Merging upstream version 1.73.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

6 files changed, 251 insertions, 224 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/bounds.rs b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
index b13de7701..ba152cd48 100644
--- a/compiler/rustc_hir_analysis/src/astconv/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
@@ -13,7 +13,7 @@ use crate::astconv::{
     AstConv, ConvertedBinding, ConvertedBindingKind, OnlySelfBounds, PredicateFilter,
 };
 use crate::bounds::Bounds;
-use crate::errors::{MultipleRelaxedDefaultBounds, ValueOfAssociatedStructAlreadySpecified};
+use crate::errors;
 
 impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// Sets `implicitly_sized` to true on `Bounds` if necessary
@@ -35,7 +35,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                     if unbound.is_none() {
                         unbound = Some(&ptr.trait_ref);
                     } else {
-                        tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
+                        tcx.sess.emit_err(errors::MultipleRelaxedDefaultBounds { span });
                     }
                 }
             }
@@ -326,7 +326,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             dup_bindings
                 .entry(assoc_item.def_id)
                 .and_modify(|prev_span| {
-                    tcx.sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
+                    tcx.sess.emit_err(errors::ValueOfAssociatedStructAlreadySpecified {
                         span: binding.span,
                         prev_span: *prev_span,
                         item_name: binding.item_name,
@@ -341,8 +341,8 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             // If we have an method return type bound, then we need to substitute
             // the method's early bound params with suitable late-bound params.
             let mut num_bound_vars = candidate.bound_vars().len();
-            let substs =
-                candidate.skip_binder().substs.extend_to(tcx, assoc_item.def_id, |param, _| {
+            let args =
+                candidate.skip_binder().args.extend_to(tcx, assoc_item.def_id, |param, _| {
                     let subst = match param.kind {
                         ty::GenericParamDefKind::Lifetime => ty::Region::new_late_bound(
                             tcx,
@@ -422,7 +422,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             // 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::bind(shifted_output).subst(tcx, substs);
+            let subst_output = ty::EarlyBinder::bind(shifted_output).instantiate(tcx, args);
 
             let bound_vars = tcx.late_bound_vars(binding.hir_id);
             ty::Binder::bind_with_vars(subst_output, bound_vars)
@@ -438,16 +438,16 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                     infer_args: false,
                 };
 
-                let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
+                let args_trait_ref_and_assoc_item = self.create_args_for_associated_item(
                     path_span,
                     assoc_item.def_id,
                     &item_segment,
-                    trait_ref.substs,
+                    trait_ref.args,
                 );
 
-                debug!(?substs_trait_ref_and_assoc_item);
+                debug!(?args_trait_ref_and_assoc_item);
 
-                tcx.mk_alias_ty(assoc_item.def_id, substs_trait_ref_and_assoc_item)
+                tcx.mk_alias_ty(assoc_item.def_id, args_trait_ref_and_assoc_item)
             })
         };
 
@@ -488,6 +488,8 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             }
         }
 
+        let assoc_item_def_id = projection_ty.skip_binder().def_id;
+        let def_kind = tcx.def_kind(assoc_item_def_id);
         match binding.kind {
             ConvertedBindingKind::Equality(..) if return_type_notation => {
                 return Err(self.tcx().sess.emit_err(
@@ -499,11 +501,9 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                 // the "projection predicate" for:
                 //
                 // `<T as Iterator>::Item = u32`
-                let assoc_item_def_id = projection_ty.skip_binder().def_id;
-                let def_kind = tcx.def_kind(assoc_item_def_id);
                 match (def_kind, term.unpack()) {
-                    (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_))
-                    | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (),
+                    (DefKind::AssocTy, ty::TermKind::Ty(_))
+                    | (DefKind::AssocConst, ty::TermKind::Const(_)) => (),
                     (_, _) => {
                         let got = if let Some(_) = term.ty() { "type" } else { "constant" };
                         let expected = tcx.def_descr(assoc_item_def_id);
@@ -516,7 +516,7 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                             format!("{expected} defined here"),
                         );
 
-                        if let hir::def::DefKind::AssocConst = def_kind
+                        if let DefKind::AssocConst = def_kind
                           && let Some(t) = term.ty() && (t.is_enum() || t.references_error())
                           && tcx.features().associated_const_equality {
                             err.span_suggestion(
@@ -528,12 +528,12 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                         }
                         let reported = err.emit();
                         term = match def_kind {
-                            hir::def::DefKind::AssocTy => Ty::new_error(tcx, reported).into(),
-                            hir::def::DefKind::AssocConst => ty::Const::new_error(
+                            DefKind::AssocTy => Ty::new_error(tcx, reported).into(),
+                            DefKind::AssocConst => ty::Const::new_error(
                                 tcx,
                                 reported,
                                 tcx.type_of(assoc_item_def_id)
-                                    .subst(tcx, projection_ty.skip_binder().substs),
+                                    .instantiate(tcx, projection_ty.skip_binder().args),
                             )
                             .into(),
                             _ => unreachable!(),
@@ -548,6 +548,15 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
                 );
             }
             ConvertedBindingKind::Constraint(ast_bounds) => {
+                match def_kind {
+                    DefKind::AssocTy => {}
+                    _ => {
+                        return Err(tcx.sess.emit_err(errors::AssocBoundOnConst {
+                            span: assoc_ident.span,
+                            descr: tcx.def_descr(assoc_item_def_id),
+                        }));
+                    }
+                }
                 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
                 //
                 // `<T as Iterator>::Item: Debug`
diff --git a/compiler/rustc_hir_analysis/src/astconv/errors.rs b/compiler/rustc_hir_analysis/src/astconv/errors.rs
index ddf99853b..bd311c98f 100644
--- a/compiler/rustc_hir_analysis/src/astconv/errors.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/errors.rs
@@ -123,7 +123,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let all_candidate_names: Vec<_> = all_candidates()
             .flat_map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
             .filter_map(|item| {
-                if item.opt_rpitit_info.is_none() && item.kind == ty::AssocKind::Type {
+                if !item.is_impl_trait_in_trait() && item.kind == ty::AssocKind::Type {
                     Some(item.name)
                 } else {
                     None
@@ -164,7 +164,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 self.tcx().associated_items(*trait_def_id).in_definition_order()
             })
             .filter_map(|item| {
-                if item.opt_rpitit_info.is_none() && item.kind == ty::AssocKind::Type {
+                if !item.is_impl_trait_in_trait() && item.kind == ty::AssocKind::Type {
                     Some(item.name)
                 } else {
                     None
@@ -197,7 +197,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
-        err.span_label(span, format!("associated type `{}` not found", assoc_name));
+        err.span_label(span, format!("associated type `{assoc_name}` not found"));
         err.emit()
     }
 
