[cmake-developers] New INTERFACE_LINK_LIBRARIES policy approach

[Stephen Kelly]

Brad King wrote:

> Now, on to exporting.  Unlike the previous iteration the policy
> affects it too.
> 
> When the policy is OLD/WARN we export only the old interface and
> not the new interface.

We spent some time figuring out how to not export the old interface if it is 
not needed, based only on what API had been used and what the policy state 
was. Adding API to make install(EXPORT) not export the old interface was 
always an option, but was disregarded before. 

Adding that API reduces complexity in my branch too. However, I think the 
complexity is worth it, and I think it would make more sense to use the 
existing checks that are in my branch, AND add the API-hammer to control 
install(EXPORT) behavior. We can also add an API to throw error if the old 
property is populated when export(INSTALL) is called. Given that the tll 
signature without a qualifier is not really needed, there's no reason to set 
the old properties anymore after the branch.

Thanks,

Steve.