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 // This counts the no of times a lifetime is used
34 #[derive(Clone, Copy, Debug)]
35 pub enum LifetimeUseSet<'tcx> {
36 One(&'tcx hir::Lifetime),
41 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
43 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
45 fn late_anon(index: &Cell<u32>) -> Region;
47 fn id(&self) -> Option<DefId>;
49 fn shifted(self, amount: u32) -> Region;
51 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
53 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
55 L: Iterator<Item = &'a hir::Lifetime>;
58 impl RegionExt for Region {
59 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
62 let def_id = hir_map.local_def_id(param.hir_id);
63 let origin = LifetimeDefOrigin::from_param(param);
64 debug!("Region::early: index={} def_id={:?}", i, def_id);
65 (param.name.modern(), Region::EarlyBound(i, def_id, origin))
68 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) {
69 let depth = ty::INNERMOST;
70 let def_id = hir_map.local_def_id(param.hir_id);
71 let origin = LifetimeDefOrigin::from_param(param);
73 "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
74 param, depth, def_id, origin,
76 (param.name.modern(), Region::LateBound(depth, def_id, origin))
79 fn late_anon(index: &Cell<u32>) -> Region {
82 let depth = ty::INNERMOST;
83 Region::LateBoundAnon(depth, i)
86 fn id(&self) -> Option<DefId> {
88 Region::Static | Region::LateBoundAnon(..) => None,
90 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
96 fn shifted(self, amount: u32) -> Region {
98 Region::LateBound(debruijn, id, origin) => {
99 Region::LateBound(debruijn.shifted_in(amount), id, origin)
101 Region::LateBoundAnon(debruijn, index) => {
102 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
108 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
110 Region::LateBound(debruijn, id, origin) => {
111 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
113 Region::LateBoundAnon(debruijn, index) => {
114 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
120 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
122 L: Iterator<Item = &'a hir::Lifetime>,
124 if let Region::EarlyBound(index, _, _) = self {
125 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
132 /// Maps the id of each lifetime reference to the lifetime decl
133 /// that it corresponds to.
135 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
136 /// actual use. It has the same data, but indexed by `DefIndex`. This
139 struct NamedRegionMap {
140 // maps from every use of a named (not anonymous) lifetime to a
141 // `Region` describing how that region is bound
142 defs: HirIdMap<Region>,
144 // the set of lifetime def ids that are late-bound; a region can
145 // be late-bound if (a) it does NOT appear in a where-clause and
146 // (b) it DOES appear in the arguments.
147 late_bound: HirIdSet,
149 // For each type and trait definition, maps type parameters
150 // to the trait object lifetime defaults computed from them.
151 object_lifetime_defaults: HirIdMap<Vec<ObjectLifetimeDefault>>,
154 struct LifetimeContext<'a, 'tcx> {
156 map: &'a mut NamedRegionMap,
159 /// This is slightly complicated. Our representation for poly-trait-refs contains a single
160 /// binder and thus we only allow a single level of quantification. However,
161 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
162 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices
163 /// correct when representing these constraints, we should only introduce one
164 /// scope. However, we want to support both locations for the quantifier and
165 /// during lifetime resolution we want precise information (so we can't
166 /// desugar in an earlier phase).
168 /// So, if we encounter a quantifier at the outer scope, we set
169 /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter
170 /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`,
171 /// then we introduce the scope at the inner quantifier.
172 trait_ref_hack: bool,
174 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
175 is_in_fn_syntax: bool,
177 /// List of labels in the function/method currently under analysis.
178 labels_in_fn: Vec<ast::Ident>,
180 /// Cache for cross-crate per-definition object lifetime defaults.
181 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
183 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
188 /// Declares lifetimes, and each can be early-bound or late-bound.
189 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
190 /// it should be shifted by the number of `Binder`s in between the
191 /// declaration `Binder` and the location it's referenced from.
193 lifetimes: FxHashMap<hir::ParamName, Region>,
195 /// if we extend this scope with another scope, what is the next index
196 /// we should use for an early-bound region?
197 next_early_index: u32,
199 /// Flag is set to true if, in this binder, `'_` would be
200 /// equivalent to a "single-use region". This is true on
201 /// impls, but not other kinds of items.
202 track_lifetime_uses: bool,
204 /// Whether or not this binder would serve as the parent
205 /// binder for opaque types introduced within. For example:
208 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
211 /// Here, the opaque types we create for the `impl Trait`
212 /// and `impl Trait2` references will both have the `foo` item
213 /// as their parent. When we get to `impl Trait2`, we find
214 /// that it is nested within the `for<>` binder -- this flag
215 /// allows us to skip that when looking for the parent binder
216 /// of the resulting opaque type.
217 opaque_type_parent: bool,
222 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
223 /// if this is a fn body, otherwise the original definitions are used.
224 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
225 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
231 /// A scope which either determines unspecified lifetimes or errors
232 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
238 /// Use a specific lifetime (if `Some`) or leave it unset (to be
239 /// inferred in a function body or potentially error outside one),
240 /// for the default choice of lifetime in a trait object type.
241 ObjectLifetimeDefault {
242 lifetime: Option<Region>,
249 #[derive(Clone, Debug)]
251 /// Use a fresh anonymous late-bound lifetime each time, by
252 /// incrementing the counter to generate sequential indices.
253 FreshLateAnon(Cell<u32>),
254 /// Always use this one lifetime.
256 /// Less or more than one lifetime were found, error on unspecified.
257 Error(Vec<ElisionFailureInfo>),
260 #[derive(Clone, Debug)]
261 struct ElisionFailureInfo {
262 /// Where we can find the argument pattern.
263 parent: Option<hir::BodyId>,
264 /// The index of the argument in the original definition.
266 lifetime_count: usize,
267 have_bound_regions: bool,
270 type ScopeRef<'a> = &'a Scope<'a>;
272 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
274 pub fn provide(providers: &mut ty::query::Providers<'_>) {
275 *providers = ty::query::Providers {
278 named_region_map: |tcx, id| {
279 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
280 tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id)
283 is_late_bound_map: |tcx, id| {
284 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
285 tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id)
288 object_lifetime_defaults_map: |tcx, id| {
289 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
290 tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id)
296 // (*) FIXME the query should be defined to take a LocalDefId
299 /// Computes the `ResolveLifetimes` map that contains data for the
300 /// entire crate. You should not read the result of this query
301 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
303 fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> &ResolveLifetimes {
304 assert_eq!(for_krate, LOCAL_CRATE);
306 let named_region_map = krate(tcx);
308 let mut rl = ResolveLifetimes::default();
310 for (hir_id, v) in named_region_map.defs {
311 let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
312 map.insert(hir_id.local_id, v);
314 for hir_id in named_region_map.late_bound {
315 let map = rl.late_bound.entry(hir_id.owner_local_def_id()).or_default();
316 map.insert(hir_id.local_id);
318 for (hir_id, v) in named_region_map.object_lifetime_defaults {
319 let map = rl.object_lifetime_defaults.entry(hir_id.owner_local_def_id()).or_default();
320 map.insert(hir_id.local_id, v);
326 fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
327 let krate = tcx.hir().krate();
328 let mut map = NamedRegionMap {
329 defs: Default::default(),
330 late_bound: Default::default(),
331 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
334 let mut visitor = LifetimeContext {
338 trait_ref_hack: false,
339 is_in_fn_syntax: false,
340 labels_in_fn: vec![],
341 xcrate_object_lifetime_defaults: Default::default(),
342 lifetime_uses: &mut Default::default(),
344 for (_, item) in &krate.items {
345 visitor.visit_item(item);
351 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
352 /// We have to account for this when computing the index of the other generic parameters.
353 /// This function returns whether there is such an implicit parameter defined on the given item.
354 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
356 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true,
361 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
362 type Map = Map<'tcx>;
364 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
365 NestedVisitorMap::All(&self.tcx.hir())
368 // We want to nest trait/impl items in their parent, but nothing else.
