Adds unsafe helpers to cast from C++ or raw IUnknown pointers to Rust IUnknown values

crates/libs/windows/src/core/interface.rs

@@ -48,6 +48,26 @@ pub unsafe trait Interface: Sized {
         raw
     }
 
+    /// Creates an `Interface` by taking ownership of the `raw` COM interface pointer.
+    ///
+    /// # Safety
+    ///
+    /// The `raw` pointer must be owned by the caller and represent a valid COM interface pointer. In other words,
+    /// it must point to a vtable beginning with the `IUnknown` function pointers and match the vtable of `Interface`.
+    unsafe fn from_raw(raw: *mut core::ffi::c_void) -> Self {
+        std::mem::transmute_copy(&raw)
+    }
+
+    /// Creates an `Interface` that is valid so long as the `raw` COM interface pointer is valid.
+    ///
+    /// # Safety
+    ///
+    /// The `raw` pointer must be a valid COM interface pointer. In other words, it must point to a vtable
+    /// beginning with the `IUnknown` function pointers and match the vtable of `Interface`.
+    unsafe fn from_raw_borrowed<'a>(raw: &'a *mut core::ffi::c_void) -> &'a Self {
+        std::mem::transmute_copy(&raw)
+    }
+
     /// Attempts to create a [`Weak`] reference to this object.
     fn downgrade(&self) -> Result<Weak<Self>> {
         self.cast::<IWeakReferenceSource>().and_then(|source| Weak::downgrade(&source))

crates/libs/windows/src/core/unknown.rs

@@ -7,28 +7,6 @@ use super::*;
 #[repr(transparent)]
 pub struct IUnknown(core::ptr::NonNull<core::ffi::c_void>);
 
-impl IUnknown {
-    /// Creates an `IUnknown` value by taking ownership of the `raw` COM interface pointer.
-    ///
-    /// # Safety
-    ///
-    /// The `raw` pointer must be owned by the caller and represent a valid COM interface pointer. In other words,
-    /// it must point to a vtable beginning with the `IUnknown` function pointers.
-    pub unsafe fn from_raw(raw: *mut core::ffi::c_void) -> Self {
-        std::mem::transmute(raw)
-    }
-
-    /// Creates a borrowed `IUnknown` that is valid so long as the `raw` COM interface pointer is valid.
-    ///
-    /// # Safety
-    ///
-    /// The `raw` pointer must be a valid COM interface pointer. In other words, it must point to a vtable
-    /// beginning with the `IUnknown` function pointers.
-    pub unsafe fn from_raw_borrowed<'a>(raw: &'a *mut core::ffi::c_void) -> &'a Self {
-        std::mem::transmute(raw)
-    }
-}
-
 #[doc(hidden)]
 #[repr(C)]
 pub struct IUnknownVtbl {

crates/tests/core/tests/unknown.rs

@@ -27,7 +27,7 @@ impl Drop for Test {
 }
 
 #[test]
-fn test() {
+fn test_unknown() {
     unsafe {
         let mut dropped = 0;
         let test: ITest = Test { drop: &mut dropped }.into();
@@ -52,3 +52,28 @@ fn test() {
         assert_eq!(dropped, 1);
     }
 }
+
+#[test]
+fn test_test() {
+    unsafe {
+        let mut dropped = 0;
+        let test: ITest = Test { drop: &mut dropped }.into();
+
+        {
+            let raw_borrowed: *mut std::ffi::c_void = test.as_raw();
+            let test_borrowed: &ITest = ITest::from_raw_borrowed(&raw_borrowed);
+            assert_eq!(test_borrowed.as_raw(), test.as_raw());
+            assert_eq!(test_borrowed.Test(), 0);
+        }
+        {
+            let raw_owned: *mut std::ffi::c_void = test.clone().into_raw();
+            let unknown_owned: ITest = ITest::from_raw(raw_owned);
+            assert_eq!(unknown_owned.as_raw(), test.as_raw());
+            assert_eq!(unknown_owned.Test(), 0);
+        }
+
+        assert_eq!(test.Test(), 0);
+        drop(test);
+        assert_eq!(dropped, 1);
+    }
+}