[CMake] Forcing a target to be built if another target is built

[Robert Maynard]

Have you thought about not doing anything in the root CMakeLists for your
testing directories but instead inside the active project you use
add_subdirectory ( it supports relative paths to handle directories not
physically nested inside it ).

On Wed, May 9, 2018 at 8:56 AM Job Noorman <job at noorman.info> wrote:

> Hi all,
>
> We have a large codebase consisting of 200+ modules. Each module is
> defined in its own subdirectory and compiled as a static library.
>
> These modules are not final products on their own but are combined to
> create "projects". We have about 15 projects that all use a subset of
> the modules to implement their functionality. The projects are
> independent in the sense that they cannot be built together; when
> running cmake, we select the project to build.
>
> To ensure that only the modules that are needed by the selected project
> are built, we took the following approach: all modules have a common
> root directory which is included using add_subdirectory with the
> EXCLUDE_FROM_ALL flag. Then, the current project's root directory is
> added without this flag. This ensures that the targets defined by the
> project and the modules that they need (but no other) are added to the
> build system. This works very well and is much nicer than having to
> define options for all optional modules to be able to disable them.
>
> There is one catch, however: each module defines an executable that runs
> its unit tests. What should happen is that if a module is built by a
> project, its unit tests are also built. However, there seems to be no
> way to define this relationship in CMake. What we would like to express
> is that "if library A is built, then executable ATest should also be
> built". Since ATest obviously links against A, we cannot use
> add_dependencies(A ATest) since this creates a circular dependency
> between an executable and a library.
>
> Note that the "option" approach briefly mentioned above would allow us
> to express this but this would be completely unwieldy in our case.
>
> Is there currently a way in CMake to express this relation between a
> library and an executable?
>
> If not, would the following suggestion make sense?: A target property
> "INTERFACE_DEPENDENCIES" could be added that would set the
> MANUALLY_ADDED_DEPENDENCIES target property of dependents. Setting this
> property on A with ATest as value would then solve my problem (note that
> I proposed adding this property for a different use case here:
> https://gitlab.kitware.com/cmake/cmake/issues/14633).
>
> Regards,
> Job
>
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