diff --git a/Cargo.lock b/Cargo.lock
index 1d7f93c789afe..6b9bb721e0186 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4303,6 +4303,13 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "rustc_next_trait_solver"
+version = "0.0.0"
+dependencies = [
+ "rustc_type_ir",
+]
+
 [[package]]
 name = "rustc_parse"
 version = "0.0.0"
@@ -4487,6 +4494,7 @@ dependencies = [
 name = "rustc_smir"
 version = "0.0.0"
 dependencies = [
+ "rustc_abi",
  "rustc_data_structures",
  "rustc_hir",
  "rustc_middle",
@@ -4571,6 +4579,7 @@ dependencies = [
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",
+ "rustc_next_trait_solver",
  "rustc_parse_format",
  "rustc_query_system",
  "rustc_session",
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 143454c71e1c4..b38a6ebd501e3 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -1591,10 +1591,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             {
                 let sig = self.tcx.fn_sig(assoc.def_id).instantiate_identity();
                 sig.inputs().skip_binder().get(0).and_then(|first| {
-                    if first.peel_refs() == rcvr_ty.peel_refs() {
-                        None
-                    } else {
+                    let impl_ty = self.tcx.type_of(*impl_did).instantiate_identity();
+                    // if the type of first arg is the same as the current impl type, we should take the first arg into assoc function
+                    if first.peel_refs() == impl_ty {
                         Some(first.ref_mutability().map_or("", |mutbl| mutbl.ref_prefix_str()))
+                    } else {
+                        None
                     }
                 })
             } else {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index ecaf9f4e16937..745c3d195ada7 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -1181,37 +1181,54 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         debug!("cmp(t1={}, t1.kind={:?}, t2={}, t2.kind={:?})", t1, t1.kind(), t2, t2.kind());
 
         // helper functions
-        fn equals<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
-            match (a.kind(), b.kind()) {
-                (a, b) if *a == *b => true,
-                (&ty::Int(_), &ty::Infer(ty::InferTy::IntVar(_)))
-                | (
-                    &ty::Infer(ty::InferTy::IntVar(_)),
-                    &ty::Int(_) | &ty::Infer(ty::InferTy::IntVar(_)),
-                )
-                | (&ty::Float(_), &ty::Infer(ty::InferTy::FloatVar(_)))
-                | (
-                    &ty::Infer(ty::InferTy::FloatVar(_)),
-                    &ty::Float(_) | &ty::Infer(ty::InferTy::FloatVar(_)),
-                ) => true,
-                _ => false,
+        let recurse = |t1, t2, values: &mut (DiagnosticStyledString, DiagnosticStyledString)| {
+            let (x1, x2) = self.cmp(t1, t2);
+            (values.0).0.extend(x1.0);
+            (values.1).0.extend(x2.0);
+        };
+
+        fn fmt_region<'tcx>(region: ty::Region<'tcx>) -> String {
+            let mut r = region.to_string();
+            if r == "'_" {
+                r.clear();
+            } else {
+                r.push(' ');
             }
+            format!("&{r}")
         }
 
-        fn push_ty_ref<'tcx>(
+        fn push_ref<'tcx>(
             region: ty::Region<'tcx>,
-            ty: Ty<'tcx>,
             mutbl: hir::Mutability,
             s: &mut DiagnosticStyledString,
         ) {
-            let mut r = region.to_string();
-            if r == "'_" {
-                r.clear();
+            s.push_highlighted(fmt_region(region));
+            s.push_highlighted(mutbl.prefix_str());
+        }
+
+        fn cmp_ty_refs<'tcx>(
+            r1: ty::Region<'tcx>,
+            mut1: hir::Mutability,
+            r2: ty::Region<'tcx>,
+            mut2: hir::Mutability,
+            ss: &mut (DiagnosticStyledString, DiagnosticStyledString),
+        ) {
+            let (r1, r2) = (fmt_region(r1), fmt_region(r2));
+            if r1 != r2 {
+                ss.0.push_highlighted(r1);
+                ss.1.push_highlighted(r2);
             } else {
-                r.push(' ');
+                ss.0.push_normal(r1);
+                ss.1.push_normal(r2);
+            }
+
+            if mut1 != mut2 {
+                ss.0.push_highlighted(mut1.prefix_str());
+                ss.1.push_highlighted(mut2.prefix_str());
+            } else {
+                ss.0.push_normal(mut1.prefix_str());
+                ss.1.push_normal(mut2.prefix_str());
             }
-            s.push_highlighted(format!("&{}{}", r, mutbl.prefix_str()));
-            s.push_normal(ty.to_string());
         }
 
         // process starts here
@@ -1310,9 +1327,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                             values.0.push_normal("_");
                             values.1.push_normal("_");
                         } else {
-                            let (x1, x2) = self.cmp(ta1, ta2);
-                            (values.0).0.extend(x1.0);
-                            (values.1).0.extend(x2.0);
+                            recurse(ta1, ta2, &mut values);
                         }
                         self.push_comma(&mut values.0, &mut values.1, len, i);
                     }
@@ -1418,27 +1433,24 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 }
             }
 
-            // When finding T != &T, highlight only the borrow
-            (&ty::Ref(r1, ref_ty1, mutbl1), _) if equals(ref_ty1, t2) => {
+            // When finding `&T != &T`, compare the references, then recurse into pointee type
+            (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2)) => {
                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
-                push_ty_ref(r1, ref_ty1, mutbl1, &mut values.0);
-                values.1.push_normal(t2.to_string());
+                cmp_ty_refs(r1, mutbl1, r2, mutbl2, &mut values);
+                recurse(ref_ty1, ref_ty2, &mut values);
                 values
             }
-            (_, &ty::Ref(r2, ref_ty2, mutbl2)) if equals(t1, ref_ty2) => {
+            // When finding T != &T, highlight the borrow
+            (&ty::Ref(r1, ref_ty1, mutbl1), _) => {
                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
-                values.0.push_normal(t1.to_string());
-                push_ty_ref(r2, ref_ty2, mutbl2, &mut values.1);
+                push_ref(r1, mutbl1, &mut values.0);
+                recurse(ref_ty1, t2, &mut values);
                 values
             }
-
-            // When encountering &T != &mut T, highlight only the borrow
-            (&ty::Ref(r1, ref_ty1, mutbl1), &ty::Ref(r2, ref_ty2, mutbl2))
-                if equals(ref_ty1, ref_ty2) =>
-            {
+            (_, &ty::Ref(r2, ref_ty2, mutbl2)) => {
                 let mut values = (DiagnosticStyledString::new(), DiagnosticStyledString::new());
-                push_ty_ref(r1, ref_ty1, mutbl1, &mut values.0);
-                push_ty_ref(r2, ref_ty2, mutbl2, &mut values.1);
+                push_ref(r2, mutbl2, &mut values.1);
+                recurse(t1, ref_ty2, &mut values);
                 values
             }
 
@@ -1448,9 +1460,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     (DiagnosticStyledString::normal("("), DiagnosticStyledString::normal("("));
                 let len = args1.len();
                 for (i, (left, right)) in args1.iter().zip(args2).enumerate() {
-                    let (x1, x2) = self.cmp(left, right);
-                    (values.0).0.extend(x1.0);
-                    (values.1).0.extend(x2.0);
+                    recurse(left, right, &mut values);
                     self.push_comma(&mut values.0, &mut values.1, len, i);
                 }
                 if len == 1 {
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 32c09e491c7ed..3a71251e73da4 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -345,37 +345,61 @@ pub struct InferCtxt<'tcx> {
 impl<'tcx> ty::InferCtxtLike for InferCtxt<'tcx> {
     type Interner = TyCtxt<'tcx>;
 
-    fn universe_of_ty(&self, ty: ty::InferTy) -> Option<ty::UniverseIndex> {
-        use InferTy::*;
-        match ty {
-            // FIXME(BoxyUwU): this is kind of jank and means that printing unresolved
-            // ty infers will give you the universe of the var it resolved to not the universe
-            // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
-            // try to print out `?0.1` it will just print `?0`.
-            TyVar(ty_vid) => match self.probe_ty_var(ty_vid) {
-                Err(universe) => Some(universe),
-                Ok(_) => None,
-            },
-            IntVar(_) | FloatVar(_) | FreshTy(_) | FreshIntTy(_) | FreshFloatTy(_) => None,
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn universe_of_ty(&self, vid: TyVid) -> Option<ty::UniverseIndex> {
+        // FIXME(BoxyUwU): this is kind of jank and means that printing unresolved
+        // ty infers will give you the universe of the var it resolved to not the universe
+        // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
+        // try to print out `?0.1` it will just print `?0`.
+        match self.probe_ty_var(vid) {
+            Err(universe) => Some(universe),
+            Ok(_) => None,
         }
     }
 
-    fn universe_of_ct(&self, ct: ty::InferConst) -> Option<ty::UniverseIndex> {
-        use ty::InferConst::*;
-        match ct {
-            // Same issue as with `universe_of_ty`
-            Var(ct_vid) => match self.probe_const_var(ct_vid) {
-                Err(universe) => Some(universe),
-                Ok(_) => None,
-            },
-            EffectVar(_) => None,
-            Fresh(_) => None,
+    fn universe_of_ct(&self, ct: ConstVid) -> Option<ty::UniverseIndex> {
+        // Same issue as with `universe_of_ty`
+        match self.probe_const_var(ct) {
+            Err(universe) => Some(universe),
+            Ok(_) => None,
         }
     }
 
     fn universe_of_lt(&self, lt: ty::RegionVid) -> Option<ty::UniverseIndex> {
         Some(self.universe_of_region_vid(lt))
     }
+
+    fn root_ty_var(&self, vid: TyVid) -> TyVid {
+        self.root_var(vid)
+    }
+
+    fn probe_ty_var(&self, vid: TyVid) -> Option<Ty<'tcx>> {
+        self.probe_ty_var(vid).ok()
+    }
+
+    fn root_lt_var(&self, vid: ty::RegionVid) -> ty::RegionVid {
+        self.root_region_var(vid)
+    }
+
+    fn probe_lt_var(&self, vid: ty::RegionVid) -> Option<ty::Region<'tcx>> {
+        let re = self
+            .inner
+            .borrow_mut()
+            .unwrap_region_constraints()
+            .opportunistic_resolve_var(self.tcx, vid);
+        if re.is_var() { None } else { Some(re) }
+    }
+
+    fn root_ct_var(&self, vid: ConstVid) -> ConstVid {
+        self.root_const_var(vid)
+    }
+
+    fn probe_ct_var(&self, vid: ConstVid) -> Option<ty::Const<'tcx>> {
+        self.probe_const_var(vid).ok()
+    }
 }
 
 /// See the `error_reporting` module for more details.
@@ -1347,6 +1371,10 @@ impl<'tcx> InferCtxt<'tcx> {
         self.inner.borrow_mut().type_variables().root_var(var)
     }
 
+    pub fn root_region_var(&self, var: ty::RegionVid) -> ty::RegionVid {
+        self.inner.borrow_mut().unwrap_region_constraints().root_var(var)
+    }
+
     pub fn root_const_var(&self, var: ty::ConstVid) -> ty::ConstVid {
         self.inner.borrow_mut().const_unification_table().find(var).vid
     }
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
index cbd8040c9f10f..5c043b1d3dd64 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/mod.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
@@ -623,6 +623,11 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
         }
     }
 
+    pub fn root_var(&mut self, vid: ty::RegionVid) -> ty::RegionVid {
+        let mut ut = self.unification_table_mut(); // FIXME(rust-lang/ena#42): unnecessary mut
+        ut.find(vid).vid
+    }
+
     fn combine_map(&mut self, t: CombineMapType) -> &mut CombineMap<'tcx> {
         match t {
             Glb => &mut self.glbs,
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index e48840fac2059..293df4f691d46 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -7,7 +7,7 @@ use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::LocalDefId;
 use rustc_macros::HashStable;
-use rustc_type_ir::{TypeFlags, WithCachedTypeInfo};
+use rustc_type_ir::{ConstTy, IntoKind, TypeFlags, WithCachedTypeInfo};
 
 mod int;
 mod kind;
@@ -26,6 +26,20 @@ use super::sty::ConstKind;
 #[rustc_pass_by_value]
 pub struct Const<'tcx>(pub(super) Interned<'tcx, WithCachedTypeInfo<ConstData<'tcx>>>);
 
+impl<'tcx> IntoKind for Const<'tcx> {
+    type Kind = ConstKind<'tcx>;
+
+    fn kind(self) -> ConstKind<'tcx> {
+        self.kind().clone()
+    }
+}
+
+impl<'tcx> ConstTy<TyCtxt<'tcx>> for Const<'tcx> {
+    fn ty(self) -> Ty<'tcx> {
+        self.ty()
+    }
+}
+
 /// Typed constant value.
 #[derive(PartialEq, Eq, PartialOrd, Ord, Hash, HashStable, TyEncodable, TyDecodable)]
 pub struct ConstData<'tcx> {
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 6ebfe778e7f21..24b613835a462 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -131,6 +131,31 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     ) -> (Self::Ty, ty::Mutability) {
         (ty, mutbl)
     }
+
+    fn mk_canonical_var_infos(self, infos: &[ty::CanonicalVarInfo<Self>]) -> Self::CanonicalVars {
+        self.mk_canonical_var_infos(infos)
+    }
+
+    fn mk_bound_ty(self, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self::Ty {
+        Ty::new_bound(self, debruijn, ty::BoundTy { var, kind: ty::BoundTyKind::Anon })
+    }
+
+    fn mk_bound_region(self, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self::Region {
+        Region::new_bound(
+            self,
+            debruijn,
+            ty::BoundRegion { var, kind: ty::BoundRegionKind::BrAnon },
+        )
+    }
+
+    fn mk_bound_const(
+        self,
+        debruijn: ty::DebruijnIndex,
+        var: ty::BoundVar,
+        ty: Self::Ty,
+    ) -> Self::Const {
+        Const::new_bound(self, debruijn, var, ty)
+    }
 }
 
 type InternedSet<'tcx, T> = ShardedHashMap<InternedInSet<'tcx, T>, ()>;
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 203c9eb65df86..71ff7021ca5de 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -65,15 +65,10 @@ use std::ops::ControlFlow;
 use std::{fmt, str};
 
 pub use crate::ty::diagnostics::*;
-pub use rustc_type_ir::AliasKind::*;
 pub use rustc_type_ir::ConstKind::{
     Bound as BoundCt, Error as ErrorCt, Expr as ExprCt, Infer as InferCt, Param as ParamCt,
     Placeholder as PlaceholderCt, Unevaluated, Value,
 };
-pub use rustc_type_ir::DynKind::*;
-pub use rustc_type_ir::InferTy::*;
-pub use rustc_type_ir::RegionKind::*;
-pub use rustc_type_ir::TyKind::*;
 pub use rustc_type_ir::*;
 
 pub use self::binding::BindingMode;
@@ -474,6 +469,14 @@ pub struct CReaderCacheKey {
 #[rustc_pass_by_value]
 pub struct Ty<'tcx>(Interned<'tcx, WithCachedTypeInfo<TyKind<'tcx>>>);
 
+impl<'tcx> IntoKind for Ty<'tcx> {
+    type Kind = TyKind<'tcx>;
+
+    fn kind(self) -> TyKind<'tcx> {
+        self.kind().clone()
+    }
+}
+
 impl EarlyParamRegion {
     /// Does this early bound region have a name? Early bound regions normally
     /// always have names except when using anonymous lifetimes (`'_`).
@@ -1545,34 +1548,42 @@ pub struct Placeholder<T> {
 
 pub type PlaceholderRegion = Placeholder<BoundRegion>;
 
-impl rustc_type_ir::Placeholder for PlaceholderRegion {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderRegion {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound.var
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: BoundRegion { var, kind: BoundRegionKind::BrAnon } }
+    }
 }
 
 pub type PlaceholderType = Placeholder<BoundTy>;
 
-impl rustc_type_ir::Placeholder for PlaceholderType {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderType {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound.var
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: BoundTy { var, kind: BoundTyKind::Anon } }
+    }
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
@@ -1584,18 +1595,22 @@ pub struct BoundConst<'tcx> {
 
 pub type PlaceholderConst = Placeholder<BoundVar>;
 
-impl rustc_type_ir::Placeholder for PlaceholderConst {
-    fn universe(&self) -> UniverseIndex {
+impl PlaceholderLike for PlaceholderConst {
+    fn universe(self) -> UniverseIndex {
         self.universe
     }
 
-    fn var(&self) -> BoundVar {
+    fn var(self) -> BoundVar {
         self.bound
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self {
+        Placeholder { universe: ui, bound: var }
+    }
 }
 
 /// When type checking, we use the `ParamEnv` to track
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index e221b4e8bec01..50a1b85b16918 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -6,7 +6,7 @@ use crate::infer::canonical::Canonical;
 use crate::ty::visit::ValidateBoundVars;
 use crate::ty::InferTy::*;
 use crate::ty::{
-    self, AdtDef, Discr, Term, Ty, TyCtxt, TypeFlags, TypeSuperVisitable, TypeVisitable,
+    self, AdtDef, Discr, IntoKind, Term, Ty, TyCtxt, TypeFlags, TypeSuperVisitable, TypeVisitable,
     TypeVisitableExt, TypeVisitor,
 };
 use crate::ty::{GenericArg, GenericArgs, GenericArgsRef};
@@ -1477,6 +1477,14 @@ impl ParamConst {
 #[rustc_pass_by_value]
 pub struct Region<'tcx>(pub Interned<'tcx, RegionKind<'tcx>>);
 
+impl<'tcx> IntoKind for Region<'tcx> {
+    type Kind = RegionKind<'tcx>;
+
+    fn kind(self) -> RegionKind<'tcx> {
+        *self
+    }
+}
+
 impl<'tcx> Region<'tcx> {
     #[inline]
     pub fn new_early_param(
diff --git a/compiler/rustc_next_trait_solver/Cargo.toml b/compiler/rustc_next_trait_solver/Cargo.toml
new file mode 100644
index 0000000000000..9d496fd8e8175
--- /dev/null
+++ b/compiler/rustc_next_trait_solver/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "rustc_next_trait_solver"
+version = "0.0.0"
+edition = "2021"
+
+[dependencies]
+rustc_type_ir = { path = "../rustc_type_ir", default-features = false }
+
+[features]
+default = ["nightly"]
+nightly = [
+    "rustc_type_ir/nightly",
+]
\ No newline at end of file
diff --git a/compiler/rustc_trait_selection/src/solve/canonicalize.rs b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
similarity index 66%
rename from compiler/rustc_trait_selection/src/solve/canonicalize.rs
rename to compiler/rustc_next_trait_solver/src/canonicalizer.rs
index 469d1f5a9cbf6..cb1f328577d02 100644
--- a/compiler/rustc_trait_selection/src/solve/canonicalize.rs
+++ b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
@@ -1,17 +1,10 @@
 use std::cmp::Ordering;
 
-use crate::infer::InferCtxt;
-use rustc_middle::infer::canonical::Canonical;
-use rustc_middle::infer::canonical::CanonicalTyVarKind;
-use rustc_middle::infer::canonical::CanonicalVarInfo;
-use rustc_middle::infer::canonical::CanonicalVarInfos;
-use rustc_middle::infer::canonical::CanonicalVarKind;
-use rustc_middle::ty::BoundRegionKind::BrAnon;
-use rustc_middle::ty::BoundTyKind;
-use rustc_middle::ty::TyCtxt;
-use rustc_middle::ty::TypeVisitableExt;
-use rustc_middle::ty::{self, Ty};
-use rustc_middle::ty::{TypeFoldable, TypeFolder, TypeSuperFoldable};
+use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
+use rustc_type_ir::{
+    self as ty, Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, ConstTy,
+    InferCtxtLike, Interner, IntoKind, PlaceholderLike,
+};
 
 /// Whether we're canonicalizing a query input or the query response.
 ///
@@ -42,23 +35,22 @@ pub enum CanonicalizeMode {
     },
 }
 
-pub struct Canonicalizer<'a, 'tcx> {
-    infcx: &'a InferCtxt<'tcx>,
+pub struct Canonicalizer<'a, Infcx: InferCtxtLike<Interner = I>, I: Interner> {
+    infcx: &'a Infcx,
     canonicalize_mode: CanonicalizeMode,
 
