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llvm-project/llvm/utils/revert_checker.py
George Burgess IV a8585654c2
[llvm][utils] skip revert-checking reverts across branches (#134108) 
e2ba1b6ffde4ec607342b1b746d1b57f0f04390a references that it reverts a
commit that's not a parent of e2ba1b6ffde4ec607342b1b746d1b57f0f04390a.

Functionally, this can (and demonstrably does) work(*), but from the
standpoint of the revert checker, it's nonsense. Print a `logging.error`
when it's detected.

Tested by running the revert checker against a commit range that
includes the aforementioned commit; the logging.error was fired
appropriately.

(*) - the specifics here are:
- the _SHA_ that was referenced was on a non-main branch, but
- the commit from the non-main branch was merged into the non-main
branch from main
- ...so the _functional_ commit being reverted was originally landed on
main, but the _SHA_ referenced from main was from a branch that was cut
before the reverted-commit was landed on main
2025-04-02 13:44:18 -07:00

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# ===----------------------------------------------------------------------===##
#
# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
# See https://llvm.org/LICENSE.txt 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,
though.
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:
```
./revert_checker.py 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 Dict, Generator, Iterable, List, NamedTuple, Optional, Tuple
assert sys.version_info >= (3, 6), "Only Python 3.6+ is supported."
# People are creative with their reverts, and heuristics are a bit difficult.
# At a glance, most reverts have "This reverts commit ${full_sha}". Many others
# have `Reverts llvm/llvm-project#${PR_NUMBER}`.
#
# By their powers combined, we should be able to automatically catch something
# like 80% of reverts with reasonable confidence. At some point, human
# intervention will always be required (e.g., I saw
# ```
# This reverts commit ${commit_sha_1} and
# also ${commit_sha_2_shorthand}
# ```
# during my sample)
_CommitMessageReverts = NamedTuple(
"_CommitMessageReverts",
[
("potential_shas", List[str]),
("potential_pr_numbers", List[int]),
],
)
def _try_parse_reverts_from_commit_message(
commit_message: str,
) -> _CommitMessageReverts:
"""Tries to parse revert SHAs and LLVM PR numbers form the commit message.
Returns:
A namedtuple containing:
- A list of potentially reverted SHAs
- A list of potentially reverted LLVM PR numbers
"""
if not commit_message:
return _CommitMessageReverts([], [])
sha_reverts = 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:
sha_reverts.append(initial_revert.group(1))
pr_numbers = [
int(x)
for x in re.findall(
r"Reverts llvm/llvm-project#(\d+)",
commit_message,
)
]
return _CommitMessageReverts(
potential_shas=sha_reverts,
potential_pr_numbers=pr_numbers,
)
def _stream_stdout(
command: List[str], cwd: Optional[str] = None
) -> Generator[str, None, None]:
with subprocess.Popen(
command,
cwd=cwd,
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],
encoding="utf-8",
stderr=subprocess.DEVNULL,
).strip()
_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 = [
"git",
"-C",
git_dir,
"log",
"^" + end_at_sha,
root_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
break
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
break
commit_message.append(line)
yield _LogEntry(sha, "\n".join(commit_message).rstrip())
def _shas_between(git_dir: str, base_ref: str, head_ref: str) -> Iterable[str]:
rev_list = [
"git",
"-C",
git_dir,
"rev-list",
"--first-parent",
f"{base_ref}..{head_ref}",
]
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],
encoding="utf-8",
).strip()
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`.
Returns:
A SHA. Note that `ref_a` will be returned if `ref_a` is a parent of
`ref_b`, and vice-versa.
"""
return subprocess.check_output(
["git", "-C", git_dir, "merge-base", ref_a, ref_b],
encoding="utf-8",
).strip()
def _load_pr_commit_mappings(
git_dir: str, root: str, min_ref: str
) -> Dict[int, List[str]]:
git_log = ["git", "log", "--format=%H %s", f"{min_ref}..{root}"]
results = collections.defaultdict(list)
pr_regex = re.compile(r"\s\(#(\d+)\)$")
for line in _stream_stdout(git_log, cwd=git_dir):
