Auto merge of #145377 - ChayimFriedman2:solver-def-id, r=lcnr

Switch next solver to use a specific associated type for trait def id

The compiler just puts `DefId` in there, but rust-analyzer uses different types for each kind of item.

See [the Zulip discussion](https://rust-lang.zulipchat.com/#narrow/channel/185405-t-compiler.2Frust-analyzer/topic/Implmentating.20New.20Trait.20Solver/near/534329794). In short, it will be a tremendous help to r-a to use specific associated types, while for the solver and the compiler it's a small change. So I ported `TraitId`, as a proof of concept and it's also likely the most impactful.

r? types

18 files changed, 234 insertions, 178 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 4990a85466e..5dbbc7297ab 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -52,7 +52,7 @@ use rustc_session::{Limit, Session};
 use rustc_span::def_id::{CRATE_DEF_ID, DefPathHash, StableCrateId};
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
 use rustc_type_ir::TyKind::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::{SolverLangItem, SolverTraitLangItem};
 pub use rustc_type_ir::lift::Lift;
 use rustc_type_ir::{
     CollectAndApply, Interner, TypeFlags, TypeFoldable, WithCachedTypeInfo, elaborate, search_graph,
@@ -93,6 +93,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
 
     type DefId = DefId;
     type LocalDefId = LocalDefId;
+    type TraitId = DefId;
     type Span = Span;
 
     type GenericArgs = ty::GenericArgsRef<'tcx>;
@@ -483,20 +484,32 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         !self.codegen_fn_attrs(def_id).target_features.is_empty()
     }
 
-    fn require_lang_item(self, lang_item: TraitSolverLangItem) -> DefId {
-        self.require_lang_item(trait_lang_item_to_lang_item(lang_item), DUMMY_SP)
+    fn require_lang_item(self, lang_item: SolverLangItem) -> DefId {
+        self.require_lang_item(solver_lang_item_to_lang_item(lang_item), DUMMY_SP)
     }
 
-    fn is_lang_item(self, def_id: DefId, lang_item: TraitSolverLangItem) -> bool {
-        self.is_lang_item(def_id, trait_lang_item_to_lang_item(lang_item))
+    fn require_trait_lang_item(self, lang_item: SolverTraitLangItem) -> DefId {
+        self.require_lang_item(solver_trait_lang_item_to_lang_item(lang_item), DUMMY_SP)
+    }
+
+    fn is_lang_item(self, def_id: DefId, lang_item: SolverLangItem) -> bool {
+        self.is_lang_item(def_id, solver_lang_item_to_lang_item(lang_item))
+    }
+
+    fn is_trait_lang_item(self, def_id: DefId, lang_item: SolverTraitLangItem) -> bool {
+        self.is_lang_item(def_id, solver_trait_lang_item_to_lang_item(lang_item))
     }
 
     fn is_default_trait(self, def_id: DefId) -> bool {
         self.is_default_trait(def_id)
     }
 
-    fn as_lang_item(self, def_id: DefId) -> Option<TraitSolverLangItem> {
-        lang_item_to_trait_lang_item(self.lang_items().from_def_id(def_id)?)
+    fn as_lang_item(self, def_id: DefId) -> Option<SolverLangItem> {
+        lang_item_to_solver_lang_item(self.lang_items().from_def_id(def_id)?)
+    }
+
+    fn as_trait_lang_item(self, def_id: DefId) -> Option<SolverTraitLangItem> {
+        lang_item_to_solver_trait_lang_item(self.lang_items().from_def_id(def_id)?)
     }
 
     fn associated_type_def_ids(self, def_id: DefId) -> impl IntoIterator<Item = DefId> {
@@ -727,16 +740,19 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
 }
 
 macro_rules! bidirectional_lang_item_map {
-    ($($name:ident),+ $(,)?) => {
-        fn trait_lang_item_to_lang_item(lang_item: TraitSolverLangItem) -> LangItem {
+    (
+        $solver_ty:ident, $to_solver:ident, $from_solver:ident;
+        $($name:ident),+ $(,)?
+    ) => {
+        fn $from_solver(lang_item: $solver_ty) -> LangItem {
             match lang_item {
-                $(TraitSolverLangItem::$name => LangItem::$name,)+
+                $($solver_ty::$name => LangItem::$name,)+
             }
         }
 
-        fn lang_item_to_trait_lang_item(lang_item: LangItem) -> Option<TraitSolverLangItem> {
+        fn $to_solver(lang_item: LangItem) -> Option<$solver_ty> {
             Some(match lang_item {
-                $(LangItem::$name => TraitSolverLangItem::$name,)+
+                $(LangItem::$name => $solver_ty::$name,)+
                 _ => return None,
             })
         }
@@ -744,40 +760,50 @@ macro_rules! bidirectional_lang_item_map {
 }
 
 bidirectional_lang_item_map! {
+    SolverLangItem, lang_item_to_solver_lang_item, solver_lang_item_to_lang_item;
+
+// tidy-alphabetical-start
+    AsyncFnKindUpvars,
+    AsyncFnOnceOutput,
+    CallOnceFuture,
+    CallRefFuture,
+    CoroutineReturn,
+    CoroutineYield,
+    DynMetadata,
+    FutureOutput,
+    Metadata,
+    Option,
+    Poll,
+// tidy-alphabetical-end
+}
+
+bidirectional_lang_item_map! {
+    SolverTraitLangItem, lang_item_to_solver_trait_lang_item, solver_trait_lang_item_to_lang_item;
+
 // tidy-alphabetical-start
     AsyncFn,
     AsyncFnKindHelper,
-    AsyncFnKindUpvars,
     AsyncFnMut,
     AsyncFnOnce,
     AsyncFnOnceOutput,
     AsyncIterator,
     BikeshedGuaranteedNoDrop,
-    CallOnceFuture,
-    CallRefFuture,
     Clone,
     Copy,
     Coroutine,
-    CoroutineReturn,
-    CoroutineYield,
     Destruct,
     DiscriminantKind,
     Drop,
-    DynMetadata,
     Fn,
     FnMut,
     FnOnce,
     FnPtrTrait,
     FusedIterator,
     Future,
-    FutureOutput,
     Iterator,
     MetaSized,
-    Metadata,
-    Option,
     PointeeSized,
     PointeeTrait,
-    Poll,
     Sized,
     TransmuteTrait,
     Tuple,
diff --git a/compiler/rustc_next_trait_solver/src/coherence.rs b/compiler/rustc_next_trait_solver/src/coherence.rs
index f8215a228f5..79219b34e29 100644
--- a/compiler/rustc_next_trait_solver/src/coherence.rs
+++ b/compiler/rustc_next_trait_solver/src/coherence.rs
@@ -295,7 +295,7 @@ where
         ControlFlow::Break(OrphanCheckEarlyExit::UncoveredTyParam(ty))
     }
 
