fix: Mispositioned TOC control on mobile due to merge conflict

fix: Show message in mobile TOC when no headings in document
fix: MenuItem with level should still have background edge-to-edge
fix: Show developer warning when creating incorrect menu item type

app/menus/TableOfContentsMenu.js

@@ -7,6 +7,7 @@ import { MenuButton, useMenuState } from "reakit/Menu";
 import Button from "components/Button";
 import ContextMenu from "components/ContextMenu";
 import Template from "components/ContextMenu/Template";
+import { type MenuItem } from "types";
 
 type Props = {|
   headings: { title: string, level: number, id: string }[],
@@ -27,6 +28,31 @@ function TableOfContentsMenu({ headings }: Props) {
     Infinity
   );
 
+  const items: MenuItem[] = React.useMemo(() => {
+    let i = [
+      {
+        type: "heading",
+        visible: true,
+        title: t("Contents"),
+      },
+      ...headings.map((heading) => ({
+        href: `#${heading.id}`,
+        title: t(heading.title),
+        level: heading.level - minHeading,
+      })),
+    ];
+
+    if (i.length === 1) {
+      i.push({
+        href: "#",
+        title: t("Headings you add to the document will appear here"),
+        disabled: true,
+      });
+    }
+
+    return i;
+  }, [t, headings, minHeading]);
+
   return (
     <>
       <MenuButton {...menu}>
@@ -41,23 +67,7 @@ function TableOfContentsMenu({ headings }: Props) {
         )}
       </MenuButton>
       <ContextMenu {...menu} aria-label={t("Table of contents")}>
-        <Template
-          {...menu}
-          items={[
-            {
-              type: "heading",
-              visible: true,
-              title: t("Contents"),
-            },
-            ...headings.map((heading) => {
-              return {
-                href: `#${heading.id}`,
-                title: t(heading.title),
-                level: heading.level - minHeading,
-              };
-            }),
-          ]}
-        />
+        <Template {...menu} items={items} />
       </ContextMenu>
     </>
   );