Merge pull request #7878 from NixOS/backport-7856-to-2.13-maintenance

[Backport 2.13-maintenance] Wait with making /etc unwritable until after build env setup

.version

@@ -1 +1 @@
-2.13.0
+2.13.3

boehmgc-coroutine-sp-fallback.diff

@@ -0,0 +1,77 @@
+diff --git a/darwin_stop_world.c b/darwin_stop_world.c
+index 3dbaa3fb..36a1d1f7 100644
+--- a/darwin_stop_world.c
++++ b/darwin_stop_world.c
+@@ -352,6 +352,7 @@ GC_INNER void GC_push_all_stacks(void)
+   int nthreads = 0;
+   word total_size = 0;
+   mach_msg_type_number_t listcount = (mach_msg_type_number_t)THREAD_TABLE_SZ;
++  size_t stack_limit;
+   if (!EXPECT(GC_thr_initialized, TRUE))
+     GC_thr_init();
+ 
+@@ -407,6 +408,19 @@ GC_INNER void GC_push_all_stacks(void)
+             GC_push_all_stack_sections(lo, hi, p->traced_stack_sect);
+           }
+           if (altstack_lo) {
++            // When a thread goes into a coroutine, we lose its original sp until
++            // control flow returns to the thread.
++            // While in the coroutine, the sp points outside the thread stack,
++            // so we can detect this and push the entire thread stack instead,
++            // as an approximation.
++            // We assume that the coroutine has similarly added its entire stack.
++            // This could be made accurate by cooperating with the application
++            // via new functions and/or callbacks.
++            stack_limit = pthread_get_stacksize_np(p->id);
++            if (altstack_lo >= altstack_hi || altstack_lo < altstack_hi - stack_limit) { // sp outside stack
++              altstack_lo = altstack_hi - stack_limit;
++            }
++
+             total_size += altstack_hi - altstack_lo;
+             GC_push_all_stack(altstack_lo, altstack_hi);
+           }
+diff --git a/pthread_stop_world.c b/pthread_stop_world.c
+index b5d71e62..aed7b0bf 100644
+--- a/pthread_stop_world.c
++++ b/pthread_stop_world.c
+@@ -768,6 +768,8 @@ STATIC void GC_restart_handler(int sig)
+ /* world is stopped.  Should not fail if it isn't.                      */
+ GC_INNER void GC_push_all_stacks(void)
+ {
++    size_t stack_limit;
++    pthread_attr_t pattr;
+     GC_bool found_me = FALSE;
+     size_t nthreads = 0;
+     int i;
+@@ -851,6 +853,31 @@ GC_INNER void GC_push_all_stacks(void)
+           hi = p->altstack + p->altstack_size;
+           /* FIXME: Need to scan the normal stack too, but how ? */
+           /* FIXME: Assume stack grows down */
++        } else {
++          if (pthread_getattr_np(p->id, &pattr)) {
++            ABORT("GC_push_all_stacks: pthread_getattr_np failed!");
++          }
++          if (pthread_attr_getstacksize(&pattr, &stack_limit)) {
++            ABORT("GC_push_all_stacks: pthread_attr_getstacksize failed!");
++          }
++          if (pthread_attr_destroy(&pattr)) {
++            ABORT("GC_push_all_stacks: pthread_attr_destroy failed!");
++          }
++          // When a thread goes into a coroutine, we lose its original sp until
++          // control flow returns to the thread.
++          // While in the coroutine, the sp points outside the thread stack,
++          // so we can detect this and push the entire thread stack instead,
++          // as an approximation.
++          // We assume that the coroutine has similarly added its entire stack.
++          // This could be made accurate by cooperating with the application
++          // via new functions and/or callbacks.
++          #ifndef STACK_GROWS_UP
++            if (lo >= hi || lo < hi - stack_limit) { // sp outside stack
++              lo = hi - stack_limit;
++            }
++          #else
++          #error "STACK_GROWS_UP not supported in boost_coroutine2 (as of june 2021), so we don't support it in Nix."
++          #endif
+         }
+         GC_push_all_stack_sections(lo, hi, traced_stack_sect);
+ #       ifdef STACK_GROWS_UP

doc/manual/local.mk

@@ -51,13 +51,13 @@ $(d)/src/SUMMARY.md: $(d)/src/SUMMARY.md.in $(d)/src/command-ref/new-cli
 $(d)/src/command-ref/new-cli: $(d)/nix.json $(d)/generate-manpage.nix $(bindir)/nix
 	@rm -rf $@
 	$(trace-gen) $(nix-eval) --write-to $@.tmp --expr 'import doc/manual/generate-manpage.nix { toplevel = builtins.readFile $<; }'
-	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	@# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
 	$(trace-gen) sed -i $@.tmp/*.md -e 's^@docroot@^../..^g'
 	@mv $@.tmp $@
 
 $(d)/src/command-ref/conf-file.md: $(d)/conf-file.json $(d)/generate-options.nix $(d)/src/command-ref/conf-file-prefix.md $(bindir)/nix
 	@cat doc/manual/src/command-ref/conf-file-prefix.md > $@.tmp
-	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	@# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
 	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-options.nix (builtins.fromJSON (builtins.readFile $<))' \
 	  | sed -e 's^@docroot@^..^g'>> $@.tmp
 	@mv $@.tmp $@
@@ -72,7 +72,7 @@ $(d)/conf-file.json: $(bindir)/nix
 
 $(d)/src/language/builtins.md: $(d)/builtins.json $(d)/generate-builtins.nix $(d)/src/language/builtins-prefix.md $(bindir)/nix
 	@cat doc/manual/src/language/builtins-prefix.md > $@.tmp
-	# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
+	@# @docroot@: https://nixos.org/manual/nix/unstable/contributing/hacking.html#docroot-variable
 	$(trace-gen) $(nix-eval) --expr 'import doc/manual/generate-builtins.nix (builtins.fromJSON (builtins.readFile $<))' \
 	  | sed -e 's^@docroot@^..^g' >> $@.tmp
 	@cat doc/manual/src/language/builtins-suffix.md >> $@.tmp

doc/manual/src/SUMMARY.md.in

@@ -66,7 +66,6 @@
   - [Hacking](contributing/hacking.md)
   - [CLI guideline](contributing/cli-guideline.md)
 - [Release Notes](release-notes/release-notes.md)
-  - [Release X.Y (202?-??-??)](release-notes/rl-next.md)
   - [Release 2.13 (2023-01-17)](release-notes/rl-2.13.md)
   - [Release 2.12 (2022-12-06)](release-notes/rl-2.12.md)
   - [Release 2.11 (2022-08-25)](release-notes/rl-2.11.md)

doc/manual/src/release-notes/rl-2.13.md

@@ -18,18 +18,14 @@
 * Instead of "antiquotation", the more common term [string interpolation](../language/string-interpolation.md) is now used consistently.
   Historical release notes were not changed.
 
-* Error traces have been reworked to provide detailed explanations and more
-  accurate error locations. A short excerpt of the trace is now shown by
-  default when an error occurs.
-
 * Allow explicitly selecting outputs in a store derivation installable, just like we can do with other sorts of installables.
   For example,
   ```shell-session
-  # nix-build /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^dev`
+  # nix build /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^dev
   ```
   now works just as
   ```shell-session
-  # nix-build glibc^dev`
+  # nix build nixpkgs#glibc^dev
   ```
   does already.
 
@@ -38,3 +34,7 @@
   for the development shell in the same way as the actual build of the
   derivation. This makes shells for `i686-linux` derivations work
   correctly on `x86_64-linux`.
+
+* You can now disable the global flake registry by setting the `flake-registry`
+  configuration option to an empty string. The same can be achieved at runtime with
+  `--flake-registry ""`.

flake.nix

@@ -9,7 +9,7 @@
 
     let
 
-      officialRelease = false;
+      officialRelease = true;
 
       version = nixpkgs.lib.fileContents ./.version + versionSuffix;
       versionSuffix =
@@ -128,9 +128,14 @@
           });
 
         propagatedDeps =
-          [ (boehmgc.override {
+          [ ((boehmgc.override {
               enableLargeConfig = true;
+            }).overrideAttrs(o: {
+              patches = (o.patches or []) ++ [
+                ./boehmgc-coroutine-sp-fallback.diff
+              ];
             })
+            )
             nlohmann_json
           ];
       };
@@ -532,6 +537,12 @@
               mkdir $out
             '';
 
+        tests.nixpkgsLibTests =
+          nixpkgs.lib.genAttrs systems (system:
+            import (nixpkgs + "/lib/tests/release.nix")
+              { pkgs = nixpkgsFor.${system}; }
+          );
+
         metrics.nixpkgs = import "${nixpkgs-regression}/pkgs/top-level/metrics.nix" {
           pkgs = nixpkgsFor.x86_64-linux;
           nixpkgs = nixpkgs-regression;
@@ -562,6 +573,7 @@
         binaryTarball = self.hydraJobs.binaryTarball.${system};
         perlBindings = self.hydraJobs.perlBindings.${system};
         installTests = self.hydraJobs.installTests.${system};
+        nixpkgsLibTests = self.hydraJobs.tests.nixpkgsLibTests.${system};
       } // (nixpkgs.lib.optionalAttrs (builtins.elem system linux64BitSystems)) {
         dockerImage = self.hydraJobs.dockerImage.${system};
       });

perl/lib/Nix/Store.xs

@@ -26,6 +26,7 @@ static ref<Store> store()
     static std::shared_ptr<Store> _store;
     if (!_store) {
         try {
+            initLibStore();
             loadConfFile();
             settings.lockCPU = false;
             _store = openStore();

src/libcmd/installables.cc

@@ -554,7 +554,7 @@ ref<eval_cache::EvalCache> openEvalCache(
             auto vFlake = state.allocValue();
             flake::callFlake(state, *lockedFlake, *vFlake);
 
-            state.forceAttrs(*vFlake, noPos, "while parsing cached flake data");
+            state.forceAttrs(*vFlake, noPos);
 
             auto aOutputs = vFlake->attrs->get(state.symbols.create("outputs"));
             assert(aOutputs);
@@ -618,7 +618,7 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
 
         else if (v.type() == nString) {
             PathSet context;
-            auto s = state->forceString(v, context, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
+            auto s = state->forceString(v, context, noPos);
             auto storePath = state->store->maybeParseStorePath(s);
             if (storePath && context.count(std::string(s))) {
                 return {{

src/libcmd/repl.cc

@@ -397,7 +397,7 @@ StringSet NixRepl::completePrefix(const std::string & prefix)
             Expr * e = parseString(expr);
             Value v;
             e->eval(*state, *env, v);
-            state->forceAttrs(v, noPos, "nevermind, it is ignored anyway");
+            state->forceAttrs(v, noPos);
 
             for (auto & i : *v.attrs) {
                 std::string_view name = state->symbols[i.name];
@@ -590,7 +590,7 @@ bool NixRepl::processLine(std::string line)
         const auto [path, line] = [&] () -> std::pair<Path, uint32_t> {
             if (v.type() == nPath || v.type() == nString) {
                 PathSet context;
-                auto path = state->coerceToPath(noPos, v, context, "while evaluating the filename to edit");
+                auto path = state->coerceToPath(noPos, v, context);
                 return {path, 0};
             } else if (v.isLambda()) {
                 auto pos = state->positions[v.lambda.fun->pos];
@@ -839,7 +839,7 @@ void NixRepl::loadFiles()
 
 void NixRepl::addAttrsToScope(Value & attrs)
 {
-    state->forceAttrs(attrs, [&]() { return attrs.determinePos(noPos); }, "while evaluating an attribute set to be merged in the global scope");
+    state->forceAttrs(attrs, [&]() { return attrs.determinePos(noPos); });
     if (displ + attrs.attrs->size() >= envSize)
         throw Error("environment full; cannot add more variables");
 
@@ -944,7 +944,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
             Bindings::iterator i = v.attrs->find(state->sDrvPath);
             PathSet context;
             if (i != v.attrs->end())
-                str << state->store->printStorePath(state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the drvPath of a derivation"));
+                str << state->store->printStorePath(state->coerceToStorePath(i->pos, *i->value, context));
             else
                 str << "???";
             str << "»";

src/libexpr/attr-path.cc

@@ -118,7 +118,7 @@ std::pair<std::string, uint32_t> findPackageFilename(EvalState & state, Value &
 
     // FIXME: is it possible to extract the Pos object instead of doing this
     //        toString + parsing?
-    auto pos = state.forceString(*v2, noPos, "while evaluating the 'meta.position' attribute of a derivation");
+    auto pos = state.forceString(*v2);
 
     auto colon = pos.rfind(':');
     if (colon == std::string::npos)

src/libexpr/eval-cache.cc

@@ -385,7 +385,7 @@ Value & AttrCursor::getValue()
     if (!_value) {
         if (parent) {
             auto & vParent = parent->first->getValue();
-            root->state.forceAttrs(vParent, noPos, "while searching for an attribute");
+            root->state.forceAttrs(vParent, noPos);
             auto attr = vParent.attrs->get(parent->second);
             if (!attr)
                 throw Error("attribute '%s' is unexpectedly missing", getAttrPathStr());
@@ -571,14 +571,14 @@ std::string AttrCursor::getString()
                 debug("using cached string attribute '%s'", getAttrPathStr());
                 return s->first;
             } else
-                root->state.error("'%s' is not a string", getAttrPathStr()).debugThrow<TypeError>();
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a string", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nString && v.type() != nPath)
-        root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
 
     return v.type() == nString ? v.string.s : v.path;
 }
@@ -613,7 +613,7 @@ string_t AttrCursor::getStringWithContext()
                     return *s;
                 }
             } else
-                root->state.error("'%s' is not a string", getAttrPathStr()).debugThrow<TypeError>();
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a string", getAttrPathStr()));
         }
     }
 
@@ -624,7 +624,7 @@ string_t AttrCursor::getStringWithContext()
     else if (v.type() == nPath)
         return {v.path, {}};
     else
-        root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a string but %s", getAttrPathStr(), showType(v.type())));
 }
 
 bool AttrCursor::getBool()
@@ -637,14 +637,14 @@ bool AttrCursor::getBool()
                 debug("using cached Boolean attribute '%s'", getAttrPathStr());
                 return *b;
             } else
-                root->state.error("'%s' is not a Boolean", getAttrPathStr()).debugThrow<TypeError>();
+                root->state.debugThrowLastTrace(TypeError("'%s' is not a Boolean", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nBool)
-        root->state.error("'%s' is not a Boolean", getAttrPathStr()).debugThrow<TypeError>();
+        root->state.debugThrowLastTrace(TypeError("'%s' is not a Boolean", getAttrPathStr()));
 
     return v.boolean;
 }
@@ -696,7 +696,7 @@ std::vector<std::string> AttrCursor::getListOfStrings()
     std::vector<std::string> res;
 
     for (auto & elem : v.listItems())
-        res.push_back(std::string(root->state.forceStringNoCtx(*elem, noPos, "while evaluating an attribute for caching")));
+        res.push_back(std::string(root->state.forceStringNoCtx(*elem)));
 
     if (root->db)
         cachedValue = {root->db->setListOfStrings(getKey(), res), res};
@@ -714,14 +714,14 @@ std::vector<Symbol> AttrCursor::getAttrs()
                 debug("using cached attrset attribute '%s'", getAttrPathStr());
                 return *attrs;
             } else
-                root->state.error("'%s' is not an attribute set", getAttrPathStr()).debugThrow<TypeError>();
+                root->state.debugThrowLastTrace(TypeError("'%s' is not an attribute set", getAttrPathStr()));
         }
     }
 
     auto & v = forceValue();
 
     if (v.type() != nAttrs)
-        root->state.error("'%s' is not an attribute set", getAttrPathStr()).debugThrow<TypeError>();
+        root->state.debugThrowLastTrace(TypeError("'%s' is not an attribute set", getAttrPathStr()));
 
     std::vector<Symbol> attrs;
     for (auto & attr : *getValue().attrs)

src/libexpr/eval-inline.hh

@@ -103,36 +103,33 @@ void EvalState::forceValue(Value & v, Callable getPos)
     else if (v.isApp())
         callFunction(*v.app.left, *v.app.right, v, noPos);
     else if (v.isBlackhole())
-        error("infinite recursion encountered").atPos(getPos()).template debugThrow<EvalError>();
+        throwEvalError(getPos(), "infinite recursion encountered");
 }
 
 
 [[gnu::always_inline]]
-inline void EvalState::forceAttrs(Value & v, const PosIdx pos, std::string_view errorCtx)
+inline void EvalState::forceAttrs(Value & v, const PosIdx pos)
 {
-    forceAttrs(v, [&]() { return pos; }, errorCtx);
+    forceAttrs(v, [&]() { return pos; });
 }
 
 
 template <typename Callable>
 [[gnu::always_inline]]
-inline void EvalState::forceAttrs(Value & v, Callable getPos, std::string_view errorCtx)
+inline void EvalState::forceAttrs(Value & v, Callable getPos)
 {
-    forceValue(v, noPos);
-    if (v.type() != nAttrs) {
-        PosIdx pos = getPos();
-        error("value is %1% while a set was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
-    }
+    forceValue(v, getPos);
+    if (v.type() != nAttrs)
+        throwTypeError(getPos(), "value is %1% while a set was expected", v);
 }
 
