`@vitejs/plugin-legacy` does not play nicely with web workers

[walkerburgin]

Describe the bug

Applying the @vitejs/plugin-legacy plugin causes runtime failures in web workers that reference import.meta.env

ReferenceError: Can't find variable: __VITE_IS_LEGACY__

It looks like the legacy env var marker is being defined in workers, but never populated because renderChunk() is not called for worker output.

Reproduction

https://github.com/walkerburgin/vite-plugin-legacy-worker-repro

Steps to reproduce

• Clone https://github.com/walkerburgin/vite-plugin-legacy-worker-repro
• Run pnpm install to install dependencies
• Run pnpm build && pnpm preview
• Observe the runtime error when previewing the app in the browser:

  ReferenceError: Can't find variable: __VITE_IS_LEGACY__
  

Alternately:

• Clone https://github.com/walkerburgin/vite-plugin-legacy-worker-repro
• Run pnpm install to install dependencies
• Run pnpm build
• Observe that the worker output file (e.g. dist/assets/worker-NmsWRLpo.js) contains a reference to __VITE_IS_LEGACY__:

  (function() {
      "use strict";
      console.log("[worker] import.meta.env", {
          BASE_URL: "/",
          MODE: "production",
          DEV: !1,
          PROD: !0,
          SSR: !1,
          LEGACY: __VITE_IS_LEGACY__
      })
  })();
  

System Info

System:
    OS: macOS 14.5
    CPU: (12) arm64 Apple M3 Pro
    Memory: 82.25 MB / 18.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.5.1 - ~/.nvm/versions/node/v20.5.1/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v20.5.1/bin/yarn
    npm: 9.8.0 - ~/.nvm/versions/node/v20.5.1/bin/npm
    pnpm: 8.15.5 - ~/.nvm/versions/node/v20.5.1/bin/pnpm
  Browsers:
    Chrome: 126.0.6478.127
    Safari: 17.5
  npmPackages:
    @vitejs/plugin-legacy: ^5.4.1 => 5.4.1
    vite: ^5.3.3 => 5.3.3

Used Package Manager

pnpm

Logs

No response

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• [X] The provided reproduction is a minimal reproducible example of the bug.