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` (#105779 (comment)) .

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`

compiler/rustc_codegen_cranelift/src/common.rs

@@ -361,7 +361,7 @@ impl<'tcx> FunctionCx<'_, '_, 'tcx> {
         self.instance.subst_mir_and_normalize_erasing_regions(
             self.tcx,
             ty::ParamEnv::reveal_all(),
-            ty::EarlyBinder(value),
+            ty::EarlyBinder::new(value),
         )
     }
 

compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs

@@ -93,7 +93,7 @@ fn make_mir_scope<'ll, 'tcx>(
             let callee = cx.tcx.subst_and_normalize_erasing_regions(
                 instance.substs,
                 ty::ParamEnv::reveal_all(),
-                ty::EarlyBinder(callee),
+                ty::EarlyBinder::new(callee),
             );
             let callee_fn_abi = cx.fn_abi_of_instance(callee, ty::List::empty());
             cx.dbg_scope_fn(callee, callee_fn_abi, None)

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -111,7 +111,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         self.instance.subst_mir_and_normalize_erasing_regions(
             self.cx.tcx(),
             ty::ParamEnv::reveal_all(),
-            ty::EarlyBinder(value),
+            ty::EarlyBinder::new(value),
         )
     }
 }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -497,7 +497,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             .try_subst_mir_and_normalize_erasing_regions(
                 *self.tcx,
                 self.param_env,
-                ty::EarlyBinder(value),
+                ty::EarlyBinder::new(value),
             )
             .map_err(|_| err_inval!(TooGeneric))
     }

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1278,7 +1278,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // params (and trait ref's late bound params). This logic is very similar to
             // `Predicate::subst_supertrait`, and it's no coincidence why.
             let shifted_output = tcx.shift_bound_var_indices(num_bound_vars, output);
-            let subst_output = ty::EarlyBinder(shifted_output).subst(tcx, substs);
+            let subst_output = ty::EarlyBinder::new(shifted_output).subst(tcx, substs);
 
             let bound_vars = tcx.late_bound_vars(binding.hir_id);
             ty::Binder::bind_with_vars(subst_output, bound_vars)

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -794,14 +794,14 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                     })
                 });
                 debug!(%ty);
-                collected_tys.insert(def_id, ty::EarlyBinder(ty));
+                collected_tys.insert(def_id, ty::EarlyBinder::new(ty));
             }
             Err(err) => {
                 let reported = tcx.sess.delay_span_bug(
                     return_span,
                     format!("could not fully resolve: {ty} => {err:?}"),
                 );
-                collected_tys.insert(def_id, ty::EarlyBinder(tcx.ty_error(reported)));
+                collected_tys.insert(def_id, ty::EarlyBinder::new(tcx.ty_error(reported)));
             }
         }
     }

compiler/rustc_hir_analysis/src/check/dropck.rs

@@ -128,7 +128,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
     // We don't need to normalize this param-env or anything, since we're only
     // substituting it with free params, so no additional param-env normalization
     // can occur on top of what has been done in the param_env query itself.
-    let param_env = ty::EarlyBinder(tcx.param_env(adt_def_id))
+    let param_env = ty::EarlyBinder::new(tcx.param_env(adt_def_id))
         .subst(tcx, adt_to_impl_substs)
         .with_constness(tcx.constness(drop_impl_def_id));
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1398,7 +1398,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             }
             let mut param_count = CountParams::default();
             let has_region = pred.visit_with(&mut param_count).is_break();
-            let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs);
+            let substituted_pred = ty::EarlyBinder::new(pred).subst(tcx, substs);
             // Don't check non-defaulted params, dependent defaults (including lifetimes)
             // or preds with multiple params.
             if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region

compiler/rustc_hir_analysis/src/collect.rs

@@ -1124,7 +1124,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<ty::PolyFnSig<
             bug!("unexpected sort of node in fn_sig(): {:?}", x);
         }
     };
-    ty::EarlyBinder(output)
+    ty::EarlyBinder::new(output)
 }
 
