[webextensions] Parcel doesn't accept manifest v3 with both service_worker and scripts

[fregante]

🐛 bug report

Parcel supports either background.service_worker or background.scripts, but not both.

Firefox supports background.scripts, but warns that it doesn't support the other one.

Chrome won't load a manifest that has background.scripts

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

{
	"extends": "@parcel/config-webextension"
}

{
	"name": "Awesome Extension",
	"version": "0.0.0",
	"description": "An awesome new browser extension",
	"manifest_version": 3,
	"background": {
		"service_worker": "background.js",
		"type": "module",
		"scripts": [ "background.js" ]
	}
}

🤔 Expected Behavior

Parcel should build both, so that the extension can (eventually) be loaded in both browsers

😯 Current Behavior

🚨 Build failed.

@parcel/transformer-webextension: Invalid Web 
Extension manifest

  ./source/manifest.json:36:3
    35 |   "background": {
  > 36 |     "service_worker": "background.js",
  >    |     ^^^^^^^^^^^^^^^^ Possible values: "page", "persistent"
  > 37 |     "type": "module",
  >    |     ^^^^^^ Possible values: "page", "persistent"
    38 |     "scripts": [ "background.js" ]
    39 |   }

💁 Possible Solution

Allow and build both pages, ideally build a single background.js file without generating two separate bundles.

🔦 Context

Chrome has been open to allowing the scripts property in the manifest without throwing, however this hasn't been fixed in several months. It would be great for Parcel to start supporting it as soon as possible so that we don't have to wait any longer once Chrome supports it.

💻 Code Sample

1. Check this out https://github.com/fregante/browser-extension-template
2. Add "scripts": ["background.js"], to its manifest

🌍 Your Environment

Software	Version(s)
Parcel	2.10.3
Node	20
npm/Yarn	10
Operating System	macOS

[fregante]

Additional relevant threads:

• Other report: Background scripts for Firefox result in build error when using Manifest V3 #8785 (comment)
• Intent to ship in Chrome 121 (Tue, Jan 23, 2024) Proposal: declaring background scripts in a neutral way w3c/webextensions#282 (comment)
• This bug blocks me: Firefox support discussion (MV2, MV3) fregante/browser-extension-template#78 (comment)

[fregante]

Chrome 121 is out and this is preventing me from building cross-browser MV3 extensions unfortunately.

[zopieux]

Per https://stackoverflow.com/a/78088358/180709 both are valid and this finally allows truly cross-browser extension packaging with Parcel.

Please allow both keys.

[tdriley]

both are valid and this finally allows truly cross-browser extension packaging with Parcel.

This is great news!

Official docs from Chrome about their MV3 manifest accepting the MV2 background values without erroring: https://developer.chrome.com/docs/extensions/whats-new#background-key-warning