Prompt to edit a corresponding .scss file when opening a .css file in vim

.vimrc

function! EditScss()
   " The current file
   let file = expand("%")

   " The current file's basename plus .scss
   let scss = expand("%:r") . ".scss"

   " If the file exists
   if filereadable(scss)
      " Prompt the user and store the user's choice (1-indexed) in a variable
      let choice = confirm("Do you want to edit " . scss . " instead?", "&Yes\n&No", 1, "Question")

      " If the user picked [Y]es
      if choice == 1
         " Set file to the escaped scss filename
         let file = fnameescape(scss)
      endif
   endif

   " e[dit] the file
   exe "e" file

   " Execute the autocommands for the file
   exe "doautocmd BufReadPost" file
endfunction

" Execute EditScss() whenever a *.css file is read
:au BufReadCmd *.css call EditScss()