Declaration.d

mixin template MixinUDACheck(T) {
	mixin("bool is" ~ T.stringof ~ " (C, string f)(C c = C.init)" ~ q{{
		foreach(UDA; __traits(getAttributes, mixin("c." ~ f))) {
			static if (is(UDA == T)) {
				return true;
			}
		}
		
		return false;
	}});
}

Usage.d

struct Test {
}

class Test2 {
	@Test
	uint x;
	uint y;
}

mixin MixinUDACheck!Test;

void main() {
	assert(isTest!(Test2, "x"));
	assert(!isTest!(Test2, "y"));
}