 fn infer_return_ty_for_fn_sig<'tcx>(
@@ -1312,7 +1312,7 @@ fn impl_trait_ref(
                 check_impl_constness(tcx, impl_.constness, ast_trait_ref),
             )
         })
-        .map(ty::EarlyBinder)
+        .map(ty::EarlyBinder::new)
 }
 
 fn check_impl_constness(

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -86,7 +86,7 @@ pub(super) fn explicit_item_bounds(
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
             let item = tcx.hir().get_by_def_id(opaque_def_id.expect_local()).expect_item();
             let opaque_ty = item.expect_opaque_ty();
-            return ty::EarlyBinder(opaque_type_bounds(
+            return ty::EarlyBinder::new(opaque_type_bounds(
                 tcx,
                 opaque_def_id.expect_local(),
                 opaque_ty.bounds,
@@ -124,7 +124,7 @@ pub(super) fn explicit_item_bounds(
         }
         _ => bug!("item_bounds called on {:?}", def_id),
     };
-    ty::EarlyBinder(bounds)
+    ty::EarlyBinder::new(bounds)
 }
 
 pub(super) fn item_bounds(

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -323,7 +323,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
                 return map[&assoc_item.trait_item_def_id.unwrap()];
             }
             Err(_) => {
-                return ty::EarlyBinder(tcx.ty_error_with_message(
+                return ty::EarlyBinder::new(tcx.ty_error_with_message(
                     DUMMY_SP,
                     "Could not collect return position impl trait in trait tys",
                 ));
@@ -497,7 +497,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
             bug!("unexpected sort of node in type_of(): {:?}", x);
         }
     };
-    ty::EarlyBinder(output)
+    ty::EarlyBinder::new(output)
 }
 
 fn infer_placeholder_type<'a>(

compiler/rustc_hir_analysis/src/outlives/explicit.rs

@@ -68,7 +68,7 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
                 }
             }
 
-            ty::EarlyBinder(required_predicates)
+            ty::EarlyBinder::new(required_predicates)
         })
     }
 }

compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs

@@ -68,12 +68,13 @@ pub(super) fn infer_predicates(
             // Therefore mark `predicates_added` as true and which will ensure
             // we walk the crates again and re-calculate predicates for all
             // items.
-            let item_predicates_len: usize =
-                global_inferred_outlives.get(&item_did.to_def_id()).map_or(0, |p| p.0.len());
+            let item_predicates_len: usize = global_inferred_outlives
+                .get(&item_did.to_def_id())
+                .map_or(0, |p| p.as_ref().skip_binder().len());
             if item_required_predicates.len() > item_predicates_len {
                 predicates_added = true;
                 global_inferred_outlives
-                    .insert(item_did.to_def_id(), ty::EarlyBinder(item_required_predicates));
+                    .insert(item_did.to_def_id(), ty::EarlyBinder::new(item_required_predicates));
             }
         }
 
@@ -137,7 +138,9 @@ fn insert_required_predicates_to_be_wf<'tcx>(
                 // 'a` holds for `Foo`.
                 debug!("Adt");
                 if let Some(unsubstituted_predicates) = global_inferred_outlives.get(&def.did()) {
-                    for (unsubstituted_predicate, &span) in &unsubstituted_predicates.0 {
+                    for (unsubstituted_predicate, &span) in
+                        unsubstituted_predicates.as_ref().skip_binder()
+                    {
                         // `unsubstituted_predicate` is `U: 'b` in the
                         // example above. So apply the substitution to
                         // get `T: 'a` (or `predicate`):
@@ -251,7 +254,7 @@ fn check_explicit_predicates<'tcx>(
     );
     let explicit_predicates = explicit_map.explicit_predicates_of(tcx, def_id);
 
-    for (outlives_predicate, &span) in &explicit_predicates.0 {
+    for (outlives_predicate, &span) in explicit_predicates.as_ref().skip_binder() {
         debug!("outlives_predicate = {:?}", &outlives_predicate);
 
