[v4] Make CSS optimization and minification configurable (#13130)

* only run Lightning CSS when passing `--minify` to the CLI

* only optimize the CSS when creating a production build

* add `optimize` option to PostCSS plugin

- The optimize option can be set to `true`, which will optimize
  (unnesting, adding browser prefixes, lowering values) and minify
- The optimize option can also be set to `{ minify: false }`, which will
  optimize but not minify.

* default `optimize` option to the true for `NODE_ENV=production`

* add `--optimize` flag to CLI

This will only optimize the CSS output without minification.

* update `--minify` description

* update changelog

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Add Android builds ([#13115](https://github.com/tailwindlabs/tailwindcss/pull/13115))
+- Make CSS optimization and minification configurable ([#13130](https://github.com/tailwindlabs/tailwindcss/pull/13130))
 
 ## [4.0.0-alpha.6] - 2024-03-07
 

packages/@tailwindcss-cli/src/commands/build/index.ts

@@ -46,9 +46,13 @@ export function options() {
     },
     '--minify': {
       type: 'boolean',
-      description: 'Minify the output',
+      description: 'Optimize and minify the output',
       alias: '-m',
     },
+    '--optimize': {
+      type: 'boolean',
+      description: 'Optimize the output without minifying',
+    },
     '--cwd': {
       type: 'string',
       description: 'The current working directory',
@@ -96,10 +100,15 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
   )
 
   // Compile the input
-  let result = optimizeCss(compile(input, candidates), {
-    file: args['--input'] ?? 'input.css',
-    minify: args['--minify'],
-  })
+  let result = compile(input, candidates)
+
+  // Optimize the output
+  if (args['--minify'] || args['--optimize']) {
+    result = optimizeCss(result, {
+      file: args['--input'] ?? 'input.css',
+      minify: args['--minify'] ?? false,
+    })
+  }
 
   // Write the output
   if (args['--output']) {
@@ -184,10 +193,15 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
         }
 
         // Compile the input
-        let result = optimizeCss(compile(input, candidates), {
-          file: args['--input'] ?? 'input.css',
-          minify: args['--minify'],
-        })
+        let result = compile(input, candidates)
+
+        // Optimize the output
+        if (args['--minify'] || args['--optimize']) {
+          result = optimizeCss(result, {
+            file: args['--input'] ?? 'input.css',
+            minify: args['--minify'] ?? false,
+          })
+        }
 
         // Write the output
         if (args['--output']) {

packages/@tailwindcss-postcss/src/index.test.ts

@@ -18,7 +18,9 @@ beforeEach(async () => {
 })
 
 test("`@import 'tailwindcss'` is replaced with the generated CSS", async () => {
-  let processor = postcss([tailwindcss({ base: `${__dirname}/fixtures/example-project` })])
+  let processor = postcss([
+    tailwindcss({ base: `${__dirname}/fixtures/example-project`, optimize: { minify: false } }),
+  ])
 
   let result = await processor.process(`@import 'tailwindcss'`, { from: INPUT_CSS_PATH })
 
@@ -47,7 +49,9 @@ test("`@import 'tailwindcss'` is replaced with the generated CSS", async () => {
 })
 
 test('output is optimized by Lightning CSS', async () => {
-  let processor = postcss([tailwindcss({ base: `${__dirname}/fixtures/example-project` })])
+  let processor = postcss([
+    tailwindcss({ base: `${__dirname}/fixtures/example-project`, optimize: { minify: false } }),
+  ])
 
   // `@apply` is used because Lightning is skipped if neither `@tailwind` nor
   // `@apply` is used.
@@ -82,7 +86,9 @@ test('output is optimized by Lightning CSS', async () => {
 })
 
 test('@apply can be used without emitting the theme in the CSS file', async () => {
-  let processor = postcss([tailwindcss({ base: `${__dirname}/fixtures/example-project` })])
+  let processor = postcss([
+    tailwindcss({ base: `${__dirname}/fixtures/example-project`, optimize: { minify: false } }),
+  ])
 
   // `@apply` is used because Lightning is skipped if neither `@tailwind` nor
   // `@apply` is used.
@@ -112,7 +118,7 @@ describe('processing without specifying a base path', () => {
   afterEach(() => unlink(filepath))
 
   test('the current working directory is used by default', async () => {
-    let processor = postcss([tailwindcss()])
+    let processor = postcss([tailwindcss({ optimize: { minify: false } })])
 
     let result = await processor.process(`@import "tailwindcss"`, { from: INPUT_CSS_PATH })
 

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

@@ -6,10 +6,14 @@ import { compile, optimizeCss } from 'tailwindcss'
 type PluginOptions = {
   // The base directory to scan for class candidates.
   base?: string
+
+  // Optimize the output CSS.
+  optimize?: boolean | { minify?: boolean }
 }
 
 function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
   let base = opts.base ?? process.cwd()
+  let optimize = opts.optimize ?? process.env.NODE_ENV === 'production'
 
   return {
     postcssPlugin: 'tailwindcss-v4',
@@ -38,7 +42,13 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
 
         function replaceCss(css: string) {
           root.removeAll()
-          root.append(postcss.parse(optimizeCss(css), result.opts))
+          let output = css
+          if (optimize) {
+            output = optimizeCss(output, {
+              minify: typeof optimize === 'object' ? optimize.minify : false,
+            })
+          }
+          root.append(postcss.parse(output, result.opts))
         }
 
         // No `@tailwind` means we don't have to look for candidates

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

@@ -61,7 +61,11 @@ export default function tailwindcss(): Plugin[] {
   }
 
   function generateCss(css: string) {
-    return optimizeCss(compile(css, Array.from(candidates)), { minify })
+    return compile(css, Array.from(candidates))
+  }
+
+  function generateOptimizedCss(css: string) {
+    return optimizeCss(generateCss(css), { minify })
   }
 
   // In dev mode, there isn't a hook to signal that we've seen all files. We use
@@ -168,7 +172,7 @@ export default function tailwindcss(): Plugin[] {
             rawSource instanceof Uint8Array ? new TextDecoder().decode(rawSource) : rawSource
 
           if (source.includes('@tailwind')) {
-            item.source = generateCss(source)
+            item.source = generateOptimizedCss(source)
           }
         }
       },