vcpkg adds target rather than host paths to CMAKE_PROGRAM_PATH

[craigscott-crascit]

Describe the bug
Calls to find_program() are generally going to want to find executables that can run on the host, not on the target architecture. At the moment, vcpkg adds the tools directory of the target triplet install area to CMAKE_PROGRAM_PATH, but not the tools directory of the host triplet's install area. When adding a host dependency that provides a tool (in my case the motivating example are things like ccache and sccache, which we are experimenting with providing via a private vcpkg registry), those tools are not able to be found due to CMAKE_PROGRAM_PATH not including the subdirectories under the host triplet's tools area.

I think adding the target triplet's tools subdirectories to CMAKE_PROGRAM_PATH is questionable, but not adding the host triplet's tools subdirectories definitely looks like a bug to me. It is currently breaking some of our projects that want to provide command line tools when using a custom target triplet.

Don't focus on the ccache and sccache part of this, I only use those as examples. There are other problems we are uncovering with trying to have those as host dependencies, but we will follow that up in separate issues and discussions. The bug report here is focused on incorrect population of the CMAKE_PROGRAM_PATH variable.

Environment

• OS: all
• Compiler: all

To Reproduce

Steps to reproduce the behavior:

1. Create a manifest file that lists at least one host dependency that provides a command line tool.
2. In the project, add a find_program() call for that command line tool.
3. Run CMake generation with the host triplet being different to the target triplet. In our case, we use a custom target triplet and the default triplet for the host.

Observe that the tool will not be found, even though vcpkg provides it in the host triplet's install area.

Expected behavior

Calls to find_program() should succeed when a host dependency provides the requested tool.

[craigscott-crascit]

It would appear that this bug only occurs if you let vcpkg determine the host triplet. If you explicitly set VCPKG_HOST_TRIPLET, then vcpkg (correctly) adds the host triplet's tools subdirectories to CMAKE_PROGRAM_PATH instead of those from the target triplet.

[craigscott-crascit]

The relevant logic appears to be

vcpkg/scripts/buildsystems/vcpkg.cmake

Lines 544 to 556 in a7b6122

	option(VCPKG_SETUP_CMAKE_PROGRAM_PATH "Enable the setup of CMAKE_PROGRAM_PATH to vcpkg paths" ON)
	set(VCPKG_CAN_USE_HOST_TOOLS OFF)
	if(DEFINED VCPKG_HOST_TRIPLET AND NOT VCPKG_HOST_TRIPLET STREQUAL "")
	set(VCPKG_CAN_USE_HOST_TOOLS ON)
	endif()
	cmake_dependent_option(VCPKG_USE_HOST_TOOLS "Setup CMAKE_PROGRAM_PATH to use host tools" ON "VCPKG_CAN_USE_HOST_TOOLS" OFF)
	unset(VCPKG_CAN_USE_HOST_TOOLS)
	if(VCPKG_SETUP_CMAKE_PROGRAM_PATH)
	set(tools_base_path "${VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}/tools")
	if(VCPKG_USE_HOST_TOOLS)
	set(tools_base_path "${VCPKG_INSTALLED_DIR}/${VCPKG_HOST_TRIPLET}/tools")
	endif()

which was added by #23322. The logic before that change was still wrong though (looks like previously the host tools were never being added to CMAKE_PROGRAM_PATH).

CC: @Neumann-A

[dg0yt]

Related: #25529

[Neumann-A]

It would appear that this bug only occurs if you let vcpkg determine the host triplet.

So I assume it works ;)
Not defining a host triplet just assumes old behavior.

In the end it comes down to CMake itself being ambiguous what find_program really means and vcpkg being undecided about it. There was also somewhere a long discussion about it but i am currently unable to find it.

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[craigscott-crascit]

Eh, why auto-stale an open, unresolved issue?

[autoantwort]

So a solution would be to rebuilt the host triplet selection in vcpkg.cmake or call vcpkg z-print-config to get the host triplet?

[github-actions]

This is an automated message. Per our repo policy, stale issues get closed if there has been no activity in the past 180 days. The issue will be automatically closed in 14 days. If you wish to keep this issue open, please add a new comment.