Rollup merge of #89001 - jackh726:binder-cleanup, r=nikomatsakis

Be explicit about using Binder::dummy

This is somewhat of a late followup to the binder refactor PR. It removes `ToPredicate` and `ToPolyTraitImpls` that hide the use of `Binder::dummy`. While this does make code a bit more verbose, it allows us be more careful about where we create binders.

Another alternative here might be to add a new trait `ToBinder` or something with a `dummy()` fn. Which could still allow grepping but allows doing something like `trait_ref.dummy()` (but I also wonder if longer-term, it would be better to be even more explicit with a `bind_with_vars(ty::List::empty())` *but* that's not clear yet.

r? ``@nikomatsakis``

Author: workingjubilee

compiler/rustc_borrowck/src/type_check/canonical.rs

@@ -89,10 +89,10 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         category: ConstraintCategory,
     ) {
         self.prove_predicates(
-            Some(ty::PredicateKind::Trait(ty::TraitPredicate {
+            Some(ty::Binder::dummy(ty::PredicateKind::Trait(ty::TraitPredicate {
                 trait_ref,
                 constness: ty::BoundConstness::NotConst,
-            })),
+            }))),
             locations,
             category,
         );

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1080,7 +1080,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     }
 
                     self.prove_predicate(
-                        ty::PredicateKind::WellFormed(inferred_ty.into()).to_predicate(self.tcx()),
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(inferred_ty.into()))
+                            .to_predicate(self.tcx()),
                         Locations::All(span),
                         ConstraintCategory::TypeAnnotation,
                     );
@@ -1316,7 +1317,8 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     obligations.obligations.push(traits::Obligation::new(
                         ObligationCause::dummy(),
                         param_env,
-                        ty::PredicateKind::WellFormed(revealed_ty.into()).to_predicate(infcx.tcx),
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(revealed_ty.into()))
+                            .to_predicate(infcx.tcx),
                     ));
                     obligations.add(
                         infcx
@@ -1599,7 +1601,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.check_call_dest(body, term, &sig, destination, term_location);
 
                 self.prove_predicates(
-                    sig.inputs_and_output.iter().map(|ty| ty::PredicateKind::WellFormed(ty.into())),
+                    sig.inputs_and_output
+                        .iter()
+                        .map(|ty| ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))),
                     term_location.to_locations(),
                     ConstraintCategory::Boring,
                 );

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -669,8 +669,10 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
         self.obligations.push(Obligation {
             cause: self.cause.clone(),
             param_env: self.param_env,
-            predicate: ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(sup, sub))
-                .to_predicate(self.infcx.tcx),
+            predicate: ty::Binder::dummy(ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(
+                sup, sub,
+            )))
+            .to_predicate(self.infcx.tcx),
             recursion_depth: 0,
         });
     }

compiler/rustc_infer/src/infer/combine.rs

@@ -360,7 +360,8 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
             self.obligations.push(Obligation::new(
                 self.trace.cause.clone(),
                 self.param_env,
-                ty::PredicateKind::WellFormed(b_ty.into()).to_predicate(self.infcx.tcx),
+                ty::Binder::dummy(ty::PredicateKind::WellFormed(b_ty.into()))
+                    .to_predicate(self.infcx.tcx),
             ));
         }
 
@@ -463,7 +464,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         self.obligations.push(Obligation::new(
             self.trace.cause.clone(),
             self.param_env,
-            predicate.to_predicate(self.tcx()),
+            ty::Binder::dummy(predicate).to_predicate(self.tcx()),
         ));
     }
 }

compiler/rustc_infer/src/infer/sub.rs

@@ -97,11 +97,11 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
                 self.fields.obligations.push(Obligation::new(
                     self.fields.trace.cause.clone(),
                     self.fields.param_env,
-                    ty::PredicateKind::Subtype(ty::SubtypePredicate {
+                    ty::Binder::dummy(ty::PredicateKind::Subtype(ty::SubtypePredicate {
                         a_is_expected: self.a_is_expected,
                         a,
                         b,
-                    })
+                    }))
                     .to_predicate(self.tcx()),
                 ));
 

compiler/rustc_infer/src/traits/engine.rs

@@ -35,7 +35,7 @@ pub trait TraitEngine<'tcx>: 'tcx {
                 cause,
                 recursion_depth: 0,
                 param_env,
-                predicate: trait_ref.without_const().to_predicate(infcx.tcx),
+                predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(infcx.tcx),
             },
         );
     }

compiler/rustc_infer/src/traits/util.rs

@@ -231,6 +231,7 @@ impl Elaborator<'tcx> {
                                 None
                             }
                         })
+                        .map(ty::Binder::dummy)
                         .map(|predicate_kind| predicate_kind.to_predicate(tcx))
                         .filter(|&predicate| visited.insert(predicate))
                         .map(|predicate| {

compiler/rustc_middle/src/ty/mod.rs

@@ -769,12 +769,6 @@ pub trait ToPolyTraitRef<'tcx> {
     fn to_poly_trait_ref(&self) -> PolyTraitRef<'tcx>;
 }
 
