bug#25152: 25.1; Customize: errors for `restricted-sexp' in `repeat'

[Drew Adams]

emacs -Q

(defcustom bar
  `(ignore)
  "..."
  :type
  '(repeat (restricted-sexp :match-alternatives (functionp)))
  :group 'emacs)

M-x customize-option bar

1. Click the INS button, to insert a new element in the list.
2. At the prompt "Lisp expression: ", hit `C-g'.

Emacs erroneously inserts two new buttons INS and DEL.
You can repeat this - click INS and you get two more such buttons.

And if you click any of the DEL buttons then you get this error:

 Symbol's function definition is void: nil

Something is quite wrong with the handling of `C-g', it seems.

This is the case also in older releases, going back to Emacs 20, at
least.


In GNU Emacs 25.1.1 (x86_64-w64-mingw32)
 of 2016-09-17 built on LAPHROAIG
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Configured using:
 'configure --without-dbus --without-compress-install CFLAGS=-static'