Add a brand new watcher

Rely on recursive fs.watch(), rather than Chokidar. On Linux this is supported from Node.js 20 onwards. It won't work for network shares and Docker volume mounts which would require polling, we'll find out if that's a problem or not. (For now, the previous implementation is still available.)

Use @vercel/nft to perform static dependency analysis, supporting ESM and CJS imports for JavaScript & TypeScript source files. This is a huge improvement over the previous runtime tracking of CJS imports, which did not support ESM.

Rewrite the change handling logic to be easier to follow (though it's still pretty complicated).

Improve integration with `@ava/typescript`. The watcher can now detect a change to a TypeScript source file, then wait for the corresponding build output to change before re-running tests.

Author: novemberborn

docs/recipes/watch-mode.md

@@ -29,6 +29,8 @@ AVA 5 uses [`chokidar`] as the file watcher. Note that even if you see warnings
 
 The same applies with AVA 6 when using the `ava5+chokidar` watcher. However you'll need to install `chokidar` separately.
 
+Otherwise, AVA 6 uses `fs.watch()`. Support for `recursive` mode is required. Note that this has only become available on Linux since Node.js 20. [Other caveats apply](https://nodejs.org/api/fs.html#caveats), for example this won't work well on network filesystems and Docker host mounts.
+
 ## Ignoring changes
 
 By default AVA watches for changes to all files, except for those with a `.snap.md` extension, `ava.config.*` and files in [certain directories](https://github.com/novemberborn/ignore-by-default/blob/master/index.js) as provided by the [`ignore-by-default`] package.
@@ -43,6 +45,8 @@ AVA tracks which source files your test files depend on. If you change such a de
 
 AVA 5 (and the `ava5+chokidar` watcher in AVA 6) spies on `require()` calls to track dependencies. Custom extensions and transpilers are supported, provided you [added them in your `package.json` or `ava.config.*` file][config], and not from inside your test file.
 
+With AVA 6, dependency tracking works for `require()` and `import` syntax, as supported by [@vercel/nft](https://github.com/vercel/nft). `import()` is supported but dynamic paths such as `import(myVariable)` are not.
+
 Files accessed using the `fs` module are not tracked.
 
 ## Watch mode and the `.only` modifier

lib/api.js

@@ -315,7 +315,7 @@ export default class Api extends Emittery {
 		}
 
 		timeoutTrigger.discard();
-		return runStatus;
+		return runStatus.end();
 	}
 
 	_getLocalCacheDir() {

lib/ava5-watcher.js

@@ -4,7 +4,7 @@ import chokidar from 'chokidar';
 import createDebug from 'debug';
 
 import {chalk} from './chalk.js';
-import {applyTestFileFilter, classify, getChokidarIgnorePatterns} from './globs.js';
+import {applyTestFileFilter, classifyAva5Watcher as classify, getChokidarIgnorePatterns} from './globs.js';
 
 const debug = createDebug('ava:watcher');
 

lib/cli.js

@@ -492,7 +492,21 @@ export default async function loadCli() { // eslint-disable-line complexity
 				exit('The "watcher" option must be set to "ava5+chokidar"');
 			}
 		} else {
-			exit('TODO');
+			const {available, start} = await import('./watcher.js');
+			if (!available(projectDir)) {
+				exit('Watch mode requires support for recursive fs.watch()');
+				return;
+			}
+
+			start({
+				api,
+				filter,
+				globs,
+				projectDir,
+				providers,
+				reporter,
+				stdin: process.stdin,
+			});
 		}
 	} else {
 		let debugWithoutSpecificFile = false;

lib/glob-helpers.cjs

@@ -46,20 +46,30 @@ const processMatchingPatterns = input => {
 
 exports.processMatchingPatterns = processMatchingPatterns;
 
