Hi again,
Here's some more info I have gathered. If I haven't set the default font in
my config file, `M-x set-frame-font` only works if there's already an open
buffer in the frame. And if I visit a new file, the ligatures are rendered
broken again, although the font is the same. So I have to change the font
again.

On Thu, 30 Jul 2020 at 23:42, Sineau Gh <sineaugh@gmail.com> wrote:

>
>
>
> > From: Sineau Gh <sineaugh@gmail.com>
>> > Date: Thu, 30 Jul 2020 17:27:36 +0430
>> > Cc: 42562@debbugs.gnu.org
>> >
>> > The problem I originally reported was not concerned with typing text,
>> but text rendered in read-only buffers
>> > (ie. dired and minibuffer).
>>
>> Then please describe the steps to reproduce this with one such
>> read-only buffer.
>>
>>
>
> > Also here's the bad news. Just now I realized that bug#41005 is not
>> solved yet. At certain combinations of
>> > characters, the ligatures are still disjointed. Also I tried to change
>> the font family, but that  didn't help either.
>> > This doesn't happen when I compiled emacs using --without-harfbuzz
>> option. I don't know if it helps but I can
>> > try to find if there's a pattern to the combinations of characters I
>> mentioned.
>>
>> Here also we would need a recipe to reproduce the problem.
>>
>> These problems are highly context dependent, and cannot be debugged
>> without a reproducer.
>
>
>
>> Thanks.
>>
>
>
>>
> Upon further investigation, I realized that in my config I have used a
> combination of `default-frame-alist` and `set-fontset-font` that I forgot
> about. So here's a reproduction I hope can be useful for you. First of all
> the case is the same for both editable buffers and read-only ones so I'm
> just using a file with following content:
> تست
> تحقیق
> به
> اصالت
>
> شرتالکو
> حقیق
> حقیقت
> سنت
> تالکو
> مدرن
> مدرنیزاسیون
> I have tested this in three cases. Please note they are basically the same
> with some minor differences, but I mention them for completeness.
> 1- If I have not set a default font in my config, the text is rendered
> with broken ligatures. And if I set the font using `M-x set-frame-font`
> then everything is okay (even if I set it again to the default font used
> for Persian / Arabic text).
>
> 2- If I use something like the following in my config files:
> `(add-to-list 'default-frame-alist '(font . "DejaVu Sans Mono-12"))`
> on init the font is rendered broken. And if I set the font using `M-x
> set-frame-font` then everything is okay. Now if I set it again to DejaVu
> Sans Mono (the font I have used in my config file), it still shows broken
> text. I have to first set it to another font and then set it again to
> DejaVu so it renders correctly.
>
> 3- If I use the following line in my config:
> `(set-frame-font "DejaVu Sans Mono-12" t t)`
> on init the font is broken. And if I set the font using `M-x
> set-frame-font` then everything is okay (like previous cases). But I can't
> set it to DejaVu Sans Mono using `M-x set-frame-font` in any way. That
> means I first tried to change the font to something different and then back
> to DejaVu and still it didn't work.
>
> I should note that I have tested this with various fonts and the result is
> the same. Also I have tested this in Org and Fundamental modes and the
> result is the same. Also I didn't add `set-fontset-font` to the mix but I
> supposed it's not going to make a difference.
>
> I hope this helps, and excuse me if it's not. Thanks for your patience.
>