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::late::diagnostics::{ForLifetimeSpanType, MissingLifetimeSpot};
9 use rustc_ast::walk_list;
10 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
11 use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
13 use rustc_hir::def::{DefKind, Res};
14 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE};
15 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
16 use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath};
17 use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind};
18 use rustc_middle::hir::map::Map;
19 use rustc_middle::middle::resolve_lifetime::*;
20 use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
21 use rustc_middle::{bug, span_bug};
22 use rustc_session::lint;
23 use rustc_span::symbol::{kw, sym, Ident, Symbol};
31 // This counts the no of times a lifetime is used
32 #[derive(Clone, Copy, Debug)]
33 pub enum LifetimeUseSet<'tcx> {
34 One(&'tcx hir::Lifetime),
39 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region);
41 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region);
43 fn late_anon(index: &Cell<u32>) -> Region;
45 fn id(&self) -> Option<DefId>;
47 fn shifted(self, amount: u32) -> Region;
49 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region;
51 fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option<Region>
53 L: Iterator<Item = &'a hir::Lifetime>;
56 impl RegionExt for Region {
57 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) {
60 let def_id = hir_map.local_def_id(param.hir_id);
61 let origin = LifetimeDefOrigin::from_param(param);
62 debug!("Region::early: index={} def_id={:?}", i, def_id);
63 (param.name.normalize_to_macros_2_0(), Region::EarlyBound(i, def_id.to_def_id(), origin))
66 fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) {
67 let depth = ty::INNERMOST;
68 let def_id = hir_map.local_def_id(param.hir_id);
69 let origin = LifetimeDefOrigin::from_param(param);
71 "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
72 param, depth, def_id, origin,
74 (param.name.normalize_to_macros_2_0(), Region::LateBound(depth, def_id.to_def_id(), origin))
77 fn late_anon(index: &Cell<u32>) -> Region {
80 let depth = ty::INNERMOST;
81 Region::LateBoundAnon(depth, i)
84 fn id(&self) -> Option<DefId> {
86 Region::Static | Region::LateBoundAnon(..) => None,
88 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
94 fn shifted(self, amount: u32) -> Region {
96 Region::LateBound(debruijn, id, origin) => {
97 Region::LateBound(debruijn.shifted_in(amount), id, origin)
99 Region::LateBoundAnon(debruijn, index) => {
100 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
106 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
108 Region::LateBound(debruijn, id, origin) => {
109 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
111 Region::LateBoundAnon(debruijn, index) => {
112 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
118 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
120 L: Iterator<Item = &'a hir::Lifetime>,
122 if let Region::EarlyBound(index, _, _) = self {
123 params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned())
130 /// Maps the id of each lifetime reference to the lifetime decl
131 /// that it corresponds to.
133 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
134 /// actual use. It has the same data, but indexed by `LocalDefId`. This
137 struct NamedRegionMap {
138 // maps from every use of a named (not anonymous) lifetime to a
139 // `Region` describing how that region is bound
140 defs: HirIdMap<Region>,
142 // the set of lifetime def ids that are late-bound; a region can
143 // be late-bound if (a) it does NOT appear in a where-clause and
144 // (b) it DOES appear in the arguments.
145 late_bound: HirIdSet,
147 // For each type and trait definition, maps type parameters
148 // to the trait object lifetime defaults computed from them.
149 object_lifetime_defaults: HirIdMap<Vec<ObjectLifetimeDefault>>,
152 crate struct LifetimeContext<'a, 'tcx> {
153 crate tcx: TyCtxt<'tcx>,
154 map: &'a mut NamedRegionMap,
157 /// This is slightly complicated. Our representation for poly-trait-refs contains a single
158 /// binder and thus we only allow a single level of quantification. However,
159 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
160 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices
161 /// correct when representing these constraints, we should only introduce one
162 /// scope. However, we want to support both locations for the quantifier and
163 /// during lifetime resolution we want precise information (so we can't
164 /// desugar in an earlier phase).
166 /// So, if we encounter a quantifier at the outer scope, we set
167 /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter
168 /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`,
169 /// then we introduce the scope at the inner quantifier.
170 trait_ref_hack: bool,
172 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
173 is_in_fn_syntax: bool,
175 is_in_const_generic: bool,
177 /// List of labels in the function/method currently under analysis.
178 labels_in_fn: Vec<Ident>,
180 /// Cache for cross-crate per-definition object lifetime defaults.
181 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
183 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
185 /// When encountering an undefined named lifetime, we will suggest introducing it in these
187 crate missing_named_lifetime_spots: Vec<MissingLifetimeSpot<'tcx>>,
192 /// Declares lifetimes, and each can be early-bound or late-bound.
193 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
194 /// it should be shifted by the number of `Binder`s in between the
195 /// declaration `Binder` and the location it's referenced from.
197 lifetimes: FxHashMap<hir::ParamName, Region>,
199 /// if we extend this scope with another scope, what is the next index
200 /// we should use for an early-bound region?
201 next_early_index: u32,
203 /// Flag is set to true if, in this binder, `'_` would be
204 /// equivalent to a "single-use region". This is true on
205 /// impls, but not other kinds of items.
206 track_lifetime_uses: bool,
208 /// Whether or not this binder would serve as the parent
209 /// binder for opaque types introduced within. For example:
212 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
215 /// Here, the opaque types we create for the `impl Trait`
216 /// and `impl Trait2` references will both have the `foo` item
217 /// as their parent. When we get to `impl Trait2`, we find
218 /// that it is nested within the `for<>` binder -- this flag
219 /// allows us to skip that when looking for the parent binder
220 /// of the resulting opaque type.
221 opaque_type_parent: bool,
226 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
227 /// if this is a fn body, otherwise the original definitions are used.
228 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
229 /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
235 /// A scope which either determines unspecified lifetimes or errors
236 /// on them (e.g., due to ambiguity). For more details, see `Elide`.
242 /// Use a specific lifetime (if `Some`) or leave it unset (to be
243 /// inferred in a function body or potentially error outside one),
244 /// for the default choice of lifetime in a trait object type.
245 ObjectLifetimeDefault {
246 lifetime: Option<Region>,
253 #[derive(Clone, Debug)]
255 /// Use a fresh anonymous late-bound lifetime each time, by
256 /// incrementing the counter to generate sequential indices.
257 FreshLateAnon(Cell<u32>),
258 /// Always use this one lifetime.
260 /// Less or more than one lifetime were found, error on unspecified.
261 Error(Vec<ElisionFailureInfo>),
262 /// Forbid lifetime elision inside of a larger scope where it would be
263 /// permitted. For example, in let position impl trait.
267 #[derive(Clone, Debug)]
268 crate struct ElisionFailureInfo {
269 /// Where we can find the argument pattern.
270 parent: Option<hir::BodyId>,
271 /// The index of the argument in the original definition.
273 lifetime_count: usize,
274 have_bound_regions: bool,
278 type ScopeRef<'a> = &'a Scope<'a>;
280 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
282 pub fn provide(providers: &mut ty::query::Providers) {
283 *providers = ty::query::Providers {
286 named_region_map: |tcx, id| tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id),
287 is_late_bound_map: |tcx, id| tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id),
288 object_lifetime_defaults_map: |tcx, id| {
289 tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id)
296 /// Computes the `ResolveLifetimes` map that contains data for the
297 /// entire crate. You should not read the result of this query
298 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
300 fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> ResolveLifetimes {
301 assert_eq!(for_krate, LOCAL_CRATE);
303 let named_region_map = krate(tcx);
305 let mut rl = ResolveLifetimes::default();
307 for (hir_id, v) in named_region_map.defs {
308 let map = rl.defs.entry(hir_id.owner).or_default();
309 map.insert(hir_id.local_id, v);
311 for hir_id in named_region_map.late_bound {
312 let map = rl.late_bound.entry(hir_id.owner).or_default();
313 map.insert(hir_id.local_id);
315 for (hir_id, v) in named_region_map.object_lifetime_defaults {
316 let map = rl.object_lifetime_defaults.entry(hir_id.owner).or_default();
317 map.insert(hir_id.local_id, v);
323 fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap {
324 let krate = tcx.hir().krate();
325 let mut map = NamedRegionMap {
326 defs: Default::default(),
327 late_bound: Default::default(),
328 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
331 let mut visitor = LifetimeContext {
335 trait_ref_hack: false,
336 is_in_fn_syntax: false,
337 is_in_const_generic: false,
338 labels_in_fn: vec![],
339 xcrate_object_lifetime_defaults: Default::default(),
340 lifetime_uses: &mut Default::default(),
341 missing_named_lifetime_spots: vec![],
343 for item in krate.items.values() {
344 visitor.visit_item(item);
350 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
351 /// We have to account for this when computing the index of the other generic parameters.