369 fn visit_nested_item(&mut self, _: hir::ItemId) {}
371 fn visit_nested_body(&mut self, body: hir::BodyId) {
372 // Each body has their own set of labels, save labels.
373 let saved = take(&mut self.labels_in_fn);
374 let body = self.tcx.hir().body(body);
375 extract_labels(self, body);
376 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
377 this.visit_body(body);
379 replace(&mut self.labels_in_fn, saved);
382 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
384 hir::ItemKind::Fn(ref sig, ref generics, _) => {
385 self.visit_early_late(None, &sig.decl, generics, |this| {
386 intravisit::walk_item(this, item);
390 hir::ItemKind::ExternCrate(_)
391 | hir::ItemKind::Use(..)
392 | hir::ItemKind::Mod(..)
393 | hir::ItemKind::ForeignMod(..)
394 | hir::ItemKind::GlobalAsm(..) => {
395 // These sorts of items have no lifetime parameters at all.
396 intravisit::walk_item(self, item);
398 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
399 // No lifetime parameters, but implied 'static.
400 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
401 self.with(scope, |_, this| intravisit::walk_item(this, item));
403 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {
404 // Currently opaque type declarations are just generated from `impl Trait`
405 // items. Doing anything on this node is irrelevant, as we currently don't need
408 hir::ItemKind::TyAlias(_, ref generics)
409 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
410 impl_trait_fn: None, ref generics, ..
412 | hir::ItemKind::Enum(_, ref generics)
413 | hir::ItemKind::Struct(_, ref generics)
414 | hir::ItemKind::Union(_, ref generics)
415 | hir::ItemKind::Trait(_, _, ref generics, ..)
416 | hir::ItemKind::TraitAlias(ref generics, ..)
417 | hir::ItemKind::Impl { ref generics, .. } => {
418 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
419 // This is not true for other kinds of items.x
420 let track_lifetime_uses = match item.kind {
421 hir::ItemKind::Impl { .. } => true,
424 // These kinds of items have only early-bound lifetime parameters.
425 let mut index = if sub_items_have_self_param(&item.kind) {
426 1 // Self comes before lifetimes
430 let mut non_lifetime_count = 0;
431 let lifetimes = generics
434 .filter_map(|param| match param.kind {
435 GenericParamKind::Lifetime { .. } => {
436 Some(Region::early(&self.tcx.hir(), &mut index, param))
438 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
439 non_lifetime_count += 1;
444 let scope = Scope::Binder {
446 next_early_index: index + non_lifetime_count,
447 opaque_type_parent: true,
451 self.with(scope, |old_scope, this| {
452 this.check_lifetime_params(old_scope, &generics.params);
453 intravisit::walk_item(this, item);
459 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
461 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
462 self.visit_early_late(None, decl, generics, |this| {
463 intravisit::walk_foreign_item(this, item);
466 hir::ForeignItemKind::Static(..) => {
467 intravisit::walk_foreign_item(self, item);
469 hir::ForeignItemKind::Type => {
470 intravisit::walk_foreign_item(self, item);
475 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
476 debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty);
477 debug!("visit_ty: ty.kind={:?}", ty.kind);
479 hir::TyKind::BareFn(ref c) => {
480 let next_early_index = self.next_early_index();
481 let was_in_fn_syntax = self.is_in_fn_syntax;
482 self.is_in_fn_syntax = true;
483 let scope = Scope::Binder {
487 .filter_map(|param| match param.kind {
488 GenericParamKind::Lifetime { .. } => {
489 Some(Region::late(&self.tcx.hir(), param))
496 track_lifetime_uses: true,
497 opaque_type_parent: false,
499 self.with(scope, |old_scope, this| {
500 // a bare fn has no bounds, so everything
501 // contained within is scoped within its binder.
502 this.check_lifetime_params(old_scope, &c.generic_params);
503 intravisit::walk_ty(this, ty);
505 self.is_in_fn_syntax = was_in_fn_syntax;
507 hir::TyKind::TraitObject(bounds, ref lifetime) => {
508 debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime);
509 for bound in bounds {
510 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
512 match lifetime.name {
513 LifetimeName::Implicit => {
514 // For types like `dyn Foo`, we should
515 // generate a special form of elided.
516 span_bug!(ty.span, "object-lifetime-default expected, not implict",);
518 LifetimeName::ImplicitObjectLifetimeDefault => {
519 // If the user does not write *anything*, we
520 // use the object lifetime defaulting
521 // rules. So e.g., `Box<dyn Debug>` becomes
522 // `Box<dyn Debug + 'static>`.
523 self.resolve_object_lifetime_default(lifetime)
525 LifetimeName::Underscore => {
526 // If the user writes `'_`, we use the *ordinary* elision
527 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
528 // resolved the same as the `'_` in `&'_ Foo`.
531 self.resolve_elided_lifetimes(vec![lifetime])
533 LifetimeName::Param(_) | LifetimeName::Static => {
534 // If the user wrote an explicit name, use that.
535 self.visit_lifetime(lifetime);
537 LifetimeName::Error => {}
540 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
541 self.visit_lifetime(lifetime_ref);
542 let scope = Scope::ObjectLifetimeDefault {
543 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
546 self.with(scope, |_, this| this.visit_ty(&mt.ty));
548 hir::TyKind::Def(item_id, lifetimes) => {
549 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
550 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
551 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
552 // ^ ^ this gets resolved in the scope of
553 // the opaque_ty generics
554 let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).kind {
555 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
556 // This arm is for `impl Trait` in the types of statics, constants and locals.
557 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
558 intravisit::walk_ty(self, ty);
561 // RPIT (return position impl trait)
562 hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, bounds, .. }) => {
565 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
568 // Resolve the lifetimes that are applied to the opaque type.
569 // These are resolved in the current scope.
570 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
571 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
572 // ^ ^this gets resolved in the current scope
573 for lifetime in lifetimes {
574 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
575 self.visit_lifetime(lifetime);
577 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
578 // and ban them. Type variables instantiated inside binders aren't
579 // well-supported at the moment, so this doesn't work.
580 // In the future, this should be fixed and this error should be removed.
581 let def = self.map.defs.get(&lifetime.hir_id).cloned();
582 if let Some(Region::LateBound(_, def_id, _)) = def {
583 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
584 // Ensure that the parent of the def is an item, not HRTB
585 let parent_id = self.tcx.hir().get_parent_node(hir_id);
586 let parent_impl_id = hir::ImplItemId { hir_id: parent_id };
587 let parent_trait_id = hir::TraitItemId { hir_id: parent_id };
588 let krate = self.tcx.hir().forest.krate();
590 if !(krate.items.contains_key(&parent_id)
591 || krate.impl_items.contains_key(&parent_impl_id)
592 || krate.trait_items.contains_key(&parent_trait_id))
598 "`impl Trait` can only capture lifetimes \
599 bound at the fn or impl level"
602 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
609 // We want to start our early-bound indices at the end of the parent scope,
610 // not including any parent `impl Trait`s.
611 let mut index = self.next_early_index_for_opaque_type();
612 debug!("visit_ty: index = {}", index);
614 let mut elision = None;
615 let mut lifetimes = FxHashMap::default();
616 let mut non_lifetime_count = 0;
617 for param in generics.params {
619 GenericParamKind::Lifetime { .. } => {
620 let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m);
621 let def_id = if let Region::EarlyBound(_, def_id, _) = reg {
626 if let hir::ParamName::Plain(param_name) = name {
627 if param_name.name == kw::UnderscoreLifetime {
628 // Pick the elided lifetime "definition" if one exists
629 // and use it to make an elision scope.
