Expose flattenColorPalette (#15318)

Resolves #15315 

It looks like we implemented this in Core but forgot to expose it from
the distributed package (the references are only used for testing
plugins internally right now). This exposes `flattenColorPalette` under
the old import path of `tailwindcss/lib/util/flattenColorPalette`.

## Test Plan

Added the following plugin to the Vite example and ensured it works as
expected:

```ts
import flattenColorPalette from 'tailwindcss/lib/util/flattenColorPalette'
import plugin from 'tailwindcss/plugin'

export default plugin(({ matchUtilities, theme }) => {
  matchUtilities(
    {
      'hover-bg': (value) => {
        return {
          '&:hover': {
            backgroundColor: value,
          },
        }
      },
    },
    { values: flattenColorPalette(theme('colors')) },
  )
})
```

<img width="462" alt="Screenshot 2024-12-06 at 11 47 44"
src="https://github.com/user-attachments/assets/11163390-053e-4c6e-8cb9-ae67184ad594">

CHANGELOG.md

@@ -7,14 +7,19 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Added
+
+- Add support for `tailwindcss/lib/util/flattenColorPalette` exports ([#15318](https://github.com/tailwindlabs/tailwindcss/pull/15318))
+
+### Fixed
+
+- Fix dependency related warnings when using `@tailwindcss/postcss` on Windows ([#15321](https://github.com/tailwindlabs/tailwindcss/pull/15321))
 
 ## [4.0.0-beta.6] - 2024-12-06
 
 ### Fixed
 
 - Ensure `@import "…" reference` never generates utilities ([#15307](https://github.com/tailwindlabs/tailwindcss/pull/15307))
-- Fix dependency related warnings when using `@tailwindcss/postcss` on Windows
 
 ## [4.0.0-beta.5] - 2024-12-04
 

packages/tailwindcss/package.json

@@ -31,6 +31,10 @@
       "require": "./src/compat/colors.cts",
       "import": "./src/compat/colors.ts"
     },
+    "./lib/util/flattenColorPalette": {
+      "require": "./src/compat/flatten-color-palette.cts",
+      "import": "./src/compat/flatten-color-palette.ts"
+    },
     "./defaultTheme": {
       "require": "./src/compat/default-theme.cts",
       "import": "./src/compat/default-theme.ts"
@@ -91,6 +95,10 @@
         "require": "./dist/colors.js",
         "import": "./dist/colors.mjs"
       },
+      "./lib/util/flattenColorPalette": {
+        "require": "./dist/flatten-color-palette.js",
+        "import": "./dist/flatten-color-palette.mjs"
+      },
       "./package.json": "./package.json",
       "./index.css": "./index.css",
       "./index": "./index.css",

packages/tailwindcss/src/compat/config.test.ts

@@ -1,7 +1,7 @@
 import { describe, expect, test, vi } from 'vitest'
 import { compile, type Config } from '..'
 import { default as plugin } from '../plugin'
-import { flattenColorPalette } from './flatten-color-palette'
+import flattenColorPalette from './flatten-color-palette'
 
 const css = String.raw
 

packages/tailwindcss/src/compat/flatten-color-palette.cts

@@ -0,0 +1,8 @@
+import flattenColorPalette from './flatten-color-palette.ts'
+
+// This file exists so that `flatten-color-palette.ts` can be written one time
+// but be compatible with both CJS and ESM. Without it we get a `.default`
+// export when using `require` in CJS.
+
+// @ts-ignore
+export = flattenColorPalette

packages/tailwindcss/src/compat/flatten-color-palette.test.ts

@@ -1,5 +1,5 @@
 import { expect, test } from 'vitest'
-import { flattenColorPalette } from './flatten-color-palette'
+import flattenColorPalette from './flatten-color-palette'
 
 test('it should handle private __CSS_VALUES__ to resolve to the right value', () => {
   expect(

packages/tailwindcss/src/compat/flatten-color-palette.ts

@@ -4,7 +4,7 @@ type Colors = {
   [key: string | number]: string | Colors
 }
 
-export function flattenColorPalette(colors: Colors) {
+export default function flattenColorPalette(colors: Colors) {
   let result: Record<string, string> = {}
 
   for (let [root, children] of Object.entries(colors ?? {})) {

packages/tailwindcss/tsup.config.ts

@@ -10,6 +10,7 @@ export default defineConfig([
       plugin: 'src/plugin.ts',
       colors: 'src/compat/colors.ts',
       'default-theme': 'src/compat/default-theme.ts',
+      'flatten-color-palette': 'src/compat/flatten-color-palette.ts',
     },
   },
   {
@@ -21,6 +22,7 @@ export default defineConfig([
       lib: 'src/index.cts',
       colors: 'src/compat/colors.cts',
       'default-theme': 'src/compat/default-theme.cts',
+      'flatten-color-palette': 'src/compat/flatten-color-palette.cts',
     },
   },
 ])