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-//
-//  Copyright 2019 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.
-//
-// -----------------------------------------------------------------------------
-// File: flag.h
-// -----------------------------------------------------------------------------
-//
-// This header file defines the `absl::Flag<T>` type for holding command-line
-// flag data, and abstractions to create, get and set such flag data.
-//
-// It is important to note that this type is **unspecified** (an implementation
-// detail) and you do not construct or manipulate actual `absl::Flag<T>`
-// instances. Instead, you define and declare flags using the
-// `ABSL_FLAG()` and `ABSL_DECLARE_FLAG()` macros, and get and set flag values
-// using the `absl::GetFlag()` and `absl::SetFlag()` functions.
-
-#ifndef ABSL_FLAGS_FLAG_H_
-#define ABSL_FLAGS_FLAG_H_
-
-#include <string>
-#include <type_traits>
-
-#include "absl/base/attributes.h"
-#include "absl/base/config.h"
-#include "absl/base/optimization.h"
-#include "absl/flags/config.h"
-#include "absl/flags/internal/flag.h"
-#include "absl/flags/internal/registry.h"
-#include "absl/strings/string_view.h"
-
-namespace absl {
-ABSL_NAMESPACE_BEGIN
-
-// Flag
-//
-// An `absl::Flag` holds a command-line flag value, providing a runtime
-// parameter to a binary. Such flags should be defined in the global namespace
-// and (preferably) in the module containing the binary's `main()` function.
-//
-// You should not construct and cannot use the `absl::Flag` type directly;
-// instead, you should declare flags using the `ABSL_DECLARE_FLAG()` macro
-// within a header file, and define your flag using `ABSL_FLAG()` within your
-// header's associated `.cc` file. Such flags will be named `FLAGS_name`.
-//
-// Example:
-//
-//    .h file
-//
-//      // Declares usage of a flag named "FLAGS_count"
-//      ABSL_DECLARE_FLAG(int, count);
-//
-//    .cc file
-//
-//      // Defines a flag named "FLAGS_count" with a default `int` value of 0.
-//      ABSL_FLAG(int, count, 0, "Count of items to process");
-//
-// No public methods of `absl::Flag<T>` are part of the Abseil Flags API.
-#if !defined(_MSC_VER) || defined(__clang__)
-template <typename T>
-using Flag = flags_internal::Flag<T>;
-#else
-// MSVC debug builds do not implement initialization with constexpr constructors
-// correctly. To work around this we add a level of indirection, so that the
-// class `absl::Flag` contains an `internal::Flag*` (instead of being an alias
-// to that class) and dynamically allocates an instance when necessary. We also
-// forward all calls to internal::Flag methods via trampoline methods. In this
-// setup the `absl::Flag` class does not have constructor and virtual methods,
-// all the data members are public and thus MSVC is able to initialize it at
-// link time. To deal with multiple threads accessing the flag for the first
-// time concurrently we use an atomic boolean indicating if flag object is
-// initialized. We also employ the double-checked locking pattern where the
-// second level of protection is a global Mutex, so if two threads attempt to
-// construct the flag concurrently only one wins.
-// This solution is based on a recomendation here:
-// https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html?childToView=648454#comment-648454
-
-namespace flags_internal {
-absl::Mutex* GetGlobalConstructionGuard();
-}  // namespace flags_internal
-
-template <typename T>
-class Flag {
- public:
-  // No constructor and destructor to ensure this is an aggregate type.
-  // Visual Studio 2015 still requires the constructor for class to be
-  // constexpr initializable.
-#if _MSC_VER <= 1900
-  constexpr Flag(const char* name, const char* filename,
-                 const flags_internal::HelpGenFunc help_gen,
-                 const flags_internal::FlagDfltGenFunc default_value_gen)
-      : name_(name),
-        filename_(filename),
-        help_gen_(help_gen),
-        default_value_gen_(default_value_gen),
-        inited_(false),
-        impl_(nullptr) {}
-#endif
-
-  flags_internal::Flag<T>& GetImpl() const {
-    if (!inited_.load(std::memory_order_acquire)) {
-      absl::MutexLock l(flags_internal::GetGlobalConstructionGuard());
-
-      if (inited_.load(std::memory_order_acquire)) {
-        return *impl_;
-      }
-
-      impl_ = new flags_internal::Flag<T>(
-          name_, filename_,
-          {flags_internal::FlagHelpMsg(help_gen_),
-           flags_internal::FlagHelpKind::kGenFunc},
-          {flags_internal::FlagDefaultSrc(default_value_gen_),
-           flags_internal::FlagDefaultKind::kGenFunc});
-      inited_.store(true, std::memory_order_release);
-    }
-
-    return *impl_;
-  }
-
-  // Public methods of `absl::Flag<T>` are NOT part of the Abseil Flags API.
