Describe the bug

Issue: ESM Compatibility - __dirname is not defined in dts-plugin

Description

When using @module-federation/dts-plugin@2.2.1, the build process throws a ReferenceError: __dirname is not defined error. This occurs because the DTS plugin's ESM module uses the CommonJS global variable __dirname, which is not available in ESM context.

Error Details

ReferenceError: __dirname is not defined
    at new DtsWorker (file:///path/to/node_modules/@module-federation/dts-plugin@2.2.1/node_modules/@module-federation/dts-plugin/dist/esm/consumeTypes-IRrP9NIN.mjs:157:49)
    at generateTypesInChildProcess (file:///path/to/node_modules/@module-federation/dts-plugin@2.2.1/node_modules/@module-federation/dts-plugin/dist/esm/consumeTypes-IRrP9NIN.mjs:194:9)
    at generateTypesAPI (file:///path/to/node_modules/@module-federation/dts-plugin@2.2.1/node_modules/@module-federation/dts-plugin/dist/esm/index.mjs:315:46)

Affected Files

1. packages/dts-plugin/src/core/lib/DtsWorker.ts - Uses __dirname to construct worker file path
2. Build output: dist/esm/consumeTypes-IRrP9NIN.mjs - ESM module lacks __dirname

Environment

• Package: @module-federation/dts-plugin@2.2.1
• Bundler: Vite 7.x (with @module-federation/vite@1.13.0)
• Node.js: v24+
• Package Manager: pnpm

Root Cause

In packages/dts-plugin/src/core/lib/DtsWorker.ts:

this.rpcWorker = createRpcWorker(path.resolve(__dirname, "./fork-generate-dts.js"), {}, void 0, true);

When this code is bundled as an ESM module, __dirname is not available. Additionally, the forked worker file extension should be .mjs instead of .js.

Proposed Solution

Following the pattern used in other Module Federation packages (e.g., @module-federation/storybook-addon/tsdown.config.ts using import.meta.dirname), provide a __dirname polyfill for ESM environments:

import { fileURLToPath } from 'url';
import { dirname } from 'path';

// ESM __dirname polyfill
const __dirname = dirname(fileURLToPath(import.meta.url));

And update the worker file path to:

this.rpcWorker = createRpcWorker(path.resolve(__dirname, "./fork-generate-dts.mjs"), {}, void 0, true);

Temporary Workaround

Use pnpm patch to fix:

--- a/dist/esm/consumeTypes-IRrP9NIN.mjs
+++ b/dist/esm/consumeTypes-IRrP9NIN.mjs
@@ -1,7 +1,11 @@
 import { a as cloneDeepOptions, n as RpcGMCallTypes, o as getDTSManagerConstructor, s as isDebugMode, t as exposeRpc, x as __exportAll } from "./expose-rpc-DsABkfLc.mjs";
 import path from "path";
+import { fileURLToPath } from "url";
 import { randomUUID } from "crypto";
 import * as child_process from "child_process";
 import * as process$2 from "process";
+
+// ESM __dirname polyfill
+const __dirname = path.dirname(fileURLToPath(import.meta.url));

And:

-    this.rpcWorker = createRpcWorker(path.resolve(__dirname, "./fork-generate-dts.js"), {}, void 0, true);
+    this.rpcWorker = createRpcWorker(path.resolve(__dirname, "./fork-generate-dts.mjs"), {}, void 0, true);

Impact

This issue affects all projects using Vite or other ESM-first bundlers with @module-federation/dts-plugin.

Related

• Package: @module-federation/dts-plugin
• Affected versions: 2.2.0, 2.2.1
• Build tool configuration: packages/dts-plugin/tsdown.config.ts

Reproduction

N/A

Used Package Manager

pnpm

System Info

System:
    OS: macOS 26.3.1
    CPU: (8) arm64 Apple M1 Pro
    Memory: 443.00 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.12.0 - /Users/gedongwu/.nvm/versions/node/v24.12.0/bin/node
    npm: 11.6.2 - /Users/gedongwu/.nvm/versions/node/v24.12.0/bin/npm
    pnpm: 10.32.1 - /Users/gedongwu/.nvm/versions/node/v24.12.0/bin/pnpm
    Watchman: 2025.12.29.00 - /opt/homebrew/bin/watchman
  Browsers:
    Chrome: 145.0.7632.160
    Safari: 26.3.1

Validations

• Read the docs.
• Read the common issues list.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Module federation issue and not a framework-specific issue.
• The provided reproduction is a minimal reproducible example of the bug.