352 /// This function returns whether there is such an implicit parameter defined on the given item.
353 fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool {
355 hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true,
360 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
361 type Map = Map<'tcx>;
363 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
364 NestedVisitorMap::All(self.tcx.hir())
367 // We want to nest trait/impl items in their parent, but nothing else.
368 fn visit_nested_item(&mut self, _: hir::ItemId) {}
370 fn visit_nested_body(&mut self, body: hir::BodyId) {
371 // Each body has their own set of labels, save labels.
372 let saved = take(&mut self.labels_in_fn);
373 let body = self.tcx.hir().body(body);
374 extract_labels(self, body);
375 self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| {
376 this.visit_body(body);
378 self.labels_in_fn = saved;
381 fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
383 hir::ItemKind::Fn(ref sig, ref generics, _) => {
384 self.missing_named_lifetime_spots.push(generics.into());
385 self.visit_early_late(None, &sig.decl, generics, |this| {
386 intravisit::walk_item(this, item);
388 self.missing_named_lifetime_spots.pop();
391 hir::ItemKind::ExternCrate(_)
392 | hir::ItemKind::Use(..)
393 | hir::ItemKind::Mod(..)
394 | hir::ItemKind::ForeignMod(..)
395 | hir::ItemKind::GlobalAsm(..) => {
396 // These sorts of items have no lifetime parameters at all.
397 intravisit::walk_item(self, item);
399 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
400 // No lifetime parameters, but implied 'static.
401 let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE };
402 self.with(scope, |_, this| intravisit::walk_item(this, item));
404 hir::ItemKind::OpaqueTy(hir::OpaqueTy { .. }) => {
405 // Opaque types are visited when we visit the
406 // `TyKind::OpaqueDef`, so that they have the lifetimes from
407 // their parent opaque_ty in scope.
409 hir::ItemKind::TyAlias(_, ref generics)
410 | hir::ItemKind::Enum(_, ref generics)
411 | hir::ItemKind::Struct(_, ref generics)
412 | hir::ItemKind::Union(_, ref generics)
413 | hir::ItemKind::Trait(_, _, ref generics, ..)
414 | hir::ItemKind::TraitAlias(ref generics, ..)
415 | hir::ItemKind::Impl { ref generics, .. } => {
416 self.missing_named_lifetime_spots.push(generics.into());
418 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
419 // This is not true for other kinds of items.x
420 let track_lifetime_uses = match item.kind {
421 hir::ItemKind::Impl { .. } => true,
424 // These kinds of items have only early-bound lifetime parameters.
425 let mut index = if sub_items_have_self_param(&item.kind) {
426 1 // Self comes before lifetimes
430 let mut non_lifetime_count = 0;
431 let lifetimes = generics
434 .filter_map(|param| match param.kind {
435 GenericParamKind::Lifetime { .. } => {
436 Some(Region::early(&self.tcx.hir(), &mut index, param))
438 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
439 non_lifetime_count += 1;
444 let scope = Scope::Binder {
446 next_early_index: index + non_lifetime_count,
447 opaque_type_parent: true,
451 self.with(scope, |old_scope, this| {
452 this.check_lifetime_params(old_scope, &generics.params);
453 intravisit::walk_item(this, item);
455 self.missing_named_lifetime_spots.pop();
460 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
462 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
463 self.visit_early_late(None, decl, generics, |this| {
464 intravisit::walk_foreign_item(this, item);
467 hir::ForeignItemKind::Static(..) => {
468 intravisit::walk_foreign_item(self, item);
470 hir::ForeignItemKind::Type => {
471 intravisit::walk_foreign_item(self, item);
476 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
477 debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty);
478 debug!("visit_ty: ty.kind={:?}", ty.kind);
480 hir::TyKind::BareFn(ref c) => {
481 let next_early_index = self.next_early_index();
482 let was_in_fn_syntax = self.is_in_fn_syntax;
483 self.is_in_fn_syntax = true;
484 let lifetime_span: Option<Span> =
485 c.generic_params.iter().rev().find_map(|param| match param.kind {
486 GenericParamKind::Lifetime { .. } => Some(param.span),
489 let (span, span_type) = if let Some(span) = lifetime_span {
490 (span.shrink_to_hi(), ForLifetimeSpanType::TypeTail)
492 (ty.span.shrink_to_lo(), ForLifetimeSpanType::TypeEmpty)
494 self.missing_named_lifetime_spots
495 .push(MissingLifetimeSpot::HigherRanked { span, span_type });
496 let scope = Scope::Binder {
500 .filter_map(|param| match param.kind {
501 GenericParamKind::Lifetime { .. } => {
502 Some(Region::late(&self.tcx.hir(), param))
509 track_lifetime_uses: true,
510 opaque_type_parent: false,
512 self.with(scope, |old_scope, this| {
513 // a bare fn has no bounds, so everything
514 // contained within is scoped within its binder.
515 this.check_lifetime_params(old_scope, &c.generic_params);
516 intravisit::walk_ty(this, ty);
518 self.missing_named_lifetime_spots.pop();
519 self.is_in_fn_syntax = was_in_fn_syntax;
521 hir::TyKind::TraitObject(bounds, ref lifetime) => {
522 debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime);
523 for bound in bounds {
524 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
526 match lifetime.name {
527 LifetimeName::Implicit => {
528 // For types like `dyn Foo`, we should
529 // generate a special form of elided.
530 span_bug!(ty.span, "object-lifetime-default expected, not implicit",);
532 LifetimeName::ImplicitObjectLifetimeDefault => {
533 // If the user does not write *anything*, we
534 // use the object lifetime defaulting
535 // rules. So e.g., `Box<dyn Debug>` becomes
536 // `Box<dyn Debug + 'static>`.
537 self.resolve_object_lifetime_default(lifetime)
539 LifetimeName::Underscore => {
540 // If the user writes `'_`, we use the *ordinary* elision
541 // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
542 // resolved the same as the `'_` in `&'_ Foo`.
545 self.resolve_elided_lifetimes(vec![lifetime])
547 LifetimeName::Param(_) | LifetimeName::Static => {
548 // If the user wrote an explicit name, use that.
549 self.visit_lifetime(lifetime);
551 LifetimeName::Error => {}
554 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
555 self.visit_lifetime(lifetime_ref);
556 let scope = Scope::ObjectLifetimeDefault {
557 lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
560 self.with(scope, |_, this| this.visit_ty(&mt.ty));
562 hir::TyKind::OpaqueDef(item_id, lifetimes) => {
563 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
564 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
565 // `type MyAnonTy<'b> = impl MyTrait<'b>;`
566 // ^ ^ this gets resolved in the scope of
567 // the opaque_ty generics
568 let opaque_ty = self.tcx.hir().expect_item(item_id.id);
569 let (generics, bounds) = match opaque_ty.kind {
570 // Named opaque `impl Trait` types are reached via `TyKind::Path`.
571 // This arm is for `impl Trait` in the types of statics, constants and locals.
572 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => {
573 intravisit::walk_ty(self, ty);
575 // Elided lifetimes are not allowed in non-return
576 // position impl Trait
577 let scope = Scope::Elision { elide: Elide::Forbid, s: self.scope };
578 self.with(scope, |_, this| {
579 intravisit::walk_item(this, opaque_ty);
584 // RPIT (return position impl trait)
585 hir::ItemKind::OpaqueTy(hir::OpaqueTy {
586 impl_trait_fn: Some(_),
590 }) => (generics, bounds),
591 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
594 // Resolve the lifetimes that are applied to the opaque type.
595 // These are resolved in the current scope.
596 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
597 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
598 // ^ ^this gets resolved in the current scope
599 for lifetime in lifetimes {
600 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
601 self.visit_lifetime(lifetime);
603 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
604 // and ban them. Type variables instantiated inside binders aren't
605 // well-supported at the moment, so this doesn't work.
606 // In the future, this should be fixed and this error should be removed.
