How to prevent cmake to not add all targets from external dependencies using modern cmake constructs

I am trying to add external dependencies to my new cmake project in the cleanest and modern cmake way possible. I want to download these dependencies during configuration time. My problem is that all the targets from external dependencies are always imported. This spams my configurations in e.g. Clion which i want to be much cleaner by default but as you can see i have several useless targets from gtest, googlebenchmark, eigen and spdlog in the figure below. The project should compile on Windows and Linux.

So my question is how to prevent this?

I watched several modern cmake videos, e.g. https://www.youtube.com/watch?v=eC9-iRN2b04 and the sources from https://cliutils.gitlab.io/modern-cmake/.

My project folder structure looks as follows

.
├── CMakeLists.txt
├── Ikarus
|   └── CMakeLists.txt
|   └── addexternalLibs.cmake
│   └── src
│       └── Ikarus
│           └── [...]
├── problems
|   └── CMakeLists.txt
|   └── [.cpp files]
├── tests
|   └── CMakeLists.txt
|   └── [.cpp files]
├── benchmarks
|   └── CMakeLists.txt
|   └── [.cpp files]

I have a top level CMakeLists.txt as follows

cmake_minimum_required(VERSION 3.16)
project(Ikarus)

add_subdirectory(Ikarus)
add_subdirectory(problems)
add_subdirectory(tests)
add_subdirectory(benchmarks)

In the folder Ikarus i want to build my Ikarus_lib which should be used by the targets defined in problems, tests and benchmarks.

The file Ikarus/CMakeLists.txt looks as follows

file(GLOB_RECURSE IKARUS_CPP_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} CONFIGURE_DEPENDS  *.cpp )


add_library(${PROJECT_NAME}_lib STATIC)
target_sources(${PROJECT_NAME}_lib PRIVATE ${IKARUS_CPP_SOURCES})

include(addexternalLibs.cmake)

target_include_directories(${PROJECT_NAME}_lib PUBLIC src)

target_link_libraries(${PROJECT_NAME}_lib PUBLIC Eigen3::Eigen
                                          PUBLIC spdlog::spdlog)

Now i want to talk about the contents of the file Ikarus/addexternalLibs.cmake where the external depencies are imported. The difficulties similar arise in benchmark and tests where i import googletest and googlebenchmark but i think i will restrict myself to the Ikarus_lib case since the difficulties are the same.

Since i want to download my dependencies during configuration time i found the nice solution using https://cmake.org/cmake/help/latest/module/FetchContent.html

The result is Ikarus/addexternalLibs.cmake:

include(FetchContent)

message("Configure Eigen: ")

FetchContent_Declare(
        eigen
        GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
        GIT_TAG 3.4
        GIT_SHALLOW TRUE
        GIT_PROGRESS TRUE
)
option(EIGEN_BUILD_DOC OFF)
option(BUILD_TESTING OFF)
option(EIGEN_LEAVE_TEST_IN_ALL_TARGET OFF)
option(EIGEN_BUILD_PKGCONFIG OFF)
FetchContent_MakeAvailable(eigen)

message("====================================")
message("Configure spdlog: ")

FetchContent_Declare(
        spdlog
        GIT_REPOSITORY https://github.com/gabime/spdlog.git
        GIT_TAG v1.8.5
        GIT_SHALLOW TRUE
        GIT_PROGRESS TRUE
)
option(SPDLOG_BUILD_SHARED OFF)
option(SPDLOG_BUILD_ALL OFF)
FetchContent_MakeAvailable(spdlog)

This solution works and i managed to deactivate some targets using the options EIGEN_BUILD_DOC OFF.... But still i have lots of different useless targets as seen in the image above which cannot be deactivated using options of the package.

I tried several other things, e.g. using EXCLUDE_FROM_ALL https://cmake.org/cmake/help/latest/prop_tgt/EXCLUDE_FROM_ALL.html as follows

FetchContent_Declare(
        eigen
        GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
        GIT_TAG 3.4
        GIT_SHALLOW TRUE
        GIT_PROGRESS TRUE
)
option(EIGEN_BUILD_DOC OFF)
option(BUILD_TESTING OFF)
option(EIGEN_LEAVE_TEST_IN_ALL_TARGET OFF)
option(EIGEN_BUILD_PKGCONFIG OFF)

FetchContent_GetProperties(eigen)
if(NOT eigen_POPULATED)
   FetchContent_Populate(Eigen)
    add_subdirectory(${eigen_SOURCE_DIR} ${eigen_BINARY_DIR} EXCLUDE_FROM_ALL)
endif()

which also works but does also adds all that targets which i don't want. Therefore, EXCLUDE_FROM_ALL does not work the way i think it works.

Another way of using EXCLUDE_FROM_ALL could be

include(FetchContent)

message("Configure Eigen: ")

FetchContent_Declare(
        eigen
        GIT_REPOSITORY https://gitlab.com/libeigen/eigen.git
        GIT_TAG 3.4
        GIT_SHALLOW TRUE
        GIT_PROGRESS TRUE
)
option(EIGEN_BUILD_DOC OFF)
option(BUILD_TESTING OFF)
option(EIGEN_LEAVE_TEST_IN_ALL_TARGET OFF)
option(EIGEN_BUILD_PKGCONFIG OFF)
FetchContent_MakeAvailable(eigen)
set_target_properties(eigen PROPERTIES EXCLUDE_FROM_ALL TRUE)

which also does not change the behaviour.

I also tried CPMAddPackage from https://github.com/cpm-cmake/CPM.cmake

CPMAddPackage(
        GITLAB_REPOSITORY libeigen/eigen
        GIT_TAG 3.4
        OPTIONS "EIGEN_BUILD_DOC NO"
                "BUILD_TESTING NO"
                "EIGEN_LEAVE_TEST_IN_ALL_TARGET YES"
                "EIGEN_BUILD_PKGCONFIG NO"
)

which also works but also adds all that targets.

So now i don't know what else to try and i think i will just keep the targets and delete them from my Clion configuration interface and hope they don't reappear. But still i want to understand what am i missing. I think this is a common problem and the solution should be very easy?

Furthermore, i know that i can just download e.g. eigen and use include_directories(...) to automatically add the headers without the targets. But on one hand this is not modern cmake as advertised in https://www.youtube.com/watch?v=eC9-iRN2b04 where using include_directories is called an anti-pattern and one should "think in modules". On the other hand this does not help for packages which are not header-only.

So how can this problem be solved elegantly? Additionally, i would appreciate every other comment to my (bad) usage of Cmake. Thanks!