bug#64780: 30.0.50; set-face-attribute can not set the medium weight of IBM Plex Mono on Windows 10

[Eli Zaretskii]

> From: Eason Huang <aqua0210@foxmail.com>
> Cc: 64780@debbugs.gnu.org
> Date: Sat, 22 Jul 2023 15:21:46 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Eason Huang <aqua0210@foxmail.com>
> >> Date: Sat, 22 Jul 2023 09:23:28 +0800
> >>
> >> I tried to use the medium weight of IBM Plex Mono font on Windows 10,
> >> and find that `set-face-attribute` can not make it works as expectd.
> >>
> >> Steps to reproduce:
> >>
> >> 1. Download IBM Plex Mono font by this link:
> >> https://github.com/IBM/plex/releases/download/v6.3.0/TrueType.zip
> >> 2. Unzip the TrueType.zip and install the IBM Plex Mono
> >> 3. Start Emacs with `emacs -Q`
> >> 4. In the `*scratch*` buffer, eval the code below:
> >> ```
> >> (set-face-attribute 'default nil :font (format
> >> "%s:pixelsize=%d:weight=medium" "IBM Plex Mono" 20))
> >>
> >> ```
> >> 5. `M-x describe-char`, will get info about font as below:
> >>  harfbuzz:-outline-IBM Plex 
> >> Mono-regular-normal-normal-mono-20-*-*-*-c-*-iso8859-1 (#x03)
> >>
> >> And you can see the regular weight is used instead.
> >
> > Emacs on MS-Windows doesn't fully support any weights except these 4
> > standard ones: regular, italic, bold, bold-italic.  AFAIU, it is a
> > limitation of the APIs we use on Windows to enumerate font families.
> 
> Thanks for your explanation.
> 
> >> The workaround recently I used:
> >>
> >> ```
> >> (set-face-attribute 'default nil :font (format
> >> "%s:pixelsize=%d:weight=medium" "IBM Plex Mono Medm" 20))
> >> ```
> >> `M-x describe-char`, will get info about font as below:
> >> harfbuzz:-outline-IBM Plex Mono 
> >> Medm-medium-normal-normal-mono-20-*-*-*-c-*-iso8859-1 (#x18)
> >>
> >> But use the `IBM Plex Mono Medm` name is not convenient for me, because
> >> I also want to switch to other weights sometimes, such as:
> >>
> >> ```
> >> (set-face-attribute 'default nil :font (format 
> >> "%s:pixelsize=%d:weight=regular" "IBM Plex Mono" 20))
> >> (set-face-attribute 'default nil :font (format 
> >> "%s:pixelsize=%d:weight=bold" "IBM Plex Mono" 20))
> >> ```
> >> It would be more consistent If we can use the `IBM Plex Mono` font name
> >> with all font weights.
> >
> > Yes, those are all aspects of the above limitation.  You could
> > configure the other faces (bold, italic, and bold-italic) explicitly
> > to use the specific members of this font's family, like you did with
> > the default face and the medium weight, but the basic problem I
> > explained above will from time to time rear its ugly head and produce
> > some unexpected results, when Emacs mutates a font to produce another
> > weight of the same family.
> 
> Thanks for mention the potential risk.
> So I will just use the regular weight on Windows if encounter issue.

OK, so I don't think we have anything else to do here, and I'm
therefore closing this bug.