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externals/vcpkg/docs/maintainers/authoring-script-ports.md

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+# Authoring Script Ports
+
+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}`).
+
+## Example
+
+```cmake
+# ${CURRENT_PACKAGES_DIR}/share/my-helper/vcpkg-port-config.cmake
+
+# This include guard ensures the file will be loaded only once
+include_guard(GLOBAL)
+
+# This is how you could pull in a transitive dependency
+include("${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")
+```