 
 [[gnu::always_inline]]
-inline void EvalState::forceList(Value & v, const PosIdx pos, std::string_view errorCtx)
+inline void EvalState::forceList(Value & v, const PosIdx pos)
 {
-    forceValue(v, noPos);
-    if (!v.isList()) {
-        error("value is %1% while a list was expected", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
-    }
+    forceValue(v, pos);
+    if (!v.isList())
+        throwTypeError(pos, "value is %1% while a list was expected", v);
 }
 
 

src/libexpr/eval.cc

@@ -318,7 +318,7 @@ static Symbol getName(const AttrName & name, EvalState & state, Env & env)
     } else {
         Value nameValue;
         name.expr->eval(state, env, nameValue);
-        state.forceStringNoCtx(nameValue, noPos, "while evaluating an attribute name");
+        state.forceStringNoCtx(nameValue);
         return state.symbols.create(nameValue.string.s);
     }
 }
@@ -414,44 +414,6 @@ static Strings parseNixPath(const std::string & s)
     return res;
 }
 
-ErrorBuilder & ErrorBuilder::atPos(PosIdx pos)
-{
-    info.errPos = state.positions[pos];
-    return *this;
-}
-
-ErrorBuilder & ErrorBuilder::withTrace(PosIdx pos, const std::string_view text)
-{
-    info.traces.push_front(Trace{ .pos = state.positions[pos], .hint = hintformat(std::string(text)), .frame = false });
-    return *this;
-}
-
-ErrorBuilder & ErrorBuilder::withFrameTrace(PosIdx pos, const std::string_view text)
-{
-    info.traces.push_front(Trace{ .pos = state.positions[pos], .hint = hintformat(std::string(text)), .frame = true });
-    return *this;
-}
-
-ErrorBuilder & ErrorBuilder::withSuggestions(Suggestions & s)
-{
-    info.suggestions = s;
-    return *this;
-}
-
-ErrorBuilder & ErrorBuilder::withFrame(const Env & env, const Expr & expr)
-{
-    // NOTE: This is abusing side-effects.
-    // TODO: check compatibility with nested debugger calls.
-    state.debugTraces.push_front(DebugTrace {
-        .pos = nullptr,
-        .expr = expr,
-        .env = env,
-        .hint = hintformat("Fake frame for debugging purposes"),
-        .isError = true
-    });
-    return *this;
-}
-
 
 EvalState::EvalState(
     const Strings & _searchPath,
@@ -684,7 +646,25 @@ void EvalState::addConstant(const std::string & name, Value * v)
 Value * EvalState::addPrimOp(const std::string & name,
     size_t arity, PrimOpFun primOp)
 {
-    return addPrimOp(PrimOp { .fun = primOp, .arity = arity, .name = name });
+    auto name2 = name.substr(0, 2) == "__" ? name.substr(2) : name;
+    auto sym = symbols.create(name2);
+
+    /* Hack to make constants lazy: turn them into a application of
+       the primop to a dummy value. */
+    if (arity == 0) {
+        auto vPrimOp = allocValue();
+        vPrimOp->mkPrimOp(new PrimOp { .fun = primOp, .arity = 1, .name = name2 });
+        Value v;
+        v.mkApp(vPrimOp, vPrimOp);
+        return addConstant(name, v);
+    }
+
+    Value * v = allocValue();
+    v->mkPrimOp(new PrimOp { .fun = primOp, .arity = arity, .name = name2 });
+    staticBaseEnv->vars.emplace_back(symbols.create(name), baseEnvDispl);
+    baseEnv.values[baseEnvDispl++] = v;
+    baseEnv.values[0]->attrs->push_back(Attr(sym, v));
+    return v;
 }
 
 
@@ -862,14 +842,176 @@ void EvalState::runDebugRepl(const Error * error, const Env & env, const Expr &
     }
 }
 
+/* Every "format" object (even temporary) takes up a few hundred bytes
+   of stack space, which is a real killer in the recursive
+   evaluator.  So here are some helper functions for throwing
+   exceptions. */
+void EvalState::throwEvalError(const PosIdx pos, const char * s, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const char * s, const std::string & s2)
+{
+    debugThrowLastTrace(EvalError(s, s2));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const std::string & s2, Env & env, Expr & expr)
+{
+    debugThrow(EvalError(ErrorInfo{
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos],
+        .suggestions = suggestions,
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s, s2),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const char * s, const std::string & s2,
+    const std::string & s3)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2, s3),
+        .errPos = positions[noPos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+    const std::string & s3)
+{
+    debugThrowLastTrace(EvalError({
+        .msg = hintfmt(s, s2, s3),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+    const std::string & s3, Env & env, Expr & expr)
+{
+    debugThrow(EvalError({
+        .msg = hintfmt(s, s2, s3),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2, Env & env, Expr & expr)
+{
+    // p1 is where the error occurred; p2 is a position mentioned in the message.
+    debugThrow(EvalError({
+        .msg = hintfmt(s, symbols[sym], positions[p2]),
+        .errPos = positions[p1]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const Value & v)
+{
+    debugThrowLastTrace(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const Value & v, Env & env, Expr & expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s)
+{
+    debugThrowLastTrace(TypeError({
+        .msg = hintfmt(s),
+        .errPos = positions[pos]
+    }));
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun,
+    const Symbol s2, Env & env, Expr &expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s,
+    const ExprLambda & fun, const Symbol s2, Env & env, Expr &expr)
+{
+    debugThrow(TypeError(ErrorInfo {
+        .msg = hintfmt(s, fun.showNamePos(*this), symbols[s2]),
+        .errPos = positions[pos],
+        .suggestions = suggestions,
+    }), env, expr);
+}
+
+void EvalState::throwTypeError(const char * s, const Value & v, Env & env, Expr &expr)
+{
+    debugThrow(TypeError({
+        .msg = hintfmt(s, showType(v)),
+        .errPos = positions[expr.getPos()],
+    }), env, expr);
+}
+
+void EvalState::throwAssertionError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(AssertionError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(UndefinedVarError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
+void EvalState::throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1, Env & env, Expr &expr)
+{
+    debugThrow(MissingArgumentError({
+        .msg = hintfmt(s, s1),
+        .errPos = positions[pos]
+    }), env, expr);
+}
+
 void EvalState::addErrorTrace(Error & e, const char * s, const std::string & s2) const
 {
     e.addTrace(nullptr, s, s2);
 }
 
-void EvalState::addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2, bool frame) const
+void EvalState::addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const
 {
-    e.addTrace(positions[pos], hintfmt(s, s2), frame);
+    e.addTrace(positions[pos], s, s2);
 }
 
 static std::unique_ptr<DebugTraceStacker> makeDebugTraceStacker(
@@ -946,7 +1088,7 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
         if (env->type == Env::HasWithExpr) {
             if (noEval) return 0;
             Value * v = allocValue();
-            evalAttrs(*env->up, (Expr *) env->values[0], *v, noPos, "<borked>");
+            evalAttrs(*env->up, (Expr *) env->values[0], *v);
             env->values[0] = v;
             env->type = Env::HasWithAttrs;
         }
@@ -956,7 +1098,7 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
             return j->value;
         }
         if (!env->prevWith)
-            error("undefined variable '%1%'", symbols[var.name]).atPos(var.pos).withFrame(*env, var).debugThrow<UndefinedVarError>();
+            throwUndefinedVarError(var.pos, "undefined variable '%1%'", symbols[var.name], *env, const_cast<ExprVar&>(var));
         for (size_t l = env->prevWith; l; --l, env = env->up) ;
     }
 }
@@ -1106,7 +1248,7 @@ void EvalState::cacheFile(
         // computation.
         if (mustBeTrivial &&
             !(dynamic_cast<ExprAttrs *>(e)))
-            error("file '%s' must be an attribute set", path).debugThrow<EvalError>();
+            throw EvalError("file '%s' must be an attribute set", path);
         eval(e, v);
     } catch (Error & e) {
         addErrorTrace(e, "while evaluating the file '%1%':", resolvedPath);
@@ -1124,31 +1266,31 @@ void EvalState::eval(Expr * e, Value & v)
 }
 
 
-inline bool EvalState::evalBool(Env & env, Expr * e, const PosIdx pos, std::string_view errorCtx)
+inline bool EvalState::evalBool(Env & env, Expr * e)
 {
-    try {
-        Value v;
-        e->eval(*this, env, v);
-        if (v.type() != nBool)
-            error("value is %1% while a Boolean was expected", showType(v)).withFrame(env, *e).debugThrow<TypeError>();
-        return v.boolean;
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
+    Value v;
+    e->eval(*this, env, v);
+    if (v.type() != nBool)
+        throwTypeError(noPos, "value is %1% while a Boolean was expected", v, env, *e);
+    return v.boolean;
 }
 
 
-inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const PosIdx pos, std::string_view errorCtx)
+inline bool EvalState::evalBool(Env & env, Expr * e, const PosIdx pos)
 {
-    try {
-        e->eval(*this, env, v);
-        if (v.type() != nAttrs)
-            error("value is %1% while a set was expected", showType(v)).withFrame(env, *e).debugThrow<TypeError>();
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
+    Value v;
+    e->eval(*this, env, v);
+    if (v.type() != nBool)
+        throwTypeError(pos, "value is %1% while a Boolean was expected", v, env, *e);
+    return v.boolean;
+}
+
+
+inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v)
+{
+    e->eval(*this, env, v);
+    if (v.type() != nAttrs)
+        throwTypeError(noPos, "value is %1% while a set was expected", v, env, *e);
 }
 
 
@@ -1221,7 +1363,7 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
            Hence we need __overrides.) */
         if (hasOverrides) {
             Value * vOverrides = (*v.attrs)[overrides->second.displ].value;
-            state.forceAttrs(*vOverrides, [&]() { return vOverrides->determinePos(noPos); }, "while evaluating the `__overrides` attribute");
+            state.forceAttrs(*vOverrides, [&]() { return vOverrides->determinePos(noPos); });
             Bindings * newBnds = state.allocBindings(v.attrs->capacity() + vOverrides->attrs->size());
             for (auto & i : *v.attrs)
                 newBnds->push_back(i);
@@ -1249,11 +1391,11 @@ void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
         state.forceValue(nameVal, i.pos);
         if (nameVal.type() == nNull)
             continue;
-        state.forceStringNoCtx(nameVal, i.pos, "while evaluating the name of a dynamic attribute");
+        state.forceStringNoCtx(nameVal);
         auto nameSym = state.symbols.create(nameVal.string.s);
         Bindings::iterator j = v.attrs->find(nameSym);
         if (j != v.attrs->end())
-            state.error("dynamic attribute '%1%' already defined at %2%", state.symbols[nameSym], state.positions[j->pos]).atPos(i.pos).withFrame(env, *this).debugThrow<EvalError>();
+            state.throwEvalError(i.pos, "dynamic attribute '%1%' already defined at %2%", nameSym, j->pos, env, *this);
 
         i.valueExpr->setName(nameSym);
         /* Keep sorted order so find can catch duplicates */
@@ -1350,14 +1492,15 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                     return;
                 }
             } else {
-                state.forceAttrs(*vAttrs, pos, "while selecting an attribute");
+                state.forceAttrs(*vAttrs, pos);
                 if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end()) {
                     std::set<std::string> allAttrNames;
                     for (auto & attr : *vAttrs->attrs)
                         allAttrNames.insert(state.symbols[attr.name]);
-                    auto suggestions = Suggestions::bestMatches(allAttrNames, state.symbols[name]);
-                    state.error("attribute '%1%' missing", state.symbols[name])
-                        .atPos(pos).withSuggestions(suggestions).withFrame(env, *this).debugThrow<EvalError>();
+                    state.throwEvalError(
+                        pos,
+                        Suggestions::bestMatches(allAttrNames, state.symbols[name]),
+                        "attribute '%1%' missing", state.symbols[name], env, *this);
                 }
             }
             vAttrs = j->value;
@@ -1452,12 +1595,7 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
             if (!lambda.hasFormals())
                 env2.values[displ++] = args[0];
             else {
-                try {
-                    forceAttrs(*args[0], lambda.pos, "while evaluating the value passed for the lambda argument");
-                } catch (Error & e) {
-                    if (pos) e.addTrace(positions[pos], "from call site");
-                    throw;
-                }
+                forceAttrs(*args[0], pos);
 
                 if (lambda.arg)
                     env2.values[displ++] = args[0];
@@ -1469,15 +1607,8 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 for (auto & i : lambda.formals->formals) {
                     auto j = args[0]->attrs->get(i.name);
                     if (!j) {
-                        if (!i.def) {
-                            error("function '%1%' called without required argument '%2%'",
-                                             (lambda.name ? std::string(symbols[lambda.name]) : "anonymous lambda"),
-                                             symbols[i.name])
-                                    .atPos(lambda.pos)
-                                    .withTrace(pos, "from call site")
-                                    .withFrame(*fun.lambda.env, lambda)
-                                    .debugThrow<TypeError>();
-                        }
+                        if (!i.def) throwTypeError(pos, "%1% called without required argument '%2%'",
+                            lambda, i.name, *fun.lambda.env, lambda);
                         env2.values[displ++] = i.def->maybeThunk(*this, env2);
                     } else {
                         attrsUsed++;
@@ -1495,15 +1626,11 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                             std::set<std::string> formalNames;
                             for (auto & formal : lambda.formals->formals)
                                 formalNames.insert(symbols[formal.name]);
-                            auto suggestions = Suggestions::bestMatches(formalNames, symbols[i.name]);
-                            error("function '%1%' called with unexpected argument '%2%'",
-                                             (lambda.name ? std::string(symbols[lambda.name]) : "anonymous lambda"),
-                                             symbols[i.name])
-                                .atPos(lambda.pos)
-                                .withTrace(pos, "from call site")
-                                .withSuggestions(suggestions)
-                                .withFrame(*fun.lambda.env, lambda)
-                                .debugThrow<TypeError>();
+                            throwTypeError(
+                                pos,
+                                Suggestions::bestMatches(formalNames, symbols[i.name]),
+                                "%1% called with unexpected argument '%2%'",
+                                lambda, i.name, *fun.lambda.env, lambda);
                         }
                     abort(); // can't happen
                 }
@@ -1526,15 +1653,11 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 lambda.body->eval(*this, env2, vCur);
             } catch (Error & e) {
                 if (loggerSettings.showTrace.get()) {
-                    addErrorTrace(
-                        e,
-                        lambda.pos,
-                        "while calling %s",
-                        lambda.name
-                        ? concatStrings("'", symbols[lambda.name], "'")
-                        : "anonymous lambda",
-                        true);
-                    if (pos) addErrorTrace(e, pos, "from call site%s", "", true);
+                    addErrorTrace(e, lambda.pos, "while calling %s",
+                        (lambda.name
+                            ? concatStrings("'", symbols[lambda.name], "'")
+                            : "anonymous lambda"));
+                    addErrorTrace(e, pos, "while evaluating call site%s", "");
                 }
                 throw;
             }
@@ -1553,17 +1676,9 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 return;
             } else {
                 /* We have all the arguments, so call the primop. */
-                auto name = vCur.primOp->name;
-
                 nrPrimOpCalls++;
-                if (countCalls) primOpCalls[name]++;
-
-                try {
-                    vCur.primOp->fun(*this, noPos, args, vCur);
-                } catch (Error & e) {
-                    addErrorTrace(e, pos, "while calling the '%1%' builtin", name);
-                    throw;
-                }
+                if (countCalls) primOpCalls[vCur.primOp->name]++;
+                vCur.primOp->fun(*this, pos, args, vCur);
 
                 nrArgs -= argsLeft;
                 args += argsLeft;
@@ -1598,20 +1713,9 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                 for (size_t i = 0; i < argsLeft; ++i)
                     vArgs[argsDone + i] = args[i];
 
