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 {
428 defs: Default::default(),
429 late_bound: Default::default(),
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: Default::default(),
441 lifetime_uses: &mut Default::default(),
443 for (_, item) in &krate.items {
444 visitor.visit_item(item);
450 /// In traits, there is an implicit `Self` type parameter which comes before the generics.
451 /// We have to account for this when computing the index of the other generic parameters.
452 /// This function returns whether there is such an implicit parameter defined on the given item.
453 fn sub_items_have_self_param(node: &hir::ItemKind) -> bool {
455 hir::ItemKind::Trait(..) |
456 hir::ItemKind::TraitAlias(..) => true,
461 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
462 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
463 NestedVisitorMap::All(&self.tcx.hir)
466 // We want to nest trait/impl items in their parent, but nothing else.
467 fn visit_nested_item(&mut self, _: hir::ItemId) {}
469 fn visit_nested_body(&mut self, body: hir::BodyId) {
470 // Each body has their own set of labels, save labels.
471 let saved = replace(&mut self.labels_in_fn, vec![]);
472 let body = self.tcx.hir.body(body);
473 extract_labels(self, body);
480 this.visit_body(body);
483 replace(&mut self.labels_in_fn, saved);
486 fn visit_item(&mut self, item: &'tcx hir::Item) {
488 hir::ItemKind::Fn(ref decl, _, ref generics, _) => {
489 self.visit_early_late(None, decl, generics, |this| {
490 intravisit::walk_item(this, item);
494 hir::ItemKind::ExternCrate(_)
495 | hir::ItemKind::Use(..)
496 | hir::ItemKind::Mod(..)
497 | hir::ItemKind::ForeignMod(..)
498 | hir::ItemKind::GlobalAsm(..) => {
499 // These sorts of items have no lifetime parameters at all.
500 intravisit::walk_item(self, item);
502 hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
503 // No lifetime parameters, but implied 'static.
504 let scope = Scope::Elision {
505 elide: Elide::Exact(Region::Static),
508 self.with(scope, |_, this| intravisit::walk_item(this, item));
510 hir::ItemKind::Existential(hir::ExistTy {
511 impl_trait_fn: Some(_),
514 // currently existential type declarations are just generated from impl Trait
515 // items. doing anything on this node is irrelevant, as we currently don't need
518 hir::ItemKind::Ty(_, ref generics)
519 | hir::ItemKind::Existential(hir::ExistTy {
524 | hir::ItemKind::Enum(_, ref generics)
525 | hir::ItemKind::Struct(_, ref generics)
526 | hir::ItemKind::Union(_, ref generics)
527 | hir::ItemKind::Trait(_, _, ref generics, ..)
528 | hir::ItemKind::TraitAlias(ref generics, ..)
529 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
530 // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
531 // This is not true for other kinds of items.x
532 let track_lifetime_uses = match item.node {
533 hir::ItemKind::Impl(..) => true,
536 // These kinds of items have only early-bound lifetime parameters.
537 let mut index = if sub_items_have_self_param(&item.node) {
538 1 // Self comes before lifetimes
542 let mut type_count = 0;
543 let lifetimes = generics
546 .filter_map(|param| match param.kind {
547 GenericParamKind::Lifetime { .. } => {
548 Some(Region::early(&self.tcx.hir, &mut index, param))
550 GenericParamKind::Type { .. } => {
556 let scope = Scope::Binder {
558 next_early_index: index + type_count,
559 abstract_type_parent: true,
563 self.with(scope, |old_scope, this| {
564 this.check_lifetime_params(old_scope, &generics.params);
565 intravisit::walk_item(this, item);
571 fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem) {
573 hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
574 self.visit_early_late(None, decl, generics, |this| {
575 intravisit::walk_foreign_item(this, item);
578 hir::ForeignItemKind::Static(..) => {
579 intravisit::walk_foreign_item(self, item);
581 hir::ForeignItemKind::Type => {
582 intravisit::walk_foreign_item(self, item);
587 fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
588 debug!("visit_ty: id={:?} ty={:?}", ty.id, ty);
590 hir::TyKind::BareFn(ref c) => {
591 let next_early_index = self.next_early_index();
592 let was_in_fn_syntax = self.is_in_fn_syntax;
593 self.is_in_fn_syntax = true;
594 let scope = Scope::Binder {
595 lifetimes: c.generic_params
597 .filter_map(|param| match param.kind {
598 GenericParamKind::Lifetime { .. } => {
599 Some(Region::late(&self.tcx.hir, param))
606 track_lifetime_uses: true,
607 abstract_type_parent: false,
609 self.with(scope, |old_scope, this| {
610 // a bare fn has no bounds, so everything
611 // contained within is scoped within its binder.
612 this.check_lifetime_params(old_scope, &c.generic_params);
613 intravisit::walk_ty(this, ty);
615 self.is_in_fn_syntax = was_in_fn_syntax;
617 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
618 for bound in bounds {
619 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
621 match lifetime.name {
622 LifetimeName::Implicit => {
623 // If the user does not write *anything*, we
624 // use the object lifetime defaulting
625 // rules. So e.g. `Box<dyn Debug>` becomes
626 // `Box<dyn Debug + 'static>`.
627 self.resolve_object_lifetime_default(lifetime)
629 LifetimeName::Underscore => {
630 // If the user writes `'_`, we use the *ordinary* elision
631 // rules. So the `'_` in e.g. `Box<dyn Debug + '_>` will be
632 // resolved the same as the `'_` in `&'_ Foo`.
635 self.resolve_elided_lifetimes(vec![lifetime])
637 LifetimeName::Param(_) | LifetimeName::Static => {
638 // If the user wrote an explicit name, use that.
639 self.visit_lifetime(lifetime);
641 LifetimeName::Error => {}
644 hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
645 self.visit_lifetime(lifetime_ref);
646 let scope = Scope::ObjectLifetimeDefault {
647 lifetime: self.map.defs.get(&lifetime_ref.id).cloned(),
650 self.with(scope, |_, this| this.visit_ty(&mt.ty));
652 hir::TyKind::Def(item_id, ref lifetimes) => {
653 // Resolve the lifetimes in the bounds to the lifetime defs in the generics.
654 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
655 // `abstract type MyAnonTy<'b>: MyTrait<'b>;`
656 // ^ ^ this gets resolved in the scope of
657 // the exist_ty generics
658 let (generics, bounds) = match self.tcx.hir.expect_item(item_id.id).node {
659 // named existential types are reached via TyKind::Path
660 // this arm is for `impl Trait` in the types of statics, constants and locals
661 hir::ItemKind::Existential(hir::ExistTy {
665 intravisit::walk_ty(self, ty);
668 // RPIT (return position impl trait)
669 hir::ItemKind::Existential(hir::ExistTy {
673 }) => (generics, bounds),
674 ref i => bug!("impl Trait pointed to non-existential type?? {:#?}", i),
677 // Resolve the lifetimes that are applied to the existential type.
678 // These are resolved in the current scope.
679 // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
680 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
681 // ^ ^this gets resolved in the current scope
682 for lifetime in lifetimes {
683 if let hir::GenericArg::Lifetime(lifetime) = lifetime {
684 self.visit_lifetime(lifetime);
686 // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
687 // and ban them. Type variables instantiated inside binders aren't
688 // well-supported at the moment, so this doesn't work.
689 // In the future, this should be fixed and this error should be removed.
