Subject: 27.0.50; Character widget unable to read newline character

From: Michael Heerdegen <[email-masked]>
Date: Sun, 17 Jun 2018 08:39:15 +0200

Hello,

a recipe for emacs -Q:

(require 'whitespace)
(customize-option 'whitespace-display-mappings)

Make a change and undo it immediately so that the contents are unchanged
but customize lets you "Set for current session".  Do that and you get
the

"error custom-variable-set: This field should contain a single
character"

If I remove the entry for the newline character, it succeeds.

For debugging purposes I changed the :valid-regexp of the character
widget definition in wid-edit.el to ".*" and it seems that the newline
character is read in as empty string.

TIA,

Michael.

In GNU Emacs 27.0.50 (build 14, x86_64-pc-linux-gnu, GTK+ Version 3.22.29)
 of 2018-06-17 built on drachen
Repository revision: adb53168e7567462a9db9ae3c9b53f588f2fe580
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Debian GNU/Linux buster/sid