[ADT] Change iterator_adaptor_base's default template arguments to forward more underlying typedefs

[timshen]

Added a test.

[timshen]

Make test compile :P.

[dblaikie]

unittests/Support/IteratorTest.cpp

101

This doesn't need to be in a test case, since none of it executes dynamically - probably just put it in a namespace (so it doesn't provide any names that might interfere with other tests)

103

Maybe worth introducing some arbitrary tag types (just random structs with helpful names like ValueType, PointerType, DifferenceType, ReferenceType) rather than using all ints - so it's clear the types aren't getting mismatched or anything?

[timshen]

Moved the compile-time test to the outer anonymous namespace.

include/llvm/ADT/iterator.h

 /// operator* implementation. Other methods can be overridden as well.
 template <
     typename DerivedT, typename WrappedIteratorT,
     typename IteratorCategoryT =
         typename std::iterator_traits<WrappedIteratorT>::iterator_category,
     typename T = typename std::iterator_traits<WrappedIteratorT>::value_type,
     typename DifferenceTypeT =
         typename std::iterator_traits<WrappedIteratorT>::difference_type,
-    typename PointerT = T *, typename ReferenceT = T &,
+    typename PointerT = typename std::conditional<
+        std::is_same<T, typename std::iterator_traits<
+                            WrappedIteratorT>::value_type>::value,
+        typename std::iterator_traits<WrappedIteratorT>::pointer, T *>::type,
+    typename ReferenceT = typename std::conditional<
+        std::is_same<T, typename std::iterator_traits<
+                            WrappedIteratorT>::value_type>::value,
+        typename std::iterator_traits<WrappedIteratorT>::reference, T &>::type,
     // Don't provide these, they are mostly to act as aliases below.
     typename WrappedTraitsT = std::iterator_traits<WrappedIteratorT>>
 class iterator_adaptor_base
     : public iterator_facade_base<DerivedT, IteratorCategoryT, T,
                                   DifferenceTypeT, PointerT, ReferenceT> {
   typedef typename iterator_adaptor_base::iterator_facade_base BaseT;
 
 protected:

unittests/Support/IteratorTest.cpp

for (int i = 0; i < 4; ++i) {
     EXPECT_EQ(Begin, I - i);
 
     test_iterator K = I++;
     EXPECT_EQ(K, std::prev(I));
   }
   EXPECT_EQ(End, I);
 }
 
+TEST(IteratorAdaptorBaseTest, ForwardTypedefs) {
+  struct WeirdIter
+      : std::iterator<std::input_iterator_tag, int, int, int, int> {};
+  struct AdaptedIter : iterator_adaptor_base<AdaptedIter, WeirdIter> {};
+  static_assert(std::is_same<typename AdaptedIter::value_type, int>::value, "");
+  static_assert(std::is_same<typename AdaptedIter::difference_type, int>::value,
+                "");
+  static_assert(std::is_same<typename AdaptedIter::pointer, int>::value, "");
+  static_assert(std::is_same<typename AdaptedIter::reference, int>::value, "");
+}
+
 } // anonymous namespace