Auto merge of #106696 - kylematsuda:early-binder, r=lcnr

Switch to `EarlyBinder` for `const_param_default` and `impl_trait_ref` queries

Part of the work to close #105779 and implement https://github.com/rust-lang/types-team/issues/78.

Several queries `X` have a `bound_X` variant that wraps the output in `EarlyBinder`. This PR adds `EarlyBinder` to the return type of  `const_param_default` and `impl_trait_ref`, and removes their `bound_X` variants.

r? `@lcnr`

11 files changed, 25 insertions, 21 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/project_goals.rs b/compiler/rustc_trait_selection/src/solve/project_goals.rs
index 3d649bea19d..e9140507192 100644
--- a/compiler/rustc_trait_selection/src/solve/project_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/project_goals.rs
@@ -110,7 +110,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
     ) {
         let tcx = acx.cx.tcx;
         let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
-        let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap();
+        let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
         if iter::zip(goal_trait_ref.substs, impl_trait_ref.skip_binder().substs)
             .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
index c69cc39acb5..a43fef5cdb0 100644
--- a/compiler/rustc_trait_selection/src/solve/trait_goals.rs
+++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs
@@ -73,7 +73,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     ) {
         let tcx = acx.cx.tcx;
 
-        let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap();
+        let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
         if iter::zip(goal.predicate.trait_ref.substs, impl_trait_ref.skip_binder().substs)
             .any(|(goal, imp)| !drcx.generic_args_may_unify(goal, imp))
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 258d2e2d28c..0edae34190c 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -80,7 +80,7 @@ pub fn overlapping_impls(
     let impl1_ref = tcx.impl_trait_ref(impl1_def_id);
     let impl2_ref = tcx.impl_trait_ref(impl2_def_id);
     let may_overlap = match (impl1_ref, impl2_ref) {
-        (Some(a), Some(b)) => iter::zip(a.substs, b.substs)
+        (Some(a), Some(b)) => iter::zip(a.skip_binder().substs, b.skip_binder().substs)
             .all(|(arg1, arg2)| drcx.generic_args_may_unify(arg1, arg2)),
         (None, None) => {
             let self_ty1 = tcx.type_of(impl1_def_id);
@@ -126,7 +126,7 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
     let header = ty::ImplHeader {
         impl_def_id,
         self_ty: tcx.bound_type_of(impl_def_id).subst(tcx, impl_substs),
-        trait_ref: tcx.bound_impl_trait_ref(impl_def_id).map(|i| i.subst(tcx, impl_substs)),
+        trait_ref: tcx.impl_trait_ref(impl_def_id).map(|i| i.subst(tcx, impl_substs)),
         predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
     };
 
@@ -461,7 +461,7 @@ pub fn orphan_check(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Result<(), OrphanChe
 
     // We only except this routine to be invoked on implementations
     // of a trait, not inherent implementations.
-    let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
+    let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().subst_identity();
     debug!("orphan_check: trait_ref={:?}", trait_ref);
 
     // If the *trait* is local to the crate, ok.
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 0c1717cff33..df57c0f60fa 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
@@ -27,7 +27,7 @@ pub fn recompute_applicable_impls<'tcx>(
             ocx.normalize(&ObligationCause::dummy(), param_env, placeholder_obligation.trait_ref);
 
         let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
-        let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap().subst(tcx, impl_substs);
+        let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().subst(tcx, impl_substs);
         let impl_trait_ref = ocx.normalize(&ObligationCause::dummy(), param_env, impl_trait_ref);
 
         if let Err(_) =
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 41a64a844ce..b23b3d34d51 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -1964,7 +1964,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     return None;
                 }
 
-                let imp = self.tcx.impl_trait_ref(def_id).unwrap();
+                let imp = self.tcx.impl_trait_ref(def_id).unwrap().skip_binder();
 
                 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
                     .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
@@ -2062,6 +2062,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         || self.tcx.is_builtin_derive(def_id)
                 })
                 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
+                .map(ty::EarlyBinder::subst_identity)
                 .filter(|trait_ref| {
                     let self_ty = trait_ref.self_ty();
                     // Avoid mentioning type parameters.
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index e599996230f..18d308f7123 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -68,7 +68,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         self.tcx.for_each_relevant_impl(trait_ref.def_id, trait_self_ty, |def_id| {
             let impl_substs = self.fresh_substs_for_item(obligation.cause.span, def_id);
-            let impl_trait_ref = tcx.bound_impl_trait_ref(def_id).unwrap().subst(tcx, impl_substs);
+            let impl_trait_ref = tcx.impl_trait_ref(def_id).unwrap().subst(tcx, impl_substs);
 
             let impl_self_ty = impl_trait_ref.self_ty();
 
