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, DiagnosticBuilder};
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, NestedVisitorMap, Visitor};
18 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
19 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind};
20 use rustc_middle::hir::map::Map;
21 use rustc_middle::middle::resolve_lifetime::*;
22 use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
23 use rustc_middle::{bug, span_bug};
24 use rustc_session::lint;
25 use rustc_span::def_id::DefId;
26 use rustc_span::symbol::{kw, sym, Ident, Symbol};
33 use tracing::{debug, span, Level};
35 // This counts the no of times a lifetime is used
36 #[derive(Clone, Copy, Debug)]
37 pub enum LifetimeUseSet<'tcx> {
38 One(&'tcx hir::Lifetime),
43 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
45 fn late(index: u32, hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
47 fn late_anon(named_late_bound_vars: u32, index: &Cell<u32>) -> Region;
49 fn id(&self) -> Option<DefId>;
51 fn shifted(self, amount: u32) -> Region;
53 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
55 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
57 L: Iterator<Item = &'a hir::Lifetime>;
60 impl RegionExt for Region {
61 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
64 let def_id = hir_map.local_def_id(param.hir_id);
65 let origin = LifetimeDefOrigin::from_param(param);
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(), origin))
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);
73 let origin = LifetimeDefOrigin::from_param(param);
75 "Region::late: idx={:?}, param={:?} depth={:?} def_id={:?} origin={:?}",
76 idx, param, depth, def_id, origin,
79 param.name.normalize_to_macros_2_0(),
80 Region::LateBound(depth, idx, def_id.to_def_id(), origin),
84 fn late_anon(named_late_bound_vars: u32, index: &Cell<u32>) -> Region {
87 let depth = ty::INNERMOST;
88 Region::LateBoundAnon(depth, named_late_bound_vars + i, i)
91 fn id(&self) -> Option<DefId> {
93 Region::Static | Region::LateBoundAnon(..) => None,
95 Region::EarlyBound(_, id, _) | Region::LateBound(_, _, id, _) | Region::Free(_, id) => {
101 fn shifted(self, amount: u32) -> Region {
103 Region::LateBound(debruijn, idx, id, origin) => {
104 Region::LateBound(debruijn.shifted_in(amount), idx, id, origin)
106 Region::LateBoundAnon(debruijn, index, anon_index) => {
107 Region::LateBoundAnon(debruijn.shifted_in(amount), index, anon_index)
113 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
115 Region::LateBound(debruijn, index, id, origin) => {
116 Region::LateBound(debruijn.shifted_out_to_binder(binder), index, id, origin)
118 Region::LateBoundAnon(debruijn, index, anon_index) => {
119 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index, anon_index)
125 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
127 L: Iterator<Item = &'a hir::Lifetime>,
129 if let Region::EarlyBound(index, _, _) = self {
130 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
137 /// Maps the id of each lifetime reference to the lifetime decl
138 /// that it corresponds to.
140 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
141 /// actual use. It has the same data, but indexed by `LocalDefId`. This
143 #[derive(Debug, Default)]
144 struct NamedRegionMap {
145 // maps from every use of a named (not anonymous) lifetime to a
146 // `Region` describing how that region is bound
147 defs: HirIdMap<Region>,
149 // the set of lifetime def ids that are late-bound; a region can
150 // be late-bound if (a) it does NOT appear in a where-clause and
151 // (b) it DOES appear in the arguments.
152 late_bound: HirIdSet,
154 // Maps relevant hir items to the bound vars on them. These include:
156 // - function pointers
159 // - bound types (like `T` in `for<'a> T<'a>: Foo`)
160 late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
162 // maps `PathSegment` `HirId`s to lifetime scopes.
163 scope_for_path: Option<FxHashMap<LocalDefId, FxHashMap<ItemLocalId, LifetimeScopeForPath>>>,
166 crate struct LifetimeContext<'a, 'tcx> {
167 crate tcx: TyCtxt<'tcx>,
168 map: &'a mut NamedRegionMap,
171 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
172 is_in_fn_syntax: bool,
174 is_in_const_generic: bool,
176 /// Indicates that we only care about the definition of a trait. This should
177 /// be false if the `Item` we are resolving lifetimes for is not a trait or
178 /// we eventually need lifetimes resolve for trait items.
179 trait_definition_only: bool,
181 /// List of labels in the function/method currently under analysis.
182 labels_in_fn: Vec<Ident>,
184 /// Cache for cross-crate per-definition object lifetime defaults.
185 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
187 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
189 /// When encountering an undefined named lifetime, we will suggest introducing it in these
191 crate missing_named_lifetime_spots: Vec<MissingLifetimeSpot<'tcx>>,
196 /// Declares lifetimes, and each can be early-bound or late-bound.
197 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
198 /// it should be shifted by the number of `Binder`s in between the
199 /// declaration `Binder` and the location it's referenced from.
201 /// We use an IndexMap here because we want these lifetimes in order
203 lifetimes: FxIndexMap<hir::ParamName, Region>,
205 /// if we extend this scope with another scope, what is the next index
206 /// we should use for an early-bound region?
207 next_early_index: u32,
209 /// Flag is set to true if, in this binder, `'_` would be
210 /// equivalent to a "single-use region". This is true on
211 /// impls, but not other kinds of items.
212 track_lifetime_uses: bool,
214 /// Whether or not this binder would serve as the parent
215 /// binder for opaque types introduced within. For example:
218 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
221 /// Here, the opaque types we create for the `impl Trait`
222 /// and `impl Trait2` references will both have the `foo` item
223 /// as their parent. When we get to `impl Trait2`, we find
224 /// that it is nested within the `for<>` binder -- this flag
225 /// allows us to skip that when looking for the parent binder
226 /// of the resulting opaque type.
227 opaque_type_parent: bool,
229 scope_type: BinderScopeType,
231 /// The late bound vars for a given item are stored by `HirId` to be
232 /// queried later. However, if we enter an elision scope, we have to
233 /// later append the elided bound vars to the list and need to know what
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 concanetate 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 `associcated_type_bounds` feature). The binders of
286 /// the innner 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 {
311 .debug_struct("Binder")
312 .field("lifetimes", lifetimes)
313 .field("next_early_index", next_early_index)
314 .field("track_lifetime_uses", track_lifetime_uses)
315 .field("opaque_type_parent", opaque_type_parent)
316 .field("scope_type", scope_type)
317 .field("hir_id", hir_id)
320 Scope::Body { id, s: _ } => {
321 f.debug_struct("Body").field("id", id).field("s", &"..").finish()
323 Scope::Elision { elide, s: _ } => {
324 f.debug_struct("Elision").field("elide", elide).field("s", &"..").finish()
326 Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
327 .debug_struct("ObjectLifetimeDefault")
328 .field("lifetime", lifetime)
331 Scope::Supertrait { lifetimes, s: _ } => f
332 .debug_struct("Supertrait")
333 .field("lifetimes", lifetimes)
336 Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
337 Scope::Root => f.debug_struct("Root").finish(),
342 #[derive(Clone, Debug)]
344 /// Use a fresh anonymous late-bound lifetime each time, by
345 /// incrementing the counter to generate sequential indices. All
346 /// anonymous lifetimes must start *after* named bound vars.
347 FreshLateAnon(u32, Cell<u32>),
348 /// Always use this one lifetime.
350 /// Less or more than one lifetime were found, error on unspecified.
351 Error(Vec<ElisionFailureInfo>),
352 /// Forbid lifetime elision inside of a larger scope where it would be
353 /// permitted. For example, in let position impl trait.
357 #[derive(Clone, Debug)]
358 crate struct ElisionFailureInfo {
359 /// Where we can find the argument pattern.
360 crate parent: Option<hir::BodyId>,
361 /// The index of the argument in the original definition.
363 crate lifetime_count: usize,
364 crate have_bound_regions: bool,
368 type ScopeRef<'a> = &'a Scope<'a>;
370 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
372 pub fn provide(providers: &mut ty::query::Providers) {
373 *providers = ty::query::Providers {
374 resolve_lifetimes_trait_definition,
377 named_region_map: |tcx, id| resolve_lifetimes_for(tcx, id).defs.get(&id),
379 object_lifetime_defaults_map: |tcx, id| {
380 let hir_id = tcx.hir().local_def_id_to_hir_id(id);
381 match tcx.hir().find(hir_id) {
382 Some(Node::Item(item)) => compute_object_lifetime_defaults(tcx, item),
386 late_bound_vars_map: |tcx, id| resolve_lifetimes_for(tcx, id).late_bound_vars.get(&id),
387 lifetime_scope_map: |tcx, id| {
388 let item_id = item_for(tcx, id);
389 do_resolve(tcx, item_id, false, true).scope_for_path.unwrap().remove(&id)
396 /// Like `resolve_lifetimes`, but does not resolve lifetimes for trait items.
397 /// Also does not generate any diagnostics.
399 /// This is ultimately a subset of the `resolve_lifetimes` work. It effectively
400 /// resolves lifetimes only within the trait "header" -- that is, the trait
401 /// and supertrait list. In contrast, `resolve_lifetimes` resolves all the
402 /// lifetimes within the trait and its items. There is room to refactor this,
403 /// for example to resolve lifetimes for each trait item in separate queries,
404 /// but it's convenient to do the entire trait at once because the lifetimes
405 /// from the trait definition are in scope within the trait items as well.
407 /// The reason for this separate call is to resolve what would otherwise
408 /// be a cycle. Consider this example:
414 /// trait Sub<'b>: for<'a> Base<'a> {
415 /// type SubItem: Sub<BaseItem = &'b u32>;
419 /// When we resolve `Sub` and all its items, we also have to resolve `Sub<BaseItem = &'b u32>`.
420 /// To figure out the index of `'b`, we have to know about the supertraits
421 /// of `Sub` so that we can determine that the `for<'a>` will be in scope.
422 /// (This is because we -- currently at least -- flatten all the late-bound
423 /// lifetimes into a single binder.) This requires us to resolve the
424 /// *trait definition* of `Sub`; basically just enough lifetime information
425 /// to look at the supertraits.
