cxx-qt-lib: implement Upcast<QGuiApplication> for QApplication

Author: jnbooth

crates/cxx-qt-lib-extras/src/gui/qapplication.rs

@@ -4,7 +4,9 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
 use core::pin::Pin;
-use cxx_qt_lib::{QByteArray, QFont, QString, QStringList, QVector};
+use cxx_qt::Upcast;
+use cxx_qt_lib::{QByteArray, QFont, QGuiApplication, QString, QStringList, QVector};
+use std::ops::Deref;
 
 #[cxx::bridge]
 mod ffi {
@@ -19,11 +21,26 @@ mod ffi {
         type QVector_QByteArray = cxx_qt_lib::QVector<QByteArray>;
         include!("cxx-qt-lib/qfont.h");
         type QFont = cxx_qt_lib::QFont;
+        include!("cxx-qt-lib/qguiapplication.h");
+        type QGuiApplication = cxx_qt_lib::QGuiApplication;
 
         include!("cxx-qt-lib-extras/qapplication.h");
         type QApplication;
     }
 
+    #[namespace = "rust::cxxqt1"]
+    unsafe extern "C++" {
+        include!("cxx-qt/casting.h");
+
+        #[doc(hidden)]
+        #[rust_name = "upcast_qapplication"]
+        unsafe fn upcastPtr(thiz: *const QApplication) -> *const QGuiApplication;
+
+        #[doc(hidden)]
+        #[rust_name = "downcast_qapplication"]
+        unsafe fn downcastPtr(base: *const QGuiApplication) -> *const QApplication;
+    }
+
     #[namespace = "rust::cxxqtlib1"]
     unsafe extern "C++" {
         #[doc(hidden)]
@@ -93,6 +110,24 @@ mod ffi {
 
 pub use ffi::QApplication;
 
+impl Upcast<QGuiApplication> for QApplication {
+    unsafe fn upcast_ptr(this: *const Self) -> *const QGuiApplication {
+        ffi::upcast_qapplication(this)
+    }
+
+    unsafe fn from_base_ptr(base: *const QGuiApplication) -> *const Self {
+        ffi::downcast_qapplication(base)
+    }
+}
+
+impl Deref for QApplication {
+    type Target = QGuiApplication;
+
+    fn deref(&self) -> &Self::Target {
+        self.upcast()
+    }
+}
+
 impl QApplication {
     /// Prepends path to the beginning of the library path list,
     /// ensuring that it is searched for libraries first.