-    fn def_id_is_local(&mut self, def_id: I::DefId) -> bool {
+    fn def_id_is_local(&mut self, def_id: impl DefId<I>) -> bool {
         match self.in_crate {
             InCrate::Local { .. } => def_id.is_local(),
             InCrate::Remote => false,
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
index a4a8317912a..be7e4dd4cda 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs
@@ -7,7 +7,7 @@ use std::ops::ControlFlow;
 
 use derive_where::derive_where;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::SolverTraitLangItem;
 use rustc_type_ir::search_graph::CandidateHeadUsages;
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{
@@ -54,7 +54,7 @@ where
 
     fn with_replaced_self_ty(self, cx: I, self_ty: I::Ty) -> Self;
 
-    fn trait_def_id(self, cx: I) -> I::DefId;
+    fn trait_def_id(self, cx: I) -> I::TraitId;
 
     /// Consider a clause, which consists of a "assumption" and some "requirements",
     /// to satisfy a goal. If the requirements hold, then attempt to satisfy our
@@ -516,80 +516,80 @@ where
         } else if cx.trait_is_alias(trait_def_id) {
             G::consider_trait_alias_candidate(self, goal)
         } else {
-            match cx.as_lang_item(trait_def_id) {
-                Some(TraitSolverLangItem::Sized) => {
+            match cx.as_trait_lang_item(trait_def_id) {
+                Some(SolverTraitLangItem::Sized) => {
                     G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::Sized)
                 }
-                Some(TraitSolverLangItem::MetaSized) => {
+                Some(SolverTraitLangItem::MetaSized) => {
                     G::consider_builtin_sizedness_candidates(self, goal, SizedTraitKind::MetaSized)
                 }
-                Some(TraitSolverLangItem::PointeeSized) => {
+                Some(SolverTraitLangItem::PointeeSized) => {
                     unreachable!("`PointeeSized` is removed during lowering");
                 }
-                Some(TraitSolverLangItem::Copy | TraitSolverLangItem::Clone) => {
+                Some(SolverTraitLangItem::Copy | SolverTraitLangItem::Clone) => {
                     G::consider_builtin_copy_clone_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Fn) => {
+                Some(SolverTraitLangItem::Fn) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
                 }
-                Some(TraitSolverLangItem::FnMut) => {
+                Some(SolverTraitLangItem::FnMut) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnMut)
                 }
-                Some(TraitSolverLangItem::FnOnce) => {
+                Some(SolverTraitLangItem::FnOnce) => {
                     G::consider_builtin_fn_trait_candidates(self, goal, ty::ClosureKind::FnOnce)
                 }
-                Some(TraitSolverLangItem::AsyncFn) => {
+                Some(SolverTraitLangItem::AsyncFn) => {
                     G::consider_builtin_async_fn_trait_candidates(self, goal, ty::ClosureKind::Fn)
                 }
-                Some(TraitSolverLangItem::AsyncFnMut) => {
+                Some(SolverTraitLangItem::AsyncFnMut) => {
                     G::consider_builtin_async_fn_trait_candidates(
                         self,
                         goal,
                         ty::ClosureKind::FnMut,
                     )
                 }
-                Some(TraitSolverLangItem::AsyncFnOnce) => {
+                Some(SolverTraitLangItem::AsyncFnOnce) => {
                     G::consider_builtin_async_fn_trait_candidates(
                         self,
                         goal,
                         ty::ClosureKind::FnOnce,
                     )
                 }
-                Some(TraitSolverLangItem::FnPtrTrait) => {
+                Some(SolverTraitLangItem::FnPtrTrait) => {
                     G::consider_builtin_fn_ptr_trait_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::AsyncFnKindHelper) => {
+                Some(SolverTraitLangItem::AsyncFnKindHelper) => {
                     G::consider_builtin_async_fn_kind_helper_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Tuple) => G::consider_builtin_tuple_candidate(self, goal),
-                Some(TraitSolverLangItem::PointeeTrait) => {
+                Some(SolverTraitLangItem::Tuple) => G::consider_builtin_tuple_candidate(self, goal),
+                Some(SolverTraitLangItem::PointeeTrait) => {
                     G::consider_builtin_pointee_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Future) => {
+                Some(SolverTraitLangItem::Future) => {
                     G::consider_builtin_future_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Iterator) => {
+                Some(SolverTraitLangItem::Iterator) => {
                     G::consider_builtin_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::FusedIterator) => {
+                Some(SolverTraitLangItem::FusedIterator) => {
                     G::consider_builtin_fused_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::AsyncIterator) => {
+                Some(SolverTraitLangItem::AsyncIterator) => {
                     G::consider_builtin_async_iterator_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Coroutine) => {
+                Some(SolverTraitLangItem::Coroutine) => {
                     G::consider_builtin_coroutine_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::DiscriminantKind) => {
+                Some(SolverTraitLangItem::DiscriminantKind) => {
                     G::consider_builtin_discriminant_kind_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::Destruct) => {
+                Some(SolverTraitLangItem::Destruct) => {
                     G::consider_builtin_destruct_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::TransmuteTrait) => {
+                Some(SolverTraitLangItem::TransmuteTrait) => {
                     G::consider_builtin_transmute_candidate(self, goal)
                 }
-                Some(TraitSolverLangItem::BikeshedGuaranteedNoDrop) => {
+                Some(SolverTraitLangItem::BikeshedGuaranteedNoDrop) => {
                     G::consider_builtin_bikeshed_guaranteed_no_drop_candidate(self, goal)
                 }
                 _ => Err(NoSolution),
@@ -600,7 +600,7 @@ where
 
         // There may be multiple unsize candidates for a trait with several supertraits:
         // `trait Foo: Bar<A> + Bar<B>` and `dyn Foo: Unsize<dyn Bar<_>>`
-        if cx.is_lang_item(trait_def_id, TraitSolverLangItem::Unsize) {
+        if cx.is_trait_lang_item(trait_def_id, SolverTraitLangItem::Unsize) {
             candidates.extend(G::consider_structural_builtin_unsize_candidates(self, goal));
         }
     }
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index d25e74e7335..7c5940828da 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -4,7 +4,7 @@
 use derive_where::derive_where;
 use rustc_type_ir::data_structures::HashMap;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::{SolverLangItem, SolverTraitLangItem};
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{
@@ -454,7 +454,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
                 nested.push(
                     ty::TraitRef::new(
                         cx,
-                        cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper),
+                        cx.require_trait_lang_item(SolverTraitLangItem::AsyncFnKindHelper),
                         [kind_ty, Ty::from_closure_kind(cx, goal_kind)],
                     )
                     .upcast(cx),
@@ -496,7 +496,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
             let args = args.as_closure();
             let bound_sig = args.sig();
             let sig = bound_sig.skip_binder();
-            let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
+            let future_trait_def_id = cx.require_trait_lang_item(SolverTraitLangItem::Future);
             // `Closure`s only implement `AsyncFn*` when their return type
             // implements `Future`.
             let mut nested = vec![
@@ -514,7 +514,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
                 }
             } else {
                 let async_fn_kind_trait_def_id =
-                    cx.require_lang_item(TraitSolverLangItem::AsyncFnKindHelper);
+                    cx.require_trait_lang_item(SolverTraitLangItem::AsyncFnKindHelper);
                 // When we don't know the closure kind (and therefore also the closure's upvars,
                 // which are computed at the same time), we must delay the computation of the
                 // generator's upvars. We do this using the `AsyncFnKindHelper`, which as a trait
@@ -532,7 +532,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
                 );
             }
 
