Sema: restrict the options to resolve the structural type of type aliases

Author: xymus

lib/AST/Decl.cpp

@@ -3437,6 +3437,8 @@ UnboundGenericType *TypeAliasDecl::getUnboundGenericType() const {
 }
 
 Type TypeAliasDecl::getStructuralType() const {
+  assert(!getGenericParams());
+  
   auto &context = getASTContext();
   return evaluateOrDefault(context.evaluator,
                            StructuralTypeRequest { const_cast<TypeAliasDecl *>(this) },

lib/Sema/TypeCheckGeneric.cpp

@@ -1012,7 +1012,13 @@ RequirementRequest::evaluate(Evaluator &evaluator,
 llvm::Expected<Type>
 swift::StructuralTypeRequest::evaluate(Evaluator &evaluator,
                                        TypeAliasDecl *D) const {
+  TypeResolutionOptions options(TypeResolverContext::TypeAliasDecl);
+  if (!D->getDeclContext()->isCascadingContextForLookup(
+        /*functionsAreNonCascading*/true)) {
+    options |= TypeResolutionFlags::KnownNonCascadingDependency;
+  }
+
   auto typeRepr = D->getUnderlyingTypeLoc().getTypeRepr();
   auto resolution = TypeResolution::forStructural(D);
-  return resolution.resolveType(typeRepr, None);
+  return resolution.resolveType(typeRepr, options);
 }