Auto merge of #112006 - kylematsuda:earlybinder-private, r=jackh726

Make `EarlyBinder`'s inner value private

Currently, `EarlyBinder(T)`'s inner value is public, which allows implicitly skipping the binder by indexing into the tuple struct (i.e., `x.0`). `@lcnr` suggested making `EarlyBinder`'s inner value private so users are required to explicitly call `skip_binder` (https://github.com/rust-lang/rust/issues/105779#issuecomment-1549933424) .

This PR makes the inner value private, adds `EarlyBinder::new` for constructing a new instance, and replaces uses of `x.0` with `x.skip_binder()` (or similar). It also adds some documentation to `EarlyBinder::skip_binder` explaining how to skip the binder of `&EarlyBinder<T>` to get `&T` now that the inner value is private (since previously we could just do `&x.0`).

r? `@lcnr`

5 files changed, 6 insertions, 8 deletions

diff --git a/compiler/rustc_ty_utils/src/assoc.rs b/compiler/rustc_ty_utils/src/assoc.rs
index ed574f22e61..0925b3956de 100644
--- a/compiler/rustc_ty_utils/src/assoc.rs
+++ b/compiler/rustc_ty_utils/src/assoc.rs
@@ -301,7 +301,7 @@ fn associated_type_for_impl_trait_in_trait(
     trait_assoc_ty.impl_defaultness(tcx.impl_defaultness(fn_def_id));
 
     // Copy type_of of the opaque.
-    trait_assoc_ty.type_of(ty::EarlyBinder(tcx.mk_opaque(
+    trait_assoc_ty.type_of(ty::EarlyBinder::new(tcx.mk_opaque(
         opaque_ty_def_id.to_def_id(),
         InternalSubsts::identity_for_item(tcx, opaque_ty_def_id),
     )));
diff --git a/compiler/rustc_ty_utils/src/consts.rs b/compiler/rustc_ty_utils/src/consts.rs
index 1219bb40098..bb723c9997a 100644
--- a/compiler/rustc_ty_utils/src/consts.rs
+++ b/compiler/rustc_ty_utils/src/consts.rs
@@ -419,7 +419,7 @@ pub fn thir_abstract_const(
 
     let root_span = body.exprs[body_id].span;
 
-    Ok(Some(ty::EarlyBinder(recurse_build(tcx, body, body_id, root_span)?)))
+    Ok(Some(ty::EarlyBinder::new(recurse_build(tcx, body, body_id, root_span)?)))
 }
 
 pub fn provide(providers: &mut Providers) {
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 16cd8bc8e69..0e5b23ca423 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -610,7 +610,7 @@ fn generator_layout<'tcx>(
 ) -> Result<Layout<'tcx>, LayoutError<'tcx>> {
     use SavedLocalEligibility::*;
     let tcx = cx.tcx;
-    let subst_field = |ty: Ty<'tcx>| EarlyBinder(ty).subst(tcx, substs);
+    let subst_field = |ty: Ty<'tcx>| EarlyBinder::new(ty).subst(tcx, substs);
 
     let Some(info) = tcx.generator_layout(def_id) else {
         return Err(LayoutError::Unknown(ty));
diff --git a/compiler/rustc_ty_utils/src/needs_drop.rs b/compiler/rustc_ty_utils/src/needs_drop.rs
index 1f9701b9322..075fde6ddb6 100644
--- a/compiler/rustc_ty_utils/src/needs_drop.rs
+++ b/compiler/rustc_ty_utils/src/needs_drop.rs
@@ -210,7 +210,7 @@ fn drop_tys_helper<'tcx>(
             match subty.kind() {
                 ty::Adt(adt_id, subst) => {
                     for subty in tcx.adt_drop_tys(adt_id.did())? {
-                        vec.push(EarlyBinder(subty).subst(tcx, subst));
+                        vec.push(EarlyBinder::new(subty).subst(tcx, subst));
                     }
                 }
                 _ => vec.push(subty),
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 65dc3c39c6a..52bc386cb00 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -44,9 +44,7 @@ fn sized_constraint_for_ty<'tcx>(
             let adt_tys = adt.sized_constraint(tcx);
             debug!("sized_constraint_for_ty({:?}) intermediate = {:?}", ty, adt_tys);
             adt_tys
-                .0
-                .iter()
-                .map(|ty| adt_tys.rebind(*ty).subst(tcx, substs))
+                .subst_iter_copied(tcx, substs)
                 .flat_map(|ty| sized_constraint_for_ty(tcx, adtdef, ty))
                 .collect()
         }
@@ -508,7 +506,7 @@ fn issue33140_self_ty(tcx: TyCtxt<'_>, def_id: DefId) -> Option<EarlyBinder<Ty<'
 
     if self_ty_matches {
         debug!("issue33140_self_ty - MATCHES!");
-        Some(EarlyBinder(self_ty))
+        Some(EarlyBinder::new(self_ty))
     } else {
         debug!("issue33140_self_ty - non-matching self type");
         None