[libcxx] r340426 - Add diagnostics for min/max algorithms when a InputIterator is used.

[Eric Fiselier via cfe-commits]

Author: ericwf
Date: Wed Aug 22 10:47:13 2018
New Revision: 340426

URL: http://llvm.org/viewvc/llvm-project?rev=340426&view=rev
Log:
Add diagnostics for min/max algorithms when a InputIterator is used.

These algorithms require a ForwardIterator or better. Ensure
we diagnose the contract violation at compile time instead of
of silently doing the wrong thing.

Further algorithms will be audited in upcoming patches.

Added:
    libcxx/trunk/test/std/algorithms/alg.sorting/alg.min.max/requires_forward_iterator.fail.cpp
Modified:
    libcxx/trunk/include/algorithm

Modified: libcxx/trunk/include/algorithm
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/algorithm?rev=340426&r1=340425&r2=340426&view=diff
==============================================================================
--- libcxx/trunk/include/algorithm (original)
+++ libcxx/trunk/include/algorithm Wed Aug 22 10:47:13 2018
@@ -2398,6 +2398,8 @@ inline _LIBCPP_INLINE_VISIBILITY _LIBCPP
 _ForwardIterator
 min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 {
+    static_assert(__is_forward_iterator<_ForwardIterator>::value,
+        "std::min_element requires a ForwardIterator");
     if (__first != __last)
     {
         _ForwardIterator __i = __first;
@@ -2462,6 +2464,8 @@ inline _LIBCPP_INLINE_VISIBILITY _LIBCPP
 _ForwardIterator
 max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 {
+    static_assert(__is_forward_iterator<_ForwardIterator>::value,
+        "std::max_element requires a ForwardIterator");
     if (__first != __last)
     {
         _ForwardIterator __i = __first;
@@ -2548,6 +2552,8 @@ _LIBCPP_CONSTEXPR_AFTER_CXX11
 std::pair<_ForwardIterator, _ForwardIterator>
 minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 {
+  static_assert(__is_forward_iterator<_ForwardIterator>::value,
+        "std::minmax_element requires a ForwardIterator");
   std::pair<_ForwardIterator, _ForwardIterator> __result(__first, __first);
   if (__first != __last)
   {

Added: libcxx/trunk/test/std/algorithms/alg.sorting/alg.min.max/requires_forward_iterator.fail.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/std/algorithms/alg.sorting/alg.min.max/requires_forward_iterator.fail.cpp?rev=340426&view=auto
==============================================================================
--- libcxx/trunk/test/std/algorithms/alg.sorting/alg.min.max/requires_forward_iterator.fail.cpp (added)
+++ libcxx/trunk/test/std/algorithms/alg.sorting/alg.min.max/requires_forward_iterator.fail.cpp Wed Aug 22 10:47:13 2018
@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// template<ForwardIterator Iter>
+//   max_element(Iter first, Iter last);
+
+#include <algorithm>
+#include <cassert>
+
+#include "test_iterators.h"
+
+int main() {
+  int arr[] = {1, 2, 3};
+  const int *b = std::begin(arr), *e = std::end(arr);
+  typedef input_iterator<const int*> Iter;
+  {
+    // expected-error at algorithm:* {{"std::min_element requires a ForwardIterator"}}
+    std::min_element(Iter(b), Iter(e));
+  }
+  {
+    // expected-error at algorithm:* {{"std::max_element requires a ForwardIterator"}}
+    std::max_element(Iter(b), Iter(e));
+  }
+  {
+    // expected-error at algorithm:* {{"std::minmax_element requires a ForwardIterator"}}
+    std::minmax_element(Iter(b), Iter(e));
+  }
+
+}