1 //! Resolution of early vs late bound lifetimes.
3 //! Name resolution for lifetimes is performed on the AST and embedded into HIR. From this
4 //! information, typechecking needs to transform the lifetime parameters into bound lifetimes.
5 //! Lifetimes can be early-bound or late-bound. Construction of typechecking terms needs to visit
6 //! the types in HIR to identify late-bound lifetimes and assign their Debruijn indices. This file
7 //! is also responsible for assigning their semantics to implicit lifetimes in trait objects.
9 use rustc_ast::walk_list;
10 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
11 use rustc_errors::struct_span_err;
13 use rustc_hir::def::{DefKind, Res};
14 use rustc_hir::def_id::LocalDefId;
15 use rustc_hir::intravisit::{self, Visitor};
16 use rustc_hir::{GenericArg, GenericParam, GenericParamKind, HirIdMap, LifetimeName, Node};
17 use rustc_middle::bug;
18 use rustc_middle::hir::map::Map;
19 use rustc_middle::hir::nested_filter;
20 use rustc_middle::middle::resolve_lifetime::*;
21 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
22 use rustc_span::def_id::DefId;
23 use rustc_span::symbol::{sym, Ident};
28 fn early(hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region);
30 fn late(index: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region);
32 fn id(&self) -> Option<DefId>;
34 fn shifted(self, amount: u32) -> Region;
36 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
39 impl RegionExt for Region {
40 fn early(hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region) {
41 let def_id = hir_map.local_def_id(param.hir_id);
42 debug!("Region::early: def_id={:?}", def_id);
43 (def_id, Region::EarlyBound(def_id.to_def_id()))
46 fn late(idx: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (LocalDefId, Region) {
47 let depth = ty::INNERMOST;
48 let def_id = hir_map.local_def_id(param.hir_id);
50 "Region::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
51 idx, param, depth, def_id,
53 (def_id, Region::LateBound(depth, idx, def_id.to_def_id()))
56 fn id(&self) -> Option<DefId> {
58 Region::Static => None,
60 Region::EarlyBound(id) | Region::LateBound(_, _, id) | Region::Free(_, id) => Some(id),
64 fn shifted(self, amount: u32) -> Region {
66 Region::LateBound(debruijn, idx, id) => {
67 Region::LateBound(debruijn.shifted_in(amount), idx, id)
73 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
75 Region::LateBound(debruijn, index, id) => {
76 Region::LateBound(debruijn.shifted_out_to_binder(binder), index, id)
83 /// Maps the id of each lifetime reference to the lifetime decl
84 /// that it corresponds to.
86 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
87 /// actual use. It has the same data, but indexed by `LocalDefId`. This
89 #[derive(Debug, Default)]
90 struct NamedRegionMap {
91 // maps from every use of a named (not anonymous) lifetime to a
92 // `Region` describing how that region is bound
93 defs: HirIdMap<Region>,
95 // Maps relevant hir items to the bound vars on them. These include:
97 // - function pointers
100 // - bound types (like `T` in `for<'a> T<'a>: Foo`)
101 late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
104 pub(crate) struct LifetimeContext<'a, 'tcx> {
105 pub(crate) tcx: TyCtxt<'tcx>,
106 map: &'a mut NamedRegionMap,
109 /// Indicates that we only care about the definition of a trait. This should
110 /// be false if the `Item` we are resolving lifetimes for is not a trait or
111 /// we eventually need lifetimes resolve for trait items.
112 trait_definition_only: bool,
117 /// Declares lifetimes, and each can be early-bound or late-bound.
118 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
119 /// it should be shifted by the number of `Binder`s in between the
120 /// declaration `Binder` and the location it's referenced from.
122 /// We use an IndexMap here because we want these lifetimes in order
124 lifetimes: FxIndexMap<LocalDefId, Region>,
126 scope_type: BinderScopeType,
128 /// The late bound vars for a given item are stored by `HirId` to be
129 /// queried later. However, if we enter an elision scope, we have to
130 /// later append the elided bound vars to the list and need to know what
136 /// If this binder comes from a where clause, specify how it was created.
137 /// This is used to diagnose inaccessible lifetimes in APIT:
138 /// ```ignore (illustrative)
139 /// fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
141 where_bound_origin: Option<hir::PredicateOrigin>,
144 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
145 /// if this is a fn body, otherwise the original definitions are used.
146 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
147 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
153 /// A scope which either determines unspecified lifetimes or errors
154 /// on them (e.g., due to ambiguity).
159 /// Use a specific lifetime (if `Some`) or leave it unset (to be
160 /// inferred in a function body or potentially error outside one),
161 /// for the default choice of lifetime in a trait object type.
162 ObjectLifetimeDefault {
163 lifetime: Option<Region>,
167 /// When we have nested trait refs, we concatenate late bound vars for inner
168 /// trait refs from outer ones. But we also need to include any HRTB
169 /// lifetimes encountered when identifying the trait that an associated type
172 lifetimes: Vec<ty::BoundVariableKind>,
183 #[derive(Copy, Clone, Debug)]
184 enum BinderScopeType {
185 /// Any non-concatenating binder scopes.
187 /// Within a syntactic trait ref, there may be multiple poly trait refs that
188 /// are nested (under the `associated_type_bounds` feature). The binders of
189 /// the inner poly trait refs are extended from the outer poly trait refs
190 /// and don't increase the late bound depth. If you had
191 /// `T: for<'a> Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope
192 /// would be `Concatenating`. This also used in trait refs in where clauses
193 /// where we have two binders `for<> T: for<> Foo` (I've intentionally left
194 /// out any lifetimes because they aren't needed to show the two scopes).
195 /// The inner `for<>` has a scope of `Concatenating`.