607 let def = self.map.defs.get(&lifetime.hir_id).cloned();
608 if let Some(Region::LateBound(_, def_id, _)) = def {
609 if let Some(def_id) = def_id.as_local() {
610 let hir_id = self.tcx.hir().as_local_hir_id(def_id);
611 // Ensure that the parent of the def is an item, not HRTB
612 let parent_id = self.tcx.hir().get_parent_node(hir_id);
613 let parent_impl_id = hir::ImplItemId { hir_id: parent_id };
614 let parent_trait_id = hir::TraitItemId { hir_id: parent_id };
615 let krate = self.tcx.hir().krate();
617 if !(krate.items.contains_key(&parent_id)
618 || krate.impl_items.contains_key(&parent_impl_id)
619 || krate.trait_items.contains_key(&parent_trait_id))
625 "`impl Trait` can only capture lifetimes \
626 bound at the fn or impl level"
629 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
636 // We want to start our early-bound indices at the end of the parent scope,
637 // not including any parent `impl Trait`s.
638 let mut index = self.next_early_index_for_opaque_type();
639 debug!("visit_ty: index = {}", index);
641 let mut elision = None;
642 let mut lifetimes = FxHashMap::default();
643 let mut non_lifetime_count = 0;
644 for param in generics.params {
646 GenericParamKind::Lifetime { .. } => {
647 let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m);
648 let def_id = if let Region::EarlyBound(_, def_id, _) = reg {
653 if let hir::ParamName::Plain(param_name) = name {
654 if param_name.name == kw::UnderscoreLifetime {
655 // Pick the elided lifetime "definition" if one exists
656 // and use it to make an elision scope.
657 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
660 lifetimes.insert(name, reg);
663 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
664 lifetimes.insert(name, reg);
667 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
668 non_lifetime_count += 1;
672 let next_early_index = index + non_lifetime_count;
674 if let Some(elision_region) = elision {
676 Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope };
677 self.with(scope, |_old_scope, this| {
678 let scope = Scope::Binder {
682 track_lifetime_uses: true,
683 opaque_type_parent: false,
685 this.with(scope, |_old_scope, this| {
686 this.visit_generics(generics);
687 for bound in bounds {
688 this.visit_param_bound(bound);
693 let scope = Scope::Binder {
697 track_lifetime_uses: true,
698 opaque_type_parent: false,
700 self.with(scope, |_old_scope, this| {
701 this.visit_generics(generics);
702 for bound in bounds {
703 this.visit_param_bound(bound);
708 _ => intravisit::walk_ty(self, ty),
712 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) {
713 use self::hir::TraitItemKind::*;
714 self.missing_named_lifetime_spots.push((&trait_item.generics).into());
715 match trait_item.kind {
718 self.visit_early_late(
719 Some(tcx.hir().get_parent_item(trait_item.hir_id)),
721 &trait_item.generics,
722 |this| intravisit::walk_trait_item(this, trait_item),
725 Type(bounds, ref ty) => {
726 let generics = &trait_item.generics;
727 let mut index = self.next_early_index();
728 debug!("visit_ty: index = {}", index);
729 let mut non_lifetime_count = 0;
730 let lifetimes = generics
733 .filter_map(|param| match param.kind {
734 GenericParamKind::Lifetime { .. } => {
735 Some(Region::early(&self.tcx.hir(), &mut index, param))
737 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
738 non_lifetime_count += 1;
743 let scope = Scope::Binder {
745 next_early_index: index + non_lifetime_count,
747 track_lifetime_uses: true,
748 opaque_type_parent: true,
750 self.with(scope, |old_scope, this| {
751 this.check_lifetime_params(old_scope, &generics.params);
752 this.visit_generics(generics);
753 for bound in bounds {
754 this.visit_param_bound(bound);
756 if let Some(ty) = ty {
762 // Only methods and types support generics.
763 assert!(trait_item.generics.params.is_empty());
764 intravisit::walk_trait_item(self, trait_item);
767 self.missing_named_lifetime_spots.pop();
770 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) {
771 use self::hir::ImplItemKind::*;
772 self.missing_named_lifetime_spots.push((&impl_item.generics).into());
773 match impl_item.kind {
776 self.visit_early_late(
777 Some(tcx.hir().get_parent_item(impl_item.hir_id)),
780 |this| intravisit::walk_impl_item(this, impl_item),
784 let generics = &impl_item.generics;
785 let mut index = self.next_early_index();
786 let mut non_lifetime_count = 0;
787 debug!("visit_ty: index = {}", index);
788 let lifetimes = generics
791 .filter_map(|param| match param.kind {
792 GenericParamKind::Lifetime { .. } => {
793 Some(Region::early(&self.tcx.hir(), &mut index, param))
795 GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => {
796 non_lifetime_count += 1;
801 let scope = Scope::Binder {
803 next_early_index: index + non_lifetime_count,
805 track_lifetime_uses: true,
806 opaque_type_parent: true,
808 self.with(scope, |old_scope, this| {
809 this.check_lifetime_params(old_scope, &generics.params);
810 this.visit_generics(generics);
815 // Only methods and types support generics.
816 assert!(impl_item.generics.params.is_empty());
817 intravisit::walk_impl_item(self, impl_item);
820 self.missing_named_lifetime_spots.pop();
823 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
824 debug!("visit_lifetime(lifetime_ref={:?})", lifetime_ref);
825 if lifetime_ref.is_elided() {
826 self.resolve_elided_lifetimes(vec![lifetime_ref]);
829 if lifetime_ref.is_static() {
830 self.insert_lifetime(lifetime_ref, Region::Static);
833 if self.is_in_const_generic && lifetime_ref.name != LifetimeName::Error {
834 self.emit_non_static_lt_in_const_generic_error(lifetime_ref);
837 self.resolve_lifetime_ref(lifetime_ref);
840 fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) {
841 for (i, segment) in path.segments.iter().enumerate() {
842 let depth = path.segments.len() - i - 1;
843 if let Some(ref args) = segment.args {
844 self.visit_segment_args(path.res, depth, args);
849 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) {
850 let output = match fd.output {
851 hir::FnRetTy::DefaultReturn(_) => None,
852 hir::FnRetTy::Return(ref ty) => Some(&**ty),
854 self.visit_fn_like_elision(&fd.inputs, output);
857 fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) {
858 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
859 for param in generics.params {
861 GenericParamKind::Lifetime { .. } => {}
862 GenericParamKind::Type { ref default, .. } => {
863 walk_list!(self, visit_param_bound, param.bounds);
864 if let Some(ref ty) = default {
868 GenericParamKind::Const { ref ty, .. } => {
869 let was_in_const_generic = self.is_in_const_generic;
870 self.is_in_const_generic = true;
871 walk_list!(self, visit_param_bound, param.bounds);
873 self.is_in_const_generic = was_in_const_generic;
877 for predicate in generics.where_clause.predicates {
879 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
882 ref bound_generic_params,
885 let lifetimes: FxHashMap<_, _> = bound_generic_params
887 .filter_map(|param| match param.kind {
888 GenericParamKind::Lifetime { .. } => {
889 Some(Region::late(&self.tcx.hir(), param))
894 if !lifetimes.is_empty() {
895 let next_early_index = self.next_early_index();
896 let scope = Scope::Binder {
900 track_lifetime_uses: true,
901 opaque_type_parent: false,
903 let result = self.with(scope, |old_scope, this| {
904 this.check_lifetime_params(old_scope, &bound_generic_params);
905 this.visit_ty(&bounded_ty);
906 this.trait_ref_hack = true;
907 walk_list!(this, visit_param_bound, bounds);
908 this.trait_ref_hack = false;
912 self.visit_ty(&bounded_ty);
913 walk_list!(self, visit_param_bound, bounds);
916 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
921 self.visit_lifetime(lifetime);
922 walk_list!(self, visit_param_bound, bounds);
924 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
929 self.visit_ty(lhs_ty);
930 self.visit_ty(rhs_ty);
936 fn visit_poly_trait_ref(
938 trait_ref: &'tcx hir::PolyTraitRef<'tcx>,
939 _modifier: hir::TraitBoundModifier,
941 debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref);
943 let should_pop_missing_lt = self.is_trait_ref_fn_scope(trait_ref);
945 let trait_ref_hack = take(&mut self.trait_ref_hack);
947 || trait_ref.bound_generic_params.iter().any(|param| match param.kind {
948 GenericParamKind::Lifetime { .. } => true,
957 "nested quantification of lifetimes"
961 let next_early_index = self.next_early_index();
962 let scope = Scope::Binder {
964 .bound_generic_params
966 .filter_map(|param| match param.kind {
967 GenericParamKind::Lifetime { .. } => {
968 Some(Region::late(&self.tcx.hir(), param))
975 track_lifetime_uses: true,
976 opaque_type_parent: false,
978 self.with(scope, |old_scope, this| {
979 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
980 walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
981 this.visit_trait_ref(&trait_ref.trait_ref);
984 self.visit_trait_ref(&trait_ref.trait_ref);
986 self.trait_ref_hack = trait_ref_hack;
987 if should_pop_missing_lt {
988 self.missing_named_lifetime_spots.pop();
993 #[derive(Copy, Clone, PartialEq)]
1007 fn original_label(span: Span) -> Original {
1008 Original { kind: ShadowKind::Label, span }
1010 fn shadower_label(span: Span) -> Shadower {
1011 Shadower { kind: ShadowKind::Label, span }
1013 fn original_lifetime(span: Span) -> Original {
1014 Original { kind: ShadowKind::Lifetime, span }
1016 fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower {
1017 Shadower { kind: ShadowKind::Lifetime, span: param.span }
1021 fn desc(&self) -> &'static str {
1023 ShadowKind::Label => "label",
1024 ShadowKind::Lifetime => "lifetime",
1029 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) {
1030 let lifetime_params: Vec<_> = params
1032 .filter_map(|param| match param.kind {
1033 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1037 let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1038 let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1040 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1045 "cannot mix in-band and explicit lifetime definitions"
1047 .span_label(*in_band_span, "in-band lifetime definition here")
1048 .span_label(*explicit_span, "explicit lifetime definition here")
1053 fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: Symbol, orig: Original, shadower: Shadower) {
1054 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1055 // lifetime/lifetime shadowing is an error
1060 "{} name `{}` shadows a \
1061 {} name that is already in scope",
1062 shadower.kind.desc(),
1067 // shadowing involving a label is only a warning, due to issues with
1068 // labels and lifetimes not being macro-hygienic.
