Deprecate the partial_match argument

docs/releases/5.0.md

@@ -213,6 +213,14 @@ The following features deprecated in Wagtail 4.0 have been fully removed. See [W
 
 Django 4.0 reached end of life on 1st April 2023 and is no longer supported by Wagtail. Django 3.2 (LTS) is still supported until April 2024.
 
+### Elasticsearch backend no longer performs partial matching on `search`
+
+The `search` method on pages, images and documents, and on the backend object returned by `wagtail.search.backends.get_search_backend()`, no longer performs partial word matching when the Elasticsearch backend is in use. Previously, a search query such as `Page.objects.search("cat")` would return results containing the word "caterpillar", while `Page.objects.search("cat", partial_match=False)` would only return results for the exact word "cat". The `search` method now always performs exact word matches, and the `partial_match` argument has no effect. This change makes the Elasticsearch backend consistent with the database-backed full-text search backends.
+
+To revert to the previous partial word matching behaviour, use the `autocomplete` method instead - for example, `Page.objects.autocomplete("cat")`. It may also be necessary to add an [](wagtailsearch_index_autocompletefield) entry for the relevant fields on the model's `search_fields` definition, as the old `SearchField("some_field", partial_match=True)` format is no longer supported.
+
+The `partial_match` argument on `search` and `SearchField` is now deprecated, and should be removed from your code; it will be dropped entirely in Wagtail 6.
+
 ### `Page.get_static_site_paths` method removed
 
 The undocumented `Page.get_static_site_paths` method (which returns a generator of URL paths for use by static site generator packages) has been removed. Packages relying on this functionality should provide their own fallback implementation.

docs/topics/search/indexing.md

@@ -110,6 +110,8 @@ These are used for performing full-text searches on your models, usually for tex
 The `partial_match` option has been deprecated. To index a field for partial matching, use `AutocompleteField` instead.
 ```
 
+(wagtailsearch_index_autocompletefield)=
+
 ### `index.AutocompleteField`
 
 These are used for autocomplete queries that match partial words. For example, a page titled `Hello World!` will be found if the user only types `Hel` into the search box.

wagtail/search/backends/base.py

@@ -8,6 +8,7 @@ from django.db.models.sql.where import SubqueryConstraint, WhereNode
 
 from wagtail.search.index import class_is_indexed, get_indexed_models
 from wagtail.search.query import MATCH_ALL, PlainText
+from wagtail.utils.deprecation import RemovedInWagtail60Warning
 
 
 class FilterError(Exception):
@@ -56,7 +57,18 @@ class BaseSearchQueryCompiler:
         self.query = query
         self.fields = fields
         self.order_by_relevance = order_by_relevance
-        self.partial_match = partial_match  # RemovedInWagtail60Warning
+        if partial_match:
+            warn(
+                "The partial_match=True argument on `search` is no longer supported. "
+                "Use the `autocomplete` method instead",
+                category=RemovedInWagtail60Warning,
+            )
+        elif partial_match is not None:
+            warn(
+                "The partial_match=False argument on `search` is no longer required "
+                "and should be removed",
+                category=RemovedInWagtail60Warning,
+            )
 
     def _get_filterable_field(self, field_attname):
         # Get field