diff --git a/Cargo.lock b/Cargo.lock
index 344e6d101f..b70b89ea54 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1863,9 +1863,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_abi"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0c6789d94fb3e6e30d62f55e99a321ba63484a8bb3b4ead338687c9ddc282d28"
+checksum = "8da95e732b424802b1f043ab4007c78a0fc515ab249587abbea4634bf5fdce9a"
 dependencies = [
  "bitflags 2.9.1",
  "ra-ap-rustc_hashes",
@@ -1875,24 +1875,24 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_ast_ir"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "aaab80bda0f05e9842e3afb7779b0bad0a4b54e0f7ba6deb5705dcf86482811d"
+checksum = "3838d9d7a3a5cdc511cfb6ad78740ce532f75a2366d3fc3b9853ea1b5c872779"
 
 [[package]]
 name = "ra-ap-rustc_hashes"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "64bd405e538102b5f699241794b2eefee39d5414c0e4bc72435e91430c51f905"
+checksum = "bdc8995d268d3bb4ece910f575ea5a063d6003e193ec155d15703b65882d53fb"
 dependencies = [
  "rustc-stable-hash",
 ]
 
 [[package]]
 name = "ra-ap-rustc_index"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "521621e271aa03b8433dad5981838278d6cfd7d2d8c9f4eb6d427f1d671f90fc"
+checksum = "ed0ccdf6e5627c6c3e54e571e52ce0bc8b94d5f0b94b7460269ca68a4706be69"
 dependencies = [
  "ra-ap-rustc_index_macros",
  "smallvec",
@@ -1900,9 +1900,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_index_macros"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "245e30f2e1fef258913cc548b36f575549c8af31cbc4649929d21deda96ceeb7"
+checksum = "bd28f42362b5c9fb9b8766c3189df02a402b13363600c6885e11027889f03ee6"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1911,9 +1911,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_lexer"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a82681f924500e888c860e60ed99e9bf702a219a69374f59116c4261525a2157"
+checksum = "f1c31a82f091b910a27ee53a86a9af28a2df10c3484e2f1bbfe70633aa84dee9"
 dependencies = [
  "memchr",
  "unicode-properties",
@@ -1922,9 +1922,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_next_trait_solver"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0c9ce51f2431fbdc7fabd2d957522b6e27f41f68ec2af74b52a6f4116352ce1a"
+checksum = "f8cac6c2b5a8924209d4ca682cbc507252c58a664911e0ef463c112882ba6f72"
 dependencies = [
  "derive-where",
  "ra-ap-rustc_index",
@@ -1935,9 +1935,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_parse_format"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "adc85ef3fdb6c084bde84857d8948dc66b752129dc8417a8614ce490e99a143f"
+checksum = "a085a1cf902dcca8abbc537faaef154bbccbbb51850f779ce5484ae3782b5d8f"
 dependencies = [
  "ra-ap-rustc_lexer",
  "rustc-literal-escaper 0.0.5",
@@ -1945,9 +1945,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_pattern_analysis"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3cd81eccf33d9528905d4e5abaa254b3129a6405d6c5f123fed9b73a3d217f35"
+checksum = "8ba32e3985367bc34856b41c7604133649d4a367eb5d7bdf50623025731459d8"
 dependencies = [
  "ra-ap-rustc_index",
  "rustc-hash 2.1.1",
@@ -1958,10 +1958,11 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_type_ir"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "11cb0da02853698d9c89e1d1c01657b9969752befd56365e8899d4310e52b373"
+checksum = "9c9911d72f75d85d21fe88374d7bcec94f2200feffb7234108a24cc3da7c3591"
 dependencies = [
+ "arrayvec",
  "bitflags 2.9.1",
  "derive-where",
  "ena",
@@ -1977,9 +1978,9 @@ dependencies = [
 
 [[package]]
 name = "ra-ap-rustc_type_ir_macros"
-version = "0.126.0"
+version = "0.128.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ffc93adeb52c483ede13bee6680466458218243ab479c04fb71bb53925a6e0ff"
+checksum = "22f539b87991683ce17cc52e62600fdf2b4a8af43952db30387edc1a576d3b43"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/Cargo.toml b/Cargo.toml
index f325027ee5..c5ffad544a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -89,14 +89,14 @@ vfs-notify = { path = "./crates/vfs-notify", version = "0.0.0" }
 vfs = { path = "./crates/vfs", version = "0.0.0" }
 edition = { path = "./crates/edition", version = "0.0.0" }
 
-ra-ap-rustc_lexer = { version = "0.126", default-features = false }
-ra-ap-rustc_parse_format = { version = "0.126", default-features = false }
-ra-ap-rustc_index = { version = "0.126", default-features = false }
-ra-ap-rustc_abi = { version = "0.126", default-features = false }
-ra-ap-rustc_pattern_analysis = { version = "0.126", default-features = false }
-ra-ap-rustc_ast_ir = { version = "0.126", default-features = false }
-ra-ap-rustc_type_ir = { version = "0.126", default-features = false }
-ra-ap-rustc_next_trait_solver = { version = "0.126", default-features = false }
+ra-ap-rustc_lexer = { version = "0.128", default-features = false }
+ra-ap-rustc_parse_format = { version = "0.128", default-features = false }
+ra-ap-rustc_index = { version = "0.128", default-features = false }
+ra-ap-rustc_abi = { version = "0.128", default-features = false }
+ra-ap-rustc_pattern_analysis = { version = "0.128", default-features = false }
+ra-ap-rustc_ast_ir = { version = "0.128", default-features = false }
+ra-ap-rustc_type_ir = { version = "0.128", default-features = false }
+ra-ap-rustc_next_trait_solver = { version = "0.128", default-features = false }
 
 # local crates that aren't published to crates.io. These should not have versions.
 
diff --git a/crates/hir-def/src/lang_item.rs b/crates/hir-def/src/lang_item.rs
index 600f206770..df0705bf90 100644
--- a/crates/hir-def/src/lang_item.rs
+++ b/crates/hir-def/src/lang_item.rs
@@ -84,6 +84,15 @@ impl LangItemTarget {
             _ => None,
         }
     }
+
+    pub fn as_adt(self) -> Option<AdtId> {
+        match self {
+            LangItemTarget::Union(it) => Some(it.into()),
+            LangItemTarget::EnumId(it) => Some(it.into()),
+            LangItemTarget::Struct(it) => Some(it.into()),
+            _ => None,
+        }
+    }
 }
 
 /// Salsa query. This will look for lang items in a specific crate.
@@ -289,6 +298,10 @@ impl LangItem {
         lang_item(db, start_crate, self).and_then(|t| t.as_trait())
     }
 
+    pub fn resolve_adt(self, db: &dyn DefDatabase, start_crate: Crate) -> Option<AdtId> {
+        lang_item(db, start_crate, self).and_then(|t| t.as_adt())
+    }
+
     pub fn resolve_enum(self, db: &dyn DefDatabase, start_crate: Crate) -> Option<EnumId> {
         lang_item(db, start_crate, self).and_then(|t| t.as_enum())
     }
diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
index fcb79e9ffb..ea8bdf8bcb 100644
--- a/crates/hir-ty/src/display.rs
+++ b/crates/hir-ty/src/display.rs
@@ -59,7 +59,7 @@ use crate::{
     lt_from_placeholder_idx,
     mir::pad16,
     next_solver::{
-        BoundExistentialPredicate, Ctor, DbInterner, GenericArgs, SolverDefId,
+        BoundExistentialPredicate, DbInterner, GenericArgs, SolverDefId,
         mapping::{
             ChalkToNextSolver, convert_args_for_result, convert_const_for_result,
             convert_region_for_result, convert_ty_for_result,
@@ -911,14 +911,13 @@ fn render_const_scalar_inner(
                 f.write_str("&")?;
                 render_const_scalar_ns(f, bytes, memory_map, t)
             }
-            TyKind::Adt(adt, _) if b.len() == 2 * size_of::<usize>() => match adt.def_id() {
-                SolverDefId::AdtId(hir_def::AdtId::StructId(s)) => {
+            TyKind::Adt(adt, _) if b.len() == 2 * size_of::<usize>() => match adt.def_id().0 {
+                hir_def::AdtId::StructId(s) => {
                     let data = f.db.struct_signature(s);
                     write!(f, "&{}", data.name.display(f.db, f.edition()))?;
                     Ok(())
                 }
-                SolverDefId::AdtId(_) => f.write_str("<unsized-enum-or-union>"),
-                _ => unreachable!(),
+                _ => f.write_str("<unsized-enum-or-union>"),
             },
             _ => {
                 let addr = usize::from_le_bytes(match b.try_into() {
@@ -966,10 +965,7 @@ fn render_const_scalar_inner(
             f.write_str(")")
         }
         TyKind::Adt(def, args) => {
-            let def = match def.def_id() {
-                SolverDefId::AdtId(def) => def,
-                _ => unreachable!(),
-            };
+            let def = def.def_id().0;
             let Ok(layout) = f.db.layout_of_adt(def, args, trait_env.clone()) else {
                 return f.write_str("<layout-error>");
             };
@@ -1300,12 +1296,7 @@ impl<'db> HirDisplay for crate::next_solver::Ty<'db> {
                 sig.hir_fmt(f)?;
             }
             TyKind::FnDef(def, args) => {
-                let def = match def {
-                    SolverDefId::FunctionId(id) => CallableDefId::FunctionId(id),
-                    SolverDefId::Ctor(Ctor::Enum(e)) => CallableDefId::EnumVariantId(e),
-                    SolverDefId::Ctor(Ctor::Struct(s)) => CallableDefId::StructId(s),
-                    _ => unreachable!(),
-                };
+                let def = def.0;
                 let sig = db
                     .callable_item_signature(def)
                     .substitute(Interner, &convert_args_for_result(interner, args.as_slice()));
@@ -1406,10 +1397,7 @@ impl<'db> HirDisplay for crate::next_solver::Ty<'db> {
                 }
             }
             TyKind::Adt(def, parameters) => {
-                let def_id = match def.def_id() {
-                    SolverDefId::AdtId(id) => id,
-                    _ => unreachable!(),
-                };
+                let def_id = def.def_id().0;
                 f.start_location_link(def_id.into());
                 match f.display_kind {
                     DisplayKind::Diagnostics | DisplayKind::Test => {
@@ -1448,7 +1436,7 @@ impl<'db> HirDisplay for crate::next_solver::Ty<'db> {
                 hir_fmt_generics(
                     f,
                     convert_args_for_result(interner, parameters.as_slice()).as_slice(Interner),
-                    def.def_id().try_into().ok(),
+                    Some(def.def_id().0.into()),
                     None,
                 )?;
             }
@@ -1466,13 +1454,9 @@ impl<'db> HirDisplay for crate::next_solver::Ty<'db> {
 