630 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
633 lifetimes.insert(name, reg);
636 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
637 lifetimes.insert(name, reg);
640 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
641 non_lifetime_count += 1;
645 let next_early_index = index + non_lifetime_count;
647 if let Some(elision_region) = elision {
649 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
650 self.with(scope, |_old_scope, this| {
651 let scope = Scope::Binder {
655 track_lifetime_uses: true,
656 opaque_type_parent: false,
658 this.with(scope, |_old_scope, this| {
659 this.visit_generics(generics);
660 for bound in bounds {
661 this.visit_param_bound(bound);
666 let scope = Scope::Binder {
670 track_lifetime_uses: true,
671 opaque_type_parent: false,
673 self.with(scope, |_old_scope, this| {
674 this.visit_generics(generics);
675 for bound in bounds {
676 this.visit_param_bound(bound);
681 _ => intravisit::walk_ty(self, ty),
685 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
686 use self::hir::TraitItemKind::*;
687 match trait_item.kind {
688 Method(ref sig, _) => {
690 self.visit_early_late(
691 Some(tcx.hir().get_parent_item(trait_item.hir_id)),
693 &trait_item.generics,
694 |this| intravisit::walk_trait_item(this, trait_item),
697 Type(bounds, ref ty) => {
698 let generics = &trait_item.generics;
699 let mut index = self.next_early_index();
700 debug!("visit_ty: index = {}", index);
701 let mut non_lifetime_count = 0;
702 let lifetimes = generics
705 .filter_map(|param| match param.kind {
706 GenericParamKind::Lifetime { .. } => {
707 Some(Region::early(&self.tcx.hir(), &mut index, param))
709 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
710 non_lifetime_count += 1;
715 let scope = Scope::Binder {
717 next_early_index: index + non_lifetime_count,
719 track_lifetime_uses: true,
720 opaque_type_parent: true,
722 self.with(scope, |_old_scope, this| {
723 this.visit_generics(generics);
724 for bound in bounds {
725 this.visit_param_bound(bound);
727 if let Some(ty) = ty {
733 // Only methods and types support generics.
734 assert!(trait_item.generics.params.is_empty());
735 intravisit::walk_trait_item(self, trait_item);
740 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
741 use self::hir::ImplItemKind::*;
742 match impl_item.kind {
743 Method(ref sig, _) => {
745 self.visit_early_late(
746 Some(tcx.hir().get_parent_item(impl_item.hir_id)),
749 |this| intravisit::walk_impl_item(this, impl_item),
753 let generics = &impl_item.generics;
754 let mut index = self.next_early_index();
755 let mut non_lifetime_count = 0;
756 debug!("visit_ty: index = {}", index);
757 let lifetimes = generics
760 .filter_map(|param| match param.kind {
761 GenericParamKind::Lifetime { .. } => {
762 Some(Region::early(&self.tcx.hir(), &mut index, param))
764 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
765 non_lifetime_count += 1;
770 let scope = Scope::Binder {
772 next_early_index: index + non_lifetime_count,
774 track_lifetime_uses: true,
775 opaque_type_parent: true,
777 self.with(scope, |_old_scope, this| {
778 this.visit_generics(generics);
782 OpaqueTy(bounds) => {
783 let generics = &impl_item.generics;
784 let mut index = self.next_early_index();
785 let mut next_early_index = index;
786 debug!("visit_ty: index = {}", index);
787 let lifetimes = generics
790 .filter_map(|param| match param.kind {
791 GenericParamKind::Lifetime { .. } => {
792 Some(Region::early(&self.tcx.hir(), &mut index, param))
794 GenericParamKind::Type { .. } => {
795 next_early_index += 1;
798 GenericParamKind::Const { .. } => {
799 next_early_index += 1;
805 let scope = Scope::Binder {
809 track_lifetime_uses: true,
810 opaque_type_parent: true,
812 self.with(scope, |_old_scope, this| {
813 this.visit_generics(generics);
814 for bound in bounds {
815 this.visit_param_bound(bound);
820 // Only methods and types support generics.
821 assert!(impl_item.generics.params.is_empty());
822 intravisit::walk_impl_item(self, impl_item);
827 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
828 debug!("visit_lifetime(lifetime_ref={:?})", lifetime_ref);
829 if lifetime_ref.is_elided() {
830 self.resolve_elided_lifetimes(vec![lifetime_ref]);
833 if lifetime_ref.is_static() {
834 self.insert_lifetime(lifetime_ref, Region::Static);
837 self.resolve_lifetime_ref(lifetime_ref);
840 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
841 for (i, segment) in path.segments.iter().enumerate() {
842 let depth = path.segments.len() - i - 1;
843 if let Some(ref args) = segment.args {
844 self.visit_segment_args(path.res, depth, args);
849 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
850 let output = match fd.output {
851 hir::FunctionRetTy::DefaultReturn(_) => None,
852 hir::FunctionRetTy::Return(ref ty) => Some(&**ty),
854 self.visit_fn_like_elision(&fd.inputs, output);
857 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
858 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
859 for param in generics.params {
861 GenericParamKind::Lifetime { .. } => {}
862 GenericParamKind::Type { ref default, .. } => {
863 walk_list!(self, visit_param_bound, param.bounds);
864 if let Some(ref ty) = default {
868 GenericParamKind::Const { ref ty, .. } => {
869 walk_list!(self, visit_param_bound, param.bounds);
874 for predicate in generics.where_clause.predicates {
876 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
879 ref bound_generic_params,
882 let lifetimes: FxHashMap<_, _> = bound_generic_params
884 .filter_map(|param| match param.kind {
885 GenericParamKind::Lifetime { .. } => {
886 Some(Region::late(&self.tcx.hir(), param))
891 if !lifetimes.is_empty() {
892 self.trait_ref_hack = true;
893 let next_early_index = self.next_early_index();
894 let scope = Scope::Binder {
898 track_lifetime_uses: true,
899 opaque_type_parent: false,
901 let result = self.with(scope, |old_scope, this| {
902 this.check_lifetime_params(old_scope, &bound_generic_params);
903 this.visit_ty(&bounded_ty);
904 walk_list!(this, visit_param_bound, bounds);
906 self.trait_ref_hack = false;
909 self.visit_ty(&bounded_ty);
910 walk_list!(self, visit_param_bound, bounds);
913 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
918 self.visit_lifetime(lifetime);
919 walk_list!(self, visit_param_bound, bounds);
921 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
926 self.visit_ty(lhs_ty);
927 self.visit_ty(rhs_ty);
933 fn visit_poly_trait_ref(
935 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
936 _modifier: hir::TraitBoundModifier,
938 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
940 if !self.trait_ref_hack
941 || trait_ref.bound_generic_params.iter().any(|param| match param.kind {
942 GenericParamKind::Lifetime { .. } => true,
946 if self.trait_ref_hack {
951 "nested quantification of lifetimes"
955 let next_early_index = self.next_early_index();
956 let scope = Scope::Binder {
958 .bound_generic_params
960 .filter_map(|param| match param.kind {
961 GenericParamKind::Lifetime { .. } => {
962 Some(Region::late(&self.tcx.hir(), param))
969 track_lifetime_uses: true,
970 opaque_type_parent: false,
972 self.with(scope, |old_scope, this| {
973 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
974 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
975 this.visit_trait_ref(&trait_ref.trait_ref)
978 self.visit_trait_ref(&trait_ref.trait_ref)
983 #[derive(Copy, Clone, PartialEq)]
997 fn original_label(span: Span) -> Original {
998 Original { kind: ShadowKind::Label, span: span }
1000 fn shadower_label(span: Span) -> Shadower {
1001 Shadower { kind: ShadowKind::Label, span: span }
1003 fn original_lifetime(span: Span) -> Original {
1004 Original { kind: ShadowKind::Lifetime, span: span }
1006 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1007 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1011 fn desc(&self) -> &'static str {
1013 ShadowKind::Label => "label",
1014 ShadowKind::Lifetime => "lifetime",
1019 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1020 let lifetime_params: Vec<_> = params
1022 .filter_map(|param| match param.kind {
1023 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1027 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1028 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1030 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1035 "cannot mix in-band and explicit lifetime definitions"
1037 .span_label(*in_band_span, "in-band lifetime definition here")
1038 .span_label(*explicit_span, "explicit lifetime definition here")
1043 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: ast::Name, orig: Original, shadower: Shadower) {
1044 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1045 // lifetime/lifetime shadowing is an error
1050 "{} name `{}` shadows a \
1051 {} name that is already in scope",
1052 shadower.kind.desc(),
1057 // shadowing involving a label is only a warning, due to issues with
1058 // labels and lifetimes not being macro-hygienic.
