code: function resolveId(details, filepath) {
    let id = '';
  
    if ('string' == typeof filepath) {
      // Only version if more than one package
      const version = details.id.includes(versionDelimiter) ? versionDelimiter + details.version : '';
      const versioned = (id, stripExtension) => {
        // Strip extension
        if (stripExtension) id = id.replace(path.extname(id), '');
        return (process.platform == 'win32' ? id.replace(/\\/g, '/') : id) + version;
      };
  
      // Resolve aliases
      id = alias.resolve(filepath, details.aliases);
      // Ignore disabled (false)
      id = id || filepath;
      // Return if resolved id
      if (!isFilepath(id)) return versioned(id, false);
      // Resolve alias to id (also handles main => id)
      id = alias.resolveReverse(id, details.aliases);
      // Return if resolved id
      if (!isFilepath(id)) return versioned(id, false);
  
      // Resolve ids from project root if nested project package
      const pkgpath = details.isNestedProjectPackage
        ? process.cwd()
        : // Resolve ids from node_modules root if npm package
          details.isNpmPackage ? details.dirname : details.pkgpath;
  
      [...details.paths, pkgpath].some(sourcepath => {
        if (filepath.includes(sourcepath)) {
          id = path.relative(sourcepath, filepath);
          return true;
        }
      });
  
      return versioned(id, true);
    }
  
    return id;
  }
docs: Resolve id for 'filepath'
  @param {Object} details
  @param {String} filepath
  @returns {String}