CMake: Make WrapVulkanHeaders target optional for QtGui consumers

If Vulkan headers are present on the system when qtbase is configured,
QtGui and QtOpenGL should be compiled with Vulkan support.

If a user project uses a Qt built with Vulkan support, but their system
is missing Vulkan headers, the project configuration needs to succeed.

The project will get compilation errors if it uses Vulkan headers, but
that's intended.

This use case was broken when fixing Vulkan to be found when building
Qt for Android.

Fix the regression with a combination of things
1) Mark the WrapVulkanHeaders package as optional (already the case)
2) Use the include directories directly when compiling Gui and OpenGL
3) Propagate WrapVulkanHeaders::WrapVulkanHeaders link requirement to
   consumers only if the target exists. It won't exist if Vulkan
   include dirs are not found

This also requires some changes in pri and prl file generation.

For prl file generation, we don't want to link to the
WrapVulkanHeaders target, so we filter out all dependencies that
use TARGET_NAME_IF_EXISTS for anything that calls
__qt_internal_walk_libs which includes qt_collect_libs.

For pri files, we make sure to generate a uses=vulkan/nolink clause
by inspecting a new _qt_is_nolink_target property on the target.

We also don't add include dirs to the pri file if the new
_qt_skip_include_dir_for_pri property is set.
This is intended for Vulkan, because there is separate qmake logic to
try and find the include dirs when configuring a user project.

As a drive-by, fix nolink handling for WrapOpenSSLHeaders.

Amends bb25536a3db657b41ae31e1690d230ef8722b57d
Amends 7b9904849fe1a43f0db8216076a9e974ebca5c78

Pick-to: 6.2
Fixes: QTBUG-95391
Change-Id: I21e2f4be5c386f9e40033e4691f4786a91ba0e2d
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

1 files changed, 37 insertions, 0 deletions

diff --git a/cmake/QtTargetHelpers.cmake b/cmake/QtTargetHelpers.cmake
index 75642c70b0..96d6982319 100644
--- a/cmake/QtTargetHelpers.cmake
+++ b/cmake/QtTargetHelpers.cmake
@@ -772,3 +772,40 @@ function(qt_internal_link_internal_platform_for_object_library target)
     # Achieve this by compiling the cpp files with the PlatformModuleInternal compile flags.
     target_link_libraries("${target}" PRIVATE Qt::PlatformModuleInternal)
 endfunction()
+
+
+# Use ${dep_target}'s include dirs when building ${target} and optionally propagate the include
+# dirs to consumers of ${target}.
+
+# Assumes ${dep_target} is an INTERFACE_LIBRARY that only propagates include dirs and ${target}
+# is a Qt module / plugin.
+#
+# Building ${target} requires ${dep_target}'s include dirs.
+#
+# User projects that don't have ${dep_target}'s headers installed in their system should still
+# configure successfully.
+#
+# To achieve that, consumers of ${target} will only get the include directories of ${dep_target}
+# if the latter package and target exists.
+#
+# A find_package(dep_target) dependency is added to ${target}'s ModuleDependencies.cmake file.
+#
+# We use target_include_directories(PRIVATE) instead of target_link_libraries(PRIVATE) because the
+# latter would propagate a mandatory LINK_ONLY dependency on the ${dep_target} in a static Qt build.
+#
+# The main use case is for propagating WrapVulkanHeaders::WrapVulkanHeaders.
+function(qt_internal_add_target_include_dirs_and_optionally_propagate target dep_target)
+    if(NOT TARGET "${target}")
+        message(FATAL_ERROR "${target} is not a valid target.")
+    endif()
+    if(NOT TARGET "${dep_target}")
+        message(FATAL_ERROR "${dep_target} is not a valid target.")
+    endif()
+
+    target_include_directories("${target}" PRIVATE
+        "$<TARGET_PROPERTY:${dep_target},INTERFACE_INCLUDE_DIRECTORIES>")
+
+    target_link_libraries("${target}" INTERFACE "$<TARGET_NAME_IF_EXISTS:${dep_target}>")
+
+    qt_record_extra_third_party_dependency("${target}" "${dep_target}")
+endfunction()