From 91e41a35936377542a3a595724a309f8732919e9 Mon Sep 17 00:00:00 2001
From: sebastien <lorber.sebastien@gmail.com>
Date: Fri, 8 Nov 2024 12:07:34 +0100
Subject: [PATCH] fix jsLoader factory ambiguity

---
 .../src/loaders/__tests__/jsLoader.test.ts    | 64 ++++++++++++++++---
 .../src/loaders/jsLoader.ts                   | 26 ++++----
 packages/docusaurus-types/src/config.d.ts     |  2 +-
 3 files changed, 68 insertions(+), 24 deletions(-)

diff --git a/packages/docusaurus-bundler/src/loaders/__tests__/jsLoader.test.ts b/packages/docusaurus-bundler/src/loaders/__tests__/jsLoader.test.ts
index 22016169b883..a3c7ea43e492 100644
--- a/packages/docusaurus-bundler/src/loaders/__tests__/jsLoader.test.ts
+++ b/packages/docusaurus-bundler/src/loaders/__tests__/jsLoader.test.ts
@@ -10,19 +10,19 @@ import {createJsLoaderFactory} from '../jsLoader';
 
 import type {RuleSetRule} from 'webpack';
 
+type SiteConfigSlice = Parameters<
+  typeof createJsLoaderFactory
+>[0]['siteConfig'];
+
 describe('createJsLoaderFactory', () => {
-  function testJsLoaderFactory(
-    siteConfig?: PartialDeep<
-      Parameters<typeof createJsLoaderFactory>[0]['siteConfig']
-    >,
-  ) {
+  function testJsLoaderFactory(siteConfig?: {
+    webpack?: SiteConfigSlice['webpack'];
+    future?: PartialDeep<SiteConfigSlice['future']>;
+  }) {
     return createJsLoaderFactory({
       siteConfig: {
         ...siteConfig,
-        webpack: {
-          jsLoader: 'babel',
-          ...siteConfig?.webpack,
-        },
+        webpack: siteConfig?.webpack,
         future: fromPartial({
           ...siteConfig?.future,
           experimental_faster: fromPartial({
@@ -43,6 +43,52 @@ describe('createJsLoaderFactory', () => {
     );
   });
 
+  it('createJsLoaderFactory accepts babel loader preset', async () => {
+    const createJsLoader = await testJsLoaderFactory({
+      webpack: {jsLoader: 'babel'},
+    });
+    expect(createJsLoader({isServer: true}).loader).toBe(
+      require.resolve('babel-loader'),
+    );
+    expect(createJsLoader({isServer: false}).loader).toBe(
+      require.resolve('babel-loader'),
+    );
+  });
+
+  it('createJsLoaderFactory accepts custom loader', async () => {
+    const createJsLoader = await testJsLoaderFactory({
+      webpack: {
+        jsLoader: (isServer) => {
+          return {loader: `my-loader-${isServer ? 'server' : 'client'}`};
+        },
+      },
+    });
+    expect(createJsLoader({isServer: true}).loader).toBe('my-loader-server');
+    expect(createJsLoader({isServer: false}).loader).toBe('my-loader-client');
+  });
+
+  it('createJsLoaderFactory rejects custom loader when using faster swc loader', async () => {
+    await expect(() =>
+      testJsLoaderFactory({
+        future: {
+          experimental_faster: {
+            swcJsLoader: true,
+          },
+        },
+        webpack: {
+          jsLoader: (isServer) => {
+            return {loader: `my-loader-${isServer ? 'server' : 'client'}`};
+          },
+        },
+      }),
+    ).rejects.toThrowErrorMatchingInlineSnapshot(`
+      "You can't use siteConfig.webpack.jsLoader and siteConfig.future.experimental_faster.swcJsLoader at the same time.
+      To avoid any configuration ambiguity, you must make an explicit choice:
+      - If you want to use Docusaurus Faster and SWC (recommended), remove siteConfig.webpack.jsLoader
+      - If you want to use a custom JS loader, use siteConfig.future.experimental_faster.swcJsLoader: false"
+    `);
+  });
+
   it('createJsLoaderFactory accepts loaders with preset', async () => {
     const createJsLoader = await testJsLoaderFactory({
       webpack: {jsLoader: 'babel'},
diff --git a/packages/docusaurus-bundler/src/loaders/jsLoader.ts b/packages/docusaurus-bundler/src/loaders/jsLoader.ts
index b6e0088ebd88..6f9213454d5d 100644
--- a/packages/docusaurus-bundler/src/loaders/jsLoader.ts
+++ b/packages/docusaurus-bundler/src/loaders/jsLoader.ts
@@ -62,26 +62,24 @@ export async function createJsLoaderFactory({
 }): Promise<ConfigureWebpackUtils['getJSLoader']> {
   const currentBundler = await getCurrentBundler({siteConfig});
   const isSWCLoader = siteConfig.future.experimental_faster.swcJsLoader;
-  if (currentBundler.name === 'rspack') {
-    return isSWCLoader
+  if (isSWCLoader) {
+    if (siteConfig.webpack?.jsLoader) {
+      throw new Error(
+        `You can't use siteConfig.webpack.jsLoader and siteConfig.future.experimental_faster.swcJsLoader at the same time.
+To avoid any configuration ambiguity, you must make an explicit choice:
+- If you want to use Docusaurus Faster and SWC (recommended), remove siteConfig.webpack.jsLoader
+- If you want to use a custom JS loader, use siteConfig.future.experimental_faster.swcJsLoader: false`,
+      );
+    }
+    return currentBundler.name === 'rspack'
       ? createRspackSwcJsLoaderFactory()
-      : BabelJsLoaderFactory;
+      : createSwcJsLoaderFactory();
   }
+
   const jsLoader = siteConfig.webpack?.jsLoader ?? 'babel';
-  if (
-    jsLoader instanceof Function &&
-    siteConfig.future?.experimental_faster.swcJsLoader
-  ) {
-    throw new Error(
-      "You can't use a custom webpack.jsLoader and experimental_faster.swcJsLoader at the same time",
-    );
-  }
   if (jsLoader instanceof Function) {
     return ({isServer}) => jsLoader(isServer);
   }
-  if (siteConfig.future?.experimental_faster.swcJsLoader) {
-    return createSwcJsLoaderFactory();
-  }
   if (jsLoader === 'babel') {
     return BabelJsLoaderFactory;
   }
diff --git a/packages/docusaurus-types/src/config.d.ts b/packages/docusaurus-types/src/config.d.ts
index 575be4a6fd57..8289e8b22282 100644
--- a/packages/docusaurus-types/src/config.d.ts
+++ b/packages/docusaurus-types/src/config.d.ts
@@ -431,7 +431,7 @@ export type DocusaurusConfig = {
     // TODO Docusaurus v4
     //  Use an object type ({isServer}) so that it conforms to jsLoaderFactory
     //  Eventually deprecate this if swc loader becomes stable?
-    jsLoader: 'babel' | ((isServer: boolean) => RuleSetRule);
+    jsLoader?: 'babel' | ((isServer: boolean) => RuleSetRule);
   };
   /** Markdown-related options. */
   markdown: MarkdownConfig;