Vim script: Syntax highlight of user-defined commands.

syntax_highlight_of_user_defined_commands.vim

augroup syntax-highlight-extension
  autocmd!
  autocmd Syntax vim call s:set_syntax_of_user_defined_commands()
augroup END

function! s:set_syntax_of_user_defined_commands()
  redir => _
  silent! command
  redir END

  let command_names = map(split(_, '\n')[1:],
        \                 'matchstr(v:val, ''^[!"b]*\s\+\zs\u\w*\ze'')')
  if empty(command_names) | return | endif

  execute 'syntax keyword vimCommand contained' join(command_names)
endfunction