remove the `Subst` trait, always use `EarlyBinder`

63 files changed, 127 insertions, 163 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index f2204c24263..69ad7f66275 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -16,7 +16,7 @@ use rustc_middle::mir::{
     FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
     ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
 };
-use rustc_middle::ty::{self, subst::Subst, suggest_constraining_type_params, PredicateKind, Ty};
+use rustc_middle::ty::{self, suggest_constraining_type_params, PredicateKind, Ty};
 use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 8cf9ed53d39..41fba8deb10 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -22,8 +22,8 @@ use rustc_hir::{BodyOwnerKind, HirId};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin};
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, InlineConstSubsts, InlineConstSubstsParts, RegionVid, Ty, TyCtxt};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use std::iter;
 
 use crate::nll::ToRegionVid;
diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
index a2f14e753ae..b52cc873f2e 100644
--- a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs
@@ -13,7 +13,7 @@ use rustc_middle::mir::pretty::display_allocation;
 use rustc_middle::traits::Reveal;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, subst::Subst, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::source_map::Span;
 use rustc_target::abi::{self, Abi};
 use std::borrow::Cow;
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs b/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
index 91f4f042517..0e3867557ad 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics/caller_location.rs
@@ -4,7 +4,6 @@ use rustc_ast::Mutability;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::layout::LayoutOf;
-use rustc_middle::ty::subst::Subst;
 use rustc_span::{Span, Symbol};
 
 use crate::interpret::{
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 4aa98cb13d8..9c95ffca19b 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -13,7 +13,6 @@ use rustc_middle::mir::{
     TerminatorKind, UnOp, START_BLOCK,
 };
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeFoldable, TypeVisitable};
 use rustc_mir_dataflow::impls::MaybeStorageLive;
 use rustc_mir_dataflow::storage::always_storage_live_locals;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 67526c22289..546ab82bc23 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -69,8 +69,8 @@ use rustc_middle::dep_graph::DepContext;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::{self, RelateResult, TypeRelation};
 use rustc_middle::ty::{
-    self, error::TypeError, Binder, List, Region, Subst, Ty, TyCtxt, TypeFoldable,
-    TypeSuperVisitable, TypeVisitable,
+    self, error::TypeError, Binder, List, Region, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
+    TypeVisitable,
 };
 use rustc_span::{sym, symbol::kw, BytePos, DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;
diff --git a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
index cb2be93589d..89a448edc9b 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs
@@ -15,8 +15,8 @@ use rustc_middle::hir::nested_filter;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::print::{FmtPrinter, PrettyPrinter, Print, Printer};
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, InferConst};
+use rustc_middle::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_middle::ty::{IsSuggestable, Ty, TyCtxt, TypeckResults};
 use rustc_session::SessionDiagnostic;
 use rustc_span::symbol::{kw, Ident};
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index 8c9ddf86632..561279e3c8e 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -8,7 +8,7 @@ use rustc_data_structures::vec_map::VecMap;
 use rustc_hir as hir;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::fold::BottomUpFolder;
-use rustc_middle::ty::subst::{GenericArgKind, Subst};
+use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{
     self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitor,
diff --git a/compiler/rustc_infer/src/infer/outlives/verify.rs b/compiler/rustc_infer/src/infer/outlives/verify.rs
index 75233495040..e344e192a76 100644
--- a/compiler/rustc_infer/src/infer/outlives/verify.rs
+++ b/compiler/rustc_infer/src/infer/outlives/verify.rs
@@ -5,7 +5,7 @@ use crate::infer::{GenericKind, VerifyBound};
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::sso::SsoHashSet;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{GenericArg, Subst};
+use rustc_middle::ty::GenericArg;
 use rustc_middle::ty::{self, EarlyBinder, OutlivesPredicate, Ty, TyCtxt};
 
 use smallvec::smallvec;
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 3d7a6230e4d..458bf4ef381 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -9,10 +9,10 @@ use crate::mir::visit::MirVisitable;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
 use crate::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
 use crate::ty::{self, List, Ty, TyCtxt};
 use crate::ty::{AdtDef, InstanceDef, ScalarInt, UserTypeAnnotationIndex};
+use crate::ty::{GenericArg, InternalSubsts, SubstsRef};
 
 use rustc_data_structures::captures::Captures;
 use rustc_errors::ErrorGuaranteed;
diff --git a/compiler/rustc_middle/src/mir/tcx.rs b/compiler/rustc_middle/src/mir/tcx.rs
index 405003156c4..b4e36076aff 100644
--- a/compiler/rustc_middle/src/mir/tcx.rs
+++ b/compiler/rustc_middle/src/mir/tcx.rs
@@ -4,7 +4,6 @@
  */
 
