Added python script suitable for using as prepare-commit-msg git hook.

1 files changed, 115 insertions, 0 deletions

diff --git a/scripts/prepare_commit_msg.py b/scripts/prepare_commit_msg.py
new file mode 100755
index 0000000000..bcb5b5faf7
--- /dev/null
+++ b/scripts/prepare_commit_msg.py
@@ -0,0 +1,115 @@
+#! /usr/bin/env python
+
+"""
+prepare-commit-msg hook for Django's repository.
+
+Adjusts commit messages on any branch:
+- Ensures the summary line ends with a period.
+
+Additionally, on stable branches:
+- Adds the [A.B.x] branch prefix if missing.
+- Adds "Backport of <sha> from main." when cherry-picking.
+
+To install:
+  1. Ensure the folder `.git/hooks` exists.
+  2. Create an executable file `.git/hooks/prepare-commit-msg` with content:
+
+#!/bin/sh
+exec python scripts/prepare_commit_msg.py "$@"
+
+"""
+
+import os
+import subprocess
+import sys
+
+
+def run(cmd):
+    return subprocess.run(cmd, capture_output=True, text=True).stdout.strip()
+
+
+def process_commit_message(lines, branch, cherry_sha=None):
+    """Adjust commit message lines for a potential backport.
+
+    - Separates body lines from trailing git comment lines.
+    - Ensure all lines ends with a period.
+    - On stable branches, adds the [A.B.x] prefix to the first line if missing.
+    - If cherry_sha is provided, appends "Backport of <sha> from main." to
+      the body if not already present.
+
+    Returns the modified lines (body + comments).
+
+    """
+    # Separate body lines from trailing git comment lines.
+    comment_start = len(lines)
+    for i in range(len(lines) - 1, -1, -1):
+        if lines[i].startswith("#"):
+            comment_start = i
+        elif lines[i].strip():
+            break
+
+    body_lines = lines[:comment_start]
+    comment_lines = lines[comment_start:]
+
+    # Strip leading and trailing blank lines from the body.
+    while body_lines and not body_lines[0].strip():
+        body_lines.pop(0)
+    while body_lines and not body_lines[-1].strip():
+        body_lines.pop()
+
+    # Nothing to do if the body is empty.
+    if not body_lines:
+        return lines
+
+    summary = body_lines[0].strip()
+
+    # Ensure summary ends with a period.
+    if not summary.endswith("."):
+        summary += "."
+
+    # On stable branches, add the [A.B.x] prefix if missing.
+    prefix = None
+    if branch.startswith("stable/"):
+        version = branch[len("stable/") :]
+        prefix = f"[{version}] "
+        if not summary.startswith(prefix):
+            summary = prefix + summary
+
+    # Capitalize the first character of the summary text (after any prefix).
+    offset = len(prefix) if prefix else 0
+    summary = summary[:offset] + summary[offset].upper() + summary[offset + 1 :]
+
+    body_lines[0] = summary + "\n"
+
+    # Add "Backport of <sha> from main." if cherry-picking and not present.
+    if cherry_sha:
+        backport_note = f"Backport of {cherry_sha} from main."
+        if backport_note not in "".join(body_lines):
+            # Strip trailing blank lines, then append note with separator.
+            while body_lines and not body_lines[-1].strip():
+                body_lines.pop()
+            body_lines.append("\n")
+            body_lines.append(backport_note + "\n")
+
+    return body_lines + comment_lines
+
+
+if __name__ == "__main__":
+    msg_path = sys.argv[1]
+
+    with open(msg_path, encoding="utf-8") as f:
+        lines = f.readlines()
+
+    branch = run(["git", "branch", "--show-current"])
+
+    cherry_sha = None
+    git_dir = run(["git", "rev-parse", "--git-dir"])
+    cherry_pick_head_path = os.path.join(git_dir, "CHERRY_PICK_HEAD")
+    if os.path.exists(cherry_pick_head_path):
+        with open(cherry_pick_head_path, encoding="utf-8") as f:
+            cherry_sha = f.read().strip()
+
+    result = process_commit_message(lines, branch, cherry_sha)
+
+    with open(msg_path, "w", encoding="utf-8") as f:
+        f.writelines(result)