bug#47162: Mouse Wheel Won't Work When Emacs Built without Any Window System

["Basil L. Contovounesios" via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> "Basil L. Contovounesios" <contovob@tcd.ie> writes:
>
>> FYI, as a result of this change mwheel is now effectively preloaded even
>> --without-x, in the sense that (featurep 'mwheel) returns non-nil even
>> when starting nox builds with -Q (see my signature for details).
>>
>> Bother or feature?
>
> Sounds like a bug -- I don't understand how adding an ;;;###autoload to
> a function would lead to Emacs being pre-built with the .el file the
> function exists in.  Unless there's something checking for that function
> during the build and then loading mwheel?  Didn't see anything like that
> in loadup.el...

My guess is the salient difference lies in lisp/loaddefs.el, where
autoload cookie results in the following additions:

--8<---------------cut here---------------start------------->8---
(defcustom mouse-wheel-mode t "\
Non-nil if Mouse-Wheel mode is enabled.
See the `mouse-wheel-mode' command
for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `mouse-wheel-mode'." :set #'custom-set-minor-mode :initialize 'custom-initialize-delay :group 'mouse :type 'boolean)

(custom-autoload 'mouse-wheel-mode "mwheel" nil)

(autoload 'mouse-wheel-mode "mwheel" "\
Toggle mouse wheel support (Mouse Wheel mode).

If called interactively, toggle `Mouse-Wheel mode'.  If the prefix
argument is positive, enable the mode, and if it is zero or negative,
disable the mode.

If called from Lisp, toggle the mode if ARG is `toggle'.  Enable the
mode if ARG is nil, omitted, or is a positive number.  Disable the
mode if ARG is a negative number.

The mode's hook is called both when the mode is enabled and when it is
disabled.

\(fn &optional ARG)" t nil)
--8<---------------cut here---------------end--------------->8---

BTW, another way to tell that mwheel is now being loaded is that the
following warnings disappear following the autoload in nox builds:

--8<---------------cut here---------------start------------->8---
In edmacro-fix-menu-commands:
edmacro.el:625:34: Warning: reference to free variable
    ‘mouse-wheel-down-event’
edmacro.el:625:57: Warning: reference to free variable ‘mouse-wheel-up-event’
edmacro.el:626:34: Warning: reference to free variable
    ‘mouse-wheel-right-event’
edmacro.el:627:34: Warning: reference to free variable
    ‘mouse-wheel-left-event’
--8<---------------cut here---------------end--------------->8---

-- 
Basil