Merge pull request #10655 from edolstra/use-source-path

Use `SourcePath` in more places

perl/lib/Nix/Store.xs

@@ -256,9 +256,8 @@ SV *
 hashPath(char * algo, int base32, char * path)
     PPCODE:
         try {
-            auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(path);
             Hash h = hashPath(
-                accessor, canonPath,
+                PosixSourceAccessor::createAtRoot(path),
                 FileIngestionMethod::Recursive, parseHashAlgo(algo));
             auto s = h.to_string(base32 ? HashFormat::Nix32 : HashFormat::Base16, false);
             XPUSHs(sv_2mortal(newSVpv(s.c_str(), 0)));
@@ -336,10 +335,9 @@ StoreWrapper::addToStore(char * srcPath, int recursive, char * algo)
     PPCODE:
         try {
             auto method = recursive ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
-            auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(srcPath);
             auto path = THIS->store->addToStore(
                 std::string(baseNameOf(srcPath)),
-                accessor, canonPath,
+                PosixSourceAccessor::createAtRoot(srcPath),
                 method, parseHashAlgo(algo));
             XPUSHs(sv_2mortal(newSVpv(THIS->store->printStorePath(path).c_str(), 0)));
         } catch (Error & e) {

src/libcmd/installables.cc

@@ -146,7 +146,7 @@ MixFlakeOptions::MixFlakeOptions()
         .category = category,
         .labels = {"flake-lock-path"},
         .handler = {[&](std::string lockFilePath) {
-            lockFlags.referenceLockFilePath = {makeFSSourceAccessor(), CanonPath(absPath(lockFilePath))};
+            lockFlags.referenceLockFilePath = {getFSSourceAccessor(), CanonPath(absPath(lockFilePath))};
         }},
         .completer = completePath
     });

src/libexpr/eval.cc

@@ -399,14 +399,14 @@ EvalState::EvalState(
     , emptyBindings(0)
     , rootFS(
         evalSettings.restrictEval || evalSettings.pureEval
-        ? ref<SourceAccessor>(AllowListSourceAccessor::create(makeFSSourceAccessor(), {},
+        ? ref<SourceAccessor>(AllowListSourceAccessor::create(getFSSourceAccessor(), {},
             [](const CanonPath & path) -> RestrictedPathError {
                 auto modeInformation = evalSettings.pureEval
                     ? "in pure evaluation mode (use '--impure' to override)"
                     : "in restricted mode";
                 throw RestrictedPathError("access to absolute path '%1%' is forbidden %2%", path, modeInformation);
             }))
-        : makeFSSourceAccessor())
+        : getFSSourceAccessor())
     , corepkgsFS(make_ref<MemorySourceAccessor>())
     , internalFS(make_ref<MemorySourceAccessor>())
     , derivationInternal{corepkgsFS->addFile(

src/libfetchers/fetch-to-store.cc

@@ -42,9 +42,9 @@ StorePath fetchToStore(
     auto storePath =
         mode == FetchMode::DryRun
         ? store.computeStorePath(
-            name, *path.accessor, path.path, method, HashAlgorithm::SHA256, {}, filter2).first
+            name, path, method, HashAlgorithm::SHA256, {}, filter2).first
         : store.addToStore(
-            name, *path.accessor, path.path, method, HashAlgorithm::SHA256, {}, filter2, repair);
+            name, path, method, HashAlgorithm::SHA256, {}, filter2, repair);
 
     if (cacheKey && mode == FetchMode::Copy)
         fetchers::getCache()->add(store, *cacheKey, {}, storePath, true);

src/libfetchers/unix/mercurial.cc

@@ -212,7 +212,7 @@ struct MercurialInputScheme : InputScheme
 
                 auto storePath = store->addToStore(
                     input.getName(),
-                    *makeFSSourceAccessor(), CanonPath { actualPath },
+                    {getFSSourceAccessor(), CanonPath(actualPath)},
                     FileIngestionMethod::Recursive, HashAlgorithm::SHA256, {},
                     filter);
 
@@ -318,7 +318,7 @@ struct MercurialInputScheme : InputScheme
 
         deletePath(tmpDir + "/.hg_archival.txt");
 
