[libc++] Improve diagnostics for non-const comparators and hashers in associative containers

Summary:
When providing a non-const-callable comparator in a map or set, the
warning diagnostic does not include the point of instantiation of
the container that triggered the warning, which makes it difficult
to track down the problem. This commit improves the diagnostic by
placing it directly in the body of the associative container.

The same change is applied to unordered associative containers, which
had a similar problem.

Finally, this commit cleans up the forward declarations of several
map and unordered_map helpers, which are not needed anymore.

<rdar://problem/41370747>

Reviewers: EricWF, mclow.lists

Subscribers: christof, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D48955

llvm-svn: 348529

1 files changed, 22 insertions, 38 deletions

diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table
index 69ed8dd8b94..6f5b183105e 100644
--- a/libcxx/include/__hash_table
+++ b/libcxx/include/__hash_table
@@ -35,15 +35,6 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <class _Key, class _Tp>
 struct __hash_value_type;
 
-template <class _Key, class _Cp, class _Hash,
-          bool =  is_empty<_Hash>::value && !__libcpp_is_final<_Hash>::value>
-class __unordered_map_hasher;
-
-template <class _Key, class _Cp, class _Pred,
-          bool = is_empty<_Pred>::value && !__libcpp_is_final<_Pred>::value
-         >
-class __unordered_map_equal;
-
 #ifndef _LIBCPP_CXX03_LANG
 template <class _Tp>
 struct __is_hash_value_type_imp : false_type {};
@@ -418,7 +409,7 @@ public:
         _LIBCPP_DEBUG_MODE(__get_db()->__insert_i(this));
     }
 
-    _LIBCPP_INLINE_VISIBILITY 
+    _LIBCPP_INLINE_VISIBILITY
     __hash_const_iterator(const __non_const_iterator& __x) _NOEXCEPT
         : __node_(__x.__node_)
     {
@@ -871,35 +862,32 @@ struct __generic_container_node_destructor<__hash_node<_Tp, _VoidPtr>, _Alloc>
 };
 #endif
 
+template <class _Key, class _Hash, class _Equal>
+struct __enforce_unordered_container_requirements {
 #ifndef _LIBCPP_CXX03_LANG
-template <class _Key, class _Hash, class _Equal, class _Alloc>
-struct __diagnose_hash_table_helper {
-  static constexpr bool __trigger_diagnostics()
-    _LIBCPP_DIAGNOSE_WARNING(__check_hash_requirements<_Key, _Hash>::value
-                         && !__invokable<_Hash const&, _Key const&>::value,
-      "the specified hash functor does not provide a const call operator")
-    _LIBCPP_DIAGNOSE_WARNING(is_copy_constructible<_Equal>::value
-                          && !__invokable<_Equal const&, _Key const&, _Key const&>::value,
-      "the specified comparator type does not provide a const call operator")
-  {
     static_assert(__check_hash_requirements<_Key, _Hash>::value,
-      "the specified hash does not meet the Hash requirements");
+    "the specified hash does not meet the Hash requirements");
     static_assert(is_copy_constructible<_Equal>::value,
-      "the specified comparator is required to be copy constructible");
-    return true;
-  }
+    "the specified comparator is required to be copy constructible");
+#endif
+    typedef int type;
 };
 
-template <class _Key, class _Value, class _Hash, class _Equal, class _Alloc>
-struct __diagnose_hash_table_helper<
-  __hash_value_type<_Key, _Value>,
-  __unordered_map_hasher<_Key, __hash_value_type<_Key, _Value>, _Hash>,
-  __unordered_map_equal<_Key, __hash_value_type<_Key, _Value>, _Equal>,
-  _Alloc>
-: __diagnose_hash_table_helper<_Key, _Hash, _Equal, _Alloc>
-{
-};
-#endif // _LIBCPP_CXX03_LANG
+template <class _Key, class _Hash, class _Equal>
+#ifndef _LIBCPP_CXX03_LANG
+    _LIBCPP_DIAGNOSE_WARNING(!__invokable<_Equal const&, _Key const&, _Key const&>::value,
+    "the specified comparator type does not provide a const call operator")
+    _LIBCPP_DIAGNOSE_WARNING(!__invokable<_Hash const&, _Key const&>::value,
+    "the specified hash functor does not provide a const call operator")
+#endif
+typename __enforce_unordered_container_requirements<_Key, _Hash, _Equal>::type
+__diagnose_unordered_container_requirements(int);
+
+// This dummy overload is used so that the compiler won't emit a spurious
+// "no matching function for call to __diagnose_unordered_xxx" diagnostic
+// when the overload above causes a hard error.
+template <class _Key, class _Hash, class _Equal>
+int __diagnose_unordered_container_requirements(void*);
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 class __hash_table
@@ -963,10 +951,6 @@ private:
     typedef allocator_traits<__pointer_allocator>          __pointer_alloc_traits;
     typedef typename __bucket_list_deleter::pointer       __node_pointer_pointer;
 
-#ifndef _LIBCPP_CXX03_LANG
-    static_assert(__diagnose_hash_table_helper<_Tp, _Hash, _Equal, _Alloc>::__trigger_diagnostics(), "");
-#endif
-
     // --- Member data begin ---
     __bucket_list                                         __bucket_list_;
     __compressed_pair<__first_node, __node_allocator>     __p1_;