1 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Name resolution for lifetimes.
13 //! Name resolution for lifetimes follows MUCH simpler rules than the
14 //! full resolve. For example, lifetime names are never exported or
15 //! used between functions, and they operate in a purely top-down
16 //! way. Therefore we break lifetime name resolution into a separate pass.
19 use hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
21 use hir::{GenericArg, GenericParam, ItemLocalId, LifetimeName, Node, ParamName};
22 use ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
24 use errors::{Applicability, DiagnosticBuilder};
26 use rustc_data_structures::sync::Lrc;
30 use std::mem::replace;
34 use syntax::symbol::keywords;
36 use util::nodemap::{DefIdMap, FxHashMap, FxHashSet, NodeMap, NodeSet};
38 use hir::intravisit::{self, NestedVisitorMap, Visitor};
39 use hir::{self, GenericParamKind, LifetimeParamKind};
41 /// The origin of a named lifetime definition.
43 /// This is used to prevent the usage of in-band lifetimes in `Fn`/`fn` syntax.
44 #[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
45 pub enum LifetimeDefOrigin {
46 // Explicit binders like `fn foo<'a>(x: &'a u8)` or elided like `impl Foo<&u32>`
48 // In-band declarations like `fn foo(x: &'a u8)`
50 // Some kind of erroneous origin
54 impl LifetimeDefOrigin {
55 fn from_param(param: &GenericParam) -> Self {
57 GenericParamKind::Lifetime { kind } => match kind {
58 LifetimeParamKind::InBand => LifetimeDefOrigin::InBand,
59 LifetimeParamKind::Explicit => LifetimeDefOrigin::ExplicitOrElided,
60 LifetimeParamKind::Elided => LifetimeDefOrigin::ExplicitOrElided,
61 LifetimeParamKind::Error => LifetimeDefOrigin::Error,
63 _ => bug!("expected a lifetime param"),
68 // This counts the no of times a lifetime is used
69 #[derive(Clone, Copy, Debug)]
70 pub enum LifetimeUseSet<'tcx> {
71 One(&'tcx hir::Lifetime),
75 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
80 /* lifetime decl */ DefId,
85 /* lifetime decl */ DefId,
88 LateBoundAnon(ty::DebruijnIndex, /* anon index */ u32),
89 Free(DefId, /* lifetime decl */ DefId),
93 fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam) -> (ParamName, Region) {
96 let def_id = hir_map.local_def_id(param.id);
97 let origin = LifetimeDefOrigin::from_param(param);
98 debug!("Region::early: index={} def_id={:?}", i, def_id);
99 (param.name.modern(), Region::EarlyBound(i, def_id, origin))
102 fn late(hir_map: &Map<'_>, param: &GenericParam) -> (ParamName, Region) {
103 let depth = ty::INNERMOST;
104 let def_id = hir_map.local_def_id(param.id);
105 let origin = LifetimeDefOrigin::from_param(param);
107 "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
108 param, depth, def_id, origin,
112 Region::LateBound(depth, def_id, origin),
116 fn late_anon(index: &Cell<u32>) -> Region {
119 let depth = ty::INNERMOST;
120 Region::LateBoundAnon(depth, i)
123 fn id(&self) -> Option<DefId> {
125 Region::Static | Region::LateBoundAnon(..) => None,
127 Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
133 fn shifted(self, amount: u32) -> Region {
135 Region::LateBound(debruijn, id, origin) => {
136 Region::LateBound(debruijn.shifted_in(amount), id, origin)
138 Region::LateBoundAnon(debruijn, index) => {
139 Region::LateBoundAnon(debruijn.shifted_in(amount), index)
145 fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
147 Region::LateBound(debruijn, id, origin) => {
148 Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
150 Region::LateBoundAnon(debruijn, index) => {
151 Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
157 fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
159 L: Iterator<Item = &'a hir::Lifetime>,
161 if let Region::EarlyBound(index, _, _) = self {
164 .and_then(|lifetime| map.defs.get(&lifetime.id).cloned())
171 /// A set containing, at most, one known element.
172 /// If two distinct values are inserted into a set, then it
173 /// becomes `Many`, which can be used to detect ambiguities.
174 #[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Debug)]
181 impl<T: PartialEq> Set1<T> {
182 pub fn insert(&mut self, value: T) {
183 if let Set1::Empty = *self {
184 *self = Set1::One(value);
187 if let Set1::One(ref old) = *self {
196 pub type ObjectLifetimeDefault = Set1<Region>;
198 /// Maps the id of each lifetime reference to the lifetime decl
199 /// that it corresponds to.
201 /// FIXME. This struct gets converted to a `ResolveLifetimes` for
202 /// actual use. It has the same data, but indexed by `DefIndex`. This
205 struct NamedRegionMap {
206 // maps from every use of a named (not anonymous) lifetime to a
207 // `Region` describing how that region is bound
208 pub defs: NodeMap<Region>,
210 // the set of lifetime def ids that are late-bound; a region can
211 // be late-bound if (a) it does NOT appear in a where-clause and
212 // (b) it DOES appear in the arguments.
213 pub late_bound: NodeSet,
215 // For each type and trait definition, maps type parameters
216 // to the trait object lifetime defaults computed from them.
217 pub object_lifetime_defaults: NodeMap<Vec<ObjectLifetimeDefault>>,
220 /// See `NamedRegionMap`.
222 pub struct ResolveLifetimes {
223 defs: FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Region>>>,
224 late_bound: FxHashMap<LocalDefId, Lrc<FxHashSet<ItemLocalId>>>,
225 object_lifetime_defaults:
226 FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
229 impl_stable_hash_for!(struct ::middle::resolve_lifetime::ResolveLifetimes {
232 object_lifetime_defaults
235 struct LifetimeContext<'a, 'tcx: 'a> {
236 tcx: TyCtxt<'a, 'tcx, 'tcx>,
237 map: &'a mut NamedRegionMap,
240 /// Deep breath. Our representation for poly trait refs contains a single
241 /// binder and thus we only allow a single level of quantification. However,
242 /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
243 /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the de Bruijn indices
244 /// correct when representing these constraints, we should only introduce one
245 /// scope. However, we want to support both locations for the quantifier and
246 /// during lifetime resolution we want precise information (so we can't
247 /// desugar in an earlier phase).
249 /// SO, if we encounter a quantifier at the outer scope, we set
250 /// trait_ref_hack to true (and introduce a scope), and then if we encounter
251 /// a quantifier at the inner scope, we error. If trait_ref_hack is false,
252 /// then we introduce the scope at the inner quantifier.
255 trait_ref_hack: bool,
257 /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
258 is_in_fn_syntax: bool,
260 /// List of labels in the function/method currently under analysis.
261 labels_in_fn: Vec<ast::Ident>,
263 /// Cache for cross-crate per-definition object lifetime defaults.
264 xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
266 lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
271 /// Declares lifetimes, and each can be early-bound or late-bound.
272 /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
273 /// it should be shifted by the number of `Binder`s in between the
274 /// declaration `Binder` and the location it's referenced from.
276 lifetimes: FxHashMap<hir::ParamName, Region>,
278 /// if we extend this scope with another scope, what is the next index
279 /// we should use for an early-bound region?
280 next_early_index: u32,
282 /// Flag is set to true if, in this binder, `'_` would be
283 /// equivalent to a "single-use region". This is true on
284 /// impls, but not other kinds of items.
285 track_lifetime_uses: bool,
287 /// Whether or not this binder would serve as the parent
288 /// binder for abstract types introduced within. For example:
290 /// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
292 /// Here, the abstract types we create for the `impl Trait`
293 /// and `impl Trait2` references will both have the `foo` item
294 /// as their parent. When we get to `impl Trait2`, we find
295 /// that it is nested within the `for<>` binder -- this flag
296 /// allows us to skip that when looking for the parent binder
297 /// of the resulting abstract type.
298 abstract_type_parent: bool,
303 /// Lifetimes introduced by a fn are scoped to the call-site for that fn,
304 /// if this is a fn body, otherwise the original definitions are used.
