1 use rustc_errors::{Applicability, ErrorReported, StashKey};
3 use rustc_hir::def::{DefKind, Res};
4 use rustc_hir::def_id::{DefId, LocalDefId};
5 use rustc_hir::intravisit;
6 use rustc_hir::intravisit::Visitor;
7 use rustc_hir::{HirId, Node};
8 use rustc_middle::hir::nested_filter;
9 use rustc_middle::ty::subst::InternalSubsts;
10 use rustc_middle::ty::util::IntTypeExt;
11 use rustc_middle::ty::{self, DefIdTree, Ty, TyCtxt, TypeFoldable, TypeFolder};
12 use rustc_span::symbol::Ident;
13 use rustc_span::{Span, DUMMY_SP};
16 use super::{bad_placeholder, is_suggestable_infer_ty};
18 /// Computes the relevant generic parameter for a potential generic const argument.
20 /// This should be called using the query `tcx.opt_const_param_of`.
21 #[instrument(level = "debug", skip(tcx))]
22 pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<DefId> {
24 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
26 match tcx.hir().get(hir_id) {
27 Node::AnonConst(_) => (),
31 let parent_node_id = tcx.hir().get_parent_node(hir_id);
32 let parent_node = tcx.hir().get(parent_node_id);
34 let (generics, arg_idx) = match parent_node {
35 // This match arm is for when the def_id appears in a GAT whose
36 // path can't be resolved without typechecking e.g.
39 // type Assoc<const N: usize>;
40 // fn foo() -> Self::Assoc<3>;
43 // In the above code we would call this query with the def_id of 3 and
44 // the parent_node we match on would be the hir node for Self::Assoc<3>
46 // `Self::Assoc<3>` cant be resolved without typchecking here as we
47 // didnt write <Self as Foo>::Assoc<3>. If we did then another match
48 // arm would handle this.
50 // I believe this match arm is only needed for GAT but I am not 100% sure - BoxyUwU
51 Node::Ty(hir_ty @ Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => {
52 // Find the Item containing the associated type so we can create an ItemCtxt.
53 // Using the ItemCtxt convert the HIR for the unresolved assoc type into a
54 // ty which is a fully resolved projection.
55 // For the code example above, this would mean converting Self::Assoc<3>
56 // into a ty::Projection(<Self as Foo>::Assoc<3>)
60 .filter(|(_, node)| matches!(node, Node::Item(_)))
64 let item_did = tcx.hir().local_def_id(item_hir_id).to_def_id();
65 let item_ctxt = &ItemCtxt::new(tcx, item_did) as &dyn crate::astconv::AstConv<'_>;
66 let ty = item_ctxt.ast_ty_to_ty(hir_ty);
68 // Iterate through the generics of the projection to find the one that corresponds to
69 // the def_id that this query was called with. We filter to only const args here as a
70 // precaution for if it's ever allowed to elide lifetimes in GAT's. It currently isn't
71 // but it can't hurt to be safe ^^
72 if let ty::Projection(projection) = ty.kind() {
73 let generics = tcx.generics_of(projection.item_def_id);
75 let arg_index = segment
80 .filter(|arg| arg.is_ty_or_const())
81 .position(|arg| arg.id() == hir_id)
84 bug!("no arg matching AnonConst in segment");
89 // I dont think it's possible to reach this but I'm not 100% sure - BoxyUwU
90 tcx.sess.delay_span_bug(
92 "unexpected non-GAT usage of an anon const",
99 ExprKind::MethodCall(segment, ..) | ExprKind::Path(QPath::TypeRelative(_, segment)),
102 let body_owner = tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
103 let tables = tcx.typeck(body_owner);
104 // This may fail in case the method/path does not actually exist.