-  // See https://abseil.io/docs/cpp/guides/flags
-  bool IsRetired() const { return GetImpl().IsRetired(); }
-  absl::string_view Name() const { return GetImpl().Name(); }
-  std::string Help() const { return GetImpl().Help(); }
-  bool IsModified() const { return GetImpl().IsModified(); }
-  bool IsSpecifiedOnCommandLine() const {
-    return GetImpl().IsSpecifiedOnCommandLine();
-  }
-  std::string Filename() const { return GetImpl().Filename(); }
-  std::string DefaultValue() const { return GetImpl().DefaultValue(); }
-  std::string CurrentValue() const { return GetImpl().CurrentValue(); }
-  template <typename U>
-  inline bool IsOfType() const {
-    return GetImpl().template IsOfType<U>();
-  }
-  T Get() const {
-    return flags_internal::FlagImplPeer::InvokeGet<T>(GetImpl());
-  }
-  void Set(const T& v) {
-    flags_internal::FlagImplPeer::InvokeSet(GetImpl(), v);
-  }
-  void InvokeCallback() { GetImpl().InvokeCallback(); }
-
-  const CommandLineFlag& Reflect() const {
-    return flags_internal::FlagImplPeer::InvokeReflect(GetImpl());
-  }
-
-  // The data members are logically private, but they need to be public for
-  // this to be an aggregate type.
-  const char* name_;
-  const char* filename_;
-  const flags_internal::HelpGenFunc help_gen_;
-  const flags_internal::FlagDfltGenFunc default_value_gen_;
-
-  mutable std::atomic<bool> inited_;
-  mutable flags_internal::Flag<T>* impl_;
-};
-#endif
-
-// GetFlag()
-//
-// Returns the value (of type `T`) of an `absl::Flag<T>` instance, by value. Do
-// not construct an `absl::Flag<T>` directly and call `absl::GetFlag()`;
-// instead, refer to flag's constructed variable name (e.g. `FLAGS_name`).
-// Because this function returns by value and not by reference, it is
-// thread-safe, but note that the operation may be expensive; as a result, avoid
-// `absl::GetFlag()` within any tight loops.
-//
-// Example:
-//
-//   // FLAGS_count is a Flag of type `int`
-//   int my_count = absl::GetFlag(FLAGS_count);
-//
-//   // FLAGS_firstname is a Flag of type `std::string`
-//   std::string first_name = absl::GetFlag(FLAGS_firstname);
-template <typename T>
-ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
-  return flags_internal::FlagImplPeer::InvokeGet<T>(flag);
-}
-
-// SetFlag()
-//
-// Sets the value of an `absl::Flag` to the value `v`. Do not construct an
-// `absl::Flag<T>` directly and call `absl::SetFlag()`; instead, use the
-// flag's variable name (e.g. `FLAGS_name`). This function is
-// thread-safe, but is potentially expensive. Avoid setting flags in general,
-// but especially within performance-critical code.
-template <typename T>
-void SetFlag(absl::Flag<T>* flag, const T& v) {
-  flags_internal::FlagImplPeer::InvokeSet(*flag, v);
-}
-
-// Overload of `SetFlag()` to allow callers to pass in a value that is
-// convertible to `T`. E.g., use this overload to pass a "const char*" when `T`
-// is `std::string`.
-template <typename T, typename V>
-void SetFlag(absl::Flag<T>* flag, const V& v) {
-  T value(v);
-  flags_internal::FlagImplPeer::InvokeSet(*flag, value);
-}
-
-// GetFlagReflectionHandle()
-//
-// Returns the reflection handle corresponding to specified Abseil Flag
-// instance. Use this handle to access flag's reflection information, like name,
-// location, default value etc.