305 /// Unspecified lifetimes are inferred, unless an elision scope is nested,
306 /// e.g. `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
312 /// A scope which either determines unspecified lifetimes or errors
313 /// on them (e.g. due to ambiguity). For more details, see `Elide`.
319 /// Use a specific lifetime (if `Some`) or leave it unset (to be
320 /// inferred in a function body or potentially error outside one),
321 /// for the default choice of lifetime in a trait object type.
322 ObjectLifetimeDefault {
323 lifetime: Option<Region>,
330 #[derive(Clone, Debug)]
332 /// Use a fresh anonymous late-bound lifetime each time, by
333 /// incrementing the counter to generate sequential indices.
334 FreshLateAnon(Cell<u32>),
335 /// Always use this one lifetime.
337 /// Less or more than one lifetime were found, error on unspecified.
338 Error(Vec<ElisionFailureInfo>),
341 #[derive(Clone, Debug)]
342 struct ElisionFailureInfo {
343 /// Where we can find the argument pattern.
344 parent: Option<hir::BodyId>,
345 /// The index of the argument in the original definition.
347 lifetime_count: usize,
348 have_bound_regions: bool,
351 type ScopeRef<'a> = &'a Scope<'a>;
353 const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
355 pub fn provide(providers: &mut ty::query::Providers<'_>) {
356 *providers = ty::query::Providers {
359 named_region_map: |tcx, id| {
360 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
361 tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id).cloned()
364 is_late_bound_map: |tcx, id| {
365 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
366 tcx.resolve_lifetimes(LOCAL_CRATE)
372 object_lifetime_defaults_map: |tcx, id| {
373 let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
374 tcx.resolve_lifetimes(LOCAL_CRATE)
375 .object_lifetime_defaults
383 // (*) FIXME the query should be defined to take a LocalDefId
386 /// Computes the `ResolveLifetimes` map that contains data for the
387 /// entire crate. You should not read the result of this query
388 /// directly, but rather use `named_region_map`, `is_late_bound_map`,
390 fn resolve_lifetimes<'tcx>(
391 tcx: TyCtxt<'_, 'tcx, 'tcx>,
393 ) -> Lrc<ResolveLifetimes> {
394 assert_eq!(for_krate, LOCAL_CRATE);
396 let named_region_map = krate(tcx);
398 let mut rl = ResolveLifetimes::default();
400 for (k, v) in named_region_map.defs {
401 let hir_id = tcx.hir.node_to_hir_id(k);
402 let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
403 Lrc::get_mut(map).unwrap().insert(hir_id.local_id, v);
405 for k in named_region_map.late_bound {
406 let hir_id = tcx.hir.node_to_hir_id(k);
407 let map = rl.late_bound
408 .entry(hir_id.owner_local_def_id())
410 Lrc::get_mut(map).unwrap().insert(hir_id.local_id);
412 for (k, v) in named_region_map.object_lifetime_defaults {
413 let hir_id = tcx.hir.node_to_hir_id(k);
414 let map = rl.object_lifetime_defaults
415 .entry(hir_id.owner_local_def_id())
419 .insert(hir_id.local_id, Lrc::new(v));
425 fn krate<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) -> NamedRegionMap {
426 let krate = tcx.hir.krate();
427 let mut map = NamedRegionMap {
429 late_bound: NodeSet(),
430 object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
433 let mut visitor = LifetimeContext {
437 trait_ref_hack: false,
438 is_in_fn_syntax: false,
439 labels_in_fn: vec![],
440 xcrate_object_lifetime_defaults: DefIdMap(),
441 lifetime_uses: &mut DefIdMap(),
443 for (_, item) in &krate.items {
444 visitor.visit_item(item);
450 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
451 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
452 NestedVisitorMap::All(&self.tcx.hir)
455 // We want to nest trait/impl items in their parent, but nothing else.
456 fn visit_nested_item(&mut self, _: hir::ItemId) {}
458 fn visit_nested_body(&mut self, body: hir::BodyId) {
459 // Each body has their own set of labels, save labels.
460 let saved = replace(&mut self.labels_in_fn, vec![]);
461 let body = self.tcx.hir.body(body);
462 extract_labels(self, body);
469 this.visit_body(body);
472 replace(&mut self.labels_in_fn, saved);
475 fn visit_item(&mut self, item: &'tcx hir::Item) {
477 hir::ItemKind::Fn(ref decl, _, ref generics, _) => {
478 self.visit_early_late(None, decl, generics, |this| {
479 intravisit::walk_item(this, item);
483 hir::ItemKind::ExternCrate(_)
484 | hir::ItemKind::Use(..)
485 | hir::ItemKind::Mod(..)
486 | hir::ItemKind::ForeignMod(..)
487 | hir::ItemKind::GlobalAsm(..) => {
488 // These sorts of items have no lifetime parameters at all.
489 intravisit::walk_item(self, item);
491 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
492 // No lifetime parameters, but implied 'static.
493 let scope = Scope::Elision {
494 elide: Elide::Exact(Region::Static),
497 self.with(scope, |_, this| intravisit::walk_item(this, item));
499 hir::ItemKind::Existential(hir::ExistTy {
500 impl_trait_fn: Some(_),
503 // currently existential type declarations are just generated from impl Trait
504 // items. doing anything on this node is irrelevant, as we currently don't need
507 hir::ItemKind::Ty(_, ref generics)
508 | hir::ItemKind::Existential(hir::ExistTy {
513 | hir::ItemKind::Enum(_, ref generics)
514 | hir::ItemKind::Struct(_, ref generics)
515 | hir::ItemKind::Union(_, ref generics)
516 | hir::ItemKind::Trait(_, _, ref generics, ..)
517 | hir::ItemKind::TraitAlias(ref generics, ..)
518 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
519 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
520 // This is not true for other kinds of items.x
521 let track_lifetime_uses = match item.node {
522 hir::ItemKind::Impl(..) => true,
525 // These kinds of items have only early bound lifetime parameters.
526 let mut index = if let hir::ItemKind::Trait(..) = item.node {
527 1 // Self comes before lifetimes
531 let mut type_count = 0;
532 let lifetimes = generics
535 .filter_map(|param| match param.kind {
536 GenericParamKind::Lifetime { .. } => {
537 Some(Region::early(&self.tcx.hir, &mut index, param))
539 GenericParamKind::Type { .. } => {
545 let scope = Scope::Binder {
547 next_early_index: index + type_count,
548 abstract_type_parent: true,
552 self.with(scope, |old_scope, this| {
553 this.check_lifetime_params(old_scope, &generics.params);
554 intravisit::walk_item(this, item);
560 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem) {
562 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
563 self.visit_early_late(None, decl, generics, |this| {
564 intravisit::walk_foreign_item(this, item);
567 hir::ForeignItemKind::Static(..) => {
568 intravisit::walk_foreign_item(self, item);
570 hir::ForeignItemKind::Type => {
571 intravisit::walk_foreign_item(self, item);
576 fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
577 debug!("visit_ty: id={:?} ty={:?}", ty.id, ty);
579 hir::TyKind::BareFn(ref c) => {
580 let next_early_index = self.next_early_index();
581 let was_in_fn_syntax = self.is_in_fn_syntax;
582 self.is_in_fn_syntax = true;
583 let scope = Scope::Binder {
584 lifetimes: c.generic_params
586 .filter_map(|param| match param.kind {
587 GenericParamKind::Lifetime { .. } => {
588 Some(Region::late(&self.tcx.hir, param))
595 track_lifetime_uses: true,
596 abstract_type_parent: false,
598 self.with(scope, |old_scope, this| {
599 // a bare fn has no bounds, so everything
600 // contained within is scoped within its binder.
601 this.check_lifetime_params(old_scope, &c.generic_params);
602 intravisit::walk_ty(this, ty);
604 self.is_in_fn_syntax = was_in_fn_syntax;
606 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
607 for bound in bounds {
608 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
610 match lifetime.name {
611 LifetimeName::Implicit => {
612 // If the user does not write *anything*, we
613 // use the object lifetime defaulting
614 // rules. So e.g. `Box<dyn Debug>` becomes
615 // `Box<dyn Debug + 'static>`.
