Subject: bug#56682: Fix the long lines font locking related slowdowns

From: Gregory Heytings <[email-masked]>
Date: Tue, 16 Aug 2022 08:26:49 +0000

>>> No, I want a simple variable that just gives the size of the narrowed 
>>> region, with nil meaning don't narrow at all.
>>
>> FWIW, I strongly object to the addition of such a variable (unless it 
>> is clearly stated that it is added temporarily and should not be used 
>> except for testing purposes).
>>
>> Adding such a variable only two weeks after locked narrowing has been 
>> introduced means that modes will have little incentive to adapt to that 
>> stronger constraint, if they can "fix" whatever problems that 
>> constraint might cause by setting that variable to nil in their 
>> initialization hooks.
>
> Modes can do that already by changing long-line-threshold to nil, don't 
> they?
>

They can indeed, but that variable is documented as "for debugging 
purposes" only.  Moreover setting that variable to nil implies that they 
deactivate all long line optimizations, which is a higher price to pay.

The way I see this is that Emacs is doing efforts to solve editing 
slowdowns as best as possible, but that there is a "last mile" that cannot 
be solved without the collaboration from major and minor modes.