This code compiles with no errors:

auto foo() {
    int x;
    return delegate() nothrow {
        return x;
    };
}
void main() {}



But with this version:

auto foo() {
    int x;
    return () nothrow {
        return x;
    };
}
void main() {}


DMD 2.059head gives:

test.d(3): expression expected, not ')'
test.d(3): found 'nothrow' when expecting ')'
test.d(3): found '{' when expecting ';' following return statement
test.d(6): unrecognized declaration


Maybe similar issues happens with other annotations.