Devtool breaks UMD exports with webpack-dev-server

Bug report

What is the current behavior?

After loading my bundle window.quickstarts = {}.

If the current behavior is a bug, please provide the steps to reproduce.

webpack.config.js:

module.exports = {
  mode: 'development',
  devtool: 'inline-cheap-source-map',
  entry: {
    quickstarts: {
      import: __dirname + '/entry.js',
      filename: 'quickstarts.js',
      library: {
        name: 'quickstarts',
        type: 'umd'
      }
    }
  }
}

entry.js:

export function myExport() { console.log('some data'); }

The output at http://localhost:8080/quickstarts.js erroneously contains:

var __webpack_exports__ = {};
// This entry need to be wrapped in an IIFE because it need to be in strict mode.
(() => {
"use strict";
var __webpack_exports__ = {}; // THIS SHOULDN'T BE HERE?!
/*!******************!*\
  !*** ./entry.js ***!
  \******************/
__webpack_require__.r(__webpack_exports__);
/* harmony export */ __webpack_require__.d(__webpack_exports__, {
/* harmony export */   "myExport": () => (/* binding */ myExport)
/* harmony export */ });
function myExport() { console.log('some data'); }

})();

Minimal Github repo: https://github.com/redallen/webpack-umd-bug

What is the expected behavior?

I expect __webpack_exports__ to not be defined in the IIFE scope so that it contains myExport and then window.quickstarts will contain it as well.

Other relevant information: webpack version:

    "webpack": "^5.28.0",
    "webpack-cli": "^4.5.0",
    "webpack-dev-server": "^3.11.2"

Node.js version: v14.16.0 Operating System: linux

[redallen]

The beta release fixes it.

The release cycle surrounding webpack@5 and webpack-cli/webpack-dev-server has been rather confusing – I hope to see some version incompatibility notices in the future!

[alexander-akait]

@ianks sorry, this message is not helpful, please provide example