[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: forward-comment and syntax-ppss

From: Dmitry Gutov
Subject: Re: forward-comment and syntax-ppss
Date: Tue, 20 Dec 2016 01:16:37 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101 Thunderbird/50.0

On 19.12.2016 16:17, Stefan Monnier wrote:

Then I misunderstood.

Maybe I worded that too strongly. How about consider the major facilities case-by-case, and see if moving widening up the stack makes sense? Just doing that for indentation and font-lock (maybe there's even nothing to change there) would be a major win already.

What is the problem that your proposal aims to fix?

To solve the "widen problem" that mixed-mode frameworks have with existing modes. Namely, when they delegate to some language-specific code, it could call `widen' before doing its work. Examples of language-specific code are the values of font-lock-keywords, indent-line-function and imenu-create-index-function (though the last one is less important).

And to solve them in a non-intrusive way that does not ask for new abstractions, and thus does not affect the rest of the discussion (about syntax-ppss, forward-comment, Info). That should simplify things.

This seems necessary to have a stable syntax cache, e.g. to have it
as a basis of comments navigation.

But if we have something like syntax-ppss-parse-start, why not use that
same info more generally when some function wants to widen (e.g. make
it also replace font-lock-dont-widen)?

I'd imagine having a new variable syntax-dont-widen, that would serve both for syntax-ppss and font-lock. Still, that does not resolve the issue of indexing by point-min.

But the problem is the linkage between the narrowing and the widening,
not between the user-command and the widening.

There are different problems. I'm most focused on the issue of code undoing narrowing willy-nilly.

In general, the command currently executed does not know who put the
narrowing nor why, so it still doesn't know what's the intention behind
it, and hence can't decide whether to widen or not, nor or much to widen.

Aside from the problem of Info (which we know can be implemented in a different way), an interactive command does know, with 98% probability, that it's the user who instituted the narrowing.

And even in Info-mode as it works now, we can provide an Info-specific widening command (bound to the usual key sequence) which would only widen to the current page instead of the whole buffer.

That's one option. But again, prog-widen doesn't solve everything, and you

Not sure which problem you're referring to.  Do you mean that when
syntax-ppss-parse-start is changed, syntax-ppss is not warned?

It can track the value of point-min, but it won't really know what to do with the caches corresponding to the previous point-min values. Keep them around? Discard some of them?

See the end of this message: http://lists.gnu.org/archive/html/emacs-devel/2016-12/msg00630.html

haven't commented on syntax-ppss's cache management ideas.

Not sure on which part you want my input.

Some help choosing would be nice. :)

I can't remember all that's
been suggested, so here's just some random opinions of mine on the
- we could/should have a macro (with-new-syntax-ppss-context
  ... &rest BODY) which runs BODY such that calls to syntax-ppss in
  there can be cached within this scope but don't use the outer
  syntax-ppss cache and don't affect it.  This could be used when
  a command wants to temporarily use an ad-hoc syntax-table (typically
  using with-syntax-table), for example.  It should probably be made to
  obey the current narrowing limits, since such uses often additionally
  want to restrict the parsing to a subpart of the buffer.

That seems sound. And, basically, all that's necessary for mixed-mode packages to work. Except for the "interleaving pieces of code" case, which I think Christopher mentioned is the case in Antlr. But that's an advanced problem.

- if we introduce a syntax-ppss-parse-start, it should not have `ppss`
  in its name, it should probably try to include some of the design of

Which ones? Having both lower and upper bound? It's not indentation specific, so using the name is out of the question, I think.

and it should probably be modified via functions
  (rather than directly via setq), so that those functions can flush the
  syntax-ppss cache when needed.

This sounds interesting. Care to add some details? Just a hook with functions that return an integer?

If we're going this way, an ability to substitute the cache, instead of just flushing it, sounds like a logical continuation of that idea. That might require a getter and setter for the cache, like we have for match-data.

We probably don't need to do that now, just keep the option open.

This said, if needed it'd probably be
  OK to have syntax-ppss auto-detect changes instead (after all,
  syntax-ppss is still implemented in Elisp, so there is a lot of room
  for speed up).

It might not we the fastest, but I'd like it to be algorithmically sound.

I wouldn't do it in indent-for-tab-command, but I agree that it should
be done in indent-according-to-mode rather than forcing every major
mode's indentation function to widen.

Shouldn't indent-for-tab-command call indent-according-to-mode, then?

Same for font-lock.  And that takes care of the two known obstacles in
the mixed-major-mode space, with very little code or changes to
the API.

Sure.  I think the current discussion is about "what should
prog-widen/syntax-ppss-parse-start look like" more than "who/when should
we call prog-widen".

I prefer to think of this as the next step.

Even if we add "something else", upon deciding that it's really needed,
later, the current proposal shouldn't hurt.

If by "current proposal" you mean to prog-widen in
indent-according-to-mode, then I agree it's a good idea.

Yes, and also agree about a similar rule for font-lock-keywords.

I really meant widen, though. Not sure what calling prog-widen in there would mean, semantically, because according to the previous discussion prog-narrowing was something a mixed-mode code would institute. But it's down the call stack from indent-according-to-mode (via a mixed-mode aware indent-line-function), not above it.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]