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::def::{DefKind, Res};
9 use rustc::hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
10 use rustc::hir::map::Map;
11 use rustc::hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
12 use rustc::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
14 use errors::{pluralize, Applicability, DiagnosticBuilder};
16 use rustc::session::Session;
17 use rustc::util::nodemap::{DefIdMap, FxHashMap, FxHashSet, HirIdMap, HirIdSet};
18 use rustc_span::symbol::{kw, sym};
22 use std::mem::{replace, take};
26 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
27 use rustc::hir::{self, GenericParamKind, LifetimeParamKind};
30 use rustc::{bug, span_bug};
31 use syntax::{help, span_err, struct_span_err, walk_list};
33 use rustc::middle::resolve_lifetime::*;
34 use rustc_error_codes::*;
36 // This counts the no of times a lifetime is used
37 #[derive(Clone, Copy, Debug)]
38 pub enum LifetimeUseSet<'tcx> {
39 One(&'tcx hir::Lifetime),
44 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
46 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
48 fn late_anon(index: &Cell<u32>) -> Region;
50 fn id(&self) -> Option<DefId>;
52 fn shifted(self, amount: u32) -> Region;
54 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
56 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
58 L: Iterator<Item = &'a hir::Lifetime>;
61 impl RegionExt for Region {
62 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
65 let def_id = hir_map.local_def_id(param.hir_id);
66 let origin = LifetimeDefOrigin::from_param(param);
67 debug!("Region::early: index={} def_id={:?}", i, def_id);
68 (param.name.modern(), Region::EarlyBound(i, def_id, origin))
71 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) {
72 let depth = ty::INNERMOST;
73 let def_id = hir_map.local_def_id(param.hir_id);
74 let origin = LifetimeDefOrigin::from_param(param);
76 "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
77 param, depth, def_id, origin,
79 (param.name.modern(), Region::LateBound(depth, def_id, origin))
82 fn late_anon(index: &Cell<u32>) -> Region {
85 let depth = ty::INNERMOST;
86 Region::LateBoundAnon(depth, i)
89 fn id(&self) -> Option<DefId> {
91 Region::Static | Region::LateBoundAnon(..) => None,
93 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
99 fn shifted(self, amount: u32) -> Region {
101 Region::LateBound(debruijn, id, origin) => {
102 Region::LateBound(debruijn.shifted_in(amount), id, origin)
104 Region::LateBoundAnon(debruijn, index) => {
105 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
111 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
113 Region::LateBound(debruijn, id, origin) => {
114 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
116 Region::LateBoundAnon(debruijn, index) => {
117 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
123 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
125 L: Iterator<Item = &'a hir::Lifetime>,
127 if let Region::EarlyBound(index, _, _) = self {
128 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
135 /// Maps the id of each lifetime reference to the lifetime decl
136 /// that it corresponds to.
138 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
139 /// actual use. It has the same data, but indexed by `DefIndex`. This
142 struct NamedRegionMap {
143 // maps from every use of a named (not anonymous) lifetime to a
144 // `Region` describing how that region is bound
145 defs: HirIdMap<Region>,
147 // the set of lifetime def ids that are late-bound; a region can
148 // be late-bound if (a) it does NOT appear in a where-clause and
149 // (b) it DOES appear in the arguments.
150 late_bound: HirIdSet,
152 // For each type and trait definition, maps type parameters
153 // to the trait object lifetime defaults computed from them.
154 object_lifetime_defaults: HirIdMap<Vec<ObjectLifetimeDefault>>,
157 struct LifetimeContext<'a, 'tcx> {
159 map: &'a mut NamedRegionMap,
162 /// This is slightly complicated. Our representation for poly-trait-refs contains a single
163 /// binder and thus we only allow a single level of quantification. However,
164 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
165 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices
166 /// correct when representing these constraints, we should only introduce one
167 /// scope. However, we want to support both locations for the quantifier and
168 /// during lifetime resolution we want precise information (so we can't
169 /// desugar in an earlier phase).
171 /// So, if we encounter a quantifier at the outer scope, we set
172 /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter
173 /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`,
174 /// then we introduce the scope at the inner quantifier.
175 trait_ref_hack: bool,
177 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
178 is_in_fn_syntax: bool,
180 /// List of labels in the function/method currently under analysis.
181 labels_in_fn: Vec<ast::Ident>,
183 /// Cache for cross-crate per-definition object lifetime defaults.
184 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
186 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
191 /// Declares lifetimes, and each can be early-bound or late-bound.
192 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
193 /// it should be shifted by the number of `Binder`s in between the
194 /// declaration `Binder` and the location it's referenced from.
196 lifetimes: FxHashMap<hir::ParamName, Region>,
198 /// if we extend this scope with another scope, what is the next index
199 /// we should use for an early-bound region?
200 next_early_index: u32,
202 /// Flag is set to true if, in this binder, `'_` would be
203 /// equivalent to a "single-use region". This is true on
204 /// impls, but not other kinds of items.
205 track_lifetime_uses: bool,
207 /// Whether or not this binder would serve as the parent
208 /// binder for opaque types introduced within. For example:
211 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
214 /// Here, the opaque types we create for the `impl Trait`
215 /// and `impl Trait2` references will both have the `foo` item
216 /// as their parent. When we get to `impl Trait2`, we find
217 /// that it is nested within the `for<>` binder -- this flag
218 /// allows us to skip that when looking for the parent binder
219 /// of the resulting opaque type.
220 opaque_type_parent: bool,
225 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
226 /// if this is a fn body, otherwise the original definitions are used.
227 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
228 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
234 /// A scope which either determines unspecified lifetimes or errors
235 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
241 /// Use a specific lifetime (if `Some`) or leave it unset (to be
242 /// inferred in a function body or potentially error outside one),
243 /// for the default choice of lifetime in a trait object type.
244 ObjectLifetimeDefault {
245 lifetime: Option<Region>,
252 #[derive(Clone, Debug)]
254 /// Use a fresh anonymous late-bound lifetime each time, by
255 /// incrementing the counter to generate sequential indices.
256 FreshLateAnon(Cell<u32>),
257 /// Always use this one lifetime.
259 /// Less or more than one lifetime were found, error on unspecified.
260 Error(Vec<ElisionFailureInfo>),
263 #[derive(Clone, Debug)]
264 struct ElisionFailureInfo {
265 /// Where we can find the argument pattern.
266 parent: Option<hir::BodyId>,
267 /// The index of the argument in the original definition.
