Add support for move-only and &&-qualified actions in WillOnce.

This provides a type-safe way for an action to express that it wants to be
called only once, or to capture move-only objects. It is a generalization of
the type system-evading hack in ByMove, with the improvement that it works for
_any_ action (including user-defined ones), and correctly expresses that the
action can only be used with WillOnce. I'll make existing actions benefit in a
future commit.

PiperOrigin-RevId: 440496139
Change-Id: I4145d191cca5655995ef41360bb126c123cb41d3

1 files changed, 310 insertions, 28 deletions

diff --git a/googlemock/test/gmock-actions_test.cc b/googlemock/test/gmock-actions_test.cc
index 233b60c..7ff5780 100644
--- a/googlemock/test/gmock-actions_test.cc
+++ b/googlemock/test/gmock-actions_test.cc
@@ -55,37 +55,170 @@
 #include "gtest/gtest-spi.h"
 #include "gtest/gtest.h"
 
+namespace testing {
 namespace {
 
-using ::testing::_;
-using ::testing::Action;
-using ::testing::ActionInterface;
-using ::testing::Assign;
-using ::testing::ByMove;
-using ::testing::ByRef;
-using ::testing::DefaultValue;
-using ::testing::DoAll;
-using ::testing::DoDefault;
-using ::testing::IgnoreResult;
-using ::testing::Invoke;
-using ::testing::InvokeWithoutArgs;
-using ::testing::MakePolymorphicAction;
-using ::testing::PolymorphicAction;
-using ::testing::Return;
-using ::testing::ReturnNew;
-using ::testing::ReturnNull;
-using ::testing::ReturnRef;
-using ::testing::ReturnRefOfCopy;
-using ::testing::ReturnRoundRobin;
-using ::testing::SetArgPointee;
-using ::testing::SetArgumentPointee;
-using ::testing::Unused;
-using ::testing::WithArgs;
 using ::testing::internal::BuiltInDefaultValue;
 
