tools/verifygitlog.py: Add script for verifying commit message format.

The main rules enforced are:
- At most 72 characters in the subject line, with a ": " in it.
- At most 75 characters per line in the body.
- No "noreply" email addresses.

tools/verifygitlog.py

+#!/usr/bin/env python3
+
+import re
+import subprocess
+import sys
+
+verbosity = 0  # Show what's going on, 0 1 or 2.
+suggestions = 1  # Set to 0 to not include lengthy suggestions in error messages.
+
+
+def verbose(*args):
+    if verbosity:
+        print(*args)
+
+
+def very_verbose(*args):
+    if verbosity > 1:
+        print(*args)
+
+
+def git_log(pretty_format, *args):
+    # Delete pretty argument from user args so it doesn't interfere with what we do.
+    args = ["git", "log"] + [arg for arg in args if "--pretty" not in args]
+    args.append("--pretty=format:" + pretty_format)
+    very_verbose("git_log", *args)
+    # Generator yielding each output line.
+    for line in subprocess.Popen(args, stdout=subprocess.PIPE).stdout:
+        yield line.decode().rstrip("\r\n")
+
+
+def verify(sha):
+    verbose("verify", sha)
+    errors = []
+    warnings = []
+
+    def error_text(err):
+        return "commit " + sha + ": " + err
+
+    def error(err):
+        errors.append(error_text(err))
+
+    def warning(err):
+        warnings.append(error_text(err))
+
+    # Author and committer email.
+    for line in git_log("%ae%n%ce", sha, "-n1"):
+        very_verbose("email", line)
+        if "noreply" in line:
+            error("Unwanted email address: " + line)
+
+    # Message body.
+    raw_body = list(git_log("%B", sha, "-n1"))
+    if not raw_body:
+        error("Message is empty")
+        return errors, warnings
+
+    # Subject line.
+    subject_line = raw_body[0]
+    very_verbose("subject_line", subject_line)
+    if not re.match(r"^[^!]+: [A-Z]+.+ .+\.$", subject_line):
+        error("Subject line should contain ': ' and end in '.': " + subject_line)
+    if len(subject_line) >= 73:
+        error("Subject line should be 72 or less characters: " + subject_line)
+
+    # Second one divides subject and body.
+    if len(raw_body) > 1 and raw_body[1]:
+        error("Second message line should be empty: " + raw_body[1])
+
+    # Message body lines.
+    for line in raw_body[2:]:
+        if len(line) >= 76:
+            error("Message lines should be 75 or less characters: " + line)
+
+    if not raw_body[-1].startswith("Signed-off-by: ") or "@" not in raw_body[-1]:
+        warning("Message should be signed-off")
+
+    return errors, warnings
+
+
+def run(args):
+    verbose("run", *args)
+    has_errors = False
+    has_warnings = False
+    for sha in git_log("%h", *args):
+        errors, warnings = verify(sha)
+        has_errors |= any(errors)
+        has_warnings |= any(warnings)
+        for err in errors:
+            print("error:", err)
+        for err in warnings:
+            print("warning:", err)
+    if has_errors or has_warnings:
+        if suggestions:
+            print("See https://github.com/micropython/micropython/blob/master/CODECONVENTIONS.md")
+    else:
+        print("ok")
+    if has_errors:
+        sys.exit(1)
+
+
+def show_help():
+    print("usage: verifygitlog.py [-v -n -h] ...")
+    print("-v  : increase verbosity, can be speficied multiple times")
+    print("-n  : do not print multi-line suggestions")
+    print("-h  : print this help message and exit")
+    print("... : arguments passed to git log to retrieve commits to verify")
+    print("      see https://www.git-scm.com/docs/git-log")
+    print("      passing no arguments at all will verify all commits")
+    print("examples:")
+    print("verifygitlog.py -n10  # Check last 10 commits")
+    print("verifygitlog.py -v master..HEAD  # Check commits since master")
+
+
+if __name__ == "__main__":
+    args = sys.argv[1:]
+    verbosity = args.count("-v")
+    suggestions = args.count("-n") == 0
+    if "-h" in args:
+        show_help()
+    else:
+        args = [arg for arg in args if arg not in ["-v", "-n", "-h"]]
+        run(args)