ci: add commit message linting to ci workflow

Author: ayushiahjolia

.github/workflows/ci.yml

@@ -12,6 +12,20 @@ on:
     branches: [ main ]
 
 jobs:
+  lint-commits:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
+      with:
+        fetch-depth: 0
+    - name: Set up Python
+      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+      with:
+        python-version: "3.12"
+    - name: Lint commit messages
+      run: python ops/lintcommit.py --range "origin/${{ github.event.pull_request.base.ref }}..${{ github.event.pull_request.head.sha }}"
+
   build:
     runs-on: ubuntu-latest
     strategy:

ops/lintcommit.py

@@ -124,29 +124,33 @@ def validate_message(message: str) -> tuple[str | None, list[str]]:
     return (error, warnings)
 
 
-def run_local() -> None:
-    """Validate local commit messages ahead of origin/main.
+def run_range(git_range: str, *, skip_dirty_check: bool = False) -> None:
+    """Validate commit messages in a git range (e.g. 'origin/main..HEAD').
 
-    If there are uncommitted changes, prints a warning and skips validation.
+    Args:
+        git_range: A git revision range like 'origin/main..HEAD'.
+        skip_dirty_check: When True, skip the uncommitted changes check
+            (useful in CI where the worktree may be clean by definition).
     """
     import subprocess
 
-    # Check for uncommitted changes
-    status: subprocess.CompletedProcess[str] = subprocess.run(
-        ["git", "status", "--porcelain"],
-        capture_output=True,
-        text=True,
-    )
-    if status.stdout.strip():
-        print(
-            "WARNING: uncommitted changes detected, skipping commit message validation.\n"
-            "Commit your changes and re-run to validate."
+    if not skip_dirty_check:
+        # Check for uncommitted changes
+        status: subprocess.CompletedProcess[str] = subprocess.run(
+            ["git", "status", "--porcelain"],
+            capture_output=True,
+            text=True,
         )
-        return
+        if status.stdout.strip():
+            print(
+                "WARNING: uncommitted changes detected, skipping commit message validation.\n"
+                "Commit your changes and re-run to validate."
+            )
+            return
 
-    # Get all commit messages ahead of origin/main
+    # Get all commit messages in the range
     result: subprocess.CompletedProcess[str] = subprocess.run(
-        ["git", "log", "origin/main..HEAD", "--format=%H%n%B%n---END---"],
+        ["git", "log", git_range, "--format=%H%n%B%n---END---"],
         capture_output=True,
         text=True,
     )
@@ -156,7 +160,7 @@ def run_local() -> None:
 
     raw: str = result.stdout.strip()
     if not raw:
-        print("No local commits ahead of origin/main")
+        print(f"No commits in range {git_range}")
         return
 
     blocks: list[str] = raw.split("---END---")
@@ -174,15 +178,21 @@ def run_local() -> None:
         if not message:
             continue
 
+        subject_line: str = message.splitlines()[0]
+
+        # Skip merge commits (auto-generated by git)
+        if subject_line.startswith("Merge "):
+            print(f"SKIP {sha}: {subject_line} (merge commit)")
+            continue
+
         error, warnings = validate_message(message)
-        subject: str = message.splitlines()[0]
 
         if error:
-            print(f"FAIL {sha}: {subject}", file=sys.stderr)
+            print(f"FAIL {sha}: {subject_line}", file=sys.stderr)
             print(f"  Error: {error}", file=sys.stderr)
             has_errors = True
         else:
-            print(f"PASS {sha}: {subject}")
+            print(f"PASS {sha}: {subject_line}")
 
         for warning in warnings:
             print(f"  Warning: {warning}")
@@ -191,8 +201,30 @@ def run_local() -> None:
         sys.exit(1)
 
 
+def run_local() -> None:
+    """Validate local commit messages ahead of origin/main."""
+    run_range("origin/main..HEAD")
+
+
 def main() -> None:
-    run_local()
+    import argparse
+
+    parser = argparse.ArgumentParser(
+        description="Lint commit messages for conventional commits compliance."
+    )
+    parser.add_argument(
+        "--range",
+        default=None,
+        dest="git_range",
+        help="Validate all commits in a git revision range (e.g. 'origin/main..HEAD'). "
+        "Skips the uncommitted-changes check (useful in CI).",
+    )
+    args = parser.parse_args()
+
+    if args.git_range is not None:
+        run_range(args.git_range, skip_dirty_check=True)
+    else:
+        run_local()
 
 
 if __name__ == "__main__":

ops/tests/test_lintcommit.py

@@ -1,6 +1,12 @@
 #!/usr/bin/env python3
 
-from ops.lintcommit import validate_message, validate_subject
+from __future__ import annotations
+
+from unittest.mock import patch
+
+import pytest
+
+from ops.lintcommit import run_range, validate_message, validate_subject
 
