diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index e9e1095a4ae5e..e6a7c08429bd4 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -57,6 +57,7 @@ use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
 use rustc_hir::def_id::{LocalDefId, LocalDefIdMap, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::{ConstArg, GenericArg, ItemLocalMap, ParamName, TraitCandidate};
 use rustc_index::{Idx, IndexSlice, IndexVec};
+use rustc_macros::extension;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
 use rustc_session::parse::{add_feature_diagnostics, feature_err};
@@ -190,15 +191,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     }
 }
 
-trait ResolverAstLoweringExt {
-    fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
-    fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
-    fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
-    fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
-    fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
-    fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
-}
-
+#[extension]
 impl ResolverAstLoweringExt for ResolverAstLowering {
     fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
         if let ExprKind::Path(None, path) = &expr.kind {
diff --git a/compiler/rustc_borrowck/src/facts.rs b/compiler/rustc_borrowck/src/facts.rs
index 68dc9a6764bfc..da14408fb6961 100644
--- a/compiler/rustc_borrowck/src/facts.rs
+++ b/compiler/rustc_borrowck/src/facts.rs
@@ -2,6 +2,7 @@ use crate::location::{LocationIndex, LocationTable};
 use crate::BorrowIndex;
 use polonius_engine::AllFacts as PoloniusFacts;
 use polonius_engine::Atom;
+use rustc_macros::extension;
 use rustc_middle::mir::Local;
 use rustc_middle::ty::{RegionVid, TyCtxt};
 use rustc_mir_dataflow::move_paths::MovePathIndex;
@@ -24,20 +25,10 @@ impl polonius_engine::FactTypes for RustcFacts {
 
 pub type AllFacts = PoloniusFacts<RustcFacts>;
 
-pub(crate) trait AllFactsExt {
+#[extension]
+pub(crate) impl AllFactsExt for AllFacts {
     /// Returns `true` if there is a need to gather `AllFacts` given the
     /// current `-Z` flags.
-    fn enabled(tcx: TyCtxt<'_>) -> bool;
-
-    fn write_to_dir(
-        &self,
-        dir: impl AsRef<Path>,
-        location_table: &LocationTable,
-    ) -> Result<(), Box<dyn Error>>;
-}
-
-impl AllFactsExt for AllFacts {
-    /// Return
     fn enabled(tcx: TyCtxt<'_>) -> bool {
         tcx.sess.opts.unstable_opts.nll_facts
             || tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled()
diff --git a/compiler/rustc_borrowck/src/place_ext.rs b/compiler/rustc_borrowck/src/place_ext.rs
index b59ab7fafa576..ac8991ccf00bd 100644
--- a/compiler/rustc_borrowck/src/place_ext.rs
+++ b/compiler/rustc_borrowck/src/place_ext.rs
@@ -1,24 +1,16 @@
 use crate::borrow_set::LocalsStateAtExit;
 use rustc_hir as hir;
+use rustc_macros::extension;
 use rustc_middle::mir::ProjectionElem;
 use rustc_middle::mir::{Body, Mutability, Place};
 use rustc_middle::ty::{self, TyCtxt};
 
-/// Extension methods for the `Place` type.
-pub trait PlaceExt<'tcx> {
+#[extension]
+pub impl<'tcx> PlaceExt<'tcx> for Place<'tcx> {
     /// Returns `true` if we can safely ignore borrows of this place.
     /// This is true whenever there is no action that the user can do
     /// to the place `self` that would invalidate the borrow. This is true
     /// for borrows of raw pointer dereferents as well as shared references.
-    fn ignore_borrow(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        body: &Body<'tcx>,
-        locals_state_at_exit: &LocalsStateAtExit,
-    ) -> bool;
-}
-
-impl<'tcx> PlaceExt<'tcx> for Place<'tcx> {
     fn ignore_borrow(
         &self,
         tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index cd2fe56ca4916..4aac392ef392e 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -6,6 +6,7 @@ use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::infer::TyCtxtInferExt as _;
 use rustc_infer::traits::{Obligation, ObligationCause};
+use rustc_macros::extension;
 use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, Ty, TyCtxt, TypeFoldable};
@@ -225,15 +226,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     }
 }
 
-pub trait InferCtxtExt<'tcx> {
-    fn infer_opaque_definition_from_instantiation(
-        &self,
-        opaque_type_key: OpaqueTypeKey<'tcx>,
-        instantiated_ty: OpaqueHiddenType<'tcx>,
-    ) -> Ty<'tcx>;
-}
-
-impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     /// Given the fully resolved, instantiated type for an opaque
     /// type, i.e., the value of an inference variable like C1 or C2
     /// (*), computes the "definition type" for an opaque type
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 90e8f1b93b294..f9a8543e28d2b 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -22,6 +22,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_hir::BodyOwnerKind;
 use rustc_index::IndexVec;
 use rustc_infer::infer::NllRegionVariableOrigin;
+use rustc_macros::extension;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, InlineConstArgs, InlineConstArgsParts, RegionVid, Ty, TyCtxt};
@@ -793,26 +794,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
     }
 }
 
-trait InferCtxtExt<'tcx> {
-    fn replace_free_regions_with_nll_infer_vars<T>(
-        &self,
-        origin: NllRegionVariableOrigin,
-        value: T,
-    ) -> T
-    where
-        T: TypeFoldable<TyCtxt<'tcx>>;
-
-    fn replace_bound_regions_with_nll_infer_vars<T>(
-        &self,
-        origin: NllRegionVariableOrigin,
-        all_outlive_scope: LocalDefId,
-        value: ty::Binder<'tcx, T>,
-        indices: &mut UniversalRegionIndices<'tcx>,
-    ) -> T
-    where
-        T: TypeFoldable<TyCtxt<'tcx>>;
-}
-
+#[extension]
 impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
     #[instrument(skip(self), level = "debug")]
     fn replace_free_regions_with_nll_infer_vars<T>(
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 287cb8809086a..9fb6103183bbc 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -14,6 +14,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{GenericArg, GenericParam, GenericParamKind, HirIdMap, LifetimeName, Node};
+use rustc_macros::extension;
 use rustc_middle::bug;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::resolve_bound_vars::*;
@@ -27,16 +28,7 @@ use std::fmt;
 
 use crate::errors;
 
