[libc++] Check correctly ref-qualified __is_callable in algorithms (llvm#73451)

changkhothuychung · web-flow · commit 8d151f804ff4 · 2024-08-01T14:08:21.000-04:00
We were only checking that the comparator was rvalue callable, when in reality the algorithms always call comparators as lvalues. This patch also refactors the tests for callable requirements and expands it to a few missing algorithms. Fixes llvm#69554
diff --git a/libcxx/include/__algorithm/equal_range.h b/libcxx/include/__algorithm/equal_range.h
@@ -62,7 +62,7 @@ __equal_range(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp
 template <class _ForwardIterator, class _Tp, class _Compare>
 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
 equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
-  static_assert(__is_callable<_Compare, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
+  static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   static_assert(is_copy_constructible<_ForwardIterator>::value, "Iterator has to be copy constructible");
   return std::__equal_range<_ClassicAlgPolicy>(
       std::move(__first),
diff --git a/libcxx/include/__algorithm/includes.h b/libcxx/include/__algorithm/includes.h
@@ -54,7 +54,7 @@ includes(_InputIterator1 __first1,
          _InputIterator2 __last2,
          _Compare __comp) {
   static_assert(
-      __is_callable<_Compare, decltype(*__first1), decltype(*__first2)>::value, "Comparator has to be callable");
+      __is_callable<_Compare&, decltype(*__first1), decltype(*__first2)>::value, "The comparator has to be callable");
 
   return std::__includes(
       std::move(__first1),
diff --git a/libcxx/include/__algorithm/is_permutation.h b/libcxx/include/__algorithm/is_permutation.h
@@ -249,8 +249,8 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __is_permutation(
 template <class _ForwardIterator1, class _ForwardIterator2, class _BinaryPredicate>
 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool is_permutation(
     _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2, _BinaryPredicate __pred) {
-  static_assert(__is_callable<_BinaryPredicate, decltype(*__first1), decltype(*__first2)>::value,
-                "The predicate has to be callable");
+  static_assert(__is_callable<_BinaryPredicate&, decltype(*__first1), decltype(*__first2)>::value,
+                "The comparator has to be callable");
 
   return std::__is_permutation<_ClassicAlgPolicy>(std::move(__first1), std::move(__last1), std::move(__first2), __pred);
 }
@@ -286,8 +286,8 @@ _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 boo
     _ForwardIterator2 __first2,
     _ForwardIterator2 __last2,
     _BinaryPredicate __pred) {
-  static_assert(__is_callable<_BinaryPredicate, decltype(*__first1), decltype(*__first2)>::value,
-                "The predicate has to be callable");
+  static_assert(__is_callable<_BinaryPredicate&, decltype(*__first1), decltype(*__first2)>::value,
+                "The comparator has to be callable");
 
   return std::__is_permutation<_ClassicAlgPolicy>(
       std::move(__first1),
diff --git a/libcxx/include/__algorithm/lower_bound.h b/libcxx/include/__algorithm/lower_bound.h
@@ -93,7 +93,7 @@ __lower_bound(_ForwardIterator __first, _Sent __last, const _Type& __value, _Com
 template <class _ForwardIterator, class _Tp, class _Compare>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
-  static_assert(__is_callable<_Compare, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
+  static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   auto __proj = std::__identity();
   return std::__lower_bound<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);
 }
diff --git a/libcxx/include/__algorithm/max_element.h b/libcxx/include/__algorithm/max_element.h
@@ -13,6 +13,7 @@
 #include <__algorithm/comp_ref_type.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_callable.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -37,6 +38,8 @@ __max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp
 template <class _ForwardIterator, class _Compare>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
+  static_assert(
+      __is_callable<_Compare&, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
   return std::__max_element<__comp_ref_type<_Compare> >(__first, __last, __comp);
 }
 
diff --git a/libcxx/include/__algorithm/min_element.h b/libcxx/include/__algorithm/min_element.h
@@ -53,7 +53,7 @@ min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
   static_assert(
       __has_forward_iterator_category<_ForwardIterator>::value, "std::min_element requires a ForwardIterator");
   static_assert(
-      __is_callable<_Compare, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
+      __is_callable<_Compare&, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
 
