Add @import "…" reference (#15228)

Closes #15219 This PR adds a new feature, `@import "…" reference` that can be used to load Tailwind CSS configuration files without adding any style rules to the CSS. The idea is that you can use this in combination with your Tailwind CSS root file when you need to have access to your full CSS config outside of the main stylesheet. A common example is for Vue, Svelte, or CSS modules: ```css @import "./tailwind.css" reference; .link { @apply underline; } ``` Importing a file as a reference will convert all `@theme` block to be `reference`, so no CSS variables will be emitted. Furthermore it will strip out all custom styles from the stylesheet. Furthermore plugins registered via `@plugin` or `@config` inside reference-mode files will not add any content to the CSS file via `addBase()`. ## Test Plan Added unit test for when we handle the import resolution and when `postcss-import` does it outside of Tailwind CSS. I also changed the Svelte and Vue integration tests to use this new syntax to ensure it works end to end. --------- Co-authored-by: Jordan Pittman <jordan@cryptica.me>
tailwindlabs · Dec 3, 2024 · 78f5b08 · 78f5b08
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Parallelize parsing of individual source files ([#15270](https://github.com/tailwindlabs/tailwindcss/pull/15270))
+- Support Vite 6 in the Vite plugin ([#15274](https://github.com/tailwindlabs/tailwindcss/issues/15274))
+- Add a new `@import "…" reference` syntax for only importing the Tailwind CSS configurations of a stylesheets ([#15228](https://github.com/tailwindlabs/tailwindcss/pull/15228))
+
 ### Fixed
 
 - Ensure absolute `url()`s inside imported CSS files are not rebased when using `@tailwindcss/vite` ([#15275](https://github.com/tailwindlabs/tailwindcss/pull/15275))
@@ -15,11 +21,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - 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
-
-- Parallelize parsing of individual source files ([#15270](https://github.com/tailwindlabs/tailwindcss/pull/15270))
-- Support Vite 6 in the Vite plugin ([#15274](https://github.com/tailwindlabs/tailwindcss/issues/15274))
-
 ## [4.0.0-beta.4] - 2024-11-29
 
 ### Fixed

diff --git a/integrations/vite/svelte.test.ts b/integrations/vite/svelte.test.ts
@@ -48,10 +48,7 @@ test(
           target: document.body,
         })
       `,
-      'src/index.css': css`
-        @import 'tailwindcss/theme' theme(reference);
-        @import 'tailwindcss/utilities';
-      `,
+      'src/index.css': css`@import 'tailwindcss' reference;`,
       'src/App.svelte': html`
         <script>
           import './index.css'

diff --git a/integrations/vite/vue.test.ts b/integrations/vite/vue.test.ts
@@ -45,15 +45,13 @@ test(
       `,
       'src/App.vue': html`
         <style>
-          @import 'tailwindcss/utilities';
-          @import 'tailwindcss/theme' theme(reference);
+          @import 'tailwindcss' reference;
           .foo {
             @apply text-red-500;
           }
         </style>
         <style scoped>
-          @import 'tailwindcss/utilities';
-          @import 'tailwindcss/theme' theme(reference);
+          @import 'tailwindcss' reference;
           :deep(.bar) {
             color: red;
           }

diff --git a/packages/tailwindcss/src/ast.ts b/packages/tailwindcss/src/ast.ts
@@ -29,7 +29,7 @@ export type Comment = {
 
 export type Context = {
   kind: 'context'
-  context: Record<string, string>
+  context: Record<string, string | boolean>
   nodes: AstNode[]
 }
 
@@ -82,7 +82,7 @@ export function comment(value: string): Comment {
   }
 }
 
-export function context(context: Record<string, string>, nodes: AstNode[]): Context {
+export function context(context: Record<string, string | boolean>, nodes: AstNode[]): Context {
   return {
     kind: 'context',
     context,
@@ -115,12 +115,12 @@ export function walk(
     utils: {
       parent: AstNode | null
       replaceWith(newNode: AstNode | AstNode[]): void
-      context: Record<string, string>
+      context: Record<string, string | boolean>
       path: AstNode[]
     },
   ) => void | WalkAction,
   parentPath: AstNode[] = [],
-  context: Record<string, string> = {},
+  context: Record<string, string | boolean> = {},
 ) {
   for (let i = 0; i < ast.length; i++) {
     let node = ast[i]
@@ -175,12 +175,12 @@ export function walkDepth(
     utils: {
       parent: AstNode | null
       path: AstNode[]
-      context: Record<string, string>
+      context: Record<string, string | boolean>
       replaceWith(newNode: AstNode[]): void
     },
   ) => void,
   parentPath: AstNode[] = [],
-  context: Record<string, string> = {},
+  context: Record<string, string | boolean> = {},
 ) {
   for (let i = 0; i < ast.length; i++) {
     let node = ast[i]