1069 tcx.sess.struct_span_warn(
1072 "{} name `{}` shadows a \
1073 {} name that is already in scope",
1074 shadower.kind.desc(),
1080 err.span_label(orig.span, "first declared here");
1081 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1085 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1086 // if one of the label shadows a lifetime or another label.
1087 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) {
1088 struct GatherLabels<'a, 'tcx> {
1090 scope: ScopeRef<'a>,
1091 labels_in_fn: &'a mut Vec<Ident>,
1095 GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn };
1096 gather.visit_body(body);
1098 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1099 type Map = intravisit::ErasedMap<'v>;
1101 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1102 NestedVisitorMap::None
1105 fn visit_expr(&mut self, ex: &hir::Expr<'_>) {
1106 if let Some(label) = expression_label(ex) {
1107 for prior_label in &self.labels_in_fn[..] {
1108 // FIXME (#24278): non-hygienic comparison
1109 if label.name == prior_label.name {
1110 signal_shadowing_problem(
1113 original_label(prior_label.span),
1114 shadower_label(label.span),
1119 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1121 self.labels_in_fn.push(label);
1123 intravisit::walk_expr(self, ex)
1127 fn expression_label(ex: &hir::Expr<'_>) -> Option<Ident> {
1128 if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None }
1131 fn check_if_label_shadows_lifetime(tcx: TyCtxt<'_>, mut scope: ScopeRef<'_>, label: Ident) {
1134 Scope::Body { s, .. }
1135 | Scope::Elision { s, .. }
1136 | Scope::ObjectLifetimeDefault { s, .. } => {
1144 Scope::Binder { ref lifetimes, s, .. } => {
1145 // FIXME (#24278): non-hygienic comparison
1147 lifetimes.get(&hir::ParamName::Plain(label.normalize_to_macros_2_0()))
1149 let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap().expect_local());
1151 signal_shadowing_problem(
1154 original_lifetime(tcx.hir().span(hir_id)),
1155 shadower_label(label.span),
1166 fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap<Vec<ObjectLifetimeDefault>> {
1167 let mut map = HirIdMap::default();
1168 for item in tcx.hir().krate().items.values() {
1170 hir::ItemKind::Struct(_, ref generics)
1171 | hir::ItemKind::Union(_, ref generics)
1172 | hir::ItemKind::Enum(_, ref generics)
1173 | hir::ItemKind::OpaqueTy(hir::OpaqueTy {
1174 ref generics, impl_trait_fn: None, ..
1176 | hir::ItemKind::TyAlias(_, ref generics)
1177 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1178 let result = object_lifetime_defaults_for_item(tcx, generics);
1181 if tcx.sess.contains_name(&item.attrs, sym::rustc_object_lifetime_default) {
1182 let object_lifetime_default_reprs: String = result
1184 .map(|set| match *set {
1185 Set1::Empty => "BaseDefault".into(),
1186 Set1::One(Region::Static) => "'static".into(),
1187 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1190 .find_map(|param| match param.kind {
1191 GenericParamKind::Lifetime { .. } => {
1193 return Some(param.name.ident().to_string().into());
1201 Set1::One(_) => bug!(),
1202 Set1::Many => "Ambiguous".into(),
1204 .collect::<Vec<Cow<'static, str>>>()
1206 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1209 map.insert(item.hir_id, result);
1217 /// Scan the bounds and where-clauses on parameters to extract bounds
1218 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1219 /// for each type parameter.
1220 fn object_lifetime_defaults_for_item(
1222 generics: &hir::Generics<'_>,
1223 ) -> Vec<ObjectLifetimeDefault> {
1224 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound<'_>]) {
1225 for bound in bounds {
1226 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1227 set.insert(lifetime.name.normalize_to_macros_2_0());
1235 .filter_map(|param| match param.kind {
1236 GenericParamKind::Lifetime { .. } => None,
1237 GenericParamKind::Type { .. } => {
1238 let mut set = Set1::Empty;
1240 add_bounds(&mut set, ¶m.bounds);
1242 let param_def_id = tcx.hir().local_def_id(param.hir_id);
1243 for predicate in generics.where_clause.predicates {
1244 // Look for `type: ...` where clauses.
1245 let data = match *predicate {
1246 hir::WherePredicate::BoundPredicate(ref data) => data,
1250 // Ignore `for<'a> type: ...` as they can change what
1251 // lifetimes mean (although we could "just" handle it).
1252 if !data.bound_generic_params.is_empty() {
1256 let res = match data.bounded_ty.kind {
1257 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res,
1261 if res == Res::Def(DefKind::TyParam, param_def_id.to_def_id()) {
1262 add_bounds(&mut set, &data.bounds);
1267 Set1::Empty => Set1::Empty,
1268 Set1::One(name) => {
1269 if name == hir::LifetimeName::Static {
1270 Set1::One(Region::Static)
1275 .filter_map(|param| match param.kind {
1276 GenericParamKind::Lifetime { .. } => Some((
1278 hir::LifetimeName::Param(param.name),
1279 LifetimeDefOrigin::from_param(param),
1284 .find(|&(_, (_, lt_name, _))| lt_name == name)
1285 .map_or(Set1::Many, |(i, (id, _, origin))| {
1286 let def_id = tcx.hir().local_def_id(id);
1287 Set1::One(Region::EarlyBound(
1295 Set1::Many => Set1::Many,
1298 GenericParamKind::Const { .. } => {
1299 // Generic consts don't impose any constraints.
1301 // We still store a dummy value here to allow generic parameters
1302 // in an arbitrary order.
