From 9f0bd78860e4ea32c570b1ffdbfca8845948a2b7 Mon Sep 17 00:00:00 2001
From: Kenneth Moreland <kmorel@sandia.gov>
Date: Thu, 29 Sep 2016 14:06:07 -0400
Subject: [PATCH] Add C++11 flags to sub-projects

Recently VTK-m was changed to require C++11. The internal builds set
properties to require C++11, but these never make it to the
configuration for projects that use the VTK-m package (i.e. not declared
in VTKmConfig.cmake).

This change adds a new CMake target, vtkm, which is an interface. It
does not point to an actual library, but it allows code that links it in
to have the appropriate compile flags.
---
 CMake/VTKmConfigureComponents.cmake |  8 +++++-
 CMake/VTKmMacros.cmake              |  2 --
 CMakeLists.txt                      | 44 ++++++++++++++---------------
 3 files changed, 28 insertions(+), 26 deletions(-)

diff --git a/CMake/VTKmConfigureComponents.cmake b/CMake/VTKmConfigureComponents.cmake
index a93d3ff1b..1be321042 100644
--- a/CMake/VTKmConfigureComponents.cmake
+++ b/CMake/VTKmConfigureComponents.cmake
@@ -107,9 +107,15 @@ macro(vtkm_configure_component_Base)
     include(VTKmCompilerOptimizations)
   endif()
 
+  # Check for the existance of the base vtkm target
+  if (TARGET vtkm)
+    set(VTKm_base_vtkm_target_FOUND True)
+  endif()
+
   vtkm_finish_configure_component(Base
-    DEPENDENT_VARIABLES Boost_FOUND
+    DEPENDENT_VARIABLES Boost_FOUND VTKm_base_vtkm_target_FOUND
     ADD_INCLUDES ${Boost_INCLUDE_DIRS}
+    ADD_LIBRARIES vtkm
     )
 endmacro()
 
diff --git a/CMake/VTKmMacros.cmake b/CMake/VTKmMacros.cmake
index 95dbabbd5..22e77dd80 100755
--- a/CMake/VTKmMacros.cmake
+++ b/CMake/VTKmMacros.cmake
@@ -584,7 +584,6 @@ function(vtkm_wrap_sources_for_cuda cuda_source_list_var)
   set(${cuda_source_list_var} ${cuda_sources} PARENT_SCOPE)
 endfunction(vtkm_wrap_sources_for_cuda)
 
-set(VTKM_HAS_AT_LEAST_ONE_LIBRARY FALSE CACHE INTERNAL "" FORCE)
 # Add a VTK-m library. The name of the library will match the "kit" name
 # (e.g. vtkm_rendering) unless the NAME argument is given.
 #
@@ -676,7 +675,6 @@ function(vtkm_library)
   vtkm_install_headers("${dir_prefix}"
     ${CMAKE_BINARY_DIR}/${VTKm_INSTALL_INCLUDE_DIR}/${dir_prefix}/${lib_name}_export.h
     )
-  set(VTKM_HAS_AT_LEAST_ONE_LIBRARY TRUE CACHE INTERNAL "" FORCE)
 endfunction(vtkm_library)
 
 # The Thrust project is not as careful as the VTKm project in avoiding warnings
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a8e4b921c..bb372b3b1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -53,6 +53,17 @@ set(VTKm_INCLUDE_DIRS
   ${CMAKE_CURRENT_SOURCE_DIR}
   )
 
+# Create an "interface" target library. This is not a real library but rather
+# holds CMake configuration that is required for CXX targets that use VTK-m
+# headers. In particular, it makes sure the appropriate C++11 version is being
+# used. (The cxx_constexpr and cxx_auto_type features happen to force C++11.
+# Directly asking for C++11 with this interface is not supported in CMake 3.3.)
+# This is also exported so that dependent CMake projects can load the same
+# configuration.
+add_library(vtkm INTERFACE)
+target_compile_features(vtkm INTERFACE cxx_constexpr cxx_auto_type)
+install(TARGETS vtkm EXPORT ${VTKm_EXPORT_NAME})
+
 # Load the base VTK-m configuration, which is required for some of the later
 # config.
 vtkm_configure_component_Base()
@@ -61,13 +72,9 @@ if(NOT VTKm_Base_FOUND)
 endif()
 
 #-----------------------------------------------------------------------------
-# Add flag to enable C++11 support.
-# Unless the user has explicitly stated to compile with a different standard
-if (NOT DEFINED CMAKE_CXX_STANDARD)
-   set(CMAKE_CXX_STANDARD 11)
-   set(CMAKE_CXX_STANDARD_REQUIRED True)
-   set(CMAKE_CXX_EXTENSIONS False)
-endif()
+# When using C++11 suport make sure you use the standard C++ extensions rather
+# than compiler-specific versions of the extensions (to preserve portability).
+set(CMAKE_CXX_EXTENSIONS False)
 
 #-----------------------------------------------------------------------------
 # Add supplemental compiler warnings, and GCC visibility support.
@@ -318,22 +325,13 @@ install(
   )
 
 # Create and install exports for external projects
-if(${VTKM_HAS_AT_LEAST_ONE_LIBRARY})
-  export(EXPORT ${VTKm_EXPORT_NAME}
-    FILE ${CMAKE_BINARY_DIR}/${VTKm_INSTALL_CONFIG_DIR}/VTKmTargets.cmake
-    )
-  install(EXPORT ${VTKm_EXPORT_NAME}
-    DESTINATION ${VTKm_INSTALL_LIB_DIR}
-    FILE VTKmTargets.cmake
-    )
-else() # No libraries built
-  file(WRITE ${CMAKE_BINARY_DIR}/${VTKm_INSTALL_CONFIG_DIR}/VTKmTargets.cmake
-    "# This build of VTK-m has no libraries to export targets for"
-    )
-  install(FILES ${CMAKE_BINARY_DIR}/${VTKm_INSTALL_CONFIG_DIR}/VTKmTargets.cmake
-    DESTINATION ${VTKm_INSTALL_LIB_DIR}
-    )
-endif()
+export(EXPORT ${VTKm_EXPORT_NAME}
+  FILE ${CMAKE_BINARY_DIR}/${VTKm_INSTALL_CONFIG_DIR}/VTKmTargets.cmake
+  )
+install(EXPORT ${VTKm_EXPORT_NAME}
+  DESTINATION ${VTKm_INSTALL_LIB_DIR}
+  FILE VTKmTargets.cmake
+  )
 
 # Enable CPack packaging
 set(CPACK_PACKAGE_DESCRIPTION_FILE ${VTKm_SOURCE_DIR}/README.md)