105 // As there is no relevant param for `def_id`, we simply return
107 let type_dependent_def = tables.type_dependent_def_id(parent_node_id)?;
113 .filter(|arg| arg.is_ty_or_const())
114 .position(|arg| arg.id() == hir_id)
117 bug!("no arg matching AnonConst in segment");
120 (tcx.generics_of(type_dependent_def), idx)
123 Node::Ty(&Ty { kind: TyKind::Path(_), .. })
124 | Node::Expr(&Expr { kind: ExprKind::Path(_) | ExprKind::Struct(..), .. })
127 let path = match parent_node {
128 Node::Ty(&Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
129 | Node::TraitRef(&TraitRef { path, .. }) => &*path,
132 ExprKind::Path(QPath::Resolved(_, path))
133 | ExprKind::Struct(&QPath::Resolved(_, path), ..),
136 let body_owner = tcx.hir().local_def_id(tcx.hir().enclosing_body_owner(hir_id));
137 let _tables = tcx.typeck(body_owner);
141 if let Some(path) = get_path_containing_arg_in_pat(pat, hir_id) {
144 tcx.sess.delay_span_bug(
145 tcx.def_span(def_id),
146 &format!("unable to find const parent for {} in pat {:?}", hir_id, pat),
152 tcx.sess.delay_span_bug(
153 tcx.def_span(def_id),
154 &format!("unexpected const parent path {:?}", parent_node),
160 // We've encountered an `AnonConst` in some path, so we need to
161 // figure out which generic parameter it corresponds to and return
162 // the relevant type.
166 .filter_map(|seg| seg.args.map(|args| (args.args, seg)))
167 .find_map(|(args, seg)| {
169 .filter(|arg| arg.is_ty_or_const())
170 .position(|arg| arg.id() == hir_id)
171 .map(|index| (index, seg))
173 let (arg_index, segment) = match filtered {
176 .delay_span_bug(tcx.def_span(def_id), "no arg matching AnonConst in path");
179 Some(inner) => inner,
182 // Try to use the segment resolution if it is valid, otherwise we
183 // default to the path resolution.
184 let res = segment.res.filter(|&r| r != Res::Err).unwrap_or(path.res);
186 let generics = match res {
187 Res::Def(DefKind::Ctor(CtorOf::Variant, _), def_id) => tcx
188 .generics_of(tcx.parent(def_id).and_then(|def_id| tcx.parent(def_id)).unwrap()),
189 Res::Def(DefKind::Variant | DefKind::Ctor(CtorOf::Struct, _), def_id) => {
190 tcx.generics_of(tcx.parent(def_id).unwrap())
192 // Other `DefKind`s don't have generics and would ICE when calling
202 | DefKind::TraitAlias
206 | DefKind::AssocConst
209 ) => tcx.generics_of(def_id),
211 tcx.sess.delay_span_bug(tcx.def_span(def_id), "anon const with Res::Err");
215 // If the user tries to specify generics on a type that does not take them,
216 // e.g. `usize<T>`, we may hit this branch, in which case we treat it as if
217 // no arguments have been passed. An error should already have been emitted.
