diff --git a/Cargo.lock b/Cargo.lock
index ad6dac97a0af3..00cce17bca2de 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3523,7 +3523,6 @@ dependencies = [
  "rustc_macros",
  "rustc_middle",
  "rustc_mir_dataflow",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3934,7 +3933,6 @@ dependencies = [
  "rustc_lint",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -3997,7 +3995,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_span",
  "rustc_target",
  "smallvec",
@@ -4215,7 +4212,6 @@ dependencies = [
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4239,7 +4235,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_span",
  "rustc_target",
  "smallvec",
@@ -4266,7 +4261,6 @@ dependencies = [
  "rustc_middle",
  "rustc_mir_build",
  "rustc_mir_dataflow",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4340,7 +4334,6 @@ dependencies = [
  "rustc_lexer",
  "rustc_macros",
  "rustc_middle",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
@@ -4564,7 +4557,6 @@ dependencies = [
  "rustc_middle",
  "rustc_parse_format",
  "rustc_query_system",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index c85ff6f5c4451..e311352c93dec 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -2574,7 +2574,6 @@ pub enum AttrStyle {
 }
 
 rustc_index::newtype_index! {
-    #[custom_encodable]
     #[debug_format = "AttrId({})"]
     pub struct AttrId {}
 }
diff --git a/compiler/rustc_ast/src/node_id.rs b/compiler/rustc_ast/src/node_id.rs
index d16741757d1f1..48081582fc320 100644
--- a/compiler/rustc_ast/src/node_id.rs
+++ b/compiler/rustc_ast/src/node_id.rs
@@ -8,6 +8,7 @@ rustc_index::newtype_index! {
     /// This is later turned into [`DefId`] and `HirId` for the HIR.
     ///
     /// [`DefId`]: rustc_span::def_id::DefId
+    #[encodable]
     #[debug_format = "NodeId({})"]
     pub struct NodeId {
         /// The [`NodeId`] used to represent the root of the crate.
diff --git a/compiler/rustc_borrowck/Cargo.toml b/compiler/rustc_borrowck/Cargo.toml
index 636817a7ce100..ec7101407eb98 100644
--- a/compiler/rustc_borrowck/Cargo.toml
+++ b/compiler/rustc_borrowck/Cargo.toml
@@ -19,7 +19,6 @@ rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_mir_dataflow = { path = "../rustc_mir_dataflow" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
index 274e0aeaaba4f..8a45f90034176 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
@@ -189,8 +189,6 @@ impl GlobalFileTable {
 }
 
 rustc_index::newtype_index! {
-    // Tell the newtype macro to not generate `Encode`/`Decode` impls.
-    #[custom_encodable]
     struct LocalFileId {}
 }
 
diff --git a/compiler/rustc_hir/src/hir_id.rs b/compiler/rustc_hir/src/hir_id.rs
index 7b741e8882dea..c40a317947c03 100644
--- a/compiler/rustc_hir/src/hir_id.rs
+++ b/compiler/rustc_hir/src/hir_id.rs
@@ -154,6 +154,7 @@ rustc_index::newtype_index! {
     /// an "item-like" to something else can be implemented by a `Vec` instead of a
     /// tree or hash map.
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct ItemLocalId {}
 }
 
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
index 7205b7a21a823..cbce8c4b8b83d 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
@@ -198,7 +198,6 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
             // entire graph when there are many connected regions.
 
             rustc_index::newtype_index! {
-                #[custom_encodable]
                 pub struct RegionId {}
             }
 
diff --git a/compiler/rustc_hir_typeck/Cargo.toml b/compiler/rustc_hir_typeck/Cargo.toml
index 0062889d2445f..b0c60304424ad 100644
--- a/compiler/rustc_hir_typeck/Cargo.toml
+++ b/compiler/rustc_hir_typeck/Cargo.toml
@@ -19,7 +19,6 @@ rustc_infer = { path = "../rustc_infer" }
 rustc_lint = { path = "../rustc_lint" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_index_macros/src/newtype.rs b/compiler/rustc_index_macros/src/newtype.rs
index 2a974fd26281c..62de5c7c6c163 100644
--- a/compiler/rustc_index_macros/src/newtype.rs
+++ b/compiler/rustc_index_macros/src/newtype.rs
@@ -22,7 +22,7 @@ impl Parse for Newtype {
         let mut debug_format: Option<Lit> = None;
         let mut max = None;
         let mut consts = Vec::new();
-        let mut encodable = true;
+        let mut encodable = false;
         let mut ord = true;
         let mut gate_rustc_only = quote! {};
         let mut gate_rustc_only_cfg = quote! { all() };
@@ -34,8 +34,8 @@ impl Parse for Newtype {
                     gate_rustc_only_cfg = quote! { feature = "nightly" };
                     false
                 }
-                "custom_encodable" => {
-                    encodable = false;
+                "encodable" => {
+                    encodable = true;
                     false
                 }
                 "no_ord_impl" => {
diff --git a/compiler/rustc_infer/Cargo.toml b/compiler/rustc_infer/Cargo.toml
index 00251a192264a..73a02a431dfc0 100644
--- a/compiler/rustc_infer/Cargo.toml
+++ b/compiler/rustc_infer/Cargo.toml
@@ -15,7 +15,6 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index ee5fa87e45db1..3bcda8b5a851f 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -56,7 +56,6 @@ struct LintLevelSets {
 }
 
 rustc_index::newtype_index! {
-    #[custom_encodable] // we don't need encoding
     struct LintStackIndex {
         const COMMAND_LINE = 0;
     }
diff --git a/compiler/rustc_middle/src/middle/region.rs b/compiler/rustc_middle/src/middle/region.rs
index b76d1d6e141d6..771801ea1d1f5 100644
--- a/compiler/rustc_middle/src/middle/region.rs
+++ b/compiler/rustc_middle/src/middle/region.rs
@@ -148,6 +148,7 @@ rustc_index::newtype_index! {
     /// * The subscope with `first_statement_index == 1` is scope of `c`,
     ///   and thus does not include EXPR_2, but covers the `...`.
     #[derive(HashStable)]
+    #[encodable]
     pub struct FirstStatementIndex {}
 }
 
diff --git a/compiler/rustc_middle/src/mir/coverage.rs b/compiler/rustc_middle/src/mir/coverage.rs
index 08d377a8695f9..ccd2cd76ad879 100644
--- a/compiler/rustc_middle/src/mir/coverage.rs
+++ b/compiler/rustc_middle/src/mir/coverage.rs
@@ -17,6 +17,7 @@ rustc_index::newtype_index! {
     /// Note that LLVM handles counter IDs as `uint32_t`, so there is no need
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
+    #[encodable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "CounterId({})"]
     pub struct CounterId {}
@@ -37,6 +38,7 @@ rustc_index::newtype_index! {
     /// Note that LLVM handles expression IDs as `uint32_t`, so there is no need
     /// to use a larger representation on the Rust side.
     #[derive(HashStable)]
+    #[encodable]
     #[max = 0xFFFF_FFFF]
     #[debug_format = "ExpressionId({})"]
     pub struct ExpressionId {}
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 874c997c23be8..113d5f7eb6c88 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -736,6 +736,7 @@ impl SourceInfo {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "_{}"]
     pub struct Local {
         const RETURN_PLACE = 0;
@@ -1171,6 +1172,7 @@ rustc_index::newtype_index! {
     /// [`CriticalCallEdges`]: ../../rustc_const_eval/transform/add_call_guards/enum.AddCallGuards.html#variant.CriticalCallEdges
     /// [guide-mir]: https://rustc-dev-guide.rust-lang.org/mir/
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "bb{}"]
     pub struct BasicBlock {
         const START_BLOCK = 0;
@@ -1305,6 +1307,7 @@ impl<'tcx> BasicBlockData<'tcx> {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "scope[{}]"]
     pub struct SourceScope {
         const OUTERMOST_SOURCE_SCOPE = 0;
@@ -1533,6 +1536,7 @@ impl UserTypeProjection {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "promoted[{}]"]
     pub struct Promoted {}
 }
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index b5dd3010d3a8b..4f98c302298e4 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -132,6 +132,7 @@ pub struct UnsafetyCheckResult {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "_{}"]
     pub struct CoroutineSavedLocal {}
 }
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index ea0e179c00de0..43c8317c0b119 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1611,6 +1611,7 @@ impl fmt::Debug for EarlyParamRegion {
 rustc_index::newtype_index! {
     /// A **region** (lifetime) **v**ariable **ID**.
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "'?{}"]
     pub struct RegionVid {}
 }
@@ -1623,6 +1624,7 @@ impl Atom for RegionVid {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "{}"]
     pub struct BoundVar {}
 }
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 914ff1fabd1bd..38e50f14b3e99 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -578,6 +578,7 @@ impl<'a, V> LocalTableInContextMut<'a, V> {
 
