fs: add ignore option to fs.watch

Add an `ignore` option to `fs.watch()` to filter filesystem events.
Supports string globs, RegExp, functions, or arrays of these.

Author: mcollina

lib/fs.js

@@ -2521,7 +2521,8 @@ function watch(filename, options, listener) {
     watcher[watchers.kFSWatchStart](path,
                                     options.persistent,
                                     options.recursive,
-                                    options.encoding);
+                                    options.encoding,
+                                    options.ignore);
   }
 
   if (listener) {

lib/internal/fs/recursive_watch.js

@@ -17,9 +17,9 @@ const {
   },
 } = require('internal/errors');
 const { getValidatedPath } = require('internal/fs/utils');
-const { kFSWatchStart, StatWatcher } = require('internal/fs/watchers');
+const { createIgnoreMatcher, kFSWatchStart, StatWatcher } = require('internal/fs/watchers');
 const { kEmptyObject } = require('internal/util');
-const { validateBoolean, validateAbortSignal } = require('internal/validators');
+const { validateBoolean, validateAbortSignal, validateIgnoreOption } = require('internal/validators');
 const {
   basename: pathBasename,
   join: pathJoin,
@@ -44,13 +44,14 @@ class FSWatcher extends EventEmitter {
   #symbolicFiles = new SafeSet();
   #rootPath = pathResolve();
   #watchingFile = false;
+  #ignoreMatcher = null;
 
   constructor(options = kEmptyObject) {
     super();
 
     assert(typeof options === 'object');
 
-    const { persistent, recursive, signal, encoding } = options;
+    const { persistent, recursive, signal, encoding, ignore } = options;
 
     // TODO(anonrig): Add non-recursive support to non-native-watcher for IBMi & AIX support.
     if (recursive != null) {
@@ -72,6 +73,9 @@ class FSWatcher extends EventEmitter {
       }
     }
 
+    validateIgnoreOption(ignore, 'options.ignore');
+    this.#ignoreMatcher = createIgnoreMatcher(ignore);
+
     this.#options = { persistent, recursive, signal, encoding };
   }
 
@@ -92,6 +96,14 @@ class FSWatcher extends EventEmitter {
     this.emit('close');
   }
 
+  #emitChange(eventType, filename) {
+    // Filter events if ignore matcher is set and filename is available
+    if (filename != null && this.#ignoreMatcher?.(filename)) {
+      return;
+    }
+    this.emit('change', eventType, filename);
+  }
+
   #unwatchFiles(file) {
     this.#symbolicFiles.delete(file);
 
@@ -120,7 +132,7 @@ class FSWatcher extends EventEmitter {
         const f = pathJoin(folder, file.name);
 
         if (!this.#files.has(f)) {
-          this.emit('change', 'rename', pathRelative(this.#rootPath, f));
+          this.#emitChange('rename', pathRelative(this.#rootPath, f));
 
           if (file.isSymbolicLink()) {
             this.#symbolicFiles.add(f);
@@ -178,20 +190,20 @@ class FSWatcher extends EventEmitter {
         this.#files.delete(file);
         this.#watchers.delete(file);
         watcher.close();
-        this.emit('change', 'rename', pathRelative(this.#rootPath, file));
+        this.#emitChange('rename', pathRelative(this.#rootPath, file));
         this.#unwatchFiles(file);
       } else if (file === this.#rootPath && this.#watchingFile) {
         // This case will only be triggered when watching a file with fs.watch
-        this.emit('change', 'change', pathBasename(file));
+        this.#emitChange('change', pathBasename(file));
       } else if (this.#symbolicFiles.has(file)) {
         // Stats from watchFile does not return correct value for currentStats.isSymbolicLink()
         // Since it is only valid when using fs.lstat(). Therefore, check the existing symbolic files.
-        this.emit('change', 'rename', pathRelative(this.#rootPath, file));
+        this.#emitChange('rename', pathRelative(this.#rootPath, file));
       } else if (currentStats.isDirectory()) {
         this.#watchFolder(file);
       } else {
         // Watching a directory will trigger a change event for child files)
-        this.emit('change', 'change', pathRelative(this.#rootPath, file));
+        this.#emitChange('change', pathRelative(this.#rootPath, file));
       }
     });
     this.#watchers.set(file, watcher);

lib/internal/fs/watchers.js

@@ -1,13 +1,15 @@
 'use strict';
 
 const {
+  ArrayIsArray,
   ArrayPrototypePush,
   ArrayPrototypeShift,
   Error,
   FunctionPrototypeCall,
   ObjectDefineProperty,
   ObjectSetPrototypeOf,
   PromiseWithResolvers,
+  RegExpPrototypeExec,
   Symbol,
 } = primordials;
 
