blob: deb49412b1ec316d8bf5f28d79cb89e92305fe2b [file] [log] [blame]
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
# See for license information.
# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
"""Checks for reverts of commits across a given git commit.
To clarify the meaning of 'across' with an example, if we had the following
commit history (where `a -> b` notes that `b` is a direct child of `a`):
123abc -> 223abc -> 323abc -> 423abc -> 523abc
And where 423abc is a revert of 223abc, this revert is considered to be 'across'
323abc. More generally, a revert A of a parent commit B is considered to be
'across' a commit C if C is a parent of A and B is a parent of C.
Please note that revert detection in general is really difficult, since merge
conflicts/etc always introduce _some_ amount of fuzziness. This script just
uses a bundle of heuristics, and is bound to ignore / incorrectly flag some
reverts. The hope is that it'll easily catch the vast majority (>90%) of them,
This is designed to be used in one of two ways: an import in Python, or run
directly from a shell. If you want to import this, the `find_reverts`
function is the thing to look at. If you'd rather use this from a shell, have a
usage example:
./ c47f97169 origin/main origin/release/12.x
This checks for all reverts from the tip of origin/main to c47f97169, which are
across the latter. It then does the same for origin/release/12.x to c47f97169.
Duplicate reverts discovered when walking both roots (origin/main and
origin/release/12.x) are deduplicated in output.
import argparse
import collections
import logging
import re
import subprocess
import sys
from typing import Generator, List, NamedTuple, Iterable
assert sys.version_info >= (3, 6), 'Only Python 3.6+ is supported.'
# People are creative with their reverts, and heuristics are a bit difficult.
# Like 90% of of reverts have "This reverts commit ${full_sha}".
# Some lack that entirely, while others have many of them specified in ad-hoc
# ways, while others use short SHAs and whatever.
# The 90% case is trivial to handle (and 100% free + automatic). The extra 10%
# starts involving human intervention, which is probably not worth it for now.
def _try_parse_reverts_from_commit_message(commit_message: str) -> List[str]:
if not commit_message:
return []
results = re.findall(r'This reverts commit ([a-f0-9]{40})\b', commit_message)
first_line = commit_message.splitlines()[0]
initial_revert = re.match(r'Revert ([a-f0-9]{6,}) "', first_line)
if initial_revert:
return results
def _stream_stdout(command: List[str]) -> Generator[str, None, None]:
with subprocess.Popen(
command, stdout=subprocess.PIPE, encoding='utf-8', errors='replace') as p:
assert p.stdout is not None # for mypy's happiness.
yield from p.stdout
def _resolve_sha(git_dir: str, sha: str) -> str:
if len(sha) == 40:
return sha
return subprocess.check_output(
['git', '-C', git_dir, 'rev-parse', sha],
_LogEntry = NamedTuple('_LogEntry', [
('sha', str),
('commit_message', str),
def _log_stream(git_dir: str, root_sha: str,
end_at_sha: str) -> Iterable[_LogEntry]:
sep = 50 * '<>'
log_command = [
'^' + end_at_sha,
'--format=' + sep + '%n%H%n%B%n',
stdout_stream = iter(_stream_stdout(log_command))
# Find the next separator line. If there's nothing to log, it may not exist.
# It might not be the first line if git feels complainy.
found_commit_header = False
for line in stdout_stream:
if line.rstrip() == sep:
found_commit_header = True
while found_commit_header:
sha = next(stdout_stream, None)
assert sha is not None, 'git died?'
sha = sha.rstrip()
commit_message = []
found_commit_header = False
for line in stdout_stream:
line = line.rstrip()
if line.rstrip() == sep:
found_commit_header = True
yield _LogEntry(sha, '\n'.join(commit_message).rstrip())
def _shas_between(git_dir: str, base_ref: str, head_ref: str) -> Iterable[str]:
rev_list = [
return (x.strip() for x in _stream_stdout(rev_list))
def _rev_parse(git_dir: str, ref: str) -> str:
return subprocess.check_output(
['git', '-C', git_dir, 'rev-parse', ref],
Revert = NamedTuple('Revert', [
('sha', str),
('reverted_sha', str),
def _find_common_parent_commit(git_dir: str, ref_a: str, ref_b: str) -> str:
"""Finds the closest common parent commit between `ref_a` and `ref_b`."""
return subprocess.check_output(
['git', '-C', git_dir, 'merge-base', ref_a, ref_b],
def find_reverts(git_dir: str, across_ref: str, root: str) -> List[Revert]:
"""Finds reverts across `across_ref` in `git_dir`, starting from `root`.
These reverts are returned in order of oldest reverts first.
across_sha = _rev_parse(git_dir, across_ref)
root_sha = _rev_parse(git_dir, root)
common_ancestor = _find_common_parent_commit(git_dir, across_sha, root_sha)
if common_ancestor != across_sha:
raise ValueError(f"{across_sha} isn't an ancestor of {root_sha} "
'(common ancestor: {common_ancestor})')
intermediate_commits = set(_shas_between(git_dir, across_sha, root_sha))
assert across_sha not in intermediate_commits
logging.debug('%d commits appear between %s and %s',
len(intermediate_commits), across_sha, root_sha)
all_reverts = []
for sha, commit_message in _log_stream(git_dir, root_sha, across_sha):
reverts = _try_parse_reverts_from_commit_message(commit_message)
if not reverts:
resolved_reverts = sorted(set(_resolve_sha(git_dir, x) for x in reverts))
for reverted_sha in resolved_reverts:
if reverted_sha in intermediate_commits:
logging.debug('Commit %s reverts %s, which happened after %s', sha,
reverted_sha, across_sha)
object_type = subprocess.check_output(
['git', '-C', git_dir, 'cat-file', '-t', reverted_sha],
except subprocess.CalledProcessError:
'Failed to resolve reverted object %s (claimed to be reverted '
'by sha %s)', reverted_sha, sha)
if object_type == 'commit':
all_reverts.append(Revert(sha, reverted_sha))
logging.error("%s claims to revert %s -- which isn't a commit -- %s", sha,
object_type, reverted_sha)
# Since `all_reverts` contains reverts in log order (e.g., newer comes before
# older), we need to reverse this to keep with our guarantee of older =
# earlier in the result.
return all_reverts
def _main() -> None:
parser = argparse.ArgumentParser(
description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
'base_ref', help='Git ref or sha to check for reverts around.')
'-C', '--git_dir', default='.', help='Git directory to use.')
'root', nargs='+', help='Root(s) to search for commits from.')
parser.add_argument('--debug', action='store_true')
opts = parser.parse_args()
format='%(asctime)s: %(levelname)s: %(filename)s:%(lineno)d: %(message)s',
level=logging.DEBUG if opts.debug else logging.INFO,
# `root`s can have related history, so we want to filter duplicate commits
# out. The overwhelmingly common case is also to have one root, and it's way
# easier to reason about output that comes in an order that's meaningful to
# git.
seen_reverts = set()
all_reverts = []
for root in opts.root:
for revert in find_reverts(opts.git_dir, opts.base_ref, root):
if revert not in seen_reverts:
for revert in all_reverts:
print(f'{revert.sha} claims to revert {revert.reverted_sha}')
if __name__ == '__main__':