Postcss: Run plugin in Once hook

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Ensure absolute `url()`s inside imported CSS files are not rebased when using `@tailwindcss/vite`
 - Fix issues with dev servers using Svelte 5 with the Vite plugin ([#15274](https://github.com/tailwindlabs/tailwindcss/issues/15274))
 - Fix resolution of imported CSS files in Vite SSR builds ([#15279](https://github.com/tailwindlabs/tailwindcss/issues/15279))
+- Ensure other plugins can run after `@tailwindcss/postcss` ([#15273](https://github.com/tailwindlabs/tailwindcss/pull/15273))
+- Rebase `url()` inside imported CSS files when using Vite with the `@tailwindcss/postcss` extension ([#15273](https://github.com/tailwindlabs/tailwindcss/pull/15273))
 
 ### Added
 

packages/@tailwindcss-postcss/src/index.test.ts

@@ -2,7 +2,6 @@ import dedent from 'dedent'
 import { unlink, writeFile } from 'node:fs/promises'
 import postcss from 'postcss'
 import { afterEach, beforeEach, describe, expect, test } from 'vitest'
-// @ts-ignore
 import tailwindcss from './index'
 
 // We give this file path to PostCSS for processing.
@@ -248,3 +247,62 @@ test('bail early when Tailwind is not used', async () => {
     }"
   `)
 })
+
+test('runs `Once` plugins in the right order', async () => {
+  let before = ''
+  let after = ''
+  let processor = postcss([
+    {
+      postcssPlugin: 'before',
+      Once(root) {
+        before = root.toString()
+      },
+    },
+    tailwindcss({ base: `${__dirname}/fixtures/example-project`, optimize: { minify: false } }),
+    {
+      postcssPlugin: 'after',
+      Once(root) {
+        after = root.toString()
+      },
+    },
+  ])
+
+  let result = await processor.process(
+    css`
+      @theme {
+        --color-red-500: red;
+      }
+      .custom-css {
+        color: theme(--color-red-500);
+      }
+    `,
+    { from: inputCssFilePath() },
+  )
+
+  expect(result.css.trim()).toMatchInlineSnapshot(`
+    ":root {
+      --color-red-500: red;
+    }
+
+    .custom-css {
+      color: red;
+    }"
+  `)
+  expect(before).toMatchInlineSnapshot(`
+    "@theme {
+      --color-red-500: red;
+    }
+    .custom-css {
+      color: theme(--color-red-500);
+    }"
+  `)
+  expect(after).toMatchInlineSnapshot(`
+    ":root {
+      --color-red-500: red;
+    }
+
+    .custom-css {
+      color: red;
+    }"
+  `)
+})

packages/@tailwindcss-postcss/src/index.ts

@@ -55,7 +55,7 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
 
       {
         postcssPlugin: 'tailwindcss',
-        async OnceExit(root, { result }) {
+        async Once(root, { result }) {
           env.DEBUG && console.time('[@tailwindcss/postcss] Total time in @tailwindcss/postcss')
           let inputFile = result.opts.from ?? ''
           let context = getContextFromCache(inputFile, opts)

packages/@tailwindcss-postcss/src/postcss-fix-relative-paths/index.ts

@@ -67,10 +67,8 @@ export default function fixRelativePathsPlugin(): Plugin {
 
   return {
     postcssPlugin: 'tailwindcss-postcss-fix-relative-paths',
-    AtRule: {
-      source: fixRelativePath,
-      plugin: fixRelativePath,
-      config: fixRelativePath,
+    Once(root) {
+      root.walkAtRules(/source|plugin|config/, fixRelativePath)
     },
   }
 }