-                auto name = primOp->primOp->name;
                 nrPrimOpCalls++;
-                if (countCalls) primOpCalls[name]++;
-
-                try {
-                    // TODO:
-                    // 1. Unify this and above code. Heavily redundant.
-                    // 2. Create a fake env (arg1, arg2, etc.) and a fake expr (arg1: arg2: etc: builtins.name arg1 arg2 etc)
-                    //    so the debugger allows to inspect the wrong parameters passed to the builtin.
-                    primOp->primOp->fun(*this, noPos, vArgs, vCur);
-                } catch (Error & e) {
-                    addErrorTrace(e, pos, "while calling the '%1%' builtin", name);
-                    throw;
-                }
+                if (countCalls) primOpCalls[primOp->primOp->name]++;
+                primOp->primOp->fun(*this, pos, vArgs, vCur);
 
                 nrArgs -= argsLeft;
                 args += argsLeft;
@@ -1624,18 +1728,14 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                heap-allocate a copy and use that instead. */
             Value * args2[] = {allocValue(), args[0]};
             *args2[0] = vCur;
-            try {
-                callFunction(*functor->value, 2, args2, vCur, functor->pos);
-            } catch (Error & e) {
-                e.addTrace(positions[pos], "while calling a functor (an attribute set with a '__functor' attribute)");
-                throw;
-            }
+            /* !!! Should we use the attr pos here? */
+            callFunction(*functor->value, 2, args2, vCur, pos);
             nrArgs--;
             args++;
         }
 
         else
-            error("attempt to call something which is not a function but %1%", showType(vCur)).atPos(pos).debugThrow<TypeError>();
+            throwTypeError(pos, "attempt to call something which is not a function but %1%", vCur);
     }
 
     vRes = vCur;
@@ -1699,12 +1799,13 @@ void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
             if (j != args.end()) {
                 attrs.insert(*j);
             } else if (!i.def) {
-                error(R"(cannot evaluate a function that has an argument without a value ('%1%')
+                throwMissingArgumentError(i.pos, R"(cannot evaluate a function that has an argument without a value ('%1%')
+
 Nix attempted to evaluate a function as a top level expression; in
 this case it must have its arguments supplied either by default
 values, or passed explicitly with '--arg' or '--argstr'. See
-https://nixos.org/manual/nix/stable/language/constructs.html#functions.)", symbols[i.name])
-                    .atPos(i.pos).withFrame(*fun.lambda.env, *fun.lambda.fun).debugThrow<MissingArgumentError>();
+https://nixos.org/manual/nix/stable/language/constructs.html#functions.)", symbols[i.name],
+                *fun.lambda.env, *fun.lambda.fun);
             }
         }
     }
@@ -1727,17 +1828,16 @@ void ExprWith::eval(EvalState & state, Env & env, Value & v)
 
 void ExprIf::eval(EvalState & state, Env & env, Value & v)
 {
-    // We cheat in the parser, and pass the position of the condition as the position of the if itself.
-    (state.evalBool(env, cond, pos, "while evaluating a branch condition") ? then : else_)->eval(state, env, v);
+    (state.evalBool(env, cond, pos) ? then : else_)->eval(state, env, v);
 }
 
 
 void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 {
-    if (!state.evalBool(env, cond, pos, "in the condition of the assert statement")) {
+    if (!state.evalBool(env, cond, pos)) {
         std::ostringstream out;
         cond->show(state.symbols, out);
-        state.error("assertion '%1%' failed", out.str()).atPos(pos).withFrame(env, *this).debugThrow<AssertionError>();
+        state.throwAssertionError(pos, "assertion '%1%' failed", out.str(), env, *this);
     }
     body->eval(state, env, v);
 }
@@ -1745,7 +1845,7 @@ void ExprAssert::eval(EvalState & state, Env & env, Value & v)
 
 void ExprOpNot::eval(EvalState & state, Env & env, Value & v)
 {
-    v.mkBool(!state.evalBool(env, e, noPos, "in the argument of the not operator")); // XXX: FIXME: !
+    v.mkBool(!state.evalBool(env, e));
 }
 
 
@@ -1753,7 +1853,7 @@ void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    v.mkBool(state.eqValues(v1, v2, pos, "while testing two values for equality"));
+    v.mkBool(state.eqValues(v1, v2));
 }
 
 
@@ -1761,33 +1861,33 @@ void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
-    v.mkBool(!state.eqValues(v1, v2, pos, "while testing two values for inequality"));
+    v.mkBool(!state.eqValues(v1, v2));
 }
 
 
 void ExprOpAnd::eval(EvalState & state, Env & env, Value & v)
 {
-    v.mkBool(state.evalBool(env, e1, pos, "in the left operand of the AND (&&) operator") && state.evalBool(env, e2, pos, "in the right operand of the AND (&&) operator"));
+    v.mkBool(state.evalBool(env, e1, pos) && state.evalBool(env, e2, pos));
 }
 
 
 void ExprOpOr::eval(EvalState & state, Env & env, Value & v)
 {
-    v.mkBool(state.evalBool(env, e1, pos, "in the left operand of the OR (||) operator") || state.evalBool(env, e2, pos, "in the right operand of the OR (||) operator"));
+    v.mkBool(state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
 }
 
 
 void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
 {
-    v.mkBool(!state.evalBool(env, e1, pos, "in the left operand of the IMPL (->) operator") || state.evalBool(env, e2, pos, "in the right operand of the IMPL (->) operator"));
+    v.mkBool(!state.evalBool(env, e1, pos) || state.evalBool(env, e2, pos));
 }
 
 
 void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
 {
     Value v1, v2;
-    state.evalAttrs(env, e1, v1, pos, "in the left operand of the update (//) operator");
-    state.evalAttrs(env, e2, v2, pos, "in the right operand of the update (//) operator");
+    state.evalAttrs(env, e1, v1);
+    state.evalAttrs(env, e2, v2);
 
     state.nrOpUpdates++;
 
@@ -1826,18 +1926,18 @@ void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
     Value v1; e1->eval(state, env, v1);
     Value v2; e2->eval(state, env, v2);
     Value * lists[2] = { &v1, &v2 };
-    state.concatLists(v, 2, lists, pos, "while evaluating one of the elements to concatenate");
+    state.concatLists(v, 2, lists, pos);
 }
 
 
-void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx)
+void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos)
 {
     nrListConcats++;
 
     Value * nonEmpty = 0;
     size_t len = 0;
     for (size_t n = 0; n < nrLists; ++n) {
-        forceList(*lists[n], pos, errorCtx);
+        forceList(*lists[n], pos);
         auto l = lists[n]->listSize();
         len += l;
         if (l) nonEmpty = lists[n];
@@ -1914,20 +2014,20 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
                 nf = n;
                 nf += vTmp.fpoint;
             } else
-                state.error("cannot add %1% to an integer", showType(vTmp)).atPos(i_pos).withFrame(env, *this).debugThrow<EvalError>();
+                state.throwEvalError(i_pos, "cannot add %1% to an integer", showType(vTmp), env, *this);
         } else if (firstType == nFloat) {
             if (vTmp.type() == nInt) {
                 nf += vTmp.integer;
             } else if (vTmp.type() == nFloat) {
                 nf += vTmp.fpoint;
             } else
-                state.error("cannot add %1% to a float", showType(vTmp)).atPos(i_pos).withFrame(env, *this).debugThrow<EvalError>();
+                state.throwEvalError(i_pos, "cannot add %1% to a float", showType(vTmp), env, *this);
         } else {
             if (s.empty()) s.reserve(es->size());
             /* skip canonization of first path, which would only be not
             canonized in the first place if it's coming from a ./${foo} type
             path */
-            auto part = state.coerceToString(i_pos, vTmp, context, false, firstType == nString, !first, "while evaluating a path segment");
+            auto part = state.coerceToString(i_pos, vTmp, context, false, firstType == nString, !first);
             sSize += part->size();
             s.emplace_back(std::move(part));
         }
@@ -1941,7 +2041,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
         v.mkFloat(nf);
     else if (firstType == nPath) {
         if (!context.empty())
-            state.error("a string that refers to a store path cannot be appended to a path").atPos(pos).withFrame(env, *this).debugThrow<EvalError>();
+            state.throwEvalError(pos, "a string that refers to a store path cannot be appended to a path", env, *this);
         v.mkPath(canonPath(str()));
     } else
         v.mkStringMove(c_str(), context);
@@ -1991,47 +2091,33 @@ void EvalState::forceValueDeep(Value & v)
 }
 
 
-NixInt EvalState::forceInt(Value & v, const PosIdx pos, std::string_view errorCtx)
+NixInt EvalState::forceInt(Value & v, const PosIdx pos)
 {
-    try {
-        forceValue(v, pos);
-        if (v.type() != nInt)
-            error("value is %1% while an integer was expected", showType(v)).debugThrow<TypeError>();
+    forceValue(v, pos);
+    if (v.type() != nInt)
+        throwTypeError(pos, "value is %1% while an integer was expected", v);
+
+    return v.integer;
+}
+
+
+NixFloat EvalState::forceFloat(Value & v, const PosIdx pos)
+{
+    forceValue(v, pos);
+    if (v.type() == nInt)
         return v.integer;
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
+    else if (v.type() != nFloat)
+        throwTypeError(pos, "value is %1% while a float was expected", v);
+    return v.fpoint;
 }
 
 
-NixFloat EvalState::forceFloat(Value & v, const PosIdx pos, std::string_view errorCtx)
+bool EvalState::forceBool(Value & v, const PosIdx pos)
 {
-    try {
-        forceValue(v, pos);
-        if (v.type() == nInt)
-            return v.integer;
-        else if (v.type() != nFloat)
-            error("value is %1% while a float was expected", showType(v)).debugThrow<TypeError>();
-        return v.fpoint;
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
-}
-
-
-bool EvalState::forceBool(Value & v, const PosIdx pos, std::string_view errorCtx)
-{
-    try {
-        forceValue(v, pos);
-        if (v.type() != nBool)
-            error("value is %1% while a Boolean was expected", showType(v)).debugThrow<TypeError>();
-        return v.boolean;
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
+    forceValue(v, pos);
+    if (v.type() != nBool)
+        throwTypeError(pos, "value is %1% while a Boolean was expected", v);
+    return v.boolean;
 }
 
 
@@ -2041,30 +2127,21 @@ bool EvalState::isFunctor(Value & fun)
 }
 
 
-void EvalState::forceFunction(Value & v, const PosIdx pos, std::string_view errorCtx)
+void EvalState::forceFunction(Value & v, const PosIdx pos)
 {
-    try {
-        forceValue(v, pos);
-        if (v.type() != nFunction && !isFunctor(v))
-            error("value is %1% while a function was expected", showType(v)).debugThrow<TypeError>();
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
-    }
+    forceValue(v, pos);
+    if (v.type() != nFunction && !isFunctor(v))
+        throwTypeError(pos, "value is %1% while a function was expected", v);
 }
 
 
-std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string_view errorCtx)
+std::string_view EvalState::forceString(Value & v, const PosIdx pos)
 {
-    try {
-        forceValue(v, pos);
-        if (v.type() != nString)
-            error("value is %1% while a string was expected", showType(v)).debugThrow<TypeError>();
-        return v.string.s;
-    } catch (Error & e) {
-        e.addTrace(positions[pos], errorCtx);
-        throw;
+    forceValue(v, pos);
+    if (v.type() != nString) {
+        throwTypeError(pos, "value is %1% while a string was expected", v);
     }
+    return v.string.s;
 }
 
 
@@ -2087,19 +2164,24 @@ NixStringContext Value::getContext(const Store & store)
 }
 
 
-std::string_view EvalState::forceString(Value & v, PathSet & context, const PosIdx pos, std::string_view errorCtx)
+std::string_view EvalState::forceString(Value & v, PathSet & context, const PosIdx pos)
 {
-    auto s = forceString(v, pos, errorCtx);
+    auto s = forceString(v, pos);
     copyContext(v, context);
     return s;
 }
 
 
-std::string_view EvalState::forceStringNoCtx(Value & v, const PosIdx pos, std::string_view errorCtx)
+std::string_view EvalState::forceStringNoCtx(Value & v, const PosIdx pos)
 {
-    auto s = forceString(v, pos, errorCtx);
+    auto s = forceString(v, pos);
     if (v.string.context) {
-        error("the string '%1%' is not allowed to refer to a store path (such as '%2%')", v.string.s, v.string.context[0]).withTrace(pos, errorCtx).debugThrow<EvalError>();
+        if (pos)
+            throwEvalError(pos, "the string '%1%' is not allowed to refer to a store path (such as '%2%')",
+                v.string.s, v.string.context[0]);
+        else
+            throwEvalError("the string '%1%' is not allowed to refer to a store path (such as '%2%')",
+                v.string.s, v.string.context[0]);
     }
     return s;
 }
@@ -2123,15 +2205,14 @@ std::optional<std::string> EvalState::tryAttrsToString(const PosIdx pos, Value &
     if (i != v.attrs->end()) {
         Value v1;
         callFunction(*i->value, v, v1, pos);
-        return coerceToString(pos, v1, context, coerceMore, copyToStore,
-                "while evaluating the result of the `toString` attribute").toOwned();
+        return coerceToString(pos, v1, context, coerceMore, copyToStore).toOwned();
     }
 
     return {};
 }
 
 BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet & context,
-    bool coerceMore, bool copyToStore, bool canonicalizePath, std::string_view errorCtx)
+    bool coerceMore, bool copyToStore, bool canonicalizePath)
 {
     forceValue(v, pos);
 
@@ -2155,12 +2236,12 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
             return std::move(*maybeString);
         auto i = v.attrs->find(sOutPath);
         if (i == v.attrs->end())
-            error("cannot coerce a set to a string", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
-        return coerceToString(pos, *i->value, context, coerceMore, copyToStore, canonicalizePath, errorCtx);
+            throwTypeError(pos, "cannot coerce a set to a string");
+        return coerceToString(pos, *i->value, context, coerceMore, copyToStore);
     }
 
     if (v.type() == nExternal)
-        return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore, errorCtx);
+        return v.external->coerceToString(positions[pos], context, coerceMore, copyToStore);
 
     if (coerceMore) {
         /* Note that `false' is represented as an empty string for
@@ -2174,13 +2255,7 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         if (v.isList()) {
             std::string result;
             for (auto [n, v2] : enumerate(v.listItems())) {
-                try {
-                    result += *coerceToString(noPos, *v2, context, coerceMore, copyToStore, canonicalizePath,
-                            "while evaluating one element of the list");
-                } catch (Error & e) {
-                    e.addTrace(positions[pos], errorCtx);
-                    throw;
-                }
+                result += *coerceToString(pos, *v2, context, coerceMore, copyToStore);
                 if (n < v.listSize() - 1
                     /* !!! not quite correct */
                     && (!v2->isList() || v2->listSize() != 0))
@@ -2190,14 +2265,14 @@ BackedStringView EvalState::coerceToString(const PosIdx pos, Value & v, PathSet
         }
     }
 
-    error("cannot coerce %1% to a string", showType(v)).withTrace(pos, errorCtx).debugThrow<TypeError>();
+    throwTypeError(pos, "cannot coerce %1% to a string", v);
 }
 
 
 StorePath EvalState::copyPathToStore(PathSet & context, const Path & path)
 {
     if (nix::isDerivation(path))
-        error("file names are not allowed to end in '%1%'", drvExtension).debugThrow<EvalError>();
+        throwEvalError("file names are not allowed to end in '%1%'", drvExtension);
 
     auto dstPath = [&]() -> StorePath
     {
@@ -2218,25 +2293,28 @@ StorePath EvalState::copyPathToStore(PathSet & context, const Path & path)
 }
 
 
-Path EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
+Path EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context)
 {
-    auto path = coerceToString(pos, v, context, false, false, true, errorCtx).toOwned();
+    auto path = coerceToString(pos, v, context, false, false).toOwned();
     if (path == "" || path[0] != '/')
-        error("string '%1%' doesn't represent an absolute path", path).withTrace(pos, errorCtx).debugThrow<EvalError>();
+        throwEvalError(pos, "string '%1%' doesn't represent an absolute path", path);
     return path;
 }
 
 
-StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
+StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, PathSet & context)
 {
-    auto path = coerceToString(pos, v, context, false, false, true, errorCtx).toOwned();
+    auto path = coerceToString(pos, v, context, false, false).toOwned();
     if (auto storePath = store->maybeParseStorePath(path))
         return *storePath;
-    error("path '%1%' is not in the Nix store", path).withTrace(pos, errorCtx).debugThrow<EvalError>();
+    throw EvalError({
+        .msg = hintfmt("path '%1%' is not in the Nix store", path),
+        .errPos = positions[pos]
+    });
 }
 
 
-bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_view errorCtx)
+bool EvalState::eqValues(Value & v1, Value & v2)
 {
     forceValue(v1, noPos);
     forceValue(v2, noPos);
@@ -2256,6 +2334,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
     if (v1.type() != v2.type()) return false;
 
     switch (v1.type()) {
+
         case nInt:
             return v1.integer == v2.integer;
 