   return std::__min_element<__comp_ref_type<_Compare> >(std::move(__first), std::move(__last), __comp);
 }
diff --git a/libcxx/include/__algorithm/minmax.h b/libcxx/include/__algorithm/minmax.h
@@ -40,7 +40,7 @@ minmax(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __
 template <class _Tp, class _Compare>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_Tp, _Tp>
 minmax(initializer_list<_Tp> __t, _Compare __comp) {
-  static_assert(__is_callable<_Compare, _Tp, _Tp>::value, "The comparator has to be callable");
+  static_assert(__is_callable<_Compare&, _Tp, _Tp>::value, "The comparator has to be callable");
   __identity __proj;
   auto __ret = std::__minmax_element_impl(__t.begin(), __t.end(), __comp, __proj);
   return pair<_Tp, _Tp>(*__ret.first, *__ret.second);
diff --git a/libcxx/include/__algorithm/minmax_element.h b/libcxx/include/__algorithm/minmax_element.h
@@ -84,7 +84,7 @@ minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __com
   static_assert(
       __has_forward_iterator_category<_ForwardIterator>::value, "std::minmax_element requires a ForwardIterator");
   static_assert(
-      __is_callable<_Compare, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
+      __is_callable<_Compare&, decltype(*__first), decltype(*__first)>::value, "The comparator has to be callable");
   auto __proj = __identity();
   return std::__minmax_element_impl(__first, __last, __comp, __proj);
 }
diff --git a/libcxx/include/__algorithm/partial_sort_copy.h b/libcxx/include/__algorithm/partial_sort_copy.h
@@ -76,8 +76,8 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
     _RandomAccessIterator __result_first,
     _RandomAccessIterator __result_last,
     _Compare __comp) {
-  static_assert(
-      __is_callable<_Compare, decltype(*__first), decltype(*__result_first)>::value, "Comparator has to be callable");
+  static_assert(__is_callable<_Compare&, decltype(*__first), decltype(*__result_first)>::value,
+                "The comparator has to be callable");
 
   auto __result = std::__partial_sort_copy<_ClassicAlgPolicy>(
       __first,
diff --git a/libcxx/include/__algorithm/search.h b/libcxx/include/__algorithm/search.h
@@ -166,8 +166,8 @@ search(_ForwardIterator1 __first1,
        _ForwardIterator2 __first2,
        _ForwardIterator2 __last2,
        _BinaryPredicate __pred) {
-  static_assert(__is_callable<_BinaryPredicate, decltype(*__first1), decltype(*__first2)>::value,
-                "BinaryPredicate has to be callable");
+  static_assert(__is_callable<_BinaryPredicate&, decltype(*__first1), decltype(*__first2)>::value,
+                "The comparator has to be callable");
   auto __proj = __identity();
   return std::__search_impl(__first1, __last1, __first2, __last2, __pred, __proj, __proj).first;
 }
diff --git a/libcxx/include/__algorithm/search_n.h b/libcxx/include/__algorithm/search_n.h
@@ -139,7 +139,7 @@ template <class _ForwardIterator, class _Size, class _Tp, class _BinaryPredicate
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator search_n(
     _ForwardIterator __first, _ForwardIterator __last, _Size __count, const _Tp& __value, _BinaryPredicate __pred) {
   static_assert(
-      __is_callable<_BinaryPredicate, decltype(*__first), const _Tp&>::value, "BinaryPredicate has to be callable");
+      __is_callable<_BinaryPredicate&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   auto __proj = __identity();
   return std::__search_n_impl(__first, __last, std::__convert_to_integral(__count), __value, __pred, __proj).first;
 }
diff --git a/libcxx/include/__algorithm/upper_bound.h b/libcxx/include/__algorithm/upper_bound.h
@@ -18,6 +18,7 @@
 #include <__iterator/advance.h>
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_callable.h>
 #include <__type_traits/is_constructible.h>
 #include <__utility/move.h>
 
@@ -50,6 +51,7 @@ __upper_bound(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp
 template <class _ForwardIterator, class _Tp, class _Compare>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 upper_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {
+  static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");
   static_assert(is_copy_constructible<_ForwardIterator>::value, "Iterator has to be copy constructible");
   return std::__upper_bound<_ClassicAlgPolicy>(
       std::move(__first), std::move(__last), __value, std::move(__comp), std::__identity());
diff --git a/libcxx/src/regex.cpp b/libcxx/src/regex.cpp
@@ -323,8 +323,8 @@ const classnames ClassNames[] = {
     {"xdigit", ctype_base::xdigit}};
 
 struct use_strcmp {
-  bool operator()(const collationnames& x, const char* y) { return strcmp(x.elem_, y) < 0; }
-  bool operator()(const classnames& x, const char* y) { return strcmp(x.elem_, y) < 0; }
+  bool operator()(const collationnames& x, const char* y) const { return strcmp(x.elem_, y) < 0; }
+  bool operator()(const classnames& x, const char* y) const { return strcmp(x.elem_, y) < 0; }
 };
 
