YouCompleteMe set flags for filetype

Question

let g:syntastic_c_compiler = 'clang'
let g:syntastic_c_compiler_options = ' -ansi -pedantic'
let g:syntastic_cpp_compiler = 'clang++'
let g:syntastic_cpp_compiler_options = ' -std=c++11 -stdlib=libc++ -pedantic

That was easy, wasn't it? How do I do the same thing with Valloric's YouCompleteMe? The "User Guide" suggests to have a seperate configuration file in each project, and manually edit the flags - which is ridiculous. How can I change the flags based on the filetype in my .ycm_extra_conf.py? My attempt:

  1 
  2 def FlagsForFile(filename, **kwargs):
  3     flags = [
  4             '-Wall',
  5             '-Wextra',
  6             '-Werror',
  7             '-pedantic'
  8     ]
  9     data = kwargs['client_data']
 10     filetype = data['&filetype']
 11     if filetype == 'c':
 12         flags += ['-ansi']
 13     elif filetype == 'cpp':
 14         flags += ['-std=c++11']
 15         flags += ['stdlib=libc++']
 16     return {
 17         'flags': flags,
 18         'do_cache': True
 19     }  

Answer 1

Nothing in the python looks wrong. The only thing you probably forgot was to set

let g:ycm_extra_conf_vim_data = ['&filetype']

in your vimrc. This tells YouCompleteMe to pass the filetype to the function. Otherwise kwargs is just empty and you probably fall through the if statements without adding anything.