1 //! Name resolution for lifetimes.
3 //! Name resolution for lifetimes follows *much* simpler rules than the
4 //! full resolve. For example, lifetime names are never exported or
5 //! used between functions, and they operate in a purely top-down
6 //! way. Therefore, we break lifetime name resolution into a separate pass.
8 use rustc::hir::map::Map;
10 use rustc::middle::resolve_lifetime::*;
11 use rustc::session::Session;
12 use rustc::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
13 use rustc::{bug, span_bug};
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
17 use rustc_hir::def::{DefKind, Res};
18 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
19 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
20 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
21 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind};
22 use rustc_span::symbol::{kw, sym};
26 use std::mem::{replace, take};
29 use syntax::walk_list;
33 use rustc_error_codes::*;
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(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
47 fn late_anon(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.modern(), Region::EarlyBound(i, def_id, origin))
70 fn late(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: param={:?} depth={:?} def_id={:?} origin={:?}",
76 param, depth, def_id, origin,
78 (param.name.modern(), Region::LateBound(depth, def_id, origin))
81 fn late_anon(index: &Cell<u32>) -> Region {
84 let depth = ty::INNERMOST;
85 Region::LateBoundAnon(depth, i)
88 fn id(&self) -> Option<DefId> {
90 Region::Static | Region::LateBoundAnon(..) => None,
92 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
98 fn shifted(self, amount: u32) -> Region {
100 Region::LateBound(debruijn, id, origin) => {
101 Region::LateBound(debruijn.shifted_in(amount), id, origin)
103 Region::LateBoundAnon(debruijn, index) => {
104 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
110 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
112 Region::LateBound(debruijn, id, origin) => {
113 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
115 Region::LateBoundAnon(debruijn, index) => {
116 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
122 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
124 L: Iterator<Item = &'a hir::Lifetime>,
126 if let Region::EarlyBound(index, _, _) = self {
127 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
134 /// Maps the id of each lifetime reference to the lifetime decl
135 /// that it corresponds to.
137 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
138 /// actual use. It has the same data, but indexed by `DefIndex`. This
141 struct NamedRegionMap {
142 // maps from every use of a named (not anonymous) lifetime to a
143 // `Region` describing how that region is bound
144 defs: HirIdMap<Region>,
146 // the set of lifetime def ids that are late-bound; a region can
147 // be late-bound if (a) it does NOT appear in a where-clause and
148 // (b) it DOES appear in the arguments.
149 late_bound: HirIdSet,
151 // For each type and trait definition, maps type parameters
152 // to the trait object lifetime defaults computed from them.
153 object_lifetime_defaults: HirIdMap<Vec<ObjectLifetimeDefault>>,
156 struct LifetimeContext<'a, 'tcx> {
158 map: &'a mut NamedRegionMap,
161 /// This is slightly complicated. Our representation for poly-trait-refs contains a single
162 /// binder and thus we only allow a single level of quantification. However,
163 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
164 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices
165 /// correct when representing these constraints, we should only introduce one
166 /// scope. However, we want to support both locations for the quantifier and
167 /// during lifetime resolution we want precise information (so we can't
168 /// desugar in an earlier phase).
170 /// So, if we encounter a quantifier at the outer scope, we set
171 /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter
172 /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`,
173 /// then we introduce the scope at the inner quantifier.
174 trait_ref_hack: bool,
176 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
177 is_in_fn_syntax: bool,
179 /// List of labels in the function/method currently under analysis.
180 labels_in_fn: Vec<ast::Ident>,
182 /// Cache for cross-crate per-definition object lifetime defaults.
183 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
185 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
190 /// Declares lifetimes, and each can be early-bound or late-bound.
191 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
192 /// it should be shifted by the number of `Binder`s in between the
193 /// declaration `Binder` and the location it's referenced from.
195 lifetimes: FxHashMap<hir::ParamName, Region>,
197 /// if we extend this scope with another scope, what is the next index
198 /// we should use for an early-bound region?
199 next_early_index: u32,
201 /// Flag is set to true if, in this binder, `'_` would be
202 /// equivalent to a "single-use region". This is true on
203 /// impls, but not other kinds of items.
204 track_lifetime_uses: bool,
206 /// Whether or not this binder would serve as the parent
207 /// binder for opaque types introduced within. For example:
210 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
213 /// Here, the opaque types we create for the `impl Trait`
214 /// and `impl Trait2` references will both have the `foo` item
215 /// as their parent. When we get to `impl Trait2`, we find
216 /// that it is nested within the `for<>` binder -- this flag
217 /// allows us to skip that when looking for the parent binder
218 /// of the resulting opaque type.
219 opaque_type_parent: bool,
224 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
225 /// if this is a fn body, otherwise the original definitions are used.
226 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
227 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
233 /// A scope which either determines unspecified lifetimes or errors
234 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
240 /// Use a specific lifetime (if `Some`) or leave it unset (to be
241 /// inferred in a function body or potentially error outside one),
242 /// for the default choice of lifetime in a trait object type.
243 ObjectLifetimeDefault {
244 lifetime: Option<Region>,
251 #[derive(Clone, Debug)]
253 /// Use a fresh anonymous late-bound lifetime each time, by
254 /// incrementing the counter to generate sequential indices.
255 FreshLateAnon(Cell<u32>),
256 /// Always use this one lifetime.
258 /// Less or more than one lifetime were found, error on unspecified.
259 Error(Vec<ElisionFailureInfo>),
262 #[derive(Clone, Debug)]
263 struct ElisionFailureInfo {
264 /// Where we can find the argument pattern.
265 parent: Option<hir::BodyId>,
266 /// The index of the argument in the original definition.
268 lifetime_count: usize,
269 have_bound_regions: bool,
272 type ScopeRef<'a> = &'a Scope<'a>;
274 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
276 pub fn provide(providers: &mut ty::query::Providers<'_>) {
277 *providers = ty::query::Providers {
280 named_region_map: |tcx, id| {
281 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
282 tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id)
285 is_late_bound_map: |tcx, id| {
286 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
287 tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id)
290 object_lifetime_defaults_map: |tcx, id| {
291 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
292 tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id)
298 // (*) FIXME the query should be defined to take a LocalDefId
301 /// Computes the `ResolveLifetimes` map that contains data for the
302 /// entire crate. You should not read the result of this query
303 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
305 fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> &ResolveLifetimes {
306 assert_eq!(for_krate, LOCAL_CRATE);
308 let named_region_map = krate(tcx);
310 let mut rl = ResolveLifetimes::default();
312 for (hir_id, v) in named_region_map.defs {
313 let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
314 map.insert(hir_id.local_id, v);
316 for hir_id in named_region_map.late_bound {
317 let map = rl.late_bound.entry(hir_id.owner_local_def_id()).or_default();
318 map.insert(hir_id.local_id);
320 for (hir_id, v) in named_region_map.object_lifetime_defaults {
321 let map = rl.object_lifetime_defaults.entry(hir_id.owner_local_def_id()).or_default();
322 map.insert(hir_id.local_id, v);
328 fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
329 let krate = tcx.hir().krate();
330 let mut map = NamedRegionMap {
331 defs: Default::default(),
332 late_bound: Default::default(),
333 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
336 let mut visitor = LifetimeContext {
340 trait_ref_hack: false,
341 is_in_fn_syntax: false,
342 labels_in_fn: vec![],
343 xcrate_object_lifetime_defaults: Default::default(),
344 lifetime_uses: &mut Default::default(),
346 for (_, item) in &krate.items {
347 visitor.visit_item(item);
353 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
354 /// We have to account for this when computing the index of the other generic parameters.
355 /// This function returns whether there is such an implicit parameter defined on the given item.
356 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
358 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true,
363 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
364 type Map = Map<'tcx>;
366 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
367 NestedVisitorMap::All(&self.tcx.hir())
370 // We want to nest trait/impl items in their parent, but nothing else.
