[libc] Add invoke / invoke_result type traits (#65750)

libc/src/__support/CPP/CMakeLists.txt

@@ -105,6 +105,8 @@ add_header_library(
     type_traits/enable_if.h
     type_traits/false_type.h
     type_traits/integral_constant.h
+    type_traits/invoke.h
+    type_traits/invoke_result.h
     type_traits/is_arithmetic.h
     type_traits/is_array.h
     type_traits/is_base_of.h

libc/src/__support/CPP/type_traits.h

@@ -18,6 +18,8 @@
 #include "src/__support/CPP/type_traits/enable_if.h"
 #include "src/__support/CPP/type_traits/false_type.h"
 #include "src/__support/CPP/type_traits/integral_constant.h"
+#include "src/__support/CPP/type_traits/invoke.h"
+#include "src/__support/CPP/type_traits/invoke_result.h"
 #include "src/__support/CPP/type_traits/is_arithmetic.h"
 #include "src/__support/CPP/type_traits/is_array.h"
 #include "src/__support/CPP/type_traits/is_base_of.h"

libc/src/__support/CPP/type_traits/invoke.h

@@ -0,0 +1,62 @@
+//===-- invoke type_traits --------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_H
+#define LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_H
+
+#include "src/__support/CPP/type_traits/always_false.h"
+#include "src/__support/CPP/type_traits/decay.h"
+#include "src/__support/CPP/type_traits/enable_if.h"
+#include "src/__support/CPP/type_traits/is_base_of.h"
+#include "src/__support/CPP/type_traits/is_pointer.h"
+#include "src/__support/CPP/type_traits/is_same.h"
+#include "src/__support/CPP/utility/forward.h"
+
+namespace __llvm_libc::cpp {
+
+namespace detail {
+
+// Catch all function and functor types.
+template <class FunctionPtrType> struct invoke_dispatcher {
+  template <class T, class... Args,
+            typename = cpp::enable_if_t<
+                cpp::is_same_v<cpp::decay_t<T>, FunctionPtrType>>>
+  static decltype(auto) call(T &&fun, Args &&...args) {
+    return cpp::forward<T>(fun)(cpp::forward<Args>(args)...);
+  }
+};
+
+// Catch pointer to member function types.
+template <class Class, class FunctionReturnType>
+struct invoke_dispatcher<FunctionReturnType Class::*> {
+  using FunctionPtrType = FunctionReturnType Class::*;
+
+  template <class T, class... Args, class DecayT = cpp::decay_t<T>>
+  static decltype(auto) call(FunctionPtrType fun, T &&t1, Args &&...args) {
+    if constexpr (cpp::is_base_of_v<Class, DecayT>) {
+      // T is a (possibly cv ref) type.
+      return (cpp::forward<T>(t1).*fun)(cpp::forward<Args>(args)...);
+    } else if constexpr (cpp::is_pointer_v<T>) {
+      // T is a pointer type.
+      return (*cpp::forward<T>(t1).*fun)(cpp::forward<Args>(args)...);
+    } else {
+      static_assert(cpp::always_false<T>);
+    }
+  }
+};
+
+} // namespace detail
+template <class Function, class... Args>
+decltype(auto) invoke(Function &&fun, Args &&...args) {
+  return detail::invoke_dispatcher<cpp::decay_t<Function>>::call(
+      cpp::forward<Function>(fun), cpp::forward<Args>(args)...);
+}
+
+} // namespace __llvm_libc::cpp
+
+#endif // LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_H

libc/src/__support/CPP/type_traits/invoke_result.h

@@ -0,0 +1,26 @@
+//===-- invoke_result type_traits -------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_RESULT_H
+#define LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_RESULT_H
+
+#include "src/__support/CPP/type_traits/invoke.h"
+#include "src/__support/CPP/type_traits/type_identity.h"
+#include "src/__support/CPP/utility/declval.h"
+
+namespace __llvm_libc::cpp {
+
+template <class F, class... Args>
+struct invoke_result : cpp::type_identity<decltype(cpp::invoke(
+                           cpp::declval<F>(), cpp::declval<Args>()...))> {};
+
+template <class F, class... Args>
+using invoke_result_t = typename invoke_result<F, Args...>::type;
+
+} // namespace __llvm_libc::cpp
+
+#endif // LLVM_LIBC_SRC_SUPPORT_CPP_TYPE_TRAITS_INVOKE_RESULT_H

libc/test/src/__support/CPP/type_traits_test.cpp

@@ -145,6 +145,119 @@ TEST(LlvmLibcTypeTraitsTest, integral_constant) {
   EXPECT_EQ((integral_constant<int, 4>::value), 4);
 }
 
