[CMake] How to use CMAKE_POLICY?

[Marcel Loose]

Hi David,

I need to set a policy to OLD, because I have wrapped a few existing 
Find*.cmake files to overcome some bugs or shortcomings. However, since 
CMake 2.8.4 (or 2.8.3, I'm not sure), this triggers a policy warning 
CMP0017 with newer versions of CMake, because some macros are now 
included from my CMAKE_MODULE_PATH and some from CMAKE_CURRENT_LIST_DIR, 
which expands to somewhere inside CMAKE_ROOT.

Best regards,
Marcel Loose.


Op 17-12-12 15:30, David Cole schreef:
> If you need to set a policy to OLD, then we have failed...
>
> Why do you need to set a policy to OLD?
>
> How can we make it work so that you don't need to do that?
>
>
>
>
> On Mon, Dec 17, 2012 at 3:58 AM, Marcel Loose <loose at astron.nl 
> <mailto:loose at astron.nl>> wrote:
>
>     Hi David,
>
>     See my remarks inline.
>
>
>     On 15/12/12 16:47, David Cole wrote:
>>     On Sat, Dec 15, 2012 at 10:33 AM, Marcel Loose
>>     <marcel.loose at zonnet.nl <mailto:marcel.loose at zonnet.nl>> wrote:
>>
>>         Thanks, that seems to work.
>>
>>         Is the idiom
>>
>>             if(POLICY CMP<NNNN>)
>>               cmake_policy(PUSH)
>>               cmake_policy(SET CMP<NNNN> OLD)
>>               cmake_policy(POP)
>>             endif()
>>
>>         one that you also need to use with newer CMakes? Or does it
>>         then suffice to do
>>
>>             cmake_policy(SET CMP<NNNN> OLD)
>>
>>
>>     I assume you really mean:
>>
>>     if(POLICY CMP<NNNN>)
>>       cmake_policy(PUSH)
>>       cmake_policy(SET CMP<NNNN> OLD)
>>     endif()
>>
>>     ...
>>     other code where the policy is set to OLD
>>     ...
>>
>>     if(POLICY CMP<NNNN>)
>>       cmake_policy(POP)
>>     endif()
>>
>     Yes, you're right. I was oversimplifying.
>>
>>     The policies are tightly tied to the minimum required version of
>>     CMake. So if you use cmake_minimum_required with a certain
>>     version number, you can write code without if(POLICY assuming
>>     that all the policies you need to set are known as of that
>>     minimum version. If they are not (and they must not be in this
>>     particular case), then you'll need the if(POLICY construct.
>>
>     So, that basically means that you need to use if(POLICY...) for
>     all policies that are not part of the minimum required version? Is
>     there a way to find out which policies exist for which version of
>     CMake?
>
>     I was hoping for a more forward compatible solution. In other
>     words, I was hoping that I could always use CMAKE_POLICY(SET...)
>     unconditionally. It's a bit of a shame that I have to clutter my
>     CMakeLists.txt and *.cmake files with these extra conditionals;
>     and have to remove them (or should I say: clean up) whenever I
>     bump the minimum required version.
>
>     What's the reason that cmake doesn't silently ignore a
>     CMAKE_POLICY(SET...) for a policy it doesn't know about?
>
>>     The other option is to bump up your minimum required version.
>     Sure, but that defeats the whole purpose of setting a minimum
>     required version. I need to be compatible with version 2.6.2.
>
>     Best regards,
>     Marcel Loose.
>
>

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