about summary refs log tree commit diff
path: root/absl
diff options
context:
space:
mode:
Diffstat (limited to 'absl')
-rw-r--r--absl/base/internal/spinlock.cc7
-rw-r--r--absl/base/internal/spinlock.h5
-rw-r--r--absl/base/internal/sysinfo.cc11
-rw-r--r--absl/base/internal/thread_identity_test.cc9
-rw-r--r--absl/base/spinlock_test_common.cc14
-rw-r--r--absl/container/node_hash_map.h6
-rw-r--r--absl/container/node_hash_set.h6
-rw-r--r--absl/flags/flag.h61
-rw-r--r--absl/flags/flag_test.cc67
-rw-r--r--absl/flags/internal/commandlineflag.cc15
-rw-r--r--absl/flags/internal/commandlineflag.h46
-rw-r--r--absl/flags/internal/commandlineflag_test.cc3
-rw-r--r--absl/flags/internal/flag.cc61
-rw-r--r--absl/flags/internal/flag.h99
-rw-r--r--absl/flags/internal/registry.cc12
-rw-r--r--absl/flags/internal/type_erased.cc4
-rw-r--r--absl/flags/internal/type_erased.h2
-rw-r--r--absl/flags/internal/usage.cc32
-rw-r--r--absl/strings/internal/str_format/arg.cc28
-rw-r--r--absl/strings/internal/str_format/arg.h85
-rw-r--r--absl/strings/internal/str_format/bind.h5
-rw-r--r--absl/strings/internal/str_format/checker.h24
-rw-r--r--absl/strings/internal/str_format/extension.h277
-rw-r--r--absl/strings/internal/str_format/extension_test.cc9
-rw-r--r--absl/strings/internal/str_format/float_conversion.cc110
-rw-r--r--absl/strings/internal/str_format/parser.cc10
-rw-r--r--absl/strings/internal/str_format/parser.h12
-rw-r--r--absl/strings/internal/str_format/parser_test.cc27
-rw-r--r--absl/strings/str_format_test.cc2
-rw-r--r--absl/synchronization/internal/create_thread_identity.cc6
-rw-r--r--absl/synchronization/internal/graphcycles.cc6
-rw-r--r--absl/synchronization/mutex.cc17
-rw-r--r--absl/time/clock.cc6
-rw-r--r--absl/time/internal/cctz/src/cctz_benchmark.cc1
-rw-r--r--absl/time/internal/cctz/src/time_zone_lookup_test.cc1
35 files changed, 646 insertions, 440 deletions
diff --git a/absl/base/internal/spinlock.cc b/absl/base/internal/spinlock.cc
index fd0c733e234b..7cac72f97f28 100644
--- a/absl/base/internal/spinlock.cc
+++ b/absl/base/internal/spinlock.cc
@@ -66,6 +66,13 @@ void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock,
   submit_profile_data.Store(fn);
 }
 
+// Static member variable definitions.
+constexpr uint32_t SpinLock::kSpinLockHeld;
+constexpr uint32_t SpinLock::kSpinLockCooperative;
+constexpr uint32_t SpinLock::kSpinLockDisabledScheduling;
+constexpr uint32_t SpinLock::kSpinLockSleeper;
+constexpr uint32_t SpinLock::kWaitTimeMask;
+
 // Uncommon constructors.
 SpinLock::SpinLock(base_internal::SchedulingMode mode)
     : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index 89e93aad0bd0..2b08a2d6e2f1 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -36,6 +36,7 @@
 #include <atomic>
 
 #include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
 #include "absl/base/dynamic_annotations.h"
 #include "absl/base/internal/low_level_scheduling.h"
 #include "absl/base/internal/raw_logging.h"
@@ -77,6 +78,10 @@ class ABSL_LOCKABLE SpinLock {
   SpinLock(base_internal::LinkerInitialized,
            base_internal::SchedulingMode mode);
 
+  // Constructor for global SpinLock instances.  See absl/base/const_init.h.
+  constexpr SpinLock(absl::ConstInitType, base_internal::SchedulingMode mode)
+      : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {}
+
   ~SpinLock() { ABSL_TSAN_MUTEX_DESTROY(this, __tsan_mutex_not_static); }
 
   // Acquire this SpinLock.
diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index c3f275ca8a28..6c69683faf67 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -344,15 +344,16 @@ pid_t GetTID() {
 #else
 
 // Fallback implementation of GetTID using pthread_getspecific.
-static once_flag tid_once;
-static pthread_key_t tid_key;
-static absl::base_internal::SpinLock tid_lock(
-    absl::base_internal::kLinkerInitialized);
+ABSL_CONST_INIT static once_flag tid_once;
+ABSL_CONST_INIT static pthread_key_t tid_key;
+ABSL_CONST_INIT static absl::base_internal::SpinLock tid_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
 
 // We set a bit per thread in this array to indicate that an ID is in
 // use. ID 0 is unused because it is the default value returned by
 // pthread_getspecific().
-static std::vector<uint32_t>* tid_array ABSL_GUARDED_BY(tid_lock) = nullptr;
+ABSL_CONST_INIT static std::vector<uint32_t> *tid_array
+    ABSL_GUARDED_BY(tid_lock) = nullptr;
 static constexpr int kBitsPerWord = 32;  // tid_array is uint32_t.
 
 // Returns the TID to tid_array.
diff --git a/absl/base/internal/thread_identity_test.cc b/absl/base/internal/thread_identity_test.cc
index 3685779ce8f5..624d5b96b6ee 100644
--- a/absl/base/internal/thread_identity_test.cc
+++ b/absl/base/internal/thread_identity_test.cc
@@ -21,6 +21,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/internal/spinlock.h"
 #include "absl/base/macros.h"
+#include "absl/base/thread_annotations.h"
 #include "absl/synchronization/internal/per_thread_sem.h"
 #include "absl/synchronization/mutex.h"
 
@@ -29,10 +30,9 @@ ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 namespace {
 
-// protects num_identities_reused
-static absl::base_internal::SpinLock map_lock(
-    absl::base_internal::kLinkerInitialized);
-static int num_identities_reused;
+ABSL_CONST_INIT static absl::base_internal::SpinLock map_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static int num_identities_reused ABSL_GUARDED_BY(map_lock);
 
 static const void* const kCheckNoIdentity = reinterpret_cast<void*>(1);
 
@@ -90,6 +90,7 @@ TEST(ThreadIdentityTest, BasicIdentityWorksThreaded) {
   // We should have recycled ThreadIdentity objects above; while (external)
   // library threads allocating their own identities may preclude some
   // reuse, we should have sufficient repetitions to exclude this.
+  absl::base_internal::SpinLockHolder l(&map_lock);
   EXPECT_LT(kNumThreads, num_identities_reused);
 }
 
diff --git a/absl/base/spinlock_test_common.cc b/absl/base/spinlock_test_common.cc
index 08f61ba86a38..b68c51a1dcde 100644
--- a/absl/base/spinlock_test_common.cc
+++ b/absl/base/spinlock_test_common.cc
@@ -56,12 +56,10 @@ namespace {
 static constexpr int kArrayLength = 10;
 static uint32_t values[kArrayLength];
 
-static SpinLock static_spinlock(base_internal::kLinkerInitialized);
-static SpinLock static_cooperative_spinlock(
-    base_internal::kLinkerInitialized,
-    base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
-static SpinLock static_noncooperative_spinlock(
-    base_internal::kLinkerInitialized, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static SpinLock static_cooperative_spinlock(
+    absl::kConstInit, base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL);
+ABSL_CONST_INIT static SpinLock static_noncooperative_spinlock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
 
 // Simple integer hash function based on the public domain lookup2 hash.
 // http://burtleburtle.net/bob/c/lookup2.c
@@ -191,10 +189,6 @@ TEST(SpinLock, WaitCyclesEncoding) {
   EXPECT_GT(expected_max_value_decoded, before_max_value_decoded);
 }
 
-TEST(SpinLockWithThreads, StaticSpinLock) {
-  ThreadedTest(&static_spinlock);
-}
-
 TEST(SpinLockWithThreads, StackSpinLock) {
   SpinLock spinlock;
   ThreadedTest(&spinlock);
diff --git a/absl/container/node_hash_map.h b/absl/container/node_hash_map.h
index fccea1841c08..174b971e99ce 100644
--- a/absl/container/node_hash_map.h
+++ b/absl/container/node_hash_map.h
@@ -514,12 +514,6 @@ class node_hash_map
   //
   // Returns the function used for comparing keys equality.
   using Base::key_eq;
-
-  ABSL_DEPRECATED("Call `hash_function()` instead.")
-  typename Base::hasher hash_funct() { return this->hash_function(); }
-
-  ABSL_DEPRECATED("Call `rehash()` instead.")
-  void resize(typename Base::size_type hint) { this->rehash(hint); }
 };
 
 // erase_if(node_hash_map<>, Pred)
diff --git a/absl/container/node_hash_set.h b/absl/container/node_hash_set.h
index ad54b6dccb50..56bab5c2c001 100644
--- a/absl/container/node_hash_set.h
+++ b/absl/container/node_hash_set.h
@@ -427,12 +427,6 @@ class node_hash_set
   //
   // Returns the function used for comparing keys equality.
   using Base::key_eq;
-
-  ABSL_DEPRECATED("Call `hash_function()` instead.")
-  typename Base::hasher hash_funct() { return this->hash_function(); }
-
-  ABSL_DEPRECATED("Call `rehash()` instead.")
-  void resize(typename Base::size_type hint) { this->rehash(hint); }
 };
 
 // erase_if(node_hash_set<>, Pred)
diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index 194a9d314fc5..8dd1b9be7af8 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -118,11 +118,12 @@ class Flag {
         return impl_;
       }
 
-      impl_ =
-          new flags_internal::Flag<T>(name_, filename_,
-                                      {flags_internal::FlagHelpMsg(help_gen_),
-                                       flags_internal::FlagHelpKind::kGenFunc},
-                                      default_value_gen_);
+      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);
     }
 
@@ -132,14 +133,12 @@ class Flag {
   // 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(); }
@@ -311,9 +310,12 @@ ABSL_NAMESPACE_END
     static std::string NonConst() { return ABSL_FLAG_IMPL_FLAGHELP(txt); } \
   }
 
-#define ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value) \
-  static void AbslFlagsInitFlag##name(void* dst) {                        \
-    absl::flags_internal::MakeFromDefaultValue<Type>(dst, default_value); \
+#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
@@ -322,29 +324,30 @@ ABSL_NAMESPACE_END
 // 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), ABSL_FLAG_IMPL_FILENAME(),    \
-      absl::flags_internal::HelpArg<AbslFlagHelpGenFor##name>(0),   \
-      &AbslFlagsInitFlag##name};                                    \
-  extern absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;   \
-  absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name =         \
+
+#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::flags_internal::HelpArg<AbslFlagHelpGenFor##name>(0),              \
+      absl::flags_internal::DefaultArg<Type, AbslFlagDefaultGenFor##name>(0)}; \
+  extern absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;              \
+  absl::flags_internal::FlagRegistrarEmpty 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 absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;     \
-  absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name =           \
+#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, &AbslFlagDefaultGenFor##name::Gen}; \
+  extern absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;              \
+  absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name =                    \
       ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name)
 #endif
 
diff --git a/absl/flags/flag_test.cc b/absl/flags/flag_test.cc
index 6fa178f1f0b9..015b1fc9dc5d 100644
--- a/absl/flags/flag_test.cc
+++ b/absl/flags/flag_test.cc
@@ -128,26 +128,27 @@ constexpr flags::FlagHelpArg help_arg{flags::FlagHelpMsg("literal help"),
 
 using String = std::string;
 
