Add release note recommending the use of AutocompleteField

docs/releases/5.1.2.md

@@ -17,3 +17,23 @@ depth: 1
  * Ensure sequence on `wagtailsearchpromotions_query` table is correctly set after migrating data (Jake Howard)
  * Change spreadsheet export headings to match listing view column headings (Christer Jensen, Sage Abdullah)
  * Fix numbers, booleans, and `None` from being exported as strings (Christer Jensen)
+
+## Upgrade considerations
+
+### Search within chooser interfaces requires `AutocompleteField` for full functionality
+
+In Wagtail 4.2, the search bar within snippet chooser interfaces (and custom choosers created via `ChooserViewSet`) returned results for partial word matches - for example, a search for "wagt" would return results containing "Wagtail" - if this was supported by the search backend in use, and at least one `AutocompleteField` was present in the model's `search_fields` definition. Otherwise, it would fall back to only matching on complete words. In Wagtail 5.0, this fallback behaviour was removed, and consequently a model with no `AutocompleteField`s in place would return no results.
+
+As of Wagtail 5.1.2, the fallback behaviour has been restored. Nevertheless, it is strongly recommended that you add `AutocompleteField` to your models' `search_fields` definitions, to ensure that users can receive search results continuously as they type. For example:
+
+```python
+from wagtail.search import index
+# ... other imports
+
+@register_snippet
+class MySnippet(index.Indexed, models.Model):
+     search_fields = [
+         index.SearchField("name"),
+         index.AutocompleteField("name"),
+     ]
+```

docs/releases/5.1.md

@@ -184,6 +184,24 @@ we have made a number of improvements to snippets as part of [RFC 85: Snippets p
 
 ## Upgrade considerations - changes affecting all projects
 
+### Search within chooser interfaces requires `AutocompleteField` for full functionality
+
+In Wagtail 4.2, the search bar within snippet chooser interfaces (and custom choosers created via `ChooserViewSet`) returned results for partial word matches - for example, a search for "wagt" would return results containing "Wagtail" - if this was supported by the search backend in use, and at least one `AutocompleteField` was present in the model's `search_fields` definition. Otherwise, it would fall back to only matching on complete words. In Wagtail 5.0, this fallback behaviour was removed, and consequently a model with no `AutocompleteField`s in place would return no results.
+
+As of Wagtail 5.1.2, the fallback behaviour has been restored. Nevertheless, it is strongly recommended that you add `AutocompleteField` to your models' `search_fields` definitions, to ensure that users can receive search results continuously as they type. For example:
+
+```python
+from wagtail.search import index
+# ... other imports
+
+@register_snippet
+class MySnippet(index.Indexed, models.Model):
+     search_fields = [
+         index.SearchField("name"),
+         index.AutocompleteField("name"),
+     ]
+```
+
 ### `GroupPagePermission` now uses Django's `Permission` model
 
 The `GroupPagePermission` model that is responsible for assigning page permissions to groups now uses Django's `Permission` model instead of a custom string. This means that the `permission_type` `CharField` has been deprecated and replaced with a `permission` `ForeignKey` to the `Permission` model.