690 let def = self.map.defs.get(&lifetime.id).cloned();
691 if let Some(Region::LateBound(_, def_id, _)) = def {
692 if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
693 // Ensure that the parent of the def is an item, not HRTB
694 let parent_id = self.tcx.hir.get_parent_node(node_id);
695 let parent_impl_id = hir::ImplItemId { node_id: parent_id };
696 let parent_trait_id = hir::TraitItemId { node_id: parent_id };
697 let krate = self.tcx.hir.forest.krate();
698 if !(krate.items.contains_key(&parent_id)
699 || krate.impl_items.contains_key(&parent_impl_id)
700 || krate.trait_items.contains_key(&parent_trait_id))
706 "`impl Trait` can only capture lifetimes \
707 bound at the fn or impl level"
709 self.uninsert_lifetime_on_error(lifetime, def.unwrap());
716 // We want to start our early-bound indices at the end of the parent scope,
717 // not including any parent `impl Trait`s.
718 let mut index = self.next_early_index_for_abstract_type();
719 debug!("visit_ty: index = {}", index);
721 let mut elision = None;
722 let mut lifetimes = FxHashMap::default();
723 let mut type_count = 0;
724 for param in &generics.params {
726 GenericParamKind::Lifetime { .. } => {
727 let (name, reg) = Region::early(&self.tcx.hir, &mut index, ¶m);
728 if let hir::ParamName::Plain(param_name) = name {
729 if param_name.name == keywords::UnderscoreLifetime.name() {
730 // Pick the elided lifetime "definition" if one exists
731 // and use it to make an elision scope.
734 lifetimes.insert(name, reg);
737 lifetimes.insert(name, reg);
740 GenericParamKind::Type { .. } => {
745 let next_early_index = index + type_count;
747 if let Some(elision_region) = elision {
748 let scope = Scope::Elision {
749 elide: Elide::Exact(elision_region),
752 self.with(scope, |_old_scope, this| {
753 let scope = Scope::Binder {
757 track_lifetime_uses: true,
758 abstract_type_parent: false,
760 this.with(scope, |_old_scope, this| {
761 this.visit_generics(generics);
762 for bound in bounds {
763 this.visit_param_bound(bound);
768 let scope = Scope::Binder {
772 track_lifetime_uses: true,
773 abstract_type_parent: false,
775 self.with(scope, |_old_scope, this| {
776 this.visit_generics(generics);
777 for bound in bounds {
778 this.visit_param_bound(bound);
783 _ => intravisit::walk_ty(self, ty),
787 fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
788 use self::hir::TraitItemKind::*;
789 match trait_item.node {
790 Method(ref sig, _) => {
792 self.visit_early_late(
793 Some(tcx.hir.get_parent(trait_item.id)),
795 &trait_item.generics,
796 |this| intravisit::walk_trait_item(this, trait_item),
799 Type(ref bounds, ref ty) => {
800 let generics = &trait_item.generics;
801 let mut index = self.next_early_index();
802 debug!("visit_ty: index = {}", index);
803 let mut type_count = 0;
804 let lifetimes = generics
807 .filter_map(|param| match param.kind {
808 GenericParamKind::Lifetime { .. } => {
809 Some(Region::early(&self.tcx.hir, &mut index, param))
811 GenericParamKind::Type { .. } => {
817 let scope = Scope::Binder {
819 next_early_index: index + type_count,
821 track_lifetime_uses: true,
822 abstract_type_parent: true,
824 self.with(scope, |_old_scope, this| {
825 this.visit_generics(generics);
826 for bound in bounds {
827 this.visit_param_bound(bound);
829 if let Some(ty) = ty {
835 // Only methods and types support generics.
836 assert!(trait_item.generics.params.is_empty());
837 intravisit::walk_trait_item(self, trait_item);
842 fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
843 use self::hir::ImplItemKind::*;
844 match impl_item.node {
845 Method(ref sig, _) => {
847 self.visit_early_late(
848 Some(tcx.hir.get_parent(impl_item.id)),
851 |this| intravisit::walk_impl_item(this, impl_item),
855 let generics = &impl_item.generics;
856 let mut index = self.next_early_index();
857 let mut next_early_index = index;
858 debug!("visit_ty: index = {}", index);
859 let lifetimes = generics
862 .filter_map(|param| match param.kind {
863 GenericParamKind::Lifetime { .. } => {
864 Some(Region::early(&self.tcx.hir, &mut index, param))
866 GenericParamKind::Type { .. } => {
867 next_early_index += 1;
872 let scope = Scope::Binder {
876 track_lifetime_uses: true,
877 abstract_type_parent: true,
879 self.with(scope, |_old_scope, this| {
880 this.visit_generics(generics);
884 Existential(ref bounds) => {
885 let generics = &impl_item.generics;
886 let mut index = self.next_early_index();
887 let mut next_early_index = index;
888 debug!("visit_ty: index = {}", index);
889 let lifetimes = generics
892 .filter_map(|param| match param.kind {
893 GenericParamKind::Lifetime { .. } => {
894 Some(Region::early(&self.tcx.hir, &mut index, param))
896 GenericParamKind::Type { .. } => {
897 next_early_index += 1;
903 let scope = Scope::Binder {
907 track_lifetime_uses: true,
908 abstract_type_parent: true,
910 self.with(scope, |_old_scope, this| {
911 this.visit_generics(generics);
912 for bound in bounds {
913 this.visit_param_bound(bound);
918 // Only methods and types support generics.