-//
-// Example:
-//
-//   std::string = absl::GetFlagReflectionHandle(FLAGS_count).DefaultValue();
-
-template <typename T>
-const CommandLineFlag& GetFlagReflectionHandle(const absl::Flag<T>& f) {
-  return flags_internal::FlagImplPeer::InvokeReflect(f);
-}
-
-ABSL_NAMESPACE_END
-}  // namespace absl
-
-
-// ABSL_FLAG()
-//
-// This macro defines an `absl::Flag<T>` instance of a specified type `T`:
-//
-//   ABSL_FLAG(T, name, default_value, help);
-//
-// where:
-//
-//   * `T` is a supported flag type (see the list of types in `marshalling.h`),
-//   * `name` designates the name of the flag (as a global variable
-//     `FLAGS_name`),
-//   * `default_value` is an expression holding the default value for this flag
-//     (which must be implicitly convertible to `T`),
-//   * `help` is the help text, which can also be an expression.
-//
-// This macro expands to a flag named 'FLAGS_name' of type 'T':
-//
-//   absl::Flag<T> FLAGS_name = ...;
-//
-// Note that all such instances are created as global variables.
-//
-// For `ABSL_FLAG()` values that you wish to expose to other translation units,
-// it is recommended to define those flags within the `.cc` file associated with
-// the header where the flag is declared.
-//
-// Note: do not construct objects of type `absl::Flag<T>` directly. Only use the
-// `ABSL_FLAG()` macro for such construction.
-#define ABSL_FLAG(Type, name, default_value, help) \
-  ABSL_FLAG_IMPL(Type, name, default_value, help)
-
-// ABSL_FLAG().OnUpdate()
-//
-// Defines a flag of type `T` with a callback attached:
-//
-//   ABSL_FLAG(T, name, default_value, help).OnUpdate(callback);
-//
-// After any setting of the flag value, the callback will be called at least
-// once. A rapid sequence of changes may be merged together into the same
-// callback. No concurrent calls to the callback will be made for the same
-// flag. Callbacks are allowed to read the current value of the flag but must
-// not mutate that flag.
-//
-// The update mechanism guarantees "eventual consistency"; if the callback
-// derives an auxiliary data structure from the flag value, it is guaranteed
-// that eventually the flag value and the derived data structure will be
-// consistent.
-//
-// Note: ABSL_FLAG.OnUpdate() does not have a public definition. Hence, this
-// comment serves as its API documentation.
-
-
-// -----------------------------------------------------------------------------
-// Implementation details below this section
-// -----------------------------------------------------------------------------
-
-// ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_NAMES
-#if !defined(_MSC_VER) || defined(__clang__)
-#define ABSL_FLAG_IMPL_FLAG_PTR(flag) flag
-#define ABSL_FLAG_IMPL_HELP_ARG(name)                      \
-  absl::flags_internal::HelpArg<AbslFlagHelpGenFor##name>( \
-      FLAGS_help_storage_##name)
-#define ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name) \
-  absl::flags_internal::DefaultArg<Type, AbslFlagDefaultGenFor##name>(0)
-#else
-#define ABSL_FLAG_IMPL_FLAG_PTR(flag) flag.GetImpl()
-#define ABSL_FLAG_IMPL_HELP_ARG(name) &AbslFlagHelpGenFor##name::NonConst
-#define ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name) &AbslFlagDefaultGenFor##name::Gen
-#endif
-
-#if ABSL_FLAGS_STRIP_NAMES
-#define ABSL_FLAG_IMPL_FLAGNAME(txt) ""
-#define ABSL_FLAG_IMPL_FILENAME() ""
-#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, false>(ABSL_FLAG_IMPL_FLAG_PTR(flag))
-#else
-#define ABSL_FLAG_IMPL_FLAGNAME(txt) txt
-#define ABSL_FLAG_IMPL_FILENAME() __FILE__
-#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, true>(ABSL_FLAG_IMPL_FLAG_PTR(flag))
-#endif
-
-// ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_HELP
-
-#if ABSL_FLAGS_STRIP_HELP
-#define ABSL_FLAG_IMPL_FLAGHELP(txt) absl::flags_internal::kStrippedFlagHelp
-#else
-#define ABSL_FLAG_IMPL_FLAGHELP(txt) txt
-#endif
-
-// AbslFlagHelpGenFor##name is used to encapsulate both immediate (method Const)
-// and lazy (method NonConst) evaluation of help message expression. We choose
-// between the two via the call to HelpArg in absl::Flag instantiation below.
