Merge InputAccessor into SourceAccessor

After the removal of the InputAccessor::fetchToStore() method, the
only remaining functionality in InputAccessor was `fingerprint` and
`getLastModified()`, and there is no reason to keep those in a
separate class.

src/libexpr/eval.cc

@@ -17,7 +17,7 @@
 #include "print.hh"
 #include "fs-input-accessor.hh"
 #include "filtering-input-accessor.hh"
-#include "memory-input-accessor.hh"
+#include "memory-source-accessor.hh"
 #include "signals.hh"
 #include "gc-small-vector.hh"
 #include "url.hh"
@@ -400,7 +400,7 @@ EvalState::EvalState(
     , emptyBindings(0)
     , rootFS(
         evalSettings.restrictEval || evalSettings.pureEval
-        ? ref<InputAccessor>(AllowListInputAccessor::create(makeFSInputAccessor(), {},
+        ? ref<SourceAccessor>(AllowListInputAccessor::create(makeFSInputAccessor(), {},
             [](const CanonPath & path) -> RestrictedPathError {
                 auto modeInformation = evalSettings.pureEval
                     ? "in pure evaluation mode (use '--impure' to override)"
@@ -408,8 +408,8 @@ EvalState::EvalState(
                 throw RestrictedPathError("access to absolute path '%1%' is forbidden %2%", path, modeInformation);
             }))
         : makeFSInputAccessor())
-    , corepkgsFS(makeMemoryInputAccessor())
+    , corepkgsFS(make_ref<MemorySourceAccessor>())
-    , internalFS(makeMemoryInputAccessor())
+    , internalFS(make_ref<MemorySourceAccessor>())
     , derivationInternal{corepkgsFS->addFile(
         CanonPath("derivation-internal.nix"),
         #include "primops/derivation.nix.gen.hh"
@@ -2766,12 +2766,12 @@ SourcePath resolveExprPath(SourcePath path)
         if (++followCount >= maxFollow)
             throw Error("too many symbolic links encountered while traversing the path '%s'", path);
         auto p = path.parent().resolveSymlinks() / path.baseName();
-        if (p.lstat().type != InputAccessor::tSymlink) break;
+        if (p.lstat().type != SourceAccessor::tSymlink) break;
         path = {path.accessor, CanonPath(p.readLink(), path.path.parent().value_or(CanonPath::root))};
     }
 
     /* If `path' refers to a directory, append `/default.nix'. */
-    if (path.resolveSymlinks().lstat().type == InputAccessor::tDirectory)
+    if (path.resolveSymlinks().lstat().type == SourceAccessor::tDirectory)
         return path / "default.nix";
 
     return path;

src/libexpr/eval.hh

@@ -9,7 +9,7 @@
 #include "symbol-table.hh"
 #include "config.hh"
 #include "experimental-features.hh"
-#include "input-accessor.hh"
+#include "source-accessor.hh"
 #include "search-path.hh"
 #include "repl-exit-status.hh"
 
@@ -33,7 +33,7 @@ class EvalState;
 class StorePath;
 struct SingleDerivedPath;
 enum RepairFlag : bool;
-struct MemoryInputAccessor;
+struct MemorySourceAccessor;
 namespace eval_cache {
     class EvalCache;
 }
@@ -229,18 +229,18 @@ public:
     /**
      * The accessor for the root filesystem.
      */
-    const ref<InputAccessor> rootFS;
+    const ref<SourceAccessor> rootFS;
 
     /**
      * The in-memory filesystem for <nix/...> paths.
      */
-    const ref<MemoryInputAccessor> corepkgsFS;
+    const ref<MemorySourceAccessor> corepkgsFS;
 
     /**
      * In-memory filesystem for internal, non-user-callable Nix
      * expressions like call-flake.nix.
      */
-    const ref<MemoryInputAccessor> internalFS;
+    const ref<MemorySourceAccessor> internalFS;
 
     const SourcePath derivationInternal;
 

src/libexpr/nixexpr.hh

@@ -92,10 +92,10 @@ struct ExprString : Expr
 
 struct ExprPath : Expr
 {
-    ref<InputAccessor> accessor;
+    ref<SourceAccessor> accessor;
     std::string s;
     Value v;
-    ExprPath(ref<InputAccessor> accessor, std::string s) : accessor(accessor), s(std::move(s))
+    ExprPath(ref<SourceAccessor> accessor, std::string s) : accessor(accessor), s(std::move(s))
     {
         v.mkPath(&*accessor, this->s.c_str());
     }

