bug#60077: 29.0.60; Is xterm modifyOtherKeys support broken?

[Eli Zaretskii <eliz@gnu.org>]

> From: Len Trigg <lenbok@gmail.com>
> Date: Thu, 15 Dec 2022 10:48:35 +1300
> 
> I often run emacs in the terminal, and usually this is inside wezterm as my
> terminal emulator. Recently wezterm has added support for the
> modifyOtherKeys xterm extension, and since then emacs M-SPC has stopped
> working in the terminal (instead it inserts "~32").
> 
> I can get M-SPC working again in wezterm by preventing emacs from enabling
> modifyOtherKeys, either by setting xterm-extra-capabilities to nil or by
> stubbing out xterm--init-modify-other-keys. Initially we thought that
> this may be a problem with wezterm, but then I tried replicating with
> xterm and exactly the same thing happens. This suggests to me that the
> issue is with emacs rather than xterm or wezterm.
> 
> To replicate:
> 
> 1) run: xterm -e emacs -nw -Q
> 2) in say *scratch* check whether M-SPC works or whether it inserts ~32
> (for me it inserts ~32)
> 
> To replicate disabling modifyOtherKeys:
> 
> 1) put the following into $HOME/test-dir/init.el
> ------
> ;; Dirty hack to not use xterm modifyOtherKeys feature
> (defun my-disable-xterm--init-modify-other-keys (orig-fun &rest args))
> (advice-add #'xterm--init-modify-other-keys :around
>             #'my-disable-xterm--init-modify-other-keys)
> ------
> 2) run: xterm -e emacs -nw --init-dir=$HOME/test-dir
> 3) in say *scratch* check whether M-SPC works or whether it inserts ~32
> (for me it works correctly)
> 
> This seems to demonstrate the out of the box behaviour being broken, but
> I don't understand enough about terminals etc to know whether there is
> some other factor at play.
> 
> Relevant link where this was discussed:
> https://github.com/CyberShadow/term-keys/issues/14

I'm not sure I understand: it sounds like you are saying that M-SPC
doesn't work in xterm, either?  (Which version of xterm. btw?)  So the
question now becomes: how did it work before that change in wezterm
for you, and why did modifyOtherKeys feature broke it?

Which terminal file in lisp/term/ was/is Emacs loading at startup when
you use wezterm?