-#define DEFINE_CONSTRUCTED_FLAG(T)                                          \
-  constexpr flags::Flag<T> f1##T("f1", "file", help_arg, &TestMakeDflt<T>); \
-  ABSL_CONST_INIT flags::Flag<T> f2##T(                                     \
-      "f2", "file",                                                         \
-      {flags::FlagHelpMsg(&TestHelpMsg), flags::FlagHelpKind::kGenFunc},    \
-      &TestMakeDflt<T>)
-
-#define TEST_CONSTRUCTED_FLAG(T) TestConstructionFor(f1##T, &f2##T);
-
-DEFINE_CONSTRUCTED_FLAG(bool);
-DEFINE_CONSTRUCTED_FLAG(int16_t);
-DEFINE_CONSTRUCTED_FLAG(uint16_t);
-DEFINE_CONSTRUCTED_FLAG(int32_t);
-DEFINE_CONSTRUCTED_FLAG(uint32_t);
-DEFINE_CONSTRUCTED_FLAG(int64_t);
-DEFINE_CONSTRUCTED_FLAG(uint64_t);
-DEFINE_CONSTRUCTED_FLAG(float);
-DEFINE_CONSTRUCTED_FLAG(double);
-DEFINE_CONSTRUCTED_FLAG(String);
-DEFINE_CONSTRUCTED_FLAG(UDT);
+#define DEFINE_CONSTRUCTED_FLAG(T, dflt, dflt_kind)                      \
+  constexpr flags::FlagDefaultArg f1default##T{                          \
+      flags::FlagDefaultSrc{dflt}, flags::FlagDefaultKind::dflt_kind};   \
+  constexpr flags::Flag<T> f1##T("f1", "file", help_arg, f1default##T);  \
+  ABSL_CONST_INIT flags::Flag<T> f2##T(                                  \
+      "f2", "file",                                                      \
+      {flags::FlagHelpMsg(&TestHelpMsg), flags::FlagHelpKind::kGenFunc}, \
+      flags::FlagDefaultArg{flags::FlagDefaultSrc(&TestMakeDflt<T>),     \
+                            flags::FlagDefaultKind::kGenFunc})
+
+DEFINE_CONSTRUCTED_FLAG(bool, true, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(int16_t, 1, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(uint16_t, 2, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(int32_t, 3, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(uint32_t, 4, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(int64_t, 5, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(uint64_t, 6, kOneWord);
+DEFINE_CONSTRUCTED_FLAG(float, 7.8, kFloat);
+DEFINE_CONSTRUCTED_FLAG(double, 9.10, kDouble);
+DEFINE_CONSTRUCTED_FLAG(String, &TestMakeDflt<String>, kGenFunc);
+DEFINE_CONSTRUCTED_FLAG(UDT, &TestMakeDflt<UDT>, kGenFunc);
 
 template <typename T>
 bool TestConstructionFor(const flags::Flag<T>& f1, flags::Flag<T>* f2) {
@@ -164,6 +165,8 @@ bool TestConstructionFor(const flags::Flag<T>& f1, flags::Flag<T>* f2) {
   return true;
 }
 
+#define TEST_CONSTRUCTED_FLAG(T) TestConstructionFor(f1##T, &f2##T);
+
 TEST_F(FlagTest, TestConstruction) {
   TEST_CONSTRUCTED_FLAG(bool);
   TEST_CONSTRUCTED_FLAG(int16_t);
@@ -443,29 +446,29 @@ TEST_F(FlagTest, TestGetSet) {
 
 TEST_F(FlagTest, TestGetViaReflection) {
   auto* handle = flags::FindCommandLineFlag("test_flag_01");
-  EXPECT_EQ(*handle->Get<bool>(), true);
+  EXPECT_EQ(*handle->TryGet<bool>(), true);
   handle = flags::FindCommandLineFlag("test_flag_02");
-  EXPECT_EQ(*handle->Get<int>(), 1234);
+  EXPECT_EQ(*handle->TryGet<int>(), 1234);
   handle = flags::FindCommandLineFlag("test_flag_03");
-  EXPECT_EQ(*handle->Get<int16_t>(), -34);
+  EXPECT_EQ(*handle->TryGet<int16_t>(), -34);
   handle = flags::FindCommandLineFlag("test_flag_04");
-  EXPECT_EQ(*handle->Get<uint16_t>(), 189);
+  EXPECT_EQ(*handle->TryGet<uint16_t>(), 189);
   handle = flags::FindCommandLineFlag("test_flag_05");
-  EXPECT_EQ(*handle->Get<int32_t>(), 10765);
+  EXPECT_EQ(*handle->TryGet<int32_t>(), 10765);
   handle = flags::FindCommandLineFlag("test_flag_06");
-  EXPECT_EQ(*handle->Get<uint32_t>(), 40000);
+  EXPECT_EQ(*handle->TryGet<uint32_t>(), 40000);
   handle = flags::FindCommandLineFlag("test_flag_07");
-  EXPECT_EQ(*handle->Get<int64_t>(), -1234567);
+  EXPECT_EQ(*handle->TryGet<int64_t>(), -1234567);
   handle = flags::FindCommandLineFlag("test_flag_08");
-  EXPECT_EQ(*handle->Get<uint64_t>(), 9876543);
+  EXPECT_EQ(*handle->TryGet<uint64_t>(), 9876543);
   handle = flags::FindCommandLineFlag("test_flag_09");
-  EXPECT_NEAR(*handle->Get<double>(), -9.876e-50, 1e-55);
+  EXPECT_NEAR(*handle->TryGet<double>(), -9.876e-50, 1e-55);
   handle = flags::FindCommandLineFlag("test_flag_10");
-  EXPECT_NEAR(*handle->Get<float>(), 1.234e12f, 1e5f);
+  EXPECT_NEAR(*handle->TryGet<float>(), 1.234e12f, 1e5f);
   handle = flags::FindCommandLineFlag("test_flag_11");
-  EXPECT_EQ(*handle->Get<std::string>(), "");
+  EXPECT_EQ(*handle->TryGet<std::string>(), "");
   handle = flags::FindCommandLineFlag("test_flag_12");
-  EXPECT_EQ(*handle->Get<absl::Duration>(), absl::Minutes(10));
+  EXPECT_EQ(*handle->TryGet<absl::Duration>(), absl::Minutes(10));
 }
 
 // --------------------------------------------------------------------
diff --git a/absl/flags/internal/commandlineflag.cc b/absl/flags/internal/commandlineflag.cc
index 90765a3eb6f3..de588c13166b 100644
--- a/absl/flags/internal/commandlineflag.cc
+++ b/absl/flags/internal/commandlineflag.cc
@@ -22,7 +22,20 @@ namespace flags_internal {
 FlagStateInterface::~FlagStateInterface() {}
 
 bool CommandLineFlag::IsRetired() const { return false; }
-bool CommandLineFlag::IsAbseilFlag() const { return true; }
+
+FlagFastTypeId PrivateHandleInterface::TypeId(const CommandLineFlag& flag) {
+  return flag.TypeId();
+}
+
+std::unique_ptr<FlagStateInterface> PrivateHandleInterface::SaveState(
+    CommandLineFlag* flag) {
+  return flag->SaveState();
+}
+
+bool PrivateHandleInterface::ValidateInputValue(const CommandLineFlag& flag,
+                                                absl::string_view value) {
+  return flag.ValidateInputValue(value);
+}
 
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
diff --git a/absl/flags/internal/commandlineflag.h b/absl/flags/internal/commandlineflag.h
index ef992f7f478d..f807fb9ab650 100644
--- a/absl/flags/internal/commandlineflag.h
+++ b/absl/flags/internal/commandlineflag.h
@@ -93,7 +93,7 @@ class CommandLineFlag {
   // Attempts to retrieve the flag value. Returns value on success,
   // absl::nullopt otherwise.
   template <typename T>
-  absl::optional<T> Get() const {
+  absl::optional<T> TryGet() const {
     if (IsRetired() || !IsOfType<T>()) {
       return absl::nullopt;
     }
@@ -130,29 +130,14 @@ class CommandLineFlag {
   virtual absl::string_view Name() const = 0;
   // Returns name of the file where this flag is defined.
   virtual std::string Filename() const = 0;
-  // Returns name of the flag's value type for some built-in types or empty
-  // string.
-  virtual absl::string_view Typename() const = 0;
   // 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;
-  // Returns true iff this is a handle to an Abseil Flag.
-  virtual bool IsAbseilFlag() const;
-  // Returns id of the flag's value type.
-  virtual FlagFastTypeId TypeId() const = 0;
-  virtual bool IsModified() const = 0;
   virtual bool IsSpecifiedOnCommandLine() const = 0;
   virtual std::string DefaultValue() const = 0;
   virtual std::string CurrentValue() const = 0;
 
-  // Interfaces to operate on validators.
-  virtual bool ValidateInputValue(absl::string_view value) const = 0;
-
-  // Interface to save flag to some persistent state. Returns current flag state
-  // or nullptr if flag does not support saving and restoring a state.
-  virtual std::unique_ptr<FlagStateInterface> SaveState() = 0;
-
   // Sets the value of the flag based on specified string `value`. If the flag
   // was successfully set to new value, it returns true. Otherwise, sets `error`
   // to indicate the error, leaves the flag unchanged, and returns false. There
@@ -174,9 +159,38 @@ class CommandLineFlag {
   ~CommandLineFlag() = default;
 
  private:
+  friend class PrivateHandleInterface;
+
+  // Returns id of the flag's value type.
+  virtual FlagFastTypeId TypeId() const = 0;
+
+  // Interface to save flag to some persistent state. Returns current flag state
+  // or nullptr if flag does not support saving and restoring a state.
+  virtual std::unique_ptr<FlagStateInterface> SaveState() = 0;
+
   // Copy-construct a new value of the flag's type in a memory referenced by
   // the dst based on the current flag's value.
   virtual void Read(void* dst) const = 0;
+
+  // Interfaces to operate on validators.
+  // Validates supplied value usign validator or parseflag routine
+  virtual bool ValidateInputValue(absl::string_view value) const = 0;
+};
+
+// This class serves as a trampoline to access private methods of
+// CommandLineFlag. This class is intended for use exclusively internally inside
+// of the Abseil Flags implementation
+class PrivateHandleInterface {
+ public:
+  // Access to CommandLineFlag::TypeId.
+  static FlagFastTypeId TypeId(const CommandLineFlag& flag);
+
+  // Access to CommandLineFlag::SaveState.
+  static std::unique_ptr<FlagStateInterface> SaveState(CommandLineFlag* flag);
+
+  // Access to CommandLineFlag::ValidateInputValue.
+  static bool ValidateInputValue(const CommandLineFlag& flag,
+                                 absl::string_view value);
 };
 
