1 // ignore-tidy-filelength
2 //! Name resolution for lifetimes.
4 //! Name resolution for lifetimes follows *much* simpler rules than the
5 //! full resolve. For example, lifetime names are never exported or
6 //! used between functions, and they operate in a purely top-down
7 //! way. Therefore, we break lifetime name resolution into a separate pass.
9 use crate::late::diagnostics::{ForLifetimeSpanType, MissingLifetimeSpot};
10 use rustc_ast::walk_list;
11 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
12 use rustc_errors::{struct_span_err, Applicability, Diagnostic};
14 use rustc_hir::def::{DefKind, Res};
15 use rustc_hir::def_id::{DefIdMap, LocalDefId};
16 use rustc_hir::hir_id::ItemLocalId;
17 use rustc_hir::intravisit::{self, Visitor};
18 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
19 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet};
20 use rustc_middle::hir::map::Map;
21 use rustc_middle::hir::nested_filter;
22 use rustc_middle::middle::resolve_lifetime::*;
23 use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
24 use rustc_middle::{bug, span_bug};
25 use rustc_session::lint;
26 use rustc_span::def_id::DefId;
27 use rustc_span::symbol::{kw, sym, Ident, Symbol};
34 use tracing::{debug, span, Level};
36 // This counts the no of times a lifetime is used
37 #[derive(Clone, Copy, Debug)]
38 pub enum LifetimeUseSet<'tcx> {
39 One(&'tcx hir::Lifetime),
44 fn early(hir_map: Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
46 fn late(index: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
48 fn late_anon(named_late_bound_vars: u32, index: &Cell<u32>) -> Region;
50 fn id(&self) -> Option<DefId>;
52 fn shifted(self, amount: u32) -> Region;
54 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
56 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
58 L: Iterator<Item = &'a hir::Lifetime>;
61 impl RegionExt for Region {
62 fn early(hir_map: Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
65 let def_id = hir_map.local_def_id(param.hir_id);
66 debug!("Region::early: index={} def_id={:?}", i, def_id);
67 (param.name.normalize_to_macros_2_0(), Region::EarlyBound(i, def_id.to_def_id()))
70 fn late(idx: u32, hir_map: Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) {
71 let depth = ty::INNERMOST;
72 let def_id = hir_map.local_def_id(param.hir_id);
74 "Region::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
75 idx, param, depth, def_id,
77 (param.name.normalize_to_macros_2_0(), Region::LateBound(depth, idx, def_id.to_def_id()))
80 fn late_anon(named_late_bound_vars: u32, index: &Cell<u32>) -> Region {
83 let depth = ty::INNERMOST;
84 Region::LateBoundAnon(depth, named_late_bound_vars + i, i)
87 fn id(&self) -> Option<DefId> {
89 Region::Static | Region::LateBoundAnon(..) => None,
91 Region::EarlyBound(_, id) | Region::LateBound(_, _, id) | Region::Free(_, id) => {
97 fn shifted(self, amount: u32) -> Region {
99 Region::LateBound(debruijn, idx, id) => {
100 Region::LateBound(debruijn.shifted_in(amount), idx, id)
102 Region::LateBoundAnon(debruijn, index, anon_index) => {
103 Region::LateBoundAnon(debruijn.shifted_in(amount), index, anon_index)
109 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
111 Region::LateBound(debruijn, index, id) => {
112 Region::LateBound(debruijn.shifted_out_to_binder(binder), index, id)
114 Region::LateBoundAnon(debruijn, index, anon_index) => {
115 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index, anon_index)
121 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
123 L: Iterator<Item = &'a hir::Lifetime>,
125 if let Region::EarlyBound(index, _) = self {
126 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
133 /// Maps the id of each lifetime reference to the lifetime decl
134 /// that it corresponds to.
136 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
137 /// actual use. It has the same data, but indexed by `LocalDefId`. This
139 #[derive(Debug, Default)]
140 struct NamedRegionMap {
141 // maps from every use of a named (not anonymous) lifetime to a
142 // `Region` describing how that region is bound
143 defs: HirIdMap<Region>,
145 // the set of lifetime def ids that are late-bound; a region can
146 // be late-bound if (a) it does NOT appear in a where-clause and
147 // (b) it DOES appear in the arguments.
148 late_bound: HirIdSet,
150 // Maps relevant hir items to the bound vars on them. These include:
152 // - function pointers
155 // - bound types (like `T` in `for<'a> T<'a>: Foo`)
156 late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
158 // maps `PathSegment` `HirId`s to lifetime scopes.
159 scope_for_path: Option<FxHashMap<LocalDefId, FxHashMap<ItemLocalId, LifetimeScopeForPath>>>,
162 crate struct LifetimeContext<'a, 'tcx> {
163 crate tcx: TyCtxt<'tcx>,
164 map: &'a mut NamedRegionMap,
167 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
168 is_in_fn_syntax: bool,
170 is_in_const_generic: bool,
172 /// Indicates that we only care about the definition of a trait. This should
173 /// be false if the `Item` we are resolving lifetimes for is not a trait or
174 /// we eventually need lifetimes resolve for trait items.
175 trait_definition_only: bool,
177 /// List of labels in the function/method currently under analysis.
178 labels_in_fn: Vec<Ident>,
180 /// Cache for cross-crate per-definition object lifetime defaults.
181 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
183 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
185 /// When encountering an undefined named lifetime, we will suggest introducing it in these
187 crate missing_named_lifetime_spots: Vec<MissingLifetimeSpot<'tcx>>,
192 /// Declares lifetimes, and each can be early-bound or late-bound.
193 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
194 /// it should be shifted by the number of `Binder`s in between the
195 /// declaration `Binder` and the location it's referenced from.
197 /// We use an IndexMap here because we want these lifetimes in order
199 lifetimes: FxIndexMap<hir::ParamName, Region>,
201 /// if we extend this scope with another scope, what is the next index
202 /// we should use for an early-bound region?
203 next_early_index: u32,
205 /// Flag is set to true if, in this binder, `'_` would be
206 /// equivalent to a "single-use region". This is true on
207 /// impls, but not other kinds of items.
208 track_lifetime_uses: bool,
210 /// Whether or not this binder would serve as the parent
211 /// binder for opaque types introduced within. For example:
214 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
217 /// Here, the opaque types we create for the `impl Trait`
218 /// and `impl Trait2` references will both have the `foo` item
219 /// as their parent. When we get to `impl Trait2`, we find
220 /// that it is nested within the `for<>` binder -- this flag
221 /// allows us to skip that when looking for the parent binder
222 /// of the resulting opaque type.
223 opaque_type_parent: bool,
225 scope_type: BinderScopeType,
227 /// The late bound vars for a given item are stored by `HirId` to be
228 /// queried later. However, if we enter an elision scope, we have to
229 /// later append the elided bound vars to the list and need to know what
235 /// In some cases not allowing late bounds allows us to avoid ICEs.
236 /// This is almost ways set to true.
237 allow_late_bound: bool,
240 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
241 /// if this is a fn body, otherwise the original definitions are used.
242 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
243 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
249 /// A scope which either determines unspecified lifetimes or errors
250 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
256 /// Use a specific lifetime (if `Some`) or leave it unset (to be
257 /// inferred in a function body or potentially error outside one),
258 /// for the default choice of lifetime in a trait object type.
259 ObjectLifetimeDefault {
260 lifetime: Option<Region>,
264 /// When we have nested trait refs, we concatenate late bound vars for inner
265 /// trait refs from outer ones. But we also need to include any HRTB
266 /// lifetimes encountered when identifying the trait that an associated type
269 lifetimes: Vec<ty::BoundVariableKind>,
280 #[derive(Copy, Clone, Debug)]
281 enum BinderScopeType {
282 /// Any non-concatenating binder scopes.
284 /// Within a syntactic trait ref, there may be multiple poly trait refs that
285 /// are nested (under the `associated_type_bounds` feature). The binders of
286 /// the inner poly trait refs are extended from the outer poly trait refs
287 /// and don't increase the late bound depth. If you had
288 /// `T: for<'a> Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope
289 /// would be `Concatenating`. This also used in trait refs in where clauses
290 /// where we have two binders `for<> T: for<> Foo` (I've intentionally left
291 /// out any lifetimes because they aren't needed to show the two scopes).
292 /// The inner `for<>` has a scope of `Concatenating`.
296 // A helper struct for debugging scopes without printing parent scopes
297 struct TruncatedScopeDebug<'a>(&'a Scope<'a>);
299 impl<'a> fmt::Debug for TruncatedScopeDebug<'a> {
300 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
312 .debug_struct("Binder")
313 .field("lifetimes", lifetimes)
314 .field("next_early_index", next_early_index)
315 .field("track_lifetime_uses", track_lifetime_uses)
316 .field("opaque_type_parent", opaque_type_parent)
317 .field("scope_type", scope_type)
318 .field("hir_id", hir_id)
320 .field("allow_late_bound", allow_late_bound)
322 Scope::Body { id, s: _ } => {
323 f.debug_struct("Body").field("id", id).field("s", &"..").finish()
325 Scope::Elision { elide, s: _ } => {
326 f.debug_struct("Elision").field("elide", elide).field("s", &"..").finish()
328 Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
329 .debug_struct("ObjectLifetimeDefault")
330 .field("lifetime", lifetime)
333 Scope::Supertrait { lifetimes, s: _ } => f
334 .debug_struct("Supertrait")
335 .field("lifetimes", lifetimes)
338 Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
339 Scope::Root => f.debug_struct("Root").finish(),
344 #[derive(Clone, Debug)]
346 /// Use a fresh anonymous late-bound lifetime each time, by
347 /// incrementing the counter to generate sequential indices. All
348 /// anonymous lifetimes must start *after* named bound vars.
349 FreshLateAnon(u32, Cell<u32>),
350 /// Always use this one lifetime.
352 /// Less or more than one lifetime were found, error on unspecified.
353 Error(Vec<ElisionFailureInfo>),
354 /// Forbid lifetime elision inside of a larger scope where it would be
355 /// permitted. For example, in let position impl trait.
359 #[derive(Clone, Debug)]
360 crate struct ElisionFailureInfo {
361 /// Where we can find the argument pattern.
362 crate parent: Option<hir::BodyId>,
363 /// The index of the argument in the original definition.
365 crate lifetime_count: usize,
366 crate have_bound_regions: bool,
370 type ScopeRef<'a> = &'a Scope<'a>;
372 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
374 pub fn provide(providers: &mut ty::query::Providers) {
375 *providers = ty::query::Providers {
376 resolve_lifetimes_trait_definition,
379 named_region_map: |tcx, id| resolve_lifetimes_for(tcx, id).defs.get(&id),
381 object_lifetime_defaults: |tcx, id| match tcx.hir().find_by_def_id(id) {
382 Some(Node::Item(item)) => compute_object_lifetime_defaults(tcx, item),
385 late_bound_vars_map: |tcx, id| resolve_lifetimes_for(tcx, id).late_bound_vars.get(&id),
386 lifetime_scope_map: |tcx, id| {
387 let item_id = item_for(tcx, id);
388 do_resolve(tcx, item_id, false, true).scope_for_path.unwrap().remove(&id)
395 /// Like `resolve_lifetimes`, but does not resolve lifetimes for trait items.
396 /// Also does not generate any diagnostics.
398 /// This is ultimately a subset of the `resolve_lifetimes` work. It effectively
399 /// resolves lifetimes only within the trait "header" -- that is, the trait
400 /// and supertrait list. In contrast, `resolve_lifetimes` resolves all the
401 /// lifetimes within the trait and its items. There is room to refactor this,
402 /// for example to resolve lifetimes for each trait item in separate queries,
403 /// but it's convenient to do the entire trait at once because the lifetimes
404 /// from the trait definition are in scope within the trait items as well.
