[cmake-developers] Printing the origin of include dirs

[Stephen Kelly]

Brad King wrote:

> If the cmProperty API were virtual then a property definition could
> specify the subclass used to represent the property.  One of the options
> could be a vector of generator expressions.

I think this idea gets complex quickly. 

The cmPropertyMap would need to hold cmProperty* and new them. cmPropertyMap 
and cmProperties are currently copied but that would have to be made 
impossible as it introduces ownership problems.

As we only currently have one potential user of this feature (the 
INCLUDE_DIRECTORIES), I'd prefer to stick with a solution which does not 
require making the cmProperty API virtual. I also see benefits for making it 
virtual, but I don't have a grasp on how much work other work it creates.

Thanks,

Steve.