fix: string annotations ClassVar bug

Author: dzherb

Lib/dataclasses.py

@@ -753,21 +753,33 @@ def _is_type(annotation, cls, a_module, a_type, is_type_predicate):
     # that's defined.  It was judged not worth it.
 
     match = _MODULE_IDENTIFIER_RE.match(annotation)
-    if match:
-        ns = None
-        module_name = match.group(1)
-        if not module_name:
-            # No module name, assume the class's module did
-            # "from dataclasses import InitVar".
-            ns = sys.modules.get(cls.__module__).__dict__
-        else:
-            # Look up module_name in the class's module.
-            module = sys.modules.get(cls.__module__)
-            if module and module.__dict__.get(module_name) is a_module:
-                ns = sys.modules.get(a_type.__module__).__dict__
-        if ns and is_type_predicate(ns.get(match.group(2)), a_module):
-            return True
-    return False
+    if not match:
+        return False
+
+    ns = None
+    module_name = match.group(1)
+    type_name = match.group(2)
+
+    if not module_name:
+        # No module name, assume the class's module did
+        # "from dataclasses import InitVar".
+        ns = sys.modules.get(cls.__module__).__dict__
+    else:
+        # Look up module_name in the class's module.
+        cls_module = sys.modules.get(cls.__module__)
+        if not cls_module:
+            return False
+
+        a_type_module = cls_module.__dict__.get(module_name)
+        if (
+            isinstance(a_type_module, types.ModuleType)
+            # Consider the case when a_type does not belong
+            # to the namespace, e.g. 'dataclasses.ClassVar[int]'
+            and a_type_module.__dict__.get(type_name) is a_type
+        ):
+            ns = sys.modules.get(a_type.__module__).__dict__
+
+    return ns and is_type_predicate(ns.get(type_name), a_module)
 
 
 def _get_field(cls, a_name, a_type, default_kw_only):

Lib/test/test_dataclasses/__init__.py

@@ -4093,10 +4093,14 @@ def test_classvar_module_level_import(self):
         from test.test_dataclasses import dataclass_module_1_str
         from test.test_dataclasses import dataclass_module_2
         from test.test_dataclasses import dataclass_module_2_str
+        from test.test_dataclasses import dataclass_module_3
+        from test.test_dataclasses import dataclass_module_3_str
 
-        for m in (dataclass_module_1, dataclass_module_1_str,
-                  dataclass_module_2, dataclass_module_2_str,
-                  ):
+        for m in (
+            dataclass_module_1, dataclass_module_1_str,
+            dataclass_module_2, dataclass_module_2_str,
+            dataclass_module_3, dataclass_module_3_str,
+        ):
             with self.subTest(m=m):
                 # There's a difference in how the ClassVars are
                 # interpreted when using string annotations or

Lib/test/test_dataclasses/_types_proxy.py

@@ -0,0 +1,6 @@
+# We need this to test a case when a type
+# is imported via some other package,
+# like ClassVar from typing_extensions instead of typing.
+# https://github.com/python/cpython/issues/133956
+from typing import ClassVar
+from dataclasses import InitVar

Lib/test/test_dataclasses/dataclass_module_3.py

@@ -0,0 +1,32 @@
+#from __future__ import annotations
+USING_STRINGS = False
+
+# dataclass_module_3.py and dataclass_module_3_str.py are identical
+# except only the latter uses string annotations.
+
+from dataclasses import dataclass
+import test.test_dataclasses._types_proxy as tp
+
+T_CV2 = tp.ClassVar[int]
+T_CV3 = tp.ClassVar
+
+T_IV2 = tp.InitVar[int]
+T_IV3 = tp.InitVar
+
+@dataclass
+class CV:
+    T_CV4 = tp.ClassVar
+    cv0: tp.ClassVar[int] = 20
+    cv1: tp.ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclass
+class IV:
+    T_IV4 = tp.InitVar
+    iv0: tp.InitVar[int]
+    iv1: tp.InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.

Lib/test/test_dataclasses/dataclass_module_3_str.py

@@ -0,0 +1,32 @@
+from __future__ import annotations
+USING_STRINGS = True
+
+# dataclass_module_3.py and dataclass_module_2_str.py are identical
+# except only the latter uses string annotations.
+
+from dataclasses import dataclass
+import test.test_dataclasses._types_proxy as tp
+
+T_CV2 = tp.ClassVar[int]
+T_CV3 = tp.ClassVar
+
+T_IV2 = tp.InitVar[int]
+T_IV3 = tp.InitVar
+
+@dataclass
+class CV:
+    T_CV4 = tp.ClassVar
+    cv0: tp.ClassVar[int] = 20
+    cv1: tp.ClassVar = 30
+    cv2: T_CV2
+    cv3: T_CV3
+    not_cv4: T_CV4  # When using string annotations, this field is not recognized as a ClassVar.
+
+@dataclass
+class IV:
+    T_IV4 = tp.InitVar
+    iv0: tp.InitVar[int]
+    iv1: tp.InitVar
+    iv2: T_IV2
+    iv3: T_IV3
+    not_iv4: T_IV4  # When using string annotations, this field is not recognized as an InitVar.