diff --git a/compiler/rustc_macros/src/serialize.rs b/compiler/rustc_macros/src/serialize.rs
index ba75517d7a66d..047066ac6815e 100644
--- a/compiler/rustc_macros/src/serialize.rs
+++ b/compiler/rustc_macros/src/serialize.rs
@@ -5,11 +5,16 @@ use syn::spanned::Spanned;
 
 pub fn type_decodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let decoder_ty = quote! { __D };
-    if !s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
-        s.add_impl_generic(parse_quote! { 'tcx });
-    }
-    s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_type_ir::codec::TyDecoder<I = ::rustc_middle::ty::TyCtxt<'tcx>>});
-    s.add_bounds(synstructure::AddBounds::Generics);
+    let bound = if s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
+        quote! { <I = ::rustc_middle::ty::TyCtxt<'tcx>> }
+    } else if s.ast().generics.type_params().any(|ty| ty.ident == "I") {
+        quote! { <I = I> }
+    } else {
+        quote! {}
+    };
+
+    s.add_impl_generic(parse_quote! {#decoder_ty: ::rustc_type_ir::codec::TyDecoder #bound });
+    s.add_bounds(synstructure::AddBounds::Fields);
 
     decodable_body(s, decoder_ty)
 }
@@ -97,12 +102,17 @@ fn decode_field(field: &syn::Field) -> proc_macro2::TokenStream {
 }
 
 pub fn type_encodable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
-    if !s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
-        s.add_impl_generic(parse_quote! {'tcx});
-    }
+    let bound = if s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
+        quote! { <I = ::rustc_middle::ty::TyCtxt<'tcx>> }
+    } else if s.ast().generics.type_params().any(|ty| ty.ident == "I") {
+        quote! { <I = I> }
+    } else {
+        quote! {}
+    };
+
     let encoder_ty = quote! { __E };
-    s.add_impl_generic(parse_quote! {#encoder_ty: ::rustc_type_ir::codec::TyEncoder<I = ::rustc_middle::ty::TyCtxt<'tcx>>});
-    s.add_bounds(synstructure::AddBounds::Generics);
+    s.add_impl_generic(parse_quote! {#encoder_ty: ::rustc_type_ir::codec::TyEncoder #bound });
+    s.add_bounds(synstructure::AddBounds::Fields);
 
     encodable_body(s, encoder_ty, false)
 }
diff --git a/compiler/rustc_type_ir/src/canonical.rs b/compiler/rustc_type_ir/src/canonical.rs
index c8e730b585ad9..ace9eade7f69b 100644
--- a/compiler/rustc_type_ir/src/canonical.rs
+++ b/compiler/rustc_type_ir/src/canonical.rs
@@ -3,18 +3,17 @@ use std::hash::Hash;
 use std::ops::ControlFlow;
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_serialize::{Decodable, Encodable};
 
 use crate::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::visit::{TypeVisitable, TypeVisitor};
-use crate::TyDecoder;
-use crate::{HashStableContext, Interner, TyEncoder, UniverseIndex};
+use crate::{HashStableContext, Interner, UniverseIndex};
 
 /// A "canonicalized" type `V` is one where all free inference
 /// variables have been rewritten to "canonical vars". These are
 /// numbered starting from 0 in order of first appearance.
 #[derive(derivative::Derivative)]
 #[derivative(Clone(bound = "V: Clone"), Hash(bound = "V: Hash"))]
+#[derive(TyEncodable, TyDecodable)]
 pub struct Canonical<I: Interner, V> {
     pub value: V,
     pub max_universe: UniverseIndex,
@@ -127,27 +126,3 @@ where
         self.variables.visit_with(folder)
     }
 }
-
-impl<I: Interner, E: TyEncoder<I = I>, V: Encodable<E>> Encodable<E> for Canonical<I, V>
-where
-    I::CanonicalVars: Encodable<E>,
-{
-    fn encode(&self, s: &mut E) {
-        self.value.encode(s);
-        self.max_universe.encode(s);
-        self.variables.encode(s);
-    }
-}
-
-impl<I: Interner, D: TyDecoder<I = I>, V: Decodable<D>> Decodable<D> for Canonical<I, V>
-where
-    I::CanonicalVars: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        Canonical {
-            value: Decodable::decode(d),
-            max_universe: Decodable::decode(d),
-            variables: Decodable::decode(d),
-        }
-    }
-}
diff --git a/compiler/rustc_type_ir/src/const_kind.rs b/compiler/rustc_type_ir/src/const_kind.rs
index cf67ba0b21a1a..33782b13ca8f5 100644
--- a/compiler/rustc_type_ir/src/const_kind.rs
+++ b/compiler/rustc_type_ir/src/const_kind.rs
@@ -1,12 +1,8 @@
 use rustc_data_structures::stable_hasher::HashStable;
 use rustc_data_structures::stable_hasher::StableHasher;
-use rustc_serialize::{Decodable, Decoder, Encodable};
 use std::fmt;
 
