Export of internal Abseil changes

--
e21e960918678629abf89ad1b694b7d4a456b434 by Greg Falcon <gfalcon@google.com>:

Roll back invoke() change due to large increases in compiler memory usage.

PiperOrigin-RevId: 315919455

--
f95872e1e1d7afdefbac94f42ea228d42d80eb6e by Greg Falcon <gfalcon@google.com>:

Rollback of invoke() changes due to compiler memory usage growth

PiperOrigin-RevId: 315911585

--
6c6c6ba6892016a2ce4703042800254fb9b15727 by Laramie Leavitt <lar@google.com>:

Move some of the common mocking code into MockHelpers.

Use MockHelpers to do mock signature detection and improve the dispatch mechansim.

PiperOrigin-RevId: 315825988

--
5e9380367d280c7fa6dbd4d0f48c31ade7f1d419 by Greg Falcon <gfalcon@google.com>:

Rename the internal implementation details Invoke and InvokeT to `invoke` and `invoke_result_t`, since these are re-implementations of C++17 library entites of the same names.

PiperOrigin-RevId: 315790467
GitOrigin-RevId: e21e960918678629abf89ad1b694b7d4a456b434
Change-Id: Ia75011f94cb033c1c9a4cb64cf14d283b91426ac

11 files changed, 212 insertions, 184 deletions

diff --git a/CMake/AbseilDll.cmake b/CMake/AbseilDll.cmake
index 07ae20fe..e25174a3 100644
--- a/CMake/AbseilDll.cmake
+++ b/CMake/AbseilDll.cmake
@@ -137,11 +137,12 @@ set(ABSL_INTERNAL_DLL_FILES
   "random/gaussian_distribution.cc"
   "random/gaussian_distribution.h"
   "random/internal/distribution_caller.h"
-  "random/internal/fast_uniform_bits.h"
   "random/internal/fastmath.h"
+  "random/internal/fast_uniform_bits.h"
   "random/internal/gaussian_distribution_gentables.cc"
   "random/internal/generate_real.h"
   "random/internal/iostream_state_saver.h"
+  "random/internal/mock_helpers.h"
   "random/internal/nonsecure_base.h"
   "random/internal/pcg_engine.h"
   "random/internal/platform.h"
diff --git a/absl/base/internal/invoke.h b/absl/base/internal/invoke.h
index ab5ad910..c4eceebd 100644
--- a/absl/base/internal/invoke.h
+++ b/absl/base/internal/invoke.h
@@ -18,19 +18,16 @@
 // [func.require]
 // Define INVOKE (f, t1, t2, ..., tN) as follows:
 // 1. (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
-//    and is_base_of_v<T, remove_reference_t<decltype(t1)>> is true;
-// 2. (t1.get().*f)(t2, ..., tN) when f is a pointer to a member function of a
-//    class T and remove_cvref_t<decltype(t1)> is a specialization of
-//    reference_wrapper;
-// 3. ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
-//    class T and t1 does not satisfy the previous two items;
-// 4. t1.*f when N == 1 and f is a pointer to data member of a class T and
-//    is_base_of_v<T, remove_reference_t<decltype(t1)>> is true;
-// 5. t1.get().*f when N == 1 and f is a pointer to data member of a class T and
-//    remove_cvref_t<decltype(t1)> is a specialization of reference_wrapper;
-// 6. (*t1).*f when N == 1 and f is a pointer to data member of a class T and t1
-//    does not satisfy the previous two items;
-// 7. f(t1, t2, ..., tN) in all other cases.
+//    and t1 is an object of type T or a reference to an object of type T or a
+//    reference to an object of a type derived from T;
+// 2. ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
+//    class T and t1 is not one of the types described in the previous item;
+// 3. t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+//    an object of type T or a reference to an object of type T or a reference
+//    to an object of a type derived from T;
+// 4. (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+//    is not one of the types described in the previous item;
+// 5. f(t1, t2, ..., tN) in all other cases.
 //
 // The implementation is SFINAE-friendly: substitution failure within Invoke()
 // isn't an error.
@@ -51,16 +48,7 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 
-template <typename T>
-struct IsReferenceWrapper : std::false_type {};
-template <typename T>
-struct IsReferenceWrapper<std::reference_wrapper<T>> : std::true_type {};
-
-template <typename T>
-using RemoveCvrefT =
-    typename std::remove_cv<typename std::remove_reference<T>::type>::type;
-
-// The seven classes below each implement one of the clauses from the definition
+// The five classes below each implement one of the clauses from the definition
 // of INVOKE. The inner class template Accept<F, Args...> checks whether the
 // clause is applicable; static function template Invoke(f, args...) does the
 // invocation.
@@ -84,10 +72,9 @@ struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
 
