code: function getDefaultTypeRoots(currentDirectory, host) {
          if (!host.directoryExists) {
              return [ts.combinePaths(currentDirectory, nodeModulesAtTypes)];
          }
          var typeRoots;
          while (true) {
              var atTypes = ts.combinePaths(currentDirectory, nodeModulesAtTypes);
              if (host.directoryExists(atTypes)) {
                  (typeRoots || (typeRoots = [])).push(atTypes);
              }
              var parent_15 = ts.getDirectoryPath(currentDirectory);
              if (parent_15 === currentDirectory) {
                  break;
              }
              currentDirectory = parent_15;
          }
          return typeRoots;
      }
docs: Returns the path to every node_modules/@types directory from some ancestor directory.
  Returns undefined if there are none.