//! Name resolution for lifetimes. //! //! Name resolution for lifetimes follows *much* simpler rules than the //! full resolve. For example, lifetime names are never exported or //! used between functions, and they operate in a purely top-down //! way. Therefore, we break lifetime name resolution into a separate pass. use crate::late::diagnostics::{ForLifetimeSpanType, MissingLifetimeSpot}; use rustc_ast::ast; use rustc_ast::attr; use rustc_ast::walk_list; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder}; use rustc_hir as hir; use rustc_hir::def::{DefKind, Res}; use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE}; use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor}; use rustc_hir::{GenericArg, GenericParam, LifetimeName, Node, ParamName, QPath}; use rustc_hir::{GenericParamKind, HirIdMap, HirIdSet, LifetimeParamKind}; use rustc_middle::hir::map::Map; use rustc_middle::middle::resolve_lifetime::*; use rustc_middle::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt}; use rustc_middle::{bug, span_bug}; use rustc_session::lint; use rustc_span::symbol::{kw, sym}; use rustc_span::Span; use std::borrow::Cow; use std::cell::Cell; use std::mem::take; use log::debug; // This counts the no of times a lifetime is used #[derive(Clone, Copy, Debug)] pub enum LifetimeUseSet<'tcx> { One(&'tcx hir::Lifetime), Many, } trait RegionExt { fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region); fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region); fn late_anon(index: &Cell) -> Region; fn id(&self) -> Option; fn shifted(self, amount: u32) -> Region; fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region; fn subst<'a, L>(self, params: L, map: &NamedRegionMap) -> Option where L: Iterator; } impl RegionExt for Region { fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam<'_>) -> (ParamName, Region) { let i = *index; *index += 1; let def_id = hir_map.local_def_id(param.hir_id); let origin = LifetimeDefOrigin::from_param(param); debug!("Region::early: index={} def_id={:?}", i, def_id); (param.name.normalize_to_macros_2_0(), Region::EarlyBound(i, def_id.to_def_id(), origin)) } fn late(hir_map: &Map<'_>, param: &GenericParam<'_>) -> (ParamName, Region) { let depth = ty::INNERMOST; let def_id = hir_map.local_def_id(param.hir_id); let origin = LifetimeDefOrigin::from_param(param); debug!( "Region::late: param={:?} depth={:?} def_id={:?} origin={:?}", param, depth, def_id, origin, ); (param.name.normalize_to_macros_2_0(), Region::LateBound(depth, def_id.to_def_id(), origin)) } fn late_anon(index: &Cell) -> Region { let i = index.get(); index.set(i + 1); let depth = ty::INNERMOST; Region::LateBoundAnon(depth, i) } fn id(&self) -> Option { match *self { Region::Static | Region::LateBoundAnon(..) => None, Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => { Some(id) } } } fn shifted(self, amount: u32) -> Region { match self { Region::LateBound(debruijn, id, origin) => { Region::LateBound(debruijn.shifted_in(amount), id, origin) } Region::LateBoundAnon(debruijn, index) => { Region::LateBoundAnon(debruijn.shifted_in(amount), index) } _ => self, } } fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region { match self { Region::LateBound(debruijn, id, origin) => { Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin) } Region::LateBoundAnon(debruijn, index) => { Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index) } _ => self, } } fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option where L: Iterator, { if let Region::EarlyBound(index, _, _) = self { params.nth(index as usize).and_then(|lifetime| map.defs.get(&lifetime.hir_id).cloned()) } else { Some(self) } } } /// Maps the id of each lifetime reference to the lifetime decl /// that it corresponds to. /// /// FIXME. This struct gets converted to a `ResolveLifetimes` for /// actual use. It has the same data, but indexed by `LocalDefId`. This /// is silly. #[derive(Default)] struct NamedRegionMap { // maps from every use of a named (not anonymous) lifetime to a // `Region` describing how that region is bound defs: HirIdMap, // the set of lifetime def ids that are late-bound; a region can // be late-bound if (a) it does NOT appear in a where-clause and // (b) it DOES appear in the arguments. late_bound: HirIdSet, // For each type and trait definition, maps type parameters // to the trait object lifetime defaults computed from them. object_lifetime_defaults: HirIdMap>, } crate struct LifetimeContext<'a, 'tcx> { crate tcx: TyCtxt<'tcx>, map: &'a mut NamedRegionMap, scope: ScopeRef<'a>, /// This is slightly complicated. Our representation for poly-trait-refs contains a single /// binder and thus we only allow a single level of quantification. However, /// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>` /// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the De Bruijn indices /// correct when representing these constraints, we should only introduce one /// scope. However, we want to support both locations for the quantifier and /// during lifetime resolution we want precise information (so we can't /// desugar in an earlier phase). /// /// So, if we encounter a quantifier at the outer scope, we set /// `trait_ref_hack` to `true` (and introduce a scope), and then if we encounter /// a quantifier at the inner scope, we error. If `trait_ref_hack` is `false`, /// then we introduce the scope at the inner quantifier. trait_ref_hack: bool, /// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax. is_in_fn_syntax: bool, /// List of labels in the function/method currently under analysis. labels_in_fn: Vec, /// Cache for cross-crate per-definition object lifetime defaults. xcrate_object_lifetime_defaults: DefIdMap>, lifetime_uses: &'a mut DefIdMap>, /// When encountering an undefined named lifetime, we will suggest introducing it in these /// places. crate missing_named_lifetime_spots: Vec>, } #[derive(Debug)] enum Scope<'a> { /// Declares lifetimes, and each can be early-bound or late-bound. /// The `DebruijnIndex` of late-bound lifetimes starts at `1` and /// it should be shifted by the number of `Binder`s in between the /// declaration `Binder` and the location it's referenced from. Binder { lifetimes: FxHashMap, /// if we extend this scope with another scope, what is the next index /// we should use for an early-bound region? next_early_index: u32, /// Flag is set to true if, in this binder, `'_` would be /// equivalent to a "single-use region". This is true on /// impls, but not other kinds of items. track_lifetime_uses: bool, /// Whether or not this binder would serve as the parent /// binder for opaque types introduced within. For example: /// /// ```text /// fn foo<'a>() -> impl for<'b> Trait> /// ``` /// /// Here, the opaque types we create for the `impl Trait` /// and `impl Trait2` references will both have the `foo` item /// as their parent. When we get to `impl Trait2`, we find /// that it is nested within the `for<>` binder -- this flag /// allows us to skip that when looking for the parent binder /// of the resulting opaque type. opaque_type_parent: bool, s: ScopeRef<'a>, }, /// Lifetimes introduced by a fn are scoped to the call-site for that fn, /// if this is a fn body, otherwise the original definitions are used. /// Unspecified lifetimes are inferred, unless an elision scope is nested, /// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`. Body { id: hir::BodyId, s: ScopeRef<'a>, }, /// A scope which either determines unspecified lifetimes or errors /// on them (e.g., due to ambiguity). For more details, see `Elide`. Elision { elide: Elide, s: ScopeRef<'a>, }, /// Use a specific lifetime (if `Some`) or leave it unset (to be /// inferred in a function body or potentially error outside one), /// for the default choice of lifetime in a trait object type. ObjectLifetimeDefault { lifetime: Option, s: ScopeRef<'a>, }, Root, } #[derive(Clone, Debug)] enum Elide { /// Use a fresh anonymous late-bound lifetime each time, by /// incrementing the counter to generate sequential indices. FreshLateAnon(Cell), /// Always use this one lifetime. Exact(Region), /// Less or more than one lifetime were found, error on unspecified. Error(Vec), } #[derive(Clone, Debug)] crate struct ElisionFailureInfo { /// Where we can find the argument pattern. parent: Option, /// The index of the argument in the original definition. index: usize, lifetime_count: usize, have_bound_regions: bool, crate span: Span, } type ScopeRef<'a> = &'a Scope<'a>; const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root; pub fn provide(providers: &mut ty::query::Providers<'_>) { *providers = ty::query::Providers { resolve_lifetimes, named_region_map: |tcx, id| tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id), is_late_bound_map: |tcx, id| tcx.resolve_lifetimes(LOCAL_CRATE).late_bound.get(&id), object_lifetime_defaults_map: |tcx, id| { tcx.resolve_lifetimes(LOCAL_CRATE).object_lifetime_defaults.get(&id) }, ..*providers }; } /// Computes the `ResolveLifetimes` map that contains data for the /// entire crate. You should not read the result of this query /// directly, but rather use `named_region_map`, `is_late_bound_map`, /// etc. fn resolve_lifetimes(tcx: TyCtxt<'_>, for_krate: CrateNum) -> ResolveLifetimes { assert_eq!(for_krate, LOCAL_CRATE); let named_region_map = krate(tcx); let mut rl = ResolveLifetimes::default(); for (hir_id, v) in named_region_map.defs { let map = rl.defs.entry(hir_id.owner).or_default(); map.insert(hir_id.local_id, v); } for hir_id in named_region_map.late_bound { let map = rl.late_bound.entry(hir_id.owner).or_default(); map.insert(hir_id.local_id); } for (hir_id, v) in named_region_map.object_lifetime_defaults { let map = rl.object_lifetime_defaults.entry(hir_id.owner).or_default(); map.insert(hir_id.local_id, v); } rl } fn krate(tcx: TyCtxt<'_>) -> NamedRegionMap { let krate = tcx.hir().krate(); let mut map = NamedRegionMap { defs: Default::default(), late_bound: Default::default(), object_lifetime_defaults: compute_object_lifetime_defaults(tcx), }; { let mut visitor = LifetimeContext { tcx, map: &mut map, scope: ROOT_SCOPE, trait_ref_hack: false, is_in_fn_syntax: false, labels_in_fn: vec![], xcrate_object_lifetime_defaults: Default::default(), lifetime_uses: &mut Default::default(), missing_named_lifetime_spots: vec![], }; for item in krate.items.values() { visitor.visit_item(item); } } map } /// In traits, there is an implicit `Self` type parameter which comes before the generics. /// We have to account for this when computing the index of the other generic parameters. /// This function returns whether there is such an implicit parameter defined on the given item. fn sub_items_have_self_param(node: &hir::ItemKind<'_>) -> bool { match *node { hir::ItemKind::Trait(..) | hir::ItemKind::TraitAlias(..) => true, _ => false, } } impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> { type Map = Map<'tcx>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::All(self.tcx.hir()) } // We want to nest trait/impl items in their parent, but nothing else. fn visit_nested_item(&mut self, _: hir::ItemId) {} fn visit_nested_body(&mut self, body: hir::BodyId) { // Each body has their own set of labels, save labels. let saved = take(&mut self.labels_in_fn); let body = self.tcx.hir().body(body); extract_labels(self, body); self.with(Scope::Body { id: body.id(), s: self.scope }, |_, this| { this.visit_body(body); }); self.labels_in_fn = saved; } fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) { match item.kind { hir::ItemKind::Fn(ref sig, ref generics, _) => { self.missing_named_lifetime_spots.push(generics.into()); self.visit_early_late(None, &sig.decl, generics, |this| { intravisit::walk_item(this, item); }); self.missing_named_lifetime_spots.pop(); } hir::ItemKind::ExternCrate(_) | hir::ItemKind::Use(..) | hir::ItemKind::Mod(..) | hir::ItemKind::ForeignMod(..) | hir::ItemKind::GlobalAsm(..) => { // These sorts of items have no lifetime parameters at all. intravisit::walk_item(self, item); } hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => { // No lifetime parameters, but implied 'static. let scope = Scope::Elision { elide: Elide::Exact(Region::Static), s: ROOT_SCOPE }; self.with(scope, |_, this| intravisit::walk_item(this, item)); } hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: Some(_), .. }) => { // Currently opaque type declarations are just generated from `impl Trait` // items. Doing anything on this node is irrelevant, as we currently don't need // it. } hir::ItemKind::TyAlias(_, ref generics) | hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, ref generics, .. }) | hir::ItemKind::Enum(_, ref generics) | hir::ItemKind::Struct(_, ref generics) | hir::ItemKind::Union(_, ref generics) | hir::ItemKind::Trait(_, _, ref generics, ..) | hir::ItemKind::TraitAlias(ref generics, ..) | hir::ItemKind::Impl { ref generics, .. } => { self.missing_named_lifetime_spots.push(generics.into()); // Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name". // This is not true for other kinds of items.x let track_lifetime_uses = match item.kind { hir::ItemKind::Impl { .. } => true, _ => false, }; // These kinds of items have only early-bound lifetime parameters. let mut index = if sub_items_have_self_param(&item.kind) { 1 // Self comes before lifetimes } else { 0 }; let mut non_lifetime_count = 0; let lifetimes = generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::early(&self.tcx.hir(), &mut index, param)) } GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => { non_lifetime_count += 1; None } }) .collect(); let scope = Scope::Binder { lifetimes, next_early_index: index + non_lifetime_count, opaque_type_parent: true, track_lifetime_uses, s: ROOT_SCOPE, }; self.with(scope, |old_scope, this| { this.check_lifetime_params(old_scope, &generics.params); intravisit::walk_item(this, item); }); self.missing_named_lifetime_spots.pop(); } } } fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) { match item.kind { hir::ForeignItemKind::Fn(ref decl, _, ref generics) => { self.visit_early_late(None, decl, generics, |this| { intravisit::walk_foreign_item(this, item); }) } hir::ForeignItemKind::Static(..) => { intravisit::walk_foreign_item(self, item); } hir::ForeignItemKind::Type => { intravisit::walk_foreign_item(self, item); } } } fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) { debug!("visit_ty: id={:?} ty={:?}", ty.hir_id, ty); debug!("visit_ty: ty.kind={:?}", ty.kind); match ty.kind { hir::TyKind::BareFn(ref c) => { let next_early_index = self.next_early_index(); let was_in_fn_syntax = self.is_in_fn_syntax; self.is_in_fn_syntax = true; let lifetime_span: Option = c.generic_params.iter().rev().find_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => Some(param.span), _ => None, }); let (span, span_type) = if let Some(span) = lifetime_span { (span.shrink_to_hi(), ForLifetimeSpanType::TypeTail) } else { (ty.span.shrink_to_lo(), ForLifetimeSpanType::TypeEmpty) }; self.missing_named_lifetime_spots .push(MissingLifetimeSpot::HigherRanked { span, span_type }); let scope = Scope::Binder { lifetimes: c .generic_params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::late(&self.tcx.hir(), param)) } _ => None, }) .collect(), s: self.scope, next_early_index, track_lifetime_uses: true, opaque_type_parent: false, }; self.with(scope, |old_scope, this| { // a bare fn has no bounds, so everything // contained within is scoped within its binder. this.check_lifetime_params(old_scope, &c.generic_params); intravisit::walk_ty(this, ty); }); self.missing_named_lifetime_spots.pop(); self.is_in_fn_syntax = was_in_fn_syntax; } hir::TyKind::TraitObject(bounds, ref lifetime) => { debug!