cxx-qt-lib: Add binding for QQmlApplicationEngine::singletonInstance

This allows accessing QObject singleton instances registered in the QML
engine (using #[qml_singleton]) from the Rust side.

Author: redstrate

CHANGELOG.md

@@ -17,6 +17,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/KDAB/cxx-qt/compare/v0.7.0...HEAD)
 
+### Added
+
+- Add binding for `singletonInstance` of `QQmlApplicationEngine`, allowing access to singleton instances registered in the QML engine.
+
 ### Fixed
 
 - Build warnings due to unused unsafe blocks since CXX 1.0.130

crates/cxx-qt-lib/include/qml/qqmlapplicationengine.h

@@ -22,6 +22,13 @@ qqmlapplicationengineNew();
 QQmlEngine&
 qqmlapplicationengineAsQQmlEngine(QQmlApplicationEngine&);
 
+#if (QT_VERSION >= QT_VERSION_CHECK(6, 5, 0))
+void*
+qqmlapplicationengineSingletonInstance(QQmlApplicationEngine& engine,
+                                       QAnyStringView uri,
+                                       QAnyStringView typeName);
+#endif
+
 }
 }
 

crates/cxx-qt-lib/src/qml/qqmlapplicationengine.cpp

@@ -22,5 +22,16 @@ qqmlapplicationengineAsQQmlEngine(QQmlApplicationEngine& engine)
   return static_cast<QQmlEngine&>(engine);
 }
 
+#if (QT_VERSION >= QT_VERSION_CHECK(6, 5, 0))
+void*
+qqmlapplicationengineSingletonInstance(QQmlApplicationEngine& engine,
+                                       QAnyStringView uri,
+                                       QAnyStringView typeName)
+{
+  return reinterpret_cast<void*>(
+    engine.singletonInstance<QObject*>(uri, typeName));
+}
+#endif
+
 }
 }

crates/cxx-qt-lib/src/qml/qqmlapplicationengine.rs

@@ -68,6 +68,9 @@ mod ffi {
 
     #[namespace = "rust::cxxqtlib1"]
     unsafe extern "C++" {
+        include!("cxx-qt-lib/common.h");
+        type c_void = crate::c_void;
+
         #[doc(hidden)]
         #[rust_name = "qqmlapplicationengine_new"]
         fn qqmlapplicationengineNew() -> UniquePtr<QQmlApplicationEngine>;
@@ -79,13 +82,33 @@ mod ffi {
         ) -> Pin<&mut QQmlEngine>;
     }
 
+    #[cfg(any(cxxqt_qt_version_at_least_7, cxxqt_qt_version_at_least_6_5))]
+    unsafe extern "C++" {
+        include!("cxx-qt-lib/qanystringview.h");
+        type QAnyStringView<'a> = crate::QAnyStringView<'a>;
+    }
+
+    #[namespace = "rust::cxxqtlib1"]
+    unsafe extern "C++" {
+        #[doc(hidden)]
+        #[rust_name = "qqmlapplicationengine_singleton_instance"]
+        #[cfg(any(cxxqt_qt_version_at_least_7, cxxqt_qt_version_at_least_6_5))]
+        fn qqmlapplicationengineSingletonInstance(
+            ptr: Pin<&mut QQmlApplicationEngine>,
+            uri: QAnyStringView,
+            typeName: QAnyStringView,
+        ) -> *mut c_void;
+    }
+
     // QQmlApplicationEngine is not a trivial to CXX and is not relocatable in Qt
     // as the following fails in C++. So we cannot mark it as a trivial type
     // and need to use references or pointers.
     // static_assert(QTypeInfo<QQmlApplicationEngine>::isRelocatable);
     impl UniquePtr<QQmlApplicationEngine> {}
 }
 
+#[cfg(any(cxxqt_qt_version_at_least_7, cxxqt_qt_version_at_least_6_5))]
+use crate::QAnyStringView;
 use crate::QQmlEngine;
 use core::pin::Pin;
 
@@ -101,4 +124,20 @@ impl QQmlApplicationEngine {
     pub fn new() -> cxx::UniquePtr<Self> {
         ffi::qqmlapplicationengine_new()
     }
+
+    /// Returns the instance of a singleton type named typeName from the module specified by uri.
+    /// This is inherently unsafe as it does not perform any type checks.
+    /// This function was introduced in Qt 6.5.
+    #[cfg(any(cxxqt_qt_version_at_least_7, cxxqt_qt_version_at_least_6_5))]
+    pub unsafe fn singleton_instance<'a, T>(
+        self: Pin<&'a mut Self>,
+        uri: QAnyStringView,
+        type_name: QAnyStringView,
+    ) -> Option<Pin<&'a mut T>> {
+        let ptr = ffi::qqmlapplicationengine_singleton_instance(self, uri, type_name);
+        if ptr.is_null() {
+            return None;
+        }
+        Some(Pin::new_unchecked(&mut *(ptr as *mut T)))
+    }
 }