Stabilize Trailing Slash API (#15331)

Closes #15330

docs/api-reference/next.config.js/trailing-slash.md

@@ -4,18 +4,13 @@ description: Configure Next.js pages to resolve with or without a trailing slash
 
 # Trailing Slash
 
-> **Warning**: This feature is **experimental and may not work as expected**.
-> You must enable the `trailingSlash` experimental option to try it.
-
 By default Next.js will redirect urls with trailing slashes to their counterpart without a trailing slash. For example `/about/` will redirect to `/about`. You can configure this behavior to act the opposite way, where urls without trailing slashes are redirected to their counterparts with trailing slashes.
 
 Open `next.config.js` and add the `trailingSlash` config:
 
 ```js
 module.exports = {
-  experimental: {
-    trailingSlash: true,
-  },
+  trailingSlash: true,
 }
 ```
 

packages/next/build/webpack-config.ts

@@ -839,7 +839,7 @@ export default async function getBaseWebpackConfig(
             }
           : {}),
         'process.env.__NEXT_TRAILING_SLASH': JSON.stringify(
-          config.experimental.trailingSlash
+          config.trailingSlash
         ),
         'process.env.__NEXT_EXPORT_TRAILING_SLASH': JSON.stringify(
           config.exportTrailingSlash

packages/next/lib/load-custom-routes.ts

@@ -357,7 +357,7 @@ export default async function loadCustomRoutes(
     loadRedirects(config),
   ])
 
-  if (config.experimental.trailingSlash) {
+  if (config.trailingSlash) {
     redirects.unshift(
       {
         source: '/:path*/:file.:ext/',

packages/next/next-server/server/config.ts

@@ -37,8 +37,8 @@ const defaultConfig: { [key: string]: any } = {
   basePath: '',
   exportTrailingSlash: false,
   sassOptions: {},
+  trailingSlash: false,
   experimental: {
-    trailingSlash: false,
     cpus: Math.max(
       1,
       (Number(process.env.CIRCLE_NODE_TOTAL) ||

test/integration/trailing-slashes/next.config.js

 module.exports = {
-  experimental: {
-    // <placeholder>
-  },
+  // trailingSlash: boolean,
   // basePath: '/docs',
 }

test/integration/trailing-slashes/test/index.test.js

@@ -178,7 +178,7 @@ function testWithTrailingSlash() {
 describe('Trailing slashes', () => {
   describe('dev mode, trailingSlash: false', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: false')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: false')
       appPort = await findPort()
       app = await launchApp(appDir, appPort)
     })
@@ -192,7 +192,7 @@ describe('Trailing slashes', () => {
 
   describe('dev mode, trailingSlash: true', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: true')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: true')
       appPort = await findPort()
       app = await launchApp(appDir, appPort)
     })
@@ -206,7 +206,7 @@ describe('Trailing slashes', () => {
 
   describe('production mode, trailingSlash: false', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: false')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: false')
       await nextBuild(appDir)
       appPort = await findPort()
       app = await nextStart(appDir, appPort)
@@ -238,7 +238,7 @@ describe('Trailing slashes', () => {
 
   describe('production mode, trailingSlash: true', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: true')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: true')
       await nextBuild(appDir)
       appPort = await findPort()
       app = await nextStart(appDir, appPort)
@@ -275,7 +275,7 @@ describe('Trailing slashes', () => {
 
   describe('dev mode, with basepath, trailingSlash: true', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: true')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: true')
       nextConfig.replace('// basePath:', 'basePath:')
       appPort = await findPort()
       app = await launchApp(appDir, appPort)
@@ -300,7 +300,7 @@ describe('Trailing slashes', () => {
 
   describe('production mode, with basepath, trailingSlash: true', () => {
     beforeAll(async () => {
-      nextConfig.replace('// <placeholder>', 'trailingSlash: true')
+      nextConfig.replace('// trailingSlash: boolean', 'trailingSlash: true')
       nextConfig.replace('// basePath:', 'basePath:')
       await nextBuild(appDir)
       appPort = await findPort()