Update documentation

doc/system/changes.adoc

@@ -11,6 +11,23 @@ http://www.boost.org/LICENSE_1_0.txt
 # Revision History
 :idprefix:
 
+## Changes in Boost 1.75
+
+* The platform-specific headers `windows_error.hpp`, `linux_error.hpp`,
+  and `cygwin_error.hpp` emit deprecation messages and are slated for
+  removal.
+* The old names for `generic_category()` and `system_category()` emit
+  deprecation messages and are slated for removal.
+* `error_condition::failed` is deprecated and is slated for removal.
+  `operator bool()` for `error_category` has been reverted to its old
+  meaning of `value() != 0`. This is done for compatibility with
+  `std::error_condition` as the next release is expected to improve
+  interoperability with `<system_error>` even further. _Note that this
+  does not affect_ `error_code::failed`, which is still alive and well.
+* The overload of `error_condition::message` that takes a buffer is
+  deprecated and is slated for removal, for the same reasons. _Note that
+  this does not affect_ `error_code::message`.
+
 ## Changes in Boost 1.74
 
 * `operator bool()` now returns `failed()` instead of `value() != 0`.

doc/system/reference.adoc

@@ -670,13 +670,16 @@ namespace boost {
       constexpr const error_category & category() const noexcept;
 
       std::string message() const;
-      char const * message( char * buffer, std::size_t len ) const noexcept;
 
-      constexpr bool failed() const noexcept;
       constexpr explicit operator bool() const noexcept;
 
       operator std::error_condition() const;
 
+      // deprecated members; do not use
+
+      char const * message( char * buffer, std::size_t len ) const noexcept;
+      constexpr bool failed() const noexcept;
+
     private: // exposition only
 
       int val_;
@@ -771,29 +774,13 @@ std::string message() const;
 +
 Returns: :: `cat_\->message( val_ )`.
 
-```
-char const * message( char * buffer, std::size_t len ) const noexcept;
-```
-[none]
-* {blank}
-+
-Returns: :: `cat_\->message( val_, buffer, len )`.
-
-```
-constexpr bool failed() const noexcept;
-```
-[none]
-* {blank}
-+
-Returns: :: `cat_\->failed( val_ )`.
-
 ```
 constexpr explicit operator bool() const noexcept;
 ```
 [none]
 * {blank}
 +
-Returns: :: `failed()`.
+Returns: :: `value() != 0`.
 
 ```
 operator std::error_condition() const;
@@ -804,6 +791,34 @@ operator std::error_condition() const;
 Returns: ::
   `std::error_condition( val_, *cat_ )`.
 
+#### Deprecated members
+
+```
+char const * message( char * buffer, std::size_t len ) const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->message( val_, buffer, len )`.
+
+WARNING: This member function is deprecated and will be removed. This is done
+      for compatibility with `std::error_condition` as the next release is
+      expected to improve interoperability with `<system_error>` even further.
+      _Note that this does not affect_ `error_code::message`.
+
+```
+constexpr bool failed() const noexcept;
+```
+[none]
+* {blank}
++
+Returns: :: `cat_\->failed( val_ )`.
+
+WARNING: This member function is deprecated and will be removed. This is done
+      for compatibility with `std::error_condition` as the next release is
+      expected to improve interoperability with `<system_error>` even further.
+      _Note that this does not affect_ `error_code::failed`.
+
 ### Nonmember functions
 
 ```