bug#12377: 24.2.50; `minibuffer-prompt-properties' should respect existing faces in prompt string

[Lars Ingebrigtsen]

It's unfortunate that read_minibuf uses this way to apply the minibuf
text properties:

        Fadd_text_properties (make_number (BEG), make_number (PT),
                              Vminibuffer_prompt_properties, Qnil);

Or rather, the design of minibuffer-prompt-properties.  It includes one
property that's pretty important for the prompt, namely `read-only', and
one that's for display only, namely `face'.  And the latter is something
that you'd want to be able to override by saying `propertize' on the
prompt, definitely.

I'm inclined to think that if the user has set any `face' properties on
the prompt, then read_minibuf should avoid setting it.  We could just
loop over the minibuffer-prompt-properties list and apply the ones that
aren't set any place in the string already?  Does that sound OK to
everybody?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no