919 assert!(impl_item.generics.params.is_empty());
920 intravisit::walk_impl_item(self, impl_item);
925 fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
926 if lifetime_ref.is_elided() {
927 self.resolve_elided_lifetimes(vec![lifetime_ref]);
930 if lifetime_ref.is_static() {
931 self.insert_lifetime(lifetime_ref, Region::Static);
934 self.resolve_lifetime_ref(lifetime_ref);
937 fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
938 for (i, segment) in path.segments.iter().enumerate() {
939 let depth = path.segments.len() - i - 1;
940 if let Some(ref args) = segment.args {
941 self.visit_segment_args(path.def, depth, args);
946 fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl) {
947 let output = match fd.output {
948 hir::DefaultReturn(_) => None,
949 hir::Return(ref ty) => Some(ty),
951 self.visit_fn_like_elision(&fd.inputs, output);
954 fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
955 check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
956 for param in &generics.params {
958 GenericParamKind::Lifetime { .. } => {}
959 GenericParamKind::Type { ref default, .. } => {
960 walk_list!(self, visit_param_bound, ¶m.bounds);
961 if let Some(ref ty) = default {
967 for predicate in &generics.where_clause.predicates {
969 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
972 ref bound_generic_params,
975 let lifetimes: FxHashMap<_, _> = bound_generic_params
977 .filter_map(|param| match param.kind {
978 GenericParamKind::Lifetime { .. } => {
979 Some(Region::late(&self.tcx.hir, param))
984 if !lifetimes.is_empty() {
985 self.trait_ref_hack = true;
986 let next_early_index = self.next_early_index();
987 let scope = Scope::Binder {
991 track_lifetime_uses: true,
992 abstract_type_parent: false,
994 let result = self.with(scope, |old_scope, this| {
995 this.check_lifetime_params(old_scope, &bound_generic_params);
996 this.visit_ty(&bounded_ty);
997 walk_list!(this, visit_param_bound, bounds);
999 self.trait_ref_hack = false;
1002 self.visit_ty(&bounded_ty);
1003 walk_list!(self, visit_param_bound, bounds);
1006 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1011 self.visit_lifetime(lifetime);
1012 walk_list!(self, visit_param_bound, bounds);
1014 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1019 self.visit_ty(lhs_ty);
1020 self.visit_ty(rhs_ty);
1026 fn visit_poly_trait_ref(
1028 trait_ref: &'tcx hir::PolyTraitRef,
1029 _modifier: hir::TraitBoundModifier,
1031 debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
1033 if !self.trait_ref_hack || trait_ref.bound_generic_params.iter().any(|param| {
1035 GenericParamKind::Lifetime { .. } => true,
1039 if self.trait_ref_hack {
1044 "nested quantification of lifetimes"
1047 let next_early_index = self.next_early_index();
1048 let scope = Scope::Binder {
1049 lifetimes: trait_ref
1050 .bound_generic_params
1052 .filter_map(|param| match param.kind {
1053 GenericParamKind::Lifetime { .. } => {
1054 Some(Region::late(&self.tcx.hir, param))
1061 track_lifetime_uses: true,
1062 abstract_type_parent: false,
1064 self.with(scope, |old_scope, this| {
1065 this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
1066 walk_list!(this, visit_generic_param, &trait_ref.bound_generic_params);
1067 this.visit_trait_ref(&trait_ref.trait_ref)
1070 self.visit_trait_ref(&trait_ref.trait_ref)
1075 #[derive(Copy, Clone, PartialEq)]
1089 fn original_label(span: Span) -> Original {
1091 kind: ShadowKind::Label,
1095 fn shadower_label(span: Span) -> Shadower {
1097 kind: ShadowKind::Label,
1101 fn original_lifetime(span: Span) -> Original {
1103 kind: ShadowKind::Lifetime,
1107 fn shadower_lifetime(param: &hir::GenericParam) -> Shadower {
1109 kind: ShadowKind::Lifetime,
1115 fn desc(&self) -> &'static str {
1117 ShadowKind::Label => "label",
1118 ShadowKind::Lifetime => "lifetime",
1123 fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_, '_, '_>, params: &P<[hir::GenericParam]>) {
1124 let lifetime_params: Vec<_> = params
1126 .filter_map(|param| match param.kind {
1127 GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
1131 let explicit = lifetime_params
1133 .find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
1134 let in_band = lifetime_params
1136 .find(|(kind, _)| *kind == LifetimeParamKind::InBand);
1138 if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
1143 "cannot mix in-band and explicit lifetime definitions"
1144 ).span_label(*in_band_span, "in-band lifetime definition here")
1145 .span_label(*explicit_span, "explicit lifetime definition here")
1150 fn signal_shadowing_problem(
1151 tcx: TyCtxt<'_, '_, '_>,
1156 let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
1157 // lifetime/lifetime shadowing is an error
1162 "{} name `{}` shadows a \
1163 {} name that is already in scope",
1164 shadower.kind.desc(),
1169 // shadowing involving a label is only a warning, due to issues with
1170 // labels and lifetimes not being macro-hygienic.
1171 tcx.sess.struct_span_warn(
1174 "{} name `{}` shadows a \
1175 {} name that is already in scope",
1176 shadower.kind.desc(),
1182 err.span_label(orig.span, "first declared here");
1183 err.span_label(shadower.span, format!("lifetime {} already in scope", name));
1187 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
1188 // if one of the label shadows a lifetime or another label.
1189 fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body) {
1190 struct GatherLabels<'a, 'tcx: 'a> {
1191 tcx: TyCtxt<'a, 'tcx, 'tcx>,
1192 scope: ScopeRef<'a>,
1193 labels_in_fn: &'a mut Vec<ast::Ident>,
1196 let mut gather = GatherLabels {
1199 labels_in_fn: &mut ctxt.labels_in_fn,
1201 gather.visit_body(body);
1203 impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
1204 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
1205 NestedVisitorMap::None
1208 fn visit_expr(&mut self, ex: &hir::Expr) {
1209 if let Some(label) = expression_label(ex) {
1210 for prior_label in &self.labels_in_fn[..] {
1211 // FIXME (#24278): non-hygienic comparison
1212 if label.name == prior_label.name {
1213 signal_shadowing_problem(
1216 original_label(prior_label.span),
1217 shadower_label(label.span),
1222 check_if_label_shadows_lifetime(self.tcx, self.scope, label);
1224 self.labels_in_fn.push(label);
1226 intravisit::walk_expr(self, ex)
1230 fn expression_label(ex: &hir::Expr) -> Option<ast::Ident> {
1232 hir::ExprKind::While(.., Some(label)) | hir::ExprKind::Loop(_, Some(label), _) => {
1239 fn check_if_label_shadows_lifetime(
1240 tcx: TyCtxt<'_, '_, '_>,
1241 mut scope: ScopeRef<'_>,
1246 Scope::Body { s, .. }
1247 | Scope::Elision { s, .. }
1248 | Scope::ObjectLifetimeDefault { s, .. } => {
1257 ref lifetimes, s, ..
1259 // FIXME (#24278): non-hygienic comparison
1260 if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
1261 let node_id = tcx.hir.as_local_node_id(def.id().unwrap()).unwrap();
1263 signal_shadowing_problem(
1266 original_lifetime(tcx.hir.span(node_id)),
1267 shadower_label(label.span),
1278 fn compute_object_lifetime_defaults(
1279 tcx: TyCtxt<'_, '_, '_>,
1280 ) -> NodeMap<Vec<ObjectLifetimeDefault>> {
1281 let mut map = NodeMap::default();
1282 for item in tcx.hir.krate().items.values() {
1284 hir::ItemKind::Struct(_, ref generics)
1285 | hir::ItemKind::Union(_, ref generics)
1286 | hir::ItemKind::Enum(_, ref generics)
1287 | hir::ItemKind::Existential(hir::ExistTy {
1289 impl_trait_fn: None,
1292 | hir::ItemKind::Ty(_, ref generics)
1293 | hir::ItemKind::Trait(_, _, ref generics, ..) => {
1294 let result = object_lifetime_defaults_for_item(tcx, generics);
1297 if attr::contains_name(&item.attrs, "rustc_object_lifetime_default") {
1298 let object_lifetime_default_reprs: String = result
1300 .map(|set| match *set {
1301 Set1::Empty => "BaseDefault".into(),
1302 Set1::One(Region::Static) => "'static".into(),
1303 Set1::One(Region::EarlyBound(mut i, _, _)) => generics
1306 .find_map(|param| match param.kind {
1307 GenericParamKind::Lifetime { .. } => {
1309 return Some(param.name.ident().to_string().into());
1317 Set1::One(_) => bug!(),
1318 Set1::Many => "Ambiguous".into(),
1320 .collect::<Vec<Cow<'static, str>>>()
1322 tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
1325 map.insert(item.id, result);
1333 /// Scan the bounds and where-clauses on parameters to extract bounds
1334 /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
1335 /// for each type parameter.