406 /// The reason for this separate call is to resolve what would otherwise
407 /// be a cycle. Consider this example:
413 /// trait Sub<'b>: for<'a> Base<'a> {
414 /// type SubItem: Sub<BaseItem = &'b u32>;
418 /// When we resolve `Sub` and all its items, we also have to resolve `Sub<BaseItem = &'b u32>`.
419 /// To figure out the index of `'b`, we have to know about the supertraits
420 /// of `Sub` so that we can determine that the `for<'a>` will be in scope.
421 /// (This is because we -- currently at least -- flatten all the late-bound
422 /// lifetimes into a single binder.) This requires us to resolve the
423 /// *trait definition* of `Sub`; basically just enough lifetime information
424 /// to look at the supertraits.
425 #[tracing::instrument(level = "debug", skip(tcx))]
426 fn resolve_lifetimes_trait_definition(
428 local_def_id: LocalDefId,
429 ) -> ResolveLifetimes {
430 convert_named_region_map(tcx, do_resolve(tcx, local_def_id, true, false))
433 /// Computes the `ResolveLifetimes` map that contains data for an entire `Item`.
434 /// You should not read the result of this query directly, but rather use
435 /// `named_region_map`, `is_late_bound_map`, etc.
436 #[tracing::instrument(level = "debug", skip(tcx))]
437 fn resolve_lifetimes(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> ResolveLifetimes {
438 convert_named_region_map(tcx, do_resolve(tcx, local_def_id, false, false))
443 local_def_id: LocalDefId,
444 trait_definition_only: bool,
445 with_scope_for_path: bool,
446 ) -> NamedRegionMap {
447 let item = tcx.hir().expect_item(local_def_id);
448 let mut named_region_map = NamedRegionMap {
449 defs: Default::default(),
450 late_bound: Default::default(),
451 late_bound_vars: Default::default(),
452 scope_for_path: with_scope_for_path.then(|| Default::default()),
454 let mut visitor = LifetimeContext {
456 map: &mut named_region_map,
458 is_in_fn_syntax: false,
459 is_in_const_generic: false,
460 trait_definition_only,
461 labels_in_fn: vec![],
462 xcrate_object_lifetime_defaults: Default::default(),
463 lifetime_uses: &mut Default::default(),
464 missing_named_lifetime_spots: vec![],
466 visitor.visit_item(item);
471 fn convert_named_region_map(tcx: TyCtxt<'_>, named_region_map: NamedRegionMap) -> ResolveLifetimes {
472 let mut rl = ResolveLifetimes::default();
474 for (hir_id, v) in named_region_map.defs {
475 let map = rl.defs.entry(hir_id.owner).or_default();
476 map.insert(hir_id.local_id, v);
478 for hir_id in named_region_map.late_bound {
479 let map = rl.late_bound.entry(hir_id.owner).or_default();
480 let def_id = tcx.hir().local_def_id(hir_id);
483 for (hir_id, v) in named_region_map.late_bound_vars {
484 let map = rl.late_bound_vars.entry(hir_id.owner).or_default();
485 map.insert(hir_id.local_id, v);
492 /// Given `any` owner (structs, traits, trait methods, etc.), does lifetime resolution.
493 /// There are two important things this does.
494 /// First, we have to resolve lifetimes for
495 /// the entire *`Item`* that contains this owner, because that's the largest "scope"
496 /// where we can have relevant lifetimes.
497 /// Second, if we are asking for lifetimes in a trait *definition*, we use `resolve_lifetimes_trait_definition`
498 /// instead of `resolve_lifetimes`, which does not descend into the trait items and does not emit diagnostics.
499 /// This allows us to avoid cycles. Importantly, if we ask for lifetimes for lifetimes that have an owner
500 /// other than the trait itself (like the trait methods or associated types), then we just use the regular
501 /// `resolve_lifetimes`.
502 fn resolve_lifetimes_for<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx ResolveLifetimes {
503 let item_id = item_for(tcx, def_id);
504 if item_id == def_id {
505 let item = tcx.hir().item(hir::ItemId { def_id: item_id });
507 hir::ItemKind::Trait(..) => tcx.resolve_lifetimes_trait_definition(item_id),
508 _ => tcx.resolve_lifetimes(item_id),
511 tcx.resolve_lifetimes(item_id)
515 /// Finds the `Item` that contains the given `LocalDefId`
516 fn item_for(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> LocalDefId {
517 match tcx.hir().find_by_def_id(local_def_id) {
518 Some(Node::Item(item)) => {
524 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
525 let mut parent_iter = tcx.hir().parent_iter(hir_id);
527 let node = parent_iter.next().map(|n| n.1);
529 Some(hir::Node::Item(item)) => break item.def_id,
530 Some(hir::Node::Crate(_)) | None => bug!("Called `item_for` on an Item."),
538 fn is_late_bound_map<'tcx>(
541 ) -> Option<(LocalDefId, &'tcx FxHashSet<LocalDefId>)> {
542 match tcx.def_kind(def_id) {
543 DefKind::AnonConst | DefKind::InlineConst => {
545 .parent(def_id.to_def_id())
546 .unwrap_or_else(|| bug!("anon const or closure without a parent"));
547 // We search for the next outer anon const or fn here
548 // while skipping closures.
550 // Note that for `AnonConst` we still just recurse until we
551 // find a function body, but who cares :shrug:
552 while tcx.is_closure(def_id) {
555 .unwrap_or_else(|| bug!("anon const or closure without a parent"));
558 tcx.is_late_bound_map(def_id.expect_local())
560 _ => resolve_lifetimes_for(tcx, def_id).late_bound.get(&def_id).map(|lt| (def_id, lt)),
564 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
565 /// We have to account for this when computing the index of the other generic parameters.
566 /// This function returns whether there is such an implicit parameter defined on the given item.
567 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
568 matches!(*node, hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..))
571 fn late_region_as_bound_region<'tcx>(tcx: TyCtxt<'tcx>, region: &Region) -> ty::BoundVariableKind {
573 Region::LateBound(_, _, def_id) => {
574 let name = tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local()));
575 ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
577 Region::LateBoundAnon(_, _, anon_idx) => {
578 ty::BoundVariableKind::Region(ty::BrAnon(*anon_idx))
580 _ => bug!("{:?} is not a late region", region),
584 #[tracing::instrument(level = "debug")]
585 fn get_lifetime_scopes_for_path(mut scope: &Scope<'_>) -> LifetimeScopeForPath {
586 let mut available_lifetimes = vec![];
589 Scope::Binder { lifetimes, s, .. } => {
590 available_lifetimes.extend(lifetimes.keys().filter_map(|p| match p {
591 hir::ParamName::Plain(ident) => Some(ident.name),
596 Scope::Body { s, .. } => {
599 Scope::Elision { elide, s } => {
600 if let Elide::Exact(_) = elide {
601 return LifetimeScopeForPath::Elided;
606 Scope::ObjectLifetimeDefault { s, .. } => {
610 return LifetimeScopeForPath::NonElided(available_lifetimes);
612 Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { s, .. } => {
619 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
620 /// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref.
621 fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) {
622 let mut scope = self.scope;
623 let mut supertrait_lifetimes = vec![];
626 Scope::Body { .. } | Scope::Root => {
627 break (vec![], BinderScopeType::Normal);
630 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
634 Scope::Supertrait { s, lifetimes } => {
635 supertrait_lifetimes = lifetimes.clone();
639 Scope::TraitRefBoundary { .. } => {
640 // We should only see super trait lifetimes if there is a `Binder` above
641 assert!(supertrait_lifetimes.is_empty());
642 break (vec![], BinderScopeType::Normal);
645 Scope::Binder { hir_id, .. } => {
646 // Nested poly trait refs have the binders concatenated
647 let mut full_binders =
648 self.map.late_bound_vars.entry(*hir_id).or_default().clone();
649 full_binders.extend(supertrait_lifetimes.into_iter());
650 break (full_binders, BinderScopeType::Concatenating);
656 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
657 type NestedFilter = nested_filter::All;
659 fn nested_visit_map(&mut self) -> Self::Map {
663 // We want to nest trait/impl items in their parent, but nothing else.
664 fn visit_nested_item(&mut self, _: hir::ItemId) {}
666 fn visit_trait_item_ref(&mut self, ii: &'tcx hir::TraitItemRef) {
667 if !self.trait_definition_only {
668 intravisit::walk_trait_item_ref(self, ii)
672 fn visit_nested_body(&mut self, body: hir::BodyId) {
673 // Each body has their own set of labels, save labels.
674 let saved = take(&mut self.labels_in_fn);
675 let body = self.tcx.hir().body(body);
676 extract_labels(self, body);
677 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
678 this.visit_body(body);
680 self.labels_in_fn = saved;
685 fk: intravisit::FnKind<'tcx>,
686 fd: &'tcx hir::FnDecl<'tcx>,
691 let name = match fk {
692 intravisit::FnKind::ItemFn(id, _, _, _) => id.name,
693 intravisit::FnKind::Method(id, _, _) => id.name,
694 intravisit::FnKind::Closure => sym::closure,
696 let name = name.as_str();
697 let span = span!(Level::DEBUG, "visit_fn", name);
698 let _enter = span.enter();
700 // Any `Binders` are handled elsewhere
701 intravisit::FnKind::ItemFn(..) | intravisit::FnKind::Method(..) => {
702 intravisit::walk_fn(self, fk, fd, b, s, hir_id)
704 intravisit::FnKind::Closure => {
705 self.map.late_bound_vars.insert(hir_id, vec![]);
706 let scope = Scope::Binder {
708 lifetimes: FxIndexMap::default(),
709 next_early_index: self.next_early_index(),
711 track_lifetime_uses: true,
712 opaque_type_parent: false,
713 scope_type: BinderScopeType::Normal,
714 allow_late_bound: true,
716 self.with(scope, move |_old_scope, this| {
717 intravisit::walk_fn(this, fk, fd, b, s, hir_id)
723 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
725 hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
726 if let Some(of_trait) = of_trait {
727 self.map.late_bound_vars.insert(of_trait.hir_ref_id, Vec::default());
733 hir::ItemKind::Fn(ref sig, ref generics, _) => {
734 self.missing_named_lifetime_spots.push(generics.into());
735 self.visit_early_late(None, item.hir_id(), &sig.decl, generics, |this| {
736 intravisit::walk_item(this, item);
738 self.missing_named_lifetime_spots.pop();
741 hir::ItemKind::ExternCrate(_)
742 | hir::ItemKind::Use(..)
743 | hir::ItemKind::Macro(..)
744 | hir::ItemKind::Mod(..)
745 | hir::ItemKind::ForeignMod { .. }
746 | hir::ItemKind::GlobalAsm(..) => {
747 // These sorts of items have no lifetime parameters at all.
748 intravisit::walk_item(self, item);
750 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
751 // No lifetime parameters, but implied 'static.
752 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
753 self.with(scope, |_, this| intravisit::walk_item(this, item));
755 hir::ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
756 // Opaque types are visited when we visit the
757 // `TyKind::OpaqueDef`, so that they have the lifetimes from
758 // their parent opaque_ty in scope.
760 // The core idea here is that since OpaqueTys are generated with the impl Trait as
761 // their owner, we can keep going until we find the Item that owns that. We then
762 // conservatively add all resolved lifetimes. Otherwise we run into problems in
763 // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`.
