Rollup merge of rust-lang#72508 - ecstatic-morse:poly-self-ty, r=nikomatsakis

Make `PolyTraitRef::self_ty` return `Binder<Ty>`

This came up during review of rust-lang#71618. The current implementation is the same as a call to `skip_binder` but harder to audit. Make it preserve binding levels and add a call to `skip_binder` at all use sites so they can be audited as part of rust-lang#72507.

Author: RalfJung

src/librustc_middle/ty/sty.rs

@@ -765,8 +765,8 @@ impl<'tcx> TraitRef<'tcx> {
 pub type PolyTraitRef<'tcx> = Binder<TraitRef<'tcx>>;
 
 impl<'tcx> PolyTraitRef<'tcx> {
-    pub fn self_ty(&self) -> Ty<'tcx> {
-        self.skip_binder().self_ty()
+    pub fn self_ty(&self) -> Binder<Ty<'tcx>> {
+        self.map_bound_ref(|tr| tr.self_ty())
     }
 
     pub fn def_id(&self) -> DefId {

src/librustc_trait_selection/traits/error_reporting/mod.rs

@@ -290,7 +290,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             (
                                 Some(format!(
                                     "`?` couldn't convert the error to `{}`",
-                                    trait_ref.self_ty(),
+                                    trait_ref.skip_binder().self_ty(),
                                 )),
                                 Some(
                                     "the question mark operation (`?`) implicitly performs a \
@@ -340,7 +340,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             if let Some(ret_span) = self.return_type_span(obligation) {
                                 err.span_label(
                                     ret_span,
-                                    &format!("expected `{}` because of this", trait_ref.self_ty()),
+                                    &format!(
+                                        "expected `{}` because of this",
+                                        trait_ref.skip_binder().self_ty()
+                                    ),
                                 );
                             }
                         }
@@ -353,7 +356,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                     "{}the trait `{}` is not implemented for `{}`",
                                     pre_message,
                                     trait_ref.print_only_trait_path(),
-                                    trait_ref.self_ty(),
+                                    trait_ref.skip_binder().self_ty(),
                                 )
                             };
 
@@ -643,7 +646,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     return;
                 }
 
-                let found_trait_ty = found_trait_ref.self_ty();
+                let found_trait_ty = match found_trait_ref.self_ty().no_bound_vars() {
+                    Some(ty) => ty,
+                    None => return,
+                };
 
                 let found_did = match found_trait_ty.kind {
                     ty::Closure(did, _) | ty::Foreign(did) | ty::FnDef(did, _) => Some(did),
@@ -1360,11 +1366,15 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
     ) {
         let get_trait_impl = |trait_def_id| {
             let mut trait_impl = None;
-            self.tcx.for_each_relevant_impl(trait_def_id, trait_ref.self_ty(), |impl_def_id| {
-                if trait_impl.is_none() {
-                    trait_impl = Some(impl_def_id);
-                }
-            });
+            self.tcx.for_each_relevant_impl(
+                trait_def_id,
+                trait_ref.skip_binder().self_ty(),
+                |impl_def_id| {
+                    if trait_impl.is_none() {
+                        trait_impl = Some(impl_def_id);
+                    }
+                },
+            );
             trait_impl
         };
         let required_trait_path = self.tcx.def_path_str(trait_ref.def_id());
@@ -1435,7 +1445,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
         let mut err = match predicate.kind() {
             ty::PredicateKind::Trait(ref data, _) => {
                 let trait_ref = data.to_poly_trait_ref();
-                let self_ty = trait_ref.self_ty();
+                let self_ty = trait_ref.skip_binder().self_ty();
                 debug!("self_ty {:?} {:?} trait_ref {:?}", self_ty, self_ty.kind, trait_ref);
 
                 if predicate.references_error() {
@@ -1564,7 +1574,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
             ty::PredicateKind::Projection(ref data) => {
                 let trait_ref = data.to_poly_trait_ref(self.tcx);
-                let self_ty = trait_ref.self_ty();
+                let self_ty = trait_ref.skip_binder().self_ty();
                 let ty = data.skip_binder().ty;
                 if predicate.references_error() {
                     return;

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -318,7 +318,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         trait_ref: ty::PolyTraitRef<'tcx>,
         body_id: hir::HirId,
     ) {
-        let self_ty = trait_ref.self_ty();
+        let self_ty = trait_ref.skip_binder().self_ty();
         let (param_ty, projection) = match &self_ty.kind {
             ty::Param(_) => (true, None),
             ty::Projection(projection) => (false, Some(projection)),
@@ -524,7 +524,11 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
         points_at_arg: bool,
     ) {
-        let self_ty = trait_ref.self_ty();
+        let self_ty = match trait_ref.self_ty().no_bound_vars() {
+            None => return,
+            Some(ty) => ty,
+        };
+
         let (def_id, output_ty, callable) = match self_ty.kind {
             ty::Closure(def_id, substs) => (def_id, substs.as_closure().sig().output(), "closure"),
             ty::FnDef(def_id, _) => (def_id, self_ty.fn_sig(self.tcx).output(), "function"),
@@ -707,7 +711,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 return;
             }
 