@@ -247,7 +247,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 "the candidate".into()
             };
 
-            let impl_ty = tcx.at(span).type_of(impl_).subst_identity();
+            let impl_ty = tcx.at(span).type_of(impl_).instantiate_identity();
             let note = format!("{title} is defined in an impl for the type `{impl_ty}`");
 
             if let Some(span) = note_span {
@@ -295,7 +295,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             let type_candidates = candidates
                 .iter()
                 .take(limit)
-                .map(|&(impl_, _)| format!("- `{}`", tcx.at(span).type_of(impl_).subst_identity()))
+                .map(|&(impl_, _)| {
+                    format!("- `{}`", tcx.at(span).type_of(impl_).instantiate_identity())
+                })
                 .collect::<Vec<_>>()
                 .join("\n");
             let additional_types = if candidates.len() > limit {
@@ -356,13 +358,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     // `<Foo as Iterator>::Item = String`.
                     let projection_ty = pred.skip_binder().projection_ty;
 
-                    let substs_with_infer_self = tcx.mk_substs_from_iter(
+                    let args_with_infer_self = tcx.mk_args_from_iter(
                         std::iter::once(Ty::new_var(tcx, ty::TyVid::from_u32(0)).into())
-                            .chain(projection_ty.substs.iter().skip(1)),
+                            .chain(projection_ty.args.iter().skip(1)),
                     );
 
                     let quiet_projection_ty =
-                        tcx.mk_alias_ty(projection_ty.def_id, substs_with_infer_self);
+                        tcx.mk_alias_ty(projection_ty.def_id, args_with_infer_self);
 
                     let term = pred.skip_binder().term;
 
@@ -391,7 +393,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .into_iter()
             .map(|error| error.root_obligation.predicate)
             .filter_map(format_pred)
-            .map(|(p, _)| format!("`{}`", p))
+            .map(|(p, _)| format!("`{p}`"))
             .collect();
         bounds.sort();
         bounds.dedup();
@@ -650,7 +652,7 @@ pub(crate) fn fn_trait_to_string(
             }
             .map(|s| {
                 // `s.empty()` checks to see if the type is the unit tuple, if so we don't want a comma
-                if parenthesized || s.is_empty() { format!("({})", s) } else { format!("({},)", s) }
+                if parenthesized || s.is_empty() { format!("({s})") } else { format!("({s},)") }
             })
             .ok(),
             _ => None,
diff --git a/compiler/rustc_hir_analysis/src/astconv/generics.rs b/compiler/rustc_hir_analysis/src/astconv/generics.rs
index 39d1d1f2d..1372cc896 100644
--- a/compiler/rustc_hir_analysis/src/astconv/generics.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/generics.rs
@@ -11,7 +11,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
 use rustc_hir::GenericArg;
 use rustc_middle::ty::{
-    self, subst, subst::SubstsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty, TyCtxt,
+    self, GenericArgsRef, GenericParamDef, GenericParamDefKind, IsSuggestable, Ty, TyCtxt,
 };
 use rustc_session::lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS;
 use rustc_span::{symbol::kw, Span};
@@ -76,12 +76,12 @@ fn generic_arg_mismatch_err(
             Res::Def(DefKind::TyParam, src_def_id) => {
                 if let Some(param_local_id) = param.def_id.as_local() {
                     let param_name = tcx.hir().ty_param_name(param_local_id);
-                    let param_type = tcx.type_of(param.def_id).subst_identity();
+                    let param_type = tcx.type_of(param.def_id).instantiate_identity();
                     if param_type.is_suggestable(tcx, false) {
                         err.span_suggestion(
                             tcx.def_span(src_def_id),
                             "consider changing this type parameter to a const parameter",
-                            format!("const {}: {}", param_name, param_type),
+                            format!("const {param_name}: {param_type}"),
                             Applicability::MaybeIncorrect,
                         );
                     };
@@ -102,7 +102,7 @@ fn generic_arg_mismatch_err(
                 err.span_suggestion(
                     arg.span(),
                     "array type provided where a `usize` was expected, try",
-                    format!("{{ {} }}", snippet),
+                    format!("{{ {snippet} }}"),
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -130,7 +130,7 @@ fn generic_arg_mismatch_err(
         } else {
             (arg.descr(), param.kind.descr())
         };
-        err.note(format!("{} arguments must be provided before {} arguments", first, last));
+        err.note(format!("{first} arguments must be provided before {last} arguments"));
         if let Some(help) = help {
             err.help(help);
         }
@@ -146,14 +146,14 @@ fn generic_arg_mismatch_err(
 ///
 /// To start, we are given the `def_id` of the thing we are
 /// creating the substitutions for, and a partial set of
-/// substitutions `parent_substs`. In general, the substitutions
+/// substitutions `parent_args`. In general, the substitutions
 /// for an item begin with substitutions for all the "parents" of
 /// that item -- e.g., for a method it might include the
 /// parameters from the impl.
 ///
 /// Therefore, the method begins by walking down these parents,
 /// starting with the outermost parent and proceed inwards until
-/// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
+/// it reaches `def_id`. For each parent `P`, it will check `parent_args`
 /// first to see if the parent's substitutions are listed in there. If so,
 /// we can append those and move on. Otherwise, it invokes the
 /// three callback functions:
@@ -168,15 +168,15 @@ fn generic_arg_mismatch_err(
 ///   instantiate a `GenericArg`.
 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
 ///   creates a suitable inference variable.
-pub fn create_substs_for_generic_args<'tcx, 'a>(
+pub fn create_args_for_parent_generic_args<'tcx, 'a>(
     tcx: TyCtxt<'tcx>,
     def_id: DefId,
-    parent_substs: &[subst::GenericArg<'tcx>],
+    parent_args: &[ty::GenericArg<'tcx>],
     has_self: bool,
     self_ty: Option<Ty<'tcx>>,
     arg_count: &GenericArgCountResult,
     ctx: &mut impl CreateSubstsForGenericArgsCtxt<'a, 'tcx>,
-) -> SubstsRef<'tcx> {
+) -> GenericArgsRef<'tcx> {
     // Collect the segments of the path; we need to substitute arguments
     // for parameters throughout the entire path (wherever there are
     // generic parameters).
@@ -191,27 +191,27 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
     // We manually build up the substitution, rather than using convenience
     // methods in `subst.rs`, so that we can iterate over the arguments and
     // parameters in lock-step linearly, instead of trying to match each pair.
-    let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
+    let mut args: SmallVec<[ty::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
     // Iterate over each segment of the path.
     while let Some((def_id, defs)) = stack.pop() {
         let mut params = defs.params.iter().peekable();
 
