[CMake] How is the linker language of a library determined?

[Robin Verschueren]

Hi Craig,

Thanks for your continued support. I was able to create a small example
that you can find here:

https://gitlab.kitware.com/cmake/cmake/issues/17453

Best regards,
Robin

On Fri, 10 Nov 2017 at 06:32 Craig Scott <craig.scott at crascit.com> wrote:

> Can you create a small, self-contained example that reproduces the
> problem? A bit more than trivial since imported targets are involved, but
> give it a go, it will help narrow down the problem. If you're able to do
> that, please then report this in the issue tracker and attach that example.
> Also include the build output highlighting where you believe the commands
> used are incorrect.
>
> On Wed, Nov 8, 2017 at 3:40 PM, Robin Verschueren <
> robin.verschueren at gmail.com> wrote:
>
>> I use the "Unix Makefiles" generator (on macOS), with clang and clang++
>> as compilers (XCode version 9).
>>
>> On Wed, 8 Nov 2017 at 03:47 Craig Scott <craig.scott at crascit.com> wrote:
>>
>>>
>>> On Wed, Nov 8, 2017 at 7:29 AM, Robin Verschueren <
>>> robin.verschueren at gmail.com> wrote:
>>>
>>>> Hi there,
>>>>
>>>> I'm building some C code into a library. The library needs to link to a
>>>> C++ static library (IMPORTED target). I'm puzzled by the following:
>>>>
>>>>    - with BUILD_SHARED_LIBS=OFF (default), everything works as
>>>>    expected and CMake sees the C library as a "C++ library" (i.e. it uses the
>>>>    C++ compiler/linker to link the two libraries together into a static
>>>>    library).
>>>>    - with BUILD_SHARED_LIBS=ON however, CMake tries to link the C
>>>>    library to the C++ library with cc (clang in my case), and I get linker
>>>>    errors.
>>>>
>>>> My questions:
>>>>
>>>> *What mechanism does CMake use to determine the linker language, and
>>>> why is it different in these two cases?* Is it because I want to link
>>>> a shared library against a static library as opposed to two static ones? Or
>>>> is BUILD_SHARED_LIBS a red herring? Does CMake have a notion of what linker
>>>> language to use for IMPORTED targets?
>>>>
>>>>
>>> Can you confirm which CMake generator type you are using? If it is the
>>> Xcode generator, do you get the same behaviour building at the command line
>>> as you do from within the IDE? I only ask because your symptoms sound
>>> eerily familiar to a problem I've seen before where linking used a
>>> different launcher from the command line compared to the IDE (see the Xcode
>>> section of this article
>>> <https://crascit.com/2016/04/09/using-ccache-with-cmake/>).
>>>
>>>
>>>
>>> --
>>> Craig Scott
>>> Melbourne, Australia
>>> https://crascit.com
>>>
>>
>
>
> --
> Craig Scott
> Melbourne, Australia
> https://crascit.com
>
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