Add basic TypeVar defaults validation

mypy/exprtotype.py

@@ -33,6 +33,7 @@
     Type,
     TypeList,
     TypeOfAny,
+    TypeOfTypeList,
     UnboundType,
     UnionType,
 )
@@ -161,9 +162,12 @@ def expr_to_unanalyzed_type(
             else:
                 raise TypeTranslationError()
         return CallableArgument(typ, name, arg_const, expr.line, expr.column)
-    elif isinstance(expr, ListExpr):
+    elif isinstance(expr, (ListExpr, TupleExpr)):
         return TypeList(
             [expr_to_unanalyzed_type(t, options, allow_new_syntax, expr) for t in expr.items],
+            TypeOfTypeList.callable_args
+            if isinstance(expr, ListExpr)
+            else TypeOfTypeList.param_spec_defaults,
             line=expr.line,
             column=expr.column,
         )

mypy/message_registry.py

@@ -181,7 +181,7 @@ def with_additional_msg(self, info: str) -> ErrorMessage:
 INVALID_TYPEVAR_ARG_BOUND: Final = 'Type argument {} of "{}" must be a subtype of {}'
 INVALID_TYPEVAR_ARG_VALUE: Final = 'Invalid type argument value for "{}"'
 TYPEVAR_VARIANCE_DEF: Final = 'TypeVar "{}" may only be a literal bool'
-TYPEVAR_BOUND_MUST_BE_TYPE: Final = 'TypeVar "bound" must be a type'
+TYPEVAR_ARG_MUST_BE_TYPE: Final = '{} "{}" must be a type'
 TYPEVAR_UNEXPECTED_ARGUMENT: Final = 'Unexpected argument to "TypeVar()"'
 UNBOUND_TYPEVAR: Final = (
     "A function returning TypeVar should receive at least "

mypy/semanal.py

@@ -4106,28 +4106,17 @@ def process_typevar_parameters(
                 if has_values:
                     self.fail("TypeVar cannot have both values and an upper bound", context)
                     return None
-                try:
-                    # We want to use our custom error message below, so we suppress
-                    # the default error message for invalid types here.
-                    analyzed = self.expr_to_analyzed_type(
-                        param_value, allow_placeholder=True, report_invalid_types=False
-                    )
-                    if analyzed is None:
-                        # Type variables are special: we need to place them in the symbol table
-                        # soon, even if upper bound is not ready yet. Otherwise avoiding
-                        # a "deadlock" in this common pattern would be tricky:
-                        #     T = TypeVar('T', bound=Custom[Any])
-                        #     class Custom(Generic[T]):
-                        #         ...
-                        analyzed = PlaceholderType(None, [], context.line)
-                    upper_bound = get_proper_type(analyzed)
-                    if isinstance(upper_bound, AnyType) and upper_bound.is_from_error:
-                        self.fail(message_registry.TYPEVAR_BOUND_MUST_BE_TYPE, param_value)
-                        # Note: we do not return 'None' here -- we want to continue
-                        # using the AnyType as the upper bound.
-                except TypeTranslationError:
-                    self.fail(message_registry.TYPEVAR_BOUND_MUST_BE_TYPE, param_value)
+                tv_arg = self.get_typevarlike_argument("TypeVar", param_name, param_value, context)
+                if tv_arg is None:
                     return None
+                upper_bound = tv_arg
+            elif param_name == "default":
+                tv_arg = self.get_typevarlike_argument(
+                    "TypeVar", param_name, param_value, context, allow_unbound_tvars=True
+                )
+                if tv_arg is None:
+                    return None
+                default = tv_arg
             elif param_name == "values":
                 # Probably using obsolete syntax with values=(...). Explain the current syntax.
                 self.fail('TypeVar "values" argument not supported', context)
@@ -4155,6 +4144,50 @@ def process_typevar_parameters(
             variance = INVARIANT
         return variance, upper_bound, default
 