   template <typename MemFunType, typename C, typename Obj, typename... Args>
   struct AcceptImpl<MemFunType C::*, Obj, Args...>
-      : std::integral_constant<
-            bool, std::is_base_of<
-                      C, typename std::remove_reference<Obj>::type>::value &&
-                      absl::is_function<MemFunType>::value> {};
+      : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
+                                         absl::is_function<MemFunType>::value> {
+  };
 
   template <typename MemFun, typename Obj, typename... Args>
   static decltype((std::declval<Obj>().*
@@ -98,41 +85,17 @@ struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
   }
 };
 
-// (t1.get().*f)(t2, ..., tN) when f is a pointer to a member function of a
-// class T and remove_cvref_t<decltype(t1)> is a specialization of
-// reference_wrapper;
-struct MemFunAndRefWrap : StrippedAccept<MemFunAndRefWrap> {
-  template <typename... Args>
-  struct AcceptImpl : std::false_type {};
-
-  template <typename MemFunType, typename C, typename RefWrap, typename... Args>
-  struct AcceptImpl<MemFunType C::*, RefWrap, Args...>
-      : std::integral_constant<
-            bool, IsReferenceWrapper<RemoveCvrefT<RefWrap>>::value &&
-                      absl::is_function<MemFunType>::value> {};
-
-  template <typename MemFun, typename RefWrap, typename... Args>
-  static decltype((std::declval<RefWrap>().get().*
-                   std::declval<MemFun>())(std::declval<Args>()...))
-  Invoke(MemFun&& mem_fun, RefWrap&& ref_wrap, Args&&... args) {
-    return (std::forward<RefWrap>(ref_wrap).get().*
-            std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
-  }
-};
-
 // ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
-// class T and t1 does not satisfy the previous two items;
+// class T and t1 is not one of the types described in the previous item.
 struct MemFunAndPtr : StrippedAccept<MemFunAndPtr> {
   template <typename... Args>
   struct AcceptImpl : std::false_type {};
 
   template <typename MemFunType, typename C, typename Ptr, typename... Args>
   struct AcceptImpl<MemFunType C::*, Ptr, Args...>
-      : std::integral_constant<
-            bool, !std::is_base_of<
-                      C, typename std::remove_reference<Ptr>::type>::value &&
-                      !IsReferenceWrapper<RemoveCvrefT<Ptr>>::value &&
-                      absl::is_function<MemFunType>::value> {};
+      : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
+                                         absl::is_function<MemFunType>::value> {
+  };
 
   template <typename MemFun, typename Ptr, typename... Args>
   static decltype(((*std::declval<Ptr>()).*
@@ -143,18 +106,17 @@ struct MemFunAndPtr : StrippedAccept<MemFunAndPtr> {
   }
 };
 
