adjust version dropdown to render for versioned products

Author: Sarah Bawabe

packages/fern-docs/bundle/src/components/header/VersionDropdown.tsx

@@ -5,6 +5,7 @@ import { FernNavigation } from "@fern-api/fdr-sdk";
 import { DocsLoader } from "@/server/docs-loader";
 import { withVersionSwitcherInfo } from "@/server/withVersionSwitcherInfo";
 
+import { isProductNode } from "../../../../../fdr-sdk/src/navigation/versions/latest/isProductNode";
 import { FaIconServer } from "../fa-icon-server";
 import {
   VersionDropdownClient,
@@ -15,6 +16,12 @@ export declare namespace VersionDropdown {
   export interface Props {}
 }
 
+/**
+ * The version dropdown is used to switch between versions at a root level or at a product level.
+ *
+ * The version dropdown is used at a root level if the root is versioned.
+ * The version dropdown is used at a product level if the root has a productgroup and the current product is versioned.
+ */
 export async function VersionDropdown({
   loader,
   currentNode,
@@ -27,30 +34,47 @@ export async function VersionDropdown({
   parents: FernNavigation.NavigationNodeParent[];
 }) {
   const root = await loader.getRoot();
-  if (root.child.type !== "versioned") {
+
+  // If the root is not versioned or a productgroup, don't render the version dropdown
+  if (root.child.type !== "versioned" && root.child.type !== "productgroup") {
     return null;
   }
 
-  const versions = root.child.children;
+  let versions: FernNavigation.VersionNode[] = [];
+
+  // Handle case where root is a productgroup and the current product is versioned OR the root is versioned
+  if (root.child.type === "productgroup") {
+    const currentProduct = parents.find(isProductNode);
+
+    // If the current product is not versioned, don't render the version dropdown
+    if (currentProduct?.child.type !== "versioned") {
+      return null;
+    }
+    versions = currentProduct.child.children;
+  } else if (root.child.type === "versioned") {
+    versions = root.child.children;
+  }
 
   if (versions.length <= 1) {
     return null;
   }
 
   const withInfo = withVersionSwitcherInfo({
     node: currentNode,
-    parents: parents,
+    parents,
     versions,
     slugMap,
   });
 
   const versionOptions = versions.map((version): VersionDropdownItem => {
     const versionInfo = withInfo.find((info) => info.id === version.versionId);
+
     const slug =
       versionInfo?.pointsTo ??
       versionInfo?.landingPage ??
       versionInfo?.slug ??
       version.slug;
+
     return {
       versionId: version.versionId,
       title: version.title,