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 crate::diagnostics::{
9 add_missing_lifetime_specifiers_label, report_missing_lifetime_specifiers,
11 use rustc::hir::map::Map;
13 use rustc::middle::resolve_lifetime::*;
14 use rustc::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
15 use rustc::{bug, span_bug};
16 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
17 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
19 use rustc_hir::def::{DefKind, Res};
20 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
21 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
22 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
23 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind};
24 use rustc_span::symbol::{kw, sym};
28 use std::mem::{replace, take};
31 use syntax::walk_list;
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, .. } = 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 missing_named_lifetime_spots = take(&mut self.missing_named_lifetime_spots);
1327 let mut this = LifetimeContext {
1331 trait_ref_hack: self.trait_ref_hack,
1332 is_in_fn_syntax: self.is_in_fn_syntax,
1334 xcrate_object_lifetime_defaults,
1336 missing_named_lifetime_spots,
1338 debug!("entering scope {:?}", this.scope);
1339 f(self.scope, &mut this);
1340 this.check_uses_for_lifetimes_defined_by_scope();
1341 debug!("exiting scope {:?}", this.scope);
1342 self.labels_in_fn = this.labels_in_fn;
1343 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1344 self.missing_named_lifetime_spots = this.missing_named_lifetime_spots;
1347 /// helper method to determine the span to remove when suggesting the
1348 /// deletion of a lifetime
1349 fn lifetime_deletion_span(
1352 generics: &hir::Generics<'_>,
1354 generics.params.iter().enumerate().find_map(|(i, param)| {
1355 if param.name.ident() == name {
1356 let mut in_band = false;
1357 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1358 if let hir::LifetimeParamKind::InBand = kind {
1365 if generics.params.len() == 1 {
1366 // if sole lifetime, remove the entire `<>` brackets
1369 // if removing within `<>` brackets, we also want to
1370 // delete a leading or trailing comma as appropriate
1371 if i >= generics.params.len() - 1 {
1372 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1374 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1384 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1385 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1386 fn suggest_eliding_single_use_lifetime(
1388 err: &mut DiagnosticBuilder<'_>,
1390 lifetime: &hir::Lifetime,
1392 let name = lifetime.name.ident();
1393 let mut remove_decl = None;
1394 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1395 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1396 remove_decl = self.lifetime_deletion_span(name, generics);
1400 let mut remove_use = None;
1401 let mut elide_use = None;
1402 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1403 for input in inputs {
1405 hir::TyKind::Rptr(lt, _) => {
1406 if lt.name.ident() == name {
1407 // include the trailing whitespace between the lifetime and type names
1408 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1413 .span_until_non_whitespace(lt_through_ty_span),
1418 hir::TyKind::Path(ref qpath) => {
1419 if let QPath::Resolved(_, path) = qpath {
1420 let last_segment = &path.segments[path.segments.len() - 1];
1421 let generics = last_segment.generic_args();
1422 for arg in generics.args.iter() {
1423 if let GenericArg::Lifetime(lt) = arg {
1424 if lt.name.ident() == name {
1425 elide_use = Some(lt.span);
1437 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1438 if let Some(parent) =
1439 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1442 Node::Item(item) => {
1443 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1444 find_arg_use_span(sig.decl.inputs);
1447 Node::ImplItem(impl_item) => {
1448 if let hir::ImplItemKind::Method(sig, _) = &impl_item.kind {
1449 find_arg_use_span(sig.decl.inputs);
1457 let msg = "elide the single-use lifetime";
1458 match (remove_decl, remove_use, elide_use) {
1459 (Some(decl_span), Some(use_span), None) => {
1460 // if both declaration and use deletion spans start at the same
1461 // place ("start at" because the latter includes trailing
1462 // whitespace), then this is an in-band lifetime
1463 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1464 err.span_suggestion(
1468 Applicability::MachineApplicable,
1471 err.multipart_suggestion(
1473 vec![(decl_span, String::new()), (use_span, String::new())],
1474 Applicability::MachineApplicable,
1478 (Some(decl_span), None, Some(use_span)) => {
1479 err.multipart_suggestion(
1481 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1482 Applicability::MachineApplicable,
1489 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1490 let defined_by = match self.scope {
1491 Scope::Binder { lifetimes, .. } => lifetimes,
1493 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1498 let mut def_ids: Vec<_> = defined_by
1500 .flat_map(|region| match region {
1501 Region::EarlyBound(_, def_id, _)
1502 | Region::LateBound(_, def_id, _)
1503 | Region::Free(_, def_id) => Some(*def_id),
