From bb78c597704935304b7d7633fdbaab6a25e9052a Mon Sep 17 00:00:00 2001
From: Jordan Pittman <jordan@cryptica.me>
Date: Tue, 29 Apr 2025 19:16:49 -0400
Subject: [PATCH] Add source map support to Vite

---
 integrations/vite/source-maps.test.ts   | 96 +++++++++++++++++++++++++
 packages/@tailwindcss-vite/src/index.ts | 22 +++++-
 2 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 integrations/vite/source-maps.test.ts

diff --git a/integrations/vite/source-maps.test.ts b/integrations/vite/source-maps.test.ts
new file mode 100644
index 000000000..299cd1167
--- /dev/null
+++ b/integrations/vite/source-maps.test.ts
@@ -0,0 +1,96 @@
+import { candidate, css, fetchStyles, html, json, retryAssertion, test, ts } from '../utils'
+
+test(
+  `dev build`,
+  {
+    fs: {
+      'package.json': json`
+        {
+          "type": "module",
+          "dependencies": {
+            "@tailwindcss/vite": "workspace:^",
+            "tailwindcss": "workspace:^"
+          },
+          "devDependencies": {
+            "lightningcss": "^1.26.0",
+            "vite": "^6"
+          }
+        }
+      `,
+      'vite.config.ts': ts`
+        import tailwindcss from '@tailwindcss/vite'
+        import { defineConfig } from 'vite'
+
+        export default defineConfig({
+          plugins: [tailwindcss()],
+          css: {
+            devSourcemap: true,
+          },
+          build: {
+            sourcemap: true,
+          },
+        })
+      `,
+      'index.html': html`
+        <head>
+          <link rel="stylesheet" href="./src/index.css" />
+        </head>
+        <body>
+          <div class="flex">Hello, world!</div>
+        </body>
+      `,
+      'src/index.css': css`
+        @import 'tailwindcss/utilities';
+        /*  */
+      `,
+    },
+  },
+  async ({ fs, spawn, expect, parseSourceMap }) => {
+    // Source maps only work in development mode in Vite
+    let process = await spawn('pnpm vite dev')
+    await process.onStdout((m) => m.includes('ready in'))
+
+    let url = ''
+    await process.onStdout((m) => {
+      let match = /Local:\s*(http.*)\//.exec(m)
+      if (match) url = match[1]
+      return Boolean(url)
+    })
+
+    let styles = await retryAssertion(async () => {
+      let styles = await fetchStyles(url, '/index.html')
+
+      // Wait until we have the right CSS
+      expect(styles).toContain(candidate`flex`)
+
+      return styles
+    })
+
+    // Make sure we can find a source map
+    let map = parseSourceMap(styles)
+
+    expect(map.at(1, 0)).toMatchObject({
+      source: null,
+      original: '(none)',
+      generated: '/*! tailwi...',
+    })
+
+    expect(map.at(2, 0)).toMatchObject({
+      source: expect.stringContaining('node_modules/tailwindcss/utilities.css'),
+      original: '@tailwind...',
+      generated: '.flex {...',
+    })
+
+    expect(map.at(3, 2)).toMatchObject({
+      source: expect.stringContaining('node_modules/tailwindcss/utilities.css'),
+      original: '@tailwind...',
+      generated: 'display: f...',
+    })
+
+    expect(map.at(4, 0)).toMatchObject({
+      source: null,
+      original: '(none)',
+      generated: '}...',
+    })
+  },
+)
diff --git a/packages/@tailwindcss-vite/src/index.ts b/packages/@tailwindcss-vite/src/index.ts
index 0a053291a..00ba92db4 100644
--- a/packages/@tailwindcss-vite/src/index.ts
+++ b/packages/@tailwindcss-vite/src/index.ts
@@ -1,4 +1,12 @@
-import { compile, env, Features, Instrumentation, normalizePath, optimize } from '@tailwindcss/node'
+import {
+  compile,
+  env,
+  Features,
+  Instrumentation,
+  normalizePath,
+  optimize,
+  toSourceMap,
+} from '@tailwindcss/node'
 import { clearRequireCache } from '@tailwindcss/node/require-cache'
 import { Scanner } from '@tailwindcss/oxide'
 import fs from 'node:fs/promises'
@@ -37,6 +45,9 @@ export default function tailwindcss(): Plugin[] {
     return new Root(
       id,
       config!.root,
+      // Currently, Vite only supports CSS source maps in development and they
+      // are off by default. Check to see if we need them or not.
+      config?.css.devSourcemap ?? false,
       customCssResolver,
       customJsResolver,
     )
@@ -108,6 +119,7 @@ export default function tailwindcss(): Plugin[] {
         DEBUG && I.start('[@tailwindcss/vite] Optimize CSS')
         result = optimize(result.code, {
           minify,
+          map: result.map,
         })
         DEBUG && I.end('[@tailwindcss/vite] Optimize CSS')
 
@@ -180,6 +192,7 @@ class Root {
     private id: string,
     private base: string,
 
+    private enableSourceMaps: boolean,
     private customCssResolver: (id: string, base: string) => Promise<string | false | undefined>,
     private customJsResolver: (id: string, base: string) => Promise<string | false | undefined>,
   ) {}
@@ -193,6 +206,7 @@ class Root {
   ): Promise<
     | {
         code: string
+        map: string | undefined
       }
     | false
   > {
@@ -227,6 +241,7 @@ class Root {
       DEBUG && I.start('Setup compiler')
       let addBuildDependenciesPromises: Promise<void>[] = []
       this.compiler = await compile(content, {
+        from: this.enableSourceMaps ? this.id : undefined,
         base: inputBase,
         shouldRewriteUrls: true,
         onDependency: (path) => {
@@ -328,8 +343,13 @@ class Root {
     let code = this.compiler.build([...this.candidates])
     DEBUG && I.end('Build CSS')
 
+    DEBUG && I.start('Build Source Map')
+    let map = this.enableSourceMaps ? toSourceMap(this.compiler.buildSourceMap()).raw : undefined
+    DEBUG && I.end('Build Source Map')
+
     return {
       code,
+      map,
     }
   }