libutil: Remove really dead code for git hashing

It's not being excersised by anything and already contains
bugs (like the fact that copyRecursive only handles the first entry
in a directory). Evidently, it can just be removed and was never used
by anything.

.github/workflows/ci.yml

@@ -174,7 +174,7 @@ jobs:
         echo "installer-url=file://$GITHUB_WORKSPACE/out" >> "$GITHUB_OUTPUT"
         TARBALL_PATH="$(find "$GITHUB_WORKSPACE/out" -name 'nix*.tar.xz' -print | head -n 1)"
         echo "tarball-path=file://$TARBALL_PATH" >> "$GITHUB_OUTPUT"
-    - uses: cachix/install-nix-action@7ec16f2c061ab07b235a7245e06ed46fe9a1cab6 # v31.8.3
+    - uses: cachix/install-nix-action@0b0e072294b088b73964f1d72dfdac0951439dbd # v31.8.4
       if: ${{ !matrix.experimental-installer }}
       with:
         install_url: ${{ format('{0}/install', steps.installer-tarball-url.outputs.installer-url) }}

doc/manual/source/command-ref/nix-build.md

@@ -36,7 +36,7 @@ to a temporary location. The tarball must include a single top-level
 directory containing at least a file named `default.nix`.
 
 `nix-build` is essentially a wrapper around
-[`nix-instantiate`](nix-instantiate.md) (to translate a high-level Nix
+[`nix-instantiate`](./nix-instantiate.md) (to translate a high-level Nix
 expression to a low-level [store derivation]) and [`nix-store
 --realise`](@docroot@/command-ref/nix-store/realise.md) (to build the store
 derivation).
@@ -52,8 +52,8 @@ derivation).
 # Options
 
 All options not listed here are passed to
-[`nix-store --realise`](nix-store/realise.md),
+[`nix-store --realise`](./nix-store/realise.md),
-except for `--arg` and `--attr` / `-A` which are passed to [`nix-instantiate`](nix-instantiate.md).
+except for `--arg` and `--attr` / `-A` which are passed to [`nix-instantiate`](./nix-instantiate.md).
 
 - <span id="opt-no-out-link">[`--no-out-link`](#opt-no-out-link)<span>
 

doc/manual/source/command-ref/nix-instantiate.md

@@ -32,7 +32,7 @@ standard input.
 
 - `--add-root` *path*
 
-  See the [corresponding option](nix-store.md) in `nix-store`.
+  See the [corresponding option](./nix-store.md) in `nix-store`.
 
 - `--parse`
 

packaging/dev-shell.nix

@@ -130,15 +130,19 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
     havePerl = stdenv.buildPlatform == stdenv.hostPlatform && stdenv.hostPlatform.isUnix;
     ignoreCrossFile = flags: builtins.filter (flag: !(lib.strings.hasInfix "cross-file" flag)) flags;
 
+    availableComponents = lib.filterAttrs (
+      k: v: lib.meta.availableOn pkgs.hostPlatform v
+    ) allComponents;
+
     activeComponents = buildInputsClosureCond isInternal (
-      lib.attrValues (finalAttrs.passthru.config.getComponents allComponents)
+      lib.attrValues (finalAttrs.passthru.config.getComponents availableComponents)
     );
 
     allComponents = lib.filterAttrs (k: v: lib.isDerivation v) pkgs.nixComponents2;
     internalDrvs = byDrvPath (
       # Drop the attr names (not present in buildInputs anyway)
-      lib.attrValues allComponents
+      lib.attrValues availableComponents
-      ++ lib.concatMap (c: lib.attrValues c.tests or { }) (lib.attrValues allComponents)
+      ++ lib.concatMap (c: lib.attrValues c.tests or { }) (lib.attrValues availableComponents)
     );
 
     isInternal =
@@ -187,19 +191,19 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
         );
 
       small =
-        (finalAttrs.finalPackage.withActiveComponents (c: {
+        (finalAttrs.finalPackage.withActiveComponents (
-          inherit (c)
+          c:
-            nix-cli
+          lib.intersectAttrs (lib.genAttrs [
-            nix-util-tests
+            "nix-cli"
-            nix-store-tests
+            "nix-util-tests"
-            nix-expr-tests
+            "nix-store-tests"
-            nix-fetchers-tests
+            "nix-expr-tests"
-            nix-flake-tests
+            "nix-fetchers-tests"
-            nix-functional-tests
+            "nix-flake-tests"
-            # Currently required
+            "nix-functional-tests"
-            nix-perl-bindings
+            "nix-perl-bindings"
-            ;
+          ] (_: null)) c
-        })).overrideAttrs
+        )).overrideAttrs
           (o: {
             mesonFlags = o.mesonFlags ++ [
               # TODO: infer from activeComponents or vice versa
@@ -269,6 +273,8 @@ pkgs.nixComponents2.nix-util.overrideAttrs (
       CXX_LD = "mold";
     };
 
+    dontUseCmakeConfigure = true;
+
     mesonFlags =
       map (transformFlag "libutil") (ignoreCrossFile pkgs.nixComponents2.nix-util.mesonFlags)
       ++ map (transformFlag "libstore") (ignoreCrossFile pkgs.nixComponents2.nix-store.mesonFlags)

src/kaitai-struct-checks/package.nix

@@ -65,6 +65,6 @@ mkMesonDerivation (finalAttrs: {
   '';
 
   meta = {
-    platforms = lib.platforms.all;
+    platforms = lib.platforms.unix;
   };
 })

src/libcmd/common-eval-args.cc

@@ -34,7 +34,7 @@ EvalSettings evalSettings{
                 auto flakeRef = parseFlakeRef(fetchSettings, std::string{rest}, {}, true, false);
                 debug("fetching flake search path element '%s''", rest);
                 auto [accessor, lockedRef] =
-                    flakeRef.resolve(fetchSettings, state.store).lazyFetch(fetchSettings, state.store);
+                    flakeRef.resolve(fetchSettings, *state.store).lazyFetch(fetchSettings, *state.store);
                 auto storePath = nix::fetchToStore(
                     state.fetchSettings,
                     *state.store,
@@ -132,7 +132,7 @@ MixEvalArgs::MixEvalArgs()
             fetchers::Attrs extraAttrs;
             if (to.subdir != "")
                 extraAttrs["dir"] = to.subdir;
-            fetchers::overrideRegistry(fetchSettings, from.input, to.input, extraAttrs);
+            fetchers::overrideRegistry(from.input, to.input, extraAttrs);
         }},
         .completer = {[&](AddCompletions & completions, size_t, std::string_view prefix) {
             completeFlakeRef(completions, openStore(), prefix);
@@ -180,7 +180,7 @@ Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
 SourcePath lookupFileArg(EvalState & state, std::string_view s, const Path * baseDir)
 {
     if (EvalSettings::isPseudoUrl(s)) {
-        auto accessor = fetchers::downloadTarball(state.store, state.fetchSettings, EvalSettings::resolvePseudoUrl(s));
+        auto accessor = fetchers::downloadTarball(*state.store, state.fetchSettings, EvalSettings::resolvePseudoUrl(s));
         auto storePath = fetchToStore(state.fetchSettings, *state.store, SourcePath(accessor), FetchMode::Copy);
         return state.storePath(storePath);
     }
@@ -188,7 +188,8 @@ SourcePath lookupFileArg(EvalState & state, std::string_view s, const Path * bas
     else if (hasPrefix(s, "flake:")) {
         experimentalFeatureSettings.require(Xp::Flakes);
         auto flakeRef = parseFlakeRef(fetchSettings, std::string(s.substr(6)), {}, true, false);
-        auto [accessor, lockedRef] = flakeRef.resolve(fetchSettings, state.store).lazyFetch(fetchSettings, state.store);
+        auto [accessor, lockedRef] =
+            flakeRef.resolve(fetchSettings, *state.store).lazyFetch(fetchSettings, *state.store);
         auto storePath = nix::fetchToStore(
             state.fetchSettings, *state.store, SourcePath(accessor), FetchMode::Copy, lockedRef.input.getName());
         state.allowPath(storePath);

src/libcmd/installables.cc

@@ -185,7 +185,6 @@ MixFlakeOptions::MixFlakeOptions()
                     }
 
                     overrideRegistry(
-                        fetchSettings,
                         fetchers::Input::fromAttrs(fetchSettings, {{"type", "indirect"}, {"id", inputName}}),
                         input3->lockedRef.input,
                         extraAttrs);
@@ -410,7 +409,7 @@ void completeFlakeRef(AddCompletions & completions, ref<Store> store, std::strin
     Args::completeDir(completions, 0, prefix);
 
     /* Look for registry entries that match the prefix. */
-    for (auto & registry : fetchers::getRegistries(fetchSettings, store)) {
+    for (auto & registry : fetchers::getRegistries(fetchSettings, *store)) {
         for (auto & entry : registry->entries) {
             auto from = entry.from.to_string();
             if (!hasPrefix(prefix, "flake:") && hasPrefix(from, "flake:")) {

src/libcmd/repl.cc

@@ -656,7 +656,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
                             + "\n\n";
             }
 
-            markdown += stripIndentation(doc->doc.view());
+            markdown += stripIndentation(doc->doc);
 
             logger->cout(trim(renderMarkdownToTerminal(markdown)));
         } else if (fallbackPos) {
@@ -739,7 +739,7 @@ void NixRepl::loadFlake(const std::string & flakeRefS)
 
     auto flakeRef = parseFlakeRef(fetchSettings, flakeRefS, cwd.string(), true);
     if (evalSettings.pureEval && !flakeRef.input.isLocked(fetchSettings))
-        throw Error("cannot use ':load-flake' on locked flake reference '%s' (use --impure to override)", flakeRefS);
+        throw Error("cannot use ':load-flake' on unlocked flake reference '%s' (use --impure to override)", flakeRefS);
 
     Value v;
 

src/libexpr-c/nix_api_value.cc

@@ -134,7 +134,7 @@ PrimOp * nix_alloc_primop(
                     .name = name,
                     .args = {},
                     .arity = (size_t) arity,
-                    .doc = &nix::StringData::make(doc),
+                    .doc = doc,
                     .fun = std::bind(nix_c_primop_wrapper, fun, user_data, _1, _2, _3, _4)};
         if (args)
             for (size_t i = 0; args[i]; i++)

src/libexpr-tests/json.cc

@@ -1,6 +1,6 @@
 #include "nix/expr/tests/libexpr.hh"
 #include "nix/expr/value-to-json.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 
 namespace nix {
 // Testing the conversion to JSON

src/libexpr-tests/value/print.cc

@@ -1,5 +1,5 @@
 #include "nix/expr/tests/libexpr.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 
 #include "nix/expr/value.hh"
 #include "nix/expr/print.hh"

src/libexpr-tests/value/value.cc

@@ -1,5 +1,5 @@
 #include "nix/expr/value.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 
 #include "nix/store/tests/libstore.hh"
 #include <gtest/gtest.h>

src/libexpr/eval.cc

@@ -51,6 +51,36 @@ using json = nlohmann::json;
 
 namespace nix {
 
+/**
+ * Just for doc strings. Not for regular string values.
+ */
+static char * allocString(size_t size)
+{
+    char * t;
+    t = (char *) GC_MALLOC_ATOMIC(size);
+    if (!t)
+        throw std::bad_alloc();
+    return t;
+}
+
+// When there's no need to write to the string, we can optimize away empty
+// string allocations.
+// This function handles makeImmutableString(std::string_view()) by returning
+// the empty string.
+/**
+ * Just for doc strings. Not for regular string values.
+ */
+static const char * makeImmutableString(std::string_view s)
+{
+    const size_t size = s.size();
+    if (size == 0)
+        return "";
+    auto t = allocString(size + 1);
+    memcpy(t, s.data(), size);
+    t[size] = '\0';
+    return t;
+}
+
 StringData & StringData::alloc(size_t size)
 {
     void * t = GC_MALLOC_ATOMIC(sizeof(StringData) + size + 1);
@@ -175,7 +205,7 @@ bool Value::isTrivial() const
 {
     return !isa<tApp, tPrimOpApp>()
            && (!isa<tThunk>()
-               || (dynamic_cast<ExprAttrs *>(thunk().expr) && ((ExprAttrs *) thunk().expr)->dynamicAttrs.empty())
+               || (dynamic_cast<ExprAttrs *>(thunk().expr) && ((ExprAttrs *) thunk().expr)->dynamicAttrs->empty())
                || dynamic_cast<ExprLambda *>(thunk().expr) || dynamic_cast<ExprList *>(thunk().expr));
 }
 
@@ -487,15 +517,16 @@ Value * EvalState::addPrimOp(PrimOp && primOp)
     if (primOp.arity == 0) {
         primOp.arity = 1;
         auto vPrimOp = allocValue();
-        vPrimOp->mkPrimOp(new PrimOp(primOp));
+        vPrimOp->mkPrimOp(new PrimOp(std::move(primOp)));
         Value v;
         v.mkApp(vPrimOp, vPrimOp);
+        auto & primOp1 = *vPrimOp->primOp();
         return addConstant(
-            primOp.name,
+            primOp1.name,
             v,
             {
                 .type = nThunk, // FIXME
-                .doc = primOp.doc,
+                .doc = primOp1.doc ? primOp1.doc->c_str() : nullptr,
             });
     }
 
@@ -535,13 +566,14 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
 {
     if (v.isPrimOp()) {
         auto v2 = &v;
-        if (auto * doc = v2->primOp()->doc)
+        auto & primOp = *v2->primOp();
+        if (primOp.doc)
             return Doc{
                 .pos = {},
-                .name = v2->primOp()->name,
+                .name = primOp.name,
-                .arity = v2->primOp()->arity,
+                .arity = primOp.arity,
-                .args = v2->primOp()->args,
+                .args = primOp.args,
-                .doc = *doc,
+                .doc = primOp.doc->c_str(),
             };
     }
     if (v.isLambda()) {
@@ -583,8 +615,9 @@ std::optional<EvalState::Doc> EvalState::getDoc(Value & v)
             .name = name,
             .arity = 0, // FIXME: figure out how deep by syntax only? It's not semantically useful though...
             .args = {},
-            /* NOTE: memory leak when compiled without GC. */
+            /* N.B. Can't use StringData here, because that would lead to an interior pointer.
-            .doc = StringData::make(s.view()),
+               NOTE: memory leak when compiled without GC. */
+            .doc = makeImmutableString(s.view()),
         };
     }
     if (isFunctor(v)) {
@@ -1193,26 +1226,26 @@ Env * ExprAttrs::buildInheritFromEnv(EvalState & state, Env & up)
 
 void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 {
-    auto bindings = state.buildBindings(attrs.size() + dynamicAttrs.size());
+    auto bindings = state.buildBindings(attrs->size() + dynamicAttrs->size());
     auto dynamicEnv = &env;
     bool sort = false;
 
     if (recursive) {
         /* Create a new environment that contains the attributes in
            this `rec'. */
-        Env & env2(state.mem.allocEnv(attrs.size()));
+        Env & env2(state.mem.allocEnv(attrs->size()));
         env2.up = &env;
         dynamicEnv = &env2;
         Env * inheritEnv = inheritFromExprs ? buildInheritFromEnv(state, env2) : nullptr;
 
-        AttrDefs::iterator overrides = attrs.find(state.s.overrides);
+        AttrDefs::iterator overrides = attrs->find(state.s.overrides);
-        bool hasOverrides = overrides != attrs.end();
+        bool hasOverrides = overrides != attrs->end();
 
         /* The recursive attributes are evaluated in the new
            environment, while the inherited attributes are evaluated
            in the original environment. */
         Displacement displ = 0;
-        for (auto & i : attrs) {
+        for (auto & i : *attrs) {
             Value * vAttr;
             if (hasOverrides && i.second.kind != AttrDef::Kind::Inherited) {
                 vAttr = state.allocValue();
@@ -1239,8 +1272,8 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
                 "while evaluating the `__overrides` attribute");
             bindings.grow(state.buildBindings(bindings.capacity() + vOverrides->attrs()->size()));
             for (auto & i : *vOverrides->attrs()) {
-                AttrDefs::iterator j = attrs.find(i.name);
+                AttrDefs::iterator j = attrs->find(i.name);
-                if (j != attrs.end()) {
+                if (j != attrs->end()) {
                     (*bindings.bindings)[j->second.displ] = i;
                     env2.values[j->second.displ] = i.value;
                 } else
@@ -1252,13 +1285,13 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
 
     else {
         Env * inheritEnv = inheritFromExprs ? buildInheritFromEnv(state, env) : nullptr;
-        for (auto & i : attrs)
+        for (auto & i : *attrs)
             bindings.insert(
                 i.first, i.second.e->maybeThunk(state, *i.second.chooseByKind(&env, &env, inheritEnv)), i.second.pos);
     }
 
     /* Dynamic attrs apply *after* rec and __overrides. */
-    for (auto & i : dynamicAttrs) {
+    for (auto & i : *dynamicAttrs) {
         Value nameVal;
         i.nameExpr->eval(state, *dynamicEnv, nameVal);
         state.forceValue(nameVal, i.pos);
@@ -1292,7 +1325,7 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
 {
     /* Create a new environment that contains the attributes in this
        `let'. */
-    Env & env2(state.mem.allocEnv(attrs->attrs.size()));
+    Env & env2(state.mem.allocEnv(attrs->attrs->size()));
     env2.up = &env;
 
     Env * inheritEnv = attrs->inheritFromExprs ? attrs->buildInheritFromEnv(state, env2) : nullptr;
@@ -1301,7 +1334,7 @@ void ExprLet::eval(EvalState & state, Env & env, Value & v)
        while the inherited attributes are evaluated in the original
        environment. */
     Displacement displ = 0;
-    for (auto & i : attrs->attrs) {
+    for (auto & i : *attrs->attrs) {
         env2.values[displ++] = i.second.e->maybeThunk(state, *i.second.chooseByKind(&env2, &env, inheritEnv));
     }
 
@@ -3157,7 +3190,7 @@ std::optional<SourcePath> EvalState::resolveLookupPathPath(const LookupPath::Pat
 
     if (EvalSettings::isPseudoUrl(value)) {
         try {
-            auto accessor = fetchers::downloadTarball(store, fetchSettings, EvalSettings::resolvePseudoUrl(value));
+            auto accessor = fetchers::downloadTarball(*store, fetchSettings, EvalSettings::resolvePseudoUrl(value));
             auto storePath = fetchToStore(fetchSettings, *store, SourcePath(accessor), FetchMode::Copy);
             return finish(this->storePath(storePath));
         } catch (Error & e) {

src/libexpr/include/nix/expr/eval.hh

@@ -108,7 +108,7 @@ struct PrimOp
     /**
      * Optional free-form documentation about the primop.
      */
-    const StringData * doc = nullptr;
+    std::optional<std::string> doc;
 
     /**
      * Add a trace item, while calling the `<name>` builtin.
@@ -156,7 +156,7 @@ struct Constant
     /**
      * Optional free-form documentation about the constant.
      */
-    const StringData * doc = nullptr;
+    const char * doc = nullptr;
 
     /**
      * Whether the constant is impure, and not available in pure mode.
@@ -837,7 +837,11 @@ public:
         std::optional<std::string> name;
         size_t arity;
         std::vector<std::string> args;
-        const StringData & doc;
+        /**
+         * Unlike the other `doc` fields in this file, this one should never be
+         * `null`.
+         */
+        const char * doc;
     };
 
     /**

src/libexpr/include/nix/expr/meson.build

@@ -31,8 +31,7 @@ headers = [ config_pub_h ] + files(
   'print.hh',
   'repl-exit-status.hh',
   'search-path.hh',
-  'string-data.hh',
+  'static-string-data.hh',
-  'string-data-static.hh',
   'symbol-table.hh',
   'value-to-json.hh',
   'value-to-xml.hh',

src/libexpr/include/nix/expr/nixexpr.hh

@@ -12,7 +12,7 @@
 #include "nix/expr/value.hh"
 #include "nix/expr/symbol-table.hh"
 #include "nix/expr/eval-error.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 #include "nix/util/pos-idx.hh"
 #include "nix/expr/counter.hh"
 #include "nix/util/pos-table.hh"
@@ -395,9 +395,13 @@ struct ExprAttrs : Expr
         }
     };
 
-    typedef std::map<Symbol, AttrDef> AttrDefs;
+    typedef std::pmr::map<Symbol, AttrDef> AttrDefs;
-    AttrDefs attrs;
+    /**
-    std::unique_ptr<std::vector<Expr *>> inheritFromExprs;
+     * attrs will never be null. we use std::optional so that we can call emplace() to re-initialize the value with a
+     * new pmr::map using a different allocator (move assignment will copy into the old allocator)
+     */
+    std::optional<AttrDefs> attrs;
+    std::unique_ptr<std::pmr::vector<Expr *>> inheritFromExprs;
 
     struct DynamicAttrDef
     {
@@ -409,13 +413,20 @@ struct ExprAttrs : Expr
             , pos(pos) {};
     };
 
-    typedef std::vector<DynamicAttrDef> DynamicAttrDefs;
+    typedef std::pmr::vector<DynamicAttrDef> DynamicAttrDefs;
-    DynamicAttrDefs dynamicAttrs;
+    /**
+     * dynamicAttrs will never be null. See comment on AttrDefs above.
+     */
+    std::optional<DynamicAttrDefs> dynamicAttrs;
     ExprAttrs(const PosIdx & pos)
         : recursive(false)
-        , pos(pos) {};
+        , pos(pos)
+        , attrs(AttrDefs{})
+        , dynamicAttrs(DynamicAttrDefs{}) {};
     ExprAttrs()
-        : recursive(false) {};
+        : recursive(false)
+        , attrs(AttrDefs{})
+        , dynamicAttrs(DynamicAttrDefs{}) {};
 
     PosIdx getPos() const override
     {

src/libexpr/include/nix/expr/parser-state.hh

@@ -5,7 +5,7 @@
 
 #include "nix/expr/eval.hh"
 #include "nix/expr/value.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 
 namespace nix {
 
@@ -126,8 +126,8 @@ inline void ParserState::addAttr(
     for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
         ExprAttrs * nested;
         if (i->symbol) {
-            ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
+            ExprAttrs::AttrDefs::iterator j = attrs->attrs->find(i->symbol);
-            if (j != attrs->attrs.end()) {
+            if (j != attrs->attrs->end()) {
                 nested = dynamic_cast<ExprAttrs *>(j->second.e);
                 if (!nested) {
                     attrPath.erase(i + 1, attrPath.end());
@@ -135,11 +135,11 @@ inline void ParserState::addAttr(
                 }
             } else {
                 nested = exprs.add<ExprAttrs>();
-                attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
+                (*attrs->attrs)[i->symbol] = ExprAttrs::AttrDef(nested, pos);
             }
         } else {
             nested = exprs.add<ExprAttrs>();
-            attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
+            attrs->dynamicAttrs->push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
         }
         attrs = nested;
     }
@@ -148,7 +148,7 @@ inline void ParserState::addAttr(
     if (i->symbol) {
         addAttr(attrs, attrPath, i->symbol, ExprAttrs::AttrDef(e, pos));
     } else {
-        attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, e, pos));
+        attrs->dynamicAttrs->push_back(ExprAttrs::DynamicAttrDef(i->expr, e, pos));
     }
 
     auto it = lexerState.positionToDocComment.find(pos);
@@ -165,8 +165,8 @@ inline void ParserState::addAttr(
 inline void
 ParserState::addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symbol, ExprAttrs::AttrDef && def)
 {
-    ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(symbol);
+    ExprAttrs::AttrDefs::iterator j = attrs->attrs->find(symbol);
-    if (j != attrs->attrs.end()) {
+    if (j != attrs->attrs->end()) {
         // This attr path is already defined. However, if both
         // e and the expr pointed by the attr path are two attribute sets,
         // we want to merge them.
@@ -181,8 +181,8 @@ ParserState::addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symb
         // See https://github.com/NixOS/nix/issues/9020.
         if (jAttrs && ae) {
             if (ae->inheritFromExprs && !jAttrs->inheritFromExprs)
-                jAttrs->inheritFromExprs = std::make_unique<std::vector<Expr *>>();
+                jAttrs->inheritFromExprs = std::make_unique<std::pmr::vector<Expr *>>();
-            for (auto & ad : ae->attrs) {
+            for (auto & ad : *ae->attrs) {
                 if (ad.second.kind == ExprAttrs::AttrDef::Kind::InheritedFrom) {
                     auto & sel = dynamic_cast<ExprSelect &>(*ad.second.e);
                     auto & from = dynamic_cast<ExprInheritFrom &>(*sel.e);
@@ -192,12 +192,12 @@ ParserState::addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symb
                 addAttr(jAttrs, attrPath, ad.first, std::move(ad.second));
                 attrPath.pop_back();
             }
-            ae->attrs.clear();
+            ae->attrs->clear();
-            jAttrs->dynamicAttrs.insert(
+            jAttrs->dynamicAttrs->insert(
-                jAttrs->dynamicAttrs.end(),
+                jAttrs->dynamicAttrs->end(),
-                std::make_move_iterator(ae->dynamicAttrs.begin()),
+                std::make_move_iterator(ae->dynamicAttrs->begin()),
-                std::make_move_iterator(ae->dynamicAttrs.end()));
+                std::make_move_iterator(ae->dynamicAttrs->end()));
-            ae->dynamicAttrs.clear();
+            ae->dynamicAttrs->clear();
             if (ae->inheritFromExprs) {
                 jAttrs->inheritFromExprs->insert(
                     jAttrs->inheritFromExprs->end(),
@@ -210,7 +210,7 @@ ParserState::addAttr(ExprAttrs * attrs, AttrPath & attrPath, const Symbol & symb
         }
     } else {
         // This attr path is not defined. Let's create it.
-        attrs->attrs.emplace(symbol, def);
+        attrs->attrs->emplace(symbol, def);
         def.e->setName(symbol);
     }
 }

src/libexpr/include/nix/expr/static-string-data.hh

@@ -1,7 +1,7 @@
 #pragma once
 ///@file
 
-#include "nix/expr/string-data.hh"
+#include "nix/expr/value.hh"
 
 namespace nix {
 

src/libexpr/include/nix/expr/string-data.hh

@@ -1,96 +0,0 @@
-#pragma once
-///@file
-
-#include <cstddef>
-#include <cstring>
-#include <memory_resource>
-#include <string_view>
-
-namespace nix {
-
-class StringData
-{
-public:
-    using size_type = std::size_t;
-
-    size_type size_;
-    char data_[];
-
-    /*
-     * This in particular ensures that we cannot have a `StringData`
-     * that we use by value, which is just what we want!
-     *
-     * Dynamically sized types aren't a thing in C++ and even flexible array
-     * members are a language extension and beyond the realm of standard C++.
-     * Technically, sizeof data_ member is 0 and the intended way to use flexible
-     * array members is to allocate sizeof(StrindData) + count * sizeof(char) bytes
-     * and the compiler will consider alignment restrictions for the FAM.
-     *
-     */
-
-    StringData(StringData &&) = delete;
-    StringData & operator=(StringData &&) = delete;
-    StringData(const StringData &) = delete;
-    StringData & operator=(const StringData &) = delete;
-    ~StringData() = default;
-
-private:
-    StringData() = delete;
-
-    explicit StringData(size_type size)
-        : size_(size)
-    {
-    }
-
-public:
-    /**
-     * Allocate StringData on the (possibly) GC-managed heap and copy
-     * the contents of s to it.
-     */
-    static const StringData & make(std::string_view s);
-
-    /**
-     * Allocate StringData on the (possibly) GC-managed heap.
-     * @param size Length of the string (without the NUL terminator).
-     */
-    static StringData & alloc(size_t size);
-
-    size_t size() const
-    {
-        return size_;
-    }
-
-    char * data() noexcept
-    {
-        return data_;
-    }
-
-    const char * data() const noexcept
-    {
-        return data_;
-    }
-
-    const char * c_str() const noexcept
-    {
-        return data_;
-    }
-
-    constexpr std::string_view view() const noexcept
-    {
-        return std::string_view(data_, size_);
-    }
-
-    template<size_t N>
-    struct Static;
-
-    static StringData & make(std::pmr::memory_resource & resource, std::string_view s)
-    {
-        auto & res =
-            *new (resource.allocate(sizeof(StringData) + s.size() + 1, alignof(StringData))) StringData(s.size());
-        std::memcpy(res.data_, s.data(), s.size());
-        res.data_[s.size()] = '\0';
-        return res;
-    }
-};
-
-} // namespace nix

src/libexpr/include/nix/expr/symbol-table.hh

@@ -3,7 +3,7 @@
 
 #include <memory_resource>
 #include "nix/expr/value.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 #include "nix/util/chunked-vector.hh"
 #include "nix/util/error.hh"
 

src/libexpr/include/nix/expr/value.hh

@@ -3,14 +3,16 @@
 
 #include <bit>
 #include <cassert>
+#include <cstddef>
+#include <cstring>
 #include <memory>
+#include <memory_resource>
 #include <span>
 #include <string_view>
 #include <type_traits>
 #include <concepts>
 
 #include "nix/expr/eval-gc.hh"
-#include "nix/expr/string-data.hh"
 #include "nix/expr/value/context.hh"
 #include "nix/util/source-path.hh"
 #include "nix/expr/print-options.hh"
@@ -191,6 +193,91 @@ public:
     friend struct Value;
 };
 