426 #[tracing::instrument(level = "debug", skip(tcx))]
427 fn resolve_lifetimes_trait_definition(
429 local_def_id: LocalDefId,
430 ) -> ResolveLifetimes {
431 convert_named_region_map(do_resolve(tcx, local_def_id, true, false))
434 /// Computes the `ResolveLifetimes` map that contains data for an entire `Item`.
435 /// You should not read the result of this query directly, but rather use
436 /// `named_region_map`, `is_late_bound_map`, etc.
437 #[tracing::instrument(level = "debug", skip(tcx))]
438 fn resolve_lifetimes(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> ResolveLifetimes {
439 convert_named_region_map(do_resolve(tcx, local_def_id, false, false))
444 local_def_id: LocalDefId,
445 trait_definition_only: bool,
446 with_scope_for_path: bool,
447 ) -> NamedRegionMap {
448 let item = tcx.hir().expect_item(local_def_id);
449 let mut named_region_map = NamedRegionMap {
450 defs: Default::default(),
451 late_bound: Default::default(),
452 late_bound_vars: Default::default(),
453 scope_for_path: with_scope_for_path.then(|| Default::default()),
455 let mut visitor = LifetimeContext {
457 map: &mut named_region_map,
459 is_in_fn_syntax: false,
460 is_in_const_generic: false,
461 trait_definition_only,
462 labels_in_fn: vec![],
463 xcrate_object_lifetime_defaults: Default::default(),
464 lifetime_uses: &mut Default::default(),
465 missing_named_lifetime_spots: vec![],
467 visitor.visit_item(item);
472 fn convert_named_region_map(named_region_map: NamedRegionMap) -> ResolveLifetimes {
473 let mut rl = ResolveLifetimes::default();
475 for (hir_id, v) in named_region_map.defs {
476 let map = rl.defs.entry(hir_id.owner).or_default();
477 map.insert(hir_id.local_id, v);
479 for hir_id in named_region_map.late_bound {
480 let map = rl.late_bound.entry(hir_id.owner).or_default();
481 map.insert(hir_id.local_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 let hir_id = tcx.hir().local_def_id_to_hir_id(local_def_id);
518 match tcx.hir().find(hir_id) {
519 Some(Node::Item(item)) => {
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<ItemLocalId>)> {
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.to_string()),
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 Map = Map<'tcx>;
659 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
660 NestedVisitorMap::All(self.tcx.hir())
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.as_str(),
693 intravisit::FnKind::Method(id, _, _) => id.as_str(),
694 intravisit::FnKind::Closure => Symbol::intern("closure").as_str(),
696 let name: &str = &name;
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,
715 self.with(scope, move |_old_scope, this| {
716 intravisit::walk_fn(this, fk, fd, b, s, hir_id)
722 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
724 hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
725 if let Some(of_trait) = of_trait {
726 self.map.late_bound_vars.insert(of_trait.hir_ref_id, Vec::default());
732 hir::ItemKind::Fn(ref sig, ref generics, _) => {
733 self.missing_named_lifetime_spots.push(generics.into());
734 self.visit_early_late(None, item.hir_id(), &sig.decl, generics, |this| {
735 intravisit::walk_item(this, item);
737 self.missing_named_lifetime_spots.pop();
740 hir::ItemKind::ExternCrate(_)
741 | hir::ItemKind::Use(..)
742 | hir::ItemKind::Macro(..)
743 | hir::ItemKind::Mod(..)
744 | hir::ItemKind::ForeignMod { .. }
745 | hir::ItemKind::GlobalAsm(..) => {
746 // These sorts of items have no lifetime parameters at all.
747 intravisit::walk_item(self, item);
749 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
750 // No lifetime parameters, but implied 'static.
751 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
752 self.with(scope, |_, this| intravisit::walk_item(this, item));
754 hir::ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
755 // Opaque types are visited when we visit the
756 // `TyKind::OpaqueDef`, so that they have the lifetimes from
757 // their parent opaque_ty in scope.
759 // The core idea here is that since OpaqueTys are generated with the impl Trait as
760 // their owner, we can keep going until we find the Item that owns that. We then
761 // conservatively add all resolved lifetimes. Otherwise we run into problems in
762 // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`.
763 for (_hir_id, node) in
764 self.tcx.hir().parent_iter(self.tcx.hir().local_def_id_to_hir_id(item.def_id))
767 hir::Node::Item(parent_item) => {
768 let resolved_lifetimes: &ResolveLifetimes =
769 self.tcx.resolve_lifetimes(item_for(self.tcx, parent_item.def_id));
770 // We need to add *all* deps, since opaque tys may want them from *us*
771 for (&owner, defs) in resolved_lifetimes.defs.iter() {
772 defs.iter().for_each(|(&local_id, region)| {
773 self.map.defs.insert(hir::HirId { owner, local_id }, *region);
776 for (&owner, late_bound) in resolved_lifetimes.late_bound.iter() {
777 late_bound.iter().for_each(|&local_id| {
778 self.map.late_bound.insert(hir::HirId { owner, local_id });
781 for (&owner, late_bound_vars) in
782 resolved_lifetimes.late_bound_vars.iter()
784 late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| {
785 self.map.late_bound_vars.insert(
786 hir::HirId { owner, local_id },
787 late_bound_vars.clone(),
793 hir::Node::Crate(_) => bug!("No Item about an OpaqueTy"),
798 hir::ItemKind::TyAlias(_, ref generics)
799 | hir::ItemKind::Enum(_, ref generics)
800 | hir::ItemKind::Struct(_, ref generics)
801 | hir::ItemKind::Union(_, ref generics)
802 | hir::ItemKind::Trait(_, _, ref generics, ..)
803 | hir::ItemKind::TraitAlias(ref generics, ..)
804 | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
805 self.missing_named_lifetime_spots.push(generics.into());
807 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
808 // This is not true for other kinds of items.
809 let track_lifetime_uses = matches!(item.kind, hir::ItemKind::Impl { .. });
810 // These kinds of items have only early-bound lifetime parameters.
811 let mut index = if sub_items_have_self_param(&item.kind) {
812 1 // Self comes before lifetimes
816 let mut non_lifetime_count = 0;
817 let lifetimes = generics
820 .filter_map(|param| match param.kind {
821 GenericParamKind::Lifetime { .. } => {
822 Some(Region::early(&self.tcx.hir(), &mut index, param))
824 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
825 non_lifetime_count += 1;
830 self.map.late_bound_vars.insert(item.hir_id(), vec![]);
831 let scope = Scope::Binder {
832 hir_id: item.hir_id(),
834 next_early_index: index + non_lifetime_count,
835 opaque_type_parent: true,
837 scope_type: BinderScopeType::Normal,
840 self.with(scope, |old_scope, this| {
841 this.check_lifetime_params(old_scope, &generics.params);
842 let scope = Scope::TraitRefBoundary { s: this.scope };
843 this.with(scope, |_, this| {
844 intravisit::walk_item(this, item);
847 self.missing_named_lifetime_spots.pop();
852 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
854 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
855 self.visit_early_late(None, item.hir_id(), decl, generics, |this| {
856 intravisit::walk_foreign_item(this, item);
859 hir::ForeignItemKind::Static(..) => {
860 intravisit::walk_foreign_item(self, item);
862 hir::ForeignItemKind::Type => {
863 intravisit::walk_foreign_item(self, item);
868 #[tracing::instrument(level = "debug", skip(self))]
869 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
871 hir::TyKind::BareFn(ref c) => {
872 let next_early_index = self.next_early_index();
873 let was_in_fn_syntax = self.is_in_fn_syntax;
874 self.is_in_fn_syntax = true;
875 let lifetime_span: Option<Span> =
876 c.generic_params.iter().rev().find_map(|param| match param.kind {
877 GenericParamKind::Lifetime { .. } => Some(param.span),
880 let (span, span_type) = if let Some(span) = lifetime_span {
881 (span.shrink_to_hi(), ForLifetimeSpanType::TypeTail)
883 (ty.span.shrink_to_lo(), ForLifetimeSpanType::TypeEmpty)
885 self.missing_named_lifetime_spots
886 .push(MissingLifetimeSpot::HigherRanked { span, span_type });
887 let (lifetimes, binders): (FxIndexMap<hir::ParamName, Region>, Vec<_>) = c
890 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
892 .map(|(late_bound_idx, param)| {
893 let pair = Region::late(late_bound_idx as u32, &self.tcx.hir(), param);
894 let r = late_region_as_bound_region(self.tcx, &pair.1);
898 self.map.late_bound_vars.insert(ty.hir_id, binders);
899 let scope = Scope::Binder {
904 track_lifetime_uses: true,
905 opaque_type_parent: false,
906 scope_type: BinderScopeType::Normal,
908 self.with(scope, |old_scope, this| {
909 // a bare fn has no bounds, so everything
910 // contained within is scoped within its binder.
911 this.check_lifetime_params(old_scope, &c.generic_params);
912 intravisit::walk_ty(this, ty);
914 self.missing_named_lifetime_spots.pop();
915 self.is_in_fn_syntax = was_in_fn_syntax;
917 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
918 debug!(?bounds, ?lifetime, "TraitObject");
919 let scope = Scope::TraitRefBoundary { s: self.scope };
920 self.with(scope, |_, this| {
921 for bound in bounds {
922 this.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
925 match lifetime.name {
926 LifetimeName::Implicit(_) => {
927 // For types like `dyn Foo`, we should
928 // generate a special form of elided.
929 span_bug!(ty.span, "object-lifetime-default expected, not implicit",);
931 LifetimeName::ImplicitObjectLifetimeDefault => {
932 // If the user does not write *anything*, we
933 // use the object lifetime defaulting
934 // rules. So e.g., `Box<dyn Debug>` becomes
935 // `Box<dyn Debug + 'static>`.
936 self.resolve_object_lifetime_default(lifetime)
938 LifetimeName::Underscore => {
939 // If the user writes `'_`, we use the *ordinary* elision
940 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
941 // resolved the same as the `'_` in `&'_ Foo`.
944 self.resolve_elided_lifetimes(&[lifetime])
946 LifetimeName::Param(_) | LifetimeName::Static => {
947 // If the user wrote an explicit name, use that.
