Add abstract interface for writing files to an Input

src/libexpr/flake/flake.cc

@@ -621,7 +621,6 @@ LockedFlake lockFlake(
             auto diff = LockFile::diff(oldLockFile, newLockFile);
 
             if (lockFlags.writeLockFile) {
-                if (auto sourcePath = topRef.input.getAccessor(state.store).first->root().getPhysicalPath()) {
                 if (auto unlockedInput = newLockFile.isUnlocked()) {
                     if (fetchSettings.warnDirty)
                         warn("will not write lock file of flake '%s' because it has an unlocked input ('%s')", topRef, *unlockedInput);
@@ -629,13 +628,9 @@ LockedFlake lockFlake(
                     if (!lockFlags.updateLockFile)
                         throw Error("flake '%s' requires lock file changes but they're not allowed due to '--no-update-lock-file'", topRef);
 
-                        CanonPath flakeDir(*sourcePath);
+                    auto path = flake->path.parent() + "flake.lock";
 
-                        auto relPath = flakeDir + "flake.lock";
+                    bool lockFileExists = path.pathExists();
-
-                        auto path = flakeDir + "flake.lock";
-
-                        bool lockFileExists = pathExists(path.abs());
 
                     if (lockFileExists) {
                         auto s = chomp(diff);
@@ -646,26 +641,21 @@ LockedFlake lockFlake(
                     } else
                         warn("creating lock file '%s'", path);
 
-                        newLockFile.write(path.abs());
-
                     std::optional<std::string> commitMessage = std::nullopt;
                     if (lockFlags.commitLockFile) {
                         std::string cm;
 
                         cm = fetchSettings.commitLockFileSummary.get();
 
-                            if (cm == "") {
+                        if (cm == "")
-                                cm = fmt("%s: %s", relPath, lockFileExists ? "Update" : "Add");
+                            cm = fmt("%s: %s", path.path.rel(), lockFileExists ? "Update" : "Add");
-                            }
 
                         cm += "\n\nFlake lock file updates:\n\n";
                         cm += filterANSIEscapes(diff, true);
                         commitMessage = cm;
                     }
 
-                        topRef.input.markChangedFile(
+                    topRef.input.putFile(path.path, fmt("%s\n", newLockFile), commitMessage);
-                            (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock",
-                            commitMessage);
 
                     /* Rewriting the lockfile changed the top-level
                        repo, so we should re-read it. FIXME: we could
@@ -678,8 +668,6 @@ LockedFlake lockFlake(
                         prevLockedRef.input.getRev() != flake->lockedRef.input.getRev())
                         warn("committed new revision '%s'", flake->lockedRef.input.getRev()->gitRev());
                 }
-                } else
-                    throw Error("cannot write modified lock file of flake '%s' (use '--no-write-lock-file' to ignore)", topRef);
             } else {
                 warn("not writing modified lock file of flake '%s':\n%s", topRef, chomp(diff));
                 flake->forceDirty = true;

src/libexpr/flake/lockfile.cc

@@ -190,12 +190,6 @@ std::ostream & operator <<(std::ostream & stream, const LockFile & lockFile)
     return stream;
 }
 
-void LockFile::write(const Path & path) const
-{
-    createDirs(dirOf(path));
-    writeFile(path, fmt("%s\n", *this));
-}
-
 std::optional<FlakeRef> LockFile::isUnlocked() const
 {
     std::unordered_set<std::shared_ptr<const Node>> nodes;

src/libexpr/flake/lockfile.hh

@@ -59,10 +59,6 @@ struct LockFile
 
     std::string to_string() const;
 
-    static LockFile read(const Path & path);
-
-    void write(const Path & path) const;
-
     /* Check whether this lock file has any unlocked inputs. If so,
        return one. */
     std::optional<FlakeRef> isUnlocked() const;

src/libfetchers/fetchers.cc

@@ -187,12 +187,13 @@ void Input::clone(const Path & destDir) const
     scheme->clone(*this, destDir);
 }
 
-void Input::markChangedFile(
+void Input::putFile(
-    std::string_view file,
+    const CanonPath & path,
+    std::string_view contents,
     std::optional<std::string> commitMsg) const
 {
     assert(scheme);
-    return scheme->markChangedFile(*this, file, commitMsg);
+    return scheme->putFile(*this, path, contents, commitMsg);
 }
 
 std::string Input::getName() const
@@ -278,9 +279,13 @@ Input InputScheme::applyOverrides(
     return input;
 }
 
-void InputScheme::markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg)
+void InputScheme::putFile(
+    const Input & input,
+    const CanonPath & path,
+    std::string_view contents,
+    std::optional<std::string> commitMsg) const
 {
-    assert(false);
+    throw Error("input '%s' does not support modifying file '%s'", input.to_string(), path);
 }
 
 void InputScheme::clone(const Input & input, const Path & destDir)

src/libfetchers/fetchers.hh

@@ -79,8 +79,9 @@ public:
 
     void clone(const Path & destDir) const;
 
