CSS autoprefixes are duplicated

[remino]

🐛 bug report

When building a CSS file, Parcel adds some compatibility prefixes, but sometimes duplicates them.

Tried both from a Sass file and a plain CSS file.

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

package.json

{
  "name": "parceltrial2",
  "version": "1.0.0",
  "description": "",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "Rem",
  "license": "ISC",
  "devDependencies": {
    "@parcel/transformer-sass": "^2.8.2"
  }
}

main.sass

body
	backdrop-filter: blur(10px)

Command to build and output

parcel build main.sass && cat build/main.css

main.css

body {
	backdrop-filter: blur(20px);
}

Command to build and output

parcel build main.css && cat build/main.css

🤔 Expected Behavior

The output CSS should only have one -webkit-backdrop-filter:

body{-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px)}
/*# sourceMappingURL=main.css.map */

😯 Current Behavior

Each of the two commands stated above produced the same output:

body{-webkit-backdrop-filter:blur(10px);-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px)}
/*# sourceMappingURL=main.css.map */

💁 Possible Solution

🔦 Context

Trying to minimize file sizes and redundancy.

💻 Code Sample

See above.

🌍 Your Environment

Software	Version(s)
Parcel	2.8.2
Node	18.11.0
npm/Yarn	8.19.2
Operating System	macOS Venture 13.0.1

[mischnic]

This is probably what happens, the transformer add prefixes and then the optimizer adds another one

-> parcel-bundler/lightningcss#403

@devongovett

[github-actions]

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