 // This macro is the "source of truth" for the list of supported flag built-in
diff --git a/absl/flags/internal/commandlineflag_test.cc b/absl/flags/internal/commandlineflag_test.cc
index c1142b7c5720..c31679f95e7a 100644
--- a/absl/flags/internal/commandlineflag_test.cc
+++ b/absl/flags/internal/commandlineflag_test.cc
@@ -67,7 +67,6 @@ TEST_F(CommandLineFlagTest, TestAttributesAccessMethods) {
   ASSERT_TRUE(flag_01);
   EXPECT_EQ(flag_01->Name(), "int_flag");
   EXPECT_EQ(flag_01->Help(), "int_flag help");
-  EXPECT_EQ(flag_01->Typename(), "");
   EXPECT_TRUE(!flag_01->IsRetired());
   EXPECT_TRUE(flag_01->IsOfType<int>());
   EXPECT_TRUE(
@@ -80,7 +79,6 @@ TEST_F(CommandLineFlagTest, TestAttributesAccessMethods) {
   ASSERT_TRUE(flag_02);
   EXPECT_EQ(flag_02->Name(), "string_flag");
   EXPECT_EQ(flag_02->Help(), "string_flag help");
-  EXPECT_EQ(flag_02->Typename(), "");
   EXPECT_TRUE(!flag_02->IsRetired());
   EXPECT_TRUE(flag_02->IsOfType<std::string>());
   EXPECT_TRUE(
@@ -93,7 +91,6 @@ TEST_F(CommandLineFlagTest, TestAttributesAccessMethods) {
   ASSERT_TRUE(flag_03);
   EXPECT_EQ(flag_03->Name(), "bool_retired_flag");
   EXPECT_EQ(flag_03->Help(), "");
-  EXPECT_EQ(flag_03->Typename(), "");
   EXPECT_TRUE(flag_03->IsRetired());
   EXPECT_TRUE(flag_03->IsOfType<bool>());
   EXPECT_EQ(flag_03->Filename(), "RETIRED");
diff --git a/absl/flags/internal/flag.cc b/absl/flags/internal/flag.cc
index 089567f7ae50..8f0777fa1dc1 100644
--- a/absl/flags/internal/flag.cc
+++ b/absl/flags/internal/flag.cc
@@ -139,19 +139,43 @@ void DynValueDeleter::operator()(void* ptr) const {
 void FlagImpl::Init() {
   new (&data_guard_) absl::Mutex;
 
-  // At this point the default_value_ always points to gen_func.
+  auto def_kind = static_cast<FlagDefaultKind>(def_kind_);
+
   switch (ValueStorageKind()) {
     case FlagValueStorageKind::kAlignedBuffer:
+      // For this storage kind the default_value_ always points to gen_func
+      // during initialization.
+      assert(def_kind == FlagDefaultKind::kGenFunc);
       (*default_value_.gen_func)(AlignedBufferValue());
       break;
     case FlagValueStorageKind::kOneWordAtomic: {
       alignas(int64_t) std::array<char, sizeof(int64_t)> buf{};
-      (*default_value_.gen_func)(buf.data());
-      auto value = absl::bit_cast<int64_t>(buf);
-      OneWordValue().store(value, std::memory_order_release);
+      switch (def_kind) {
+        case FlagDefaultKind::kOneWord:
+          std::memcpy(buf.data(), &default_value_.one_word,
+                      sizeof(default_value_.one_word));
+          break;
+        case FlagDefaultKind::kFloat:
+          std::memcpy(buf.data(), &default_value_.float_value,
+                      sizeof(default_value_.float_value));
+          break;
+        case FlagDefaultKind::kDouble:
+          std::memcpy(buf.data(), &default_value_.double_value,
+                      sizeof(default_value_.double_value));
+          break;
+        default:
+          assert(def_kind == FlagDefaultKind::kGenFunc);
+          (*default_value_.gen_func)(buf.data());
+          break;
+      }
+      OneWordValue().store(absl::bit_cast<int64_t>(buf),
+                           std::memory_order_release);
       break;
     }
     case FlagValueStorageKind::kTwoWordsAtomic: {
+      // For this storage kind the default_value_ always points to gen_func
+      // during initialization.
+      assert(def_kind == FlagDefaultKind::kGenFunc);
       alignas(AlignedTwoWords) std::array<char, sizeof(AlignedTwoWords)> buf{};
       (*default_value_.gen_func)(buf.data());
       auto atomic_value = absl::bit_cast<AlignedTwoWords>(buf);
@@ -196,11 +220,23 @@ void FlagImpl::AssertValidType(FlagFastTypeId rhs_type_id,
 
 std::unique_ptr<void, DynValueDeleter> FlagImpl::MakeInitValue() const {
   void* res = nullptr;
-  if (DefaultKind() == FlagDefaultKind::kDynamicValue) {
-    res = flags_internal::Clone(op_, default_value_.dynamic_value);
-  } else {
-    res = flags_internal::Alloc(op_);
-    (*default_value_.gen_func)(res);
+  switch (DefaultKind()) {
+    case FlagDefaultKind::kDynamicValue:
+      res = flags_internal::Clone(op_, default_value_.dynamic_value);
+      break;
+    case FlagDefaultKind::kGenFunc:
+      res = flags_internal::Alloc(op_);
+      (*default_value_.gen_func)(res);
+      break;
+    case FlagDefaultKind::kOneWord:
+      res = flags_internal::Clone(op_, &default_value_.one_word);
+      break;
+    case FlagDefaultKind::kFloat:
+      res = flags_internal::Clone(op_, &default_value_.float_value);
+      break;
+    case FlagDefaultKind::kDouble:
+      res = flags_internal::Clone(op_, &default_value_.double_value);
+      break;
   }
   return {res, DynValueDeleter{op_}};
 }
@@ -235,8 +271,6 @@ std::string FlagImpl::Filename() const {
   return flags_internal::GetUsageConfig().normalize_filename(filename_);
 }
 
-absl::string_view FlagImpl::Typename() const { return ""; }
-
 std::string FlagImpl::Help() const {
   return HelpSourceKind() == FlagHelpKind::kLiteral ? help_.literal
                                                     : help_.gen_func();
@@ -246,11 +280,6 @@ FlagFastTypeId FlagImpl::TypeId() const {
   return flags_internal::FastTypeId(op_);
 }
 
-bool FlagImpl::IsModified() const {
-  absl::MutexLock l(DataGuard());
-  return modified_;
-}
-
 bool FlagImpl::IsSpecifiedOnCommandLine() const {
   absl::MutexLock l(DataGuard());
   return on_command_line_;
diff --git a/absl/flags/internal/flag.h b/absl/flags/internal/flag.h
index 6da25aa9454a..b2208824508d 100644
--- a/absl/flags/internal/flag.h
+++ b/absl/flags/internal/flag.h
@@ -206,12 +206,72 @@ using FlagDfltGenFunc = void (*)(void*);
 union FlagDefaultSrc {
   constexpr explicit FlagDefaultSrc(FlagDfltGenFunc gen_func_arg)
       : gen_func(gen_func_arg) {}
+  template <typename T>
+  constexpr explicit FlagDefaultSrc(T one_word_value)
+      : one_word(static_cast<int64_t>(one_word_value)) {}
+  constexpr explicit FlagDefaultSrc(float f) : float_value(f) {}
+  constexpr explicit FlagDefaultSrc(double d) : double_value(d) {}
 
   void* dynamic_value;
   FlagDfltGenFunc gen_func;
+  int64_t one_word;
+  float float_value;
+  double double_value;
+};
+
+enum class FlagDefaultKind : uint8_t {
+  kDynamicValue = 0,
+  kGenFunc = 1,
+  kOneWord = 2,
+  kFloat = 3,
+  kDouble = 4
+};
+
+struct FlagDefaultArg {
+  FlagDefaultSrc source;
+  FlagDefaultKind kind;
 };
 
-enum class FlagDefaultKind : uint8_t { kDynamicValue = 0, kGenFunc = 1 };
+// This struct and corresponding overload to InitDefaultValue are used to
+// facilitate usage of {} as default value in ABSL_FLAG macro.
+// TODO(rogeeff): Fix handling types with explicit constructors.
+struct EmptyBraces {};
+
+template <typename T>
+constexpr T InitDefaultValue(T t) {
+  return t;
+}
+
+template <typename T>
+constexpr T InitDefaultValue(EmptyBraces) {
+  return T{};
+}
+
+template <typename ValueT, typename GenT,
+          typename std::enable_if<std::is_integral<ValueT>::value, int>::type =
+              (GenT{}, 0)>
+constexpr FlagDefaultArg DefaultArg(int) {
+  return {FlagDefaultSrc(GenT{}.value), FlagDefaultKind::kOneWord};
+}
+
+template <typename ValueT, typename GenT,
+          typename std::enable_if<std::is_same<ValueT, float>::value,
+                                  int>::type = (GenT{}, 0)>
+constexpr FlagDefaultArg DefaultArg(int) {
+  return {FlagDefaultSrc(GenT{}.value), FlagDefaultKind::kFloat};
+}
+
+template <typename ValueT, typename GenT,
+          typename std::enable_if<std::is_same<ValueT, double>::value,
+                                  int>::type = (GenT{}, 0)>
+constexpr FlagDefaultArg DefaultArg(int) {
+  return {FlagDefaultSrc(GenT{}.value), FlagDefaultKind::kDouble};
+}
+
+template <typename ValueT, typename GenT>
+constexpr FlagDefaultArg DefaultArg(char) {
+  return {FlagDefaultSrc(&GenT::Gen), FlagDefaultKind::kGenFunc};
+}
 
 ///////////////////////////////////////////////////////////////////////////////
 // Flag current value auxiliary structs.
@@ -356,19 +416,19 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
  public:
   constexpr FlagImpl(const char* name, const char* filename, FlagOpFn op,
                      FlagHelpArg help, FlagValueStorageKind value_kind,
-                     FlagDfltGenFunc default_value_gen)
+                     FlagDefaultArg default_arg)
       : name_(name),
         filename_(filename),
         op_(op),
         help_(help.source),
         help_source_kind_(static_cast<uint8_t>(help.kind)),
         value_storage_kind_(static_cast<uint8_t>(value_kind)),
-        def_kind_(static_cast<uint8_t>(FlagDefaultKind::kGenFunc)),
+        def_kind_(static_cast<uint8_t>(default_arg.kind)),
         modified_(false),
         on_command_line_(false),
         counter_(0),
         callback_(nullptr),
-        default_value_(default_value_gen),
+        default_value_(default_arg.source),
         data_guard_{} {}
 
   // Constant access methods
@@ -444,10 +504,8 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
   // CommandLineFlag interface implementation
   absl::string_view Name() const override;
   std::string Filename() const override;
-  absl::string_view Typename() const override;
   std::string Help() const override;
   FlagFastTypeId TypeId() const override;
-  bool IsModified() const override ABSL_LOCKS_EXCLUDED(*DataGuard());
   bool IsSpecifiedOnCommandLine() const override
       ABSL_LOCKS_EXCLUDED(*DataGuard());
   std::string DefaultValue() const override ABSL_LOCKS_EXCLUDED(*DataGuard());
@@ -492,9 +550,10 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
 
   // Mutable flag's state (guarded by `data_guard_`).
 