("visit_ty: TraitObject(bounds={:?}, lifetime={:?})", bounds, lifetime); for bound in bounds { self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None); } match lifetime.name { LifetimeName::Implicit => { // For types like `dyn Foo`, we should // generate a special form of elided. span_bug!(ty.span, "object-lifetime-default expected, not implicit",); } LifetimeName::ImplicitObjectLifetimeDefault => { // If the user does not write *anything*, we // use the object lifetime defaulting // rules. So e.g., `Box` becomes // `Box`. self.resolve_object_lifetime_default(lifetime) } LifetimeName::Underscore => { // If the user writes `'_`, we use the *ordinary* elision // rules. So the `'_` in e.g., `Box` will be // resolved the same as the `'_` in `&'_ Foo`. // // cc #48468 self.resolve_elided_lifetimes(vec![lifetime]) } LifetimeName::Param(_) | LifetimeName::Static => { // If the user wrote an explicit name, use that. self.visit_lifetime(lifetime); } LifetimeName::Error => {} } } hir::TyKind::Rptr(ref lifetime_ref, ref mt) => { self.visit_lifetime(lifetime_ref); let scope = Scope::ObjectLifetimeDefault { lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(), s: self.scope, }; self.with(scope, |_, this| this.visit_ty(&mt.ty)); } hir::TyKind::Def(item_id, lifetimes) => { // Resolve the lifetimes in the bounds to the lifetime defs in the generics. // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to // `type MyAnonTy<'b> = impl MyTrait<'b>;` // ^ ^ this gets resolved in the scope of // the opaque_ty generics let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).kind { // Named opaque `impl Trait` types are reached via `TyKind::Path`. // This arm is for `impl Trait` in the types of statics, constants and locals. hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn: None, .. }) => { intravisit::walk_ty(self, ty); return; } // RPIT (return position impl trait) hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, bounds, .. }) => { (generics, bounds) } ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i), }; // Resolve the lifetimes that are applied to the opaque type. // These are resolved in the current scope. // `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to // `fn foo<'a>() -> MyAnonTy<'a> { ... }` // ^ ^this gets resolved in the current scope for lifetime in lifetimes { if let hir::GenericArg::Lifetime(lifetime) = lifetime { self.visit_lifetime(lifetime); // Check for predicates like `impl for<'a> Trait>` // and ban them. Type variables instantiated inside binders aren't // well-supported at the moment, so this doesn't work. // In the future, this should be fixed and this error should be removed. let def = self.map.defs.get(&lifetime.hir_id).cloned(); if let Some(Region::LateBound(_, def_id, _)) = def { if let Some(def_id) = def_id.as_local() { let hir_id = self.tcx.hir().as_local_hir_id(def_id); // Ensure that the parent of the def is an item, not HRTB let parent_id = self.tcx.hir().get_parent_node(hir_id); let parent_impl_id = hir::ImplItemId { hir_id: parent_id }; let parent_trait_id = hir::TraitItemId { hir_id: parent_id }; let krate = self.tcx.hir().krate(); if !(krate.items.contains_key(&parent_id) || krate.impl_items.contains_key(&parent_impl_id) || krate.trait_items.contains_key(&parent_trait_id)) { struct_span_err!( self.tcx.sess, lifetime.span, E0657, "`impl Trait` can only capture lifetimes \ bound at the fn or impl level" ) .emit(); self.uninsert_lifetime_on_error(lifetime, def.unwrap()); } } } } } // We want to start our early-bound indices at the end of the parent scope, // not including any parent `impl Trait`s. let mut index = self.next_early_index_for_opaque_type(); debug!("visit_ty: index = {}", index); let mut elision = None; let mut lifetimes = FxHashMap::default(); let mut non_lifetime_count = 0; for param in generics.params { match param.kind { GenericParamKind::Lifetime { .. } => { let (name, reg) = Region::early(&self.tcx.hir(), &mut index, ¶m); let def_id = if let Region::EarlyBound(_, def_id, _) = reg { def_id } else { bug!(); }; if let hir::ParamName::Plain(param_name) = name { if param_name.name == kw::UnderscoreLifetime { // Pick the elided lifetime "definition" if one exists // and use it to make an elision scope. self.lifetime_uses.insert(def_id, LifetimeUseSet::Many); elision = Some(reg); } else { lifetimes.insert(name, reg); } } else { self.lifetime_uses.insert(def_id, LifetimeUseSet::Many); lifetimes.insert(name, reg); } } GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => { non_lifetime_count += 1; } } } let next_early_index = index + non_lifetime_count; if let Some(elision_region) = elision { let scope = Scope::Elision { elide: Elide::Exact(elision_region), s: self.scope }; self.with(scope, |_old_scope, this| { let scope = Scope::Binder { lifetimes, next_early_index, s: this.scope, track_lifetime_uses: true, opaque_type_parent: false, }; this.with(scope, |_old_scope, this| { this.visit_generics(generics); for bound in bounds { this.visit_param_bound(bound); } }); }); } else { let scope = Scope::Binder { lifetimes, next_early_index, s: self.scope, track_lifetime_uses: true, opaque_type_parent: false, }; self.with(scope, |_old_scope, this| { this.visit_generics(generics); for bound in bounds { this.visit_param_bound(bound); } }); } } _ => intravisit::walk_ty(self, ty), } } fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) { use self::hir::TraitItemKind::*; self.missing_named_lifetime_spots.push((&trait_item.generics).into()); match trait_item.kind { Fn(ref sig, _) => { let tcx = self.tcx; self.visit_early_late( Some(tcx.hir().get_parent_item(trait_item.hir_id)), &sig.decl, &trait_item.generics, |this| intravisit::walk_trait_item(this, trait_item), ); } Type(bounds, ref ty) => { let generics = &trait_item.generics; let mut index = self.next_early_index(); debug!("visit_ty: index = {}", index); let mut non_lifetime_count = 0; let lifetimes = generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::early(&self.tcx.hir(), &mut index, param)) } GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => { non_lifetime_count += 1; None } }) .collect(); let scope = Scope::Binder { lifetimes, next_early_index: index + non_lifetime_count, s: self.scope, track_lifetime_uses: true, opaque_type_parent: true, }; self.with(scope, |old_scope, this| { this.check_lifetime_params(old_scope, &generics.params); this.visit_generics(generics); for bound in bounds { this.visit_param_bound(bound); } if let Some(ty) = ty { this.visit_ty(ty); } }); } Const(_, _) => { // Only methods and types support generics. assert!(trait_item.generics.params.is_empty()); intravisit::walk_trait_item(self, trait_item); } } self.missing_named_lifetime_spots.pop(); } fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) { use self::hir::ImplItemKind::*; self.missing_named_lifetime_spots.push((&impl_item.generics).into()); match impl_item.kind { Fn(ref sig, _) => { let tcx = self.tcx; self.visit_early_late( Some(tcx.hir().get_parent_item(impl_item.hir_id)), &sig.decl, &impl_item.generics, |this| intravisit::walk_impl_item(this, impl_item), ) } TyAlias(ref ty) => { let generics = &impl_item.generics; let mut index = self.next_early_index(); let mut non_lifetime_count = 0; debug!("visit_ty: index = {}", index); let lifetimes = generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::early(&self.tcx.hir(), &mut index, param)) } GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => { non_lifetime_count += 1; None } }) .collect(); let scope = Scope::Binder { lifetimes, next_early_index: index + non_lifetime_count, s: self.scope, track_lifetime_uses: true, opaque_type_parent: true, }; self.with(scope, |old_scope, this| { this.check_lifetime_params(old_scope, &generics.params); this.visit_generics(generics); this.visit_ty(ty); }); } OpaqueTy(bounds) => { let generics = &impl_item.generics; let mut index = self.next_early_index(); let mut next_early_index = index; debug!("visit_ty: index = {}", index); let lifetimes = generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::early(&self.tcx.hir(), &mut index, param)) } GenericParamKind::Type { .. } => { next_early_index += 1; None } GenericParamKind::Const { .. } => { next_early_index += 1; None } }) .collect(); let scope = Scope::Binder { lifetimes, next_early_index, s: self.scope, track_lifetime_uses: true, opaque_type_parent: true, }; self.with(scope, |_old_scope, this| { this.visit_generics(generics); for bound in bounds { this.visit_param_bound(bound); } }); } Const(_, _) => { // Only methods and types support generics. assert!(impl_item.generics.params.is_empty()); intravisit::walk_impl_item(self, impl_item); } } self.missing_named_lifetime_spots.pop(); } fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) { debug!("visit_lifetime(lifetime_ref={:?})", lifetime_ref); if lifetime_ref.is_elided() { self.resolve_elided_lifetimes(vec![lifetime_ref]); return; } if lifetime_ref.is_static() { self.insert_lifetime(lifetime_ref, Region::Static); return; } self.resolve_lifetime_ref(lifetime_ref); } fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _: hir::HirId) { for (i, segment) in path.segments.iter().enumerate() { let depth = path.segments.len() - i - 1; if let Some(ref args) = segment.args { self.visit_segment_args(path.res, depth, args); } } } fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl<'tcx>) { let output = match fd.output { hir::FnRetTy::DefaultReturn(_) => None, hir::FnRetTy::Return(ref ty) => Some(&**ty), }; self.visit_fn_like_elision(&fd.inputs, output); } fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) { check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params); for param in generics.params { match param.kind { GenericParamKind::Lifetime { .. } => {} GenericParamKind::Type { ref default, .. } => { walk_list!(self, visit_param_bound, param.bounds); if let Some(ref ty) = default { self.visit_ty(&ty); } } GenericParamKind::Const { ref ty, .. } => { walk_list!