bug#31641: 26.1; iter-do variable not left unused warning

[Noam Postavsky <npostavs@gmail.com>]

tags 31641 + confirmed
severity 31641 minor
quit

Christopher Wellons <wellons@nullprogram.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#)