-use crate::{
-    DebruijnIndex, DebugWithInfcx, HashStableContext, InferCtxtLike, Interner, TyDecoder,
-    TyEncoder, WithInfcx,
-};
+use crate::{DebruijnIndex, DebugWithInfcx, HashStableContext, InferCtxtLike, Interner, WithInfcx};
 
 use self::ConstKind::*;
 
@@ -20,6 +16,7 @@ use self::ConstKind::*;
     Ord = "feature_allow_slow_enum",
     Hash(bound = "")
 )]
+#[derive(TyEncodable, TyDecodable)]
 pub enum ConstKind<I: Interner> {
     /// A const generic parameter.
     Param(I::ParamConst),
@@ -92,67 +89,6 @@ where
     }
 }
 
-impl<I: Interner, D: TyDecoder<I = I>> Decodable<D> for ConstKind<I>
-where
-    I::ParamConst: Decodable<D>,
-    I::InferConst: Decodable<D>,
-    I::BoundConst: Decodable<D>,
-    I::PlaceholderConst: Decodable<D>,
-    I::AliasConst: Decodable<D>,
-    I::ValueConst: Decodable<D>,
-    I::ErrorGuaranteed: Decodable<D>,
-    I::ExprConst: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        match Decoder::read_usize(d) {
-            0 => Param(Decodable::decode(d)),
-            1 => Infer(Decodable::decode(d)),
-            2 => Bound(Decodable::decode(d), Decodable::decode(d)),
-            3 => Placeholder(Decodable::decode(d)),
-            4 => Unevaluated(Decodable::decode(d)),
-            5 => Value(Decodable::decode(d)),
-            6 => Error(Decodable::decode(d)),
-            7 => Expr(Decodable::decode(d)),
-            _ => panic!(
-                "{}",
-                format!(
-                    "invalid enum variant tag while decoding `{}`, expected 0..{}",
-                    "ConstKind", 8,
-                )
-            ),
-        }
-    }
-}
-
-impl<I: Interner, E: TyEncoder<I = I>> Encodable<E> for ConstKind<I>
-where
-    I::ParamConst: Encodable<E>,
-    I::InferConst: Encodable<E>,
-    I::BoundConst: Encodable<E>,
-    I::PlaceholderConst: Encodable<E>,
-    I::AliasConst: Encodable<E>,
-    I::ValueConst: Encodable<E>,
-    I::ErrorGuaranteed: Encodable<E>,
-    I::ExprConst: Encodable<E>,
-{
-    fn encode(&self, e: &mut E) {
-        let disc = const_kind_discriminant(self);
-        match self {
-            Param(p) => e.emit_enum_variant(disc, |e| p.encode(e)),
-            Infer(i) => e.emit_enum_variant(disc, |e| i.encode(e)),
-            Bound(d, b) => e.emit_enum_variant(disc, |e| {
-                d.encode(e);
-                b.encode(e);
-            }),
-            Placeholder(p) => e.emit_enum_variant(disc, |e| p.encode(e)),
-            Unevaluated(u) => e.emit_enum_variant(disc, |e| u.encode(e)),
-            Value(v) => e.emit_enum_variant(disc, |e| v.encode(e)),
-            Error(er) => e.emit_enum_variant(disc, |e| er.encode(e)),
-            Expr(ex) => e.emit_enum_variant(disc, |e| ex.encode(e)),
-        }
-    }
-}
-
 impl<I: Interner> PartialEq for ConstKind<I> {
     fn eq(&self, other: &Self) -> bool {
         match (self, other) {
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index a056fbeda9811..e8785fff2efcd 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -10,6 +10,8 @@
 #![deny(rustc::diagnostic_outside_of_impl)]
 #![allow(internal_features)]
 
