Add option --commit-lock-file

src/libexpr/flake/flake.cc

@@ -321,15 +321,15 @@ static std::string diffLockFiles(const LockedInputs & oldLocks, const LockedInpu
 
     while (i != oldFlat.end() || j != newFlat.end()) {
         if (j != newFlat.end() && (i == oldFlat.end() || i->first > j->first)) {
-            res += fmt("  added '%s': '%s'\n", concatStringsSep("/", j->first), j->second->lockedRef);
+            res += fmt("* Added '%s': '%s'\n", concatStringsSep("/", j->first), j->second->lockedRef);
             ++j;
         } else if (i != oldFlat.end() && (j == newFlat.end() || i->first < j->first)) {
-            res += fmt("  removed '%s'\n", concatStringsSep("/", i->first));
+            res += fmt("* Removed '%s'\n", concatStringsSep("/", i->first));
             ++i;
         } else {
             if (!(i->second->lockedRef == j->second->lockedRef)) {
                 assert(i->second->lockedRef.to_string() != j->second->lockedRef.to_string());
-                res += fmt("  updated '%s': '%s' -> '%s'\n",
+                res += fmt("* Updated '%s': '%s' -> '%s'\n",
                     concatStringsSep("/", i->first),
                     i->second->lockedRef,
                     j->second->lockedRef);
@@ -558,8 +558,10 @@ LockedFlake lockFlake(
     /* Check whether we need to / can write the new lock file. */
     if (!(newLockFile == oldLockFile)) {
 
+        auto diff = diffLockFiles(oldLockFile, newLockFile);
+
         if (!(oldLockFile == LockFile()))
-            printInfo("inputs of flake '%s' changed:\n%s", topRef, chomp(diffLockFiles(oldLockFile, newLockFile)));
+            printInfo("inputs of flake '%s' changed:\n%s", topRef, chomp(diff));
 
         if (lockFlags.writeLockFile) {
             if (auto sourcePath = topRef.input->getSourcePath()) {
@@ -572,7 +574,9 @@ LockedFlake lockFlake(
 
                     auto path = *sourcePath + (topRef.subdir == "" ? "" : "/" + topRef.subdir) + "/flake.lock";
 
-                    if (pathExists(path))
+                    bool lockFileExists = pathExists(path);
+
+                    if (lockFileExists)
                         warn("updating lock file '%s'", path);
                     else
                         warn("creating lock file '%s'", path);
@@ -580,7 +584,10 @@ LockedFlake lockFlake(
                     newLockFile.write(path);
 
                     topRef.input->markChangedFile(
-                        (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock");
+                        (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock",
+                        lockFlags.commitLockFile
+                        ? std::optional<std::string>(fmt("flake.lock: %s\n\nFlake input changes:\n\n%s", lockFileExists ? "Update" : "Add", diff))
+                        : std::nullopt);
 
                     /* Rewriting the lockfile changed the top-level
                        repo, so we should re-read it. FIXME: we could

src/libexpr/flake/flake.hh

@@ -78,6 +78,9 @@ struct LockFlags
        allowed. */
     bool allowMutable = true;
 
+    /* Whether to commit changes to flake.lock. */
+    bool commitLockFile = false;
+
     /* Flake inputs to be overriden. */
     std::map<InputPath, FlakeRef> inputOverrides;
 

src/libstore/fetchers/fetchers.hh

@@ -62,8 +62,10 @@ struct Input : std::enable_shared_from_this<Input>
 
     virtual std::optional<Path> getSourcePath() const { return {}; }
 
-    // FIXME: should merge with getSourcePath().
+    virtual void markChangedFile(
-    virtual void markChangedFile(std::string_view file) const { assert(false); }
+        std::string_view file,
+        std::optional<std::string> commitMsg) const
+    { assert(false); }
 
     virtual void clone(const Path & destDir) const
     {

src/libstore/fetchers/git.cc

@@ -169,17 +169,17 @@ struct GitInput : Input
             return url.path;
         return {};
     }
-
+    void markChangedFile(std::string_view file, std::optional<std::string> commitMsg) const override
-    void markChangedFile(std::string_view file) const override
     {
         auto sourcePath = getSourcePath();
         assert(sourcePath);
+
         runProgram("git", true,
-            { "-C", *sourcePath, "add",
+            { "-C", *sourcePath, "add", "--force", "--intent-to-add", std::string(file) });
-              "--force",
+
-              "--intent-to-add",
+        if (commitMsg)
-              std::string(file)
+            runProgram("git", true,
-            });
+                { "-C", *sourcePath, "commit", std::string(file), "-m", *commitMsg });
     }
 
     std::pair<bool, std::string> getActualUrl() const

src/libstore/fetchers/mercurial.cc

@@ -84,15 +84,18 @@ struct MercurialInput : Input
         return {};
     }
 
-    void markChangedFile(std::string_view file) const override
+    void markChangedFile(std::string_view file, std::optional<std::string> commitMsg) const override
     {
         auto sourcePath = getSourcePath();
         assert(sourcePath);
+
         // FIXME: shut up if file is already tracked.
         runProgram("hg", true,
-            { "add",
+            { "add", *sourcePath + "/" + std::string(file) });
-              *sourcePath + "/" + std::string(file)
+
-            });
+        if (commitMsg)
+            runProgram("hg", true,
+                { "commit", *sourcePath + "/" + std::string(file), "-m", *commitMsg });
     }
 
     std::pair<bool, std::string> getActualUrl() const

src/nix/installables.cc

@@ -39,6 +39,11 @@ MixFlakeOptions::MixFlakeOptions()
         .description("don't use flake registries")
         .set(&lockFlags.useRegistries, false);
 
+    mkFlag()
+        .longName("commit-lock-file")
+        .description("commit changes to the lock file")
+        .set(&lockFlags.commitLockFile, true);
+
     mkFlag()
         .longName("update-input")
         .description("update a specific flake input")

tests/flakes.sh

@@ -170,10 +170,9 @@ nix build -o $TEST_ROOT/result $flake2Dir#bar --no-update-lock-file 2>&1 | grep
 # But it should succeed without that flag.
 nix build -o $TEST_ROOT/result $flake2Dir#bar --no-write-lock-file
 nix build -o $TEST_ROOT/result $flake2Dir#bar --no-update-lock-file 2>&1 | grep 'requires lock file changes'
-nix build -o $TEST_ROOT/result $flake2Dir#bar
+nix build -o $TEST_ROOT/result $flake2Dir#bar --commit-lock-file
 [[ -e $flake2Dir/flake.lock ]]
-git -C $flake2Dir add flake.lock
+[[ -z $(git -C $flake2Dir diff master) ]]
-git -C $flake2Dir commit flake.lock -m 'Add flake.lock'
 
 # Rerunning the build should not change the lockfile.
 nix build -o $TEST_ROOT/result $flake2Dir#bar
@@ -291,11 +290,7 @@ git -C $flake3Dir commit -m 'Add nonFlakeInputs'
 
 # Check whether `nix build` works with a lockfile which is missing a
 # nonFlakeInputs.
-nix build -o $TEST_ROOT/result $flake3Dir#sth
+nix build -o $TEST_ROOT/result $flake3Dir#sth --commit-lock-file
-
-git -C $flake3Dir add flake.lock
-
-git -C $flake3Dir commit -m 'Update nonFlakeInputs'
 
 nix build -o $TEST_ROOT/result flake3#fnord
 [[ $(cat $TEST_ROOT/result) = FNORD ]]