Easier way to debug file scanner

[jlarmstrongiv]

Currently, to debug the file scanner, @wongjn provided these helpful instructions:

To debug which folders or files tailwind is scanning I think you'd need to:

1. Clone this repo.
2. Add a logging statement within the oxide rust code somewhere.
3. Compile it.
4. Use your compiled version in your project.

Otherwise, consider providing a git repo of a project that exhibits the unexpected behavior without simplifying it down, and it should help regardless.

It would be great to toggle a debug log ${time} ${filePath} using an environment variable or tailwindcss config setting.

The scanner will never be perfect for every project, and there are many common problems:

• the automatic scanner scans more than it needs
• the automatic scanner misses needed files
• users accidentally include files that needn’t be scanned
• users accidentally forget a folder
• bespoke monorepo setups

Providing debug information will make it easier for everyone to debug these issues on their projects and contribute fixes back to tailwindcss.

Some users have issues compiling the rust builds, and improving it will make reporting bugs with simple reproductions faster, easier, and less burdensome for users and maintainers alike.

Just a cursory search shows that there are many people running into this issue:

• "@tailwindcss/vite": "4.0.8" and "@tailwindcss/vite": "4.0.9" have massively increased load times for the CSS in Vite. #16911
• `@tailwindcss/vite@^4.0.8` is not able to find classes from component based config and components #16958
• All @tailwindcss/cli commands handing forever docker builds #17781
• Cli should not scan unauthorized directories #17803
• No classes generated in monorepo setup with Yarn PnP #17739
• Vite is very slow if a large GeoJson file is in the backend folder #17699
• Latest tailwindcss and @tailwindcss/vite packages don't compile DaisyUI styles in Nuxt 3 Layers architecture #17648
• @source Not Working as Expected During Build Process #17601
• twcss very slow in dev, >30s to load page after hmr update/ssr reload #17581
• [4.1.1] Tailwindcss v4.1.x too slower，twenty times slower than 4.0.x #17522
• `@tailwindcss/vite@^4.0.8` is not able to find classes from component based config and components #16958

[RobinMalfait]

Hey!

We merged some changes that will improve the debugability of the scanner. #17906

Essentially, once we release this in the next version, you could use DEBUG=* as an environment variable. This could lead to a lot of tools spamming your stdout/stderr with information but we will write to a tailwindcss-<pid>.log file and append to that file when logs come in.