@@ -2274,7 +2353,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
         case nList:
             if (v1.listSize() != v2.listSize()) return false;
             for (size_t n = 0; n < v1.listSize(); ++n)
-                if (!eqValues(*v1.listElems()[n], *v2.listElems()[n], pos, errorCtx)) return false;
+                if (!eqValues(*v1.listElems()[n], *v2.listElems()[n])) return false;
             return true;
 
         case nAttrs: {
@@ -2284,7 +2363,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
                 Bindings::iterator i = v1.attrs->find(sOutPath);
                 Bindings::iterator j = v2.attrs->find(sOutPath);
                 if (i != v1.attrs->end() && j != v2.attrs->end())
-                    return eqValues(*i->value, *j->value, pos, errorCtx);
+                    return eqValues(*i->value, *j->value);
             }
 
             if (v1.attrs->size() != v2.attrs->size()) return false;
@@ -2292,7 +2371,7 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
             /* Otherwise, compare the attributes one by one. */
             Bindings::iterator i, j;
             for (i = v1.attrs->begin(), j = v2.attrs->begin(); i != v1.attrs->end(); ++i, ++j)
-                if (i->name != j->name || !eqValues(*i->value, *j->value, pos, errorCtx))
+                if (i->name != j->name || !eqValues(*i->value, *j->value))
                     return false;
 
             return true;
@@ -2309,7 +2388,9 @@ bool EvalState::eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_v
             return v1.fpoint == v2.fpoint;
 
         default:
-            error("cannot compare %1% with %2%", showType(v1), showType(v2)).withTrace(pos, errorCtx).debugThrow<EvalError>();
+            throwEvalError("cannot compare %1% with %2%",
+                showType(v1),
+                showType(v2));
     }
 }
 
@@ -2433,13 +2514,12 @@ void EvalState::printStats()
 }
 
 
-std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, std::string_view errorCtx) const
+std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const
 {
-    auto e = TypeError({
-        .msg = hintfmt("cannot coerce %1% to a string", showType())
+    throw TypeError({
+        .msg = hintfmt("cannot coerce %1% to a string", showType()),
+        .errPos = pos
     });
-    e.addTrace(pos, errorCtx);
-    throw e;
 }
 
 

src/libexpr/eval.hh

@@ -86,43 +86,6 @@ struct DebugTrace {
 
 void debugError(Error * e, Env & env, Expr & expr);
 
-class ErrorBuilder
-{
-    private:
-        EvalState & state;
-        ErrorInfo info;
-
-        ErrorBuilder(EvalState & s, ErrorInfo && i): state(s), info(i) { }
-
-    public:
-        template<typename... Args>
-        [[nodiscard, gnu::noinline]]
-        static ErrorBuilder * create(EvalState & s, const Args & ... args)
-        {
-            return new ErrorBuilder(s, ErrorInfo { .msg = hintfmt(args...) });
-        }
-
-        [[nodiscard, gnu::noinline]]
-        ErrorBuilder & atPos(PosIdx pos);
-
-        [[nodiscard, gnu::noinline]]
-        ErrorBuilder & withTrace(PosIdx pos, const std::string_view text);
-
-        [[nodiscard, gnu::noinline]]
-        ErrorBuilder & withFrameTrace(PosIdx pos, const std::string_view text);
-
-        [[nodiscard, gnu::noinline]]
-        ErrorBuilder & withSuggestions(Suggestions & s);
-
-        [[nodiscard, gnu::noinline]]
-        ErrorBuilder & withFrame(const Env & e, const Expr & ex);
-
-        template<class ErrorType>
-        [[gnu::noinline, gnu::noreturn]]
-        void debugThrow();
-};
-
-
 class EvalState : public std::enable_shared_from_this<EvalState>
 {
 public:
@@ -182,36 +145,30 @@ public:
 
     template<class E>
     [[gnu::noinline, gnu::noreturn]]
-    void debugThrowLastTrace(E && error)
+    void debugThrow(E && error, const Env & env, const Expr & expr)
     {
-        debugThrow(error, nullptr, nullptr);
-    }
-
-    template<class E>
-    [[gnu::noinline, gnu::noreturn]]
-    void debugThrow(E && error, const Env * env, const Expr * expr)
-    {
-        if (debugRepl && ((env && expr) || !debugTraces.empty())) {
-            if (!env || !expr) {
-                const DebugTrace & last = debugTraces.front();
-                env = &last.env;
-                expr = &last.expr;
-            }
-            runDebugRepl(&error, *env, *expr);
-        }
+        if (debugRepl)
+            runDebugRepl(&error, env, expr);
 
         throw std::move(error);
     }
 
-    ErrorBuilder * errorBuilder;
+    template<class E>
+    [[gnu::noinline, gnu::noreturn]]
+    void debugThrowLastTrace(E && e)
+    {
+        // Call this in the situation where Expr and Env are inaccessible.
+        // The debugger will start in the last context that's in the
+        // DebugTrace stack.
+        if (debugRepl && !debugTraces.empty()) {
+            const DebugTrace & last = debugTraces.front();
+            runDebugRepl(&e, last.env, last.expr);
+        }
 
-    template<typename... Args>
-    [[nodiscard, gnu::noinline]]
-    ErrorBuilder & error(const Args & ... args) {
-        errorBuilder = ErrorBuilder::create(*this, args...);
-        return *errorBuilder;
+        throw std::move(e);
     }
 
+
 private:
     SrcToStore srcToStore;
 
@@ -325,8 +282,8 @@ public:
     /* Evaluation the expression, then verify that it has the expected
        type. */
     inline bool evalBool(Env & env, Expr * e);
-    inline bool evalBool(Env & env, Expr * e, const PosIdx pos, std::string_view errorCtx);
-    inline void evalAttrs(Env & env, Expr * e, Value & v, const PosIdx pos, std::string_view errorCtx);
+    inline bool evalBool(Env & env, Expr * e, const PosIdx pos);
+    inline void evalAttrs(Env & env, Expr * e, Value & v);
 
     /* If `v' is a thunk, enter it and overwrite `v' with the result
        of the evaluation of the thunk.  If `v' is a delayed function
@@ -342,25 +299,89 @@ public:
     void forceValueDeep(Value & v);
 
     /* Force `v', and then verify that it has the expected type. */
-    NixInt forceInt(Value & v, const PosIdx pos, std::string_view errorCtx);
-    NixFloat forceFloat(Value & v, const PosIdx pos, std::string_view errorCtx);
-    bool forceBool(Value & v, const PosIdx pos, std::string_view errorCtx);
+    NixInt forceInt(Value & v, const PosIdx pos);
+    NixFloat forceFloat(Value & v, const PosIdx pos);
+    bool forceBool(Value & v, const PosIdx pos);
 
-    void forceAttrs(Value & v, const PosIdx pos, std::string_view errorCtx);
+    void forceAttrs(Value & v, const PosIdx pos);
 
     template <typename Callable>
-    inline void forceAttrs(Value & v, Callable getPos, std::string_view errorCtx);
+    inline void forceAttrs(Value & v, Callable getPos);
 
-    inline void forceList(Value & v, const PosIdx pos, std::string_view errorCtx);
-    void forceFunction(Value & v, const PosIdx pos, std::string_view errorCtx); // either lambda or primop
-    std::string_view forceString(Value & v, const PosIdx pos, std::string_view errorCtx);
-    std::string_view forceString(Value & v, PathSet & context, const PosIdx pos, std::string_view errorCtx);
-    std::string_view forceStringNoCtx(Value & v, const PosIdx pos, std::string_view errorCtx);
+    inline void forceList(Value & v, const PosIdx pos);
+    void forceFunction(Value & v, const PosIdx pos); // either lambda or primop
+    std::string_view forceString(Value & v, const PosIdx pos = noPos);
+    std::string_view forceString(Value & v, PathSet & context, const PosIdx pos = noPos);
+    std::string_view forceStringNoCtx(Value & v, const PosIdx pos = noPos);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2, const std::string & s3,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const char * s, const std::string & s2, const std::string & s3);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const char * s, const std::string & s2, const std::string & s3);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx pos, const Suggestions & suggestions, const char * s, const std::string & s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwEvalError(const PosIdx p1, const char * s, const Symbol sym, const PosIdx p2,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const Value & v,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const char * s, const ExprLambda & fun, const Symbol s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const PosIdx pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol s2,
+        Env & env, Expr & expr);
+    [[gnu::noinline, gnu::noreturn]]
+    void throwTypeError(const char * s, const Value & v,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwAssertionError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwUndefinedVarError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
+
+    [[gnu::noinline, gnu::noreturn]]
+    void throwMissingArgumentError(const PosIdx pos, const char * s, const std::string & s1,
+        Env & env, Expr & expr);
 
     [[gnu::noinline]]
     void addErrorTrace(Error & e, const char * s, const std::string & s2) const;
     [[gnu::noinline]]
-    void addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2, bool frame = false) const;
+    void addErrorTrace(Error & e, const PosIdx pos, const char * s, const std::string & s2) const;
 
 public:
     /* Return true iff the value `v' denotes a derivation (i.e. a
@@ -376,18 +397,17 @@ public:
        referenced paths are copied to the Nix store as a side effect. */
     BackedStringView coerceToString(const PosIdx pos, Value & v, PathSet & context,
         bool coerceMore = false, bool copyToStore = true,
-        bool canonicalizePath = true,
-        std::string_view errorCtx = "");
+        bool canonicalizePath = true);
 
     StorePath copyPathToStore(PathSet & context, const Path & path);
 
     /* Path coercion.  Converts strings, paths and derivations to a
        path.  The result is guaranteed to be a canonicalised, absolute
        path.  Nothing is copied to the store. */
-    Path coerceToPath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx);
+    Path coerceToPath(const PosIdx pos, Value & v, PathSet & context);
 
     /* Like coerceToPath, but the result must be a store path. */
-    StorePath coerceToStorePath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx);
+    StorePath coerceToStorePath(const PosIdx pos, Value & v, PathSet & context);
 
 public:
 
@@ -447,7 +467,7 @@ public:
 
     /* Do a deep equality test between two values.  That is, list
        elements and attributes are compared recursively. */
-    bool eqValues(Value & v1, Value & v2, const PosIdx pos, std::string_view errorCtx);
+    bool eqValues(Value & v1, Value & v2);
 
     bool isFunctor(Value & fun);
 
@@ -482,7 +502,7 @@ public:
     void mkThunk_(Value & v, Expr * expr);
     void mkPos(Value & v, PosIdx pos);
 
-    void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx);
+    void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos);
 
     /* Print statistics. */
     void printStats();
@@ -645,13 +665,6 @@ extern EvalSettings evalSettings;
 
 static const std::string corepkgsPrefix{"/__corepkgs__/"};
 
-template<class ErrorType>
-void ErrorBuilder::debugThrow()
-{
-    // NOTE: We always use the -LastTrace version as we push the new trace in withFrame()
-    state.debugThrowLastTrace(ErrorType(info));
-}
-
 }
 
 #include "eval-inline.hh"

src/libexpr/flake/flake.cc

@@ -259,28 +259,28 @@ static Flake getFlake(
             if (setting.value->type() == nString)
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
-                    std::string(state.forceStringNoCtx(*setting.value, setting.pos, "")));
+                    std::string(state.forceStringNoCtx(*setting.value, setting.pos)));
             else if (setting.value->type() == nPath) {
                 PathSet emptyContext = {};
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
-                    state.coerceToString(setting.pos, *setting.value, emptyContext, false, true, true, "") .toOwned());
+                    state.coerceToString(setting.pos, *setting.value, emptyContext, false, true, true) .toOwned());
             }
             else if (setting.value->type() == nInt)
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
-                    state.forceInt(*setting.value, setting.pos, ""));
+                    state.forceInt(*setting.value, setting.pos));
             else if (setting.value->type() == nBool)
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
-                    Explicit<bool> { state.forceBool(*setting.value, setting.pos, "") });
+                    Explicit<bool> { state.forceBool(*setting.value, setting.pos) });
             else if (setting.value->type() == nList) {
                 std::vector<std::string> ss;
                 for (auto elem : setting.value->listItems()) {
                     if (elem->type() != nString)
                         throw TypeError("list element in flake configuration setting '%s' is %s while a string is expected",
                             state.symbols[setting.name], showType(*setting.value));
-                    ss.emplace_back(state.forceStringNoCtx(*elem, setting.pos, ""));
+                    ss.emplace_back(state.forceStringNoCtx(*elem, setting.pos));
                 }
                 flake.config.settings.emplace(state.symbols[setting.name], ss);
             }
@@ -741,7 +741,7 @@ void callFlake(EvalState & state,
 
 static void prim_getFlake(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    std::string flakeRefS(state.forceStringNoCtx(*args[0], pos, "while evaluating the argument passed to builtins.getFlake"));
+    std::string flakeRefS(state.forceStringNoCtx(*args[0], pos));
     auto flakeRef = parseFlakeRef(flakeRefS, {}, true);
     if (evalSettings.pureEval && !flakeRef.input.isLocked())
         throw Error("cannot call 'getFlake' on unlocked flake reference '%s', at %s (use --impure to override)", flakeRefS, state.positions[pos]);

src/libexpr/get-drvs.cc

@@ -51,7 +51,7 @@ std::string DrvInfo::queryName() const
     if (name == "" && attrs) {
         auto i = attrs->find(state->sName);
         if (i == attrs->end()) throw TypeError("derivation name missing");
-        name = state->forceStringNoCtx(*i->value, noPos, "while evaluating the 'name' attribute of a derivation");
+        name = state->forceStringNoCtx(*i->value);
     }
     return name;
 }
@@ -61,7 +61,7 @@ std::string DrvInfo::querySystem() const
 {
     if (system == "" && attrs) {
         auto i = attrs->find(state->sSystem);
-        system = i == attrs->end() ? "unknown" : state->forceStringNoCtx(*i->value, i->pos, "while evaluating the 'system' attribute of a derivation");
+        system = i == attrs->end() ? "unknown" : state->forceStringNoCtx(*i->value, i->pos);
     }
     return system;
 }
@@ -75,7 +75,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
         if (i == attrs->end())
             drvPath = {std::nullopt};
         else
-            drvPath = {state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the 'drvPath' attribute of a derivation")};
+            drvPath = {state->coerceToStorePath(i->pos, *i->value, context)};
     }
     return drvPath.value_or(std::nullopt);
 }
@@ -95,7 +95,7 @@ StorePath DrvInfo::queryOutPath() const
         Bindings::iterator i = attrs->find(state->sOutPath);
         PathSet context;
         if (i != attrs->end())
-            outPath = state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the output path of a derivation");
+            outPath = state->coerceToStorePath(i->pos, *i->value, context);
     }
     if (!outPath)
         throw UnimplementedError("CA derivations are not yet supported");
@@ -109,23 +109,23 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         /* Get the ‘outputs’ list. */
         Bindings::iterator i;
         if (attrs && (i = attrs->find(state->sOutputs)) != attrs->end()) {
-            state->forceList(*i->value, i->pos, "while evaluating the 'outputs' attribute of a derivation");
+            state->forceList(*i->value, i->pos);
 
             /* For each output... */
             for (auto elem : i->value->listItems()) {
-                std::string output(state->forceStringNoCtx(*elem, i->pos, "while evaluating the name of an output of a derivation"));
+                std::string output(state->forceStringNoCtx(*elem, i->pos));
 
                 if (withPaths) {
                     /* Evaluate the corresponding set. */
                     Bindings::iterator out = attrs->find(state->symbols.create(output));
                     if (out == attrs->end()) continue; // FIXME: throw error?
-                    state->forceAttrs(*out->value, i->pos, "while evaluating an output of a derivation");
+                    state->forceAttrs(*out->value, i->pos);
 
                     /* And evaluate its ‘outPath’ attribute. */
                     Bindings::iterator outPath = out->value->attrs->find(state->sOutPath);
                     if (outPath == out->value->attrs->end()) continue; // FIXME: throw error?
                     PathSet context;
-                    outputs.emplace(output, state->coerceToStorePath(outPath->pos, *outPath->value, context, "while evaluating an output path of a derivation"));
+                    outputs.emplace(output, state->coerceToStorePath(outPath->pos, *outPath->value, context));
                 } else
                     outputs.emplace(output, std::nullopt);
             }
@@ -137,7 +137,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
         return outputs;
 
     Bindings::iterator i;
-    if (attrs && (i = attrs->find(state->sOutputSpecified)) != attrs->end() && state->forceBool(*i->value, i->pos, "while evaluating the 'outputSpecified' attribute of a derivation")) {
+    if (attrs && (i = attrs->find(state->sOutputSpecified)) != attrs->end() && state->forceBool(*i->value, i->pos)) {
         Outputs result;
         auto out = outputs.find(queryOutputName());
         if (out == outputs.end())
@@ -169,7 +169,7 @@ std::string DrvInfo::queryOutputName() const
 {
     if (outputName == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sOutputName);
-        outputName = i != attrs->end() ? state->forceStringNoCtx(*i->value, noPos, "while evaluating the output name of a derivation") : "";
+        outputName = i != attrs->end() ? state->forceStringNoCtx(*i->value) : "";
     }
     return outputName;
 }
@@ -181,7 +181,7 @@ Bindings * DrvInfo::getMeta()
     if (!attrs) return 0;
     Bindings::iterator a = attrs->find(state->sMeta);
     if (a == attrs->end()) return 0;
-    state->forceAttrs(*a->value, a->pos, "while evaluating the 'meta' attribute of a derivation");
+    state->forceAttrs(*a->value, a->pos);
     meta = a->value->attrs;
     return meta;
 }
@@ -382,7 +382,7 @@ static void getDerivations(EvalState & state, Value & vIn,
                    `recurseForDerivations = true' attribute. */
                 if (i->value->type() == nAttrs) {
                     Bindings::iterator j = i->value->attrs->find(state.sRecurseForDerivations);
-                    if (j != i->value->attrs->end() && state.forceBool(*j->value, j->pos, "while evaluating the attribute `recurseForDerivations`"))
+                    if (j != i->value->attrs->end() && state.forceBool(*j->value, j->pos))
                         getDerivations(state, *i->value, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
                 }
             }

src/libexpr/nixexpr.hh

@@ -8,6 +8,7 @@
 #include "error.hh"
 #include "chunked-vector.hh"
 
