Add var to BoundRegion. Add query to get bound vars for applicable items.

compiler/rustc_hir/src/hir.rs

@@ -402,7 +402,7 @@ pub enum TraitBoundModifier {
 /// `typeck::collect::compute_bounds` matches these against
 /// the "special" built-in traits (see `middle::lang_items`) and
 /// detects `Copy`, `Send` and `Sync`.
-#[derive(Debug, HashStable_Generic)]
+#[derive(Clone, Debug, HashStable_Generic)]
 pub enum GenericBound<'hir> {
     Trait(PolyTraitRef<'hir>, TraitBoundModifier),
     // FIXME(davidtwco): Introduce `PolyTraitRef::LangItem`
@@ -2556,7 +2556,7 @@ pub enum UseKind {
 /// that the `ref_id` is for. Note that `ref_id`'s value is not the `HirId` of the
 /// trait being referred to but just a unique `HirId` that serves as a key
 /// within the resolution map.
-#[derive(Debug, HashStable_Generic)]
+#[derive(Clone, Debug, HashStable_Generic)]
 pub struct TraitRef<'hir> {
     pub path: &'hir Path<'hir>,
     // Don't hash the `ref_id`. It is tracked via the thing it is used to access.
@@ -2575,7 +2575,7 @@ impl TraitRef<'_> {
     }
 }
 
-#[derive(Debug, HashStable_Generic)]
+#[derive(Clone, Debug, HashStable_Generic)]
 pub struct PolyTraitRef<'hir> {
     /// The `'a` in `for<'a> Foo<&'a T>`.
     pub bound_generic_params: &'hir [GenericParam<'hir>],

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

@@ -621,7 +621,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
         r: ty::Region<'tcx>,
     ) -> ty::Region<'tcx> {
         let var = self.canonical_var(info, r.into());
-        let br = ty::BoundRegion { kind: ty::BrAnon(var.as_u32()) };
+        let br = ty::BoundRegion { var, kind: ty::BrAnon(var.as_u32()) };
         let region = ty::ReLateBound(self.binder_index, br);
         self.tcx().mk_region(region)
     }

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

@@ -439,7 +439,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
                         // We only allow a `ty::INNERMOST` index in substitutions.
                         assert_eq!(debruijn, ty::INNERMOST);
-                        opt_values[br.assert_bound_var()] = Some(*original_value);
+                        opt_values[br.var] = Some(*original_value);
                     }
                 }
                 GenericArgKind::Const(result_value) => {

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

@@ -71,11 +71,10 @@ where
     if var_values.var_values.is_empty() {
         value
     } else {
-        let fld_r =
-            |br: ty::BoundRegion| match var_values.var_values[br.assert_bound_var()].unpack() {
-                GenericArgKind::Lifetime(l) => l,
-                r => bug!("{:?} is a region but value is {:?}", br, r),
-            };
+        let fld_r = |br: ty::BoundRegion| match var_values.var_values[br.var].unpack() {
+            GenericArgKind::Lifetime(l) => l,
+            r => bug!("{:?} is a region but value is {:?}", br, r),
+        };
 
         let fld_t = |bound_ty: ty::BoundTy| match var_values.var_values[bound_ty.var].unpack() {
             GenericArgKind::Type(ty) => ty,

compiler/rustc_middle/src/ich/impls_ty.rs

@@ -70,16 +70,16 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::RegionKind {
             ty::ReEmpty(universe) => {
                 universe.hash_stable(hcx, hasher);
             }
-            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrAnon(i) }) => {
+            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrAnon(i), .. }) => {
                 db.hash_stable(hcx, hasher);
                 i.hash_stable(hcx, hasher);
             }
-            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrNamed(def_id, name) }) => {
+            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrNamed(def_id, name), .. }) => {
                 db.hash_stable(hcx, hasher);
                 def_id.hash_stable(hcx, hasher);
                 name.hash_stable(hcx, hasher);
             }
-            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrEnv }) => {
+            ty::ReLateBound(db, ty::BoundRegion { kind: ty::BrEnv, .. }) => {
                 db.hash_stable(hcx, hasher);
             }
             ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, index, name }) => {

compiler/rustc_middle/src/infer/canonical.rs

@@ -314,7 +314,8 @@ impl<'tcx> CanonicalVarValues<'tcx> {
                         tcx.mk_ty(ty::Bound(ty::INNERMOST, ty::BoundVar::from_u32(i).into())).into()
                     }
                     GenericArgKind::Lifetime(..) => {
-                        let br = ty::BoundRegion { kind: ty::BrAnon(i) };
+                        let br =
+                            ty::BoundRegion { var: ty::BoundVar::from_u32(i), kind: ty::BrAnon(i) };
                         tcx.mk_region(ty::ReLateBound(ty::INNERMOST, br)).into()
                     }
                     GenericArgKind::Const(ct) => tcx

compiler/rustc_middle/src/middle/resolve_lifetime.rs

@@ -83,4 +83,6 @@ pub struct ResolveLifetimes {
     /// be late-bound if (a) it does NOT appear in a where-clause and
     /// (b) it DOES appear in the arguments.
     pub late_bound: FxHashMap<LocalDefId, FxHashSet<ItemLocalId>>,
+
+    pub late_bound_vars: FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Vec<ty::BoundVariableKind>>>,
 }

compiler/rustc_middle/src/query/mod.rs

@@ -1290,6 +1290,10 @@ rustc_queries! {
         -> Option<Vec<ObjectLifetimeDefault>> {
         desc { "looking up lifetime defaults for a region on an item" }
     }
+    query late_bound_vars_map(_: LocalDefId)
+        -> Option<&'tcx FxHashMap<ItemLocalId, Vec<ty::BoundVariableKind>>> {
+        desc { "looking up late bound vars" }
+    }
 
     query visibility(def_id: DefId) -> ty::Visibility {
         eval_always

compiler/rustc_middle/src/ty/context.rs

@@ -810,7 +810,7 @@ impl CanonicalUserType<'tcx> {
                             ty::ReLateBound(debruijn, br) => {
                                 // We only allow a `ty::INNERMOST` index in substitutions.
                                 assert_eq!(*debruijn, ty::INNERMOST);
-                                cvar == br.assert_bound_var()
+                                cvar == br.var
                             }
                             _ => false,
                         },
@@ -2672,6 +2672,17 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn object_lifetime_defaults(self, id: HirId) -> Option<Vec<ObjectLifetimeDefault>> {
         self.object_lifetime_defaults_map(id.owner)
     }
+
+    pub fn late_bound_vars(self, id: HirId) -> &'tcx List<ty::BoundVariableKind> {
+        self.mk_bound_variable_kinds(
+            self.late_bound_vars_map(id.owner)
+                .and_then(|map| map.get(&id.local_id).cloned())
+                .unwrap_or_else(|| {
+                    bug!("No bound vars found for {:?} ({:?})", self.hir().node_to_string(id), id)
+                })
+                .iter(),
+        )
+    }
 }
 
 impl TyCtxtAt<'tcx> {

compiler/rustc_middle/src/ty/fold.rs

@@ -634,6 +634,42 @@ impl<'tcx> TyCtxt<'tcx> {
         .0
     }
 
+    pub fn shift_bound_var_indices<T>(self, bound_vars: usize, value: T) -> T
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        self.replace_escaping_bound_vars(
+            value,
+            |r| {
+                self.mk_region(ty::ReLateBound(
+                    ty::INNERMOST,
+                    ty::BoundRegion {
+                        var: ty::BoundVar::from_usize(r.var.as_usize() + bound_vars),
+                        kind: r.kind,
+                    },
+                ))
+            },
+            |t| {
+                self.mk_ty(ty::Bound(
+                    ty::INNERMOST,
+                    ty::BoundTy {
+                        var: ty::BoundVar::from_usize(t.var.as_usize() + bound_vars),
+                        kind: t.kind,
+                    },
+                ))
+            },
+            |c, ty| {
+                self.mk_const(ty::Const {
+                    val: ty::ConstKind::Bound(
+                        ty::INNERMOST,
+                        ty::BoundVar::from_usize(c.as_usize() + bound_vars),
+                    ),
+                    ty,
+                })
+            },
+        )
+    }
+
     /// Returns a set of all late-bound regions that are constrained
     /// by `value`, meaning that if we instantiate those LBR with
     /// variables and equate `value` with something else, those
@@ -695,16 +731,21 @@ impl<'tcx> TyCtxt<'tcx> {
         T: TypeFoldable<'tcx>,
     {
         let mut counter = 0;
-        Binder::bind(
-            self.replace_late_bound_regions(sig, |_| {
-                let br = ty::BoundRegion { kind: ty::BrAnon(counter) };
+        let inner = self
+            .replace_late_bound_regions(sig, |_| {
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_u32(counter),
+                    kind: ty::BrAnon(counter),
+                };
                 let r = self.mk_region(ty::ReLateBound(ty::INNERMOST, br));
                 counter += 1;
                 r
             })
-            .0,
-            self,
-        )
+            .0;
+        let bound_vars = self.mk_bound_variable_kinds(
+            (0..counter).map(|i| ty::BoundVariableKind::Region(ty::BrAnon(i))),
+        );
+        Binder::bind_with_vars(inner, bound_vars)
     }
 }
 
@@ -777,27 +818,105 @@ impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
     }
 
     fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
-        use std::collections::btree_map::Entry;
         match r {
-            ty::ReLateBound(index, br) if *index == self.binder_index => match br.kind {
-                ty::BrNamed(_def_id, _name) => {
-                    // FIXME
-                }
+            ty::ReLateBound(index, _br) if *index == self.binder_index => {
+                bug!("{:?} {:?}", index, _br)
+            }
 
