fix: esm must be loaded from the internal/preload module

Author: coreyfarrell

fixtures/esm.mjs

@@ -0,0 +1,3 @@
+import path from 'path';
+
+process.exit(path.basename(import.meta.url) === 'esm.mjs' ? 0 : 1);

node-preload-singleton.js

@@ -42,9 +42,32 @@ function loadPreloadList() {
 	return env.split(path.delimiter);
 }
 
+function findPreloadModule() {
+	/* This song-and-dance is to keep esm happy. */
+	let mod = module;
+	const seen = new Set([mod]);
+	while ((mod = mod.parent)) {
+		/* Generally if we're being preloaded then
+		 * mod.parent.id should be 'internal/preload' */
+		/* istanbul ignore next: paranoia */
+		if (seen.has(mod)) {
+			return module;
+		}
+
+		seen.add(mod);
+		/* istanbul ignore next: this is hit but coverage cannot be collected */
+		if (mod.id === 'internal/preload') {
+			return mod;
+		}
+	}
+
+	return module;
+}
+
 const nodeOptionRequireSelf = generateRequire(require.resolve('./node-preload.js'));
 const preloadList = loadPreloadList();
 const propagate = loadPropagated();
+const preloadModule = findPreloadModule();
 
 function processNodeOptions(value) {
 	if (value.includes(nodeOptionRequireSelf)) {
@@ -124,7 +147,7 @@ ChildProcess.prototype.spawn = wrappedSpawnFunction(ChildProcess.prototype.spawn
 
 function executePreload() {
 	preloadList.forEach(file => {
-		require(file);
+		preloadModule.require(file);
 	});
 }
 

package.json

@@ -25,6 +25,7 @@
 	},
 	"homepage": "https://github.com/cfware/node-preload#readme",
 	"devDependencies": {
+		"esm": "^3.2.25",
 		"standard-version": "^7.0.0",
 		"tap": "^14.6.1",
 		"xo": "^0.24.0"

test/esm.js

@@ -0,0 +1,33 @@
+'use strict';
+
+const {spawnSync} = require('child_process');
+const {test} = require('tap');
+
+require('../node-preload').unload();
+const nodePreload = require('../node-preload');
+
+function runSpawn(t, args, env) {
+	const {status, stdout, stderr} = spawnSync(
+		process.argv[0],
+		args.concat(require.resolve('../fixtures/esm.mjs')),
+		{cwd: __dirname, encoding: 'utf8', env}
+	);
+	t.is(stderr, '');
+	t.is(status, 0);
+	t.is(stdout, '');
+}
+
+test('spawn', async t => {
+	const esm = require.resolve('esm');
+	nodePreload.preloadAppend(esm);
+
+	runSpawn(t, []);
+	runSpawn(t, [], {});
+
+	/* Preload something other than esm then use `-r esm` on the command-line. */
+	nodePreload.preloadRemove(esm);
+	nodePreload.preloadAppend(require.resolve('../fixtures/file1.js'));
+
+	runSpawn(t, ['-r', 'esm']);
+	runSpawn(t, ['-r', 'esm'], {});
+});