Export of internal Abseil changes

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f8fe0f483378c7520d8f8bdfabe4b20de4d96c7e by Andy Soffer <asoffer@google.com>:

Ensure that Invoke can support C++17 in the sense that noexcept is part of the type.

PiperOrigin-RevId: 261730155

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bf796ab71653a80498f9374bc8c5111d065c64ba by Abseil Team <absl-team@google.com>:

Fix typo in static_assert message for copy/move constructible by replacing "by" with "be".

PiperOrigin-RevId: 261713992

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8c7c17c40d03a322f304a2fd73ed34462dbf265a by Andy Soffer <asoffer@google.com>:

Add absl::is_function drop-in replacement for std::is_function. Some standard
libraries incorrectly implement std::is_function in a few corner cases. In
particular, libstdc++ functions marked noexcept.

The trick being used here is that function types decay to pointers. After
excluding cases like is_class, etc, we can distinguish function types by
testing for this decay.

Many thanks to ericwf@ for essentially writing this CL.

PiperOrigin-RevId: 261705008

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c5adf42d0a132c2525d17a719329eab2ffe0aa94 by Abseil Team <absl-team@google.com>:

Add microbenchmark for StrSplit that uses delimiter ByAnyChar.

PiperOrigin-RevId: 261424010

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66a342f9381ec56be2fe3aa5b3193dd3538a9740 by Andy Soffer <asoffer@google.com>:

CMake support for Abseil Random

This change touches almost build-related files for CMake almost exclusively. The one minor exception is random/internal/salted_seed_seq.h. The default warnings configuration for one of our CI builds requests not having named but unused parameters. The change in this file cleans up that warning.

PiperOrigin-RevId: 261192369
GitOrigin-RevId: f8fe0f483378c7520d8f8bdfabe4b20de4d96c7e
Change-Id: I05f662baacfe78750651535aa658f61c2327bc44

2 files changed, 33 insertions, 0 deletions

diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h
index c08e3754689b..927244e09dfb 100644
--- a/absl/meta/type_traits.h
+++ b/absl/meta/type_traits.h
@@ -224,6 +224,23 @@ struct disjunction<> : std::false_type {};
 template <typename T>
 struct negation : std::integral_constant<bool, !T::value> {};
 
+// is_function()
+//
+// Determines whether the passed type `T` is a function type.
+//
+// This metafunction is designed to be a drop-in replacement for the C++11
+// `std::is_function()` metafunction for platforms that have incomplete C++11
+// support (such as libstdc++ 4.x).
+//
+// This metafunction works because appending `const` to a type does nothing to
+// function types and reference types (and forms a const-qualified type
+// otherwise).
+template <typename T>
+struct is_function
+    : std::integral_constant<
+          bool, !(std::is_reference<T>::value ||
+                  std::is_const<typename std::add_const<T>::type>::value)> {};
+
 // is_trivially_destructible()
 //
 // Determines whether the passed type `T` is trivially destructable.
diff --git a/absl/meta/type_traits_test.cc b/absl/meta/type_traits_test.cc
index 82b1be51065e..a7a9c5c917ff 100644
--- a/absl/meta/type_traits_test.cc
+++ b/absl/meta/type_traits_test.cc
@@ -385,6 +385,22 @@ class Base {
 #define ABSL_GCC_BUG_TRIVIALLY_CONSTRUCTIBLE_ON_ARRAY_OF_NONTRIVIAL 1
 #endif
 
+TEST(TypeTraitsTest, TestIsFunction) {
+  struct Callable {
+    void operator()() {}
+  };
+  EXPECT_TRUE(absl::is_function<void()>::value);
+  EXPECT_TRUE(absl::is_function<void()&>::value);
+  EXPECT_TRUE(absl::is_function<void() const>::value);
+  EXPECT_TRUE(absl::is_function<void() noexcept>::value);
+  EXPECT_TRUE(absl::is_function<void(...) noexcept>::value);
+
+  EXPECT_FALSE(absl::is_function<void(*)()>::value);
+  EXPECT_FALSE(absl::is_function<void(&)()>::value);
+  EXPECT_FALSE(absl::is_function<int>::value);
+  EXPECT_FALSE(absl::is_function<Callable>::value);
+}
+
 TEST(TypeTraitsTest, TestTrivialDestructor) {
   // Verify that arithmetic types and pointers have trivial destructors.
   EXPECT_TRUE(absl::is_trivially_destructible<bool>::value);