-            let mut suggested_ty = trait_ref.self_ty();
+            let mut suggested_ty = match trait_ref.self_ty().no_bound_vars() {
+                Some(ty) => ty,
+                None => return,
+            };
 
             for refs_remaining in 0..refs_number {
                 if let ty::Ref(_, inner_ty, _) = suggested_ty.kind {
@@ -829,6 +836,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         span: Span,
         trait_ref: &ty::Binder<ty::TraitRef<'tcx>>,
     ) {
+        let is_empty_tuple =
+            |ty: ty::Binder<Ty<'_>>| ty.skip_binder().kind == ty::Tuple(ty::List::empty());
+
         let hir = self.tcx.hir();
         let parent_node = hir.get_parent_node(obligation.cause.body_id);
         let node = hir.find(parent_node);
@@ -840,7 +850,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             if let hir::ExprKind::Block(blk, _) = &body.value.kind {
                 if sig.decl.output.span().overlaps(span)
                     && blk.expr.is_none()
-                    && "()" == &trait_ref.self_ty().to_string()
+                    && is_empty_tuple(trait_ref.self_ty())
                 {
                     // FIXME(estebank): When encountering a method with a trait
                     // bound not satisfied in the return type with a body that has
@@ -1271,7 +1281,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 ObligationCauseCode::DerivedObligation(derived_obligation)
                 | ObligationCauseCode::BuiltinDerivedObligation(derived_obligation)
                 | ObligationCauseCode::ImplDerivedObligation(derived_obligation) => {
-                    let ty = derived_obligation.parent_trait_ref.self_ty();
+                    let ty = derived_obligation.parent_trait_ref.skip_binder().self_ty();
                     debug!(
                         "maybe_note_obligation_cause_for_async_await: \
                             parent_trait_ref={:?} self_ty.kind={:?}",
@@ -1917,7 +1927,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
                 let impls_future = self.tcx.type_implements_trait((
                     future_trait,
-                    self_ty,
+                    self_ty.skip_binder(),
                     ty::List::empty(),
                     obligation.param_env,
                 ));
@@ -1933,7 +1943,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                 let projection_ty = ty::ProjectionTy {
                     // `T`
                     substs: self.tcx.mk_substs_trait(
-                        trait_ref.self_ty(),
+                        trait_ref.self_ty().skip_binder(),
                         self.fresh_substs_for_item(span, item_def_id),
                     ),
                     // `Future::Output`

src/librustc_trait_selection/traits/specialize/mod.rs

@@ -496,7 +496,7 @@ fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Option<String>
     for (p, _) in predicates {
         if let Some(poly_trait_ref) = p.to_opt_poly_trait_ref() {
             if Some(poly_trait_ref.def_id()) == sized_trait {
-                types_without_default_bounds.remove(poly_trait_ref.self_ty());
+                types_without_default_bounds.remove(poly_trait_ref.self_ty().skip_binder());
                 continue;
             }
         }

src/librustc_typeck/check/mod.rs

@@ -3813,7 +3813,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         trait_ref: ty::PolyTraitRef<'tcx>,
         expected_vid: ty::TyVid,
     ) -> bool {
-        let self_ty = self.shallow_resolve(trait_ref.self_ty());
+        let self_ty = self.shallow_resolve(trait_ref.skip_binder().self_ty());
         debug!(
             "self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?}, expected_vid={:?})",
             trait_ref, self_ty, expected_vid

src/librustdoc/clean/mod.rs

@@ -500,7 +500,7 @@ impl<'a> Clean<WherePredicate> for ty::PolyTraitPredicate<'a> {
     fn clean(&self, cx: &DocContext<'_>) -> WherePredicate {
         let poly_trait_ref = self.map_bound(|pred| pred.trait_ref);
         WherePredicate::BoundPredicate {
-            ty: poly_trait_ref.self_ty().clean(cx),
+            ty: poly_trait_ref.skip_binder().self_ty().clean(cx),
             bounds: vec![poly_trait_ref.clean(cx)],
         }
     }
@@ -755,7 +755,7 @@ impl<'a, 'tcx> Clean<Generics> for (&'a ty::Generics, ty::GenericPredicates<'tcx
                 let mut projection = None;
                 let param_idx = (|| {
                     if let Some(trait_ref) = p.to_opt_poly_trait_ref() {
-                        if let ty::Param(param) = trait_ref.self_ty().kind {
+                        if let ty::Param(param) = trait_ref.skip_binder().self_ty().kind {
                             return Some(param.index);
                         }
                     } else if let Some(outlives) = p.to_opt_type_outlives() {

src/tools/clippy/clippy_lints/src/future_not_send.rs

@@ -95,7 +95,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FutureNotSend {
                                         let trait_ref = trait_pred.to_poly_trait_ref();
                                         db.note(&*format!(
                                             "`{}` doesn't implement `{}`",
-                                            trait_ref.self_ty(),
+                                            trait_ref.skip_binder().self_ty(),
                                             trait_ref.print_only_trait_path(),
                                         ));
                                     }