bug#57652: 29.0.50; Warning setting attribute of face ‘term’

[David Ponce <da_vid@orange.fr>]

On 08/09/2022 07:02, Po Lu wrote:
> David Ponce <da_vid@orange.fr> writes:
> 
>> diff --git a/term.el b/term.el
>> index 797fb18074..c564a5429a 100644
>> --- a/term.el
>> +++ b/term.el
>> @@ -755,17 +755,19 @@ ansi-term-color-vector
>>      term-color-bright-cyan
>>      term-color-bright-white])
>>
>> -(defcustom term-default-fg-color nil
>> -  "If non-nil, default color for foreground in Term mode."
>> +(defcustom term-default-fg-color 'unspecified
>> +  "Default color for foreground in Term mode."
>>     :group 'term
>> -  :type '(choice (const nil) (string :tag "color")))
>> +  :type '(choice (const unspecified)
>> +                 (string :tag "color")))
> 
> Doesn't that change behavior?
> 
> i.e. wouldn't it be better to test that term-default-fg-color is not nil
> wherever the face is actually made that color?

To be honest I don't know.  I reread the spec that says:

    "Apart from the values given below, each face attribute can have the
value ‘unspecified’.  This special value means that the face doesn’t
specify that attribute directly.  An ‘unspecified’ attribute tells Emacs
to refer instead to a parent face (see the description ‘:inherit’
attribute below); or, failing that, to an underlying face (*note
Displaying Faces::).  (However, ‘unspecified’ is not a valid value in
‘defface’.)"

So it seems that unspecified is not allowed in defface.  So, how to 
specify a missing attribute excepted by using nil in the defface used in 
term.el?

(defface term
   `((t
      :foreground ,term-default-fg-color
      :background ,term-default-bg-color
      :inherit default))
   "Default face to use in Term mode."
   :group 'term)

Thanks!