Auto merge of #52984 - fabric-and-ink:remove-canonical-var, r=scalexm

Replace CanonicalVar with DebruijnIndex

Close #49887

13 files changed, 65 insertions, 49 deletions

diff --git a/src/librustc/ich/impls_ty.rs b/src/librustc/ich/impls_ty.rs
index 2a3d40c0e3f..642eb110066 100644
--- a/src/librustc/ich/impls_ty.rs
+++ b/src/librustc/ich/impls_ty.rs
@@ -147,7 +147,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for ty::RegionVid {
     }
 }
 
-impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::CanonicalVar {
+impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::BoundTyIndex {
     #[inline]
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'gcx>,
@@ -915,7 +915,7 @@ impl_stable_hash_for!(enum ty::InferTy {
     FreshTy(a),
     FreshIntTy(a),
     FreshFloatTy(a),
-    CanonicalTy(a),
+    BoundTy(a),
 });
 
 impl<'a, 'gcx> HashStable<StableHashingContext<'a>>
diff --git a/src/librustc/infer/canonical/canonicalizer.rs b/src/librustc/infer/canonical/canonicalizer.rs
index 8c87c2a01c0..2b085a3407c 100644
--- a/src/librustc/infer/canonical/canonicalizer.rs
+++ b/src/librustc/infer/canonical/canonicalizer.rs
@@ -23,7 +23,7 @@ use infer::InferCtxt;
 use std::sync::atomic::Ordering;
 use ty::fold::{TypeFoldable, TypeFolder};
 use ty::subst::Kind;
-use ty::{self, CanonicalVar, Lift, List, Ty, TyCtxt, TypeFlags};
+use ty::{self, BoundTy, BoundTyIndex, Lift, List, Ty, TyCtxt, TypeFlags};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::indexed_vec::Idx;
@@ -225,7 +225,7 @@ struct Canonicalizer<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
     query_state: &'cx mut OriginalQueryValues<'tcx>,
     // Note that indices is only used once `var_values` is big enough to be
     // heap-allocated.
-    indices: FxHashMap<Kind<'tcx>, CanonicalVar>,
+    indices: FxHashMap<Kind<'tcx>, BoundTyIndex>,
     canonicalize_region_mode: &'cx dyn CanonicalizeRegionMode,
     needs_canonical_flags: TypeFlags,
 }
@@ -283,7 +283,7 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for Canonicalizer<'cx, 'gcx, 'tcx>
                 bug!("encountered a fresh type during canonicalization")
             }
 
-            ty::Infer(ty::CanonicalTy(_)) => {
+            ty::Infer(ty::BoundTy(_)) => {
                 bug!("encountered a canonical type during canonicalization")
             }
 
@@ -393,7 +393,7 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
     /// or returns an existing variable if `kind` has already been
     /// seen. `kind` is expected to be an unbound variable (or
     /// potentially a free region).
-    fn canonical_var(&mut self, info: CanonicalVarInfo, kind: Kind<'tcx>) -> CanonicalVar {
+    fn canonical_var(&mut self, info: CanonicalVarInfo, kind: Kind<'tcx>) -> BoundTy {
         let Canonicalizer {
             variables,
             query_state,
@@ -408,12 +408,12 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
         // avoid allocations in those cases. We also don't use `indices` to
         // determine if a kind has been seen before until the limit of 8 has
         // been exceeded, to also avoid allocations for `indices`.
-        if !var_values.spilled() {
+        let var = if !var_values.spilled() {
             // `var_values` is stack-allocated. `indices` isn't used yet. Do a
             // direct linear search of `var_values`.
             if let Some(idx) = var_values.iter().position(|&k| k == kind) {
                 // `kind` is already present in `var_values`.
-                CanonicalVar::new(idx)
+                BoundTyIndex::new(idx)
             } else {
                 // `kind` isn't present in `var_values`. Append it. Likewise
                 // for `info` and `variables`.
@@ -428,11 +428,11 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
                     *indices = var_values
                         .iter()
                         .enumerate()
-                        .map(|(i, &kind)| (kind, CanonicalVar::new(i)))
+                        .map(|(i, &kind)| (kind, BoundTyIndex::new(i)))
                         .collect();
                 }
                 // The cv is the index of the appended element.
-                CanonicalVar::new(var_values.len() - 1)
+                BoundTyIndex::new(var_values.len() - 1)
             }
         } else {
             // `var_values` is large. Do a hashmap search via `indices`.
@@ -440,8 +440,13 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
                 variables.push(info);
                 var_values.push(kind);
                 assert_eq!(variables.len(), var_values.len());
-                CanonicalVar::new(variables.len() - 1)
+                BoundTyIndex::new(variables.len() - 1)
             })
+        };
+
+        BoundTy {
+            level: ty::INNERMOST,
+            var,
         }
     }
 
