[1.11.x] Fixed #28038 -- Restored casting to text of builtin lookups on PostgreSQL.

Reverted 658f1e8 which broke code using __icontains's implicit cast to ::text
on ArrayField.

Thanks Peter J. Farrell for the report.

Backport of a354c69055fd818e612ce22eaa2da0576a4b89ee from master

3 files changed, 11 insertions, 2 deletions

diff --git a/django/db/backends/postgresql/operations.py b/django/db/backends/postgresql/operations.py
index fecea0f826..a66cb0c563 100644
--- a/django/db/backends/postgresql/operations.py
+++ b/django/db/backends/postgresql/operations.py
@@ -83,8 +83,6 @@ class DatabaseOperations(BaseDatabaseOperations):
                            'istartswith', 'endswith', 'iendswith', 'regex', 'iregex'):
             if internal_type in ('IPAddressField', 'GenericIPAddressField'):
                 lookup = "HOST(%s)"
-            elif internal_type in ('CharField', 'TextField'):
-                lookup = '%s'
             else:
                 lookup = "%s::text"
 
diff --git a/docs/releases/1.11.1.txt b/docs/releases/1.11.1.txt
index 101988819a..d1e054bb18 100644
--- a/docs/releases/1.11.1.txt
+++ b/docs/releases/1.11.1.txt
@@ -12,3 +12,6 @@ Bugfixes
 * Made migrations respect ``Index``’s ``name`` argument. If you created a
   named index with Django 1.11, ``makemigrations`` will create a migration to
   recreate the index with the correct name (:ticket:`28051`).
+
+* Fixed a crash when using a ``__icontains`` lookup on a ``ArrayField``
+  (:ticket:`28038`).
diff --git a/tests/postgres_tests/test_array.py b/tests/postgres_tests/test_array.py
index 69ae5f3cda..a11b60e261 100644
--- a/tests/postgres_tests/test_array.py
+++ b/tests/postgres_tests/test_array.py
@@ -216,6 +216,14 @@ class TestQuerying(PostgreSQLTestCase):
             self.objs[1:3]
         )
 
+    def test_icontains(self):
+        # Using the __icontains lookup with ArrayField is inefficient.
+        instance = CharArrayModel.objects.create(field=['FoO'])
+        self.assertSequenceEqual(
+            CharArrayModel.objects.filter(field__icontains='foo'),
+            [instance]
+        )
+
     def test_contains_charfield(self):
         # Regression for #22907
         self.assertSequenceEqual(