[cxx-interop] Add test for iterator conformances with nested typedefs

Follow-up to 34f6cd3.

Author: egorzhdan

test/Interop/Cxx/stdlib/overlay/Inputs/custom-iterator.h

@@ -259,6 +259,29 @@ struct HasCustomRACIteratorTag {
   }
 };
 
+struct HasCustomInheritedRACIteratorTag {
+  struct CustomTag0 : public std::random_access_iterator_tag {};
+  using CustomTag1 = CustomTag0;
+  struct CustomTag2 : public CustomTag1 {};
+  using CustomTag3 = CustomTag2;
+  using CustomTag4 = CustomTag3;
+
+  int value;
+  using iterator_category = CustomTag4;
+  const int &operator*() const { return value; }
+  HasCustomInheritedRACIteratorTag &operator++() {
+    value++;
+    return *this;
+  }
+  void operator+=(int x) { value += x; }
+  int operator-(const HasCustomInheritedRACIteratorTag &x) const {
+    return value - x.value;
+  }
+  bool operator==(const HasCustomInheritedRACIteratorTag &other) const {
+    return value == other.value;
+  }
+};
+
 struct HasCustomIteratorTagInline {
   struct iterator_category : public std::input_iterator_tag {};
 

test/Interop/Cxx/stdlib/overlay/custom-iterator-module-interface.swift

@@ -66,6 +66,23 @@
 // CHECK:   static func == (lhs: HasCustomRACIteratorTag, other: HasCustomRACIteratorTag) -> Bool
 // CHECK: }
 
+// CHECK: struct HasCustomInheritedRACIteratorTag : UnsafeCxxRandomAccessIterator, UnsafeCxxInputIterator {
+// CHECK:   func successor() -> HasCustomInheritedRACIteratorTag
+// CHECK:   var pointee: Int32 { get }
+// CHECK:   typealias Pointee = Int32
+// CHECK:   typealias Distance = Int32
+// CHECK:   struct CustomTag0 {
+// CHECK:     init()
+// CHECK:   }
+// CHECK:   typealias CustomTag1 = HasCustomInheritedRACIteratorTag.CustomTag0
+// CHECK:   struct CustomTag2 {
+// CHECK:     init()
+// CHECK:   }
+// CHECK:   typealias CustomTag3 = HasCustomInheritedRACIteratorTag.CustomTag2
+// CHECK:   typealias CustomTag4 = HasCustomInheritedRACIteratorTag.CustomTag3
+// CHECK:   typealias iterator_category = HasCustomInheritedRACIteratorTag.CustomTag4
+// CHECK: }
+
 // CHECK: struct HasCustomIteratorTagInline : UnsafeCxxInputIterator {
 // CHECK:   func successor() -> HasCustomIteratorTagInline
 // CHECK:   var pointee: Int32 { get }