616 self.resolve_object_lifetime_default(lifetime)
618 LifetimeName::Underscore => {
619 // If the user writes `'_`, we use the *ordinary* elision
620 // rules. So the `'_` in e.g. `Box<dyn Debug + '_>` will be
621 // resolved the same as the `'_` in `&'_ Foo`.
624 self.resolve_elided_lifetimes(vec![lifetime])
626 LifetimeName::Param(_) | LifetimeName::Static => {
627 // If the user wrote an explicit name, use that.
628 self.visit_lifetime(lifetime);
630 LifetimeName::Error => {}
633 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
634 self.visit_lifetime(lifetime_ref);
635 let scope = Scope::ObjectLifetimeDefault {
636 lifetime: self.map.defs.get(&lifetime_ref.id).cloned(),
639 self.with(scope, |_, this| this.visit_ty(&mt.ty));
641 hir::TyKind::Def(item_id, ref lifetimes) => {
642 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
643 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
644 // `abstract type MyAnonTy<'b>: MyTrait<'b>;`
645 // ^ ^ this gets resolved in the scope of
646 // the exist_ty generics
647 let (generics, bounds) = match self.tcx.hir.expect_item(item_id.id).node {
648 // named existential types are reached via TyKind::Path
649 // this arm is for `impl Trait` in the types of statics, constants and locals
650 hir::ItemKind::Existential(hir::ExistTy {
654 intravisit::walk_ty(self, ty);
657 // RPIT (return position impl trait)
658 hir::ItemKind::Existential(hir::ExistTy {
662 }) => (generics, bounds),
663 ref i => bug!("impl Trait pointed to non-existential type?? {:#?}", i),
666 // Resolve the lifetimes that are applied to the existential type.
667 // These are resolved in the current scope.
668 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
669 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
670 // ^ ^this gets resolved in the current scope
671 for lifetime in lifetimes {
672 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
673 self.visit_lifetime(lifetime);
675 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
676 // and ban them. Type variables instantiated inside binders aren't
677 // well-supported at the moment, so this doesn't work.
678 // In the future, this should be fixed and this error should be removed.
679 let def = self.map.defs.get(&lifetime.id).cloned();
680 if let Some(Region::LateBound(_, def_id, _)) = def {
681 if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
682 // Ensure that the parent of the def is an item, not HRTB
683 let parent_id = self.tcx.hir.get_parent_node(node_id);
684 let parent_impl_id = hir::ImplItemId { node_id: parent_id };
685 let parent_trait_id = hir::TraitItemId { node_id: parent_id };
686 let krate = self.tcx.hir.forest.krate();
687 if !(krate.items.contains_key(&parent_id)
688 || krate.impl_items.contains_key(&parent_impl_id)
689 || krate.trait_items.contains_key(&parent_trait_id))
695 "`impl Trait` can only capture lifetimes \
696 bound at the fn or impl level"
698 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
705 // We want to start our early-bound indices at the end of the parent scope,
706 // not including any parent `impl Trait`s.
707 let mut index = self.next_early_index_for_abstract_type();
708 debug!("visit_ty: index = {}", index);
710 let mut elision = None;
711 let mut lifetimes = FxHashMap::default();
712 let mut type_count = 0;
713 for param in &generics.params {
715 GenericParamKind::Lifetime { .. } => {
716 let (name, reg) = Region::early(&self.tcx.hir, &mut index, ¶m);
717 if let hir::ParamName::Plain(param_name) = name {
718 if param_name.name == keywords::UnderscoreLifetime.name() {
719 // Pick the elided lifetime "definition" if one exists
720 // and use it to make an elision scope.
723 lifetimes.insert(name, reg);
726 lifetimes.insert(name, reg);
729 GenericParamKind::Type { .. } => {
734 let next_early_index = index + type_count;
736 if let Some(elision_region) = elision {
737 let scope = Scope::Elision {
738 elide: Elide::Exact(elision_region),
741 self.with(scope, |_old_scope, this| {
742 let scope = Scope::Binder {
746 track_lifetime_uses: true,
747 abstract_type_parent: false,
749 this.with(scope, |_old_scope, this| {
750 this.visit_generics(generics);
751 for bound in bounds {
752 this.visit_param_bound(bound);
757 let scope = Scope::Binder {
761 track_lifetime_uses: true,
762 abstract_type_parent: false,
764 self.with(scope, |_old_scope, this| {
765 this.visit_generics(generics);
766 for bound in bounds {
767 this.visit_param_bound(bound);
772 _ => intravisit::walk_ty(self, ty),
776 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
777 use self::hir::TraitItemKind::*;
778 match trait_item.node {
779 Method(ref sig, _) => {
781 self.visit_early_late(
782 Some(tcx.hir.get_parent(trait_item.id)),
784 &trait_item.generics,
785 |this| intravisit::walk_trait_item(this, trait_item),
788 Type(ref bounds, ref ty) => {
789 let generics = &trait_item.generics;
790 let mut index = self.next_early_index();
791 debug!("visit_ty: index = {}", index);
792 let mut type_count = 0;
793 let lifetimes = generics
796 .filter_map(|param| match param.kind {
797 GenericParamKind::Lifetime { .. } => {
798 Some(Region::early(&self.tcx.hir, &mut index, param))
800 GenericParamKind::Type { .. } => {
806 let scope = Scope::Binder {
808 next_early_index: index + type_count,
810 track_lifetime_uses: true,
811 abstract_type_parent: true,
813 self.with(scope, |_old_scope, this| {
814 this.visit_generics(generics);
815 for bound in bounds {
816 this.visit_param_bound(bound);
818 if let Some(ty) = ty {
824 // Only methods and types support generics.
825 assert!(trait_item.generics.params.is_empty());
826 intravisit::walk_trait_item(self, trait_item);
831 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
832 use self::hir::ImplItemKind::*;
833 match impl_item.node {
834 Method(ref sig, _) => {
836 self.visit_early_late(
837 Some(tcx.hir.get_parent(impl_item.id)),
840 |this| intravisit::walk_impl_item(this, impl_item),
844 let generics = &impl_item.generics;
845 let mut index = self.next_early_index();
846 let mut next_early_index = index;
847 debug!("visit_ty: index = {}", index);
848 let lifetimes = generics
851 .filter_map(|param| match param.kind {
852 GenericParamKind::Lifetime { .. } => {
853 Some(Region::early(&self.tcx.hir, &mut index, param))
855 GenericParamKind::Type { .. } => {
856 next_early_index += 1;
861 let scope = Scope::Binder {
865 track_lifetime_uses: true,
866 abstract_type_parent: true,
868 self.with(scope, |_old_scope, this| {
869 this.visit_generics(generics);
873 Existential(ref bounds) => {
874 let generics = &impl_item.generics;
875 let mut index = self.next_early_index();
876 let mut next_early_index = index;
877 debug!("visit_ty: index = {}", index);
878 let lifetimes = generics
881 .filter_map(|param| match param.kind {
882 GenericParamKind::Lifetime { .. } => {
883 Some(Region::early(&self.tcx.hir, &mut index, param))
885 GenericParamKind::Type { .. } => {
886 next_early_index += 1;
892 let scope = Scope::Binder {
896 track_lifetime_uses: true,
897 abstract_type_parent: true,
899 self.with(scope, |_old_scope, this| {
900 this.visit_generics(generics);
901 for bound in bounds {
902 this.visit_param_bound(bound);
907 // Only methods and types support generics.
