export default function watch(
  initialGlobalConfig: Config.GlobalConfig,
  contexts: Array<Context>,
  outputStream: NodeJS.WriteStream,
  hasteMapInstances: Array<HasteMap>,
  stdin: NodeJS.ReadStream = process.stdin,
  hooks: JestHook = new JestHook(),
  filter?: Filter,
): Promise<void> {
  // `globalConfig` will be constantly updated and reassigned as a result of
  // watch mode interactions.
  let globalConfig = initialGlobalConfig;
  let activePlugin: WatchPlugin | null;

  globalConfig = updateGlobalConfig(globalConfig, {
    mode: globalConfig.watch ? 'watch' : 'watchAll',
    passWithNoTests: true,
  });

  const updateConfigAndRun = ({
    bail,
    changedSince,
    collectCoverage,
    collectCoverageFrom,
    collectCoverageOnlyFrom,
    coverageDirectory,
    coverageReporters,
    mode,
    notify,
    notifyMode,
    onlyFailures,
    reporters,
    testNamePattern,
    testPathPattern,
    updateSnapshot,
    verbose,
  }: AllowedConfigOptions = {}) => {
    const previousUpdateSnapshot = globalConfig.updateSnapshot;
    globalConfig = updateGlobalConfig(globalConfig, {
      bail,
      changedSince,
      collectCoverage,
      collectCoverageFrom,
      collectCoverageOnlyFrom,
      coverageDirectory,
      coverageReporters,
      mode,
      notify,
      notifyMode,
      onlyFailures,
      reporters,
      testNamePattern,
      testPathPattern,
      updateSnapshot,
      verbose,
    });

    startRun(globalConfig);
    globalConfig = updateGlobalConfig(globalConfig, {
      // updateSnapshot is not sticky after a run.
      updateSnapshot:
        previousUpdateSnapshot === 'all' ? 'none' : previousUpdateSnapshot,
    });
  };

  const watchPlugins: Array<WatchPlugin> = INTERNAL_PLUGINS.map(
    InternalPlugin => new InternalPlugin({stdin, stdout: outputStream}),
  );
  watchPlugins.forEach((plugin: WatchPlugin) => {
    const hookSubscriber = hooks.getSubscriber();
    if (plugin.apply) {
      plugin.apply(hookSubscriber);
    }
  });

  if (globalConfig.watchPlugins != null) {
    const watchPluginKeys: WatchPluginKeysMap = new Map();
    for (const plugin of watchPlugins) {
      const reservedInfo =
        RESERVED_KEY_PLUGINS.get(plugin.constructor as WatchPluginClass) ||
        ({} as ReservedInfo);
      const key = reservedInfo.key || getPluginKey(plugin, globalConfig);
      if (!key) {
        continue;
      }
      const {forbiddenOverwriteMessage} = reservedInfo;
      watchPluginKeys.set(key, {
        forbiddenOverwriteMessage,
        overwritable: forbiddenOverwriteMessage == null,
        plugin,
      });
    }

    for (const pluginWithConfig of globalConfig.watchPlugins) {
      let plugin: WatchPlugin;
      try {
        const ThirdPartyPlugin = require(pluginWithConfig.path);
        plugin = new ThirdPartyPlugin({
          config: pluginWithConfig.config,
          stdin,
//.........这里部分代码省略.........

 const emitFileChange = () => {
   if (hooks.isUsed('onFileChange')) {
     const projects = searchSources.map(({context, searchSource}) => ({
       config: context.config,
       testPaths: searchSource.findMatchingTests('').tests.map(t => t.path),
     }));
     hooks.getEmitter().onFileChange({projects});
   }
 };

      onComplete: results => {
        isRunning = false;
        hooks.getEmitter().onTestRunComplete(results);

        // Create a new testWatcher instance so that re-runs won't be blocked.
        // The old instance that was passed to Jest will still be interrupted
        // and prevent test runs from the previous run.
        testWatcher = new TestWatcher({isWatchMode: true});

        // Do not show any Watch Usage related stuff when running in a
        // non-interactive environment
        if (isInteractive) {
          if (shouldDisplayWatchUsage) {
            outputStream.write(usage(globalConfig, watchPlugins));
            shouldDisplayWatchUsage = false; // hide Watch Usage after first run
            isWatchUsageDisplayed = true;
          } else {
            outputStream.write(showToggleUsagePrompt());
            shouldDisplayWatchUsage = false;
            isWatchUsageDisplayed = false;
          }
        } else {
          outputStream.write('\n');
        }
        failedTestsCache.setTestResults(results.testResults);
      },

  const startRun = (
    globalConfig: Config.GlobalConfig,
  ): Promise<void | null> => {
    if (isRunning) {
      return Promise.resolve(null);
    }

    testWatcher = new TestWatcher({isWatchMode: true});
    isInteractive && outputStream.write(specialChars.CLEAR);
    preRunMessagePrint(outputStream);
    isRunning = true;
    const configs = contexts.map(context => context.config);
    const changedFilesPromise = getChangedFilesPromise(globalConfig, configs);
    return runJest({
      changedFilesPromise,
      contexts,
      failedTestsCache,
      filter,
      globalConfig,
      jestHooks: hooks.getEmitter(),
      onComplete: results => {
        isRunning = false;
        hooks.getEmitter().onTestRunComplete(results);

        // Create a new testWatcher instance so that re-runs won't be blocked.
        // The old instance that was passed to Jest will still be interrupted
        // and prevent test runs from the previous run.
        testWatcher = new TestWatcher({isWatchMode: true});

        // Do not show any Watch Usage related stuff when running in a
        // non-interactive environment
        if (isInteractive) {
          if (shouldDisplayWatchUsage) {
            outputStream.write(usage(globalConfig, watchPlugins));
            shouldDisplayWatchUsage = false; // hide Watch Usage after first run
            isWatchUsageDisplayed = true;
          } else {
            outputStream.write(showToggleUsagePrompt());
            shouldDisplayWatchUsage = false;
            isWatchUsageDisplayed = false;
          }
        } else {
          outputStream.write('\n');
        }
        failedTestsCache.setTestResults(results.testResults);
      },
      outputStream,
      startRun,
      testWatcher,
    }).catch(error =>
      // Errors thrown inside `runJest`, e.g. by resolvers, are caught here for
      // continuous watch mode execution. We need to reprint them to the
      // terminal and give just a little bit of extra space so they fit below
      // `preRunMessagePrint` message nicely.
      console.error(
        '\n\n' +
          formatExecError(error, contexts[0].config, {noStackTrace: false}),
      ),
    );
  };