bpo-36470: Allow dataclasses.replace() to handle InitVars with default values (GH-20867) (GH-25200)

Co-Authored-By: Claudiu Popa <pcmanticore@gmail.com>

Automerge-Triggered-By: GH:ericvsmith
(cherry picked from commit 75220674c07abfc90c2cd7862d04cfa2e2354450)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>

Co-authored-by: Zackery Spytz <zspytz@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index b20103b..31caae9 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -3245,6 +3245,24 @@ class TestReplace(unittest.TestCase):
         c = replace(c, x=3, y=5)
         self.assertEqual(c.x, 15)
 
+    def test_initvar_with_default_value(self):
+        @dataclass
+        class C:
+            x: int
+            y: InitVar[int] = None
+            z: InitVar[int] = 42
+
+            def __post_init__(self, y, z):
+                if y is not None:
+                    self.x += y
+                if z is not None:
+                    self.x += z
+
+        c = C(x=1, y=10, z=1)
+        self.assertEqual(replace(c), C(x=12))
+        self.assertEqual(replace(c, y=4), C(x=12, y=4, z=42))
+        self.assertEqual(replace(c, y=4, z=1), C(x=12, y=4, z=1))
+
     def test_recursive_repr(self):
         @dataclass
         class C: