Auto merge of #96883 - jackh726:early-binder-2, r=oli-obk

Add EarlyBinder

Chalk has no concept of `Param` (https://github.com/rust-lang/chalk/blob/e0ade19d139bc784384acc6736cd960c91dd55a1/chalk-ir/src/lib.rs#L579) or `ReEarlyBound` (https://github.com/rust-lang/chalk/blob/e0ade19d139bc784384acc6736cd960c91dd55a1/chalk-ir/src/lib.rs#L1308). Everything  is just "bound" - the equivalent of rustc's late-bound. It's not completely clear yet whether to move everything to the same time of binder in rustc or add `Param` and `ReEarlyBound` in Chalk.

Either way, tracking when we have or haven't already substituted out these in rustc can be helpful.

As a first step, I'm just adding a `EarlyBinder` newtype that is required to call `subst`. I also add a couple "transparent" `bound_*` wrappers around a couple query that are often immediately substituted.

r? `@nikomatsakis`

2 files changed, 8 insertions, 6 deletions

diff --git a/compiler/rustc_ty_utils/src/needs_drop.rs b/compiler/rustc_ty_utils/src/needs_drop.rs
index c5fc4e4c661..9ad44d14d61 100644
--- a/compiler/rustc_ty_utils/src/needs_drop.rs
+++ b/compiler/rustc_ty_utils/src/needs_drop.rs
@@ -5,7 +5,7 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::util::{needs_drop_components, AlwaysRequiresDrop};
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, EarlyBinder, Ty, TyCtxt};
 use rustc_session::Limit;
 use rustc_span::{sym, DUMMY_SP};
 
@@ -204,7 +204,7 @@ 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(subty.subst(tcx, subst));
+                        vec.push(EarlyBinder(subty).subst(tcx, subst));
                     }
                 }
                 _ => vec.push(subty),
@@ -237,7 +237,7 @@ fn drop_tys_helper<'tcx>(
             Ok(Vec::new())
         } else {
             let field_tys = adt_def.all_fields().map(|field| {
-                let r = tcx.type_of(field.did).subst(tcx, substs);
+                let r = tcx.bound_type_of(field.did).subst(tcx, substs);
                 debug!("drop_tys_helper: Subst into {:?} with {:?} gettng {:?}", field, substs, r);
                 r
             });
diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs
index 6ad71bdb481..23700e653e3 100644
--- a/compiler/rustc_ty_utils/src/ty.rs
+++ b/compiler/rustc_ty_utils/src/ty.rs
@@ -2,7 +2,9 @@ use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::subst::Subst;
-use rustc_middle::ty::{self, Binder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt};
+use rustc_middle::ty::{
+    self, Binder, EarlyBinder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt,
+};
 use rustc_span::{sym, Span};
 use rustc_trait_selection::traits;
 
@@ -33,7 +35,7 @@ fn sized_constraint_for_ty<'tcx>(
             debug!("sized_constraint_for_ty({:?}) intermediate = {:?}", ty, adt_tys);
             adt_tys
                 .iter()
-                .map(|ty| ty.subst(tcx, substs))
+                .map(|ty| EarlyBinder(*ty).subst(tcx, substs))
                 .flat_map(|ty| sized_constraint_for_ty(tcx, adtdef, ty))
                 .collect()
         }
@@ -442,7 +444,7 @@ pub fn conservative_is_privately_uninhabited_raw<'tcx>(
             //     one uninhabited field.
             def.variants().iter().all(|var| {
                 var.fields.iter().any(|field| {
-                    let ty = tcx.type_of(field.did).subst(tcx, substs);
+                    let ty = tcx.bound_type_of(field.did).subst(tcx, substs);
                     tcx.conservative_is_privately_uninhabited(param_env.and(ty))
                 })
             })