@tailwindcss/upgrade should add source(none) when content is defined in the legacy tailwind.config.js

[Bouhnosaure]

Hi !

When migrating from Tailwind CSS v3 to v4 using npx @tailwindcss/upgrade, the tool converts the legacy content property from tailwind.config.js into @source directives inside the CSS entrypoint.

That's cool but it does not enforce it as I've read after spending a lot of time understanding why the builds are different on my two identical servers causing one to be without CSS after using my tool to upload and purge my CDN.

However, in v4 the default behavior is to scan all files except those ignored by .gitignore. This can lead to unexpected behavior if the legacy config previously restricted scanning to specific directories only.

For instance, in the .gitignore of laravel the storage/framework is not ignored, but it's files are ignored inside the folder by another .gitignore. So if you have a shared storage folder with old cached views, this can lead to different files on same codebase, not due to tailwind but due to the missing source(none) when upgrading from V3 to V4.

Legacy config:

/** @type {import('tailwindcss').Config} */
module.exports = {
  content: [
    './resources/views/components/store/**/*.blade.php',
    './resources/views/livewire/store/**/*.blade.php', 
    './resources/views/store/**/*.blade.php',
    './resources/assets/store/**/*.js'
  ],
  // ...
}

After upgrade to V4:

@import 'tailwindcss';

@source './resources/views/components/store/**/*.blade.php';
@source './resources/views/livewire/store/**/*.blade.php';
@source './resources/views/store/**/*.blade.php';
@source './resources/assets/store/**/*.js';

Expected behavior when the legacy config has explicit content paths (indicating intentional restriction), the upgrade tool should generate:

@import 'tailwindcss' source(none);

@source './resources/views/components/store/**/*.blade.php';
@source './resources/views/livewire/store/**/*.blade.php';
@source './resources/views/store/**/*.blade.php';
@source './resources/assets/store/**/*.js';

For me it can make more deterministic builds, better migration experience and prevent cache pollution when building assets

Thanks !

Alex