Allow to use Final and ClassVar after Python 3.13 (#18358)

This PR allows to use Final and ClassVar after python 3.13

I saw this [PR](#10478)

and I saw recent changes of python 3.13
https://docs.python.org/3/library/typing.html#typing.Final

Final now can be nested with ClassVar. so I added a version check!

---------

Co-authored-by: triumph1 <[email protected]>
Co-authored-by: hauntsaninja <[email protected]>

Author: 3 people

mypy/semanal.py

@@ -3658,7 +3658,11 @@ def unwrap_final(self, s: AssignmentStmt) -> bool:
         else:
             s.type = s.unanalyzed_type.args[0]
 
-        if s.type is not None and self.is_classvar(s.type):
+        if (
+            s.type is not None
+            and self.options.python_version < (3, 13)
+            and self.is_classvar(s.type)
+        ):
             self.fail("Variable should not be annotated with both ClassVar and Final", s)
             return False
 
@@ -7358,6 +7362,7 @@ def type_analyzer(
         allow_unbound_tvars: bool = False,
         allow_placeholder: bool = False,
         allow_typed_dict_special_forms: bool = False,
+        allow_final: bool = False,
         allow_param_spec_literals: bool = False,
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
@@ -7379,6 +7384,7 @@ def type_analyzer(
             report_invalid_types=report_invalid_types,
             allow_placeholder=allow_placeholder,
             allow_typed_dict_special_forms=allow_typed_dict_special_forms,
+            allow_final=allow_final,
             allow_param_spec_literals=allow_param_spec_literals,
             allow_unpack=allow_unpack,
             prohibit_self_type=prohibit_self_type,
@@ -7403,6 +7409,7 @@ def anal_type(
         allow_unbound_tvars: bool = False,
         allow_placeholder: bool = False,
         allow_typed_dict_special_forms: bool = False,
+        allow_final: bool = False,
         allow_param_spec_literals: bool = False,
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
@@ -7439,6 +7446,7 @@ def anal_type(
             allow_tuple_literal=allow_tuple_literal,
             allow_placeholder=allow_placeholder,
             allow_typed_dict_special_forms=allow_typed_dict_special_forms,
+            allow_final=allow_final,
             allow_param_spec_literals=allow_param_spec_literals,
             allow_unpack=allow_unpack,
             report_invalid_types=report_invalid_types,

mypy/typeanal.py

@@ -226,6 +226,7 @@ def __init__(
         allow_unbound_tvars: bool = False,
         allow_placeholder: bool = False,
         allow_typed_dict_special_forms: bool = False,
+        allow_final: bool = True,
         allow_param_spec_literals: bool = False,
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
@@ -261,6 +262,8 @@ def __init__(
         self.allow_placeholder = allow_placeholder
         # Are we in a context where Required[] is allowed?
         self.allow_typed_dict_special_forms = allow_typed_dict_special_forms
+        # Set True when we analyze ClassVar else False
+        self.allow_final = allow_final
         # Are we in a context where ParamSpec literals are allowed?
         self.allow_param_spec_literals = allow_param_spec_literals
         # Are we in context where literal "..." specifically is allowed?
@@ -607,11 +610,12 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                     code=codes.VALID_TYPE,
                 )
             else:
-                self.fail(
-                    "Final can be only used as an outermost qualifier in a variable annotation",
-                    t,
-                    code=codes.VALID_TYPE,
-                )
+                if not self.allow_final:
+                    self.fail(
+                        "Final can be only used as an outermost qualifier in a variable annotation",
+                        t,
+                        code=codes.VALID_TYPE,
+                    )
             return AnyType(TypeOfAny.from_error)
         elif fullname == "typing.Tuple" or (
             fullname == "builtins.tuple"
@@ -692,7 +696,7 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                     "ClassVar[...] must have at most one type argument", t, code=codes.VALID_TYPE
                 )
                 return AnyType(TypeOfAny.from_error)
-            return self.anal_type(t.args[0])
+            return self.anal_type(t.args[0], allow_final=self.options.python_version >= (3, 13))
         elif fullname in NEVER_NAMES:
             return UninhabitedType()
         elif fullname in LITERAL_TYPE_NAMES:
@@ -1878,11 +1882,13 @@ def anal_type(
         allow_unpack: bool = False,
         allow_ellipsis: bool = False,
         allow_typed_dict_special_forms: bool = False,
+        allow_final: bool = False,
     ) -> Type:
         if nested:
             self.nesting_level += 1
         old_allow_typed_dict_special_forms = self.allow_typed_dict_special_forms
         self.allow_typed_dict_special_forms = allow_typed_dict_special_forms
+        self.allow_final = allow_final
         old_allow_ellipsis = self.allow_ellipsis
         self.allow_ellipsis = allow_ellipsis
         old_allow_unpack = self.allow_unpack

test-data/unit/check-final.test

@@ -194,6 +194,7 @@ def g(x: int) -> Final[int]: ...  # E: Final can be only used as an outermost qu
 [out]
 
 [case testFinalDefiningNotInMethodExtensions]
+# flags: --python-version 3.14
 from typing_extensions import Final
 
 def f(x: Final[int]) -> int: ...  # E: Final can be only used as an outermost qualifier in a variable annotation
@@ -1128,6 +1129,7 @@ class A:
 [builtins fixtures/tuple.pyi]
 
 [case testFinalUsedWithClassVar]
+# flags: --python-version 3.12
 from typing import Final, ClassVar
 
 class A:
@@ -1136,6 +1138,15 @@ class A:
     c: ClassVar[Final] = 1  # E: Final can be only used as an outermost qualifier in a variable annotation
 [out]
 
+[case testFinalUsedWithClassVarAfterPy313]
+# flags: --python-version 3.13
+from typing import Final, ClassVar
+
+class A:
+    a: Final[ClassVar[int]] = 1
+    b: ClassVar[Final[int]] = 1
+    c: ClassVar[Final] = 1
+
 [case testFinalClassWithAbstractMethod]
 from typing import final
 from abc import ABC, abstractmethod