CMake cannot find the header files of a git submodule - c++

Question

I have two git repositories with CMake, one is a game engine, and the other is a game that I am making with the game engine.
It turns out, this game engine has a submodule that is included in the project's CMakeLists.txt, and in the game repository, the game engine is added as a submodule that is also included in CMakeLists.txt. However, when compiling the two projects, the Game Engine compiles everything normal without errors, I update the game repository to update the submodules, and when compiling the game, it does not find the game engine submodule for some unknown reason.
Game Engine CMakeLists:
cmake_minimum_required(VERSION 3.8)
set(PROJECT_NAME "Enel")
set(CMAKE_CXX_STANDARD 17)
project(${PROJECT_NAME} VERSION 0.1.0)
include_directories(
"${PROJECT_SOURCE_DIR}/include"
"${PROJECT_SOURCE_DIR}/src"
"${PROJECT_SOURCE_DIR}/libs/spdlog/include"
"${PROJECT_SOURCE_DIR}/libs/spdlog/src"
)
file(GLOB SRC_FILES
"${PROJECT_SOURCE_DIR}/include/**/*.h"
"${PROJECT_SOURCE_DIR}/include/**/*.hh"
"${PROJECT_SOURCE_DIR}/include/**/*.hpp"
"${PROJECT_SOURCE_DIR}/src/**/*.c"
"${PROJECT_SOURCE_DIR}/src/**/*.cc"
"${PROJECT_SOURCE_DIR}/src/**/*.cpp"
)
add_library(${PROJECT_NAME} STATIC ${SRC_FILES})
Game CMakeLists:
cmake_minimum_required(VERSION 3.8)
set(PROJECT_NAME "Minicraft")
set(CMAKE_CXX_STANDARD 17)
project(${PROJECT_NAME} VERSION 0.1.0)
include_directories(
"${PROJECT_SOURCE_DIR}/include"
"${PROJECT_SOURCE_DIR}/src"
"${PROJECT_SOURCE_DIR}/libs/enel/include"
"${PROJECT_SOURCE_DIR}/libs/enel/src"
)
link_directories(${PROJECT_SOURCE_DIR}/libs/enel)
file(GLOB SRC_FILES
"${PROJECT_SOURCE_DIR}/include/**/*.h"
"${PROJECT_SOURCE_DIR}/include/**/*.hh"
"${PROJECT_SOURCE_DIR}/include/**/*.hpp"
"${PROJECT_SOURCE_DIR}/src/**/*.c"
"${PROJECT_SOURCE_DIR}/src/**/*.cc"
"${PROJECT_SOURCE_DIR}/src/**/*.cpp"
"${PROJECT_SOURCE_DIR}/libs/enel/src/**/*.c"
"${PROJECT_SOURCE_DIR}/libs/enel/src/**/*.cc"
"${PROJECT_SOURCE_DIR}/libs/enel/src/**/*.cpp"
"${PROJECT_SOURCE_DIR}/libs/enel/include/**/*.h"
"${PROJECT_SOURCE_DIR}/libs/enel/include/**/*.hh"
"${PROJECT_SOURCE_DIR}/libs/enel/include/**/*.hpp"
)
add_executable(${PROJECT_NAME} ${SRC_FILES})
Build Output:
[ 33%] Building CXX object CMakeFiles/Minicraft.dir/src/MC/Game.cc.o
In file included from /home/yorichii/repos/minicraft/libs/enel/include/Enel/Platform/EntryPoint.hh:4,
from /home/yorichii/repos/minicraft/src/MC/Game.cc:2:
/home/yorichii/repos/minicraft/libs/enel/include/Enel/Util/Log.hh:3:10: fatal error: spdlog/spdlog.h: Arquivo ou diretório inexistente
3 | #include <spdlog/spdlog.h>
| ^~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/Minicraft.dir/build.make:76: CMakeFiles/Minicraft.dir/src/MC/Game.cc.o] Erro 1
make[1]: *** [CMakeFiles/Makefile2:76: CMakeFiles/Minicraft.dir/all] Erro 2
make: *** [Makefile:84: all] Erro 2

Answer 1

If you use directory based property like include_directory or link_directory, you'll have to repeat requirements:
include_directories(
"${PROJECT_SOURCE_DIR}/include"
"${PROJECT_SOURCE_DIR}/src"
"${PROJECT_SOURCE_DIR}/libs/enel/include"
"${PROJECT_SOURCE_DIR}/libs/enel/src"
# Repeat all requirements
"${PROJECT_SOURCE_DIR}/libs/enel/libs/spdlog/include"
"${PROJECT_SOURCE_DIR}/libs/enel/libs/spdlog/src"
)
This is why you should strongly consider target based property, as all modern build system are using, including modern CMake:
In Enel:
cmake_minimum_required(VERSION 3.8)
set(PROJECT_NAME "Enel")
set(CMAKE_CXX_STANDARD 17)
project(${PROJECT_NAME} VERSION 0.1.0)
# If you can install spdlog in a local directory in the project,
# prefer find_package(spdlog REQUIRED)
add_subdirectrory(libs/spdlog)
file(GLOB SRC_FILES
"strongly/consider/not/globbing/**/*.cpp"
)
add_library(Enel STATIC ${SRC_FILES})
target_link_libraries(Enel PUBLIC spdlog)
target_include_directories(Enel PUBLIC src include)
Then in your game, do this:
cmake_minimum_required(VERSION 3.8)
set(PROJECT_NAME "Minicraft")
set(CMAKE_CXX_STANDARD 17)
project(${PROJECT_NAME} VERSION 0.1.0)
add_subdirectory(libs/enel)
file(GLOB SRC_FILES
...
)
add_executable(Minicraft ${SRC_FILES})
# Links to all required libraries, add all required include directories
target_link_libraries(Minicraft PUBLIC Enel)
target_include_directory(Minicraft PUBLIC include src)