From 39b95c965aada6bab37c803b24067bbb26644f38 Mon Sep 17 00:00:00 2001
From: Maybe Waffle <waffle.lapkin@gmail.com>
Date: Wed, 26 Apr 2023 11:59:51 +0000
Subject: [PATCH] Don't return a `Binder` from `TraitRef::identity`

---
 compiler/rustc_middle/src/ty/sty.rs                   |  8 ++------
 .../src/traits/error_reporting/ambiguity.rs           |  2 +-
 .../rustc_trait_selection/src/traits/object_safety.rs | 11 ++++++-----
 3 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 1849a66fa8f..e1d3690b679 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -855,12 +855,8 @@ pub fn from_method(
 
     /// Returns a `TraitRef` of the form `P0: Foo<P1..Pn>` where `Pi`
     /// are the parameters defined on trait.
-    pub fn identity(tcx: TyCtxt<'tcx>, def_id: DefId) -> Binder<'tcx, TraitRef<'tcx>> {
-        ty::Binder::dummy(ty::TraitRef::new(
-            tcx,
-            def_id,
-            InternalSubsts::identity_for_item(tcx, def_id),
-        ))
+    pub fn identity(tcx: TyCtxt<'tcx>, def_id: DefId) -> TraitRef<'tcx> {
+        ty::TraitRef::new(tcx, def_id, InternalSubsts::identity_for_item(tcx, def_id))
     }
 
     pub fn with_self_ty(self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> Self {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
index 0475f24d87c..7ab652761a4 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
@@ -87,7 +87,7 @@ pub fn recompute_applicable_impls<'tcx>(
         if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = kind.skip_binder()
             && param_env_candidate_may_apply(kind.rebind(trait_pred))
         {
-            if kind.rebind(trait_pred.trait_ref) == ty::TraitRef::identity(tcx, trait_pred.def_id()) {
+            if kind.rebind(trait_pred.trait_ref) == ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_pred.def_id())) {
                 ambiguities.push(Ambiguity::ParamEnv(tcx.def_span(trait_pred.def_id())))
             } else {
                 ambiguities.push(Ambiguity::ParamEnv(span))
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 3f526e70522..6cb9b213852 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -279,7 +279,7 @@ fn predicates_reference_self(
     trait_def_id: DefId,
     supertraits_only: bool,
 ) -> SmallVec<[Span; 1]> {
-    let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
+    let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, trait_def_id));
     let predicates = if supertraits_only {
         tcx.super_predicates_of(trait_def_id)
     } else {
@@ -661,9 +661,9 @@ fn object_ty_for_trait<'tcx>(
     let trait_ref = ty::TraitRef::identity(tcx, trait_def_id);
     debug!(?trait_ref);
 
-    let trait_predicate = trait_ref.map_bound(|trait_ref| {
-        ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref))
-    });
+    let trait_predicate = ty::Binder::dummy(ty::ExistentialPredicate::Trait(
+        ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref),
+    ));
     debug!(?trait_predicate);
 
     let pred: ty::Predicate<'tcx> = trait_ref.to_predicate(tcx);
@@ -880,7 +880,8 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
 
                     // Compute supertraits of current trait lazily.
                     if self.supertraits.is_none() {
-                        let trait_ref = ty::TraitRef::identity(self.tcx, self.trait_def_id);
+                        let trait_ref =
+                            ty::Binder::dummy(ty::TraitRef::identity(self.tcx, self.trait_def_id));
                         self.supertraits = Some(
                             traits::supertraits(self.tcx, trait_ref).map(|t| t.def_id()).collect(),
                         );