Fixed #24938 -- Added PostgreSQL trigram support.

tests/postgres_tests/migrations/0001_setup_extensions.py

@@ -5,12 +5,13 @@ from django.db import migrations
 
 try:
     from django.contrib.postgres.operations import (
-        CreateExtension, HStoreExtension, UnaccentExtension,
+        CreateExtension, HStoreExtension, TrigramExtension, UnaccentExtension,
     )
 except ImportError:
     from django.test import mock
     CreateExtension = mock.Mock()
     HStoreExtension = mock.Mock()
+    TrigramExtension = mock.Mock()
     UnaccentExtension = mock.Mock()
 
 
@@ -21,5 +22,6 @@ class Migration(migrations.Migration):
         # dash in its name.
         CreateExtension('uuid-ossp'),
         HStoreExtension(),
+        TrigramExtension(),
         UnaccentExtension(),
     ]

tests/postgres_tests/test_trigram.py

@@ -0,0 +1,53 @@
+from django.contrib.postgres.search import TrigramDistance, TrigramSimilarity
+from django.test import modify_settings
+
+from . import PostgreSQLTestCase
+from .models import CharFieldModel, TextFieldModel
+
+
+@modify_settings(INSTALLED_APPS={'append': 'django.contrib.postgres'})
+class TrigramTest(PostgreSQLTestCase):
+    Model = CharFieldModel
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.Model.objects.bulk_create([
+            cls.Model(field='Matthew'),
+            cls.Model(field='Cat sat on mat.'),
+            cls.Model(field='Dog sat on rug.'),
+        ])
+
+    def test_trigram_search(self):
+        self.assertQuerysetEqual(
+            self.Model.objects.filter(field__trigram_similar='Mathew'),
+            ['Matthew'],
+            transform=lambda instance: instance.field,
+        )
+
+    def test_trigram_similarity(self):
+        search = 'Bat sat on cat.'
+        self.assertQuerysetEqual(
+            self.Model.objects.filter(
+                field__trigram_similar=search,
+            ).annotate(similarity=TrigramSimilarity('field', search)).order_by('-similarity'),
+            [('Cat sat on mat.', 0.625), ('Dog sat on rug.', 0.333333)],
+            transform=lambda instance: (instance.field, instance.similarity),
+            ordered=True,
+        )
+
+    def test_trigram_similarity_alternate(self):
+        self.assertQuerysetEqual(
+            self.Model.objects.annotate(
+                distance=TrigramDistance('field', 'Bat sat on cat.'),
+            ).filter(distance__lte=0.7).order_by('distance'),
+            [('Cat sat on mat.', 0.375), ('Dog sat on rug.', 0.666667)],
+            transform=lambda instance: (instance.field, instance.distance),
+            ordered=True,
+        )
+
+
+class TrigramTextFieldTest(TrigramTest):
+    """
+    TextField has the same behavior as CharField regarding trigram lookups.
+    """
+    Model = TextFieldModel