How to make vcpkg use (s)ccache from cmake preset

[Arndt-MBE]

I use vcpkg in manifest mode in my project, which is configured by cmake presets.
Integration of vcpkg via CMAKE_TOOLCHAIN_FILE works fine, and the compiler cache (sccache in my case) is integrated via CMAKE_CXX_COMPILER_LAUNCHER in the actual build process.
But I have not yet found out how to make vcpkg use sccache as the CMAKE_CXX_COMPILER_LAUNCHER in its cmake builds.
I read that vcpkg unsets all CMAKE_* environment variables, so I tried to VCPKG_CHAINLOAD_TOOLCHAIN_FILE with the content set(CMAKE_CXX_COMPILER_LAUNCHER "sccache"), but that has no effect.

Do you know a good way to make vcpkg accept a CMAKE_CXX_COMPILER_LAUNCHER?

[Neumann-A]

Variables from your CMake project are not forwarded to vcpkg. You need to adjust the toolchain vcpkg internally uses.

[Arndt-MBE]

Isn't that what VCPKG_CHAINLOAD_TOOLCHAIN_FILE does, like through an official backdoor?

[Neumann-A]

No. Only if it is directly set in the triplet.

That variable is meant to load another toolchain alongside vcpkg.cmake for your project.

[Arndt-MBE]

#30191 is about a very similar question, although not specific to presets.