-    variables: &'a mut Vec<ty::GenericArg<'tcx>>,
-    primitive_var_infos: Vec<CanonicalVarInfo<'tcx>>,
+    variables: &'a mut Vec<I::GenericArg>,
+    primitive_var_infos: Vec<CanonicalVarInfo<I>>,
     binder_index: ty::DebruijnIndex,
 }
 
-impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
-    #[instrument(level = "debug", skip(infcx), ret)]
-    pub fn canonicalize<T: TypeFoldable<TyCtxt<'tcx>>>(
-        infcx: &'a InferCtxt<'tcx>,
+impl<'a, Infcx: InferCtxtLike<Interner = I>, I: Interner> Canonicalizer<'a, Infcx, I> {
+    pub fn canonicalize<T: TypeFoldable<I>>(
+        infcx: &'a Infcx,
         canonicalize_mode: CanonicalizeMode,
-        variables: &'a mut Vec<ty::GenericArg<'tcx>>,
+        variables: &'a mut Vec<I::GenericArg>,
         value: T,
-    ) -> Canonical<'tcx, T> {
+    ) -> ty::Canonical<I, T> {
         let mut canonicalizer = Canonicalizer {
             infcx,
             canonicalize_mode,
@@ -69,15 +61,16 @@ impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
         };
 
         let value = value.fold_with(&mut canonicalizer);
-        assert!(!value.has_infer(), "unexpected infer in {value:?}");
-        assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
+        // FIXME: Restore these assertions. Should we uplift type flags?
+        // assert!(!value.has_infer(), "unexpected infer in {value:?}");
+        // assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
 
         let (max_universe, variables) = canonicalizer.finalize();
 
         Canonical { max_universe, variables, value }
     }
 
-    fn finalize(self) -> (ty::UniverseIndex, CanonicalVarInfos<'tcx>) {
+    fn finalize(self) -> (ty::UniverseIndex, I::CanonicalVars) {
         let mut var_infos = self.primitive_var_infos;
         // See the rustc-dev-guide section about how we deal with universes
         // during canonicalization in the new solver.
@@ -105,7 +98,7 @@ impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
                     .max()
                     .unwrap_or(ty::UniverseIndex::ROOT);
 
-                let var_infos = self.infcx.tcx.mk_canonical_var_infos(&var_infos);
+                let var_infos = self.infcx.interner().mk_canonical_var_infos(&var_infos);
                 return (max_universe, var_infos);
             }
         }
@@ -131,7 +124,7 @@ impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
         let mut existential_in_new_uv = false;
         let mut next_orig_uv = Some(ty::UniverseIndex::ROOT);
         while let Some(orig_uv) = next_orig_uv.take() {
-            let mut update_uv = |var: &mut CanonicalVarInfo<'tcx>, orig_uv, is_existential| {
+            let mut update_uv = |var: &mut CanonicalVarInfo<I>, orig_uv, is_existential| {
                 let uv = var.universe();
                 match uv.cmp(&orig_uv) {
                     Ordering::Less => (), // Already updated
@@ -187,19 +180,22 @@ impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
             }
         }
 
-        let var_infos = self.infcx.tcx.mk_canonical_var_infos(&var_infos);
+        let var_infos = self.infcx.interner().mk_canonical_var_infos(&var_infos);
         (curr_compressed_uv, var_infos)
     }
 }
 
-impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
-    fn interner(&self) -> TyCtxt<'tcx> {
-        self.infcx.tcx
+impl<Infcx: InferCtxtLike<Interner = I>, I: Interner> TypeFolder<I>
+    for Canonicalizer<'_, Infcx, I>
+{
+    fn interner(&self) -> I {
+        self.infcx.interner()
     }
 
-    fn fold_binder<T>(&mut self, t: ty::Binder<'tcx, T>) -> ty::Binder<'tcx, T>
+    fn fold_binder<T>(&mut self, t: I::Binder<T>) -> I::Binder<T>
     where
-        T: TypeFoldable<TyCtxt<'tcx>>,
+        T: TypeFoldable<I>,
+        I::Binder<T>: TypeSuperFoldable<I>,
     {
         self.binder_index.shift_in(1);
         let t = t.super_fold_with(self);
@@ -207,21 +203,8 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
         t
     }
 
-    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        if let ty::ReVar(vid) = *r {
-            let resolved_region = self
-                .infcx
-                .inner
-                .borrow_mut()
-                .unwrap_region_constraints()
-                .opportunistic_resolve_var(self.infcx.tcx, vid);
-            assert_eq!(
-                r, resolved_region,
-                "region var should have been resolved, {r} -> {resolved_region}"
-            );
-        }
-
-        let kind = match *r {
+    fn fold_region(&mut self, r: I::Region) -> I::Region {
+        let kind = match r.kind() {
             ty::ReBound(..) => return r,
 
             // We may encounter `ReStatic` in item signatures or the hidden type
@@ -237,9 +220,11 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
                 CanonicalizeMode::Response { .. } => return r,
             },
 
-            ty::ReLateParam(_) | ty::ReEarlyParam(_) => match self.canonicalize_mode {
+            ty::ReEarlyParam(_) | ty::ReLateParam(_) => match self.canonicalize_mode {
                 CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
-                CanonicalizeMode::Response { .. } => bug!("unexpected region in response: {r:?}"),
+                CanonicalizeMode::Response { .. } => {
+                    panic!("unexpected region in response: {r:?}")
+                }
             },
 
             ty::RePlaceholder(placeholder) => match self.canonicalize_mode {
@@ -248,20 +233,32 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
                 CanonicalizeMode::Response { max_input_universe } => {
                     // If we have a placeholder region inside of a query, it must be from
                     // a new universe.
-                    if max_input_universe.can_name(placeholder.universe) {
-                        bug!("new placeholder in universe {max_input_universe:?}: {r:?}");
+                    if max_input_universe.can_name(placeholder.universe()) {
+                        panic!("new placeholder in universe {max_input_universe:?}: {r:?}");
                     }
                     CanonicalVarKind::PlaceholderRegion(placeholder)
                 }
             },
 
-            ty::ReVar(_) => match self.canonicalize_mode {
-                CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
-                CanonicalizeMode::Response { .. } => {
-                    CanonicalVarKind::Region(self.infcx.universe_of_region(r))
-                }
-            },
+            ty::ReVar(vid) => {
+                assert_eq!(
+                    self.infcx.root_lt_var(vid),
+                    vid,
+                    "region vid should have been resolved fully before canonicalization"
+                );
+                assert_eq!(
+                    self.infcx.probe_lt_var(vid),
+                    None,
+                    "region vid should have been resolved fully before canonicalization"
+                );
 
+                match self.canonicalize_mode {
+                    CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
+                    CanonicalizeMode::Response { .. } => {
+                        CanonicalVarKind::Region(self.infcx.universe_of_lt(vid).unwrap())
+                    }
+                }
+            }
             ty::ReError(_) => return r,
         };
 
@@ -271,55 +268,60 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
                 self.variables.iter().position(|&v| v == r.into()).map(ty::BoundVar::from)
             }
         };
+
         let var = existing_bound_var.unwrap_or_else(|| {
             let var = ty::BoundVar::from(self.variables.len());
             self.variables.push(r.into());
             self.primitive_var_infos.push(CanonicalVarInfo { kind });
             var
         });
-        let br = ty::BoundRegion { var, kind: BrAnon };
-        ty::Region::new_bound(self.interner(), self.binder_index, br)
+
+        self.interner().mk_bound_region(self.binder_index, var)
     }
 
-    fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        let kind = match *t.kind() {
-            ty::Infer(ty::TyVar(vid)) => {
-                assert_eq!(self.infcx.root_var(vid), vid, "ty vid should have been resolved");
-                let Err(ui) = self.infcx.probe_ty_var(vid) else {
-                    bug!("ty var should have been resolved: {t}");
-                };
-                CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui))
-            }
-            ty::Infer(ty::IntVar(vid)) => {
-                assert_eq!(self.infcx.opportunistic_resolve_int_var(vid), t);
-                CanonicalVarKind::Ty(CanonicalTyVarKind::Int)
-            }
-            ty::Infer(ty::FloatVar(vid)) => {
-                assert_eq!(self.infcx.opportunistic_resolve_float_var(vid), t);
-                CanonicalVarKind::Ty(CanonicalTyVarKind::Float)
-            }
-            ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
-                bug!("fresh var during canonicalization: {t:?}")
-            }
+    fn fold_ty(&mut self, t: I::Ty) -> I::Ty
+    where
+        I::Ty: TypeSuperFoldable<I>,
+    {
+        let kind = match t.kind() {
+            ty::Infer(i) => match i {
+                ty::TyVar(vid) => {
+                    assert_eq!(
+                        self.infcx.root_ty_var(vid),
+                        vid,
+                        "ty vid should have been resolved fully before canonicalization"
+                    );
+                    assert_eq!(
+                        self.infcx.probe_ty_var(vid),
+                        None,
+                        "ty vid should have been resolved fully before canonicalization"
+                    );
+
+                    CanonicalVarKind::Ty(CanonicalTyVarKind::General(
+                        self.infcx
+                            .universe_of_ty(vid)
+                            .unwrap_or_else(|| panic!("ty var should have been resolved: {t:?}")),
+                    ))
+                }
+                ty::IntVar(_) => CanonicalVarKind::Ty(CanonicalTyVarKind::Int),
+                ty::FloatVar(_) => CanonicalVarKind::Ty(CanonicalTyVarKind::Float),
+                ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_) => {
+                    todo!()
+                }
+            },
             ty::Placeholder(placeholder) => match self.canonicalize_mode {
-                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(ty::Placeholder {
-                    universe: placeholder.universe,
-                    bound: ty::BoundTy {
-                        var: ty::BoundVar::from_usize(self.variables.len()),
-                        kind: ty::BoundTyKind::Anon,
-                    },
-                }),
+                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
+                    placeholder.universe(),
+                    self.variables.len().into(),
+                )),
                 CanonicalizeMode::Response { .. } => CanonicalVarKind::PlaceholderTy(placeholder),
             },
             ty::Param(_) => match self.canonicalize_mode {
-                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(ty::Placeholder {
-                    universe: ty::UniverseIndex::ROOT,
-                    bound: ty::BoundTy {
-                        var: ty::BoundVar::from_usize(self.variables.len()),
-                        kind: ty::BoundTyKind::Anon,
-                    },
-                }),
-                CanonicalizeMode::Response { .. } => bug!("param ty in response: {t:?}"),
+                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
+                    ty::UniverseIndex::ROOT,
+                    self.variables.len().into(),
+                )),
+                CanonicalizeMode::Response { .. } => panic!("param ty in response: {t:?}"),
             },
             ty::Bool
             | ty::Char
@@ -354,44 +356,38 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
                 var
             }),
         );
-        let bt = ty::BoundTy { var, kind: BoundTyKind::Anon };
-        Ty::new_bound(self.infcx.tcx, self.binder_index, bt)
+
+        self.interner().mk_bound_ty(self.binder_index, var)
     }
 
-    fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
+    fn fold_const(&mut self, c: I::Const) -> I::Const
+    where
+        I::Const: TypeSuperFoldable<I>,
+    {
         let kind = match c.kind() {
-            ty::ConstKind::Infer(ty::InferConst::Var(vid)) => {
-                assert_eq!(
-                    self.infcx.root_const_var(vid),
-                    vid,
-                    "const var should have been resolved"
-                );
-                let Err(ui) = self.infcx.probe_const_var(vid) else {
-                    bug!("const var should have been resolved");
-                };
-                // FIXME: we should fold this ty eventually
-                CanonicalVarKind::Const(ui, c.ty())
-            }
-            ty::ConstKind::Infer(ty::InferConst::EffectVar(vid)) => {
-                assert_eq!(
-                    self.infcx.root_effect_var(vid),
-                    vid,
-                    "effect var should have been resolved"
-                );
-                let None = self.infcx.probe_effect_var(vid) else {
-                    bug!("effect var should have been resolved");
-                };
-                CanonicalVarKind::Effect
-            }
-            ty::ConstKind::Infer(ty::InferConst::Fresh(_)) => {
-                bug!("fresh var during canonicalization: {c:?}")
+            ty::ConstKind::Infer(i) => {
+                // FIXME: we should fold the ty too eventually
+                match i {
+                    ty::InferConst::Var(vid) => {
+                        assert_eq!(
+                            self.infcx.root_ct_var(vid),
+                            vid,
+                            "region vid should have been resolved fully before canonicalization"
+                        );
+                        assert_eq!(
+                            self.infcx.probe_ct_var(vid),
+                            None,
+                            "region vid should have been resolved fully before canonicalization"
+                        );
+                        CanonicalVarKind::Const(self.infcx.universe_of_ct(vid).unwrap(), c.ty())
+                    }
+                    ty::InferConst::EffectVar(_) => CanonicalVarKind::Effect,
+                    ty::InferConst::Fresh(_) => todo!(),
+                }
             }
             ty::ConstKind::Placeholder(placeholder) => match self.canonicalize_mode {
                 CanonicalizeMode::Input => CanonicalVarKind::PlaceholderConst(
-                    ty::Placeholder {
-                        universe: placeholder.universe,
-                        bound: ty::BoundVar::from(self.variables.len()),
-                    },
+                    PlaceholderLike::new(placeholder.universe(), self.variables.len().into()),
                     c.ty(),
                 ),
                 CanonicalizeMode::Response { .. } => {
@@ -400,13 +396,10 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
             },
             ty::ConstKind::Param(_) => match self.canonicalize_mode {
                 CanonicalizeMode::Input => CanonicalVarKind::PlaceholderConst(
-                    ty::Placeholder {
-                        universe: ty::UniverseIndex::ROOT,
-                        bound: ty::BoundVar::from(self.variables.len()),
-                    },
+                    PlaceholderLike::new(ty::UniverseIndex::ROOT, self.variables.len().into()),
                     c.ty(),
                 ),
-                CanonicalizeMode::Response { .. } => bug!("param ty in response: {c:?}"),
+                CanonicalizeMode::Response { .. } => panic!("param ty in response: {c:?}"),
             },
             ty::ConstKind::Bound(_, _)
             | ty::ConstKind::Unevaluated(_)
@@ -423,6 +416,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
                 var
             }),
         );
-        ty::Const::new_bound(self.infcx.tcx, self.binder_index, var, c.ty())
+
+        self.interner().mk_bound_const(self.binder_index, var, c.ty())
     }
 }
diff --git a/compiler/rustc_next_trait_solver/src/lib.rs b/compiler/rustc_next_trait_solver/src/lib.rs
new file mode 100644
index 0000000000000..e5fc8f755e0a9
--- /dev/null
+++ b/compiler/rustc_next_trait_solver/src/lib.rs
@@ -0,0 +1 @@
+pub mod canonicalizer;
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 9064cb6e87522..e49282e638ab4 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -218,20 +218,21 @@ where
                     return ControlFlow::Continue(());
                 }
 
-                let kind = match kind {
-                    ty::Inherent | ty::Projection => "associated type",
-                    ty::Weak => "type alias",
-                    ty::Opaque => unreachable!(),
-                };
                 self.def_id_visitor.visit_def_id(
                     data.def_id,
-                    kind,
+                    match kind {
+                        ty::Inherent | ty::Projection => "associated type",
+                        ty::Weak => "type alias",
+                        ty::Opaque => unreachable!(),
+                    },
                     &LazyDefPathStr { def_id: data.def_id, tcx },
                 )?;
 
                 // This will also visit args if necessary, so we don't need to recurse.
                 return if V::SHALLOW {
                     ControlFlow::Continue(())
+                } else if kind == ty::Projection {
+                    self.visit_projection_ty(data)
                 } else {
                     data.args.iter().try_for_each(|subst| subst.visit_with(self))
                 };
diff --git a/compiler/rustc_smir/Cargo.toml b/compiler/rustc_smir/Cargo.toml
index 836ea046ffea1..c9e23efcb10c6 100644
--- a/compiler/rustc_smir/Cargo.toml
+++ b/compiler/rustc_smir/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
+rustc_abi = { path = "../rustc_abi" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_middle = { path = "../rustc_middle" }
diff --git a/compiler/rustc_smir/src/rustc_smir/alloc.rs b/compiler/rustc_smir/src/rustc_smir/alloc.rs
index 850a52ce275f1..48cb164c308a7 100644
--- a/compiler/rustc_smir/src/rustc_smir/alloc.rs
+++ b/compiler/rustc_smir/src/rustc_smir/alloc.rs
@@ -2,6 +2,7 @@ use rustc_middle::mir::{
     interpret::{alloc_range, AllocRange, Pointer},
     ConstValue,
 };
+use stable_mir::Error;
 
 use crate::rustc_smir::{Stable, Tables};
 use stable_mir::mir::Mutability;
@@ -26,23 +27,35 @@ pub fn new_allocation<'tcx>(
     const_value: ConstValue<'tcx>,
     tables: &mut Tables<'tcx>,
 ) -> Allocation {
-    match const_value {
+    try_new_allocation(ty, const_value, tables).unwrap()
+}
+
+#[allow(rustc::usage_of_qualified_ty)]
+pub fn try_new_allocation<'tcx>(
+    ty: rustc_middle::ty::Ty<'tcx>,
+    const_value: ConstValue<'tcx>,
+    tables: &mut Tables<'tcx>,
+) -> Result<Allocation, Error> {
+    Ok(match const_value {
         ConstValue::Scalar(scalar) => {
             let size = scalar.size();
             let align = tables
                 .tcx
                 .layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(ty))
-                .unwrap()
+                .map_err(|e| e.stable(tables))?
                 .align;
             let mut allocation = rustc_middle::mir::interpret::Allocation::uninit(size, align.abi);
             allocation
                 .write_scalar(&tables.tcx, alloc_range(rustc_target::abi::Size::ZERO, size), scalar)
-                .unwrap();
+                .map_err(|e| e.stable(tables))?;
             allocation.stable(tables)
         }
         ConstValue::ZeroSized => {
-            let align =
-                tables.tcx.layout_of(rustc_middle::ty::ParamEnv::empty().and(ty)).unwrap().align;
+            let align = tables
+                .tcx
+                .layout_of(rustc_middle::ty::ParamEnv::empty().and(ty))
+                .map_err(|e| e.stable(tables))?
+                .align;
             new_empty_allocation(align.abi)
         }
         ConstValue::Slice { data, meta } => {
@@ -51,8 +64,10 @@ pub fn new_allocation<'tcx>(
             let scalar_ptr = rustc_middle::mir::interpret::Scalar::from_pointer(ptr, &tables.tcx);
             let scalar_meta =
                 rustc_middle::mir::interpret::Scalar::from_target_usize(meta, &tables.tcx);
-            let layout =
-                tables.tcx.layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(ty)).unwrap();
+            let layout = tables
+                .tcx
+                .layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(ty))
+                .map_err(|e| e.stable(tables))?;
             let mut allocation =
                 rustc_middle::mir::interpret::Allocation::uninit(layout.size, layout.align.abi);
             allocation
@@ -61,14 +76,14 @@ pub fn new_allocation<'tcx>(
                     alloc_range(rustc_target::abi::Size::ZERO, tables.tcx.data_layout.pointer_size),
                     scalar_ptr,
                 )
-                .unwrap();
+                .map_err(|e| e.stable(tables))?;
             allocation
                 .write_scalar(
                     &tables.tcx,
                     alloc_range(tables.tcx.data_layout.pointer_size, scalar_meta.size()),
                     scalar_meta,
                 )
-                .unwrap();
+                .map_err(|e| e.stable(tables))?;
             allocation.stable(tables)
         }
         ConstValue::Indirect { alloc_id, offset } => {
@@ -76,11 +91,11 @@ pub fn new_allocation<'tcx>(
             let ty_size = tables
                 .tcx
                 .layout_of(rustc_middle::ty::ParamEnv::reveal_all().and(ty))
-                .unwrap()
+                .map_err(|e| e.stable(tables))?
                 .size;
             allocation_filter(&alloc.0, alloc_range(offset, ty_size), tables)
         }
-    }
+    })
 }
 
