Allow completely disabling deprecated APIs with CMake option OVM_ENABLE_DEPRECATED_APIS

At some point in the future, we should switch the default to OFF.

src/CMakeLists.txt

 include (ACGCommon)
 
+set(OVM_ENABLE_DEPRECATED_APIS ON CACHE BOOL "Support deprecated OpenVolumeMesh APIs")
+
+configure_file (
+    "${CMAKE_CURRENT_SOURCE_DIR}/Config/DeprecationConfig.hh.in"
+    "${CMAKE_CURRENT_BINARY_DIR}/Config/DeprecationConfig.hh"
+)
+
 include_directories (
   ..
   ${CMAKE_CURRENT_SOURCE_DIR}
@@ -10,6 +17,7 @@ set (directories
   .
   OpenVolumeMesh/Attribs
   OpenVolumeMesh/Core
+  OpenVolumeMesh/Config
   OpenVolumeMesh/FileManager
   OpenVolumeMesh/Geometry
   OpenVolumeMesh/Mesh
@@ -32,6 +40,11 @@ else ()
     set_target_properties (OpenVolumeMesh PROPERTIES VERSION ${OPENVOLUMEMESH_VERSION_MAJOR}.${OPENVOLUMEMESH_VERSION_MINOR}
                                           SOVERSION ${OPENVOLUMEMESH_VERSION_MAJOR}.${OPENVOLUMEMESH_VERSION_MINOR} )
 endif ()
+foreach(TARGET_NAME OpenVolumeMesh OpenVolumeMeshStatic)
+    if (TARGET ${TARGET_NAME})
+        target_include_directories(${TARGET_NAME} PUBLIC "${CMAKE_CURRENT_BINARY_DIR}/Config/")
+    endif()
+endforeach(TARGET_NAME)
 
 # Only install if the project name matches OpenVolumeMesh.
 if (NOT APPLE AND ${PROJECT_NAME} MATCHES "OpenVolumeMesh")
@@ -50,6 +63,10 @@ install(DIRECTORY .
         PATTERN "Debian*" EXCLUDE)
 endif ()
 
+# install config files
+install( FILES ${CMAKE_CURRENT_BINARY_DIR}/Config/DeprecationConfig.hh
+           DESTINATION include/OpenVolumeMesh/Config )
+
 # Only build unittests and file converter
 # if not built as external library
 if(${PROJECT_NAME} MATCHES "OpenVolumeMesh")

src/Config/DeprecationConfig.hh.in

+#pragma once
+
+#cmakedefine01  OVM_ENABLE_DEPRECATED_APIS
+

src/OpenVolumeMesh/Core/OpenVolumeMeshHandle.hh

@@ -81,8 +81,10 @@ public:
 
 	void idx(const int& _idx) { idx_ = _idx; }
 
+#if OVM_ENABLE_DEPRECATED_APIS
     OVM_DEPRECATED("use explicit .idx() instead")
     inline operator int() const { return idx_; }
+#endif
 
 	void reset() { idx_ = -1; }
 

src/OpenVolumeMesh/Core/PropertyPtr.hh

@@ -96,10 +96,12 @@ public:
     const_iterator end() const { return ptr::shared_ptr<PropT>::get()->end(); }
     iterator end() { return ptr::shared_ptr<PropT>::get()->end(); }
 
+#if OVM_ENABLE_DEPRECATED_APIS
     OVM_DEPRECATED("use handles to index properties")
     reference operator[](size_t _idx) { return (*ptr::shared_ptr<PropT>::get())[_idx]; }
     OVM_DEPRECATED("use handles to index properties")
     const_reference operator[](size_t _idx) const { return (*ptr::shared_ptr<PropT>::get())[_idx]; }
+#endif
 
     reference operator[](const EntityHandleT& _h) { return (*ptr::shared_ptr<PropT>::get())[_h.idx()]; }
     const_reference operator[](const EntityHandleT& _h) const { return (*ptr::shared_ptr<PropT>::get())[_h.uidx()]; }

src/OpenVolumeMesh/System/Deprecation.hh

 #pragma once
 
+#include "DeprecationConfig.hh"
+
 #if defined(__cplusplus) && (__cplusplus >= 201402L)
 #  define OVM_DEPRECATED(msg) [[deprecated(msg)]]
 #elif defined(__GNUC__) || defined(__clang__)