+namespace invoke_detail {
+
+enum State { INIT = 0, A_APPLY_CALLED, B_APPLY_CALLED };
+
+struct A {
+  State state = INIT;
+  virtual ~A() {}
+  virtual void apply() { state = A_APPLY_CALLED; }
+};
+
+struct B : public A {
+  virtual ~B() {}
+  virtual void apply() { state = B_APPLY_CALLED; }
+};
+
+void free_function() {}
+int free_function_return_5() { return 5; }
+int free_function_passtrough(int value) { return value; }
+
+struct Delegate {
+  int (*ptr)(int) = &free_function_passtrough;
+};
+
+template <int tag> struct Tag {
+  static constexpr int value = tag;
+};
+
+struct Functor {
+  auto operator()() & { return Tag<0>(); }
+  auto operator()() const & { return Tag<1>(); }
+  auto operator()() && { return Tag<2>(); }
+  auto operator()() const && { return Tag<3>(); }
+
+  const Tag<0> &operator()(const Tag<0> &a) { return a; }
+  const Tag<0> &&operator()(const Tag<0> &&a) { return cpp::move(a); }
+  Tag<1> operator()(Tag<1> a) { return a; }
+};
+
+} // namespace invoke_detail
+
+TEST(LlvmLibcTypeTraitsTest, invoke) {
+  using namespace invoke_detail;
+  { // member function call
+    A a;
+    EXPECT_EQ(a.state, INIT);
+    invoke(&A::apply, a);
+    EXPECT_EQ(a.state, A_APPLY_CALLED);
+  }
+  { // overriden member function call
+    B b;
+    EXPECT_EQ(b.state, INIT);
+    invoke(&A::apply, b);
+    EXPECT_EQ(b.state, B_APPLY_CALLED);
+  }
+  { // free function
+    invoke(&free_function);
+    EXPECT_EQ(invoke(&free_function_return_5), 5);
+    EXPECT_EQ(invoke(&free_function_passtrough, 1), 1);
+  }
+  { // pointer member function call
+    Delegate d;
+    EXPECT_EQ(invoke(&Delegate::ptr, d, 2), 2);
+  }
+  { // Functor with several ref qualifier
+    Functor f;
+    const Functor cf;
+    EXPECT_EQ(invoke(f).value, 0);
+    EXPECT_EQ(invoke(cf).value, 1);
+    EXPECT_EQ(invoke(move(f)).value, 2);
+    EXPECT_EQ(invoke(move(cf)).value, 3);
+  }
+  { // lambda
+    EXPECT_EQ(invoke([]() -> int { return 2; }), 2);
+    EXPECT_EQ(invoke([](int value) -> int { return value; }, 1), 1);
+
+    const auto lambda = [](int) { return 0; };
+    EXPECT_EQ(invoke(lambda, 1), 0);
+  }
+}
+
+TEST(LlvmLibcTypeTraitsTest, invoke_result) {
+  using namespace invoke_detail;
+  EXPECT_TRUE((is_same_v<invoke_result_t<void (A::*)(), A>, void>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<void (A::*)(), B>, void>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<void (*)()>, void>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<int (*)()>, int>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<int (*)(int), int>, int>));
+  EXPECT_TRUE((
+      is_same_v<invoke_result_t<int (*Delegate::*)(int), Delegate, int>, int>));
+  // Functor with several ref qualifiers
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor &>, Tag<0>>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor const &>, Tag<1>>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor &&>, Tag<2>>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor const &&>, Tag<3>>));
+  // Functor with several arg qualifiers
+  EXPECT_TRUE(
+      (is_same_v<invoke_result_t<Functor &&, Tag<0> &>, const Tag<0> &>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor, Tag<0>>, const Tag<0> &&>));
+  EXPECT_TRUE((is_same_v<invoke_result_t<Functor, Tag<1>>, Tag<1>>));
+  {
+    auto lambda = []() {};
+    EXPECT_TRUE((is_same_v<invoke_result_t<decltype(lambda)>, void>));
+  }
+  {
+    auto lambda = []() { return 0; };
+    EXPECT_TRUE((is_same_v<invoke_result_t<decltype(lambda)>, int>));
+  }
+  {
+    auto lambda = [](int) -> double { return 0; };
+    EXPECT_TRUE((is_same_v<invoke_result_t<decltype(lambda), int>, double>));
+  }
+}
+
 using IntegralAndFloatingTypes =
     testing::TypeList<bool, char, short, int, long, long long, unsigned char,
                       unsigned short, unsigned int, unsigned long,

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -296,6 +296,8 @@ libc_support_library(
         "src/__support/CPP/type_traits/enable_if.h",
         "src/__support/CPP/type_traits/false_type.h",
         "src/__support/CPP/type_traits/integral_constant.h",
+        "src/__support/CPP/type_traits/invoke.h",
+        "src/__support/CPP/type_traits/invoke_result.h",
         "src/__support/CPP/type_traits/is_arithmetic.h",
         "src/__support/CPP/type_traits/is_array.h",
         "src/__support/CPP/type_traits/is_base_of.h",
@@ -334,6 +336,7 @@ libc_support_library(
         "src/__support/CPP/type_traits/type_identity.h",
         "src/__support/CPP/type_traits/void_t.h",
         "src/__support/CPP/utility/declval.h",
+        "src/__support/CPP/utility/forward.h",
     ],
     deps = [
         ":__support_macros_attributes",