Re: [Emacs-diffs] comment-cache 223d16f 2/3: Apply `comment-depth' text properties when calling `back_comment'.

[Dmitry Gutov]

On 03/14/2016 03:30 AM, Stefan Monnier wrote:

> > So I have to wonder why the "get out of a comment" feature is used in C/l
> > mode so much that it becomes a bottleneck, and you get significant
> > improvement in performance by dropping the caching logic to C. That is, of
> > course, not a nice thing to ask considering the overall complexity of CC
> > Mode, but still.
>
> Hmm... I get the impression that maybe there's some confusion here.
> The current "get out of a comment" feature doesn't use syntax-ppss.

Maybe I should rephrase that: why is it important to be a lot faster 
than syntax-ppss? Because speed seems to be the main advantage that 
Alan's proposal has.

Would using your syntax-ppss approach instead chip away at the reported 
80% improvement in the synthetic test, or will it be about as fast?

(As an aside: we do have `comment-beginning', which delegates to 
syntax-ppss. But it doesn't seem to be widely used.)

> > I don't see anything comparable to 10 second waiting described in
> > http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22884, when doing a comparable
> > operation in a 5000-line Ruby file.
>
> Ruby's comment syntax is easier to parse backward than C's (because
> there's only one syntax style, rather than 2),

There are two:

#

and

=begin
=end

The latter one gets handled in ruby-syntax-propertize, so I don't know 
if it's relevant.