Given a type as follows:

typedef union
{
    int W;
    struct
    {
        short S1;
        short S2;
    };
} Test;

Creating a variable and accessing the fields as follows

Test t;
t.

autocomplete only shows the entry W, even though typing S1 or S2 is valid code. See also screenshot.

Types like these are very common in the supporting codebase of microcontrollers (in my case, ARM Cortex-M3) so changing the inner struct to something with a name is not desireable. See also the screenshot attached.