emitSiteMessages infra for site errors/warnings

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 +1,67 @@
+/**
+ * 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 [];
+};
+
+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);
+}