1336 fn object_lifetime_defaults_for_item(
1337 tcx: TyCtxt<'_, '_, '_>,
1338 generics: &hir::Generics,
1339 ) -> Vec<ObjectLifetimeDefault> {
1340 fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound]) {
1341 for bound in bounds {
1342 if let hir::GenericBound::Outlives(ref lifetime) = *bound {
1343 set.insert(lifetime.name.modern());
1351 .filter_map(|param| match param.kind {
1352 GenericParamKind::Lifetime { .. } => None,
1353 GenericParamKind::Type { .. } => {
1354 let mut set = Set1::Empty;
1356 add_bounds(&mut set, ¶m.bounds);
1358 let param_def_id = tcx.hir.local_def_id(param.id);
1359 for predicate in &generics.where_clause.predicates {
1360 // Look for `type: ...` where clauses.
1361 let data = match *predicate {
1362 hir::WherePredicate::BoundPredicate(ref data) => data,
1366 // Ignore `for<'a> type: ...` as they can change what
1367 // lifetimes mean (although we could "just" handle it).
1368 if !data.bound_generic_params.is_empty() {
1372 let def = match data.bounded_ty.node {
1373 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.def,
1377 if def == Def::TyParam(param_def_id) {
1378 add_bounds(&mut set, &data.bounds);
1383 Set1::Empty => Set1::Empty,
1384 Set1::One(name) => {
1385 if name == hir::LifetimeName::Static {
1386 Set1::One(Region::Static)
1391 .filter_map(|param| match param.kind {
1392 GenericParamKind::Lifetime { .. } => Some((
1394 hir::LifetimeName::Param(param.name),
1395 LifetimeDefOrigin::from_param(param),
1400 .find(|&(_, (_, lt_name, _))| lt_name == name)
1401 .map_or(Set1::Many, |(i, (id, _, origin))| {
1402 let def_id = tcx.hir.local_def_id(id);
1403 Set1::One(Region::EarlyBound(i as u32, def_id, origin))
1407 Set1::Many => Set1::Many,
1414 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
1415 // FIXME(#37666) this works around a limitation in the region inferencer
1416 fn hack<F>(&mut self, f: F)
1418 F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
1423 fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
1425 F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
1427 let LifetimeContext {
1433 let labels_in_fn = replace(&mut self.labels_in_fn, vec![]);
1434 let xcrate_object_lifetime_defaults =
1435 replace(&mut self.xcrate_object_lifetime_defaults, DefIdMap::default());
1436 let mut this = LifetimeContext {
1440 trait_ref_hack: self.trait_ref_hack,
1441 is_in_fn_syntax: self.is_in_fn_syntax,
1443 xcrate_object_lifetime_defaults,
1444 lifetime_uses: lifetime_uses,
1446 debug!("entering scope {:?}", this.scope);
1447 f(self.scope, &mut this);
1448 this.check_uses_for_lifetimes_defined_by_scope();
1449 debug!("exiting scope {:?}", this.scope);
1450 self.labels_in_fn = this.labels_in_fn;
1451 self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
1454 /// helper method to determine the span to remove when suggesting the
1455 /// deletion of a lifetime
1456 fn lifetime_deletion_span(&self, name: ast::Ident, generics: &hir::Generics) -> Option<Span> {
1457 generics.params.iter().enumerate().find_map(|(i, param)| {
1458 if param.name.ident() == name {
1459 let mut in_band = false;
1460 if let hir::GenericParamKind::Lifetime { kind } = param.kind {
1461 if let hir::LifetimeParamKind::InBand = kind {
1468 if generics.params.len() == 1 {
1469 // if sole lifetime, remove the entire `<>` brackets
1472 // if removing within `<>` brackets, we also want to
1473 // delete a leading or trailing comma as appropriate
1474 if i >= generics.params.len() - 1 {
1475 Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
1477 Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
1487 // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
1488 fn suggest_eliding_single_use_lifetime(
1489 &self, err: &mut DiagnosticBuilder<'_>, def_id: DefId, lifetime: &hir::Lifetime
1491 // FIXME: future work: also suggest `impl Foo<'_>` for `impl<'a> Foo<'a>`
1492 let name = lifetime.name.ident();
1493 let mut remove_decl = None;
1494 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1495 if let Some(generics) = self.tcx.hir.get_generics(parent_def_id) {
1496 remove_decl = self.lifetime_deletion_span(name, generics);
1500 let mut remove_use = None;
1501 let mut find_arg_use_span = |inputs: &hir::HirVec<hir::Ty>| {
1502 for input in inputs {
1503 if let hir::TyKind::Rptr(lt, _) = input.node {
1504 if lt.name.ident() == name {
1505 // include the trailing whitespace between the ampersand and the type name
1506 let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
1508 self.tcx.sess.source_map()
1509 .span_until_non_whitespace(lt_through_ty_span)
1516 if let Node::Lifetime(hir_lifetime) = self.tcx.hir.get(lifetime.id) {
1517 if let Some(parent) = self.tcx.hir.find(self.tcx.hir.get_parent(hir_lifetime.id)) {
1519 Node::Item(item) => {
1520 if let hir::ItemKind::Fn(decl, _, _, _) = &item.node {
1521 find_arg_use_span(&decl.inputs);
1524 Node::ImplItem(impl_item) => {
1525 if let hir::ImplItemKind::Method(sig, _) = &impl_item.node {
1526 find_arg_use_span(&sig.decl.inputs);
1534 if let (Some(decl_span), Some(use_span)) = (remove_decl, remove_use) {
1535 // if both declaration and use deletion spans start at the same
1536 // place ("start at" because the latter includes trailing
1537 // whitespace), then this is an in-band lifetime
1538 if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
1539 err.span_suggestion_with_applicability(
1541 "elide the single-use lifetime",
1543 Applicability::MachineApplicable,
1546 err.multipart_suggestion_with_applicability(
1547 "elide the single-use lifetime",
1548 vec![(decl_span, String::new()), (use_span, String::new())],
1549 Applicability::MachineApplicable,
1555 fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
1556 let defined_by = match self.scope {
1557 Scope::Binder { lifetimes, .. } => lifetimes,
1559 debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
1564 let mut def_ids: Vec<_> = defined_by
1566 .flat_map(|region| match region {
1567 Region::EarlyBound(_, def_id, _)
1568 | Region::LateBound(_, def_id, _)
1569 | Region::Free(_, def_id) => Some(*def_id),
1571 Region::LateBoundAnon(..) | Region::Static => None,
1575 // ensure that we issue lints in a repeatable order
1576 def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
1578 for def_id in def_ids {
1580 "check_uses_for_lifetimes_defined_by_scope: def_id = {:?}",
1584 let lifetimeuseset = self.lifetime_uses.remove(&def_id);
1587 "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
1591 match lifetimeuseset {
1592 Some(LifetimeUseSet::One(lifetime)) => {
1593 let node_id = self.tcx.hir.as_local_node_id(def_id).unwrap();
1594 debug!("node id first={:?}", node_id);
1595 if let Some((id, span, name)) = match self.tcx.hir.get(node_id) {
1596 Node::Lifetime(hir_lifetime) => Some((
1599 hir_lifetime.name.ident(),
1601 Node::GenericParam(param) => {
1602 Some((param.id, param.span, param.name.ident()))
1606 debug!("id = {:?} span = {:?} name = {:?}", node_id, span, name);
1608 if name == keywords::UnderscoreLifetime.ident() {
1612 let mut err = self.tcx.struct_span_lint_node(
1613 lint::builtin::SINGLE_USE_LIFETIMES,
1616 &format!("lifetime parameter `{}` only used once", name),
1619 if span == lifetime.span {
1620 // spans are the same for in-band lifetime declarations
1621 err.span_label(span, "this lifetime is only used here");
1623 err.span_label(span, "this lifetime...");
1624 err.span_label(lifetime.span, "...is used only here");
1626 self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
1630 Some(LifetimeUseSet::Many) => {
1631 debug!("Not one use lifetime");
1634 let node_id = self.tcx.hir.as_local_node_id(def_id).unwrap();
1635 if let Some((id, span, name)) = match self.tcx.hir.get(node_id) {
1636 Node::Lifetime(hir_lifetime) => Some((
1639 hir_lifetime.name.ident(),
1641 Node::GenericParam(param) => {
1642 Some((param.id, param.span, param.name.ident()))
1646 debug!("id ={:?} span = {:?} name = {:?}", node_id, span, name);
1647 let mut err = self.tcx.struct_span_lint_node(
1648 lint::builtin::UNUSED_LIFETIMES,
1651 &format!("lifetime parameter `{}` never used", name),
1653 if let Some(parent_def_id) = self.tcx.parent(def_id) {
1654 if let Some(generics) = self.tcx.hir.get_generics(parent_def_id) {
1655 let unused_lt_span = self.lifetime_deletion_span(name, generics);
1656 if let Some(span) = unused_lt_span {
1657 err.span_suggestion_with_applicability(
1659 "elide the unused lifetime",
1661 Applicability::MachineApplicable,
1673 /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
1675 /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
1676 /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
1677 /// within type bounds; those are early bound lifetimes, and the rest are late bound.
