Register migrateImport to ensure it actually runs (#14769)

This PR makes sure the `migrateImport` codemod is properly registered so
that it runs as part of the upgrade process.

## Test plan

This PR adds a new `v3` playground with an `upgrade` script that you can
use to run the upgrade from the local package. When you add a
non-prefixed `@import` to the v3 example, the paths are now properly
updated with no errors logged:


https://github.com/user-attachments/assets/85949bbb-756b-4ee2-8ac0-234fe1b2ca39

---------

Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Philipp Spiess <hello@philippspiess.com>

Author: adamwathan

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Ensure individual logical property utilities are sorted later than left/right pair utilities ([#14777](https://github.com/tailwindlabs/tailwindcss/pull/14777))
+- _Upgrade (experimental)_: Ensure `@import` statements for relative CSS files are actually migrated to use relative path syntax ([#14769](https://github.com/tailwindlabs/tailwindcss/pull/14769))
 
 ## [4.0.0-alpha.29] - 2024-10-23
 

integrations/upgrade/index.test.ts

@@ -1775,6 +1775,7 @@ test(
       /* Inject missing @config due to nested imports with tailwind imports */
       @import './root.4/base.css';
       @import './root.4/utilities.css';
+      @config '../tailwind.config.ts';
 
       /*
         The default border color has changed to \`currentColor\` in Tailwind CSS v4,
@@ -1808,7 +1809,6 @@ test(
           border-width: 0;
         }
       }
-      @config '../tailwind.config.ts';
 
       --- ./src/root.5.css ---
       @import './root.5/tailwind.css';
@@ -1963,3 +1963,80 @@ test(
     `)
   },
 )
+
+test(
+  'relative imports without a relative path prefix are migrated to include a relative path prefix',
+  {
+    fs: {
+      'package.json': json`
+        {
+          "dependencies": {
+            "tailwindcss": "workspace:^",
+            "@tailwindcss/upgrade": "workspace:^"
+          }
+        }
+      `,
+      'tailwind.config.js': js`module.exports = {}`,
+      'src/index.css': css`
+        @import 'tailwindcss/base';
+        @import 'tailwindcss/components';
+        @import 'styles/components';
+        @import 'tailwindcss/utilities';
+      `,
+      'src/styles/components.css': css`
+        .btn {
+          @apply bg-black px-4 py-2 rounded-md text-white font-medium hover:bg-zinc-800;
+        }
+      `,
+    },
+  },
+  async ({ fs, exec }) => {
+    await exec('npx @tailwindcss/upgrade --force')
+
+    expect(await fs.dumpFiles('./src/**/*.css')).toMatchInlineSnapshot(`
+      "
+      --- ./src/index.css ---
+      @import 'tailwindcss';
+      @import './styles/components.css' layer(components);
+
+      /*
+        The default border color has changed to \`currentColor\` in Tailwind CSS v4,
+        so we've added these compatibility styles to make sure everything still
+        looks the same as it did with Tailwind CSS v3.
+
+        If we ever want to remove these styles, we need to add an explicit border
+        color utility to any element that depends on these defaults.
+      */
+      @layer base {
+        *,
+        ::after,
+        ::before,
+        ::backdrop,
+        ::file-selector-button {
+          border-color: var(--color-gray-200, currentColor);
+        }
+      }
+      /*
+        Form elements have a 1px border by default in Tailwind CSS v4, so we've
+        added these compatibility styles to make sure everything still looks the
+        same as it did with Tailwind CSS v3.
+
+        If we ever want to remove these styles, we need to add \`border-0\` to
+        any form elements that shouldn't have a border.
+      */
+      @layer base {
+        input:where(:not([type='button'], [type='reset'], [type='submit'])),
+        select,
+        textarea {
+          border-width: 0;
+        }
+      }
+
+      --- ./src/styles/components.css ---
+      .btn {
+        @apply bg-black px-4 py-2 rounded-md text-white font-medium hover:bg-zinc-800;
+      }
+      "
+    `)
+  },
+)