@@ -22,6 +24,8 @@ const {
 
 const {
   kEmptyObject,
+  isWindows,
+  isMacOS,
 } = require('internal/util');
 
 const {
@@ -48,6 +52,7 @@ const { toNamespacedPath } = require('path');
 const {
   validateAbortSignal,
   validateBoolean,
+  validateIgnoreOption,
   validateObject,
   validateUint32,
   validateInteger,
@@ -60,6 +65,8 @@ const {
   },
 } = require('buffer');
 
+const { isRegExp } = require('internal/util/types');
+
 const assert = require('internal/assert');
 
 const kOldStatus = Symbol('kOldStatus');
@@ -71,6 +78,54 @@ const KFSStatWatcherRefCount = Symbol('KFSStatWatcherRefCount');
 const KFSStatWatcherMaxRefCount = Symbol('KFSStatWatcherMaxRefCount');
 const kFSStatWatcherAddOrCleanRef = Symbol('kFSStatWatcherAddOrCleanRef');
 
+let minimatch;
+function lazyMinimatch() {
+  minimatch ??= require('internal/deps/minimatch/index');
+  return minimatch;
+}
+
+/**
+ * Creates an ignore matcher function from the ignore option.
+ * @param {string | RegExp | Function | Array} ignore - The ignore patterns
+ * @returns {Function | null} A function that returns true if filename should be ignored
+ */
+function createIgnoreMatcher(ignore) {
+  if (ignore == null) return null;
+  const matchers = ArrayIsArray(ignore) ? ignore : [ignore];
+  const compiled = [];
+
+  for (let i = 0; i < matchers.length; i++) {
+    const matcher = matchers[i];
+    if (typeof matcher === 'string') {
+      const mm = new (lazyMinimatch().Minimatch)(matcher, {
+        __proto__: null,
+        nocase: isWindows || isMacOS,
+        windowsPathsNoEscape: true,
+        nonegate: true,
+        nocomment: true,
+        optimizationLevel: 2,
+        platform: process.platform,
+        // matchBase allows patterns without slashes to match the basename
+        // e.g., '*.log' matches 'subdir/file.log'
+        matchBase: true,
+      });
+      ArrayPrototypePush(compiled, (filename) => mm.match(filename));
+    } else if (isRegExp(matcher)) {
+      ArrayPrototypePush(compiled, (filename) => RegExpPrototypeExec(matcher, filename) !== null);
+    } else {
+      // Function
+      ArrayPrototypePush(compiled, matcher);
+    }
+  }
+
+  return (filename) => {
+    for (let i = 0; i < compiled.length; i++) {
+      if (compiled[i](filename)) return true;
+    }
+    return false;
+  };
+}
+
 function emitStop(self) {
   self.emit('stop');
 }
@@ -199,6 +254,7 @@ function FSWatcher() {
 
   this._handle = new FSEvent();
   this._handle[owner_symbol] = this;
+  this._ignoreMatcher = null;
 
   this._handle.onchange = (status, eventType, filename) => {
     // TODO(joyeecheung): we may check self._handle.initialized here
@@ -219,6 +275,10 @@ function FSWatcher() {
       error.filename = filename;
       this.emit('error', error);
     } else {
+      // Filter events if ignore matcher is set and filename is available
+      if (filename != null && this._ignoreMatcher?.(filename)) {
+        return;
+      }
       this.emit('change', eventType, filename);
     }
   };
@@ -235,7 +295,8 @@ ObjectSetPrototypeOf(FSWatcher, EventEmitter);
 FSWatcher.prototype[kFSWatchStart] = function(filename,
                                               persistent,
                                               recursive,
-                                              encoding) {
+                                              encoding,
+                                              ignore) {
   if (this._handle === null) {  // closed
     return;
   }
@@ -246,6 +307,10 @@ FSWatcher.prototype[kFSWatchStart] = function(filename,
 
   filename = getValidatedPath(filename, 'filename');
 