+class StringData
+{
+public:
+    using size_type = std::size_t;
+
+    size_type size_;
+    char data_[];
+
+    /*
+     * This in particular ensures that we cannot have a `StringData`
+     * that we use by value, which is just what we want!
+     *
+     * Dynamically sized types aren't a thing in C++ and even flexible array
+     * members are a language extension and beyond the realm of standard C++.
+     * Technically, sizeof data_ member is 0 and the intended way to use flexible
+     * array members is to allocate sizeof(StrindData) + count * sizeof(char) bytes
+     * and the compiler will consider alignment restrictions for the FAM.
+     *
+     */
+
+    StringData(StringData &&) = delete;
+    StringData & operator=(StringData &&) = delete;
+    StringData(const StringData &) = delete;
+    StringData & operator=(const StringData &) = delete;
+    ~StringData() = default;
+
+private:
+    StringData() = delete;
+
+    explicit StringData(size_type size)
+        : size_(size)
+    {
+    }
+
+public:
+    /**
+     * Allocate StringData on the (possibly) GC-managed heap and copy
+     * the contents of s to it.
+     */
+    static const StringData & make(std::string_view s);
+
+    /**
+     * Allocate StringData on the (possibly) GC-managed heap.
+     * @param size Length of the string (without the NUL terminator).
+     */
+    static StringData & alloc(size_t size);
+
+    size_t size() const
+    {
+        return size_;
+    }
+
+    char * data() noexcept
+    {
+        return data_;
+    }
+
+    const char * data() const noexcept
+    {
+        return data_;
+    }
+
+    const char * c_str() const noexcept
+    {
+        return data_;
+    }
+
+    constexpr std::string_view view() const noexcept
+    {
+        return std::string_view(data_, size_);
+    }
+
+    template<size_t N>
+    struct Static;
+
+    static StringData & make(std::pmr::memory_resource & resource, std::string_view s)
+    {
+        auto & res =
+            *new (resource.allocate(sizeof(StringData) + s.size() + 1, alignof(StringData))) StringData(s.size());
+        std::memcpy(res.data_, s.data(), s.size());
+        res.data_[s.size()] = '\0';
+        return res;
+    }
+};
+
 namespace detail {
 
 /**

src/libexpr/nixexpr.cc

@@ -74,9 +74,9 @@ void ExprOpHasAttr::show(const SymbolTable & symbols, std::ostream & str) const
 
 void ExprAttrs::showBindings(const SymbolTable & symbols, std::ostream & str) const
 {
-    typedef const decltype(attrs)::value_type * Attr;
+    typedef const AttrDefs::value_type * Attr;
     std::vector<Attr> sorted;
-    for (auto & i : attrs)
+    for (auto & i : *attrs)
         sorted.push_back(&i);
     std::sort(sorted.begin(), sorted.end(), [&](Attr a, Attr b) {
         std::string_view sa = symbols[a->first], sb = symbols[b->first];
@@ -122,7 +122,7 @@ void ExprAttrs::showBindings(const SymbolTable & symbols, std::ostream & str) co
             str << "; ";
         }
     }
-    for (auto & i : dynamicAttrs) {
+    for (auto & i : *dynamicAttrs) {
         str << "\"${";
         i.nameExpr->show(symbols, str);
         str << "}\" = ";
@@ -401,15 +401,26 @@ ExprAttrs::bindInheritSources(EvalState & es, const std::shared_ptr<const Static
 
 void ExprAttrs::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
+    // Move storage into the Exprs arena
+    {
+        auto arena = es.mem.exprs.alloc;
+        AttrDefs newAttrs{std::move(*attrs), arena};
+        attrs.emplace(std::move(newAttrs), arena);
+        DynamicAttrDefs newDynamicAttrs{std::move(*dynamicAttrs), arena};
+        dynamicAttrs.emplace(std::move(newDynamicAttrs), arena);
+        if (inheritFromExprs)
+            inheritFromExprs = std::make_unique<std::pmr::vector<Expr *>>(std::move(*inheritFromExprs), arena);
+    }
+
     if (es.debugRepl)
         es.exprEnvs.insert(std::make_pair(this, env));
 
     if (recursive) {
         auto newEnv = [&]() -> std::shared_ptr<const StaticEnv> {
-            auto newEnv = std::make_shared<StaticEnv>(nullptr, env, attrs.size());
+            auto newEnv = std::make_shared<StaticEnv>(nullptr, env, attrs->size());
 
             Displacement displ = 0;
-            for (auto & i : attrs)
+            for (auto & i : *attrs)
                 newEnv->vars.emplace_back(i.first, i.second.displ = displ++);
             return newEnv;
         }();
@@ -417,20 +428,20 @@ void ExprAttrs::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv>
         // No need to sort newEnv since attrs is in sorted order.
 
         auto inheritFromEnv = bindInheritSources(es, newEnv);
-        for (auto & i : attrs)
+        for (auto & i : *attrs)
             i.second.e->bindVars(es, i.second.chooseByKind(newEnv, env, inheritFromEnv));
 
-        for (auto & i : dynamicAttrs) {
+        for (auto & i : *dynamicAttrs) {
             i.nameExpr->bindVars(es, newEnv);
             i.valueExpr->bindVars(es, newEnv);
         }
     } else {
         auto inheritFromEnv = bindInheritSources(es, env);
 
-        for (auto & i : attrs)
+        for (auto & i : *attrs)
             i.second.e->bindVars(es, i.second.chooseByKind(env, env, inheritFromEnv));
 
-        for (auto & i : dynamicAttrs) {
+        for (auto & i : *dynamicAttrs) {
             i.nameExpr->bindVars(es, env);
             i.valueExpr->bindVars(es, env);
         }
@@ -486,10 +497,10 @@ void ExprCall::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
 void ExprLet::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env)
 {
     auto newEnv = [&]() -> std::shared_ptr<const StaticEnv> {
-        auto newEnv = std::make_shared<StaticEnv>(nullptr, env, attrs->attrs.size());
+        auto newEnv = std::make_shared<StaticEnv>(nullptr, env, attrs->attrs->size());
 
         Displacement displ = 0;
-        for (auto & i : attrs->attrs)
+        for (auto & i : *attrs->attrs)
             newEnv->vars.emplace_back(i.first, i.second.displ = displ++);
         return newEnv;
     }();
@@ -497,7 +508,7 @@ void ExprLet::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
     // No need to sort newEnv since attrs->attrs is in sorted order.
 
     auto inheritFromEnv = attrs->bindInheritSources(es, newEnv);
-    for (auto & i : attrs->attrs)
+    for (auto & i : *attrs->attrs)
         i.second.e->bindVars(es, i.second.chooseByKind(newEnv, env, inheritFromEnv));
 
     if (es.debugRepl)

src/libexpr/parser.y

@@ -211,7 +211,7 @@ expr_function
   | WITH expr ';' expr_function
     { $$ = state->exprs.add<ExprWith>(CUR_POS, $2, $4); }
   | LET binds IN_KW expr_function
-    { if (!$2->dynamicAttrs.empty())
+    { if (!$2->dynamicAttrs->empty())
         throw ParseError({
             .msg = HintFmt("dynamic attributes not allowed in let"),
             .pos = state->positions[CUR_POS]
@@ -413,9 +413,9 @@ binds1
   | binds[accum] INHERIT attrs ';'
     { $$ = $accum;
       for (auto & [i, iPos] : $attrs) {
-          if ($accum->attrs.find(i.symbol) != $accum->attrs.end())
+          if ($accum->attrs->find(i.symbol) != $accum->attrs->end())
-              state->dupAttr(i.symbol, iPos, $accum->attrs[i.symbol].pos);
+              state->dupAttr(i.symbol, iPos, (*$accum->attrs)[i.symbol].pos);
-          $accum->attrs.emplace(
+          $accum->attrs->emplace(
               i.symbol,
               ExprAttrs::AttrDef(state->exprs.add<ExprVar>(iPos, i.symbol), iPos, ExprAttrs::AttrDef::Kind::Inherited));
       }
@@ -423,13 +423,13 @@ binds1
   | binds[accum] INHERIT '(' expr ')' attrs ';'
     { $$ = $accum;
       if (!$accum->inheritFromExprs)
-          $accum->inheritFromExprs = std::make_unique<std::vector<Expr *>>();
+          $accum->inheritFromExprs = std::make_unique<std::pmr::vector<Expr *>>();
       $accum->inheritFromExprs->push_back($expr);
       auto from = state->exprs.add<ExprInheritFrom>(state->at(@expr), $accum->inheritFromExprs->size() - 1);
       for (auto & [i, iPos] : $attrs) {
-          if ($accum->attrs.find(i.symbol) != $accum->attrs.end())
+          if ($accum->attrs->find(i.symbol) != $accum->attrs->end())
-              state->dupAttr(i.symbol, iPos, $accum->attrs[i.symbol].pos);
+              state->dupAttr(i.symbol, iPos, (*$accum->attrs)[i.symbol].pos);
-          $accum->attrs.emplace(
+          $accum->attrs->emplace(
               i.symbol,
               ExprAttrs::AttrDef(
                   state->exprs.add<ExprSelect>(state->exprs.alloc, iPos, from, i.symbol),

src/libexpr/primops/context.cc

@@ -1,6 +1,5 @@
 #include "nix/expr/primops.hh"
 #include "nix/expr/eval-inline.hh"
-#include "nix/expr/string-data-static.hh"
 #include "nix/store/derivations.hh"
 #include "nix/store/store-api.hh"
 #include "nix/store/globals.hh"
@@ -18,9 +17,9 @@ static void prim_unsafeDiscardStringContext(EvalState & state, const PosIdx pos,
 static RegisterPrimOp primop_unsafeDiscardStringContext({
     .name = "__unsafeDiscardStringContext",
     .args = {"s"},
-    .doc = &R"(
+    .doc = R"(
         Discard the [string context](@docroot@/language/string-context.md) from a value that can be coerced to a string.
-    )"_sds,
+    )",
     .fun = prim_unsafeDiscardStringContext,
 });
 
@@ -34,7 +33,7 @@ static void prim_hasContext(EvalState & state, const PosIdx pos, Value ** args,
 static RegisterPrimOp primop_hasContext(
     {.name = "__hasContext",
      .args = {"s"},
-     .doc = &R"(
+     .doc = R"(
       Return `true` if string *s* has a non-empty context.
       The context can be obtained with
       [`getContext`](#builtins-getContext).
@@ -51,7 +50,7 @@ static RegisterPrimOp primop_hasContext(
       > then throw "package name cannot contain string context"
       > else { ${name} = meta; }
       > ```
-    )"_sds,
+    )",
      .fun = prim_hasContext});
 
 static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx pos, Value ** args, Value & v)
@@ -76,7 +75,7 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx p
 static RegisterPrimOp primop_unsafeDiscardOutputDependency(
     {.name = "__unsafeDiscardOutputDependency",
      .args = {"s"},
-     .doc = &R"(
+     .doc = R"(
       Create a copy of the given string where every
       [derivation deep](@docroot@/language/string-context.md#string-context-element-derivation-deep)
       string context element is turned into a
@@ -92,7 +91,7 @@ static RegisterPrimOp primop_unsafeDiscardOutputDependency(
       Replacing a constant string context element with a "derivation deep" element is a safe operation that just enlargens the string context without forgetting anything.
 
       [`builtins.addDrvOutputDependencies`]: #builtins-addDrvOutputDependencies
-    )"_sds,
+    )",
      .fun = prim_unsafeDiscardOutputDependency});
 
 static void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, Value ** args, Value & v)
@@ -144,7 +143,7 @@ static void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, V
 static RegisterPrimOp primop_addDrvOutputDependencies(
     {.name = "__addDrvOutputDependencies",
      .args = {"s"},
-     .doc = &R"(
+     .doc = R"(
       Create a copy of the given string where a single
       [constant](@docroot@/language/string-context.md#string-context-constant)
       string context element is turned into a
@@ -157,7 +156,7 @@ static RegisterPrimOp primop_addDrvOutputDependencies(
       The latter is supported so this function is idempotent.
 
       This is the opposite of [`builtins.unsafeDiscardOutputDependency`](#builtins-unsafeDiscardOutputDependency).
-    )"_sds,
+    )",
      .fun = prim_addDrvOutputDependencies});
 
 /* Extract the context of a string as a structured Nix value.
@@ -231,7 +230,7 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value ** args,
 static RegisterPrimOp primop_getContext(
     {.name = "__getContext",
      .args = {"s"},
-     .doc = &R"(
+     .doc = R"(
       Return the string context of *s*.
 
       The string context tracks references to derivations within a string.
@@ -249,7 +248,7 @@ static RegisterPrimOp primop_getContext(
       ```
       { "/nix/store/arhvjaf6zmlyn8vh8fgn55rpwnxq0n7l-a.drv" = { outputs = [ "out" ]; }; }
       ```
-    )"_sds,
+    )",
      .fun = prim_getContext});
 
 /* Append the given context to a given string.

src/libexpr/primops/fetchClosure.cc

@@ -1,5 +1,4 @@
 #include "nix/expr/primops.hh"
-#include "nix/expr/string-data-static.hh"
 #include "nix/store/store-open.hh"
 #include "nix/store/realisation.hh"
 #include "nix/store/make-content-addressed.hh"
@@ -217,7 +216,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value ** args
 static RegisterPrimOp primop_fetchClosure({
     .name = "__fetchClosure",
     .args = {"args"},
-    .doc = &R"(
+    .doc = R"(
       Fetch a store path [closure](@docroot@/glossary.md#gloss-closure) from a binary cache, and return the store path as a string with context.
 
       This function can be invoked in three ways that we will discuss in order of preference.
@@ -285,7 +284,7 @@ static RegisterPrimOp primop_fetchClosure({
       `fetchClosure` is similar to [`builtins.storePath`](#builtins-storePath) in that it allows you to use a previously built store path in a Nix expression.
       However, `fetchClosure` is more reproducible because it specifies a binary cache from which the path can be fetched.
       Also, using content-addressed store paths does not require users to configure [`trusted-public-keys`](@docroot@/command-ref/conf-file.md#conf-trusted-public-keys) to ensure their authenticity.
-    )"_sds,
+    )",
     .fun = prim_fetchClosure,
     .experimentalFeature = Xp::FetchClosure,
 });

src/libexpr/primops/fetchMercurial.cc

@@ -81,7 +81,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value ** ar
         attrs.insert_or_assign("rev", rev->gitRev());
     auto input = fetchers::Input::fromAttrs(state.fetchSettings, std::move(attrs));
 
-    auto [storePath, input2] = input.fetchToStore(state.fetchSettings, state.store);
+    auto [storePath, input2] = input.fetchToStore(state.fetchSettings, *state.store);
 
     auto attrs2 = state.buildBindings(8);
     state.mkStorePathString(storePath, attrs2.alloc(state.s.outPath));

src/libexpr/primops/fetchTree.cc

@@ -2,7 +2,6 @@
 #include "nix/expr/primops.hh"
 #include "nix/expr/eval-inline.hh"
 #include "nix/expr/eval-settings.hh"
-#include "nix/expr/string-data-static.hh"
 #include "nix/store/store-api.hh"
 #include "nix/fetchers/fetchers.hh"
 #include "nix/store/filetransfer.hh"
@@ -195,7 +194,7 @@ static void fetchTree(
     }
 
     if (!state.settings.pureEval && !input.isDirect() && experimentalFeatureSettings.isEnabled(Xp::Flakes))
-        input = lookupInRegistries(state.fetchSettings, state.store, input, fetchers::UseRegistries::Limited).first;
+        input = lookupInRegistries(state.fetchSettings, *state.store, input, fetchers::UseRegistries::Limited).first;
 
     if (state.settings.pureEval && !input.isLocked(state.fetchSettings)) {
         if (input.getNarHash())
@@ -221,7 +220,7 @@ static void fetchTree(
     }
 
     auto cachedInput =
-        state.inputCache->getAccessor(state.fetchSettings, state.store, input, fetchers::UseRegistries::No);
+        state.inputCache->getAccessor(state.fetchSettings, *state.store, input, fetchers::UseRegistries::No);
 
     auto storePath = state.mountInput(cachedInput.lockedInput, input, cachedInput.accessor);
 
@@ -236,229 +235,127 @@ static void prim_fetchTree(EvalState & state, const PosIdx pos, Value ** args, V
 static RegisterPrimOp primop_fetchTree({
     .name = "fetchTree",
     .args = {"input"},
-    .doc = &R"(
+    .doc = []() -> std::string {
-      Fetch a file system tree or a plain file using one of the supported backends and return an attribute set with:
+        std::string doc = stripIndentation(R"(
+          Fetch a file system tree or a plain file using one of the supported backends and return an attribute set with:
 
-      - the resulting fixed-output [store path](@docroot@/store/store-path.md)
+          - the resulting fixed-output [store path](@docroot@/store/store-path.md)
-      - the corresponding [NAR](@docroot@/store/file-system-object/content-address.md#serial-nix-archive) hash
+          - the corresponding [NAR](@docroot@/store/file-system-object/content-address.md#serial-nix-archive) hash
-      - backend-specific metadata (currently not documented). <!-- TODO: document output attributes -->
+          - backend-specific metadata (currently not documented). <!-- TODO: document output attributes -->
 
-      *input* must be an attribute set with the following attributes:
+          *input* must be an attribute set with the following attributes:
 
-      - `type` (String, required)
+          - `type` (String, required)
 
-        One of the [supported source types](#source-types).
+            One of the [supported source types](#source-types).
-        This determines other required and allowed input attributes.
+            This determines other required and allowed input attributes.
 
-      - `narHash` (String, optional)
+          - `narHash` (String, optional)
 
-        The `narHash` parameter can be used to substitute the source of the tree.
+            The `narHash` parameter can be used to substitute the source of the tree.
-        It also allows for verification of tree contents that may not be provided by the underlying transfer mechanism.
+            It also allows for verification of tree contents that may not be provided by the underlying transfer mechanism.
-        If `narHash` is set, the source is first looked up is the Nix store and [substituters](@docroot@/command-ref/conf-file.md#conf-substituters), and only fetched if not available.
+            If `narHash` is set, the source is first looked up is the Nix store and [substituters](@docroot@/command-ref/conf-file.md#conf-substituters), and only fetched if not available.
 
-      A subset of the output attributes of `fetchTree` can be re-used for subsequent calls to `fetchTree` to produce the same result again.
+          A subset of the output attributes of `fetchTree` can be re-used for subsequent calls to `fetchTree` to produce the same result again.
-      That is, `fetchTree` is idempotent.
+          That is, `fetchTree` is idempotent.
 
-      Downloads are cached in `$XDG_CACHE_HOME/nix`.
+          Downloads are cached in `$XDG_CACHE_HOME/nix`.
-      The remote source is fetched from the network if both are true:
+          The remote source is fetched from the network if both are true:
-      - A NAR hash is supplied and the corresponding store path is not [valid](@docroot@/glossary.md#gloss-validity), that is, not available in the store
+          - A NAR hash is supplied and the corresponding store path is not [valid](@docroot@/glossary.md#gloss-validity), that is, not available in the store
 
-        > **Note**
+            > **Note**
-        >
-        > [Substituters](@docroot@/command-ref/conf-file.md#conf-substituters) are not used in fetching.
-
-      - There is no cache entry or the cache entry is older than [`tarball-ttl`](@docroot@/command-ref/conf-file.md#conf-tarball-ttl)
-
-      ## Source types
-
-      The following source types and associated input attributes are supported.
-
-      <!-- TODO: It would be soooo much more predictable to work with (and
-      document) if `fetchTree` was a curried call with the first parameter for
-      `type` or an attribute like `builtins.fetchTree.git`! -->
-
-      - `"file"`
-
-        Place a plain file into the Nix store.
-        This is similar to [`builtins.fetchurl`](@docroot@/language/builtins.md#builtins-fetchurl)
-
-        - `url` (String, required)
-
-          Supported protocols:
-
-          - `https`
-
-            > **Example**
             >
-            > ```nix
+            > [Substituters](@docroot@/command-ref/conf-file.md#conf-substituters) are not used in fetching.
-            > fetchTree {
-            >   type = "file";
-            >   url = "https://example.com/index.html";
-            > }
-            > ```
 
-          - `http`
+          - There is no cache entry or the cache entry is older than [`tarball-ttl`](@docroot@/command-ref/conf-file.md#conf-tarball-ttl)
 
-            Insecure HTTP transfer for legacy sources.
+          ## Source types
 
-            > **Warning**
+          The following source types and associated input attributes are supported.
-            >
-            > HTTP performs no encryption or authentication.
-            > Use a `narHash` known in advance to ensure the output has expected contents.
 
-          - `file`
+          <!-- TODO: It would be soooo much more predictable to work with (and
+          document) if `fetchTree` was a curried call with the first parameter for
+          `type` or an attribute like `builtins.fetchTree.git`! -->
+        )");
 
-            A file on the local file system.
+        auto indentString = [](std::string const & str, std::string const & indent) {
+            std::string result;
+            std::istringstream stream(str);
+            std::string line;
+            bool first = true;
+            while (std::getline(stream, line)) {
+                if (!first)
+                    result += "\n";
+                result += indent + line;
+                first = false;
+            }
+            return result;
+        };
 
-            > **Example**
+        for (const auto & [schemeName, scheme] : fetchers::getAllInputSchemes()) {
-            >
+            doc += "\n- `" + quoteString(schemeName, '"') + "`\n\n";
-            > ```nix
+            doc += indentString(scheme->schemeDescription(), "  ");
-            > fetchTree {
+            if (!doc.empty() && doc.back() != '\n')
-            >   type = "file";
+                doc += "\n";
-            >   url = "file:///home/eelco/nix/README.md";
-            > }
-            > ```
 
-      - `"git"`
+            for (const auto & [attrName, attribute] : scheme->allowedAttrs()) {
+                doc += "\n  - `" + attrName + "` (" + attribute.type + ", "
+                       + (attribute.required ? "required" : "optional") + ")\n\n";
+                doc += indentString(stripIndentation(attribute.doc), "    ");
+                if (!doc.empty() && doc.back() != '\n')
+                    doc += "\n";
+            }
+        }
 
-        Fetch a Git tree and copy it to the Nix store.
+        doc += "\n" + stripIndentation(R"(
-        This is similar to [`builtins.fetchGit`](@docroot@/language/builtins.md#builtins-fetchGit).
+          The following input types are still subject to change:
 
-        - `allRefs` (Bool, optional)
+          - `"path"`
+          - `"github"`
+          - `"gitlab"`
+          - `"sourcehut"`
+          - `"mercurial"`
 
-          By default, this has no effect. This becomes relevant only once `shallow` cloning is disabled.
+         *input* can also be a [URL-like reference](@docroot@/command-ref/new-cli/nix3-flake.md#flake-references).
-
+         The additional input types and the URL-like syntax requires the [`flakes` experimental feature](@docroot@/development/experimental-features.md#xp-feature-flakes) to be enabled.
-          Whether to fetch all references (eg. branches and tags) of the repository.
-          With this argument being true, it's possible to load a `rev` from *any* `ref`.
-          (Without setting this option, only `rev`s from the specified `ref` are supported).
-
-          Default: `false`
-
-        - `lastModified` (Integer, optional)
-
-          Unix timestamp of the fetched commit.
-
-          If set, pass through the value to the output attribute set.
-          Otherwise, generated from the fetched Git tree.
-
-        - `lfs` (Bool, optional)
-
-          Fetch any [Git LFS](https://git-lfs.com/) files.
-
-          Default: `false`
-
-        - `ref` (String, optional)
-
-          By default, this has no effect. This becomes relevant only once `shallow` cloning is disabled.
-
-          A [Git reference](https://git-scm.com/book/en/v2/Git-Internals-Git-References), such as a branch or tag name.
-
-          Default: `"HEAD"`
-
-        - `rev` (String, optional)
-
-          A Git revision; a commit hash.
-
-          Default: the tip of `ref`
-
-        - `revCount` (Integer, optional)
-
-          Number of revisions in the history of the Git repository before the fetched commit.
-
-          If set, pass through the value to the output attribute set.
-          Otherwise, generated from the fetched Git tree.
-
-        - `shallow` (Bool, optional)
-
-          Make a shallow clone when fetching the Git tree.
-          When this is enabled, the options `ref` and `allRefs` have no effect anymore.
-
-          Default: `true`
-
-        - `submodules` (Bool, optional)
-
-          Also fetch submodules if available.
-
-          Default: `false`
-
-        - `url` (String, required)
-
-          The URL formats supported are the same as for Git itself.
 
           > **Example**
           >
+          > Fetch a GitHub repository using the attribute set representation:
+          >
           > ```nix
-          > fetchTree {
+          > builtins.fetchTree {
-          >   type = "git";
+          >   type = "github";
-          >   url = "git@github.com:NixOS/nixpkgs.git";
+          >   owner = "NixOS";
+          >   repo = "nixpkgs";
+          >   rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
+          > }
+          > ```
+          >
+          > This evaluates to the following attribute set:
+          >
+          > ```nix
+          > {
+          >   lastModified = 1686503798;
+          >   lastModifiedDate = "20230611171638";
+          >   narHash = "sha256-rA9RqKP9OlBrgGCPvfd5HVAXDOy8k2SmPtB/ijShNXc=";
+          >   outPath = "/nix/store/l5m6qlvfs9sdw14ja3qbzpglcjlb6j1x-source";
+          >   rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
+          >   shortRev = "ae2e6b3";
           > }
           > ```
 
-          > **Note**
+          > **Example**
           >
-          > If the URL points to a local directory, and no `ref` or `rev` is given, Nix only considers files added to the Git index, as listed by `git ls-files` but use the *current file contents* of the Git working directory.
+          > Fetch the same GitHub repository using the URL-like syntax:
+          >
+          >   ```nix
+          >   builtins.fetchTree "github:NixOS/nixpkgs/ae2e6b3958682513d28f7d633734571fb18285dd"
+          >   ```
+        )");
 
-      - `"tarball"`
+        return doc;
-
+    }(),
-        Download a tar archive and extract it into the Nix store.
-        This has the same underlying implementation as [`builtins.fetchTarball`](@docroot@/language/builtins.md#builtins-fetchTarball)
-
-        - `url` (String, required)
-
-           > **Example**
-           >
-           > ```nix
-           > fetchTree {
-           >   type = "tarball";
-           >   url = "https://github.com/NixOS/nixpkgs/tarball/nixpkgs-23.11";
-           > }
-           > ```
-
-      The following input types are still subject to change:
-
-      - `"path"`
-      - `"github"`
-      - `"gitlab"`
-      - `"sourcehut"`
-      - `"mercurial"`
-
-     *input* can also be a [URL-like reference](@docroot@/command-ref/new-cli/nix3-flake.md#flake-references).
-     The additional input types and the URL-like syntax requires the [`flakes` experimental feature](@docroot@/development/experimental-features.md#xp-feature-flakes) to be enabled.
-
-      > **Example**
-      >
-      > Fetch a GitHub repository using the attribute set representation:
-      >
-      > ```nix
-      > builtins.fetchTree {
-      >   type = "github";
-      >   owner = "NixOS";
-      >   repo = "nixpkgs";
-      >   rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
-      > }
-      > ```
-      >
-      > This evaluates to the following attribute set:
-      >
-      > ```nix
-      > {
-      >   lastModified = 1686503798;
-      >   lastModifiedDate = "20230611171638";
-      >   narHash = "sha256-rA9RqKP9OlBrgGCPvfd5HVAXDOy8k2SmPtB/ijShNXc=";
-      >   outPath = "/nix/store/l5m6qlvfs9sdw14ja3qbzpglcjlb6j1x-source";
-      >   rev = "ae2e6b3958682513d28f7d633734571fb18285dd";
-      >   shortRev = "ae2e6b3";
-      > }
-      > ```
-
-      > **Example**
-      >
-      > Fetch the same GitHub repository using the URL-like syntax:
-      >
-      >   ```nix
-      >   builtins.fetchTree "github:NixOS/nixpkgs/ae2e6b3958682513d28f7d633734571fb18285dd"
-      >   ```
-    )"_sds,
     .fun = prim_fetchTree,
     .experimentalFeature = Xp::FetchTree,
 });
@@ -583,10 +480,10 @@ static void fetch(
     auto storePath = unpack ? fetchToStore(
                                   state.fetchSettings,
                                   *state.store,
-                                  fetchers::downloadTarball(state.store, state.fetchSettings, *url),
+                                  fetchers::downloadTarball(*state.store, state.fetchSettings, *url),
                                   FetchMode::Copy,
                                   name)
-                            : fetchers::downloadFile(state.store, state.fetchSettings, *url, name).storePath;
+                            : fetchers::downloadFile(*state.store, state.fetchSettings, *url, name).storePath;
 
     if (expectedHash) {
         auto hash = unpack ? state.store->queryPathInfo(storePath)->narHash
@@ -618,7 +515,7 @@ static void prim_fetchurl(EvalState & state, const PosIdx pos, Value ** args, Va
 static RegisterPrimOp primop_fetchurl({
     .name = "__fetchurl",
     .args = {"arg"},
-    .doc = &R"(
+    .doc = R"(
       Download the specified URL and return the path of the downloaded file.
       `arg` can be either a string denoting the URL, or an attribute set with the following attributes:
 
@@ -632,7 +529,7 @@ static RegisterPrimOp primop_fetchurl({
         characters that are invalid for the store.
 
