Reduce the number of RefCells in InferCtxt.

src/librustc/infer/canonical/canonicalizer.rs

@@ -317,7 +317,9 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
                 let r = self
                     .infcx
                     .unwrap()
-                    .borrow_region_constraints()
+                    .inner
+                    .borrow_mut()
+                    .unwrap_region_constraints()
                     .opportunistic_resolve_var(self.tcx, vid);
                 debug!(
                     "canonical: region var found with vid {:?}, \
@@ -621,7 +623,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
 
     /// Returns the universe in which `vid` is defined.
     fn region_var_universe(&self, vid: ty::RegionVid) -> ty::UniverseIndex {
-        self.infcx.unwrap().borrow_region_constraints().var_universe(vid)
+        self.infcx.unwrap().inner.borrow_mut().unwrap_region_constraints().var_universe(vid)
     }
 
     /// Creates a canonical variable (with the given `info`)

src/librustc/infer/combine.rs

@@ -74,8 +74,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         match (&a.kind, &b.kind) {
             // Relate integral variables to other types
             (&ty::Infer(ty::IntVar(a_id)), &ty::Infer(ty::IntVar(b_id))) => {
-                self.int_unification_table
+                self.inner
                     .borrow_mut()
+                    .int_unification_table
                     .unify_var_var(a_id, b_id)
                     .map_err(|e| int_unification_error(a_is_expected, e))?;
                 Ok(a)
@@ -95,8 +96,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
 
             // Relate floating-point variables to other types
             (&ty::Infer(ty::FloatVar(a_id)), &ty::Infer(ty::FloatVar(b_id))) => {
-                self.float_unification_table
+                self.inner
                     .borrow_mut()
+                    .float_unification_table
                     .unify_var_var(a_id, b_id)
                     .map_err(|e| float_unification_error(relation.a_is_expected(), e))?;
                 Ok(a)
@@ -131,8 +133,8 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
             return Ok(a);
         }
 
-        let a = replace_if_possible(self.const_unification_table.borrow_mut(), a);
-        let b = replace_if_possible(self.const_unification_table.borrow_mut(), b);
+        let a = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table, a);
+        let b = replace_if_possible(&mut self.inner.borrow_mut().const_unification_table, b);
 
         let a_is_expected = relation.a_is_expected();
 
@@ -141,8 +143,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
                 ty::ConstKind::Infer(InferConst::Var(a_vid)),
                 ty::ConstKind::Infer(InferConst::Var(b_vid)),
             ) => {
-                self.const_unification_table
+                self.inner
                     .borrow_mut()
+                    .const_unification_table
                     .unify_var_var(a_vid, b_vid)
                     .map_err(|e| const_unification_error(a_is_expected, e))?;
                 return Ok(a);
@@ -174,8 +177,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         vid: ty::ConstVid<'tcx>,
         value: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        self.const_unification_table
+        self.inner
             .borrow_mut()
+            .const_unification_table
             .unify_var_value(
                 vid,
                 ConstVarValue {
@@ -196,8 +200,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         vid: ty::IntVid,
         val: ty::IntVarValue,
     ) -> RelateResult<'tcx, Ty<'tcx>> {
-        self.int_unification_table
+        self.inner
             .borrow_mut()
+            .int_unification_table
             .unify_var_value(vid, Some(val))
             .map_err(|e| int_unification_error(vid_is_expected, e))?;
         match val {
@@ -212,8 +217,9 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
         vid: ty::FloatVid,
         val: ast::FloatTy,
     ) -> RelateResult<'tcx, Ty<'tcx>> {
-        self.float_unification_table
+        self.inner
             .borrow_mut()
+            .float_unification_table
             .unify_var_value(vid, Some(ty::FloatVarValue(val)))
             .map_err(|e| float_unification_error(vid_is_expected, e))?;
         Ok(self.tcx.mk_mach_float(val))
@@ -260,7 +266,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         use self::RelationDir::*;
 
