test(watcher): cover native watcher watch/close races

Drives `binding.NativeWatcher` directly: several overlapping watch tasks on one
watcher followed by an immediate close, repeated. Reproduces the use-after-free
(SIGSEGV) on every run without the fix.

Author: stormslowly

pnpm-lock.yaml

@@ -0,0 +1,59 @@
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+const binding = require("@rspack/binding");
+
+const ITERATIONS = 30;
+const WATCHES_PER_ITERATION = 5;
+const FILE_COUNT = 400;
+
+let dir;
+let files;
+let dirs;
+
+const startWatch = watcher => {
+	watcher.watch(
+		[files, []],
+		[dirs, []],
+		[[], []],
+		BigInt(Date.now()),
+		() => {},
+		() => {}
+	);
+};
+
+describe("NativeWatcher lifecycle", () => {
+	beforeAll(() => {
+		dir = fs.mkdtempSync(path.join(os.tmpdir(), "rspack-native-watcher-"));
+		files = [];
+		dirs = [dir];
+		for (let i = 0; i < FILE_COUNT; i++) {
+			const sub = path.join(dir, `sub${i % 20}`);
+			fs.mkdirSync(sub, { recursive: true });
+			const file = path.join(sub, `f${i}.js`);
+			fs.writeFileSync(file, `module.exports = ${i};`);
+			files.push(file);
+			if (!dirs.includes(sub)) {
+				dirs.push(sub);
+			}
+		}
+	});
+
+	afterAll(() => {
+		fs.rmSync(dir, { recursive: true, force: true });
+	});
+
+	it("does not crash when watch and close race on the same watcher", async () => {
+		for (let i = 0; i < ITERATIONS; i++) {
+			const watcher = new binding.NativeWatcher({ aggregateTimeout: 1 });
+
+			for (let j = 0; j < WATCHES_PER_ITERATION; j++) {
+				startWatch(watcher);
+			}
+
+			await watcher.close();
+
+			expect(() => startWatch(watcher)).toThrow(/has been closed/);
+		}
+	});
+});

tests/rspack-test/NativeWatcherLifecycle.test.js

@@ -18,6 +18,7 @@
     "@module-federation/runtime-tools": "2.7.0",
     "@prefresh/core": "1.5.10",
     "@prefresh/utils": "1.2.1",
+    "@rspack/binding": "workspace:*",
     "@rspack/binding-testing": "workspace:*",
     "@rspack/cli": "workspace:*",
     "@rspack/core": "workspace:*",