integrations/utils.ts

@@ -620,11 +620,3 @@ async function gracefullyRemove(dir: string) {
     await fs.rm(dir, { recursive: true, force: true })
   }
 }
-
-async function dirExists(dir: string): Promise<boolean> {
-  try {
-    return await fs.stat(dir).then((stat) => stat.isDirectory())
-  } catch {
-    return false
-  }
-}

packages/@tailwindcss-upgrade/src/migrate.ts

@@ -8,6 +8,7 @@ import { migrateAtApply } from './codemods/migrate-at-apply'
 import { migrateAtLayerUtilities } from './codemods/migrate-at-layer-utilities'
 import { migrateBorderCompatibility } from './codemods/migrate-border-compatibility'
 import { migrateConfig } from './codemods/migrate-config'
+import { migrateImport } from './codemods/migrate-import'
 import { migrateMediaScreen } from './codemods/migrate-media-screen'
 import { migrateMissingLayers } from './codemods/migrate-missing-layers'
 import { migrateTailwindDirectives } from './codemods/migrate-tailwind-directives'
@@ -37,6 +38,7 @@ export async function migrateContents(
   }
 
   return postcss()
+    .use(migrateImport())
     .use(migrateAtApply(options))
     .use(migrateMediaScreen(options))
     .use(migrateVariantsDirective())
@@ -84,9 +86,20 @@ export async function analyze(stylesheets: Stylesheet[]) {
             : process.cwd()
 
           // Resolve the import to a file path
-          let resolvedPath: string | false
+          let resolvedPath: string | false = false
           try {
-            resolvedPath = resolveCssId(id, basePath)
+            // We first try to resolve the file as relative to the current file
+            // to mimic the behavior of `postcss-import` since that's what was
+            // used to resolve imports in Tailwind CSS v3.
+            if (id[0] !== '.') {
+              try {
+                resolvedPath = resolveCssId(`./${id}`, basePath)
+              } catch {}
+            }
+
+            if (!resolvedPath) {
+              resolvedPath = resolveCssId(id, basePath)
+            }
           } catch (err) {
             console.warn(`Failed to resolve import: ${id}. Skipping.`)
             console.error(err)

playgrounds/v3/.eslintrc.json

@@ -0,0 +1,7 @@
+{
+  "extends": "next/core-web-vitals",
+  "rules": {
+    "react/no-unescaped-entities": "off",
+    "react/jsx-no-comment-textnodes": "off"
+  }
+}

playgrounds/v3/.gitignore

@@ -0,0 +1,36 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+.yarn/install-state.gz
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# local env files
+.env*.local
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts

playgrounds/v3/app/globals.css

@@ -0,0 +1,3 @@
+@import 'tailwindcss/base';
+@import 'tailwindcss/components';
+@import 'tailwindcss/utilities';

playgrounds/v3/app/layout.tsx

@@ -0,0 +1,23 @@
+import type { Metadata } from 'next'
+import { Inter } from 'next/font/google'
+import './globals.css'
+
+const inter = Inter({ subsets: ['latin'] })
+
+export const metadata: Metadata = {
+  title: 'Create Next App',
+  description: 'Generated by create next app',
+}
+
+export default function RootLayout({
+  children,
+}: Readonly<{
+  children: React.ReactNode
+}>) {
+  return (
+    <html lang="en" className="[&_h1]:font-thin">
+      <head>{/* <script src="https://cdn.tailwindcss.com"></script> */}</head>
+      <body className={inter.className}>{children}</body>
+    </html>
+  )
+}

playgrounds/v3/app/page.tsx

@@ -0,0 +1,3 @@
+export default function Home() {
+  return <h1 className="text-3xl font-bold underline border ring">Hello world!</h1>
+}

playgrounds/v3/next.config.mjs

@@ -0,0 +1,4 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {}
+
+export default nextConfig