gitlab CI: apply some basic validity checks on the commit messages

Let's stop merge requests from users that don't set their git author name and
email address. Aside from it looking stange in the history it'll also make it
virtually impossible to ever find that user again should something important
arise in the future - especially if we switch off gitlab.

The rest is basic style, short subject lines, Signed-off-by lines and correct
formatting.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
[bentiss: use /usr/bin/env python3 as requested by the CI]
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

.gitlab-ci.yml

@@ -135,6 +135,27 @@ variables:
 #                                                               #
 #################################################################
 
+
+check-commit:
+  image: $FEDORA_CONTAINER_IMAGE
+  stage: prep
+  script:
+    - pip3 install GitPython
+    - pip3 install pytest
+    - |
+      pytest --junitxml=results.xml \
+             --tb=line \
+             --assert=plain \
+             ./.gitlab-ci/check-commit.py
+  except:
+    - master@libinput/libinput
+  variables:
+    GIT_DEPTH: 100
+    FEDORA_VERSION: 31
+  artifacts:
+    reports:
+      junit: results.xml
+
 #
 # This stage will recreate the container images only if the image
 # is too old or if it is missing some dependencies.

.gitlab-ci/check-commit.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+#
+# This script tests a few things against the commit messages, search for
+# `def test_` to see the actual tests run.
+
+import git
+import os
+import pytest
+
+# Environment variables set by gitlab
+CI_COMMIT_SHA = os.environ['CI_COMMIT_SHA']
+CI_MERGE_REQUEST_TARGET_BRANCH_NAME = 'master'
+CI_SERVER_HOST = os.environ['CI_SERVER_HOST']
+
+# We need to add the real libinput as remote, our origin here is the user's
+# fork.
+repo = git.Repo('.')
+upstream = repo.create_remote('upstream', f'https://{CI_SERVER_HOST}/libinput/libinput.git')
+upstream.fetch()
+
+sha = CI_COMMIT_SHA
+branch = CI_MERGE_REQUEST_TARGET_BRANCH_NAME
+
+commits = list(repo.iter_commits(f'upstream/{branch}..{sha}'))
+
+
+def error(commit, message, long_message=''):
+    if long_message:
+        long_message = '\n\n\t' + long_message.replace('\n', '\n\t')
+    return f'on commit {str(commit)[:8]} "{commit.summary}": {message}{long_message}'
+
+
+@pytest.mark.parametrize('commit', commits)
+class TestCommits:
+    def test_author_email(self, commit):
+        assert '@users.noreply.gitlab.freedesktop.org' not in commit.author.email, \
+            error(commit, 'git author email invalid',
+                  ('Please set your name and email with the commands\n',
+                   '    git config --global user.name Your Name\n'
+                   '    git config --global user.email your.email@provider.com\n'))
+
+    def test_signed_off_by(self, commit):
+        if not commit.message.startswith('Revert "'):
+            assert 'Signed-off-by:' in commit.message, \
+                error(commit, 'missing Signed-off-by tag',
+                      'Please add the required "Signed-off-by: author information" line to the commit message')
+
+    def test_fixup(self, commit):
+        assert not commit.message.startswith('fixup!'), \
+            error(commit, 'Remove fixup! tag',
+                  'Leftover "fixup!" commit message detected, please squash')
+        assert not commit.message.startswith('squash!'), \
+            error(commit, 'Remove squash! tag',
+                  'Leftover "squash!" commit message detected, please squash')
+
+    def test_line_length(self, commit):
+        lines = commit.message.split('\n')
+        first_line = lines[0]
+
+        assert len(first_line) < 85, \
+            error(commit, 'Commit message subject line too long')
+
+        try:
+            second_line = lines[1]
+            assert second_line == '', \
+                error(commit, 'Second line in commit message must be emtpy')
+        except IndexError:
+            pass