-  // If def_kind_ == kDynamicValue, default_value_ holds a dynamically allocated
-  // value.
-  uint8_t def_kind_ : 1 ABSL_GUARDED_BY(*DataGuard());
+  // def_kind_ is not guard by DataGuard() since it is accessed in Init without
+  // locks. If necessary we can decrease number of bits used to 2 by folding
+  // one_word storage cases.
+  uint8_t def_kind_ : 3;
   // Has this flag's value been modified?
   bool modified_ : 1 ABSL_GUARDED_BY(*DataGuard());
   // Has this flag been specified on command line.
@@ -530,10 +589,10 @@ class FlagImpl final : public flags_internal::CommandLineFlag {
 template <typename T>
 class Flag {
  public:
-  constexpr Flag(const char* name, const char* filename, const FlagHelpArg help,
-                 const FlagDfltGenFunc default_value_gen)
+  constexpr Flag(const char* name, const char* filename, FlagHelpArg help,
+                 const FlagDefaultArg default_arg)
       : impl_(name, filename, &FlagOps<T>, help,
-              flags_internal::StorageKind<T>(), default_value_gen),
+              flags_internal::StorageKind<T>(), default_arg),
         value_() {}
 
   T Get() const {
@@ -560,9 +619,7 @@ class Flag {
   // CommandLineFlag interface
   absl::string_view Name() const { return impl_.Name(); }
   std::string Filename() const { return impl_.Filename(); }
-  absl::string_view Typename() const { return ""; }
   std::string Help() const { return impl_.Help(); }
-  bool IsModified() const { return impl_.IsModified(); }
   bool IsSpecifiedOnCommandLine() const {
     return impl_.IsSpecifiedOnCommandLine();
   }
@@ -662,20 +719,6 @@ class FlagRegistrar {
   Flag<T>* flag_;  // Flag being registered (not owned).
 };
 
-// This struct and corresponding overload to MakeDefaultValue are used to
-// facilitate usage of {} as default value in ABSL_FLAG macro.
-struct EmptyBraces {};
-
-template <typename T>
-void MakeFromDefaultValue(void* dst, T t) {
-  new (dst) T(std::move(t));
-}
-
-template <typename T>
-void MakeFromDefaultValue(void* dst, EmptyBraces) {
-  new (dst) T{};
-}
-
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/flags/internal/registry.cc b/absl/flags/internal/registry.cc
index eb619c7086ad..62b5b40d88b8 100644
--- a/absl/flags/internal/registry.cc
+++ b/absl/flags/internal/registry.cc
@@ -127,14 +127,13 @@ void FlagRegistry::RegisterFlag(CommandLineFlag* flag) {
               (flag->IsRetired() ? old_flag->Filename() : flag->Filename()),
               "'."),
           true);
-    } else if (flag->TypeId() != old_flag->TypeId()) {
+    } else if (flags_internal::PrivateHandleInterface::TypeId(*flag) !=
+               flags_internal::PrivateHandleInterface::TypeId(*old_flag)) {
       flags_internal::ReportUsageError(
           absl::StrCat("Flag '", flag->Name(),
                        "' was defined more than once but with "
                        "differing types. Defined in files '",
-                       old_flag->Filename(), "' and '", flag->Filename(),
-                       "' with types '", old_flag->Typename(), "' and '",
-                       flag->Typename(), "', respectively."),
+                       old_flag->Filename(), "' and '", flag->Filename(), "'."),
           true);
     } else if (old_flag->IsRetired()) {
       // Retired flag can just be deleted.
@@ -206,7 +205,8 @@ class FlagSaverImpl {
   void SaveFromRegistry() {
     assert(backup_registry_.empty());  // call only once!
     flags_internal::ForEachFlag([&](flags_internal::CommandLineFlag* flag) {
-      if (auto flag_state = flag->SaveState()) {
+      if (auto flag_state =
+              flags_internal::PrivateHandleInterface::SaveState(flag)) {
         backup_registry_.emplace_back(std::move(flag_state));
       }
     });
@@ -290,11 +290,9 @@ class RetiredFlagObj final : public flags_internal::CommandLineFlag {
  private:
   absl::string_view Name() const override { return name_; }
   std::string Filename() const override { return "RETIRED"; }
-  absl::string_view Typename() const override { return ""; }
   FlagFastTypeId TypeId() const override { return type_id_; }
   std::string Help() const override { return ""; }
   bool IsRetired() const override { return true; }
-  bool IsModified() const override { return false; }
   bool IsSpecifiedOnCommandLine() const override { return false; }
   std::string DefaultValue() const override { return ""; }
   std::string CurrentValue() const override { return ""; }
diff --git a/absl/flags/internal/type_erased.cc b/absl/flags/internal/type_erased.cc
index 75b4cdf891a8..5038625be761 100644
--- a/absl/flags/internal/type_erased.cc
+++ b/absl/flags/internal/type_erased.cc
@@ -72,7 +72,9 @@ bool IsValidFlagValue(absl::string_view name, absl::string_view value) {
   CommandLineFlag* flag = flags_internal::FindCommandLineFlag(name);
 
   return flag != nullptr &&
-         (flag->IsRetired() || flag->ValidateInputValue(value));
+         (flag->IsRetired() ||
+          flags_internal::PrivateHandleInterface::ValidateInputValue(*flag,
+                                                                     value));
 }
 
 // --------------------------------------------------------------------
diff --git a/absl/flags/internal/type_erased.h b/absl/flags/internal/type_erased.h
index 188429c77129..ffe319bad945 100644
--- a/absl/flags/internal/type_erased.h
+++ b/absl/flags/internal/type_erased.h
@@ -75,7 +75,7 @@ inline bool GetByName(absl::string_view name, T* dst) {
   CommandLineFlag* flag = flags_internal::FindCommandLineFlag(name);
   if (!flag) return false;
 
-  if (auto val = flag->Get<T>()) {
+  if (auto val = flag->TryGet<T>()) {
     *dst = *val;
     return true;
   }
diff --git a/absl/flags/internal/usage.cc b/absl/flags/internal/usage.cc
index a9a5cba94de8..9d856c87a6c0 100644
--- a/absl/flags/internal/usage.cc
+++ b/absl/flags/internal/usage.cc
@@ -54,27 +54,6 @@ ABSL_NAMESPACE_BEGIN
 namespace flags_internal {
 namespace {
 
-absl::string_view TypenameForHelp(const flags_internal::CommandLineFlag& flag) {
-  // Only report names of v1 built-in types
-#define HANDLE_V1_BUILTIN_TYPE(t) \
-  if (flag.IsOfType<t>()) {       \
-    return #t;                    \
-  }
-
-  HANDLE_V1_BUILTIN_TYPE(bool);
-  HANDLE_V1_BUILTIN_TYPE(int32_t);
-  HANDLE_V1_BUILTIN_TYPE(int64_t);
-  HANDLE_V1_BUILTIN_TYPE(uint64_t);
-  HANDLE_V1_BUILTIN_TYPE(double);
-#undef HANDLE_V1_BUILTIN_TYPE
-
-  if (flag.IsOfType<std::string>()) {
-    return "string";
-  }
-
-  return "";
-}
-
 // This class is used to emit an XML element with `tag` and `text`.
 // It adds opening and closing tags and escapes special characters in the text.
 // For example:
@@ -212,23 +191,20 @@ void FlagHelpHumanReadable(const flags_internal::CommandLineFlag& flag,
   // Flag help.
   printer.Write(absl::StrCat("(", flag.Help(), ");"), /*wrap_line=*/true);
 
-  // Flag data type (for V1 flags only).
-  if (!flag.IsAbseilFlag() && !flag.IsRetired()) {
-    printer.Write(absl::StrCat("type: ", TypenameForHelp(flag), ";"));
-  }
-
   // The listed default value will be the actual default from the flag
   // definition in the originating source file, unless the value has
   // subsequently been modified using SetCommandLineOption() with mode
   // SET_FLAGS_DEFAULT.
   std::string dflt_val = flag.DefaultValue();
+  std::string curr_val = flag.CurrentValue();
+  bool is_modified = curr_val != dflt_val;
+
   if (flag.IsOfType<std::string>()) {
     dflt_val = absl::StrCat("\"", dflt_val, "\"");
   }
   printer.Write(absl::StrCat("default: ", dflt_val, ";"));
 
-  if (flag.IsModified()) {
-    std::string curr_val = flag.CurrentValue();
+  if (is_modified) {
     if (flag.IsOfType<std::string>()) {
       curr_val = absl::StrCat("\"", curr_val, "\"");
     }
diff --git a/absl/strings/internal/str_format/arg.cc b/absl/strings/internal/str_format/arg.cc
index 12842276a8e0..a112071c43a7 100644
--- a/absl/strings/internal/str_format/arg.cc
+++ b/absl/strings/internal/str_format/arg.cc
@@ -315,7 +315,7 @@ bool ConvertFloatArg(T v, const ConversionSpec conv, FormatSinkImpl *sink) {
 
 inline bool ConvertStringArg(string_view v, const ConversionSpec conv,
                              FormatSinkImpl *sink) {
-  if (conv.conversion_char() != ConversionChar::s) return false;
+  if (conv.conversion_char() != FormatConversionCharInternal::s) return false;
   if (conv.is_basic()) {
     sink->Append(v);
     return true;
@@ -327,22 +327,22 @@ inline bool ConvertStringArg(string_view v, const ConversionSpec conv,
 }  // namespace
 
 // ==================== Strings ====================
-ConvertResult<Conv::s> FormatConvertImpl(const std::string &v,
-                                         const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
+StringConvertResult FormatConvertImpl(const std::string &v,
+                                      const ConversionSpec conv,
+                                      FormatSinkImpl *sink) {
   return {ConvertStringArg(v, conv, sink)};
 }
 
-ConvertResult<Conv::s> FormatConvertImpl(string_view v,
-                                         const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
+StringConvertResult FormatConvertImpl(string_view v, const ConversionSpec conv,
+                                      FormatSinkImpl *sink) {
   return {ConvertStringArg(v, conv, sink)};
 }
 
-ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char *v,
-                                                   const ConversionSpec conv,
-                                                   FormatSinkImpl *sink) {
-  if (conv.conversion_char() == ConversionChar::p)
+ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::p)>
+FormatConvertImpl(const char *v, const ConversionSpec conv,
+                  FormatSinkImpl *sink) {
+  if (conv.conversion_char() == FormatConversionCharInternal::p)
     return {FormatConvertImpl(VoidPtr(v), conv, sink).value};
   size_t len;
   if (v == nullptr) {
@@ -357,9 +357,9 @@ ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char *v,
 }
 