+
 namespace nix {
 
 

src/libexpr/parser.y

@@ -400,21 +400,21 @@ expr_op
   | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {new ExprInt(0), $2}); }
   | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
   | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
-  | expr_op '<' expr_op { $$ = new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__lessThan")), {$1, $3}); }
-  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__lessThan")), {$3, $1})); }
-  | expr_op '>' expr_op { $$ = new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__lessThan")), {$3, $1}); }
-  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__lessThan")), {$1, $3})); }
-  | expr_op AND expr_op { $$ = new ExprOpAnd(makeCurPos(@2, data), $1, $3); }
-  | expr_op OR expr_op { $$ = new ExprOpOr(makeCurPos(@2, data), $1, $3); }
-  | expr_op IMPL expr_op { $$ = new ExprOpImpl(makeCurPos(@2, data), $1, $3); }
-  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(makeCurPos(@2, data), $1, $3); }
+  | expr_op '<' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$1, $3}); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$3, $1})); }
+  | expr_op '>' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$3, $1}); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__lessThan")), {$1, $3})); }
+  | expr_op AND expr_op { $$ = new ExprOpAnd(CUR_POS, $1, $3); }
+  | expr_op OR expr_op { $$ = new ExprOpOr(CUR_POS, $1, $3); }
+  | expr_op IMPL expr_op { $$ = new ExprOpImpl(CUR_POS, $1, $3); }
+  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(CUR_POS, $1, $3); }
   | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
   | expr_op '+' expr_op
-    { $$ = new ExprConcatStrings(makeCurPos(@2, data), false, new std::vector<std::pair<PosIdx, Expr *> >({{makeCurPos(@1, data), $1}, {makeCurPos(@3, data), $3}})); }
-  | expr_op '-' expr_op { $$ = new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__sub")), {$1, $3}); }
-  | expr_op '*' expr_op { $$ = new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__mul")), {$1, $3}); }
-  | expr_op '/' expr_op { $$ = new ExprCall(makeCurPos(@2, data), new ExprVar(data->symbols.create("__div")), {$1, $3}); }
-  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(makeCurPos(@2, data), $1, $3); }
+    { $$ = new ExprConcatStrings(CUR_POS, false, new std::vector<std::pair<PosIdx, Expr *>>({{makeCurPos(@1, data), $1}, {makeCurPos(@3, data), $3}})); }
+  | expr_op '-' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__sub")), {$1, $3}); }
+  | expr_op '*' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__mul")), {$1, $3}); }
+  | expr_op '/' expr_op { $$ = new ExprCall(CUR_POS, new ExprVar(data->symbols.create("__div")), {$1, $3}); }
+  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(CUR_POS, $1, $3); }
   | expr_app
   ;
 
@@ -782,13 +782,13 @@ Path EvalState::findFile(SearchPath & searchPath, const std::string_view path, c
     if (hasPrefix(path, "nix/"))
         return concatStrings(corepkgsPrefix, path.substr(4));
 
-    debugThrow(ThrownError({
+    debugThrowLastTrace(ThrownError({
         .msg = hintfmt(evalSettings.pureEval
             ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
             : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
             path),
         .errPos = positions[pos]
-    }), 0, 0);
+    }));
 }
 
 

src/libexpr/primops/context.cc

@@ -8,7 +8,7 @@ namespace nix {
 static void prim_unsafeDiscardStringContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardStringContext");
+    auto s = state.coerceToString(pos, *args[0], context);
     v.mkString(*s);
 }
 
@@ -18,7 +18,7 @@ static RegisterPrimOp primop_unsafeDiscardStringContext("__unsafeDiscardStringCo
 static void prim_hasContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.hasContext");
+    state.forceString(*args[0], context, pos);
     v.mkBool(!context.empty());
 }
 
@@ -34,7 +34,7 @@ static RegisterPrimOp primop_hasContext("__hasContext", 1, prim_hasContext);
 static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardOutputDependency");
+    auto s = state.coerceToString(pos, *args[0], context);
 
     PathSet context2;
     for (auto && p : context) {
@@ -80,18 +80,16 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
         Strings outputs;
     };
     PathSet context;
-    state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.getContext");
+    state.forceString(*args[0], context, pos);
     auto contextInfos = std::map<StorePath, ContextInfo>();
     for (const auto & p : context) {
-        Path drv;
-        std::string output;
         NixStringContextElem ctx = NixStringContextElem::parse(*state.store, p);
         std::visit(overloaded {
             [&](NixStringContextElem::DrvDeep & d) {
                 contextInfos[d.drvPath].allOutputs = true;
             },
             [&](NixStringContextElem::Built & b) {
-                contextInfos[b.drvPath].outputs.emplace_back(std::move(output));
+                contextInfos[b.drvPath].outputs.emplace_back(std::move(b.output));
             },
             [&](NixStringContextElem::Opaque & o) {
                 contextInfos[o.path].path = true;
@@ -132,9 +130,9 @@ static RegisterPrimOp primop_getContext("__getContext", 1, prim_getContext);
 static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     PathSet context;
-    auto orig = state.forceString(*args[0], context, noPos, "while evaluating the first argument passed to builtins.appendContext");
+    auto orig = state.forceString(*args[0], context, pos);
 
-    state.forceAttrs(*args[1], pos, "while evaluating the second argument passed to builtins.appendContext");
+    state.forceAttrs(*args[1], pos);
 
     auto sPath = state.symbols.create("path");
     auto sAllOutputs = state.symbols.create("allOutputs");
@@ -142,24 +140,24 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
         const auto & name = state.symbols[i.name];
         if (!state.store->isStorePath(name))
             throw EvalError({
-                .msg = hintfmt("context key '%s' is not a store path", name),
+                .msg = hintfmt("Context key '%s' is not a store path", name),
                 .errPos = state.positions[i.pos]
             });
         if (!settings.readOnlyMode)
             state.store->ensurePath(state.store->parseStorePath(name));
-        state.forceAttrs(*i.value, i.pos, "while evaluating the value of a string context");
+        state.forceAttrs(*i.value, i.pos);
         auto iter = i.value->attrs->find(sPath);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, iter->pos, "while evaluating the `path` attribute of a string context"))
+            if (state.forceBool(*iter->value, iter->pos))
                 context.emplace(name);
         }
 
         iter = i.value->attrs->find(sAllOutputs);
         if (iter != i.value->attrs->end()) {
-            if (state.forceBool(*iter->value, iter->pos, "while evaluating the `allOutputs` attribute of a string context")) {
+            if (state.forceBool(*iter->value, iter->pos)) {
                 if (!isDerivation(name)) {
                     throw EvalError({
-                        .msg = hintfmt("tried to add all-outputs context of %s, which is not a derivation, to a string", name),
+                        .msg = hintfmt("Tried to add all-outputs context of %s, which is not a derivation, to a string", name),
                         .errPos = state.positions[i.pos]
                     });
                 }
@@ -169,15 +167,15 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
 
         iter = i.value->attrs->find(state.sOutputs);
         if (iter != i.value->attrs->end()) {
-            state.forceList(*iter->value, iter->pos, "while evaluating the `outputs` attribute of a string context");
+            state.forceList(*iter->value, iter->pos);
             if (iter->value->listSize() && !isDerivation(name)) {
                 throw EvalError({
-                    .msg = hintfmt("tried to add derivation output context of %s, which is not a derivation, to a string", name),
+                    .msg = hintfmt("Tried to add derivation output context of %s, which is not a derivation, to a string", name),
                     .errPos = state.positions[i.pos]
                 });
             }
             for (auto elem : iter->value->listItems()) {
-                auto outputName = state.forceStringNoCtx(*elem, iter->pos, "while evaluating an output name within a string context");
+                auto outputName = state.forceStringNoCtx(*elem, iter->pos);
                 context.insert(concatStrings("!", outputName, "!", name));
             }
         }

src/libexpr/primops/fetchClosure.cc

@@ -7,7 +7,7 @@ namespace nix {
 
 static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.fetchClosure");
+    state.forceAttrs(*args[0], pos);
 
     std::optional<std::string> fromStoreUrl;
     std::optional<StorePath> fromPath;
@@ -19,8 +19,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
 
         if (attrName == "fromPath") {
             PathSet context;
-            fromPath = state.coerceToStorePath(attr.pos, *attr.value, context,
-                    "while evaluating the 'fromPath' attribute passed to builtins.fetchClosure");
+            fromPath = state.coerceToStorePath(attr.pos, *attr.value, context);
         }
 
         else if (attrName == "toPath") {
@@ -28,14 +27,12 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
             toCA = true;
             if (attr.value->type() != nString || attr.value->string.s != std::string("")) {
                 PathSet context;
-                toPath = state.coerceToStorePath(attr.pos, *attr.value, context,
-                        "while evaluating the 'toPath' attribute passed to builtins.fetchClosure");
+                toPath = state.coerceToStorePath(attr.pos, *attr.value, context);
             }
         }
 
         else if (attrName == "fromStore")
-            fromStoreUrl = state.forceStringNoCtx(*attr.value, attr.pos,
-                    "while evaluating the 'fromStore' attribute passed to builtins.fetchClosure");
+            fromStoreUrl = state.forceStringNoCtx(*attr.value, attr.pos);
 
         else
             throw Error({

src/libexpr/primops/fetchMercurial.cc

@@ -19,21 +19,23 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
 
     if (args[0]->type() == nAttrs) {
 
+        state.forceAttrs(*args[0], pos);
+
         for (auto & attr : *args[0]->attrs) {
             std::string_view n(state.symbols[attr.name]);
             if (n == "url")
-                url = state.coerceToString(attr.pos, *attr.value, context, false, false, "while evaluating the `url` attribute passed to builtins.fetchMercurial").toOwned();
+                url = state.coerceToString(attr.pos, *attr.value, context, false, false).toOwned();
             else if (n == "rev") {
                 // Ugly: unlike fetchGit, here the "rev" attribute can
                 // be both a revision or a branch/tag name.
-                auto value = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `rev` attribute passed to builtins.fetchMercurial");
+                auto value = state.forceStringNoCtx(*attr.value, attr.pos);
                 if (std::regex_match(value.begin(), value.end(), revRegex))
                     rev = Hash::parseAny(value, htSHA1);
                 else
                     ref = value;
             }
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `name` attribute passed to builtins.fetchMercurial");
+                name = state.forceStringNoCtx(*attr.value, attr.pos);
             else
                 throw EvalError({
                     .msg = hintfmt("unsupported argument '%s' to 'fetchMercurial'", state.symbols[attr.name]),
@@ -48,7 +50,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
             });
 
     } else
-        url = state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to builtins.fetchMercurial").toOwned();
+        url = state.coerceToString(pos, *args[0], context, false, false).toOwned();
 
     // FIXME: git externals probably can be used to bypass the URI
     // whitelist. Ah well.

src/libexpr/primops/fetchTree.cc

@@ -102,7 +102,7 @@ static void fetchTree(
     state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
-        state.forceAttrs(*args[0], pos, "while evaluating the argument passed to builtins.fetchTree");
+        state.forceAttrs(*args[0], pos);
 
         fetchers::Attrs attrs;
 
@@ -112,7 +112,7 @@ static void fetchTree(
                     .msg = hintfmt("unexpected attribute 'type'"),
                     .errPos = state.positions[pos]
                 }));
-            type = state.forceStringNoCtx(*aType->value, aType->pos, "while evaluating the `type` attribute passed to builtins.fetchTree");
+            type = state.forceStringNoCtx(*aType->value, aType->pos);
         } else if (!type)
             state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
@@ -125,7 +125,7 @@ static void fetchTree(
             if (attr.name == state.sType) continue;
             state.forceValue(*attr.value, attr.pos);
             if (attr.value->type() == nPath || attr.value->type() == nString) {
-                auto s = state.coerceToString(attr.pos, *attr.value, context, false, false, "").toOwned();
+                auto s = state.coerceToString(attr.pos, *attr.value, context, false, false).toOwned();
                 attrs.emplace(state.symbols[attr.name],
                     state.symbols[attr.name] == "url"
                     ? type == "git"
@@ -151,7 +151,7 @@ static void fetchTree(
 
         input = fetchers::Input::fromAttrs(std::move(attrs));
     } else {
-        auto url = state.coerceToString(pos, *args[0], context, false, false, "while evaluating the first argument passed to the fetcher").toOwned();
+        auto url = state.coerceToString(pos, *args[0], context, false, false).toOwned();
 
         if (type == "git") {
             fetchers::Attrs attrs;
@@ -195,14 +195,16 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
 
     if (args[0]->type() == nAttrs) {
 
+        state.forceAttrs(*args[0], pos);
+
         for (auto & attr : *args[0]->attrs) {
             std::string_view n(state.symbols[attr.name]);
             if (n == "url")
-                url = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the url we should fetch");
+                url = state.forceStringNoCtx(*attr.value, attr.pos);
             else if (n == "sha256")
-                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the sha256 of the content we should fetch"), htSHA256);
+                expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos), htSHA256);
             else if (n == "name")
-                name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the name of the content we should fetch");
+                name = state.forceStringNoCtx(*attr.value, attr.pos);
             else
                 state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("unsupported argument '%s' to '%s'", n, who),
@@ -216,7 +218,10 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
                 .errPos = state.positions[pos]
             }));
     } else
-        url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");
+        url = state.forceStringNoCtx(*args[0], pos);
+
+    if (who == "fetchTarball")
+        url = evalSettings.resolvePseudoUrl(*url);
 
     state.checkURI(*url);
 

src/libexpr/primops/fromTOML.cc

@@ -7,7 +7,7 @@ namespace nix {
 
 static void prim_fromTOML(EvalState & state, const PosIdx pos, Value * * args, Value & val)
 {
-    auto toml = state.forceStringNoCtx(*args[0], pos, "while evaluating the argument passed to builtins.fromTOML");
+    auto toml = state.forceStringNoCtx(*args[0], pos);
 
     std::istringstream tomlStream(std::string{toml});
 