-            let future_output_def_id = cx.require_lang_item(TraitSolverLangItem::FutureOutput);
+            let future_output_def_id = cx.require_lang_item(SolverLangItem::FutureOutput);
             let future_output_ty = Ty::new_projection(cx, future_output_def_id, [sig.output()]);
             Ok((
                 bound_sig.rebind(AsyncCallableRelevantTypes {
@@ -581,13 +581,13 @@ fn fn_item_to_async_callable<I: Interner>(
     bound_sig: ty::Binder<I, ty::FnSig<I>>,
 ) -> Result<(ty::Binder<I, AsyncCallableRelevantTypes<I>>, Vec<I::Predicate>), NoSolution> {
     let sig = bound_sig.skip_binder();
-    let future_trait_def_id = cx.require_lang_item(TraitSolverLangItem::Future);
+    let future_trait_def_id = cx.require_trait_lang_item(SolverTraitLangItem::Future);
     // `FnDef` and `FnPtr` only implement `AsyncFn*` when their
     // return type implements `Future`.
     let nested = vec![
         bound_sig.rebind(ty::TraitRef::new(cx, future_trait_def_id, [sig.output()])).upcast(cx),
     ];
-    let future_output_def_id = cx.require_lang_item(TraitSolverLangItem::FutureOutput);
+    let future_output_def_id = cx.require_lang_item(SolverLangItem::FutureOutput);
     let future_output_ty = Ty::new_projection(cx, future_output_def_id, [sig.output()]);
     Ok((
         bound_sig.rebind(AsyncCallableRelevantTypes {
@@ -633,7 +633,7 @@ fn coroutine_closure_to_ambiguous_coroutine<I: Interner>(
     args: ty::CoroutineClosureArgs<I>,
     sig: ty::CoroutineClosureSignature<I>,
 ) -> I::Ty {
-    let upvars_projection_def_id = cx.require_lang_item(TraitSolverLangItem::AsyncFnKindUpvars);
+    let upvars_projection_def_id = cx.require_lang_item(SolverLangItem::AsyncFnKindUpvars);
     let tupled_upvars_ty = Ty::new_projection(
         cx,
         upvars_projection_def_id,
@@ -732,7 +732,7 @@ pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
     cx: I,
     self_ty: I::Ty,
 ) -> Result<Vec<ty::TraitRef<I>>, NoSolution> {
-    let destruct_def_id = cx.require_lang_item(TraitSolverLangItem::Destruct);
+    let destruct_def_id = cx.require_trait_lang_item(SolverTraitLangItem::Destruct);
 
     match self_ty.kind() {
         // `ManuallyDrop` is trivially `[const] Destruct` as we do not run any drop glue on it.
@@ -751,7 +751,7 @@ pub(in crate::solve) fn const_conditions_for_destruct<I: Interner>(
                 Some(AdtDestructorKind::NotConst) => return Err(NoSolution),
                 // `Drop` impl exists, and it's const. Require `Ty: [const] Drop` to hold.
                 Some(AdtDestructorKind::Const) => {
-                    let drop_def_id = cx.require_lang_item(TraitSolverLangItem::Drop);
+                    let drop_def_id = cx.require_trait_lang_item(SolverTraitLangItem::Drop);
                     let drop_trait_ref = ty::TraitRef::new(cx, drop_def_id, [self_ty]);
                     const_conditions.push(drop_trait_ref);
                 }
@@ -869,7 +869,7 @@ where
 
     // FIXME(associated_const_equality): Also add associated consts to
     // the requirements here.
-    for associated_type_def_id in cx.associated_type_def_ids(trait_ref.def_id) {
+    for associated_type_def_id in cx.associated_type_def_ids(trait_ref.def_id.into()) {
         // associated types that require `Self: Sized` do not show up in the built-in
         // implementation of `Trait for dyn Trait`, and can be dropped here.
         if cx.generics_require_sized_self(associated_type_def_id) {
diff --git a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
index b7ae9994c62..229345065b1 100644
--- a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs
@@ -3,7 +3,7 @@
 
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::SolverTraitLangItem;
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::solve::inspect::ProbeKind;
 use rustc_type_ir::{self as ty, Interner, TypingMode, elaborate};
@@ -33,7 +33,7 @@ where
         self.with_replaced_self_ty(cx, self_ty)
     }
 
-    fn trait_def_id(self, _: I) -> I::DefId {
+    fn trait_def_id(self, _: I) -> I::TraitId {
         self.def_id()
     }
 
@@ -237,7 +237,7 @@ where
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
         let output_is_sized_pred = inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [output])
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
         });
         let requirements = cx
             .const_conditions(def_id)
diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs
index c2745c878dc..710b59f662a 100644
--- a/compiler/rustc_next_trait_solver/src/solve/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/mod.rs
@@ -130,7 +130,7 @@ where
         }
     }
 
-    fn compute_dyn_compatible_goal(&mut self, trait_def_id: I::DefId) -> QueryResult<I> {
+    fn compute_dyn_compatible_goal(&mut self, trait_def_id: I::TraitId) -> QueryResult<I> {
         if self.cx().trait_is_dyn_compatible(trait_def_id) {
             self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
         } else {
diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
index 93434dce79f..cfdf2007391 100644
--- a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs
@@ -5,7 +5,7 @@ mod opaque_types;
 
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::{SolverLangItem, SolverTraitLangItem};
 use rustc_type_ir::solve::SizedTraitKind;
 use rustc_type_ir::{self as ty, Interner, NormalizesTo, PredicateKind, Upcast as _};
 use tracing::instrument;
@@ -103,7 +103,7 @@ where
         self.with_replaced_self_ty(cx, self_ty)
     }
 
-    fn trait_def_id(self, cx: I) -> I::DefId {
+    fn trait_def_id(self, cx: I) -> I::TraitId {
         self.trait_def_id(cx)
     }
 
@@ -456,7 +456,7 @@ where
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
         let output_is_sized_pred = tupled_inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [output])
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
         });
 
         let pred = tupled_inputs_and_output
@@ -503,7 +503,11 @@ where
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
         let output_is_sized_pred = tupled_inputs_and_output_and_coroutine.map_bound(
             |AsyncCallableRelevantTypes { output_coroutine_ty: output_ty, .. }| {
-                ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [output_ty])
+                ty::TraitRef::new(
+                    cx,
+                    cx.require_trait_lang_item(SolverTraitLangItem::Sized),
+                    [output_ty],
+                )
             },
         );
 