199 // A helper struct for debugging scopes without printing parent scopes
200 struct TruncatedScopeDebug<'a>(&'a Scope<'a>);
202 impl<'a> fmt::Debug for TruncatedScopeDebug<'a> {
203 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
205 Scope::Binder { lifetimes, scope_type, hir_id, where_bound_origin, s: _ } => f
206 .debug_struct("Binder")
207 .field("lifetimes", lifetimes)
208 .field("scope_type", scope_type)
209 .field("hir_id", hir_id)
210 .field("where_bound_origin", where_bound_origin)
213 Scope::Body { id, s: _ } => {
214 f.debug_struct("Body").field("id", id).field("s", &"..").finish()
216 Scope::Elision { s: _ } => f.debug_struct("Elision").field("s", &"..").finish(),
217 Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
218 .debug_struct("ObjectLifetimeDefault")
219 .field("lifetime", lifetime)
222 Scope::Supertrait { lifetimes, s: _ } => f
223 .debug_struct("Supertrait")
224 .field("lifetimes", lifetimes)
227 Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
228 Scope::Root => f.debug_struct("Root").finish(),
233 type ScopeRef<'a> = &'a Scope<'a>;
235 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
237 pub fn provide(providers: &mut ty::query::Providers) {
238 *providers = ty::query::Providers {
239 resolve_lifetimes_trait_definition,
242 named_region_map: |tcx, id| resolve_lifetimes_for(tcx, id).defs.get(&id),
244 object_lifetime_default,
245 late_bound_vars_map: |tcx, id| resolve_lifetimes_for(tcx, id).late_bound_vars.get(&id),
251 /// Like `resolve_lifetimes`, but does not resolve lifetimes for trait items.
252 /// Also does not generate any diagnostics.
254 /// This is ultimately a subset of the `resolve_lifetimes` work. It effectively
255 /// resolves lifetimes only within the trait "header" -- that is, the trait
256 /// and supertrait list. In contrast, `resolve_lifetimes` resolves all the
257 /// lifetimes within the trait and its items. There is room to refactor this,
258 /// for example to resolve lifetimes for each trait item in separate queries,
259 /// but it's convenient to do the entire trait at once because the lifetimes
260 /// from the trait definition are in scope within the trait items as well.
262 /// The reason for this separate call is to resolve what would otherwise
263 /// be a cycle. Consider this example:
265 /// ```ignore UNSOLVED (maybe @jackh726 knows what lifetime parameter to give Sub)
269 /// trait Sub<'b>: for<'a> Base<'a> {
270 /// type SubItem: Sub<BaseItem = &'b u32>;
274 /// When we resolve `Sub` and all its items, we also have to resolve `Sub<BaseItem = &'b u32>`.
275 /// To figure out the index of `'b`, we have to know about the supertraits
276 /// of `Sub` so that we can determine that the `for<'a>` will be in scope.
277 /// (This is because we -- currently at least -- flatten all the late-bound
278 /// lifetimes into a single binder.) This requires us to resolve the
279 /// *trait definition* of `Sub`; basically just enough lifetime information
280 /// to look at the supertraits.
281 #[tracing::instrument(level = "debug", skip(tcx))]
282 fn resolve_lifetimes_trait_definition(
284 local_def_id: LocalDefId,
285 ) -> ResolveLifetimes {
286 convert_named_region_map(do_resolve(tcx, local_def_id, true))
289 /// Computes the `ResolveLifetimes` map that contains data for an entire `Item`.
290 /// You should not read the result of this query directly, but rather use
291 /// `named_region_map`, `is_late_bound_map`, etc.
292 #[tracing::instrument(level = "debug", skip(tcx))]
293 fn resolve_lifetimes(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> ResolveLifetimes {
294 convert_named_region_map(do_resolve(tcx, local_def_id, false))
299 local_def_id: LocalDefId,
300 trait_definition_only: bool,
301 ) -> NamedRegionMap {
302 let item = tcx.hir().expect_item(local_def_id);
303 let mut named_region_map =
304 NamedRegionMap { defs: Default::default(), late_bound_vars: Default::default() };
305 let mut visitor = LifetimeContext {
307 map: &mut named_region_map,
309 trait_definition_only,
311 visitor.visit_item(item);
316 fn convert_named_region_map(named_region_map: NamedRegionMap) -> ResolveLifetimes {
317 let mut rl = ResolveLifetimes::default();
319 for (hir_id, v) in named_region_map.defs {
320 let map = rl.defs.entry(hir_id.owner).or_default();
321 map.insert(hir_id.local_id, v);
323 for (hir_id, v) in named_region_map.late_bound_vars {
324 let map = rl.late_bound_vars.entry(hir_id.owner).or_default();
325 map.insert(hir_id.local_id, v);
332 /// Given `any` owner (structs, traits, trait methods, etc.), does lifetime resolution.
333 /// There are two important things this does.
334 /// First, we have to resolve lifetimes for
335 /// the entire *`Item`* that contains this owner, because that's the largest "scope"
336 /// where we can have relevant lifetimes.
337 /// Second, if we are asking for lifetimes in a trait *definition*, we use `resolve_lifetimes_trait_definition`
338 /// instead of `resolve_lifetimes`, which does not descend into the trait items and does not emit diagnostics.
339 /// This allows us to avoid cycles. Importantly, if we ask for lifetimes for lifetimes that have an owner
340 /// other than the trait itself (like the trait methods or associated types), then we just use the regular
341 /// `resolve_lifetimes`.
342 fn resolve_lifetimes_for<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx ResolveLifetimes {
343 let item_id = item_for(tcx, def_id);
344 if item_id == def_id {
345 let item = tcx.hir().item(hir::ItemId { def_id: item_id });
347 hir::ItemKind::Trait(..) => tcx.resolve_lifetimes_trait_definition(item_id),
348 _ => tcx.resolve_lifetimes(item_id),
351 tcx.resolve_lifetimes(item_id)
355 /// Finds the `Item` that contains the given `LocalDefId`
356 fn item_for(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> LocalDefId {
357 match tcx.hir().find_by_def_id(local_def_id) {
358 Some(Node::Item(item)) => {
364 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
365 let mut parent_iter = tcx.hir().parent_iter(hir_id);
367 let node = parent_iter.next().map(|n| n.1);
369 Some(hir::Node::Item(item)) => break item.def_id,
370 Some(hir::Node::Crate(_)) | None => bug!("Called `item_for` on an Item."),
378 fn late_region_as_bound_region<'tcx>(tcx: TyCtxt<'tcx>, region: &Region) -> ty::BoundVariableKind {
380 Region::LateBound(_, _, def_id) => {
381 let name = tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local()));
382 ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
384 _ => bug!("{:?} is not a late region", region),
388 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
389 /// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref.
