Rollup merge of #117586 - compiler-errors:the-canonicalizer, r=lcnr

Uplift the (new solver) canonicalizer into `rustc_next_trait_solver`

Uplifts the new trait solver's canonicalizer into a new crate called `rustc_next_trait_solver`.

The crate name is literally a bikeshed-avoidance name, so let's not block this PR on that -- renames are welcome later.

There are a host of other changes that were required to make this possible:
* Expose a `ConstTy` trait to get the `Interner::Ty` from a `Interner::Const`.
* Expose some constructor methods to construct `Bound` variants. These are currently methods defined on the interner themselves, but they could be pulled into traits later.
* Expose a `IntoKind` trait to turn a `Ty`/`Const`/`Region` into their corresponding `*Kind`s.
* Some minor tweaks to other APIs in `rustc_type_ir`.

The canonicalizer code itself is best reviewed **with whitespace ignored.**

r? ``@lcnr``

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"
@@ -4571,6 +4578,7 @@ dependencies = [
  "rustc_infer",
  "rustc_macros",
  "rustc_middle",
+ "rustc_next_trait_solver",
  "rustc_parse_format",
  "rustc_query_system",
  "rustc_session",

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> {
+    fn interner(&self) -> TyCtxt<'tcx> {
-        use InferTy::*;
+        self.tcx
-        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
+    fn universe_of_ty(&self, vid: TyVid) -> Option<ty::UniverseIndex> {
-            // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
+        // FIXME(BoxyUwU): this is kind of jank and means that printing unresolved
-            // try to print out `?0.1` it will just print `?0`.
+        // ty infers will give you the universe of the var it resolved to not the universe
-            TyVar(ty_vid) => match self.probe_ty_var(ty_vid) {
+        // it actually had. It also means that if you have a `?0.1` and infer it to `u8` then
-                Err(universe) => Some(universe),
+        // try to print out `?0.1` it will just print `?0`.
-                Ok(_) => None,
+        match self.probe_ty_var(vid) {
-            },
+            Err(universe) => Some(universe),
-            IntVar(_) | FloatVar(_) | FreshTy(_) | FreshIntTy(_) | FreshFloatTy(_) => None,
+            Ok(_) => None,
         }
     }
 
-    fn universe_of_ct(&self, ct: ty::InferConst) -> Option<ty::UniverseIndex> {
+    fn universe_of_ct(&self, ct: ConstVid) -> Option<ty::UniverseIndex> {
-        use ty::InferConst::*;
+        // Same issue as with `universe_of_ty`
-        match ct {
+        match self.probe_const_var(ct) {
-            // Same issue as with `universe_of_ty`
+            Err(universe) => Some(universe),
-            Var(ct_vid) => match self.probe_const_var(ct_vid) {
+            Ok(_) => None,
-                Err(universe) => Some(universe),
-                Ok(_) => None,
-            },
-            EffectVar(_) => None,
-            Fresh(_) => 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
     }

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,

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> {

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>, ()>;

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 {
+impl PlaceholderLike for PlaceholderRegion {
-    fn universe(&self) -> UniverseIndex {
+    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 {
+impl PlaceholderLike for PlaceholderType {
-    fn universe(&self) -> UniverseIndex {
+    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 {
+impl PlaceholderLike for PlaceholderConst {
-    fn universe(&self) -> UniverseIndex {
+    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

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(

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",
+]

compiler/rustc_next_trait_solver/src/canonicalizer.rs

@@ -1,17 +1,10 @@
 use std::cmp::Ordering;
 
-use crate::infer::InferCtxt;
+use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
-use rustc_middle::infer::canonical::Canonical;
+use rustc_type_ir::{
-use rustc_middle::infer::canonical::CanonicalTyVarKind;
+    self as ty, Canonical, CanonicalTyVarKind, CanonicalVarInfo, CanonicalVarKind, ConstTy,
-use rustc_middle::infer::canonical::CanonicalVarInfo;
+    InferCtxtLike, Interner, IntoKind, PlaceholderLike,
-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};
 
 /// Whether we're canonicalizing a query input or the query response.
 ///
@@ -42,23 +35,22 @@ pub enum CanonicalizeMode {
     },
 }
 
-pub struct Canonicalizer<'a, 'tcx> {
+pub struct Canonicalizer<'a, Infcx: InferCtxtLike<Interner = I>, I: Interner> {
-    infcx: &'a InferCtxt<'tcx>,
+    infcx: &'a Infcx,
     canonicalize_mode: CanonicalizeMode,
 
-    variables: &'a mut Vec<ty::GenericArg<'tcx>>,
+    variables: &'a mut Vec<I::GenericArg>,
-    primitive_var_infos: Vec<CanonicalVarInfo<'tcx>>,
+    primitive_var_infos: Vec<CanonicalVarInfo<I>>,
     binder_index: ty::DebruijnIndex,
 }
 
-impl<'a, 'tcx> Canonicalizer<'a, 'tcx> {
+impl<'a, Infcx: InferCtxtLike<Interner = I>, I: Interner> Canonicalizer<'a, Infcx, I> {
-    #[instrument(level = "debug", skip(infcx), ret)]
+    pub fn canonicalize<T: TypeFoldable<I>>(
-    pub fn canonicalize<T: TypeFoldable<TyCtxt<'tcx>>>(
+        infcx: &'a Infcx,
-        infcx: &'a InferCtxt<'tcx>,
         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:?}");
+        // FIXME: Restore these assertions. Should we uplift type flags?
-        assert!(!value.has_placeholders(), "unexpected placeholders in {value:?}");
+        // 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> {
+impl<Infcx: InferCtxtLike<Interner = I>, I: Interner> TypeFolder<I>
-    fn interner(&self) -> TyCtxt<'tcx> {
+    for Canonicalizer<'_, Infcx, I>
-        self.infcx.tcx
+{
+    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> {
+    fn fold_region(&mut self, r: I::Region) -> I::Region {
-        if let ty::ReVar(vid) = *r {
+        let kind = match r.kind() {
-            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 {
             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) {
+                    if max_input_universe.can_name(placeholder.universe()) {
-                        bug!("new placeholder in universe {max_input_universe:?}: {r:?}");
+                        panic!("new placeholder in universe {max_input_universe:?}: {r:?}");
                     }
                     CanonicalVarKind::PlaceholderRegion(placeholder)
                 }
             },
 
