Export of internal Abseil changes

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20b3acaff75d05315f272747956b01405adccafb by Greg Falcon <gfalcon@google.com>:

Re-import of CCTZ from GitHub, with new ABSL_NAMESPACE_ transform applied.

PiperOrigin-RevId: 285564474

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4d9e3fcabcea33c8b0b69f094ad2eddc0fa19557 by Derek Mauro <dmauro@google.com>:

Moves the disabling of a warning to before the function begins.

MSVC apparently requires this for warnings in the range 4700-4999.
https://docs.microsoft.com/en-us/cpp/preprocessor/warning?redirectedfrom=MSDN&view=vs-2019

PiperOrigin-RevId: 285516232

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4a060cbeda76e89693c50276ae5b62cbf0fff39a by Derek Mauro <dmauro@google.com>:

MSVC: Fixes uniform_real_distribution_test in opt mode

Disables a constant arithmetic overflow warning in a test that tests
the behavior on overflow. This should be tested because a user might
have this warning disabled.

PiperOrigin-RevId: 285452242

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548ab2f4cbe59bd6f6bf493af4f9ea765c4fa949 by Andy Soffer <asoffer@google.com>:

Release absl::bind_front, a C++11-compliant work-alike type for the C++20
std::bind_front.

PiperOrigin-RevId: 285247872
GitOrigin-RevId: 20b3acaff75d05315f272747956b01405adccafb
Change-Id: I00fe45939246cba9bfc7be375d67787d2eb57cd3

1 files changed, 152 insertions, 0 deletions

diff --git a/absl/functional/bind_front.h b/absl/functional/bind_front.h
new file mode 100644
index 000000000000..4c61d0ecfd12
--- /dev/null
+++ b/absl/functional/bind_front.h
@@ -0,0 +1,152 @@
+// Copyright 2018 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.
+
+// `absl::bind_front()` returns a functor by binding a number of arguments to
+// the front of a provided functor, allowing you to avoid known problems with
+// `std::bind()`.  It is a form of partial function application
+// https://en.wikipedia.org/wiki/Partial_application.
+//
+// Like `std::bind()` it is implicitly convertible to `std::function`.  In
+// particular, it may be used as a simpler replacement for `std::bind()` in most
+// cases, as it does not require  placeholders to be specified.  More
+// importantly, it provides more reliable correctness guarantees than
+// `std::bind()`.
+//
+// absl::bind_front(a...) can be seen as storing the results of
+// std::make_tuple(a...).
+//
+// Example: Binding a free function.
+//
+//   int Minus(int a, int b) { return a - b; }
+//
+//   assert(absl::bind_front(Minus)(3, 2) == 3 - 2);
+//   assert(absl::bind_front(Minus, 3)(2) == 3 - 2);
+//   assert(absl::bind_front(Minus, 3, 2)() == 3 - 2);
+//
+// Example: Binding a member function.
+//
+//   struct Math {
+//     int Double(int a) const { return 2 * a; }
+//   };
+//
+//   Math math;
+//
+//   assert(absl::bind_front(&Math::Double)(&math, 3) == 2 * 3);
+//   // Stores a pointer to math inside the functor.
+//   assert(absl::bind_front(&Math::Double, &math)(3) == 2 * 3);
+//   // Stores a copy of math inside the functor.
+//   assert(absl::bind_front(&Math::Double, math)(3) == 2 * 3);
+//   // Stores std::unique_ptr<Math> inside the functor.
+//   assert(absl::bind_front(&Math::Double,
+//                           std::unique_ptr<Math>(new Math))(3) == 2 * 3);
+//
+// Example: Using `absl::bind_front()`, instead of `std::bind()`, with
+//          `std::function`.
+//
+//   class FileReader {
+//    public:
+//     void ReadFileAsync(const std::string& filename, std::string* content,
+//                        const std::function<void()>& done) {
+//       // Calls Executor::Schedule(std::function<void()>).
+//       Executor::DefaultExecutor()->Schedule(
+//           absl::bind_front(&FileReader::BlockingRead, this,
+//                            filename, content, done));
+//     }
+//
+//    private:
+//     void BlockingRead(const std::string& filename, std::string* content,
+//                       const std::function<void()>& done) {
+//       CHECK_OK(file::GetContents(filename, content, {}));
+//       done();
+//     }
+//   };
+//
+// `absl::bind_front()` stores bound arguments explicitly using the type passed
+// rather than implicitly based on the type accepted by its functor.
+//
+// Example: Binding arguments explicitly.
+//
+//   void LogStringView(absl::string_view sv) {
+//     LOG(INFO) << sv;
+//   }
+//
+//   Executor* e = Executor::DefaultExecutor();
+//   std::string s = "hello";
+//   absl::string_view sv = s;
+//
+//   // absl::bind_front(LogStringView, arg) makes a copy of arg and stores it.
+//   e->Schedule(absl::bind_front(LogStringView, sv)); // ERROR: dangling
+//                                                     // string_view.
+//
+//   e->Schedule(absl::bind_front(LogStringView, s));  // OK: stores a copy of
+//                                                     // s.
+//
+// To store some of the arguments passed to `absl::bind_front()` by reference,
+//  use std::ref()` and `std::cref()`.
+//
+// Example: Storing some of the bound arguments by reference.
+//
+//   class Service {
+//    public:
+//     void Serve(const Request& req, std::function<void()>* done) {
+//       // The request protocol buffer won't be deleted until done is called.
+//       // It's safe to store a reference to it inside the functor.
+//       Executor::DefaultExecutor()->Schedule(
+//           absl::bind_front(&Service::BlockingServe, this, std::cref(req),
+//           done));
+//     }
+//
+//    private:
+//     void BlockingServe(const Request& req, std::function<void()>* done);
+//   };
+//
+// Example: Storing bound arguments by reference.
+//
+//   void Print(const string& a, const string& b) { LOG(INFO) << a << b; }
+//
+//   std::string hi = "Hello, ";
+//   std::vector<std::string> names = {"Chuk", "Gek"};
+//   // Doesn't copy hi.
+//   for_each(names.begin(), names.end(),
+//            absl::bind_front(Print, std::ref(hi)));
+//
+//   // DO NOT DO THIS: the functor may outlive "hi", resulting in
+//   // dangling references.
+//   foo->DoInFuture(absl::bind_front(Print, std::ref(hi), "Guest"));  // BAD!
+//   auto f = absl::bind_front(Print, std::ref(hi), "Guest"); // BAD!
+
+#ifndef ABSL_FUNCTIONAL_BIND_FRONT_H_
+#define ABSL_FUNCTIONAL_BIND_FRONT_H_
+
+#include "absl/functional/internal/front_binder.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// Binds the first N arguments of an invocable object and stores them by value,
+// except types of std::reference_wrapper which are 'unwound' and stored by
+// reference.
+template <class F, class... BoundArgs>
+constexpr functional_internal::bind_front_t<F, BoundArgs...> bind_front(
+    F&& func, BoundArgs&&... args) {
+  return functional_internal::bind_front_t<F, BoundArgs...>(
+      absl::in_place, absl::forward<F>(func),
+      absl::forward<BoundArgs>(args)...);
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_FUNCTIONAL_BIND_FRONT_H_