908 assert!(impl_item.generics.params.is_empty());
909 intravisit::walk_impl_item(self, impl_item);
914 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
915 if lifetime_ref.is_elided() {
916 self.resolve_elided_lifetimes(vec![lifetime_ref]);
919 if lifetime_ref.is_static() {
920 self.insert_lifetime(lifetime_ref, Region::Static);
923 self.resolve_lifetime_ref(lifetime_ref);
926 fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
927 for (i, segment) in path.segments.iter().enumerate() {
928 let depth = path.segments.len() - i - 1;
929 if let Some(ref args) = segment.args {
930 self.visit_segment_args(path.def, depth, args);
935 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl) {
936 let output = match fd.output {
937 hir::DefaultReturn(_) => None,
938 hir::Return(ref ty) => Some(ty),
940 self.visit_fn_like_elision(&fd.inputs, output);
943 fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
944 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
945 for param in &generics.params {
947 GenericParamKind::Lifetime { .. } => {}
948 GenericParamKind::Type { ref default, .. } => {
949 walk_list!(self, visit_param_bound, ¶m.bounds);
950 if let Some(ref ty) = default {
956 for predicate in &generics.where_clause.predicates {
958 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
961 ref bound_generic_params,
964 let lifetimes: FxHashMap<_, _> = bound_generic_params
966 .filter_map(|param| match param.kind {
967 GenericParamKind::Lifetime { .. } => {
968 Some(Region::late(&self.tcx.hir, param))
973 if !lifetimes.is_empty() {
974 self.trait_ref_hack = true;
975 let next_early_index = self.next_early_index();
976 let scope = Scope::Binder {
980 track_lifetime_uses: true,
981 abstract_type_parent: false,
983 let result = self.with(scope, |old_scope, this| {
984 this.check_lifetime_params(old_scope, &bound_generic_params);
985 this.visit_ty(&bounded_ty);
986 walk_list!(this, visit_param_bound, bounds);
988 self.trait_ref_hack = false;
991 self.visit_ty(&bounded_ty);
992 walk_list!(self, visit_param_bound, bounds);
995 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1000 self.visit_lifetime(lifetime);
1001 walk_list!(self, visit_param_bound, bounds);
1003 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1008 self.visit_ty(lhs_ty);
1009 self.visit_ty(rhs_ty);
1015 fn visit_poly_trait_ref(
1017 trait_ref: &'tcx hir::PolyTraitRef,
1018 _modifier: hir::TraitBoundModifier,
1020 debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
1022 if !self.trait_ref_hack || trait_ref.bound_generic_params.iter().any(|param| {
1024 GenericParamKind::Lifetime { .. } => true,
1028 if self.trait_ref_hack {
1033 "nested quantification of lifetimes"
1036 let next_early_index = self.next_early_index();
1037 let scope = Scope::Binder {
1038 lifetimes: trait_ref
1039 .bound_generic_params
1041 .filter_map(|param| match param.kind {
1042 GenericParamKind::Lifetime { .. } => {
1043 Some(Region::late(&self.tcx.hir, param))
1050 track_lifetime_uses: true,
1051 abstract_type_parent: false,
1053 self.with(scope, |old_scope, this| {
1054 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
1055 walk_list!(this, visit_generic_param, &trait_ref.bound_generic_params);
1056 this.visit_trait_ref(&trait_ref.trait_ref)
1059 self.visit_trait_ref(&trait_ref.trait_ref)
1064 #[derive(Copy, Clone, PartialEq)]
1078 fn original_label(span: Span) -> Original {
1080 kind: ShadowKind::Label,
1084 fn shadower_label(span: Span) -> Shadower {
1086 kind: ShadowKind::Label,
1090 fn original_lifetime(span: Span) -> Original {
1092 kind: ShadowKind::Lifetime,
1096 fn shadower_lifetime(param: &hir::GenericParam) -> Shadower {
1098 kind: ShadowKind::Lifetime,
1104 fn desc(&self) -> &'static str {
1106 ShadowKind::Label => "label",
1107 ShadowKind::Lifetime => "lifetime",
1112 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_, '_, '_>, params: &P<[hir::GenericParam]>) {
1113 let lifetime_params: Vec<_> = params
1115 .filter_map(|param| match param.kind {
1116 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1120 let explicit = lifetime_params
1122 .find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1123 let in_band = lifetime_params
1125 .find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1127 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1132 "cannot mix in-band and explicit lifetime definitions"
1133 ).span_label(*in_band_span, "in-band lifetime definition here")
1134 .span_label(*explicit_span, "explicit lifetime definition here")
1139 fn signal_shadowing_problem(
1140 tcx: TyCtxt<'_, '_, '_>,
1145 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1146 // lifetime/lifetime shadowing is an error
1151 "{} name `{}` shadows a \
1152 {} name that is already in scope",
1153 shadower.kind.desc(),
1158 // shadowing involving a label is only a warning, due to issues with
1159 // labels and lifetimes not being macro-hygienic.
1160 tcx.sess.struct_span_warn(
1163 "{} name `{}` shadows a \
1164 {} name that is already in scope",
1165 shadower.kind.desc(),
1171 err.span_label(orig.span, "first declared here");
1172 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1176 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1177 // if one of the label shadows a lifetime or another label.
1178 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body) {
1179 struct GatherLabels<'a, 'tcx: 'a> {
1180 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1181 scope: ScopeRef<'a>,
1182 labels_in_fn: &'a mut Vec<ast::Ident>,
1185 let mut gather = GatherLabels {
1188 labels_in_fn: &mut ctxt.labels_in_fn,
1190 gather.visit_body(body);
1192 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1193 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
1194 NestedVisitorMap::None
1197 fn visit_expr(&mut self, ex: &hir::Expr) {
1198 if let Some(label) = expression_label(ex) {
1199 for prior_label in &self.labels_in_fn[..] {
1200 // FIXME (#24278): non-hygienic comparison
1201 if label.name == prior_label.name {
1202 signal_shadowing_problem(
1205 original_label(prior_label.span),
1206 shadower_label(label.span),
1211 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1213 self.labels_in_fn.push(label);
1215 intravisit::walk_expr(self, ex)
1219 fn expression_label(ex: &hir::Expr) -> Option<ast::Ident> {
1221 hir::ExprKind::While(.., Some(label)) | hir::ExprKind::Loop(_, Some(label), _) => {
1228 fn check_if_label_shadows_lifetime(
1229 tcx: TyCtxt<'_, '_, '_>,
1230 mut scope: ScopeRef<'_>,
1235 Scope::Body { s, .. }
1236 | Scope::Elision { s, .. }
1237 | Scope::ObjectLifetimeDefault { s, .. } => {
1246 ref lifetimes, s, ..
1248 // FIXME (#24278): non-hygienic comparison
1249 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1250 let node_id = tcx.hir.as_local_node_id(def.id().unwrap()).unwrap();
1252 signal_shadowing_problem(
1255 original_lifetime(tcx.hir.span(node_id)),
1256 shadower_label(label.span),
1267 fn compute_object_lifetime_defaults(
1268 tcx: TyCtxt<'_, '_, '_>,
1269 ) -> NodeMap<Vec<ObjectLifetimeDefault>> {
1270 let mut map = NodeMap();
1271 for item in tcx.hir.krate().items.values() {
1273 hir::ItemKind::Struct(_, ref generics)
1274 | hir::ItemKind::Union(_, ref generics)
1275 | hir::ItemKind::Enum(_, ref generics)
1276 | hir::ItemKind::Existential(hir::ExistTy {
1278 impl_trait_fn: None,
1281 | hir::ItemKind::Ty(_, ref generics)
1282 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1283 let result = object_lifetime_defaults_for_item(tcx, generics);
1286 if attr::contains_name(&item.attrs, "rustc_object_lifetime_default") {
1287 let object_lifetime_default_reprs: String = result
1289 .map(|set| match *set {
1290 Set1::Empty => "BaseDefault".into(),
1291 Set1::One(Region::Static) => "'static".into(),
1292 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1295 .find_map(|param| match param.kind {
1296 GenericParamKind::Lifetime { .. } => {
1298 return Some(param.name.ident().to_string().into());
1306 Set1::One(_) => bug!(),
1307 Set1::Many => "Ambiguous".into(),
1309 .collect::<Vec<Cow<'static, str>>>()
1311 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1314 map.insert(item.id, result);
1322 /// Scan the bounds and where-clauses on parameters to extract bounds
1323 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1324 /// for each type parameter.
