Method check_overload_call

mypy/checkexpr.py:2769–2912

Checks a call to an overloaded function.

(
        self,
        callee: Overloaded,
        args: list[Expression],
        arg_kinds: list[ArgKind],
        arg_names: Sequence[str | None] | None,
        callable_name: str | None,
        object_type: Type | None,
        context: Context,
    )

                )

    def check_overload_call(
        self,
        callee: Overloaded,
        args: list[Expression],
        arg_kinds: list[ArgKind],
        arg_names: Sequence[str | None] | None,
        callable_name: str | None,
        object_type: Type | None,
        context: Context,
    ) -> tuple[Type, Type]:
        """Checks a call to an overloaded function."""
        # Normalize unpacked kwargs before checking the call.
        callee = callee.with_unpacked_kwargs()
        arg_types = self.infer_arg_types_in_empty_context(args)
        # Step 1: Filter call targets to remove ones where the argument counts don't match
        plausible_targets = self.plausible_overload_call_targets(
            arg_types, arg_kinds, arg_names, callee
        )

        # Step 2: If the arguments contain a union, we try performing union math first,
        #         instead of picking the first matching overload.
        #         This is because picking the first overload often ends up being too greedy:
        #         for example, when we have a fallback alternative that accepts an unrestricted
        #         typevar. See https://github.com/python/mypy/issues/4063 for related discussion.
        erased_targets: list[CallableType] | None = None
        inferred_types: list[Type] | None = None
        unioned_result: tuple[Type, Type] | None = None

        # Determine whether we need to encourage union math. This should be generally safe,
        # as union math infers better results in the vast majority of cases, but it is very
        # computationally intensive.
        none_type_var_overlap = self.possible_none_type_var_overlap(arg_types, plausible_targets)
        union_interrupted = False  # did we try all union combinations?
        if any(self.real_union(arg) for arg in arg_types):
            try:
                with self.msg.filter_errors():
                    unioned_return = self.union_overload_result(
                        plausible_targets,
                        args,
                        arg_types,
                        arg_kinds,
                        arg_names,
                        callable_name,
                        object_type,
                        none_type_var_overlap,
                        context,
                    )
            except TooManyUnions:
                union_interrupted = True
            else:
                # Record if we succeeded. Next we need to see if maybe normal procedure
                # gives a narrower type.
                if unioned_return:
                    returns = [u[0] for u in unioned_return]
                    inferred_types = [u[1] for u in unioned_return]
                    # Note that we use `combine_function_signatures` instead of just returning
                    # a union of inferred callables because for example a call
                    # Union[int -> int, str -> str](Union[int, str]) is invalid and