src/libexpr/tests/error_traces.cc

@@ -1,94 +0,0 @@
-#include <gmock/gmock.h>
-#include <gtest/gtest.h>
-
-#include "libexprtests.hh"
-
-namespace nix {
-
-    using namespace testing;
-
-    // Testing eval of PrimOp's
-    class ErrorTraceTest : public LibExprTest { };
-
-#define ASSERT_TRACE1(args, type, message)                                  \
-        ASSERT_THROW(                                                       \
-            try {                                                           \
-                eval("builtins." args);                                     \
-            } catch (BaseError & e) {                                       \
-                ASSERT_EQ(PrintToString(e.info().msg),                      \
-                          PrintToString(message));                          \
-                auto trace = e.info().traces.rbegin();                      \
-                ASSERT_EQ(PrintToString(trace->hint),                       \
-                          PrintToString(hintfmt("while calling the '%s' builtin", "genericClosure"))); \
-                throw;                                                      \
-            }                                                               \
-            , type                                                          \
-        )
-
-#define ASSERT_TRACE2(args, type, message, context)                         \
-        ASSERT_THROW(                                                       \
-            try {                                                           \
-                eval("builtins." args);                                     \
-            } catch (BaseError & e) {                                       \
-                ASSERT_EQ(PrintToString(e.info().msg),                      \
-                          PrintToString(message));                          \
-                auto trace = e.info().traces.rbegin();                      \
-                ASSERT_EQ(PrintToString(trace->hint),                       \
-                          PrintToString(context));                          \
-                ++trace;                                                    \
-                ASSERT_EQ(PrintToString(trace->hint),                       \
-                          PrintToString(hintfmt("while calling the '%s' builtin", "genericClosure"))); \
-                throw;                                                      \
-            }                                                               \
-            , type                                                          \
-        )
-
-    TEST_F(ErrorTraceTest, genericClosure) { \
-        ASSERT_TRACE2("genericClosure 1",
-                      TypeError,
-                      hintfmt("value is %s while a set was expected", "an integer"),
-                      hintfmt("while evaluating the first argument passed to builtins.genericClosure"));
-
-        ASSERT_TRACE1("genericClosure {}",
-                      TypeError,
-                      hintfmt("attribute '%s' missing %s", "startSet", normaltxt("in the attrset passed as argument to builtins.genericClosure")));
-
-        ASSERT_TRACE2("genericClosure { startSet = 1; }",
-                      TypeError,
-                      hintfmt("value is %s while a list was expected", "an integer"),
-                      hintfmt("while evaluating the 'startSet' attribute passed as argument to builtins.genericClosure"));
-
-        // Okay:      "genericClosure { startSet = []; }"
-
-        ASSERT_TRACE2("genericClosure { startSet = [{ key = 1;}]; operator = true; }",
-                      TypeError,
-                      hintfmt("value is %s while a function was expected", "a Boolean"),
-                      hintfmt("while evaluating the 'operator' attribute passed as argument to builtins.genericClosure"));
-
-        ASSERT_TRACE2("genericClosure { startSet = [{ key = 1;}]; operator = item: true; }",
-                      TypeError,
-                      hintfmt("value is %s while a list was expected", "a Boolean"),
-                      hintfmt("while evaluating the return value of the `operator` passed to builtins.genericClosure")); // TODO: inconsistent naming
-
-        ASSERT_TRACE2("genericClosure { startSet = [{ key = 1;}]; operator = item: [ true ]; }",
-                      TypeError,
-                      hintfmt("value is %s while a set was expected", "a Boolean"),
-                      hintfmt("while evaluating one of the elements generated by (or initially passed to) builtins.genericClosure"));
-
-        ASSERT_TRACE1("genericClosure { startSet = [{ key = 1;}]; operator = item: [ {} ]; }",
-                      TypeError,
-                      hintfmt("attribute '%s' missing %s", "key", normaltxt("in one of the attrsets generated by (or initially passed to) builtins.genericClosure")));
-
-        ASSERT_TRACE2("genericClosure { startSet = [{ key = 1;}]; operator = item: [{ key = ''a''; }]; }",
-                      EvalError,
-                      hintfmt("cannot compare %s with %s", "a string", "an integer"),
-                      hintfmt("while comparing the `key` attributes of two genericClosure elements"));
-
-        ASSERT_TRACE2("genericClosure { startSet = [ true ]; operator = item: [{ key = ''a''; }]; }",
-                      TypeError,
-                      hintfmt("value is %s while a set was expected", "a Boolean"),
-                      hintfmt("while evaluating one of the elements generated by (or initially passed to) builtins.genericClosure"));
-
-    }
-
-} /* namespace nix */

src/libexpr/tests/primops.cc

@@ -823,10 +823,4 @@ namespace nix {
         for (const auto [n, elem] : enumerate(v.listItems()))
             ASSERT_THAT(*elem, IsStringEq(expected[n]));
     }
-
-    TEST_F(PrimOpTest, genericClosure_not_strict) {
-        // Operator should not be used when startSet is empty
-        auto v = eval("builtins.genericClosure { startSet = []; }");
-        ASSERT_THAT(v, IsListOfSize(0));
-    }
 } /* namespace nix */

src/libexpr/value.hh

@@ -89,7 +89,7 @@ class ExternalValueBase
     /* Coerce the value to a string. Defaults to uncoercable, i.e. throws an
      * error.
      */
-    virtual std::string coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore, std::string_view errorCtx) const;
+    virtual std::string coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const;
 
     /* Compare to another value of the same type. Defaults to uncomparable,
      * i.e. always false.

src/libmain/shared.cc

@@ -404,6 +404,8 @@ int handleExceptions(const std::string & programName, std::function<void()> fun)
         return 1;
     } catch (BaseError & e) {
         logError(e.info());
+        if (e.hasTrace() && !loggerSettings.showTrace.get())
+            printError("(use '--show-trace' to show detailed location information)");
         return e.status;
     } catch (std::bad_alloc & e) {
         printError(error + "out of memory");

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

@@ -663,7 +663,8 @@ void LocalDerivationGoal::startBuilder()
            nobody account.  The latter is kind of a hack to support
            Samba-in-QEMU. */
         createDirs(chrootRootDir + "/etc");
-        chownToBuilder(chrootRootDir + "/etc");
+        if (parsedDrv->useUidRange())
+            chownToBuilder(chrootRootDir + "/etc");
 
         if (parsedDrv->useUidRange() && (!buildUser || buildUser->getUIDCount() < 65536))
             throw Error("feature 'uid-range' requires the setting '%s' to be enabled", settings.autoAllocateUids.name);
@@ -1907,6 +1908,10 @@ void LocalDerivationGoal::runChild()
                 }
             }
 
+            /* Make /etc unwritable */
+            if (!parsedDrv->useUidRange())
+                chmod_(chrootRootDir + "/etc", 0555);
+
             /* Unshare this mount namespace. This is necessary because
                pivot_root() below changes the root of the mount
                namespace. This means that the call to setns() in

src/libstore/derivations.hh

@@ -13,6 +13,7 @@
 
 namespace nix {
 
+class Store;
 
 /* Abstract syntax of derivations. */
 

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

@@ -56,7 +56,7 @@ public:
     void init() override
     {
         // FIXME: do this lazily?
-        if (auto cacheInfo = diskCache->cacheExists(cacheUri)) {
+        if (auto cacheInfo = diskCache->upToDateCacheExists(cacheUri)) {
             wantMassQuery.setDefault(cacheInfo->wantMassQuery);
             priority.setDefault(cacheInfo->priority);
         } else {

src/libstore/nar-info-disk-cache.cc

@@ -84,11 +84,10 @@ public:
 
     Sync<State> _state;
 
-    NarInfoDiskCacheImpl()
+    NarInfoDiskCacheImpl(Path dbPath = getCacheDir() + "/nix/binary-cache-v6.sqlite")
     {
         auto state(_state.lock());
 
-        Path dbPath = getCacheDir() + "/nix/binary-cache-v6.sqlite";
         createDirs(dirOf(dbPath));
 
         state->db = SQLite(dbPath);
@@ -98,7 +97,7 @@ public:
         state->db.exec(schema);
 
         state->insertCache.create(state->db,
-            "insert or replace into BinaryCaches(url, timestamp, storeDir, wantMassQuery, priority) values (?, ?, ?, ?, ?)");
+            "insert into BinaryCaches(url, timestamp, storeDir, wantMassQuery, priority) values (?1, ?2, ?3, ?4, ?5) on conflict (url) do update set timestamp = ?2, storeDir = ?3, wantMassQuery = ?4, priority = ?5 returning id;");
 
         state->queryCache.create(state->db,
             "select id, storeDir, wantMassQuery, priority from BinaryCaches where url = ? and timestamp > ?");
@@ -166,6 +165,8 @@ public:
         return i->second;
     }
 
+private:
+
     std::optional<Cache> queryCacheRaw(State & state, const std::string & uri)
     {
         auto i = state.caches.find(uri);
@@ -173,15 +174,21 @@ public:
             auto queryCache(state.queryCache.use()(uri)(time(0) - cacheInfoTtl));
             if (!queryCache.next())
                 return std::nullopt;
-            state.caches.emplace(uri,
-                Cache{(int) queryCache.getInt(0), queryCache.getStr(1), queryCache.getInt(2) != 0, (int) queryCache.getInt(3)});
+            auto cache = Cache {
+                .id = (int) queryCache.getInt(0),
+                .storeDir = queryCache.getStr(1),
+                .wantMassQuery = queryCache.getInt(2) != 0,
+                .priority = (int) queryCache.getInt(3),
+            };
+            state.caches.emplace(uri, cache);
         }
         return getCache(state, uri);
     }
 
-    void createCache(const std::string & uri, const Path & storeDir, bool wantMassQuery, int priority) override
+public:
+    int createCache(const std::string & uri, const Path & storeDir, bool wantMassQuery, int priority) override
     {
-        retrySQLite<void>([&]() {
+        return retrySQLite<int>([&]() {
             auto state(_state.lock());
             SQLiteTxn txn(state->db);
 
@@ -190,17 +197,29 @@ public:
             auto cache(queryCacheRaw(*state, uri));
 
             if (cache)
-                return;
+                return cache->id;
 
-            state->insertCache.use()(uri)(time(0))(storeDir)(wantMassQuery)(priority).exec();
-            assert(sqlite3_changes(state->db) == 1);
-            state->caches[uri] = Cache{(int) sqlite3_last_insert_rowid(state->db), storeDir, wantMassQuery, priority};
+            Cache ret {
+                .id = -1, // set below
+                .storeDir = storeDir,
+                .wantMassQuery = wantMassQuery,
+                .priority = priority,
+            };
+
+            {
+                auto r(state->insertCache.use()(uri)(time(0))(storeDir)(wantMassQuery)(priority));
+                assert(r.next());
+                ret.id = (int) r.getInt(0);
+            }
+
+            state->caches[uri] = ret;
 
             txn.commit();
+            return ret.id;
         });
     }
 
-    std::optional<CacheInfo> cacheExists(const std::string & uri) override
+    std::optional<CacheInfo> upToDateCacheExists(const std::string & uri) override
     {
         return retrySQLite<std::optional<CacheInfo>>([&]() -> std::optional<CacheInfo> {
             auto state(_state.lock());
@@ -208,6 +227,7 @@ public:
             if (!cache)
                 return std::nullopt;
             return CacheInfo {
+                .id = cache->id,
                 .wantMassQuery = cache->wantMassQuery,
                 .priority = cache->priority
             };
@@ -371,4 +391,9 @@ ref<NarInfoDiskCache> getNarInfoDiskCache()
     return cache;
 }
 
+ref<NarInfoDiskCache> getTestNarInfoDiskCache(Path dbPath)
+{
+    return make_ref<NarInfoDiskCacheImpl>(dbPath);
+}
+
 }

src/libstore/nar-info-disk-cache.hh

@@ -13,16 +13,17 @@ public:
 
     virtual ~NarInfoDiskCache() { }
 
-    virtual void createCache(const std::string & uri, const Path & storeDir,
+    virtual int createCache(const std::string & uri, const Path & storeDir,
         bool wantMassQuery, int priority) = 0;
 
     struct CacheInfo
     {
+        int id;
         bool wantMassQuery;
         int priority;
     };
 
-    virtual std::optional<CacheInfo> cacheExists(const std::string & uri) = 0;
+    virtual std::optional<CacheInfo> upToDateCacheExists(const std::string & uri) = 0;
 
     virtual std::pair<Outcome, std::shared_ptr<NarInfo>> lookupNarInfo(
         const std::string & uri, const std::string & hashPart) = 0;
@@ -45,4 +46,6 @@ public:
    multiple threads. */
 ref<NarInfoDiskCache> getNarInfoDiskCache();
 
+ref<NarInfoDiskCache> getTestNarInfoDiskCache(Path dbPath);
+
 }

src/libstore/outputs-spec.cc

@@ -1,8 +1,10 @@
-#include "util.hh"
-#include "outputs-spec.hh"
-#include "nlohmann/json.hpp"
-
 #include <regex>
+#include <nlohmann/json.hpp>
+
+#include "util.hh"
+#include "regex-combinators.hh"
+#include "outputs-spec.hh"
+#include "path-regex.hh"
 
 namespace nix {
 
@@ -18,10 +20,14 @@ bool OutputsSpec::contains(const std::string & outputName) const
     }, raw());
 }
 
+static std::string outputSpecRegexStr =
+    regex::either(
+        regex::group(R"(\*)"),
+        regex::group(regex::list(nameRegexStr)));
 
 std::optional<OutputsSpec> OutputsSpec::parseOpt(std::string_view s)
 {
-    static std::regex regex(R"((\*)|([a-z]+(,[a-z]+)*))");
+    static std::regex regex(std::string { outputSpecRegexStr });
 
     std::smatch match;
     std::string s2 { s }; // until some improves std::regex
@@ -42,7 +48,7 @@ OutputsSpec OutputsSpec::parse(std::string_view s)
 {
     std::optional spec = parseOpt(s);
     if (!spec)
-        throw Error("Invalid outputs specifier: '%s'", s);
+        throw Error("invalid outputs specifier '%s'", s);
     return *spec;
 }
 
@@ -65,7 +71,7 @@ std::pair<std::string_view, ExtendedOutputsSpec> ExtendedOutputsSpec::parse(std:
 {
     std::optional spec = parseOpt(s);
     if (!spec)
-        throw Error("Invalid extended outputs specifier: '%s'", s);
+        throw Error("invalid extended outputs specifier '%s'", s);
     return *spec;
 }
 
@@ -163,7 +169,7 @@ void adl_serializer<OutputsSpec>::to_json(json & json, OutputsSpec t) {
         [&](const OutputsSpec::Names & names) {
             json = names;
         },
-    }, t);
+    }, t.raw());
 }
 
 
@@ -183,7 +189,7 @@ void adl_serializer<ExtendedOutputsSpec>::to_json(json & json, ExtendedOutputsSp
         [&](const ExtendedOutputsSpec::Explicit & e) {
             adl_serializer<OutputsSpec>::to_json(json, e);
         },
-    }, t);
+    }, t.raw());
 }
 
 }

src/libstore/path-regex.hh

@@ -0,0 +1,7 @@
+#pragma once
+
+namespace nix {
+
+static constexpr std::string_view nameRegexStr = R"([0-9a-zA-Z\+\-\._\?=]+)";
+
+}

src/libstore/path.cc

@@ -8,8 +8,10 @@ static void checkName(std::string_view path, std::string_view name)
 {
     if (name.empty())
         throw BadStorePath("store path '%s' has an empty name", path);
-    if (name.size() > 211)
-        throw BadStorePath("store path '%s' has a name longer than 211 characters", path);
+    if (name.size() > StorePath::MaxPathLen)
+        throw BadStorePath("store path '%s' has a name longer than '%d characters",
+            StorePath::MaxPathLen, path);
+    // See nameRegexStr for the definition
     for (auto c : name)
         if (!((c >= '0' && c <= '9')
                 || (c >= 'a' && c <= 'z')

src/libstore/path.hh

@@ -5,7 +5,6 @@
 
 namespace nix {
 
-class Store;
 struct Hash;
 
 class StorePath
@@ -17,6 +16,8 @@ public:
     /* Size of the hash part of store paths, in base-32 characters. */
     constexpr static size_t HashLen = 32; // i.e. 160 bits
 
+    constexpr static size_t MaxPathLen = 211;
+
     StorePath() = delete;
 
     StorePath(std::string_view baseName);

src/libstore/realisation.hh

@@ -7,6 +7,8 @@
 
 namespace nix {
 
+class Store;
+
 struct DrvOutput {
     // The hash modulo of the derivation
     Hash drvHash;

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

@@ -238,7 +238,7 @@ struct S3BinaryCacheStoreImpl : virtual S3BinaryCacheStoreConfig, public virtual
 
     void init() override
     {
-        if (auto cacheInfo = diskCache->cacheExists(getUri())) {
+        if (auto cacheInfo = diskCache->upToDateCacheExists(getUri())) {
             wantMassQuery.setDefault(cacheInfo->wantMassQuery);
             priority.setDefault(cacheInfo->priority);
         } else {

src/libstore/sqlite.cc

@@ -41,6 +41,15 @@ SQLiteError::SQLiteError(const char *path, const char *errMsg, int errNo, int ex
         throw SQLiteError(path, errMsg, err, exterr, offset, std::move(hf));
 }
 
+static void traceSQL(void * x, const char * sql)
+{
+    // wacky delimiters:
+    //   so that we're quite unambiguous without escaping anything
+    // notice instead of trace:
+    //   so that this can be enabled without getting the firehose in our face.
+    notice("SQL<[%1%]>", sql);
+};
+
 SQLite::SQLite(const Path & path, bool create)
 {
     // useSQLiteWAL also indicates what virtual file system we need.  Using
@@ -58,6 +67,11 @@ SQLite::SQLite(const Path & path, bool create)
     if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
         SQLiteError::throw_(db, "setting timeout");
 