1325 fn object_lifetime_defaults_for_item(
1326 tcx: TyCtxt<'_, '_, '_>,
1327 generics: &hir::Generics,
1328 ) -> Vec<ObjectLifetimeDefault> {
1329 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound]) {
1330 for bound in bounds {
1331 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1332 set.insert(lifetime.name.modern());
1340 .filter_map(|param| match param.kind {
1341 GenericParamKind::Lifetime { .. } => None,
1342 GenericParamKind::Type { .. } => {
1343 let mut set = Set1::Empty;
1345 add_bounds(&mut set, ¶m.bounds);
1347 let param_def_id = tcx.hir.local_def_id(param.id);
1348 for predicate in &generics.where_clause.predicates {
1349 // Look for `type: ...` where clauses.
1350 let data = match *predicate {
1351 hir::WherePredicate::BoundPredicate(ref data) => data,
1355 // Ignore `for<'a> type: ...` as they can change what
1356 // lifetimes mean (although we could "just" handle it).
1357 if !data.bound_generic_params.is_empty() {
1361 let def = match data.bounded_ty.node {
1362 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.def,
1366 if def == Def::TyParam(param_def_id) {
1367 add_bounds(&mut set, &data.bounds);
1372 Set1::Empty => Set1::Empty,
1373 Set1::One(name) => {
1374 if name == hir::LifetimeName::Static {
1375 Set1::One(Region::Static)
1380 .filter_map(|param| match param.kind {
1381 GenericParamKind::Lifetime { .. } => Some((
1383 hir::LifetimeName::Param(param.name),
1384 LifetimeDefOrigin::from_param(param),
1389 .find(|&(_, (_, lt_name, _))| lt_name == name)
1390 .map_or(Set1::Many, |(i, (id, _, origin))| {
1391 let def_id = tcx.hir.local_def_id(id);
1392 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1396 Set1::Many => Set1::Many,
1403 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1404 // FIXME(#37666) this works around a limitation in the region inferencer
1405 fn hack<F>(&mut self, f: F)
1407 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1412 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1414 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1416 let LifetimeContext {
1422 let labels_in_fn = replace(&mut self.labels_in_fn, vec![]);
1423 let xcrate_object_lifetime_defaults =
1424 replace(&mut self.xcrate_object_lifetime_defaults, DefIdMap());
1425 let mut this = LifetimeContext {
1429 trait_ref_hack: self.trait_ref_hack,
1430 is_in_fn_syntax: self.is_in_fn_syntax,
1432 xcrate_object_lifetime_defaults,
1433 lifetime_uses: lifetime_uses,
1435 debug!("entering scope {:?}", this.scope);
1436 f(self.scope, &mut this);
1437 this.check_uses_for_lifetimes_defined_by_scope();
1438 debug!("exiting scope {:?}", this.scope);
1439 self.labels_in_fn = this.labels_in_fn;
1440 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1443 /// helper method to determine the span to remove when suggesting the
1444 /// deletion of a lifetime
1445 fn lifetime_deletion_span(&self, name: ast::Ident, generics: &hir::Generics) -> Option<Span> {
1446 if generics.params.len() == 1 {
1447 // if sole lifetime, remove the `<>` brackets
1450 generics.params.iter().enumerate().find_map(|(i, param)| {
1451 if param.name.ident() == name {
1452 // We also want to delete a leading or trailing comma
1454 if i >= generics.params.len() - 1 {
1455 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1457 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1466 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1467 let defined_by = match self.scope {
1468 Scope::Binder { lifetimes, .. } => lifetimes,
1470 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1475 let mut def_ids: Vec<_> = defined_by
1477 .flat_map(|region| match region {
1478 Region::EarlyBound(_, def_id, _)
1479 | Region::LateBound(_, def_id, _)
1480 | Region::Free(_, def_id) => Some(*def_id),
1482 Region::LateBoundAnon(..) | Region::Static => None,
1486 // ensure that we issue lints in a repeatable order
1487 def_ids.sort_by_key(|&def_id| self.tcx.def_path_hash(def_id));
1489 for def_id in def_ids {
1491 "check_uses_for_lifetimes_defined_by_scope: def_id = {:?}",
1495 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1498 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1502 match lifetimeuseset {
1503 Some(LifetimeUseSet::One(lifetime)) => {
1504 let node_id = self.tcx.hir.as_local_node_id(def_id).unwrap();
1505 debug!("node id first={:?}", node_id);
1506 if let Some((id, span, name)) = match self.tcx.hir.get(node_id) {
1507 Node::Lifetime(hir_lifetime) => Some((
1510 hir_lifetime.name.ident(),
1512 Node::GenericParam(param) => {
1513 Some((param.id, param.span, param.name.ident()))
1517 debug!("id = {:?} span = {:?} name = {:?}", node_id, span, name);
1518 let mut err = self.tcx.struct_span_lint_node(
1519 lint::builtin::SINGLE_USE_LIFETIMES,
1522 &format!("lifetime parameter `{}` only used once", name),
1524 err.span_label(span, "this lifetime...");
1525 err.span_label(lifetime.span, "...is used only here");
1529 Some(LifetimeUseSet::Many) => {
1530 debug!("Not one use lifetime");
1533 let node_id = self.tcx.hir.as_local_node_id(def_id).unwrap();
1534 if let Some((id, span, name)) = match self.tcx.hir.get(node_id) {
1535 Node::Lifetime(hir_lifetime) => Some((
1538 hir_lifetime.name.ident(),
1540 Node::GenericParam(param) => {
1541 Some((param.id, param.span, param.name.ident()))
1545 debug!("id ={:?} span = {:?} name = {:?}", node_id, span, name);
1546 let mut err = self.tcx.struct_span_lint_node(
1547 lint::builtin::UNUSED_LIFETIMES,
1550 &format!("lifetime parameter `{}` never used", name),
1552 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1553 if let Some(generics) = self.tcx.hir.get_generics(parent_def_id) {
1554 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1555 if let Some(span) = unused_lt_span {
1556 err.span_suggestion_with_applicability(
1560 Applicability::MachineApplicable,
1572 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1574 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1575 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1576 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1580 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1582 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1583 /// lifetimes may be interspersed together.
1585 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1586 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1587 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1588 /// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
1589 /// ordering is not important there.
1590 fn visit_early_late<F>(
1592 parent_id: Option<ast::NodeId>,
1593 decl: &'tcx hir::FnDecl,
1594 generics: &'tcx hir::Generics,
1597 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1599 insert_late_bound_lifetimes(self.map, decl, generics);
1601 // Find the start of nested early scopes, e.g. in methods.
1603 if let Some(parent_id) = parent_id {
1604 let parent = self.tcx.hir.expect_item(parent_id);
1605 if let hir::ItemKind::Trait(..) = parent.node {
1606 index += 1; // Self comes first.
1609 hir::ItemKind::Trait(_, _, ref generics, ..)
1610 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
1611 index += generics.params.len() as u32;
1617 let mut type_count = 0;
1618 let lifetimes = generics
1621 .filter_map(|param| match param.kind {
1622 GenericParamKind::Lifetime { .. } => {
1623 if self.map.late_bound.contains(¶m.id) {
1624 Some(Region::late(&self.tcx.hir, param))
1626 Some(Region::early(&self.tcx.hir, &mut index, param))
1629 GenericParamKind::Type { .. } => {
1635 let next_early_index = index + type_count;
1637 let scope = Scope::Binder {
1641 abstract_type_parent: true,
1642 track_lifetime_uses: false,
1644 self.with(scope, move |old_scope, this| {
1645 this.check_lifetime_params(old_scope, &generics.params);
1646 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1650 fn next_early_index_helper(&self, only_abstract_type_parent: bool) -> u32 {
1651 let mut scope = self.scope;
1654 Scope::Root => return 0,
1658 abstract_type_parent,
1660 } if (!only_abstract_type_parent || abstract_type_parent) =>
1662 return next_early_index
1665 Scope::Binder { s, .. }
1666 | Scope::Body { s, .. }
1667 | Scope::Elision { s, .. }
1668 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1673 /// Returns the next index one would use for an early-bound-region
1674 /// if extending the current scope.
