Do not allow ClassVar and Final in TypedDict and NamedTuple (#18281)

Closes #18220

Author: sobolevn

mypy/checker.py

@@ -3565,7 +3565,7 @@ def check_final(self, s: AssignmentStmt | OperatorAssignmentStmt | AssignmentExp
         else:
             lvs = [s.lvalue]
         is_final_decl = s.is_final_def if isinstance(s, AssignmentStmt) else False
-        if is_final_decl and self.scope.active_class():
+        if is_final_decl and (active_class := self.scope.active_class()):
             lv = lvs[0]
             assert isinstance(lv, RefExpr)
             if lv.node is not None:
@@ -3579,6 +3579,9 @@ def check_final(self, s: AssignmentStmt | OperatorAssignmentStmt | AssignmentExp
                     # then we already reported the error about missing r.h.s.
                     isinstance(s, AssignmentStmt)
                     and s.type is not None
+                    # Avoid extra error message for NamedTuples,
+                    # they were reported during semanal
+                    and not active_class.is_named_tuple
                 ):
                     self.msg.final_without_value(s)
         for lv in lvs:

mypy/semanal.py

@@ -3646,7 +3646,12 @@ def unwrap_final(self, s: AssignmentStmt) -> bool:
         invalid_bare_final = False
         if not s.unanalyzed_type.args:
             s.type = None
-            if isinstance(s.rvalue, TempNode) and s.rvalue.no_rhs:
+            if (
+                isinstance(s.rvalue, TempNode)
+                and s.rvalue.no_rhs
+                # Filter duplicate errors, we already reported this:
+                and not (self.type and self.type.is_named_tuple)
+            ):
                 invalid_bare_final = True
                 self.fail("Type in Final[...] can only be omitted if there is an initializer", s)
         else:
@@ -7351,6 +7356,7 @@ def type_analyzer(
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
         prohibit_self_type: str | None = None,
+        prohibit_special_class_field_types: str | None = None,
         allow_type_any: bool = False,
     ) -> TypeAnalyser:
         if tvar_scope is None:
@@ -7370,6 +7376,7 @@ def type_analyzer(
             allow_param_spec_literals=allow_param_spec_literals,
             allow_unpack=allow_unpack,
             prohibit_self_type=prohibit_self_type,
+            prohibit_special_class_field_types=prohibit_special_class_field_types,
             allow_type_any=allow_type_any,
         )
         tpan.in_dynamic_func = bool(self.function_stack and self.function_stack[-1].is_dynamic())
@@ -7394,6 +7401,7 @@ def anal_type(
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
         prohibit_self_type: str | None = None,
+        prohibit_special_class_field_types: str | None = None,
         allow_type_any: bool = False,
     ) -> Type | None:
         """Semantically analyze a type.
@@ -7429,6 +7437,7 @@ def anal_type(
             allow_unpack=allow_unpack,
             report_invalid_types=report_invalid_types,
             prohibit_self_type=prohibit_self_type,
+            prohibit_special_class_field_types=prohibit_special_class_field_types,
             allow_type_any=allow_type_any,
         )
         tag = self.track_incomplete_refs()

mypy/semanal_namedtuple.py

@@ -191,6 +191,7 @@ def check_namedtuple_classdef(
                         stmt.type,
                         allow_placeholder=not self.api.is_func_scope(),
                         prohibit_self_type="NamedTuple item type",
+                        prohibit_special_class_field_types="NamedTuple",
                     )
                     if analyzed is None:
                         # Something is incomplete. We need to defer this named tuple.
@@ -483,6 +484,7 @@ def parse_namedtuple_fields_with_types(
                     type,
                     allow_placeholder=not self.api.is_func_scope(),
                     prohibit_self_type="NamedTuple item type",
+                    prohibit_special_class_field_types="NamedTuple",
                 )
                 # Workaround #4987 and avoid introducing a bogus UnboundType
                 if isinstance(analyzed, UnboundType):

mypy/semanal_shared.py

@@ -185,6 +185,7 @@ def anal_type(
         allow_placeholder: bool = False,
         report_invalid_types: bool = True,
         prohibit_self_type: str | None = None,
+        prohibit_special_class_field_types: str | None = None,
     ) -> Type | None:
         raise NotImplementedError
 

mypy/semanal_typeddict.py

@@ -330,6 +330,7 @@ def analyze_typeddict_classdef_fields(
                         allow_typed_dict_special_forms=True,
                         allow_placeholder=not self.api.is_func_scope(),
                         prohibit_self_type="TypedDict item type",
+                        prohibit_special_class_field_types="TypedDict",
                     )
                     if analyzed is None:
                         return None, [], [], set(), set()  # Need to defer
@@ -561,6 +562,7 @@ def parse_typeddict_fields_with_types(
                 allow_typed_dict_special_forms=True,
                 allow_placeholder=not self.api.is_func_scope(),
                 prohibit_self_type="TypedDict item type",
+                prohibit_special_class_field_types="TypedDict",
             )
             if analyzed is None:
                 return None

