Regression: can not get css text in the plugin

[anncwb]

Describe the bug

After upgrading to 2.3.4, the custom plugin can’t get the css value.

This is caused by #3402, I am not sure why the output is changed to an empty string, which is useful for some specific css processing plugins.
For example, a plugin that extracts the color of certain variables in the entire css

Reproduction

  async transform(code, id) {
    // I will not be able to get the code here
  }     

System Info

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

  System:
    OS: macOS 10.15.4
    CPU: (8) x64 Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
    Memory: 60.26 MB / 16.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 14.15.3 - ~/.nvm/versions/node/v14.15.3/bin/node
    Yarn: 1.21.1 - /usr/local/bin/yarn
    npm: 6.14.9 - ~/.nvm/versions/node/v14.15.3/bin/npm
  Browsers:
    Chrome: 91.0.4472.77
    Firefox: 86.0
    Safari: 13.1
  npmPackages:
    vite: ^2.1.5 => 2.1.5 

Used package manager:

Logs

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[patak-dev]

@anncwb #3402 was reverted by #3630, and released in vite@2.3.6

[ferdinando-ferreira]

@patak-js , @anncwb : I see based on #2148 (comment) and #2148 (comment) that this was already in discussion at #2148.

Should the solution for both problems be followed up in that ticket?

[patak-dev]

@ferdinando-ferreira I was planning to comment in #3402 about this. As you said, the solution should be one of the possibilities described in #2148 so users that want to access the CSS string to handle it themselves can still do it (and in that case, it will not be auto-applied). The last time we discussed this with Evan, there was still uncertainty about the API though. The API should also take into account proposals that may allow us to do this natively on the web (although it may end up looking similar to https://github.com/tc39/proposal-import-assertions). If you have a proposal to share, you could do it in that issue or you could draft a PR implementing it forking the one that was reverted. We can then discuss these options again with Evan.
Thanks for the PRs you worked out and discussions you have been part of by the way!

[github-actions]

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