treewide: Get rid of PosixSourceAccessor::createAtRoot

We'd like to split out the implementation into Unix/Windows-specific
parts to more easily iterate on improving UNIX accessors to make use
of dirfd-based operations (or even openat2). This should be hidden behind
the appropriate interface and not exposed as a static member function of
the PosixSourceAccessor.

src/libutil/archive.cc

@@ -103,7 +103,8 @@ void SourceAccessor::dumpPath(const CanonPath & path, Sink & sink, PathFilter &
 
 time_t dumpPathAndGetMtime(const Path & path, Sink & sink, PathFilter & filter)
 {
-    auto path2 = PosixSourceAccessor::createAtRoot(path, /*trackLastModified=*/true);
+    SourcePath path2 = {
+        makeFSSourceAccessor(std::filesystem::path{}, /*trackLastModified=*/true), CanonPath(absPath(path))};
     path2.dumpPath(sink, filter);
     return path2.accessor->getLastModified().value();
 }

src/libutil/include/nix/util/posix-source-accessor.hh

@@ -43,36 +43,6 @@ public:
 
     std::optional<std::filesystem::path> getPhysicalPath(const CanonPath & path) override;
 
-    /**
-     * Create a `PosixSourceAccessor` and `SourcePath` corresponding to
-     * some native path.
-     *
-     * @param Whether the accessor should return a non-null getLastModified.
-     * When true the accessor must be used only by a single thread.
-     *
-     * The `PosixSourceAccessor` is rooted as far up the tree as
-     * possible, (e.g. on Windows it could scoped to a drive like
-     * `C:\`). This allows more `..` parent accessing to work.
-     *
-     * @note When `path` is trusted user input, canonicalize it using
-     * `std::filesystem::canonical`, `makeParentCanonical`, `std::filesystem::weakly_canonical`, etc,
-     * as appropriate for the use case. At least weak canonicalization is
-     * required for the `SourcePath` to do anything useful at the location it
-     * points to.
-     *
-     * @note A canonicalizing behavior is not built in `createAtRoot` so that
-     * callers do not accidentally introduce symlink-related security vulnerabilities.
-     * Furthermore, `createAtRoot` does not know whether the file pointed to by
-     * `path` should be resolved if it is itself a symlink. In other words,
-     * `createAtRoot` can not decide between aforementioned `canonical`, `makeParentCanonical`, etc. for its callers.
-     *
-     * See
-     * [`std::filesystem::path::root_path`](https://en.cppreference.com/w/cpp/filesystem/path/root_path)
-     * and
-     * [`std::filesystem::path::relative_path`](https://en.cppreference.com/w/cpp/filesystem/path/relative_path).
-     */
-    static SourcePath createAtRoot(const std::filesystem::path & path, bool trackLastModified = false);
-
     std::optional<std::time_t> getLastModified() override
     {
         return trackLastModified ? std::optional{mtime} : std::nullopt;

src/libutil/include/nix/util/source-accessor.hh

@@ -233,7 +233,7 @@ ref<SourceAccessor> getFSSourceAccessor();
  * elements, and that absolute symlinks are resolved relative to
  * `root`.
  */
-ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root);
+ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root, bool trackLastModified = false);
 
 /**
  * Construct an accessor that presents a "union" view of a vector of

src/libutil/posix-source-accessor.cc

@@ -1,7 +1,5 @@
 #include "nix/util/posix-source-accessor.hh"
-#include "nix/util/source-path.hh"
 #include "nix/util/signals.hh"
-#include "nix/util/sync.hh"
 
 #include <boost/unordered/concurrent_flat_map.hpp>
 
@@ -20,15 +18,6 @@ PosixSourceAccessor::PosixSourceAccessor()
 {
 }
 
-SourcePath PosixSourceAccessor::createAtRoot(const std::filesystem::path & path, bool trackLastModified)
-{
-    std::filesystem::path path2 = absPath(path);
-    return {
-        make_ref<PosixSourceAccessor>(path2.root_path(), trackLastModified),
-        CanonPath{path2.relative_path().string()},
-    };
-}
-
 std::filesystem::path PosixSourceAccessor::makeAbsPath(const CanonPath & path)
 {
     return root.empty()    ? (std::filesystem::path{path.abs()})
@@ -219,8 +208,8 @@ ref<SourceAccessor> getFSSourceAccessor()
     return rootFS;
 }
 
-ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root)
+ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root, bool trackLastModified)
 {
-    return make_ref<PosixSourceAccessor>(std::move(root));
+    return make_ref<PosixSourceAccessor>(std::move(root), trackLastModified);
 }
 } // namespace nix

src/nix/add-to-store.cc

@@ -38,7 +38,7 @@ struct CmdAddToStore : MixDryRun, StoreCommand
         if (!namePart)
             namePart = baseNameOf(path);
 
-        auto sourcePath = PosixSourceAccessor::createAtRoot(makeParentCanonical(path));
+        SourcePath sourcePath = makeFSSourceAccessor(makeParentCanonical(path));
 
         auto storePath = dryRun ? store->computeStorePath(*namePart, sourcePath, caMethod, hashAlgo, {}).first
                                 : store->addToStoreSlow(*namePart, sourcePath, caMethod, hashAlgo, {}).path;

src/nix/hash.cc

@@ -85,9 +85,7 @@ struct CmdHashBase : Command
                     return std::make_unique<HashSink>(hashAlgo);
             };
 
-            auto makeSourcePath = [&]() -> SourcePath {
-                return PosixSourceAccessor::createAtRoot(makeParentCanonical(path));
-            };
+            auto makeSourcePath = [&]() -> SourcePath { return makeFSSourceAccessor(makeParentCanonical(path)); };
 
             Hash h{HashAlgorithm::SHA256}; // throwaway def to appease C++
             switch (mode) {

src/nix/nix-store/nix-store.cc

@@ -191,7 +191,7 @@ static void opAdd(Strings opFlags, Strings opArgs)
         throw UsageError("unknown flag");
 
     for (auto & i : opArgs) {
-        auto sourcePath = PosixSourceAccessor::createAtRoot(makeParentCanonical(i));
+        SourcePath sourcePath = makeFSSourceAccessor(makeParentCanonical(i));
         cout << fmt("%s\n", store->printStorePath(store->addToStore(std::string(baseNameOf(i)), sourcePath)));
     }
 }
@@ -215,7 +215,7 @@ static void opAddFixed(Strings opFlags, Strings opArgs)
     opArgs.pop_front();
 
     for (auto & i : opArgs) {
-        auto sourcePath = PosixSourceAccessor::createAtRoot(makeParentCanonical(i));
+        SourcePath sourcePath = makeFSSourceAccessor(makeParentCanonical(i));
         std::cout << fmt(
             "%s\n", store->printStorePath(store->addToStoreSlow(baseNameOf(i), sourcePath, method, hashAlgo).path));
     }

src/perl/lib/Nix/Store.xs

@@ -256,7 +256,7 @@ hashPath(char * algo, int base32, char * path)
     PPCODE:
         try {
             Hash h = hashPath(
-                PosixSourceAccessor::createAtRoot(path),
+                SourcePath{getFSSourceAccessor(), CanonPath(absPath(Path(path)))},
                 FileIngestionMethod::NixArchive, parseHashAlgo(algo)).first;
             auto s = h.to_string(base32 ? HashFormat::Nix32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
@@ -336,7 +336,7 @@ StoreWrapper::addToStore(char * srcPath, int recursive, char * algo)
             auto method = recursive ? ContentAddressMethod::Raw::NixArchive : ContentAddressMethod::Raw::Flat;
             auto path = THIS->store->addToStore(
                 std::string(baseNameOf(srcPath)),
-                PosixSourceAccessor::createAtRoot(srcPath),
+                SourcePath{getFSSourceAccessor(), CanonPath(absPath(Path(srcPath)))},
                 method, parseHashAlgo(algo));
             XPUSHs(sv_2mortal(newSVpv(THIS->store->printStorePath(path).c_str(), 0)));
         } catch (Error & e) {