1059 tcx.sess.struct_span_warn(
1062 "{} name `{}` shadows a \
1063 {} name that is already in scope",
1064 shadower.kind.desc(),
1070 err.span_label(orig.span, "first declared here");
1071 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1075 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1076 // if one of the label shadows a lifetime or another label.
1077 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1078 struct GatherLabels<'a, 'tcx> {
1080 scope: ScopeRef<'a>,
1081 labels_in_fn: &'a mut Vec<ast::Ident>,
1085 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1086 gather.visit_body(body);
1088 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1091 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1092 NestedVisitorMap::None
1095 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1096 if let Some(label) = expression_label(ex) {
1097 for prior_label in &self.labels_in_fn[..] {
1098 // FIXME (#24278): non-hygienic comparison
1099 if label.name == prior_label.name {
1100 signal_shadowing_problem(
1103 original_label(prior_label.span),
1104 shadower_label(label.span),
1109 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1111 self.labels_in_fn.push(label);
1113 intravisit::walk_expr(self, ex)
1117 fn expression_label(ex: &hir::Expr<'_>) -> Option<ast::Ident> {
1118 if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None }
1121 fn check_if_label_shadows_lifetime(
1123 mut scope: ScopeRef<'_>,
1128 Scope::Body { s, .. }
1129 | Scope::Elision { s, .. }
1130 | Scope::ObjectLifetimeDefault { s, .. } => {
1138 Scope::Binder { ref lifetimes, s, .. } => {
1139 // FIXME (#24278): non-hygienic comparison
1140 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1141 let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
1143 signal_shadowing_problem(
1146 original_lifetime(tcx.hir().span(hir_id)),
1147 shadower_label(label.span),
1158 fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap<Vec<ObjectLifetimeDefault>> {
1159 let mut map = HirIdMap::default();
1160 for item in tcx.hir().krate().items.values() {
1162 hir::ItemKind::Struct(_, ref generics)
1163 | hir::ItemKind::Union(_, ref generics)
1164 | hir::ItemKind::Enum(_, ref generics)
1165 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1166 ref generics, impl_trait_fn: None, ..
1168 | hir::ItemKind::TyAlias(_, ref generics)
1169 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1170 let result = object_lifetime_defaults_for_item(tcx, generics);
1173 if attr::contains_name(&item.attrs, sym::rustc_object_lifetime_default) {
1174 let object_lifetime_default_reprs: String = result
1176 .map(|set| match *set {
1177 Set1::Empty => "BaseDefault".into(),
1178 Set1::One(Region::Static) => "'static".into(),
1179 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1182 .find_map(|param| match param.kind {
1183 GenericParamKind::Lifetime { .. } => {
1185 return Some(param.name.ident().to_string().into());
1193 Set1::One(_) => bug!(),
1194 Set1::Many => "Ambiguous".into(),
1196 .collect::<Vec<Cow<'static, str>>>()
1198 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1201 map.insert(item.hir_id, result);
1209 /// Scan the bounds and where-clauses on parameters to extract bounds
1210 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1211 /// for each type parameter.
1212 fn object_lifetime_defaults_for_item(
1214 generics: &hir::Generics<'_>,
1215 ) -> Vec<ObjectLifetimeDefault> {
1216 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1217 for bound in bounds {
1218 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1219 set.insert(lifetime.name.modern());
1227 .filter_map(|param| match param.kind {
1228 GenericParamKind::Lifetime { .. } => None,
1229 GenericParamKind::Type { .. } => {
1230 let mut set = Set1::Empty;
1232 add_bounds(&mut set, ¶m.bounds);
1234 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1235 for predicate in generics.where_clause.predicates {
1236 // Look for `type: ...` where clauses.
1237 let data = match *predicate {
1238 hir::WherePredicate::BoundPredicate(ref data) => data,
1242 // Ignore `for<'a> type: ...` as they can change what
1243 // lifetimes mean (although we could "just" handle it).
1244 if !data.bound_generic_params.is_empty() {
1248 let res = match data.bounded_ty.kind {
1249 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1253 if res == Res::Def(DefKind::TyParam, param_def_id) {
1254 add_bounds(&mut set, &data.bounds);
1259 Set1::Empty => Set1::Empty,
1260 Set1::One(name) => {
1261 if name == hir::LifetimeName::Static {
1262 Set1::One(Region::Static)
1267 .filter_map(|param| match param.kind {
1268 GenericParamKind::Lifetime { .. } => Some((
1270 hir::LifetimeName::Param(param.name),
1271 LifetimeDefOrigin::from_param(param),
1276 .find(|&(_, (_, lt_name, _))| lt_name == name)
1277 .map_or(Set1::Many, |(i, (id, _, origin))| {
1278 let def_id = tcx.hir().local_def_id(id);
1279 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1283 Set1::Many => Set1::Many,
1286 GenericParamKind::Const { .. } => {
1287 // Generic consts don't impose any constraints.
1294 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1295 // FIXME(#37666) this works around a limitation in the region inferencer
1296 fn hack<F>(&mut self, f: F)
1298 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1303 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1305 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1307 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1308 let labels_in_fn = take(&mut self.labels_in_fn);
1309 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1310 let mut this = LifetimeContext {
1314 trait_ref_hack: self.trait_ref_hack,
1315 is_in_fn_syntax: self.is_in_fn_syntax,
1317 xcrate_object_lifetime_defaults,
1318 lifetime_uses: lifetime_uses,
1320 debug!("entering scope {:?}", this.scope);
1321 f(self.scope, &mut this);
1322 this.check_uses_for_lifetimes_defined_by_scope();
1323 debug!("exiting scope {:?}", this.scope);
1324 self.labels_in_fn = this.labels_in_fn;
1325 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1328 /// helper method to determine the span to remove when suggesting the
1329 /// deletion of a lifetime
1330 fn lifetime_deletion_span(
1333 generics: &hir::Generics<'_>,
1335 generics.params.iter().enumerate().find_map(|(i, param)| {
1336 if param.name.ident() == name {
1337 let mut in_band = false;
1338 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1339 if let hir::LifetimeParamKind::InBand = kind {
1346 if generics.params.len() == 1 {
1347 // if sole lifetime, remove the entire `<>` brackets
1350 // if removing within `<>` brackets, we also want to
1351 // delete a leading or trailing comma as appropriate
1352 if i >= generics.params.len() - 1 {
1353 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1355 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1365 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1366 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1367 fn suggest_eliding_single_use_lifetime(
1369 err: &mut DiagnosticBuilder<'_>,
1371 lifetime: &hir::Lifetime,
1373 let name = lifetime.name.ident();
1374 let mut remove_decl = None;
1375 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1376 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1377 remove_decl = self.lifetime_deletion_span(name, generics);
1381 let mut remove_use = None;
1382 let mut elide_use = None;
1383 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1384 for input in inputs {
1386 hir::TyKind::Rptr(lt, _) => {
1387 if lt.name.ident() == name {
1388 // include the trailing whitespace between the lifetime and type names
1389 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1394 .span_until_non_whitespace(lt_through_ty_span),
1399 hir::TyKind::Path(ref qpath) => {
1400 if let QPath::Resolved(_, path) = qpath {
1401 let last_segment = &path.segments[path.segments.len() - 1];
1402 let generics = last_segment.generic_args();
1403 for arg in generics.args.iter() {
1404 if let GenericArg::Lifetime(lt) = arg {
1405 if lt.name.ident() == name {
1406 elide_use = Some(lt.span);
1418 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1419 if let Some(parent) =
1420 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1423 Node::Item(item) => {
1424 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1425 find_arg_use_span(sig.decl.inputs);
1428 Node::ImplItem(impl_item) => {