-            ty::ReVar(_) => match self.canonicalize_mode {
+            ty::ReVar(vid) => {
-                CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
+                assert_eq!(
-                CanonicalizeMode::Response { .. } => {
+                    self.infcx.root_lt_var(vid),
-                    CanonicalVarKind::Region(self.infcx.universe_of_region(r))
+                    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> {
+    fn fold_ty(&mut self, t: I::Ty) -> I::Ty
-        let kind = match *t.kind() {
+    where
-            ty::Infer(ty::TyVar(vid)) => {
+        I::Ty: TypeSuperFoldable<I>,
-                assert_eq!(self.infcx.root_var(vid), vid, "ty vid should have been resolved");
+    {
-                let Err(ui) = self.infcx.probe_ty_var(vid) else {
+        let kind = match t.kind() {
-                    bug!("ty var should have been resolved: {t}");
+            ty::Infer(i) => match i {
-                };
+                ty::TyVar(vid) => {
-                CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui))
+                    assert_eq!(
-            }
+                        self.infcx.root_ty_var(vid),
-            ty::Infer(ty::IntVar(vid)) => {
+                        vid,
-                assert_eq!(self.infcx.opportunistic_resolve_int_var(vid), t);
+                        "ty vid should have been resolved fully before canonicalization"
-                CanonicalVarKind::Ty(CanonicalTyVarKind::Int)
+                    );
-            }
+                    assert_eq!(
-            ty::Infer(ty::FloatVar(vid)) => {
+                        self.infcx.probe_ty_var(vid),
-                assert_eq!(self.infcx.opportunistic_resolve_float_var(vid), t);
+                        None,
-                CanonicalVarKind::Ty(CanonicalTyVarKind::Float)
+                        "ty vid should have been resolved fully before canonicalization"
-            }
+                    );
-            ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
+
-                bug!("fresh var during canonicalization: {t:?}")
+                    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 {
+                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
-                    universe: placeholder.universe,
+                    placeholder.universe(),
-                    bound: ty::BoundTy {
+                    self.variables.len().into(),
-                        var: ty::BoundVar::from_usize(self.variables.len()),
+                )),
-                        kind: ty::BoundTyKind::Anon,
-                    },
-                }),
                 CanonicalizeMode::Response { .. } => CanonicalVarKind::PlaceholderTy(placeholder),
             },
             ty::Param(_) => match self.canonicalize_mode {
-                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(ty::Placeholder {
+                CanonicalizeMode::Input => CanonicalVarKind::PlaceholderTy(PlaceholderLike::new(
-                    universe: ty::UniverseIndex::ROOT,
+                    ty::UniverseIndex::ROOT,
-                    bound: ty::BoundTy {
+                    self.variables.len().into(),
-                        var: ty::BoundVar::from_usize(self.variables.len()),
+                )),
-                        kind: ty::BoundTyKind::Anon,
+                CanonicalizeMode::Response { .. } => panic!("param ty in response: {t:?}"),
-                    },
-                }),
-                CanonicalizeMode::Response { .. } => bug!("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)) => {
+            ty::ConstKind::Infer(i) => {
-                assert_eq!(
+                // FIXME: we should fold the ty too eventually
-                    self.infcx.root_const_var(vid),
+                match i {
-                    vid,
+                    ty::InferConst::Var(vid) => {
-                    "const var should have been resolved"
+                        assert_eq!(
-                );
+                            self.infcx.root_ct_var(vid),
-                let Err(ui) = self.infcx.probe_const_var(vid) else {
+                            vid,
-                    bug!("const var should have been resolved");
+                            "region vid should have been resolved fully before canonicalization"
-                };
+                        );
-                // FIXME: we should fold this ty eventually
+                        assert_eq!(
-                CanonicalVarKind::Const(ui, c.ty())
+                            self.infcx.probe_ct_var(vid),
-            }
+                            None,
-            ty::ConstKind::Infer(ty::InferConst::EffectVar(vid)) => {
+                            "region vid should have been resolved fully before canonicalization"
-                assert_eq!(
+                        );
-                    self.infcx.root_effect_var(vid),
+                        CanonicalVarKind::Const(self.infcx.universe_of_ct(vid).unwrap(), c.ty())
-                    vid,
+                    }
-                    "effect var should have been resolved"
+                    ty::InferConst::EffectVar(_) => CanonicalVarKind::Effect,
-                );
+                    ty::InferConst::Fresh(_) => todo!(),
-                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::Placeholder(placeholder) => match self.canonicalize_mode {
                 CanonicalizeMode::Input => CanonicalVarKind::PlaceholderConst(
-                    ty::Placeholder {
+                    PlaceholderLike::new(placeholder.universe(), self.variables.len().into()),
-                        universe: placeholder.universe,
-                        bound: ty::BoundVar::from(self.variables.len()),
-                    },
                     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 {
+                    PlaceholderLike::new(ty::UniverseIndex::ROOT, self.variables.len().into()),
-                        universe: ty::UniverseIndex::ROOT,
-                        bound: ty::BoundVar::from(self.variables.len()),
-                    },
                     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())
     }
 }

compiler/rustc_next_trait_solver/src/lib.rs

@@ -0,0 +1 @@
+pub mod canonicalizer;

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" }

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;

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;

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::Ty(CanonicalTyVarKind::General(ui)) => ui,
-            CanonicalVarKind::Region(ui) => *ui,
+            CanonicalVarKind::Region(ui) => ui,
-            CanonicalVarKind::Const(ui, _) => *ui,
+            CanonicalVarKind::Const(ui, _) => ui,
             CanonicalVarKind::PlaceholderTy(placeholder) => placeholder.universe(),
             CanonicalVarKind::PlaceholderRegion(placeholder) => placeholder.universe(),
             CanonicalVarKind::PlaceholderConst(placeholder, _) => placeholder.universe(),

