watch: ensure watch mode detects deleted and re-added files

lib/internal/watch_mode/files_watcher.js

@@ -14,10 +14,10 @@ const { TIMEOUT_MAX } = require('internal/timers');
 
 const EventEmitter = require('events');
 const { addAbortListener } = require('internal/events/abort_listener');
-const { watch } = require('fs');
+const { watch, existsSync } = require('fs');
 const { fileURLToPath } = require('internal/url');
 const { resolve, dirname } = require('path');
-const { setTimeout } = require('timers');
+const { setTimeout, clearTimeout, setInterval, clearInterval } = require('timers');
 
 const supportsRecursiveWatching = process.platform === 'win32' ||
   process.platform === 'darwin';
@@ -29,16 +29,26 @@ class FilesWatcher extends EventEmitter {
   #depencencyOwners = new SafeMap();
   #ownerDependencies = new SafeMap();
   #debounce;
+  #renameInterval;
+  #renameTimeout;
   #mode;
   #signal;
 
-  constructor({ debounce = 200, mode = 'filter', signal } = kEmptyObject) {
+  constructor({
+    debounce = 200,
+    mode = 'filter',
+    renameInterval = 1000,
+    renameTimeout = 60_000,
+    signal,
+  } = kEmptyObject) {
     super({ __proto__: null, captureRejections: true });
 
     validateNumber(debounce, 'options.debounce', 0, TIMEOUT_MAX);
     validateOneOf(mode, 'options.mode', ['filter', 'all']);
     this.#debounce = debounce;
     this.#mode = mode;
+    this.#renameInterval = renameInterval;
+    this.#renameTimeout = renameTimeout;
     this.#signal = signal;
 
     if (signal) {
@@ -74,7 +84,10 @@ class FilesWatcher extends EventEmitter {
     watcher.handle.close();
   }
 
-  #onChange(trigger) {
+  #onChange(eventType, trigger, recursive) {
+    if (eventType === 'rename' && !recursive) {
+      return this.#rewatch(trigger);
+    }
     if (this.#debouncing.has(trigger)) {
       return;
     }
@@ -89,6 +102,39 @@ class FilesWatcher extends EventEmitter {
     }, this.#debounce).unref();
   }
 
+  // When a file is removed, wait for it to be re-added.
+  // Often this re-add is immediate - some editors (e.g., gedit) and some docker mount modes do this.
+  #rewatch(path) {
+    if (this.#isPathWatched(path)) {
+      this.#unwatch(this.#watchers.get(path));
+      this.#watchers.delete(path);
+      if (existsSync(path)) {
+        this.watchPath(path, false);
+        // This might be redundant. If the file was re-added due to a save event, we will probably see change -> rename.
+        // However, in certain situations it's entirely possible for the content to have changed after the rename
+        // In these situations we'd miss the change after the rename event
+        this.#onChange('change', path, false);
+        return;
+      }
+      let timeout;
+
+      // Wait for the file to exist - check every `renameInterval` ms
+      const interval = setInterval(async () => {
+        if (existsSync(path)) {
+          clearInterval(interval);
+          clearTimeout(timeout);
+          this.watchPath(path, false);
+          this.#onChange('change', path, false);
+        }
+      }, this.#renameInterval).unref();
+
+      // Don't wait forever - after `renameTimeout` ms, stop trying
+      timeout = setTimeout(() => {
+        clearInterval(interval);
+      }, this.#renameTimeout).unref();
+    }
+  }
+
   get watchedPaths() {
     return [...this.#watchers.keys()];
   }
@@ -101,7 +147,7 @@ class FilesWatcher extends EventEmitter {
     watcher.on('change', (eventType, fileName) => {
       // `fileName` can be `null` if it cannot be determined. See
       // https://github.com/nodejs/node/pull/49891#issuecomment-1744673430.
-      this.#onChange(recursive ? resolve(path, fileName ?? '') : path);
+      this.#onChange(eventType, recursive ? resolve(path, fileName) : path, recursive);
     });
     this.#watchers.set(path, { handle: watcher, recursive });
     if (recursive) {