764 for (_hir_id, node) in
765 self.tcx.hir().parent_iter(self.tcx.hir().local_def_id_to_hir_id(item.def_id))
768 hir::Node::Item(parent_item) => {
769 let resolved_lifetimes: &ResolveLifetimes =
770 self.tcx.resolve_lifetimes(item_for(self.tcx, parent_item.def_id));
771 // We need to add *all* deps, since opaque tys may want them from *us*
772 for (&owner, defs) in resolved_lifetimes.defs.iter() {
773 defs.iter().for_each(|(&local_id, region)| {
774 self.map.defs.insert(hir::HirId { owner, local_id }, *region);
777 for (&owner, late_bound) in resolved_lifetimes.late_bound.iter() {
778 late_bound.iter().for_each(|&id| {
779 let hir_id = self.tcx.local_def_id_to_hir_id(id);
780 debug_assert_eq!(owner, hir_id.owner);
781 self.map.late_bound.insert(hir_id);
784 for (&owner, late_bound_vars) in
785 resolved_lifetimes.late_bound_vars.iter()
787 late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| {
788 self.map.late_bound_vars.insert(
789 hir::HirId { owner, local_id },
790 late_bound_vars.clone(),
796 hir::Node::Crate(_) => bug!("No Item about an OpaqueTy"),
801 hir::ItemKind::TyAlias(_, ref generics)
802 | hir::ItemKind::Enum(_, ref generics)
803 | hir::ItemKind::Struct(_, ref generics)
804 | hir::ItemKind::Union(_, ref generics)
805 | hir::ItemKind::Trait(_, _, ref generics, ..)
806 | hir::ItemKind::TraitAlias(ref generics, ..)
807 | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
808 self.missing_named_lifetime_spots.push(generics.into());
810 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
811 // This is not true for other kinds of items.
812 let track_lifetime_uses = matches!(item.kind, hir::ItemKind::Impl { .. });
813 // These kinds of items have only early-bound lifetime parameters.
814 let mut index = if sub_items_have_self_param(&item.kind) {
815 1 // Self comes before lifetimes
819 let mut non_lifetime_count = 0;
820 let lifetimes = generics
823 .filter_map(|param| match param.kind {
824 GenericParamKind::Lifetime { .. } => {
825 Some(Region::early(self.tcx.hir(), &mut index, param))
827 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
828 non_lifetime_count += 1;
833 self.map.late_bound_vars.insert(item.hir_id(), vec![]);
834 let scope = Scope::Binder {
835 hir_id: item.hir_id(),
837 next_early_index: index + non_lifetime_count,
838 opaque_type_parent: true,
840 scope_type: BinderScopeType::Normal,
842 allow_late_bound: false,
844 self.with(scope, |old_scope, this| {
845 this.check_lifetime_params(old_scope, &generics.params);
846 let scope = Scope::TraitRefBoundary { s: this.scope };
847 this.with(scope, |_, this| {
848 intravisit::walk_item(this, item);
851 self.missing_named_lifetime_spots.pop();
856 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
858 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
859 self.visit_early_late(None, item.hir_id(), decl, generics, |this| {
860 intravisit::walk_foreign_item(this, item);
863 hir::ForeignItemKind::Static(..) => {
864 intravisit::walk_foreign_item(self, item);
866 hir::ForeignItemKind::Type => {
867 intravisit::walk_foreign_item(self, item);
872 #[tracing::instrument(level = "debug", skip(self))]
873 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
875 hir::TyKind::BareFn(ref c) => {
876 let next_early_index = self.next_early_index();
877 let was_in_fn_syntax = self.is_in_fn_syntax;
878 self.is_in_fn_syntax = true;
879 let lifetime_span: Option<Span> =
880 c.generic_params.iter().rev().find_map(|param| match param.kind {
881 GenericParamKind::Lifetime { .. } => Some(param.span),
884 let (span, span_type) = if let Some(span) = lifetime_span {
885 (span.shrink_to_hi(), ForLifetimeSpanType::TypeTail)
887 (ty.span.shrink_to_lo(), ForLifetimeSpanType::TypeEmpty)
889 self.missing_named_lifetime_spots
890 .push(MissingLifetimeSpot::HigherRanked { span, span_type });
891 let (lifetimes, binders): (FxIndexMap<hir::ParamName, Region>, Vec<_>) = c
894 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
896 .map(|(late_bound_idx, param)| {
897 let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
898 let r = late_region_as_bound_region(self.tcx, &pair.1);
902 self.map.late_bound_vars.insert(ty.hir_id, binders);
903 let scope = Scope::Binder {
908 track_lifetime_uses: true,
909 opaque_type_parent: false,
910 scope_type: BinderScopeType::Normal,
911 allow_late_bound: true,
913 self.with(scope, |old_scope, this| {
914 // a bare fn has no bounds, so everything
915 // contained within is scoped within its binder.
916 this.check_lifetime_params(old_scope, &c.generic_params);
917 intravisit::walk_ty(this, ty);
919 self.missing_named_lifetime_spots.pop();
920 self.is_in_fn_syntax = was_in_fn_syntax;
922 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
923 debug!(?bounds, ?lifetime, "TraitObject");
924 let scope = Scope::TraitRefBoundary { s: self.scope };
925 self.with(scope, |_, this| {
926 for bound in bounds {
927 this.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
930 match lifetime.name {
931 LifetimeName::Implicit(_) => {
932 // For types like `dyn Foo`, we should
933 // generate a special form of elided.
934 span_bug!(ty.span, "object-lifetime-default expected, not implicit",);
936 LifetimeName::ImplicitObjectLifetimeDefault => {
937 // If the user does not write *anything*, we
938 // use the object lifetime defaulting
939 // rules. So e.g., `Box<dyn Debug>` becomes
940 // `Box<dyn Debug + 'static>`.
941 self.resolve_object_lifetime_default(lifetime)
943 LifetimeName::Underscore => {
944 // If the user writes `'_`, we use the *ordinary* elision
945 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
946 // resolved the same as the `'_` in `&'_ Foo`.
949 self.resolve_elided_lifetimes(&[lifetime])
951 LifetimeName::Param(_) | LifetimeName::Static => {
952 // If the user wrote an explicit name, use that.
953 self.visit_lifetime(lifetime);
955 LifetimeName::Error => {}
958 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
959 self.visit_lifetime(lifetime_ref);
960 let scope = Scope::ObjectLifetimeDefault {
961 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
964 self.with(scope, |_, this| this.visit_ty(&mt.ty));
966 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
967 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
968 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
969 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
970 // ^ ^ this gets resolved in the scope of
971 // the opaque_ty generics
972 let opaque_ty = self.tcx.hir().item(item_id);
973 let (generics, bounds) = match opaque_ty.kind {
974 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
975 // This arm is for `impl Trait` in the types of statics, constants and locals.
976 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
977 origin: hir::OpaqueTyOrigin::TyAlias,
980 intravisit::walk_ty(self, ty);
982 // Elided lifetimes are not allowed in non-return
983 // position impl Trait
984 let scope = Scope::TraitRefBoundary { s: self.scope };
985 self.with(scope, |_, this| {
986 let scope = Scope::Elision { elide: Elide::Forbid, s: this.scope };
987 this.with(scope, |_, this| {
988 intravisit::walk_item(this, opaque_ty);
994 // RPIT (return position impl trait)
995 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
996 origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
1000 }) => (generics, bounds),
1001 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
1004 // Resolve the lifetimes that are applied to the opaque type.
1005 // These are resolved in the current scope.
1006 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
1007 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
1008 // ^ ^this gets resolved in the current scope
1009 for lifetime in lifetimes {
1010 let hir::GenericArg::Lifetime(lifetime) = lifetime else {
1013 self.visit_lifetime(lifetime);
1015 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
1016 // and ban them. Type variables instantiated inside binders aren't
1017 // well-supported at the moment, so this doesn't work.
1018 // In the future, this should be fixed and this error should be removed.
1019 let def = self.map.defs.get(&lifetime.hir_id).cloned();
1020 let Some(Region::LateBound(_, _, def_id)) = def else {
1023 let Some(def_id) = def_id.as_local() else {
1026 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
1027 // Ensure that the parent of the def is an item, not HRTB
1028 let parent_id = self.tcx.hir().get_parent_node(hir_id);
1029 if !parent_id.is_owner() {
1030 if !self.trait_definition_only {
1035 "`impl Trait` can only capture lifetimes \
1036 bound at the fn or impl level"
1040 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
1044 // We want to start our early-bound indices at the end of the parent scope,
1045 // not including any parent `impl Trait`s.
1046 let mut index = self.next_early_index_for_opaque_type();
1049 let mut elision = None;
1050 let mut lifetimes = FxIndexMap::default();
1051 let mut non_lifetime_count = 0;
1052 for param in generics.params {
1054 GenericParamKind::Lifetime { .. } => {
1055 let (name, reg) = Region::early(self.tcx.hir(), &mut index, ¶m);
1056 let Region::EarlyBound(_, def_id) = reg else {
1059 // We cannot predict what lifetimes are unused in opaque type.
1060 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
1061 if let hir::ParamName::Plain(Ident {
1062 name: kw::UnderscoreLifetime,
1066 // Pick the elided lifetime "definition" if one exists
1067 // and use it to make an elision scope.
1068 elision = Some(reg);
1070 lifetimes.insert(name, reg);
1073 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1074 non_lifetime_count += 1;
1078 let next_early_index = index + non_lifetime_count;
1079 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
1081 if let Some(elision_region) = elision {
1083 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
1084 self.with(scope, |_old_scope, this| {
1085 let scope = Scope::Binder {
1090 track_lifetime_uses: true,
1091 opaque_type_parent: false,
1092 scope_type: BinderScopeType::Normal,
1093 allow_late_bound: false,
1095 this.with(scope, |_old_scope, this| {
1096 this.visit_generics(generics);
1097 let scope = Scope::TraitRefBoundary { s: this.scope };
1098 this.with(scope, |_, this| {
1099 for bound in bounds {
1100 this.visit_param_bound(bound);
1106 let scope = Scope::Binder {
1111 track_lifetime_uses: true,
1112 opaque_type_parent: false,
1113 scope_type: BinderScopeType::Normal,
1114 allow_late_bound: false,
1116 self.with(scope, |_old_scope, this| {
1117 let scope = Scope::TraitRefBoundary { s: this.scope };
1118 this.with(scope, |_, this| {
1119 this.visit_generics(generics);
1120 for bound in bounds {
1121 this.visit_param_bound(bound);
1127 _ => intravisit::walk_ty(self, ty),
1131 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1132 use self::hir::TraitItemKind::*;
1133 match trait_item.kind {
1135 self.missing_named_lifetime_spots.push((&trait_item.generics).into());
1137 self.visit_early_late(
1138 Some(tcx.hir().get_parent_item(trait_item.hir_id())),
1139 trait_item.hir_id(),
1141 &trait_item.generics,
1142 |this| intravisit::walk_trait_item(this, trait_item),
1144 self.missing_named_lifetime_spots.pop();
1146 Type(bounds, ref ty) => {
1147 self.missing_named_lifetime_spots.push((&trait_item.generics).into());
1148 let generics = &trait_item.generics;
1149 let mut index = self.next_early_index();
1150 debug!("visit_ty: index = {}", index);
1151 let mut non_lifetime_count = 0;
1152 let lifetimes = generics
1155 .filter_map(|param| match param.kind {
1156 GenericParamKind::Lifetime { .. } => {
1157 Some(Region::early(self.tcx.hir(), &mut index, param))
1159 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1160 non_lifetime_count += 1;
1165 self.map.late_bound_vars.insert(trait_item.hir_id(), vec![]);
1166 let scope = Scope::Binder {
1167 hir_id: trait_item.hir_id(),
1169 next_early_index: index + non_lifetime_count,
1171 track_lifetime_uses: true,
1172 opaque_type_parent: true,
1173 scope_type: BinderScopeType::Normal,
1174 allow_late_bound: false,
1176 self.with(scope, |old_scope, this| {
1177 this.check_lifetime_params(old_scope, &generics.params);
1178 let scope = Scope::TraitRefBoundary { s: this.scope };
1179 this.with(scope, |_, this| {
1180 this.visit_generics(generics);
1181 for bound in bounds {
1182 this.visit_param_bound(bound);
1184 if let Some(ty) = ty {
1189 self.missing_named_lifetime_spots.pop();
1192 // Only methods and types support generics.
