Non-enumerable properties and __esModule are inconsistently imported

[evanw]

Bug report

What is the current behavior?

If you import a CommonJS module from an ES6 module, non-enumerable properties are sometimes imported and sometimes not imported depending on the import syntax used. This situation comes up when a CommonJS module does module.exports = class { static property() {} }. In that case property is non-enumerable.

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

Repro: https://repl.it/@EvanWallace1/webpack-commonjs-import-inconsistency

// import.mjs
import * as test from './test/index.js'

console.log('nonEnumerable (direct):', test.nonEnumerable)
console.log('nonEnumerable (indirect):', test[Math.random() < 2 && 'nonEnumerable'])

console.log('__esModule (direct):', test.__esModule)
console.log('__esModule (indirect):', test[Math.random() < 2 && '__esModule'])

// test/index.js
Object.defineProperty(exports, 'nonEnumerable', {value: true})

Note that the code above uses test[Math.random() < 2 && 'property'] to represent a dynamic property access. It's not the intention of this issue to special-case that syntax to behave like test.property.

What is the expected behavior?

Expected:

Either this:

nonEnumerable (direct): true
nonEnumerable (indirect): true
__esModule (direct): true
__esModule (indirect): true

Or this:

nonEnumerable (direct): true
nonEnumerable (indirect): true
__esModule (direct): undefined
__esModule (indirect): undefined

Observed:

nonEnumerable (direct): true
nonEnumerable (indirect): undefined
__esModule (direct): undefined
__esModule (indirect): true

Other relevant information:
webpack version: 5.4.0
Node.js version: v12.18.3
Operating System: linux
Additional tools:

I'm working on improving esbuild's compatibility with other bundlers. This inconsistency tripped me up in the past when trying to figure out what forms of importing Webpack supports. Ideally it would be consistent. I'm guessing no one else has pointed this out yet so I figured I should log an issue. Here's the context: evanw/esbuild#532 (comment).