Macro generate_index_type

macro_rules! generate_index_type {
    ($name:ident) => { ... };
    ($name:ident, $pretty_name:expr) => { ... };
}

Generate an Index index type. We use it because we need manipulate a lot of different indices (for various kinds of declarations, variables, blocks, etc.). For sanity, we prevent any confusion between the different kinds of indices by using different types. The following macro allows us to easily derive those types.

The name parameter should contain the name of the module to declare. The pretty_name parameter is used to implement Id::to_pretty_string; if not provided, it defaults to name.