1 //! Name resolution for lifetimes.
3 //! Name resolution for lifetimes follows *much* simpler rules than the
4 //! full resolve. For example, lifetime names are never exported or
5 //! used between functions, and they operate in a purely top-down
6 //! way. Therefore, we break lifetime name resolution into a separate pass.
8 use rustc::hir::map::Map;
10 use rustc::middle::resolve_lifetime::*;
11 use rustc::session::Session;
12 use rustc::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
13 use rustc::{bug, span_bug};
14 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
17 use rustc_hir::def::{DefKind, Res};
18 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
19 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
20 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
21 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind};
22 use rustc_span::symbol::{kw, sym};
26 use std::mem::{replace, take};
29 use syntax::walk_list;
33 use rustc_error_codes::*;
35 // This counts the no of times a lifetime is used
36 #[derive(Clone, Copy, Debug)]
37 pub enum LifetimeUseSet<'tcx> {
38 One(&'tcx hir::Lifetime),
43 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
45 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
47 fn late_anon(index: &Cell<u32>) -> Region;
49 fn id(&self) -> Option<DefId>;
51 fn shifted(self, amount: u32) -> Region;
53 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
55 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
57 L: Iterator<Item = &'a hir::Lifetime>;
60 impl RegionExt for Region {
61 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
64 let def_id = hir_map.local_def_id(param.hir_id);
65 let origin = LifetimeDefOrigin::from_param(param);
66 debug!("Region::early: index={} def_id={:?}", i, def_id);
67 (param.name.modern(), Region::EarlyBound(i, def_id, origin))
70 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) {
71 let depth = ty::INNERMOST;
72 let def_id = hir_map.local_def_id(param.hir_id);
73 let origin = LifetimeDefOrigin::from_param(param);
75 "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
76 param, depth, def_id, origin,
78 (param.name.modern(), Region::LateBound(depth, def_id, origin))
81 fn late_anon(index: &Cell<u32>) -> Region {
84 let depth = ty::INNERMOST;
85 Region::LateBoundAnon(depth, i)
88 fn id(&self) -> Option<DefId> {
90 Region::Static | Region::LateBoundAnon(..) => None,
92 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
98 fn shifted(self, amount: u32) -> Region {
100 Region::LateBound(debruijn, id, origin) => {
101 Region::LateBound(debruijn.shifted_in(amount), id, origin)
103 Region::LateBoundAnon(debruijn, index) => {
104 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
110 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
112 Region::LateBound(debruijn, id, origin) => {
113 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
115 Region::LateBoundAnon(debruijn, index) => {
116 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
122 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
124 L: Iterator<Item = &'a hir::Lifetime>,
126 if let Region::EarlyBound(index, _, _) = self {
127 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
134 /// Maps the id of each lifetime reference to the lifetime decl
135 /// that it corresponds to.
137 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
138 /// actual use. It has the same data, but indexed by `DefIndex`. This
141 struct NamedRegionMap {
142 // maps from every use of a named (not anonymous) lifetime to a
143 // `Region` describing how that region is bound
144 defs: HirIdMap<Region>,
146 // the set of lifetime def ids that are late-bound; a region can
147 // be late-bound if (a) it does NOT appear in a where-clause and
148 // (b) it DOES appear in the arguments.
149 late_bound: HirIdSet,
151 // For each type and trait definition, maps type parameters
152 // to the trait object lifetime defaults computed from them.
153 object_lifetime_defaults: HirIdMap<Vec<ObjectLifetimeDefault>>,
156 struct LifetimeContext<'a, 'tcx> {
158 map: &'a mut NamedRegionMap,
161 /// This is slightly complicated. Our representation for poly-trait-refs contains a single
162 /// binder and thus we only allow a single level of quantification. However,
163 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
164 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices
165 /// correct when representing these constraints, we should only introduce one
166 /// scope. However, we want to support both locations for the quantifier and
167 /// during lifetime resolution we want precise information (so we can't
168 /// desugar in an earlier phase).
170 /// So, if we encounter a quantifier at the outer scope, we set
171 /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter
172 /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`,
173 /// then we introduce the scope at the inner quantifier.
174 trait_ref_hack: bool,
176 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
177 is_in_fn_syntax: bool,
179 /// List of labels in the function/method currently under analysis.
180 labels_in_fn: Vec<ast::Ident>,
182 /// Cache for cross-crate per-definition object lifetime defaults.
183 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
185 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
187 /// When encountering an undefined named lifetime, we will suggest introducing it in these
189 missing_named_lifetime_spots: Vec<&'tcx hir::Generics<'tcx>>,
194 /// Declares lifetimes, and each can be early-bound or late-bound.
195 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
196 /// it should be shifted by the number of `Binder`s in between the
197 /// declaration `Binder` and the location it's referenced from.
199 lifetimes: FxHashMap<hir::ParamName, Region>,
201 /// if we extend this scope with another scope, what is the next index
202 /// we should use for an early-bound region?
203 next_early_index: u32,
205 /// Flag is set to true if, in this binder, `'_` would be
206 /// equivalent to a "single-use region". This is true on
207 /// impls, but not other kinds of items.
208 track_lifetime_uses: bool,
210 /// Whether or not this binder would serve as the parent
211 /// binder for opaque types introduced within. For example:
214 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
217 /// Here, the opaque types we create for the `impl Trait`
218 /// and `impl Trait2` references will both have the `foo` item
219 /// as their parent. When we get to `impl Trait2`, we find
220 /// that it is nested within the `for<>` binder -- this flag
221 /// allows us to skip that when looking for the parent binder
222 /// of the resulting opaque type.
223 opaque_type_parent: bool,
228 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
229 /// if this is a fn body, otherwise the original definitions are used.
230 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
231 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
237 /// A scope which either determines unspecified lifetimes or errors
238 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
244 /// Use a specific lifetime (if `Some`) or leave it unset (to be
245 /// inferred in a function body or potentially error outside one),
246 /// for the default choice of lifetime in a trait object type.
247 ObjectLifetimeDefault {
248 lifetime: Option<Region>,
255 #[derive(Clone, Debug)]
257 /// Use a fresh anonymous late-bound lifetime each time, by
258 /// incrementing the counter to generate sequential indices.
259 FreshLateAnon(Cell<u32>),
260 /// Always use this one lifetime.
262 /// Less or more than one lifetime were found, error on unspecified.
263 Error(Vec<ElisionFailureInfo>),
266 #[derive(Clone, Debug)]
267 struct ElisionFailureInfo {
268 /// Where we can find the argument pattern.
269 parent: Option<hir::BodyId>,
270 /// The index of the argument in the original definition.
272 lifetime_count: usize,
273 have_bound_regions: bool,
276 type ScopeRef<'a> = &'a Scope<'a>;
278 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
280 pub fn provide(providers: &mut ty::query::Providers<'_>) {
281 *providers = ty::query::Providers {
284 named_region_map: |tcx, id| {
285 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
286 tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id)
289 is_late_bound_map: |tcx, id| {
290 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
291 tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id)
294 object_lifetime_defaults_map: |tcx, id| {
295 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
296 tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id)
302 // (*) FIXME the query should be defined to take a LocalDefId
305 /// Computes the `ResolveLifetimes` map that contains data for the
306 /// entire crate. You should not read the result of this query
307 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
309 fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> &ResolveLifetimes {
310 assert_eq!(for_krate, LOCAL_CRATE);
312 let named_region_map = krate(tcx);
314 let mut rl = ResolveLifetimes::default();
316 for (hir_id, v) in named_region_map.defs {
317 let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
318 map.insert(hir_id.local_id, v);
320 for hir_id in named_region_map.late_bound {
321 let map = rl.late_bound.entry(hir_id.owner_local_def_id()).or_default();
322 map.insert(hir_id.local_id);
324 for (hir_id, v) in named_region_map.object_lifetime_defaults {
325 let map = rl.object_lifetime_defaults.entry(hir_id.owner_local_def_id()).or_default();
326 map.insert(hir_id.local_id, v);
332 fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
333 let krate = tcx.hir().krate();
334 let mut map = NamedRegionMap {
335 defs: Default::default(),
336 late_bound: Default::default(),
337 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
340 let mut visitor = LifetimeContext {
344 trait_ref_hack: false,
345 is_in_fn_syntax: false,
346 labels_in_fn: vec![],
347 xcrate_object_lifetime_defaults: Default::default(),
348 lifetime_uses: &mut Default::default(),
349 missing_named_lifetime_spots: vec![],
351 for (_, item) in &krate.items {
352 visitor.visit_item(item);
358 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
359 /// We have to account for this when computing the index of the other generic parameters.