 use crate::mir::*;
-use crate::ty::subst::Subst;
 use crate::ty::{self, Ty, TyCtxt};
 use rustc_hir as hir;
 use rustc_target::abi::VariantIdx;
diff --git a/compiler/rustc_middle/src/ty/abstract_const.rs b/compiler/rustc_middle/src/ty/abstract_const.rs
index 8f79b4705ad..8e0a1f1f9ac 100644
--- a/compiler/rustc_middle/src/ty/abstract_const.rs
+++ b/compiler/rustc_middle/src/ty/abstract_const.rs
@@ -1,7 +1,7 @@
 //! A subset of a mir body used for const evaluatability checking.
 use crate::mir;
 use crate::ty::visit::TypeVisitable;
-use crate::ty::{self, subst::Subst, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt};
+use crate::ty::{self, DelaySpanBugEmitted, EarlyBinder, SubstsRef, Ty, TyCtxt};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def_id::DefId;
 use std::cmp;
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 4a9fbc5511c..10c5933574f 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -15,7 +15,6 @@ use crate::mir::{
 use crate::thir::Thir;
 use crate::traits;
 use crate::ty::query::{self, TyCtxtAt};
-use crate::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSubsts};
 use crate::ty::{
     self, AdtDef, AdtDefData, AdtKind, Binder, BindingMode, BoundVar, CanonicalPolyFnSig,
     ClosureSizeProfileData, Const, ConstS, ConstVid, DefIdTree, ExistentialPredicate, FloatTy,
@@ -24,6 +23,7 @@ use crate::ty::{
     RegionKind, ReprOptions, TraitObjectVisitor, Ty, TyKind, TyS, TyVar, TyVid, TypeAndMut, UintTy,
     Visibility,
 };
+use crate::ty::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef, UserSubsts};
 use rustc_ast as ast;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
diff --git a/compiler/rustc_middle/src/ty/generics.rs b/compiler/rustc_middle/src/ty/generics.rs
index 0c8bdde9c8b..19754d1453f 100644
--- a/compiler/rustc_middle/src/ty/generics.rs
+++ b/compiler/rustc_middle/src/ty/generics.rs
@@ -1,6 +1,5 @@
 use crate::ty;
-use crate::ty::subst::{Subst, SubstsRef};
-use crate::ty::EarlyBinder;
+use crate::ty::{EarlyBinder, SubstsRef};
 use rustc_ast as ast;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::DefId;
diff --git a/compiler/rustc_middle/src/ty/instance.rs b/compiler/rustc_middle/src/ty/instance.rs
index 9afd6620756..6c1414f7b8a 100644
--- a/compiler/rustc_middle/src/ty/instance.rs
+++ b/compiler/rustc_middle/src/ty/instance.rs
@@ -1,9 +1,7 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::print::{FmtPrinter, Printer};
-use crate::ty::subst::{InternalSubsts, Subst};
-use crate::ty::{
-    self, EarlyBinder, SubstsRef, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitable,
-};
+use crate::ty::{self, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitable};
+use crate::ty::{EarlyBinder, InternalSubsts, SubstsRef};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::Namespace;
 use rustc_hir::def_id::{CrateNum, DefId};
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 13a6cf19009..b53ec21b764 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -1,7 +1,6 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::mir::{GeneratorLayout, GeneratorSavedLocal};
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::subst::Subst;
 use crate::ty::{
     self, layout_sanity_check::sanity_check_layout, subst::SubstsRef, EarlyBinder, ReprOptions, Ty,
     TyCtxt, TypeVisitable,
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index e8fe37e7dab..ac4cad8e5d2 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -89,9 +89,9 @@ pub use self::sty::BoundRegionKind::*;
 pub use self::sty::{
     Article, Binder, BoundRegion, BoundRegionKind, BoundTy, BoundTyKind, BoundVar,
     BoundVariableKind, CanonicalPolyFnSig, ClosureSubsts, ClosureSubstsParts, ConstVid,
-    EarlyBinder, EarlyBoundRegion, ExistentialPredicate, ExistentialProjection,
-    ExistentialTraitRef, FnSig, FreeRegion, GenSig, GeneratorSubsts, GeneratorSubstsParts,
-    InlineConstSubsts, InlineConstSubstsParts, ParamConst, ParamTy, PolyExistentialProjection,
+    EarlyBoundRegion, ExistentialPredicate, ExistentialProjection, ExistentialTraitRef, FnSig,
+    FreeRegion, GenSig, GeneratorSubsts, GeneratorSubstsParts, InlineConstSubsts,
+    InlineConstSubstsParts, ParamConst, ParamTy, PolyExistentialProjection,
     PolyExistentialTraitRef, PolyFnSig, PolyGenSig, PolyTraitRef, ProjectionTy, Region, RegionKind,
     RegionVid, TraitRef, TyKind, TypeAndMut, UpvarSubsts, VarianceDiagInfo,
 };
diff --git a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
index 9db5a289484..fe303e21b65 100644
--- a/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
+++ b/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs
@@ -10,8 +10,7 @@
 use crate::mir;
 use crate::traits::query::NoSolution;
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder};
-use crate::ty::subst::{Subst, SubstsRef};
-use crate::ty::{self, EarlyBinder, Ty, TyCtxt};
+use crate::ty::{self, EarlyBinder, SubstsRef, Ty, TyCtxt};
 