-// t1.*f when N == 1 and f is a pointer to data member of a class T and
-// is_base_of_v<T, remove_reference_t<decltype(t1)>> is true;
+// t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+// an object of type T or a reference to an object of type T or a reference
+// to an object of a type derived from T.
 struct DataMemAndRef : StrippedAccept<DataMemAndRef> {
   template <typename... Args>
   struct AcceptImpl : std::false_type {};
 
   template <typename R, typename C, typename Obj>
   struct AcceptImpl<R C::*, Obj>
-      : std::integral_constant<
-            bool, std::is_base_of<
-                      C, typename std::remove_reference<Obj>::type>::value &&
-                      !absl::is_function<R>::value> {};
+      : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
+                                         !absl::is_function<R>::value> {};
 
   template <typename DataMem, typename Ref>
   static decltype(std::declval<Ref>().*std::declval<DataMem>()) Invoke(
@@ -163,39 +125,16 @@ struct DataMemAndRef : StrippedAccept<DataMemAndRef> {
   }
 };
 
-// t1.get().*f when N == 1 and f is a pointer to data member of a class T and
-// remove_cvref_t<decltype(t1)> is a specialization of reference_wrapper;
-struct DataMemAndRefWrap : StrippedAccept<DataMemAndRefWrap> {
-  template <typename... Args>
-  struct AcceptImpl : std::false_type {};
-
-  template <typename R, typename C, typename RefWrap>
-  struct AcceptImpl<R C::*, RefWrap>
-      : std::integral_constant<
-            bool, IsReferenceWrapper<RemoveCvrefT<RefWrap>>::value &&
-                      !absl::is_function<R>::value> {};
-
-  template <typename DataMem, typename RefWrap>
-  static decltype(std::declval<RefWrap>().get().*std::declval<DataMem>())
-  Invoke(DataMem&& data_mem, RefWrap&& ref_wrap) {
-    return std::forward<RefWrap>(ref_wrap).get().*
-           std::forward<DataMem>(data_mem);
-  }
-};
-
-// (*t1).*f when N == 1 and f is a pointer to data member of a class T and t1
-// does not satisfy the previous two items;
+// (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+// is not one of the types described in the previous item.
 struct DataMemAndPtr : StrippedAccept<DataMemAndPtr> {
   template <typename... Args>
   struct AcceptImpl : std::false_type {};
 
   template <typename R, typename C, typename Ptr>
   struct AcceptImpl<R C::*, Ptr>
-      : std::integral_constant<
-            bool, !std::is_base_of<
-                      C, typename std::remove_reference<Ptr>::type>::value &&
-                      !IsReferenceWrapper<RemoveCvrefT<Ptr>>::value &&
-                      !absl::is_function<R>::value> {};
+      : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
+                                         !absl::is_function<R>::value> {};
 
   template <typename DataMem, typename Ptr>
   static decltype((*std::declval<Ptr>()).*std::declval<DataMem>()) Invoke(
@@ -221,18 +160,12 @@ struct Invoker {
   typedef typename std::conditional<
       MemFunAndRef::Accept<Args...>::value, MemFunAndRef,
       typename std::conditional<
-          MemFunAndRefWrap::Accept<Args...>::value, MemFunAndRefWrap,
+          MemFunAndPtr::Accept<Args...>::value, MemFunAndPtr,
           typename std::conditional<
-              MemFunAndPtr::Accept<Args...>::value, MemFunAndPtr,
-              typename std::conditional<
-                  DataMemAndRef::Accept<Args...>::value, DataMemAndRef,
-                  typename std::conditional<
-                      DataMemAndRefWrap::Accept<Args...>::value,
-                      DataMemAndRefWrap,
-                      typename std::conditional<
-                          DataMemAndPtr::Accept<Args...>::value, DataMemAndPtr,
-                          Callable>::type>::type>::type>::type>::type>::type
-      type;
+              DataMemAndRef::Accept<Args...>::value, DataMemAndRef,
+              typename std::conditional<DataMemAndPtr::Accept<Args...>::value,
+                                        DataMemAndPtr, Callable>::type>::type>::
+          type>::type type;
 };
 
