bug#41343: tab-bar-mode: Close tab on mouse-2 click

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: stefankangas@gmail.com,  41343@debbugs.gnu.org
> Date: Wed, 04 Aug 2021 23:13:12 +0300
> 
> > Do we really have to hard-code the mouse button this way, including
> > explicit values in C?  Why is that necessary or justified?
> 
> In tab-line.el it was very easy to bind mouse-2 to close the tab:
> 
>   (defvar tab-line-tab-map
>     (let ((map (make-sparse-keymap)))
>       (define-key map [tab-line mouse-1] 'tab-line-select-tab)
>       (define-key map [tab-line mouse-2] 'tab-line-close-tab)
> 
> But it's impossible to do the same for the menu-bar and the tool-bar
> and so in the tab-bar too.

Why not?  What prevents that?

> Ot do you mean adding an integer variable that holds
> a number of the mouse button used to close the tab?
> For example, tab-bar-close-tab-mouse-button = 2.

I think we should explore such possibilities only after we understand
why normal key bindings don't work.