-trait RegionExt {
-    fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg);
-
-    fn late(index: u32, param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg);
-
-    fn id(&self) -> Option<DefId>;
-
-    fn shifted(self, amount: u32) -> ResolvedArg;
-}
-
+#[extension]
 impl RegionExt for ResolvedArg {
     fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) {
         debug!("ResolvedArg::early: def_id={:?}", param.def_id);
diff --git a/compiler/rustc_infer/src/infer/canonical/instantiate.rs b/compiler/rustc_infer/src/infer/canonical/instantiate.rs
index f6b583151fdf3..54940a2b4988c 100644
--- a/compiler/rustc_infer/src/infer/canonical/instantiate.rs
+++ b/compiler/rustc_infer/src/infer/canonical/instantiate.rs
@@ -13,12 +13,16 @@ use rustc_middle::ty::{self, TyCtxt};
 
 /// FIXME(-Znext-solver): This or public because it is shared with the
 /// new trait solver implementation. We should deduplicate canonicalization.
-pub trait CanonicalExt<'tcx, V> {
+#[extension]
+pub impl<'tcx, V> CanonicalExt<'tcx, V> for Canonical<'tcx, V> {
     /// Instantiate the wrapped value, replacing each canonical value
     /// with the value given in `var_values`.
     fn instantiate(&self, tcx: TyCtxt<'tcx>, var_values: &CanonicalVarValues<'tcx>) -> V
     where
-        V: TypeFoldable<TyCtxt<'tcx>>;
+        V: TypeFoldable<TyCtxt<'tcx>>,
+    {
+        self.instantiate_projected(tcx, var_values, |value| value.clone())
+    }
 
     /// Allows one to apply a instantiation to some subset of
     /// `self.value`. Invoke `projection_fn` with `self.value` to get
@@ -26,24 +30,6 @@ pub trait CanonicalExt<'tcx, V> {
     /// variables bound in `self` (usually this extracts from subset
     /// of `self`). Apply the instantiation `var_values` to this value
     /// V, replacing each of the canonical variables.
-    fn instantiate_projected<T>(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        var_values: &CanonicalVarValues<'tcx>,
-        projection_fn: impl FnOnce(&V) -> T,
-    ) -> T
-    where
-        T: TypeFoldable<TyCtxt<'tcx>>;
-}
-
-impl<'tcx, V> CanonicalExt<'tcx, V> for Canonical<'tcx, V> {
-    fn instantiate(&self, tcx: TyCtxt<'tcx>, var_values: &CanonicalVarValues<'tcx>) -> V
-    where
-        V: TypeFoldable<TyCtxt<'tcx>>,
-    {
-        self.instantiate_projected(tcx, var_values, |value| value.clone())
-    }
-
     fn instantiate_projected<T>(
         &self,
         tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 104bf4a5be873..37efafc5972f2 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -2786,19 +2786,8 @@ pub enum FailureCode {
     Error0644,
 }
 
-pub trait ObligationCauseExt<'tcx> {
-    fn as_failure_code(&self, terr: TypeError<'tcx>) -> FailureCode;
-
-    fn as_failure_code_diag(
-        &self,
-        terr: TypeError<'tcx>,
-        span: Span,
-        subdiags: Vec<TypeErrorAdditionalDiags>,
-    ) -> ObligationCauseFailureCode;
-    fn as_requirement_str(&self) -> &'static str;
-}
-
-impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
+#[extension]
+pub impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
     fn as_failure_code(&self, terr: TypeError<'tcx>) -> FailureCode {
         use self::FailureCode::*;
         use crate::traits::ObligationCauseCode::*;
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 2caf3b3cc9364..b9ebd685ca9f2 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -626,11 +626,8 @@ pub struct InferCtxtBuilder<'tcx> {
     next_trait_solver: bool,
 }
 
-pub trait TyCtxtInferExt<'tcx> {
-    fn infer_ctxt(self) -> InferCtxtBuilder<'tcx>;
-}
-
-impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> TyCtxtInferExt<'tcx> for TyCtxt<'tcx> {
     fn infer_ctxt(self) -> InferCtxtBuilder<'tcx> {
         InferCtxtBuilder {
             tcx: self,
diff --git a/compiler/rustc_infer/src/traits/engine.rs b/compiler/rustc_infer/src/traits/engine.rs
index 64b9714c7c086..79a29e2496807 100644
--- a/compiler/rustc_infer/src/traits/engine.rs
+++ b/compiler/rustc_infer/src/traits/engine.rs
@@ -52,18 +52,8 @@ pub trait TraitEngine<'tcx>: 'tcx {
     ) -> Vec<PredicateObligation<'tcx>>;
 }
 
-pub trait TraitEngineExt<'tcx> {
-    fn register_predicate_obligations(
-        &mut self,
-        infcx: &InferCtxt<'tcx>,
-        obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
-    );
-
-    #[must_use]
-    fn select_all_or_error(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>>;
-}
-
-impl<'tcx, T: ?Sized + TraitEngine<'tcx>> TraitEngineExt<'tcx> for T {
+#[extension]
+pub impl<'tcx, T: ?Sized + TraitEngine<'tcx>> TraitEngineExt<'tcx> for T {
     fn register_predicate_obligations(
         &mut self,
         infcx: &InferCtxt<'tcx>,
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 2b34f5daaf63f..1fb04f5bbfe34 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/compiler/rustc_middle/src/ty/layout.rs
@@ -23,20 +23,8 @@ use std::fmt;
 use std::num::NonZero;
 use std::ops::Bound;
 
-pub trait IntegerExt {
-    fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>, signed: bool) -> Ty<'tcx>;
-    fn from_int_ty<C: HasDataLayout>(cx: &C, ity: ty::IntTy) -> Integer;
-    fn from_uint_ty<C: HasDataLayout>(cx: &C, uty: ty::UintTy) -> Integer;
-    fn repr_discr<'tcx>(
-        tcx: TyCtxt<'tcx>,
-        ty: Ty<'tcx>,
-        repr: &ReprOptions,
-        min: i128,
-        max: i128,
-    ) -> (Integer, bool);
-}
-
-impl IntegerExt for Integer {
+#[extension]
+pub impl IntegerExt for Integer {
     #[inline]
     fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>, signed: bool) -> Ty<'tcx> {
         match (*self, signed) {
@@ -123,12 +111,8 @@ impl IntegerExt for Integer {
     }
 }
 
-pub trait PrimitiveExt {
-    fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
-    fn to_int_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
-}
-
-impl PrimitiveExt for Primitive {
+#[extension]
+pub impl PrimitiveExt for Primitive {
     #[inline]
     fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
         match *self {
diff --git a/compiler/rustc_middle/src/ty/util.rs b/compiler/rustc_middle/src/ty/util.rs
index 2addfa37f8b4d..98d19083aaba7 100644
--- a/compiler/rustc_middle/src/ty/util.rs
+++ b/compiler/rustc_middle/src/ty/util.rs
@@ -96,13 +96,8 @@ impl<'tcx> Discr<'tcx> {
     }
 }
 