 /// Creates an `Allocation` only from information within the `AllocRange`.
diff --git a/compiler/rustc_smir/src/rustc_smir/context.rs b/compiler/rustc_smir/src/rustc_smir/context.rs
index b10dfe8591414..341c69e932777 100644
--- a/compiler/rustc_smir/src/rustc_smir/context.rs
+++ b/compiler/rustc_smir/src/rustc_smir/context.rs
@@ -11,18 +11,29 @@ use stable_mir::compiler_interface::Context;
 use stable_mir::mir::alloc::GlobalAlloc;
 use stable_mir::mir::mono::{InstanceDef, StaticDef};
 use stable_mir::mir::Body;
+use stable_mir::target::{MachineInfo, MachineSize};
 use stable_mir::ty::{
     AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, Const, FieldDef, FnDef, GenericArgs,
-    LineInfo, PolyFnSig, RigidTy, Span, TyKind, VariantDef,
+    LineInfo, PolyFnSig, RigidTy, Span, Ty, TyKind, VariantDef,
 };
 use stable_mir::{self, Crate, CrateItem, DefId, Error, Filename, ItemKind, Symbol};
 use std::cell::RefCell;
 
 use crate::rustc_internal::{internal, RustcInternal};
 use crate::rustc_smir::builder::BodyBuilder;
-use crate::rustc_smir::{new_item_kind, smir_crate, Stable, Tables};
+use crate::rustc_smir::{alloc, new_item_kind, smir_crate, Stable, Tables};
 
 impl<'tcx> Context for TablesWrapper<'tcx> {
+    fn target_info(&self) -> MachineInfo {
+        let mut tables = self.0.borrow_mut();
+        MachineInfo {
+            endian: tables.tcx.data_layout.endian.stable(&mut *tables),
+            pointer_width: MachineSize::from_bits(
+                tables.tcx.data_layout.pointer_size.bits().try_into().unwrap(),
+            ),
+        }
+    }
+
     fn entry_fn(&self) -> Option<stable_mir::CrateItem> {
         let mut tables = self.0.borrow_mut();
         let tcx = tables.tcx;
@@ -382,6 +393,21 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         Instance::resolve_closure(tables.tcx, def_id, args_ref, closure_kind).stable(&mut *tables)
     }
 
+    fn eval_instance(&self, def: InstanceDef, const_ty: Ty) -> Result<Allocation, Error> {
+        let mut tables = self.0.borrow_mut();
+        let instance = tables.instances[def];
+        let result = tables.tcx.const_eval_instance(
+            ParamEnv::reveal_all(),
+            instance,
+            Some(tables.tcx.def_span(instance.def_id())),
+        );
+        result
+            .map(|const_val| {
+                alloc::try_new_allocation(const_ty.internal(&mut *tables), const_val, &mut *tables)
+            })
+            .map_err(|e| e.stable(&mut *tables))?
+    }
+
     fn eval_static_initializer(&self, def: StaticDef) -> Result<Allocation, Error> {
         let mut tables = self.0.borrow_mut();
         let def_id = def.0.internal(&mut *tables);
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/error.rs b/compiler/rustc_smir/src/rustc_smir/convert/error.rs
new file mode 100644
index 0000000000000..6c582b799f867
--- /dev/null
+++ b/compiler/rustc_smir/src/rustc_smir/convert/error.rs
@@ -0,0 +1,22 @@
+//! Handle the conversion of different internal errors into a stable version.
+//!
+//! Currently we encode everything as [stable_mir::Error], which is represented as a string.
+use crate::rustc_smir::{Stable, Tables};
+use rustc_middle::mir::interpret::AllocError;
+use rustc_middle::ty::layout::LayoutError;
+
+impl<'tcx> Stable<'tcx> for LayoutError<'tcx> {
+    type T = stable_mir::Error;
+
+    fn stable(&self, _tables: &mut Tables<'tcx>) -> Self::T {
+        stable_mir::Error::new(format!("{self:?}"))
+    }
+}
+
+impl<'tcx> Stable<'tcx> for AllocError {
+    type T = stable_mir::Error;
+
+    fn stable(&self, _tables: &mut Tables<'tcx>) -> Self::T {
+        stable_mir::Error::new(format!("{self:?}"))
+    }
+}
diff --git a/compiler/rustc_smir/src/rustc_smir/convert/mod.rs b/compiler/rustc_smir/src/rustc_smir/convert/mod.rs
index ce575f269caa1..7d8339ab50366 100644
--- a/compiler/rustc_smir/src/rustc_smir/convert/mod.rs
+++ b/compiler/rustc_smir/src/rustc_smir/convert/mod.rs
@@ -5,6 +5,7 @@ use stable_mir::ty::{IndexedVal, VariantIdx};
 
 use crate::rustc_smir::{Stable, Tables};
 
+mod error;
 mod mir;
 mod ty;
 
@@ -76,3 +77,14 @@ impl<'tcx> Stable<'tcx> for rustc_span::Span {
         tables.create_span(*self)
     }
 }
+
+impl<'tcx> Stable<'tcx> for rustc_abi::Endian {
+    type T = stable_mir::target::Endian;
+
+    fn stable(&self, _tables: &mut Tables<'tcx>) -> Self::T {
+        match self {
+            rustc_abi::Endian::Little => stable_mir::target::Endian::Little,
+            rustc_abi::Endian::Big => stable_mir::target::Endian::Big,
+        }
+    }
+}
diff --git a/compiler/rustc_trait_selection/Cargo.toml b/compiler/rustc_trait_selection/Cargo.toml
index 7d098180b9314..29c0d8b5ff172 100644
--- a/compiler/rustc_trait_selection/Cargo.toml
+++ b/compiler/rustc_trait_selection/Cargo.toml
@@ -15,6 +15,7 @@ rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
+rustc_next_trait_solver = { path = "../rustc_next_trait_solver" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc_session = { path = "../rustc_session" }
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
index da2f16e97608a..7457ba837f505 100644
--- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
+++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/canonical.rs
@@ -9,7 +9,6 @@
 //!
 //! [c]: https://rustc-dev-guide.rust-lang.org/solve/canonicalization.html
 use super::{CanonicalInput, Certainty, EvalCtxt, Goal};
-use crate::solve::canonicalize::{CanonicalizeMode, Canonicalizer};
 use crate::solve::{
     inspect, response_no_constraints_raw, CanonicalResponse, QueryResult, Response,
 };
@@ -27,6 +26,7 @@ use rustc_middle::traits::solve::{
 };
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{self, BoundVar, GenericArgKind, Ty, TyCtxt, TypeFoldable};
+use rustc_next_trait_solver::canonicalizer::{CanonicalizeMode, Canonicalizer};
 use rustc_span::DUMMY_SP;
 use std::iter;
 use std::ops::Deref;
diff --git a/compiler/rustc_trait_selection/src/solve/mod.rs b/compiler/rustc_trait_selection/src/solve/mod.rs
index cf3f94e26e402..0ab099ef0c8d1 100644
--- a/compiler/rustc_trait_selection/src/solve/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/mod.rs
@@ -30,7 +30,6 @@ use rustc_middle::ty::{
 
 mod alias_relate;
 mod assembly;
-mod canonicalize;
 mod eval_ctxt;
 mod fulfill;
 pub mod inspect;
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
index e87e585ef0b72..cd09aaff2d97d 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs
@@ -157,18 +157,10 @@ where
         }
 
         let mut region_constraints = QueryRegionConstraints::default();
-        let (output, error_info, mut obligations) =
-            Q::fully_perform_into(self, infcx, &mut region_constraints)
-                .map_err(|_| {
-                    infcx.tcx.sess.span_delayed_bug(span, format!("error performing {self:?}"))
-                })
-                .and_then(|(output, error_info, obligations, certainty)| match certainty {
-                    Certainty::Proven => Ok((output, error_info, obligations)),
-                    Certainty::Ambiguous => Err(infcx
-                        .tcx
-                        .sess
-                        .span_delayed_bug(span, format!("ambiguity performing {self:?}"))),
-                })?;
+        let (output, error_info, mut obligations, _) =
+            Q::fully_perform_into(self, infcx, &mut region_constraints).map_err(|_| {
+                infcx.tcx.sess.span_delayed_bug(span, format!("error performing {self:?}"))
+            })?;
 
         // Typically, instantiating NLL query results does not
         // create obligations. However, in some cases there
diff --git a/compiler/rustc_type_ir/src/canonical.rs b/compiler/rustc_type_ir/src/canonical.rs
index d2768703297e3..572c6f201d379 100644
--- a/compiler/rustc_type_ir/src/canonical.rs
+++ b/compiler/rustc_type_ir/src/canonical.rs
@@ -4,7 +4,7 @@ use std::ops::ControlFlow;
 
 use crate::fold::{FallibleTypeFolder, TypeFoldable};
 use crate::visit::{TypeVisitable, TypeVisitor};
-use crate::{Interner, Placeholder, UniverseIndex};
+use crate::{Interner, PlaceholderLike, UniverseIndex};
 
 /// A "canonicalized" type `V` is one where all free inference
 /// variables have been rewritten to "canonical vars". These are
@@ -157,7 +157,7 @@ where
 }
 
 impl<I: Interner> CanonicalVarInfo<I> {
-    pub fn universe(&self) -> UniverseIndex {
+    pub fn universe(self) -> UniverseIndex {
         self.kind.universe()
     }
 
@@ -305,11 +305,11 @@ where
 }
 
 impl<I: Interner> CanonicalVarKind<I> {
-    pub fn universe(&self) -> UniverseIndex {
+    pub fn universe(self) -> UniverseIndex {
         match self {
-            CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui)) => *ui,
-            CanonicalVarKind::Region(ui) => *ui,
-            CanonicalVarKind::Const(ui, _) => *ui,
+            CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui)) => ui,
+            CanonicalVarKind::Region(ui) => ui,
+            CanonicalVarKind::Const(ui, _) => ui,
             CanonicalVarKind::PlaceholderTy(placeholder) => placeholder.universe(),
             CanonicalVarKind::PlaceholderRegion(placeholder) => placeholder.universe(),
             CanonicalVarKind::PlaceholderConst(placeholder, _) => placeholder.universe(),
diff --git a/compiler/rustc_type_ir/src/const_kind.rs b/compiler/rustc_type_ir/src/const_kind.rs
index 409033a2d8d0e..879de58f10054 100644
--- a/compiler/rustc_type_ir/src/const_kind.rs
+++ b/compiler/rustc_type_ir/src/const_kind.rs
@@ -81,7 +81,7 @@ impl<I: Interner> DebugWithInfcx<I> for ConstKind<I> {
         match this.data {
             Param(param) => write!(f, "{param:?}"),
             Infer(var) => write!(f, "{:?}", &this.wrap(var)),
-            Bound(debruijn, var) => crate::debug_bound_var(f, *debruijn, var.clone()),
+            Bound(debruijn, var) => crate::debug_bound_var(f, *debruijn, var),
             Placeholder(placeholder) => write!(f, "{placeholder:?}"),
             Unevaluated(uv) => {
                 write!(f, "{:?}", &this.wrap(uv))
@@ -146,15 +146,15 @@ impl<I: Interner> DebugWithInfcx<I> for InferConst {
         this: WithInfcx<'_, Infcx, &Self>,
         f: &mut core::fmt::Formatter<'_>,
     ) -> core::fmt::Result {
-        match this.infcx.universe_of_ct(*this.data) {
-            None => write!(f, "{:?}", this.data),
-            Some(universe) => match *this.data {
-                InferConst::Var(vid) => write!(f, "?{}_{}c", vid.index(), universe.index()),
-                InferConst::EffectVar(vid) => write!(f, "?{}_{}e", vid.index(), universe.index()),
-                InferConst::Fresh(_) => {
-                    unreachable!()
-                }
+        match *this.data {
+            InferConst::Var(vid) => match this.infcx.universe_of_ct(vid) {
+                None => write!(f, "{:?}", this.data),
+                Some(universe) => write!(f, "?{}_{}c", vid.index(), universe.index()),
             },
+            InferConst::EffectVar(vid) => write!(f, "?{}e", vid.index()),
+            InferConst::Fresh(_) => {
+                unreachable!()
+            }
         }
     }
 }
diff --git a/compiler/rustc_type_ir/src/debug.rs b/compiler/rustc_type_ir/src/debug.rs
index db29ec9da8c9e..8998001ec20ec 100644
--- a/compiler/rustc_type_ir/src/debug.rs
+++ b/compiler/rustc_type_ir/src/debug.rs
@@ -1,35 +1,50 @@
-use crate::{InferConst, InferTy, Interner, UniverseIndex};
+use crate::{ConstVid, InferCtxtLike, Interner, TyVid, UniverseIndex};
 
 use core::fmt;
 use std::marker::PhantomData;
 
-pub trait InferCtxtLike {
-    type Interner: Interner;
+pub struct NoInfcx<I>(PhantomData<I>);
 
-    fn universe_of_ty(&self, ty: InferTy) -> Option<UniverseIndex>;
+impl<I: Interner> InferCtxtLike for NoInfcx<I> {
+    type Interner = I;
 
-    fn universe_of_lt(
-        &self,
-        lt: <Self::Interner as Interner>::InferRegion,
-    ) -> Option<UniverseIndex>;
+    fn interner(&self) -> Self::Interner {
+        unreachable!()
+    }
 
-    fn universe_of_ct(&self, ct: InferConst) -> Option<UniverseIndex>;
-}
+    fn universe_of_ty(&self, _ty: TyVid) -> Option<UniverseIndex> {
+        None
+    }
 
-pub struct NoInfcx<I>(PhantomData<I>);
+    fn universe_of_lt(&self, _lt: I::InferRegion) -> Option<UniverseIndex> {
+        None
+    }
 
-impl<I: Interner> InferCtxtLike for NoInfcx<I> {
-    type Interner = I;
+    fn universe_of_ct(&self, _ct: ConstVid) -> Option<UniverseIndex> {
+        None
+    }
+
+    fn root_ty_var(&self, vid: TyVid) -> TyVid {
+        vid
+    }
 
-    fn universe_of_ty(&self, _ty: InferTy) -> Option<UniverseIndex> {
+    fn probe_ty_var(&self, _vid: TyVid) -> Option<I::Ty> {
         None
     }
 
-    fn universe_of_ct(&self, _ct: InferConst) -> Option<UniverseIndex> {
+    fn root_lt_var(&self, vid: I::InferRegion) -> I::InferRegion {
+        vid
+    }
+
+    fn probe_lt_var(&self, _vid: I::InferRegion) -> Option<I::Region> {
         None
     }
 
-    fn universe_of_lt(&self, _lt: <I as Interner>::InferRegion) -> Option<UniverseIndex> {
+    fn root_ct_var(&self, vid: ConstVid) -> ConstVid {
+        vid
+    }
+
+    fn probe_ct_var(&self, _vid: ConstVid) -> Option<I::Const> {
         None
     }
 }
diff --git a/compiler/rustc_type_ir/src/infcx.rs b/compiler/rustc_type_ir/src/infcx.rs
new file mode 100644
index 0000000000000..681f129a50b7c
--- /dev/null
+++ b/compiler/rustc_type_ir/src/infcx.rs
@@ -0,0 +1,40 @@
+use crate::{ConstVid, Interner, TyVid, UniverseIndex};
+
+pub trait InferCtxtLike {
+    type Interner: Interner;
+
+    fn interner(&self) -> Self::Interner;
+
+    fn universe_of_ty(&self, ty: TyVid) -> Option<UniverseIndex>;
+
+    /// Resolve `TyVid` to its root `TyVid`.
+    fn root_ty_var(&self, vid: TyVid) -> TyVid;
+
+    /// Resolve `TyVid` to its inferred type, if it has been equated with a non-infer type.
+    fn probe_ty_var(&self, vid: TyVid) -> Option<<Self::Interner as Interner>::Ty>;
+
+    fn universe_of_lt(
+        &self,
+        lt: <Self::Interner as Interner>::InferRegion,
+    ) -> Option<UniverseIndex>;
+
+    /// Resolve `InferRegion` to its root `InferRegion`.
+    fn root_lt_var(
+        &self,
+        vid: <Self::Interner as Interner>::InferRegion,
+    ) -> <Self::Interner as Interner>::InferRegion;
+
+    /// Resolve `InferRegion` to its inferred region, if it has been equated with a non-infer region.
+    fn probe_lt_var(
+        &self,
+        vid: <Self::Interner as Interner>::InferRegion,
+    ) -> Option<<Self::Interner as Interner>::Region>;
+
+    fn universe_of_ct(&self, ct: ConstVid) -> Option<UniverseIndex>;
+
+    /// Resolve `ConstVid` to its root `ConstVid`.
+    fn root_ct_var(&self, vid: ConstVid) -> ConstVid;
+
+    /// Resolve `ConstVid` to its inferred type, if it has been equated with a non-infer type.
+    fn probe_ct_var(&self, vid: ConstVid) -> Option<<Self::Interner as Interner>::Const>;
+}
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index 300b0bf090d7b..c262302133bee 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -2,75 +2,113 @@ use smallvec::SmallVec;
 use std::fmt::Debug;
 use std::hash::Hash;
 
-use crate::{BoundVar, DebugWithInfcx, Mutability, UniverseIndex};
+use crate::{
+    BoundVar, CanonicalVarInfo, ConstKind, DebruijnIndex, DebugWithInfcx, Mutability, RegionKind,
+    TyKind, UniverseIndex,
+};
 
 pub trait Interner: Sized {
-    type DefId: Clone + Debug + Hash + Ord;
-    type AdtDef: Clone + Debug + Hash + Ord;
+    type DefId: Copy + Debug + Hash + Ord;
+    type AdtDef: Copy + Debug + Hash + Ord;
 
-    type GenericArgs: Clone
+    type GenericArgs: Copy
         + DebugWithInfcx<Self>
         + Hash
         + Ord
         + IntoIterator<Item = Self::GenericArg>;
-    type GenericArg: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type Term: Clone + Debug + Hash + Ord;
+    type GenericArg: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type Term: Copy + Debug + Hash + Ord;
 
     type Binder<T>;
-    type TypeAndMut: Clone + Debug + Hash + Ord;
-    type CanonicalVars: Clone + Debug + Hash + Eq;
+    type TypeAndMut: Copy + Debug + Hash + Ord;
+    type CanonicalVars: Copy + Debug + Hash + Eq + IntoIterator<Item = CanonicalVarInfo<Self>>;
 
     // Kinds of tys
-    type Ty: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type Tys: Clone + Debug + Hash + Ord + IntoIterator<Item = Self::Ty>;
-    type AliasTy: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type ParamTy: Clone + Debug + Hash + Ord;
-    type BoundTy: Clone + Debug + Hash + Ord;
-    type PlaceholderTy: Clone + Debug + Hash + Ord + Placeholder;
+    type Ty: Copy
+        + DebugWithInfcx<Self>
+        + Hash
+        + Ord
+        + Into<Self::GenericArg>
+        + IntoKind<Kind = TyKind<Self>>;
+    type Tys: Copy + Debug + Hash + Ord + IntoIterator<Item = Self::Ty>;
+    type AliasTy: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type ParamTy: Copy + Debug + Hash + Ord;
+    type BoundTy: Copy + Debug + Hash + Ord;
+    type PlaceholderTy: Copy + Debug + Hash + Ord + PlaceholderLike;
 
     // Things stored inside of tys
-    type ErrorGuaranteed: Clone + Debug + Hash + Ord;
-    type BoundExistentialPredicates: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type PolyFnSig: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type AllocId: Clone + Debug + Hash + Ord;
+    type ErrorGuaranteed: Copy + Debug + Hash + Ord;
+    type BoundExistentialPredicates: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type PolyFnSig: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type AllocId: Copy + Debug + Hash + Ord;
 
