Subject: Re: bug#65380: [PATCH] Add command to copy contents in a diff-mode buffer

From: Eli Zaretskii <[email-masked]>
Date: Sun, 18 Aug 2024 21:00:19 +0300

> From: Philip Kaludercic <[email-masked]>
> Cc: [email-masked],  [email-masked]
> Date: Sun, 18 Aug 2024 16:20:52 +0000
> 
> >> To fix this I have written a general macro for subr.el to restore
> >> the scroll position:
> >
> > Let's first make sure we understand what happens here before we add
> > such a macro.  (It also has some conceptual problems of its own, but
> > let's defer that until we actually sure it is needed.)
> 
> It is not needed, but I would be interested in what the conceptual
> errors are.

Forcing window-start has some side-effects that could look like bugs.
For example, the window's vscroll is reset, and if the original window
started its display with an overlay or display property,
set-window-start will not necessarily restore the original display,
due to boring technical issues.

So my recommendation is to avoid calling set-window-start as a means
to return to some previous display, because it is not guaranteed that
you can do it like that.