         // Get the actual variable that b_vid has been inferred to
-        debug_assert!(self.infcx.type_variables.borrow_mut().probe(b_vid).is_unknown());
+        debug_assert!(self.infcx.inner.borrow_mut().type_variables.probe(b_vid).is_unknown());
 
         debug!("instantiate(a_ty={:?} dir={:?} b_vid={:?})", a_ty, dir, b_vid);
 
@@ -280,7 +286,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
             "instantiate(a_ty={:?}, dir={:?}, b_vid={:?}, generalized b_ty={:?})",
             a_ty, dir, b_vid, b_ty
         );
-        self.infcx.type_variables.borrow_mut().instantiate(b_vid, b_ty);
+        self.infcx.inner.borrow_mut().type_variables.instantiate(b_vid, b_ty);
 
         if needs_wf {
             self.obligations.push(Obligation::new(
@@ -338,7 +344,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
 
         debug!("generalize: ambient_variance = {:?}", ambient_variance);
 
-        let for_universe = match self.infcx.type_variables.borrow_mut().probe(for_vid) {
+        let for_universe = match self.infcx.inner.borrow_mut().type_variables.probe(for_vid) {
             v @ TypeVariableValue::Known { .. } => {
                 panic!("instantiating {:?} which has a known value {:?}", for_vid, v,)
             }
@@ -350,7 +356,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         let mut generalize = Generalizer {
             infcx: self.infcx,
             span: self.trace.cause.span,
-            for_vid_sub_root: self.infcx.type_variables.borrow_mut().sub_root_var(for_vid),
+            for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables.sub_root_var(for_vid),
             for_universe,
             ambient_variance,
             needs_wf: false,
@@ -502,17 +508,16 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
         // us from creating infinitely sized types.
         match t.kind {
             ty::Infer(ty::TyVar(vid)) => {
-                let mut variables = self.infcx.type_variables.borrow_mut();
-                let vid = variables.root_var(vid);
-                let sub_vid = variables.sub_root_var(vid);
+                let vid = self.infcx.inner.borrow_mut().type_variables.root_var(vid);
+                let sub_vid = self.infcx.inner.borrow_mut().type_variables.sub_root_var(vid);
                 if sub_vid == self.for_vid_sub_root {
                     // If sub-roots are equal, then `for_vid` and
                     // `vid` are related via subtyping.
                     Err(TypeError::CyclicTy(self.root_ty))
                 } else {
-                    match variables.probe(vid) {
+                    let probe = self.infcx.inner.borrow_mut().type_variables.probe(vid);
+                    match probe {
                         TypeVariableValue::Known { value: u } => {
-                            drop(variables);
                             debug!("generalize: known value {:?}", u);
                             self.relate(&u, &u)
                         }
@@ -536,8 +541,13 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                                 ty::Covariant | ty::Contravariant => (),
                             }
 
-                            let origin = *variables.var_origin(vid);
-                            let new_var_id = variables.new_var(self.for_universe, false, origin);
+                            let origin =
+                                *self.infcx.inner.borrow_mut().type_variables.var_origin(vid);
+                            let new_var_id = self.infcx.inner.borrow_mut().type_variables.new_var(
+                                self.for_universe,
+                                false,
+                                origin,
+                            );
                             let u = self.tcx().mk_ty_var(new_var_id);
                             debug!("generalize: replacing original vid={:?} with new={:?}", vid, u);
                             Ok(u)
@@ -612,7 +622,7 @@ impl TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
 
         match c.val {
             ty::ConstKind::Infer(InferConst::Var(vid)) => {
-                let mut variable_table = self.infcx.const_unification_table.borrow_mut();
+                let variable_table = &mut self.infcx.inner.borrow_mut().const_unification_table;
                 let var_value = variable_table.probe_value(vid);
                 match var_value.val {
                     ConstVariableValue::Known { value: u } => self.relate(&u, &u),

src/librustc/infer/equate.rs

@@ -72,14 +72,14 @@ impl TypeRelation<'tcx> for Equate<'combine, 'infcx, 'tcx> {
         }
 