+    def get_typevarlike_argument(
+        self,
+        typevarlike_name: str,
+        param_name: str,
+        param_value: Expression,
+        context: Context,
+        *,
+        allow_unbound_tvars: bool = False,
+        allow_param_spec_literals: bool = False,
+    ) -> ProperType | None:
+        try:
+            # We want to use our custom error message below, so we suppress
+            # the default error message for invalid types here.
+            analyzed = self.expr_to_analyzed_type(
+                param_value,
+                allow_placeholder=True,
+                report_invalid_types=False,
+                allow_unbound_tvars=allow_unbound_tvars,
+                allow_param_spec_literals=allow_param_spec_literals,
+            )
+            if analyzed is None:
+                # Type variables are special: we need to place them in the symbol table
+                # soon, even if upper bound is not ready yet. Otherwise avoiding
+                # a "deadlock" in this common pattern would be tricky:
+                #     T = TypeVar('T', bound=Custom[Any])
+                #     class Custom(Generic[T]):
+                #         ...
+                analyzed = PlaceholderType(None, [], context.line)
+            typ = get_proper_type(analyzed)
+            if isinstance(typ, AnyType) and typ.is_from_error:
+                self.fail(
+                    message_registry.TYPEVAR_ARG_MUST_BE_TYPE.format(typevarlike_name, param_name),
+                    param_value,
+                )
+                # Note: we do not return 'None' here -- we want to continue
+                # using the AnyType as the upper bound.
+            return typ
+        except TypeTranslationError:
+            self.fail(
+                message_registry.TYPEVAR_ARG_MUST_BE_TYPE.format(typevarlike_name, param_name),
+                param_value,
+            )
+            return None
+
     def extract_typevarlike_name(self, s: AssignmentStmt, call: CallExpr) -> str | None:
         if not call:
             return None
@@ -4187,13 +4220,47 @@ def process_paramspec_declaration(self, s: AssignmentStmt) -> bool:
         if name is None:
             return False
 
-        # ParamSpec is different from a regular TypeVar:
-        # arguments are not semantically valid. But, allowed in runtime.
-        # So, we need to warn users about possible invalid usage.
-        if len(call.args) > 1:
-            self.fail("Only the first argument to ParamSpec has defined semantics", s)
+        n_values = call.arg_kinds[1:].count(ARG_POS)
+        if n_values != 0:
+            self.fail("Only the first positional argument to ParamSpec has defined semantics", s)
 
         default: Type = AnyType(TypeOfAny.from_omitted_generics)
+        for param_value, param_name in zip(
+            call.args[1 + n_values :], call.arg_names[1 + n_values :]
+        ):
+            if param_name == "default":
+                tv_arg = self.get_typevarlike_argument(
+                    "ParamSpec",
+                    param_name,
+                    param_value,
+                    s,
+                    allow_unbound_tvars=True,
+                    allow_param_spec_literals=True,
+                )
+                if tv_arg is None:
+                    return False
+                default = tv_arg
+                if isinstance(tv_arg, Parameters):
+                    for i, arg_type in enumerate(tv_arg.arg_types):
+                        typ = get_proper_type(arg_type)
+                        if isinstance(typ, AnyType) and typ.is_from_error:
+                            self.fail(
+                                f"Argument {i} of ParamSpec default must be a type", param_value
+                            )
+                elif not isinstance(default, (AnyType, UnboundType)):
+                    self.fail(
+                        "The default argument to ParamSpec must be a tuple expression, ellipsis, or a ParamSpec",
+                        param_value,
+                    )
+                    default = AnyType(TypeOfAny.from_error)
+            else:
+                # ParamSpec is different from a regular TypeVar:
+                # arguments are not semantically valid. But, allowed in runtime.
+                # So, we need to warn users about possible invalid usage.
+                self.fail(
+                    "The variance and bound arguments to ParamSpec do not have defined semantics yet",
+                    s,
+                )
 
         # PEP 612 reserves the right to define bound, covariant and contravariant arguments to
         # ParamSpec in a later PEP. If and when that happens, we should do something
@@ -4227,10 +4294,34 @@ def process_typevartuple_declaration(self, s: AssignmentStmt) -> bool:
         if not call:
             return False
 