                 projection_ty.hir_fmt(f)?;
             }
-            TyKind::Foreign(type_alias) => {
-                let alias = match type_alias {
-                    SolverDefId::TypeAliasId(id) => id,
-                    _ => unreachable!(),
-                };
-                let type_alias = db.type_alias_signature(alias);
-                f.start_location_link(alias.into());
+            TyKind::Foreign(alias) => {
+                let type_alias = db.type_alias_signature(alias.0);
+                f.start_location_link(alias.0.into());
                 write!(f, "{}", type_alias.name.display(f.db, f.edition()))?;
                 f.end_location_link();
             }
@@ -1549,10 +1533,7 @@ impl<'db> HirDisplay for crate::next_solver::Ty<'db> {
                 }
             }
             TyKind::Closure(id, substs) => {
-                let id = match id {
-                    SolverDefId::InternedClosureId(id) => id,
-                    _ => unreachable!(),
-                };
+                let id = id.0;
                 let substs = convert_args_for_result(interner, substs.as_slice());
                 if f.display_kind.is_source_code() {
                     if !f.display_kind.allows_opaque() {
diff --git a/crates/hir-ty/src/layout.rs b/crates/hir-ty/src/layout.rs
index f8abb3b7f6..2020a8b34b 100644
--- a/crates/hir-ty/src/layout.rs
+++ b/crates/hir-ty/src/layout.rs
@@ -25,7 +25,7 @@ use crate::{
     consteval_nextsolver::try_const_usize,
     db::HirDatabase,
     next_solver::{
-        DbInterner, GenericArgs, ParamEnv, SolverDefId, Ty, TyKind, TypingMode,
+        DbInterner, GenericArgs, ParamEnv, Ty, TyKind, TypingMode,
         infer::{DbInternerInferExt, traits::ObligationCause},
         mapping::{ChalkToNextSolver, convert_args_for_result},
         project::solve_normalize::deeply_normalize,
@@ -323,14 +323,10 @@ pub fn layout_of_ty_query<'db>(
             ptr.valid_range_mut().start = 1;
             Layout::scalar(dl, ptr)
         }
-        TyKind::Closure(c, args) => {
-            let id = match c {
-                SolverDefId::InternedClosureId(id) => id,
-                _ => unreachable!(),
-            };
-            let def = db.lookup_intern_closure(id);
+        TyKind::Closure(id, args) => {
+            let def = db.lookup_intern_closure(id.0);
             let infer = db.infer(def.0);
-            let (captures, _) = infer.closure_info(&id.into());
+            let (captures, _) = infer.closure_info(&id.0.into());
             let fields = captures
                 .iter()
                 .map(|it| {
diff --git a/crates/hir-ty/src/method_resolution.rs b/crates/hir-ty/src/method_resolution.rs
index a234312173..ac85bf7950 100644
--- a/crates/hir-ty/src/method_resolution.rs
+++ b/crates/hir-ty/src/method_resolution.rs
@@ -163,10 +163,7 @@ impl TyFingerprint {
                 rustc_ast_ir::Mutability::Mut => TyFingerprint::RawPtr(Mutability::Mut),
                 rustc_ast_ir::Mutability::Not => TyFingerprint::RawPtr(Mutability::Not),
             },
-            TyKind::Foreign(def) => {
-                let SolverDefId::TypeAliasId(def) = def else { unreachable!() };
-                TyFingerprint::ForeignType(crate::to_foreign_def_id(def))
-            }
+            TyKind::Foreign(def) => TyFingerprint::ForeignType(crate::to_foreign_def_id(def.0)),
             TyKind::Dynamic(bounds, _, _) => {
                 let trait_ref = bounds
                     .as_slice()
diff --git a/crates/hir-ty/src/mir/eval.rs b/crates/hir-ty/src/mir/eval.rs
index c60ace85be..ca7467d385 100644
--- a/crates/hir-ty/src/mir/eval.rs
+++ b/crates/hir-ty/src/mir/eval.rs
@@ -42,7 +42,7 @@ use crate::{
     layout::{Layout, LayoutError, RustcEnumVariantIdx},
     method_resolution::{is_dyn_method, lookup_impl_const},
     next_solver::{
-        Ctor, DbInterner, SolverDefId,
+        DbInterner,
         mapping::{ChalkToNextSolver, convert_args_for_result, convert_ty_for_result},
     },
     static_lifetime,
@@ -2366,8 +2366,8 @@ impl<'db> Evaluator<'db> {
                 let new_id = self.vtable_map.id(ty);
                 self.write_memory(addr, &new_id.to_le_bytes())?;
             }
-            TyKind::Adt(id, args) => match id.def_id() {
-                SolverDefId::AdtId(AdtId::StructId(s)) => {
+            TyKind::Adt(id, args) => match id.def_id().0 {
+                AdtId::StructId(s) => {
                     for (i, (_, ty)) in self.db.field_types_ns(s.into()).iter().enumerate() {
                         let offset = layout.fields.offset(i).bytes_usize();
                         let ty = ty.instantiate(interner, args);
@@ -2380,8 +2380,8 @@ impl<'db> Evaluator<'db> {
                         )?;
                     }
                 }
-                SolverDefId::AdtId(AdtId::UnionId(_)) => (),
-                SolverDefId::AdtId(AdtId::EnumId(e)) => {
+                AdtId::UnionId(_) => (),
+                AdtId::EnumId(e) => {
                     if let Some((ev, layout)) = detect_variant_from_bytes(
                         &layout,
                         self.db,
@@ -2402,7 +2402,6 @@ impl<'db> Evaluator<'db> {
                         }
                     }
                 }
-                _ => unreachable!(),
             },
             TyKind::Tuple(tys) => {
                 for (id, ty) in tys.iter().enumerate() {
@@ -2472,38 +2471,24 @@ impl<'db> Evaluator<'db> {
         let interner = DbInterner::new_with(self.db, None, None);
         use rustc_type_ir::TyKind;
         match next_ty.kind() {
-            TyKind::FnDef(def, generic_args) => {
-                let def = match def {
-                    SolverDefId::FunctionId(id) => CallableDefId::FunctionId(id),
-                    SolverDefId::Ctor(Ctor::Struct(s)) => CallableDefId::StructId(s),
-                    SolverDefId::Ctor(Ctor::Enum(e)) => CallableDefId::EnumVariantId(e),
-                    _ => unreachable!(),
-                };
-                self.exec_fn_def(
-                    def,
-                    &convert_args_for_result(interner, generic_args.as_slice()),
-                    destination,
-                    args,
-                    locals,
-                    target_bb,
-                    span,
-                )
-            }
-            TyKind::Closure(id, generic_args) => {
-                let id = match id {
-                    SolverDefId::InternedClosureId(id) => id,
-                    _ => unreachable!(),
-                };
-                self.exec_closure(
-                    id.into(),
-                    bytes.slice(0..0),
-                    &convert_args_for_result(interner, generic_args.as_slice()),
-                    destination,
-                    args,
-                    locals,
-                    span,
-                )
-            }
+            TyKind::FnDef(def, generic_args) => self.exec_fn_def(
+                def.0,
+                &convert_args_for_result(interner, generic_args.as_slice()),
+                destination,
+                args,
+                locals,
+                target_bb,
+                span,
+            ),
+            TyKind::Closure(id, generic_args) => self.exec_closure(
+                id.0.into(),
+                bytes.slice(0..0),
+                &convert_args_for_result(interner, generic_args.as_slice()),
+                destination,
+                args,
+                locals,
+                span,
+            ),
             _ => Err(MirEvalError::InternalError("function pointer to non function".into())),
         }
     }
diff --git a/crates/hir-ty/src/next_solver/def_id.rs b/crates/hir-ty/src/next_solver/def_id.rs
index 8bbc6e3370..a9c572d3f3 100644
--- a/crates/hir-ty/src/next_solver/def_id.rs
+++ b/crates/hir-ty/src/next_solver/def_id.rs
@@ -1,8 +1,8 @@
 //! Definition of `SolverDefId`
 
 use hir_def::{
-    AdtId, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId, ImplId, StaticId, StructId,
-    TraitId, TypeAliasId, UnionId,
+    AdtId, CallableDefId, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId, ImplId,
+    StaticId, StructId, TraitId, TypeAliasId, UnionId,
 };
 use rustc_type_ir::inherent;
 use stdx::impl_from;
@@ -42,7 +42,8 @@ impl_from!(
     TypeAliasId,
     InternedClosureId,
     InternedCoroutineId,
-    InternedOpaqueTyId
+    InternedOpaqueTyId,
+    Ctor
     for SolverDefId
 );
 
