diff --git a/src/libcmd/common-eval-args.cc b/src/libcmd/common-eval-args.cc
index 0a4b7d114..14837de92 100644
--- a/src/libcmd/common-eval-args.cc
+++ b/src/libcmd/common-eval-args.cc
@@ -94,7 +94,7 @@ SourcePath lookupFileArg(EvalState & state, std::string_view s)
     if (isUri(s)) {
         auto storePath = fetchers::downloadTarball(
             state.store, resolveUri(s), "source", false).first;
-        auto accessor = makeFSInputAccessor(CanonPath(state.store->toRealPath(storePath)));
+        auto accessor = makeStorePathAccessor(state.store, storePath);
         state.registerAccessor(accessor);
         return {accessor, CanonPath::root};
     } else if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 71228743b..4d69a5d75 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -791,7 +791,7 @@ SourcePath EvalState::findFile(SearchPath & searchPath, const std::string_view p
         try {
             auto storePath = fetchers::downloadTarball(
                 store, resolveUri(elem.second), "source", false).first;
-            auto accessor = makeFSInputAccessor(CanonPath(store->toRealPath(storePath)));
+            auto accessor = makeStorePathAccessor(store, storePath);
             registerAccessor(accessor);
             res.emplace(SourcePath {accessor, CanonPath::root});
         } catch (FileTransferError & e) {
diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 66063a324..5b3dde436 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -115,32 +115,40 @@ bool Input::contains(const Input & other) const
 
 std::pair<StorePath, Input> Input::fetchToStore(ref<Store> store) const
 {
-    if (!scheme)
-        throw Error("cannot fetch unsupported input '%s'", attrsToJSON(toAttrs()));
-
     auto [storePath, input] = [&]() -> std::pair<StorePath, Input> {
         try {
-            return scheme->fetchToStore(store, *this);
+            auto [accessor, input2] = getAccessor(store);
+
+            // FIXME: add an optimisation for the case where the
+            // accessor is an FSInputAccessor pointing to a store
+            // path.
+            auto source = sinkToSource([&, accessor{accessor}](Sink & sink) {
+                accessor->dumpPath(CanonPath::root, sink);
+            });
+
+            auto storePath = store->addToStoreFromDump(*source, input2.getName());
+
+            return {storePath, input2};
         } catch (Error & e) {
             e.addTrace({}, "while fetching the input '%s'", to_string());
             throw;
         }
     }();
 
-    checkLocked(*store, storePath, input);
-
     return {std::move(storePath), input};
 }
 
-void Input::checkLocked(Store & store, const StorePath & storePath, Input & input) const
+void Input::checkLocks(Input & input) const
 {
+    #if 0
     auto narHash = store.queryPathInfo(storePath)->narHash;
     input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
+    #endif
 
     if (auto prevNarHash = getNarHash()) {
-        if (narHash != *prevNarHash)
-            throw Error((unsigned int) 102, "NAR hash mismatch in input '%s' (%s), expected '%s', got '%s'",
-                to_string(), store.printStorePath(storePath), prevNarHash->to_string(SRI, true), narHash.to_string(SRI, true));
+        if (input.getNarHash() != prevNarHash)
+            throw Error((unsigned int) 102, "NAR hash mismatch in input '%s', expected '%s'",
+                to_string(), prevNarHash->to_string(SRI, true));
     }
 
     if (auto prevLastModified = getLastModified()) {
@@ -155,9 +163,12 @@ void Input::checkLocked(Store & store, const StorePath & storePath, Input & inpu
                 input.to_string(), *prevRevCount);
     }
 
+    // FIXME
+    #if 0
     input.locked = true;
 
     assert(input.hasAllInfo());
+    #endif
 }
 
 std::pair<ref<InputAccessor>, Input> Input::getAccessor(ref<Store> store) const
@@ -166,7 +177,9 @@ std::pair<ref<InputAccessor>, Input> Input::getAccessor(ref<Store> store) const
         throw Error("cannot fetch unsupported input '%s'", attrsToJSON(toAttrs()));
 
     try {
-        return scheme->getAccessor(store, *this);
+        auto [accessor, final] = scheme->getAccessor(store, *this);
+        checkLocks(final);
+        return {accessor, std::move(final)};
     } catch (Error & e) {
         e.addTrace({}, "while fetching the input '%s'", to_string());
         throw;
@@ -262,7 +275,7 @@ std::optional<std::string> Input::getFingerprint(ref<Store> store) const
     return scheme->getFingerprint(store, *this);
 }
 
