Codegen/Semantics Boundary

January 8, 2026 · View on GitHub

This document defines the stable interface between semantics and codegen in the compiler.

Contract

Semantics produces a whole-program, codegen-oriented artifact:

Codegen consumes this view as its only source of program-wide semantic meaning.

A single program-wide TypeArena shared across all modules in the compilation unit.
A program-wide EffectInterner (canonical effect rows) used by typing and codegen.
Deterministic, stable iteration order for codegen-relevant indexes (modules, impl sets, instance sets).
Codegen-facing indexes for:
- type descriptors/layout information
- nominal ownership/instances
- trait dispatch inputs (impl sets and method mappings)
- call-site lowering info (targets, type arguments, instance keys, trait-dispatch flags)
- primitive type ids used by lowering

TypeId and EffectRowId are globally meaningful within a compilation unit.
Nominal identity is represented canonically via SymbolRef ({ moduleId, symbol }).
Call-site resolution has already happened; codegen does not re-run overload/trait resolution.

Import or read typing internals (TypingResult, TypeTable, FunctionStore, ObjectStore, TraitStore, etc).
Use binding/import metadata to resolve semantic identity (other than WASM import wiring).
Walk typing stores to reconstruct layouts, ancestry, or dispatch tables.