bug#64596: 30.0.50; On FIXME: in src/buffer.c:1481 (force-mode-line-update)

[Ihor Radchenko <yantar92@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Ihor Radchenko <yantar92@posteo.net>
>> Cc: Eli Zaretskii <eliz@gnu.org>, 64596@debbugs.gnu.org
>> Date: Sun, 16 Jul 2023 10:22:38 +0000
>> 
>> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> 
>> >>   . prevent_redisplay_optimizations_p flag of a buffer
>> >>   . must_be_updated_p flag of a window
>> >
>> > No idea what these mean.
>> > The name `must_be_updated_p` makes it sound to me like it's redundant
>> > with the `redisplay` flag above.
>> 
>> I agree about must_be_updated_p. I had exactly same though that it is
>> redundant with redisplay flag when reading the code.
>
> Actually, the must_be_updated_p flag is not for xdisp.c, i.e. not for
> redisplay_window and its subroutines.  It is for update_window, which
> is the last, 3rd, stage of a redisplay cycle, most of the code of
> which is in dispnew.c.  That's where the newly computed glyph matrix
> of a window is compared to its current matrix, and Emacs decides what,
> if anything, should be actually written to the glass.  What happens
> with this flag is that redisplay_window and friends _set_ this flag
> for windows that dispnew.c _must_ update.  The flag is tested in
> dispnew.c, see there for its use and comments.

I see.

I have to say that these flag names are very disorienting.
I have first seen this flag while reading xdisp.c, and it was not obvious
at all what it does.

The name must_be_updated has no link with glyph matrix terminology, and
it is only explained in the commentary in window.h. But then, at the
point of reading commentary I was not yet familiar with xdisp...

-- 
Ihor Radchenko // yantar92,
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