layout.d.ts: Layout type - merge extracted ids union

typescript/types/layout.d.ts

@@ -1,5 +1,8 @@
 type Prev = [never, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
 
+type UnionToIntersection<U> =
+  (U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never
+
 type ExtractIds<T extends Layout.Hierarchy, Depth extends Prev[number] = 9> =
   [Depth] extends [never]
   ? never
@@ -15,7 +18,7 @@ type ExtractIds<T extends Layout.Hierarchy, Depth extends Prev[number] = 9> =
 
 declare module Layout {
   type Layouter<T extends Hierarchy> =
-    ExtractIds<T>
+    UnionToIntersection<ExtractIds<T>>
     &
     {
       // these actually change T