-        auto storePath = store->addToStore(name, *makeFSSourceAccessor(), CanonPath { tmpDir });
+        auto storePath = store->addToStore(name, {getFSSourceAccessor(), CanonPath(tmpDir)});
 
         Attrs infoAttrs({
             {"rev", input.getRev()->gitRev()},

src/libstore/binary-cache-store.cc

@@ -442,8 +442,7 @@ void BinaryCacheStore::queryPathInfoUncached(const StorePath & storePath,
 
 StorePath BinaryCacheStore::addToStore(
     std::string_view name,
-    SourceAccessor & accessor,
+    const SourcePath & path,
-    const CanonPath & path,
     ContentAddressMethod method,
     HashAlgorithm hashAlgo,
     const StorePathSet & references,
@@ -454,10 +453,10 @@ StorePath BinaryCacheStore::addToStore(
        non-recursive+sha256 so we can just use the default
        implementation of this method in terms of addToStoreFromDump. */
 
-    auto h = hashPath(accessor, path, method.getFileIngestionMethod(), hashAlgo, filter);
+    auto h = hashPath(path, method.getFileIngestionMethod(), hashAlgo, filter);
 
     auto source = sinkToSource([&](Sink & sink) {
-        accessor.dumpPath(path, sink, filter);
+        path.dumpPath(sink, filter);
     });
     return addToStoreCommon(*source, repair, CheckSigs, [&](HashResult nar) {
         ValidPathInfo info {

src/libstore/binary-cache-store.hh

@@ -133,8 +133,7 @@ public:
 
     StorePath addToStore(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & path,
-        const CanonPath & srcPath,
         ContentAddressMethod method,
         HashAlgorithm hashAlgo,
         const StorePathSet & references,

src/libstore/legacy-ssh-store.hh

@@ -60,8 +60,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
 
     StorePath addToStore(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & path,
-        const CanonPath & srcPath,
         ContentAddressMethod method,
         HashAlgorithm hashAlgo,
         const StorePathSet & references,

src/libstore/store-api.cc

@@ -167,14 +167,13 @@ StorePath StoreDirConfig::makeFixedOutputPathFromCA(std::string_view name, const
 
 std::pair<StorePath, Hash> StoreDirConfig::computeStorePath(
     std::string_view name,
-    SourceAccessor & accessor,
+    const SourcePath & path,
-    const CanonPath & path,
     ContentAddressMethod method,
     HashAlgorithm hashAlgo,
     const StorePathSet & references,
     PathFilter & filter) const
 {
-    auto h = hashPath(accessor, path, method.getFileIngestionMethod(), hashAlgo, filter);
+    auto h = hashPath(path, method.getFileIngestionMethod(), hashAlgo, filter);
     return {
         makeFixedOutputPathFromCA(
             name,
@@ -192,8 +191,7 @@ std::pair<StorePath, Hash> StoreDirConfig::computeStorePath(
 
 StorePath Store::addToStore(
     std::string_view name,
-    SourceAccessor & accessor,
+    const SourcePath & path,
-    const CanonPath & path,
     ContentAddressMethod method,
     HashAlgorithm hashAlgo,
     const StorePathSet & references,
@@ -214,7 +212,7 @@ StorePath Store::addToStore(
         break;
     }
     auto source = sinkToSource([&](Sink & sink) {
-        dumpPath(accessor, path, sink, fsm, filter);
+        dumpPath(path, sink, fsm, filter);
     });
     return addToStoreFromDump(*source, name, fsm, method, hashAlgo, references, repair);
 }
@@ -343,8 +341,7 @@ digraph graphname {
 */
 ValidPathInfo Store::addToStoreSlow(
     std::string_view name,
-    SourceAccessor & accessor,
+    const SourcePath & srcPath,
-    const CanonPath & srcPath,
     ContentAddressMethod method, HashAlgorithm hashAlgo,
     const StorePathSet & references,
     std::optional<Hash> expectedCAHash)
@@ -366,7 +363,7 @@ ValidPathInfo Store::addToStoreSlow(
        srcPath. The fact that we use scratchpadSink as a temporary buffer here
        is an implementation detail. */
     auto fileSource = sinkToSource([&](Sink & scratchpadSink) {
-        accessor.dumpPath(srcPath, scratchpadSink);
+        srcPath.dumpPath(scratchpadSink);
     });
 