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) {
+        match *this.data {
-            None => write!(f, "{:?}", this.data),
+            InferConst::Var(vid) => match this.infcx.universe_of_ct(vid) {
-            Some(universe) => match *this.data {
+                None => write!(f, "{:?}", this.data),
-                InferConst::Var(vid) => write!(f, "?{}_{}c", vid.index(), universe.index()),
+                Some(universe) => write!(f, "?{}_{}c", vid.index(), universe.index()),
-                InferConst::EffectVar(vid) => write!(f, "?{}_{}e", vid.index(), universe.index()),
-                InferConst::Fresh(_) => {
-                    unreachable!()
-                }
             },
+            InferConst::EffectVar(vid) => write!(f, "?{}e", vid.index()),
+            InferConst::Fresh(_) => {
+                unreachable!()
+            }
         }
     }
 }

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;
-
-    fn universe_of_ty(&self, ty: InferTy) -> Option<UniverseIndex>;
-
-    fn universe_of_lt(
-        &self,
-        lt: <Self::Interner as Interner>::InferRegion,
-    ) -> Option<UniverseIndex>;
-
-    fn universe_of_ct(&self, ct: InferConst) -> Option<UniverseIndex>;
-}
-
 pub struct NoInfcx<I>(PhantomData<I>);
 
 impl<I: Interner> InferCtxtLike for NoInfcx<I> {
     type Interner = I;
 
-    fn universe_of_ty(&self, _ty: InferTy) -> Option<UniverseIndex> {
+    fn interner(&self) -> Self::Interner {
+        unreachable!()
+    }
+
+    fn universe_of_ty(&self, _ty: TyVid) -> Option<UniverseIndex> {
         None
     }
 
-    fn universe_of_ct(&self, _ct: InferConst) -> Option<UniverseIndex> {
+    fn universe_of_lt(&self, _lt: I::InferRegion) -> Option<UniverseIndex> {
         None
     }
 
-    fn universe_of_lt(&self, _lt: <I as Interner>::InferRegion) -> Option<UniverseIndex> {
+    fn universe_of_ct(&self, _ct: ConstVid) -> Option<UniverseIndex> {
+        None
+    }
+
+    fn root_ty_var(&self, vid: TyVid) -> TyVid {
+        vid
+    }
+
+    fn probe_ty_var(&self, _vid: TyVid) -> Option<I::Ty> {
+        None
+    }
+
+    fn root_lt_var(&self, vid: I::InferRegion) -> I::InferRegion {
+        vid
+    }
+
+    fn probe_lt_var(&self, _vid: I::InferRegion) -> Option<I::Region> {
+        None
+    }
+
+    fn root_ct_var(&self, vid: ConstVid) -> ConstVid {
+        vid
+    }
+
+    fn probe_ct_var(&self, _vid: ConstVid) -> Option<I::Const> {
         None
     }
 }

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>;
+}

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 DefId: Copy + Debug + Hash + Ord;
-    type AdtDef: Clone + 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 GenericArg: Copy + DebugWithInfcx<Self> + Hash + Ord;
-    type Term: Clone + Debug + Hash + Ord;
+    type Term: Copy + Debug + Hash + Ord;
 
     type Binder<T>;
-    type TypeAndMut: Clone + Debug + Hash + Ord;
+    type TypeAndMut: Copy + Debug + Hash + Ord;
-    type CanonicalVars: Clone + Debug + Hash + Eq;
+    type CanonicalVars: Copy + Debug + Hash + Eq + IntoIterator<Item = CanonicalVarInfo<Self>>;
 
     // Kinds of tys
-    type Ty: Clone + DebugWithInfcx<Self> + Hash + Ord;
+    type Ty: Copy
-    type Tys: Clone + Debug + Hash + Ord + IntoIterator<Item = Self::Ty>;
+        + DebugWithInfcx<Self>
-    type AliasTy: Clone + DebugWithInfcx<Self> + Hash + Ord;
+        + Hash
-    type ParamTy: Clone + Debug + Hash + Ord;
+        + Ord
-    type BoundTy: Clone + Debug + Hash + Ord;
+        + Into<Self::GenericArg>
-    type PlaceholderTy: Clone + Debug + Hash + Ord + Placeholder;
+        + 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 ErrorGuaranteed: Copy + Debug + Hash + Ord;
-    type BoundExistentialPredicates: Clone + DebugWithInfcx<Self> + Hash + Ord;
+    type BoundExistentialPredicates: Copy + DebugWithInfcx<Self> + Hash + Ord;
-    type PolyFnSig: Clone + DebugWithInfcx<Self> + Hash + Ord;
+    type PolyFnSig: Copy + DebugWithInfcx<Self> + Hash + Ord;
-    type AllocId: Clone + Debug + Hash + Ord;
+    type AllocId: Copy + Debug + Hash + Ord;
 
