[cmake-developers] Support for imported targets in CMAKE_REQUIRED_LIBRARIES

Brad King brad.king at kitware.com
Fri Jan 20 09:25:29 EST 2012


On 1/19/2012 11:49 AM, Alexander Neundorf wrote:
> On Thursday 19 January 2012, Brad King wrote:
>> I think a full solution to this will end up duplicating a lot of the logic
>> that CMake already has in its C++ code for link dependency analysis.  I
>> wonder if instead you could modify the signature of try_compile to accept
>> the LINK_LIBRARIES as a formal argument.  Then teach the C++ code to
>> resolve the imported targets and take care of the link interfaces.
>
> I'll have a look at that too.
> What things exactly do you have in mind additionally ?

Rather than jumping to an implementation of my proposal let's think through
the interface.  The src-file signature of try_compile is currently:

  try_compile(RESULT_VAR <bindir> <srcfile>
              [CMAKE_FLAGS flags...]
              [COMPILE_DEFINITIONS flags...]
              [OUTPUT_VARIABLE <var>]
              [COPY_FILE <fileName>])

The CMakeLists.txt it generates includes the line

   TARGET_LINK_LIBRARIES(cmTryCompileExec ${LINK_LIBRARIES})

so right now one uses the CMAKE_FLAGS option to pass -DLINK_LIBRARIES=...
to specify link libraries.  The try_compile command has no chance to
recognize which options are libraries.  Instead, let's add a LINK_LIBRARIES
option to try_compile:

  try_compile(RESULT_VAR <bindir> <srcfile>
              ... [LINK_LIBRARIES libs...] ...)

Then the implementation of the command can evaluate the "libs..." arguments
in a context where imported targets are known.  Loop over each library.
For those that this->Makefile->FindTargetToUse() returns a target, verify
that it is IMPORTED, and then call target->GetLinkInformation(config),
where config is the try-compile's configuration.  The return value of
that will be a cmComputeLinkInformation object from which you can query
the link line.

-Brad



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