CMake Error: Attempt to add link library to target which is not built in this directory (only when policy CMP0079 is set to NEW)

Question

I want to link the component "fsm" into my executable (main.cpp). "fsm" is dependent on "taskmap". So I was trying to figure out how to configure cmake to recognise my libraries the correct way, but the configuration always fails with the following errors:

Errors (yielded while configuring):

[cmake] CMake Error at components/taskmap/CMakeLists.txt:9 (target_link_libraries):
[cmake]   Attempt to add link library "taskmap" to target "sample_project" which is
[cmake]   not built in this directory.
[cmake] 
[cmake]   This is allowed only when policy CMP0079 is set to NEW.
[cmake] Call Stack (most recent call first):
[cmake]   CMakeLists.txt:8 (include)
[cmake] 
[cmake] 
[cmake] CMake Error at components/fsm/CMakeLists.txt:8 (target_link_libraries):
[cmake]   Attempt to add link library "fsm" to target "sample_project" which is not
[cmake]   built in this directory.
[cmake] 
[cmake]   This is allowed only when policy CMP0079 is set to NEW.
[cmake] Call Stack (most recent call first):
[cmake]   CMakeLists.txt:9 (include)

My directory structure:

project
├───CMakeLists.txt
├───components
│   ├───fsm
│   │   ├───fsm.cpp
│   │   ├───CMakeLists.txt
│   │   └───include
│   │       └───fsm.hpp
│   └───taskmap
│       ├───CMakeLists.txt
│       └───include
│           └───taskmap.hpp
└───main
    ├───main.cpp
    └───CMakeLists.txt

CMakeLists.txt (toplevel):

cmake_minimum_required(VERSION 3.0.0)
project(sample_project VERSION 0.1.0)

include(CTest)
enable_testing()

add_subdirectory(main)
include(components/taskmap/CMakeLists.txt)
include(components/fsm/CMakeLists.txt)

set(CPACK_PROJECT_NAME ${PROJECT_NAME})
set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
include(CPack)

main/CMakeLists.txt:

add_executable(sample_project main.cpp)

components/fsm/CMakeLists.txt:

add_library(
    fsm
    fsm.cpp
    include/fsm.h
)

target_include_directories(fsm PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
target_link_libraries(sample_project PRIVATE fsm)

components/taskmap/CMakeLists.txt:

add_library(
    taskmap
    include/taskmap.h
)

set_target_properties(taskmap PROPERTIES LINKER_LANGUAGE CXX)

target_include_directories(taskmap PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
target_link_libraries(sample_project PRIVATE taskmap)

I can't really make a lot out of this error and have done some research:

CMake: Attempted to add link library to target which is not built in this directory

This person tried to target_link_libraries() in the toplevel CMakeLists.txt, even though the executables are added in a subordered CMakeLists.txt. Apparently target_link_libraries() needs to be called from the CMakeLists.txt where the target is specified (except if the directory scope remains the same, see below).

Alternative to calling target_link_libraries in subdirectory

This person attempted to use target_link_libraries() with the "link to"-target not specified in the same directory as the newly created target (because a new subdirectory scope was entered). I think this is somewhat related to my problem, so I switched to use include() directives instead of add_subdirectory(), but the error stays the same.

So nothing helped so far. Any clues on what I'm doing wrong?