On Sa, 14 Apr 2018, Ivan Brennan wrote:
> When your plugin wants to provide an event the user can hook into, it could
> broadcast a User autocommand:
>
> function! foo#do_it()
> call s:do_thing()
> doautocmd User FooDidIt
> endfunction
>
> If the user's vimrc contains,
>
> augroup MyGroup
> autocmd!
> autocmd User FooDidIt call MyHandler()
> augroup END
>
> then MyHandler() will be called any time foo#do_it() runs.
>
> If the user *does not* set up any such autocommand, however, any time
> foo#do_it() runs, Vim displays "No matching autocommands".
>
> You could suppress these messages by prefixing doautocmd with "silent", but
> that would also suppress any messages a handler tries to display. So most
> plugins wrap doautocmd in a conditional:
>
> function! foo#do_it()
> call s:do_thing()
> if exists('#User#FooThing')
> doautocmd User FooThing
> endif
> endfunction
>
> When providing an event the user can hook into, I'd think it's better to
> decouple the plugin from any knowledge/concern about what, if anything, has
> been set up to listen for the event. But we're forced to run this check,
> given how doautocmd works.
>
> More importantly, the exists() check is inaccurate in some cases. For
> example, the following are two autocommand definitions are equivalent,
>
> autocmd User FooBar,FooBaz call MyHandler()
> autocmd User Foo{Bar,Baz} call MyHandler()
>
> but exists('#User#FooBar') will return true for the first and false for the
> second.
>
> I can see the usefulness of displaying No matching autocommands for debugging
> purposes, but beyond that it seems like bad behavior.
>
> Am I thinking about this the wrong way?
You are probably right. However most plugins I have seen usually do not
bother and use `:sil doautocmd User ...` So perhaps nothing to worry
about?
Best,
Christian
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