Subject: bug#23917: Please consider making Bug #23917 a blocker for 25.1 (was Re: org-capture: Capture template ‘g’: Match data clobbered by buffer modification hooks)

From: Eli Zaretskii <[email-masked]>
Date: Wed, 20 Jul 2016 17:55:11 +0300

> From: Stefan Monnier <[email-masked]>
> Cc: [email-masked],  [email-masked],  [email-masked],  [email-masked],  [email-masked]
> Date: Tue, 19 Jul 2016 21:50:07 -0400
> 
> > Do we care that using save-match-data in every call to replace-match
> > might mean a performance hit?
> 
> I do but:
> - to be honest, it's probably lost in the noise.
> - if we copy search_regs.start and search_regs.end with something like
>   alloca+memcpy (instead of calling Fmatch_data), the cost should be even more
>   lost in the noise.  Especially if you consider that the current code
>   already loops through the match-data to adjust it.
> - it's the best fix we've found so far.

What about Noam's suggestion:

> Is it not possible to adjust the match data *before* calling buffer
> modification hooks?  Seems to me the root of the problem is that buffer
> modification hooks get to see this invalid intermediate state where the
> match data is out of sync with the buffer.

Is it OK to adjust the match data before actually making the
replacement?  If so, I think it's a simpler solution.

> PS: I can think of one (theoretical) other/better way to fix this
>     problem: move the match-data adjustment so it's done within
>     replace_range before running the after-change-functions.

Isn't that almost the same as what Noam suggested?