218 tcx.sess.delay_span_bug(
219 tcx.def_span(def_id),
220 &format!("unexpected anon const res {:?} in path: {:?}", res, path),
226 (generics, arg_index)
231 debug!(?parent_node);
232 debug!(?generics, ?arg_idx);
236 .filter(|param| param.kind.is_ty_or_const())
237 .nth(match generics.has_self && generics.parent.is_none() {
241 .and_then(|param| match param.kind {
242 ty::GenericParamDefKind::Const { .. } => {
250 fn get_path_containing_arg_in_pat<'hir>(
251 pat: &'hir hir::Pat<'hir>,
253 ) -> Option<&'hir hir::Path<'hir>> {
256 let is_arg_in_path = |p: &hir::Path<'_>| {
259 .filter_map(|seg| seg.args)
260 .flat_map(|args| args.args)
261 .any(|arg| arg.id() == arg_id)
263 let mut arg_path = None;
264 pat.walk(|pat| match pat.kind {
265 PatKind::Struct(QPath::Resolved(_, path), _, _)
266 | PatKind::TupleStruct(QPath::Resolved(_, path), _, _)
267 | PatKind::Path(QPath::Resolved(_, path))
268 if is_arg_in_path(path) =>
270 arg_path = Some(path);
278 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
279 let def_id = def_id.expect_local();
282 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
284 let icx = ItemCtxt::new(tcx, def_id.to_def_id());
286 match tcx.hir().get(hir_id) {
287 Node::TraitItem(item) => match item.kind {
288 TraitItemKind::Fn(..) => {
289 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
290 tcx.mk_fn_def(def_id.to_def_id(), substs)
292 TraitItemKind::Const(ty, body_id) => body_id
293 .and_then(|body_id| {
294 if is_suggestable_infer_ty(ty) {
295 Some(infer_placeholder_type(
296 tcx, def_id, body_id, ty.span, item.ident, "constant",
302 .unwrap_or_else(|| icx.to_ty(ty)),
303 TraitItemKind::Type(_, Some(ty)) => icx.to_ty(ty),
304 TraitItemKind::Type(_, None) => {
305 span_bug!(item.span, "associated type missing default");
309 Node::ImplItem(item) => match item.kind {
310 ImplItemKind::Fn(..) => {
311 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
312 tcx.mk_fn_def(def_id.to_def_id(), substs)
314 ImplItemKind::Const(ty, body_id) => {
315 if is_suggestable_infer_ty(ty) {
316 infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident, "constant")
321 ImplItemKind::TyAlias(ty) => {
322 if tcx.impl_trait_ref(tcx.hir().get_parent_item(hir_id)).is_none() {
323 check_feature_inherent_assoc_ty(tcx, item.span);
330 Node::Item(item) => {
332 ItemKind::Static(ty, .., body_id) => {
333 if is_suggestable_infer_ty(ty) {
334 infer_placeholder_type(
346 ItemKind::Const(ty, body_id) => {
347 if is_suggestable_infer_ty(ty) {
348 infer_placeholder_type(
349 tcx, def_id, body_id, ty.span, item.ident, "constant",
355 ItemKind::TyAlias(self_ty, _)
356 | ItemKind::Impl(hir::Impl { self_ty, .. }) => icx.to_ty(self_ty),
357 ItemKind::Fn(..) => {
358 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
359 tcx.mk_fn_def(def_id.to_def_id(), substs)
361 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
362 let def = tcx.adt_def(def_id);
363 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
364 tcx.mk_adt(def, substs)
366 ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::TyAlias, .. }) => {
367 find_opaque_ty_constraints(tcx, def_id)
369 // Opaque types desugared from `impl Trait`.
370 ItemKind::OpaqueTy(OpaqueTy { origin: hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner), .. }) => {
371 let concrete_ty = tcx
373 .concrete_opaque_types
374 .get_value_matching(|(key, _)| key.def_id == def_id.to_def_id())
377 tcx.sess.delay_span_bug(
380 "owner {:?} has no opaque type for {:?} in its typeck results",
384 if let Some(ErrorReported) =
385 tcx.typeck(owner).tainted_by_errors
388 // owner fn prevented us from populating
389 // the `concrete_opaque_types` table.
392 // We failed to resolve the opaque type or it
393 // resolves to itself. Return the non-revealed
394 // type, which should result in E0720.
397 InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
401 debug!("concrete_ty = {:?}", concrete_ty);
405 | ItemKind::TraitAlias(..)
406 | ItemKind::Macro(..)
408 | ItemKind::ForeignMod { .. }
409 | ItemKind::GlobalAsm(..)
410 | ItemKind::ExternCrate(..)
