Allow ParamSpecArgs to be unpacked (#13459)

Author: AlexWaygood

mypy/checker.py

@@ -194,6 +194,7 @@
     TypeTranslator,
     TypeType,
     TypeVarId,
+    TypeVarLikeType,
     TypeVarType,
     UnboundType,
     UninhabitedType,
@@ -3161,7 +3162,7 @@ def check_multi_assignment(
         # TODO: maybe elsewhere; redundant.
         rvalue_type = get_proper_type(rv_type or self.expr_checker.accept(rvalue))
 
-        if isinstance(rvalue_type, TypeVarType):
+        if isinstance(rvalue_type, TypeVarLikeType):
             rvalue_type = get_proper_type(rvalue_type.upper_bound)
 
         if isinstance(rvalue_type, UnionType):

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

@@ -1092,3 +1092,23 @@ def func(callback: Callable[P, str]) -> Callable[P, str]:
         return 'baz'
     return inner
 [builtins fixtures/paramspec.pyi]
+
+[case testUnpackingParamsSpecArgsAndKwargs]
+from typing import Callable
+from typing_extensions import ParamSpec
+
+P = ParamSpec("P")
+
+def func(callback: Callable[P, str]) -> Callable[P, str]:
+    def inner(*args: P.args, **kwargs: P.kwargs) -> str:
+        a, *b = args
+        reveal_type(a)  # N: Revealed type is "builtins.object"
+        reveal_type(b)  # N: Revealed type is "builtins.list[builtins.object]"
+        c, *d = kwargs
+        reveal_type(c)  # N: Revealed type is "builtins.str"
+        reveal_type(d)  # N: Revealed type is "builtins.list[builtins.str]"
+        e = {**kwargs}
+        reveal_type(e)  # N: Revealed type is "builtins.dict[builtins.str, builtins.object]"
+        return "foo"
+    return inner
+[builtins fixtures/paramspec.pyi]