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 37b40a2f75a..241ae0275ce 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -521,8 +521,10 @@ fn is_impossible_method(tcx: TyCtxt<'_>, (impl_def_id, trait_item_def_id): (DefI
 
     let generics = tcx.generics_of(trait_item_def_id);
     let predicates = tcx.predicates_of(trait_item_def_id);
-    let impl_trait_ref =
-        tcx.impl_trait_ref(impl_def_id).expect("expected impl to correspond to trait");
+    let impl_trait_ref = tcx
+        .impl_trait_ref(impl_def_id)
+        .expect("expected impl to correspond to trait")
+        .subst_identity();
     let param_env = tcx.param_env(impl_def_id);
 
     let mut visitor = ReferencesOnlyParentGenerics { tcx, generics, trait_item_def_id };
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 8c291d1595d..e29ad30d5f2 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -357,7 +357,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 // Before we create the substitutions and everything, first
                 // consider a "quick reject". This avoids creating more types
                 // and so forth that we need to.
-                let impl_trait_ref = self.tcx().bound_impl_trait_ref(impl_def_id).unwrap();
+                let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap();
                 if self.fast_reject_trait_refs(obligation, &impl_trait_ref.0) {
                     return;
                 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 305902af7c8..ba4e668f52d 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2335,7 +2335,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         impl_def_id: DefId,
         obligation: &TraitObligation<'tcx>,
     ) -> Normalized<'tcx, SubstsRef<'tcx>> {
-        let impl_trait_ref = self.tcx().bound_impl_trait_ref(impl_def_id).unwrap();
+        let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap();
         match self.match_impl(impl_def_id, impl_trait_ref, obligation) {
             Ok(substs) => substs,
             Err(()) => {
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index a251a508b48..3b796c623c0 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -87,7 +87,7 @@ pub fn translate_substs<'tcx>(
         param_env, source_impl, source_substs, target_node
     );
     let source_trait_ref =
-        infcx.tcx.bound_impl_trait_ref(source_impl).unwrap().subst(infcx.tcx, &source_substs);
+        infcx.tcx.impl_trait_ref(source_impl).unwrap().subst(infcx.tcx, &source_substs);
 
     // translate the Self and Param parts of the substitution, since those
     // vary across impls
@@ -148,7 +148,7 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId,
 
     // create a parameter environment corresponding to a (placeholder) instantiation of impl1
     let penv = tcx.param_env(impl1_def_id);
-    let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap();
+    let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap().subst_identity();
 
     // Create an infcx, taking the predicates of impl1 as assumptions:
     let infcx = tcx.infer_ctxt().build();
@@ -431,7 +431,7 @@ fn report_conflicting_impls<'tcx>(
 pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Option<String> {
     use std::fmt::Write;
 
-    let trait_ref = tcx.impl_trait_ref(impl_def_id)?;
+    let trait_ref = tcx.impl_trait_ref(impl_def_id)?.subst_identity();
     let mut w = "impl".to_owned();
 
     let substs = InternalSubsts::identity_for_item(tcx, impl_def_id);
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index 02b06677740..6411206a5a4 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -48,7 +48,7 @@ trait ChildrenExt<'tcx> {
 impl<'tcx> ChildrenExt<'tcx> for Children {
     /// Insert an impl into this set of children without comparing to any existing impls.
     fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
-        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
+        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().skip_binder();
         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
         {
             debug!("insert_blindly: impl_def_id={:?} st={:?}", impl_def_id, st);
@@ -63,7 +63,7 @@ impl<'tcx> ChildrenExt<'tcx> for Children {
     /// an impl with a parent. The impl must be present in the list of
     /// children already.
     fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
-        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
+        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().skip_binder();
         let vec: &mut Vec<DefId>;
         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
         {
@@ -181,7 +181,7 @@ impl<'tcx> ChildrenExt<'tcx> for Children {
             if le && !ge {
                 debug!(
                     "descending as child of TraitRef {:?}",
-                    tcx.impl_trait_ref(possible_sibling).unwrap()
+                    tcx.impl_trait_ref(possible_sibling).unwrap().subst_identity()
                 );
 
                 // The impl specializes `possible_sibling`.
@@ -189,7 +189,7 @@ impl<'tcx> ChildrenExt<'tcx> for Children {
             } else if ge && !le {
                 debug!(
                     "placing as parent of TraitRef {:?}",
-                    tcx.impl_trait_ref(possible_sibling).unwrap()
+                    tcx.impl_trait_ref(possible_sibling).unwrap().subst_identity()
                 );
 
                 replace_children.push(possible_sibling);
@@ -275,7 +275,8 @@ impl<'tcx> GraphExt<'tcx> for Graph {
     ) -> Result<Option<FutureCompatOverlapError<'tcx>>, OverlapError<'tcx>> {
         assert!(impl_def_id.is_local());
 
-        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
+        // FIXME: use `EarlyBinder` in `self.children`
+        let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap().skip_binder();
         let trait_def_id = trait_ref.def_id;
 
         debug!(
@@ -388,7 +389,7 @@ pub(crate) fn assoc_def(
     impl_def_id: DefId,
     assoc_def_id: DefId,
 ) -> Result<LeafDef, ErrorGuaranteed> {
-    let trait_def_id = tcx.impl_trait_ref(impl_def_id).unwrap().def_id;
+    let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
     let trait_def = tcx.trait_def(trait_def_id);
 
     // This function may be called while we are still building the