[CMake] Why isn't target_link_libraries not enough in some cases?

[Saad Khattak]

Hi,

I am fetching and building SDL2 using FetchContent and then using
target_link_libraries(MyExe SDL2) in the hopes that the required include
directories and libraries will be added populated properly. The example
project can be found here:

https://github.com/samaursa/cmake_fetch_content_SDL2

Unfortunately, it seems that I have to manually specify the include
directories. Although target_link_directories(...) does take care of the
linking against the correct libraries. When it comes to my own CMake
enabled libraries, I do not have to specify the include directories.

This is problematic when installing my libraries or executables that depend
on SDL2 because the include directory for SDL is absolute (
https://cmake.org/Bug/view.php?id=15788).

Is SDL2 setup incorrectly or is there something I am overlooking?

Here is the CMakeLists.txt in the above mentioned example:
------------------------------------------------------------------------------------->

cmake_minimum_required(VERSION 3.11)

project(testProj)

include(FetchContent)

FetchContent_Declare(
  SDL2
  GIT_REPOSITORY "https://github.com/spurious/SDL-mirror"
  )

FetchContent_GetProperties(SDL2)
if(NOT sdl2_POPULATED)
  FetchContent_Populate(SDL2)
  message(STATUS "Catch source dir: ${sdl2_SOURCE_DIR}")
  message(STATUS "Catch binary dir: ${sdl2_BINARY_DIR}")
  add_subdirectory(${sdl2_SOURCE_DIR} ${sdl2_BINARY_DIR})
endif()

add_executable(testExe
  main.cpp
  )

message(STATUS "Catch include dir: ${sdl2_SOURCE_DIR}/include")

target_link_libraries(testExe SDL2)

# the following line is necessary, target_link_libraries for SDL2
# does not automatically set the correct include directories
target_include_directories(testExe PUBLIC ${sdl2_SOURCE_DIR}/include)

<-------------------------------------------------------------------------------------

Regards,
Saad
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