1505 Region::LateBoundAnon(..) | Region::Static => None,
1509 // ensure that we issue lints in a repeatable order
1510 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1512 for def_id in def_ids {
1513 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1515 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1518 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1522 match lifetimeuseset {
1523 Some(LifetimeUseSet::One(lifetime)) => {
1524 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1525 debug!("hir id first={:?}", hir_id);
1526 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1527 Node::Lifetime(hir_lifetime) => Some((
1528 hir_lifetime.hir_id,
1530 hir_lifetime.name.ident(),
1532 Node::GenericParam(param) => {
1533 Some((param.hir_id, param.span, param.name.ident()))
1537 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1538 if name.name == kw::UnderscoreLifetime {
1542 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1543 if let Some(parent_hir_id) =
1544 self.tcx.hir().as_local_hir_id(parent_def_id)
1546 // lifetimes in `derive` expansions don't count (Issue #53738)
1550 .attrs(parent_hir_id)
1552 .any(|attr| attr.check_name(sym::automatically_derived))
1559 let mut err = self.tcx.struct_span_lint_hir(
1560 lint::builtin::SINGLE_USE_LIFETIMES,
1563 &format!("lifetime parameter `{}` only used once", name),
1566 if span == lifetime.span {
1567 // spans are the same for in-band lifetime declarations
1568 err.span_label(span, "this lifetime is only used here");
1570 err.span_label(span, "this lifetime...");
1571 err.span_label(lifetime.span, "...is used only here");
1573 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1577 Some(LifetimeUseSet::Many) => {
1578 debug!("not one use lifetime");
1581 let hir_id = self.tcx.hir().as_local_hir_id(def_id).unwrap();
1582 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1583 Node::Lifetime(hir_lifetime) => Some((
1584 hir_lifetime.hir_id,
1586 hir_lifetime.name.ident(),
1588 Node::GenericParam(param) => {
1589 Some((param.hir_id, param.span, param.name.ident()))
1593 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1594 let mut err = self.tcx.struct_span_lint_hir(
1595 lint::builtin::UNUSED_LIFETIMES,
1598 &format!("lifetime parameter `{}` never used", name),
1600 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1601 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1602 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1603 if let Some(span) = unused_lt_span {
1604 err.span_suggestion(
1606 "elide the unused lifetime",
1608 Applicability::MachineApplicable,
1620 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1622 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1623 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1624 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1628 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1630 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1631 /// lifetimes may be interspersed together.
1633 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1634 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1635 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1636 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1637 /// ordering is not important there.
1638 fn visit_early_late<F>(
1640 parent_id: Option<hir::HirId>,
1641 decl: &'tcx hir::FnDecl<'tcx>,
1642 generics: &'tcx hir::Generics<'tcx>,
1645 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1647 insert_late_bound_lifetimes(self.map, decl, generics);
1649 // Find the start of nested early scopes, e.g., in methods.
1651 if let Some(parent_id) = parent_id {
1652 let parent = self.tcx.hir().expect_item(parent_id);
1653 if sub_items_have_self_param(&parent.kind) {
1654 index += 1; // Self comes before lifetimes
1657 hir::ItemKind::Trait(_, _, ref generics, ..)
1658 | hir::ItemKind::Impl { ref generics, .. } => {
1659 index += generics.params.len() as u32;
1665 let mut non_lifetime_count = 0;
1666 let lifetimes = generics
1669 .filter_map(|param| match param.kind {
1670 GenericParamKind::Lifetime { .. } => {
1671 if self.map.late_bound.contains(¶m.hir_id) {
1672 Some(Region::late(&self.tcx.hir(), param))
1674 Some(Region::early(&self.tcx.hir(), &mut index, param))
1677 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1678 non_lifetime_count += 1;
1683 let next_early_index = index + non_lifetime_count;
1685 let scope = Scope::Binder {
1689 opaque_type_parent: true,
1690 track_lifetime_uses: false,
1692 self.with(scope, move |old_scope, this| {
1693 this.check_lifetime_params(old_scope, &generics.params);
1694 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1698 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1699 let mut scope = self.scope;
1702 Scope::Root => return 0,
1704 Scope::Binder { next_early_index, opaque_type_parent, .. }
1705 if (!only_opaque_type_parent || opaque_type_parent) =>
1707 return next_early_index;
1710 Scope::Binder { s, .. }
1711 | Scope::Body { s, .. }
1712 | Scope::Elision { s, .. }
1713 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1718 /// Returns the next index one would use for an early-bound-region
1719 /// if extending the current scope.
