fix(v2): improve dx sidebar config, ability to have no sidebars file (#4775)

* Improve sidebar config

* Edit message

* fix some little issues in the way undefined/false sidebars are handled

* remove old error message as it has been moved to a better place

Co-authored-by: Nam Hoang Le <nam.hoang.le@mgm-tp.com>
Co-authored-by: slorber <lorber.sebastien@gmail.com>

packages/docusaurus-plugin-content-docs/src/sidebars.ts

@@ -254,18 +254,29 @@ export const DefaultSidebars: UnprocessedSidebars = {
   ],
 };
 
+export const DisabledSidebars: UnprocessedSidebars = {};
+
 // TODO refactor: make async
-export function loadSidebars(sidebarFilePath: string): UnprocessedSidebars {
-  if (!sidebarFilePath) {
-    throw new Error(`sidebarFilePath not provided: ${sidebarFilePath}`);
+export function loadSidebars(
+  sidebarFilePath: string | false | undefined,
+): UnprocessedSidebars {
+  // false => no sidebars
+  if (sidebarFilePath === false) {
+    return DisabledSidebars;
   }
 
-  // No sidebars file: by default we use the file-system structure to generate the sidebar
-  // See https://github.com/facebook/docusaurus/pull/4582
-  if (!fs.existsSync(sidebarFilePath)) {
+  // undefined => defaults to autogenerated sidebars
+  if (typeof sidebarFilePath === 'undefined') {
     return DefaultSidebars;
   }
 
+  // unexisting sidebars file: no sidebars
+  // Note: this edge case can happen on versioned docs, not current version
+  // We avoid creating empty versioned sidebars file with the CLI
+  if (!fs.existsSync(sidebarFilePath)) {
+    return DisabledSidebars;
+  }
+
   // We don't want sidebars to be cached because of hot reloading.
   const sidebarJson = importFresh(sidebarFilePath) as SidebarsJSON;
   return normalizeSidebars(sidebarJson);