390 fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) {
391 let mut scope = self.scope;
392 let mut supertrait_lifetimes = vec![];
395 Scope::Body { .. } | Scope::Root => {
396 break (vec![], BinderScopeType::Normal);
399 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
403 Scope::Supertrait { s, lifetimes } => {
404 supertrait_lifetimes = lifetimes.clone();
408 Scope::TraitRefBoundary { .. } => {
409 // We should only see super trait lifetimes if there is a `Binder` above
410 assert!(supertrait_lifetimes.is_empty());
411 break (vec![], BinderScopeType::Normal);
414 Scope::Binder { hir_id, .. } => {
415 // Nested poly trait refs have the binders concatenated
416 let mut full_binders =
417 self.map.late_bound_vars.entry(*hir_id).or_default().clone();
418 full_binders.extend(supertrait_lifetimes.into_iter());
419 break (full_binders, BinderScopeType::Concatenating);
425 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
426 type NestedFilter = nested_filter::All;
428 fn nested_visit_map(&mut self) -> Self::Map {
432 // We want to nest trait/impl items in their parent, but nothing else.
433 fn visit_nested_item(&mut self, _: hir::ItemId) {}
435 fn visit_trait_item_ref(&mut self, ii: &'tcx hir::TraitItemRef) {
436 if !self.trait_definition_only {
437 intravisit::walk_trait_item_ref(self, ii)
441 fn visit_nested_body(&mut self, body: hir::BodyId) {
442 let body = self.tcx.hir().body(body);
443 self.with(Scope::Body { id: body.id(), s: self.scope }, |this| {
444 this.visit_body(body);
448 fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
449 if let hir::ExprKind::Closure(hir::Closure {
450 binder, bound_generic_params, fn_decl, ..
453 if let &hir::ClosureBinder::For { span: for_sp, .. } = binder {
454 fn span_of_infer(ty: &hir::Ty<'_>) -> Option<Span> {
455 struct V(Option<Span>);
457 impl<'v> Visitor<'v> for V {
458 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
460 _ if self.0.is_some() => (),
461 hir::TyKind::Infer => {
462 self.0 = Some(t.span);
464 _ => intravisit::walk_ty(self, t),
474 let infer_in_rt_sp = match fn_decl.output {
475 hir::FnRetTy::DefaultReturn(sp) => Some(sp),
476 hir::FnRetTy::Return(ty) => span_of_infer(ty),
479 let infer_spans = fn_decl
482 .filter_map(span_of_infer)
483 .chain(infer_in_rt_sp)
484 .collect::<Vec<_>>();
486 if !infer_spans.is_empty() {
490 "implicit types in closure signatures are forbidden when `for<...>` is present",
492 .span_label(for_sp, "`for<...>` is here")
497 let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) =
500 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
502 .map(|(late_bound_idx, param)| {
503 let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
504 let r = late_region_as_bound_region(self.tcx, &pair.1);
509 self.map.late_bound_vars.insert(e.hir_id, binders);
510 let scope = Scope::Binder {
514 scope_type: BinderScopeType::Normal,
515 where_bound_origin: None,
518 self.with(scope, |this| {
519 // a closure has no bounds, so everything
520 // contained within is scoped within its binder.
521 intravisit::walk_expr(this, e)
524 intravisit::walk_expr(self, e)
528 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
530 hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
531 if let Some(of_trait) = of_trait {
532 self.map.late_bound_vars.insert(of_trait.hir_ref_id, Vec::default());
538 hir::ItemKind::Fn(_, ref generics, _) => {
539 self.visit_early_late(item.hir_id(), generics, |this| {
540 intravisit::walk_item(this, item);
544 hir::ItemKind::ExternCrate(_)
545 | hir::ItemKind::Use(..)
546 | hir::ItemKind::Macro(..)
547 | hir::ItemKind::Mod(..)
548 | hir::ItemKind::ForeignMod { .. }
549 | hir::ItemKind::GlobalAsm(..) => {
550 // These sorts of items have no lifetime parameters at all.
551 intravisit::walk_item(self, item);
553 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
554 // No lifetime parameters, but implied 'static.
555 self.with(Scope::Elision { s: self.scope }, |this| {
556 intravisit::walk_item(this, item)
559 hir::ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
560 // Opaque types are visited when we visit the
561 // `TyKind::OpaqueDef`, so that they have the lifetimes from
562 // their parent opaque_ty in scope.
564 // The core idea here is that since OpaqueTys are generated with the impl Trait as
565 // their owner, we can keep going until we find the Item that owns that. We then
566 // conservatively add all resolved lifetimes. Otherwise we run into problems in
567 // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`.
568 for (_hir_id, node) in
569 self.tcx.hir().parent_iter(self.tcx.hir().local_def_id_to_hir_id(item.def_id))
572 hir::Node::Item(parent_item) => {
573 let resolved_lifetimes: &ResolveLifetimes =
574 self.tcx.resolve_lifetimes(item_for(self.tcx, parent_item.def_id));
575 // We need to add *all* deps, since opaque tys may want them from *us*
576 for (&owner, defs) in resolved_lifetimes.defs.iter() {
577 defs.iter().for_each(|(&local_id, region)| {
578 self.map.defs.insert(hir::HirId { owner, local_id }, *region);
581 for (&owner, late_bound_vars) in
582 resolved_lifetimes.late_bound_vars.iter()
584 late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| {
585 self.map.late_bound_vars.insert(
586 hir::HirId { owner, local_id },
587 late_bound_vars.clone(),
593 hir::Node::Crate(_) => bug!("No Item about an OpaqueTy"),
598 hir::ItemKind::TyAlias(_, ref generics)
599 | hir::ItemKind::Enum(_, ref generics)
600 | hir::ItemKind::Struct(_, ref generics)
601 | hir::ItemKind::Union(_, ref generics)
602 | hir::ItemKind::Trait(_, _, ref generics, ..)
603 | hir::ItemKind::TraitAlias(ref generics, ..)
604 | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
605 // These kinds of items have only early-bound lifetime parameters.
