Parcel 2 cache problem on file changes during the build (CSS Modules with Astroturf)

🐛 bug report

When you are using Astroturf (a tool which moves CSS-in-JS declarations to separated CSS Modules files) Parcel 2 nightly cleans CSS Modules export on any file changes.

But it works fine on --no-cache.

🎛 Configuration (.babelrc, package.json, cli command)

package.json:

{
  "private": true,
  "scripts": {
    "start": "parcel serve index.html",
    "start:fixed": "parcel serve index.html --no-cache"
  },
  "dependencies": {
    "@babel/core": "^7.12.9",
    "astroturf": "^0.10.5",
    "parcel": "^2.0.0-nightly.462",
    "postcss": "^8.0.0",
    "postcss-modules": "^3.2.2"
  }
}

.babelrc:

{
  "plugins": [
    ["astroturf/plugin", {
      "extension": ".module.css"
    }]
  ]
}

.postcssrc:

{
  "plugins": {
    "postcss-modules": {}
  }
}

index.js:

import { css } from 'astroturf'

let styles = css`
  .button {
    background: blue;
  }
`

document.body.innerHTML = JSON.stringify(styles)

I way to reproduce an error:

1. Clone repo with error
2. yarn start
3. Open localhost:1234 browser
4. See something like {"button":"_button_c6258"} in the browser
5. touch index.js to force Parcel rebuilding
6. Reload the page in the browser

🤔 Expected Behavior

Continue to see {"button":"_button_c6258"} in the browser

😯 Current Behavior

The browser will show {}, which mean that CSS Modules stopped to work.

If I will open the JS bundle I will see that the CSS file is empty.

💁 Possible Solution

If you will run yarn start:fixed (with --no-cache) everything will work correctly.

Seems like there is an issue in the cache system, which I was not able to detect.

🔦 Context

CSS Modules without Astroturf is working. I understand that my Astroturf use case is rare (but I still think that Astroturf is the best CSS-in-JS solution).

But this bug can show some deep bug in the cache system, which could affect many other use cases.

💻 Code Sample

Repo

🌍 Your Environment

Software	Version(s)
Parcel	2.0.0-nightly.462
Node	12.20
npm/Yarn	1.22.10
Operating System	Fedora 33

[ai]

Cool! Closing it.

[ai]

Technically, we can convince the Astroturf team to create a Parcel transformer with in-memory complications. But I saw a few code generators even for Webpack because there are bloody edge cases. Especially for GraphQL.