 #[derive(Debug, Copy, Clone, HashStable, TyEncodable, TyDecodable)]
 pub enum NormalizationError<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/print/mod.rs b/compiler/rustc_middle/src/ty/print/mod.rs
index d57cf8f0149..e0a8d58f8a7 100644
--- a/compiler/rustc_middle/src/ty/print/mod.rs
+++ b/compiler/rustc_middle/src/ty/print/mod.rs
@@ -1,4 +1,4 @@
-use crate::ty::subst::{GenericArg, Subst};
+use crate::ty::GenericArg;
 use crate::ty::{self, DefIdTree, Ty, TyCtxt};
 
 use rustc_data_structures::fx::FxHashSet;
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 97bddb93eb4..b6cd5396b1d 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1,9 +1,9 @@
 use crate::mir::interpret::{AllocRange, GlobalAlloc, Pointer, Provenance, Scalar};
-use crate::ty::subst::{GenericArg, GenericArgKind, Subst};
 use crate::ty::{
     self, ConstInt, DefIdTree, ParamConst, ScalarInt, Term, TermKind, Ty, TyCtxt, TypeFoldable,
     TypeSuperFoldable, TypeSuperVisitable, TypeVisitable,
 };
+use crate::ty::{GenericArg, GenericArgKind};
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_data_structures::sso::SsoHashSet;
diff --git a/compiler/rustc_middle/src/ty/relate.rs b/compiler/rustc_middle/src/ty/relate.rs
index af31f54981f..0d97d4acdfc 100644
--- a/compiler/rustc_middle/src/ty/relate.rs
+++ b/compiler/rustc_middle/src/ty/relate.rs
@@ -5,8 +5,8 @@
 //! subtyping, type equality, etc.
 
 use crate::ty::error::{ExpectedFound, TypeError};
-use crate::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
 use crate::ty::{self, ImplSubject, Term, TermKind, Ty, TyCtxt, TypeFoldable};
+use crate::ty::{GenericArg, GenericArgKind, SubstsRef};
 use rustc_hir as ast;
 use rustc_hir::def_id::DefId;
 use rustc_span::DUMMY_SP;
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 2d78c0c8656..d2f73f274f8 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -3,7 +3,7 @@
 #![allow(rustc::usage_of_ty_tykind)]
 
 use crate::infer::canonical::Canonical;
-use crate::ty::subst::{GenericArg, InternalSubsts, Subst, SubstsRef};
+use crate::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
 use crate::ty::visit::ValidateBoundVars;
 use crate::ty::InferTy::*;
 use crate::ty::{
@@ -551,7 +551,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         layout.variant_fields.iter().map(move |variant| {
             variant
                 .iter()
-                .map(move |field| EarlyBinder(layout.field_tys[*field]).subst(tcx, self.substs))
+                .map(move |field| ty::EarlyBinder(layout.field_tys[*field]).subst(tcx, self.substs))
         })
     }
 
@@ -915,77 +915,6 @@ impl<'tcx> PolyExistentialTraitRef<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
-#[derive(Encodable, Decodable, HashStable)]
-pub struct EarlyBinder<T>(pub T);
-
-/// For early binders, you should first call `subst` before using any visitors.
-impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
-impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
-
-impl<T> EarlyBinder<T> {
-    pub fn as_ref(&self) -> EarlyBinder<&T> {
-        EarlyBinder(&self.0)
-    }
-
-    pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
-    where
-        F: FnOnce(&T) -> U,
-    {
-        self.as_ref().map_bound(f)
-    }
-
-    pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
-    where
-        F: FnOnce(T) -> U,
-    {
-        let value = f(self.0);
-        EarlyBinder(value)
-    }
-
-    pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
-    where
-        F: FnOnce(T) -> Result<U, E>,
-    {
-        let value = f(self.0)?;
-        Ok(EarlyBinder(value))
-    }
-
-    pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
-        EarlyBinder(value)
-    }
-}
-
-impl<T> EarlyBinder<Option<T>> {
-    pub fn transpose(self) -> Option<EarlyBinder<T>> {
-        self.0.map(|v| EarlyBinder(v))
-    }
-}
-
-impl<T, U> EarlyBinder<(T, U)> {
-    pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
-        (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
-    }
-}
-
-pub struct EarlyBinderIter<T> {
-    t: T,
-}
-
-impl<T: IntoIterator> EarlyBinder<T> {
-    pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
-        EarlyBinderIter { t: self.0.into_iter() }
-    }
-}
-
-impl<T: Iterator> Iterator for EarlyBinderIter<T> {
-    type Item = EarlyBinder<T::Item>;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        self.t.next().map(|i| EarlyBinder(i))
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum BoundVariableKind {
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 8e69bf067d0..a939be32fff 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -497,18 +497,79 @@ impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &'tcx ty::List<T> {
     }
 }
 