1675 fn next_early_index(&self) -> u32 {
1676 self.next_early_index_helper(true)
1679 /// Returns the next index one would use for an `impl Trait` that
1680 /// is being converted into an `abstract type`. This will be the
1681 /// next early index from the enclosing item, for the most
1682 /// part. See the `abstract_type_parent` field for more info.
1683 fn next_early_index_for_abstract_type(&self) -> u32 {
1684 self.next_early_index_helper(false)
1687 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1688 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1690 // If we've already reported an error, just ignore `lifetime_ref`.
1691 if let LifetimeName::Error = lifetime_ref.name {
1695 // Walk up the scope chain, tracking the number of fn scopes
1696 // that we pass through, until we find a lifetime with the
1697 // given name or we run out of scopes.
1699 let mut late_depth = 0;
1700 let mut scope = self.scope;
1701 let mut outermost_body = None;
1704 Scope::Body { id, s } => {
1705 outermost_body = Some(id);
1714 ref lifetimes, s, ..
1716 match lifetime_ref.name {
1717 LifetimeName::Param(param_name) => {
1718 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1719 break Some(def.shifted(late_depth));
1722 _ => bug!("expected LifetimeName::Param"),
1729 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1735 if let Some(mut def) = result {
1736 if let Region::EarlyBound(..) = def {
1737 // Do not free early-bound regions, only late-bound ones.
1738 } else if let Some(body_id) = outermost_body {
1739 let fn_id = self.tcx.hir.body_owner(body_id);
1740 match self.tcx.hir.get(fn_id) {
1741 Node::Item(&hir::Item {
1742 node: hir::ItemKind::Fn(..),
1745 | Node::TraitItem(&hir::TraitItem {
1746 node: hir::TraitItemKind::Method(..),
1749 | Node::ImplItem(&hir::ImplItem {
1750 node: hir::ImplItemKind::Method(..),
1753 let scope = self.tcx.hir.local_def_id(fn_id);
1754 def = Region::Free(scope, def.id().unwrap());
1760 // Check for fn-syntax conflicts with in-band lifetime definitions
1761 if self.is_in_fn_syntax {
1763 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1764 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1769 "lifetimes used in `fn` or `Fn` syntax must be \
1770 explicitly declared using `<...>` binders"
1771 ).span_label(lifetime_ref.span, "in-band lifetime definition")
1776 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1777 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1778 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1779 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1780 | Region::LateBoundAnon(..)
1781 | Region::Free(..) => {}
1785 self.insert_lifetime(lifetime_ref, def);
1791 "use of undeclared lifetime name `{}`",
1793 ).span_label(lifetime_ref.span, "undeclared lifetime")
1798 fn visit_segment_args(&mut self, def: Def, depth: usize, generic_args: &'tcx hir::GenericArgs) {
1799 if generic_args.parenthesized {
1800 let was_in_fn_syntax = self.is_in_fn_syntax;
1801 self.is_in_fn_syntax = true;
1802 self.visit_fn_like_elision(generic_args.inputs(), Some(&generic_args.bindings[0].ty));
1803 self.is_in_fn_syntax = was_in_fn_syntax;
1807 let mut elide_lifetimes = true;
1808 let lifetimes = generic_args
1811 .filter_map(|arg| match arg {
1812 hir::GenericArg::Lifetime(lt) => {
1813 if !lt.is_elided() {
1814 elide_lifetimes = false;
1821 if elide_lifetimes {
1822 self.resolve_elided_lifetimes(lifetimes);
1824 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1827 // Figure out if this is a type/trait segment,
1828 // which requires object lifetime defaults.
1829 let parent_def_id = |this: &mut Self, def_id: DefId| {
1830 let def_key = this.tcx.def_key(def_id);
1832 krate: def_id.krate,
1833 index: def_key.parent.expect("missing parent"),
1836 let type_def_id = match def {
1837 Def::AssociatedTy(def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1838 Def::Variant(def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1840 | Def::Union(def_id)
1842 | Def::TyAlias(def_id)
1843 | Def::Trait(def_id) if depth == 0 =>
1850 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1852 let mut scope = self.scope;
1855 Scope::Root => break false,
1857 Scope::Body { .. } => break true,
1859 Scope::Binder { s, .. }
1860 | Scope::Elision { s, .. }
1861 | Scope::ObjectLifetimeDefault { s, .. } => {
1868 let map = &self.map;
1869 let unsubst = if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
1870 &map.object_lifetime_defaults[&id]
1873 self.xcrate_object_lifetime_defaults
1875 .or_insert_with(|| {
1876 tcx.generics_of(def_id)
1879 .filter_map(|param| match param.kind {
1880 GenericParamDefKind::Type {
1881 object_lifetime_default,
1883 } => Some(object_lifetime_default),
1884 GenericParamDefKind::Lifetime => None,
1891 .map(|set| match *set {
1892 Set1::Empty => if in_body {
1895 Some(Region::Static)
1898 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
1899 GenericArg::Lifetime(lt) => Some(lt),
1902 r.subst(lifetimes, map)
1910 for arg in &generic_args.args {
1912 GenericArg::Lifetime(_) => {}
1913 GenericArg::Type(ty) => {
1914 if let Some(<) = object_lifetime_defaults.get(i) {
1915 let scope = Scope::ObjectLifetimeDefault {
1919 self.with(scope, |_, this| this.visit_ty(ty));
1928 for b in &generic_args.bindings {
1929 self.visit_assoc_type_binding(b);
1933 fn visit_fn_like_elision(&mut self, inputs: &'tcx [hir::Ty], output: Option<&'tcx P<hir::Ty>>) {
1934 debug!("visit_fn_like_elision: enter");
1935 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
1936 let arg_scope = Scope::Elision {
1937 elide: arg_elide.clone(),
1940 self.with(arg_scope, |_, this| {
1941 for input in inputs {
1942 this.visit_ty(input);
1945 Scope::Elision { ref elide, .. } => {
1946 arg_elide = elide.clone();
1952 let output = match output {
1957 debug!("visit_fn_like_elision: determine output");
1959 // Figure out if there's a body we can get argument names from,
1960 // and whether there's a `self` argument (treated specially).
1961 let mut assoc_item_kind = None;
1962 let mut impl_self = None;
1963 let parent = self.tcx.hir.get_parent_node(output.id);
1964 let body = match self.tcx.hir.get(parent) {
1965 // `fn` definitions and methods.
1966 Node::Item(&hir::Item {
1967 node: hir::ItemKind::Fn(.., body),
1971 Node::TraitItem(&hir::TraitItem {
1972 node: hir::TraitItemKind::Method(_, ref m),
1975 if let hir::ItemKind::Trait(.., ref trait_items) = self.tcx
1977 .expect_item(self.tcx.hir.get_parent(parent))
1980 assoc_item_kind = trait_items
1982 .find(|ti| ti.id.node_id == parent)
1986 hir::TraitMethod::Required(_) => None,
1987 hir::TraitMethod::Provided(body) => Some(body),
1991 Node::ImplItem(&hir::ImplItem {
1992 node: hir::ImplItemKind::Method(_, body),
1995 if let hir::ItemKind::Impl(.., ref self_ty, ref impl_items) = self.tcx
1997 .expect_item(self.tcx.hir.get_parent(parent))
2000 impl_self = Some(self_ty);
2001 assoc_item_kind = impl_items
2003 .find(|ii| ii.id.node_id == parent)
2009 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2010 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2011 // Everything else (only closures?) doesn't
2012 // actually enjoy elision in return types.
2014 self.visit_ty(output);
2019 let has_self = match assoc_item_kind {
2020 Some(hir::AssociatedItemKind::Method { has_self }) => has_self,
2024 // In accordance with the rules for lifetime elision, we can determine
2025 // what region to use for elision in the output type in two ways.
2026 // First (determined here), if `self` is by-reference, then the
2027 // implied output region is the region of the self parameter.
2029 // Look for `self: &'a Self` - also desugared from `&'a self`,
2030 // and if that matches, use it for elision and return early.