-                ty::BrAnon(var) => match self.vars.entry(var) {
-                    Entry::Vacant(entry) => {
-                        entry.insert(ty::BoundVariableKind::Region(br.kind));
+            _ => (),
+        };
+
+        r.super_visit_with(self)
+    }
+}
+
+pub struct ValidateBoundVars<'tcx> {
+    bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
+    binder_index: ty::DebruijnIndex,
+    // We may encounter the same variable at different levels of binding, so
+    // this can't just be `Ty`
+    visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
+}
+
+impl<'tcx> ValidateBoundVars<'tcx> {
+    pub fn new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self {
+        ValidateBoundVars {
+            bound_vars,
+            binder_index: ty::INNERMOST,
+            visited: SsoHashSet::default(),
+        }
+    }
+}
+
+impl<'tcx> TypeVisitor<'tcx> for ValidateBoundVars<'tcx> {
+    type BreakTy = ();
+
+    fn visit_binder<T: TypeFoldable<'tcx>>(
+        &mut self,
+        t: &Binder<'tcx, T>,
+    ) -> ControlFlow<Self::BreakTy> {
+        self.binder_index.shift_in(1);
+        let result = t.super_visit_with(self);
+        self.binder_index.shift_out(1);
+        result
+    }
+
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+        if t.outer_exclusive_binder < self.binder_index
+            || !self.visited.insert((self.binder_index, t))
+        {
+            return ControlFlow::BREAK;
+        }
+        match *t.kind() {
+            ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
+                if self.bound_vars.len() <= bound_ty.var.as_usize() {
+                    panic!("Not enough bound vars: {:?} not found in {:?}", t, self.bound_vars);
+                }
+                let list_var = self.bound_vars[bound_ty.var.as_usize()];
+                match list_var {
+                    ty::BoundVariableKind::Ty(kind) => {
+                        if kind != bound_ty.kind {
+                            panic!(
+                                "Mismatched type kinds: {:?} doesn't var in list {:?}",
+                                bound_ty.kind, list_var
+                            );
+                        }
                     }
-                    Entry::Occupied(entry) => match entry.get() {
-                        ty::BoundVariableKind::Region(_) => {}
-                        _ => bug!("Conflicting bound vars"),
-                    },
-                },
-
-                ty::BrEnv => {
-                    // FIXME
+                    _ => panic!(
+                        "Mismatched bound variable kinds! Expected type, found {:?}",
+                        list_var
+                    ),
                 }
-            },
+            }
+
+            _ => (),
+        };
+
+        t.super_visit_with(self)
+    }
+
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
+        match r {
+            ty::ReLateBound(index, br) if *index == self.binder_index => {
+                if self.bound_vars.len() <= br.var.as_usize() {
+                    panic!("Not enough bound vars: {:?} not found in {:?}", *br, self.bound_vars);
+                }
+                let list_var = self.bound_vars[br.var.as_usize()];
+                match list_var {
+                    ty::BoundVariableKind::Region(kind) => {
+                        if kind != br.kind {
+                            panic!(
+                                "Mismatched region kinds: {:?} doesn't match var ({:?}) in list ({:?})",
+                                br.kind, list_var, self.bound_vars
+                            );
+                        }
+                    }
+                    _ => panic!(
+                        "Mismatched bound variable kinds! Expected region, found {:?}",
+                        list_var
+                    ),
+                }
+            }
 
             _ => (),
         };

compiler/rustc_middle/src/ty/layout.rs

@@ -1,3 +1,4 @@
+// ignore-tidy-filelength
 use crate::ich::StableHashingContext;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir::{GeneratorLayout, GeneratorSavedLocal};
@@ -2481,21 +2482,42 @@ impl<'tcx> ty::Instance<'tcx> {
             ty::Closure(def_id, substs) => {
                 let sig = substs.as_closure().sig();
 
-                let env_ty = tcx.closure_env_ty(def_id, substs).unwrap();
-                sig.map_bound(|sig| {
+                let bound_vars = tcx.mk_bound_variable_kinds(
+                    sig.bound_vars()
+                        .iter()
+                        .chain(iter::once(ty::BoundVariableKind::Region(ty::BrEnv))),
+                );
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(bound_vars.len() - 1),
+                    kind: ty::BoundRegionKind::BrEnv,
+                };
+                let env_region = ty::ReLateBound(ty::INNERMOST, br);
+                let env_ty = tcx.closure_env_ty(def_id, substs, env_region).unwrap();
+
+                let sig = sig.skip_binder();
+                ty::Binder::bind_with_vars(
                     tcx.mk_fn_sig(
-                        iter::once(env_ty.skip_binder()).chain(sig.inputs().iter().cloned()),
+                        iter::once(env_ty).chain(sig.inputs().iter().cloned()),
                         sig.output(),
                         sig.c_variadic,
                         sig.unsafety,
                         sig.abi,
-                    )
-                })
+                    ),
+                    bound_vars,
+                )
             }
             ty::Generator(_, substs, _) => {
                 let sig = substs.as_generator().poly_sig();
 
-                let br = ty::BoundRegion { kind: ty::BrEnv };
+                let bound_vars = tcx.mk_bound_variable_kinds(
+                    sig.bound_vars()
+                        .iter()
+                        .chain(iter::once(ty::BoundVariableKind::Region(ty::BrEnv))),
+                );
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(bound_vars.len() - 1),
+                    kind: ty::BoundRegionKind::BrEnv,
+                };
                 let env_region = ty::ReLateBound(ty::INNERMOST, br);
                 let env_ty = tcx.mk_mut_ref(tcx.mk_region(env_region), ty);
 
@@ -2504,21 +2526,21 @@ impl<'tcx> ty::Instance<'tcx> {
                 let pin_substs = tcx.intern_substs(&[env_ty.into()]);
                 let env_ty = tcx.mk_adt(pin_adt_ref, pin_substs);
 
-                sig.map_bound(|sig| {
-                    let state_did = tcx.require_lang_item(LangItem::GeneratorState, None);
-                    let state_adt_ref = tcx.adt_def(state_did);
-                    let state_substs =
-                        tcx.intern_substs(&[sig.yield_ty.into(), sig.return_ty.into()]);
-                    let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
-
+                let sig = sig.skip_binder();
+                let state_did = tcx.require_lang_item(LangItem::GeneratorState, None);
+                let state_adt_ref = tcx.adt_def(state_did);
+                let state_substs = tcx.intern_substs(&[sig.yield_ty.into(), sig.return_ty.into()]);
+                let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
+                ty::Binder::bind_with_vars(
                     tcx.mk_fn_sig(
                         [env_ty, sig.resume_ty].iter(),
                         &ret_ty,
                         false,
                         hir::Unsafety::Normal,
                         rustc_target::spec::abi::Abi::Rust,
-                    )
-                })
+                    ),
+                    bound_vars,
+                )
             }
             _ => bug!("unexpected type {:?} in Instance::fn_sig", ty),
         }

compiler/rustc_middle/src/ty/mod.rs

@@ -543,10 +543,33 @@ impl<'tcx> Predicate<'tcx> {
         // substitution code expects equal binding levels in the values
         // from the substitution and the value being substituted into, and
         // this trick achieves that).
-        let substs = trait_ref.skip_binder().substs;
-        let pred = self.kind().skip_binder();
-        let new = pred.subst(tcx, substs);
-        tcx.reuse_or_mk_predicate(self, ty::Binder::bind(new, tcx))
+
+        // Working through the second example:
+        // trait_ref: for<'x> T: Foo1<'^0.0>; substs: [T, '^0.0]
+        // predicate: for<'b> Self: Bar1<'a, '^0.0>; substs: [Self, 'a, '^0.0]
+        // We want to end up with:
+        //     for<'x, 'b> T: Bar1<'^0.0, '^0.1>
+        // To do this:
+        // 1) We must shift all bound vars in predicate by the length
+        //    of trait ref's bound vars. So, we would end up with predicate like
+        //    Self: Bar1<'a, '^0.1>
+        // 2) We can then apply the trait substs to this, ending up with
+        //    T: Bar1<'^0.0, '^0.1>
+        // 3) Finally, to create the final bound vars, we concatenate the bound
+        //    vars of the trait ref with those of the predicate:
+        //    ['x, 'b]
+        let bound_pred = self.kind();
+        let pred_bound_vars = bound_pred.bound_vars();
+        let trait_bound_vars = trait_ref.bound_vars();
+        // 1) Self: Bar1<'a, '^0.0> -> Self: Bar1<'a, '^0.1>
+        let shifted_pred =
+            tcx.shift_bound_var_indices(trait_bound_vars.len(), bound_pred.skip_binder());
+        // 2) Self: Bar1<'a, '^0.1> -> T: Bar1<'^0.0, '^0.1>
+        let new = shifted_pred.subst(tcx, trait_ref.skip_binder().substs);
+        // 3) ['x] + ['b] -> ['x, 'b]
+        let bound_vars =
+            tcx.mk_bound_variable_kinds(trait_bound_vars.iter().chain(pred_bound_vars));
+        tcx.reuse_or_mk_predicate(self, ty::Binder::bind_with_vars(new, bound_vars))
     }
 }
 

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

@@ -1636,7 +1636,7 @@ impl<F: fmt::Write> PrettyPrinter<'tcx> for FmtPrinter<'_, 'tcx, F> {
                 data.name != kw::Empty && data.name != kw::UnderscoreLifetime
             }
 
-            ty::ReLateBound(_, ty::BoundRegion { kind: br })
+            ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
             | ty::ReFree(ty::FreeRegion { bound_region: br, .. })
             | ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
                 if let ty::BrNamed(_, name) = br {
@@ -1715,7 +1715,7 @@ impl<F: fmt::Write> FmtPrinter<'_, '_, F> {
                     return Ok(self);
                 }
             }
-            ty::ReLateBound(_, ty::BoundRegion { kind: br })
+            ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
             | ty::ReFree(ty::FreeRegion { bound_region: br, .. })
             | ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
                 if let ty::BrNamed(_, name) = br {
@@ -1821,7 +1821,8 @@ impl<F: fmt::Write> FmtPrinter<'_, 'tcx, F> {
                     ty::BrNamed(DefId::local(CRATE_DEF_INDEX), name)
                 }
             };
-            self.tcx.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { kind }))
+            self.tcx
+                .mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { var: br.var, kind }))
         });
         start_or_continue(&mut self, "", "> ")?;
 