-ParsedURL InputScheme::toURL(const Input & input)
+ParsedURL InputScheme::toURL(const Input & input) const
 {
     throw Error("don't know how to convert input '%s' to a URL", attrsToJSON(input.attrs));
 }
@@ -270,7 +283,7 @@ ParsedURL InputScheme::toURL(const Input & input)
 Input InputScheme::applyOverrides(
     const Input & input,
     std::optional<std::string> ref,
-    std::optional<Hash> rev)
+    std::optional<Hash> rev) const
 {
     if (ref)
         throw Error("don't know how to set branch/tag name of input '%s' to '%s'", input.to_string(), *ref);
@@ -288,31 +301,9 @@ void InputScheme::putFile(
     throw Error("input '%s' does not support modifying file '%s'", input.to_string(), path);
 }
 
-void InputScheme::clone(const Input & input, const Path & destDir)
+void InputScheme::clone(const Input & input, const Path & destDir) const
 {
     throw Error("do not know how to clone input '%s'", input.to_string());
 }
 
-std::pair<StorePath, Input> InputScheme::fetchToStore(ref<Store> store, const Input & input)
-{
-    auto [accessor, input2] = getAccessor(store, input);
-
-    auto source = sinkToSource([&, accessor{accessor}](Sink & sink) {
-        accessor->dumpPath(CanonPath::root, sink);
-    });
-
-    auto storePath = store->addToStoreFromDump(*source, "source");
-
-    return {storePath, input2};
-}
-
-std::pair<ref<InputAccessor>, Input> InputScheme::getAccessor(ref<Store> store, const Input & input)
-{
-    auto [storePath, input2] = fetchToStore(store, input);
-
-    input.checkLocked(*store, storePath, input2);
-
-    return {makeFSInputAccessor(CanonPath(store->toRealPath(storePath))), input2};
-}
-
 }
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 97bc4c20f..2a03dcaad 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -100,7 +100,7 @@ public:
 
 private:
 
-    void checkLocked(Store & store, const StorePath & storePath, Input & input) const;
+    void checkLocks(Input & input) const;
 };
 
 /* The InputScheme represents a type of fetcher.  Each fetcher
@@ -116,20 +116,20 @@ struct InputScheme
     virtual ~InputScheme()
     { }
 
-    virtual std::optional<Input> inputFromURL(const ParsedURL & url) = 0;
+    virtual std::optional<Input> inputFromURL(const ParsedURL & url) const = 0;
 
-    virtual std::optional<Input> inputFromAttrs(const Attrs & attrs) = 0;
+    virtual std::optional<Input> inputFromAttrs(const Attrs & attrs) const = 0;
 
-    virtual ParsedURL toURL(const Input & input);
+    virtual ParsedURL toURL(const Input & input) const;
 
-    virtual bool hasAllInfo(const Input & input) = 0;
+    virtual bool hasAllInfo(const Input & input) const = 0;
 
     virtual Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev);
+        std::optional<Hash> rev) const;
 
-    virtual void clone(const Input & input, const Path & destDir);
+    virtual void clone(const Input & input, const Path & destDir) const;
 
     virtual void putFile(
         const Input & input,
@@ -137,13 +137,7 @@ struct InputScheme
         std::string_view contents,
         std::optional<std::string> commitMsg) const;
 
-    /* Note: the default implementations of fetchToStore() and
-       getAccessor() are defined using the other, so implementations
-       have to override at least one. */
-
-    virtual std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & input);
-
-    virtual std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input);
+    virtual std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const = 0;
 
     virtual std::optional<CanonPath> isRelative(const Input & input) const
     { return std::nullopt; }
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index f1cbbdae3..2218f594b 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -140,7 +140,7 @@ bool isNotDotGitDirectory(const Path & path)
 
 struct GitInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "git" &&
             url.scheme != "git+http" &&
@@ -169,7 +169,7 @@ struct GitInputScheme : InputScheme
         return inputFromAttrs(attrs);
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "git") return {};
 