         // If we have already computed substitutions for parents, we can use those directly.
         while let Some(&param) = params.peek() {
-            if let Some(&kind) = parent_substs.get(param.index as usize) {
-                substs.push(kind);
+            if let Some(&kind) = parent_args.get(param.index as usize) {
+                args.push(kind);
                 params.next();
             } else {
                 break;
             }
         }
 
-        // `Self` is handled first, unless it's been handled in `parent_substs`.
+        // `Self` is handled first, unless it's been handled in `parent_args`.
         if has_self {
             if let Some(&param) = params.peek() {
                 if param.index == 0 {
                     if let GenericParamDefKind::Type { .. } = param.kind {
-                        substs.push(
+                        args.push(
                             self_ty
                                 .map(|ty| ty.into())
                                 .unwrap_or_else(|| ctx.inferred_kind(None, param, true)),
@@ -226,7 +226,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
         let (generic_args, infer_args) = ctx.args_for_def_id(def_id);
 
         let args_iter = generic_args.iter().flat_map(|generic_args| generic_args.args.iter());
-        let mut args = args_iter.clone().peekable();
+        let mut args_iter = args_iter.clone().peekable();
 
         // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
         // If we later encounter a lifetime, we know that the arguments were provided in the
@@ -239,7 +239,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
             // provided, matching them with the generic parameters we expect.
             // Mismatches can occur as a result of elided lifetimes, or for malformed
             // input. We try to handle both sensibly.
-            match (args.peek(), params.peek()) {
+            match (args_iter.peek(), params.peek()) {
                 (Some(&arg), Some(&param)) => {
                     match (arg, &param.kind, arg_count.explicit_late_bound) {
                         (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
@@ -253,8 +253,8 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                             GenericParamDefKind::Const { .. },
                             _,
                         ) => {
-                            substs.push(ctx.provided_kind(param, arg));
-                            args.next();
+                            args.push(ctx.provided_kind(param, arg));
+                            args_iter.next();
                             params.next();
                         }
                         (
@@ -264,7 +264,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                         ) => {
                             // We expected a lifetime argument, but got a type or const
                             // argument. That means we're inferring the lifetimes.
-                            substs.push(ctx.inferred_kind(None, param, infer_args));
+                            args.push(ctx.inferred_kind(None, param, infer_args));
                             force_infer_lt = Some((arg, param));
                             params.next();
                         }
@@ -273,7 +273,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                             // the presence of explicit late bounds. This is most likely
                             // due to the presence of the explicit bound so we're just going to
                             // ignore it.
-                            args.next();
+                            args_iter.next();
                         }
                         (_, _, _) => {
                             // We expected one kind of parameter, but the user provided
@@ -304,7 +304,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                                         "reorder the arguments: {}: `<{}>`",
                                         param_types_present
                                             .into_iter()
-                                            .map(|ord| format!("{}s", ord))
+                                            .map(|ord| format!("{ord}s"))
                                             .collect::<Vec<String>>()
                                             .join(", then "),
                                         ordered_params
@@ -327,7 +327,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                             // errors. In this case, we're simply going to ignore the argument
                             // and any following arguments. The rest of the parameters will be
                             // inferred.
-                            while args.next().is_some() {}
+                            while args_iter.next().is_some() {}
                         }
                     }
                 }
@@ -360,7 +360,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                 (None, Some(&param)) => {
                     // If there are fewer arguments than parameters, it means
                     // we're inferring the remaining arguments.
-                    substs.push(ctx.inferred_kind(Some(&substs), param, infer_args));
+                    args.push(ctx.inferred_kind(Some(&args), param, infer_args));
                     params.next();
                 }
 
@@ -369,7 +369,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
         }
     }
 
-    tcx.mk_substs(&substs)
+    tcx.mk_args(&args)
 }
 
 /// Checks that the correct number of generic arguments have been provided.
diff --git a/compiler/rustc_hir_analysis/src/astconv/lint.rs b/compiler/rustc_hir_analysis/src/astconv/lint.rs
index 05a3ab63d..1bd1270be 100644
--- a/compiler/rustc_hir_analysis/src/astconv/lint.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/lint.rs
@@ -34,9 +34,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             let param_name = generics.params.next_type_param_name(None);
 
             let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
-                (span, format!(", {}: {}", param_name, impl_trait_name))
+                (span, format!(", {param_name}: {impl_trait_name}"))
             } else {
-                (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
+                (generics.span, format!("<{param_name}: {impl_trait_name}>"))
             };
             diag.multipart_suggestion(
             format!("alternatively use a blanket \
@@ -86,7 +86,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 ));
             }
 
-            if self_ty.span.edition().rust_2021() {
+            if self_ty.span.edition().at_least_rust_2021() {
                 let msg = "trait objects must include the `dyn` keyword";
                 let label = "add `dyn` keyword before this trait";
                 let mut diag =
diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 3d6984628..668763f9b 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -9,7 +9,7 @@ mod lint;
 mod object_safety;
 
 use crate::astconv::errors::prohibit_assoc_ty_binding;
-use crate::astconv::generics::{check_generic_arg_count, create_substs_for_generic_args};
+use crate::astconv::generics::{check_generic_arg_count, create_args_for_parent_generic_args};
 use crate::bounds::Bounds;
 use crate::collect::HirPlaceholderCollector;
 use crate::errors::{AmbiguousLifetimeBound, TypeofReservedKeywordUsed};
@@ -29,9 +29,10 @@ use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
 use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::middle::stability::AllowUnstable;
-use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
 use rustc_middle::ty::GenericParamDefKind;
-use rustc_middle::ty::{self, Const, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{
+    self, Const, GenericArgKind, GenericArgsRef, IsSuggestable, Ty, TyCtxt, TypeVisitableExt,
+};
 use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
@@ -220,14 +221,14 @@ pub trait CreateSubstsForGenericArgsCtxt<'a, 'tcx> {
         &mut self,
         param: &ty::GenericParamDef,
         arg: &GenericArg<'_>,
-    ) -> subst::GenericArg<'tcx>;
+    ) -> ty::GenericArg<'tcx>;
 
     fn inferred_kind(
         &mut self,
-        substs: Option<&[subst::GenericArg<'tcx>]>,
+        args: Option<&[ty::GenericArg<'tcx>]>,
         param: &ty::GenericParamDef,
         infer_args: bool,
-    ) -> subst::GenericArg<'tcx>;
+    ) -> ty::GenericArg<'tcx>;
 }
 