@@ -1865,7 +1866,7 @@ impl<F: fmt::Write> FmtPrinter<'_, 'tcx, F> {
         struct LateBoundRegionNameCollector<'a>(&'a mut FxHashSet<Symbol>);
         impl<'tcx> ty::fold::TypeVisitor<'tcx> for LateBoundRegionNameCollector<'_> {
             fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
-                if let ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name) }) = *r {
+                if let ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name), .. }) = *r {
                     self.0.insert(name);
                 }
                 r.super_visit_with(self)

compiler/rustc_middle/src/ty/sty.rs

@@ -6,6 +6,7 @@ use self::TyKind::*;
 
 use crate::infer::canonical::Canonical;
 use crate::ty::fold::BoundVarsCollector;
+use crate::ty::fold::ValidateBoundVars;
 use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::InferTy::{self, *};
 use crate::ty::{
@@ -63,22 +64,10 @@ pub enum BoundRegionKind {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, TyEncodable, TyDecodable, Debug, PartialOrd, Ord)]
 #[derive(HashStable)]
 pub struct BoundRegion {
+    pub var: BoundVar,
     pub kind: BoundRegionKind,
 }
 
-impl BoundRegion {
-    /// When canonicalizing, we replace unbound inference variables and free
-    /// regions with anonymous late bound regions. This method asserts that
-    /// we have an anonymous late bound region, which hence may refer to
-    /// a canonical variable.
-    pub fn assert_bound_var(&self) -> BoundVar {
-        match self.kind {
-            BoundRegionKind::BrAnon(var) => BoundVar::from_u32(var),
-            _ => bug!("bound region is not anonymous"),
-        }
-    }
-}
-
 impl BoundRegionKind {
     pub fn is_named(&self) -> bool {
         match *self {
@@ -987,13 +976,17 @@ where
         value.visit_with(&mut collector);
         Binder(value, collector.into_vars(tcx))
     }
+
+    pub fn bind_with_vars(value: T, vars: &'tcx List<BoundVariableKind>) -> Binder<'tcx, T> {
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(vars);
+            value.visit_with(&mut validator);
+        }
+        Binder(value, vars)
+    }
 }
 
 impl<'tcx, T> Binder<'tcx, T> {
-    pub fn bind_with_vars(value: T, vars: &'tcx List<BoundVariableKind>) -> Binder<'tcx, T> {
-        Binder(value, vars)
-    }
-
     /// Skips the binder and returns the "bound" value. This is a
     /// risky thing to do because it's easy to get confused about
     /// De Bruijn indices and the like. It is usually better to
@@ -1022,18 +1015,31 @@ impl<'tcx, T> Binder<'tcx, T> {
         Binder(&self.0, self.1)
     }
 
-    pub fn map_bound_ref<F, U>(&self, f: F) -> Binder<'tcx, U>
+    pub fn map_bound_ref_unchecked<F, U>(&self, f: F) -> Binder<'tcx, U>
+    where
+        F: FnOnce(&T) -> U,
+    {
+        let value = f(&self.0);
+        Binder(value, self.1)
+    }
+
+    pub fn map_bound_ref<F, U: TypeFoldable<'tcx>>(&self, f: F) -> Binder<'tcx, U>
     where
         F: FnOnce(&T) -> U,
     {
         self.as_ref().map_bound(f)
     }
 
-    pub fn map_bound<F, U>(self, f: F) -> Binder<'tcx, U>
+    pub fn map_bound<F, U: TypeFoldable<'tcx>>(self, f: F) -> Binder<'tcx, U>
     where
         F: FnOnce(T) -> U,
     {
-        Binder(f(self.0), self.1)
+        let value = f(self.0);
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(self.1);
+            value.visit_with(&mut validator);
+        }
+        Binder(value, self.1)
     }
 
     /// Wraps a `value` in a binder, using the same bound variables as the
@@ -1045,7 +1051,14 @@ impl<'tcx, T> Binder<'tcx, T> {
     /// don't actually track bound vars. However, semantically, it is different
     /// because bound vars aren't allowed to change here, whereas they are
     /// in `bind`. This may be (debug) asserted in the future.
-    pub fn rebind<U>(&self, value: U) -> Binder<'tcx, U> {
+    pub fn rebind<U>(&self, value: U) -> Binder<'tcx, U>
+    where
+        U: TypeFoldable<'tcx>,
+    {
+        if cfg!(debug_assertions) {
+            let mut validator = ValidateBoundVars::new(self.bound_vars());
+            value.visit_with(&mut validator);
+        }
         Binder(value, self.1)
     }
 
@@ -1066,20 +1079,6 @@ impl<'tcx, T> Binder<'tcx, T> {
         if self.0.has_escaping_bound_vars() { None } else { Some(self.skip_binder()) }
     }
 
-    /// Given two things that have the same binder level,
-    /// and an operation that wraps on their contents, executes the operation
-    /// and then wraps its result.
-    ///
-    /// `f` should consider bound regions at depth 1 to be free, and
-    /// anything it produces with bound regions at depth 1 will be
-    /// bound in the resulting return value.
-    pub fn fuse<U, F, R>(self, u: Binder<'tcx, U>, f: F) -> Binder<'tcx, R>
-    where
-        F: FnOnce(T, U) -> R,
-    {
-        Binder(f(self.0, u.0), self.1)
-    }
-
     /// Splits the contents into two things that share the same binder
     /// level as the original, returning two distinct binders.
     ///
@@ -1204,7 +1203,7 @@ pub type PolyFnSig<'tcx> = Binder<'tcx, FnSig<'tcx>>;
 impl<'tcx> PolyFnSig<'tcx> {
     #[inline]
     pub fn inputs(&self) -> Binder<'tcx, &'tcx [Ty<'tcx>]> {
-        self.map_bound_ref(|fn_sig| fn_sig.inputs())
+        self.map_bound_ref_unchecked(|fn_sig| fn_sig.inputs())
     }
     #[inline]
     pub fn input(&self, index: usize) -> ty::Binder<'tcx, Ty<'tcx>> {

compiler/rustc_middle/src/ty/util.rs

@@ -499,18 +499,18 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         closure_def_id: DefId,
         closure_substs: SubstsRef<'tcx>,
-    ) -> Option<ty::Binder<'tcx, Ty<'tcx>>> {
+        env_region: ty::RegionKind,
+    ) -> Option<Ty<'tcx>> {
         let closure_ty = self.mk_closure(closure_def_id, closure_substs);
-        let br = ty::BoundRegion { kind: ty::BrEnv };
-        let env_region = ty::ReLateBound(ty::INNERMOST, br);
         let closure_kind_ty = closure_substs.as_closure().kind_ty();
         let closure_kind = closure_kind_ty.to_opt_closure_kind()?;
+        debug_assert!(!closure_ty.has_escaping_bound_vars());
         let env_ty = match closure_kind {
             ty::ClosureKind::Fn => self.mk_imm_ref(self.mk_region(env_region), closure_ty),
             ty::ClosureKind::FnMut => self.mk_mut_ref(self.mk_region(env_region), closure_ty),
             ty::ClosureKind::FnOnce => closure_ty,
         };
-        Some(ty::Binder::bind(env_ty, self))
+        Some(env_ty)
     }
 
     /// Returns `true` if the node pointed to by `def_id` is a `static` item.

compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs

@@ -502,7 +502,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         // lifetimes without names with the value `'0`.
         match ty.kind() {
             ty::Ref(
-                ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br })
+                ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br, .. })
                 | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
                 _,
                 _,
@@ -523,7 +523,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let region = match ty.kind() {
             ty::Ref(region, _, _) => {
                 match region {
-                    ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br })
+                    ty::RegionKind::ReLateBound(_, ty::BoundRegion { kind: br, .. })
                     | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
                         printer.region_highlight_mode.highlighting_bound_region(*br, counter)
                     }

compiler/rustc_mir/src/borrow_check/universal_regions.rs

@@ -596,24 +596,38 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
                 assert_eq!(self.mir_def.did.to_def_id(), def_id);
                 let closure_sig = substs.as_closure().sig();
                 let inputs_and_output = closure_sig.inputs_and_output();
-                let closure_ty = tcx.closure_env_ty(def_id, substs).unwrap();
-                ty::Binder::fuse(closure_ty, inputs_and_output, |closure_ty, inputs_and_output| {
-                    // The "inputs" of the closure in the
-                    // signature appear as a tuple.  The MIR side
-                    // flattens this tuple.
-                    let (&output, tuplized_inputs) = inputs_and_output.split_last().unwrap();
-                    assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
-                    let inputs = match tuplized_inputs[0].kind() {
-                        ty::Tuple(inputs) => inputs,
-                        _ => bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]),
-                    };
+                let bound_vars = tcx.mk_bound_variable_kinds(
+                    inputs_and_output
+                        .bound_vars()
+                        .iter()
+                        .chain(iter::once(ty::BoundVariableKind::Region(ty::BrEnv))),
+                );
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(bound_vars.len() - 1),
+                    kind: ty::BrEnv,
+                };
+                let env_region = ty::ReLateBound(ty::INNERMOST, br);
+                let closure_ty = tcx.closure_env_ty(def_id, substs, env_region).unwrap();
 
+                // The "inputs" of the closure in the
+                // signature appear as a tuple.  The MIR side
+                // flattens this tuple.
+                let (&output, tuplized_inputs) =
+                    inputs_and_output.skip_binder().split_last().unwrap();
+                assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
+                let inputs = match tuplized_inputs[0].kind() {
+                    ty::Tuple(inputs) => inputs,
+                    _ => bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]),
+                };
+
+                ty::Binder::bind_with_vars(
                     tcx.mk_type_list(
                         iter::once(closure_ty)
                             .chain(inputs.iter().map(|k| k.expect_ty()))
                             .chain(iter::once(output)),
-                    )
-                })
+                    ),
+                    bound_vars,
+                )
             }
 
             DefiningTy::Generator(def_id, substs, movability) => {

compiler/rustc_mir_build/src/build/mod.rs

@@ -252,8 +252,13 @@ fn liberated_closure_env_ty(
         _ => bug!("closure expr does not have closure type: {:?}", closure_ty),
     };
 
-    let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs).unwrap();
-    tcx.erase_late_bound_regions(closure_env_ty)
+    let bound_vars =
+        tcx.mk_bound_variable_kinds(std::iter::once(ty::BoundVariableKind::Region(ty::BrEnv)));
+    let br =
+        ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind: ty::BrEnv };
+    let env_region = ty::ReLateBound(ty::INNERMOST, br);
+    let closure_env_ty = tcx.closure_env_ty(closure_def_id, closure_substs, env_region).unwrap();
+    tcx.erase_late_bound_regions(ty::Binder::bind_with_vars(closure_env_ty, bound_vars))
 }
 
 #[derive(Debug, PartialEq, Eq)]

compiler/rustc_resolve/src/late.rs

@@ -34,6 +34,7 @@ use tracing::debug;
 
 mod diagnostics;
 crate mod lifetimes;
+crate mod supertraits;
 
 type Res = def::Res<NodeId>;
 

compiler/rustc_resolve/src/late/supertraits.rs

@@ -0,0 +1,60 @@
+use smallvec::{smallvec, SmallVec};
+
+use rustc_data_structures::fx::FxHashSet;
+use rustc_hir::def_id::DefId;
+use rustc_middle::ty::{self, TyCtxt};
+
+pub struct Elaborator<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]>,
+    visited: FxHashSet<DefId>,
+}
+
+#[allow(dead_code)]
+pub fn supertraits<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> Elaborator<'tcx> {
+    Elaborator { tcx, stack: smallvec![(def_id, smallvec![])], visited: Default::default() }
+}
+
+impl<'tcx> Elaborator<'tcx> {
+    fn elaborate(&mut self, def_id: DefId, bound_vars: &SmallVec<[ty::BoundVariableKind; 8]>) {
+        let tcx = self.tcx;
+
+        let predicates = tcx.super_predicates_of(def_id);
+        let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
+            let bound_predicate = pred.kind();
+            match bound_predicate.skip_binder() {
+                ty::PredicateKind::Trait(data, _) => {
+                    // The order here needs to match what we would get from `subst_supertrait`
+                    let pred_bound_vars = bound_predicate.bound_vars();
+                    let mut all_bound_vars = bound_vars.clone();
+                    all_bound_vars.extend(pred_bound_vars.iter());
+                    let super_def_id = data.trait_ref.def_id;
+                    Some((super_def_id, all_bound_vars))
+                }
+                _ => None,
+            }
+        });
+
+        let visited = &mut self.visited;
+        let obligations = obligations.filter(|o| visited.insert(o.0));
+        self.stack.extend(obligations);
+    }
+}
+
+impl<'tcx> Iterator for Elaborator<'tcx> {
+    type Item = (DefId, SmallVec<[ty::BoundVariableKind; 8]>);
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.stack.len(), None)
+    }
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.stack.pop() {
+            Some((def_id, bound_vars)) => {
+                self.elaborate(def_id, &bound_vars);
+                Some((def_id, bound_vars))
+            }
+            None => None,
+        }
+    }
+}

compiler/rustc_symbol_mangling/src/v0.rs

@@ -318,7 +318,7 @@ impl Printer<'tcx> for SymbolMangler<'tcx> {
 
             // Late-bound lifetimes use indices starting at 1,
             // see `BinderLevel` for more details.
-            ty::ReLateBound(debruijn, ty::BoundRegion { kind: ty::BrAnon(i) }) => {
+            ty::ReLateBound(debruijn, ty::BoundRegion { kind: ty::BrAnon(i), .. }) => {
                 let binder = &self.binders[self.binders.len() - 1 - debruijn.index()];
                 let depth = binder.lifetime_depths.start + i;
 

compiler/rustc_traits/src/chalk/db.rs

@@ -735,7 +735,10 @@ fn bound_vars_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> {
             .into(),
 
         ty::GenericParamDefKind::Lifetime => {
-            let br = ty::BoundRegion { kind: ty::BrAnon(substs.len() as u32) };
+            let br = ty::BoundRegion {
+                var: ty::BoundVar::from_usize(substs.len()),
+                kind: ty::BrAnon(substs.len() as u32),
+            };
             tcx.mk_region(ty::RegionKind::ReLateBound(ty::INNERMOST, br)).into()
         }
 

compiler/rustc_traits/src/chalk/lowering.rs

@@ -434,17 +434,11 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'t
             ReEarlyBound(_) => {
                 panic!("Should have already been substituted.");
             }
-            ReLateBound(db, br) => match br.kind {
-                ty::BoundRegionKind::BrAnon(var) => {
-                    chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
-                        chalk_ir::DebruijnIndex::new(db.as_u32()),
-                        var as usize,
-                    ))
-                    .intern(interner)
-                }
-                ty::BoundRegionKind::BrNamed(_def_id, _name) => unimplemented!(),
-                ty::BrEnv => unimplemented!(),
-            },
+            ReLateBound(db, br) => chalk_ir::LifetimeData::BoundVar(chalk_ir::BoundVar::new(
+                chalk_ir::DebruijnIndex::new(db.as_u32()),
+                br.var.as_usize(),
+            ))
+            .intern(interner),
             ReFree(_) => unimplemented!(),
             ReStatic => chalk_ir::LifetimeData::Static.intern(interner),
             ReVar(_) => unimplemented!(),
@@ -467,7 +461,10 @@ impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'t
         let kind = match self.data(interner) {
             chalk_ir::LifetimeData::BoundVar(var) => ty::RegionKind::ReLateBound(
                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
-                ty::BoundRegion { kind: ty::BrAnon(var.index as u32) },
+                ty::BoundRegion {
+                    var: ty::BoundVar::from_usize(var.index),
+                    kind: ty::BrAnon(var.index as u32),
+                },
             ),
             chalk_ir::LifetimeData::InferenceVar(_var) => unimplemented!(),
             chalk_ir::LifetimeData::Placeholder(p) => {
@@ -900,7 +897,7 @@ impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
                     },
                 },
 
-                ty::BrEnv => unimplemented!(),
+                ty::BoundRegionKind::BrEnv => unimplemented!(),
             },
 
             ty::ReEarlyBound(_re) => {
@@ -948,7 +945,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
             ty::ReLateBound(index, br) if *index == self.binder_index => match br.kind {
                 ty::BrNamed(def_id, _name) => match self.named_parameters.get(&def_id) {
                     Some(idx) => {
-                        let new_br = ty::BoundRegion { kind: ty::BrAnon(*idx) };
+                        let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx) };
                         return self.tcx.mk_region(RegionKind::ReLateBound(*index, new_br));
                     }
                     None => panic!("Missing `BrNamed`."),
@@ -1031,12 +1028,16 @@ impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
             // This covers any region variables in a goal, right?
             ty::ReEarlyBound(_re) => match self.named_regions.get(&_re.def_id) {
                 Some(idx) => {
-                    let br = ty::BoundRegion { kind: ty::BrAnon(*idx) };
+                    let br = ty::BoundRegion {
+                        var: ty::BoundVar::from_u32(*idx),
+                        kind: ty::BrAnon(*idx),
+                    };
                     self.tcx.mk_region(RegionKind::ReLateBound(self.binder_index, br))
                 }
                 None => {
                     let idx = self.named_regions.len() as u32;
-                    let br = ty::BoundRegion { kind: ty::BrAnon(idx) };
+                    let br =
+                        ty::BoundRegion { var: ty::BoundVar::from_u32(idx), kind: ty::BrAnon(idx) };
                     self.named_regions.insert(_re.def_id, idx);
                     self.tcx.mk_region(RegionKind::ReLateBound(self.binder_index, br))
                 }

compiler/rustc_typeck/src/astconv/generics.rs

@@ -166,7 +166,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         parent_substs: &[subst::GenericArg<'tcx>],
         has_self: bool,
         self_ty: Option<Ty<'tcx>>,
-        arg_count: GenericArgCountResult,
+        arg_count: &GenericArgCountResult,
         ctx: &mut impl CreateSubstsForGenericArgsCtxt<'a, 'tcx>,
     ) -> SubstsRef<'tcx> {
         // Collect the segments of the path; we need to substitute arguments

compiler/rustc_typeck/src/astconv/mod.rs

@@ -210,14 +210,20 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let r = match tcx.named_region(lifetime.hir_id) {
             Some(rl::Region::Static) => tcx.lifetimes.re_static,
 
-            Some(rl::Region::LateBound(debruijn, _, id, _)) => {
-                let name = lifetime_name(id.expect_local());
-                let br = ty::BoundRegion { kind: ty::BrNamed(id, name) };
+            Some(rl::Region::LateBound(debruijn, index, def_id, _)) => {
+                let name = lifetime_name(def_id.expect_local());
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_u32(index),
+                    kind: ty::BrNamed(def_id, name),
+                };
                 tcx.mk_region(ty::ReLateBound(debruijn, br))
             }
 
-            Some(rl::Region::LateBoundAnon(debruijn, _index, anon_index)) => {
-                let br = ty::BoundRegion { kind: ty::BrAnon(anon_index) };
+            Some(rl::Region::LateBoundAnon(debruijn, index, anon_index)) => {
+                let br = ty::BoundRegion {
+                    var: ty::BoundVar::from_u32(index),
+                    kind: ty::BrAnon(anon_index),
+                };
                 tcx.mk_region(ty::ReLateBound(debruijn, br))
             }
 
@@ -266,7 +272,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         def_id: DefId,
         item_segment: &hir::PathSegment<'_>,
     ) -> SubstsRef<'tcx> {
-        let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
+        let (substs, _) = self.create_substs_for_ast_path(
             span,
             def_id,
             &[],
@@ -275,6 +281,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             item_segment.infer_args,
             None,
         );
+        let assoc_bindings = self.create_assoc_bindings_for_generic_args(item_segment.args());
 
         if let Some(b) = assoc_bindings.first() {
             Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
@@ -314,6 +321,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
     /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
     /// lists: `[Vec<u8>, u8, 'a]`.
+    #[tracing::instrument(level = "debug", skip(self, span))]
     fn create_substs_for_ast_path<'a>(
         &self,
         span: Span,
@@ -323,15 +331,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         generic_args: &'a hir::GenericArgs<'_>,
         infer_args: bool,
         self_ty: Option<Ty<'tcx>>,
-    ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
+    ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
         // If the type is parameterized by this region, then replace this
         // region with the current anon region binding (in other words,
         // whatever & would get replaced with).
-        debug!(
-            "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
-                generic_args={:?})",
-            def_id, self_ty, generic_args
-        );
 
         let tcx = self.tcx();
         let generics = tcx.generics_of(def_id);
@@ -367,7 +370,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // here and so associated type bindings will be handled regardless of whether there are any
         // non-`Self` generic parameters.
         if generics.params.len() == 0 {
-            return (tcx.intern_substs(&[]), vec![], arg_count);
+            return (tcx.intern_substs(&[]), arg_count);
         }
 
         let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
@@ -540,7 +543,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             parent_substs,
             self_ty.is_some(),
             self_ty,
-            arg_count.clone(),
+            &arg_count,
             &mut substs_ctx,
         );
 
@@ -551,6 +554,18 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             generic_args.args.is_empty(),
         );
 
+        debug!(
+            "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
+            generics, self_ty, substs
+        );
+
+        (substs, arg_count)
+    }
+
+    fn create_assoc_bindings_for_generic_args<'a>(
+        &self,
+        generic_args: &'a hir::GenericArgs<'_>,
+    ) -> Vec<ConvertedBinding<'a, 'tcx>> {
         // Convert associated-type bindings or constraints into a separate vector.
         // Example: Given this:
         //
@@ -581,12 +596,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             })
             .collect();
 
-        debug!(
-            "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
-            generics, self_ty, substs
-        );
-
-        (substs, assoc_bindings, arg_count)
+        assoc_bindings
     }
 
     crate fn create_substs_for_associated_item(
@@ -636,55 +646,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         )
     }
 
-    /// The given trait-ref must actually be a trait.
-    pub(super) fn instantiate_poly_trait_ref_inner(
-        &self,
-        trait_ref: &hir::TraitRef<'_>,
-        span: Span,
-        constness: Constness,
-        self_ty: Ty<'tcx>,
-        bounds: &mut Bounds<'tcx>,
-        speculative: bool,
-    ) -> GenericArgCountResult {
-        let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
-
-        debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
-
-        self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
-
-        let (substs, assoc_bindings, arg_count) = self.create_substs_for_ast_trait_ref(
-            trait_ref.path.span,
-            trait_def_id,
-            self_ty,
-            trait_ref.path.segments.last().unwrap(),
-        );
-        let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs), self.tcx());
-
-        bounds.trait_bounds.push((poly_trait_ref, span, constness));
-
-        let mut dup_bindings = FxHashMap::default();
-        for binding in &assoc_bindings {
-            // Specify type to assert that error was already reported in `Err` case.
-            let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
-                trait_ref.hir_ref_id,
-                poly_trait_ref,
-                binding,
-                bounds,
-                speculative,
-                &mut dup_bindings,
-                binding.span,
-            );
-            // Okay to ignore `Err` because of `ErrorReported` (see above).
-        }
-
-        debug!(
-            "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
-            trait_ref, bounds, poly_trait_ref
-        );
-
-        arg_count
-    }
-
     /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
     /// a full trait reference. The resulting trait reference is returned. This may also generate
     /// auxiliary bounds, which are added to `bounds`.
@@ -704,21 +665,55 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
     /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
     /// however.
+    #[tracing::instrument(level = "debug", skip(self, span, constness, bounds, speculative))]
     pub fn instantiate_poly_trait_ref(
         &self,
-        poly_trait_ref: &hir::PolyTraitRef<'_>,
+        trait_ref: &hir::TraitRef<'_>,
+        span: Span,
         constness: Constness,
         self_ty: Ty<'tcx>,
         bounds: &mut Bounds<'tcx>,
+        speculative: bool,
     ) -> GenericArgCountResult {
-        self.instantiate_poly_trait_ref_inner(
-            &poly_trait_ref.trait_ref,
-            poly_trait_ref.span,
-            constness,
+        let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
+
+        self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
+
+        let tcx = self.tcx();
+        let bound_vars = tcx.late_bound_vars(trait_ref.hir_ref_id);
+        debug!(?bound_vars);
+
+        let (substs, arg_count) = self.create_substs_for_ast_trait_ref(
+            trait_ref.path.span,
+            trait_def_id,
             self_ty,
-            bounds,
-            false,
-        )
+            trait_ref.path.segments.last().unwrap(),
+        );
+        let assoc_bindings = self
+            .create_assoc_bindings_for_generic_args(trait_ref.path.segments.last().unwrap().args());
+
+        let poly_trait_ref =
+            ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
+
+        debug!(?poly_trait_ref, ?assoc_bindings);
+        bounds.trait_bounds.push((poly_trait_ref, span, constness));
+
+        let mut dup_bindings = FxHashMap::default();
+        for binding in &assoc_bindings {
+            // Specify type to assert that error was already reported in `Err` case.
+            let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
+                trait_ref.hir_ref_id,
+                poly_trait_ref,
+                binding,
+                bounds,
+                speculative,
+                &mut dup_bindings,
+                binding.span,
+            );
+            // Okay to ignore `Err` because of `ErrorReported` (see above).
+        }
+
+        arg_count
     }
 
     pub fn instantiate_lang_item_trait_ref(
@@ -732,7 +727,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     ) {
         let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
 
-        let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
+        let (substs, _) = self.create_substs_for_ast_path(
             span,
             trait_def_id,
             &[],
@@ -741,7 +736,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             false,
             Some(self_ty),
         );
-        let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs), self.tcx());
+        let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
+        let tcx = self.tcx();
+        let bound_vars = tcx.late_bound_vars(hir_id);
+        let poly_trait_ref =
+            ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
         bounds.trait_bounds.push((poly_trait_ref, span, Constness::NotConst));
 
         let mut dup_bindings = FxHashMap::default();
@@ -765,23 +764,23 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Ty<'tcx>,
         trait_segment: &hir::PathSegment<'_>,
     ) -> ty::TraitRef<'tcx> {
-        let (substs, assoc_bindings, _) =
+        let (substs, _) =
             self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
+        let assoc_bindings = self.create_assoc_bindings_for_generic_args(trait_segment.args());
         if let Some(b) = assoc_bindings.first() {
             Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
         }
         ty::TraitRef::new(trait_def_id, substs)
     }
 
+    #[tracing::instrument(level = "debug", skip(self, span))]
     fn create_substs_for_ast_trait_ref<'a>(
         &self,
         span: Span,
         trait_def_id: DefId,
         self_ty: Ty<'tcx>,
         trait_segment: &'a hir::PathSegment<'a>,
-    ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
-        debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
-
+    ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
         self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
 
         self.create_substs_for_ast_path(
@@ -803,7 +802,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     }
 
     // Returns `true` if a bounds list includes `?Sized`.
-    pub fn is_unsized(&self, ast_bounds: &[&hir::GenericBound<'_>], span: Span) -> bool {
+    pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
         let tcx = self.tcx();
 
         // Try to find an unbound in bounds.
@@ -858,28 +857,44 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// **A note on binders:** there is an implied binder around
     /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
     /// for more details.
+    #[tracing::instrument(level = "debug", skip(self, bounds))]
     fn add_bounds(
         &self,
         param_ty: Ty<'tcx>,
-        ast_bounds: &[&hir::GenericBound<'_>],
+        ast_bounds: &[hir::GenericBound<'_>],
         bounds: &mut Bounds<'tcx>,
+        bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
     ) {
         let constness = self.default_constness_for_trait_bounds();
         for ast_bound in ast_bounds {
             match *ast_bound {
                 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
-                    self.instantiate_poly_trait_ref(b, constness, param_ty, bounds);
+                    self.instantiate_poly_trait_ref(
+                        &b.trait_ref,
+                        b.span,
+                        constness,
+                        param_ty,
+                        bounds,
+                        false,
+                    );
                 }
                 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
-                    self.instantiate_poly_trait_ref(b, Constness::NotConst, param_ty, bounds);
+                    self.instantiate_poly_trait_ref(
+                        &b.trait_ref,
+                        b.span,
+                        Constness::NotConst,
+                        param_ty,
+                        bounds,
+                        false,
+                    );
                 }
                 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
                 hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => self
                     .instantiate_lang_item_trait_ref(
-                        *lang_item, *span, *hir_id, args, param_ty, bounds,
+                        lang_item, span, hir_id, args, param_ty, bounds,
                     ),
                 hir::GenericBound::Outlives(ref l) => bounds.region_bounds.push((
-                    ty::Binder::bind(self.ast_region_to_region(l, None), self.tcx()),
+                    ty::Binder::bind_with_vars(self.ast_region_to_region(l, None), bound_vars),
                     l.span,
                 )),
             }
@@ -909,7 +924,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         sized_by_default: SizedByDefault,
         span: Span,
     ) -> Bounds<'tcx> {
-        let ast_bounds: Vec<_> = ast_bounds.iter().collect();
         self.compute_bounds_inner(param_ty, &ast_bounds, sized_by_default, span)
     }
 
@@ -929,7 +943,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             if let Some(trait_ref) = ast_bound.trait_ref() {
                 if let Some(trait_did) = trait_ref.trait_def_id() {
                     if self.tcx().trait_may_define_assoc_type(trait_did, assoc_name) {
-                        result.push(ast_bound);
+                        result.push(ast_bound.clone());
                     }
                 }
             }
@@ -941,13 +955,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     fn compute_bounds_inner(
         &self,
         param_ty: Ty<'tcx>,
-        ast_bounds: &[&hir::GenericBound<'_>],
+        ast_bounds: &[hir::GenericBound<'_>],
         sized_by_default: SizedByDefault,
         span: Span,
     ) -> Bounds<'tcx> {
         let mut bounds = Bounds::default();
 
-        self.add_bounds(param_ty, ast_bounds, &mut bounds);
+        self.add_bounds(param_ty, ast_bounds, &mut bounds, ty::List::empty());
 
         bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
             if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
@@ -964,6 +978,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
     /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
     /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
+    #[tracing::instrument(
+        level = "debug",
+        skip(self, bounds, speculative, dup_bindings, path_span)
+    )]
     fn add_predicates_for_ast_type_binding(
         &self,
         hir_ref_id: hir::HirId,
@@ -990,7 +1008,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         //
         // We want to produce `<B as SuperTrait<i32>>::T == foo`.
 
-        debug!(?hir_ref_id, ?trait_ref, ?binding, ?bounds, "add_predicates_for_ast_type_binding",);
         let tcx = self.tcx();
 
         let candidate =
@@ -1140,10 +1157,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 //
                 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
                 // parameter to have a skipped binder.
-                let param_ty =
-                    tcx.mk_projection(assoc_ty.def_id, projection_ty.skip_binder().substs);
-                let ast_bounds: Vec<_> = ast_bounds.iter().collect();
-                self.add_bounds(param_ty, &ast_bounds, bounds);
+                let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
+                self.add_bounds(param_ty, ast_bounds, bounds, candidate.bound_vars());
             }
         }
         Ok(())
@@ -1177,10 +1192,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
                 ..
             } = self.instantiate_poly_trait_ref(
-                trait_bound,
+                &trait_bound.trait_ref,
+                trait_bound.span,
                 Constness::NotConst,
                 dummy_self,
                 &mut bounds,
+                false,
             ) {
                 potential_assoc_types.extend(cur_potential_assoc_types);
             }
@@ -2169,12 +2186,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
     }
 
-    /// Parses the programmer's textual representation of a type into our
-    /// internal notion of a type.
     pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
         self.ast_ty_to_ty_inner(ast_ty, false)
     }
 
+    /// Parses the programmer's textual representation of a type into our
+    /// internal notion of a type.
+    ///
     /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
     /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
     #[tracing::instrument(level = "debug", skip(self))]
@@ -2200,6 +2218,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
 
                 tcx.mk_fn_ptr(self.ty_of_fn(
+                    ast_ty.hir_id,
                     bf.unsafety,
                     bf.abi,
                     &bf.decl,
@@ -2242,7 +2261,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
             hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
                 let def_id = tcx.require_lang_item(lang_item, Some(span));
-                let (substs, _, _) = self.create_substs_for_ast_path(
+                let (substs, _) = self.create_substs_for_ast_path(
                     span,
                     def_id,
                     &[],
@@ -2279,7 +2298,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         result_ty
     }
 
-    pub fn impl_trait_ty_to_ty(
+    fn impl_trait_ty_to_ty(
         &self,
         def_id: DefId,
         lifetimes: &[hir::GenericArg<'_>],
@@ -2340,6 +2359,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
     pub fn ty_of_fn(
         &self,
+        hir_id: hir::HirId,
         unsafety: hir::Unsafety,
         abi: abi::Abi,
         decl: &hir::FnDecl<'_>,
@@ -2350,6 +2370,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         debug!("ty_of_fn");
 
         let tcx = self.tcx();
+        let bound_vars = tcx.late_bound_vars(hir_id);
+        debug!(?bound_vars);
 
         // We proactively collect all the inferred type params to emit a single error per fn def.
         let mut visitor = PlaceholderHirTyCollector::default();
@@ -2369,10 +2391,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         debug!("ty_of_fn: output_ty={:?}", output_ty);
 
-        let bare_fn_ty = ty::Binder::bind(
-            tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi),
-            tcx,
-        );
+        let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
+        let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
 
         if !self.allow_ty_infer() {
             // We always collect the spans for placeholder types when evaluating `fn`s, but we

compiler/rustc_typeck/src/check/closure.rs

@@ -69,7 +69,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let expr_def_id = self.tcx.hir().local_def_id(expr.hir_id);
 
         let ClosureSignatures { bound_sig, liberated_sig } =
-            self.sig_of_closure(expr_def_id.to_def_id(), decl, body, expected_sig);
+            self.sig_of_closure(expr.hir_id, expr_def_id.to_def_id(), decl, body, expected_sig);
 
         debug!("check_closure: ty_of_closure returns {:?}", liberated_sig);
 
@@ -288,15 +288,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
     fn sig_of_closure(
         &self,
+        hir_id: hir::HirId,
         expr_def_id: DefId,
         decl: &hir::FnDecl<'_>,
         body: &hir::Body<'_>,
         expected_sig: Option<ExpectedSig<'tcx>>,
     ) -> ClosureSignatures<'tcx> {
         if let Some(e) = expected_sig {
-            self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
+            self.sig_of_closure_with_expectation(hir_id, expr_def_id, decl, body, e)
         } else {
-            self.sig_of_closure_no_expectation(expr_def_id, decl, body)
+            self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body)
         }
     }
 
@@ -304,13 +305,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// types that the user gave into a signature.
     fn sig_of_closure_no_expectation(
         &self,
+        hir_id: hir::HirId,
         expr_def_id: DefId,
         decl: &hir::FnDecl<'_>,
         body: &hir::Body<'_>,
     ) -> ClosureSignatures<'tcx> {
         debug!("sig_of_closure_no_expectation()");
 
-        let bound_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
+        let bound_sig = self.supplied_sig_of_closure(hir_id, expr_def_id, decl, body);
 
         self.closure_sigs(expr_def_id, body, bound_sig)
     }
@@ -364,6 +366,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ///   regions with depth 1, which are bound then by the closure.
     fn sig_of_closure_with_expectation(
         &self,
+        hir_id: hir::HirId,
         expr_def_id: DefId,
         decl: &hir::FnDecl<'_>,
         body: &hir::Body<'_>,
@@ -375,7 +378,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // expectation if things don't see to match up with what we
         // expect.
         if expected_sig.sig.c_variadic() != decl.c_variadic {
-            return self.sig_of_closure_no_expectation(expr_def_id, decl, body);
+            return self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body);
         } else if expected_sig.sig.skip_binder().inputs_and_output.len() != decl.inputs.len() + 1 {
             return self.sig_of_closure_with_mismatched_number_of_arguments(
                 expr_def_id,
@@ -411,9 +414,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Along the way, it also writes out entries for types that the user
         // wrote into our typeck results, which are then later used by the privacy
         // check.
-        match self.check_supplied_sig_against_expectation(expr_def_id, decl, body, &closure_sigs) {
+        match self.check_supplied_sig_against_expectation(
+            hir_id,
+            expr_def_id,
+            decl,
+            body,
+            &closure_sigs,
+        ) {
             Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
-            Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
+            Err(_) => return self.sig_of_closure_no_expectation(hir_id, expr_def_id, decl, body),
         }
 
         closure_sigs
@@ -460,6 +469,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// strategy.
     fn check_supplied_sig_against_expectation(
         &self,
+        hir_id: hir::HirId,
         expr_def_id: DefId,
         decl: &hir::FnDecl<'_>,
         body: &hir::Body<'_>,
@@ -469,7 +479,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         //
         // (See comment on `sig_of_closure_with_expectation` for the
         // meaning of these letters.)
-        let supplied_sig = self.supplied_sig_of_closure(expr_def_id, decl, body);
+        let supplied_sig = self.supplied_sig_of_closure(hir_id, expr_def_id, decl, body);
 
         debug!("check_supplied_sig_against_expectation: supplied_sig={:?}", supplied_sig);
 
@@ -534,6 +544,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Also, record this closure signature for later.
     fn supplied_sig_of_closure(
         &self,
+        hir_id: hir::HirId,
         expr_def_id: DefId,
         decl: &hir::FnDecl<'_>,
         body: &hir::Body<'_>,
@@ -545,6 +556,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             decl, body.generator_kind,
         );
 
+        let bound_vars = self.tcx.late_bound_vars(hir_id);
+
         // First, convert the types that the user supplied (if any).
         let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
         let supplied_return = match decl.output {
@@ -571,7 +584,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             },
         };
 
-        let result = ty::Binder::bind(
+        let result = ty::Binder::bind_with_vars(
             self.tcx.mk_fn_sig(
                 supplied_arguments,
                 supplied_return,
@@ -579,7 +592,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 hir::Unsafety::Normal,
                 Abi::RustCall,
             ),
-            self.tcx,
+            bound_vars,
         );
 
         debug!("supplied_sig_of_closure: result={:?}", result);

