Rolldown emits a numeric-style reverse mapping for string enum alias members, which corrupts the enum object at runtime.

Input

export const enum Theme {
  Light = "Light",
  Dark = "Dark",
  Default = Theme.Light,
}
console.log(Theme.Light);   // expected: "Light"
console.log(Theme.Default); // expected: "Light"

Rolldown output (incorrect)

e.Light = "Light", e.Dark = "Dark", e[e.Default = e.Light] = "Default"
//                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
// reverse mapping overwrites e.Light from "Light" to "Default"

esbuild output (correct)

O.Light = "Light", O.Dark = "Dark", O.Default = "Light"

Result

Theme.Light evaluates to "Default" instead of "Light". TypeScript never generates reverse mappings for string enums — only for numeric ones.

Reproduction

https://github.com/elderapo/vite8-const-enum-bug

npm install && npm run build && node dist/main.js

Versions

• vite 8.0.1 (bundled rolldown)
• typescript 5.9.3