 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
@@ -291,13 +292,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
     /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
     /// returns an appropriate set of substitutions for this particular reference to `I`.
-    pub fn ast_path_substs_for_ty(
+    pub fn ast_path_args_for_ty(
         &self,
         span: Span,
         def_id: DefId,
         item_segment: &hir::PathSegment<'_>,
-    ) -> SubstsRef<'tcx> {
-        let (substs, _) = self.create_substs_for_ast_path(
+    ) -> GenericArgsRef<'tcx> {
+        let (args, _) = self.create_args_for_ast_path(
             span,
             def_id,
             &[],
@@ -311,7 +312,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             prohibit_assoc_ty_binding(self.tcx(), b.span, Some((item_segment, span)));
         }
 
-        substs
+        args
     }
 
     /// Given the type/lifetime/const arguments provided to some path (along with
@@ -330,7 +331,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// 2. The path in question is the path to the trait `std::ops::Index`,
     ///    which will have been resolved to a `def_id`
     /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
-    ///    parameters are returned in the `SubstsRef`, the associated type bindings like
+    ///    parameters are returned in the `GenericArgsRef`, the associated type bindings like
     ///    `Output = u32` are returned from `create_assoc_bindings_for_generic_args`.
     ///
     /// Note that the type listing given here is *exactly* what the user provided.
@@ -341,22 +342,22 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
     /// ```
     ///
-    /// We have the parent substs are the substs for the parent trait:
+    /// We have the parent args are the args for the parent trait:
     /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
-    /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
+    /// type itself: `['a]`. The returned `GenericArgsRef` concatenates these two
     /// lists: `[Vec<u8>, u8, 'a]`.
     #[instrument(level = "debug", skip(self, span), ret)]
-    fn create_substs_for_ast_path<'a>(
+    fn create_args_for_ast_path<'a>(
         &self,
         span: Span,
         def_id: DefId,
-        parent_substs: &[subst::GenericArg<'tcx>],
+        parent_args: &[ty::GenericArg<'tcx>],
         seg: &hir::PathSegment<'_>,
         generic_args: &'a hir::GenericArgs<'_>,
         infer_args: bool,
         self_ty: Option<Ty<'tcx>>,
         constness: ty::BoundConstness,
-    ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
+    ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
         // If the type is parameterized by this region, then replace this
         // region with the current anon region binding (in other words,
         // whatever & would get replaced with).
@@ -369,7 +370,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             if generics.parent.is_some() {
                 // The parent is a trait so it should have at least one subst
                 // for the `Self` type.
-                assert!(!parent_substs.is_empty())
+                assert!(!parent_args.is_empty())
             } else {
                 // This item (presumably a trait) needs a self-type.
                 assert!(self_ty.is_some());
@@ -395,7 +396,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // here and so associated type bindings will be handled regardless of whether there are any
         // non-`Self` generic parameters.
         if generics.params.is_empty() {
-            return (tcx.mk_substs(parent_substs), arg_count);
+            return (tcx.mk_args(parent_args), arg_count);
         }
 
         struct SubstsForAstPathCtxt<'a, 'tcx> {
@@ -421,7 +422,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 &mut self,
                 param: &ty::GenericParamDef,
                 arg: &GenericArg<'_>,
-            ) -> subst::GenericArg<'tcx> {
+            ) -> ty::GenericArg<'tcx> {
                 let tcx = self.astconv.tcx();
 
                 let mut handle_ty_args = |has_default, ty: &hir::Ty<'_>| {
@@ -483,10 +484,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             fn inferred_kind(
                 &mut self,
-                substs: Option<&[subst::GenericArg<'tcx>]>,
+                args: Option<&[ty::GenericArg<'tcx>]>,
                 param: &ty::GenericParamDef,
                 infer_args: bool,
-            ) -> subst::GenericArg<'tcx> {
+            ) -> ty::GenericArg<'tcx> {
                 let tcx = self.astconv.tcx();
                 match param.kind {
                     GenericParamDefKind::Lifetime => self
@@ -506,15 +507,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     GenericParamDefKind::Type { has_default, .. } => {
                         if !infer_args && has_default {
                             // No type parameter provided, but a default exists.
-                            let substs = substs.unwrap();
-                            if substs.iter().any(|arg| match arg.unpack() {
+                            let args = args.unwrap();
+                            if args.iter().any(|arg| match arg.unpack() {
                                 GenericArgKind::Type(ty) => ty.references_error(),
                                 _ => false,
                             }) {
                                 // Avoid ICE #86756 when type error recovery goes awry.
                                 return Ty::new_misc_error(tcx).into();
                             }
-                            tcx.at(self.span).type_of(param.def_id).subst(tcx, substs).into()
+                            tcx.at(self.span).type_of(param.def_id).instantiate(tcx, args).into()
                         } else if infer_args {
                             self.astconv.ty_infer(Some(param), self.span).into()
                         } else {
@@ -531,8 +532,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         if let Err(guar) = ty.error_reported() {
                             return ty::Const::new_error(tcx, guar, ty).into();
                         }
+                        // FIXME(effects) see if we should special case effect params here
                         if !infer_args && has_default {
-                            tcx.const_param_default(param.def_id).subst(tcx, substs.unwrap()).into()
+                            tcx.const_param_default(param.def_id)
+                                .instantiate(tcx, args.unwrap())
+                                .into()
                         } else {
                             if infer_args {
                                 self.astconv.ct_infer(ty, Some(param), self.span).into()
@@ -546,7 +550,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
-        let mut substs_ctx = SubstsForAstPathCtxt {
+        let mut args_ctx = SubstsForAstPathCtxt {
             astconv: self,
             def_id,
             span,
@@ -554,14 +558,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             inferred_params: vec![],
             infer_args,
         };
-        let substs = create_substs_for_generic_args(
+        let args = create_args_for_parent_generic_args(
             tcx,
             def_id,
-            parent_substs,
+            parent_args,
             self_ty.is_some(),
             self_ty,
             &arg_count,
-            &mut substs_ctx,
+            &mut args_ctx,
         );
 
         if let ty::BoundConstness::ConstIfConst = constness
@@ -570,7 +574,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             tcx.sess.emit_err(crate::errors::ConstBoundForNonConstTrait { span } );
         }
 
-        (substs, arg_count)
+        (args, arg_count)
     }
 
     fn create_assoc_bindings_for_generic_args<'a>(
@@ -617,21 +621,21 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         assoc_bindings
     }
 