     /* tapped provides the same data as fileSource, but we also write all the
@@ -389,13 +386,12 @@ ValidPathInfo Store::addToStoreSlow(
     auto hash = method == FileIngestionMethod::Recursive && hashAlgo == HashAlgorithm::SHA256
         ? narHash
         : method == FileIngestionMethod::Git
-        ? git::dumpHash(hashAlgo, accessor, srcPath).hash
+        ? git::dumpHash(hashAlgo, srcPath).hash
         : caHashSink.finish().first;
 
     if (expectedCAHash && expectedCAHash != hash)
         throw Error("hash mismatch for '%s'", srcPath);
 
-
     ValidPathInfo info {
         *this,
         name,
@@ -412,7 +408,7 @@ ValidPathInfo Store::addToStoreSlow(
 
     if (!isValidPath(info.path)) {
         auto source = sinkToSource([&](Sink & scratchpadSink) {
-            accessor.dumpPath(srcPath, scratchpadSink);
+            srcPath.dumpPath(scratchpadSink);
         });
         addToStore(info, *source);
     }

src/libstore/store-api.hh

@@ -439,8 +439,7 @@ public:
      */
     virtual StorePath addToStore(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & path,
-        const CanonPath & path,
         ContentAddressMethod method = FileIngestionMethod::Recursive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = StorePathSet(),
@@ -454,8 +453,7 @@ public:
      */
     ValidPathInfo addToStoreSlow(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & path,
-        const CanonPath & path,
         ContentAddressMethod method = FileIngestionMethod::Recursive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = StorePathSet(),

src/libstore/store-dir-config.hh

@@ -13,6 +13,8 @@
 
 namespace nix {
 
+struct SourcePath;
+
 MakeError(BadStorePath, Error);
 
 struct StoreDirConfig : public Config
@@ -94,8 +96,7 @@ struct StoreDirConfig : public Config
      */
     std::pair<StorePath, Hash> computeStorePath(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & path,
-        const CanonPath & path,
         ContentAddressMethod method = FileIngestionMethod::Recursive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = {},

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

@@ -1306,8 +1306,7 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual In
 
     StorePath addToStore(
         std::string_view name,
-        SourceAccessor & accessor,
+        const SourcePath & srcPath,
-        const CanonPath & srcPath,
         ContentAddressMethod method,
         HashAlgorithm hashAlgo,
         const StorePathSet & references,
@@ -2485,7 +2484,6 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             /* FIXME optimize and deduplicate with addToStore */
             std::string oldHashPart { scratchPath->hashPart() };
             auto got = [&]{
-                PosixSourceAccessor accessor;
                 auto fim = outputHash.method.getFileIngestionMethod();
                 switch (fim) {
                 case FileIngestionMethod::Flat:
@@ -2494,15 +2492,15 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
                     HashModuloSink caSink { outputHash.hashAlgo, oldHashPart };
                     auto fim = outputHash.method.getFileIngestionMethod();
                     dumpPath(
-                        accessor, CanonPath { actualPath },
+                        {getFSSourceAccessor(), CanonPath(actualPath)},
                         caSink,
                         (FileSerialisationMethod) fim);
                     return caSink.finish().first;
                 }
                 case FileIngestionMethod::Git: {
                     return git::dumpHash(
-                        outputHash.hashAlgo, accessor,
+                        outputHash.hashAlgo,
-                        CanonPath { tmpDir + "/tmp" }).hash;
+                        {getFSSourceAccessor(), CanonPath(tmpDir + "/tmp")}).hash;
                 }
                 }
                 assert(false);
@@ -2529,9 +2527,8 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             }
 
