Support loading plugins in CSS

packages/tailwindcss-language-server/src/lib/env.ts

@@ -1,6 +1,6 @@
 import Module from 'node:module'
 import * as path from 'node:path'
-import resolveFrom from '../util/resolveFrom'
+import { resolveFrom } from '../util/resolveFrom'
 
 process.env.TAILWIND_MODE = 'build'
 process.env.TAILWIND_DISABLE_TOUCH = 'true'

packages/tailwindcss-language-server/src/project-locator.ts

@@ -11,7 +11,7 @@ import type { AtRule, Message } from 'postcss'
 import { type DocumentSelector, DocumentSelectorPriority } from './projects'
 import { CacheMap } from './cache-map'
 import { getPackageRoot } from './util/get-package-root'
-import resolveFrom from './util/resolveFrom'
+import { resolveFrom } from './util/resolveFrom'
 import { type Feature, supportedFeatures } from '@tailwindcss/language-service/src/features'
 import { extractSourceDirectives, resolveCssImports } from './css'
 import { normalizeDriveLetter, normalizePath, pathToFileURL } from './utils'
@@ -132,15 +132,18 @@ export class ProjectLocator {
 
     console.log(JSON.stringify({ tailwind }))
 
-    // A JS/TS config file was loaded from an `@config`` directive in a CSS file
+    // A JS/TS config file was loaded from an `@config` directive in a CSS file
+    // This is only relevant for v3 projects so we'll do some feature detection
+    // to verify if this is supported in the current version of Tailwind.
     if (config.type === 'js' && config.source === 'css') {
       // We only allow local versions of Tailwind to use `@config` directives
       if (tailwind.isDefaultVersion) {
         return null
       }
 
-      // This version of Tailwind doesn't support `@config` directives
-      if (!tailwind.features.includes('css-at-config')) {
+      // This version of Tailwind doesn't support considering `@config` directives
+      // as a project on their own.
+      if (!tailwind.features.includes('css-at-config-as-project')) {
         return null
       }
     }
@@ -310,8 +313,12 @@ export class ProjectLocator {
       // If the CSS file couldn't be read for some reason, skip it
       if (!file.content) continue
 
+      // Look for `@import`, `@tailwind`, `@theme`, `@config`, etc…
+      if (!file.isMaybeTailwindRelated()) continue
+
       // Find `@config` directives in CSS files and resolve them to the actual
-      // config file that they point to.
+      // config file that they point to. This is only relevant for v3 which
+      // we'll verify after config resolution.
       let configPath = file.configPathInCss()
       if (configPath) {
         // We don't need the content for this file anymore
@@ -327,14 +334,9 @@ export class ProjectLocator {
             content: [],
           })),
         )
-        continue
       }
 
-      // Look for `@import` or `@tailwind` directives
-      if (file.isMaybeTailwindRelated()) {
-        imports.push(file)
-        continue
-      }
+      imports.push(file)
     }
 
     // Resolve imports in all the CSS files
@@ -636,6 +638,9 @@ class FileEntry {
    * Look for `@config` directives in a CSS file and return the path to the config
    * file that it points to. This path is (possibly) relative to the CSS file so
    * it must be resolved to an absolute path before returning.
+   *
+   * This is only useful for v3 projects. While v4 can use `@config` directives
+   * the CSS file is still considered the "config" rather than the JS file.
    */
   configPathInCss(): string | null {
     if (!this.content) return null
@@ -649,21 +654,21 @@ class FileEntry {
   }
 
   /**
-   * Look for `@import` or `@tailwind` directives in a CSS file. This means that
+   * Look for tailwind-specific directives in a CSS file. This means that it
    * participates in the CSS "graph" for the project and we need to traverse
    * the graph to find all the CSS files that are considered entrypoints.
    */
   isMaybeTailwindRelated(): boolean {
     if (!this.content) return false
 
-    let HAS_IMPORT = /@import\s*(?<config>'[^']+'|"[^"]+");/
+    let HAS_IMPORT = /@import\s*('[^']+'|"[^"]+");/
     let HAS_TAILWIND = /@tailwind\s*[^;]+;/
-    let HAS_THEME = /@theme\s*\{/
+    let HAS_DIRECTIVE = /@(theme|plugin|config|utility|variant|apply)\s*[^;{]+[;{]/
 
     return (
       HAS_IMPORT.test(this.content) ||
       HAS_TAILWIND.test(this.content) ||
-      HAS_THEME.test(this.content)
+      HAS_DIRECTIVE.test(this.content)
     )
   }
 }

packages/tailwindcss-language-server/src/projects.ts

@@ -24,7 +24,7 @@ import * as path from 'path'
 import * as fs from 'fs'
 import findUp from 'find-up'
 import picomatch from 'picomatch'
-import resolveFrom, { setPnpApi } from './util/resolveFrom'
+import { resolveFrom, setPnpApi } from './util/resolveFrom'
 import type { AtRule, Container, Node, Result } from 'postcss'
 import Hook from './lib/hook'
 import * as semver from '@tailwindcss/language-service/src/util/semver'

packages/tailwindcss-language-server/src/tw.ts

@@ -36,7 +36,7 @@ import normalizePath from 'normalize-path'
 import * as path from 'path'
 import type * as chokidar from 'chokidar'
 import picomatch from 'picomatch'
-import resolveFrom from './util/resolveFrom'
+import { resolveFrom } from './util/resolveFrom'
 import * as parcel from './watcher/index.js'
 import { equal } from '@tailwindcss/language-service/src/util/array'
 import { CONFIG_GLOB, CSS_GLOB, PACKAGE_LOCK_GLOB } from './lib/constants'

packages/tailwindcss-language-server/src/util/resolveFrom.ts

@@ -16,7 +16,7 @@ export function setPnpApi(newPnpApi: any): void {
   resolver = recreateResolver()
 }
 
