feat(next-dev): reenable turbopack beta message (#55116)

### What?
Minor PR brings back turbopack beta message. We'll need to improve the actual checks per progress, but that might need auditing what's working vs not later.


Closes WEB-1517

packages/next-swc/crates/next-core/src/next_config.rs

@@ -84,6 +84,7 @@ pub struct NextConfig {
     pub transpile_packages: Option<Vec<String>>,
     pub modularize_imports: Option<IndexMap<String, ModularizeImportPackageConfig>>,
     sass_options: Option<serde_json::Value>,
+    trailing_slash: bool,
 
     // Partially supported
     pub compiler: Option<CompilerConfig>,
@@ -119,7 +120,6 @@ pub struct NextConfig {
     static_page_generation_timeout: f64,
     swc_minify: Option<bool>,
     target: Option<String>,
-    trailing_slash: bool,
     typescript: TypeScriptConfig,
     use_file_system_public_routes: bool,
     webpack: Option<serde_json::Value>,
@@ -413,7 +413,7 @@ pub struct ExperimentalConfig {
     pub swc_plugins: Option<Vec<(String, serde_json::Value)>>,
 
     // unsupported
-    adjust_font_fallbacks: Option<bool>,
+    optimize_package_imports: Option<Vec<String>>,
     adjust_font_fallbacks_with_size_adjust: Option<bool>,
     allow_middleware_response_body: Option<bool>,
     amp: Option<serde_json::Value>,

packages/next/src/cli/next-dev.ts

@@ -22,6 +22,7 @@ import {
   getReservedPortExplanation,
   isPortIsReserved,
 } from '../lib/helpers/get-reserved-port'
+import { validateTurboNextConfig } from '../lib/turbopack-warning'
 
 let dir: string
 let config: NextConfigComplete
@@ -227,6 +228,11 @@ const nextDev: CliCommand = async (args) => {
 
   if (args['--turbo']) {
     process.env.TURBOPACK = '1'
+    await validateTurboNextConfig({
+      isCustomTurbopack: !!process.env.__INTERNAL_CUSTOM_TURBOPACK_BINDINGS,
+      ...devServerOptions,
+      isDev: true,
+    })
   }
 
   const distDir = path.join(dir, config.distDir ?? '.next')

packages/next/src/lib/turbopack-warning.ts

@@ -6,6 +6,7 @@ import { PHASE_DEVELOPMENT_SERVER } from '../shared/lib/constants'
 const supportedTurbopackNextConfigOptions = [
   'configFileName',
   'env',
+  'basePath',
   'modularizeImports',
   'compiler.emotion',
   'compiler.relay',
@@ -19,6 +20,9 @@ const supportedTurbopackNextConfigOptions = [
   'reactStrictMode',
   'swcMinify',
   'transpilePackages',
+  'trailingSlash',
+  'i18n.locales',
+  'i18n.defaultLocale',
   'sassOptions.includePaths',
   'experimental.serverComponentsExternalPackages',
   'experimental.turbo',
@@ -214,7 +218,17 @@ export async function validateTurboNextConfig({
       babelrc
     )})\n  ${`Babel is not yet supported. To use Turbopack at the moment,\n  you'll need to remove your usage of Babel.`}`
   }
-  if (unsupportedConfig.length) {
+
+  if (
+    unsupportedConfig.length === 1 &&
+    unsupportedConfig[0] === 'experimental.optimizePackageImports'
+  ) {
+    console.warn(
+      `\n${chalk.yellow('Warning:')} ${chalk.cyan(
+        'experimental.optimizePackageImports'
+      )} is not yet supported by Turbopack and will be ignored.`
+    )
+  } else if (unsupportedConfig.length) {
     unsupportedParts += `\n\n- Unsupported Next.js configuration option(s) (${chalk.cyan(
       'next.config.js'
     )})\n  ${`To use Turbopack, remove the following configuration options:\n${unsupportedConfig

test/turbopack-tests-manifest.js

@@ -131,7 +131,6 @@ const enabledTests = [
   'test/integration/ssg-dynamic-routes-404-page/test/index.test.js',
   'test/integration/static-404/test/index.test.js',
   'test/integration/static-page-name/test/index.test.js',
-  'test/integration/trailing-slash-dist/test/index.test.js',
   'test/integration/trailing-slashes-href-resolving/test/index.test.js',
   'test/production/app-dir-hide-suppressed-error-during-next-export/index.test.ts',
   'test/production/app-dir-prefetch-non-iso-url/index.test.ts',
@@ -141,6 +140,9 @@ const enabledTests = [
   'test/production/jest/transpile-packages.test.ts',
   'test/production/postcss-plugin-config-as-string/index.test.ts',
   'test/production/suppo.ts',
+
+  // disabled due to nextConfig.distDir
+  //'test/integration/trailing-slash-dist/test/index.test.js',
 ]
 
 module.exports = { enabledTests }