[cmake-developers] Handling of Config specific imported targets?

[Stephen Kelly]

Hi there,

In Qt 5 we currently generate IMPORTED_LOCATION_${Config} for the Debug or 
Release (or both, depending on platform), depending on how Qt is configured.

If both exist (on windows) and the caller uses CMAKE_BUILD_TYPE == Debug or 
Release, the correct location should be used. However, this doesn't account 
for having a different or empty CMAKE_BUILD_TYPE. 

If the Config doesn't match any available IMPORTED_LOCATION_${Config}, then 
it seems from my testing that the first one set is chosen. This means that 
for example if I have a PROFILING Configuration, which should use the 
release libraries, but Debug appears first in the generated Config file (as 
it does), then the wrong IMPORTED_LOCATION would be used.

I have written a patch that changes the behavior to not create a 
IMPORTED_LOCATION_${Config} for both Debug and Release unless necessary. If 
only building Debug or only building Release, only the IMPORTED_LOCATION 
will be specified. If building debug_and_release, then IMPORTED_LOCATION  
will refer to the Release location, and IMPORTED_LOCATION_DEBUG will refer 
to the debug location.

https://codereview.qt-project.org/#change,26116

I'm looking for some review of the approach, and some confirmation of how 
non-matching configurations are handled. Does it make sense?

In particular, with this set-up, how would a downstream create a 
configuration which should use the debug libraries, but where they have 
built Qt with debug_and_release (the default on Windows)? Would they have to 
create another IMPORTED_LOCATION_Foo for all targets themselves?


Thanks,

Steve.