diff --git a/packages/tailwindcss/src/compat/apply-compat-hooks.ts b/packages/tailwindcss/src/compat/apply-compat-hooks.ts
@@ -34,8 +34,9 @@ export async function applyCompatibilityHooks({
   globs: { origin?: string; pattern: string }[]
 }) {
   let features = Features.None
-  let pluginPaths: [{ id: string; base: string }, CssPluginOptions | null][] = []
-  let configPaths: { id: string; base: string }[] = []
+  let pluginPaths: [{ id: string; base: string; reference: boolean }, CssPluginOptions | null][] =
+    []
+  let configPaths: { id: string; base: string; reference: boolean }[] = []
 
   walk(ast, (node, { parent, replaceWith, context }) => {
     if (node.kind !== 'at-rule') return
@@ -95,7 +96,7 @@ export async function applyCompatibilityHooks({
       }
 
       pluginPaths.push([
-        { id: pluginPath, base: context.base },
+        { id: pluginPath, base: context.base as string, reference: !!context.reference },
         Object.keys(options).length > 0 ? options : null,
       ])
 
@@ -114,7 +115,11 @@ export async function applyCompatibilityHooks({
         throw new Error('`@config` cannot be nested.')
       }
 
-      configPaths.push({ id: node.params.slice(1, -1), base: context.base })
+      configPaths.push({
+        id: node.params.slice(1, -1),
+        base: context.base as string,
+        reference: !!context.reference,
+      })
       replaceWith([])
       features |= Features.JsPluginCompat
       return
@@ -153,23 +158,25 @@ export async function applyCompatibilityHooks({
 
   let [configs, pluginDetails] = await Promise.all([
     Promise.all(
-      configPaths.map(async ({ id, base }) => {
+      configPaths.map(async ({ id, base, reference }) => {
         let loaded = await loadModule(id, base, 'config')
         return {
           path: id,
           base: loaded.base,
           config: loaded.module as UserConfig,
+          reference,
         }
       }),
     ),
     Promise.all(
-      pluginPaths.map(async ([{ id, base }, pluginOptions]) => {
+      pluginPaths.map(async ([{ id, base, reference }, pluginOptions]) => {
         let loaded = await loadModule(id, base, 'plugin')
         return {
           path: id,
           base: loaded.base,
           plugin: loaded.module as Plugin,
           options: pluginOptions,
+          reference,
         }
       }),
     ),
@@ -203,22 +210,32 @@ function upgradeToFullPluginSupport({
     path: string
     base: string
     config: UserConfig
+    reference: boolean
   }[]
   pluginDetails: {
     path: string
     base: string
     plugin: Plugin
     options: CssPluginOptions | null
+    reference: boolean
   }[]
 }) {
   let features = Features.None
   let pluginConfigs = pluginDetails.map((detail) => {
     if (!detail.options) {
-      return { config: { plugins: [detail.plugin] }, base: detail.base }
+      return {
+        config: { plugins: [detail.plugin] },
+        base: detail.base,
+        reference: detail.reference,
+      }
     }
 
     if ('__isOptionsFunction' in detail.plugin) {
-      return { config: { plugins: [detail.plugin(detail.options)] }, base: detail.base }
+      return {
+        config: { plugins: [detail.plugin(detail.options)] },
+        base: detail.base,
+        reference: detail.reference,
+      }
     }
 
     throw new Error(`The plugin "${detail.path}" does not accept options`)
@@ -227,9 +244,9 @@ function upgradeToFullPluginSupport({
   let userConfig = [...pluginConfigs, ...configs]
 
   let { resolvedConfig } = resolveConfig(designSystem, [
-    { config: createCompatConfig(designSystem.theme), base },
+    { config: createCompatConfig(designSystem.theme), base, reference: true },
     ...userConfig,
-    { config: { plugins: [darkModePlugin] }, base },
+    { config: { plugins: [darkModePlugin] }, base, reference: true },
   ])
   let { resolvedConfig: resolvedUserConfig, replacedThemeKeys } = resolveConfig(
     designSystem,
@@ -242,8 +259,8 @@ function upgradeToFullPluginSupport({
     },
   })
 