@@ -192,7 +192,7 @@ struct GitInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         if (url.scheme != "git") url.scheme = "git+" + url.scheme;
@@ -203,7 +203,7 @@ struct GitInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         bool maybeDirty = !input.getRef();
         bool shallow = maybeGetBoolAttr(input.attrs, "shallow").value_or(false);
@@ -215,7 +215,7 @@ struct GitInputScheme : InputScheme
     Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto res(input);
         if (rev) res.attrs.insert_or_assign("rev", rev->gitRev());
@@ -225,7 +225,7 @@ struct GitInputScheme : InputScheme
         return res;
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto repoInfo = getRepoInfo(input);
 
@@ -394,7 +394,7 @@ struct GitInputScheme : InputScheme
         return repoInfo;
     }
 
-    std::set<CanonPath> listFiles(const RepoInfo & repoInfo)
+    std::set<CanonPath> listFiles(const RepoInfo & repoInfo) const
     {
         auto gitOpts = Strings({ "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "ls-files", "-z" });
         if (repoInfo.submodules)
@@ -409,14 +409,14 @@ struct GitInputScheme : InputScheme
         return res;
     }
 
-    void updateRev(Input & input, const RepoInfo & repoInfo, const std::string & ref)
+    void updateRev(Input & input, const RepoInfo & repoInfo, const std::string & ref) const
     {
         if (!input.getRev())
             input.attrs.insert_or_assign("rev",
                 Hash::parseAny(chomp(runProgram("git", true, { "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "rev-parse", ref })), htSHA1).gitRev());
     }
 
-    uint64_t getLastModified(const RepoInfo & repoInfo, const std::string & repoDir, const std::string & ref)
+    uint64_t getLastModified(const RepoInfo & repoInfo, const std::string & repoDir, const std::string & ref) const
     {
         return
             repoInfo.hasHead
@@ -426,7 +426,7 @@ struct GitInputScheme : InputScheme
             : 0;
     }
 
-    uint64_t getRevCount(const RepoInfo & repoInfo, const std::string & repoDir, const Hash & rev)
+    uint64_t getRevCount(const RepoInfo & repoInfo, const std::string & repoDir, const Hash & rev) const
     {
         // FIXME: cache this.
         return
@@ -437,7 +437,7 @@ struct GitInputScheme : InputScheme
             : 0;
     }
 
-    std::string getDefaultRef(const RepoInfo & repoInfo)
+    std::string getDefaultRef(const RepoInfo & repoInfo) const
     {
         auto head = repoInfo.isLocal
             ? readHead(repoInfo.url)
@@ -449,11 +449,14 @@ struct GitInputScheme : InputScheme
         return *head;
     }
 
-    std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & _input) override
+    StorePath fetchToStore(
+        ref<Store> store,
+        RepoInfo & repoInfo,
+        Input & input) const
     {
-        Input input(_input);
+        assert(!repoInfo.isDirty);
 
-        auto repoInfo = getRepoInfo(input);
+        auto origRev = input.getRev();
 
         std::string name = input.getName();
 
@@ -466,15 +469,21 @@ struct GitInputScheme : InputScheme
             });
         };
 
-        auto makeResult = [&](const Attrs & infoAttrs, StorePath && storePath)
-            -> std::pair<StorePath, Input>
+        auto makeResult = [&](const Attrs & infoAttrs, const StorePath & storePath) -> StorePath
         {
             assert(input.getRev());
-            assert(!_input.getRev() || _input.getRev() == input.getRev());
+            assert(!origRev || origRev == input.getRev());
             if (!repoInfo.shallow)
                 input.attrs.insert_or_assign("revCount", getIntAttr(infoAttrs, "revCount"));
             input.attrs.insert_or_assign("lastModified", getIntAttr(infoAttrs, "lastModified"));
-            return {std::move(storePath), input};
+
+            // FIXME: remove?
+            //input.attrs.erase("narHash");
+            auto narHash = store->queryPathInfo(storePath)->narHash;
+            input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
+            input.locked = true;
+
+            return storePath;
         };
 
         if (input.getRev()) {
@@ -482,9 +491,6 @@ struct GitInputScheme : InputScheme
                 return makeResult(res->first, std::move(res->second));
         }
 
