Add Transitive casting and testing code

crates/cxx-qt-gen/src/generator/rust/fragment.rs

@@ -78,7 +78,7 @@ impl GeneratedRustFragment {
                 }
             }],
             cxx_qt_mod_contents: vec![parse_quote! {
-                impl ::cxx_qt::Upcast<#base_qualified> for #struct_name {
+                unsafe impl ::cxx_qt::Upcast<#base_qualified> for #struct_name {
                     unsafe fn upcast_ptr(this: *const Self) -> *const #base_qualified {
                         #upcast_fn_qualified(this)
                     }

crates/cxx-qt-gen/test_outputs/cfgs.rs

@@ -668,7 +668,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<QObjectEnabledCxxQtSignalClosuresignal_enabled>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectEnabled {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectEnabled {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QObjectEnabled_upcastPtr(this)
     }
@@ -847,7 +847,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<QObjectDisabledCxxQtSignalClosuresignal_enabled>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectDisabled {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectDisabled {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QObjectDisabled_upcastPtr(this)
     }
@@ -878,7 +878,7 @@ impl ::cxx_qt::CxxQtType for ffi::QObjectDisabled {
         ffi::cxx_qt_ffi_QObjectDisabled_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectExternEnabled {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectExternEnabled {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QObjectExternEnabled_upcastPtr(this)
     }
@@ -1048,7 +1048,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     >,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectExternDisabled {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectExternDisabled {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QObjectExternDisabled_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/inheritance.rs

@@ -130,7 +130,7 @@ mod inheritance {
         type QObject = cxx_qt::QObject;
     }
 }
-impl ::cxx_qt::Upcast<inheritance::QAbstractItemModel> for inheritance::MyObject {
+unsafe impl ::cxx_qt::Upcast<inheritance::QAbstractItemModel> for inheritance::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const inheritance::QAbstractItemModel {
         inheritance::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
@@ -158,15 +158,15 @@ impl ::cxx_qt::CxxQtType for inheritance::MyObject {
         inheritance::cxx_qt_ffi_MyObject_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for inheritance::QPushButton {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for inheritance::QPushButton {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         inheritance::cxx_qt_ffi_QPushButton_upcastPtr(this)
     }
     unsafe fn from_base_ptr(base: *const ::cxx_qt::QObject) -> *const Self {
         inheritance::cxx_qt_ffi_QPushButton_downcastPtr(base)
     }
 }
-impl ::cxx_qt::Upcast<inheritance::QPushButton> for inheritance::QPushButtonChild {
+unsafe impl ::cxx_qt::Upcast<inheritance::QPushButton> for inheritance::QPushButtonChild {
     unsafe fn upcast_ptr(this: *const Self) -> *const inheritance::QPushButton {
         inheritance::cxx_qt_ffi_QPushButtonChild_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/invokables.rs

@@ -326,7 +326,7 @@ impl cxx_qt::Threading for ffi::MyObject {
 pub struct MyObjectCxxQtThreadQueuedFn {
     inner: std::boxed::Box<dyn FnOnce(core::pin::Pin<&mut ffi::MyObject>) + Send>,
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/passthrough_and_naming.rs

@@ -648,7 +648,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<MyObjectCxxQtSignalClosureready>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<ffi::QStringListModel> for ffi::MyObject {
+unsafe impl ::cxx_qt::Upcast<ffi::QStringListModel> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ffi::QStringListModel {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
@@ -822,7 +822,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<SecondObjectCxxQtSignalClosureready>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::SecondObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::SecondObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_SecondObject_upcastPtr(this)
     }
@@ -850,7 +850,7 @@ impl ::cxx_qt::CxxQtType for ffi::SecondObject {
         ffi::cxx_qt_ffi_SecondObject_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyRustName {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyRustName {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_MyCxxName_upcastPtr(this)
     }
@@ -878,15 +878,15 @@ impl ::cxx_qt::CxxQtType for ffi::MyRustName {
         ffi::cxx_qt_ffi_MyCxxName_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QPushButton {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QPushButton {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QPushButton_upcastPtr(this)
     }
     unsafe fn from_base_ptr(base: *const ::cxx_qt::QObject) -> *const Self {
         ffi::cxx_qt_ffi_QPushButton_downcastPtr(base)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::ExternObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::ExternObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_ExternObjectCpp_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/properties.rs

@@ -1052,7 +1052,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<MyObjectCxxQtSignalClosuremy_on_changed>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/qenum.rs