948 self.visit_lifetime(lifetime);
950 LifetimeName::Error => {}
953 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
954 self.visit_lifetime(lifetime_ref);
955 let scope = Scope::ObjectLifetimeDefault {
956 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
959 self.with(scope, |_, this| this.visit_ty(&mt.ty));
961 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
962 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
963 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
964 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
965 // ^ ^ this gets resolved in the scope of
966 // the opaque_ty generics
967 let opaque_ty = self.tcx.hir().item(item_id);
968 let (generics, bounds) = match opaque_ty.kind {
969 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
970 // This arm is for `impl Trait` in the types of statics, constants and locals.
971 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
972 origin: hir::OpaqueTyOrigin::TyAlias,
975 intravisit::walk_ty(self, ty);
977 // Elided lifetimes are not allowed in non-return
978 // position impl Trait
979 let scope = Scope::TraitRefBoundary { s: self.scope };
980 self.with(scope, |_, this| {
981 let scope = Scope::Elision { elide: Elide::Forbid, s: this.scope };
982 this.with(scope, |_, this| {
983 intravisit::walk_item(this, opaque_ty);
989 // RPIT (return position impl trait)
990 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
991 origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
995 }) => (generics, bounds),
996 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
999 // Resolve the lifetimes that are applied to the opaque type.
1000 // These are resolved in the current scope.
1001 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
1002 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
1003 // ^ ^this gets resolved in the current scope
1004 for lifetime in lifetimes {
1005 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
1006 self.visit_lifetime(lifetime);
1008 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
1009 // and ban them. Type variables instantiated inside binders aren't
1010 // well-supported at the moment, so this doesn't work.
1011 // In the future, this should be fixed and this error should be removed.
1012 let def = self.map.defs.get(&lifetime.hir_id).cloned();
1013 if let Some(Region::LateBound(_, _, def_id, _)) = def {
1014 if let Some(def_id) = def_id.as_local() {
1015 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
1016 // Ensure that the parent of the def is an item, not HRTB
1017 let parent_id = self.tcx.hir().get_parent_node(hir_id);
1018 // FIXME(cjgillot) Can this check be replaced by
1019 // `let parent_is_item = parent_id.is_owner();`?
1020 let parent_is_item =
1021 if let Some(parent_def_id) = parent_id.as_owner() {
1023 self.tcx.hir().krate().owners.get(parent_def_id),
1030 if !parent_is_item {
1031 if !self.trait_definition_only {
1036 "`impl Trait` can only capture lifetimes \
1037 bound at the fn or impl level"
1041 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
1048 // We want to start our early-bound indices at the end of the parent scope,
1049 // not including any parent `impl Trait`s.
1050 let mut index = self.next_early_index_for_opaque_type();
1053 let mut elision = None;
1054 let mut lifetimes = FxIndexMap::default();
1055 let mut non_lifetime_count = 0;
1056 for param in generics.params {
1058 GenericParamKind::Lifetime { .. } => {
1059 let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m);
1060 let Region::EarlyBound(_, def_id, _) = reg else {
1063 // We cannot predict what lifetimes are unused in opaque type.
1064 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
1065 if let hir::ParamName::Plain(Ident {
1066 name: kw::UnderscoreLifetime,
1070 // Pick the elided lifetime "definition" if one exists
1071 // and use it to make an elision scope.
1072 elision = Some(reg);
1074 lifetimes.insert(name, reg);
1077 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1078 non_lifetime_count += 1;
1082 let next_early_index = index + non_lifetime_count;
1083 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
1085 if let Some(elision_region) = elision {
1087 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
1088 self.with(scope, |_old_scope, this| {
1089 let scope = Scope::Binder {
1094 track_lifetime_uses: true,
1095 opaque_type_parent: false,
1096 scope_type: BinderScopeType::Normal,
1098 this.with(scope, |_old_scope, this| {
1099 this.visit_generics(generics);
1100 let scope = Scope::TraitRefBoundary { s: this.scope };
1101 this.with(scope, |_, this| {
1102 for bound in bounds {
1103 this.visit_param_bound(bound);
1109 let scope = Scope::Binder {
1114 track_lifetime_uses: true,
1115 opaque_type_parent: false,
1116 scope_type: BinderScopeType::Normal,
1118 self.with(scope, |_old_scope, this| {
1119 let scope = Scope::TraitRefBoundary { s: this.scope };
1120 this.with(scope, |_, this| {
1121 this.visit_generics(generics);
1122 for bound in bounds {
1123 this.visit_param_bound(bound);
1129 _ => intravisit::walk_ty(self, ty),
1133 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1134 use self::hir::TraitItemKind::*;
1135 match trait_item.kind {
1137 self.missing_named_lifetime_spots.push((&trait_item.generics).into());
1139 self.visit_early_late(
1140 Some(tcx.hir().get_parent_did(trait_item.hir_id())),
1141 trait_item.hir_id(),
1143 &trait_item.generics,
1144 |this| intravisit::walk_trait_item(this, trait_item),
1146 self.missing_named_lifetime_spots.pop();
1148 Type(bounds, ref ty) => {
1149 self.missing_named_lifetime_spots.push((&trait_item.generics).into());
1150 let generics = &trait_item.generics;
1151 let mut index = self.next_early_index();
1152 debug!("visit_ty: index = {}", index);
1153 let mut non_lifetime_count = 0;
1154 let lifetimes = generics
1157 .filter_map(|param| match param.kind {
1158 GenericParamKind::Lifetime { .. } => {
1159 Some(Region::early(&self.tcx.hir(), &mut index, param))
1161 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1162 non_lifetime_count += 1;
1167 self.map.late_bound_vars.insert(trait_item.hir_id(), vec![]);
1168 let scope = Scope::Binder {
1169 hir_id: trait_item.hir_id(),
1171 next_early_index: index + non_lifetime_count,
1173 track_lifetime_uses: true,
1174 opaque_type_parent: true,
1175 scope_type: BinderScopeType::Normal,
1177 self.with(scope, |old_scope, this| {
1178 this.check_lifetime_params(old_scope, &generics.params);
1179 let scope = Scope::TraitRefBoundary { s: this.scope };
1180 this.with(scope, |_, this| {
1181 this.visit_generics(generics);
1182 for bound in bounds {
1183 this.visit_param_bound(bound);
1185 if let Some(ty) = ty {
1190 self.missing_named_lifetime_spots.pop();
1193 // Only methods and types support generics.
1194 assert!(trait_item.generics.params.is_empty());
1195 self.missing_named_lifetime_spots.push(MissingLifetimeSpot::Static);
1196 intravisit::walk_trait_item(self, trait_item);
1197 self.missing_named_lifetime_spots.pop();
1202 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1203 use self::hir::ImplItemKind::*;
1204 match impl_item.kind {
1206 self.missing_named_lifetime_spots.push((&impl_item.generics).into());
1208 self.visit_early_late(
1209 Some(tcx.hir().get_parent_did(impl_item.hir_id())),
1212 &impl_item.generics,
1213 |this| intravisit::walk_impl_item(this, impl_item),
1215 self.missing_named_lifetime_spots.pop();
1217 TyAlias(ref ty) => {
1218 let generics = &impl_item.generics;
1219 self.missing_named_lifetime_spots.push(generics.into());
1220 let mut index = self.next_early_index();
1221 let mut non_lifetime_count = 0;
1222 debug!("visit_ty: index = {}", index);
1223 let lifetimes: FxIndexMap<hir::ParamName, Region> = generics
1226 .filter_map(|param| match param.kind {
1227 GenericParamKind::Lifetime { .. } => {
1228 Some(Region::early(&self.tcx.hir(), &mut index, param))
1230 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
1231 non_lifetime_count += 1;
1236 self.map.late_bound_vars.insert(ty.hir_id, vec![]);
1237 let scope = Scope::Binder {
1240 next_early_index: index + non_lifetime_count,
1242 track_lifetime_uses: true,
1243 opaque_type_parent: true,
1244 scope_type: BinderScopeType::Normal,
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 if !self.trait_definition_only {
1340 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
1342 let scope = Scope::TraitRefBoundary { s: self.scope };
1343 self.with(scope, |_, this| {
1344 for param in generics.params {
1346 GenericParamKind::Lifetime { .. } => {}
1347 GenericParamKind::Type { ref default, .. } => {
1348 walk_list!(this, visit_param_bound, param.bounds);
1349 if let Some(ref ty) = default {
1353 GenericParamKind::Const { ref ty, .. } => {
1354 let was_in_const_generic = this.is_in_const_generic;
1355 this.is_in_const_generic = true;
1356 walk_list!(this, visit_param_bound, param.bounds);
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,
1399 this.with(scope, |old_scope, this| {
1400 this.check_lifetime_params(old_scope, &bound_generic_params);
1401 this.visit_ty(&bounded_ty);
1402 walk_list!(this, visit_param_bound, bounds);
1405 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1410 this.visit_lifetime(lifetime);
1411 walk_list!(this, visit_param_bound, bounds);
1413 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1418 this.visit_ty(lhs_ty);
1419 this.visit_ty(rhs_ty);
1426 fn visit_param_bound(&mut self, bound: &'tcx hir::GenericBound<'tcx>) {
1428 hir::GenericBound::LangItemTrait(_, _, hir_id, _) => {
1429 // FIXME(jackh726): This is pretty weird. `LangItemTrait` doesn't go
1430 // through the regular poly trait ref code, so we don't get another
1431 // chance to introduce a binder. For now, I'm keeping the existing logic
1432 // of "if there isn't a Binder scope above us, add one", but I
1433 // imagine there's a better way to go about this.
