Set cmake minimum version in a centralized place

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>

CMakeLists.txt

@@ -14,7 +14,13 @@ if( "${CMAKE_CURRENT_SOURCE_DIR}" STREQUAL "${CMAKE_SOURCE_DIR}" )
 
 ##### general package setup #####################
 
-  cmake_minimum_required( VERSION 3.5 )
+  # building tde-cmake requires reading the minimum required version
+  # from the source files, because there may be a different version
+  # of tde-cmake already installed in the system. Trying to build
+  # tde-cmake with a lower minimum version would not be allowed then.
+
+  include( ${CMAKE_SOURCE_DIR}/modules/TDEVersion.cmake )
+  cmake_minimum_required( VERSION ${TDE_CMAKE_MINIMUM_VERSION} )
   project( tde-cmake-rules )
 
 

modules/TDEMacros.cmake

@@ -16,13 +16,20 @@
 #################################################
 
 
+#################################################
+#####
+##### Need cmake minimum version
+
+include( TDEVersion )
+
+
 #################################################
 #####
 ##### initialization...
 
 if( NOT TDE_CMAKE_ROOT )
-  if( "${CMAKE_VERSION}" VERSION_LESS "3.5" )
-    message( FATAL_ERROR "CMake >= 3.5.0 required" )
+  if( "${CMAKE_VERSION}" VERSION_LESS "${TDE_CMAKE_MINIMUM_VERSION}" )
+    message( FATAL_ERROR "CMake >= ${TDE_CMAKE_MINIMUM_VERSION} required" )
   endif()
 
   if( ${CMAKE_CURRENT_LIST_DIR} STREQUAL ${CMAKE_ROOT}/Modules )
@@ -83,7 +90,6 @@ include( CheckCXXSourceCompiles )
 include( CheckLinkerFlag OPTIONAL )
 include( CheckSymbolExists )
 include( CheckTypeSize )
-include( TDEVersion )
 
 
 #################################################

modules/TDEVersion.cmake

@@ -9,6 +9,11 @@
 #
 #################################################
 
+# Centralized place where to set the minimum cmake version required in TDE
+
+set( TDE_CMAKE_MINIMUM_VERSION 3.5 )
+
+
 #################################################
 #####
 ##### tde_set_project_version