Merge pull request #8042 from lheckemann/alt-lockfiles

Allow specifying alternative paths for reading/writing flake locks

2 files changed, 28 insertions, 12 deletions

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 81e94848a..b7025aecb 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -334,10 +334,14 @@ LockedFlake lockFlake(
     }
 
     try {
+        if (!fetchSettings.allowDirty && lockFlags.referenceLockFilePath) {
+            throw Error("reference lock file was provided, but the `allow-dirty` setting is set to false");
+        }
 
         // FIXME: symlink attack
         auto oldLockFile = LockFile::read(
-            flake.sourceInfo->actualPath + "/" + flake.lockedRef.subdir + "/flake.lock");
+            lockFlags.referenceLockFilePath.value_or(
+                flake.sourceInfo->actualPath + "/" + flake.lockedRef.subdir + "/flake.lock"));
 
         debug("old lock file: %s", oldLockFile);
 
@@ -619,13 +623,20 @@ LockedFlake lockFlake(
 
         debug("new lock file: %s", newLockFile);
 
+        auto relPath = (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock";
+        auto sourcePath = topRef.input.getSourcePath();
+        auto outputLockFilePath = sourcePath ? std::optional{*sourcePath + "/" + relPath} : std::nullopt;
+        if (lockFlags.outputLockFilePath) {
+            outputLockFilePath = lockFlags.outputLockFilePath;
+        }
+
         /* Check whether we need to / can write the new lock file. */
-        if (!(newLockFile == oldLockFile)) {
+        if (newLockFile != oldLockFile || lockFlags.outputLockFilePath) {
 
             auto diff = LockFile::diff(oldLockFile, newLockFile);
 
             if (lockFlags.writeLockFile) {
-                if (auto sourcePath = topRef.input.getSourcePath()) {
+                if (outputLockFilePath) {
                     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);
@@ -633,25 +644,24 @@ 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);
 
-                        auto relPath = (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock";
-
-                        auto path = *sourcePath + "/" + relPath;
-
-                        bool lockFileExists = pathExists(path);
+                        bool lockFileExists = pathExists(*outputLockFilePath);
 
                         if (lockFileExists) {
                             auto s = chomp(diff);
                             if (s.empty())
-                                warn("updating lock file '%s'", path);
+                                warn("updating lock file '%s'", *outputLockFilePath);
                             else
-                                warn("updating lock file '%s':\n%s", path, s);
+                                warn("updating lock file '%s':\n%s", *outputLockFilePath, s);
                         } else
-                            warn("creating lock file '%s'", path);
+                            warn("creating lock file '%s'", *outputLockFilePath);
 
-                        newLockFile.write(path);
+                        newLockFile.write(*outputLockFilePath);
 
                         std::optional<std::string> commitMessage = std::nullopt;
                         if (lockFlags.commitLockFile) {
+                            if (lockFlags.outputLockFilePath) {
+                                throw Error("--commit-lock-file and --output-lock-file are currently incompatible");
+                            }
                             std::string cm;
 
                             cm = fetchSettings.commitLockFileSummary.get();
diff --git a/src/libexpr/flake/flake.hh b/src/libexpr/flake/flake.hh
index 3cb39d766..b6f710288 100644
--- a/src/libexpr/flake/flake.hh
+++ b/src/libexpr/flake/flake.hh
@@ -118,6 +118,12 @@ struct LockFlags
     /* Whether to commit changes to flake.lock. */
     bool commitLockFile = false;
 
+    /* The path to a lock file to read instead of the `flake.lock` file in the top-level flake */
+    std::optional<std::string> referenceLockFilePath;
+
+    /* The path to a lock file to write to instead of the `flake.lock` file in the top-level flake */
+    std::optional<Path> outputLockFilePath;
+
     /* Flake inputs to be overridden. */
     std::map<InputPath, FlakeRef> inputOverrides;