A lot of refactoring to remove more Binder::binds

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

@@ -525,10 +525,10 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         result_subst: &'a CanonicalVarValues<'tcx>,
     ) -> impl Iterator<Item = PredicateObligation<'tcx>> + 'a + Captures<'tcx> {
         unsubstituted_region_constraints.iter().map(move |&constraint| {
-            let ty::OutlivesPredicate(k1, r2) =
-                substitute_value(self.tcx, result_subst, constraint).skip_binder();
+            let predicate = substitute_value(self.tcx, result_subst, constraint);
+            let ty::OutlivesPredicate(k1, r2) = predicate.skip_binder();
 
-            let predicate = match k1.unpack() {
+            let atom = match k1.unpack() {
                 GenericArgKind::Lifetime(r1) => {
                     ty::PredicateAtom::RegionOutlives(ty::OutlivesPredicate(r1, r2))
                 }
@@ -540,8 +540,9 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                     // encounter this branch.
                     span_bug!(cause.span, "unexpected const outlives {:?}", constraint);
                 }
-            }
-            .potentially_quantified(self.tcx, ty::PredicateKind::ForAll);
+            };
+            let predicate =
+                predicate.rebind(atom).potentially_quantified(self.tcx, ty::PredicateKind::ForAll);
 
             Obligation::new(cause.clone(), param_env, predicate)
         })

compiler/rustc_infer/src/infer/combine.rs

@@ -551,7 +551,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
-        Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))
+        Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
     }
 
     fn relate_item_substs(
@@ -833,7 +833,7 @@ impl TypeRelation<'tcx> for ConstInferUnifier<'_, 'tcx> {
     where
         T: Relate<'tcx>,
     {
-        Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))
+        Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
     }
 
     fn tys(&mut self, t: Ty<'tcx>, _t: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -1008,6 +1008,6 @@ where
         self.first_free_index.shift_in(1);
         let result = self.relate(a.skip_binder(), a.skip_binder())?;
         self.first_free_index.shift_out(1);
-        Ok(ty::Binder::bind(result))
+        Ok(a.rebind(result))
     }
 }

compiler/rustc_middle/src/ty/_match.rs

@@ -118,6 +118,6 @@ impl TypeRelation<'tcx> for Match<'tcx> {
     where
         T: Relate<'tcx>,
     {
-        Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))
+        Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))
     }
 }

compiler/rustc_middle/src/ty/context.rs

@@ -299,6 +299,7 @@ pub struct ResolvedOpaqueTy<'tcx> {
 /// Here, we would store the type `T`, the span of the value `x`, the "scope-span" for
 /// the scope that contains `x`, the expr `T` evaluated from, and the span of `foo.await`.
 #[derive(TyEncodable, TyDecodable, Clone, Debug, Eq, Hash, PartialEq, HashStable)]
+#[derive(TypeFoldable)]
 pub struct GeneratorInteriorTypeCause<'tcx> {
     /// Type of the captured binding.
     pub ty: Ty<'tcx>,
@@ -423,7 +424,7 @@ pub struct TypeckResults<'tcx> {
 
     /// Stores the type, expression, span and optional scope span of all types
     /// that are live across the yield of this generator (if a generator).
-    pub generator_interior_types: Vec<GeneratorInteriorTypeCause<'tcx>>,
+    pub generator_interior_types: ty::Binder<Vec<GeneratorInteriorTypeCause<'tcx>>>,
 
     /// We sometimes treat byte string literals (which are of type `&[u8; N]`)
     /// as `&[u8]`, depending on the pattern  in which they are used.
@@ -455,7 +456,7 @@ impl<'tcx> TypeckResults<'tcx> {
             concrete_opaque_types: Default::default(),
             closure_captures: Default::default(),
             closure_min_captures: Default::default(),
-            generator_interior_types: Default::default(),
+            generator_interior_types: ty::Binder::dummy(Default::default()),
             treat_byte_string_as_slice: Default::default(),
         }
     }

compiler/rustc_middle/src/ty/mod.rs

@@ -1149,17 +1149,16 @@ pub enum PredicateAtom<'tcx> {
     TypeWellFormedFromEnv(Ty<'tcx>),
 }
 