371 fn visit_nested_item(&mut self, _: hir::ItemId) {}
373 fn visit_nested_body(&mut self, body: hir::BodyId) {
374 // Each body has their own set of labels, save labels.
375 let saved = take(&mut self.labels_in_fn);
376 let body = self.tcx.hir().body(body);
377 extract_labels(self, body);
378 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
379 this.visit_body(body);
381 replace(&mut self.labels_in_fn, saved);
384 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
386 hir::ItemKind::Fn(ref sig, ref generics, _) => {
387 self.visit_early_late(None, &sig.decl, generics, |this| {
388 intravisit::walk_item(this, item);
392 hir::ItemKind::ExternCrate(_)
393 | hir::ItemKind::Use(..)
394 | hir::ItemKind::Mod(..)
395 | hir::ItemKind::ForeignMod(..)
396 | hir::ItemKind::GlobalAsm(..) => {
397 // These sorts of items have no lifetime parameters at all.
398 intravisit::walk_item(self, item);
400 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
401 // No lifetime parameters, but implied 'static.
402 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
403 self.with(scope, |_, this| intravisit::walk_item(this, item));
405 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {
406 // Currently opaque type declarations are just generated from `impl Trait`
407 // items. Doing anything on this node is irrelevant, as we currently don't need
410 hir::ItemKind::TyAlias(_, ref generics)
411 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
412 impl_trait_fn: None, ref generics, ..
414 | hir::ItemKind::Enum(_, ref generics)
415 | hir::ItemKind::Struct(_, ref generics)
416 | hir::ItemKind::Union(_, ref generics)
417 | hir::ItemKind::Trait(_, _, ref generics, ..)
418 | hir::ItemKind::TraitAlias(ref generics, ..)
419 | hir::ItemKind::Impl { ref generics, .. } => {
420 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
421 // This is not true for other kinds of items.x
422 let track_lifetime_uses = match item.kind {
423 hir::ItemKind::Impl { .. } => true,
426 // These kinds of items have only early-bound lifetime parameters.
427 let mut index = if sub_items_have_self_param(&item.kind) {
428 1 // Self comes before lifetimes
432 let mut non_lifetime_count = 0;
433 let lifetimes = generics
436 .filter_map(|param| match param.kind {
437 GenericParamKind::Lifetime { .. } => {
438 Some(Region::early(&self.tcx.hir(), &mut index, param))
440 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
441 non_lifetime_count += 1;
446 let scope = Scope::Binder {
448 next_early_index: index + non_lifetime_count,
449 opaque_type_parent: true,
453 self.with(scope, |old_scope, this| {
454 this.check_lifetime_params(old_scope, &generics.params);
455 intravisit::walk_item(this, item);
461 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
463 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
464 self.visit_early_late(None, decl, generics, |this| {
465 intravisit::walk_foreign_item(this, item);
468 hir::ForeignItemKind::Static(..) => {
469 intravisit::walk_foreign_item(self, item);
471 hir::ForeignItemKind::Type => {
472 intravisit::walk_foreign_item(self, item);
477 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
478 debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty);
479 debug!("visit_ty: ty.kind={:?}", ty.kind);
481 hir::TyKind::BareFn(ref c) => {
482 let next_early_index = self.next_early_index();
483 let was_in_fn_syntax = self.is_in_fn_syntax;
484 self.is_in_fn_syntax = true;
485 let scope = Scope::Binder {
489 .filter_map(|param| match param.kind {
490 GenericParamKind::Lifetime { .. } => {
491 Some(Region::late(&self.tcx.hir(), param))
498 track_lifetime_uses: true,
499 opaque_type_parent: false,
501 self.with(scope, |old_scope, this| {
502 // a bare fn has no bounds, so everything
503 // contained within is scoped within its binder.
504 this.check_lifetime_params(old_scope, &c.generic_params);
505 intravisit::walk_ty(this, ty);
507 self.is_in_fn_syntax = was_in_fn_syntax;
509 hir::TyKind::TraitObject(bounds, ref lifetime) => {
510 debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime);
511 for bound in bounds {
512 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
514 match lifetime.name {
515 LifetimeName::Implicit => {
516 // For types like `dyn Foo`, we should
517 // generate a special form of elided.
518 span_bug!(ty.span, "object-lifetime-default expected, not implict",);
520 LifetimeName::ImplicitObjectLifetimeDefault => {
521 // If the user does not write *anything*, we
522 // use the object lifetime defaulting
523 // rules. So e.g., `Box<dyn Debug>` becomes
524 // `Box<dyn Debug + 'static>`.
525 self.resolve_object_lifetime_default(lifetime)
527 LifetimeName::Underscore => {
528 // If the user writes `'_`, we use the *ordinary* elision
529 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
530 // resolved the same as the `'_` in `&'_ Foo`.
533 self.resolve_elided_lifetimes(vec![lifetime])
535 LifetimeName::Param(_) | LifetimeName::Static => {
536 // If the user wrote an explicit name, use that.
537 self.visit_lifetime(lifetime);
539 LifetimeName::Error => {}
542 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
543 self.visit_lifetime(lifetime_ref);
544 let scope = Scope::ObjectLifetimeDefault {
545 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
548 self.with(scope, |_, this| this.visit_ty(&mt.ty));
550 hir::TyKind::Def(item_id, lifetimes) => {
551 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
552 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
553 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
554 // ^ ^ this gets resolved in the scope of
555 // the opaque_ty generics
556 let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).kind {
557 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
558 // This arm is for `impl Trait` in the types of statics, constants and locals.
559 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
560 intravisit::walk_ty(self, ty);
563 // RPIT (return position impl trait)
564 hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, bounds, .. }) => {
567 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
570 // Resolve the lifetimes that are applied to the opaque type.
571 // These are resolved in the current scope.
572 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
573 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
574 // ^ ^this gets resolved in the current scope
575 for lifetime in lifetimes {
576 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
577 self.visit_lifetime(lifetime);
579 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
580 // and ban them. Type variables instantiated inside binders aren't
581 // well-supported at the moment, so this doesn't work.
582 // In the future, this should be fixed and this error should be removed.
583 let def = self.map.defs.get(&lifetime.hir_id).cloned();
584 if let Some(Region::LateBound(_, def_id, _)) = def {
585 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
586 // Ensure that the parent of the def is an item, not HRTB
587 let parent_id = self.tcx.hir().get_parent_node(hir_id);
588 let parent_impl_id = hir::ImplItemId { hir_id: parent_id };
589 let parent_trait_id = hir::TraitItemId { hir_id: parent_id };
590 let krate = self.tcx.hir().forest.krate();
592 if !(krate.items.contains_key(&parent_id)
593 || krate.impl_items.contains_key(&parent_impl_id)
594 || krate.trait_items.contains_key(&parent_trait_id))
600 "`impl Trait` can only capture lifetimes \
601 bound at the fn or impl level"
604 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
611 // We want to start our early-bound indices at the end of the parent scope,
612 // not including any parent `impl Trait`s.
613 let mut index = self.next_early_index_for_opaque_type();
614 debug!("visit_ty: index = {}", index);
616 let mut elision = None;
617 let mut lifetimes = FxHashMap::default();
618 let mut non_lifetime_count = 0;
619 for param in generics.params {
621 GenericParamKind::Lifetime { .. } => {
622 let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m);
623 let def_id = if let Region::EarlyBound(_, def_id, _) = reg {
628 if let hir::ParamName::Plain(param_name) = name {
629 if param_name.name == kw::UnderscoreLifetime {
630 // Pick the elided lifetime "definition" if one exists
631 // and use it to make an elision scope.