 // The result type of Invoke<F, Args...>.
diff --git a/absl/base/invoke_test.cc b/absl/base/invoke_test.cc
index 994d36b9..6aa613c9 100644
--- a/absl/base/invoke_test.cc
+++ b/absl/base/invoke_test.cc
@@ -158,56 +158,31 @@ TEST(InvokeTest, MemberFunction) {
   std::unique_ptr<const Class> cp(new Class);
   std::unique_ptr<volatile Class> vp(new Class);
 
-  Class c;
-  std::reference_wrapper<Class> ref(c);
-  std::reference_wrapper<const Class> ref_const(c);
-  const std::reference_wrapper<Class> const_ref(c);
-  std::reference_wrapper<volatile Class> ref_volatile(c);
-
   EXPECT_EQ(1, Invoke(&Class::Method, p, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::Method, p.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::Method, *p, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::Method, ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::Method, const_ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::Method, std::move(ref), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::RefMethod, p, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::RefMethod, p.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::RefMethod, *p, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::RefMethod, ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::RefMethod, const_ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::RefMethod, std::move(ref), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::RefRefMethod, std::move(*p), 3, 2));  // NOLINT
   EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, p, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, p.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, *p, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, const_ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::NoExceptMethod, std::move(ref), 3, 2));
 
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, p, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, p.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, *p, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::ConstMethod, ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::ConstMethod, const_ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::ConstMethod, std::move(ref), 3, 2));
 
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, cp, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, cp.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, *cp, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::ConstMethod, ref_const, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::ConstMethod, std::move(ref_const), 3, 2));
 
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, p, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, p.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, *p, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::VolatileMethod, ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::VolatileMethod, const_ref, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::VolatileMethod, std::move(ref), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, vp, 3, 2));
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, vp.get(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::VolatileMethod, *vp, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::VolatileMethod, ref_volatile, 3, 2));
-  EXPECT_EQ(1, Invoke(&Class::VolatileMethod, std::move(ref_volatile), 3, 2));
 
   EXPECT_EQ(1, Invoke(&Class::Method, make_unique<Class>(), 3, 2));
   EXPECT_EQ(1, Invoke(&Class::ConstMethod, make_unique<Class>(), 3, 2));
@@ -217,15 +192,8 @@ TEST(InvokeTest, MemberFunction) {
 TEST(InvokeTest, DataMember) {
   std::unique_ptr<Class> p(new Class{42});
   std::unique_ptr<const Class> cp(new Class{42});
-  Class c{42};
-  std::reference_wrapper<Class> ref(c);
-  std::reference_wrapper<const Class> ref_const(c);
-  const std::reference_wrapper<Class> const_ref(c);
   EXPECT_EQ(42, Invoke(&Class::member, p));
   EXPECT_EQ(42, Invoke(&Class::member, *p));
-  EXPECT_EQ(42, Invoke(&Class::member, ref));
-  EXPECT_EQ(42, Invoke(&Class::member, const_ref));
-  EXPECT_EQ(42, Invoke(&Class::member, std::move(ref)));
   EXPECT_EQ(42, Invoke(&Class::member, p.get()));
 
   Invoke(&Class::member, p) = 42;
@@ -233,8 +201,6 @@ TEST(InvokeTest, DataMember) {
 
   EXPECT_EQ(42, Invoke(&Class::member, cp));
   EXPECT_EQ(42, Invoke(&Class::member, *cp));
-  EXPECT_EQ(42, Invoke(&Class::member, ref_const));
-  EXPECT_EQ(42, Invoke(&Class::member, std::move(ref_const)));
   EXPECT_EQ(42, Invoke(&Class::member, cp.get()));
 }
 
diff --git a/absl/functional/bind_front_test.cc b/absl/functional/bind_front_test.cc
index 92b6e8e5..4801a81c 100644
--- a/absl/functional/bind_front_test.cc
+++ b/absl/functional/bind_front_test.cc
@@ -228,23 +228,4 @@ TEST(BindTest, Mangling) {
   absl::bind_front(ManglingCall{}, 1, 3.3)("A");
 }
 