-    pub fn create_substs_for_associated_item(
+    pub fn create_args_for_associated_item(
         &self,
         span: Span,
         item_def_id: DefId,
         item_segment: &hir::PathSegment<'_>,
-        parent_substs: SubstsRef<'tcx>,
-    ) -> SubstsRef<'tcx> {
+        parent_args: GenericArgsRef<'tcx>,
+    ) -> GenericArgsRef<'tcx> {
         debug!(
-            "create_substs_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
+            "create_args_for_associated_item(span: {:?}, item_def_id: {:?}, item_segment: {:?}",
             span, item_def_id, item_segment
         );
-        let (args, _) = self.create_substs_for_ast_path(
+        let (args, _) = self.create_args_for_ast_path(
             span,
             item_def_id,
-            parent_substs,
+            parent_args,
             item_segment,
             item_segment.args(),
             item_segment.infer_args,
@@ -656,7 +660,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         &self,
         trait_ref: &hir::TraitRef<'_>,
         self_ty: Ty<'tcx>,
-        constness: ty::BoundConstness,
     ) -> ty::TraitRef<'tcx> {
         self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1.iter(), |_| {});
 
@@ -666,7 +669,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             self_ty,
             trait_ref.path.segments.last().unwrap(),
             true,
-            constness,
+            ty::BoundConstness::NotConst,
         )
     }
 
@@ -687,7 +690,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Ty<'tcx>,
         only_self_bounds: OnlySelfBounds,
     ) -> GenericArgCountResult {
-        let (substs, arg_count) = self.create_substs_for_ast_path(
+        let (generic_args, arg_count) = self.create_args_for_ast_path(
             trait_ref_span,
             trait_def_id,
             &[],
@@ -704,11 +707,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
 
-        let poly_trait_ref =
-            ty::Binder::bind_with_vars(ty::TraitRef::new(tcx, trait_def_id, substs), bound_vars);
+        let poly_trait_ref = ty::Binder::bind_with_vars(
+            ty::TraitRef::new(tcx, trait_def_id, generic_args),
+            bound_vars,
+        );
 
         debug!(?poly_trait_ref, ?assoc_bindings);
-        bounds.push_trait_bound(tcx, poly_trait_ref, span, constness, polarity);
+        bounds.push_trait_bound(tcx, poly_trait_ref, span, polarity);
 
         let mut dup_bindings = FxHashMap::default();
         for binding in &assoc_bindings {
@@ -844,9 +849,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Ty<'tcx>,
         trait_segment: &hir::PathSegment<'_>,
         is_impl: bool,
+        // FIXME(effects) move all host param things in astconv to hir lowering
         constness: ty::BoundConstness,
     ) -> ty::TraitRef<'tcx> {
-        let (substs, _) = self.create_substs_for_ast_trait_ref(
+        let (generic_args, _) = self.create_args_for_ast_trait_ref(
             span,
             trait_def_id,
             self_ty,
@@ -857,11 +863,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         if let Some(b) = trait_segment.args().bindings.first() {
             prohibit_assoc_ty_binding(self.tcx(), b.span, Some((trait_segment, span)));
         }
-        ty::TraitRef::new(self.tcx(), trait_def_id, substs)
+        ty::TraitRef::new(self.tcx(), trait_def_id, generic_args)
     }
 
     #[instrument(level = "debug", skip(self, span))]
-    fn create_substs_for_ast_trait_ref<'a>(
+    fn create_args_for_ast_trait_ref<'a>(
         &self,
         span: Span,
         trait_def_id: DefId,
@@ -869,10 +875,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         trait_segment: &'a hir::PathSegment<'a>,
         is_impl: bool,
         constness: ty::BoundConstness,
-    ) -> (SubstsRef<'tcx>, GenericArgCountResult) {
+    ) -> (GenericArgsRef<'tcx>, GenericArgCountResult) {
         self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment, is_impl);
 
-        self.create_substs_for_ast_path(
+        self.create_args_for_ast_path(
             span,
             trait_def_id,
             &[],
@@ -902,19 +908,21 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         did: DefId,
         item_segment: &hir::PathSegment<'_>,
     ) -> Ty<'tcx> {
-        let substs = self.ast_path_substs_for_ty(span, did, item_segment);
-        let ty = self.tcx().at(span).type_of(did);
+        let tcx = self.tcx();
+        let args = self.ast_path_args_for_ty(span, did, item_segment);
+        let ty = tcx.at(span).type_of(did);
 
-        if matches!(self.tcx().def_kind(did), DefKind::TyAlias)
-            && (ty.skip_binder().has_opaque_types() || self.tcx().features().lazy_type_alias)
+        if let DefKind::TyAlias { lazy } = tcx.def_kind(did)
+            && (lazy || ty.skip_binder().has_opaque_types())
         {
             // Type aliases referring to types that contain opaque types (but aren't just directly
-            // referencing a single opaque type) get encoded as a type alias that normalization will
+            // referencing a single opaque type) as well as those defined in crates that have the
+            // feature `lazy_type_alias` enabled get encoded as a type alias that normalization will
             // then actually instantiate the where bounds of.
-            let alias_ty = self.tcx().mk_alias_ty(did, substs);
-            Ty::new_alias(self.tcx(), ty::Weak, alias_ty)
+            let alias_ty = tcx.mk_alias_ty(did, args);
+            Ty::new_alias(tcx, ty::Weak, alias_ty)
         } else {
-            ty.subst(self.tcx(), substs)
+            ty.instantiate(tcx, args)
         }
     }
 
@@ -1123,7 +1131,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ty_param_name
                 )
             };
-            err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
+            err.span_label(span, format!("ambiguous associated type `{assoc_name}`"));
 