-// Just call `foo.subst(tcx, substs)` to perform a substitution across `foo`.
-#[rustc_on_unimplemented(message = "Calling `subst` must now be done through an `EarlyBinder`")]
-pub trait Subst<'tcx>: Sized {
-    type Inner;
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable)]
+pub struct EarlyBinder<T>(pub T);
 
-    fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner;
+/// For early binders, you should first call `subst` before using any visitors.
+impl<'tcx, T> !TypeFoldable<'tcx> for ty::EarlyBinder<T> {}
+impl<'tcx, T> !TypeVisitable<'tcx> for ty::EarlyBinder<T> {}
+
+impl<T> EarlyBinder<T> {
+    pub fn as_ref(&self) -> EarlyBinder<&T> {
+        EarlyBinder(&self.0)
+    }
+
+    pub fn map_bound_ref<F, U>(&self, f: F) -> EarlyBinder<U>
+    where
+        F: FnOnce(&T) -> U,
+    {
+        self.as_ref().map_bound(f)
+    }
+
+    pub fn map_bound<F, U>(self, f: F) -> EarlyBinder<U>
+    where
+        F: FnOnce(T) -> U,
+    {
+        let value = f(self.0);
+        EarlyBinder(value)
+    }
+
+    pub fn try_map_bound<F, U, E>(self, f: F) -> Result<EarlyBinder<U>, E>
+    where
+        F: FnOnce(T) -> Result<U, E>,
+    {
+        let value = f(self.0)?;
+        Ok(EarlyBinder(value))
+    }
+
+    pub fn rebind<U>(&self, value: U) -> EarlyBinder<U> {
+        EarlyBinder(value)
+    }
+}
+
+impl<T> EarlyBinder<Option<T>> {
+    pub fn transpose(self) -> Option<EarlyBinder<T>> {
+        self.0.map(|v| EarlyBinder(v))
+    }
 }
 
-impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for ty::EarlyBinder<T> {
-    type Inner = T;
+impl<T, U> EarlyBinder<(T, U)> {
+    pub fn transpose_tuple2(self) -> (EarlyBinder<T>, EarlyBinder<U>) {
+        (EarlyBinder(self.0.0), EarlyBinder(self.0.1))
+    }
+}
+
+pub struct EarlyBinderIter<T> {
+    t: T,
+}
+
+impl<T: IntoIterator> EarlyBinder<T> {
+    pub fn transpose_iter(self) -> EarlyBinderIter<T::IntoIter> {
+        EarlyBinderIter { t: self.0.into_iter() }
+    }
+}
+
+impl<T: Iterator> Iterator for EarlyBinderIter<T> {
+    type Item = EarlyBinder<T::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.t.next().map(|i| EarlyBinder(i))
+    }
+}
 
-    fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner {
+impl<'tcx, T: TypeFoldable<'tcx>> ty::EarlyBinder<T> {
+    pub fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> T {
         let mut folder = SubstFolder { tcx, substs, binders_passed: 0 };
         self.0.fold_with(&mut folder)
     }
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 23ad4d27d8e..d93aab04e99 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -3,11 +3,11 @@
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::ty::layout::IntegerExt;
 use crate::ty::query::TyCtxtAt;
-use crate::ty::subst::{GenericArgKind, Subst, SubstsRef};
 use crate::ty::{
     self, DefIdTree, FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
     TypeVisitable,
 };
+use crate::ty::{GenericArgKind, SubstsRef};
 use rustc_apfloat::Float as _;
 use rustc_ast as ast;
 use rustc_attr::{self as attr, SignedInt, UnsignedInt};
diff --git a/compiler/rustc_mir_build/src/build/matches/test.rs b/compiler/rustc_mir_build/src/build/matches/test.rs
index 47d05a6e32c..1b141483766 100644
--- a/compiler/rustc_mir_build/src/build/matches/test.rs
+++ b/compiler/rustc_mir_build/src/build/matches/test.rs
@@ -14,8 +14,8 @@ use rustc_hir::{LangItem, RangeEnd};
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
-use rustc_middle::ty::subst::{GenericArg, Subst};
 use rustc_middle::ty::util::IntTypeExt;
+use rustc_middle::ty::GenericArg;
 use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
 use rustc_span::symbol::{sym, Symbol};
diff --git a/compiler/rustc_mir_build/src/thir/cx/mod.rs b/compiler/rustc_mir_build/src/thir/cx/mod.rs
index 3ef1b263ffd..1d95d6b53fb 100644
--- a/compiler/rustc_mir_build/src/thir/cx/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/mod.rs
@@ -15,7 +15,7 @@ use rustc_hir::HirId;
 use rustc_hir::Node;
 use rustc_middle::middle::region;
 use rustc_middle::thir::*;
-use rustc_middle::ty::{self, RvalueScopes, Subst, TyCtxt};
+use rustc_middle::ty::{self, RvalueScopes, TyCtxt};
 use rustc_span::Span;
 
