Merge bitcoin/bitcoin#24853: lint: Convert lint-git-commit-check.sh to Python

f27fcd9 lint: Convert lint-git-commit-check.sh to Python (Dimitri)

Pull request description:

  A port of `/test/lint/lint-git-commit-check.sh` to a Python-script as part of the request of #24783 . Checked for output-consistency.

ACKs for top commit:
  laanwj:
    re-ACK f27fcd9

Tree-SHA512: afc4a662f4aec1796c023b98a875c1591940ecdfc709eefe2df29d33e51e807c3c2e2b5c410aa3ad1cd3f6f8207f5c15b638637ff9f5659cafa7543bbe8a0bae

Author: laanwj

test/lint/lint-git-commit-check.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2020-2022 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Linter to check that commit messages have a new line before the body
+# or no body at all
+
+import argparse
+import os
+import sys
+
+from subprocess import check_output
+
+
+def parse_args():
+    """Parse command line arguments."""
+    parser = argparse.ArgumentParser(
+        description="""
+            Linter to check that commit messages have a new line before
+            the body or no body at all.
+        """,
+        epilog=f"""
+            You can manually set the commit-range with the COMMIT_RANGE
+            environment variable (e.g. "COMMIT_RANGE='47ba2c3...ee50c9e'
+            {sys.argv[0]}"). Defaults to current merge base when neither
+            prev-commits nor the environment variable is set.
+        """)
+
+    parser.add_argument("--prev-commits", "-p", required=False, help="The previous n commits to check")
+
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+    exit_code = 0
+
+    if not os.getenv("COMMIT_RANGE"):
+        if args.prev_commits:
+            commit_range = "HEAD~" + args.prev_commits + "...HEAD"
+        else:
+            # This assumes that the target branch of the pull request will be master.
+            merge_base = check_output(["git", "merge-base", "HEAD", "master"], universal_newlines=True, encoding="utf8").rstrip("\n")
+            commit_range = merge_base + "..HEAD"
+    else:
+        commit_range = os.getenv("COMMIT_RANGE")
+
+    commit_hashes = check_output(["git", "log", commit_range, "--format=%H"], universal_newlines=True, encoding="utf8").splitlines()
+
+    for hash in commit_hashes:
+        commit_info = check_output(["git", "log", "--format=%B", "-n", "1", hash], universal_newlines=True, encoding="utf8").splitlines()
+        if len(commit_info) >= 2:
+            if commit_info[1]:
+                print(f"The subject line of commit hash {hash} is followed by a non-empty line. Subject lines should always be followed by a blank line.")
+                exit_code = 1
+
+    sys.exit(exit_code)
+
+
+if __name__ == "__main__":
+    main()