fix: Lazy init message formatter for improved tree shaking in case useTranslations is only used in Server Components

docs/components/CodeSnippets.tsx

@@ -334,7 +334,7 @@ function buildOutput() {
         <span style={{color: 'var(--shiki-color-text)'}}> kB</span>
         <span style={{color: 'var(--shiki-color-text)'}}>{'     '}</span>
         <span style={{color: 'var(--shiki-token-string-expression)'}}>
-          87.6 kB
+          89.7 kB
         </span>
       </span>
       <span className="line">
@@ -344,7 +344,7 @@ function buildOutput() {
         <span style={{color: 'var(--shiki-color-text)'}}> B</span>
         <span style={{color: 'var(--shiki-color-text)'}}>{'      '}</span>
         <span style={{color: 'var(--shiki-token-string-expression)'}}>
-          86.2 kB
+          89.3 kB
         </span>
       </span>
       <span className="line">
@@ -354,7 +354,7 @@ function buildOutput() {
         <span style={{color: 'var(--shiki-color-text)'}}> kB</span>
         <span style={{color: 'var(--shiki-color-text)'}}>{'    '}</span>
         <span style={{color: 'var(--shiki-token-string-expression)'}}>
-          89.3 kB
+          91.1 kB
         </span>
       </span>
       <span className="line"> </span>

packages/next-intl/.size-limit.ts

@@ -0,0 +1,48 @@
+import type {SizeLimitConfig} from 'size-limit';
+
+const config: SizeLimitConfig = [
+  {
+    path: 'dist/production/index.react-client.js',
+    limit: '14.084 KB'
+  },
+  {
+    path: 'dist/production/index.react-server.js',
+    limit: '14.665 KB'
+  },
+  {
+    path: 'dist/production/navigation.react-client.js',
+    limit: '3.155 KB'
+  },
+  {
+    path: 'dist/production/navigation.react-server.js',
+    limit: '15.975 KB'
+  },
+  {
+    path: 'dist/production/server.react-client.js',
+    limit: '1 KB'
+  },
+  {
+    path: 'dist/production/server.react-server.js',
+    limit: '13.975 KB'
+  },
+  {
+    path: 'dist/production/middleware.js',
+    limit: '9.535 KB'
+  },
+  {
+    path: 'dist/production/routing.js',
+    limit: '0 KB'
+  },
+  {
+    path: 'dist/esm/index.react-client.js',
+    import: '*',
+    limit: '14.265 kB'
+  },
+  {
+    path: 'dist/esm/index.react-client.js',
+    import: '{NextIntlClientProvider}',
+    limit: '1.425 kB'
+  }
+];
+
+module.exports = config;

packages/next-intl/package.json

@@ -96,7 +96,7 @@
   "devDependencies": {
     "@arethetypeswrong/cli": "^0.15.3",
     "@edge-runtime/vm": "^3.2.0",
-    "@size-limit/preset-big-lib": "^8.2.6",
+    "@size-limit/preset-big-lib": "^11.1.4",
     "@testing-library/react": "^16.0.0",
     "@types/negotiator": "^0.6.3",
     "@types/node": "^20.14.5",
@@ -112,43 +112,9 @@
     "react-dom": "^18.3.1",
     "rollup": "^4.18.0",
     "rollup-plugin-preserve-directives": "0.4.0",
-    "size-limit": "^8.2.6",
+    "size-limit": "^11.1.4",
     "typescript": "^5.5.3",
     "vitest": "^2.0.2"
   },
-  "prettier": "../../.prettierrc.json",
-  "size-limit": [
-    {
-      "path": "dist/production/index.react-client.js",
-      "limit": "16.055 KB"
-    },
-    {
-      "path": "dist/production/index.react-server.js",
-      "limit": "16.875 KB"
-    },
-    {
-      "path": "dist/production/navigation.react-client.js",
-      "limit": "3.55 KB"
-    },
-    {
-      "path": "dist/production/navigation.react-server.js",
-      "limit": "18.355 KB"
-    },
-    {
-      "path": "dist/production/server.react-client.js",
-      "limit": "1 KB"
-    },
-    {
-      "path": "dist/production/server.react-server.js",
-      "limit": "16.025 KB"
-    },
-    {
-      "path": "dist/production/middleware.js",
-      "limit": "11.515 KB"
-    },
-    {
-      "path": "dist/production/routing.js",
-      "limit": "0 KB"
-    }
-  ]
+  "prettier": "../../.prettierrc.json"
 }

