Remove experimental.newNextLinkBehavior as it's stable (#54720)

Cleans up some code that is not used anymore as this feature went stable
in Next.js 13.

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packages/next-codemod/bin/cli.ts

@@ -132,7 +132,7 @@ const TRANSFORMER_INQUIRER_CHOICES = [
     value: 'cra-to-next',
   },
   {
-    name: 'new-link: Ensures your <Link> usage is backwards compatible. Used in combination with experimental newNextLinkBehavior',
+    name: 'new-link: Ensures your <Link> usage is backwards compatible.',
     value: 'new-link',
   },
   {

packages/next-swc/crates/next-core/js/src/build/client/app-turbopack.ts

@@ -1,6 +1,3 @@
-// @ts-expect-error
-process.env.__NEXT_NEW_LINK_BEHAVIOR = true
-
 // eslint-disable-next-line no-undef
 self.__next_require__ = __turbopack_require__
 

packages/next-swc/crates/next-core/js/src/entry/app-renderer.tsx

@@ -25,8 +25,6 @@ import { IncrementalCache } from 'next/dist/server/lib/incremental-cache'
 
 installRequireAndChunkLoad()
 
-process.env.__NEXT_NEW_LINK_BEHAVIOR = 'true'
-
 const MIME_TEXT_HTML_UTF8 = 'text/html; charset=utf-8'
 
 startOperationStreamHandler(async (renderData: RenderData, respond) => {

packages/next-swc/crates/next-core/js/src/entry/app/hydrate.tsx

@@ -25,8 +25,6 @@ globalThis.__next_require__ = (data) => {
 }
 globalThis.__next_chunk_load__ = __turbopack_load__
 
-process.env.__NEXT_NEW_LINK_BEHAVIOR = 'true'
-
 const appElement = document
 
 const getCacheKey = () => {

packages/next/src/build/jest/jest.ts

@@ -1,7 +1,6 @@
 import { loadEnvConfig } from '@next/env'
 import { resolve, join } from 'path'
 import loadConfig from '../../server/config'
-import type { NextConfigComplete } from '../../server/config-shared'
 import { PHASE_TEST } from '../../shared/lib/constants'
 import loadJsConfig from '../load-jsconfig'
 import * as Log from '../output/log'
@@ -31,13 +30,9 @@ function loadClosestPackageJson(dir: string, attempts = 1): any {
 }
 
 /** Loads dotenv files and sets environment variables based on next config. */
-function setUpEnv(dir: string, nextConfig: NextConfigComplete) {
+function setUpEnv(dir: string) {
   const dev = false
   loadEnvConfig(dir, dev, Log)
-
-  if (nextConfig.experimental.newNextLinkBehavior) {
-    process.env.__NEXT_NEW_LINK_BEHAVIOR = 'true'
-  }
 }
 
 /*
@@ -82,7 +77,7 @@ export default function nextJest(options: { dir?: string } = {}) {
         const findPagesDirResult = findPagesDir(resolvedDir, isAppDirEnabled)
         hasServerComponents = !!findPagesDirResult.appDir
         pagesDir = findPagesDirResult.pagesDir
-        setUpEnv(resolvedDir, nextConfig)
+        setUpEnv(resolvedDir)
         // TODO: revisit when bug in SWC is fixed that strips `.css`
         const result = await loadJsConfig(resolvedDir, nextConfig)
         jsConfig = result.jsConfig

packages/next/src/build/webpack-config.ts

@@ -280,9 +280,6 @@ export function getDefineEnv({
     'process.env.__NEXT_MANUAL_CLIENT_BASE_PATH': JSON.stringify(
       config.experimental.manualClientBasePath
     ),
-    'process.env.__NEXT_NEW_LINK_BEHAVIOR': JSON.stringify(
-      config.experimental.newNextLinkBehavior
-    ),
     'process.env.__NEXT_CLIENT_ROUTER_FILTER_ENABLED': JSON.stringify(
       config.experimental.clientRouterFilter
     ),

packages/next/src/client/link.tsx

@@ -276,8 +276,7 @@ const Link = React.forwardRef<HTMLAnchorElement, LinkPropsReal>(
       onClick,
       onMouseEnter: onMouseEnterProp,
       onTouchStart: onTouchStartProp,
-      // @ts-expect-error this is inlined as a literal boolean not a string
-      legacyBehavior = process.env.__NEXT_NEW_LINK_BEHAVIOR === false,
+      legacyBehavior = false,
       ...restProps
     } = props
 

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

@@ -358,9 +358,6 @@ const configSchema = {
           enum: ['strict', 'flexible'] as any,
           type: 'string',
         },
-        newNextLinkBehavior: {
-          type: 'boolean',
-        },
         nextScriptWorkers: {
           type: 'boolean',
         },

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

@@ -165,7 +165,6 @@ export interface ExperimentalConfig {
   optimisticClientCache?: boolean
   middlewarePrefetch?: 'strict' | 'flexible'
   manualClientBasePath?: boolean
-  newNextLinkBehavior?: boolean
   // custom path to a cache handler to use
   incrementalCacheHandlerPath?: string
   disablePostcssPresetEnv?: boolean
@@ -709,7 +708,6 @@ export const defaultConfig: NextConfig = {
     middlewarePrefetch: 'flexible',
     optimisticClientCache: true,
     manualClientBasePath: false,
-    newNextLinkBehavior: true,
     cpus: Math.max(
       1,
       (Number(process.env.CIRCLE_NODE_TOTAL) ||