269 lifetime_count: usize,
270 have_bound_regions: bool,
273 type ScopeRef<'a> = &'a Scope<'a>;
275 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
277 pub fn provide(providers: &mut ty::query::Providers<'_>) {
278 *providers = ty::query::Providers {
281 named_region_map: |tcx, id| {
282 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
283 tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id)
286 is_late_bound_map: |tcx, id| {
287 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
288 tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id)
291 object_lifetime_defaults_map: |tcx, id| {
292 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
293 tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id)
299 // (*) FIXME the query should be defined to take a LocalDefId
302 /// Computes the `ResolveLifetimes` map that contains data for the
303 /// entire crate. You should not read the result of this query
304 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
306 fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> &ResolveLifetimes {
307 assert_eq!(for_krate, LOCAL_CRATE);
309 let named_region_map = krate(tcx);
311 let mut rl = ResolveLifetimes::default();
313 for (hir_id, v) in named_region_map.defs {
314 let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
315 map.insert(hir_id.local_id, v);
317 for hir_id in named_region_map.late_bound {
318 let map = rl.late_bound.entry(hir_id.owner_local_def_id()).or_default();
319 map.insert(hir_id.local_id);
321 for (hir_id, v) in named_region_map.object_lifetime_defaults {
322 let map = rl.object_lifetime_defaults.entry(hir_id.owner_local_def_id()).or_default();
323 map.insert(hir_id.local_id, v);
329 fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
330 let krate = tcx.hir().krate();
331 let mut map = NamedRegionMap {
332 defs: Default::default(),
333 late_bound: Default::default(),
334 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
337 let mut visitor = LifetimeContext {
341 trait_ref_hack: false,
342 is_in_fn_syntax: false,
343 labels_in_fn: vec![],
344 xcrate_object_lifetime_defaults: Default::default(),
345 lifetime_uses: &mut Default::default(),
347 for (_, item) in &krate.items {
348 visitor.visit_item(item);
354 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
355 /// We have to account for this when computing the index of the other generic parameters.
356 /// This function returns whether there is such an implicit parameter defined on the given item.
357 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
359 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true,
364 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
365 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
366 NestedVisitorMap::All(&self.tcx.hir())
369 // We want to nest trait/impl items in their parent, but nothing else.
370 fn visit_nested_item(&mut self, _: hir::ItemId) {}
372 fn visit_nested_body(&mut self, body: hir::BodyId) {
373 // Each body has their own set of labels, save labels.
374 let saved = take(&mut self.labels_in_fn);
375 let body = self.tcx.hir().body(body);
376 extract_labels(self, body);
377 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
378 this.visit_body(body);
380 replace(&mut self.labels_in_fn, saved);
383 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
385 hir::ItemKind::Fn(ref sig, ref generics, _) => {
386 self.visit_early_late(None, &sig.decl, generics, |this| {
387 intravisit::walk_item(this, item);
391 hir::ItemKind::ExternCrate(_)
392 | hir::ItemKind::Use(..)
393 | hir::ItemKind::Mod(..)
394 | hir::ItemKind::ForeignMod(..)
395 | hir::ItemKind::GlobalAsm(..) => {
396 // These sorts of items have no lifetime parameters at all.
397 intravisit::walk_item(self, item);
399 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
400 // No lifetime parameters, but implied 'static.
401 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
402 self.with(scope, |_, this| intravisit::walk_item(this, item));
404 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {
405 // Currently opaque type declarations are just generated from `impl Trait`
406 // items. Doing anything on this node is irrelevant, as we currently don't need
409 hir::ItemKind::TyAlias(_, ref generics)
410 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
411 impl_trait_fn: None, ref generics, ..
413 | hir::ItemKind::Enum(_, ref generics)
414 | hir::ItemKind::Struct(_, ref generics)
415 | hir::ItemKind::Union(_, ref generics)
416 | hir::ItemKind::Trait(_, _, ref generics, ..)
417 | hir::ItemKind::TraitAlias(ref generics, ..)
418 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
419 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
420 // This is not true for other kinds of items.x
421 let track_lifetime_uses = match item.kind {
422 hir::ItemKind::Impl(..) => true,
425 // These kinds of items have only early-bound lifetime parameters.
426 let mut index = if sub_items_have_self_param(&item.kind) {
427 1 // Self comes before lifetimes
431 let mut non_lifetime_count = 0;
432 let lifetimes = generics
435 .filter_map(|param| match param.kind {
436 GenericParamKind::Lifetime { .. } => {
437 Some(Region::early(&self.tcx.hir(), &mut index, param))
439 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
440 non_lifetime_count += 1;
445 let scope = Scope::Binder {
447 next_early_index: index + non_lifetime_count,
448 opaque_type_parent: true,
452 self.with(scope, |old_scope, this| {
453 this.check_lifetime_params(old_scope, &generics.params);
454 intravisit::walk_item(this, item);
460 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
462 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
463 self.visit_early_late(None, decl, generics, |this| {
464 intravisit::walk_foreign_item(this, item);
467 hir::ForeignItemKind::Static(..) => {
468 intravisit::walk_foreign_item(self, item);
470 hir::ForeignItemKind::Type => {
471 intravisit::walk_foreign_item(self, item);
476 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
477 debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty);
478 debug!("visit_ty: ty.kind={:?}", ty.kind);
480 hir::TyKind::BareFn(ref c) => {
481 let next_early_index = self.next_early_index();
482 let was_in_fn_syntax = self.is_in_fn_syntax;
483 self.is_in_fn_syntax = true;
484 let scope = Scope::Binder {
488 .filter_map(|param| match param.kind {
489 GenericParamKind::Lifetime { .. } => {
490 Some(Region::late(&self.tcx.hir(), param))
497 track_lifetime_uses: true,
498 opaque_type_parent: false,
500 self.with(scope, |old_scope, this| {
501 // a bare fn has no bounds, so everything
502 // contained within is scoped within its binder.
503 this.check_lifetime_params(old_scope, &c.generic_params);
504 intravisit::walk_ty(this, ty);
506 self.is_in_fn_syntax = was_in_fn_syntax;
508 hir::TyKind::TraitObject(bounds, ref lifetime) => {
509 debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime);
510 for bound in bounds {
511 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
513 match lifetime.name {
514 LifetimeName::Implicit => {
515 // For types like `dyn Foo`, we should
516 // generate a special form of elided.
517 span_bug!(ty.span, "object-lifetime-default expected, not implict",);
519 LifetimeName::ImplicitObjectLifetimeDefault => {
520 // If the user does not write *anything*, we
521 // use the object lifetime defaulting
522 // rules. So e.g., `Box<dyn Debug>` becomes
523 // `Box<dyn Debug + 'static>`.
524 self.resolve_object_lifetime_default(lifetime)
526 LifetimeName::Underscore => {
527 // If the user writes `'_`, we use the *ordinary* elision
528 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
529 // resolved the same as the `'_` in `&'_ Foo`.
532 self.resolve_elided_lifetimes(vec![lifetime])
534 LifetimeName::Param(_) | LifetimeName::Static => {
535 // If the user wrote an explicit name, use that.
536 self.visit_lifetime(lifetime);
538 LifetimeName::Error => {}
541 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
542 self.visit_lifetime(lifetime_ref);
543 let scope = Scope::ObjectLifetimeDefault {
544 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
547 self.with(scope, |_, this| this.visit_ty(&mt.ty));
549 hir::TyKind::Def(item_id, lifetimes) => {
550 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
551 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
552 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
553 // ^ ^ this gets resolved in the scope of
554 // the opaque_ty generics
555 let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).kind {
556 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
557 // This arm is for `impl Trait` in the types of statics, constants and locals.
