Declaration Type Pattern Architecture

Public syntax and semantics are specified in Generics, Interfaces, and Methods. This document owns the compiler architecture for v0.11.0 Phase 5.

Boundary

instance, conform, and destruct headers use declaration type patterns. A pattern slot introduces a bare binder; it does not accept an arbitrary type expression. func, method, nominal type, interface, construction, coercion, and literal generic lists remain explicit name declarations.

The parser derives one ordered GenericParamList from first occurrences in pattern slots. This is not a synthetic, spanless list: each parameter points to its first authored occurrence, and later occurrences resolve to the same declaration identity.

Refinement

The AST stores where T = Type as a directed binder refinement, not as symmetric type equality. Validation requires the left name to identify a pattern binder, forbids a second refinement of the same binder, and rejects a right side that recursively mentions the refined binder. Projection equality remains a separate predicate with its existing symmetric relation semantics.

One normalized substitution map applies refinements after receiver/interface pattern matching. All consumers use that service; no consumer scans a where clause or presentation string to rediscover refinements.

Coherence

Pattern overlap is satisfiability, not textual equality. Binder names are alpha-renamed, repeated positions add equality constraints, and refinements contribute their normalized concrete shape. Two conformances conflict when both their interface and target patterns can match one concrete pair. Inherent declarations conflict only when overlapping target patterns export the same method name. A nominal family has one independent destructor declaration.

Destruction is intentionally uniform across a nominal family. A destruct declaration has no where clause and must mention every target slot through one distinct binder. Allowing a type's need for destruction to vary by refinement would make generic ownership and ABI decisions conditional. Refined instances remain method-only declaration patterns.

Nocter rejects overlap rather than selecting the more concrete declaration. This keeps lookup, ownership, lowering, and editor results independent of declaration and import order.

Consumer Rule

Parser validation, resolver signatures, type checking, conditional conformance, associated-type normalization, drop discovery, buildability, lowering, formatter output, AST JSON, hover, completion, navigation, references, rename, and semantic tokens consume authored binder identities or normalized pattern results. None may infer declaration parameters from unresolved symbol-table failures or parse normalized display text.