feat(content-docs): sidebar category linking to document or auto-generated index page (#5830)

Co-authored-by: Joshua Chen <sidachen2003@gmail.com>
Co-authored-by: Armano <armano2@users.noreply.github.com>
Co-authored-by: Alexey Pyltsyn <lex61rus@gmail.com>

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

@@ -0,0 +1,57 @@
+/**
+ * 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 {CategoryGeneratedIndexMetadata, DocMetadataBase} from './types';
+import {SidebarItemCategoryWithGeneratedIndex} from './sidebars/types';
+import {SidebarsUtils, toNavigationLink} from './sidebars/utils';
+import {createDocsByIdIndex} from './docs';
+
+function getCategoryGeneratedIndexMetadata({
+  category,
+  sidebarsUtils,
+  docsById,
+}: {
+  category: SidebarItemCategoryWithGeneratedIndex;
+  sidebarsUtils: SidebarsUtils;
+  docsById: Record<string, DocMetadataBase>;
+}): CategoryGeneratedIndexMetadata {
+  const {sidebarName, previous, next} =
+    sidebarsUtils.getCategoryGeneratedIndexNavigation(category.link.permalink);
+  if (!sidebarName) {
+    throw new Error('unexpected');
+  }
+
+  return {
+    title: category.link.title ?? category.label,
+    description: category.link.description,
+    slug: category.link.slug,
+    permalink: category.link.permalink,
+    sidebar: sidebarName,
+    previous: toNavigationLink(previous, docsById),
+    next: toNavigationLink(next, docsById),
+  };
+}
+
+export function getCategoryGeneratedIndexMetadataList({
+  docs,
+  sidebarsUtils,
+}: {
+  sidebarsUtils: SidebarsUtils;
+  docs: DocMetadataBase[];
+}): CategoryGeneratedIndexMetadata[] {
+  const docsById = createDocsByIdIndex(docs);
+
+  const categoryGeneratedIndexItems =
+    sidebarsUtils.getCategoryGeneratedIndexList();
+  return categoryGeneratedIndexItems.map((category) =>
+    getCategoryGeneratedIndexMetadata({
+      category,
+      sidebarsUtils,
+      docsById,
+    }),
+  );
+}