     // Kinds of consts
-    type Const: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type AliasConst: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type PlaceholderConst: Clone + Debug + Hash + Ord + Placeholder;
-    type ParamConst: Clone + Debug + Hash + Ord;
-    type BoundConst: Clone + Debug + Hash + Ord;
-    type ValueConst: Clone + Debug + Hash + Ord;
-    type ExprConst: Clone + DebugWithInfcx<Self> + Hash + Ord;
+    type Const: Copy
+        + DebugWithInfcx<Self>
+        + Hash
+        + Ord
+        + Into<Self::GenericArg>
+        + IntoKind<Kind = ConstKind<Self>>
+        + ConstTy<Self>;
+    type AliasConst: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type PlaceholderConst: Copy + Debug + Hash + Ord + PlaceholderLike;
+    type ParamConst: Copy + Debug + Hash + Ord;
+    type BoundConst: Copy + Debug + Hash + Ord;
+    type ValueConst: Copy + Debug + Hash + Ord;
+    type ExprConst: Copy + DebugWithInfcx<Self> + Hash + Ord;
 
     // Kinds of regions
-    type Region: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type EarlyParamRegion: Clone + Debug + Hash + Ord;
-    type BoundRegion: Clone + Debug + Hash + Ord;
-    type LateParamRegion: Clone + Debug + Hash + Ord;
-    type InferRegion: Clone + DebugWithInfcx<Self> + Hash + Ord;
-    type PlaceholderRegion: Clone + Debug + Hash + Ord + Placeholder;
+    type Region: Copy
+        + DebugWithInfcx<Self>
+        + Hash
+        + Ord
+        + Into<Self::GenericArg>
+        + IntoKind<Kind = RegionKind<Self>>;
+    type EarlyParamRegion: Copy + Debug + Hash + Ord;
+    type LateParamRegion: Copy + Debug + Hash + Ord;
+    type BoundRegion: Copy + Debug + Hash + Ord;
+    type InferRegion: Copy + DebugWithInfcx<Self> + Hash + Ord;
+    type PlaceholderRegion: Copy + Debug + Hash + Ord + PlaceholderLike;
 
     // Predicates
-    type Predicate: Clone + Debug + Hash + Eq;
-    type TraitPredicate: Clone + Debug + Hash + Eq;
-    type RegionOutlivesPredicate: Clone + Debug + Hash + Eq;
-    type TypeOutlivesPredicate: Clone + Debug + Hash + Eq;
-    type ProjectionPredicate: Clone + Debug + Hash + Eq;
-    type NormalizesTo: Clone + Debug + Hash + Eq;
-    type SubtypePredicate: Clone + Debug + Hash + Eq;
-    type CoercePredicate: Clone + Debug + Hash + Eq;
-    type ClosureKind: Clone + Debug + Hash + Eq;
+    type Predicate: Copy + Debug + Hash + Eq;
+    type TraitPredicate: Copy + Debug + Hash + Eq;
+    type RegionOutlivesPredicate: Copy + Debug + Hash + Eq;
+    type TypeOutlivesPredicate: Copy + Debug + Hash + Eq;
+    type ProjectionPredicate: Copy + Debug + Hash + Eq;
+    type NormalizesTo: Copy + Debug + Hash + Eq;
+    type SubtypePredicate: Copy + Debug + Hash + Eq;
+    type CoercePredicate: Copy + Debug + Hash + Eq;
+    type ClosureKind: Copy + Debug + Hash + Eq;
 
     fn ty_and_mut_to_parts(ty_and_mut: Self::TypeAndMut) -> (Self::Ty, Mutability);
+
+    fn mk_canonical_var_infos(self, infos: &[CanonicalVarInfo<Self>]) -> Self::CanonicalVars;
+
+    // FIXME: We should not have all these constructors on `Interner`, but as functions on some trait.
+    fn mk_bound_ty(self, debruijn: DebruijnIndex, var: BoundVar) -> Self::Ty;
+    fn mk_bound_region(self, debruijn: DebruijnIndex, var: BoundVar) -> Self::Region;
+    fn mk_bound_const(self, debruijn: DebruijnIndex, var: BoundVar, ty: Self::Ty) -> Self::Const;
 }
 
 /// Common capabilities of placeholder kinds
-pub trait Placeholder {
-    fn universe(&self) -> UniverseIndex;
-    fn var(&self) -> BoundVar;
+pub trait PlaceholderLike {
+    fn universe(self) -> UniverseIndex;
+    fn var(self) -> BoundVar;
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self;
+
+    fn new(ui: UniverseIndex, var: BoundVar) -> Self;
+}
+
+pub trait IntoKind {
+    type Kind;
+
+    fn kind(self) -> Self::Kind;
+}
+
+pub trait ConstTy<I: Interner> {
+    fn ty(self) -> I::Ty;
 }
 
 /// Imagine you have a function `F: FnOnce(&[T]) -> R`, plus an iterator `iter`
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index 2aeb4230bb83c..200963ff7c5c8 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -4,6 +4,7 @@
 )]
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
+#![allow(rustc::usage_of_ty_tykind)]
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 
 #[cfg(feature = "nightly")]
@@ -35,6 +36,7 @@ mod canonical;
 mod const_kind;
 mod debug;
 mod flags;
+mod infcx;
 mod interner;
 mod predicate_kind;
 mod region_kind;
@@ -43,13 +45,19 @@ pub use canonical::*;
 #[cfg(feature = "nightly")]
 pub use codec::*;
 pub use const_kind::*;
-pub use debug::{DebugWithInfcx, InferCtxtLike, WithInfcx};
+pub use debug::{DebugWithInfcx, WithInfcx};
 pub use flags::*;
+pub use infcx::InferCtxtLike;
 pub use interner::*;
 pub use predicate_kind::*;
 pub use region_kind::*;
 pub use ty_info::*;
 pub use ty_kind::*;
+pub use AliasKind::*;
+pub use DynKind::*;
+pub use InferTy::*;
+pub use RegionKind::*;
+pub use TyKind::*;
 
 rustc_index::newtype_index! {
     /// A [De Bruijn index][dbi] is a standard means of representing
@@ -337,6 +345,12 @@ impl UniverseIndex {
     }
 }
 
+impl Default for UniverseIndex {
+    fn default() -> Self {
+        Self::ROOT
+    }
+}
+
 rustc_index::newtype_index! {
     #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
     #[encodable]
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 3d4e7f77a4f2c..a7a5cae254ccd 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -1,5 +1,3 @@
-#![allow(rustc::usage_of_ty_tykind)]
-
 #[cfg(feature = "nightly")]
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 #[cfg(feature = "nightly")]
@@ -394,7 +392,7 @@ impl<I: Interner> DebugWithInfcx<I> for TyKind<I> {
             Float(float) => write!(f, "{float:?}"),
             Adt(d, s) => {
                 write!(f, "{d:?}")?;
-                let mut s = s.clone().into_iter();
+                let mut s = s.into_iter();
                 let first = s.next();
                 match first {
                     Some(first) => write!(f, "<{:?}", first)?,
@@ -412,7 +410,7 @@ impl<I: Interner> DebugWithInfcx<I> for TyKind<I> {
             Array(t, c) => write!(f, "[{:?}; {:?}]", &this.wrap(t), &this.wrap(c)),
             Slice(t) => write!(f, "[{:?}]", &this.wrap(t)),
             RawPtr(p) => {
-                let (ty, mutbl) = I::ty_and_mut_to_parts(p.clone());
+                let (ty, mutbl) = I::ty_and_mut_to_parts(*p);
                 match mutbl {
                     Mutability::Mut => write!(f, "*mut "),
                     Mutability::Not => write!(f, "*const "),
@@ -442,7 +440,7 @@ impl<I: Interner> DebugWithInfcx<I> for TyKind<I> {
             Tuple(t) => {
                 write!(f, "(")?;
                 let mut count = 0;
-                for ty in t.clone() {
+                for ty in *t {
                     if count > 0 {
                         write!(f, ", ")?;
                     }
@@ -820,15 +818,15 @@ impl<I: Interner> DebugWithInfcx<I> for InferTy {
         this: WithInfcx<'_, Infcx, &Self>,
         f: &mut fmt::Formatter<'_>,
     ) -> fmt::Result {
-        use InferTy::*;
-        match this.infcx.universe_of_ty(*this.data) {
-            None => write!(f, "{:?}", this.data),
-            Some(universe) => match *this.data {
-                TyVar(ty_vid) => write!(f, "?{}_{}t", ty_vid.index(), universe.index()),
-                IntVar(_) | FloatVar(_) | FreshTy(_) | FreshIntTy(_) | FreshFloatTy(_) => {
-                    unreachable!()
+        match this.data {
+            InferTy::TyVar(vid) => {
+                if let Some(universe) = this.infcx.universe_of_ty(*vid) {
+                    write!(f, "?{}_{}t", vid.index(), universe.index())
+                } else {
+                    write!(f, "{:?}", this.data)
                 }
-            },
+            }
+            _ => write!(f, "{:?}", this.data),
         }
     }
 }
diff --git a/compiler/stable_mir/src/compiler_interface.rs b/compiler/stable_mir/src/compiler_interface.rs
index 7916d04250d57..17c5212fb9cd4 100644
--- a/compiler/stable_mir/src/compiler_interface.rs
+++ b/compiler/stable_mir/src/compiler_interface.rs
@@ -8,6 +8,7 @@ use std::cell::Cell;
 use crate::mir::alloc::{AllocId, GlobalAlloc};
 use crate::mir::mono::{Instance, InstanceDef, StaticDef};
 use crate::mir::Body;
+use crate::target::MachineInfo;
 use crate::ty::{
     AdtDef, AdtKind, Allocation, ClosureDef, ClosureKind, Const, FieldDef, FnDef, GenericArgs,
     GenericPredicates, Generics, ImplDef, ImplTrait, LineInfo, PolyFnSig, RigidTy, Span, TraitDecl,
@@ -150,6 +151,9 @@ pub trait Context {
     /// Evaluate a static's initializer.
     fn eval_static_initializer(&self, def: StaticDef) -> Result<Allocation, Error>;
 
+    /// Try to evaluate an instance into a constant.
+    fn eval_instance(&self, def: InstanceDef, const_ty: Ty) -> Result<Allocation, Error>;
+
     /// Retrieve global allocation for the given allocation ID.
     fn global_alloc(&self, id: AllocId) -> GlobalAlloc;
 
@@ -157,6 +161,9 @@ pub trait Context {
     fn vtable_allocation(&self, global_alloc: &GlobalAlloc) -> Option<AllocId>;
     fn krate(&self, def_id: DefId) -> Crate;
     fn instance_name(&self, def: InstanceDef, trimmed: bool) -> Symbol;
+
+    /// Return information about the target machine.
+    fn target_info(&self) -> MachineInfo;
 }
 
 // A thread local variable that stores a pointer to the tables mapping between TyCtxt
diff --git a/compiler/stable_mir/src/error.rs b/compiler/stable_mir/src/error.rs
index bb5e1a34180ba..c6da3ae41d34b 100644
--- a/compiler/stable_mir/src/error.rs
+++ b/compiler/stable_mir/src/error.rs
@@ -6,11 +6,11 @@
 
 use std::convert::From;
 use std::fmt::{Debug, Display, Formatter};
-use std::{error, fmt};
+use std::{error, fmt, io};
 
 macro_rules! error {
      ($fmt: literal $(,)?) => { Error(format!($fmt)) };
-     ($fmt: literal, $($arg:tt)*) => { Error(format!($fmt, $($arg:tt)*)) };
+     ($fmt: literal, $($arg:tt)*) => { Error(format!($fmt, $($arg)*)) };
  }
 
 /// An error type used to represent an error that has already been reported by the compiler.
@@ -79,3 +79,9 @@ where
 
 impl error::Error for Error {}
 impl<T> error::Error for CompilerError<T> where T: Display + Debug {}
+
+impl From<io::Error> for Error {
+    fn from(value: io::Error) -> Self {
+        Error(value.to_string())
+    }
+}
diff --git a/compiler/stable_mir/src/lib.rs b/compiler/stable_mir/src/lib.rs
index 1e7495009d8de..8c66bfb2e9890 100644
--- a/compiler/stable_mir/src/lib.rs
+++ b/compiler/stable_mir/src/lib.rs
@@ -39,6 +39,7 @@ pub mod compiler_interface;
 #[macro_use]
 pub mod error;
 pub mod mir;
+pub mod target;
 pub mod ty;
 pub mod visitor;
 
diff --git a/compiler/stable_mir/src/mir/alloc.rs b/compiler/stable_mir/src/mir/alloc.rs
index af951bcef8c1e..c780042ff261c 100644
--- a/compiler/stable_mir/src/mir/alloc.rs
+++ b/compiler/stable_mir/src/mir/alloc.rs
@@ -1,7 +1,9 @@
 //! This module provides methods to retrieve allocation information, such as static variables.
 use crate::mir::mono::{Instance, StaticDef};
+use crate::target::{Endian, MachineInfo};
 use crate::ty::{Allocation, Binder, ExistentialTraitRef, IndexedVal, Ty};
-use crate::with;
+use crate::{with, Error};
+use std::io::Read;
 
 /// An allocation in the SMIR global memory can be either a function pointer,
 /// a static, or a "real" allocation with some data in it.
@@ -38,7 +40,7 @@ impl GlobalAlloc {
 }
 
 /// A unique identification number for each provenance
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
 pub struct AllocId(usize);
 
 impl IndexedVal for AllocId {
@@ -49,3 +51,33 @@ impl IndexedVal for AllocId {
         self.0
     }
 }
+
+/// Utility function used to read an allocation data into a unassigned integer.
+pub(crate) fn read_target_uint(mut bytes: &[u8]) -> Result<u128, Error> {
+    let mut buf = [0u8; std::mem::size_of::<u128>()];
+    match MachineInfo::target_endianess() {
+        Endian::Little => {
+            bytes.read(&mut buf)?;
+            Ok(u128::from_le_bytes(buf))
+        }
+        Endian::Big => {
+            bytes.read(&mut buf[16 - bytes.len()..])?;
+            Ok(u128::from_be_bytes(buf))
+        }
+    }
+}
+
+/// Utility function used to read an allocation data into an assigned integer.
+pub(crate) fn read_target_int(mut bytes: &[u8]) -> Result<i128, Error> {
+    let mut buf = [0u8; std::mem::size_of::<i128>()];
+    match MachineInfo::target_endianess() {
+        Endian::Little => {
+            bytes.read(&mut buf)?;
+            Ok(i128::from_le_bytes(buf))
+        }
+        Endian::Big => {
+            bytes.read(&mut buf[16 - bytes.len()..])?;
+            Ok(i128::from_be_bytes(buf))
+        }
+    }
+}
diff --git a/compiler/stable_mir/src/mir/body.rs b/compiler/stable_mir/src/mir/body.rs
index 90bd7aa7d1872..663275d9a0f8c 100644
--- a/compiler/stable_mir/src/mir/body.rs
+++ b/compiler/stable_mir/src/mir/body.rs
@@ -21,7 +21,7 @@ pub struct Body {
     pub(super) arg_count: usize,
 
     /// Debug information pertaining to user variables, including captures.
-    pub(super) var_debug_info: Vec<VarDebugInfo>,
+    pub var_debug_info: Vec<VarDebugInfo>,
 }
 
 pub type BasicBlockIdx = usize;
@@ -616,6 +616,24 @@ pub struct VarDebugInfo {
     pub argument_index: Option<u16>,
 }
 
+impl VarDebugInfo {
+    /// Return a local variable if this info is related to one.
+    pub fn local(&self) -> Option<Local> {
+        match &self.value {
+            VarDebugInfoContents::Place(place) if place.projection.is_empty() => Some(place.local),
+            VarDebugInfoContents::Place(_) | VarDebugInfoContents::Const(_) => None,
+        }
+    }
+
+    /// Return a constant if this info is related to one.
+    pub fn constant(&self) -> Option<&ConstOperand> {
+        match &self.value {
+            VarDebugInfoContents::Place(_) => None,
+            VarDebugInfoContents::Const(const_op) => Some(const_op),
+        }
+    }
+}
+
 pub type SourceScope = u32;
 
 #[derive(Clone, Debug, Eq, PartialEq)]
@@ -832,7 +850,7 @@ pub enum MutBorrowKind {
     ClosureCapture,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Mutability {
     Not,
     Mut,
diff --git a/compiler/stable_mir/src/mir/mono.rs b/compiler/stable_mir/src/mir/mono.rs
index 5c27f9281de65..bc5d4a3b8f477 100644
--- a/compiler/stable_mir/src/mir/mono.rs
+++ b/compiler/stable_mir/src/mir/mono.rs
@@ -132,6 +132,14 @@ impl Instance {
     pub fn is_empty_shim(&self) -> bool {
         self.kind == InstanceKind::Shim && with(|cx| cx.is_empty_drop_shim(self.def))
     }
+
+    /// Try to constant evaluate the instance into a constant with the given type.
+    ///
+    /// This can be used to retrieve a constant that represents an intrinsic return such as
+    /// `type_id`.
+    pub fn try_const_eval(&self, const_ty: Ty) -> Result<Allocation, Error> {
+        with(|cx| cx.eval_instance(self.def, const_ty))
+    }
 }
 
 impl Debug for Instance {
@@ -212,7 +220,7 @@ impl TryFrom<CrateItem> for StaticDef {
     type Error = crate::Error;
 
     fn try_from(value: CrateItem) -> Result<Self, Self::Error> {
-        if matches!(value.kind(), ItemKind::Static | ItemKind::Const) {
+        if matches!(value.kind(), ItemKind::Static) {
             Ok(StaticDef(value.0))
         } else {
             Err(Error::new(format!("Expected a static item, but found: {value:?}")))
diff --git a/compiler/stable_mir/src/target.rs b/compiler/stable_mir/src/target.rs
new file mode 100644
index 0000000000000..bed1dbc4c003c
--- /dev/null
+++ b/compiler/stable_mir/src/target.rs
@@ -0,0 +1,50 @@
+//! Provide information about the machine that this is being compiled into.
+
+use crate::compiler_interface::with;
+
+/// The properties of the target machine being compiled into.
+#[derive(Clone, PartialEq, Eq)]
+pub struct MachineInfo {
+    pub endian: Endian,
+    pub pointer_width: MachineSize,
+}
+
+impl MachineInfo {
+    pub fn target() -> MachineInfo {
+        with(|cx| cx.target_info().clone())
+    }
+
+    pub fn target_endianess() -> Endian {
+        with(|cx| cx.target_info().endian)
+    }
+
+    pub fn target_pointer_width() -> MachineSize {
+        with(|cx| cx.target_info().pointer_width)
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum Endian {
+    Little,
+    Big,
+}
+
+/// Represent the size of a component.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct MachineSize {
+    num_bits: usize,
+}
+
+impl MachineSize {
+    pub fn bytes(self) -> usize {
+        self.num_bits / 8
+    }
+
+    pub fn bits(self) -> usize {
+        self.num_bits
+    }
+
+    pub fn from_bits(num_bits: usize) -> MachineSize {
+        MachineSize { num_bits }
+    }
+}
diff --git a/compiler/stable_mir/src/ty.rs b/compiler/stable_mir/src/ty.rs
index c922264f8a365..bea7702bd34bf 100644
--- a/compiler/stable_mir/src/ty.rs
+++ b/compiler/stable_mir/src/ty.rs
@@ -4,9 +4,11 @@ use super::{
     with, DefId, Error, Symbol,
 };
 use crate::crate_def::CrateDef;
-use crate::mir::alloc::AllocId;
+use crate::mir::alloc::{read_target_int, read_target_uint, AllocId};
+use crate::target::MachineInfo;
 use crate::{Filename, Opaque};
 use std::fmt::{self, Debug, Display, Formatter};
+use std::ops::Range;
 
 #[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct Ty(pub usize);
@@ -366,6 +368,19 @@ pub enum IntTy {
     I128,
 }
 
+impl IntTy {
+    pub fn num_bytes(self) -> usize {
+        match self {
+            IntTy::Isize => crate::target::MachineInfo::target_pointer_width().bytes().into(),
+            IntTy::I8 => 1,
+            IntTy::I16 => 2,
+            IntTy::I32 => 4,
+            IntTy::I64 => 8,
+            IntTy::I128 => 16,
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum UintTy {
     Usize,
@@ -376,6 +391,19 @@ pub enum UintTy {
     U128,
 }
 
