Macro shader_struct

macro_rules! shader_struct {
    { @sum $( $size:expr ; )* } => { ... };
    { @size $ty:ty } => { ... };
    { @max } => { ... };
    { @max $size:expr ; } => { ... };
    { @max $size:expr ; $( $rest:expr ; )+ } => { ... };
    { @sum_size $( $ty:ty )* } => { ... };
    { @max_size $( $ty:ty )* } => { ... };
    { $struct:ident [
        $( $num:tt $field:ident => $ty:ty ),* $(,)?
    ] } => { ... };
}