632 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
635 lifetimes.insert(name, reg);
638 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
639 lifetimes.insert(name, reg);
642 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
643 non_lifetime_count += 1;
647 let next_early_index = index + non_lifetime_count;
649 if let Some(elision_region) = elision {
651 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
652 self.with(scope, |_old_scope, this| {
653 let scope = Scope::Binder {
657 track_lifetime_uses: true,
658 opaque_type_parent: false,
660 this.with(scope, |_old_scope, this| {
661 this.visit_generics(generics);
662 for bound in bounds {
663 this.visit_param_bound(bound);
668 let scope = Scope::Binder {
672 track_lifetime_uses: true,
673 opaque_type_parent: false,
675 self.with(scope, |_old_scope, this| {
676 this.visit_generics(generics);
677 for bound in bounds {
678 this.visit_param_bound(bound);
683 _ => intravisit::walk_ty(self, ty),
687 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
688 use self::hir::TraitItemKind::*;
689 match trait_item.kind {
690 Method(ref sig, _) => {
692 self.visit_early_late(
693 Some(tcx.hir().get_parent_item(trait_item.hir_id)),
695 &trait_item.generics,
696 |this| intravisit::walk_trait_item(this, trait_item),
699 Type(bounds, ref ty) => {
700 let generics = &trait_item.generics;
701 let mut index = self.next_early_index();
702 debug!("visit_ty: index = {}", index);
703 let mut non_lifetime_count = 0;
704 let lifetimes = generics
707 .filter_map(|param| match param.kind {
708 GenericParamKind::Lifetime { .. } => {
709 Some(Region::early(&self.tcx.hir(), &mut index, param))
711 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
712 non_lifetime_count += 1;
717 let scope = Scope::Binder {
719 next_early_index: index + non_lifetime_count,
721 track_lifetime_uses: true,
722 opaque_type_parent: true,
724 self.with(scope, |_old_scope, this| {
725 this.visit_generics(generics);
726 for bound in bounds {
727 this.visit_param_bound(bound);
729 if let Some(ty) = ty {
735 // Only methods and types support generics.
736 assert!(trait_item.generics.params.is_empty());
737 intravisit::walk_trait_item(self, trait_item);
742 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
743 use self::hir::ImplItemKind::*;
744 match impl_item.kind {
745 Method(ref sig, _) => {
747 self.visit_early_late(
748 Some(tcx.hir().get_parent_item(impl_item.hir_id)),
751 |this| intravisit::walk_impl_item(this, impl_item),
755 let generics = &impl_item.generics;
756 let mut index = self.next_early_index();
757 let mut non_lifetime_count = 0;
758 debug!("visit_ty: index = {}", index);
759 let lifetimes = generics
762 .filter_map(|param| match param.kind {
763 GenericParamKind::Lifetime { .. } => {
764 Some(Region::early(&self.tcx.hir(), &mut index, param))
766 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
767 non_lifetime_count += 1;
772 let scope = Scope::Binder {
774 next_early_index: index + non_lifetime_count,
776 track_lifetime_uses: true,
777 opaque_type_parent: true,
779 self.with(scope, |_old_scope, this| {
780 this.visit_generics(generics);
784 OpaqueTy(bounds) => {
785 let generics = &impl_item.generics;
786 let mut index = self.next_early_index();
787 let mut next_early_index = index;
788 debug!("visit_ty: index = {}", index);
789 let lifetimes = generics
792 .filter_map(|param| match param.kind {
793 GenericParamKind::Lifetime { .. } => {
794 Some(Region::early(&self.tcx.hir(), &mut index, param))
796 GenericParamKind::Type { .. } => {
797 next_early_index += 1;
800 GenericParamKind::Const { .. } => {
801 next_early_index += 1;
807 let scope = Scope::Binder {
811 track_lifetime_uses: true,
812 opaque_type_parent: true,
814 self.with(scope, |_old_scope, this| {
815 this.visit_generics(generics);
816 for bound in bounds {
817 this.visit_param_bound(bound);
822 // Only methods and types support generics.
823 assert!(impl_item.generics.params.is_empty());
824 intravisit::walk_impl_item(self, impl_item);
829 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
830 debug!("visit_lifetime(lifetime_ref={:?})", lifetime_ref);
831 if lifetime_ref.is_elided() {
832 self.resolve_elided_lifetimes(vec![lifetime_ref]);
835 if lifetime_ref.is_static() {
836 self.insert_lifetime(lifetime_ref, Region::Static);
839 self.resolve_lifetime_ref(lifetime_ref);
842 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
843 for (i, segment) in path.segments.iter().enumerate() {
844 let depth = path.segments.len() - i - 1;
845 if let Some(ref args) = segment.args {
846 self.visit_segment_args(path.res, depth, args);
851 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
852 let output = match fd.output {
853 hir::FunctionRetTy::DefaultReturn(_) => None,
854 hir::FunctionRetTy::Return(ref ty) => Some(&**ty),
856 self.visit_fn_like_elision(&fd.inputs, output);
859 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
860 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
861 for param in generics.params {
863 GenericParamKind::Lifetime { .. } => {}
864 GenericParamKind::Type { ref default, .. } => {
865 walk_list!(self, visit_param_bound, param.bounds);
866 if let Some(ref ty) = default {
870 GenericParamKind::Const { ref ty, .. } => {
871 walk_list!(self, visit_param_bound, param.bounds);
876 for predicate in generics.where_clause.predicates {
878 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
881 ref bound_generic_params,
884 let lifetimes: FxHashMap<_, _> = bound_generic_params
886 .filter_map(|param| match param.kind {
887 GenericParamKind::Lifetime { .. } => {
888 Some(Region::late(&self.tcx.hir(), param))
893 if !lifetimes.is_empty() {
894 self.trait_ref_hack = true;
895 let next_early_index = self.next_early_index();
896 let scope = Scope::Binder {
900 track_lifetime_uses: true,
901 opaque_type_parent: false,
903 let result = self.with(scope, |old_scope, this| {
904 this.check_lifetime_params(old_scope, &bound_generic_params);
905 this.visit_ty(&bounded_ty);
906 walk_list!(this, visit_param_bound, bounds);
908 self.trait_ref_hack = false;
911 self.visit_ty(&bounded_ty);
912 walk_list!(self, visit_param_bound, bounds);
915 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
920 self.visit_lifetime(lifetime);
921 walk_list!(self, visit_param_bound, bounds);
923 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
928 self.visit_ty(lhs_ty);
929 self.visit_ty(rhs_ty);
935 fn visit_poly_trait_ref(
937 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
938 _modifier: hir::TraitBoundModifier,
940 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
942 if !self.trait_ref_hack
943 || trait_ref.bound_generic_params.iter().any(|param| match param.kind {
944 GenericParamKind::Lifetime { .. } => true,
948 if self.trait_ref_hack {
953 "nested quantification of lifetimes"
957 let next_early_index = self.next_early_index();
958 let scope = Scope::Binder {
960 .bound_generic_params
962 .filter_map(|param| match param.kind {
963 GenericParamKind::Lifetime { .. } => {
964 Some(Region::late(&self.tcx.hir(), param))
971 track_lifetime_uses: true,
972 opaque_type_parent: false,
974 self.with(scope, |old_scope, this| {
975 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
976 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
977 this.visit_trait_ref(&trait_ref.trait_ref)
980 self.visit_trait_ref(&trait_ref.trait_ref)
985 #[derive(Copy, Clone, PartialEq)]
999 fn original_label(span: Span) -> Original {
1000 Original { kind: ShadowKind::Label, span: span }
1002 fn shadower_label(span: Span) -> Shadower {
1003 Shadower { kind: ShadowKind::Label, span: span }
1005 fn original_lifetime(span: Span) -> Original {
1006 Original { kind: ShadowKind::Lifetime, span: span }
1008 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1009 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1013 fn desc(&self) -> &'static str {
1015 ShadowKind::Label => "label",
1016 ShadowKind::Lifetime => "lifetime",
1021 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1022 let lifetime_params: Vec<_> = params
1024 .filter_map(|param| match param.kind {
1025 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1029 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1030 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1032 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1037 "cannot mix in-band and explicit lifetime definitions"
1039 .span_label(*in_band_span, "in-band lifetime definition here")
1040 .span_label(*explicit_span, "explicit lifetime definition here")
1045 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: ast::Name, orig: Original, shadower: Shadower) {
1046 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1047 // lifetime/lifetime shadowing is an error
1052 "{} name `{}` shadows a \
1053 {} name that is already in scope",
1054 shadower.kind.desc(),
1059 // shadowing involving a label is only a warning, due to issues with
1060 // labels and lifetimes not being macro-hygienic.