-        if (repoInfo.isDirty)
-            return fetchFromWorkdir(store, repoInfo, std::move(input));
-
         auto originalRef = input.getRef();
         auto ref = originalRef ? *originalRef : getDefaultRef(repoInfo);
         input.attrs.insert_or_assign("ref", ref);
@@ -674,7 +680,7 @@ struct GitInputScheme : InputScheme
             infoAttrs.insert_or_assign("revCount",
                 getRevCount(repoInfo, repoDir, rev));
 
-        if (!_input.getRev())
+        if (!origRev)
             getCache()->add(
                 store,
                 unlockedAttrs,
@@ -692,45 +698,27 @@ struct GitInputScheme : InputScheme
         return makeResult(infoAttrs, std::move(storePath));
     }
 
-    std::pair<StorePath, Input> fetchFromWorkdir(
-        ref<Store> store,
-        const RepoInfo & repoInfo,
-        Input input)
-    {
-        /* This is an unclean working tree. So copy all tracked
-           files. */
-        repoInfo.checkDirty();
-
-        auto files = listFiles(repoInfo);
-
-        CanonPath repoDir(repoInfo.url);
-
-        PathFilter filter = [&](const Path & p) -> bool {
-            return CanonPath(p).removePrefix(repoDir).isAllowed(files);
-        };
-
-        auto storePath = store->addToStore(input.getName(), repoInfo.url, FileIngestionMethod::Recursive, htSHA256, filter);
-
-        // FIXME: maybe we should use the timestamp of the last
-        // modified dirty file?
-        input.attrs.insert_or_assign(
-            "lastModified",
-            getLastModified(repoInfo, repoInfo.url, "HEAD"));
-
-        return {std::move(storePath), input};
-    }
-
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
         Input input(_input);
 
         auto repoInfo = getRepoInfo(input);
 
+        auto makeNotAllowedError = [url{repoInfo.url}](const CanonPath & path) -> RestrictedPathError
+        {
+            if (nix::pathExists(path.abs()))
+                return RestrictedPathError("access to path '%s' is forbidden because it is not under Git control; maybe you should 'git add' it to the repository '%s'?", path, url);
+            else
+                return RestrictedPathError("path '%s' does not exist in Git repository '%s'", path, url);
+        };
+
         /* Unless we're using the working tree, copy the tree into the
            Nix store. TODO: We could have an accessor for fetching
            files from the Git repository directly. */
-        if (input.getRef() || input.getRev() || !repoInfo.isLocal)
-            return InputScheme::getAccessor(store, input);
+        if (input.getRef() || input.getRev() || !repoInfo.isLocal) {
+            auto storePath = fetchToStore(store, repoInfo, input);
+            return {makeStorePathAccessor(store, storePath, std::move(makeNotAllowedError)), input};
+        }
 
         repoInfo.checkDirty();
 
@@ -753,14 +741,6 @@ struct GitInputScheme : InputScheme
             "lastModified",
             getLastModified(repoInfo, repoInfo.url, ref));
 
-        auto makeNotAllowedError = [url{repoInfo.url}](const CanonPath & path) -> RestrictedPathError
-        {
-            if (nix::pathExists(path.abs()))
-                return RestrictedPathError("access to path '%s' is forbidden because it is not under Git control; maybe you should 'git add' it to the repository '%s'?", path, url);
-            else
-                return RestrictedPathError("path '%s' does not exist in Git repository '%s'", path, url);
-        };
-
         return {makeFSInputAccessor(CanonPath(repoInfo.url), listFiles(repoInfo), std::move(makeNotAllowedError)), input};
     }
 };
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 5409594f7..4005a1f48 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -26,11 +26,11 @@ std::regex hostRegex(hostRegexS, std::regex::ECMAScript);
 
 struct GitArchiveInputScheme : InputScheme
 {
-    virtual std::string type() = 0;
+    virtual std::string type() const = 0;
 
     virtual std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const = 0;
 
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != type()) return {};
 
@@ -100,7 +100,7 @@ struct GitArchiveInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != type()) return {};
 
@@ -116,7 +116,7 @@ struct GitArchiveInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto owner = getStrAttr(input.attrs, "owner");
         auto repo = getStrAttr(input.attrs, "repo");
@@ -132,7 +132,7 @@ struct GitArchiveInputScheme : InputScheme
         };
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return input.getRev() &&
             true; // FIXME
@@ -142,7 +142,7 @@ struct GitArchiveInputScheme : InputScheme
     Input applyOverrides(
         const Input & _input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto input(_input);
         if (rev && ref)
@@ -185,7 +185,7 @@ struct GitArchiveInputScheme : InputScheme
 
     virtual DownloadUrl getDownloadUrl(const Input & input) const = 0;
 
