dnscms: add alt and attribution on images to search index

dnscms/images/models.py

@@ -5,6 +5,7 @@ from grapple.models import (
     GraphQLString,
 )
 from wagtail.images.models import AbstractImage, AbstractRendition, Image
+from wagtail.search import index
 
 
 class CustomImage(AbstractImage):
@@ -48,6 +49,15 @@ class CustomImage(AbstractImage):
         GraphQLString("attribution"),
     ]
 
+    # Wagtail indexes title, description and tags. Editors describe the picture
+    # in `alt` rather than in `description`, so it is boosted alongside title.
+    search_fields = AbstractImage.search_fields + [
+        index.SearchField("alt", boost=10),
+        index.AutocompleteField("alt"),
+        index.SearchField("attribution"),
+        index.AutocompleteField("attribution"),
+    ]
+
 
 class Rendition(AbstractRendition):
     image = models.ForeignKey(CustomImage, on_delete=models.CASCADE, related_name="renditions")