How to use the @vuepress/shared-utils.logger.debug function in @vuepress/shared-utils

pagesWatcher.on('add', spawnUpdate('add'))
  pagesWatcher.on('unlink', spawnUpdate('unlink'))
  pagesWatcher.on('addDir', spawnUpdate('addDir'))
  pagesWatcher.on('unlinkDir', spawnUpdate('unlinkDir'))

  const watchFiles = [
    '.vuepress/config.js',
    '.vuepress/config.yml',
    '.vuepress/config.toml'
  ].concat(
    (
      ctx.siteConfig.extraWatchFiles || []
    ).map(file => normalizeWatchFilePath(file, ctx.sourceDir))
  )

  logger.debug('watchFiles', watchFiles)

  // watch config file
  const configWatcher = chokidar.watch(watchFiles, {
    cwd: sourceDir,
    ignoreInitial: true
  })
  configWatcher.on('change', spawnUpdate('change'))

  // also listen for frontmatter changes from markdown files
  frontmatterEmitter.on('update', () => update('frontmatter or headers change'))

  // resolve webpack config
  let config = createClientConfig(ctx)

  config
    .plugin('html')

if (inferredUserDocsDirectory && sourceDir !== inferredUserDocsDirectory) {
      logUnknownCommand(cli)
      console.log()
      logger.tip(`Did you miss to specify the target docs dir? e.g. ${chalk.cyan(`vuepress ${commandName} [targetDir]`)}.`)
      logger.tip(`A custom command registered by a plugin requires VuePress to locate your site configuration like ${chalk.cyan('vuepress dev')} or ${chalk.cyan('vuepress build')}.`)
      console.log()
      process.exit(1)
    }

    if (!inferredUserDocsDirectory) {
      logUnknownCommand(cli)
      process.exit(1)
    }

    logger.debug('Custom command', chalk.cyan(commandName))
    CLI({
      async beforeParse (subCli) {
        const app = createApp({
          sourceDir: sourceDir,
          ...options,
          ...commandoptions
        })
        await app.process()
        app.pluginAPI.applySyncOption('extendCli', subCli, app)
        console.log()
      },
      async afterParse (subCli) {
        if (!subCli.matchedCommand) {
          logUnknownCommand(subCli)
          console.log()
        }

cli.on('command:*', async () => {
    const { args, options: commandoptions } = cli

    logger.debug('global_options', options)
    logger.debug('cli_options', commandoptions)
    logger.debug('cli_args', args)

    const [commandName] = args
    const sourceDir = args[1] ? path.resolve(args[1]) : pwd
    const inferredUserDocsDirectory = await inferUserDocsDirectory(pwd)
    logger.developer('inferredUserDocsDirectory', inferredUserDocsDirectory)
    logger.developer('sourceDir', sourceDir)

    if (inferredUserDocsDirectory && sourceDir !== inferredUserDocsDirectory) {
      logUnknownCommand(cli)
      console.log()
      logger.tip(`Did you miss to specify the target docs dir? e.g. ${chalk.cyan(`vuepress ${commandName} [targetDir]`)}.`)
      logger.tip(`A custom command registered by a plugin requires VuePress to locate your site configuration like ${chalk.cyan('vuepress dev')} or ${chalk.cyan('vuepress build')}.`)
      console.log()
      process.exit(1)
    }

constructor (options = {}) {
    this.isProd = process.env.NODE_ENV === 'production'
    this.options = options
    this.sourceDir = this.options.sourceDir || path.join(__dirname, 'docs.fallback')
    logger.debug('sourceDir', this.sourceDir)
    if (!fs.existsSync(this.sourceDir)) {
      logger.warn(`Source directory doesn't exist: ${chalk.yellow(this.sourceDir)}`)
    }

    this.vuepressDir = path.resolve(this.sourceDir, '.vuepress')
    this.libDir = path.join(__dirname, '../')
  }

.action((sourceDir = '.', commandOptions) => {
      const { debug, silent } = commandOptions

      logger.setOptions({ logLevel: silent ? 1 : debug ? 4 : 3 })
      logger.debug('global_options', options)
      logger.debug('build_options', commandOptions)
      env.setOptions({ isDebug: debug, isTest: process.env.NODE_ENV === 'test' })

      wrapCommand(build)({
        sourceDir: path.resolve(sourceDir),
        ...options,
        ...commandOptions
      })
    })

applySyncOption (name, ...args) {
    logger.debug('applySyncOption: ' + name)
    this.getOption(name).apply(...args)
    return this
  }

watchUserConfig () {
    this.watchFiles = [
      '.vuepress/config.js',
      '.vuepress/config.yml',
      '.vuepress/config.toml'
    ].concat(
      (
        this.context.siteConfig.extraWatchFiles || []
      ).map(file => normalizeWatchFilePath(file, this.context.sourceDir))
    )

    logger.debug('watchFiles', this.watchFiles)

    this.configWatcher = chokidar.watch(this.watchFiles, {
      cwd: this.context.sourceDir,
      ignoreInitial: true
    })

    this.configWatcher.on('change', target => this.handleUpdate('change', target))
  }

logger.warn(e.message)
        return this
      }
    }

    if (plugin.multiple !== true) {
      const duplicateIndex = this._pluginQueue.findIndex(({ name }) => name === plugin.name)
      if (duplicateIndex !== -1) {
        this._pluginQueue.splice(duplicateIndex, 1)
      }
    }

    this._pluginQueue.push(plugin)

    if (plugin.plugins) {
      logger.debug(`Plugins defined at ${chalk.gray(plugin.name)}`, plugin.plugins)
      this.useByPluginsConfig(plugin.plugins)
    }

    return this
  }