bug#38749: 27.0.50; objc-mode: wrong imenu item

[Alan Mackenzie]

Hello, HaiJun.

On Tue, Jan 07, 2020 at 10:09:49 +0800, HaiJun Zhang wrote:
> 在 2020年1月7日 +0800 AM2:08，Alan Mackenzie <acm@muc.de>，写道：
> > I've just spent some time fixing a more serious bug in the
> > Objective-C imenu mechanism. This only occurs when I invoke imenu
> > through the keyboard (e.g. with M-x imenu), which might explain why
> > it's survived so long without detection. If I invoke imenu with a
> > mouse click, it works.

> > Anyhow, with nsfns.m, do M-x imenu <tab> C <tab> and select any
> > item.  This works. Now do M-x imenu. This throws the error "Wrong
> > type argument: stringp, nil".

> > I've fixed this now, but haven't committed the fix yet.

It turns out, that bug had been fixed in the Emacs core version of CC
Mode back in 2012.  ;-)

> Thanks.

> > Back to your bug - clearly what is happening is that the regular
> > expression search for functions is finding things in comments (such as
> > "Copyright (C)") which look like functions but aren't. This is easy
> > enough to fix, by checking for comments and strings, but comes with a
> > fairly stiff time penalty. On my 2½ year old Ryzen machine, scanning
> > the freshly visited Objc buffer currently takes 0.0196s. With the check
> > for comments/strings, it takes 0.0650s.

> > That's a factor of ~3.25 slower. On a slower machine (factor 3) with a
> > larger file (factor 3) this could mean the scanning would take 0.6s
> > rather than 0.2s. This might be slow enough to annoy somebody a little.

I tried the timings again this evening, and I no longer see this factor
of ~3 slowdown.  In fact just a few 10s of percent.

So I've committed this fix, both to standalone CC Mode and the emacs-27
branch at savannah (from where it will soon find its way to the master
branch).

> I'm not familiar with objc. What about searching the char '{' after
> the current pattern? But then I see the following snippet in nsfns.m:

This isn't needed any more

> static Lisp_Object
> interpret_services_menu (NSMenu *menu, Lisp_Object prefix, Lisp_Object old)
> /* —————————————————————————————————————
>    Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
>    ————————————————————————————————————— */
> {

Could I ask you to try out the new code, and if everything's OK, we can
close the bug as fixed.

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).