From 6439c7fe238d14f10b9b4cfae328ec408e8dfde4 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 28 Mar 2024 12:17:17 -0400
Subject: [PATCH] Require foldability part of interner item bounds, remove
 redundant where clauses

---
 .../src/canonicalizer.rs                      | 10 +---
 compiler/rustc_type_ir/src/fold.rs            | 51 ++++---------------
 compiler/rustc_type_ir/src/interner.rs        |  8 ++-
 3 files changed, 20 insertions(+), 49 deletions(-)

diff --git a/compiler/rustc_next_trait_solver/src/canonicalizer.rs b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
index a7148c88864..1899517c0e2 100644
--- a/compiler/rustc_next_trait_solver/src/canonicalizer.rs
+++ b/compiler/rustc_next_trait_solver/src/canonicalizer.rs
@@ -296,10 +296,7 @@ fn fold_region(&mut self, r: I::Region) -> I::Region {
         Region::new_anon_bound(self.interner(), self.binder_index, var)
     }
 
-    fn fold_ty(&mut self, t: I::Ty) -> I::Ty
-    where
-        I::Ty: TypeSuperFoldable<I>,
-    {
+    fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
         let kind = match t.kind() {
             ty::Infer(i) => match i {
                 ty::TyVar(vid) => {
@@ -378,10 +375,7 @@ fn fold_ty(&mut self, t: I::Ty) -> I::Ty
         Ty::new_anon_bound(self.interner(), self.binder_index, var)
     }
 
-    fn fold_const(&mut self, c: I::Const) -> I::Const
-    where
-        I::Const: TypeSuperFoldable<I>,
-    {
+    fn fold_const(&mut self, c: I::Const) -> I::Const {
         // We could canonicalize all consts with static types, but the only ones we
         // *really* need to worry about are the ones that we end up putting into `CanonicalVarKind`
         // since canonical vars can't reference other canonical vars.
diff --git a/compiler/rustc_type_ir/src/fold.rs b/compiler/rustc_type_ir/src/fold.rs
index 8d402588398..01bb3d73dbd 100644
--- a/compiler/rustc_type_ir/src/fold.rs
+++ b/compiler/rustc_type_ir/src/fold.rs
@@ -136,31 +136,21 @@ fn fold_binder<T>(&mut self, t: I::Binder<T>) -> I::Binder<T>
         t.super_fold_with(self)
     }
 
-    fn fold_ty(&mut self, t: I::Ty) -> I::Ty
-    where
-        I::Ty: TypeSuperFoldable<I>,
-    {
+    fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
         t.super_fold_with(self)
     }
 
     // The default region folder is a no-op because `Region` is non-recursive
-    // and has no `super_fold_with` method to call. That also explains the
-    // lack of `I::Region: TypeSuperFoldable<I>` bound on this method.
+    // and has no `super_fold_with` method to call.
     fn fold_region(&mut self, r: I::Region) -> I::Region {
         r
     }
 
-    fn fold_const(&mut self, c: I::Const) -> I::Const
-    where
-        I::Const: TypeSuperFoldable<I>,
-    {
+    fn fold_const(&mut self, c: I::Const) -> I::Const {
         c.super_fold_with(self)
     }
 
-    fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate
-    where
-        I::Predicate: TypeSuperFoldable<I>,
-    {
+    fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
         p.super_fold_with(self)
     }
 }
@@ -185,31 +175,21 @@ fn try_fold_binder<T>(&mut self, t: I::Binder<T>) -> Result<I::Binder<T>, Self::
         t.try_super_fold_with(self)
     }
 
-    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Self::Error>
-    where
-        I::Ty: TypeSuperFoldable<I>,
-    {
+    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Self::Error> {
         t.try_super_fold_with(self)
     }
 
     // The default region folder is a no-op because `Region` is non-recursive
-    // and has no `super_fold_with` method to call. That also explains the
-    // lack of `I::Region: TypeSuperFoldable<I>` bound on this method.
+    // and has no `super_fold_with` method to call.
     fn try_fold_region(&mut self, r: I::Region) -> Result<I::Region, Self::Error> {
         Ok(r)
     }
 
-    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Self::Error>
-    where
-        I::Const: TypeSuperFoldable<I>,
-    {
+    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Self::Error> {
         c.try_super_fold_with(self)
     }
 
-    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Self::Error>
-    where
-        I::Predicate: TypeSuperFoldable<I>,
-    {
+    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Self::Error> {
         p.try_super_fold_with(self)
     }
 }
@@ -234,10 +214,7 @@ fn try_fold_binder<T>(&mut self, t: I::Binder<T>) -> Result<I::Binder<T>, Never>
         Ok(self.fold_binder(t))
     }
 
-    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Never>
-    where
-        I::Ty: TypeSuperFoldable<I>,
-    {
+    fn try_fold_ty(&mut self, t: I::Ty) -> Result<I::Ty, Never> {
         Ok(self.fold_ty(t))
     }
 
@@ -245,17 +222,11 @@ fn try_fold_region(&mut self, r: I::Region) -> Result<I::Region, Never> {
         Ok(self.fold_region(r))
     }
 
-    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Never>
-    where
-        I::Const: TypeSuperFoldable<I>,
-    {
+    fn try_fold_const(&mut self, c: I::Const) -> Result<I::Const, Never> {
         Ok(self.fold_const(c))
     }
 
-    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Never>
-    where
-        I::Predicate: TypeSuperFoldable<I>,
-    {
+    fn try_fold_predicate(&mut self, p: I::Predicate) -> Result<I::Predicate, Never> {
         Ok(self.fold_predicate(p))
     }
 }
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index d941195eecc..7a2885dd3bb 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -85,7 +85,13 @@ pub trait Interner: Sized + Copy {
     type PlaceholderRegion: Copy + Debug + Hash + Eq + PlaceholderLike;
 
     // Predicates
-    type Predicate: Copy + Debug + Hash + Eq + TypeSuperVisitable<Self> + Flags;
+    type Predicate: Copy
+        + Debug
+        + Hash
+        + Eq
+        + TypeSuperVisitable<Self>
+        + TypeSuperFoldable<Self>
+        + Flags;
     type TraitPredicate: Copy + Debug + Hash + Eq;
     type RegionOutlivesPredicate: Copy + Debug + Hash + Eq;
     type TypeOutlivesPredicate: Copy + Debug + Hash + Eq;