Re: Mysterious fontification/C++ context issue - Patch for beginning-of-defun-raw.

[martin rudalics <rudalics@gmx.at>]

 >>M-> ran almost instantaneously before `beginning-of-defun-raw' changed.
 >>And you did fill CC Mode's cache already before the change.  I could
 >>imagine it's because font-locking runs `beginning-of-defun' repeatedly
 >>for decreasing buffer positions and the `syntax-ppss' cache doesn't
 >>handle these cases optimally.
 >
 >
 > I thought "no, can't be, 'cause I was careful to treat this correctly", so
 > I went and measured it to give a clear proof of it, and much to my surprise
 > you seemed to be right:
 >
 > parse-partial-sexp on the whole buffer takes about 0.08 seconds on my laptop
 > (1.2GHz P-III M, maybe running at 800MHz at that time).  syntax-ppss on that
 > same buffer takes about 0.24s (about 3 times slower: not great, but seemed
 > possible), but
 >
 >            (syntax-ppss (point-max))
 >            (syntax-ppss (- (point-max) 2000))
 >            (syntax-ppss (- (point-max) 4000))
 >
 > takes a good 1.8s which doesn't make any sense.

I got approximately that far when I wrote the lines above.

 > After the shock (thinking,
 > god, I was wrong, how could that be?), I realized that these numbers didn't
 > make any sense.

I simply felt puzzled and didn't dig any further.

 > And sure enough the problem was that in xdisp.c
 > syntax-begin-function is not nil but set to c-beginning-of-syntax which
 > doesn't make any sense: if you don't want to use a heuristic, then set the
 > damn thing to nil.
 >
 > This variable is set to c-beginning-of-defun in cc-mode.el via
 > font-lock-beginning-of-syntax-function which is set via font-lock-defaults.

Does that mean we got the `_c_-beginning-of-defun' behavior through the
back-door?  All that code existed before the open-paren-... change.

 > -	  c-beginning-of-syntax
 > +	  nil

Jumping to the end of xdisp.c still takes four seconds.  I continue to
feel puzzled.  Note that Alan binds `syntax-begin-function' to nil in
his `beginning-of-defun-raw' hence why should this have any impact in
the first place?  I must take another look in the basements of that.