-pub trait IntTypeExt {
-    fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
-    fn disr_incr<'tcx>(&self, tcx: TyCtxt<'tcx>, val: Option<Discr<'tcx>>) -> Option<Discr<'tcx>>;
-    fn initial_discriminant<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Discr<'tcx>;
-}
-
-impl IntTypeExt for IntegerType {
+#[extension]
+pub impl IntTypeExt for IntegerType {
     fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
         match self {
             IntegerType::Pointer(true) => tcx.types.isize,
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index ef4a0f52f9ea7..8406880477e4d 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -17,49 +17,8 @@ use std::fmt::Debug;
 
 pub use rustc_infer::infer::*;
 
-pub trait InferCtxtExt<'tcx> {
-    fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool;
-
-    fn type_is_sized_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool;
-
-    /// Check whether a `ty` implements given trait(trait_def_id) without side-effects.
-    ///
-    /// The inputs are:
-    ///
-    /// - the def-id of the trait
-    /// - the type parameters of the trait, including the self-type
-    /// - the parameter environment
-    ///
-    /// Invokes `evaluate_obligation`, so in the event that evaluating
-    /// `Ty: Trait` causes overflow, EvaluatedToErrStackDependent
-    /// (or EvaluatedToAmbigStackDependent) will be returned.
-    fn type_implements_trait(
-        &self,
-        trait_def_id: DefId,
-        params: impl IntoIterator<Item: Into<GenericArg<'tcx>>>,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> traits::EvaluationResult;
-
-    /// Returns `Some` if a type implements a trait shallowly, without side-effects,
-    /// along with any errors that would have been reported upon further obligation
-    /// processing.
-    ///
-    /// - If this returns `Some([])`, then the trait holds modulo regions.
-    /// - If this returns `Some([errors..])`, then the trait has an impl for
-    /// the self type, but some nested obligations do not hold.
-    /// - If this returns `None`, no implementation that applies could be found.
-    ///
-    /// FIXME(-Znext-solver): Due to the recursive nature of the new solver,
-    /// this will probably only ever return `Some([])` or `None`.
-    fn type_implements_trait_shallow(
-        &self,
-        trait_def_id: DefId,
-        ty: Ty<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> Option<Vec<traits::FulfillmentError<'tcx>>>;
-}
-
-impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     fn type_is_copy_modulo_regions(&self, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
         let ty = self.resolve_vars_if_possible(ty);
 
@@ -81,6 +40,17 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, lang_item)
     }
 
+    /// Check whether a `ty` implements given trait(trait_def_id) without side-effects.
+    ///
+    /// The inputs are:
+    ///
+    /// - the def-id of the trait
+    /// - the type parameters of the trait, including the self-type
+    /// - the parameter environment
+    ///
+    /// Invokes `evaluate_obligation`, so in the event that evaluating
+    /// `Ty: Trait` causes overflow, EvaluatedToErrStackDependent
+    /// (or EvaluatedToAmbigStackDependent) will be returned.
     #[instrument(level = "debug", skip(self, params), ret)]
     fn type_implements_trait(
         &self,
@@ -99,6 +69,17 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         self.evaluate_obligation(&obligation).unwrap_or(traits::EvaluationResult::EvaluatedToErr)
     }
 
+    /// Returns `Some` if a type implements a trait shallowly, without side-effects,
+    /// along with any errors that would have been reported upon further obligation
+    /// processing.
+    ///
+    /// - If this returns `Some([])`, then the trait holds modulo regions.
+    /// - If this returns `Some([errors..])`, then the trait has an impl for
+    /// the self type, but some nested obligations do not hold.
+    /// - If this returns `None`, no implementation that applies could be found.
+    ///
+    /// FIXME(-Znext-solver): Due to the recursive nature of the new solver,
+    /// this will probably only ever return `Some([])` or `None`.
     fn type_implements_trait_shallow(
         &self,
         trait_def_id: DefId,
@@ -124,19 +105,8 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     }
 }
 
-pub trait InferCtxtBuilderExt<'tcx> {
-    fn enter_canonical_trait_query<K, R>(
-        self,
-        canonical_key: &Canonical<'tcx, K>,
-        operation: impl FnOnce(&ObligationCtxt<'_, 'tcx>, K) -> Result<R, NoSolution>,
-    ) -> Result<CanonicalQueryResponse<'tcx, R>, NoSolution>
-    where
-        K: TypeFoldable<TyCtxt<'tcx>>,
-        R: Debug + TypeFoldable<TyCtxt<'tcx>>,
-        Canonical<'tcx, QueryResponse<'tcx, R>>: ArenaAllocatable<'tcx>;
-}
-
-impl<'tcx> InferCtxtBuilderExt<'tcx> for InferCtxtBuilder<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtBuilderExt<'tcx> for InferCtxtBuilder<'tcx> {
     /// The "main method" for a canonicalized trait query. Given the
     /// canonical key `canonical_key`, this method will create a new
     /// inference context, instantiate the key, and run your operation
diff --git a/compiler/rustc_trait_selection/src/regions.rs b/compiler/rustc_trait_selection/src/regions.rs
index 756db7cc2063f..dc9edb6063d75 100644
--- a/compiler/rustc_trait_selection/src/regions.rs
+++ b/compiler/rustc_trait_selection/src/regions.rs
@@ -3,20 +3,14 @@ use rustc_infer::infer::{InferCtxt, RegionResolutionError};
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::ObligationCause;
 
-pub trait InferCtxtRegionExt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
     /// Resolve regions, using the deep normalizer to normalize any type-outlives
     /// obligations in the process. This is in `rustc_trait_selection` because
     /// we need to normalize.
     ///
     /// Prefer this method over `resolve_regions_with_normalize`, unless you are
     /// doing something specific for normalization.
-    fn resolve_regions(
-        &self,
-        outlives_env: &OutlivesEnvironment<'tcx>,
-    ) -> Vec<RegionResolutionError<'tcx>>;
-}
-
-impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
     fn resolve_regions(
         &self,
         outlives_env: &OutlivesEnvironment<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
index 803379af005f9..3abdc4a333053 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
@@ -131,22 +131,12 @@ pub enum GenerateProofTree {
     Never,
 }
 
