Add blanket implementation of QObjectExt

- All objects which upcast to QObject now have QObjectExt implemented
- Via transitive casting and using the QObjectExt trait, any descendent of QObject can access its methods

Author: BenFordTytherington

crates/cxx-qt-lib/src/core/qobject.rs

@@ -3,6 +3,7 @@
 //
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
+use cxx_qt::casting::Upcast;
 pub use cxx_qt::QObject;
 use std::pin::Pin;
 
@@ -33,6 +34,9 @@ pub mod ffi {
 
         #[rust_name = "set_parent"]
         pub unsafe fn setParent(self: Pin<&mut Self>, parent: *mut QObjectExternal);
+
+        #[rust_name = "dump_object_info"]
+        fn dumpObjectInfo(&self);
     }
 }
 
@@ -49,9 +53,11 @@ pub trait QObjectExt {
 
     fn object_name(&self) -> QString;
 
-    fn parent(&self) -> *mut Self;
+    fn parent(&self) -> *mut QObjectExternal;
 
     fn set_parent(self: Pin<&mut Self>, parent: &Self);
+
+    fn dump_object_info(&self);
 }
 
 /// Used to convert the QObject type from the library type to the C++ type, as a pin
@@ -70,31 +76,38 @@ fn cast(obj: &QObject) -> &QObjectExternal {
     }
 }
 
-impl QObjectExt for QObject {
+impl<T> QObjectExt for T
+where
+    T: Upcast<QObject>,
+{
     fn block_signals(self: Pin<&mut Self>, block: bool) -> bool {
-        cast_pin(self).block_signals(block)
+        cast_pin(self.upcast_pin()).block_signals(block)
     }
 
     fn signals_blocked(&self) -> bool {
-        cast(self).signals_blocked()
+        cast(self.upcast()).signals_blocked()
     }
 
     fn set_object_name(self: Pin<&mut Self>, name: &QString) {
-        cast_pin(self).set_object_name(name)
+        cast_pin(self.upcast_pin()).set_object_name(name)
     }
 
     fn object_name(&self) -> QString {
-        cast(self).object_name()
+        cast(self.upcast()).object_name()
     }
 
-    fn parent(&self) -> *mut Self {
-        cast(self).parent() as *mut Self
+    fn parent(&self) -> *mut QObjectExternal {
+        cast(self.upcast()).parent()
     }
 
     fn set_parent(self: Pin<&mut Self>, parent: &Self) {
+        let s = cast_pin(self.upcast_pin());
         unsafe {
-            cast_pin(self)
-                .set_parent(cast(parent) as *const QObjectExternal as *mut QObjectExternal);
+            s.set_parent(cast(parent.upcast()) as *const QObjectExternal as *mut QObjectExternal)
         }
     }
+
+    fn dump_object_info(&self) {
+        cast(self.upcast()).dump_object_info()
+    }
 }

crates/cxx-qt/src/lib.rs

@@ -9,7 +9,7 @@
 //!
 //! See the [book](https://kdab.github.io/cxx-qt/book/) for more information.
 
-use std::{fs::File, io::Write, path::Path};
+use std::{fs::File, io::Write, path::Path, pin::Pin};
 
 #[doc(hidden)]
 pub mod casting;
@@ -125,6 +125,26 @@ pub use threading::{CxxQtThread, ThreadingQueueError};
 #[doc(hidden)]
 pub use static_assertions;
 
+/// This trait provides wrappers for objects which are QObjects or can be turned into a [QObject].
+/// It is automatically implemented for any types which implement [casting::Upcast] to a [QObject].
+pub trait AsObject {
+    /// Cast self reference into a [QObject] reference
+    fn as_qobject(&self) -> &QObject;
+
+    /// Cast pinned mutable reference into a pinned mutable [QObject] reference
+    fn as_qobject_mut(self: Pin<&mut Self>) -> Pin<&mut QObject>;
+}
+
+impl<T: casting::Upcast<QObject>> AsObject for T {
+    fn as_qobject(&self) -> &QObject {
+        self.upcast()
+    }
+
+    fn as_qobject_mut(self: Pin<&mut Self>) -> Pin<&mut QObject> {
+        self.upcast_pin()
+    }
+}
+
 /// This trait is automatically implemented for all QObject types generated by CXX-Qt.
 /// It provides information about the inner Rust struct that is wrapped by the QObject, as well as the methods
 /// that Cxx-Qt will generate for the QObject.

crates/cxx-qt/src/qobject.rs

@@ -14,10 +14,6 @@ mod ffi {
         /// Most methods available on this type are within the [cxx_qt_lib::core::QObjectExt] trait,
         /// which needs to be imported in order to access these.
         type QObject;
-
-        #[cxx_name = "dumpObjectInfo"]
-        /// Dump information about this QObjects name and signals
-        fn dump_object_info(&self);
     }
 }