1309 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1310 // FIXME(#37666) this works around a limitation in the region inferencer
1311 fn hack<F>(&mut self, f: F)
1313 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1318 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1320 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1322 let LifetimeContext { tcx, map, lifetime_uses, .. } = self;
1323 let labels_in_fn = take(&mut self.labels_in_fn);
1324 let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults);
1325 let missing_named_lifetime_spots = take(&mut self.missing_named_lifetime_spots);
1326 let mut this = LifetimeContext {
1330 trait_ref_hack: self.trait_ref_hack,
1331 is_in_fn_syntax: self.is_in_fn_syntax,
1332 is_in_const_generic: self.is_in_const_generic,
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(&self, name: Ident, generics: &hir::Generics<'_>) -> Option<Span> {
1350 generics.params.iter().enumerate().find_map(|(i, param)| {
1351 if param.name.ident() == name {
1352 let mut in_band = false;
1353 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1354 if let hir::LifetimeParamKind::InBand = kind {
1361 if generics.params.len() == 1 {
1362 // if sole lifetime, remove the entire `<>` brackets
1365 // if removing within `<>` brackets, we also want to
1366 // delete a leading or trailing comma as appropriate
1367 if i >= generics.params.len() - 1 {
1368 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1370 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1380 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1381 // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)`
1382 fn suggest_eliding_single_use_lifetime(
1384 err: &mut DiagnosticBuilder<'_>,
1386 lifetime: &hir::Lifetime,
1388 let name = lifetime.name.ident();
1389 let mut remove_decl = None;
1390 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1391 if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
1392 remove_decl = self.lifetime_deletion_span(name, generics);
1396 let mut remove_use = None;
1397 let mut elide_use = None;
1398 let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| {
1399 for input in inputs {
1401 hir::TyKind::Rptr(lt, _) => {
1402 if lt.name.ident() == name {
1403 // include the trailing whitespace between the lifetime and type names
1404 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1409 .span_until_non_whitespace(lt_through_ty_span),
1414 hir::TyKind::Path(ref qpath) => {
1415 if let QPath::Resolved(_, path) = qpath {
1416 let last_segment = &path.segments[path.segments.len() - 1];
1417 let generics = last_segment.generic_args();
1418 for arg in generics.args.iter() {
1419 if let GenericArg::Lifetime(lt) = arg {
1420 if lt.name.ident() == name {
1421 elide_use = Some(lt.span);
1433 if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) {
1434 if let Some(parent) =
1435 self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id))
1438 Node::Item(item) => {
1439 if let hir::ItemKind::Fn(sig, _, _) = &item.kind {
1440 find_arg_use_span(sig.decl.inputs);
1443 Node::ImplItem(impl_item) => {
1444 if let hir::ImplItemKind::Fn(sig, _) = &impl_item.kind {
1445 find_arg_use_span(sig.decl.inputs);
1453 let msg = "elide the single-use lifetime";
1454 match (remove_decl, remove_use, elide_use) {
1455 (Some(decl_span), Some(use_span), None) => {
1456 // if both declaration and use deletion spans start at the same
1457 // place ("start at" because the latter includes trailing
1458 // whitespace), then this is an in-band lifetime
1459 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1460 err.span_suggestion(
1464 Applicability::MachineApplicable,
1467 err.multipart_suggestion(
1469 vec![(decl_span, String::new()), (use_span, String::new())],
1470 Applicability::MachineApplicable,
1474 (Some(decl_span), None, Some(use_span)) => {
1475 err.multipart_suggestion(
1477 vec![(decl_span, String::new()), (use_span, "'_".to_owned())],
1478 Applicability::MachineApplicable,
1485 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1486 let defined_by = match self.scope {
1487 Scope::Binder { lifetimes, .. } => lifetimes,
1489 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1494 let mut def_ids: Vec<_> = defined_by
1496 .flat_map(|region| match region {
1497 Region::EarlyBound(_, def_id, _)
1498 | Region::LateBound(_, def_id, _)
1499 | Region::Free(_, def_id) => Some(*def_id),
1501 Region::LateBoundAnon(..) | Region::Static => None,
1505 // ensure that we issue lints in a repeatable order
1506 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1508 for def_id in def_ids {
1509 debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id);
1511 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1514 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1518 match lifetimeuseset {
1519 Some(LifetimeUseSet::One(lifetime)) => {
1520 let hir_id = self.tcx.hir().as_local_hir_id(def_id.expect_local());
1521 debug!("hir id first={:?}", hir_id);
1522 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1523 Node::Lifetime(hir_lifetime) => Some((
1524 hir_lifetime.hir_id,
1526 hir_lifetime.name.ident(),
1528 Node::GenericParam(param) => {
1529 Some((param.hir_id, param.span, param.name.ident()))
1533 debug!("id = {:?} span = {:?} name = {:?}", id, span, name);
1534 if name.name == kw::UnderscoreLifetime {
1538 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1539 if let Some(def_id) = parent_def_id.as_local() {
1540 let parent_hir_id = self.tcx.hir().as_local_hir_id(def_id);
1541 // lifetimes in `derive` expansions don't count (Issue #53738)
1542 if self.tcx.hir().attrs(parent_hir_id).iter().any(|attr| {
1543 self.tcx.sess.check_name(attr, sym::automatically_derived)
1550 self.tcx.struct_span_lint_hir(
1551 lint::builtin::SINGLE_USE_LIFETIMES,
1555 let mut err = lint.build(&format!(
1556 "lifetime parameter `{}` only used once",
1559 if span == lifetime.span {
1560 // spans are the same for in-band lifetime declarations
1561 err.span_label(span, "this lifetime is only used here");
1563 err.span_label(span, "this lifetime...");
1564 err.span_label(lifetime.span, "...is used only here");
1566 self.suggest_eliding_single_use_lifetime(
1567 &mut err, def_id, lifetime,
1574 Some(LifetimeUseSet::Many) => {
1575 debug!("not one use lifetime");
1578 let hir_id = self.tcx.hir().as_local_hir_id(def_id.expect_local());
1579 if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) {
1580 Node::Lifetime(hir_lifetime) => Some((
1581 hir_lifetime.hir_id,
1583 hir_lifetime.name.ident(),
1585 Node::GenericParam(param) => {
1586 Some((param.hir_id, param.span, param.name.ident()))
1590 debug!("id ={:?} span = {:?} name = {:?}", id, span, name);
1591 self.tcx.struct_span_lint_hir(
1592 lint::builtin::UNUSED_LIFETIMES,
1597 .build(&format!("lifetime parameter `{}` never used", name));
1598 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1599 if let Some(generics) =
1600 self.tcx.hir().get_generics(parent_def_id)
1602 let unused_lt_span =
1603 self.lifetime_deletion_span(name, generics);
1604 if let Some(span) = unused_lt_span {
1605 err.span_suggestion(
1607 "elide the unused lifetime",
1609 Applicability::MachineApplicable,
1623 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1625 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1626 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1627 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1631 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1633 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1634 /// lifetimes may be interspersed together.
1636 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1637 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1638 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1639 /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the
1640 /// ordering is not important there.
1641 fn visit_early_late<F>(
1643 parent_id: Option<hir::HirId>,
1644 decl: &'tcx hir::FnDecl<'tcx>,
1645 generics: &'tcx hir::Generics<'tcx>,
1648 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1650 insert_late_bound_lifetimes(self.map, decl, generics);
1652 // Find the start of nested early scopes, e.g., in methods.
1654 if let Some(parent_id) = parent_id {
1655 let parent = self.tcx.hir().expect_item(parent_id);
1656 if sub_items_have_self_param(&parent.kind) {
1657 index += 1; // Self comes before lifetimes
1660 hir::ItemKind::Trait(_, _, ref generics, ..)
1661 | hir::ItemKind::Impl { ref generics, .. } => {
1662 index += generics.params.len() as u32;
1668 let mut non_lifetime_count = 0;
1669 let lifetimes = generics
1672 .filter_map(|param| match param.kind {
1673 GenericParamKind::Lifetime { .. } => {
1674 if self.map.late_bound.contains(¶m.hir_id) {
1675 Some(Region::late(&self.tcx.hir(), param))
1677 Some(Region::early(&self.tcx.hir(), &mut index, param))
1680 GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
1681 non_lifetime_count += 1;
1686 let next_early_index = index + non_lifetime_count;
1688 let scope = Scope::Binder {
1692 opaque_type_parent: true,
1693 track_lifetime_uses: false,
1695 self.with(scope, move |old_scope, this| {
1696 this.check_lifetime_params(old_scope, &generics.params);
1697 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1701 fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 {
1702 let mut scope = self.scope;
1705 Scope::Root => return 0,
1707 Scope::Binder { next_early_index, opaque_type_parent, .. }
1708 if (!only_opaque_type_parent || opaque_type_parent) =>
1710 return next_early_index;
1713 Scope::Binder { s, .. }
1714 | Scope::Body { s, .. }
1715 | Scope::Elision { s, .. }
1716 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1721 /// Returns the next index one would use for an early-bound-region
1722 /// if extending the current scope.
1723 fn next_early_index(&self) -> u32 {
1724 self.next_early_index_helper(true)
1727 /// Returns the next index one would use for an `impl Trait` that
1728 /// is being converted into an opaque type alias `impl Trait`. This will be the
1729 /// next early index from the enclosing item, for the most
1730 /// part. See the `opaque_type_parent` field for more info.
1731 fn next_early_index_for_opaque_type(&self) -> u32 {
1732 self.next_early_index_helper(false)
1735 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1736 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1738 // If we've already reported an error, just ignore `lifetime_ref`.
