cmake: find gtk3 and build the gtk3 platformtheme

Change-Id: I7db7321a2fd5ea0eda1924f3dece3b1c86d87d10
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

cmake/FindGTK3.cmake

@@ -0,0 +1,3 @@
+include(FindPkgConfig)
+
+pkg_check_modules(GTK3 "gtk+-3.0 >= 3.6" IMPORTED_TARGET)

src/plugins/CMakeLists.txt

@@ -1,6 +1,7 @@
 if(QT_FEATURE_gui)
     add_subdirectory(imageformats)
     add_subdirectory(platforms)
+    add_subdirectory(platformthemes)
 
     if (NOT ANDROID AND QT_FEATURE_library)
         add_subdirectory(generic)

src/plugins/platformthemes/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Generated from platformthemes.pro.
+
+if (QT_FEATURE_dbus AND QT_FEATURE_regularexpression)
+#     TODO add_subdirectory(xdgdesktopportal)
+endif()
+
+if (QT_FEATURE_widgets AND QT_FEATURE_gtk3)
+    add_subdirectory(gtk3)
+endif()
+

src/plugins/platformthemes/gtk3/CMakeLists.txt

@@ -0,0 +1,29 @@
+# Generated from gtk3.pro.
+
+find_package(GTK3)
+find_package(X11)
+
+#####################################################################
+## qgtk3 Plugin:
+#####################################################################
+
+add_qt_plugin(qgtk3
+    TYPE platformthemes
+    SOURCES
+        main.cpp
+        qgtk3dialoghelpers.cpp qgtk3dialoghelpers.h
+        qgtk3menu.cpp qgtk3menu.h
+        qgtk3theme.cpp qgtk3theme.h
+    DEFINES
+        GDK_VERSION_MIN_REQUIRED=GDK_VERSION_3_6
+    LIBRARIES
+        Qt::CorePrivate
+        Qt::GuiPrivate
+        Qt::ThemeSupportPrivate
+        PkgConfig::GTK3
+        X11::X11
+    # CONFIG = "X11"
+    # PLUGIN_CLASS_NAME = "QGtk3ThemePlugin"
+    # PLUGIN_EXTENDS = "-"
+    # _LOADED = "qt_plugin"
+)

src/widgets/configure.cmake

@@ -6,6 +6,8 @@
 
 #### Libraries
 
+find_package(GTK3)
+set_package_properties(GTK3 PROPERTIES TYPE OPTIONAL)
 
 
 #### Tests
@@ -17,7 +19,7 @@
 qt_feature("gtk3" PRIVATE
     LABEL "GTK+"
     AUTODETECT NOT APPLE
-    CONDITION QT_FEATURE_glib AND libs.gtk3 OR FIXME
+    CONDITION QT_FEATURE_glib AND GTK3_FOUND
 )
 qt_feature("style_fusion" PRIVATE
     LABEL "Fusion"

util/cmake/configurejson2cmake.py

@@ -57,6 +57,7 @@ def map_library(lib: str) -> Union[str, LibraryMapping, List[str]]:
        'gbm': 'gbm',
        'glib': 'GLIB2',
        'gnu_iconv': None,
+       'gtk3': 'GTK3',
        'harfbuzz': 'harfbuzz',
        'host_dbus': None,
        'icu': ['ICU', 'COMPONENTS', 'i18n', 'uc', 'data'],