Creation of LTS branch "lts_2020_02_25"20200225

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  - ecc0033b54847f6c9ee37dbb0be8aa17e5b6d37b Always enable proper symbolize implementation on Windows ... by Loo Rong Jie <loorongjie@gmail.com>
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  - e9f9000c7c80993cb589d011616b7a8016e42f4a Fix ABSL_WAITER_MODE detection for mingw (#342) by Joe Sylve <Joe.Sylve@gmail.com>
  - abea769b551f7a100f540967cb95debdb0080df8 Fix ABSL_HAVE_ALARM check on mingw (#341) by Joe Sylve <Joe.Sylve@gmail.com>
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  - 0302d1e5fa4fcdd1763b7d1bb3212943b1ae911d supppress unused variable warning for gcc (#372) by Martin <pizzard@users.noreply.github.com>
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  - 36910d3d7e9fccadd6603f232d0c4f54dcd47c7e [bazel] Add fixes for --incompatible_load_cc_rules_from_b... by Yannic <contact@yannic-bonenberger.com>
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GitOrigin-RevId: 0033c9ea91a52ade7c6b725aa2ef3cbe15463421
Change-Id: I8a2b70063cb3ab40c6943a6db0fe40cae71ed8d7

1 files changed, 145 insertions, 25 deletions

diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index 28925927..cff02c1f 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -29,16 +29,21 @@
 #ifndef ABSL_FLAGS_FLAG_H_
 #define ABSL_FLAGS_FLAG_H_
 
+#include <string>
+#include <type_traits>
+
 #include "absl/base/attributes.h"
 #include "absl/base/casts.h"
+#include "absl/base/config.h"
 #include "absl/flags/config.h"
 #include "absl/flags/declare.h"
 #include "absl/flags/internal/commandlineflag.h"
 #include "absl/flags/internal/flag.h"
+#include "absl/flags/internal/registry.h"
 #include "absl/flags/marshalling.h"
 
 namespace absl {
-inline namespace lts_2019_08_08 {
+ABSL_NAMESPACE_BEGIN
 
 // Flag
 //
@@ -64,8 +69,103 @@ inline namespace lts_2019_08_08 {
 //      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},
+                                      default_value_gen_);
+      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(); }
+  bool IsAbseilFlag() const { return GetImpl()->IsAbseilFlag(); }
+  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();
+  }
+  absl::string_view Typename() const { return GetImpl()->Typename(); }
+  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 GetImpl()->Get(); }
+  bool AtomicGet(T* v) const { return GetImpl()->AtomicGet(v); }
+  void Set(const T& v) { GetImpl()->Set(v); }
+  void SetCallback(const flags_internal::FlagCallbackFunc mutation_callback) {
+    GetImpl()->SetCallback(mutation_callback);
+  }
+  void InvokeCallback() { GetImpl()->InvokeCallback(); }
+
+  // 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()
 //
@@ -84,23 +184,10 @@ using Flag = flags_internal::Flag<T>;
 //   // FLAGS_firstname is a Flag of type `std::string`
 //   std::string first_name = absl::GetFlag(FLAGS_firstname);
 template <typename T>
-T GetFlag(const absl::Flag<T>& flag) {
-#define ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE(BIT) \
-  static_assert(                                    \
-      !std::is_same<T, BIT>::value,                 \
-      "Do not specify explicit template parameters to absl::GetFlag");
-  ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE)
-#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE
-
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
   return flag.Get();
 }
 
-// Overload for `GetFlag()` for types that support lock-free reads.
-#define ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT(T) \
-  extern T GetFlag(const absl::Flag<T>& flag);
-ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT)
-#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT
-
 // SetFlag()
 //
 // Sets the value of an `absl::Flag` to the value `v`. Do not construct an
@@ -122,7 +209,7 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
   flag->Set(value);
 }
 
-}  // inline namespace lts_2019_08_08
+ABSL_NAMESPACE_END
 }  // namespace absl
 
 
@@ -186,13 +273,23 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
 #if ABSL_FLAGS_STRIP_NAMES
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) ""
 #define ABSL_FLAG_IMPL_FILENAME() ""
+#if !defined(_MSC_VER) || defined(__clang__)
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
   absl::flags_internal::FlagRegistrar<T, false>(&flag)
 #else
+#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
+  absl::flags_internal::FlagRegistrar<T, false>(flag.GetImpl())
+#endif
+#else
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) txt
 #define ABSL_FLAG_IMPL_FILENAME() __FILE__
+#if !defined(_MSC_VER) || defined(__clang__)
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
   absl::flags_internal::FlagRegistrar<T, true>(&flag)
+#else
+#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
+  absl::flags_internal::FlagRegistrar<T, true>(flag.GetImpl())
+#endif
 #endif
 
 // ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_HELP
@@ -203,9 +300,19 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
 #define ABSL_FLAG_IMPL_FLAGHELP(txt) txt
 #endif
 
-#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt) \
-  static std::string AbslFlagsWrapHelp##name() {       \
-    return ABSL_FLAG_IMPL_FLAGHELP(txt);               \
+// 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.
+#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt)                     \
+  struct AbslFlagHelpGenFor##name {                                        \
+    template <typename T = void>                                           \
+    static constexpr const char* Const() {                                 \
+      return absl::flags_internal::HelpConstexprWrap(                      \
+          ABSL_FLAG_IMPL_FLAGHELP(txt));                                   \
+    }                                                                      \
+    static std::string NonConst() { return ABSL_FLAG_IMPL_FLAGHELP(txt); } \
   }
 
 #define ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value)   \
@@ -218,17 +325,30 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
 // 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.
+#if !defined(_MSC_VER) || defined(__clang__)
 #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), &AbslFlagsWrapHelp##name,     \
-      ABSL_FLAG_IMPL_FILENAME(),                                    \
-      &absl::flags_internal::FlagMarshallingOps<Type>,              \
-      &AbslFlagsInitFlag##name);                                    \
+  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::flags_internal::HelpArg<AbslFlagHelpGenFor##name>(0),   \
+      &AbslFlagsInitFlag##name};                                    \
   extern bool FLAGS_no##name;                                       \
   bool FLAGS_no##name = ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name)
+#else
+// MSVC version uses aggregate initialization. We also do not try to
+// optimize away help wrapper.
+#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(),      \
+      &AbslFlagHelpGenFor##name::NonConst, &AbslFlagsInitFlag##name}; \
+  extern bool FLAGS_no##name;                                         \
+  bool FLAGS_no##name = ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name)
+#endif
 
 // ABSL_RETIRED_FLAG
 //