[automerge] Adjust automerge ignore to cope with deleted files (#22)

The `git restore --ours` command is not able to cope with the case where
a file was deleted in the destination branch. This adjusts the automerge
script to use a combination of `git ls-files --deleted` and `git rm` to
make sure these are handled correctly for ignored files.

Author: pratlucas

arm-software/ci/automerge.py

@@ -47,6 +47,21 @@ def run_cmd(self, args: list[str], check: bool = True) -> str:
         return git_process.stdout
 
 
+def restore_changes_to_ignored_files(git_repo: Git, ignore_list: list[str]) -> None:
+    if not ignore_list:
+        return
+    # Make sure any files deleted by us stay deleted.
+    # Note that any deleted files in the working tree at this point are conflicts
+    ls_files_output = git_repo.run_cmd(["ls-files", "--deleted", "--deduplicate"] + ignore_list)
+    deleted_by_us = ls_files_output.splitlines()
+    if deleted_by_us:
+        git_repo.run_cmd(["rm"] + deleted_by_us)
+    # Next, restore ignored files in the index
+    git_repo.run_cmd(["restore", "--staged"] + ignore_list)
+    # And finally, restore ignored files in the working tree
+    git_repo.run_cmd(["restore", "--ours", "--worktree"] + ignore_list)
+
+
 def has_unresolved_conflicts(git_repo: Git) -> bool:
     diff_output = git_repo.run_cmd(["diff", "--name-only", "--diff-filter=U"])
     diff_output = diff_output.strip()
@@ -59,13 +74,11 @@ def prefix_current_commit_message(git_repo: Git) -> None:
     git_repo.run_cmd(["commit", "--amend", "--message=" + commit_msg])
 
 
-def merge_commit(git_repo: Git, to_branch: str, commit_hash: str, dry_run: bool) -> None:
+def merge_commit(git_repo: Git, to_branch: str, commit_hash: str, ignored_paths: list[str], dry_run: bool) -> None:
     logger.info("Merging commit %s into %s", commit_hash, to_branch)
     git_repo.run_cmd(["switch", to_branch])
     git_repo.run_cmd(["merge", commit_hash, "--no-commit", "--no-ff"], check=False)
-    # Ensure all paths that should be ignored stay unchanged
-    git_repo.run_cmd(["restore", "--staged", f"--pathspec-from-file={MERGE_IGNORE_PATHSPEC_FILE}"])
-    git_repo.run_cmd(["restore", "--ours", "--worktree", f"--pathspec-from-file={MERGE_IGNORE_PATHSPEC_FILE}"])
+    restore_changes_to_ignored_files(git_repo, ignored_paths)
     if has_unresolved_conflicts(git_repo):
         logger.info("Merge failed")
         git_repo.run_cmd(["merge", "--abort"])
@@ -171,9 +184,12 @@ def main():
 
         git_repo = Git(args.repo_path)
 
+        with open(MERGE_IGNORE_PATHSPEC_FILE) as ignored_paths_file:
+            ignored_paths = ignored_paths_file.readlines()
+
         merge_commits = get_merge_commit_list(git_repo, args.from_branch, args.to_branch)
         for commit_hash in merge_commits:
-            merge_commit(git_repo, args.to_branch, commit_hash, args.dry_run)
+            merge_commit(git_repo, args.to_branch, commit_hash, ignored_paths, args.dry_run)
     except MergeConflictError as conflict:
         process_conflict(
             git_repo,