bug#4911: mouse-face property should merge face attributes, not replace

[Basil L. Contovounesios]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> To reproduce:
>
> (insert (propertize "hello" 'face 'underline 'mouse-face 'highlight))
>
> and put the mouse pointer over the "hello": The underline goes away.

Isn't this long-standing and documented behaviour?  It can be worked
around to an extent by defining mouse-face in terms of face:

  (insert (propertize "hello" 'face 'underline
                      'mouse-face '(:inherit (highlight underline))))

> I think it might make sense to merge the properties...  but, on the
> other hand, this may make the text illegible.

Indeed, I'm not sure this makes sense in the general case, but I'm no
expert.

Thanks,

-- 
Basil