-// If help message expression is constexpr evaluable compiler will optimize
-// away this whole struct.
-// TODO(rogeeff): place these generated structs into local namespace and apply
-// ABSL_INTERNAL_UNIQUE_SHORT_NAME.
-// TODO(rogeeff): Apply __attribute__((nodebug)) to FLAGS_help_storage_##name
-#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt)                       \
-  struct AbslFlagHelpGenFor##name {                                          \
-    /* The expression is run in the caller as part of the   */               \
-    /* default value argument. That keeps temporaries alive */               \
-    /* long enough for NonConst to work correctly.          */               \
-    static constexpr absl::string_view Value(                                \
-        absl::string_view v = ABSL_FLAG_IMPL_FLAGHELP(txt)) {                \
-      return v;                                                              \
-    }                                                                        \
-    static std::string NonConst() { return std::string(Value()); }           \
-  };                                                                         \
-  constexpr auto FLAGS_help_storage_##name ABSL_INTERNAL_UNIQUE_SMALL_NAME() \
-      ABSL_ATTRIBUTE_SECTION_VARIABLE(flags_help_cold) =                     \
-          absl::flags_internal::HelpStringAsArray<AbslFlagHelpGenFor##name>( \
-              0);
-
-#define ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value)     \
-  struct AbslFlagDefaultGenFor##name {                                        \
-    Type value = absl::flags_internal::InitDefaultValue<Type>(default_value); \
-    static void Gen(void* p) {                                                \
-      new (p) Type(AbslFlagDefaultGenFor##name{}.value);                      \
-    }                                                                         \
-  };
-
-// ABSL_FLAG_IMPL
-//
-// Note: Name of registrar object is not arbitrary. It is used to "grab"
-// global name for FLAGS_no<flag_name> symbol, thus preventing the possibility
-// of defining two flags with names foo and nofoo.
-#define ABSL_FLAG_IMPL(Type, name, default_value, help)                       \
-  namespace absl /* block flags in namespaces */ {}                           \
-  ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value)           \
-  ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, help)                             \
-  ABSL_CONST_INIT absl::Flag<Type> FLAGS_##name{                              \
-      ABSL_FLAG_IMPL_FLAGNAME(#name), ABSL_FLAG_IMPL_FILENAME(),              \
-      ABSL_FLAG_IMPL_HELP_ARG(name), ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name)}; \
-  extern absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;             \
-  absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name =                   \
-      ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name)
-
-// ABSL_RETIRED_FLAG
-//
-// Designates the flag (which is usually pre-existing) as "retired." A retired
-// flag is a flag that is now unused by the program, but may still be passed on
-// the command line, usually by production scripts. A retired flag is ignored
-// and code can't access it at runtime.
-//
-// This macro registers a retired flag with given name and type, with a name
-// identical to the name of the original flag you are retiring. The retired
-// flag's type can change over time, so that you can retire code to support a
-// custom flag type.
-//
-// This macro has the same signature as `ABSL_FLAG`. To retire a flag, simply
-// replace an `ABSL_FLAG` definition with `ABSL_RETIRED_FLAG`, leaving the
-// arguments unchanged (unless of course you actually want to retire the flag
-// type at this time as well).
-//
-// `default_value` is only used as a double check on the type. `explanation` is
-// unused.
-// TODO(rogeeff): replace RETIRED_FLAGS with FLAGS once forward declarations of
-// retired flags are cleaned up.
-#define ABSL_RETIRED_FLAG(type, name, default_value, explanation)      \
-  static absl::flags_internal::RetiredFlag<type> RETIRED_FLAGS_##name; \
-  ABSL_ATTRIBUTE_UNUSED static const auto RETIRED_FLAGS_REG_##name =   \
-      (RETIRED_FLAGS_##name.Retire(#name),                             \
-       ::absl::flags_internal::FlagRegistrarEmpty{})
-
-#endif  // ABSL_FLAGS_FLAG_H_