2031 let is_self_ty = |def: Def| {
2032 if let Def::SelfTy(..) = def {
2036 // Can't always rely on literal (or implied) `Self` due
2037 // to the way elision rules were originally specified.
2038 let impl_self = impl_self.map(|ty| &ty.node);
2039 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) = impl_self {
2041 // Whitelist the types that unambiguously always
2042 // result in the same type constructor being used
2043 // (it can't differ between `Self` and `self`).
2044 Def::Struct(_) | Def::Union(_) | Def::Enum(_) | Def::PrimTy(_) => {
2045 return def == path.def
2054 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = inputs[0].node {
2055 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.node {
2056 if is_self_ty(path.def) {
2057 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
2058 let scope = Scope::Elision {
2059 elide: Elide::Exact(lifetime),
2062 self.with(scope, |_, this| this.visit_ty(output));
2070 // Second, if there was exactly one lifetime (either a substitution or a
2071 // reference) in the arguments, then any anonymous regions in the output
2072 // have that lifetime.
2073 let mut possible_implied_output_region = None;
2074 let mut lifetime_count = 0;
2075 let arg_lifetimes = inputs
2078 .skip(has_self as usize)
2080 let mut gather = GatherLifetimes {
2082 outer_index: ty::INNERMOST,
2083 have_bound_regions: false,
2084 lifetimes: Default::default(),
2086 gather.visit_ty(input);
2088 lifetime_count += gather.lifetimes.len();
2090 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2091 // there's a chance that the unique lifetime of this
2092 // iteration will be the appropriate lifetime for output
2093 // parameters, so lets store it.
2094 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2097 ElisionFailureInfo {
2100 lifetime_count: gather.lifetimes.len(),
2101 have_bound_regions: gather.have_bound_regions,
2106 let elide = if lifetime_count == 1 {
2107 Elide::Exact(possible_implied_output_region.unwrap())
2109 Elide::Error(arg_lifetimes)
2112 debug!("visit_fn_like_elision: elide={:?}", elide);
2114 let scope = Scope::Elision {
2118 self.with(scope, |_, this| this.visit_ty(output));
2119 debug!("visit_fn_like_elision: exit");
2121 struct GatherLifetimes<'a> {
2122 map: &'a NamedRegionMap,
2123 outer_index: ty::DebruijnIndex,
2124 have_bound_regions: bool,
2125 lifetimes: FxHashSet<Region>,
2128 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2129 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2130 NestedVisitorMap::None
2133 fn visit_ty(&mut self, ty: &hir::Ty) {
2134 if let hir::TyKind::BareFn(_) = ty.node {
2135 self.outer_index.shift_in(1);
2137 if let hir::TyKind::TraitObject(ref bounds, ref lifetime) = ty.node {
2138 for bound in bounds {
2139 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2142 // Stay on the safe side and don't include the object
2143 // lifetime default (which may not end up being used).
2144 if !lifetime.is_elided() {
2145 self.visit_lifetime(lifetime);
2148 intravisit::walk_ty(self, ty);
2150 if let hir::TyKind::BareFn(_) = ty.node {
2151 self.outer_index.shift_out(1);
2155 fn visit_generic_param(&mut self, param: &hir::GenericParam) {
2156 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2157 // FIXME(eddyb) Do we want this? It only makes a difference
2158 // if this `for<'a>` lifetime parameter is never used.
2159 self.have_bound_regions = true;
2162 intravisit::walk_generic_param(self, param);
2165 fn visit_poly_trait_ref(
2167 trait_ref: &hir::PolyTraitRef,
2168 modifier: hir::TraitBoundModifier,
2170 self.outer_index.shift_in(1);
2171 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2172 self.outer_index.shift_out(1);
2175 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2176 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
2178 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2179 if debruijn < self.outer_index =>
2181 self.have_bound_regions = true;
2185 .insert(lifetime.shifted_out_to_binder(self.outer_index));
2193 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2194 if lifetime_refs.is_empty() {
2198 let span = lifetime_refs[0].span;
2199 let mut late_depth = 0;
2200 let mut scope = self.scope;
2203 // Do not assign any resolution, it will be inferred.
2204 Scope::Body { .. } => return,
2206 Scope::Root => break None,
2208 Scope::Binder { s, .. } => {
2213 Scope::Elision { ref elide, .. } => {
2214 let lifetime = match *elide {
2215 Elide::FreshLateAnon(ref counter) => {
2216 for lifetime_ref in lifetime_refs {
2217 let lifetime = Region::late_anon(counter).shifted(late_depth);
2218 self.insert_lifetime(lifetime_ref, lifetime);
2222 Elide::Exact(l) => l.shifted(late_depth),
2223 Elide::Error(ref e) => break Some(e),
2225 for lifetime_ref in lifetime_refs {
2226 self.insert_lifetime(lifetime_ref, lifetime);
2231 Scope::ObjectLifetimeDefault { s, .. } => {
2237 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2239 if let Some(params) = error {
2240 if lifetime_refs.len() == 1 {
2241 self.report_elision_failure(&mut err, params);
2248 fn report_elision_failure(
2250 db: &mut DiagnosticBuilder<'_>,
2251 params: &[ElisionFailureInfo],
2253 let mut m = String::new();
2254 let len = params.len();
2256 let elided_params: Vec<_> = params
2259 .filter(|info| info.lifetime_count > 0)
2262 let elided_len = elided_params.len();
2264 for (i, info) in elided_params.into_iter().enumerate() {
2265 let ElisionFailureInfo {
2272 let help_name = if let Some(body) = parent {
2273 let arg = &self.tcx.hir.body(body).arguments[index];
2274 format!("`{}`", self.tcx.hir.node_to_pretty_string(arg.pat.id))
2276 format!("argument {}", index + 1)
2284 "one of {}'s {} {}lifetimes",
2287 if have_bound_regions { "free " } else { "" }
2292 if elided_len == 2 && i == 0 {
2294 } else if i + 2 == elided_len {
2295 m.push_str(", or ");
2296 } else if i != elided_len - 1 {
2304 "this function's return type contains a borrowed value, but \
2305 there is no value for it to be borrowed from"
2307 help!(db, "consider giving it a 'static lifetime");
2308 } else if elided_len == 0 {
2311 "this function's return type contains a borrowed value with \
2312 an elided lifetime, but the lifetime cannot be derived from \
2317 "consider giving it an explicit bounded or 'static \
2320 } else if elided_len == 1 {
2323 "this function's return type contains a borrowed value, but \
2324 the signature does not say which {} it is borrowed from",
2330 "this function's return type contains a borrowed value, but \
2331 the signature does not say whether it is borrowed from {}",
2337 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2338 let mut late_depth = 0;
2339 let mut scope = self.scope;
2340 let lifetime = loop {
2342 Scope::Binder { s, .. } => {
2347 Scope::Root | Scope::Elision { .. } => break Region::Static,
2349 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2351 Scope::ObjectLifetimeDefault {
2352 lifetime: Some(l), ..
2356 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2359 fn check_lifetime_params(
2361 old_scope: ScopeRef<'_>,
2362 params: &'tcx [hir::GenericParam],
2364 let lifetimes: Vec<_> = params
2366 .filter_map(|param| match param.kind {
2367 GenericParamKind::Lifetime { .. } => Some((param, param.name)),
2371 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2372 if let hir::ParamName::Plain(_) = lifetime_i_name {
2373 let name = lifetime_i_name.ident().name;
2374 if name == keywords::UnderscoreLifetime.name()
2375 || name == keywords::StaticLifetime.name()
2377 let mut err = struct_span_err!(
2381 "invalid lifetime parameter name: `{}`",
2382 lifetime_i.name.ident(),
2386 format!("{} is a reserved lifetime name", name),
2392 // It is a hard error to shadow a lifetime within the same scope.
2393 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2394 if lifetime_i_name == lifetime_j_name {
2399 "lifetime name `{}` declared twice in the same scope",
2400 lifetime_j.name.ident()
2401 ).span_label(lifetime_j.span, "declared twice")
2402 .span_label(lifetime_i.span, "previous declaration here")
2407 // It is a soft error to shadow a lifetime within a parent scope.