1434 let (binders, scope_type) = self.poly_trait_ref_binder_info();
1436 self.map.late_bound_vars.insert(*hir_id, binders);
1437 let scope = Scope::Binder {
1439 lifetimes: FxIndexMap::default(),
1441 next_early_index: self.next_early_index(),
1442 track_lifetime_uses: true,
1443 opaque_type_parent: false,
1446 self.with(scope, |_, this| {
1447 intravisit::walk_param_bound(this, bound);
1450 _ => intravisit::walk_param_bound(self, bound),
1454 fn visit_poly_trait_ref(
1456 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
1457 _modifier: hir::TraitBoundModifier,
1459 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
1461 let should_pop_missing_lt = self.is_trait_ref_fn_scope(trait_ref);
1463 let next_early_index = self.next_early_index();
1464 let (mut binders, scope_type) = self.poly_trait_ref_binder_info();
1466 let initial_bound_vars = binders.len() as u32;
1467 let mut lifetimes: FxIndexMap<hir::ParamName, Region> = FxIndexMap::default();
1468 let binders_iter = trait_ref
1469 .bound_generic_params
1471 .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
1473 .map(|(late_bound_idx, param)| {
1474 let pair = Region::late(
1475 initial_bound_vars + late_bound_idx as u32,
1479 let r = late_region_as_bound_region(self.tcx, &pair.1);
1480 lifetimes.insert(pair.0, pair.1);
1483 binders.extend(binders_iter);
1486 self.map.late_bound_vars.insert(trait_ref.trait_ref.hir_ref_id, binders);
1488 // Always introduce a scope here, even if this is in a where clause and
1489 // we introduced the binders around the bounded Ty. In that case, we
1490 // just reuse the concatenation functionality also present in nested trait
1492 let scope = Scope::Binder {
1493 hir_id: trait_ref.trait_ref.hir_ref_id,
1497 track_lifetime_uses: true,
1498 opaque_type_parent: false,
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 check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1550 let lifetime_params: Vec<_> = params
1552 .filter_map(|param| match param.kind {
1553 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1557 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1558 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1560 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1565 "cannot mix in-band and explicit lifetime definitions"
1567 .span_label(*in_band_span, "in-band lifetime definition here")
1568 .span_label(*explicit_span, "explicit lifetime definition here")
1573 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: Symbol, orig: Original, shadower: Shadower) {
1574 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1575 // lifetime/lifetime shadowing is an error
1580 "{} name `{}` shadows a \
1581 {} name that is already in scope",
1582 shadower.kind.desc(),
1587 // shadowing involving a label is only a warning, due to issues with
1588 // labels and lifetimes not being macro-hygienic.
1589 tcx.sess.struct_span_warn(
1592 "{} name `{}` shadows a \
1593 {} name that is already in scope",
1594 shadower.kind.desc(),
1600 err.span_label(orig.span, "first declared here");
1601 err.span_label(shadower.span, format!("{} `{}` already in scope", orig.kind.desc(), name));
1605 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1606 // if one of the label shadows a lifetime or another label.
1607 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1608 struct GatherLabels<'a, 'tcx> {
1610 scope: ScopeRef<'a>,
1611 labels_in_fn: &'a mut Vec<Ident>,
1615 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1616 gather.visit_body(body);
1618 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1619 type Map = intravisit::ErasedMap<'v>;
1621 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1622 NestedVisitorMap::None
1625 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1626 if let Some(label) = expression_label(ex) {
1627 for prior_label in &self.labels_in_fn[..] {
1628 // FIXME (#24278): non-hygienic comparison
1629 if label.name == prior_label.name {
1630 signal_shadowing_problem(
1633 original_label(prior_label.span),
1634 shadower_label(label.span),
1639 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1641 self.labels_in_fn.push(label);
1643 intravisit::walk_expr(self, ex)
1647 fn expression_label(ex: &hir::Expr<'_>) -> Option<Ident> {
1649 hir::ExprKind::Loop(_, Some(label), ..) => Some(label.ident),
1650 hir::ExprKind::Block(_, Some(label)) => Some(label.ident),
1655 fn check_if_label_shadows_lifetime(tcx: TyCtxt<'_>, mut scope: ScopeRef<'_>, label: Ident) {
1658 Scope::Body { s, .. }
1659 | Scope::Elision { s, .. }
1660 | Scope::ObjectLifetimeDefault { s, .. }
1661 | Scope::Supertrait { s, .. }
1662 | Scope::TraitRefBoundary { s, .. } => {
1670 Scope::Binder { ref lifetimes, s, .. } => {
1671 // FIXME (#24278): non-hygienic comparison
1673 lifetimes.get(&hir::ParamName::Plain(label.normalize_to_macros_2_0()))
1676 tcx.hir().local_def_id_to_hir_id(def.id().unwrap().expect_local());
1678 signal_shadowing_problem(
1681 original_lifetime(tcx.hir().span(hir_id)),
1682 shadower_label(label.span),
1693 fn compute_object_lifetime_defaults(
1695 item: &hir::Item<'_>,
1696 ) -> Option<Vec<ObjectLifetimeDefault>> {
1698 hir::ItemKind::Struct(_, ref generics)
1699 | hir::ItemKind::Union(_, ref generics)
1700 | hir::ItemKind::Enum(_, ref generics)
1701 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1703 origin: hir::OpaqueTyOrigin::TyAlias,
1706 | hir::ItemKind::TyAlias(_, ref generics)
1707 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1708 let result = object_lifetime_defaults_for_item(tcx, generics);
1711 let attrs = tcx.hir().attrs(item.hir_id());
1712 if tcx.sess.contains_name(attrs, sym::rustc_object_lifetime_default) {
1713 let object_lifetime_default_reprs: String = result
1715 .map(|set| match *set {
1716 Set1::Empty => "BaseDefault".into(),
1717 Set1::One(Region::Static) => "'static".into(),
1718 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1721 .find_map(|param| match param.kind {
1722 GenericParamKind::Lifetime { .. } => {
1724 return Some(param.name.ident().to_string().into());
1732 Set1::One(_) => bug!(),
1733 Set1::Many => "Ambiguous".into(),
1735 .collect::<Vec<Cow<'static, str>>>()
1737 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1746 /// Scan the bounds and where-clauses on parameters to extract bounds
1747 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1748 /// for each type parameter.
1749 fn object_lifetime_defaults_for_item(
1751 generics: &hir::Generics<'_>,
1752 ) -> Vec<ObjectLifetimeDefault> {
1753 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1754 for bound in bounds {
1755 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1756 set.insert(lifetime.name.normalize_to_macros_2_0());
1764 .filter_map(|param| match param.kind {
1765 GenericParamKind::Lifetime { .. } => None,
1766 GenericParamKind::Type { .. } => {
1767 let mut set = Set1::Empty;
1769 add_bounds(&mut set, ¶m.bounds);
1771 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1772 for predicate in generics.where_clause.predicates {
1773 // Look for `type: ...` where clauses.
1774 let data = match *predicate {
1775 hir::WherePredicate::BoundPredicate(ref data) => data,
1779 // Ignore `for<'a> type: ...` as they can change what
1780 // lifetimes mean (although we could "just" handle it).
1781 if !data.bound_generic_params.is_empty() {
1785 let res = match data.bounded_ty.kind {
1786 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1790 if res == Res::Def(DefKind::TyParam, param_def_id.to_def_id()) {
1791 add_bounds(&mut set, &data.bounds);
1796 Set1::Empty => Set1::Empty,
1797 Set1::One(name) => {
1798 if name == hir::LifetimeName::Static {
1799 Set1::One(Region::Static)
1804 .filter_map(|param| match param.kind {
1805 GenericParamKind::Lifetime { .. } => Some((
1807 hir::LifetimeName::Param(param.name),
1808 LifetimeDefOrigin::from_param(param),
1813 .find(|&(_, (_, lt_name, _))| lt_name == name)
1814 .map_or(Set1::Many, |(i, (id, _, origin))| {
1815 let def_id = tcx.hir().local_def_id(id);
1816 Set1::One(Region::EarlyBound(
1824 Set1::Many => Set1::Many,
1827 GenericParamKind::Const { .. } => {
1828 // Generic consts don't impose any constraints.
1830 // We still store a dummy value here to allow generic parameters
1831 // in an arbitrary order.