+    if (getEnv("NIX_DEBUG_SQLITE_TRACES") == "1") {
+        // To debug sqlite statements; trace all of them
+        sqlite3_trace(db, &traceSQL, nullptr);
+    }
+
     exec("pragma foreign_keys = 1");
 }
 

src/libstore/tests/libstoretests.hh

@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+#include <gmock/gmock.h>
+
+#include "store-api.hh"
+
+namespace nix {
+
+class LibStoreTest : public ::testing::Test {
+    public:
+        static void SetUpTestSuite() {
+            initLibStore();
+        }
+
+    protected:
+        LibStoreTest()
+            : store(openStore("dummy://"))
+        { }
+
+        ref<Store> store;
+};
+
+
+} /* namespace nix */

src/libstore/tests/nar-info-disk-cache.cc

@@ -0,0 +1,122 @@
+#include "nar-info-disk-cache.hh"
+
+#include <gtest/gtest.h>
+#include "sqlite.hh"
+#include <sqlite3.h>
+
+
+namespace nix {
+
+TEST(NarInfoDiskCacheImpl, create_and_read) {
+    // This is a large single test to avoid some setup overhead.
+
+    int prio = 12345;
+    bool wantMassQuery = true;
+
+    Path tmpDir = createTempDir();
+    AutoDelete delTmpDir(tmpDir);
+    Path dbPath(tmpDir + "/test-narinfo-disk-cache.sqlite");
+
+    int savedId;
+    int barId;
+    SQLite db;
+    SQLiteStmt getIds;
+
+    {
+        auto cache = getTestNarInfoDiskCache(dbPath);
+
+        // Set up "background noise" and check that different caches receive different ids
+        {
+            auto bc1 = cache->createCache("https://bar", "/nix/storedir", wantMassQuery, prio);
+            auto bc2 = cache->createCache("https://xyz", "/nix/storedir", false, 12);
+            ASSERT_NE(bc1, bc2);
+            barId = bc1;
+        }
+
+        // Check that the fields are saved and returned correctly. This does not test
+        // the select statement yet, because of in-memory caching.
+        savedId = cache->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);;
+        {
+            auto r = cache->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+            ASSERT_EQ(savedId, r->id);
+        }
+
+        // We're going to pay special attention to the id field because we had a bug
+        // that changed it.
+        db = SQLite(dbPath);
+        getIds.create(db, "select id from BinaryCaches where url = 'http://foo'");
+
+        {
+            auto q(getIds.use());
+            ASSERT_TRUE(q.next());
+            ASSERT_EQ(savedId, q.getInt(0));
+            ASSERT_FALSE(q.next());
+        }
+
+        // Pretend that the caches are older, but keep one up to date, as "background noise"
+        db.exec("update BinaryCaches set timestamp = timestamp - 1 - 7 * 24 * 3600 where url <> 'https://xyz';");
+
+        // This shows that the in-memory cache works
+        {
+            auto r = cache->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+        }
+    }
+
+    {
+        // We can't clear the in-memory cache, so we use a new cache object. This is
+        // more realistic anyway.
+        auto cache2 = getTestNarInfoDiskCache(dbPath);
+
+        {
+            auto r = cache2->upToDateCacheExists("http://foo");
+            ASSERT_FALSE(r);
+        }
+
+        // "Update", same data, check that the id number is reused
+        cache2->createCache("http://foo", "/nix/storedir", wantMassQuery, prio);
+
+        {
+            auto r = cache2->upToDateCacheExists("http://foo");
+            ASSERT_TRUE(r);
+            ASSERT_EQ(r->priority, prio);
+            ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+            ASSERT_EQ(r->id, savedId);
+        }
+
+        {
+            auto q(getIds.use());
+            ASSERT_TRUE(q.next());
+            auto currentId = q.getInt(0);
+            ASSERT_FALSE(q.next());
+            ASSERT_EQ(currentId, savedId);
+        }
+
+        // Check that the fields can be modified, and the id remains the same
+        {
+            auto r0 = cache2->upToDateCacheExists("https://bar");
+            ASSERT_FALSE(r0);
+
+            cache2->createCache("https://bar", "/nix/storedir", !wantMassQuery, prio + 10);
+            auto r = cache2->upToDateCacheExists("https://bar");
+            ASSERT_EQ(r->wantMassQuery, !wantMassQuery);
+            ASSERT_EQ(r->priority, prio + 10);
+            ASSERT_EQ(r->id, barId);
+        }
+
+        // // Force update (no use case yet; we only retrieve cache metadata when stale based on timestamp)
+        // {
+        //     cache2->createCache("https://bar", "/nix/storedir", wantMassQuery, prio + 20);
+        //     auto r = cache2->upToDateCacheExists("https://bar");
+        //     ASSERT_EQ(r->wantMassQuery, wantMassQuery);
+        //     ASSERT_EQ(r->priority, prio + 20);
+        // }
+    }
+}
+
+}

src/libstore/tests/outputs-spec.cc

@@ -40,6 +40,20 @@ TEST(OutputsSpec, names_out) {
     ASSERT_EQ(expected.to_string(), str);
 }
 
+TEST(OutputsSpec, names_underscore) {
+    std::string_view str = "a_b";
+    OutputsSpec expected = OutputsSpec::Names { "a_b" };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
+TEST(OutputsSpec, names_numberic) {
+    std::string_view str = "01";
+    OutputsSpec expected = OutputsSpec::Names { "01" };
+    ASSERT_EQ(OutputsSpec::parse(str), expected);
+    ASSERT_EQ(expected.to_string(), str);
+}
+
 TEST(OutputsSpec, names_out_bin) {
     OutputsSpec expected = OutputsSpec::Names { "out", "bin" };
     ASSERT_EQ(OutputsSpec::parse("out,bin"), expected);

src/libstore/tests/path.cc

@@ -0,0 +1,66 @@
+#include <regex>
+
+#include <nlohmann/json.hpp>
+#include <gtest/gtest.h>
+
+#include "path-regex.hh"
+#include "store-api.hh"
+
+#include "libstoretests.hh"
+
+namespace nix {
+
+#define STORE_DIR "/nix/store/"
+#define HASH_PART "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q"
+
+class StorePathTest : public LibStoreTest
+{
+};
+
+static std::regex nameRegex { std::string { nameRegexStr } };
+
+#define TEST_DONT_PARSE(NAME, STR)                           \
+    TEST_F(StorePathTest, bad_ ## NAME) {                    \
+        std::string_view str =                               \
+            STORE_DIR HASH_PART "-" STR;                     \
+        ASSERT_THROW(                                        \
+            store->parseStorePath(str),                      \
+            BadStorePath);                                   \
+        std::string name { STR };                            \
+        EXPECT_FALSE(std::regex_match(name, nameRegex));     \
+    }
+
+TEST_DONT_PARSE(empty, "")
+TEST_DONT_PARSE(garbage, "&*()")
+TEST_DONT_PARSE(double_star, "**")
+TEST_DONT_PARSE(star_first, "*,foo")
+TEST_DONT_PARSE(star_second, "foo,*")
+TEST_DONT_PARSE(bang, "foo!o")
+
+#undef TEST_DONT_PARSE
+
+#define TEST_DO_PARSE(NAME, STR)                             \
+    TEST_F(StorePathTest, good_ ## NAME) {                   \
+        std::string_view str =                               \
+            STORE_DIR HASH_PART "-" STR;                     \
+        auto p = store->parseStorePath(str);                 \
+        std::string name { p.name() };                       \
+        EXPECT_TRUE(std::regex_match(name, nameRegex));      \
+    }
+
+// 0-9 a-z A-Z + - . _ ? =
+
+TEST_DO_PARSE(numbers, "02345")
+TEST_DO_PARSE(lower_case, "foo")
+TEST_DO_PARSE(upper_case, "FOO")
+TEST_DO_PARSE(plus, "foo+bar")
+TEST_DO_PARSE(dash, "foo-dev")
+TEST_DO_PARSE(underscore, "foo_bar")
+TEST_DO_PARSE(period, "foo.txt")
+TEST_DO_PARSE(question_mark, "foo?why")
+TEST_DO_PARSE(equals_sign, "foo=foo")
+
+#undef TEST_DO_PARSE
+
+
+}

src/libutil/error.cc

@@ -9,9 +9,9 @@ namespace nix {
 
 const std::string nativeSystem = SYSTEM;
 
-void BaseError::addTrace(std::shared_ptr<AbstractPos> && e, hintformat hint, bool frame)
+void BaseError::addTrace(std::shared_ptr<AbstractPos> && e, hintformat hint)
 {
-    err.traces.push_front(Trace { .pos = std::move(e), .hint = hint, .frame = frame });
+    err.traces.push_front(Trace { .pos = std::move(e), .hint = hint });
 }
 
 // c++ std::exception descendants must have a 'const char* what()' function.
@@ -200,125 +200,13 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
 
     auto noSource = ANSI_ITALIC " (source not available)" ANSI_NORMAL "\n";
 
-    /*
-     * Traces
-     * ------
-     *
-     *  The semantics of traces is a bit weird. We have only one option to
-     *  print them and to make them verbose (--show-trace). In the code they
-     *  are always collected, but they are not printed by default. The code
-     *  also collects more traces when the option is on. This means that there
-     *  is no way to print the simplified traces at all.
-     *
-     *  I (layus) designed the code to attach positions to a restricted set of
-     *  messages. This means that we have  a lot of traces with no position at
-     *  all, including most of the base error messages. For example "type
-     *  error: found a string while a set was expected" has no position, but
-     *  will come with several traces detailing it's precise relation to the
-     *  closest know position. This makes erroring without printing traces
-     *  quite useless.
-     *
-     *  This is why I introduced the idea to always print a few traces on
-     *  error. The number 3 is quite arbitrary, and was selected so as not to
-     *  clutter the console on error. For the same reason, a trace with an
-     *  error position takes more space, and counts as two traces towards the
-     *  limit.
-     *
-     *  The rest is truncated, unless --show-trace is passed. This preserves
-     *  the same bad semantics of --show-trace to both show the trace and
-     *  augment it with new data. Not too sure what is the best course of
-     *  action.
-     *
-     *  The issue is that it is fundamentally hard to provide a trace for a
-     *  lazy language. The trace will only cover the current spine of the
-     *  evaluation, missing things that have been evaluated before. For
-     *  example, most type errors are hard to inspect because there is not
-     *  trace for the faulty value. These errors should really print the faulty
-     *  value itself.
-     *
-     *  In function calls, the --show-trace flag triggers extra traces for each
-     *  function invocation. These work as scopes, allowing to follow the
-     *  current spine of the evaluation graph. Without that flag, the error
-     *  trace should restrict itself to a restricted prefix of that trace,
-     *  until the first scope. If we ever get to such a precise error
-     *  reporting, there would be no need to add an arbitrary limit here. We
-     *  could always print the full trace, and it would just be small without
-     *  the flag.
-     *
-     *  One idea I had is for XxxError.addTrace() to perform nothing if one
-     *  scope has already been traced. Alternatively, we could stop here when
-     *  we encounter such a scope instead of after an arbitrary number of
-     *  traces. This however requires to augment traces with the notion of
-     *  "scope".
-     *
-     *  This is particularly visible in code like evalAttrs(...) where we have
-     *  to make a decision between the two following options.
-     *
-     *  ``` long traces
-     *  inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const Pos & pos, std::string_view errorCtx)
-     *  {
-     *      try {
-     *          e->eval(*this, env, v);
-     *          if (v.type() != nAttrs)
-     *              throwTypeError("value is %1% while a set was expected", v);
-     *      } catch (Error & e) {
-     *          e.addTrace(pos, errorCtx);
-     *          throw;
-     *      }
-     *  }
-     *  ```
-     *
-     *  ``` short traces
-     *  inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v, const Pos & pos, std::string_view errorCtx)
-     *  {
-     *      e->eval(*this, env, v);
-     *      try {
-     *          if (v.type() != nAttrs)
-     *              throwTypeError("value is %1% while a set was expected", v);
-     *      } catch (Error & e) {
-     *          e.addTrace(pos, errorCtx);
-     *          throw;
-     *      }
-     *  }
-     *  ```
-     *
-     *  The second example can be rewritten more concisely, but kept in this
-     *  form to highlight the symmetry. The first option adds more information,
-     *  because whatever caused an error down the line, in the generic eval
-     *  function, will get annotated with the code location that uses and
-     *  required it. The second option is less verbose, but does not provide
-     *  any context at all as to where and why a failing value was required.
-     *
-     *  Scopes would fix that, by adding context only when --show-trace is
-     *  passed, and keeping the trace terse otherwise.
-     *
-     */
-
-    // Enough indent to align with with the `... `
-    // prepended to each element of the trace
-    auto ellipsisIndent = "  ";
-
-    bool frameOnly = false;
-    if (!einfo.traces.empty()) {
-        size_t count = 0;
+    // traces
+    if (showTrace && !einfo.traces.empty()) {
         for (const auto & trace : einfo.traces) {
-            if (!showTrace && count > 3) {
-                oss << "\n" << ANSI_WARNING "(stack trace truncated; use '--show-trace' to show the full trace)" ANSI_NORMAL << "\n";
-                break;
-            }
-
-            if (trace.hint.str().empty()) continue;
-            if (frameOnly && !trace.frame) continue;
-
-            count++;
-            frameOnly = trace.frame;
-
             oss << "\n" << "… " << trace.hint.str() << "\n";
 
             if (trace.pos) {
-                count++;
-
-                oss << "\n" << ellipsisIndent << ANSI_BLUE << "at " ANSI_WARNING << *trace.pos << ANSI_NORMAL << ":";
+                oss << "\n" << ANSI_BLUE << "at " ANSI_WARNING << *trace.pos << ANSI_NORMAL << ":";
 
                 if (auto loc = trace.pos->getCodeLines()) {
                     oss << "\n";

src/libutil/error.hh

@@ -86,7 +86,6 @@ void printCodeLines(std::ostream & out,
 struct Trace {
     std::shared_ptr<AbstractPos> pos;
     hintformat hint;
-    bool frame;
 };
 
 struct ErrorInfo {
@@ -115,8 +114,6 @@ protected:
 public:
     unsigned int status = 1; // exit status
 
-    BaseError(const BaseError &) = default;
-
     template<typename... Args>
     BaseError(unsigned int status, const Args & ... args)
         : err { .level = lvlError, .msg = hintfmt(args...) }
@@ -155,22 +152,15 @@ public:
     const std::string & msg() const { return calcWhat(); }
     const ErrorInfo & info() const { calcWhat(); return err; }
 
-    void pushTrace(Trace trace)
-    {
-        err.traces.push_front(trace);
-    }
-
     template<typename... Args>
-    void addTrace(std::shared_ptr<AbstractPos> && e, std::string_view fs, const Args & ... args)
+    void addTrace(std::shared_ptr<AbstractPos> && e, const std::string & fs, const Args & ... args)
     {
-        addTrace(std::move(e), hintfmt(std::string(fs), args...));
+        addTrace(std::move(e), hintfmt(fs, args...));
     }
 
-    void addTrace(std::shared_ptr<AbstractPos> && e, hintformat hint, bool frame = false);
+    void addTrace(std::shared_ptr<AbstractPos> && e, hintformat hint);
 
     bool hasTrace() const { return !err.traces.empty(); }
-
-    const ErrorInfo & info() { return err; };
 };
 
 #define MakeError(newClass, superClass) \

src/libutil/regex-combinators.hh

@@ -0,0 +1,30 @@
+#pragma once
+
+#include <string_view>
+
+namespace nix::regex {
+
+// TODO use constexpr string building like
+// https://github.com/akrzemi1/static_string/blob/master/include/ak_toolkit/static_string.hpp
+
+static inline std::string either(std::string_view a, std::string_view b)
+{
+    return std::string { a } + "|" + b;
+}
+
+static inline std::string group(std::string_view a)
+{
+    return std::string { "(" } + a + ")";
+}
+
+static inline std::string many(std::string_view a)
+{
+    return std::string { "(?:" } + a + ")*";
+}
+
+static inline std::string list(std::string_view a)
+{
+    return std::string { a } + many(group("," + a));
+}
+
+}

src/nix-env/user-env.cc

@@ -134,9 +134,9 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     state.forceValue(topLevel, [&]() { return topLevel.determinePos(noPos); });
     PathSet context;
     Attr & aDrvPath(*topLevel.attrs->find(state.sDrvPath));
-    auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, *aDrvPath.value, context, "");
+    auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, *aDrvPath.value, context);
     Attr & aOutPath(*topLevel.attrs->find(state.sOutPath));
-    auto topLevelOut = state.coerceToStorePath(aOutPath.pos, *aOutPath.value, context, "");
+    auto topLevelOut = state.coerceToStorePath(aOutPath.pos, *aOutPath.value, context);
 
     /* Realise the resulting store expression. */
     debug("building user environment");

src/nix/bundle.cc

@@ -97,13 +97,13 @@ struct CmdBundle : InstallableCommand
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
         PathSet context2;
-        auto drvPath = evalState->coerceToStorePath(attr1->pos, *attr1->value, context2, "");
+        auto drvPath = evalState->coerceToStorePath(attr1->pos, *attr1->value, context2);
 
         auto attr2 = vRes->attrs->get(evalState->sOutPath);
         if (!attr2)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
-        auto outPath = evalState->coerceToStorePath(attr2->pos, *attr2->value, context2, "");
+        auto outPath = evalState->coerceToStorePath(attr2->pos, *attr2->value, context2);
 
         store->buildPaths({
             DerivedPath::Built {
@@ -118,7 +118,7 @@ struct CmdBundle : InstallableCommand
             auto * attr = vRes->attrs->get(evalState->sName);
             if (!attr)
                 throw Error("attribute 'name' missing");
-            outLink = evalState->forceStringNoCtx(*attr->value, attr->pos, "");
+            outLink = evalState->forceStringNoCtx(*attr->value, attr->pos);
         }
 
