bug#20466: 25.0.50; REGRESSION in `isearch-mode-map': <backspace> is not translated to DEL

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 29 Apr 2015 22:19:48 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> This regression was apparently introduced in Emacs 24.4.
> 
> (define-key isearch-mode-map (kbd "DEL") 
>             (lambda () (interactive) (message "@@@@@@@@@@@@@@@@")))
> 
> During Isearch, hit the Backspace key.  `DEL' is not used, so the
> message is not seen.  `isearch-mode-map' shows that `DEL' is correctly
> bound to the above command, but `<backspace>' is bound to
> `isearch-delete-char'.  It is not translated to `DEL', as is the case in
> Emacs generally (still), but it instead now has its own explicit binding
> in `isearch-mode-map'.
> 
> Why?  This is an unexpected (and unnecessary?) obstacle for users.

The "why" part was answered by Artur, who pointed to the bug report
which triggered that change.

> It is an incompatible change, and I see nothing in NEWS about it.

It's not really incompatible, but I agree that it would be good to
document the change, although I don't believe we document changes in
keybindings in general.

May I ask what kind of real-life use case is behind this?  I learned
long ago that if you want to change the binding of DEL, you had better
changed the binding of Backspace accordingly at the same time, because
there's no guarantee Backspace will not be bound in any particular
mode.  So why you are showing a use case that violates this simple
rule?