feat(v2): support external links and linking to docs from other sidebars (#1052)

* feat(sidebar): support external links and linking to docs from other sidebars

* Update styles.css

v2/lib/load/docs/sidebars.js

@@ -2,6 +2,110 @@ const fs = require('fs-extra');
 const path = require('path');
 const {idx} = require('../utils');
 
+/**
+ * Check that item contains only allowed keys
+ *
+ * @param {Object} item
+ * @param {Array<string>} keys
+ */
+function assertItem(item, keys) {
+  const unknownKeys = Object.keys(item).filter(
+    key => !keys.includes(key) && key !== 'type',
+  );
+
+  if (unknownKeys.length) {
+    throw new Error(
+      `Unknown sidebar item keys: ${unknownKeys}. Item: ${JSON.stringify(
+        item,
+      )}`,
+    );
+  }
+}
+
+/**
+ * Normalizes recursively category and all its children. Ensures, that at the end
+ * each item will be an object with the corresponding type
+ *
+ * @param {Array<Object>} category
+ * @param {number} [level=0]
+ *
+ * @return {Array<Object>}
+ */
+function normalizeCategory(category, level = 0) {
+  if (level === 2) {
+    throw new Error(
+      `Can not process ${
+        category.label
+      } category. Categories can be nested only one level deep.`,
+    );
+  }
+
+  assertItem(category, ['items', 'label']);
+
+  if (!Array.isArray(category.items)) {
+    throw new Error(
+      `Error loading ${category.label} category. Category items must be array.`,
+    );
+  }
+
+  const items = category.items.map(item => {
+    switch (item.type) {
+      case 'category':
+        return normalizeCategory(item, level + 1);
+      case 'link':
+        assertItem(item, ['href', 'label']);
+        break;
+      case 'ref':
+        assertItem(item, ['id', 'label']);
+        break;
+      default:
+        if (typeof item === 'string') {
+          return {
+            type: 'doc',
+            id: item,
+          };
+        }
+
+        if (item.type !== 'doc') {
+          throw new Error(`Unknown sidebar item type: ${item.type}`);
+        }
+
+        assertItem(item, ['id', 'label']);
+        break;
+    }
+
+    return item;
+  });
+
+  return {...category, items};
+}
+
+/**
+ * Converts sidebars object to mapping to arrays of sidebar item objects
+ *
+ * @param  {{[key: string]: Object}} sidebars
+ *
+ * @return {{[key: string]: Array<Object>}}
+ */
+function normalizeSidebar(sidebars) {
+  return Object.entries(sidebars).reduce((acc, [sidebarId, sidebar]) => {
+    let normalizedSidebar = sidebar;
+
+    if (!Array.isArray(sidebar)) {
+      // convert sidebar to a more generic structure
+      normalizedSidebar = Object.entries(sidebar).map(([label, items]) => ({
+        type: 'category',
+        label,
+        items,
+      }));
+    }
+
+    acc[sidebarId] = normalizedSidebar.map(item => normalizeCategory(item));
+
+    return acc;
+  }, {});
+}
+
 module.exports = function loadSidebars({siteDir, env}, deleteCache = true) {
   let allSidebars = {};
 
@@ -34,5 +138,6 @@ module.exports = function loadSidebars({siteDir, env}, deleteCache = true) {
       });
     }
   }
-  return allSidebars;
+
+  return normalizeSidebar(allSidebars);
 };