360 /// This function returns whether there is such an implicit parameter defined on the given item.
361 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
363 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true,
368 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
369 type Map = Map<'tcx>;
371 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
372 NestedVisitorMap::All(&self.tcx.hir())
375 // We want to nest trait/impl items in their parent, but nothing else.
376 fn visit_nested_item(&mut self, _: hir::ItemId) {}
378 fn visit_nested_body(&mut self, body: hir::BodyId) {
379 // Each body has their own set of labels, save labels.
380 let saved = take(&mut self.labels_in_fn);
381 let body = self.tcx.hir().body(body);
382 extract_labels(self, body);
383 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
384 this.visit_body(body);
386 replace(&mut self.labels_in_fn, saved);
389 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
391 hir::ItemKind::Fn(ref sig, ref generics, _) => {
392 self.missing_named_lifetime_spots.push(generics);
393 self.visit_early_late(None, &sig.decl, generics, |this| {
394 intravisit::walk_item(this, item);
396 self.missing_named_lifetime_spots.pop();
399 hir::ItemKind::ExternCrate(_)
400 | hir::ItemKind::Use(..)
401 | hir::ItemKind::Mod(..)
402 | hir::ItemKind::ForeignMod(..)
403 | hir::ItemKind::GlobalAsm(..) => {
404 // These sorts of items have no lifetime parameters at all.
405 intravisit::walk_item(self, item);
407 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
408 // No lifetime parameters, but implied 'static.
409 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
410 self.with(scope, |_, this| intravisit::walk_item(this, item));
412 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => {
413 // Currently opaque type declarations are just generated from `impl Trait`
414 // items. Doing anything on this node is irrelevant, as we currently don't need
417 hir::ItemKind::TyAlias(_, ref generics)
418 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
419 impl_trait_fn: None, ref generics, ..
421 | hir::ItemKind::Enum(_, ref generics)
422 | hir::ItemKind::Struct(_, ref generics)
423 | hir::ItemKind::Union(_, ref generics)
424 | hir::ItemKind::Trait(_, _, ref generics, ..)
425 | hir::ItemKind::TraitAlias(ref generics, ..)
426 | hir::ItemKind::Impl { ref generics, .. } => {
427 self.missing_named_lifetime_spots.push(generics);
429 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
430 // This is not true for other kinds of items.x
431 let track_lifetime_uses = match item.kind {
432 hir::ItemKind::Impl { .. } => true,
435 // These kinds of items have only early-bound lifetime parameters.
436 let mut index = if sub_items_have_self_param(&item.kind) {
437 1 // Self comes before lifetimes
441 let mut non_lifetime_count = 0;
442 let lifetimes = generics
445 .filter_map(|param| match param.kind {
446 GenericParamKind::Lifetime { .. } => {
447 Some(Region::early(&self.tcx.hir(), &mut index, param))
449 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
450 non_lifetime_count += 1;
455 let scope = Scope::Binder {
457 next_early_index: index + non_lifetime_count,
458 opaque_type_parent: true,
462 self.with(scope, |old_scope, this| {
463 this.check_lifetime_params(old_scope, &generics.params);
464 intravisit::walk_item(this, item);
466 self.missing_named_lifetime_spots.pop();
471 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
473 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
474 self.visit_early_late(None, decl, generics, |this| {
475 intravisit::walk_foreign_item(this, item);
478 hir::ForeignItemKind::Static(..) => {
479 intravisit::walk_foreign_item(self, item);
481 hir::ForeignItemKind::Type => {
482 intravisit::walk_foreign_item(self, item);
487 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
488 debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty);
489 debug!("visit_ty: ty.kind={:?}", ty.kind);
491 hir::TyKind::BareFn(ref c) => {
492 let next_early_index = self.next_early_index();
493 let was_in_fn_syntax = self.is_in_fn_syntax;
494 self.is_in_fn_syntax = true;
495 let scope = Scope::Binder {
499 .filter_map(|param| match param.kind {
500 GenericParamKind::Lifetime { .. } => {
501 Some(Region::late(&self.tcx.hir(), param))
508 track_lifetime_uses: true,
509 opaque_type_parent: false,
511 self.with(scope, |old_scope, this| {
512 // a bare fn has no bounds, so everything
513 // contained within is scoped within its binder.
514 this.check_lifetime_params(old_scope, &c.generic_params);
515 intravisit::walk_ty(this, ty);
517 self.is_in_fn_syntax = was_in_fn_syntax;
519 hir::TyKind::TraitObject(bounds, ref lifetime) => {
520 debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime);
521 for bound in bounds {
522 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
524 match lifetime.name {
525 LifetimeName::Implicit => {
526 // For types like `dyn Foo`, we should
527 // generate a special form of elided.
528 span_bug!(ty.span, "object-lifetime-default expected, not implict",);
530 LifetimeName::ImplicitObjectLifetimeDefault => {
531 // If the user does not write *anything*, we
532 // use the object lifetime defaulting
533 // rules. So e.g., `Box<dyn Debug>` becomes
534 // `Box<dyn Debug + 'static>`.
535 self.resolve_object_lifetime_default(lifetime)
537 LifetimeName::Underscore => {
538 // If the user writes `'_`, we use the *ordinary* elision
539 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
540 // resolved the same as the `'_` in `&'_ Foo`.
543 self.resolve_elided_lifetimes(vec![lifetime])
545 LifetimeName::Param(_) | LifetimeName::Static => {
546 // If the user wrote an explicit name, use that.
547 self.visit_lifetime(lifetime);
549 LifetimeName::Error => {}
552 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
553 self.visit_lifetime(lifetime_ref);
554 let scope = Scope::ObjectLifetimeDefault {
555 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
558 self.with(scope, |_, this| this.visit_ty(&mt.ty));
560 hir::TyKind::Def(item_id, lifetimes) => {
561 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
562 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
563 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
564 // ^ ^ this gets resolved in the scope of
565 // the opaque_ty generics
566 let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).kind {
567 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
568 // This arm is for `impl Trait` in the types of statics, constants and locals.
569 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
570 intravisit::walk_ty(self, ty);
573 // RPIT (return position impl trait)
574 hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, bounds, .. }) => {
577 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
580 // Resolve the lifetimes that are applied to the opaque type.
581 // These are resolved in the current scope.
582 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
583 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
584 // ^ ^this gets resolved in the current scope
585 for lifetime in lifetimes {
586 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
587 self.visit_lifetime(lifetime);
589 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
590 // and ban them. Type variables instantiated inside binders aren't
591 // well-supported at the moment, so this doesn't work.
592 // In the future, this should be fixed and this error should be removed.
593 let def = self.map.defs.get(&lifetime.hir_id).cloned();
594 if let Some(Region::LateBound(_, def_id, _)) = def {
595 if let Some(hir_id) = self.tcx.hir().as_local_hir_id(def_id) {
596 // Ensure that the parent of the def is an item, not HRTB
597 let parent_id = self.tcx.hir().get_parent_node(hir_id);
598 let parent_impl_id = hir::ImplItemId { hir_id: parent_id };
599 let parent_trait_id = hir::TraitItemId { hir_id: parent_id };
600 let krate = self.tcx.hir().forest.krate();
602 if !(krate.items.contains_key(&parent_id)
603 || krate.impl_items.contains_key(&parent_impl_id)
604 || krate.trait_items.contains_key(&parent_trait_id))
610 "`impl Trait` can only capture lifetimes \
611 bound at the fn or impl level"
614 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
621 // We want to start our early-bound indices at the end of the parent scope,
622 // not including any parent `impl Trait`s.
