Update protobuf-config-version.cmake.in to correctly set the required variables (PACKAGE_VERSION_EXACT, PACKAGE_VERSION_COMPATIBLE, PACKAGE_VERSION_UNSUITABLE)

cmake/protobuf-config-version.cmake.in

@@ -1 +1,36 @@
+# This is a basic version file for the Config-mode of find_package().
+# It is derived from the format suggested in the CMake module
+# CMakePackageConfigHelpers. introduced in CMake 2.8.8.
+# If the cmake_minimum_required version is ever bumped to 2.8.8 or
+# above, this file may be deleted and replaced with a call to
+# write_basic_package_version_file(...)
+
 set(PACKAGE_VERSION @protobuf_VERSION@)
+
+if(PACKAGE_VERSION VERSION_LESS PACKAGE_FIND_VERSION)
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+else()
+
+  if(PACKAGE_FIND_VERSION_MAJOR STREQUAL @protobuf_VERSION_MAJOR@)
+    set(PACKAGE_VERSION_COMPATIBLE TRUE)
+  else()
+    set(PACKAGE_VERSION_COMPATIBLE FALSE)
+  endif()
+
+  if(PACKAGE_FIND_VERSION STREQUAL PACKAGE_VERSION)
+      set(PACKAGE_VERSION_EXACT TRUE)
+  endif()
+endif()
+
+
+# if the installed or the using project don't have CMAKE_SIZEOF_VOID_P set, ignore it:
+if("${CMAKE_SIZEOF_VOID_P}" STREQUAL "" OR "@CMAKE_SIZEOF_VOID_P@" STREQUAL "")
+   return()
+endif()
+
+# check that the installed version has the same 32/64bit-ness as the one which is currently searching:
+if(NOT CMAKE_SIZEOF_VOID_P STREQUAL "@CMAKE_SIZEOF_VOID_P@")
+  math(EXPR installedBits "@CMAKE_SIZEOF_VOID_P@ * 8")
+  set(PACKAGE_VERSION "${PACKAGE_VERSION} (${installedBits}bit)")
+  set(PACKAGE_VERSION_UNSUITABLE TRUE)
+endif()