-  for (let { handler } of resolvedConfig.plugins) {
-    handler(pluginApi)
+  for (let { handler, reference } of resolvedConfig.plugins) {
+    handler(reference ? { ...pluginApi, addBase: () => {} } : pluginApi)
   }
 
   // Merge the user-configured theme keys into the design system. The compat

diff --git a/packages/tailwindcss/src/compat/config/resolve-config.ts b/packages/tailwindcss/src/compat/config/resolve-config.ts
@@ -15,6 +15,7 @@ export interface ConfigFile {
   path?: string
   base: string
   config: UserConfig
+  reference: boolean
 }
 
 interface ResolutionContext {
@@ -128,25 +129,28 @@ export type PluginUtils = {
   colors: typeof colors
 }
 
-function extractConfigs(ctx: ResolutionContext, { config, base, path }: ConfigFile): void {
+function extractConfigs(
+  ctx: ResolutionContext,
+  { config, base, path, reference }: ConfigFile,
+): void {
   let plugins: PluginWithConfig[] = []
 
   // Normalize plugins so they share the same shape
   for (let plugin of config.plugins ?? []) {
     if ('__isOptionsFunction' in plugin) {
       // Happens with `plugin.withOptions()` when no options were passed:
       // e.g. `require("my-plugin")` instead of `require("my-plugin")(options)`
-      plugins.push(plugin())
+      plugins.push({ ...plugin(), reference })
     } else if ('handler' in plugin) {
       // Happens with `plugin(…)`:
       // e.g. `require("my-plugin")`
       //
       // or with `plugin.withOptions()` when the user passed options:
       // e.g. `require("my-plugin")(options)`
-      plugins.push(plugin)
+      plugins.push({ ...plugin, reference })
     } else {
       // Just a plain function without using the plugin(…) API
-      plugins.push({ handler: plugin })
+      plugins.push({ handler: plugin, reference })
     }
   }
 
@@ -158,15 +162,15 @@ function extractConfigs(ctx: ResolutionContext, { config, base, path }: ConfigFi
   }
 
   for (let preset of config.presets ?? []) {
-    extractConfigs(ctx, { path, base, config: preset })
+    extractConfigs(ctx, { path, base, config: preset, reference })
   }
 
   // Apply configs from plugins
   for (let plugin of plugins) {
     ctx.plugins.push(plugin)
 
     if (plugin.config) {
-      extractConfigs(ctx, { path, base, config: plugin.config })
+      extractConfigs(ctx, { path, base, config: plugin.config, reference: !!plugin.reference })
     }
   }
 

diff --git a/packages/tailwindcss/src/compat/plugin-api.test.ts b/packages/tailwindcss/src/compat/plugin-api.test.ts
@@ -1490,6 +1490,52 @@ describe('theme', async () => {
   })
 })
 
+describe('addBase', () => {
+  test('does not create rules when imported via `@import "…" reference`', async () => {
+    let input = css`
+      @tailwind utilities;
+      @plugin "outside";
+      @import './inside.css' reference;
+    `
+
+    let compiler = await compile(input, {
+      loadModule: async (id, base) => {
+        if (id === 'inside') {
+          return {
+            base,
+            module: plugin(function ({ addBase }) {
+              addBase({ inside: { color: 'red' } })
+            }),
+          }
+        }
+        return {
+          base,
+          module: plugin(function ({ addBase }) {
+            addBase({ outside: { color: 'red' } })
+          }),
+        }
+      },
+      async loadStylesheet() {
+        return {
+          content: css`
+            @plugin "inside";
+          `,
+          base: '',
+        }
+      },
+    })
+
+    expect(compiler.build([])).toMatchInlineSnapshot(`
+      "@layer base {
+        outside {
+          color: red;
+        }
+      }
+      "
+    `)
+  })
+})
+
 describe('addVariant', () => {
   test('addVariant with string selector', async () => {
     let { build } = await compile(

diff --git a/packages/tailwindcss/src/compat/plugin-api.ts b/packages/tailwindcss/src/compat/plugin-api.ts
@@ -17,7 +17,13 @@ import * as SelectorParser from './selector-parser'
 
 export type Config = UserConfig
 export type PluginFn = (api: PluginAPI) => void
-export type PluginWithConfig = { handler: PluginFn; config?: UserConfig }
+export type PluginWithConfig = { 
+  handler: PluginFn;
+  config?: UserConfig;
+
+  /** @internal */
+  reference?: boolean
+}
 export type PluginWithOptions<T> = {
   (options?: T): PluginWithConfig
   __isOptionsFunction: true