-pub trait InferCtxtEvalExt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtEvalExt<'tcx> for InferCtxt<'tcx> {
     /// Evaluates a goal from **outside** of the trait solver.
     ///
     /// Using this while inside of the solver is wrong as it uses a new
     /// search graph which would break cycle detection.
-    fn evaluate_root_goal(
-        &self,
-        goal: Goal<'tcx, ty::Predicate<'tcx>>,
-        generate_proof_tree: GenerateProofTree,
-    ) -> (
-        Result<(bool, Certainty, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), NoSolution>,
-        Option<inspect::GoalEvaluation<'tcx>>,
-    );
-}
-
-impl<'tcx> InferCtxtEvalExt<'tcx> for InferCtxt<'tcx> {
     #[instrument(level = "debug", skip(self))]
     fn evaluate_root_goal(
         &self,
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
index eab5962443696..406f4c2f6151e 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
@@ -17,14 +17,8 @@ use crate::solve::inspect::ProofTreeBuilder;
 use crate::traits::StructurallyNormalizeExt;
 use crate::traits::TraitEngineExt;
 
-pub trait InferCtxtSelectExt<'tcx> {
-    fn select_in_new_trait_solver(
-        &self,
-        obligation: &PolyTraitObligation<'tcx>,
-    ) -> SelectionResult<'tcx, Selection<'tcx>>;
-}
-
-impl<'tcx> InferCtxtSelectExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtSelectExt<'tcx> for InferCtxt<'tcx> {
     fn select_in_new_trait_solver(
         &self,
         obligation: &PolyTraitObligation<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
index f33d0f397ce9e..1c6c2ff594a1b 100644
--- a/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
+++ b/compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
@@ -216,15 +216,8 @@ pub trait ProofTreeVisitor<'tcx> {
     fn visit_goal(&mut self, goal: &InspectGoal<'_, 'tcx>) -> ControlFlow<Self::BreakTy>;
 }
 
-pub trait ProofTreeInferCtxtExt<'tcx> {
-    fn visit_proof_tree<V: ProofTreeVisitor<'tcx>>(
-        &self,
-        goal: Goal<'tcx, ty::Predicate<'tcx>>,
-        visitor: &mut V,
-    ) -> ControlFlow<V::BreakTy>;
-}
-
-impl<'tcx> ProofTreeInferCtxtExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> ProofTreeInferCtxtExt<'tcx> for InferCtxt<'tcx> {
     fn visit_proof_tree<V: ProofTreeVisitor<'tcx>>(
         &self,
         goal: Goal<'tcx, ty::Predicate<'tcx>>,
diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs
index 94a3cef8ad14e..11e1e72e04e23 100644
--- a/compiler/rustc_trait_selection/src/solve/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/mod.rs
@@ -61,10 +61,7 @@ enum GoalEvaluationKind {
     Nested { is_normalizes_to_hack: IsNormalizesToHack },
 }
 
-trait CanonicalResponseExt {
-    fn has_no_inference_or_external_constraints(&self) -> bool;
-}
-
+#[extension]
 impl<'tcx> CanonicalResponseExt for Canonical<'tcx, Response<'tcx>> {
     fn has_no_inference_or_external_constraints(&self) -> bool {
         self.value.external_constraints.region_constraints.is_empty()
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index caf950037fdfd..b234b8a9d0327 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -27,11 +27,8 @@ use rustc_middle::ty::TypeFoldable;
 use rustc_middle::ty::Variance;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
-pub trait TraitEngineExt<'tcx> {
-    fn new(infcx: &InferCtxt<'tcx>) -> Box<Self>;
-}
-
-impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
+#[extension]
+pub impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
     fn new(infcx: &InferCtxt<'tcx>) -> Box<Self> {
         if infcx.next_trait_solver() {
             Box::new(NextFulfillmentCtxt::new(infcx))
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
index 15d064d4036ea..80581d01f6b0a 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs
@@ -11,38 +11,8 @@ use super::ArgKind;
 
 pub use rustc_infer::traits::error_reporting::*;
 
-pub trait InferCtxtExt<'tcx> {
-    /// Given some node representing a fn-like thing in the HIR map,
-    /// returns a span and `ArgKind` information that describes the
-    /// arguments it expects. This can be supplied to
-    /// `report_arg_count_mismatch`.
-    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
-
-    /// Reports an error when the number of arguments needed by a
-    /// trait match doesn't match the number that the expression
-    /// provides.
-    fn report_arg_count_mismatch(
-        &self,
-        span: Span,
-        found_span: Option<Span>,
-        expected_args: Vec<ArgKind>,
-        found_args: Vec<ArgKind>,
-        is_closure: bool,
-        closure_pipe_span: Option<Span>,
-    ) -> DiagnosticBuilder<'tcx>;
-
-    /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
-    /// in that order, and returns the generic type corresponding to the
-    /// argument of that trait (corresponding to the closure arguments).
-    fn type_implements_fn_trait(
-        &self,
-        param_env: ty::ParamEnv<'tcx>,
-        ty: ty::Binder<'tcx, Ty<'tcx>>,
-        polarity: ty::ImplPolarity,
-    ) -> Result<(ty::ClosureKind, ty::Binder<'tcx, Ty<'tcx>>), ()>;
-}
-
-impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     /// Given some node representing a fn-like thing in the HIR map,
     /// returns a span and `ArgKind` information that describes the
     /// arguments it expects. This can be supplied to
@@ -229,6 +199,9 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         err
     }
 
+    /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
+    /// in that order, and returns the generic type corresponding to the
+    /// argument of that trait (corresponding to the closure arguments).
     fn type_implements_fn_trait(
         &self,
         param_env: ty::ParamEnv<'tcx>,
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 f0773fd1671e2..7d7f415c7bb7a 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
@@ -23,24 +23,6 @@ use crate::errors::{
 
 use crate::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt;
 
-pub trait TypeErrCtxtExt<'tcx> {
-    /*private*/
-    fn impl_similar_to(
-        &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> Option<(DefId, GenericArgsRef<'tcx>)>;
-
-    /*private*/
-    fn describe_enclosure(&self, def_id: LocalDefId) -> Option<&'static str>;
-
-    fn on_unimplemented_note(
-        &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> OnUnimplementedNote;
-}
-
 /// The symbols which are always allowed in a format string
 static ALLOWED_FORMAT_SYMBOLS: &[Symbol] = &[
     kw::SelfUpper,
@@ -56,7 +38,8 @@ static ALLOWED_FORMAT_SYMBOLS: &[Symbol] = &[
     sym::Trait,
 ];
 
-impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
+#[extension]
+pub impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn impl_similar_to(
         &self,
         trait_ref: ty::PolyTraitRef<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 335e6ff28226e..58c731a8ed7f4 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -106,279 +106,6 @@ impl<'tcx, 'a> CoroutineData<'tcx, 'a> {
     }
 }
 
