EarlyBinder and instantiating parameters
Summary
Overview of how Rust's EarlyBinder handles instantiation of generic parameters when types from outside an item refer to inner generics. The guide explains that to obtain a concrete type, the outer generic arguments must be applied via EarlyBinder::instantiate, converting a binder-wrapped type into the inner value with all parameters substituted. It also mentions the instantiate_identity path for inside-binder scenarios and notes that index mismatches are errors caught during name resolution, with a short note on related code paths such as FieldDef::ty during type checking.