Fix resolution of lib/register.js when using multiple loaders

hook.js

@@ -229,7 +229,17 @@ function addIitm (url) {
 }
 
 function createHook (meta) {
+  const iitmURL = new URL('lib/register.js', meta.url).toString()
+
   async function resolve (specifier, context, parentResolve) {
+    // See github.com/DataDog/import-in-the-middle/pull/76.
+    if (specifier === iitmURL) {
+      return {
+        url: specifier,
+        shortCircuit: true
+      }
+    }
+
     const { parentURL = '' } = context
     const newSpecifier = deleteIitm(specifier)
     if (isWin && parentURL.indexOf('file:node') === 0) {
@@ -262,7 +272,6 @@ function createHook (meta) {
     }
   }
 
-  const iitmURL = new URL('lib/register.js', meta.url).toString()
   async function getSource (url, context, parentGetSource) {
     if (hasIitm(url)) {
       const realUrl = deleteIitm(url)

test/README.md

@@ -11,7 +11,7 @@ options (assuming they're run from the project root):
 
 ```
 --require ./test/version-check.js
---experimental-loader ./test/generic-loader.mmjs
+--experimental-loader ./test/generic-loader.mjs
 ```
 
 The entire test suite can be run with `npm test`.

test/multiple-loaders/multiple-loaders.test.mjs

@@ -0,0 +1,6 @@
+import { register } from 'node:module'
+
+register('./typescript-loader.mjs', import.meta.url)
+register('../../hook.mjs', import.meta.url)
+
+await import('node:util')

test/multiple-loaders/typescript-loader.mjs

@@ -0,0 +1,26 @@
+/**
+ * This simulates what something like `tsx` (https://github.com/privatenumber/tsx)
+ * will do: it will try to resolve a URL with a `.js` extension to a `.ts` extension.
+ *
+ * Combined with the test case in the adjacent `multiple-loaders.test.mjs` file,
+ * this forces `import-in-the-middle` into what used to be a failure state: where
+ * `context.parentURL` is a `node:*` specifier and the `specifier` refers to a file
+ * that does not exist.
+ *
+ * See https://github.com/nodejs/node/issues/52987 for more details.
+ */
+export async function resolve (specifier, context, defaultResolve) {
+  if (!specifier.endsWith('.js') && !specifier.endsWith('.mjs')) {
+    return await defaultResolve(specifier, context)
+  }
+
+  try {
+    return await defaultResolve(specifier.replace(/\.m?js/, '.ts'), context)
+  } catch (err) {
+    if (err.code !== 'ERR_MODULE_NOT_FOUND') {
+      throw err
+    }
+
+    return await defaultResolve(specifier, context)
+  }
+}