411 | ItemKind::Use(..) => {
414 "compute_type_of_item: unexpected item type: {:?}",
421 Node::ForeignItem(foreign_item) => match foreign_item.kind {
422 ForeignItemKind::Fn(..) => {
423 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
424 tcx.mk_fn_def(def_id.to_def_id(), substs)
426 ForeignItemKind::Static(t, _) => icx.to_ty(t),
427 ForeignItemKind::Type => tcx.mk_foreign(def_id.to_def_id()),
430 Node::Ctor(&ref def) | Node::Variant(Variant { data: ref def, .. }) => match *def {
431 VariantData::Unit(..) | VariantData::Struct(..) => {
432 tcx.type_of(tcx.hir().get_parent_item(hir_id))
434 VariantData::Tuple(..) => {
435 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
436 tcx.mk_fn_def(def_id.to_def_id(), substs)
440 Node::Field(field) => icx.to_ty(field.ty),
442 Node::Expr(&Expr { kind: ExprKind::Closure(..), .. }) => tcx.typeck(def_id).node_type(hir_id),
444 Node::AnonConst(_) if let Some(param) = tcx.opt_const_param_of(def_id) => {
445 // We defer to `type_of` of the corresponding parameter
446 // for generic arguments.
450 Node::AnonConst(_) => {
451 let parent_node = tcx.hir().get(tcx.hir().get_parent_node(hir_id));
453 Node::Ty(&Ty { kind: TyKind::Array(_, ref constant), .. })
454 | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
455 if constant.hir_id() == hir_id =>
459 Node::Ty(&Ty { kind: TyKind::Typeof(ref e), .. }) if e.hir_id == hir_id => {
460 tcx.typeck(def_id).node_type(e.hir_id)
463 Node::Expr(&Expr { kind: ExprKind::ConstBlock(ref anon_const), .. })
464 if anon_const.hir_id == hir_id =>
466 let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
467 substs.as_inline_const().ty()
470 Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
471 | Node::Item(&Item { kind: ItemKind::GlobalAsm(asm), .. })
472 if asm.operands.iter().any(|(op, _op_sp)| match op {
473 hir::InlineAsmOperand::Const { anon_const } => anon_const.hir_id == hir_id,
477 tcx.typeck(def_id).node_type(hir_id)
480 Node::Variant(Variant { disr_expr: Some(ref e), .. }) if e.hir_id == hir_id => tcx
481 .adt_def(tcx.hir().get_parent_item(hir_id))
486 Node::GenericParam(&GenericParam {
487 hir_id: param_hir_id,
488 kind: GenericParamKind::Const { default: Some(ct), .. },
490 }) if ct.hir_id == hir_id => tcx.type_of(tcx.hir().local_def_id(param_hir_id)),
492 x => tcx.ty_error_with_message(
494 &format!("unexpected const parent in type_of(): {:?}", x),
499 Node::GenericParam(param) => match ¶m.kind {
500 GenericParamKind::Type { default: Some(ty), .. }
501 | GenericParamKind::Const { ty, .. } => icx.to_ty(ty),
502 x => bug!("unexpected non-type Node::GenericParam: {:?}", x),
506 bug!("unexpected sort of node in type_of(): {:?}", x);
511 #[instrument(skip(tcx), level = "debug")]
512 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
513 /// laid for "higher-order pattern unification".
514 /// This ensures that inference is tractable.
515 /// In particular, definitions of opaque types can only use other generics as arguments,
516 /// and they cannot repeat an argument. Example:
519 /// type Foo<A, B> = impl Bar<A, B>;
521 /// // Okay -- `Foo` is applied to two distinct, generic types.
522 /// fn a<T, U>() -> Foo<T, U> { .. }
524 /// // Not okay -- `Foo` is applied to `T` twice.
525 /// fn b<T>() -> Foo<T, T> { .. }
527 /// // Not okay -- `Foo` is applied to a non-generic type.
