mochapack/src/webpack/compiler/createWatchCompiler.ts

mocha cli with webpack support

import _ from 'lodash'
import Watching from 'webpack/lib/Watching'
import { Compiler } from 'webpack'

export type WatchCompiler = {
  watch: () => void
  pause: () => void
  getWatchOptions: () => {
    aggregateTimeout: number
    ignored?: RegExp | string
    poll?: number | boolean
  }
}

const noop = () => undefined
export default function createWatchCompiler(
  compiler: Compiler,
  watchOptions: {}
): WatchCompiler {
  // this ugly statement to create a watch compiler is unfortunately necessary,
  // as webpack clears the file timestamps with the official compiler.watch()
  const createWatcher = () => new Watching(compiler, watchOptions, noop)
  let watchCompiler = null

  return {
    watch() {
      if (watchCompiler === null) {
        watchCompiler = createWatcher()
      } else {
        // @ts-ignore
        const times = compiler.watchFileSystem.watcher.getTimes()
        // check if we can store some collected file timestamps
        // the non-empty check is necessary as the times will be reseted after .close()
        // and we don't want to reset already existing timestamps
        if (Object.keys(times).length > 0) {
          const timesMap = new Map(
            Object.keys(times).map(key => [key, times[key]])
          )
          // set already collected file timestamps to cache compiled files
          // webpack will do this only after a file change, but that will not happen when we add or delete files
          // and this means that we have to test the whole test suite again ...
          compiler.fileTimestamps = timesMap // eslint-disable-line no-param-reassign
          compiler.contextTimestamps = timesMap // eslint-disable-line no-param-reassign
        }

        watchCompiler.close(() => {
          watchCompiler = createWatcher()
        })
      }
    },
    pause() {
      if (watchCompiler !== null && watchCompiler.watcher) {
        watchCompiler.watcher.pause()
      }
    },
    getWatchOptions() {
      // 200 is the default value by webpack
      return _.get(watchCompiler, 'watchOptions', { aggregateTimeout: 200 })
    }
  }
}