             let mut where_bounds = vec![];
             for bound in bounds {
@@ -1267,9 +1275,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 "you might have meant to specify type parameters on enum \
                                  `{type_name}`"
                             );
-                            let Some(args) = assoc_segment.args else { return; };
+                            let Some(args) = assoc_segment.args else {
+                                return;
+                            };
                             // Get the span of the generics args *including* the leading `::`.
-                            let args_span = assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
+                            let args_span =
+                                assoc_segment.ident.span.shrink_to_hi().to(args.span_ext);
                             if tcx.generics_of(adt_def.did()).count() == 0 {
                                 // FIXME(estebank): we could also verify that the arguments being
                                 // work for the `enum`, instead of just looking if it takes *any*.
@@ -1281,49 +1292,56 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 );
                                 return;
                             }
-                            let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span) else {
+                            let Ok(snippet) = tcx.sess.source_map().span_to_snippet(args_span)
+                            else {
                                 err.note(msg);
                                 return;
                             };
-                            let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
-                                hir::QPath::Resolved(_, path)
-                            ) = &qself.kind {
-                                // If the path segment already has type params, we want to overwrite
-                                // them.
-                                match &path.segments {
-                                    // `segment` is the previous to last element on the path,
-                                    // which would normally be the `enum` itself, while the last
-                                    // `_` `PathSegment` corresponds to the variant.
-                                    [.., hir::PathSegment {
-                                        ident,
-                                        args,
-                                        res: Res::Def(DefKind::Enum, _),
-                                        ..
-                                    }, _] => (
-                                        // We need to include the `::` in `Type::Variant::<Args>`
-                                        // to point the span to `::<Args>`, not just `<Args>`.
-                                        ident.span.shrink_to_hi().to(args.map_or(
-                                            ident.span.shrink_to_hi(),
-                                            |a| a.span_ext)),
-                                        false,
-                                    ),
-                                    [segment] => (
-                                        // We need to include the `::` in `Type::Variant::<Args>`
-                                        // to point the span to `::<Args>`, not just `<Args>`.
-                                        segment.ident.span.shrink_to_hi().to(segment.args.map_or(
-                                            segment.ident.span.shrink_to_hi(),
-                                            |a| a.span_ext)),
-                                        kw::SelfUpper == segment.ident.name,
-                                    ),
-                                    _ => {
-                                        err.note(msg);
-                                        return;
+                            let (qself_sugg_span, is_self) =
+                                if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) =
+                                    &qself.kind
+                                {
+                                    // If the path segment already has type params, we want to overwrite
+                                    // them.
+                                    match &path.segments {
+                                        // `segment` is the previous to last element on the path,
+                                        // which would normally be the `enum` itself, while the last
+                                        // `_` `PathSegment` corresponds to the variant.
+                                        [
+                                            ..,
+                                            hir::PathSegment {
+                                                ident,
+                                                args,
+                                                res: Res::Def(DefKind::Enum, _),
+                                                ..
+                                            },
+                                            _,
+                                        ] => (
+                                            // We need to include the `::` in `Type::Variant::<Args>`
+                                            // to point the span to `::<Args>`, not just `<Args>`.
+                                            ident.span.shrink_to_hi().to(args
+                                                .map_or(ident.span.shrink_to_hi(), |a| a.span_ext)),
+                                            false,
+                                        ),
+                                        [segment] => (
+                                            // We need to include the `::` in `Type::Variant::<Args>`
+                                            // to point the span to `::<Args>`, not just `<Args>`.
+                                            segment.ident.span.shrink_to_hi().to(segment
+                                                .args
+                                                .map_or(segment.ident.span.shrink_to_hi(), |a| {
+                                                    a.span_ext
+                                                })),
+                                            kw::SelfUpper == segment.ident.name,
+                                        ),
+                                        _ => {
+                                            err.note(msg);
+                                            return;
+                                        }
                                     }
-                                }
-                            } else {
-                                err.note(msg);
-                                return;
-                            };
+                                } else {
+                                    err.note(msg);
+                                    return;
+                                };
                             let suggestion = vec![
                                 if is_self {
                                     // Account for people writing `Self::Variant::<Args>`, where
@@ -1373,7 +1391,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 };
 
                 self.one_bound_for_assoc_type(
-                    || traits::supertraits(tcx, ty::Binder::dummy(trait_ref.subst_identity())),
+                    || {
+                        traits::supertraits(
+                            tcx,
+                            ty::Binder::dummy(trait_ref.instantiate_identity()),
+                        )
+                    },
                     kw::SelfUpper,
                     assoc_ident,
                     span,
@@ -1387,7 +1410,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             _ => {
                 let reported = if variant_resolution.is_some() {
                     // Variant in type position
-                    let msg = format!("expected type, found variant `{}`", assoc_ident);
+                    let msg = format!("expected type, found variant `{assoc_ident}`");
                     tcx.sess.span_err(span, msg)
                 } else if qself_ty.is_enum() {
                     let mut err = struct_span_err!(
@@ -1418,12 +1441,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     } else {
                         err.span_label(
                             assoc_ident.span,
-                            format!("variant not found in `{}`", qself_ty),
+                            format!("variant not found in `{qself_ty}`"),
                         );
                     }
 
                     if let Some(sp) = tcx.hir().span_if_local(adt_def.did()) {
-                        err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
+                        err.span_label(sp, format!("variant `{assoc_ident}` not found here"));
                     }
 
                     err.emit()
@@ -1442,7 +1465,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     let traits: Vec<_> =
                         self.probe_traits_that_match_assoc_ty(qself_ty, assoc_ident);
 
-                    // Don't print `TyErr` to the user.
+                    // Don't print `ty::Error` to the user.
                     self.report_ambiguous_associated_type(
                         span,
                         &[qself_ty.to_string()],
@@ -1455,7 +1478,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         };
 
         let trait_did = bound.def_id();
-        let Some(assoc_ty_did) = self.lookup_assoc_ty(assoc_ident, hir_ref_id, span, trait_did) else {
+        let Some(assoc_ty_did) = self.lookup_assoc_ty(assoc_ident, hir_ref_id, span, trait_did)
+        else {
             // Assume that if it's not matched, there must be a const defined with the same name
             // but it was used in a type position.
             let msg = format!("found associated const `{assoc_ident}` when type was expected");
@@ -1609,8 +1633,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         let ocx = ObligationCtxt::new(&infcx);
                         ocx.register_obligations(obligations.clone());
 
-                        let impl_substs = infcx.fresh_substs_for_item(span, impl_);
-                        let impl_ty = tcx.type_of(impl_).subst(tcx, impl_substs);
+                        let impl_args = infcx.fresh_args_for_item(span, impl_);
+                        let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args);
                         let impl_ty = ocx.normalize(&cause, param_env, impl_ty);
 
                         // Check that the self types can be related.
@@ -1622,7 +1646,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         }
 
                         // Check whether the impl imposes obligations we have to worry about.
-                        let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_substs);
+                        let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args);
                         let impl_bounds = ocx.normalize(&cause, param_env, impl_bounds);
                         let impl_obligations = traits::predicates_for_generics(
                             |_, _| cause.clone(),
@@ -1654,18 +1678,17 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         if let Some((impl_, (assoc_item, def_scope))) = applicable_candidates.pop() {
             self.check_assoc_ty(assoc_item, name, def_scope, block, span);
 
