refactor: make locales array immutable (#74037)

To improve memory efficiency, this marks all the locale arrays as readonly. This ensures that there's no undefined behaviour from accidentally mutating the array, and allows us to use the locales array as a stable reference for a future optimization PR.
vercel · Dec 17, 2024 · 4f5df6a · 4f5df6a
1 parent d5fc05b
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Showing 16 changed files with 52 additions and 39 deletions.
diff --git a/packages/next/src/build/index.ts b/packages/next/src/build/index.ts
@@ -377,13 +377,13 @@ export type RoutesManifest = {
   dynamicRoutes: Array<ManifestRoute>
   dataRoutes: Array<ManifestDataRoute>
   i18n?: {
-    domains?: Array<{
+    domains?: ReadonlyArray<{
       http?: true
       domain: string
-      locales?: string[]
+      locales?: readonly string[]
       defaultLocale: string
     }>
-    locales: string[]
+    locales: readonly string[]
     defaultLocale: string
     localeDetection?: false
   }
@@ -473,7 +473,11 @@ async function writeClientSsgManifest(
     buildId,
     distDir,
     locales,
-  }: { buildId: string; distDir: string; locales: string[] }
+  }: {
+    buildId: string
+    distDir: string
+    locales: readonly string[] | undefined
+  }
 ) {
   const ssgPages = new Set<string>(
     [
@@ -3622,7 +3626,7 @@ export default async function build(
         await writeClientSsgManifest(prerenderManifest, {
           distDir,
           buildId,
-          locales: config.i18n?.locales || [],
+          locales: config.i18n?.locales,
         })
       } else {
         await writePrerenderManifest(distDir, {

diff --git a/packages/next/src/build/static-paths/pages.ts b/packages/next/src/build/static-paths/pages.ts
@@ -19,7 +19,7 @@ export async function buildPagesStaticPaths({
   page: string
   getStaticPaths: GetStaticPaths
   configFileName: string
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
 }): Promise<StaticPathsResult> {
   const prerenderedRoutes: PrerenderedRoute[] = []
@@ -28,7 +28,13 @@ export async function buildPagesStaticPaths({
 
   // Get the default list of allowed params.
   const routeParameterKeys = Object.keys(_routeMatcher(page))
-  const staticPathsResult = await getStaticPaths({ locales, defaultLocale })
+  const staticPathsResult = await getStaticPaths({
+    // We create a copy here to avoid having the types of `getStaticPaths`
+    // change. This ensures that users can't mutate this array and have it
+    // poison the reference.
+    locales: [...(locales ?? [])],
+    defaultLocale,
+  })
 
   const expectedReturnVal =
     `Expected: { paths: [], fallback: boolean }\n` +

diff --git a/packages/next/src/build/utils.ts b/packages/next/src/build/utils.ts
@@ -981,7 +981,7 @@ export async function isPageStatic({
   configFileName: string
   runtimeEnvConfig: any
   httpAgentOptions: NextConfigComplete['httpAgentOptions']
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
   parentId?: any
   edgeInfo?: any

diff --git a/packages/next/src/client/get-domain-locale.ts b/packages/next/src/client/get-domain-locale.ts
@@ -8,8 +8,8 @@ const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 export function getDomainLocale(
   path: string,
   locale?: string | false,
-  locales?: string[],
-  domainLocales?: DomainLocale[]
+  locales?: readonly string[],
+  domainLocales?: readonly DomainLocale[]
 ) {
   if (process.env.__NEXT_I18N_SUPPORT) {
     const normalizeLocalePath: typeof NormalizeFn =

diff --git a/packages/next/src/server/accept-header.ts b/packages/next/src/server/accept-header.ts
@@ -12,7 +12,7 @@ interface Options {
 
 function parse(
   raw: string,
-  preferences: string[] | undefined,
+  preferences: readonly string[] | undefined,
   options: Options
 ) {
   const lowers = new Map<string, { orig: string; pos: number }>()
@@ -127,7 +127,7 @@ function parse(
   return preferred
 }
 
