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bug#26486: 25.1.91; unused var warning from cconv.el can't be suppressed

From: Lars Ingebrigtsen
Subject: bug#26486: 25.1.91; unused var warning from cconv.el can't be suppressed
Date: Mon, 05 Jul 2021 17:17:06 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)

Noam Postavsky <npostavs@users.sourceforge.net> writes:

> This happens also without a macro.
> ;; -*- lexical-binding: t; byte-compile-warnings: nil  -*-
> (with-no-warnings (let (unused)))

This currently gives a warning about both an unused variable and an
empty let body.

The following seemingly straightforward patch fixes both these things,
I'd appreciate it if somebody had a look over it first, though.  :-)
(So Stefan M added to the CCs.)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 70999648d4..d97bc1073b 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -325,6 +325,7 @@ byte-compile-warnings
   docstrings  docstrings that are too wide (longer than 80 characters,
               or `fill-column', whichever is bigger)
   suspicious  constructs that usually don't do what the coder wanted.
+  empty-body  the body of a binding form is empty.
 If the list begins with `not', then the remaining elements specify warnings to
 suppress.  For example, (not mapcar) will suppress warnings about mapcar."
diff --git a/lisp/emacs-lisp/cconv.el b/lisp/emacs-lisp/cconv.el
index f663710902..f1579cda8b 100644
--- a/lisp/emacs-lisp/cconv.el
+++ b/lisp/emacs-lisp/cconv.el
@@ -259,7 +259,8 @@ cconv--warn-unused-msg
               (not (intern-soft var))
               (eq ?_ (aref (symbol-name var) 0))
              ;; As a special exception, ignore "ignore".
-             (eq var 'ignored))
+             (eq var 'ignored)
+              (not (byte-compile-warning-enabled-p 'unbound var)))
        (let ((suggestions (help-uni-confusable-suggestions (symbol-name var))))
          (format "Unused lexical %s `%S'%s"
                  varkind var
diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
index df864464b7..e9c2eb3fee 100644
--- a/lisp/emacs-lisp/macroexp.el
+++ b/lisp/emacs-lisp/macroexp.el
@@ -319,14 +319,16 @@ macroexp--expand-all
       (`(,(and fun (or 'let 'let*)) . ,(or `(,bindings . ,body)
        (macroexp--cons fun
-                       (macroexp--cons (macroexp--all-clauses bindings 1)
-                                       (if (null body)
-                                           (macroexp-unprogn
-                                            (macroexp-warn-and-return
-                                             (format "Empty %s body" fun)
-                                             nil t))
-                                         (macroexp--all-forms body))
-                                       (cdr form))
+                       (macroexp--cons
+                        (macroexp--all-clauses bindings 1)
+                        (if (null body)
+                            (macroexp-unprogn
+                             (macroexp-warn-and-return
+                              (and (byte-compile-warning-enabled-p 'empty-body)
+                                   (format "Empty %s body" fun))
+                              nil t))
+                          (macroexp--all-forms body))
+                        (cdr form))
       (`(,(and fun `(lambda . ,_)) . ,args)
        ;; Embedded lambda in function position.

(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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