Export of internal Abseil changes

--
d447fdcb801036cf08197eece193a5a706661120 by Gennadiy Rozental <rogeeff@google.com>:

Eliminate the need for static function holding help message. This decreases the cost of ABSL_FLAG abstraction by 120 bytes under clang.

PiperOrigin-RevId: 281107806

--
0aa6b91189f0e8b2381438c33465673a7ae02487 by Derek Mauro <dmauro@google.com>:

Disable the weak symbol CCTZ extension in the time test_util
on MinGW, which does not support it.

PiperOrigin-RevId: 280719769

--
67322c41c3e776eb541de90fa4526bdb49422eb6 by Abseil Team <absl-team@google.com>:

Tune PeriodicSampler implementation (for internal-use only)

PiperOrigin-RevId: 280708943

--
3a48c346340c7ed03816645cd327e1ff07729aa4 by Abseil Team <absl-team@google.com>:

Clean up public headers not to have warnings for "-Wcomma"

PiperOrigin-RevId: 280695373

--
981acd1ef3b13a83a84f04f11c8931f4ed4451c9 by Matthew Brown <matthewbr@google.com>:

Release absl::int128.

PiperOrigin-RevId: 280690817

--
d30fae9d2ec30b81322d2eb5afe7e13e45b4b422 by Derek Mauro <dmauro@google.com>:

Fix -Wundef warnings in random platform detection

PiperOrigin-RevId: 280669598
GitOrigin-RevId: d447fdcb801036cf08197eece193a5a706661120
Change-Id: Ie5e10e567c54b7de211833607689f233d4ddf734

5 files changed, 92 insertions, 62 deletions

diff --git a/absl/flags/internal/commandlineflag.cc b/absl/flags/internal/commandlineflag.cc
index caf33bc4..88f91e16 100644
--- a/absl/flags/internal/commandlineflag.cc
+++ b/absl/flags/internal/commandlineflag.cc
@@ -56,12 +56,5 @@ std::string CommandLineFlag::Filename() const {
   return flags_internal::GetUsageConfig().normalize_filename(filename_);
 }
 
-std::string HelpText::GetHelpText() const {
-  if (help_function_) return help_function_();
-  if (help_message_) return help_message_;
-
-  return {};
-}
-
 }  // namespace flags_internal
 }  // namespace absl
diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h
index 13a3352e..7964f1bf 100644
--- a/absl/flags/internal/commandlineflag.h
+++ b/absl/flags/internal/commandlineflag.h
@@ -60,14 +60,6 @@ enum ValueSource {
   kProgrammaticChange,
 };
 
-// Signature for the help generation function used as an argument for the
-// absl::Flag constructor.
-using HelpGenFunc = std::string (*)();
-
-// Signature for the function generating the initial flag value based (usually
-// based on default value supplied in flag's definition)
-using InitialValGenFunc = void* (*)();
-
 extern const char kStrippedFlagHelp[];
 
 // The per-type function
@@ -149,34 +141,6 @@ inline size_t Sizeof(FlagOpFn op) {
       op(flags_internal::kSizeof, nullptr, nullptr)));
 }
 
-// Holds either a pointer to help text or a function which produces it.  This is
-// needed for supporting both static initialization of Flags while supporting
-// the legacy registration framework.  We can't use absl::variant<const char*,
-// const char*(*)()> since anybody passing 0 or nullptr in to a CommandLineFlag
-// would find an ambiguity.
-class HelpText {
- public:
-  static constexpr HelpText FromFunctionPointer(const HelpGenFunc fn) {
-    return HelpText(fn, nullptr);
-  }
-  static constexpr HelpText FromStaticCString(const char* msg) {
-    return HelpText(nullptr, msg);
-  }
-
-  std::string GetHelpText() const;
-
-  HelpText() = delete;
-  HelpText(const HelpText&) = default;
-  HelpText(HelpText&&) = default;
-
- private:
-  explicit constexpr HelpText(const HelpGenFunc fn, const char* msg)
-      : help_function_(fn), help_message_(msg) {}
-
-  HelpGenFunc help_function_;
-  const char* help_message_;
-};
-
 // Handle to FlagState objects. Specific flag state objects will restore state
 // of a flag produced this flag state from method CommandLineFlag::SaveState().
 class FlagStateInterface {
@@ -190,9 +154,8 @@ class FlagStateInterface {
 // Holds all information for a flag.
 class CommandLineFlag {
  public:
-  constexpr CommandLineFlag(const char* name, HelpText help_text,
-                            const char* filename)
-      : name_(name), help_(help_text), filename_(filename) {}
+  constexpr CommandLineFlag(const char* name, const char* filename)
+      : name_(name), filename_(filename) {}
 
