CI: Check commit message compliance

This commit adds these checks.
- Title consists of module name(s) and subject or just subject.
- If there are two or more module names, the module names has to be
  separated by a comma followed by an optional space.
- First word of the subject is starting from an upper case letter and
  remaining characters in the first word are lower case letters.
  "Don't" and a word with a hyphen at the middle are also acceptable.
- The title is 72 characters at max including module prefix.
- If the subject exceed 50 characters excluding the module prefix,
  display a warning message.
- Titles for commits of revert and merge are ignored.
- Full description lines are 72 columns max.
  Links and co-author names are excluded from this check.

.github/workflows/commit-msg.yml

@@ -0,0 +1,24 @@
+name: Commit Message Check
+
+on: [pull_request]
+
+jobs:
+  commit-message-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup environment
+        run: |
+          pip3 install -U gitpython
+
+      - name: Fetch commits
+        run: |
+          gh api repos/${{ github.repository }}/pulls/${{ github.event.number }}/commits > commits.json
+        env:
+          GH_TOKEN: ${{ github.token }}
+
+      - name: Check the log messages
+        run: |
+          ./CI/check-log-msg.py --verbose --json commits.json

CI/check-log-msg.py

@@ -0,0 +1,213 @@
+#! /bin/env python3
+
+import git
+import re
+
+title_limit = 72
+title_text_limit = 50
+title_text_re = re.compile(r"([A-Z][a-z]*(-[a-z]+)*|Don't) .*[^.]$")
+description_line_limit = 72
+description_line_ignore_re = re.compile(r'(^Co-Authored-By:|^ *(\[[1-9][0-9]*\] |)https?://[^ ]*$)')
+
+LOG_ERROR = 100
+LOG_WARNING = 200
+LOG_INFO = 300
+loglevel_threashold = LOG_WARNING
+
+
+def find_directory_name(name, tree, max_depth):
+    for t in tree.trees:
+        if name == t.name:
+            return True
+    if max_depth > 1:
+        for t in tree.trees:
+            if find_directory_name(name, t, max_depth - 1):
+                return True
+    return False
+
+
+def check_path(path, tree):
+    paths = path.split('/', 1)
+    name = paths[0]
+    if len(paths) == 1:
+        return find_directory_name(name, tree, 1)
+    else:
+        for t in tree.trees:
+            if name == t.name:
+                return check_path(paths[1], t)
+    return False
+
+
+def find_toplevel_file(name, blobs):
+    for b in blobs:
+        n = b.name
+        if n[0] == '.':
+            n = n[1:]
+        n = n.split('.', 1)[0]
+        if name == n:
+            return True
+
+
+def find_submodule_name(name, submodules):
+    for s in submodules:
+        sname = s.name.split('/')[-1]
+        if name == sname:
+            return True
+
+
+class CommitFromJson:
+    '''Helper class to provide the same interface as git.Commit.'''
+    def __init__(self, obj, repo):
+        self._obj = obj
+        self.message = obj['commit']['message']
+        self.hexsha = obj['sha']
+        self.repo = repo
+        # Below is not exactly same as git.Commit but provided because better than nothing.
+        self.tree = repo.tree()
+
+
+class Checker:
+    def __init__(self, repo):
+        self.has_error = False
+        self.current_commit = None
+        self.repo = repo
+
+    def blog(self, level, txt):
+        if level > loglevel_threashold:
+            return
+        if level == LOG_ERROR:
+            self.has_error = True
+            s_level = "Error: "
+        elif level == LOG_WARNING:
+            s_level = "Warning: "
+        elif level == LOG_INFO:
+            s_level = "Info: "
+        print('{level}commit {hexsha}: {txt}'.format(level=s_level, hexsha=self.current_commit.hexsha[:9], txt=txt))
+
+    def check_module_names(self, names):
+        for name in names:
+            if name.find('/') >= 0:
+                if check_path(name, self.current_commit.tree):
+                    return True
+            else:
+                if find_directory_name(name, self.current_commit.tree, 3):
+                    return True
+                if find_toplevel_file(name, self.current_commit.tree.blobs):
+                    return True
+                # TODO: Cannot handle removed submodules. Implement to parse .gitmodules file.