1193 assert!(trait_item.generics.params.is_empty());
1194 self.missing_named_lifetime_spots.push(MissingLifetimeSpot::Static);
1195 intravisit::walk_trait_item(self, trait_item);
1196 self.missing_named_lifetime_spots.pop();
1201 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1202 use self::hir::ImplItemKind::*;
1203 match impl_item.kind {
1205 self.missing_named_lifetime_spots.push((&impl_item.generics).into());
1207 self.visit_early_late(
1208 Some(tcx.hir().get_parent_item(impl_item.hir_id())),
1211 &impl_item.generics,
1212 |this| intravisit::walk_impl_item(this, impl_item),
1214 self.missing_named_lifetime_spots.pop();
1216 TyAlias(ref ty) => {
1217 let generics = &impl_item.generics;
1218 self.missing_named_lifetime_spots.push(generics.into());
1219 let mut index = self.next_early_index();
1220 let mut non_lifetime_count = 0;
1221 debug!("visit_ty: index = {}", index);
1222 let lifetimes: FxIndexMap<hir::ParamName, Region> = generics
1225 .filter_map(|param| match param.kind {
1226 GenericParamKind::Lifetime { .. } => {
1227 Some(Region::early(self.tcx.hir(), &mut index, param))
1229 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
1230 non_lifetime_count += 1;
1235 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
1236 let scope = Scope::Binder {
1239 next_early_index: index + non_lifetime_count,
1241 track_lifetime_uses: true,
1242 opaque_type_parent: true,
1243 scope_type: BinderScopeType::Normal,
1244 allow_late_bound: true,
1246 self.with(scope, |old_scope, this| {
1247 this.check_lifetime_params(old_scope, &generics.params);
1248 let scope = Scope::TraitRefBoundary { s: this.scope };
1249 this.with(scope, |_, this| {
1250 this.visit_generics(generics);
1254 self.missing_named_lifetime_spots.pop();
1257 // Only methods and types support generics.
1258 assert!(impl_item.generics.params.is_empty());
1259 self.missing_named_lifetime_spots.push(MissingLifetimeSpot::Static);
1260 intravisit::walk_impl_item(self, impl_item);
1261 self.missing_named_lifetime_spots.pop();
1266 #[tracing::instrument(level = "debug", skip(self))]
1267 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1268 if lifetime_ref.is_elided() {
1269 self.resolve_elided_lifetimes(&[lifetime_ref]);
1272 if lifetime_ref.is_static() {
1273 self.insert_lifetime(lifetime_ref, Region::Static);
1276 if self.is_in_const_generic && lifetime_ref.name != LifetimeName::Error {
1277 self.emit_non_static_lt_in_const_generic_error(lifetime_ref);
1280 self.resolve_lifetime_ref(lifetime_ref);
1283 fn visit_assoc_type_binding(&mut self, type_binding: &'tcx hir::TypeBinding<'_>) {
1284 let scope = self.scope;
1285 if let Some(scope_for_path) = self.map.scope_for_path.as_mut() {
1286 // We add lifetime scope information for `Ident`s in associated type bindings and use
1287 // the `HirId` of the type binding as the key in `LifetimeMap`
1288 let lifetime_scope = get_lifetime_scopes_for_path(scope);
1289 let map = scope_for_path.entry(type_binding.hir_id.owner).or_default();
1290 map.insert(type_binding.hir_id.local_id, lifetime_scope);
1292 hir::intravisit::walk_assoc_type_binding(self, type_binding);
1295 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
1296 for (i, segment) in path.segments.iter().enumerate() {
1297 let depth = path.segments.len() - i - 1;
1298 if let Some(ref args) = segment.args {
1299 self.visit_segment_args(path.res, depth, args);
1302 let scope = self.scope;
1303 if let Some(scope_for_path) = self.map.scope_for_path.as_mut() {
1304 // Add lifetime scope information to path segment. Note we cannot call `visit_path_segment`
1305 // here because that call would yield to resolution problems due to `walk_path_segment`
1306 // being called, which processes the path segments generic args, which we have already
1307 // processed using `visit_segment_args`.
1308 let lifetime_scope = get_lifetime_scopes_for_path(scope);
1309 if let Some(hir_id) = segment.hir_id {
1310 let map = scope_for_path.entry(hir_id.owner).or_default();
1311 map.insert(hir_id.local_id, lifetime_scope);
1317 fn visit_path_segment(&mut self, path_span: Span, path_segment: &'tcx hir::PathSegment<'tcx>) {
1318 let scope = self.scope;
1319 if let Some(scope_for_path) = self.map.scope_for_path.as_mut() {
1320 let lifetime_scope = get_lifetime_scopes_for_path(scope);
1321 if let Some(hir_id) = path_segment.hir_id {
1322 let map = scope_for_path.entry(hir_id.owner).or_default();
1323 map.insert(hir_id.local_id, lifetime_scope);
1327 intravisit::walk_path_segment(self, path_span, path_segment);
1330 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
1331 let output = match fd.output {
1332 hir::FnRetTy::DefaultReturn(_) => None,
1333 hir::FnRetTy::Return(ref ty) => Some(&**ty),
1335 self.visit_fn_like_elision(&fd.inputs, output);
1338 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
1339 let scope = Scope::TraitRefBoundary { s: self.scope };
1340 self.with(scope, |_, this| {
1341 for param in generics.params {
1343 GenericParamKind::Lifetime { .. } => {}
1344 GenericParamKind::Type { ref default, .. } => {
1345 walk_list!(this, visit_param_bound, param.bounds);
1346 if let Some(ref ty) = default {
1350 GenericParamKind::Const { ref ty, default } => {
1351 let was_in_const_generic = this.is_in_const_generic;
1352 this.is_in_const_generic = true;
1353 walk_list!(this, visit_param_bound, param.bounds);
1355 if let Some(default) = default {
1356 this.visit_body(this.tcx.hir().body(default.body));
1358 this.is_in_const_generic = was_in_const_generic;
1362 for predicate in generics.where_clause.predicates {
1364 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1367 ref bound_generic_params,
1370 let (lifetimes, binders): (FxIndexMap<hir::ParamName, Region>, Vec<_>) =
1371 bound_generic_params
1374 matches!(param.kind, GenericParamKind::Lifetime { .. })
1377 .map(|(late_bound_idx, param)| {
1379 Region::late(late_bound_idx as u32, this.tcx.hir(), param);
1380 let r = late_region_as_bound_region(this.tcx, &pair.1);
1384 this.map.late_bound_vars.insert(bounded_ty.hir_id, binders.clone());
1385 let next_early_index = this.next_early_index();
1386 // Even if there are no lifetimes defined here, we still wrap it in a binder
1387 // scope. If there happens to be a nested poly trait ref (an error), that
1388 // will be `Concatenating` anyways, so we don't have to worry about the depth
1390 let scope = Scope::Binder {
1391 hir_id: bounded_ty.hir_id,
1395 track_lifetime_uses: true,
1396 opaque_type_parent: false,
1397 scope_type: BinderScopeType::Normal,
1398 allow_late_bound: true,
1400 this.with(scope, |old_scope, this| {
1401 this.check_lifetime_params(old_scope, &bound_generic_params);
1402 this.visit_ty(&bounded_ty);
1403 walk_list!(this, visit_param_bound, bounds);
1406 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1411 this.visit_lifetime(lifetime);
1412 walk_list!(this, visit_param_bound, bounds);
1414 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1419 this.visit_ty(lhs_ty);
1420 this.visit_ty(rhs_ty);
1427 fn visit_param_bound(&mut self, bound: &'tcx hir::GenericBound<'tcx>) {
1429 hir::GenericBound::LangItemTrait(_, _, hir_id, _) => {
1430 // FIXME(jackh726): This is pretty weird. `LangItemTrait` doesn't go
1431 // through the regular poly trait ref code, so we don't get another
1432 // chance to introduce a binder. For now, I'm keeping the existing logic
1433 // of "if there isn't a Binder scope above us, add one", but I
1434 // imagine there's a better way to go about this.
1435 let (binders, scope_type) = self.poly_trait_ref_binder_info();
1437 self.map.late_bound_vars.insert(*hir_id, binders);
1438 let scope = Scope::Binder {
1440 lifetimes: FxIndexMap::default(),
1442 next_early_index: self.next_early_index(),
1443 track_lifetime_uses: true,
1444 opaque_type_parent: false,
1446 allow_late_bound: true,
1448 self.with(scope, |_, this| {
1449 intravisit::walk_param_bound(this, bound);
1452 _ => intravisit::walk_param_bound(self, bound),
1456 fn visit_poly_trait_ref(
1458 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
1459 _modifier: hir::TraitBoundModifier,
1461 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
1463 let should_pop_missing_lt = self.is_trait_ref_fn_scope(trait_ref);
1465 let next_early_index = self.next_early_index();
1466 let (mut binders, scope_type) = self.poly_trait_ref_binder_info();
1468 let initial_bound_vars = binders.len() as u32;
1469 let mut lifetimes: FxIndexMap<hir::ParamName, Region> = FxIndexMap::default();
1470 let binders_iter = trait_ref
1471 .bound_generic_params
1473 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
1475 .map(|(late_bound_idx, param)| {
1477 Region::late(initial_bound_vars + late_bound_idx as u32, self.tcx.hir(), param);
1478 let r = late_region_as_bound_region(self.tcx, &pair.1);
1479 lifetimes.insert(pair.0, pair.1);
1482 binders.extend(binders_iter);
1485 self.map.late_bound_vars.insert(trait_ref.trait_ref.hir_ref_id, binders);
1487 // Always introduce a scope here, even if this is in a where clause and
1488 // we introduced the binders around the bounded Ty. In that case, we
1489 // just reuse the concatenation functionality also present in nested trait
1491 let scope = Scope::Binder {
1492 hir_id: trait_ref.trait_ref.hir_ref_id,
1496 track_lifetime_uses: true,
1497 opaque_type_parent: false,
1499 allow_late_bound: true,
1501 self.with(scope, |old_scope, this| {
1502 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
1503 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
1504 this.visit_trait_ref(&trait_ref.trait_ref);
1507 if should_pop_missing_lt {
1508 self.missing_named_lifetime_spots.pop();
1513 #[derive(Copy, Clone, PartialEq)]
1527 fn original_label(span: Span) -> Original {
1528 Original { kind: ShadowKind::Label, span }
1530 fn shadower_label(span: Span) -> Shadower {
1531 Shadower { kind: ShadowKind::Label, span }
1533 fn original_lifetime(span: Span) -> Original {
1534 Original { kind: ShadowKind::Lifetime, span }
1536 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1537 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1541 fn desc(&self) -> &'static str {
1543 ShadowKind::Label => "label",
1544 ShadowKind::Lifetime => "lifetime",
1549 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: Symbol, orig: Original, shadower: Shadower) {
1550 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1551 // lifetime/lifetime shadowing is an error
1556 "{} name `{}` shadows a \
1557 {} name that is already in scope",
1558 shadower.kind.desc(),
1564 // shadowing involving a label is only a warning, due to issues with
1565 // labels and lifetimes not being macro-hygienic.
1566 tcx.sess.struct_span_warn(
1569 "{} name `{}` shadows a \
1570 {} name that is already in scope",
1571 shadower.kind.desc(),
1577 err.span_label(orig.span, "first declared here");
1578 err.span_label(shadower.span, format!("{} `{}` already in scope", orig.kind.desc(), name));
1582 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1583 // if one of the label shadows a lifetime or another label.