             {
-                PosixSourceAccessor accessor;
                 HashResult narHashAndSize = hashPath(
-                    accessor, CanonPath { actualPath },
+                    {getFSSourceAccessor(), CanonPath(actualPath)},
                     FileSerialisationMethod::Recursive, HashAlgorithm::SHA256);
                 newInfo0.narHash = narHashAndSize.first;
                 newInfo0.narSize = narHashAndSize.second;
@@ -2553,9 +2550,8 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
                         std::string { scratchPath->hashPart() },
                         std::string { requiredFinalPath.hashPart() });
                 rewriteOutput(outputRewrites);
-                PosixSourceAccessor accessor;
                 HashResult narHashAndSize = hashPath(
-                    accessor, CanonPath { actualPath },
+                    {getFSSourceAccessor(), CanonPath(actualPath)},
                     FileSerialisationMethod::Recursive, HashAlgorithm::SHA256);
                 ValidPathInfo newInfo0 { requiredFinalPath, narHashAndSize.first };
                 newInfo0.narSize = narHashAndSize.second;

src/libstore/unix/build/worker.cc

@@ -530,7 +530,7 @@ bool Worker::pathContentsGood(const StorePath & path)
         res = false;
     else {
         Hash current = hashPath(
-            *store.getFSAccessor(), CanonPath { store.printStorePath(path) },
+            {store.getFSAccessor(), CanonPath(store.printStorePath(path))},
             FileIngestionMethod::Recursive, info->narHash.algo);
         Hash nullHash(HashAlgorithm::SHA256);
         res = info->narHash == nullHash || info->narHash == current;

src/libstore/unix/local-store.cc

@@ -1132,12 +1132,12 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
                             specified.hash.algo,
                             std::string { info.path.hashPart() },
                         };
-                        dumpPath(*accessor, path, caSink, (FileSerialisationMethod) fim);
+                        dumpPath({accessor, path}, caSink, (FileSerialisationMethod) fim);
                         h = caSink.finish().first;
                         break;
                     }
                     case FileIngestionMethod::Git:
-                        h = git::dumpHash(specified.hash.algo, *accessor, path).hash;
+                        h = git::dumpHash(specified.hash.algo, {accessor, path}).hash;
                         break;
                     }
                     ContentAddress {
@@ -1247,14 +1247,12 @@ StorePath LocalStore::addToStoreFromDump(
 
     auto [dumpHash, size] = hashSink->finish();
 
-    PosixSourceAccessor accessor;
-
     auto desc = ContentAddressWithReferences::fromParts(
         hashMethod,
         methodsMatch
             ? dumpHash
             : hashPath(
-                accessor, CanonPath { tempPath },
+                {getFSSourceAccessor(), CanonPath(tempPath)},
                 hashMethod.getFileIngestionMethod(), hashAlgo),
         {
             .others = references,
@@ -1394,7 +1392,7 @@ bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
             Path linkPath = linksDir + "/" + link.name;
             PosixSourceAccessor accessor;
             std::string hash = hashPath(
-                accessor, CanonPath { linkPath },
+                {getFSSourceAccessor(), CanonPath(linkPath)},
                 FileIngestionMethod::Recursive, HashAlgorithm::SHA256).to_string(HashFormat::Nix32, false);
             if (hash != link.name) {
                 printError("link '%s' was modified! expected hash '%s', got '%s'",

src/libstore/unix/optimise-store.cc

@@ -148,9 +148,8 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
        contents of the symlink (i.e. the result of readlink()), not
        the contents of the target (which may not even exist). */
     Hash hash = ({
-        PosixSourceAccessor accessor;
         hashPath(
-            accessor, CanonPath { path },
+            {make_ref<PosixSourceAccessor>(), CanonPath(path)},
             FileSerialisationMethod::Recursive, HashAlgorithm::SHA256).first;
     });
     debug("'%1%' has hash '%2%'", path, hash.to_string(HashFormat::Nix32, true));
@@ -163,9 +162,8 @@ void LocalStore::optimisePath_(Activity * act, OptimiseStats & stats,
         auto stLink = lstat(linkPath);
         if (st.st_size != stLink.st_size
             || (repair && hash != ({
-                PosixSourceAccessor accessor;
                 hashPath(
-                    accessor, CanonPath { linkPath },
+                    {make_ref<PosixSourceAccessor>(), CanonPath(linkPath)},
                     FileSerialisationMethod::Recursive, HashAlgorithm::SHA256).first;
            })))
         {

src/libutil/archive.cc

@@ -8,6 +8,7 @@
 #include "archive.hh"
 #include "config.hh"
 #include "posix-source-accessor.hh"
+#include "source-path.hh"
 #include "file-system.hh"
 #include "signals.hh"
 