1838 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1839 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1841 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1843 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1844 let labels_in_fn = take(&mut self.labels_in_fn);
1845 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1846 let missing_named_lifetime_spots = take(&mut self.missing_named_lifetime_spots);
1847 let mut this = LifetimeContext {
1851 is_in_fn_syntax: self.is_in_fn_syntax,
1852 is_in_const_generic: self.is_in_const_generic,
1853 trait_definition_only: self.trait_definition_only,
1855 xcrate_object_lifetime_defaults,
1857 missing_named_lifetime_spots,
1859 let span = tracing::debug_span!("scope", scope = ?TruncatedScopeDebug(&this.scope));
1861 let _enter = span.enter();
1862 f(self.scope, &mut this);
1863 if !self.trait_definition_only {
1864 this.check_uses_for_lifetimes_defined_by_scope();
1867 self.labels_in_fn = this.labels_in_fn;
1868 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1869 self.missing_named_lifetime_spots = this.missing_named_lifetime_spots;
1872 /// helper method to determine the span to remove when suggesting the
1873 /// deletion of a lifetime
1874 fn lifetime_deletion_span(&self, name: Ident, generics: &hir::Generics<'_>) -> Option<Span> {
1875 generics.params.iter().enumerate().find_map(|(i, param)| {
1876 if param.name.ident() == name {
1877 let in_band = matches!(
1879 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::InBand }
1883 } else if generics.params.len() == 1 {
1884 // if sole lifetime, remove the entire `<>` brackets
1887 // if removing within `<>` brackets, we also want to
1888 // delete a leading or trailing comma as appropriate
1889 if i >= generics.params.len() - 1 {
1890 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1892 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1901 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1902 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1903 fn suggest_eliding_single_use_lifetime(
1905 err: &mut DiagnosticBuilder<'_>,
1907 lifetime: &hir::Lifetime,
1909 let name = lifetime.name.ident();
1910 let remove_decl = self
1913 .and_then(|parent_def_id| self.tcx.hir().get_generics(parent_def_id))
1914 .and_then(|generics| self.lifetime_deletion_span(name, generics));
1916 let mut remove_use = None;
1917 let mut elide_use = None;
1918 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1919 for input in inputs {
1921 hir::TyKind::Rptr(lt, _) => {
1922 if lt.name.ident() == name {
1923 // include the trailing whitespace between the lifetime and type names
1924 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1929 .span_until_non_whitespace(lt_through_ty_span),
1934 hir::TyKind::Path(QPath::Resolved(_, path)) => {
1935 let last_segment = &path.segments[path.segments.len() - 1];
1936 let generics = last_segment.args();
1937 for arg in generics.args.iter() {
1938 if let GenericArg::Lifetime(lt) = arg {
1939 if lt.name.ident() == name {
1940 elide_use = Some(lt.span);
1951 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1952 if let Some(parent) =
1953 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1956 Node::Item(item) => {
1957 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1958 find_arg_use_span(sig.decl.inputs);
1961 Node::ImplItem(impl_item) => {
1962 if let hir::ImplItemKind::Fn(sig, _) = &impl_item.kind {
1963 find_arg_use_span(sig.decl.inputs);
1971 let msg = "elide the single-use lifetime";
1972 match (remove_decl, remove_use, elide_use) {
1973 (Some(decl_span), Some(use_span), None) => {
1974 // if both declaration and use deletion spans start at the same
1975 // place ("start at" because the latter includes trailing
1976 // whitespace), then this is an in-band lifetime
1977 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1978 err.span_suggestion(
1982 Applicability::MachineApplicable,
1985 err.multipart_suggestion(
1987 vec![(decl_span, String::new()), (use_span, String::new())],
1988 Applicability::MachineApplicable,
1992 (Some(decl_span), None, Some(use_span)) => {
1993 err.multipart_suggestion(
1995 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1996 Applicability::MachineApplicable,
2003 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
2004 let defined_by = match self.scope {
2005 Scope::Binder { lifetimes, .. } => lifetimes,
2007 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
2012 let mut def_ids: Vec<_> = defined_by
2014 .flat_map(|region| match region {
2015 Region::EarlyBound(_, def_id, _)
2016 | Region::LateBound(_, _, def_id, _)
2017 | Region::Free(_, def_id) => Some(*def_id),
2019 Region::LateBoundAnon(..) | Region::Static => None,
2023 // ensure that we issue lints in a repeatable order
2024 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
2026 'lifetimes: for def_id in def_ids {
2027 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
2029 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
2032 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
2036 match lifetimeuseset {
2037 Some(LifetimeUseSet::One(lifetime)) => {
2038 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2039 debug!("hir id first={:?}", hir_id);
2040 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
2041 Node::Lifetime(hir_lifetime) => Some((
2042 hir_lifetime.hir_id,
2044 hir_lifetime.name.ident(),
2046 Node::GenericParam(param) => {
2047 Some((param.hir_id, param.span, param.name.ident()))
2051 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
2052 if name.name == kw::UnderscoreLifetime {
2056 if let Some(parent_def_id) = self.tcx.parent(def_id) {
2057 if let Some(def_id) = parent_def_id.as_local() {
2058 let parent_hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
2059 // lifetimes in `derive` expansions don't count (Issue #53738)
2063 .attrs(parent_hir_id)
2065 .any(|attr| attr.has_name(sym::automatically_derived))
2070 // opaque types generated when desugaring an async function can have a single
2071 // use lifetime even if it is explicitly denied (Issue #77175)
2072 if let hir::Node::Item(hir::Item {
2073 kind: hir::ItemKind::OpaqueTy(ref opaque),
2075 }) = self.tcx.hir().get(parent_hir_id)
2077 if !matches!(opaque.origin, hir::OpaqueTyOrigin::AsyncFn(..)) {
2078 continue 'lifetimes;
2080 // We want to do this only if the liftime identifier is already defined
2081 // in the async function that generated this. Otherwise it could be
2082 // an opaque type defined by the developer and we still want this
2083 // lint to fail compilation
2084 for p in opaque.generics.params {
2085 if defined_by.contains_key(&p.name) {
2086 continue 'lifetimes;
2093 self.tcx.struct_span_lint_hir(
2094 lint::builtin::SINGLE_USE_LIFETIMES,
2098 let mut err = lint.build(&format!(
2099 "lifetime parameter `{}` only used once",
2102 if span == lifetime.span {
2103 // spans are the same for in-band lifetime declarations
2104 err.span_label(span, "this lifetime is only used here");
2106 err.span_label(span, "this lifetime...");
2107 err.span_label(lifetime.span, "...is used only here");
2109 self.suggest_eliding_single_use_lifetime(
2110 &mut err, def_id, lifetime,
2117 Some(LifetimeUseSet::Many) => {
2118 debug!("not one use lifetime");
2121 let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2122 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
2123 Node::Lifetime(hir_lifetime) => Some((
2124 hir_lifetime.hir_id,
2126 hir_lifetime.name.ident(),
2128 Node::GenericParam(param) => {
2129 Some((param.hir_id, param.span, param.name.ident()))
2133 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
2134 self.tcx.struct_span_lint_hir(
2135 lint::builtin::UNUSED_LIFETIMES,
2140 .build(&format!("lifetime parameter `{}` never used", name));
2141 if let Some(parent_def_id) = self.tcx.parent(def_id) {
2142 if let Some(generics) =
2143 self.tcx.hir().get_generics(parent_def_id)
2145 let unused_lt_span =
2146 self.lifetime_deletion_span(name, generics);
2147 if let Some(span) = unused_lt_span {
2148 err.span_suggestion(
2150 "elide the unused lifetime",
2152 Applicability::MachineApplicable,
2166 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
2168 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
2169 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
2170 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
2174 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
2176 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
2177 /// lifetimes may be interspersed together.
2179 /// If early bound lifetimes are present, we separate them into their own list (and likewise
2180 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
2181 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
2182 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
2183 /// ordering is not important there.
2184 fn visit_early_late<F>(
2186 parent_id: Option<LocalDefId>,
2188 decl: &'tcx hir::FnDecl<'tcx>,
2189 generics: &'tcx hir::Generics<'tcx>,
2192 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
2194 insert_late_bound_lifetimes(self.map, decl, generics);
2196 // Find the start of nested early scopes, e.g., in methods.
2197 let mut next_early_index = 0;
2198 if let Some(parent_id) = parent_id {
2199 let parent = self.tcx.hir().expect_item(parent_id);
2200 if sub_items_have_self_param(&parent.kind) {
2201 next_early_index += 1; // Self comes before lifetimes
2204 hir::ItemKind::Trait(_, _, ref generics, ..)
2205 | hir::ItemKind::Impl(hir::Impl { ref generics, .. }) => {
2206 next_early_index += generics.params.len() as u32;
2212 let mut non_lifetime_count = 0;
2213 let mut named_late_bound_vars = 0;
2214 let lifetimes: FxIndexMap<hir::ParamName, Region> = generics
2217 .filter_map(|param| match param.kind {
2218 GenericParamKind::Lifetime { .. } => {
2219 if self.map.late_bound.contains(¶m.hir_id) {
2220 let late_bound_idx = named_late_bound_vars;
2221 named_late_bound_vars += 1;
2222 Some(Region::late(late_bound_idx, &self.tcx.hir(), param))
2224 Some(Region::early(&self.tcx.hir(), &mut next_early_index, param))
2227 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
2228 non_lifetime_count += 1;
2233 let next_early_index = next_early_index + non_lifetime_count;
2235 let binders: Vec<_> = generics
2239 matches!(param.kind, GenericParamKind::Lifetime { .. })
2240 && self.map.late_bound.contains(¶m.hir_id)
2243 .map(|(late_bound_idx, param)| {
2244 let pair = Region::late(late_bound_idx as u32, &self.tcx.hir(), param);
2245 late_region_as_bound_region(self.tcx, &pair.1)
2248 self.map.late_bound_vars.insert(hir_id, binders);
2249 let scope = Scope::Binder {
2254 opaque_type_parent: true,
2255 track_lifetime_uses: false,
2256 scope_type: BinderScopeType::Normal,
2258 self.with(scope, move |old_scope, this| {
2259 this.check_lifetime_params(old_scope, &generics.params);
2264 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
2265 let mut scope = self.scope;
2268 Scope::Root => return 0,
2270 Scope::Binder { next_early_index, opaque_type_parent, .. }
2271 if (!only_opaque_type_parent || opaque_type_parent) =>
2273 return next_early_index;
2276 Scope::Binder { s, .. }
2277 | Scope::Body { s, .. }
2278 | Scope::Elision { s, .. }
2279 | Scope::ObjectLifetimeDefault { s, .. }
2280 | Scope::Supertrait { s, .. }
2281 | Scope::TraitRefBoundary { s, .. } => scope = s,
2286 /// Returns the next index one would use for an early-bound-region
2287 /// if extending the current scope.
2288 fn next_early_index(&self) -> u32 {
2289 self.next_early_index_helper(true)
2292 /// Returns the next index one would use for an `impl Trait` that
2293 /// is being converted into an opaque type alias `impl Trait`. This will be the
2294 /// next early index from the enclosing item, for the most
2295 /// part. See the `opaque_type_parent` field for more info.
2296 fn next_early_index_for_opaque_type(&self) -> u32 {
2297 self.next_early_index_helper(false)
2300 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2301 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
2303 // If we've already reported an error, just ignore `lifetime_ref`.
2304 if let LifetimeName::Error = lifetime_ref.name {
2308 // Walk up the scope chain, tracking the number of fn scopes
2309 // that we pass through, until we find a lifetime with the
2310 // given name or we run out of scopes.
2312 let mut late_depth = 0;
2313 let mut scope = self.scope;
2314 let mut outermost_body = None;
2317 Scope::Body { id, s } => {
2318 // Non-static lifetimes are prohibited in anonymous constants without
2319 // `generic_const_exprs`.
2320 self.maybe_emit_forbidden_non_static_lifetime_error(id, lifetime_ref);
2322 outermost_body = Some(id);
2330 Scope::Binder { ref lifetimes, scope_type, s, .. } => {
2331 match lifetime_ref.name {
2332 LifetimeName::Param(param_name) => {
2333 if let Some(&def) = lifetimes.get(¶m_name.normalize_to_macros_2_0())
2335 break Some(def.shifted(late_depth));
2338 _ => bug!("expected LifetimeName::Param"),
2341 BinderScopeType::Normal => late_depth += 1,
2342 BinderScopeType::Concatenating => {}
2347 Scope::Elision { s, .. }
2348 | Scope::ObjectLifetimeDefault { s, .. }
2349 | Scope::Supertrait { s, .. }
2350 | Scope::TraitRefBoundary { s, .. } => {
2356 if let Some(mut def) = result {
2357 if let Region::EarlyBound(..) = def {
2358 // Do not free early-bound regions, only late-bound ones.
