martin rudalics <rudalics@gmx.at> writes:
>> [1] Compare:
>>
>> (let ((prompt "foobar "))
>>    (add-face-text-property 3 6 'warning nil prompt)
>>    (yes-or-no-p prompt))
>>
>> With:
>>
>> (let ((prompt "foobar "))
>>    (add-face-text-property 3 6 'warning nil prompt)
>>    (y-or-n-p prompt))
>
> 'y-or-n-p' propertizes the prompt rigidly as
>
>                     (read-key (propertize (if (memq answer scroll-actions)
>                                               prompt
>                                             (concat "Please answer y or n.  "
>                                                     prompt))
>                                           'face 'minibuffer-prompt)))))
>
> while 'yes-or-no-p' carefully applies 'minibuffer-prompt-properties'
> to any text properties provided with PROMPT.

Well, that's interesting.

I dug into yes-or-no-p until I came across `read_minibuf()'; is this the
code you are referring to?

    if (PT > BEG)
      {
        Fput_text_property (make_fixnum (BEG), make_fixnum (PT),
                            Qfront_sticky, Qt, Qnil);
        Fput_text_property (make_fixnum (BEG), make_fixnum (PT),
                            Qrear_nonsticky, Qt, Qnil);
        Fput_text_property (make_fixnum (BEG), make_fixnum (PT),
                            Qfield, Qt, Qnil);
        if (CONSP (Vminibuffer_prompt_properties))
          {
            /* We want to apply all properties from
               `minibuffer-prompt-properties' to the region normally,
               but if the `face' property is present, add that
               property to the end of the face properties to avoid
               overwriting faces. */
            Lisp_Object list = Vminibuffer_prompt_properties;
            while (CONSP (list))
              {
                Lisp_Object key = XCAR (list);
                list = XCDR (list);
                if (CONSP (list))
                  {
                    Lisp_Object val = XCAR (list);
                    list = XCDR (list);
                    if (EQ (key, Qface))
                      Fadd_face_text_property (make_fixnum (BEG),
                                               make_fixnum (PT), val, Qt, Qnil);
                    else
                      Fput_text_property (make_fixnum (BEG), make_fixnum (PT),
                                          key, val, Qnil);
                  }
              }
          }
      }

If one were to fix the issue of y-or-n-p hardcoding the face property,
what would be the best way to go?

1. Make a C DEFUN out of this snippet, and have it called by
   `read_minibuf()' and `y-or-n-p'.

2. Re-implement this snippet as an Elisp defun, and have it called by
   `read_minibuf()' and `y-or-n-p'.

3. (Re-implement this snippet within `y-or-n-p'.)

(FWIW, the attached patch seems to work as a workaround, but I assume
solutions 1 or 2 would be better, by virtue of reusing code)