fix crash in split_for_callable when passing values to variadic generics

Author: a12k

mypy/checkexpr.py

@@ -4966,7 +4966,9 @@ class C(Generic[T, Unpack[Ts]]): ...
         if not vars or not any(isinstance(v, TypeVarTupleType) for v in vars):
             return list(args)
         # TODO: in future we may want to support type application to variadic functions.
-        assert t.is_type_obj()
+        if not t.is_type_obj():
+            self.chk.fail(f"Invalid type argument: type expected, for {args[0]!r}", ctx)
+            return [AnyType(TypeOfAny.from_error)] * len(vars)
         info = t.type_object()
         # We reuse the logic from semanal phase to reduce code duplication.
         fake = Instance(info, args, line=ctx.line, column=ctx.column)

test-data/unit/check-typevar-tuple.test

@@ -2754,3 +2754,20 @@ class X(Generic[Unpack[Ts]]):
 def c(t: X[Concatenate[int, ...]]) -> None:  # E: Cannot use "[int, VarArg(Any), KwArg(Any)]" for TypeVarTuple, only for ParamSpec
     reveal_type(t)  # N: Revealed type is "__main__.X[Unpack[builtins.tuple[Any, ...]]]"
 [builtins fixtures/tuple.pyi]
+
+[case testTypeVarTupleLiteralValueAsTypeArgument]
+# flags: --python-version 3.12
+from typing import TypeVarTuple, Generic, Unpack
+
+Ts = TypeVarTuple('Ts')
+
+def fn[*T]() -> None:
+    pass
+
+class C(Generic[*Ts]):
+    pass
+
+x = C[1, 2, 3]() # E: Invalid type: try using Literal[1] instead? \
+                 # E: Invalid type: try using Literal[2] instead? \
+                 # E: Invalid type: try using Literal[3] instead?
+[builtins fixtures/tuple.pyi]