-impl<'tcx> ToPolyTraitRef<'tcx> for TraitRef<'tcx> {
-    fn to_poly_trait_ref(&self) -> PolyTraitRef<'tcx> {
-        ty::Binder::dummy(*self)
-    }
-}
-
 impl<'tcx> ToPolyTraitRef<'tcx> for PolyTraitPredicate<'tcx> {
     fn to_poly_trait_ref(&self) -> PolyTraitRef<'tcx> {
         self.map_bound_ref(|trait_pred| trait_pred.trait_ref)
@@ -792,23 +786,6 @@ impl ToPredicate<'tcx> for Binder<'tcx, PredicateKind<'tcx>> {
     }
 }
 
-impl ToPredicate<'tcx> for PredicateKind<'tcx> {
-    #[inline(always)]
-    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        tcx.mk_predicate(Binder::dummy(self))
-    }
-}
-
-impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<TraitRef<'tcx>> {
-    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        PredicateKind::Trait(ty::TraitPredicate {
-            trait_ref: self.value,
-            constness: self.constness,
-        })
-        .to_predicate(tcx)
-    }
-}
-
 impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<PolyTraitRef<'tcx>> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
         self.value

compiler/rustc_middle/src/ty/sty.rs

@@ -844,8 +844,11 @@ impl<'tcx> TraitRef<'tcx> {
 
     /// Returns a `TraitRef` of the form `P0: Foo<P1..Pn>` where `Pi`
     /// are the parameters defined on trait.
-    pub fn identity(tcx: TyCtxt<'tcx>, def_id: DefId) -> TraitRef<'tcx> {
-        TraitRef { def_id, substs: InternalSubsts::identity_for_item(tcx, def_id) }
+    pub fn identity(tcx: TyCtxt<'tcx>, def_id: DefId) -> Binder<'tcx, TraitRef<'tcx>> {
+        ty::Binder::dummy(TraitRef {
+            def_id,
+            substs: InternalSubsts::identity_for_item(tcx, def_id),
+        })
     }
 
     #[inline]

compiler/rustc_trait_selection/src/autoderef.rs

@@ -135,7 +135,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         let obligation = traits::Obligation::new(
             cause.clone(),
             self.param_env,
-            trait_ref.without_const().to_predicate(tcx),
+            ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
         );
         if !self.infcx.predicate_may_hold(&obligation) {
             debug!("overloaded_deref_ty: cannot match obligation");

compiler/rustc_trait_selection/src/infer.rs

@@ -120,7 +120,7 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
             cause: traits::ObligationCause::dummy(),
             param_env,
             recursion_depth: 0,
-            predicate: trait_ref.without_const().to_predicate(self.tcx),
+            predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx),
         };
         self.evaluate_obligation(&obligation).unwrap_or(traits::EvaluationResult::EvaluatedToErr)
     }

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

@@ -726,7 +726,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             let new_obligation = Obligation::new(
                 ObligationCause::dummy(),
                 param_env,
-                new_trait_ref.without_const().to_predicate(self.tcx),
+                ty::Binder::dummy(new_trait_ref).without_const().to_predicate(self.tcx),
             );
 
             if self.predicate_must_hold_modulo_regions(&new_obligation) {

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -418,7 +418,8 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                 | ty::PredicateKind::Coerce(_)
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..) => {
-                    let pred = infcx.replace_bound_vars_with_placeholders(binder);
+                    let pred =
+                        ty::Binder::dummy(infcx.replace_bound_vars_with_placeholders(binder));
                     ProcessResult::Changed(mk_pending(vec![
                         obligation.with(pred.to_predicate(self.selcx.tcx())),
                     ]))

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -140,7 +140,8 @@ pub fn type_known_to_meet_bound_modulo_regions<'a, 'tcx>(
         infcx.tcx.def_path_str(def_id)
     );
 
-    let trait_ref = ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) };
+    let trait_ref =
+        ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) });
     let obligation = Obligation {
         param_env,
         cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -250,7 +250,7 @@ fn predicates_reference_self(
     trait_def_id: DefId,
     supertraits_only: bool,
 ) -> SmallVec<[Span; 1]> {
-    let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id));
+    let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
     let predicates = if supertraits_only {
         tcx.super_predicates_of(trait_def_id)
     } else {
@@ -554,11 +554,11 @@ fn object_ty_for_trait<'tcx>(
 
     let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
 
-    let trait_predicate = ty::Binder::dummy(ty::ExistentialPredicate::Trait(
-        ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref),
-    ));
+    let trait_predicate = trait_ref.map_bound(|trait_ref| {
+        ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref))
+    });
 
-    let mut associated_types = traits::supertraits(tcx, ty::Binder::dummy(trait_ref))
+    let mut associated_types = traits::supertraits(tcx, trait_ref)
         .flat_map(|super_trait_ref| {
             tcx.associated_items(super_trait_ref.def_id())
                 .in_definition_order()
@@ -671,10 +671,10 @@ fn receiver_is_dispatchable<'tcx>(
         let param_env = tcx.param_env(method.def_id);
 
