bug#43631: 28.0.50; CC Mode multiline strings grinds performance to a halt

[Theodor Thornhill via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Alan Mackenzie <acm@muc.de> writes:

> Hello, Theo.
>

[...]
>> I see that when I remove 'c-before-change-check-unbalanced-strings from
>> 'c-get-state-before-change-functions' the performance degradation
>> ceases.  I'm not sure what else is affected by that change, so not sure
>> if that can be counted as a fix as far as 'csharp-mode' is concerned.
>
> I would strongly recommend you not to make such a change, at least not
> without a good deal of matching changes elsewhere.  ;-)

Yeah, I put it back in some time ago ;)

>
> It seems the bit in c-b-c-check-unbalanced-strings dealing with
> multiline strings was written on the assumption that buffers containing
> such would be small.
>
> With multiline strings, _any_ change involving quote characters can flip
> the string/non-string characterisation from point all the way to the end
> of the buffer.  In the worst case scenario, this potentially big region
> needs to be analysed and have syntax-table text properties throughout
> the entire region changed.
>
> The current problem is that c-b-c-check-u-strings is doing this analysis
> for every buffer change.  This was easier to code, but has led to
> performance problems on buffers which aren't small.  The solution to
> this will have to involve restricting this analysis to when quote marks
> or the c-multiline-string-start-char get inserted or removed.  That way,
> there should only be an occasional and tolerable delay when one of these
> characters is inserted/removed.
>
> I'll be looking at this in the coming days.
>

Thats very interesting, and thanks!

--
Theo