         // Careful: If we are inferring the effects of a `dyn Trait<..>`

compiler/rustc_hir_analysis/src/outlives/mod.rs

@@ -98,24 +98,27 @@ fn inferred_outlives_crate(tcx: TyCtxt<'_>, (): ()) -> CratePredicatesMap<'_> {
     let predicates = global_inferred_outlives
         .iter()
         .map(|(&def_id, set)| {
-            let predicates = &*tcx.arena.alloc_from_iter(set.0.iter().filter_map(
-                |(ty::OutlivesPredicate(kind1, region2), &span)| {
-                    match kind1.unpack() {
-                        GenericArgKind::Type(ty1) => Some((
-                            ty::Clause::TypeOutlives(ty::OutlivesPredicate(ty1, *region2)),
-                            span,
-                        )),
-                        GenericArgKind::Lifetime(region1) => Some((
-                            ty::Clause::RegionOutlives(ty::OutlivesPredicate(region1, *region2)),
-                            span,
-                        )),
-                        GenericArgKind::Const(_) => {
-                            // Generic consts don't impose any constraints.
-                            None
+            let predicates =
+                &*tcx.arena.alloc_from_iter(set.as_ref().skip_binder().iter().filter_map(
+                    |(ty::OutlivesPredicate(kind1, region2), &span)| {
+                        match kind1.unpack() {
+                            GenericArgKind::Type(ty1) => Some((
+                                ty::Clause::TypeOutlives(ty::OutlivesPredicate(ty1, *region2)),
+                                span,
+                            )),
+                            GenericArgKind::Lifetime(region1) => Some((
+                                ty::Clause::RegionOutlives(ty::OutlivesPredicate(
+                                    region1, *region2,
+                                )),
+                                span,
+                            )),
+                            GenericArgKind::Const(_) => {
+                                // Generic consts don't impose any constraints.
+                                None
+                            }
                         }
-                    }
-                },
-            ));
+                    },
+                ));
             (def_id, predicates)
         })
         .collect();

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1386,7 +1386,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // the referenced item.
         let ty = tcx.type_of(def_id);
         assert!(!substs.has_escaping_bound_vars());
-        assert!(!ty.0.has_escaping_bound_vars());
+        assert!(!ty.skip_binder().has_escaping_bound_vars());
         let ty_substituted = self.normalize(span, ty.subst(tcx, substs));
 
         if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -293,7 +293,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ) -> impl Iterator<Item = ty::Region<'tcx>> {
         let tcx = self.tcx;
         let bounds = tcx.item_bounds(alias_ty.def_id);
-        trace!("{:#?}", bounds.0);
+        trace!("{:#?}", bounds.skip_binder());
         bounds
             .subst_iter(tcx, alias_ty.substs)
             .filter_map(|p| p.to_opt_type_outlives())

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -851,7 +851,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         } else {
             tcx.arena.alloc_from_iter(lazy.decode((self, tcx)))
         };
-        ty::EarlyBinder(&*output)
+        ty::EarlyBinder::new(&*output)
     }
 
     fn get_variant(

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1727,7 +1727,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             ty::Closure(_, substs) => {
                 let constness = self.tcx.constness(def_id.to_def_id());
                 self.tables.constness.set_some(def_id.to_def_id().index, constness);
-                record!(self.tables.fn_sig[def_id.to_def_id()] <- ty::EarlyBinder(substs.as_closure().sig()));
+                record!(self.tables.fn_sig[def_id.to_def_id()] <- ty::EarlyBinder::new(substs.as_closure().sig()));
             }
 
             _ => bug!("closure that is neither generator nor closure"),

compiler/rustc_middle/src/mir/mod.rs

@@ -476,7 +476,7 @@ impl<'tcx> Body<'tcx> {
     /// Returns the return type; it always return first element from `local_decls` array.
     #[inline]
     pub fn bound_return_ty(&self) -> ty::EarlyBinder<Ty<'tcx>> {
-        ty::EarlyBinder(self.local_decls[RETURN_PLACE].ty)
+        ty::EarlyBinder::new(self.local_decls[RETURN_PLACE].ty)
     }
 
