[3.9] bpo-45662: Fix the repr of InitVar with a type alias to the built-in class (GH-29291) (GH-29924)

For example, InitVar[list[int]].
(cherry picked from commit 1fd4de5)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Author: miss-islington

Lib/dataclasses.py

@@ -207,7 +207,7 @@ def __init__(self, type):
         self.type = type
 
     def __repr__(self):
-        if isinstance(self.type, type):
+        if isinstance(self.type, type) and not isinstance(self.type, GenericAlias):
             type_name = self.type.__name__
         else:
             # typing objects, e.g. List[int]

Lib/test/test_dataclasses.py

@@ -1125,6 +1125,8 @@ def test_init_var_preserve_type(self):
         self.assertEqual(repr(InitVar[int]), 'dataclasses.InitVar[int]')
         self.assertEqual(repr(InitVar[List[int]]),
                          'dataclasses.InitVar[typing.List[int]]')
+        self.assertEqual(repr(InitVar[list[int]]),
+                         'dataclasses.InitVar[list[int]]')
 
     def test_init_var_inheritance(self):
         # Note that this deliberately tests that a dataclass need not

Misc/NEWS.d/next/Library/2021-10-28-22-58-14.bpo-45662.sJd7Ir.rst

@@ -0,0 +1,2 @@
+Fix the repr of :data:`dataclasses.InitVar` with a type alias to the
+built-in class, e.g. ``InitVar[list[int]]``.