packages/next-intl/src/react-server/index.test.tsx

@@ -1,14 +1,14 @@
 import React from 'react';
 import {describe, expect, vi, it} from 'vitest';
 import {getTranslations} from '../server.react-server';
-import {renderToStream} from './utils';
+import {renderToStream} from './testUtils';
 import {
-  createTranslator,
   useFormatter,
   useLocale,
   useMessages,
   useNow,
-  useTranslations
+  useTranslations,
+  _createCache
 } from '.';
 
 vi.mock('react');
@@ -32,10 +32,9 @@ vi.mock('../../src/server/react-server/RequestLocale', () => ({
 
 vi.mock('use-intl/core', async (importActual) => {
   const actual: any = await importActual();
-  const {createTranslator: actualCreateTranslator} = actual;
   return {
     ...actual,
-    createTranslator: vi.fn(actualCreateTranslator)
+    _createCache: vi.fn(actual._createCache)
   };
 });
 
@@ -73,8 +72,7 @@ describe('performance', () => {
   });
 
   it('shares a formatter cache between `useTranslations` and `getTranslations`', async () => {
-    // First invocation
-    // (simulate React rendering)
+    // First invocation (simulate React rendering)
     try {
       useTranslations('Component');
     } catch (promiseOrError) {
@@ -89,12 +87,7 @@ describe('performance', () => {
     // Second invocation with a different namespace
     await getTranslations('Component2');
 
-    // Verify the cached formatters are shared
-    expect(vi.mocked(createTranslator).mock.calls[0][0]._formatters).toBe(
-      vi.mocked(createTranslator).mock.calls[1][0]._formatters
-    );
-    expect(vi.mocked(createTranslator).mock.calls.length).toBe(2);
-
-    vi.mocked(createTranslator).mockReset();
+    expect(vi.mocked(_createCache).mock.calls.length).toBe(1);
+    vi.mocked(_createCache).mockReset();
   });
 });

packages/next-intl/src/react-server/useTranslations.test.tsx

@@ -1,6 +1,6 @@
 import React, {cache} from 'react';
 import {describe, expect, it, vi, beforeEach} from 'vitest';
-import {renderToStream} from './utils';
+import {renderToStream} from './testUtils';
 import {createTranslator, useTranslations} from '.';
 
 vi.mock('../../src/server/react-server/createRequestConfig', () => ({

packages/next-intl/src/server/react-server/getConfig.tsx

@@ -1,5 +1,10 @@
 import {cache} from 'react';
-import {initializeConfig, IntlConfig, _createFormatters} from 'use-intl/core';
+import {
+  initializeConfig,
+  IntlConfig,
+  _createIntlFormatters,
+  _createCache
+} from 'use-intl/core';
 import {getRequestLocale} from './RequestLocale';
 import createRequestConfig from './createRequestConfig';
 
@@ -52,22 +57,26 @@ async function receiveRuntimeConfigImpl(
 }
 const receiveRuntimeConfig = cache(receiveRuntimeConfigImpl);
 
-const getFormatters = cache(_createFormatters);
+const getFormatters = cache(_createIntlFormatters);
+const getCache = cache(_createCache);
 
 async function getConfigImpl(localeOverride?: string): Promise<
   IntlConfig & {
     getMessageFallback: NonNullable<IntlConfig['getMessageFallback']>;
     now: NonNullable<IntlConfig['now']>;
     onError: NonNullable<IntlConfig['onError']>;
     timeZone: NonNullable<IntlConfig['timeZone']>;
-    _formatters: ReturnType<typeof _createFormatters>;
+    _formatters: ReturnType<typeof _createIntlFormatters>;
   }
 > {
   const runtimeConfig = await receiveRuntimeConfig(
     createRequestConfig,
     localeOverride
   );
-  return {...initializeConfig(runtimeConfig), _formatters: getFormatters()};
+  return {
+    ...initializeConfig(runtimeConfig),
+    _formatters: getFormatters(getCache())
+  };
 }
 const getConfig = cache(getConfigImpl);
 export default getConfig;

packages/use-intl/.size-limit.ts

@@ -0,0 +1,24 @@
+import type {SizeLimitConfig} from 'size-limit';
+
+const config: SizeLimitConfig = [
+  {
+    name: './ (ESM)',
+    import: '*',
+    path: 'dist/esm/index.js',
+    limit: '14.065 kB'
+  },
+  {
+    name: './ (no useTranslations, ESM)',
+    path: 'dist/esm/index.js',
+    import:
+      '{IntlProvider, useLocale, useNow, useTimeZone, useMessages, useFormatter}',
+    limit: '2.865 kB'
+  },
+  {
+    name: './ (CJS)',
+    path: 'dist/production/index.js',
+    limit: '15.65 kB'
+  }
+];
+
+module.exports = config;

