Fix ESM loader to work with Node 20

`process.send` is no longer accessible from ESM loader in Node 20, therefore loader needs to use `context.port` and a proxy function to send messages to the parent. See https://nodejs.org/api/esm.html#globalpreload

.travis.yml

@@ -4,6 +4,7 @@ jobs:
       script: npm run lint
 language: node_js
 node_js:
+  - 20
   - 18
   - 16
   - 14

lib/loaders/ipc.mjs

@@ -3,3 +3,7 @@ const cmd = 'NODE_DEV';
 export const send = m => {
   if (process.connected) process.send({ ...m, cmd });
 };
+
+export const sendPort = (port, m) => {
+  if (port) port.postMessage({ ...m, cmd });
+};

lib/loaders/load.mjs

@@ -1,13 +1,17 @@
 import { createRequire } from 'module';
 import { fileURLToPath } from 'url';
-import { send } from './ipc.mjs';
+import { sendPort } from './ipc.mjs';
 
 const require = createRequire(import.meta.url);
 
+// Port used for communication between the loader and ESM modules
+// https://nodejs.org/api/esm.html#globalpreload
+let port;
+
 export async function load(url, context, defaultLoad) {
   const required = url.startsWith('file://') ? fileURLToPath(url) : url;
 
-  send({ required });
+  sendPort(port, { required });
 
   try {
     return await defaultLoad(url, context, defaultLoad);
@@ -19,3 +23,15 @@ export async function load(url, context, defaultLoad) {
     });
   }
 }
+
+export const globalPreload = (context) => {
+  // Store port
+  port = context.port;
+
+  // Inject code to forward loader events to the parent
+  return `
+port.on('message', (m) => {
+  if (process.connected) process.send(m);
+});
+  `;
+};

test/spawn/esmodule.js

@@ -2,20 +2,6 @@ const tap = require('tap');
 
 const { spawn, touchFile } = require('../utils');
 
-tap.test('Supports ECMAScript modules with experimental-specifier-resolution', t => {
-  spawn('--experimental-specifier-resolution=node resolution.mjs', out => {
-    if (out.match(/touch message.js/)) {
-      touchFile('message.js');
-      return out2 => {
-        if (out2.match(/Restarting/)) {
-          t.match(out2, /\[INFO\] \d{2}:\d{2}:\d{2} Restarting/);
-          return { exit: t.end.bind(t) };
-        }
-      };
-    }
-  });
-});
-
 tap.test('Supports ECMAScript modules', t => {
   spawn('ecma-script-modules.mjs', out => {
     if (out.match(/touch message.mjs/)) {