-export function acceptLanguage(header = '', preferences?: string[]) {
+export function acceptLanguage(header = '', preferences?: readonly string[]) {
   return (
     parse(header, preferences, {
       type: 'accept-language',

diff --git a/packages/next/src/server/base-server.ts b/packages/next/src/server/base-server.ts
@@ -1437,7 +1437,7 @@ export default abstract class Server<
         }
         const normalizeResult = normalizeLocalePath(
           removePathPrefix(parsedUrl.pathname, this.nextConfig.basePath || ''),
-          this.nextConfig.i18n?.locales || []
+          this.nextConfig.i18n?.locales
         )
 
         if (normalizeResult.detectedLocale) {

diff --git a/packages/next/src/server/config-shared.ts b/packages/next/src/server/config-shared.ts
@@ -23,20 +23,20 @@ export type NextConfigComplete = Required<NextConfig> & {
   configFileName: string
 }
 
-export type I18NDomains = DomainLocale[]
+export type I18NDomains = readonly DomainLocale[]
 
 export interface I18NConfig {
   defaultLocale: string
   domains?: I18NDomains
   localeDetection?: false
-  locales: string[]
+  locales: readonly string[]
 }
 
 export interface DomainLocale {
   defaultLocale: string
   domain: string
   http?: true
-  locales?: string[]
+  locales?: readonly string[]
 }
 
 export interface ESLintConfig {

diff --git a/packages/next/src/server/dev/static-paths-worker.ts b/packages/next/src/server/dev/static-paths-worker.ts
@@ -55,7 +55,7 @@ export async function loadStaticPaths({
   pathname: string
   config: RuntimeConfig
   httpAgentOptions: NextConfigComplete['httpAgentOptions']
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
   isAppPath: boolean
   page: string

diff --git a/packages/next/src/server/render.tsx b/packages/next/src/server/render.tsx
@@ -142,9 +142,9 @@ class ServerRouter implements NextRouter {
   isFallback: boolean
   locale?: string
   isReady: boolean
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
-  domainLocales?: DomainLocale[]
+  domainLocales?: readonly DomainLocale[]
   isPreview: boolean
   isLocaleDomain: boolean
 
@@ -156,9 +156,9 @@ class ServerRouter implements NextRouter {
     isReady: boolean,
     basePath: string,
     locale?: string,
-    locales?: string[],
+    locales?: readonly string[],
     defaultLocale?: string,
-    domainLocales?: DomainLocale[],
+    domainLocales?: readonly DomainLocale[],
     isPreview?: boolean,
     isLocaleDomain?: boolean
   ) {
@@ -261,9 +261,9 @@ export type RenderOptsPartial = {
   nextFontManifest?: DeepReadonly<NextFontManifest>
   distDir?: string
   locale?: string
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
-  domainLocales?: DomainLocale[]
+  domainLocales?: readonly DomainLocale[]
   disableOptimizedLoading?: boolean
   supportsDynamicResponse: boolean
   isBot?: boolean
@@ -848,7 +848,7 @@ export async function renderToHTMLImpl(
             ...(isPreview
               ? { draftMode: true, preview: true, previewData: previewData }
               : undefined),
-            locales: renderOpts.locales,
+            locales: [...(renderOpts.locales ?? [])],
             locale: renderOpts.locale,
             defaultLocale: renderOpts.defaultLocale,
             revalidateReason: renderOpts.isOnDemandRevalidate
@@ -1071,7 +1071,10 @@ export async function renderToHTMLImpl(
             ...(previewData !== false
               ? { draftMode: true, preview: true, previewData: previewData }
               : undefined),
-            locales: renderOpts.locales,
+            // We create a copy here to avoid having the types of
+            // `getServerSideProps` change. This ensures that users can't
+            // mutate this array and have it poison the reference.
+            locales: [...(renderOpts.locales ?? [])],
             locale: renderOpts.locale,
             defaultLocale: renderOpts.defaultLocale,
           })

diff --git a/packages/next/src/server/require.ts b/packages/next/src/server/require.ts
@@ -19,7 +19,7 @@ const pagePathCache = !isDev ? new LRUCache<string | null>(1000) : null
 export function getMaybePagePath(
   page: string,
   distDir: string,
-  locales: string[] | undefined,
+  locales: readonly string[] | undefined,
   isAppPath: boolean
 ): string | null {
   const cacheKey = `${page}:${distDir}:${locales}:${isAppPath}`