1681 /// fn foo<'a,'b,'c,T:Trait<'b>>(...)
1683 /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
1684 /// lifetimes may be interspersed together.
1686 /// If early bound lifetimes are present, we separate them into their own list (and likewise
1687 /// for late bound). They will be numbered sequentially, starting from the lowest index that is
1688 /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
1689 /// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
1690 /// ordering is not important there.
1691 fn visit_early_late<F>(
1693 parent_id: Option<ast::NodeId>,
1694 decl: &'tcx hir::FnDecl,
1695 generics: &'tcx hir::Generics,
1698 F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
1700 insert_late_bound_lifetimes(self.map, decl, generics);
1702 // Find the start of nested early scopes, e.g. in methods.
1704 if let Some(parent_id) = parent_id {
1705 let parent = self.tcx.hir.expect_item(parent_id);
1706 if sub_items_have_self_param(&parent.node) {
1707 index += 1; // Self comes before lifetimes
1710 hir::ItemKind::Trait(_, _, ref generics, ..)
1711 | hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
1712 index += generics.params.len() as u32;
1718 let mut type_count = 0;
1719 let lifetimes = generics
1722 .filter_map(|param| match param.kind {
1723 GenericParamKind::Lifetime { .. } => {
1724 if self.map.late_bound.contains(¶m.id) {
1725 Some(Region::late(&self.tcx.hir, param))
1727 Some(Region::early(&self.tcx.hir, &mut index, param))
1730 GenericParamKind::Type { .. } => {
1736 let next_early_index = index + type_count;
1738 let scope = Scope::Binder {
1742 abstract_type_parent: true,
1743 track_lifetime_uses: false,
1745 self.with(scope, move |old_scope, this| {
1746 this.check_lifetime_params(old_scope, &generics.params);
1747 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
1751 fn next_early_index_helper(&self, only_abstract_type_parent: bool) -> u32 {
1752 let mut scope = self.scope;
1755 Scope::Root => return 0,
1759 abstract_type_parent,
1761 } if (!only_abstract_type_parent || abstract_type_parent) =>
1763 return next_early_index
1766 Scope::Binder { s, .. }
1767 | Scope::Body { s, .. }
1768 | Scope::Elision { s, .. }
1769 | Scope::ObjectLifetimeDefault { s, .. } => scope = s,
1774 /// Returns the next index one would use for an early-bound-region
1775 /// if extending the current scope.
1776 fn next_early_index(&self) -> u32 {
1777 self.next_early_index_helper(true)
1780 /// Returns the next index one would use for an `impl Trait` that
1781 /// is being converted into an `abstract type`. This will be the
1782 /// next early index from the enclosing item, for the most
1783 /// part. See the `abstract_type_parent` field for more info.
1784 fn next_early_index_for_abstract_type(&self) -> u32 {
1785 self.next_early_index_helper(false)
1788 fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
1789 debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
1791 // If we've already reported an error, just ignore `lifetime_ref`.
1792 if let LifetimeName::Error = lifetime_ref.name {
1796 // Walk up the scope chain, tracking the number of fn scopes
1797 // that we pass through, until we find a lifetime with the
1798 // given name or we run out of scopes.
1800 let mut late_depth = 0;
1801 let mut scope = self.scope;
1802 let mut outermost_body = None;
1805 Scope::Body { id, s } => {
1806 outermost_body = Some(id);
1815 ref lifetimes, s, ..
1817 match lifetime_ref.name {
1818 LifetimeName::Param(param_name) => {
1819 if let Some(&def) = lifetimes.get(¶m_name.modern()) {
1820 break Some(def.shifted(late_depth));
1823 _ => bug!("expected LifetimeName::Param"),
1830 Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
1836 if let Some(mut def) = result {
1837 if let Region::EarlyBound(..) = def {
1838 // Do not free early-bound regions, only late-bound ones.
1839 } else if let Some(body_id) = outermost_body {
1840 let fn_id = self.tcx.hir.body_owner(body_id);
1841 match self.tcx.hir.get(fn_id) {
1842 Node::Item(&hir::Item {
1843 node: hir::ItemKind::Fn(..),
1846 | Node::TraitItem(&hir::TraitItem {
1847 node: hir::TraitItemKind::Method(..),
1850 | Node::ImplItem(&hir::ImplItem {
1851 node: hir::ImplItemKind::Method(..),
1854 let scope = self.tcx.hir.local_def_id(fn_id);
1855 def = Region::Free(scope, def.id().unwrap());
1861 // Check for fn-syntax conflicts with in-band lifetime definitions
1862 if self.is_in_fn_syntax {
1864 Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
1865 | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
1870 "lifetimes used in `fn` or `Fn` syntax must be \
1871 explicitly declared using `<...>` binders"
1872 ).span_label(lifetime_ref.span, "in-band lifetime definition")
1877 | Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1878 | Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
1879 | Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
1880 | Region::LateBound(_, _, LifetimeDefOrigin::Error)
1881 | Region::LateBoundAnon(..)
1882 | Region::Free(..) => {}
1886 self.insert_lifetime(lifetime_ref, def);
1892 "use of undeclared lifetime name `{}`",
1894 ).span_label(lifetime_ref.span, "undeclared lifetime")
1899 fn visit_segment_args(&mut self, def: Def, depth: usize, generic_args: &'tcx hir::GenericArgs) {
1900 if generic_args.parenthesized {
1901 let was_in_fn_syntax = self.is_in_fn_syntax;
1902 self.is_in_fn_syntax = true;
1903 self.visit_fn_like_elision(generic_args.inputs(), Some(&generic_args.bindings[0].ty));
1904 self.is_in_fn_syntax = was_in_fn_syntax;
1908 let mut elide_lifetimes = true;
1909 let lifetimes = generic_args
1912 .filter_map(|arg| match arg {
1913 hir::GenericArg::Lifetime(lt) => {
1914 if !lt.is_elided() {
1915 elide_lifetimes = false;
1922 if elide_lifetimes {
1923 self.resolve_elided_lifetimes(lifetimes);
1925 lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
1928 // Figure out if this is a type/trait segment,
1929 // which requires object lifetime defaults.
