disabling implicit cast for std::variants

[Tich-fr]

Hello there !

I'm currently trying to wrap a function that looks like this :

auto test_variant_with_int(std::variant<bool, int> value) {
	return std::visit(make_visitor(
		[](bool x) { return absl::StrFormat("bool:%i", x); },
		[](std::int64_t x) { return absl::StrFormat("int:%i", x); }
	), value);
}

This works as expected until on the python side I call the function with an integer that has value.bit_length() > 31, so for example foo = test_variant_with_int(9223372036854775808). In that case the value cannot be cast to int because of the overflow so instead it is implicitely casted to bool.

I'd have expected a TypeError, like what I'd get if I passed a string or anything else. Looking at https://github.com/pybind/pybind11/blob/master/include/pybind11/stl.h#L323 there is a convert parameter that seems to disable implicit casts. Is there a way to control this from the client code ?

[Edit]

Note that when binding a C++ function that looks like auto bar(int value), calling the function on python side with an int that has value.bit_length() > 31 throws a TypeError just as expected.