         let infcx = self.fields.infcx;
-        let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
-        let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
+        let a = infcx.inner.borrow_mut().type_variables.replace_if_possible(a);
+        let b = infcx.inner.borrow_mut().type_variables.replace_if_possible(b);
 
         debug!("{}.tys: replacements ({:?}, {:?})", self.tag(), a, b);
 
         match (&a.kind, &b.kind) {
             (&ty::Infer(TyVar(a_id)), &ty::Infer(TyVar(b_id))) => {
-                infcx.type_variables.borrow_mut().equate(a_id, b_id);
+                infcx.inner.borrow_mut().type_variables.equate(a_id, b_id);
             }
 
             (&ty::Infer(TyVar(a_id)), _) => {
@@ -105,7 +105,12 @@ impl TypeRelation<'tcx> for Equate<'combine, 'infcx, 'tcx> {
     ) -> RelateResult<'tcx, ty::Region<'tcx>> {
         debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
         let origin = Subtype(box self.fields.trace.clone());
-        self.fields.infcx.borrow_region_constraints().make_eqregion(origin, a, b);
+        self.fields
+            .infcx
+            .inner
+            .borrow_mut()
+            .unwrap_region_constraints()
+            .make_eqregion(origin, a, b);
         Ok(a)
     }
 

src/librustc/infer/error_reporting/need_type_info.rs

@@ -47,9 +47,12 @@ impl<'a, 'tcx> FindLocalByTypeVisitor<'a, 'tcx> {
                 if ty.walk().any(|inner_ty| {
                     inner_ty == self.target_ty
                         || match (&inner_ty.kind, &self.target_ty.kind) {
-                            (&Infer(TyVar(a_vid)), &Infer(TyVar(b_vid))) => {
-                                self.infcx.type_variables.borrow_mut().sub_unified(a_vid, b_vid)
-                            }
+                            (&Infer(TyVar(a_vid)), &Infer(TyVar(b_vid))) => self
+                                .infcx
+                                .inner
+                                .borrow_mut()
+                                .type_variables
+                                .sub_unified(a_vid, b_vid),
                             _ => false,
                         }
                 }) {
@@ -166,7 +169,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         highlight: Option<ty::print::RegionHighlightMode>,
     ) -> (String, Option<Span>, Cow<'static, str>, Option<String>, Option<&'static str>) {
         if let ty::Infer(ty::TyVar(ty_vid)) = ty.kind {
-            let ty_vars = self.type_variables.borrow();
+            let ty_vars = &self.inner.borrow().type_variables;
             let var_origin = ty_vars.var_origin(ty_vid);
             if let TypeVariableOriginKind::TypeParameterDefinition(name, def_id) = var_origin.kind {
                 let parent_def_id = def_id.and_then(|def_id| self.tcx.parent(def_id));
@@ -224,7 +227,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let ty_to_string = |ty: Ty<'tcx>| -> String {
             let mut s = String::new();
             let mut printer = ty::print::FmtPrinter::new(self.tcx, &mut s, Namespace::TypeNS);
-            let ty_vars = self.type_variables.borrow();
+            let ty_vars = &self.inner.borrow().type_variables;
             let getter = move |ty_vid| {
                 let var_origin = ty_vars.var_origin(ty_vid);
                 if let TypeVariableOriginKind::TypeParameterDefinition(name, _) = var_origin.kind {

src/librustc/infer/freshen.rs

@@ -154,14 +154,15 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
 
         match t.kind {
             ty::Infer(ty::TyVar(v)) => {
-                let opt_ty = self.infcx.type_variables.borrow_mut().probe(v).known();
+                let opt_ty = self.infcx.inner.borrow_mut().type_variables.probe(v).known();
                 self.freshen_ty(opt_ty, ty::TyVar(v), ty::FreshTy)
             }
 
             ty::Infer(ty::IntVar(v)) => self.freshen_ty(
                 self.infcx
-                    .int_unification_table
+                    .inner
                     .borrow_mut()
+                    .int_unification_table
                     .probe_value(v)
                     .map(|v| v.to_type(tcx)),
                 ty::IntVar(v),
@@ -170,8 +171,9 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
 