   // Virtual destructor
   virtual void Destroy() const = 0;
@@ -203,7 +166,6 @@ class CommandLineFlag {
 
   // Non-polymorphic access methods.
   absl::string_view Name() const { return name_; }
-  std::string Help() const { return help_.GetHelpText(); }
   absl::string_view Typename() const;
   std::string Filename() const;
 
@@ -250,6 +212,8 @@ class CommandLineFlag {
 
   // Polymorphic access methods
 
+  // Returns help message associated with this flag
+  virtual std::string Help() const = 0;
   // Returns true iff this object corresponds to retired flag
   virtual bool IsRetired() const { return false; }
   // Returns true iff this is a handle to an Abseil Flag.
@@ -285,12 +249,11 @@ class CommandLineFlag {
   // flag's value type.
   virtual void CheckDefaultValueParsingRoundtrip() const = 0;
 
-  // Constant configuration for a particular flag.
  protected:
   ~CommandLineFlag() = default;
 
+  // Constant configuration for a particular flag.
   const char* const name_;      // Flags name passed to ABSL_FLAG as second arg.
-  const HelpText help_;         // The function generating help message.
   const char* const filename_;  // The file name where ABSL_FLAG resides.
 
  private:
diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc
index 061113d7..d087f79e 100644
--- a/absl/flags/internal/flag.cc
+++ b/absl/flags/internal/flag.cc
@@ -85,6 +85,11 @@ void FlagImpl::Destroy() const {
   delete locks_;
 }
 
+std::string FlagImpl::Help() const {
+  return help_source_kind_ == FlagHelpSrcKind::kLiteral ? help_.literal
+                                                        : help_.gen_func();
+}
+
 bool FlagImpl::IsModified() const {
   absl::MutexLock l(DataGuard());
   return modified_;
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index ce0ccf2d..d7990254 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -61,6 +61,68 @@ class FlagState : public flags_internal::FlagStateInterface {
   int64_t counter_;
 };
 
+// This is help argument for absl::Flag encapsulating the string literal pointer
+// or pointer to function generating it as well as enum descriminating two
+// cases.
+using HelpGenFunc = std::string (*)();
+
+union FlagHelpSrc {
+  constexpr explicit FlagHelpSrc(const char* help_msg) : literal(help_msg) {}
+  constexpr explicit FlagHelpSrc(HelpGenFunc help_gen) : gen_func(help_gen) {}
+
+  const char* literal;
+  HelpGenFunc gen_func;
+};
+
+enum class FlagHelpSrcKind : int8_t { kLiteral, kGenFunc };
+
+struct HelpInitArg {
+  FlagHelpSrc source;
+  FlagHelpSrcKind kind;
+};
+
+// HelpConstexprWrap is used by struct AbslFlagHelpGenFor##name generated by
+// ABSL_FLAG macro. It is only used to silence the compiler in the case where
+// help message expression is not constexpr and does not have type const char*.
+// If help message expression is indeed constexpr const char* HelpConstexprWrap
+// is just a trivial identity function.
+template <typename T>
+const char* HelpConstexprWrap(const T&) {
+  return nullptr;
+}
+constexpr const char* HelpConstexprWrap(const char* p) { return p; }
+constexpr const char* HelpConstexprWrap(char* p) { return p; }
+
+// These two HelpArg overloads allows us to select at compile time one of two
+// way to pass Help argument to absl::Flag. We'll be passing
+// AbslFlagHelpGenFor##name as T and integer 0 as a single argument to prefer
+// first overload if possible. If T::Const is evaluatable on constexpr
+// context (see non template int parameter below) we'll choose first overload.
+// In this case the help message expression is immediately evaluated and is used
+// to construct the absl::Flag. No additionl code is generated by ABSL_FLAG.
+// Otherwise SFINAE kicks in and first overload is dropped from the
+// consideration, in which case the second overload will be used. The second
+// overload does not attempt to evaluate the help message expression
+// immediately and instead delays the evaluation by returing the function
+// pointer (&T::NonConst) genering the help message when necessary. This is
+// evaluatable in constexpr context, but the cost is an extra function being
+// generated in the ABSL_FLAG code.
+template <typename T, int = (T::Const(), 1)>
+constexpr flags_internal::HelpInitArg HelpArg(int) {
+  return {flags_internal::FlagHelpSrc(T::Const()),
+          flags_internal::FlagHelpSrcKind::kLiteral};
+}
+
+template <typename T>
+constexpr flags_internal::HelpInitArg HelpArg(char) {
+  return {flags_internal::FlagHelpSrc(&T::NonConst),
+          flags_internal::FlagHelpSrcKind::kGenFunc};
+}
+
+// Signature for the function generating the initial flag value based (usually
+// based on default value supplied in flag's definition)
+using InitialValGenFunc = void* (*)();
+
 // Signature for the mutation callback used by watched Flags
 // The callback is noexcept.
 // TODO(rogeeff): add noexcept after C++17 support is added.
@@ -74,15 +136,19 @@ class FlagImpl {
  public:
   constexpr FlagImpl(const flags_internal::FlagOpFn op,
                      const flags_internal::FlagMarshallingOpFn marshalling_op,
-                     const flags_internal::InitialValGenFunc initial_value_gen)
+                     const flags_internal::InitialValGenFunc initial_value_gen,
+                     const HelpInitArg help)
       : op_(op),
         marshalling_op_(marshalling_op),
-        initial_value_gen_(initial_value_gen) {}
+        initial_value_gen_(initial_value_gen),
+        help_(help.source),
+        help_source_kind_(help.kind) {}
 
