Ignore Rails runtime dirs in Tailwind source scanning

[nehanakrani]

This excludes Rails runtime directories from the default Tailwind source scan.

Tailwind watches generated files under directories like log, tmp, and storage by default, which can trigger unnecessary rebuilds in development. The default generated application.css now opts those directories out with @source not.

Fixes #491.

Tests:

• bundle exec bin/test

[flavorjones]

@nehanakrani Thanks for opening this pull request.

There's a bit of history here, and I'm not sure that this pull request addresses the issue.

The original bug report on this project is #491 as you noted in the description. That issue references an upstream issue tailwindlabs/tailwindcss#15684 which as far as I know is still unresolved.

I attempted to test the approach in this PR by:

• creating a new rails app rails new test-tailwind-source --css=tailwind
• in that project dir, rails generate scaffold post title:string body:text published:boolean
• bin/setup
• edit app/assets/tailwind/application.css with @source note (see below for details)
• bin/rails server in terminal 1
• bin/rails tailwindcss:watch in terminal 2

The contents of app/assets/tailwind/application.css are:

@import "tailwindcss";
@source not "../../../log";
@source not "../../../tmp";
@source not "../../../storage";

And the original problem still manifests: when I make a request to the development server, and the log is appended-to, then I see tailwind kick off a scan:

bin/rails tailwindcss:watch
≈ tailwindcss v4.2.4

Done in 65ms
Done in 2ms
Done in 2ms
Done in 1ms
Done in 1ms
Done in 2ms
Done in 1ms

Can you help me understand:

1. whether I have correctly understood the problem you're trying to solve
2. if you see this issue fixed on your system if you follow the above steps

Thank you!