GNU bug report logs - #45619
No warning when pcase-let is binding dynamic variable

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Message #46 received at 45619 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Michael Heerdegen <michael_heerdegen <at> web.de>, jixiuf <jixiuf <at> qq.com>,
 45619 <at> debbugs.gnu.org
Subject: Re: bug#45619: 28.0.50; pcase-let on MacOS doesn't work
Date: Sat, 12 Feb 2022 09:56:37 -0500

Lars Ingebrigtsen [2022-02-12 08:46:02] wrote:
> Michael Heerdegen <michael_heerdegen <at> web.de> writes:
>>> (pcase-let ((`(,default-directory) '( "/tmp/")))
>>>     (call-interactively 'find-file))
>>>
>>> Expected behavior: Find file in "/tmp/"
>>> Observed behavior: Find file in "~"
>>
>> AFAICT the issue here is that `pcase-let' always creates lexically
>> scoped bindings, even for special variables.  That can be surprising.
>>
>> @Stefan, what can we do?  Document better?  Add compiler warnings?  Or
>> is it possible to "fix" this?
> I tried the form in Emacs 29, and I got the expected behaviour here.  So
> was this fixed since this bug was reported?  (But I only tested on Debian.)

Hmm... I doubt it's fixed in all cases.
I still think pcase should emit a warning when asked to bind
a dynamically scoped variable.


        Stefan

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