bug#71741: 30.0.60; Wrong type argument: number-or-marker-p after C-x C-+ in eww

[Jim Porter <jporterbugs@gmail.com>]

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On 6/23/2024 4:24 PM, Stefan Kangas wrote:
> epg@pretzelnet.org writes:
> 
>> To reproduce:
>> - emacs -Q
>> - M-x eww RET gnu.org RET C-x C-+
>>
>> Expected:
>> Text is scaled up without error.
>>
>> Actual:
>> Text is scaled up, but with an error:
>>
>> run-hooks: Wrong type argument: number-or-marker-p, default
> 
> I can reproduce this bug.  Copying in Po Lu.

I was just looking at image scaling in an unrelated bug, so I had 
already swapped in all the necessary mental context for this. Here's a 
patch.

The second part fixes a closely-related issue: the scaling didn't work 
for sliced images (you can get a sliced image by zooming it: put point 
on the image and press "z").

Fixing that required fixing a bug in 'get-display-property': it only 
returned the CAR of the display property value. To maintain backwards 
compatibility, I changed it so that it still returns the CAR if there's 
only one element, but it now returns the whole list if there are 
multiple elements. I don't love this, and maybe we should always return 
a list, but I'll leave that decision to others (for what it's worth, 
'get-display-property' is new in Emacs 29, so there hopefully aren't too 
many uses of it out in the wild yet).

I think the first patch is definitely worth merging to Emacs 30, but the 
second I'm neutral on. Maybe we should fix 'get-display-property' now?

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From a2f3d51f70efa1b65c9308e3445ada16d4211586 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Sun, 23 Jun 2024 16:59:00 -0700
Subject: [PATCH 1/2] Fix rescaling of images via 'text-scale-mode' in EWW

* lisp/net/eww.el (eww--rescale-images): Handle a :scale of 'default'
(bug#71741).
---
 lisp/net/eww.el | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/lisp/net/eww.el b/lisp/net/eww.el
index fd8f80065b1..94bfd333fa9 100644
--- a/lisp/net/eww.el
+++ b/lisp/net/eww.el
@@ -1371,12 +1371,16 @@ eww--rescale-images
       (goto-char (point-min))
       (while-let ((match (text-property-search-forward
                           'display nil (lambda (_ value) (imagep value)))))
-        (let ((image (prop-match-value match)))
-          (unless (image-property image :original-scale)
-            (setf (image-property image :original-scale)
-                  (or (image-property image :scale) 1)))
+        (let* ((image (prop-match-value match))
+               (original-scale (or (image-property image :original-scale)
+                                   (setf (image-property image :original-scale)
+                                         (or (image-property image :scale)
+                                             'default)))))
+          (when (eq original-scale 'default)
+            (setq original-scale (image-compute-scaling-factor
+                                  image-scaling-factor)))
           (setf (image-property image :scale)
-                (* (image-property image :original-scale) scaling)))))))
+                (* original-scale scaling)))))))
 
 (defun eww--url-at-point ()
   "`thing-at-point' provider function."
-- 
2.25.1


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From 55a7b2ea1220cdf7d0aa511e4f65b0d021162b44 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Sun, 23 Jun 2024 17:27:24 -0700
Subject: [PATCH 2/2] Support rescaling sliced images in EWW via
 'text-scale-mode'

* src/xdisp.c (find_display_property): When the property value has
multiple elements, return the whole list.

* lisp/net/eww.el (eww--rescale-images): Use 'get-display-property'.

* doc/lispref/display.texi (Display Property): Describe the new
'get-display-property' behavior.
---
 doc/lispref/display.texi |  6 ++++--
 lisp/net/eww.el          |  9 +++++++--
 src/xdisp.c              | 24 ++++++++++++++++++------
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 34096196df4..67b64df75fd 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -5182,8 +5182,10 @@ Display Property
 This convenience function can be used to get a specific display
 property, no matter whether the @code{display} property is a vector, a
 list or a simple property.  This is like @code{get-text-property}
-(@pxref{Examining Properties}), but works on the @code{display}
-property only.
+(@pxref{Examining Properties}), but works on the @code{display} property
+only.  For properties with a single value (e.g.@: @code{height}, this
+returns the value itself; for properties with a list of values (e.g.@:
+@code{slice}), this returns the list of values.
 
 @var{position} is the position in the buffer or string to examine, and
 @var{prop} is the @code{display} property to return.  The optional
diff --git a/lisp/net/eww.el b/lisp/net/eww.el
index 94bfd333fa9..907b35f8565 100644
--- a/lisp/net/eww.el
+++ b/lisp/net/eww.el
@@ -1370,8 +1370,13 @@ eww--rescale-images
     (save-excursion
       (goto-char (point-min))
       (while-let ((match (text-property-search-forward
-                          'display nil (lambda (_ value) (imagep value)))))
-        (let* ((image (prop-match-value match))
+                          'display nil
+                          (lambda (_ value)
+                            (and value (get-display-property
+                                        nil 'image nil value))))))
+        (let* ((image (cons 'image
+                            (get-display-property nil 'image nil
+                                                  (prop-match-value match))))
                (original-scale (or (image-property image :original-scale)
                                    (setf (image-property image :original-scale)
                                          (or (image-property image :scale)
diff --git a/src/xdisp.c b/src/xdisp.c
index 18ac5b69d7e..8c7e8e5cb43 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -5549,6 +5549,7 @@ setup_for_ellipsis (struct it *it, int len)
 static Lisp_Object
 find_display_property (Lisp_Object disp, Lisp_Object prop)
 {
+  Lisp_Object elem;
   if (NILP (disp))
     return Qnil;
   /* We have a vector of display specs.  */
@@ -5556,11 +5557,11 @@ find_display_property (Lisp_Object disp, Lisp_Object prop)
     {
       for (ptrdiff_t i = 0; i < ASIZE (disp); i++)
 	{
-	  Lisp_Object elem = AREF (disp, i);
+	  elem = AREF (disp, i);
 	  if (CONSP (elem)
 	      && CONSP (XCDR (elem))
 	      && EQ (XCAR (elem), prop))
-	    return XCAR (XCDR (elem));
+	    goto found;
 	}
       return Qnil;
     }
@@ -5570,11 +5571,11 @@ find_display_property (Lisp_Object disp, Lisp_Object prop)
     {
       while (!NILP (disp))
 	{
-	  Lisp_Object elem = XCAR (disp);
+	  elem = XCAR (disp);
 	  if (CONSP (elem)
 	      && CONSP (XCDR (elem))
 	      && EQ (XCAR (elem), prop))
-	    return XCAR (XCDR (elem));
+	    goto found;
 
 	  /* Check that we have a proper list before going to the next
 	     element.  */
@@ -5589,9 +5590,20 @@ find_display_property (Lisp_Object disp, Lisp_Object prop)
   else if (CONSP (disp)
 	   && CONSP (XCDR (disp))
 	   && EQ (XCAR (disp), prop))
-    return XCAR (XCDR (disp));
+    {
+      elem = disp;
+      goto found;
+    }
+
+  return Qnil;
+
+ found:
+  /* If the property value is a list of one element, just return the
+     CAR. */
+  if (NILP (XCDR (XCDR (elem))))
+    return XCAR (XCDR (elem));
   else
-    return Qnil;
+    return XCDR (elem);
 }
 
 static Lisp_Object
-- 
2.25.1