mrhlpr: use Part-of trailer instead of adding MR ID to subject

We are planning to migrate to marge-bot for handling merging commits,
and with it adopt a new way of linking commits to their source MRs.

Using a trailer with Part-of: !MR-ID results in the commits being linked
to the MR, and the GitLab web interface inserting a hyperlink in its
place making it easier to jump to the source MR.

Let's adopt this for MRs we still merge manually now.

Use the full URL to the MR rather than just the ID, this way if we ever
split or merge repos it will still be easily possible to trace commits
back to their original MRs.

Signed-off-by: Caleb Connolly <caleb@postmarketos.org>

mrhlpr/data/msg_filter_add_commit_id.py

@@ -16,22 +16,41 @@ if not mrhlpr_msg_filter_mr_id:
     exit(1)
 
 
-line_number = 0
-suffix = " (MR " + mrhlpr_msg_filter_mr_id + ")"
+line_count = 0
+empty_lines = 0
+trailer = f"Part-of: {mrhlpr_msg_filter_mr_id}"
+emit_trailer = True
+have_trailers = False
 for line in sys.stdin:
     line = line.rstrip()
-    line_number += 1
+    line_count += 1
 
-    # Add the suffix in the first line
-    if line_number == 1:
-        if line.endswith(suffix):
-            print(line)
-        else:
-            print(line + suffix)
+    # Don't emit the trailer if the commit already has it
+    if line == trailer:
+        emit_trailer = False
     else:
-        # Make sure we have an empty line after the first one
-        if line_number == 2 and line != "":
-            print()
+        # Count empty lines since the last non-empty line
+        if line == "":
+            empty_lines += 1
+        else:
+            empty_lines = 0
+
+        if any(
+            line.lower().startswith(prefix)
+            for prefix in [
+                "signed-off-by: ",
+                "co-developed-by: ",
+                "change-id: ",
+                "co-authoured-by: ",
+                "part-of: ",
+            ]
+        ):
+            have_trailers = True
+
+    print(line)
 
-        # Print all other lines without modification
-        print(line)
+if emit_trailer:
+    # Print a blank line before the trailer section unless we already have trailers
+    if empty_lines == 0 and not have_trailers:
+        print()
+    print(trailer)

mrhlpr/mr.py

@@ -125,6 +125,17 @@ def get_status(
     )
 
 
+def get_url(mr_id: int, origin: Optional[GitLabOrigin] = None) -> str:
+    """Get the URL to the merge request on the GitLab server.
+
+    :param mr_id: merge request ID
+    :param origin: gitlab origin information, see gitlab.parse_git_origin()
+    :returns: URL to the merge request"""
+    if not origin:
+        origin = gitlab.parse_git_origin()
+    return f"https://{origin.host}/{origin.project_id}/-/merge_requests/{mr_id}"
+
+
 def get_artifacts_zip(mr_id: int, no_cache: bool, origin: GitLabOrigin) -> str:
     """Download artifacts from the GitLab API.
 
@@ -326,11 +337,12 @@ def commits_have_mr_id(commits: list[str], mr_id: int) -> bool:
 
     :param commits: return value from git.commits_on_top_of()
     :returns: True if the MR-ID is in each subject, False otherwise"""
+    mr_url = get_url(mr_id)
     for commit in commits:
-        subject = git.run(["show", "-s", "--format=%s", commit])
-        if subject is None:
+        body = git.run(["show", "-s", "--format=%b", commit])
+        if body is None:
             raise RuntimeError
-        if not subject.endswith(" (MR " + str(mr_id) + ")"):
+        if f"Part-of: {mr_url}" not in body:
             return False
     return True
 
@@ -416,7 +428,7 @@ def run_git_filter_branch(
     env = os.environ.copy()
     env["FILTER_BRANCH_SQUELCH_WARNING"] = "1"
     if mr_id:
-        env["MRHLPR_MSG_FILTER_MR_ID"] = str(mr_id)
+        env["MRHLPR_MSG_FILTER_MR_ID"] = get_url(mr_id)
     if label:
         env["MRHLPR_LABEL"] = ci_labels[label]
 
@@ -455,7 +467,7 @@ def fixmsg(
         raise RuntimeError(msg)
     os.chdir(ret)
 
-    print("Appending ' (MR " + str(mr_id) + ")' to commits and signing them...")  # noqa: E501
+    print("Adding ' Part-of: !" + str(mr_id) + "' trailer to commits and signing them...")  # noqa: E501
     run_git_filter_branch("msg_filter_add_commit_id.py", f"origin/{target_branch}", mr_id)
 
     if skip_build: