bug#67404: 30.0.50; Issue with :box face attribute

[Mauro Aranda <maurooaranda@gmail.com>]

On 26/11/23 07:27, Eli Zaretskii wrote:

 >> Date: Thu, 23 Nov 2023 16:23:15 +0100
 >> From: David Ponce <da_vid@orange.fr>
 >>
 >> Hello,
 >>
 >> The below face with specified :box attribute can be defined and further
 >> used without problem:
 >>
 >> (defface test-face
 >>    '((t
 >>       (:box (:style released-button :line-width (3 . 0)))
 >>       ))
 >>    "Test face.")
 >>
 >> (insert (propertize "XXXXX" 'face 'test-face))
 >>
 >> However, it is not possible to apply any change to this face with
 >> `customize-face', for example to change :line-width (3 . 0) to
 >> :line-width (2 . 0), or to add a :foreground color, etc. This fails
 >> with the message "set-face-attribute: Invalid face box: :line-width,
 >> <value>, :style, <value>", and the :box attribute is discarded.
 >>
 >> AFAICS, :box attribute with any zero :line-width value works as
 >> expected: the box line with zero width is not displayed. But zero is
 >> not considered as a valid value by `set-face-attribute' (in fact, the
 >> internal function `internal-set-lisp-face-attribute').
 >>
 >> For consistency, a zero :line-width value either should be accepted by
 >> `internal-set-lisp-face-attribute', or never accepted at all.
 >
 > Mauro, any comments about these issues?

Hi Eli,

Not really, no.  The widget used for line-width just assumes 0 is a
valid value.  I don't know if that's the case or not, it is not
explicitly documented in the ELisp manual and I don't really know the
xfaces.c code.

For some reason, the code that rejects a value of 0 in
Finternal_set_lisp_face_attribute doesn't complain (maybe it does not
get to run?) when using defface, but it does complain when Customize
tries to set it, by calling face-spec-set.

Sorry I can't be of any more help right now.