use auto detected newline instead of hardcoded \n for line splitting

Author: Tom Ferdinandt

pre_commit_hooks/file_contents_sorter.py

@@ -29,18 +29,21 @@ def sort_file_contents(
     unique: bool = False,
 ) -> int:
     before = list(f)
+    # detect the line ending style of the file, based on the first line
+    new_line = b'\r\n' if before and before[0].endswith(b'\r\n') else b'\n'
+
     lines: Iterable[bytes] = (
-        line.rstrip(b'\n\r') for line in before if line.strip()
+        line.rstrip(new_line) for line in before if line.strip()
     )
     if unique:
         lines = set(lines)
     after = sorted(lines, key=key)
 
     before_string = b''.join(before)
-    after_string = b'\n'.join(after)
+    after_string = new_line.join(after)
 
     if after_string:
-        after_string += b'\n'
+        after_string += new_line
 
     if before_string == after_string:
         return PASS

tests/file_contents_sorter_test.py

@@ -12,11 +12,14 @@
     (
         (b'', [], PASS, b''),
         (b'\n', [], FAIL, b''),
+        (b'\r\n', [], FAIL, b''),
         (b'\n\n', [], FAIL, b''),
         (b'lonesome\n', [], PASS, b'lonesome\n'),
         (b'missing_newline', [], FAIL, b'missing_newline\n'),
         (b'newline\nmissing', [], FAIL, b'missing\nnewline\n'),
         (b'missing\nnewline', [], FAIL, b'missing\nnewline\n'),
+        (b'newline\r\nmissing', [], FAIL, b'missing\r\nnewline\r\n'),
+        (b'missing\r\nnewline', [], FAIL, b'missing\r\nnewline\r\n'),
         (b'alpha\nbeta\n', [], PASS, b'alpha\nbeta\n'),
         (b'beta\nalpha\n', [], FAIL, b'alpha\nbeta\n'),
         (b'C\nc\n', [], PASS, b'C\nc\n'),
@@ -25,6 +28,8 @@
         (b'@\n-\n_\n#\n', [], FAIL, b'#\n-\n@\n_\n'),
         (b'extra\n\n\nwhitespace\n', [], FAIL, b'extra\nwhitespace\n'),
         (b'whitespace\n\n\nextra\n', [], FAIL, b'extra\nwhitespace\n'),
+        (b'on\r\nwindows\r\n', [], PASS, b'on\r\nwindows\r\n'),
+        (b'extra\r\n\r\n\r\nwindows\r\n', [], FAIL, b'extra\r\nwindows\r\n'),
         (
             b'fee\nFie\nFoe\nfum\n',
             [],