checkstyle: Work around bug in difflib

If a file misses the newline at the end it gets detected by checkstyle,
but the resulting patch is incorrect and does not apply. It took me a
while to understand that it wasn't me using checkstyle incorrectly, but
that the patch was faulty. The bug itself is in difflib and dates back to
2008.

To reproduce:
- Remove trailing newline from a file
- git add the file
- run ./utils/checkstyle.py -s | patch -p0

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

utils/checkstyle.py

@@ -168,6 +168,12 @@ def parse_diff(diff):
             hunk = DiffHunk(line)
 
         elif hunk is not None:
+            # Work around https://github.com/python/cpython/issues/46395
+            # See https://www.gnu.org/software/diffutils/manual/html_node/Incomplete-Lines.html
+            if line[-1] != '\n':
+                hunk.append(line + '\n')
+                line = '\\ No newline at end of file\n'
+
             hunk.append(line)
 
     if hunk: