From dae078e521c3932c66436cbdbfaf5294a1842901 Mon Sep 17 00:00:00 2001
From: Joerg Bornemann <joerg.bornemann@qt.io>
Date: Thu, 24 Sep 2020 12:02:44 +0200
Subject: [PATCH] CMake: Export 3rdparty dependency find_package calls of
 private modules

Consider a Qt module with a 3rdparty library target in
PRIVATE_MODULE_INTERFACE, e.g. XKB::XKB in Qt6::GuiPrivate. Consumers of
GuiPrivate automatically depend on XKB::XKB. In order to do that they
must find_package(XKB ...). As all find_package calls for GuiPrivate are
in the same place as the ones for Gui, this package must be marked as
optional. Otherwise all consumers of Qt6::Gui would have to have the
xkbcommon package installed too.

This patch exports find_package calls for every 3rdparty public
dependency of private modules and marks them as optional.

Change-Id: Ia1eeb09c29927fb6634ef08b477684ed6f123267
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
---
 cmake/QtPostProcessHelpers.cmake | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/cmake/QtPostProcessHelpers.cmake b/cmake/QtPostProcessHelpers.cmake
index 56b2d5e56fe..4f8106dfaed 100644
--- a/cmake/QtPostProcessHelpers.cmake
+++ b/cmake/QtPostProcessHelpers.cmake
@@ -25,7 +25,7 @@ macro(qt_collect_third_party_deps target)
     endif()
     unset(_target_is_static)
 
-    foreach(dep ${${depends_var}})
+    foreach(dep ${${depends_var}} ${optional_public_depends})
         # Gather third party packages that should be found when using the Qt module.
         # Also handle nolink target dependencies.
         string(REGEX REPLACE "_nolink$" "" base_dep "${dep}")
@@ -44,6 +44,9 @@ macro(qt_collect_third_party_deps target)
             if(dep_seen EQUAL -1 AND package_name)
                 list(APPEND third_party_deps_seen ${dep})
                 get_target_property(package_is_optional ${dep} INTERFACE_QT_PACKAGE_IS_OPTIONAL)
+                if(NOT package_is_optional AND dep IN_LIST optional_public_depends)
+                    set(package_is_optional TRUE)
+                endif()
                 get_target_property(package_version ${dep} INTERFACE_QT_PACKAGE_VERSION)
                 if(NOT package_version)
                     set(package_version "")
@@ -76,6 +79,11 @@ function(qt_internal_create_module_depends_file target)
 
     get_target_property(public_depends "${target}" INTERFACE_LINK_LIBRARIES)
 
+    unset(optional_public_depends)
+    if(TARGET "${target}Private")
+        get_target_property(optional_public_depends "${target}Private" INTERFACE_LINK_LIBRARIES)
+    endif()
+
     # Used for collecting Qt module dependencies that should be find_package()'d in
     # ModuleDependencies.cmake.
     get_target_property(target_deps "${target}" _qt_target_deps)
@@ -227,6 +235,7 @@ function(qt_internal_create_plugin_depends_file target)
     get_target_property(depends "${target}" LINK_LIBRARIES)
     get_target_property(public_depends "${target}" INTERFACE_LINK_LIBRARIES)
     get_target_property(target_deps "${target}" _qt_target_deps)
+    unset(optional_public_depends)
     set(target_deps_seen "")
 
     qt_collect_third_party_deps(${target})
@@ -288,6 +297,8 @@ function(qt_internal_create_qt6_dependencies_file)
     # This is the actual target we're querying.
     set(actual_target Platform)
     get_target_property(public_depends "${actual_target}" INTERFACE_LINK_LIBRARIES)
+    unset(depends)
+    unset(optional_public_depends)
 
     # We need to collect third party deps that are set on the public Platform target,
     # like Threads::Threads.