refactor(bundler): target the current Node.js version for server builds, remove the hardcoded 26.0.0 clamp (AI-assisted) (#12781)

SWC no longer falls back to ES5 for Node.js versions newer than its
Browserslist data: it now skips all transforms for them, like Babel
(swc-project/swc#11457, shipped in every Rspack 2.x).

The server target is the current Node.js version without its pre-release
tag, because SWC panics on versions like "27.0.0-rc.1".

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: slorber

packages/docusaurus-bundler/src/__tests__/browserslist.test.ts

@@ -0,0 +1,39 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {afterEach, describe, expect, it, vi} from 'vitest';
+import {getTargets} from '../browserslist';
+
+const realNodeVersion = process.versions.node;
+
+function stubNodeVersion(version: string) {
+  Object.defineProperty(process.versions, 'node', {value: version});
+}
+
+describe('getTargets', () => {
+  describe('server', () => {
+    afterEach(() => {
+      stubNodeVersion(realNodeVersion);
+      vi.unstubAllEnvs();
+    });
+
+    it('targets the current Node.js version', () => {
+      stubNodeVersion('26.8.1');
+      expect(getTargets({isServer: true})).toEqual(['node 26.8.1']);
+    });
+
+    it('removes the pre-release tag of the current Node.js version', () => {
+      stubNodeVersion('27.0.0-rc.1');
+      expect(getTargets({isServer: true})).toEqual(['node 27.0.0']);
+    });
+
+    it('targets the DOCUSAURUS_SERVER_NODE_TARGET env variable', () => {
+      vi.stubEnv('DOCUSAURUS_SERVER_NODE_TARGET', '24.18.0');
+      expect(getTargets({isServer: true})).toEqual(['node 24.18.0']);
+    });
+  });
+});

packages/docusaurus-bundler/src/browserslist.ts

@@ -8,7 +8,6 @@
 import browserslist from 'browserslist';
 import semver from 'semver';
 import {browserslistToTargets, type TransformOptions} from 'lightningcss';
-import type {CurrentBundler} from '@docusaurus/types';
 
 // Used when the site doesn't provide its own Browserslist config
 // See https://web.dev/baseline
@@ -18,14 +17,8 @@ const DefaultBrowserslistQueries = ['baseline widely available'];
  * The targets the client or server bundle is compiled for, like
  * `['chrome 120', 'firefox 115']` or `['node 24.11.1']`
  */
-export function getTargets({
-  isServer,
-  bundlerName,
-}: {
-  isServer: boolean;
-  bundlerName: CurrentBundler['name'];
-}): string[] {
-  return isServer ? getServerTargets({bundlerName}) : getClientTargets();
+export function getTargets({isServer}: {isServer: boolean}): string[] {
+  return isServer ? getServerTargets() : getClientTargets();
 }
 
 export function getClientQueries(): string[] {
@@ -42,41 +35,16 @@ function getClientTargets(): string[] {
   return browserslist(getClientQueries());
 }
 
-export function getServerTargets({
-  bundlerName,
-}: {
-  bundlerName: CurrentBundler['name'];
-}): string[] {
+// SWC skips all transforms for Node versions newer than its Browserslist data
+// See https://github.com/swc-project/swc/pull/11457
+export function getServerTargets(): string[] {
   // Escape hatch env variable
   if (process.env.DOCUSAURUS_SERVER_NODE_TARGET) {
     return [`node ${process.env.DOCUSAURUS_SERVER_NODE_TARGET}`];
   }
-  // For server builds, we want to use the current Node version as target
-  // But we can't pass a target that Browserslist doesn't know about yet
-  const nodeTarget = getMinVersion(
-    process.versions.node,
-    getLastBrowserslistKnownNodeVersion(bundlerName),
-  );
-  return [`node ${nodeTarget}`];
-}
-
-// TODO this is not accurate
-//  for Rspack we should read from the built-in browserslist data
-//  see https://github.com/facebook/docusaurus/pull/11496
-function getLastBrowserslistKnownNodeVersion(
-  bundlerName: CurrentBundler['name'],
-): string {
-  if (bundlerName === 'rspack') {
-    // TODO hardcoded value until Rspack exposes its Browserslist data
-    //  see https://github.com/facebook/docusaurus/pull/11496
-    return '26.0.0';
-  }
-  // browserslist('last 1 node versions')[0]!.replace('node ', '')
-  return browserslist.nodeVersions.at(-1)!;
-}
-
-function getMinVersion(v1: string, v2: string): string {
-  return semver.lt(v1, v2) ? v1 : v2;
+  // SWC panics on pre-release versions like "27.0.0-rc.1"
+  const nodeVersion = semver.coerce(process.versions.node)!.version;
+  return [`node ${nodeVersion}`];
 }
 
 // LightningCSS doesn't expose any type for minimizer-webpack-plugin setup

packages/docusaurus-bundler/src/loaders/jsLoader.ts

@@ -29,7 +29,7 @@ function createRspackSwcJsLoaderFactory(): ConfigureWebpackUtils['getJSLoader']
   return ({isServer}) => {
     return {
       loader,
-      options: getSwcLoaderOptions({isServer, bundlerName: 'rspack'}),
+      options: getSwcLoaderOptions({isServer}),
     };
   };
 }

packages/docusaurus-bundler/src/swc.ts

@@ -7,19 +7,16 @@
 
 import {getClientQueries, getServerTargets} from './browserslist';
 import type {SwcLoaderOptions} from '@rspack/core';
-import type {CurrentBundler} from '@docusaurus/types';
 
 export function getSwcLoaderOptions({
   isServer,
-  bundlerName,
 }: {
   isServer: boolean;
-  bundlerName: CurrentBundler['name'];
 }): SwcLoaderOptions {
   return {
     env: {
       // Rspack resolves the client queries with its own Browserslist data
-      targets: isServer ? getServerTargets({bundlerName}) : getClientQueries(),
+      targets: isServer ? getServerTargets() : getClientQueries(),
     },
     jsc: {
       parser: {

packages/docusaurus/src/webpack/base.ts

@@ -118,7 +118,7 @@ export async function createBaseConfig({
       // Changing the target browsers or Node.js version must evict the cache
       // The same Browserslist queries can match other browsers over time and
       // after data upgrades, for example "baseline widely available"
-      getTargets({isServer, bundlerName: props.currentBundler.name}),
+      getTargets({isServer}),
       // The plugin code computing loader options is not a build dependency
       // Upgrading a third-party plugin must evict the cache
       siteMetadata.pluginVersions,