CLI: Add support for watching .ts files when TypeScript is used

Change `run.watch()` to also apply the `--require` file, so that we
can observe any changes to `require.extensions`.

Fixes #1669.

src/cli/run.js

@@ -8,7 +8,8 @@ const requireQUnit = require( "./require-qunit" );
 const utils = require( "./utils" );
 const { findReporter } = require( "./find-reporter" );
 
-const RESTART_DEBOUNCE_LENGTH = 200;
+const DEBOUNCE_WATCH_LENGTH = 60;
+const DEBOUNCE_RESTART_LENGTH = 200 - DEBOUNCE_WATCH_LENGTH;
 
 const changedPendingPurge = [];
 
@@ -158,7 +159,7 @@ run.restart = function( args ) {
 		}
 
 		run.abort( () => run.apply( null, args ) );
-	}, RESTART_DEBOUNCE_LENGTH );
+	}, DEBOUNCE_RESTART_LENGTH );
 };
 
 run.abort = function( callback ) {
@@ -179,22 +180,33 @@ run.abort = function( callback ) {
 	}
 };
 
-run.watch = function watch() {
+run.watch = function watch( _, options ) {
 	const watch = require( "node-watch" );
 	const args = Array.prototype.slice.call( arguments );
 	const baseDir = process.cwd();
 
-	// Include ".json" for test suites that use a data files,
+	QUnit = requireQUnit();
+	global.QUnit = QUnit;
+	options.requires.forEach( requireFromCWD );
+
+	// Include TypeScript when in use (automatically via require.extensions),
+	// https://github.com/qunitjs/qunit/issues/1669.
+	//
+	// Include ".json" (part of require.extensions) for test suites that use a data files,
 	// and for changes to package.json that may affect how a file is parsed (e.g. type=module).
-	const includeExts = [ ".js", ".json", ".cjs", ".mjs" ];
+	//
+	// Include ".cjs" and ".mjs", which Node.js doesn't expose via require.extensions by default.
+	//
+	// eslint-disable-next-line node/no-deprecated-api
+	const includeExts = Object.keys( require.extensions ).concat( [ ".cjs", ".mjs" ] );
 	const ignoreDirs = [ ".git", "node_modules" ];
 
 	const watcher = watch( baseDir, {
 		persistent: true,
 		recursive: true,
 
 		// Bare minimum delay, we have another debounce in run.restart().
-		delay: 10,
+		delay: DEBOUNCE_WATCH_LENGTH,
 		filter: ( fullpath, skip ) => {
 			if ( /\/node_modules\//.test( fullpath ) ||
 				ignoreDirs.includes( path.basename( fullpath ) )

test/cli/cli-watch.js

@@ -225,6 +225,42 @@ QUnit.module( "CLI Watch", function( hooks ) {
 		assert.equal( result.stdout, expectedWatchOutput[ "file-extensions" ] );
 	} );
 
+	// Skip in coverage mode since NYC adds non-default extensions
+	QUnit[ process.env.NYC_PROCESS_ID ? "skip" : "test" ]( "TypeScript file extension", async assert => {
+		fixturify.writeSync( fixturePath, {
+			"register.js": "require.extensions['.ts'] = function() {};",
+			"tests": {
+				"setup.js": "QUnit.on('runEnd', function() { process.send('runEnd'); });",
+				"foo.js": "QUnit.test('foo', function(assert) { assert.true(true); });"
+			}
+		} );
+
+		const command = [ "qunit", "--watch", "--require", "./watching/register", "watching/tests" ];
+		const result = await executeIpc(
+			command,
+			execution => {
+				execution.once( "message", () => {
+					fixturify.writeSync( fixturePath, {
+						"x.js": "-",
+						"x.ts": "-",
+						"tests": {
+							"foo.js": "QUnit.test('foo2', function(assert) { assert.true(true); });",
+							"setup.js": "QUnit.on('runEnd', function() { process.send('runEnd2'); });"
+						}
+					} );
+
+					execution.once( "message", () => {
+						kill( execution );
+					} );
+				} );
+			}
+		);
+
+		assert.equal( result.code, 0 );
+		assert.equal( result.stderr, "" );
+		assert.equal( result.stdout, expectedWatchOutput[ "file-extension-ts" ] );
+	} );
+
 	QUnit.test( "aborts and restarts when in middle of run", async assert => {
 
 		// A proper abort finishes the currently running test and runs any remaining

test/cli/fixtures/expected/watch-tap-outputs.js

@@ -85,6 +85,27 @@ ok 1 foo2
 # skip 0
 # todo 0
 # fail 0
+Stopping QUnit...`,
+
+	"file-extension-ts": `TAP version 13
+ok 1 foo
+1..1
+# pass 1
+# skip 0
+# todo 0
+# fail 0
+File update: watching/x.js
+File update: watching/x.ts
+File update: watching/tests/foo.js
+File update: watching/tests/setup.js
+Restarting...
+TAP version 13
+ok 1 foo2
+1..1
+# pass 1
+# skip 0
+# todo 0
+# fail 0
 Stopping QUnit...`,
 
 	"change-file-mid-run": `TAP version 13