@@ -145,3 +146,59 @@ macro_rules! declare_id_wrapper {
 }
 
 declare_id_wrapper!(TraitIdWrapper, TraitId);
+declare_id_wrapper!(TypeAliasIdWrapper, TypeAliasId);
+declare_id_wrapper!(ClosureIdWrapper, InternedClosureId);
+declare_id_wrapper!(CoroutineIdWrapper, InternedCoroutineId);
+declare_id_wrapper!(AdtIdWrapper, AdtId);
+declare_id_wrapper!(ImplIdWrapper, ImplId);
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+pub struct CallableIdWrapper(pub CallableDefId);
+
+impl std::fmt::Debug for CallableIdWrapper {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Debug::fmt(&self.0, f)
+    }
+}
+impl From<CallableIdWrapper> for CallableDefId {
+    #[inline]
+    fn from(value: CallableIdWrapper) -> CallableDefId {
+        value.0
+    }
+}
+impl From<CallableDefId> for CallableIdWrapper {
+    #[inline]
+    fn from(value: CallableDefId) -> CallableIdWrapper {
+        Self(value)
+    }
+}
+impl From<CallableIdWrapper> for SolverDefId {
+    #[inline]
+    fn from(value: CallableIdWrapper) -> SolverDefId {
+        match value.0 {
+            CallableDefId::FunctionId(it) => it.into(),
+            CallableDefId::StructId(it) => Ctor::Struct(it).into(),
+            CallableDefId::EnumVariantId(it) => Ctor::Enum(it).into(),
+        }
+    }
+}
+impl TryFrom<SolverDefId> for CallableIdWrapper {
+    type Error = ();
+    #[inline]
+    fn try_from(value: SolverDefId) -> Result<Self, Self::Error> {
+        match value {
+            SolverDefId::FunctionId(it) => Ok(Self(it.into())),
+            SolverDefId::Ctor(Ctor::Struct(it)) => Ok(Self(it.into())),
+            SolverDefId::Ctor(Ctor::Enum(it)) => Ok(Self(it.into())),
+            _ => Err(()),
+        }
+    }
+}
+impl<'db> inherent::DefId<DbInterner<'db>> for CallableIdWrapper {
+    fn as_local(self) -> Option<SolverDefId> {
+        Some(self.into())
+    }
+    fn is_local(self) -> bool {
+        true
+    }
+}
diff --git a/crates/hir-ty/src/next_solver/infer/canonical/canonicalizer.rs b/crates/hir-ty/src/next_solver/infer/canonical/canonicalizer.rs
index 5d11525cd1..beaac11a2d 100644
--- a/crates/hir-ty/src/next_solver/infer/canonical/canonicalizer.rs
+++ b/crates/hir-ty/src/next_solver/infer/canonical/canonicalizer.rs
@@ -10,9 +10,8 @@ use rustc_index::Idx;
 use rustc_type_ir::InferTy::{self, FloatVar, IntVar, TyVar};
 use rustc_type_ir::inherent::{Const as _, IntoKind as _, Region as _, SliceLike, Ty as _};
 use rustc_type_ir::{
-    BoundVar, CanonicalQueryInput, CanonicalTyVarKind, DebruijnIndex, Flags, InferConst,
-    RegionKind, TypeFlags, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
-    UniverseIndex,
+    BoundVar, CanonicalQueryInput, DebruijnIndex, Flags, InferConst, RegionKind, TyVid, TypeFlags,
+    TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt, UniverseIndex,
 };
 use smallvec::SmallVec;
 use tracing::debug;
@@ -316,6 +315,13 @@ struct Canonicalizer<'cx, 'db> {
     // Note that indices is only used once `var_values` is big enough to be
     // heap-allocated.
     indices: FxHashMap<GenericArg<'db>, BoundVar>,
+    /// Maps each `sub_unification_table_root_var` to the index of the first
+    /// variable which used it.
+    ///
+    /// This means in case two type variables have the same sub relations root,
+    /// we set the `sub_root` of the second variable to the position of the first.
+    /// Otherwise the `sub_root` of each type variable is just its own position.
+    sub_root_lookup_table: FxHashMap<TyVid, usize>,
     canonicalize_mode: &'cx dyn CanonicalizeMode,
     needs_canonical_flags: TypeFlags,
 
@@ -384,10 +390,9 @@ impl<'cx, 'db> TypeFolder<DbInterner<'db>> for Canonicalizer<'cx, 'db> {
                             // FIXME: perf problem described in #55921.
                             ui = UniverseIndex::ROOT;
                         }
-                        self.canonicalize_ty_var(
-                            CanonicalVarKind::Ty(CanonicalTyVarKind::General(ui)),
-                            t,
-                        )
+
+                        let sub_root = self.get_or_insert_sub_root(vid);
+                        self.canonicalize_ty_var(CanonicalVarKind::Ty { ui, sub_root }, t)
                     }
                 }
             }
@@ -397,7 +402,7 @@ impl<'cx, 'db> TypeFolder<DbInterner<'db>> for Canonicalizer<'cx, 'db> {
                 if nt != t {
                     self.fold_ty(nt)
                 } else {
-                    self.canonicalize_ty_var(CanonicalVarKind::Ty(CanonicalTyVarKind::Int), t)
+                    self.canonicalize_ty_var(CanonicalVarKind::Int, t)
                 }
             }
             TyKind::Infer(FloatVar(vid)) => {
@@ -405,7 +410,7 @@ impl<'cx, 'db> TypeFolder<DbInterner<'db>> for Canonicalizer<'cx, 'db> {
                 if nt != t {
                     self.fold_ty(nt)
                 } else {
-                    self.canonicalize_ty_var(CanonicalVarKind::Ty(CanonicalTyVarKind::Float), t)
+                    self.canonicalize_ty_var(CanonicalVarKind::Float, t)
                 }
             }
 
@@ -579,6 +584,7 @@ impl<'cx, 'db> Canonicalizer<'cx, 'db> {
             variables: SmallVec::from_slice(base.variables.as_slice()),
             query_state,
             indices: FxHashMap::default(),
+            sub_root_lookup_table: Default::default(),
             binder_index: DebruijnIndex::ZERO,
         };
         if canonicalizer.query_state.var_values.spilled() {
@@ -673,6 +679,13 @@ impl<'cx, 'db> Canonicalizer<'cx, 'db> {
         }
     }
 
+    fn get_or_insert_sub_root(&mut self, vid: TyVid) -> BoundVar {
+        let root_vid = self.infcx.sub_unification_table_root_var(vid);
+        let idx =
+            *self.sub_root_lookup_table.entry(root_vid).or_insert_with(|| self.variables.len());
+        BoundVar::from(idx)
+    }
+
     /// Replaces the universe indexes used in `var_values` with their index in
     /// `query_state.universe_map`. This minimizes the maximum universe used in
     /// the canonicalized value.
@@ -692,9 +705,9 @@ impl<'cx, 'db> Canonicalizer<'cx, 'db> {
         self.variables
             .iter()
             .map(|v| match *v {
-                CanonicalVarKind::Ty(CanonicalTyVarKind::Int | CanonicalTyVarKind::Float) => *v,
-                CanonicalVarKind::Ty(CanonicalTyVarKind::General(u)) => {
-                    CanonicalVarKind::Ty(CanonicalTyVarKind::General(reverse_universe_map[&u]))
+                CanonicalVarKind::Int | CanonicalVarKind::Float => *v,
+                CanonicalVarKind::Ty { ui, sub_root } => {
+                    CanonicalVarKind::Ty { ui: reverse_universe_map[&ui], sub_root }
                 }
                 CanonicalVarKind::Region(u) => CanonicalVarKind::Region(reverse_universe_map[&u]),
                 CanonicalVarKind::Const(u) => CanonicalVarKind::Const(reverse_universe_map[&u]),
diff --git a/crates/hir-ty/src/next_solver/infer/canonical/mod.rs b/crates/hir-ty/src/next_solver/infer/canonical/mod.rs
index ec41111ed8..d0669f5c3b 100644
--- a/crates/hir-ty/src/next_solver/infer/canonical/mod.rs
+++ b/crates/hir-ty/src/next_solver/infer/canonical/mod.rs
@@ -32,9 +32,10 @@ use crate::next_solver::{
 };
 use instantiate::CanonicalExt;
 use rustc_index::IndexVec;
+use rustc_type_ir::inherent::IntoKind;
 use rustc_type_ir::{
-    AliasRelationDirection, AliasTyKind, CanonicalTyVarKind, CanonicalVarKind, InferTy,
-    TypeFoldable, UniverseIndex, Upcast, Variance,
+    AliasRelationDirection, AliasTyKind, CanonicalVarKind, InferTy, TypeFoldable, UniverseIndex,
+    Upcast, Variance,
     inherent::{SliceLike, Ty as _},
     relate::{
         Relate, TypeRelation, VarianceDiagInfo,
@@ -78,27 +79,13 @@ impl<'db> InferCtxt<'db> {
             .chain((1..=canonical.max_universe.as_u32()).map(|_| self.create_next_universe()))
             .collect();
 
