libstdc++: Add macros for the inline namespace std::_V2

Use macros to open and close the inline namespace _V2 that is used for
ABI versioning of individual components such as chrono::system_clock.

This allows the namespace to be hidden in the docs generated by Doxygen,
so that we document std::foo instead of std::_V2::foo.

This also makes it easy to remove that namespace entirely for the
gnu-versioned-namespace build, where everything is already versioned as
std::__8 and there are no backwards compatibility guarantees.

libstdc++-v3/ChangeLog:

	* doc/doxygen/user.cfg.in (PREDEFINED): Expand new macros to
	nothing.
	* include/bits/c++config (_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE)
	(_GLIBCXX_END_INLINE_ABI_NAMESPACE): Define new macros.
	* include/bits/algorithmfwd.h (_V2::__rotate): Use new macros
	for the namespace.
	* include/bits/chrono.h (chrono::_V2::system_clock): Likewise.
	* include/bits/stl_algo.h (_V2::__rotate): Likewise.
	* include/std/condition_variable (_V2::condition_variable_any):
	Likewise.
	* include/std/system_error (_V2::error_category): Likewise.

7 files changed, 28 insertions, 18 deletions

diff --git a/libstdc++-v3/doc/doxygen/user.cfg.in b/libstdc++-v3/doc/doxygen/user.cfg.in
index b9babc3..2dbed72 100644
--- a/libstdc++-v3/doc/doxygen/user.cfg.in
+++ b/libstdc++-v3/doc/doxygen/user.cfg.in
@@ -2347,6 +2347,8 @@ PREDEFINED             = __cplusplus=202002L \
                          "_GLIBCXX_END_NAMESPACE_CONTAINER= " \
                          "_GLIBCXX_END_NAMESPACE_CXX11= " \
                          "_GLIBCXX_END_NAMESPACE_LDBL= " \
+			 "-D_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(X)= " \
+			 "-D_GLIBCXX_END_INLINE_ABI_NAMESPACE(X)= " \
                          "_GLIBCXX_TEMPLATE_ARGS=...  " \
                          "_GLIBCXX_DEPRECATED= " \
                          "_GLIBCXX_DEPRECATED_SUGGEST(E)= " \
diff --git a/libstdc++-v3/include/bits/algorithmfwd.h b/libstdc++-v3/include/bits/algorithmfwd.h
index 5271a90..aacc34e 100644
--- a/libstdc++-v3/include/bits/algorithmfwd.h
+++ b/libstdc++-v3/include/bits/algorithmfwd.h
@@ -601,13 +601,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     _OIter
     reverse_copy(_BIter, _BIter, _OIter);
 
-  inline namespace _V2
-  {
-    template<typename _FIter>
-      _GLIBCXX20_CONSTEXPR
-      _FIter
-      rotate(_FIter, _FIter, _FIter);
-  }
+_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
+
+  template<typename _FIter>
+    _GLIBCXX20_CONSTEXPR
+    _FIter
+    rotate(_FIter, _FIter, _FIter);
+
+_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
   template<typename _FIter, typename _OIter>
     _GLIBCXX20_CONSTEXPR
diff --git a/libstdc++-v3/include/bits/c++config b/libstdc++-v3/include/bits/c++config
index 2798b97..150b0bc 100644
--- a/libstdc++-v3/include/bits/c++config
+++ b/libstdc++-v3/include/bits/c++config
@@ -345,13 +345,16 @@ namespace __gnu_cxx
 # define _GLIBCXX_DEFAULT_ABI_TAG
 #endif
 
-// Defined if inline namespaces are used for versioning.
+// Non-zero if inline namespaces are used for versioning the entire library.
 #define _GLIBCXX_INLINE_VERSION 
 
-// Inline namespace for symbol versioning.
 #if _GLIBCXX_INLINE_VERSION
+// Inline namespace for symbol versioning of (nearly) everything in std.
 # define _GLIBCXX_BEGIN_NAMESPACE_VERSION namespace __8 {
 # define _GLIBCXX_END_NAMESPACE_VERSION }
+// Unused when everything in std is versioned anyway.
+# define _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(X)
+# define _GLIBCXX_END_INLINE_ABI_NAMESPACE(X)
 
 namespace std
 {
@@ -376,8 +379,12 @@ _GLIBCXX_END_NAMESPACE_VERSION
 }
 
 #else
+// Unused.
 # define _GLIBCXX_BEGIN_NAMESPACE_VERSION
 # define _GLIBCXX_END_NAMESPACE_VERSION
+// Used to version individual components, e.g. std::_V2::error_category.
+# define _GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(X) inline namespace X {
+# define _GLIBCXX_END_INLINE_ABI_NAMESPACE(X)   } // inline namespace X
 #endif
 
 // Inline namespaces for special modes: debug, parallel.
diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h
index 4218985..745f9a8 100644
--- a/libstdc++-v3/include/bits/chrono.h
+++ b/libstdc++-v3/include/bits/chrono.h
@@ -1099,7 +1099,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // compatibility definitions for previous versions.  At some
     // point, when these clocks settle down, the inlined namespaces
     // can be removed.  XXX GLIBCXX_ABI Deprecated
-    inline namespace _V2 {
+_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 
     /**
      *  @brief System clock.
@@ -1171,7 +1171,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     */
     using high_resolution_clock = system_clock;
 
-    } // end inline namespace _V2
+_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
 #if __cplusplus >= 202002L
     /// @addtogroup chrono
diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 1f07b9e..6619ff7 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1190,8 +1190,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return __m;
     }
 
-  inline namespace _V2
-  {
+_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 
   /// This is a helper function for the rotate algorithm.
   template<typename _ForwardIterator>
@@ -1398,7 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 			   std::__iterator_category(__first));
     }
 
-  } // namespace _V2
+_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
   /**
    *  @brief Copy a sequence, rotating its elements.
diff --git a/libstdc++-v3/include/std/condition_variable b/libstdc++-v3/include/std/condition_variable
index 2a23e65..06c4ff9 100644
--- a/libstdc++-v3/include/std/condition_variable
+++ b/libstdc++-v3/include/std/condition_variable
@@ -234,7 +234,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     void (*_M_cb)(void*);
   };
 
-  inline namespace _V2 {
+_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 
   /// condition_variable_any
   // Like above, but mutex is not required to have try_lock.
@@ -439,7 +439,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
   };
 
-  } // end inline namespace
+_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
   /// @} group condition_variables
 _GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/include/std/system_error b/libstdc++-v3/include/std/system_error
index 45a1d28..dcef94e 100644
--- a/libstdc++-v3/include/std/system_error
+++ b/libstdc++-v3/include/std/system_error
@@ -77,7 +77,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif // C++17
   /// @}
 
-  inline namespace _V2 {
+_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
 
   /** @addtogroup diagnostics
    * @{
@@ -168,7 +168,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   _GLIBCXX_CONST const error_category& system_category() noexcept;
 
   /// @}
-  } // end inline namespace
+
+_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
 
   /** @addtogroup diagnostics
    * @{