-// This trait is public to expose the diagnostics methods to clippy.
-pub trait TypeErrCtxtExt<'tcx> {
-    fn suggest_restricting_param_bound(
-        &self,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-        associated_item: Option<(&'static str, Ty<'tcx>)>,
-        body_id: LocalDefId,
-    );
-
-    fn suggest_dereferences(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn get_closure_name(
-        &self,
-        def_id: DefId,
-        err: &mut Diagnostic,
-        msg: Cow<'static, str>,
-    ) -> Option<Symbol>;
-
-    fn suggest_fn_call(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn check_for_binding_assigned_block_without_tail_expression(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    );
-
-    fn suggest_add_clone_to_arg(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn extract_callable_info(
-        &self,
-        body_id: LocalDefId,
-        param_env: ty::ParamEnv<'tcx>,
-        found: Ty<'tcx>,
-    ) -> Option<(DefIdOrName, Ty<'tcx>, Vec<Ty<'tcx>>)>;
-
-    fn suggest_add_reference_to_arg(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-        has_custom_message: bool,
-    ) -> bool;
-
-    fn suggest_borrowing_for_object_cast(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-        self_ty: Ty<'tcx>,
-        object_ty: Ty<'tcx>,
-    );
-
-    fn suggest_remove_reference(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn suggest_remove_await(&self, obligation: &PredicateObligation<'tcx>, err: &mut Diagnostic);
-
-    fn suggest_change_mut(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    );
-
-    fn suggest_semicolon_removal(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        span: Span,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn return_type_span(&self, obligation: &PredicateObligation<'tcx>) -> Option<Span>;
-
-    fn suggest_impl_trait(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn point_at_returns_when_relevant(
-        &self,
-        err: &mut DiagnosticBuilder<'tcx>,
-        obligation: &PredicateObligation<'tcx>,
-    );
-
-    fn report_closure_arg_mismatch(
-        &self,
-        span: Span,
-        found_span: Option<Span>,
-        found: ty::PolyTraitRef<'tcx>,
-        expected: ty::PolyTraitRef<'tcx>,
-        cause: &ObligationCauseCode<'tcx>,
-        found_node: Option<Node<'_>>,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> DiagnosticBuilder<'tcx>;
-
-    fn note_conflicting_fn_args(
-        &self,
-        err: &mut Diagnostic,
-        cause: &ObligationCauseCode<'tcx>,
-        expected: Ty<'tcx>,
-        found: Ty<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-    );
-
-    fn note_conflicting_closure_bounds(
-        &self,
-        cause: &ObligationCauseCode<'tcx>,
-        err: &mut DiagnosticBuilder<'tcx>,
-    );
-
-    fn suggest_fully_qualified_path(
-        &self,
-        err: &mut Diagnostic,
-        item_def_id: DefId,
-        span: Span,
-        trait_ref: DefId,
-    );
-
-    fn maybe_note_obligation_cause_for_async_await(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> bool;
-
-    fn note_obligation_cause_for_async_await(
-        &self,
-        err: &mut Diagnostic,
-        interior_or_upvar_span: CoroutineInteriorOrUpvar,
-        is_async: bool,
-        outer_coroutine: Option<DefId>,
-        trait_pred: ty::TraitPredicate<'tcx>,
-        target_ty: Ty<'tcx>,
-        obligation: &PredicateObligation<'tcx>,
-        next_code: Option<&ObligationCauseCode<'tcx>>,
-    );
-
-    fn note_obligation_cause_code<T>(
-        &self,
-        body_id: LocalDefId,
-        err: &mut Diagnostic,
-        predicate: T,
-        param_env: ty::ParamEnv<'tcx>,
-        cause_code: &ObligationCauseCode<'tcx>,
-        obligated_types: &mut Vec<Ty<'tcx>>,
-        seen_requirements: &mut FxHashSet<DefId>,
-    ) where
-        T: ToPredicate<'tcx>;
-
-    /// Suggest to await before try: future? => future.await?
-    fn suggest_await_before_try(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-        span: Span,
-    );
-
-    fn suggest_floating_point_literal(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_ref: &ty::PolyTraitRef<'tcx>,
-    );
-
-    fn suggest_derive(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    );
-
-    fn suggest_dereferencing_index(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        err: &mut Diagnostic,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    );
-
-    fn suggest_option_method_if_applicable(
-        &self,
-        failed_pred: ty::Predicate<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        err: &mut Diagnostic,
-        expr: &hir::Expr<'_>,
-    );
-
-    fn note_function_argument_obligation(
-        &self,
-        body_id: LocalDefId,
-        err: &mut Diagnostic,
-        arg_hir_id: HirId,
-        parent_code: &ObligationCauseCode<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        predicate: ty::Predicate<'tcx>,
-        call_hir_id: HirId,
-    );
-
-    fn look_for_iterator_item_mistakes(
-        &self,
-        assocs_in_this_method: &[Option<(Span, (DefId, Ty<'tcx>))>],
-        typeck_results: &TypeckResults<'tcx>,
-        type_diffs: &[TypeError<'tcx>],
-        param_env: ty::ParamEnv<'tcx>,
-        path_segment: &hir::PathSegment<'_>,
-        args: &[hir::Expr<'_>],
-        err: &mut Diagnostic,
-    );
-
-    fn point_at_chain(
-        &self,
-        expr: &hir::Expr<'_>,
-        typeck_results: &TypeckResults<'tcx>,
-        type_diffs: Vec<TypeError<'tcx>>,
-        param_env: ty::ParamEnv<'tcx>,
-        err: &mut Diagnostic,
-    );
-
-    fn probe_assoc_types_at_expr(
-        &self,
-        type_diffs: &[TypeError<'tcx>],
-        span: Span,
-        prev_ty: Ty<'tcx>,
-        body_id: hir::HirId,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> Vec<Option<(Span, (DefId, Ty<'tcx>))>>;
-
-    fn suggest_convert_to_slice(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        candidate_impls: &[ImplCandidate<'tcx>],
-        span: Span,
-    );
-
-    fn explain_hrtb_projection(
-        &self,
-        diag: &mut Diagnostic,
-        pred: ty::PolyTraitPredicate<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        cause: &ObligationCause<'tcx>,
-    );
-
-    fn suggest_desugaring_async_fn_in_trait(
-        &self,
-        err: &mut Diagnostic,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-    );
-}
-
 fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
     (
         generics.tail_span_for_predicate_suggestion(),
@@ -509,7 +236,8 @@ pub fn suggest_restriction<'tcx>(
     }
 }
 
-impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
+#[extension]
+pub impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn suggest_restricting_param_bound(
         &self,
         err: &mut Diagnostic,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
index 68b1a0d4e61cd..92992de64ffb9 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
@@ -57,78 +57,8 @@ use super::{
 
 pub use rustc_infer::traits::error_reporting::*;
 
-pub trait TypeErrCtxtExt<'tcx> {
-    fn build_overflow_error<T>(
-        &self,
-        predicate: &T,
-        span: Span,
-        suggest_increasing_limit: bool,
-    ) -> DiagnosticBuilder<'tcx>
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>;
-
-    fn report_overflow_error<T>(
-        &self,
-        predicate: &T,
-        span: Span,
-        suggest_increasing_limit: bool,
-        mutate: impl FnOnce(&mut Diagnostic),
-    ) -> !
-    where
-        T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>;
-
-    fn report_overflow_no_abort(&self, obligation: PredicateObligation<'tcx>) -> ErrorGuaranteed;
-
-    fn report_fulfillment_errors(&self, errors: Vec<FulfillmentError<'tcx>>) -> ErrorGuaranteed;
-
-    fn report_overflow_obligation<T>(
-        &self,
-        obligation: &Obligation<'tcx, T>,
-        suggest_increasing_limit: bool,
-    ) -> !
-    where
-        T: ToPredicate<'tcx> + Clone;
-
-    fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
-
-    fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
-
-    /// The `root_obligation` parameter should be the `root_obligation` field
-    /// from a `FulfillmentError`. If no `FulfillmentError` is available,
-    /// then it should be the same as `obligation`.
-    fn report_selection_error(
-        &self,
-        obligation: PredicateObligation<'tcx>,
-        root_obligation: &PredicateObligation<'tcx>,
-        error: &SelectionError<'tcx>,
-    ) -> ErrorGuaranteed;
-
-    fn emit_specialized_closure_kind_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-    ) -> Option<ErrorGuaranteed>;
-
-    fn fn_arg_obligation(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> Result<(), ErrorGuaranteed>;
-
-    fn try_conversion_context(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        trait_ref: ty::TraitRef<'tcx>,
-        err: &mut Diagnostic,
-    ) -> bool;
-
-    fn report_const_param_not_wf(
-        &self,
-        ty: Ty<'tcx>,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> DiagnosticBuilder<'tcx>;
-}
-
-impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
+#[extension]
+pub impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn report_fulfillment_errors(
         &self,
         mut errors: Vec<FulfillmentError<'tcx>>,
@@ -382,6 +312,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err.emit()
     }
 
+    /// The `root_obligation` parameter should be the `root_obligation` field
+    /// from a `FulfillmentError`. If no `FulfillmentError` is available,
+    /// then it should be the same as `obligation`.
     fn report_selection_error(
         &self,
         mut obligation: PredicateObligation<'tcx>,
@@ -1393,209 +1326,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     }
 }
 
-pub(super) trait InferCtxtPrivExt<'tcx> {
-    // returns if `cond` not occurring implies that `error` does not occur - i.e., that
-    // `error` occurring implies that `cond` occurs.
-    fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool;
-
-    fn report_fulfillment_error(&self, error: &FulfillmentError<'tcx>) -> ErrorGuaranteed;
-
-    fn report_projection_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        error: &MismatchedProjectionTypes<'tcx>,
-    ) -> ErrorGuaranteed;
-
-    fn maybe_detailed_projection_msg(
-        &self,
-        pred: ty::ProjectionPredicate<'tcx>,
-        normalized_ty: ty::Term<'tcx>,
-        expected_ty: ty::Term<'tcx>,
-    ) -> Option<String>;
-
-    fn fuzzy_match_tys(
-        &self,
-        a: Ty<'tcx>,
-        b: Ty<'tcx>,
-        ignoring_lifetimes: bool,
-    ) -> Option<CandidateSimilarity>;
-
-    fn describe_closure(&self, kind: hir::ClosureKind) -> &'static str;
-
-    fn find_similar_impl_candidates(
-        &self,
-        trait_pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> Vec<ImplCandidate<'tcx>>;
-
-    fn report_similar_impl_candidates(
-        &self,
-        impl_candidates: &[ImplCandidate<'tcx>],
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        body_def_id: LocalDefId,
-        err: &mut Diagnostic,
-        other: bool,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> bool;
-
-    fn report_similar_impl_candidates_for_root_obligation(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        trait_predicate: ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
-        body_def_id: LocalDefId,
-        err: &mut Diagnostic,
-    );
-
-    /// Gets the parent trait chain start
-    fn get_parent_trait_ref(
-        &self,
-        code: &ObligationCauseCode<'tcx>,
-    ) -> Option<(Ty<'tcx>, Option<Span>)>;
-
-    /// If the `Self` type of the unsatisfied trait `trait_ref` implements a trait
-    /// with the same path as `trait_ref`, a help message about
-    /// a probable version mismatch is added to `err`
-    fn note_version_mismatch(
-        &self,
-        err: &mut Diagnostic,
-        trait_ref: &ty::PolyTraitRef<'tcx>,
-    ) -> bool;
-
-    /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
-    /// `trait_ref`.
-    ///
-    /// For this to work, `new_self_ty` must have no escaping bound variables.
-    fn mk_trait_obligation_with_new_self_ty(
-        &self,
-        param_env: ty::ParamEnv<'tcx>,
-        trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
-    ) -> PredicateObligation<'tcx>;
-
-    fn maybe_report_ambiguity(&self, obligation: &PredicateObligation<'tcx>) -> ErrorGuaranteed;
-
-    fn predicate_can_apply(
-        &self,
-        param_env: ty::ParamEnv<'tcx>,
-        pred: ty::PolyTraitPredicate<'tcx>,
-    ) -> bool;
-
-    fn note_obligation_cause(&self, err: &mut Diagnostic, obligation: &PredicateObligation<'tcx>);
-
-    fn suggest_unsized_bound_if_applicable(
-        &self,
-        err: &mut Diagnostic,
-        obligation: &PredicateObligation<'tcx>,
-    );
-
-    fn annotate_source_of_ambiguity(
-        &self,
-        err: &mut Diagnostic,
-        impls: &[ambiguity::Ambiguity],
-        predicate: ty::Predicate<'tcx>,
-    );
-
-    fn maybe_suggest_unsized_generics(&self, err: &mut Diagnostic, span: Span, node: Node<'tcx>);
-
-    fn maybe_indirection_for_unsized(
-        &self,
-        err: &mut Diagnostic,
-        item: &'tcx Item<'tcx>,
-        param: &'tcx GenericParam<'tcx>,
-    ) -> bool;
-
-    fn is_recursive_obligation(
-        &self,
-        obligated_types: &mut Vec<Ty<'tcx>>,
-        cause_code: &ObligationCauseCode<'tcx>,
-    ) -> bool;
-
-    fn get_standard_error_message(
-        &self,
-        trait_predicate: &ty::PolyTraitPredicate<'tcx>,
-        message: Option<String>,
-        predicate_is_const: bool,
-        append_const_msg: Option<AppendConstMessage>,
-        post_message: String,
-    ) -> String;
-
-    fn get_safe_transmute_error_and_reason(
-        &self,
-        obligation: PredicateObligation<'tcx>,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        span: Span,
-    ) -> GetSafeTransmuteErrorAndReason;
-
-    fn add_tuple_trait_message(
-        &self,
-        obligation_cause_code: &ObligationCauseCode<'tcx>,
-        err: &mut Diagnostic,
-    );
-
-    fn try_to_add_help_message(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        trait_predicate: &ty::PolyTraitPredicate<'tcx>,
-        err: &mut Diagnostic,
-        span: Span,
-        is_fn_trait: bool,
-        suggested: bool,
-        unsatisfied_const: bool,
-    );
-
-    fn add_help_message_for_fn_trait(
-        &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        err: &mut Diagnostic,
-        implemented_kind: ty::ClosureKind,
-        params: ty::Binder<'tcx, Ty<'tcx>>,
-    );
-
-    fn maybe_add_note_for_unsatisfied_const(
-        &self,
-        trait_predicate: &ty::PolyTraitPredicate<'tcx>,
-        err: &mut Diagnostic,
-        span: Span,
-    ) -> UnsatisfiedConst;
-
-    fn report_closure_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        closure_def_id: DefId,
-        found_kind: ty::ClosureKind,
-        kind: ty::ClosureKind,
-        trait_prefix: &'static str,
-    ) -> DiagnosticBuilder<'tcx>;
-
-    fn report_cyclic_signature_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-        expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-        terr: TypeError<'tcx>,
-    ) -> DiagnosticBuilder<'tcx>;
-
-    fn report_opaque_type_auto_trait_leakage(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        def_id: DefId,
-    ) -> DiagnosticBuilder<'tcx>;
-
-    fn report_signature_mismatch_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        span: Span,
-        found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-        expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-    ) -> Result<DiagnosticBuilder<'tcx>, ErrorGuaranteed>;
-
-    fn report_not_const_evaluatable_error(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-        span: Span,
-    ) -> Result<DiagnosticBuilder<'tcx>, ErrorGuaranteed>;
-}
-
-impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
+#[extension]
+pub(super) impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     // returns if `cond` not occurring implies that `error` does not occur - i.e., that
     // `error` occurring implies that `cond` occurs.
     fn error_implies(&self, cond: ty::Predicate<'tcx>, error: ty::Predicate<'tcx>) -> bool {
@@ -2414,6 +2146,10 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         suggested
     }
 