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -1462,7 +1462,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 &[][..],
                 has_self,
                 self_ty,
-                arg_count,
+                &arg_count,
                 &mut CreateCtorSubstsContext {
                     fcx: self,
                     span,

compiler/rustc_typeck/src/check/generator_interior.rs

@@ -186,7 +186,10 @@ pub fn resolve_interior<'a, 'tcx>(
                 // which means that none of the regions inside relate to any other, even if
                 // typeck had previously found constraints that would cause them to be related.
                 let folded = fcx.tcx.fold_regions(erased, &mut false, |_, current_depth| {
-                    let br = ty::BoundRegion { kind: ty::BrAnon(counter) };
+                    let br = ty::BoundRegion {
+                        var: ty::BoundVar::from_u32(counter),
+                        kind: ty::BrAnon(counter),
+                    };
                     let r = fcx.tcx.mk_region(ty::ReLateBound(current_depth, br));
                     counter += 1;
                     r
@@ -202,11 +205,15 @@ pub fn resolve_interior<'a, 'tcx>(
 
     // Extract type components to build the witness type.
     let type_list = fcx.tcx.mk_type_list(type_causes.iter().map(|cause| cause.ty));
-    let witness = fcx.tcx.mk_generator_witness(ty::Binder::bind(type_list, fcx.tcx));
+    let bound_vars = fcx.tcx.mk_bound_variable_kinds(
+        (0..counter).map(|i| ty::BoundVariableKind::Region(ty::BrAnon(i))),
+    );
+    let witness =
+        fcx.tcx.mk_generator_witness(ty::Binder::bind_with_vars(type_list, bound_vars.clone()));
 
     // Store the generator types and spans into the typeck results for this generator.
     visitor.fcx.inh.typeck_results.borrow_mut().generator_interior_types =
-        ty::Binder::bind(type_causes, fcx.tcx);
+        ty::Binder::bind_with_vars(type_causes, bound_vars);
 
     debug!(
         "types in generator after region replacement {:?}, span = {:?}",

compiler/rustc_typeck/src/check/intrinsic.rs

@@ -101,12 +101,21 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     let intrinsic_name = tcx.item_name(it.def_id.to_def_id());
     let name_str = intrinsic_name.as_str();
 
+    let bound_vars = tcx.mk_bound_variable_kinds(
+        [ty::BoundVariableKind::Region(ty::BrAnon(0)), ty::BoundVariableKind::Region(ty::BrEnv)]
+            .iter()
+            .copied(),
+    );
     let mk_va_list_ty = |mutbl| {
         tcx.lang_items().va_list().map(|did| {
-            let region = tcx
-                .mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { kind: ty::BrAnon(0) }));
-            let env_region =
-                tcx.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { kind: ty::BrEnv }));
+            let region = tcx.mk_region(ty::ReLateBound(
+                ty::INNERMOST,
+                ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon(0) },
+            ));
+            let env_region = tcx.mk_region(ty::ReLateBound(
+                ty::INNERMOST,
+                ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BrEnv },
+            ));
             let va_list_ty = tcx.type_of(did).subst(tcx, &[region.into()]);
             (tcx.mk_ref(env_region, ty::TypeAndMut { ty: va_list_ty, mutbl }), va_list_ty)
         })
@@ -305,7 +314,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                     tcx.associated_items(tcx.lang_items().discriminant_kind_trait().unwrap());
                 let discriminant_def_id = assoc_items.in_definition_order().next().unwrap().def_id;
 
-                let br = ty::BoundRegion { kind: ty::BrAnon(0) };
+                let br = ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon(0) };
                 (
                     1,
                     vec![
@@ -366,7 +375,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
         (n_tps, inputs, output, unsafety)
     };
     let sig = tcx.mk_fn_sig(inputs.into_iter(), output, false, unsafety, Abi::RustIntrinsic);
-    let sig = ty::Binder::bind(sig, tcx);
+    let sig = ty::Binder::bind_with_vars(sig, bound_vars);
     equate_intrinsic_type(tcx, it, n_tps, sig)
 }
 

compiler/rustc_typeck/src/check/method/confirm.rs

@@ -381,7 +381,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
             parent_substs,
             false,
             None,
-            arg_count_correct,
+            &arg_count_correct,
             &mut MethodSubstsCtxt { cfcx: self, pick, seg },
         )
     }

compiler/rustc_typeck/src/check/mod.rs

@@ -497,6 +497,7 @@ fn typeck_with_fallback<'tcx>(
                 let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id);
                 <dyn AstConv<'_>>::ty_of_fn(
                     &fcx,
+                    id,
                     header.unsafety,
                     header.abi,
                     decl,

compiler/rustc_typeck/src/collect.rs

@@ -1712,6 +1712,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
                 }
                 None => <dyn AstConv<'_>>::ty_of_fn(
                     &icx,
+                    hir_id,
                     sig.header.unsafety,
                     sig.header.abi,
                     &sig.decl,
@@ -1729,6 +1730,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
             ..
         }) => <dyn AstConv<'_>>::ty_of_fn(
             &icx,
+            hir_id,
             header.unsafety,
             header.abi,
             decl,
@@ -2082,6 +2084,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
         match predicate {
             hir::WherePredicate::BoundPredicate(bound_pred) => {
                 let ty = icx.to_ty(&bound_pred.bounded_ty);
+                let bound_vars = icx.tcx.late_bound_vars(bound_pred.bounded_ty.hir_id);
 
                 // Keep the type around in a dummy predicate, in case of no bounds.
                 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
@@ -2097,12 +2100,12 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
                     } else {
                         let span = bound_pred.bounded_ty.span;
                         let re_root_empty = tcx.lifetimes.re_root_empty;
-                        let predicate = ty::Binder::bind(
+                        let predicate = ty::Binder::bind_with_vars(
                             ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
                                 ty,
                                 re_root_empty,
                             )),
-                            tcx,
+                            bound_vars,
                         );
                         predicates.insert((predicate.to_predicate(tcx), span));
                     }
@@ -2120,10 +2123,12 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
                             let mut bounds = Bounds::default();
                             let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
                                 &icx,
-                                &poly_trait_ref,
+                                &poly_trait_ref.trait_ref,
+                                poly_trait_ref.span,
                                 constness,
                                 ty,
                                 &mut bounds,
+                                false,
                             );
                             predicates.extend(bounds.predicates(tcx, ty));
                         }
@@ -2146,11 +2151,11 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericP
                             let region =
                                 <dyn AstConv<'_>>::ast_region_to_region(&icx, lifetime, None);
                             predicates.insert((
-                                ty::Binder::bind(
+                                ty::Binder::bind_with_vars(
                                     ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(
                                         ty, region,
                                     )),
-                                    tcx,
+                                    bound_vars,
                                 )
                                 .to_predicate(tcx),
                                 lifetime.span,
@@ -2373,7 +2378,14 @@ fn predicates_from_bound<'tcx>(
             };
 
             let mut bounds = Bounds::default();
-            let _ = astconv.instantiate_poly_trait_ref(tr, constness, param_ty, &mut bounds);
+            let _ = astconv.instantiate_poly_trait_ref(
+                &tr.trait_ref,
+                tr.span,
+                constness,
+                param_ty,
+                &mut bounds,
+                false,
+            );
             bounds.predicates(astconv.tcx(), param_ty)
         }
         hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
@@ -2409,8 +2421,10 @@ fn compute_sig_of_foreign_fn_decl<'tcx>(
     } else {
         hir::Unsafety::Unsafe
     };
+    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
     let fty = <dyn AstConv<'_>>::ty_of_fn(
         &ItemCtxt::new(tcx, def_id),
+        hir_id,
         unsafety,
         abi,
         decl,

compiler/rustc_typeck/src/lib.rs

@@ -430,7 +430,7 @@ pub fn hir_ty_to_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
     let env_node_id = tcx.hir().get_parent_item(hir_ty.hir_id);
     let env_def_id = tcx.hir().local_def_id(env_node_id);
     let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
-    item_cx.to_ty(hir_ty)
+    AstConv::ast_ty_to_ty(&item_cx, hir_ty)
 }
 
 pub fn hir_trait_to_predicates<'tcx>(
@@ -445,7 +445,7 @@ pub fn hir_trait_to_predicates<'tcx>(
     let env_def_id = tcx.hir().local_def_id(env_hir_id);
     let item_cx = self::collect::ItemCtxt::new(tcx, env_def_id.to_def_id());
     let mut bounds = Bounds::default();
-    let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref_inner(
+    let _ = <dyn AstConv<'_>>::instantiate_poly_trait_ref(
         &item_cx,
         hir_trait,
         DUMMY_SP,

src/librustdoc/clean/mod.rs

@@ -411,7 +411,7 @@ impl Clean<Option<Lifetime>> for ty::RegionKind {
     fn clean(&self, _cx: &mut DocContext<'_>) -> Option<Lifetime> {
         match *self {
             ty::ReStatic => Some(Lifetime::statik()),
-            ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name) }) => {
+            ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrNamed(_, name), .. }) => {
                 Some(Lifetime(name))
             }
             ty::ReEarlyBound(ref data) => Some(Lifetime(data.name)),

src/librustdoc/clean/utils.rs

@@ -97,7 +97,7 @@ fn external_generic_args(
         .iter()
         .filter_map(|kind| match kind.unpack() {
             GenericArgKind::Lifetime(lt) => match lt {
-                ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrAnon(_) }) => {
+                ty::ReLateBound(_, ty::BoundRegion { kind: ty::BrAnon(_), .. }) => {
                     Some(GenericArg::Lifetime(Lifetime::elided()))
                 }
                 _ => lt.clean(cx).map(GenericArg::Lifetime),

src/test/incremental/hashes/function_interfaces.rs

@@ -118,7 +118,7 @@ pub fn type_parameter<T>() {}
 pub fn lifetime_parameter() {}
 
 #[cfg(not(cfail1))]
-#[rustc_clean(cfg = "cfail2", except = "hir_owner, hir_owner_nodes, generics_of")]
+#[rustc_clean(cfg = "cfail2", except = "hir_owner, hir_owner_nodes, generics_of,fn_sig")]
 #[rustc_clean(cfg = "cfail3")]
 pub fn lifetime_parameter<'a>() {}
 