       Not available in [restricted evaluation mode](@docroot@/command-ref/conf-file.md#conf-restrict-eval).
-    )"_sds,
+    )",
     .fun = prim_fetchurl,
 });
 
@@ -644,7 +541,7 @@ static void prim_fetchTarball(EvalState & state, const PosIdx pos, Value ** args
 static RegisterPrimOp primop_fetchTarball({
     .name = "fetchTarball",
     .args = {"args"},
-    .doc = &R"(
+    .doc = R"(
       Download the specified URL, unpack it and return the path of the
       unpacked tree. The file must be a tape archive (`.tar`) compressed
       with `gzip`, `bzip2` or `xz`. If the tarball consists of a
@@ -682,7 +579,7 @@ static RegisterPrimOp primop_fetchTarball({
       ```
 
       Not available in [restricted evaluation mode](@docroot@/command-ref/conf-file.md#conf-restrict-eval).
-    )"_sds,
+    )",
     .fun = prim_fetchTarball,
 });
 
@@ -695,7 +592,7 @@ static void prim_fetchGit(EvalState & state, const PosIdx pos, Value ** args, Va
 static RegisterPrimOp primop_fetchGit({
     .name = "fetchGit",
     .args = {"args"},
-    .doc = &R"(
+    .doc = R"(
       Fetch a path from git. *args* can be a URL, in which case the HEAD
       of the repo at that URL is fetched. Otherwise, it can be an
       attribute with the following attributes (all except `url` optional):
@@ -898,7 +795,7 @@ static RegisterPrimOp primop_fetchGit({
       given, `fetchGit` uses the current content of the checked-out
       files, even if they are not committed or added to Git's index. It
       only considers files added to the Git repository, as listed by `git ls-files`.
-    )"_sds,
+    )",
     .fun = prim_fetchGit,
 });
 

src/libexpr/primops/fromTOML.cc

@@ -1,6 +1,6 @@
 #include "nix/expr/primops.hh"
 #include "nix/expr/eval-inline.hh"
-#include "nix/expr/string-data-static.hh"
+#include "nix/expr/static-string-data.hh"
 
 #include "expr-config-private.hh"
 
@@ -170,10 +170,10 @@ static void prim_fromTOML(EvalState & state, const PosIdx pos, Value ** args, Va
     }
 }
 
-static RegisterPrimOp primop_fromTOML({
+static RegisterPrimOp primop_fromTOML(
-    .name = "fromTOML",
+    {.name = "fromTOML",
-    .args = {"e"},
+     .args = {"e"},
-    .doc = &R"(
+     .doc = R"(
       Convert a TOML string to a Nix value. For example,
 
       ```nix
@@ -186,8 +186,7 @@ static RegisterPrimOp primop_fromTOML({
       ```
 
       returns the value `{ s = "a"; table = { y = 2; }; x = 1; }`.
-    )"_sds,
+    )",
-    .fun = prim_fromTOML,
+     .fun = prim_fromTOML});
-});
 
 } // namespace nix

src/libfetchers-tests/git.cc

@@ -196,7 +196,7 @@ TEST_F(GitTest, submodulePeriodSupport)
             {"ref", "main"},
         });
 
-    auto [accessor, i] = input.getAccessor(settings, store);
+    auto [accessor, i] = input.getAccessor(settings, *store);
 
     ASSERT_EQ(accessor->readFile(CanonPath("deps/sub/lib.txt")), "hello from submodule\n");
 }

src/libfetchers/fetchers.cc

@@ -6,6 +6,7 @@
 #include "nix/fetchers/fetch-settings.hh"
 #include "nix/fetchers/fetch-to-store.hh"
 #include "nix/util/url.hh"
+#include "nix/util/archive.hh"
 
 #include <nlohmann/json.hpp>
 
@@ -26,18 +27,9 @@ void registerInputScheme(std::shared_ptr<InputScheme> && inputScheme)
         throw Error("Input scheme with name %s already registered", schemeName);
 }
 
-nlohmann::json dumpRegisterInputSchemeInfo()
+const InputSchemeMap & getAllInputSchemes()
 {
-    using nlohmann::json;
+    return inputSchemes();
-
-    auto res = json::object();
-
-    for (auto & [name, scheme] : inputSchemes()) {
-        auto & r = res[name] = json::object();
-        r["allowedAttrs"] = scheme->allowedAttrs();
-    }
-
-    return res;
 }
 
 Input Input::fromURL(const Settings & settings, const std::string & url, bool requireTree)
@@ -119,7 +111,7 @@ Input Input::fromAttrs(const Settings & settings, Attrs && attrs)
     return std::move(*res);
 }
 
-std::optional<std::string> Input::getFingerprint(ref<Store> store) const
+std::optional<std::string> Input::getFingerprint(Store & store) const
 {
     if (!scheme)
         return std::nullopt;
@@ -198,7 +190,7 @@ bool Input::contains(const Input & other) const
 }
 
 // FIXME: remove
-std::pair<StorePath, Input> Input::fetchToStore(const Settings & settings, ref<Store> store) const
+std::pair<StorePath, Input> Input::fetchToStore(const Settings & settings, Store & store) const
 {
     if (!scheme)
         throw Error("cannot fetch unsupported input '%s'", attrsToJSON(toAttrs()));
@@ -208,9 +200,9 @@ std::pair<StorePath, Input> Input::fetchToStore(const Settings & settings, ref<S
             auto [accessor, result] = getAccessorUnchecked(settings, store);
 
             auto storePath =
-                nix::fetchToStore(settings, *store, SourcePath(accessor), FetchMode::Copy, result.getName());
+                nix::fetchToStore(settings, store, SourcePath(accessor), FetchMode::Copy, result.getName());
 
-            auto narHash = store->queryPathInfo(storePath)->narHash;
+            auto narHash = store.queryPathInfo(storePath)->narHash;
             result.attrs.insert_or_assign("narHash", narHash.to_string(HashFormat::SRI, true));
 
             result.attrs.insert_or_assign("__final", Explicit<bool>(true));
@@ -297,7 +289,7 @@ void Input::checkLocks(Input specified, Input & result)
     }
 }
 
-std::pair<ref<SourceAccessor>, Input> Input::getAccessor(const Settings & settings, ref<Store> store) const
+std::pair<ref<SourceAccessor>, Input> Input::getAccessor(const Settings & settings, Store & store) const
 {
     try {
         auto [accessor, result] = getAccessorUnchecked(settings, store);
@@ -313,7 +305,7 @@ std::pair<ref<SourceAccessor>, Input> Input::getAccessor(const Settings & settin
     }
 }
 
-std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(const Settings & settings, ref<Store> store) const
+std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(const Settings & settings, Store & store) const
 {
     // FIXME: cache the accessor
 
@@ -333,13 +325,13 @@ std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(const Settings
     */
     if (isFinal() && getNarHash()) {
         try {
-            auto storePath = computeStorePath(*store);
+            auto storePath = computeStorePath(store);
 
-            store->ensurePath(storePath);
+            store.ensurePath(storePath);
 
-            debug("using substituted/cached input '%s' in '%s'", to_string(), store->printStorePath(storePath));
+            debug("using substituted/cached input '%s' in '%s'", to_string(), store.printStorePath(storePath));
 
-            auto accessor = store->requireStoreObjectAccessor(storePath);
+            auto accessor = store.requireStoreObjectAccessor(storePath);
 
             accessor->fingerprint = getFingerprint(store);
 
@@ -349,7 +341,7 @@ std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(const Settings
             if (accessor->fingerprint) {
                 ContentAddressMethod method = ContentAddressMethod::Raw::NixArchive;
                 auto cacheKey = makeFetchToStoreCacheKey(getName(), *accessor->fingerprint, method, "/");
-                settings.getCache()->upsert(cacheKey, *store, {}, storePath);
+                settings.getCache()->upsert(cacheKey, store, {}, storePath);
             }
 
             accessor->setPathDisplay("«" + to_string() + "»");
@@ -377,10 +369,10 @@ Input Input::applyOverrides(std::optional<std::string> ref, std::optional<Hash>
     return scheme->applyOverrides(*this, ref, rev);
 }
 
-void Input::clone(const Settings & settings, const Path & destDir) const
+void Input::clone(const Settings & settings, Store & store, const std::filesystem::path & destDir) const
 {
     assert(scheme);
-    scheme->clone(settings, *this, destDir);
+    scheme->clone(settings, store, *this, destDir);
 }
 
 std::optional<std::filesystem::path> Input::getSourcePath() const
@@ -493,9 +485,19 @@ void InputScheme::putFile(
     throw Error("input '%s' does not support modifying file '%s'", input.to_string(), path);
 }
 
-void InputScheme::clone(const Settings & settings, const Input & input, const Path & destDir) const
+void InputScheme::clone(
+    const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir) const
 {
-    throw Error("do not know how to clone input '%s'", input.to_string());
+    if (std::filesystem::exists(destDir))
+        throw Error("cannot clone into existing path %s", destDir);
+
+    auto [accessor, input2] = getAccessor(settings, store, input);
+
+    Activity act(*logger, lvlTalkative, actUnknown, fmt("copying '%s' to %s...", input2.to_string(), destDir));
+
+    auto source = sinkToSource([&](Sink & sink) { accessor->dumpPath(CanonPath::root, sink); });
+
+    restorePath(destDir, *source);
 }
 
 std::optional<ExperimentalFeature> InputScheme::experimentalFeature() const

src/libfetchers/git-lfs-fetch.cc

@@ -209,7 +209,7 @@ std::vector<nlohmann::json> Fetch::fetchUrls(const std::vector<Pointer> & pointe
     auto url = api.endpoint + "/objects/batch";
     const auto & authHeader = api.authHeader;
     FileTransferRequest request(parseURL(url));
-    request.method = HttpMethod::POST;
+    request.method = HttpMethod::Post;
     Headers headers;
     if (authHeader.has_value())
         headers.push_back({"Authorization", *authHeader});

src/libfetchers/git.cc

@@ -194,28 +194,183 @@ struct GitInputScheme : InputScheme
         return "git";
     }
 
-    StringSet allowedAttrs() const override
+    std::string schemeDescription() const override
     {
-        return {
+        return stripIndentation(R"(
-            "url",
+          Fetch a Git tree and copy it to the Nix store.
-            "ref",
+          This is similar to [`builtins.fetchGit`](@docroot@/language/builtins.md#builtins-fetchGit).
-            "rev",
+        )");
-            "shallow",
+    }
-            "submodules",
+
-            "lfs",
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
-            "exportIgnore",
+    {
-            "lastModified",
+        static const std::map<std::string, AttributeInfo> attrs = {
-            "revCount",
+            {
-            "narHash",
+                "url",
-            "allRefs",
+                {
-            "name",
+                    .type = "String",
-            "dirtyRev",
+                    .required = true,
-            "dirtyShortRev",
+                    .doc = R"(
-            "verifyCommit",
+                      The URL formats supported are the same as for Git itself.
-            "keytype",
+
-            "publicKey",
+                      > **Example**
-            "publicKeys",
+                      >
+                      > ```nix
+                      > fetchTree {
+                      >   type = "git";
+                      >   url = "git@github.com:NixOS/nixpkgs.git";
+                      > }
+                      > ```
+
+                      > **Note**
+                      >
+                      > If the URL points to a local directory, and no `ref` or `rev` is given, Nix only considers files added to the Git index, as listed by `git ls-files` but uses the *current file contents* of the Git working directory.
+                    )",
+                },
+            },
+            {
+                "ref",
+                {
+                    .type = "String",
+                    .required = false,
+                    .doc = R"(
+                      By default, this has no effect. This becomes relevant only once `shallow` cloning is disabled.
+
+                      A [Git reference](https://git-scm.com/book/en/v2/Git-Internals-Git-References), such as a branch or tag name.
+
+                      Default: `"HEAD"`
+                    )",
+                },
+            },
+            {
+                "rev",
+                {
+                    .type = "String",
+                    .required = false,
+                    .doc = R"(
+                      A Git revision; a commit hash.
+
+                      Default: the tip of `ref`
+                    )",
+                },
+            },
+            {
+                "shallow",
+                {
+                    .type = "Bool",
+                    .required = false,
+                    .doc = R"(
+                      Make a shallow clone when fetching the Git tree.
+                      When this is enabled, the options `ref` and `allRefs` have no effect anymore.
+
+                      Default: `true`
+                    )",
+                },
+            },
+            {
+                "submodules",
+                {
+                    .type = "Bool",
+                    .required = false,
+                    .doc = R"(
+                      Also fetch submodules if available.
+
+                      Default: `false`
+                    )",
+                },
+            },
+            {
+                "lfs",
+                {
+                    .type = "Bool",
+                    .required = false,
+                    .doc = R"(
+                      Fetch any [Git LFS](https://git-lfs.com/) files.
+
+                      Default: `false`
+                    )",
+                },
+            },
+            {
+                "exportIgnore",
+                {},
+            },
+            {
+                "lastModified",
+                {
+                    .type = "Integer",
+                    .required = false,
+                    .doc = R"(
+                      Unix timestamp of the fetched commit.
+
+                      If set, pass through the value to the output attribute set.
+                      Otherwise, generated from the fetched Git tree.
+                    )",
+                },
+            },
+            {
+                "revCount",
+                {
+                    .type = "Integer",
+                    .required = false,
+                    .doc = R"(
+                      Number of revisions in the history of the Git repository before the fetched commit.
+
+                      If set, pass through the value to the output attribute set.
+                      Otherwise, generated from the fetched Git tree.
+                    )",
+                },
+            },
+            {
+                "narHash",
+                {},
+            },
+            {
+                "allRefs",
+                {
+                    .type = "Bool",
+                    .required = false,
+                    .doc = R"(
+                      By default, this has no effect. This becomes relevant only once `shallow` cloning is disabled.
+
+                      Whether to fetch all references (eg. branches and tags) of the repository.
+                      With this argument being true, it's possible to load a `rev` from *any* `ref`.
+                      (Without setting this option, only `rev`s from the specified `ref` are supported).
+
+                      Default: `false`
+                    )",
+                },
+            },
+            {
+                "name",
+                {},
+            },
+            {
+                "dirtyRev",
+                {},
+            },
+            {
+                "dirtyShortRev",
+                {},
+            },
+            {
+                "verifyCommit",
+                {},
+            },
+            {
+                "keytype",
+                {},
+            },
+            {
+                "publicKey",
+                {},
+            },
+            {
+                "publicKeys",
+                {},
+            },
         };
+        return attrs;
     }
 
     std::optional<Input> inputFromAttrs(const Settings & settings, const Attrs & attrs) const override
@@ -278,7 +433,8 @@ struct GitInputScheme : InputScheme
         return res;
     }
 
-    void clone(const Settings & settings, const Input & input, const Path & destDir) const override
+    void clone(const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto repoInfo = getRepoInfo(input);
 
@@ -623,7 +779,7 @@ struct GitInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessorFromCommit(const Settings & settings, ref<Store> store, RepoInfo & repoInfo, Input && input) const
+    getAccessorFromCommit(const Settings & settings, Store & store, RepoInfo & repoInfo, Input && input) const
     {
         assert(!repoInfo.workdirInfo.isDirty);
 
@@ -797,7 +953,7 @@ struct GitInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessorFromWorkdir(const Settings & settings, ref<Store> store, RepoInfo & repoInfo, Input && input) const
+    getAccessorFromWorkdir(const Settings & settings, Store & store, RepoInfo & repoInfo, Input && input) const
     {
         auto repoPath = repoInfo.getPath().value();
 
@@ -881,7 +1037,7 @@ struct GitInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         Input input(_input);
 
@@ -903,7 +1059,7 @@ struct GitInputScheme : InputScheme
         return {accessor, std::move(final)};
     }
 
-    std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
+    std::optional<std::string> getFingerprint(Store & store, const Input & input) const override
     {
         auto makeFingerprint = [&](const Hash & rev) {
             return rev.gitRev() + (getSubmodulesAttr(input) ? ";s" : "") + (getExportIgnoreAttr(input) ? ";e" : "")

src/libfetchers/github.cc

@@ -110,18 +110,43 @@ struct GitArchiveInputScheme : InputScheme
         return input;
     }
 
-    StringSet allowedAttrs() const override
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
     {
-        return {
+        static const std::map<std::string, AttributeInfo> attrs = {
-            "owner",
+            {
-            "repo",
+                "owner",
-            "ref",
+                {},
-            "rev",
+            },
-            "narHash",
+            {
-            "lastModified",
+                "repo",
-            "host",
+                {},
-            "treeHash",
+            },
+            {
+                "ref",
+                {},
+            },
+            {
+                "rev",
+                {},
+            },
+            {
+                "narHash",
+                {},
+            },
+            {
+                "lastModified",
+                {},
+            },
+            {
+                "host",
+                {},
+            },
+            {
+                "treeHash",
+                {},
+            },
         };
+        return attrs;
     }
 
     std::optional<Input> inputFromAttrs(const fetchers::Settings & settings, const Attrs & attrs) const override
@@ -233,7 +258,7 @@ struct GitArchiveInputScheme : InputScheme
         std::optional<Hash> treeHash;
     };
 
-    virtual RefInfo getRevFromRef(const Settings & settings, nix::ref<Store> store, const Input & input) const = 0;
+    virtual RefInfo getRevFromRef(const Settings & settings, nix::Store & store, const Input & input) const = 0;
 
     virtual DownloadUrl getDownloadUrl(const Settings & settings, const Input & input) const = 0;
 
@@ -243,7 +268,7 @@ struct GitArchiveInputScheme : InputScheme
         time_t lastModified;
     };
 
-    std::pair<Input, TarballInfo> downloadArchive(const Settings & settings, ref<Store> store, Input input) const
+    std::pair<Input, TarballInfo> downloadArchive(const Settings & settings, Store & store, Input input) const
     {
         if (!maybeGetStrAttr(input.attrs, "ref"))
             input.attrs.insert_or_assign("ref", "HEAD");
@@ -316,7 +341,7 @@ struct GitArchiveInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         auto [input, tarballInfo] = downloadArchive(settings, store, _input);
 
@@ -345,7 +370,7 @@ struct GitArchiveInputScheme : InputScheme
         return Xp::Flakes;
     }
 
-    std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
+    std::optional<std::string> getFingerprint(Store & store, const Input & input) const override
     {
         if (auto rev = input.getRev())
             return rev->gitRev();
@@ -361,6 +386,12 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return "github";
     }
 
+    std::string schemeDescription() const override
+    {
+        // TODO
+        return "";
+    }
+
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
         // Github supports PAT/OAuth2 tokens and HTTP Basic
@@ -387,7 +418,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return getStrAttr(input.attrs, "repo");
     }
 
-    RefInfo getRevFromRef(const Settings & settings, nix::ref<Store> store, const Input & input) const override
+    RefInfo getRevFromRef(const Settings & settings, nix::Store & store, const Input & input) const override
     {
         auto host = getHost(input);
         auto url = fmt(
@@ -401,7 +432,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
 
         auto downloadResult = downloadFile(store, settings, url, "source", headers);
         auto json = nlohmann::json::parse(
-            store->requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
+            store.requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
 
         return RefInfo{
             .rev = Hash::parseAny(std::string{json["sha"]}, HashAlgorithm::SHA1),
@@ -426,12 +457,13 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const Path & destDir) const override
+    void clone(const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = getHost(input);
         Input::fromURL(settings, fmt("git+https://%s/%s/%s.git", host, getOwner(input), getRepo(input)))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 
@@ -442,6 +474,12 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return "gitlab";
     }
 
+    std::string schemeDescription() const override
+    {
+        // TODO
+        return "";
+    }
+
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
         // Gitlab supports 4 kinds of authorization, two of which are
@@ -461,7 +499,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return std::make_pair(token.substr(0, fldsplit), token.substr(fldsplit + 1));
     }
 
-    RefInfo getRevFromRef(const Settings & settings, nix::ref<Store> store, const Input & input) const override
+    RefInfo getRevFromRef(const Settings & settings, nix::Store & store, const Input & input) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // See rate limiting note below
@@ -476,7 +514,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
 
         auto downloadResult = downloadFile(store, settings, url, "source", headers);
         auto json = nlohmann::json::parse(
-            store->requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
+            store.requireStoreObjectAccessor(downloadResult.storePath)->readFile(CanonPath::root));
 
         if (json.is_array() && json.size() >= 1 && json[0]["id"] != nullptr) {
             return RefInfo{.rev = Hash::parseAny(std::string(json[0]["id"]), HashAlgorithm::SHA1)};
@@ -507,7 +545,8 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const Path & destDir) const override
+    void clone(const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // FIXME: get username somewhere
@@ -515,7 +554,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
             settings,
             fmt("git+https://%s/%s/%s.git", host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 
@@ -526,6 +565,12 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         return "sourcehut";
     }
 
+    std::string schemeDescription() const override
+    {
+        // TODO
+        return "";
+    }
+
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
         // SourceHut supports both PAT and OAuth2. See
@@ -536,7 +581,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         // Once it is implemented, however, should work as expected.
     }
 
-    RefInfo getRevFromRef(const Settings & settings, nix::ref<Store> store, const Input & input) const override
+    RefInfo getRevFromRef(const Settings & settings, nix::Store & store, const Input & input) const override
     {
         // TODO: In the future, when the sourcehut graphql API is implemented for mercurial
         // and with anonymous access, this method should use it instead.
@@ -552,7 +597,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         std::string refUri;
         if (ref == "HEAD") {
             auto downloadFileResult = downloadFile(store, settings, fmt("%s/HEAD", base_url), "source", headers);
-            auto contents = store->requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
+            auto contents = store.requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
 
             auto remoteLine = git::parseLsRemoteLine(getLine(contents).first);
             if (!remoteLine) {
@@ -565,7 +610,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         std::regex refRegex(refUri);
 
         auto downloadFileResult = downloadFile(store, settings, fmt("%s/info/refs", base_url), "source", headers);
-        auto contents = store->requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
+        auto contents = store.requireStoreObjectAccessor(downloadFileResult.storePath)->readFile(CanonPath::root);
         std::istringstream is(contents);
 
         std::string line;
@@ -596,14 +641,15 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         return DownloadUrl{parseURL(url), headers};
     }
 
-    void clone(const Settings & settings, const Input & input, const Path & destDir) const override
+    void clone(const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir)
+        const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("git.sr.ht");
         Input::fromURL(
             settings,
             fmt("git+https://%s/%s/%s", host, getStrAttr(input.attrs, "owner"), getStrAttr(input.attrs, "repo")))
             .applyOverrides(input.getRef(), input.getRev())
-            .clone(settings, destDir);
+            .clone(settings, store, destDir);
     }
 };
 

src/libfetchers/include/nix/fetchers/fetchers.hh

@@ -113,7 +113,7 @@ public:
      * Fetch the entire input into the Nix store, returning the
      * location in the Nix store and the locked input.
      */
-    std::pair<StorePath, Input> fetchToStore(const Settings & settings, ref<Store> store) const;
+    std::pair<StorePath, Input> fetchToStore(const Settings & settings, Store & store) const;
 
     /**
      * Check the locking attributes in `result` against
@@ -133,17 +133,17 @@ public:
      * input without copying it to the store. Also return a possibly
      * unlocked input.
      */
-    std::pair<ref<SourceAccessor>, Input> getAccessor(const Settings & settings, ref<Store> store) const;
+    std::pair<ref<SourceAccessor>, Input> getAccessor(const Settings & settings, Store & store) const;
 
 private:
 
-    std::pair<ref<SourceAccessor>, Input> getAccessorUnchecked(const Settings & settings, ref<Store> store) const;
+    std::pair<ref<SourceAccessor>, Input> getAccessorUnchecked(const Settings & settings, Store & store) const;
 
 public:
 
     Input applyOverrides(std::optional<std::string> ref, std::optional<Hash> rev) const;
 
-    void clone(const Settings & settings, const Path & destDir) const;
+    void clone(const Settings & settings, Store & store, const std::filesystem::path & destDir) const;
 
     std::optional<std::filesystem::path> getSourcePath() const;
 
@@ -173,7 +173,7 @@ public:
      *
      * This is not a stable identifier between Nix versions, but not guaranteed to change either.
      */
-    std::optional<std::string> getFingerprint(ref<Store> store) const;
+    std::optional<std::string> getFingerprint(Store & store) const;
 };
 
 /**
@@ -203,20 +203,34 @@ struct InputScheme
      */
     virtual std::string_view schemeName() const = 0;
 
+    /**
+     * Longform description of this scheme, for documentation purposes.
+     */
+    virtual std::string schemeDescription() const = 0;
+
+    // TODO remove these defaults
+    struct AttributeInfo
+    {
+        const char * type = "String";
+        bool required = true;
+        const char * doc = "";
+    };
+
     /**
      * Allowed attributes in an attribute set that is converted to an
-     * input.
+     * input, and documentation for each attribute.
      *
-     * `type` is not included from this set, because the `type` field is
+     * `type` is not included from this map, because the `type` field is
       parsed first to choose which scheme; `type` is always required.
      */
-    virtual StringSet allowedAttrs() const = 0;
+    virtual const std::map<std::string, AttributeInfo> & allowedAttrs() const = 0;
 
     virtual ParsedURL toURL(const Input & input) const;
 
     virtual Input applyOverrides(const Input & input, std::optional<std::string> ref, std::optional<Hash> rev) const;
 
-    virtual void clone(const Settings & settings, const Input & input, const Path & destDir) const;
+    virtual void
+    clone(const Settings & settings, Store & store, const Input & input, const std::filesystem::path & destDir) const;
 
     virtual std::optional<std::filesystem::path> getSourcePath(const Input & input) const;
 
@@ -227,7 +241,7 @@ struct InputScheme
         std::optional<std::string> commitMsg) const;
 
     virtual std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & input) const = 0;
+    getAccessor(const Settings & settings, Store & store, const Input & input) const = 0;
 
     /**
      * Is this `InputScheme` part of an experimental feature?
@@ -239,7 +253,7 @@ struct InputScheme
         return true;
     }
 
-    virtual std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const
+    virtual std::optional<std::string> getFingerprint(Store & store, const Input & input) const
     {
         return std::nullopt;
     }
@@ -263,7 +277,12 @@ struct InputScheme
 
 void registerInputScheme(std::shared_ptr<InputScheme> && fetcher);
 
-nlohmann::json dumpRegisterInputSchemeInfo();
+using InputSchemeMap = std::map<std::string_view, std::shared_ptr<InputScheme>>;
+
+/**
+ * Use this for docs, not for finding a specific scheme
+ */
+const InputSchemeMap & getAllInputSchemes();
 
 struct PublicKey
 {

src/libfetchers/include/nix/fetchers/input-cache.hh

@@ -16,7 +16,7 @@ struct InputCache
     };
 
     CachedResult
-    getAccessor(const Settings & settings, ref<Store> store, const Input & originalInput, UseRegistries useRegistries);
+    getAccessor(const Settings & settings, Store & store, const Input & originalInput, UseRegistries useRegistries);
 
     struct CachedInput
     {

src/libfetchers/include/nix/fetchers/registry.hh

@@ -13,8 +13,6 @@ namespace nix::fetchers {
 
 struct Registry
 {
-    const Settings & settings;
-
     enum RegistryType {
         Flag = 0,
         User = 1,
@@ -34,9 +32,8 @@ struct Registry
 
     std::vector<Entry> entries;
 
-    Registry(const Settings & settings, RegistryType type)
+    Registry(RegistryType type)
-        : settings{settings}
+        : type{type}
-        , type{type}
     {
     }
 
@@ -57,9 +54,9 @@ std::shared_ptr<Registry> getCustomRegistry(const Settings & settings, const Pat
 
 Path getUserRegistryPath();
 
-Registries getRegistries(const Settings & settings, ref<Store> store);
+Registries getRegistries(const Settings & settings, Store & store);
 
-void overrideRegistry(const Settings & settings, const Input & from, const Input & to, const Attrs & extraAttrs);
+void overrideRegistry(const Input & from, const Input & to, const Attrs & extraAttrs);
 
 enum class UseRegistries : int {
     No,
@@ -72,6 +69,6 @@ enum class UseRegistries : int {
  * use the registries for which the filter function returns true.
  */
 std::pair<Input, Attrs>
-lookupInRegistries(const Settings & settings, ref<Store> store, const Input & input, UseRegistries useRegistries);
+lookupInRegistries(const Settings & settings, Store & store, const Input & input, UseRegistries useRegistries);
 
 } // namespace nix::fetchers

src/libfetchers/include/nix/fetchers/tarball.hh

@@ -25,7 +25,7 @@ struct DownloadFileResult
 };
 
 DownloadFileResult downloadFile(
-    ref<Store> store,
+    Store & store,
     const Settings & settings,
     const std::string & url,
     const std::string & name,
@@ -43,6 +43,6 @@ struct DownloadTarballResult
  * Download and import a tarball into the Git cache. The result is the
  * Git tree hash of the root directory.
  */
-ref<SourceAccessor> downloadTarball(ref<Store> store, const Settings & settings, const std::string & url);
+ref<SourceAccessor> downloadTarball(Store & store, const Settings & settings, const std::string & url);
 
 } // namespace nix::fetchers

src/libfetchers/indirect.cc

@@ -60,14 +60,33 @@ struct IndirectInputScheme : InputScheme
         return "indirect";
     }
 
-    StringSet allowedAttrs() const override
+    std::string schemeDescription() const override
     {
-        return {
+        // TODO
-            "id",
+        return "";
-            "ref",
+    }
-            "rev",
+
-            "narHash",
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
+    {
+        static const std::map<std::string, AttributeInfo> attrs = {
+            {
+                "id",
+                {},
+            },
+            {
+                "ref",
+                {},
+            },
+            {
+                "rev",
+                {},
+            },
+            {
+                "narHash",
+                {},
+            },
         };
+        return attrs;
     }
 
     std::optional<Input> inputFromAttrs(const Settings & settings, const Attrs & attrs) const override
@@ -107,7 +126,7 @@ struct IndirectInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & input) const override
     {
         throw Error("indirect input '%s' cannot be fetched directly", input.to_string());
     }

src/libfetchers/input-cache.cc

@@ -6,7 +6,7 @@
 namespace nix::fetchers {
 
 InputCache::CachedResult InputCache::getAccessor(
-    const Settings & settings, ref<Store> store, const Input & originalInput, UseRegistries useRegistries)
+    const Settings & settings, Store & store, const Input & originalInput, UseRegistries useRegistries)
 {
     auto fetched = lookup(originalInput);
     Input resolvedInput = originalInput;

src/libfetchers/mercurial.cc

@@ -68,16 +68,41 @@ struct MercurialInputScheme : InputScheme
         return "hg";
     }
 
