bug#73752: 29.4; Ligatures are randomly rendered with extra spaces

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 27 Oct 2024 16:32:34 -0400
> Cc: visuweshm@gmail.com, luangruo@yahoo.com, 73752@debbugs.gnu.org
> From: Yixuan Chen <xuan@xlk.me>
> 
> On 10/27/24 16:07, Eli Zaretskii wrote:
> > To convince me that this is really happening (although I'm unable to
> > understand how it could, given how Emacs faces work), you will need to
> > show some code which generates such a situation in a reproducible
> > manner, and then show me by using "M-x describe-text-properties" and
> > "C-u C-x =" that indeed the same characters in the same face are shown
> > on different lines with different metrics.
> 
> OK, here you go.

Not exactly what I asked for, or understood how the problem manifests
itself...

> "screenshot1.png" shows the bugged display. Here's the result of 
> "describe-text-properties",
> > There are text properties here:
> >   face                 (face12 font-lock-string-face)
> >   fontified            t

But this is a completely different issue.  There's no indentation
here, right?  You are saying that in the "bad" display there's some
extra space between the ligature and the following quote, right?  Is
that extra space a real SPC glyph or is it just that the ligature is
considered "wider"?  What happens if you put the cursor on the ▷
ligature in the "bad" display -- does the block cursor then take up
all the space up to the next quote?