Plugin API: Allow custom utilities to start with @

[philipp-spiess]

Closes #14791

Add support to the JS Plugin interop layer for utilities that start with @. This ensures no breaking when trying to load plugins that contribute utilities like @container from @tailwindcss/container-queries (even though the @container utility is now part of core).

Test Plan

Added the @tailwindcss/container-queries plugin to to the Vite example:

However, in order for the Vite example to load the extension, I also had to apply the following patch:

I think this is related to our dev system though, the compiled plugin file is going to be a flat file with no requires in our public release.

[philipp-spiess]

• Plugin API: Allow custom utilities to start with @ #14793 👈
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[adamwathan]

Wondering if we should actually support this or not, given that this is meant to try and solve the issue of the @tailwindcss/container-queries plugin not working when upgrading to v4 but the real solution is just not installing the plugin since it exists in core in v4 already, and adding the plugin means you have two overlapping sets of utilities now.

It probably makes sense for this to work from a sort of grammar perspective, but still wonder what the real "fix" is for someone upgrading with the container queries plugin installed.

Brain dump of potential options:

• Remove that plugin as part of the codemod process
• Detect that it's being used somehow and basically reject it + warn the user
• Both of those?

[philipp-spiess]

@adamwathan Agree that this is not the solution for @tailwindcss/container-queries and we want to make the codemod handle it too. I will create a ticket for it to look into it. Maybe removing it and explaining to the user is enough? That said I do think that there might be other plugins using @ in the utility names out there and it seems reasonable enough to support that (it's a 1 character change in the interop layer after all).

[philipp-spiess]

Removed the test case referencing @tailwindcss/container-queries like we discussed.