[libc++] Fix PR35491 - std::array of zero-size doesn't work with non-default constructible types.

Summary:
This patch fixes llvm.org/PR35491 and LWG2157  (https://cplusplus.github.io/LWG/issue2157)

The fix attempts to maintain ABI compatibility by replacing the array with a instance of `aligned_storage`.

Reviewers: mclow.lists, EricWF

Reviewed By: EricWF

Subscribers: lichray, cfe-commits

Differential Revision: https://reviews.llvm.org/D41223

llvm-svn: 324526

1 files changed, 71 insertions, 0 deletions

diff --git a/libcxx/test/std/containers/sequences/array/compare.fail.cpp b/libcxx/test/std/containers/sequences/array/compare.fail.cpp
new file mode 100644
index 00000000000..2aa7cd896d9
--- /dev/null
+++ b/libcxx/test/std/containers/sequences/array/compare.fail.cpp
@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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>
+
+// bool operator==(array<T, N> const&, array<T, N> const&);
+// bool operator!=(array<T, N> const&, array<T, N> const&);
+// bool operator<(array<T, N> const&, array<T, N> const&);
+// bool operator<=(array<T, N> const&, array<T, N> const&);
+// bool operator>(array<T, N> const&, array<T, N> const&);
+// bool operator>=(array<T, N> const&, array<T, N> const&);
+
+
+#include <array>
+#include <vector>
+#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"
+
+template <class Array>
+void test_compare(const Array& LHS, const Array& RHS) {
+  typedef std::vector<typename Array::value_type> Vector;
+  const Vector LHSV(LHS.begin(), LHS.end());
+  const Vector RHSV(RHS.begin(), RHS.end());
+  assert((LHS == RHS) == (LHSV == RHSV));
+  assert((LHS != RHS) == (LHSV != RHSV));
+  assert((LHS < RHS) == (LHSV < RHSV));
+  assert((LHS <= RHS) == (LHSV <= RHSV));
+  assert((LHS > RHS) == (LHSV > RHSV));
+  assert((LHS >= RHS) == (LHSV >= RHSV));
+}
+
+template <int Dummy> struct NoCompare {};
+
+int main()
+{
+  {
+    typedef NoCompare<0> T;
+    typedef std::array<T, 3> C;
+    C c1 = {{}};
+    // expected-error@algorithm:* 2 {{invalid operands to binary expression}}
+    TEST_IGNORE_NODISCARD (c1 == c1);
+    TEST_IGNORE_NODISCARD (c1 < c1);
+  }
+  {
+    typedef NoCompare<1> T;
+    typedef std::array<T, 3> C;
+    C c1 = {{}};
+    // expected-error@algorithm:* 2 {{invalid operands to binary expression}}
+    TEST_IGNORE_NODISCARD (c1 != c1);
+    TEST_IGNORE_NODISCARD (c1 > c1);
+  }
+  {
+    typedef NoCompare<2> T;
+    typedef std::array<T, 0> C;
+    C c1 = {{}};
+    // expected-error@algorithm:* 2 {{invalid operands to binary expression}}
+    TEST_IGNORE_NODISCARD (c1 == c1);
+    TEST_IGNORE_NODISCARD (c1 < c1);
+  }
+}