add ?Sized bounds to traits in #[pin_data] macro

The `#[pin_data]` macro uses some auxiliary traits to ensure that a user
does not implement `Drop` for the annotated struct, as that is unsound
and can lead to UB. However, if the struct that is annotated is
`!Sized`, the current bounds do not work, because `Sized` is an implicit
bound for generics.

This is *not* a soundness hole of pin-init, as it currently is
impossible to construct an unsized struct using pin-init.

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

internal/src/pin_data.rs

@@ -223,7 +223,7 @@ fn generate_drop_impl(
             // if it also implements `Drop`
             trait MustNotImplDrop {}
             #[expect(drop_bounds)]
-            impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
+            impl<T: ::core::ops::Drop + ?::core::marker::Sized> MustNotImplDrop for T {}
             impl #impl_generics MustNotImplDrop for #ident #ty_generics
                 #whr
             {}
@@ -232,7 +232,7 @@ fn generate_drop_impl(
             // `PinnedDrop` as the parameter to `#[pin_data]`.
             #[expect(non_camel_case_types)]
             trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
-            impl<T: ::pin_init::PinnedDrop>
+            impl<T: ::pin_init::PinnedDrop + ?::core::marker::Sized>
                 UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
             impl #impl_generics
                 UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for #ident #ty_generics

tests/ui/expand/pin-data.expanded.rs

@@ -113,11 +113,12 @@ const _: () = {
     {}
     trait MustNotImplDrop {}
     #[expect(drop_bounds)]
-    impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
+    impl<T: ::core::ops::Drop + ?::core::marker::Sized> MustNotImplDrop for T {}
     impl MustNotImplDrop for Foo {}
     #[expect(non_camel_case_types)]
     trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
-    impl<T: ::pin_init::PinnedDrop> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop
-    for T {}
+    impl<
+        T: ::pin_init::PinnedDrop + ?::core::marker::Sized,
+    > UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
     impl UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Foo {}
 };