+                if find_submodule_name(name, self.current_commit.repo.submodules):
+                    return True
+        self.blog(LOG_ERROR, "unknown module name '%s'" % name)
+
+    def check_message_title(self, title):
+        title_split = title.split(': ', 1)
+        if len(title_split) == 2:
+            self.check_module_names(re.split(r', ?', title_split[0]))
+            title_text = title_split[1]
+        else:
+            title_text = title_split[0]
+
+        if len(title) > title_limit:
+            self.blog(LOG_ERROR, 'Too long title, %d characters, limit %d:\n  %s' % (len(title), title_limit, title))
+        elif len(title_text) > title_text_limit:
+            self.blog(LOG_WARNING, 'Too long title excluding module prefix, %d characters, recommended %d:\n  %s' % (
+                len(title_text), title_text_limit, title_text))
+
+        if not title_text_re.match(title_text):
+            self.blog(LOG_ERROR, 'Invalid title text:\n  %s' % title_text)
+            self.has_error = True
+
+    def check_message_body(self, body):
+        for line in body.split('\n'):
+            if description_line_ignore_re.match(line):
+                continue
+            if len(line) > description_line_limit and line.find(' ') > 0:
+                self.blog(LOG_ERROR, 'Too long description in a line, %d characters, limit %d:\n  %s' % (
+                    len(line), description_line_limit, line))
+        pass
+
+    def check_message(self, c):
+        self.current_commit = c
+        self.blog(LOG_INFO, "Checking commit '%s'" % c.message.split('\n', 1)[0])
+
+        msg = c.message.split('\n', 2)
+        if len(msg) == 0:
+            self.blog(LOG_ERROR, 'Commit message is empty.')
+            return True
+
+        if re.match(r'Revert ', msg[0]):
+            return False
+        if re.match(r'Merge [0-9a-f]{40} into [0-9a-f]{40}$', msg[0]):
+            return False
+        if re.match(r'Merge pull request', msg[0]):
+            return False
+
+        if len(msg) > 0:
+            self.check_message_title(msg[0])
+        if len(msg) > 1:
+            if len(msg[1]):
+                self.blog(LOG_ERROR, '2nd line is not empty.')
+        if len(msg) > 2:
+            self.check_message_body(msg[2])
+
+    def check_commits(self, commits):
+        for c in self.repo.iter_commits(commits):
+            self.check_message(c)
+
+    def check_by_json(self, commits):
+        for obj in commits:
+            c = CommitFromJson(obj, self.repo)
+            self.check_message(c)
+
+
+def open_or_stdin(name):
+    if name == '-':
+        import sys
+        return sys.stdin
+    else:
+        return open(name)
+
+
+help_epilog = """
+examples:
+  Check commit messages taken from GitHub REST API:
+    gh api repos/obsproject/obs-studio/pulls/5248/commits > commits.json
+    %(prog)s -j commits.json
+  Check commit messages from git log:
+    %(prog)s -c origin/master..
+"""
+
+
+def main():
+    import sys
+    import argparse
+    parser = argparse.ArgumentParser(prog=sys.argv[0],
+                                     description='Log message compliance checker',
+                                     formatter_class=argparse.RawDescriptionHelpFormatter,
+                                     epilog=help_epilog)
+    parser.add_argument('--commits', '-c', default=None, help='Revision range')
+    parser.add_argument('--json', '-j', default=None, help='JSON file to take the log messages')
+    parser.add_argument('--verbose', '-v', action='count', default=0, help='Increase verbosity')
+    parser.add_argument('--quiet', '-q', action='count', default=0, help='Decrease verbosity')
+    args = parser.parse_args()
+
+    global loglevel_threashold
+    loglevel_threashold += args.verbose * 100 - args.quiet * 100
+
+    checker = Checker(git.Repo('.'))
+
+    if args.commits:
+        checker.check_commits(args.commits)
+
+    if args.json:
+        with open_or_stdin(args.json) as f:
+            import json
+            obj = json.load(f)
+            checker.check_by_json(obj)
+
+    if checker.has_error:
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    ret = main()