fs: add promise support to linux watcher

lib/internal/fs/promises.js

@@ -89,6 +89,7 @@ const {
 const { EventEmitterMixin } = require('internal/event_target');
 const { StringDecoder } = require('string_decoder');
 const { watch } = require('internal/fs/watchers');
+const linuxWatcher = require('internal/fs/watch/linux');
 const { isIterable } = require('internal/streams/utils');
 const assert = require('internal/assert');
 
@@ -120,6 +121,7 @@ const getDirectoryEntriesPromise = promisify(getDirents);
 const validateRmOptionsPromise = promisify(validateRmOptions);
 
 const isWindows = process.platform === 'win32';
+const isLinux = process.platform === 'linux';
 
 let cpPromises;
 function lazyLoadCpPromises() {
@@ -917,6 +919,21 @@ async function readFile(path, options) {
   return handleFdClose(readFileHandle(fd, options), fd.close);
 }
 
+function _watch(filename, options) {
+  options = getOptions(options, { persistent: true, recursive: false, encoding: 'utf8' });
+
+  // TODO(anonrig): Remove this when/if libuv supports it.
+  // libuv does not support recursive file watch on Linux due to
+  // the limitations of inotify.
+  if (options.recursive && isLinux) {
+    const watcher = new linuxWatcher.FSWatcher(options);
+    watcher[linuxWatcher.kFSWatchStart](filename);
+    return watcher;
+  }
+
+  return watch(filename, options);
+}
+
 module.exports = {
   exports: {
     access,
@@ -947,7 +964,7 @@ module.exports = {
     writeFile,
     appendFile,
     readFile,
-    watch,
+    watch: _watch,
     constants,
   },
 

lib/internal/fs/watch/linux.js

@@ -1,11 +1,12 @@
 'use strict';
 
+const { SafeMap, Symbol, StringPrototypeStartsWith, SymbolAsyncIterator, Promise } = primordials;
+
+const { ERR_FEATURE_UNAVAILABLE_ON_PLATFORM } = require('internal/errors');
+const { kEmptyObject } = require('internal/util');
+const { validateObject, validateString } = require('internal/validators');
 const { EventEmitter } = require('events');
 const path = require('path');
-const { SafeMap, Symbol, StringPrototypeStartsWith } = primordials;
-const { validateObject, validateString } = require('internal/validators');
-const { kEmptyObject } = require('internal/util');
-const { ERR_FEATURE_UNAVAILABLE_ON_PLATFORM } = require('internal/errors');
 
 const kFSWatchStart = Symbol('kFSWatchStart');
 
@@ -185,6 +186,25 @@ class FSWatcher extends EventEmitter {
     // This is kept to have the same API with FSWatcher
     throw new ERR_FEATURE_UNAVAILABLE_ON_PLATFORM('unref');
   }
+
+  async next() {
+    if (this.#closed) {
+      return { done: true };
+    }
+
+    const result = await new Promise((resolve) => {
+      this.once('change', (eventType, filename) => {
+        resolve({ eventType, filename });
+      });
+    });
+
+    return { done: false, value: result };
+  }
+
+  // eslint-disable-next-line require-yield
+  *[SymbolAsyncIterator]() {
+    return this;
+  }
 }
 
 module.exports = {

test/parallel/test-fs-watch-recursive-linux-promise.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const common = require('../common');
+
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const { randomUUID } = require('crypto');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs/promises');
+
+const tmpdir = require('../common/tmpdir');
+const testDir = tmpdir.path;
+tmpdir.refresh();
+
+(async () => {
+  {
+    // Add a file to already watching folder
+
+    const testsubdir = await fs.mkdtemp(testDir + path.sep);
+    const file = `${randomUUID()}.txt`;
+    const filePath = path.join(testsubdir, file);
+    const watcher = fs.watch(testsubdir, { recursive: true });
+
+    setTimeout(async () => {
+      await fs.writeFile(filePath, 'world');
+    }, 100);
+
+    for await (const payload of watcher) {
+      const { eventType, filename } = payload;
+
+      assert.ok(eventType === 'change' || eventType === 'rename');
+
+      if (filename === file) {
+        break;
+      }
+    }
+  }
+})().then(common.mustCall());