1061 tcx.sess.struct_span_warn(
1064 "{} name `{}` shadows a \
1065 {} name that is already in scope",
1066 shadower.kind.desc(),
1072 err.span_label(orig.span, "first declared here");
1073 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1077 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1078 // if one of the label shadows a lifetime or another label.
1079 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1080 struct GatherLabels<'a, 'tcx> {
1082 scope: ScopeRef<'a>,
1083 labels_in_fn: &'a mut Vec<ast::Ident>,
1087 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1088 gather.visit_body(body);
1090 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1093 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1094 NestedVisitorMap::None
1097 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1098 if let Some(label) = expression_label(ex) {
1099 for prior_label in &self.labels_in_fn[..] {
1100 // FIXME (#24278): non-hygienic comparison
1101 if label.name == prior_label.name {
1102 signal_shadowing_problem(
1105 original_label(prior_label.span),
1106 shadower_label(label.span),
1111 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1113 self.labels_in_fn.push(label);
1115 intravisit::walk_expr(self, ex)
1119 fn expression_label(ex: &hir::Expr<'_>) -> Option<ast::Ident> {
1120 if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None }
1123 fn check_if_label_shadows_lifetime(
1125 mut scope: ScopeRef<'_>,
1130 Scope::Body { s, .. }
1131 | Scope::Elision { s, .. }
1132 | Scope::ObjectLifetimeDefault { s, .. } => {
1140 Scope::Binder { ref lifetimes, s, .. } => {
1141 // FIXME (#24278): non-hygienic comparison
1142 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1143 let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
1145 signal_shadowing_problem(
1148 original_lifetime(tcx.hir().span(hir_id)),
1149 shadower_label(label.span),
1160 fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap<Vec<ObjectLifetimeDefault>> {
1161 let mut map = HirIdMap::default();
1162 for item in tcx.hir().krate().items.values() {
1164 hir::ItemKind::Struct(_, ref generics)
1165 | hir::ItemKind::Union(_, ref generics)
1166 | hir::ItemKind::Enum(_, ref generics)
1167 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1168 ref generics, impl_trait_fn: None, ..
1170 | hir::ItemKind::TyAlias(_, ref generics)
1171 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1172 let result = object_lifetime_defaults_for_item(tcx, generics);
1175 if attr::contains_name(&item.attrs, sym::rustc_object_lifetime_default) {
1176 let object_lifetime_default_reprs: String = result
1178 .map(|set| match *set {
1179 Set1::Empty => "BaseDefault".into(),
1180 Set1::One(Region::Static) => "'static".into(),
1181 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1184 .find_map(|param| match param.kind {
1185 GenericParamKind::Lifetime { .. } => {
1187 return Some(param.name.ident().to_string().into());
1195 Set1::One(_) => bug!(),
1196 Set1::Many => "Ambiguous".into(),
1198 .collect::<Vec<Cow<'static, str>>>()
1200 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1203 map.insert(item.hir_id, result);
1211 /// Scan the bounds and where-clauses on parameters to extract bounds
1212 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1213 /// for each type parameter.
1214 fn object_lifetime_defaults_for_item(
1216 generics: &hir::Generics<'_>,
1217 ) -> Vec<ObjectLifetimeDefault> {
1218 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1219 for bound in bounds {
1220 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1221 set.insert(lifetime.name.modern());
1229 .filter_map(|param| match param.kind {
1230 GenericParamKind::Lifetime { .. } => None,
1231 GenericParamKind::Type { .. } => {
1232 let mut set = Set1::Empty;
1234 add_bounds(&mut set, ¶m.bounds);
1236 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1237 for predicate in generics.where_clause.predicates {
1238 // Look for `type: ...` where clauses.
1239 let data = match *predicate {
1240 hir::WherePredicate::BoundPredicate(ref data) => data,
1244 // Ignore `for<'a> type: ...` as they can change what
1245 // lifetimes mean (although we could "just" handle it).
1246 if !data.bound_generic_params.is_empty() {
1250 let res = match data.bounded_ty.kind {
1251 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1255 if res == Res::Def(DefKind::TyParam, param_def_id) {
1256 add_bounds(&mut set, &data.bounds);
1261 Set1::Empty => Set1::Empty,
1262 Set1::One(name) => {
1263 if name == hir::LifetimeName::Static {
1264 Set1::One(Region::Static)
1269 .filter_map(|param| match param.kind {
1270 GenericParamKind::Lifetime { .. } => Some((
1272 hir::LifetimeName::Param(param.name),
1273 LifetimeDefOrigin::from_param(param),
1278 .find(|&(_, (_, lt_name, _))| lt_name == name)
1279 .map_or(Set1::Many, |(i, (id, _, origin))| {
1280 let def_id = tcx.hir().local_def_id(id);
1281 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1285 Set1::Many => Set1::Many,
1288 GenericParamKind::Const { .. } => {
1289 // Generic consts don't impose any constraints.
1296 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1297 // FIXME(#37666) this works around a limitation in the region inferencer
1298 fn hack<F>(&mut self, f: F)
1300 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1305 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1307 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1309 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1310 let labels_in_fn = take(&mut self.labels_in_fn);
1311 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1312 let mut this = LifetimeContext {
1316 trait_ref_hack: self.trait_ref_hack,
1317 is_in_fn_syntax: self.is_in_fn_syntax,
1319 xcrate_object_lifetime_defaults,
1320 lifetime_uses: lifetime_uses,
1322 debug!("entering scope {:?}", this.scope);
1323 f(self.scope, &mut this);
1324 this.check_uses_for_lifetimes_defined_by_scope();
1325 debug!("exiting scope {:?}", this.scope);
1326 self.labels_in_fn = this.labels_in_fn;
1327 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1330 /// helper method to determine the span to remove when suggesting the
1331 /// deletion of a lifetime
1332 fn lifetime_deletion_span(
1335 generics: &hir::Generics<'_>,
1337 generics.params.iter().enumerate().find_map(|(i, param)| {
1338 if param.name.ident() == name {
1339 let mut in_band = false;
1340 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1341 if let hir::LifetimeParamKind::InBand = kind {
1348 if generics.params.len() == 1 {
1349 // if sole lifetime, remove the entire `<>` brackets
1352 // if removing within `<>` brackets, we also want to
1353 // delete a leading or trailing comma as appropriate
1354 if i >= generics.params.len() - 1 {
1355 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1357 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1367 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1368 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1369 fn suggest_eliding_single_use_lifetime(
1371 err: &mut DiagnosticBuilder<'_>,
1373 lifetime: &hir::Lifetime,
1375 let name = lifetime.name.ident();
1376 let mut remove_decl = None;
1377 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1378 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1379 remove_decl = self.lifetime_deletion_span(name, generics);
1383 let mut remove_use = None;
1384 let mut elide_use = None;
1385 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1386 for input in inputs {
1388 hir::TyKind::Rptr(lt, _) => {
1389 if lt.name.ident() == name {
1390 // include the trailing whitespace between the lifetime and type names
1391 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1396 .span_until_non_whitespace(lt_through_ty_span),
1401 hir::TyKind::Path(ref qpath) => {
1402 if let QPath::Resolved(_, path) = qpath {
1403 let last_segment = &path.segments[path.segments.len() - 1];
1404 let generics = last_segment.generic_args();
1405 for arg in generics.args.iter() {
1406 if let GenericArg::Lifetime(lt) = arg {
1407 if lt.name.ident() == name {
1408 elide_use = Some(lt.span);
1420 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1421 if let Some(parent) =
1422 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1425 Node::Item(item) => {
1426 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1427 find_arg_use_span(sig.decl.inputs);
1430 Node::ImplItem(impl_item) => {
1431 if let hir::ImplItemKind::Method(sig, _) = &impl_item.kind {
1432 find_arg_use_span(sig.decl.inputs);
1440 let msg = "elide the single-use lifetime";
1441 match (remove_decl, remove_use, elide_use) {
1442 (Some(decl_span), Some(use_span), None) => {
1443 // if both declaration and use deletion spans start at the same
1444 // place ("start at" because the latter includes trailing
1445 // whitespace), then this is an in-band lifetime
1446 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1447 err.span_suggestion(
1451 Applicability::MachineApplicable,
1454 err.multipart_suggestion(
1456 vec![(decl_span, String::new()), (use_span, String::new())],
1457 Applicability::MachineApplicable,
1461 (Some(decl_span), None, Some(use_span)) => {
1462 err.multipart_suggestion(
1464 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1465 Applicability::MachineApplicable,
1472 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1473 let defined_by = match self.scope {
1474 Scope::Binder { lifetimes, .. } => lifetimes,
1476 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1481 let mut def_ids: Vec<_> = defined_by
1483 .flat_map(|region| match region {
1484 Region::EarlyBound(_, def_id, _)
1485 | Region::LateBound(_, def_id, _)
1486 | Region::Free(_, def_id) => Some(*def_id),
1488 Region::LateBoundAnon(..) | Region::Static => None,
1492 // ensure that we issue lints in a repeatable order
1493 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1495 for def_id in def_ids {
1496 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1498 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1501 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1505 match lifetimeuseset {
1506 Some(LifetimeUseSet::One(lifetime)) => {
1507 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1508 debug!("hir id first={:?}", hir_id);
1509 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1510 Node::Lifetime(hir_lifetime) => Some((
1511 hir_lifetime.hir_id,
1513 hir_lifetime.name.ident(),
1515 Node::GenericParam(param) => {
1516 Some((param.hir_id, param.span, param.name.ident()))
1520 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1521 if name.name == kw::UnderscoreLifetime {
1525 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1526 if let Some(parent_hir_id) =
1527 self.tcx.hir().as_local_hir_id(parent_def_id)
1529 // lifetimes in `derive` expansions don't count (Issue #53738)
1533 .attrs(parent_hir_id)
1535 .any(|attr| attr.check_name(sym::automatically_derived))
1542 let mut err = self.tcx.struct_span_lint_hir(
1543 lint::builtin::SINGLE_USE_LIFETIMES,
1546 &format!("lifetime parameter `{}` only used once", name),
1549 if span == lifetime.span {
1550 // spans are the same for in-band lifetime declarations
1551 err.span_label(span, "this lifetime is only used here");
1553 err.span_label(span, "this lifetime...");
1554 err.span_label(lifetime.span, "...is used only here");
1556 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1560 Some(LifetimeUseSet::Many) => {
1561 debug!("not one use lifetime");
1564 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1565 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1566 Node::Lifetime(hir_lifetime) => Some((
1567 hir_lifetime.hir_id,
1569 hir_lifetime.name.ident(),
1571 Node::GenericParam(param) => {
1572 Some((param.hir_id, param.span, param.name.ident()))
1576 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1577 let mut err = self.tcx.struct_span_lint_hir(
1578 lint::builtin::UNUSED_LIFETIMES,
1581 &format!("lifetime parameter `{}` never used", name),
1583 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1584 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1585 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1586 if let Some(span) = unused_lt_span {
1587 err.span_suggestion(
1589 "elide the unused lifetime",
1591 Applicability::MachineApplicable,
1603 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1605 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1606 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1607 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1611 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1613 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1614 /// lifetimes may be interspersed together.
1616 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1617 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1618 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1619 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1620 /// ordering is not important there.
1621 fn visit_early_late<F>(
1623 parent_id: Option<hir::HirId>,
1624 decl: &'tcx hir::FnDecl<'tcx>,
1625 generics: &'tcx hir::Generics<'tcx>,
1628 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1630 insert_late_bound_lifetimes(self.map, decl, generics);
1632 // Find the start of nested early scopes, e.g., in methods.
1634 if let Some(parent_id) = parent_id {
1635 let parent = self.tcx.hir().expect_item(parent_id);
1636 if sub_items_have_self_param(&parent.kind) {
1637 index += 1; // Self comes before lifetimes
1640 hir::ItemKind::Trait(_, _, ref generics, ..)
1641 | hir::ItemKind::Impl { ref generics, .. } => {
1642 index += generics.params.len() as u32;
1648 let mut non_lifetime_count = 0;
1649 let lifetimes = generics
1652 .filter_map(|param| match param.kind {
1653 GenericParamKind::Lifetime { .. } => {
1654 if self.map.late_bound.contains(¶m.hir_id) {
1655 Some(Region::late(&self.tcx.hir(), param))
1657 Some(Region::early(&self.tcx.hir(), &mut index, param))
1660 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1661 non_lifetime_count += 1;
1666 let next_early_index = index + non_lifetime_count;
1668 let scope = Scope::Binder {
1672 opaque_type_parent: true,
1673 track_lifetime_uses: false,
1675 self.with(scope, move |old_scope, this| {
1676 this.check_lifetime_params(old_scope, &generics.params);
1677 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1681 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1682 let mut scope = self.scope;
1685 Scope::Root => return 0,
1687 Scope::Binder { next_early_index, opaque_type_parent, .. }
1688 if (!only_opaque_type_parent || opaque_type_parent) =>
1690 return next_early_index;
1693 Scope::Binder { s, .. }
1694 | Scope::Body { s, .. }
1695 | Scope::Elision { s, .. }
1696 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1701 /// Returns the next index one would use for an early-bound-region
1702 /// if extending the current scope.
1703 fn next_early_index(&self) -> u32 {
1704 self.next_early_index_helper(true)
1707 /// Returns the next index one would use for an `impl Trait` that
1708 /// is being converted into an opaque type alias `impl Trait`. This will be the
1709 /// next early index from the enclosing item, for the most
1710 /// part. See the `opaque_type_parent` field for more info.
1711 fn next_early_index_for_opaque_type(&self) -> u32 {
1712 self.next_early_index_helper(false)
1715 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1716 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1718 // If we've already reported an error, just ignore `lifetime_ref`.
1719 if let LifetimeName::Error = lifetime_ref.name {
1723 // Walk up the scope chain, tracking the number of fn scopes
1724 // that we pass through, until we find a lifetime with the
1725 // given name or we run out of scopes.
1727 let mut late_depth = 0;
1728 let mut scope = self.scope;
1729 let mut outermost_body = None;
1732 Scope::Body { id, s } => {
1733 outermost_body = Some(id);
1741 Scope::Binder { ref lifetimes, s, .. } => {
1742 match lifetime_ref.name {
1743 LifetimeName::Param(param_name) => {
1744 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1745 break Some(def.shifted(late_depth));
1748 _ => bug!("expected LifetimeName::Param"),
1755 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1761 if let Some(mut def) = result {
1762 if let Region::EarlyBound(..) = def {
1763 // Do not free early-bound regions, only late-bound ones.
1764 } else if let Some(body_id) = outermost_body {
1765 let fn_id = self.tcx.hir().body_owner(body_id);
1766 match self.tcx.hir().get(fn_id) {
1767 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1768 | Node::TraitItem(&hir::TraitItem {
1769 kind: hir::TraitItemKind::Method(..),
1772 | Node::ImplItem(&hir::ImplItem {
1773 kind: hir::ImplItemKind::Method(..), ..