mypy/typeanal.py

@@ -229,6 +229,7 @@ def __init__(
         allow_unpack: bool = False,
         report_invalid_types: bool = True,
         prohibit_self_type: str | None = None,
+        prohibit_special_class_field_types: str | None = None,
         allowed_alias_tvars: list[TypeVarLikeType] | None = None,
         allow_type_any: bool = False,
         alias_type_params_names: list[str] | None = None,
@@ -275,6 +276,8 @@ def __init__(
         # Names of type aliases encountered while analysing a type will be collected here.
         self.aliases_used: set[str] = set()
         self.prohibit_self_type = prohibit_self_type
+        # Set when we analyze TypedDicts or NamedTuples, since they are special:
+        self.prohibit_special_class_field_types = prohibit_special_class_field_types
         # Allow variables typed as Type[Any] and type (useful for base classes).
         self.allow_type_any = allow_type_any
         self.allow_type_var_tuple = False
@@ -596,11 +599,18 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
         elif fullname == "typing.Any" or fullname == "builtins.Any":
             return AnyType(TypeOfAny.explicit, line=t.line, column=t.column)
         elif fullname in FINAL_TYPE_NAMES:
-            self.fail(
-                "Final can be only used as an outermost qualifier in a variable annotation",
-                t,
-                code=codes.VALID_TYPE,
-            )
+            if self.prohibit_special_class_field_types:
+                self.fail(
+                    f"Final[...] can't be used inside a {self.prohibit_special_class_field_types}",
+                    t,
+                    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,
+                )
             return AnyType(TypeOfAny.from_error)
         elif fullname == "typing.Tuple" or (
             fullname == "builtins.tuple"
@@ -668,6 +678,12 @@ def try_analyze_special_unbound_type(self, t: UnboundType, fullname: str) -> Typ
                 self.fail(
                     "Invalid type: ClassVar nested inside other type", t, code=codes.VALID_TYPE
                 )
+            if self.prohibit_special_class_field_types:
+                self.fail(
+                    f"ClassVar[...] can't be used inside a {self.prohibit_special_class_field_types}",
+                    t,
+                    code=codes.VALID_TYPE,
+                )
             if len(t.args) == 0:
                 return AnyType(TypeOfAny.from_omitted_generics, line=t.line, column=t.column)
             if len(t.args) != 1:

test-data/unit/check-namedtuple.test

@@ -1441,3 +1441,22 @@ def bar() -> None:
             misspelled_var_name  # E: Name "misspelled_var_name" is not defined
 [builtins fixtures/tuple.pyi]
 [typing fixtures/typing-namedtuple.pyi]
+
+
+[case testNamedTupleFinalAndClassVar]
+from typing import NamedTuple, Final, ClassVar
+
+class My(NamedTuple):
+    a: Final      # E: Final[...] can't be used inside a NamedTuple
+    b: Final[int] # E: Final[...] can't be used inside a NamedTuple
+    c: ClassVar       # E: ClassVar[...] can't be used inside a NamedTuple
+    d: ClassVar[int]  # E: ClassVar[...] can't be used inside a NamedTuple
+
+Func = NamedTuple('Func', [
+    ('a', Final),         # E: Final[...] can't be used inside a NamedTuple
+    ('b', Final[int]),    # E: Final[...] can't be used inside a NamedTuple
+    ('c', ClassVar),      # E: ClassVar[...] can't be used inside a NamedTuple
+    ('d', ClassVar[int]), # E: ClassVar[...] can't be used inside a NamedTuple
+])
+[builtins fixtures/tuple.pyi]
+[typing fixtures/typing-namedtuple.pyi]

test-data/unit/check-typeddict.test

@@ -4053,3 +4053,22 @@ d: D = {"a": 1, "b": "x"}
 c: C = d  # E: Incompatible types in assignment (expression has type "D", variable has type "C")
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
+
+
+[case testTypedDictFinalAndClassVar]
+from typing import TypedDict, Final, ClassVar
+
+class My(TypedDict):
+    a: Final      # E: Final[...] can't be used inside a TypedDict
+    b: Final[int] # E: Final[...] can't be used inside a TypedDict
+    c: ClassVar       # E: ClassVar[...] can't be used inside a TypedDict
+    d: ClassVar[int]  # E: ClassVar[...] can't be used inside a TypedDict
+
+Func = TypedDict('Func', {
+    'a': Final,         # E: Final[...] can't be used inside a TypedDict
+    'b': Final[int],    # E: Final[...] can't be used inside a TypedDict
+    'c': ClassVar,      # E: ClassVar[...] can't be used inside a TypedDict
+    'd': ClassVar[int], # E: ClassVar[...] can't be used inside a TypedDict
+})
+[builtins fixtures/dict.pyi]
+[typing fixtures/typing-typeddict.pyi]

test-data/unit/fixtures/typing-namedtuple.pyi

@@ -8,6 +8,7 @@ Optional = 0
 Self = 0
 Tuple = 0
 ClassVar = 0
+Final = 0
 
 T = TypeVar('T')
 T_co = TypeVar('T_co', covariant=True)

test-data/unit/fixtures/typing-typeddict.pyi

@@ -28,6 +28,7 @@ Required = 0
 NotRequired = 0
 ReadOnly = 0
 Self = 0
+ClassVar = 0
 
 T = TypeVar('T')
 T_co = TypeVar('T_co', covariant=True)