558 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
559 intravisit::walk_ty(self, ty);
562 // RPIT (return position impl trait)
563 hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, bounds, .. }) => {
566 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
569 // Resolve the lifetimes that are applied to the opaque type.
570 // These are resolved in the current scope.
571 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
572 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
573 // ^ ^this gets resolved in the current scope
574 for lifetime in lifetimes {
575 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
576 self.visit_lifetime(lifetime);
578 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
579 // and ban them. Type variables instantiated inside binders aren't
580 // well-supported at the moment, so this doesn't work.
581 // In the future, this should be fixed and this error should be removed.
582 let def = self.map.defs.get(&lifetime.hir_id).cloned();
583 if let Some(Region::LateBound(_, def_id, _)) = def {
584 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
585 // Ensure that the parent of the def is an item, not HRTB
586 let parent_id = self.tcx.hir().get_parent_node(hir_id);
587 let parent_impl_id = hir::ImplItemId { hir_id: parent_id };
588 let parent_trait_id = hir::TraitItemId { hir_id: parent_id };
589 let krate = self.tcx.hir().forest.krate();
591 if !(krate.items.contains_key(&parent_id)
592 || krate.impl_items.contains_key(&parent_impl_id)
593 || krate.trait_items.contains_key(&parent_trait_id))
599 "`impl Trait` can only capture lifetimes \
600 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::DefaultReturn(_) => None,
852 hir::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"
954 let next_early_index = self.next_early_index();
955 let scope = Scope::Binder {
957 .bound_generic_params
959 .filter_map(|param| match param.kind {
960 GenericParamKind::Lifetime { .. } => {
961 Some(Region::late(&self.tcx.hir(), param))
968 track_lifetime_uses: true,
969 opaque_type_parent: false,
971 self.with(scope, |old_scope, this| {
972 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
973 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
974 this.visit_trait_ref(&trait_ref.trait_ref)
977 self.visit_trait_ref(&trait_ref.trait_ref)
982 #[derive(Copy, Clone, PartialEq)]
996 fn original_label(span: Span) -> Original {
997 Original { kind: ShadowKind::Label, span: span }
999 fn shadower_label(span: Span) -> Shadower {
1000 Shadower { kind: ShadowKind::Label, span: span }
1002 fn original_lifetime(span: Span) -> Original {
1003 Original { kind: ShadowKind::Lifetime, span: span }
1005 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1006 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1010 fn desc(&self) -> &'static str {
1012 ShadowKind::Label => "label",
1013 ShadowKind::Lifetime => "lifetime",
1018 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1019 let lifetime_params: Vec<_> = params
1021 .filter_map(|param| match param.kind {
1022 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1026 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1027 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1029 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1034 "cannot mix in-band and explicit lifetime definitions"
1036 .span_label(*in_band_span, "in-band lifetime definition here")
1037 .span_label(*explicit_span, "explicit lifetime definition here")
1042 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: ast::Name, orig: Original, shadower: Shadower) {
1043 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1044 // lifetime/lifetime shadowing is an error
1049 "{} name `{}` shadows a \
1050 {} name that is already in scope",
1051 shadower.kind.desc(),
1056 // shadowing involving a label is only a warning, due to issues with
1057 // labels and lifetimes not being macro-hygienic.
1058 tcx.sess.struct_span_warn(
1061 "{} name `{}` shadows a \
1062 {} name that is already in scope",
1063 shadower.kind.desc(),
1069 err.span_label(orig.span, "first declared here");
1070 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1074 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1075 // if one of the label shadows a lifetime or another label.
1076 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1077 struct GatherLabels<'a, 'tcx> {
1079 scope: ScopeRef<'a>,
1080 labels_in_fn: &'a mut Vec<ast::Ident>,
1084 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1085 gather.visit_body(body);
1087 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1088 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
1089 NestedVisitorMap::None
1092 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1093 if let Some(label) = expression_label(ex) {
1094 for prior_label in &self.labels_in_fn[..] {
1095 // FIXME (#24278): non-hygienic comparison
1096 if label.name == prior_label.name {
1097 signal_shadowing_problem(
1100 original_label(prior_label.span),
1101 shadower_label(label.span),
1106 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1108 self.labels_in_fn.push(label);
1110 intravisit::walk_expr(self, ex)
1114 fn expression_label(ex: &hir::Expr<'_>) -> Option<ast::Ident> {
1115 if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None }
1118 fn check_if_label_shadows_lifetime(
1120 mut scope: ScopeRef<'_>,
1125 Scope::Body { s, .. }
1126 | Scope::Elision { s, .. }
1127 | Scope::ObjectLifetimeDefault { s, .. } => {
1135 Scope::Binder { ref lifetimes, s, .. } => {
1136 // FIXME (#24278): non-hygienic comparison
1137 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1138 let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
1140 signal_shadowing_problem(
1143 original_lifetime(tcx.hir().span(hir_id)),
1144 shadower_label(label.span),
1155 fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap<Vec<ObjectLifetimeDefault>> {
1156 let mut map = HirIdMap::default();
1157 for item in tcx.hir().krate().items.values() {
1159 hir::ItemKind::Struct(_, ref generics)
1160 | hir::ItemKind::Union(_, ref generics)
1161 | hir::ItemKind::Enum(_, ref generics)
1162 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1163 ref generics, impl_trait_fn: None, ..
1165 | hir::ItemKind::TyAlias(_, ref generics)
1166 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1167 let result = object_lifetime_defaults_for_item(tcx, generics);
1170 if attr::contains_name(&item.attrs, sym::rustc_object_lifetime_default) {
1171 let object_lifetime_default_reprs: String = result
1173 .map(|set| match *set {
1174 Set1::Empty => "BaseDefault".into(),
1175 Set1::One(Region::Static) => "'static".into(),
1176 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1179 .find_map(|param| match param.kind {
1180 GenericParamKind::Lifetime { .. } => {
1182 return Some(param.name.ident().to_string().into());
1190 Set1::One(_) => bug!(),
1191 Set1::Many => "Ambiguous".into(),
1193 .collect::<Vec<Cow<'static, str>>>()
1195 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1198 map.insert(item.hir_id, result);
1206 /// Scan the bounds and where-clauses on parameters to extract bounds
1207 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1208 /// for each type parameter.
1209 fn object_lifetime_defaults_for_item(
1211 generics: &hir::Generics<'_>,
1212 ) -> Vec<ObjectLifetimeDefault> {
1213 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1214 for bound in bounds {
1215 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1216 set.insert(lifetime.name.modern());
1224 .filter_map(|param| match param.kind {
1225 GenericParamKind::Lifetime { .. } => None,
1226 GenericParamKind::Type { .. } => {
1227 let mut set = Set1::Empty;
1229 add_bounds(&mut set, ¶m.bounds);
1231 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1232 for predicate in generics.where_clause.predicates {
1233 // Look for `type: ...` where clauses.
1234 let data = match *predicate {
1235 hir::WherePredicate::BoundPredicate(ref data) => data,
1239 // Ignore `for<'a> type: ...` as they can change what
1240 // lifetimes mean (although we could "just" handle it).
