Ensure deterministic SSR builds in @tailwindcss/vite (#13457)

* ensure we wait in the `build` step as well

It looks like when running `astro build` we only run this `build` step
and not the `dev` step where we already use the `waitForRequestsIdle`
code.

Adding this to the `build` part as well does generate the correct
result.

* update changelog

* fix typo

* add comment

* Don’t run transforms more than necessary

* Don’t remove modules from the graph during SSR

* Update changelog

* Add `preview` script

---------

Co-authored-by: Jordan Pittman <jordan@cryptica.me>

Author: RobinMalfait

CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Fixed
+
+- Ensure deterministic SSR builds in `@tailwindcss/vite` ([#13457](https://github.com/tailwindlabs/tailwindcss/pull/13457))
 
 ## [4.0.0-alpha.13] - 2024-04-04
 

packages/@tailwindcss-vite/src/index.ts

@@ -7,24 +7,36 @@ import type { Plugin, Rollup, Update, ViteDevServer } from 'vite'
 export default function tailwindcss(): Plugin[] {
   let server: ViteDevServer | null = null
   let candidates = new Set<string>()
-  // In serve mode, we treat this as a set, storing storing empty strings.
+  // In serve mode this is treated as a set — the content doesn't matter.
   // In build mode, we store file contents to use them in renderChunk.
-  let cssModules: Record<string, string> = {}
+  let cssModules: Record<
+    string,
+    {
+      content: string
+      handled: boolean
+    }
+  > = {}
+  let isSSR = false
   let minify = false
   let cssPlugins: readonly Plugin[] = []
 
   // Trigger update to all CSS modules
-  function updateCssModules() {
+  function updateCssModules(isSSR: boolean) {
     // If we're building then we don't need to update anything
     if (!server) return
 
     let updates: Update[] = []
     for (let id of Object.keys(cssModules)) {
       let cssModule = server.moduleGraph.getModuleById(id)
       if (!cssModule) {
-        // It is safe to remove the item here since we're iterating on a copy of
-        // the keys.
-        delete cssModules[id]
+        // Note: Removing this during SSR is not safe and will produce
+        // inconsistent results based on the timing of the removal and
+        // the order / timing of transforms.
+        if (!isSSR) {
+          // It is safe to remove the item here since we're iterating on a copy
+          // of the keys.
+          delete cssModules[id]
+        }
         continue
       }
 
@@ -85,7 +97,7 @@ export default function tailwindcss(): Plugin[] {
       try {
         // Directly call the plugin's transform function to process the
         // generated CSS. In build mode, this updates the chunks later used to
-        // generate the bundle. In serve mode, the transformed souce should be
+        // generate the bundle. In serve mode, the transformed source should be
         // applied in transform.
         let result = await transformHandler.call(transformPluginContext, css, id)
         if (!result) continue
@@ -113,16 +125,21 @@ export default function tailwindcss(): Plugin[] {
 
       async configResolved(config) {
         minify = config.build.cssMinify !== false
-        // Apply the vite:css plugin to generated CSS for transformations like
-        // URL path rewriting and image inlining.
-        //
-        // In build mode, since renderChunk runs after all transformations, we
-        // need to also apply vite:css-post.
-        cssPlugins = config.plugins.filter((plugin) =>
-          ['vite:css', ...(config.command === 'build' ? ['vite:css-post'] : [])].includes(
-            plugin.name,
-          ),
-        )
+        isSSR = config.build.ssr !== false && config.build.ssr !== undefined
+
+        let allowedPlugins = [
+          // Apply the vite:css plugin to generated CSS for transformations like
+          // URL path rewriting and image inlining.
+          'vite:css',
+
+          // In build mode, since renderChunk runs after all transformations, we
+          // need to also apply vite:css-post.
+          ...(config.command === 'build' ? ['vite:css-post'] : []),
+        ]
+
+        cssPlugins = config.plugins.filter((plugin) => {
+          return allowedPlugins.includes(plugin.name)
+        })
       },
 
       // Scan index.html for candidates
@@ -134,18 +151,18 @@ export default function tailwindcss(): Plugin[] {
         // CSS update will cause an infinite loop. We only trigger if the
         // candidates have been updated.
         if (updated) {
-          updateCssModules()
+          updateCssModules(isSSR)
         }
       },
 
       // Scan all non-CSS files for candidates
-      transform(src, id) {
+      transform(src, id, options) {
         if (id.includes('/.vite/')) return
         let extension = getExtension(id)
         if (extension === '' || extension === 'css') return
 
         scan(src, extension)
-        updateCssModules()
+        updateCssModules(options?.ssr ?? false)
       },
     },
 
@@ -163,7 +180,7 @@ export default function tailwindcss(): Plugin[] {
         if (!isTailwindCssFile(id, src)) return
 
         // In serve mode, we treat cssModules as a set, ignoring the value.
-        cssModules[id] = ''
+        cssModules[id] = { content: '', handled: true }
 
         if (!options?.ssr) {
           // Wait until all other files have been processed, so we can extract
@@ -184,15 +201,26 @@ export default function tailwindcss(): Plugin[] {
 
       transform(src, id) {
         if (!isTailwindCssFile(id, src)) return
-        cssModules[id] = src
+        cssModules[id] = { content: src, handled: false }
       },
 
       // renderChunk runs in the bundle generation stage after all transforms.
       // We must run before `enforce: post` so the updated chunks are picked up
       // by vite:css-post.
       async renderChunk(_code, _chunk) {
-        for (let [cssFile, css] of Object.entries(cssModules)) {
-          await transformWithPlugins(this, cssFile, generateOptimizedCss(css))
+        for (let [id, file] of Object.entries(cssModules)) {
+          if (file.handled) {
+            continue
+          }
+
+          let css = generateOptimizedCss(file.content)
+
+          // These plugins have side effects which, during build, results in CSS
+          // being written to the output dir. We need to run them here to ensure
+          // the CSS is written before the bundle is generated.
+          await transformWithPlugins(this, id, css)
+
+          file.handled = true
         }
       },
     },

playgrounds/vite/package.json

@@ -5,7 +5,8 @@
   "scripts": {
     "lint": "tsc --noEmit",
     "dev": "bun --bun vite ./src --config ./vite.config.ts",
-    "build": "bun --bun vite build ./src --outDir ../dist --config ./vite.config.ts --emptyOutDir"
+    "build": "bun --bun vite build ./src --outDir ../dist --config ./vite.config.ts --emptyOutDir",
+    "preview": "bun --bun vite preview"
   },
   "dependencies": {
     "@tailwindcss/vite": "workspace:^",