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MEP-75 Phase 11: Interface and Abstract Class Bridge (Hierarchy)

Status: LANDED 2026-05-30 00:33 (GMT+7)

Goal​

Implement hierarchy analysis for PHP class/interface relationships under package3/php/externemit/hierarchy.go. Given a ReflectionSurface, build an index of which classes extend which parents, which concrete classes implement each interface, and which classes are abstract. Use this index to emit extern type declarations with annotations listing concrete subtypes.

Design​

BuildHierarchy(surface) constructs a Hierarchy struct with five maps:

  • ClassByFQCN - all classes indexed by FQCN
  • InterfaceByFQCN - all interfaces indexed by FQCN
  • ImplementorsOf - interface FQCN to list of implementing class FQCNs
  • SubclassesOf - parent FQCN to list of direct child FQCNs
  • AbstractClasses - set of abstract class FQCNs

ConcreteImplementors(ifaceFQCN) filters ImplementorsOf to non-abstract classes.

AllSubclasses(fqcn) performs a DFS walk over SubclassesOf to collect all transitive subclasses (cycle-safe via seen map).

EmitAbstractBridge(surface) emits extern type declarations for:

  • Abstract classes, with a comment listing concrete (non-abstract) subclass handles
  • Interfaces, with a comment listing concrete implementor handles

Concrete classes are skipped since they are handled by the main Emit() path.

Files Landed​

  • package3/php/externemit/hierarchy.go -- Hierarchy + BuildHierarchy + EmitAbstractBridge
  • package3/php/externemit/hierarchy_test.go -- 14 test functions

Test Coverage​

  • ClassByFQCN and InterfaceByFQCN indexing
  • AbstractClasses set membership
  • SubclassesOf direct child mapping
  • ImplementorsOf interface-to-class mapping
  • AllSubclasses transitive DFS walk
  • AllSubclasses no-cycle guard on leaf nodes
  • ConcreteImplementors filters abstract classes
  • InterfacesOf known and unknown class
  • EmitAbstractBridge emits extern type for abstract classes
  • EmitAbstractBridge emits concrete subclasses annotation
  • EmitAbstractBridge emits Interface implementors annotation
  • EmitAbstractBridge returns empty output for empty surface
  • EmitAbstractBridge skips concrete-only surfaces