1241 if !data.bound_generic_params.is_empty() {
1245 let res = match data.bounded_ty.kind {
1246 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1250 if res == Res::Def(DefKind::TyParam, param_def_id) {
1251 add_bounds(&mut set, &data.bounds);
1256 Set1::Empty => Set1::Empty,
1257 Set1::One(name) => {
1258 if name == hir::LifetimeName::Static {
1259 Set1::One(Region::Static)
1264 .filter_map(|param| match param.kind {
1265 GenericParamKind::Lifetime { .. } => Some((
1267 hir::LifetimeName::Param(param.name),
1268 LifetimeDefOrigin::from_param(param),
1273 .find(|&(_, (_, lt_name, _))| lt_name == name)
1274 .map_or(Set1::Many, |(i, (id, _, origin))| {
1275 let def_id = tcx.hir().local_def_id(id);
1276 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1280 Set1::Many => Set1::Many,
1283 GenericParamKind::Const { .. } => {
1284 // Generic consts don't impose any constraints.
1291 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1292 // FIXME(#37666) this works around a limitation in the region inferencer
1293 fn hack<F>(&mut self, f: F)
1295 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1300 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1302 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1304 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1305 let labels_in_fn = take(&mut self.labels_in_fn);
1306 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1307 let mut this = LifetimeContext {
1311 trait_ref_hack: self.trait_ref_hack,
1312 is_in_fn_syntax: self.is_in_fn_syntax,
1314 xcrate_object_lifetime_defaults,
1315 lifetime_uses: lifetime_uses,
1317 debug!("entering scope {:?}", this.scope);
1318 f(self.scope, &mut this);
1319 this.check_uses_for_lifetimes_defined_by_scope();
1320 debug!("exiting scope {:?}", this.scope);
1321 self.labels_in_fn = this.labels_in_fn;
1322 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1325 /// helper method to determine the span to remove when suggesting the
1326 /// deletion of a lifetime
1327 fn lifetime_deletion_span(
1330 generics: &hir::Generics<'_>,
1332 generics.params.iter().enumerate().find_map(|(i, param)| {
1333 if param.name.ident() == name {
1334 let mut in_band = false;
1335 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1336 if let hir::LifetimeParamKind::InBand = kind {
1343 if generics.params.len() == 1 {
1344 // if sole lifetime, remove the entire `<>` brackets
1347 // if removing within `<>` brackets, we also want to
1348 // delete a leading or trailing comma as appropriate
1349 if i >= generics.params.len() - 1 {
1350 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1352 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1362 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1363 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1364 fn suggest_eliding_single_use_lifetime(
1366 err: &mut DiagnosticBuilder<'_>,
1368 lifetime: &hir::Lifetime,
1370 let name = lifetime.name.ident();
1371 let mut remove_decl = None;
1372 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1373 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1374 remove_decl = self.lifetime_deletion_span(name, generics);
1378 let mut remove_use = None;
1379 let mut elide_use = None;
1380 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1381 for input in inputs {
1383 hir::TyKind::Rptr(lt, _) => {
1384 if lt.name.ident() == name {
1385 // include the trailing whitespace between the lifetime and type names
1386 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1391 .span_until_non_whitespace(lt_through_ty_span),
1396 hir::TyKind::Path(ref qpath) => {
1397 if let QPath::Resolved(_, path) = qpath {
1398 let last_segment = &path.segments[path.segments.len() - 1];
1399 let generics = last_segment.generic_args();
1400 for arg in generics.args.iter() {
1401 if let GenericArg::Lifetime(lt) = arg {
1402 if lt.name.ident() == name {
1403 elide_use = Some(lt.span);
1415 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1416 if let Some(parent) =
1417 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1420 Node::Item(item) => {
1421 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1422 find_arg_use_span(sig.decl.inputs);
1425 Node::ImplItem(impl_item) => {
1426 if let hir::ImplItemKind::Method(sig, _) = &impl_item.kind {
1427 find_arg_use_span(sig.decl.inputs);
1435 let msg = "elide the single-use lifetime";
1436 match (remove_decl, remove_use, elide_use) {
1437 (Some(decl_span), Some(use_span), None) => {
1438 // if both declaration and use deletion spans start at the same
1439 // place ("start at" because the latter includes trailing
1440 // whitespace), then this is an in-band lifetime
1441 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1442 err.span_suggestion(
1446 Applicability::MachineApplicable,
1449 err.multipart_suggestion(
1451 vec![(decl_span, String::new()), (use_span, String::new())],
1452 Applicability::MachineApplicable,
1456 (Some(decl_span), None, Some(use_span)) => {
1457 err.multipart_suggestion(
1459 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1460 Applicability::MachineApplicable,
1467 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1468 let defined_by = match self.scope {
1469 Scope::Binder { lifetimes, .. } => lifetimes,
1471 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1476 let mut def_ids: Vec<_> = defined_by
1478 .flat_map(|region| match region {
1479 Region::EarlyBound(_, def_id, _)
1480 | Region::LateBound(_, def_id, _)
1481 | Region::Free(_, def_id) => Some(*def_id),
1483 Region::LateBoundAnon(..) | Region::Static => None,
1487 // ensure that we issue lints in a repeatable order
1488 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1490 for def_id in def_ids {
1491 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1493 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1496 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1500 match lifetimeuseset {
1501 Some(LifetimeUseSet::One(lifetime)) => {
1502 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1503 debug!("hir id first={:?}", hir_id);
1504 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1505 Node::Lifetime(hir_lifetime) => Some((
1506 hir_lifetime.hir_id,
1508 hir_lifetime.name.ident(),
1510 Node::GenericParam(param) => {
1511 Some((param.hir_id, param.span, param.name.ident()))
1515 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1516 if name.name == kw::UnderscoreLifetime {
1520 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1521 if let Some(parent_hir_id) =
1522 self.tcx.hir().as_local_hir_id(parent_def_id)
1524 // lifetimes in `derive` expansions don't count (Issue #53738)
1528 .attrs(parent_hir_id)
1530 .any(|attr| attr.check_name(sym::automatically_derived))
1537 let mut err = self.tcx.struct_span_lint_hir(
1538 lint::builtin::SINGLE_USE_LIFETIMES,
1541 &format!("lifetime parameter `{}` only used once", name),
1544 if span == lifetime.span {
1545 // spans are the same for in-band lifetime declarations
1546 err.span_label(span, "this lifetime is only used here");
1548 err.span_label(span, "this lifetime...");
1549 err.span_label(lifetime.span, "...is used only here");
1551 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1555 Some(LifetimeUseSet::Many) => {
1556 debug!("not one use lifetime");
1559 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1560 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1561 Node::Lifetime(hir_lifetime) => Some((
1562 hir_lifetime.hir_id,
1564 hir_lifetime.name.ident(),
1566 Node::GenericParam(param) => {
1567 Some((param.hir_id, param.span, param.name.ident()))
1571 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1572 let mut err = self.tcx.struct_span_lint_hir(
1573 lint::builtin::UNUSED_LIFETIMES,
1576 &format!("lifetime parameter `{}` never used", name),
1578 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1579 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1580 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1581 if let Some(span) = unused_lt_span {
1582 err.span_suggestion(
1584 "elide the unused lifetime",
1586 Applicability::MachineApplicable,
1598 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1600 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1601 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1602 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1606 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1608 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1609 /// lifetimes may be interspersed together.