 pub(crate) fn thir_body<'tcx>(
diff --git a/compiler/rustc_mir_transform/src/const_prop.rs b/compiler/rustc_mir_transform/src/const_prop.rs
index 53f33a7a0ba..08ba3f9941d 100644
--- a/compiler/rustc_mir_transform/src/const_prop.rs
+++ b/compiler/rustc_mir_transform/src/const_prop.rs
@@ -17,7 +17,7 @@ use rustc_middle::mir::{
     RETURN_PLACE,
 };
 use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{self, ConstKind, Instance, ParamEnv, Ty, TyCtxt, TypeVisitable};
 use rustc_span::{def_id::DefId, Span};
 use rustc_target::abi::{self, HasDataLayout, Size, TargetDataLayout};
diff --git a/compiler/rustc_mir_transform/src/const_prop_lint.rs b/compiler/rustc_mir_transform/src/const_prop_lint.rs
index 37e78f4ac07..f16efb365f3 100644
--- a/compiler/rustc_mir_transform/src/const_prop_lint.rs
+++ b/compiler/rustc_mir_transform/src/const_prop_lint.rs
@@ -21,7 +21,7 @@ use rustc_middle::mir::{
     TerminatorKind, UnOp, RETURN_PLACE,
 };
 use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{self, ConstInt, Instance, ParamEnv, ScalarInt, Ty, TyCtxt, TypeVisitable};
 use rustc_session::lint;
 use rustc_span::Span;
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
index 294af2455d0..ef8d6bb6559 100644
--- a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -8,7 +8,6 @@ use rustc_index::vec::Idx;
 use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{Ty, TyCtxt};
 
 /// Constructs the types used when accessing a Box's pointer
diff --git a/compiler/rustc_mir_transform/src/function_item_references.rs b/compiler/rustc_mir_transform/src/function_item_references.rs
index 2e4fe1e3e5d..0568eb2ffa6 100644
--- a/compiler/rustc_mir_transform/src/function_item_references.rs
+++ b/compiler/rustc_mir_transform/src/function_item_references.rs
@@ -3,11 +3,7 @@ use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
-use rustc_middle::ty::{
-    self,
-    subst::{GenericArgKind, Subst, SubstsRef},
-    EarlyBinder, PredicateKind, Ty, TyCtxt,
-};
+use rustc_middle::ty::{self, EarlyBinder, GenericArgKind, PredicateKind, SubstsRef, Ty, TyCtxt};
 use rustc_session::lint::builtin::FUNCTION_ITEM_REFERENCES;
 use rustc_span::{symbol::sym, Span};
 use rustc_target::spec::abi::Abi;
diff --git a/compiler/rustc_mir_transform/src/generator.rs b/compiler/rustc_mir_transform/src/generator.rs
index 705cf776fb2..c833de3a8a7 100644
--- a/compiler/rustc_mir_transform/src/generator.rs
+++ b/compiler/rustc_mir_transform/src/generator.rs
@@ -61,9 +61,8 @@ use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::mir::dump_mir;
 use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
 use rustc_middle::mir::*;
-use rustc_middle::ty::subst::{Subst, SubstsRef};
-use rustc_middle::ty::GeneratorSubsts;
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
+use rustc_middle::ty::{GeneratorSubsts, SubstsRef};
 use rustc_mir_dataflow::impls::{
     MaybeBorrowedLocals, MaybeLiveLocals, MaybeRequiresStorage, MaybeStorageLive,
 };
diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index d00a384cb44..b60bd3cea23 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -7,7 +7,6 @@ use rustc_index::vec::Idx;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_span::def_id::DefId;
diff --git a/compiler/rustc_mir_transform/src/shim.rs b/compiler/rustc_mir_transform/src/shim.rs
index 88213620029..6ca58ee458c 100644
--- a/compiler/rustc_mir_transform/src/shim.rs
+++ b/compiler/rustc_mir_transform/src/shim.rs
@@ -3,7 +3,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::*;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{self, EarlyBinder, GeneratorSubsts, Ty, TyCtxt};
 use rustc_target::abi::VariantIdx;
 
diff --git a/compiler/rustc_symbol_mangling/src/v0.rs b/compiler/rustc_symbol_mangling/src/v0.rs
index 79d0ef69ba7..18e7e74741a 100644
--- a/compiler/rustc_symbol_mangling/src/v0.rs
+++ b/compiler/rustc_symbol_mangling/src/v0.rs
@@ -7,10 +7,10 @@ use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::ty::layout::IntegerExt;
 use rustc_middle::ty::print::{Print, Printer};
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
 use rustc_middle::ty::{
     self, EarlyBinder, FloatTy, Instance, IntTy, Ty, TyCtxt, TypeVisitable, UintTy,
 };
+use rustc_middle::ty::{GenericArg, GenericArgKind};
 use rustc_span::symbol::kw;
 use rustc_target::abi::Integer;
 use rustc_target::spec::abi::Abi;
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 292787d4dbb..94de8abce19 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -22,7 +22,6 @@ use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::traits::specialization_graph::OverlapMode;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitor};
 use rustc_span::symbol::sym;
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index e11a4220144..07e470dc2ae 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -4,7 +4,7 @@ use super::{
 use crate::infer::InferCtxt;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{Subst, SubstsRef};
+use rustc_middle::ty::SubstsRef;
 use rustc_middle::ty::{self, GenericParamDefKind};
 use rustc_span::symbol::sym;
 use std::iter;
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 40596078f04..104a465a3b5 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -34,12 +34,11 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{
-    self, DefIdTree, GenericParamDefKind, Subst, ToPredicate, Ty, TyCtxt, TypeSuperVisitable,
-    VtblEntry,
+    self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeSuperVisitable, VtblEntry,
 };
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_span::{sym, Span};
 use smallvec::SmallVec;
 