1775 let scope = self.tcx.hir().local_def_id(fn_id);
1776 def = Region::Free(scope, def.id().unwrap());
1782 // Check for fn-syntax conflicts with in-band lifetime definitions
1783 if self.is_in_fn_syntax {
1785 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1786 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1791 "lifetimes used in `fn` or `Fn` syntax must be \
1792 explicitly declared using `<...>` binders"
1794 .span_label(lifetime_ref.span, "in-band lifetime definition")
1799 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1800 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1801 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1802 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1803 | Region::LateBoundAnon(..)
1804 | Region::Free(..) => {}
1808 self.insert_lifetime(lifetime_ref, def);
1814 "use of undeclared lifetime name `{}`",
1817 .span_label(lifetime_ref.span, "undeclared lifetime")
1822 fn visit_segment_args(
1826 generic_args: &'tcx hir::GenericArgs<'tcx>,
1829 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1830 res, depth, generic_args,
1833 if generic_args.parenthesized {
1834 let was_in_fn_syntax = self.is_in_fn_syntax;
1835 self.is_in_fn_syntax = true;
1836 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1837 self.is_in_fn_syntax = was_in_fn_syntax;
1841 let mut elide_lifetimes = true;
1842 let lifetimes = generic_args
1845 .filter_map(|arg| match arg {
1846 hir::GenericArg::Lifetime(lt) => {
1847 if !lt.is_elided() {
1848 elide_lifetimes = false;
1855 if elide_lifetimes {
1856 self.resolve_elided_lifetimes(lifetimes);
1858 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1861 // Figure out if this is a type/trait segment,
1862 // which requires object lifetime defaults.
1863 let parent_def_id = |this: &mut Self, def_id: DefId| {
1864 let def_key = this.tcx.def_key(def_id);
1865 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1867 let type_def_id = match res {
1868 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1869 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1870 Res::Def(DefKind::Struct, def_id)
1871 | Res::Def(DefKind::Union, def_id)
1872 | Res::Def(DefKind::Enum, def_id)
1873 | Res::Def(DefKind::TyAlias, def_id)
1874 | Res::Def(DefKind::Trait, def_id)
1882 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1884 // Compute a vector of defaults, one for each type parameter,
1885 // per the rules given in RFCs 599 and 1156. Example:
1888 // struct Foo<'a, T: 'a, U> { }
1891 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1892 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1893 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1896 // Therefore, we would compute `object_lifetime_defaults` to a
1897 // vector like `['x, 'static]`. Note that the vector only
1898 // includes type parameters.
1899 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1901 let mut scope = self.scope;
1904 Scope::Root => break false,
1906 Scope::Body { .. } => break true,
1908 Scope::Binder { s, .. }
1909 | Scope::Elision { s, .. }
1910 | Scope::ObjectLifetimeDefault { s, .. } => {
1917 let map = &self.map;
1918 let unsubst = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
1919 &map.object_lifetime_defaults[&id]
1922 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1923 tcx.generics_of(def_id)
1926 .filter_map(|param| match param.kind {
1927 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1928 Some(object_lifetime_default)
1930 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1935 debug!("visit_segment_args: unsubst={:?}", unsubst);
1938 .map(|set| match *set {
1943 Some(Region::Static)
1947 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1948 GenericArg::Lifetime(lt) => Some(lt),
1951 r.subst(lifetimes, map)
1958 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1961 for arg in generic_args.args {
1963 GenericArg::Lifetime(_) => {}
1964 GenericArg::Type(ty) => {
1965 if let Some(<) = object_lifetime_defaults.get(i) {
1966 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1967 self.with(scope, |_, this| this.visit_ty(ty));
1973 GenericArg::Const(ct) => {
1974 self.visit_anon_const(&ct.value);
1979 // Hack: when resolving the type `XX` in binding like `dyn
1980 // Foo<'b, Item = XX>`, the current object-lifetime default
1981 // would be to examine the trait `Foo` to check whether it has
1982 // a lifetime bound declared on `Item`. e.g., if `Foo` is
1983 // declared like so, then the default object lifetime bound in
1984 // `XX` should be `'b`:
1992 // but if we just have `type Item;`, then it would be
1993 // `'static`. However, we don't get all of this logic correct.
1995 // Instead, we do something hacky: if there are no lifetime parameters
1996 // to the trait, then we simply use a default object lifetime
1997 // bound of `'static`, because there is no other possibility. On the other hand,
1998 // if there ARE lifetime parameters, then we require the user to give an
1999 // explicit bound for now.
2001 // This is intended to leave room for us to implement the
2002 // correct behavior in the future.
2003 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
2004 GenericArg::Lifetime(_) => true,
2008 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2009 for b in generic_args.bindings {
2010 let scope = Scope::ObjectLifetimeDefault {
2011 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2014 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2018 fn visit_fn_like_elision(
2020 inputs: &'tcx [hir::Ty<'tcx>],
2021 output: Option<&'tcx hir::Ty<'tcx>>,
2023 debug!("visit_fn_like_elision: enter");
2024 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2025 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2026 self.with(arg_scope, |_, this| {
2027 for input in inputs {
2028 this.visit_ty(input);
2031 Scope::Elision { ref elide, .. } => {
2032 arg_elide = elide.clone();
2038 let output = match output {
2043 debug!("visit_fn_like_elision: determine output");
2045 // Figure out if there's a body we can get argument names from,
2046 // and whether there's a `self` argument (treated specially).
2047 let mut assoc_item_kind = None;
2048 let mut impl_self = None;
2049 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2050 let body = match self.tcx.hir().get(parent) {
2051 // `fn` definitions and methods.
2052 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2054 Node::TraitItem(&hir::TraitItem {
2055 kind: hir::TraitItemKind::Method(_, ref m), ..
2057 if let hir::ItemKind::Trait(.., ref trait_items) =
2058 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2061 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2064 hir::TraitMethod::Required(_) => None,
2065 hir::TraitMethod::Provided(body) => Some(body),
2069 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Method(_, body), .. }) => {
2070 if let hir::ItemKind::Impl { ref self_ty, ref items, .. } =
2071 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2073 impl_self = Some(self_ty);
2075 items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2080 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2081 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2082 // Everything else (only closures?) doesn't
2083 // actually enjoy elision in return types.
2085 self.visit_ty(output);
2090 let has_self = match assoc_item_kind {
2091 Some(hir::AssocItemKind::Method { has_self }) => has_self,
2095 // In accordance with the rules for lifetime elision, we can determine
2096 // what region to use for elision in the output type in two ways.
2097 // First (determined here), if `self` is by-reference, then the
2098 // implied output region is the region of the self parameter.
2100 struct SelfVisitor<'a> {
2101 map: &'a NamedRegionMap,
2102 impl_self: Option<&'a hir::TyKind<'a>>,
2103 lifetime: Set1<Region>,
2106 impl SelfVisitor<'_> {
2107 // Look for `self: &'a Self` - also desugared from `&'a self`,
2108 // and if that matches, use it for elision and return early.
2109 fn is_self_ty(&self, res: Res) -> bool {
2110 if let Res::SelfTy(..) = res {
2114 // Can't always rely on literal (or implied) `Self` due
2115 // to the way elision rules were originally specified.
2116 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2120 // Whitelist the types that unambiguously always
2121 // result in the same type constructor being used
2122 // (it can't differ between `Self` and `self`).
2123 Res::Def(DefKind::Struct, _)
2124 | Res::Def(DefKind::Union, _)
2125 | Res::Def(DefKind::Enum, _)
2126 | Res::PrimTy(_) => return res == path.res,
2135 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2138 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2139 NestedVisitorMap::None
2142 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2143 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2144 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2146 if self.is_self_ty(path.res) {
2147 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2148 self.lifetime.insert(*lifetime);
2153 intravisit::walk_ty(self, ty)
2157 let mut visitor = SelfVisitor {
2159 impl_self: impl_self.map(|ty| &ty.kind),
2160 lifetime: Set1::Empty,
2162 visitor.visit_ty(&inputs[0]);
2163 if let Set1::One(lifetime) = visitor.lifetime {
2164 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2165 self.with(scope, |_, this| this.visit_ty(output));
2170 // Second, if there was exactly one lifetime (either a substitution or a
2171 // reference) in the arguments, then any anonymous regions in the output
2172 // have that lifetime.
