GNU bug report logs - #14883
warning about unused returned value from some ert shoulds

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Message #3 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: submit <at> debbugs.gnu.org
Subject: warning about unused returned value from some ert shoulds
Date: Tue, 16 Jul 2013 16:17:05 -0400

Package: emacs
Version: 24.3
Severity: minor

Compiling a file with contents:

    ;; -*- lexical-binding: t; -*-
    (require 'ert)
    (require 'cl-lib)
    (defvar foo-test 1)
    (should foo-test)
    (cl-assert foo-test)

results in a warning (for some reason, only when lexical-binding is t):

   foo.el:5:1:Warning: value returned from (car value-94600) is unused

The warning is from the `should'. Obviously it is a bogus warning
because the whole point of the should is to test the return value.
The similar cl-assert does not trigger a warning, because internally
cl-assert is written differently.

This is the same issue as http://debbugs.gnu.org/10969, for what is now
cl-pop.

byte-optimize-form-code-walker has special handling for the standard
`pop' macro so as not to warn about unused return values from (pop foo).
It would be nice if there was a general way to get the same result for
arbitrary macros (sort of the opposite of side-effect-free?), but I
don't see how.

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