1611 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1612 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1613 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1614 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1615 /// ordering is not important there.
1616 fn visit_early_late<F>(
1618 parent_id: Option<hir::HirId>,
1619 decl: &'tcx hir::FnDecl<'tcx>,
1620 generics: &'tcx hir::Generics<'tcx>,
1623 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1625 insert_late_bound_lifetimes(self.map, decl, generics);
1627 // Find the start of nested early scopes, e.g., in methods.
1629 if let Some(parent_id) = parent_id {
1630 let parent = self.tcx.hir().expect_item(parent_id);
1631 if sub_items_have_self_param(&parent.kind) {
1632 index += 1; // Self comes before lifetimes
1635 hir::ItemKind::Trait(_, _, ref generics, ..)
1636 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
1637 index += generics.params.len() as u32;
1643 let mut non_lifetime_count = 0;
1644 let lifetimes = generics
1647 .filter_map(|param| match param.kind {
1648 GenericParamKind::Lifetime { .. } => {
1649 if self.map.late_bound.contains(¶m.hir_id) {
1650 Some(Region::late(&self.tcx.hir(), param))
1652 Some(Region::early(&self.tcx.hir(), &mut index, param))
1655 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1656 non_lifetime_count += 1;
1661 let next_early_index = index + non_lifetime_count;
1663 let scope = Scope::Binder {
1667 opaque_type_parent: true,
1668 track_lifetime_uses: false,
1670 self.with(scope, move |old_scope, this| {
1671 this.check_lifetime_params(old_scope, &generics.params);
1672 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1676 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1677 let mut scope = self.scope;
1680 Scope::Root => return 0,
1682 Scope::Binder { next_early_index, opaque_type_parent, .. }
1683 if (!only_opaque_type_parent || opaque_type_parent) =>
1685 return next_early_index;
1688 Scope::Binder { s, .. }
1689 | Scope::Body { s, .. }
1690 | Scope::Elision { s, .. }
1691 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1696 /// Returns the next index one would use for an early-bound-region
1697 /// if extending the current scope.
1698 fn next_early_index(&self) -> u32 {
1699 self.next_early_index_helper(true)
1702 /// Returns the next index one would use for an `impl Trait` that
1703 /// is being converted into an opaque type alias `impl Trait`. This will be the
1704 /// next early index from the enclosing item, for the most
1705 /// part. See the `opaque_type_parent` field for more info.
1706 fn next_early_index_for_opaque_type(&self) -> u32 {
1707 self.next_early_index_helper(false)
1710 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1711 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1713 // If we've already reported an error, just ignore `lifetime_ref`.
1714 if let LifetimeName::Error = lifetime_ref.name {
1718 // Walk up the scope chain, tracking the number of fn scopes
1719 // that we pass through, until we find a lifetime with the
1720 // given name or we run out of scopes.
1722 let mut late_depth = 0;
1723 let mut scope = self.scope;
1724 let mut outermost_body = None;
1727 Scope::Body { id, s } => {
1728 outermost_body = Some(id);
1736 Scope::Binder { ref lifetimes, s, .. } => {
1737 match lifetime_ref.name {
1738 LifetimeName::Param(param_name) => {
1739 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1740 break Some(def.shifted(late_depth));
1743 _ => bug!("expected LifetimeName::Param"),
1750 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1756 if let Some(mut def) = result {
1757 if let Region::EarlyBound(..) = def {
1758 // Do not free early-bound regions, only late-bound ones.
1759 } else if let Some(body_id) = outermost_body {
1760 let fn_id = self.tcx.hir().body_owner(body_id);
1761 match self.tcx.hir().get(fn_id) {
1762 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1763 | Node::TraitItem(&hir::TraitItem {
1764 kind: hir::TraitItemKind::Method(..),
1767 | Node::ImplItem(&hir::ImplItem {
1768 kind: hir::ImplItemKind::Method(..), ..
1770 let scope = self.tcx.hir().local_def_id(fn_id);
1771 def = Region::Free(scope, def.id().unwrap());
1777 // Check for fn-syntax conflicts with in-band lifetime definitions
1778 if self.is_in_fn_syntax {
1780 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1781 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1786 "lifetimes used in `fn` or `Fn` syntax must be \
1787 explicitly declared using `<...>` binders"
1789 .span_label(lifetime_ref.span, "in-band lifetime definition")
1794 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1795 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1796 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1797 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1798 | Region::LateBoundAnon(..)
1799 | Region::Free(..) => {}
1803 self.insert_lifetime(lifetime_ref, def);
1809 "use of undeclared lifetime name `{}`",
1812 .span_label(lifetime_ref.span, "undeclared lifetime")
1817 fn visit_segment_args(
1821 generic_args: &'tcx hir::GenericArgs<'tcx>,
1824 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1825 res, depth, generic_args,
1828 if generic_args.parenthesized {
1829 let was_in_fn_syntax = self.is_in_fn_syntax;
1830 self.is_in_fn_syntax = true;
1831 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1832 self.is_in_fn_syntax = was_in_fn_syntax;
1836 let mut elide_lifetimes = true;
1837 let lifetimes = generic_args
1840 .filter_map(|arg| match arg {
1841 hir::GenericArg::Lifetime(lt) => {
1842 if !lt.is_elided() {
1843 elide_lifetimes = false;
1850 if elide_lifetimes {
1851 self.resolve_elided_lifetimes(lifetimes);
1853 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1856 // Figure out if this is a type/trait segment,
1857 // which requires object lifetime defaults.
1858 let parent_def_id = |this: &mut Self, def_id: DefId| {
1859 let def_key = this.tcx.def_key(def_id);
1860 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1862 let type_def_id = match res {
1863 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1864 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1865 Res::Def(DefKind::Struct, def_id)
1866 | Res::Def(DefKind::Union, def_id)
1867 | Res::Def(DefKind::Enum, def_id)
1868 | Res::Def(DefKind::TyAlias, def_id)
1869 | Res::Def(DefKind::Trait, def_id)
1877 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1879 // Compute a vector of defaults, one for each type parameter,
1880 // per the rules given in RFCs 599 and 1156. Example:
1883 // struct Foo<'a, T: 'a, U> { }
1886 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1887 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1888 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1891 // Therefore, we would compute `object_lifetime_defaults` to a
1892 // vector like `['x, 'static]`. Note that the vector only
1893 // includes type parameters.
