Re: Limits of multiline font-lock

[Adam Porter <adam@alphapapa.net>]

Hi Michael,

Please forgive the "blast from the past"; going through some old mail 
from the list I saw this message of yours that I missed.

On 9/18/19 21:05, Michael Heerdegen wrote:
> Adam Porter <adam@alphapapa.net> writes:
> 
>> You might be interested in this package I published recently.  It
>> implements depth-based syntax highlighting for Lisp and some other
>> languages.
>>
>> https://github.com/alphapapa/prism.el
> 
> Nice.  Could it go to Gnu Elpa?

Yes, I think I will submit it to GNU ELPA one of these days.  It's more 
mature now than it was then.

>> However, I have discovered a performance issue in the case of sexps that
>> span large portions of the buffer (e.g. in my init files, I have some
>> large use-package forms that contain many functions and span hundreds of
>> lines).  If I could solve that, it would be great, but it works fine for
>> most code.
> 
> If you use `font-lock-extend-region-functions', all of font-lock uses
> the extended region, right?  I guess basing your functionality on
> jit-lock-register could be better.  If finding the beginning-of-defun
> and identifying the levels is what causes the main cost, it wouldn't
> help much, however.

IIRC that performance issue turned out to be a bug elsewhere in the 
code; once solved, the issue with large forms spanning many lines was no 
longer a problem.

> My use case is a bit simpler since I only have to deal with Lisp.  What
> modes does prism support btw?  What are reasons why some languages are
> not supported?

Prism has two modes, one for whitespace-significant languages and one 
for all others.  It seems to generally work well, especially since some 
recent bug fixes.

The liability, to the extent that there is one, is that syntax tables 
can affect how delimiters and comments are detected, and some major 
modes may not use them in a way that makes such detection possible, e.g. 
using Emacs regexps' syntax types and syntax-ppss parsing.

Now that treesitter is in Emacs, I'm guessing that it might be helpful 
as a backend for some languages, so I may look into that in the future.