Support shebang executable checks outside git repos

pre_commit_hooks/check_shebang_scripts_are_executable.py

@@ -2,20 +2,34 @@
 from __future__ import annotations
 
 import argparse
+import os
 import shlex
 import sys
 from collections.abc import Sequence
 
 from pre_commit_hooks.check_executables_have_shebangs import EXECUTABLE_VALUES
 from pre_commit_hooks.check_executables_have_shebangs import git_ls_files
 from pre_commit_hooks.check_executables_have_shebangs import has_shebang
+from pre_commit_hooks.util import cmd_output
 
 
 def check_shebangs(paths: list[str]) -> int:
-    # Cannot optimize on non-executability here if we intend this check to
-    # work on win32 -- and that's where problems caused by non-executability
-    # (elsewhere) are most likely to arise from.
-    return _check_git_filemode(paths)
+    fs_tracks_executable_bit = cmd_output(
+        'git', 'config', 'core.fileMode', retcode=None,
+    ).strip()
+
+    # Fall back to Git's file mode when the filesystem cannot reliably
+    # track executable bits, as is commonly the case on Windows.
+    if fs_tracks_executable_bit == 'false':  # pragma: win32 cover
+        return _check_git_filemode(paths)
+    else:  # pragma: win32 no cover
+        retv = 0
+        for path in paths:
+            if has_shebang(path) and not os.access(path, os.X_OK):
+                _message(path)
+                retv = 1
+
+        return retv
 
 
 def _check_git_filemode(paths: Sequence[str]) -> int:

tests/check_shebang_scripts_are_executable_test.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import os
+import sys
 
 import pytest
 
@@ -9,6 +10,30 @@
 from pre_commit_hooks.check_shebang_scripts_are_executable import main
 from pre_commit_hooks.util import cmd_output
 
+skip_win32 = pytest.mark.skipif(
+    sys.platform == 'win32',
+    reason="non-git checks aren't relevant on windows",
+)
+
+
+@skip_win32  # pragma: win32 no cover
+@pytest.mark.parametrize(
+    ('content', 'mode', 'expected'),
+    (
+        pytest.param('#!python', '+x', 0, id='shebang with executable'),
+        pytest.param('#!python', '-x', 1, id='shebang without executable'),
+        pytest.param('', '+x', 0, id='no shebang with executable'),
+        pytest.param('', '-x', 0, id='no shebang without executable'),
+    ),
+)
+def test_non_git_executable_shebang(tmpdir, content, mode, expected):
+    with tmpdir.as_cwd():
+        path = tmpdir.join('path')
+        path.write(content)
+        cmd_output('chmod', mode, str(path))
+
+        assert main((str(path),)) == expected
+
 
 def test_check_git_filemode_passing(tmpdir):
     with tmpdir.as_cwd():