From: Juri Linkov <juri@linkov.net>
To: Alan Mackenzie <acm@muc.de>
Cc: Jayden Navarro <jayden@yugabyte.com>, 36328@debbugs.gnu.org
Subject: bug#36328: 26.2; Args out of range on search-and-replace of *.cc file
Date: Mon, 24 Jun 2019 22:18:53 +0300 [thread overview]
Message-ID: <87d0j27wiu.fsf@mail.linkov.net> (raw)
In-Reply-To: <20190624075218.GA4781@ACM> (Alan Mackenzie's message of "Mon, 24 Jun 2019 07:52:18 +0000")
Hello, Alan.
>> I think first we should try to narrow down the source of this match
>> data leak.
>
> Is there really such a thing as a match data leak? I don't think there's
> any convention that the match data are preserved over large bits of code,
> particularly when different libraries are involved. There is nothing
> documented in the Elisp manual that I can see.
Yes, it seems such match-data leak is considered at least undesirable.
I remember efforts to replace string-match with string-match-p in
potentially unsafe places and to wrap more code in save-match-data.
But I guess such efforts are futile since this task is endless.
Usually it's enough for a function that cares about preserving match-data
to protect it from mutation.
>> Then we could decide what is the best solution. Currently I see no
>> such place in isearch-lazy-highlight-new-loop that calls external code.
>
> isearch-lazy-highlight-new-loop calls (sit-for 0), which calls redisplay,
> which calls font locking.
You are right that it's too much to expect that the match-data will be
preserved after redisplay, and we can't find and fix all places that
change match-data, so save-match-data needs be added to perform-replace
somewhere to protect match-data.
Since (sit-for 0) is unsafe for match-data, the first candidate to be
wrapped in save-match-data is (sit-for 0) itself in isearch-lazy-highlight-new-loop.
But perhaps more correct would be to use save-match-data in the same
function that cares about preserving its match-data, so the second
candidate to use save-match-data is perform-replace. Then the need
of using save-match-data will be self-evident for everyone who will
look at the code in perform-replace: here we use match-data, and here
we protect it in the same function.
next prev parent reply other threads:[~2019-06-24 19:18 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-21 23:03 bug#36328: 26.2; Args out of range on search-and-replace of *.cc file Jayden Navarro
[not found] ` <mailman.612.1561158667.10840.bug-gnu-emacs@gnu.org>
2019-06-22 13:25 ` Alan Mackenzie
2019-06-22 14:25 ` Jayden Navarro
2019-06-22 14:51 ` Juanma Barranquero
2019-06-22 16:09 ` Jayden Navarro
2019-06-22 20:50 ` Alan Mackenzie
2019-06-22 21:27 ` Jayden Navarro
2019-06-22 22:38 ` Jayden Navarro
2019-06-22 23:02 ` Jayden Navarro
2019-06-23 12:22 ` Alan Mackenzie
2019-06-23 16:14 ` Jayden Navarro
2019-06-23 19:32 ` Alan Mackenzie
2019-06-23 21:19 ` Juri Linkov
2019-06-23 21:42 ` Jayden Navarro
2019-06-24 19:05 ` Juri Linkov
2019-06-24 20:03 ` Jayden Navarro
2019-06-24 7:52 ` Alan Mackenzie
2019-06-24 19:18 ` Juri Linkov [this message]
2019-06-25 9:47 ` Alan Mackenzie
2019-06-25 19:58 ` Juri Linkov
2019-07-04 21:09 ` Juri Linkov
2019-07-05 6:11 ` Eli Zaretskii
2019-07-05 19:12 ` Juri Linkov
2019-10-02 23:53 ` Stefan Kangas
2019-06-23 20:10 ` bug#36328: [jayden@yugabyte.com: Re: bug#36328: 26.2; Args out of range on search-and-replace of *.cc file] Alan Mackenzie
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