+impl UintTy {
+    pub fn num_bytes(self) -> usize {
+        match self {
+            UintTy::Usize => crate::target::MachineInfo::target_pointer_width().bytes().into(),
+            UintTy::U8 => 1,
+            UintTy::U16 => 2,
+            UintTy::U32 => 4,
+            UintTy::U64 => 8,
+            UintTy::U128 => 16,
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum FloatTy {
     F32,
@@ -821,21 +849,21 @@ pub struct BoundTy {
 pub type Bytes = Vec<Option<u8>>;
 pub type Size = usize;
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Hash)]
 pub struct Prov(pub AllocId);
 pub type Align = u64;
 pub type Promoted = u32;
 pub type InitMaskMaterialized = Vec<u64>;
 
 /// Stores the provenance information of pointers stored in memory.
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub struct ProvenanceMap {
     /// Provenance in this map applies from the given offset for an entire pointer-size worth of
     /// bytes. Two entries in this map are always at least a pointer size apart.
     pub ptrs: Vec<(Size, Prov)>,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub struct Allocation {
     pub bytes: Bytes,
     pub provenance: ProvenanceMap,
@@ -843,6 +871,74 @@ pub struct Allocation {
     pub mutability: Mutability,
 }
 
+impl Allocation {
+    /// Get a vector of bytes for an Allocation that has been fully initialized
+    pub fn raw_bytes(&self) -> Result<Vec<u8>, Error> {
+        self.bytes
+            .iter()
+            .copied()
+            .collect::<Option<Vec<_>>>()
+            .ok_or_else(|| error!("Found uninitialized bytes: `{:?}`", self.bytes))
+    }
+
+    /// Read a uint value from the specified range.
+    pub fn read_partial_uint(&self, range: Range<usize>) -> Result<u128, Error> {
+        if range.end - range.start > 16 {
+            return Err(error!("Allocation is bigger than largest integer"));
+        }
+        if range.end > self.bytes.len() {
+            return Err(error!(
+                "Range is out of bounds. Allocation length is `{}`, but requested range `{:?}`",
+                self.bytes.len(),
+                range
+            ));
+        }
+        let raw = self.bytes[range]
+            .iter()
+            .copied()
+            .collect::<Option<Vec<_>>>()
+            .ok_or_else(|| error!("Found uninitialized bytes: `{:?}`", self.bytes))?;
+        read_target_uint(&raw)
+    }
+
+    /// Read this allocation and try to convert it to an unassigned integer.
+    pub fn read_uint(&self) -> Result<u128, Error> {
+        if self.bytes.len() > 16 {
+            return Err(error!("Allocation is bigger than largest integer"));
+        }
+        let raw = self.raw_bytes()?;
+        read_target_uint(&raw)
+    }
+
+    /// Read this allocation and try to convert it to a signed integer.
+    pub fn read_int(&self) -> Result<i128, Error> {
+        if self.bytes.len() > 16 {
+            return Err(error!("Allocation is bigger than largest integer"));
+        }
+        let raw = self.raw_bytes()?;
+        read_target_int(&raw)
+    }
+
+    /// Read this allocation and try to convert it to a boolean.
+    pub fn read_bool(&self) -> Result<bool, Error> {
+        match self.read_int()? {
+            0 => Ok(false),
+            1 => Ok(true),
+            val @ _ => Err(error!("Unexpected value for bool: `{val}`")),
+        }
+    }
+
+    /// Read this allocation as a pointer and return whether it represents a `null` pointer.
+    pub fn is_null(&self) -> Result<bool, Error> {
+        let len = self.bytes.len();
+        let ptr_len = MachineInfo::target_pointer_width().bytes();
+        if len != ptr_len {
+            return Err(error!("Expected width of pointer (`{ptr_len}`), but found: `{len}`"));
+        }
+        Ok(self.read_uint()? == 0 && self.provenance.ptrs.is_empty())
+    }
+}
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ConstantKind {
     Allocated(Allocation),
diff --git a/tests/ui-fulldeps/stable-mir/check_allocation.rs b/tests/ui-fulldeps/stable-mir/check_allocation.rs
index 170b1fd73b16f..88c41537d9f85 100644
--- a/tests/ui-fulldeps/stable-mir/check_allocation.rs
+++ b/tests/ui-fulldeps/stable-mir/check_allocation.rs
@@ -23,12 +23,16 @@ extern crate stable_mir;
 
 use rustc_middle::ty::TyCtxt;
 use rustc_smir::rustc_internal;
-use stable_mir::{CrateItem, CrateItems, ItemKind};
 use stable_mir::crate_def::CrateDef;
 use stable_mir::mir::alloc::GlobalAlloc;
-use stable_mir::mir::mono::StaticDef;
+use stable_mir::mir::mono::{Instance, InstanceKind, StaticDef};
+use stable_mir::mir::{Body, TerminatorKind};
+use stable_mir::ty::{Allocation, ConstantKind, RigidTy, TyKind};
+use stable_mir::{CrateItem, CrateItems, ItemKind};
 use std::ascii::Char;
 use std::assert_matches::assert_matches;
+use std::cmp::{max, min};
+use std::collections::HashMap;
 use std::io::Write;
 use std::ops::ControlFlow;
 
@@ -40,6 +44,9 @@ fn test_stable_mir(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
     let items = stable_mir::all_local_items();
     check_foo(*get_item(&items, (ItemKind::Static, "FOO")).unwrap());
     check_bar(*get_item(&items, (ItemKind::Static, "BAR")).unwrap());
+    check_len(*get_item(&items, (ItemKind::Static, "LEN")).unwrap());
+    check_other_consts(*get_item(&items, (ItemKind::Fn, "other_consts")).unwrap());
+    check_type_id(*get_item(&items, (ItemKind::Fn, "check_type_id")).unwrap());
     ControlFlow::Continue(())
 }
 
@@ -76,6 +83,110 @@ fn check_bar(item: CrateItem) {
     assert_eq!(allocation.bytes[0].unwrap(), Char::CapitalB.to_u8());
     assert_eq!(allocation.bytes[1].unwrap(), Char::SmallA.to_u8());
     assert_eq!(allocation.bytes[2].unwrap(), Char::SmallR.to_u8());
+    assert_eq!(std::str::from_utf8(&allocation.raw_bytes().unwrap()), Ok("Bar"));
+}
+
+/// Check the allocation data for constants used in `other_consts` function.
+fn check_other_consts(item: CrateItem) {
+    // Instance body will force constant evaluation.
+    let body = Instance::try_from(item).unwrap().body().unwrap();
+    let assigns = collect_consts(&body);
+    assert_eq!(assigns.len(), 9);
+    for (name, alloc) in assigns {
+        match name.as_str() {
+            "_max_u128" => {
+                assert_eq!(alloc.read_uint(), Ok(u128::MAX), "Failed parsing allocation: {alloc:?}")
+            }
+            "_min_i128" => {
+                assert_eq!(alloc.read_int(), Ok(i128::MIN), "Failed parsing allocation: {alloc:?}")
+            }
+            "_max_i8" => {
+                assert_eq!(
+                    alloc.read_int().unwrap() as i8,
+                    i8::MAX,
+                    "Failed parsing allocation: {alloc:?}"
+                )
+            }
+            "_char" => {
+                assert_eq!(
+                    char::from_u32(alloc.read_uint().unwrap() as u32),
+                    Some('x'),
+                    "Failed parsing allocation: {alloc:?}"
+                )
+            }
+            "_false" => {
+                assert_eq!(alloc.read_bool(), Ok(false), "Failed parsing allocation: {alloc:?}")
+            }
+            "_true" => {
+                assert_eq!(alloc.read_bool(), Ok(true), "Failed parsing allocation: {alloc:?}")
+            }
+            "_ptr" => {
+                assert_eq!(alloc.is_null(), Ok(false), "Failed parsing allocation: {alloc:?}")
+            }
+            "_null_ptr" => {
+                assert_eq!(alloc.is_null(), Ok(true), "Failed parsing allocation: {alloc:?}")
+            }
+            "_tuple" => {
+                // The order of fields is not guaranteed.
+                let first = alloc.read_partial_uint(0..4).unwrap();
+                let second = alloc.read_partial_uint(4..8).unwrap();
+                assert_eq!(max(first, second) as u32, u32::MAX);
+                assert_eq!(min(first, second), 10);
+            }
+            _ => {
+                unreachable!("{name} -- {alloc:?}")
+            }
+        }
+    }
+}
+
+/// Check that we can retrieve the type id of char and bool, and that they have different values.
+fn check_type_id(item: CrateItem) {
+    let body = Instance::try_from(item).unwrap().body().unwrap();
+    let mut ids: Vec<u128> = vec![];
+    for term in body.blocks.iter().map(|bb| &bb.terminator) {
+        match &term.kind {
+            TerminatorKind::Call { func, destination, .. } => {
+                let TyKind::RigidTy(ty) = func.ty(body.locals()).unwrap().kind() else {
+                    unreachable!()
+                };
+                let RigidTy::FnDef(def, args) = ty else { unreachable!() };
+                let instance = Instance::resolve(def, &args).unwrap();
+                assert_eq!(instance.kind, InstanceKind::Intrinsic);
+                let dest_ty = destination.ty(body.locals()).unwrap();
+                let alloc = instance.try_const_eval(dest_ty).unwrap();
+                ids.push(alloc.read_uint().unwrap());
+            }
+            _ => { /* Do nothing */ }
+        }
+    }
+    assert_eq!(ids.len(), 2);
+    assert_ne!(ids[0], ids[1]);
+}
+
+/// Collects all the constant assignments.
+pub fn collect_consts(body: &Body) -> HashMap<String, &Allocation> {
+    body.var_debug_info
+        .iter()
+        .filter_map(|info| {
+            info.constant().map(|const_op| {
+                let ConstantKind::Allocated(alloc) = const_op.const_.kind() else { unreachable!() };
+                (info.name.clone(), alloc)
+            })
+        })
+        .collect::<HashMap<_, _>>()
+}
+
+/// Check the allocation data for `LEN`.
+///
+/// ```no_run
+/// static LEN: usize = 2;
+/// ```
+fn check_len(item: CrateItem) {
+    let def = StaticDef::try_from(item).unwrap();
+    let alloc = def.eval_initializer().unwrap();
+    assert!(alloc.provenance.ptrs.is_empty());
+    assert_eq!(alloc.read_uint(), Ok(2));
 }
 
 // Use internal API to find a function in a crate.
@@ -83,9 +194,7 @@ fn get_item<'a>(
     items: &'a CrateItems,
     item: (ItemKind, &str),
 ) -> Option<&'a stable_mir::CrateItem> {
-    items.iter().find(|crate_item| {
-        (item.0 == crate_item.kind()) && crate_item.name() == item.1
-    })
+    items.iter().find(|crate_item| (item.0 == crate_item.kind()) && crate_item.name() == item.1)
 }
 
 /// This test will generate and analyze a dummy crate using the stable mir.
@@ -109,11 +218,36 @@ fn generate_input(path: &str) -> std::io::Result<()> {
     write!(
         file,
         r#"
+    #![feature(core_intrinsics)]
+    use std::intrinsics::type_id;
+
+    static LEN: usize = 2;
     static FOO: [&str; 2] = ["hi", "there"];
     static BAR: &str = "Bar";
+    const NULL: *const u8 = std::ptr::null();
+    const TUPLE: (u32, u32) = (10, u32::MAX);
+
+    fn other_consts() {{
+        let _max_u128 = u128::MAX;
+        let _min_i128 = i128::MIN;
+        let _max_i8 = i8::MAX;
+        let _char = 'x';
+        let _false = false;
+        let _true = true;
+        let _ptr = &BAR;
+        let _null_ptr: *const u8 = NULL;
+        let _tuple = TUPLE;
+    }}
+
+    fn check_type_id() {{
+        let _char_id = type_id::<char>();
+        let _bool_id = type_id::<bool>();
+    }}
 
     pub fn main() {{
         println!("{{FOO:?}}! {{BAR}}");
+        assert_eq!(FOO.len(), LEN);
+        other_consts();
     }}"#
     )?;
     Ok(())
diff --git a/tests/ui/associated-consts/associated-const-impl-wrong-lifetime.stderr b/tests/ui/associated-consts/associated-const-impl-wrong-lifetime.stderr
index 6037122a365d9..1304bef4211d0 100644
--- a/tests/ui/associated-consts/associated-const-impl-wrong-lifetime.stderr
+++ b/tests/ui/associated-consts/associated-const-impl-wrong-lifetime.stderr
@@ -4,8 +4,8 @@ error[E0308]: const not compatible with trait
 LL |     const NAME: &'a str = "unit";
    |     ^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected reference `&'static str`
-              found reference `&'a str`
+   = note: expected reference `&'static _`
+              found reference `&'a _`
 note: the lifetime `'a` as defined here...
   --> $DIR/associated-const-impl-wrong-lifetime.rs:6:6
    |
diff --git a/tests/ui/associated-types/dont-suggest-cyclic-constraint.stderr b/tests/ui/associated-types/dont-suggest-cyclic-constraint.stderr
index 606084aea34a6..1b4694a2125a6 100644
--- a/tests/ui/associated-types/dont-suggest-cyclic-constraint.stderr
+++ b/tests/ui/associated-types/dont-suggest-cyclic-constraint.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     debug_assert_eq!(iter.next(), Some(value));
    |                                   ^^^^^^^^^^^ expected `Option<<I as Iterator>::Item>`, found `Option<&<I as Iterator>::Item>`
    |
-   = note: expected enum `Option<<I as Iterator>::Item>`
-              found enum `Option<&<I as Iterator>::Item>`
+   = note: expected enum `Option<_>`
+              found enum `Option<&_>`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.stderr b/tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.stderr
index 34aded73da55b..54df0edf5a8e4 100644
--- a/tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.stderr
+++ b/tests/ui/async-await/in-trait/async-example-desugared-boxed-in-trait.stderr
@@ -9,8 +9,8 @@ note: type in trait
    |
 LL |     fn foo(&self) -> Pin<Box<dyn Future<Output = i32> + '_>>;
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: expected signature `fn(&i32) -> Pin<Box<dyn Future<Output = i32>>>`
-              found signature `fn(&i32) -> impl Future<Output = i32>`
+   = note: expected signature `fn(&_) -> Pin<Box<dyn Future<Output = i32>>>`
+              found signature `fn(&_) -> impl Future<Output = i32>`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr b/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
index 7ebea3c03d36f..54d8f26f4ea8e 100644
--- a/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
+++ b/tests/ui/borrowck/regions-bound-missing-bound-in-impl.stderr
@@ -22,8 +22,8 @@ error[E0308]: method not compatible with trait
 LL |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected signature `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
-              found signature `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
+   = note: expected signature `fn(&'a _, Inv<'c>, Inv<'c>, Inv<'_>)`
+              found signature `fn(&'a _, Inv<'_>, Inv<'c>, Inv<'_>)`
 note: the lifetime `'c` as defined here...
   --> $DIR/regions-bound-missing-bound-in-impl.rs:27:24
    |
@@ -41,8 +41,8 @@ error[E0308]: method not compatible with trait
 LL |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected signature `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'_>)`
-              found signature `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'_>)`
+   = note: expected signature `fn(&'a _, Inv<'c>, Inv<'c>, Inv<'_>)`
+              found signature `fn(&'a _, Inv<'_>, Inv<'c>, Inv<'_>)`
 note: the lifetime `'c` as defined here...
   --> $DIR/regions-bound-missing-bound-in-impl.rs:27:24
    |
diff --git a/tests/ui/box/issue-82446.stderr b/tests/ui/box/issue-82446.stderr
index 568d23c2cb791..66daaceffb156 100644
--- a/tests/ui/box/issue-82446.stderr
+++ b/tests/ui/box/issue-82446.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |         val
    |         ^^^ expected `Box<dyn MyTrait>`, found `&Box<dyn MyTrait>`
    |
-   = note: expected struct `Box<(dyn MyTrait + 'static)>`
-           found reference `&Box<(dyn MyTrait + 'static)>`
+   = note: expected struct `Box<_>`
+           found reference `&Box<_>`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/closure-expected-type/expect-fn-supply-fn.stderr b/tests/ui/closure-expected-type/expect-fn-supply-fn.stderr
index e6ddc60689779..e010f0502f833 100644
--- a/tests/ui/closure-expected-type/expect-fn-supply-fn.stderr
+++ b/tests/ui/closure-expected-type/expect-fn-supply-fn.stderr
@@ -25,8 +25,8 @@ error[E0308]: mismatched types
 LL |     with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
    |                                                 ^ one type is more general than the other
    |
-   = note: expected fn pointer `fn(&u32)`
-              found fn pointer `for<'a> fn(&'a u32)`
+   = note: expected fn pointer `fn(&_)`
+              found fn pointer `for<'a> fn(&'a _)`
 
 error[E0308]: mismatched types
   --> $DIR/expect-fn-supply-fn.rs:39:50
@@ -34,8 +34,8 @@ error[E0308]: mismatched types
 LL |     with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
    |                                                  ^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a> fn(&'a u32)`
-              found fn pointer `fn(&u32)`
+   = note: expected fn pointer `for<'a> fn(&'a _)`
+              found fn pointer `fn(&_)`
 
 error[E0308]: mismatched types
   --> $DIR/expect-fn-supply-fn.rs:48:50
@@ -43,8 +43,8 @@ error[E0308]: mismatched types
 LL |     with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
    |                                                  ^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a> fn(&'a u32)`
-              found fn pointer `fn(&u32)`
+   = note: expected fn pointer `for<'a> fn(&'a _)`
+              found fn pointer `fn(&_)`
 
 error: aborting due to 5 previous errors
 
diff --git a/tests/ui/closures/multiple-fn-bounds.stderr b/tests/ui/closures/multiple-fn-bounds.stderr
index d510fc585f651..325652ef14ce5 100644
--- a/tests/ui/closures/multiple-fn-bounds.stderr
+++ b/tests/ui/closures/multiple-fn-bounds.stderr
@@ -6,8 +6,8 @@ LL |     foo(move |x| v);
    |     |
    |     expected due to this
    |
-   = note: expected closure signature `fn(char) -> _`
-              found closure signature `for<'a> fn(&'a char) -> _`
+   = note: expected closure signature `fn(_) -> _`
+              found closure signature `for<'a> fn(&'a _) -> _`
 note: closure inferred to have a different signature due to this bound
   --> $DIR/multiple-fn-bounds.rs:1:11
    |
diff --git a/tests/ui/fn/fn-pointer-mismatch.rs b/tests/ui/fn/fn-pointer-mismatch.rs
index 0597478cb4292..1c50d8b0f8b2d 100644
--- a/tests/ui/fn/fn-pointer-mismatch.rs
+++ b/tests/ui/fn/fn-pointer-mismatch.rs
@@ -35,20 +35,20 @@ fn main() {
     // suggest removing reference
     let c: fn(u32) -> u32 = &foo;
     //~^ ERROR mismatched types
-    //~| expected fn pointer `fn(u32) -> u32`
-    //~| found reference `&fn(u32) -> u32 {foo}`
+    //~| expected fn pointer `fn(_) -> _`
+    //~| found reference `&fn(_) -> _ {foo}`
 
     // suggest using reference
     let d: &fn(u32) -> u32 = foo;
     //~^ ERROR mismatched types
-    //~| expected reference `&fn(u32) -> u32`
-    //~| found fn item `fn(u32) -> u32 {foo}`
+    //~| expected reference `&fn(_) -> _`
+    //~| found fn item `fn(_) -> _ {foo}`
 
     // suggest casting with reference
     let e: &fn(u32) -> u32 = &foo;
     //~^ ERROR mismatched types
-    //~| expected reference `&fn(u32) -> u32`
-    //~| found reference `&fn(u32) -> u32 {foo}`
+    //~| expected reference `&fn(_) -> _`
+    //~| found reference `&fn(_) -> _ {foo}`
 