@@ -150,7 +150,7 @@ pub fn lifetime_bound<'a, T>() {}
 #[cfg(not(cfail1))]
 #[rustc_clean(
     cfg = "cfail2",
-    except = "hir_owner, hir_owner_nodes, generics_of, type_of, predicates_of"
+    except = "hir_owner, hir_owner_nodes, generics_of, type_of, predicates_of,fn_sig"
 )]
 #[rustc_clean(cfg = "cfail3")]
 pub fn lifetime_bound<'a, T: 'a>() {}
@@ -183,7 +183,7 @@ pub fn second_lifetime_bound<'a, 'b, T: 'a>() {}
 #[cfg(not(cfail1))]
 #[rustc_clean(
     cfg = "cfail2",
-    except = "hir_owner, hir_owner_nodes, generics_of, type_of, predicates_of"
+    except = "hir_owner, hir_owner_nodes, generics_of, type_of, predicates_of,fn_sig"
 )]
 #[rustc_clean(cfg = "cfail3")]
 pub fn second_lifetime_bound<'a, 'b, T: 'a + 'b>() {}

src/test/incremental/hashes/inherent_impls.rs

@@ -312,7 +312,7 @@ impl Foo {
     // if we lower generics before the body, then the `HirId` for
     // things in the body will be affected. So if you start to see
     // `typeck` appear dirty, that might be the cause. -nmatsakis
-    #[rustc_clean(cfg="cfail2", except="hir_owner,hir_owner_nodes")]
+    #[rustc_clean(cfg="cfail2", except="hir_owner,hir_owner_nodes,fn_sig")]
     #[rustc_clean(cfg="cfail3")]
     pub fn add_lifetime_parameter_to_method<'a>(&self) { }
 }
@@ -360,7 +360,7 @@ impl Foo {
 impl Foo {
     #[rustc_clean(
         cfg="cfail2",
-        except="hir_owner,hir_owner_nodes,generics_of,predicates_of,type_of"
+        except="hir_owner,hir_owner_nodes,generics_of,predicates_of,type_of,fn_sig"
     )]
     #[rustc_clean(cfg="cfail3")]
     pub fn add_lifetime_bound_to_lifetime_param_of_method<'a, 'b: 'a>(&self) { }
@@ -388,7 +388,7 @@ impl Foo {
     // body will be affected. So if you start to see `typeck`
     // appear dirty, that might be the cause. -nmatsakis
     #[rustc_clean(cfg="cfail2", except="hir_owner,hir_owner_nodes,generics_of,predicates_of,\
-                                        type_of")]
+                                        type_of,fn_sig")]
     #[rustc_clean(cfg="cfail3")]
     pub fn add_lifetime_bound_to_type_param_of_method<'a, T: 'a>(&self) { }
 }

src/test/ui/associated-type-bounds/hrtb.rs

@@ -0,0 +1,65 @@
+// check-pass
+
+#![feature(associated_type_bounds)]
+
+trait A<'a> {}
+trait B<'b> {}
+fn foo<T>()
+where
+    for<'a> T: A<'a> + 'a,
+{
+}
+trait C<'c>: for<'a> A<'a> + for<'b> B<'b> {
+    type As;
+}
+struct D<T>
+where
+    T: for<'c> C<'c, As: A<'c>>,
+{
+    t: std::marker::PhantomData<T>,
+}
+
+trait E<'e> {
+    type As;
+}
+trait F<'f>: for<'a> A<'a> + for<'e> E<'e> {}
+struct G<T>
+where
+    for<'f> T: F<'f, As: E<'f>> + 'f,
+{
+    t: std::marker::PhantomData<T>,
+}
+
+trait I<'a, 'b, 'c> {
+    type As;
+}
+trait H<'d, 'e>: for<'f> I<'d, 'f, 'e> + 'd {}
+fn foo2<T>()
+where
+    T: for<'g> H<'g, 'g, As: for<'h> H<'h, 'g> + 'g>,
+{
+}
+
+fn foo3<T>()
+where
+    T: for<'i> H<'i, 'i, As: for<'j> H<'j, 'i, As: for<'k> I<'i, 'k, 'j> + 'j> + 'i>,
+{
+}
+fn foo4<T>()
+where
+    T: for<'l, 'i> H<'l, 'i, As: for<'j> H<'j, 'i, As: for<'k> I<'l, 'k, 'j> + 'j> + 'i>,
+{
+}
+
+struct X<'x, 'y> {
+    x: std::marker::PhantomData<&'x ()>,
+    y: std::marker::PhantomData<&'y ()>,
+}
+
+fn foo5<T>()
+where
+    T: for<'l, 'i> H<'l, 'i, As: for<'j> H<'j, 'i, As: for<'k> H<'j, 'k, As = X<'j, 'k>> + 'j> + 'i>
+{
+}
+
+fn main() {}

src/test/ui/hrtb/complex.rs

@@ -9,12 +9,20 @@ trait C<'c>: for<'a> A<'a> + for<'b> B<'b> {
 struct D<T> where T: for<'c> C<'c, As=&'c ()> {
     t: std::marker::PhantomData<T>,
 }
-trait E<'e> {
+trait E<'e, 'g> {
     type As;
 }
-trait F<'f>: for<'a> A<'a> + for<'e> E<'e> {}
+trait F<'f>: for<'a> A<'a> + for<'e> E<'e, 'f> {}
 struct G<T> where T: for<'f> F<'f, As=&'f ()> {
     t: std::marker::PhantomData<T>,
 }
+trait H<'a, 'b> {
+    type As;
+}
+trait I<'a>: for<'b> H<'a, 'b> {}
+
+struct J<T> where T: for<'i> I<'i, As=&'i ()> {
+    t: std::marker::PhantomData<T>,
+}
 
 fn main() {}

src/test/ui/nll/closure-requirements/escape-argument-callee.stderr

@@ -6,7 +6,7 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
    |
    = note: defining type: test::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) mut &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) i32)),
+               for<'r, 's, 't0> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) mut &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) i32)),
                (),
            ]
 

src/test/ui/nll/closure-requirements/escape-argument.stderr

@@ -6,7 +6,7 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
    |
    = note: defining type: test::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) mut &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) i32)),
+               for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) mut &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) i32)),
                (),
            ]
 

src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr

@@ -10,7 +10,7 @@ LL | |         },
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) &'_#3r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>)),
+               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) &'_#3r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#4r

src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr

@@ -11,7 +11,7 @@ LL | |     });
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) u32>)),
+               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 4, kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 5, kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#3r

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr

@@ -10,7 +10,7 @@ LL | |     })
    |
    = note: defining type: case1::{closure#0} with closure substs [
                i32,
-               for<'r> extern "rust-call" fn((std::cell::Cell<&'_#1r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>)),
+               for<'r> extern "rust-call" fn((std::cell::Cell<&'_#1r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>)),
                (),
            ]
 
@@ -49,7 +49,7 @@ LL | |     })
    |
    = note: defining type: case2::{closure#0} with closure substs [
                i32,
-               for<'r> extern "rust-call" fn((std::cell::Cell<&'_#1r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>)),
+               for<'r> extern "rust-call" fn((std::cell::Cell<&'_#1r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>)),
                (),
            ]
    = note: number of external vids: 2

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr

@@ -12,7 +12,7 @@ LL | |     });
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t2) }) u32>)),
+               for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 4, kind: BrNamed('t2) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#2r

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr

@@ -12,7 +12,7 @@ LL | |     });
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) u32>)),
+               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 4, kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 5, kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#3r

src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr

@@ -11,7 +11,7 @@ LL | |     });
    |
    = note: defining type: test::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>)),
+               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#3r

src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr

@@ -10,7 +10,7 @@ LL | |         },
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>)),
+               for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#3r

src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr

@@ -11,7 +11,7 @@ LL | |     });
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>)),
+               for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 4, kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#2r

src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr

@@ -11,7 +11,7 @@ LL | |     });
    |
    = note: defining type: supply::{closure#0} with closure substs [
                i16,
-               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('t1) }) u32>)),
+               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 2, kind: BrNamed('t0) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 4, kind: BrNamed('t2) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) u32>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 5, kind: BrNamed('t3) }) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BoundRegion { var: 3, kind: BrNamed('t1) }) u32>)),
                (),
            ]
    = note: late-bound region is '_#3r

src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr

@@ -6,7 +6,7 @@ LL |     expect_sig(|a, b| b); // ought to return `a`
    |
    = note: defining type: test::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) i32)) -> &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) i32,
+               for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) i32, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) i32)) -> &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) i32,
                (),
            ]
 

src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr

@@ -6,7 +6,7 @@ LL |     twice(cell, value, |a, b| invoke(a, b));
    |
    = note: defining type: generic::<T>::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((std::option::Option<std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) ()>>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) T)),
+               for<'r, 's> extern "rust-call" fn((std::option::Option<std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) ()>>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) T)),
                (),
            ]
    = note: number of external vids: 2
@@ -31,7 +31,7 @@ LL |     twice(cell, value, |a, b| invoke(a, b));
    |
    = note: defining type: generic_fail::<T>::{closure#0} with closure substs [
                i16,
-               for<'r, 's> extern "rust-call" fn((std::option::Option<std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('r) }) ()>>, &ReLateBound(DebruijnIndex(0), BoundRegion { kind: BrNamed('s) }) T)),
+               for<'r, 's> extern "rust-call" fn((std::option::Option<std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BoundRegion { var: 0, kind: BrNamed('r) }) ()>>, &ReLateBound(DebruijnIndex(0), BoundRegion { var: 1, kind: BrNamed('s) }) T)),
                (),
            ]
    = note: late-bound region is '_#2r