Export of internal Abseil changes

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487c7a754a3b93bc0f9de14bdced48007a96ae55 by Greg Falcon <gfalcon@google.com>:

Add support for absl::Hash to hash unordered containers.  These can now be hashed directly, as well as combined in AbslHashValue implementations.

This also adds a new method, `H::combine_unordered()`, to the public AbslHashValue hash state API.  This allows users to implement hash specializations for their own unordered collection types.

A traits class, `H::is_hashable<T>`, is also added to the hash state API.  H::is_hashable<T>::value reflects whether type T is considered hashable by the AbslHashValue framework.  This allows users to properly SFINAE templated versions of AbslHashValue.  (The AbslHashValue implementation added to raw_hash_set shows an example of its use.)

PiperOrigin-RevId: 422856706
GitOrigin-RevId: 487c7a754a3b93bc0f9de14bdced48007a96ae55
Change-Id: Id31fd4ccba282f8c9ae6fcee6ae0ad0f7879f456

1 files changed, 35 insertions, 0 deletions

diff --git a/absl/hash/internal/spy_hash_state.h b/absl/hash/internal/spy_hash_state.h
index c0831208..09728266 100644
--- a/absl/hash/internal/spy_hash_state.h
+++ b/absl/hash/internal/spy_hash_state.h
@@ -15,6 +15,7 @@
 #ifndef ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_
 #define ABSL_HASH_INTERNAL_SPY_HASH_STATE_H_
 
+#include <algorithm>
 #include <ostream>
 #include <string>
 #include <vector>
@@ -167,6 +168,24 @@ class SpyHashStateImpl : public HashStateBase<SpyHashStateImpl<T>> {
 
   using SpyHashStateImpl::HashStateBase::combine_contiguous;
 
+  template <typename CombinerT>
+  static SpyHashStateImpl RunCombineUnordered(SpyHashStateImpl state,
+                                              CombinerT combiner) {
+    UnorderedCombinerCallback cb;
+
+    combiner(SpyHashStateImpl<void>{}, std::ref(cb));
+
+    std::sort(cb.element_hash_representations.begin(),
+              cb.element_hash_representations.end());
+    state.hash_representation_.insert(state.hash_representation_.end(),
+                                      cb.element_hash_representations.begin(),
+                                      cb.element_hash_representations.end());
+    if (cb.error && cb.error->has_value()) {
+      state.error_ = std::move(cb.error);
+    }
+    return state;
+  }
+
   absl::optional<std::string> error() const {
     if (moved_from_) {
       return "Returned a moved-from instance of the hash state object.";
@@ -178,6 +197,22 @@ class SpyHashStateImpl : public HashStateBase<SpyHashStateImpl<T>> {
   template <typename U>
   friend class SpyHashStateImpl;
 
+  struct UnorderedCombinerCallback {
+    std::vector<std::string> element_hash_representations;
+    std::shared_ptr<absl::optional<std::string>> error;
+
+    // The inner spy can have a different type.
+    template <typename U>
+    void operator()(SpyHashStateImpl<U>& inner) {
+      element_hash_representations.push_back(
+          absl::StrJoin(inner.hash_representation_, ""));
+      if (inner.error_->has_value()) {
+        error = std::move(inner.error_);
+      }
+      inner = SpyHashStateImpl<void>{};
+    }
+  };
+
   // This is true if SpyHashStateImpl<T> has been passed to a call of
   // AbslHashValue with the wrong type. This detects that the user called
   // AbslHashValue directly (because the hash state type does not match).