Auto merge of #114358 - matthiaskrgr:rollup-d810m9e, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #114178 (Account for macros when suggesting a new let binding)
 - #114199 (Don't unsize coerce infer vars in select in new solver)
 - #114301 (Don't check unnecessarily that impl trait is RPIT)
 - #114314 (Tweaks to `adt_sized_constraint`)
 - #114322 (Fix invalid slice coercion suggestion reported in turbofish)
 - #114340 ([rustc_attr][nit] Replace `filter` + `is_some` with `map_or`.)

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -150,7 +150,7 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
 
         ty::Adt(def, args) => {
             let sized_crit = def.sized_constraint(ecx.tcx());
-            Ok(sized_crit.iter_instantiated_copied(ecx.tcx(), args).collect())
+            Ok(sized_crit.iter_instantiated(ecx.tcx(), args).collect())
         }
     }
 }

compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs

@@ -235,7 +235,10 @@ fn rematch_unsize<'tcx>(
         goal.param_env,
         &mut nested,
     );
+
     match (a_ty.kind(), b_ty.kind()) {
+        // Don't try to coerce `?0` to `dyn Trait`
+        (ty::Infer(ty::TyVar(_)), _) | (_, ty::Infer(ty::TyVar(_))) => Ok(None),
         // Stall any ambiguous upcasting goals, since we can't rematch those
         (ty::Dynamic(_, _, ty::Dyn), ty::Dynamic(_, _, ty::Dyn)) => match certainty {
             Certainty::Yes => Ok(Some(ImplSource::Builtin(source, nested))),

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -3030,8 +3030,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 self.report_similar_impl_candidates_for_root_obligation(&obligation, *trait_predicate, body_def_id, err);
             }
 
-            self.maybe_suggest_convert_to_slice(
+            self.suggest_convert_to_slice(
                 err,
+                obligation,
                 trait_ref,
                 impl_candidates.as_slice(),
                 span,

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -398,9 +398,10 @@ pub trait TypeErrCtxtExt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
     ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>;
 
-    fn maybe_suggest_convert_to_slice(
+    fn suggest_convert_to_slice(
         &self,
         err: &mut Diagnostic,
+        obligation: &PredicateObligation<'tcx>,
         trait_ref: ty::PolyTraitRef<'tcx>,
         candidate_impls: &[ImplCandidate<'tcx>],
         span: Span,
@@ -3944,13 +3945,20 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     /// If the type that failed selection is an array or a reference to an array,
     /// but the trait is implemented for slices, suggest that the user converts
     /// the array into a slice.
-    fn maybe_suggest_convert_to_slice(
+    fn suggest_convert_to_slice(
         &self,
         err: &mut Diagnostic,
+        obligation: &PredicateObligation<'tcx>,
         trait_ref: ty::PolyTraitRef<'tcx>,
         candidate_impls: &[ImplCandidate<'tcx>],
         span: Span,
     ) {
+        // We can only suggest the slice coersion for function arguments since the suggestion
+        // would make no sense in turbofish or call
+        let ObligationCauseCode::FunctionArgumentObligation { .. } = obligation.cause.code() else {
+            return;
+        };
+
         // Three cases where we can make a suggestion:
         // 1. `[T; _]` (array of T)
         // 2. `&[T; _]` (reference to array of T)

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2099,7 +2099,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
                 Where(
                     obligation
                         .predicate
-                        .rebind(sized_crit.iter_instantiated_copied(self.tcx(), args).collect()),
+                        .rebind(sized_crit.iter_instantiated(self.tcx(), args).collect()),
                 )
             }