1429 if let hir::ImplItemKind::Method(sig, _) = &impl_item.kind {
1430 find_arg_use_span(sig.decl.inputs);
1438 let msg = "elide the single-use lifetime";
1439 match (remove_decl, remove_use, elide_use) {
1440 (Some(decl_span), Some(use_span), None) => {
1441 // if both declaration and use deletion spans start at the same
1442 // place ("start at" because the latter includes trailing
1443 // whitespace), then this is an in-band lifetime
1444 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1445 err.span_suggestion(
1449 Applicability::MachineApplicable,
1452 err.multipart_suggestion(
1454 vec![(decl_span, String::new()), (use_span, String::new())],
1455 Applicability::MachineApplicable,
1459 (Some(decl_span), None, Some(use_span)) => {
1460 err.multipart_suggestion(
1462 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1463 Applicability::MachineApplicable,
1470 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1471 let defined_by = match self.scope {
1472 Scope::Binder { lifetimes, .. } => lifetimes,
1474 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1479 let mut def_ids: Vec<_> = defined_by
1481 .flat_map(|region| match region {
1482 Region::EarlyBound(_, def_id, _)
1483 | Region::LateBound(_, def_id, _)
1484 | Region::Free(_, def_id) => Some(*def_id),
1486 Region::LateBoundAnon(..) | Region::Static => None,
1490 // ensure that we issue lints in a repeatable order
1491 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1493 for def_id in def_ids {
1494 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1496 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1499 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1503 match lifetimeuseset {
1504 Some(LifetimeUseSet::One(lifetime)) => {
1505 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1506 debug!("hir id first={:?}", hir_id);
1507 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1508 Node::Lifetime(hir_lifetime) => Some((
1509 hir_lifetime.hir_id,
1511 hir_lifetime.name.ident(),
1513 Node::GenericParam(param) => {
1514 Some((param.hir_id, param.span, param.name.ident()))
1518 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1519 if name.name == kw::UnderscoreLifetime {
1523 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1524 if let Some(parent_hir_id) =
1525 self.tcx.hir().as_local_hir_id(parent_def_id)
1527 // lifetimes in `derive` expansions don't count (Issue #53738)
1531 .attrs(parent_hir_id)
1533 .any(|attr| attr.check_name(sym::automatically_derived))
1540 let mut err = self.tcx.struct_span_lint_hir(
1541 lint::builtin::SINGLE_USE_LIFETIMES,
1544 &format!("lifetime parameter `{}` only used once", name),
1547 if span == lifetime.span {
1548 // spans are the same for in-band lifetime declarations
1549 err.span_label(span, "this lifetime is only used here");
1551 err.span_label(span, "this lifetime...");
1552 err.span_label(lifetime.span, "...is used only here");
1554 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1558 Some(LifetimeUseSet::Many) => {
1559 debug!("not one use lifetime");
1562 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1563 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1564 Node::Lifetime(hir_lifetime) => Some((
1565 hir_lifetime.hir_id,
1567 hir_lifetime.name.ident(),
1569 Node::GenericParam(param) => {
1570 Some((param.hir_id, param.span, param.name.ident()))
1574 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1575 let mut err = self.tcx.struct_span_lint_hir(
1576 lint::builtin::UNUSED_LIFETIMES,
1579 &format!("lifetime parameter `{}` never used", name),
1581 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1582 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1583 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1584 if let Some(span) = unused_lt_span {
1585 err.span_suggestion(
1587 "elide the unused lifetime",
1589 Applicability::MachineApplicable,
1601 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1603 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1604 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1605 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1609 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1611 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1612 /// lifetimes may be interspersed together.
1614 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1615 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1616 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1617 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1618 /// ordering is not important there.
1619 fn visit_early_late<F>(
1621 parent_id: Option<hir::HirId>,
1622 decl: &'tcx hir::FnDecl<'tcx>,
1623 generics: &'tcx hir::Generics<'tcx>,
1626 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1628 insert_late_bound_lifetimes(self.map, decl, generics);
1630 // Find the start of nested early scopes, e.g., in methods.
1632 if let Some(parent_id) = parent_id {
1633 let parent = self.tcx.hir().expect_item(parent_id);
1634 if sub_items_have_self_param(&parent.kind) {
1635 index += 1; // Self comes before lifetimes
1638 hir::ItemKind::Trait(_, _, ref generics, ..)
1639 | hir::ItemKind::Impl { ref generics, .. } => {
1640 index += generics.params.len() as u32;
1646 let mut non_lifetime_count = 0;
1647 let lifetimes = generics
1650 .filter_map(|param| match param.kind {
1651 GenericParamKind::Lifetime { .. } => {
1652 if self.map.late_bound.contains(¶m.hir_id) {
1653 Some(Region::late(&self.tcx.hir(), param))
1655 Some(Region::early(&self.tcx.hir(), &mut index, param))
1658 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1659 non_lifetime_count += 1;
1664 let next_early_index = index + non_lifetime_count;
1666 let scope = Scope::Binder {
1670 opaque_type_parent: true,
1671 track_lifetime_uses: false,
1673 self.with(scope, move |old_scope, this| {
1674 this.check_lifetime_params(old_scope, &generics.params);
1675 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1679 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1680 let mut scope = self.scope;
1683 Scope::Root => return 0,
1685 Scope::Binder { next_early_index, opaque_type_parent, .. }
1686 if (!only_opaque_type_parent || opaque_type_parent) =>
1688 return next_early_index;
1691 Scope::Binder { s, .. }
1692 | Scope::Body { s, .. }
1693 | Scope::Elision { s, .. }
1694 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1699 /// Returns the next index one would use for an early-bound-region
1700 /// if extending the current scope.
1701 fn next_early_index(&self) -> u32 {
1702 self.next_early_index_helper(true)
1705 /// Returns the next index one would use for an `impl Trait` that
1706 /// is being converted into an opaque type alias `impl Trait`. This will be the
1707 /// next early index from the enclosing item, for the most
1708 /// part. See the `opaque_type_parent` field for more info.
1709 fn next_early_index_for_opaque_type(&self) -> u32 {
1710 self.next_early_index_helper(false)
1713 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1714 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1716 // If we've already reported an error, just ignore `lifetime_ref`.
1717 if let LifetimeName::Error = lifetime_ref.name {
1721 // Walk up the scope chain, tracking the number of fn scopes
1722 // that we pass through, until we find a lifetime with the
1723 // given name or we run out of scopes.
1725 let mut late_depth = 0;
1726 let mut scope = self.scope;
1727 let mut outermost_body = None;
1730 Scope::Body { id, s } => {
1731 outermost_body = Some(id);
1739 Scope::Binder { ref lifetimes, s, .. } => {
1740 match lifetime_ref.name {
1741 LifetimeName::Param(param_name) => {
1742 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1743 break Some(def.shifted(late_depth));
1746 _ => bug!("expected LifetimeName::Param"),
1753 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1759 if let Some(mut def) = result {
1760 if let Region::EarlyBound(..) = def {
1761 // Do not free early-bound regions, only late-bound ones.
1762 } else if let Some(body_id) = outermost_body {
1763 let fn_id = self.tcx.hir().body_owner(body_id);
1764 match self.tcx.hir().get(fn_id) {
1765 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1766 | Node::TraitItem(&hir::TraitItem {
1767 kind: hir::TraitItemKind::Method(..),
1770 | Node::ImplItem(&hir::ImplItem {
1771 kind: hir::ImplItemKind::Method(..), ..
