Wait a sec... where we link against "telepathy-qt target"? I see only ${TELEPATHY_QT5_LIBRARIES} and IMO it was just wrong to treat LIBRARIES variable as targets.

Starting from 0.9.8 we have TelepathyQt5::Core target that exports linked libraries (thought as Qt5::Xml is not a part of the public API, it is not added to the link list to prevent "overlinking".
I admit I could mess it up, but the new targets worked well for me: https://github.com/TelepathyIM/telepathy-morse/commit/997100a07e6464d85c2cbd3ce56049eebae310c6

That would require bumping the telepathy-qt dependency, no? I think we're past the dependency freeze for 19.12

Yes, probably it would be better to land this patch for now.
Long story short — I rewrote targets for TelepathyQt, because we exported them under the same name as the library files. CMake doesn't allow to export a target under multiple names, nor add_library(telepathy-qt5 ALIAS TelepathyQt5::Core). It is sad that we relied on ${TELEPATHY_QT5_LIBRARIES} that had not the recommended full path (like /usr/lib/libtelepathy-qt5.so.0.9.7) or the lookup path and linking flag (such as -L/usr/lib -ltelepathy-qt5), but just the "telepathy-qt5" name that happened to match the odd target name.

I considered addition of "add_library(telepathy-qt5 UNKNOWN IMPORTED)" with manual iteration and coping of the target properties from TelepathyQt5::Core to telepathy-qt5 but it seemed like too big workaround for the use that I consider as invalid.

I would suggest to make it clear that there is new version that works:

if(TELEPATHY_QT5_VERSION VERSION_LESS "0.9.8")
    target_link_libraries (KTpCommonInternals
        PUBLIC
            Qt5::DBus
            Qt5::Xml
            # ${TELEPATHY_QT5_LIB_DIR}/lib${TELEPATHY_QT5_LIBRARIES}.so.0.${TELEPATHY_QT5_VERSION}
            ${TELEPATHY_QT5_LIBRARIES}
    )
else()
    target_link_libraries (KTpCommonInternals
        PUBLIC
            TelepathyQt5::Core
    )
endif()

What about pushing this as-is for 19.12 and bumping the dependency and using the new target on master (19.12 is already branched)

In D25269#561463, @arojas wrote:

What about pushing this as-is for 19.12 and bumping the dependency and using the new target on master (19.12 is already branched)

Meh :-(. I realized that a distribution can't update to telepathy-qt-0.9.8 because it'll break KTp. That said, I actually need your patch to land in 19.12 at the very least. Or maybe I have to release a hotfix for TpQt, but there is no nice solution to copy an imported target. I actually checked if KTp use the target, but didn't found that weird-named "telepathy-qt5" target in the link list and thought that we use the legacy variable-based approach (TELEPATHY_QT5_LIBRARIES, etc).

Hey-ho! One-line fix 😄 :facepalm: :

if(NOT TELEPATHY_QT5_VERSION VERSION_LESS "0.9.8") # Use NOT VERSION_LESS because VERSION_GREATER_EQUAL is not available until CMake-3.7
    set(TELEPATHY_QT5_LIBRARIES TelepathyQt5::Core)
endif()