[clang-format] Support new file formatting with vim

[jsji]

Summary

The vim Formatonsave integration is not working if we create a new file directly using vim.
eg: vi -V9t.log t.cpp

It will not able to format the buffer.

Traceback (most recent call last):

File "<string>", line 1, in <module>
File "...clang/tools/clang-format/clang-format.py", line 156, in <module>
  main()
File "...clang/tools/clang-format/clang-format.py", line 80, in main
  with open(vim.current.buffer.name, 'r') as f:

FileNotFoundError: [Errno 2] No such file or directory: '...t.cpp'

This patch check the file before we try to open it.

[owenpan]

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

49

Can you move it up to keep the module names sorted?

80–81

[jsji]

Address comments.

[owenpan]

LGTM

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

 # :endfunction
 #
 # It operates on the current, potentially unsaved buffer and does not create
 # or save any files. To revert a formatting, just undo.
 from __future__ import absolute_import, division, print_function
 
 import difflib
 import json
+import os.path
 import platform
 import subprocess
 import sys
 import vim
 
 # set g:clang_format_path to the path to clang-format if it is not on the path
 # Change this to the full path if clang-format is not on the path.
 binary = 'clang-format'
 if vim.eval('exists("g:clang_format_path")') == "1":
   binary = vim.eval('g:clang_format_path')
 
 # Change this to format according to other formatting styles. See the output of
 # 'clang-format --help' for a list of supported styles. The default looks for
def main():
   encoding = vim.eval("&encoding")
   buf = get_buffer(encoding)
   # Join the buffer into a single string with a terminating newline
   text = ('\n'.join(buf) + '\n').encode(encoding)
 
   # Determine range to format.
   if vim.eval('exists("l:lines")') == '1':
     lines = ['-lines', vim.eval('l:lines')]
-  elif vim.eval('exists("l:formatdiff")') == '1':
+  elif vim.eval('exists("l:formatdiff")') == '1' and \
+       os.path.exists(vim.current.buffer.name):
     with open(vim.current.buffer.name, 'r') as f:
       ondisk = f.read().splitlines();
     sequence = difflib.SequenceMatcher(None, ondisk, vim.current.buffer)
     lines = []
     for op in reversed(sequence.get_opcodes()):
       if op[0] not in ['equal', 'delete']:
         lines += ['-lines', '%s:%s' % (op[3] + 1, op[4])]
     if lines == []: