CMake: Create a Qt5::<ModuleName>Private target for each module

Make it depend on the corresponding Private target of each
dependency.  This way, user code can write

 find_package(Qt5Gui REQUIRED)

 add_executable(hello hello.cpp)

 target_link_libraries(hello Qt5::GuiPrivate)

and get the private include directories for both Qt5Core and Qt5Gui.

Don't create the Private target if any of the private include
directories do not exist.  This way, if user code uses one of the
targets, CMake will issue an error if the private include directories do
not exist.  Unfortunately the error is somewhat cryptic (eg, 'the
"Qt5::CorePrivate" was not found'), but this is still an improvement
over an error at compile time.

This is an improvement on the situation described in QTBUG-37417 using
Modern CMake features.

Change-Id: I034f8216c3ec64d1a3309682456a713cac9bf854
Reviewed-by: Kai Pastor <dg0yt@darc.de>
Reviewed-by: Stephen Kelly <steveire@gmail.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in b/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
index d2358cae4b..866ace6c5c 100644
--- a/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
+++ b/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
@@ -166,6 +166,8 @@ if (NOT TARGET Qt5::$${CMAKE_MODULE_NAME})
     endif()
 !!ENDIF
 
+    set(Qt5$${CMAKE_MODULE_NAME}_OWN_PRIVATE_INCLUDE_DIRS ${Qt5$${CMAKE_MODULE_NAME}_PRIVATE_INCLUDE_DIRS})
+
     set(_Qt5$${CMAKE_MODULE_NAME}_FIND_DEPENDENCIES_REQUIRED)
     if (Qt5$${CMAKE_MODULE_NAME}_FIND_REQUIRED)
         set(_Qt5$${CMAKE_MODULE_NAME}_FIND_DEPENDENCIES_REQUIRED REQUIRED)
@@ -243,6 +245,29 @@ if (NOT TARGET Qt5::$${CMAKE_MODULE_NAME})
     set_property(TARGET Qt5::$${CMAKE_MODULE_NAME} PROPERTY
       INTERFACE_COMPILE_DEFINITIONS $${MODULE_DEFINE})
 
+    set(_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIRS_EXIST TRUE)
+    foreach (_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIR ${Qt5$${CMAKE_MODULE_NAME}_OWN_PRIVATE_INCLUDE_DIRS})
+        if (NOT EXISTS ${_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIR})
+            set(_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIRS_EXIST FALSE)
+        endif()
+    endforeach()
+
+    if (_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIRS_EXIST)
+        add_library(Qt5::$${CMAKE_MODULE_NAME}Private INTERFACE IMPORTED)
+        set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}Private PROPERTY
+            INTERFACE_INCLUDE_DIRECTORIES ${Qt5$${CMAKE_MODULE_NAME}_OWN_PRIVATE_INCLUDE_DIRS}
+        )
+        set(_Qt5$${CMAKE_MODULE_NAME}_PRIVATEDEPS)
+        foreach(dep ${_Qt5$${CMAKE_MODULE_NAME}_LIB_DEPENDENCIES})
+            if (TARGET ${dep}Private)
+                list(APPEND _Qt5$${CMAKE_MODULE_NAME}_PRIVATEDEPS ${dep}Private)
+            endif()
+        endforeach()
+        set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}Private PROPERTY
+            INTERFACE_LINK_LIBRARIES Qt5::$${CMAKE_MODULE_NAME} ${_Qt5$${CMAKE_MODULE_NAME}_PRIVATEDEPS}
+        )
+    endif()
+
 !!IF !equals(TEMPLATE, aux)
 !!IF !isEmpty(CMAKE_RELEASE_TYPE)
 !!IF !isEmpty(CMAKE_STATIC_WINDOWS_BUILD)