[3.1.x] Fixed #32007 -- Fixed queryset crash with Q() annotation and aggregation.

Thanks Gordon Wrigley for the report.

Regression in 8a6df55f2dd5131282084a4edfd48f63fbf8c69a.
Backport of eaf9764d3bb25970da89de5799d8d308715628ba from master

3 files changed, 17 insertions, 0 deletions

diff --git a/django/db/models/sql/where.py b/django/db/models/sql/where.py
index bf0828dc8b..795eff8395 100644
--- a/django/db/models/sql/where.py
+++ b/django/db/models/sql/where.py
@@ -159,6 +159,9 @@ class WhereNode(tree.Node):
         clone.relabel_aliases(change_map)
         return clone
 
+    def copy(self):
+        return self.clone()
+
     @classmethod
     def _contains_aggregate(cls, obj):
         if isinstance(obj, tree.Node):
diff --git a/docs/releases/3.1.2.txt b/docs/releases/3.1.2.txt
index f9e45370ab..fa820c78ee 100644
--- a/docs/releases/3.1.2.txt
+++ b/docs/releases/3.1.2.txt
@@ -16,3 +16,6 @@ Bugfixes
   attribute returned incorrectly ``True`` for ``GROUP BY`` queries (e.g.
   ``.annotate().values()``) on models with ``Meta.ordering``. A model's
   ``Meta.ordering`` doesn't affect such queries (:ticket:`31990`).
+
+* Fixed a regression in Django 3.1 where a queryset would crash if it contained
+  an aggregation and a ``Q`` object annotation (:ticket:`32007`).
diff --git a/tests/annotations/tests.py b/tests/annotations/tests.py
index aa3682b86b..e42a04bb60 100644
--- a/tests/annotations/tests.py
+++ b/tests/annotations/tests.py
@@ -186,6 +186,17 @@ class NonAggregateAnnotationTestCase(TestCase):
         self.assertEqual(book.combined, 13410.0)
         self.assertEqual(book.rating_count, 1)
 
+    def test_q_expression_annotation_with_aggregation(self):
+        book = Book.objects.filter(isbn='159059725').annotate(
+            isnull_pubdate=ExpressionWrapper(
+                Q(pubdate__isnull=True),
+                output_field=BooleanField(),
+            ),
+            rating_count=Count('rating'),
+        ).first()
+        self.assertEqual(book.isnull_pubdate, False)
+        self.assertEqual(book.rating_count, 1)
+
     def test_aggregate_over_annotation(self):
         agg = Author.objects.annotate(other_age=F('age')).aggregate(otherage_sum=Sum('other_age'))
         other_agg = Author.objects.aggregate(age_sum=Sum('age'))