The following compiles with the old ABI:
contract C {
event Changed(string indexed name);
function f() public {
emit Changed("Notin'");
}
}
But fails with ABIEncoderV2 (found here):
indexevent.sol:4:17: Error: Indexed reference types cannot yet be used with ABIEncoderV2.
event Changed(string indexed name);
^-----------------^