-        if len(call.args) > 1:
-            self.fail("Only the first argument to TypeVarTuple has defined semantics", s)
+        n_values = call.arg_kinds[1:].count(ARG_POS)
+        if n_values != 0:
+            self.fail(
+                "Only the first positional argument to TypeVarTuple has defined semantics", s
+            )
 
         default: Type = AnyType(TypeOfAny.from_omitted_generics)
+        for param_value, param_name in zip(
+            call.args[1 + n_values :], call.arg_names[1 + n_values :]
+        ):
+            if param_name == "default":
+                tv_arg = self.get_typevarlike_argument(
+                    "TypeVarTuple", param_name, param_value, s, allow_unbound_tvars=True
+                )
+                if tv_arg is None:
+                    return False
+                default = tv_arg
+                if not isinstance(default, UnpackType):
+                    self.fail(
+                        "The default argument to TypeVarTuple must be an Unpacked tuple",
+                        param_value,
+                    )
+                    default = AnyType(TypeOfAny.from_error)
+            else:
+                self.fail(
+                    "The variance and bound arguments to TypeVarTuple do not have defined semantics yet",
+                    s,
+                )
 
         if not self.incomplete_feature_enabled(TYPE_VAR_TUPLE, s):
             return False
@@ -6324,6 +6415,8 @@ def expr_to_analyzed_type(
         report_invalid_types: bool = True,
         allow_placeholder: bool = False,
         allow_type_any: bool = False,
+        allow_unbound_tvars: bool = False,
+        allow_param_spec_literals: bool = False,
     ) -> Type | None:
         if isinstance(expr, CallExpr):
             # This is a legacy syntax intended mostly for Python 2, we keep it for
@@ -6352,6 +6445,8 @@ def expr_to_analyzed_type(
             report_invalid_types=report_invalid_types,
             allow_placeholder=allow_placeholder,
             allow_type_any=allow_type_any,
+            allow_unbound_tvars=allow_unbound_tvars,
+            allow_param_spec_literals=allow_param_spec_literals,
         )
 
     def analyze_type_expr(self, expr: Expression) -> None:

mypy/typeanal.py

@@ -72,6 +72,7 @@
     TypedDictType,
     TypeList,
     TypeOfAny,
+    TypeOfTypeList,
     TypeQuery,
     TypeType,
     TypeVarLikeType,
@@ -896,10 +897,12 @@ def visit_type_list(self, t: TypeList) -> Type:
             else:
                 return AnyType(TypeOfAny.from_error)
         else:
+            s = "[...]" if t.list_type == TypeOfTypeList.callable_args else "(...)"
             self.fail(
-                'Bracketed expression "[...]" is not valid as a type', t, code=codes.VALID_TYPE
+                f'Bracketed expression "{s}" is not valid as a type', t, code=codes.VALID_TYPE
             )
-            self.note('Did you mean "List[...]"?', t)
+            if t.list_type == TypeOfTypeList.callable_args:
+                self.note('Did you mean "List[...]"?', t)
             return AnyType(TypeOfAny.from_error)
 
     def visit_callable_argument(self, t: CallableArgument) -> Type:

mypy/types.py

@@ -197,6 +197,17 @@ class TypeOfAny:
     suggestion_engine: Final = 9
 
 
+class TypeOfTypeList:
+    """This class describes the different types of TypeList."""
+
+    __slots__ = ()
+
+    # List expressions for callable args
+    callable_args: Final = 1
+    # Tuple expressions for ParamSpec defaults
+    param_spec_defaults: Final = 2
+
+
 def deserialize_type(data: JsonDict | str) -> Type:
     if isinstance(data, str):
         return Instance.deserialize(data)
@@ -994,13 +1005,20 @@ class TypeList(ProperType):
     types before they are processed into Callable types.
     """
 
-    __slots__ = ("items",)
+    __slots__ = ("items", "list_type")
 
     items: list[Type]
 
-    def __init__(self, items: list[Type], line: int = -1, column: int = -1) -> None:
+    def __init__(
+        self,
+        items: list[Type],
+        list_type: int = TypeOfTypeList.callable_args,
+        line: int = -1,
+        column: int = -1,
+    ) -> None:
         super().__init__(line, column)
         self.items = items
+        self.list_type = list_type
 
     def accept(self, visitor: TypeVisitor[T]) -> T:
         assert isinstance(visitor, SyntheticTypeVisitor)
@@ -1014,7 +1032,11 @@ def __hash__(self) -> int:
         return hash(tuple(self.items))
 
     def __eq__(self, other: object) -> bool:
-        return isinstance(other, TypeList) and self.items == other.items
+        return (
+            isinstance(other, TypeList)
+            and self.items == other.items
+            and self.list_type == other.list_type
+        )
 