623 let mut index = self.next_early_index_for_opaque_type();
624 debug!("visit_ty: index = {}", index);
626 let mut elision = None;
627 let mut lifetimes = FxHashMap::default();
628 let mut non_lifetime_count = 0;
629 for param in generics.params {
631 GenericParamKind::Lifetime { .. } => {
632 let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m);
633 let def_id = if let Region::EarlyBound(_, def_id, _) = reg {
638 if let hir::ParamName::Plain(param_name) = name {
639 if param_name.name == kw::UnderscoreLifetime {
640 // Pick the elided lifetime "definition" if one exists
641 // and use it to make an elision scope.
642 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
645 lifetimes.insert(name, reg);
648 self.lifetime_uses.insert(def_id.clone(), LifetimeUseSet::Many);
649 lifetimes.insert(name, reg);
652 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
653 non_lifetime_count += 1;
657 let next_early_index = index + non_lifetime_count;
659 if let Some(elision_region) = elision {
661 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
662 self.with(scope, |_old_scope, this| {
663 let scope = Scope::Binder {
667 track_lifetime_uses: true,
668 opaque_type_parent: false,
670 this.with(scope, |_old_scope, this| {
671 this.visit_generics(generics);
672 for bound in bounds {
673 this.visit_param_bound(bound);
678 let scope = Scope::Binder {
682 track_lifetime_uses: true,
683 opaque_type_parent: false,
685 self.with(scope, |_old_scope, this| {
686 this.visit_generics(generics);
687 for bound in bounds {
688 this.visit_param_bound(bound);
693 _ => intravisit::walk_ty(self, ty),
697 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
698 use self::hir::TraitItemKind::*;
699 self.missing_named_lifetime_spots.push(&trait_item.generics);
700 match trait_item.kind {
701 Method(ref sig, _) => {
703 self.visit_early_late(
704 Some(tcx.hir().get_parent_item(trait_item.hir_id)),
706 &trait_item.generics,
707 |this| intravisit::walk_trait_item(this, trait_item),
710 Type(bounds, ref ty) => {
711 let generics = &trait_item.generics;
712 let mut index = self.next_early_index();
713 debug!("visit_ty: index = {}", index);
714 let mut non_lifetime_count = 0;
715 let lifetimes = generics
718 .filter_map(|param| match param.kind {
719 GenericParamKind::Lifetime { .. } => {
720 Some(Region::early(&self.tcx.hir(), &mut index, param))
722 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
723 non_lifetime_count += 1;
728 let scope = Scope::Binder {
730 next_early_index: index + non_lifetime_count,
732 track_lifetime_uses: true,
733 opaque_type_parent: true,
735 self.with(scope, |_old_scope, this| {
736 this.visit_generics(generics);
737 for bound in bounds {
738 this.visit_param_bound(bound);
740 if let Some(ty) = ty {
746 // Only methods and types support generics.
747 assert!(trait_item.generics.params.is_empty());
748 intravisit::walk_trait_item(self, trait_item);
751 self.missing_named_lifetime_spots.pop();
754 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
755 use self::hir::ImplItemKind::*;
756 self.missing_named_lifetime_spots.push(&impl_item.generics);
757 match impl_item.kind {
758 Method(ref sig, _) => {
760 self.visit_early_late(
761 Some(tcx.hir().get_parent_item(impl_item.hir_id)),
764 |this| intravisit::walk_impl_item(this, impl_item),
768 let generics = &impl_item.generics;
769 let mut index = self.next_early_index();
770 let mut non_lifetime_count = 0;
771 debug!("visit_ty: index = {}", index);
772 let lifetimes = generics
775 .filter_map(|param| match param.kind {
776 GenericParamKind::Lifetime { .. } => {
777 Some(Region::early(&self.tcx.hir(), &mut index, param))
779 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
780 non_lifetime_count += 1;
785 let scope = Scope::Binder {
787 next_early_index: index + non_lifetime_count,
789 track_lifetime_uses: true,
790 opaque_type_parent: true,
792 self.with(scope, |_old_scope, this| {
793 this.visit_generics(generics);
797 OpaqueTy(bounds) => {
798 let generics = &impl_item.generics;
799 let mut index = self.next_early_index();
800 let mut next_early_index = index;
801 debug!("visit_ty: index = {}", index);
802 let lifetimes = generics
805 .filter_map(|param| match param.kind {
806 GenericParamKind::Lifetime { .. } => {
807 Some(Region::early(&self.tcx.hir(), &mut index, param))
809 GenericParamKind::Type { .. } => {
810 next_early_index += 1;
813 GenericParamKind::Const { .. } => {
814 next_early_index += 1;
820 let scope = Scope::Binder {
824 track_lifetime_uses: true,
825 opaque_type_parent: true,
827 self.with(scope, |_old_scope, this| {
828 this.visit_generics(generics);
829 for bound in bounds {
830 this.visit_param_bound(bound);
835 // Only methods and types support generics.
836 assert!(impl_item.generics.params.is_empty());
837 intravisit::walk_impl_item(self, impl_item);
840 self.missing_named_lifetime_spots.pop();
843 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
844 debug!("visit_lifetime(lifetime_ref={:?})", lifetime_ref);
845 if lifetime_ref.is_elided() {
846 self.resolve_elided_lifetimes(vec![lifetime_ref]);
849 if lifetime_ref.is_static() {
850 self.insert_lifetime(lifetime_ref, Region::Static);
853 self.resolve_lifetime_ref(lifetime_ref);
856 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
857 for (i, segment) in path.segments.iter().enumerate() {
858 let depth = path.segments.len() - i - 1;
859 if let Some(ref args) = segment.args {
860 self.visit_segment_args(path.res, depth, args);
865 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
866 let output = match fd.output {
867 hir::FunctionRetTy::DefaultReturn(_) => None,
868 hir::FunctionRetTy::Return(ref ty) => Some(&**ty),
870 self.visit_fn_like_elision(&fd.inputs, output);
873 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
874 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
875 for param in generics.params {
877 GenericParamKind::Lifetime { .. } => {}
878 GenericParamKind::Type { ref default, .. } => {
879 walk_list!(self, visit_param_bound, param.bounds);
880 if let Some(ref ty) = default {
884 GenericParamKind::Const { ref ty, .. } => {
885 walk_list!(self, visit_param_bound, param.bounds);
890 for predicate in generics.where_clause.predicates {
892 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
895 ref bound_generic_params,
898 let lifetimes: FxHashMap<_, _> = bound_generic_params
900 .filter_map(|param| match param.kind {
901 GenericParamKind::Lifetime { .. } => {
902 Some(Region::late(&self.tcx.hir(), param))
907 if !lifetimes.is_empty() {
908 self.trait_ref_hack = true;
909 let next_early_index = self.next_early_index();
910 let scope = Scope::Binder {
914 track_lifetime_uses: true,
915 opaque_type_parent: false,
917 let result = self.with(scope, |old_scope, this| {
918 this.check_lifetime_params(old_scope, &bound_generic_params);
919 this.visit_ty(&bounded_ty);
920 walk_list!(this, visit_param_bound, bounds);
922 self.trait_ref_hack = false;
925 self.visit_ty(&bounded_ty);
926 walk_list!(self, visit_param_bound, bounds);
929 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
934 self.visit_lifetime(lifetime);
935 walk_list!(self, visit_param_bound, bounds);
937 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
942 self.visit_ty(lhs_ty);
943 self.visit_ty(rhs_ty);
949 fn visit_poly_trait_ref(
951 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
952 _modifier: hir::TraitBoundModifier,
954 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
956 if !self.trait_ref_hack
957 || trait_ref.bound_generic_params.iter().any(|param| match param.kind {
958 GenericParamKind::Lifetime { .. } => true,
962 if self.trait_ref_hack {
967 "nested quantification of lifetimes"
971 let next_early_index = self.next_early_index();
972 let scope = Scope::Binder {
974 .bound_generic_params
976 .filter_map(|param| match param.kind {
977 GenericParamKind::Lifetime { .. } => {
978 Some(Region::late(&self.tcx.hir(), param))
985 track_lifetime_uses: true,
986 opaque_type_parent: false,
988 self.with(scope, |old_scope, this| {
989 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
990 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
991 this.visit_trait_ref(&trait_ref.trait_ref)
994 self.visit_trait_ref(&trait_ref.trait_ref)
999 #[derive(Copy, Clone, PartialEq)]
1013 fn original_label(span: Span) -> Original {
1014 Original { kind: ShadowKind::Label, span: span }
1016 fn shadower_label(span: Span) -> Shadower {
1017 Shadower { kind: ShadowKind::Label, span: span }
1019 fn original_lifetime(span: Span) -> Original {
1020 Original { kind: ShadowKind::Lifetime, span: span }
1022 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1023 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1027 fn desc(&self) -> &'static str {
1029 ShadowKind::Label => "label",
1030 ShadowKind::Lifetime => "lifetime",
1035 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1036 let lifetime_params: Vec<_> = params
1038 .filter_map(|param| match param.kind {
1039 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1043 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1044 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1046 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1051 "cannot mix in-band and explicit lifetime definitions"
1053 .span_label(*in_band_span, "in-band lifetime definition here")
1054 .span_label(*explicit_span, "explicit lifetime definition here")
1059 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: ast::Name, orig: Original, shadower: Shadower) {
1060 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1061 // lifetime/lifetime shadowing is an error
1066 "{} name `{}` shadows a \
1067 {} name that is already in scope",
1068 shadower.kind.desc(),
1073 // shadowing involving a label is only a warning, due to issues with
1074 // labels and lifetimes not being macro-hygienic.