src/libexpr/parser-state.hh

@@ -44,7 +44,7 @@ struct ParserState
     Expr * result;
     SourcePath basePath;
     PosTable::Origin origin;
-    const ref<InputAccessor> rootFS;
+    const ref<SourceAccessor> rootFS;
     const Expr::AstSymbols & s;
 
     void dupAttr(const AttrPath & attrPath, const PosIdx pos, const PosIdx prevPos);

src/libexpr/parser.y

@@ -41,7 +41,7 @@ Expr * parseExprFromBuf(
     const SourcePath & basePath,
     SymbolTable & symbols,
     PosTable & positions,
-    const ref<InputAccessor> rootFS,
+    const ref<SourceAccessor> rootFS,
     const Expr::AstSymbols & astSymbols);
 
 }
@@ -291,7 +291,7 @@ path_start
     /* add back in the trailing '/' to the first segment */
     if ($1.p[$1.l-1] == '/' && $1.l > 1)
       path += "/";
-    $$ = new ExprPath(ref<InputAccessor>(state->rootFS), std::move(path));
+    $$ = new ExprPath(ref<SourceAccessor>(state->rootFS), std::move(path));
   }
   | HPATH {
     if (evalSettings.pureEval) {
@@ -301,7 +301,7 @@ path_start
         );
     }
     Path path(getHome() + std::string($1.p + 1, $1.l - 1));
-    $$ = new ExprPath(ref<InputAccessor>(state->rootFS), std::move(path));
+    $$ = new ExprPath(ref<SourceAccessor>(state->rootFS), std::move(path));
   }
   ;
 
@@ -430,7 +430,7 @@ Expr * parseExprFromBuf(
     const SourcePath & basePath,
     SymbolTable & symbols,
     PosTable & positions,
-    const ref<InputAccessor> rootFS,
+    const ref<SourceAccessor> rootFS,
     const Expr::AstSymbols & astSymbols)
 {
     yyscan_t scanner;

src/libexpr/primops.cc

@@ -1828,12 +1828,12 @@ static RegisterPrimOp primop_hashFile({
     .fun = prim_hashFile,
 });
 
-static Value * fileTypeToString(EvalState & state, InputAccessor::Type type)
+static Value * fileTypeToString(EvalState & state, SourceAccessor::Type type)
 {
     return
-        type == InputAccessor::Type::tRegular ? &state.vStringRegular :
+        type == SourceAccessor::Type::tRegular ? &state.vStringRegular :
-        type == InputAccessor::Type::tDirectory ? &state.vStringDirectory :
+        type == SourceAccessor::Type::tDirectory ? &state.vStringDirectory :
-        type == InputAccessor::Type::tSymlink ? &state.vStringSymlink :
+        type == SourceAccessor::Type::tSymlink ? &state.vStringSymlink :
         &state.vStringUnknown;
 }
 

src/libexpr/value.hh

@@ -7,7 +7,6 @@
 
 #include "symbol-table.hh"
 #include "value/context.hh"
-#include "input-accessor.hh"
 #include "source-path.hh"
 #include "print-options.hh"
 
@@ -217,7 +216,7 @@ public:
     };
 
     struct Path {
-        InputAccessor * accessor;
+        SourceAccessor * accessor;
         const char * path;
     };
 
@@ -335,7 +334,7 @@ public:
     void mkPath(const SourcePath & path);
     void mkPath(std::string_view path);
 
-    inline void mkPath(InputAccessor * accessor, const char * path)
+    inline void mkPath(SourceAccessor * accessor, const char * path)
     {
         finishValue(tPath, { .path = { .accessor = accessor, .path = path } });
     }

src/libfetchers/fetchers.cc

@@ -1,6 +1,5 @@
 #include "fetchers.hh"
 #include "store-api.hh"
-#include "input-accessor.hh"
 #include "source-path.hh"
 #include "fetch-to-store.hh"
 #include "json-utils.hh"
@@ -238,7 +237,7 @@ void InputScheme::checkLocks(const Input & specified, const Input & final) const
     }
 }
 
-std::pair<ref<InputAccessor>, Input> Input::getAccessor(ref<Store> store) const
+std::pair<ref<SourceAccessor>, Input> Input::getAccessor(ref<Store> store) const
 {
     try {
         auto [accessor, final] = getAccessorUnchecked(store);
@@ -252,7 +251,7 @@ std::pair<ref<InputAccessor>, Input> Input::getAccessor(ref<Store> store) const
     }
 }
 
