c - Expansion of module_param() macro: a struct with a single member or a bitfield?

The linux kernel module_param() macro expands into several instructions, some of them using numbers (sizes) that are calculated as follow (I only paste here relevant code):

sizeof(struct { int:- ! !(((00400|00040|00004)) < 0 || ((00400|00040|00004)) > 0777 || (((00400|00040|00004)) & 2)); })

Could somebody enlighten me what is that int:- ! !(NUMBER) doing?

Actually, I have several questions:
1) why define a struct with a single member?
2) why do not name that member? (or is the member's name... "int", just like the type?)
3) what is the meaning of that int:- ! !(NUMBER) expression? Is that a struct field? A bitfield?
4) what is the meaning and the final result of the above sizeof()?

Thank you very much.