             ty::Infer(ty::FloatVar(v)) => self.freshen_ty(
                 self.infcx
-                    .float_unification_table
+                    .inner
                     .borrow_mut()
+                    .float_unification_table
                     .probe_value(v)
                     .map(|v| v.to_type(tcx)),
                 ty::FloatVar(v),
@@ -225,8 +227,14 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
     fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
         match ct.val {
             ty::ConstKind::Infer(ty::InferConst::Var(v)) => {
-                let opt_ct =
-                    self.infcx.const_unification_table.borrow_mut().probe_value(v).val.known();
+                let opt_ct = self
+                    .infcx
+                    .inner
+                    .borrow_mut()
+                    .const_unification_table
+                    .probe_value(v)
+                    .val
+                    .known();
                 return self.freshen_const(
                     opt_ct,
                     ty::InferConst::Var(v),

src/librustc/infer/fudge.rs

@@ -8,11 +8,10 @@ use super::{ConstVariableOrigin, RegionVariableOrigin};
 use rustc_data_structures::unify as ut;
 use ut::UnifyKey;
 
-use std::cell::RefMut;
 use std::ops::Range;
 
 fn const_vars_since_snapshot<'tcx>(
-    mut table: RefMut<'_, ut::UnificationTable<ut::InPlace<ConstVid<'tcx>>>>,
+    table: &mut ut::UnificationTable<ut::InPlace<ConstVid<'tcx>>>,
     snapshot: &ut::Snapshot<ut::InPlace<ConstVid<'tcx>>>,
 ) -> (Range<ConstVid<'tcx>>, Vec<ConstVariableOrigin>) {
     let range = table.vars_since_snapshot(snapshot);
@@ -82,23 +81,18 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     // going to be popped, so we will have to
                     // eliminate any references to them.
 
-                    let type_vars = self
-                        .type_variables
-                        .borrow_mut()
-                        .vars_since_snapshot(&snapshot.type_snapshot);
-                    let int_vars = self
-                        .int_unification_table
-                        .borrow_mut()
-                        .vars_since_snapshot(&snapshot.int_snapshot);
-                    let float_vars = self
-                        .float_unification_table
-                        .borrow_mut()
-                        .vars_since_snapshot(&snapshot.float_snapshot);
-                    let region_vars = self
-                        .borrow_region_constraints()
+                    let mut inner = self.inner.borrow_mut();
+                    let type_vars =
+                        inner.type_variables.vars_since_snapshot(&snapshot.type_snapshot);
+                    let int_vars =
+                        inner.int_unification_table.vars_since_snapshot(&snapshot.int_snapshot);
+                    let float_vars =
+                        inner.float_unification_table.vars_since_snapshot(&snapshot.float_snapshot);
+                    let region_vars = inner
+                        .unwrap_region_constraints()
                         .vars_since_snapshot(&snapshot.region_constraints_snapshot);
                     let const_vars = const_vars_since_snapshot(
-                        self.const_unification_table.borrow_mut(),
+                        &mut inner.const_unification_table,
                         &snapshot.const_snapshot,
                     );
 
@@ -166,7 +160,9 @@ impl<'a, 'tcx> TypeFolder<'tcx> for InferenceFudger<'a, 'tcx> {
                     // variables to their binding anyhow, we know
                     // that it is unbound, so we can just return
                     // it.
-                    debug_assert!(self.infcx.type_variables.borrow_mut().probe(vid).is_unknown());
+                    debug_assert!(
+                        self.infcx.inner.borrow_mut().type_variables.probe(vid).is_unknown()
+                    );
                     ty
                 }
             }

src/librustc/infer/glb.rs

@@ -66,7 +66,12 @@ impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
         debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
 
         let origin = Subtype(box self.fields.trace.clone());
-        Ok(self.fields.infcx.borrow_region_constraints().glb_regions(self.tcx(), origin, a, b))
+        Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().glb_regions(
+            self.tcx(),
+            origin,
+            a,
+            b,
+        ))
     }
 
     fn consts(

src/librustc/infer/higher_ranked/mod.rs

@@ -138,7 +138,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             return Ok(());
         }
 