+extern crate self as rustc_type_ir;
+
 #[macro_use]
 extern crate bitflags;
 #[macro_use]
diff --git a/compiler/rustc_type_ir/src/predicate_kind.rs b/compiler/rustc_type_ir/src/predicate_kind.rs
index 23117fdd53109..48662d4264235 100644
--- a/compiler/rustc_type_ir/src/predicate_kind.rs
+++ b/compiler/rustc_type_ir/src/predicate_kind.rs
@@ -1,18 +1,16 @@
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-use rustc_serialize::Decoder;
-use rustc_serialize::{Decodable, Encodable};
 use std::fmt;
 use std::ops::ControlFlow;
 
 use crate::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::visit::{TypeVisitable, TypeVisitor};
 use crate::{HashStableContext, Interner};
-use crate::{TyDecoder, TyEncoder};
 
 /// A clause is something that can appear in where bounds or be inferred
 /// by implied bounds.
 #[derive(derivative::Derivative)]
 #[derivative(Clone(bound = ""), Hash(bound = ""))]
+#[derive(TyEncodable, TyDecodable)]
 pub enum ClauseKind<I: Interner> {
     /// Corresponds to `where Foo: Bar<A, B, C>`. `Foo` here would be
     /// the `Self` type of the trait reference and `A`, `B`, and `C`
@@ -161,65 +159,9 @@ where
     }
 }
 
-impl<I: Interner, D: TyDecoder<I = I>> Decodable<D> for ClauseKind<I>
-where
-    I::Ty: Decodable<D>,
-    I::Const: Decodable<D>,
-    I::GenericArg: Decodable<D>,
-    I::TraitPredicate: Decodable<D>,
-    I::ProjectionPredicate: Decodable<D>,
-    I::TypeOutlivesPredicate: Decodable<D>,
-    I::RegionOutlivesPredicate: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        match Decoder::read_usize(d) {
-            0 => ClauseKind::Trait(Decodable::decode(d)),
-            1 => ClauseKind::RegionOutlives(Decodable::decode(d)),
-            2 => ClauseKind::TypeOutlives(Decodable::decode(d)),
-            3 => ClauseKind::Projection(Decodable::decode(d)),
-            4 => ClauseKind::ConstArgHasType(Decodable::decode(d), Decodable::decode(d)),
-            5 => ClauseKind::WellFormed(Decodable::decode(d)),
-            6 => ClauseKind::ConstEvaluatable(Decodable::decode(d)),
-            _ => panic!(
-                "{}",
-                format!(
-                    "invalid enum variant tag while decoding `{}`, expected 0..{}",
-                    "ClauseKind", 7,
-                )
-            ),
-        }
-    }
-}
-
-impl<I: Interner, E: TyEncoder> Encodable<E> for ClauseKind<I>
-where
-    I::Ty: Encodable<E>,
-    I::Const: Encodable<E>,
-    I::GenericArg: Encodable<E>,
-    I::TraitPredicate: Encodable<E>,
-    I::ProjectionPredicate: Encodable<E>,
-    I::TypeOutlivesPredicate: Encodable<E>,
-    I::RegionOutlivesPredicate: Encodable<E>,
-{
-    fn encode(&self, s: &mut E) {
-        let discriminant = clause_kind_discriminant(self);
-        match self {
-            ClauseKind::Trait(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-            ClauseKind::RegionOutlives(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-            ClauseKind::TypeOutlives(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-            ClauseKind::Projection(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-            ClauseKind::ConstArgHasType(c, t) => s.emit_enum_variant(discriminant, |s| {
-                c.encode(s);
-                t.encode(s);
-            }),
-            ClauseKind::WellFormed(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-            ClauseKind::ConstEvaluatable(p) => s.emit_enum_variant(discriminant, |s| p.encode(s)),
-        }
-    }
-}
-
 #[derive(derivative::Derivative)]
 #[derivative(Clone(bound = ""), Hash(bound = ""))]
+#[derive(TyEncodable, TyDecodable)]
 pub enum PredicateKind<I: Interner> {
     /// Prove a clause
     Clause(ClauseKind<I>),
@@ -418,83 +360,6 @@ where
     }
 }
 