1720 fn next_early_index(&self) -> u32 {
1721 self.next_early_index_helper(true)
1724 /// Returns the next index one would use for an `impl Trait` that
1725 /// is being converted into an opaque type alias `impl Trait`. This will be the
1726 /// next early index from the enclosing item, for the most
1727 /// part. See the `opaque_type_parent` field for more info.
1728 fn next_early_index_for_opaque_type(&self) -> u32 {
1729 self.next_early_index_helper(false)
1732 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1733 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1735 // If we've already reported an error, just ignore `lifetime_ref`.
1736 if let LifetimeName::Error = lifetime_ref.name {
1740 // Walk up the scope chain, tracking the number of fn scopes
1741 // that we pass through, until we find a lifetime with the
1742 // given name or we run out of scopes.
1744 let mut late_depth = 0;
1745 let mut scope = self.scope;
1746 let mut outermost_body = None;
1749 Scope::Body { id, s } => {
1750 outermost_body = Some(id);
1758 Scope::Binder { ref lifetimes, s, .. } => {
1759 match lifetime_ref.name {
1760 LifetimeName::Param(param_name) => {
1761 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1762 break Some(def.shifted(late_depth));
1765 _ => bug!("expected LifetimeName::Param"),
1772 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1778 if let Some(mut def) = result {
1779 if let Region::EarlyBound(..) = def {
1780 // Do not free early-bound regions, only late-bound ones.
1781 } else if let Some(body_id) = outermost_body {
1782 let fn_id = self.tcx.hir().body_owner(body_id);
1783 match self.tcx.hir().get(fn_id) {
1784 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1785 | Node::TraitItem(&hir::TraitItem {
1786 kind: hir::TraitItemKind::Method(..),
1789 | Node::ImplItem(&hir::ImplItem {
1790 kind: hir::ImplItemKind::Method(..), ..
1792 let scope = self.tcx.hir().local_def_id(fn_id);
1793 def = Region::Free(scope, def.id().unwrap());
1799 // Check for fn-syntax conflicts with in-band lifetime definitions
1800 if self.is_in_fn_syntax {
1802 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1803 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1808 "lifetimes used in `fn` or `Fn` syntax must be \
1809 explicitly declared using `<...>` binders"
1811 .span_label(lifetime_ref.span, "in-band lifetime definition")
1816 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1817 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1818 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1819 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1820 | Region::LateBoundAnon(..)
1821 | Region::Free(..) => {}
1825 self.insert_lifetime(lifetime_ref, def);
1827 let mut err = struct_span_err!(
1831 "use of undeclared lifetime name `{}`",
1834 err.span_label(lifetime_ref.span, "undeclared lifetime");
1835 if !self.is_in_fn_syntax {
1836 for generics in &self.missing_named_lifetime_spots {
1837 let (span, sugg) = match &generics.params {
1838 [] => (generics.span, format!("<{}>", lifetime_ref)),
1839 [param, ..] => (param.span.shrink_to_lo(), format!("{}, ", lifetime_ref)),
1841 err.span_suggestion(
1843 &format!("consider introducing lifetime `{}` here", lifetime_ref),
1845 Applicability::MaybeIncorrect,
1853 fn visit_segment_args(
1857 generic_args: &'tcx hir::GenericArgs<'tcx>,
1860 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1861 res, depth, generic_args,
1864 if generic_args.parenthesized {
1865 let was_in_fn_syntax = self.is_in_fn_syntax;
1866 self.is_in_fn_syntax = true;
1867 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1868 self.is_in_fn_syntax = was_in_fn_syntax;
1872 let mut elide_lifetimes = true;
1873 let lifetimes = generic_args
1876 .filter_map(|arg| match arg {
1877 hir::GenericArg::Lifetime(lt) => {
1878 if !lt.is_elided() {
1879 elide_lifetimes = false;
1886 if elide_lifetimes {
1887 self.resolve_elided_lifetimes(lifetimes);
1889 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1892 // Figure out if this is a type/trait segment,
1893 // which requires object lifetime defaults.
