bug#61215: 29.0.60; font-lock broken in diff-mode with long lines

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: Gregory Heytings <gregory@heytings.org>,  61215@debbugs.gnu.org
> Date: Mon, 27 Feb 2023 20:28:33 +0200
> 
> >> After debugging I discovered that the problem is not caused by font-lock
> >> in diff-mode.  The problem is in easy-mmode-define-navigation.
> >> diff-mode uses it to navigate diff hunks.  It supports such a feature
> >> that when the user narrowed the diff buffer, it puts narrowing back
> >> after moving to the next hunk.  But this fails when the diff buffer
> >> is narrowed automatically by long-line-optimizations.  If there is
> >> no way to distinguish whether the narrowing is automatic by long-lines
> >> or manual by the user, this patch fixes the problem.  It works without
> >> errors, and even highlights first 250000 characters of the long line:
> >
> > Thanks.
> >
> > Maybe Gregory (CC'ed) can help here and tell whether there's a better
> > solution.
> 
> It seems there is no better solution?

I think you should be able to use the new facilities to distinguish
between user narrowing and that due to long-line-optimizations.