 rustc_index::newtype_index! {
     #[derive(HashStable)]
+    #[encodable]
     #[debug_format = "UserType({})"]
     pub struct UserTypeAnnotationIndex {
         const START_INDEX = 0;
diff --git a/compiler/rustc_mir_build/Cargo.toml b/compiler/rustc_mir_build/Cargo.toml
index 6dceacd75a543..db54223405230 100644
--- a/compiler/rustc_mir_build/Cargo.toml
+++ b/compiler/rustc_mir_build/Cargo.toml
@@ -17,7 +17,6 @@ rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_mir_dataflow/Cargo.toml b/compiler/rustc_mir_dataflow/Cargo.toml
index 61664eb2a6fb0..7199db677c464 100644
--- a/compiler/rustc_mir_dataflow/Cargo.toml
+++ b/compiler/rustc_mir_dataflow/Cargo.toml
@@ -16,7 +16,6 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
diff --git a/compiler/rustc_mir_transform/Cargo.toml b/compiler/rustc_mir_transform/Cargo.toml
index 0448e9d276d4e..81d1e0e4ffd3c 100644
--- a/compiler/rustc_mir_transform/Cargo.toml
+++ b/compiler/rustc_mir_transform/Cargo.toml
@@ -20,7 +20,6 @@ rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_mir_build = { path = "../rustc_mir_build" }
 rustc_mir_dataflow = { path = "../rustc_mir_dataflow" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_passes/Cargo.toml b/compiler/rustc_passes/Cargo.toml
index 40c3811e054e6..592b42d4701fe 100644
--- a/compiler/rustc_passes/Cargo.toml
+++ b/compiler/rustc_passes/Cargo.toml
@@ -19,7 +19,6 @@ rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_query_system/src/dep_graph/serialized.rs b/compiler/rustc_query_system/src/dep_graph/serialized.rs
index e97ef8072045d..a70f4138cfb53 100644
--- a/compiler/rustc_query_system/src/dep_graph/serialized.rs
+++ b/compiler/rustc_query_system/src/dep_graph/serialized.rs
@@ -54,6 +54,7 @@ use std::marker::PhantomData;
 // unused so that we can store multiple index types in `CompressedHybridIndex`,
 // and use those bits to encode which index type it contains.
 rustc_index::newtype_index! {
+    #[encodable]
     #[max = 0x7FFF_FFFF]
     pub struct SerializedDepNodeIndex {}
 }
diff --git a/compiler/rustc_span/src/def_id.rs b/compiler/rustc_span/src/def_id.rs
index 595babc26ae68..595456e6d6a17 100644
--- a/compiler/rustc_span/src/def_id.rs
+++ b/compiler/rustc_span/src/def_id.rs
@@ -13,7 +13,6 @@ pub type StableCrateIdMap =
     indexmap::IndexMap<StableCrateId, CrateNum, BuildHasherDefault<Unhasher>>;
 
 rustc_index::newtype_index! {
-    #[custom_encodable]
     #[debug_format = "crate{}"]
     pub struct CrateNum {}
 }
@@ -213,7 +212,6 @@ rustc_index::newtype_index! {
     /// A DefIndex is an index into the hir-map for a crate, identifying a
     /// particular definition. It should really be considered an interned
     /// shorthand for a particular DefPath.
-    #[custom_encodable] // (only encodable in metadata)
     #[debug_format = "DefIndex({})"]
     pub struct DefIndex {
         /// The crate root is always assigned index 0 by the AST Map code,
@@ -222,6 +220,7 @@ rustc_index::newtype_index! {
     }
 }
 
+// njn: I don't understand these
 impl<E: Encoder> Encodable<E> for DefIndex {
     default fn encode(&self, _: &mut E) {
         panic!("cannot encode `DefIndex` with `{}`", std::any::type_name::<E>());
diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index 988ff57254c53..8c6600c4e531f 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -60,7 +60,6 @@ pub struct SyntaxContextData {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
-    #[custom_encodable]
     pub struct ExpnIndex {}
 }
 