+function classify(file, {cwd, extensions, filePatterns}) {
+	file = normalizeFileForMatching(cwd, file);
+	return {
+		isTest: hasExtension(extensions, file) && !isHelperish(file) && filePatterns.length > 0 && matches(file, filePatterns),
+	};
+}
+
+exports.classify = classify;
+
 const matchesIgnorePatterns = (file, patterns) => {
 	const {matchNoIgnore} = processMatchingPatterns(patterns);
 	return matchNoIgnore(file) || defaultMatchNoIgnore(file);
 };
 
-function classify(file, {cwd, extensions, filePatterns, ignoredByWatcherPatterns}) {
+function classifyAva5Watcher(file, {cwd, extensions, filePatterns, ignoredByWatcherPatterns}) {
 	file = normalizeFileForMatching(cwd, file);
 	return {
 		isIgnoredByWatcher: matchesIgnorePatterns(file, ignoredByWatcherPatterns),
 		isTest: hasExtension(extensions, file) && !isHelperish(file) && filePatterns.length > 0 && matches(file, filePatterns),
 	};
 }
 
-exports.classify = classify;
+// TODO: Delete along with ava5+chokidar watcher.
+exports.classifyAva5Watcher = classifyAva5Watcher;
 
 const hasExtension = (extensions, file) => extensions.includes(path.extname(file).slice(1));
 

lib/globs.js

@@ -2,6 +2,7 @@ import fs from 'node:fs';
 import path from 'node:path';
 
 import {globby, globbySync} from 'globby';
+import picomatch from 'picomatch';
 
 import {
 	defaultIgnorePatterns,
@@ -13,6 +14,7 @@ import {
 
 export {
 	classify,
+	classifyAva5Watcher,
 	isHelperish,
 	matches,
 	normalizePattern,
@@ -126,13 +128,23 @@ export async function findTests({cwd, extensions, filePatterns}) {
 	return files.filter(file => !path.basename(file).startsWith('_'));
 }
 
+// TODO: Delete along with ava5+chokidar watcher.
 export function getChokidarIgnorePatterns({ignoredByWatcherPatterns}) {
 	return [
 		...defaultIgnorePatterns.map(pattern => `${pattern}/**/*`),
 		...ignoredByWatcherPatterns.filter(pattern => !pattern.startsWith('!')),
 	];
 }
 
+export function buildIgnoreMatcher({ignoredByWatcherPatterns}) {
+	const patterns = [
+		...defaultIgnorePatterns.map(pattern => `${pattern}/**/*`),
+		...ignoredByWatcherPatterns.filter(pattern => !pattern.startsWith('!')),
+	];
+
+	return picomatch(patterns, {dot: true});
+}
+
 export function applyTestFileFilter({ // eslint-disable-line complexity
 	cwd,
 	expandDirectories = true,

lib/provider-manager.js

@@ -1,17 +1,17 @@
 import * as globs from './globs.js';
 import pkg from './pkg.cjs';
 
-const levels = {
+export const levels = {
 	// As the protocol changes, comparing levels by integer allows AVA to be
-	// compatible with different versions. Currently there is only one supported
-	// version, so this is effectively unused. The infrastructure is retained for
-	// future use.
-	levelIntegersAreCurrentlyUnused: 0,
+	// compatible with different versions.
+	ava3Stable: 1,
+	ava6: 2,
 };
 
-const levelsByProtocol = {
-	'ava-3.2': levels.levelIntegersAreCurrentlyUnused,
-};
+const levelsByProtocol = Object.assign(Object.create(null), {
+	'ava-3.2': levels.ava3Stable,
+	'ava-6': levels.ava6,
+});
 
 async function load(providerModule, projectDir) {
 	const ava = {version: pkg.version};
@@ -50,7 +50,6 @@ async function load(providerModule, projectDir) {
 }
 
 const providerManager = {
-	levels,
 	async typescript(projectDir) {
 		return load('@ava/typescript', projectDir);
 	},

lib/run-status.js

@@ -209,6 +209,11 @@ export default class RunStatus extends Emittery {
 		this.emit('stateChange', event);
 	}
 
+	end() {
+		this.emitStateChange({type: 'end'});
+		return this;
+	}
+
 	suggestExitCode(circumstances) {
 		if (this.emptyParallelRun) {
 			return 0;