-impl<I: Interner, D: TyDecoder<I = I>> Decodable<D> for PredicateKind<I>
-where
-    I::DefId: Decodable<D>,
-    I::Const: Decodable<D>,
-    I::GenericArgs: Decodable<D>,
-    I::Term: Decodable<D>,
-    I::CoercePredicate: Decodable<D>,
-    I::SubtypePredicate: Decodable<D>,
-    I::ClosureKind: Decodable<D>,
-    ClauseKind<I>: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        match Decoder::read_usize(d) {
-            0 => PredicateKind::Clause(Decodable::decode(d)),
-            1 => PredicateKind::ObjectSafe(Decodable::decode(d)),
-            2 => PredicateKind::ClosureKind(
-                Decodable::decode(d),
-                Decodable::decode(d),
-                Decodable::decode(d),
-            ),
-            3 => PredicateKind::Subtype(Decodable::decode(d)),
-            4 => PredicateKind::Coerce(Decodable::decode(d)),
-            5 => PredicateKind::ConstEquate(Decodable::decode(d), Decodable::decode(d)),
-            6 => PredicateKind::Ambiguous,
-            7 => PredicateKind::AliasRelate(
-                Decodable::decode(d),
-                Decodable::decode(d),
-                Decodable::decode(d),
-            ),
-            _ => panic!(
-                "{}",
-                format!(
-                    "invalid enum variant tag while decoding `{}`, expected 0..{}",
-                    "PredicateKind", 8,
-                )
-            ),
-        }
-    }
-}
-
-impl<I: Interner, E: TyEncoder> Encodable<E> for PredicateKind<I>
-where
-    I::DefId: Encodable<E>,
-    I::Const: Encodable<E>,
-    I::GenericArgs: Encodable<E>,
-    I::Term: Encodable<E>,
-    I::CoercePredicate: Encodable<E>,
-    I::SubtypePredicate: Encodable<E>,
-    I::ClosureKind: Encodable<E>,
-    ClauseKind<I>: Encodable<E>,
-{
-    fn encode(&self, s: &mut E) {
-        let discriminant = predicate_kind_discriminant(self);
-        match self {
-            PredicateKind::Clause(c) => s.emit_enum_variant(discriminant, |s| c.encode(s)),
-            PredicateKind::ObjectSafe(d) => s.emit_enum_variant(discriminant, |s| d.encode(s)),
-            PredicateKind::ClosureKind(d, g, k) => s.emit_enum_variant(discriminant, |s| {
-                d.encode(s);
-                g.encode(s);
-                k.encode(s);
-            }),
-            PredicateKind::Subtype(c) => s.emit_enum_variant(discriminant, |s| c.encode(s)),
-            PredicateKind::Coerce(c) => s.emit_enum_variant(discriminant, |s| c.encode(s)),
-            PredicateKind::ConstEquate(a, b) => s.emit_enum_variant(discriminant, |s| {
-                a.encode(s);
-                b.encode(s);
-            }),
-            PredicateKind::Ambiguous => s.emit_enum_variant(discriminant, |_s| {}),
-            PredicateKind::AliasRelate(a, b, d) => s.emit_enum_variant(discriminant, |s| {
-                a.encode(s);
-                b.encode(s);
-                d.encode(s);
-            }),
-        }
-    }
-}
-
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Copy)]
 #[derive(HashStable_Generic, Encodable, Decodable)]
 pub enum AliasRelationDirection {
diff --git a/compiler/rustc_type_ir/src/region_kind.rs b/compiler/rustc_type_ir/src/region_kind.rs
index 72f86fc069299..69ed5badaea38 100644
--- a/compiler/rustc_type_ir/src/region_kind.rs
+++ b/compiler/rustc_type_ir/src/region_kind.rs
@@ -1,12 +1,8 @@
 use rustc_data_structures::stable_hasher::HashStable;
 use rustc_data_structures::stable_hasher::StableHasher;
-use rustc_serialize::{Decodable, Decoder, Encodable};
 use std::fmt;
 