1075 tcx.sess.struct_span_warn(
1078 "{} name `{}` shadows a \
1079 {} name that is already in scope",
1080 shadower.kind.desc(),
1086 err.span_label(orig.span, "first declared here");
1087 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1091 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1092 // if one of the label shadows a lifetime or another label.
1093 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1094 struct GatherLabels<'a, 'tcx> {
1096 scope: ScopeRef<'a>,
1097 labels_in_fn: &'a mut Vec<ast::Ident>,
1101 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1102 gather.visit_body(body);
1104 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1107 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
1108 NestedVisitorMap::None
1111 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1112 if let Some(label) = expression_label(ex) {
1113 for prior_label in &self.labels_in_fn[..] {
1114 // FIXME (#24278): non-hygienic comparison
1115 if label.name == prior_label.name {
1116 signal_shadowing_problem(
1119 original_label(prior_label.span),
1120 shadower_label(label.span),
1125 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1127 self.labels_in_fn.push(label);
1129 intravisit::walk_expr(self, ex)
1133 fn expression_label(ex: &hir::Expr<'_>) -> Option<ast::Ident> {
1134 if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None }
1137 fn check_if_label_shadows_lifetime(
1139 mut scope: ScopeRef<'_>,
1144 Scope::Body { s, .. }
1145 | Scope::Elision { s, .. }
1146 | Scope::ObjectLifetimeDefault { s, .. } => {
1154 Scope::Binder { ref lifetimes, s, .. } => {
1155 // FIXME (#24278): non-hygienic comparison
1156 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1157 let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
1159 signal_shadowing_problem(
1162 original_lifetime(tcx.hir().span(hir_id)),
1163 shadower_label(label.span),
1174 fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap<Vec<ObjectLifetimeDefault>> {
1175 let mut map = HirIdMap::default();
1176 for item in tcx.hir().krate().items.values() {
1178 hir::ItemKind::Struct(_, ref generics)
1179 | hir::ItemKind::Union(_, ref generics)
1180 | hir::ItemKind::Enum(_, ref generics)
1181 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1182 ref generics, impl_trait_fn: None, ..
1184 | hir::ItemKind::TyAlias(_, ref generics)
1185 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1186 let result = object_lifetime_defaults_for_item(tcx, generics);
1189 if attr::contains_name(&item.attrs, sym::rustc_object_lifetime_default) {
1190 let object_lifetime_default_reprs: String = result
1192 .map(|set| match *set {
1193 Set1::Empty => "BaseDefault".into(),
1194 Set1::One(Region::Static) => "'static".into(),
1195 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1198 .find_map(|param| match param.kind {
1199 GenericParamKind::Lifetime { .. } => {
1201 return Some(param.name.ident().to_string().into());
1209 Set1::One(_) => bug!(),
1210 Set1::Many => "Ambiguous".into(),
1212 .collect::<Vec<Cow<'static, str>>>()
1214 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1217 map.insert(item.hir_id, result);
1225 /// Scan the bounds and where-clauses on parameters to extract bounds
1226 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1227 /// for each type parameter.
1228 fn object_lifetime_defaults_for_item(
1230 generics: &hir::Generics<'_>,
1231 ) -> Vec<ObjectLifetimeDefault> {
1232 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1233 for bound in bounds {
1234 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1235 set.insert(lifetime.name.modern());
1243 .filter_map(|param| match param.kind {
1244 GenericParamKind::Lifetime { .. } => None,
1245 GenericParamKind::Type { .. } => {
1246 let mut set = Set1::Empty;
1248 add_bounds(&mut set, ¶m.bounds);
1250 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1251 for predicate in generics.where_clause.predicates {
1252 // Look for `type: ...` where clauses.
1253 let data = match *predicate {
1254 hir::WherePredicate::BoundPredicate(ref data) => data,
1258 // Ignore `for<'a> type: ...` as they can change what
1259 // lifetimes mean (although we could "just" handle it).
1260 if !data.bound_generic_params.is_empty() {
1264 let res = match data.bounded_ty.kind {
1265 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1269 if res == Res::Def(DefKind::TyParam, param_def_id) {
1270 add_bounds(&mut set, &data.bounds);
1275 Set1::Empty => Set1::Empty,
1276 Set1::One(name) => {
1277 if name == hir::LifetimeName::Static {
1278 Set1::One(Region::Static)
1283 .filter_map(|param| match param.kind {
1284 GenericParamKind::Lifetime { .. } => Some((
1286 hir::LifetimeName::Param(param.name),
1287 LifetimeDefOrigin::from_param(param),
1292 .find(|&(_, (_, lt_name, _))| lt_name == name)
1293 .map_or(Set1::Many, |(i, (id, _, origin))| {
1294 let def_id = tcx.hir().local_def_id(id);
1295 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1299 Set1::Many => Set1::Many,
1302 GenericParamKind::Const { .. } => {
1303 // Generic consts don't impose any constraints.
