[llvm-dev] Clang/GCC overload resolution disagreement

[TellowKrinkle via llvm-dev]

Given the following code:

struct A {};
struct B: public A {
	explicit B(A a) {}
};
struct C: public B {};
B yay(const C& thing) {
	return B(thing);
}

Clang uses B’s copy constructor, while GCC refuses to compile, claiming an ambiguity between B’s copy constructor and the explicit B(A) constructor

Which compiler is correct here?

Live example: https://gcc.godbolt.org/z/3doW5d