-std::pair<ref<InputAccessor>, Input> Input::getAccessorUnchecked(ref<Store> store) const
+std::pair<ref<SourceAccessor>, Input> Input::getAccessorUnchecked(ref<Store> store) const
 {
     // FIXME: cache the accessor
 

src/libfetchers/fetchers.hh

@@ -11,7 +11,7 @@
 #include <memory>
 #include <nlohmann/json_fwd.hpp>
 
-namespace nix { class Store; class StorePath; struct InputAccessor; }
+namespace nix { class Store; class StorePath; struct SourceAccessor; }
 
 namespace nix::fetchers {
 
@@ -84,15 +84,15 @@ public:
     std::pair<StorePath, Input> fetchToStore(ref<Store> store) const;
 
     /**
-     * Return an InputAccessor that allows access to files in the
+     * Return a `SourceAccessor` that allows access to files in the
      * input without copying it to the store. Also return a possibly
      * unlocked input.
      */
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store) const;
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store) const;
 
 private:
 
-    std::pair<ref<InputAccessor>, Input> getAccessorUnchecked(ref<Store> store) const;
+    std::pair<ref<SourceAccessor>, Input> getAccessorUnchecked(ref<Store> store) const;
 
 public:
 
@@ -185,7 +185,7 @@ struct InputScheme
         std::string_view contents,
         std::optional<std::string> commitMsg) const;
 
-    virtual std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const = 0;
+    virtual std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const = 0;
 
     /**
      * Is this `InputScheme` part of an experimental feature?

src/libfetchers/filtering-input-accessor.cc

@@ -13,13 +13,13 @@ bool FilteringInputAccessor::pathExists(const CanonPath & path)
     return isAllowed(path) && next->pathExists(prefix / path);
 }
 
-std::optional<InputAccessor::Stat> FilteringInputAccessor::maybeLstat(const CanonPath & path)
+std::optional<SourceAccessor::Stat> FilteringInputAccessor::maybeLstat(const CanonPath & path)
 {
     checkAccess(path);
     return next->maybeLstat(prefix / path);
 }
 
-InputAccessor::DirEntries FilteringInputAccessor::readDirectory(const CanonPath & path)
+SourceAccessor::DirEntries FilteringInputAccessor::readDirectory(const CanonPath & path)
 {
     checkAccess(path);
     DirEntries entries;
@@ -54,7 +54,7 @@ struct AllowListInputAccessorImpl : AllowListInputAccessor
     std::set<CanonPath> allowedPrefixes;
 
     AllowListInputAccessorImpl(
-        ref<InputAccessor> next,
+        ref<SourceAccessor> next,
         std::set<CanonPath> && allowedPrefixes,
         MakeNotAllowedError && makeNotAllowedError)
         : AllowListInputAccessor(SourcePath(next), std::move(makeNotAllowedError))
@@ -73,7 +73,7 @@ struct AllowListInputAccessorImpl : AllowListInputAccessor
 };
 
 ref<AllowListInputAccessor> AllowListInputAccessor::create(
-    ref<InputAccessor> next,
+    ref<SourceAccessor> next,
     std::set<CanonPath> && allowedPrefixes,
     MakeNotAllowedError && makeNotAllowedError)
 {

src/libfetchers/filtering-input-accessor.hh

@@ -1,6 +1,5 @@
 #pragma once
 
-#include "input-accessor.hh"
 #include "source-path.hh"
 
 namespace nix {
@@ -17,9 +16,9 @@ typedef std::function<RestrictedPathError(const CanonPath & path)> MakeNotAllowe
  * control. Subclasses should override `isAllowed()` to implement an
  * access control policy. The error message is customized at construction.
  */
-struct FilteringInputAccessor : InputAccessor
+struct FilteringInputAccessor : SourceAccessor
 {
-    ref<InputAccessor> next;
+    ref<SourceAccessor> next;
     CanonPath prefix;
     MakeNotAllowedError makeNotAllowedError;
 
@@ -67,7 +66,7 @@ struct AllowListInputAccessor : public FilteringInputAccessor
     virtual void allowPrefix(CanonPath prefix) = 0;
 
     static ref<AllowListInputAccessor> create(
-        ref<InputAccessor> next,
+        ref<SourceAccessor> next,
         std::set<CanonPath> && allowedPrefixes,
         MakeNotAllowedError && makeNotAllowedError);
 

src/libfetchers/fs-input-accessor.cc

@@ -4,22 +4,17 @@
 
 namespace nix {
 
-struct FSInputAccessor : InputAccessor, PosixSourceAccessor
+ref<SourceAccessor> makeFSInputAccessor()
 {
-    using PosixSourceAccessor::PosixSourceAccessor;
+    return make_ref<PosixSourceAccessor>();
-};
-
-ref<InputAccessor> makeFSInputAccessor()
-{
-    return make_ref<FSInputAccessor>();
 }
 