-        let canonical_inference_vars =
-            self.instantiate_canonical_vars(canonical.variables, |ui| universes[ui]);
-        let result = canonical.instantiate(self.interner, &canonical_inference_vars);
-        (result, canonical_inference_vars)
-    }
-
-    /// Given the "infos" about the canonical variables from some
-    /// canonical, creates fresh variables with the same
-    /// characteristics (see `instantiate_canonical_var` for
-    /// details). You can then use `instantiate` to instantiate the
-    /// canonical variable with these inference variables.
-    fn instantiate_canonical_vars(
-        &self,
-        variables: CanonicalVars<'db>,
-        universe_map: impl Fn(UniverseIndex) -> UniverseIndex,
-    ) -> CanonicalVarValues<'db> {
-        CanonicalVarValues {
-            var_values: self.interner.mk_args_from_iter(
-                variables.iter().map(|info| self.instantiate_canonical_var(info, &universe_map)),
-            ),
-        }
+        let var_values = CanonicalVarValues::instantiate(
+            self.interner,
+            canonical.variables,
+            |var_values, info| self.instantiate_canonical_var(info, var_values, |ui| universes[ui]),
+        );
+        let result = canonical.instantiate(self.interner, &var_values);
+        (result, var_values)
     }
 
     /// Given the "info" about a canonical variable, creates a fresh
@@ -112,22 +99,28 @@ impl<'db> InferCtxt<'db> {
     pub fn instantiate_canonical_var(
         &self,
         cv_info: CanonicalVarKind<DbInterner<'db>>,
+        previous_var_values: &[GenericArg<'db>],
         universe_map: impl Fn(UniverseIndex) -> UniverseIndex,
     ) -> GenericArg<'db> {
         match cv_info {
-            CanonicalVarKind::Ty(ty_kind) => {
-                let ty = match ty_kind {
-                    CanonicalTyVarKind::General(ui) => {
-                        self.next_ty_var_in_universe(universe_map(ui))
+            CanonicalVarKind::Ty { ui, sub_root } => {
+                let vid = self.next_ty_var_id_in_universe(universe_map(ui));
+                // If this inference variable is related to an earlier variable
+                // via subtyping, we need to add that info to the inference context.
+                if let Some(prev) = previous_var_values.get(sub_root.as_usize()) {
+                    if let TyKind::Infer(InferTy::TyVar(sub_root)) = prev.expect_ty().kind() {
+                        self.sub_unify_ty_vids_raw(vid, sub_root);
+                    } else {
+                        unreachable!()
                     }
-
-                    CanonicalTyVarKind::Int => self.next_int_var(),
-
-                    CanonicalTyVarKind::Float => self.next_float_var(),
-                };
-                ty.into()
+                }
+                Ty::new_var(self.interner, vid).into()
             }
 
+            CanonicalVarKind::Int => self.next_int_var().into(),
+
+            CanonicalVarKind::Float => self.next_float_var().into(),
+
             CanonicalVarKind::PlaceholderTy(PlaceholderTy { universe, bound }) => {
                 let universe_mapped = universe_map(universe);
                 let placeholder_mapped = PlaceholderTy { universe: universe_mapped, bound };
diff --git a/crates/hir-ty/src/next_solver/infer/context.rs b/crates/hir-ty/src/next_solver/infer/context.rs
index 93fd6eeab3..45ce7e6f6c 100644
--- a/crates/hir-ty/src/next_solver/infer/context.rs
+++ b/crates/hir-ty/src/next_solver/infer/context.rs
@@ -313,4 +313,12 @@ impl<'db> rustc_type_ir::InferCtxtLike for InferCtxt<'db> {
     fn reset_opaque_types(&self) {
         let _ = self.take_opaque_types();
     }
+
+    fn sub_unification_table_root_var(&self, var: rustc_type_ir::TyVid) -> rustc_type_ir::TyVid {
+        self.sub_unification_table_root_var(var)
+    }
+
+    fn sub_unify_ty_vids_raw(&self, a: rustc_type_ir::TyVid, b: rustc_type_ir::TyVid) {
+        self.sub_unify_ty_vids_raw(a, b);
+    }
 }
diff --git a/crates/hir-ty/src/next_solver/infer/mod.rs b/crates/hir-ty/src/next_solver/infer/mod.rs
index 2630f2a8cc..ce6c941287 100644
--- a/crates/hir-ty/src/next_solver/infer/mod.rs
+++ b/crates/hir-ty/src/next_solver/infer/mod.rs
@@ -1019,6 +1019,14 @@ impl<'db> InferCtxt<'db> {
             }
         }
     }
+
+    fn sub_unification_table_root_var(&self, var: rustc_type_ir::TyVid) -> rustc_type_ir::TyVid {
+        self.inner.borrow_mut().type_variables().sub_unification_table_root_var(var)
+    }
+
+    fn sub_unify_ty_vids_raw(&self, a: rustc_type_ir::TyVid, b: rustc_type_ir::TyVid) {
+        self.inner.borrow_mut().type_variables().sub_unify(a, b);
+    }
 }
 
 /// Helper for [InferCtxt::ty_or_const_infer_var_changed] (see comment on that), currently
diff --git a/crates/hir-ty/src/next_solver/infer/snapshot/undo_log.rs b/crates/hir-ty/src/next_solver/infer/snapshot/undo_log.rs
index 0fa6421f51..28ae56f4ee 100644
--- a/crates/hir-ty/src/next_solver/infer/snapshot/undo_log.rs
+++ b/crates/hir-ty/src/next_solver/infer/snapshot/undo_log.rs
@@ -25,7 +25,7 @@ pub struct Snapshot {
 pub(crate) enum UndoLog<'db> {
     DuplicateOpaqueType,
     OpaqueTypes(OpaqueTypeKey<'db>, Option<OpaqueHiddenType<'db>>),
-    TypeVariables(sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'db>>>),
+    TypeVariables(type_variable::UndoLog<'db>),
     ConstUnificationTable(sv::UndoLog<ut::Delegate<ConstVidKey<'db>>>),
     IntUnificationTable(sv::UndoLog<ut::Delegate<IntVid>>),
     FloatUnificationTable(sv::UndoLog<ut::Delegate<FloatVid>>),
@@ -51,6 +51,8 @@ impl_from! {
     RegionConstraintCollector(region_constraints::UndoLog<'db>),
 
     TypeVariables(sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'db>>>),
+    TypeVariables(sv::UndoLog<ut::Delegate<type_variable::TyVidSubKey>>),
+    TypeVariables(type_variable::UndoLog<'db>),
     IntUnificationTable(sv::UndoLog<ut::Delegate<IntVid>>),
     FloatUnificationTable(sv::UndoLog<ut::Delegate<FloatVid>>),
 
diff --git a/crates/hir-ty/src/next_solver/infer/type_variable.rs b/crates/hir-ty/src/next_solver/infer/type_variable.rs
index 5217308af4..b640039af6 100644
--- a/crates/hir-ty/src/next_solver/infer/type_variable.rs
+++ b/crates/hir-ty/src/next_solver/infer/type_variable.rs
@@ -17,12 +17,48 @@ use crate::next_solver::SolverDefId;
 use crate::next_solver::Ty;
 use crate::next_solver::infer::InferCtxtUndoLogs;
 
+/// Represents a single undo-able action that affects a type inference variable.
+#[derive(Clone)]
+pub(crate) enum UndoLog<'tcx> {
+    EqRelation(sv::UndoLog<ut::Delegate<TyVidEqKey<'tcx>>>),
+    SubRelation(sv::UndoLog<ut::Delegate<TyVidSubKey>>),
+}
+
+/// Convert from a specific kind of undo to the more general UndoLog
+impl<'db> From<sv::UndoLog<ut::Delegate<TyVidEqKey<'db>>>> for UndoLog<'db> {
+    fn from(l: sv::UndoLog<ut::Delegate<TyVidEqKey<'db>>>) -> Self {
+        UndoLog::EqRelation(l)
+    }
+}
+
+/// Convert from a specific kind of undo to the more general UndoLog
+impl<'db> From<sv::UndoLog<ut::Delegate<TyVidSubKey>>> for UndoLog<'db> {
+    fn from(l: sv::UndoLog<ut::Delegate<TyVidSubKey>>) -> Self {
+        UndoLog::SubRelation(l)
+    }
+}
+
 impl<'db> Rollback<sv::UndoLog<ut::Delegate<TyVidEqKey<'db>>>> for TypeVariableStorage<'db> {
     fn reverse(&mut self, undo: sv::UndoLog<ut::Delegate<TyVidEqKey<'db>>>) {
         self.eq_relations.reverse(undo)
     }
 }
 
+impl<'tcx> Rollback<sv::UndoLog<ut::Delegate<TyVidSubKey>>> for TypeVariableStorage<'tcx> {
+    fn reverse(&mut self, undo: sv::UndoLog<ut::Delegate<TyVidSubKey>>) {
+        self.sub_unification_table.reverse(undo)
+    }
+}
+
+impl<'tcx> Rollback<UndoLog<'tcx>> for TypeVariableStorage<'tcx> {
+    fn reverse(&mut self, undo: UndoLog<'tcx>) {
+        match undo {
+            UndoLog::EqRelation(undo) => self.eq_relations.reverse(undo),
+            UndoLog::SubRelation(undo) => self.sub_unification_table.reverse(undo),
+        }
+    }
+}
+
 #[derive(Clone, Default)]
 pub(crate) struct TypeVariableStorage<'db> {
     /// The origins of each type variable.
@@ -31,6 +67,25 @@ pub(crate) struct TypeVariableStorage<'db> {
     /// constraint `?X == ?Y`. This table also stores, for each key,
     /// the known value.
     eq_relations: ut::UnificationTableStorage<TyVidEqKey<'db>>,
+    /// Only used by `-Znext-solver` and for diagnostics. Tracks whether
+    /// type variables are related via subtyping at all, ignoring which of
+    /// the two is the subtype.
+    ///
+    /// When reporting ambiguity errors, we sometimes want to
+    /// treat all inference vars which are subtypes of each
+    /// others as if they are equal. For this case we compute
+    /// the transitive closure of our subtype obligations here.
+    ///
+    /// E.g. when encountering ambiguity errors, we want to suggest
+    /// specifying some method argument or to add a type annotation
+    /// to a local variable. Because subtyping cannot change the
+    /// shape of a type, it's fine if the cause of the ambiguity error
+    /// is only related to the suggested variable via subtyping.
+    ///
+    /// Even for something like `let x = returns_arg(); x.method();` the
+    /// type of `x` is only a supertype of the argument of `returns_arg`. We
+    /// still want to suggest specifying the type of the argument.
+    sub_unification_table: ut::UnificationTableStorage<TyVidSubKey>,
 }
 
