# Copyright 2018 Andrey Semashev
# Distributed under the Boost Software License, Version 1.0.
# (See accompanying file LICENSE.txt or copy at
# https://www.bfgroup.xyz/b2/LICENSE.txt)

import feature ;

#| tag::doc[]

[[bbv2.builtin.features.visibility]]`visibility`::
*Allowed values:* `global`, `protected`, `hidden`.
+
Specifies the default symbol visibility in compiled binaries. Not all values
are supported on all platforms and on some platforms (for example, Windows)
symbol visibility is not supported at all.
+
The supported values have the following meaning:
+
`global`::: a.k.a. "default" in gcc documentation. Global symbols are
  considered public, they are exported from shared libraries and can be
  redefined by another shared library or executable.
`protected`::: a.k.a. "symbolic". Protected symbols are exported from shared
  ibraries but cannot be redefined by another shared library or executable.
  This mode is not supported on some platforms, for example OS X.
`hidden`::: Hidden symbols are not exported from shared libraries and cannot
  be redefined by a different shared library or executable loaded in a process.
  In this mode, public symbols have to be explicitly marked in the source code
  to be exported from shared libraries. This is the recommended mode.
+
By default compiler default visibility mode is used (no compiler flags are
added).
+
NOTE: In Boost super-project Jamroot file this property is set to the default
value of `hidden`. This means that Boost libraries are built with hidden
visibility by default, unless the user overrides it with a different
`visibility` or a library sets a different `local-visibility` (see below).

|# # end::doc[]

feature.feature visibility
    : global protected hidden
    : optional composite propagated ;

feature.compose <visibility>global : <local-visibility>global ;
feature.compose <visibility>protected : <local-visibility>protected ;
feature.compose <visibility>hidden : <local-visibility>hidden ;