GNU bug report logs - #5734
23.1.94; (forward-sexp N) at the very end of large latex-mode buffer takes time proportional to N

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Message #8 received at 5734 <at> debbugs.gnu.org (full text, mbox):

From: Chong Yidong <cyd <at> stupidchicken.com>
To: joaotavora <at> gmail.com (Joao Tavora)
Cc: 5734 <at> debbugs.gnu.org
Subject: Re: 23.1.94;
	(forward-sexp N) at the very end of large latex-mode buffer takes
	time proportional to N
Date: Thu, 25 Mar 2010 15:17:12 -0400

> start with `emacs -Q'
> M-x eval-expression RET (insert (make-string 100000 ?a)) RET
> M-x eval-expression RET (latex-mode)                     RET
> M-x eval-expression RET (forward-sexp 200)               RET
> M-x eval-expression RET (forward-sexp 500)               RET
> M-x eval-expression RET (forward-sexp (point-max))       RET

> In some versions of emacs this does not happen, notably my earlier
> Carbon Emacs "GNU Emacs 22.3.1 (i386-apple-darwin9.7.0, Carbon Version
> 1.6.0) of 2009-07-26 on gs674-seijiz.local" after loading some lisp
> libraries (don't know which), like the ones I have bellow (autopair,
> yasnippet).

I can reproduce this slowness even on Emacs 22.3.  It arises because
tex-mode wants to be able to signal an error if point is in a containing
expression that ends prematurely, so it does a bit of backtracking.
(This is the `skip-syntax-backward' call in latex-forward-sexp-1).

I'm not sure what the best way to fix this is, though.

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