hl-line face used as default in 26.1

Question

When I use emacs 24.3.1 and run

/usr/bin/emacs -Q

Then M-< followed by M-xglobal-hl-line-mode and M-xdescribe-face, emacs asks me

Describe face (default `font-lock-comment-delimiter-face'):

But when I use 26.1 and run

/usr/local/bin/emacs -Q

and run exactly the same commands, emacs asks me

Describe face (default ‘hl-line’):

I have to turn hl-line off to get the name of the point's face. What causes this difference and is there a way to get the old behaviour back?

Update:

It seems

(get-char-property (point) 'face)

returns hl-line in 26.1, but returns the actual face in 24.3.1.

Answer 1

You are right that describe-face ultimately calls get-char-property (via face-at-point). get-char-property, unlike its cousin get-text-property, doesn't return just text properties, but also overlay properties. And that's how hl-line-mode works: By setting the face property on an overlay.

A cursory glance at Emacs' git repository at savannah.gnu.org, doesn't tell me when and why there was some change. Anyways, you could argue that interactive functions like M-x describe-char should special case hl-line-mode. (Or: That might lead to confusion, so maybe not.) Be that as it may be, a possible temporary fix could be to use advice:

(defun my-face-at-point ()
  (let ((face (get-text-property (point) 'face)))
    (or (and (face-list-p face)
             (car face))
        (and (symbolp face)
             face))))

(defun my-describe-face (&rest ignore)
  (interactive (list (read-face-name "Describe face"
                                     (or (my-face-at-point) 'default)
                                     t)))
  ;; This only needs to change the `interactive` spec, so:
  nil)

(eval-after-load "hl-line"
  '(advice-add 'describe-face :before #'my-describe-face))

You'd have to do that for every interactive function that is affected by this, though, e.g. M-x customize-face, too.

Answer 2

At the particular location of interest in the current buffer, type C-u C-x = and that will pull up a *Help* buffer that describes the various faces, text properties, overlays and additional information ... There may be many things happening, and something may be trumping/superseding something else.

As to the default face that is proposed by describe-face if the user were to just press enter without actually inputting any particular face, or as to the difference between various versions of Emacs, I will leave that to another forum participant to create an alternative answer.