Register comparison classes at the field level instead of overriding get_comparison_class on panels

wagtail/admin/compare.py

@@ -11,7 +11,7 @@ from django.utils.translation import gettext_lazy as _
 from taggit.managers import TaggableManager
 
 from wagtail.core import blocks
-from wagtail.core.fields import RichTextField
+from wagtail.core.fields import RichTextField, StreamField
 from wagtail.utils.registry import ModelFieldRegistry
 
 
@@ -319,6 +319,9 @@ class StreamFieldComparison(FieldComparison):
             ).to_html()
 
 
+register_comparison_class(StreamField, comparison_class=StreamFieldComparison)
+
+
 class ChoiceFieldComparison(FieldComparison):
     def htmldiff(self):
         val_a = force_str(

wagtail/admin/edit_handlers.py

@@ -603,8 +603,7 @@ class FieldPanel(EditHandler):
 
 
 class RichTextFieldPanel(FieldPanel):
-    def get_comparison_class(self):
-        return compare.RichTextFieldComparison
+    pass
 
 
 class BaseChooserPanel(FieldPanel):
@@ -1012,9 +1011,6 @@ class StreamFieldPanel(FieldPanel):
 
         return classes
 
-    def get_comparison_class(self):
-        return compare.StreamFieldComparison
-
     def id_for_label(self):
         # a StreamField may consist of many input fields, so it's not meaningful to
         # attach the label to any specific one

wagtail/images/apps.py

@@ -24,3 +24,13 @@ class WagtailImagesAppConfig(AppConfig):
         register_form_field_override(
             ForeignKey, to=Image, override={"widget": AdminImageChooser}
         )
+
+        # Set up image ForeignKeys to use ImageFieldComparison as the comparison class
+        # when comparing page revisions
+        from wagtail.admin.compare import register_comparison_class
+
+        from .edit_handlers import ImageFieldComparison
+
+        register_comparison_class(
+            ForeignKey, to=Image, comparison_class=ImageFieldComparison
+        )

wagtail/images/edit_handlers.py

@@ -5,8 +5,7 @@ from wagtail.admin.edit_handlers import BaseChooserPanel
 
 
 class ImageChooserPanel(BaseChooserPanel):
-    def get_comparison_class(self):
-        return ImageFieldComparison
+    pass
 
 
 class ImageFieldComparison(ForeignObjectComparison):