CMake: Split off private module config packages

[ChangeLog][CMake] Private Qt modules have been split off into separate
Qt6FooPrivate CMake config packages. A call to find_package(Qt6Foo) will
now implicitly find_package(Qt6FooPrivate). It's not an error if
Qt6FooPrivate isn't available as it may be the case on certain Linux
distros that split their Qt module packages into private and public
parts.

For every public module Qt6Foo that has an associated Qt6FooPrivate
module, create a separate Qt6FooPrivate CMake config package.

Let Qt6FooPrivate find Qt6Foo. This is a required dependency.

Let Qt6Foo find Qt6FooPrivate if it's available. A message of log level
VERBOSE is issued if Qt6FooPrivate is not found.

Implementation notes: In QtModuleConfig.cmake.in, we pull in the private
module. This is not part of the *Dependencies.cmake file, because

1. The Qt6FooPrivate package references the Qt6::Foo target, therefore
it must be available. And Qt6FooDependencies.cmake is loaded before
creating targets.

2. The dependency needs to be optional, and we don't have facilities for
optional dependencies in Qt6FooDependencies yet.

3. We'd have to avoid recursion, because of the Qt6FooPrivate -> Qt6Foo
dependency.

Fixes: QTBUG-87776
Pick-to: 6.9
Change-Id: I8f23f07da7ca76486f87b759e197174c11e13534
Reviewed-by: Alexey Edelev <[email protected]>

1 files changed, 17 insertions, 0 deletions

diff --git a/cmake/QtPostProcessHelpers.cmake b/cmake/QtPostProcessHelpers.cmake
index 6ecb0c492dc..974b588822d 100644
--- a/cmake/QtPostProcessHelpers.cmake
+++ b/cmake/QtPostProcessHelpers.cmake
@@ -143,6 +143,15 @@ function(qt_internal_remove_qt_dependency_duplicates out_deps deps)
 endfunction()
 
 function(qt_internal_create_module_depends_file target)
+    set(no_value_options "")
+    set(single_value_options "")
+    set(multi_value_options
+        EXTRA_PACKAGE_DEPENDENCIES
+    )
+    cmake_parse_arguments(PARSE_ARGV 1 arg
+        "${no_value_options}" "${single_value_options}" "${multi_value_options}"
+    )
+
     get_target_property(target_type "${target}" TYPE)
     set(is_interface_lib FALSE)
     if(target_type STREQUAL "INTERFACE_LIBRARY")
@@ -173,6 +182,9 @@ function(qt_internal_create_module_depends_file target)
     if(NOT extra_depends MATCHES "-NOTFOUND$")
         list(APPEND target_deps "${extra_depends}")
     endif()
+    if(DEFINED arg_EXTRA_PACKAGE_DEPENDENCIES)
+        list(APPEND target_deps "${arg_EXTRA_PACKAGE_DEPENDENCIES}")
+    endif()
 
     # Extra 3rd party targets who's packages should be considered dependencies.
     get_target_property(extra_third_party_deps "${target}" _qt_extra_third_party_dep_targets)
@@ -467,6 +479,11 @@ function(qt_internal_create_depends_files)
 
     foreach (target ${repo_known_modules})
         qt_internal_create_module_depends_file(${target})
+        if(TARGET "${target}Private")
+            qt_internal_create_module_depends_file(${target}Private
+                EXTRA_PACKAGE_DEPENDENCIES "${INSTALL_CMAKE_NAMESPACE}${target};${PROJECT_VERSION}"
+            )
+        endif()
     endforeach()
 
     foreach (target ${QT_KNOWN_PLUGINS})