(self, visit_param_bound, param.bounds); self.visit_ty(&ty); } } } for predicate in generics.where_clause.predicates { match predicate { &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate { ref bounded_ty, bounds, ref bound_generic_params, .. }) => { let lifetimes: FxHashMap<_, _> = bound_generic_params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::late(&self.tcx.hir(), param)) } _ => None, }) .collect(); if !lifetimes.is_empty() { self.trait_ref_hack = true; let next_early_index = self.next_early_index(); let scope = Scope::Binder { lifetimes, s: self.scope, next_early_index, track_lifetime_uses: true, opaque_type_parent: false, }; let result = self.with(scope, |old_scope, this| { this.check_lifetime_params(old_scope, &bound_generic_params); this.visit_ty(&bounded_ty); walk_list!(this, visit_param_bound, bounds); }); self.trait_ref_hack = false; result } else { self.visit_ty(&bounded_ty); walk_list!(self, visit_param_bound, bounds); } } &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate { ref lifetime, bounds, .. }) => { self.visit_lifetime(lifetime); walk_list!(self, visit_param_bound, bounds); } &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate { ref lhs_ty, ref rhs_ty, .. }) => { self.visit_ty(lhs_ty); self.visit_ty(rhs_ty); } } } } fn visit_poly_trait_ref( &mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>, _modifier: hir::TraitBoundModifier, ) { debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref); let should_pop_missing_lt = self.is_trait_ref_fn_scope(trait_ref); if !self.trait_ref_hack || trait_ref.bound_generic_params.iter().any(|param| match param.kind { GenericParamKind::Lifetime { .. } => true, _ => false, }) { if self.trait_ref_hack { struct_span_err!( self.tcx.sess, trait_ref.span, E0316, "nested quantification of lifetimes" ) .emit(); } let next_early_index = self.next_early_index(); let scope = Scope::Binder { lifetimes: trait_ref .bound_generic_params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(Region::late(&self.tcx.hir(), param)) } _ => None, }) .collect(), s: self.scope, next_early_index, track_lifetime_uses: true, opaque_type_parent: false, }; self.with(scope, |old_scope, this| { this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params); walk_list!(this, visit_generic_param, trait_ref.bound_generic_params); this.visit_trait_ref(&trait_ref.trait_ref); }) } else { self.visit_trait_ref(&trait_ref.trait_ref); } if should_pop_missing_lt { self.missing_named_lifetime_spots.pop(); } } } #[derive(Copy, Clone, PartialEq)] enum ShadowKind { Label, Lifetime, } struct Original { kind: ShadowKind, span: Span, } struct Shadower { kind: ShadowKind, span: Span, } fn original_label(span: Span) -> Original { Original { kind: ShadowKind::Label, span } } fn shadower_label(span: Span) -> Shadower { Shadower { kind: ShadowKind::Label, span } } fn original_lifetime(span: Span) -> Original { Original { kind: ShadowKind::Lifetime, span } } fn shadower_lifetime(param: &hir::GenericParam<'_>) -> Shadower { Shadower { kind: ShadowKind::Lifetime, span: param.span } } impl ShadowKind { fn desc(&self) -> &'static str { match *self { ShadowKind::Label => "label", ShadowKind::Lifetime => "lifetime", } } } fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_>, params: &[hir::GenericParam<'_>]) { let lifetime_params: Vec<_> = params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)), _ => None, }) .collect(); let explicit = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::Explicit); let in_band = lifetime_params.iter().find(|(kind, _)| *kind == LifetimeParamKind::InBand); if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) { struct_span_err!( tcx.sess, *in_band_span, E0688, "cannot mix in-band and explicit lifetime definitions" ) .span_label(*in_band_span, "in-band lifetime definition here") .span_label(*explicit_span, "explicit lifetime definition here") .emit(); } } fn signal_shadowing_problem(tcx: TyCtxt<'_>, name: ast::Name, orig: Original, shadower: Shadower) { let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) { // lifetime/lifetime shadowing is an error struct_span_err!( tcx.sess, shadower.span, E0496, "{} name `{}` shadows a \ {} name that is already in scope", shadower.kind.desc(), name, orig.kind.desc() ) } else { // shadowing involving a label is only a warning, due to issues with // labels and lifetimes not being macro-hygienic. tcx.sess.struct_span_warn( shadower.span, &format!( "{} name `{}` shadows a \ {} name that is already in scope", shadower.kind.desc(), name, orig.kind.desc() ), ) }; err.span_label(orig.span, "first declared here"); err.span_label(shadower.span, format!("lifetime {} already in scope", name)); err.emit(); } // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning // if one of the label shadows a lifetime or another label. fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body<'_>) { struct GatherLabels<'a, 'tcx> { tcx: TyCtxt<'tcx>, scope: ScopeRef<'a>, labels_in_fn: &'a mut Vec, } let mut gather = GatherLabels { tcx: ctxt.tcx, scope: ctxt.scope, labels_in_fn: &mut ctxt.labels_in_fn }; gather.visit_body(body); impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> { type Map = intravisit::ErasedMap<'v>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } fn visit_expr(&mut self, ex: &hir::Expr<'_>) { if let Some(label) = expression_label(ex) { for prior_label in &self.labels_in_fn[..] { // FIXME (#24278): non-hygienic comparison if label.name == prior_label.name { signal_shadowing_problem( self.tcx, label.name, original_label(prior_label.span), shadower_label(label.span), ); } } check_if_label_shadows_lifetime(self.tcx, self.scope, label); self.labels_in_fn.push(label); } intravisit::walk_expr(self, ex) } } fn expression_label(ex: &hir::Expr<'_>) -> Option { if let hir::ExprKind::Loop(_, Some(label), _) = ex.kind { Some(label.ident) } else { None } } fn check_if_label_shadows_lifetime( tcx: TyCtxt<'_>, mut scope: ScopeRef<'_>, label: ast::Ident, ) { loop { match *scope { Scope::Body { s, .. } | Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => { scope = s; } Scope::Root => { return; } Scope::Binder { ref lifetimes, s, .. } => { // FIXME (#24278): non-hygienic comparison if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.normalize_to_macros_2_0())) { let hir_id = tcx.hir().as_local_hir_id(def.id().unwrap().expect_local()); signal_shadowing_problem( tcx, label.name, original_lifetime(tcx.hir().span(hir_id)), shadower_label(label.span), ); return; } scope = s; } } } } } fn compute_object_lifetime_defaults(tcx: TyCtxt<'_>) -> HirIdMap> { let mut map = HirIdMap::default(); for item in tcx.hir().krate().items.values() { match item.kind { hir::ItemKind::Struct(_, ref generics) | hir::ItemKind::Union(_, ref generics) | hir::ItemKind::Enum(_, ref generics) | hir::ItemKind::OpaqueTy(hir::OpaqueTy { ref generics, impl_trait_fn: None, .. }) | hir::ItemKind::TyAlias(_, ref generics) | hir::ItemKind::Trait(_, _, ref generics, ..) => { let result = object_lifetime_defaults_for_item(tcx, generics); // Debugging aid. if attr::contains_name(&item.attrs, sym::rustc_object_lifetime_default) { let object_lifetime_default_reprs: String = result .iter() .map(|set| match *set { Set1::Empty => "BaseDefault".into(), Set1::One(Region::Static) => "'static".into(), Set1::One(Region::EarlyBound(mut i, _, _)) => generics .params .iter() .find_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { if i == 0 { return Some(param.name.ident().to_string().into()); } i -= 1; None } _ => None, }) .unwrap(), Set1::One(_) => bug!(), Set1::Many => "Ambiguous".into(), }) .collect::>>() .join(","); tcx.sess.span_err(item.span, &object_lifetime_default_reprs); } map.insert(item.hir_id, result); } _ => {} } } map } /// Scan the bounds and where-clauses on parameters to extract bounds /// of the form `T:'a` so as to determine the `ObjectLifetimeDefault` /// for each type parameter. fn object_lifetime_defaults_for_item( tcx: TyCtxt<'_>, generics: &hir::Generics<'_>, ) -> Vec { fn add_bounds(set: &mut Set1, bounds: &[hir::GenericBound<'_>]) { for bound in bounds { if let hir::GenericBound::Outlives(ref lifetime) = *bound { set.insert(lifetime.name.normalize_to_macros_2_0()); } } } generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => None, GenericParamKind::Type { .. } => { let mut set = Set1::Empty; add_bounds(&mut set, ¶m.bounds); let param_def_id = tcx.hir().local_def_id(param.hir_id); for predicate in generics.where_clause.predicates { // Look for `type: ...` where clauses. let data = match *predicate { hir::WherePredicate::BoundPredicate(ref data) => data, _ => continue, }; // Ignore `for<'a> type: ...` as they can change what // lifetimes mean (although we could "just" handle it). if !data.bound_generic_params.is_empty() { continue; } let res = match data.bounded_ty.kind { hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.res, _ => continue, }; if res == Res::Def(DefKind::TyParam, param_def_id.to_def_id()) { add_bounds(&mut set, &data.bounds); } } Some(match set { Set1::Empty => Set1::Empty, Set1::One(name) => { if name == hir::LifetimeName::Static { Set1::One(Region::Static) } else { generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => Some(( param.hir_id, hir::LifetimeName::Param(param.name), LifetimeDefOrigin::from_param(param), )), _ => None, }) .enumerate() .find(|&(_, (_, lt_name, _))| lt_name == name) .map_or(Set1::Many, |(i, (id, _, origin))| { let def_id = tcx.hir().local_def_id(id); Set1::One(Region::EarlyBound( i as u32, def_id.to_def_id(), origin, )) }) } } Set1::Many => Set1::Many, }) } GenericParamKind::Const { .. } => { // Generic consts don't impose any constraints. None } }) .collect() } impl<'a, 'tcx> LifetimeContext<'a, 'tcx> { // FIXME(#37666) this works around a limitation in the region inferencer fn hack(&mut self, f: F) where F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>), { f(self) } fn with(&mut self, wrap_scope: Scope<'_>, f: F) where F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>), { let LifetimeContext { tcx, map, lifetime_uses, .. } = self; let labels_in_fn = take(&mut self.labels_in_fn); let xcrate_object_lifetime_defaults = take(&mut self.xcrate_object_lifetime_defaults); let missing_named_lifetime_spots = take(&mut self.missing_named_lifetime_spots); let mut this = LifetimeContext { tcx: *tcx, map, scope: &wrap_scope, trait_ref_hack: self.trait_ref_hack, is_in_fn_syntax: self.is_in_fn_syntax, labels_in_fn, xcrate_object_lifetime_defaults, lifetime_uses, missing_named_lifetime_spots, }; debug!("entering scope {:?}", this.scope); f(self.scope, &mut this); this.check_uses_for_lifetimes_defined_by_scope(); debug!("exiting scope {:?