Warn on invalid *args and **kwargs with ParamSpec

mypy/semanal.py

@@ -843,6 +843,7 @@ def analyze_func_def(self, defn: FuncDef) -> None:
                 defn.type = result
                 self.add_type_alias_deps(analyzer.aliases_used)
                 self.check_function_signature(defn)
+                self.check_paramspec_definition(defn.type)
                 if isinstance(defn, FuncDef):
                     assert isinstance(defn.type, CallableType)
                     defn.type = set_callable_name(defn.type, defn)
@@ -1282,6 +1283,28 @@ def check_function_signature(self, fdef: FuncItem) -> None:
         elif len(sig.arg_types) > len(fdef.arguments):
             self.fail("Type signature has too many arguments", fdef, blocker=True)
 
+    def check_paramspec_definition(self, func: CallableType) -> None:
+        param_spec_var = next(
+            (var for var in func.variables if isinstance(var, ParamSpecType)), None
+        )
+        if param_spec_var:
+            args = func.var_arg()
+            kwargs = func.kw_arg()
+            if args is None and kwargs is None:
+                return  # Looks like this function does not have starred args
+
+            args_type = args.typ if args is not None else None
+            kwargs_type = kwargs.typ if kwargs is not None else None
+
+            if not isinstance(args_type, ParamSpecType) or not isinstance(
+                kwargs_type, ParamSpecType
+            ):
+                self.fail(
+                    f'ParamSpec must have "*args" typed as "{param_spec_var.name}.args" and "**kwargs" typed as "{param_spec_var.name}.kwargs"',
+                    func,
+                    code=codes.VALID_TYPE,
+                )
+
     def visit_decorator(self, dec: Decorator) -> None:
         self.statement = dec
         # TODO: better don't modify them at all.

mypy/typeanal.py

@@ -863,6 +863,7 @@ def visit_callable_type(self, t: CallableType, nested: bool = True) -> Type:
                 ]
             else:
                 arg_types = self.anal_array(t.arg_types, nested=nested)
+
             ret = t.copy_modified(
                 arg_types=arg_types,
                 ret_type=self.anal_type(t.ret_type, nested=nested),

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

@@ -1166,3 +1166,24 @@ def func3(callback: Callable[P1, str]) -> Callable[P1, str]:
         return "foo"
     return inner
 [builtins fixtures/paramspec.pyi]
+
+
+[case testInvalidDefinitions]
+from typing import Callable, ParamSpec
+
+P = ParamSpec('P')
+
+def c1(f: Callable[P, int], *args: P.args, **kwargs: P.kwargs) -> int: ...
+def c2(f: Callable[P, int]) -> int: ...
+
+def f1(f: Callable[P, int], *args, **kwargs: P.kwargs) -> int: ...  # E: ParamSpec must have "*args" typed as "P.args" and "**kwargs" typed as "P.kwargs"
+def f2(f: Callable[P, int], *args: P.args, **kwargs) -> int: ...  # E: ParamSpec must have "*args" typed as "P.args" and "**kwargs" typed as "P.kwargs"
+def f3(f: Callable[P, int], *args: P.args) -> int: ...  # E: ParamSpec must have "*args" typed as "P.args" and "**kwargs" typed as "P.kwargs"
+def f4(f: Callable[P, int], **kwargs: P.kwargs) -> int: ...  # E: ParamSpec must have "*args" typed as "P.args" and "**kwargs" typed as "P.kwargs"
+def f5(f: Callable[P, int], *args, **kwargs) -> int: ...  # E: ParamSpec must have "*args" typed as "P.args" and "**kwargs" typed as "P.kwargs"
+
+# Error message test:
+P1 = ParamSpec('P1')
+
+def m1(f: Callable[P1, int], *a, **k: P1.kwargs) -> int: ...  # E: ParamSpec must have "*args" typed as "P1.args" and "**kwargs" typed as "P1.kwargs"
+[builtins fixtures/paramspec.pyi]