-#if !GTEST_OS_WINDOWS_MOBILE
-using ::testing::SetErrnoAndReturn;
-#endif
+TEST(TypeTraits, Negation) {
+  // Direct use with std types.
+  static_assert(std::is_base_of<std::false_type,
+                                internal::negation<std::true_type>>::value,
+                "");
+
+  static_assert(std::is_base_of<std::true_type,
+                                internal::negation<std::false_type>>::value,
+                "");
+
+  // With other types that fit the requirement of a value member that is
+  // convertible to bool.
+  static_assert(std::is_base_of<
+                    std::true_type,
+                    internal::negation<std::integral_constant<int, 0>>>::value,
+                "");
+
+  static_assert(std::is_base_of<
+                    std::false_type,
+                    internal::negation<std::integral_constant<int, 1>>>::value,
+                "");
+
+  static_assert(std::is_base_of<
+                    std::false_type,
+                    internal::negation<std::integral_constant<int, -1>>>::value,
+                "");
+}
+
+// Weird false/true types that aren't actually bool constants (but should still
+// be legal according to [meta.logical] because `bool(T::value)` is valid), are
+// distinct from std::false_type and std::true_type, and are distinct from other
+// instantiations of the same template.
+//
+// These let us check finicky details mandated by the standard like
+// "std::conjunction should evaluate to a type that inherits from the first
+// false-y input".
+template <int>
+struct MyFalse : std::integral_constant<int, 0> {};
+
+template <int>
+struct MyTrue : std::integral_constant<int, -1> {};
+
+TEST(TypeTraits, Conjunction) {
+  // Base case: always true.
+  static_assert(std::is_base_of<std::true_type, internal::conjunction<>>::value,
+                "");
+
+  // One predicate: inherits from that predicate, regardless of value.
+  static_assert(
+      std::is_base_of<MyFalse<0>, internal::conjunction<MyFalse<0>>>::value,
+      "");
+
+  static_assert(
+      std::is_base_of<MyTrue<0>, internal::conjunction<MyTrue<0>>>::value, "");
+
+  // Multiple predicates, with at least one false: inherits from that one.
+  static_assert(
+      std::is_base_of<MyFalse<1>, internal::conjunction<MyTrue<0>, MyFalse<1>,
+                                                        MyTrue<2>>>::value,
+      "");
+
+  static_assert(
+      std::is_base_of<MyFalse<1>, internal::conjunction<MyTrue<0>, MyFalse<1>,
+                                                        MyFalse<2>>>::value,
+      "");
+
+  // Short circuiting: in the case above, additional predicates need not even
+  // define a value member.
+  struct Empty {};
+  static_assert(
+      std::is_base_of<MyFalse<1>, internal::conjunction<MyTrue<0>, MyFalse<1>,
+                                                        Empty>>::value,
+      "");
+
+  // All predicates true: inherits from the last.
+  static_assert(
+      std::is_base_of<MyTrue<2>, internal::conjunction<MyTrue<0>, MyTrue<1>,
+                                                       MyTrue<2>>>::value,
+      "");
+}
+
+TEST(TypeTraits, Disjunction) {
+  // Base case: always false.
+  static_assert(
+      std::is_base_of<std::false_type, internal::disjunction<>>::value, "");
+
+  // One predicate: inherits from that predicate, regardless of value.
+  static_assert(
+      std::is_base_of<MyFalse<0>, internal::disjunction<MyFalse<0>>>::value,
+      "");
+
+  static_assert(
+      std::is_base_of<MyTrue<0>, internal::disjunction<MyTrue<0>>>::value, "");
+
+  // Multiple predicates, with at least one true: inherits from that one.
+  static_assert(
+      std::is_base_of<MyTrue<1>, internal::disjunction<MyFalse<0>, MyTrue<1>,
+                                                       MyFalse<2>>>::value,
+      "");
+
+  static_assert(
+      std::is_base_of<MyTrue<1>, internal::disjunction<MyFalse<0>, MyTrue<1>,
+                                                       MyTrue<2>>>::value,
+      "");
+
+  // Short circuiting: in the case above, additional predicates need not even
+  // define a value member.
+  struct Empty {};
+  static_assert(
+      std::is_base_of<MyTrue<1>, internal::disjunction<MyFalse<0>, MyTrue<1>,
+                                                       Empty>>::value,
+      "");
+
+  // All predicates false: inherits from the last.
+  static_assert(
+      std::is_base_of<MyFalse<2>, internal::disjunction<MyFalse<0>, MyFalse<1>,
+                                                        MyFalse<2>>>::value,
+      "");
+}
+
+TEST(TypeTraits, IsInvocableRV) {
+  struct C {
+    int operator()() const { return 0; }
+    void operator()(int) & {}
+    std::string operator()(int) && { return ""; };
+  };
+
+  // The first overload is callable for const and non-const rvalues and lvalues.
+  // It can be used to obtain an int, void, or anything int is convertible too.
+  static_assert(internal::is_callable_r<int, C>::value, "");
+  static_assert(internal::is_callable_r<int, C&>::value, "");
+  static_assert(internal::is_callable_r<int, const C>::value, "");
+  static_assert(internal::is_callable_r<int, const C&>::value, "");
+
+  static_assert(internal::is_callable_r<void, C>::value, "");
+  static_assert(internal::is_callable_r<char, C>::value, "");
+
+  // It's possible to provide an int. If it's given to an lvalue, the result is
+  // void. Otherwise it is std::string (which is also treated as allowed for a
+  // void result type).
+  static_assert(internal::is_callable_r<void, C&, int>::value, "");
+  static_assert(!internal::is_callable_r<int, C&, int>::value, "");
+  static_assert(!internal::is_callable_r<std::string, C&, int>::value, "");
+  static_assert(!internal::is_callable_r<void, const C&, int>::value, "");
+
+  static_assert(internal::is_callable_r<std::string, C, int>::value, "");
+  static_assert(internal::is_callable_r<void, C, int>::value, "");
+  static_assert(!internal::is_callable_r<int, C, int>::value, "");
+
+  // It's not possible to provide other arguments.
+  static_assert(!internal::is_callable_r<void, C, std::string>::value, "");
+  static_assert(!internal::is_callable_r<void, C, int, int>::value, "");
+
+  // Nothing should choke when we try to call other arguments besides directly
+  // callable objects, but they should not show up as callable.
+  static_assert(!internal::is_callable_r<void, int>::value, "");
+  static_assert(!internal::is_callable_r<void, void (C::*)()>::value, "");
+  static_assert(!internal::is_callable_r<void, void (C::*)(), C*>::value, "");
+}
 
 // Tests that BuiltInDefaultValue<T*>::Get() returns NULL.
 TEST(BuiltInDefaultValueTest, IsNullForPointerTypes) {
@@ -1428,6 +1561,154 @@ TEST(MockMethodTest, CanTakeMoveOnlyValue) {
   EXPECT_EQ(42, *saved);
 }
 