1310 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1311 // FIXME(#37666) this works around a limitation in the region inferencer
1312 fn hack<F>(&mut self, f: F)
1314 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1319 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1321 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1323 let LifetimeContext { tcx, map, lifetime_uses, missing_named_lifetime_spots, .. } = self;
1324 let labels_in_fn = take(&mut self.labels_in_fn);
1325 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1326 let mut this = LifetimeContext {
1330 trait_ref_hack: self.trait_ref_hack,
1331 is_in_fn_syntax: self.is_in_fn_syntax,
1333 xcrate_object_lifetime_defaults,
1335 missing_named_lifetime_spots: missing_named_lifetime_spots.to_vec(),
1337 debug!("entering scope {:?}", this.scope);
1338 f(self.scope, &mut this);
1339 this.check_uses_for_lifetimes_defined_by_scope();
1340 debug!("exiting scope {:?}", this.scope);
1341 self.labels_in_fn = this.labels_in_fn;
1342 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1345 /// helper method to determine the span to remove when suggesting the
1346 /// deletion of a lifetime
1347 fn lifetime_deletion_span(
1350 generics: &hir::Generics<'_>,
1352 generics.params.iter().enumerate().find_map(|(i, param)| {
1353 if param.name.ident() == name {
1354 let mut in_band = false;
1355 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1356 if let hir::LifetimeParamKind::InBand = kind {
1363 if generics.params.len() == 1 {
1364 // if sole lifetime, remove the entire `<>` brackets
1367 // if removing within `<>` brackets, we also want to
1368 // delete a leading or trailing comma as appropriate
1369 if i >= generics.params.len() - 1 {
1370 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1372 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1382 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1383 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1384 fn suggest_eliding_single_use_lifetime(
1386 err: &mut DiagnosticBuilder<'_>,
1388 lifetime: &hir::Lifetime,
1390 let name = lifetime.name.ident();
1391 let mut remove_decl = None;
1392 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1393 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1394 remove_decl = self.lifetime_deletion_span(name, generics);
1398 let mut remove_use = None;
1399 let mut elide_use = None;
1400 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1401 for input in inputs {
1403 hir::TyKind::Rptr(lt, _) => {
1404 if lt.name.ident() == name {
1405 // include the trailing whitespace between the lifetime and type names
1406 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1411 .span_until_non_whitespace(lt_through_ty_span),
1416 hir::TyKind::Path(ref qpath) => {
1417 if let QPath::Resolved(_, path) = qpath {
1418 let last_segment = &path.segments[path.segments.len() - 1];
1419 let generics = last_segment.generic_args();
1420 for arg in generics.args.iter() {
1421 if let GenericArg::Lifetime(lt) = arg {
1422 if lt.name.ident() == name {
1423 elide_use = Some(lt.span);
1435 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1436 if let Some(parent) =
1437 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1440 Node::Item(item) => {
1441 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1442 find_arg_use_span(sig.decl.inputs);
1445 Node::ImplItem(impl_item) => {
1446 if let hir::ImplItemKind::Method(sig, _) = &impl_item.kind {
1447 find_arg_use_span(sig.decl.inputs);
1455 let msg = "elide the single-use lifetime";
1456 match (remove_decl, remove_use, elide_use) {
1457 (Some(decl_span), Some(use_span), None) => {
1458 // if both declaration and use deletion spans start at the same
1459 // place ("start at" because the latter includes trailing
1460 // whitespace), then this is an in-band lifetime
1461 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1462 err.span_suggestion(
1466 Applicability::MachineApplicable,
1469 err.multipart_suggestion(
1471 vec![(decl_span, String::new()), (use_span, String::new())],
1472 Applicability::MachineApplicable,
1476 (Some(decl_span), None, Some(use_span)) => {
1477 err.multipart_suggestion(
1479 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1480 Applicability::MachineApplicable,
1487 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1488 let defined_by = match self.scope {
1489 Scope::Binder { lifetimes, .. } => lifetimes,
1491 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1496 let mut def_ids: Vec<_> = defined_by
1498 .flat_map(|region| match region {
1499 Region::EarlyBound(_, def_id, _)
1500 | Region::LateBound(_, def_id, _)
1501 | Region::Free(_, def_id) => Some(*def_id),
1503 Region::LateBoundAnon(..) | Region::Static => None,
1507 // ensure that we issue lints in a repeatable order
1508 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1510 for def_id in def_ids {
1511 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1513 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1516 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1520 match lifetimeuseset {
1521 Some(LifetimeUseSet::One(lifetime)) => {
1522 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1523 debug!("hir id first={:?}", hir_id);
1524 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1525 Node::Lifetime(hir_lifetime) => Some((
1526 hir_lifetime.hir_id,
1528 hir_lifetime.name.ident(),
1530 Node::GenericParam(param) => {
1531 Some((param.hir_id, param.span, param.name.ident()))
1535 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1536 if name.name == kw::UnderscoreLifetime {
1540 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1541 if let Some(parent_hir_id) =
1542 self.tcx.hir().as_local_hir_id(parent_def_id)
1544 // lifetimes in `derive` expansions don't count (Issue #53738)
1548 .attrs(parent_hir_id)
1550 .any(|attr| attr.check_name(sym::automatically_derived))
1557 let mut err = self.tcx.struct_span_lint_hir(
1558 lint::builtin::SINGLE_USE_LIFETIMES,
1561 &format!("lifetime parameter `{}` only used once", name),
1564 if span == lifetime.span {
1565 // spans are the same for in-band lifetime declarations
1566 err.span_label(span, "this lifetime is only used here");
1568 err.span_label(span, "this lifetime...");
1569 err.span_label(lifetime.span, "...is used only here");
1571 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1575 Some(LifetimeUseSet::Many) => {
1576 debug!("not one use lifetime");
1579 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1580 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1581 Node::Lifetime(hir_lifetime) => Some((
1582 hir_lifetime.hir_id,
1584 hir_lifetime.name.ident(),
1586 Node::GenericParam(param) => {
1587 Some((param.hir_id, param.span, param.name.ident()))
1591 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1592 let mut err = self.tcx.struct_span_lint_hir(
1593 lint::builtin::UNUSED_LIFETIMES,
1596 &format!("lifetime parameter `{}` never used", name),
1598 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1599 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1600 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1601 if let Some(span) = unused_lt_span {
1602 err.span_suggestion(
1604 "elide the unused lifetime",
1606 Applicability::MachineApplicable,
1618 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1620 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1621 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1622 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1626 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1628 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1629 /// lifetimes may be interspersed together.
1631 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1632 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1633 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1634 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1635 /// ordering is not important there.
1636 fn visit_early_late<F>(
1638 parent_id: Option<hir::HirId>,
1639 decl: &'tcx hir::FnDecl<'tcx>,
1640 generics: &'tcx hir::Generics<'tcx>,
1643 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1645 insert_late_bound_lifetimes(self.map, decl, generics);
1647 // Find the start of nested early scopes, e.g., in methods.
1649 if let Some(parent_id) = parent_id {
1650 let parent = self.tcx.hir().expect_item(parent_id);
1651 if sub_items_have_self_param(&parent.kind) {
1652 index += 1; // Self comes before lifetimes
1655 hir::ItemKind::Trait(_, _, ref generics, ..)
1656 | hir::ItemKind::Impl { ref generics, .. } => {
1657 index += generics.params.len() as u32;
1663 let mut non_lifetime_count = 0;
1664 let lifetimes = generics
1667 .filter_map(|param| match param.kind {
1668 GenericParamKind::Lifetime { .. } => {
1669 if self.map.late_bound.contains(¶m.hir_id) {
1670 Some(Region::late(&self.tcx.hir(), param))
1672 Some(Region::early(&self.tcx.hir(), &mut index, param))
1675 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1676 non_lifetime_count += 1;
1681 let next_early_index = index + non_lifetime_count;
1683 let scope = Scope::Binder {
1687 opaque_type_parent: true,
1688 track_lifetime_uses: false,
1690 self.with(scope, move |old_scope, this| {
1691 this.check_lifetime_params(old_scope, &generics.params);
1692 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1696 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1697 let mut scope = self.scope;
1700 Scope::Root => return 0,
1702 Scope::Binder { next_early_index, opaque_type_parent, .. }
1703 if (!only_opaque_type_parent || opaque_type_parent) =>
1705 return next_early_index;
1708 Scope::Binder { s, .. }
1709 | Scope::Body { s, .. }
1710 | Scope::Elision { s, .. }
1711 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1716 /// Returns the next index one would use for an early-bound-region
1717 /// if extending the current scope.
1718 fn next_early_index(&self) -> u32 {
1719 self.next_early_index_helper(true)
1722 /// Returns the next index one would use for an `impl Trait` that
1723 /// is being converted into an opaque type alias `impl Trait`. This will be the
1724 /// next early index from the enclosing item, for the most
1725 /// part. See the `opaque_type_parent` field for more info.
1726 fn next_early_index_for_opaque_type(&self) -> u32 {
1727 self.next_early_index_helper(false)
1730 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1731 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1733 // If we've already reported an error, just ignore `lifetime_ref`.
1734 if let LifetimeName::Error = lifetime_ref.name {
1738 // Walk up the scope chain, tracking the number of fn scopes
1739 // that we pass through, until we find a lifetime with the
1740 // given name or we run out of scopes.
1742 let mut late_depth = 0;
1743 let mut scope = self.scope;
1744 let mut outermost_body = None;
1747 Scope::Body { id, s } => {
1748 outermost_body = Some(id);
1756 Scope::Binder { ref lifetimes, s, .. } => {
1757 match lifetime_ref.name {
1758 LifetimeName::Param(param_name) => {
1759 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1760 break Some(def.shifted(late_depth));
1763 _ => bug!("expected LifetimeName::Param"),
1770 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1776 if let Some(mut def) = result {
1777 if let Region::EarlyBound(..) = def {
1778 // Do not free early-bound regions, only late-bound ones.
1779 } else if let Some(body_id) = outermost_body {
1780 let fn_id = self.tcx.hir().body_owner(body_id);
1781 match self.tcx.hir().get(fn_id) {
1782 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1783 | Node::TraitItem(&hir::TraitItem {
1784 kind: hir::TraitItemKind::Method(..),
1787 | Node::ImplItem(&hir::ImplItem {
1788 kind: hir::ImplItemKind::Method(..), ..
