My project is a game engine, and it currently looks something like this:

/build
/engine
    /include
        /engine.h
    /src
        /enginepch.h
        ...
    /vendor
        /header_only
            /include
                /header1.h
                ...
        /need_to_compile
        ...
    CMakeLists.txt
/testbed
    /stuffForTestingEngine
    CMakeLists.txt
CMakeLists.txt

My includePath has engine/vendor/** and engine/src/** and I’m doing all my coding in VSCode with the C/C++ ms-vscode extension.

./engine/CMakeLists.txt is as such:

project(engine)

# config "need_to_compile

# ...and I configured everything that needed compilation here: glm, glad, openal, libpng and glfw.

# linking

add_library(engine SHARED
    src/core/application.cpp
    src/core/engine.cpp
    # etc. These are all my source files.
)
add_library(engine::engine ALIAS engine)

target_include_directories(engine PUBLIC 
    ${engine_SOURCE_DIR}/include
)
target_include_directories(engine PRIVATE
    ${PROJECT_SOURCE_DIR}/vendor
)
target_precompile_headers(engine PRIVATE src/enginepch.h)

target_link_libraries(engine PUBLIC 
    glfw 
    png 
    openal
    glad
    glm::glm
) 

This setup and pch.h file worked great with all the std stuff, such as <chrono> and <string>.

As soon as I tried including any header_only lib in my pch file, it broke. For example:

# This works!
#include <glm/glm.hpp>

# These didn't.
#include <spdlog/spdlog.h>
#include <entt/entt.h>
#include <stb_image/stb_image.h>

I tried many variations of the #include statement, such as “lib”, “lib.h”, “lib/lib.h”, , <lib/lib.h> and <lib.h>. None worked.

I tried including these header_only libs in CMakeLists, either by linking to an alias or adding a include_directory, but that didn’t work.

I suspect that my setup is wrong, or that I have a fatal misunderstanding of what CMake/the compiler is doing.