From cee95e6172f2ea3dbf8cfd4214562cfc92f95392 Mon Sep 17 00:00:00 2001
From: Adam Johnson <me@adamj.eu>
Date: Thu, 29 Aug 2024 18:52:31 +0100
Subject: [PATCH] Fixed #35717 -- Reduced Create/RemoveCollation operations
 when optimizing migrations.

---
 django/contrib/postgres/operations.py   |  5 +++++
 tests/postgres_tests/test_operations.py | 20 +++++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/django/contrib/postgres/operations.py b/django/contrib/postgres/operations.py
index 1ee5fbc2e2c2..84360febf90f 100644
--- a/django/contrib/postgres/operations.py
+++ b/django/contrib/postgres/operations.py
@@ -237,6 +237,11 @@ def describe(self):
     def migration_name_fragment(self):
         return "create_collation_%s" % self.name.lower()
 
+    def reduce(self, operation, app_label):
+        if isinstance(operation, RemoveCollation) and self.name == operation.name:
+            return []
+        return super().reduce(operation, app_label)
+
 
 class RemoveCollation(CollationOperation):
     """Remove a collation."""
diff --git a/tests/postgres_tests/test_operations.py b/tests/postgres_tests/test_operations.py
index f344d4ae743c..322f38148b5d 100644
--- a/tests/postgres_tests/test_operations.py
+++ b/tests/postgres_tests/test_operations.py
@@ -318,7 +318,7 @@ def test_drop_nonexistent_extension(self):
 
 
 @unittest.skipUnless(connection.vendor == "postgresql", "PostgreSQL specific tests.")
-class CreateCollationTests(PostgreSQLTestCase):
+class CreateCollationTests(OptimizerTestBase, PostgreSQLTestCase):
     app_label = "test_allow_create_collation"
 
     @override_settings(DATABASE_ROUTERS=[NoMigrationRouter()])
@@ -459,6 +459,24 @@ def test_writer(self):
             "),",
         )
 
+    def test_reduce_create_remove(self):
+        self.assertOptimizesTo(
+            [
+                CreateCollation(
+                    "sample_collation",
+                    "und-u-ks-level2",
+                    provider="icu",
+                    deterministic=False,
+                ),
+                RemoveCollation(
+                    "sample_collation",
+                    # Different locale
+                    "de-u-ks-level1",
+                ),
+            ],
+            [],
+        )
+
 
 @unittest.skipUnless(connection.vendor == "postgresql", "PostgreSQL specific tests.")
 class RemoveCollationTests(PostgreSQLTestCase):