1894 let parent_def_id = |this: &mut Self, def_id: DefId| {
1895 let def_key = this.tcx.def_key(def_id);
1896 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1898 let type_def_id = match res {
1899 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1900 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1901 Res::Def(DefKind::Struct, def_id)
1902 | Res::Def(DefKind::Union, def_id)
1903 | Res::Def(DefKind::Enum, def_id)
1904 | Res::Def(DefKind::TyAlias, def_id)
1905 | Res::Def(DefKind::Trait, def_id)
1913 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1915 // Compute a vector of defaults, one for each type parameter,
1916 // per the rules given in RFCs 599 and 1156. Example:
1919 // struct Foo<'a, T: 'a, U> { }
1922 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1923 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1924 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1927 // Therefore, we would compute `object_lifetime_defaults` to a
1928 // vector like `['x, 'static]`. Note that the vector only
1929 // includes type parameters.
1930 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1932 let mut scope = self.scope;
1935 Scope::Root => break false,
1937 Scope::Body { .. } => break true,
1939 Scope::Binder { s, .. }
1940 | Scope::Elision { s, .. }
1941 | Scope::ObjectLifetimeDefault { s, .. } => {
1948 let map = &self.map;
1949 let unsubst = if let Some(id) = self.tcx.hir().as_local_hir_id(def_id) {
1950 &map.object_lifetime_defaults[&id]
1953 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1954 tcx.generics_of(def_id)
1957 .filter_map(|param| match param.kind {
1958 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1959 Some(object_lifetime_default)
1961 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1966 debug!("visit_segment_args: unsubst={:?}", unsubst);
1969 .map(|set| match *set {
1974 Some(Region::Static)
1978 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1979 GenericArg::Lifetime(lt) => Some(lt),
1982 r.subst(lifetimes, map)
1989 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1992 for arg in generic_args.args {
1994 GenericArg::Lifetime(_) => {}
1995 GenericArg::Type(ty) => {
1996 if let Some(<) = object_lifetime_defaults.get(i) {
1997 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1998 self.with(scope, |_, this| this.visit_ty(ty));
2004 GenericArg::Const(ct) => {
2005 self.visit_anon_const(&ct.value);
2010 // Hack: when resolving the type `XX` in binding like `dyn
2011 // Foo<'b, Item = XX>`, the current object-lifetime default
2012 // would be to examine the trait `Foo` to check whether it has
2013 // a lifetime bound declared on `Item`. e.g., if `Foo` is
2014 // declared like so, then the default object lifetime bound in
2015 // `XX` should be `'b`:
2023 // but if we just have `type Item;`, then it would be
2024 // `'static`. However, we don't get all of this logic correct.
2026 // Instead, we do something hacky: if there are no lifetime parameters
2027 // to the trait, then we simply use a default object lifetime
2028 // bound of `'static`, because there is no other possibility. On the other hand,
2029 // if there ARE lifetime parameters, then we require the user to give an
2030 // explicit bound for now.
2032 // This is intended to leave room for us to implement the
2033 // correct behavior in the future.
2034 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
2035 GenericArg::Lifetime(_) => true,
2039 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2040 for b in generic_args.bindings {
2041 let scope = Scope::ObjectLifetimeDefault {
2042 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2045 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2049 fn visit_fn_like_elision(
2051 inputs: &'tcx [hir::Ty<'tcx>],
2052 output: Option<&'tcx hir::Ty<'tcx>>,
2054 debug!("visit_fn_like_elision: enter");
2055 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2056 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2057 self.with(arg_scope, |_, this| {
2058 for input in inputs {
2059 this.visit_ty(input);
2062 Scope::Elision { ref elide, .. } => {
2063 arg_elide = elide.clone();
2069 let output = match output {
2074 debug!("visit_fn_like_elision: determine output");
2076 // Figure out if there's a body we can get argument names from,
2077 // and whether there's a `self` argument (treated specially).
2078 let mut assoc_item_kind = None;
2079 let mut impl_self = None;
2080 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2081 let body = match self.tcx.hir().get(parent) {
2082 // `fn` definitions and methods.
2083 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2085 Node::TraitItem(&hir::TraitItem {
2086 kind: hir::TraitItemKind::Method(_, ref m), ..