-    std::pair<StorePath, Input> downloadArchive(ref<Store> store, Input input)
+    std::pair<StorePath, Input> downloadArchive(ref<Store> store, Input input) const
     {
         if (!maybeGetStrAttr(input.attrs, "ref")) input.attrs.insert_or_assign("ref", "HEAD");
 
@@ -228,7 +228,7 @@ struct GitArchiveInputScheme : InputScheme
         return {res.storePath, input};
     }
 
-    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const override
     {
         auto [storePath, input2] = downloadArchive(store, input);
 
@@ -242,7 +242,7 @@ struct GitArchiveInputScheme : InputScheme
 
 struct GitHubInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "github"; }
+    std::string type() const override { return "github"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -291,7 +291,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("github.com");
         Input::fromURL(fmt("git+https://%s/%s/%s.git",
@@ -303,7 +303,7 @@ struct GitHubInputScheme : GitArchiveInputScheme
 
 struct GitLabInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "gitlab"; }
+    std::string type() const override { return "gitlab"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -358,7 +358,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("gitlab.com");
         // FIXME: get username somewhere
@@ -371,7 +371,7 @@ struct GitLabInputScheme : GitArchiveInputScheme
 
 struct SourceHutInputScheme : GitArchiveInputScheme
 {
-    std::string type() override { return "sourcehut"; }
+    std::string type() const override { return "sourcehut"; }
 
     std::optional<std::pair<std::string, std::string>> accessHeaderFromToken(const std::string & token) const override
     {
@@ -445,7 +445,7 @@ struct SourceHutInputScheme : GitArchiveInputScheme
         return DownloadUrl { url, headers };
     }
 
-    void clone(const Input & input, const Path & destDir) override
+    void clone(const Input & input, const Path & destDir) const override
     {
         auto host = maybeGetStrAttr(input.attrs, "host").value_or("git.sr.ht");
         Input::fromURL(fmt("git+https://%s/%s/%s",
diff --git a/src/libfetchers/indirect.cc b/src/libfetchers/indirect.cc
index 32ee6719d..bd4ecf320 100644
--- a/src/libfetchers/indirect.cc
+++ b/src/libfetchers/indirect.cc
@@ -7,7 +7,7 @@ std::regex flakeRegex("[a-zA-Z][a-zA-Z0-9_-]*", std::regex::ECMAScript);
 
 struct IndirectInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "flake") return {};
 
@@ -50,7 +50,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "indirect") return {};
 
@@ -68,7 +68,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         ParsedURL url;
         url.scheme = "flake";
@@ -78,7 +78,7 @@ struct IndirectInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return false;
     }
@@ -86,7 +86,7 @@ struct IndirectInputScheme : InputScheme
     Input applyOverrides(
         const Input & _input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto input(_input);
         if (rev) input.attrs.insert_or_assign("rev", rev->gitRev());
@@ -94,7 +94,7 @@ struct IndirectInputScheme : InputScheme
         return input;
     }
 
-    std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & input) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const override
     {
         throw Error("indirect input '%s' cannot be fetched directly", input.to_string());
     }
diff --git a/src/libfetchers/input-accessor.cc b/src/libfetchers/input-accessor.cc
index 55aecd839..5df447f01 100644
--- a/src/libfetchers/input-accessor.cc
+++ b/src/libfetchers/input-accessor.cc
@@ -1,5 +1,6 @@
 #include "input-accessor.hh"
 #include "util.hh"
+#include "store-api.hh"
 
 #include <atomic>
 
@@ -235,6 +236,14 @@ ref<FSInputAccessor> makeFSInputAccessor(
     return make_ref<FSInputAccessorImpl>(root, std::move(allowedPaths), std::move(makeNotAllowedError));
 }
 
+ref<FSInputAccessor> makeStorePathAccessor(
+    ref<Store> store,
+    const StorePath & storePath,
+    MakeNotAllowedError && makeNotAllowedError)
+{
+    return makeFSInputAccessor(CanonPath(store->toRealPath(storePath)), {}, std::move(makeNotAllowedError));
+}
+
 std::ostream & operator << (std::ostream & str, const SourcePath & path)
 {
     str << path.to_string();
diff --git a/src/libfetchers/input-accessor.hh b/src/libfetchers/input-accessor.hh
index 28bf38bce..2c0be75ff 100644
--- a/src/libfetchers/input-accessor.hh
+++ b/src/libfetchers/input-accessor.hh
@@ -10,6 +10,8 @@ namespace nix {
 MakeError(RestrictedPathError, Error);
 
 struct SourcePath;
+class StorePath;
+class Store;
 
 struct InputAccessor : public std::enable_shared_from_this<InputAccessor>
 {
@@ -91,6 +93,11 @@ ref<FSInputAccessor> makeFSInputAccessor(
     std::optional<std::set<CanonPath>> && allowedPaths = {},
     MakeNotAllowedError && makeNotAllowedError = {});
 
+ref<FSInputAccessor> makeStorePathAccessor(
+    ref<Store> store,
+    const StorePath & storePath,
+    MakeNotAllowedError && makeNotAllowedError = {});
+
 struct SourcePath;
 
 struct MemoryInputAccessor : InputAccessor
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index a10fc0a63..ccd504e15 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -43,7 +43,7 @@ static std::string runHg(const Strings & args, const std::optional<std::string>
 
 struct MercurialInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "hg+http" &&
             url.scheme != "hg+https" &&
@@ -69,7 +69,7 @@ struct MercurialInputScheme : InputScheme
         return inputFromAttrs(attrs);
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "hg") return {};
 
@@ -89,7 +89,7 @@ struct MercurialInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         url.scheme = "hg+" + url.scheme;
@@ -98,7 +98,7 @@ struct MercurialInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         // FIXME: ugly, need to distinguish between dirty and clean
         // default trees.
@@ -108,7 +108,7 @@ struct MercurialInputScheme : InputScheme
     Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
-        std::optional<Hash> rev) override
+        std::optional<Hash> rev) const override
     {
         auto res(input);
         if (rev) res.attrs.insert_or_assign("rev", rev->gitRev());
@@ -148,9 +148,9 @@ struct MercurialInputScheme : InputScheme
         return {isLocal, isLocal ? url.path : url.base};
     }
 
-    std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & _input) override
+    StorePath fetchToStore(ref<Store> store, Input & input) const
     {
-        Input input(_input);
+        auto origRev = input.getRev();
 
         auto name = input.getName();
 
@@ -200,7 +200,7 @@ struct MercurialInputScheme : InputScheme
 
                 auto storePath = store->addToStore(input.getName(), actualPath, FileIngestionMethod::Recursive, htSHA256, filter);
 
-                return {std::move(storePath), input};
+                return storePath;
             }
         }
 
@@ -224,13 +224,13 @@ struct MercurialInputScheme : InputScheme
             });
         };
 
-        auto makeResult = [&](const Attrs & infoAttrs, StorePath && storePath)
-            -> std::pair<StorePath, Input>
+        auto makeResult = [&](const Attrs & infoAttrs, const StorePath & storePath) -> StorePath
         {
             assert(input.getRev());
-            assert(!_input.getRev() || _input.getRev() == input.getRev());
+            assert(!origRev || origRev == input.getRev());
             input.attrs.insert_or_assign("revCount", getIntAttr(infoAttrs, "revCount"));
-            return {std::move(storePath), input};
+            input.locked = true;
+            return storePath;
         };
 
         if (input.getRev()) {
@@ -310,7 +310,7 @@ struct MercurialInputScheme : InputScheme
             {"revCount", (uint64_t) revCount},
         });
 
-        if (!_input.getRev())
+        if (!origRev)
             getCache()->add(
                 store,
                 unlockedAttrs,
@@ -327,6 +327,15 @@ struct MercurialInputScheme : InputScheme
 
         return makeResult(infoAttrs, std::move(storePath));
     }
+
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
+    {
+        Input input(_input);
+
+        auto storePath = fetchToStore(store, input);
+
+        return {makeStorePathAccessor(store, storePath), input};
+    }
 };
 
 static auto rMercurialInputScheme = OnStartup([] { registerInputScheme(std::make_unique<MercurialInputScheme>()); });
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index ea056861b..4d3dad679 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -6,7 +6,7 @@ namespace nix::fetchers {
 
 struct PathInputScheme : InputScheme
 {
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (url.scheme != "path") return {};
 