2173 let mut possible_implied_output_region = None;
2174 let mut lifetime_count = 0;
2175 let arg_lifetimes = inputs
2178 .skip(has_self as usize)
2180 let mut gather = GatherLifetimes {
2182 outer_index: ty::INNERMOST,
2183 have_bound_regions: false,
2184 lifetimes: Default::default(),
2186 gather.visit_ty(input);
2188 lifetime_count += gather.lifetimes.len();
2190 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2191 // there's a chance that the unique lifetime of this
2192 // iteration will be the appropriate lifetime for output
2193 // parameters, so lets store it.
2194 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2197 ElisionFailureInfo {
2200 lifetime_count: gather.lifetimes.len(),
2201 have_bound_regions: gather.have_bound_regions,
2206 let elide = if lifetime_count == 1 {
2207 Elide::Exact(possible_implied_output_region.unwrap())
2209 Elide::Error(arg_lifetimes)
2212 debug!("visit_fn_like_elision: elide={:?}", elide);
2214 let scope = Scope::Elision { elide, s: self.scope };
2215 self.with(scope, |_, this| this.visit_ty(output));
2216 debug!("visit_fn_like_elision: exit");
2218 struct GatherLifetimes<'a> {
2219 map: &'a NamedRegionMap,
2220 outer_index: ty::DebruijnIndex,
2221 have_bound_regions: bool,
2222 lifetimes: FxHashSet<Region>,
2225 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2228 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2229 NestedVisitorMap::None
2232 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2233 if let hir::TyKind::BareFn(_) = ty.kind {
2234 self.outer_index.shift_in(1);
2237 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2238 for bound in bounds {
2239 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2242 // Stay on the safe side and don't include the object
2243 // lifetime default (which may not end up being used).
2244 if !lifetime.is_elided() {
2245 self.visit_lifetime(lifetime);
2249 intravisit::walk_ty(self, ty);
2252 if let hir::TyKind::BareFn(_) = ty.kind {
2253 self.outer_index.shift_out(1);
2257 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2258 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2259 // FIXME(eddyb) Do we want this? It only makes a difference
2260 // if this `for<'a>` lifetime parameter is never used.
2261 self.have_bound_regions = true;
2264 intravisit::walk_generic_param(self, param);
2267 fn visit_poly_trait_ref(
2269 trait_ref: &hir::PolyTraitRef<'_>,
2270 modifier: hir::TraitBoundModifier,
2272 self.outer_index.shift_in(1);
2273 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2274 self.outer_index.shift_out(1);
2277 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2278 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2280 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2281 if debruijn < self.outer_index =>
2283 self.have_bound_regions = true;
2286 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2294 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2295 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2297 if lifetime_refs.is_empty() {
2301 let span = lifetime_refs[0].span;
2302 let mut late_depth = 0;
2303 let mut scope = self.scope;
2304 let mut lifetime_names = FxHashSet::default();
2307 // Do not assign any resolution, it will be inferred.
2308 Scope::Body { .. } => return,
2310 Scope::Root => break None,
2312 Scope::Binder { s, ref lifetimes, .. } => {
2313 // collect named lifetimes for suggestions
2314 for name in lifetimes.keys() {
2315 if let hir::ParamName::Plain(name) = name {
2316 lifetime_names.insert(*name);
2323 Scope::Elision { ref elide, ref s, .. } => {
2324 let lifetime = match *elide {
2325 Elide::FreshLateAnon(ref counter) => {
2326 for lifetime_ref in lifetime_refs {
2327 let lifetime = Region::late_anon(counter).shifted(late_depth);
2328 self.insert_lifetime(lifetime_ref, lifetime);
2332 Elide::Exact(l) => l.shifted(late_depth),
2333 Elide::Error(ref e) => {
2334 if let Scope::Binder { ref lifetimes, .. } = s {
2335 // collect named lifetimes for suggestions
2336 for name in lifetimes.keys() {
2337 if let hir::ParamName::Plain(name) = name {
2338 lifetime_names.insert(*name);
2345 for lifetime_ref in lifetime_refs {
2346 self.insert_lifetime(lifetime_ref, lifetime);
2351 Scope::ObjectLifetimeDefault { s, .. } => {
2357 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2358 let mut add_label = true;
2360 if let Some(params) = error {
2361 if lifetime_refs.len() == 1 {
2362 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2366 add_missing_lifetime_specifiers_label(
2369 lifetime_refs.len(),
2371 self.tcx.sess.source_map().span_to_snippet(span).ok().as_ref().map(|s| s.as_str()),
2378 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2379 match self.tcx.sess.source_map().span_to_snippet(span) {
2380 Ok(ref snippet) => {
2381 let (sugg, applicability) = if snippet == "&" {
2382 ("&'static ".to_owned(), Applicability::MachineApplicable)
2383 } else if snippet == "'_" {
2384 ("'static".to_owned(), Applicability::MachineApplicable)
2386 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2388 db.span_suggestion(span, msg, sugg, applicability);
2398 fn report_elision_failure(
2400 db: &mut DiagnosticBuilder<'_>,
2401 params: &[ElisionFailureInfo],
2404 let mut m = String::new();
2405 let len = params.len();
2407 let elided_params: Vec<_> =
2408 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2410 let elided_len = elided_params.len();
2412 for (i, info) in elided_params.into_iter().enumerate() {
2413 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions } = info;
2415 let help_name = if let Some(ident) =
2416 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2418 format!("`{}`", ident)
2420 format!("argument {}", index + 1)
2428 "one of {}'s {} {}lifetimes",
2431 if have_bound_regions { "free " } else { "" }
2436 if elided_len == 2 && i == 0 {
2438 } else if i + 2 == elided_len {
2439 m.push_str(", or ");
2440 } else if i != elided_len - 1 {
2447 "this function's return type contains a borrowed value, \
2448 but there is no value for it to be borrowed from",
2450 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2451 } else if elided_len == 0 {
2453 "this function's return type contains a borrowed value with \
2454 an elided lifetime, but the lifetime cannot be derived from \
2457 let msg = "consider giving it an explicit bounded or 'static lifetime";
2458 self.suggest_lifetime(db, span, msg)
2459 } else if elided_len == 1 {
2461 "this function's return type contains a borrowed value, \
2462 but the signature does not say which {} it is borrowed from",
2468 "this function's return type contains a borrowed value, \
2469 but the signature does not say whether it is borrowed from {}",
2476 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2477 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2478 let mut late_depth = 0;
2479 let mut scope = self.scope;
2480 let lifetime = loop {
2482 Scope::Binder { s, .. } => {
2487 Scope::Root | Scope::Elision { .. } => break Region::Static,
2489 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2491 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2494 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2497 fn check_lifetime_params(
2499 old_scope: ScopeRef<'_>,
2500 params: &'tcx [hir::GenericParam<'tcx>],
2502 let lifetimes: Vec<_> = params
2504 .filter_map(|param| match param.kind {
2505 GenericParamKind::Lifetime { .. } => Some((param, param.name.modern())),
2509 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2510 if let hir::ParamName::Plain(_) = lifetime_i_name {
2511 let name = lifetime_i_name.ident().name;
2512 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2513 let mut err = struct_span_err!(
2517 "invalid lifetime parameter name: `{}`",
2518 lifetime_i.name.ident(),
2522 format!("{} is a reserved lifetime name", name),
2528 // It is a hard error to shadow a lifetime within the same scope.
2529 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2530 if lifetime_i_name == lifetime_j_name {
2535 "lifetime name `{}` declared twice in the same scope",
2536 lifetime_j.name.ident()
2538 .span_label(lifetime_j.span, "declared twice")
2539 .span_label(lifetime_i.span, "previous declaration here")
2544 // It is a soft error to shadow a lifetime within a parent scope.