 
 # region validate_subject: valid subjects
@@ -151,3 +157,117 @@ def test_empty_message() -> None:
 def test_invalid_subject_in_message() -> None:
     error, _ = validate_message("invalid title")
     assert error == "missing colon (:) char"
+
+
+# region run_range
+
+
+def _make_git_log_output(*messages: str) -> str:
+    """Build fake ``git log --format=%H%n%B%n---END---`` output."""
+    blocks: list[str] = []
+    for i, msg in enumerate(messages):
+        sha = f"abc{i:04d}" + "0" * 33  # 40-char fake SHA
+        blocks.append(f"{sha}\n{msg}\n---END---")
+    return "\n".join(blocks)
+
+
+def _completed(stdout: str = "", stderr: str = "", returncode: int = 0):
+    """Shorthand for a ``subprocess.CompletedProcess``."""
+    from subprocess import CompletedProcess
+
+    return CompletedProcess(
+        args=[], returncode=returncode, stdout=stdout, stderr=stderr
+    )
+
+
+@patch("subprocess.run")
+def test_run_range_all_valid(mock_run, capsys) -> None:
+    log_output = _make_git_log_output(
+        "feat: add new feature",
+        "fix(sdk): resolve issue",
+    )
+    mock_run.return_value = _completed(stdout=log_output)
+
+    run_range("origin/main..HEAD", skip_dirty_check=True)
+
+    out = capsys.readouterr().out
+    assert "PASS" in out
+    assert out.count("PASS") == 2
+
+
+@patch("subprocess.run")
+def test_run_range_with_invalid_commit(mock_run, capsys) -> None:
+    log_output = _make_git_log_output(
+        "feat: add new feature",
+        "bad commit no colon",
+    )
+    mock_run.return_value = _completed(stdout=log_output)
+
+    with pytest.raises(SystemExit, match="1"):
+        run_range("origin/main..HEAD", skip_dirty_check=True)
+
+    captured = capsys.readouterr()
+    assert "PASS" in captured.out
+    assert "FAIL" in captured.err
+
+
+@patch("subprocess.run")
+def test_run_range_empty(mock_run, capsys) -> None:
+    mock_run.return_value = _completed(stdout="")
+
+    run_range("origin/main..HEAD", skip_dirty_check=True)
+
+    out = capsys.readouterr().out
+    assert "No commits in range" in out
+
+
+@patch("subprocess.run")
+def test_run_range_git_failure(mock_run) -> None:
+    mock_run.return_value = _completed(returncode=1, stderr="fatal: bad range")
+
+    with pytest.raises(SystemExit, match="1"):
+        run_range("bad..range", skip_dirty_check=True)
+
+
+@patch("subprocess.run")
+def test_run_range_dirty_worktree_skips(mock_run, capsys) -> None:
+    """When skip_dirty_check=False and worktree is dirty, validation is skipped."""
+    mock_run.return_value = _completed(stdout=" M ops/lintcommit.py\n")
+
+    run_range("origin/main..HEAD", skip_dirty_check=False)
+
+    out = capsys.readouterr().out
+    assert "uncommitted changes" in out
+    # git log should never have been called (only git status)
+    mock_run.assert_called_once()
+
+
+@patch("subprocess.run")
+def test_run_range_skips_merge_commits(mock_run, capsys) -> None:
+    log_output = _make_git_log_output(
+        "Merge branch 'main' into ci_linter",
+        "feat: add new feature",
+    )
+    mock_run.return_value = _completed(stdout=log_output)
+
+    run_range("origin/main..HEAD", skip_dirty_check=True)
+
+    out = capsys.readouterr().out
+    assert "SKIP" in out
+    assert "merge commit" in out
+    assert "PASS" in out
+    assert out.count("PASS") == 1
+
+
+@patch("subprocess.run")
+def test_run_range_warnings_printed(mock_run, capsys) -> None:
+    log_output = _make_git_log_output(
+        "feat: add thing\n\n" + "x" * 80,
+    )
+    mock_run.return_value = _completed(stdout=log_output)
+
+    run_range("origin/main..HEAD", skip_dirty_check=True)
+
+    out = capsys.readouterr().out
+    assert "PASS" in out
+    assert "exceeds 72 chars" in out