Arenas, interning, index newtypes and the small data structures the rest of the compiler is built out of.

Design: spec/03-architecture.md. Layer rank 0, see spec/18-package-layout.md.

Nothing in here knows anything about C. That is deliberate: this is the one crate every other crate depends on, so anything C-specific that leaks in here becomes impossible to avoid later.

Status

The index newtypes and the interner are real and used. The arena is a thin wrapper for now and grows with M2.

This crate is tier 3 in spec/18-package-layout.md section 18.5: its Rust API is explicitly unstable and will change without a major version bump.