@@ -515,7 +519,7 @@ where
                      coroutine_return_ty,
                  }| {
                     let (projection_term, term) = if cx
-                        .is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::CallOnceFuture)
+                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::CallOnceFuture)
                     {
                         (
                             ty::AliasTerm::new(
@@ -526,7 +530,7 @@ where
                             output_coroutine_ty.into(),
                         )
                     } else if cx
-                        .is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::CallRefFuture)
+                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::CallRefFuture)
                     {
                         (
                             ty::AliasTerm::new(
@@ -540,10 +544,9 @@ where
                             ),
                             output_coroutine_ty.into(),
                         )
-                    } else if cx.is_lang_item(
-                        goal.predicate.def_id(),
-                        TraitSolverLangItem::AsyncFnOnceOutput,
-                    ) {
+                    } else if cx
+                        .is_lang_item(goal.predicate.def_id(), SolverLangItem::AsyncFnOnceOutput)
+                    {
                         (
                             ty::AliasTerm::new(
                                 cx,
@@ -637,7 +640,7 @@ where
         goal: Goal<I, Self>,
     ) -> Result<Candidate<I>, NoSolution> {
         let cx = ecx.cx();
-        let metadata_def_id = cx.require_lang_item(TraitSolverLangItem::Metadata);
+        let metadata_def_id = cx.require_lang_item(SolverLangItem::Metadata);
         assert_eq!(metadata_def_id, goal.predicate.def_id());
         let metadata_ty = match goal.predicate.self_ty().kind() {
             ty::Bool
@@ -664,7 +667,7 @@ where
             ty::Str | ty::Slice(_) => Ty::new_usize(cx),
 
             ty::Dynamic(_, _, ty::Dyn) => {
-                let dyn_metadata = cx.require_lang_item(TraitSolverLangItem::DynMetadata);
+                let dyn_metadata = cx.require_lang_item(SolverLangItem::DynMetadata);
                 cx.type_of(dyn_metadata)
                     .instantiate(cx, &[I::GenericArg::from(goal.predicate.self_ty())])
             }
@@ -678,7 +681,7 @@ where
                     ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
                         let sized_predicate = ty::TraitRef::new(
                             cx,
-                            cx.require_lang_item(TraitSolverLangItem::Sized),
+                            cx.require_trait_lang_item(SolverTraitLangItem::Sized),
                             [I::GenericArg::from(goal.predicate.self_ty())],
                         );
                         ecx.add_goal(GoalSource::Misc, goal.with(cx, sized_predicate));
@@ -821,10 +824,10 @@ where
             // coroutine yield ty `Poll<Option<I>>`.
             let wrapped_expected_ty = Ty::new_adt(
                 cx,
-                cx.adt_def(cx.require_lang_item(TraitSolverLangItem::Poll)),
+                cx.adt_def(cx.require_lang_item(SolverLangItem::Poll)),
                 cx.mk_args(&[Ty::new_adt(
                     cx,
-                    cx.adt_def(cx.require_lang_item(TraitSolverLangItem::Option)),
+                    cx.adt_def(cx.require_lang_item(SolverLangItem::Option)),
                     cx.mk_args(&[expected_ty.into()]),
                 )
                 .into()]),
@@ -853,10 +856,9 @@ where
 
         let coroutine = args.as_coroutine();
 
-        let term = if cx.is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::CoroutineReturn)
-        {
+        let term = if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::CoroutineReturn) {
             coroutine.return_ty().into()
-        } else if cx.is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::CoroutineYield) {
+        } else if cx.is_lang_item(goal.predicate.def_id(), SolverLangItem::CoroutineYield) {
             coroutine.yield_ty().into()
         } else {
             panic!("unexpected associated item `{:?}` for `{self_ty:?}`", goal.predicate.def_id())
@@ -983,13 +985,13 @@ where
         target_container_def_id: I::DefId,
     ) -> Result<I::GenericArgs, NoSolution> {
         let cx = self.cx();
-        Ok(if target_container_def_id == impl_trait_ref.def_id {
+        Ok(if target_container_def_id == impl_trait_ref.def_id.into() {
             // Default value from the trait definition. No need to rebase.
             goal.predicate.alias.args
         } else if target_container_def_id == impl_def_id {
             // Same impl, no need to fully translate, just a rebase from
             // the trait is sufficient.
-            goal.predicate.alias.args.rebase_onto(cx, impl_trait_ref.def_id, impl_args)
+            goal.predicate.alias.args.rebase_onto(cx, impl_trait_ref.def_id.into(), impl_args)
         } else {
             let target_args = self.fresh_args_for_item(target_container_def_id);
             let target_trait_ref =
@@ -1004,7 +1006,7 @@ where
                     .iter_instantiated(cx, target_args)
                     .map(|pred| goal.with(cx, pred)),
             );
-            goal.predicate.alias.args.rebase_onto(cx, impl_trait_ref.def_id, target_args)
+            goal.predicate.alias.args.rebase_onto(cx, impl_trait_ref.def_id.into(), target_args)
         })
     }
 }
diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
index 891ecab041a..cdcfebf2909 100644
--- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs
@@ -3,7 +3,7 @@
 use rustc_type_ir::data_structures::IndexSet;
 use rustc_type_ir::fast_reject::DeepRejectCtxt;
 use rustc_type_ir::inherent::*;
-use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::lang_items::SolverTraitLangItem;
 use rustc_type_ir::solve::{CanonicalResponse, SizedTraitKind};
 use rustc_type_ir::{
     self as ty, Interner, Movability, PredicatePolarity, TraitPredicate, TraitRef,
@@ -39,7 +39,7 @@ where
         self.with_replaced_self_ty(cx, self_ty)
     }
 
-    fn trait_def_id(self, _: I) -> I::DefId {
+    fn trait_def_id(self, _: I) -> I::TraitId {
         self.def_id()
     }
 
@@ -131,8 +131,8 @@ where
     ) -> Result<(), NoSolution> {
         fn trait_def_id_matches<I: Interner>(
             cx: I,
-            clause_def_id: I::DefId,
-            goal_def_id: I::DefId,
+            clause_def_id: I::TraitId,
+            goal_def_id: I::TraitId,
             polarity: PredicatePolarity,
         ) -> bool {
             clause_def_id == goal_def_id
@@ -141,8 +141,8 @@ where
             //
             // `PointeeSized` bounds are syntactic sugar for a lack of bounds so don't need this.
                 || (polarity == PredicatePolarity::Positive
-                    && cx.is_lang_item(clause_def_id, TraitSolverLangItem::Sized)
-                    && cx.is_lang_item(goal_def_id, TraitSolverLangItem::MetaSized))
+                    && cx.is_trait_lang_item(clause_def_id, SolverTraitLangItem::Sized)
+                    && cx.is_trait_lang_item(goal_def_id, SolverTraitLangItem::MetaSized))
         }
 
         if let Some(trait_clause) = assumption.as_trait_clause()
@@ -177,8 +177,8 @@ where
         // are syntactic sugar for a lack of bounds so don't need this.
         // We don't need to check polarity, `fast_reject_assumption` already rejected non-`Positive`
         // polarity `Sized` assumptions as matching non-`Positive` `MetaSized` goals.
-        if ecx.cx().is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::MetaSized)
-            && ecx.cx().is_lang_item(trait_clause.def_id(), TraitSolverLangItem::Sized)
+        if ecx.cx().is_trait_lang_item(goal.predicate.def_id(), SolverTraitLangItem::MetaSized)
+            && ecx.cx().is_trait_lang_item(trait_clause.def_id(), SolverTraitLangItem::Sized)
         {
             let meta_sized_clause =
                 trait_predicate_with_def_id(ecx.cx(), trait_clause, goal.predicate.def_id());
@@ -263,7 +263,7 @@ where
 
         ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
             let nested_obligations = cx
-                .predicates_of(goal.predicate.def_id())
+                .predicates_of(goal.predicate.def_id().into())
                 .iter_instantiated(cx, goal.predicate.trait_ref.args)
                 .map(|p| goal.with(cx, p));
             // While you could think of trait aliases to have a single builtin impl
@@ -372,7 +372,7 @@ where
         // A built-in `Fn` impl only holds if the output is sized.
         // (FIXME: technically we only need to check this if the type is a fn ptr...)
         let output_is_sized_pred = tupled_inputs_and_output.map_bound(|(_, output)| {
-            ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [output])
+            ty::TraitRef::new(cx, cx.require_trait_lang_item(SolverTraitLangItem::Sized), [output])
         });
 
         let pred = tupled_inputs_and_output
@@ -414,7 +414,7 @@ where
             |AsyncCallableRelevantTypes { output_coroutine_ty, .. }| {
                 ty::TraitRef::new(
                     cx,
-                    cx.require_lang_item(TraitSolverLangItem::Sized),
+                    cx.require_trait_lang_item(SolverTraitLangItem::Sized),
                     [output_coroutine_ty],
                 )
             },
@@ -757,7 +757,7 @@ where
                             cx,
                             ty::TraitRef::new(
                                 cx,
-                                cx.require_lang_item(TraitSolverLangItem::Copy),
+                                cx.require_trait_lang_item(SolverTraitLangItem::Copy),
                                 [ty],
                             ),
                         ),
@@ -857,7 +857,7 @@ where
 fn trait_predicate_with_def_id<I: Interner>(
     cx: I,
     clause: ty::Binder<I, ty::TraitPredicate<I>>,
-    did: I::DefId,
+    did: I::TraitId,
 ) -> I::Clause {
     clause
         .map_bound(|c| TraitPredicate {
@@ -956,7 +956,11 @@ where
                 GoalSource::ImplWhereBound,
                 goal.with(
                     cx,
-                    ty::TraitRef::new(cx, cx.require_lang_item(TraitSolverLangItem::Sized), [a_ty]),
+                    ty::TraitRef::new(
+                        cx,
+                        cx.require_trait_lang_item(SolverTraitLangItem::Sized),
+                        [a_ty],
+                    ),
                 ),
             );
 
@@ -981,7 +985,7 @@ where
         // We may upcast to auto traits that are either explicitly listed in
         // the object type's bounds, or implied by the principal trait ref's
         // supertraits.
-        let a_auto_traits: IndexSet<I::DefId> = a_data
+        let a_auto_traits: IndexSet<I::TraitId> = a_data
             .auto_traits()
             .into_iter()
             .chain(a_data.principal_def_id().into_iter().flat_map(|principal_def_id| {
@@ -1143,7 +1147,7 @@ where
                 cx,
                 ty::TraitRef::new(
                     cx,
-                    cx.require_lang_item(TraitSolverLangItem::Unsize),
+                    cx.require_trait_lang_item(SolverTraitLangItem::Unsize),
                     [a_tail_ty, b_tail_ty],
                 ),
             ),
@@ -1208,7 +1212,9 @@ where
             // takes precedence over the structural auto trait candidate being
             // assembled.
             ty::Coroutine(def_id, _)
-                if self.cx().is_lang_item(goal.predicate.def_id(), TraitSolverLangItem::Unpin) =>
+                if self
+                    .cx()
+                    .is_trait_lang_item(goal.predicate.def_id(), SolverTraitLangItem::Unpin) =>
             {
                 match self.cx().coroutine_movability(def_id) {
                     Movability::Static => Some(Err(NoSolution)),
diff --git a/compiler/rustc_type_ir/src/elaborate.rs b/compiler/rustc_type_ir/src/elaborate.rs
index dc15cc3eb55..2f7c78d497a 100644
--- a/compiler/rustc_type_ir/src/elaborate.rs
+++ b/compiler/rustc_type_ir/src/elaborate.rs
@@ -4,7 +4,7 @@ use smallvec::smallvec;
 
 use crate::data_structures::HashSet;
 use crate::inherent::*;
-use crate::lang_items::TraitSolverLangItem;
+use crate::lang_items::SolverTraitLangItem;
 use crate::outlives::{Component, push_outlives_components};
 use crate::{self as ty, Interner, Upcast as _};
 
@@ -140,7 +140,7 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
         // is present.
         if self.elaborate_sized == ElaborateSized::No
             && let Some(did) = clause.as_trait_clause().map(|c| c.def_id())
-            && self.cx.is_lang_item(did, TraitSolverLangItem::Sized)
+            && self.cx.is_trait_lang_item(did, SolverTraitLangItem::Sized)
         {
             return;
         }
@@ -166,7 +166,7 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
                 // Get predicates implied by the trait, or only super predicates if we only care about self predicates.
                 match self.mode {
                     Filter::All => self.extend_deduped(
-                        cx.explicit_implied_predicates_of(data.def_id())
+                        cx.explicit_implied_predicates_of(data.def_id().into())
                             .iter_identity()
                             .enumerate()
                             .map(map_to_child_clause),
@@ -181,13 +181,15 @@ impl<I: Interner, O: Elaboratable<I>> Elaborator<I, O> {
             }
             // `T: [const] Trait` implies `T: [const] Supertrait`.
             ty::ClauseKind::HostEffect(data) => self.extend_deduped(
-                cx.explicit_implied_const_bounds(data.def_id()).iter_identity().map(|trait_ref| {
-                    elaboratable.child(
-                        trait_ref
-                            .to_host_effect_clause(cx, data.constness)
-                            .instantiate_supertrait(cx, bound_clause.rebind(data.trait_ref)),
-                    )
-                }),
+                cx.explicit_implied_const_bounds(data.def_id().into()).iter_identity().map(
+                    |trait_ref| {
+                        elaboratable.child(
+                            trait_ref
+                                .to_host_effect_clause(cx, data.constness)
+                                .instantiate_supertrait(cx, bound_clause.rebind(data.trait_ref)),
+                        )
+                    },
+                ),
             ),
             ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_max, r_min)) => {
                 // We know that `T: 'a` for some type `T`. We can
@@ -312,8 +314,8 @@ impl<I: Interner, O: Elaboratable<I>> Iterator for Elaborator<I, O> {
 /// and to make size estimates for vtable layout computation.
 pub fn supertrait_def_ids<I: Interner>(
     cx: I,
-    trait_def_id: I::DefId,
-) -> impl Iterator<Item = I::DefId> {
+    trait_def_id: I::TraitId,
+) -> impl Iterator<Item = I::TraitId> {
     let mut set = HashSet::default();
     let mut stack = vec![trait_def_id];
 
diff --git a/compiler/rustc_type_ir/src/error.rs b/compiler/rustc_type_ir/src/error.rs
index e8840bcfaca..eb5b6b4a1b4 100644
--- a/compiler/rustc_type_ir/src/error.rs
+++ b/compiler/rustc_type_ir/src/error.rs
@@ -38,7 +38,7 @@ pub enum TypeError<I: Interner> {
 