2359 } else if let Some(body_id) = outermost_body {
2360 let fn_id = self.tcx.hir().body_owner(body_id);
2361 match self.tcx.hir().get(fn_id) {
2362 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
2363 | Node::TraitItem(&hir::TraitItem {
2364 kind: hir::TraitItemKind::Fn(..), ..
2366 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
2367 let scope = self.tcx.hir().local_def_id(fn_id);
2368 def = Region::Free(scope.to_def_id(), def.id().unwrap());
2374 // Check for fn-syntax conflicts with in-band lifetime definitions
2375 if !self.trait_definition_only && self.is_in_fn_syntax {
2377 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
2378 | Region::LateBound(_, _, _, LifetimeDefOrigin::InBand) => {
2383 "lifetimes used in `fn` or `Fn` syntax must be \
2384 explicitly declared using `<...>` binders"
2386 .span_label(lifetime_ref.span, "in-band lifetime definition")
2391 | Region::EarlyBound(
2394 LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error,
2396 | Region::LateBound(
2400 LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error,
2402 | Region::LateBoundAnon(..)
2403 | Region::Free(..) => {}
2407 self.insert_lifetime(lifetime_ref, def);
2409 self.emit_undeclared_lifetime_error(lifetime_ref);
2413 fn visit_segment_args(
2417 generic_args: &'tcx hir::GenericArgs<'tcx>,
2420 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
2421 res, depth, generic_args,
2424 if generic_args.parenthesized {
2425 let was_in_fn_syntax = self.is_in_fn_syntax;
2426 self.is_in_fn_syntax = true;
2427 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
2428 self.is_in_fn_syntax = was_in_fn_syntax;
2432 let mut elide_lifetimes = true;
2433 let lifetimes: Vec<_> = generic_args
2436 .filter_map(|arg| match arg {
2437 hir::GenericArg::Lifetime(lt) => {
2438 if !lt.is_elided() {
2439 elide_lifetimes = false;
2446 // We short-circuit here if all are elided in order to pluralize
2448 if elide_lifetimes {
2449 self.resolve_elided_lifetimes(&lifetimes);
2451 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
2454 // Figure out if this is a type/trait segment,
2455 // which requires object lifetime defaults.
2456 let parent_def_id = |this: &mut Self, def_id: DefId| {
2457 let def_key = this.tcx.def_key(def_id);
2458 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
2460 let type_def_id = match res {
2461 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
2462 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
2470 ) if depth == 0 => Some(def_id),
2474 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
2476 // Compute a vector of defaults, one for each type parameter,
2477 // per the rules given in RFCs 599 and 1156. Example:
2480 // struct Foo<'a, T: 'a, U> { }
2483 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
2484 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
2485 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
2488 // Therefore, we would compute `object_lifetime_defaults` to a
2489 // vector like `['x, 'static]`. Note that the vector only
2490 // includes type parameters.
2491 let object_lifetime_defaults = type_def_id.map_or_else(Vec::new, |def_id| {
2493 let mut scope = self.scope;
2496 Scope::Root => break false,
2498 Scope::Body { .. } => break true,
2500 Scope::Binder { s, .. }
2501 | Scope::Elision { s, .. }
2502 | Scope::ObjectLifetimeDefault { s, .. }
2503 | Scope::Supertrait { s, .. }
2504 | Scope::TraitRefBoundary { s, .. } => {
2511 let map = &self.map;
2512 let set_to_region = |set: &ObjectLifetimeDefault| match *set {
2517 Some(Region::Static)
2521 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
2522 GenericArg::Lifetime(lt) => Some(lt),
2525 r.subst(lifetimes, map)
2529 if let Some(def_id) = def_id.as_local() {
2530 let id = self.tcx.hir().local_def_id_to_hir_id(def_id);
2531 self.tcx.object_lifetime_defaults(id).unwrap().iter().map(set_to_region).collect()
2534 self.xcrate_object_lifetime_defaults
2536 .or_insert_with(|| {
2537 tcx.generics_of(def_id)
2540 .filter_map(|param| match param.kind {
2541 GenericParamDefKind::Type { object_lifetime_default, .. } => {
2542 Some(object_lifetime_default)
2544 GenericParamDefKind::Lifetime
2545 | GenericParamDefKind::Const { .. } => None,
2555 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
2558 for arg in generic_args.args {
2560 GenericArg::Lifetime(_) => {}
2561 GenericArg::Type(ty) => {
2562 if let Some(<) = object_lifetime_defaults.get(i) {
2563 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
2564 self.with(scope, |_, this| this.visit_ty(ty));
2570 GenericArg::Const(ct) => {
2571 self.visit_anon_const(&ct.value);
2573 GenericArg::Infer(inf) => {
2574 self.visit_id(inf.hir_id);
2575 if inf.kind.is_type() {
2582 // Hack: when resolving the type `XX` in binding like `dyn
2583 // Foo<'b, Item = XX>`, the current object-lifetime default
2584 // would be to examine the trait `Foo` to check whether it has
2585 // a lifetime bound declared on `Item`. e.g., if `Foo` is
2586 // declared like so, then the default object lifetime bound in
2587 // `XX` should be `'b`:
2595 // but if we just have `type Item;`, then it would be
2596 // `'static`. However, we don't get all of this logic correct.
2598 // Instead, we do something hacky: if there are no lifetime parameters
2599 // to the trait, then we simply use a default object lifetime
2600 // bound of `'static`, because there is no other possibility. On the other hand,
2601 // if there ARE lifetime parameters, then we require the user to give an
2602 // explicit bound for now.
2604 // This is intended to leave room for us to implement the
2605 // correct behavior in the future.
2606 let has_lifetime_parameter =
2607 generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
2609 // Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or
2610 // in the trait ref `YY<...>` in `Item: YY<...>`.
2611 for binding in generic_args.bindings {
2612 let scope = Scope::ObjectLifetimeDefault {
2613 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2616 if let Some(type_def_id) = type_def_id {
2617 let lifetimes = LifetimeContext::supertrait_hrtb_lifetimes(
2622 self.with(scope, |_, this| {
2623 let scope = Scope::Supertrait {
2624 lifetimes: lifetimes.unwrap_or_default(),
2627 this.with(scope, |_, this| this.visit_assoc_type_binding(binding));
2630 self.with(scope, |_, this| this.visit_assoc_type_binding(binding));
2635 /// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the
2636 /// associated type name and starting trait.
2637 /// For example, imagine we have
2639 /// trait Foo<'a, 'b> {
2642 /// trait Bar<'b>: for<'a> Foo<'a, 'b> {}
2643 /// trait Bar: for<'b> Bar<'b> {}
2645 /// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on
2646 /// the starting trait `Bar`, we would return `Some(['b, 'a])`.
2647 fn supertrait_hrtb_lifetimes(
2651 ) -> Option<Vec<ty::BoundVariableKind>> {
2652 let trait_defines_associated_type_named = |trait_def_id: DefId| {
2653 tcx.associated_items(trait_def_id)
2654 .find_by_name_and_kind(tcx, assoc_name, ty::AssocKind::Type, trait_def_id)
2658 use smallvec::{smallvec, SmallVec};
2659 let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> =
2660 smallvec![(def_id, smallvec![])];
2661 let mut visited: FxHashSet<DefId> = FxHashSet::default();
2663 let (def_id, bound_vars) = match stack.pop() {
2667 // See issue #83753. If someone writes an associated type on a non-trait, just treat it as
2668 // there being no supertrait HRTBs.
2669 match tcx.def_kind(def_id) {
2670 DefKind::Trait | DefKind::TraitAlias | DefKind::Impl => {}
2674 if trait_defines_associated_type_named(def_id) {
2675 break Some(bound_vars.into_iter().collect());
2678 tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name)));
2679 let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
2680 let bound_predicate = pred.kind();
2681 match bound_predicate.skip_binder() {
2682 ty::PredicateKind::Trait(data) => {
2683 // The order here needs to match what we would get from `subst_supertrait`
2684 let pred_bound_vars = bound_predicate.bound_vars();
2685 let mut all_bound_vars = bound_vars.clone();
2686 all_bound_vars.extend(pred_bound_vars.iter());
2687 let super_def_id = data.trait_ref.def_id;
2688 Some((super_def_id, all_bound_vars))
2694 let obligations = obligations.filter(|o| visited.insert(o.0));
2695 stack.extend(obligations);
2699 #[tracing::instrument(level = "debug", skip(self))]
2700 fn visit_fn_like_elision(
2702 inputs: &'tcx [hir::Ty<'tcx>],
2703 output: Option<&'tcx hir::Ty<'tcx>>,
2705 debug!("visit_fn_like_elision: enter");
2706 let mut scope = &*self.scope;
2709 Scope::Binder { hir_id, .. } => {
2712 Scope::ObjectLifetimeDefault { ref s, .. }
2713 | Scope::Elision { ref s, .. }
2714 | Scope::Supertrait { ref s, .. }
2715 | Scope::TraitRefBoundary { ref s, .. } => {
2718 Scope::Root | Scope::Body { .. } => {
2719 // See issues #83907 and #83693. Just bail out from looking inside.
2720 self.tcx.sess.delay_span_bug(
2721 rustc_span::DUMMY_SP,
2722 "In fn_like_elision without appropriate scope above",
2728 // While not strictly necessary, we gather anon lifetimes *before* actually
2729 // visiting the argument types.
2730 let mut gather = GatherAnonLifetimes { anon_count: 0 };
2731 for input in inputs {
2732 gather.visit_ty(input);
2734 trace!(?gather.anon_count);
2735 let late_bound_vars = self.map.late_bound_vars.entry(hir_id).or_default();
2736 let named_late_bound_vars = late_bound_vars.len() as u32;
2737 late_bound_vars.extend(
2738 (0..gather.anon_count).map(|var| ty::BoundVariableKind::Region(ty::BrAnon(var))),
2740 let arg_scope = Scope::Elision {
2741 elide: Elide::FreshLateAnon(named_late_bound_vars, Cell::new(0)),
2744 self.with(arg_scope, |_, this| {
2745 for input in inputs {
2746 this.visit_ty(input);
2750 let output = match output {
2755 debug!("determine output");
2757 // Figure out if there's a body we can get argument names from,
2758 // and whether there's a `self` argument (treated specially).