-impl<'tcx> PredicateAtom<'tcx> {
+impl<'tcx> Binder<PredicateAtom<'tcx>> {
     /// Wraps `self` with the given qualifier if this predicate has any unbound variables.
     pub fn potentially_quantified(
         self,
         tcx: TyCtxt<'tcx>,
         qualifier: impl FnOnce(Binder<PredicateAtom<'tcx>>) -> PredicateKind<'tcx>,
     ) -> Predicate<'tcx> {
-        if self.has_escaping_bound_vars() {
-            qualifier(Binder::bind(self))
-        } else {
-            PredicateKind::Atom(self)
+        match self.no_bound_vars() {
+            Some(atom) => PredicateKind::Atom(atom),
+            None => qualifier(self),
         }
         .to_predicate(tcx)
     }
@@ -1252,7 +1251,11 @@ impl<'tcx> Predicate<'tcx> {
         let substs = trait_ref.skip_binder().substs;
         let pred = self.skip_binders();
         let new = pred.subst(tcx, substs);
-        if new != pred { new.potentially_quantified(tcx, PredicateKind::ForAll) } else { self }
+        if new != pred {
+            ty::Binder::bind(new).potentially_quantified(tcx, PredicateKind::ForAll)
+        } else {
+            self
+        }
     }
 }
 
@@ -1279,6 +1282,10 @@ impl<'tcx> PolyTraitPredicate<'tcx> {
         // Ok to skip binder since trait `DefId` does not care about regions.
         self.skip_binder().def_id()
     }
+
+    pub fn self_ty(self) -> ty::Binder<Ty<'tcx>> {
+        self.map_bound(|trait_ref| trait_ref.self_ty())
+    }
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
@@ -1403,37 +1410,39 @@ impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<PolyTraitRef<'tcx>> {
 
 impl<'tcx> ToPredicate<'tcx> for ConstnessAnd<PolyTraitPredicate<'tcx>> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        PredicateAtom::Trait(self.value.skip_binder(), self.constness)
+        self.value
+            .map_bound(|value| PredicateAtom::Trait(value, self.constness))
             .potentially_quantified(tcx, PredicateKind::ForAll)
     }
 }
 
 impl<'tcx> ToPredicate<'tcx> for PolyRegionOutlivesPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        PredicateAtom::RegionOutlives(self.skip_binder())
+        self.map_bound(|value| PredicateAtom::RegionOutlives(value))
             .potentially_quantified(tcx, PredicateKind::ForAll)
     }
 }
 
 impl<'tcx> ToPredicate<'tcx> for PolyTypeOutlivesPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        PredicateAtom::TypeOutlives(self.skip_binder())
+        self.map_bound(|value| PredicateAtom::TypeOutlives(value))
             .potentially_quantified(tcx, PredicateKind::ForAll)
     }
 }
 
 impl<'tcx> ToPredicate<'tcx> for PolyProjectionPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        PredicateAtom::Projection(self.skip_binder())
+        self.map_bound(|value| PredicateAtom::Projection(value))
             .potentially_quantified(tcx, PredicateKind::ForAll)
     }
 }
 
 impl<'tcx> Predicate<'tcx> {
     pub fn to_opt_poly_trait_ref(self) -> Option<ConstnessAnd<PolyTraitRef<'tcx>>> {
-        match self.skip_binders() {
+        let predicate = self.bound_atom();
+        match predicate.skip_binder() {
             PredicateAtom::Trait(t, constness) => {
-                Some(ConstnessAnd { constness, value: ty::Binder::bind(t.trait_ref) })
+                Some(ConstnessAnd { constness, value: predicate.rebind(t.trait_ref) })
             }
             PredicateAtom::Projection(..)
             | PredicateAtom::Subtype(..)
@@ -1449,8 +1458,9 @@ impl<'tcx> Predicate<'tcx> {
     }
 
     pub fn to_opt_type_outlives(self) -> Option<PolyTypeOutlivesPredicate<'tcx>> {
-        match self.skip_binders() {
-            PredicateAtom::TypeOutlives(data) => Some(ty::Binder::bind(data)),
+        let predicate = self.bound_atom();
+        match predicate.skip_binder() {
+            PredicateAtom::TypeOutlives(data) => Some(predicate.rebind(data)),
             PredicateAtom::Trait(..)
             | PredicateAtom::Projection(..)
             | PredicateAtom::Subtype(..)

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

@@ -1151,9 +1151,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
     ) -> DiagnosticBuilder<'tcx> {
         crate fn build_fn_sig_string<'tcx>(
             tcx: TyCtxt<'tcx>,
-            trait_ref: ty::TraitRef<'tcx>,
+            trait_ref: ty::PolyTraitRef<'tcx>,
         ) -> String {
-            let inputs = trait_ref.substs.type_at(1);
+            let inputs = trait_ref.skip_binder().substs.type_at(1);
             let sig = if let ty::Tuple(inputs) = inputs.kind() {
                 tcx.mk_fn_sig(
                     inputs.iter().map(|k| k.expect_ty()),
@@ -1171,7 +1171,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     abi::Abi::Rust,
                 )
             };
-            ty::Binder::bind(sig).to_string()
+            trait_ref.rebind(sig).to_string()
         }
 
         let argument_is_closure = expected_ref.skip_binder().substs.type_at(0).is_closure();
@@ -1183,17 +1183,12 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             if argument_is_closure { "closure" } else { "function" }
         );
 