@@ -110,9 +111,9 @@ void SourceAccessor::dumpPath(
 
 time_t dumpPathAndGetMtime(const Path & path, Sink & sink, PathFilter & filter)
 {
-    auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(path);
+    auto path2 = PosixSourceAccessor::createAtRoot(path);
-    accessor.dumpPath(canonPath, sink, filter);
+    path2.dumpPath(sink, filter);
-    return accessor.mtime;
+    return path2.accessor.dynamic_pointer_cast<PosixSourceAccessor>()->mtime;
 }
 
 void dumpPath(const Path & path, Sink & sink, PathFilter & filter)

src/libutil/file-content-address.cc

@@ -1,6 +1,7 @@
 #include "file-content-address.hh"
 #include "archive.hh"
 #include "git.hh"
+#include "source-path.hh"
 
 namespace nix {
 
@@ -68,17 +69,17 @@ std::string_view renderFileIngestionMethod(FileIngestionMethod method)
 
 
 void dumpPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     Sink & sink,
     FileSerialisationMethod method,
     PathFilter & filter)
 {
     switch (method) {
     case FileSerialisationMethod::Flat:
-        accessor.readFile(path, sink);
+        path.readFile(sink);
         break;
     case FileSerialisationMethod::Recursive:
-        accessor.dumpPath(path, sink, filter);
+        path.dumpPath(sink, filter);
         break;
     }
 }
@@ -101,27 +102,27 @@ void restorePath(
 
 
 HashResult hashPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     FileSerialisationMethod method, HashAlgorithm ha,
     PathFilter & filter)
 {
     HashSink sink { ha };
-    dumpPath(accessor, path, sink, method, filter);
+    dumpPath(path, sink, method, filter);
     return sink.finish();
 }
 
 
 Hash hashPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     FileIngestionMethod method, HashAlgorithm ht,
     PathFilter & filter)
 {
     switch (method) {
     case FileIngestionMethod::Flat:
     case FileIngestionMethod::Recursive:
-        return hashPath(accessor, path, (FileSerialisationMethod) method, ht, filter).first;
+        return hashPath(path, (FileSerialisationMethod) method, ht, filter).first;
     case FileIngestionMethod::Git:
-        return git::dumpHash(ht, accessor, path, filter).hash;
+        return git::dumpHash(ht, path, filter).hash;
     }
     assert(false);
 }

