libstdc++: Improve doxygen docs for std::allocator

libstdc++-v3/ChangeLog:

	* doc/doxygen/user.cfg.in (PREDEFINED): Define __allocator_base
	so that Doxygen shows the right base-class for std::allocator.
	* include/bits/alloc_traits.h: Improve doxygen docs.
	* include/bits/allocator.h: Likewise.
	* include/bits/new_allocator.h: Likewise.
	* include/ext/new_allocator.h: Likewise.

(cherry picked from commit 171f41f124bc1d5d80a395d27833a578cceba9e7)

4 files changed, 41 insertions, 10 deletions

diff --git a/libstdc++-v3/include/bits/alloc_traits.h b/libstdc++-v3/include/bits/alloc_traits.h
index 25496bc..4f40b36 100644
--- a/libstdc++-v3/include/bits/alloc_traits.h
+++ b/libstdc++-v3/include/bits/alloc_traits.h
@@ -661,6 +661,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { return __rhs; }
     };
 
+  /// @cond undocumented
 #if __cplusplus < 201703L
   template<typename _Alloc>
     inline void
@@ -818,8 +819,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __a.deallocate(__a.allocate(1u), 1u);
     };
 #endif
+  /// @endcond
 #endif // C++11
 
+  /// @cond undocumented
+
   /**
    * Destroy a range of objects using the supplied allocator.  For
    * non-default allocators we do not optimize away invocation of
@@ -849,6 +853,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       std::_Destroy(__first, __last);
     }
+  /// @endcond
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
diff --git a/libstdc++-v3/include/bits/allocator.h b/libstdc++-v3/include/bits/allocator.h
index a4b80d9..aec0b37 100644
--- a/libstdc++-v3/include/bits/allocator.h
+++ b/libstdc++-v3/include/bits/allocator.h
@@ -67,7 +67,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // explicit specialization, with the historical ABI properties, but with
   // the same members that are present in the primary template.
 
-  /// allocator<void> specialization.
+  /** std::allocator<void> specialization.
+   *
+   * @headerfile memory
+   */
   template<>
     class allocator<void>
     {
@@ -119,6 +122,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  for further details.
    *
    *  @tparam  _Tp  Type of allocated object.
+   *
+   *  @headerfile memory
    */
   template<typename _Tp>
     class allocator : public __allocator_base<_Tp>
@@ -214,6 +219,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       // Inherit everything else.
     };
 
+  /** Equality comparison for std::allocator objects
+   *
+   * @return true, for all std::allocator objects.
+   * @relates std::allocator
+   */
   template<typename _T1, typename _T2>
     inline _GLIBCXX20_CONSTEXPR bool
     operator==(const allocator<_T1>&, const allocator<_T2>&)
@@ -228,6 +238,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return false; }
 #endif
 
+  /// @cond undocumented
+
   // Invalid allocator<cv T> partial specializations.
   // allocator_traits::rebind_alloc can be used to form a valid allocator type.
   template<typename _Tp>
@@ -330,6 +342,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
     };
 #endif
+  /// @endcond
 
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
diff --git a/libstdc++-v3/include/bits/new_allocator.h b/libstdc++-v3/include/bits/new_allocator.h
index d066d01..e9eb103 100644
--- a/libstdc++-v3/include/bits/new_allocator.h
+++ b/libstdc++-v3/include/bits/new_allocator.h
@@ -43,14 +43,21 @@ namespace std _GLIBCXX_VISIBILITY(default)
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /**
-   *  @brief  An allocator that uses global new, as per C++03 [20.4.1].
-   *  @ingroup allocators
+   * @brief  An allocator that uses global `new`, as per C++03 [20.4.1].
+   * @ingroup allocators
    *
-   *  This is precisely the allocator defined in the C++ Standard.
-   *    - all allocation calls operator new
-   *    - all deallocation calls operator delete
+   * This is precisely the allocator defined in the C++ Standard.
+   *   - all allocation calls `operator new`
+   *   - all deallocation calls `operator delete`
    *
-   *  @tparam  _Tp  Type of allocated object.
+   * This is the default base-class implementation of `std::allocator`,
+   * and is also the base-class of the `__gnu_cxx::new_allocator` extension.
+   * You should use either `std::allocator` or `__gnu_cxx::new_allocator`
+   * instead of using this directly.
+   *
+   * @tparam  _Tp  Type of allocated object.
+   *
+   * @headerfile memory
    */
   template<typename _Tp>
     class __new_allocator
diff --git a/libstdc++-v3/include/ext/new_allocator.h b/libstdc++-v3/include/ext/new_allocator.h
index b8f5fcc..96e6523 100644
--- a/libstdc++-v3/include/ext/new_allocator.h
+++ b/libstdc++-v3/include/ext/new_allocator.h
@@ -36,14 +36,20 @@ namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /**
-   *  @brief  An allocator that uses global new, as per C++03 [20.4.1].
+   *  @brief  An allocator that uses global `new`, as per C++03 [20.4.1].
    *  @ingroup allocators
    *
    *  This is precisely the allocator defined in the C++ Standard.
-   *    - all allocation calls operator new
-   *    - all deallocation calls operator delete
+   *    - all allocation calls `operator new`
+   *    - all deallocation calls `operator delete`
+   *
+   *  This is a non-standard extension that can be used to guarantee
+   *  allocation from `new` even if the library has been configured to
+   *  use a different implementation for `std::allocator`.
    *
    *  @tparam  _Tp  Type of allocated object.
+   *
+   *  @headerfile ext/new_allocator.h
    */
   template<typename _Tp>
     class new_allocator : public std::__new_allocator<_Tp>