-ref<InputAccessor> makeFSInputAccessor(std::filesystem::path root)
+ref<SourceAccessor> makeFSInputAccessor(std::filesystem::path root)
 {
-    return make_ref<FSInputAccessor>(std::move(root));
+    return make_ref<PosixSourceAccessor>(std::move(root));
 }
 
-ref<InputAccessor> makeStorePathAccessor(
+ref<SourceAccessor> makeStorePathAccessor(
     ref<Store> store,
     const StorePath & storePath)
 {

src/libfetchers/fs-input-accessor.hh

@@ -1,6 +1,5 @@
 #pragma once
 
-#include "input-accessor.hh"
 #include "source-path.hh"
 
 namespace nix {
@@ -8,11 +7,11 @@ namespace nix {
 class StorePath;
 class Store;
 
-ref<InputAccessor> makeFSInputAccessor();
+ref<SourceAccessor> makeFSInputAccessor();
 
-ref<InputAccessor> makeFSInputAccessor(std::filesystem::path root);
+ref<SourceAccessor> makeFSInputAccessor(std::filesystem::path root);
 
-ref<InputAccessor> makeStorePathAccessor(
+ref<SourceAccessor> makeStorePathAccessor(
     ref<Store> store,
     const StorePath & storePath);
 

src/libfetchers/git-utils.cc

@@ -1,8 +1,5 @@
 #include "git-utils.hh"
 #include "fs-input-accessor.hh"
-#include "input-accessor.hh"
-#include "filtering-input-accessor.hh"
-#include "memory-input-accessor.hh"
 #include "cache.hh"
 #include "finally.hh"
 #include "processes.hh"
@@ -338,9 +335,9 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
      */
     ref<GitInputAccessor> getRawAccessor(const Hash & rev);
 
-    ref<InputAccessor> getAccessor(const Hash & rev, bool exportIgnore) override;
+    ref<SourceAccessor> getAccessor(const Hash & rev, bool exportIgnore) override;
 
-    ref<InputAccessor> getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError e) override;
+    ref<SourceAccessor> getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError e) override;
 
     ref<GitFileSystemObjectSink> getFileSystemObjectSink() override;
 
@@ -477,7 +474,7 @@ ref<GitRepo> GitRepo::openRepo(const std::filesystem::path & path, bool create,
 /**
  * Raw git tree input accessor.
  */
-struct GitInputAccessor : InputAccessor
+struct GitInputAccessor : SourceAccessor
 {
     ref<GitRepoImpl> repo;
     Tree root;
@@ -710,7 +707,7 @@ struct GitExportIgnoreInputAccessor : CachingFilteringInputAccessor {
     ref<GitRepoImpl> repo;
     std::optional<Hash> rev;
 
-    GitExportIgnoreInputAccessor(ref<GitRepoImpl> repo, ref<InputAccessor> next, std::optional<Hash> rev)
+    GitExportIgnoreInputAccessor(ref<GitRepoImpl> repo, ref<SourceAccessor> next, std::optional<Hash> rev)
         : CachingFilteringInputAccessor(next, [&](const CanonPath & path) {
             return RestrictedPathError(fmt("'%s' does not exist because it was fetched with exportIgnore enabled", path));
         })
@@ -928,7 +925,7 @@ ref<GitInputAccessor> GitRepoImpl::getRawAccessor(const Hash & rev)
     return make_ref<GitInputAccessor>(self, rev);
 }
 
-ref<InputAccessor> GitRepoImpl::getAccessor(const Hash & rev, bool exportIgnore)
+ref<SourceAccessor> GitRepoImpl::getAccessor(const Hash & rev, bool exportIgnore)
 {
     auto self = ref<GitRepoImpl>(shared_from_this());
     ref<GitInputAccessor> rawGitAccessor = getRawAccessor(rev);
@@ -940,20 +937,20 @@ ref<InputAccessor> GitRepoImpl::getAccessor(const Hash & rev, bool exportIgnore)
     }
 }
 
