CMake: Add Qt6 forward compatible CMake API and targets

Create Qt:: versionless targets for libraries and tools. So
Qt::Core will link to Qt5::Core.

Add additional feature properties to targets, with the same name
they have in Qt6: QT_ENABLED_PUBLIC_FEATURES,
QT_DISABLED_PUBLIC_FEATURES, QT_ENABLED_PRIVATE_FEATURES,
QT_DISABLED_PRIVATE_FEATURES, to be forward-compatible with Qt6.
Prefix properties with INTERFACE_ for interface libraries.

Create functions with no major version in their prefix, so qt_foo
instead of qt5_foo.
The non-versioned functions will call the versioned functions,
depending on the value of QT_DEFAULT_MAJOR_VERSION, which can be
set by an application developer before finding the Qt package.

Set QT_DEFAULT_MAJOR_VERSION to 5 if the value has not been defined
in the current scope.

Application developers can set QT_NO_CREATE_VERSIONLESS_FUNCTIONS to
TRUE before calling find_package(Qt5) to suppress creation of the
non-versioned functions.

Application developers can set QT_NO_CREATE_VERSIONLESS_TARGETS to
TRUE before calling find_package(Qt5) to suppress creation of the
non-versioned targets.

Setting these can be useful when both find_package(Qt5) and
find_package(Qt6) are in the same project.
If none of these are set by the user, then the first find_package(Qt5)
will create versionless targets with the major version being "5",
which means the second find_package(Qt6) will not create versionless
targets.

Handle versionless plugin names in qt_import_plugins, so both
Qt::QCocoaIntegrationPlugin and Qt5/6::QCocoaIntegrationPlugin
are recognized by the function.

Allow specifying multiple types in EXCLUDE_BY_TYPE in
qt_import_plugins, to be consitent with the Qt 6 version.

Make sure to set the QT_PLUGIN_CLASS_NAME property to compatible with
Qt 6.

Task-number: QTBUG-74137
Task-number: QTBUG-80477
Change-Id: Ib89d090ea6f7794d7debd64f03f29da963a17ca7
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

2 files changed, 48 insertions, 5 deletions

diff --git a/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in b/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
index 26d4c17e6c..01dda9b0c3 100644
--- a/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
+++ b/mkspecs/features/data/cmake/Qt5BasicConfig.cmake.in
@@ -406,6 +406,15 @@ if (NOT TARGET Qt5::$${CMAKE_MODULE_NAME})
     add_library(Qt5::$${CMAKE_MODULE_NAME} SHARED IMPORTED)
 !!ENDIF
 !!ENDIF
+
+    # Add a versionless target, for compatibility with Qt6.
+    if(NOT \"${QT_NO_CREATE_VERSIONLESS_TARGETS}\" AND NOT TARGET Qt::$${CMAKE_MODULE_NAME})
+        add_library(Qt::$${CMAKE_MODULE_NAME} INTERFACE IMPORTED)
+        set_target_properties(Qt::$${CMAKE_MODULE_NAME} PROPERTIES
+            INTERFACE_LINK_LIBRARIES \"Qt5::$${CMAKE_MODULE_NAME}\"
+        )
+    endif()
+
 !!IF !equals(TEMPLATE, aux)
 !!IF !isEmpty(CMAKE_BUILD_IS_FRAMEWORK)
     set_property(TARGET Qt5::$${CMAKE_MODULE_NAME} PROPERTY FRAMEWORK 1)
@@ -420,6 +429,20 @@ if (NOT TARGET Qt5::$${CMAKE_MODULE_NAME})
     set_property(TARGET Qt5::$${CMAKE_MODULE_NAME} PROPERTY INTERFACE_QT_ENABLED_FEATURES $$join(QT.$${MODULE}.enabled_features, ";"))
     set_property(TARGET Qt5::$${CMAKE_MODULE_NAME} PROPERTY INTERFACE_QT_DISABLED_FEATURES $$join(QT.$${MODULE}.disabled_features, ";"))
 
+    # Qt 6 forward compatible properties.
+    set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}
+                 PROPERTY $${CMAKE_FEATURE_PROPERTY_PREFIX}QT_ENABLED_PUBLIC_FEATURES
+                 $$join(QT.$${MODULE}.enabled_features, ";"))
+    set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}
+                 PROPERTY $${CMAKE_FEATURE_PROPERTY_PREFIX}QT_DISABLED_PUBLIC_FEATURES
+                 $$join(QT.$${MODULE}.disabled_features, ";"))
+    set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}
+                 PROPERTY $${CMAKE_FEATURE_PROPERTY_PREFIX}QT_ENABLED_PRIVATE_FEATURES
+                 $$join(QT.$${MODULE}_private.enabled_features, ";"))
+    set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}
+                 PROPERTY $${CMAKE_FEATURE_PROPERTY_PREFIX}QT_DISABLED_PRIVATE_FEATURES
+                 $$join(QT.$${MODULE}_private.disabled_features, ";"))
+
     set_property(TARGET Qt5::$${CMAKE_MODULE_NAME} PROPERTY INTERFACE_QT_PLUGIN_TYPES \"$${CMAKE_MODULE_PLUGIN_TYPES}\")
 
