Ports can expose functions for other ports to consume during their build. For
example, the vcpkg-cmake helper port exposes the vcpkg_cmake_configure()
helper function. Packaging common scripts into a shared helper port makes
maintenance easier because all consumers can be updated from a single place.
Because the scripts come from a port, they can be versioned and depended upon
via all the same mechanisms as any other port.
Script ports are implemented via the vcpkg-port-config.cmake extension
mechanism. Before invoking the portfile.cmake of a port, vcpkg will first
import share/<port>/vcpkg-port-config.cmake from each direct dependency. If
the direct dependency is a host dependency, the import will be performed in the
host installed tree (e.g.
${HOST_INSTALLED_DIR}/share/<port>/vcpkg-port-config.cmake).
Only direct dependencies are considered for vcpkg-port-config.cmake inclusion.
This means that if a script port relies on another script port, it must
explicitly import the vcpkg-port-config.cmake of its dependency.
Script-to-script dependencies should not be marked as host. The dependency from
a target port to a script should be marked host, which means that scripts should
always already be natively compiling. By making script-to-script dependencies
"host": false, it ensures that one script can depend upon the other being in
its same install directory.
Ports should never provide a vcpkg-port-config.cmake file under a different
share/ subdirectory than the current port (${PORT}).
# ${CURRENT_PACKAGES_DIR}/share/my-helper/vcpkg-port-config.cmake
# This include guard ensures the file will be loaded only once
include_guard(GLOBAL)
# This is how you could pull in a transitive dependency
include("${CMAKE_CURRENT_LIST_DIR}/../my-other-helper/vcpkg-port-config.cmake")
# Finally, it is convention to put each public function into a separate file with a matching name
include("${CMAKE_CURRENT_LIST_DIR}/my_helper_function_01.cmake")
include("${CMAKE_CURRENT_LIST_DIR}/my_helper_function_02.cmake")
include("${CMAKE_CURRENT_LIST_DIR}/my_helper_function_03.cmake")