Re: The unwarranted scrolling assumption

[Eli Zaretskii]

> From: Lennart Borgman <address@hidden>
> Date: Sat, 19 Jun 2010 02:18:13 +0200
> Cc: address@hidden
> 
> I just checked the code. w->current_matrix->begv/zv is only set in
> 
>   mark_window_display_accurate_1 (w, accurate_p)
> 
> That means that it has the value needed to set clip_changed as I suggested.

You cannot base such general conclusions on what the code does now.
Each API and each member of the structures we use _must_ live up to
their contract, as documented in the source.  Any new code _must_
follow those contracts, or else it will break Emacs some day, if not
today.

> >> IOW, we still need to find out why reconsider_clip_changes fails to
> >> reset the clip_changed flag.
> 
> I think I have explained that several times. narrow_to_region etc sets
> clip_changed to 1 without ever caring about the state redisplay is in.

That is true, but then reconsider_clip_changes is supposed to fix the
value for redisplay's purposes.  The question is: why it seemingly
fails in your case, when you lean on the <down> key, in the original
recipe you posted?

> I could go into more details, but is that necessary?

Yes, it's necessary.  Without understanding the reasons of why
reconsider_clip_changes fails, your patch cannot be accepted, because
the need in such a patch and its correctness cannot be established.

But please do not "go into details" of how narrow_to_region is wrong
in setting the clip_changed flag.  That is not the issue here.  The
issue is what happens in reconsider_clip_changes, that prevents it
from resetting the clip_changed flag.