-            // FIXME(fmease): Currently creating throwaway `parent_substs` to please
-            // `create_substs_for_associated_item`. Modify the latter instead (or sth. similar) to
-            // not require the parent substs logic.
-            let parent_substs = InternalSubsts::identity_for_item(tcx, impl_);
-            let substs =
-                self.create_substs_for_associated_item(span, assoc_item, segment, parent_substs);
-            let substs = tcx.mk_substs_from_iter(
+            // FIXME(fmease): Currently creating throwaway `parent_args` to please
+            // `create_args_for_associated_item`. Modify the latter instead (or sth. similar) to
+            // not require the parent args logic.
+            let parent_args = ty::GenericArgs::identity_for_item(tcx, impl_);
+            let args = self.create_args_for_associated_item(span, assoc_item, segment, parent_args);
+            let args = tcx.mk_args_from_iter(
                 std::iter::once(ty::GenericArg::from(self_ty))
-                    .chain(substs.into_iter().skip(parent_substs.len())),
+                    .chain(args.into_iter().skip(parent_args.len())),
             );
 
-            let ty = Ty::new_alias(tcx, ty::Inherent, tcx.mk_alias_ty(assoc_item, substs));
+            let ty = Ty::new_alias(tcx, ty::Inherent, tcx.mk_alias_ty(assoc_item, args));
 
             return Ok(Some((ty, assoc_item)));
         }
@@ -1769,9 +1792,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         .any(|impl_def_id| {
                             let trait_ref = tcx.impl_trait_ref(impl_def_id);
                             trait_ref.is_some_and(|trait_ref| {
-                                let impl_ = trait_ref.subst(
+                                let impl_ = trait_ref.instantiate(
                                     tcx,
-                                    infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id),
+                                    infcx.fresh_args_for_item(DUMMY_SP, impl_def_id),
                                 );
                                 let value = tcx.fold_regions(qself_ty, |_, _| tcx.lifetimes.re_erased);
                                 // FIXME: Don't bother dealing with non-lifetime binders here...
@@ -1814,7 +1837,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
 
-            let parent_def_id = def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
+            let parent_def_id = def_id
+                .as_local()
+                .map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
                 .map(|hir_id| tcx.hir().get_parent_item(hir_id).to_def_id());
 
             debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
@@ -1835,7 +1860,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative
                     })
                     .filter_map(|impl_def_id| tcx.impl_trait_ref(impl_def_id))
-                    .map(|impl_| impl_.subst_identity().self_ty())
+                    .map(|impl_| impl_.instantiate_identity().self_ty())
                     // We don't care about blanket impls.
                     .filter(|self_ty| !self_ty.has_non_region_param())
                     .map(|self_ty| tcx.erase_regions(self_ty).to_string())
@@ -1850,7 +1875,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 &[path_str],
                 item_segment.ident.name,
             );
-            return Ty::new_error(tcx,reported)
+            return Ty::new_error(tcx, reported);
         };
 
         debug!("qpath_to_ty: self_type={:?}", self_ty);
@@ -1864,16 +1889,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             constness,
         );
 
-        let item_substs = self.create_substs_for_associated_item(
-            span,
-            item_def_id,
-            item_segment,
-            trait_ref.substs,
-        );
+        let item_args =
+            self.create_args_for_associated_item(span, item_def_id, item_segment, trait_ref.args);
 
         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 
-        Ty::new_projection(tcx, item_def_id, item_substs)
+        Ty::new_projection(tcx, item_def_id, item_args)
     }
 
     pub fn prohibit_generics<'a>(
@@ -2128,19 +2149,19 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let span = path.span;
         match path.res {
-            Res::Def(DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder, did) => {
+            Res::Def(DefKind::OpaqueTy, did) => {
                 // Check for desugared `impl Trait`.
                 assert!(tcx.is_type_alias_impl_trait(did));
                 let item_segment = path.segments.split_last().unwrap();
                 self.prohibit_generics(item_segment.1.iter(), |err| {
                     err.note("`impl Trait` types can't have type parameters");
                 });
-                let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
-                Ty::new_opaque(tcx, did, substs)
+                let args = self.ast_path_args_for_ty(span, did, item_segment.0);
+                Ty::new_opaque(tcx, did, args)
             }
             Res::Def(
                 DefKind::Enum
-                | DefKind::TyAlias
+                | DefKind::TyAlias { .. }
                 | DefKind::Struct
                 | DefKind::Union
                 | DefKind::ForeignTy,
@@ -2220,7 +2241,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 // `Self` in impl (we know the concrete type).
                 assert_eq!(opt_self_ty, None);
                 // Try to evaluate any array length constants.
-                let ty = tcx.at(span).type_of(def_id).subst_identity();
+                let ty = tcx.at(span).type_of(def_id).instantiate_identity();
                 let span_of_impl = tcx.span_of_impl(def_id);
                 self.prohibit_generics(path.segments.iter(), |err| {
                     let def_id = match *ty.kind() {
@@ -2439,7 +2460,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         // If this is an RPITIT and we are using the new RPITIT lowering scheme, we
                         // generate the def_id of an associated type for the trait and return as
                         // type a projection.
-                        let def_id = if in_trait && tcx.lower_impl_trait_in_trait_to_assoc_ty() {
+                        let def_id = if in_trait {
                             tcx.associated_type_for_impl_trait_in_trait(local_def_id).to_def_id()
                         } else {
                             local_def_id.to_def_id()
@@ -2458,7 +2479,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
             &hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
                 let def_id = tcx.require_lang_item(lang_item, Some(span));
-                let (substs, _) = self.create_substs_for_ast_path(
+                let (args, _) = self.create_args_for_ast_path(
                     span,
                     def_id,
                     &[],
@@ -2468,7 +2489,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     None,
                     ty::BoundConstness::NotConst,
                 );
-                tcx.at(span).type_of(def_id).subst(tcx, substs)
+                tcx.at(span).type_of(def_id).instantiate(tcx, args)
             }
             hir::TyKind::Array(ty, length) => {
                 let length = match length {
@@ -2481,7 +2502,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 Ty::new_array_with_const_len(tcx, self.ast_ty_to_ty(ty), length)
             }
             hir::TyKind::Typeof(e) => {
-                let ty_erased = tcx.type_of(e.def_id).subst_identity();
+                let ty_erased = tcx.type_of(e.def_id).instantiate_identity();
                 let ty = tcx.fold_regions(ty_erased, |r, _| {
                     if r.is_erased() { tcx.lifetimes.re_static } else { r }
                 });
@@ -2523,7 +2544,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let generics = tcx.generics_of(def_id);
 
         debug!("impl_trait_ty_to_ty: generics={:?}", generics);
-        let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
+        let args = ty::GenericArgs::for_item(tcx, def_id, |param, _| {
             // We use `generics.count() - lifetimes.len()` here instead of `generics.parent_count`
             // since return-position impl trait in trait squashes all of the generics from its source fn
             // into its own generics, so the opaque's "own" params isn't always just lifetimes.
@@ -2537,12 +2558,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 tcx.mk_param_from_def(param)
             }
         });
-        debug!("impl_trait_ty_to_ty: substs={:?}", substs);
+        debug!("impl_trait_ty_to_ty: args={:?}", args);
 
         if in_trait {
-            Ty::new_projection(tcx, def_id, substs)
+            Ty::new_projection(tcx, def_id, args)
         } else {
-            Ty::new_opaque(tcx, def_id, substs)
+            Ty::new_opaque(tcx, def_id, args)
         }
     }
 