-use crate::{
-    DebruijnIndex, DebugWithInfcx, HashStableContext, InferCtxtLike, Interner, TyDecoder,
-    TyEncoder, WithInfcx,
-};
+use crate::{DebruijnIndex, DebugWithInfcx, HashStableContext, InferCtxtLike, Interner, WithInfcx};
 
 use self::RegionKind::*;
 
@@ -125,6 +121,7 @@ use self::RegionKind::*;
     Ord = "feature_allow_slow_enum",
     Hash(bound = "")
 )]
+#[derive(TyEncodable, TyDecodable)]
 pub enum RegionKind<I: Interner> {
     /// Region bound in a type or fn declaration which will be
     /// substituted 'early' -- that is, at the same time when type
@@ -245,72 +242,6 @@ impl<I: Interner> fmt::Debug for RegionKind<I> {
     }
 }
 
-// This is manually implemented because a derive would require `I: Encodable`
-impl<I: Interner, E: TyEncoder<I = I>> Encodable<E> for RegionKind<I>
-where
-    I::EarlyBoundRegion: Encodable<E>,
-    I::BoundRegion: Encodable<E>,
-    I::FreeRegion: Encodable<E>,
-    I::InferRegion: Encodable<E>,
-    I::PlaceholderRegion: Encodable<E>,
-{
-    fn encode(&self, e: &mut E) {
-        let disc = regionkind_discriminant(self);
-        match self {
-            ReEarlyBound(a) => e.emit_enum_variant(disc, |e| {
-                a.encode(e);
-            }),
-            ReLateBound(a, b) => e.emit_enum_variant(disc, |e| {
-                a.encode(e);
-                b.encode(e);
-            }),
-            ReFree(a) => e.emit_enum_variant(disc, |e| {
-                a.encode(e);
-            }),
-            ReStatic => e.emit_enum_variant(disc, |_| {}),
-            ReVar(a) => e.emit_enum_variant(disc, |e| {
-                a.encode(e);
-            }),
-            RePlaceholder(a) => e.emit_enum_variant(disc, |e| {
-                a.encode(e);
-            }),
-            ReErased => e.emit_enum_variant(disc, |_| {}),
-            ReError(_) => e.emit_enum_variant(disc, |_| {}),
-        }
-    }
-}
-
-// This is manually implemented because a derive would require `I: Decodable`
-impl<I: Interner, D: TyDecoder<I = I>> Decodable<D> for RegionKind<I>
-where
-    I::EarlyBoundRegion: Decodable<D>,
-    I::BoundRegion: Decodable<D>,
-    I::FreeRegion: Decodable<D>,
-    I::InferRegion: Decodable<D>,
-    I::PlaceholderRegion: Decodable<D>,
-    I::ErrorGuaranteed: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        match Decoder::read_usize(d) {
-            0 => ReEarlyBound(Decodable::decode(d)),
-            1 => ReLateBound(Decodable::decode(d), Decodable::decode(d)),
-            2 => ReFree(Decodable::decode(d)),
-            3 => ReStatic,
-            4 => ReVar(Decodable::decode(d)),
-            5 => RePlaceholder(Decodable::decode(d)),
-            6 => ReErased,
-            7 => ReError(Decodable::decode(d)),
-            _ => panic!(
-                "{}",
-                format!(
-                    "invalid enum variant tag while decoding `{}`, expected 0..{}",
-                    "RegionKind", 8,
-                )
-            ),
-        }
-    }
-}
-
 // This is not a derived impl because a derive would require `I: HashStable`
 impl<CTX: HashStableContext, I: Interner> HashStable<CTX> for RegionKind<I>
 where
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 2138c27334134..09a9a332269ef 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -2,14 +2,11 @@
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::unify::{EqUnifyValue, UnifyKey};
-use rustc_serialize::{Decodable, Decoder, Encodable};
 use std::fmt;
 use std::mem::discriminant;
 