-struct Adder {
-  int add(int v2) const { return v + v2; }
-  int v;
-};
-
-TEST(BindTest, InvokeSemantics) {
-  Struct s1 = {"value"};
-  auto f1 = absl::bind_front(&Struct::value);
-  EXPECT_EQ(f1(s1), "value");
-  EXPECT_EQ(f1(&s1), "value");
-  EXPECT_EQ(f1(std::ref(s1)), "value");
-
-  Adder add_100 = {100};
-  auto f2 = absl::bind_front(&Adder::add);
-  EXPECT_EQ(f2(add_100, 23), 123);
-  EXPECT_EQ(f2(&add_100, 45), 145);
-  EXPECT_EQ(f2(std::ref(add_100), 67), 167);
-}
-
 }  // namespace
diff --git a/absl/random/CMakeLists.txt b/absl/random/CMakeLists.txt
index 8875b309..ade9ea10 100644
--- a/absl/random/CMakeLists.txt
+++ b/absl/random/CMakeLists.txt
@@ -69,6 +69,21 @@ absl_cc_test(
 # Internal-only target, do not depend on directly.
 absl_cc_library(
   NAME
+    random_internal_mock_helpers
+  HDRS
+    "internal/mock_helpers.h"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  LINKOPTS
+    ${ABSL_DEFAULT_LINKOPTS}
+  DEPS
+    absl::fast_type_id
+    absl::optional
+)
+
+# Internal-only target, do not depend on directly.
+absl_cc_library(
+  NAME
     random_internal_mock_overload_set
   HDRS
     "internal/mock_overload_set.h"
@@ -78,7 +93,7 @@ absl_cc_library(
     ${ABSL_DEFAULT_LINKOPTS}
   DEPS
     absl::random_mocking_bit_gen
-    absl::fast_type_id
+    absl::random_internal_mock_helpers
   TESTONLY
 )
 
diff --git a/absl/random/bit_gen_ref.h b/absl/random/bit_gen_ref.h
index 00e36248..9555460f 100644
--- a/absl/random/bit_gen_ref.h
+++ b/absl/random/bit_gen_ref.h
@@ -53,6 +53,7 @@ struct is_urbg<
 
 template <typename>
 struct DistributionCaller;
+class MockHelpers;
 
 }  // namespace random_internal
 
@@ -171,6 +172,7 @@ class BitGenRef {
 
   template <typename>
   friend struct ::absl::random_internal::DistributionCaller;  // for InvokeMock
+  friend class ::absl::random_internal::MockHelpers;          // for InvokeMock
 };
 
 ABSL_NAMESPACE_END
diff --git a/absl/random/internal/BUILD.bazel b/absl/random/internal/BUILD.bazel
index 3ab1177d..d81477ff 100644
--- a/absl/random/internal/BUILD.bazel
+++ b/absl/random/internal/BUILD.bazel
@@ -485,11 +485,20 @@ cc_test(
 )
 
 cc_library(
+    name = "mock_helpers",
+    hdrs = ["mock_helpers.h"],
+    deps = [
+        "//absl/base:fast_type_id",
+        "//absl/types:optional",
+    ],
+)
+
+cc_library(
     name = "mock_overload_set",
     testonly = 1,
     hdrs = ["mock_overload_set.h"],
     deps = [
-        "//absl/base:fast_type_id",
+        ":mock_helpers",
         "//absl/random:mocking_bit_gen",
         "@com_google_googletest//:gtest",
     ],
diff --git a/absl/random/internal/distribution_caller.h b/absl/random/internal/distribution_caller.h
index 87a76845..fc81b787 100644
--- a/absl/random/internal/distribution_caller.h
+++ b/absl/random/internal/distribution_caller.h
@@ -52,23 +52,25 @@ struct DistributionCaller {
 
