Hir is the "high-level IR". It is a simpified, somewhat resolved version of the bare AST.
All the data for a fn-body is stored in these tables.a
A list of "HIR indices" of type
The HIR has a number of kinds of indices that reach into it. This enum brings them together into a sort of "meta index". It's useful sometimes.
A trait used to add extra information to fn-body debugs. You can specialize it and you will get a callback for each item that lets you add extra fields etc.
Trait implemented by the various kinds of indices that reach into the HIR; allows us to grab the vector that they correspond to.
Trait for the various types for which a span can be had --
corresponds to all the index types plus