What is the recommended way of managing features for my package?

[crgnam]

I have a library I'm looking to add to vcpkg at somepoint (currently private and on a private registry within my org).

There is an optional feature for building a GUI preview tool for somethings, which I currently set by adding the following to my root CMakeLists.txt:

option(BUILD_GUI "Build the GUI components" OFF)

if(BUILD_GUI)
    set(BUILD_VULKAN ON)
    list(APPEND VCPKG_MANIFEST_FEATURES "gui")
    message("Building GUI components")
endif()

Then in later CMakeLists.txt I test if(BUILD_GUI) to configure the correct things to build.

Then in my vcpkg.json manifest file, I add the following:

"features": {
    "gui": {
        "description": "Build GUI Applications",
        "dependencies": [
            "glfw3",
            {
                "name": "imgui",
                "features": [
                    "glfw-binding",
                    "vulkan-binding"
                ]
            }
        ]
    }
}

The idea being you can simply set the -DBUILD_GUI when building the project, and then by updating VCPKG_MANIFEST_FEATURES with the correct keyword, it will fetch the necessary dependencies.

This works perfectly when developing my library, however when attempting to install from my private registry, it does not seem possible to configure a specific CMake option without using a custom-overlay, which doesn't seem like the right solution. Obviously what could be done is to set the feature directly in the manifest file, but then my existing logic within various CMakeLists.txt would be broken.

Would it therefore be correct to reorganize my logic to be centered around whether or not the necessary dependencies have been installed via specifying the feature? And similarly, is it possible to use this system to specify options that do not explicitly require any additional dependencies? Say, for example, I wanted to optionally build some command-line applications alongside my library. Could I allow a user to specify an apps feature in their manifest file using:

"dependencies": [
    {
        "name": "mylib",
        "features": [
            "gui", 
            "apps"
        ]
    }
]

that my CMake could detect and build those applications? It just feels like requiring a custom-overlay for building additional components is the wrong solution but perhaps I'm just misunderstanding.

[crgnam]

It looks like this is where the vcpkg_check_features() command comes in handy: https://learn.microsoft.com/en-us/vcpkg/maintainers/functions/vcpkg_check_features

If a feature has been enabled, you can use this function to set a CMake variable.