Honor visibility properties for all target types (#15556)

The <LANG>_VISIBILITY_PRESET and VISIBILITY_INLINES_HIDDEN were first
merged in commit v2.8.12~322 (Merge topic 'VISIBILITY_PRESET-property',
2013-06-05) but worked only for shared libraries and executables with
exports.  Prior to commit v3.0.0-rc1~581^2 (GenerateExportHeader:
Deprecate add_compiler_export_flags function., 2013-09-02) the
add_compiler_export_flags function was used to add visibility flags to
all targets.

The visibility flags are useful for sources in all target types because
they may be later linked into shared libraries or executables with
exports.  Introduce policy CMP0063 to enable them for all target types
while preserving compatibility with existing projects that do not expect
this.

1 files changed, 26 insertions, 0 deletions

diff --git a/Help/policy/CMP0063.rst b/Help/policy/CMP0063.rst
new file mode 100644
index 0000000..298e9c2
--- /dev/null
+++ b/Help/policy/CMP0063.rst
@@ -0,0 +1,26 @@
+CMP0063
+-------
+
+Honor visibility properties for all target types.
+
+The :prop_tgt:`<LANG>_VISIBILITY_PRESET` and
+:prop_tgt:`VISIBILITY_INLINES_HIDDEN` target properties affect visibility
+of symbols during dynamic linking.  When first introduced these properties
+affected compilation of sources only in shared libraries, module libraries,
+and executables with the :prop_tgt:`ENABLE_EXPORTS` property set.  This
+was sufficient for the basic use cases of shared libraries and executables
+with plugins.  However, some sources may be compiled as part of static
+libraries or object libraries and then linked into a shared library later.
+CMake 3.3 and above prefer to honor these properties for sources compiled
+in all target types.  This policy preserves compatibility for projects
+expecting the properties to work only for some target types.
+
+The ``OLD`` behavior for this policy is to ignore the visibility properties
+for static libraries, object libraries, and executables without exports.
+The ``NEW`` behavior for this policy is to honor the visibility properties
+for all target types.
+
+This policy was introduced in CMake version 3.3.  CMake version
+|release| warns when the policy is not set and uses ``OLD`` behavior.  Use
+the :command:`cmake_policy()` command to set it to ``OLD`` or ``NEW``
+explicitly.