1790 let scope = self.tcx.hir().local_def_id(fn_id);
1791 def = Region::Free(scope, def.id().unwrap());
1797 // Check for fn-syntax conflicts with in-band lifetime definitions
1798 if self.is_in_fn_syntax {
1800 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1801 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1806 "lifetimes used in `fn` or `Fn` syntax must be \
1807 explicitly declared using `<...>` binders"
1809 .span_label(lifetime_ref.span, "in-band lifetime definition")
1814 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1815 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1816 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1817 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1818 | Region::LateBoundAnon(..)
1819 | Region::Free(..) => {}
1823 self.insert_lifetime(lifetime_ref, def);
1825 let mut err = struct_span_err!(
1829 "use of undeclared lifetime name `{}`",
1832 err.span_label(lifetime_ref.span, "undeclared lifetime");
1833 if !self.is_in_fn_syntax {
1834 for generics in &self.missing_named_lifetime_spots {
1835 let (span, sugg) = match &generics.params {
1836 [] => (generics.span, format!("<{}>", lifetime_ref)),
1837 [param, ..] => (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref)),
1839 err.span_suggestion(
1841 &format!("consider introducing lifetime `{}` here", lifetime_ref),
1843 Applicability::MaybeIncorrect,
1851 fn visit_segment_args(
1855 generic_args: &'tcx hir::GenericArgs<'tcx>,
1858 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1859 res, depth, generic_args,
1862 if generic_args.parenthesized {
1863 let was_in_fn_syntax = self.is_in_fn_syntax;
1864 self.is_in_fn_syntax = true;
1865 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1866 self.is_in_fn_syntax = was_in_fn_syntax;
1870 let mut elide_lifetimes = true;
1871 let lifetimes = generic_args
1874 .filter_map(|arg| match arg {
1875 hir::GenericArg::Lifetime(lt) => {
1876 if !lt.is_elided() {
1877 elide_lifetimes = false;
1884 if elide_lifetimes {
1885 self.resolve_elided_lifetimes(lifetimes);
1887 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1890 // Figure out if this is a type/trait segment,
1891 // which requires object lifetime defaults.
1892 let parent_def_id = |this: &mut Self, def_id: DefId| {
1893 let def_key = this.tcx.def_key(def_id);
1894 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1896 let type_def_id = match res {
1897 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1898 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1899 Res::Def(DefKind::Struct, def_id)
1900 | Res::Def(DefKind::Union, def_id)
1901 | Res::Def(DefKind::Enum, def_id)
1902 | Res::Def(DefKind::TyAlias, def_id)
1903 | Res::Def(DefKind::Trait, def_id)
1911 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1913 // Compute a vector of defaults, one for each type parameter,
1914 // per the rules given in RFCs 599 and 1156. Example:
1917 // struct Foo<'a, T: 'a, U> { }
1920 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1921 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1922 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1925 // Therefore, we would compute `object_lifetime_defaults` to a
1926 // vector like `['x, 'static]`. Note that the vector only
1927 // includes type parameters.
1928 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1930 let mut scope = self.scope;
1933 Scope::Root => break false,
1935 Scope::Body { .. } => break true,
1937 Scope::Binder { s, .. }
1938 | Scope::Elision { s, .. }
1939 | Scope::ObjectLifetimeDefault { s, .. } => {
1946 let map = &self.map;
1947 let unsubst = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
1948 &map.object_lifetime_defaults[&id]
1951 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1952 tcx.generics_of(def_id)
1955 .filter_map(|param| match param.kind {
1956 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1957 Some(object_lifetime_default)
1959 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1964 debug!("visit_segment_args: unsubst={:?}", unsubst);
1967 .map(|set| match *set {
1972 Some(Region::Static)
1976 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1977 GenericArg::Lifetime(lt) => Some(lt),
1980 r.subst(lifetimes, map)
1987 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1990 for arg in generic_args.args {
1992 GenericArg::Lifetime(_) => {}
1993 GenericArg::Type(ty) => {
1994 if let Some(<) = object_lifetime_defaults.get(i) {
1995 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1996 self.with(scope, |_, this| this.visit_ty(ty));
2002 GenericArg::Const(ct) => {
2003 self.visit_anon_const(&ct.value);
2008 // Hack: when resolving the type `XX` in binding like `dyn
2009 // Foo<'b, Item = XX>`, the current object-lifetime default
2010 // would be to examine the trait `Foo` to check whether it has
2011 // a lifetime bound declared on `Item`. e.g., if `Foo` is
2012 // declared like so, then the default object lifetime bound in
2013 // `XX` should be `'b`:
2021 // but if we just have `type Item;`, then it would be
2022 // `'static`. However, we don't get all of this logic correct.
2024 // Instead, we do something hacky: if there are no lifetime parameters
2025 // to the trait, then we simply use a default object lifetime
2026 // bound of `'static`, because there is no other possibility. On the other hand,
2027 // if there ARE lifetime parameters, then we require the user to give an
2028 // explicit bound for now.
2030 // This is intended to leave room for us to implement the
2031 // correct behavior in the future.
2032 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
2033 GenericArg::Lifetime(_) => true,
2037 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2038 for b in generic_args.bindings {
2039 let scope = Scope::ObjectLifetimeDefault {
2040 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2043 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2047 fn visit_fn_like_elision(
2049 inputs: &'tcx [hir::Ty<'tcx>],
2050 output: Option<&'tcx hir::Ty<'tcx>>,
2052 debug!("visit_fn_like_elision: enter");
2053 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2054 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2055 self.with(arg_scope, |_, this| {
2056 for input in inputs {
2057 this.visit_ty(input);
2060 Scope::Elision { ref elide, .. } => {
2061 arg_elide = elide.clone();
2067 let output = match output {
2072 debug!("visit_fn_like_elision: determine output");
2074 // Figure out if there's a body we can get argument names from,
2075 // and whether there's a `self` argument (treated specially).
2076 let mut assoc_item_kind = None;
2077 let mut impl_self = None;
2078 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2079 let body = match self.tcx.hir().get(parent) {
2080 // `fn` definitions and methods.
2081 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2083 Node::TraitItem(&hir::TraitItem {
2084 kind: hir::TraitItemKind::Method(_, ref m), ..
2086 if let hir::ItemKind::Trait(.., ref trait_items) =
2087 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2090 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2093 hir::TraitMethod::Required(_) => None,
2094 hir::TraitMethod::Provided(body) => Some(body),
2098 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Method(_, body), .. }) => {
2099 if let hir::ItemKind::Impl { ref self_ty, ref items, .. } =
2100 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2102 impl_self = Some(self_ty);
2104 items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2109 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2110 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2111 // Everything else (only closures?) doesn't
2112 // actually enjoy elision in return types.
2114 self.visit_ty(output);
2119 let has_self = match assoc_item_kind {
2120 Some(hir::AssocItemKind::Method { has_self }) => has_self,
2124 // In accordance with the rules for lifetime elision, we can determine
2125 // what region to use for elision in the output type in two ways.
2126 // First (determined here), if `self` is by-reference, then the
2127 // implied output region is the region of the self parameter.
2129 struct SelfVisitor<'a> {
2130 map: &'a NamedRegionMap,
2131 impl_self: Option<&'a hir::TyKind<'a>>,
2132 lifetime: Set1<Region>,
2135 impl SelfVisitor<'_> {
2136 // Look for `self: &'a Self` - also desugared from `&'a self`,
2137 // and if that matches, use it for elision and return early.
2138 fn is_self_ty(&self, res: Res) -> bool {
2139 if let Res::SelfTy(..) = res {
2143 // Can't always rely on literal (or implied) `Self` due
2144 // to the way elision rules were originally specified.
2145 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2149 // Whitelist the types that unambiguously always
2150 // result in the same type constructor being used
2151 // (it can't differ between `Self` and `self`).
