Subject: bug#53294: 29.0.50; Indirect font changes incorrectly affecting original buffer

From: Andrew Hyatt <[email-masked]>
Date: Mon, 17 Jan 2022 21:24:24 -0500

On Mon, Jan 17, 2022 at 04:47 PM Stefan Monnier 
<[email-masked]> wrote: 

>>> - In `face-remap.el`, refrain from modifying the 
>>> `face-remapping-alist` 
>>>   by side-effects (i.e. avoid `delq`, `setcdr`, and friends). 
>>>  - Add a `make-indirect-buffer-hook` and arrange for 
>>> `face-remap.el` to 
>>>   add a function there that does a deep enough copy of 
>>>   `face-remapping-alist`. 
>>>  - Remember that indirect buffers are an attractive nuisance 
>>> and should 
>>>   be deprecated (but note that I suspect the same bug affects 
>>>   `clone-buffer` because it doesn't make a deep enough copy of 
>>>   `face-remapping-alist` either). 
>> 
>> The last one tells me we are better with leaving this sleeping 
>> dog lie. 
> 
> Actually, looking back at the code, I see we already have the 
> needed hook (tho called from `clone-indirect-buffer`), so I 
> think the better option is to change `make-indirect-buffer` so 
> it runs `clone-indirect-buffer-hook` (when called with a non-nil 
> `clone` arg) instead of having `clone-indirect-buffer` run it. 
> And then in `face-remap.el` add a function to that hook which 
> copies `face-remapping-alist`. 
> 
> An intermediate option is to change the Org code to use 
> `clone-indirect-buffer` instead of `make-indirect-buffer` (but 
> that still requires the `face-remap.el` addition to the hook). 
> 
> [ Sorry Andrew for not noticing your earlier patch which does 
> something 
>   similar to my first suggestion above.  ] 
> 
> Andrew, would you be willing to write that patch?
>  
>         Stefan 

That sounds reasonable, I can do that. In fact, I just did this 
based on your suggestions, and it does work well. The only weird 
thing is that I had to pull `clone-indirect-buffer-hook' into the 
c code, because that's where `make-indirect-buffer' is. Let me 
know if that seems wrong.

I've attached the patch, please let me know if there is an issue. 
I have commit access, so I can just commit it myself after your OK 
(if so, I'll wait for a week or so to see if Eli has a comment as 
well before checkin).