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

[Dmitry Gutov <dgutov@yandex.ru>]

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On 06.08.2022 14:49, Gregory Heytings wrote:
> 
>>> Just like depicted on my latest screenshot for downloadify.js: the 
>>> beginning of the narrowed region ended up inside a string, and as a 
>>> result several screenfuls were entirely mis-fontified, with strings 
>>> and non-strings inverted.
>>
>> Yes, and IMNSHO responsiveness is more important than correctness in 
>> these cases.
>>
> 
> Especially given that the said correctness has always been relative.  So 
> it's not like we're leaving the aven of 100% correctness and falling 
> into the hell of 10% correctness.  A more reasonable view of the 
> situation is that we had 90% correctness and now have,

As someone who worked on different major mode and syntax-ppss itself a 
little, that feels moderately insulting.

No: we strive to close to 100% correctness in supporting language syntax 
and can often reach it with moderate effort (programming-wise).

> in files with 
> "loo long lines" and only in those files, 60% correctness.

Does the attached screenshot look like 60% correctness to you?

To me, it's more like -60%. Or at least, that's what the utility of such 
highlighting will be (negative).

And I didn't have to hunt for this screenshot, tweaking parameters, or 
files, or window sizes here and there.

This is just how half of dictionary.json looks with Emacs from master on 
default settings.

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