-ref<InputAccessor> GitRepoImpl::getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError makeNotAllowedError)
+ref<SourceAccessor> GitRepoImpl::getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError makeNotAllowedError)
 {
     auto self = ref<GitRepoImpl>(shared_from_this());
     /* In case of an empty workdir, return an empty in-memory tree. We
        cannot use AllowListInputAccessor because it would return an
        error for the root (and we can't add the root to the allow-list
        since that would allow access to all its children). */
-    ref<InputAccessor> fileAccessor =
+    ref<SourceAccessor> fileAccessor =
         wd.files.empty()
-        ? makeEmptyInputAccessor()
+        ? makeEmptySourceAccessor()
         : AllowListInputAccessor::create(
             makeFSInputAccessor(path),
             std::set<CanonPath> { wd.files },
-            std::move(makeNotAllowedError)).cast<InputAccessor>();
+            std::move(makeNotAllowedError)).cast<SourceAccessor>();
     if (exportIgnore)
         return make_ref<GitExportIgnoreInputAccessor>(self, fileAccessor, std::nullopt);
     else

src/libfetchers/git-utils.hh

@@ -1,7 +1,6 @@
 #pragma once
 
 #include "filtering-input-accessor.hh"
-#include "input-accessor.hh"
 #include "fs-sink.hh"
 
 namespace nix {
@@ -75,9 +74,9 @@ struct GitRepo
 
     virtual bool hasObject(const Hash & oid) = 0;
 
-    virtual ref<InputAccessor> getAccessor(const Hash & rev, bool exportIgnore) = 0;
+    virtual ref<SourceAccessor> getAccessor(const Hash & rev, bool exportIgnore) = 0;
 
-    virtual ref<InputAccessor> getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError makeNotAllowedError) = 0;
+    virtual ref<SourceAccessor> getAccessor(const WorkdirInfo & wd, bool exportIgnore, MakeNotAllowedError makeNotAllowedError) = 0;
 
     virtual ref<GitFileSystemObjectSink> getFileSystemObjectSink() = 0;
 

src/libfetchers/github.cc

@@ -272,7 +272,7 @@ struct GitArchiveInputScheme : InputScheme
         return {std::move(input), tarballInfo};
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         auto [input, tarballInfo] = downloadArchive(store, _input);
 

src/libfetchers/indirect.cc

@@ -97,7 +97,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const override
     {
         throw Error("indirect input '%s' cannot be fetched directly", input.to_string());
     }

src/libfetchers/memory-input-accessor.cc

@@ -1,29 +0,0 @@
-#include "memory-input-accessor.hh"
-#include "memory-source-accessor.hh"
-#include "source-path.hh"
-
-namespace nix {
-
-struct MemoryInputAccessorImpl : MemoryInputAccessor, MemorySourceAccessor
-{
-    SourcePath addFile(CanonPath path, std::string && contents) override
-    {
-        return {
-            ref(shared_from_this()),
-            MemorySourceAccessor::addFile(path, std::move(contents))
-        };
-    }
-};
-
-ref<MemoryInputAccessor> makeMemoryInputAccessor()
-{
-    return make_ref<MemoryInputAccessorImpl>();
-}
-
-ref<InputAccessor> makeEmptyInputAccessor()
-{
-    static auto empty = makeMemoryInputAccessor().cast<InputAccessor>();
-    return empty;
-}
-
-}

src/libfetchers/memory-input-accessor.hh

@@ -1,18 +0,0 @@
-#include "input-accessor.hh"
-#include "source-path.hh"
-
-namespace nix {
-
-/**
- * An input accessor for an in-memory file system.
- */
-struct MemoryInputAccessor : InputAccessor
-{
-    virtual SourcePath addFile(CanonPath path, std::string && contents) = 0;
-};
-
-ref<MemoryInputAccessor> makeMemoryInputAccessor();
-
-ref<InputAccessor> makeEmptyInputAccessor();
-
-}

src/libfetchers/mounted-input-accessor.cc

@@ -2,11 +2,11 @@
 
 namespace nix {
 
-struct MountedInputAccessor : InputAccessor
+struct MountedInputAccessor : SourceAccessor
 {
-    std::map<CanonPath, ref<InputAccessor>> mounts;
+    std::map<CanonPath, ref<SourceAccessor>> mounts;
 
-    MountedInputAccessor(std::map<CanonPath, ref<InputAccessor>> _mounts)
+    MountedInputAccessor(std::map<CanonPath, ref<SourceAccessor>> _mounts)
         : mounts(std::move(_mounts))
     {
         displayPrefix.clear();
@@ -53,7 +53,7 @@ struct MountedInputAccessor : InputAccessor
         return displayPrefix + accessor->showPath(subpath) + displaySuffix;
     }
 
-    std::pair<ref<InputAccessor>, CanonPath> resolve(CanonPath path)
+    std::pair<ref<SourceAccessor>, CanonPath> resolve(CanonPath path)
     {
         // Find the nearest parent of `path` that is a mount point.
         std::vector<std::string> subpath;
@@ -71,7 +71,7 @@ struct MountedInputAccessor : InputAccessor
     }
 };
 
