Arbitrary self types v2: Weak, NonNull hints

Various types can be used as method receivers, such as Rc<>, Box<> and
Arc<>. The arbitrary self types v2 work allows further types to be made
method receivers by implementing the Receiver trait.

With that in mind, it may come as a surprise to people when certain
common types do not implement Receiver and thus cannot be used as a
method receiver.

The RFC for arbitrary self types v2 therefore proposes emitting specific
lint hints for these cases:
* NonNull
* Weak
* Raw pointers

The code already emits a hint for this third case, in that it advises
folks that the `arbitrary_self_types_pointers` feature may meet their
need. This PR adds diagnostic hints for the Weak and NonNull cases.

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index a2df0ba265c..0c3ed9b5c60 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -249,6 +249,12 @@ hir_analysis_invalid_receiver_ty_help =
 hir_analysis_invalid_receiver_ty_help_no_arbitrary_self_types =
     consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
+hir_analysis_invalid_receiver_ty_help_nonnull_note =
+    `NonNull` does not implement `Receiver` because it has methods that may shadow the referent; consider wrapping your `NonNull` in a newtype wrapper for which you implement `Receiver`
+
+hir_analysis_invalid_receiver_ty_help_weak_note =
+    `Weak` does not implement `Receiver` because it has methods that may shadow the referent; consider wrapping your `Weak` in a newtype wrapper for which you implement `Receiver`
+
 hir_analysis_invalid_receiver_ty_no_arbitrary_self_types = invalid `self` parameter type: `{$receiver_ty}`
     .note = type of `self` must be `Self` or a type that dereferences to it