dart2js attributes the wrong type to super tearoffs

[fishythefish]

The following code incorrectly prints true instead of false.

class Foo {
  int f() => 42;
}

class Bar extends Foo {
  void test() {
    var f = super.f;
    print(f is int);
  }
}

void main() {
  Bar().test();
}

We build an HInvokeSuper node for the super.f access here:

sdk/pkg/compiler/lib/src/ssa/builder_kernel.dart

Lines 5292 to 5299 in ce7fcff

	_buildInvokeSuper(
	_elementMap.getSelector(node),
	_elementMap.getClass(_containingClass(node)),
	member,
	const <HInstruction>[],
	const <DartType>[],
	sourceInformation);
	}

The problem is that this is indistinguishable from the node we would have built for the method invocation super.f():

sdk/pkg/compiler/lib/src/ssa/builder_kernel.dart

Lines 5331 to 5338 in ce7fcff

	_buildInvokeSuper(
	_elementMap.getSelector(node),
	_elementMap.getClass(_containingClass(node)),
	member,
	arguments,
	typeArguments,
	sourceInformation);
	}

When we build the node, we attempt to determine the type by inspecting the member:

sdk/pkg/compiler/lib/src/ssa/builder_kernel.dart

Lines 5251 to 5255 in ce7fcff

	if (target is FunctionEntity) {
	typeMask = _typeInferenceMap.getReturnTypeOf(target);
	} else {
	typeMask = _abstractValueDomain.dynamicType;
	}

Of course, in both super.f and super.f(), the member is the same FunctionEntity, but only in the latter case does it make sense to use the return type.