@@ -449,8 +454,9 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
         let info = CanonicalVarInfo {
             kind: CanonicalVarKind::Region,
         };
-        let cvar = self.canonical_var(info, r.into());
-        self.tcx().mk_region(ty::ReCanonical(cvar))
+        let b = self.canonical_var(info, r.into());
+        debug_assert_eq!(ty::INNERMOST, b.level);
+        self.tcx().mk_region(ty::ReCanonical(b.var))
     }
 
     /// Given a type variable `ty_var` of the given kind, first check
@@ -466,8 +472,9 @@ impl<'cx, 'gcx, 'tcx> Canonicalizer<'cx, 'gcx, 'tcx> {
             let info = CanonicalVarInfo {
                 kind: CanonicalVarKind::Ty(ty_kind),
             };
-            let cvar = self.canonical_var(info, ty_var.into());
-            self.tcx().mk_infer(ty::InferTy::CanonicalTy(cvar))
+            let b = self.canonical_var(info, ty_var.into());
+            debug_assert_eq!(ty::INNERMOST, b.level);
+            self.tcx().mk_infer(ty::InferTy::BoundTy(b))
         }
     }
 }
diff --git a/src/librustc/infer/canonical/mod.rs b/src/librustc/infer/canonical/mod.rs
index 1863f08930f..e3bd407d17a 100644
--- a/src/librustc/infer/canonical/mod.rs
+++ b/src/librustc/infer/canonical/mod.rs
@@ -40,7 +40,7 @@ use std::ops::Index;
 use syntax::source_map::Span;
 use ty::fold::TypeFoldable;
 use ty::subst::Kind;
-use ty::{self, CanonicalVar, Lift, Region, List, TyCtxt};
+use ty::{self, BoundTyIndex, Lift, Region, List, TyCtxt};
 
 mod canonicalizer;
 
@@ -72,7 +72,7 @@ impl<'gcx> UseSpecializedDecodable for CanonicalVarInfos<'gcx> {}
 /// canonicalized query response.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub struct CanonicalVarValues<'tcx> {
-    pub var_values: IndexVec<CanonicalVar, Kind<'tcx>>,
+    pub var_values: IndexVec<BoundTyIndex, Kind<'tcx>>,
 }
 
 /// When we canonicalize a value to form a query, we wind up replacing
@@ -264,7 +264,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         span: Span,
         variables: &List<CanonicalVarInfo>,
     ) -> CanonicalVarValues<'tcx> {
-        let var_values: IndexVec<CanonicalVar, Kind<'tcx>> = variables
+        let var_values: IndexVec<BoundTyIndex, Kind<'tcx>> = variables
             .iter()
             .map(|info| self.fresh_inference_var_for_canonical_var(span, *info))
             .collect();
@@ -367,10 +367,10 @@ BraceStructLiftImpl! {
     } where R: Lift<'tcx>
 }
 
-impl<'tcx> Index<CanonicalVar> for CanonicalVarValues<'tcx> {
+impl<'tcx> Index<BoundTyIndex> for CanonicalVarValues<'tcx> {
     type Output = Kind<'tcx>;
 
-    fn index(&self, value: CanonicalVar) -> &Kind<'tcx> {
+    fn index(&self, value: BoundTyIndex) -> &Kind<'tcx> {
         &self.var_values[value]
     }
 }
diff --git a/src/librustc/infer/canonical/query_response.rs b/src/librustc/infer/canonical/query_response.rs
index b9edc9f51ea..38788186eb0 100644
--- a/src/librustc/infer/canonical/query_response.rs
+++ b/src/librustc/infer/canonical/query_response.rs
@@ -35,7 +35,7 @@ use traits::{FulfillmentContext, TraitEngine};
 use traits::{Obligation, ObligationCause, PredicateObligation};
 use ty::fold::TypeFoldable;
 use ty::subst::{Kind, UnpackedKind};
-use ty::{self, CanonicalVar, Lift, Ty, TyCtxt};
+use ty::{self, BoundTyIndex, Lift, Ty, TyCtxt};
 