2088 if let hir::ItemKind::Trait(.., ref trait_items) =
2089 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2092 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2095 hir::TraitMethod::Required(_) => None,
2096 hir::TraitMethod::Provided(body) => Some(body),
2100 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Method(_, body), .. }) => {
2101 if let hir::ItemKind::Impl { ref self_ty, ref items, .. } =
2102 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2104 impl_self = Some(self_ty);
2106 items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2111 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2112 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2113 // Everything else (only closures?) doesn't
2114 // actually enjoy elision in return types.
2116 self.visit_ty(output);
2121 let has_self = match assoc_item_kind {
2122 Some(hir::AssocItemKind::Method { has_self }) => has_self,
2126 // In accordance with the rules for lifetime elision, we can determine
2127 // what region to use for elision in the output type in two ways.
2128 // First (determined here), if `self` is by-reference, then the
2129 // implied output region is the region of the self parameter.
2131 struct SelfVisitor<'a> {
2132 map: &'a NamedRegionMap,
2133 impl_self: Option<&'a hir::TyKind<'a>>,
2134 lifetime: Set1<Region>,
2137 impl SelfVisitor<'_> {
2138 // Look for `self: &'a Self` - also desugared from `&'a self`,
2139 // and if that matches, use it for elision and return early.
2140 fn is_self_ty(&self, res: Res) -> bool {
2141 if let Res::SelfTy(..) = res {
2145 // Can't always rely on literal (or implied) `Self` due
2146 // to the way elision rules were originally specified.
2147 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2151 // Whitelist the types that unambiguously always
2152 // result in the same type constructor being used
2153 // (it can't differ between `Self` and `self`).
2154 Res::Def(DefKind::Struct, _)
2155 | Res::Def(DefKind::Union, _)
2156 | Res::Def(DefKind::Enum, _)
2157 | Res::PrimTy(_) => return res == path.res,
2166 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2169 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2170 NestedVisitorMap::None
2173 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2174 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2175 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2177 if self.is_self_ty(path.res) {
2178 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2179 self.lifetime.insert(*lifetime);
2184 intravisit::walk_ty(self, ty)
2188 let mut visitor = SelfVisitor {
2190 impl_self: impl_self.map(|ty| &ty.kind),
2191 lifetime: Set1::Empty,
2193 visitor.visit_ty(&inputs[0]);
2194 if let Set1::One(lifetime) = visitor.lifetime {
2195 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2196 self.with(scope, |_, this| this.visit_ty(output));
2201 // Second, if there was exactly one lifetime (either a substitution or a
2202 // reference) in the arguments, then any anonymous regions in the output
2203 // have that lifetime.
2204 let mut possible_implied_output_region = None;
2205 let mut lifetime_count = 0;
2206 let arg_lifetimes = inputs
2209 .skip(has_self as usize)
2211 let mut gather = GatherLifetimes {
2213 outer_index: ty::INNERMOST,
2214 have_bound_regions: false,
2215 lifetimes: Default::default(),
2217 gather.visit_ty(input);
2219 lifetime_count += gather.lifetimes.len();
2221 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2222 // there's a chance that the unique lifetime of this
2223 // iteration will be the appropriate lifetime for output
2224 // parameters, so lets store it.
2225 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2228 ElisionFailureInfo {
2231 lifetime_count: gather.lifetimes.len(),
2232 have_bound_regions: gather.have_bound_regions,
2237 let elide = if lifetime_count == 1 {
2238 Elide::Exact(possible_implied_output_region.unwrap())
2240 Elide::Error(arg_lifetimes)
2243 debug!("visit_fn_like_elision: elide={:?}", elide);
2245 let scope = Scope::Elision { elide, s: self.scope };
2246 self.with(scope, |_, this| this.visit_ty(output));
2247 debug!("visit_fn_like_elision: exit");
2249 struct GatherLifetimes<'a> {
2250 map: &'a NamedRegionMap,
2251 outer_index: ty::DebruijnIndex,
2252 have_bound_regions: bool,
2253 lifetimes: FxHashSet<Region>,
2256 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2259 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2260 NestedVisitorMap::None
2263 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2264 if let hir::TyKind::BareFn(_) = ty.kind {
2265 self.outer_index.shift_in(1);
2268 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2269 for bound in bounds {
2270 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2273 // Stay on the safe side and don't include the object
2274 // lifetime default (which may not end up being used).
