Simplify From impls from implement macro

microsoft · May 11, 2022 · 94d335e · 94d335e
1 parent 2eddbfa
commit 94d335e
Showing 1 changed file with 10 additions and 14 deletions.
diff --git a/crates/libs/implement/src/lib.rs b/crates/libs/implement/src/lib.rs
@@ -53,10 +53,10 @@ pub fn implement(attributes: proc_macro::TokenStream, original_type: proc_macro:
             impl <#constraints> ::core::convert::From<#original_ident::<#(#generics,)*>> for #interface_ident {
                 fn from(this: #original_ident::<#(#generics,)*>) -> Self {
                     let this = #impl_ident::<#(#generics,)*>::new(this);
-                    let mut this = ::std::boxed::Box::new(this);
-                    let vtable_ptr = &mut this.vtables.#offset as *mut *const <#interface_ident as ::windows::core::Interface>::Vtable;
-                    let _ = ::std::boxed::Box::leak(this);
-                    unsafe { ::core::mem::transmute_copy(&vtable_ptr) }
+                    let mut this = ::core::mem::ManuallyDrop::new(::std::boxed::Box::new(this));
+                    let vtable_ptr = &this.vtables.#offset;
+                    // SAFETY: interfaces are in-memory equivalent to pointers to their vtables.
+                    unsafe { ::core::mem::transmute(vtable_ptr) }
                 }
             }
             impl <#constraints> ::windows::core::AsImpl<#original_ident::<#(#generics,)*>> for #interface_ident {
@@ -163,23 +163,19 @@ pub fn implement(attributes: proc_macro::TokenStream, original_type: proc_macro:
         }
         impl <#constraints> ::core::convert::From<#original_ident::<#(#generics,)*>> for ::windows::core::IUnknown {
             fn from(this: #original_ident::<#(#generics,)*>) -> Self {
+                let this = #impl_ident::<#(#generics,)*>::new(this);
+                let boxed = ::core::mem::ManuallyDrop::new(::std::boxed::Box::new(this));
                 unsafe {
-                    let this = #impl_ident::<#(#generics,)*>::new(this);
-                    let ptr = ::std::boxed::Box::into_raw(::std::boxed::Box::new(this));
-                    ::core::mem::transmute_copy(&::core::ptr::NonNull::new_unchecked(
-                        &mut (*ptr).identity as *mut _ as _
-                    ))
+                    ::core::mem::transmute(&boxed.identity)
                 }
             }
         }
         impl <#constraints> ::core::convert::From<#original_ident::<#(#generics,)*>> for ::windows::core::IInspectable {
             fn from(this: #original_ident::<#(#generics,)*>) -> Self {
+                let this = #impl_ident::<#(#generics,)*>::new(this);
+                let boxed = ::core::mem::ManuallyDrop::new(::std::boxed::Box::new(this));
                 unsafe {
-                    let this = #impl_ident::<#(#generics,)*>::new(this);
-                    let ptr = ::std::boxed::Box::into_raw(::std::boxed::Box::new(this));
-                    ::core::mem::transmute_copy(&::core::ptr::NonNull::new_unchecked(
-                        &mut (*ptr).identity as *mut _ as _
-                    ))
+                    ::core::mem::transmute(&boxed.identity)
                 }
             }
         }