bug#25558: Spurious warnings with variables mentioned only pcase guard patterns

bug#25558: Spurious warnings with variables mentioned only pcase guard patterns

[Clément Pit--Claudel]

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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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bug#25558: Spurious warnings with variables mentioned only pcase guard patterns

[npostavs]

forcemerge 16771 25558
quit

Clément Pit--Claudel <clement.pitclaudel@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.

bug#25558: Spurious warnings with variables mentioned only pcase guard patterns

[Lars Ingebrigtsen]

Yuri Khan <yuri.v.khan@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