-    StringSet allowedAttrs() const override
+    std::string schemeDescription() const override
     {
-        return {
+        // TODO
-            "url",
+        return "";
-            "ref",
+    }
-            "rev",
+
-            "revCount",
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
-            "narHash",
+    {
-            "name",
+        static const std::map<std::string, AttributeInfo> attrs = {
+            {
+                "url",
+                {},
+            },
+            {
+                "ref",
+                {},
+            },
+            {
+                "rev",
+                {},
+            },
+            {
+                "revCount",
+                {},
+            },
+            {
+                "narHash",
+                {},
+            },
+            {
+                "name",
+                {},
+            },
         };
+        return attrs;
     }
 
     std::optional<Input> inputFromAttrs(const Settings & settings, const Attrs & attrs) const override
@@ -154,7 +179,7 @@ struct MercurialInputScheme : InputScheme
         return {isLocal, isLocal ? renderUrlPathEnsureLegal(url.path) : url.to_string()};
     }
 
-    StorePath fetchToStore(const Settings & settings, ref<Store> store, Input & input) const
+    StorePath fetchToStore(const Settings & settings, Store & store, Input & input) const
     {
         auto origRev = input.getRev();
 
@@ -205,7 +230,7 @@ struct MercurialInputScheme : InputScheme
                     return files.count(file);
                 };
 
-                auto storePath = store->addToStore(
+                auto storePath = store.addToStore(
                     input.getName(),
                     {getFSSourceAccessor(), CanonPath(actualPath)},
                     ContentAddressMethod::Raw::NixArchive,
@@ -226,7 +251,7 @@ struct MercurialInputScheme : InputScheme
                     "Hash '%s' is not supported by Mercurial. Only sha1 is supported.",
                     rev.to_string(HashFormat::Base16, true));
 
-            return Cache::Key{"hgRev", {{"store", store->storeDir}, {"name", name}, {"rev", input.getRev()->gitRev()}}};
+            return Cache::Key{"hgRev", {{"store", store.storeDir}, {"name", name}, {"rev", input.getRev()->gitRev()}}};
         };
 
         auto makeResult = [&](const Attrs & infoAttrs, const StorePath & storePath) -> StorePath {
@@ -246,7 +271,7 @@ struct MercurialInputScheme : InputScheme
 
         /* If we have a rev, check if we have a cached store path. */
         if (auto rev = input.getRev()) {
-            if (auto res = settings.getCache()->lookupStorePath(revInfoKey(*rev), *store))
+            if (auto res = settings.getCache()->lookupStorePath(revInfoKey(*rev), store))
                 return makeResult(res->value, res->storePath);
         }
 
@@ -300,7 +325,7 @@ struct MercurialInputScheme : InputScheme
 
         /* Now that we have the rev, check the cache again for a
            cached store path. */
-        if (auto res = settings.getCache()->lookupStorePath(revInfoKey(rev), *store))
+        if (auto res = settings.getCache()->lookupStorePath(revInfoKey(rev), store))
             return makeResult(res->value, res->storePath);
 
         Path tmpDir = createTempDir();
@@ -310,7 +335,7 @@ struct MercurialInputScheme : InputScheme
 
         deletePath(tmpDir + "/.hg_archival.txt");
 
-        auto storePath = store->addToStore(name, {getFSSourceAccessor(), CanonPath(tmpDir)});
+        auto storePath = store.addToStore(name, {getFSSourceAccessor(), CanonPath(tmpDir)});
 
         Attrs infoAttrs({
             {"revCount", (uint64_t) revCount},
@@ -319,18 +344,18 @@ struct MercurialInputScheme : InputScheme
         if (!origRev)
             settings.getCache()->upsert(refToRevKey, {{"rev", rev.gitRev()}});
 
-        settings.getCache()->upsert(revInfoKey(rev), *store, infoAttrs, storePath);
+        settings.getCache()->upsert(revInfoKey(rev), store, infoAttrs, storePath);
 
         return makeResult(infoAttrs, std::move(storePath));
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         Input input(_input);
 
         auto storePath = fetchToStore(settings, store, input);
-        auto accessor = store->requireStoreObjectAccessor(storePath);
+        auto accessor = store.requireStoreObjectAccessor(storePath);
 
         accessor->setPathDisplay("«" + input.to_string() + "»");
 
@@ -342,7 +367,7 @@ struct MercurialInputScheme : InputScheme
         return (bool) input.getRev();
     }
 
-    std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
+    std::optional<std::string> getFingerprint(Store & store, const Input & input) const override
     {
         if (auto rev = input.getRev())
             return rev->gitRev();

src/libfetchers/path.cc

@@ -40,20 +40,42 @@ struct PathInputScheme : InputScheme
         return "path";
     }
 
-    StringSet allowedAttrs() const override
+    std::string schemeDescription() const override
     {
-        return {
+        // TODO
-            "path",
+        return "";
+    }
+
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
+    {
+        static const std::map<std::string, AttributeInfo> attrs = {
+            {
+                "path",
+                {},
+            },
             /* Allow the user to pass in "fake" tree info
                attributes. This is useful for making a pinned tree work
                the same as the repository from which is exported (e.g.
                path:/nix/store/...-source?lastModified=1585388205&rev=b0c285...).
              */
-            "rev",
+            {
-            "revCount",
+                "rev",
-            "lastModified",
+                {},
-            "narHash",
+            },
+            {
+                "revCount",
+                {},
+            },
+            {
+                "lastModified",
+                {},
+            },
+            {
+                "narHash",
+                {},
+            },
         };
+        return attrs;
     }
 
     std::optional<Input> inputFromAttrs(const Settings & settings, const Attrs & attrs) const override
@@ -117,7 +139,7 @@ struct PathInputScheme : InputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         Input input(_input);
         auto path = getStrAttr(input.attrs, "path");
@@ -125,31 +147,31 @@ struct PathInputScheme : InputScheme
         auto absPath = getAbsPath(input);
 
         // FIXME: check whether access to 'path' is allowed.
-        auto storePath = store->maybeParseStorePath(absPath.string());
+        auto storePath = store.maybeParseStorePath(absPath.string());
 
         if (storePath)
-            store->addTempRoot(*storePath);
+            store.addTempRoot(*storePath);
 
         time_t mtime = 0;
-        if (!storePath || storePath->name() != "source" || !store->isValidPath(*storePath)) {
+        if (!storePath || storePath->name() != "source" || !store.isValidPath(*storePath)) {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying %s to the store", absPath));
             // FIXME: try to substitute storePath.
             auto src = sinkToSource(
                 [&](Sink & sink) { mtime = dumpPathAndGetMtime(absPath.string(), sink, defaultPathFilter); });
-            storePath = store->addToStoreFromDump(*src, "source");
+            storePath = store.addToStoreFromDump(*src, "source");
         }
 
-        auto accessor = store->requireStoreObjectAccessor(*storePath);
+        auto accessor = store.requireStoreObjectAccessor(*storePath);
 
         // To prevent `fetchToStore()` copying the path again to Nix
         // store, pre-create an entry in the fetcher cache.
-        auto info = store->queryPathInfo(*storePath);
+        auto info = store.queryPathInfo(*storePath);
         accessor->fingerprint =
-            fmt("path:%s", store->queryPathInfo(*storePath)->narHash.to_string(HashFormat::SRI, true));
+            fmt("path:%s", store.queryPathInfo(*storePath)->narHash.to_string(HashFormat::SRI, true));
         settings.getCache()->upsert(
             makeFetchToStoreCacheKey(
                 input.getName(), *accessor->fingerprint, ContentAddressMethod::Raw::NixArchive, "/"),
-            *store,
+            store,
             {},
             *storePath);
 

src/libfetchers/registry.cc

@@ -14,10 +14,10 @@ std::shared_ptr<Registry> Registry::read(const Settings & settings, const Source
 {
     debug("reading registry '%s'", path);
 
-    auto registry = std::make_shared<Registry>(settings, type);
+    auto registry = std::make_shared<Registry>(type);
 
     if (!path.pathExists())
-        return std::make_shared<Registry>(settings, type);
+        return std::make_shared<Registry>(type);
 
     try {
 
@@ -125,23 +125,23 @@ std::shared_ptr<Registry> getCustomRegistry(const Settings & settings, const Pat
     return customRegistry;
 }
 
-std::shared_ptr<Registry> getFlagRegistry(const Settings & settings)
+std::shared_ptr<Registry> getFlagRegistry()
 {
-    static auto flagRegistry = std::make_shared<Registry>(settings, Registry::Flag);
+    static auto flagRegistry = std::make_shared<Registry>(Registry::Flag);
     return flagRegistry;
 }
 
-void overrideRegistry(const Settings & settings, const Input & from, const Input & to, const Attrs & extraAttrs)
+void overrideRegistry(const Input & from, const Input & to, const Attrs & extraAttrs)
 {
-    getFlagRegistry(settings)->add(from, to, extraAttrs);
+    getFlagRegistry()->add(from, to, extraAttrs);
 }
 
-static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, ref<Store> store)
+static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, Store & store)
 {
     static auto reg = [&]() {
         auto path = settings.flakeRegistry.get();
         if (path == "") {
-            return std::make_shared<Registry>(settings, Registry::Global); // empty registry
+            return std::make_shared<Registry>(Registry::Global); // empty registry
         }
 
         return Registry::read(
@@ -149,9 +149,9 @@ static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, re
             [&] -> SourcePath {
                 if (!isAbsolute(path)) {
                     auto storePath = downloadFile(store, settings, path, "flake-registry.json").storePath;
-                    if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
+                    if (auto store2 = dynamic_cast<LocalFSStore *>(&store))
                         store2->addPermRoot(storePath, getCacheDir() + "/flake-registry.json");
-                    return {store->requireStoreObjectAccessor(storePath)};
+                    return {store.requireStoreObjectAccessor(storePath)};
                 } else {
                     return SourcePath{getFSSourceAccessor(), CanonPath{path}}.resolveSymlinks();
                 }
@@ -162,10 +162,10 @@ static std::shared_ptr<Registry> getGlobalRegistry(const Settings & settings, re
     return reg;
 }
 
-Registries getRegistries(const Settings & settings, ref<Store> store)
+Registries getRegistries(const Settings & settings, Store & store)
 {
     Registries registries;
-    registries.push_back(getFlagRegistry(settings));
+    registries.push_back(getFlagRegistry());
     registries.push_back(getUserRegistry(settings));
     registries.push_back(getSystemRegistry(settings));
     registries.push_back(getGlobalRegistry(settings, store));
@@ -173,7 +173,7 @@ Registries getRegistries(const Settings & settings, ref<Store> store)
 }
 
 std::pair<Input, Attrs>
-lookupInRegistries(const Settings & settings, ref<Store> store, const Input & _input, UseRegistries useRegistries)
+lookupInRegistries(const Settings & settings, Store & store, const Input & _input, UseRegistries useRegistries)
 {
     Attrs extraAttrs;
     int n = 0;

src/libfetchers/tarball.cc

@@ -13,7 +13,7 @@
 namespace nix::fetchers {
 
 DownloadFileResult downloadFile(
-    ref<Store> store,
+    Store & store,
     const Settings & settings,
     const std::string & url,
     const std::string & name,
@@ -28,7 +28,7 @@ DownloadFileResult downloadFile(
             {"name", name},
         }}};
 
-    auto cached = settings.getCache()->lookupStorePath(key, *store);
+    auto cached = settings.getCache()->lookupStorePath(key, store);
 
     auto useCached = [&]() -> DownloadFileResult {
         return {
@@ -74,7 +74,7 @@ DownloadFileResult downloadFile(
         dumpString(res.data, sink);
         auto hash = hashString(HashAlgorithm::SHA256, res.data);
         auto info = ValidPathInfo::makeFromCA(
-            *store,
+            store,
             name,
             FixedOutputInfo{
                 .method = FileIngestionMethod::Flat,
@@ -84,7 +84,7 @@ DownloadFileResult downloadFile(
             hashString(HashAlgorithm::SHA256, sink.s));
         info.narSize = sink.s.size();
         auto source = StringSource{sink.s};
-        store->addToStore(info, source, NoRepair, NoCheckSigs);
+        store.addToStore(info, source, NoRepair, NoCheckSigs);
         storePath = std::move(info.path);
     }
 
@@ -93,7 +93,7 @@ DownloadFileResult downloadFile(
         key.second.insert_or_assign("url", url);
         assert(!res.urls.empty());
         infoAttrs.insert_or_assign("url", *res.urls.rbegin());
-        settings.getCache()->upsert(key, *store, infoAttrs, *storePath);
+        settings.getCache()->upsert(key, store, infoAttrs, *storePath);
     }
 
     return {
@@ -214,7 +214,7 @@ static DownloadTarballResult downloadTarball_(
     return attrsToResult(infoAttrs);
 }
 
-ref<SourceAccessor> downloadTarball(ref<Store> store, const Settings & settings, const std::string & url)
+ref<SourceAccessor> downloadTarball(Store & store, const Settings & settings, const std::string & url)
 {
     /* Go through Input::getAccessor() to ensure that the resulting
        accessor has a fingerprint. */
@@ -278,7 +278,7 @@ struct CurlInputScheme : InputScheme
            HTTP request. Now that we've processed the Nix-specific
            attributes above, remove them so we don't also send them as
            part of the HTTP request. */
-        for (auto & param : allowedAttrs())
+        for (auto & [param, _] : allowedAttrs())
             url.query.erase(param);
 
         input.attrs.insert_or_assign("type", std::string{schemeName()});
@@ -286,18 +286,83 @@ struct CurlInputScheme : InputScheme
         return input;
     }
 
-    StringSet allowedAttrs() const override
+    static const std::map<std::string, AttributeInfo> & allowedAttrsImpl()
     {
-        return {
+        static const std::map<std::string, AttributeInfo> attrs = {
-            "type",
+            {
-            "url",
+                "url",
-            "narHash",
+                {
-            "name",
+                    .type = "String",
-            "unpack",
+                    .required = true,
-            "rev",
+                    .doc = R"(
-            "revCount",
+                      Supported protocols:
-            "lastModified",
+
+                      - `https`
+
+                        > **Example**
+                        >
+                        > ```nix
+                        > fetchTree {
+                        >   type = "file";
+                        >   url = "https://example.com/index.html";
+                        > }
+                        > ```
+
+                      - `http`
+
+                        Insecure HTTP transfer for legacy sources.
+
+                        > **Warning**
+                        >
+                        > HTTP performs no encryption or authentication.
+                        > Use a `narHash` known in advance to ensure the output has expected contents.
+
+                      - `file`
+
+                        A file on the local file system.
+
+                        > **Example**
+                        >
+                        > ```nix
+                        > fetchTree {
+                        >   type = "file";
+                        >   url = "file:///home/eelco/nix/README.md";
+                        > }
+                        > ```
+                    )",
+                },
+            },
+            {
+                "narHash",
+                {},
+            },
+            {
+                "name",
+                {},
+            },
+            {
+                "unpack",
+                {},
+            },
+            {
+                "rev",
+                {},
+            },
+            {
+                "revCount",
+                {},
+            },
+            {
+                "lastModified",
+                {},
+            },
         };
+        return attrs;
+    }
+
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
+    {
+        return allowedAttrsImpl();
     }
 
     std::optional<Input> inputFromAttrs(const Settings & settings, const Attrs & attrs) const override
@@ -332,6 +397,14 @@ struct FileInputScheme : CurlInputScheme
         return "file";
     }
 
+    std::string schemeDescription() const override
+    {
+        return stripIndentation(R"(
+          Place a plain file into the Nix store.
+          This is similar to [`builtins.fetchurl`](@docroot@/language/builtins.md#builtins-fetchurl)
+        )");
+    }
+
     bool isValidURL(const ParsedURL & url, bool requireTree) const override
     {
         auto parsedUrlScheme = parseUrlScheme(url.scheme);
@@ -341,7 +414,7 @@ struct FileInputScheme : CurlInputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         auto input(_input);
 
@@ -351,10 +424,10 @@ struct FileInputScheme : CurlInputScheme
            tarballs. */
         auto file = downloadFile(store, settings, getStrAttr(input.attrs, "url"), input.getName());
 
-        auto narHash = store->queryPathInfo(file.storePath)->narHash;
+        auto narHash = store.queryPathInfo(file.storePath)->narHash;
         input.attrs.insert_or_assign("narHash", narHash.to_string(HashFormat::SRI, true));
 
-        auto accessor = ref{store->getFSAccessor(file.storePath)};
+        auto accessor = ref{store.getFSAccessor(file.storePath)};
 
         accessor->setPathDisplay("«" + input.to_string() + "»");
 
@@ -369,6 +442,34 @@ struct TarballInputScheme : CurlInputScheme
         return "tarball";
     }
 
+    std::string schemeDescription() const override
+    {
+        return stripIndentation(R"(
+          Download a tar archive and extract it into the Nix store.
+          This has the same underlying implementation as [`builtins.fetchTarball`](@docroot@/language/builtins.md#builtins-fetchTarball)
+        )");
+    }
+
+    const std::map<std::string, AttributeInfo> & allowedAttrs() const override
+    {
+        static const std::map<std::string, AttributeInfo> attrs = [] {
+            auto attrs = CurlInputScheme::allowedAttrsImpl();
+            // Override the "url" attribute to add tarball-specific example
+            attrs["url"].doc = R"(
+              > **Example**
+              >
+              > ```nix
+              > fetchTree {
+              >   type = "tarball";
+              >   url = "https://github.com/NixOS/nixpkgs/tarball/nixpkgs-23.11";
+              > }
+              > ```
+            )";
+            return attrs;
+        }();
+        return attrs;
+    }
+
     bool isValidURL(const ParsedURL & url, bool requireTree) const override
     {
         auto parsedUrlScheme = parseUrlScheme(url.scheme);
@@ -379,7 +480,7 @@ struct TarballInputScheme : CurlInputScheme
     }
 
     std::pair<ref<SourceAccessor>, Input>
-    getAccessor(const Settings & settings, ref<Store> store, const Input & _input) const override
+    getAccessor(const Settings & settings, Store & store, const Input & _input) const override
     {
         auto input(_input);
 
@@ -404,7 +505,7 @@ struct TarballInputScheme : CurlInputScheme
         return {result.accessor, input};
     }
 
-    std::optional<std::string> getFingerprint(ref<Store> store, const Input & input) const override
+    std::optional<std::string> getFingerprint(Store & store, const Input & input) const override
     {
         if (auto narHash = input.getNarHash())
             return narHash->to_string(HashFormat::SRI, true);

src/libflake/flake-primops.cc

@@ -19,7 +19,6 @@
 #include "nix/expr/eval-settings.hh"
 #include "nix/expr/symbol-table.hh"
 #include "nix/expr/value.hh"
-#include "nix/expr/string-data-static.hh"
 #include "nix/fetchers/attrs.hh"
 #include "nix/fetchers/fetchers.hh"
 #include "nix/util/configuration.hh"
@@ -63,7 +62,7 @@ PrimOp getFlake(const Settings & settings)
     return PrimOp{
         .name = "__getFlake",
         .args = {"args"},
-        .doc = &R"(
+        .doc = R"(
           Fetch a flake from a flake reference, and return its output attributes and some metadata. For example:
 
           ```nix
@@ -77,7 +76,7 @@ PrimOp getFlake(const Settings & settings)
           ```nix
           (builtins.getFlake "github:edolstra/dwarffs").rev
           ```
-        )"_sds,
+        )",
         .fun = prim_getFlake,
         .experimentalFeature = Xp::Flakes,
     };
@@ -105,7 +104,7 @@ static void prim_parseFlakeRef(EvalState & state, const PosIdx pos, Value ** arg
 nix::PrimOp parseFlakeRef({
     .name = "__parseFlakeRef",
     .args = {"flake-ref"},
-    .doc = &R"(
+    .doc = R"(
       Parse a flake reference, and return its exploded form.
 
       For example:
@@ -119,7 +118,7 @@ nix::PrimOp parseFlakeRef({
       ```nix
       { dir = "lib"; owner = "NixOS"; ref = "23.05"; repo = "nixpkgs"; type = "github"; }
       ```
-    )"_sds,
+    )",
     .fun = prim_parseFlakeRef,
     .experimentalFeature = Xp::Flakes,
 });
@@ -163,7 +162,7 @@ static void prim_flakeRefToString(EvalState & state, const PosIdx pos, Value **
 nix::PrimOp flakeRefToString({
     .name = "__flakeRefToString",
     .args = {"attrs"},
-    .doc = &R"(
+    .doc = R"(
       Convert a flake reference from attribute set format to URL format.
 
       For example:
@@ -179,7 +178,7 @@ nix::PrimOp flakeRefToString({
       ```nix
       "github:NixOS/nixpkgs/23.05?dir=lib"
       ```
-    )"_sds,
+    )",
     .fun = prim_flakeRefToString,
     .experimentalFeature = Xp::Flakes,
 });

src/libflake/flake.cc

@@ -373,7 +373,7 @@ static Flake getFlake(
 {
     // Fetch a lazy tree first.
     auto cachedInput =
-        state.inputCache->getAccessor(state.fetchSettings, state.store, originalRef.input, useRegistries);
+        state.inputCache->getAccessor(state.fetchSettings, *state.store, originalRef.input, useRegistries);
 
     auto subdir = fetchers::maybeGetStrAttr(cachedInput.extraAttrs, "dir").value_or(originalRef.subdir);
     auto resolvedRef = FlakeRef(std::move(cachedInput.resolvedInput), subdir);
@@ -390,7 +390,7 @@ static Flake getFlake(
         // FIXME: need to remove attrs that are invalidated by the changed input attrs, such as 'narHash'.
         newLockedRef.input.attrs.erase("narHash");
         auto cachedInput2 = state.inputCache->getAccessor(
-            state.fetchSettings, state.store, newLockedRef.input, fetchers::UseRegistries::No);
+            state.fetchSettings, *state.store, newLockedRef.input, fetchers::UseRegistries::No);
         cachedInput.accessor = cachedInput2.accessor;
         lockedRef = FlakeRef(std::move(cachedInput2.lockedInput), newLockedRef.subdir);
     }
@@ -756,7 +756,7 @@ lockFlake(const Settings & settings, EvalState & state, const FlakeRef & topRef,
                                     return {*resolvedPath, *input.ref};
                                 } else {
                                     auto cachedInput = state.inputCache->getAccessor(
-                                        state.fetchSettings, state.store, input.ref->input, useRegistriesInputs);
+                                        state.fetchSettings, *state.store, input.ref->input, useRegistriesInputs);
 
                                     auto lockedRef = FlakeRef(std::move(cachedInput.lockedInput), input.ref->subdir);
 
@@ -975,7 +975,7 @@ void callFlake(EvalState & state, const LockedFlake & lockedFlake, Value & vRes)
     state.callFunction(*vCallFlake, args, vRes, noPos);
 }
 
-std::optional<Fingerprint> LockedFlake::getFingerprint(ref<Store> store, const fetchers::Settings & fetchSettings) const
+std::optional<Fingerprint> LockedFlake::getFingerprint(Store & store, const fetchers::Settings & fetchSettings) const
 {
     if (lockFile.isUnlocked(fetchSettings))
         return std::nullopt;
@@ -1005,7 +1005,7 @@ Flake::~Flake() {}
 ref<eval_cache::EvalCache> openEvalCache(EvalState & state, ref<const LockedFlake> lockedFlake)
 {
     auto fingerprint = state.settings.useEvalCache && state.settings.pureEval
-                           ? lockedFlake->getFingerprint(state.store, state.fetchSettings)
+                           ? lockedFlake->getFingerprint(*state.store, state.fetchSettings)
                            : std::nullopt;
     auto rootLoader = [&state, lockedFlake]() {
         /* For testing whether the evaluation cache is

src/libflake/flakeref.cc

@@ -64,8 +64,8 @@ std::ostream & operator<<(std::ostream & str, const FlakeRef & flakeRef)
     return str;
 }
 
-FlakeRef FlakeRef::resolve(
+FlakeRef
-    const fetchers::Settings & fetchSettings, ref<Store> store, fetchers::UseRegistries useRegistries) const
+FlakeRef::resolve(const fetchers::Settings & fetchSettings, Store & store, fetchers::UseRegistries useRegistries) const
 {
     auto [input2, extraAttrs] = lookupInRegistries(fetchSettings, store, input, useRegistries);
     return FlakeRef(std::move(input2), fetchers::maybeGetStrAttr(extraAttrs, "dir").value_or(subdir));
@@ -289,7 +289,7 @@ FlakeRef FlakeRef::fromAttrs(const fetchers::Settings & fetchSettings, const fet
 }
 
 std::pair<ref<SourceAccessor>, FlakeRef>
-FlakeRef::lazyFetch(const fetchers::Settings & fetchSettings, ref<Store> store) const
+FlakeRef::lazyFetch(const fetchers::Settings & fetchSettings, Store & store) const
 {
     auto [accessor, lockedInput] = input.getAccessor(fetchSettings, store);
     return {accessor, FlakeRef(std::move(lockedInput), subdir)};

src/libflake/include/nix/flake/flake.hh

@@ -135,7 +135,7 @@ struct LockedFlake
      */
     std::map<ref<Node>, SourcePath> nodePaths;
 
-    std::optional<Fingerprint> getFingerprint(ref<Store> store, const fetchers::Settings & fetchSettings) const;
+    std::optional<Fingerprint> getFingerprint(Store & store, const fetchers::Settings & fetchSettings) const;
 };
 
 struct LockFlags

src/libflake/include/nix/flake/flakeref.hh

@@ -73,13 +73,12 @@ struct FlakeRef
 
     FlakeRef resolve(
         const fetchers::Settings & fetchSettings,
-        ref<Store> store,
+        Store & store,
         fetchers::UseRegistries useRegistries = fetchers::UseRegistries::All) const;
 
     static FlakeRef fromAttrs(const fetchers::Settings & fetchSettings, const fetchers::Attrs & attrs);
 
-    std::pair<ref<SourceAccessor>, FlakeRef>
+    std::pair<ref<SourceAccessor>, FlakeRef> lazyFetch(const fetchers::Settings & fetchSettings, Store & store) const;
-    lazyFetch(const fetchers::Settings & fetchSettings, ref<Store> store) const;
 
     /**
      * Canonicalize a flakeref for the purpose of comparing "old" and

src/libstore-c/meson.build

@@ -35,6 +35,8 @@ include_dirs = [ include_directories('.') ]
 
 headers = files(
   'nix_api_store.h',
+  'nix_api_store/derivation.h',
+  'nix_api_store/store_path.h',
 )
 
 # TODO don't install this once tests don't use it and/or move the header into `libstore`, non-`c`

src/libstore-c/nix_api_store.h

@@ -12,6 +12,8 @@
  */
 
 #include "nix_api_util.h"
+#include "nix_api_store/store_path.h"
+#include "nix_api_store/derivation.h"
 #include <stdbool.h>
 
 #ifdef __cplusplus
@@ -21,10 +23,6 @@ extern "C" {
 
 /** @brief Reference to a Nix store */
 typedef struct Store Store;
-/** @brief Nix store path */
-typedef struct StorePath StorePath;
-/** @brief Nix Derivation */
-typedef struct nix_derivation nix_derivation;
 
 /**
  * @brief Initializes the Nix store library
@@ -118,30 +116,6 @@ nix_store_get_storedir(nix_c_context * context, Store * store, nix_get_string_ca
  */
 StorePath * nix_store_parse_path(nix_c_context * context, Store * store, const char * path);
 
-/**
- * @brief Get the path name (e.g. "name" in /nix/store/...-name)
- *
- * @param[in] store_path the path to get the name from
- * @param[in] callback called with the name
- * @param[in] user_data arbitrary data, passed to the callback when it's called.
- */
-void nix_store_path_name(const StorePath * store_path, nix_get_string_callback callback, void * user_data);
-
-/**
- * @brief Copy a StorePath
- *
- * @param[in] p the path to copy
- * @return a new StorePath
- */
-StorePath * nix_store_path_clone(const StorePath * p);
-
-/** @brief Deallocate a StorePath
- *
- * Does not fail.
- * @param[in] p the path to free
- */
-void nix_store_path_free(StorePath * p);
-
 /**
  * @brief Check if a StorePath is valid (i.e. that corresponding store object and its closure of references exists in
  * the store)
@@ -229,14 +203,6 @@ nix_derivation * nix_derivation_from_json(nix_c_context * context, Store * store
  */
 StorePath * nix_add_derivation(nix_c_context * context, Store * store, nix_derivation * derivation);
 