 pub(crate) struct TypeVariableTable<'a, 'db> {
@@ -112,6 +167,17 @@ impl<'db> TypeVariableTable<'_, 'db> {
         debug_assert!(self.probe(a).is_unknown());
         debug_assert!(self.probe(b).is_unknown());
         self.eq_relations().union(a, b);
+        self.sub_unification_table().union(a, b);
+    }
+
+    /// Records that `a` and `b` are related via subtyping. We don't track
+    /// which of the two is the subtype.
+    ///
+    /// Precondition: neither `a` nor `b` are known.
+    pub(crate) fn sub_unify(&mut self, a: TyVid, b: TyVid) {
+        debug_assert!(self.probe(a).is_unknown());
+        debug_assert!(self.probe(b).is_unknown());
+        self.sub_unification_table().union(a, b);
     }
 
     /// Instantiates `vid` with the type `ty`.
@@ -141,6 +207,10 @@ impl<'db> TypeVariableTable<'_, 'db> {
     ///   for improving error messages.
     pub(crate) fn new_var(&mut self, universe: UniverseIndex, origin: TypeVariableOrigin) -> TyVid {
         let eq_key = self.eq_relations().new_key(TypeVariableValue::Unknown { universe });
+
+        let sub_key = self.sub_unification_table().new_key(());
+        debug_assert_eq!(eq_key.vid, sub_key.vid);
+
         let index = self.storage.values.push(TypeVariableData { origin });
         debug_assert_eq!(eq_key.vid, index);
 
@@ -163,6 +233,18 @@ impl<'db> TypeVariableTable<'_, 'db> {
         self.eq_relations().find(vid).vid
     }
 
+    /// Returns the "root" variable of `vid` in the `sub_unification_table`
+    /// equivalence table. All type variables that have been are related via
+    /// equality or subtyping will yield the same root variable (per the
+    /// union-find algorithm), so `sub_unification_table_root_var(a)
+    /// == sub_unification_table_root_var(b)` implies that:
+    /// ```text
+    /// exists X. (a <: X || X <: a) && (b <: X || X <: b)
+    /// ```
+    pub(crate) fn sub_unification_table_root_var(&mut self, vid: TyVid) -> TyVid {
+        self.sub_unification_table().find(vid).vid
+    }
+
     /// Retrieves the type to which `vid` has been instantiated, if
     /// any.
     pub(crate) fn probe(&mut self, vid: TyVid) -> TypeVariableValue<'db> {
@@ -180,6 +262,11 @@ impl<'db> TypeVariableTable<'_, 'db> {
         self.storage.eq_relations.with_log(self.undo_log)
     }
 
+    #[inline]
+    fn sub_unification_table(&mut self) -> super::UnificationTable<'_, 'db, TyVidSubKey> {
+        self.storage.sub_unification_table.with_log(self.undo_log)
+    }
+
     /// Returns indices of all variables that are not yet
     /// instantiated.
     pub(crate) fn unresolved_variables(&mut self) -> Vec<TyVid> {
@@ -228,6 +315,36 @@ impl<'db> ut::UnifyKey for TyVidEqKey<'db> {
     fn tag() -> &'static str {
         "TyVidEqKey"
     }
+    fn order_roots(a: Self, _: &Self::Value, b: Self, _: &Self::Value) -> Option<(Self, Self)> {
+        if a.vid.as_u32() < b.vid.as_u32() { Some((a, b)) } else { Some((b, a)) }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub(crate) struct TyVidSubKey {
+    vid: TyVid,
+}
+
+impl From<TyVid> for TyVidSubKey {
+    #[inline] // make this function eligible for inlining - it is quite hot.
+    fn from(vid: TyVid) -> Self {
+        TyVidSubKey { vid }
+    }
+}
+
+impl ut::UnifyKey for TyVidSubKey {
+    type Value = ();
+    #[inline]
+    fn index(&self) -> u32 {
+        self.vid.as_u32()
+    }
+    #[inline]
+    fn from_index(i: u32) -> TyVidSubKey {
+        TyVidSubKey { vid: TyVid::from_u32(i) }
+    }
+    fn tag() -> &'static str {
+        "TyVidSubKey"
+    }
 }
 
 impl<'db> ut::UnifyValue for TypeVariableValue<'db> {
diff --git a/crates/hir-ty/src/next_solver/infer/unify_key.rs b/crates/hir-ty/src/next_solver/infer/unify_key.rs
index b9afb45ba8..dc913b262a 100644
--- a/crates/hir-ty/src/next_solver/infer/unify_key.rs
+++ b/crates/hir-ty/src/next_solver/infer/unify_key.rs
@@ -139,6 +139,9 @@ impl<'db> UnifyKey for ConstVidKey<'db> {
     fn tag() -> &'static str {
         "ConstVidKey"
     }
+    fn order_roots(a: Self, _: &Self::Value, b: Self, _: &Self::Value) -> Option<(Self, Self)> {
+        if a.vid.as_u32() < b.vid.as_u32() { Some((a, b)) } else { Some((b, a)) }
+    }
 }
 
 impl<'db> UnifyValue for ConstVariableValue<'db> {
diff --git a/crates/hir-ty/src/next_solver/interner.rs b/crates/hir-ty/src/next_solver/interner.rs
index 5709beaefc..0f512fdaf8 100644
--- a/crates/hir-ty/src/next_solver/interner.rs
+++ b/crates/hir-ty/src/next_solver/interner.rs
@@ -19,7 +19,7 @@ use rustc_type_ir::error::TypeError;
 use rustc_type_ir::inherent::{
     AdtDef as _, GenericArgs as _, GenericsOf, IntoKind, SliceLike as _, Span as _,
 };
-use rustc_type_ir::lang_items::{SolverLangItem, SolverTraitLangItem};
+use rustc_type_ir::lang_items::{SolverAdtLangItem, SolverLangItem, SolverTraitLangItem};
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{
     AliasTerm, AliasTermKind, AliasTy, AliasTyKind, EarlyBinder, FlagComputation, Flags,
@@ -47,8 +47,9 @@ use crate::method_resolution::{ALL_FLOAT_FPS, ALL_INT_FPS, TyFingerprint};
 use crate::next_solver::infer::InferCtxt;
 use crate::next_solver::util::{ContainsTypeErrors, explicit_item_bounds, for_trait_impls};
 use crate::next_solver::{
-    BoundConst, CanonicalVarKind, FxIndexMap, InternedWrapperNoDebug, RegionAssumptions,
-    SolverContext, SolverDefIds, TraitIdWrapper,
+    AdtIdWrapper, BoundConst, CallableIdWrapper, CanonicalVarKind, ClosureIdWrapper,
+    CoroutineIdWrapper, FxIndexMap, ImplIdWrapper, InternedWrapperNoDebug, RegionAssumptions,
+    SolverContext, SolverDefIds, TraitIdWrapper, TypeAliasIdWrapper,
 };
 use crate::{ConstScalar, FnAbi, Interner, db::HirDatabase};
 
@@ -609,8 +610,8 @@ impl AdtDef {
 }
 
 impl<'db> inherent::AdtDef<DbInterner<'db>> for AdtDef {
-    fn def_id(self) -> <DbInterner<'db> as rustc_type_ir::Interner>::DefId {
-        SolverDefId::AdtId(self.inner().id)
+    fn def_id(self) -> AdtIdWrapper {
+        self.inner().id.into()
     }
 
     fn is_struct(self) -> bool {
@@ -889,6 +890,13 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
     type LocalDefId = SolverDefId;
     type LocalDefIds = SolverDefIds;
     type TraitId = TraitIdWrapper;
+    type ForeignId = TypeAliasIdWrapper;
+    type FunctionId = CallableIdWrapper;
+    type ClosureId = ClosureIdWrapper;
+    type CoroutineClosureId = CoroutineIdWrapper;
+    type CoroutineId = CoroutineIdWrapper;
+    type AdtId = AdtIdWrapper;
+    type ImplId = ImplIdWrapper;
     type Span = Span;
 
     type GenericArgs = GenericArgs<'db>;
@@ -1103,12 +1111,8 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         self.db().ty_ns(def_id)
     }
 
-    fn adt_def(self, adt_def_id: Self::DefId) -> Self::AdtDef {
-        let def_id = match adt_def_id {
-            SolverDefId::AdtId(adt_id) => adt_id,
-            _ => panic!("Invalid DefId passed to adt_def"),
-        };
-        AdtDef::new(def_id, self)
+    fn adt_def(self, def_id: Self::AdtId) -> Self::AdtDef {
+        AdtDef::new(def_id.0, self)
     }
 
     fn alias_ty_kind(self, alias: rustc_type_ir::AliasTy<Self>) -> AliasTyKind {
@@ -1219,24 +1223,16 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
 
     fn fn_sig(
         self,
-        def_id: Self::DefId,
+        def_id: Self::FunctionId,
     ) -> EarlyBinder<Self, rustc_type_ir::Binder<Self, rustc_type_ir::FnSig<Self>>> {
-        let id = match def_id {
-            SolverDefId::FunctionId(id) => CallableDefId::FunctionId(id),
-            SolverDefId::Ctor(ctor) => match ctor {
-                super::Ctor::Struct(struct_id) => CallableDefId::StructId(struct_id),
-                super::Ctor::Enum(enum_variant_id) => CallableDefId::EnumVariantId(enum_variant_id),
-            },
-            def => unreachable!("{:?}", def),
-        };
-        self.db().callable_item_signature_ns(id)
+        self.db().callable_item_signature_ns(def_id.0)
     }
 