2759 let mut assoc_item_kind = None;
2760 let mut impl_self = None;
2761 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2762 let body = match self.tcx.hir().get(parent) {
2763 // `fn` definitions and methods.
2764 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2766 Node::TraitItem(&hir::TraitItem { kind: hir::TraitItemKind::Fn(_, ref m), .. }) => {
2767 if let hir::ItemKind::Trait(.., ref trait_items) =
2768 self.tcx.hir().expect_item(self.tcx.hir().get_parent_did(parent)).kind
2771 trait_items.iter().find(|ti| ti.id.hir_id() == parent).map(|ti| ti.kind);
2774 hir::TraitFn::Required(_) => None,
2775 hir::TraitFn::Provided(body) => Some(body),
2779 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body), .. }) => {
2780 if let hir::ItemKind::Impl(hir::Impl { ref self_ty, ref items, .. }) =
2781 self.tcx.hir().expect_item(self.tcx.hir().get_parent_did(parent)).kind
2783 impl_self = Some(self_ty);
2785 items.iter().find(|ii| ii.id.hir_id() == parent).map(|ii| ii.kind);
2790 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2791 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2792 // Everything else (only closures?) doesn't
2793 // actually enjoy elision in return types.
2795 self.visit_ty(output);
2800 let has_self = match assoc_item_kind {
2801 Some(hir::AssocItemKind::Fn { has_self }) => has_self,
2805 // In accordance with the rules for lifetime elision, we can determine
2806 // what region to use for elision in the output type in two ways.
2807 // First (determined here), if `self` is by-reference, then the
2808 // implied output region is the region of the self parameter.
2810 struct SelfVisitor<'a> {
2811 map: &'a NamedRegionMap,
2812 impl_self: Option<&'a hir::TyKind<'a>>,
2813 lifetime: Set1<Region>,
2816 impl SelfVisitor<'_> {
2817 // Look for `self: &'a Self` - also desugared from `&'a self`,
2818 // and if that matches, use it for elision and return early.
2819 fn is_self_ty(&self, res: Res) -> bool {
2820 if let Res::SelfTy(..) = res {
2824 // Can't always rely on literal (or implied) `Self` due
2825 // to the way elision rules were originally specified.
2826 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2830 // Permit the types that unambiguously always
2831 // result in the same type constructor being used
2832 // (it can't differ between `Self` and `self`).
2833 Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _)
2834 | Res::PrimTy(_) => return res == path.res,
2843 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2844 type Map = intravisit::ErasedMap<'a>;
2846 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2847 NestedVisitorMap::None
2850 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2851 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2852 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2854 if self.is_self_ty(path.res) {
2855 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2856 self.lifetime.insert(*lifetime);
2861 intravisit::walk_ty(self, ty)
2865 let mut visitor = SelfVisitor {
2867 impl_self: impl_self.map(|ty| &ty.kind),
2868 lifetime: Set1::Empty,
2870 visitor.visit_ty(&inputs[0]);
2871 if let Set1::One(lifetime) = visitor.lifetime {
2872 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2873 self.with(scope, |_, this| this.visit_ty(output));
2878 // Second, if there was exactly one lifetime (either a substitution or a
2879 // reference) in the arguments, then any anonymous regions in the output
2880 // have that lifetime.
2881 let mut possible_implied_output_region = None;
2882 let mut lifetime_count = 0;
2883 let arg_lifetimes = inputs
2886 .skip(has_self as usize)
2888 let mut gather = GatherLifetimes {
2890 outer_index: ty::INNERMOST,
2891 have_bound_regions: false,
2892 lifetimes: Default::default(),
2894 gather.visit_ty(input);
2896 lifetime_count += gather.lifetimes.len();
2898 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2899 // there's a chance that the unique lifetime of this
2900 // iteration will be the appropriate lifetime for output
2901 // parameters, so lets store it.
2902 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2905 ElisionFailureInfo {
2908 lifetime_count: gather.lifetimes.len(),
2909 have_bound_regions: gather.have_bound_regions,
2915 let elide = if lifetime_count == 1 {
2916 Elide::Exact(possible_implied_output_region.unwrap())
2918 Elide::Error(arg_lifetimes)
2923 let scope = Scope::Elision { elide, s: self.scope };
2924 self.with(scope, |_, this| this.visit_ty(output));
2926 struct GatherLifetimes<'a> {
2927 map: &'a NamedRegionMap,
2928 outer_index: ty::DebruijnIndex,
2929 have_bound_regions: bool,
2930 lifetimes: FxHashSet<Region>,
2933 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2934 type Map = intravisit::ErasedMap<'v>;
2936 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2937 NestedVisitorMap::None
2940 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2941 if let hir::TyKind::BareFn(_) = ty.kind {
2942 self.outer_index.shift_in(1);
2945 hir::TyKind::TraitObject(bounds, ref lifetime, _) => {
2946 for bound in bounds {
2947 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2950 // Stay on the safe side and don't include the object
2951 // lifetime default (which may not end up being used).
2952 if !lifetime.is_elided() {
2953 self.visit_lifetime(lifetime);
2957 intravisit::walk_ty(self, ty);
2960 if let hir::TyKind::BareFn(_) = ty.kind {
2961 self.outer_index.shift_out(1);
2965 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2966 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2967 // FIXME(eddyb) Do we want this? It only makes a difference
2968 // if this `for<'a>` lifetime parameter is never used.
2969 self.have_bound_regions = true;
2972 intravisit::walk_generic_param(self, param);
2975 fn visit_poly_trait_ref(
2977 trait_ref: &hir::PolyTraitRef<'_>,
2978 modifier: hir::TraitBoundModifier,
2980 self.outer_index.shift_in(1);
2981 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2982 self.outer_index.shift_out(1);
2985 fn visit_param_bound(&mut self, bound: &hir::GenericBound<'_>) {
2986 if let hir::GenericBound::LangItemTrait { .. } = bound {
2987 self.outer_index.shift_in(1);
2988 intravisit::walk_param_bound(self, bound);
2989 self.outer_index.shift_out(1);
2991 intravisit::walk_param_bound(self, bound);
2995 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2996 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2998 Region::LateBound(debruijn, _, _, _)
2999 | Region::LateBoundAnon(debruijn, _, _)
3000 if debruijn < self.outer_index =>
3002 self.have_bound_regions = true;
3005 // FIXME(jackh726): nested trait refs?
3006 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
3013 struct GatherAnonLifetimes {
3016 impl<'v> Visitor<'v> for GatherAnonLifetimes {
3017 type Map = intravisit::ErasedMap<'v>;
3019 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3020 NestedVisitorMap::None
3023 #[instrument(skip(self), level = "trace")]
3024 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
3025 // If we enter a `BareFn`, then we enter a *new* binding scope
3026 if let hir::TyKind::BareFn(_) = ty.kind {
3029 intravisit::walk_ty(self, ty);
3032 fn visit_generic_args(
3035 generic_args: &'v hir::GenericArgs<'v>,
3037 // parenthesized args enter a new elison scope
3038 if generic_args.parenthesized {
3041 intravisit::walk_generic_args(self, path_span, generic_args)
3044 #[instrument(skip(self), level = "trace")]
3045 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
3046 if lifetime_ref.is_elided() {
3047 self.anon_count += 1;
3053 fn resolve_elided_lifetimes(&mut self, lifetime_refs: &[&'tcx hir::Lifetime]) {
3054 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
3056 if lifetime_refs.is_empty() {
3060 let mut late_depth = 0;
3061 let mut scope = self.scope;
3062 let mut lifetime_names = FxHashSet::default();
3063 let mut lifetime_spans = vec![];
3066 // Do not assign any resolution, it will be inferred.
3067 Scope::Body { .. } => break Ok(()),
3069 Scope::Root => break Err(None),
3071 Scope::Binder { s, ref lifetimes, scope_type, .. } => {
3072 // collect named lifetimes for suggestions
3073 for name in lifetimes.keys() {
3074 if let hir::ParamName::Plain(name) = name {
3075 lifetime_names.insert(name.name);
3076 lifetime_spans.push(name.span);
3080 BinderScopeType::Normal => late_depth += 1,
3081 BinderScopeType::Concatenating => {}
3087 elide: Elide::FreshLateAnon(named_late_bound_vars, ref counter),
3090 for lifetime_ref in lifetime_refs {
3092 Region::late_anon(named_late_bound_vars, counter).shifted(late_depth);
3094 self.insert_lifetime(lifetime_ref, lifetime);
3099 Scope::Elision { elide: Elide::Exact(l), .. } => {
3100 let lifetime = l.shifted(late_depth);
3101 for lifetime_ref in lifetime_refs {
3102 self.insert_lifetime(lifetime_ref, lifetime);
3107 Scope::Elision { elide: Elide::Error(ref e), ref s, .. } => {
3111 Scope::Binder { ref lifetimes, s, .. } => {
3112 // Collect named lifetimes for suggestions.
3113 for name in lifetimes.keys() {
3114 if let hir::ParamName::Plain(name) = name {
3115 lifetime_names.insert(name.name);
3116 lifetime_spans.push(name.span);
3121 Scope::ObjectLifetimeDefault { ref s, .. }
3122 | Scope::Elision { ref s, .. }
3123 | Scope::TraitRefBoundary { ref s, .. } => {
3129 break Err(Some(&e[..]));
3132 Scope::Elision { elide: Elide::Forbid, .. } => break Err(None),
3134 Scope::ObjectLifetimeDefault { s, .. }
3135 | Scope::Supertrait { s, .. }
3136 | Scope::TraitRefBoundary { s, .. } => {
3142 let error = match error {
3144 self.report_elided_lifetime_in_ty(lifetime_refs);
3147 Err(error) => error,
3150 // If we specifically need the `scope_for_path` map, then we're in the
3151 // diagnostic pass and we don't want to emit more errors.
