Normalize paths on windows to forward slashes

pre_commit/commands/run.py

@@ -34,6 +34,12 @@ def filter_by_include_exclude(names, include, exclude):
 
 class Classifier(object):
     def __init__(self, filenames):
+        # on windows we normalize all filenames to use forward slashes
+        # this makes it easier to filter using the `files:` regex
+        # this also makes improperly quoted shell-based hooks work better
+        # see #1173
+        if os.altsep == '/' and os.sep == '\\':
+            filenames = (f.replace(os.sep, os.altsep) for f in filenames)
         self.filenames = [f for f in filenames if os.path.lexists(f)]
         self._types_cache = {}
 

tests/commands/run_test.py

@@ -7,6 +7,7 @@ import pipes
 import subprocess
 import sys
 
+import mock
 import pytest
 
 import pre_commit.constants as C
@@ -782,7 +783,7 @@ def test_files_running_subdir(repo_with_passing_hook, tempdir_factory):
                 '--files', 'foo.py',
                 tempdir_factory=tempdir_factory,
             )
-        assert 'subdir/foo.py'.replace('/', os.sep) in stdout
+        assert 'subdir/foo.py' in stdout
 
 
 @pytest.mark.parametrize(
@@ -826,6 +827,23 @@ def test_classifier_removes_dne():
     assert classifier.filenames == []
 
 
+def test_classifier_normalizes_filenames_on_windows_to_forward_slashes(tmpdir):
+    with tmpdir.as_cwd():
+        tmpdir.join('a/b/c').ensure()
+        with mock.patch.object(os, 'altsep', '/'):
+            with mock.patch.object(os, 'sep', '\\'):
+                classifier = Classifier((r'a\b\c',))
+                assert classifier.filenames == ['a/b/c']
+
+
+def test_classifier_does_not_normalize_backslashes_non_windows(tmpdir):
+    with mock.patch.object(os.path, 'lexists', return_value=True):
+        with mock.patch.object(os, 'altsep', None):
+            with mock.patch.object(os, 'sep', '/'):
+                classifier = Classifier((r'a/b\c',))
+                assert classifier.filenames == [r'a/b\c']
+
+
 @pytest.fixture
 def some_filenames():
     return (