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Re: end-of-defun is fubsr.

From: Stefan Monnier
Subject: Re: end-of-defun is fubsr.
Date: Tue, 03 Feb 2009 21:21:02 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux)

> Visit src/buffer.c, goto L313 which contains the closing brace of DEFUN
> Fget_file_buffer, put point AFTER the "}".  Or put point on the next line
> (L314).  In either case C-M-e leaves point at BOL315.  

Oh, so we just disagree about what is the correct behavior.  As far as
I'm concerned, if C-M-e gets you to BOL315, that means that the end of
the function is BOL315, which implies that EOL313 is inside the
function, so it's correct for C-M-e to just move to BOL315.

> If one were to define a variable end-of-defun-RAW-function, which is
> defined to leave point just after the last bit of the function,

That's what end-of-defun-function should do, indeed.

> perhaps that would work, but it would break existing 3rd party code.

Like which code?

>> Unless by "the problem" you're talking about the performance problem, in
>> which case I understand that each time we call BOD (except for the first
>> call), we know that we're "outside" of a defun (unless there's nesting,
>> of course) but we don't tell that to BOD which may have to redo the work
>> of figuring it out.

> WILL have to do the work.

No: in most cases, beginning-of-defun-raw just uses a simple regexp and
doesn't try to determine its position in the syntax tree before doing
its job.  This is pretty much how C-mode's beginning-of-defun worked in
Emacs-21 and incidentally it worked (for the cases I care about) much
better than the current code.

> Now, I wonder, who could that have been?  ;-)  Oh, how I'd love just to
> get rid of these stupid K&R declarations, which NOBODY uses at all
> nowadays, except on >20 year old code bases.  ;-)  Why don't we flush
> them out of Emacs C source?  (No, you don't have to answer.)

Feel free to remove support for those things in C-mode.  If that can
solve the performance issues, I'm all for it.  After all, Emacs-21
didn't get it right and I haven't heard significant complains about it.
It's not like Emacs is always expected to understand every little bit of
a language's syntax anyway.

>> > It's changed from "move to next end of function" to "move to the end of
>> > the function at whose beginning we now are",

>> Right.  As you may notice, the second is a subset of the first (with
>> a few caveats for nested functions, of course, but that shouldn't matter
>> for C-mode), so if your implementation works for the first, it should
>> work for the second as well.  It's called backward compatibility.

> c-end-of-defun's functionality "needs" to stay the same to support other
> Emacsen.  For Emacs-23's EOD-function, It would barely need to be more
> than
>      (search-forward-regexp "{")
>      (backward-char)
>      (foward-sexp)

Yes, simplicity of implementation of EOD-function was indeed an
important motivation in my code changes.

>> > and its default value is `forward-sexp'.  `c-end-of-defun' was a good
>> > fit for the variable as it formerly was, but is now
>> > severely suboptimal.

>> At most by a factor of 2.  I.e. if it's slow now, it sure wasn't
>> zippy before.

> By a factor a great deal more than 2, highly dependent on ARG.

The only case I care about for now is when ARG=1.  As long as this case
is slow, there's no point complaining that end-of-defun makes it too
slow for ARG=106.

>> >> Not sure about restoring the previous semantics.  But I could agree to
>> >> the additional ARG argument, which could even let it "take over" (so
>> >> beginning-of-defun-raw is not called in that case).
>> > :-)  Let's do it!
>> I knew you'd like it.
> :-)

I'm still wondering whether we couldn't just turn end-of-defun into
a simple variant of

   (BOD-raw N)
   (funcall EOD-function)

> OK.  I think I can see what you're saying, now.  Were you thinking of any
> (non CC Mode) languages in particular?  Did this ever get discussed on
> emacs-devel?  I might well have been asleep at the time.

No, I don't remember discussing it much.  It did come out of
a discussion where it became apparent that end-of-defun was broken
(especially when called with negative args).


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