1584 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1585 struct GatherLabels<'a, 'tcx> {
1587 scope: ScopeRef<'a>,
1588 labels_in_fn: &'a mut Vec<Ident>,
1592 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1593 gather.visit_body(body);
1595 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1596 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1597 if let Some(label) = expression_label(ex) {
1598 for prior_label in &self.labels_in_fn[..] {
1599 // FIXME (#24278): non-hygienic comparison
1600 if label.name == prior_label.name {
1601 signal_shadowing_problem(
1604 original_label(prior_label.span),
1605 shadower_label(label.span),
1610 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1612 self.labels_in_fn.push(label);
1614 intravisit::walk_expr(self, ex)
1618 fn expression_label(ex: &hir::Expr<'_>) -> Option<Ident> {
1620 hir::ExprKind::Loop(_, Some(label), ..) => Some(label.ident),
1621 hir::ExprKind::Block(_, Some(label)) => Some(label.ident),
1626 fn check_if_label_shadows_lifetime(tcx: TyCtxt<'_>, mut scope: ScopeRef<'_>, label: Ident) {
1629 Scope::Body { s, .. }
1630 | Scope::Elision { s, .. }
1631 | Scope::ObjectLifetimeDefault { s, .. }
1632 | Scope::Supertrait { s, .. }
1633 | Scope::TraitRefBoundary { s, .. } => {
1641 Scope::Binder { ref lifetimes, s, .. } => {
1642 // FIXME (#24278): non-hygienic comparison
1644 lifetimes.get(&hir::ParamName::Plain(label.normalize_to_macros_2_0()))
1646 signal_shadowing_problem(
1649 original_lifetime(tcx.def_span(def.id().unwrap().expect_local())),
1650 shadower_label(label.span),
1661 fn compute_object_lifetime_defaults<'tcx>(
1663 item: &hir::Item<'_>,
1664 ) -> Option<&'tcx [ObjectLifetimeDefault]> {
1666 hir::ItemKind::Struct(_, ref generics)
1667 | hir::ItemKind::Union(_, ref generics)
1668 | hir::ItemKind::Enum(_, ref generics)
1669 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1671 origin: hir::OpaqueTyOrigin::TyAlias,
1674 | hir::ItemKind::TyAlias(_, ref generics)
1675 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1676 let result = object_lifetime_defaults_for_item(tcx, generics);
1679 let attrs = tcx.hir().attrs(item.hir_id());
1680 if tcx.sess.contains_name(attrs, sym::rustc_object_lifetime_default) {
1681 let object_lifetime_default_reprs: String = result
1683 .map(|set| match *set {
1684 Set1::Empty => "BaseDefault".into(),
1685 Set1::One(Region::Static) => "'static".into(),
1686 Set1::One(Region::EarlyBound(mut i, _)) => generics
1689 .find_map(|param| match param.kind {
1690 GenericParamKind::Lifetime { .. } => {
1692 return Some(param.name.ident().to_string().into());
1700 Set1::One(_) => bug!(),
1701 Set1::Many => "Ambiguous".into(),
1703 .collect::<Vec<Cow<'static, str>>>()
1705 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1714 /// Scan the bounds and where-clauses on parameters to extract bounds
1715 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1716 /// for each type parameter.
1717 fn object_lifetime_defaults_for_item<'tcx>(
1719 generics: &hir::Generics<'_>,
1720 ) -> &'tcx [ObjectLifetimeDefault] {
1721 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1722 for bound in bounds {
1723 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1724 set.insert(lifetime.name.normalize_to_macros_2_0());
1729 let process_param = |param: &hir::GenericParam<'_>| match param.kind {
1730 GenericParamKind::Lifetime { .. } => None,
1731 GenericParamKind::Type { .. } => {
1732 let mut set = Set1::Empty;
1734 add_bounds(&mut set, ¶m.bounds);
1736 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1737 for predicate in generics.where_clause.predicates {
1738 // Look for `type: ...` where clauses.
1739 let hir::WherePredicate::BoundPredicate(ref data) = *predicate else { continue };
1741 // Ignore `for<'a> type: ...` as they can change what
1742 // lifetimes mean (although we could "just" handle it).
1743 if !data.bound_generic_params.is_empty() {
1747 let res = match data.bounded_ty.kind {
1748 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1752 if res == Res::Def(DefKind::TyParam, param_def_id.to_def_id()) {
1753 add_bounds(&mut set, &data.bounds);
1758 Set1::Empty => Set1::Empty,
1759 Set1::One(name) => {
1760 if name == hir::LifetimeName::Static {
1761 Set1::One(Region::Static)
1766 .filter_map(|param| match param.kind {
1767 GenericParamKind::Lifetime { .. } => {
1768 Some((param.hir_id, hir::LifetimeName::Param(param.name)))
1773 .find(|&(_, (_, lt_name))| lt_name == name)
1774 .map_or(Set1::Many, |(i, (id, _))| {
1775 let def_id = tcx.hir().local_def_id(id);
1776 Set1::One(Region::EarlyBound(i as u32, def_id.to_def_id()))
1780 Set1::Many => Set1::Many,
1783 GenericParamKind::Const { .. } => {
1784 // Generic consts don't impose any constraints.
1786 // We still store a dummy value here to allow generic parameters
1787 // in an arbitrary order.
1792 tcx.arena.alloc_from_iter(generics.params.iter().filter_map(process_param))
1795 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1796 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1798 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1800 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1801 let labels_in_fn = take(&mut self.labels_in_fn);
1802 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1803 let missing_named_lifetime_spots = take(&mut self.missing_named_lifetime_spots);
1804 let mut this = LifetimeContext {
1808 is_in_fn_syntax: self.is_in_fn_syntax,
1809 is_in_const_generic: self.is_in_const_generic,
1810 trait_definition_only: self.trait_definition_only,
1812 xcrate_object_lifetime_defaults,
1814 missing_named_lifetime_spots,
1816 let span = tracing::debug_span!("scope", scope = ?TruncatedScopeDebug(&this.scope));
1818 let _enter = span.enter();
1819 f(self.scope, &mut this);
1820 if !self.trait_definition_only {
1821 this.check_uses_for_lifetimes_defined_by_scope();
1824 self.labels_in_fn = this.labels_in_fn;
1825 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1826 self.missing_named_lifetime_spots = this.missing_named_lifetime_spots;
1829 /// helper method to determine the span to remove when suggesting the
1830 /// deletion of a lifetime
1831 fn lifetime_deletion_span(&self, name: Ident, generics: &hir::Generics<'_>) -> Option<Span> {
1832 generics.params.iter().enumerate().find_map(|(i, param)| {
1833 if param.name.ident() == name {
1834 if generics.params.len() == 1 {
1835 // if sole lifetime, remove the entire `<>` brackets
1838 // if removing within `<>` brackets, we also want to
1839 // delete a leading or trailing comma as appropriate
1840 if i >= generics.params.len() - 1 {
1841 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1843 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1852 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1853 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1854 fn suggest_eliding_single_use_lifetime(
1856 err: &mut Diagnostic,
1858 lifetime: &hir::Lifetime,
1860 let name = lifetime.name.ident();
1861 let remove_decl = self
1864 .and_then(|parent_def_id| parent_def_id.as_local())
1865 .and_then(|parent_def_id| self.tcx.hir().get_generics(parent_def_id))
1866 .and_then(|generics| self.lifetime_deletion_span(name, generics));
1868 let mut remove_use = None;
1869 let mut elide_use = None;
1870 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1871 for input in inputs {
1873 hir::TyKind::Rptr(lt, _) => {
1874 if lt.name.ident() == name {
1875 // include the trailing whitespace between the lifetime and type names
1876 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1881 .span_until_non_whitespace(lt_through_ty_span),
1886 hir::TyKind::Path(QPath::Resolved(_, path)) => {
1887 let last_segment = &path.segments[path.segments.len() - 1];
1888 let generics = last_segment.args();
1889 for arg in generics.args.iter() {
1890 if let GenericArg::Lifetime(lt) = arg {
1891 if lt.name.ident() == name {
1892 elide_use = Some(lt.span);
1903 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1904 if let Some(parent) =
1905 self.tcx.hir().find_by_def_id(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1908 Node::Item(item) => {
1909 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1910 find_arg_use_span(sig.decl.inputs);
1913 Node::ImplItem(impl_item) => {
1914 if let hir::ImplItemKind::Fn(sig, _) = &impl_item.kind {
1915 find_arg_use_span(sig.decl.inputs);
1923 let msg = "elide the single-use lifetime";
1924 match (remove_decl, remove_use, elide_use) {
1925 (Some(decl_span), Some(use_span), None) => {
1926 // if both declaration and use deletion spans start at the same
1927 // place ("start at" because the latter includes trailing
1928 // whitespace), then this is an in-band lifetime
1929 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1930 err.span_suggestion(
1934 Applicability::MachineApplicable,
1937 err.multipart_suggestion(
1939 vec![(decl_span, String::new()), (use_span, String::new())],
1940 Applicability::MachineApplicable,
1944 (Some(decl_span), None, Some(use_span)) => {
1945 err.multipart_suggestion(
1947 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1948 Applicability::MachineApplicable,
1955 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1956 let Scope::Binder { lifetimes: defined_by, .. } = self.scope else {
1957 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1961 let def_ids: Vec<_> = defined_by
1963 .flat_map(|region| match region {
1964 Region::EarlyBound(_, def_id)
1965 | Region::LateBound(_, _, def_id)
1966 | Region::Free(_, def_id) => Some(*def_id),
1968 Region::LateBoundAnon(..) | Region::Static => None,
1972 'lifetimes: for def_id in def_ids {
1973 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1975 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1978 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1982 match lifetimeuseset {
1983 Some(LifetimeUseSet::One(lifetime)) => {
1985 if let Some((id, span, name)) =
1986 match self.tcx.hir().get_by_def_id(def_id.expect_local()) {
1987 Node::Lifetime(hir_lifetime) => Some((
1988 hir_lifetime.hir_id,
1990 hir_lifetime.name.ident(),
1992 Node::GenericParam(param) => {
1993 Some((param.hir_id, param.span, param.name.ident()))
1998 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1999 if name.name == kw::UnderscoreLifetime {
2003 if let Some(parent_def_id) = self.tcx.parent(def_id) {
2004 if let Some(def_id) = parent_def_id.as_local() {
2005 // lifetimes in `derive` expansions don't count (Issue #53738)
2008 .get_attrs(def_id.to_def_id())
2010 .any(|attr| attr.has_name(sym::automatically_derived))
2015 // opaque types generated when desugaring an async function can have a single
2016 // use lifetime even if it is explicitly denied (Issue #77175)
2017 if let hir::Node::Item(hir::Item {
2018 kind: hir::ItemKind::OpaqueTy(ref opaque),
2020 }) = self.tcx.hir().get_by_def_id(def_id)
2022 if !matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn(..)) {
2023 continue 'lifetimes;
2025 // We want to do this only if the lifetime identifier is already defined
2026 // in the async function that generated this. Otherwise it could be
2027 // an opaque type defined by the developer and we still want this
2028 // lint to fail compilation
2029 for p in opaque.generics.params {
2030 if defined_by.contains_key(&p.name) {
2031 continue 'lifetimes;
2038 self.tcx.struct_span_lint_hir(
2039 lint::builtin::SINGLE_USE_LIFETIMES,
2043 let mut err = lint.build(&format!(
2044 "lifetime parameter `{}` only used once",
2047 if span == lifetime.span {
2048 // spans are the same for in-band lifetime declarations
2049 err.span_label(span, "this lifetime is only used here");
2051 err.span_label(span, "this lifetime...");
2052 err.span_label(lifetime.span, "...is used only here");
2054 self.suggest_eliding_single_use_lifetime(
2055 &mut err, def_id, lifetime,
2062 Some(LifetimeUseSet::Many) => {
2063 debug!("not one use lifetime");
2066 if let Some((id, span, name)) =
2067 match self.tcx.hir().get_by_def_id(def_id.expect_local()) {
2068 Node::Lifetime(hir_lifetime) => Some((
2069 hir_lifetime.hir_id,
2071 hir_lifetime.name.ident(),
2073 Node::GenericParam(param) => {
2074 Some((param.hir_id, param.span, param.name.ident()))
2079 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
2080 self.tcx.struct_span_lint_hir(
2081 lint::builtin::UNUSED_LIFETIMES,
2086 .build(&format!("lifetime parameter `{}` never used", name));
2087 if let Some(parent_def_id) = self.tcx.parent(def_id) {
2088 if let Some(generics) =
2089 self.tcx.hir().get_generics(parent_def_id.expect_local())
2091 let unused_lt_span =
2092 self.lifetime_deletion_span(name, generics);
2093 if let Some(span) = unused_lt_span {
2094 err.span_suggestion(
2096 "elide the unused lifetime",
2098 Applicability::MachineApplicable,
2112 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
2114 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
2115 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
2116 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
2120 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
2122 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
2123 /// lifetimes may be interspersed together.