1930 let parent_def_id = |this: &mut Self, def_id: DefId| {
1931 let def_key = this.tcx.def_key(def_id);
1933 krate: def_id.krate,
1934 index: def_key.parent.expect("missing parent"),
1937 let type_def_id = match def {
1938 Def::AssociatedTy(def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
1939 Def::Variant(def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
1941 | Def::Union(def_id)
1943 | Def::TyAlias(def_id)
1944 | Def::Trait(def_id) if depth == 0 =>
1951 let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
1953 let mut scope = self.scope;
1956 Scope::Root => break false,
1958 Scope::Body { .. } => break true,
1960 Scope::Binder { s, .. }
1961 | Scope::Elision { s, .. }
1962 | Scope::ObjectLifetimeDefault { s, .. } => {
1969 let map = &self.map;
1970 let unsubst = if let Some(id) = self.tcx.hir.as_local_node_id(def_id) {
1971 &map.object_lifetime_defaults[&id]
1974 self.xcrate_object_lifetime_defaults
1976 .or_insert_with(|| {
1977 tcx.generics_of(def_id)
1980 .filter_map(|param| match param.kind {
1981 GenericParamDefKind::Type {
1982 object_lifetime_default,
1984 } => Some(object_lifetime_default),
1985 GenericParamDefKind::Lifetime => None,
1992 .map(|set| match *set {
1993 Set1::Empty => if in_body {
1996 Some(Region::Static)
1999 let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
2000 GenericArg::Lifetime(lt) => Some(lt),
2003 r.subst(lifetimes, map)
2011 for arg in &generic_args.args {
2013 GenericArg::Lifetime(_) => {}
2014 GenericArg::Type(ty) => {
2015 if let Some(<) = object_lifetime_defaults.get(i) {
2016 let scope = Scope::ObjectLifetimeDefault {
2020 self.with(scope, |_, this| this.visit_ty(ty));
2029 for b in &generic_args.bindings {
2030 self.visit_assoc_type_binding(b);
2034 fn visit_fn_like_elision(&mut self, inputs: &'tcx [hir::Ty], output: Option<&'tcx P<hir::Ty>>) {
2035 debug!("visit_fn_like_elision: enter");
2036 let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
2037 let arg_scope = Scope::Elision {
2038 elide: arg_elide.clone(),
2041 self.with(arg_scope, |_, this| {
2042 for input in inputs {
2043 this.visit_ty(input);
2046 Scope::Elision { ref elide, .. } => {
2047 arg_elide = elide.clone();
2053 let output = match output {
2058 debug!("visit_fn_like_elision: determine output");
2060 // Figure out if there's a body we can get argument names from,
2061 // and whether there's a `self` argument (treated specially).
2062 let mut assoc_item_kind = None;
2063 let mut impl_self = None;
2064 let parent = self.tcx.hir.get_parent_node(output.id);
2065 let body = match self.tcx.hir.get(parent) {
2066 // `fn` definitions and methods.
2067 Node::Item(&hir::Item {
2068 node: hir::ItemKind::Fn(.., body),
2072 Node::TraitItem(&hir::TraitItem {
2073 node: hir::TraitItemKind::Method(_, ref m),
2076 if let hir::ItemKind::Trait(.., ref trait_items) = self.tcx
2078 .expect_item(self.tcx.hir.get_parent(parent))
2081 assoc_item_kind = trait_items
2083 .find(|ti| ti.id.node_id == parent)
2087 hir::TraitMethod::Required(_) => None,
2088 hir::TraitMethod::Provided(body) => Some(body),
2092 Node::ImplItem(&hir::ImplItem {
2093 node: hir::ImplItemKind::Method(_, body),
2096 if let hir::ItemKind::Impl(.., ref self_ty, ref impl_items) = self.tcx
2098 .expect_item(self.tcx.hir.get_parent(parent))
2101 impl_self = Some(self_ty);
2102 assoc_item_kind = impl_items
2104 .find(|ii| ii.id.node_id == parent)
2110 // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
2111 Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
2112 // Everything else (only closures?) doesn't
2113 // actually enjoy elision in return types.
2115 self.visit_ty(output);
2120 let has_self = match assoc_item_kind {
2121 Some(hir::AssociatedItemKind::Method { has_self }) => has_self,
2125 // In accordance with the rules for lifetime elision, we can determine
2126 // what region to use for elision in the output type in two ways.
2127 // First (determined here), if `self` is by-reference, then the
2128 // implied output region is the region of the self parameter.
2130 // Look for `self: &'a Self` - also desugared from `&'a self`,
2131 // and if that matches, use it for elision and return early.
2132 let is_self_ty = |def: Def| {
2133 if let Def::SelfTy(..) = def {
2137 // Can't always rely on literal (or implied) `Self` due
2138 // to the way elision rules were originally specified.
2139 let impl_self = impl_self.map(|ty| &ty.node);
2140 if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) = impl_self {
2142 // Whitelist the types that unambiguously always
2143 // result in the same type constructor being used
2144 // (it can't differ between `Self` and `self`).
2145 Def::Struct(_) | Def::Union(_) | Def::Enum(_) | Def::PrimTy(_) => {
2146 return def == path.def
2155 if let hir::TyKind::Rptr(lifetime_ref, ref mt) = inputs[0].node {
2156 if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.node {
2157 if is_self_ty(path.def) {
2158 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
2159 let scope = Scope::Elision {
2160 elide: Elide::Exact(lifetime),
2163 self.with(scope, |_, this| this.visit_ty(output));
2171 // Second, if there was exactly one lifetime (either a substitution or a
2172 // reference) in the arguments, then any anonymous regions in the output
2173 // have that lifetime.
2174 let mut possible_implied_output_region = None;
2175 let mut lifetime_count = 0;
2176 let arg_lifetimes = inputs
2179 .skip(has_self as usize)
2181 let mut gather = GatherLifetimes {
2183 outer_index: ty::INNERMOST,
2184 have_bound_regions: false,
2185 lifetimes: Default::default(),
2187 gather.visit_ty(input);
2189 lifetime_count += gather.lifetimes.len();
2191 if lifetime_count == 1 && gather.lifetimes.len() == 1 {
2192 // there's a chance that the unique lifetime of this
2193 // iteration will be the appropriate lifetime for output
2194 // parameters, so lets store it.
2195 possible_implied_output_region = gather.lifetimes.iter().cloned().next();
2198 ElisionFailureInfo {
2201 lifetime_count: gather.lifetimes.len(),
2202 have_bound_regions: gather.have_bound_regions,
2207 let elide = if lifetime_count == 1 {
2208 Elide::Exact(possible_implied_output_region.unwrap())
2210 Elide::Error(arg_lifetimes)
2213 debug!("visit_fn_like_elision: elide={:?}", elide);
2215 let scope = Scope::Elision {
2219 self.with(scope, |_, this| this.visit_ty(output));
2220 debug!("visit_fn_like_elision: exit");
2222 struct GatherLifetimes<'a> {
2223 map: &'a NamedRegionMap,
2224 outer_index: ty::DebruijnIndex,
2225 have_bound_regions: bool,
2226 lifetimes: FxHashSet<Region>,
2229 impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
2230 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2231 NestedVisitorMap::None
2234 fn visit_ty(&mut self, ty: &hir::Ty) {
2235 if let hir::TyKind::BareFn(_) = ty.node {
2236 self.outer_index.shift_in(1);
2238 if let hir::TyKind::TraitObject(ref bounds, ref lifetime) = ty.node {
2239 for bound in bounds {
2240 self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
2243 // Stay on the safe side and don't include the object
2244 // lifetime default (which may not end up being used).