 // ==================== Raw pointers ====================
-ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, const ConversionSpec conv,
-                                         FormatSinkImpl *sink) {
-  if (conv.conversion_char() != ConversionChar::p) return {false};
+ArgConvertResult<FormatConversionCharSetInternal::p> FormatConvertImpl(
+    VoidPtr v, const ConversionSpec conv, FormatSinkImpl *sink) {
+  if (conv.conversion_char() != FormatConversionCharInternal::p) return {false};
   if (!v.value) {
     sink->Append("(nil)");
     return {true};
diff --git a/absl/strings/internal/str_format/arg.h b/absl/strings/internal/str_format/arg.h
index 1c36e3098c49..f4ac940ab43f 100644
--- a/absl/strings/internal/str_format/arg.h
+++ b/absl/strings/internal/str_format/arg.h
@@ -31,10 +31,11 @@ template <typename T, typename = void>
 struct HasUserDefinedConvert : std::false_type {};
 
 template <typename T>
-struct HasUserDefinedConvert<
-    T, void_t<decltype(AbslFormatConvert(
-           std::declval<const T&>(), std::declval<ConversionSpec>(),
-           std::declval<FormatSink*>()))>> : std::true_type {};
+struct HasUserDefinedConvert<T, void_t<decltype(AbslFormatConvert(
+                                    std::declval<const T&>(),
+                                    std::declval<const FormatConversionSpec&>(),
+                                    std::declval<FormatSink*>()))>>
+    : std::true_type {};
 
 template <typename T>
 class StreamedWrapper;
@@ -52,25 +53,36 @@ struct VoidPtr {
       : value(ptr ? reinterpret_cast<uintptr_t>(ptr) : 0) {}
   uintptr_t value;
 };
-ConvertResult<Conv::p> FormatConvertImpl(VoidPtr v, ConversionSpec conv,
-                                         FormatSinkImpl* sink);
+
+template <FormatConversionCharSet C>
+struct ArgConvertResult {
+  bool value;
+};
+
+template <FormatConversionCharSet C>
+constexpr FormatConversionCharSet ExtractCharSet(ArgConvertResult<C>) {
+  return C;
+}
+
+using StringConvertResult =
+    ArgConvertResult<FormatConversionCharSetInternal::s>;
+ArgConvertResult<FormatConversionCharSetInternal::p> FormatConvertImpl(
+    VoidPtr v, ConversionSpec conv, FormatSinkImpl* sink);
 
 // Strings.
-ConvertResult<Conv::s> FormatConvertImpl(const std::string& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink);
-ConvertResult<Conv::s> FormatConvertImpl(string_view v, ConversionSpec conv,
-                                         FormatSinkImpl* sink);
-ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char* v,
-                                                   ConversionSpec conv,
-                                                   FormatSinkImpl* sink);
-template <class AbslCord,
-          typename std::enable_if<
-              std::is_same<AbslCord, absl::Cord>::value>::type* = nullptr>
-ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink) {
-  if (conv.conversion_char() != ConversionChar::s) {
+StringConvertResult FormatConvertImpl(const std::string& v, ConversionSpec conv,
+                                      FormatSinkImpl* sink);
+StringConvertResult FormatConvertImpl(string_view v, ConversionSpec conv,
+                                      FormatSinkImpl* sink);
+ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::s, FormatConversionCharSetInternal::p)>
+FormatConvertImpl(const char* v, ConversionSpec conv, FormatSinkImpl* sink);
+template <class AbslCord, typename std::enable_if<std::is_same<
+                              AbslCord, absl::Cord>::value>::type* = nullptr>
+StringConvertResult FormatConvertImpl(const AbslCord& value,
+                                      ConversionSpec conv,
+                                      FormatSinkImpl* sink) {
+  if (conv.conversion_char() != FormatConversionCharInternal::s) {
     return {false};
   }
 
@@ -107,9 +119,12 @@ ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
   return {true};
 }
 
-using IntegralConvertResult =
-    ConvertResult<Conv::c | Conv::kNumeric | Conv::kStar>;
-using FloatingConvertResult = ConvertResult<Conv::kFloating>;
+using IntegralConvertResult = ArgConvertResult<FormatConversionCharSetUnion(
+    FormatConversionCharSetInternal::c,
+    FormatConversionCharSetInternal::kNumeric,
+    FormatConversionCharSetInternal::kStar)>;
+using FloatingConvertResult =
+    ArgConvertResult<FormatConversionCharSetInternal::kFloating>;
 
 // Floats.
 FloatingConvertResult FormatConvertImpl(float v, ConversionSpec conv,
@@ -169,9 +184,9 @@ typename std::enable_if<std::is_enum<T>::value &&
 FormatConvertImpl(T v, ConversionSpec conv, FormatSinkImpl* sink);
 
 template <typename T>
-ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<T>& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* out) {
+StringConvertResult FormatConvertImpl(const StreamedWrapper<T>& v,
+                                      ConversionSpec conv,
+                                      FormatSinkImpl* out) {
   std::ostringstream oss;
   oss << v.v_;
   if (!oss) return {false};
@@ -182,12 +197,12 @@ ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<T>& v,
 // until after FormatCountCapture is fully defined.
 struct FormatCountCaptureHelper {
   template <class T = int>
-  static ConvertResult<Conv::n> ConvertHelper(const FormatCountCapture& v,
-                                              ConversionSpec conv,
-                                              FormatSinkImpl* sink) {
+  static ArgConvertResult<FormatConversionCharSetInternal::n> ConvertHelper(
+      const FormatCountCapture& v, ConversionSpec conv, FormatSinkImpl* sink) {
     const absl::enable_if_t<sizeof(T) != 0, FormatCountCapture>& v2 = v;
 
-    if (conv.conversion_char() != str_format_internal::ConversionChar::n) {
+    if (conv.conversion_char() !=
+        str_format_internal::FormatConversionCharInternal::n) {
       return {false};
     }
     *v2.p_ = static_cast<int>(sink->size());
@@ -196,9 +211,8 @@ struct FormatCountCaptureHelper {
 };
 
 template <class T = int>
-ConvertResult<Conv::n> FormatConvertImpl(const FormatCountCapture& v,
-                                         ConversionSpec conv,
-                                         FormatSinkImpl* sink) {
+ArgConvertResult<FormatConversionCharSetInternal::n> FormatConvertImpl(
+    const FormatCountCapture& v, ConversionSpec conv, FormatSinkImpl* sink) {
   return FormatCountCaptureHelper::ConvertHelper(v, conv, sink);
 }
 
@@ -381,7 +395,8 @@ class FormatArgImpl {
   template <typename T>
   static bool Dispatch(Data arg, ConversionSpec spec, void* out) {
     // A `none` conv indicates that we want the `int` conversion.
-    if (ABSL_PREDICT_FALSE(spec.conversion_char() == ConversionChar::kNone)) {
+    if (ABSL_PREDICT_FALSE(spec.conversion_char() ==
+                           FormatConversionCharInternal::kNone)) {
       return ToInt<T>(arg, static_cast<int*>(out), std::is_integral<T>(),
                       std::is_enum<T>());
     }
diff --git a/absl/strings/internal/str_format/bind.h b/absl/strings/internal/str_format/bind.h
index d30fdf5078d4..05105d8d5c9c 100644
--- a/absl/strings/internal/str_format/bind.h
+++ b/absl/strings/internal/str_format/bind.h
@@ -189,9 +189,8 @@ class StreamedWrapper {
 
  private:
   template <typename S>
-  friend ConvertResult<Conv::s> FormatConvertImpl(const StreamedWrapper<S>& v,
-                                                  ConversionSpec conv,
-                                                  FormatSinkImpl* out);
+  friend ArgConvertResult<FormatConversionCharSetInternal::s> FormatConvertImpl(
+      const StreamedWrapper<S>& v, ConversionSpec conv, FormatSinkImpl* out);
   const T& v_;
 };
 
diff --git a/absl/strings/internal/str_format/checker.h b/absl/strings/internal/str_format/checker.h
index 8993a79b9580..73ef05ff44b3 100644
--- a/absl/strings/internal/str_format/checker.h
+++ b/absl/strings/internal/str_format/checker.h
@@ -25,10 +25,12 @@ constexpr bool AllOf(bool b, T... t) {
 }
 
 template <typename Arg>
-constexpr Conv ArgumentToConv() {
-  return decltype(str_format_internal::FormatConvertImpl(
-      std::declval<const Arg&>(), std::declval<const ConversionSpec&>(),
-      std::declval<FormatSinkImpl*>()))::kConv;
+constexpr FormatConversionCharSet ArgumentToConv() {
+  return absl::str_format_internal::ExtractCharSet(
+      decltype(str_format_internal::FormatConvertImpl(
+          std::declval<const Arg&>(),
+          std::declval<const FormatConversionSpecImpl&>(),
+          std::declval<FormatSinkImpl*>())){});
 }
 
 #ifdef ABSL_INTERNAL_ENABLE_FORMAT_CHECKER
@@ -39,14 +41,14 @@ constexpr bool ContainsChar(const char* chars, char c) {
 
 // A constexpr compatible list of Convs.
 struct ConvList {
-  const Conv* array;
+  const FormatConversionCharSet* array;
   int count;
 
   // We do the bound check here to avoid having to do it on the callers.
-  // Returning an empty Conv has the same effect as short circuiting because it
-  // will never match any conversion.
-  constexpr Conv operator[](int i) const {
-    return i < count ? array[i] : Conv{};
+  // Returning an empty FormatConversionCharSet has the same effect as
+  // short circuiting because it will never match any conversion.
+  constexpr FormatConversionCharSet operator[](int i) const {
+    return i < count ? array[i] : FormatConversionCharSet{};
   }
 
   constexpr ConvList without_front() const {
@@ -57,7 +59,7 @@ struct ConvList {
 template <size_t count>
 struct ConvListT {
   // Make sure the array has size > 0.
-  Conv list[count ? count : 1];
+  FormatConversionCharSet list[count ? count : 1];
 };
 
 constexpr char GetChar(string_view str, size_t index) {
@@ -310,7 +312,7 @@ class FormatParser {
   ConvList args_;
 };
 
-template <Conv... C>
+template <FormatConversionCharSet... C>
 constexpr bool ValidFormatImpl(string_view format) {
   return FormatParser(format,
                       {ConvListT<sizeof...(C)>{{C...}}.list, sizeof...(C)})
diff --git a/absl/strings/internal/str_format/extension.h b/absl/strings/internal/str_format/extension.h
index fb31a9db415e..f0cffe1e6d6c 100644
--- a/absl/strings/internal/str_format/extension.h
+++ b/absl/strings/internal/str_format/extension.h
@@ -30,7 +30,10 @@
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
+
 namespace str_format_internal {
+enum class FormatConversionCharSet : uint64_t;
+enum class FormatConversionChar : uint8_t;
 
 class FormatRawSinkImpl {
  public:
@@ -149,13 +152,39 @@ struct Flags {
   X_VAL(g) X_SEP X_VAL(G) X_SEP X_VAL(a) X_SEP X_VAL(A) X_SEP \
   /* misc */ \
   X_VAL(n) X_SEP X_VAL(p)
+// clang-format on
 
-enum class FormatConversionChar : uint8_t {
+// This type should not be referenced, it exists only to provide labels
+// internally that match the values declared in FormatConversionChar in
+// str_format.h. This is meant to allow internal libraries to use the same
+// declared interface type as the public interface
+// (absl::StrFormatConversionChar) while keeping the definition in a public
+// header.
+// Internal libraries should use the form
+// `FormatConversionCharInternal::c`, `FormatConversionCharInternal::kNone` for
+// comparisons.  Use in switch statements is not recommended due to a bug in how
+// gcc 4.9 -Wswitch handles declared but undefined enums.
+struct FormatConversionCharInternal {
+  FormatConversionCharInternal() = delete;
+
+ private:
+  // clang-format off
+  enum class Enum : uint8_t {
     c, C, s, S,              // text
     d, i, o, u, x, X,        // int
     f, F, e, E, g, G, a, A,  // float
     n, p,                    // misc
     kNone
+  };
+  // clang-format on
+ public:
+#define ABSL_INTERNAL_X_VAL(id)              \
+  static constexpr FormatConversionChar id = \
+      static_cast<FormatConversionChar>(Enum::id);
+  ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL, )
+#undef ABSL_INTERNAL_X_VAL
+  static constexpr FormatConversionChar kNone =
+      static_cast<FormatConversionChar>(Enum::kNone);
 };
 // clang-format on
 