m = pr_regex.search(line)
if not m:
continue
pr_number = int(m.group(1))
sha = line.split(None, 1)[0]
# N.B., these are kept in log (read: reverse chronological) order,
# which is what's expected by `find_reverts`.
results[pr_number].append(sha)
return results
# N.B., max_pr_lookback's default of 20K commits is arbitrary, but should be
# enough for the 99% case of reverts: rarely should someone land a cleanish
# revert of a >6 month old change...
def find_reverts(
git_dir: str, across_ref: str, root: str, max_pr_lookback: int = 20000
) -> List[Revert]:
"""Finds reverts across `across_ref` in `git_dir`, starting from `root`.
These reverts are returned in order of oldest reverts first.
Args:
git_dir: git directory to find reverts in.
across_ref: the ref to find reverts across.
root: the 'main' ref to look for reverts on.
max_pr_lookback: this function uses heuristics to map PR numbers to
SHAs. These heuristics require that commit history from `root` to
`some_parent_of_root` is loaded in memory. `max_pr_lookback` is how
many commits behind `across_ref` should be loaded in memory.
"""
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 = []
# Lazily load PR <-> commit mappings, since it can be expensive.
pr_commit_mappings = None
for sha, commit_message in _log_stream(git_dir, root_sha, across_sha):
reverts, pr_reverts = _try_parse_reverts_from_commit_message(
commit_message,
)
if pr_reverts:
if pr_commit_mappings is None:
logging.info(
"Loading PR <-> commit mappings. This may take a moment..."
)
pr_commit_mappings = _load_pr_commit_mappings(
git_dir, root_sha, f"{across_sha}~{max_pr_lookback}"
)
logging.info(
"Loaded %d PR <-> commit mappings", len(pr_commit_mappings)
)
for reverted_pr_number in pr_reverts:
reverted_shas = pr_commit_mappings.get(reverted_pr_number)
if not reverted_shas:
logging.warning(
"No SHAs for reverted PR %d (commit %s)",
reverted_pr_number,
sha,
)
continue
logging.debug(
"Inferred SHAs %s for reverted PR %d (commit %s)",
reverted_shas,
reverted_pr_number,
sha,
)
reverts.extend(reverted_shas)
if not reverts:
continue
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,
)
continue
try:
object_type = subprocess.check_output(
["git", "-C", git_dir, "cat-file", "-t", reverted_sha],
encoding="utf-8",
stderr=subprocess.DEVNULL,
).strip()
except subprocess.CalledProcessError:
logging.warning(
"Failed to resolve reverted object %s (claimed to be reverted "
"by sha %s)",
reverted_sha,
sha,
)
continue
if object_type != "commit":
logging.error(
"%s claims to revert the %s %s, which isn't a commit",
sha,
object_type,
reverted_sha,
)
continue
# Rarely, reverts will cite SHAs on other branches (e.g., revert
# commit says it reverts a commit with SHA ${X}, but ${X} is not a
# parent of the revert). This can happen if e.g., the revert has
# been mirrored to another branch. Treat them the same as
# reverts of non-commits.
if _find_common_parent_commit(git_dir, sha, reverted_sha) != reverted_sha:
logging.error(
"%s claims to revert %s, which is a commit that is not "
"a parent of the revert",
sha,
reverted_sha,
)
continue
all_reverts.append(Revert(sha, 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.
all_reverts.reverse()
return all_reverts
def _main() -> None:
parser = argparse.ArgumentParser(
description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter
)
parser.add_argument("base_ref", help="Git ref or sha to check for reverts around.")
parser.add_argument("-C", "--git_dir", default=".", help="Git directory to use.")
parser.add_argument("root", nargs="+", help="Root(s) to search for commits from.")
parser.add_argument("--debug", action="store_true")
parser.add_argument(
"-u",
"--review_url",
action="store_true",
help="Format SHAs as llvm review URLs",
)
opts = parser.parse_args()
logging.basicConfig(
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:
seen_reverts.add(revert)
all_reverts.append(revert)
sha_prefix = (
"https://github.com/llvm/llvm-project/commit/" if opts.review_url else ""
)
for revert in all_reverts:
sha_fmt = f"{sha_prefix}{revert.sha}"
reverted_sha_fmt = f"{sha_prefix}{revert.reverted_sha}"
print(f"{sha_fmt} claims to revert {reverted_sha_fmt}")
if __name__ == "__main__":
_main()
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