528 /// fn b<T>() -> Foo<T, u32> { .. }
531 fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
532 use rustc_hir::{Expr, ImplItem, Item, TraitItem};
534 struct ConstraintLocator<'tcx> {
537 /// def_id of the opaque type whose defining uses are being checked
540 /// as we walk the defining uses, we are checking that all of them
541 /// define the same hidden type. This variable is set to `Some`
542 /// with the first type that we find, and then later types are
543 /// checked against it (we also carry the span of that first
545 found: Option<(Span, Ty<'tcx>)>,
548 impl ConstraintLocator<'_> {
549 #[instrument(skip(self), level = "debug")]
550 fn check(&mut self, def_id: LocalDefId) {
551 // Don't try to check items that cannot possibly constrain the type.
552 if !self.tcx.has_typeck_results(def_id) {
553 debug!("no constraint: no typeck results");
556 // Calling `mir_borrowck` can lead to cycle errors through
557 // const-checking, avoid calling it if we don't have to.
558 if !self.tcx.typeck(def_id).concrete_opaque_types.contains(&self.def_id) {
559 debug!("no constraints in typeck results");
562 // Use borrowck to get the type with unerased regions.
563 let concrete_opaque_types = &self.tcx.mir_borrowck(def_id).concrete_opaque_types;
564 debug!(?concrete_opaque_types);
565 for (opaque_type_key, concrete_type) in concrete_opaque_types {
566 if opaque_type_key.def_id != self.def_id {
567 // Ignore constraints for other opaque types.
571 debug!(?concrete_type, ?opaque_type_key.substs, "found constraint");
573 // FIXME(oli-obk): trace the actual span from inference to improve errors.
574 let span = self.tcx.def_span(def_id);
576 if let Some((prev_span, prev_ty)) = self.found {
577 if *concrete_type != prev_ty && !(*concrete_type, prev_ty).references_error() {
579 // Found different concrete types for the opaque type.
580 let mut err = self.tcx.sess.struct_span_err(
582 "concrete type differs from previous defining opaque type use",
586 format!("expected `{}`, got `{}`", prev_ty, concrete_type),
588 err.span_note(prev_span, "previous use here");
592 self.found = Some((span, concrete_type));
598 impl<'tcx> intravisit::Visitor<'tcx> for ConstraintLocator<'tcx> {
599 type NestedFilter = nested_filter::All;
601 fn nested_visit_map(&mut self) -> Self::Map {
604 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
605 if let hir::ExprKind::Closure(..) = ex.kind {
606 let def_id = self.tcx.hir().local_def_id(ex.hir_id);
609 intravisit::walk_expr(self, ex);
611 fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
612 debug!("find_existential_constraints: visiting {:?}", it);
613 // The opaque type itself or its children are not within its reveal scope.
614 if it.def_id.to_def_id() != self.def_id {
615 self.check(it.def_id);
616 intravisit::walk_item(self, it);
619 fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
620 debug!("find_existential_constraints: visiting {:?}", it);
621 // The opaque type itself or its children are not within its reveal scope.
622 if it.def_id.to_def_id() != self.def_id {
623 self.check(it.def_id);
624 intravisit::walk_impl_item(self, it);
627 fn visit_trait_item(&mut self, it: &'tcx TraitItem<'tcx>) {
628 debug!("find_existential_constraints: visiting {:?}", it);
629 self.check(it.def_id);
630 intravisit::walk_trait_item(self, it);
634 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
635 let scope = tcx.hir().get_defining_scope(hir_id);
636 let mut locator = ConstraintLocator { def_id: def_id.to_def_id(), tcx, found: None };
638 debug!("find_opaque_ty_constraints: scope={:?}", scope);
640 if scope == hir::CRATE_HIR_ID {
641 tcx.hir().walk_toplevel_module(&mut locator);
643 debug!("find_opaque_ty_constraints: scope={:?}", tcx.hir().get(scope));
644 match tcx.hir().get(scope) {
645 // We explicitly call `visit_*` methods, instead of using `intravisit::walk_*` methods
646 // This allows our visitor to process the defining item itself, causing
647 // it to pick up any 'sibling' defining uses.