606 let lifetimes = generics
609 .filter_map(|param| match param.kind {
610 GenericParamKind::Lifetime { .. } => {
611 Some(Region::early(self.tcx.hir(), param))
613 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
616 self.map.late_bound_vars.insert(item.hir_id(), vec![]);
617 let scope = Scope::Binder {
618 hir_id: item.hir_id(),
620 scope_type: BinderScopeType::Normal,
622 where_bound_origin: None,
624 self.with(scope, |this| {
625 let scope = Scope::TraitRefBoundary { s: this.scope };
626 this.with(scope, |this| {
627 intravisit::walk_item(this, item);
634 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
636 hir::ForeignItemKind::Fn(_, _, ref generics) => {
637 self.visit_early_late(item.hir_id(), generics, |this| {
638 intravisit::walk_foreign_item(this, item);
641 hir::ForeignItemKind::Static(..) => {
642 intravisit::walk_foreign_item(self, item);
644 hir::ForeignItemKind::Type => {
645 intravisit::walk_foreign_item(self, item);
650 #[tracing::instrument(level = "debug", skip(self))]
651 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
653 hir::TyKind::BareFn(ref c) => {
654 let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) = c
657 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
659 .map(|(late_bound_idx, param)| {
660 let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
661 let r = late_region_as_bound_region(self.tcx, &pair.1);
665 self.map.late_bound_vars.insert(ty.hir_id, binders);
666 let scope = Scope::Binder {
670 scope_type: BinderScopeType::Normal,
671 where_bound_origin: None,
673 self.with(scope, |this| {
674 // a bare fn has no bounds, so everything
675 // contained within is scoped within its binder.
676 intravisit::walk_ty(this, ty);
679 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
680 debug!(?bounds, ?lifetime, "TraitObject");
681 let scope = Scope::TraitRefBoundary { s: self.scope };
682 self.with(scope, |this| {
683 for bound in bounds {
684 this.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
687 match lifetime.name {
688 LifetimeName::ImplicitObjectLifetimeDefault => {
689 // If the user does not write *anything*, we
690 // use the object lifetime defaulting
691 // rules. So e.g., `Box<dyn Debug>` becomes
692 // `Box<dyn Debug + 'static>`.
693 self.resolve_object_lifetime_default(lifetime)
695 LifetimeName::Infer => {
696 // If the user writes `'_`, we use the *ordinary* elision
697 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
698 // resolved the same as the `'_` in `&'_ Foo`.
702 LifetimeName::Param(..) | LifetimeName::Static => {
703 // If the user wrote an explicit name, use that.
704 self.visit_lifetime(lifetime);
706 LifetimeName::Error => {}
709 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
710 self.visit_lifetime(lifetime_ref);
711 let scope = Scope::ObjectLifetimeDefault {
712 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
715 self.with(scope, |this| this.visit_ty(&mt.ty));
717 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
718 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
719 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
720 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
721 // ^ ^ this gets resolved in the scope of
722 // the opaque_ty generics
723 let opaque_ty = self.tcx.hir().item(item_id);
724 let (generics, bounds) = match opaque_ty.kind {
725 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
726 origin: hir::OpaqueTyOrigin::TyAlias,
729 intravisit::walk_ty(self, ty);
731 // Elided lifetimes are not allowed in non-return
732 // position impl Trait
733 let scope = Scope::TraitRefBoundary { s: self.scope };
734 self.with(scope, |this| {
735 let scope = Scope::Elision { s: this.scope };
736 this.with(scope, |this| {
737 intravisit::walk_item(this, opaque_ty);
743 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
744 origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
748 }) => (generics, bounds),
749 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
752 // Resolve the lifetimes that are applied to the opaque type.
753 // These are resolved in the current scope.
754 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
755 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
756 // ^ ^this gets resolved in the current scope
757 for lifetime in lifetimes {
758 let hir::GenericArg::Lifetime(lifetime) = lifetime else {
761 self.visit_lifetime(lifetime);
763 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
764 // and ban them. Type variables instantiated inside binders aren't
765 // well-supported at the moment, so this doesn't work.
766 // In the future, this should be fixed and this error should be removed.
767 let def = self.map.defs.get(&lifetime.hir_id).cloned();
768 let Some(Region::LateBound(_, _, def_id)) = def else {
771 let Some(def_id) = def_id.as_local() else {
774 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
775 // Ensure that the parent of the def is an item, not HRTB
776 let parent_id = self.tcx.hir().get_parent_node(hir_id);
777 if !parent_id.is_owner() {
778 if !self.trait_definition_only {
783 "`impl Trait` can only capture lifetimes \
784 bound at the fn or impl level"
788 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
790 if let hir::Node::Item(hir::Item {
791 kind: hir::ItemKind::OpaqueTy { .. }, ..
792 }) = self.tcx.hir().get(parent_id)
794 if !self.trait_definition_only {
795 let mut err = self.tcx.sess.struct_span_err(
797 "higher kinded lifetime bounds on nested opaque types are not supported yet",
799 err.span_note(self.tcx.def_span(def_id), "lifetime declared here");
802 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
806 // We want to start our early-bound indices at the end of the parent scope,
807 // not including any parent `impl Trait`s.
808 let mut lifetimes = FxIndexMap::default();
809 debug!(?generics.params);
810 for param in generics.params {
812 GenericParamKind::Lifetime { .. } => {
813 let (def_id, reg) = Region::early(self.tcx.hir(), ¶m);
814 lifetimes.insert(def_id, reg);
816 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {}
819 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
821 let scope = Scope::Binder {
825 scope_type: BinderScopeType::Normal,
826 where_bound_origin: None,
828 self.with(scope, |this| {
829 let scope = Scope::TraitRefBoundary { s: this.scope };
830 this.with(scope, |this| {
831 this.visit_generics(generics);
832 for bound in bounds {
833 this.visit_param_bound(bound);
838 _ => intravisit::walk_ty(self, ty),
842 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
843 use self::hir::TraitItemKind::*;
844 match trait_item.kind {
846 self.visit_early_late(trait_item.hir_id(), &trait_item.generics, |this| {
847 intravisit::walk_trait_item(this, trait_item)
850 Type(bounds, ref ty) => {
851 let generics = &trait_item.generics;
852 let lifetimes = generics
855 .filter_map(|param| match param.kind {
856 GenericParamKind::Lifetime { .. } => {
857 Some(Region::early(self.tcx.hir(), param))
859 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
862 self.map.late_bound_vars.insert(trait_item.hir_id(), vec![]);
863 let scope = Scope::Binder {
864 hir_id: trait_item.hir_id(),
867 scope_type: BinderScopeType::Normal,
868 where_bound_origin: None,
870 self.with(scope, |this| {
871 let scope = Scope::TraitRefBoundary { s: this.scope };
872 this.with(scope, |this| {
873 this.visit_generics(generics);
874 for bound in bounds {
875 this.visit_param_bound(bound);
877 if let Some(ty) = ty {
884 // Only methods and types support generics.