packages/use-intl/package.json

@@ -71,7 +71,7 @@
   },
   "devDependencies": {
     "@arethetypeswrong/cli": "^0.15.3",
-    "@size-limit/preset-big-lib": "^8.2.6",
+    "@size-limit/preset-big-lib": "^11.1.4",
     "@testing-library/react": "^16.0.0",
     "@types/node": "^20.14.5",
     "@types/react": "^18.3.3",
@@ -83,16 +83,10 @@
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "rollup": "^4.18.0",
-    "size-limit": "^8.2.6",
+    "size-limit": "^11.1.4",
     "tinyspy": "^3.0.0",
     "typescript": "^5.5.3",
     "vitest": "^2.0.2"
   },
-  "prettier": "../../.prettierrc.json",
-  "size-limit": [
-    {
-      "path": "dist/production/index.js",
-      "limit": "15.545 kB"
-    }
-  ]
+  "prettier": "../../.prettierrc.json"
 }

packages/use-intl/src/core/IntlConfig.tsx

@@ -1,7 +1,7 @@
 import type AbstractIntlMessages from './AbstractIntlMessages';
-import Formats from './Formats';
-import IntlError from './IntlError';
-import TimeZone from './TimeZone';
+import type Formats from './Formats';
+import type IntlError from './IntlError';
+import type TimeZone from './TimeZone';
 import type {RichTranslationValues} from './TranslationValues';
 
 /**

packages/use-intl/src/core/NumberFormatOptions.tsx

@@ -1,4 +1,4 @@
-import {Formats} from 'intl-messageformat';
+import type {Formats} from 'intl-messageformat';
 
 // Use the already bundled version of `NumberFormat` from `@formatjs/ecma402-abstract`
 // that comes with `intl-messageformat`

packages/use-intl/src/core/createBaseTranslator.tsx

@@ -17,12 +17,36 @@ import TranslationValues, {
 } from './TranslationValues';
 import convertFormatsToIntlMessageFormat from './convertFormatsToIntlMessageFormat';
 import {defaultGetMessageFallback, defaultOnError} from './defaults';
-import {Formatters} from './formatters';
+import {
+  Formatters,
+  IntlCache,
+  IntlFormatters,
+  memoFn,
+  MessageFormatter
+} from './formatters';
 import joinPath from './joinPath';
 import MessageKeys from './utils/MessageKeys';
 import NestedKeyOf from './utils/NestedKeyOf';
 import NestedValueOf from './utils/NestedValueOf';
 
+// Placed here for improved tree shaking. Somehow when this is placed in
+// `formatters.tsx`, then it can't be shaken off from `next-intl`.
+function createMessageFormatter(
+  cache: IntlCache,
+  intlFormatters: IntlFormatters
+): MessageFormatter {
+  const getMessageFormat = memoFn(
+    (...args: ConstructorParameters<typeof IntlMessageFormat>) =>
+      new IntlMessageFormat(args[0], args[1], args[2], {
+        formatters: intlFormatters,
+        ...args[3]
+      }),
+    cache.message
+  );
+
+  return getMessageFormat;
+}
+
 function resolvePath(
   locale: string,
   messages: AbstractIntlMessages | undefined,
@@ -125,6 +149,7 @@ function getMessagesOrError<Messages extends AbstractIntlMessages>(
 }
 
 export type CreateBaseTranslatorProps<Messages> = InitializedIntlConfig & {
+  cache: IntlCache;
   formatters: Formatters;
   defaultTranslationValues?: RichTranslationValues;
   namespace?: string;
@@ -169,6 +194,7 @@ function createBaseTranslatorImpl<
   Messages extends AbstractIntlMessages,
   NestedKey extends NestedKeyOf<Messages>
 >({
+  cache,
   defaultTranslationValues,
   formats: globalFormats,
   formatters,
@@ -247,6 +273,12 @@ function createBaseTranslatorImpl<
     const plainMessage = getPlainMessage(message as string, values);
     if (plainMessage) return plainMessage;
 
+    // Lazy init the message formatter for better tree
+    // shaking in case message formatting is not used.
+    if (!formatters.getMessageFormat) {
+      formatters.getMessageFormat = createMessageFormatter(cache, formatters);
+    }
+
     try {
       messageFormat = formatters.getMessageFormat(
         message,