   // Default implementation of distribution caller.
   template <typename DistrT, typename... Args>
-  static inline typename DistrT::result_type Impl(std::false_type, URBG* urbg,
-                                                  Args&&... args) {
+  static typename DistrT::result_type Impl(std::false_type, URBG* urbg,
+                                           Args&&... args) {
     DistrT dist(std::forward<Args>(args)...);
     return dist(*urbg);
   }
 
   // Mock implementation of distribution caller.
+  // The underlying KeyT must match the KeyT constructed by MockOverloadSet.
   template <typename DistrT, typename... Args>
-  static inline typename DistrT::result_type Impl(std::true_type, URBG* urbg,
-                                                  Args&&... args) {
+  static typename DistrT::result_type Impl(std::true_type, URBG* urbg,
+                                           Args&&... args) {
     using ResultT = typename DistrT::result_type;
     using ArgTupleT = std::tuple<absl::decay_t<Args>...>;
+    using KeyT = ResultT(DistrT, ArgTupleT);
+
     ArgTupleT arg_tuple(std::forward<Args>(args)...);
     ResultT result;
-    if (!urbg->InvokeMock(
-            ::absl::base_internal::FastTypeId<ResultT(DistrT, ArgTupleT)>(),
-            &arg_tuple, &result)) {
+    if (!urbg->InvokeMock(::absl::base_internal::FastTypeId<KeyT>(), &arg_tuple,
+                          &result)) {
       auto dist = absl::make_from_tuple<DistrT>(arg_tuple);
       result = dist(*urbg);
     }
@@ -77,7 +79,7 @@ struct DistributionCaller {
 
