/** Creates a rollup bundle of a specified JavaScript file.*/
  private async createRollupBundle(config: RollupBundleConfig) {
    const bundleOptions = {
      context: 'this',
      external: Object.keys(rollupGlobals),
      input: config.entry,
      onwarn: (message: string) => {
        // TODO(jelbourn): figure out *why* rollup warns about certain symbols not being found
        // when those symbols don't appear to be in the input file in the first place.
        if (/but never used/.test(message)) {
          return false;
        }

        console.warn(message);
      },
      plugins: [
        rollupRemoveLicensesPlugin,
      ]
    };

    const writeOptions = {
      name: config.moduleName || 'ng.flexLayout',
      amd: {id: config.importName},
      banner: buildConfig.licenseBanner,
      format: config.format,
      file: config.dest,
      globals: rollupGlobals,
      sourcemap: true
    };

    // For UMD bundles, we need to adjust the `external` bundle option in order to include
    // all necessary code in the bundle.
    if (config.format === 'umd') {
      bundleOptions.plugins.push(rollupNodeResolutionPlugin());

      // For all UMD bundles, we want to exclude tslib from the `external` bundle option so that
      // it is inlined into the bundle.
      let external = Object.keys(rollupGlobals);
      external.splice(external.indexOf('tslib'), 1);

      // If each secondary entry-point is re-exported at the root, we want to exlclude those
      // secondary entry-points from the rollup globals because we want the UMD for this package
      // to include *all* of the sources for those entry-points.
      if (this.buildPackage.exportsSecondaryEntryPointsAtRoot &&
          config.moduleName === `ng.${this.buildPackage.name}`) {

        const importRegex = new RegExp(`@angular/${this.buildPackage.name}/.+`);
        external = external.filter(e => !importRegex.test(e));

        // Use the rollup-alias plugin to map imports of the form `@angular/material/button`
        // to the actual file location so that rollup can resolve the imports (otherwise they
        // will be treated as external dependencies and not included in the bundle).
        bundleOptions.plugins.push(
            rollupAlias(this.getResolvedSecondaryEntryPointImportPaths(config.dest)));
      }

      bundleOptions.external = external;
    }

    return rollup.rollup(bundleOptions).then((bundle: any) => bundle.write(writeOptions));
  }

  /** Creates a rollup bundle of a specified JavaScript file.*/
  private async createRollupBundle(config: RollupBundleConfig) {
    const bundleOptions = {
      context: 'this',
      external: Object.keys(rollupExternals),
      input: config.entry,
      onwarn: (message: string) => {
        if (/but never used/.test(message)) {
          return false;
        }
        console.warn(message);
      },
      plugins: [
        rollupRemoveLicensesPlugin,
        rollupNodeResolutionPlugin(),
        rollupAlias(this.getResolvedSecondaryEntryPointImportPaths(config.dest))
      ]
    };

    const writeOptions = {
      name: config.moduleName || 'ng.web',
      amd: { id: config.importName },
      globals: rollupGlobals,
      file: config.dest,
      format: config.format,
      banner: buildConfig.licenseBanner,
      sourcemap: false
    };

    bundleOptions.plugins.push(commonjs({
      include: 'node_modules/**'
    }));

    // Only transpile es5 / umd packages
    if (!config.es6) {
      bundleOptions.plugins.push(babel({
        include: 'node_modules/**'
      }));
    }

    // For UMD bundles, we need to adjust the `external` bundle option in order to include
    // all necessary code in the bundle.
    if (config.format === 'umd') {
      // bundleOptions.plugins.push(minify());

      // For all UMD bundles, we want to exclude tslib from the `external` bundle option so that
      // it is inlined into the bundle.
      let external = Object.keys(rollupGlobals);
      external.splice(external.indexOf('tslib'), 1);

      // If each secondary entry-point is re-exported at the root, we want to exclude those
      // secondary entry-points from the rollup globals because we want the UMD for the
      // primary entry-point to include *all* of the sources for those entry-points.
      if (this.buildPackage.exportsSecondaryEntryPointsAtRoot &&
        config.moduleName === `ng.${this.buildPackage.name}`) {

        const importRegex = new RegExp(`@angular-mdc/${this.buildPackage.name}/.+`);
        external = external.filter(e => !importRegex.test(e));
      }

      bundleOptions.external = external;
    }

    return rollup.rollup(bundleOptions).then((bundle: any) => bundle.write(writeOptions));
  }