1773 let scope = self.tcx.hir().local_def_id(fn_id);
1774 def = Region::Free(scope, def.id().unwrap());
1780 // Check for fn-syntax conflicts with in-band lifetime definitions
1781 if self.is_in_fn_syntax {
1783 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1784 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1789 "lifetimes used in `fn` or `Fn` syntax must be \
1790 explicitly declared using `<...>` binders"
1792 .span_label(lifetime_ref.span, "in-band lifetime definition")
1797 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1798 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1799 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1800 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1801 | Region::LateBoundAnon(..)
1802 | Region::Free(..) => {}
1806 self.insert_lifetime(lifetime_ref, def);
1812 "use of undeclared lifetime name `{}`",
1815 .span_label(lifetime_ref.span, "undeclared lifetime")
1820 fn visit_segment_args(
1824 generic_args: &'tcx hir::GenericArgs<'tcx>,
1827 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1828 res, depth, generic_args,
1831 if generic_args.parenthesized {
1832 let was_in_fn_syntax = self.is_in_fn_syntax;
1833 self.is_in_fn_syntax = true;
1834 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1835 self.is_in_fn_syntax = was_in_fn_syntax;
1839 let mut elide_lifetimes = true;
1840 let lifetimes = generic_args
1843 .filter_map(|arg| match arg {
1844 hir::GenericArg::Lifetime(lt) => {
1845 if !lt.is_elided() {
1846 elide_lifetimes = false;
1853 if elide_lifetimes {
1854 self.resolve_elided_lifetimes(lifetimes);
1856 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1859 // Figure out if this is a type/trait segment,
1860 // which requires object lifetime defaults.
1861 let parent_def_id = |this: &mut Self, def_id: DefId| {
1862 let def_key = this.tcx.def_key(def_id);
1863 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1865 let type_def_id = match res {
1866 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1867 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1868 Res::Def(DefKind::Struct, def_id)
1869 | Res::Def(DefKind::Union, def_id)
1870 | Res::Def(DefKind::Enum, def_id)
1871 | Res::Def(DefKind::TyAlias, def_id)
1872 | Res::Def(DefKind::Trait, def_id)
1880 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1882 // Compute a vector of defaults, one for each type parameter,
1883 // per the rules given in RFCs 599 and 1156. Example:
1886 // struct Foo<'a, T: 'a, U> { }
1889 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1890 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1891 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1894 // Therefore, we would compute `object_lifetime_defaults` to a
1895 // vector like `['x, 'static]`. Note that the vector only
1896 // includes type parameters.
1897 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1899 let mut scope = self.scope;
1902 Scope::Root => break false,
1904 Scope::Body { .. } => break true,
1906 Scope::Binder { s, .. }
1907 | Scope::Elision { s, .. }
1908 | Scope::ObjectLifetimeDefault { s, .. } => {
1915 let map = &self.map;
1916 let unsubst = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
1917 &map.object_lifetime_defaults[&id]
1920 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1921 tcx.generics_of(def_id)
1924 .filter_map(|param| match param.kind {
1925 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1926 Some(object_lifetime_default)
1928 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1933 debug!("visit_segment_args: unsubst={:?}", unsubst);
1936 .map(|set| match *set {
1941 Some(Region::Static)
1945 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1946 GenericArg::Lifetime(lt) => Some(lt),
1949 r.subst(lifetimes, map)
1956 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1959 for arg in generic_args.args {
1961 GenericArg::Lifetime(_) => {}
1962 GenericArg::Type(ty) => {
1963 if let Some(<) = object_lifetime_defaults.get(i) {
1964 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1965 self.with(scope, |_, this| this.visit_ty(ty));
1971 GenericArg::Const(ct) => {
1972 self.visit_anon_const(&ct.value);
1977 // Hack: when resolving the type `XX` in binding like `dyn
1978 // Foo<'b, Item = XX>`, the current object-lifetime default
1979 // would be to examine the trait `Foo` to check whether it has
1980 // a lifetime bound declared on `Item`. e.g., if `Foo` is
1981 // declared like so, then the default object lifetime bound in
1982 // `XX` should be `'b`:
1990 // but if we just have `type Item;`, then it would be
1991 // `'static`. However, we don't get all of this logic correct.
1993 // Instead, we do something hacky: if there are no lifetime parameters
1994 // to the trait, then we simply use a default object lifetime
1995 // bound of `'static`, because there is no other possibility. On the other hand,
1996 // if there ARE lifetime parameters, then we require the user to give an
1997 // explicit bound for now.
1999 // This is intended to leave room for us to implement the
2000 // correct behavior in the future.
2001 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
2002 GenericArg::Lifetime(_) => true,
2006 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2007 for b in generic_args.bindings {
2008 let scope = Scope::ObjectLifetimeDefault {
2009 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2012 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2016 fn visit_fn_like_elision(
2018 inputs: &'tcx [hir::Ty<'tcx>],
2019 output: Option<&'tcx hir::Ty<'tcx>>,
2021 debug!("visit_fn_like_elision: enter");
2022 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2023 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2024 self.with(arg_scope, |_, this| {
2025 for input in inputs {
2026 this.visit_ty(input);
2029 Scope::Elision { ref elide, .. } => {
2030 arg_elide = elide.clone();
2036 let output = match output {
2041 debug!("visit_fn_like_elision: determine output");
2043 // Figure out if there's a body we can get argument names from,
2044 // and whether there's a `self` argument (treated specially).
2045 let mut assoc_item_kind = None;
2046 let mut impl_self = None;
2047 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2048 let body = match self.tcx.hir().get(parent) {
2049 // `fn` definitions and methods.
2050 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2052 Node::TraitItem(&hir::TraitItem {
2053 kind: hir::TraitItemKind::Method(_, ref m), ..
2055 if let hir::ItemKind::Trait(.., ref trait_items) =
2056 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2059 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2062 hir::TraitMethod::Required(_) => None,
2063 hir::TraitMethod::Provided(body) => Some(body),
2067 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Method(_, body), .. }) => {
2068 if let hir::ItemKind::Impl { ref self_ty, ref items, .. } =
2069 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2071 impl_self = Some(self_ty);
2073 items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2078 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2079 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2080 // Everything else (only closures?) doesn't
2081 // actually enjoy elision in return types.
2083 self.visit_ty(output);
2088 let has_self = match assoc_item_kind {
2089 Some(hir::AssocItemKind::Method { has_self }) => has_self,
2093 // In accordance with the rules for lifetime elision, we can determine
2094 // what region to use for elision in the output type in two ways.
2095 // First (determined here), if `self` is by-reference, then the
2096 // implied output region is the region of the self parameter.
2098 struct SelfVisitor<'a> {
2099 map: &'a NamedRegionMap,
2100 impl_self: Option<&'a hir::TyKind<'a>>,
2101 lifetime: Set1<Region>,
2104 impl SelfVisitor<'_> {
2105 // Look for `self: &'a Self` - also desugared from `&'a self`,
2106 // and if that matches, use it for elision and return early.
2107 fn is_self_ty(&self, res: Res) -> bool {
2108 if let Res::SelfTy(..) = res {
2112 // Can't always rely on literal (or implied) `Self` due
2113 // to the way elision rules were originally specified.
2114 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2118 // Whitelist the types that unambiguously always
2119 // result in the same type constructor being used
2120 // (it can't differ between `Self` and `self`).
2121 Res::Def(DefKind::Struct, _)
2122 | Res::Def(DefKind::Union, _)
2123 | Res::Def(DefKind::Enum, _)
2124 | Res::PrimTy(_) => return res == path.res,
2133 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2136 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2137 NestedVisitorMap::None
2140 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2141 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2142 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2144 if self.is_self_ty(path.res) {
2145 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2146 self.lifetime.insert(*lifetime);
2151 intravisit::walk_ty(self, ty)
2155 let mut visitor = SelfVisitor {
2157 impl_self: impl_self.map(|ty| &ty.kind),
2158 lifetime: Set1::Empty,
2160 visitor.visit_ty(&inputs[0]);
2161 if let Set1::One(lifetime) = visitor.lifetime {
2162 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2163 self.with(scope, |_, this| this.visit_ty(output));
2168 // Second, if there was exactly one lifetime (either a substitution or a
2169 // reference) in the arguments, then any anonymous regions in the output
2170 // have that lifetime.
