GNU bug report logs - #25558
Spurious warnings with variables mentioned only pcase guard patterns

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Clément Pit--Claudel <clement.pitclaudel <at> live.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Spurious warnings with variables mentioned only pcase guard patterns
Date: Fri, 27 Jan 2017 19:14:54 -0500

[Message part 1 (text/plain, inline)]

The following causes a warning (unused variable 'b'):

  (pcase '(1 2) ((and `(,a ,b) (guard (equal a b))) a))

This is due to pcase let-binding 'a' twice; once around the guard test ('(equal a b)'), and once around the body ('a').

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Message #8 received at 25558 <at> debbugs.gnu.org (full text, mbox):

From: npostavs <at> users.sourceforge.net
To: Clément Pit--Claudel <clement.pitclaudel <at> live.com>
Cc: 25558 <at> debbugs.gnu.org
Subject: Re: bug#25558: Spurious warnings with variables mentioned only pcase
 guard patterns
Date: Fri, 27 Jan 2017 19:24:41 -0500

forcemerge 16771 25558
quit

Clément Pit--Claudel <clement.pitclaudel <at> live.com> writes:

> The following causes a warning (unused variable 'b'):
>
>   (pcase '(1 2) ((and `(,a ,b) (guard (equal a b))) a))
>
> This is due to pcase let-binding 'a' twice; once around the guard test ('(equal a b)'), and once around the body ('a').

This was reported as #16771.  It seems difficult to fix, unfortunately.

Message #17 received at 25558 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Yuri Khan <yuri.v.khan <at> gmail.com>
Cc: 27545 <at> debbugs.gnu.org, 25558 <at> debbugs.gnu.org
Subject: Re: bug#25558: Spurious warnings with variables mentioned only
 pcase guard patterns
Date: Fri, 03 Sep 2021 10:49:09 +0200

Yuri Khan <yuri.v.khan <at> gmail.com> writes:

> C-x C-f test.el RET
>
> ;; -*- lexical-binding: t -*-
>
> (defun foo (x)
>   (pcase x
>     ((and `(,bar ,baz)
>           (guard (eq bar 'quux)))
>      baz)))
>
> C-x C-s
> M-x byte-compile RET test.el RET
>
> Observed output:
>
> Compiling file /home/yuri/test.el at Sat Jul  1 16:27:36 2017
> test.el:3:1:Warning: Unused lexical variable ‘bar’

I can reproduce this in Emacs 26.1, but not in Emacs 28, so I'm guessing
that this is fixed, and I'm closing this bug report.  If there's still
problems here, please respond to the debbugs address and we'll reopen.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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