885 assert!(trait_item.generics.params.is_empty());
886 intravisit::walk_trait_item(self, trait_item);
891 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
892 use self::hir::ImplItemKind::*;
893 match impl_item.kind {
894 Fn(..) => self.visit_early_late(impl_item.hir_id(), &impl_item.generics, |this| {
895 intravisit::walk_impl_item(this, impl_item)
898 let generics = &impl_item.generics;
899 let lifetimes: FxIndexMap<LocalDefId, Region> = generics
902 .filter_map(|param| match param.kind {
903 GenericParamKind::Lifetime { .. } => {
904 Some(Region::early(self.tcx.hir(), param))
906 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => None,
909 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
910 let scope = Scope::Binder {
914 scope_type: BinderScopeType::Normal,
915 where_bound_origin: None,
917 self.with(scope, |this| {
918 let scope = Scope::TraitRefBoundary { s: this.scope };
919 this.with(scope, |this| {
920 this.visit_generics(generics);
926 // Only methods and types support generics.
927 assert!(impl_item.generics.params.is_empty());
928 intravisit::walk_impl_item(self, impl_item);
933 #[tracing::instrument(level = "debug", skip(self))]
934 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
935 match lifetime_ref.name {
936 hir::LifetimeName::Static => self.insert_lifetime(lifetime_ref, Region::Static),
937 hir::LifetimeName::Param(param_def_id, _) => {
938 self.resolve_lifetime_ref(param_def_id, lifetime_ref)
940 // If we've already reported an error, just ignore `lifetime_ref`.
941 hir::LifetimeName::Error => {}
942 // Those will be resolved by typechecking.
943 hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {}
947 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
948 for (i, segment) in path.segments.iter().enumerate() {
949 let depth = path.segments.len() - i - 1;
950 if let Some(ref args) = segment.args {
951 self.visit_segment_args(path.res, depth, args);
958 fk: intravisit::FnKind<'tcx>,
959 fd: &'tcx hir::FnDecl<'tcx>,
960 body_id: hir::BodyId,
964 let output = match fd.output {
965 hir::FnRetTy::DefaultReturn(_) => None,
966 hir::FnRetTy::Return(ref ty) => Some(&**ty),
968 self.visit_fn_like_elision(&fd.inputs, output, matches!(fk, intravisit::FnKind::Closure));
969 intravisit::walk_fn_kind(self, fk);
970 self.visit_nested_body(body_id)
973 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
974 let scope = Scope::TraitRefBoundary { s: self.scope };
975 self.with(scope, |this| {
976 for param in generics.params {
978 GenericParamKind::Lifetime { .. } => {}
979 GenericParamKind::Type { ref default, .. } => {
980 if let Some(ref ty) = default {
984 GenericParamKind::Const { ref ty, default } => {
986 if let Some(default) = default {
987 this.visit_body(this.tcx.hir().body(default.body));
992 for predicate in generics.predicates {
994 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
997 ref bound_generic_params,
1001 let (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) =
1002 bound_generic_params
1005 matches!(param.kind, GenericParamKind::Lifetime { .. })
1008 .map(|(late_bound_idx, param)| {
1010 Region::late(late_bound_idx as u32, this.tcx.hir(), param);
1011 let r = late_region_as_bound_region(this.tcx, &pair.1);
1015 this.map.late_bound_vars.insert(bounded_ty.hir_id, binders.clone());
1016 // Even if there are no lifetimes defined here, we still wrap it in a binder
1017 // scope. If there happens to be a nested poly trait ref (an error), that
1018 // will be `Concatenating` anyways, so we don't have to worry about the depth
1020 let scope = Scope::Binder {
1021 hir_id: bounded_ty.hir_id,
1024 scope_type: BinderScopeType::Normal,
1025 where_bound_origin: Some(origin),
1027 this.with(scope, |this| {
1028 this.visit_ty(&bounded_ty);
1029 walk_list!(this, visit_param_bound, bounds);
1032 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1037 this.visit_lifetime(lifetime);
1038 walk_list!(this, visit_param_bound, bounds);
1040 if lifetime.name != hir::LifetimeName::Static {
1041 for bound in bounds {
1042 let hir::GenericBound::Outlives(ref lt) = bound else {
1045 if lt.name != hir::LifetimeName::Static {
1048 this.insert_lifetime(lt, Region::Static);
1054 "unnecessary lifetime parameter `{}`",
1055 lifetime.name.ident(),
1059 "you can use the `'static` lifetime directly, in place of `{}`",
1060 lifetime.name.ident(),
1066 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1071 this.visit_ty(lhs_ty);
1072 this.visit_ty(rhs_ty);
1079 fn visit_param_bound(&mut self, bound: &'tcx hir::GenericBound<'tcx>) {
1081 hir::GenericBound::LangItemTrait(_, _, hir_id, _) => {
1082 // FIXME(jackh726): This is pretty weird. `LangItemTrait` doesn't go
1083 // through the regular poly trait ref code, so we don't get another
1084 // chance to introduce a binder. For now, I'm keeping the existing logic
1085 // of "if there isn't a Binder scope above us, add one", but I
1086 // imagine there's a better way to go about this.
