-----
enum string value = "foo";

struct A
{
    void test(A a)
    {
        auto x = a.value;
    }
}

void main() { }
-----

$ dmd test.d
Error: function expected before (), not "foo" of type string

It looks like the compiler attempted to do UFCS on a non-function. The above message is reproduced with:

auto x = value(a);