     Sorts(ExpectedFound<I::Ty>),
     ArgumentSorts(ExpectedFound<I::Ty>, usize),
-    Traits(ExpectedFound<I::DefId>),
+    Traits(ExpectedFound<I::TraitId>),
     VariadicMismatch(ExpectedFound<bool>),
 
     /// Instantiating a type variable with the given type would have
diff --git a/compiler/rustc_type_ir/src/fast_reject.rs b/compiler/rustc_type_ir/src/fast_reject.rs
index d88c88fc6f3..5a05630e1bd 100644
--- a/compiler/rustc_type_ir/src/fast_reject.rs
+++ b/compiler/rustc_type_ir/src/fast_reject.rs
@@ -130,7 +130,7 @@ pub fn simplify_type<I: Interner>(
         ty::RawPtr(_, mutbl) => Some(SimplifiedType::Ptr(mutbl)),
         ty::Dynamic(trait_info, ..) => match trait_info.principal_def_id() {
             Some(principal_def_id) if !cx.trait_is_auto(principal_def_id) => {
-                Some(SimplifiedType::Trait(principal_def_id))
+                Some(SimplifiedType::Trait(principal_def_id.into()))
             }
             _ => Some(SimplifiedType::MarkerTraitObject),
         },
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 569570b5783..64063b1a365 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -649,11 +649,11 @@ pub trait DefId<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
 pub trait BoundExistentialPredicates<I: Interner>:
     Copy + Debug + Hash + Eq + Relate<I> + SliceLike<Item = ty::Binder<I, ty::ExistentialPredicate<I>>>
 {
-    fn principal_def_id(self) -> Option<I::DefId>;
+    fn principal_def_id(self) -> Option<I::TraitId>;
 
     fn principal(self) -> Option<ty::Binder<I, ty::ExistentialTraitRef<I>>>;
 
-    fn auto_traits(self) -> impl IntoIterator<Item = I::DefId>;
+    fn auto_traits(self) -> impl IntoIterator<Item = I::TraitId>;
 
     fn projection_bounds(
         self,
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index e3231244577..21fe7879b29 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -8,7 +8,7 @@ use rustc_index::bit_set::DenseBitSet;
 use crate::fold::TypeFoldable;
 use crate::inherent::*;
 use crate::ir_print::IrPrint;
-use crate::lang_items::TraitSolverLangItem;
+use crate::lang_items::{SolverLangItem, SolverTraitLangItem};
 use crate::relate::Relate;
 use crate::solve::{CanonicalInput, ExternalConstraintsData, PredefinedOpaquesData, QueryResult};
 use crate::visit::{Flags, TypeVisitable};
@@ -38,6 +38,13 @@ pub trait Interner:
 
     type DefId: DefId<Self>;
     type LocalDefId: Copy + Debug + Hash + Eq + Into<Self::DefId> + TypeFoldable<Self>;
+    /// A `DefId` of a trait.
+    ///
+    /// In rustc this is just a `DefId`, but rust-analyzer uses different types for different items.
+    ///
+    /// Note: The `TryFrom<DefId>` always succeeds (in rustc), so don't use it to check if some `DefId`
+    /// is a trait!
+    type TraitId: DefId<Self> + Into<Self::DefId> + TryFrom<Self::DefId, Error: std::fmt::Debug>;
     type Span: Span<Self>;
 
     type GenericArgs: GenericArgs<Self>;
@@ -271,7 +278,7 @@ pub trait Interner:
 
     fn explicit_super_predicates_of(
         self,
-        def_id: Self::DefId,
+        def_id: Self::TraitId,
     ) -> ty::EarlyBinder<Self, impl IntoIterator<Item = (Self::Clause, Self::Span)>>;
 
     fn explicit_implied_predicates_of(
@@ -302,19 +309,25 @@ pub trait Interner:
 
     fn has_target_features(self, def_id: Self::DefId) -> bool;
 
-    fn require_lang_item(self, lang_item: TraitSolverLangItem) -> Self::DefId;
+    fn require_lang_item(self, lang_item: SolverLangItem) -> Self::DefId;
+
+    fn require_trait_lang_item(self, lang_item: SolverTraitLangItem) -> Self::TraitId;
+
+    fn is_lang_item(self, def_id: Self::DefId, lang_item: SolverLangItem) -> bool;
+
+    fn is_trait_lang_item(self, def_id: Self::TraitId, lang_item: SolverTraitLangItem) -> bool;
 
-    fn is_lang_item(self, def_id: Self::DefId, lang_item: TraitSolverLangItem) -> bool;
+    fn is_default_trait(self, def_id: Self::TraitId) -> bool;
 
-    fn is_default_trait(self, def_id: Self::DefId) -> bool;
+    fn as_lang_item(self, def_id: Self::DefId) -> Option<SolverLangItem>;
 
-    fn as_lang_item(self, def_id: Self::DefId) -> Option<TraitSolverLangItem>;
+    fn as_trait_lang_item(self, def_id: Self::TraitId) -> Option<SolverTraitLangItem>;
 
     fn associated_type_def_ids(self, def_id: Self::DefId) -> impl IntoIterator<Item = Self::DefId>;
 
     fn for_each_relevant_impl(
         self,
-        trait_def_id: Self::DefId,
+        trait_def_id: Self::TraitId,
         self_ty: Self::Ty,
         f: impl FnMut(Self::DefId),
     );
@@ -329,20 +342,20 @@ pub trait Interner:
 
     fn impl_polarity(self, impl_def_id: Self::DefId) -> ty::ImplPolarity;
 
-    fn trait_is_auto(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_auto(self, trait_def_id: Self::TraitId) -> bool;
 
-    fn trait_is_coinductive(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_coinductive(self, trait_def_id: Self::TraitId) -> bool;
 
-    fn trait_is_alias(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_alias(self, trait_def_id: Self::TraitId) -> bool;
 
-    fn trait_is_dyn_compatible(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_dyn_compatible(self, trait_def_id: Self::TraitId) -> bool;
 
-    fn trait_is_fundamental(self, def_id: Self::DefId) -> bool;
+    fn trait_is_fundamental(self, def_id: Self::TraitId) -> bool;
 
-    fn trait_may_be_implemented_via_object(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_may_be_implemented_via_object(self, trait_def_id: Self::TraitId) -> bool;
 