-    void markChangedFile(
+    void putFile(
-        std::string_view file,
+        const CanonPath & path,
+        std::string_view contents,
         std::optional<std::string> commitMsg) const;
 
     std::string getName() const;
@@ -130,7 +131,11 @@ struct InputScheme
 
     virtual void clone(const Input & input, const Path & destDir);
 
-    virtual void markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg);
+    virtual void putFile(
+        const Input & input,
+        const CanonPath & path,
+        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

src/libfetchers/git.cc

@@ -245,17 +245,28 @@ struct GitInputScheme : InputScheme
         runProgram("git", true, args);
     }
 
-    void markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg) override
+    void putFile(
+        const Input & input,
+        const CanonPath & path,
+        std::string_view contents,
+        std::optional<std::string> commitMsg) const
     {
         auto repoInfo = getRepoInfo(input);
-        assert(repoInfo.isLocal);
+        if (!repoInfo.isLocal)
+            throw Error("cannot commit '%s' to Git repository '%s' because it's not a working tree", path, input.to_string());
+
+        auto absPath = CanonPath(repoInfo.url) + path;
+
+        // FIXME: make sure that absPath is not a symlink that escapes
+        // the repo.
+        writeFile(absPath.abs(), contents);
 
         runProgram("git", true,
-            { "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "add", "--force", "--intent-to-add", "--", std::string(file) });
+            { "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "add", "--force", "--intent-to-add", "--", std::string(path.rel()) });
 
         if (commitMsg)
             runProgram("git", true,
-                { "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "commit", std::string(file), "-m", *commitMsg });
+                { "-C", repoInfo.url, "--git-dir", repoInfo.gitDir, "commit", std::string(path.rel()), "-m", *commitMsg });
     }
 
     struct RepoInfo
@@ -292,7 +303,7 @@ struct GitInputScheme : InputScheme
         std::string gitDir = ".git";
     };
 
-    RepoInfo getRepoInfo(const Input & input)
+    RepoInfo getRepoInfo(const Input & input) const
     {
         auto checkHashType = [&](const std::optional<Hash> & hash)
         {

src/libfetchers/mercurial.cc

@@ -116,18 +116,29 @@ struct MercurialInputScheme : InputScheme
         return res;
     }
 
-    void markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg) override
+    void putFile(
+        const Input & input,
+        const CanonPath & path,
+        std::string_view contents,
+        std::optional<std::string> commitMsg) const
     {
-        auto [isLocal, path] = getActualUrl(input);
+        auto [isLocal, repoPath] = getActualUrl(input);
-        assert(isLocal);
+        if (!isLocal)
+            throw Error("cannot commit '%s' to Mercurial repository '%s' because it's not a working tree", path, input.to_string());
+
+        auto absPath = CanonPath(repoPath) + path;
+
+        // FIXME: make sure that absPath is not a symlink that escapes
+        // the repo.
+        writeFile(absPath.abs(), contents);
 
         // FIXME: shut up if file is already tracked.
         runHg(
-            { "add", path + "/" + file });
+            { "add", absPath.abs() });
 
         if (commitMsg)
             runHg(
-                { "commit", path + "/" + file, "-m", *commitMsg });
+                { "commit", absPath.abs(), "-m", *commitMsg });
     }
 
     std::pair<bool, std::string> getActualUrl(const Input & input) const

src/libfetchers/path.cc

@@ -80,12 +80,20 @@ struct PathInputScheme : InputScheme
         return true;
     }
 
-    void markChangedFile(const Input & input, std::string_view file, std::optional<std::string> commitMsg) override
+    void putFile(
+        const Input & input,
+        const CanonPath & path,
+        std::string_view contents,
+        std::optional<std::string> commitMsg) const
     {
-        // nothing to do
+        auto absPath = CanonPath(getAbsPath(input)) + path;
+
+        // FIXME: make sure that absPath is not a symlink that escapes
+        // the repo.
+        writeFile(absPath.abs(), contents);
     }
 
-    CanonPath getAbsPath(ref<Store> store, const Input & input) const
+    CanonPath getAbsPath(const Input & input) const
     {
         auto path = getStrAttr(input.attrs, "path");
 
@@ -97,7 +105,7 @@ struct PathInputScheme : InputScheme
 
     std::pair<ref<InputAccessor>, Input> getAccessor(ref<Store> store, const Input & input) override
     {
-        auto absPath = getAbsPath(store, input);
+        auto absPath = getAbsPath(input);
         auto input2(input);
         input2.attrs.emplace("path", (std::string) absPath.abs());
         return {makeFSInputAccessor(absPath), std::move(input2)};
@@ -109,7 +117,7 @@ struct PathInputScheme : InputScheme
            locked, so just use the path as its fingerprint. Maybe we
            should restrict this to CA paths but that's not
            super-important. */
-        auto path = getAbsPath(store, input);
+        auto path = getAbsPath(input);
         if (store->isInStore(path.abs()))
             return path.abs();
         return std::nullopt;