2125 /// If early bound lifetimes are present, we separate them into their own list (and likewise
2126 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
2127 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
2128 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
2129 /// ordering is not important there.
2130 fn visit_early_late<F>(
2132 parent_id: Option<LocalDefId>,
2134 decl: &'tcx hir::FnDecl<'tcx>,
2135 generics: &'tcx hir::Generics<'tcx>,
2138 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
2140 insert_late_bound_lifetimes(self.map, decl, generics);
2142 // Find the start of nested early scopes, e.g., in methods.
2143 let mut next_early_index = 0;
2144 if let Some(parent_id) = parent_id {
2145 let parent = self.tcx.hir().expect_item(parent_id);
2146 if sub_items_have_self_param(&parent.kind) {
2147 next_early_index += 1; // Self comes before lifetimes
2150 hir::ItemKind::Trait(_, _, ref generics, ..)
2151 | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
2152 next_early_index += generics.params.len() as u32;
2158 let mut non_lifetime_count = 0;
2159 let mut named_late_bound_vars = 0;
2160 let lifetimes: FxIndexMap<hir::ParamName, Region> = generics
2163 .filter_map(|param| match param.kind {
2164 GenericParamKind::Lifetime { .. } => {
2165 if self.map.late_bound.contains(¶m.hir_id) {
2166 let late_bound_idx = named_late_bound_vars;
2167 named_late_bound_vars += 1;
2168 Some(Region::late(late_bound_idx, self.tcx.hir(), param))
2170 Some(Region::early(self.tcx.hir(), &mut next_early_index, param))
2173 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
2174 non_lifetime_count += 1;
2179 let next_early_index = next_early_index + non_lifetime_count;
2181 let binders: Vec<_> = generics
2185 matches!(param.kind, GenericParamKind::Lifetime { .. })
2186 && self.map.late_bound.contains(¶m.hir_id)
2189 .map(|(late_bound_idx, param)| {
2190 let pair = Region::late(late_bound_idx as u32, self.tcx.hir(), param);
2191 late_region_as_bound_region(self.tcx, &pair.1)
2194 self.map.late_bound_vars.insert(hir_id, binders);
2195 let scope = Scope::Binder {
2200 opaque_type_parent: true,
2201 track_lifetime_uses: false,
2202 scope_type: BinderScopeType::Normal,
2203 allow_late_bound: true,
2205 self.with(scope, move |old_scope, this| {
2206 this.check_lifetime_params(old_scope, &generics.params);
2211 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
2212 let mut scope = self.scope;
2215 Scope::Root => return 0,
2217 Scope::Binder { next_early_index, opaque_type_parent, .. }
2218 if (!only_opaque_type_parent || opaque_type_parent) =>
2220 return next_early_index;
2223 Scope::Binder { s, .. }
2224 | Scope::Body { s, .. }
2225 | Scope::Elision { s, .. }
2226 | Scope::ObjectLifetimeDefault { s, .. }
2227 | Scope::Supertrait { s, .. }
2228 | Scope::TraitRefBoundary { s, .. } => scope = s,
2233 /// Returns the next index one would use for an early-bound-region
2234 /// if extending the current scope.
2235 fn next_early_index(&self) -> u32 {
2236 self.next_early_index_helper(true)
2239 /// Returns the next index one would use for an `impl Trait` that
2240 /// is being converted into an opaque type alias `impl Trait`. This will be the
2241 /// next early index from the enclosing item, for the most
2242 /// part. See the `opaque_type_parent` field for more info.
2243 fn next_early_index_for_opaque_type(&self) -> u32 {
2244 self.next_early_index_helper(false)
2247 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2248 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
2250 // If we've already reported an error, just ignore `lifetime_ref`.
2251 if let LifetimeName::Error = lifetime_ref.name {
2255 // Walk up the scope chain, tracking the number of fn scopes
2256 // that we pass through, until we find a lifetime with the
2257 // given name or we run out of scopes.
2259 let mut late_depth = 0;
2260 let mut scope = self.scope;
2261 let mut outermost_body = None;
2264 Scope::Body { id, s } => {
2265 // Non-static lifetimes are prohibited in anonymous constants without
2266 // `generic_const_exprs`.
2267 self.maybe_emit_forbidden_non_static_lifetime_error(id, lifetime_ref);
2269 outermost_body = Some(id);
2277 Scope::Binder { ref lifetimes, scope_type, s, .. } => {
2278 match lifetime_ref.name {
2279 LifetimeName::Param(param_name) => {
2280 if let Some(&def) = lifetimes.get(¶m_name.normalize_to_macros_2_0())
2282 break Some(def.shifted(late_depth));
2285 _ => bug!("expected LifetimeName::Param"),
2288 BinderScopeType::Normal => late_depth += 1,
2289 BinderScopeType::Concatenating => {}
2294 Scope::Elision { s, .. }
2295 | Scope::ObjectLifetimeDefault { s, .. }
2296 | Scope::Supertrait { s, .. }
2297 | Scope::TraitRefBoundary { s, .. } => {
2303 if let Some(mut def) = result {
2304 if let Region::EarlyBound(..) = def {
2305 // Do not free early-bound regions, only late-bound ones.
2306 } else if let Some(body_id) = outermost_body {
2307 let fn_id = self.tcx.hir().body_owner(body_id);
2308 match self.tcx.hir().get(fn_id) {
2309 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
2310 | Node::TraitItem(&hir::TraitItem {
2311 kind: hir::TraitItemKind::Fn(..), ..
2313 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
2314 let scope = self.tcx.hir().local_def_id(fn_id);
2315 def = Region::Free(scope.to_def_id(), def.id().unwrap());
2321 self.insert_lifetime(lifetime_ref, def);
2323 self.emit_undeclared_lifetime_error(lifetime_ref);
2327 fn visit_segment_args(
2331 generic_args: &'tcx hir::GenericArgs<'tcx>,
2334 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
2335 res, depth, generic_args,
2338 if generic_args.parenthesized {
2339 let was_in_fn_syntax = self.is_in_fn_syntax;
2340 self.is_in_fn_syntax = true;
2341 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
2342 self.is_in_fn_syntax = was_in_fn_syntax;
2346 let mut elide_lifetimes = true;
2347 let lifetimes: Vec<_> = generic_args
2350 .filter_map(|arg| match arg {
2351 hir::GenericArg::Lifetime(lt) => {
2352 if !lt.is_elided() {
2353 elide_lifetimes = false;
2360 // We short-circuit here if all are elided in order to pluralize
2362 if elide_lifetimes {
2363 self.resolve_elided_lifetimes(&lifetimes);
2365 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
2368 // Figure out if this is a type/trait segment,
2369 // which requires object lifetime defaults.
2370 let parent_def_id = |this: &mut Self, def_id: DefId| {
2371 let def_key = this.tcx.def_key(def_id);
2372 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
2374 let type_def_id = match res {
2375 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
2376 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
2384 ) if depth == 0 => Some(def_id),
2388 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
2390 // Compute a vector of defaults, one for each type parameter,
2391 // per the rules given in RFCs 599 and 1156. Example:
2394 // struct Foo<'a, T: 'a, U> { }
2397 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
2398 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
2399 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
2402 // Therefore, we would compute `object_lifetime_defaults` to a
2403 // vector like `['x, 'static]`. Note that the vector only
2404 // includes type parameters.
2405 let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
2407 let mut scope = self.scope;
2410 Scope::Root => break false,
2412 Scope::Body { .. } => break true,
2414 Scope::Binder { s, .. }
2415 | Scope::Elision { s, .. }
2416 | Scope::ObjectLifetimeDefault { s, .. }
2417 | Scope::Supertrait { s, .. }
2418 | Scope::TraitRefBoundary { s, .. } => {
2425 let map = &self.map;
2426 let set_to_region = |set: &ObjectLifetimeDefault| match *set {
2431 Some(Region::Static)
2435 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
2436 GenericArg::Lifetime(lt) => Some(lt),
2439 r.subst(lifetimes, map)
2443 if let Some(def_id) = def_id.as_local() {
2444 let id = self.tcx.hir().local_def_id_to_hir_id(def_id);
2446 .object_lifetime_defaults(id.owner)
2453 self.xcrate_object_lifetime_defaults
2455 .or_insert_with(|| {
2456 tcx.generics_of(def_id)
2459 .filter_map(|param| match param.kind {
2460 GenericParamDefKind::Type { object_lifetime_default, .. } => {
2461 Some(object_lifetime_default)
2463 GenericParamDefKind::Const { .. } => Some(Set1::Empty),
2464 GenericParamDefKind::Lifetime => None,
2474 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
2477 for arg in generic_args.args {
2479 GenericArg::Lifetime(_) => {}
2480 GenericArg::Type(ty) => {
2481 if let Some(<) = object_lifetime_defaults.get(i) {
2482 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
2483 self.with(scope, |_, this| this.visit_ty(ty));
2489 GenericArg::Const(ct) => {
2490 self.visit_anon_const(&ct.value);
2493 GenericArg::Infer(inf) => {
2494 self.visit_id(inf.hir_id);
2500 // Hack: when resolving the type `XX` in binding like `dyn
2501 // Foo<'b, Item = XX>`, the current object-lifetime default
2502 // would be to examine the trait `Foo` to check whether it has
2503 // a lifetime bound declared on `Item`. e.g., if `Foo` is
2504 // declared like so, then the default object lifetime bound in
2505 // `XX` should be `'b`:
2513 // but if we just have `type Item;`, then it would be
2514 // `'static`. However, we don't get all of this logic correct.
2516 // Instead, we do something hacky: if there are no lifetime parameters
2517 // to the trait, then we simply use a default object lifetime
2518 // bound of `'static`, because there is no other possibility. On the other hand,
2519 // if there ARE lifetime parameters, then we require the user to give an
2520 // explicit bound for now.
2522 // This is intended to leave room for us to implement the
2523 // correct behavior in the future.
2524 let has_lifetime_parameter =
2525 generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
2527 // Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or
2528 // in the trait ref `YY<...>` in `Item: YY<...>`.
2529 for binding in generic_args.bindings {
2530 let scope = Scope::ObjectLifetimeDefault {
2531 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2534 if let Some(type_def_id) = type_def_id {
2535 let lifetimes = LifetimeContext::supertrait_hrtb_lifetimes(
2540 self.with(scope, |_, this| {
2541 let scope = Scope::Supertrait {
2542 lifetimes: lifetimes.unwrap_or_default(),
2545 this.with(scope, |_, this| this.visit_assoc_type_binding(binding));
2548 self.with(scope, |_, this| this.visit_assoc_type_binding(binding));
2553 /// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the
2554 /// associated type name and starting trait.