3152 if self.map.scope_for_path.is_some() {
3153 self.tcx.sess.delay_span_bug(
3154 rustc_span::DUMMY_SP,
3155 "Encountered unexpected errors during diagnostics related part",
3160 let mut spans: Vec<_> = lifetime_refs.iter().map(|lt| lt.span).collect();
3162 let mut spans_dedup = spans.clone();
3163 spans_dedup.dedup();
3164 let spans_with_counts: Vec<_> = spans_dedup
3166 .map(|sp| (sp, spans.iter().filter(|nsp| *nsp == &sp).count()))
3169 let mut err = self.report_missing_lifetime_specifiers(spans.clone(), lifetime_refs.len());
3171 if let Some(params) = error {
3172 // If there's no lifetime available, suggest `'static`.
3173 if self.report_elision_failure(&mut err, params) && lifetime_names.is_empty() {
3174 lifetime_names.insert(kw::StaticLifetime);
3178 self.add_missing_lifetime_specifiers_label(
3183 error.unwrap_or(&[]),
3188 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
3189 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
3190 let mut late_depth = 0;
3191 let mut scope = self.scope;
3192 let lifetime = loop {
3194 Scope::Binder { s, scope_type, .. } => {
3196 BinderScopeType::Normal => late_depth += 1,
3197 BinderScopeType::Concatenating => {}
3202 Scope::Root | Scope::Elision { .. } => break Region::Static,
3204 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
3206 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
3208 Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { s, .. } => {
3213 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
3216 fn check_lifetime_params(
3218 old_scope: ScopeRef<'_>,
3219 params: &'tcx [hir::GenericParam<'tcx>],
3221 let lifetimes: Vec<_> = params
3223 .filter_map(|param| match param.kind {
3224 GenericParamKind::Lifetime { .. } => {
3225 Some((param, param.name.normalize_to_macros_2_0()))
3230 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
3231 if let hir::ParamName::Plain(_) = lifetime_i_name {
3232 let name = lifetime_i_name.ident().name;
3233 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
3234 let mut err = struct_span_err!(
3238 "invalid lifetime parameter name: `{}`",
3239 lifetime_i.name.ident(),
3243 format!("{} is a reserved lifetime name", name),
3249 // It is a hard error to shadow a lifetime within the same scope.
3250 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
3251 if lifetime_i_name == lifetime_j_name {
3256 "lifetime name `{}` declared twice in the same scope",
3257 lifetime_j.name.ident()
3259 .span_label(lifetime_j.span, "declared twice")
3260 .span_label(lifetime_i.span, "previous declaration here")
3265 // It is a soft error to shadow a lifetime within a parent scope.
3266 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
3268 for bound in lifetime_i.bounds {
3270 hir::GenericBound::Outlives(ref lt) => match lt.name {
3271 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
3273 "use of `'_` in illegal place, but not caught by lowering",
3275 hir::LifetimeName::Static => {
3276 self.insert_lifetime(lt, Region::Static);
3280 lifetime_i.span.to(lt.span),
3282 "unnecessary lifetime parameter `{}`",
3283 lifetime_i.name.ident(),
3287 "you can use the `'static` lifetime directly, in place of `{}`",
3288 lifetime_i.name.ident(),
3292 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit(_) => {
3293 self.resolve_lifetime_ref(lt);
3295 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
3296 self.tcx.sess.delay_span_bug(
3298 "lowering generated `ImplicitObjectLifetimeDefault` \
3299 outside of an object type",
3302 hir::LifetimeName::Error => {
3303 // No need to do anything, error already reported.
3312 fn check_lifetime_param_for_shadowing(
3314 mut old_scope: ScopeRef<'_>,
3315 param: &'tcx hir::GenericParam<'tcx>,
3317 for label in &self.labels_in_fn {
3318 // FIXME (#24278): non-hygienic comparison
3319 if param.name.ident().name == label.name {
3320 signal_shadowing_problem(
3323 original_label(label.span),
3324 shadower_lifetime(¶m),
3332 Scope::Body { s, .. }
3333 | Scope::Elision { s, .. }
3334 | Scope::ObjectLifetimeDefault { s, .. }
3335 | Scope::Supertrait { s, .. }
3336 | Scope::TraitRefBoundary { s, .. } => {
3344 Scope::Binder { ref lifetimes, s, .. } => {
3345 if let Some(&def) = lifetimes.get(¶m.name.normalize_to_macros_2_0()) {
3347 self.tcx.hir().local_def_id_to_hir_id(def.id().unwrap().expect_local());
3349 signal_shadowing_problem(
3351 param.name.ident().name,
3352 original_lifetime(self.tcx.hir().span(hir_id)),
3353 shadower_lifetime(¶m),
3364 /// Returns `true` if, in the current scope, replacing `'_` would be
3365 /// equivalent to a single-use lifetime.
3366 fn track_lifetime_uses(&self) -> bool {
3367 let mut scope = self.scope;
3370 Scope::Root => break false,
3372 // Inside of items, it depends on the kind of item.
3373 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
3375 // Inside a body, `'_` will use an inference variable,
3377 Scope::Body { .. } => break true,
3379 // A lifetime only used in a fn argument could as well
3380 // be replaced with `'_`, as that would generate a
3382 Scope::Elision { elide: Elide::FreshLateAnon(..), .. } => break true,
3384 // In the return type or other such place, `'_` is not
3385 // going to make a fresh name, so we cannot
3386 // necessarily replace a single-use lifetime with
3389 elide: Elide::Exact(_) | Elide::Error(_) | Elide::Forbid, ..
3392 Scope::ObjectLifetimeDefault { s, .. }
3393 | Scope::Supertrait { s, .. }
3394 | Scope::TraitRefBoundary { s, .. } => scope = s,
3399 #[tracing::instrument(level = "debug", skip(self))]
3400 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
3402 node = ?self.tcx.hir().node_to_string(lifetime_ref.hir_id),
3403 span = ?self.tcx.sess.source_map().span_to_diagnostic_string(lifetime_ref.span)
3405 self.map.defs.insert(lifetime_ref.hir_id, def);
3408 Region::LateBoundAnon(..) | Region::Static => {
3409 // These are anonymous lifetimes or lifetimes that are not declared.
3412 Region::Free(_, def_id)
3413 | Region::LateBound(_, _, def_id, _)
3414 | Region::EarlyBound(_, def_id, _) => {
3415 // A lifetime declared by the user.
3416 let track_lifetime_uses = self.track_lifetime_uses();
3417 debug!(?track_lifetime_uses);
3418 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
3419 debug!("first use of {:?}", def_id);
3420 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
3422 debug!("many uses of {:?}", def_id);
3423 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
3429 /// Sometimes we resolve a lifetime, but later find that it is an
3430 /// error (esp. around impl trait). In that case, we remove the
3431 /// entry into `map.defs` so as not to confuse later code.
3432 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
3433 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
3434 assert_eq!(old_value, Some(bad_def));
3438 /// Detects late-bound lifetimes and inserts them into
3439 /// `map.late_bound`.
3441 /// A region declared on a fn is **late-bound** if:
3442 /// - it is constrained by an argument type;
3443 /// - it does not appear in a where-clause.
3445 /// "Constrained" basically means that it appears in any type but
3446 /// not amongst the inputs to a projection. In other words, `<&'a
3447 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
3448 #[tracing::instrument(level = "debug", skip(map))]
3449 fn insert_late_bound_lifetimes(
3450 map: &mut NamedRegionMap,
3451 decl: &hir::FnDecl<'_>,
3452 generics: &hir::Generics<'_>,
3454 let mut constrained_by_input = ConstrainedCollector::default();
3455 for arg_ty in decl.inputs {
3456 constrained_by_input.visit_ty(arg_ty);
3459 let mut appears_in_output = AllCollector::default();
3460 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
3462 debug!(?constrained_by_input.regions);
3464 // Walk the lifetimes that appear in where clauses.
3466 // Subtle point: because we disallow nested bindings, we can just
3467 // ignore binders here and scrape up all names we see.
3468 let mut appears_in_where_clause = AllCollector::default();
3469 appears_in_where_clause.visit_generics(generics);
3471 for param in generics.params {
3472 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
3473 if !param.bounds.is_empty() {
3474 // `'a: 'b` means both `'a` and `'b` are referenced
3475 appears_in_where_clause
3477 .insert(hir::LifetimeName::Param(param.name.normalize_to_macros_2_0()));
3482 debug!(?appears_in_where_clause.regions);
3484 // Late bound regions are those that:
3485 // - appear in the inputs
3486 // - do not appear in the where-clauses
3487 // - are not implicitly captured by `impl Trait`
3488 for param in generics.params {
3490 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
3492 // Neither types nor consts are late-bound.
3493 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
3496 let lt_name = hir::LifetimeName::Param(param.name.normalize_to_macros_2_0());
3497 // appears in the where clauses? early-bound.
3498 if appears_in_where_clause.regions.contains(<_name) {
3502 // does not appear in the inputs, but appears in the return type? early-bound.
3503 if !constrained_by_input.regions.contains(<_name)
3504 && appears_in_output.regions.contains(<_name)
3509 debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.hir_id);
3511 let inserted = map.late_bound.insert(param.hir_id);
3512 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
3518 struct ConstrainedCollector {
3519 regions: FxHashSet<hir::LifetimeName>,
3522 impl<'v> Visitor<'v> for ConstrainedCollector {
3523 type Map = intravisit::ErasedMap<'v>;
3525 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3526 NestedVisitorMap::None
3529 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
3532 hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
3534 // ignore lifetimes appearing in associated type
3535 // projections, as they are not *constrained*
3539 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
3540 // consider only the lifetimes on the final
3541 // segment; I am not sure it's even currently
3542 // valid to have them elsewhere, but even if it
3543 // is, those would be potentially inputs to
3545 if let Some(last_segment) = path.segments.last() {
3546 self.visit_path_segment(path.span, last_segment);
3551 intravisit::walk_ty(self, ty);
3556 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
3557 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());
3562 struct AllCollector {
3563 regions: FxHashSet<hir::LifetimeName>,
3566 impl<'v> Visitor<'v> for AllCollector {
3567 type Map = intravisit::ErasedMap<'v>;
3569 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
3570 NestedVisitorMap::None
3573 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
3574 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());