Add Transitive casting and testing code (#1252)

* Add Transitive casting and testing code

* Add Transitive casting and testing code

* Add book entry and rename macro

Author: BenFordTytherington

book/src/concepts/casting.md

@@ -15,7 +15,7 @@ or a `#[base = T]` attribute. See the [attributes documentation](../bridge/attri
 
 ## Accessing the base class
 
-To access the methods of a base class in Rust, use the `Upcast` trait like so `use cxx_qt::Upcast;`.
+To access the methods of a base class in Rust, use the `Upcast` trait like so `use cxx_qt::casting::Upcast;`.
 Objects with base classes can then be accessed with the following methods
 
 | Self Type        | Method         |
@@ -41,3 +41,17 @@ The child can then be accessed in the same manner, with the following methods
 These will return an `Option<T>`, as it is possible that downcasting will fail,
 if the type is not actually of the given subclass,
 and these also return in the same format as the self type, e.g. `downcast()` returns `Option<&Sub>`, etc...
+
+## Transitive casting
+
+Given 3 types, where there is a grandparent relationship, e.g. that using 2 casts, you can go from A -> B -> C,
+CXX-Qt inlcudes a macro for automatically implementing a cast between A and C. This property also extends for longer chains.
+For example, if you have a deeply nested set of inheritance, you can quickly generate helpers to cast from your child type to any of its ancestors.
+
+```rust, ignore
+use cxx_qt::impl_transitive_cast;
+
+impl_transitive_cast!(A, B, C, D);
+```
+
+Will generate casting from A -> C, and A -> D, **provided** A -> B -> C -> D is already implemented.

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::casting::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

@@ -677,7 +677,7 @@ 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::casting::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)
     }
@@ -864,7 +864,7 @@ 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::casting::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)
     }
@@ -895,7 +895,7 @@ 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::casting::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)
     }
@@ -1073,7 +1073,7 @@ cxx_qt::static_assertions::assert_eq_size!(
     >,
     [usize; 2]
 );
-impl ::cxx_qt::Upcast<::cxx_qt::QObject> for ffi::QObjectExternDisabled {
+unsafe impl ::cxx_qt::casting::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::casting::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::casting::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::casting::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::casting::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

@@ -659,7 +659,7 @@ 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::casting::Upcast<ffi::QStringListModel> for ffi::MyObject {
     unsafe fn upcast_ptr(this: *const Self) -> *const ffi::QStringListModel {
         ffi::cxx_qt_ffi_MyObject_upcastPtr(this)
     }
@@ -839,7 +839,7 @@ 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::casting::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)
     }
@@ -867,7 +867,7 @@ 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::casting::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)
     }
@@ -895,15 +895,15 @@ 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::casting::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::casting::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

@@ -1110,7 +1110,7 @@ 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::casting::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::casting::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::casting::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

@@ -464,7 +464,7 @@ 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::casting::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)
     }
@@ -492,7 +492,7 @@ 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::casting::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

@@ -5,7 +5,7 @@
 use crate::{QList, QString};
 use core::mem::MaybeUninit;
 use cxx::{type_id, ExternType};
-use cxx_qt::Upcast;
+use cxx_qt::casting::Upcast;
 use std::fmt;
 use std::ops::{Deref, DerefMut};
 
@@ -204,7 +204,7 @@ 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)
     }