@@ -163,56 +192,56 @@ inline FormatConversionChar FormatConversionCharFromChar(char c) {
   switch (c) {
 #define ABSL_INTERNAL_X_VAL(id) \
   case #id[0]:                  \
-    return FormatConversionChar::id;
+    return FormatConversionCharInternal::id;
     ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL, )
 #undef ABSL_INTERNAL_X_VAL
   }
-  return FormatConversionChar::kNone;
+  return FormatConversionCharInternal::kNone;
 }
 
 inline bool FormatConversionCharIsUpper(FormatConversionChar c) {
-  switch (c) {
-    case FormatConversionChar::X:
-    case FormatConversionChar::F:
-    case FormatConversionChar::E:
-    case FormatConversionChar::G:
-    case FormatConversionChar::A:
-      return true;
-    default:
-      return false;
+  if (c == FormatConversionCharInternal::X ||
+      c == FormatConversionCharInternal::F ||
+      c == FormatConversionCharInternal::E ||
+      c == FormatConversionCharInternal::G ||
+      c == FormatConversionCharInternal::A) {
+    return true;
+  } else {
+    return false;
   }
 }
 
 inline bool FormatConversionCharIsFloat(FormatConversionChar c) {
-  switch (c) {
-    case FormatConversionChar::a:
-    case FormatConversionChar::e:
-    case FormatConversionChar::f:
-    case FormatConversionChar::g:
-    case FormatConversionChar::A:
-    case FormatConversionChar::E:
-    case FormatConversionChar::F:
-    case FormatConversionChar::G:
-      return true;
-    default:
-      return false;
+  if (c == FormatConversionCharInternal::a ||
+      c == FormatConversionCharInternal::e ||
+      c == FormatConversionCharInternal::f ||
+      c == FormatConversionCharInternal::g ||
+      c == FormatConversionCharInternal::A ||
+      c == FormatConversionCharInternal::E ||
+      c == FormatConversionCharInternal::F ||
+      c == FormatConversionCharInternal::G) {
+    return true;
+  } else {
+    return false;
   }
 }
 
 inline char FormatConversionCharToChar(FormatConversionChar c) {
-  switch (c) {
-#define ABSL_INTERNAL_X_VAL(e)  \
-  case FormatConversionChar::e: \
+  if (c == FormatConversionCharInternal::kNone) {
+    return '\0';
+
+#define ABSL_INTERNAL_X_VAL(e)                       \
+  } else if (c == FormatConversionCharInternal::e) { \
     return #e[0];
 #define ABSL_INTERNAL_X_SEP
-    ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL,
-                                           ABSL_INTERNAL_X_SEP)
-    case FormatConversionChar::kNone:
-      return '\0';
+  ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_X_VAL,
+                                         ABSL_INTERNAL_X_SEP)
+  } else {
+    return '\0';
+  }
+
 #undef ABSL_INTERNAL_X_VAL
 #undef ABSL_INTERNAL_X_SEP
-  }
-  return '\0';
 }
 
 // The associated char.
@@ -224,7 +253,7 @@ inline std::ostream& operator<<(std::ostream& os, FormatConversionChar v) {
 
 struct FormatConversionSpecImplFriend;
 
-class FormatConversionSpec {
+class FormatConversionSpecImpl {
  public:
   // Width and precison are not specified, no flags are set.
   bool is_basic() const { return flags_.basic; }
@@ -237,7 +266,7 @@ class FormatConversionSpec {
   FormatConversionChar conversion_char() const {
     // Keep this field first in the struct . It generates better code when
     // accessing it when ConversionSpec is passed by value in registers.
-    static_assert(offsetof(FormatConversionSpec, conv_) == 0, "");
+    static_assert(offsetof(FormatConversionSpecImpl, conv_) == 0, "");
     return conv_;
   }
 
@@ -248,37 +277,62 @@ class FormatConversionSpec {
   // negative value.
   int precision() const { return precision_; }
 
+  template <typename T>
+  T Wrap() {
+    return T(*this);
+  }
+
  private:
   friend struct str_format_internal::FormatConversionSpecImplFriend;
-  FormatConversionChar conv_ = FormatConversionChar::kNone;
+  FormatConversionChar conv_ = FormatConversionCharInternal::kNone;
   Flags flags_;
   int width_;
   int precision_;
 };
 
 struct FormatConversionSpecImplFriend final {
-  static void SetFlags(Flags f, FormatConversionSpec* conv) {
+  static void SetFlags(Flags f, FormatConversionSpecImpl* conv) {
     conv->flags_ = f;
   }
   static void SetConversionChar(FormatConversionChar c,
-                                FormatConversionSpec* conv) {
+                                FormatConversionSpecImpl* conv) {
     conv->conv_ = c;
   }
-  static void SetWidth(int w, FormatConversionSpec* conv) { conv->width_ = w; }
-  static void SetPrecision(int p, FormatConversionSpec* conv) {
+  static void SetWidth(int w, FormatConversionSpecImpl* conv) {
+    conv->width_ = w;
+  }
+  static void SetPrecision(int p, FormatConversionSpecImpl* conv) {
     conv->precision_ = p;
   }
-  static std::string FlagsToString(const FormatConversionSpec& spec) {
+  static std::string FlagsToString(const FormatConversionSpecImpl& spec) {
     return spec.flags_.ToString();
   }
 };
 
-constexpr uint64_t FormatConversionCharToConvValue(char conv) {
+// Type safe OR operator.
+// We need this for two reasons:
+//  1. operator| on enums makes them decay to integers and the result is an
+//     integer. We need the result to stay as an enum.
+//  2. We use "enum class" which would not work even if we accepted the decay.
+constexpr FormatConversionCharSet FormatConversionCharSetUnion(
+    FormatConversionCharSet a) {
+  return a;
+}
+
+template <typename... CharSet>
+constexpr FormatConversionCharSet FormatConversionCharSetUnion(
+    FormatConversionCharSet a, CharSet... rest) {
+  return static_cast<FormatConversionCharSet>(
+      static_cast<uint64_t>(a) |
+      static_cast<uint64_t>(FormatConversionCharSetUnion(rest...)));
+}
+
+constexpr uint64_t FormatConversionCharToConvInt(char conv) {
   return
-#define ABSL_INTERNAL_CHAR_SET_CASE(c)                                       \
-  conv == #c[0]                                                              \
-      ? (uint64_t{1} << (1 + static_cast<uint8_t>(FormatConversionChar::c))) \
-      :
+#define ABSL_INTERNAL_CHAR_SET_CASE(c)                                        \
+  conv == #c[0] ? (uint64_t{1} << (1 + static_cast<uint8_t>(                  \
+                                           FormatConversionCharInternal::c))) \
+                :
       ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef ABSL_INTERNAL_CHAR_SET_CASE
                   conv == '*'
@@ -286,20 +340,31 @@ constexpr uint64_t FormatConversionCharToConvValue(char conv) {
           : 0;
 }
 
-enum class FormatConversionCharSet : uint64_t {
-#define ABSL_INTERNAL_CHAR_SET_CASE(c) \
-  c = FormatConversionCharToConvValue(#c[0]),
+constexpr FormatConversionCharSet FormatConversionCharToConvValue(char conv) {
+  return static_cast<FormatConversionCharSet>(
+      FormatConversionCharToConvInt(conv));
+}
+
+struct FormatConversionCharSetInternal {
+#define ABSL_INTERNAL_CHAR_SET_CASE(c)         \
+  static constexpr FormatConversionCharSet c = \
+      FormatConversionCharToConvValue(#c[0]);
   ABSL_INTERNAL_CONVERSION_CHARS_EXPAND_(ABSL_INTERNAL_CHAR_SET_CASE, )
 #undef ABSL_INTERNAL_CHAR_SET_CASE
 
   // Used for width/precision '*' specification.
-  kStar = FormatConversionCharToConvValue('*'),
-  // Some predefined values:
-  kIntegral = d | i | u | o | x | X,
-  kFloating = a | e | f | g | A | E | F | G,
-  kNumeric = kIntegral | kFloating,
-  kString = s,
-  kPointer = p
+  static constexpr FormatConversionCharSet kStar =
+      FormatConversionCharToConvValue('*');
+
+  // Some predefined values (TODO(matthewbr), delete any that are unused).
+  static constexpr FormatConversionCharSet kIntegral =
+      FormatConversionCharSetUnion(d, i, u, o, x, X);
+  static constexpr FormatConversionCharSet kFloating =
+      FormatConversionCharSetUnion(a, e, f, g, A, E, F, G);
+  static constexpr FormatConversionCharSet kNumeric =
+      FormatConversionCharSetUnion(kIntegral, kFloating);
+  static constexpr FormatConversionCharSet kString = s;
+  static constexpr FormatConversionCharSet kPointer = p;
 };
 
 // Type safe OR operator.
@@ -309,8 +374,7 @@ enum class FormatConversionCharSet : uint64_t {
 //  2. We use "enum class" which would not work even if we accepted the decay.
 constexpr FormatConversionCharSet operator|(FormatConversionCharSet a,
                                             FormatConversionCharSet b) {
-  return FormatConversionCharSet(static_cast<uint64_t>(a) |
-                                 static_cast<uint64_t>(b));
+  return FormatConversionCharSetUnion(a, b);
 }
 
 // Overloaded conversion functions to support absl::ParsedFormat.
@@ -331,7 +395,8 @@ void ToFormatConversionCharSet(T) = delete;
 
 // Checks whether `c` exists in `set`.
 constexpr bool Contains(FormatConversionCharSet set, char c) {
-  return (static_cast<uint64_t>(set) & FormatConversionCharToConvValue(c)) != 0;
+  return (static_cast<uint64_t>(set) &
+          static_cast<uint64_t>(FormatConversionCharToConvValue(c))) != 0;
 }
 
 // Checks whether all the characters in `c` are contained in `set`
@@ -341,19 +406,6 @@ constexpr bool Contains(FormatConversionCharSet set,
          static_cast<uint64_t>(c);
 }
 
-// Return type of the AbslFormatConvert() functions.
-// The FormatConversionCharSet template parameter is used to inform the
-// framework of what conversion characters are supported by that
-// AbslFormatConvert routine.
-template <FormatConversionCharSet C>
-struct FormatConvertResult {
-  static constexpr FormatConversionCharSet kConv = C;
-  bool value;
-};
-
-template <FormatConversionCharSet C>
-constexpr FormatConversionCharSet FormatConvertResult<C>::kConv;
-
 // Return capacity - used, clipped to a minimum of 0.
 inline size_t Excess(size_t used, size_t capacity) {
   return used < capacity ? capacity - used : 0;
@@ -361,10 +413,85 @@ inline size_t Excess(size_t used, size_t capacity) {
 
