Emacs treatment of match-data during change hooks

Emacs treatment of match-data during change hooks

[Barry OReilly]

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Investigating bug 14281[1], I found this passage in the Elisp
manual[2]:

   The functions you use in these [change] hooks should save and
   restore the match data if they do anything that uses regular
   expressions; otherwise, they will interfere in bizarre ways with
   the editing operations that call them.

I suppose that caveat would pin the bug on one of the third party
packages I use. However, why couldn't Emacs save off the match-data
itself and restore it after the after-change-functions? Is there any
legit situation where a change hook would want to change the
match-data in effect after the change hook returns?

[1] https://lists.gnu.org/archive/html/bug-gnu-emacs/2013-04/msg00703.html
[2]
http://www.gnu.org/software/emacs/manual/html_node/elisp/Change-Hooks.html

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Re: Emacs treatment of match-data during change hooks

[Stefan Monnier]

> I suppose that caveat would pin the bug on one of the third party
> packages I use. However, why couldn't Emacs save off the match-data
> itself and restore it after the after-change-functions? Is there any
> legit situation where a change hook would want to change the
> match-data in effect after the change hook returns?

There are many cases where an after-change-function won't use regular
expressions at all.


        Stefan