 } // namespace
diff --git a/libcxx/test/libcxx/algorithms/callable-requirements-rvalue.compile.pass.cpp b/libcxx/test/libcxx/algorithms/callable-requirements-rvalue.compile.pass.cpp
@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// <algorithm>
+
+// Make sure that we don't error out when passing a comparator that is lvalue callable
+// but not rvalue callable to algorithms. While it is technically ill-formed for users
+// to provide us such predicates, this test is useful for libc++ to ensure that we check
+// predicate requirements correctly (i.e. that we check them on lvalues and not on
+// rvalues). See https://github.com/llvm/llvm-project/issues/69554 for additional
+// context.
+
+#include <algorithm>
+
+#include "test_macros.h"
+
+struct NotRvalueCallable {
+  bool operator()(int a, int b) const& { return a < b; }
+  bool operator()(int, int) && = delete;
+};
+
+void f() {
+  int a[] = {1, 2, 3, 4};
+  (void)std::lower_bound(a, a + 4, 0, NotRvalueCallable{});
+  (void)std::upper_bound(a, a + 4, 0, NotRvalueCallable{});
+  (void)std::minmax({1, 2, 3}, NotRvalueCallable{});
+  (void)std::minmax_element(a, a + 4, NotRvalueCallable{});
+  (void)std::min_element(a, a + 4, NotRvalueCallable{});
+  (void)std::max_element(a, a + 4, NotRvalueCallable{});
+  (void)std::is_permutation(a, a + 4, a, NotRvalueCallable{});
+#if TEST_STD_VER >= 14
+  (void)std::is_permutation(a, a + 4, a, a + 4, NotRvalueCallable{});
+#endif
+  (void)std::includes(a, a + 4, a, a + 4, NotRvalueCallable{});
+  (void)std::equal_range(a, a + 4, 0, NotRvalueCallable{});
+  (void)std::partial_sort_copy(a, a + 4, a, a + 4, NotRvalueCallable{});
+  (void)std::search(a, a + 4, a, a + 4, NotRvalueCallable{});
+  (void)std::search_n(a, a + 4, 4, 0, NotRvalueCallable{});
+}
diff --git a/libcxx/test/libcxx/algorithms/callable-requirements.verify.cpp b/libcxx/test/libcxx/algorithms/callable-requirements.verify.cpp
@@ -0,0 +1,118 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// Ignore spurious errors after the initial static_assert failure.
+// ADDITIONAL_COMPILE_FLAGS: -Xclang -verify-ignore-unexpected=error
+
+// <algorithm>
+
+// Check that calling a classic STL algorithm with various non-callable comparators is diagnosed.
+
+#include <algorithm>
+
+#include "test_macros.h"
+
+struct NotCallable {
+  bool compare(int a, int b) const { return a < b; }
+};
+
+struct NotMutableCallable {
+  bool operator()(int a, int b) = delete;
+  bool operator()(int a, int b) const { return a < b; }
+};
+
+void f() {
+  int a[] = {1, 2, 3, 4};
+  {
+    (void)std::lower_bound(a, a + 4, 0, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::upper_bound(a, a + 4, 0, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::minmax({1, 2, 3}, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::minmax_element(a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::min_element(a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::max_element(a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::is_permutation(a, a + 4, a, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+#if TEST_STD_VER >= 14
+    (void)std::is_permutation(a, a + 4, a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+#endif
+
+    (void)std::includes(a, a + 4, a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::equal_range(a, a + 4, 0, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::partial_sort_copy(a, a + 4, a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::search(a, a + 4, a, a + 4, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::search_n(a, a + 4, 4, 0, &NotCallable::compare);
+    // expected-error@*:* {{The comparator has to be callable}}
+  }
+
+  {
+    (void)std::lower_bound(a, a + 4, 0, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::upper_bound(a, a + 4, 0, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::minmax({1, 2, 3}, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::minmax_element(a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::min_element(a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::max_element(a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::is_permutation(a, a + 4, a, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+#if TEST_STD_VER >= 14
+    (void)std::is_permutation(a, a + 4, a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+#endif
+
+    (void)std::includes(a, a + 4, a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::equal_range(a, a + 4, 0, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::partial_sort_copy(a, a + 4, a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::search(a, a + 4, a, a + 4, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+
+    (void)std::search_n(a, a + 4, 4, 0, NotMutableCallable{});
+    // expected-error@*:* {{The comparator has to be callable}}
+  }
+}
diff --git a/libcxx/test/libcxx/algorithms/callable.verify.cpp b/libcxx/test/libcxx/algorithms/callable.verify.cpp
diff --git a/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp b/libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp
@@ -26,35 +26,35 @@ struct Proj {
     constexpr explicit Proj(int *copies) : copies_(copies) {}
     constexpr Proj(const Proj& rhs) : copies_(rhs.copies_) { *copies_ += 1; }
     constexpr Proj& operator=(const Proj&) = default;
-    constexpr void *operator()(T) const { return nullptr; }
+    constexpr void* operator()(T) const { return nullptr; }
 };
 