 impl<'cx, 'gcx, 'tcx> InferCtxtBuilder<'cx, 'gcx, 'tcx> {
     /// The "main method" for a canonicalized trait query. Given the
@@ -273,7 +273,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         for (index, original_value) in original_values.var_values.iter().enumerate() {
             // ...with the value `v_r` of that variable from the query.
             let result_value = query_response.substitute_projected(self.tcx, &result_subst, |v| {
-                &v.var_values[CanonicalVar::new(index)]
+                &v.var_values[BoundTyIndex::new(index)]
             });
             match (original_value.unpack(), result_value.unpack()) {
                 (UnpackedKind::Lifetime(ty::ReErased), UnpackedKind::Lifetime(ty::ReErased)) => {
@@ -408,7 +408,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         // is directly equal to one of the canonical variables in the
         // result, then we can type the corresponding value from the
         // input. See the example above.
-        let mut opt_values: IndexVec<CanonicalVar, Option<Kind<'tcx>>> =
+        let mut opt_values: IndexVec<BoundTyIndex, Option<Kind<'tcx>>> =
             IndexVec::from_elem_n(None, query_response.variables.len());
 
         // In terms of our example above, we are iterating over pairs like:
@@ -417,9 +417,9 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
             match result_value.unpack() {
                 UnpackedKind::Type(result_value) => {
                     // e.g., here `result_value` might be `?0` in the example above...
-                    if let ty::Infer(ty::InferTy::CanonicalTy(index)) = result_value.sty {
+                    if let ty::Infer(ty::InferTy::BoundTy(b)) = result_value.sty {
                         // in which case we would set `canonical_vars[0]` to `Some(?U)`.
-                        opt_values[index] = Some(*original_value);
+                        opt_values[b.var] = Some(*original_value);
                     }
                 }
                 UnpackedKind::Lifetime(result_value) => {
@@ -440,7 +440,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                 .variables
                 .iter()
                 .enumerate()
-                .map(|(index, info)| opt_values[CanonicalVar::new(index)].unwrap_or_else(||
+                .map(|(index, info)| opt_values[BoundTyIndex::new(index)].unwrap_or_else(||
                     self.fresh_inference_var_for_canonical_var(cause.span, *info)
                 ))
                 .collect(),
@@ -470,7 +470,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         // canonical variable; this is taken from
         // `query_response.var_values` after applying the substitution
         // `result_subst`.
-        let substituted_query_response = |index: CanonicalVar| -> Kind<'tcx> {
+        let substituted_query_response = |index: BoundTyIndex| -> Kind<'tcx> {
             query_response.substitute_projected(self.tcx, &result_subst, |v| &v.var_values[index])
         };
 
@@ -526,12 +526,12 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         cause: &ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         variables1: &OriginalQueryValues<'tcx>,
-        variables2: impl Fn(CanonicalVar) -> Kind<'tcx>,
+        variables2: impl Fn(BoundTyIndex) -> Kind<'tcx>,
     ) -> InferResult<'tcx, ()> {
         self.commit_if_ok(|_| {
             let mut obligations = vec![];
             for (index, value1) in variables1.var_values.iter().enumerate() {
-                let value2 = variables2(CanonicalVar::new(index));
+                let value2 = variables2(BoundTyIndex::new(index));
 
                 match (value1.unpack(), value2.unpack()) {
                     (UnpackedKind::Type(v1), UnpackedKind::Type(v2)) => {
diff --git a/src/librustc/infer/canonical/substitute.rs b/src/librustc/infer/canonical/substitute.rs
index f3fe01d5fd1..03441c3dee3 100644
--- a/src/librustc/infer/canonical/substitute.rs
+++ b/src/librustc/infer/canonical/substitute.rs
@@ -85,10 +85,11 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for CanonicalVarValuesSubst<'cx, 'g
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
         match t.sty {
-            ty::Infer(ty::InferTy::CanonicalTy(c)) => {
-                match self.var_values.var_values[c].unpack() {
+            ty::Infer(ty::InferTy::BoundTy(b)) => {
+                debug_assert_eq!(ty::INNERMOST, b.level);
+                match self.var_values.var_values[b.var].unpack() {
                     UnpackedKind::Type(ty) => ty,
-                    r => bug!("{:?} is a type but value is {:?}", c, r),
+                    r => bug!("{:?} is a type but value is {:?}", b, r),
                 }
             }
             _ => {
diff --git a/src/librustc/infer/freshen.rs b/src/librustc/infer/freshen.rs
index c7785d83171..1647f259db9 100644
--- a/src/librustc/infer/freshen.rs
+++ b/src/librustc/infer/freshen.rs
@@ -171,7 +171,7 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
                 t
             }
 