2408 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2410 for bound in &lifetime_i.bounds {
2412 hir::GenericBound::Outlives(lt) => match lt.name {
2413 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2415 "use of `'_` in illegal place, but not caught by lowering",
2417 hir::LifetimeName::Static => {
2418 self.insert_lifetime(lt, Region::Static);
2422 lifetime_i.span.to(lt.span),
2424 "unnecessary lifetime parameter `{}`",
2425 lifetime_i.name.ident(),
2429 "you can use the `'static` lifetime directly, in place of `{}`",
2430 lifetime_i.name.ident(),
2434 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2435 self.resolve_lifetime_ref(lt);
2437 hir::LifetimeName::Error => {
2438 // No need to do anything, error already reported.
2447 fn check_lifetime_param_for_shadowing(
2449 mut old_scope: ScopeRef<'_>,
2450 param: &'tcx hir::GenericParam,
2452 for label in &self.labels_in_fn {
2453 // FIXME (#24278): non-hygienic comparison
2454 if param.name.ident().name == label.name {
2455 signal_shadowing_problem(
2458 original_label(label.span),
2459 shadower_lifetime(¶m),
2467 Scope::Body { s, .. }
2468 | Scope::Elision { s, .. }
2469 | Scope::ObjectLifetimeDefault { s, .. } => {
2478 ref lifetimes, s, ..
2480 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2481 let node_id = self.tcx.hir.as_local_node_id(def.id().unwrap()).unwrap();
2483 signal_shadowing_problem(
2485 param.name.ident().name,
2486 original_lifetime(self.tcx.hir.span(node_id)),
2487 shadower_lifetime(¶m),
2498 /// Returns true if, in the current scope, replacing `'_` would be
2499 /// equivalent to a single-use lifetime.
2500 fn track_lifetime_uses(&self) -> bool {
2501 let mut scope = self.scope;
2504 Scope::Root => break false,
2506 // Inside of items, it depends on the kind of item.
2508 track_lifetime_uses,
2510 } => break track_lifetime_uses,
2512 // Inside a body, `'_` will use an inference variable,
2514 Scope::Body { .. } => break true,
2516 // A lifetime only used in a fn argument could as well
2517 // be replaced with `'_`, as that would generate a
2520 elide: Elide::FreshLateAnon(_),
2524 // In the return type or other such place, `'_` is not
2525 // going to make a fresh name, so we cannot
2526 // necessarily replace a single-use lifetime with
2529 elide: Elide::Exact(_),
2533 elide: Elide::Error(_),
2537 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2542 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2543 if lifetime_ref.id == ast::DUMMY_NODE_ID {
2546 "lifetime reference not renumbered, \
2547 probably a bug in syntax::fold"
2552 "insert_lifetime: {} resolved to {:?} span={:?}",
2553 self.tcx.hir.node_to_string(lifetime_ref.id),
2555 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2557 self.map.defs.insert(lifetime_ref.id, def);
2560 Region::LateBoundAnon(..) | Region::Static => {
2561 // These are anonymous lifetimes or lifetimes that are not declared.
2564 Region::Free(_, def_id)
2565 | Region::LateBound(_, def_id, _)
2566 | Region::EarlyBound(_, def_id, _) => {
2567 // A lifetime declared by the user.
2568 let track_lifetime_uses = self.track_lifetime_uses();
2570 "insert_lifetime: track_lifetime_uses={}",
2573 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2574 debug!("insert_lifetime: first use of {:?}", def_id);
2576 .insert(def_id, LifetimeUseSet::One(lifetime_ref));
2578 debug!("insert_lifetime: many uses of {:?}", def_id);
2579 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2585 /// Sometimes we resolve a lifetime, but later find that it is an
2586 /// error (esp. around impl trait). In that case, we remove the
2587 /// entry into `map.defs` so as not to confuse later code.
2588 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2589 let old_value = self.map.defs.remove(&lifetime_ref.id);
2590 assert_eq!(old_value, Some(bad_def));
2594 /// Detects late-bound lifetimes and inserts them into
2595 /// `map.late_bound`.
2597 /// A region declared on a fn is **late-bound** if:
2598 /// - it is constrained by an argument type;
2599 /// - it does not appear in a where-clause.
2601 /// "Constrained" basically means that it appears in any type but
2602 /// not amongst the inputs to a projection. In other words, `<&'a
2603 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2604 fn insert_late_bound_lifetimes(
2605 map: &mut NamedRegionMap,
2607 generics: &hir::Generics,
2610 "insert_late_bound_lifetimes(decl={:?}, generics={:?})",
2614 let mut constrained_by_input = ConstrainedCollector::default();
2615 for arg_ty in &decl.inputs {
2616 constrained_by_input.visit_ty(arg_ty);
2619 let mut appears_in_output = AllCollector {
2620 regions: Default::default(),
2622 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2625 "insert_late_bound_lifetimes: constrained_by_input={:?}",
2626 constrained_by_input.regions
2629 // Walk the lifetimes that appear in where clauses.
2631 // Subtle point: because we disallow nested bindings, we can just
2632 // ignore binders here and scrape up all names we see.
2633 let mut appears_in_where_clause = AllCollector {
2634 regions: Default::default(),
2636 appears_in_where_clause.visit_generics(generics);
2638 for param in &generics.params {
2639 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2640 if !param.bounds.is_empty() {
2641 // `'a: 'b` means both `'a` and `'b` are referenced
2642 appears_in_where_clause
2644 .insert(hir::LifetimeName::Param(param.name.modern()));
2650 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2651 appears_in_where_clause.regions
2654 // Late bound regions are those that:
2655 // - appear in the inputs
2656 // - do not appear in the where-clauses
2657 // - are not implicitly captured by `impl Trait`
2658 for param in &generics.params {
2660 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2662 // Types are not late-bound.
2663 hir::GenericParamKind::Type { .. } => continue,
2666 let lt_name = hir::LifetimeName::Param(param.name.modern());
2667 // appears in the where clauses? early-bound.
2668 if appears_in_where_clause.regions.contains(<_name) {
2672 // does not appear in the inputs, but appears in the return type? early-bound.
2673 if !constrained_by_input.regions.contains(<_name)
2674 && appears_in_output.regions.contains(<_name)
2680 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2685 let inserted = map.late_bound.insert(param.id);
2686 assert!(inserted, "visited lifetime {:?} twice", param.id);
2692 struct ConstrainedCollector {
2693 regions: FxHashSet<hir::LifetimeName>,
2696 impl<'v> Visitor<'v> for ConstrainedCollector {
2697 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2698 NestedVisitorMap::None
2701 fn visit_ty(&mut self, ty: &'v hir::Ty) {
2703 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2704 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2705 // ignore lifetimes appearing in associated type
2706 // projections, as they are not *constrained*
2710 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2711 // consider only the lifetimes on the final
2712 // segment; I am not sure it's even currently
2713 // valid to have them elsewhere, but even if it
2714 // is, those would be potentially inputs to
2716 if let Some(last_segment) = path.segments.last() {
2717 self.visit_path_segment(path.span, last_segment);
2722 intravisit::walk_ty(self, ty);
2727 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2728 self.regions.insert(lifetime_ref.name.modern());
2732 struct AllCollector {
2733 regions: FxHashSet<hir::LifetimeName>,
2736 impl<'v> Visitor<'v> for AllCollector {
2737 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2738 NestedVisitorMap::None
2741 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2742 self.regions.insert(lifetime_ref.name.modern());
2747 pub fn report_missing_lifetime_specifiers(
2751 ) -> DiagnosticBuilder<'_> {
2752 let mut err = struct_span_err!(
2756 "missing lifetime specifier{}",
2757 if count > 1 { "s" } else { "" }
2760 let msg: Cow<'static, str> = if count > 1 {
2761 format!("expected {} lifetime parameters", count).into()
2763 "expected lifetime parameter".into()
2766 err.span_label(span, msg);