     /// Returns `true` if this is an `unsafe trait`.
-    fn trait_is_unsafe(self, trait_def_id: Self::DefId) -> bool;
+    fn trait_is_unsafe(self, trait_def_id: Self::TraitId) -> bool;
 
     fn is_impl_trait_in_trait(self, def_id: Self::DefId) -> bool;
 
diff --git a/compiler/rustc_type_ir/src/lang_items.rs b/compiler/rustc_type_ir/src/lang_items.rs
index f9994448e28..31f8f5be588 100644
--- a/compiler/rustc_type_ir/src/lang_items.rs
+++ b/compiler/rustc_type_ir/src/lang_items.rs
@@ -1,40 +1,46 @@
 /// Lang items used by the new trait solver. This can be mapped to whatever internal
 /// representation of `LangItem`s used in the underlying compiler implementation.
-pub enum TraitSolverLangItem {
+pub enum SolverLangItem {
+    // tidy-alphabetical-start
+    AsyncFnKindUpvars,
+    AsyncFnOnceOutput,
+    CallOnceFuture,
+    CallRefFuture,
+    CoroutineReturn,
+    CoroutineYield,
+    DynMetadata,
+    FutureOutput,
+    Metadata,
+    Option,
+    Poll,
+    // tidy-alphabetical-end
+}
+
+pub enum SolverTraitLangItem {
     // tidy-alphabetical-start
     AsyncFn,
     AsyncFnKindHelper,
-    AsyncFnKindUpvars,
     AsyncFnMut,
     AsyncFnOnce,
     AsyncFnOnceOutput,
     AsyncIterator,
     BikeshedGuaranteedNoDrop,
-    CallOnceFuture,
-    CallRefFuture,
     Clone,
     Copy,
     Coroutine,
-    CoroutineReturn,
-    CoroutineYield,
     Destruct,
     DiscriminantKind,
     Drop,
-    DynMetadata,
     Fn,
     FnMut,
     FnOnce,
     FnPtrTrait,
     FusedIterator,
     Future,
-    FutureOutput,
     Iterator,
     MetaSized,
-    Metadata,
-    Option,
     PointeeSized,
     PointeeTrait,
-    Poll,
     Sized,
     TransmuteTrait,
     Tuple,
diff --git a/compiler/rustc_type_ir/src/predicate.rs b/compiler/rustc_type_ir/src/predicate.rs
index b53eb099c4b..a3300b88c43 100644
--- a/compiler/rustc_type_ir/src/predicate.rs
+++ b/compiler/rustc_type_ir/src/predicate.rs
@@ -58,7 +58,7 @@ where
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
 )]
 pub struct TraitRef<I: Interner> {
-    pub def_id: I::DefId,
+    pub def_id: I::TraitId,
     pub args: I::GenericArgs,
     /// This field exists to prevent the creation of `TraitRef` without
     /// calling [`TraitRef::new_from_args`].
@@ -68,32 +68,32 @@ pub struct TraitRef<I: Interner> {
 impl<I: Interner> Eq for TraitRef<I> {}
 
 impl<I: Interner> TraitRef<I> {
-    pub fn new_from_args(interner: I, trait_def_id: I::DefId, args: I::GenericArgs) -> Self {
-        interner.debug_assert_args_compatible(trait_def_id, args);
+    pub fn new_from_args(interner: I, trait_def_id: I::TraitId, args: I::GenericArgs) -> Self {
+        interner.debug_assert_args_compatible(trait_def_id.into(), args);
         Self { def_id: trait_def_id, args, _use_trait_ref_new_instead: () }
     }
 
     pub fn new(
         interner: I,
-        trait_def_id: I::DefId,
+        trait_def_id: I::TraitId,
         args: impl IntoIterator<Item: Into<I::GenericArg>>,
     ) -> Self {
         let args = interner.mk_args_from_iter(args.into_iter().map(Into::into));
         Self::new_from_args(interner, trait_def_id, args)
     }
 
-    pub fn from_assoc(interner: I, trait_id: I::DefId, args: I::GenericArgs) -> TraitRef<I> {
-        let generics = interner.generics_of(trait_id);
+    pub fn from_assoc(interner: I, trait_id: I::TraitId, args: I::GenericArgs) -> TraitRef<I> {
+        let generics = interner.generics_of(trait_id.into());
         TraitRef::new(interner, trait_id, args.iter().take(generics.count()))
     }
 
     /// Returns a `TraitRef` of the form `P0: Foo<P1..Pn>` where `Pi`
     /// are the parameters defined on trait.
-    pub fn identity(interner: I, def_id: I::DefId) -> TraitRef<I> {
+    pub fn identity(interner: I, def_id: I::TraitId) -> TraitRef<I> {
         TraitRef::new_from_args(
             interner,
             def_id,
-            I::GenericArgs::identity_for_item(interner, def_id),
+            I::GenericArgs::identity_for_item(interner, def_id.into()),
         )
     }
 
@@ -116,7 +116,7 @@ impl<I: Interner> ty::Binder<I, TraitRef<I>> {
         self.map_bound_ref(|tr| tr.self_ty())
     }
 
-    pub fn def_id(&self) -> I::DefId {
+    pub fn def_id(&self) -> I::TraitId {
         self.skip_binder().def_id
     }
 
@@ -155,7 +155,7 @@ impl<I: Interner> TraitPredicate<I> {
         }
     }
 
-    pub fn def_id(self) -> I::DefId {
+    pub fn def_id(self) -> I::TraitId {
         self.trait_ref.def_id
     }
 
@@ -165,7 +165,7 @@ impl<I: Interner> TraitPredicate<I> {
 }
 
 impl<I: Interner> ty::Binder<I, TraitPredicate<I>> {
-    pub fn def_id(self) -> I::DefId {
+    pub fn def_id(self) -> I::TraitId {
         // Ok to skip binder since trait `DefId` does not care about regions.
         self.skip_binder().def_id()
     }
@@ -285,7 +285,7 @@ pub enum ExistentialPredicate<I: Interner> {
     /// E.g., `Iterator::Item = T`.
     Projection(ExistentialProjection<I>),
     /// E.g., `Send`.
-    AutoTrait(I::DefId),
+    AutoTrait(I::TraitId),
 }
 
 impl<I: Interner> Eq for ExistentialPredicate<I> {}
@@ -301,13 +301,14 @@ impl<I: Interner> ty::Binder<I, ExistentialPredicate<I>> {
                 self.rebind(p.with_self_ty(cx, self_ty)).upcast(cx)
             }
             ExistentialPredicate::AutoTrait(did) => {
-                let generics = cx.generics_of(did);
+                let generics = cx.generics_of(did.into());
                 let trait_ref = if generics.count() == 1 {
                     ty::TraitRef::new(cx, did, [self_ty])
                 } else {
                     // If this is an ill-formed auto trait, then synthesize
                     // new error args for the missing generics.
-                    let err_args = GenericArgs::extend_with_error(cx, did, &[self_ty.into()]);
+                    let err_args =
+                        GenericArgs::extend_with_error(cx, did.into(), &[self_ty.into()]);
                     ty::TraitRef::new_from_args(cx, did, err_args)
                 };
                 self.rebind(trait_ref).upcast(cx)
@@ -330,7 +331,7 @@ impl<I: Interner> ty::Binder<I, ExistentialPredicate<I>> {
     derive(Decodable_NoContext, Encodable_NoContext, HashStable_NoContext)
 )]
 pub struct ExistentialTraitRef<I: Interner> {
-    pub def_id: I::DefId,
+    pub def_id: I::TraitId,
     pub args: I::GenericArgs,
     /// This field exists to prevent the creation of `ExistentialTraitRef` without
     /// calling [`ExistentialTraitRef::new_from_args`].
@@ -340,14 +341,14 @@ pub struct ExistentialTraitRef<I: Interner> {
 impl<I: Interner> Eq for ExistentialTraitRef<I> {}
 
 impl<I: Interner> ExistentialTraitRef<I> {
-    pub fn new_from_args(interner: I, trait_def_id: I::DefId, args: I::GenericArgs) -> Self {
-        interner.debug_assert_existential_args_compatible(trait_def_id, args);
+    pub fn new_from_args(interner: I, trait_def_id: I::TraitId, args: I::GenericArgs) -> Self {
+        interner.debug_assert_existential_args_compatible(trait_def_id.into(), args);
         Self { def_id: trait_def_id, args, _use_existential_trait_ref_new_instead: () }
     }
 
     pub fn new(
         interner: I,
-        trait_def_id: I::DefId,
+        trait_def_id: I::TraitId,
         args: impl IntoIterator<Item: Into<I::GenericArg>>,
     ) -> Self {
         let args = interner.mk_args_from_iter(args.into_iter().map(Into::into));
@@ -378,7 +379,7 @@ impl<I: Interner> ExistentialTraitRef<I> {
 }
 
 impl<I: Interner> ty::Binder<I, ExistentialTraitRef<I>> {
-    pub fn def_id(&self) -> I::DefId {
+    pub fn def_id(&self) -> I::TraitId {
         self.skip_binder().def_id
     }
 
