Run a vim formatter conditionally

Question

I have a callback setup-ed that auto-formats the code automatically after saving the buffer (depending on the file type). I'd like to avoid this behavior for very long files. Is it possible to make :w behave the same as :noa w , when the file is longer than N lines?

Answer 1

A direct implementation of your requirement would be by mapping :w . Through the use of :help map-expr , you can dynamically react to conditions (here: the number of lines in the buffer):

:nnoremap <expr> :w ':' . (line('$') >= 1000 ? 'noa ' : '') . 'w'

Note that there are more robust approaches for overriding built-in Ex commands. (For example cmdalias.vim - Create aliases for Vim commands .)

Recommended alternative

The advantage of the mapping is that you directly see what effect it has (though you have to remember what effects :noautocmd has here), and you can influence / override it easily.

However, it won't work with mappings or plugins that invoke :update directly. I would prefer to modify the callback setup instead. You probably have something like

:autocmd BufWritePost <buffer> call AutoFormat()

I would introduce a boolean flag that guards this:

:autocmd BufWritePost <buffer> if exists('b:AutoFormat') && b:AutoFormat | call AutoFormat() | endif

And then setup a hook that initializes it:

:autocmd BufWritePre <buffer> if ! exists('b:AutoFormat') | let b:AutoFormat = (line('$') < 1000) | endif

This way, you see whether auto-formatting is enabled (you can even put b:AutoFormat into your statusline), and you can tweak the behavior by manipulating the flag:

:let b:AutoFormat = 0   " Turn off auto-formatting even though the buffer is small.
:let b:AutoFormat = 1   " Force auto-formatting even though it's a large buffer.