     // OK
     let mut z: fn(u32) -> u32 = foo as fn(u32) -> u32;
diff --git a/tests/ui/fn/fn-pointer-mismatch.stderr b/tests/ui/fn/fn-pointer-mismatch.stderr
index 87ece845b83a8..9cda11639d0f5 100644
--- a/tests/ui/fn/fn-pointer-mismatch.stderr
+++ b/tests/ui/fn/fn-pointer-mismatch.stderr
@@ -6,8 +6,8 @@ LL |     let g = if n % 2 == 0 { &foo } else { &bar };
    |                             |
    |                             expected because of this
    |
-   = note: expected reference `&fn(u32) -> u32 {foo}`
-              found reference `&fn(u32) -> u32 {bar}`
+   = note: expected reference `&fn(_) -> _ {foo}`
+              found reference `&fn(_) -> _ {bar}`
    = note: different fn items have unique types, even if their signatures are the same
    = help: consider casting both fn items to fn pointers using `as fn(u32) -> u32`
 
@@ -47,8 +47,8 @@ LL |     let c: fn(u32) -> u32 = &foo;
    |            |
    |            expected due to this
    |
-   = note: expected fn pointer `fn(u32) -> u32`
-               found reference `&fn(u32) -> u32 {foo}`
+   = note: expected fn pointer `fn(_) -> _`
+               found reference `&fn(_) -> _ {foo}`
 help: consider removing the reference
    |
 LL |     let c: fn(u32) -> u32 = foo;
@@ -62,8 +62,8 @@ LL |     let d: &fn(u32) -> u32 = foo;
    |            |
    |            expected due to this
    |
-   = note: expected reference `&fn(u32) -> u32`
-                found fn item `fn(u32) -> u32 {foo}`
+   = note: expected reference `&fn(_) -> _`
+                found fn item `fn(_) -> _ {foo}`
 help: consider using a reference
    |
 LL |     let d: &fn(u32) -> u32 = &foo;
@@ -77,8 +77,8 @@ LL |     let e: &fn(u32) -> u32 = &foo;
    |            |
    |            expected due to this
    |
-   = note: expected reference `&fn(u32) -> u32`
-              found reference `&fn(u32) -> u32 {foo}`
+   = note: expected reference `&fn(_) -> _`
+              found reference `&fn(_) -> _ {foo}`
    = note: fn items are distinct from fn pointers
 help: consider casting to a fn pointer
    |
diff --git a/tests/ui/generic-associated-types/issue-88360.stderr b/tests/ui/generic-associated-types/issue-88360.stderr
index 64cd55e684c65..49d36acadd657 100644
--- a/tests/ui/generic-associated-types/issue-88360.stderr
+++ b/tests/ui/generic-associated-types/issue-88360.stderr
@@ -9,8 +9,8 @@ LL |     fn copy(&self) -> Self::Gat<'_> where T: Copy {
 LL |         *self.test()
    |         ^^^^^^^^^^^^ expected `&T`, found type parameter `T`
    |
-   = note:   expected reference `&T`
-           found type parameter `T`
+   = note:   expected reference `&_`
+           found type parameter `_`
 help: consider removing deref here
    |
 LL -         *self.test()
diff --git a/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.stderr b/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.stderr
index 7cb7edfafeb66..d7f0860a026ac 100644
--- a/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.stderr
+++ b/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.stderr
@@ -8,8 +8,8 @@ LL | / check! { bound_a_b_ret_a_vs_bound_a_ret_a: (for<'a,'b> fn(&'a u32, &'b u3
 LL | | for<'a>    fn(&'a u32, &'a u32) -> &'a u32) }
    | |_____________________________________________- in this macro invocation
    |
-   = note: expected enum `Option<for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32>`
-              found enum `Option<for<'a> fn(&'a u32, &'a u32) -> &'a u32>`
+   = note: expected enum `Option<for<'a, 'b> fn(&'a _, &'b _) -> &'a _>`
+              found enum `Option<for<'a> fn(&'a _, &'a _) -> &'a _>`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_vs_free_x.stderr b/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_vs_free_x.stderr
index c6adbd91e7860..9b5ca3b2056aa 100644
--- a/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_vs_free_x.stderr
+++ b/tests/ui/higher-ranked/subtype/hr-subtype.bound_a_vs_free_x.stderr
@@ -8,8 +8,8 @@ LL | / check! { bound_a_vs_free_x: (for<'a> fn(&'a u32),
 LL | | fn(&'x u32)) }
    | |______________- in this macro invocation
    |
-   = note: expected enum `Option<for<'a> fn(&'a u32)>`
-              found enum `Option<fn(&u32)>`
+   = note: expected enum `Option<for<'a> fn(&'a _)>`
+              found enum `Option<fn(&_)>`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
diff --git a/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-fn.stderr b/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-fn.stderr
index f269babcf71aa..2d6b8063f69ff 100644
--- a/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-fn.stderr
+++ b/tests/ui/higher-ranked/trait-bounds/hrtb-exists-forall-fn.stderr
@@ -6,8 +6,8 @@ LL |     let _: for<'b> fn(&'b u32) = foo();
    |            |
    |            expected due to this
    |
-   = note: expected fn pointer `for<'b> fn(&'b u32)`
-              found fn pointer `fn(&u32)`
+   = note: expected fn pointer `for<'b> fn(&'b _)`
+              found fn pointer `fn(&_)`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/impl-trait/in-trait/specialization-broken.stderr b/tests/ui/impl-trait/in-trait/specialization-broken.stderr
index 25c0adeddbd7e..b8a8e2401b229 100644
--- a/tests/ui/impl-trait/in-trait/specialization-broken.stderr
+++ b/tests/ui/impl-trait/in-trait/specialization-broken.stderr
@@ -15,8 +15,8 @@ note: type in trait
    |
 LL |     fn bar(&self) -> impl Sized;
    |                      ^^^^^^^^^^
-   = note: expected signature `fn(&U) -> impl Sized`
-              found signature `fn(&U) -> U`
+   = note: expected signature `fn(&_) -> impl Sized`
+              found signature `fn(&_) -> U`
 
 error: method with return-position `impl Trait` in trait cannot be specialized
   --> $DIR/specialization-broken.rs:15:5
diff --git a/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr b/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
index fe765271bd2fe..07ac1a37e75ce 100644
--- a/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
+++ b/tests/ui/impl-trait/recursive-type-alias-impl-trait-declaration-too-subtle.stderr
@@ -18,8 +18,8 @@ LL |         fn eq(&self, _other: &(Foo, i32)) -> bool {
    |                              expected `a::Bar`, found opaque type
    |                              help: change the parameter type to match the trait: `&(a::Bar, i32)`
    |
-   = note: expected signature `fn(&a::Bar, &(a::Bar, i32)) -> _`
-              found signature `fn(&a::Bar, &(a::Foo, i32)) -> _`
+   = note: expected signature `fn(&a::Bar, &(a::Bar, _)) -> _`
+              found signature `fn(&a::Bar, &(a::Foo, _)) -> _`
 
 error: unconstrained opaque type
   --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:18:16
@@ -41,8 +41,8 @@ LL |         fn eq(&self, _other: &(Bar, i32)) -> bool {
    |                              expected opaque type, found `b::Bar`
    |                              help: change the parameter type to match the trait: `&(b::Foo, i32)`
    |
-   = note: expected signature `fn(&b::Bar, &(b::Foo, i32)) -> _`
-              found signature `fn(&b::Bar, &(b::Bar, i32)) -> _`
+   = note: expected signature `fn(&b::Bar, &(b::Foo, _)) -> _`
+              found signature `fn(&b::Bar, &(b::Bar, _)) -> _`
 note: this item must have the opaque type in its signature in order to be able to register hidden types
   --> $DIR/recursive-type-alias-impl-trait-declaration-too-subtle.rs:24:12
    |
diff --git a/tests/ui/implied-bounds/issue-100690.stderr b/tests/ui/implied-bounds/issue-100690.stderr
index 49f2fcd0a677b..df069d875cebc 100644
--- a/tests/ui/implied-bounds/issue-100690.stderr
+++ b/tests/ui/implied-bounds/issue-100690.stderr
@@ -6,8 +6,8 @@ LL |         real_dispatch(f)
    |         |
    |         required by a bound introduced by this call
    |
-   = note: expected a closure with arguments `(&mut UIView<'a, T>,)`
-              found a closure with arguments `(&mut UIView<'_, T>,)`
+   = note: expected a closure with arguments `(&mut UIView<'a, _>,)`
+              found a closure with arguments `(&mut UIView<'_, _>,)`
 note: required by a bound in `real_dispatch`
   --> $DIR/issue-100690.rs:9:8
    |
diff --git a/tests/ui/issues/issue-17905-2.stderr b/tests/ui/issues/issue-17905-2.stderr
index 88b5fbec6cf03..c66cb2224897d 100644
--- a/tests/ui/issues/issue-17905-2.stderr
+++ b/tests/ui/issues/issue-17905-2.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn say(self: &Pair<&str, isize>) {
    |                  ^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected struct `Pair<&str, _>`
-              found struct `Pair<&str, _>`
+   = note: expected struct `Pair<&_, _>`
+              found struct `Pair<&_, _>`
 note: the anonymous lifetime defined here...
   --> $DIR/issue-17905-2.rs:8:24
    |
@@ -23,8 +23,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn say(self: &Pair<&str, isize>) {
    |                  ^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected struct `Pair<&str, _>`
-              found struct `Pair<&str, _>`
+   = note: expected struct `Pair<&_, _>`
+              found struct `Pair<&_, _>`
 note: the anonymous lifetime as defined here...
   --> $DIR/issue-17905-2.rs:5:5
    |
diff --git a/tests/ui/issues/issue-20225.stderr b/tests/ui/issues/issue-20225.stderr
index b34aa8e1ff5ae..2d24a5bbd50ab 100644
--- a/tests/ui/issues/issue-20225.stderr
+++ b/tests/ui/issues/issue-20225.stderr
@@ -9,8 +9,8 @@ LL |   extern "rust-call" fn call(&self, (_,): (T,)) {}
    |                                           expected `&'a T`, found type parameter `T`
    |                                           help: change the parameter type to match the trait: `(&'a T,)`
    |
-   = note: expected signature `extern "rust-call" fn(&Foo, (&'a T,))`
-              found signature `extern "rust-call" fn(&Foo, (T,))`
+   = note: expected signature `extern "rust-call" fn(&Foo, (&'a _,))`
+              found signature `extern "rust-call" fn(&Foo, (_,))`
 
 error[E0053]: method `call_mut` has an incompatible type for trait
   --> $DIR/issue-20225.rs:11:51
@@ -23,8 +23,8 @@ LL |   extern "rust-call" fn call_mut(&mut self, (_,): (T,)) {}
    |                                                   expected `&'a T`, found type parameter `T`
    |                                                   help: change the parameter type to match the trait: `(&'a T,)`
    |
-   = note: expected signature `extern "rust-call" fn(&mut Foo, (&'a T,))`
-              found signature `extern "rust-call" fn(&mut Foo, (T,))`
+   = note: expected signature `extern "rust-call" fn(&mut Foo, (&'a _,))`
+              found signature `extern "rust-call" fn(&mut Foo, (_,))`
 
 error[E0053]: method `call_once` has an incompatible type for trait
   --> $DIR/issue-20225.rs:18:47
@@ -38,8 +38,8 @@ LL |   extern "rust-call" fn call_once(self, (_,): (T,)) {}
    |                                               expected `&'a T`, found type parameter `T`
    |                                               help: change the parameter type to match the trait: `(&'a T,)`
    |
-   = note: expected signature `extern "rust-call" fn(Foo, (&'a T,))`
-              found signature `extern "rust-call" fn(Foo, (T,))`
+   = note: expected signature `extern "rust-call" fn(Foo, (&'a _,))`
+              found signature `extern "rust-call" fn(Foo, (_,))`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/issues/issue-24322.stderr b/tests/ui/issues/issue-24322.stderr
index b260d02738854..d078069addcfb 100644
--- a/tests/ui/issues/issue-24322.stderr
+++ b/tests/ui/issues/issue-24322.stderr
@@ -6,8 +6,8 @@ LL |     let x: &fn(&B) -> u32 = &B::func;
    |            |
    |            expected due to this
    |
-   = note: expected reference `&for<'a> fn(&'a B) -> u32`
-              found reference `&for<'a> fn(&'a B) -> u32 {B::func}`
+   = note: expected reference `&for<'a> fn(&'a B) -> _`
+              found reference `&for<'a> fn(&'a B) -> _ {B::func}`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/issues/issue-37884.stderr b/tests/ui/issues/issue-37884.stderr
index 633abeb6f2266..b7c0095d682a2 100644
--- a/tests/ui/issues/issue-37884.stderr
+++ b/tests/ui/issues/issue-37884.stderr
@@ -4,8 +4,8 @@ error[E0308]: method not compatible with trait
 LL |     fn next(&'a mut self) -> Option<Self::Item>
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected signature `fn(&mut RepeatMut<'a, T>) -> Option<_>`
-              found signature `fn(&'a mut RepeatMut<'a, T>) -> Option<_>`
+   = note: expected signature `fn(&mut RepeatMut<'_, _>) -> Option<_>`
+              found signature `fn(&'a mut RepeatMut<'_, _>) -> Option<_>`
 note: the anonymous lifetime as defined here...
   --> $DIR/issue-37884.rs:6:5
    |
diff --git a/tests/ui/let-else/let-else-binding-explicit-mut-annotated.stderr b/tests/ui/let-else/let-else-binding-explicit-mut-annotated.stderr
index 065787cab08ff..1d41335036e56 100644
--- a/tests/ui/let-else/let-else-binding-explicit-mut-annotated.stderr
+++ b/tests/ui/let-else/let-else-binding-explicit-mut-annotated.stderr
@@ -6,8 +6,8 @@ LL |     let Some(n): &mut Option<i32> = &&Some(5i32) else { return };
    |                  |
    |                  expected due to this
    |
-   = note: expected mutable reference `&mut Option<i32>`
-                      found reference `&&Option<i32>`
+   = note: expected mutable reference `&mut Option<_>`
+                      found reference `&&Option<_>`
 
 error[E0308]: mismatched types
   --> $DIR/let-else-binding-explicit-mut-annotated.rs:13:37
@@ -17,8 +17,8 @@ LL |     let Some(n): &mut Option<i32> = &&mut Some(5i32) else { return };
    |                  |
    |                  expected due to this
    |
-   = note: expected mutable reference `&mut Option<i32>`
-                      found reference `&&mut Option<i32>`
+   = note: expected mutable reference `&mut Option<_>`
+                      found reference `&&mut Option<_>`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/lifetimes/issue-79187-2.stderr b/tests/ui/lifetimes/issue-79187-2.stderr
index 86a4ac4132e44..e8115bb6b064f 100644
--- a/tests/ui/lifetimes/issue-79187-2.stderr
+++ b/tests/ui/lifetimes/issue-79187-2.stderr
@@ -54,8 +54,8 @@ error[E0308]: mismatched types
 LL |     take_foo(|a: &i32| a);
    |     ^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
-   = note: expected reference `&i32`
-              found reference `&i32`
+   = note: expected reference `&_`
+              found reference `&_`
 note: the lifetime requirement is introduced here
   --> $DIR/issue-79187-2.rs:5:21
    |
@@ -68,8 +68,8 @@ error[E0308]: mismatched types
 LL |     take_foo(|a: &i32| -> &i32 { a });
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
-   = note: expected reference `&i32`
-              found reference `&i32`
+   = note: expected reference `&_`
+              found reference `&_`
 note: the lifetime requirement is introduced here
   --> $DIR/issue-79187-2.rs:5:21
    |
diff --git a/tests/ui/lub-glb/old-lub-glb-hr-noteq1.leak.stderr b/tests/ui/lub-glb/old-lub-glb-hr-noteq1.leak.stderr
index c3d7960de5641..10e3fc9286895 100644
--- a/tests/ui/lub-glb/old-lub-glb-hr-noteq1.leak.stderr
+++ b/tests/ui/lub-glb/old-lub-glb-hr-noteq1.leak.stderr
@@ -12,8 +12,8 @@ LL | |
 LL | |     };
    | |_____- `match` arms have incompatible types
    |
-   = note: expected fn pointer `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
-              found fn pointer `for<'a> fn(&'a u8, &'a u8) -> &'a u8`
+   = note: expected fn pointer `for<'a, 'b> fn(&'a _, &'b _) -> &'a _`
+              found fn pointer `for<'a> fn(&'a _, &'a _) -> &'a _`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/lub-glb/old-lub-glb-hr-noteq1.noleak.stderr b/tests/ui/lub-glb/old-lub-glb-hr-noteq1.noleak.stderr
index 8e4a514c7c6b8..bf77875fa7a2a 100644
--- a/tests/ui/lub-glb/old-lub-glb-hr-noteq1.noleak.stderr
+++ b/tests/ui/lub-glb/old-lub-glb-hr-noteq1.noleak.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |         _ => y,
    |              ^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
-              found fn pointer `for<'a> fn(&'a u8, &'a u8) -> &'a u8`
+   = note: expected fn pointer `for<'a, 'b> fn(&'a _, &'b _) -> &'a _`
+              found fn pointer `for<'a> fn(&'a _, &'a _) -> &'a _`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/lub-glb/old-lub-glb-hr-noteq2.leak.stderr b/tests/ui/lub-glb/old-lub-glb-hr-noteq2.leak.stderr
index a1958cc436adc..1c8925e0bfbcf 100644
--- a/tests/ui/lub-glb/old-lub-glb-hr-noteq2.leak.stderr
+++ b/tests/ui/lub-glb/old-lub-glb-hr-noteq2.leak.stderr
@@ -11,8 +11,8 @@ LL | |
 LL | |     };
    | |_____- `match` arms have incompatible types
    |
-   = note: expected fn pointer `for<'a> fn(&'a u8, &'a u8) -> &'a u8`
-              found fn pointer `for<'a, 'b> fn(&'a u8, &'b u8) -> &'a u8`
+   = note: expected fn pointer `for<'a> fn(&'a _, &'a _) -> &'a _`
+              found fn pointer `for<'a, 'b> fn(&'a _, &'b _) -> &'a _`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/mir/field-projection-mutating-context.stderr b/tests/ui/mir/field-projection-mutating-context.stderr
index 62c9e55a44bb5..c7289c0f07c75 100644
--- a/tests/ui/mir/field-projection-mutating-context.stderr
+++ b/tests/ui/mir/field-projection-mutating-context.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     let Foo(ref mut y): Foo<fn(&'static str)> = x;
    |             ^^^^^^^^^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a> fn(&'a str)`
-              found fn pointer `fn(&str)`
+   = note: expected fn pointer `for<'a> fn(&'a _)`
+              found fn pointer `fn(&_)`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/mismatched_types/closure-arg-type-mismatch.stderr b/tests/ui/mismatched_types/closure-arg-type-mismatch.stderr
index 760e3327b776a..e9808b8699186 100644
--- a/tests/ui/mismatched_types/closure-arg-type-mismatch.stderr
+++ b/tests/ui/mismatched_types/closure-arg-type-mismatch.stderr
@@ -6,8 +6,8 @@ LL |     a.iter().map(|_: (u32, u32)| 45);
    |              |
    |              expected due to this
    |
-   = note: expected closure signature `fn(&(u32, u32)) -> _`
-              found closure signature `fn((u32, u32)) -> _`
+   = note: expected closure signature `fn(&(_, _)) -> _`
+              found closure signature `fn((_, _)) -> _`
 note: required by a bound in `map`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider adjusting the signature so it borrows its argument
diff --git a/tests/ui/mismatched_types/issue-36053-2.stderr b/tests/ui/mismatched_types/issue-36053-2.stderr
index bac27788a2dc6..292525daa3d6b 100644
--- a/tests/ui/mismatched_types/issue-36053-2.stderr
+++ b/tests/ui/mismatched_types/issue-36053-2.stderr
@@ -6,8 +6,8 @@ LL |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                |
    |                                expected due to this
    |
-   = note: expected closure signature `for<'a> fn(&'a &str) -> _`
-              found closure signature `for<'a> fn(&'a str) -> _`
+   = note: expected closure signature `for<'a> fn(&'a &_) -> _`
+              found closure signature `for<'a> fn(&'a _) -> _`
 note: required by a bound in `filter`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 help: consider adjusting the signature so it borrows its argument
diff --git a/tests/ui/mismatched_types/normalize-fn-sig.stderr b/tests/ui/mismatched_types/normalize-fn-sig.stderr
index 2166de85f1fec..0fb3975c3c29d 100644
--- a/tests/ui/mismatched_types/normalize-fn-sig.stderr
+++ b/tests/ui/mismatched_types/normalize-fn-sig.stderr
@@ -6,8 +6,8 @@ LL |     needs_i32_ref_fn(foo::<()>);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected fn pointer `fn(&'static i32, i32)`
-                 found fn item `fn(i32, &'static i32) {foo::<()>}`
+   = note: expected fn pointer `fn(&'static _, _)`
+                 found fn item `fn(_, &'static _) {foo::<()>}`
 note: function defined here
   --> $DIR/normalize-fn-sig.rs:11:4
    |
diff --git a/tests/ui/moves/assignment-of-clone-call-on-ref-due-to-missing-bound.stderr b/tests/ui/moves/assignment-of-clone-call-on-ref-due-to-missing-bound.stderr
index 821661f1a568e..6a9d76f7998c9 100644
--- a/tests/ui/moves/assignment-of-clone-call-on-ref-due-to-missing-bound.stderr
+++ b/tests/ui/moves/assignment-of-clone-call-on-ref-due-to-missing-bound.stderr
@@ -6,8 +6,8 @@ LL |             let mut x: HashSet<Day> = v.clone();
    |                        |
    |                        expected due to this
    |
-   = note: expected struct `HashSet<Day>`
-           found reference `&HashSet<Day>`
+   = note: expected struct `HashSet<_>`
+           found reference `&HashSet<_>`
 note: `HashSet<Day>` does not implement `Clone`, so `&HashSet<Day>` was cloned instead
   --> $DIR/assignment-of-clone-call-on-ref-due-to-missing-bound.rs:18:39
    |
diff --git a/tests/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr b/tests/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr
index 7d76c916d6ddc..58fd7776f2f00 100644
--- a/tests/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr
+++ b/tests/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     let a: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
    |                                                          ^^^^^^^^^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32`
-              found fn pointer `for<'a> fn(&'a u32, &'a u32) -> &'a u32`
+   = note: expected fn pointer `for<'a, 'b> fn(&'a _, &'b _) -> &'a _`
+              found fn pointer `for<'a> fn(&'a _, &'a _) -> &'a _`
 