 use crate::HashStableContext;
 use crate::Interner;
-use crate::TyDecoder;
-use crate::TyEncoder;
 use crate::{DebruijnIndex, DebugWithInfcx, InferCtxtLike, WithInfcx};
 
 use self::TyKind::*;
@@ -122,6 +119,7 @@ pub enum AliasKind {
     Ord = "feature_allow_slow_enum",
     Hash(bound = "")
 )]
+#[derive(TyEncodable, TyDecodable)]
 pub enum TyKind<I: Interner> {
     /// The primitive boolean type. Written as `bool`.
     Bool,
@@ -472,178 +470,6 @@ impl<I: Interner> fmt::Debug for TyKind<I> {
     }
 }
 
-// This is manually implemented because a derive would require `I: Encodable`
-impl<I: Interner, E: TyEncoder<I = I>> Encodable<E> for TyKind<I>
-where
-    I::ErrorGuaranteed: Encodable<E>,
-    I::AdtDef: Encodable<E>,
-    I::GenericArgs: Encodable<E>,
-    I::DefId: Encodable<E>,
-    I::Ty: Encodable<E>,
-    I::Const: Encodable<E>,
-    I::Region: Encodable<E>,
-    I::TypeAndMut: Encodable<E>,
-    I::PolyFnSig: Encodable<E>,
-    I::BoundExistentialPredicates: Encodable<E>,
-    I::Tys: Encodable<E>,
-    I::AliasTy: Encodable<E>,
-    I::ParamTy: Encodable<E>,
-    I::BoundTy: Encodable<E>,
-    I::PlaceholderTy: Encodable<E>,
-    I::InferTy: Encodable<E>,
-    I::AllocId: Encodable<E>,
-{
-    fn encode(&self, e: &mut E) {
-        let disc = tykind_discriminant(self);
-        match self {
-            Bool => e.emit_enum_variant(disc, |_| {}),
-            Char => e.emit_enum_variant(disc, |_| {}),
-            Int(i) => e.emit_enum_variant(disc, |e| {
-                i.encode(e);
-            }),
-            Uint(u) => e.emit_enum_variant(disc, |e| {
-                u.encode(e);
-            }),
-            Float(f) => e.emit_enum_variant(disc, |e| {
-                f.encode(e);
-            }),
-            Adt(adt, args) => e.emit_enum_variant(disc, |e| {
-                adt.encode(e);
-                args.encode(e);
-            }),
-            Foreign(def_id) => e.emit_enum_variant(disc, |e| {
-                def_id.encode(e);
-            }),
-            Str => e.emit_enum_variant(disc, |_| {}),
-            Array(t, c) => e.emit_enum_variant(disc, |e| {
-                t.encode(e);
-                c.encode(e);
-            }),
-            Slice(t) => e.emit_enum_variant(disc, |e| {
-                t.encode(e);
-            }),
-            RawPtr(tam) => e.emit_enum_variant(disc, |e| {
-                tam.encode(e);
-            }),
-            Ref(r, t, m) => e.emit_enum_variant(disc, |e| {
-                r.encode(e);
-                t.encode(e);
-                m.encode(e);
-            }),
-            FnDef(def_id, args) => e.emit_enum_variant(disc, |e| {
-                def_id.encode(e);
-                args.encode(e);
-            }),
-            FnPtr(polyfnsig) => e.emit_enum_variant(disc, |e| {
-                polyfnsig.encode(e);
-            }),
-            Dynamic(l, r, repr) => e.emit_enum_variant(disc, |e| {
-                l.encode(e);
-                r.encode(e);
-                repr.encode(e);
-            }),
-            Closure(def_id, args) => e.emit_enum_variant(disc, |e| {
-                def_id.encode(e);
-                args.encode(e);
-            }),
-            Coroutine(def_id, args, m) => e.emit_enum_variant(disc, |e| {
-                def_id.encode(e);
-                args.encode(e);
-                m.encode(e);
-            }),
-            CoroutineWitness(def_id, args) => e.emit_enum_variant(disc, |e| {
-                def_id.encode(e);
-                args.encode(e);
-            }),
