Watcher backends: simplify ignore functions, remove anymatch dependen…

…cy (#1407)

Summary:
We currently use the [`anymatch`](https://www.npmjs.com/package/anymatch) dependency to evaluate ignore patterns in watcher backends. `anymatch` handles various input types including globs and arrays of globs/regexps

However, since D67285745, it's become clear that the `ignored` param is only ever a `?RegExp`, so we hardly use any of `anymatch` and can simply `test()` paths, and remove the dependency.

One subtlety to note that this change makes explicit, is that `anymatch` converts all input paths to posix separators before testing against the input `RegExp` (see block comment). We do the same in this diff so that the change is behaviour-preserving - however, this isn't a convention in Metro and should be revisited (maybe in a breaking change).

Note that we don't need to handle other kinds of path normalisation (like `anymatch` does with [`normalize-path`](https://www.npmjs.com/package/normalize-path)) because watcher backends must already emit normal paths, with no trailing separators. 

Changelog: Internal


Differential Revision: D67259981

packages/metro-file-map/package.json

@@ -13,7 +13,6 @@
   },
   "license": "MIT",
   "dependencies": {
-    "anymatch": "^3.0.3",
     "debug": "^2.2.0",
     "fb-watchman": "^2.0.0",
     "flow-enums-runtime": "^0.0.6",

packages/metro-file-map/src/watchers/FSEventsWatcher.js

@@ -14,8 +14,6 @@ import type {ChangeEventMetadata} from '../flow-types';
 import type {FSEvents} from 'fsevents';
 
 import {isIncluded, recReaddir, typeFromStat} from './common';
-// $FlowFixMe[untyped-import] - anymatch
-import anymatch from 'anymatch';
 import EventEmitter from 'events';
 import {promises as fsPromises} from 'fs';
 import * as path from 'path';
@@ -63,7 +61,11 @@ export default class FSEventsWatcher extends EventEmitter {
 
   constructor(
     dir: string,
-    opts: $ReadOnly<{
+    {
+      ignored,
+      glob,
+      dot,
+    }: $ReadOnly<{
       ignored: ?RegExp,
       glob: string | $ReadOnlyArray<string>,
       dot: boolean,
@@ -78,10 +80,14 @@ export default class FSEventsWatcher extends EventEmitter {
 
     super();
 
-    this.dot = opts.dot || false;
-    this.ignored = opts.ignored;
-    this.glob = Array.isArray(opts.glob) ? opts.glob : [opts.glob];
-    this.doIgnore = opts.ignored ? anymatch(opts.ignored) : () => false;
+    this.dot = dot || false;
+    this.ignored = ignored;
+    this.glob = Array.isArray(glob) ? glob : [glob];
+    this.doIgnore = ignored
+      ? // No need to normalise Windows paths to posix because this backend
+        // only runs on macOS, and backends always emit system-native paths.
+        (filePath: string) => ignored.test(filePath)
+      : () => false;
 
     this.root = path.resolve(dir);
 

packages/metro-file-map/src/watchers/common.js

@@ -19,8 +19,6 @@
 import type {ChangeEventMetadata} from '../flow-types';
 import type {Stats} from 'fs';
 
-// $FlowFixMe[untyped-import] - Write libdefs for `anymatch`
-const anymatch = require('anymatch');
 // $FlowFixMe[untyped-import] - Write libdefs for `micromatch`
 const micromatch = require('micromatch');
 const platform = require('os').platform();
@@ -74,8 +72,10 @@ export const assignOptions = function (
   if (!Array.isArray(watcher.globs)) {
     watcher.globs = [watcher.globs];
   }
-  watcher.doIgnore =
-    opts.ignored != null ? anymatch(opts.ignored) : () => false;
+  const ignored = watcher.ignored;
+  watcher.doIgnore = ignored
+    ? filePath => posixPathMatchesPattern(ignored, filePath)
+    : () => false;
 
   if (opts.watchman == true && opts.watchmanPath != null) {
     watcher.watchmanPath = opts.watchmanPath;
@@ -105,6 +105,21 @@ export function isIncluded(
   return micromatch.some(relativePath, globs, {dot});
 }
 
+/**
+ * Whether the given filePath matches the given RegExp, after converting
+ * (on Windows only) system separators to posix separators.
+ *
+ * Conversion to posix is for backwards compatibility with the previous
+ * anymatch matcher, which normlises all inputs[1]. This may not be consistent
+ * with other parts of metro-file-map.
+ *
+ * [1]: https://github.com/micromatch/anymatch/blob/3.1.1/index.js#L50
+ */
+const posixPathMatchesPattern: (pattern: RegExp, filePath: string) => boolean =
+  path.sep === '/'
+    ? (pattern, filePath) => pattern.test(filePath)
+    : (pattern, filePath) => pattern.test(filePath.replaceAll(path.sep, '/'));
+
 /**
  * Traverse a directory recursively calling `callback` on every directory.
  */
@@ -117,8 +132,13 @@ export function recReaddir(
   errorCallback: Error => void,
   ignored: ?RegExp,
 ) {
-  walker(dir)
-    .filterDir(currentDir => !anymatch(ignored, currentDir))
+  const walk = walker(dir);
+  if (ignored) {
+    walk.filterDir(
+      (currentDir: string) => !posixPathMatchesPattern(ignored, currentDir),
+    );
+  }
+  walk
     .on('dir', normalizeProxy(dirCallback))
     .on('file', normalizeProxy(fileCallback))
     .on('symlink', normalizeProxy(symlinkCallback))