[cmake-developers] A policy for Policies

[Stephen Kelly]

Stephen Kelly wrote:

> Setting a policy to REQUIRED_IF_USED in the cmake source means that if
> someone tries
> 
>  cmake_policy(SET CMP0011 OLD)
> 
> they will get an informative error instead of no warning.

Actually, that's not correct, sorry I wrote the explanation too quickly. 
What I described is actually REQUIRED_ALWAYS.

REQUIRED_IF_USED means that if the policy behavior is hit (ie, relying on 
old CMP0011 behavior), *and* the code has 

 cmake_policy(SET CMP0011 OLD)

*then* they get an informative error. 

If they set the policy (with cmake_policy or with cmake_minimum_required), 
but already don't rely on OLD behavior, then there is no new error.

Thanks,

Steve.