[5.2.x] Fixed #36173 -- Stabilized identity of Concat with an explicit output_field.

When Expression.__init__() overrides make use of *args, **kwargs
captures their argument values are respectively bound as a tuple and
dict instances. These composite values might themselves contain values
that require special identity treatments such as Concat(output_field)
as it's a Field instance.

Refs #30628 which introduced bound Field differentiation but lacked
argument captures handling.

Thanks erchenstein for the report.

Backport of df2c4952df6d93c575fb8a3c853dc9d4c2449f36 from main

2 files changed, 37 insertions, 0 deletions

diff --git a/tests/db_functions/text/test_concat.py b/tests/db_functions/text/test_concat.py
index 6e4cb91d3a..ffcd19fad6 100644
--- a/tests/db_functions/text/test_concat.py
+++ b/tests/db_functions/text/test_concat.py
@@ -107,3 +107,17 @@ class ConcatTests(TestCase):
             ctx.captured_queries[0]["sql"].count("::text"),
             1 if connection.vendor == "postgresql" else 0,
         )
+
+    def test_equal(self):
+        self.assertEqual(
+            Concat("foo", "bar", output_field=TextField()),
+            Concat("foo", "bar", output_field=TextField()),
+        )
+        self.assertNotEqual(
+            Concat("foo", "bar", output_field=TextField()),
+            Concat("foo", "bar", output_field=CharField()),
+        )
+        self.assertNotEqual(
+            Concat("foo", "bar", output_field=TextField()),
+            Concat("bar", "foo", output_field=TextField()),
+        )
diff --git a/tests/expressions/tests.py b/tests/expressions/tests.py
index cfa33b6f45..89601de85b 100644
--- a/tests/expressions/tests.py
+++ b/tests/expressions/tests.py
@@ -1433,6 +1433,29 @@ class SimpleExpressionTests(SimpleTestCase):
             Expression(TestModel._meta.get_field("other_field")),
         )
 
+        class InitCaptureExpression(Expression):
+            def __init__(self, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+
+        # The identity of expressions that obscure their __init__() signature
+        # with *args and **kwargs cannot be determined when bound with
+        # different combinations or *args and **kwargs.
+        self.assertNotEqual(
+            InitCaptureExpression(IntegerField()),
+            InitCaptureExpression(output_field=IntegerField()),
+        )
+
+        # However, they should be considered equal when their bindings are
+        # equal.
+        self.assertEqual(
+            InitCaptureExpression(IntegerField()),
+            InitCaptureExpression(IntegerField()),
+        )
+        self.assertEqual(
+            InitCaptureExpression(output_field=IntegerField()),
+            InitCaptureExpression(output_field=IntegerField()),
+        )
+
     def test_hash(self):
         self.assertEqual(hash(Expression()), hash(Expression()))
         self.assertEqual(