Macro repr_c_struct_has_padding 

macro_rules! repr_c_struct_has_padding {
    ($t:ty, [$($ts:tt),*]) => { ... };
    (@field ([$t:ty])) => { ... };
    (@field ($t:ty)) => { ... };
    (@field [$t:ty]) => { ... };
    (@field $t:ty) => { ... };
}

Does the repr(C) struct type $t have padding?

$ts is the list of the type of every field in $t. $t must be a repr(C) struct type, or else struct_has_padding!’s result may be meaningless.