-ref<InputAccessor> makeMountedInputAccessor(std::map<CanonPath, ref<InputAccessor>> mounts)
+ref<SourceAccessor> makeMountedInputAccessor(std::map<CanonPath, ref<SourceAccessor>> mounts)
 {
     return make_ref<MountedInputAccessor>(std::move(mounts));
 }

src/libfetchers/mounted-input-accessor.hh

@@ -1,9 +1,9 @@
 #pragma once
 
-#include "input-accessor.hh"
+#include "source-accessor.hh"
 
 namespace nix {
 
-ref<InputAccessor> makeMountedInputAccessor(std::map<CanonPath, ref<InputAccessor>> mounts);
+ref<SourceAccessor> makeMountedInputAccessor(std::map<CanonPath, ref<SourceAccessor>> mounts);
 
 }

src/libfetchers/path.cc

@@ -114,7 +114,7 @@ struct PathInputScheme : InputScheme
         throw Error("cannot fetch input '%s' because it uses a relative path", input.to_string());
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         Input input(_input);
         std::string absPath;

src/libfetchers/tarball.cc

@@ -297,7 +297,7 @@ struct FileInputScheme : CurlInputScheme
                 : (!requireTree && !hasTarballExtension(url.path)));
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         auto input(_input);
 
@@ -332,7 +332,7 @@ struct TarballInputScheme : CurlInputScheme
                 : (requireTree || hasTarballExtension(url.path)));
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         auto input(_input);
 

src/libfetchers/tarball.hh

@@ -8,7 +8,7 @@
 
 namespace nix {
 class Store;
-struct InputAccessor;
+struct SourceAccessor;
 }
 
 namespace nix::fetchers {
@@ -32,7 +32,7 @@ struct DownloadTarballResult
     Hash treeHash;
     time_t lastModified;
     std::optional<std::string> immutableUrl;
-    ref<InputAccessor> accessor;
+    ref<SourceAccessor> accessor;
 };
 
 /**

src/libfetchers/unix/git.cc

@@ -495,7 +495,7 @@ struct GitInputScheme : InputScheme
         }
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessorFromCommit(
+    std::pair<ref<SourceAccessor>, Input> getAccessorFromCommit(
         ref<Store> store,
         RepoInfo & repoInfo,
         Input && input) const
@@ -629,7 +629,7 @@ struct GitInputScheme : InputScheme
            input accessor consisting of the accessor for the top-level
            repo and the accessors for the submodules. */
         if (getSubmodulesAttr(input)) {
-            std::map<CanonPath, nix::ref<InputAccessor>> mounts;
+            std::map<CanonPath, nix::ref<SourceAccessor>> mounts;
 
             for (auto & [submodule, submoduleRev] : repo->getSubmodules(rev, exportIgnore)) {
                 auto resolved = repo->resolveSubmoduleUrl(submodule.url);
@@ -665,7 +665,7 @@ struct GitInputScheme : InputScheme
         return {accessor, std::move(input)};
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessorFromWorkdir(
+    std::pair<ref<SourceAccessor>, Input> getAccessorFromWorkdir(
         ref<Store> store,
         RepoInfo & repoInfo,
         Input && input) const
@@ -679,7 +679,7 @@ struct GitInputScheme : InputScheme
 
         auto exportIgnore = getExportIgnoreAttr(input);
 
-        ref<InputAccessor> accessor =
+        ref<SourceAccessor> accessor =
             repo->getAccessor(repoInfo.workdirInfo,
                 exportIgnore,
                 makeNotAllowedError(repoInfo.url));
@@ -690,7 +690,7 @@ struct GitInputScheme : InputScheme
            consisting of the accessor for the top-level repo and the
            accessors for the submodule workdirs. */
         if (getSubmodulesAttr(input) && !repoInfo.workdirInfo.submodules.empty()) {
-            std::map<CanonPath, nix::ref<InputAccessor>> mounts;
+            std::map<CanonPath, nix::ref<SourceAccessor>> mounts;
 
             for (auto & submodule : repoInfo.workdirInfo.submodules) {
                 auto submodulePath = CanonPath(repoInfo.url) / submodule.path;
@@ -755,7 +755,7 @@ struct GitInputScheme : InputScheme
         return {accessor, std::move(input)};
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         Input input(_input);
 

src/libfetchers/unix/mercurial.cc

@@ -346,7 +346,7 @@ struct MercurialInputScheme : InputScheme
         return makeResult(infoAttrs, std::move(storePath));
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    std::pair<ref<SourceAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         Input input(_input);
 

