[libc++][ranges] fix `std::search_n` incorrect `static_assert`

[huixie90]

Summary

[libc++][ranges] fix std::search_n incorrect static_assert
see more detail in https://reviews.llvm.org/D124079?#3661721

[jloser]

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

189

Nit: can we give a better name to this function?

[huixie90]

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

189

Any suggestions? I agree it is a terrible name. It is my failed attempt to give it a reasonable name

[jloser]

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

189

Maybe test_binary_predicate_callable? Note the camel case instead to match that of test_constexpr for example.

[ldionne]

Should we add a similar test in std::search and others that have a similar pattern?

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

189

Suggestion -- don't give it a name. Define it in main like this instead:

// test bug reported in https://reviews.llvm.org/D124079?#3661721
{
  A a[]       = {A(1, 2), A(2, 3), A(2, 4)};
  int value   = 2;
  auto result = std::search_n(a, a + 3, 1, value, Pred());
  assert(result == a + 1);
}

[huixie90]

In D130124#3663907, @ldionne wrote:

Should we add a similar test in std::search and others that have a similar pattern?

std::search takes two ranges so it is slightly different. But yes it is worthwhile checking other algorithms which take a range and a value to see if they work properly

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

189

good suggestion. thanks

[huixie90]

address comments

[bgraur]

Thanks a lot for the quick fix!!

libcxx/include/__algorithm/search_n.h

 }
 
 template <class _ForwardIterator, class _Size, class _Tp, class _BinaryPredicate>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17
 _ForwardIterator search_n(_ForwardIterator __first, _ForwardIterator __last,
                           _Size __count,
                           const _Tp& __value,
                           _BinaryPredicate __pred) {
-  static_assert(__is_callable<_BinaryPredicate, decltype(*__first), decltype(*__last)>::value,
+  static_assert(__is_callable<_BinaryPredicate, decltype(*__first), const _Tp&>::value,
                 "BinaryPredicate has to be callable");
   auto __proj = __identity();
   return std::__search_n_impl(__first, __last, std::__convert_to_integral(__count), __value, __pred, __proj).first;
 }
 
 template <class _ForwardIterator, class _Size, class _Tp>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17
 _ForwardIterator search_n(_ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value) {
   typedef typename iterator_traits<_ForwardIterator>::value_type __v;
   return std::search_n(__first, __last, std::__convert_to_integral(__count), __value, __equal_to<__v, _Tp>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___ALGORITHM_SEARCH_N_H

libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp

test()
     assert(count_equal::count <= sc);
     count_equal::count = 0;
 
     // Check that we properly convert the size argument to an integral.
     TEST_IGNORE_NODISCARD std::search_n(Iter(ic), Iter(ic+sc), UserDefinedIntegral<unsigned>(4), 0, count_equal());
     count_equal::count = 0;
 }
 
+// test bug reported in https://reviews.llvm.org/D124079?#3661721
+class A {
+public:
+  A(int x, int y) : x_(x), y_(y) {}
+  int x() const { return x_; }
+  int y() const { return y_; }
+
+private:
+  int x_;
+  int y_;
+};
+
+struct Pred {
+  bool operator()(const A& l, int r) const { return l.x() == r; }
+};
+
+void testStaticAssertBug() {
+  A a[]       = {A(1, 2), A(2, 3), A(2, 4)};
+  int value   = 2;
+  auto result = std::search_n(a, a + 3, 1, value, Pred());
+  assert(result == a + 1);
+}
+
 int main(int, char**)
 {
     test<forward_iterator<const int*> >();
     test<bidirectional_iterator<const int*> >();
     test<random_access_iterator<const int*> >();
-
+    testStaticAssertBug();
 #if TEST_STD_VER > 17
     static_assert(test_constexpr());
 #endif
 
   return 0;
 }