   // Default implementation of distribution caller.
   template <typename DistrT, typename... Args>
-  static inline typename DistrT::result_type Call(URBG* urbg, Args&&... args) {
+  static typename DistrT::result_type Call(URBG* urbg, Args&&... args) {
     return Impl<DistrT, Args...>(HasInvokeMock{}, urbg,
                                  std::forward<Args>(args)...);
   }
diff --git a/absl/random/internal/mock_helpers.h b/absl/random/internal/mock_helpers.h
new file mode 100644
index 00000000..9af27ab3
--- /dev/null
+++ b/absl/random/internal/mock_helpers.h
@@ -0,0 +1,127 @@
+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_RANDOM_INTERNAL_MOCK_HELPERS_H_
+#define ABSL_RANDOM_INTERNAL_MOCK_HELPERS_H_
+
+#include <tuple>
+#include <type_traits>
+
+#include "absl/base/internal/fast_type_id.h"
+#include "absl/types/optional.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace random_internal {
+
+// MockHelpers works in conjunction with MockOverloadSet, MockingBitGen, and
+// BitGenRef to enable the mocking capability for absl distribution functions.
+//
+// MockingBitGen registers mocks based on the typeid of a mock signature, KeyT,
+// which is used to generate a unique id.
+//
+// KeyT is a signature of the form:
+//   result_type(discriminator_type, std::tuple<args...>)
+// The mocked function signature will be composed from KeyT as:
+//   result_type(args...)
+//
+class MockHelpers {
+  using IdType = ::absl::base_internal::FastTypeIdType;
+
+  // Given a key signature type used to index the mock, extract the components.
+  // KeyT is expected to have the form:
+  //   result_type(discriminator_type, arg_tuple_type)
+  template <typename KeyT>
+  struct KeySignature;
+
+  template <typename ResultT, typename DiscriminatorT, typename ArgTupleT>
+  struct KeySignature<ResultT(DiscriminatorT, ArgTupleT)> {
+    using result_type = ResultT;
+    using discriminator_type = DiscriminatorT;
+    using arg_tuple_type = ArgTupleT;
+  };
+
+  // Detector for InvokeMock.
+  template <class T>
+  using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock(
+      std::declval<IdType>(), std::declval<void*>(), std::declval<void*>()));
+
+  // Empty implementation of InvokeMock.
+  template <typename KeyT, typename ReturnT, typename ArgTupleT, typename URBG,
+            typename... Args>
+  static absl::optional<ReturnT> InvokeMockImpl(char, URBG*, Args&&...) {
+    return absl::nullopt;
+  }
+
+  // Non-empty implementation of InvokeMock.
+  template <typename KeyT, typename ReturnT, typename ArgTupleT, typename URBG,
+            typename = invoke_mock_t<URBG>, typename... Args>
+  static absl::optional<ReturnT> InvokeMockImpl(int, URBG* urbg,
+                                                Args&&... args) {
+    ArgTupleT arg_tuple(std::forward<Args>(args)...);
+    ReturnT result;
+    if (urbg->InvokeMock(::absl::base_internal::FastTypeId<KeyT>(), &arg_tuple,
+                         &result)) {
+      return result;
+    }
+    return absl::nullopt;
+  }
+
+ public:
+  // Invoke a mock for the KeyT (may or may not be a signature).
+  //
+  // KeyT is used to generate a typeid-based lookup key for the mock.
+  // KeyT is a signature of the form:
+  //   result_type(discriminator_type, std::tuple<args...>)
+  // The mocked function signature will be composed from KeyT as:
+  //   result_type(args...)
+  //
+  // An instance of arg_tuple_type must be constructable from Args..., since
+  // the underlying mechanism requires a pointer to an argument tuple.
+  template <typename KeyT, typename URBG, typename... Args>
+  static auto MaybeInvokeMock(URBG* urbg, Args&&... args)
+      -> absl::optional<typename KeySignature<KeyT>::result_type> {
+    // Use function overloading to dispatch to the implemenation since
+    // more modern patterns (e.g. require + constexpr) are not supported in all
+    // compiler configurations.
+    return InvokeMockImpl<KeyT, typename KeySignature<KeyT>::result_type,
+                          typename KeySignature<KeyT>::arg_tuple_type, URBG>(
+        0, urbg, std::forward<Args>(args)...);
+  }
+
+  // Acquire a mock for the KeyT (may or may not be a signature).
+  //
+  // KeyT is used to generate a typeid-based lookup for the mock.
+  // KeyT is a signature of the form:
+  //   result_type(discriminator_type, std::tuple<args...>)
+  // The mocked function signature will be composed from KeyT as:
+  //   result_type(args...)
+  template <typename KeyT, typename MockURBG>
+  static auto MockFor(MockURBG& m) -> decltype(
+      std::declval<MockURBG>()
+          .template RegisterMock<typename KeySignature<KeyT>::result_type,
+                                 typename KeySignature<KeyT>::arg_tuple_type>(
+              std::declval<IdType>())) {
+    return m.template RegisterMock<typename KeySignature<KeyT>::result_type,
+                                   typename KeySignature<KeyT>::arg_tuple_type>(
+        ::absl::base_internal::FastTypeId<KeyT>());
+  }
+};
+
+}  // namespace random_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_RANDOM_INTERNAL_MOCK_HELPERS_H_
diff --git a/absl/random/internal/mock_overload_set.h b/absl/random/internal/mock_overload_set.h
index 60561b51..dccc6cee 100644
--- a/absl/random/internal/mock_overload_set.h
+++ b/absl/random/internal/mock_overload_set.h
@@ -20,7 +20,7 @@
 