1087 let (binders, scope_type) = self.poly_trait_ref_binder_info();
1089 self.map.late_bound_vars.insert(*hir_id, binders);
1090 let scope = Scope::Binder {
1092 lifetimes: FxIndexMap::default(),
1095 where_bound_origin: None,
1097 self.with(scope, |this| {
1098 intravisit::walk_param_bound(this, bound);
1101 _ => intravisit::walk_param_bound(self, bound),
1105 fn visit_poly_trait_ref(
1107 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
1108 _modifier: hir::TraitBoundModifier,
1110 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
1112 let (mut binders, scope_type) = self.poly_trait_ref_binder_info();
1114 let initial_bound_vars = binders.len() as u32;
1115 let mut lifetimes: FxIndexMap<LocalDefId, Region> = FxIndexMap::default();
1116 let binders_iter = trait_ref
1117 .bound_generic_params
1119 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
1121 .map(|(late_bound_idx, param)| {
1123 Region::late(initial_bound_vars + late_bound_idx as u32, self.tcx.hir(), param);
1124 let r = late_region_as_bound_region(self.tcx, &pair.1);
1125 lifetimes.insert(pair.0, pair.1);
1128 binders.extend(binders_iter);
1131 self.map.late_bound_vars.insert(trait_ref.trait_ref.hir_ref_id, binders);
1133 // Always introduce a scope here, even if this is in a where clause and
1134 // we introduced the binders around the bounded Ty. In that case, we
1135 // just reuse the concatenation functionality also present in nested trait
1137 let scope = Scope::Binder {
1138 hir_id: trait_ref.trait_ref.hir_ref_id,
1142 where_bound_origin: None,
1144 self.with(scope, |this| {
1145 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
1146 this.visit_trait_ref(&trait_ref.trait_ref);
1151 fn object_lifetime_default<'tcx>(
1153 param_def_id: DefId,
1154 ) -> Option<ObjectLifetimeDefault> {
1155 let param_def_id = param_def_id.expect_local();
1156 let parent_def_id = tcx.local_parent(param_def_id);
1157 let generics = tcx.hir().get_generics(parent_def_id)?;
1158 let param_hir_id = tcx.local_def_id_to_hir_id(param_def_id);
1159 let param = generics.params.iter().find(|p| p.hir_id == param_hir_id)?;
1161 // Scan the bounds and where-clauses on parameters to extract bounds
1162 // of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1163 // for each type parameter.
1165 GenericParamKind::Lifetime { .. } => None,
1166 GenericParamKind::Type { .. } => {
1167 let mut set = Set1::Empty;
1169 // Look for `type: ...` where clauses.
1170 for bound in generics.bounds_for_param(param_def_id) {
1171 // Ignore `for<'a> type: ...` as they can change what
1172 // lifetimes mean (although we could "just" handle it).
1173 if !bound.bound_generic_params.is_empty() {
1177 for bound in bound.bounds {
1178 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1179 set.insert(lifetime.name.normalize_to_macros_2_0());
1185 Set1::Empty => ObjectLifetimeDefault::Empty,
1186 Set1::One(hir::LifetimeName::Static) => ObjectLifetimeDefault::Static,
1187 Set1::One(hir::LifetimeName::Param(param_def_id, _)) => {
1188 ObjectLifetimeDefault::Param(param_def_id.to_def_id())
1190 _ => ObjectLifetimeDefault::Ambiguous,
1193 GenericParamKind::Const { .. } => {
1194 // Generic consts don't impose any constraints.
1196 // We still store a dummy value here to allow generic parameters
1197 // in an arbitrary order.
1198 Some(ObjectLifetimeDefault::Empty)
1203 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1204 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1206 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1208 let LifetimeContext { tcx, map, .. } = self;
1209 let mut this = LifetimeContext {
1213 trait_definition_only: self.trait_definition_only,
1215 let span = tracing::debug_span!("scope", scope = ?TruncatedScopeDebug(&this.scope));
1217 let _enter = span.enter();
1222 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1224 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1225 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1226 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1230 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1232 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1233 /// lifetimes may be interspersed together.
1235 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1236 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1237 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1238 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1239 /// ordering is not important there.
1240 fn visit_early_late<F>(
1243 generics: &'tcx hir::Generics<'tcx>,
1246 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1248 let mut named_late_bound_vars = 0;
1249 let lifetimes: FxIndexMap<LocalDefId, Region> = generics
1252 .filter_map(|param| match param.kind {
1253 GenericParamKind::Lifetime { .. } => {
1254 if self.tcx.is_late_bound(param.hir_id) {
1255 let late_bound_idx = named_late_bound_vars;
1256 named_late_bound_vars += 1;
1257 Some(Region::late(late_bound_idx, self.tcx.hir(), param))
1259 Some(Region::early(self.tcx.hir(), param))
1262 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
1266 let binders: Vec<_> = generics
1270 matches!(param.kind, GenericParamKind::Lifetime { .. })
1271 && self.tcx.is_late_bound(param.hir_id)
1274 .map(|(late_bound_idx, param)| {
1275 let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
1276 late_region_as_bound_region(self.tcx, &pair.1)
1279 self.map.late_bound_vars.insert(hir_id, binders);
1280 let scope = Scope::Binder {
1284 scope_type: BinderScopeType::Normal,
1285 where_bound_origin: None,
1287 self.with(scope, walk);
1290 #[tracing::instrument(level = "debug", skip(self))]
1291 fn resolve_lifetime_ref(
1293 region_def_id: LocalDefId,
1294 lifetime_ref: &'tcx hir::Lifetime,
1296 // Walk up the scope chain, tracking the number of fn scopes
1297 // that we pass through, until we find a lifetime with the
1298 // given name or we run out of scopes.
1300 let mut late_depth = 0;
1301 let mut scope = self.scope;
1302 let mut outermost_body = None;
1305 Scope::Body { id, s } => {
1306 outermost_body = Some(id);
1314 Scope::Binder { ref lifetimes, scope_type, s, where_bound_origin, .. } => {
1315 if let Some(&def) = lifetimes.get(®ion_def_id) {
1316 break Some(def.shifted(late_depth));
1319 BinderScopeType::Normal => late_depth += 1,
1320 BinderScopeType::Concatenating => {}
1322 // Fresh lifetimes in APIT used to be allowed in async fns and forbidden in
1324 if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin
1325 && let hir::LifetimeName::Param(_, hir::ParamName::Fresh) = lifetime_ref.name
1326 && let hir::IsAsync::NotAsync = self.tcx.asyncness(lifetime_ref.hir_id.owner)
1327 && !self.tcx.features().anonymous_lifetime_in_impl_trait
1329 rustc_session::parse::feature_err(
1330 &self.tcx.sess.parse_sess,
1331 sym::anonymous_lifetime_in_impl_trait,
1333 "anonymous lifetimes in `impl Trait` are unstable",
1340 Scope::Elision { s, .. }
1341 | Scope::ObjectLifetimeDefault { s, .. }
1342 | Scope::Supertrait { s, .. }
1343 | Scope::TraitRefBoundary { s, .. } => {
1349 if let Some(mut def) = result {
1350 if let Region::EarlyBound(..) = def {
1351 // Do not free early-bound regions, only late-bound ones.
1352 } else if let Some(body_id) = outermost_body {
1353 let fn_id = self.tcx.hir().body_owner(body_id);
1354 match self.tcx.hir().get(fn_id) {
1355 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1356 | Node::TraitItem(&hir::TraitItem {
1357 kind: hir::TraitItemKind::Fn(..), ..
