For examples to successfully find not yet installed Config files in a
prefix cross-build, both CMAKE_FIND_ROOT_PATH and CMAKE_PREFIX_PATH
need to be adjusted when toolchain files set
CMAKE_FIND_ROOT_PATH_MODE_PACKAGE to ONLY.
Before this change, we lacked two things.
1) If the chain-loaded toolchain file sets CMAKE_FIND_ROOT_PATH
(instead of appending), then the initial value of CMAKE_FIND_ROOT_PATH
that was passed by ExternalProject's initial cache would be
overridden.
2) The prefixes we passed via QT_EXAMPLES_CMAKE_PREFIX_PATH did not
end in lib/cmake, to work around the path re-rooting problem in CMake.
We can handle both of these points by using
QT_ADDITIONAL_PACKAGES_PREFIX_PATH which was introduced for Conan
usage.
Each value assigned to QT_ADDITIONAL_PACKAGES_PREFIX_PATH
gets prepended to CMAKE_FIND_ROOT_PATH by qt.toolchain.cmake AFTER the
original toolchain file is chain-loaded.
And each value also gets lib/cmake appended and assigned to
both CMAKE_PREFIX_PATH and _qt_additional_packages_prefix_paths (used
by Qt6Config.cmake.in to work with find_package + NO_DEFAULT_PATH).
This is exactly what we need to ensure examples build.
Pick-to: 6.2 6.3
Task-number: QTBUG-96232
Change-Id: I11a52457ff795a6661a3a7b68e823e0615d0ce89
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
c89da21249