bug#53729: 29.0.50; Tamil text not shaped in modeline

[Eli Zaretskii <eliz@gnu.org>]

> From: Visuwesh <visuweshm@gmail.com>
> Cc: 53729@debbugs.gnu.org
> Date: Thu, 03 Feb 2022 13:37:09 +0530
> 
> > Strange.  I guess the only way of investigating this is to step with
> > GDB into the code which renders the mode line, and see which font
> > specifically is being used there?
> >
> 
> I suppose so but I'm confident that "Noto Serif Tamil" is the font used
> in the modeline.  The only other Tamil font I have installed is "Noto
> Sans Tamil" and I can easily make out the difference between the two.
> Font selection does not seem to be the problem, at least.

It could be that Emacs selects some variant of Noto Serif Tamil (some
weight or maybe width) which causes this.

Btw, can you try this with other fonts and see if any of them displays
the buffer name correctly in the mode line?

> In either case, I think I can only get to this in two weeks.  And is the
> information in etc/DEBUG all I need (except the breakpoint which will be
> provided?)?

It should get you started, yes.  There are special commands defined in
src/.gdbinit that will help showing Lisp objects, and feel free to ask
for guidance if you aren't sure how to proceed or have any questions.

> You're right.  In the OP, even simple combinations like க + ் is not
> rendered right: the dot should be on top of க but in the buffer name, it
> is next to it.  However, Emacs seems to have no problem shaping க + ி.
> The grossest of all is க + ு where the combined letter should be க plus
> some kind of arc that surrounds the letter i.e., கு (hopefully Emacs
> renders this fine on your end, if not, I guess I could write it down on
> paper and send a picture).

OK, thanks.

One more question: which version of HarfBuzz do you have installed
there?