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index f2779ce2db1..a54b725753c 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -18,10 +18,10 @@ use rustc_errors::{FatalError, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::abstract_const::{walk_abstract_const, AbstractConst};
-use rustc_middle::ty::subst::{GenericArg, InternalSubsts, Subst};
 use rustc_middle::ty::{
     self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
+use rustc_middle::ty::{GenericArg, InternalSubsts};
 use rustc_middle::ty::{Predicate, ToPredicate};
 use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
 use rustc_span::symbol::Symbol;
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index a25fb854316..6f41cbeb7af 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -30,7 +30,6 @@ use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
 use rustc_middle::ty::DefIdTree;
 use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index 40acabf622a..88000d46978 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -13,7 +13,6 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_infer::traits::Normalized;
 use rustc_middle::mir;
 use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable};
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitor};
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index d1deef78407..8b24e83ffa4 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -11,8 +11,8 @@ use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::GrowableBitSet;
 use rustc_infer::infer::InferOk;
 use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType;
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, GenericParamDefKind, Ty, TyCtxt};
+use rustc_middle::ty::{GenericArg, GenericArgKind, InternalSubsts, SubstsRef};
 use rustc_middle::ty::{ToPolyTraitRef, ToPredicate};
 use rustc_span::def_id::DefId;
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 75bd2c89f54..cff6b61ee33 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -37,7 +37,7 @@ use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::relate::TypeRelation;
-use rustc_middle::ty::subst::{Subst, SubstsRef};
+use rustc_middle::ty::SubstsRef;
 use rustc_middle::ty::{self, EarlyBinder, PolyProjectionPredicate, ToPolyTraitRef, ToPredicate};
 use rustc_middle::ty::{Ty, TyCtxt, TypeFoldable, TypeVisitable};
 use rustc_span::symbol::sym;
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index 7d299e30ae0..56a88749c46 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -19,8 +19,8 @@ use crate::traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCau
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_errors::{struct_span_err, EmissionGuarantee, LintDiagnosticBuilder};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, ImplSubject, TyCtxt};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
 use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
 use rustc_span::{Span, DUMMY_SP};
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 0f5dff01c66..5206e9f649b 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -5,8 +5,8 @@ use smallvec::SmallVec;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{GenericArg, Subst, SubstsRef};
 use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{GenericArg, SubstsRef};
 
 use super::{Normalized, Obligation, ObligationCause, PredicateObligation, SelectionContext};
 pub use rustc_infer::traits::{self, util::*};
diff --git a/compiler/rustc_traits/src/chalk/db.rs b/compiler/rustc_traits/src/chalk/db.rs
index ff5ca0cbcb7..0de28b82661 100644
--- a/compiler/rustc_traits/src/chalk/db.rs
+++ b/compiler/rustc_traits/src/chalk/db.rs
@@ -7,8 +7,8 @@
 //! `crate::chalk::lowering` (to lower rustc types into Chalk types).
 
 use rustc_middle::traits::ChalkRustInterner as RustInterner;
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, AssocKind, EarlyBinder, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 
 use rustc_ast::ast;
 use rustc_attr as attr;
diff --git a/compiler/rustc_traits/src/dropck_outlives.rs b/compiler/rustc_traits/src/dropck_outlives.rs
index a20de08b4ef..7fb7c689550 100644
--- a/compiler/rustc_traits/src/dropck_outlives.rs
+++ b/compiler/rustc_traits/src/dropck_outlives.rs
@@ -4,7 +4,7 @@ use rustc_infer::infer::canonical::{Canonical, QueryResponse};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{self, EarlyBinder, ParamEnvAnd, Ty, TyCtxt};
 use rustc_span::source_map::{Span, DUMMY_SP};
 use rustc_trait_selection::traits::query::dropck_outlives::trivial_dropck_outlives;
diff --git a/compiler/rustc_traits/src/type_op.rs b/compiler/rustc_traits/src/type_op.rs
index 1bb6506b367..ff7d1ef00cc 100644
--- a/compiler/rustc_traits/src/type_op.rs
+++ b/compiler/rustc_traits/src/type_op.rs
@@ -5,10 +5,10 @@ use rustc_infer::infer::canonical::{Canonical, QueryResponse};
 use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::{ObligationCauseCode, TraitEngineExt as _};
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{GenericArg, Subst, UserSelfTy, UserSubsts};
 use rustc_middle::ty::{
     self, EarlyBinder, FnSig, Lift, PolyFnSig, Ty, TyCtxt, TypeFoldable, Variance,
 };
+use rustc_middle::ty::{GenericArg, UserSelfTy, UserSubsts};
 use rustc_middle::ty::{ParamEnv, ParamEnvAnd, Predicate, ToPredicate};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
diff --git a/compiler/rustc_ty_utils/src/needs_drop.rs b/compiler/rustc_ty_utils/src/needs_drop.rs
index ab5a3d8ae48..ba987c6f763 100644
--- a/compiler/rustc_ty_utils/src/needs_drop.rs
+++ b/compiler/rustc_ty_utils/src/needs_drop.rs
@@ -2,7 +2,6 @@
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::util::{needs_drop_components, AlwaysRequiresDrop};
 use rustc_middle::ty::{self, EarlyBinder, Ty, TyCtxt};
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 9266e4e3f6e..f7db39dfec3 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -1,7 +1,6 @@
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
 use rustc_trait_selection::traits;
 
diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index 6d2ba7c1c95..5432fdbb5e8 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -26,7 +26,7 @@ use rustc_hir::intravisit::{walk_generics, Visitor as _};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
 use rustc_middle::middle::stability::AllowUnstable;
-use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
+use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
 use rustc_middle::ty::DynKind;
 use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::ty::{
diff --git a/compiler/rustc_typeck/src/check/_match.rs b/compiler/rustc_typeck/src/check/_match.rs
index 20332e75c42..27329f8eab4 100644
--- a/compiler/rustc_typeck/src/check/_match.rs
+++ b/compiler/rustc_typeck/src/check/_match.rs
@@ -4,7 +4,7 @@ use rustc_errors::{Applicability, MultiSpan};
 use rustc_hir::{self as hir, ExprKind};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_infer::traits::Obligation;
-use rustc_middle::ty::{self, Subst, ToPredicate, Ty};
+use rustc_middle::ty::{self, ToPredicate, Ty};
 use rustc_span::Span;
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::{
diff --git a/compiler/rustc_typeck/src/check/callee.rs b/compiler/rustc_typeck/src/check/callee.rs
index 0d35c2479dd..c82a31e65cf 100644
--- a/compiler/rustc_typeck/src/check/callee.rs
+++ b/compiler/rustc_typeck/src/check/callee.rs
@@ -17,7 +17,7 @@ use rustc_infer::{
 use rustc_middle::ty::adjustment::{
     Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability,
 };
-use rustc_middle::ty::subst::{Subst, SubstsRef};
+use rustc_middle::ty::SubstsRef;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::{sym, Ident};
diff --git a/compiler/rustc_typeck/src/check/closure.rs b/compiler/rustc_typeck/src/check/closure.rs
index 9b943b160f3..a13d73c471b 100644
--- a/compiler/rustc_typeck/src/check/closure.rs
+++ b/compiler/rustc_typeck/src/check/closure.rs
@@ -3,7 +3,6 @@
 use super::{check_fn, Expectation, FnCtxt, GeneratorTypes};
 
