From b56cbdd23834a65682c0b46f367f8679e83bc894 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Fri, 18 Sep 2020 15:55:15 -0700
Subject: Abseil LTS 20200923

What's New:
* `absl::StatusOr<T>` has been released. See our [blog
  post](https://abseil.io/blog/2020-091021-status) for more
  information.
* Abseil Flags reflection interfaces have been released.
* Abseil Flags memory usage has been significantly optimized.
* Abseil now supports a "hardened" build mode. This build mode enables
  runtime checks that guard against programming errors that may lead
  to security vulnerabilities.

Notable Fixes:
* Sanitizer dynamic annotations like `AnnotateRWLockCreate` that are
  also defined by the compiler sanitizer implementation are no longer
  also defined by Abseil.
* Sanitizer macros are now prefixed with `ABSL_` to avoid naming collisions.
* Sanitizer usage is now automatically detected and no longer requires
  macros like `ADDRESS_SANITIZER` to be defined on the command line.

Breaking Changes:
* Abseil no longer contains a `dynamic_annotations` library. Users
  using a supported build system (Bazel or CMake) are unaffected by
  this, but users manually specifying link libraries may get an error
  about a missing linker input.

Baseline: 7680a5f8efe32de4753baadbd63e74e59d95bac1
Cherry picks: None
---
 absl/container/internal/hash_policy_traits.h | 31 +++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

(limited to 'absl/container/internal/hash_policy_traits.h')

diff --git a/absl/container/internal/hash_policy_traits.h b/absl/container/internal/hash_policy_traits.h
index 3e1209c6..46c97b18 100644
--- a/absl/container/internal/hash_policy_traits.h
+++ b/absl/container/internal/hash_policy_traits.h
@@ -17,6 +17,7 @@
 
 #include <cstddef>
 #include <memory>
+#include <new>
 #include <type_traits>
 #include <utility>
 
@@ -29,15 +30,34 @@ namespace container_internal {
 // Defines how slots are initialized/destroyed/moved.
 template <class Policy, class = void>
 struct hash_policy_traits {
+  // The type of the keys stored in the hashtable.
+  using key_type = typename Policy::key_type;
+
  private:
   struct ReturnKey {
-    // We return `Key` here.
+    // When C++17 is available, we can use std::launder to provide mutable
+    // access to the key for use in node handle.
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
+    template <class Key,
+              absl::enable_if_t<std::is_lvalue_reference<Key>::value, int> = 0>
+    static key_type& Impl(Key&& k, int) {
+      return *std::launder(
+          const_cast<key_type*>(std::addressof(std::forward<Key>(k))));
+    }
+#endif
+
+    template <class Key>
+    static Key Impl(Key&& k, char) {
+      return std::forward<Key>(k);
+    }
+
     // When Key=T&, we forward the lvalue reference.
     // When Key=T, we return by value to avoid a dangling reference.
     // eg, for string_hash_map.
     template <class Key, class... Args>
-    Key operator()(Key&& k, const Args&...) const {
-      return std::forward<Key>(k);
+    auto operator()(Key&& k, const Args&...) const
+        -> decltype(Impl(std::forward<Key>(k), 0)) {
+      return Impl(std::forward<Key>(k), 0);
     }
   };
 
@@ -52,9 +72,6 @@ struct hash_policy_traits {
   // The actual object stored in the hash table.
   using slot_type = typename Policy::slot_type;
 
-  // The type of the keys stored in the hashtable.
-  using key_type = typename Policy::key_type;
-
   // The argument type for insertions into the hashtable. This is different
   // from value_type for increased performance. See initializer_list constructor
   // and insert() member functions for more details.
@@ -156,7 +173,7 @@ struct hash_policy_traits {
   // Returns the "key" portion of the slot.
   // Used for node handle manipulation.
   template <class P = Policy>
-  static auto key(slot_type* slot)
+  static auto mutable_key(slot_type* slot)
       -> decltype(P::apply(ReturnKey(), element(slot))) {
     return P::apply(ReturnKey(), element(slot));
   }
-- 
cgit v1.2.3