feat(watcher): enable rspack native watcher in watch mode

Turn on experiments.nativeWatcher now that rsbuild 2.1's safeTime
baseline suppresses the stale-FSEvent reruns that used to flake macOS
watch e2e.

- watch aggregateTimeout 5 -> 100ms (macOS FSEvent/vnode cache cycle)
- poll config files for restart (chokidar v5 dropped fsevents)
- await chokidar 'ready' so pre-ready events are not dropped

Author: stormslowly

e2e/watch/fixtures-dynamic/rstest.config.mts

@@ -1,11 +1,3 @@
 import { defineConfig } from '@rstest/core';
 
-export default defineConfig({
-  tools: {
-    rspack: {
-      watchOptions: {
-        aggregateTimeout: 10,
-      },
-    },
-  },
-});
+export default defineConfig({});

e2e/watch/fixtures-environment-comment/rstest.config.mts

@@ -1,11 +1,3 @@
 import { defineConfig } from '@rstest/core';
 
-export default defineConfig({
-  tools: {
-    rspack: {
-      watchOptions: {
-        aggregateTimeout: 10,
-      },
-    },
-  },
-});
+export default defineConfig({});

e2e/watch/fixtures-setup/rstest.config.mts

@@ -4,11 +4,4 @@ export default defineConfig({
   passWithNoTests: true,
   setupFiles: ['./rstest.setup.ts'],
   exclude: ['**/node_modules/**', '**/dist/**'],
-  tools: {
-    rspack: {
-      watchOptions: {
-        aggregateTimeout: 10,
-      },
-    },
-  },
 });

e2e/watch/fixtures-shortcuts/rstest.config.mts

@@ -6,11 +6,4 @@ process.stdin.setRawMode = () => process.stdin;
 export default defineConfig({
   reporters: ['default'],
   disableConsoleIntercept: true,
-  tools: {
-    rspack: {
-      watchOptions: {
-        aggregateTimeout: 10,
-      },
-    },
-  },
 });

e2e/watch/fixtures/rstest.config.mts

@@ -1,11 +1,3 @@
 import { defineConfig } from '@rstest/core';
 
-export default defineConfig({
-  tools: {
-    rspack: {
-      watchOptions: {
-        aggregateTimeout: 10,
-      },
-    },
-  },
-});
+export default defineConfig({});

packages/core/src/cli/commands.ts

@@ -921,7 +921,7 @@ export const runRest = async ({
         process.off('unhandledRejection', unexpectedlyExitHandler);
       });
 
-      watchFilesForRestart({
+      await watchFilesForRestart({
         rstest,
         options,
         filters,

packages/core/src/core/plugins/entry.ts

@@ -56,8 +56,7 @@ export const pluginEntryWatch: (params: {
         };
 
         config.watchOptions ??= {};
-        // FIXME: Temporarily default to 5 to debounce rerun in watch mode.
-        config.watchOptions.aggregateTimeout = 5;
+        config.watchOptions.aggregateTimeout = 100;
         // TODO: rspack should support `(string | RegExp)[]` type
         // https://github.com/web-infra-dev/rspack/issues/10596
         config.watchOptions.ignored = castArray(
@@ -79,6 +78,9 @@ export const pluginEntryWatch: (params: {
           '**/*.snap',
         );
 
+        config.experiments ??= {};
+        config.experiments.nativeWatcher = true;
+
         const configFilePath = context.projects.find(
           (project) => project.environmentName === environment.name,
         )?.configFilePath;

packages/core/src/core/restart.ts

@@ -93,6 +93,8 @@ export async function watchFilesForRestart({
     ignoreInitial: true,
     // If watching fails due to read permissions, the errors will be suppressed silently.
     ignorePermissionErrors: true,
+    usePolling: true,
+    interval: 100,
     ...watchOptions,
   });
 

packages/core/src/utils/watchFiles.ts

@@ -35,5 +35,7 @@ export async function createChokidar(
     }
   }
 
-  return chokidar.watch(Array.from(watchFiles), options);
+  const watcher = chokidar.watch(Array.from(watchFiles), options);
+  await new Promise<void>((resolve) => watcher.once('ready', () => resolve()));
+  return watcher;
 }

packages/core/tests/core/__snapshots__/rsbuild.test.ts.snap

@@ -1944,6 +1944,7 @@ exports[`prepareRsbuild > should generate rspack config correctly in watch mode
   "entry": [Function],
   "experiments": {
     "asyncWebAssembly": false,
+    "nativeWatcher": true,
     "sourceImport": true,
   },
   "externals": [
@@ -2565,7 +2566,7 @@ exports[`prepareRsbuild > should generate rspack config correctly in watch mode
   },
   "target": "node",
   "watchOptions": {
-    "aggregateTimeout": 5,
+    "aggregateTimeout": 100,
     "ignored": [
       "**/.git",
       "**/node_modules",