anchor.diff:      final declarationId = inputs.first;
       final type = inputs.second;
   
  -    if (type.simpleTypes.length > 1) {
  -      throw CompilerError.unsupportedFeature(
  -        'Nested types are not yet supported.',
  -      );
  -    }
  -
       // Step 1: Look for traits/classes in outer modules in the same file.
       final localResult = _resolveAstUserTypeInFile(context, declarationId, type);
       if (localResult.isSome) return localResult.value;
  
positive.code:     // Step 2: Search use-lines.
      final resourceId = declarationId.resourceId;
      final simpleType = type.simpleTypes.first.name;
      final importedModules = findModuleInUseLines(
        context,
        Tuple4(resourceId, simpleType.name, simpleType.span, false),
      );
      if (importedModules is None) {
        throw CompilerError.typeNotFound(
          'Type `${simpleType.name}` could not be resolved.',
          location: ErrorLocation(resourceId, type.simpleTypes.first.span),
        );
      }
  
      final resultDeclarationId =
          moduleIdToDeclarationId(context, importedModules.value);
      if (resultDeclarationId.isModule) {
        throw CompilerError.typeNotFound(
          'Type `${simpleType.name}` could not be resolved.',
  
negative.code:     }
      assert(resultDeclarationId.isTrait || resultDeclarationId.isClass);
      return hir.CandyType.user(
        moduleId.parent,
        resultDeclarationId.simplePath.last.nameOrNull,
      );
    },
  