2171 let mut possible_implied_output_region = None;
2172 let mut lifetime_count = 0;
2173 let arg_lifetimes = inputs
2176 .skip(has_self as usize)
2178 let mut gather = GatherLifetimes {
2180 outer_index: ty::INNERMOST,
2181 have_bound_regions: false,
2182 lifetimes: Default::default(),
2184 gather.visit_ty(input);
2186 lifetime_count += gather.lifetimes.len();
2188 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2189 // there's a chance that the unique lifetime of this
2190 // iteration will be the appropriate lifetime for output
2191 // parameters, so lets store it.
2192 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2195 ElisionFailureInfo {
2198 lifetime_count: gather.lifetimes.len(),
2199 have_bound_regions: gather.have_bound_regions,
2204 let elide = if lifetime_count == 1 {
2205 Elide::Exact(possible_implied_output_region.unwrap())
2207 Elide::Error(arg_lifetimes)
2210 debug!("visit_fn_like_elision: elide={:?}", elide);
2212 let scope = Scope::Elision { elide, s: self.scope };
2213 self.with(scope, |_, this| this.visit_ty(output));
2214 debug!("visit_fn_like_elision: exit");
2216 struct GatherLifetimes<'a> {
2217 map: &'a NamedRegionMap,
2218 outer_index: ty::DebruijnIndex,
2219 have_bound_regions: bool,
2220 lifetimes: FxHashSet<Region>,
2223 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2226 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2227 NestedVisitorMap::None
2230 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2231 if let hir::TyKind::BareFn(_) = ty.kind {
2232 self.outer_index.shift_in(1);
2235 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2236 for bound in bounds {
2237 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2240 // Stay on the safe side and don't include the object
2241 // lifetime default (which may not end up being used).
2242 if !lifetime.is_elided() {
2243 self.visit_lifetime(lifetime);
2247 intravisit::walk_ty(self, ty);
2250 if let hir::TyKind::BareFn(_) = ty.kind {
2251 self.outer_index.shift_out(1);
2255 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2256 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2257 // FIXME(eddyb) Do we want this? It only makes a difference
2258 // if this `for<'a>` lifetime parameter is never used.
2259 self.have_bound_regions = true;
2262 intravisit::walk_generic_param(self, param);
2265 fn visit_poly_trait_ref(
2267 trait_ref: &hir::PolyTraitRef<'_>,
2268 modifier: hir::TraitBoundModifier,
2270 self.outer_index.shift_in(1);
2271 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2272 self.outer_index.shift_out(1);
2275 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2276 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2278 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2279 if debruijn < self.outer_index =>
2281 self.have_bound_regions = true;
2284 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2292 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2293 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2295 if lifetime_refs.is_empty() {
2299 let span = lifetime_refs[0].span;
2300 let mut late_depth = 0;
2301 let mut scope = self.scope;
2302 let mut lifetime_names = FxHashSet::default();
2305 // Do not assign any resolution, it will be inferred.
2306 Scope::Body { .. } => return,
2308 Scope::Root => break None,
2310 Scope::Binder { s, ref lifetimes, .. } => {
2311 // collect named lifetimes for suggestions
2312 for name in lifetimes.keys() {
2313 if let hir::ParamName::Plain(name) = name {
2314 lifetime_names.insert(*name);
2321 Scope::Elision { ref elide, ref s, .. } => {
2322 let lifetime = match *elide {
2323 Elide::FreshLateAnon(ref counter) => {
2324 for lifetime_ref in lifetime_refs {
2325 let lifetime = Region::late_anon(counter).shifted(late_depth);
2326 self.insert_lifetime(lifetime_ref, lifetime);
2330 Elide::Exact(l) => l.shifted(late_depth),
2331 Elide::Error(ref e) => {
2332 if let Scope::Binder { ref lifetimes, .. } = s {
2333 // collect named lifetimes for suggestions
2334 for name in lifetimes.keys() {
2335 if let hir::ParamName::Plain(name) = name {
2336 lifetime_names.insert(*name);
2343 for lifetime_ref in lifetime_refs {
2344 self.insert_lifetime(lifetime_ref, lifetime);
2349 Scope::ObjectLifetimeDefault { s, .. } => {
2355 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2356 let mut add_label = true;
2358 if let Some(params) = error {
2359 if lifetime_refs.len() == 1 {
2360 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2364 add_missing_lifetime_specifiers_label(
2367 lifetime_refs.len(),
2369 self.tcx.sess.source_map().span_to_snippet(span).ok().as_ref().map(|s| s.as_str()),
2376 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2377 match self.tcx.sess.source_map().span_to_snippet(span) {
2378 Ok(ref snippet) => {
2379 let (sugg, applicability) = if snippet == "&" {
2380 ("&'static ".to_owned(), Applicability::MachineApplicable)
2381 } else if snippet == "'_" {
2382 ("'static".to_owned(), Applicability::MachineApplicable)
2384 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2386 db.span_suggestion(span, msg, sugg, applicability);
2396 fn report_elision_failure(
2398 db: &mut DiagnosticBuilder<'_>,
2399 params: &[ElisionFailureInfo],
2402 let mut m = String::new();
2403 let len = params.len();
2405 let elided_params: Vec<_> =
2406 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2408 let elided_len = elided_params.len();
2410 for (i, info) in elided_params.into_iter().enumerate() {
2411 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions } = info;
2413 let help_name = if let Some(ident) =
2414 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2416 format!("`{}`", ident)
2418 format!("argument {}", index + 1)
2426 "one of {}'s {} {}lifetimes",
2429 if have_bound_regions { "free " } else { "" }
2434 if elided_len == 2 && i == 0 {
2436 } else if i + 2 == elided_len {
2437 m.push_str(", or ");
2438 } else if i != elided_len - 1 {
2445 "this function's return type contains a borrowed value, \
2446 but there is no value for it to be borrowed from",
2448 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2449 } else if elided_len == 0 {
2451 "this function's return type contains a borrowed value with \
2452 an elided lifetime, but the lifetime cannot be derived from \
2455 let msg = "consider giving it an explicit bounded or 'static lifetime";
2456 self.suggest_lifetime(db, span, msg)
2457 } else if elided_len == 1 {
2459 "this function's return type contains a borrowed value, \
2460 but the signature does not say which {} it is borrowed from",
2466 "this function's return type contains a borrowed value, \
2467 but the signature does not say whether it is borrowed from {}",
2474 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2475 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2476 let mut late_depth = 0;
2477 let mut scope = self.scope;
2478 let lifetime = loop {
2480 Scope::Binder { s, .. } => {
2485 Scope::Root | Scope::Elision { .. } => break Region::Static,
2487 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2489 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2492 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2495 fn check_lifetime_params(
2497 old_scope: ScopeRef<'_>,
2498 params: &'tcx [hir::GenericParam<'tcx>],
2500 let lifetimes: Vec<_> = params
2502 .filter_map(|param| match param.kind {
2503 GenericParamKind::Lifetime { .. } => Some((param, param.name.modern())),
2507 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2508 if let hir::ParamName::Plain(_) = lifetime_i_name {
2509 let name = lifetime_i_name.ident().name;
2510 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2511 let mut err = struct_span_err!(
2515 "invalid lifetime parameter name: `{}`",
2516 lifetime_i.name.ident(),
2520 format!("{} is a reserved lifetime name", name),
2526 // It is a hard error to shadow a lifetime within the same scope.
2527 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2528 if lifetime_i_name == lifetime_j_name {
2533 "lifetime name `{}` declared twice in the same scope",
2534 lifetime_j.name.ident()
2536 .span_label(lifetime_j.span, "declared twice")
2537 .span_label(lifetime_i.span, "previous declaration here")
2542 // It is a soft error to shadow a lifetime within a parent scope.
