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>

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)

tests/auto/cmake/CMakeLists.txt

@@ -97,6 +97,7 @@ if (NOT WIN32 OR (WIN32 AND NOT CMAKE_VERSION VERSION_LESS 2.8.11))
     expect_pass(test_add_binary_resources_delayed_file BINARY test_add_binary_resources_delayed_file)
 endif()
 expect_pass(test_private_includes)
+expect_pass(test_private_targets)
 expect_pass(test_testlib_definitions)
 expect_pass(test_json_plugin_includes)
 

tests/auto/cmake/test_private_targets/CMakeLists.txt

@@ -0,0 +1,9 @@
+
+cmake_minimum_required(VERSION 3.0)
+
+project(test_private_targets)
+
+find_package(Qt5Gui REQUIRED)
+
+add_executable(testapp main.cpp)
+target_link_libraries(testapp Qt5::GuiPrivate)

tests/auto/cmake/test_private_targets/main.cpp

@@ -0,0 +1,53 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 Stephen Kelly <steveire@gmail.com>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QGuiApplication>
+
+#include <private/qwindow_p.h>
+#include <private/qobject_p.h>
+#include <QtGui/private/qwindow_p.h>
+#include <QtCore/private/qobject_p.h>
+
+int main(int argc, char **argv)
+{
+    QGuiApplication app(argc, argv);
+
+    QWindow window;
+
+    auto windowPrivate = QWindowPrivate::get(&window);
+
+    if (windowPrivate->visible)
+        return 1;
+
+    auto objectPrivate = QObjectPrivate::get(&window);
+
+    auto mo = window.metaObject();
+
+    // Should be 0
+    return objectPrivate->signalIndex("destroyed()", &mo);
+}