bug#63271: 29.0.90; broken mouse-face

[Stephen Berman]

On Tue, 09 May 2023 16:35:50 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: Eli Zaretskii <eliz@gnu.org>,  juri@linkov.net,  63271@debbugs.gnu.org
>> Date: Tue, 09 May 2023 15:12:06 +0200
>>
>> On Tue, 09 May 2023 20:52:24 +0800 Po Lu <luangruo@yahoo.com> wrote:
>>
>> > What if you change the font driver in use to something else, like X?
>> > i.e.
>> >
>> >   (set-frame-parameter (selected-frame) 'font-backend "x")
>>
>> With that the highlighting problem in fundamental-mode vanishes: all
>> problematic strings show mouse-highlighting. (FTR, with the "x"
>> font-backend, the default face here is displayed with adobe-courier and
>> variable-pitch face is displayed with adobe-helvetica.)
>
> Does changing the font backend also changes the font used for the
> variable-pitch face?  If it does, then perhaps you could force Emacs
> to use the same font by customizing the variable-pitch face?  Since we
> already know that the font somehow affects this issue, we need to try
> to use the same font with different backends, to be sure it's the
> backend that counts, not the font.

As I noted previously, here with ftcrhb variable-pitch face is displayed
with DejaVu Sans.  When I change the font-backend to "x", variable-pitch
face is displayed with adobe-helvetica, as noted, but when I change its
Font Family attribute to DejaVu Sans, the "TODO" string in
fundamental-mode, propertized to inherit variable-pitch, is displayed
with adobe-times.  So it seems that DejaVu Sans cannot be used by the x
font-backend.

Steve Berman