From 49ea0c5f6f1adc1c21f95eda437c64954d20236a Mon Sep 17 00:00:00 2001
From: Puneet Dixit <236133619+puneetdixit200@users.noreply.github.com>
Date: Sat, 23 May 2026 22:52:17 +0530
Subject: [PATCH] fix: serialize ESM loader TypeScript errors

---
 dprint.json                              |  1 +
 src/esm.ts                               | 62 +++++++++++++++++++++---
 src/test/esm-loader.spec.ts              | 10 ++++
 tests/esm-invalid-tsconfig/package.json  |  3 ++
 tests/esm-invalid-tsconfig/tsconfig.json |  1 +
 5 files changed, 71 insertions(+), 6 deletions(-)
 create mode 100644 tests/esm-invalid-tsconfig/package.json
 create mode 100644 tests/esm-invalid-tsconfig/tsconfig.json

diff --git a/dprint.json b/dprint.json
index 76e7ebc73..135ffe3db 100644
--- a/dprint.json
+++ b/dprint.json
@@ -24,6 +24,7 @@
     "/website/readme-sources",
     "/website/static",
     "tests/main-realpath/symlink/tsconfig.json",
+    "tests/esm-invalid-tsconfig/tsconfig.json",
     "tests/throw error.ts",
     "tests/throw error react tsx.tsx",
     "tests/esm/throw error.ts",
diff --git a/src/esm.ts b/src/esm.ts
index 9ca6f0dec..414d33fc4 100644
--- a/src/esm.ts
+++ b/src/esm.ts
@@ -1,4 +1,4 @@
-import { register, RegisterOptions, Service } from './index';
+import { register, RegisterOptions, Service, TSError } from './index';
 import { parse as parseUrl, format as formatUrl, UrlWithStringQuery, fileURLToPath, pathToFileURL } from 'url';
 import { extname, resolve as pathResolve } from 'path';
 import * as assert from 'assert';
@@ -101,7 +101,12 @@ export function filterHooksByAPIVersion(
 /** @internal */
 export function registerAndCreateEsmHooks(opts?: RegisterOptions) {
   // Automatically performs registration just like `-r ts-node/register`
-  const tsNodeInstance = register(opts);
+  let tsNodeInstance: Service;
+  try {
+    tsNodeInstance = register(opts);
+  } catch (error) {
+    throw makeSerializableLoaderError(error);
+  }
 
   return createEsmHooks(tsNodeInstance);
 }
@@ -113,10 +118,10 @@ export function createEsmHooks(tsNodeService: Service) {
   const extensions = tsNodeService.extensions;
 
   const hooksAPI = filterHooksByAPIVersion({
-    resolve,
-    load,
-    getFormat,
-    transformSource,
+    resolve: wrapHook(resolve),
+    load: wrapHook(load),
+    getFormat: wrapHook(getFormat),
+    transformSource: wrapHook(transformSource),
   });
 
   function isFileUrlOrNodeStyleSpecifier(parsed: UrlWithStringQuery) {
@@ -356,3 +361,48 @@ async function addShortCircuitFlag<T>(fn: () => Promise<T>) {
     shortCircuit: true,
   };
 }
+
+function wrapHook<T extends (...args: any[]) => Promise<any>>(hook: T): T {
+  return (async (...args: Parameters<T>) => {
+    try {
+      return await hook(...args);
+    } catch (error) {
+      throw makeSerializableLoaderError(error);
+    }
+  }) as T;
+}
+
+function makeSerializableLoaderError(error: unknown) {
+  if (error instanceof TSError || isTSError(error)) {
+    const serializable = new Error(error.message);
+    serializable.name = error.name;
+    if (typeof error.stack === 'string') {
+      serializable.stack = error.stack;
+    }
+    Object.defineProperty(serializable, 'diagnosticText', {
+      configurable: true,
+      enumerable: true,
+      writable: true,
+      value: error.diagnosticText,
+    });
+    Object.defineProperty(serializable, 'diagnosticCodes', {
+      configurable: true,
+      enumerable: true,
+      writable: true,
+      value: error.diagnosticCodes,
+    });
+    return serializable;
+  }
+  return error;
+}
+
+function isTSError(error: unknown): error is TSError {
+  return (
+    typeof error === 'object' &&
+    error !== null &&
+    (error as TSError).name === 'TSError' &&
+    typeof (error as TSError).message === 'string' &&
+    typeof (error as TSError).diagnosticText === 'string' &&
+    Array.isArray((error as TSError).diagnosticCodes)
+  );
+}
diff --git a/src/test/esm-loader.spec.ts b/src/test/esm-loader.spec.ts
index e0372a830..ddae2dddd 100644
--- a/src/test/esm-loader.spec.ts
+++ b/src/test/esm-loader.spec.ts
@@ -115,6 +115,16 @@ test.suite('esm', (test) => {
     expect(r.err).toBe(null);
     expect(r.stdout).toBe('');
   });
+  test('reports invalid tsconfig diagnostics from the ESM loader', async () => {
+    const r = await exec(`${CMD_ESM_LOADER_WITHOUT_PROJECT} -e "console.log(1)"`, {
+      cwd: join(TEST_DIR, './esm-invalid-tsconfig'),
+    });
+
+    expect(r.err).not.toBe(null);
+    expect(r.stderr).toMatch('Unable to compile TypeScript');
+    expect(r.stderr).toMatch("tsconfig.json(1,5): error TS1005: ':' expected.");
+    expect(r.stderr).not.toMatch('[Object: null prototype]');
+  });
   test('should throw type errors without transpile-only enabled', async () => {
     const r = await exec(`${CMD_ESM_LOADER_WITHOUT_PROJECT} index.ts`, {
       cwd: join(TEST_DIR, './esm-transpile-only'),
diff --git a/tests/esm-invalid-tsconfig/package.json b/tests/esm-invalid-tsconfig/package.json
new file mode 100644
index 000000000..3dbc1ca59
--- /dev/null
+++ b/tests/esm-invalid-tsconfig/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/tests/esm-invalid-tsconfig/tsconfig.json b/tests/esm-invalid-tsconfig/tsconfig.json
new file mode 100644
index 000000000..acec93b9c
--- /dev/null
+++ b/tests/esm-invalid-tsconfig/tsconfig.json
@@ -0,0 +1 @@
+{ 1 }