         // Self: Unsize<U>
-        let unsize_predicate = ty::TraitRef {
+        let unsize_predicate = ty::Binder::dummy(ty::TraitRef {
             def_id: unsize_did,
             substs: tcx.mk_substs_trait(tcx.types.self_param, &[unsized_self_ty.into()]),
-        }
+        })
         .without_const()
         .to_predicate(tcx);
 
@@ -689,7 +689,9 @@ fn receiver_is_dispatchable<'tcx>(
                     }
                 });
 
-            ty::TraitRef { def_id: unsize_did, substs }.without_const().to_predicate(tcx)
+            ty::Binder::dummy(ty::TraitRef { def_id: unsize_did, substs })
+                .without_const()
+                .to_predicate(tcx)
         };
 
         let caller_bounds: Vec<Predicate<'tcx>> = param_env
@@ -703,10 +705,10 @@ fn receiver_is_dispatchable<'tcx>(
 
     // Receiver: DispatchFromDyn<Receiver[Self => U]>
     let obligation = {
-        let predicate = ty::TraitRef {
+        let predicate = ty::Binder::dummy(ty::TraitRef {
             def_id: dispatch_from_dyn_did,
             substs: tcx.mk_substs_trait(receiver_ty, &[unsized_receiver_ty.into()]),
-        }
+        })
         .without_const()
         .to_predicate(tcx);
 
@@ -789,8 +791,7 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeFoldable<'tcx>>(
 
                     // Compute supertraits of current trait lazily.
                     if self.supertraits.is_none() {
-                        let trait_ref =
-                            ty::Binder::dummy(ty::TraitRef::identity(self.tcx, self.trait_def_id));
+                        let trait_ref = ty::TraitRef::identity(self.tcx, self.trait_def_id);
                         self.supertraits = Some(
                             traits::supertraits(self.tcx, trait_ref).map(|t| t.def_id()).collect(),
                         );

compiler/rustc_trait_selection/src/traits/project.rs

@@ -27,7 +27,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
 use rustc_middle::ty::subst::Subst;
-use rustc_middle::ty::{self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, WithConstness};
 use rustc_span::symbol::sym;
 
 use std::collections::BTreeMap;
@@ -1028,7 +1028,7 @@ fn normalize_to_error<'a, 'tcx>(
     cause: ObligationCause<'tcx>,
     depth: usize,
 ) -> NormalizedTy<'tcx> {
-    let trait_ref = projection_ty.trait_ref(selcx.tcx()).to_poly_trait_ref();
+    let trait_ref = ty::Binder::dummy(projection_ty.trait_ref(selcx.tcx()));
     let trait_obligation = Obligation {
         cause,
         recursion_depth: depth,
@@ -1290,7 +1290,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
 
     // If we are resolving `<T as TraitRef<...>>::Item == Type`,
     // start out by selecting the predicate `T as TraitRef<...>`:
-    let poly_trait_ref = obligation.predicate.trait_ref(selcx.tcx()).to_poly_trait_ref();
+    let poly_trait_ref = ty::Binder::dummy(obligation.predicate.trait_ref(selcx.tcx()));
     let trait_obligation = obligation.with(poly_trait_ref.to_poly_trait_predicate());
     let _ = selcx.infcx().commit_if_ok(|_| {
         let impl_source = match selcx.select(&trait_obligation) {

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

@@ -141,6 +141,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             let placeholder_trait_predicate =
                 self.infcx().replace_bound_vars_with_placeholders(trait_predicate);
             let placeholder_self_ty = placeholder_trait_predicate.self_ty();
+            let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
             let (def_id, substs) = match *placeholder_self_ty.kind() {
                 ty::Projection(proj) => (proj.item_def_id, proj.substs),
                 ty::Opaque(def_id, substs) => (def_id, substs),
@@ -164,7 +165,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             obligations.extend(self.infcx.commit_if_ok(|_| {
                 self.infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .sup(placeholder_trait_predicate.trait_ref.to_poly_trait_ref(), candidate.value)
+                    .sup(placeholder_trait_predicate.to_poly_trait_ref(), candidate.value)
                     .map(|InferOk { obligations, .. }| obligations)
                     .map_err(|_| Unimplemented)
             })?);
@@ -646,7 +647,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             obligations.push(Obligation::new(
                 obligation.cause.clone(),
                 obligation.param_env,
-                ty::PredicateKind::ClosureKind(closure_def_id, substs, kind)
+                ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, substs, kind))
                     .to_predicate(self.tcx()),
             ));
         }
@@ -898,10 +899,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
 
                 // We can only make objects from sized types.
-                let tr = ty::TraitRef::new(
+                let tr = ty::Binder::dummy(ty::TraitRef::new(
                     tcx.require_lang_item(LangItem::Sized, None),
                     tcx.mk_substs_trait(source, &[]),
-                );
+                ));
                 nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx)));
 
                 // If the type is `Foo + 'a`, ensure that the type

compiler/rustc_trait_selection/src/traits/util.rs

@@ -248,7 +248,7 @@ pub fn predicate_for_trait_ref<'tcx>(
         cause,
         param_env,
         recursion_depth,
-        predicate: trait_ref.without_const().to_predicate(tcx),
+        predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
     }
 }