-/**
- * @brief Deallocate a `nix_derivation`
- *
- * Does not fail.
- * @param[in] drv the derivation to free
- */
-void nix_derivation_free(nix_derivation * drv);
-
 /**
  * @brief Copy the closure of `path` from `srcStore` to `dstStore`.
  *

src/libstore-c/nix_api_store/derivation.h

@@ -0,0 +1,38 @@
+#ifndef NIX_API_STORE_DERIVATION_H
+#define NIX_API_STORE_DERIVATION_H
+/**
+ * @defgroup libstore_derivation Derivation
+ * @ingroup libstore
+ * @brief Derivation operations that don't require a Store
+ * @{
+ */
+/** @file
+ * @brief Derivation operations
+ */
+
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @brief Nix Derivation */
+typedef struct nix_derivation nix_derivation;
+
+/**
+ * @brief Deallocate a `nix_derivation`
+ *
+ * Does not fail.
+ * @param[in] drv the derivation to free
+ */
+void nix_derivation_free(nix_derivation * drv);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/**
+ * @}
+ */
+#endif // NIX_API_STORE_DERIVATION_H

src/libstore-c/nix_api_store/store_path.h

@@ -0,0 +1,54 @@
+#ifndef NIX_API_STORE_STORE_PATH_H
+#define NIX_API_STORE_STORE_PATH_H
+/**
+ * @defgroup libstore_storepath StorePath
+ * @ingroup libstore
+ * @brief Store path operations that don't require a Store
+ * @{
+ */
+/** @file
+ * @brief Store path operations
+ */
+
+#include "nix_api_util.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+// cffi start
+
+/** @brief Nix store path */
+typedef struct StorePath StorePath;
+
+/**
+ * @brief Copy a StorePath
+ *
+ * @param[in] p the path to copy
+ * @return a new StorePath
+ */
+StorePath * nix_store_path_clone(const StorePath * p);
+
+/** @brief Deallocate a StorePath
+ *
+ * Does not fail.
+ * @param[in] p the path to free
+ */
+void nix_store_path_free(StorePath * p);
+
+/**
+ * @brief Get the path name (e.g. "<name>" in /nix/store/<hash>-<name>)
+ *
+ * @param[in] store_path the path to get the name from
+ * @param[in] callback called with the name
+ * @param[in] user_data arbitrary data, passed to the callback when it's called.
+ */
+void nix_store_path_name(const StorePath * store_path, nix_get_string_callback callback, void * user_data);
+
+// cffi end
+#ifdef __cplusplus
+}
+#endif
+/**
+ * @}
+ */
+#endif // NIX_API_STORE_STORE_PATH_H

src/libstore-tests/data/derivation/ca/all_set.json

@@ -4,10 +4,13 @@
   "allowSubstitutes": false,
   "exportReferencesGraph": {
     "refs1": [
-      "/164j69y6zir9z0339n8pjigg3rckinlr77bxsavzizdaaljb7nh9"
+      {
+        "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+        "output": "out"
+      }
     ],
     "refs2": [
-      "/nix/store/qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"
+      "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"
     ]
   },
   "impureEnvVars": [
@@ -20,18 +23,36 @@
   "outputChecks": {
     "forAllOutputs": {
       "allowedReferences": [
-        "/164j69y6zir9z0339n8pjigg3rckinlr77bxsavzizdaaljb7nh9"
+        {
+          "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+          "output": "out"
+        }
       ],
       "allowedRequisites": [
-        "/0nr45p69vn6izw9446wsh9bng9nndhvn19kpsm4n96a5mycw0s4z",
+        {
-        "bin"
+          "drvPath": "self",
+          "output": "bin"
+        },
+        {
+          "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+          "output": "dev"
+        }
       ],
       "disallowedReferences": [
-        "/0nyw57wm2iicnm9rglvjmbci3ikmcp823czdqdzdcgsnnwqps71g",
+        {
-        "dev"
+          "drvPath": "self",
+          "output": "dev"
+        },
+        {
+          "drvPath": "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv",
+          "output": "out"
+        }
       ],
       "disallowedRequisites": [
-        "/07f301yqyz8c6wf6bbbavb2q39j4n8kmcly1s09xadyhgy6x2wr8"
+        {
+          "drvPath": "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv",
+          "output": "dev"
+        }
       ],
       "ignoreSelfRefs": true,
       "maxClosureSize": null,

src/libstore-tests/data/derivation/ca/structuredAttrs_all_set.json

@@ -4,10 +4,13 @@
   "allowSubstitutes": false,
   "exportReferencesGraph": {
     "refs1": [
-      "/164j69y6zir9z0339n8pjigg3rckinlr77bxsavzizdaaljb7nh9"
+      {
+        "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+        "output": "out"
+      }
     ],
     "refs2": [
-      "/nix/store/qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"
+      "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"
     ]
   },
   "impureEnvVars": [
@@ -23,11 +26,20 @@
         "allowedReferences": null,
         "allowedRequisites": null,
         "disallowedReferences": [
-          "/0nyw57wm2iicnm9rglvjmbci3ikmcp823czdqdzdcgsnnwqps71g",
+          {
-          "dev"
+            "drvPath": "self",
+            "output": "dev"
+          },
+          {
+            "drvPath": "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv",
+            "output": "out"
+          }
         ],
         "disallowedRequisites": [
-          "/07f301yqyz8c6wf6bbbavb2q39j4n8kmcly1s09xadyhgy6x2wr8"
+          {
+            "drvPath": "qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv",
+            "output": "dev"
+          }
         ],
         "ignoreSelfRefs": false,
         "maxClosureSize": null,
@@ -44,11 +56,20 @@
       },
       "out": {
         "allowedReferences": [
-          "/164j69y6zir9z0339n8pjigg3rckinlr77bxsavzizdaaljb7nh9"
+          {
+            "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+            "output": "out"
+          }
         ],
         "allowedRequisites": [
-          "/0nr45p69vn6izw9446wsh9bng9nndhvn19kpsm4n96a5mycw0s4z",
+          {
-          "bin"
+            "drvPath": "self",
+            "output": "bin"
+          },
+          {
+            "drvPath": "j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv",
+            "output": "dev"
+          }
         ],
         "disallowedReferences": [],
         "disallowedRequisites": [],

src/libstore-tests/data/derivation/ia/all_set.json

@@ -4,10 +4,10 @@
   "allowSubstitutes": false,
   "exportReferencesGraph": {
     "refs1": [
-      "/nix/store/p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
+      "p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
     ],
     "refs2": [
-      "/nix/store/vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv"
+      "vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv"
     ]
   },
   "impureEnvVars": [
@@ -20,18 +20,24 @@
   "outputChecks": {
     "forAllOutputs": {
       "allowedReferences": [
-        "/nix/store/p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
+        "p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
       ],
       "allowedRequisites": [
-        "/nix/store/z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev",
+        {
-        "bin"
+          "drvPath": "self",
+          "output": "bin"
+        },
+        "z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev"
       ],
       "disallowedReferences": [
-        "/nix/store/r5cff30838majxk5mp3ip2diffi8vpaj-bar",
+        {
-        "dev"
+          "drvPath": "self",
+          "output": "dev"
+        },
+        "r5cff30838majxk5mp3ip2diffi8vpaj-bar"
       ],
       "disallowedRequisites": [
-        "/nix/store/9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev"
+        "9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev"
       ],
       "ignoreSelfRefs": true,
       "maxClosureSize": null,

src/libstore-tests/data/derivation/ia/structuredAttrs_all_set.json

@@ -4,10 +4,10 @@
   "allowSubstitutes": false,
   "exportReferencesGraph": {
     "refs1": [
-      "/nix/store/p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
+      "p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
     ],
     "refs2": [
-      "/nix/store/vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv"
+      "vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv"
     ]
   },
   "impureEnvVars": [
@@ -23,11 +23,14 @@
         "allowedReferences": null,
         "allowedRequisites": null,
         "disallowedReferences": [
-          "/nix/store/r5cff30838majxk5mp3ip2diffi8vpaj-bar",
+          {
-          "dev"
+            "drvPath": "self",
+            "output": "dev"
+          },
+          "r5cff30838majxk5mp3ip2diffi8vpaj-bar"
         ],
         "disallowedRequisites": [
-          "/nix/store/9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev"
+          "9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev"
         ],
         "ignoreSelfRefs": false,
         "maxClosureSize": null,
@@ -44,11 +47,14 @@
       },
       "out": {
         "allowedReferences": [
-          "/nix/store/p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
+          "p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"
         ],
         "allowedRequisites": [
-          "/nix/store/z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev",
+          {
-          "bin"
+            "drvPath": "self",
+            "output": "bin"
+          },
+          "z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev"
         ],
         "disallowedReferences": [],
         "disallowedRequisites": [],

src/libstore-tests/derivation-advanced-attrs.cc

@@ -3,7 +3,7 @@
 
 #include "nix/util/experimental-features.hh"
 #include "nix/store/derivations.hh"
-#include "nix/store/derivations.hh"
+#include "nix/store/derived-path.hh"
 #include "nix/store/derivation-options.hh"
 #include "nix/store/parsed-derivations.hh"
 #include "nix/util/types.hh"
@@ -17,7 +17,7 @@ namespace nix {
 using namespace nlohmann;
 
 class DerivationAdvancedAttrsTest : public JsonCharacterizationTest<Derivation>,
-                                    public JsonCharacterizationTest<DerivationOptions>,
+                                    public JsonCharacterizationTest<DerivationOptions<SingleDerivedPath>>,
                                     public LibStoreTest
 {
 protected:
@@ -42,7 +42,8 @@ public:
     {
         this->readTest(fileName, [&](auto encoded) {
             auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
-            DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+            auto options = derivationOptionsFromStructuredAttrs(
+                *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
             EXPECT_EQ(options.getRequiredSystemFeatures(got), expectedFeatures);
         });
     }
@@ -51,11 +52,14 @@ public:
      * Helper function to test DerivationOptions parsing and comparison
      */
     void testDerivationOptions(
-        const std::string & fileName, const DerivationOptions & expected, const StringSet & expectedSystemFeatures)
+        const std::string & fileName,
+        const DerivationOptions<SingleDerivedPath> & expected,
+        const StringSet & expectedSystemFeatures)
     {
         this->readTest(fileName, [&](auto encoded) {
             auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
-            DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+            auto options = derivationOptionsFromStructuredAttrs(
+                *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
 
             EXPECT_EQ(options, expected);
             EXPECT_EQ(options.getRequiredSystemFeatures(got), expectedSystemFeatures);
@@ -131,22 +135,38 @@ TEST_ATERM_JSON(advancedAttributes_structuredAttrs_defaults, "advanced-attribute
  * Since these are both repeated and sensative opaque values, it makes
  * sense to give them names in this file.
  */
-static std::string pathFoo = "/nix/store/p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo",
+static SingleDerivedPath
-                   pathFooDev = "/nix/store/z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev",
+    pathFoo = SingleDerivedPath::Opaque{StorePath{"p0hax2lzvjpfc2gwkk62xdglz0fcqfzn-foo"}},
-                   pathBar = "/nix/store/r5cff30838majxk5mp3ip2diffi8vpaj-bar",
+    pathFooDev = SingleDerivedPath::Opaque{StorePath{"z0rjzy29v9k5qa4nqpykrbzirj7sd43v-foo-dev"}},
-                   pathBarDev = "/nix/store/9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev",
+    pathBar = SingleDerivedPath::Opaque{StorePath{"r5cff30838majxk5mp3ip2diffi8vpaj-bar"}},
-                   pathBarDrvIA = "/nix/store/vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv",
+    pathBarDev = SingleDerivedPath::Opaque{StorePath{"9b61w26b4avv870dw0ymb6rw4r1hzpws-bar-dev"}},
-                   pathBarDrvCA = "/nix/store/qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv",
+    pathBarDrvIA = SingleDerivedPath::Opaque{StorePath{"vj2i49jm2868j2fmqvxm70vlzmzvgv14-bar.drv"}},
-                   placeholderFoo = "/164j69y6zir9z0339n8pjigg3rckinlr77bxsavzizdaaljb7nh9",
+    pathBarDrvCA = SingleDerivedPath::Opaque{StorePath{"qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"}},
-                   placeholderFooDev = "/0nr45p69vn6izw9446wsh9bng9nndhvn19kpsm4n96a5mycw0s4z",
+    placeholderFoo =
-                   placeholderBar = "/0nyw57wm2iicnm9rglvjmbci3ikmcp823czdqdzdcgsnnwqps71g",
+        SingleDerivedPath::Built{
-                   placeholderBarDev = "/07f301yqyz8c6wf6bbbavb2q39j4n8kmcly1s09xadyhgy6x2wr8";
+            .drvPath = makeConstantStorePathRef(StorePath{"j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv"}),
+            .output = "out",
+        },
+    placeholderFooDev =
+        SingleDerivedPath::Built{
+            .drvPath = makeConstantStorePathRef(StorePath{"j56sf12rxpcv5swr14vsjn5cwm6bj03h-foo.drv"}),
+            .output = "dev",
+        },
+    placeholderBar =
+        SingleDerivedPath::Built{
+            .drvPath = makeConstantStorePathRef(StorePath{"qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"}),
+            .output = "out",
+        },
+    placeholderBarDev = SingleDerivedPath::Built{
+        .drvPath = makeConstantStorePathRef(StorePath{"qnml92yh97a6fbrs2m5qg5cqlc8vni58-bar.drv"}),
+        .output = "dev",
+    };
 
-using ExportReferencesMap = decltype(DerivationOptions::exportReferencesGraph);
+using ExportReferencesMap = decltype(DerivationOptions<SingleDerivedPath>::exportReferencesGraph);
 
-static const DerivationOptions advancedAttributes_defaults = {
+static const DerivationOptions<SingleDerivedPath> advancedAttributes_defaults = {
     .outputChecks =
-        DerivationOptions::OutputChecks{
+        DerivationOptions<SingleDerivedPath>::OutputChecks{
             .ignoreSelfRefs = true,
         },
     .unsafeDiscardReferences = {},
@@ -167,7 +187,8 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_defaults)
     this->readTest("advanced-attributes-defaults.drv", [&](auto encoded) {
         auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
 
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+        auto options = derivationOptionsFromStructuredAttrs(
+            *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
 
         EXPECT_TRUE(!got.structuredAttrs);
 
@@ -192,9 +213,9 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_defaults)
 
 TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes)
 {
-    DerivationOptions expected = {
+    DerivationOptions<SingleDerivedPath> expected = {
         .outputChecks =
-            DerivationOptions::OutputChecks{
+            DerivationOptions<SingleDerivedPath>::OutputChecks{
                 .ignoreSelfRefs = true,
             },
         .unsafeDiscardReferences = {},
@@ -212,12 +233,13 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes)
     this->readTest("advanced-attributes.drv", [&](auto encoded) {
         auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
 
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+        auto options = derivationOptionsFromStructuredAttrs(
+            *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
 
         EXPECT_TRUE(!got.structuredAttrs);
 
         // Reset fields that vary between test cases to enable whole-object comparison
-        options.outputChecks = DerivationOptions::OutputChecks{.ignoreSelfRefs = true};
+        options.outputChecks = DerivationOptions<SingleDerivedPath>::OutputChecks{.ignoreSelfRefs = true};
         options.exportReferencesGraph = {};
 
         EXPECT_EQ(options, expected);
@@ -227,14 +249,14 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes)
     });
 };
 
-DerivationOptions advancedAttributes_ia = {
+DerivationOptions<SingleDerivedPath> advancedAttributes_ia = {
     .outputChecks =
-        DerivationOptions::OutputChecks{
+        DerivationOptions<SingleDerivedPath>::OutputChecks{
             .ignoreSelfRefs = true,
-            .allowedReferences = StringSet{pathFoo},
+            .allowedReferences = std::set<DrvRef<SingleDerivedPath>>{pathFoo},
-            .disallowedReferences = StringSet{pathBar, "dev"},
+            .disallowedReferences = std::set<DrvRef<SingleDerivedPath>>{pathBar, OutputName{"dev"}},
-            .allowedRequisites = StringSet{pathFooDev, "bin"},
+            .allowedRequisites = std::set<DrvRef<SingleDerivedPath>>{pathFooDev, OutputName{"bin"}},
-            .disallowedRequisites = StringSet{pathBarDev},
+            .disallowedRequisites = std::set<DrvRef<SingleDerivedPath>>{pathBarDev},
         },
     .unsafeDiscardReferences = {},
     .passAsFile = {},
@@ -257,14 +279,14 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes_ia)
     testDerivationOptions("advanced-attributes.drv", advancedAttributes_ia, {"rainbow", "uid-range"});
 };
 
-DerivationOptions advancedAttributes_ca = {
+DerivationOptions<SingleDerivedPath> advancedAttributes_ca = {
     .outputChecks =
-        DerivationOptions::OutputChecks{
+        DerivationOptions<SingleDerivedPath>::OutputChecks{
             .ignoreSelfRefs = true,
-            .allowedReferences = StringSet{placeholderFoo},
+            .allowedReferences = std::set<DrvRef<SingleDerivedPath>>{placeholderFoo},
-            .disallowedReferences = StringSet{placeholderBar, "dev"},
+            .disallowedReferences = std::set<DrvRef<SingleDerivedPath>>{placeholderBar, OutputName{"dev"}},
-            .allowedRequisites = StringSet{placeholderFooDev, "bin"},
+            .allowedRequisites = std::set<DrvRef<SingleDerivedPath>>{placeholderFooDev, OutputName{"bin"}},
-            .disallowedRequisites = StringSet{placeholderBarDev},
+            .disallowedRequisites = std::set<DrvRef<SingleDerivedPath>>{placeholderBarDev},
         },
     .unsafeDiscardReferences = {},
     .passAsFile = {},
@@ -287,8 +309,8 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes)
     testDerivationOptions("advanced-attributes.drv", advancedAttributes_ca, {"rainbow", "uid-range", "ca-derivations"});
 };
 
-DerivationOptions advancedAttributes_structuredAttrs_defaults = {
+DerivationOptions<SingleDerivedPath> advancedAttributes_structuredAttrs_defaults = {
-    .outputChecks = std::map<std::string, DerivationOptions::OutputChecks>{},
+    .outputChecks = std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks>{},
     .unsafeDiscardReferences = {},
     .passAsFile = {},
     .exportReferencesGraph = {},
@@ -307,7 +329,8 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs_d
     this->readTest("advanced-attributes-structured-attrs-defaults.drv", [&](auto encoded) {
         auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
 
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+        auto options = derivationOptionsFromStructuredAttrs(
+            *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
 
         EXPECT_TRUE(got.structuredAttrs);
 
@@ -332,11 +355,11 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs_default
 
 TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs)
 {
-    DerivationOptions expected = {
+    DerivationOptions<SingleDerivedPath> expected = {
         .outputChecks =
-            std::map<std::string, DerivationOptions::OutputChecks>{
+            std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks>{
                 {"dev",
-                 DerivationOptions::OutputChecks{
+                 DerivationOptions<SingleDerivedPath>::OutputChecks{
                      .maxSize = 789,
                      .maxClosureSize = 5909,
                  }},
@@ -357,7 +380,8 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs)
     this->readTest("advanced-attributes-structured-attrs.drv", [&](auto encoded) {
         auto got = parseDerivation(*this->store, std::move(encoded), "foo", this->mockXpSettings);
 
-        DerivationOptions options = DerivationOptions::fromStructuredAttrs(got.env, got.structuredAttrs);
+        auto options = derivationOptionsFromStructuredAttrs(
+            *this->store, got.inputDrvs, got.env, get(got.structuredAttrs), true, this->mockXpSettings);
 
         EXPECT_TRUE(got.structuredAttrs);
 
@@ -365,7 +389,8 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs)
         {
             // Delete all keys but "dev" in options.outputChecks
             auto * outputChecksMapP =
-                std::get_if<std::map<std::string, DerivationOptions::OutputChecks>>(&options.outputChecks);
+                std::get_if<std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks>>(
+                    &options.outputChecks);
             ASSERT_TRUE(outputChecksMapP);
             auto & outputChecksMap = *outputChecksMapP;
             auto devEntry = outputChecksMap.find("dev");
@@ -385,21 +410,21 @@ TYPED_TEST(DerivationAdvancedAttrsBothTest, advancedAttributes_structuredAttrs)
     });
 };
 
-DerivationOptions advancedAttributes_structuredAttrs_ia = {
+DerivationOptions<SingleDerivedPath> advancedAttributes_structuredAttrs_ia = {
     .outputChecks =
-        std::map<std::string, DerivationOptions::OutputChecks>{
+        std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks>{
             {"out",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
-                 .allowedReferences = StringSet{pathFoo},
+                 .allowedReferences = std::set<DrvRef<SingleDerivedPath>>{pathFoo},
-                 .allowedRequisites = StringSet{pathFooDev, "bin"},
+                 .allowedRequisites = std::set<DrvRef<SingleDerivedPath>>{pathFooDev, OutputName{"bin"}},
              }},
             {"bin",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
-                 .disallowedReferences = StringSet{pathBar, "dev"},
+                 .disallowedReferences = std::set<DrvRef<SingleDerivedPath>>{pathBar, OutputName{"dev"}},
-                 .disallowedRequisites = StringSet{pathBarDev},
+                 .disallowedRequisites = std::set<DrvRef<SingleDerivedPath>>{pathBarDev},
              }},
             {"dev",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
                  .maxSize = 789,
                  .maxClosureSize = 5909,
              }},
@@ -427,21 +452,21 @@ TEST_F(DerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs)
         "advanced-attributes-structured-attrs.drv", advancedAttributes_structuredAttrs_ia, {"rainbow", "uid-range"});
 };
 
-DerivationOptions advancedAttributes_structuredAttrs_ca = {
+DerivationOptions<SingleDerivedPath> advancedAttributes_structuredAttrs_ca = {
     .outputChecks =
-        std::map<std::string, DerivationOptions::OutputChecks>{
+        std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks>{
             {"out",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
-                 .allowedReferences = StringSet{placeholderFoo},
+                 .allowedReferences = std::set<DrvRef<SingleDerivedPath>>{placeholderFoo},
-                 .allowedRequisites = StringSet{placeholderFooDev, "bin"},
+                 .allowedRequisites = std::set<DrvRef<SingleDerivedPath>>{placeholderFooDev, OutputName{"bin"}},
              }},
             {"bin",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
-                 .disallowedReferences = StringSet{placeholderBar, "dev"},
+                 .disallowedReferences = std::set<DrvRef<SingleDerivedPath>>{placeholderBar, OutputName{"dev"}},
-                 .disallowedRequisites = StringSet{placeholderBarDev},
+                 .disallowedRequisites = std::set<DrvRef<SingleDerivedPath>>{placeholderBarDev},
              }},
             {"dev",
-             DerivationOptions::OutputChecks{
+             DerivationOptions<SingleDerivedPath>::OutputChecks{
                  .maxSize = 789,
                  .maxClosureSize = 5909,
              }},
@@ -471,14 +496,16 @@ TEST_F(CaDerivationAdvancedAttrsTest, advancedAttributes_structuredAttrs)
         {"rainbow", "uid-range", "ca-derivations"});
 };
 
-#define TEST_JSON_OPTIONS(FIXUTURE, VAR, VAR2)                                                             \
+#define TEST_JSON_OPTIONS(FIXUTURE, VAR, VAR2)                                               \
-    TEST_F(FIXUTURE, DerivationOptions_##VAR##_from_json)                                                  \
+    TEST_F(FIXUTURE, DerivationOptions_##VAR##_from_json)                                    \
-    {                                                                                                      \
+    {                                                                                        \
-        this->JsonCharacterizationTest<DerivationOptions>::readJsonTest(#VAR, advancedAttributes_##VAR2);  \
+        this->JsonCharacterizationTest<DerivationOptions<SingleDerivedPath>>::readJsonTest(  \
-    }                                                                                                      \
+            #VAR, advancedAttributes_##VAR2);                                                \
-    TEST_F(FIXUTURE, DerivationOptions_##VAR##_to_json)                                                    \
+    }                                                                                        \
-    {                                                                                                      \
+    TEST_F(FIXUTURE, DerivationOptions_##VAR##_to_json)                                      \
-        this->JsonCharacterizationTest<DerivationOptions>::writeJsonTest(#VAR, advancedAttributes_##VAR2); \
+    {                                                                                        \
+        this->JsonCharacterizationTest<DerivationOptions<SingleDerivedPath>>::writeJsonTest( \
+            #VAR, advancedAttributes_##VAR2);                                                \
     }
 
 TEST_JSON_OPTIONS(DerivationAdvancedAttrsTest, defaults, defaults)

src/libstore/build/derivation-building-goal.cc

@@ -32,14 +32,6 @@ DerivationBuildingGoal::DerivationBuildingGoal(
     , drv{std::make_unique<Derivation>(drv)}
     , buildMode(buildMode)
 {
-    try {
-        drvOptions =
-            std::make_unique<DerivationOptions>(DerivationOptions::fromStructuredAttrs(drv.env, drv.structuredAttrs));
-    } catch (Error & e) {
-        e.addTrace({}, "while parsing derivation '%s'", worker.store.printStorePath(drvPath));
-        throw;
-    }
-
     name = fmt("building derivation '%s'", worker.store.printStorePath(drvPath));
     trace("created");
 
@@ -206,6 +198,38 @@ Goal::Co DerivationBuildingGoal::gaveUpOnSubstitution(bool storeDerivation)
 
 Goal::Co DerivationBuildingGoal::tryToBuild()
 {
+    auto drvOptions = [&] {
+        DerivationOptions<SingleDerivedPath> temp;
+        try {
+            temp =
+                derivationOptionsFromStructuredAttrs(worker.store, drv->inputDrvs, drv->env, get(drv->structuredAttrs));
+        } catch (Error & e) {
+            e.addTrace({}, "while parsing derivation '%s'", worker.store.printStorePath(drvPath));
+            throw;
+        }
+
+        auto res = tryResolve(
+            temp,
+            [&](ref<const SingleDerivedPath> drvPath, const std::string & outputName) -> std::optional<StorePath> {
+                try {
+                    return resolveDerivedPath(
+                        worker.store, SingleDerivedPath::Built{drvPath, outputName}, &worker.evalStore);
+                } catch (Error &) {
+                    return std::nullopt;
+                }
+            });
+
+        /* The derivation must have all of its inputs gotten this point,
+           so the resolution will surely succeed.
+
+           (Actually, we shouldn't even enter this goal until we have a
+           resolved derivation, or derivation with only input addressed
+           transitive inputs, so this should be a no-opt anyways.)
+         */
+        assert(res);
+        return *res;
+    }();
+
     std::map<std::string, InitialOutput> initialOutputs;
 
     /* Recheck at this point. In particular, whereas before we were
@@ -344,13 +368,13 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
         /* Don't do a remote build if the derivation has the attribute
            `preferLocalBuild' set.  Also, check and repair modes are only
            supported for local builds. */
-        bool buildLocally = (buildMode != bmNormal || drvOptions->willBuildLocally(worker.store, *drv))
+        bool buildLocally = (buildMode != bmNormal || drvOptions.willBuildLocally(worker.store, *drv))
                             && settings.maxBuildJobs.get() != 0;
 
         if (buildLocally) {
             useHook = false;
         } else {
-            switch (tryBuildHook(initialOutputs)) {
+            switch (tryBuildHook(initialOutputs, drvOptions)) {
             case rpAccept:
                 /* Yes, it has started doing so.  Wait until we get
                    EOF from the hook. */
@@ -379,7 +403,7 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
 
                 externalBuilder = settings.findExternalDerivationBuilderIfSupported(*drv);
 
-                if (!externalBuilder && !drvOptions->canBuildLocally(worker.store, *drv)) {
+                if (!externalBuilder && !drvOptions.canBuildLocally(worker.store, *drv)) {
                     auto msg =
                         fmt("Cannot build '%s'.\n"
                             "Reason: " ANSI_RED "required system or feature not available" ANSI_NORMAL
@@ -388,7 +412,7 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
                             "Current system: '%s' with features {%s}",
                             Magenta(worker.store.printStorePath(drvPath)),
                             Magenta(drv->platform),
-                            concatStringsSep(", ", drvOptions->getRequiredSystemFeatures(*drv)),
+                            concatStringsSep(", ", drvOptions.getRequiredSystemFeatures(*drv)),
                             Magenta(settings.thisSystem),
                             concatStringsSep<StringSet>(", ", worker.store.Store::config.systemFeatures));
 
@@ -586,7 +610,7 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
             }
 
             try {
-                desugaredEnv = DesugaredEnv::create(worker.store, *drv, *drvOptions, inputPaths);
+                desugaredEnv = DesugaredEnv::create(worker.store, *drv, drvOptions, inputPaths);
             } catch (BuildError & e) {
                 outputLocks.unlock();
                 worker.permanentFailure = true;
@@ -597,7 +621,7 @@ Goal::Co DerivationBuildingGoal::tryToBuild()
                 .drvPath = drvPath,
                 .buildResult = buildResult,
                 .drv = *drv,
-                .drvOptions = *drvOptions,
+                .drvOptions = drvOptions,
                 .inputPaths = inputPaths,
                 .initialOutputs = initialOutputs,
                 .buildMode = buildMode,
@@ -803,7 +827,8 @@ BuildError DerivationBuildingGoal::fixupBuilderFailureErrorMessage(BuilderFailur
     return BuildError{e.status, msg};
 }
 
-HookReply DerivationBuildingGoal::tryBuildHook(const std::map<std::string, InitialOutput> & initialOutputs)
+HookReply DerivationBuildingGoal::tryBuildHook(
+    const std::map<std::string, InitialOutput> & initialOutputs, const DerivationOptions<StorePath> & drvOptions)
 {
 #ifdef _WIN32 // TODO enable build hook on Windows
     return rpDecline;
@@ -820,7 +845,7 @@ HookReply DerivationBuildingGoal::tryBuildHook(const std::map<std::string, Initi
 
         /* Send the request to the hook. */
         worker.hook->sink << "try" << (worker.getNrLocalBuilds() < settings.maxBuildJobs ? 1 : 0) << drv->platform
-                          << worker.store.printStorePath(drvPath) << drvOptions->getRequiredSystemFeatures(*drv);
+                          << worker.store.printStorePath(drvPath) << drvOptions.getRequiredSystemFeatures(*drv);
         worker.hook->sink.flush();
 
