Repository: pre-commit/pre-commit-hooks

Issue:
double-quote-string-fixer change linebreak on windows
I'm using `mixed-line-ending` and  `double-quote-string-fixer` on windows'
If `double-quote-string-fixer` changes file content, origin `LF` ending will be convert to `CRLF` ending.

Discussion:

Patch:
diff --git a/pre_commit_hooks/string_fixer.py b/pre_commit_hooks/string_fixer.py
index a5ea1ea..a41b737 100644
--- a/pre_commit_hooks/string_fixer.py
+++ b/pre_commit_hooks/string_fixer.py
@@ -31,13 +31,13 @@ def handle_match(token_text):  # type: (str) -> str
 def get_line_offsets_by_line_no(src):  # type: (str) -> List[int]
     # Padded so we can index with line number
     offsets = [-1, 0]
-    for line in src.splitlines():
-        offsets.append(offsets[-1] + len(line) + 1)
+    for line in src.splitlines(True):
+        offsets.append(offsets[-1] + len(line))
     return offsets
 
 
 def fix_strings(filename):  # type: (str) -> int
-    with io.open(filename, encoding='UTF-8') as f:
+    with io.open(filename, encoding='UTF-8', newline='') as f:
         contents = f.read()
     line_offsets = get_line_offsets_by_line_no(contents)
 
@@ -58,8 +58,8 @@ def fix_strings(filename):  # type: (str) -> int
 
     new_contents = ''.join(splitcontents)
     if contents != new_contents:
-        with io.open(filename, 'w', encoding='UTF-8') as write_handle:
-            write_handle.write(new_contents)
+        with io.open(filename, 'w', encoding='UTF-8', newline='') as f:
+            f.write(new_contents)
         return 1
     else:
         return 0


Test patch:
diff --git a/tests/string_fixer_test.py b/tests/string_fixer_test.py
index a65213b..4adca4a 100644
--- a/tests/string_fixer_test.py
+++ b/tests/string_fixer_test.py
@@ -44,8 +44,15 @@ TESTS = (
 
 @pytest.mark.parametrize(('input_s', 'output', 'expected_retval'), TESTS)
 def test_rewrite(input_s, output, expected_retval, tmpdir):
-    path = tmpdir.join('file.txt')
+    path = tmpdir.join('file.py')
     path.write(input_s)
     retval = main([path.strpath])
     assert path.read() == output
     assert retval == expected_retval
+
+
+def test_rewrite_crlf(tmpdir):
+    f = tmpdir.join('f.py')
+    f.write_binary(b'"foo"\r\n"bar"\r\n')
+    assert main((f.strpath,))
+    assert f.read_binary() == b"'foo'\r\n'bar'\r\n"