-            ty::Infer(ty::CanonicalTy(..)) =>
+            ty::Infer(ty::BoundTy(..)) =>
                 bug!("encountered canonical ty during freshening"),
 
             ty::Generator(..) |
diff --git a/src/librustc/traits/select.rs b/src/librustc/traits/select.rs
index 39c623de677..49f37179354 100644
--- a/src/librustc/traits/select.rs
+++ b/src/librustc/traits/select.rs
@@ -2421,7 +2421,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             ty::Infer(ty::TyVar(_)) => Ambiguous,
 
             ty::UnnormalizedProjection(..)
-            | ty::Infer(ty::CanonicalTy(_))
+            | ty::Infer(ty::BoundTy(_))
             | ty::Infer(ty::FreshTy(_))
             | ty::Infer(ty::FreshIntTy(_))
             | ty::Infer(ty::FreshFloatTy(_)) => {
@@ -2506,7 +2506,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             }
 
             ty::UnnormalizedProjection(..)
-            | ty::Infer(ty::CanonicalTy(_))
+            | ty::Infer(ty::BoundTy(_))
             | ty::Infer(ty::FreshTy(_))
             | ty::Infer(ty::FreshIntTy(_))
             | ty::Infer(ty::FreshFloatTy(_)) => {
@@ -2549,7 +2549,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             | ty::Param(..)
             | ty::Foreign(..)
             | ty::Projection(..)
-            | ty::Infer(ty::CanonicalTy(_))
+            | ty::Infer(ty::BoundTy(_))
             | ty::Infer(ty::TyVar(_))
             | ty::Infer(ty::FreshTy(_))
             | ty::Infer(ty::FreshIntTy(_))
diff --git a/src/librustc/ty/error.rs b/src/librustc/ty/error.rs
index d886d5ed204..ed6e372fe76 100644
--- a/src/librustc/ty/error.rs
+++ b/src/librustc/ty/error.rs
@@ -217,7 +217,7 @@ impl<'a, 'gcx, 'lcx, 'tcx> ty::TyS<'tcx> {
             ty::Infer(ty::TyVar(_)) => "inferred type".into(),
             ty::Infer(ty::IntVar(_)) => "integral variable".into(),
             ty::Infer(ty::FloatVar(_)) => "floating-point variable".into(),
-            ty::Infer(ty::CanonicalTy(_)) |
+            ty::Infer(ty::BoundTy(_)) |
             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
diff --git a/src/librustc/ty/flags.rs b/src/librustc/ty/flags.rs
index 10a90dfc8a8..a7b21688fbe 100644
--- a/src/librustc/ty/flags.rs
+++ b/src/librustc/ty/flags.rs
@@ -122,7 +122,7 @@ impl FlagComputation {
                     ty::FreshTy(_) |
                     ty::FreshIntTy(_) |
                     ty::FreshFloatTy(_) |
-                    ty::CanonicalTy(_) => {
+                    ty::BoundTy(_) => {
                         self.add_flags(TypeFlags::HAS_CANONICAL_VARS);
                     }
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 760114a5838..5602ce479c8 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -63,7 +63,7 @@ use rustc_data_structures::stable_hasher::{StableHasher, StableHasherResult,
 
 use hir;
 
-pub use self::sty::{Binder, CanonicalVar, DebruijnIndex, INNERMOST};
+pub use self::sty::{Binder, BoundTy, BoundTyIndex, DebruijnIndex, INNERMOST};
 pub use self::sty::{FnSig, GenSig, PolyFnSig, PolyGenSig};
 pub use self::sty::{InferTy, ParamTy, ProjectionTy, ExistentialPredicate};
 pub use self::sty::{ClosureSubsts, GeneratorSubsts, UpvarSubsts, TypeAndMut};
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index cc6e6b2861e..82891583870 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -1165,7 +1165,7 @@ pub enum RegionKind {
     ReClosureBound(RegionVid),
 