2152 Res::Def(DefKind::Struct, _)
2153 | Res::Def(DefKind::Union, _)
2154 | Res::Def(DefKind::Enum, _)
2155 | Res::PrimTy(_) => return res == path.res,
2164 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2167 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2168 NestedVisitorMap::None
2171 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2172 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2173 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2175 if self.is_self_ty(path.res) {
2176 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2177 self.lifetime.insert(*lifetime);
2182 intravisit::walk_ty(self, ty)
2186 let mut visitor = SelfVisitor {
2188 impl_self: impl_self.map(|ty| &ty.kind),
2189 lifetime: Set1::Empty,
2191 visitor.visit_ty(&inputs[0]);
2192 if let Set1::One(lifetime) = visitor.lifetime {
2193 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2194 self.with(scope, |_, this| this.visit_ty(output));
2199 // Second, if there was exactly one lifetime (either a substitution or a
2200 // reference) in the arguments, then any anonymous regions in the output
2201 // have that lifetime.
2202 let mut possible_implied_output_region = None;
2203 let mut lifetime_count = 0;
2204 let arg_lifetimes = inputs
2207 .skip(has_self as usize)
2209 let mut gather = GatherLifetimes {
2211 outer_index: ty::INNERMOST,
2212 have_bound_regions: false,
2213 lifetimes: Default::default(),
2215 gather.visit_ty(input);
2217 lifetime_count += gather.lifetimes.len();
2219 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2220 // there's a chance that the unique lifetime of this
2221 // iteration will be the appropriate lifetime for output
2222 // parameters, so lets store it.
2223 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2226 ElisionFailureInfo {
2229 lifetime_count: gather.lifetimes.len(),
2230 have_bound_regions: gather.have_bound_regions,
2235 let elide = if lifetime_count == 1 {
2236 Elide::Exact(possible_implied_output_region.unwrap())
2238 Elide::Error(arg_lifetimes)
2241 debug!("visit_fn_like_elision: elide={:?}", elide);
2243 let scope = Scope::Elision { elide, s: self.scope };
2244 self.with(scope, |_, this| this.visit_ty(output));
2245 debug!("visit_fn_like_elision: exit");
2247 struct GatherLifetimes<'a> {
2248 map: &'a NamedRegionMap,
2249 outer_index: ty::DebruijnIndex,
2250 have_bound_regions: bool,
2251 lifetimes: FxHashSet<Region>,
2254 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2257 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2258 NestedVisitorMap::None
2261 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2262 if let hir::TyKind::BareFn(_) = ty.kind {
2263 self.outer_index.shift_in(1);
2266 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2267 for bound in bounds {
2268 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2271 // Stay on the safe side and don't include the object
2272 // lifetime default (which may not end up being used).
2273 if !lifetime.is_elided() {
2274 self.visit_lifetime(lifetime);
2278 intravisit::walk_ty(self, ty);
2281 if let hir::TyKind::BareFn(_) = ty.kind {
2282 self.outer_index.shift_out(1);
2286 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2287 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2288 // FIXME(eddyb) Do we want this? It only makes a difference
2289 // if this `for<'a>` lifetime parameter is never used.
2290 self.have_bound_regions = true;
2293 intravisit::walk_generic_param(self, param);
2296 fn visit_poly_trait_ref(
2298 trait_ref: &hir::PolyTraitRef<'_>,
2299 modifier: hir::TraitBoundModifier,
2301 self.outer_index.shift_in(1);
2302 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2303 self.outer_index.shift_out(1);
2306 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2307 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2309 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2310 if debruijn < self.outer_index =>
2312 self.have_bound_regions = true;
2315 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2323 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2324 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2326 if lifetime_refs.is_empty() {
2330 let span = lifetime_refs[0].span;
2331 let mut late_depth = 0;
2332 let mut scope = self.scope;
2333 let mut lifetime_names = FxHashSet::default();
2336 // Do not assign any resolution, it will be inferred.
2337 Scope::Body { .. } => return,
2339 Scope::Root => break None,
2341 Scope::Binder { s, ref lifetimes, .. } => {
2342 // collect named lifetimes for suggestions
2343 for name in lifetimes.keys() {
2344 if let hir::ParamName::Plain(name) = name {
2345 lifetime_names.insert(*name);
2352 Scope::Elision { ref elide, ref s, .. } => {
2353 let lifetime = match *elide {
2354 Elide::FreshLateAnon(ref counter) => {
2355 for lifetime_ref in lifetime_refs {
2356 let lifetime = Region::late_anon(counter).shifted(late_depth);
2357 self.insert_lifetime(lifetime_ref, lifetime);
2361 Elide::Exact(l) => l.shifted(late_depth),
2362 Elide::Error(ref e) => {
2363 if let Scope::Binder { ref lifetimes, .. } = s {
2364 // collect named lifetimes for suggestions
2365 for name in lifetimes.keys() {
2366 if let hir::ParamName::Plain(name) = name {
2367 lifetime_names.insert(*name);
2374 for lifetime_ref in lifetime_refs {
2375 self.insert_lifetime(lifetime_ref, lifetime);
2380 Scope::ObjectLifetimeDefault { s, .. } => {
2386 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2387 let mut add_label = true;
2389 if let Some(params) = error {
2390 if lifetime_refs.len() == 1 {
2391 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2395 add_missing_lifetime_specifiers_label(
2398 lifetime_refs.len(),
2400 self.tcx.sess.source_map().span_to_snippet(span).ok().as_ref().map(|s| s.as_str()),
2407 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2408 match self.tcx.sess.source_map().span_to_snippet(span) {
2409 Ok(ref snippet) => {
2410 let (sugg, applicability) = if snippet == "&" {
2411 ("&'static ".to_owned(), Applicability::MachineApplicable)
2412 } else if snippet == "'_" {
2413 ("'static".to_owned(), Applicability::MachineApplicable)
2415 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2417 db.span_suggestion(span, msg, sugg, applicability);
2427 fn report_elision_failure(
2429 db: &mut DiagnosticBuilder<'_>,
2430 params: &[ElisionFailureInfo],
2433 let mut m = String::new();
2434 let len = params.len();
2436 let elided_params: Vec<_> =
2437 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2439 let elided_len = elided_params.len();
2441 for (i, info) in elided_params.into_iter().enumerate() {
2442 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions } = info;
2444 let help_name = if let Some(ident) =
2445 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2447 format!("`{}`", ident)
2449 format!("argument {}", index + 1)
2457 "one of {}'s {} {}lifetimes",
2460 if have_bound_regions { "free " } else { "" }
2465 if elided_len == 2 && i == 0 {
2467 } else if i + 2 == elided_len {
2468 m.push_str(", or ");
2469 } else if i != elided_len - 1 {
2476 "this function's return type contains a borrowed value, \
2477 but there is no value for it to be borrowed from",
2479 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2480 } else if elided_len == 0 {
2482 "this function's return type contains a borrowed value with \
2483 an elided lifetime, but the lifetime cannot be derived from \
2486 let msg = "consider giving it an explicit bounded or 'static lifetime";
2487 self.suggest_lifetime(db, span, msg)
2488 } else if elided_len == 1 {
2490 "this function's return type contains a borrowed value, \
2491 but the signature does not say which {} it is borrowed from",
2497 "this function's return type contains a borrowed value, \
2498 but the signature does not say whether it is borrowed from {}",
2505 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2506 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2507 let mut late_depth = 0;
2508 let mut scope = self.scope;
2509 let lifetime = loop {
2511 Scope::Binder { s, .. } => {
2516 Scope::Root | Scope::Elision { .. } => break Region::Static,
2518 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2520 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2523 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2526 fn check_lifetime_params(
2528 old_scope: ScopeRef<'_>,
2529 params: &'tcx [hir::GenericParam<'tcx>],
2531 let lifetimes: Vec<_> = params
2533 .filter_map(|param| match param.kind {
2534 GenericParamKind::Lifetime { .. } => Some((param, param.name.modern())),
2538 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2539 if let hir::ParamName::Plain(_) = lifetime_i_name {
2540 let name = lifetime_i_name.ident().name;
2541 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2542 let mut err = struct_span_err!(
2546 "invalid lifetime parameter name: `{}`",
2547 lifetime_i.name.ident(),
2551 format!("{} is a reserved lifetime name", name),
2557 // It is a hard error to shadow a lifetime within the same scope.
