This PR improves the DX by showing all the Lightning CSS warnings when
using a "production" build (or using `--optimize` or `--minify` flags
when using the CLI).
Right now Tailwind CSS itself doesn't care about the exact syntax you
are using in the CSS as long as it looks valid. We do this because
otherwise we would have to parse a lot more CSS syntax and validate it
even though it would be valid CSS in 99.99% of the cases.
Even worse, if you want to use newer CSS syntax that Tailwind CSS
doesn't validate yet, then you would get warnings for valid CSS.
Another reason why we don't do this is because the browser already does
a great job at ignoring invalid CSS.
So the linked issue #15872 would still silently fail in development
mode. In this case, everything would work, except the shadow with the
invalid syntax.
But in production mode, you would now get a proper warning from
Lightning CSS, because they try to optimize the CSS and remove invalid
CSS.
One potential issue here is that we run Lightning CSS on the generated
CSS, not on the input CSS. So the current output shows the warnings in
the output CSS not the input CSS. Any thoughts if we would just skip the
line numbers?
## Test plan
1. Everything works as before
2. In production mode, you would get warnings printed to the terminal.
This is done in `@tailwindcss/node` so the CLI/Vite/PostCSS plugins
would all get the same behavior.
Screenshots:
If you have a single issue:
<img width="977" height="441" alt="image"
src="https://github.com/user-attachments/assets/7b061ee9-b74f-4b40-aa05-cff67a21dfcc"
/>
If you have multiple issues:
<img width="2170" height="711" alt="image"
src="https://github.com/user-attachments/assets/a5bc9b0a-964b-465f-80f3-d30dd467e69c"
/>
Fixes: #15872
In Tailwind v4 the CSS file is the main entry point to your project and
is generally configured via `@theme`. However, given that all v3
projects were configured via a `tailwind.config.js` file we definitely
need to support those. This PR adds support for loading existing
Tailwind config files by adding an `@config` directive to the CSS —
similar to how v3 supported multiple config files except that this is
now _required_ to use a config file.
You can load a config file like so:
```
@import "tailwindcss";
@config "./path/to/tailwind.config.js";
```
A few notes:
- Both CommonJS and ESM config files are supported (loaded directly via
`import()` in Node)
- This is not yet supported in Intellisense or Prettier — should
hopefully land next week
- TypeScript is **not yet** supported in the config file — this will be
handled in a future PR.
---------
Co-authored-by: Philipp Spiess <hello@philippspiess.com>
Co-authored-by: Adam Wathan <adam.wathan@gmail.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