 error[E0308]: mismatched types
   --> $DIR/hr-fn-aaa-as-aba.rs:20:12
@@ -13,8 +13,8 @@ error[E0308]: mismatched types
 LL |     let _: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32`
-              found fn pointer `for<'a> fn(&'a u32, &'a u32) -> &'a u32`
+   = note: expected fn pointer `for<'a, 'b> fn(&'a _, &'b _) -> &'a _`
+              found fn pointer `for<'a> fn(&'a _, &'a _) -> &'a _`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/nll/relate_tys/universe-violation.stderr b/tests/ui/nll/relate_tys/universe-violation.stderr
index b585eee0769db..a538a59a495dc 100644
--- a/tests/ui/nll/relate_tys/universe-violation.stderr
+++ b/tests/ui/nll/relate_tys/universe-violation.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     let b: fn(&u32) -> &u32 = a;
    |                               ^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'a> fn(&'a u32) -> &'a u32`
-              found fn pointer `fn(&u32) -> &u32`
+   = note: expected fn pointer `for<'a> fn(&'a _) -> &'a _`
+              found fn pointer `fn(&_) -> &_`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/nll/trait-associated-constant.stderr b/tests/ui/nll/trait-associated-constant.stderr
index f6277508eebf5..371f7860d4da7 100644
--- a/tests/ui/nll/trait-associated-constant.stderr
+++ b/tests/ui/nll/trait-associated-constant.stderr
@@ -4,8 +4,8 @@ error[E0308]: const not compatible with trait
 LL |     const AC: Option<&'c str> = None;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
    |
-   = note: expected enum `Option<&'b str>`
-              found enum `Option<&'c str>`
+   = note: expected enum `Option<&'b _>`
+              found enum `Option<&'c _>`
 note: the lifetime `'c` as defined here...
   --> $DIR/trait-associated-constant.rs:20:18
    |
diff --git a/tests/ui/or-patterns/inconsistent-modes.stderr b/tests/ui/or-patterns/inconsistent-modes.stderr
index f6367ef823405..19618d336f883 100644
--- a/tests/ui/or-patterns/inconsistent-modes.stderr
+++ b/tests/ui/or-patterns/inconsistent-modes.stderr
@@ -57,8 +57,8 @@ LL |     let (Ok(ref a) | Err(ref mut a)): Result<&u8, &mut u8> = Ok(&0);
    |             |            types differ in mutability
    |             first introduced with type `&&u8` here
    |
-   = note:      expected reference `&&u8`
-           found mutable reference `&mut &mut u8`
+   = note:      expected reference `&&_`
+           found mutable reference `&mut &mut _`
    = note: a binding must have the same type in all alternatives
 
 error[E0308]: mismatched types
diff --git a/tests/ui/privacy/auxiliary/issue-117997.rs b/tests/ui/privacy/auxiliary/issue-117997.rs
new file mode 100644
index 0000000000000..6f71cc2ba3570
--- /dev/null
+++ b/tests/ui/privacy/auxiliary/issue-117997.rs
@@ -0,0 +1,35 @@
+// no-prefer-dynamic
+// compile-flags: --crate-type=rlib
+
+pub use impl_mod::TraitImplementer as Implementer;
+
+pub use trait_mod::get_assoc;
+
+mod impl_mod {
+    use crate::trait_mod::TraitWithAssocType;
+
+    pub struct TraitImplementer {}
+    pub struct AssociatedType {}
+
+    impl AssociatedType {
+        pub fn method_on_assoc(&self) -> i32 {
+            todo!()
+        }
+    }
+
+    impl TraitWithAssocType for TraitImplementer {
+        type AssocType = AssociatedType;
+    }
+}
+
+mod trait_mod {
+    use crate::Implementer;
+
+    pub fn get_assoc() -> <Implementer as TraitWithAssocType>::AssocType {
+        todo!()
+    }
+
+    pub trait TraitWithAssocType {
+        type AssocType;
+    }
+}
diff --git a/tests/ui/privacy/issue-117997.rs b/tests/ui/privacy/issue-117997.rs
new file mode 100644
index 0000000000000..d8284ef29970c
--- /dev/null
+++ b/tests/ui/privacy/issue-117997.rs
@@ -0,0 +1,8 @@
+// aux-build:issue-117997.rs
+// build-pass
+
+extern crate issue_117997;
+
+pub fn main() {
+    issue_117997::get_assoc().method_on_assoc();
+}
diff --git a/tests/ui/privacy/private-in-public.rs b/tests/ui/privacy/private-in-public.rs
index 3fff2d517106b..7b8e0fbe6b64a 100644
--- a/tests/ui/privacy/private-in-public.rs
+++ b/tests/ui/privacy/private-in-public.rs
@@ -106,6 +106,7 @@ mod aliases_pub {
     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
     //~^ WARNING type `aliases_pub::Priv` is more private than the item `aliases_pub::f3`
     //~| WARNING associated type `aliases_pub::PrivTr::Assoc` is more private than the item `aliases_pub::f3`
+    //~^^^ WARNING trait `aliases_pub::PrivTr` is more private than the item `aliases_pub::f3`
 
     impl PrivUseAlias {
         pub fn f(arg: Priv) {}
@@ -135,6 +136,7 @@ mod aliases_priv {
     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
     //~^ WARNING type `aliases_priv::Priv` is more private than the item `aliases_priv::f3`
     //~| WARNING associated type `aliases_priv::PrivTr::Assoc` is more private than the item `aliases_priv::f3`
+    //~^^^ WARNING trait `aliases_priv::PrivTr` is more private than the item `aliases_priv::f3`
 }
 
 mod aliases_params {
diff --git a/tests/ui/privacy/private-in-public.stderr b/tests/ui/privacy/private-in-public.stderr
index 49cc2e19bf0a6..ff3061337ff05 100644
--- a/tests/ui/privacy/private-in-public.stderr
+++ b/tests/ui/privacy/private-in-public.stderr
@@ -288,6 +288,18 @@ note: but associated type `aliases_pub::PrivTr::Assoc` is only usable at visibil
 LL |         type Assoc = m::Pub3;
    |         ^^^^^^^^^^
 
+warning: trait `aliases_pub::PrivTr` is more private than the item `aliases_pub::f3`
+  --> $DIR/private-in-public.rs:106:5
+   |
+LL |     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_pub::f3` is reachable at visibility `pub(crate)`
+   |
+note: but trait `aliases_pub::PrivTr` is only usable at visibility `pub(self)`
+  --> $DIR/private-in-public.rs:100:5
+   |
+LL |     trait PrivTr {
+   |     ^^^^^^^^^^^^
+
 warning: type `aliases_pub::Priv` is more private than the item `aliases_pub::f3`
   --> $DIR/private-in-public.rs:106:5
    |
@@ -301,76 +313,88 @@ LL |     struct Priv;
    |     ^^^^^^^^^^^
 
 warning: type `Priv1` is more private than the item `aliases_priv::f1`
-  --> $DIR/private-in-public.rs:133:5
+  --> $DIR/private-in-public.rs:134:5
    |
 LL |     pub fn f1(arg: PrivUseAlias) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_priv::f1` is reachable at visibility `pub(crate)`
    |
 note: but type `Priv1` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:118:5
+  --> $DIR/private-in-public.rs:119:5
    |
 LL |     struct Priv1;
    |     ^^^^^^^^^^^^
 
 warning: type `Priv2` is more private than the item `aliases_priv::f2`
-  --> $DIR/private-in-public.rs:134:5
+  --> $DIR/private-in-public.rs:135:5
    |
 LL |     pub fn f2(arg: PrivAlias) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_priv::f2` is reachable at visibility `pub(crate)`
    |
 note: but type `Priv2` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:119:5
+  --> $DIR/private-in-public.rs:120:5
    |
 LL |     struct Priv2;
    |     ^^^^^^^^^^^^
 
 warning: associated type `aliases_priv::PrivTr::Assoc` is more private than the item `aliases_priv::f3`
-  --> $DIR/private-in-public.rs:135:5
+  --> $DIR/private-in-public.rs:136:5
    |
 LL |     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_priv::f3` is reachable at visibility `pub(crate)`
    |
 note: but associated type `aliases_priv::PrivTr::Assoc` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:129:9
+  --> $DIR/private-in-public.rs:130:9
    |
 LL |         type Assoc = Priv3;
    |         ^^^^^^^^^^
 
+warning: trait `aliases_priv::PrivTr` is more private than the item `aliases_priv::f3`
+  --> $DIR/private-in-public.rs:136:5
+   |
+LL |     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_priv::f3` is reachable at visibility `pub(crate)`
+   |
+note: but trait `aliases_priv::PrivTr` is only usable at visibility `pub(self)`
+  --> $DIR/private-in-public.rs:129:5
+   |
+LL |     trait PrivTr {
+   |     ^^^^^^^^^^^^
+
 warning: type `aliases_priv::Priv` is more private than the item `aliases_priv::f3`
-  --> $DIR/private-in-public.rs:135:5
+  --> $DIR/private-in-public.rs:136:5
    |
 LL |     pub fn f3(arg: <Priv as PrivTr>::Assoc) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_priv::f3` is reachable at visibility `pub(crate)`
    |
 note: but type `aliases_priv::Priv` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:116:5
+  --> $DIR/private-in-public.rs:117:5
    |
 LL |     struct Priv;
    |     ^^^^^^^^^^^
 
 warning: type `aliases_params::Priv` is more private than the item `aliases_params::f2`
-  --> $DIR/private-in-public.rs:145:5
+  --> $DIR/private-in-public.rs:147:5
    |
 LL |     pub fn f2(arg: PrivAliasGeneric) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_params::f2` is reachable at visibility `pub(crate)`
    |
 note: but type `aliases_params::Priv` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:141:5
+  --> $DIR/private-in-public.rs:143:5
    |
 LL |     struct Priv;
    |     ^^^^^^^^^^^
 
 warning: type `aliases_params::Priv` is more private than the item `aliases_params::f3`
-  --> $DIR/private-in-public.rs:147:5
+  --> $DIR/private-in-public.rs:149:5
    |
 LL |     pub fn f3(arg: Result<u8>) {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ function `aliases_params::f3` is reachable at visibility `pub(crate)`
    |
 note: but type `aliases_params::Priv` is only usable at visibility `pub(self)`
-  --> $DIR/private-in-public.rs:141:5
+  --> $DIR/private-in-public.rs:143:5
    |
 LL |     struct Priv;
    |     ^^^^^^^^^^^
 
-warning: 31 warnings emitted
+warning: 33 warnings emitted
 
diff --git a/tests/ui/range/issue-73553-misinterp-range-literal.stderr b/tests/ui/range/issue-73553-misinterp-range-literal.stderr
index 52efa241d0b12..15e55708c3785 100644
--- a/tests/ui/range/issue-73553-misinterp-range-literal.stderr
+++ b/tests/ui/range/issue-73553-misinterp-range-literal.stderr
@@ -6,8 +6,8 @@ LL |     demo(tell(1)..tell(10));
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&std::ops::Range<usize>`
-                 found struct `std::ops::Range<usize>`
+   = note: expected reference `&std::ops::Range<_>`
+                 found struct `std::ops::Range<_>`
 note: function defined here
   --> $DIR/issue-73553-misinterp-range-literal.rs:3:4
    |
diff --git a/tests/ui/regions/issue-101280.stderr b/tests/ui/regions/issue-101280.stderr
index 70953808b8168..48deb99494bee 100644
--- a/tests/ui/regions/issue-101280.stderr
+++ b/tests/ui/regions/issue-101280.stderr
@@ -6,8 +6,8 @@ LL | fn f<'r>(f: fn(Cell<(&'r i32, &i32)>)) -> Ty {
 LL |     f
    |     ^ one type is more general than the other
    |
-   = note: expected fn pointer `for<'r> fn(Cell<(&'r i32, &'r i32)>)`
-              found fn pointer `for<'a> fn(Cell<(&'r i32, &'a i32)>)`
+   = note: expected fn pointer `for<'r> fn(Cell<(&'r _, &'r _)>)`
+              found fn pointer `for<'a> fn(Cell<(&'r _, &'a _)>)`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/regions/region-lifetime-bounds-on-fns-where-clause.stderr b/tests/ui/regions/region-lifetime-bounds-on-fns-where-clause.stderr
index 03d5a0be7235e..d8269514befd9 100644
--- a/tests/ui/regions/region-lifetime-bounds-on-fns-where-clause.stderr
+++ b/tests/ui/regions/region-lifetime-bounds-on-fns-where-clause.stderr
@@ -6,8 +6,8 @@ LL |     let _: fn(&mut &isize, &mut &isize) = a;
    |            |
    |            expected due to this
    |
-   = note: expected fn pointer `for<'a, 'b, 'c, 'd> fn(&'a mut &'b isize, &'c mut &'d isize)`
-                 found fn item `for<'a, 'b> fn(&'a mut &isize, &'b mut &isize) {a::<'_, '_>}`
+   = note: expected fn pointer `for<'a, 'b, 'c, 'd> fn(&'a mut &'b _, &'c mut &'d _)`
+                 found fn item `for<'a, 'b> fn(&'a mut &_, &'b mut &_) {a::<'_, '_>}`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.stderr b/tests/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.stderr
index 250571f1556d8..e383f352b9e97 100644
--- a/tests/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.stderr
+++ b/tests/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.stderr
@@ -6,8 +6,8 @@ LL |     let _: fn(&mut &isize, &mut &isize, &mut &isize) = a;
    |            |
    |            expected due to this
    |
-   = note: expected fn pointer `for<'a, 'b, 'c, 'd, 'e, 'f> fn(&'a mut &'b isize, &'c mut &'d isize, &'e mut &'f isize)`
-                 found fn item `for<'a, 'b, 'c> fn(&'a mut &isize, &'b mut &isize, &'c mut &isize) {a::<'_, '_, '_>}`
+   = note: expected fn pointer `for<'a, 'b, 'c, 'd, 'e, 'f> fn(&'a mut &'b _, &'c mut &'d _, &'e mut &'f _)`
+                 found fn item `for<'a, 'b, 'c> fn(&'a mut &_, &'b mut &_, &'c mut &_) {a::<'_, '_, '_>}`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/regions/regions-lifetime-bounds-on-fns.stderr b/tests/ui/regions/regions-lifetime-bounds-on-fns.stderr
index 31dd7efe067cf..989e91c702b83 100644
--- a/tests/ui/regions/regions-lifetime-bounds-on-fns.stderr
+++ b/tests/ui/regions/regions-lifetime-bounds-on-fns.stderr
@@ -6,8 +6,8 @@ LL |     let _: fn(&mut &isize, &mut &isize) = a;
    |            |
    |            expected due to this
    |
-   = note: expected fn pointer `for<'a, 'b, 'c, 'd> fn(&'a mut &'b isize, &'c mut &'d isize)`
-                 found fn item `for<'a, 'b> fn(&'a mut &isize, &'b mut &isize) {a::<'_, '_>}`
+   = note: expected fn pointer `for<'a, 'b, 'c, 'd> fn(&'a mut &'b _, &'c mut &'d _)`
+                 found fn item `for<'a, 'b> fn(&'a mut &_, &'b mut &_) {a::<'_, '_>}`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/resolve/resolve-inconsistent-binding-mode.stderr b/tests/ui/resolve/resolve-inconsistent-binding-mode.stderr
index c805c9eb125c8..6e44c280f758d 100644
--- a/tests/ui/resolve/resolve-inconsistent-binding-mode.stderr
+++ b/tests/ui/resolve/resolve-inconsistent-binding-mode.stderr
@@ -62,8 +62,8 @@ LL |         Opts::A(ref mut i) | Opts::B(ref i) => {}
    |                 |
    |                 first introduced with type `&mut isize` here
    |
-   = note: expected mutable reference `&mut isize`
-                      found reference `&isize`
+   = note: expected mutable reference `&mut _`
+                      found reference `&_`
    = note: in the same arm, a binding must have the same type in all alternatives
 
 error: aborting due to 6 previous errors
diff --git a/tests/ui/rfcs/rfc-2005-default-binding-mode/lit.stderr b/tests/ui/rfcs/rfc-2005-default-binding-mode/lit.stderr
index 181f57899a910..970a9c151c18f 100644
--- a/tests/ui/rfcs/rfc-2005-default-binding-mode/lit.stderr
+++ b/tests/ui/rfcs/rfc-2005-default-binding-mode/lit.stderr
@@ -6,8 +6,8 @@ LL |     match &s {
 LL |             "abc" => true,
    |             ^^^^^ expected `&&str`, found `&str`
    |
-   = note: expected reference `&&str`
-              found reference `&'static str`
+   = note: expected reference `&&_`
+              found reference `&'static _`
 
