Extract some crawl and watch management out of index.js

Summary:
Refactoring to begin the work of bringing crawl+watch closer together.

This simply pulls some code out of the bloated `index.js` into a `Watcher` class, which is responsible for managing crawl and watch backends.

The API is likely to change, but for now sticks to `crawl()` / `watch()` as separate instance methods (reflecting the current architecture) to minimise the churn in this diff.

Changelog: Internal

Reviewed By: motiz88

Differential Revision: D39891465

fbshipit-source-id: 8e3616847380bea7acf7117479a0a9a90526e19e

packages/metro-file-map/src/Watcher.js

@@ -0,0 +1,186 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow strict-local
+ */
+
+import type {
+  Console,
+  CrawlerOptions,
+  FileData,
+  InternalData,
+  Path,
+  PerfLogger,
+} from './flow-types';
+import type {WatcherOptions as WatcherBackendOptions} from './watchers/common';
+import type {Stats} from 'fs';
+
+import watchmanCrawl from './crawlers/watchman';
+import nodeCrawl from './crawlers/node';
+import WatchmanWatcher from './watchers/WatchmanWatcher';
+import FSEventsWatcher from './watchers/FSEventsWatcher';
+// $FlowFixMe[untyped-import] - it's a fork: https://github.com/facebook/jest/pull/10919
+import NodeWatcher from './watchers/NodeWatcher';
+
+const debug = require('debug')('Metro:Watcher');
+
+const MAX_WAIT_TIME = 240000;
+
+type WatcherOptions = {
+  abortSignal: AbortSignal,
+  computeSha1: boolean,
+  console: Console,
+  enableSymlinks: boolean,
+  extensions: $ReadOnlyArray<string>,
+  forceNodeFilesystemAPI: boolean,
+  ignore: string => boolean,
+  ignorePattern: RegExp,
+  initialData: InternalData,
+  perfLogger: ?PerfLogger,
+  roots: $ReadOnlyArray<string>,
+  rootDir: string,
+  useWatchman: boolean,
+  watch: boolean,
+  watchmanDeferStates: $ReadOnlyArray<string>,
+};
+
+interface WatcherBackend {
+  close(): Promise<void>;
+}
+
+export class Watcher {
+  _options: WatcherOptions;
+  _backends: $ReadOnlyArray<WatcherBackend> = [];
+
+  constructor(options: WatcherOptions) {
+    this._options = options;
+  }
+
+  async crawl(): Promise<?(
+    | Promise<{
+        changedFiles?: FileData,
+        hasteMap: InternalData,
+        removedFiles: FileData,
+      }>
+    | {changedFiles?: FileData, hasteMap: InternalData, removedFiles: FileData}
+  )> {
+    this._options.perfLogger?.point('crawl_start');
+
+    const options = this._options;
+    const ignore = (filePath: string) => options.ignore(filePath);
+    const crawl = options.useWatchman ? watchmanCrawl : nodeCrawl;
+    const crawlerOptions: CrawlerOptions = {
+      abortSignal: options.abortSignal,
+      computeSha1: options.computeSha1,
+      data: options.initialData,
+      enableSymlinks: options.enableSymlinks,
+      extensions: options.extensions,
+      forceNodeFilesystemAPI: options.forceNodeFilesystemAPI,
+      ignore,
+      perfLogger: options.perfLogger,
+      rootDir: options.rootDir,
+      roots: options.roots,
+    };
+
+    const retry = (error: Error) => {
+      if (crawl === watchmanCrawl) {
+        options.console.warn(
+          'metro-file-map: Watchman crawl failed. Retrying once with node ' +
+            'crawler.\n' +
+            "  Usually this happens when watchman isn't running. Create an " +
+            "empty `.watchmanconfig` file in your project's root folder or " +
+            'initialize a git or hg repository in your project.\n' +
+            '  ' +
+            error.toString(),
+        );
+        return nodeCrawl(crawlerOptions).catch(e => {
+          throw new Error(
+            'Crawler retry failed:\n' +
+              `  Original error: ${error.message}\n` +
+              `  Retry error: ${e.message}\n`,
+          );
+        });
+      }
+
+      throw error;
+    };
+
+    const logEnd = <T>(result: T): T => {
+      this._options.perfLogger?.point('crawl_end');
+      return result;
+    };
+
+    try {
+      return crawl(crawlerOptions).catch(retry).then(logEnd);
+    } catch (error) {
+      return retry(error).then(logEnd);
+    }
+  }
+
+  async watch(
+    onChange: (
+      type: string,
+      filePath: string,
+      root: string,
+      stat?: Stats,
+    ) => void,
+  ) {
+    const {extensions, ignorePattern, useWatchman} = this._options;
+
+    // WatchmanWatcher > FSEventsWatcher > sane.NodeWatcher
+    const WatcherImpl = useWatchman
+      ? WatchmanWatcher
+      : FSEventsWatcher.isSupported()
+      ? FSEventsWatcher
+      : NodeWatcher;
+
+    let watcher = 'node';
+    if (WatcherImpl === WatchmanWatcher) {
+      watcher = 'watchman';
+    } else if (WatcherImpl === FSEventsWatcher) {
+      watcher = 'fsevents';
+    }
+    debug(`Using watcher: ${watcher}`);
+    this._options.perfLogger?.annotate({string: {watcher}});
+
+    const createWatcherBackend = (root: Path): Promise<WatcherBackend> => {
+      const watcherOptions: WatcherBackendOptions = {
+        dot: true,
+        glob: [
+          // Ensure we always include package.json files, which are crucial for
+          /// module resolution.
+          '**/package.json',
+          ...extensions.map(extension => '**/*.' + extension),
+        ],
+        ignored: ignorePattern,
+        watchmanDeferStates: this._options.watchmanDeferStates,
+      };
+      const watcher = new WatcherImpl(root, watcherOptions);
+
+      return new Promise((resolve, reject) => {
+        const rejectTimeout = setTimeout(
+          () => reject(new Error('Failed to start watch mode.')),
+          MAX_WAIT_TIME,
+        );
+
+        watcher.once('ready', () => {
+          clearTimeout(rejectTimeout);
+          watcher.on('all', onChange);
+          resolve(watcher);
+        });
+      });
+    };
+
+    this._backends = await Promise.all(
+      this._options.roots.map(createWatcherBackend),
+    );
+  }
+
+  async close() {
+    await Promise.all(this._backends.map(watcher => watcher.close()));
+  }
+}