     /// Gets the location of the terminator for the given block.

compiler/rustc_middle/src/ty/adt.rs

@@ -573,7 +573,7 @@ impl<'tcx> AdtDef<'tcx> {
     /// Due to normalization being eager, this applies even if
     /// the associated type is behind a pointer (e.g., issue #31299).
     pub fn sized_constraint(self, tcx: TyCtxt<'tcx>) -> ty::EarlyBinder<&'tcx [Ty<'tcx>]> {
-        ty::EarlyBinder(tcx.adt_sized_constraint(self.did()))
+        ty::EarlyBinder::new(tcx.adt_sized_constraint(self.did()))
     }
 }
 

compiler/rustc_middle/src/ty/consts.rs

@@ -254,5 +254,5 @@ pub fn const_param_default(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBind
             "`const_param_default` expected a generic parameter with a constant"
         ),
     };
-    ty::EarlyBinder(Const::from_anon_const(tcx, default_def_id))
+    ty::EarlyBinder::new(Const::from_anon_const(tcx, default_def_id))
 }

compiler/rustc_middle/src/ty/generics.rs

@@ -343,7 +343,7 @@ impl<'tcx> GenericPredicates<'tcx> {
         substs: SubstsRef<'tcx>,
     ) -> impl Iterator<Item = (Predicate<'tcx>, Span)> + DoubleEndedIterator + ExactSizeIterator
     {
-        EarlyBinder(self.predicates).subst_iter_copied(tcx, substs)
+        EarlyBinder::new(self.predicates).subst_iter_copied(tcx, substs)
     }
 
     #[instrument(level = "debug", skip(self, tcx))]
@@ -358,7 +358,7 @@ impl<'tcx> GenericPredicates<'tcx> {
         }
         instantiated
             .predicates
-            .extend(self.predicates.iter().map(|(p, _)| EarlyBinder(*p).subst(tcx, substs)));
+            .extend(self.predicates.iter().map(|(p, _)| EarlyBinder::new(*p).subst(tcx, substs)));
         instantiated.spans.extend(self.predicates.iter().map(|(_, sp)| *sp));
     }
 

compiler/rustc_middle/src/ty/inhabitedness/inhabited_predicate.rs

@@ -158,7 +158,7 @@ impl<'tcx> InhabitedPredicate<'tcx> {
     fn subst_opt(self, tcx: TyCtxt<'tcx>, substs: ty::SubstsRef<'tcx>) -> Option<Self> {
         match self {
             Self::ConstIsZero(c) => {
-                let c = ty::EarlyBinder(c).subst(tcx, substs);
+                let c = ty::EarlyBinder::new(c).subst(tcx, substs);
                 let pred = match c.kind().try_to_target_usize(tcx) {
                     Some(0) => Self::True,
                     Some(1..) => Self::False,
@@ -167,7 +167,7 @@ impl<'tcx> InhabitedPredicate<'tcx> {
                 Some(pred)
             }
             Self::GenericType(t) => {
-                Some(ty::EarlyBinder(t).subst(tcx, substs).inhabited_predicate(tcx))
+                Some(ty::EarlyBinder::new(t).subst(tcx, substs).inhabited_predicate(tcx))
             }
             Self::And(&[a, b]) => match a.subst_opt(tcx, substs) {
                 None => b.subst_opt(tcx, substs).map(|b| a.and(tcx, b)),

compiler/rustc_middle/src/ty/mod.rs

@@ -764,7 +764,7 @@ impl<'tcx> Predicate<'tcx> {
         let shifted_pred =
             tcx.shift_bound_var_indices(trait_bound_vars.len(), bound_pred.skip_binder());
         // 2) Self: Bar1<'a, '^0.1> -> T: Bar1<'^0.0, '^0.1>
-        let new = EarlyBinder(shifted_pred).subst(tcx, trait_ref.skip_binder().substs);
+        let new = EarlyBinder::new(shifted_pred).subst(tcx, trait_ref.skip_binder().substs);
         // 3) ['x] + ['b] -> ['x, 'b]
         let bound_vars =
             tcx.mk_bound_variable_kinds_from_iter(trait_bound_vars.iter().chain(pred_bound_vars));

