Set Minimum C++ Standard on CMake Targets

To fix OpenDDS#4478

cmake/import_common.cmake

@@ -360,6 +360,10 @@ function(_opendds_import_group_targets group libs exes)
           INTERFACE_COMPILE_OPTIONS "${${var_prefix}_COMPILE_OPTIONS}"
       )
 
+      if(NOT CMAKE_VERSION VERSION_LESS "3.11.0" AND OPENDDS_CXX_STD)
+        target_compile_features(${target} INTERFACE "cxx_std_${OPENDDS_CXX_STD}")
+      endif()
+
       set(mpc_ext_proj_var "${group_prefix}_MPC_EXTERNAL_PROJECT")
       if(DEFINED "${mpc_ext_proj_var}")
         add_dependencies(${target} "${${mpc_ext_proj_var}}")

cmake/init.cmake

@@ -279,6 +279,15 @@ if(NOT DEFINED ACE_ROOT)
   set(ACE_BIN_DIR "${ACE_ROOT}/bin")
 endif()
 _opendds_get_version(OPENDDS_ACE_VERSION ACE "${ACE_ROOT}")
+if(NOT DEFINED OPENDDS_CXX_STD)
+  if(NOT OPENDDS_ACE_VERSION VERSION_LESS "7.0.0")
+    set(OPENDDS_CXX_STD 14)
+  elseif(OPENDDS_CXX11)
+    set(OPENDDS_CXX_STD 11)
+  else()
+    set(OPENDDS_CXX_STD 98)
+  endif()
+endif()
 
 if(NOT DEFINED TAO_ROOT)
   if(OPENDDS_USE_PREFIX_PATH)

cmake/opendds_build_helpers.cmake

@@ -29,6 +29,10 @@ function(_opendds_library target)
 
   _opendds_alias(${target})
 
+  if(OPENDDS_CXX_STD)
+    target_compile_features(${target} PUBLIC "cxx_std_${OPENDDS_CXX_STD}")
+  endif()
+
   # Put library in BINARY_DIR/lib
   set_target_properties(${target} PROPERTIES
     RUNTIME_OUTPUT_DIRECTORY "${OPENDDS_LIB_DIR}"
@@ -84,6 +88,10 @@ function(_opendds_executable target)
   _opendds_alias(${target})
   set_target_properties(${target} PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${OPENDDS_BIN_DIR}")
 
+  if(OPENDDS_CXX_STD)
+    target_compile_features(${target} PRIVATE "cxx_std_${OPENDDS_CXX_STD}")
+  endif()
+
   if(NOT arg_NO_INSTALL)
     install(TARGETS ${target}
       EXPORT opendds_targets

docs/devguide/building/cmake.rst

@@ -826,6 +826,16 @@ Features
   Default depends on the compiler being used.
   Has no effect when building OpenDDS using CMake.
 
+.. cmake:var:: OPENDDS_CXX_STD
+
+  .. versionadded:: 3.28
+
+  If defined, then this value is prefixed with ``cxx_std_`` and passed to `target_compile_features <https://cmake.org/cmake/help/latest/command/target_compile_features.html>`__ for all targets.
+  The valid values are the standards in `CMAKE_CXX_KNOWN_FEATURES <https://cmake.org/cmake/help/latest/prop_gbl/CMAKE_CXX_KNOWN_FEATURES.html#high-level-meta-features-indicating-c-standard-support>`__ without the leading ``cxx_std_``.
+  This is the minimum C++ standard required to use the ACE, TAO, and OpenDDS libraries.
+  When building OpenDDS using CMake, it's also the minimum C++ standard used to build OpenDDS.
+  The default depends on the version of ACE being used.
+
 .. cmake:var:: OPENDDS_DEBUG
   :no-contents-entry:
 

docs/devguide/building/index.rst

@@ -694,7 +694,7 @@ A few things to note:
 
 - Native-built host tools, like :term:`opendds_idl`, have to be configured and built separately and provided to the target build using :cmake:var:`OPENDDS_HOST_TOOLS`.
 - The host tools will build its own ACE/TAO for the host system, but this can be overridden using :cmake:var:`OPENDDS_ACE` on the host build and :cmake:var:`OPENDDS_ACE_TAO_HOST_TOOLS` on the target build.
-- If the target platform isn't automatically supported, then ACE/TAO will have to be :ref:`built serperatly <cmake-ace-tao-manual>`.
+- If the target platform isn't automatically supported, then ACE/TAO will have to be :ref:`built separately <cmake-ace-tao-manual>`.
 
 Android
 ^^^^^^^

docs/news.d/cmake-cxx-std.rst

@@ -0,0 +1,7 @@
+.. news-prs: 4481
+
+.. news-start-section: Fixes
+.. news-start-section: Building with CMake
+- Fixed :ghissue:`building with CMake and Apple Clang on macOS <4478>` without setting ``-DCMAKE_CXX_STANDARD=14`` or using ACE 6 by setting :cmake:var:`OPENDDS_CXX_STD` when ACE 7 is used.
+.. news-end-section
+.. news-end-section