[CMake] Where is QT_USE_IMPORTED_TARGETS not safe to use?

[Stephen Kelly]

Wups, sent a moment to early...

Stephen Kelly wrote:

> Clinton Stimpson wrote:
>> It means the target must be created again with something like
>> add_library(Qt4::QtCore UNKNOWN IMPORTED)
>> 
>> If GrantleeConfig.cmake were to do this:
>> SET(QT_USE_IMPORTED_TARGETS 1)
>> find_package(Qt4 REQUIRED)
>> 
>> then the imported targets would satisfy the Qt4::QtCore reference and
>> others from your GrantleeTargets-debug.
>> 
>>> 
>>> > The GrantleeConfig.cmake could set QT_USE_IMPORTED_TARGETS and a
>>> > find_package(Qt4) to recreated those imported targets.
>>> 
>>> Ok, so maybe setting cis the thing that needs to
>>> be done 'again' by project B?
>> 
>> Yes, or preferably in your GrantleeConfig.cmake so project B doesn't have
>> to do it.
>> 
> 
> I tried creating the error scenario, but it does work even if the
> downstream does not set QT_USE_IMPORTED_TARGETS and even if I don't put it
> in GrantleeConfig either. Qt4::QtCore is never interpreted as a file path
> because FindQt4.cmake sets it unconditionally, and only conditionally sets
> QT_QTCORE_LIBRARY to Qt4::QtCore based on QT_USE_IMPORTED_TARGETS.


That means that if GrantleeTarget-debug uses

IMPORTED_LINK_INTERFACE_LIBRARIES_DEBUG "Qt4::QtCore"

then the Qt4::QtCore will never be interpreted as a file on disk and the 
comment in the file:

> This
> means when a project B then uses project A, these imported targets must be
> created again, otherwise e.g. "Qt4__QtCore" will be interpreted as name of 
> a library file on disk, and not as a target, and linking will fail.

is not correct. Right?

Also, it means that I don't have to use 

SET(QT_USE_IMPORTED_TARGETS 1)
find_package(Qt4 REQUIRED)

in my GrantleeConfig?

Thanks,

Steve.