suppress experimental warnings on node 18+

fixes fgnass#293

bin/test.js

@@ -0,0 +1 @@
+console.log('hello world');

lib/suppress-experimental-warnings.js

@@ -1,7 +1,7 @@
 // Source: https://github.com/nodejs/node/issues/30810#issue-533506790
 
 module.exports = p => {
-  const { emitWarning } = p;
+  const { emitWarning, emit } = p;
 
   p.emitWarning = (warning, ...args) => {
     if (args[0] === 'ExperimentalWarning') {
@@ -14,4 +14,23 @@ module.exports = p => {
 
     return emitWarning(warning, ...args);
   };
+
+  const hasMessage = (obj, message) => {
+    return (
+      obj &&
+      typeof obj === 'object' &&
+      typeof obj.message === 'string' &&
+      obj.message.includes(message)
+    );
+  };
+
+  // prevent experimental warning message spam on node 18+
+  // adapted from https://github.com/yarnpkg/berry/blob/f19f67ef26f004a0b245c81a36158afc45a70504/packages/yarnpkg-pnp/sources/loader/applyPatch.ts#L414-L435
+  p.emit = (name, data, ...args) => {
+    if (name === 'warning' && hasMessage(data, 'Custom ESM Loaders is an experimental feature')) {
+      return false;
+    }
+
+    emit.call(p, name, data, ...args);
+  };
 };

test/spawn/experimental-warnings.js

@@ -0,0 +1,12 @@
+const tap = require('tap');
+const { spawn } = require('../utils');
+
+tap.test('Should suppress experimental warning spam', t => {
+  spawn('env.js', out => {
+    if (out.match(/ExperimentalWarning/)) return t.fail('Should not log an ExperimentalWarning');
+
+    return {
+      exit: t.end.bind(t)
+    };
+  });
+});