[libc++] Remove the constexpr hash<vector<bool>> extension

libcxx/docs/ReleaseNotes/21.rst

@@ -80,6 +80,9 @@ Deprecations and Removals
 - The ``_LIBCPP_VERBOSE_ABORT_NOT_NOEXCEPT`` has been removed, making ``std::__libcpp_verbose_abort``
   unconditionally ``noexcept``.
 
+- libc++ no longer adds ``constexpr`` to ``std::hash<std::vector<bool, A>>::operator()``, as the ``constexpr`` addition
+  since C++20 was an unintended extension.
+
 - TODO: The non-conforming extension ``packaged_task::result_type`` has been removed in LLVM 21.
 
 Potentially breaking changes

libcxx/include/__vector/vector_bool.h

@@ -512,7 +512,7 @@ class vector<bool, _Allocator> {
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __move_assign_alloc(vector&, false_type) _NOEXCEPT {}
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 size_t __hash_code() const _NOEXCEPT;
+  _LIBCPP_HIDE_FROM_ABI size_t __hash_code() const _NOEXCEPT;
 
   friend class __bit_reference<vector>;
   friend class __bit_const_reference<vector>;
@@ -1093,7 +1093,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 bool vector<bool, _Allocator>::__invariants() cons
 }
 
 template <class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 size_t vector<bool, _Allocator>::__hash_code() const _NOEXCEPT {
+size_t vector<bool, _Allocator>::__hash_code() const _NOEXCEPT {
   size_t __h = 0;
   // do middle whole words
   size_type __n         = __size_;
@@ -1110,8 +1110,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 size_t vector<bool, _Allocator>::__hash_code() con
 
 template <class _Allocator>
 struct hash<vector<bool, _Allocator> > : public __unary_function<vector<bool, _Allocator>, size_t> {
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 size_t
-  operator()(const vector<bool, _Allocator>& __vec) const _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI size_t operator()(const vector<bool, _Allocator>& __vec) const _NOEXCEPT {
     return __vec.__hash_code();
   }
 };

libcxx/test/std/containers/sequences/vector.bool/enabled_hash.pass.cpp

@@ -19,19 +19,14 @@
 #include "test_macros.h"
 #include "min_allocator.h"
 
-TEST_CONSTEXPR_CXX20 bool test() {
+void test() {
   test_hash_enabled<std::vector<bool> >();
   test_hash_enabled<std::vector<bool, min_allocator<bool>>>();
-
-  return true;
 }
 
 int main(int, char**) {
   test_library_hash_specializations_available();
   test();
-#if TEST_STD_VER > 17
-  static_assert(test());
-#endif
 
   return 0;
 }

libcxx/test/std/containers/sequences/vector.bool/vector_bool.pass.cpp

@@ -14,8 +14,6 @@
 //     size_t operator()(T val) const;
 // };
 
-// Not very portable
-
 #include <vector>
 #include <cassert>
 #include <iterator>
@@ -24,35 +22,29 @@
 #include "test_macros.h"
 #include "min_allocator.h"
 
-TEST_CONSTEXPR_CXX20 bool tests() {
-  {
-    typedef std::vector<bool> T;
-    typedef std::hash<T> H;
+template <class VB>
+TEST_CONSTEXPR_CXX20 void test() {
+  typedef std::hash<VB> H;
 #if TEST_STD_VER <= 14
-    static_assert((std::is_same<H::argument_type, T>::value), "");
-    static_assert((std::is_same<H::result_type, std::size_t>::value), "");
+  static_assert((std::is_same<typename H::argument_type, VB>::value), "");
+  static_assert((std::is_same<typename H::result_type, std::size_t>::value), "");
 #endif
-    ASSERT_NOEXCEPT(H()(T()));
-
-    bool ba[] = {true, false, true, true, false};
-    T vb(std::begin(ba), std::end(ba));
-    H h;
-    assert(h(vb) != 0);
+  ASSERT_NOEXCEPT(H()(VB()));
+
+  bool ba[] = {true, false, true, true, false};
+  VB vb(std::begin(ba), std::end(ba));
+  H h;
+  if (!TEST_IS_CONSTANT_EVALUATED) {
+    const std::size_t hash_value = h(vb);
+    assert(h(vb) == hash_value);
+    LIBCPP_ASSERT(hash_value != 0);
   }
+}
+
+TEST_CONSTEXPR_CXX20 bool tests() {
+  test<std::vector<bool> >();
 #if TEST_STD_VER >= 11
-  {
-    typedef std::vector<bool, min_allocator<bool>> T;
-    typedef std::hash<T> H;
-#  if TEST_STD_VER <= 14
-    static_assert((std::is_same<H::argument_type, T>::value), "");
-    static_assert((std::is_same<H::result_type, std::size_t>::value), "");
-#  endif
-    ASSERT_NOEXCEPT(H()(T()));
-    bool ba[] = {true, false, true, true, false};
-    T vb(std::begin(ba), std::end(ba));
-    H h;
-    assert(h(vb) != 0);
-  }
+  test<std::vector<bool, min_allocator<bool>>>();
 #endif
 
   return true;