 error[E0308]: mismatched types
   --> $DIR/lit.rs:16:9
diff --git a/tests/ui/rfcs/rfc-2528-type-changing-struct-update/issue-92010-trait-bound-not-satisfied.stderr b/tests/ui/rfcs/rfc-2528-type-changing-struct-update/issue-92010-trait-bound-not-satisfied.stderr
index 61aae850a9438..86f2d9b6ec800 100644
--- a/tests/ui/rfcs/rfc-2528-type-changing-struct-update/issue-92010-trait-bound-not-satisfied.stderr
+++ b/tests/ui/rfcs/rfc-2528-type-changing-struct-update/issue-92010-trait-bound-not-satisfied.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |     fn y(&self, y: f64) -> Self { P{y, .. self.clone() } }
    |                                           ^^^^^^^^^^^^ expected `P<T>`, found `&P<T>`
    |
-   = note: expected struct `P<T>`
-           found reference `&P<T>`
+   = note: expected struct `P<_>`
+           found reference `&P<_>`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/static/static-reference-to-fn-1.stderr b/tests/ui/static/static-reference-to-fn-1.stderr
index ce9b6a739cfcc..6bf64974ef59b 100644
--- a/tests/ui/static/static-reference-to-fn-1.stderr
+++ b/tests/ui/static/static-reference-to-fn-1.stderr
@@ -4,8 +4,8 @@ error[E0308]: mismatched types
 LL |         func: &foo,
    |               ^^^^ expected `&fn() -> Option<isize>`, found `&fn() -> Option<isize> {foo}`
    |
-   = note: expected reference `&fn() -> Option<isize>`
-              found reference `&fn() -> Option<isize> {foo}`
+   = note: expected reference `&fn() -> Option<_>`
+              found reference `&fn() -> Option<_> {foo}`
    = note: fn items are distinct from fn pointers
 help: consider casting to a fn pointer
    |
diff --git a/tests/ui/suggestions/as-ref.stderr b/tests/ui/suggestions/as-ref.stderr
index c5b2bb1260f35..a42e2af316415 100644
--- a/tests/ui/suggestions/as-ref.stderr
+++ b/tests/ui/suggestions/as-ref.stderr
@@ -78,8 +78,8 @@ LL |     let y: Option<&usize> = x;
    |            |
    |            expected due to this
    |
-   = note:   expected enum `Option<&usize>`
-           found reference `&Option<usize>`
+   = note:   expected enum `Option<&_>`
+           found reference `&Option<_>`
 help: try using `.as_ref()` to convert `&Option<usize>` to `Option<&usize>`
    |
 LL |     let y: Option<&usize> = x.as_ref();
@@ -93,8 +93,8 @@ LL |     let y: Result<&usize, &usize> = x;
    |            |
    |            expected due to this
    |
-   = note:   expected enum `Result<&usize, &usize>`
-           found reference `&Result<usize, usize>`
+   = note:   expected enum `Result<&_, &_>`
+           found reference `&Result<_, _>`
 help: try using `.as_ref()` to convert `&Result<usize, usize>` to `Result<&usize, &usize>`
    |
 LL |     let y: Result<&usize, &usize> = x.as_ref();
@@ -108,8 +108,8 @@ LL |     let y: Result<&usize, usize> = x;
    |            |
    |            expected due to this
    |
-   = note:   expected enum `Result<&usize, usize>`
-           found reference `&Result<usize, usize>`
+   = note:   expected enum `Result<&_, _>`
+           found reference `&Result<_, _>`
 
 error[E0308]: mismatched types
   --> $DIR/as-ref.rs:22:42
diff --git a/tests/ui/suggestions/clone-on-unconstrained-borrowed-type-param.stderr b/tests/ui/suggestions/clone-on-unconstrained-borrowed-type-param.stderr
index 8c973995c34bd..afbb9c32d516e 100644
--- a/tests/ui/suggestions/clone-on-unconstrained-borrowed-type-param.stderr
+++ b/tests/ui/suggestions/clone-on-unconstrained-borrowed-type-param.stderr
@@ -8,8 +8,8 @@ LL | fn wat<T>(t: &T) -> T {
 LL |     t.clone()
    |     ^^^^^^^^^ expected type parameter `T`, found `&T`
    |
-   = note: expected type parameter `T`
-                   found reference `&T`
+   = note: expected type parameter `_`
+                   found reference `&_`
 note: `T` does not implement `Clone`, so `&T` was cloned instead
   --> $DIR/clone-on-unconstrained-borrowed-type-param.rs:3:5
    |
diff --git a/tests/ui/suggestions/method-access-to-range-literal-typo.stderr b/tests/ui/suggestions/method-access-to-range-literal-typo.stderr
index 54a16b8efa748..b1fb0254cd9cf 100644
--- a/tests/ui/suggestions/method-access-to-range-literal-typo.stderr
+++ b/tests/ui/suggestions/method-access-to-range-literal-typo.stderr
@@ -18,8 +18,8 @@ LL |     fn method(&self) -> Option<&Vec<u8>> {
 LL |         self.option..as_ref().map(|x| x)
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Option<&Vec<u8>>`, found `Range<Option<Vec<u8>>>`
    |
-   = note: expected enum `Option<&Vec<u8>>`
-            found struct `std::ops::Range<Option<Vec<u8>>>`
+   = note: expected enum `Option<&Vec<_>>`
+            found struct `std::ops::Range<Option<Vec<_>>>`
 help: you likely meant to write a method call instead of a range
    |
 LL -         self.option..as_ref().map(|x| x)
diff --git a/tests/ui/suggestions/mut-ref-reassignment.stderr b/tests/ui/suggestions/mut-ref-reassignment.stderr
index b86a04c7cd3d1..a225b34f8c30b 100644
--- a/tests/ui/suggestions/mut-ref-reassignment.stderr
+++ b/tests/ui/suggestions/mut-ref-reassignment.stderr
@@ -32,8 +32,8 @@ LL | fn suggestion2(opt: &mut Option<String>) {
 LL |     opt = Some(String::new())
    |           ^^^^^^^^^^^^^^^^^^^ expected `&mut Option<String>`, found `Option<String>`
    |
-   = note: expected mutable reference `&mut Option<String>`
-                           found enum `Option<String>`
+   = note: expected mutable reference `&mut Option<_>`
+                           found enum `Option<_>`
 help: consider dereferencing here to assign to the mutably borrowed value
    |
 LL |     *opt = Some(String::new())
diff --git a/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.fixed b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.fixed
new file mode 100644
index 0000000000000..6e679134d636c
--- /dev/null
+++ b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.fixed
@@ -0,0 +1,16 @@
+// run-rustfix
+
+struct A {}
+
+impl A {
+    fn hello(_a: i32) {}
+    fn test(_a: Self, _b: i32) {}
+}
+
+fn main() {
+    let _a = A {};
+    A::hello(1);
+    //~^ ERROR no method named `hello` found
+    A::test(_a, 1);
+    //~^ ERROR no method named `test` found
+}
diff --git a/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.rs b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.rs
new file mode 100644
index 0000000000000..67c2cc1bed561
--- /dev/null
+++ b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.rs
@@ -0,0 +1,16 @@
+// run-rustfix
+
+struct A {}
+
+impl A {
+    fn hello(_a: i32) {}
+    fn test(_a: Self, _b: i32) {}
+}
+
+fn main() {
+    let _a = A {};
+    _a.hello(1);
+    //~^ ERROR no method named `hello` found
+    _a.test(1);
+    //~^ ERROR no method named `test` found
+}
diff --git a/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.stderr b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.stderr
new file mode 100644
index 0000000000000..ed227cbab3967
--- /dev/null
+++ b/tests/ui/suggestions/suggest-assoc-fn-call-without-receiver.stderr
@@ -0,0 +1,41 @@
+error[E0599]: no method named `hello` found for struct `A` in the current scope
+  --> $DIR/suggest-assoc-fn-call-without-receiver.rs:12:8
+   |
+LL | struct A {}
+   | -------- method `hello` not found for this struct
+...
+LL |     _a.hello(1);
+   |     ---^^^^^---
+   |     |  |
+   |     |  this is an associated function, not a method
+   |     help: use associated function syntax instead: `A::hello(1)`
+   |
+   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
+note: the candidate is defined in an impl for the type `A`
+  --> $DIR/suggest-assoc-fn-call-without-receiver.rs:6:5
+   |
+LL |     fn hello(_a: i32) {}
+   |     ^^^^^^^^^^^^^^^^^
+
+error[E0599]: no method named `test` found for struct `A` in the current scope
+  --> $DIR/suggest-assoc-fn-call-without-receiver.rs:14:8
+   |
+LL | struct A {}
+   | -------- method `test` not found for this struct
+...
+LL |     _a.test(1);
+   |     ---^^^^---
+   |     |  |
+   |     |  this is an associated function, not a method
+   |     help: use associated function syntax instead: `A::test(_a, 1)`
+   |
+   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
+note: the candidate is defined in an impl for the type `A`
+  --> $DIR/suggest-assoc-fn-call-without-receiver.rs:7:5
+   |
+LL |     fn test(_a: Self, _b: i32) {}
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0599`.
diff --git a/tests/ui/traits/impl-method-mismatch.stderr b/tests/ui/traits/impl-method-mismatch.stderr
index 2655d465f2363..2061fc78575a0 100644
--- a/tests/ui/traits/impl-method-mismatch.stderr
+++ b/tests/ui/traits/impl-method-mismatch.stderr
@@ -9,8 +9,8 @@ note: type in trait
    |
 LL |     fn jumbo(&self, x: &usize) -> usize;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: expected signature `fn(&usize, &usize) -> usize`
-              found signature `unsafe fn(&usize, &usize)`
+   = note: expected signature `fn(&_, &_) -> usize`
+              found signature `unsafe fn(&_, &_)`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/traits/wrong-mul-method-signature.stderr b/tests/ui/traits/wrong-mul-method-signature.stderr
index 25a92f5ec12a7..91162cbc1231f 100644
--- a/tests/ui/traits/wrong-mul-method-signature.stderr
+++ b/tests/ui/traits/wrong-mul-method-signature.stderr
@@ -7,8 +7,8 @@ LL |     fn mul(self, s: &f64) -> Vec1 {
    |                     expected `f64`, found `&f64`
    |                     help: change the parameter type to match the trait: `f64`
    |
-   = note: expected signature `fn(Vec1, f64) -> Vec1`
-              found signature `fn(Vec1, &f64) -> Vec1`
+   = note: expected signature `fn(Vec1, _) -> Vec1`
+              found signature `fn(Vec1, &_) -> Vec1`
 
 error[E0053]: method `mul` has an incompatible type for trait
   --> $DIR/wrong-mul-method-signature.rs:33:21
diff --git a/tests/ui/type/type-check/point-at-inference-2.stderr b/tests/ui/type/type-check/point-at-inference-2.stderr
index 1d2777ad69a21..8b559ffff7e3b 100644
--- a/tests/ui/type/type-check/point-at-inference-2.stderr
+++ b/tests/ui/type/type-check/point-at-inference-2.stderr
@@ -25,8 +25,8 @@ LL |     bar(v);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected struct `Vec<i32>`
-              found struct `Vec<&i32>`
+   = note: expected struct `Vec<_>`
+              found struct `Vec<&_>`
 note: function defined here
   --> $DIR/point-at-inference-2.rs:1:4
    |
@@ -43,8 +43,8 @@ LL |     bar(v);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected struct `Vec<i32>`
-              found struct `Vec<&i32>`
+   = note: expected struct `Vec<_>`
+              found struct `Vec<&_>`
 note: function defined here
   --> $DIR/point-at-inference-2.rs:1:4
    |
diff --git a/tests/ui/type/type-mismatch.stderr b/tests/ui/type/type-mismatch.stderr
index ce6f29d354fd1..aca96978ac91a 100644
--- a/tests/ui/type/type-mismatch.stderr
+++ b/tests/ui/type/type-mismatch.stderr
@@ -382,8 +382,8 @@ LL |     want::<&Foo<foo>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo>`
-                 found struct `Foo<foo>`
+   = note: expected reference `&Foo<_>`
+                 found struct `Foo<_>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
@@ -402,8 +402,8 @@ LL |     want::<&Foo<foo, B>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo, B>`
-                 found struct `Foo<foo>`
+   = note: expected reference `&Foo<_, B>`
+                 found struct `Foo<_, A>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
@@ -546,8 +546,8 @@ LL |     want::<&Foo<foo>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo>`
-                 found struct `Foo<foo, B>`
+   = note: expected reference `&Foo<_, A>`
+                 found struct `Foo<_, B>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
@@ -562,8 +562,8 @@ LL |     want::<&Foo<foo, B>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo, B>`
-                 found struct `Foo<foo, B>`
+   = note: expected reference `&Foo<_, _>`
+                 found struct `Foo<_, _>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
@@ -726,8 +726,8 @@ LL |     want::<&Foo<foo>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo>`
-                 found struct `Foo<foo, B, A>`
+   = note: expected reference `&Foo<_, A, B>`
+                 found struct `Foo<_, B, A>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
@@ -742,8 +742,8 @@ LL |     want::<&Foo<foo, B>>(f);
    |     |
    |     arguments to this function are incorrect
    |
-   = note: expected reference `&Foo<foo, B>`
-                 found struct `Foo<foo, B, A>`
+   = note: expected reference `&Foo<_, _, B>`
+                 found struct `Foo<_, _, A>`
 note: function defined here
   --> $DIR/type-mismatch.rs:14:4
    |
diff --git a/tests/ui/typeck/bad-index-due-to-nested.stderr b/tests/ui/typeck/bad-index-due-to-nested.stderr
index 0b705d467ffb4..bd7fd0392c378 100644
--- a/tests/ui/typeck/bad-index-due-to-nested.stderr
+++ b/tests/ui/typeck/bad-index-due-to-nested.stderr
@@ -44,8 +44,8 @@ LL | fn index<'a, K, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
 LL |     map[k]
    |         ^ expected `&K`, found type parameter `K`
    |
-   = note:   expected reference `&K`
-           found type parameter `K`
+   = note:   expected reference `&_`
+           found type parameter `_`
 help: consider borrowing here
    |
 LL |     map[&k]
@@ -59,8 +59,8 @@ LL | fn index<'a, K, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
 LL |     map[k]
    |     ^^^^^^ expected `&V`, found type parameter `V`
    |
-   = note:   expected reference `&'a V`
-           found type parameter `V`
+   = note:   expected reference `&'a _`
+           found type parameter `_`
 help: consider borrowing here
    |
 LL |     &map[k]
diff --git a/tests/ui/typeck/mismatched-map-under-self.stderr b/tests/ui/typeck/mismatched-map-under-self.stderr
index 41391720a28c5..13678b4b82727 100644
--- a/tests/ui/typeck/mismatched-map-under-self.stderr
+++ b/tests/ui/typeck/mismatched-map-under-self.stderr
@@ -12,8 +12,8 @@ note: type in trait
    |
 LL |     fn values(&self) -> Self::Values;
    |               ^^^^^
-   = note: expected signature `fn(&Option<T>)`
-              found signature `fn(Option<T>)`
+   = note: expected signature `fn(&Option<_>)`
+              found signature `fn(Option<_>)`
 
 error[E0631]: type mismatch in function arguments
   --> $DIR/mismatched-map-under-self.rs:12:18
diff --git a/tests/ui/ufcs/ufcs-explicit-self-bad.rs b/tests/ui/ufcs/ufcs-explicit-self-bad.rs
index 9b0f99a189a76..3bb3d906d110b 100644
--- a/tests/ui/ufcs/ufcs-explicit-self-bad.rs
+++ b/tests/ui/ufcs/ufcs-explicit-self-bad.rs
@@ -39,12 +39,12 @@ impl<'a, T> SomeTrait for &'a Bar<T> {
     //~| ERROR has an incompatible type for trait
     fn dummy3(self: &&Bar<T>) {}
     //~^ ERROR mismatched `self` parameter type
-    //~| expected reference `&'a Bar<T>`
-    //~| found reference `&Bar<T>`
+    //~| expected reference `&'a Bar<_>`
+    //~| found reference `&Bar<_>`
     //~| lifetime mismatch
     //~| ERROR mismatched `self` parameter type
-    //~| expected reference `&'a Bar<T>`
-    //~| found reference `&Bar<T>`
+    //~| expected reference `&'a Bar<_>`
+    //~| found reference `&Bar<_>`
     //~| lifetime mismatch
 }
 
diff --git a/tests/ui/ufcs/ufcs-explicit-self-bad.stderr b/tests/ui/ufcs/ufcs-explicit-self-bad.stderr
index 0efaa41d48a1c..4c2cb0eb7536a 100644
--- a/tests/ui/ufcs/ufcs-explicit-self-bad.stderr
+++ b/tests/ui/ufcs/ufcs-explicit-self-bad.stderr
@@ -31,8 +31,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn dummy2(self: &Bar<T>) {}
    |                     ^^^^^^^ lifetime mismatch
    |
-   = note: expected reference `&'a Bar<T>`
-              found reference `&Bar<T>`
+   = note: expected reference `&'a Bar<_>`
+              found reference `&Bar<_>`
 note: the anonymous lifetime defined here...
   --> $DIR/ufcs-explicit-self-bad.rs:37:21
    |
@@ -50,8 +50,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn dummy2(self: &Bar<T>) {}
    |                     ^^^^^^^ lifetime mismatch
    |
-   = note: expected reference `&'a Bar<T>`
-              found reference `&Bar<T>`
+   = note: expected reference `&'a Bar<_>`
+              found reference `&Bar<_>`
 note: the lifetime `'a` as defined here...
   --> $DIR/ufcs-explicit-self-bad.rs:35:6
    |
@@ -69,8 +69,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn dummy3(self: &&Bar<T>) {}
    |                     ^^^^^^^^ lifetime mismatch
    |
-   = note: expected reference `&'a Bar<T>`
-              found reference `&Bar<T>`
+   = note: expected reference `&'a Bar<_>`
+              found reference `&Bar<_>`
 note: the anonymous lifetime defined here...
   --> $DIR/ufcs-explicit-self-bad.rs:40:22
    |
@@ -88,8 +88,8 @@ error[E0308]: mismatched `self` parameter type
 LL |     fn dummy3(self: &&Bar<T>) {}
    |                     ^^^^^^^^ lifetime mismatch
    |
-   = note: expected reference `&'a Bar<T>`
-              found reference `&Bar<T>`
+   = note: expected reference `&'a Bar<_>`
+              found reference `&Bar<_>`
 note: the lifetime `'a` as defined here...
   --> $DIR/ufcs-explicit-self-bad.rs:35:6
    |
@@ -115,8 +115,8 @@ note: type in trait
    |
 LL |     fn dummy2(&self);
    |               ^^^^^
-   = note: expected signature `fn(&&'a Bar<T>)`
-              found signature `fn(&Bar<T>)`
+   = note: expected signature `fn(&&'a Bar<_>)`
+              found signature `fn(&Bar<_>)`
 
 error: aborting due to 8 previous errors
 
diff --git a/tests/ui/unsafe/unsafe-trait-impl.rs b/tests/ui/unsafe/unsafe-trait-impl.rs
index 1fc84ca02560d..9fd9ff65288d9 100644
--- a/tests/ui/unsafe/unsafe-trait-impl.rs
+++ b/tests/ui/unsafe/unsafe-trait-impl.rs
@@ -7,8 +7,8 @@ trait Foo {
 impl Foo for u32 {
     fn len(&self) -> u32 { *self }
     //~^ ERROR method `len` has an incompatible type for trait
-    //~| expected signature `unsafe fn(&u32) -> _`
-    //~| found signature `fn(&u32) -> _`
+    //~| expected signature `unsafe fn(&_) -> _`
+    //~| found signature `fn(&_) -> _`
 }
 
 fn main() { }
diff --git a/tests/ui/unsafe/unsafe-trait-impl.stderr b/tests/ui/unsafe/unsafe-trait-impl.stderr
index db5200e1c2030..5888b674d4fb4 100644
--- a/tests/ui/unsafe/unsafe-trait-impl.stderr
+++ b/tests/ui/unsafe/unsafe-trait-impl.stderr
@@ -9,8 +9,8 @@ note: type in trait
    |
 LL |     unsafe fn len(&self) -> u32;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: expected signature `unsafe fn(&u32) -> _`
-              found signature `fn(&u32) -> _`
+   = note: expected signature `unsafe fn(&_) -> _`
+              found signature `fn(&_) -> _`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/wf/unnormalized-projection-guides-inference.rs b/tests/ui/wf/unnormalized-projection-guides-inference.rs
new file mode 100644
index 0000000000000..ca2d6c2e882d0
--- /dev/null
+++ b/tests/ui/wf/unnormalized-projection-guides-inference.rs
@@ -0,0 +1,24 @@
+// The WF requirements of the *unnormalized* form of type annotations
+// can guide inference.
+// check-pass
+
+pub trait EqualTo {
+    type Ty;
+}
+impl<X> EqualTo for X {
+    type Ty = X;
+}
+
+trait MyTrait<U: EqualTo<Ty = Self>> {
+    type Out;
+}
+impl<T, U: EqualTo<Ty = T>> MyTrait<U> for T {
+    type Out = ();
+}
+
+fn main() {
+    let _: <_ as MyTrait<u8>>::Out;
+    // We shoud be able to infer a value for the inference variable above.
+    // The WF of the unnormalized projection requires `u8: EqualTo<Ty = _>`,
+    // which is sufficient to guide inference.
+}