In the following example nothing is highlighted

int foo()
{
    union
    {
        int foo1;
        int foo2;
    };
    foo1 = 42;
}

Adding another nested type (even a forward declaration) surprisingly fixes highlighting...

int foo()
{
    union
    {
        int foo1;
        int foo2;
    };
    foo1 = 42;
    struct Foo;
}

foo1 and foo2 don't appear in autocomplete on both cases.