[CMake] transitive linkage of OBJECT library targets

[Robert Maynard]

This is a known limitation of the current design. Only directly linked
object library objects are propagated.

For more details on why see: https://gitlab.kitware.com/cmake/cmake/issues/18090

On Wed, May 22, 2019 at 1:48 AM Richard Szabo <sz.richard at gmail.com> wrote:
>
> Hi cmakers
>
> I'm trying to get the following example working:
> ```
> cmake_minimum_required(VERSION 3.14)
> project(test_object_lib_nesting)
>
> set(CMAKE_CXX_STANDARD 14)
>
> add_library(first_object_lib OBJECT first.cpp)
>
> add_library(second_object_lib OBJECT second.cpp)
>
> target_link_libraries(second_object_lib first_object_lib)
>
> add_executable(test_object_lib_nesting main.cpp)
>
> target_link_libraries(test_object_lib_nesting second_object_lib)
> ```
>
> The problem I have that the linker command line will have only the
> second.cpp.o for linking the first.cpp.o will not be added as link
> object to the exe. Causing missing symbols on exe linkage.
>
> How to transitively resolve and link "nested" Object library targets ?.
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