From: Lars Ingebrigtsen <larsi@gnus.org>
To: Noam Postavsky <npostavs@gmail.com>
Cc: Christopher Wellons <wellons@nullprogram.com>,
31641@debbugs.gnu.org, Stefan Monnier <monnier@iro.umontreal.ca>
Subject: bug#31641: 26.1; iter-do variable not left unused warning
Date: Thu, 04 Feb 2021 11:05:24 +0100 [thread overview]
Message-ID: <87czxgtafv.fsf@gnus.org> (raw)
In-Reply-To: <87in76cdpd.fsf@gmail.com> (Noam Postavsky's message of "Tue, 29 May 2018 18:13:50 -0400")
Noam Postavsky <npostavs@gmail.com> writes:
>> When byte-compiling an iter-do form with a variable intended to be
>> left unused, the compiler emits a false warning:
>>
>> ;;; -*- lexical-binding: t; -*-
>> (require 'generator)
>> (iter-do (_ i))
>> ;; -> "Warning: variable ‘_’ not left unused"
>
> Looking at the expansion, I guess the setf should be dropped if the
> variable name starts with _.
>
> (let (_
> #3=#:iter-do-result11
> (#1=#:iter-do-iterator-done8 nil)
> (#2=#:iter-do-iterator10 i))
> (while (not #1#)
> (condition-case #4=#:iter-do-condition9
> (setf _ (iter-next #2#))
> (iter-end-of-sequence
> (setf #3# (cdr #4#))
> (setf #1# t)))
> (unless #1#))
> #3#)
The following patch does this, but I'm not sure whether this is correct
or not -- in other cases, the _ convention just removes the warning, but
doesn't change the semantics.
I wondered whether we could just suppress this warning like this:
,(if (string-match-p "\\`_" (symbol-name var))
`(with-suppressed-warnings ((not-unused ,var))
(setf ,var (iter-next ,it-symbol)))
`(setf ,var (iter-next ,it-symbol)))
But no, cconv--analyze-use is called too early, and would have to be
taught about `with-suppressed-warnings'... which, looking at the code,
isn't immediately obvious how to do.
So does anybody have any ideas here?
diff --git a/lisp/emacs-lisp/generator.el b/lisp/emacs-lisp/generator.el
index 9eb6d95964..0b644cc72c 100644
--- a/lisp/emacs-lisp/generator.el
+++ b/lisp/emacs-lisp/generator.el
@@ -731,7 +731,10 @@ iter-do
(,it-symbol ,iterator))
(while (not ,done-symbol)
(condition-case ,condition-symbol
- (setf ,var (iter-next ,it-symbol))
+ ;; Variables that start with an underscore shouldn't be set.
+ ,(if (string-match-p "\\`_" (symbol-name var))
+ nil
+ `(setf ,var (iter-next ,it-symbol)))
(iter-end-of-sequence
(setf ,result-symbol (cdr ,condition-symbol))
(setf ,done-symbol t)))
--
(domestic pets only, the antidote for overdose, milk.)
bloggy blog: http://lars.ingebrigtsen.no
next prev parent reply other threads:[~2021-02-04 10:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-29 13:12 bug#31641: 26.1; iter-do variable not left unused warning Christopher Wellons
2018-05-29 22:13 ` Noam Postavsky
2021-02-04 10:05 ` Lars Ingebrigtsen [this message]
2021-02-04 16:36 ` Stefan Monnier
2021-02-05 8:53 ` Lars Ingebrigtsen
2021-02-05 15:03 ` Stefan Monnier
2021-02-06 10:31 ` Lars Ingebrigtsen
2021-02-05 17:12 ` Basil L. Contovounesios
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