bug#8711: 24.0.50; binding _ to unused values with lexical-binding

[Lawrence Mitchell <wence@gmx.li>]

Helmut Eller wrote:
> There seems be no way to avoid a warning in code like this:

> ;; -*- lexical-binding: t -*-
> (eval-when-compile (require 'cl))
> (defun foo (x) (destructuring-bind (_) x))
> (defun bar (x) (destructuring-bind (_) x (ignore _)))

> In foo the compiler complains because _ is never used and
> it bar it complains because it is used.

This latter is because cconv-analyse-use is not smart enough when
checking for use of variables starting with an underscore.

;; -*- lexical-binding: t -*-

(let ((_ nil))
  (ignore _))

=>

Warning: variable `_' not left unused.

This despite ignore not touching it.

Lawrence
-- 
Lawrence Mitchell <wence@gmx.li>