diff --git a/packages/next/src/shared/lib/i18n/detect-domain-locale.ts b/packages/next/src/shared/lib/i18n/detect-domain-locale.ts
@@ -1,7 +1,7 @@
 import type { DomainLocale } from '../../../server/config-shared'
 
 export function detectDomainLocale(
-  domainItems?: DomainLocale[],
+  domainItems?: readonly DomainLocale[],
   hostname?: string,
   detectedLocale?: string
 ) {

diff --git a/packages/next/src/shared/lib/i18n/normalize-locale-path.ts b/packages/next/src/shared/lib/i18n/normalize-locale-path.ts
@@ -14,7 +14,7 @@ export interface PathLocale {
  */
 export function normalizeLocalePath(
   pathname: string,
-  locales?: string[]
+  locales?: readonly string[]
 ): PathLocale {
   let detectedLocale: string | undefined
   // first item will be empty string from splitting at first char

diff --git a/packages/next/src/shared/lib/router/router.ts b/packages/next/src/shared/lib/router/router.ts
@@ -348,9 +348,9 @@ export type BaseRouter = {
   asPath: string
   basePath: string
   locale?: string | undefined
-  locales?: string[] | undefined
+  locales?: readonly string[] | undefined
   defaultLocale?: string | undefined
-  domainLocales?: DomainLocale[] | undefined
+  domainLocales?: readonly DomainLocale[] | undefined
   isLocaleDomain: boolean
 }
 
@@ -681,9 +681,9 @@ export default class Router implements BaseRouter {
   isSsr: boolean
   _inFlightRoute?: string | undefined
   _shallow?: boolean | undefined
-  locales?: string[] | undefined
+  locales?: readonly string[] | undefined
   defaultLocale?: string | undefined
-  domainLocales?: DomainLocale[] | undefined
+  domainLocales?: readonly DomainLocale[] | undefined
   isReady: boolean
   isLocaleDomain: boolean
   isFirstPopStateEvent = true
@@ -735,9 +735,9 @@ export default class Router implements BaseRouter {
       err?: Error
       isFallback: boolean
       locale?: string
-      locales?: string[]
+      locales?: readonly string[]
       defaultLocale?: string
-      domainLocales?: DomainLocale[]
+      domainLocales?: readonly DomainLocale[]
       isPreview?: boolean
     }
   ) {

diff --git a/packages/next/src/shared/lib/router/utils/get-next-pathname-info.ts b/packages/next/src/shared/lib/router/utils/get-next-pathname-info.ts
@@ -39,7 +39,7 @@ interface Options {
    */
   nextConfig?: {
     basePath?: string
-    i18n?: { locales?: string[] } | null
+    i18n?: { locales?: readonly string[] } | null
     trailingSlash?: boolean
   }
 

diff --git a/packages/next/src/shared/lib/router/utils/resolve-rewrites.ts b/packages/next/src/shared/lib/router/utils/resolve-rewrites.ts
@@ -17,7 +17,7 @@ export default function resolveRewrites(
   },
   query: ParsedUrlQuery,
   resolveHref: (path: string) => string,
-  locales?: string[]
+  locales?: readonly string[]
 ): {
   matchedPage: boolean
   parsedAs: ParsedRelativeUrl

diff --git a/packages/next/src/shared/lib/utils.ts b/packages/next/src/shared/lib/utils.ts
@@ -107,9 +107,9 @@ export type NEXT_DATA = {
   gip?: boolean
   appGip?: boolean
   locale?: string
-  locales?: string[]
+  locales?: readonly string[]
   defaultLocale?: string
-  domainLocales?: DomainLocale[]
+  domainLocales?: readonly DomainLocale[]
   scriptLoader?: any[]
   isPreview?: boolean
   notFoundSrcPage?: string
@@ -150,7 +150,7 @@ export interface NextPageContext {
   /**
    * All configured locales
    */
-  locales?: string[]
+  locales?: readonly string[]
   /**
    * The configured default locale
    */