2555 /// For example, imagine we have
2557 /// trait Foo<'a, 'b> {
2560 /// trait Bar<'b>: for<'a> Foo<'a, 'b> {}
2561 /// trait Bar: for<'b> Bar<'b> {}
2563 /// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on
2564 /// the starting trait `Bar`, we would return `Some(['b, 'a])`.
2565 fn supertrait_hrtb_lifetimes(
2569 ) -> Option<Vec<ty::BoundVariableKind>> {
2570 let trait_defines_associated_type_named = |trait_def_id: DefId| {
2571 tcx.associated_items(trait_def_id)
2572 .find_by_name_and_kind(tcx, assoc_name, ty::AssocKind::Type, trait_def_id)
2576 use smallvec::{smallvec, SmallVec};
2577 let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> =
2578 smallvec![(def_id, smallvec![])];
2579 let mut visited: FxHashSet<DefId> = FxHashSet::default();
2581 let Some((def_id, bound_vars)) = stack.pop() else {
2584 // See issue #83753. If someone writes an associated type on a non-trait, just treat it as
2585 // there being no supertrait HRTBs.
2586 match tcx.def_kind(def_id) {
2587 DefKind::Trait | DefKind::TraitAlias | DefKind::Impl => {}
2591 if trait_defines_associated_type_named(def_id) {
2592 break Some(bound_vars.into_iter().collect());
2595 tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name)));
2596 let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
2597 let bound_predicate = pred.kind();
2598 match bound_predicate.skip_binder() {
2599 ty::PredicateKind::Trait(data) => {
2600 // The order here needs to match what we would get from `subst_supertrait`
2601 let pred_bound_vars = bound_predicate.bound_vars();
2602 let mut all_bound_vars = bound_vars.clone();
2603 all_bound_vars.extend(pred_bound_vars.iter());
2604 let super_def_id = data.trait_ref.def_id;
2605 Some((super_def_id, all_bound_vars))
2611 let obligations = obligations.filter(|o| visited.insert(o.0));
2612 stack.extend(obligations);
2616 #[tracing::instrument(level = "debug", skip(self))]
2617 fn visit_fn_like_elision(
2619 inputs: &'tcx [hir::Ty<'tcx>],
2620 output: Option<&'tcx hir::Ty<'tcx>>,
2622 debug!("visit_fn_like_elision: enter");
2623 let mut scope = &*self.scope;
2626 Scope::Binder { hir_id, allow_late_bound: true, .. } => {
2629 Scope::ObjectLifetimeDefault { ref s, .. }
2630 | Scope::Elision { ref s, .. }
2631 | Scope::Supertrait { ref s, .. }
2632 | Scope::TraitRefBoundary { ref s, .. } => {
2636 | Scope::Body { .. }
2637 | Scope::Binder { allow_late_bound: false, .. } => {
2638 // See issues #83907 and #83693. Just bail out from looking inside.
2639 // See the issue #95023 for not allowing late bound
2640 self.tcx.sess.delay_span_bug(
2641 rustc_span::DUMMY_SP,
2642 "In fn_like_elision without appropriate scope above",
2648 // While not strictly necessary, we gather anon lifetimes *before* actually
2649 // visiting the argument types.
2650 let mut gather = GatherAnonLifetimes { anon_count: 0 };
2651 for input in inputs {
2652 gather.visit_ty(input);
2654 trace!(?gather.anon_count);
2655 let late_bound_vars = self.map.late_bound_vars.entry(hir_id).or_default();
2656 let named_late_bound_vars = late_bound_vars.len() as u32;
2657 late_bound_vars.extend(
2658 (0..gather.anon_count).map(|var| ty::BoundVariableKind::Region(ty::BrAnon(var))),
2660 let arg_scope = Scope::Elision {
2661 elide: Elide::FreshLateAnon(named_late_bound_vars, Cell::new(0)),
2664 self.with(arg_scope, |_, this| {
2665 for input in inputs {
2666 this.visit_ty(input);
2670 let Some(output) = output else { return };
2672 debug!("determine output");
2674 // Figure out if there's a body we can get argument names from,
2675 // and whether there's a `self` argument (treated specially).
2676 let mut assoc_item_kind = None;
2677 let mut impl_self = None;
2678 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2679 let body = match self.tcx.hir().get(parent) {
2680 // `fn` definitions and methods.
2681 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2683 Node::TraitItem(&hir::TraitItem { kind: hir::TraitItemKind::Fn(_, ref m), .. }) => {
2684 if let hir::ItemKind::Trait(.., ref trait_items) =
2685 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2688 trait_items.iter().find(|ti| ti.id.hir_id() == parent).map(|ti| ti.kind);
2691 hir::TraitFn::Required(_) => None,
2692 hir::TraitFn::Provided(body) => Some(body),
2696 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body), .. }) => {
2697 if let hir::ItemKind::Impl(hir::Impl { ref self_ty, ref items, .. }) =
2698 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2700 impl_self = Some(self_ty);
2702 items.iter().find(|ii| ii.id.hir_id() == parent).map(|ii| ii.kind);
2707 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2708 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2709 // Everything else (only closures?) doesn't
2710 // actually enjoy elision in return types.
2712 self.visit_ty(output);
2717 let has_self = match assoc_item_kind {
2718 Some(hir::AssocItemKind::Fn { has_self }) => has_self,
2722 // In accordance with the rules for lifetime elision, we can determine
2723 // what region to use for elision in the output type in two ways.
2724 // First (determined here), if `self` is by-reference, then the
2725 // implied output region is the region of the self parameter.
2727 struct SelfVisitor<'a> {
2728 map: &'a NamedRegionMap,
2729 impl_self: Option<&'a hir::TyKind<'a>>,
2730 lifetime: Set1<Region>,
2733 impl SelfVisitor<'_> {
2734 // Look for `self: &'a Self` - also desugared from `&'a self`,
2735 // and if that matches, use it for elision and return early.
2736 fn is_self_ty(&self, res: Res) -> bool {
2737 if let Res::SelfTy { .. } = res {
2741 // Can't always rely on literal (or implied) `Self` due
2742 // to the way elision rules were originally specified.
2743 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2747 // Permit the types that unambiguously always
2748 // result in the same type constructor being used
2749 // (it can't differ between `Self` and `self`).
2750 Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _)
2751 | Res::PrimTy(_) => return res == path.res,
2760 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2761 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2762 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2763 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2765 if self.is_self_ty(path.res) {
2766 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2767 self.lifetime.insert(*lifetime);
2772 intravisit::walk_ty(self, ty)
2776 let mut visitor = SelfVisitor {
2778 impl_self: impl_self.map(|ty| &ty.kind),
2779 lifetime: Set1::Empty,
2781 visitor.visit_ty(&inputs[0]);
2782 if let Set1::One(lifetime) = visitor.lifetime {
2783 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2784 self.with(scope, |_, this| this.visit_ty(output));
2789 // Second, if there was exactly one lifetime (either a substitution or a
2790 // reference) in the arguments, then any anonymous regions in the output
2791 // have that lifetime.
2792 let mut possible_implied_output_region = None;
2793 let mut lifetime_count = 0;
2794 let arg_lifetimes = inputs
2797 .skip(has_self as usize)
2799 let mut gather = GatherLifetimes {
2801 outer_index: ty::INNERMOST,
2802 have_bound_regions: false,
2803 lifetimes: Default::default(),
2805 gather.visit_ty(input);
2807 lifetime_count += gather.lifetimes.len();
2809 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2810 // there's a chance that the unique lifetime of this
2811 // iteration will be the appropriate lifetime for output
2812 // parameters, so lets store it.
2813 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2816 ElisionFailureInfo {
2819 lifetime_count: gather.lifetimes.len(),
2820 have_bound_regions: gather.have_bound_regions,
2826 let elide = if lifetime_count == 1 {
2827 Elide::Exact(possible_implied_output_region.unwrap())
2829 Elide::Error(arg_lifetimes)
2834 let scope = Scope::Elision { elide, s: self.scope };
2835 self.with(scope, |_, this| this.visit_ty(output));
2837 struct GatherLifetimes<'a> {
2838 map: &'a NamedRegionMap,
2839 outer_index: ty::DebruijnIndex,
2840 have_bound_regions: bool,
2841 lifetimes: FxHashSet<Region>,
2844 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2845 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2846 if let hir::TyKind::BareFn(_) = ty.kind {
2847 self.outer_index.shift_in(1);
2850 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2851 for bound in bounds {
2852 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2855 // Stay on the safe side and don't include the object
2856 // lifetime default (which may not end up being used).
2857 if !lifetime.is_elided() {
2858 self.visit_lifetime(lifetime);
2862 intravisit::walk_ty(self, ty);
2865 if let hir::TyKind::BareFn(_) = ty.kind {
2866 self.outer_index.shift_out(1);
2870 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2871 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2872 // FIXME(eddyb) Do we want this? It only makes a difference
2873 // if this `for<'a>` lifetime parameter is never used.
2874 self.have_bound_regions = true;
2877 intravisit::walk_generic_param(self, param);
2880 fn visit_poly_trait_ref(
2882 trait_ref: &hir::PolyTraitRef<'_>,
2883 modifier: hir::TraitBoundModifier,
2885 self.outer_index.shift_in(1);
2886 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2887 self.outer_index.shift_out(1);
2890 fn visit_param_bound(&mut self, bound: &hir::GenericBound<'_>) {
2891 if let hir::GenericBound::LangItemTrait { .. } = bound {
2892 self.outer_index.shift_in(1);
2893 intravisit::walk_param_bound(self, bound);
2894 self.outer_index.shift_out(1);
2896 intravisit::walk_param_bound(self, bound);
2900 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2901 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2903 Region::LateBound(debruijn, _, _)
2904 | Region::LateBoundAnon(debruijn, _, _)
2905 if debruijn < self.outer_index =>
2907 self.have_bound_regions = true;
2910 // FIXME(jackh726): nested trait refs?
2911 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2918 struct GatherAnonLifetimes {
2921 impl<'v> Visitor<'v> for GatherAnonLifetimes {
2922 #[instrument(skip(self), level = "trace")]
2923 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2924 // If we enter a `BareFn`, then we enter a *new* binding scope
2925 if let hir::TyKind::BareFn(_) = ty.kind {
2928 intravisit::walk_ty(self, ty);
2931 fn visit_generic_args(
2934 generic_args: &'v hir::GenericArgs<'v>,
2936 // parenthesized args enter a new elision scope
2937 if generic_args.parenthesized {
2940 intravisit::walk_generic_args(self, path_span, generic_args)
2943 #[instrument(skip(self), level = "trace")]
2944 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2945 if lifetime_ref.is_elided() {
2946 self.anon_count += 1;
2952 fn resolve_elided_lifetimes(&mut self, lifetime_refs: &[&'tcx hir::Lifetime]) {
2953 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2955 if lifetime_refs.is_empty() {
2959 let mut late_depth = 0;
2960 let mut scope = self.scope;
2961 let mut lifetime_names = FxHashSet::default();
2962 let mut lifetime_spans = vec![];
2965 // Do not assign any resolution, it will be inferred.