1894 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1896 let mut scope = self.scope;
1899 Scope::Root => break false,
1901 Scope::Body { .. } => break true,
1903 Scope::Binder { s, .. }
1904 | Scope::Elision { s, .. }
1905 | Scope::ObjectLifetimeDefault { s, .. } => {
1912 let map = &self.map;
1913 let unsubst = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
1914 &map.object_lifetime_defaults[&id]
1917 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1918 tcx.generics_of(def_id)
1921 .filter_map(|param| match param.kind {
1922 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1923 Some(object_lifetime_default)
1925 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1930 debug!("visit_segment_args: unsubst={:?}", unsubst);
1933 .map(|set| match *set {
1938 Some(Region::Static)
1942 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1943 GenericArg::Lifetime(lt) => Some(lt),
1946 r.subst(lifetimes, map)
1953 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1956 for arg in generic_args.args {
1958 GenericArg::Lifetime(_) => {}
1959 GenericArg::Type(ty) => {
1960 if let Some(<) = object_lifetime_defaults.get(i) {
1961 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1962 self.with(scope, |_, this| this.visit_ty(ty));
1968 GenericArg::Const(ct) => {
1969 self.visit_anon_const(&ct.value);
1974 // Hack: when resolving the type `XX` in binding like `dyn
1975 // Foo<'b, Item = XX>`, the current object-lifetime default
1976 // would be to examine the trait `Foo` to check whether it has
1977 // a lifetime bound declared on `Item`. e.g., if `Foo` is
1978 // declared like so, then the default object lifetime bound in
1979 // `XX` should be `'b`:
1987 // but if we just have `type Item;`, then it would be
1988 // `'static`. However, we don't get all of this logic correct.
1990 // Instead, we do something hacky: if there are no lifetime parameters
1991 // to the trait, then we simply use a default object lifetime
1992 // bound of `'static`, because there is no other possibility. On the other hand,
1993 // if there ARE lifetime parameters, then we require the user to give an
1994 // explicit bound for now.
1996 // This is intended to leave room for us to implement the
1997 // correct behavior in the future.
1998 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
1999 GenericArg::Lifetime(_) => true,
2003 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2004 for b in generic_args.bindings {
2005 let scope = Scope::ObjectLifetimeDefault {
2006 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2009 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2013 fn visit_fn_like_elision(
2015 inputs: &'tcx [hir::Ty<'tcx>],
2016 output: Option<&'tcx hir::Ty<'tcx>>,
2018 debug!("visit_fn_like_elision: enter");
2019 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2020 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2021 self.with(arg_scope, |_, this| {
2022 for input in inputs {
2023 this.visit_ty(input);
2026 Scope::Elision { ref elide, .. } => {
2027 arg_elide = elide.clone();
2033 let output = match output {
2038 debug!("visit_fn_like_elision: determine output");
2040 // Figure out if there's a body we can get argument names from,
2041 // and whether there's a `self` argument (treated specially).
2042 let mut assoc_item_kind = None;
2043 let mut impl_self = None;
2044 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2045 let body = match self.tcx.hir().get(parent) {
2046 // `fn` definitions and methods.
2047 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2049 Node::TraitItem(&hir::TraitItem {
2050 kind: hir::TraitItemKind::Method(_, ref m), ..
2052 if let hir::ItemKind::Trait(.., ref trait_items) =
2053 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2056 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2059 hir::TraitMethod::Required(_) => None,
2060 hir::TraitMethod::Provided(body) => Some(body),
2064 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Method(_, body), .. }) => {
2065 if let hir::ItemKind::Impl(.., ref self_ty, ref impl_items) =
2066 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2068 impl_self = Some(self_ty);
2070 impl_items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2075 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2076 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2077 // Everything else (only closures?) doesn't
2078 // actually enjoy elision in return types.
2080 self.visit_ty(output);
2085 let has_self = match assoc_item_kind {
2086 Some(hir::AssocItemKind::Method { has_self }) => has_self,
2090 // In accordance with the rules for lifetime elision, we can determine
2091 // what region to use for elision in the output type in two ways.
2092 // First (determined here), if `self` is by-reference, then the
2093 // implied output region is the region of the self parameter.
2095 struct SelfVisitor<'a> {
2096 map: &'a NamedRegionMap,
2097 impl_self: Option<&'a hir::TyKind<'a>>,
2098 lifetime: Set1<Region>,
2101 impl SelfVisitor<'_> {
2102 // Look for `self: &'a Self` - also desugared from `&'a self`,
2103 // and if that matches, use it for elision and return early.
2104 fn is_self_ty(&self, res: Res) -> bool {
2105 if let Res::SelfTy(..) = res {
2109 // Can't always rely on literal (or implied) `Self` due
2110 // to the way elision rules were originally specified.
2111 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2115 // Whitelist the types that unambiguously always
2116 // result in the same type constructor being used
2117 // (it can't differ between `Self` and `self`).
2118 Res::Def(DefKind::Struct, _)
2119 | Res::Def(DefKind::Union, _)
2120 | Res::Def(DefKind::Enum, _)
2121 | Res::PrimTy(_) => return res == path.res,
2130 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2131 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'a> {
2132 NestedVisitorMap::None
2135 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2136 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2137 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2139 if self.is_self_ty(path.res) {
2140 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2141 self.lifetime.insert(*lifetime);
2146 intravisit::walk_ty(self, ty)
2150 let mut visitor = SelfVisitor {
2152 impl_self: impl_self.map(|ty| &ty.kind),
2153 lifetime: Set1::Empty,
2155 visitor.visit_ty(&inputs[0]);
2156 if let Set1::One(lifetime) = visitor.lifetime {
2157 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2158 self.with(scope, |_, this| this.visit_ty(output));
2163 // Second, if there was exactly one lifetime (either a substitution or a
2164 // reference) in the arguments, then any anonymous regions in the output
2165 // have that lifetime.
2166 let mut possible_implied_output_region = None;
2167 let mut lifetime_count = 0;
2168 let arg_lifetimes = inputs
2171 .skip(has_self as usize)
2173 let mut gather = GatherLifetimes {
2175 outer_index: ty::INNERMOST,
2176 have_bound_regions: false,
2177 lifetimes: Default::default(),
2179 gather.visit_ty(input);
2181 lifetime_count += gather.lifetimes.len();
2183 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2184 // there's a chance that the unique lifetime of this
2185 // iteration will be the appropriate lifetime for output
2186 // parameters, so lets store it.
2187 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2190 ElisionFailureInfo {
2193 lifetime_count: gather.lifetimes.len(),
2194 have_bound_regions: gather.have_bound_regions,
2199 let elide = if lifetime_count == 1 {
2200 Elide::Exact(possible_implied_output_region.unwrap())
2202 Elide::Error(arg_lifetimes)
2205 debug!("visit_fn_like_elision: elide={:?}", elide);
2207 let scope = Scope::Elision { elide, s: self.scope };
2208 self.with(scope, |_, this| this.visit_ty(output));
2209 debug!("visit_fn_like_elision: exit");
2211 struct GatherLifetimes<'a> {
2212 map: &'a NamedRegionMap,
2213 outer_index: ty::DebruijnIndex,
2214 have_bound_regions: bool,
2215 lifetimes: FxHashSet<Region>,
2218 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2219 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2220 NestedVisitorMap::None
2223 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2224 if let hir::TyKind::BareFn(_) = ty.kind {
2225 self.outer_index.shift_in(1);
2228 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2229 for bound in bounds {
2230 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2233 // Stay on the safe side and don't include the object
2234 // lifetime default (which may not end up being used).
