Null-coalescing operator cast before test against null issue

[yuxiaomao]

Here is a code which works with 4.3.4 but not with 5.0 ( https://try.haxe.org/#3F583427 ): in 5.0, using ?? cause onEnd first being cast to EndFun before test against null.

Thanks to Rudy I found that the test fail after this commit 39642c9 ( #11425 )

class Test {
	var onEnd : Void -> Void = null;
	public function new() {
	}

	public function call(f : EndFun ) {
		f();
		trace("call " + f);
	}

	static function main()
	{
		var m = new Test();
		m.call(m.onEnd == null ? function() {trace("somefunc1");} : m.onEnd); // ok
		m.call(m.onEnd ?? function() {trace("somefunc2");}); // Runtime error null access f
	}
}

@:callable abstract EndFun(Void -> Void) {
	@:from public static function fromFun( f : Void -> Void ) : EndFun {
		return cast function() {
			f();
			f = () -> throw "double end";
		};
	}
}

[kLabz]

(added to hotfix candidates because #11425 is in there and this issues shouldn't be missed if #11425 is to be included in 4.3.x)

[Simn]

Hmm... the problem here is that the expected type is EndFun because that's what call wants as an argument, and then we pass a Void->Void to it and that causes a cast. That cast should clearly happen after the null-check though, not before.