-    fn coroutine_movability(self, def_id: Self::DefId) -> rustc_ast_ir::Movability {
+    fn coroutine_movability(self, def_id: Self::CoroutineId) -> rustc_ast_ir::Movability {
         unimplemented!()
     }
 
-    fn coroutine_for_closure(self, def_id: Self::DefId) -> Self::DefId {
+    fn coroutine_for_closure(self, def_id: Self::CoroutineId) -> Self::CoroutineId {
         unimplemented!()
     }
 
@@ -1361,13 +1357,9 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
 
     fn impl_super_outlives(
         self,
-        impl_def_id: Self::DefId,
+        impl_id: Self::ImplId,
     ) -> EarlyBinder<Self, impl IntoIterator<Item = Self::Clause>> {
-        let impl_id = match impl_def_id {
-            SolverDefId::ImplId(id) => id,
-            _ => unreachable!(),
-        };
-        let trait_ref = self.db().impl_trait_ns(impl_id).expect("expected an impl of trait");
+        let trait_ref = self.db().impl_trait_ns(impl_id.0).expect("expected an impl of trait");
         trait_ref.map_bound(|trait_ref| {
             let clause: Clause<'_> = trait_ref.upcast(self);
             Clauses::new_from_iter(
@@ -1392,7 +1384,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         EarlyBinder::bind([unimplemented!()])
     }
 
-    fn has_target_features(self, def_id: Self::DefId) -> bool {
+    fn has_target_features(self, def_id: Self::FunctionId) -> bool {
         false
     }
 
@@ -1407,8 +1399,6 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
             SolverLangItem::DynMetadata => LangItem::DynMetadata,
             SolverLangItem::FutureOutput => LangItem::FutureOutput,
             SolverLangItem::Metadata => LangItem::Metadata,
-            SolverLangItem::Option => LangItem::Option,
-            SolverLangItem::Poll => LangItem::Poll,
         };
         let target = hir_def::lang_item::lang_item(
             self.db(),
@@ -1468,24 +1458,33 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
             .into()
     }
 
-    #[allow(clippy::match_like_matches_macro)]
-    fn is_lang_item(self, def_id: Self::DefId, lang_item: SolverLangItem) -> bool {
-        use SolverLangItem::*;
+    fn require_adt_lang_item(self, lang_item: SolverAdtLangItem) -> AdtIdWrapper {
+        let lang_item = match lang_item {
+            SolverAdtLangItem::Option => LangItem::Option,
+            SolverAdtLangItem::Poll => LangItem::Poll,
+        };
+        lang_item
+            .resolve_adt(self.db(), self.krate.expect("Must have self.krate"))
+            .unwrap_or_else(|| panic!("Lang item {lang_item:?} required but not found."))
+            .into()
+    }
 
-        // FIXME: derive PartialEq on SolverLangItem
+    fn is_lang_item(self, def_id: Self::DefId, lang_item: SolverLangItem) -> bool {
         self.as_lang_item(def_id)
             .map_or(false, |l| std::mem::discriminant(&l) == std::mem::discriminant(&lang_item))
     }
 
-    #[allow(clippy::match_like_matches_macro)]
     fn is_trait_lang_item(self, def_id: Self::TraitId, lang_item: SolverTraitLangItem) -> bool {
-        use SolverTraitLangItem::*;
-
-        // FIXME: derive PartialEq on SolverTraitLangItem
         self.as_trait_lang_item(def_id)
             .map_or(false, |l| std::mem::discriminant(&l) == std::mem::discriminant(&lang_item))
     }
 
+    fn is_adt_lang_item(self, def_id: Self::AdtId, lang_item: SolverAdtLangItem) -> bool {
+        // FIXME: derive PartialEq on SolverTraitLangItem
+        self.as_adt_lang_item(def_id)
+            .map_or(false, |l| std::mem::discriminant(&l) == std::mem::discriminant(&lang_item))
+    }
+
     fn as_lang_item(self, def_id: Self::DefId) -> Option<SolverLangItem> {
         let def_id: AttrDefId = match def_id {
             SolverDefId::TraitId(id) => id.into(),
@@ -1505,9 +1504,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
             DynMetadata,
             CoroutineReturn,
             CoroutineYield,
-            Poll,
             FutureOutput,
-            Option,
             AsyncFnOnceOutput,
             CallRefFuture,
             CallOnceFuture,
@@ -1556,6 +1553,19 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         )
     }
 
+    fn as_adt_lang_item(self, def_id: Self::AdtId) -> Option<SolverAdtLangItem> {
+        let def_id: AttrDefId = def_id.0.into();
+        let lang_item = self.db().lang_attr(def_id)?;
+        as_lang_item!(
+            SolverAdtLangItem, lang_item;
+
+            ignore = {}
+
+            Option,
+            Poll,
+        )
+    }
+
     fn associated_type_def_ids(self, def_id: Self::DefId) -> impl IntoIterator<Item = Self::DefId> {
         let trait_ = match def_id {
             SolverDefId::TraitId(id) => id,
@@ -1568,7 +1578,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         self,
         trait_: Self::TraitId,
         self_ty: Self::Ty,
-        mut f: impl FnMut(Self::DefId),
+        mut f: impl FnMut(Self::ImplId),
     ) {
         let trait_ = trait_.0;
         let self_ty_fp = TyFingerprint::for_trait_impl_ns(&self_ty);
@@ -1595,7 +1605,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
                             continue;
                         }
 
-                        f(SolverDefId::ImplId(i));
+                        f(i.into());
                     }
                     ControlFlow::Continue(())
                 },
@@ -1618,7 +1628,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
                                 continue;
                             }
 
-                            f(SolverDefId::ImplId(i));
+                            f(i.into());
                         }
                     }
                     ControlFlow::Continue(())
@@ -1632,7 +1642,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         true
     }
 
-    fn impl_is_default(self, impl_def_id: Self::DefId) -> bool {
+    fn impl_is_default(self, impl_def_id: Self::ImplId) -> bool {
         // FIXME
         false
     }
@@ -1640,26 +1650,16 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
     #[tracing::instrument(skip(self), ret)]
     fn impl_trait_ref(
         self,
-        impl_def_id: Self::DefId,
+        impl_id: Self::ImplId,
     ) -> EarlyBinder<Self, rustc_type_ir::TraitRef<Self>> {
-        let impl_id = match impl_def_id {
-            SolverDefId::ImplId(id) => id,
-            _ => panic!("Unexpected SolverDefId in impl_trait_ref"),
-        };
-
         let db = self.db();
-
-        db.impl_trait_ns(impl_id)
+        db.impl_trait_ns(impl_id.0)
             // ImplIds for impls where the trait ref can't be resolved should never reach trait solving
             .expect("invalid impl passed to trait solver")
     }
 
-    fn impl_polarity(self, impl_def_id: Self::DefId) -> rustc_type_ir::ImplPolarity {
-        let impl_id = match impl_def_id {
-            SolverDefId::ImplId(id) => id,
-            _ => unreachable!(),
-        };
-        let impl_data = self.db().impl_signature(impl_id);
+    fn impl_polarity(self, impl_id: Self::ImplId) -> rustc_type_ir::ImplPolarity {
+        let impl_data = self.db().impl_signature(impl_id.0);
         if impl_data.flags.contains(ImplFlags::NEGATIVE) {
             ImplPolarity::Negative
         } else {
@@ -1701,33 +1701,29 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         panic!("Bug encountered in next-trait-solver.")
     }
 
-    fn is_general_coroutine(self, coroutine_def_id: Self::DefId) -> bool {
+    fn is_general_coroutine(self, coroutine_def_id: Self::CoroutineId) -> bool {
         // FIXME(next-solver)
         true
     }
 
-    fn coroutine_is_async(self, coroutine_def_id: Self::DefId) -> bool {
+    fn coroutine_is_async(self, coroutine_def_id: Self::CoroutineId) -> bool {
         // FIXME(next-solver)
         true
     }
 
-    fn coroutine_is_gen(self, coroutine_def_id: Self::DefId) -> bool {
+    fn coroutine_is_gen(self, coroutine_def_id: Self::CoroutineId) -> bool {
         // FIXME(next-solver)
         false
     }
 
-    fn coroutine_is_async_gen(self, coroutine_def_id: Self::DefId) -> bool {
+    fn coroutine_is_async_gen(self, coroutine_def_id: Self::CoroutineId) -> bool {
         // FIXME(next-solver)
         false
     }
 
-    fn unsizing_params_for_adt(self, adt_def_id: Self::DefId) -> Self::UnsizingParams {
-        let id = match adt_def_id {
-            SolverDefId::AdtId(id) => id,
-            _ => unreachable!(),
-        };
-        let def = AdtDef::new(id, self);
-        let num_params = self.generics_of(adt_def_id).count();
+    fn unsizing_params_for_adt(self, id: Self::AdtId) -> Self::UnsizingParams {
+        let def = AdtDef::new(id.0, self);
+        let num_params = self.generics_of(id.into()).count();
 
         let maybe_unsizing_param_idx = |arg: GenericArg<'db>| match arg.kind() {
             GenericArgKind::Type(ty) => match ty.kind() {
@@ -1835,15 +1831,15 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         EarlyBinder::bind([])
     }
 