-        self.borrow_region_constraints().leak_check(
+        self.inner.borrow_mut().unwrap_region_constraints().leak_check(
             self.tcx,
             overly_polymorphic,
             placeholder_map,

src/librustc/infer/lattice.rs

@@ -56,8 +56,8 @@ where
     }
 
     let infcx = this.infcx();
-    let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
-    let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
+    let a = infcx.inner.borrow_mut().type_variables.replace_if_possible(a);
+    let b = infcx.inner.borrow_mut().type_variables.replace_if_possible(b);
     match (&a.kind, &b.kind) {
         // If one side is known to be a variable and one is not,
         // create a variable (`v`) to represent the LUB. Make sure to

src/librustc/infer/lub.rs

@@ -66,7 +66,12 @@ impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> {
         debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
 
         let origin = Subtype(box self.fields.trace.clone());
-        Ok(self.fields.infcx.borrow_region_constraints().lub_regions(self.tcx(), origin, a, b))
+        Ok(self.fields.infcx.inner.borrow_mut().unwrap_region_constraints().lub_regions(
+            self.tcx(),
+            origin,
+            a,
+            b,
+        ))
     }
 
     fn consts(

src/librustc/infer/nll_relate/mod.rs

@@ -322,7 +322,7 @@ where
         match value_ty.kind {
             ty::Infer(ty::TyVar(value_vid)) => {
                 // Two type variables: just equate them.
-                self.infcx.type_variables.borrow_mut().equate(vid, value_vid);
+                self.infcx.inner.borrow_mut().type_variables.equate(vid, value_vid);
                 return Ok(value_ty);
             }
 
@@ -343,7 +343,7 @@ where
             assert!(!generalized_ty.has_infer_types());
         }
 
-        self.infcx.type_variables.borrow_mut().instantiate(vid, generalized_ty);
+        self.infcx.inner.borrow_mut().type_variables.instantiate(vid, generalized_ty);
 
         // The generalized values we extract from `canonical_var_values` have
         // been fully instantiated and hence the set of scopes we have
@@ -373,7 +373,7 @@ where
             delegate: &mut self.delegate,
             first_free_index: ty::INNERMOST,
             ambient_variance: self.ambient_variance,
-            for_vid_sub_root: self.infcx.type_variables.borrow_mut().sub_root_var(for_vid),
+            for_vid_sub_root: self.infcx.inner.borrow_mut().type_variables.sub_root_var(for_vid),
             universe,
         };
 
@@ -870,7 +870,7 @@ where
             }
 
             ty::Infer(ty::TyVar(vid)) => {
-                let mut variables = self.infcx.type_variables.borrow_mut();
+                let variables = &mut self.infcx.inner.borrow_mut().type_variables;
                 let vid = variables.root_var(vid);
                 let sub_vid = variables.sub_root_var(vid);
                 if sub_vid == self.for_vid_sub_root {
@@ -972,7 +972,7 @@ where
                 bug!("unexpected inference variable encountered in NLL generalization: {:?}", a);
             }
             ty::ConstKind::Infer(InferConst::Var(vid)) => {
-                let mut variable_table = self.infcx.const_unification_table.borrow_mut();
+                let variable_table = &mut self.infcx.inner.borrow_mut().const_unification_table;
                 let var_value = variable_table.probe_value(vid);
                 match var_value.val.known() {
                     Some(u) => self.relate(&u, &u),

src/librustc/infer/outlives/obligations.rs

@@ -82,7 +82,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     ) {
         debug!("register_region_obligation(body_id={:?}, obligation={:?})", body_id, obligation);
 
