Re: RFR cc-langs.el: change syntax for @ in Java

[Alan Mackenzie <acm@muc.de>]

Hello, Filipp.

On Mon, Apr 12, 2021 at 20:33:39 +0300, Filipp Gunbin wrote:
> Hi Alan,

> On 12/04/2021 13:36 +0000, Alan Mackenzie wrote:

> > I've had a more thorough look at it.  In cc-langs.el, there are several
> > places where @ is treated as a symbol character, namely:

> I've checked those places before submitting the patch, and I think they
> should stay without change.

OK, thanks!

> > L375: c-make-mode-syntax-table (which you have proposed modifying)
> > L419: c-identifier-syntax-modifications
> > L636: c-symbol-start

> I see no problem in leaving them as-is, because they will just continue
> to match @ with the following chars as a whole.  It's just when you need
> more fine-grained distinction, then you could check if it's prefix or
> symbol.

> Prefix syntax is defined so that prefix chars are part of the following
> expression, that's exactly the case of Java annotations.

Prefix syntax hasn't been used in CC Mode up till now, so it will be
something of an experiment.

> > L1969: c-paragraph-start (I think this one only applies in comments)

> Yes, this is for javadoc tags, which start with @, and appear only in
> comments, like:

> /**
>  * @param my-param ..
>  */

> > L2198: c-class-decl-kwds (The "@interface" keyword)

> @interface is a keyword which declares the annotation interface itself.

> I would really hope that syntax tables do not affect parsing/matching of
> keywords.  If they don't, then this place doesn't need to be changed,
> either.

> > We need to consider whether to amend some or all of these places, so
> > that @ ceases to be a (starting) character of an identifier.

> I don't think it should cease to be.

OK.

> > I'm also a bit worried that in

> >     @NonNull
> >     @TestClass
> >     @FooBar
> >     public class Annotations {

> > , the last line gets parsed as ((annotation-top-cont 21)), where it
> > really ought to be a topmost-intro.  But this problem is present without
> > your patch, anyway.

> > In summary, I think the motivation for the change (highlighting symbols
> > correctly) is valid, but the change is going to be more involved than
> > the patch you've supplied.

This is, I'm sure, a separate problem.

> It's not about highlighting, but rather about "extracting" @, to be able
> to request the non-@ part separately.

> But maybe I'm missing something.

You've just told me you've looked into things more thoroughly than you
told me before.  Thanks!

I now agree with you that we should commit this change, both to CC Mode
and to Emacs.  Do you want me to do this (with your name), or would you
prefer to do it yourself (at least in Emacs)?

> Thanks.
> Filipp

-- 
Alan Mackenzie (Nuremberg, Germany).