2275 if !lifetime.is_elided() {
2276 self.visit_lifetime(lifetime);
2280 intravisit::walk_ty(self, ty);
2283 if let hir::TyKind::BareFn(_) = ty.kind {
2284 self.outer_index.shift_out(1);
2288 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2289 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2290 // FIXME(eddyb) Do we want this? It only makes a difference
2291 // if this `for<'a>` lifetime parameter is never used.
2292 self.have_bound_regions = true;
2295 intravisit::walk_generic_param(self, param);
2298 fn visit_poly_trait_ref(
2300 trait_ref: &hir::PolyTraitRef<'_>,
2301 modifier: hir::TraitBoundModifier,
2303 self.outer_index.shift_in(1);
2304 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2305 self.outer_index.shift_out(1);
2308 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2309 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2311 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2312 if debruijn < self.outer_index =>
2314 self.have_bound_regions = true;
2317 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2325 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2326 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2328 if lifetime_refs.is_empty() {
2332 let span = lifetime_refs[0].span;
2333 let mut late_depth = 0;
2334 let mut scope = self.scope;
2335 let mut lifetime_names = FxHashSet::default();
2338 // Do not assign any resolution, it will be inferred.
2339 Scope::Body { .. } => return,
2341 Scope::Root => break None,
2343 Scope::Binder { s, ref lifetimes, .. } => {
2344 // collect named lifetimes for suggestions
2345 for name in lifetimes.keys() {
2346 if let hir::ParamName::Plain(name) = name {
2347 lifetime_names.insert(*name);
2354 Scope::Elision { ref elide, ref s, .. } => {
2355 let lifetime = match *elide {
2356 Elide::FreshLateAnon(ref counter) => {
2357 for lifetime_ref in lifetime_refs {
2358 let lifetime = Region::late_anon(counter).shifted(late_depth);
2359 self.insert_lifetime(lifetime_ref, lifetime);
2363 Elide::Exact(l) => l.shifted(late_depth),
2364 Elide::Error(ref e) => {
2365 if let Scope::Binder { ref lifetimes, .. } = s {
2366 // collect named lifetimes for suggestions
2367 for name in lifetimes.keys() {
2368 if let hir::ParamName::Plain(name) = name {
2369 lifetime_names.insert(*name);
2376 for lifetime_ref in lifetime_refs {
2377 self.insert_lifetime(lifetime_ref, lifetime);
2382 Scope::ObjectLifetimeDefault { s, .. } => {
2388 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2389 let mut add_label = true;
2391 if let Some(params) = error {
2392 if lifetime_refs.len() == 1 {
2393 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2397 add_missing_lifetime_specifiers_label(
2400 lifetime_refs.len(),
2402 self.tcx.sess.source_map().span_to_snippet(span).ok().as_ref().map(|s| s.as_str()),
2403 &self.missing_named_lifetime_spots,
2410 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2411 match self.tcx.sess.source_map().span_to_snippet(span) {
2412 Ok(ref snippet) => {
2413 let (sugg, applicability) = if snippet == "&" {
2414 ("&'static ".to_owned(), Applicability::MachineApplicable)
2415 } else if snippet == "'_" {
2416 ("'static".to_owned(), Applicability::MachineApplicable)
2418 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2420 db.span_suggestion(span, msg, sugg, applicability);
2430 fn report_elision_failure(
2432 db: &mut DiagnosticBuilder<'_>,
2433 params: &[ElisionFailureInfo],
2436 let mut m = String::new();
2437 let len = params.len();
2439 let elided_params: Vec<_> =
2440 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2442 let elided_len = elided_params.len();
2444 for (i, info) in elided_params.into_iter().enumerate() {
2445 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions } = info;
2447 let help_name = if let Some(ident) =
2448 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2450 format!("`{}`", ident)
2452 format!("argument {}", index + 1)
2460 "one of {}'s {} {}lifetimes",
2463 if have_bound_regions { "free " } else { "" }
2468 if elided_len == 2 && i == 0 {
2470 } else if i + 2 == elided_len {
2471 m.push_str(", or ");
2472 } else if i != elided_len - 1 {
2479 "this function's return type contains a borrowed value, \
2480 but there is no value for it to be borrowed from",
2482 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2483 } else if elided_len == 0 {
2485 "this function's return type contains a borrowed value with \
2486 an elided lifetime, but the lifetime cannot be derived from \
2489 let msg = "consider giving it an explicit bounded or 'static lifetime";
2490 self.suggest_lifetime(db, span, msg)
2491 } else if elided_len == 1 {
2493 "this function's return type contains a borrowed value, \
2494 but the signature does not say which {} it is borrowed from",
2500 "this function's return type contains a borrowed value, \
2501 but the signature does not say whether it is borrowed from {}",
2508 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2509 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2510 let mut late_depth = 0;
2511 let mut scope = self.scope;
2512 let lifetime = loop {
2514 Scope::Binder { s, .. } => {
2519 Scope::Root | Scope::Elision { .. } => break Region::Static,
2521 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2523 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2526 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2529 fn check_lifetime_params(
2531 old_scope: ScopeRef<'_>,
2532 params: &'tcx [hir::GenericParam<'tcx>],
2534 let lifetimes: Vec<_> = params
2536 .filter_map(|param| match param.kind {
2537 GenericParamKind::Lifetime { .. } => Some((param, param.name.modern())),
2541 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2542 if let hir::ParamName::Plain(_) = lifetime_i_name {
2543 let name = lifetime_i_name.ident().name;
2544 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2545 let mut err = struct_span_err!(
2549 "invalid lifetime parameter name: `{}`",
2550 lifetime_i.name.ident(),
2554 format!("{} is a reserved lifetime name", name),
2560 // It is a hard error to shadow a lifetime within the same scope.
