bug#46819: 28.0.50; Undesireable warning: Empty let body from the `benchmark-run' implementation

[Matt Armstrong]

This behavior began with Stefan's recent commit d41a4ad4ae (*
lisp/emacs-lisp/macroexp.el ;; (macroexp--expand-all): Warn on empty let
bodies, 2021-02-15)

`benchmark-run' has a timing `doloop' with an empty body, which `doloop`
expands to a `let` with an empty body (in the lexical-binding case).

Save the following into my-benchmark-warning.el

----------------------------------------------------------------------
;;; Code:

(require 'benchmark)

(defun my-list-benchmark ()
  "Lorem ipsum dolor."
  (benchmark-run 100
    (list 1 2 3)))

(provide 'my-benchmark-warning)
;;; my-benchmark-warning.el ends here
----------------------------------------------------------------------

Then run this and you'll see the interaction below:

----------------------------------------------------------------------
% ./src/emacs -Q --batch -f batch-byte-compile ./my-benchmark-warning.el

In my-list-benchmark:
./my-benchmark-warning.el:32:8: Warning: Empty let body
----------------------------------------------------------------------





In GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin20.3.0, NS appkit-2022.30 
Version 11.2.1 (Build 20D74))
 of 2021-02-27 built on matts-mbp-2016.lan
Repository revision: de33de1a660283f45a10acfaedef20c460553dbd
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2022
System Description:  macOS 11.2.1

Configured using:
 'configure --without-info'

Configured features:
ACL GLIB GMP GNUTLS JPEG JSON LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER
PNG RSVG THREADS TIFF TOOLKIT_SCROLL_BARS ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Special

Minor modes in effect:
  winner-mode: t
  electric-pair-mode: t
  auto-insert-mode: t
  display-time-mode: t
  show-paren-mode: t
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  magit-auto-revert-mode: t
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  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  global-flycheck-mode: t
  which-key-mode: t
  override-global-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

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/Users/matt/git/notmuch/emacs/coolj hides 
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/Users/matt/git/notmuch/emacs/notmuch-wash hides 
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/Users/matt/git/notmuch/emacs/notmuch-maildir-fcc hides 
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/Users/matt/git/notmuch/emacs/notmuch-compat hides 
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/Users/matt/git/notmuch/emacs/notmuch-address hides 
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/Users/matt/git/notmuch/emacs/rstdoc hides 
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/Users/matt/git/notmuch/emacs/notmuch-lib hides 
/Users/matt/.emacs.d/elpa/notmuch-0.31.3/notmuch-lib
/Users/matt/git/notmuch/emacs/notmuch-print hides 
/Users/matt/.emacs.d/elpa/notmuch-0.31.3/notmuch-print
/Users/matt/git/notmuch/emacs/notmuch-draft hides 
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/Users/matt/git/notmuch/emacs/notmuch-jump hides 
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/Users/matt/git/notmuch/emacs/notmuch-parser hides 
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/Users/matt/git/notmuch/emacs/notmuch-query hides 
/Users/matt/.emacs.d/elpa/notmuch-0.31.3/notmuch-query
/Users/matt/git/notmuch/emacs/notmuch-message hides 
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/Users/matt/git/notmuch/emacs/notmuch-hello hides 
/Users/matt/.emacs.d/elpa/notmuch-0.31.3/notmuch-hello
/Users/matt/git/notmuch/emacs/notmuch-crypto hides 
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/Users/matt/git/notmuch/emacs/make-deps hides 
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/Users/matt/git/notmuch/emacs/notmuch-company hides 
/Users/matt/.emacs.d/elpa/notmuch-0.31.3/notmuch-company

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slime-fancy-inspector slime-c-p-c slime-editing-commands slime-autodoc
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window text-properties overlay sha1 md5 base64 format env code-pages
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Memory information:
((conses 16 766437 32631)
 (symbols 48 56488 4)
 (strings 32 248491 4562)
 (string-bytes 1 7334590)
 (vectors 16 89116)
 (vector-slots 8 956750 71031)
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