@@ -169,7 +169,7 @@ mod ffi {
         type QObject = cxx_qt::QObject;
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
@@ -197,7 +197,7 @@ impl ::cxx_qt::CxxQtType for ffi::MyObject {
         ffi::cxx_qt_ffi_MyObject_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyRenamedObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyRenamedObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_CxxName_upcastPtr(this)
     }

crates/cxx-qt-gen/test_outputs/signals.rs

@@ -455,7 +455,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     cxx_qt::signalhandler::CxxQtSignalHandler<MyObjectCxxQtSignalClosurenewData>,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
@@ -483,7 +483,7 @@ impl ::cxx_qt::CxxQtType for ffi::MyObject {
         ffi::cxx_qt_ffi_MyObject_unsafeRustMut(self)
     }
 }
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QTimer {
+unsafe impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QTimer {
     unsafe fn upcast_ptr(this: *const Self) -> *const ::cxx_qt::QObject {
         ffi::cxx_qt_ffi_QTimer_upcastPtr(this)
     }

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

@@ -207,7 +207,7 @@ impl DerefMut for QStringList {
     }
 }
 
-impl Upcast<QList_QString> for QStringList {
+unsafe impl Upcast<QList_QString> for QStringList {
     unsafe fn upcast_ptr(this: *const Self) -> *const QList_QString {
         ffi::upcast_qstringlist(this)
     }

crates/cxx-qt/src/lib.rs

@@ -130,7 +130,7 @@ pub trait Threading: Sized {
 /// This trait is automatically implemented by CXX-Qt and you most likely do not need to manually implement it.
 /// Allows upcasting to either [QObject] or the provided base class of a type.
 /// Will not be implemented if no types inherit from [QObject] or have the `#[base = T]` attribute.
-pub trait Upcast<T> {
+pub unsafe trait Upcast<T> {
     #[doc(hidden)]
     /// # Safety
     ///

examples/qml_features/rust/src/custom_base_class.rs

@@ -10,9 +10,10 @@
 #[cxx_qt::bridge]
 pub mod qobject {
     // ANCHOR: book_base_include
-    unsafe extern "C++" {
+    unsafe extern "C++Qt" {
         include!(<QtCore/QAbstractListModel>);
         /// Base for Qt type
+        #[qobject]
         type QAbstractListModel;
     }
     // ANCHOR_END: book_base_include
@@ -272,11 +273,51 @@ pub mod qobject {
     }
 }
 
-use crate::custom_base_class::qobject::CustomBaseClass;
+macro_rules! impl_transitive_cast {
+    ($first:ty, $second:ty, $third:ty) => {
+        unsafe impl cxx_qt::Upcast<$third> for $first {
+            unsafe fn upcast_ptr(this: *const Self) -> *const $third {
+                let base = Self::upcast_ptr(this);
+                <$second as Upcast<$third>>::upcast_ptr(base)
+            }
+
+            unsafe fn from_base_ptr(base: *const $third) -> *const Self {
+                let base = <$second as Upcast<$third>>::from_base_ptr(base);
+                if base.is_null() {
+                    std::ptr::null()
+                } else {
+                    Self::from_base_ptr(base)
+                }
+            }
+        }
+    };
+}
+
+macro_rules! chain_cast {
+    ($first:ty, $second:ty, $third:ty) => {
+        impl_transitive_cast!($first, $second, $third);
+    };
+
+    ($first:ty, $second:ty, $third:ty, $($rest:ty),*) => {
+        impl_transitive_cast!($first, $second, $third);
+        $(impl_transitive_cast!($first, $third, $rest);)*
+    };
+}
+
+use crate::custom_base_class::qobject::{
+    AbstractBaseClass, CustomBaseClass, QAbstractListModel, QObject,
+};
 use core::pin::Pin;
-use cxx_qt::{CxxQtType, Threading};
+use cxx_qt::{CxxQtType, Threading, Upcast};
 use cxx_qt_lib::{QByteArray, QHash, QHashPair_i32_QByteArray, QModelIndex, QVariant, QVector};
 
+chain_cast!(
+    CustomBaseClass,
+    AbstractBaseClass,
+    QAbstractListModel,
+    QObject
+);
+
 impl Default for qobject::State {
     fn default() -> Self {
         Self::Idle
@@ -300,6 +341,12 @@ pub struct CustomBaseClassRust {
 impl qobject::CustomBaseClass {
     /// Virtual method for logging type
     pub fn log(self: &CustomBaseClass) {
+        let _abs: &AbstractBaseClass = self.upcast();
+        let _qabs: &QAbstractListModel = self.upcast();
+        let qobj: &QObject = self.upcast();
+
+        qobj.dump_object_info();
+
         println!(
             "state: {}\npending adds: {}\nid: {}\nvector: {:?}\n",
             self.state.repr, self.pending_adds, self.id, self.vector