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

[Visuwesh]

[ஞாயிறு, பிப்ரவரி 13 2022] Eli Zaretskii wrote:

>> From: Visuwesh <visuweshm@gmail.com>
>> Cc: 53729@debbugs.gnu.org
>> Date: Thu, 10 Feb 2022 18:39:42 +0530
>> 
>> I tried all the Tamil fonts in Google fonts and to ease the checking
>> process, I wrote the following Elisp snippet:
>> 
>> [...]
>> 
>> and the buffer name in the modeline has the right shaping!  This is the
>> case for _every_ font I tried: including Noto Serif Tamil.  But if I
>> open a file named "அக்னிச்சிறகுகள்.pdf", the shaping is as in the OP.
>
> What happens if you turn off auto-composition mode before repeating
> the above experiment?  Do you see any difference in the buffer name
> produced by you and the buffer name produced by Emacs when visiting
> that file?

If I turn off global-auto-composition-mode and do the above, none of the
text is shaped i.e., the buffer name produced by me and the buffer name
produced by Emacs both are not shaped.  Turning it on again and visiting
the file does not produce the right shaping either (but the buffer
created by me does).

I did this out of curiosity: in dired, I typed C M-n when over the file
and added ".1" to the end of new file name, and when I visit this file,
the buffer name is shaped properly.  [ The new filename is
அக்னிச்சிறகுகள்.pdf.1 ]

I'm not sure if this has to do with the filename since when I yank the
file name from dired and create an empty file (M-x
dired-create-empty-file) by that name in another directory and visit it,
Emacs shapes the buffer name properly.

In either case, here's the filename as yanked from dired:
அக்னிச்சிறகுகள்.pdf
If this doesn't do it, then I guess I can send you the file off-list.