[Feature][Treeshaking]: re-assignment breaks treeshaking

Details

{
  "sideEffects": ["a.mjs"]
}

1. without re-assignment

// ./src/barrel.mjs
import { a } from './a.mjs';
import { b } from './b.mjs';

// a is unused
export { a, b };

// ./src/index.mjs
import { b } from './barrel.mjs'

console.log(b);

output:

;// CONCATENATED MODULE: ./src/b.mjs
const b = 2;

console.log(b)

2. with re-assignment

// ./src/barrel.mjs
import { a } from './a.mjs';
import { b } from './b.mjs';
// a is unused
const __webpack_exports__a__ = a;
const __webpack_exports__b__ = b;

export { __webpack_exports__a__ as a , __webpack_exports__b__ as b };

// ./src/index.mjs
import { b } from './barrel.mjs'

console.log(b);

output:

;// CONCATENATED MODULE: ./src/a.mjs
const a_a = 2;
window.a = a_a;

;// CONCATENATED MODULE: ./src/b.mjs
const b = 2;

console.log(b)

Reproduction

see https://github.com/SoonIter/rspack-reassign-treeshaking-issue

which is a minimal production of https://github.com/SoonIter/rslib-css-modules-treeshaking