2561 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2562 if lifetime_i_name == lifetime_j_name {
2567 "lifetime name `{}` declared twice in the same scope",
2568 lifetime_j.name.ident()
2570 .span_label(lifetime_j.span, "declared twice")
2571 .span_label(lifetime_i.span, "previous declaration here")
2576 // It is a soft error to shadow a lifetime within a parent scope.
2577 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2579 for bound in lifetime_i.bounds {
2581 hir::GenericBound::Outlives(ref lt) => match lt.name {
2582 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2584 "use of `'_` in illegal place, but not caught by lowering",
2586 hir::LifetimeName::Static => {
2587 self.insert_lifetime(lt, Region::Static);
2591 lifetime_i.span.to(lt.span),
2593 "unnecessary lifetime parameter `{}`",
2594 lifetime_i.name.ident(),
2598 "you can use the `'static` lifetime directly, in place of `{}`",
2599 lifetime_i.name.ident(),
2603 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2604 self.resolve_lifetime_ref(lt);
2606 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2607 self.tcx.sess.delay_span_bug(
2609 "lowering generated `ImplicitObjectLifetimeDefault` \
2610 outside of an object type",
2613 hir::LifetimeName::Error => {
2614 // No need to do anything, error already reported.
2623 fn check_lifetime_param_for_shadowing(
2625 mut old_scope: ScopeRef<'_>,
2626 param: &'tcx hir::GenericParam<'tcx>,
2628 for label in &self.labels_in_fn {
2629 // FIXME (#24278): non-hygienic comparison
2630 if param.name.ident().name == label.name {
2631 signal_shadowing_problem(
2634 original_label(label.span),
2635 shadower_lifetime(¶m),
2643 Scope::Body { s, .. }
2644 | Scope::Elision { s, .. }
2645 | Scope::ObjectLifetimeDefault { s, .. } => {
2653 Scope::Binder { ref lifetimes, s, .. } => {
2654 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2655 let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap()).unwrap();
2657 signal_shadowing_problem(
2659 param.name.ident().name,
2660 original_lifetime(self.tcx.hir().span(hir_id)),
2661 shadower_lifetime(¶m),
2672 /// Returns `true` if, in the current scope, replacing `'_` would be
2673 /// equivalent to a single-use lifetime.
2674 fn track_lifetime_uses(&self) -> bool {
2675 let mut scope = self.scope;
2678 Scope::Root => break false,
2680 // Inside of items, it depends on the kind of item.
2681 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2683 // Inside a body, `'_` will use an inference variable,
2685 Scope::Body { .. } => break true,
2687 // A lifetime only used in a fn argument could as well
2688 // be replaced with `'_`, as that would generate a
2690 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2692 // In the return type or other such place, `'_` is not
2693 // going to make a fresh name, so we cannot
2694 // necessarily replace a single-use lifetime with
2696 Scope::Elision { elide: Elide::Exact(_), .. } => break false,
2697 Scope::Elision { elide: Elide::Error(_), .. } => break false,
2699 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2704 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2705 if lifetime_ref.hir_id == hir::DUMMY_HIR_ID {
2708 "lifetime reference not renumbered, \
2709 probably a bug in syntax::fold"
2714 "insert_lifetime: {} resolved to {:?} span={:?}",
2715 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2717 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2719 self.map.defs.insert(lifetime_ref.hir_id, def);
2722 Region::LateBoundAnon(..) | Region::Static => {
2723 // These are anonymous lifetimes or lifetimes that are not declared.