2545 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2547 for bound in lifetime_i.bounds {
2549 hir::GenericBound::Outlives(ref lt) => match lt.name {
2550 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2552 "use of `'_` in illegal place, but not caught by lowering",
2554 hir::LifetimeName::Static => {
2555 self.insert_lifetime(lt, Region::Static);
2559 lifetime_i.span.to(lt.span),
2561 "unnecessary lifetime parameter `{}`",
2562 lifetime_i.name.ident(),
2566 "you can use the `'static` lifetime directly, in place of `{}`",
2567 lifetime_i.name.ident(),
2571 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2572 self.resolve_lifetime_ref(lt);
2574 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2575 self.tcx.sess.delay_span_bug(
2577 "lowering generated `ImplicitObjectLifetimeDefault` \
2578 outside of an object type",
2581 hir::LifetimeName::Error => {
2582 // No need to do anything, error already reported.
2591 fn check_lifetime_param_for_shadowing(
2593 mut old_scope: ScopeRef<'_>,
2594 param: &'tcx hir::GenericParam<'tcx>,
2596 for label in &self.labels_in_fn {
2597 // FIXME (#24278): non-hygienic comparison
2598 if param.name.ident().name == label.name {
2599 signal_shadowing_problem(
2602 original_label(label.span),
2603 shadower_lifetime(¶m),
2611 Scope::Body { s, .. }
2612 | Scope::Elision { s, .. }
2613 | Scope::ObjectLifetimeDefault { s, .. } => {
2621 Scope::Binder { ref lifetimes, s, .. } => {
2622 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2623 let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
2625 signal_shadowing_problem(
2627 param.name.ident().name,
2628 original_lifetime(self.tcx.hir().span(hir_id)),
2629 shadower_lifetime(¶m),
2640 /// Returns `true` if, in the current scope, replacing `'_` would be
2641 /// equivalent to a single-use lifetime.
2642 fn track_lifetime_uses(&self) -> bool {
2643 let mut scope = self.scope;
2646 Scope::Root => break false,
2648 // Inside of items, it depends on the kind of item.
2649 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2651 // Inside a body, `'_` will use an inference variable,
2653 Scope::Body { .. } => break true,
2655 // A lifetime only used in a fn argument could as well
2656 // be replaced with `'_`, as that would generate a
2658 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2660 // In the return type or other such place, `'_` is not
2661 // going to make a fresh name, so we cannot
2662 // necessarily replace a single-use lifetime with
2664 Scope::Elision { elide: Elide::Exact(_), .. } => break false,
2665 Scope::Elision { elide: Elide::Error(_), .. } => break false,
2667 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2672 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2673 if lifetime_ref.hir_id == hir::DUMMY_HIR_ID {
2676 "lifetime reference not renumbered, \
2677 probably a bug in syntax::fold"
2682 "insert_lifetime: {} resolved to {:?} span={:?}",
2683 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2685 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2687 self.map.defs.insert(lifetime_ref.hir_id, def);
2690 Region::LateBoundAnon(..) | Region::Static => {
2691 // These are anonymous lifetimes or lifetimes that are not declared.
2694 Region::Free(_, def_id)
2695 | Region::LateBound(_, def_id, _)
2696 | Region::EarlyBound(_, def_id, _) => {
2697 // A lifetime declared by the user.
2698 let track_lifetime_uses = self.track_lifetime_uses();
2699 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2700 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2701 debug!("insert_lifetime: first use of {:?}", def_id);
2702 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2704 debug!("insert_lifetime: many uses of {:?}", def_id);
2705 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2711 /// Sometimes we resolve a lifetime, but later find that it is an
2712 /// error (esp. around impl trait). In that case, we remove the
2713 /// entry into `map.defs` so as not to confuse later code.
2714 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2715 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2716 assert_eq!(old_value, Some(bad_def));
2720 /// Detects late-bound lifetimes and inserts them into
2721 /// `map.late_bound`.
2723 /// A region declared on a fn is **late-bound** if:
2724 /// - it is constrained by an argument type;
2725 /// - it does not appear in a where-clause.
2727 /// "Constrained" basically means that it appears in any type but
2728 /// not amongst the inputs to a projection. In other words, `<&'a
2729 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2730 fn insert_late_bound_lifetimes(
2731 map: &mut NamedRegionMap,
2732 decl: &hir::FnDecl<'_>,
2733 generics: &hir::Generics<'_>,
2735 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2737 let mut constrained_by_input = ConstrainedCollector::default();
2738 for arg_ty in decl.inputs {
2739 constrained_by_input.visit_ty(arg_ty);
2742 let mut appears_in_output = AllCollector::default();
2743 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2745 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2747 // Walk the lifetimes that appear in where clauses.
2749 // Subtle point: because we disallow nested bindings, we can just
2750 // ignore binders here and scrape up all names we see.
2751 let mut appears_in_where_clause = AllCollector::default();
2752 appears_in_where_clause.visit_generics(generics);
2754 for param in generics.params {
2755 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2756 if !param.bounds.is_empty() {
2757 // `'a: 'b` means both `'a` and `'b` are referenced
2758 appears_in_where_clause
2760 .insert(hir::LifetimeName::Param(param.name.modern()));
2766 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2767 appears_in_where_clause.regions
2770 // Late bound regions are those that:
2771 // - appear in the inputs
2772 // - do not appear in the where-clauses
2773 // - are not implicitly captured by `impl Trait`
2774 for param in generics.params {
2776 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2778 // Neither types nor consts are late-bound.
2779 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2782 let lt_name = hir::LifetimeName::Param(param.name.modern());
2783 // appears in the where clauses? early-bound.
2784 if appears_in_where_clause.regions.contains(<_name) {
2788 // does not appear in the inputs, but appears in the return type? early-bound.
2789 if !constrained_by_input.regions.contains(<_name)
2790 && appears_in_output.regions.contains(<_name)
2796 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2801 let inserted = map.late_bound.insert(param.hir_id);
2802 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2808 struct ConstrainedCollector {
2809 regions: FxHashSet<hir::LifetimeName>,
2812 impl<'v> Visitor<'v> for ConstrainedCollector {
2815 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2816 NestedVisitorMap::None
2819 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2821 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2822 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2823 // ignore lifetimes appearing in associated type
2824 // projections, as they are not *constrained*
2828 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2829 // consider only the lifetimes on the final
2830 // segment; I am not sure it's even currently
2831 // valid to have them elsewhere, but even if it
2832 // is, those would be potentially inputs to
2834 if let Some(last_segment) = path.segments.last() {
2835 self.visit_path_segment(path.span, last_segment);
2840 intravisit::walk_ty(self, ty);
2845 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2846 self.regions.insert(lifetime_ref.name.modern());
2851 struct AllCollector {
2852 regions: FxHashSet<hir::LifetimeName>,
2855 impl<'v> Visitor<'v> for AllCollector {
2858 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2859 NestedVisitorMap::None
2862 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2863 self.regions.insert(lifetime_ref.name.modern());
2868 fn report_missing_lifetime_specifiers(
2872 ) -> DiagnosticBuilder<'_> {
2873 struct_span_err!(sess, span, E0106, "missing lifetime specifier{}", pluralize!(count))
2876 fn add_missing_lifetime_specifiers_label(
2877 err: &mut DiagnosticBuilder<'_>,
2880 lifetime_names: &FxHashSet<ast::Ident>,
2881 snippet: Option<&str>,
2884 err.span_label(span, format!("expected {} lifetime parameters", count));
2885 } else if let (1, Some(name), Some("&")) =
2886 (lifetime_names.len(), lifetime_names.iter().next(), snippet)
2888 err.span_suggestion(
2890 "consider using the named lifetime",
2891 format!("&{} ", name),
2892 Applicability::MaybeIncorrect,
2895 err.span_label(span, "expected lifetime parameter");