Fix TS2742 error when inferring exported Config type (#19707)

Type aliases get resolved through to `UserConfig` during declaration
emit, which lives in a hashed internal DTS chunk with no stable import
path, causing TS2742. This is 100% backwards-compatible because type
aliases and interfaces are structurally comparable.

Fixes: #15844
Fixes: #19706
Fixes: #15458

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

Author: 3 people

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Canonicalization: migrate arbitrary `:has()` variants from `[&:has(…)]` to `has-[…]` ([#19991](https://github.com/tailwindlabs/tailwindcss/pull/19991))
 - Upgrade: don’t migrate inline `style` attributes ([#19918](https://github.com/tailwindlabs/tailwindcss/pull/19918))
 - Allow multiple `@utility` definitions with the same name but different value types ([#19777](https://github.com/tailwindlabs/tailwindcss/pull/19777))
+- Export missing `PluginWithConfig` type from `tailwindcss/plugin` to fix errors when inferring plugin config types ([#19707](https://github.com/tailwindlabs/tailwindcss/pull/19707))
 
 ## [4.2.4] - 2026-04-21
 

integrations/cli/config.test.ts

@@ -126,6 +126,72 @@ test(
   },
 )
 
+// https://github.com/tailwindlabs/tailwindcss/issues/19706
+test(
+  'Config files (TS, valid types)',
+  {
+    fs: {
+      'package.json': json`
+        {
+          "type": "module",
+          "dependencies": {
+            "tailwindcss": "workspace:^",
+            "@tailwindcss/cli": "workspace:^"
+          },
+          "devDependencies": {
+            "typescript": "^5.9.3"
+          }
+        }
+      `,
+      'tsconfig.json': json`
+        {
+          "compilerOptions": {
+            "target": "ES2022",
+            "module": "NodeNext",
+            "moduleResolution": "NodeNext",
+            "declaration": true,
+            "composite": true,
+            "outDir": "./.build",
+            "skipLibCheck": true
+          },
+          "include": ["tailwind.config.ts"]
+        }
+      `,
+      'index.html': html`
+        <div class="text-primary"></div>
+      `,
+      'tailwind.config.ts': ts`
+        import type { Config } from 'tailwindcss'
+
+        function defineConfig(config: Config): Config {
+          return config
+        }
+
+        export default defineConfig({
+          theme: {
+            extend: {
+              colors: {
+                primary: 'blue',
+              },
+            },
+          },
+        })
+      `,
+      'src/index.css': css`
+        @import 'tailwindcss';
+        @config '../tailwind.config.ts';
+      `,
+    },
+  },
+  async ({ fs, exec }) => {
+    // We expect that these commands don't crash:
+    await exec('pnpm tsc -b')
+    await exec('pnpm tailwindcss --input src/index.css --output dist/out.css')
+
+    await fs.expectFileToContain('dist/out.css', [candidate`text-primary`])
+  },
+)
+
 test(
   'Config files (CJS, watch mode)',
   {

integrations/cli/plugins.test.ts

@@ -1,4 +1,4 @@
-import { candidate, css, html, json, test } from '../utils'
+import { candidate, css, html, json, test, ts } from '../utils'
 
 test(
   'builds the `@tailwindcss/typography` plugin utilities',
@@ -207,3 +207,88 @@ test(
     ])
   },
 )
+
+// https://github.com/tailwindlabs/tailwindcss/issues/15844
+test(
+  'builds CSS with a custom plugin compiled from TypeScript',
+  {
+    fs: {
+      'package.json': json`
+        {
+          "type": "module",
+          "dependencies": {
+            "tailwindcss": "workspace:^",
+            "@tailwindcss/cli": "workspace:^"
+          },
+          "devDependencies": {
+            "typescript": "^5.7.2"
+          }
+        }
+      `,
+      'tsconfig.json': json`
+        {
+          "compilerOptions": {
+            "target": "ES2022",
+            "module": "NodeNext",
+            "moduleResolution": "NodeNext",
+            "declaration": true,
+            "composite": true,
+            "rootDir": "./src",
+            "outDir": "./.build",
+            "skipLibCheck": true
+          },
+          "include": ["src/**/*.ts"]
+        }
+      `,
+      'index.html': html`
+        <div class="test-red"></div>
+      `,
+      'src/index.css': css`
+        @import 'tailwindcss';
+        @plugin '../.build/plugin.js';
+      `,
+      'src/plugin.ts': ts`
+        import plugin from 'tailwindcss/plugin'
+
+        export const typedPlugin = plugin(() => {
+          return ({ matchComponents }) => {
+            matchComponents(
+              {
+                test: (content: string) => ({
+                  color: content,
+                }),
+              },
+              {
+                values: {
+                  red: 'red',
+                },
+              },
+            )
+          }
+        })
+
+        export default plugin(({ matchComponents }) => {
+          matchComponents(
+            {
+              test: (content: string) => ({
+                color: content,
+              }),
+            },
+            {
+              values: {
+                red: 'red',
+              },
+            },
+          )
+        })
+      `,
+    },
+  },
+  async ({ fs, exec }) => {
+    // We expect that these commands don't crash:
+    await exec('pnpm tsc -b')
+    await exec('pnpm tailwindcss --input src/index.css --output dist/out.css')
+
+    await fs.expectFileToContain('dist/out.css', [candidate`test-red`])
+  },
+)

packages/tailwindcss/src/index.ts

@@ -34,7 +34,8 @@ import { segment } from './utils/segment'
 import { topologicalSort } from './utils/topological-sort'
 import { compoundsForSelectors, IS_VALID_VARIANT_NAME, substituteAtVariant } from './variants'
 import { walk, WalkAction } from './walk'
-export type Config = UserConfig
+
+export interface Config extends UserConfig {}
 
 const IS_VALID_PREFIX = /^[a-z]+$/
 

packages/tailwindcss/src/plugin.ts

@@ -41,5 +41,6 @@ export type {
   PluginFn as PluginCreator,
   Plugin as PluginsConfig,
   PluginUtils,
+  PluginWithConfig,
   ThemeConfig,
 }