+  // Validate and create the ignore matcher
+  validateIgnoreOption(ignore, 'options.ignore');
+  this._ignoreMatcher = createIgnoreMatcher(ignore);
+
   const err = this._handle.start(toNamespacedPath(filename),
                                  persistent,
                                  recursive,
@@ -319,13 +384,15 @@ async function* watch(filename, options = kEmptyObject) {
     maxQueue = 2048,
     overflow = 'ignore',
     signal,
+    ignore,
   } = options;
 
   validateBoolean(persistent, 'options.persistent');
   validateBoolean(recursive, 'options.recursive');
   validateInteger(maxQueue, 'options.maxQueue');
   validateOneOf(overflow, 'options.overflow', ['ignore', 'error']);
   validateAbortSignal(signal, 'options.signal');
+  validateIgnoreOption(ignore, 'options.ignore');
 
   if (encoding && !isEncoding(encoding)) {
     const reason = 'is invalid encoding';
@@ -336,6 +403,7 @@ async function* watch(filename, options = kEmptyObject) {
     throw new AbortError(undefined, { cause: signal.reason });
 
   const handle = new FSEvent();
+  const ignoreMatcher = createIgnoreMatcher(ignore);
   let { promise, resolve } = PromiseWithResolvers();
   const queue = [];
   const oncancel = () => {
@@ -361,6 +429,10 @@ async function* watch(filename, options = kEmptyObject) {
         resolve();
         return;
       }
+      // Filter events if ignore matcher is set and filename is available
+      if (filename != null && ignoreMatcher?.(filename)) {
+        return;
+      }
       if (queue.length < maxQueue) {
         ArrayPrototypePush(queue, { __proto__: null, eventType, filename });
         resolve();
@@ -409,6 +481,7 @@ async function* watch(filename, options = kEmptyObject) {
 }
 
 module.exports = {
+  createIgnoreMatcher,
   FSWatcher,
   StatWatcher,
   kFSWatchStart,

lib/internal/validators.js

@@ -35,6 +35,7 @@ const { normalizeEncoding } = require('internal/util');
 const {
   isAsyncFunction,
   isArrayBufferView,
+  isRegExp,
 } = require('internal/util/types');
 const { signals } = internalBinding('constants').os;
 
@@ -575,6 +576,38 @@ const validateLinkHeaderValue = hideStackFrames((hints) => {
   );
 });
 
+/**
+ * Validates a single ignore option element (string, RegExp, or Function).
+ * @param {*} value
+ * @param {string} name
+ */
+const validateIgnoreOptionElement = hideStackFrames((value, name) => {
+  if (typeof value === 'string') {
+    if (value.length === 0)
+      throw new ERR_INVALID_ARG_VALUE(name, value, 'must be a non-empty string');
+    return;
+  }
+  if (isRegExp(value)) return;
+  if (typeof value === 'function') return;
+  throw new ERR_INVALID_ARG_TYPE(name, ['string', 'RegExp', 'Function'], value);
+});
+
+/**
+ * Validates the ignore option for fs.watch.
+ * @param {*} value
+ * @param {string} name
+ */
+const validateIgnoreOption = hideStackFrames((value, name) => {
+  if (value == null) return;
+  if (ArrayIsArray(value)) {
+    for (let i = 0; i < value.length; i++) {
+      validateIgnoreOptionElement(value[i], `${name}[${i}]`);
+    }
+    return;
+  }
+  validateIgnoreOptionElement(value, name);
+});
+
 // 1. Returns false for undefined and NaN
 // 2. Returns true for finite numbers
 // 3. Throws ERR_INVALID_ARG_TYPE for non-numbers
@@ -628,6 +661,7 @@ module.exports = {
   validateDictionary,
   validateEncoding,
   validateFunction,
+  validateIgnoreOption,
   validateInt32,
   validateInteger,
   validateNumber,