     // Kinds of consts
-    type Const: Clone + DebugWithInfcx<Self> + Hash + Ord;
+    type Const: Copy
-    type AliasConst: Clone + DebugWithInfcx<Self> + Hash + Ord;
+        + DebugWithInfcx<Self>
-    type PlaceholderConst: Clone + Debug + Hash + Ord + Placeholder;
+        + Hash
-    type ParamConst: Clone + Debug + Hash + Ord;
+        + Ord
-    type BoundConst: Clone + Debug + Hash + Ord;
+        + Into<Self::GenericArg>
-    type ValueConst: Clone + Debug + Hash + Ord;
+        + IntoKind<Kind = ConstKind<Self>>
-    type ExprConst: Clone + DebugWithInfcx<Self> + Hash + Ord;
+        + 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 Region: Copy
-    type EarlyParamRegion: Clone + Debug + Hash + Ord;
+        + DebugWithInfcx<Self>
-    type BoundRegion: Clone + Debug + Hash + Ord;
+        + Hash
-    type LateParamRegion: Clone + Debug + Hash + Ord;
+        + Ord
-    type InferRegion: Clone + DebugWithInfcx<Self> + Hash + Ord;
+        + Into<Self::GenericArg>
-    type PlaceholderRegion: Clone + Debug + Hash + Ord + Placeholder;
+        + 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 Predicate: Copy + Debug + Hash + Eq;
-    type TraitPredicate: Clone + Debug + Hash + Eq;
+    type TraitPredicate: Copy + Debug + Hash + Eq;
-    type RegionOutlivesPredicate: Clone + Debug + Hash + Eq;
+    type RegionOutlivesPredicate: Copy + Debug + Hash + Eq;
-    type TypeOutlivesPredicate: Clone + Debug + Hash + Eq;
+    type TypeOutlivesPredicate: Copy + Debug + Hash + Eq;
-    type ProjectionPredicate: Clone + Debug + Hash + Eq;
+    type ProjectionPredicate: Copy + Debug + Hash + Eq;
-    type NormalizesTo: Clone + Debug + Hash + Eq;
+    type NormalizesTo: Copy + Debug + Hash + Eq;
-    type SubtypePredicate: Clone + Debug + Hash + Eq;
+    type SubtypePredicate: Copy + Debug + Hash + Eq;
-    type CoercePredicate: Clone + Debug + Hash + Eq;
+    type CoercePredicate: Copy + Debug + Hash + Eq;
-    type ClosureKind: Clone + 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 {
+pub trait PlaceholderLike {
-    fn universe(&self) -> UniverseIndex;
+    fn universe(self) -> UniverseIndex;
-    fn var(&self) -> BoundVar;
+    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`

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]

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.data {
-        match this.infcx.universe_of_ty(*this.data) {
+            InferTy::TyVar(vid) => {
-            None => write!(f, "{:?}", this.data),
+                if let Some(universe) = this.infcx.universe_of_ty(*vid) {
-            Some(universe) => match *this.data {
+                    write!(f, "?{}_{}t", vid.index(), universe.index())
-                TyVar(ty_vid) => write!(f, "?{}_{}t", ty_vid.index(), universe.index()),
+                } else {
-                IntVar(_) | FloatVar(_) | FreshTy(_) | FreshIntTy(_) | FreshFloatTy(_) => {
+                    write!(f, "{:?}", this.data)
-                    unreachable!()
                 }
-            },
+            }
+            _ => write!(f, "{:?}", this.data),
         }
     }
 }