1359 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
1360 let scope = self.tcx.hir().local_def_id(fn_id);
1361 def = Region::Free(scope.to_def_id(), def.id().unwrap());
1367 self.insert_lifetime(lifetime_ref, def);
1371 // We may fail to resolve higher-ranked lifetimes that are mentionned by APIT.
1372 // AST-based resolution does not care for impl-trait desugaring, which are the
1373 // responibility of lowering. This may create a mismatch between the resolution
1374 // AST found (`region_def_id`) which points to HRTB, and what HIR allows.
1376 // fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {}
1379 // In such case, walk back the binders to diagnose it properly.
1380 let mut scope = self.scope;
1384 where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
1386 let mut err = self.tcx.sess.struct_span_err(
1388 "`impl Trait` can only mention lifetimes bound at the fn or impl level",
1390 err.span_note(self.tcx.def_span(region_def_id), "lifetime declared here");
1394 Scope::Root => break,
1395 Scope::Binder { s, .. }
1396 | Scope::Body { s, .. }
1397 | Scope::Elision { s, .. }
1398 | Scope::ObjectLifetimeDefault { s, .. }
1399 | Scope::Supertrait { s, .. }
1400 | Scope::TraitRefBoundary { s, .. } => {
1406 self.tcx.sess.delay_span_bug(
1408 &format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,),
1412 fn visit_segment_args(
1416 generic_args: &'tcx hir::GenericArgs<'tcx>,
1419 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1420 res, depth, generic_args,
1423 if generic_args.parenthesized {
1424 self.visit_fn_like_elision(
1425 generic_args.inputs(),
1426 Some(generic_args.bindings[0].ty()),
1432 for arg in generic_args.args {
1433 if let hir::GenericArg::Lifetime(lt) = arg {
1434 self.visit_lifetime(lt);
1438 // Figure out if this is a type/trait segment,
1439 // which requires object lifetime defaults.
1440 let type_def_id = match res {
1441 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(self.tcx.parent(def_id)),
1442 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(self.tcx.parent(def_id)),
1450 ) if depth == 0 => Some(def_id),
1454 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1456 // Compute a vector of defaults, one for each type parameter,
1457 // per the rules given in RFCs 599 and 1156. Example:
1460 // struct Foo<'a, T: 'a, U> { }
1463 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1464 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1465 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1468 // Therefore, we would compute `object_lifetime_defaults` to a
1469 // vector like `['x, 'static]`. Note that the vector only
1470 // includes type parameters.
1471 let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
1473 let mut scope = self.scope;
1476 Scope::Root => break false,
1478 Scope::Body { .. } => break true,
1480 Scope::Binder { s, .. }
1481 | Scope::Elision { s, .. }
1482 | Scope::ObjectLifetimeDefault { s, .. }
1483 | Scope::Supertrait { s, .. }
1484 | Scope::TraitRefBoundary { s, .. } => {
1491 let map = &self.map;
1492 let generics = self.tcx.generics_of(def_id);
1493 let set_to_region = |set: ObjectLifetimeDefault| match set {
1494 ObjectLifetimeDefault::Empty => {
1498 Some(Region::Static)
1501 ObjectLifetimeDefault::Static => Some(Region::Static),
1502 ObjectLifetimeDefault::Param(param_def_id) => {
1503 let index = generics.param_def_id_to_index[¶m_def_id];
1504 generic_args.args.get(index as usize).and_then(|arg| match arg {
1505 GenericArg::Lifetime(lt) => map.defs.get(<.hir_id).copied(),
1509 ObjectLifetimeDefault::Ambiguous => None,
1514 .filter_map(|param| self.tcx.object_lifetime_default(param.def_id))
1519 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1522 for arg in generic_args.args {
1524 GenericArg::Lifetime(_) => {}
1525 GenericArg::Type(ty) => {
1526 if let Some(<) = object_lifetime_defaults.get(i) {
1527 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1528 self.with(scope, |this| this.visit_ty(ty));
1534 GenericArg::Const(ct) => {
1535 self.visit_anon_const(&ct.value);
1538 GenericArg::Infer(inf) => {
1539 self.visit_id(inf.hir_id);
1545 // Hack: when resolving the type `XX` in binding like `dyn
1546 // Foo<'b, Item = XX>`, the current object-lifetime default
1547 // would be to examine the trait `Foo` to check whether it has
1548 // a lifetime bound declared on `Item`. e.g., if `Foo` is
1549 // declared like so, then the default object lifetime bound in
1550 // `XX` should be `'b`:
1558 // but if we just have `type Item;`, then it would be
1559 // `'static`. However, we don't get all of this logic correct.
1561 // Instead, we do something hacky: if there are no lifetime parameters
1562 // to the trait, then we simply use a default object lifetime
1563 // bound of `'static`, because there is no other possibility. On the other hand,
1564 // if there ARE lifetime parameters, then we require the user to give an
1565 // explicit bound for now.
1567 // This is intended to leave room for us to implement the
1568 // correct behavior in the future.
1569 let has_lifetime_parameter =
1570 generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
1572 // Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or
1573 // in the trait ref `YY<...>` in `Item: YY<...>`.
1574 for binding in generic_args.bindings {
1575 let scope = Scope::ObjectLifetimeDefault {
1576 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
1579 if let Some(type_def_id) = type_def_id {
1580 let lifetimes = LifetimeContext::supertrait_hrtb_lifetimes(
1585 self.with(scope, |this| {
1586 let scope = Scope::Supertrait {
1587 lifetimes: lifetimes.unwrap_or_default(),
1590 this.with(scope, |this| this.visit_assoc_type_binding(binding));
1593 self.with(scope, |this| this.visit_assoc_type_binding(binding));
1598 /// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the
1599 /// associated type name and starting trait.
1600 /// For example, imagine we have
1601 /// ```ignore (illustrative)
1602 /// trait Foo<'a, 'b> {
1605 /// trait Bar<'b>: for<'a> Foo<'a, 'b> {}
1606 /// trait Bar: for<'b> Bar<'b> {}
1608 /// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on
1609 /// the starting trait `Bar`, we would return `Some(['b, 'a])`.
