Make is_revert stricter, to match GCCs changelog scripts

Reverts like
https://gcc.gnu.org/cgit/gcc/commit/?id=eec8da328cf1f91db302ab4cee803e269e68ad33
are let through by the hooks, but then lead to failures in the changelog
generating script:
https://inbox.sourceware.org/gccadmin/20260415001632.71DF64BA23C4@sourceware.org/

This check should prevent that.

Author: ArsenArsen

hooks/config.py

@@ -93,6 +93,7 @@
     "hooks.no-precommit-check": {"default": (), "type": tuple},
     "hooks.no-rh-character-range-check": {"default": False, "type": bool},
     "hooks.no-rh-style-checks": {"default": (), "type": tuple},
+    "hooks.no-rh-near-revert-check": {"default": False, "type": bool},
     "hooks.no-style-checks": {"default": (), "type": tuple},
     "hooks.pre-receive-hook": {"default": None},
     "hooks.post-receive-hook": {"default": None},

hooks/pre_commit_checks.py

@@ -309,6 +309,29 @@ def check_missing_ticket_number(commit):
     )
 
 
+def reject_almost_reversions(commit):
+    """Raise InvalidUpdate if the commit's revlog contains "This reverts
+    commit" in it.
+
+    The GCC ChangeLog scripts expect a line that contains that sentence to also
+    contain a reference to the commit being reverted.  If this line is altered,
+    therefore, they will fail.
+
+    PARAMETERS
+        commit: A CommitInfo object corresponding to the commit being checked.
+    """
+    if git_config("hooks.no-rh-near-revert-check"):
+        return
+
+    if "This reverts commit" in commit.raw_revlog:
+        raise InvalidUpdate(
+            "Commit %s looks like it was intended as a revert." % commit.rev,
+            "",
+            "When reverting, you should leave the 'This reverts commit'",
+            "line unaltered.",
+        )
+
+
 def check_revision_history(commit):
     """Apply pre-commit checks to the commit's revision history.
 
@@ -321,6 +344,7 @@ def check_revision_history(commit):
         return
 
     # Various checks on the revision history...
+    reject_almost_reversions(commit)
     ensure_iso_8859_15_only(commit)
     ensure_empty_line_after_subject(commit)
     reject_lines_too_long(commit)

hooks/updates/commits.py

@@ -4,6 +4,19 @@
 from io_utils import safe_decode
 from updates.mailinglists import expanded_mailing_list
 from utils import debug
+import re
+
+
+_REVERT_COMMIT_RE = re.compile(
+    r"^This reverts commit (?P<hash>[0-9a-f]+)\.$",
+    re.M
+)
+"""A regex that matches the same revert lines as ``revert_regex`` does in
+``contrib/gcc-changelog/git_commit.py``.
+
+Note that this regex is matched against an entire body of a commit rather than
+each line in it, though.
+"""
 
 
 class CommitInfo(object):
@@ -235,11 +248,7 @@ def is_revert(self):
         revision log of such commits, hoping that a user is not deleting
         them afterwards.
         """
-        if "This reverts commit" in self.raw_revlog:
-            return True
-
-        # No recognizable pattern. Probably not a revert commit.
-        return False
+        return bool(_REVERT_COMMIT_RE.search(self.raw_revlog));
 
     @classmethod
     def __all_files_from_commit_rev(cls, rev):