 // Type alias for use during migration.
 using ConversionChar = FormatConversionChar;
-using ConversionSpec = FormatConversionSpec;
+using ConversionSpec = FormatConversionSpecImpl;
 using Conv = FormatConversionCharSet;
-template <FormatConversionCharSet C>
-using ConvertResult = FormatConvertResult<C>;
+
+class FormatConversionSpec {
+ public:
+  // Width and precison are not specified, no flags are set.
+  bool is_basic() const { return impl_.is_basic(); }
+  bool has_left_flag() const { return impl_.has_left_flag(); }
+  bool has_show_pos_flag() const { return impl_.has_show_pos_flag(); }
+  bool has_sign_col_flag() const { return impl_.has_sign_col_flag(); }
+  bool has_alt_flag() const { return impl_.has_alt_flag(); }
+  bool has_zero_flag() const { return impl_.has_zero_flag(); }
+
+  FormatConversionChar conversion_char() const {
+    return impl_.conversion_char();
+  }
+
+  // Returns the specified width. If width is unspecfied, it returns a negative
+  // value.
+  int width() const { return impl_.width(); }
+  // Returns the specified precision. If precision is unspecfied, it returns a
+  // negative value.
+  int precision() const { return impl_.precision(); }
+
+ private:
+  explicit FormatConversionSpec(
+      str_format_internal::FormatConversionSpecImpl impl)
+      : impl_(impl) {}
+
+  friend str_format_internal::FormatConversionSpecImpl;
+
+  absl::str_format_internal::FormatConversionSpecImpl impl_;
+};
+
+// clang-format off
+enum class FormatConversionChar : uint8_t {
+  c, C, s, S,              // text
+  d, i, o, u, x, X,        // int
+  f, F, e, E, g, G, a, A,  // float
+  n, p                     // misc
+};
+// clang-format on
+
+enum class FormatConversionCharSet : uint64_t {
+  // text
+  c = str_format_internal::FormatConversionCharToConvInt('c'),
+  C = str_format_internal::FormatConversionCharToConvInt('C'),
+  s = str_format_internal::FormatConversionCharToConvInt('s'),
+  S = str_format_internal::FormatConversionCharToConvInt('S'),
+  // integer
+  d = str_format_internal::FormatConversionCharToConvInt('d'),
+  i = str_format_internal::FormatConversionCharToConvInt('i'),
+  o = str_format_internal::FormatConversionCharToConvInt('o'),
+  u = str_format_internal::FormatConversionCharToConvInt('u'),
+  x = str_format_internal::FormatConversionCharToConvInt('x'),
+  X = str_format_internal::FormatConversionCharToConvInt('X'),
+  // Float
+  f = str_format_internal::FormatConversionCharToConvInt('f'),
+  F = str_format_internal::FormatConversionCharToConvInt('F'),
+  e = str_format_internal::FormatConversionCharToConvInt('e'),
+  E = str_format_internal::FormatConversionCharToConvInt('E'),
+  g = str_format_internal::FormatConversionCharToConvInt('g'),
+  G = str_format_internal::FormatConversionCharToConvInt('G'),
+  a = str_format_internal::FormatConversionCharToConvInt('a'),
+  A = str_format_internal::FormatConversionCharToConvInt('A'),
+  // misc
+  n = str_format_internal::FormatConversionCharToConvInt('n'),
+  p = str_format_internal::FormatConversionCharToConvInt('p'),
+
+  // Used for width/precision '*' specification.
+  kStar = str_format_internal::FormatConversionCharToConvInt('*'),
+
+  // Some predefined values:
+  kIntegral = d | i | u | o | x | X,
+  kFloating = a | e | f | g | A | E | F | G,
+  kNumeric = kIntegral | kFloating,
+  kString = s,
+  kPointer = p,
+};
 
 }  // namespace str_format_internal
 
diff --git a/absl/strings/internal/str_format/extension_test.cc b/absl/strings/internal/str_format/extension_test.cc
index 561eaa36b845..0a023f9c0333 100644
--- a/absl/strings/internal/str_format/extension_test.cc
+++ b/absl/strings/internal/str_format/extension_test.cc
@@ -80,13 +80,4 @@ TEST(FormatExtensionTest, SinkAppendChars) {
     EXPECT_EQ(actual, expected);
   }
 }
-
-TEST(FormatExtensionTest, CustomSink) {
-  my_namespace::UserDefinedType sink;
-  absl::Format(&sink, "There were %04d little %s.", 3, "pigs");
-  EXPECT_EQ("There were 0003 little pigs.", sink.Value());
-  absl::Format(&sink, "And %-3llx bad wolf!", 1);
-  EXPECT_EQ("There were 0003 little pigs.And 1   bad wolf!", sink.Value());
-}
-
 }  // namespace
diff --git a/absl/strings/internal/str_format/float_conversion.cc b/absl/strings/internal/str_format/float_conversion.cc
index d5a1ee40bc67..d6858cfffd95 100644
--- a/absl/strings/internal/str_format/float_conversion.cc
+++ b/absl/strings/internal/str_format/float_conversion.cc
@@ -403,70 +403,62 @@ bool FloatToSink(const Float v, const ConversionSpec &conv,
 
   Buffer buffer;
 
-  switch (conv.conversion_char()) {
-    case ConversionChar::f:
-    case ConversionChar::F:
-      if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer,
-                                             nullptr)) {
-        return FallbackToSnprintf(v, conv, sink);
-      }
-      if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
-      break;
+  FormatConversionChar c = conv.conversion_char();
 
-    case ConversionChar::e:
-    case ConversionChar::E:
-      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
-                                                 &exp)) {
-        return FallbackToSnprintf(v, conv, sink);
+  if (c == FormatConversionCharInternal::f ||
+      c == FormatConversionCharInternal::F) {
+    if (!FloatToBuffer<FormatStyle::Fixed>(decomposed, precision, &buffer,
+                                           nullptr)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+  } else if (c == FormatConversionCharInternal::e ||
+             c == FormatConversionCharInternal::E) {
+    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                               &exp)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+    PrintExponent(
+        exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
+        &buffer);
+  } else if (c == FormatConversionCharInternal::g ||
+             c == FormatConversionCharInternal::G) {
+    precision = std::max(0, precision - 1);
+    if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
+                                               &exp)) {
+      return FallbackToSnprintf(v, conv, sink);
+    }
+    if (precision + 1 > exp && exp >= -4) {
+      if (exp < 0) {
+        // Have 1.23456, needs 0.00123456
+        // Move the first digit
+        buffer.begin[1] = *buffer.begin;
+        // Add some zeros
+        for (; exp < -1; ++exp) *buffer.begin-- = '0';
+        *buffer.begin-- = '.';
+        *buffer.begin = '0';
+      } else if (exp > 0) {
+        // Have 1.23456, needs 1234.56
+        // Move the '.' exp positions to the right.
+        std::rotate(buffer.begin + 1, buffer.begin + 2, buffer.begin + exp + 2);
       }
-      if (!conv.has_alt_flag() && buffer.back() == '.') buffer.pop_back();
+      exp = 0;
+    }
+    if (!conv.has_alt_flag()) {
+      while (buffer.back() == '0') buffer.pop_back();
+      if (buffer.back() == '.') buffer.pop_back();
+    }
+    if (exp) {
       PrintExponent(
           exp, FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
           &buffer);
-      break;
-
-    case ConversionChar::g:
-    case ConversionChar::G:
-      precision = std::max(0, precision - 1);
-      if (!FloatToBuffer<FormatStyle::Precision>(decomposed, precision, &buffer,
-                                                 &exp)) {
-        return FallbackToSnprintf(v, conv, sink);
-      }
-      if (precision + 1 > exp && exp >= -4) {
-        if (exp < 0) {
-          // Have 1.23456, needs 0.00123456
-          // Move the first digit
-          buffer.begin[1] = *buffer.begin;
-          // Add some zeros
-          for (; exp < -1; ++exp) *buffer.begin-- = '0';
-          *buffer.begin-- = '.';
-          *buffer.begin = '0';
-        } else if (exp > 0) {
-          // Have 1.23456, needs 1234.56
-          // Move the '.' exp positions to the right.
-          std::rotate(buffer.begin + 1, buffer.begin + 2,
-                      buffer.begin + exp + 2);
-        }
-        exp = 0;
-      }
-      if (!conv.has_alt_flag()) {
-        while (buffer.back() == '0') buffer.pop_back();
-        if (buffer.back() == '.') buffer.pop_back();
-      }
-      if (exp) {
-        PrintExponent(
-            exp,
-            FormatConversionCharIsUpper(conv.conversion_char()) ? 'E' : 'e',
-            &buffer);
-      }
-      break;
-
-    case ConversionChar::a:
-    case ConversionChar::A:
-      return FallbackToSnprintf(v, conv, sink);
-
-    default:
-      return false;
+    }
+  } else if (c == FormatConversionCharInternal::a ||
+             c == FormatConversionCharInternal::A) {
+    return FallbackToSnprintf(v, conv, sink);
+  } else {
+    return false;
   }
 
   WriteBufferToSink(sign_char,
diff --git a/absl/strings/internal/str_format/parser.cc b/absl/strings/internal/str_format/parser.cc
index aab68db94bca..61132739b875 100644
--- a/absl/strings/internal/str_format/parser.cc
+++ b/absl/strings/internal/str_format/parser.cc
@@ -17,7 +17,7 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace str_format_internal {
 
-using CC = ConversionChar;
+using CC = FormatConversionCharInternal;
 using LM = LengthMod;
 
 ABSL_CONST_INIT const ConvTag kTags[256] = {
@@ -296,15 +296,17 @@ struct ParsedFormatBase::ParsedFormatConsumer {
   char* data_pos;
 };
 
-ParsedFormatBase::ParsedFormatBase(string_view format, bool allow_ignored,
-                                   std::initializer_list<Conv> convs)
+ParsedFormatBase::ParsedFormatBase(
+    string_view format, bool allow_ignored,
+    std::initializer_list<FormatConversionCharSet> convs)
     : data_(format.empty() ? nullptr : new char[format.size()]) {
   has_error_ = !ParseFormatString(format, ParsedFormatConsumer(this)) ||
                !MatchesConversions(allow_ignored, convs);
 }
 
 bool ParsedFormatBase::MatchesConversions(
-    bool allow_ignored, std::initializer_list<Conv> convs) const {
+    bool allow_ignored,
+    std::initializer_list<FormatConversionCharSet> convs) const {
   std::unordered_set<int> used;
   auto add_if_valid_conv = [&](int pos, char c) {
       if (static_cast<size_t>(pos) > convs.size() ||
diff --git a/absl/strings/internal/str_format/parser.h b/absl/strings/internal/str_format/parser.h
index 7d966517256b..fd2dc9704507 100644
--- a/absl/strings/internal/str_format/parser.h
+++ b/absl/strings/internal/str_format/parser.h
@@ -67,7 +67,7 @@ struct UnboundConversion {
 
   Flags flags;
   LengthMod length_mod = LengthMod::none;
-  ConversionChar conv = FormatConversionChar::kNone;
+  FormatConversionChar conv = FormatConversionCharInternal::kNone;
 };
 
 // Consume conversion spec prefix (not including '%') of [p, end) if valid.
@@ -186,8 +186,9 @@ constexpr bool EnsureConstexpr(string_view s) {
 
 class ParsedFormatBase {
  public:
-  explicit ParsedFormatBase(string_view format, bool allow_ignored,
-                            std::initializer_list<Conv> convs);
+  explicit ParsedFormatBase(
+      string_view format, bool allow_ignored,
+      std::initializer_list<FormatConversionCharSet> convs);
 
