More review comments

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

@@ -6,7 +6,6 @@ pub mod verify;
 
 use rustc_middle::traits::query::OutlivesBound;
 use rustc_middle::ty;
-use rustc_middle::ty::fold::TypeFoldable;
 
 pub fn explicit_outlives_bounds<'tcx>(
     param_env: ty::ParamEnv<'tcx>,
@@ -16,9 +15,8 @@ pub fn explicit_outlives_bounds<'tcx>(
         .caller_bounds()
         .into_iter()
         .map(ty::Predicate::kind)
-        .map(ty::Binder::skip_binder)
-        .filter(|atom| !atom.has_escaping_bound_vars())
-        .filter_map(move |atom| match atom {
+        .filter_map(ty::Binder::no_bound_vars)
+        .filter_map(move |kind| match kind {
             ty::PredicateKind::Projection(..)
             | ty::PredicateKind::Trait(..)
             | ty::PredicateKind::Subtype(..)

compiler/rustc_middle/src/ty/context.rs

@@ -133,13 +133,13 @@ impl<'tcx> CtxtInterners<'tcx> {
     }
 
     #[inline(never)]
-    fn intern_predicate(&self, binder: Binder<PredicateKind<'tcx>>) -> &'tcx PredicateInner<'tcx> {
+    fn intern_predicate(&self, kind: Binder<PredicateKind<'tcx>>) -> &'tcx PredicateInner<'tcx> {
         self.predicate
-            .intern(binder, |binder| {
-                let flags = super::flags::FlagComputation::for_predicate(binder);
+            .intern(kind, |kind| {
+                let flags = super::flags::FlagComputation::for_predicate(kind);
 
                 let predicate_struct = PredicateInner {
-                    binder,
+                    kind,
                     flags: flags.flags,
                     outer_exclusive_binder: flags.outer_exclusive_binder,
                 };
@@ -1936,7 +1936,7 @@ impl<'tcx> Borrow<TyKind<'tcx>> for Interned<'tcx, TyS<'tcx>> {
 // N.B., an `Interned<PredicateInner>` compares and hashes as a `PredicateKind`.
 impl<'tcx> PartialEq for Interned<'tcx, PredicateInner<'tcx>> {
     fn eq(&self, other: &Interned<'tcx, PredicateInner<'tcx>>) -> bool {
-        self.0.binder == other.0.binder
+        self.0.kind == other.0.kind
     }
 }
 
@@ -1944,13 +1944,13 @@ impl<'tcx> Eq for Interned<'tcx, PredicateInner<'tcx>> {}
 
 impl<'tcx> Hash for Interned<'tcx, PredicateInner<'tcx>> {
     fn hash<H: Hasher>(&self, s: &mut H) {
-        self.0.binder.hash(s)
+        self.0.kind.hash(s)
     }
 }
 
 impl<'tcx> Borrow<Binder<PredicateKind<'tcx>>> for Interned<'tcx, PredicateInner<'tcx>> {
     fn borrow<'a>(&'a self) -> &'a Binder<PredicateKind<'tcx>> {
-        &self.0.binder
+        &self.0.kind
     }
 }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -1030,7 +1030,7 @@ impl<'tcx> GenericPredicates<'tcx> {
 
 #[derive(Debug)]
 crate struct PredicateInner<'tcx> {
-    binder: Binder<PredicateKind<'tcx>>,
+    kind: Binder<PredicateKind<'tcx>>,
     flags: TypeFlags,
     /// See the comment for the corresponding field of [TyS].
     outer_exclusive_binder: ty::DebruijnIndex,
@@ -1060,21 +1060,21 @@ impl Hash for Predicate<'_> {
 impl<'tcx> Eq for Predicate<'tcx> {}
 
 impl<'tcx> Predicate<'tcx> {
-    /// Converts this to a `Binder<PredicateKind<'tcx>>`. If the value was an
-    /// `Atom`, then it is not allowed to contain escaping bound vars.
+    /// Gets the inner `Binder<PredicateKind<'tcx>>`.
     pub fn kind(self) -> Binder<PredicateKind<'tcx>> {
-        self.inner.binder
+        self.inner.kind
     }
 
-    pub fn kind_ref(self) -> &'tcx Binder<PredicateKind<'tcx>> {
-        &self.inner.binder
+    /// Like `kind` but returns a reference. Only needed because of encoding.
+    pub(super) fn kind_ref(self) -> &'tcx Binder<PredicateKind<'tcx>> {
+        &self.inner.kind
     }
 }
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for Predicate<'tcx> {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         let PredicateInner {
-            ref binder,
+            ref kind,
 
             // The other fields just provide fast access to information that is
             // also contained in `kind`, so no need to hash them.
@@ -1082,7 +1082,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for Predicate<'tcx> {
             outer_exclusive_binder: _,
         } = self.inner;
 
-        binder.hash_stable(hcx, hasher);
+        kind.hash_stable(hcx, hasher);
     }
 }
 
@@ -1221,7 +1221,7 @@ impl<'tcx> Predicate<'tcx> {
         let substs = trait_ref.skip_binder().substs;
         let pred = self.kind().skip_binder();
         let new = pred.subst(tcx, substs);
-        if new != pred { ty::Binder::bind(new).to_predicate(tcx) } else { self }
+        tcx.reuse_or_mk_predicate(self, ty::Binder::bind(new))
     }
 }
 
@@ -1352,7 +1352,6 @@ impl ToPredicate<'tcx> for Binder<PredicateKind<'tcx>> {
 impl ToPredicate<'tcx> for PredicateKind<'tcx> {
     #[inline(always)]
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
-        debug_assert!(!self.has_escaping_bound_vars(), "escaping bound vars for {:?}", self);
         tcx.mk_predicate(Binder::dummy(self))
     }
 }

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -623,10 +623,6 @@ pub trait PrettyPrinter<'tcx>:
                     p!("impl");
                     for (predicate, _) in bounds {
                         let predicate = predicate.subst(self.tcx(), substs);
-                        // Note: We can't use `to_opt_poly_trait_ref` here as `predicate`
-                        // may contain unbound variables. We therefore do this manually.
-                        //
-                        // FIXME(lcnr): Find out why exactly this is the case :)
                         let bound_predicate = predicate.kind();
                         if let ty::PredicateKind::Trait(pred, _) = bound_predicate.skip_binder() {
                             let trait_ref = bound_predicate.rebind(pred.trait_ref);

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -1017,12 +1017,12 @@ impl<'tcx> TypeFoldable<'tcx> for ty::Region<'tcx> {
 
 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
     fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
-        let new = self.inner.binder.fold_with(folder);
+        let new = self.inner.kind.fold_with(folder);
         folder.tcx().reuse_or_mk_predicate(self, new)
     }
 
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
-        self.inner.binder.visit_with(visitor)
+        self.inner.kind.visit_with(visitor)
     }
 
     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {

src/librustdoc/clean/mod.rs

@@ -1684,8 +1684,6 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                 let mut bounds = bounds
                     .iter()
                     .filter_map(|bound| {
-                        // Note: The substs of opaque types can contain unbound variables,
-                        // meaning that we have to use `ignore_quantifiers_with_unbound_vars` here.
                         let bound_predicate = bound.kind();
                         let trait_ref = match bound_predicate.skip_binder() {
                             ty::PredicateKind::Trait(tr, _constness) => {