 struct Less {
-    constexpr bool operator()(void*, void*) const { return false; }
+  constexpr bool operator()(void*, void*) const { return false; }
 };
 
 struct Equal {
-    constexpr bool operator()(void*, void*) const { return true; }
+  constexpr bool operator()(void*, void*) const { return true; }
 };
 
 struct UnaryVoid {
-    constexpr void operator()(void*) const {}
+  constexpr void operator()(void*) const {}
 };
 
 struct UnaryTrue {
-    constexpr bool operator()(void*) const { return true; }
+  constexpr bool operator()(void*) const { return true; }
 };
 
 struct NullaryValue {
-    constexpr std::nullptr_t operator()() const { return nullptr; }
+  constexpr std::nullptr_t operator()() const { return nullptr; }
 };
 
 struct UnaryTransform {
-    constexpr T operator()(void*) const { return T(); }
+  constexpr T operator()(void*) const { return T(); }
 };
 
 struct BinaryTransform {
-    constexpr T operator()(void*, void*) const { return T(); }
+  constexpr T operator()(void*, void*) const { return T(); }
 };
 
 constexpr bool all_the_algorithms()
diff --git a/libcxx/test/libcxx/algorithms/robust_against_cpp20_hostile_iterators.compile.pass.cpp b/libcxx/test/libcxx/algorithms/robust_against_cpp20_hostile_iterators.compile.pass.cpp
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.is_permutation/is_permutation_pred.pass.cpp
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_n_pred.pass.cpp
diff --git a/libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_pred.pass.cpp b/libcxx/test/std/algorithms/alg.nonmodifying/alg.search/search_pred.pass.cpp
diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.merge/inplace_merge_comp.pass.cpp
diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/stable_sort_comp.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/stable_sort_comp.pass.cpp

Original file line number	Diff line number	Diff line change
`@@ -93,7 +93,7 @@ __lower_bound(_ForwardIterator __first, _Sent __last, const _Type& __value, _Com`
`93`	`93`	`template <class _ForwardIterator, class _Tp, class _Compare>`
`94`	`94`	`_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator`
`95`	`95`	`lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value, _Compare __comp) {`
`96`		`- static_assert(__is_callable<_Compare, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");`
	`96`	`+ static_assert(__is_callable<_Compare&, decltype(*__first), const _Tp&>::value, "The comparator has to be callable");`
`97`	`97`	`auto __proj = std::__identity();`
`98`	`98`	`return std::__lower_bound<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);`
`99`	`99`	`}`
Original file line number	Diff line number	Diff line change
`@@ -53,7 +53,7 @@ min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)`
`53`	`53`	`static_assert(`
`54`	`54`	`__has_forward_iterator_category<_ForwardIterator>::value, "std::min_element requires a ForwardIterator");`
`55`	`55`	`static_assert(`
`56`		`- __is_callable<_Compare, decltype(__first), decltype(__first)>::value, "The comparator has to be callable");`
	`56`	`+ __is_callable<_Compare&, decltype(__first), decltype(__first)>::value, "The comparator has to be callable");`
`57`	`57`
`58`	`58`	`return std::__min_element<__comp_ref_type<_Compare> >(std::move(__first), std::move(__last), __comp);`
`59`	`59`	`}`
Original file line number	Diff line number	Diff line change
`@@ -84,7 +84,7 @@ minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __com`
`84`	`84`	`static_assert(`
`85`	`85`	`__has_forward_iterator_category<_ForwardIterator>::value, "std::minmax_element requires a ForwardIterator");`
`86`	`86`	`static_assert(`
`87`		`- __is_callable<_Compare, decltype(__first), decltype(__first)>::value, "The comparator has to be callable");`
	`87`	`+ __is_callable<_Compare&, decltype(__first), decltype(__first)>::value, "The comparator has to be callable");`
`88`	`88`	`auto __proj = __identity();`
`89`	`89`	`return std::__minmax_element_impl(__first, __last, __comp, __proj);`
`90`	`90`	`}`