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include "absl/base/internal/fast_type_id.h"
+#include "absl/random/internal/mock_helpers.h"
 #include "absl/random/mocking_bit_gen.h"
 
 namespace absl {
@@ -37,22 +37,19 @@ struct MockSingleOverload;
 // `mock_single_overload.gmock_Call(...)`. Because expectations are stored on
 // the MockingBitGen (an argument passed inside `Call(...)`), this forwards to
 // arguments to MockingBitGen::Register.
+//
+// The underlying KeyT must match the KeyT constructed by DistributionCaller.
 template <typename DistrT, typename Ret, typename... Args>
 struct MockSingleOverload<DistrT, Ret(MockingBitGen&, Args...)> {
   static_assert(std::is_same<typename DistrT::result_type, Ret>::value,
                 "Overload signature must have return type matching the "
                 "distribution result_type.");
-  using ArgTupleT = std::tuple<Args...>;
+  using KeyT = Ret(DistrT, std::tuple<Args...>);
   auto gmock_Call(
       absl::MockingBitGen& gen,  // NOLINT(google-runtime-references)
       const ::testing::Matcher<Args>&... matchers)
-      -> decltype(gen.RegisterMock<Ret, ArgTupleT>(
-                         std::declval<::absl::base_internal::FastTypeIdType>())
-                      .gmock_Call(matchers...)) {
-    return gen
-        .RegisterMock<Ret, ArgTupleT>(
-            ::absl::base_internal::FastTypeId<Ret(DistrT, ArgTupleT)>())
-        .gmock_Call(matchers...);
+      -> decltype(MockHelpers::MockFor<KeyT>(gen).gmock_Call(matchers...)) {
+    return MockHelpers::MockFor<KeyT>(gen).gmock_Call(matchers...);
   }
 };
 
@@ -61,18 +58,14 @@ struct MockSingleOverload<DistrT, Ret(Arg, MockingBitGen&, Args...)> {
   static_assert(std::is_same<typename DistrT::result_type, Ret>::value,
                 "Overload signature must have return type matching the "
                 "distribution result_type.");
-  using ArgTupleT = std::tuple<Arg, Args...>;
+  using KeyT = Ret(DistrT, std::tuple<Arg, Args...>);
   auto gmock_Call(
       const ::testing::Matcher<Arg>& matcher,
       absl::MockingBitGen& gen,  // NOLINT(google-runtime-references)
       const ::testing::Matcher<Args>&... matchers)
-      -> decltype(gen.RegisterMock<Ret, ArgTupleT>(
-                         std::declval<::absl::base_internal::FastTypeIdType>())
-                      .gmock_Call(matcher, matchers...)) {
-    return gen
-        .RegisterMock<Ret, ArgTupleT>(
-            ::absl::base_internal::FastTypeId<Ret(DistrT, ArgTupleT)>())
-        .gmock_Call(matcher, matchers...);
+      -> decltype(MockHelpers::MockFor<KeyT>(gen).gmock_Call(matcher,
+                                                             matchers...)) {
+    return MockHelpers::MockFor<KeyT>(gen).gmock_Call(matcher, matchers...);
   }
 };
 
diff --git a/absl/random/mocking_bit_gen.h b/absl/random/mocking_bit_gen.h
index c3c7d44d..6d2f2c83 100644
--- a/absl/random/mocking_bit_gen.h
+++ b/absl/random/mocking_bit_gen.h
@@ -53,10 +53,9 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 
 namespace random_internal {
-template <typename, typename>
-struct MockSingleOverload;
 template <typename>
 struct DistributionCaller;
+class MockHelpers;
 
 }  // namespace random_internal
 class BitGenRef;
@@ -216,11 +215,11 @@ class MockingBitGen {
   std::vector<std::function<void()>> deleters_;
   absl::BitGen gen_;
 
-  template <typename, typename>
-  friend struct ::absl::random_internal::MockSingleOverload;  // for Register
   template <typename>
   friend struct ::absl::random_internal::DistributionCaller;  // for InvokeMock
   friend class ::absl::BitGenRef;                             // for InvokeMock
+  friend class ::absl::random_internal::MockHelpers;  // for RegisterMock,
+                                                      // InvokeMock
 };
 
 ABSL_NAMESPACE_END