bug#21200: 25.0.50; xdisp.c: infinite loop when using invisibility specs

[Eli Zaretskii]

> Date: Thu, 6 Aug 2015 18:26:05 +0000
> From: Pip Cet <pipcet@gmail.com>
> 
> with the current git tree (revision 0aec2aac), I'm running into
> problems with an infinite loop in xdisp.c which I believe to be fixed
> by this patch, which is reasonably obvious:
> 
> diff --git a/src/xdisp.c b/src/xdisp.c
> index e45cb87..7b221d4 100644
> --- a/src/xdisp.c
> +++ b/src/xdisp.c
> @@ -4221,6 +4221,8 @@ handle_invisible_prop (struct it *it)
>            if (invis == 2)
>              display_ellipsis_p = true;
>          }
> +
> +              charpos = end_charpos;
>          }
>        while (invis != 0 && endpos < len);
> 
> in this loop:
> 
>       do
>         {
>           end_charpos = Fnext_single_property_change (charpos, Qinvisible,
>                               it->string, limit);
>           if (INTEGERP (end_charpos))
>         {
>           endpos = XFASTINT (end_charpos);
>           charpos = end_charpos;
>           prop = Fget_text_property (end_charpos, Qinvisible, it->string);
>           invis = TEXT_PROP_MEANS_INVISIBLE (prop);
>           if (invis == 2)
>             display_ellipsis_p = true;
>         }
>         }
>       while (invis != 0 && endpos < len);
> 
> Without the patch, we keep calling Fnext_property_change with the same
> arguments and expecting a different result, which obviously never
> happens. In fact it seems to me we only need one of charpos and
> end_charpos as the code currently stands, anyway. However, charpos =
> f(..., charpos, ...) might cause confusion.
> 
> I can provide more detail if necessary, but as I said, it's a fairly
> obvious bug.

Yes, please provide the details, and preferably also a recipe where
you see the loop.

Thanks.