   // Forces destruction of the Flag's data.
   void Destroy() const;
 
   // Constant access methods
+  std::string Help() const;
   bool IsModified() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu);
   bool IsSpecifiedOnCommandLine() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu);
   std::string DefaultValue() const ABSL_LOCKS_EXCLUDED(locks_->primary_mu);
@@ -149,9 +215,12 @@ class FlagImpl {
   absl::Mutex* DataGuard() const ABSL_LOCK_RETURNED(locks_->primary_mu);
 
   // Immutable Flag's data.
-  const FlagOpFn op_;                          // Type-specific handler
-  const FlagMarshallingOpFn marshalling_op_;   // Marshalling ops handler
-  const InitialValGenFunc initial_value_gen_;  // Makes flag's initial value
+  const FlagOpFn op_;                          // Type-specific handler.
+  const FlagMarshallingOpFn marshalling_op_;   // Marshalling ops handler.
+  const InitialValGenFunc initial_value_gen_;  // Makes flag's initial value.
+  const FlagHelpSrc help_;  // Help message literal or function to generate it.
+  // Indicates if help message was supplied as literal or generator func.
+  const FlagHelpSrcKind help_source_kind_;
 
   // Mutable Flag's data. (guarded by locks_->primary_mu).
   // Indicates that locks_, cur_ and def_ fields have been lazily initialized.
@@ -191,14 +260,13 @@ class FlagImpl {
 template <typename T>
 class Flag final : public flags_internal::CommandLineFlag {
  public:
-  constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
+  constexpr Flag(const char* name, const flags_internal::HelpInitArg help,
                  const char* filename,
                  const flags_internal::FlagMarshallingOpFn marshalling_op,
                  const flags_internal::InitialValGenFunc initial_value_gen)
-      : flags_internal::CommandLineFlag(
-            name, flags_internal::HelpText::FromFunctionPointer(help_gen),
-            filename),
-        impl_(&flags_internal::FlagOps<T>, marshalling_op, initial_value_gen) {}
+      : flags_internal::CommandLineFlag(name, filename),
+        impl_(&flags_internal::FlagOps<T>, marshalling_op, initial_value_gen,
+              help) {}
 
   T Get() const {
     // See implementation notes in CommandLineFlag::Get().
@@ -222,6 +290,7 @@ class Flag final : public flags_internal::CommandLineFlag {
   }
 
   // CommandLineFlag interface
+  std::string Help() const override { return impl_.Help(); }
   bool IsModified() const override { return impl_.IsModified(); }
   bool IsSpecifiedOnCommandLine() const override {
     return impl_.IsSpecifiedOnCommandLine();
diff --git a/absl/flags/internal/registry.cc b/absl/flags/internal/registry.cc
index ae7671a9..52d9f3c7 100644
--- a/absl/flags/internal/registry.cc
+++ b/absl/flags/internal/registry.cc
@@ -276,9 +276,8 @@ namespace {
 class RetiredFlagObj final : public flags_internal::CommandLineFlag {
  public:
   constexpr RetiredFlagObj(const char* name, FlagOpFn ops)
-      : flags_internal::CommandLineFlag(
-            name, flags_internal::HelpText::FromStaticCString(nullptr),
-            /*filename=*/"RETIRED"),
+      : flags_internal::CommandLineFlag(name,
+                                        /*filename=*/"RETIRED"),
         op_(ops) {}
 
  private:
@@ -288,6 +287,7 @@ class RetiredFlagObj final : public flags_internal::CommandLineFlag {
   }
 
   flags_internal::FlagOpFn TypeId() const override { return op_; }
+  std::string Help() const override { return ""; }
   bool IsRetired() const override { return true; }
   bool IsModified() const override { return false; }
   bool IsSpecifiedOnCommandLine() const override { return false; }