Refs #35149 -- Made equivalent db_default alterations noops.

This allows for an easier transition of preserving the literal nature of
non-compilable db_default.

django/db/backends/base/schema.py

@@ -1640,6 +1640,14 @@ def _field_should_be_altered(self, old_field, new_field, ignore=None):
         ):
             old_kwargs.pop("to", None)
             new_kwargs.pop("to", None)
+        # db_default can take many form but result in the same SQL.
+        if (
+            old_kwargs.get("db_default")
+            and new_kwargs.get("db_default")
+            and self.db_default_sql(old_field) == self.db_default_sql(new_field)
+        ):
+            old_kwargs.pop("db_default")
+            new_kwargs.pop("db_default")
         return self.quote_name(old_field.column) != self.quote_name(
             new_field.column
         ) or (old_path, old_args, old_kwargs) != (new_path, new_args, new_kwargs)

tests/schema/tests.py

@@ -2316,6 +2316,23 @@ class Meta:
         columns = self.column_classes(Author)
         self.assertIn("(missing)", columns["description"][1].default)
 
+    @isolate_apps("schema")
+    def test_db_default_equivalent_sql_noop(self):
+        class Author(Model):
+            name = TextField(db_default=Value("foo"))
+
+            class Meta:
+                app_label = "schema"
+
+        with connection.schema_editor() as editor:
+            editor.create_model(Author)
+
+        new_field = TextField(db_default="foo")
+        new_field.set_attributes_from_name("name")
+        new_field.model = Author
+        with connection.schema_editor() as editor, self.assertNumQueries(0):
+            editor.alter_field(Author, Author._meta.get_field("name"), new_field)
+
     @skipUnlessDBFeature(
         "supports_column_check_constraints", "can_introspect_check_constraints"
     )