@@ -32,7 +32,7 @@ struct PathInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         if (maybeGetStrAttr(attrs, "type") != "path") return {};
 
@@ -54,7 +54,7 @@ struct PathInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto query = attrsToQuery(input.attrs);
         query.erase("path");
@@ -75,7 +75,7 @@ struct PathInputScheme : InputScheme
             return CanonPath(path);
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return true;
     }
@@ -103,7 +103,7 @@ 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) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) const override
     {
         auto absPath = getAbsPath(input);
         auto input2(input);
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index ab8f847dd..964a10124 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -185,7 +185,7 @@ struct CurlInputScheme : InputScheme
 
     virtual bool isValidURL(const ParsedURL & url) const = 0;
 
-    std::optional<Input> inputFromURL(const ParsedURL & url) override
+    std::optional<Input> inputFromURL(const ParsedURL & url) const override
     {
         if (!isValidURL(url))
             return std::nullopt;
@@ -203,7 +203,7 @@ struct CurlInputScheme : InputScheme
         return input;
     }
 
-    std::optional<Input> inputFromAttrs(const Attrs & attrs) override
+    std::optional<Input> inputFromAttrs(const Attrs & attrs) const override
     {
         auto type = maybeGetStrAttr(attrs, "type");
         if (type != inputType()) return {};
@@ -220,7 +220,7 @@ struct CurlInputScheme : InputScheme
         return input;
     }
 
-    ParsedURL toURL(const Input & input) override
+    ParsedURL toURL(const Input & input) const override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         // NAR hashes are preferred over file hashes since tar/zip
@@ -230,7 +230,7 @@ struct CurlInputScheme : InputScheme
         return url;
     }
 
-    bool hasAllInfo(const Input & input) override
+    bool hasAllInfo(const Input & input) const override
     {
         return true;
     }
@@ -250,10 +250,18 @@ struct FileInputScheme : CurlInputScheme
                     : !hasTarballExtension(url.path));
     }
 
-    std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & input) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
+        auto input(_input);
+
         auto file = downloadFile(store, getStrAttr(input.attrs, "url"), input.getName(), false);
-        return {std::move(file.storePath), input};
+
+        // FIXME: remove?
+        auto narHash = store->queryPathInfo(file.storePath)->narHash;
+        input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
+        input.locked = true;
+
+        return {makeStorePathAccessor(store, file.storePath), input};
     }
 };
 
@@ -271,12 +279,18 @@ struct TarballInputScheme : CurlInputScheme
                     : hasTarballExtension(url.path));
     }
 
-    std::pair<StorePath, Input> fetchToStore(ref<Store> store, const Input & input) override
+    std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & _input) const override
     {
-        return {
-            downloadTarball(store, getStrAttr(input.attrs, "url"), input.getName(), false).first,
-            input
-        };
+        auto input(_input);
+
+        auto storePath = downloadTarball(store, getStrAttr(input.attrs, "url"), input.getName(), false).first;
+
+        // FIXME: remove?
+        auto narHash = store->queryPathInfo(storePath)->narHash;
+        input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
+        input.locked = true;
+
+        return {makeStorePathAccessor(store, storePath), input};
     }
 };
 
diff --git a/tests/fetchGit.sh b/tests/fetchGit.sh
index 166bccfc7..108be4c02 100644
--- a/tests/fetchGit.sh
+++ b/tests/fetchGit.sh
@@ -120,6 +120,7 @@ git -C $repo commit -m 'Bla3' -a
 path4=$(nix eval --impure --refresh --raw --expr "(builtins.fetchGit file://$repo).outPath")
 [[ $path2 = $path4 ]]
 
+status=0
 nix eval --impure --raw --expr "(builtins.fetchGit { url = $repo; rev = \"$rev2\"; narHash = \"sha256-B5yIPHhEm0eysJKEsO7nqxprh9vcblFxpJG11gXJus1=\"; }).outPath" || status=$?
 [[ "$status" = "102" ]]
 
@@ -223,4 +224,5 @@ rm -rf $repo/.git
 
 # should succeed for a repo without commits
 git init $repo
+git -C $repo add hello # need to add at least one file to cause the root of the repo to be visible
 path10=$(nix eval --impure --raw --expr "(builtins.fetchGit \"file://$repo\").outPath")