refactor(faster,bundler,core): improve js loader DX

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'},

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;
   }

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;

packages/docusaurus/src/server/__tests__/siteMessages.test.ts

@@ -0,0 +1,66 @@
+/**
+ * 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 path from 'path';
+import {fromPartial} from '@total-typescript/shoehorn';
+import {collectAllSiteMessages} from '../siteMessages';
+
+function siteDirFixture(name: string) {
+  return path.resolve(__dirname, '__fixtures__', 'siteMessages', name);
+}
+
+describe('collectAllSiteMessages', () => {
+  describe('uselessBabelConfigMessages', () => {
+    async function getMessagesFor({
+      siteDir,
+      swcJsLoader,
+    }: {
+      siteDir: string;
+      swcJsLoader: boolean;
+    }) {
+      return collectAllSiteMessages(
+        fromPartial({
+          site: {
+            props: {
+              siteDir,
+              siteConfig: {
+                future: {
+                  experimental_faster: {
+                    swcJsLoader,
+                  },
+                },
+              },
+            },
+          },
+        }),
+      );
+    }
+
+    it('warns for useless babel config file when SWC enabled', async () => {
+      const messages = await getMessagesFor({
+        siteDir: siteDirFixture('siteWithBabelConfigFile'),
+        swcJsLoader: true,
+      });
+      expect(messages).toMatchInlineSnapshot(`
+              [
+                {
+                  "message": "Your site is using the SWC js loader. You can safely remove the Babel config file at \`packages/docusaurus/src/server/__tests__/__fixtures__/siteMessages/siteWithBabelConfigFile/babel.config.js\`.",
+                  "type": "warning",
+                },
+              ]
+          `);
+    });
+
+    it('does not warn for babel config file when SWC disabled', async () => {
+      const messages = await getMessagesFor({
+        siteDir: siteDirFixture('siteWithBabelConfigFile'),
+        swcJsLoader: false,
+      });
+      expect(messages).toMatchInlineSnapshot(`[]`);
+    });
+  });
+});

packages/docusaurus/src/server/site.ts

@@ -27,6 +27,7 @@ import {
 import {generateSiteFiles} from './codegen/codegen';
 import {getRoutesPaths, handleDuplicateRoutes} from './routes';
 import {createSiteStorage} from './storage';
+import {emitSiteMessages} from './siteMessages';
 import type {LoadPluginsResult} from './plugins/plugins';
 import type {
   DocusaurusConfig,
@@ -54,7 +55,9 @@ export type LoadContextParams = {
   localizePath?: boolean;
 };
 
-export type LoadSiteParams = LoadContextParams;
+export type LoadSiteParams = LoadContextParams & {
+  isReload?: boolean;
+};
 
 export type Site = {
   props: Props;
@@ -236,7 +239,7 @@ async function createSiteFiles({
  * lifecycles to generate content and other data. It is side-effect-ful because
  * it generates temp files in the `.docusaurus` folder for the bundler.
  */
-export async function loadSite(params: LoadContextParams): Promise<Site> {
+export async function loadSite(params: LoadSiteParams): Promise<Site> {
   const context = await PerfLogger.async('Load context', () =>
     loadContext(params),
   );
@@ -252,14 +255,22 @@ export async function loadSite(params: LoadContextParams): Promise<Site> {
     globalData,
   });
 
+  // For now, we don't re-emit messages on site reloads, it's too verbose
+  if (!params.isReload) {
+    await emitSiteMessages({site});
+  }
+
   return site;
 }
 
 export async function reloadSite(site: Site): Promise<Site> {
   // TODO this can be optimized, for example:
   //  - plugins loading same data as before should not recreate routes/bundles
   //  - codegen does not need to re-run if nothing changed
-  return loadSite(site.params);
+  return loadSite({
+    ...site.params,
+    isReload: true,
+  });
 }
 
 export async function reloadSitePlugin(

packages/docusaurus/src/server/siteMessages.ts

@@ -0,0 +1,69 @@
+/**
+ * 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 path from 'path';
+import _ from 'lodash';
+import {getCustomBabelConfigFilePath} from '@docusaurus/babel';
+import logger from '@docusaurus/logger';
+import type {Site} from './site';
+
+type Params = {site: Site};
+
+type SiteMessage = {type: 'warning' | 'error'; message: string};
+
+type SiteMessageCreator = (params: Params) => Promise<SiteMessage[]>;
+
+const uselessBabelConfigMessages: SiteMessageCreator = async ({site}) => {
+  const {
+    props: {siteDir, siteConfig},
+  } = site;
+  if (siteConfig.future.experimental_faster.swcJsLoader) {
+    const babelConfigFilePath = await getCustomBabelConfigFilePath(siteDir);
+    if (babelConfigFilePath) {
+      return [
+        {
+          type: 'warning',
+          message: `Your site is using the SWC js loader. You can safely remove the Babel config file at ${logger.code(
+            path.relative(process.cwd(), babelConfigFilePath),
+          )}.`,
+        },
+      ];
+    }
+  }
+  return [];
+};
+
+export async function collectAllSiteMessages(
+  params: Params,
+): Promise<SiteMessage[]> {
+  const messageCreators: SiteMessageCreator[] = [uselessBabelConfigMessages];
+  return (
+    await Promise.all(
+      messageCreators.map((createMessages) => createMessages(params)),
+    )
+  ).flat();
+}
+
+function printSiteMessages(siteMessages: SiteMessage[]): void {
+  const [errors, warnings] = _.partition(
+    siteMessages,
+    (sm) => sm.type === 'error',
+  );
+  if (errors.length > 0) {
+    logger.error(`Docusaurus site errors:
+- ${errors.map((sm) => sm.message).join('\n- ')}`);
+  }
+  if (warnings.length > 0) {
+    logger.warn(`Docusaurus site warnings:
+- ${warnings.map((sm) => sm.message).join('\n- ')}`);
+  }
+}
+
+export async function emitSiteMessages(params: Params): Promise<void> {
+  const siteMessages = await collectAllSiteMessages(params);
+  printSiteMessages(siteMessages);
+}