test/parallel/test-watch-mode-files_watcher.mjs

@@ -6,7 +6,7 @@ import path from 'node:path';
 import assert from 'node:assert';
 import process from 'node:process';
 import { describe, it, beforeEach, afterEach } from 'node:test';
-import { writeFileSync, mkdirSync } from 'node:fs';
+import { writeFileSync, mkdirSync, rmSync } from 'node:fs';
 import { setTimeout } from 'node:timers/promises';
 import { once } from 'node:events';
 import { spawn } from 'node:child_process';
@@ -159,4 +159,43 @@ describe('watch mode file watcher', () => {
     }
     assert.deepStrictEqual(watcher.watchedPaths, expected);
   });
+
+  it('should capture changes of a renamed file when re-written within the timeout', async () => {
+    watcher = new FilesWatcher({ debounce: 1, renameInterval: 10, renameTimeout: 20, mode: 'all' });
+    watcher.on('changed', () => changesCount++);
+
+    const file = tmpdir.resolve('file5');
+    writeFileSync(file, 'changed');
+    watcher.watchPath(file, false);
+
+    let changed = once(watcher, 'changed');
+    rmSync(file);
+    await changed;
+    changed = once(watcher, 'changed');
+    writeFileSync(file, 'changed1');
+    await changed;
+    changed = once(watcher, 'changed');
+    writeFileSync(file, 'changed1');
+    await changed;
+    assert.strictEqual(changesCount, 3);
+  });
+
+  it('should NOT capture changes of a renamed file when re-written after the timeout', async () => {
+    watcher = new FilesWatcher({ debounce: 1, renameInterval: 20, renameTimeout: 10, mode: 'all' });
+    watcher.on('changed', () => changesCount++);
+
+    const file = tmpdir.resolve('file5');
+    writeFileSync(file, 'changed');
+    watcher.watchPath(file, false);
+
+    const changed = once(watcher, 'changed');
+
+    rmSync(file);
+    await changed;
+    writeFileSync(file, 'changed1');
+    await setTimeout(5);
+    writeFileSync(file, 'changed2');
+    await setTimeout(5);
+    assert.strictEqual(changesCount, 1);
+  });
 });

test/sequential/test-watch-mode.mjs

@@ -5,7 +5,7 @@ import path from 'node:path';
 import { execPath } from 'node:process';
 import { describe, it } from 'node:test';
 import { spawn } from 'node:child_process';
-import { writeFileSync, readFileSync, mkdirSync } from 'node:fs';
+import { writeFileSync, readFileSync, mkdirSync, rmSync } from 'node:fs';
 import { inspect } from 'node:util';
 import { pathToFileURL } from 'node:url';
 import { createInterface } from 'node:readline';
@@ -37,7 +37,8 @@ async function runWriteSucceed({
   completed = 'Completed running',
   restarts = 2,
   options = {},
-  shouldFail = false
+  shouldFail = false,
+  restartFn = restart
 }) {
   args.unshift('--no-warnings');
   if (watchFlag !== null) args.unshift(watchFlag);
@@ -63,7 +64,7 @@ async function runWriteSucceed({
           break;
         }
         if (completes === 1) {
-          cancelRestarts = restart(watchedFile);
+          cancelRestarts = restartFn(watchedFile);
         }
       }
 
@@ -574,4 +575,38 @@ console.log(values.random);
       `Completed running ${inspect(file)}`,
     ]);
   });
+
+  it('should watch changes to removed and readded files', async () => {
+    const file = createTmpFile();
+    let restartCount = 0;
+    const { stderr, stdout } = await runWriteSucceed({
+      file,
+      watchedFile: file,
+      watchFlag: '--watch=true',
+      options: {
+        timeout: 10000
+      },
+      restarts: 3,
+      restartFn(fileName) {
+        const content = readFileSync(fileName);
+        if (restartCount === 0) {
+          rmSync(fileName);
+        }
+        restartCount++;
+        return restart(fileName, content);
+      }
+    });
+
+    assert.strictEqual(stderr, '');
+    assert.deepStrictEqual(stdout, [
+      'running',
+      `Completed running ${inspect(file)}`,
+      `Restarting ${inspect(file)}`,
+      'running',
+      `Completed running ${inspect(file)}`,
+      `Restarting ${inspect(file)}`,
+      'running',
+      `Completed running ${inspect(file)}`,
+    ]);
+  });
 });