+    /// Creates a `PredicateObligation` with `new_self_ty` replacing the existing type in the
+    /// `trait_ref`.
+    ///
+    /// For this to work, `new_self_ty` must have no escaping bound variables.
     fn mk_trait_obligation_with_new_self_ty(
         &self,
         param_env: ty::ParamEnv<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index 52631d4353bfa..c4e8ea45dd32e 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -11,25 +11,6 @@ pub use rustc_middle::traits::query::OutlivesBound;
 
 pub type BoundsCompat<'a, 'tcx: 'a> = impl Iterator<Item = OutlivesBound<'tcx>> + 'a;
 pub type Bounds<'a, 'tcx: 'a> = impl Iterator<Item = OutlivesBound<'tcx>> + 'a;
-pub trait InferCtxtExt<'a, 'tcx> {
-    /// Do *NOT* call this directly.
-    fn implied_bounds_tys_compat(
-        &'a self,
-        param_env: ty::ParamEnv<'tcx>,
-        body_id: LocalDefId,
-        tys: &'a FxIndexSet<Ty<'tcx>>,
-        compat: bool,
-    ) -> BoundsCompat<'a, 'tcx>;
-
-    /// If `-Z no-implied-bounds-compat` is set, calls `implied_bounds_tys_compat`
-    /// with `compat` set to `true`, otherwise `false`.
-    fn implied_bounds_tys(
-        &'a self,
-        param_env: ty::ParamEnv<'tcx>,
-        body_id: LocalDefId,
-        tys: &'a FxIndexSet<Ty<'tcx>>,
-    ) -> Bounds<'a, 'tcx>;
-}
 
 /// Implied bounds are region relationships that we deduce
 /// automatically. The idea is that (e.g.) a caller must check that a
@@ -130,7 +111,9 @@ fn implied_outlives_bounds<'a, 'tcx>(
     bounds
 }
 
-impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
+    /// Do *NOT* call this directly.
     fn implied_bounds_tys_compat(
         &'a self,
         param_env: ParamEnv<'tcx>,
@@ -142,6 +125,8 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
             .flat_map(move |ty| implied_outlives_bounds(self, param_env, body_id, *ty, compat))
     }
 
+    /// If `-Z no-implied-bounds-compat` is set, calls `implied_bounds_tys_compat`
+    /// with `compat` set to `true`, otherwise `false`.
     fn implied_bounds_tys(
         &'a self,
         param_env: ParamEnv<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 049877bc5fed4..807540a1720a2 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -52,12 +52,22 @@ pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::AliasTy<'tcx>>;
 
 pub(super) struct InProgress;
 
-pub trait NormalizeExt<'tcx> {
+#[extension]
+pub impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
     /// Normalize a value using the `AssocTypeNormalizer`.
     ///
     /// This normalization should be used when the type contains inference variables or the
     /// projection may be fallible.
-    fn normalize<T: TypeFoldable<TyCtxt<'tcx>>>(&self, t: T) -> InferOk<'tcx, T>;
+    fn normalize<T: TypeFoldable<TyCtxt<'tcx>>>(&self, value: T) -> InferOk<'tcx, T> {
+        if self.infcx.next_trait_solver() {
+            InferOk { value, obligations: Vec::new() }
+        } else {
+            let mut selcx = SelectionContext::new(self.infcx);
+            let Normalized { value, obligations } =
+                normalize_with_depth(&mut selcx, self.param_env, self.cause.clone(), 0, value);
+            InferOk { value, obligations }
+        }
+    }
 
