From 3b8b26a0971a09628c125f166855dfbc1d2fd891 Mon Sep 17 00:00:00 2001
From: "zhiwei.meng" <zhiwei.meng@magna.com>
Date: Wed, 1 Apr 2026 17:16:02 +0800
Subject: [PATCH] Add "--check" option support to end_of_file_fixer hook

---
 pre_commit_hooks/end_of_file_fixer.py | 20 ++++++----
 tests/end_of_file_fixer_test.py       | 56 +++++++++++++++++++--------
 2 files changed, 52 insertions(+), 24 deletions(-)

diff --git a/pre_commit_hooks/end_of_file_fixer.py b/pre_commit_hooks/end_of_file_fixer.py
index a88425c..bb00fec 100644
--- a/pre_commit_hooks/end_of_file_fixer.py
+++ b/pre_commit_hooks/end_of_file_fixer.py
@@ -6,7 +6,7 @@ from collections.abc import Sequence
 from typing import IO
 
 
-def fix_file(file_obj: IO[bytes]) -> int:
+def fix_file(file_obj: IO[bytes], check_only=False) -> int:
     # Test for newline at end of file
     # Empty files will throw IOError here
     try:
@@ -18,7 +18,8 @@ def fix_file(file_obj: IO[bytes]) -> int:
     if last_character not in {b'\n', b'\r'} and last_character != b'':
         # Needs this seek for windows, otherwise IOError
         file_obj.seek(0, os.SEEK_END)
-        file_obj.write(b'\n')
+        if not check_only:
+            file_obj.write(b'\n')
         return 1
 
     while last_character in {b'\n', b'\r'}:
@@ -27,7 +28,8 @@ def fix_file(file_obj: IO[bytes]) -> int:
             # If we've reached the beginning of the file and it is all
             # linebreaks then we can make this file empty
             file_obj.seek(0)
-            file_obj.truncate()
+            if not check_only:
+                file_obj.truncate()
             return 1
 
         # Go back two bytes and read a character
@@ -43,7 +45,8 @@ def fix_file(file_obj: IO[bytes]) -> int:
             return 0
         elif remaining.startswith(sequence):
             file_obj.seek(position + len(sequence))
-            file_obj.truncate()
+            if not check_only:
+                file_obj.truncate()
             return 1
 
     return 0
@@ -51,6 +54,7 @@ def fix_file(file_obj: IO[bytes]) -> int:
 
 def main(argv: Sequence[str] | None = None) -> int:
     parser = argparse.ArgumentParser()
+    parser.add_argument('--check', action='store_true', help='Check without fixing')
     parser.add_argument('filenames', nargs='*', help='Filenames to fix')
     args = parser.parse_args(argv)
 
@@ -59,11 +63,13 @@ def main(argv: Sequence[str] | None = None) -> int:
     for filename in args.filenames:
         # Read as binary so we can read byte-by-byte
         with open(filename, 'rb+') as file_obj:
-            ret_for_file = fix_file(file_obj)
+            ret_for_file = fix_file(file_obj, args.check)
             if ret_for_file:
-                print(f'Fixing {filename}')
+                if args.check:
+                    print(f'Wrong ending of file: {filename}')
+                else:
+                    print(f'Fixing {filename}')
             retv |= ret_for_file
-
     return retv
 
 
diff --git a/tests/end_of_file_fixer_test.py b/tests/end_of_file_fixer_test.py
index 8a5d889..a5349d5 100644
--- a/tests/end_of_file_fixer_test.py
+++ b/tests/end_of_file_fixer_test.py
@@ -10,34 +10,56 @@ from pre_commit_hooks.end_of_file_fixer import main
 
 # Input, expected return value, expected output
 TESTS = (
-    (b'foo\n', 0, b'foo\n'),
-    (b'', 0, b''),
-    (b'\n\n', 1, b''),
-    (b'\n\n\n\n', 1, b''),
-    (b'foo', 1, b'foo\n'),
-    (b'foo\n\n\n', 1, b'foo\n'),
-    (b'\xe2\x98\x83', 1, b'\xe2\x98\x83\n'),
-    (b'foo\r\n', 0, b'foo\r\n'),
-    (b'foo\r\n\r\n\r\n', 1, b'foo\r\n'),
-    (b'foo\r', 0, b'foo\r'),
-    (b'foo\r\r\r\r', 1, b'foo\r'),
+    (b'foo\n', 0, b'foo\n', None),
+    (b'', 0, b'', None),
+    (b'\n\n', 1, b'', None),
+    (b'\n\n\n\n', 1, b'', None),
+    (b'foo', 1, b'foo\n', None),
+    (b'foo\n\n\n', 1, b'foo\n', None),
+    (b'\xe2\x98\x83', 1, b'\xe2\x98\x83\n', None),
+    (b'foo\r\n', 0, b'foo\r\n', None),
+    (b'foo\r\n\r\n\r\n', 1, b'foo\r\n', None),
+    (b'foo\r', 0, b'foo\r', None),
+    (b'foo\r\r\r\r', 1, b'foo\r', None),
+
+    (b'foo\n', 0, b'foo\n', '--check'),
+    (b'', 0, b'', '--check'),
+    (b'\n\n', 1, b'\n\n', '--check'),
+    (b'\n\n\n\n', 1, b'\n\n\n\n', '--check'),
+    (b'foo', 1, b'foo', '--check'),
+    (b'foo\n\n\n', 1, b'foo\n\n\n', '--check'),
+    (b'\xe2\x98\x83', 1, b'\xe2\x98\x83', '--check'),
+    (b'foo\r\n', 0, b'foo\r\n', '--check'),
+    (b'foo\r\n\r\n\r\n', 1, b'foo\r\n\r\n\r\n', '--check'),
+    (b'foo\r', 0, b'foo\r', '--check'),
+    (b'foo\r\r\r\r', 1, b'foo\r\r\r\r', '--check'),
 )
 
 
-@pytest.mark.parametrize(('input_s', 'expected_retval', 'output'), TESTS)
-def test_fix_file(input_s, expected_retval, output):
+@pytest.mark.parametrize(('input_s', 'expected_retval', 'output', 'options'), TESTS)
+def test_fix_file(input_s, expected_retval, output, options):
+    if options is None:
+        options = []
+    elif isinstance(options, str):
+        options = [options]
+
     file_obj = io.BytesIO(input_s)
-    ret = fix_file(file_obj)
+    ret = fix_file(file_obj, "--check" in [*options])
     assert file_obj.getvalue() == output
     assert ret == expected_retval
 
 
-@pytest.mark.parametrize(('input_s', 'expected_retval', 'output'), TESTS)
-def test_integration(input_s, expected_retval, output, tmpdir):
+@pytest.mark.parametrize(('input_s', 'expected_retval', 'output', 'options'), TESTS)
+def test_integration(input_s, expected_retval, output, options, tmpdir):
     path = tmpdir.join('file.txt')
     path.write_binary(input_s)
 
-    ret = main([str(path)])
+    if options is None:
+        options = []
+    elif isinstance(options, str):
+        options = [options]
+
+    ret = main([*options, str(path)])
     file_output = path.read_binary()
 
     assert file_output == output