From e7e8eb44a30bcab004a582760752b5eb3fcd6e91 Mon Sep 17 00:00:00 2001
From: Paolo Melchiorre <paolo@melchiorre.org>
Date: Wed, 27 Sep 2023 22:24:04 +0200
Subject: [PATCH] Fixed #34877 -- Fixed migrations crash when adding
 GeneratedField with output_field with params.

---
 django/db/models/fields/generated.py      |  3 +++
 tests/model_fields/test_generatedfield.py |  7 +++++++
 tests/schema/tests.py                     | 20 +++++++++++++++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/django/db/models/fields/generated.py b/django/db/models/fields/generated.py
index 225d3e9d12..abafc3ad27 100644
--- a/django/db/models/fields/generated.py
+++ b/django/db/models/fields/generated.py
@@ -159,3 +159,6 @@ class GeneratedField(Field):
 
     def db_parameters(self, connection):
         return self.output_field.db_parameters(connection)
+
+    def db_type_parameters(self, connection):
+        return self.output_field.db_type_parameters(connection)
diff --git a/tests/model_fields/test_generatedfield.py b/tests/model_fields/test_generatedfield.py
index 3184f77d87..d965940465 100644
--- a/tests/model_fields/test_generatedfield.py
+++ b/tests/model_fields/test_generatedfield.py
@@ -181,6 +181,13 @@ class GeneratedFieldTestMixin:
             field._resolved_expression.output_field.db_type(connection),
         )
 
+    @skipUnlessDBFeature("supports_collation_on_charfield")
+    def test_db_type_parameters(self):
+        db_type_parameters = self.output_field_model._meta.get_field(
+            "lower_name"
+        ).db_type_parameters(connection)
+        self.assertEqual(db_type_parameters["max_length"], 11)
+
     def test_model_with_params(self):
         m = self.params_model.objects.create()
         m = self._refresh_if_needed(m)
diff --git a/tests/schema/tests.py b/tests/schema/tests.py
index 340399c0bf..68b6442794 100644
--- a/tests/schema/tests.py
+++ b/tests/schema/tests.py
@@ -2,6 +2,7 @@ import datetime
 import itertools
 import unittest
 from copy import copy
+from decimal import Decimal
 from unittest import mock
 
 from django.core.exceptions import FieldError
@@ -52,7 +53,7 @@ from django.db.models import (
     Value,
 )
 from django.db.models.fields.json import KT, KeyTextTransform
-from django.db.models.functions import Abs, Cast, Collate, Lower, Random, Upper
+from django.db.models.functions import Abs, Cast, Collate, Lower, Random, Round, Upper
 from django.db.models.indexes import IndexExpression
 from django.db.transaction import TransactionManagementError, atomic
 from django.test import TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature
@@ -829,6 +830,23 @@ class SchemaTests(TransactionTestCase):
             False,
         )
 
+    @isolate_apps("schema")
+    @skipUnlessDBFeature("supports_stored_generated_columns")
+    def test_add_generated_field_with_output_field(self):
+        class GeneratedFieldOutputFieldModel(Model):
+            price = DecimalField(max_digits=7, decimal_places=2)
+            vat_price = GeneratedField(
+                expression=Round(F("price") * Value(Decimal("1.22")), 2),
+                db_persist=True,
+                output_field=DecimalField(max_digits=8, decimal_places=2),
+            )
+
+            class Meta:
+                app_label = "schema"
+
+        with connection.schema_editor() as editor:
+            editor.create_model(GeneratedFieldOutputFieldModel)
+
     @isolate_apps("schema")
     def test_add_auto_field(self):
         class AddAutoFieldModel(Model):