1739 if let LifetimeName::Error = lifetime_ref.name {
1743 // Walk up the scope chain, tracking the number of fn scopes
1744 // that we pass through, until we find a lifetime with the
1745 // given name or we run out of scopes.
1747 let mut late_depth = 0;
1748 let mut scope = self.scope;
1749 let mut outermost_body = None;
1752 Scope::Body { id, s } => {
1753 outermost_body = Some(id);
1761 Scope::Binder { ref lifetimes, s, .. } => {
1762 match lifetime_ref.name {
1763 LifetimeName::Param(param_name) => {
1764 if let Some(&def) = lifetimes.get(¶m_name.normalize_to_macros_2_0())
1766 break Some(def.shifted(late_depth));
1769 _ => bug!("expected LifetimeName::Param"),
1776 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1782 if let Some(mut def) = result {
1783 if let Region::EarlyBound(..) = def {
1784 // Do not free early-bound regions, only late-bound ones.
1785 } else if let Some(body_id) = outermost_body {
1786 let fn_id = self.tcx.hir().body_owner(body_id);
1787 match self.tcx.hir().get(fn_id) {
1788 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. })
1789 | Node::TraitItem(&hir::TraitItem {
1790 kind: hir::TraitItemKind::Fn(..), ..
1792 | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => {
1793 let scope = self.tcx.hir().local_def_id(fn_id);
1794 def = Region::Free(scope.to_def_id(), def.id().unwrap());
1800 // Check for fn-syntax conflicts with in-band lifetime definitions
1801 if self.is_in_fn_syntax {
1803 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1804 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1809 "lifetimes used in `fn` or `Fn` syntax must be \
1810 explicitly declared using `<...>` binders"
1812 .span_label(lifetime_ref.span, "in-band lifetime definition")
1817 | Region::EarlyBound(
1820 LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error,
1822 | Region::LateBound(
1825 LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error,
1827 | Region::LateBoundAnon(..)
1828 | Region::Free(..) => {}
1832 self.insert_lifetime(lifetime_ref, def);
1834 self.emit_undeclared_lifetime_error(lifetime_ref);
1838 fn visit_segment_args(
1842 generic_args: &'tcx hir::GenericArgs<'tcx>,
1845 "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})",
1846 res, depth, generic_args,
1849 if generic_args.parenthesized {
1850 let was_in_fn_syntax = self.is_in_fn_syntax;
1851 self.is_in_fn_syntax = true;
1852 self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty()));
1853 self.is_in_fn_syntax = was_in_fn_syntax;
1857 let mut elide_lifetimes = true;
1858 let lifetimes = generic_args
1861 .filter_map(|arg| match arg {
1862 hir::GenericArg::Lifetime(lt) => {
1863 if !lt.is_elided() {
1864 elide_lifetimes = false;
1871 if elide_lifetimes {
1872 self.resolve_elided_lifetimes(lifetimes);
1874 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1877 // Figure out if this is a type/trait segment,
1878 // which requires object lifetime defaults.
1879 let parent_def_id = |this: &mut Self, def_id: DefId| {
1880 let def_key = this.tcx.def_key(def_id);
1881 DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") }
1883 let type_def_id = match res {
1884 Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1885 Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1893 ) if depth == 0 => Some(def_id),
1897 debug!("visit_segment_args: type_def_id={:?}", type_def_id);
1899 // Compute a vector of defaults, one for each type parameter,
1900 // per the rules given in RFCs 599 and 1156. Example:
1903 // struct Foo<'a, T: 'a, U> { }
1906 // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default
1907 // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound)
1908 // and `dyn Baz` to `dyn Baz + 'static` (because there is no
1911 // Therefore, we would compute `object_lifetime_defaults` to a
1912 // vector like `['x, 'static]`. Note that the vector only
1913 // includes type parameters.
1914 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1916 let mut scope = self.scope;
1919 Scope::Root => break false,
1921 Scope::Body { .. } => break true,
1923 Scope::Binder { s, .. }
1924 | Scope::Elision { s, .. }
1925 | Scope::ObjectLifetimeDefault { s, .. } => {
1932 let map = &self.map;
1933 let unsubst = if let Some(def_id) = def_id.as_local() {
1934 let id = self.tcx.hir().as_local_hir_id(def_id);
1935 &map.object_lifetime_defaults[&id]
1938 self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| {
1939 tcx.generics_of(def_id)
1942 .filter_map(|param| match param.kind {
1943 GenericParamDefKind::Type { object_lifetime_default, .. } => {
1944 Some(object_lifetime_default)
1946 GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None,
1951 debug!("visit_segment_args: unsubst={:?}", unsubst);
1954 .map(|set| match *set {
1959 Some(Region::Static)
1963 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1964 GenericArg::Lifetime(lt) => Some(lt),
1967 r.subst(lifetimes, map)
1974 debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults);
1977 for arg in generic_args.args {
1979 GenericArg::Lifetime(_) => {}
1980 GenericArg::Type(ty) => {
1981 if let Some(<) = object_lifetime_defaults.get(i) {
1982 let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope };
1983 self.with(scope, |_, this| this.visit_ty(ty));
1989 GenericArg::Const(ct) => {
1990 self.visit_anon_const(&ct.value);
1995 // Hack: when resolving the type `XX` in binding like `dyn
1996 // Foo<'b, Item = XX>`, the current object-lifetime default
1997 // would be to examine the trait `Foo` to check whether it has
1998 // a lifetime bound declared on `Item`. e.g., if `Foo` is
1999 // declared like so, then the default object lifetime bound in
2000 // `XX` should be `'b`:
2008 // but if we just have `type Item;`, then it would be
2009 // `'static`. However, we don't get all of this logic correct.
2011 // Instead, we do something hacky: if there are no lifetime parameters
2012 // to the trait, then we simply use a default object lifetime
2013 // bound of `'static`, because there is no other possibility. On the other hand,
2014 // if there ARE lifetime parameters, then we require the user to give an
2015 // explicit bound for now.
2017 // This is intended to leave room for us to implement the
2018 // correct behavior in the future.
2019 let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg {
2020 GenericArg::Lifetime(_) => true,
2024 // Resolve lifetimes found in the type `XX` from `Item = XX` bindings.
2025 for b in generic_args.bindings {
2026 let scope = Scope::ObjectLifetimeDefault {
2027 lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) },
2030 self.with(scope, |_, this| this.visit_assoc_type_binding(b));
2034 fn visit_fn_like_elision(
2036 inputs: &'tcx [hir::Ty<'tcx>],
2037 output: Option<&'tcx hir::Ty<'tcx>>,
2039 debug!("visit_fn_like_elision: enter");
2040 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2041 let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope };
2042 self.with(arg_scope, |_, this| {
2043 for input in inputs {
2044 this.visit_ty(input);
2047 Scope::Elision { ref elide, .. } => {
2048 arg_elide = elide.clone();
2054 let output = match output {
2059 debug!("visit_fn_like_elision: determine output");
2061 // Figure out if there's a body we can get argument names from,
2062 // and whether there's a `self` argument (treated specially).
2063 let mut assoc_item_kind = None;
2064 let mut impl_self = None;
2065 let parent = self.tcx.hir().get_parent_node(output.hir_id);
2066 let body = match self.tcx.hir().get(parent) {
2067 // `fn` definitions and methods.
2068 Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body),
2070 Node::TraitItem(&hir::TraitItem { kind: hir::TraitItemKind::Fn(_, ref m), .. }) => {
2071 if let hir::ItemKind::Trait(.., ref trait_items) =
2072 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2075 trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind);
2078 hir::TraitFn::Required(_) => None,
2079 hir::TraitFn::Provided(body) => Some(body),
2083 Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body), .. }) => {
2084 if let hir::ItemKind::Impl { ref self_ty, ref items, .. } =
2085 self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind
2087 impl_self = Some(self_ty);
2089 items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind);
2094 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2095 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2096 // Everything else (only closures?) doesn't
2097 // actually enjoy elision in return types.
2099 self.visit_ty(output);
2104 let has_self = match assoc_item_kind {
2105 Some(hir::AssocItemKind::Fn { has_self }) => has_self,
2109 // In accordance with the rules for lifetime elision, we can determine
2110 // what region to use for elision in the output type in two ways.
2111 // First (determined here), if `self` is by-reference, then the
2112 // implied output region is the region of the self parameter.
