[cmake-developers] CMake 2.8.12 transitive link regression?

[Stephen Kelly]

Brad King wrote:

> On 10/30/2013 11:20 AM, Brad King wrote:
>> Also please add the corresponding test case and base the topic
>> on v2.8.12~2 so we can merge it for 2.8.12.1 after it passes
>> in 'next'.
> 
> Thanks.  It appears that ImplementationIsInterface bypasses the
> checks for EXPORT_LINK_INTERFACE_LIBRARIES and produces the
> IMPORTED_LINK_INTERFACE_LIBRARIES properties even when CMP0022
> is set to NEW.


  cmake_minimum_required(VERSION 2.8.12.1)

  project(foo)

  add_library(foo SHARED foo.cpp)
  add_library(bar SHARED foo.cpp)
  target_link_libraries(bar foo)

  export(TARGETS foo bar FILE myTargets.cmake)

It is not obvious to the user that they are causing their downstreams to 
depend on CMake 2.8.12. There was no warning about it (because there is no 
bug in the code), no build error and no export error.

By populating INTERFACE_LINK_LIBRARIES instead, the result would be that 
downstreams require 2.8.12. If that's what you want I can change this when 
the policy is NEW. I think that's fine. If they care about their 
downstreams, they'd test or examine their export files when they bump their 
cmake version requirement.

Or maybe I can export both INTERFACE_LINK_LIBRARIES and 
IMPORTED_LINK_INTERFACE_LIBRARIES. But then, when could we ever not export 
IMPORTED_LINK_INTERFACE_LIBRARIES? As this case is mostly just resulting 
from a 'very ingrained' pattern of not making the link interface explicit, I 
don't think it matters if we always export IMPORTED_LINK_INTERFACE_LIBRARIES 
in this case. We stop exporting it when the user makes their link interface 
explicit. However, if they do the migration to 2.8.12 (no output from cmake) 
and then later make their link interface explicit (no output from cmake), 
then downstream now require 2.8.12. I think that's fine. If they care about 
their downstreams they need to test or examine their export files in this 
case too.

Or we could make it a CMP0022-NEW-error to export a target which has link 
dependencies and no explicit link interface and 
EXPORT_LINK_INTERFACE_LIBRARIES is not used. I think this is still my 
preference. Everything else is very messy. 

Thanks,

Steve.