Make Ref work with more than just interface types (#3394)

crates/libs/core/src/ref.rs

@@ -1,24 +1,29 @@
 use super::*;
-use core::ffi::c_void;
 use core::marker::PhantomData;
 use core::mem::transmute;
 
 /// A borrowed type with the same memory layout as the type itself that can be used to construct ABI-compatible function signatures.
 #[repr(transparent)]
 pub struct Ref<'a, T: Type<T>>(T::Abi, PhantomData<&'a T>);
 
-impl<T: Type<T, Default = Option<T>, Abi = *mut c_void>> Ref<'_, T> {
+impl<T: Type<T>> Ref<'_, T> {
     /// Returns `true` if the argument is null.
     pub fn is_null(&self) -> bool {
-        self.0.is_null()
+        T::is_null(&self.0)
     }
 
-    /// Converts the argument to a [Result<&T>] reference.
+    /// Converts the argument to a [`Result<&T>`] reference.
     pub fn ok(&self) -> Result<&T> {
-        if self.0.is_null() {
-            Err(Error::from_hresult(imp::E_POINTER))
+        self.as_ref()
+            .ok_or_else(|| Error::from_hresult(imp::E_POINTER))
+    }
+
+    /// Converts the argument to a [`Option<&T>`] reference.
+    pub fn as_ref(&self) -> Option<&T> {
+        if self.is_null() {
+            None
         } else {
-            unsafe { Ok(self.assume_init()) }
+            unsafe { Some(self.assume_init_ref()) }
         }
     }
 
@@ -27,25 +32,18 @@ impl<T: Type<T, Default = Option<T>, Abi = *mut c_void>> Ref<'_, T> {
     /// # Panics
     ///
     /// Panics if the argument is null.
+    #[track_caller]
     pub fn unwrap(&self) -> &T {
-        if self.0.is_null() {
-            panic!("called `Ref::unwrap` on a null value")
-        } else {
-            unsafe { self.assume_init() }
-        }
+        self.as_ref().expect("called `Ref::unwrap` on a null value")
     }
 
-    /// Converts the argument to an [Option<T>] by cloning the reference.
+    /// Converts the argument to an [`Option<T>`] by cloning the reference.
     pub fn cloned(&self) -> Option<T> {
-        if self.0.is_null() {
-            None
-        } else {
-            unsafe { Some(self.assume_init().clone()) }
-        }
+        self.as_ref().cloned()
     }
 
-    unsafe fn assume_init(&self) -> &T {
-        unsafe { transmute::<&*mut c_void, &T>(&self.0) }
+    unsafe fn assume_init_ref(&self) -> &T {
+        unsafe { T::assume_init_ref(&self.0) }
     }
 }
 

crates/libs/core/src/type.rs

@@ -19,7 +19,8 @@ pub trait Type<T: TypeKind, C = <T as TypeKind>::TypeKind>: TypeKind + Sized + C
     type Abi;
     type Default;
 
-    /// # Safety
+    fn is_null(abi: &Self::Abi) -> bool;
+    unsafe fn assume_init_ref(abi: &Self::Abi) -> &Self;
     unsafe fn from_abi(abi: Self::Abi) -> Result<Self>;
     fn from_default(default: &Self::Default) -> Result<Self>;
 }
@@ -31,6 +32,14 @@ where
     type Abi = *mut core::ffi::c_void;
     type Default = Option<Self>;
 
+    fn is_null(abi: &Self::Abi) -> bool {
+        abi.is_null()
+    }
+
+    unsafe fn assume_init_ref(abi: &Self::Abi) -> &Self {
+        unsafe { core::mem::transmute::<&*mut core::ffi::c_void, &T>(abi) }
+    }
+
     unsafe fn from_abi(abi: Self::Abi) -> Result<Self> {
         unsafe {
             if !abi.is_null() {
@@ -53,6 +62,14 @@ where
     type Abi = core::mem::MaybeUninit<Self>;
     type Default = Self;
 
+    fn is_null(_: &Self::Abi) -> bool {
+        false
+    }
+
+    unsafe fn assume_init_ref(abi: &Self::Abi) -> &Self {
+        unsafe { abi.assume_init_ref() }
+    }
+
     unsafe fn from_abi(abi: Self::Abi) -> Result<Self> {
         unsafe { Ok(abi.assume_init()) }
     }
@@ -69,6 +86,14 @@ where
     type Abi = Self;
     type Default = Self;
 
+    fn is_null(_: &Self::Abi) -> bool {
+        false
+    }
+
+    unsafe fn assume_init_ref(abi: &Self::Abi) -> &Self {
+        abi
+    }
+
     unsafe fn from_abi(abi: Self::Abi) -> Result<Self> {
         Ok(abi)
     }

crates/tests/winrt/ref_params/src/interop.cpp

@@ -15,6 +15,11 @@ struct Test : implements<Test, ITest>
 
     int32_t Input(ITest const& input)
     {
+        if (!input)
+        {
+            throw hresult_error(E_POINTER);
+        }
+
         return input.Current();
     }
 

crates/tests/winrt/ref_params/tests/test.rs

@@ -32,6 +32,7 @@ fn test_interface(test: &ITest) -> Result<()> {
 
     assert_eq!(test.Input(&one_two_three)?, 123);
     assert_eq!(test.Input(&four_five_six)?, 456);
+    assert_eq!(test.Input(None).unwrap_err().code(), HRESULT(-2147467261)); // E_POINTER
 
     let mut seven_eight_nine = None;
     test.Output(789, &mut seven_eight_nine)?;

crates/tests/winrt/reference/src/lib.rs

@@ -7,7 +7,7 @@ unsafe extern "system" fn DllGetActivationFactory(
     name: Ref<HSTRING>,
     factory: OutRef<IActivationFactory>,
 ) -> HRESULT {
-    if *name == "test_reference.Reference" {
+    if name.unwrap() == "test_reference.Reference" {
         factory.write(Some(ReferenceFactory.into())).into()
     } else {
         _ = factory.write(None);