Rollup merge of #134264 - adetaylor:weak-and-nonnull, r=compiler-errors

Arbitrary self types v2: Weak & NonNull diagnostics

This builds on top of #134262 which is more urgent to review and merge first. I'll likely rebase this PR once that lands.

This is the first part of the diagnostic enhancements planned for Arbitrary Self Types v2.

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.

Tracking issue #44874

r? `@wesleywiser`

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
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -44,6 +44,7 @@ use {rustc_ast as ast, rustc_hir as hir};
 use crate::autoderef::Autoderef;
 use crate::collect::CollectItemTypesVisitor;
 use crate::constrained_generic_params::{Parameter, identify_constrained_generic_params};
+use crate::errors::InvalidReceiverTyHint;
 use crate::{errors, fluent_generated as fluent};
 
 pub(super) struct WfCheckingCtxt<'a, 'tcx> {
@@ -1749,7 +1750,18 @@ fn check_method_receiver<'tcx>(
             {
                 match receiver_validity_err {
                     ReceiverValidityError::DoesNotDeref if arbitrary_self_types_level.is_some() => {
-                        tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty })
+                        let hint = match receiver_ty
+                            .builtin_deref(false)
+                            .unwrap_or(receiver_ty)
+                            .ty_adt_def()
+                            .and_then(|adt_def| tcx.get_diagnostic_name(adt_def.did()))
+                        {
+                            Some(sym::RcWeak | sym::ArcWeak) => Some(InvalidReceiverTyHint::Weak),
+                            Some(sym::NonNull) => Some(InvalidReceiverTyHint::NonNull),
+                            _ => None,
+                        };
+
+                        tcx.dcx().emit_err(errors::InvalidReceiverTy { span, receiver_ty, hint })
                     }
                     ReceiverValidityError::DoesNotDeref => {
                         tcx.dcx().emit_err(errors::InvalidReceiverTyNoArbitrarySelfTypes {

compiler/rustc_hir_analysis/src/errors.rs

@@ -1655,6 +1655,14 @@ pub(crate) struct NonConstRange {
     pub span: Span,
 }
 
+#[derive(Subdiagnostic)]
+pub(crate) enum InvalidReceiverTyHint {
+    #[note(hir_analysis_invalid_receiver_ty_help_weak_note)]
+    Weak,
+    #[note(hir_analysis_invalid_receiver_ty_help_nonnull_note)]
+    NonNull,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_analysis_invalid_receiver_ty_no_arbitrary_self_types, code = E0307)]
 #[note]
@@ -1673,6 +1681,8 @@ pub(crate) struct InvalidReceiverTy<'tcx> {
     #[primary_span]
     pub span: Span,
     pub receiver_ty: Ty<'tcx>,
+    #[subdiagnostic]
+    pub hint: Option<InvalidReceiverTyHint>,
 }
 
 #[derive(Diagnostic)]