         /* Read the first line of input, which should be a word indicating

src/libstore/build/derivation-check.cc

@@ -11,7 +11,7 @@ void checkOutputs(
     Store & store,
     const StorePath & drvPath,
     const decltype(Derivation::outputs) & drvOutputs,
-    const decltype(DerivationOptions::outputChecks) & outputChecks,
+    const decltype(DerivationOptions<StorePath>::outputChecks) & outputChecks,
     const std::map<std::string, ValidPathInfo> & outputs)
 {
     std::map<Path, const ValidPathInfo &> outputsByPath;
@@ -85,7 +85,7 @@ void checkOutputs(
             return std::make_pair(std::move(pathsDone), closureSize);
         };
 
-        auto applyChecks = [&](const DerivationOptions::OutputChecks & checks) {
+        auto applyChecks = [&](const DerivationOptions<StorePath>::OutputChecks & checks) {
             if (checks.maxSize && info.narSize > *checks.maxSize)
                 throw BuildError(
                     BuildResult::Failure::OutputRejected,
@@ -105,28 +105,33 @@ void checkOutputs(
                         *checks.maxClosureSize);
             }
 
-            auto checkRefs = [&](const StringSet & value, bool allowed, bool recursive) {
+            auto checkRefs = [&](const std::set<DrvRef<StorePath>> & value, bool allowed, bool recursive) {
                 /* Parse a list of reference specifiers.  Each element must
                    either be a store path, or the symbolic name of the output
                    of the derivation (such as `out'). */
                 StorePathSet spec;
                 for (auto & i : value) {
-                    if (store.isStorePath(i))
+                    std::visit(
-                        spec.insert(store.parseStorePath(i));
+                        overloaded{
-                    else if (auto output = get(outputs, i))
+                            [&](const StorePath & path) { spec.insert(path); },
-                        spec.insert(output->path);
+                            [&](const OutputName & refOutputName) {
-                    else {
+                                if (auto output = get(outputs, refOutputName))
-                        std::string outputsListing =
+                                    spec.insert(output->path);
-                            concatMapStringsSep(", ", outputs, [](auto & o) { return o.first; });
+                                else {
-                        throw BuildError(
+                                    std::string outputsListing =
-                            BuildResult::Failure::OutputRejected,
+                                        concatMapStringsSep(", ", outputs, [](auto & o) { return o.first; });
-                            "derivation '%s' output check for '%s' contains an illegal reference specifier '%s',"
+                                    throw BuildError(
-                            " expected store path or output name (one of [%s])",
+                                        BuildResult::Failure::OutputRejected,
-                            store.printStorePath(drvPath),
+                                        "derivation '%s' output check for '%s' contains output name '%s',"
-                            outputName,
+                                        " but this is not a valid output of this derivation."
-                            i,
+                                        " (Valid outputs are [%s].)",
-                            outputsListing);
+                                        store.printStorePath(drvPath),
-                    }
+                                        outputName,
+                                        refOutputName,
+                                        outputsListing);
+                                }
+                            }},
+                        i);
                 }
 
                 auto used = recursive ? getClosure(info.path).first : info.references;
@@ -180,8 +185,8 @@ void checkOutputs(
 
         std::visit(
             overloaded{
-                [&](const DerivationOptions::OutputChecks & checks) { applyChecks(checks); },
+                [&](const DerivationOptions<StorePath>::OutputChecks & checks) { applyChecks(checks); },
-                [&](const std::map<std::string, DerivationOptions::OutputChecks> & checksPerOutput) {
+                [&](const std::map<std::string, DerivationOptions<StorePath>::OutputChecks> & checksPerOutput) {
                     if (auto outputChecks = get(checksPerOutput, outputName))
 
                         applyChecks(*outputChecks);

src/libstore/build/derivation-check.hh

@@ -21,7 +21,7 @@ void checkOutputs(
     Store & store,
     const StorePath & drvPath,
     const decltype(Derivation::outputs) & drvOutputs,
-    const decltype(DerivationOptions::outputChecks) & drvOptions,
+    const decltype(DerivationOptions<StorePath>::outputChecks) & drvOptions,
     const std::map<std::string, ValidPathInfo> & outputs);
 
 } // namespace nix

src/libstore/build/derivation-env-desugar.cc

@@ -18,7 +18,10 @@ std::string & DesugaredEnv::atFileEnvPair(std::string_view name, std::string fil
 }
 
 DesugaredEnv DesugaredEnv::create(
-    Store & store, const Derivation & drv, const DerivationOptions & drvOptions, const StorePathSet & inputPaths)
+    Store & store,
+    const Derivation & drv,
+    const DerivationOptions<StorePath> & drvOptions,
+    const StorePathSet & inputPaths)
 {
     DesugaredEnv res;
 
@@ -46,7 +49,7 @@ DesugaredEnv DesugaredEnv::create(
         }
 
         /* Handle exportReferencesGraph(), if set. */
-        for (auto & [fileName, storePaths] : drvOptions.getParsedExportReferencesGraph(store)) {
+        for (auto & [fileName, storePaths] : drvOptions.exportReferencesGraph) {
             /* Write closure info to <fileName>. */
             res.extraFiles.insert_or_assign(
                 fileName, store.makeValidityRegistration(store.exportReferences(storePaths, inputPaths), false, false));

src/libstore/build/derivation-goal.cc

@@ -64,9 +64,10 @@ Goal::Co DerivationGoal::haveDerivation(bool storeDerivation)
 {
     trace("have derivation");
 
-    auto drvOptions = [&]() -> DerivationOptions {
+    auto drvOptions = [&]() -> DerivationOptions<SingleDerivedPath> {
         try {
-            return DerivationOptions::fromStructuredAttrs(drv->env, drv->structuredAttrs);
+            return derivationOptionsFromStructuredAttrs(
+                worker.store, drv->inputDrvs, drv->env, get(drv->structuredAttrs));
         } catch (Error & e) {
             e.addTrace({}, "while parsing derivation '%s'", worker.store.printStorePath(drvPath));
             throw;

src/libstore/derivation-options.cc

@@ -2,15 +2,18 @@
 #include "nix/util/json-utils.hh"
 #include "nix/store/parsed-derivations.hh"
 #include "nix/store/derivations.hh"
+#include "nix/store/derived-path.hh"
 #include "nix/store/store-api.hh"
 #include "nix/util/types.hh"
 #include "nix/util/util.hh"
 #include "nix/store/globals.hh"
+#include "nix/util/variant-wrapper.hh"
 
 #include <optional>
 #include <string>
 #include <variant>
 #include <regex>
+#include <ranges>
 
 namespace nix {
 
@@ -90,14 +93,38 @@ getStringSetAttr(const StringMap & env, const StructuredAttrs * parsed, const st
     return ss ? (std::optional{StringSet{ss->begin(), ss->end()}}) : (std::optional<StringSet>{});
 }
 
-using OutputChecks = DerivationOptions::OutputChecks;
+template<typename Inputs>
+using OutputChecks = DerivationOptions<Inputs>::OutputChecks;
 
-using OutputChecksVariant = std::variant<OutputChecks, std::map<std::string, OutputChecks>>;
+template<typename Inputs>
+using OutputChecksVariant = std::variant<OutputChecks<Inputs>, std::map<std::string, OutputChecks<Inputs>>>;
 
-DerivationOptions DerivationOptions::fromStructuredAttrs(
+DerivationOptions<StorePath> derivationOptionsFromStructuredAttrs(
-    const StringMap & env, const std::optional<StructuredAttrs> & parsed, bool shouldWarn)
+    const StoreDirConfig & store,
+    const StringMap & env,
+    const StructuredAttrs * parsed,
+    bool shouldWarn,
+    const ExperimentalFeatureSettings & mockXpSettings)
 {
-    return fromStructuredAttrs(env, parsed ? &*parsed : nullptr);
+    /* Use the SingleDerivedPath version with empty inputDrvs, then
+       resolve. */
+    DerivedPathMap<StringSet> emptyInputDrvs{};
+    auto singleDerivedPathOptions =
+        derivationOptionsFromStructuredAttrs(store, emptyInputDrvs, env, parsed, shouldWarn, mockXpSettings);
+
+    /* "Resolve" all SingleDerivedPath inputs to StorePath. */
+    auto resolved = tryResolve(
+        singleDerivedPathOptions,
+        [&](ref<const SingleDerivedPath> drvPath, const std::string & outputName) -> std::optional<StorePath> {
+            // there should be nothing to resolve
+            assert(false);
+        });
+
+    /* Since we should never need to call the call back, there should be
+       no way it fails. */
+    assert(resolved);
+
+    return *resolved;
 }
 
 static void flatten(const nlohmann::json & value, StringSet & res)
@@ -111,10 +138,63 @@ static void flatten(const nlohmann::json & value, StringSet & res)
         throw Error("'exportReferencesGraph' value is not an array or a string");
 }
 
-DerivationOptions
+DerivationOptions<SingleDerivedPath> derivationOptionsFromStructuredAttrs(
-DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAttrs * parsed, bool shouldWarn)
+    const StoreDirConfig & store,
+    const DerivedPathMap<StringSet> & inputDrvs,
+    const StringMap & env,
+    const StructuredAttrs * parsed,
+    bool shouldWarn,
+    const ExperimentalFeatureSettings & mockXpSettings)
 {
-    DerivationOptions defaults = {};
+    DerivationOptions<SingleDerivedPath> defaults = {};
+
+    std::map<std::string, SingleDerivedPath::Built> placeholders;
+    if (mockXpSettings.isEnabled(Xp::CaDerivations)) {
+        /* Initialize placeholder map from inputDrvs */
+        auto initPlaceholders = [&](this const auto & initPlaceholders,
+                                    ref<const SingleDerivedPath> basePath,
+                                    const DerivedPathMap<StringSet>::ChildNode & node) -> void {
+            for (const auto & outputName : node.value) {
+                auto built = SingleDerivedPath::Built{
+                    .drvPath = basePath,
+                    .output = outputName,
+                };
+                placeholders.insert_or_assign(
+                    DownstreamPlaceholder::fromSingleDerivedPathBuilt(built, mockXpSettings).render(),
+                    std::move(built));
+            }
+
+            for (const auto & [outputName, childNode] : node.childMap) {
+                initPlaceholders(
+                    make_ref<const SingleDerivedPath>(SingleDerivedPath::Built{
+                        .drvPath = basePath,
+                        .output = outputName,
+                    }),
+                    childNode);
+            }
+        };
+
+        for (const auto & [drvPath, outputs] : inputDrvs.map) {
+            auto basePath = make_ref<const SingleDerivedPath>(SingleDerivedPath::Opaque{drvPath});
+            initPlaceholders(basePath, outputs);
+        }
+    }
+
+    auto parseSingleDerivedPath = [&](const std::string & pathS) -> SingleDerivedPath {
+        if (auto it = placeholders.find(pathS); it != placeholders.end())
+            return it->second;
+        else
+            return SingleDerivedPath::Opaque{store.toStorePath(pathS).first};
+    };
+
+    auto parseRef = [&](const std::string & pathS) -> DrvRef<SingleDerivedPath> {
+        if (auto it = placeholders.find(pathS); it != placeholders.end())
+            return it->second;
+        if (store.isStorePath(pathS))
+            return SingleDerivedPath::Opaque{store.toStorePath(pathS).first};
+        else
+            return pathS;
+    };
 
     if (shouldWarn && parsed) {
         auto & structuredAttrs = parsed->structuredAttrs;
@@ -146,14 +226,14 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
     }
 
     return {
-        .outputChecks = [&]() -> OutputChecksVariant {
+        .outputChecks = [&]() -> OutputChecksVariant<SingleDerivedPath> {
             if (parsed) {
                 auto & structuredAttrs = parsed->structuredAttrs;
 
-                std::map<std::string, OutputChecks> res;
+                std::map<std::string, OutputChecks<SingleDerivedPath>> res;
                 if (auto * outputChecks = get(structuredAttrs, "outputChecks")) {
                     for (auto & [outputName, output_] : getObject(*outputChecks)) {
-                        OutputChecks checks;
+                        OutputChecks<SingleDerivedPath> checks;
 
                         auto & output = getObject(output_);
 
@@ -163,13 +243,14 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
                         if (auto maxClosureSize = get(output, "maxClosureSize"))
                             checks.maxClosureSize = maxClosureSize->get<uint64_t>();
 
-                        auto get_ = [&output = output](const std::string & name) -> std::optional<StringSet> {
+                        auto get_ =
+                            [&](const std::string & name) -> std::optional<std::set<DrvRef<SingleDerivedPath>>> {
                             if (auto i = get(output, name)) {
-                                StringSet res;
+                                std::set<DrvRef<SingleDerivedPath>> res;
                                 for (auto j = i->begin(); j != i->end(); ++j) {
                                     if (!j->is_string())
                                         throw Error("attribute '%s' must be a list of strings", name);
-                                    res.insert(j->get<std::string>());
+                                    res.insert(parseRef(j->get<std::string>()));
                                 }
                                 return res;
                             }
@@ -178,7 +259,7 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
 
                         res.insert_or_assign(
                             outputName,
-                            OutputChecks{
+                            OutputChecks<SingleDerivedPath>{
                                 .maxSize = [&]() -> std::optional<uint64_t> {
                                     if (auto maxSize = get(output, "maxSize"))
                                         return maxSize->get<uint64_t>();
@@ -192,21 +273,32 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
                                         return std::nullopt;
                                 }(),
                                 .allowedReferences = get_("allowedReferences"),
-                                .disallowedReferences = get_("disallowedReferences").value_or(StringSet{}),
+                                .disallowedReferences =
+                                    get_("disallowedReferences").value_or(std::set<DrvRef<SingleDerivedPath>>{}),
                                 .allowedRequisites = get_("allowedRequisites"),
-                                .disallowedRequisites = get_("disallowedRequisites").value_or(StringSet{}),
+                                .disallowedRequisites =
+                                    get_("disallowedRequisites").value_or(std::set<DrvRef<SingleDerivedPath>>{}),
                             });
                     }
                 }
                 return res;
             } else {
-                return OutputChecks{
+                auto parseRefSet = [&](const std::optional<StringSet> optionalStringSet)
+                    -> std::optional<std::set<DrvRef<SingleDerivedPath>>> {
+                    if (!optionalStringSet)
+                        return std::nullopt;
+                    auto range = *optionalStringSet | std::views::transform(parseRef);
+                    return std::set<DrvRef<SingleDerivedPath>>(range.begin(), range.end());
+                };
+                return OutputChecks<SingleDerivedPath>{
                     // legacy non-structured-attributes case
                     .ignoreSelfRefs = true,
-                    .allowedReferences = getStringSetAttr(env, parsed, "allowedReferences"),
+                    .allowedReferences = parseRefSet(getStringSetAttr(env, parsed, "allowedReferences")),
-                    .disallowedReferences = getStringSetAttr(env, parsed, "disallowedReferences").value_or(StringSet{}),
+                    .disallowedReferences = parseRefSet(getStringSetAttr(env, parsed, "disallowedReferences"))
-                    .allowedRequisites = getStringSetAttr(env, parsed, "allowedRequisites"),
+                                                .value_or(std::set<DrvRef<SingleDerivedPath>>{}),
-                    .disallowedRequisites = getStringSetAttr(env, parsed, "disallowedRequisites").value_or(StringSet{}),
+                    .allowedRequisites = parseRefSet(getStringSetAttr(env, parsed, "allowedRequisites")),
+                    .disallowedRequisites = parseRefSet(getStringSetAttr(env, parsed, "disallowedRequisites"))
+                                                .value_or(std::set<DrvRef<SingleDerivedPath>>{}),
                 };
             }
         }(),
@@ -245,16 +337,19 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
             }(),
         .exportReferencesGraph =
             [&] {
-                std::map<std::string, StringSet> ret;
+                std::map<std::string, std::set<SingleDerivedPath>> ret;
 
                 if (parsed) {
                     auto * e = optionalValueAt(parsed->structuredAttrs, "exportReferencesGraph");
                     if (!e || !e->is_object())
                         return ret;
-                    for (auto & [key, value] : getObject(*e)) {
+                    for (auto & [key, storePathsJson] : getObject(*e)) {
                         StringSet ss;
-                        flatten(value, ss);
+                        flatten(storePathsJson, ss);
-                        ret.insert_or_assign(key, std::move(ss));
+                        std::set<SingleDerivedPath> storePaths;
+                        for (auto & s : ss)
+                            storePaths.insert(parseSingleDerivedPath(s));
+                        ret.insert_or_assign(key, std::move(storePaths));
                     }
                 } else {
                     auto s = getOr(env, "exportReferencesGraph", "");
@@ -268,7 +363,7 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
                             throw Error("invalid file name '%s' in 'exportReferencesGraph'", fileName);
 
                         auto & storePathS = *i++;
-                        ret.insert_or_assign(std::move(fileName), StringSet{storePathS});
+                        ret.insert_or_assign(std::move(fileName), std::set{parseSingleDerivedPath(storePathS)});
                     }
                 }
                 return ret;
@@ -286,28 +381,8 @@ DerivationOptions::fromStructuredAttrs(const StringMap & env, const StructuredAt
     };
 }
 
-std::map<std::string, StorePathSet>
+template<typename Input>
-DerivationOptions::getParsedExportReferencesGraph(const StoreDirConfig & store) const
+StringSet DerivationOptions<Input>::getRequiredSystemFeatures(const BasicDerivation & drv) const
-{
-    std::map<std::string, StorePathSet> res;
-
-    for (auto & [fileName, ss] : exportReferencesGraph) {
-        StorePathSet storePaths;
-        for (auto & storePathS : ss) {
-            if (!store.isInStore(storePathS))
-                throw BuildError(
-                    BuildResult::Failure::InputRejected,
-                    "'exportReferencesGraph' contains a non-store path '%1%'",
-                    storePathS);
-            storePaths.insert(store.toStorePath(storePathS).first);
-        }
-        res.insert_or_assign(fileName, storePaths);
-    }
-
-    return res;
-}
-
-StringSet DerivationOptions::getRequiredSystemFeatures(const BasicDerivation & drv) const
 {
     // FIXME: cache this?
     StringSet res;
@@ -318,7 +393,8 @@ StringSet DerivationOptions::getRequiredSystemFeatures(const BasicDerivation & d
     return res;
 }
 
-bool DerivationOptions::canBuildLocally(Store & localStore, const BasicDerivation & drv) const
+template<typename Input>
+bool DerivationOptions<Input>::canBuildLocally(Store & localStore, const BasicDerivation & drv) const
 {
     if (drv.platform != settings.thisSystem.get() && !settings.extraPlatforms.get().count(drv.platform)
         && !drv.isBuiltin())
@@ -334,42 +410,194 @@ bool DerivationOptions::canBuildLocally(Store & localStore, const BasicDerivatio
     return true;
 }
 
-bool DerivationOptions::willBuildLocally(Store & localStore, const BasicDerivation & drv) const
+template<typename Input>
+bool DerivationOptions<Input>::willBuildLocally(Store & localStore, const BasicDerivation & drv) const
 {
     return preferLocalBuild && canBuildLocally(localStore, drv);
 }
 
-bool DerivationOptions::substitutesAllowed() const
+template<typename Input>
+bool DerivationOptions<Input>::substitutesAllowed() const
 {
     return settings.alwaysAllowSubstitutes ? true : allowSubstitutes;
 }
 
-bool DerivationOptions::useUidRange(const BasicDerivation & drv) const
+template<typename Input>
+bool DerivationOptions<Input>::useUidRange(const BasicDerivation & drv) const
 {
     return getRequiredSystemFeatures(drv).count("uid-range");
 }
 
+std::optional<DerivationOptions<StorePath>> tryResolve(
+    const DerivationOptions<SingleDerivedPath> & drvOptions,
+    std::function<std::optional<StorePath>(ref<const SingleDerivedPath> drvPath, const std::string & outputName)>
+        queryResolutionChain)
+{
+    auto tryResolvePath = [&](const SingleDerivedPath & input) -> std::optional<StorePath> {
+        return std::visit(
+            overloaded{
+                [](const SingleDerivedPath::Opaque & p) -> std::optional<StorePath> { return p.path; },
+                [&](const SingleDerivedPath::Built & p) -> std::optional<StorePath> {
+                    return queryResolutionChain(p.drvPath, p.output);
+                }},
+            input.raw());
+    };
+
+    auto tryResolveRef = [&](const DrvRef<SingleDerivedPath> & ref) -> std::optional<DrvRef<StorePath>> {
+        return std::visit(
+            overloaded{
+                [](const OutputName & outputName) -> std::optional<DrvRef<StorePath>> { return outputName; },
+                [&](const SingleDerivedPath & input) -> std::optional<DrvRef<StorePath>> {
+                    return tryResolvePath(input);
+                }},
+            ref);
+    };
+
+    auto tryResolveRefSet =
+        [&](const std::set<DrvRef<SingleDerivedPath>> & refSet) -> std::optional<std::set<DrvRef<StorePath>>> {
+        std::set<DrvRef<StorePath>> resolvedSet;
+        for (const auto & ref : refSet) {
+            auto resolvedRef = tryResolveRef(ref);
+            if (!resolvedRef)
+                return std::nullopt;
+            resolvedSet.insert(*resolvedRef);
+        }
+        return resolvedSet;
+    };
+
+    // Helper function to try resolving OutputChecks using functional style
+    auto tryResolveOutputChecks = [&](const DerivationOptions<SingleDerivedPath>::OutputChecks & checks)
+        -> std::optional<DerivationOptions<StorePath>::OutputChecks> {
+        std::optional<std::set<DrvRef<StorePath>>> resolvedAllowedReferences;
+        if (checks.allowedReferences) {
+            resolvedAllowedReferences = tryResolveRefSet(*checks.allowedReferences);
+            if (!resolvedAllowedReferences)
+                return std::nullopt;
+        }
+
+        std::optional<std::set<DrvRef<StorePath>>> resolvedAllowedRequisites;
+        if (checks.allowedRequisites) {
+            resolvedAllowedRequisites = tryResolveRefSet(*checks.allowedRequisites);
+            if (!resolvedAllowedRequisites)
+                return std::nullopt;
+        }
+
+        auto resolvedDisallowedReferences = tryResolveRefSet(checks.disallowedReferences);
+        if (!resolvedDisallowedReferences)
+            return std::nullopt;
+
+        auto resolvedDisallowedRequisites = tryResolveRefSet(checks.disallowedRequisites);
+        if (!resolvedDisallowedRequisites)
+            return std::nullopt;
+
+        return DerivationOptions<StorePath>::OutputChecks{
+            .ignoreSelfRefs = checks.ignoreSelfRefs,
+            .maxSize = checks.maxSize,
+            .maxClosureSize = checks.maxClosureSize,
+            .allowedReferences = resolvedAllowedReferences,
+            .disallowedReferences = *resolvedDisallowedReferences,
+            .allowedRequisites = resolvedAllowedRequisites,
+            .disallowedRequisites = *resolvedDisallowedRequisites,
+        };
+    };
+
+    // Helper function to resolve exportReferencesGraph using functional style
+    auto tryResolveExportReferencesGraph = [&](const std::map<std::string, std::set<SingleDerivedPath>> & exportGraph)
+        -> std::optional<std::map<std::string, std::set<StorePath>>> {
+        std::map<std::string, std::set<StorePath>> resolved;
+        for (const auto & [name, inputPaths] : exportGraph) {
+            std::set<StorePath> resolvedPaths;
+            for (const auto & inputPath : inputPaths) {
+                auto resolvedPath = tryResolvePath(inputPath);
+                if (!resolvedPath)
+                    return std::nullopt;
+                resolvedPaths.insert(*resolvedPath);
+            }
+            resolved.emplace(name, std::move(resolvedPaths));
+        }
+        return resolved;
+    };
+
+    // Resolve outputChecks using functional style with std::visit
+    auto resolvedOutputChecks = std::visit(
+        overloaded{
+            [&](const DerivationOptions<SingleDerivedPath>::OutputChecks & checks)
+                -> std::optional<std::variant<
+                    DerivationOptions<StorePath>::OutputChecks,
+                    std::map<std::string, DerivationOptions<StorePath>::OutputChecks>>> {
+                auto resolved = tryResolveOutputChecks(checks);
+                if (!resolved)
+                    return std::nullopt;
+                return std::variant<
+                    DerivationOptions<StorePath>::OutputChecks,
+                    std::map<std::string, DerivationOptions<StorePath>::OutputChecks>>(*resolved);
+            },
+            [&](const std::map<std::string, DerivationOptions<SingleDerivedPath>::OutputChecks> & checksMap)
+                -> std::optional<std::variant<
+                    DerivationOptions<StorePath>::OutputChecks,
+                    std::map<std::string, DerivationOptions<StorePath>::OutputChecks>>> {
+                std::map<std::string, DerivationOptions<StorePath>::OutputChecks> resolvedMap;
+                for (const auto & [outputName, checks] : checksMap) {
+                    auto resolved = tryResolveOutputChecks(checks);
+                    if (!resolved)
+                        return std::nullopt;
+                    resolvedMap.emplace(outputName, *resolved);
+                }
+                return std::variant<
+                    DerivationOptions<StorePath>::OutputChecks,
+                    std::map<std::string, DerivationOptions<StorePath>::OutputChecks>>(resolvedMap);
+            }},
+        drvOptions.outputChecks);
+
+    if (!resolvedOutputChecks)
+        return std::nullopt;
+
+    // Resolve exportReferencesGraph
+    auto resolvedExportGraph = tryResolveExportReferencesGraph(drvOptions.exportReferencesGraph);
+    if (!resolvedExportGraph)
+        return std::nullopt;
+
+    // Return resolved DerivationOptions using designated initializers
+    return DerivationOptions<StorePath>{
+        .outputChecks = *resolvedOutputChecks,
+        .unsafeDiscardReferences = drvOptions.unsafeDiscardReferences,
+        .passAsFile = drvOptions.passAsFile,
+        .exportReferencesGraph = *resolvedExportGraph,
+        .additionalSandboxProfile = drvOptions.additionalSandboxProfile,
+        .noChroot = drvOptions.noChroot,
+        .impureHostDeps = drvOptions.impureHostDeps,
+        .impureEnvVars = drvOptions.impureEnvVars,
+        .allowLocalNetworking = drvOptions.allowLocalNetworking,
+        .requiredSystemFeatures = drvOptions.requiredSystemFeatures,
+        .preferLocalBuild = drvOptions.preferLocalBuild,
+        .allowSubstitutes = drvOptions.allowSubstitutes,
+    };
+}
+
+template struct DerivationOptions<StorePath>;
+template struct DerivationOptions<SingleDerivedPath>;
+
 } // namespace nix
 
 namespace nlohmann {
 
 using namespace nix;
 
-DerivationOptions adl_serializer<DerivationOptions>::from_json(const json & json_)
+DerivationOptions<SingleDerivedPath> adl_serializer<DerivationOptions<SingleDerivedPath>>::from_json(const json & json_)
 {
     auto & json = getObject(json_);
 
     return {
-        .outputChecks = [&]() -> OutputChecksVariant {
+        .outputChecks = [&]() -> OutputChecksVariant<SingleDerivedPath> {
             auto outputChecks = getObject(valueAt(json, "outputChecks"));
 
             auto forAllOutputsOpt = optionalValueAt(outputChecks, "forAllOutputs");
             auto perOutputOpt = optionalValueAt(outputChecks, "perOutput");
 
             if (forAllOutputsOpt && !perOutputOpt) {
-                return static_cast<OutputChecks>(*forAllOutputsOpt);
+                return static_cast<OutputChecks<SingleDerivedPath>>(*forAllOutputsOpt);
             } else if (perOutputOpt && !forAllOutputsOpt) {
-                return static_cast<std::map<std::string, OutputChecks>>(*perOutputOpt);
+                return static_cast<std::map<std::string, OutputChecks<SingleDerivedPath>>>(*perOutputOpt);
             } else {
                 throw Error("Exactly one of 'perOutput' or 'forAllOutputs' is required");
             }
@@ -377,7 +605,7 @@ DerivationOptions adl_serializer<DerivationOptions>::from_json(const json & json
 
         .unsafeDiscardReferences = valueAt(json, "unsafeDiscardReferences"),
         .passAsFile = getStringSet(valueAt(json, "passAsFile")),
-        .exportReferencesGraph = getMap<StringSet>(getObject(valueAt(json, "exportReferencesGraph")), getStringSet),
+        .exportReferencesGraph = valueAt(json, "exportReferencesGraph"),
 
         .additionalSandboxProfile = getString(valueAt(json, "additionalSandboxProfile")),
         .noChroot = getBoolean(valueAt(json, "noChroot")),
@@ -391,16 +619,17 @@ DerivationOptions adl_serializer<DerivationOptions>::from_json(const json & json
     };
 }
 
-void adl_serializer<DerivationOptions>::to_json(json & json, const DerivationOptions & o)
+void adl_serializer<DerivationOptions<SingleDerivedPath>>::to_json(
+    json & json, const DerivationOptions<SingleDerivedPath> & o)
 {
     json["outputChecks"] = std::visit(
         overloaded{
-            [&](const OutputChecks & checks) {
+            [&](const OutputChecks<SingleDerivedPath> & checks) {
                 nlohmann::json outputChecks;
                 outputChecks["forAllOutputs"] = checks;
                 return outputChecks;
             },
-            [&](const std::map<std::string, OutputChecks> & checksPerOutput) {
+            [&](const std::map<std::string, OutputChecks<SingleDerivedPath>> & checksPerOutput) {
                 nlohmann::json outputChecks;
                 outputChecks["perOutput"] = checksPerOutput;
                 return outputChecks;
@@ -423,7 +652,7 @@ void adl_serializer<DerivationOptions>::to_json(json & json, const DerivationOpt
     json["allowSubstitutes"] = o.allowSubstitutes;
 }
 