2245 if !lifetime.is_elided() {
2246 self.visit_lifetime(lifetime);
2249 intravisit::walk_ty(self, ty);
2251 if let hir::TyKind::BareFn(_) = ty.node {
2252 self.outer_index.shift_out(1);
2256 fn visit_generic_param(&mut self, param: &hir::GenericParam) {
2257 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2258 // FIXME(eddyb) Do we want this? It only makes a difference
2259 // if this `for<'a>` lifetime parameter is never used.
2260 self.have_bound_regions = true;
2263 intravisit::walk_generic_param(self, param);
2266 fn visit_poly_trait_ref(
2268 trait_ref: &hir::PolyTraitRef,
2269 modifier: hir::TraitBoundModifier,
2271 self.outer_index.shift_in(1);
2272 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
2273 self.outer_index.shift_out(1);
2276 fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
2277 if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
2279 Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
2280 if debruijn < self.outer_index =>
2282 self.have_bound_regions = true;
2286 .insert(lifetime.shifted_out_to_binder(self.outer_index));
2294 fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
2295 if lifetime_refs.is_empty() {
2299 let span = lifetime_refs[0].span;
2300 let mut late_depth = 0;
2301 let mut scope = self.scope;
2304 // Do not assign any resolution, it will be inferred.
2305 Scope::Body { .. } => return,
2307 Scope::Root => break None,
2309 Scope::Binder { s, .. } => {
2314 Scope::Elision { ref elide, .. } => {
2315 let lifetime = match *elide {
2316 Elide::FreshLateAnon(ref counter) => {
2317 for lifetime_ref in lifetime_refs {
2318 let lifetime = Region::late_anon(counter).shifted(late_depth);
2319 self.insert_lifetime(lifetime_ref, lifetime);
2323 Elide::Exact(l) => l.shifted(late_depth),
2324 Elide::Error(ref e) => break Some(e),
2326 for lifetime_ref in lifetime_refs {
2327 self.insert_lifetime(lifetime_ref, lifetime);
2332 Scope::ObjectLifetimeDefault { s, .. } => {
2338 let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
2339 let mut add_label = true;
2341 if let Some(params) = error {
2342 if lifetime_refs.len() == 1 {
2343 add_label = add_label && self.report_elision_failure(&mut err, params, span);
2347 add_missing_lifetime_specifiers_label(&mut err, span, lifetime_refs.len());
2353 fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
2354 match self.tcx.sess.source_map().span_to_snippet(span) {
2355 Ok(ref snippet) => {
2356 let (sugg, applicability) = if snippet == "&" {
2357 ("&'static ".to_owned(), Applicability::MachineApplicable)
2358 } else if snippet == "'_" {
2359 ("'static".to_owned(), Applicability::MachineApplicable)
2361 (format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
2363 db.span_suggestion_with_applicability(span, msg, sugg, applicability);
2373 fn report_elision_failure(
2375 db: &mut DiagnosticBuilder<'_>,
2376 params: &[ElisionFailureInfo],
2379 let mut m = String::new();
2380 let len = params.len();
2382 let elided_params: Vec<_> = params
2385 .filter(|info| info.lifetime_count > 0)
2388 let elided_len = elided_params.len();
2390 for (i, info) in elided_params.into_iter().enumerate() {
2391 let ElisionFailureInfo {
2398 let help_name = if let Some(body) = parent {
2399 let arg = &self.tcx.hir.body(body).arguments[index];
2400 format!("`{}`", self.tcx.hir.node_to_pretty_string(arg.pat.id))
2402 format!("argument {}", index + 1)
2410 "one of {}'s {} {}lifetimes",
2413 if have_bound_regions { "free " } else { "" }
2418 if elided_len == 2 && i == 0 {
2420 } else if i + 2 == elided_len {
2421 m.push_str(", or ");
2422 } else if i != elided_len - 1 {
2430 "this function's return type contains a borrowed value, but \
2431 there is no value for it to be borrowed from"
2433 self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
2434 } else if elided_len == 0 {
2437 "this function's return type contains a borrowed value with \
2438 an elided lifetime, but the lifetime cannot be derived from \
2441 let msg = "consider giving it an explicit bounded or 'static lifetime";
2442 self.suggest_lifetime(db, span, msg)
2443 } else if elided_len == 1 {
2446 "this function's return type contains a borrowed value, but \
2447 the signature does not say which {} it is borrowed from",
2454 "this function's return type contains a borrowed value, but \
2455 the signature does not say whether it is borrowed from {}",
2462 fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
2463 let mut late_depth = 0;
2464 let mut scope = self.scope;
2465 let lifetime = loop {
2467 Scope::Binder { s, .. } => {
2472 Scope::Root | Scope::Elision { .. } => break Region::Static,
2474 Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
2476 Scope::ObjectLifetimeDefault {
2477 lifetime: Some(l), ..
2481 self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
2484 fn check_lifetime_params(
2486 old_scope: ScopeRef<'_>,
2487 params: &'tcx [hir::GenericParam],
2489 let lifetimes: Vec<_> = params
2491 .filter_map(|param| match param.kind {
2492 GenericParamKind::Lifetime { .. } => Some((param, param.name)),
2496 for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
2497 if let hir::ParamName::Plain(_) = lifetime_i_name {
2498 let name = lifetime_i_name.ident().name;
2499 if name == keywords::UnderscoreLifetime.name()
2500 || name == keywords::StaticLifetime.name()
2502 let mut err = struct_span_err!(
2506 "invalid lifetime parameter name: `{}`",
2507 lifetime_i.name.ident(),
2511 format!("{} is a reserved lifetime name", name),
2517 // It is a hard error to shadow a lifetime within the same scope.
2518 for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
2519 if lifetime_i_name == lifetime_j_name {
2524 "lifetime name `{}` declared twice in the same scope",
2525 lifetime_j.name.ident()
2526 ).span_label(lifetime_j.span, "declared twice")
2527 .span_label(lifetime_i.span, "previous declaration here")
2532 // It is a soft error to shadow a lifetime within a parent scope.
2533 self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
2535 for bound in &lifetime_i.bounds {
2537 hir::GenericBound::Outlives(lt) => match lt.name {
2538 hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
2540 "use of `'_` in illegal place, but not caught by lowering",
2542 hir::LifetimeName::Static => {
2543 self.insert_lifetime(lt, Region::Static);
2547 lifetime_i.span.to(lt.span),
2549 "unnecessary lifetime parameter `{}`",
2550 lifetime_i.name.ident(),
2554 "you can use the `'static` lifetime directly, in place of `{}`",
2555 lifetime_i.name.ident(),
2559 hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
2560 self.resolve_lifetime_ref(lt);
2562 hir::LifetimeName::Error => {
2563 // No need to do anything, error already reported.
