bug#62675: 29.0.60; emoji-zoom-increase interacts badly with faces

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Wed, 05 Apr 2023 11:45:35 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> Thatʼs not a valid 'face property, unless Iʼm misreading (info
    >> "(elisp) Special Properties"), plus the ':height 1.331' bit is wrong,
    >> thatʼs (expt 1.1 3), not (expt 1.1 4). Yet it works, the height has
    >> been increased.

    Eli> The first "+" doesn't increase the height, though.

Hmm, youʼre right. Although if I then move to a different place in the
buffer, and do 'C-x 8 e +' it does increase the height first time. Is
this an interaction with font-lock?

Oh, and it doesnʼt work at eob. And increase followed by decrease
doesnʼt get you back to :height 1.0. And thereʼs no reset. I think
Iʼll only fix the first one on emacs-29 :-)

    >> Is this a bug in our interpretation of 'face properties?

    Eli> Face properties can be specified in many strange ways, and the fact
    Eli> that some invalid specifications seem to "work" doesn't mean we have a
    Eli> bug, it just means some invalid faces fall through the cracks.

OK. Iʼll make the code match the documented behaviour, and not worry
about it too much 😀

    >> I can fix the code in `emoji-zoom-increase' to produce something like
    >> 
    >> ((:height 1.4641000000000004) font-lock-comment-delimiter-face)
    >> 
    >> instead

    Eli> Please do, and thanks.  We don't need to understand why some bug seems
    Eli> to work, it is enough to fix the bug.

This seems to work:

diff --git a/lisp/international/emoji.el b/lisp/international/emoji.el
index bcd4aac4f29..a9ed6e79cc9 100644
--- a/lisp/international/emoji.el
+++ b/lisp/international/emoji.el
@@ -708,22 +708,24 @@ emoji-zoom-increase
 FACTOR is the multiplication factor for the size."
   (interactive)
   (set-transient-map emoji-zoom-map t nil "Zoom with %k")
-  (let* ((factor (or factor 1.1))
-         (old (get-text-property (point) 'face))
-         (height (or (and (consp old)
-                          (plist-get old :height))
-                     1.0))
-         (inhibit-read-only t))
-    (with-silent-modifications
-      (if (consp old)
-          (add-text-properties
-           (point) (1+ (point))
-           (list 'face (plist-put (copy-sequence old) :height (* height factor))
-                 'rear-nonsticky t))
-        (add-face-text-property (point) (1+ (point))
-                                (list :height (* height factor)))
-        (put-text-property (point) (1+ (point))
-                           'rear-nonsticky t)))))
+  (unless (eobp)
+    (let* ((factor (or factor 1.1))
+           (old (get-text-property (point) 'face))
+           (height (or (and (consp old)
+                            (plist-get (car old) :height))
+                       1.0))
+           (inhibit-read-only t))
+      (with-silent-modifications
+        (if (consp old)
+            (add-text-properties
+             (point) (1+ (point))
+             (list 'face (cons (plist-put (car old) :height (* height factor))
+                               (cdr old))
+                   'rear-nonsticky t))
+          (add-face-text-property (point) (1+ (point))
+                                  (list :height (* height factor)))
+          (put-text-property (point) (1+ (point))
+                             'rear-nonsticky t))))))
 
 ;;;###autoload
 (defun emoji-zoom-decrease ()

Robert
--