     set(_Qt5$${CMAKE_MODULE_NAME}_PRIVATE_DIRS_EXIST TRUE)
@@ -443,6 +466,14 @@ if (NOT TARGET Qt5::$${CMAKE_MODULE_NAME})
         set_property(TARGET Qt5::$${CMAKE_MODULE_NAME}Private PROPERTY
             INTERFACE_LINK_LIBRARIES Qt5::$${CMAKE_MODULE_NAME} ${_Qt5$${CMAKE_MODULE_NAME}_PRIVATEDEPS}
         )
+
+        # Add a versionless target, for compatibility with Qt6.
+        if(NOT \"${QT_NO_CREATE_VERSIONLESS_TARGETS}\" AND NOT TARGET Qt::$${CMAKE_MODULE_NAME}Private)
+            add_library(Qt::$${CMAKE_MODULE_NAME}Private INTERFACE IMPORTED)
+            set_target_properties(Qt::$${CMAKE_MODULE_NAME}Private PROPERTIES
+                INTERFACE_LINK_LIBRARIES \"Qt5::$${CMAKE_MODULE_NAME}Private\"
+            )
+        endif()
     endif()
 
 !!IF !equals(TEMPLATE, aux)
diff --git a/mkspecs/features/data/cmake/Qt5PluginTarget.cmake.in b/mkspecs/features/data/cmake/Qt5PluginTarget.cmake.in
index 7b70cfed09..b550a52c60 100644
--- a/mkspecs/features/data/cmake/Qt5PluginTarget.cmake.in
+++ b/mkspecs/features/data/cmake/Qt5PluginTarget.cmake.in
@@ -75,19 +75,30 @@ endif()
 set(_user_specified_genex
     \"$<IN_LIST:Qt5::$$CMAKE_PLUGIN_NAME,${_manual_plugins_genex};${_plugin_type_genex}>\"
 )
+set(_user_specified_genex_versionless
+    \"$<IN_LIST:Qt::$$CMAKE_PLUGIN_NAME,${_manual_plugins_genex};${_plugin_type_genex}>\"
+)
 string(CONCAT _plugin_genex
     \"$<$<OR:\"
-        # Add this plugin if it\'s in the list of manual plugins or plugins for the type
+        # Add this plugin if it\'s in the list of manually specified plugins or in the list of
+        # explicitly included plugin types.
         \"${_user_specified_genex},\"
-        # Add this plugin if the list of plugins for the type is empty, the PLUGIN_EXTENDS
-        # is either empty or equal to the module name, and the user hasn\'t blacklisted it
+        \"${_user_specified_genex_versionless},\"
+        # Add this plugin if all of the following are true:
+        # 1) the list of explicitly included plugin types is empty
+        # 2) the QT_PLUGIN_EXTENDS property for the plugin is empty or equal to the current
+        #    module name
+        # 3) the user hasn\'t explicitly excluded the plugin.
         \"$<AND:\"
             \"$<STREQUAL:${_plugin_type_genex},>,\"
             \"$<OR:\"
-                \"$<STREQUAL:$<TARGET_PROPERTY:Qt5::$${CMAKE_PLUGIN_NAME},QT_PLUGIN_EXTENDS>,Qt5::$${CMAKE_MODULE_NAME}>,\"
+                # FIXME: The value of CMAKE_MODULE_NAME seems to be wrong (e.g for Svg plugin
+                # it should be Qt::Svg instead of Qt::Gui).
+                \"$<STREQUAL:$<TARGET_PROPERTY:Qt5::$${CMAKE_PLUGIN_NAME},QT_PLUGIN_EXTENDS>,Qt::$${CMAKE_MODULE_NAME}>,\"
                 \"$<STREQUAL:$<TARGET_PROPERTY:Qt5::$${CMAKE_PLUGIN_NAME},QT_PLUGIN_EXTENDS>,>\"
             \">,\"
-            \"$<NOT:$<IN_LIST:Qt5::$${CMAKE_PLUGIN_NAME},${_no_plugins_genex}>>\"
+            \"$<NOT:$<IN_LIST:Qt5::$${CMAKE_PLUGIN_NAME},${_no_plugins_genex}>>,\"
+            \"$<NOT:$<IN_LIST:Qt::$${CMAKE_PLUGIN_NAME},${_no_plugins_genex}>>\"
         \">\"
     \">:Qt5::$$CMAKE_PLUGIN_NAME>\"
 )
@@ -100,3 +111,4 @@ set_property(TARGET Qt5::$${CMAKE_PLUGIN_NAME} APPEND PROPERTY INTERFACE_LINK_LI
 !!ENDIF
 set_property(TARGET Qt5::$${CMAKE_PLUGIN_NAME} PROPERTY QT_PLUGIN_TYPE \"$$CMAKE_PLUGIN_TYPE\")
 set_property(TARGET Qt5::$${CMAKE_PLUGIN_NAME} PROPERTY QT_PLUGIN_EXTENDS \"$$CMAKE_PLUGIN_EXTENDS\")
+set_property(TARGET Qt5::$${CMAKE_PLUGIN_NAME} PROPERTY QT_PLUGIN_CLASS_NAME \"$$CMAKE_PLUGIN_NAME\")