2572 fn check_lifetime_param_for_shadowing(
2574 mut old_scope: ScopeRef<'_>,
2575 param: &'tcx hir::GenericParam,
2577 for label in &self.labels_in_fn {
2578 // FIXME (#24278): non-hygienic comparison
2579 if param.name.ident().name == label.name {
2580 signal_shadowing_problem(
2583 original_label(label.span),
2584 shadower_lifetime(¶m),
2592 Scope::Body { s, .. }
2593 | Scope::Elision { s, .. }
2594 | Scope::ObjectLifetimeDefault { s, .. } => {
2603 ref lifetimes, s, ..
2605 if let Some(&def) = lifetimes.get(¶m.name.modern()) {
2606 let node_id = self.tcx.hir.as_local_node_id(def.id().unwrap()).unwrap();
2608 signal_shadowing_problem(
2610 param.name.ident().name,
2611 original_lifetime(self.tcx.hir.span(node_id)),
2612 shadower_lifetime(¶m),
2623 /// Returns true if, in the current scope, replacing `'_` would be
2624 /// equivalent to a single-use lifetime.
2625 fn track_lifetime_uses(&self) -> bool {
2626 let mut scope = self.scope;
2629 Scope::Root => break false,
2631 // Inside of items, it depends on the kind of item.
2633 track_lifetime_uses,
2635 } => break track_lifetime_uses,
2637 // Inside a body, `'_` will use an inference variable,
2639 Scope::Body { .. } => break true,
2641 // A lifetime only used in a fn argument could as well
2642 // be replaced with `'_`, as that would generate a
2645 elide: Elide::FreshLateAnon(_),
2649 // In the return type or other such place, `'_` is not
2650 // going to make a fresh name, so we cannot
2651 // necessarily replace a single-use lifetime with
2654 elide: Elide::Exact(_),
2658 elide: Elide::Error(_),
2662 Scope::ObjectLifetimeDefault { s, .. } => scope = s,
2667 fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
2668 if lifetime_ref.id == ast::DUMMY_NODE_ID {
2671 "lifetime reference not renumbered, \
2672 probably a bug in syntax::fold"
2677 "insert_lifetime: {} resolved to {:?} span={:?}",
2678 self.tcx.hir.node_to_string(lifetime_ref.id),
2680 self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
2682 self.map.defs.insert(lifetime_ref.id, def);
2685 Region::LateBoundAnon(..) | Region::Static => {
2686 // These are anonymous lifetimes or lifetimes that are not declared.
2689 Region::Free(_, def_id)
2690 | Region::LateBound(_, def_id, _)
2691 | Region::EarlyBound(_, def_id, _) => {
2692 // A lifetime declared by the user.
2693 let track_lifetime_uses = self.track_lifetime_uses();
2695 "insert_lifetime: track_lifetime_uses={}",
2698 if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
2699 debug!("insert_lifetime: first use of {:?}", def_id);
2701 .insert(def_id, LifetimeUseSet::One(lifetime_ref));
2703 debug!("insert_lifetime: many uses of {:?}", def_id);
2704 self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
2710 /// Sometimes we resolve a lifetime, but later find that it is an
2711 /// error (esp. around impl trait). In that case, we remove the
2712 /// entry into `map.defs` so as not to confuse later code.
2713 fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
2714 let old_value = self.map.defs.remove(&lifetime_ref.id);
2715 assert_eq!(old_value, Some(bad_def));
2719 /// Detects late-bound lifetimes and inserts them into
2720 /// `map.late_bound`.
2722 /// A region declared on a fn is **late-bound** if:
2723 /// - it is constrained by an argument type;
2724 /// - it does not appear in a where-clause.
2726 /// "Constrained" basically means that it appears in any type but
2727 /// not amongst the inputs to a projection. In other words, `<&'a
2728 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
2729 fn insert_late_bound_lifetimes(
2730 map: &mut NamedRegionMap,
2732 generics: &hir::Generics,
2735 "insert_late_bound_lifetimes(decl={:?}, generics={:?})",
2739 let mut constrained_by_input = ConstrainedCollector::default();
2740 for arg_ty in &decl.inputs {
2741 constrained_by_input.visit_ty(arg_ty);
2744 let mut appears_in_output = AllCollector::default();
2745 intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
2748 "insert_late_bound_lifetimes: constrained_by_input={:?}",
2749 constrained_by_input.regions
2752 // Walk the lifetimes that appear in where clauses.
2754 // Subtle point: because we disallow nested bindings, we can just
2755 // ignore binders here and scrape up all names we see.
2756 let mut appears_in_where_clause = AllCollector::default();
2757 appears_in_where_clause.visit_generics(generics);
2759 for param in &generics.params {
2760 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
2761 if !param.bounds.is_empty() {
2762 // `'a: 'b` means both `'a` and `'b` are referenced
2763 appears_in_where_clause
2765 .insert(hir::LifetimeName::Param(param.name.modern()));
2771 "insert_late_bound_lifetimes: appears_in_where_clause={:?}",
2772 appears_in_where_clause.regions
2775 // Late bound regions are those that:
2776 // - appear in the inputs
2777 // - do not appear in the where-clauses
2778 // - are not implicitly captured by `impl Trait`
2779 for param in &generics.params {
2781 hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
2783 // Types are not late-bound.
2784 hir::GenericParamKind::Type { .. } => continue,
2787 let lt_name = hir::LifetimeName::Param(param.name.modern());
2788 // appears in the where clauses? early-bound.
2789 if appears_in_where_clause.regions.contains(<_name) {
2793 // does not appear in the inputs, but appears in the return type? early-bound.
2794 if !constrained_by_input.regions.contains(<_name)
2795 && appears_in_output.regions.contains(<_name)
2801 "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
2806 let inserted = map.late_bound.insert(param.id);
2807 assert!(inserted, "visited lifetime {:?} twice", param.id);
2813 struct ConstrainedCollector {
2814 regions: FxHashSet<hir::LifetimeName>,
2817 impl<'v> Visitor<'v> for ConstrainedCollector {
2818 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2819 NestedVisitorMap::None
2822 fn visit_ty(&mut self, ty: &'v hir::Ty) {
2824 hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
2825 | hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
2826 // ignore lifetimes appearing in associated type
2827 // projections, as they are not *constrained*
2831 hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
2832 // consider only the lifetimes on the final
2833 // segment; I am not sure it's even currently
2834 // valid to have them elsewhere, but even if it
2835 // is, those would be potentially inputs to
2837 if let Some(last_segment) = path.segments.last() {
2838 self.visit_path_segment(path.span, last_segment);
2843 intravisit::walk_ty(self, ty);
2848 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2849 self.regions.insert(lifetime_ref.name.modern());
2854 struct AllCollector {
2855 regions: FxHashSet<hir::LifetimeName>,
2858 impl<'v> Visitor<'v> for AllCollector {
2859 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
2860 NestedVisitorMap::None
2863 fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
2864 self.regions.insert(lifetime_ref.name.modern());
2869 fn report_missing_lifetime_specifiers(
2873 ) -> DiagnosticBuilder<'_> {
2878 "missing lifetime specifier{}",
2879 if count > 1 { "s" } else { "" }
2883 fn add_missing_lifetime_specifiers_label(
2884 err: &mut DiagnosticBuilder<'_>,
2889 err.span_label(span, format!("expected {} lifetime parameters", count));
2891 err.span_label(span, "expected lifetime parameter");