-        self.region_obligations.borrow_mut().push((body_id, obligation));
+        self.inner.borrow_mut().region_obligations.push((body_id, obligation));
     }
 
     pub fn register_region_obligation_with_cause(
@@ -103,7 +103,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
     /// Trait queries just want to pass back type obligations "as is"
     pub fn take_registered_region_obligations(&self) -> Vec<(hir::HirId, RegionObligation<'tcx>)> {
-        ::std::mem::take(&mut *self.region_obligations.borrow_mut())
+        ::std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
     /// Process the region obligations that must be proven (during

src/librustc/infer/resolve.rs

@@ -75,9 +75,12 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticTypeAndRegionResolver<'a, 'tcx>
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         match *r {
-            ty::ReVar(rid) => {
-                self.infcx.borrow_region_constraints().opportunistic_resolve_var(self.tcx(), rid)
-            }
+            ty::ReVar(rid) => self
+                .infcx
+                .inner
+                .borrow_mut()
+                .unwrap_region_constraints()
+                .opportunistic_resolve_var(self.tcx(), rid),
             _ => r,
         }
     }
@@ -120,7 +123,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
                 // Since we called `shallow_resolve` above, this must
                 // be an (as yet...) unresolved inference variable.
                 let ty_var_span = if let ty::TyVar(ty_vid) = infer_ty {
-                    let ty_vars = self.infcx.type_variables.borrow();
+                    let ty_vars = &self.infcx.inner.borrow().type_variables;
                     if let TypeVariableOrigin {
                         kind: TypeVariableOriginKind::TypeParameterDefinition(_, _),
                         span,

src/librustc/infer/sub.rs

@@ -80,8 +80,8 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
         }
 
         let infcx = self.fields.infcx;
-        let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
-        let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
+        let a = infcx.inner.borrow_mut().type_variables.replace_if_possible(a);
+        let b = infcx.inner.borrow_mut().type_variables.replace_if_possible(b);
         match (&a.kind, &b.kind) {
             (&ty::Infer(TyVar(a_vid)), &ty::Infer(TyVar(b_vid))) => {
                 // Shouldn't have any LBR here, so we can safely put
@@ -95,7 +95,7 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
                 // have to record in the `type_variables` tracker that
                 // the two variables are equal modulo subtyping, which
                 // is important to the occurs check later on.
-                infcx.type_variables.borrow_mut().sub(a_vid, b_vid);
+                infcx.inner.borrow_mut().type_variables.sub(a_vid, b_vid);
                 self.fields.obligations.push(Obligation::new(
                     self.fields.trace.cause.clone(),
                     self.fields.param_env,
@@ -140,7 +140,12 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
         // from the "cause" field, we could perhaps give more tailored
         // error messages.
         let origin = SubregionOrigin::Subtype(box self.fields.trace.clone());
-        self.fields.infcx.borrow_region_constraints().make_subregion(origin, a, b);
+        self.fields
+            .infcx
+            .inner
+            .borrow_mut()
+            .unwrap_region_constraints()
+            .make_subregion(origin, a, b);
 
         Ok(a)
     }

src/librustc/infer/unify_key.rs

@@ -4,7 +4,6 @@ use rustc_data_structures::unify::{EqUnifyValue, NoError, UnificationTable, Unif
 use rustc_span::symbol::Symbol;
 use rustc_span::{Span, DUMMY_SP};
 
-use std::cell::RefMut;
 use std::cmp;
 use std::marker::PhantomData;
 
@@ -214,7 +213,7 @@ impl<'tcx> UnifyValue for ConstVarValue<'tcx> {
 impl<'tcx> EqUnifyValue for &'tcx ty::Const<'tcx> {}
 
 pub fn replace_if_possible(
-    mut table: RefMut<'_, UnificationTable<InPlace<ty::ConstVid<'tcx>>>>,
+    table: &mut UnificationTable<InPlace<ty::ConstVid<'tcx>>>,
     c: &'tcx ty::Const<'tcx>,
 ) -> &'tcx ty::Const<'tcx> {
     if let ty::Const { val: ty::ConstKind::Infer(InferConst::Var(vid)), .. } = c {

src/librustc/traits/auto_trait.rs

@@ -199,12 +199,22 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 panic!("Unable to fulfill trait {:?} for '{:?}': {:?}", trait_did, ty, e)
             });
 
