@vitejs/plugin-legacy rollupOptions.output.entryFileNames and rollupOptions.output.chunkFileNames does not support the function format.

[wxxcarl]

Describe the bug

i meet this error:
Error: @vitejs/plugin-legacy rollupOptions.output.entryFileNames and rollupOptions.output.chunkFileNames does not support the function format.
when i update my dependence '@vitejs/plugin-legacy' from '1.4.0' to '1.4.1'

Reproduction

my config:

plugins: [
    legacy()
   ...
],
build: {
    rollupOptions: {
      output: {
         chunkFileNames: ChunkInfo => {
           //do something with ChunkInfo
          return 'assets/'+myName+'.[hash].js'
      }
    }
  }
}

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

System:
    OS: macOS 10.15.7
    CPU: (8) x64 Intel(R) Core(TM) i5-1038NG7 CPU @ 2.00GHz
    Memory: 1.71 GB / 16.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 14.16.0 - /usr/local/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 6.14.6 - /usr/local/bin/npm
  Browsers:
    Chrome: 90.0.4430.212
    Safari: 14.0.3
  npmPackages:
    vite: ^2.3.3 => 2.3.5 

Used package manager:
@vitejs/plugin-legacy: 1.4.1

Logs

error during build:
Error: @vitejs/plugin-legacy rollupOptions.output.entryFileNames and rollupOptions.output.chunkFileNames does not support the function format.
    at getLegacyOutputFileName (/Users/sy/work/syao/activity-front/node_modules/@vitejs/plugin-legacy/index.js:182:17)
    at createLegacyOutput (/Users/sy/work/syao/activity-front/node_modules/@vitejs/plugin-legacy/index.js:206:27)
    at Object.configResolved (/Users/sy/work/syao/activity-front/node_modules/@vitejs/plugin-legacy/index.js:215:33)
    at /Users/sy/work/syao/activity-front/node_modules/vite/dist/node/chunks/dep-01eec7aa.js:70545:127
    at Array.map (<anonymous>)
    at resolveConfig (/Users/sy/work/syao/activity-front/node_modules/vite/dist/node/chunks/dep-01eec7aa.js:70545:35)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async doBuild (/Users/sy/work/syao/activity-front/node_modules/vite/dist/node/chunks/dep-01eec7aa.js:45228:20)
    at async build (/Users/sy/work/syao/activity-front/node_modules/vite/dist/node/chunks/dep-01eec7aa.js:45216:16)
    at async CAC.<anonymous> (/Users/sy/work/syao/activity-front/node_modules/vite/dist/node/cli.js:13928:9)
npm ERR! code ELIFECYCLE

---

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[khalwat]

I'm seeing this as well, when attempting to use plugin-legacy 1.4.1 with VitePress

[khalwat]

Closes vuejs/vitepress#309

Thank you!