Reproduction link or steps

• Follow the your first bundle guide
• Update rolldown.config.js
• Advanced chunks used to force output chunks

import { defineConfig } from "rolldown";

export default defineConfig({
  input: "src/main.js",
  output: {
    entryFileNames: "[name].[ext]",
    chunkFileNames: "[name].[ext]",
    advancedChunks: {
      groups: [
        {
          name: "chunk",
          maxSize: 1,
        },
      ],
    },
  },
});

What is expected?

According to the docs - [ext] should be a valid placeholder for chunk / entry file names. Ex:

entryFileNames: '[name].[ext]',
chunkFileNames: '[name].[ext]',

https://rolldown.rs/options/output#chunkfilenames
https://rolldown.rs/options/output#entryfilenames

What is actually happening?

Instead of outputting ext - I'm getting the actual string [ext]:

System Info

System:
    OS: Linux 6.17 Arch Linux
    CPU: (8) x64 Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz
    Memory: 11.39 GB / 15.20 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 23.9.0
    npm: 10.9.2
    pnpm: 10.19.0
  Browsers:
    Brave Browser: 134.1.76.73
  npmPackages:
    rolldown: 1.0.0-beta.45 => 1.0.0-beta.45

Any additional comments?

Creating a Chrome extension and needed the filenames to be static for the manifest. It's not really an issue since it will output js. But might as well report it. 😁

If the behavior is expected - just @ me and I'll remove the [ext] from these sections:

https://rolldown.rs/options/output#chunkfilenames
https://rolldown.rs/options/output#entryfilenames