Add a workaround for Microsoft's non-conformant std::system_error.

Author: chriskohlhoff

asio/boostify.pl

@@ -310,6 +310,13 @@ sub copy_source_file
         last if $line =~ /boostify: non-boost docs end here/;
       }
     }
+    elsif ($line =~ /boostify: non-boost code starts here/)
+    { 
+      while ($line = <$input>)
+      {
+        last if $line =~ /boostify: non-boost code ends here/;
+      }
+    }
     elsif ($line =~ /^$/ && $needs_doc_link)
     {
       $needs_doc_link = 0;

asio/include/asio/detail/impl/throw_error.ipp

@@ -33,8 +33,23 @@ void do_throw_error(const asio::error_code& err)
 
 void do_throw_error(const asio::error_code& err, const char* location)
 {
+  // boostify: non-boost code starts here
+#if defined(ASIO_MSVC) && defined(ASIO_HAS_STD_SYSTEM_ERROR)
+  // Microsoft's implementation of std::system_error is non-conformant in that
+  // it ignores the error code's message when a "what" string is supplied. We'll
+  // work around this by explicitly formatting the "what" string.
+  std::string what_msg = location;
+  what_msg += ": ";
+  what_msg += err.message();
+  asio::system_error e(err, what_msg);
+  asio::detail::throw_exception(e);
+#else // defined(ASIO_MSVC) && defined(ASIO_HAS_STD_SYSTEM_ERROR)
+  // boostify: non-boost code ends here
   asio::system_error e(err, location);
   asio::detail::throw_exception(e);
+  // boostify: non-boost code starts here
+#endif // defined(ASIO_MSVC) && defined(ASIO_HAS_STD_SYSTEM_ERROR)
+  // boostify: non-boost code ends here
 }
 
 } // namespace detail