Re: Issue with hide-ifdef and cc-mode

[Ergus]

Hi Eli:

On Sun, May 30, 2021 at 09:53:15PM +0300, Eli Zaretskii wrote:
> > 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.
This part is fine for me. In my use case using 0 or 1 should be defined
as numeric values right? so I don't need to define anything. For more
complex cases I understand these commands are very useful; but not in
this simple case.

> > 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.

I mean:

#if 0
<CODE>
#endif

M-x hide-ifdef-mode
M-x hide-ifdef-toggle-shadowing

does not shadows the region.

I need to explicitly call 
M-x hide-ifdefs

But also

If I change after that #if 0 -> #if 1; the shadow does not disappears
inmediately. So I need to call: M-x hide-ifdefs again.

This is the part that I think may be automatized. Calling hide-ifdefs
every time is annoying.

Emacs is smart enough to recognize when the user modifies a
cpp-macro. And multi-line code highlight is simple like /* */ does... 

What I am missing here?