-DerivationOptions::OutputChecks adl_serializer<DerivationOptions::OutputChecks>::from_json(const json & json_)
+OutputChecks<SingleDerivedPath> adl_serializer<OutputChecks<SingleDerivedPath>>::from_json(const json & json_)
 {
     auto & json = getObject(json_);
 
@@ -431,14 +660,16 @@ DerivationOptions::OutputChecks adl_serializer<DerivationOptions::OutputChecks>:
         .ignoreSelfRefs = getBoolean(valueAt(json, "ignoreSelfRefs")),
         .maxSize = ptrToOwned<uint64_t>(getNullable(valueAt(json, "maxSize"))),
         .maxClosureSize = ptrToOwned<uint64_t>(getNullable(valueAt(json, "maxClosureSize"))),
-        .allowedReferences = ptrToOwned<StringSet>(getNullable(valueAt(json, "allowedReferences"))),
+        .allowedReferences =
-        .disallowedReferences = getStringSet(valueAt(json, "disallowedReferences")),
+            ptrToOwned<std::set<DrvRef<SingleDerivedPath>>>(getNullable(valueAt(json, "allowedReferences"))),
-        .allowedRequisites = ptrToOwned<StringSet>(getNullable(valueAt(json, "allowedRequisites"))),
+        .disallowedReferences = valueAt(json, "disallowedReferences"),
-        .disallowedRequisites = getStringSet(valueAt(json, "disallowedRequisites")),
+        .allowedRequisites =
+            ptrToOwned<std::set<DrvRef<SingleDerivedPath>>>(getNullable(valueAt(json, "allowedRequisites"))),
+        .disallowedRequisites = valueAt(json, "disallowedRequisites"),
     };
 }
 
-void adl_serializer<DerivationOptions::OutputChecks>::to_json(json & json, const DerivationOptions::OutputChecks & c)
+void adl_serializer<OutputChecks<SingleDerivedPath>>::to_json(json & json, const OutputChecks<SingleDerivedPath> & c)
 {
     json["ignoreSelfRefs"] = c.ignoreSelfRefs;
     json["maxSize"] = c.maxSize;

src/libstore/derivations.cc

@@ -13,6 +13,7 @@
 #include <boost/container/small_vector.hpp>
 #include <boost/unordered/concurrent_flat_map.hpp>
 #include <nlohmann/json.hpp>
+#include <optional>
 
 namespace nix {
 
@@ -791,71 +792,63 @@ std::string outputPathName(std::string_view drvName, OutputNameView outputName)
 
 DerivationType BasicDerivation::type() const
 {
-    std::set<std::string_view> inputAddressedOutputs, fixedCAOutputs, floatingCAOutputs, deferredIAOutputs,
-        impureOutputs;
     std::optional<HashAlgorithm> floatingHashAlgo;
+    std::optional<DerivationType> ty;
+
+    auto decide = [&](DerivationType newTy) {
+        if (!ty)
+            ty = newTy;
+        else if (ty.value() != newTy)
+            throw Error("can't mix derivation output types");
+        else if (ty.value() == DerivationType::ContentAddressed{.sandboxed = false, .fixed = true})
+            // FIXME: Experimental feature?
+            throw Error("only one fixed output is allowed for now");
+    };
 
     for (auto & i : outputs) {
         std::visit(
             overloaded{
-                [&](const DerivationOutput::InputAddressed &) { inputAddressedOutputs.insert(i.first); },
+                [&](const DerivationOutput::InputAddressed &) {
-                [&](const DerivationOutput::CAFixed &) { fixedCAOutputs.insert(i.first); },
+                    decide(
-                [&](const DerivationOutput::CAFloating & dof) {
+                        DerivationType::InputAddressed{
-                    floatingCAOutputs.insert(i.first);
+                            .deferred = false,
-                    if (!floatingHashAlgo) {
+                        });
-                        floatingHashAlgo = dof.hashAlgo;
-                    } else {
-                        if (*floatingHashAlgo != dof.hashAlgo)
-                            throw Error("all floating outputs must use the same hash algorithm");
-                    }
                 },
-                [&](const DerivationOutput::Deferred &) { deferredIAOutputs.insert(i.first); },
+                [&](const DerivationOutput::CAFixed &) {
-                [&](const DerivationOutput::Impure &) { impureOutputs.insert(i.first); },
+                    decide(
+                        DerivationType::ContentAddressed{
+                            .sandboxed = false,
+                            .fixed = true,
+                        });
+                    if (i.first != "out"sv)
+                        throw Error("single fixed output must be named \"out\"");
+                },
+                [&](const DerivationOutput::CAFloating & dof) {
+                    decide(
+                        DerivationType::ContentAddressed{
+                            .sandboxed = true,
+                            .fixed = false,
+                        });
+                    if (!floatingHashAlgo)
+                        floatingHashAlgo = dof.hashAlgo;
+                    else if (*floatingHashAlgo != dof.hashAlgo)
+                        throw Error("all floating outputs must use the same hash algorithm");
+                },
+                [&](const DerivationOutput::Deferred &) {
+                    decide(
+                        DerivationType::InputAddressed{
+                            .deferred = true,
+                        });
+                },
+                [&](const DerivationOutput::Impure &) { decide(DerivationType::Impure{}); },
             },
             i.second.raw);
     }
 
-    if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty()
+    if (!ty)
-        && deferredIAOutputs.empty() && impureOutputs.empty())
         throw Error("must have at least one output");
 
-    if (!inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty()
+    return ty.value();
-        && deferredIAOutputs.empty() && impureOutputs.empty())
-        return DerivationType::InputAddressed{
-            .deferred = false,
-        };
-
-    if (inputAddressedOutputs.empty() && !fixedCAOutputs.empty() && floatingCAOutputs.empty()
-        && deferredIAOutputs.empty() && impureOutputs.empty()) {
-        if (fixedCAOutputs.size() > 1)
-            // FIXME: Experimental feature?
-            throw Error("only one fixed output is allowed for now");
-        if (*fixedCAOutputs.begin() != "out"sv)
-            throw Error("single fixed output must be named \"out\"");
-        return DerivationType::ContentAddressed{
-            .sandboxed = false,
-            .fixed = true,
-        };
-    }
-
-    if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && !floatingCAOutputs.empty()
-        && deferredIAOutputs.empty() && impureOutputs.empty())
-        return DerivationType::ContentAddressed{
-            .sandboxed = true,
-            .fixed = false,
-        };
-
-    if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty()
-        && !deferredIAOutputs.empty() && impureOutputs.empty())
-        return DerivationType::InputAddressed{
-            .deferred = true,
-        };
-
-    if (inputAddressedOutputs.empty() && fixedCAOutputs.empty() && floatingCAOutputs.empty()
-        && deferredIAOutputs.empty() && !impureOutputs.empty())
-        return DerivationType::Impure{};
-
-    throw Error("can't mix derivation output types");
 }
 
 DrvHashes drvHashes;

src/libstore/downstream-placeholder.cc

@@ -1,5 +1,6 @@
 #include "nix/store/downstream-placeholder.hh"
 #include "nix/store/derivations.hh"
+#include "nix/util/json-utils.hh"
 
 namespace nix {
 
@@ -49,3 +50,45 @@ DownstreamPlaceholder DownstreamPlaceholder::fromSingleDerivedPathBuilt(
 }
 
 } // namespace nix
+
+namespace nlohmann {
+
+using namespace nix;
+
+template<typename Item>
+DrvRef<Item> adl_serializer<DrvRef<Item>>::from_json(const json & json)
+{
+    // OutputName case: { "drvPath": "self", "output": <output> }
+    if (json.type() == nlohmann::json::value_t::object) {
+        auto & obj = getObject(json);
+        if (auto * drvPath_ = get(obj, "drvPath")) {
+            auto & drvPath = *drvPath_;
+            if (drvPath.type() == nlohmann::json::value_t::string && getString(drvPath) == "self") {
+                return getString(valueAt(obj, "output"));
+            }
+        }
+    }
+
+    // Input case
+    return adl_serializer<Item>::from_json(json);
+}
+
+template<typename Item>
+void adl_serializer<DrvRef<Item>>::to_json(json & json, const DrvRef<Item> & ref)
+{
+    std::visit(
+        overloaded{
+            [&](const OutputName & outputName) {
+                json = nlohmann::json::object();
+                json["drvPath"] = "self";
+                json["output"] = outputName;
+            },
+            [&](const Item & item) { json = item; },
+        },
+        ref);
+}
+
+template struct adl_serializer<nix::DrvRef<StorePath>>;
+template struct adl_serializer<nix::DrvRef<SingleDerivedPath>>;
+
+} // namespace nlohmann

src/libstore/filetransfer.cc

@@ -151,15 +151,23 @@ struct curlFileTransfer : public FileTransfer
             }
         }
 
-        void failEx(std::exception_ptr ex)
+        void failEx(std::exception_ptr ex) noexcept
         {
             assert(!done);
             done = true;
+            try {
+                std::rethrow_exception(ex);
+            } catch (nix::Error & e) {
+                /* Add more context to the error message. */
+                e.addTrace({}, "during %s of '%s'", Uncolored(request.verb()), request.uri.to_string());
+            } catch (...) {
+                /* Can't add more context to the error. */
+            }
             callback.rethrow(ex);
         }
 
         template<class T>
-        void fail(T && e)
+        void fail(T && e) noexcept
         {
             failEx(std::make_exception_ptr(std::forward<T>(e)));
         }
@@ -168,32 +176,30 @@ struct curlFileTransfer : public FileTransfer
         std::shared_ptr<FinishSink> decompressionSink;
         std::optional<StringSink> errorSink;
 
-        std::exception_ptr writeException;
+        std::exception_ptr callbackException;
 
-        size_t writeCallback(void * contents, size_t size, size_t nmemb)
+        size_t writeCallback(void * contents, size_t size, size_t nmemb) noexcept
-        {
+        try {
-            try {
+            size_t realSize = size * nmemb;
-                size_t realSize = size * nmemb;
+            result.bodySize += realSize;
-                result.bodySize += realSize;
 
-                if (!decompressionSink) {
+            if (!decompressionSink) {
-                    decompressionSink = makeDecompressionSink(encoding, finalSink);
+                decompressionSink = makeDecompressionSink(encoding, finalSink);
-                    if (!successfulStatuses.count(getHTTPStatus())) {
+                if (!successfulStatuses.count(getHTTPStatus())) {
-                        // In this case we want to construct a TeeSink, to keep
+                    // In this case we want to construct a TeeSink, to keep
-                        // the response around (which we figure won't be big
+                    // the response around (which we figure won't be big
-                        // like an actual download should be) to improve error
+                    // like an actual download should be) to improve error
-                        // messages.
+                    // messages.
-                        errorSink = StringSink{};
+                    errorSink = StringSink{};
-                    }
                 }
-
-                (*decompressionSink)({(char *) contents, realSize});
-
-                return realSize;
-            } catch (...) {
-                writeException = std::current_exception();
-                return 0;
             }
+
+            (*decompressionSink)({(char *) contents, realSize});
+
+            return realSize;
+        } catch (...) {
+            callbackException = std::current_exception();
+            return 0;
         }
 
         static size_t writeCallbackWrapper(void * contents, size_t size, size_t nmemb, void * userp)
@@ -209,8 +215,8 @@ struct curlFileTransfer : public FileTransfer
                 result.urls.push_back(effectiveUriCStr);
         }
 
-        size_t headerCallback(void * contents, size_t size, size_t nmemb)
+        size_t headerCallback(void * contents, size_t size, size_t nmemb) noexcept
-        {
+        try {
             size_t realSize = size * nmemb;
             std::string line((char *) contents, realSize);
             printMsg(lvlVomit, "got header for '%s': %s", request.uri, trim(line));
@@ -263,6 +269,15 @@ struct curlFileTransfer : public FileTransfer
                 }
             }
             return realSize;
+        } catch (...) {
+#if LIBCURL_VERSION_NUM >= 0x075700
+            /* https://curl.se/libcurl/c/CURLOPT_HEADERFUNCTION.html:
+               You can also abort the transfer by returning CURL_WRITEFUNC_ERROR. */
+            callbackException = std::current_exception();
+            return CURL_WRITEFUNC_ERROR;
+#else
+            return realSize;
+#endif
         }
 
         static size_t headerCallbackWrapper(void * contents, size_t size, size_t nmemb, void * userp)
@@ -270,14 +285,17 @@ struct curlFileTransfer : public FileTransfer
             return ((TransferItem *) userp)->headerCallback(contents, size, nmemb);
         }
 
-        int progressCallback(curl_off_t dltotal, curl_off_t dlnow)
+        int progressCallback(curl_off_t dltotal, curl_off_t dlnow) noexcept
-        {
+        try {
-            try {
+            act.progress(dlnow, dltotal);
-                act.progress(dlnow, dltotal);
-            } catch (nix::Interrupted &) {
-                assert(getInterrupted());
-            }
             return getInterrupted();
+        } catch (nix::Interrupted &) {
+            assert(getInterrupted());
+            return 1;
+        } catch (...) {
+            /* Something unexpected has happened like logger throwing an exception. */
+            callbackException = std::current_exception();
+            return 1;
         }
 
         static int progressCallbackWrapper(
@@ -288,11 +306,14 @@ struct curlFileTransfer : public FileTransfer
             return item.progressCallback(isUpload ? ultotal : dltotal, isUpload ? ulnow : dlnow);
         }
 
-        static int debugCallback(CURL * handle, curl_infotype type, char * data, size_t size, void * userptr)
+        static int debugCallback(CURL * handle, curl_infotype type, char * data, size_t size, void * userptr) noexcept
-        {
+        try {
             if (type == CURLINFO_TEXT)
                 vomit("curl: %s", chomp(std::string(data, size)));
             return 0;
+        } catch (...) {
+            /* Swallow the exception. Nothing left to do. */
+            return 0;
         }
 
         size_t readCallback(char * buffer, size_t size, size_t nitems) noexcept
@@ -302,6 +323,7 @@ struct curlFileTransfer : public FileTransfer
         } catch (EndOfFile &) {
             return 0;
         } catch (...) {
+            callbackException = std::current_exception();
             return CURL_READFUNC_ABORT;
         }
 
@@ -333,6 +355,7 @@ struct curlFileTransfer : public FileTransfer
             }
             return CURL_SEEKFUNC_OK;
         } catch (...) {
+            callbackException = std::current_exception();
             return CURL_SEEKFUNC_FAIL;
         }
 
@@ -386,17 +409,17 @@ struct curlFileTransfer : public FileTransfer
             if (settings.downloadSpeed.get() > 0)
                 curl_easy_setopt(req, CURLOPT_MAX_RECV_SPEED_LARGE, (curl_off_t) (settings.downloadSpeed.get() * 1024));
 
-            if (request.method == HttpMethod::HEAD)
+            if (request.method == HttpMethod::Head)
                 curl_easy_setopt(req, CURLOPT_NOBODY, 1);
 
-            if (request.method == HttpMethod::DELETE)
+            if (request.method == HttpMethod::Delete)
                 curl_easy_setopt(req, CURLOPT_CUSTOMREQUEST, "DELETE");
 
             if (request.data) {
-                if (request.method == HttpMethod::POST) {
+                if (request.method == HttpMethod::Post) {
                     curl_easy_setopt(req, CURLOPT_POST, 1L);
                     curl_easy_setopt(req, CURLOPT_POSTFIELDSIZE_LARGE, (curl_off_t) request.data->sizeHint);
-                } else if (request.method == HttpMethod::PUT) {
+                } else if (request.method == HttpMethod::Put) {
                     curl_easy_setopt(req, CURLOPT_UPLOAD, 1L);
                     curl_easy_setopt(req, CURLOPT_INFILESIZE_LARGE, (curl_off_t) request.data->sizeHint);
                 } else {
@@ -476,7 +499,7 @@ struct curlFileTransfer : public FileTransfer
                 try {
                     decompressionSink->finish();
                 } catch (...) {
-                    writeException = std::current_exception();
+                    callbackException = std::current_exception();
                 }
             }
 
@@ -485,8 +508,8 @@ struct curlFileTransfer : public FileTransfer
                 httpStatus = 304;
             }
 
-            if (writeException)
+            if (callbackException)
-                failEx(writeException);
+                failEx(callbackException);
 
             else if (code == CURLE_OK && successfulStatuses.count(httpStatus)) {
                 result.cached = httpStatus == 304;

src/libstore/http-binary-cache-store.cc

@@ -120,7 +120,7 @@ bool HttpBinaryCacheStore::fileExists(const std::string & path)
 
     try {
         FileTransferRequest request(makeRequest(path));
-        request.method = HttpMethod::HEAD;
+        request.method = HttpMethod::Head;
         getFileTransfer()->download(request);
         return true;
     } catch (FileTransferError & e) {
@@ -141,7 +141,7 @@ void HttpBinaryCacheStore::upload(
     std::optional<Headers> headers)
 {
     auto req = makeRequest(path);
-    req.method = HttpMethod::PUT;
+    req.method = HttpMethod::Put;
 
     if (headers) {
         req.headers.reserve(req.headers.size() + headers->size());

src/libstore/include/nix/store/build/derivation-builder.hh

@@ -69,7 +69,7 @@ struct DerivationBuilderParams
      *
      * @todo this should be part of `Derivation`.
      */
-    const DerivationOptions & drvOptions;
+    const DerivationOptions<StorePath> & drvOptions;
 
     // The remainder is state held during the build.
 

src/libstore/include/nix/store/build/derivation-building-goal.hh

@@ -52,8 +52,6 @@ private:
      */
     std::unique_ptr<Derivation> drv;
 
-    std::unique_ptr<DerivationOptions> drvOptions;
-
     /**
      * The remainder is state held during the build.
      */
@@ -115,7 +113,8 @@ private:
     /**
      * Is the build hook willing to perform the build?
      */
-    HookReply tryBuildHook(const std::map<std::string, InitialOutput> & initialOutputs);
+    HookReply tryBuildHook(
+        const std::map<std::string, InitialOutput> & initialOutputs, const DerivationOptions<StorePath> & drvOptions);
 
     /**
      * Open a log file and a pipe to it.

src/libstore/include/nix/store/build/derivation-env-desugar.hh

@@ -8,6 +8,7 @@ namespace nix {
 
 class Store;
 struct Derivation;
+template<typename Input>
 struct DerivationOptions;
 
 /**
@@ -77,7 +78,10 @@ struct DesugaredEnv
      * just part of `Derivation`.
      */
     static DesugaredEnv create(
-        Store & store, const Derivation & drv, const DerivationOptions & drvOptions, const StorePathSet & inputPaths);
+        Store & store,
+        const Derivation & drv,
+        const DerivationOptions<StorePath> & drvOptions,
+        const StorePathSet & inputPaths);
 };
 
 } // namespace nix

src/libstore/include/nix/store/derivation-options.hh

@@ -8,7 +8,8 @@
 
 #include "nix/util/types.hh"
 #include "nix/util/json-impls.hh"
-#include "nix/store/path.hh"
+#include "nix/store/store-dir-config.hh"
+#include "nix/store/downstream-placeholder.hh"
 
 namespace nix {
 
@@ -17,6 +18,9 @@ struct StoreDirConfig;
 struct BasicDerivation;
 struct StructuredAttrs;
 
+template<typename V>
+struct DerivedPathMap;
+
 /**
  * This represents all the special options on a `Derivation`.
  *
@@ -34,6 +38,7 @@ struct StructuredAttrs;
  * separately. That would be nice to separate concerns, and not make any
  * environment variable names magical.
  */
+template<typename Input>
 struct DerivationOptions
 {
     struct OutputChecks
@@ -41,13 +46,15 @@ struct DerivationOptions
         bool ignoreSelfRefs = false;
         std::optional<uint64_t> maxSize, maxClosureSize;
 
+        using DrvRef = nix::DrvRef<Input>;
+
         /**
          * env: allowedReferences
          *
          * A value of `nullopt` indicates that the check is skipped.
          * This means that all references are allowed.
          */
-        std::optional<StringSet> allowedReferences;
+        std::optional<std::set<DrvRef>> allowedReferences;
 
         /**
          * env: disallowedReferences
@@ -55,21 +62,21 @@ struct DerivationOptions
          * No needed for `std::optional`, because skipping the check is
          * the same as disallowing the references.
          */
-        StringSet disallowedReferences;
+        std::set<DrvRef> disallowedReferences;
 
         /**
          * env: allowedRequisites
          *
          * See `allowedReferences`
          */
-        std::optional<StringSet> allowedRequisites;
+        std::optional<std::set<DrvRef>> allowedRequisites;
 
         /**
          * env: disallowedRequisites
          *
          * See `disallowedReferences`
          */
-        StringSet disallowedRequisites;
+        std::set<DrvRef> disallowedRequisites;
 
         bool operator==(const OutputChecks &) const = default;
     };
@@ -116,23 +123,7 @@ struct DerivationOptions
      * attributes give to the builder. The set of paths in the original JSON
      * is replaced with a list of `PathInfo` in JSON format.
      */
-    std::map<std::string, StringSet> exportReferencesGraph;
+    std::map<std::string, std::set<Input>> exportReferencesGraph;
-
-    /**
-     * Once a derivations is resolved, the strings in in
-     * `exportReferencesGraph` should all be store paths (with possible
-     * suffix paths, but those are discarded).
-     *
-     * @return The parsed path set for for each key in the map.
-     *
-     * @todo Ideally, `exportReferencesGraph` would just store
-     * `StorePath`s for this, but we can't just do that, because for CA
-     * derivations they is actually in general `DerivedPath`s (via
-     * placeholder strings) until the derivation is resolved and exact
-     * inputs store paths are known. We can use better types for that
-     * too, but that is a longer project.
-     */
-    std::map<std::string, StorePathSet> getParsedExportReferencesGraph(const StoreDirConfig & store) const;
 
     /**
      * env: __sandboxProfile
@@ -185,18 +176,6 @@ struct DerivationOptions
 
     bool operator==(const DerivationOptions &) const = default;
 
-    /**
-     * Parse this information from its legacy encoding as part of the
-     * environment. This should not be used with nice greenfield formats
-     * (e.g. JSON) but is necessary for supporting old formats (e.g.
-     * ATerm).
-     */
-    static DerivationOptions
-    fromStructuredAttrs(const StringMap & env, const StructuredAttrs * parsed, bool shouldWarn = true);
-
-    static DerivationOptions
-    fromStructuredAttrs(const StringMap & env, const std::optional<StructuredAttrs> & parsed, bool shouldWarn = true);
-
     /**
      * @param drv Must be the same derivation we parsed this from. In
      * the future we'll flip things around so a `BasicDerivation` has
@@ -222,7 +201,49 @@ struct DerivationOptions
     bool useUidRange(const BasicDerivation & drv) const;
 };
 
+extern template struct DerivationOptions<StorePath>;
+extern template struct DerivationOptions<SingleDerivedPath>;
+
+struct DerivationOutput;
+
+/**
+ * Parse this information from its legacy encoding as part of the
+ * environment. This should not be used with nice greenfield formats
+ * (e.g. JSON) but is necessary for supporting old formats (e.g.
+ * ATerm).
+ */
+DerivationOptions<SingleDerivedPath> derivationOptionsFromStructuredAttrs(
+    const StoreDirConfig & store,
+    const DerivedPathMap<StringSet> & inputDrvs,
+    const StringMap & env,
+    const StructuredAttrs * parsed,
+    bool shouldWarn = true,
+    const ExperimentalFeatureSettings & mockXpSettings = experimentalFeatureSettings);
+
+DerivationOptions<StorePath> derivationOptionsFromStructuredAttrs(
+    const StoreDirConfig & store,
+    const StringMap & env,
+    const StructuredAttrs * parsed,
+    bool shouldWarn = true,
+    const ExperimentalFeatureSettings & mockXpSettings = experimentalFeatureSettings);
+
+/**
+ * This is the counterpart of `Derivation::tryResolve`. In particular,
+ * it takes the same sort of callback, which is used to reolve
+ * non-constant deriving paths.
+ *
+ * We need this function when resolving a derivation, and we will use
+ * this as part of that if/when `Derivation` includes
+ * `DerivationOptions`
+ */
+std::optional<DerivationOptions<StorePath>> tryResolve(
+    const DerivationOptions<SingleDerivedPath> & drvOptions,
+    std::function<std::optional<StorePath>(ref<const SingleDerivedPath> drvPath, const std::string & outputName)>
+        queryResolutionChain);
+
 }; // namespace nix
 
-JSON_IMPL(DerivationOptions);
+JSON_IMPL(nix::DerivationOptions<nix::StorePath>);
-JSON_IMPL(DerivationOptions::OutputChecks)
+JSON_IMPL(nix::DerivationOptions<nix::SingleDerivedPath>);
+JSON_IMPL(nix::DerivationOptions<nix::StorePath>::OutputChecks)
+JSON_IMPL(nix::DerivationOptions<nix::SingleDerivedPath>::OutputChecks)

src/libstore/include/nix/store/downstream-placeholder.hh

@@ -2,11 +2,23 @@
 ///@file
 
 #include "nix/util/hash.hh"
+#include "nix/util/json-impls.hh"
 #include "nix/store/path.hh"
 #include "nix/store/derived-path.hh"
 
 namespace nix {
 
+/**
+ * A reference is either to a to-be-registered output (by name),
+ * or to an already-registered store object (by `Input`).
+ *
+ * `Ref<SingleDerivedPath` is a representation of something that can be
+ * turned into a placeholder. (Regular own-output placeholder in the
+ * first case, `DownstreamPlaceholder` in the second case.)
+ */
+template<typename Input>
+using DrvRef = std::variant<OutputName, Input>;
+
 /**
  * Downstream Placeholders are opaque and almost certainly unique values
  * used to allow derivations to refer to store objects which are yet to
@@ -92,3 +104,17 @@ public:
 };
 
 } // namespace nix
+
+namespace nlohmann {
+
+template<typename Item>
+struct adl_serializer<nix::DrvRef<Item>>
+{
+    static nix::DrvRef<Item> from_json(const json & json);
+    static void to_json(json & json, const nix::DrvRef<Item> & t);
+};
+
+extern template struct adl_serializer<nix::DrvRef<nix::StorePath>>;
+extern template struct adl_serializer<nix::DrvRef<nix::SingleDerivedPath>>;
+
+} // namespace nlohmann

src/libstore/include/nix/store/filetransfer.hh

@@ -87,11 +87,11 @@ extern const unsigned int RETRY_TIME_MS_DEFAULT;
  * HTTP methods supported by FileTransfer.
  */
 enum struct HttpMethod {
-    GET,
+    Get,
-    PUT,
+    Put,
-    HEAD,
+    Head,
-    POST,
+    Post,
-    DELETE,
+    Delete,
 };
 
 /**
@@ -110,7 +110,7 @@ struct FileTransferRequest
     VerbatimURL uri;
     Headers headers;
     std::string expectedETag;
-    HttpMethod method = HttpMethod::GET;
+    HttpMethod method = HttpMethod::Get;
     size_t tries = fileTransferSettings.tries;
     unsigned int baseRetryTimeMs = RETRY_TIME_MS_DEFAULT;
     ActivityId parentAct;
@@ -164,14 +164,14 @@ struct FileTransferRequest
     std::string verb() const
     {
         switch (method) {
-        case HttpMethod::HEAD:
+        case HttpMethod::Head:
-        case HttpMethod::GET:
+        case HttpMethod::Get:
             return "download";
-        case HttpMethod::PUT:
+        case HttpMethod::Put:
-        case HttpMethod::POST:
+        case HttpMethod::Post:
             assert(data);
             return "upload";
-        case HttpMethod::DELETE:
+        case HttpMethod::Delete:
             return "delet";
         }
         unreachable();

src/libstore/include/nix/store/parsed-derivations.hh

@@ -9,6 +9,7 @@
 namespace nix {
 
 class Store;
+template<typename Input>
 struct DerivationOptions;
 struct DerivationOutput;
 
