bug#64759: Broken faces

[Mauro Aranda]

Juri Linkov <juri@linkov.net> writes:

> It seems adding non-empty definitions in bug#64655
> were intended to workaround a bug in cus-edit.el,
> not to fix it.
>
> Maybe Mauro could help to fix it (Cc'ed)
> without requiring non-nil definitions
> that anyway can not be fixed outside of
> the Emacs source tree, i.e. in numerous
> user init files and external packages.

I don't think it is a bug in Custom.  Custom will allow the user to edit
the face and set/save or whatever, even if it's definition is
(defface foo nil "...")

But it seems to me that it's better to define it like this:
(defface foo '((t nil)) "...")
so that the face gets a face-defface-spec property.

So maybe the definition for display-time-date-and-time should be changed
to:
(defface display-time-date-and-time
  '((t nil))
  "Face for `display-time-format'."
  :group 'mode-line-faces
  :version "30.1")

instead that making it inherit from mode-line?