2543 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2545 for bound in lifetime_i.bounds {
2547 hir::GenericBound::Outlives(ref lt) => match lt.name {
2548 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2550 "use of `'_` in illegal place, but not caught by lowering",
2552 hir::LifetimeName::Static => {
2553 self.insert_lifetime(lt, Region::Static);
2557 lifetime_i.span.to(lt.span),
2559 "unnecessary lifetime parameter `{}`",
2560 lifetime_i.name.ident(),
2564 "you can use the `'static` lifetime directly, in place of `{}`",
2565 lifetime_i.name.ident(),
2569 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2570 self.resolve_lifetime_ref(lt);
2572 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2573 self.tcx.sess.delay_span_bug(
2575 "lowering generated `ImplicitObjectLifetimeDefault` \
2576 outside of an object type",
2579 hir::LifetimeName::Error => {
2580 // No need to do anything, error already reported.
2589 fn check_lifetime_param_for_shadowing(
2591 mut old_scope: ScopeRef<'_>,
2592 param: &'tcx hir::GenericParam<'tcx>,
2594 for label in &self.labels_in_fn {
2595 // FIXME (#24278): non-hygienic comparison
2596 if param.name.ident().name == label.name {
2597 signal_shadowing_problem(
2600 original_label(label.span),
2601 shadower_lifetime(¶m),
2609 Scope::Body { s, .. }
2610 | Scope::Elision { s, .. }
2611 | Scope::ObjectLifetimeDefault { s, .. } => {
2619 Scope::Binder { ref lifetimes, s, .. } => {
2620 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2621 let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
2623 signal_shadowing_problem(
2625 param.name.ident().name,
2626 original_lifetime(self.tcx.hir().span(hir_id)),
2627 shadower_lifetime(¶m),
2638 /// Returns `true` if, in the current scope, replacing `'_` would be
2639 /// equivalent to a single-use lifetime.
2640 fn track_lifetime_uses(&self) -> bool {
2641 let mut scope = self.scope;
2644 Scope::Root => break false,
2646 // Inside of items, it depends on the kind of item.
2647 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2649 // Inside a body, `'_` will use an inference variable,
2651 Scope::Body { .. } => break true,
2653 // A lifetime only used in a fn argument could as well
2654 // be replaced with `'_`, as that would generate a
2656 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2658 // In the return type or other such place, `'_` is not
2659 // going to make a fresh name, so we cannot
2660 // necessarily replace a single-use lifetime with
2662 Scope::Elision { elide: Elide::Exact(_), .. } => break false,
2663 Scope::Elision { elide: Elide::Error(_), .. } => break false,
2665 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2670 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2671 if lifetime_ref.hir_id == hir::DUMMY_HIR_ID {
2674 "lifetime reference not renumbered, \
2675 probably a bug in syntax::fold"
2680 "insert_lifetime: {} resolved to {:?} span={:?}",
2681 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2683 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2685 self.map.defs.insert(lifetime_ref.hir_id, def);
2688 Region::LateBoundAnon(..) | Region::Static => {
2689 // These are anonymous lifetimes or lifetimes that are not declared.
2692 Region::Free(_, def_id)
2693 | Region::LateBound(_, def_id, _)
2694 | Region::EarlyBound(_, def_id, _) => {
2695 // A lifetime declared by the user.
2696 let track_lifetime_uses = self.track_lifetime_uses();
2697 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2698 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2699 debug!("insert_lifetime: first use of {:?}", def_id);
2700 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2702 debug!("insert_lifetime: many uses of {:?}", def_id);
2703 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2709 /// Sometimes we resolve a lifetime, but later find that it is an
2710 /// error (esp. around impl trait). In that case, we remove the
2711 /// entry into `map.defs` so as not to confuse later code.
2712 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2713 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2714 assert_eq!(old_value, Some(bad_def));
2718 /// Detects late-bound lifetimes and inserts them into
2719 /// `map.late_bound`.
2721 /// A region declared on a fn is **late-bound** if:
2722 /// - it is constrained by an argument type;
2723 /// - it does not appear in a where-clause.
2725 /// "Constrained" basically means that it appears in any type but
2726 /// not amongst the inputs to a projection. In other words, `<&'a
2727 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2728 fn insert_late_bound_lifetimes(
2729 map: &mut NamedRegionMap,
2730 decl: &hir::FnDecl<'_>,
2731 generics: &hir::Generics<'_>,
2733 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2735 let mut constrained_by_input = ConstrainedCollector::default();
2736 for arg_ty in decl.inputs {
2737 constrained_by_input.visit_ty(arg_ty);
2740 let mut appears_in_output = AllCollector::default();
2741 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2743 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2745 // Walk the lifetimes that appear in where clauses.
2747 // Subtle point: because we disallow nested bindings, we can just
2748 // ignore binders here and scrape up all names we see.
2749 let mut appears_in_where_clause = AllCollector::default();
2750 appears_in_where_clause.visit_generics(generics);
2752 for param in generics.params {
2753 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2754 if !param.bounds.is_empty() {
2755 // `'a: 'b` means both `'a` and `'b` are referenced
2756 appears_in_where_clause
2758 .insert(hir::LifetimeName::Param(param.name.modern()));
2764 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2765 appears_in_where_clause.regions
2768 // Late bound regions are those that:
2769 // - appear in the inputs
2770 // - do not appear in the where-clauses
2771 // - are not implicitly captured by `impl Trait`
2772 for param in generics.params {
2774 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2776 // Neither types nor consts are late-bound.
2777 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2780 let lt_name = hir::LifetimeName::Param(param.name.modern());
2781 // appears in the where clauses? early-bound.
2782 if appears_in_where_clause.regions.contains(<_name) {
2786 // does not appear in the inputs, but appears in the return type? early-bound.
2787 if !constrained_by_input.regions.contains(<_name)
2788 && appears_in_output.regions.contains(<_name)
2794 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2799 let inserted = map.late_bound.insert(param.hir_id);
2800 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2806 struct ConstrainedCollector {
2807 regions: FxHashSet<hir::LifetimeName>,
2810 impl<'v> Visitor<'v> for ConstrainedCollector {
2813 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2814 NestedVisitorMap::None
2817 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2819 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2820 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2821 // ignore lifetimes appearing in associated type
2822 // projections, as they are not *constrained*
2826 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2827 // consider only the lifetimes on the final
2828 // segment; I am not sure it's even currently
2829 // valid to have them elsewhere, but even if it
2830 // is, those would be potentially inputs to
2832 if let Some(last_segment) = path.segments.last() {
2833 self.visit_path_segment(path.span, last_segment);
2838 intravisit::walk_ty(self, ty);
2843 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2844 self.regions.insert(lifetime_ref.name.modern());
2849 struct AllCollector {
2850 regions: FxHashSet<hir::LifetimeName>,
2853 impl<'v> Visitor<'v> for AllCollector {
2856 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2857 NestedVisitorMap::None
2860 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2861 self.regions.insert(lifetime_ref.name.modern());
2866 fn report_missing_lifetime_specifiers(
2870 ) -> DiagnosticBuilder<'_> {
2871 struct_span_err!(sess, span, E0106, "missing lifetime specifier{}", pluralize!(count))
2874 fn add_missing_lifetime_specifiers_label(
2875 err: &mut DiagnosticBuilder<'_>,
2878 lifetime_names: &FxHashSet<ast::Ident>,
2879 snippet: Option<&str>,
2882 err.span_label(span, format!("expected {} lifetime parameters", count));
2883 } else if let (1, Some(name), Some("&")) =
2884 (lifetime_names.len(), lifetime_names.iter().next(), snippet)
2886 err.span_suggestion(
2888 "consider using the named lifetime",
2889 format!("&{} ", name),
2890 Applicability::MaybeIncorrect,
2893 err.span_label(span, "expected lifetime parameter");