Re: Issue with hide-ifdef and cc-mode

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 30 May 2021 20:14:11 +0200
> From: Ergus <spacibba@aol.com>
> Cc: emacs-devel@gnu.org, Alan Mackenzie <acm@muc.de>
> 
> I didn't know I need to manually call hide-ifdefs every time I change
> the preprocessor argument. Because none of this is documented in the
> manual. But also calling that makes the functionality pretty
> sub-optimal.

Please be sure to read the commentary at the beginning of hideif.el,
it explains quite a lot.

> It is bad that this functionality works fine out of the box either in
> vim and in VS Code and other editors but not in emacs without user
> explicit intervention.

??? How can Emacs know which preprocessor symbols are defined and
which undefined?  You have "C-c @ d" and "C-c @ u" to tell Emacs which
symbols are defined and which undefined.

> So I am not sure how difficult may be to do it automatic without killing
> the performance... Like font-lock does with everything else... Soes it
> really kills performance to add his to font-lock?

I'm not sure I understand: what do you need to automate?  Once you
turn on hiding, the display automatically changes as you define and
undefine preprocessor symbols.