@@ -2688,14 +2709,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let hir = tcx.hir();
 
         let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
-            hir.get(fn_hir_id) else { return None };
+            hir.get(fn_hir_id)
+        else {
+            return None;
+        };
         let i = hir.get_parent(fn_hir_id).expect_item().expect_impl();
 
-        let trait_ref = self.instantiate_mono_trait_ref(
-            i.of_trait.as_ref()?,
-            self.ast_ty_to_ty(i.self_ty),
-            ty::BoundConstness::NotConst,
-        );
+        let trait_ref =
+            self.instantiate_mono_trait_ref(i.of_trait.as_ref()?, self.ast_ty_to_ty(i.self_ty));
 
         let assoc = tcx.associated_items(trait_ref.def_id).find_by_name_and_kind(
             tcx,
@@ -2704,9 +2725,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             trait_ref.def_id,
         )?;
 
-        let fn_sig = tcx.fn_sig(assoc.def_id).subst(
+        let fn_sig = tcx.fn_sig(assoc.def_id).instantiate(
             tcx,
-            trait_ref.substs.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
+            trait_ref.args.extend_to(tcx, assoc.def_id, |param, _| tcx.mk_param_from_def(param)),
         );
         let fn_sig = tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), fn_sig);
 
@@ -2729,7 +2750,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 ty::BrNamed(_, kw::UnderscoreLifetime) | ty::BrAnon(..) | ty::BrEnv => {
                     "an anonymous lifetime".to_string()
                 }
-                ty::BrNamed(_, name) => format!("lifetime `{}`", name),
+                ty::BrNamed(_, name) => format!("lifetime `{name}`"),
             };
 
             let mut err = generate_err(&br_name);
diff --git a/compiler/rustc_hir_analysis/src/astconv/object_safety.rs b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
index 9227ee934..30c2ab8f5 100644
--- a/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
@@ -62,11 +62,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             match bound_pred.skip_binder() {
                 ty::ClauseKind::Trait(trait_pred) => {
                     assert_eq!(trait_pred.polarity, ty::ImplPolarity::Positive);
-                    trait_bounds.push((
-                        bound_pred.rebind(trait_pred.trait_ref),
-                        span,
-                        trait_pred.constness,
-                    ));
+                    trait_bounds.push((bound_pred.rebind(trait_pred.trait_ref), span));
                 }
                 ty::ClauseKind::Projection(proj) => {
                     projection_bounds.push((bound_pred.rebind(proj), span));
@@ -86,7 +82,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // Expand trait aliases recursively and check that only one regular (non-auto) trait
         // is used and no 'maybe' bounds are used.
         let expanded_traits =
-            traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b, _)| (a, b)));
+            traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b)| (a, b)));
 
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
             .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
@@ -126,7 +122,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         if regular_traits.is_empty() && auto_traits.is_empty() {
             let trait_alias_span = trait_bounds
                 .iter()
-                .map(|&(trait_ref, _, _)| trait_ref.def_id())
+                .map(|&(trait_ref, _)| trait_ref.def_id())
                 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
                 .map(|trait_ref| tcx.def_span(trait_ref));
             let reported =
@@ -157,10 +153,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let regular_traits_refs_spans = trait_bounds
             .into_iter()
-            .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
+            .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
-        for (base_trait_ref, span, constness) in regular_traits_refs_spans {
-            assert_eq!(constness, ty::BoundConstness::NotConst);
+        for (base_trait_ref, span) in regular_traits_refs_spans {
             let base_pred: ty::Predicate<'tcx> = base_trait_ref.to_predicate(tcx);
             for pred in traits::elaborate(tcx, [base_pred]) {
                 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", pred);
@@ -173,7 +168,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             tcx.associated_items(pred.def_id())
                                 .in_definition_order()
                                 .filter(|item| item.kind == ty::AssocKind::Type)
-                                .filter(|item| item.opt_rpitit_info.is_none())
+                                .filter(|item| !item.is_impl_trait_in_trait())
                                 .map(|item| item.def_id),
                         );
                     }
@@ -262,8 +257,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let mut missing_type_params = vec![];
                 let mut references_self = false;
                 let generics = tcx.generics_of(trait_ref.def_id);
-                let substs: Vec<_> = trait_ref
-                    .substs
+                let args: Vec<_> = trait_ref
+                    .args
                     .iter()
                     .enumerate()
                     .skip(1) // Remove `Self` for `ExistentialPredicate`.
@@ -279,7 +274,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         arg
                     })
                     .collect();
-                let substs = tcx.mk_substs(&substs);
+                let args = tcx.mk_args(&args);
 
                 let span = i.bottom().1;
                 let empty_generic_args = hir_trait_bounds.iter().any(|hir_bound| {
@@ -310,7 +305,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     err.emit();
                 }
 
-                ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
+                ty::ExistentialTraitRef { def_id: trait_ref.def_id, args }
             })
         });
 
@@ -325,7 +320,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
                     // Like for trait refs, verify that `dummy_self` did not leak inside default type
                     // parameters.
-                    let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
+                    let references_self = b.projection_ty.args.iter().skip(1).any(|arg| {
                         if arg.walk().any(|arg| arg == dummy_self.into()) {
                             return true;
                         }
@@ -336,9 +331,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             span,
                             "trait object projection bounds reference `Self`",
                         );
-                        let substs: Vec<_> = b
+                        let args: Vec<_> = b
                             .projection_ty
-                            .substs
+                            .args
                             .iter()
                             .map(|arg| {
                                 if arg.walk().any(|arg| arg == dummy_self.into()) {
@@ -347,7 +342,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 arg
                             })
                             .collect();
-                        b.projection_ty.substs = tcx.mk_substs(&substs);
+                        b.projection_ty.args = tcx.mk_args(&args);
                     }
 
                     ty::ExistentialProjection::erase_self_ty(tcx, b)