2966 Scope::Body { .. } => break Ok(()),
2968 Scope::Root => break Err(None),
2970 Scope::Binder { s, ref lifetimes, scope_type, .. } => {
2971 // collect named lifetimes for suggestions
2972 for name in lifetimes.keys() {
2973 if let hir::ParamName::Plain(name) = name {
2974 lifetime_names.insert(name.name);
2975 lifetime_spans.push(name.span);
2979 BinderScopeType::Normal => late_depth += 1,
2980 BinderScopeType::Concatenating => {}
2986 elide: Elide::FreshLateAnon(named_late_bound_vars, ref counter),
2989 for lifetime_ref in lifetime_refs {
2991 Region::late_anon(named_late_bound_vars, counter).shifted(late_depth);
2993 self.insert_lifetime(lifetime_ref, lifetime);
2998 Scope::Elision { elide: Elide::Exact(l), .. } => {
2999 let lifetime = l.shifted(late_depth);
3000 for lifetime_ref in lifetime_refs {
3001 self.insert_lifetime(lifetime_ref, lifetime);
3006 Scope::Elision { elide: Elide::Error(ref e), ref s, .. } => {
3010 Scope::Binder { ref lifetimes, s, .. } => {
3011 // Collect named lifetimes for suggestions.
3012 for name in lifetimes.keys() {
3013 if let hir::ParamName::Plain(name) = name {
3014 lifetime_names.insert(name.name);
3015 lifetime_spans.push(name.span);
3020 Scope::ObjectLifetimeDefault { ref s, .. }
3021 | Scope::Elision { ref s, .. }
3022 | Scope::TraitRefBoundary { ref s, .. } => {
3028 break Err(Some(&e[..]));
3031 Scope::Elision { elide: Elide::Forbid, .. } => break Err(None),
3033 Scope::ObjectLifetimeDefault { s, .. }
3034 | Scope::Supertrait { s, .. }
3035 | Scope::TraitRefBoundary { s, .. } => {
3041 let error = match error {
3043 self.report_elided_lifetime_in_ty(lifetime_refs);
3046 Err(error) => error,
3049 // If we specifically need the `scope_for_path` map, then we're in the
3050 // diagnostic pass and we don't want to emit more errors.
3051 if self.map.scope_for_path.is_some() {
3052 self.tcx.sess.delay_span_bug(
3053 rustc_span::DUMMY_SP,
3054 "Encountered unexpected errors during diagnostics related part",
3059 let mut spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
3061 let mut spans_dedup = spans.clone();
3062 spans_dedup.dedup();
3063 let spans_with_counts: Vec<_> = spans_dedup
3065 .map(|sp| (sp, spans.iter().filter(|nsp| *nsp == &sp).count()))
3068 let mut err = self.report_missing_lifetime_specifiers(spans.clone(), lifetime_refs.len());
3070 if let Some(params) = error {
3071 // If there's no lifetime available, suggest `'static`.
3072 if self.report_elision_failure(&mut err, params) && lifetime_names.is_empty() {
3073 lifetime_names.insert(kw::StaticLifetime);
3077 self.add_missing_lifetime_specifiers_label(
3082 error.unwrap_or(&[]),
3087 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
3088 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
3089 let mut late_depth = 0;
3090 let mut scope = self.scope;
3091 let lifetime = loop {
3093 Scope::Binder { s, scope_type, .. } => {
3095 BinderScopeType::Normal => late_depth += 1,
3096 BinderScopeType::Concatenating => {}
3101 Scope::Root | Scope::Elision { .. } => break Region::Static,
3103 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
3105 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
3107 Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { s, .. } => {
3112 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
3115 fn check_lifetime_params(
3117 old_scope: ScopeRef<'_>,
3118 params: &'tcx [hir::GenericParam<'tcx>],
3120 let lifetimes: Vec<_> = params
3122 .filter_map(|param| match param.kind {
3123 GenericParamKind::Lifetime { .. } => {
3124 Some((param, param.name.normalize_to_macros_2_0()))
3129 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
3130 if let hir::ParamName::Plain(_) = lifetime_i_name {
3131 let name = lifetime_i_name.ident().name;
3132 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
3133 let mut err = struct_span_err!(
3137 "invalid lifetime parameter name: `{}`",
3138 lifetime_i.name.ident(),
3142 format!("{} is a reserved lifetime name", name),
3148 // It is a hard error to shadow a lifetime within the same scope.
3149 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
3150 if lifetime_i_name == lifetime_j_name {
3155 "lifetime name `{}` declared twice in the same scope",
3156 lifetime_j.name.ident()
3158 .span_label(lifetime_j.span, "declared twice")
3159 .span_label(lifetime_i.span, "previous declaration here")
3164 // It is a soft error to shadow a lifetime within a parent scope.
3165 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
3167 for bound in lifetime_i.bounds {
3169 hir::GenericBound::Outlives(ref lt) => match lt.name {
3170 hir::LifetimeName::Underscore => {
3171 self.tcx.sess.delay_span_bug(
3173 "use of `'_` in illegal place, but not caught by lowering",
3176 hir::LifetimeName::Static => {
3177 self.insert_lifetime(lt, Region::Static);
3181 lifetime_i.span.to(lt.span),
3183 "unnecessary lifetime parameter `{}`",
3184 lifetime_i.name.ident(),
3188 "you can use the `'static` lifetime directly, in place of `{}`",
3189 lifetime_i.name.ident(),
3193 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit(_) => {
3194 self.resolve_lifetime_ref(lt);
3196 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
3197 self.tcx.sess.delay_span_bug(
3199 "lowering generated `ImplicitObjectLifetimeDefault` \
3200 outside of an object type",
3203 hir::LifetimeName::Error => {
3204 // No need to do anything, error already reported.
3213 fn check_lifetime_param_for_shadowing(
3215 mut old_scope: ScopeRef<'_>,
3216 param: &'tcx hir::GenericParam<'tcx>,
3218 for label in &self.labels_in_fn {
3219 // FIXME (#24278): non-hygienic comparison
3220 if param.name.ident().name == label.name {
3221 signal_shadowing_problem(
3224 original_label(label.span),
3225 shadower_lifetime(¶m),
3233 Scope::Body { s, .. }
3234 | Scope::Elision { s, .. }
3235 | Scope::ObjectLifetimeDefault { s, .. }
3236 | Scope::Supertrait { s, .. }
3237 | Scope::TraitRefBoundary { s, .. } => {
3245 Scope::Binder { ref lifetimes, s, .. } => {
3246 if let Some(&def) = lifetimes.get(¶m.name.normalize_to_macros_2_0()) {
3247 signal_shadowing_problem(
3249 param.name.ident().name,
3250 original_lifetime(self.tcx.def_span(def.id().unwrap())),
3251 shadower_lifetime(¶m),
3262 /// Returns `true` if, in the current scope, replacing `'_` would be
3263 /// equivalent to a single-use lifetime.
3264 fn track_lifetime_uses(&self) -> bool {
3265 let mut scope = self.scope;
3268 Scope::Root => break false,
3270 // Inside of items, it depends on the kind of item.
3271 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
3273 // Inside a body, `'_` will use an inference variable,
3275 Scope::Body { .. } => break true,
3277 // A lifetime only used in a fn argument could as well
3278 // be replaced with `'_`, as that would generate a
3280 Scope::Elision { elide: Elide::FreshLateAnon(..), .. } => break true,
3282 // In the return type or other such place, `'_` is not
3283 // going to make a fresh name, so we cannot
3284 // necessarily replace a single-use lifetime with
3287 elide: Elide::Exact(_) | Elide::Error(_) | Elide::Forbid, ..
3290 Scope::ObjectLifetimeDefault { s, .. }
3291 | Scope::Supertrait { s, .. }
3292 | Scope::TraitRefBoundary { s, .. } => scope = s,
3297 #[tracing::instrument(level = "debug", skip(self))]
3298 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
3300 node = ?self.tcx.hir().node_to_string(lifetime_ref.hir_id),
3301 span = ?self.tcx.sess.source_map().span_to_diagnostic_string(lifetime_ref.span)
3303 self.map.defs.insert(lifetime_ref.hir_id, def);
3306 Region::LateBoundAnon(..) | Region::Static => {
3307 // These are anonymous lifetimes or lifetimes that are not declared.
3310 Region::Free(_, def_id)
3311 | Region::LateBound(_, _, def_id)
3312 | Region::EarlyBound(_, def_id) => {
3313 // A lifetime declared by the user.
3314 let track_lifetime_uses = self.track_lifetime_uses();
3315 debug!(?track_lifetime_uses);
3316 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
3317 debug!("first use of {:?}", def_id);
3318 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
3320 debug!("many uses of {:?}", def_id);
3321 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
3327 /// Sometimes we resolve a lifetime, but later find that it is an
3328 /// error (esp. around impl trait). In that case, we remove the
3329 /// entry into `map.defs` so as not to confuse later code.
3330 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
3331 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
3332 assert_eq!(old_value, Some(bad_def));
3336 /// Detects late-bound lifetimes and inserts them into
3337 /// `map.late_bound`.
3339 /// A region declared on a fn is **late-bound** if:
3340 /// - it is constrained by an argument type;
3341 /// - it does not appear in a where-clause.
3343 /// "Constrained" basically means that it appears in any type but
3344 /// not amongst the inputs to a projection. In other words, `<&'a
3345 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
3346 #[tracing::instrument(level = "debug", skip(map))]
3347 fn insert_late_bound_lifetimes(
3348 map: &mut NamedRegionMap,
3349 decl: &hir::FnDecl<'_>,
3350 generics: &hir::Generics<'_>,
3352 let mut constrained_by_input = ConstrainedCollector::default();
3353 for arg_ty in decl.inputs {
3354 constrained_by_input.visit_ty(arg_ty);
3357 let mut appears_in_output = AllCollector::default();
3358 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
3360 debug!(?constrained_by_input.regions);
3362 // Walk the lifetimes that appear in where clauses.
3364 // Subtle point: because we disallow nested bindings, we can just
3365 // ignore binders here and scrape up all names we see.
3366 let mut appears_in_where_clause = AllCollector::default();
3367 appears_in_where_clause.visit_generics(generics);
3369 for param in generics.params {
3370 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
3371 if !param.bounds.is_empty() {
3372 // `'a: 'b` means both `'a` and `'b` are referenced
3373 appears_in_where_clause
3375 .insert(hir::LifetimeName::Param(param.name.normalize_to_macros_2_0()));
3380 debug!(?appears_in_where_clause.regions);
3382 // Late bound regions are those that:
3383 // - appear in the inputs
3384 // - do not appear in the where-clauses
3385 // - are not implicitly captured by `impl Trait`
3386 for param in generics.params {
3388 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
3390 // Neither types nor consts are late-bound.
3391 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
3394 let lt_name = hir::LifetimeName::Param(param.name.normalize_to_macros_2_0());
3395 // appears in the where clauses? early-bound.
3396 if appears_in_where_clause.regions.contains(<_name) {
3400 // does not appear in the inputs, but appears in the return type? early-bound.
3401 if !constrained_by_input.regions.contains(<_name)
3402 && appears_in_output.regions.contains(<_name)
3407 debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.hir_id);
3409 let inserted = map.late_bound.insert(param.hir_id);
3410 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
3416 struct ConstrainedCollector {
3417 regions: FxHashSet<hir::LifetimeName>,
3420 impl<'v> Visitor<'v> for ConstrainedCollector {
3421 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
3424 hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
3426 // ignore lifetimes appearing in associated type
3427 // projections, as they are not *constrained*
3431 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
3432 // consider only the lifetimes on the final
3433 // segment; I am not sure it's even currently
3434 // valid to have them elsewhere, but even if it
3435 // is, those would be potentially inputs to
3437 if let Some(last_segment) = path.segments.last() {
3438 self.visit_path_segment(path.span, last_segment);
3443 intravisit::walk_ty(self, ty);
3448 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
3449 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());
3454 struct AllCollector {
3455 regions: FxHashSet<hir::LifetimeName>,
3458 impl<'v> Visitor<'v> for AllCollector {
3459 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
3460 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());