@@ -47,7 +48,7 @@ struct StructuredAttrs
 
     nlohmann::json::object_t prepareStructuredAttrs(
         Store & store,
-        const DerivationOptions & drvOptions,
+        const DerivationOptions<StorePath> & drvOptions,
         const StorePathSet & inputPaths,
         const DerivationOutputs & outputs) const;
 

src/libstore/local-store.cc

@@ -1246,10 +1246,8 @@ StorePath LocalStore::addToStoreFromDump(
 
     auto desc = ContentAddressWithReferences::fromParts(
         hashMethod,
-        methodsMatch
+        methodsMatch ? dumpHash
-            ? dumpHash
+                     : hashPath(makeFSSourceAccessor(tempPath), hashMethod.getFileIngestionMethod(), hashAlgo).first,
-            : hashPath(PosixSourceAccessor::createAtRoot(tempPath), hashMethod.getFileIngestionMethod(), hashAlgo)
-                  .first,
         {
             .others = references,
             // caller is not capable of creating a self-reference, because this is content-addressed without modulus
@@ -1385,11 +1383,9 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
             checkInterrupt();
             auto name = link.path().filename();
             printMsg(lvlTalkative, "checking contents of %s", name);
-            std::string hash = hashPath(
+            std::string hash =
-                                   PosixSourceAccessor::createAtRoot(link.path()),
+                hashPath(makeFSSourceAccessor(link.path()), FileIngestionMethod::NixArchive, HashAlgorithm::SHA256)
-                                   FileIngestionMethod::NixArchive,
+                    .first.to_string(HashFormat::Nix32, false);
-                                   HashAlgorithm::SHA256)
-                                   .first.to_string(HashFormat::Nix32, false);
             if (hash != name.string()) {
                 printError("link %s was modified! expected hash %s, got '%s'", link.path(), name, hash);
                 if (repair) {

src/libstore/misc.cc

@@ -225,11 +225,12 @@ MissingPaths Store::queryMissing(const std::vector<DerivedPath> & targets)
                         return;
 
                     auto drv = make_ref<Derivation>(derivationFromPath(drvPath));
-                    DerivationOptions drvOptions;
+                    DerivationOptions<SingleDerivedPath> drvOptions;
                     try {
                         // FIXME: this is a lot of work just to get the value
                         // of `allowSubstitutes`.
-                        drvOptions = DerivationOptions::fromStructuredAttrs(drv->env, drv->structuredAttrs);
+                        drvOptions = derivationOptionsFromStructuredAttrs(
+                            *this, drv->inputDrvs, drv->env, get(drv->structuredAttrs));
                     } catch (Error & e) {
                         e.addTrace({}, "while parsing derivation '%s'", printStorePath(drvPath));
                         throw;

src/libstore/optimise-store.cc

@@ -172,7 +172,7 @@ void LocalStore::optimisePath_(
         auto stLink = lstat(linkPath.string());
         if (st.st_size != stLink.st_size || (repair && hash != ({
                                                            hashPath(
-                                                               PosixSourceAccessor::createAtRoot(linkPath),
+                                                               makeFSSourceAccessor(linkPath),
                                                                FileSerialisationMethod::NixArchive,
                                                                HashAlgorithm::SHA256)
                                                                .hash;

src/libstore/parsed-derivations.cc

@@ -100,7 +100,7 @@ static nlohmann::json pathInfoToJSON(Store & store, const StorePathSet & storePa
 
 nlohmann::json::object_t StructuredAttrs::prepareStructuredAttrs(
     Store & store,
-    const DerivationOptions & drvOptions,
+    const DerivationOptions<StorePath> & drvOptions,
     const StorePathSet & inputPaths,
     const DerivationOutputs & outputs) const
 {
@@ -114,8 +114,8 @@ nlohmann::json::object_t StructuredAttrs::prepareStructuredAttrs(
     json["outputs"] = std::move(outputsJson);
 
     /* Handle exportReferencesGraph. */
-    for (auto & [key, storePaths] : drvOptions.getParsedExportReferencesGraph(store)) {
+    for (auto & [key, storePaths] : drvOptions.exportReferencesGraph) {
-        json[key] = pathInfoToJSON(store, store.exportReferences(storePaths, storePaths));
+        json[key] = pathInfoToJSON(store, store.exportReferences(storePaths, inputPaths));
     }
 
     return json;

src/libstore/s3-binary-cache-store.cc

@@ -295,7 +295,7 @@ std::string S3BinaryCacheStore::createMultipartUpload(
     url.query["uploads"] = "";
     req.uri = VerbatimURL(url);
 
-    req.method = HttpMethod::POST;
+    req.method = HttpMethod::Post;
     StringSource payload{std::string_view("")};
     req.data = {payload};
     req.mimeType = mimeType;
@@ -325,7 +325,7 @@ S3BinaryCacheStore::uploadPart(std::string_view key, std::string_view uploadId,
     }
 
     auto req = makeRequest(key);
-    req.method = HttpMethod::PUT;
+    req.method = HttpMethod::Put;
     req.setupForS3();
 
     auto url = req.uri.parsed();
@@ -355,7 +355,7 @@ void S3BinaryCacheStore::abortMultipartUpload(std::string_view key, std::string_
         auto url = req.uri.parsed();
         url.query["uploadId"] = uploadId;
         req.uri = VerbatimURL(url);
-        req.method = HttpMethod::DELETE;
+        req.method = HttpMethod::Delete;
 
         getFileTransfer()->enqueueFileTransfer(req).get();
     } catch (...) {
@@ -372,7 +372,7 @@ void S3BinaryCacheStore::completeMultipartUpload(
     auto url = req.uri.parsed();
     url.query["uploadId"] = uploadId;
     req.uri = VerbatimURL(url);
-    req.method = HttpMethod::POST;
+    req.method = HttpMethod::Post;
 
     std::string xml = "<CompleteMultipartUpload>";
     for (const auto & [idx, etag] : enumerate(partEtags)) {

src/libutil-c/nix_api_util.cc

@@ -36,7 +36,7 @@ nix_err nix_context_error(nix_c_context * context)
         const char * demangled = abi::__cxa_demangle(typeid(e).name(), 0, 0, &status);
         if (demangled) {
             context->name = demangled;
-            // todo: free(demangled);
+            free((void *) demangled);
         } else {
             context->name = typeid(e).name();
         }

src/libutil/archive.cc

@@ -200,54 +200,54 @@ static void parse(FileSystemObjectSink & sink, Source & source, const CanonPath
     }
 
     else if (type == "directory") {
-        sink.createDirectory(path);
+        sink.createDirectory(path, [&](FileSystemObjectSink & dirSink, const CanonPath & relDirPath) {
+            std::map<Path, int, CaseInsensitiveCompare> names;
 
-        std::map<Path, int, CaseInsensitiveCompare> names;
+            std::string prevName;
 
-        std::string prevName;
+            while (1) {
+                auto tag = getString();
 
-        while (1) {
+                if (tag == ")")
-            auto tag = getString();
+                    break;
 
-            if (tag == ")")
+                if (tag != "entry")
-                break;
+                    throw badArchive("expected tag 'entry' or ')', got '%s'", tag);
 
-            if (tag != "entry")
+                expectTag("(");
-                throw badArchive("expected tag 'entry' or ')', got '%s'", tag);
 
-            expectTag("(");
+                expectTag("name");
 
-            expectTag("name");
+                auto name = getString();
+                if (name.empty() || name == "." || name == ".." || name.find('/') != std::string::npos
+                    || name.find((char) 0) != std::string::npos)
+                    throw badArchive("NAR contains invalid file name '%1%'", name);
+                if (name <= prevName)
+                    throw badArchive("NAR directory is not sorted");
+                prevName = name;
+                if (archiveSettings.useCaseHack) {
+                    auto i = names.find(name);
+                    if (i != names.end()) {
+                        debug("case collision between '%1%' and '%2%'", i->first, name);
+                        name += caseHackSuffix;
+                        name += std::to_string(++i->second);
+                        auto j = names.find(name);
+                        if (j != names.end())
+                            throw badArchive(
+                                "NAR contains file name '%s' that collides with case-hacked file name '%s'",
+                                prevName,
+                                j->first);
+                    } else
+                        names[name] = 0;
+                }
 
-            auto name = getString();
+                expectTag("node");
-            if (name.empty() || name == "." || name == ".." || name.find('/') != std::string::npos
+
-                || name.find((char) 0) != std::string::npos)
+                parse(dirSink, source, relDirPath / name);
-                throw badArchive("NAR contains invalid file name '%1%'", name);
+
-            if (name <= prevName)
+                expectTag(")");
-                throw badArchive("NAR directory is not sorted");
-            prevName = name;
-            if (archiveSettings.useCaseHack) {
-                auto i = names.find(name);
-                if (i != names.end()) {
-                    debug("case collision between '%1%' and '%2%'", i->first, name);
-                    name += caseHackSuffix;
-                    name += std::to_string(++i->second);
-                    auto j = names.find(name);
-                    if (j != names.end())
-                        throw badArchive(
-                            "NAR contains file name '%s' that collides with case-hacked file name '%s'",
-                            prevName,
-                            j->first);
-                } else
-                    names[name] = 0;
             }
-
+        });
-            expectTag("node");
-
-            parse(sink, source, path / name);
-
-            expectTag(")");
-        }
     }
 
     else if (type == "symlink") {

src/libutil/fs-sink.cc

@@ -14,44 +14,6 @@
 
 namespace nix {
 
-void copyRecursive(SourceAccessor & accessor, const CanonPath & from, FileSystemObjectSink & sink, const CanonPath & to)
-{
-    auto stat = accessor.lstat(from);
-
-    switch (stat.type) {
-    case SourceAccessor::tSymlink: {
-        sink.createSymlink(to, accessor.readLink(from));
-        break;
-    }
-
-    case SourceAccessor::tRegular: {
-        sink.createRegularFile(to, [&](CreateRegularFileSink & crf) {
-            if (stat.isExecutable)
-                crf.isExecutable();
-            accessor.readFile(from, crf, [&](uint64_t size) { crf.preallocateContents(size); });
-        });
-        break;
-    }
-
-    case SourceAccessor::tDirectory: {
-        sink.createDirectory(to);
-        for (auto & [name, _] : accessor.readDirectory(from)) {
-            copyRecursive(accessor, from / name, sink, to / name);
-            break;
-        }
-        break;
-    }
-
-    case SourceAccessor::tChar:
-    case SourceAccessor::tBlock:
-    case SourceAccessor::tSocket:
-    case SourceAccessor::tFifo:
-    case SourceAccessor::tUnknown:
-    default:
-        throw Error("file '%1%' has an unsupported type of %2%", from, stat.typeString());
-    }
-}
-
 struct RestoreSinkSettings : Config
 {
     Setting<bool> preallocateContents{
@@ -70,11 +32,60 @@ static std::filesystem::path append(const std::filesystem::path & src, const Can
     return dst;
 }
 
+#ifndef _WIN32
+void RestoreSink::createDirectory(const CanonPath & path, DirectoryCreatedCallback callback)
+{
+    if (path.isRoot()) {
+        createDirectory(path);
+        callback(*this, path);
+        return;
+    }
+
+    createDirectory(path);
+    assert(dirFd); // If that's not true the above call must have thrown an exception.
+
+    RestoreSink dirSink{startFsync};
+    dirSink.dstPath = append(dstPath, path);
+    dirSink.dirFd = ::openat(dirFd.get(), path.rel_c_str(), O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+
+    if (!dirSink.dirFd)
+        throw SysError("opening directory '%s'", dirSink.dstPath.string());
+
+    callback(dirSink, CanonPath::root);
+}
+#endif
+
 void RestoreSink::createDirectory(const CanonPath & path)
 {
     auto p = append(dstPath, path);
+
+#ifndef _WIN32
+    if (dirFd) {
+        if (path.isRoot())
+            /* Trying to create a directory that we already have a file descriptor for. */
+            throw Error("path '%s' already exists", p.string());
+
+        if (::mkdirat(dirFd.get(), path.rel_c_str(), 0777) == -1)
+            throw SysError("creating directory '%s'", p.string());
+
+        return;
+    }
+#endif
+
     if (!std::filesystem::create_directory(p))
         throw Error("path '%s' already exists", p.string());
+
+#ifndef _WIN32
+    if (path.isRoot()) {
+        assert(!dirFd); // Handled above
+
+        /* Open directory for further *at operations relative to the sink root
+           directory. */
+        dirFd = open(p.c_str(), O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+        if (!dirFd)
+            throw SysError("creating directory '%1%'", p.string());
+    }
+#endif
 };
 
 struct RestoreRegularFile : CreateRegularFileSink
@@ -114,7 +125,14 @@ void RestoreSink::createRegularFile(const CanonPath & path, std::function<void(C
             FILE_ATTRIBUTE_NORMAL,
             NULL)
 #else
-        open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666)
+        [&]() {
+            /* O_EXCL together with O_CREAT ensures symbolic links in the last
+              component are not followed. */
+            constexpr int flags = O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC;
+            if (!dirFd)
+                return ::open(p.c_str(), flags, 0666);
+            return ::openat(dirFd.get(), path.rel_c_str(), flags, 0666);
+        }();
 #endif
         ;
     if (!crf.fd)
@@ -161,6 +179,13 @@ void RestoreRegularFile::operator()(std::string_view data)
 void RestoreSink::createSymlink(const CanonPath & path, const std::string & target)
 {
     auto p = append(dstPath, path);
+#ifndef _WIN32
+    if (dirFd) {
+        if (::symlinkat(requireCString(target), dirFd.get(), path.rel_c_str()) == -1)
+            throw SysError("creating symlink from '%1%' -> '%2%'", p.string(), target);
+        return;
+    }
+#endif
     nix::createSymlink(target, p.string());
 }
 

src/libutil/git.cc

@@ -217,29 +217,6 @@ std::optional<Mode> convertMode(SourceAccessor::Type type)
     }
 }
 
-void restore(FileSystemObjectSink & sink, Source & source, HashAlgorithm hashAlgo, std::function<RestoreHook> hook)
-{
-    parse(sink, CanonPath::root, source, BlobMode::Regular, hashAlgo, [&](CanonPath name, TreeEntry entry) {
-        auto [accessor, from] = hook(entry.hash);
-        auto stat = accessor->lstat(from);
-        auto gotOpt = convertMode(stat.type);
-        if (!gotOpt)
-            throw Error(
-                "file '%s' (git hash %s) has an unsupported type",
-                from,
-                entry.hash.to_string(HashFormat::Base16, false));
-        auto & got = *gotOpt;
-        if (got != entry.mode)
-            throw Error(
-                "git mode of file '%s' (git hash %s) is %o but expected %o",
-                from,
-                entry.hash.to_string(HashFormat::Base16, false),
-                (RawMode) got,
-                (RawMode) entry.mode);
-        copyRecursive(*accessor, from, sink, name);
-    });
-}
-
 void dumpBlobPrefix(uint64_t size, Sink & sink, const ExperimentalFeatureSettings & xpSettings)
 {
     xpSettings.require(Xp::GitHashing);

src/libutil/include/nix/util/fs-sink.hh

@@ -36,6 +36,23 @@ struct FileSystemObjectSink
 
     virtual void createDirectory(const CanonPath & path) = 0;
 
+    using DirectoryCreatedCallback = std::function<void(FileSystemObjectSink & dirSink, const CanonPath & dirRelPath)>;
+
+    /**
+     * Create a directory and invoke a callback with a pair of sink + CanonPath
+     * of the created subdirectory relative to dirSink.
+     *
+     * @note This allows for UNIX RestoreSink implementations to implement
+     * *at-style accessors that always keep an open file descriptor for the
+     * freshly created directory. Use this when it's important to disallow any
+     * intermediate path components from being symlinks.
+     */
+    virtual void createDirectory(const CanonPath & path, DirectoryCreatedCallback callback)
+    {
+        createDirectory(path);
+        callback(*this, path);
+    }
+
     /**
      * This function in general is no re-entrant. Only one file can be
      * written at a time.
@@ -82,6 +99,18 @@ struct NullFileSystemObjectSink : FileSystemObjectSink
 struct RestoreSink : FileSystemObjectSink
 {
     std::filesystem::path dstPath;
+#ifndef _WIN32
+    /**
+     * File descriptor for the directory located at dstPath. Used for *at
+     * operations relative to this file descriptor. This sink must *never*
+     * follow intermediate symlinks (starting from dstPath) in case a file
+     * collision is encountered for various reasons like case-insensitivity or
+     * other types on normalization. using appropriate *at system calls and traversing
+     * only one path component at a time ensures that writing is race-free and is
+     * is not susceptible to symlink replacement.
+     */
+    AutoCloseFD dirFd;
+#endif
     bool startFsync = false;
 
     explicit RestoreSink(bool startFsync)
@@ -91,6 +120,10 @@ struct RestoreSink : FileSystemObjectSink
 
     void createDirectory(const CanonPath & path) override;
 
+#ifndef _WIN32
+    void createDirectory(const CanonPath & path, DirectoryCreatedCallback callback) override;
+#endif
+
     void createRegularFile(const CanonPath & path, std::function<void(CreateRegularFileSink &)>) override;
 
     void createSymlink(const CanonPath & path, const std::string & target) override;

src/libutil/include/nix/util/git.hh

@@ -136,13 +136,6 @@ std::optional<Mode> convertMode(SourceAccessor::Type type);
  */
 using RestoreHook = SourcePath(Hash);
 
-/**
- * Wrapper around `parse` and `RestoreSink`
- *
- * @param hashAlgo must be `HashAlgo::SHA1` or `HashAlgo::SHA256` for now.
- */
-void restore(FileSystemObjectSink & sink, Source & source, HashAlgorithm hashAlgo, std::function<RestoreHook> hook);
-
 /**
  * Dumps a single file to a sink
  *

src/libutil/include/nix/util/strings.hh

@@ -166,4 +166,10 @@ public:
     }
 };
 
+/**
+ * Check that the string does not contain any NUL bytes and return c_str().
+ * @throws Error if str contains '\0' bytes.
+ */
+const char * requireCString(const std::string & str);
+
 } // namespace nix

src/libutil/include/nix/util/terminal.hh

@@ -4,7 +4,15 @@
 #include <limits>
 #include <string>
 
+#include "nix/util/file-descriptor.hh"
+
 namespace nix {
+
+/**
+ * Determine whether \param fd is a terminal.
+ */
+bool isTTY(Descriptor fd);
+
 /**
  * Determine whether ANSI escape sequences are appropriate for the
  * present output.

src/libutil/include/nix/util/util.hh

@@ -242,6 +242,28 @@ std::string stripIndentation(std::string_view s);
  */
 std::pair<std::string_view, std::string_view> getLine(std::string_view s);
 
+/**
+ * Get a pointer to the contents of a `std::optional` if it is set, or a
+ * null pointer otherise.
+ *
+ * Const version.
+ */
+template<class T>
+const T * get(const std::optional<T> & opt)
+{
+    return opt ? &*opt : nullptr;
+}
+
+/**
+ * Non-const counterpart of `const T * get(const std::optional<T>)`.
+ * Takes a mutable reference, but returns a mutable pointer.
+ */
+template<class T>
+T * get(std::optional<T> & opt)
+{
+    return opt ? &*opt : nullptr;
+}
+
 /**
  * Get a value for the specified key from an associate container.
  */

src/libutil/strings.cc

@@ -5,6 +5,7 @@
 #include "nix/util/strings-inline.hh"
 #include "nix/util/os-string.hh"
 #include "nix/util/error.hh"
+#include "nix/util/util.hh"
 
 namespace nix {
 
@@ -152,4 +153,14 @@ std::string optionalBracket(std::string_view prefix, std::string_view content, s
     return result;
 }
 
+const char * requireCString(const std::string & s)
+{
+    if (std::memchr(s.data(), '\0', s.size())) [[unlikely]] {
+        using namespace std::string_view_literals;
+        auto str = replaceStrings(s, "\0"sv, "␀"sv);
+        throw Error("string '%s' with null (\\0) bytes used where it's not allowed", str);
+    }
+    return s.c_str();
+}
+
 } // namespace nix

src/libutil/terminal.cc

@@ -64,6 +64,16 @@ inline std::pair<int, size_t> charWidthUTF8Helper(std::string_view s)
 
 namespace nix {
 
+bool isTTY(Descriptor fd)
+{
+#ifndef _WIN32
+    return isatty(fd);
+#else
+    DWORD mode;
+    return GetConsoleMode(fd, &mode);
+#endif
+}
+
 bool isTTY()
 {
     static const bool tty = isatty(STDERR_FILENO) && getEnv("TERM").value_or("dumb") != "dumb"

src/libutil/url.cc

@@ -327,8 +327,11 @@ Path renderUrlPathEnsureLegal(const std::vector<std::string> & urlPath)
         /* This is only really valid for UNIX. Windows has more restrictions. */
         if (comp.contains('/'))
             throw BadURL("URL path component '%s' contains '/', which is not allowed in file names", comp);
-        if (comp.contains(char(0)))
+        if (comp.contains(char(0))) {
-            throw BadURL("URL path component '%s' contains NUL byte which is not allowed", comp);
+            using namespace std::string_view_literals;
+            auto str = replaceStrings(comp, "\0"sv, "␀"sv);
+            throw BadURL("URL path component '%s' contains NUL byte which is not allowed", str);
+        }
     }
 
     return concatStringsSep("/", urlPath);

src/nix/cat.cc

@@ -75,7 +75,7 @@ struct CmdCatNar : StoreCommand, MixCat
 
     void run(ref<Store> store) override
     {
-        AutoCloseFD fd = open(narPath.c_str(), O_RDONLY);
+        AutoCloseFD fd = toDescriptor(open(narPath.c_str(), O_RDONLY));
         if (!fd)
             throw SysError("opening NAR file '%s'", narPath);
         auto source = FdSource{fd.get()};

src/nix/dump-path.cc

@@ -1,13 +1,14 @@
 #include "nix/cmd/command.hh"
 #include "nix/store/store-api.hh"
 #include "nix/util/archive.hh"
+#include "nix/util/terminal.hh"
 
 using namespace nix;
 
 static FdSink getNarSink()
 {
     auto fd = getStandardOutput();
-    if (isatty(fd))
+    if (isTTY(fd))
         throw UsageError("refusing to write NAR to a terminal");
     return FdSink(std::move(fd));
 }

src/nix/flake-prefetch-inputs.cc

@@ -45,7 +45,7 @@ struct CmdFlakePrefetchInputs : FlakeCommand
             if (auto lockedNode = dynamic_cast<const LockedNode *>(&node)) {
                 try {
                     Activity act(*logger, lvlInfo, actUnknown, fmt("fetching '%s'", lockedNode->lockedRef));
-                    auto accessor = lockedNode->lockedRef.input.getAccessor(fetchSettings, store).first;
+                    auto accessor = lockedNode->lockedRef.input.getAccessor(fetchSettings, *store).first;
                     fetchToStore(
                         fetchSettings, *store, accessor, FetchMode::Copy, lockedNode->lockedRef.input.getName());
                 } catch (Error & e) {

src/nix/flake.cc

@@ -240,7 +240,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                 j["lastModified"] = *lastModified;
             j["path"] = storePath;
             j["locks"] = lockedFlake.lockFile.toJSON().first;
-            if (auto fingerprint = lockedFlake.getFingerprint(store, fetchSettings))
+            if (auto fingerprint = lockedFlake.getFingerprint(*store, fetchSettings))
                 j["fingerprint"] = fingerprint->to_string(HashFormat::Base16, false);
             printJSON(j);
         } else {
@@ -260,7 +260,7 @@ struct CmdFlakeMetadata : FlakeCommand, MixJSON
                 logger->cout(
                     ANSI_BOLD "Last modified:" ANSI_NORMAL " %s",
                     std::put_time(std::localtime(&*lastModified), "%F %T"));
-            if (auto fingerprint = lockedFlake.getFingerprint(store, fetchSettings))
+            if (auto fingerprint = lockedFlake.getFingerprint(*store, fetchSettings))
                 logger->cout(
                     ANSI_BOLD "Fingerprint:" ANSI_NORMAL "   %s", fingerprint->to_string(HashFormat::Base16, false));
 
@@ -1019,7 +1019,7 @@ struct CmdFlakeNew : CmdFlakeInitCommon
 
 struct CmdFlakeClone : FlakeCommand
 {
-    Path destDir;
+    std::filesystem::path destDir;
 
     std::string description() override
     {
@@ -1049,7 +1049,7 @@ struct CmdFlakeClone : FlakeCommand
         if (destDir.empty())
             throw Error("missing flag '--dest'");
 
-        getFlakeRef().resolve(fetchSettings, store).input.clone(fetchSettings, destDir);
+        getFlakeRef().resolve(fetchSettings, *store).input.clone(fetchSettings, *store, destDir);
     }
 };
 
@@ -1100,7 +1100,7 @@ struct CmdFlakeArchive : FlakeCommand, MixJSON, MixDryRun, MixNoCheckSigs
                     std::optional<StorePath> storePath;
                     if (!(*inputNode)->lockedRef.input.isRelative()) {
                         storePath = dryRun ? (*inputNode)->lockedRef.input.computeStorePath(*store)
-                                           : (*inputNode)->lockedRef.input.fetchToStore(fetchSettings, store).first;
+                                           : (*inputNode)->lockedRef.input.fetchToStore(fetchSettings, *store).first;
                         sources.insert(*storePath);
                     }
                     if (json) {
@@ -1498,8 +1498,8 @@ struct CmdFlakePrefetch : FlakeCommand, MixJSON
     void run(ref<Store> store) override
     {
         auto originalRef = getFlakeRef();
-        auto resolvedRef = originalRef.resolve(fetchSettings, store);
+        auto resolvedRef = originalRef.resolve(fetchSettings, *store);
-        auto [accessor, lockedRef] = resolvedRef.lazyFetch(getEvalState()->fetchSettings, store);
+        auto [accessor, lockedRef] = resolvedRef.lazyFetch(getEvalState()->fetchSettings, *store);
         auto storePath =
             fetchToStore(getEvalState()->fetchSettings, *store, accessor, FetchMode::Copy, lockedRef.input.getName());
         auto hash = store->queryPathInfo(storePath)->narHash;

src/nix/ls.cc

@@ -145,7 +145,7 @@ struct CmdLsNar : Command, MixLs
 
     void run() override
     {
-        AutoCloseFD fd = open(narPath.c_str(), O_RDONLY);
+        AutoCloseFD fd = toDescriptor(open(narPath.c_str(), O_RDONLY));
         if (!fd)
             throw SysError("opening NAR file '%s'", narPath);
         auto source = FdSource{fd.get()};

src/nix/main.cc

@@ -193,20 +193,38 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs, virtual RootArgs
 
     std::string dumpCli()
     {
-        auto res = nlohmann::json::object();
+        using nlohmann::json;
+
+        auto res = json::object();
 
         res["args"] = toJSON();
 
-        auto stores = nlohmann::json::object();
+        {
-        for (auto & [storeName, implem] : Implementations::registered()) {
+            auto & stores = res["stores"] = json::object();
-            auto & j = stores[storeName];
+            for (auto & [storeName, implem] : Implementations::registered()) {
-            j["doc"] = implem.doc;
+                auto & j = stores[storeName];
-            j["uri-schemes"] = implem.uriSchemes;
+                j["doc"] = implem.doc;
-            j["settings"] = implem.getConfig()->toJSON();
+                j["uri-schemes"] = implem.uriSchemes;
-            j["experimentalFeature"] = implem.experimentalFeature;
+                j["settings"] = implem.getConfig()->toJSON();
+                j["experimentalFeature"] = implem.experimentalFeature;
+            }
         }
-        res["stores"] = std::move(stores);
+
-        res["fetchers"] = fetchers::dumpRegisterInputSchemeInfo();
+        {
+            auto & fetchers = res["fetchers"] = json::object();
+
+            for (const auto & [schemeName, scheme] : fetchers::getAllInputSchemes()) {
+                auto & s = fetchers[schemeName] = json::object();
+                s["description"] = scheme->schemeDescription();
+                auto & attrs = s["allowedAttrs"] = json::object();
+                for (auto & [fieldName, field] : scheme->allowedAttrs()) {
+                    auto & f = attrs[fieldName] = json::object();
+                    f["type"] = field.type;
+                    f["required"] = field.required;
+                    f["doc"] = stripIndentation(field.doc);
+                }
+            }
+        };
 
         return res.dump();
     }
@@ -440,7 +458,7 @@ void mainWrapped(int argc, char ** argv)
             if (!primOp->doc)
                 continue;
             b["args"] = primOp->args;
-            b["doc"] = trim(stripIndentation(primOp->doc->view()));
+            b["doc"] = trim(stripIndentation(*primOp->doc));
             if (primOp->experimentalFeature)
                 b["experimental-feature"] = primOp->experimentalFeature;
             builtinsJson.emplace(state.symbols[builtin.name], std::move(b));
@@ -449,7 +467,7 @@ void mainWrapped(int argc, char ** argv)
             auto b = nlohmann::json::object();
             if (!info.doc)
                 continue;
-            b["doc"] = trim(stripIndentation(info.doc->view()));
+            b["doc"] = trim(stripIndentation(info.doc));
             b["type"] = showType(info.type, false);
             if (info.impureOnly)
                 b["impure-only"] = true;

src/nix/nix-build/nix-build.cc

@@ -554,9 +554,9 @@ static void main_nix_build(int argc, char ** argv)
         env["NIX_STORE"] = store->storeDir;
         env["NIX_BUILD_CORES"] = fmt("%d", settings.buildCores ? settings.buildCores : settings.getDefaultCores());
 
-        DerivationOptions drvOptions;
+        DerivationOptions<StorePath> drvOptions;
         try {
-            drvOptions = DerivationOptions::fromStructuredAttrs(drv.env, drv.structuredAttrs);
+            drvOptions = derivationOptionsFromStructuredAttrs(*store, drv.env, get(drv.structuredAttrs));
         } catch (Error & e) {
             e.addTrace({}, "while parsing derivation '%s'", store->printStorePath(packageInfo.requireDrvPath()));
             throw;

src/nix/nix-channel/nix-channel.cc

@@ -121,7 +121,7 @@ static void update(const StringSet & channelNames)
             // We want to download the url to a file to see if it's a tarball while also checking if we
             // got redirected in the process, so that we can grab the various parts of a nix channel
             // definition from a consistent location if the redirect changes mid-download.
-            auto result = fetchers::downloadFile(store, fetchSettings, url, std::string(baseNameOf(url)));
+            auto result = fetchers::downloadFile(*store, fetchSettings, url, std::string(baseNameOf(url)));
             url = result.effectiveUrl;
 
             bool unpacked = false;
@@ -139,10 +139,10 @@ static void update(const StringSet & channelNames)
             if (!unpacked) {
                 // Download the channel tarball.
                 try {
-                    result = fetchers::downloadFile(store, fetchSettings, url + "/nixexprs.tar.xz", "nixexprs.tar.xz");
+                    result = fetchers::downloadFile(*store, fetchSettings, url + "/nixexprs.tar.xz", "nixexprs.tar.xz");
                 } catch (FileTransferError & e) {
                     result =
-                        fetchers::downloadFile(store, fetchSettings, url + "/nixexprs.tar.bz2", "nixexprs.tar.bz2");
+                        fetchers::downloadFile(*store, fetchSettings, url + "/nixexprs.tar.bz2", "nixexprs.tar.bz2");
                 }
             }
             // Regardless of where it came from, add the expression representing this channel to accumulated expression