         // TODO: will crash if not a localFSStore?

src/nix/eval.cc

@@ -112,7 +112,7 @@ struct CmdEval : MixJSON, InstallableCommand
 
         else if (raw) {
             stopProgressBar();
-            std::cout << *state->coerceToString(noPos, *v, context, "while generating the eval command output");
+            std::cout << *state->coerceToString(noPos, *v, context);
         }
 
         else if (json) {

src/nix/flake.cc

@@ -126,12 +126,12 @@ static void enumerateOutputs(EvalState & state, Value & vFlake,
     std::function<void(const std::string & name, Value & vProvide, const PosIdx pos)> callback)
 {
     auto pos = vFlake.determinePos(noPos);
-    state.forceAttrs(vFlake, pos, "while evaluating a flake to get its outputs");
+    state.forceAttrs(vFlake, pos);
 
     auto aOutputs = vFlake.attrs->get(state.symbols.create("outputs"));
     assert(aOutputs);
 
-    state.forceAttrs(*aOutputs->value, pos, "while evaluating the outputs of a flake");
+    state.forceAttrs(*aOutputs->value, pos);
 
     auto sHydraJobs = state.symbols.create("hydraJobs");
 
@@ -391,13 +391,13 @@ struct CmdFlakeCheck : FlakeCommand
 
         checkHydraJobs = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
             try {
-                state->forceAttrs(v, pos, "");
+                state->forceAttrs(v, pos);
 
                 if (state->isDerivation(v))
                     throw Error("jobset should not be a derivation at top-level");
 
                 for (auto & attr : *v.attrs) {
-                    state->forceAttrs(*attr.value, attr.pos, "");
+                    state->forceAttrs(*attr.value, attr.pos);
                     auto attrPath2 = concatStrings(attrPath, ".", state->symbols[attr.name]);
                     if (state->isDerivation(*attr.value)) {
                         Activity act(*logger, lvlChatty, actUnknown,
@@ -419,7 +419,7 @@ struct CmdFlakeCheck : FlakeCommand
                     fmt("checking NixOS configuration '%s'", attrPath));
                 Bindings & bindings(*state->allocBindings(0));
                 auto vToplevel = findAlongAttrPath(*state, "config.system.build.toplevel", bindings, v).first;
-                state->forceValue(*vToplevel, pos);
+                state->forceAttrs(*vToplevel, pos);
                 if (!state->isDerivation(*vToplevel))
                     throw Error("attribute 'config.system.build.toplevel' is not a derivation");
             } catch (Error & e) {
@@ -433,12 +433,12 @@ struct CmdFlakeCheck : FlakeCommand
                 Activity act(*logger, lvlChatty, actUnknown,
                     fmt("checking template '%s'", attrPath));
 
-                state->forceAttrs(v, pos, "");
+                state->forceAttrs(v, pos);
 
                 if (auto attr = v.attrs->get(state->symbols.create("path"))) {
                     if (attr->name == state->symbols.create("path")) {
                         PathSet context;
-                        auto path = state->coerceToPath(attr->pos, *attr->value, context, "");
+                        auto path = state->coerceToPath(attr->pos, *attr->value, context);
                         if (!store->isInStore(path))
                             throw Error("template '%s' has a bad 'path' attribute");
                         // TODO: recursively check the flake in 'path'.
@@ -447,7 +447,7 @@ struct CmdFlakeCheck : FlakeCommand
                     throw Error("template '%s' lacks attribute 'path'", attrPath);
 
                 if (auto attr = v.attrs->get(state->symbols.create("description")))
-                    state->forceStringNoCtx(*attr->value, attr->pos, "");
+                    state->forceStringNoCtx(*attr->value, attr->pos);
                 else
                     throw Error("template '%s' lacks attribute 'description'", attrPath);
 
@@ -504,11 +504,11 @@ struct CmdFlakeCheck : FlakeCommand
                             warn("flake output attribute '%s' is deprecated; use '%s' instead", name, replacement);
 
                         if (name == "checks") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
-                                state->forceAttrs(*attr.value, attr.pos, "");
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs) {
                                     auto drvPath = checkDerivation(
                                         fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
@@ -524,7 +524,7 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "formatter") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
@@ -535,11 +535,11 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "packages" || name == "devShells") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
-                                state->forceAttrs(*attr.value, attr.pos, "");
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkDerivation(
                                         fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
@@ -548,11 +548,11 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "apps") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
-                                state->forceAttrs(*attr.value, attr.pos, "");
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs)
                                     checkApp(
                                         fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),
@@ -561,7 +561,7 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "defaultPackage" || name == "devShell") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
@@ -572,7 +572,7 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "defaultApp") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
@@ -583,7 +583,7 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "legacyPackages") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 checkSystemName(state->symbols[attr.name], attr.pos);
                                 // FIXME: do getDerivations?
@@ -594,7 +594,7 @@ struct CmdFlakeCheck : FlakeCommand
                             checkOverlay(name, vOutput, pos);
 
                         else if (name == "overlays") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
                                 checkOverlay(fmt("%s.%s", name, state->symbols[attr.name]),
                                     *attr.value, attr.pos);
@@ -604,14 +604,14 @@ struct CmdFlakeCheck : FlakeCommand
                             checkModule(name, vOutput, pos);
 
                         else if (name == "nixosModules") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
                                 checkModule(fmt("%s.%s", name, state->symbols[attr.name]),
                                     *attr.value, attr.pos);
                         }
 
                         else if (name == "nixosConfigurations") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
                                 checkNixOSConfiguration(fmt("%s.%s", name, state->symbols[attr.name]),
                                     *attr.value, attr.pos);
@@ -624,14 +624,14 @@ struct CmdFlakeCheck : FlakeCommand
                             checkTemplate(name, vOutput, pos);
 
                         else if (name == "templates") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs)
                                 checkTemplate(fmt("%s.%s", name, state->symbols[attr.name]),
                                     *attr.value, attr.pos);
                         }
 
                         else if (name == "defaultBundler") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
@@ -642,11 +642,11 @@ struct CmdFlakeCheck : FlakeCommand
                         }
 
                         else if (name == "bundlers") {
-                            state->forceAttrs(vOutput, pos, "");
+                            state->forceAttrs(vOutput, pos);
                             for (auto & attr : *vOutput.attrs) {
                                 const auto & attr_name = state->symbols[attr.name];
                                 checkSystemName(attr_name, attr.pos);
-                                state->forceAttrs(*attr.value, attr.pos, "");
+                                state->forceAttrs(*attr.value, attr.pos);
                                 for (auto & attr2 : *attr.value->attrs) {
                                     checkBundler(
                                         fmt("%s.%s.%s", name, attr_name, state->symbols[attr2.name]),

src/nix/main.cc

@@ -199,7 +199,7 @@ static void showHelp(std::vector<std::string> subcommand, MultiCommand & topleve
     if (!attr)
         throw UsageError("Nix has no subcommand '%s'", concatStringsSep("", subcommand));
 
-    auto markdown = state.forceString(*attr->value, noPos, "while evaluating the lowdown help text");
+    auto markdown = state.forceString(*attr->value);
 
     RunPager pager;
     std::cout << renderMarkdownToTerminal(markdown) << "\n";

src/nix/prefetch.cc

@@ -28,17 +28,17 @@ std::string resolveMirrorUrl(EvalState & state, const std::string & url)
     Value vMirrors;
     // FIXME: use nixpkgs flake
     state.eval(state.parseExprFromString("import <nixpkgs/pkgs/build-support/fetchurl/mirrors.nix>", "."), vMirrors);
-    state.forceAttrs(vMirrors, noPos, "while evaluating the set of all mirrors");
+    state.forceAttrs(vMirrors, noPos);
 
     auto mirrorList = vMirrors.attrs->find(state.symbols.create(mirrorName));
     if (mirrorList == vMirrors.attrs->end())
         throw Error("unknown mirror name '%s'", mirrorName);
-    state.forceList(*mirrorList->value, noPos, "while evaluating one mirror configuration");
+    state.forceList(*mirrorList->value, noPos);
 
     if (mirrorList->value->listSize() < 1)
         throw Error("mirror URL '%s' did not expand to anything", url);
 
-    std::string mirror(state.forceString(*mirrorList->value->listElems()[0], noPos, "while evaluating the first available mirror"));
+    std::string mirror(state.forceString(*mirrorList->value->listElems()[0]));
     return mirror + (hasSuffix(mirror, "/") ? "" : "/") + s.substr(p + 1);
 }
 
@@ -196,29 +196,29 @@ static int main_nix_prefetch_url(int argc, char * * argv)
             Value vRoot;
             state->evalFile(path, vRoot);
             Value & v(*findAlongAttrPath(*state, attrPath, autoArgs, vRoot).first);
-            state->forceAttrs(v, noPos, "while evaluating the source attribute to prefetch");
+            state->forceAttrs(v, noPos);
 
             /* Extract the URL. */
             auto * attr = v.attrs->get(state->symbols.create("urls"));
             if (!attr)
                 throw Error("attribute 'urls' missing");
-            state->forceList(*attr->value, noPos, "while evaluating the urls to prefetch");
+            state->forceList(*attr->value, noPos);
             if (attr->value->listSize() < 1)
                 throw Error("'urls' list is empty");
-            url = state->forceString(*attr->value->listElems()[0], noPos, "while evaluating the first url from the urls list");
+            url = state->forceString(*attr->value->listElems()[0]);
 
             /* Extract the hash mode. */
             auto attr2 = v.attrs->get(state->symbols.create("outputHashMode"));
             if (!attr2)
                 printInfo("warning: this does not look like a fetchurl call");
             else
-                unpack = state->forceString(*attr2->value, noPos, "while evaluating the outputHashMode of the source to prefetch") == "recursive";
+                unpack = state->forceString(*attr2->value) == "recursive";
 
             /* Extract the name. */
             if (!name) {
                 auto attr3 = v.attrs->get(state->symbols.create("name"));
                 if (!attr3)
-                    name = state->forceString(*attr3->value, noPos, "while evaluating the name of the source to prefetch");
+                    name = state->forceString(*attr3->value);
             }
         }
 

src/nix/upgrade-nix.cc

@@ -144,7 +144,7 @@ struct CmdUpgradeNix : MixDryRun, StoreCommand
         Bindings & bindings(*state->allocBindings(0));
         auto v2 = findAlongAttrPath(*state, settings.thisSystem, bindings, *v).first;
 
-        return store->parseStorePath(state->forceString(*v2, noPos, "while evaluating the path tho latest nix version"));
+        return store->parseStorePath(state->forceString(*v2));
     }
 };
 

tests/build.sh

@@ -42,20 +42,21 @@ nix build -f multiple-outputs.nix --json 'a^*' --no-link | jq --exit-status '
 nix build -f multiple-outputs.nix --json e --no-link | jq --exit-status '
   (.[0] |
     (.drvPath | match(".*multiple-outputs-e.drv")) and
-    (.outputs | keys == ["a", "b"]))
+    (.outputs | keys == ["a_a", "b"]))
 '
 
 # But not when it's overriden.
-nix build -f multiple-outputs.nix --json e^a --no-link | jq --exit-status '
+nix build -f multiple-outputs.nix --json e^a_a --no-link
+nix build -f multiple-outputs.nix --json e^a_a --no-link | jq --exit-status '
   (.[0] |
     (.drvPath | match(".*multiple-outputs-e.drv")) and
-    (.outputs | keys == ["a"]))
+    (.outputs | keys == ["a_a"]))
 '
 
 nix build -f multiple-outputs.nix --json 'e^*' --no-link | jq --exit-status '
   (.[0] |
     (.drvPath | match(".*multiple-outputs-e.drv")) and
-    (.outputs | keys == ["a", "b", "c"]))
+    (.outputs | keys == ["a_a", "b", "c"]))
 '
 
 # Test building from raw store path to drv not expression.
@@ -88,7 +89,7 @@ nix build "$drv^first,second" --no-link --json | jq --exit-status '
     (.outputs |
       (keys | length == 2) and
       (.first | match(".*multiple-outputs-a-first")) and
-	  (.second | match(".*multiple-outputs-a-second"))))
+      (.second | match(".*multiple-outputs-a-second"))))
 '
 
 nix build "$drv^*" --no-link --json | jq --exit-status '
@@ -97,14 +98,14 @@ nix build "$drv^*" --no-link --json | jq --exit-status '
     (.outputs |
       (keys | length == 2) and
       (.first | match(".*multiple-outputs-a-first")) and
-	  (.second | match(".*multiple-outputs-a-second"))))
+      (.second | match(".*multiple-outputs-a-second"))))
 '
 
 # Make sure that `--impure` works (regression test for https://github.com/NixOS/nix/issues/6488)
 nix build --impure -f multiple-outputs.nix --json e --no-link | jq --exit-status '
   (.[0] |
     (.drvPath | match(".*multiple-outputs-e.drv")) and
-    (.outputs | keys == ["a", "b"]))
+    (.outputs | keys == ["a_a", "b"]))
 '
 
 testNormalization () {

tests/lang/eval-okay-context-introspection.exp

@@ -1 +1 @@
-true
+[ true true true true true true ]

tests/lang/eval-okay-context-introspection.nix

@@ -18,7 +18,24 @@ let
     };
   };
 
-  legit-context = builtins.getContext "${path}${drv.outPath}${drv.foo.outPath}${drv.drvPath}";
+  combo-path = "${path}${drv.outPath}${drv.foo.outPath}${drv.drvPath}";
+  legit-context = builtins.getContext combo-path;
 
-  constructed-context = builtins.getContext (builtins.appendContext "" desired-context);
-in legit-context == constructed-context
+  reconstructed-path = builtins.appendContext
+    (builtins.unsafeDiscardStringContext combo-path)
+    desired-context;
+
+  # Eta rule for strings with context.
+  etaRule = str:
+    str == builtins.appendContext
+      (builtins.unsafeDiscardStringContext str)
+      (builtins.getContext str);
+
+in [
+  (legit-context == desired-context)
+  (reconstructed-path == combo-path)
+  (etaRule "foo")
+  (etaRule drv.drvPath)
+  (etaRule drv.foo.outPath)
+  (etaRule (builtins.unsafeDiscardOutputDependency drv.drvPath))
+]

tests/linux-sandbox.sh

@@ -37,3 +37,6 @@ nix-build check.nix -A nondeterministic --sandbox-paths /nix/store --no-out-link
 (! nix-build check.nix -A nondeterministic --sandbox-paths /nix/store --no-out-link --check -K 2> $TEST_ROOT/log)
 if grep -q 'error: renaming' $TEST_ROOT/log; then false; fi
 grep -q 'may not be deterministic' $TEST_ROOT/log
+
+# Test that sandboxed builds cannot write to /etc easily
+(! nix-build -E 'with import ./config.nix; mkDerivation { name = "etc-write"; buildCommand = "echo > /etc/test"; }' --no-out-link --sandbox-paths /nix/store)

tests/multiple-outputs.nix

@@ -91,9 +91,9 @@ rec {
 
   e = mkDerivation {
     name = "multiple-outputs-e";
-    outputs = [ "a" "b" "c" ];
-    meta.outputsToInstall = [ "a" "b" ];
-    buildCommand = "mkdir $a $b $c";
+    outputs = [ "a_a" "b" "c" ];
+    meta.outputsToInstall = [ "a_a" "b" ];
+    buildCommand = "mkdir $a_a $b $c";
   };
 
   independent = mkDerivation {
@@ -117,4 +117,14 @@ rec {
       '';
   };
 
+  invalid-output-name-1 = mkDerivation {
+    name = "invalid-output-name-1";
+    outputs = [ "out/"];
+  };
+
+  invalid-output-name-2 = mkDerivation {
+    name = "invalid-output-name-2";
+    outputs = [ "x" "foo$"];
+  };
+
 }

tests/multiple-outputs.sh

@@ -83,3 +83,6 @@ nix-store --gc --keep-derivations --keep-outputs
 nix-store --gc --print-roots
 rm -rf $NIX_STORE_DIR/.links
 rmdir $NIX_STORE_DIR
+
+nix build -f multiple-outputs.nix invalid-output-name-1 2>&1 | grep 'contains illegal character'
+nix build -f multiple-outputs.nix invalid-output-name-2 2>&1 | grep 'contains illegal character'

tests/systemd-nspawn.nix

@@ -56,12 +56,12 @@ runCommand "test"
     # Make /run a tmpfs to shut up a systemd warning.
     mkdir /run
     mount -t tmpfs none /run
-    chmod 0700 /run
 
     mount -t cgroup2 none /sys/fs/cgroup
 
     mkdir -p $out
 
+    chmod +w /etc
     touch /etc/os-release
     echo a5ea3f98dedc0278b6f3cc8c37eeaeac > /etc/machine-id