     /// Deeply normalizes `value`, replacing all aliases which can by normalized in
     /// the current environment. In the new solver this errors in case normalization
@@ -73,25 +83,6 @@ pub trait NormalizeExt<'tcx> {
     /// existing fulfillment context in the old solver. Once we also eagerly prove goals with
     /// the old solver or have removed the old solver, remove `traits::fully_normalize` and
     /// rename this function to `At::fully_normalize`.
-    fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
-        self,
-        value: T,
-        fulfill_cx: &mut dyn TraitEngine<'tcx>,
-    ) -> Result<T, Vec<FulfillmentError<'tcx>>>;
-}
-
-impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
-    fn normalize<T: TypeFoldable<TyCtxt<'tcx>>>(&self, value: T) -> InferOk<'tcx, T> {
-        if self.infcx.next_trait_solver() {
-            InferOk { value, obligations: Vec::new() }
-        } else {
-            let mut selcx = SelectionContext::new(self.infcx);
-            let Normalized { value, obligations } =
-                normalize_with_depth(&mut selcx, self.param_env, self.cause.clone(), 0, value);
-            InferOk { value, obligations }
-        }
-    }
-
     fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
         self,
         value: T,
diff --git a/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
index a050b30317a05..e56ad101d2997 100644
--- a/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
@@ -4,32 +4,8 @@ use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::InferCtxt;
 use crate::traits::{EvaluationResult, OverflowError, PredicateObligation, SelectionContext};
 
-pub trait InferCtxtExt<'tcx> {
-    fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool;
-
-    fn predicate_must_hold_considering_regions(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> bool;
-
-    fn predicate_must_hold_modulo_regions(&self, obligation: &PredicateObligation<'tcx>) -> bool;
-
-    fn evaluate_obligation(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> Result<EvaluationResult, OverflowError>;
-
-    // Helper function that canonicalizes and runs the query. If an
-    // overflow results, we re-run it in the local context so we can
-    // report a nice error.
-    /*crate*/
-    fn evaluate_obligation_no_overflow(
-        &self,
-        obligation: &PredicateObligation<'tcx>,
-    ) -> EvaluationResult;
-}
-
-impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
+#[extension]
+pub impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     /// Evaluates whether the predicate can be satisfied (by any means)
     /// in the given `ParamEnv`.
     fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool {
@@ -114,9 +90,9 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         }
     }
 
-    // Helper function that canonicalizes and runs the query. If an
-    // overflow results, we re-run it in the local context so we can
-    // report a nice error.
+    /// Helper function that canonicalizes and runs the query. If an
+    /// overflow results, we re-run it in the local context so we can
+    /// report a nice error.
     fn evaluate_obligation_no_overflow(
         &self,
         obligation: &PredicateObligation<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index 0b73fefd2da9d..7dd8a990c3fd6 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -22,20 +22,8 @@ use super::NoSolution;
 
 pub use rustc_middle::traits::query::NormalizationResult;
 
-pub trait QueryNormalizeExt<'tcx> {
-    /// Normalize a value using the `QueryNormalizer`.
-    ///
-    /// This normalization should *only* be used when the projection does not
-    /// have possible ambiguity or may not be well-formed.
-    ///
-    /// After codegen, when lifetimes do not matter, it is preferable to instead
-    /// use [`TyCtxt::normalize_erasing_regions`], which wraps this procedure.
-    fn query_normalize<T>(self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
-    where
-        T: TypeFoldable<TyCtxt<'tcx>>;
-}
-
-impl<'cx, 'tcx> QueryNormalizeExt<'tcx> for At<'cx, 'tcx> {
+#[extension]
+pub impl<'cx, 'tcx> QueryNormalizeExt<'tcx> for At<'cx, 'tcx> {
     /// Normalize `value` in the context of the inference context,
     /// yielding a resulting type, or an error if `value` cannot be
     /// normalized. If you don't care about regions, you should prefer
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index e9a592bdee799..57e3f72a2f3de 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -33,19 +33,7 @@ enum Inserted<'tcx> {
     ShouldRecurseOn(DefId),
 }
 
-trait ChildrenExt<'tcx> {
-    fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId);
-    fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId);
-
-    fn insert(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        impl_def_id: DefId,
-        simplified_self: Option<SimplifiedType>,
-        overlap_mode: OverlapMode,
-    ) -> Result<Inserted<'tcx>, OverlapError<'tcx>>;
-}
-
+#[extension]
 impl<'tcx> ChildrenExt<'tcx> for Children {
     /// Insert an impl into this set of children without comparing to any existing impls.
     fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
@@ -247,22 +235,8 @@ where
     }
 }
 
-pub trait GraphExt<'tcx> {
-    /// Insert a local impl into the specialization graph. If an existing impl
-    /// conflicts with it (has overlap, but neither specializes the other),
-    /// information about the area of overlap is returned in the `Err`.
-    fn insert(
-        &mut self,
-        tcx: TyCtxt<'tcx>,
-        impl_def_id: DefId,
-        overlap_mode: OverlapMode,
-    ) -> Result<Option<FutureCompatOverlapError<'tcx>>, OverlapError<'tcx>>;
-
-    /// Insert cached metadata mapping from a child impl back to its parent.
-    fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'tcx>, parent: DefId, child: DefId);
-}
-
-impl<'tcx> GraphExt<'tcx> for Graph {
+#[extension]
+pub impl<'tcx> GraphExt<'tcx> for Graph {
     /// Insert a local impl into the specialization graph. If an existing impl
     /// conflicts with it (has overlap, but neither specializes the other),
     /// information about the area of overlap is returned in the `Err`.
diff --git a/compiler/rustc_trait_selection/src/traits/structural_normalize.rs b/compiler/rustc_trait_selection/src/traits/structural_normalize.rs
index ed5d01d7048e6..7b0a4a69501ad 100644
--- a/compiler/rustc_trait_selection/src/traits/structural_normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/structural_normalize.rs
@@ -5,15 +5,8 @@ use rustc_middle::ty::{self, Ty};
 
 use crate::traits::{NormalizeExt, Obligation};
 
-pub trait StructurallyNormalizeExt<'tcx> {
-    fn structurally_normalize(
-        &self,
-        ty: Ty<'tcx>,
-        fulfill_cx: &mut dyn TraitEngine<'tcx>,
-    ) -> Result<Ty<'tcx>, Vec<FulfillmentError<'tcx>>>;
-}
-
-impl<'tcx> StructurallyNormalizeExt<'tcx> for At<'_, 'tcx> {
+#[extension]
+pub impl<'tcx> StructurallyNormalizeExt<'tcx> for At<'_, 'tcx> {
     fn structurally_normalize(
         &self,
         ty: Ty<'tcx>,