src/libutil/file-content-address.hh

@@ -7,6 +7,8 @@
 
 namespace nix {
 
+struct SourcePath;
+
 /**
  * An enumeration of the ways we can serialize file system
  * objects.
@@ -45,7 +47,7 @@ std::string_view renderFileSerialisationMethod(FileSerialisationMethod method);
  * Dump a serialization of the given file system object.
  */
 void dumpPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     Sink & sink,
     FileSerialisationMethod method,
     PathFilter & filter = defaultPathFilter);
@@ -72,7 +74,7 @@ void restorePath(
  * ```
  */
 HashResult hashPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     FileSerialisationMethod method, HashAlgorithm ha,
     PathFilter & filter = defaultPathFilter);
 
@@ -138,7 +140,7 @@ std::string_view renderFileIngestionMethod(FileIngestionMethod method);
  * useful defined for a merkle format.
  */
 Hash hashPath(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     FileIngestionMethod method, HashAlgorithm ha,
     PathFilter & filter = defaultPathFilter);
 

src/libutil/git.cc

@@ -8,7 +8,6 @@
 #include "signals.hh"
 #include "config.hh"
 #include "hash.hh"
-#include "posix-source-accessor.hh"
 
 #include "git.hh"
 #include "serialise.hh"
@@ -269,18 +268,18 @@ void dumpTree(const Tree & entries, Sink & sink,
 
 
 Mode dump(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     Sink & sink,
     std::function<DumpHook> hook,
     PathFilter & filter,
     const ExperimentalFeatureSettings & xpSettings)
 {
-    auto st = accessor.lstat(path);
+    auto st = path.lstat();
 
     switch (st.type) {
     case SourceAccessor::tRegular:
     {
-        accessor.readFile(path, sink, [&](uint64_t size) {
+        path.readFile(sink, [&](uint64_t size) {
             dumpBlobPrefix(size, sink, xpSettings);
         });
         return st.isExecutable
@@ -291,9 +290,9 @@ Mode dump(
     case SourceAccessor::tDirectory:
     {
         Tree entries;
-        for (auto & [name, _] : accessor.readDirectory(path)) {
+        for (auto & [name, _] : path.readDirectory()) {
             auto child = path / name;
-            if (!filter(child.abs())) continue;
+            if (!filter(child.path.abs())) continue;
 
             auto entry = hook(child);
 
@@ -309,7 +308,7 @@ Mode dump(
 
     case SourceAccessor::tSymlink:
     {
-        auto target = accessor.readLink(path);
+        auto target = path.readLink();
         dumpBlobPrefix(target.size(), sink, xpSettings);
         sink(target);
         return Mode::Symlink;
@@ -323,13 +322,14 @@ Mode dump(
 
 
 TreeEntry dumpHash(
-        HashAlgorithm ha,
+    HashAlgorithm ha,
-        SourceAccessor & accessor, const CanonPath & path, PathFilter & filter)
+    const SourcePath & path,
+    PathFilter & filter)
 {
     std::function<DumpHook> hook;
-    hook = [&](const CanonPath & path) -> TreeEntry {
+    hook = [&](const SourcePath & path) -> TreeEntry {
         auto hashSink = HashSink(ha);
-        auto mode = dump(accessor, path, hashSink, hook, filter);
+        auto mode = dump(path, hashSink, hook, filter);
         auto hash = hashSink.finish().first;
         return {
             .mode = mode,

src/libutil/git.hh

@@ -8,7 +8,7 @@
 #include "types.hh"
 #include "serialise.hh"
 #include "hash.hh"
-#include "source-accessor.hh"
+#include "source-path.hh"
 #include "fs-sink.hh"
 
 namespace nix::git {
@@ -125,7 +125,7 @@ std::optional<Mode> convertMode(SourceAccessor::Type type);
  * Given a `Hash`, return a `SourceAccessor` and `CanonPath` pointing to
  * the file system object with that path.
  */
-using RestoreHook = std::pair<SourceAccessor *, CanonPath>(Hash);
+using RestoreHook = SourcePath(Hash);
 
 /**
  * Wrapper around `parse` and `RestoreSink`
@@ -157,10 +157,10 @@ void dumpTree(
  * Note that if the child is a directory, its child in must also be so
  * processed in order to compute this information.
  */
-using DumpHook = TreeEntry(const CanonPath & path);
+using DumpHook = TreeEntry(const SourcePath & path);
 
 Mode dump(
-    SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
     Sink & sink,
     std::function<DumpHook> hook,
     PathFilter & filter = defaultPathFilter,
@@ -172,9 +172,9 @@ Mode dump(
  * A smaller wrapper around `dump`.
  */
 TreeEntry dumpHash(
-            HashAlgorithm ha,
