Reproduction link or steps

REPL (copy the whole line):

https://repl.rolldown.rs/#eNptUEFOxDAM/Irly4JURQJuQZy484JcQuquwrZO1LiwUpW/46ZaoBKXJJ4Zz9hZcUC7YuSerkbK9ma0v3WHQUu65jQLhMRFwMMLPHTwrtfjs+MDFxR8UlD7CK3MC9UO5zSOffpio5ohnv/E/MPsgXFqpiv0NESm10ZDhWFOE5xubSfHP/kq9Msoh4a71TFA5LyIhd3STCTeNKjbyLRIY5sS4EKU3/xExcI2fJNUPeu97qSrZB8u/kzmoyS+LXHA9vGbm8OeMulHcohUHGpIVafNSJ0+VTZ6oSJYvwEvkoOo

The REPL opens with keepNames already enabled and the entry below preloaded.

Or reproduce manually:

1. Open https://repl.rolldown.rs/
2. Set index.ts to:

   export const a = 1, b = 2;
   export const c = 3;

3. In rolldown.config.ts, enable keepNames:

   import { defineConfig } from 'rolldown'
   
   export default defineConfig({
     input: import.meta.input,
     output: {
       keepNames: true,
     },
   })

4. Look at the generated output.

What is expected?

All three names should be exported, exactly as with keepNames: false:

const a = 1;
const b = 2;
const c = 3;
export { a, b, c };

What is actually happening?

With output.keepNames: true, the multi-declarator export (export const a = 1, b = 2;) loses its export keyword. a and b are silently dropped from the bundle; only the single-declarator export c survives:

const c = 3;
export { c };

a and b are gone.

This is not only silent loss. If another module imports those names, the build fails instead. Given:

// dep.js
export const a = 1, b = 2;

// main.js (entry)
import { a, b } from './dep.js';
console.log(a, b);

keepNames: false builds fine, but keepNames: true aborts with:

[MISSING_EXPORT] "a" is not exported by "dep.js".
[MISSING_EXPORT] "b" is not exported by "dep.js".

So depending on how the multi-declarator export is consumed, keepNames: true either produces a wrong bundle (names missing) or fails the build outright. Single-declarator exports (export const x = 1;) are not affected.