v4: A theme key of `1` does not work in JS configs

[gylxan]

What version of Tailwind CSS are you using?

4.1.15

What build tool (or framework if it abstracts the build tool) are you using?

vite 7.1.12

What version of Node.js are you using?

22

What browser are you using?

Chrome

What operating system are you using?

macOS, Windows

Reproduction URL

https://stackblitz.com/edit/vite-react-tailwind-apth9whe

Describe your issue

We are building libraries in our company and provide a Tailwind Preset from version 3.
In this preset we have color entries like adaptive-bg-basic-level-1(-pressed and -hovered).
Same for level-2 and level-3

For some reason with the new @config directive, level-2 and level-3 are working, but level-1 preset configurations aren't.

//preset.js
export default {
  theme: {
    colors: {
      adaptive: {
        bg: {
          basic: {
            level: {
              1: { // Does not work with @config
                DEFAULT: 'color-mix(in srgb,light-dark(#ffffff, #16181b) calc(<alpha-value> * 100%), transparent)',
                hovered: 'color-mix(in srgb,light-dark(#f3f3f5, #2e3036) calc(<alpha-value> * 100%), transparent)',
                pressed: 'color-mix(in srgb,light-dark(#edeef0, #3b3e44) calc(<alpha-value> * 100%), transparent)',
              },
              2: {
                DEFAULT: 'color-mix(in srgb,light-dark(#f3f3f5, #222428) calc(<alpha-value> * 100%), transparent)',
                hovered: 'color-mix(in srgb,light-dark(#edeef0, #3b3e44) calc(<alpha-value> * 100%), transparent)',
                pressed: 'color-mix(in srgb,light-dark(#e1e2e6, #484b53) calc(<alpha-value> * 100%), transparent)',
              },
              3: {
                DEFAULT: 'color-mix(in srgb,light-dark(#edeef0, #2e3036) calc(<alpha-value> * 100%), transparent)',
                hovered: 'color-mix(in srgb,light-dark(#e1e2e6, #16181b) calc(<alpha-value> * 100%), transparent)',
                pressed: 'color-mix(in srgb,light-dark(#c3c7ce, #0d0e11) calc(<alpha-value> * 100%), transparent)',
              },
            },
          },
        },
      },
    },
  },
}

[thecrypticace]

Minimal config reproduction:

@import "tailwindcss";
@config "./tailwind.config.js";

export default {
  theme: {
    colors: {
      foo: {
        1: { DEFAULT: '#ffffff', hovered: '#f3f3f5' },
        2: { DEFAULT: '#f3f3f5', hovered: '#edeef0' },
      },
    },
  },
}

Setting the 1 key to a string works but the object form doesn't.

The problem comes from our internal key path generation + conversion:

In the above example colors.foo.1.DEFAULT and colors.foo.1.hovered want to turn into normal theme keys: --color-foo-1: … and --color-foo-1-hovered. However, in other cases the 1 means we want to act like tuple syntax in configs which have a different theme key convention:

e.g. fontSize.xs.1.lineHeight -> --font-size-xs--line-height.

This probably means that we have to either special case the color namespaces or we have to generate both. 🤔