Function ensureValidRuntimeType

packages/executor/src/execution/execute.ts:1343–1399

(
  runtimeTypeName: unknown,
  exeContext: ExecutionContext,
  returnType: GraphQLAbstractType,
  fieldNodes: Array<FieldNode>,
  info: GraphQLResolveInfo,
  result: unknown,
)

}

function ensureValidRuntimeType(
  runtimeTypeName: unknown,
  exeContext: ExecutionContext,
  returnType: GraphQLAbstractType,
  fieldNodes: Array<FieldNode>,
  info: GraphQLResolveInfo,
  result: unknown,
): GraphQLObjectType {
  if (runtimeTypeName == null) {
    throw createGraphQLError(
      `Abstract type "${returnType.name}" must resolve to an Object type at runtime for field "${info.parentType.name}.${info.fieldName}". Either the "${returnType.name}" type should provide a "resolveType" function or each possible type should provide an "isTypeOf" function.`,
      { nodes: fieldNodes },
    );
  }

  // releases before 16.0.0 supported returning `GraphQLObjectType` from `resolveType`
  // TODO: remove in 17.0.0 release
  if (isObjectType(runtimeTypeName)) {
    if (versionInfo.major >= 16) {
      throw createGraphQLError(
        'Support for returning GraphQLObjectType from resolveType was removed in graphql-js@16.0.0 please return type name instead.',
      );
    }
    runtimeTypeName = runtimeTypeName.name;
  }

  if (typeof runtimeTypeName !== 'string') {
    throw createGraphQLError(
      `Abstract type "${returnType.name}" must resolve to an Object type at runtime for field "${info.parentType.name}.${info.fieldName}" with ` +
        `value ${inspect(result)}, received "${inspect(runtimeTypeName)}".`,
    );
  }

  const runtimeType = exeContext.schema.getType(runtimeTypeName);
  if (runtimeType == null) {
    throw createGraphQLError(
      `Abstract type "${returnType.name}" was resolved to a type "${runtimeTypeName}" that does not exist inside the schema.`,
      { nodes: fieldNodes },
    );
  }

  if (!isObjectType(runtimeType)) {
    throw createGraphQLError(
      `Abstract type "${returnType.name}" was resolved to a non-object type "${runtimeTypeName}".`,
      { nodes: fieldNodes },
    );
  }

  if (!exeContext.schema.isSubType(returnType, runtimeType)) {
    throw createGraphQLError(
      `Runtime Object type "${runtimeType.name}" is not a possible type for "${returnType.name}".`,
      { nodes: fieldNodes },
    );
  }

  return runtimeType;
}