docs(blog-only): add warning and improve error log (facebook#9839)

packages/docusaurus-plugin-content-docs/src/client/index.ts

@@ -86,10 +86,20 @@ export const useAllDocsData = (): {[pluginId: string]: GlobalPluginData} =>
       }
     | undefined) ?? StableEmptyObject;
 
-export const useDocsData = (pluginId: string | undefined): GlobalPluginData =>
-  usePluginData('docusaurus-plugin-content-docs', pluginId, {
-    failfast: true,
-  }) as GlobalPluginData;
+export const useDocsData = (pluginId: string | undefined): GlobalPluginData => {
+  try {
+    return usePluginData('docusaurus-plugin-content-docs', pluginId, {
+      failfast: true,
+    }) as GlobalPluginData;
+  } catch (error) {
+    throw new Error(
+      `You are using a feature of the Docusaurus docs plugin, but this plugin does not seem to be enabled${
+        pluginId === 'Default' ? '' : ` (pluginId=${pluginId}`
+      }`,
+      {cause: error as Error},
+    );
+  }
+};
 
 // TODO this feature should be provided by docusaurus core
 export function useActivePlugin(

website/docs/blog.mdx

@@ -625,6 +625,12 @@ Don't forget to delete the existing homepage at `./src/pages/index.js` or else t
 
 :::
 
+:::warning
+
+If you disable the docs plugin, don't forget to delete references to the docs plugin elsewhere in your configuration file. Notably, make sure to remove the docs-related navbar items.
+
+:::
+
 :::tip
 
 There's also a "Docs-only mode" for those who only want to use the docs. Read [Docs-only mode](./guides/docs/docs-introduction.mdx) for detailed instructions or a more elaborate explanation of `routeBasePath`.