compiler/rustc_middle/src/ty/print/mod.rs

@@ -123,7 +123,7 @@ pub trait Printer<'tcx>: Sized {
                         impl_trait_ref.map(|i| i.subst(self.tcx(), substs)),
                     )
                 } else {
-                    (self_ty.0, impl_trait_ref.map(|i| i.0))
+                    (self_ty.subst_identity(), impl_trait_ref.map(|i| i.subst_identity()))
                 };
                 self.print_impl_path(def_id, substs, self_ty, impl_trait_ref)
             }

compiler/rustc_middle/src/ty/sty.rs

@@ -568,7 +568,7 @@ impl<'tcx> GeneratorSubsts<'tcx> {
         let layout = tcx.generator_layout(def_id).unwrap();
         layout.variant_fields.iter().map(move |variant| {
             variant.iter().map(move |field| {
-                ty::EarlyBinder(layout.field_tys[*field].ty).subst(tcx, self.substs)
+                ty::EarlyBinder::new(layout.field_tys[*field].ty).subst(tcx, self.substs)
             })
         })
     }
@@ -2366,7 +2366,7 @@ impl<'tcx> Ty<'tcx> {
 
             ty::Tuple(tys) => tys.iter().all(|ty| ty.is_trivially_sized(tcx)),
 
-            ty::Adt(def, _substs) => def.sized_constraint(tcx).0.is_empty(),
+            ty::Adt(def, _substs) => def.sized_constraint(tcx).skip_binder().is_empty(),
 
             ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => false,
 

compiler/rustc_middle/src/ty/subst.rs

@@ -538,13 +538,17 @@ impl<'tcx, T: TypeVisitable<TyCtxt<'tcx>>> TypeVisitable<TyCtxt<'tcx>> for &'tcx
 /// [`subst_identity`](EarlyBinder::subst_identity) or [`skip_binder`](EarlyBinder::skip_binder).
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 #[derive(Encodable, Decodable, HashStable)]
-pub struct EarlyBinder<T>(pub T);
+pub struct EarlyBinder<T>(T);
 
 /// For early binders, you should first call `subst` before using any visitors.
 impl<'tcx, T> !TypeFoldable<TyCtxt<'tcx>> for ty::EarlyBinder<T> {}
 impl<'tcx, T> !TypeVisitable<TyCtxt<'tcx>> for ty::EarlyBinder<T> {}
 
 impl<T> EarlyBinder<T> {
+    pub fn new(inner: T) -> EarlyBinder<T> {
+        EarlyBinder(inner)
+    }
+
     pub fn as_ref(&self) -> EarlyBinder<&T> {
         EarlyBinder(&self.0)
     }
@@ -582,6 +586,9 @@ impl<T> EarlyBinder<T> {
     /// arguments of an `FnSig`). Otherwise, consider using
     /// [`subst_identity`](EarlyBinder::subst_identity).
     ///
+    /// To skip the binder on `x: &EarlyBinder<T>` to obtain `&T`, leverage
+    /// [`EarlyBinder::as_ref`](EarlyBinder::as_ref): `x.as_ref().skip_binder()`.
+    ///
     /// See also [`Binder::skip_binder`](super::Binder::skip_binder), which is
     /// the analogous operation on [`super::Binder`].
     pub fn skip_binder(self) -> T {

compiler/rustc_middle/src/ty/util.rs

@@ -709,7 +709,7 @@ impl<'tcx> TyCtxt<'tcx> {
             .as_ref()
             .map_or_else(|| [].iter(), |l| l.field_tys.iter())
             .filter(|decl| !decl.ignore_for_traits)
-            .map(|decl| ty::EarlyBinder(decl.ty))
+            .map(|decl| ty::EarlyBinder::new(decl.ty))
     }
 
     /// Normalizes all opaque types in the given value, replacing them