2235 if !lifetime.is_elided() {
2236 self.visit_lifetime(lifetime);
2240 intravisit::walk_ty(self, ty);
2243 if let hir::TyKind::BareFn(_) = ty.kind {
2244 self.outer_index.shift_out(1);
2248 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2249 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2250 // FIXME(eddyb) Do we want this? It only makes a difference
2251 // if this `for<'a>` lifetime parameter is never used.
2252 self.have_bound_regions = true;
2255 intravisit::walk_generic_param(self, param);
2258 fn visit_poly_trait_ref(
2260 trait_ref: &hir::PolyTraitRef<'_>,
2261 modifier: hir::TraitBoundModifier,
2263 self.outer_index.shift_in(1);
2264 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2265 self.outer_index.shift_out(1);
2268 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2269 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2271 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2272 if debruijn < self.outer_index =>
2274 self.have_bound_regions = true;
2277 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2285 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2286 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2288 if lifetime_refs.is_empty() {
2292 let span = lifetime_refs[0].span;
2293 let mut late_depth = 0;
2294 let mut scope = self.scope;
2295 let mut lifetime_names = FxHashSet::default();
2298 // Do not assign any resolution, it will be inferred.
2299 Scope::Body { .. } => return,
2301 Scope::Root => break None,
2303 Scope::Binder { s, ref lifetimes, .. } => {
2304 // collect named lifetimes for suggestions
2305 for name in lifetimes.keys() {
2306 if let hir::ParamName::Plain(name) = name {
2307 lifetime_names.insert(*name);
2314 Scope::Elision { ref elide, ref s, .. } => {
2315 let lifetime = match *elide {
2316 Elide::FreshLateAnon(ref counter) => {
2317 for lifetime_ref in lifetime_refs {
2318 let lifetime = Region::late_anon(counter).shifted(late_depth);
2319 self.insert_lifetime(lifetime_ref, lifetime);
2323 Elide::Exact(l) => l.shifted(late_depth),
2324 Elide::Error(ref e) => {
2325 if let Scope::Binder { ref lifetimes, .. } = s {
2326 // collect named lifetimes for suggestions
2327 for name in lifetimes.keys() {
2328 if let hir::ParamName::Plain(name) = name {
2329 lifetime_names.insert(*name);
2336 for lifetime_ref in lifetime_refs {
2337 self.insert_lifetime(lifetime_ref, lifetime);
2342 Scope::ObjectLifetimeDefault { s, .. } => {
2348 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2349 let mut add_label = true;
2351 if let Some(params) = error {
2352 if lifetime_refs.len() == 1 {
2353 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2357 add_missing_lifetime_specifiers_label(
2360 lifetime_refs.len(),
2362 self.tcx.sess.source_map().span_to_snippet(span).ok().as_ref().map(|s| s.as_str()),
2369 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2370 match self.tcx.sess.source_map().span_to_snippet(span) {
2371 Ok(ref snippet) => {
2372 let (sugg, applicability) = if snippet == "&" {
2373 ("&'static ".to_owned(), Applicability::MachineApplicable)
2374 } else if snippet == "'_" {
2375 ("'static".to_owned(), Applicability::MachineApplicable)
2377 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2379 db.span_suggestion(span, msg, sugg, applicability);
2389 fn report_elision_failure(
2391 db: &mut DiagnosticBuilder<'_>,
2392 params: &[ElisionFailureInfo],
2395 let mut m = String::new();
2396 let len = params.len();
2398 let elided_params: Vec<_> =
2399 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2401 let elided_len = elided_params.len();
2403 for (i, info) in elided_params.into_iter().enumerate() {
2404 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions } = info;
2406 let help_name = if let Some(ident) =
2407 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2409 format!("`{}`", ident)
2411 format!("argument {}", index + 1)
2419 "one of {}'s {} {}lifetimes",
2422 if have_bound_regions { "free " } else { "" }
2427 if elided_len == 2 && i == 0 {
2429 } else if i + 2 == elided_len {
2430 m.push_str(", or ");
2431 } else if i != elided_len - 1 {
2439 "this function's return type contains a borrowed value, but \
2440 there is no value for it to be borrowed from"
2442 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2443 } else if elided_len == 0 {
2446 "this function's return type contains a borrowed value with \
2447 an elided lifetime, but the lifetime cannot be derived from \
2450 let msg = "consider giving it an explicit bounded or 'static lifetime";
2451 self.suggest_lifetime(db, span, msg)
2452 } else if elided_len == 1 {
2455 "this function's return type contains a borrowed value, but \
2456 the signature does not say which {} it is borrowed from",
2463 "this function's return type contains a borrowed value, but \
2464 the signature does not say whether it is borrowed from {}",
2471 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2472 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2473 let mut late_depth = 0;
2474 let mut scope = self.scope;
2475 let lifetime = loop {
2477 Scope::Binder { s, .. } => {
2482 Scope::Root | Scope::Elision { .. } => break Region::Static,
2484 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2486 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2489 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2492 fn check_lifetime_params(
2494 old_scope: ScopeRef<'_>,
2495 params: &'tcx [hir::GenericParam<'tcx>],
2497 let lifetimes: Vec<_> = params
2499 .filter_map(|param| match param.kind {
2500 GenericParamKind::Lifetime { .. } => Some((param, param.name.modern())),
2504 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2505 if let hir::ParamName::Plain(_) = lifetime_i_name {
2506 let name = lifetime_i_name.ident().name;
2507 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2508 let mut err = struct_span_err!(
2512 "invalid lifetime parameter name: `{}`",
2513 lifetime_i.name.ident(),
2517 format!("{} is a reserved lifetime name", name),
2523 // It is a hard error to shadow a lifetime within the same scope.
2524 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2525 if lifetime_i_name == lifetime_j_name {
2530 "lifetime name `{}` declared twice in the same scope",
2531 lifetime_j.name.ident()
2533 .span_label(lifetime_j.span, "declared twice")
2534 .span_label(lifetime_i.span, "previous declaration here")
2539 // It is a soft error to shadow a lifetime within a parent scope.
2540 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2542 for bound in lifetime_i.bounds {
2544 hir::GenericBound::Outlives(ref lt) => match lt.name {
2545 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2547 "use of `'_` in illegal place, but not caught by lowering",
2549 hir::LifetimeName::Static => {
2550 self.insert_lifetime(lt, Region::Static);
2554 lifetime_i.span.to(lt.span),
2556 "unnecessary lifetime parameter `{}`",
2557 lifetime_i.name.ident(),
2561 "you can use the `'static` lifetime directly, in place of `{}`",
2562 lifetime_i.name.ident(),
2566 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2567 self.resolve_lifetime_ref(lt);
2569 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2570 self.tcx.sess.delay_span_bug(
2572 "lowering generated `ImplicitObjectLifetimeDefault` \
2573 outside of an object type",
2576 hir::LifetimeName::Error => {
2577 // No need to do anything, error already reported.