-            let body_id_map: FxHashMap<_, _> =
-                infcx.region_obligations.borrow().iter().map(|&(id, _)| (id, vec![])).collect();
+            let body_id_map: FxHashMap<_, _> = infcx
+                .inner
+                .borrow()
+                .region_obligations
+                .iter()
+                .map(|&(id, _)| (id, vec![]))
+                .collect();
 
             infcx.process_registered_region_obligations(&body_id_map, None, full_env);
 
-            let region_data = infcx.borrow_region_constraints().region_constraint_data().clone();
+            let region_data = infcx
+                .inner
+                .borrow_mut()
+                .unwrap_region_constraints()
+                .region_constraint_data()
+                .clone();
 
             let vid_to_region = self.map_vid_to_region(&region_data);
 

src/librustc/traits/project.rs

@@ -454,7 +454,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
     // bounds. It might be the case that we want two distinct caches,
     // or else another kind of cache entry.
 
-    let cache_result = infcx.projection_cache.borrow_mut().try_start(cache_key);
+    let cache_result = infcx.inner.borrow_mut().projection_cache.try_start(cache_key);
     match cache_result {
         Ok(()) => {}
         Err(ProjectionCacheEntry::Ambiguous) => {
@@ -528,7 +528,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             // Once we have inferred everything we need to know, we
             // can ignore the `obligations` from that point on.
             if infcx.unresolved_type_vars(&ty.value).is_none() {
-                infcx.projection_cache.borrow_mut().complete_normalized(cache_key, &ty);
+                infcx.inner.borrow_mut().projection_cache.complete_normalized(cache_key, &ty);
             // No need to extend `obligations`.
             } else {
                 obligations.extend(ty.obligations);
@@ -590,7 +590,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             };
 
             let cache_value = prune_cache_value_obligations(infcx, &result);
-            infcx.projection_cache.borrow_mut().insert_ty(cache_key, cache_value);
+            infcx.inner.borrow_mut().projection_cache.insert_ty(cache_key, cache_value);
             obligations.extend(result.obligations);
             Some(result.value)
         }
@@ -601,7 +601,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
                 projected_ty
             );
             let result = Normalized { value: projected_ty, obligations: vec![] };
-            infcx.projection_cache.borrow_mut().insert_ty(cache_key, result.clone());
+            infcx.inner.borrow_mut().projection_cache.insert_ty(cache_key, result.clone());
             // No need to extend `obligations`.
             Some(result.value)
         }
@@ -610,7 +610,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
                 "opt_normalize_projection_type: \
                     too many candidates"
             );
-            infcx.projection_cache.borrow_mut().ambiguous(cache_key);
+            infcx.inner.borrow_mut().projection_cache.ambiguous(cache_key);
             None
         }
         Err(ProjectionTyError::TraitSelectionError(_)) => {
@@ -620,7 +620,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             // Trait`, which when processed will cause the error to be
             // reported later
 
-            infcx.projection_cache.borrow_mut().error(cache_key);
+            infcx.inner.borrow_mut().projection_cache.error(cache_key);
             let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
             obligations.extend(result.obligations);
             Some(result.value)

src/librustc/traits/select.rs

@@ -511,7 +511,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         if let Some(key) =
                             ProjectionCacheKey::from_poly_projection_predicate(self, data)
                         {
-                            self.infcx.projection_cache.borrow_mut().complete(key);
+                            self.infcx.inner.borrow_mut().projection_cache.complete(key);
                         }
                         result
                     }

src/librustc_traits/chalk_context/resolvent_ops.rs

@@ -226,7 +226,9 @@ impl TypeRelation<'tcx> for AnswerSubstitutor<'cx, 'tcx> {
         let b = match b {
             &ty::ReVar(vid) => self
                 .infcx
-                .borrow_region_constraints()
+                .inner
+                .borrow_mut()
+                .unwrap_region_constraints()
                 .opportunistic_resolve_var(self.infcx.tcx, vid),
 
             other => other,