1610 fn supertrait_hrtb_lifetimes(
1614 ) -> Option<Vec<ty::BoundVariableKind>> {
1615 let trait_defines_associated_type_named = |trait_def_id: DefId| {
1616 tcx.associated_items(trait_def_id)
1617 .find_by_name_and_kind(tcx, assoc_name, ty::AssocKind::Type, trait_def_id)
1621 use smallvec::{smallvec, SmallVec};
1622 let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> =
1623 smallvec![(def_id, smallvec![])];
1624 let mut visited: FxHashSet<DefId> = FxHashSet::default();
1626 let Some((def_id, bound_vars)) = stack.pop() else {
1629 // See issue #83753. If someone writes an associated type on a non-trait, just treat it as
1630 // there being no supertrait HRTBs.
1631 match tcx.def_kind(def_id) {
1632 DefKind::Trait | DefKind::TraitAlias | DefKind::Impl => {}
1636 if trait_defines_associated_type_named(def_id) {
1637 break Some(bound_vars.into_iter().collect());
1640 tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name)));
1641 let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
1642 let bound_predicate = pred.kind();
1643 match bound_predicate.skip_binder() {
1644 ty::PredicateKind::Trait(data) => {
1645 // The order here needs to match what we would get from `subst_supertrait`
1646 let pred_bound_vars = bound_predicate.bound_vars();
1647 let mut all_bound_vars = bound_vars.clone();
1648 all_bound_vars.extend(pred_bound_vars.iter());
1649 let super_def_id = data.trait_ref.def_id;
1650 Some((super_def_id, all_bound_vars))
1656 let obligations = obligations.filter(|o| visited.insert(o.0));
1657 stack.extend(obligations);
1661 #[tracing::instrument(level = "debug", skip(self))]
1662 fn visit_fn_like_elision(
1664 inputs: &'tcx [hir::Ty<'tcx>],
1665 output: Option<&'tcx hir::Ty<'tcx>>,
1668 self.with(Scope::Elision { s: self.scope }, |this| {
1669 for input in inputs {
1670 this.visit_ty(input);
1672 if !in_closure && let Some(output) = output {
1673 this.visit_ty(output);
1676 if in_closure && let Some(output) = output {
1677 self.visit_ty(output);
1681 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1682 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
1683 let mut late_depth = 0;
1684 let mut scope = self.scope;
1685 let lifetime = loop {
1687 Scope::Binder { s, scope_type, .. } => {
1689 BinderScopeType::Normal => late_depth += 1,
1690 BinderScopeType::Concatenating => {}
1695 Scope::Root | Scope::Elision { .. } => break Region::Static,
1697 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
1699 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
1701 Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { s, .. } => {
1706 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
1709 #[tracing::instrument(level = "debug", skip(self))]
1710 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
1712 node = ?self.tcx.hir().node_to_string(lifetime_ref.hir_id),
1713 span = ?self.tcx.sess.source_map().span_to_diagnostic_string(lifetime_ref.span)
1715 self.map.defs.insert(lifetime_ref.hir_id, def);
1718 /// Sometimes we resolve a lifetime, but later find that it is an
1719 /// error (esp. around impl trait). In that case, we remove the
1720 /// entry into `map.defs` so as not to confuse later code.
1721 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
1722 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
1723 assert_eq!(old_value, Some(bad_def));
1727 /// Detects late-bound lifetimes and inserts them into
1730 /// A region declared on a fn is **late-bound** if:
1731 /// - it is constrained by an argument type;
1732 /// - it does not appear in a where-clause.
1734 /// "Constrained" basically means that it appears in any type but
1735 /// not amongst the inputs to a projection. In other words, `<&'a
1736 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
1737 fn is_late_bound_map(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<&FxIndexSet<LocalDefId>> {
1738 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
1739 let decl = tcx.hir().fn_decl_by_hir_id(hir_id)?;
1740 let generics = tcx.hir().get_generics(def_id)?;
1742 let mut late_bound = FxIndexSet::default();
1744 let mut constrained_by_input = ConstrainedCollector::default();
1745 for arg_ty in decl.inputs {
1746 constrained_by_input.visit_ty(arg_ty);
1749 let mut appears_in_output = AllCollector::default();
1750 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
1752 debug!(?constrained_by_input.regions);
1754 // Walk the lifetimes that appear in where clauses.
1756 // Subtle point: because we disallow nested bindings, we can just
1757 // ignore binders here and scrape up all names we see.
1758 let mut appears_in_where_clause = AllCollector::default();
1759 appears_in_where_clause.visit_generics(generics);
1760 debug!(?appears_in_where_clause.regions);
1762 // Late bound regions are those that:
1763 // - appear in the inputs
1764 // - do not appear in the where-clauses
1765 // - are not implicitly captured by `impl Trait`
1766 for param in generics.params {
1768 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
1770 // Neither types nor consts are late-bound.
1771 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
1774 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1776 // appears in the where clauses? early-bound.
1777 if appears_in_where_clause.regions.contains(¶m_def_id) {
1781 // does not appear in the inputs, but appears in the return type? early-bound.
1782 if !constrained_by_input.regions.contains(¶m_def_id)
1783 && appears_in_output.regions.contains(¶m_def_id)
1788 debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.hir_id);
1790 let inserted = late_bound.insert(param_def_id);
1791 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
1794 debug!(?late_bound);
1795 return Some(tcx.arena.alloc(late_bound));
1798 struct ConstrainedCollector {
1799 regions: FxHashSet<LocalDefId>,
1802 impl<'v> Visitor<'v> for ConstrainedCollector {
1803 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
1806 hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
1808 // ignore lifetimes appearing in associated type
1809 // projections, as they are not *constrained*
1813 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
1814 // consider only the lifetimes on the final
1815 // segment; I am not sure it's even currently
1816 // valid to have them elsewhere, but even if it
1817 // is, those would be potentially inputs to
1819 if let Some(last_segment) = path.segments.last() {
1820 self.visit_path_segment(path.span, last_segment);
1825 intravisit::walk_ty(self, ty);
1830 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
1831 if let hir::LifetimeName::Param(def_id, _) = lifetime_ref.name {
1832 self.regions.insert(def_id);
1838 struct AllCollector {
1839 regions: FxHashSet<LocalDefId>,
1842 impl<'v> Visitor<'v> for AllCollector {
1843 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
1844 if let hir::LifetimeName::Param(def_id, _) = lifetime_ref.name {
1845 self.regions.insert(def_id);