1const NextError = error{NextError};
 2const OtherError = error{OutOfMemory};
 3
 4export fn entry() void {
 5    const a: ?NextError!i32 = foo();
 6    _ = a;
 7}
 8
 9fn foo() ?OtherError!i32 {
10    return null;
11}
12
13// error
14//
15// :5:34: error: expected type '?error{NextError}!i32', found '?error{OutOfMemory}!i32'
16// :5:34: note: optional type child 'error{OutOfMemory}!i32' cannot cast into optional type child 'error{NextError}!i32'
17// :5:34: note: 'error.OutOfMemory' not a member of destination error set