2726 Region::Free(_, def_id)
2727 | Region::LateBound(_, def_id, _)
2728 | Region::EarlyBound(_, def_id, _) => {
2729 // A lifetime declared by the user.
2730 let track_lifetime_uses = self.track_lifetime_uses();
2731 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2732 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2733 debug!("insert_lifetime: first use of {:?}", def_id);
2734 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2736 debug!("insert_lifetime: many uses of {:?}", def_id);
2737 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2743 /// Sometimes we resolve a lifetime, but later find that it is an
2744 /// error (esp. around impl trait). In that case, we remove the
2745 /// entry into `map.defs` so as not to confuse later code.
2746 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2747 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2748 assert_eq!(old_value, Some(bad_def));
2752 /// Detects late-bound lifetimes and inserts them into
2753 /// `map.late_bound`.
2755 /// A region declared on a fn is **late-bound** if:
2756 /// - it is constrained by an argument type;
2757 /// - it does not appear in a where-clause.
2759 /// "Constrained" basically means that it appears in any type but
2760 /// not amongst the inputs to a projection. In other words, `<&'a
2761 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2762 fn insert_late_bound_lifetimes(
2763 map: &mut NamedRegionMap,
2764 decl: &hir::FnDecl<'_>,
2765 generics: &hir::Generics<'_>,
2767 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2769 let mut constrained_by_input = ConstrainedCollector::default();
2770 for arg_ty in decl.inputs {
2771 constrained_by_input.visit_ty(arg_ty);
2774 let mut appears_in_output = AllCollector::default();
2775 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2777 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2779 // Walk the lifetimes that appear in where clauses.
2781 // Subtle point: because we disallow nested bindings, we can just
2782 // ignore binders here and scrape up all names we see.
2783 let mut appears_in_where_clause = AllCollector::default();
2784 appears_in_where_clause.visit_generics(generics);
2786 for param in generics.params {
2787 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2788 if !param.bounds.is_empty() {
2789 // `'a: 'b` means both `'a` and `'b` are referenced
2790 appears_in_where_clause
2792 .insert(hir::LifetimeName::Param(param.name.modern()));
2798 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2799 appears_in_where_clause.regions
2802 // Late bound regions are those that:
2803 // - appear in the inputs
2804 // - do not appear in the where-clauses
2805 // - are not implicitly captured by `impl Trait`
2806 for param in generics.params {
2808 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2810 // Neither types nor consts are late-bound.
2811 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2814 let lt_name = hir::LifetimeName::Param(param.name.modern());
2815 // appears in the where clauses? early-bound.
2816 if appears_in_where_clause.regions.contains(<_name) {
2820 // does not appear in the inputs, but appears in the return type? early-bound.
2821 if !constrained_by_input.regions.contains(<_name)
2822 && appears_in_output.regions.contains(<_name)
2828 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2833 let inserted = map.late_bound.insert(param.hir_id);
2834 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2840 struct ConstrainedCollector {
2841 regions: FxHashSet<hir::LifetimeName>,
2844 impl<'v> Visitor<'v> for ConstrainedCollector {
2847 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2848 NestedVisitorMap::None
2851 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2853 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2854 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2855 // ignore lifetimes appearing in associated type
2856 // projections, as they are not *constrained*
2860 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2861 // consider only the lifetimes on the final
2862 // segment; I am not sure it's even currently
2863 // valid to have them elsewhere, but even if it
2864 // is, those would be potentially inputs to
2866 if let Some(last_segment) = path.segments.last() {
2867 self.visit_path_segment(path.span, last_segment);
2872 intravisit::walk_ty(self, ty);
2877 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2878 self.regions.insert(lifetime_ref.name.modern());
2883 struct AllCollector {
2884 regions: FxHashSet<hir::LifetimeName>,
2887 impl<'v> Visitor<'v> for AllCollector {
2890 fn nested_visit_map(&mut self) -> NestedVisitorMap<'_, Self::Map> {
2891 NestedVisitorMap::None
2894 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2895 self.regions.insert(lifetime_ref.name.modern());