2586 fn check_lifetime_param_for_shadowing(
2588 mut old_scope: ScopeRef<'_>,
2589 param: &'tcx hir::GenericParam<'tcx>,
2591 for label in &self.labels_in_fn {
2592 // FIXME (#24278): non-hygienic comparison
2593 if param.name.ident().name == label.name {
2594 signal_shadowing_problem(
2597 original_label(label.span),
2598 shadower_lifetime(¶m),
2606 Scope::Body { s, .. }
2607 | Scope::Elision { s, .. }
2608 | Scope::ObjectLifetimeDefault { s, .. } => {
2616 Scope::Binder { ref lifetimes, s, .. } => {
2617 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2618 let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
2620 signal_shadowing_problem(
2622 param.name.ident().name,
2623 original_lifetime(self.tcx.hir().span(hir_id)),
2624 shadower_lifetime(¶m),
2635 /// Returns `true` if, in the current scope, replacing `'_` would be
2636 /// equivalent to a single-use lifetime.
2637 fn track_lifetime_uses(&self) -> bool {
2638 let mut scope = self.scope;
2641 Scope::Root => break false,
2643 // Inside of items, it depends on the kind of item.
2644 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2646 // Inside a body, `'_` will use an inference variable,
2648 Scope::Body { .. } => break true,
2650 // A lifetime only used in a fn argument could as well
2651 // be replaced with `'_`, as that would generate a
2653 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2655 // In the return type or other such place, `'_` is not
2656 // going to make a fresh name, so we cannot
2657 // necessarily replace a single-use lifetime with
2659 Scope::Elision { elide: Elide::Exact(_), .. } => break false,
2660 Scope::Elision { elide: Elide::Error(_), .. } => break false,
2662 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2667 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2668 if lifetime_ref.hir_id == hir::DUMMY_HIR_ID {
2671 "lifetime reference not renumbered, \
2672 probably a bug in syntax::fold"
2677 "insert_lifetime: {} resolved to {:?} span={:?}",
2678 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2680 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2682 self.map.defs.insert(lifetime_ref.hir_id, def);
2685 Region::LateBoundAnon(..) | Region::Static => {
2686 // These are anonymous lifetimes or lifetimes that are not declared.
2689 Region::Free(_, def_id)
2690 | Region::LateBound(_, def_id, _)
2691 | Region::EarlyBound(_, def_id, _) => {
2692 // A lifetime declared by the user.
2693 let track_lifetime_uses = self.track_lifetime_uses();
2694 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2695 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2696 debug!("insert_lifetime: first use of {:?}", def_id);
2697 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2699 debug!("insert_lifetime: many uses of {:?}", def_id);
2700 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2706 /// Sometimes we resolve a lifetime, but later find that it is an
2707 /// error (esp. around impl trait). In that case, we remove the
2708 /// entry into `map.defs` so as not to confuse later code.
2709 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2710 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2711 assert_eq!(old_value, Some(bad_def));
2715 /// Detects late-bound lifetimes and inserts them into
2716 /// `map.late_bound`.
2718 /// A region declared on a fn is **late-bound** if:
2719 /// - it is constrained by an argument type;
2720 /// - it does not appear in a where-clause.
2722 /// "Constrained" basically means that it appears in any type but
2723 /// not amongst the inputs to a projection. In other words, `<&'a
2724 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2725 fn insert_late_bound_lifetimes(
2726 map: &mut NamedRegionMap,
2727 decl: &hir::FnDecl<'_>,
2728 generics: &hir::Generics<'_>,
2730 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2732 let mut constrained_by_input = ConstrainedCollector::default();
2733 for arg_ty in decl.inputs {
2734 constrained_by_input.visit_ty(arg_ty);
2737 let mut appears_in_output = AllCollector::default();
2738 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2740 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2742 // Walk the lifetimes that appear in where clauses.
2744 // Subtle point: because we disallow nested bindings, we can just
2745 // ignore binders here and scrape up all names we see.
2746 let mut appears_in_where_clause = AllCollector::default();
2747 appears_in_where_clause.visit_generics(generics);
2749 for param in generics.params {
2750 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2751 if !param.bounds.is_empty() {
2752 // `'a: 'b` means both `'a` and `'b` are referenced
2753 appears_in_where_clause
2755 .insert(hir::LifetimeName::Param(param.name.modern()));
2761 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2762 appears_in_where_clause.regions
2765 // Late bound regions are those that:
2766 // - appear in the inputs
2767 // - do not appear in the where-clauses
2768 // - are not implicitly captured by `impl Trait`
2769 for param in generics.params {
2771 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2773 // Neither types nor consts are late-bound.
2774 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2777 let lt_name = hir::LifetimeName::Param(param.name.modern());
2778 // appears in the where clauses? early-bound.
2779 if appears_in_where_clause.regions.contains(<_name) {
2783 // does not appear in the inputs, but appears in the return type? early-bound.
2784 if !constrained_by_input.regions.contains(<_name)
2785 && appears_in_output.regions.contains(<_name)
2791 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2796 let inserted = map.late_bound.insert(param.hir_id);
2797 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2803 struct ConstrainedCollector {
2804 regions: FxHashSet<hir::LifetimeName>,
2807 impl<'v> Visitor<'v> for ConstrainedCollector {
2808 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2809 NestedVisitorMap::None
2812 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2814 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2815 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2816 // ignore lifetimes appearing in associated type
2817 // projections, as they are not *constrained*
2821 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2822 // consider only the lifetimes on the final
2823 // segment; I am not sure it's even currently
2824 // valid to have them elsewhere, but even if it
2825 // is, those would be potentially inputs to
2827 if let Some(last_segment) = path.segments.last() {
2828 self.visit_path_segment(path.span, last_segment);
2833 intravisit::walk_ty(self, ty);
2838 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2839 self.regions.insert(lifetime_ref.name.modern());
2844 struct AllCollector {
2845 regions: FxHashSet<hir::LifetimeName>,
2848 impl<'v> Visitor<'v> for AllCollector {
2849 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2850 NestedVisitorMap::None
2853 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2854 self.regions.insert(lifetime_ref.name.modern());
2859 fn report_missing_lifetime_specifiers(
2863 ) -> DiagnosticBuilder<'_> {
2864 struct_span_err!(sess, span, E0106, "missing lifetime specifier{}", pluralize!(count))
2867 fn add_missing_lifetime_specifiers_label(
2868 err: &mut DiagnosticBuilder<'_>,
2871 lifetime_names: &FxHashSet<ast::Ident>,
2872 snippet: Option<&str>,
2875 err.span_label(span, format!("expected {} lifetime parameters", count));
2876 } else if let (1, Some(name), Some("&")) =
2877 (lifetime_names.len(), lifetime_names.iter().next(), snippet)
2879 err.span_suggestion(
2881 "consider using the named lifetime",
2882 format!("&{} ", name),
2883 Applicability::MaybeIncorrect,
2886 err.span_label(span, "expected lifetime parameter");