   ParsedFormatBase(const ParsedFormatBase& other) { *this = other; }
 
@@ -234,8 +235,9 @@ class ParsedFormatBase {
  private:
   // Returns whether the conversions match and if !allow_ignored it verifies
   // that all conversions are used by the format.
-  bool MatchesConversions(bool allow_ignored,
-                          std::initializer_list<Conv> convs) const;
+  bool MatchesConversions(
+      bool allow_ignored,
+      std::initializer_list<FormatConversionCharSet> convs) const;
 
   struct ParsedFormatConsumer;
 
diff --git a/absl/strings/internal/str_format/parser_test.cc b/absl/strings/internal/str_format/parser_test.cc
index 51eb53f5a4cf..26f5bec6bcff 100644
--- a/absl/strings/internal/str_format/parser_test.cc
+++ b/absl/strings/internal/str_format/parser_test.cc
@@ -46,13 +46,13 @@ TEST(ConversionCharTest, Names) {
   };
   // clang-format off
   const Expectation kExpect[] = {
-#define X(c) {ConversionChar::c, #c[0]}
+#define X(c) {FormatConversionCharInternal::c, #c[0]}
     X(c), X(C), X(s), X(S),                          // text
     X(d), X(i), X(o), X(u), X(x), X(X),              // int
     X(f), X(F), X(e), X(E), X(g), X(G), X(a), X(A),  // float
     X(n), X(p),                                      // misc
 #undef X
-    {ConversionChar::kNone, '\0'},
+    {FormatConversionCharInternal::kNone, '\0'},
   };
   // clang-format on
   for (auto e : kExpect) {
@@ -349,7 +349,8 @@ TEST_F(ParsedFormatTest, ValueSemantics) {
   ParsedFormatBase p2 = p1;  // copy construct (empty)
   EXPECT_EQ(SummarizeParsedFormat(p1), SummarizeParsedFormat(p2));
 
-  p1 = ParsedFormatBase("hello%s", true, {Conv::s});  // move assign
+  p1 = ParsedFormatBase("hello%s", true,
+                        {FormatConversionCharSetInternal::s});  // move assign
   EXPECT_EQ("[hello]{s:1$s}", SummarizeParsedFormat(p1));
 
   ParsedFormatBase p3 = p1;  // copy construct (nonempty)
@@ -377,9 +378,9 @@ TEST_F(ParsedFormatTest, Parsing) {
   const ExpectParse kExpect[] = {
       {"", {}, ""},
       {"ab", {}, "[ab]"},
-      {"a%d", {Conv::d}, "[a]{d:1$d}"},
-      {"a%+d", {Conv::d}, "[a]{+d:1$d}"},
-      {"a% d", {Conv::d}, "[a]{ d:1$d}"},
+      {"a%d", {FormatConversionCharSetInternal::d}, "[a]{d:1$d}"},
+      {"a%+d", {FormatConversionCharSetInternal::d}, "[a]{+d:1$d}"},
+      {"a% d", {FormatConversionCharSetInternal::d}, "[a]{ d:1$d}"},
       {"a%b %d", {}, "[a]!"},  // stop after error
   };
   for (const auto& e : kExpect) {
@@ -391,13 +392,13 @@ TEST_F(ParsedFormatTest, Parsing) {
 
 TEST_F(ParsedFormatTest, ParsingFlagOrder) {
   const ExpectParse kExpect[] = {
-      {"a%+ 0d", {Conv::d}, "[a]{+ 0d:1$d}"},
-      {"a%+0 d", {Conv::d}, "[a]{+0 d:1$d}"},
-      {"a%0+ d", {Conv::d}, "[a]{0+ d:1$d}"},
-      {"a% +0d", {Conv::d}, "[a]{ +0d:1$d}"},
-      {"a%0 +d", {Conv::d}, "[a]{0 +d:1$d}"},
-      {"a% 0+d", {Conv::d}, "[a]{ 0+d:1$d}"},
-      {"a%+   0+d", {Conv::d}, "[a]{+   0+d:1$d}"},
+      {"a%+ 0d", {FormatConversionCharSetInternal::d}, "[a]{+ 0d:1$d}"},
+      {"a%+0 d", {FormatConversionCharSetInternal::d}, "[a]{+0 d:1$d}"},
+      {"a%0+ d", {FormatConversionCharSetInternal::d}, "[a]{0+ d:1$d}"},
+      {"a% +0d", {FormatConversionCharSetInternal::d}, "[a]{ +0d:1$d}"},
+      {"a%0 +d", {FormatConversionCharSetInternal::d}, "[a]{0 +d:1$d}"},
+      {"a% 0+d", {FormatConversionCharSetInternal::d}, "[a]{ 0+d:1$d}"},
+      {"a%+   0+d", {FormatConversionCharSetInternal::d}, "[a]{+   0+d:1$d}"},
   };
   for (const auto& e : kExpect) {
     SCOPED_TRACE(e.in);
diff --git a/absl/strings/str_format_test.cc b/absl/strings/str_format_test.cc
index f0d1f0ad28a7..160f4c6186f5 100644
--- a/absl/strings/str_format_test.cc
+++ b/absl/strings/str_format_test.cc
@@ -450,7 +450,7 @@ struct SummarizeConsumer {
     if (conv.precision.is_from_arg()) {
       *out += "." + std::to_string(conv.precision.get_from_arg()) + "$*";
     }
-    *out += FormatConversionCharToChar(conv.conv);
+    *out += str_format_internal::FormatConversionCharToChar(conv.conv);
     *out += "}";
     return true;
   }
diff --git a/absl/synchronization/internal/create_thread_identity.cc b/absl/synchronization/internal/create_thread_identity.cc
index fa0070a9fc99..53a71b342b9f 100644
--- a/absl/synchronization/internal/create_thread_identity.cc
+++ b/absl/synchronization/internal/create_thread_identity.cc
@@ -32,9 +32,9 @@ namespace synchronization_internal {
 
 // ThreadIdentity storage is persistent, we maintain a free-list of previously
 // released ThreadIdentity objects.
-static base_internal::SpinLock freelist_lock(
-    base_internal::kLinkerInitialized);
-static base_internal::ThreadIdentity* thread_identity_freelist;
+ABSL_CONST_INIT static base_internal::SpinLock freelist_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static base_internal::ThreadIdentity* thread_identity_freelist;
 
 // A per-thread destructor for reclaiming associated ThreadIdentity objects.
 // Since we must preserve their storage we cache them for re-use.
diff --git a/absl/synchronization/internal/graphcycles.cc b/absl/synchronization/internal/graphcycles.cc
index 6a2bcdf68175..19f9aab5b1a5 100644
--- a/absl/synchronization/internal/graphcycles.cc
+++ b/absl/synchronization/internal/graphcycles.cc
@@ -51,9 +51,9 @@ namespace {
 
 // Avoid LowLevelAlloc's default arena since it calls malloc hooks in
 // which people are doing things like acquiring Mutexes.
-static absl::base_internal::SpinLock arena_mu(
-    absl::base_internal::kLinkerInitialized);
-static base_internal::LowLevelAlloc::Arena* arena;
+ABSL_CONST_INIT static absl::base_internal::SpinLock arena_mu(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static base_internal::LowLevelAlloc::Arena* arena;
 
 static void InitArenaIfNecessary() {
   arena_mu.Lock();
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 8cda5a1ce093..1f8a696e08ee 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -207,12 +207,12 @@ static void AtomicClearBits(std::atomic<intptr_t>* pv, intptr_t bits,
 //------------------------------------------------------------------
 
 // Data for doing deadlock detection.
-static absl::base_internal::SpinLock deadlock_graph_mu(
-    absl::base_internal::kLinkerInitialized);
+ABSL_CONST_INIT static absl::base_internal::SpinLock deadlock_graph_mu(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
 
-// graph used to detect deadlocks.
-static GraphCycles *deadlock_graph ABSL_GUARDED_BY(deadlock_graph_mu)
-    ABSL_PT_GUARDED_BY(deadlock_graph_mu);
+// Graph used to detect deadlocks.
+ABSL_CONST_INIT static GraphCycles *deadlock_graph
+    ABSL_GUARDED_BY(deadlock_graph_mu) ABSL_PT_GUARDED_BY(deadlock_graph_mu);
 
 //------------------------------------------------------------------
 // An event mechanism for debugging mutex use.
@@ -273,13 +273,12 @@ static const struct {
     {0, "SignalAll on "},
 };
 
-static absl::base_internal::SpinLock synch_event_mu(
-    absl::base_internal::kLinkerInitialized);
-// protects synch_event
+ABSL_CONST_INIT static absl::base_internal::SpinLock synch_event_mu(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
 
 // Hash table size; should be prime > 2.
 // Can't be too small, as it's used for deadlock detection information.
-static const uint32_t kNSynchEvent = 1031;
+static constexpr uint32_t kNSynchEvent = 1031;
 
 static struct SynchEvent {     // this is a trivial hash table for the events
   // struct is freed when refcount reaches 0
diff --git a/absl/time/clock.cc b/absl/time/clock.cc
index 3b895c38e968..e5c423c7e4fc 100644
--- a/absl/time/clock.cc
+++ b/absl/time/clock.cc
@@ -226,9 +226,9 @@ static_assert(((kMinNSBetweenSamples << (kScale + 1)) >> (kScale + 1)) ==
 
 // A reader-writer lock protecting the static locations below.
 // See SeqAcquire() and SeqRelease() above.
-static absl::base_internal::SpinLock lock(
-    absl::base_internal::kLinkerInitialized);
-static std::atomic<uint64_t> seq(0);
+ABSL_CONST_INIT static absl::base_internal::SpinLock lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+ABSL_CONST_INIT static std::atomic<uint64_t> seq(0);
 
 // data from a sample of the kernel's time value
 struct TimeSampleAtomic {
diff --git a/absl/time/internal/cctz/src/cctz_benchmark.cc b/absl/time/internal/cctz/src/cctz_benchmark.cc
index d30a644e09d7..a402760d19e0 100644
--- a/absl/time/internal/cctz/src/cctz_benchmark.cc
+++ b/absl/time/internal/cctz/src/cctz_benchmark.cc
@@ -280,6 +280,7 @@ const char* const kTimeZoneNames[] = {"Africa/Abidjan",
                                       "America/North_Dakota/Beulah",
                                       "America/North_Dakota/Center",
                                       "America/North_Dakota/New_Salem",
+                                      "America/Nuuk",
                                       "America/Ojinaga",
                                       "America/Panama",
                                       "America/Pangnirtung",
diff --git a/absl/time/internal/cctz/src/time_zone_lookup_test.cc b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
index 35911ce56448..0b0c1a3b72c6 100644
--- a/absl/time/internal/cctz/src/time_zone_lookup_test.cc
+++ b/absl/time/internal/cctz/src/time_zone_lookup_test.cc
@@ -211,6 +211,7 @@ const char* const kTimeZoneNames[] = {"Africa/Abidjan",
                                       "America/North_Dakota/Beulah",
                                       "America/North_Dakota/Center",
                                       "America/North_Dakota/New_Salem",
+                                      "America/Nuuk",
                                       "America/Ojinaga",
                                       "America/Panama",
                                       "America/Pangnirtung",