setting filetype with reference/variable in vim

Question

I'm trying to improve the command from neovim help that show diff between buffer and original file.

problem is the new buffer opens without syntax highlighting because it has no file type. so I tried to save the filetype into variables and registers but I'm unable to use it in the setf command later (even manually)

Here's my latest attempt:

command! DiffOrig call setreg('f', &filetype) | vert new | set buftype=nofile | read ++edit # | 0d_
    \ | diffthis | setf @f | wincmd p | diffthis

In this attempt I manage to save the original filetype to register, but I don't manage to use it as argument for setf.

How can I make it work?

Matt · Accepted Answer · 2020-08-07 13:56:19Z

2

VimScript sets a strong difference between "commands" and "expressions" (including "variables"). Only few commands accept expressions, while others, like set or setfiletype, only accept strings. This is why one has to use execute so often. Yet in this case, simple let is more than enough. Here is a complete implementation of DiffOrig with filetype set:

command! -bar DiffOrig
    \   vnew +setlocal\ buftype=nofile
    \ | let &filetype = getbufvar(0, '&filetype')
    \ | read ++edit #
    \ | 1delete_
    \ | diffthis
    \ | wincmd p
    \ | diffthis

edited Aug 7, 2020 at 13:56

answered Aug 7, 2020 at 7:16

Matt

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2 Comments

prophet-five Over a year ago

Thanks for the great answer! Just one thing to clear - does the backslash after the set means call the buffer [space] ?

Matt Over a year ago

@prophet-five See :h +cmd

bk2204 · Accepted Answer · 2020-08-07 02:42:41Z

2

You can do this by using let: let &ft=@f. :setf only takes literal strings.

This may also be tidier in a function, where you could use a local variable instead of a register. If you want to do that, you can define a private function by prefixing the function name with s:, and then referring to it with <SID>. So something like this:

function! s:DoDiffOrig()
  let oldft=&ft
  " ...
  let &ft=oldft
  wincmd p
  diffthis
endfunction

command! DiffOrig call <SID>DoDiffOrig()<CR>

answered Aug 7, 2020 at 2:42

bk2204

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