From 0eaaadd47fa00baabe12be3ed736aa016b6d327e Mon Sep 17 00:00:00 2001
From: Ben Cail <bcail@crossway.org>
Date: Tue, 17 Sep 2024 15:10:39 -0400
Subject: [PATCH] Fixed #35180 -- Recreated PostgreSQL _like indexes when
 changing between TextField and CharField field types.

---
 django/db/backends/postgresql/schema.py | 23 +++++++++----
 tests/schema/tests.py                   | 45 +++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 7 deletions(-)

diff --git a/django/db/backends/postgresql/schema.py b/django/db/backends/postgresql/schema.py
index 0c8548a5d6..75bf331472 100644
--- a/django/db/backends/postgresql/schema.py
+++ b/django/db/backends/postgresql/schema.py
@@ -140,6 +140,13 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                     return sequence["name"]
         return None
 
+    def _is_changing_type_of_indexed_text_column(self, old_field, old_type, new_type):
+        return (old_field.db_index or old_field.unique) and (
+            (old_type.startswith("varchar") and not new_type.startswith("varchar"))
+            or (old_type.startswith("text") and not new_type.startswith("text"))
+            or (old_type.startswith("citext") and not new_type.startswith("citext"))
+        )
+
     def _alter_column_type_sql(
         self, model, old_field, new_field, new_type, old_collation, new_collation
     ):
@@ -147,11 +154,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # different type.
         old_db_params = old_field.db_parameters(connection=self.connection)
         old_type = old_db_params["type"]
-        if (old_field.db_index or old_field.unique) and (
-            (old_type.startswith("varchar") and not new_type.startswith("varchar"))
-            or (old_type.startswith("text") and not new_type.startswith("text"))
-            or (old_type.startswith("citext") and not new_type.startswith("citext"))
-        ):
+        if self._is_changing_type_of_indexed_text_column(old_field, old_type, new_type):
             index_name = self._create_index_name(
                 model._meta.db_table, [old_field.column], suffix="_like"
             )
@@ -277,8 +280,14 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
             strict,
         )
         # Added an index? Create any PostgreSQL-specific indexes.
-        if (not (old_field.db_index or old_field.unique) and new_field.db_index) or (
-            not old_field.unique and new_field.unique
+        if (
+            (not (old_field.db_index or old_field.unique) and new_field.db_index)
+            or (not old_field.unique and new_field.unique)
+            or (
+                self._is_changing_type_of_indexed_text_column(
+                    old_field, old_type, new_type
+                )
+            )
         ):
             like_index_statement = self._create_like_index_sql(model, new_field)
             if like_index_statement is not None:
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 33a4bc527b..935267c2d6 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -5223,6 +5223,51 @@ class SchemaTests(TransactionTestCase):
             ["schema_tag_slug_2c418ba3_like", "schema_tag_slug_key"],
         )
 
+    @isolate_apps("schema")
+    @unittest.skipUnless(connection.vendor == "postgresql", "PostgreSQL specific")
+    def test_indexed_charfield_to_textfield(self):
+        class SimpleModel(Model):
+            field1 = CharField(max_length=10, db_index=True)
+
+            class Meta:
+                app_label = "schema"
+
+        with connection.schema_editor() as editor:
+            editor.create_model(SimpleModel)
+        self.assertEqual(
+            self.get_constraints_for_column(SimpleModel, "field1"),
+            [
+                "schema_simplemodel_field1_f07a3d6a",
+                "schema_simplemodel_field1_f07a3d6a_like",
+            ],
+        )
+        # Change to TextField.
+        old_field1 = SimpleModel._meta.get_field("field1")
+        new_field1 = TextField(db_index=True)
+        new_field1.set_attributes_from_name("field1")
+        with connection.schema_editor() as editor:
+            editor.alter_field(SimpleModel, old_field1, new_field1, strict=True)
+        self.assertEqual(
+            self.get_constraints_for_column(SimpleModel, "field1"),
+            [
+                "schema_simplemodel_field1_f07a3d6a",
+                "schema_simplemodel_field1_f07a3d6a_like",
+            ],
+        )
+        # Change back to CharField.
+        old_field1 = SimpleModel._meta.get_field("field1")
+        new_field1 = CharField(max_length=10, db_index=True)
+        new_field1.set_attributes_from_name("field1")
+        with connection.schema_editor() as editor:
+            editor.alter_field(SimpleModel, old_field1, new_field1, strict=True)
+        self.assertEqual(
+            self.get_constraints_for_column(SimpleModel, "field1"),
+            [
+                "schema_simplemodel_field1_f07a3d6a",
+                "schema_simplemodel_field1_f07a3d6a_like",
+            ],
+        )
+
     def test_alter_field_add_index_to_integerfield(self):
         # Create the table and verify no initial indexes.
         with connection.schema_editor() as editor: