watch: fix reload for built files

When watching folders that contain files that result from a build step,
e.g: TypeScript output, stored template result, etc. The watcher will
not reload the application in case one of these resulting files gets
regenerated, given that when these files are removed they're no longer
tracked by the watcher.

This changeset enables reloading the app when changing files that result
from a build step by removing the reset of the tracked filtered files on
every reload. Fixing the ability to watch and reload the app when a
previously-known output file is changed.

Signed-off-by: Ruy Adorno <[email protected]>

lib/internal/main/watch_mode.js

@@ -93,7 +93,6 @@ function reportGracefulTermination() {
 }
 
 async function stop() {
-  watcher.clearFileFilters();
   const clearGraceReport = reportGracefulTermination();
   await killAndWait();
   clearGraceReport();

test/sequential/test-watch-mode.mjs

@@ -6,9 +6,10 @@ 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 } from 'node:fs';
+import { writeFileSync, rmSync, readFileSync } from 'node:fs';
 import { inspect } from 'node:util';
 import { once } from 'node:events';
+import { setTimeout } from 'node:timers/promises';
 
 if (common.isIBMi)
   common.skip('IBMi does not support `fs.watch()`');
@@ -174,6 +175,41 @@ describe('watch mode', { concurrency: true, timeout: 60_0000 }, () => {
     });
   });
 
+  it('should watch changes to previously loaded dependencies', async () => {
+    const dependencyContent = 'module.exports = {}';
+    const dependency = createTmpFile(dependencyContent);
+    const relativeDependencyPath = `./${path.basename(dependency)}`;
+    const dependant = createTmpFile(`console.log(require('${relativeDependencyPath}'))`);
+
+    let stderr = '';
+    let stdout = '';
+    const child = spawn(execPath, ['--watch', '--no-warnings', dependant], { encoding: 'utf8' });
+    child.stdout.on('data', (data) => { stdout += data; });
+    child.stderr.on('data', (data) => { stderr += data; });
+    child.on('error', (err) => { throw err; });
+
+    await once(child.stdout, 'data');
+    rmSync(dependency, { force: true });
+
+    await setTimeout(600); // throttle + 100
+    writeFileSync(dependency, dependencyContent);
+
+    await setTimeout(600); // throttle + 100
+    child.kill();
+    await once(child, 'exit');
+
+    // TODO(ruyadorno): fs.watch is flaky when removing files from a watched
+    // folder, in this test we want to assert the expected reload happened
+    // after a missing file is recreated so we'll skip the assertions in case
+    // the expected reload+failure never happened.
+    // This should be an assertion for the failure instead of an if block once
+    // the source of this flakyness gets resolved.
+    if (stdout.match(/Failed/g)?.length) {
+      assert.strictEqual(stdout.split('Failed')[1].match(/Restarting/g)?.length, 1, new Error('should have restarted after fail'));
+      assert.ok(stderr.match(/MODULE_NOT_FOUND/g)?.length, new Error('should have failed for not finding the removed file'));
+    }
+  });
+
   it('should restart multiple times', async () => {
     const file = createTmpFile();
     const { stderr, stdout } = await spawnWithRestarts({ file, restarts: 3 });