@@ -439,7 +440,7 @@ impl<I: Interner> ExistentialProjection<I> {
         let def_id = interner.parent(self.def_id);
         let args_count = interner.generics_of(def_id).count() - 1;
         let args = interner.mk_args(&self.args.as_slice()[..args_count]);
-        ExistentialTraitRef { def_id, args, _use_existential_trait_ref_new_instead: () }
+        ExistentialTraitRef::new_from_args(interner, def_id.try_into().unwrap(), args)
     }
 
     pub fn with_self_ty(&self, interner: I, self_ty: I::Ty) -> ProjectionPredicate<I> {
@@ -675,7 +676,7 @@ impl<I: Interner> AliasTerm<I> {
         )
     }
 
-    pub fn trait_def_id(self, interner: I) -> I::DefId {
+    pub fn trait_def_id(self, interner: I) -> I::TraitId {
         assert!(
             matches!(
                 self.kind(interner),
@@ -683,7 +684,7 @@ impl<I: Interner> AliasTerm<I> {
             ),
             "expected a projection"
         );
-        interner.parent(self.def_id)
+        interner.parent(self.def_id).try_into().unwrap()
     }
 
     /// Extracts the underlying trait reference and own args from this projection.
@@ -787,7 +788,7 @@ impl<I: Interner> ProjectionPredicate<I> {
         }
     }
 
-    pub fn trait_def_id(self, interner: I) -> I::DefId {
+    pub fn trait_def_id(self, interner: I) -> I::TraitId {
         self.projection_term.trait_def_id(interner)
     }
 
@@ -799,7 +800,7 @@ impl<I: Interner> ProjectionPredicate<I> {
 impl<I: Interner> ty::Binder<I, ProjectionPredicate<I>> {
     /// Returns the `DefId` of the trait of the associated item being projected.
     #[inline]
-    pub fn trait_def_id(&self, cx: I) -> I::DefId {
+    pub fn trait_def_id(&self, cx: I) -> I::TraitId {
         self.skip_binder().projection_term.trait_def_id(cx)
     }
 
@@ -847,7 +848,7 @@ impl<I: Interner> NormalizesTo<I> {
         Self { alias: self.alias.with_replaced_self_ty(interner, self_ty), ..self }
     }
 
-    pub fn trait_def_id(self, interner: I) -> I::DefId {
+    pub fn trait_def_id(self, interner: I) -> I::TraitId {
         self.alias.trait_def_id(interner)
     }
 
@@ -884,13 +885,13 @@ impl<I: Interner> HostEffectPredicate<I> {
         Self { trait_ref: self.trait_ref.with_replaced_self_ty(interner, self_ty), ..self }
     }
 
-    pub fn def_id(self) -> I::DefId {
+    pub fn def_id(self) -> I::TraitId {
         self.trait_ref.def_id
     }
 }
 
 impl<I: Interner> ty::Binder<I, HostEffectPredicate<I>> {
-    pub fn def_id(self) -> I::DefId {
+    pub fn def_id(self) -> I::TraitId {
         // Ok to skip binder since trait `DefId` does not care about regions.
         self.skip_binder().def_id()
     }
diff --git a/compiler/rustc_type_ir/src/predicate_kind.rs b/compiler/rustc_type_ir/src/predicate_kind.rs
index ff92a0070cc..785d41929cf 100644
--- a/compiler/rustc_type_ir/src/predicate_kind.rs
+++ b/compiler/rustc_type_ir/src/predicate_kind.rs
@@ -68,7 +68,7 @@ pub enum PredicateKind<I: Interner> {
     Clause(ClauseKind<I>),
 
     /// Trait must be dyn-compatible.
-    DynCompatible(I::DefId),
+    DynCompatible(I::TraitId),
 
     /// `T1 <: T2`
     ///
diff --git a/compiler/rustc_type_ir/src/solve/mod.rs b/compiler/rustc_type_ir/src/solve/mod.rs
index 1497236039f..b6d362d77c4 100644
--- a/compiler/rustc_type_ir/src/solve/mod.rs
+++ b/compiler/rustc_type_ir/src/solve/mod.rs
@@ -7,7 +7,7 @@ use derive_where::derive_where;
 use rustc_macros::{Decodable_NoContext, Encodable_NoContext, HashStable_NoContext};
 use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Generic};
 
-use crate::lang_items::TraitSolverLangItem;
+use crate::lang_items::SolverTraitLangItem;
 use crate::search_graph::PathKind;
 use crate::{self as ty, Canonical, CanonicalVarValues, Interner, Upcast};
 
@@ -386,10 +386,10 @@ pub enum SizedTraitKind {
 
 impl SizedTraitKind {
     /// Returns `DefId` of corresponding language item.
-    pub fn require_lang_item<I: Interner>(self, cx: I) -> I::DefId {
-        cx.require_lang_item(match self {
-            SizedTraitKind::Sized => TraitSolverLangItem::Sized,
-            SizedTraitKind::MetaSized => TraitSolverLangItem::MetaSized,
+    pub fn require_lang_item<I: Interner>(self, cx: I) -> I::TraitId {
+        cx.require_trait_lang_item(match self {
+            SizedTraitKind::Sized => SolverTraitLangItem::Sized,
+            SizedTraitKind::MetaSized => SolverTraitLangItem::MetaSized,
         })
     }
 }
diff --git a/tests/ui-fulldeps/internal-lints/import-of-type-ir-traits.rs b/tests/ui-fulldeps/internal-lints/import-of-type-ir-traits.rs
index 3fdd65d6c87..965fd832722 100644
--- a/tests/ui-fulldeps/internal-lints/import-of-type-ir-traits.rs
+++ b/tests/ui-fulldeps/internal-lints/import-of-type-ir-traits.rs
@@ -8,7 +8,7 @@ extern crate rustc_type_ir;
 
 use rustc_type_ir::Interner;
 
-fn foo<I: Interner>(cx: I, did: I::DefId) {
+fn foo<I: Interner>(cx: I, did: I::TraitId) {
     let _ = cx.trait_is_unsafe(did);
     //~^ ERROR do not use `rustc_type_ir::Interner` or `rustc_type_ir::InferCtxtLike` unless you're inside of the trait solver
 }