649 // For example, this code:
652 // type Blah = impl Debug;
653 // let my_closure = || -> Blah { true };
657 // requires us to explicitly process `foo()` in order
658 // to notice the defining usage of `Blah`.
659 Node::Item(it) => locator.visit_item(it),
660 Node::ImplItem(it) => locator.visit_impl_item(it),
661 Node::TraitItem(it) => locator.visit_trait_item(it),
662 other => bug!("{:?} is not a valid scope for an opaque type item", other),
666 match locator.found {
669 let span = tcx.def_span(def_id);
670 tcx.sess.span_err(span, "could not find defining uses");
676 fn infer_placeholder_type<'a>(
679 body_id: hir::BodyId,
684 // Attempts to make the type nameable by turning FnDefs into FnPtrs.
685 struct MakeNameable<'tcx> {
690 impl<'tcx> MakeNameable<'tcx> {
691 fn new(tcx: TyCtxt<'tcx>) -> Self {
692 MakeNameable { success: true, tcx }
696 impl<'tcx> TypeFolder<'tcx> for MakeNameable<'tcx> {
697 fn tcx(&self) -> TyCtxt<'tcx> {
701 fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
707 ty::FnDef(def_id, _) => self.tcx.mk_fn_ptr(self.tcx.fn_sig(*def_id)),
708 // FIXME: non-capturing closures should also suggest a function pointer
709 ty::Closure(..) | ty::Generator(..) => {
710 self.success = false;
713 _ => ty.super_fold_with(self),
718 let ty = tcx.diagnostic_only_typeck(def_id).node_type(body_id.hir_id);
720 // If this came from a free `const` or `static mut?` item,
721 // then the user may have written e.g. `const A = 42;`.
722 // In this case, the parser has stashed a diagnostic for
723 // us to improve in typeck so we do that now.
724 match tcx.sess.diagnostic().steal_diagnostic(span, StashKey::ItemNoType) {
726 if !ty.references_error() {
727 // The parser provided a sub-optimal `HasPlaceholders` suggestion for the type.
728 // We are typeck and have the real type, so remove that and suggest the actual type.
729 err.suggestions.clear();
731 // Suggesting unnameable types won't help.
732 let mut mk_nameable = MakeNameable::new(tcx);
733 let ty = mk_nameable.fold_ty(ty);
734 let sugg_ty = if mk_nameable.success { Some(ty) } else { None };
735 if let Some(sugg_ty) = sugg_ty {
738 &format!("provide a type for the {item}", item = kind),
739 format!("{}: {}", item_ident, sugg_ty),
740 Applicability::MachineApplicable,
744 tcx.hir().body(body_id).value.span,
745 &format!("however, the inferred type `{}` cannot be named", ty),
753 let mut diag = bad_placeholder(tcx, "type", vec![span], kind);
755 if !ty.references_error() {
756 let mut mk_nameable = MakeNameable::new(tcx);
757 let ty = mk_nameable.fold_ty(ty);
758 let sugg_ty = if mk_nameable.success { Some(ty) } else { None };
759 if let Some(sugg_ty) = sugg_ty {
760 diag.span_suggestion(
762 "replace with the correct type",
764 Applicability::MaybeIncorrect,
768 tcx.hir().body(body_id).value.span,
769 &format!("however, the inferred type `{}` cannot be named", ty),
778 // Typeck doesn't expect erased regions to be returned from `type_of`.
779 tcx.fold_regions(ty, &mut false, |r, _| match r {
780 ty::ReErased => tcx.lifetimes.re_static,
785 fn check_feature_inherent_assoc_ty(tcx: TyCtxt<'_>, span: Span) {
786 if !tcx.features().inherent_associated_types {
787 use rustc_session::parse::feature_err;
788 use rustc_span::symbol::sym;
790 &tcx.sess.parse_sess,
791 sym::inherent_associated_types,
793 "inherent associated types are unstable",