-            Never => e.emit_enum_variant(disc, |_| {}),
-            Tuple(args) => e.emit_enum_variant(disc, |e| {
-                args.encode(e);
-            }),
-            Alias(k, p) => e.emit_enum_variant(disc, |e| {
-                k.encode(e);
-                p.encode(e);
-            }),
-            Param(p) => e.emit_enum_variant(disc, |e| {
-                p.encode(e);
-            }),
-            Bound(d, b) => e.emit_enum_variant(disc, |e| {
-                d.encode(e);
-                b.encode(e);
-            }),
-            Placeholder(p) => e.emit_enum_variant(disc, |e| {
-                p.encode(e);
-            }),
-            Infer(i) => e.emit_enum_variant(disc, |e| {
-                i.encode(e);
-            }),
-            Error(d) => e.emit_enum_variant(disc, |e| {
-                d.encode(e);
-            }),
-        }
-    }
-}
-
-// This is manually implemented because a derive would require `I: Decodable`
-impl<I: Interner, D: TyDecoder<I = I>> Decodable<D> for TyKind<I>
-where
-    I::ErrorGuaranteed: Decodable<D>,
-    I::AdtDef: Decodable<D>,
-    I::GenericArgs: Decodable<D>,
-    I::DefId: Decodable<D>,
-    I::Ty: Decodable<D>,
-    I::Const: Decodable<D>,
-    I::Region: Decodable<D>,
-    I::TypeAndMut: Decodable<D>,
-    I::PolyFnSig: Decodable<D>,
-    I::BoundExistentialPredicates: Decodable<D>,
-    I::Tys: Decodable<D>,
-    I::AliasTy: Decodable<D>,
-    I::ParamTy: Decodable<D>,
-    I::AliasTy: Decodable<D>,
-    I::BoundTy: Decodable<D>,
-    I::PlaceholderTy: Decodable<D>,
-    I::InferTy: Decodable<D>,
-    I::AllocId: Decodable<D>,
-{
-    fn decode(d: &mut D) -> Self {
-        match Decoder::read_usize(d) {
-            0 => Bool,
-            1 => Char,
-            2 => Int(Decodable::decode(d)),
-            3 => Uint(Decodable::decode(d)),
-            4 => Float(Decodable::decode(d)),
-            5 => Adt(Decodable::decode(d), Decodable::decode(d)),
-            6 => Foreign(Decodable::decode(d)),
-            7 => Str,
-            8 => Array(Decodable::decode(d), Decodable::decode(d)),
-            9 => Slice(Decodable::decode(d)),
-            10 => RawPtr(Decodable::decode(d)),
-            11 => Ref(Decodable::decode(d), Decodable::decode(d), Decodable::decode(d)),
-            12 => FnDef(Decodable::decode(d), Decodable::decode(d)),
-            13 => FnPtr(Decodable::decode(d)),
-            14 => Dynamic(Decodable::decode(d), Decodable::decode(d), Decodable::decode(d)),
-            15 => Closure(Decodable::decode(d), Decodable::decode(d)),
-            16 => Coroutine(Decodable::decode(d), Decodable::decode(d), Decodable::decode(d)),
-            17 => CoroutineWitness(Decodable::decode(d), Decodable::decode(d)),
-            18 => Never,
-            19 => Tuple(Decodable::decode(d)),
-            20 => Alias(Decodable::decode(d), Decodable::decode(d)),
-            21 => Param(Decodable::decode(d)),
-            22 => Bound(Decodable::decode(d), Decodable::decode(d)),
-            23 => Placeholder(Decodable::decode(d)),
-            24 => Infer(Decodable::decode(d)),
-            25 => Error(Decodable::decode(d)),
-            _ => panic!(
-                "{}",
-                format!(
-                    "invalid enum variant tag while decoding `{}`, expected 0..{}",
-                    "TyKind", 26,
-                )
-            ),
-        }
-    }
-}
-
 // This is not a derived impl because a derive would require `I: HashStable`
 #[allow(rustc::usage_of_ty_tykind)]
 impl<CTX: HashStableContext, I: Interner> HashStable<CTX> for TyKind<I>