CMake updates to better handle C++ standard specification and propagation to apps consistently

Author: andrewfb

proj/cmake/libcinder_target.cmake

@@ -79,20 +79,43 @@ if( CINDER_MSW AND MSVC )
     endif()
 endif()
 
-target_compile_features( cinder PUBLIC cxx_std_17 )
+# Determine C++ standard for Cinder (default 17, allow user override)
+if( CMAKE_CXX_STANDARD )
+    set( CINDER_CXX_STANDARD ${CMAKE_CXX_STANDARD} )
+else()
+    set( CINDER_CXX_STANDARD 17 )
+endif()
+
+# Validate minimum
+if( CINDER_CXX_STANDARD LESS 17 )
+    message( FATAL_ERROR "Cinder requires C++17 or later. CMAKE_CXX_STANDARD is set to ${CINDER_CXX_STANDARD}" )
+endif()
+
+# Set C++ standard for cinder target
+target_compile_features( cinder PUBLIC cxx_std_${CINDER_CXX_STANDARD} )
+
+# Determine CXX_EXTENSIONS: default OFF (prevents "namespace linux" issue)
+# Only enable if user explicitly sets CMAKE_CXX_EXTENSIONS=ON
+if( DEFINED CMAKE_CXX_EXTENSIONS )
+    set( CINDER_CXX_EXTENSIONS ${CMAKE_CXX_EXTENSIONS} )
+else()
+    set( CINDER_CXX_EXTENSIONS OFF )
+endif()
+
 set_target_properties( cinder PROPERTIES
-    CXX_STANDARD 17
+    CXX_STANDARD ${CINDER_CXX_STANDARD}
     CXX_STANDARD_REQUIRED ON
-    CXX_EXTENSIONS OFF
+    CXX_EXTENSIONS ${CINDER_CXX_EXTENSIONS}
 )
 
 # This file will contain all dependencies, includes, definition, compiler flags and so on..
 export( TARGETS cinder FILE ${PROJECT_BINARY_DIR}/${CINDER_LIB_DIRECTORY}/cinderTargets.cmake )
 
 # And this command will generate a file on the ${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}
 # that applications have to pull in order to link successfully with Cinder and its dependencies.
-# This specific cinderConfig.cmake file will just hold a path to the above mention 
+# This specific cinderConfig.cmake file will just hold a path to the above mention
 # cinderTargets.cmake file which holds the actual info.
+# CINDER_CXX_STANDARD and CINDER_CXX_EXTENSIONS will be substituted into the template
 configure_file( ${CMAKE_CURRENT_LIST_DIR}/modules/cinderConfig.buildtree.cmake.in
     "${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/cinderConfig.cmake"
 )

proj/cmake/modules/cinderConfig.buildtree.cmake.in

@@ -1,5 +1,10 @@
 if( NOT TARGET cinder${CINDER_LIB_SUFFIX} )
     include( "${PROJECT_BINARY_DIR}/${CINDER_LIB_DIRECTORY}/cinderTargets.cmake" )
+
+    # Record the C++ standard and extensions setting Cinder was built with
+    # These will be inherited by apps unless they explicitly override
+    set( CINDER_CXX_STANDARD @CINDER_CXX_STANDARD@ )
+    set( CINDER_CXX_EXTENSIONS @CINDER_CXX_EXTENSIONS@ )
 endif()
 
 

proj/cmake/modules/cinderMakeApp.cmake

@@ -129,6 +129,36 @@ function( ci_make_app )
 	target_include_directories( ${ARG_APP_NAME} PUBLIC ${ARG_INCLUDES} )
 	target_link_libraries( ${ARG_APP_NAME} PUBLIC cinder ${ARG_LIBRARIES} )
 
+	# Determine C++ standard: user override > Cinder's standard > 17
+	if( CMAKE_CXX_STANDARD )
+		set( APP_CXX_STANDARD ${CMAKE_CXX_STANDARD} )
+	elseif( DEFINED CINDER_CXX_STANDARD )
+		set( APP_CXX_STANDARD ${CINDER_CXX_STANDARD} )
+	else()
+		set( APP_CXX_STANDARD 17 )
+	endif()
+
+	if( APP_CXX_STANDARD LESS 17 )
+		message( FATAL_ERROR "Cinder requires C++17 or later. App is configured to use C++${APP_CXX_STANDARD}" )
+	endif()
+
+	target_compile_features( ${ARG_APP_NAME} PUBLIC cxx_std_${APP_CXX_STANDARD} )
+
+	# Determine CXX_EXTENSIONS: inherit from Cinder, or default OFF (prevents "namespace linux" issue)
+	if( DEFINED CMAKE_CXX_EXTENSIONS )
+		set( APP_CXX_EXTENSIONS ${CMAKE_CXX_EXTENSIONS} )
+	elseif( DEFINED CINDER_CXX_EXTENSIONS )
+		set( APP_CXX_EXTENSIONS ${CINDER_CXX_EXTENSIONS} )
+	else()
+		set( APP_CXX_EXTENSIONS OFF )
+	endif()
+
+	set_target_properties( ${ARG_APP_NAME} PROPERTIES
+		CXX_STANDARD ${APP_CXX_STANDARD}
+		CXX_STANDARD_REQUIRED ON
+		CXX_EXTENSIONS ${APP_CXX_EXTENSIONS}
+	)
+
 	if( MSVC )
 		# Ignore Specific Default Libraries for Debug build
 		set_target_properties( ${ARG_APP_NAME} PROPERTIES LINK_FLAGS_DEBUG "/NODEFAULTLIB:LIBCMT /NODEFAULTLIB:LIBCPMT" )