[libcxx] Add checks for unique value of array<T, 0>.begin() and array<T, 0>.end() .

[amakc11]

Summary

The standard section array.zero requires the return value of begin() and end() methods of a zero-sized array to be unique. Eric Fiselier clarifies: "That unique value cannot be null, and must be properly aligned". This patch adds checks for the first part of this clarification: unique value returned by these methods cannot be null.

[ldionne]

test/std/containers/sequences/array/begin.pass.cpp

49

Comparing the iterator to nullptr assumes the iterators to be pointers, which I don't think is required. They're only required to be contiguous iterators.

[amakc11]

In libc++ these array iterators declared as follows:

typedef value_type*                        iterator;
typedef const value_type*                  const_iterator;

The asserts changed to LIBCPP_ASSERTs.

[ldionne]

Ahh, you're right. Ok, LGTM.

[ldionne]

Committed as r348509.

test/std/containers/sequences/array/begin.pass.cpp

49

This doesn't compile because you're missing an include of "test_macros.h". Please make a habit of running the tests before submitting a review.

[amakc11]

Sorry. Fixed.

[mclow.lists]

In D55366#1321351, @amakc11 wrote:

In libc++ these array iterators declared as follows:

typedef value_type*                        iterator;
typedef const value_type*                  const_iterator;

Yes, but that's just true for libc++. Other library maintainers use these tests, too.
(and frankly, I screwed up when I implemented <array>. Those iterators should not be pointers)

[amakc11]

In D55366#1321692, @mclow.lists wrote:

Yes, but that's just true for libc++. Other library maintainers use these tests, too.

It is also true for GNU libstdc++.

test/std/containers/sequences/array/begin.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is dual licensed under the MIT and the University of Illinois Open
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 // <array>
 
 // iterator begin();
 
 #include <array>
 #include <cassert>
 
+#include "test_macros.h"
+
 // std::array is explicitly allowed to be initialized with A a = { init-list };.
 // Disable the missing braces warning for this reason.
 #include "disable_missing_braces_warning.h"
 
 struct NoDefault {
   NoDefault(int) {}
 };
 
int main()
         assert(&*i == c.data());
         *i = 5.5;
         assert(c[0] == 5.5);
     }
     {
       typedef NoDefault T;
       typedef std::array<T, 0> C;
       C c = {};
-      assert(c.begin() == c.end());
+      C::iterator ib, ie;
+      ib = c.begin();
+      ie = c.end();
+      assert(ib == ie);
+      LIBCPP_ASSERT(ib != nullptr);
+      LIBCPP_ASSERT(ie != nullptr);
     }
 }