src/libutil/input-accessor.hh

@@ -1,27 +0,0 @@
-#pragma once
-///@file
-
-#include "source-accessor.hh"
-#include "ref.hh"
-#include "repair-flag.hh"
-
-namespace nix {
-
-MakeError(RestrictedPathError, Error);
-
-struct InputAccessor : virtual SourceAccessor, std::enable_shared_from_this<InputAccessor>
-{
-    std::optional<std::string> fingerprint;
-
-    /**
-     * Return the maximum last-modified time of the files in this
-     * tree, if available.
-     */
-    virtual std::optional<time_t> getLastModified()
-    {
-        return std::nullopt;
-    }
-
-};
-
-}

src/libutil/memory-source-accessor.cc

@@ -108,7 +108,7 @@ std::string MemorySourceAccessor::readLink(const CanonPath & path)
         throw Error("file '%s' is not a symbolic link", path);
 }
 
-CanonPath MemorySourceAccessor::addFile(CanonPath path, std::string && contents)
+SourcePath MemorySourceAccessor::addFile(CanonPath path, std::string && contents)
 {
     auto * f = open(path, File { File::Regular {} });
     if (!f)
@@ -118,7 +118,7 @@ CanonPath MemorySourceAccessor::addFile(CanonPath path, std::string && contents)
     else
         throw Error("file '%s' is not a regular file", path);
 
-    return path;
+    return SourcePath{ref(shared_from_this()), path};
 }
 
 
@@ -184,4 +184,10 @@ void MemorySink::createSymlink(const Path & path, const std::string & target)
         throw Error("file '%s' is not a symbolic link", path);
 }
 
+ref<SourceAccessor> makeEmptySourceAccessor()
+{
+    static auto empty = make_ref<MemorySourceAccessor>().cast<SourceAccessor>();
+    return empty;
+}
+
 }

src/libutil/memory-source-accessor.hh

@@ -1,4 +1,4 @@
-#include "source-accessor.hh"
+#include "source-path.hh"
 #include "fs-sink.hh"
 #include "variant-wrapper.hh"
 
@@ -69,7 +69,7 @@ struct MemorySourceAccessor : virtual SourceAccessor
      */
     File * open(const CanonPath & path, std::optional<File> create);
 
-    CanonPath addFile(CanonPath path, std::string && contents);
+    SourcePath addFile(CanonPath path, std::string && contents);
 };
 
 /**

src/libutil/source-accessor.hh

@@ -35,7 +35,7 @@ enum class SymlinkResolution {
  * filesystem-like entities (such as the real filesystem, tarballs or
  * Git repositories).
  */
-struct SourceAccessor
+struct SourceAccessor : std::enable_shared_from_this<SourceAccessor>
 {
     const size_t number;
 
@@ -168,6 +168,30 @@ struct SourceAccessor
     CanonPath resolveSymlinks(
         const CanonPath & path,
         SymlinkResolution mode = SymlinkResolution::Full);
+
+    /**
+     * A string that uniquely represents the contents of this
+     * accessor. This is used for caching lookups (see `fetchToStore()`).
+     */
+    std::optional<std::string> fingerprint;
+
+    /**
+     * Return the maximum last-modified time of the files in this
+     * tree, if available.
+     */
+    virtual std::optional<time_t> getLastModified()
+    { return std::nullopt; }
 };
 
+/**
+ * Return a source accessor that contains only an empty root directory.
+ */
+ref<SourceAccessor> makeEmptySourceAccessor();
+
+/**
+ * Exception thrown when accessing a filtered path (see
+ * `FilteringInputAccessor`).
+ */
+MakeError(RestrictedPathError, Error);
+
 }

src/libutil/source-path.cc

@@ -18,13 +18,13 @@ std::string SourcePath::readFile() const
 bool SourcePath::pathExists() const
 { return accessor->pathExists(path); }
 
-InputAccessor::Stat SourcePath::lstat() const
+SourceAccessor::Stat SourcePath::lstat() const
 { return accessor->lstat(path); }
 
-std::optional<InputAccessor::Stat> SourcePath::maybeLstat() const
+std::optional<SourceAccessor::Stat> SourcePath::maybeLstat() const
 { return accessor->maybeLstat(path); }
 
