Reject ParamSpec-typed callables calls with insufficient arguments (#17323)

Fixes #14571.

When type checking a call of a `ParamSpec`-typed callable, currently
there is an incorrect "fast path" (if there are two arguments of shape
`(*args: P.args, **kwargs: P.kwargs)`, accept), which breaks with
`Concatenate` (such call was accepted even for `Concatenate[int, P]`).

Also there was no checking that args and kwargs are actually present:
since `*args` and `**kwargs` are not required, their absence was
silently accepted.

Author: sterliakov

mypy/checkexpr.py

@@ -1756,7 +1756,11 @@ def check_callable_call(
                 )
 
         param_spec = callee.param_spec()
-        if param_spec is not None and arg_kinds == [ARG_STAR, ARG_STAR2]:
+        if (
+            param_spec is not None
+            and arg_kinds == [ARG_STAR, ARG_STAR2]
+            and len(formal_to_actual) == 2
+        ):
             arg1 = self.accept(args[0])
             arg2 = self.accept(args[1])
             if (
@@ -2362,6 +2366,9 @@ def check_argument_count(
                 # Positional argument when expecting a keyword argument.
                 self.msg.too_many_positional_arguments(callee, context)
                 ok = False
+            elif callee.param_spec() is not None and not formal_to_actual[i]:
+                self.msg.too_few_arguments(callee, context, actual_names)
+                ok = False
         return ok
 
     def check_for_extra_actual_arguments(
@@ -2763,9 +2770,9 @@ def plausible_overload_call_targets(
     ) -> list[CallableType]:
         """Returns all overload call targets that having matching argument counts.
 
-        If the given args contains a star-arg (*arg or **kwarg argument), this method
-        will ensure all star-arg overloads appear at the start of the list, instead
-        of their usual location.
+        If the given args contains a star-arg (*arg or **kwarg argument, including
+        ParamSpec), this method will ensure all star-arg overloads appear at the start
+        of the list, instead of their usual location.
 
         The only exception is if the starred argument is something like a Tuple or a
         NamedTuple, which has a definitive "shape". If so, we don't move the corresponding
@@ -2793,9 +2800,13 @@ def has_shape(typ: Type) -> bool:
             formal_to_actual = map_actuals_to_formals(
                 arg_kinds, arg_names, typ.arg_kinds, typ.arg_names, lambda i: arg_types[i]
             )
-
             with self.msg.filter_errors():
-                if self.check_argument_count(
+                if typ.param_spec() is not None:
+                    # ParamSpec can be expanded in a lot of different ways. We may try
+                    # to expand it here instead, but picking an impossible overload
+                    # is safe: it will be filtered out later.
+                    star_matches.append(typ)
+                elif self.check_argument_count(
                     typ, arg_types, arg_kinds, arg_names, formal_to_actual, None
                 ):
                     if args_have_var_arg and typ.is_var_arg:

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

@@ -2192,3 +2192,114 @@ parametrize(_test, Case(1, b=2), Case(3, b=4))
 parametrize(_test, Case(1, 2), Case(3))
 parametrize(_test, Case(1, 2), Case(3, b=4))
 [builtins fixtures/paramspec.pyi]
+
+[case testRunParamSpecInsufficientArgs]
+from typing_extensions import ParamSpec, Concatenate
+from typing import Callable
+
+_P = ParamSpec("_P")
+
+def run(predicate: Callable[_P, None], *args: _P.args, **kwargs: _P.kwargs) -> None:  # N: "run" defined here
+    predicate()  # E: Too few arguments
+    predicate(*args)  # E: Too few arguments
+    predicate(**kwargs)  # E: Too few arguments
+    predicate(*args, **kwargs)
+
+def fn() -> None: ...
+def fn_args(x: int) -> None: ...
+def fn_posonly(x: int, /) -> None: ...
+
+run(fn)
+run(fn_args, 1)
+run(fn_args, x=1)
+run(fn_posonly, 1)
+run(fn_posonly, x=1)  # E: Unexpected keyword argument "x" for "run"
+
+[builtins fixtures/paramspec.pyi]
+
+[case testRunParamSpecConcatenateInsufficientArgs]
+from typing_extensions import ParamSpec, Concatenate
+from typing import Callable
+
+_P = ParamSpec("_P")
+
+def run(predicate: Callable[Concatenate[int, _P], None], *args: _P.args, **kwargs: _P.kwargs) -> None:  # N: "run" defined here
+    predicate()  # E: Too few arguments
+    predicate(1)  # E: Too few arguments
+    predicate(1, *args)  # E: Too few arguments
+    predicate(1, *args)  # E: Too few arguments
+    predicate(1, **kwargs)  # E: Too few arguments
+    predicate(*args, **kwargs)  # E: Argument 1 has incompatible type "*_P.args"; expected "int"
+    predicate(1, *args, **kwargs)
+
+def fn() -> None: ...
+def fn_args(x: int, y: str) -> None: ...
+def fn_posonly(x: int, /) -> None: ...
+def fn_posonly_args(x: int, /, y: str) -> None: ...
+
+run(fn)  # E: Argument 1 to "run" has incompatible type "Callable[[], None]"; expected "Callable[[int], None]"
+run(fn_args, 1, 'a')  # E: Too many arguments for "run" \
+                      # E: Argument 2 to "run" has incompatible type "int"; expected "str"
+run(fn_args, y='a')
+run(fn_args, 'a')
+run(fn_posonly)
+run(fn_posonly, x=1)  # E: Unexpected keyword argument "x" for "run"
+run(fn_posonly_args)  # E: Missing positional argument "y" in call to "run"
+run(fn_posonly_args, 'a')
+run(fn_posonly_args, y='a')
+
+[builtins fixtures/paramspec.pyi]
+
+[case testRunParamSpecConcatenateInsufficientArgsInDecorator]
+from typing_extensions import ParamSpec, Concatenate
+from typing import Callable
+
+P = ParamSpec("P")
+
+def decorator(fn: Callable[Concatenate[str, P], None]) -> Callable[P, None]:
+    def inner(*args: P.args, **kwargs: P.kwargs) -> None:
+        fn("value")  # E: Too few arguments
+        fn("value", *args)  # E: Too few arguments
+        fn("value", **kwargs)  # E: Too few arguments
+        fn(*args, **kwargs)  # E: Argument 1 has incompatible type "*P.args"; expected "str"
+        fn("value", *args, **kwargs)
+    return inner
+
+@decorator
+def foo(s: str, s2: str) -> None: ...
+
+[builtins fixtures/paramspec.pyi]
+
+[case testRunParamSpecOverload]
+from typing_extensions import ParamSpec
+from typing import Callable, NoReturn, TypeVar, Union, overload
+
+P = ParamSpec("P")
+T = TypeVar("T")
+
+@overload
+def capture(
+    sync_fn: Callable[P, NoReturn],
+    *args: P.args,
+    **kwargs: P.kwargs,
+) -> int: ...
+@overload
+def capture(
+    sync_fn: Callable[P, T],
+    *args: P.args,
+    **kwargs: P.kwargs,
+) -> Union[T, int]: ...
+def capture(
+    sync_fn: Callable[P, T],
+    *args: P.args,
+    **kwargs: P.kwargs,
+) -> Union[T, int]:
+    return sync_fn(*args, **kwargs)
+
+def fn() -> str: return ''
+def err() -> NoReturn: ...
+
+reveal_type(capture(fn))  # N: Revealed type is "Union[builtins.str, builtins.int]"
+reveal_type(capture(err))  # N: Revealed type is "builtins.int"
+
+[builtins fixtures/paramspec.pyi]