Export of internal Abseil changes

--
30e5e00a54cabc50118a3e1055826ea02a0d32e4 by Gennadiy Rozental <rogeeff@google.com>:

Move flag help into flag_cold section.

To facilitate this we set flag help not in a constructor, but during flag registration. This allows us to place flag name as static variable inside non constexpr lambda and invoke it immediately in FlagRegistrar argument location.

PiperOrigin-RevId: 312432625

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efd91b05152b68df648cff5ba38e9669a817c12f by Gennadiy Rozental <rogeeff@google.com>:

Make CommandLineFlag public.

PiperOrigin-RevId: 312404666

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dc7f5fb73487766fa8a76d6b97d28116e5334445 by Mark Barolak <mbar@google.com>:

Internal change.

PiperOrigin-RevId: 312297164
GitOrigin-RevId: 30e5e00a54cabc50118a3e1055826ea02a0d32e4
Change-Id: Ic46ab011bb804645264572caddff0becba5f9170

1 files changed, 42 insertions, 49 deletions

diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index ca7d581f..f84853ea 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -37,7 +37,6 @@
 #include "absl/base/config.h"
 #include "absl/flags/config.h"
 #include "absl/flags/declare.h"
-#include "absl/flags/internal/commandlineflag.h"
 #include "absl/flags/internal/flag.h"
 #include "absl/flags/internal/registry.h"
 #include "absl/flags/marshalling.h"
@@ -265,27 +264,29 @@ ABSL_NAMESPACE_END
 // -----------------------------------------------------------------------------
 
 // ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_NAMES
+#if !defined(_MSC_VER) || defined(__clang__)
+#define ABSL_FLAG_IMPL_FLAG_PTR(flag) &flag
+#define ABSL_FLAG_IMPL_HELP_ARG(name)                      \
+  absl::flags_internal::HelpArg<AbslFlagHelpGenFor##name>( \
+      FLAGS_help_storage_##name)
+#define ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name) \
+  absl::flags_internal::DefaultArg<Type, AbslFlagDefaultGenFor##name>(0)
+#else
+#define ABSL_FLAG_IMPL_FLAG_PTR(flag) flag.GetImpl()
+#define ABSL_FLAG_IMPL_HELP_ARG(name) &AbslFlagHelpGenFor##name::NonConst
+#define ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name) &AbslFlagDefaultGenFor##name::Gen
+#endif
 
 #if ABSL_FLAGS_STRIP_NAMES
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) ""
 #define ABSL_FLAG_IMPL_FILENAME() ""
-#if !defined(_MSC_VER) || defined(__clang__)
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, false>(&flag)
-#else
-#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, false>(flag.GetImpl())
-#endif
+  absl::flags_internal::FlagRegistrar<T, false>(ABSL_FLAG_IMPL_FLAG_PTR(flag))
 #else
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) txt
 #define ABSL_FLAG_IMPL_FILENAME() __FILE__
-#if !defined(_MSC_VER) || defined(__clang__)
-#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, true>(&flag)
-#else
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
-  absl::flags_internal::FlagRegistrar<T, true>(flag.GetImpl())
-#endif
+  absl::flags_internal::FlagRegistrar<T, true>(ABSL_FLAG_IMPL_FLAG_PTR(flag))
 #endif
 
 // ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_HELP
@@ -301,15 +302,24 @@ ABSL_NAMESPACE_END
 // between the two via the call to HelpArg in absl::Flag instantiation below.
 // If help message expression is constexpr evaluable compiler will optimize
 // away this whole struct.
-#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt)                     \
-  struct AbslFlagHelpGenFor##name {                                        \
-    template <typename T = void>                                           \
-    static constexpr const char* Const() {                                 \
-      return absl::flags_internal::HelpConstexprWrap(                      \
-          ABSL_FLAG_IMPL_FLAGHELP(txt));                                   \
-    }                                                                      \
-    static std::string NonConst() { return ABSL_FLAG_IMPL_FLAGHELP(txt); } \
-  }
+// TODO(rogeeff): place these generated structs into local namespace and apply
+// ABSL_INTERNAL_UNIQUE_SHORT_NAME.
+// TODO(rogeeff): Apply __attribute__((nodebug)) to FLAGS_help_storage_##name
+#define ABSL_FLAG_IMPL_DECLARE_HELP_WRAPPER(name, txt)                       \
+  struct AbslFlagHelpGenFor##name {                                          \
+    /* The expression is run in the caller as part of the   */               \
+    /* default value argument. That keeps temporaries alive */               \
+    /* long enough for NonConst to work correctly.          */               \
+    static constexpr absl::string_view Value(                                \
+        absl::string_view v = ABSL_FLAG_IMPL_FLAGHELP(txt)) {                \
+      return v;                                                              \
+    }                                                                        \
+    static std::string NonConst() { return std::string(Value()); }           \
+  };                                                                         \
+  constexpr auto FLAGS_help_storage_##name ABSL_INTERNAL_UNIQUE_SMALL_NAME() \
+      ABSL_ATTRIBUTE_SECTION_VARIABLE(flags_help_cold) =                     \
+          absl::flags_internal::HelpStringAsArray<AbslFlagHelpGenFor##name>( \
+              0);
 
 #define ABSL_FLAG_IMPL_DECLARE_DEF_VAL_WRAPPER(name, Type, default_value)     \
   struct AbslFlagDefaultGenFor##name {                                        \
@@ -317,40 +327,23 @@ ABSL_NAMESPACE_END
     static void Gen(void* p) {                                                \
       new (p) Type(AbslFlagDefaultGenFor##name{}.value);                      \
     }                                                                         \
-  }
+  };
 
 // ABSL_FLAG_IMPL
 //
 // Note: Name of registrar object is not arbitrary. It is used to "grab"
 // global name for FLAGS_no<flag_name> symbol, thus preventing the possibility
 // of defining two flags with names foo and nofoo.
-#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),              \
-      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, &AbslFlagDefaultGenFor##name::Gen}; \
-  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_FLAG_IMPL_HELP_ARG(name), ABSL_FLAG_IMPL_DEFAULT_ARG(Type, name)}; \
+  extern absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name;             \
+  absl::flags_internal::FlagRegistrarEmpty FLAGS_no##name =                   \
       ABSL_FLAG_IMPL_REGISTRAR(Type, FLAGS_##name)
-#endif
 
 // ABSL_RETIRED_FLAG
 //