Repository: pre-commit/pre-commit-hooks

Issue:
check-executables-have-shebangs not correct on windows
does not seem to work right on windows

i am dealing with a primarily linux / python project but on a windows machine.

i have set `git config core.filemode false`

i created a new file and stage and i verify that filemode is 644:
```
>git ls-files -s newfile.py
100644 3edd36f71bf2081c70a0eaf39dec6980d0a9f791 0       newfile.py
```

but hook still fails

```
hookid: check-executables-have-shebangs

newfile.py: marked executable but has no (or invalid) shebang!
  If it isn't supposed to be executable, try: chmod -x newfile.py
  If it is supposed to be executable, double-check its shebang.
```

why is this file causing error?

Discussion:
mxr: @asottile I  can't request a review in the GitHub UI but this should be ready for review now

Patch:
diff --git a/pre_commit_hooks/check_executables_have_shebangs.py b/pre_commit_hooks/check_executables_have_shebangs.py
index c34c7b7..1c50ea0 100644
--- a/pre_commit_hooks/check_executables_have_shebangs.py
+++ b/pre_commit_hooks/check_executables_have_shebangs.py
@@ -2,26 +2,60 @@
 import argparse
 import shlex
 import sys
+from typing import List
 from typing import Optional
 from typing import Sequence
+from typing import Set
 
+from pre_commit_hooks.util import cmd_output
 
-def check_has_shebang(path: str) -> int:
+EXECUTABLE_VALUES = frozenset(('1', '3', '5', '7'))
+
+
+def check_executables(paths: List[str]) -> int:
+    if sys.platform == 'win32':  # pragma: win32 cover
+        return _check_git_filemode(paths)
+    else:  # pragma: win32 no cover
+        retv = 0
+        for path in paths:
+            if not _check_has_shebang(path):
+                _message(path)
+                retv = 1
+
+        return retv
+
+
+def _check_git_filemode(paths: Sequence[str]) -> int:
+    outs = cmd_output('git', 'ls-files', '--stage', '--', *paths)
+    seen: Set[str] = set()
+    for out in outs.splitlines():
+        metadata, path = out.split('\t')
+        tagmode = metadata.split(' ', 1)[0]
+
+        is_executable = any(b in EXECUTABLE_VALUES for b in tagmode[-3:])
+        has_shebang = _check_has_shebang(path)
+        if is_executable and not has_shebang:
+            _message(path)
+            seen.add(path)
+
+    return int(bool(seen))
+
+
+def _check_has_shebang(path: str) -> int:
     with open(path, 'rb') as f:
         first_bytes = f.read(2)
 
-    if first_bytes != b'#!':
-        quoted = shlex.quote(path)
-        print(
-            f'{path}: marked executable but has no (or invalid) shebang!\n'
-            f"  If it isn't supposed to be executable, try: "
-            f'`chmod -x {quoted}`\n'
-            f'  If it is supposed to be executable, double-check its shebang.',
-            file=sys.stderr,
-        )
-        return 1
-    else:
-        return 0
+    return first_bytes == b'#!'
+
+
+def _message(path: str) -> None:
+    print(
+        f'{path}: marked executable but has no (or invalid) shebang!\n'
+        f"  If it isn't supposed to be executable, try: "
+        f'`chmod -x {shlex.quote(path)}`\n'
+        f'  If it is supposed to be executable, double-check its shebang.',
+        file=sys.stderr,
+    )
 
 
 def main(argv: Optional[Sequence[str]] = None) -> int:
@@ -29,12 +63,7 @@ def main(argv: Optional[Sequence[str]] = None) -> int:
     parser.add_argument('filenames', nargs='*')
     args = parser.parse_args(argv)
 
-    retv = 0
-
-    for filename in args.filenames:
-        retv |= check_has_shebang(filename)
-
-    return retv
+    return check_executables(args.filenames)
 
 
 if __name__ == '__main__':


Test patch:
diff --git a/tests/check_executables_have_shebangs_test.py b/tests/check_executables_have_shebangs_test.py
index 15f0c79..3b77612 100644
--- a/tests/check_executables_have_shebangs_test.py
+++ b/tests/check_executables_have_shebangs_test.py
@@ -1,8 +1,19 @@
+import os
+import sys
+
 import pytest
 
+from pre_commit_hooks import check_executables_have_shebangs
 from pre_commit_hooks.check_executables_have_shebangs 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', (
         b'#!/bin/bash\nhello world\n',
@@ -17,6 +28,7 @@ def test_has_shebang(content, tmpdir):
     assert main((path.strpath,)) == 0
 
 
+@skip_win32  # pragma: win32 no cover
 @pytest.mark.parametrize(
     'content', (
         b'',
@@ -24,7 +36,6 @@ def test_has_shebang(content, tmpdir):
         b'\n#!python\n',
         b'python\n',
         '☃'.encode(),
-
     ),
 )
 def test_bad_shebang(content, tmpdir, capsys):
@@ -33,3 +44,67 @@ def test_bad_shebang(content, tmpdir, capsys):
     assert main((path.strpath,)) == 1
     _, stderr = capsys.readouterr()
     assert stderr.startswith(f'{path}: marked executable but')
+
+
+def test_check_git_filemode_passing(tmpdir):
+    with tmpdir.as_cwd():
+        cmd_output('git', 'init', '.')
+
+        f = tmpdir.join('f')
+        f.write('#!/usr/bin/env bash')
+        f_path = str(f)
+        cmd_output('chmod', '+x', f_path)
+        cmd_output('git', 'add', f_path)
+        cmd_output('git', 'update-index', '--chmod=+x', f_path)
+
+        g = tmpdir.join('g').ensure()
+        g_path = str(g)
+        cmd_output('git', 'add', g_path)
+
+        # this is potentially a problem, but not something the script intends
+        # to check for -- we're only making sure that things that are
+        # executable have shebangs
+        h = tmpdir.join('h')
+        h.write('#!/usr/bin/env bash')
+        h_path = str(h)
+        cmd_output('git', 'add', h_path)
+
+        files = (f_path, g_path, h_path)
+        assert check_executables_have_shebangs._check_git_filemode(files) == 0
+
+
+def test_check_git_filemode_failing(tmpdir):
+    with tmpdir.as_cwd():
+        cmd_output('git', 'init', '.')
+
+        f = tmpdir.join('f').ensure()
+        f_path = str(f)
+        cmd_output('chmod', '+x', f_path)
+        cmd_output('git', 'add', f_path)
+        cmd_output('git', 'update-index', '--chmod=+x', f_path)
+
+        files = (f_path,)
+        assert check_executables_have_shebangs._check_git_filemode(files) == 1
+
+
+@pytest.mark.parametrize(
+    ('content', 'mode', 'expected'),
+    (
+        pytest.param('#!python', '+x', 0, id='shebang with executable'),
+        pytest.param('#!python', '-x', 0, id='shebang without executable'),
+        pytest.param('', '+x', 1, id='no shebang with executable'),
+        pytest.param('', '-x', 0, id='no shebang without executable'),
+    ),
+)
+def test_git_executable_shebang(temp_git_dir, content, mode, expected):
+    with temp_git_dir.as_cwd():
+        path = temp_git_dir.join('path')
+        path.write(content)
+        cmd_output('git', 'add', str(path))
+        cmd_output('chmod', mode, str(path))
+        cmd_output('git', 'update-index', f'--chmod={mode}', str(path))
+
+        # simulate how identify choses that something is executable
+        filenames = [path for path in [str(path)] if os.access(path, os.X_OK)]
+
+        assert main(filenames) == expected