Simplify nested indexed access types

ahejlsberg · ahejlsberg · commit 55d4d7b5c637 · 2018-06-03T08:57:15.000-07:00
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -8881,7 +8881,9 @@ namespace ts {
                 return type.simplified === circularConstraintType ? type : type.simplified;
             }
             type.simplified = circularConstraintType;
-            const objectType = type.objectType;
+            // We recursively simplify the object type as it may in turn be an indexed access type. For example, with
+            // '{ [P in T]: { [Q in U]: number } }[T][U]' we want to first simplify the inner indexed access type.
+            const objectType = getSimplifiedType(type.objectType);
             if (objectType.flags & TypeFlags.Intersection && isGenericObjectType(objectType)) {
                 // Given an indexed access type T[K], if T is an intersection containing one or more generic types and one or
                 // more object types with only a string index signature, e.g. '(U & V & { [x: string]: D })[K]', return a