testsuite/tests/GCC__stricter_revert_pattern/bare_repo_config

@@ -0,0 +1,95 @@
+[hooks]
+	from-domain = gcc.gnu.org
+	mailinglist = /git/gcc.git/hooks-bin/email_to.py
+
+	# We do not want to force a maximum line length in commit
+	# revision logs, as they get in the way of copy-pasting
+	# debugging session, error messages, logs, etc.
+	max-rh-line-length = 0
+
+	# We allow a 0.5MiB email diff maximum.
+	max-email-diff-size = 524288
+
+	# Reject merge commits on a certain number of branches:
+	#  - on master: We request that people rebase their changes
+	#    before pushing instead (merge commits tend to confuse
+	#    git newcomers).
+	#  - on release: We apply the same policy to release branches
+	#    as we have on master.
+	reject-merge-commits = refs/heads/master,refs/heads/trunk,refs/heads/releases/.*
+
+	# The URL where we can inspect the commit, inserted in the commit
+	# notification email, and also copy sent to the file-commit-cmd.
+	commit-url = "https://gcc.gnu.org/g:%(rev)s"
+
+	# This style checker does nothing at present.
+	style-checker = /git/gcc.git/hooks-bin/style_checker
+
+	# Send a copy to bugzilla if a commit has a PR number in it.
+	# The script is a wrapper around
+	# /sourceware/infra/bin/email-to-bugzilla.
+	file-commit-cmd = "/git/gcc.git/hooks-bin/email-to-bugzilla-filtered"
+
+	# Work around <https://github.com/AdaCore/git-hooks/issues/9>
+	# to allow larger merges.
+	max-commit-emails = 5000
+
+	# Allow deliberate merges to use the default commit message.
+	# Branches that do not allow merge commits are listed in
+	# reject-merge-commits.
+	disable-merge-commit-checks = true
+
+	# Do not send emails for commits that are already in the
+	# repository being added to development branches or user or
+	# vendor branches (through merges or rebases).
+	email-new-commits-only = refs/heads/devel/.*
+	email-new-commits-only = refs/users/.*
+	email-new-commits-only = refs/vendors/.*
+
+	# GCC-specific ref naming conventions for user and vendor
+	# branches.
+	branch-ref-namespace = refs/users/[^/]*/heads/.*
+	branch-ref-namespace = refs/vendors/[^/]*/heads/.*
+
+	# GCC-specific ref naming conventions for user and vendor
+	# tags.
+	tag-ref-namespace = refs/users/[^/]*/tags/.*
+	tag-ref-namespace = refs/vendors/[^/]*/tags/.*
+
+	# Branch deletion is disabled by default.
+	restrict-branch-deletion = true
+
+	# Branch deletion is allowed for user and vendor branches.
+	allow-delete-branch = refs/users/[^/]*/heads/.*
+	allow-delete-branch = refs/vendors/[^/]*/heads/.*
+
+	# Non-fast-forward updates are allowed in the user and vendor
+	# namespaces.
+	allow-non-fast-forward = refs/users/.*
+	allow-non-fast-forward = refs/vendors/.*
+
+	# Message to give for rejected branch deletion.
+	rejected-branch-deletion-tip = Branch deletion is only allowed for user and vendor branches.  If another branch was created by mistake, contact an administrator to delete it on the server with git update-ref.  If a development branch is dead, also contact an administrator to move it under refs/dead/heads/ rather than deleting it.
+
+	# Commit messages should not be restricted to ISO-8859-15.
+	no-rh-character-range-check = true
+
+	# Custom checker script for each new commit of each ref being
+	# updated.  This makes several checks on the commit message,
+	# including for ChangeLog formatting and contents.
+	commit-extra-checker = /git/gcc.git/hooks-bin/commit_checker
+
+	# Custom checker script for ref updates.  This checks for
+	# branch naming conventions and not introducing new references
+	# to the git-svn history.
+	update-hook = /git/gcc.git/hooks-bin/update_hook
+
+	# Custom email formatter.  This inserts GCC monotonically
+	# increasing commit ids in the commit emails.
+	commit-email-formatter = /git/gcc.git/hooks-bin/commit_email_formatter
+
+	# For GCC/Rust development that happens outside of GCC proper,
+	# <https://rust-gcc.github.io/>, the Git commit messages
+	# don't always adhere to standard GCC style; see
+	# <https://github.com/Rust-GCC/gccrs/issues/143>.
+	no-precommit-check = refs/heads/devel/rust/.*

testsuite/tests/GCC__stricter_revert_pattern/hooks_config

@@ -0,0 +1,14 @@
+def test_push_bad_revert_commit(testcase):
+    """Try pushing master..."""
+    p = testcase.run("git push origin trunk".split())
+    testcase.assertNotEqual(p.status, 0, p.image)
+    testcase.assertRunOutputEqual(p, """\
+remote: *** Commit df3a09266b6685060fb1e11268922b491e3e5cd8 looks like it was intended as a revert.
+remote: ***
+remote: *** When reverting, you should leave the 'This reverts commit'
+remote: *** line unaltered.
+remote: error: hook declined to update refs/heads/trunk
+To ../bare/repo.git/
+ ! [remote rejected] trunk -> trunk (hook declined)
+error: failed to push some refs to '../bare/repo.git/'
+""")