clang-format: Smarter replacement in the vim integration.

With this fix, only changed regions will be replaced in vim's buffer.
Thereby, marks should mostly be left intact. Furthermore, this is a
better fix for the performance problem in conjunction with
'foldmethod=syntax' (see r186660).

llvm-svn: 186789

clang/tools/clang-format/clang-format.py

@@ -17,6 +17,7 @@
 # It operates on the current, potentially unsaved buffer and does not create
 # or save any files. To revert a formatting, just undo.
 
+import difflib
 import json
 import subprocess
 import sys
@@ -67,10 +68,8 @@ else:
   lines = stdout.split('\n')
   output = json.loads(lines[0])
   lines = lines[1:]
-  if '\n'.join(lines) != text:
-    common_length = min(len(buf), len(lines))
-    buf[:common_length] = lines[:common_length]
-    for line in lines[len(buf):]:
-      buf.append(line)
-    del buf[len(lines):]
-    vim.command('goto %d' % (output['Cursor'] + 1))
+  sequence = difflib.SequenceMatcher(None, vim.current.buffer, lines)
+  for op in sequence.get_opcodes():
+    if op[0] is not 'equal':
+      vim.current.buffer[op[1]:op[2]] = lines[op[3]:op[4]]
+  vim.command('goto %d' % (output['Cursor'] + 1))