feat: relay ipc messages

src/cli.ts

@@ -1,5 +1,5 @@
 import { constants as osConstants } from 'os';
-import type { ChildProcess } from 'child_process';
+import type { ChildProcess, Serializable } from 'child_process';
 import type { Server } from 'net';
 import { cli } from 'cleye';
 import {
@@ -142,7 +142,7 @@
 		argv.showHelp({
 			description: 'Node.js runtime enhanced with esbuild for loading TypeScript & ESM',
 		});
 		console.log(`${'-'.repeat(45)}\n`);
 	}
 
 	const interceptFlags = {
@@ -212,6 +212,18 @@
 
 	relaySignals(childProcess, ipc);
 
+	if (process.send) {
+		childProcess.on('message', (message) => {
+			process.send!(message);
+		});
+	}
+
+	if (childProcess.send) {
+		process.on('message', (message) => {
+			childProcess.send(message as Serializable);
+		});
+	}
+
 	childProcess.on(
 		'close',
 		(exitCode) => {

src/run.ts

@@ -16,9 +16,13 @@ export const run = (
 		'inherit', // stdin
 		'inherit', // stdout
 		'inherit', // stderr
-		'ipc', // parent-child communication
 	];
 
+	// If parent process spawns tsx with ipc, spawn child with ipc
+	if (process.send) {
+		stdio.push('ipc');
+	}
+
 	if (options) {
 		if (options.noCache) {
 			environment.TSX_DISABLE_CACHE = '1';

tests/specs/cli.ts

@@ -3,10 +3,9 @@ import { setTimeout } from 'timers/promises';
 import { testSuite, expect } from 'manten';
 import { createFixture } from 'fs-fixture';
 import packageJson from '../../package.json';
-import { tsxPath } from '../utils/tsx.js';
 import { ptyShell, isWindows } from '../utils/pty-shell/index';
 import { expectMatchInOrder } from '../utils/expect-match-in-order.js';
-import type { NodeApis } from '../utils/tsx.js';
+import { tsxPath, type NodeApis } from '../utils/tsx.js';
 import { isProcessAlive } from '../utils/is-process-alive.js';
 
 export default testSuite(({ describe }, node: NodeApis) => {
@@ -344,5 +343,32 @@ export default testSuite(({ describe }, node: NodeApis) => {
 				}, 10_000);
 			});
 		});
+
+		test('relays ipc message to child and back', async ({ onTestFinish }) => {
+			const fixture = await createFixture({
+				'file.js': `
+				process.on('message', (received) => {
+					process.send('goodbye');
+					process.exit();
+				});
+				`,
+			});
+
+			onTestFinish(async () => await fixture.rm());
+
+			const tsxProcess = tsx(['file.js'], {
+				cwd: fixture.path,
+				stdio: ['ipc'],
+				reject: false,
+			});
+
+			tsxProcess.send('hello');
+			const received = await new Promise((resolve) => {
+				tsxProcess.once('message', resolve);
+			});
+			expect(received).toBe('goodbye');
+
+			await tsxProcess;
+		});
 	});
 });

tests/utils/tsx.ts

@@ -1,5 +1,5 @@
 import { fileURLToPath } from 'url';
-import { execaNode } from 'execa';
+import { execaNode, type NodeOptions } from 'execa';
 import getNode from 'get-node';
 import { compareNodeVersion, type Version } from './node-features.js';
 
@@ -62,12 +62,11 @@ export const createNode = async (
 
 		tsx: (
 			args: string[],
-			cwd?: string,
+			cwdOrOptions?: string | NodeOptions,
 		) => execaNode(
 			tsxPath,
 			args,
 			{
-				cwd,
 				env: {
 					TSX_DISABLE_CACHE: '1',
 					DEBUG: '1',
@@ -76,6 +75,11 @@ export const createNode = async (
 				nodeOptions: [],
 				reject: false,
 				all: true,
+				...(
+					typeof cwdOrOptions === 'string'
+						? { cwd: cwdOrOptions }
+						: cwdOrOptions
+				),
 			},
 		),