     /// Canonicalized region, used only when preparing a trait query.
-    ReCanonical(CanonicalVar),
+    ReCanonical(BoundTyIndex),
 }
 
 impl<'tcx> serialize::UseSpecializedDecodable for Region<'tcx> {}
@@ -1217,14 +1217,22 @@ pub enum InferTy {
     FreshIntTy(u32),
     FreshFloatTy(u32),
 
-    /// Canonicalized type variable, used only when preparing a trait query.
-    CanonicalTy(CanonicalVar),
+    /// Bound type variable, used only when preparing a trait query.
+    BoundTy(BoundTy),
 }
 
 newtype_index! {
-    pub struct CanonicalVar { .. }
+    pub struct BoundTyIndex { .. }
 }
 
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
+pub struct BoundTy {
+    pub level: DebruijnIndex,
+    pub var: BoundTyIndex,
+}
+
+impl_stable_hash_for!(struct BoundTy { level, var });
+
 /// A `ProjectionPredicate` for an `ExistentialTraitRef`.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 pub struct ExistentialProjection<'tcx> {
@@ -1919,7 +1927,7 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
 
             ty::Infer(ty::TyVar(_)) => false,
 
-            ty::Infer(ty::CanonicalTy(_)) |
+            ty::Infer(ty::BoundTy(_)) |
             ty::Infer(ty::FreshTy(_)) |
             ty::Infer(ty::FreshIntTy(_)) |
             ty::Infer(ty::FreshFloatTy(_)) =>
diff --git a/src/librustc/ty/subst.rs b/src/librustc/ty/subst.rs
index 64cfba7df6e..02b5d36ecce 100644
--- a/src/librustc/ty/subst.rs
+++ b/src/librustc/ty/subst.rs
@@ -12,7 +12,7 @@
 
 use hir::def_id::DefId;
 use infer::canonical::Canonical;
-use ty::{self, CanonicalVar, Lift, List, Ty, TyCtxt};
+use ty::{self, BoundTyIndex, Lift, List, Ty, TyCtxt};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 
 use serialize::{self, Encodable, Encoder, Decodable, Decoder};
@@ -553,10 +553,10 @@ impl CanonicalUserSubsts<'tcx> {
             return false;
         }
 
-        self.value.substs.iter().zip(CanonicalVar::new(0)..).all(|(kind, cvar)| {
+        self.value.substs.iter().zip(BoundTyIndex::new(0)..).all(|(kind, cvar)| {
             match kind.unpack() {
                 UnpackedKind::Type(ty) => match ty.sty {
-                    ty::Infer(ty::CanonicalTy(cvar1)) => cvar == cvar1,
+                    ty::Infer(ty::BoundTy(ref b)) => cvar == b.var,
                     _ => false,
                 },
 
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index bfa2203cc04..709b8445265 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -984,7 +984,7 @@ define_print! {
                     ty::TyVar(_) => write!(f, "_"),
                     ty::IntVar(_) => write!(f, "{}", "{integer}"),
                     ty::FloatVar(_) => write!(f, "{}", "{float}"),
-                    ty::CanonicalTy(_) => write!(f, "_"),
+                    ty::BoundTy(_) => write!(f, "_"),
                     ty::FreshTy(v) => write!(f, "FreshTy({})", v),
                     ty::FreshIntTy(v) => write!(f, "FreshIntTy({})", v),
                     ty::FreshFloatTy(v) => write!(f, "FreshFloatTy({})", v)
@@ -996,7 +996,7 @@ define_print! {
                 ty::TyVar(ref v) => write!(f, "{:?}", v),
                 ty::IntVar(ref v) => write!(f, "{:?}", v),
                 ty::FloatVar(ref v) => write!(f, "{:?}", v),
-                ty::CanonicalTy(v) => write!(f, "?{:?}", v.index()),
+                ty::BoundTy(v) => write!(f, "?{:?}", v.var.index()),
                 ty::FreshTy(v) => write!(f, "FreshTy({:?})", v),
                 ty::FreshIntTy(v) => write!(f, "FreshIntTy({:?})", v),
                 ty::FreshFloatTy(v) => write!(f, "FreshFloatTy({:?})", v)