2114 struct SelfVisitor<'a> {
2115 map: &'a NamedRegionMap,
2116 impl_self: Option<&'a hir::TyKind<'a>>,
2117 lifetime: Set1<Region>,
2120 impl SelfVisitor<'_> {
2121 // Look for `self: &'a Self` - also desugared from `&'a self`,
2122 // and if that matches, use it for elision and return early.
2123 fn is_self_ty(&self, res: Res) -> bool {
2124 if let Res::SelfTy(..) = res {
2128 // Can't always rely on literal (or implied) `Self` due
2129 // to the way elision rules were originally specified.
2130 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) =
2134 // Permit the types that unambiguously always
2135 // result in the same type constructor being used
2136 // (it can't differ between `Self` and `self`).
2137 Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _)
2138 | Res::PrimTy(_) => return res == path.res,
2147 impl<'a> Visitor<'a> for SelfVisitor<'a> {
2148 type Map = intravisit::ErasedMap<'a>;
2150 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2151 NestedVisitorMap::None
2154 fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) {
2155 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind {
2156 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind
2158 if self.is_self_ty(path.res) {
2159 if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2160 self.lifetime.insert(*lifetime);
2165 intravisit::walk_ty(self, ty)
2169 let mut visitor = SelfVisitor {
2171 impl_self: impl_self.map(|ty| &ty.kind),
2172 lifetime: Set1::Empty,
2174 visitor.visit_ty(&inputs[0]);
2175 if let Set1::One(lifetime) = visitor.lifetime {
2176 let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope };
2177 self.with(scope, |_, this| this.visit_ty(output));
2182 // Second, if there was exactly one lifetime (either a substitution or a
2183 // reference) in the arguments, then any anonymous regions in the output
2184 // have that lifetime.
2185 let mut possible_implied_output_region = None;
2186 let mut lifetime_count = 0;
2187 let arg_lifetimes = inputs
2190 .skip(has_self as usize)
2192 let mut gather = GatherLifetimes {
2194 outer_index: ty::INNERMOST,
2195 have_bound_regions: false,
2196 lifetimes: Default::default(),
2198 gather.visit_ty(input);
2200 lifetime_count += gather.lifetimes.len();
2202 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2203 // there's a chance that the unique lifetime of this
2204 // iteration will be the appropriate lifetime for output
2205 // parameters, so lets store it.
2206 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2209 ElisionFailureInfo {
2212 lifetime_count: gather.lifetimes.len(),
2213 have_bound_regions: gather.have_bound_regions,
2219 let elide = if lifetime_count == 1 {
2220 Elide::Exact(possible_implied_output_region.unwrap())
2222 Elide::Error(arg_lifetimes)
2225 debug!("visit_fn_like_elision: elide={:?}", elide);
2227 let scope = Scope::Elision { elide, s: self.scope };
2228 self.with(scope, |_, this| this.visit_ty(output));
2229 debug!("visit_fn_like_elision: exit");
2231 struct GatherLifetimes<'a> {
2232 map: &'a NamedRegionMap,
2233 outer_index: ty::DebruijnIndex,
2234 have_bound_regions: bool,
2235 lifetimes: FxHashSet<Region>,
2238 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2239 type Map = intravisit::ErasedMap<'v>;
2241 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2242 NestedVisitorMap::None
2245 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
2246 if let hir::TyKind::BareFn(_) = ty.kind {
2247 self.outer_index.shift_in(1);
2250 hir::TyKind::TraitObject(bounds, ref lifetime) => {
2251 for bound in bounds {
2252 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2255 // Stay on the safe side and don't include the object
2256 // lifetime default (which may not end up being used).
2257 if !lifetime.is_elided() {
2258 self.visit_lifetime(lifetime);
2262 intravisit::walk_ty(self, ty);
2265 if let hir::TyKind::BareFn(_) = ty.kind {
2266 self.outer_index.shift_out(1);
2270 fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) {
2271 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2272 // FIXME(eddyb) Do we want this? It only makes a difference
2273 // if this `for<'a>` lifetime parameter is never used.
2274 self.have_bound_regions = true;
2277 intravisit::walk_generic_param(self, param);
2280 fn visit_poly_trait_ref(
2282 trait_ref: &hir::PolyTraitRef<'_>,
2283 modifier: hir::TraitBoundModifier,
2285 self.outer_index.shift_in(1);
2286 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2287 self.outer_index.shift_out(1);
2290 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2291 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) {
2293 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2294 if debruijn < self.outer_index =>
2296 self.have_bound_regions = true;
2299 self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index));
2307 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2308 debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs);
2310 if lifetime_refs.is_empty() {
2314 let span = lifetime_refs[0].span;
2315 let mut late_depth = 0;
2316 let mut scope = self.scope;
2317 let mut lifetime_names = FxHashSet::default();
2320 // Do not assign any resolution, it will be inferred.
2321 Scope::Body { .. } => return,
2323 Scope::Root => break None,
2325 Scope::Binder { s, ref lifetimes, .. } => {
2326 // collect named lifetimes for suggestions
2327 for name in lifetimes.keys() {
2328 if let hir::ParamName::Plain(name) = name {
2329 lifetime_names.insert(*name);
2336 Scope::Elision { ref elide, ref s, .. } => {
2337 let lifetime = match *elide {
2338 Elide::FreshLateAnon(ref counter) => {
2339 for lifetime_ref in lifetime_refs {
2340 let lifetime = Region::late_anon(counter).shifted(late_depth);
2341 self.insert_lifetime(lifetime_ref, lifetime);
2345 Elide::Exact(l) => l.shifted(late_depth),
2346 Elide::Error(ref e) => {
2347 if let Scope::Binder { ref lifetimes, .. } = s {
2348 // collect named lifetimes for suggestions
2349 for name in lifetimes.keys() {
2350 if let hir::ParamName::Plain(name) = name {
2351 lifetime_names.insert(*name);
2357 Elide::Forbid => break None,
2359 for lifetime_ref in lifetime_refs {
2360 self.insert_lifetime(lifetime_ref, lifetime);
2365 Scope::ObjectLifetimeDefault { s, .. } => {
2371 let mut err = self.report_missing_lifetime_specifiers(span, lifetime_refs.len());
2373 if let Some(params) = error {
2374 // If there's no lifetime available, suggest `'static`.
2375 if self.report_elision_failure(&mut err, params) && lifetime_names.is_empty() {
2376 lifetime_names.insert(Ident::with_dummy_span(kw::StaticLifetime));
2379 self.add_missing_lifetime_specifiers_label(
2382 lifetime_refs.len(),
2384 error.map(|p| &p[..]).unwrap_or(&[]),
2389 fn report_elision_failure(
2391 db: &mut DiagnosticBuilder<'_>,
2392 params: &[ElisionFailureInfo],
2393 ) -> bool /* add `'static` lifetime to lifetime list */ {
2394 let mut m = String::new();
2395 let len = params.len();
2397 let elided_params: Vec<_> =
2398 params.iter().cloned().filter(|info| info.lifetime_count > 0).collect();
2400 let elided_len = elided_params.len();
2402 for (i, info) in elided_params.into_iter().enumerate() {
2403 let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions, span } =
2406 db.span_label(span, "");
2407 let help_name = if let Some(ident) =
2408 parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident())
2410 format!("`{}`", ident)
2412 format!("argument {}", index + 1)
2420 "one of {}'s {} {}lifetimes",
2423 if have_bound_regions { "free " } else { "" }
2428 if elided_len == 2 && i == 0 {
2430 } else if i + 2 == elided_len {
2431 m.push_str(", or ");
2432 } else if i != elided_len - 1 {
2439 "this function's return type contains a borrowed value, \
2440 but there is no value for it to be borrowed from",
2443 } else if elided_len == 0 {
2445 "this function's return type contains a borrowed value with \
2446 an elided lifetime, but the lifetime cannot be derived from \
2450 } else if elided_len == 1 {
2452 "this function's return type contains a borrowed value, \
2453 but the signature does not say which {} it is borrowed from",
2459 "this function's return type contains a borrowed value, \
2460 but the signature does not say whether it is borrowed from {}",
2467 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2468 debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref);
2469 let mut late_depth = 0;
2470 let mut scope = self.scope;
2471 let lifetime = loop {
2473 Scope::Binder { s, .. } => {
2478 Scope::Root | Scope::Elision { .. } => break Region::Static,
2480 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2482 Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
2485 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2488 fn check_lifetime_params(
2490 old_scope: ScopeRef<'_>,
2491 params: &'tcx [hir::GenericParam<'tcx>],
2493 let lifetimes: Vec<_> = params
2495 .filter_map(|param| match param.kind {
2496 GenericParamKind::Lifetime { .. } => {
2497 Some((param, param.name.normalize_to_macros_2_0()))
2502 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2503 if let hir::ParamName::Plain(_) = lifetime_i_name {
2504 let name = lifetime_i_name.ident().name;
2505 if name == kw::UnderscoreLifetime || name == kw::StaticLifetime {
2506 let mut err = struct_span_err!(
2510 "invalid lifetime parameter name: `{}`",
2511 lifetime_i.name.ident(),
2515 format!("{} is a reserved lifetime name", name),
2521 // It is a hard error to shadow a lifetime within the same scope.
2522 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2523 if lifetime_i_name == lifetime_j_name {
2528 "lifetime name `{}` declared twice in the same scope",
2529 lifetime_j.name.ident()
2531 .span_label(lifetime_j.span, "declared twice")
2532 .span_label(lifetime_i.span, "previous declaration here")
2537 // It is a soft error to shadow a lifetime within a parent scope.
2538 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2540 for bound in lifetime_i.bounds {
2542 hir::GenericBound::Outlives(ref lt) => match lt.name {
2543 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2545 "use of `'_` in illegal place, but not caught by lowering",
2547 hir::LifetimeName::Static => {
2548 self.insert_lifetime(lt, Region::Static);
2552 lifetime_i.span.to(lt.span),
2554 "unnecessary lifetime parameter `{}`",
2555 lifetime_i.name.ident(),
2559 "you can use the `'static` lifetime directly, in place of `{}`",
2560 lifetime_i.name.ident(),
2564 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2565 self.resolve_lifetime_ref(lt);
2567 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2568 self.tcx.sess.delay_span_bug(
2570 "lowering generated `ImplicitObjectLifetimeDefault` \
2571 outside of an object type",
2574 hir::LifetimeName::Error => {
2575 // No need to do anything, error already reported.
2584 fn check_lifetime_param_for_shadowing(
2586 mut old_scope: ScopeRef<'_>,
2587 param: &'tcx hir::GenericParam<'tcx>,
2589 for label in &self.labels_in_fn {
2590 // FIXME (#24278): non-hygienic comparison
2591 if param.name.ident().name == label.name {
2592 signal_shadowing_problem(
2595 original_label(label.span),
2596 shadower_lifetime(¶m),
2604 Scope::Body { s, .. }
2605 | Scope::Elision { s, .. }
2606 | Scope::ObjectLifetimeDefault { s, .. } => {
2614 Scope::Binder { ref lifetimes, s, .. } => {
2615 if let Some(&def) = lifetimes.get(¶m.name.normalize_to_macros_2_0()) {
2617 self.tcx.hir().as_local_hir_id(def.id().unwrap().expect_local());
2619 signal_shadowing_problem(
2621 param.name.ident().name,
2622 original_lifetime(self.tcx.hir().span(hir_id)),
2623 shadower_lifetime(¶m),
2634 /// Returns `true` if, in the current scope, replacing `'_` would be
2635 /// equivalent to a single-use lifetime.
2636 fn track_lifetime_uses(&self) -> bool {
2637 let mut scope = self.scope;
2640 Scope::Root => break false,
2642 // Inside of items, it depends on the kind of item.
2643 Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses,
2645 // Inside a body, `'_` will use an inference variable,
2647 Scope::Body { .. } => break true,
2649 // A lifetime only used in a fn argument could as well
2650 // be replaced with `'_`, as that would generate a
2652 Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true,
2654 // In the return type or other such place, `'_` is not
2655 // going to make a fresh name, so we cannot
2656 // necessarily replace a single-use lifetime with
2659 elide: Elide::Exact(_) | Elide::Error(_) | Elide::Forbid, ..
2662 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2667 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2669 "insert_lifetime: {} resolved to {:?} span={:?}",
2670 self.tcx.hir().node_to_string(lifetime_ref.hir_id),
2672 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2674 self.map.defs.insert(lifetime_ref.hir_id, def);
2677 Region::LateBoundAnon(..) | Region::Static => {
2678 // These are anonymous lifetimes or lifetimes that are not declared.
2681 Region::Free(_, def_id)
2682 | Region::LateBound(_, def_id, _)
2683 | Region::EarlyBound(_, def_id, _) => {
2684 // A lifetime declared by the user.
2685 let track_lifetime_uses = self.track_lifetime_uses();
2686 debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses);
2687 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2688 debug!("insert_lifetime: first use of {:?}", def_id);
2689 self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref));
2691 debug!("insert_lifetime: many uses of {:?}", def_id);
2692 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2698 /// Sometimes we resolve a lifetime, but later find that it is an
2699 /// error (esp. around impl trait). In that case, we remove the
2700 /// entry into `map.defs` so as not to confuse later code.
2701 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2702 let old_value = self.map.defs.remove(&lifetime_ref.hir_id);
2703 assert_eq!(old_value, Some(bad_def));
2707 /// Detects late-bound lifetimes and inserts them into
2708 /// `map.late_bound`.
2710 /// A region declared on a fn is **late-bound** if:
2711 /// - it is constrained by an argument type;
2712 /// - it does not appear in a where-clause.
2714 /// "Constrained" basically means that it appears in any type but
2715 /// not amongst the inputs to a projection. In other words, `<&'a
2716 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2717 fn insert_late_bound_lifetimes(
2718 map: &mut NamedRegionMap,
2719 decl: &hir::FnDecl<'_>,
2720 generics: &hir::Generics<'_>,
2722 debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
2724 let mut constrained_by_input = ConstrainedCollector::default();
2725 for arg_ty in decl.inputs {
2726 constrained_by_input.visit_ty(arg_ty);
2729 let mut appears_in_output = AllCollector::default();
2730 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2732 debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions);
2734 // Walk the lifetimes that appear in where clauses.
2736 // Subtle point: because we disallow nested bindings, we can just
2737 // ignore binders here and scrape up all names we see.
2738 let mut appears_in_where_clause = AllCollector::default();
2739 appears_in_where_clause.visit_generics(generics);
2741 for param in generics.params {
2742 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2743 if !param.bounds.is_empty() {
2744 // `'a: 'b` means both `'a` and `'b` are referenced
2745 appears_in_where_clause
2747 .insert(hir::LifetimeName::Param(param.name.normalize_to_macros_2_0()));
2753 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2754 appears_in_where_clause.regions
2757 // Late bound regions are those that:
2758 // - appear in the inputs
2759 // - do not appear in the where-clauses
2760 // - are not implicitly captured by `impl Trait`
2761 for param in generics.params {
2763 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2765 // Neither types nor consts are late-bound.
2766 hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
2769 let lt_name = hir::LifetimeName::Param(param.name.normalize_to_macros_2_0());
2770 // appears in the where clauses? early-bound.
2771 if appears_in_where_clause.regions.contains(<_name) {
2775 // does not appear in the inputs, but appears in the return type? early-bound.
2776 if !constrained_by_input.regions.contains(<_name)
2777 && appears_in_output.regions.contains(<_name)
2783 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2788 let inserted = map.late_bound.insert(param.hir_id);
2789 assert!(inserted, "visited lifetime {:?} twice", param.hir_id);
2795 struct ConstrainedCollector {
2796 regions: FxHashSet<hir::LifetimeName>,
2799 impl<'v> Visitor<'v> for ConstrainedCollector {
2800 type Map = intravisit::ErasedMap<'v>;
2802 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2803 NestedVisitorMap::None
2806 fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
2809 hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..),
2811 // ignore lifetimes appearing in associated type
2812 // projections, as they are not *constrained*
2816 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2817 // consider only the lifetimes on the final
2818 // segment; I am not sure it's even currently
2819 // valid to have them elsewhere, but even if it
2820 // is, those would be potentially inputs to
2822 if let Some(last_segment) = path.segments.last() {
2823 self.visit_path_segment(path.span, last_segment);
2828 intravisit::walk_ty(self, ty);
2833 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2834 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());
2839 struct AllCollector {
2840 regions: FxHashSet<hir::LifetimeName>,
2843 impl<'v> Visitor<'v> for AllCollector {
2844 type Map = intravisit::ErasedMap<'v>;
2846 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2847 NestedVisitorMap::None
2850 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2851 self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0());