Re: Bug in ftdetect?

Fullquote, because I am CC'ing Bram for comment

On Mi, 24 Mai 2017, 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').
>
> 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:
>
> diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
> index 36ee57e8e..e0fbbfb9b 100644
> --- a/src/ex_cmds2.c
> +++ b/src/ex_cmds2.c
> @@ -2757,8 +2757,22 @@ ex_next(exarg_T *eap)
> {
> if (*eap->arg != NUL) /* redefine file list */
> {
> + /* do_arglist() could trigger BufNew events, which might
> + * in turn trigger expensive FileType and Syntax autocommands
> + * prevent this for now */
> +#if defined(FEAT_AUTOCMD) && defined(FEAT_SYN_HL)
> + char_u *save_ei = au_event_disable(",Filetype");
> +