diff mbox series

[v2,3/3] devtool: upgrade: diff git-log-style changelogs by commit hash

Message ID 20260804060205.179715-4-daniel.turull@ericsson.com
State Under Review
Headers show
Series devtool: upgrade: improve changelog extraction for git-log-style ChangeLogs | expand

Commit Message

Daniel Turull Aug. 4, 2026, 6:02 a.m. UTC
From: Daniel Turull <daniel.turull@ericsson.com>

Files like nghttp2's ChangeLog are the literal output of `git log`,
regenerated wholesale on every release. New commits are prepended, so
every existing commit shifts position even though its content is
unchanged. A textual diff sees that shift as removed/added lines
instead of showing just the commits that were actually added.

Diff these files structurally instead: compare commit hashes between
the old and new file to tell moved commits from genuinely new ones,
and report the subject lines of the new commits. Falls back to the
existing line-based diff for changelogs that aren't git-log output.

AI-Generated: Kiro with Claude Sonnet 5
Signed-off-by: Daniel Turull <daniel.turull@ericsson.com>
---
 scripts/lib/devtool/upgrade.py | 64 +++++++++++++++++++++++++++++-----
 1 file changed, 55 insertions(+), 9 deletions(-)
diff mbox series

Patch

diff --git a/scripts/lib/devtool/upgrade.py b/scripts/lib/devtool/upgrade.py
index 6883c99cce..856110c803 100644
--- a/scripts/lib/devtool/upgrade.py
+++ b/scripts/lib/devtool/upgrade.py
@@ -589,6 +589,43 @@  def _resolve_rst_includes(content, srctree):
     return ''.join(result)
 
 
+_GIT_LOG_COMMIT_RE = re.compile(r'^commit ([0-9a-f]{7,40})\b.*$', re.MULTILINE)
+
+def _diff_git_log_changelog(old_content, new_content):
+    """Diff a ChangeLog that is itself `git log` output (e.g. nghttp2),
+    regenerated wholesale on every release. New commits get prepended, so
+    old ones shift position even though unchanged, which a textual diff
+    would wrongly show as removed/added lines. Compare commit hashes
+    instead: hashes already in old_content are just moved, anything else
+    is new. Returns the new commits' subject lines as one string, or
+    None if either file doesn't look like git log output."""
+    old_hashes = set(_GIT_LOG_COMMIT_RE.findall(old_content))
+    new_commits = _GIT_LOG_COMMIT_RE.split(new_content)[1:]  # [hash, block, hash, block, ...]
+    if not old_hashes or not new_commits:
+        return None
+
+    subjects = []
+    for commit_hash, block in zip(new_commits[0::2], new_commits[1::2]):
+        if commit_hash in old_hashes:
+            continue
+        # `git log` separates headers (Author:, Date:, etc.) from the
+        # commit message with a blank line; drop the leading blank line
+        # left over from splitting on "commit <hash>", then skip the
+        # headers up to the next blank line to get just the message.
+        lines = block.splitlines()
+        while lines and not lines[0].strip():
+            lines.pop(0)
+        blank_at = next((i for i, l in enumerate(lines) if not l.strip()), len(lines))
+        message_lines = [l.strip() for l in lines[blank_at:] if l.strip()]
+        # Skip the 'Merge pull request ...' line GitHub adds as the first
+        # message line of a merge commit; the actual change subject is the
+        # next line, and keeping the merge line would duplicate it.
+        subject = next((l for l in message_lines if not l.startswith('Merge pull request ')), None)
+        if subject and (not subjects or subjects[-1] != subject):
+            subjects.append(subject)
+    return '\n'.join(subjects) if subjects else None
+
+
 def _git_show_file(srctree, ref, fname):
     """Return the content of fname at ref. Changelogs occasionally contain
     non-UTF-8 bytes (e.g. Latin-1 author names), which bb.process.run()
@@ -642,15 +679,24 @@  def _extract_changelog(srctree, pn, old_ver, new_ver, old_tag, new_tag, workspac
             for fname in changed_files:
                 basename = os.path.basename(fname).lower()
                 if basename in _CHANGELOG_BASENAMES:
-                    diff_out, _ = _run('git diff %s %s -- %s' % (old_tag, new_tag, shlex.quote(fname)), srctree)
-                    if diff_out.strip():
-                        lines = [line[1:] for line in diff_out.splitlines()
-                                 if line.startswith('+') and not line.startswith('+++')]
-                        if lines:
-                            candidate = '\n'.join(lines)
-                            if not changelog_content or len(candidate) > len(changelog_content):
-                                changelog_content = candidate
-                                changelog_fname = fname
+                    candidate = None
+                    try:
+                        old_file = _git_show_file(srctree, old_tag, fname)
+                        new_file = _git_show_file(srctree, new_tag, fname)
+                        candidate = _diff_git_log_changelog(old_file, new_file)
+                    except bb.process.ExecutionError:
+                        pass
+                    if candidate is None:
+                        try:
+                            diff_out, _ = _run('git diff %s %s -- %s' % (old_tag, new_tag, shlex.quote(fname)), srctree)
+                        except UnicodeDecodeError:
+                            diff_out = ''
+                        added_lines = [line[1:] for line in diff_out.splitlines()
+                                       if line.startswith('+') and not line.startswith('+++')]
+                        candidate = '\n'.join(added_lines) if added_lines else None
+                    if candidate and (not changelog_content or len(candidate) > len(changelog_content)):
+                        changelog_content = candidate
+                        changelog_fname = fname
     except bb.process.ExecutionError as e:
         logger.warning('Changelog file extraction failed: %s' % str(e))