 
 class UnpackType(ProperType):
@@ -3041,6 +3063,8 @@ def visit_type_var(self, t: TypeVarType) -> str:
             s = f"{t.name}`{t.id}"
         if self.id_mapper and t.upper_bound:
             s += f"(upper_bound={t.upper_bound.accept(self)})"
+        if t.has_default():
+            s += f" = {t.default.accept(self)}"
         return s
 
     def visit_param_spec(self, t: ParamSpecType) -> str:
@@ -3056,6 +3080,8 @@ def visit_param_spec(self, t: ParamSpecType) -> str:
             s += f"{t.name_with_suffix()}`{t.id}"
         if t.prefix.arg_types:
             s += "]"
+        if t.has_default():
+            s += f" = {t.default.accept(self)}"
         return s
 
     def visit_parameters(self, t: Parameters) -> str:
@@ -3094,6 +3120,8 @@ def visit_type_var_tuple(self, t: TypeVarTupleType) -> str:
         else:
             # Named type variable type.
             s = f"{t.name}`{t.id}"
+        if t.has_default():
+            s += f" = {t.default.accept(self)}"
         return s
 
     def visit_callable_type(self, t: CallableType) -> str:
@@ -3130,6 +3158,8 @@ def visit_callable_type(self, t: CallableType) -> str:
             if s:
                 s += ", "
             s += f"*{n}.args, **{n}.kwargs"
+            if param_spec.has_default():
+                s += f" = {param_spec.default.accept(self)}"
 
         s = f"({s})"
 
@@ -3148,12 +3178,18 @@ def visit_callable_type(self, t: CallableType) -> str:
                         vals = f"({', '.join(val.accept(self) for val in var.values)})"
                         vs.append(f"{var.name} in {vals}")
                     elif not is_named_instance(var.upper_bound, "builtins.object"):
-                        vs.append(f"{var.name} <: {var.upper_bound.accept(self)}")
+                        vs.append(
+                            f"{var.name} <: {var.upper_bound.accept(self)}{f' = {var.default.accept(self)}' if var.has_default() else ''}"
+                        )
                     else:
-                        vs.append(var.name)
+                        vs.append(
+                            f"{var.name}{f' = {var.default.accept(self)}' if var.has_default()  else ''}"
+                        )
                 else:
-                    # For other TypeVarLikeTypes, just use the name
-                    vs.append(var.name)
+                    # For other TypeVarLikeTypes, use the name and default
+                    vs.append(
+                        f"{var.name}{f' = {var.default.accept(self)}' if var.has_default() else ''}"
+                    )
             s = f"[{', '.join(vs)}] {s}"
 
         return f"def {s}"

test-data/unit/check-parameter-specification.test

@@ -6,11 +6,11 @@ P = ParamSpec('P')
 [case testInvalidParamSpecDefinitions]
 from typing import ParamSpec
 
-P1 = ParamSpec("P1", covariant=True)  # E: Only the first argument to ParamSpec has defined semantics
-P2 = ParamSpec("P2", contravariant=True)  # E: Only the first argument to ParamSpec has defined semantics
-P3 = ParamSpec("P3", bound=int)  # E: Only the first argument to ParamSpec has defined semantics
-P4 = ParamSpec("P4", int, str)  # E: Only the first argument to ParamSpec has defined semantics
-P5 = ParamSpec("P5", covariant=True, bound=int)  # E: Only the first argument to ParamSpec has defined semantics
+P1 = ParamSpec("P1", covariant=True)  # E: The variance and bound arguments to ParamSpec do not have defined semantics yet
+P2 = ParamSpec("P2", contravariant=True)  # E: The variance and bound arguments to ParamSpec do not have defined semantics yet
+P3 = ParamSpec("P3", bound=int)  # E: The variance and bound arguments to ParamSpec do not have defined semantics yet
+P4 = ParamSpec("P4", int, str)  # E: Only the first positional argument to ParamSpec has defined semantics
+P5 = ParamSpec("P5", covariant=True, bound=int)  # E: The variance and bound arguments to ParamSpec do not have defined semantics yet
 [builtins fixtures/paramspec.pyi]
 
 [case testParamSpecLocations]