[CMake] cache behaviour

[pellegrini]

Hello CMakers,

I saw this question turning around several times but I do not really 
understand why
the explanations do not suit with my problem. Sorry in advance for the 
redundancy.

Here is my 'problem':

I have a CMakeLists.txt file that starts with:

     ##########################################################
     cmake_minimum_required(VERSION 2.8.0 FATAL_ERROR)

     option(GUI "Build the GUI on top of the console programs." ON)

     if(DEFINED CMAKE_BUILD_TYPE)
         set(CMAKE_BUILD_TYPE ${CMAKE_BUILD_TYPE} CACHE STRING "" FORCE)
     else()
         set(CMAKE_BUILD_TYPE Release CACHE STRING "" FORCE)
     endif()
     message(STATUS "Setting build type to ${CMAKE_BUILD_TYPE}")

     if(DEFINED CMAKE_Fortran_COMPILER)
         set(CMAKE_Fortran_COMPILER ${CMAKE_Fortran_COMPILER} CACHE 
STRING "" FORCE)
     else()
         set(CMAKE_Fortran_COMPILER ifort CACHE STRING "" FORCE)
     endif()
     message(STATUS "Setting compiler to ${CMAKE_Fortran_COMPILER}")

     project(sxtalsoft Fortran RC)

     bla bla bla ...
     ##########################################################

When I run it a first time in an empty directory with

     cmake -G"NMake Makefiles" -DCMAKE_Fortran_COMPILER=ifort 
-DCMAKE_BUILD_TYPE=Release ..\..\.

I get:

-- Setting build type to Release
-- Setting compiler to ifort
-- The Fortran compiler identification is Intel
-- Check for working Fortran compiler: C:/Intel/Composer 
XE/bin/ia32/ifort.exe
-- Check for working Fortran compiler: C:/Intel/Composer 
XE/bin/ia32/ifort.exe  -- works
-- Detecting Fortran compiler ABI info
-- Detecting Fortran compiler ABI info - done
-- Checking whether C:/Intel/Composer XE/bin/ia32/ifort.exe supports 
Fortran 90
-- Checking whether C:/Intel/Composer XE/bin/ia32/ifort.exe supports 
Fortran 90 -- yes
-- Configuring done
-- Generating done
-- Build files have been written to: 
C:/Users/pellegrini/work/diffraction/sxtalsoft/build/ifort

If a run it a second time WITHOUT deleting the CMakeCache.txt file with

     cmake -G"NMake Makefiles" -DCMAKE_Fortran_COMPILER=ifort 
-DCMAKE_BUILD_TYPE=Debug ..\..\.

I get this time:

-- Setting build type to Debug
-- Setting compiler to ifort
-- Configuring done
You have changed variables that require your cache to be deleted.
Configure will be re-run and you may have to reset some variables.
The following variables have changed:
CMAKE_Fortran_COMPILER= ifort

-- Setting build type to Release
-- Setting compiler to ifort
-- The Fortran compiler identification is Intel
-- Check for working Fortran compiler: C:/Intel/Composer 
XE/bin/ia32/ifort.exe
-- Check for working Fortran compiler: C:/Intel/Composer 
XE/bin/ia32/ifort.exe  -- works
-- Detecting Fortran compiler ABI info
-- Detecting Fortran compiler ABI info - done
-- Checking whether C:/Intel/Composer XE/bin/ia32/ifort.exe supports 
Fortran 90
-- Checking whether C:/Intel/Composer XE/bin/ia32/ifort.exe supports 
Fortran 90 -- yes
-- Configuring done
-- Generating done
-- Build files have been written to: 
C:/Users/pellegrini/work/diffraction/sxtalsoft/build/ifort

There are two things that puzzle me here. The first is: why cmake detect 
a change in the compiler
type as it did not change its value in the command line between the two 
calls ? The second is why
during the rerun the CMAKE_BUILD_TYPE is set back to Release and not to 
the value set in the command
line i.e. Debug ?

Is my implementation not correct or is this some cache behaviour that I 
still do not get ?

thanks a lot

Eric