feat(3p/absl): import StatusOr from tensorflow

Additionally, add tests for the macros. A future CL will enable the tests in CI.

Change-Id: Id4445a1aa65bf6751b87606f37654f3fc6d20efc
Tested-By: kanepyork <rikingcoding@gmail.com>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1274
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI

third_party/abseil_cpp/absl/status/statusor_internals.h

@@ -0,0 +1,250 @@
+/* Copyright 2017 The TensorFlow Authors. All Rights Reserved.
+
+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
+
+    http://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_STATUS_STATUSOR_INTERNALS_H_
+#define ABSL_STATUS_STATUSOR_INTERNALS_H_
+
+#include "absl/status/status.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace internal_statusor {
+
+class Helper {
+ public:
+  // Move type-agnostic error handling to the .cc.
+  static void HandleInvalidStatusCtorArg(Status*);
+  ABSL_ATTRIBUTE_NORETURN static void Crash(const Status& status);
+};
+
+// Construct an instance of T in `p` through placement new, passing Args... to
+// the constructor.
+// This abstraction is here mostly for the gcc performance fix.
+template <typename T, typename... Args>
+void PlacementNew(void* p, Args&&... args) {
+#if defined(__GNUC__) && !defined(__clang__)
+  // Teach gcc that 'p' cannot be null, fixing code size issues.
+  if (p == nullptr) __builtin_unreachable();
+#endif
+  new (p) T(std::forward<Args>(args)...);
+}
+
+// Helper base class to hold the data and all operations.
+// We move all this to a base class to allow mixing with the appropriate
+// TraitsBase specialization.
+template <typename T>
+class StatusOrData {
+  template <typename U>
+  friend class StatusOrData;
+
+ public:
+  StatusOrData() = delete;
+
+  StatusOrData(const StatusOrData& other) {
+    if (other.ok()) {
+      MakeValue(other.data_);
+      MakeStatus();
+    } else {
+      MakeStatus(other.status_);
+    }
+  }
+
+  StatusOrData(StatusOrData&& other) noexcept {
+    if (other.ok()) {
+      MakeValue(std::move(other.data_));
+      MakeStatus();
+    } else {
+      MakeStatus(other.status_);
+    }
+  }
+
+  template <typename U>
+  StatusOrData(const StatusOrData<U>& other) {
+    if (other.ok()) {
+      MakeValue(other.data_);
+      MakeStatus();
+    } else {
+      MakeStatus(other.status_);
+    }
+  }
+
+  template <typename U>
+  StatusOrData(StatusOrData<U>&& other) {
+    if (other.ok()) {
+      MakeValue(std::move(other.data_));
+      MakeStatus();
+    } else {
+      MakeStatus(other.status_);
+    }
+  }
+
+  explicit StatusOrData(const T& value) : data_(value) { MakeStatus(); }
+  explicit StatusOrData(T&& value) : data_(std::move(value)) { MakeStatus(); }
+
+  explicit StatusOrData(const Status& status) : status_(status) {
+    EnsureNotOk();
+  }
+  explicit StatusOrData(Status&& status) : status_(std::move(status)) {
+    EnsureNotOk();
+  }
+
+  StatusOrData& operator=(const StatusOrData& other) {
+    if (this == &other) return *this;
+    if (other.ok())
+      Assign(other.data_);
+    else
+      Assign(other.status_);
+    return *this;
+  }
+
+  StatusOrData& operator=(StatusOrData&& other) {
+    if (this == &other) return *this;
+    if (other.ok())
+      Assign(std::move(other.data_));
+    else
+      Assign(std::move(other.status_));
+    return *this;
+  }
+
+  ~StatusOrData() {
+    if (ok()) {
+      status_.~Status();
+      data_.~T();
+    } else {
+      status_.~Status();
+    }
+  }
+
+  void Assign(const T& value) {
+    if (ok()) {
+      data_.~T();
+      MakeValue(value);
+    } else {
+      MakeValue(value);
+      status_ = OkStatus();
+    }
+  }
+
+  void Assign(T&& value) {
+    if (ok()) {
+      data_.~T();
+      MakeValue(std::move(value));
+    } else {
+      MakeValue(std::move(value));
+      status_ = OkStatus();
+    }
+  }
+
+  void Assign(const Status& status) {
+    Clear();
+    status_ = status;
+    EnsureNotOk();
+  }
+
+  void Assign(Status&& status) {
+    Clear();
+    // Note that we copy instead of moving the status here so that
+    // status.~StatusOrData() can call ok() without invoking UB.
+    status_ = status;
+    EnsureNotOk();
+  }
+
+  bool ok() const { return status_.ok(); }
+
+ protected:
+  // status_ will always be active after the constructor.
+  // We make it a union to be able to initialize exactly how we need without
+  // waste.
+  // Eg. in the copy constructor we use the default constructor of Status in
+  // the ok() path to avoid an extra Ref call.
+  union {
+    Status status_;
+  };
+
+  // data_ is active iff status_.ok()==true
+  struct Dummy {};
+  union {
+    // When T is const, we need some non-const object we can cast to void* for
+    // the placement new. dummy_ is that object.
+    Dummy dummy_;
+    T data_;
+  };
+
+  void Clear() {
+    if (ok()) data_.~T();
+  }
+
+  void EnsureOk() const {
+    if (!ok()) Helper::Crash(status_);
+  }
+
+  void EnsureNotOk() {
+    if (ok()) Helper::HandleInvalidStatusCtorArg(&status_);
+  }
+
+  // Construct the value (ie. data_) through placement new with the passed
+  // argument.
+  template <typename Arg>
+  void MakeValue(Arg&& arg) {
+    internal_statusor::PlacementNew<T>(&dummy_, std::forward<Arg>(arg));
+  }
+
+  // Construct the status (ie. status_) through placement new with the passed
+  // argument.
+  template <typename... Args>
+  void MakeStatus(Args&&... args) {
+    internal_statusor::PlacementNew<Status>(&status_,
+                                            std::forward<Args>(args)...);
+  }
+};
+
+// Helper base class to allow implicitly deleted constructors and assignment
+// operations in StatusOr.
+// TraitsBase will explicitly delete what it can't support and StatusOr will
+// inherit that behavior implicitly.
+template <bool Copy, bool Move>
+struct TraitsBase {
+  TraitsBase() = default;
+  TraitsBase(const TraitsBase&) = default;
+  TraitsBase(TraitsBase&&) = default;
+  TraitsBase& operator=(const TraitsBase&) = default;
+  TraitsBase& operator=(TraitsBase&&) = default;
+};
+
+template <>
+struct TraitsBase<false, true> {
+  TraitsBase() = default;
+  TraitsBase(const TraitsBase&) = delete;
+  TraitsBase(TraitsBase&&) = default;
+  TraitsBase& operator=(const TraitsBase&) = delete;
+  TraitsBase& operator=(TraitsBase&&) = default;
+};
+
+template <>
+struct TraitsBase<false, false> {
+  TraitsBase() = default;
+  TraitsBase(const TraitsBase&) = delete;
+  TraitsBase(TraitsBase&&) = delete;
+  TraitsBase& operator=(const TraitsBase&) = delete;
+  TraitsBase& operator=(TraitsBase&&) = delete;
+};
+
+}  // namespace internal_statusor
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STATUS_STATUSOR_INTERNALS_H_