Intern types for canonical identity#29570
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Introduce a two-tier type model separating canonical identity from source-level type annotations: - `Type` is a `Copy` `u32` handle into a session-scoped `TypeInterner`. Equality, hashing, and ordering are O(1). - `TypeKind` is the enum that was previously called `Type`, carrying the source shape (nested `TypeNode` children, integer variants, composites, and so on). - `TypeNode` is the AST-level wrapper: a `TypeKind`, its `Span`, and a cached `Type` handle. `TypeNode::new(interner, kind, span)` is the sole constructor that populates the handle; `PartialEq` and `Hash` delegate to it. Future generics work needs canonical identity for types so monomorphization can key on `Type` directly, and every pass benefits from O(1) equality replacing recursive structural comparison. Keeping `TypeNode` distinct from `Type` preserves per-occurrence spans that diagnostics rely on, which a pure interner handle would drop.
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Introduce a two-tier type model separating canonical identity from source-level type annotations:
Typeis aCopyu32handle into a session-scopedTypeInterner. Equality, hashing, and ordering are O(1).TypeKindis the enum that was previously calledType, carrying the source shape (nestedTypeNodechildren, integer variants, composites, and so on).TypeNodeis the AST-level wrapper: aTypeKind, itsSpan, and a cachedTypehandle.TypeNode::new(interner, kind, span)is the sole constructor that populates the handle;PartialEqandHashdelegate to it.Future generics work needs canonical identity for types so monomorphization can key on
Typedirectly, and every pass benefits from O(1) equality replacing recursive structural comparison. KeepingTypeNodedistinct fromTypepreserves per-occurrence spans that diagnostics rely on, which a pure interner handle would drop.