+// It should be possible to use callables with an &&-qualified call operator
+// with WillOnce, since they will be called only once. This allows actions to
+// contain and manipulate move-only types.
+TEST(MockMethodTest, ActionHasRvalueRefQualifiedCallOperator) {
+  struct Return17 {
+    int operator()() && { return 17; }
+  };
+
+  // Action is directly compatible with mocked function type.
+  {
+    MockFunction<int()> mock;
+    EXPECT_CALL(mock, Call).WillOnce(Return17());
+
+    EXPECT_EQ(17, mock.AsStdFunction()());
+  }
+
+  // Action doesn't want mocked function arguments.
+  {
+    MockFunction<int(int)> mock;
+    EXPECT_CALL(mock, Call).WillOnce(Return17());
+
+    EXPECT_EQ(17, mock.AsStdFunction()(0));
+  }
+}
+
+// Edge case: if an action has both a const-qualified and an &&-qualified call
+// operator, there should be no "ambiguous call" errors. The &&-qualified
+// operator should be used by WillOnce (since it doesn't need to retain the
+// action beyond one call), and the const-qualified one by WillRepeatedly.
+TEST(MockMethodTest, ActionHasMultipleCallOperators) {
+  struct ReturnInt {
+    int operator()() && { return 17; }
+    int operator()() const& { return 19; }
+  };
+
+  // Directly compatible with mocked function type.
+  {
+    MockFunction<int()> mock;
+    EXPECT_CALL(mock, Call).WillOnce(ReturnInt()).WillRepeatedly(ReturnInt());
+
+    EXPECT_EQ(17, mock.AsStdFunction()());
+    EXPECT_EQ(19, mock.AsStdFunction()());
+    EXPECT_EQ(19, mock.AsStdFunction()());
+  }
+
+  // Ignores function arguments.
+  {
+    MockFunction<int(int)> mock;
+    EXPECT_CALL(mock, Call).WillOnce(ReturnInt()).WillRepeatedly(ReturnInt());
+
+    EXPECT_EQ(17, mock.AsStdFunction()(0));
+    EXPECT_EQ(19, mock.AsStdFunction()(0));
+    EXPECT_EQ(19, mock.AsStdFunction()(0));
+  }
+}
+
+// WillOnce should have no problem coping with a move-only action, whether it is
+// &&-qualified or not.
+TEST(MockMethodTest, MoveOnlyAction) {
+  // &&-qualified
+  {
+    struct Return17 {
+      Return17() = default;
+      Return17(Return17&&) = default;
+
+      Return17(const Return17&) = delete;
+      Return17 operator=(const Return17&) = delete;
+
+      int operator()() && { return 17; }
+    };
+
+    MockFunction<int()> mock;
+    EXPECT_CALL(mock, Call).WillOnce(Return17());
+    EXPECT_EQ(17, mock.AsStdFunction()());
+  }
+
+  // Not &&-qualified
+  {
+    struct Return17 {
+      Return17() = default;
+      Return17(Return17&&) = default;
+
+      Return17(const Return17&) = delete;
+      Return17 operator=(const Return17&) = delete;
+
+      int operator()() const { return 17; }
+    };
+
+    MockFunction<int()> mock;
+    EXPECT_CALL(mock, Call).WillOnce(Return17());
+    EXPECT_EQ(17, mock.AsStdFunction()());
+  }
+}
+
+// It should be possible to use an action that returns a value with a mock
+// function that doesn't, both through WillOnce and WillRepeatedly.
+TEST(MockMethodTest, ActionReturnsIgnoredValue) {
+  struct ReturnInt {
+    int operator()() const { return 0; }
+  };
+
+  MockFunction<void()> mock;
+  EXPECT_CALL(mock, Call).WillOnce(ReturnInt()).WillRepeatedly(ReturnInt());
+
+  mock.AsStdFunction()();
+  mock.AsStdFunction()();
+}
+
+// Despite the fanciness around move-only actions and so on, it should still be
+// possible to hand an lvalue reference to a copyable action to WillOnce.
+TEST(MockMethodTest, WillOnceCanAcceptLvalueReference) {
+  MockFunction<int()> mock;
+
+  const auto action = [] { return 17; };
+  EXPECT_CALL(mock, Call).WillOnce(action);
+
+  EXPECT_EQ(17, mock.AsStdFunction()());
+}
+
+// A callable that doesn't use SFINAE to restrict its call operator's overload
+// set, but is still picky about which arguments it will accept.
+struct StaticAssertSingleArgument {
+  template <typename... Args>
+  static constexpr bool CheckArgs() {
+    static_assert(sizeof...(Args) == 1, "");
+    return true;
+  }
+
+  template <typename... Args, bool = CheckArgs<Args...>()>
+  int operator()(Args...) const {
+    return 17;
+  }
+};
+
+// WillOnce and WillRepeatedly should both work fine with naïve implementations
+// of actions that don't use SFINAE to limit the overload set for their call
+// operator. If they are compatible with the actual mocked signature, we
+// shouldn't probe them with no arguments and trip a static_assert.
+TEST(MockMethodTest, ActionSwallowsAllArguments) {
+  MockFunction<int(int)> mock;
+  EXPECT_CALL(mock, Call)
+      .WillOnce(StaticAssertSingleArgument{})
+      .WillRepeatedly(StaticAssertSingleArgument{});
+
+  EXPECT_EQ(17, mock.AsStdFunction()(0));
+  EXPECT_EQ(17, mock.AsStdFunction()(0));
+}
+
 // Tests for std::function based action.
 
 int Add(int val, int& ref, int* ptr) {  // NOLINT
@@ -1552,7 +1833,8 @@ TEST(ActionMacro, LargeArity) {
                                    14, 15, 16, 17, 18, 19)));
 }
 
-}  // Unnamed namespace
+}  // namespace
+}  // namespace testing
 
 #ifdef _MSC_VER
 #if _MSC_VER == 1900