CMake Interface project - doesn't build with gcc Linux

[TS-RyanShear]

Working on a cross compilation project. Project builds, runs and works as expected compiling with MSVC. Switching over to gcc (Ubuntu system), when I run make I get this error:

fatal error: nlohmann/json.hpp: No such file or directory
   11 | #include <nlohmann/json.hpp>

I'm using CMake / VCPKG for my project.

The project it fails on is an INTERFACE project, which I just have a couple of header files to help define behavior, as interfacing intended. This project compiles with no warning or errors with msvc. Is there something special I need to handle for the Linux adaption of it?

here is my cmake file:

cmake_minimum_required(VERSION 3.13)

# Find Nlohmann JSON
find_package(nlohmann_json CONFIG REQUIRED)

project(CPP.Interfaces LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)

file(GLOB_RECURSE SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/Sources/*.h")

# Create the header-only library target
add_library(CPP.Interfaces INTERFACE ${SOURCES})

# Specify the include files for the library
target_include_directories(CPP.Interfaces INTERFACE
    ${CMAKE_CURRENT_SOURCE_DIR}/Sources
)

target_link_libraries(CPP.Interfaces
    INTERFACE nlohmann_json::nlohmann_json
)

Any help is greatly appreciated.

[gregmarr]

https://github.com/nlohmann/json?tab=readme-ov-file#cmake says to use PRIVATE. I don't know if that would have any effect.

[TS-RyanShear]

I read that as well. I was hoping to keep this project as just an interface project, and haven't really thought of converting to a traditional library. Setting the value to private breaks the CMake interpreter for both Windows and Linux.

[cmake] CMake Error at CPP.Interfaces/CMakeLists.txt:20 (target_link_libraries):
[cmake]   INTERFACE library can only be used with the INTERFACE keyword of
[cmake]   target_link_libraries

I brought it up due to it being successfully used in Windows and not Linux, backwards from my experiences.