Fixed #29166 -- Fixed crash in When() expression with a list argument.

Thanks Matthew Pava for the report and Tim Graham and Carlton Gibson for
reviews.
Regression in 19b2dfd1bfe7fd716dd3d8bfa5f972070d83b42f.

3 files changed, 27 insertions, 1 deletions

diff --git a/django/db/models/expressions.py b/django/db/models/expressions.py
index 8c67839616..307ee97db5 100644
--- a/django/db/models/expressions.py
+++ b/django/db/models/expressions.py
@@ -369,7 +369,12 @@ class BaseExpression:
 
     def __hash__(self):
         path, args, kwargs = self.deconstruct()
-        return hash((path,) + args + tuple(kwargs.items()))
+        kwargs = kwargs.copy()
+        output_field = type(kwargs.pop('output_field', None))
+        return hash((path, output_field) + args + tuple([
+            (key, tuple(value)) if isinstance(value, list) else (key, value)
+            for key, value in kwargs.items()
+        ]))
 
 
 class Expression(BaseExpression, Combinable):
diff --git a/docs/releases/2.0.3.txt b/docs/releases/2.0.3.txt
index c0c9ebb782..348af75bc0 100644
--- a/docs/releases/2.0.3.txt
+++ b/docs/releases/2.0.3.txt
@@ -21,3 +21,6 @@ Bugfixes
 * Made ``Q.deconstruct()`` deterministic with multiple keyword arguments
   (:ticket:`29125`). You may need to modify ``Q``'s in existing migrations, or
   accept an autogenerated migration.
+
+* Fixed a regression where a ``When()`` expression with a list argument crashes
+  (:ticket:`29166`).
diff --git a/tests/expressions_case/tests.py b/tests/expressions_case/tests.py
index 90aba36031..a688dc073d 100644
--- a/tests/expressions_case/tests.py
+++ b/tests/expressions_case/tests.py
@@ -1288,6 +1288,24 @@ class CaseDocumentationExamples(TestCase):
             transform=attrgetter('name', 'account_type')
         )
 
+    def test_hash(self):
+        expression_1 = Case(
+            When(account_type__in=[Client.REGULAR, Client.GOLD], then=1),
+            default=2,
+            output_field=models.IntegerField(),
+        )
+        expression_2 = Case(
+            When(account_type__in=(Client.REGULAR, Client.GOLD), then=1),
+            default=2,
+            output_field=models.IntegerField(),
+        )
+        expression_3 = Case(When(account_type__in=[Client.REGULAR, Client.GOLD], then=1), default=2)
+        expression_4 = Case(When(account_type__in=[Client.PLATINUM, Client.GOLD], then=2), default=1)
+        self.assertEqual(hash(expression_1), hash(expression_2))
+        self.assertNotEqual(hash(expression_2), hash(expression_3))
+        self.assertNotEqual(hash(expression_1), hash(expression_4))
+        self.assertNotEqual(hash(expression_3), hash(expression_4))
+
 
 class CaseWhenTests(SimpleTestCase):
     def test_only_when_arguments(self):