Fail the release when docstrfmt verifies nothing

The 1.6.0 release job ran docstrfmt over the changelog, was told
"0 files was checked", and treated the zero as success. The pre-commit
docstrfmt hook agreed, so the fail-closed check at the end of the
release passed and the commit went to main past the ruleset bypass,
where pre-commit.ci then rejected it.

Drop the bespoke docstrfmt call so the hooks are the only formatter,
and verify the result: the changelog check must both succeed and
report the file it inspected. A run that formats nothing now stops
the release instead of shipping.

Author: gaborbernat

tasks/release.py

@@ -2,8 +2,10 @@
 
 from __future__ import annotations
 
+import re
+
 from pathlib import Path
-from subprocess import call, check_call
+from subprocess import call, check_call, run
 
 from git import Commit, Remote, Repo, TagReference
 from packaging.version import Version
@@ -15,6 +17,7 @@
 CHANGELOG_FRAGMENTS_DIR = ROOT_SRC_DIR / 'docs' / 'changelog'
 MAJOR_FRAGMENT_TYPES = frozenset({'removal'})
 MINOR_FRAGMENT_TYPES = frozenset({'feature', 'deprecation'})
+CHECKED_FILE_COUNT = re.compile(r'(\d+) files? was checked')
 
 
 def main(version_str: str, *, push: bool) -> None:
@@ -80,20 +83,37 @@ def create_release_commit(repo: Repo, version: Version) -> Commit:
     update_version_file(version)
     print('build changelog from fragments with towncrier')
     check_call(['towncrier', 'build', '--yes', '--version', version.public], cwd=str(ROOT_SRC_DIR))  # noqa: S603
-    # towncrier appends the issue reference past docstrfmt's width budget, so its raw output can run over the
-    # limit; reflow it here with a pinned docstrfmt instead of trusting the release job's isolated hook env,
-    # which passed over-long lines into 1.5.1 and left a changelog that failed pre-commit everywhere else.
-    check_call(['docstrfmt', '--line-length', '120', 'CHANGELOG.rst'], cwd=str(ROOT_SRC_DIR))
     call(['pre-commit', 'run', '--all-files'], cwd=str(ROOT_SRC_DIR))
     call(['pre-commit', 'run', '--all-files'], cwd=str(ROOT_SRC_DIR))
     repo.git.add('src/build/__init__.py', 'CHANGELOG.rst', 'docs/changelog/*')
     check_call(['pre-commit', 'run', '--all-files', '--show-diff-on-failure'], cwd=str(ROOT_SRC_DIR))
     if repo.is_dirty(index=False, working_tree=True, untracked_files=False):
         msg = 'Pre-commit hooks modified files after final run. This indicates an environment inconsistency.'
         raise RuntimeError(msg)
+    verify_changelog_formatted()
     return repo.index.commit(f'chore: prepare for {version}')
 
 
+def verify_changelog_formatted() -> None:
+    # 1.6.0 shipped a changelog that every other environment reformats: the release runner's docstrfmt inspected no
+    # files and still exited 0, so the hook reported success. Require the check to name a file it actually looked at.
+    # The width is the one the docstrfmt hook passes in .pre-commit-config.yaml.
+    result = run(
+        ['docstrfmt', '--check', '--ignore-cache', '--line-length', '120', 'CHANGELOG.rst'],
+        capture_output=True,
+        check=False,
+        cwd=str(ROOT_SRC_DIR),
+        encoding='utf-8',
+    )
+    report = (result.stderr or result.stdout).strip()
+    if result.returncode:
+        msg = f'CHANGELOG.rst is not formatted the way the docstrfmt hook expects:\n{report}'
+        raise RuntimeError(msg)
+    if (checked := CHECKED_FILE_COUNT.search(report)) is None or not int(checked[1]):
+        msg = f'docstrfmt inspected no files, leaving CHANGELOG.rst unverified:\n{report}'
+        raise RuntimeError(msg)
+
+
 def update_version_file(version: Version) -> None:
     content = VERSION_FILE.read_text(encoding='utf-8')
     lines = content.splitlines(keepends=True)