-InputAccessor::DirEntries SourcePath::readDirectory() const
+SourceAccessor::DirEntries SourcePath::readDirectory() const
 { return accessor->readDirectory(path); }
 
 std::string SourcePath::readLink() const

src/libutil/source-path.hh

@@ -7,7 +7,7 @@
 
 #include "ref.hh"
 #include "canon-path.hh"
-#include "input-accessor.hh"
+#include "source-accessor.hh"
 
 namespace nix {
 
@@ -19,10 +19,10 @@ namespace nix {
  */
 struct SourcePath
 {
-    ref<InputAccessor> accessor;
+    ref<SourceAccessor> accessor;
     CanonPath path;
 
-    SourcePath(ref<InputAccessor> accessor, CanonPath path = CanonPath::root)
+    SourcePath(ref<SourceAccessor> accessor, CanonPath path = CanonPath::root)
         : accessor(std::move(accessor))
         , path(std::move(path))
     { }
@@ -51,19 +51,19 @@ struct SourcePath
      * Return stats about this `SourcePath`, or throw an exception if
      * it doesn't exist.
      */
-    InputAccessor::Stat lstat() const;
+    SourceAccessor::Stat lstat() const;
 
     /**
      * Return stats about this `SourcePath`, or std::nullopt if it
      * doesn't exist.
      */
-    std::optional<InputAccessor::Stat> maybeLstat() const;
+    std::optional<SourceAccessor::Stat> maybeLstat() const;
 
     /**
      * If this `SourcePath` denotes a directory (not a symlink),
      * return its directory entries; otherwise throw an error.
      */
-    InputAccessor::DirEntries readDirectory() const;
+    SourceAccessor::DirEntries readDirectory() const;
 
     /**
      * If this `SourcePath` denotes a symlink, return its target;

src/nix-env/nix-env.cc

@@ -94,11 +94,11 @@ static bool parseInstallSourceOptions(Globals & globals,
 }
 
 
-static bool isNixExpr(const SourcePath & path, struct InputAccessor::Stat & st)
+static bool isNixExpr(const SourcePath & path, struct SourceAccessor::Stat & st)
 {
     return
-        st.type == InputAccessor::tRegular
+        st.type == SourceAccessor::tRegular
-        || (st.type == InputAccessor::tDirectory && (path / "default.nix").resolveSymlinks().pathExists());
+        || (st.type == SourceAccessor::tDirectory && (path / "default.nix").resolveSymlinks().pathExists());
 }
 
 
@@ -119,14 +119,14 @@ static void getAllExprs(EvalState & state,
 
         auto path2 = (path / i).resolveSymlinks();
 
-        InputAccessor::Stat st;
+        SourceAccessor::Stat st;
         try {
             st = path2.lstat();
         } catch (Error &) {
             continue; // ignore dangling symlinks in ~/.nix-defexpr
         }
 
-        if (isNixExpr(path2, st) && (st.type != InputAccessor::tRegular || hasSuffix(path2.baseName(), ".nix"))) {
+        if (isNixExpr(path2, st) && (st.type != SourceAccessor::tRegular || hasSuffix(path2.baseName(), ".nix"))) {
             /* Strip off the `.nix' filename suffix (if applicable),
                otherwise the attribute cannot be selected with the
                `-A' option.  Useful if you want to stick a Nix
@@ -149,7 +149,7 @@ static void getAllExprs(EvalState & state,
                 throw Error("too many Nix expressions in directory '%1%'", path);
             attrs.alloc(attrName).mkApp(&state.getBuiltin("import"), vArg);
         }
-        else if (st.type == InputAccessor::tDirectory)
+        else if (st.type == SourceAccessor::tDirectory)
             /* `path2' is a directory (with no default.nix in it);
                recurse into it. */
             getAllExprs(state, path2, seen, attrs);
@@ -171,7 +171,7 @@ static void loadSourceExpr(EvalState & state, const SourcePath & path, Value & v
        set flat, not nested, to make it easier for a user to have a
        ~/.nix-defexpr directory that includes some system-wide
        directory). */
-    else if (st.type == InputAccessor::tDirectory) {
+    else if (st.type == SourceAccessor::tDirectory) {
         auto attrs = state.buildBindings(maxAttrs);
         attrs.insert(state.symbols.create("_combineChannels"), &state.vEmptyList);
         StringSet seen;

src/nix/main.cc

@@ -14,7 +14,7 @@
 #include "finally.hh"
 #include "loggers.hh"
 #include "markdown.hh"
-#include "memory-input-accessor.hh"
+#include "memory-source-accessor.hh"
 #include "terminal.hh"
 #include "users.hh"
 

tests/unit/libexpr/primops.cc

@@ -2,7 +2,6 @@
 #include <gtest/gtest.h>
 
 #include "eval-settings.hh"
-#include "memory-input-accessor.hh"
 
 #include "tests/libexpr.hh"