-export default function resolveFrom(from?: string, id?: string): string {
+export function resolveFrom(from?: string, id?: string): string {
   // Network share path on Windows
   if (id.startsWith('\\\\')) return id
 

packages/tailwindcss-language-server/src/util/v4/design-system.ts

@@ -1,7 +1,10 @@
 import type { DesignSystem } from '@tailwindcss/language-service/src/util/v4'
 
 import postcss from 'postcss'
+import * as path from 'node:path'
 import { resolveCssImports } from '../../css'
+import { resolveFrom } from '../resolveFrom'
+import { pathToFileURL } from 'tailwindcss-language-server/src/utils'
 
 const HAS_V4_IMPORT = /@import\s*(?:'tailwindcss'|"tailwindcss")/
 const HAS_V4_THEME = /@theme\s*\{/
@@ -18,6 +21,37 @@ export async function isMaybeV4(css: string): Promise<boolean> {
   return HAS_V4_THEME.test(css) || HAS_V4_IMPORT.test(css)
 }
 
+/**
+ * Create a loader function that can load plugins and config files relative to
+ * the CSS file that uses them. However, we don't want missing files to prevent
+ * everything from working so we'll let the error handler decide how to proceed.
+ *
+ * @param {object} param0
+ * @returns
+ */
+function createLoader<T>({
+  filepath,
+  onError,
+}: {
+  filepath: string
+  onError: (id: string, error: unknown) => T
+}) {
+  let baseDir = path.dirname(filepath)
+  let cacheKey = `${+Date.now()}`
+
+  return async function loadFile(id: string) {
+    try {
+      let resolved = resolveFrom(baseDir, id)
+      let url = pathToFileURL(resolved)
+      url.searchParams.append('t', cacheKey)
+
+      return await import(url.href).then((m) => m.default ?? m)
+    } catch (err) {
+      return onError(id, err)
+    }
+  }
+}
+
 export async function loadDesignSystem(
   tailwindcss: any,
   filepath: string,
@@ -38,9 +72,23 @@ export async function loadDesignSystem(
 
   // Step 3: Take the resolved CSS and pass it to v4's `loadDesignSystem`
   let design: DesignSystem = await tailwindcss.__unstable__loadDesignSystem(resolved.css, {
-    loadPlugin() {
-      return () => {}
-    },
+    loadPlugin: createLoader({
+      filepath,
+      onError(id, err) {
+        console.error(`Unable to load plugin: ${id}`, err)
+
+        return () => {}
+      },
+    }),
+
+    loadConfig: createLoader({
+      filepath,
+      onError(id, err) {
+        console.error(`Unable to load config: ${id}`, err)
+
+        return {}
+      },
+    }),
   })
 
   // Step 4: Augment the design system with some additional APIs that the LSP needs

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/app.css

@@ -0,0 +1,17 @@
+@import 'tailwindcss';
+
+/* Load ESM versions */
+@config './esm/my-config.mjs';
+@plugin './esm/my-plugin.mjs';
+
+/* Load Common JS versions */
+@config './cjs/my-config.cjs';
+@plugin './cjs/my-plugin.cjs';
+
+/* Load TypeScript versions */
+@config './ts/my-config.ts';
+@plugin './ts/my-plugin.ts';
+
+/* Attempt to load files that do not exist */
+@config './missing-confg.mjs';
+@plugin './missing-plugin.mjs';

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/cjs/my-config.cjs

@@ -0,0 +1,9 @@
+module.exports = {
+  theme: {
+    extend: {
+      colors: {
+        'cjs-from-config': 'black',
+      },
+    },
+  },
+}

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/cjs/my-plugin.cjs

@@ -0,0 +1,16 @@
+const plugin = require('tailwindcss/plugin')
+
+module.exports = plugin(
+  () => {
+    //
+  },
+  {
+    theme: {
+      extend: {
+        colors: {
+          'cjs-from-plugin': 'black',
+        },
+      },
+    },
+  },
+)

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/esm/my-config.mjs

@@ -0,0 +1,9 @@
+export default {
+  theme: {
+    extend: {
+      colors: {
+        'esm-from-config': 'black',
+      },
+    },
+  },
+}

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/esm/my-plugin.mjs

@@ -0,0 +1,16 @@
+import plugin from 'tailwindcss/plugin'
+
+export default plugin(
+  () => {
+    //
+  },
+  {
+    theme: {
+      extend: {
+        colors: {
+          'esm-from-plugin': 'black',
+        },
+      },
+    },
+  },
+)

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "tailwindcss": "file:tailwindcss.tgz"
+  }
+}

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/ts/my-config.ts

@@ -0,0 +1,11 @@
+import type { Config } from 'tailwindcss'
+
+export default {
+  theme: {
+    extend: {
+      colors: {
+        'ts-from-config': 'black',
+      },
+    },
+  },
+} satisfies Config

packages/tailwindcss-language-server/tests/fixtures/v4/css-loading-js/ts/my-plugin.ts

@@ -0,0 +1,17 @@
+import type { PluginAPI } from 'tailwindcss'
+import plugin from 'tailwindcss/plugin'
+
+export default plugin(
+  (api: PluginAPI) => {
+    //
+  },
+  {
+    theme: {
+      extend: {
+        colors: {
+          'ts-from-plugin': 'black',
+        },
+      },
+    },
+  },
+)