-    fn fn_is_const(self, def_id: Self::DefId) -> bool {
-        let id = match def_id {
-            SolverDefId::FunctionId(id) => id,
-            _ => unreachable!(),
+    fn fn_is_const(self, id: Self::FunctionId) -> bool {
+        let id = match id.0 {
+            CallableDefId::FunctionId(id) => id,
+            _ => return false,
         };
         self.db().function_signature(id).flags.contains(FnFlags::CONST)
     }
 
-    fn impl_is_const(self, def_id: Self::DefId) -> bool {
+    fn impl_is_const(self, def_id: Self::ImplId) -> bool {
         false
     }
 
@@ -1877,7 +1873,7 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
 
     fn coroutine_hidden_types(
         self,
-        def_id: Self::DefId,
+        def_id: Self::CoroutineId,
     ) -> EarlyBinder<Self, rustc_type_ir::Binder<Self, rustc_type_ir::CoroutineWitnessTypes<Self>>>
     {
         // FIXME(next-solver)
@@ -1896,11 +1892,11 @@ impl<'db> rustc_type_ir::Interner for DbInterner<'db> {
         self.db().trait_signature(trait_.0).flags.contains(TraitFlags::UNSAFE)
     }
 
-    fn impl_self_is_guaranteed_unsized(self, def_id: Self::DefId) -> bool {
+    fn impl_self_is_guaranteed_unsized(self, def_id: Self::ImplId) -> bool {
         false
     }
 
-    fn impl_specializes(self, impl_def_id: Self::DefId, victim_def_id: Self::DefId) -> bool {
+    fn impl_specializes(self, impl_def_id: Self::ImplId, victim_def_id: Self::ImplId) -> bool {
         false
     }
 
@@ -2020,6 +2016,12 @@ macro_rules! TrivialTypeTraversalImpls {
 TrivialTypeTraversalImpls! {
     SolverDefId,
     TraitIdWrapper,
+    TypeAliasIdWrapper,
+    CallableIdWrapper,
+    ClosureIdWrapper,
+    CoroutineIdWrapper,
+    AdtIdWrapper,
+    ImplIdWrapper,
     Pattern<'db>,
     Safety,
     FnAbi,
diff --git a/crates/hir-ty/src/next_solver/mapping.rs b/crates/hir-ty/src/next_solver/mapping.rs
index 57a56b3f0c..eb2cc69167 100644
--- a/crates/hir-ty/src/next_solver/mapping.rs
+++ b/crates/hir-ty/src/next_solver/mapping.rs
@@ -243,12 +243,10 @@ impl<'db> ChalkToNextSolver<'db, Ty<'db>> for chalk_ir::Ty<Interner> {
                 }
                 chalk_ir::TyKind::FnDef(fn_def_id, substitution) => {
                     let def_id = CallableDefId::from_chalk(interner.db(), *fn_def_id);
-                    let id: SolverDefId = match def_id {
-                        CallableDefId::FunctionId(id) => id.into(),
-                        CallableDefId::StructId(id) => SolverDefId::Ctor(Ctor::Struct(id)),
-                        CallableDefId::EnumVariantId(id) => SolverDefId::Ctor(Ctor::Enum(id)),
-                    };
-                    rustc_type_ir::TyKind::FnDef(id, substitution.to_nextsolver(interner))
+                    rustc_type_ir::TyKind::FnDef(
+                        def_id.into(),
+                        substitution.to_nextsolver(interner),
+                    )
                 }
                 chalk_ir::TyKind::Str => rustc_type_ir::TyKind::Str,
                 chalk_ir::TyKind::Never => rustc_type_ir::TyKind::Never,
@@ -271,7 +269,7 @@ impl<'db> ChalkToNextSolver<'db, Ty<'db>> for chalk_ir::Ty<Interner> {
                     )
                 }
                 chalk_ir::TyKind::Foreign(foreign_def_id) => rustc_type_ir::TyKind::Foreign(
-                    SolverDefId::TypeAliasId(crate::from_foreign_def_id(*foreign_def_id)),
+                    crate::from_foreign_def_id(*foreign_def_id).into(),
                 ),
                 chalk_ir::TyKind::Error => rustc_type_ir::TyKind::Error(ErrorGuaranteed),
                 chalk_ir::TyKind::Dyn(dyn_ty) => {
@@ -734,15 +732,13 @@ impl<'db, T: HasInterner<Interner = Interner> + ChalkToNextSolver<'db, U>, U>
             interner,
             self.binders.iter(Interner).map(|k| match &k.kind {
                 chalk_ir::VariableKind::Ty(ty_variable_kind) => match ty_variable_kind {
-                    TyVariableKind::General => rustc_type_ir::CanonicalVarKind::Ty(
-                        rustc_type_ir::CanonicalTyVarKind::General(UniverseIndex::ROOT),
-                    ),
-                    TyVariableKind::Integer => {
-                        rustc_type_ir::CanonicalVarKind::Ty(rustc_type_ir::CanonicalTyVarKind::Int)
-                    }
-                    TyVariableKind::Float => rustc_type_ir::CanonicalVarKind::Ty(
-                        rustc_type_ir::CanonicalTyVarKind::Float,
-                    ),
+                    // FIXME(next-solver): the info is incorrect, but we have no way to store the information in Chalk.
+                    TyVariableKind::General => rustc_type_ir::CanonicalVarKind::Ty {
+                        ui: UniverseIndex::ROOT,
+                        sub_root: BoundVar::from_u32(0),
+                    },
+                    TyVariableKind::Integer => rustc_type_ir::CanonicalVarKind::Int,
+                    TyVariableKind::Float => rustc_type_ir::CanonicalVarKind::Float,
                 },
                 chalk_ir::VariableKind::Lifetime => {
                     rustc_type_ir::CanonicalVarKind::Region(UniverseIndex::ROOT)
@@ -767,24 +763,20 @@ impl<'db, T: NextSolverToChalk<'db, U>, U: HasInterner<Interner = Interner>>
         let binders = chalk_ir::CanonicalVarKinds::from_iter(
             Interner,
             self.variables.iter().map(|v| match v {
-                rustc_type_ir::CanonicalVarKind::Ty(
-                    rustc_type_ir::CanonicalTyVarKind::General(ui),
-                ) => chalk_ir::CanonicalVarKind::new(
-                    chalk_ir::VariableKind::Ty(TyVariableKind::General),
-                    chalk_ir::UniverseIndex { counter: ui.as_usize() },
+                rustc_type_ir::CanonicalVarKind::Ty { ui, sub_root: _ } => {
+                    chalk_ir::CanonicalVarKind::new(
+                        chalk_ir::VariableKind::Ty(TyVariableKind::General),
+                        chalk_ir::UniverseIndex { counter: ui.as_usize() },
+                    )
+                }
+                rustc_type_ir::CanonicalVarKind::Int => chalk_ir::CanonicalVarKind::new(
+                    chalk_ir::VariableKind::Ty(TyVariableKind::Integer),
+                    chalk_ir::UniverseIndex::root(),
+                ),
+                rustc_type_ir::CanonicalVarKind::Float => chalk_ir::CanonicalVarKind::new(
+                    chalk_ir::VariableKind::Ty(TyVariableKind::Float),
+                    chalk_ir::UniverseIndex::root(),
                 ),
-                rustc_type_ir::CanonicalVarKind::Ty(rustc_type_ir::CanonicalTyVarKind::Int) => {
-                    chalk_ir::CanonicalVarKind::new(
-                        chalk_ir::VariableKind::Ty(TyVariableKind::Integer),
-                        chalk_ir::UniverseIndex::root(),
-                    )
-                }
-                rustc_type_ir::CanonicalVarKind::Ty(rustc_type_ir::CanonicalTyVarKind::Float) => {
-                    chalk_ir::CanonicalVarKind::new(
-                        chalk_ir::VariableKind::Ty(TyVariableKind::Float),
-                        chalk_ir::UniverseIndex::root(),
-                    )
-                }
                 rustc_type_ir::CanonicalVarKind::Region(ui) => chalk_ir::CanonicalVarKind::new(
                     chalk_ir::VariableKind::Lifetime,
                     chalk_ir::UniverseIndex { counter: ui.as_usize() },
@@ -1520,13 +1512,7 @@ pub(crate) fn convert_ty_for_result<'db>(interner: DbInterner<'db>, ty: Ty<'db>)
             TyKind::Slice(ty)
         }
 