 use crate::astconv::AstConv;
-use crate::rustc_middle::ty::subst::Subst;
 use hir::def::DefKind;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
diff --git a/compiler/rustc_typeck/src/check/compare_method.rs b/compiler/rustc_typeck/src/check/compare_method.rs
index 0c6d8f26f1d..7c0b815e42a 100644
--- a/compiler/rustc_typeck/src/check/compare_method.rs
+++ b/compiler/rustc_typeck/src/check/compare_method.rs
@@ -12,8 +12,8 @@ use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKi
 use rustc_infer::infer::{self, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
 use rustc_middle::ty::util::ExplicitSelf;
+use rustc_middle::ty::InternalSubsts;
 use rustc_middle::ty::{
     self, AssocItem, DefIdTree, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable,
 };
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
index a40478db969..70b9c732ff4 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
@@ -20,14 +20,12 @@ use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
 use rustc_infer::infer::{InferOk, InferResult};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{
-    self, GenericArgKind, InternalSubsts, Subst, SubstsRef, UserSelfTy, UserSubsts,
-};
 use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{
     self, AdtKind, CanonicalUserType, DefIdTree, EarlyBinder, GenericParamDefKind, ToPolyTraitRef,
     ToPredicate, Ty, UserType,
 };
+use rustc_middle::ty::{GenericArgKind, InternalSubsts, SubstsRef, UserSelfTy, UserSubsts};
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
@@ -559,7 +557,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
     pub fn register_wf_obligation(
         &self,
-        arg: subst::GenericArg<'tcx>,
+        arg: ty::GenericArg<'tcx>,
         span: Span,
         code: traits::ObligationCauseCode<'tcx>,
     ) {
@@ -1271,7 +1269,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 &mut self,
                 param: &ty::GenericParamDef,
                 arg: &GenericArg<'_>,
-            ) -> subst::GenericArg<'tcx> {
+            ) -> ty::GenericArg<'tcx> {
                 match (&param.kind, arg) {
                     (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
                         <dyn AstConv<'_>>::ast_region_to_region(self.fcx, lt, Some(param)).into()
@@ -1295,10 +1293,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             fn inferred_kind(
                 &mut self,
-                substs: Option<&[subst::GenericArg<'tcx>]>,
+                substs: Option<&[ty::GenericArg<'tcx>]>,
                 param: &ty::GenericParamDef,
                 infer_args: bool,
-            ) -> subst::GenericArg<'tcx> {
+            ) -> ty::GenericArg<'tcx> {
                 let tcx = self.fcx.tcx();
                 match param.kind {
                     GenericParamDefKind::Lifetime => {
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs b/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
index ee0ad7b5d0a..c32d1309031 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs
@@ -14,7 +14,7 @@ use rustc_hir::{
 use rustc_infer::infer::{self, TyCtxtInferExt};
 use rustc_infer::traits::{self, StatementAsExpression};
 use rustc_middle::lint::in_external_macro;
-use rustc_middle::ty::{self, Binder, IsSuggestable, Subst, ToPredicate, Ty};
+use rustc_middle::ty::{self, Binder, IsSuggestable, ToPredicate, Ty};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_trait_selection::infer::InferCtxtExt;
diff --git a/compiler/rustc_typeck/src/check/intrinsic.rs b/compiler/rustc_typeck/src/check/intrinsic.rs
index c7425ff7865..ae484b4feda 100644
--- a/compiler/rustc_typeck/src/check/intrinsic.rs
+++ b/compiler/rustc_typeck/src/check/intrinsic.rs
@@ -10,7 +10,6 @@ use crate::require_same_types;
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_target::spec::abi::Abi;
diff --git a/compiler/rustc_typeck/src/check/method/confirm.rs b/compiler/rustc_typeck/src/check/method/confirm.rs
index 59fd5c315ae..30731cbd03d 100644
--- a/compiler/rustc_typeck/src/check/method/confirm.rs
+++ b/compiler/rustc_typeck/src/check/method/confirm.rs
@@ -10,7 +10,7 @@ use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast};
 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::subst::{self, Subst, SubstsRef};
+use rustc_middle::ty::subst::{self, SubstsRef};
 use rustc_middle::ty::{self, GenericParamDefKind, Ty};
 use rustc_span::Span;
 use rustc_trait_selection::traits;
diff --git a/compiler/rustc_typeck/src/check/method/mod.rs b/compiler/rustc_typeck/src/check/method/mod.rs
index 249e9c66ba7..3fe9bea2299 100644
--- a/compiler/rustc_typeck/src/check/method/mod.rs
+++ b/compiler/rustc_typeck/src/check/method/mod.rs
@@ -18,7 +18,6 @@ use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Namespace};
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::{self, InferOk};
-use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::subst::{InternalSubsts, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TypeVisitable};
 use rustc_span::symbol::Ident;
diff --git a/compiler/rustc_typeck/src/check/method/probe.rs b/compiler/rustc_typeck/src/check/method/probe.rs
index e9f55ab3406..6cd7ced01a3 100644
--- a/compiler/rustc_typeck/src/check/method/probe.rs
+++ b/compiler/rustc_typeck/src/check/method/probe.rs
@@ -19,9 +19,9 @@ use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitable};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::lev_distance::{
diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs
index cfae63e4a06..618b01fc55f 100644
--- a/compiler/rustc_typeck/src/check/mod.rs
+++ b/compiler/rustc_typeck/src/check/mod.rs
@@ -112,8 +112,8 @@ use rustc_hir::{HirIdMap, ImplicitSelfKind, Node};
 use rustc_index::bit_set::BitSet;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef};
 use rustc_middle::ty::{self, Ty, TyCtxt, UserType};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::config;
 use rustc_session::parse::feature_err;
 use rustc_session::Session;
diff --git a/compiler/rustc_typeck/src/check/wfcheck.rs b/compiler/rustc_typeck/src/check/wfcheck.rs
index 27b3da8ab3d..fd5df0d9fa1 100644
--- a/compiler/rustc_typeck/src/check/wfcheck.rs
+++ b/compiler/rustc_typeck/src/check/wfcheck.rs
@@ -12,12 +12,12 @@ use rustc_infer::infer::outlives::obligations::TypeOutlives;
 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts, Subst};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{
     self, AdtKind, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable,
     TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
+use rustc_middle::ty::{GenericArgKind, InternalSubsts};
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
diff --git a/compiler/rustc_typeck/src/outlives/implicit_infer.rs b/compiler/rustc_typeck/src/outlives/implicit_infer.rs
index 3b779280eda..064a70107fe 100644
--- a/compiler/rustc_typeck/src/outlives/implicit_infer.rs
+++ b/compiler/rustc_typeck/src/outlives/implicit_infer.rs
@@ -1,8 +1,8 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt};
+use rustc_middle::ty::{GenericArg, GenericArgKind};
 use rustc_span::Span;
 
 use super::explicit::ExplicitPredicatesMap;