@@ -80,7 +79,6 @@ impl fmt::Debug for ExpnId {
 
 rustc_index::newtype_index! {
     /// A unique ID associated with a macro invocation and expansion.
-    #[custom_encodable]
     #[no_ord_impl]
     #[debug_format = "expn{}"]
     pub struct LocalExpnId {}
diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs
index b00567e87c656..c1fbc2980a97e 100644
--- a/compiler/rustc_target/src/abi/mod.rs
+++ b/compiler/rustc_target/src/abi/mod.rs
@@ -42,6 +42,7 @@ rustc_index::newtype_index! {
     /// `d` is `FieldIdx(1)` in `VariantIdx(1)`, and
     /// `f` is `FieldIdx(1)` in `VariantIdx(0)`.
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct FieldIdx {}
 }
 
@@ -57,6 +58,7 @@ rustc_index::newtype_index! {
     /// `struct`s, `tuples`, and `unions`s are considered to have a single variant
     /// with variant index zero, aka [`FIRST_VARIANT`].
     #[derive(HashStable_Generic)]
+    #[encodable]
     pub struct VariantIdx {
         /// Equivalent to `VariantIdx(0)`.
         const FIRST_VARIANT = 0;
diff --git a/compiler/rustc_trait_selection/Cargo.toml b/compiler/rustc_trait_selection/Cargo.toml
index 667ee3d4e1c69..7d098180b9314 100644
--- a/compiler/rustc_trait_selection/Cargo.toml
+++ b/compiler/rustc_trait_selection/Cargo.toml
@@ -17,7 +17,6 @@ rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_query_system = { path = "../rustc_query_system" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }
 rustc_target = { path = "../rustc_target" }
diff --git a/compiler/rustc_type_ir/src/const_kind.rs b/compiler/rustc_type_ir/src/const_kind.rs
index a5f90421de5f7..765cbceb7d1c9 100644
--- a/compiler/rustc_type_ir/src/const_kind.rs
+++ b/compiler/rustc_type_ir/src/const_kind.rs
@@ -95,6 +95,7 @@ impl<I: Interner> DebugWithInfcx<I> for ConstKind<I> {
 
 rustc_index::newtype_index! {
     /// A **`const`** **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}c"]
     #[gate_rustc_only]
     pub struct ConstVid {}
@@ -108,6 +109,7 @@ rustc_index::newtype_index! {
     /// relate an effect variable with a normal one, we would ICE, which can catch bugs
     /// where we are not correctly using the effect var for an effect param. Fallback
     /// is also implemented on top of having separate effect and normal const variables.
+    #[encodable]
     #[debug_format = "?{}e"]
     #[gate_rustc_only]
     pub struct EffectVid {}
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index acea7aa46f6f5..67ed154f1bd74 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -92,6 +92,7 @@ rustc_index::newtype_index! {
     ///
     /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+    #[encodable]
     #[debug_format = "DebruijnIndex({})"]
     #[gate_rustc_only]
     pub struct DebruijnIndex {
@@ -293,6 +294,7 @@ rustc_index::newtype_index! {
     /// type -- an idealized representative of "types in general" that we
     /// use for checking generic functions.
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
+    #[encodable]
     #[debug_format = "U{}"]
     #[gate_rustc_only]
     pub struct UniverseIndex {}
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 494eeaf3dc881..a3e94d5c13787 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -622,6 +622,7 @@ pub struct FloatVarValue(pub FloatTy);
 
 rustc_index::newtype_index! {
     /// A **ty**pe **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}t"]
     #[gate_rustc_only]
     pub struct TyVid {}
@@ -629,6 +630,7 @@ rustc_index::newtype_index! {
 
 rustc_index::newtype_index! {
     /// An **int**egral (`u32`, `i32`, `usize`, etc.) type **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}i"]
     #[gate_rustc_only]
     pub struct IntVid {}
@@ -636,6 +638,7 @@ rustc_index::newtype_index! {
 
 rustc_index::newtype_index! {
     /// A **float**ing-point (`f32` or `f64`) type **v**ariable **ID**.
+    #[encodable]
     #[debug_format = "?{}f"]
     #[gate_rustc_only]
     pub struct FloatVid {}