+    HashAlgorithm ha,
-            SourceAccessor & accessor, const CanonPath & path,
+    const SourcePath & path,
-            PathFilter & filter = defaultPathFilter);
+    PathFilter & filter = defaultPathFilter);
 
 /**
  * A line from the output of `git ls-remote --symref`.

src/libutil/posix-source-accessor.cc

@@ -1,4 +1,5 @@
 #include "posix-source-accessor.hh"
+#include "source-path.hh"
 #include "signals.hh"
 #include "sync.hh"
 
@@ -17,11 +18,11 @@ PosixSourceAccessor::PosixSourceAccessor()
     : PosixSourceAccessor(std::filesystem::path {})
 { }
 
-std::pair<PosixSourceAccessor, CanonPath> PosixSourceAccessor::createAtRoot(const std::filesystem::path & path)
+SourcePath PosixSourceAccessor::createAtRoot(const std::filesystem::path & path)
 {
     std::filesystem::path path2 = absPath(path.string());
     return {
-        PosixSourceAccessor { path2.root_path() },
+        make_ref<PosixSourceAccessor>(path2.root_path()),
         CanonPath { path2.relative_path().string() },
     };
 }
@@ -166,7 +167,7 @@ void PosixSourceAccessor::assertNoSymlinks(CanonPath path)
     }
 }
 
-ref<SourceAccessor> makeFSSourceAccessor()
+ref<SourceAccessor> getFSSourceAccessor()
 {
     static auto rootFS = make_ref<PosixSourceAccessor>();
     return rootFS;

src/libutil/posix-source-accessor.hh

@@ -4,6 +4,8 @@
 
 namespace nix {
 
+struct SourcePath;
+
 /**
  * A source accessor that uses the Unix filesystem.
  */
@@ -53,7 +55,7 @@ struct PosixSourceAccessor : virtual SourceAccessor
      * and
      * [`std::filesystem::path::relative_path`](https://en.cppreference.com/w/cpp/filesystem/path/relative_path).
      */
-    static std::pair<PosixSourceAccessor, CanonPath> createAtRoot(const std::filesystem::path & path);
+    static SourcePath createAtRoot(const std::filesystem::path & path);
 
 private:
 

src/libutil/source-accessor.hh

@@ -197,10 +197,13 @@ MakeError(RestrictedPathError, Error);
 /**
  * Return an accessor for the root filesystem.
  */
-ref<SourceAccessor> makeFSSourceAccessor();
+ref<SourceAccessor> getFSSourceAccessor();
 
 /**
- * Return an accessor for the filesystem rooted at `root`.
+ * Construct an accessor for the filesystem rooted at `root`. Note
+ * that it is not possible to escape `root` by appending `..` path
+ * elements, and that absolute symlinks are resolved relative to
+ * `root`.
  */
 ref<SourceAccessor> makeFSSourceAccessor(std::filesystem::path root);
 

src/libutil/source-path.hh

@@ -41,6 +41,11 @@ struct SourcePath
      */
     std::string readFile() const;
 
+    void readFile(
+        Sink & sink,
+        std::function<void(uint64_t)> sizeCallback = [](uint64_t size){}) const
+    { return accessor->readFile(path, sink, sizeCallback); }
+
     /**
      * Return whether this `SourcePath` denotes a file (of any type)
      * that exists

src/nix-store/nix-store.cc

@@ -184,7 +184,7 @@ static void opAdd(Strings opFlags, Strings opArgs)
     for (auto & i : opArgs) {
         auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(i);
         cout << fmt("%s\n", store->printStorePath(store->addToStore(
-            std::string(baseNameOf(i)), accessor, canonPath)));
+            std::string(baseNameOf(i)), {accessor, canonPath})));
     }
 }
 
@@ -209,8 +209,7 @@ static void opAddFixed(Strings opFlags, Strings opArgs)
         auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(i);
         std::cout << fmt("%s\n", store->printStorePath(store->addToStoreSlow(
             baseNameOf(i),
-            accessor,
+            {accessor, canonPath},
-            canonPath,
             method,
             hashAlgo).path));
     }
@@ -562,8 +561,7 @@ static void registerValidity(bool reregister, bool hashGiven, bool canonicalise)
 #endif
             if (!hashGiven) {
                 HashResult hash = hashPath(
-                    *store->getFSAccessor(false), CanonPath { store->printStorePath(info->path) },
+                    {store->getFSAccessor(false), CanonPath { store->printStorePath(info->path) }},
-
                     FileSerialisationMethod::Recursive, HashAlgorithm::SHA256);
                 info->narHash = hash.first;
                 info->narSize = hash.second;

src/nix/add-to-store.cc

@@ -41,9 +41,9 @@ struct CmdAddToStore : MixDryRun, StoreCommand
 