-        let found_str = format!(
-            "expected signature of `{}`",
-            build_fn_sig_string(self.tcx, found.skip_binder())
-        );
+        let found_str = format!("expected signature of `{}`", build_fn_sig_string(self.tcx, found));
         err.span_label(span, found_str);
 
         let found_span = found_span.unwrap_or(span);
-        let expected_str = format!(
-            "found signature of `{}`",
-            build_fn_sig_string(self.tcx, expected_ref.skip_binder())
-        );
+        let expected_str =
+            format!("found signature of `{}`", build_fn_sig_string(self.tcx, expected_ref));
         err.span_label(found_span, expected_str);
 
         err
@@ -1422,7 +1417,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // generator frame. Bound regions are preserved by
             // `erase_regions` and so we must also call
             // `erase_late_bound_regions`.
-            let ty_erased = self.tcx.erase_late_bound_regions(ty::Binder::bind(ty));
+            let ty_erased = self.tcx.erase_late_bound_regions(ty);
             let ty_erased = self.tcx.erase_regions(ty_erased);
             let eq = ty::TyS::same_type(ty_erased, target_ty_erased);
             debug!(
@@ -1440,18 +1435,21 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             interior_or_upvar_span = upvars.iter().find_map(|(upvar_id, upvar)| {
                 let upvar_ty = typeck_results.node_type(*upvar_id);
                 let upvar_ty = self.resolve_vars_if_possible(upvar_ty);
-                if ty_matches(&upvar_ty) {
+                if ty_matches(ty::Binder::dummy(upvar_ty)) {
                     Some(GeneratorInteriorOrUpvar::Upvar(upvar.span))
                 } else {
                     None
                 }
             });
         };
 
-        if let Some(cause) = typeck_results
-            .generator_interior_types
-            .iter()
-            .find(|ty::GeneratorInteriorTypeCause { ty, .. }| ty_matches(ty))
+        // The generator interior types share the same binders
+        if let Some(cause) =
+            typeck_results.generator_interior_types.as_ref().skip_binder().iter().find(
+                |ty::GeneratorInteriorTypeCause { ty, .. }| {
+                    ty_matches(typeck_results.generator_interior_types.rebind(ty))
+                },
+            )
         {
             // Check to see if any awaited expressions have the target type.
             let from_awaited_ty = visitor
@@ -1464,7 +1462,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         "maybe_note_obligation_cause_for_async_await: await_expr={:?}",
                         await_expr
                     );
-                    ty_matches(ty)
+                    ty_matches(ty::Binder::dummy(ty))
                 })
                 .map(|expr| expr.span);
             let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -418,11 +418,11 @@ fn virtual_call_violation_for_method<'tcx>(
     }
 
     for (i, &input_ty) in sig.skip_binder().inputs()[1..].iter().enumerate() {
-        if contains_illegal_self_type_reference(tcx, trait_def_id, input_ty) {
+        if contains_illegal_self_type_reference(tcx, trait_def_id, sig.rebind(input_ty)) {
             return Some(MethodViolationCode::ReferencesSelfInput(i));
         }
     }
-    if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output().skip_binder()) {
+    if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output()) {
         return Some(MethodViolationCode::ReferencesSelfOutput);
     }
 

compiler/rustc_trait_selection/src/traits/project.rs

@@ -951,7 +951,7 @@ 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_trait_ref.to_poly_trait_ref();
+    let poly_trait_ref = ty::Binder::dummy(*obligation_trait_ref);
     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) {
@@ -1247,7 +1247,9 @@ fn confirm_discriminant_kind_candidate<'cx, 'tcx>(
         ty: self_ty.discriminant_ty(tcx),
     };
 
-    confirm_param_env_candidate(selcx, obligation, ty::Binder::bind(predicate), false)
+    // We get here from `poly_project_and_unify_type` which replaces bound vars
+    // with placeholders, so dummy is okay here.
+    confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
 }
 
 fn confirm_fn_pointer_candidate<'cx, 'tcx>(

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

@@ -259,10 +259,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) -> ImplSourceAutoImplData<PredicateObligation<'tcx>> {
         debug!(?obligation, ?trait_def_id, "confirm_auto_impl_candidate");
 
-        let types = obligation.predicate.map_bound(|inner| {
-            let self_ty = self.infcx.shallow_resolve(inner.self_ty());
-            self.constituent_types_for_ty(self_ty)
-        });
+        let self_ty = self.infcx.shallow_resolve(obligation.predicate.self_ty());
+        let types = self.constituent_types_for_ty(self_ty);
         self.vtable_auto_impl(obligation, trait_def_id, types)
     }