Start designing an official or community-driven vcpkg dependency provider implementation

[theblackunknown]

This discussion is about starting implementing a CMake dependency provider for vcpkg the proper way.

Based on search for similar discussions, there are a couple of past/pending efforts but they seem to be on hold given the last update date:

• WIP: Dep providier shenanigans #31062
• [vcpkg] Controlling top-level find_package #27950 (comment)

Ideally I would like to start making an "official" implementation for this but based on #27950 (comment) maybe this is not desirable and we would provide a community driven one, the same way we do for triplet useful for the community but not tested on the CI ?

I do believe we can start one without breaking backward compatibility with the current scripts/buildsystems/vcpkg.cmake, for example we can create another scripts/buildsystems(/community)/vcpkg-dependency-provider.cmake which share common code with the former.

[Neumann-A]

The question rather is:
What would be the benefit of it? cmake dependency providers are just an upstream blessed overwrite of find_package

[Neumann-A]

Concretely we would have a consistent approach to bring dependency in a project

You don't need dependency providers to use CMAKE_TOP_LEVEL_INCLUDE. You can already use it with vcpkg.cmake. But be aware that this has implications for try_compile since CMAKE_TOOLCHAIN_FILE is passed on but CMAKE_TOP_LEVEL_INCLUDE is not

[theblackunknown]

I thought that your PR #31062 showed the minimal required change to make vcpkg.cmake works as a dependency provider ?

The current implementation overrides find_package implementation and does not call cmake_language(SET_DEPENDENCY_PROVIDER ...) so it does not look like this can work, am I missing something ?

[Neumann-A]

I thought that your PR #31062 showed the minimal required change to make vcpkg.cmake works as a dependency provider ?

The problem is you will still need to have the find_package override since vcpkg-cmake-wrapper.cmake requires it. So for versioning and backward compat it is always needed

[theblackunknown]

Good point ! I forgot about those vcpkg-cmake-wrapper.cmake, but maybe this is something a dependency provider could implement as well as part of its find_package override ?
It would make sense in my opinion as using find_package(BYPASS_PROVIDER ...) will then rightfully skip those too.

[dg0yt]

Find something better than vcpkg-cmake-wrapper.cmake could be desired: Wrappers don't see the normal find_package interface variables.