         auto storePath = dryRun
             ? store->computeStorePath(
-                *namePart, accessor, path2, caMethod, hashAlgo, {}).first
+                *namePart, {accessor, path2}, caMethod, hashAlgo, {}).first
             : store->addToStoreSlow(
-                *namePart, accessor, path2, caMethod, hashAlgo, {}).path;
+                *namePart, {accessor, path2}, caMethod, hashAlgo, {}).path;
 
         logger->cout("%s", store->printStorePath(storePath));
     }

src/nix/hash.cc

@@ -87,30 +87,29 @@ struct CmdHashBase : Command
                     return std::make_unique<HashSink>(hashAlgo);
             };
 
-            auto [accessor_, canonPath] = PosixSourceAccessor::createAtRoot(path);
+            auto path2 = PosixSourceAccessor::createAtRoot(path);
-            auto & accessor = accessor_;
             Hash h { HashAlgorithm::SHA256 }; // throwaway def to appease C++
             switch (mode) {
             case FileIngestionMethod::Flat:
             case FileIngestionMethod::Recursive:
             {
                 auto hashSink = makeSink();
-                dumpPath(accessor, canonPath, *hashSink, (FileSerialisationMethod) mode);
+                dumpPath(path2, *hashSink, (FileSerialisationMethod) mode);
                 h = hashSink->finish().first;
                 break;
             }
             case FileIngestionMethod::Git: {
                 std::function<git::DumpHook> hook;
-                hook = [&](const CanonPath & path) -> git::TreeEntry {
+                hook = [&](const SourcePath & path) -> git::TreeEntry {
                     auto hashSink = makeSink();
-                    auto mode = dump(accessor, path, *hashSink, hook);
+                    auto mode = dump(path, *hashSink, hook);
                     auto hash = hashSink->finish().first;
                     return {
                         .mode = mode,
                         .hash = hash,
                     };
                 };
-                h = hook(canonPath).hash;
+                h = hook(path2).hash;
                 break;
             }
             }

src/nix/prefetch.cc

@@ -125,9 +125,8 @@ std::tuple<StorePath, Hash> prefetchFile(
         Activity act(*logger, lvlChatty, actUnknown,
             fmt("adding '%s' to the store", url));
 
-        auto [accessor, canonPath] = PosixSourceAccessor::createAtRoot(tmpFile);
         auto info = store->addToStoreSlow(
-            *name, accessor, canonPath,
+            *name, PosixSourceAccessor::createAtRoot(tmpFile),
             ingestionMethod, hashAlgo, {}, expectedHash);
         storePath = info.path;
         assert(info.ca);

tests/unit/libutil/git.cc

@@ -154,8 +154,8 @@ TEST_F(GitTest, tree_write) {
 TEST_F(GitTest, both_roundrip) {
     using File = MemorySourceAccessor::File;
 
-    MemorySourceAccessor files;
+    auto files = make_ref<MemorySourceAccessor>();
-    files.root = File::Directory {
+    files->root = File::Directory {
         .contents {
             {
                 "foo",
@@ -189,12 +189,12 @@ TEST_F(GitTest, both_roundrip) {
     std::map<Hash, std::string> cas;
 
     std::function<DumpHook> dumpHook;
-    dumpHook = [&](const CanonPath & path) {
+    dumpHook = [&](const SourcePath & path) {
         StringSink s;
         HashSink hashSink { HashAlgorithm::SHA1 };
         TeeSink s2 { s, hashSink };
         auto mode = dump(
-            files, path, s2, dumpHook,
+            path, s2, dumpHook,
             defaultPathFilter, mockXpSettings);
         auto hash = hashSink.finish().first;
         cas.insert_or_assign(hash, std::move(s.s));
@@ -204,11 +204,11 @@ TEST_F(GitTest, both_roundrip) {
         };
     };
 
-    auto root = dumpHook(CanonPath::root);
+    auto root = dumpHook({files});
 
-    MemorySourceAccessor files2;
+    auto files2 = make_ref<MemorySourceAccessor>();
 
-    MemorySink sinkFiles2 { files2 };
+    MemorySink sinkFiles2 { *files2 };
 
     std::function<void(const Path, const Hash &, BlobMode)> mkSinkHook;
     mkSinkHook = [&](auto prefix, auto & hash, auto blobMode) {
@@ -229,7 +229,7 @@ TEST_F(GitTest, both_roundrip) {
 
     mkSinkHook("", root.hash, BlobMode::Regular);
 
-    ASSERT_EQ(files, files2);
+    ASSERT_EQ(*files, *files2);
 }
 
 TEST(GitLsRemote, parseSymrefLineWithReference) {