Allow customizing input/output via env variables

[thewatts]

The Rails assets:precompile task internally calls bin/rails tailwindcss:build, which uses hardcoded input/output file paths. Previously, the only way to customize these paths was to bypass the Rails integration entirely and use the Tailwind CLI directly (via bundle exec tailwindcss).

This change introduces TAILWINDCSS_INPUT_FILE and TAILWINDCSS_OUTPUT_FILE environment variables that allow users to override the default paths while still using the standard assets:precompile workflow.

This is useful for projects with non-standard asset structures or when integrating with custom build pipelines.

[flavorjones]

Hi @thewatts, thanks for suggesting this change.

I'd like to understand the problem you're hoping to solve -- that is, why do you want to change these file names?

I'm asking questions because this implementation seems like it's only a partial solution that doesn't address the many places these paths are assumed after installation:

• the .gitignore file
• the experimental engine support feature
• the clobber rake task
• upgrade functionality (see lib/install/upgrade_tailwindcss.rb)

And I'm hoping that by understanding what problem is driving your contribution, that I can make some helpful suggestions. Thank you!

[manuelmeurer]

Hi @flavorjones, I just found this PR, since I have the same wish as @thewatts to be able to customize the input and output file(s). 😄
My use-case is that my app has several "namespaces", which map to separate URLs and have separate styling.
Thus I'd like to have separate CSS files, one for each namespace, to allow for customizing TW and plugins, add custom CSS etc.

I understand that this is not a trivial change, since as you mentioned the default paths are assumed at different locations, but maybe it's worthwile adding this customization nevertheless?
For now, I'm using the TW CLI instead of the Rake tasks, but of course that's not optimal.