[5.0.x] Fixed #35422 -- Fixed migrations crash when altering Generate…

…dField referencing rename field.

Thanks Sarah Boyce for the report and Simon Charette for the
implementation idea.

Backport of 91a4b9a from main.

django/db/backends/base/schema.py

@@ -3,6 +3,7 @@
 from datetime import datetime
 
 from django.conf import settings
+from django.core.exceptions import FieldError
 from django.db.backends.ddl_references import (
     Columns,
     Expressions,
@@ -832,6 +833,7 @@ def alter_field(self, model, old_field, new_field, strict=False):
         old_type = old_db_params["type"]
         new_db_params = new_field.db_parameters(connection=self.connection)
         new_type = new_db_params["type"]
+        modifying_generated_field = False
         if (old_type is None and old_field.remote_field is None) or (
             new_type is None and new_field.remote_field is None
         ):
@@ -870,13 +872,19 @@ def alter_field(self, model, old_field, new_field, strict=False):
                 "through= on M2M fields)" % (old_field, new_field)
             )
         elif old_field.generated != new_field.generated or (
-            new_field.generated
-            and (
-                old_field.db_persist != new_field.db_persist
-                or old_field.generated_sql(self.connection)
-                != new_field.generated_sql(self.connection)
-            )
+            new_field.generated and old_field.db_persist != new_field.db_persist
         ):
+            modifying_generated_field = True
+        elif new_field.generated:
+            try:
+                old_field_sql = old_field.generated_sql(self.connection)
+            except FieldError:
+                # Field used in a generated field was renamed.
+                modifying_generated_field = True
+            else:
+                new_field_sql = new_field.generated_sql(self.connection)
+                modifying_generated_field = old_field_sql != new_field_sql
+        if modifying_generated_field:
             raise ValueError(
                 f"Modifying GeneratedFields is not supported - the field {new_field} "
                 "must be removed and re-added with the new definition."

django/db/backends/mysql/features.py

@@ -173,6 +173,18 @@ def django_test_skips(self):
                     },
                 }
             )
+        if not self.connection.mysql_is_mariadb:
+            skips.update(
+                {
+                    "MySQL doesn't allow renaming columns referenced by generated "
+                    "columns": {
+                        "migrations.test_operations.OperationTests."
+                        "test_invalid_generated_field_changes_on_rename_stored",
+                        "migrations.test_operations.OperationTests."
+                        "test_invalid_generated_field_changes_on_rename_virtual",
+                    },
+                }
+            )
         return skips
 
     @cached_property

docs/releases/5.0.5.txt

@@ -27,3 +27,6 @@ Bugfixes
 * Fixed a bug in Django 5.0 that caused a migration crash when a
   ``GeneratedField`` was added before any of the referenced fields from its
   ``expression`` definition (:ticket:`35359`).
+
+* Fixed a bug in Django 5.0 that caused a migration crash when altering a
+  ``GeneratedField`` referencing a rename field (:ticket:`35422`).

tests/migrations/test_operations.py

@@ -5926,6 +5926,50 @@ def test_invalid_generated_field_changes_stored(self):
     def test_invalid_generated_field_changes_virtual(self):
         self._test_invalid_generated_field_changes(db_persist=False)
 
+    def _test_invalid_generated_field_changes_on_rename(self, db_persist):
+        app_label = "test_igfcor"
+        operation = migrations.AddField(
+            "Pony",
+            "modified_pink",
+            models.GeneratedField(
+                expression=F("pink") + F("pink"),
+                output_field=models.IntegerField(),
+                db_persist=db_persist,
+            ),
+        )
+        project_state, new_state = self.make_test_state(app_label, operation)
+        # Add generated column.
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        # Rename field used in the generated field.
+        operations = [
+            migrations.RenameField("Pony", "pink", "renamed_pink"),
+            migrations.AlterField(
+                "Pony",
+                "modified_pink",
+                models.GeneratedField(
+                    expression=F("renamed_pink"),
+                    output_field=models.IntegerField(),
+                    db_persist=db_persist,
+                ),
+            ),
+        ]
+        msg = (
+            "Modifying GeneratedFields is not supported - the field "
+            f"{app_label}.Pony.modified_pink must be removed and re-added with the "
+            "new definition."
+        )
+        with self.assertRaisesMessage(ValueError, msg):
+            self.apply_operations(app_label, new_state, operations)
+
+    @skipUnlessDBFeature("supports_stored_generated_columns")
+    def test_invalid_generated_field_changes_on_rename_stored(self):
+        self._test_invalid_generated_field_changes_on_rename(db_persist=True)
+
+    @skipUnlessDBFeature("supports_virtual_generated_columns")
+    def test_invalid_generated_field_changes_on_rename_virtual(self):
+        self._test_invalid_generated_field_changes_on_rename(db_persist=False)
+
     @skipUnlessDBFeature(
         "supports_stored_generated_columns",
         "supports_virtual_generated_columns",