cmake linking libraries with internal dependency - cmake

Question

First of all, I'm not sure if the way I setup my project is correct but it's like this,
A cmake project called Lib has two subdirectories Animal and Dog. Both are static libraries but Dog depends on Animal.
Lib's CMakeLists.txt
cmake_minimum_required(VERSION 3.16.3)
project(Lib VERSION 1.0.0 DESCRIPTION "My package." LANGUAGES CXX)
add_subdirectory(Animal)
add_subdirectory(Dog)
install(EXPORT LibConfig
FILE LibConfig.cmake
NAMESPACE Lib::
DESTINATION lib/Lib/cmake
)
Animal/CmakeLists.txt
set(TARGET_NAME Animal)
add_library(${TARGET_NAME}
src/Animal.cpp
)
target_include_directories(${TARGET_NAME} PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>
)
install(TARGETS ${TARGET_NAME} EXPORT LibConfig
ARCHIVE DESTINATION lib
LIBRARY DESTINATION lib
RUNTIME DESTINATION bin
)
install(DIRECTORY include/
DESTINATION include/${TARGET_NAME}
FILES_MATCHING PATTERN "*.hpp")
Dog/CMakeLists.txt. I'm not sure how to depend on Animal.
set(TARGET_NAME Dog)
add_library(${TARGET_NAME}
src/Dog.cpp
)
target_include_directories(${TARGET_NAME}
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>
PRIVATE
$<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/Animal/include>
)
target_link_libraries(${TARGET_NAME}
PRIVATE
Animal
)
install(TARGETS ${TARGET_NAME} EXPORT LibConfig
ARCHIVE DESTINATION lib
LIBRARY DESTINATION lib
RUNTIME DESTINATION bin
)
install(DIRECTORY include/
DESTINATION include/${TARGET_NAME}
FILES_MATCHING PATTERN "*.hpp")
This uses the library.
cmake_minimum_required(VERSION 3.10.2)
project(UseLib)
find_package(Lib REQUIRED)
add_executable(${PROJECT_NAME}
main.cpp
)
target_link_libraries(${PROJECT_NAME}
Lib::Dog
)
main.cpp
#include <Dog/Dog.hpp>
int main()
{
Dog d;
return 0;
}
The libraries compile fine but when I use it in a project I get an error saying Dog can't find the Animal header.
.../include/Dog/Dog.hpp:3:10: fatal error: Animal.hpp: No such file or directory
#include "Animal.hpp"
^~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/UseLib.dir/build.make:63: CMakeFiles/UseLib.dir/main.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:76: CMakeFiles/UseLib.dir/all] Error 2
make: *** [Makefile:84: all] Error 2

Answer 1

Dog is not finding Animal because in Dog.hpp I have #include "Animal.hpp" but I have the headers installed in its own subdirectory so external projects includes it this way #include <Animal/Animal.hpp>. It's something I didn't understand.
target_include_directories(${TARGET_NAME}
PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>
$<INSTALL_INTERFACE:include/Animal>
)