2558 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2559 if lifetime_i_name == lifetime_j_name {
2564 "lifetime name `{}` declared twice in the same scope",
2565 lifetime_j.name.ident()
2567 .span_label(lifetime_j.span, "declared twice")
2568 .span_label(lifetime_i.span, "previous declaration here")
2573 // It is a soft error to shadow a lifetime within a parent scope.
2574 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2576 for bound in lifetime_i.bounds {
2578 hir::GenericBound::Outlives(ref lt) => match lt.name {
2579 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2581 "use of `'_` in illegal place, but not caught by lowering",
2583 hir::LifetimeName::Static => {
2584 self.insert_lifetime(lt, Region::Static);
2588 lifetime_i.span.to(lt.span),
2590 "unnecessary lifetime parameter `{}`",
2591 lifetime_i.name.ident(),
2595 "you can use the `'static` lifetime directly, in place of `{}`",
2596 lifetime_i.name.ident(),
2600 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2601 self.resolve_lifetime_ref(lt);
2603 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2604 self.tcx.sess.delay_span_bug(
2606 "lowering generated `ImplicitObjectLifetimeDefault` \
2607 outside of an object type",
2610 hir::LifetimeName::Error => {
2611 // No need to do anything, error already reported.
2620 fn check_lifetime_param_for_shadowing(
2622 mut old_scope: ScopeRef<'_>,
2623 param: &'tcx hir::GenericParam<'tcx>,
2625 for label in &self.labels_in_fn {
2626 // FIXME (#24278): non-hygienic comparison
2627 if param.name.ident().name == label.name {
2628 signal_shadowing_problem(
2631 original_label(label.span),
2632 shadower_lifetime(¶m),
2640 Scope::Body { s, .. }
2641 | Scope::Elision { s, .. }
2642 | Scope::ObjectLifetimeDefault { s, .. } => {
2650 Scope::Binder { ref lifetimes, s, .. } => {
2651 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2652 let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
2654 signal_shadowing_problem(
2656 param.name.ident().name,
2657 original_lifetime(self.tcx.hir().span(hir_id)),
2658 shadower_lifetime(¶m),
2669 /// Returns `true` if, in the current scope, replacing `'_` would be
2670 /// equivalent to a single-use lifetime.
2671 fn track_lifetime_uses(&self) -> bool {
2672 let mut scope = self.scope;
2675 Scope::Root => break false,
2677 // Inside of items, it depends on the kind of item.
2678 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2680 // Inside a body, `'_` will use an inference variable,
2682 Scope::Body { .. } => break true,
2684 // A lifetime only used in a fn argument could as well
2685 // be replaced with `'_`, as that would generate a
2687 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2689 // In the return type or other such place, `'_` is not
2690 // going to make a fresh name, so we cannot
2691 // necessarily replace a single-use lifetime with
2693 Scope::Elision { elide: Elide::Exact(_), .. } => break false,
2694 Scope::Elision { elide: Elide::Error(_), .. } => break false,
2696 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2701 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2702 if lifetime_ref.hir_id == hir::DUMMY_HIR_ID {
2705 "lifetime reference not renumbered, \
2706 probably a bug in syntax::fold"
2711 "insert_lifetime: {} resolved to {:?} span={:?}",
2712 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2714 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2716 self.map.defs.insert(lifetime_ref.hir_id, def);
2719 Region::LateBoundAnon(..) | Region::Static => {
2720 // These are anonymous lifetimes or lifetimes that are not declared.
2723 Region::Free(_, def_id)
2724 | Region::LateBound(_, def_id, _)
2725 | Region::EarlyBound(_, def_id, _) => {
2726 // A lifetime declared by the user.
2727 let track_lifetime_uses = self.track_lifetime_uses();
2728 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2729 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2730 debug!("insert_lifetime: first use of {:?}", def_id);
2731 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2733 debug!("insert_lifetime: many uses of {:?}", def_id);
2734 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2740 /// Sometimes we resolve a lifetime, but later find that it is an
2741 /// error (esp. around impl trait). In that case, we remove the
2742 /// entry into `map.defs` so as not to confuse later code.
2743 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2744 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2745 assert_eq!(old_value, Some(bad_def));
2749 /// Detects late-bound lifetimes and inserts them into
2750 /// `map.late_bound`.
2752 /// A region declared on a fn is **late-bound** if:
2753 /// - it is constrained by an argument type;
2754 /// - it does not appear in a where-clause.
2756 /// "Constrained" basically means that it appears in any type but
2757 /// not amongst the inputs to a projection. In other words, `<&'a
2758 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2759 fn insert_late_bound_lifetimes(
2760 map: &mut NamedRegionMap,
2761 decl: &hir::FnDecl<'_>,
2762 generics: &hir::Generics<'_>,
2764 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2766 let mut constrained_by_input = ConstrainedCollector::default();
2767 for arg_ty in decl.inputs {
2768 constrained_by_input.visit_ty(arg_ty);
2771 let mut appears_in_output = AllCollector::default();
2772 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2774 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2776 // Walk the lifetimes that appear in where clauses.
2778 // Subtle point: because we disallow nested bindings, we can just
2779 // ignore binders here and scrape up all names we see.
2780 let mut appears_in_where_clause = AllCollector::default();
2781 appears_in_where_clause.visit_generics(generics);
2783 for param in generics.params {
2784 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2785 if !param.bounds.is_empty() {
2786 // `'a: 'b` means both `'a` and `'b` are referenced
2787 appears_in_where_clause
2789 .insert(hir::LifetimeName::Param(param.name.modern()));
2795 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2796 appears_in_where_clause.regions
2799 // Late bound regions are those that:
2800 // - appear in the inputs
2801 // - do not appear in the where-clauses
2802 // - are not implicitly captured by `impl Trait`
2803 for param in generics.params {
2805 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2807 // Neither types nor consts are late-bound.
2808 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2811 let lt_name = hir::LifetimeName::Param(param.name.modern());
2812 // appears in the where clauses? early-bound.
2813 if appears_in_where_clause.regions.contains(<_name) {
2817 // does not appear in the inputs, but appears in the return type? early-bound.
2818 if !constrained_by_input.regions.contains(<_name)
2819 && appears_in_output.regions.contains(<_name)
2825 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2830 let inserted = map.late_bound.insert(param.hir_id);
2831 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2837 struct ConstrainedCollector {
2838 regions: FxHashSet<hir::LifetimeName>,
2841 impl<'v> Visitor<'v> for ConstrainedCollector {
2844 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2845 NestedVisitorMap::None
2848 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2850 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2851 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2852 // ignore lifetimes appearing in associated type
2853 // projections, as they are not *constrained*
2857 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2858 // consider only the lifetimes on the final
2859 // segment; I am not sure it's even currently
2860 // valid to have them elsewhere, but even if it
2861 // is, those would be potentially inputs to
2863 if let Some(last_segment) = path.segments.last() {
2864 self.visit_path_segment(path.span, last_segment);
2869 intravisit::walk_ty(self, ty);
2874 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2875 self.regions.insert(lifetime_ref.name.modern());
2880 struct AllCollector {
2881 regions: FxHashSet<hir::LifetimeName>,
2884 impl<'v> Visitor<'v> for AllCollector {
2887 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2888 NestedVisitorMap::None
2891 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2892 self.regions.insert(lifetime_ref.name.modern());
2897 fn report_missing_lifetime_specifiers(
2901 ) -> DiagnosticBuilder<'_> {
2902 struct_span_err!(sess, span, E0106, "missing lifetime specifier{}", pluralize!(count))
2905 fn add_missing_lifetime_specifiers_label(
2906 err: &mut DiagnosticBuilder<'_>,
2909 lifetime_names: &FxHashSet<ast::Ident>,
2910 snippet: Option<&str>,
2913 err.span_label(span, format!("expected {} lifetime parameters", count));
2914 } else if let (1, Some(name), Some("&")) =
2915 (lifetime_names.len(), lifetime_names.iter().next(), snippet)
2917 err.span_suggestion(
2919 "consider using the named lifetime",
2920 format!("&{} ", name),
2921 Applicability::MaybeIncorrect,
2924 err.span_label(span, "expected lifetime parameter");