Continuous Integration: Export warnings as warning annotations in Git…

…Hub Actions

src/crystal/tests/index.py

@@ -1,3 +1,4 @@
+from contextlib import contextmanager
 from crystal.tests import (
     test_addgroup,
     test_addrooturl,
@@ -34,7 +35,7 @@
 import sys
 import time
 import traceback
-from typing import Any, Callable, Coroutine, Dict, List, Optional, Tuple
+from typing import Any, Callable, Coroutine, Dict, List, Iterator, Optional, Tuple
 from unittest import SkipTest
 import warnings
 
@@ -232,3 +233,27 @@ def _run_tests(test_names: List[str]) -> bool:
         print()
 
     return is_ok
+
+
+@contextmanager
+def _warnings_sent_to_ci() -> Iterator[None]:
+    if not _running_in_ci():
+        yield
+        return
+
+    super_showwarning = warnings.showwarning  # capture
+
+    def showwarning(message, category, filename, lineno, file=None, line=None):
+        # Syntax: https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#example-setting-a-warning-message
+        print(f'::warning file={filename},line={lineno}::{message}')
+        return super_showwarning(message, category, filename, lineno, file, line)
+
+    warnings.showwarning = showwarning
+    try:
+        yield
+    finally:
+        warnings.showwarning = super_showwarning
+
+
+def _running_in_ci() -> bool:
+    return os.environ.get('GITHUB_ACTIONS') == 'true'