Re: Bug in ftdetect?

Christian Brabandt wrote:

> On Mi, 24 Mai 2017, fREW Schmidt wrote:
>
> > Yes. "If I replace the contents of /usr/share/vim/vim80/syntax/vb.vim with `let
> > b:current_syntax = "vb"` everything is fast and, as I would hope, the support
> > files are not loaded N times per buffer but instead exactly once." 
>
> Well, I see the problem, although I cannot reproduce it.
>
> The markdown syntax script sources the html syntax script and that one
> does include a couple of other syntax scripts, like css.vim,
> javascript.vim and also vb.vim. However from my testing vb.vim is not
> guilty alone. If I uncomment vb.vim, the overall loading time only
> shrinks by 0.2 seconds or so (it needs here a total of around 7
> seconds). So you would need to disable all other to be included syntax
> scripts as well (for a test, you could set main_syntax='java').

I haven't read the whole thread, but I suspect that the trick is to set
b:current_syntax (to anything), which will cause further syntax scripts to bail
out. Anyway, this is all working around the actual problem.

> However, I think you might have found a bug here. Your ftdetect script
> does this:
>
> autocmd BufNew,BufNewFile,BufRead *.md :set filetype=markdown
>
> The :args command does fill the argument list, calls ex_next() which
> calls eventually alist_set() and then iterates over the argument list
> and calls adlist_add(). This will finally call buflist_add() which in
> turn calls buflist_new(), which triggers the BufNew autocommand, which
> then triggers the FileType and finally the Syntax autocommands. So in
> the end, we are iterating over the whole list of arguments and call
> autocommands, for buffers that are not even going to be displayed next.
>
> So I wonder, if we can't do a little bit better, similar to how vimgrep
> sets the eventignore option to prevent at least the expensive FileType
> autocommand:

I'm quite sure this will make other things fail. Just don't use BufNew for
detecting the filetype, that is the cause of the problem. The file type should
only be detected when the buffer is loaded. Doing it earlier indeed causes the
overhead experienced.

--
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