-        rustc_type_ir::TyKind::Foreign(foreign) => {
-            let def_id = match foreign {
-                SolverDefId::TypeAliasId(id) => id,
-                _ => unreachable!(),
-            };
-            TyKind::Foreign(to_foreign_def_id(def_id))
-        }
+        rustc_type_ir::TyKind::Foreign(foreign) => TyKind::Foreign(to_foreign_def_id(foreign.0)),
         rustc_type_ir::TyKind::Pat(_, _) => unimplemented!(),
         rustc_type_ir::TyKind::RawPtr(ty, mutability) => {
             let mutability = match mutability {
@@ -1537,40 +1523,22 @@ pub(crate) fn convert_ty_for_result<'db>(interner: DbInterner<'db>, ty: Ty<'db>)
             TyKind::Raw(mutability, ty)
         }
         rustc_type_ir::TyKind::FnDef(def_id, args) => {
-            let id = match def_id {
-                SolverDefId::FunctionId(id) => CallableDefId::FunctionId(id),
-                SolverDefId::Ctor(Ctor::Struct(id)) => CallableDefId::StructId(id),
-                SolverDefId::Ctor(Ctor::Enum(id)) => CallableDefId::EnumVariantId(id),
-                _ => unreachable!(),
-            };
             let subst = convert_args_for_result(interner, args.as_slice());
-            TyKind::FnDef(id.to_chalk(interner.db()), subst)
+            TyKind::FnDef(def_id.0.to_chalk(interner.db()), subst)
         }
 
         rustc_type_ir::TyKind::Closure(def_id, args) => {
-            let id = match def_id {
-                SolverDefId::InternedClosureId(id) => id,
-                _ => unreachable!(),
-            };
             let subst = convert_args_for_result(interner, args.as_slice());
-            TyKind::Closure(id.into(), subst)
+            TyKind::Closure(def_id.0.into(), subst)
         }
         rustc_type_ir::TyKind::CoroutineClosure(_, _) => unimplemented!(),
         rustc_type_ir::TyKind::Coroutine(def_id, args) => {
-            let id = match def_id {
-                SolverDefId::InternedCoroutineId(id) => id,
-                _ => unreachable!(),
-            };
             let subst = convert_args_for_result(interner, args.as_slice());
-            TyKind::Coroutine(id.into(), subst)
+            TyKind::Coroutine(def_id.0.into(), subst)
         }
         rustc_type_ir::TyKind::CoroutineWitness(def_id, args) => {
-            let id = match def_id {
-                SolverDefId::InternedCoroutineId(id) => id,
-                _ => unreachable!(),
-            };
             let subst = convert_args_for_result(interner, args.as_slice());
-            TyKind::CoroutineWitness(id.into(), subst)
+            TyKind::CoroutineWitness(def_id.0.into(), subst)
         }
 
         rustc_type_ir::TyKind::UnsafeBinder(_) => unimplemented!(),
diff --git a/crates/hir-ty/src/next_solver/solver.rs b/crates/hir-ty/src/next_solver/solver.rs
index 385149d784..c7591c0c77 100644
--- a/crates/hir-ty/src/next_solver/solver.rs
+++ b/crates/hir-ty/src/next_solver/solver.rs
@@ -10,6 +10,7 @@ use rustc_type_ir::{
 };
 
 use crate::next_solver::mapping::NextSolverToChalk;
+use crate::next_solver::{CanonicalVarKind, ImplIdWrapper};
 use crate::{
     TraitRefExt,
     db::HirDatabase,
@@ -117,13 +118,14 @@ impl<'db> SolverDelegate for SolverContext<'db> {
         canonical.instantiate(self.cx(), &values)
     }
 
-    fn instantiate_canonical_var_with_infer(
+    fn instantiate_canonical_var(
         &self,
-        cv_info: rustc_type_ir::CanonicalVarKind<Self::Interner>,
-        _span: <Self::Interner as rustc_type_ir::Interner>::Span,
+        kind: CanonicalVarKind<'db>,
+        span: <Self::Interner as Interner>::Span,
+        var_values: &[GenericArg<'db>],
         universe_map: impl Fn(rustc_type_ir::UniverseIndex) -> rustc_type_ir::UniverseIndex,
-    ) -> <Self::Interner as rustc_type_ir::Interner>::GenericArg {
-        self.0.instantiate_canonical_var(cv_info, universe_map)
+    ) -> GenericArg<'db> {
+        self.0.instantiate_canonical_var(kind, var_values, universe_map)
     }
 
     fn add_item_bounds_for_hidden_type(
@@ -146,12 +148,8 @@ impl<'db> SolverDelegate for SolverContext<'db> {
         &self,
         goal_trait_ref: rustc_type_ir::TraitRef<Self::Interner>,
         trait_assoc_def_id: <Self::Interner as rustc_type_ir::Interner>::DefId,
-        impl_def_id: <Self::Interner as rustc_type_ir::Interner>::DefId,
+        impl_id: ImplIdWrapper,
     ) -> Result<Option<<Self::Interner as rustc_type_ir::Interner>::DefId>, ErrorGuaranteed> {
-        let impl_id = match impl_def_id {
-            SolverDefId::ImplId(id) => id,
-            _ => panic!("Unexpected SolverDefId"),
-        };
         let trait_assoc_id = match trait_assoc_def_id {
             SolverDefId::TypeAliasId(id) => id,
             _ => panic!("Unexpected SolverDefId"),
@@ -160,7 +158,7 @@ impl<'db> SolverDelegate for SolverContext<'db> {
             .0
             .interner
             .db()
-            .impl_trait(impl_id)
+            .impl_trait(impl_id.0)
             // ImplIds for impls where the trait ref can't be resolved should never reach solver
             .expect("invalid impl passed to next-solver")
             .into_value_and_skipped_binders()
@@ -168,7 +166,7 @@ impl<'db> SolverDelegate for SolverContext<'db> {
         let trait_ = trait_ref.hir_trait_id();
         let trait_data = trait_.trait_items(self.0.interner.db());
         let id =
-            impl_id.impl_items(self.0.interner.db()).items.iter().find_map(|item| -> Option<_> {
+            impl_id.0.impl_items(self.0.interner.db()).items.iter().find_map(|item| -> Option<_> {
                 match item {
                     (_, AssocItemId::TypeAliasId(type_alias)) => {
                         let name = &self.0.interner.db().type_alias_signature(*type_alias).name;
diff --git a/crates/hir-ty/src/next_solver/ty.rs b/crates/hir-ty/src/next_solver/ty.rs
index 4794e2d604..e1c29160ad 100644
--- a/crates/hir-ty/src/next_solver/ty.rs
+++ b/crates/hir-ty/src/next_solver/ty.rs
@@ -20,7 +20,9 @@ use rustc_type_ir::{
 use salsa::plumbing::{AsId, FromId};
 use smallvec::SmallVec;
 
-use crate::next_solver::GenericArg;
+use crate::next_solver::{
+    CallableIdWrapper, ClosureIdWrapper, CoroutineIdWrapper, GenericArg, TypeAliasIdWrapper,
+};
 use crate::{
     db::HirDatabase,
     interner::InternedWrapperNoDebug,
@@ -599,10 +601,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
         Ty::new(interner, TyKind::Adt(adt_def, args))
     }
 
-    fn new_foreign(
-        interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
-    ) -> Self {
+    fn new_foreign(interner: DbInterner<'db>, def_id: TypeAliasIdWrapper) -> Self {
         Ty::new(interner, TyKind::Foreign(def_id))
     }
 
@@ -617,7 +616,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_coroutine(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: CoroutineIdWrapper,
         args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         Ty::new(interner, TyKind::Coroutine(def_id, args))
@@ -625,7 +624,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_coroutine_closure(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: CoroutineIdWrapper,
         args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         Ty::new(interner, TyKind::CoroutineClosure(def_id, args))
@@ -633,7 +632,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_closure(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: ClosureIdWrapper,
         args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         Ty::new(interner, TyKind::Closure(def_id, args))
@@ -641,7 +640,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_coroutine_witness(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: CoroutineIdWrapper,
         args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         Ty::new(interner, TyKind::CoroutineWitness(def_id, args))
@@ -649,7 +648,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_coroutine_witness_for_coroutine(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: CoroutineIdWrapper,
         coroutine_args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         // HACK: Coroutine witness types are lifetime erased, so they
@@ -714,7 +713,7 @@ impl<'db> rustc_type_ir::inherent::Ty<DbInterner<'db>> for Ty<'db> {
 
     fn new_fn_def(
         interner: DbInterner<'db>,
-        def_id: <DbInterner<'db> as rustc_type_ir::Interner>::DefId,
+        def_id: CallableIdWrapper,
         args: <DbInterner<'db> as rustc_type_ir::Interner>::GenericArgs,
     ) -> Self {
         Ty::new(interner, TyKind::FnDef(def_id, args))
diff --git a/crates/hir-ty/src/next_solver/util.rs b/crates/hir-ty/src/next_solver/util.rs
index 50b96a160e..97d3ea72c9 100644
--- a/crates/hir-ty/src/next_solver/util.rs
+++ b/crates/hir-ty/src/next_solver/util.rs
@@ -532,17 +532,14 @@ pub(crate) fn mini_canonicalize<'db, T: TypeFoldable<DbInterner<'db>>>(
         max_universe: UniverseIndex::from_u32(1),
         variables: CanonicalVars::new_from_iter(
             context.cx(),
-            vars.iter().map(|(k, v)| match (*k).kind() {
+            vars.iter().enumerate().map(|(idx, (k, v))| match (*k).kind() {
                 GenericArgKind::Type(ty) => match ty.kind() {
-                    TyKind::Int(..) | TyKind::Uint(..) => {
-                        rustc_type_ir::CanonicalVarKind::Ty(rustc_type_ir::CanonicalTyVarKind::Int)
-                    }
-                    TyKind::Float(..) => rustc_type_ir::CanonicalVarKind::Ty(
-                        rustc_type_ir::CanonicalTyVarKind::Float,
-                    ),
-                    _ => rustc_type_ir::CanonicalVarKind::Ty(
-                        rustc_type_ir::CanonicalTyVarKind::General(UniverseIndex::ZERO),
-                    ),
+                    TyKind::Int(..) | TyKind::Uint(..) => rustc_type_ir::CanonicalVarKind::Int,
+                    TyKind::Float(..) => rustc_type_ir::CanonicalVarKind::Float,
+                    _ => rustc_type_ir::CanonicalVarKind::Ty {
+                        ui: UniverseIndex::ZERO,
+                        sub_root: BoundVar::from_usize(idx),
+                    },
                 },
                 GenericArgKind::Lifetime(_) => {
                     rustc_type_ir::CanonicalVarKind::Region(UniverseIndex::ZERO)