}", this.scope); self.labels_in_fn = this.labels_in_fn; self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults; self.missing_named_lifetime_spots = this.missing_named_lifetime_spots; } /// helper method to determine the span to remove when suggesting the /// deletion of a lifetime fn lifetime_deletion_span( &self, name: ast::Ident, generics: &hir::Generics<'_>, ) -> Option { generics.params.iter().enumerate().find_map(|(i, param)| { if param.name.ident() == name { let mut in_band = false; if let hir::GenericParamKind::Lifetime { kind } = param.kind { if let hir::LifetimeParamKind::InBand = kind { in_band = true; } } if in_band { Some(param.span) } else { if generics.params.len() == 1 { // if sole lifetime, remove the entire `<>` brackets Some(generics.span) } else { // if removing within `<>` brackets, we also want to // delete a leading or trailing comma as appropriate if i >= generics.params.len() - 1 { Some(generics.params[i - 1].span.shrink_to_hi().to(param.span)) } else { Some(param.span.to(generics.params[i + 1].span.shrink_to_lo())) } } } } else { None } }) } // helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)` // or from `fn rah<'a>(T<'a>)` to `fn rah(T<'_>)` fn suggest_eliding_single_use_lifetime( &self, err: &mut DiagnosticBuilder<'_>, def_id: DefId, lifetime: &hir::Lifetime, ) { let name = lifetime.name.ident(); let mut remove_decl = None; if let Some(parent_def_id) = self.tcx.parent(def_id) { if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) { remove_decl = self.lifetime_deletion_span(name, generics); } } let mut remove_use = None; let mut elide_use = None; let mut find_arg_use_span = |inputs: &[hir::Ty<'_>]| { for input in inputs { match input.kind { hir::TyKind::Rptr(lt, _) => { if lt.name.ident() == name { // include the trailing whitespace between the lifetime and type names let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi()); remove_use = Some( self.tcx .sess .source_map() .span_until_non_whitespace(lt_through_ty_span), ); break; } } hir::TyKind::Path(ref qpath) => { if let QPath::Resolved(_, path) = qpath { let last_segment = &path.segments[path.segments.len() - 1]; let generics = last_segment.generic_args(); for arg in generics.args.iter() { if let GenericArg::Lifetime(lt) = arg { if lt.name.ident() == name { elide_use = Some(lt.span); break; } } } break; } } _ => {} } } }; if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.hir_id) { if let Some(parent) = self.tcx.hir().find(self.tcx.hir().get_parent_item(hir_lifetime.hir_id)) { match parent { Node::Item(item) => { if let hir::ItemKind::Fn(sig, _, _) = &item.kind { find_arg_use_span(sig.decl.inputs); } } Node::ImplItem(impl_item) => { if let hir::ImplItemKind::Fn(sig, _) = &impl_item.kind { find_arg_use_span(sig.decl.inputs); } } _ => {} } } } let msg = "elide the single-use lifetime"; match (remove_decl, remove_use, elide_use) { (Some(decl_span), Some(use_span), None) => { // if both declaration and use deletion spans start at the same // place ("start at" because the latter includes trailing // whitespace), then this is an in-band lifetime if decl_span.shrink_to_lo() == use_span.shrink_to_lo() { err.span_suggestion( use_span, msg, String::new(), Applicability::MachineApplicable, ); } else { err.multipart_suggestion( msg, vec![(decl_span, String::new()), (use_span, String::new())], Applicability::MachineApplicable, ); } } (Some(decl_span), None, Some(use_span)) => { err.multipart_suggestion( msg, vec![(decl_span, String::new()), (use_span, "'_".to_owned())], Applicability::MachineApplicable, ); } _ => {} } } fn check_uses_for_lifetimes_defined_by_scope(&mut self) { let defined_by = match self.scope { Scope::Binder { lifetimes, .. } => lifetimes, _ => { debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope"); return; } }; let mut def_ids: Vec<_> = defined_by .values() .flat_map(|region| match region { Region::EarlyBound(_, def_id, _) | Region::LateBound(_, def_id, _) | Region::Free(_, def_id) => Some(*def_id), Region::LateBoundAnon(..) | Region::Static => None, }) .collect(); // ensure that we issue lints in a repeatable order def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id)); for def_id in def_ids { debug!("check_uses_for_lifetimes_defined_by_scope: def_id = {:?}", def_id); let lifetimeuseset = self.lifetime_uses.remove(&def_id); debug!( "check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}", lifetimeuseset ); match lifetimeuseset { Some(LifetimeUseSet::One(lifetime)) => { let hir_id = self.tcx.hir().as_local_hir_id(def_id.expect_local()); debug!("hir id first={:?}", hir_id); if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) { Node::Lifetime(hir_lifetime) => Some(( hir_lifetime.hir_id, hir_lifetime.span, hir_lifetime.name.ident(), )), Node::GenericParam(param) => { Some((param.hir_id, param.span, param.name.ident())) } _ => None, } { debug!("id = {:?} span = {:?} name = {:?}", id, span, name); if name.name == kw::UnderscoreLifetime { continue; } if let Some(parent_def_id) = self.tcx.parent(def_id) { if let Some(def_id) = parent_def_id.as_local() { let parent_hir_id = self.tcx.hir().as_local_hir_id(def_id); // lifetimes in `derive` expansions don't count (Issue #53738) if self .tcx .hir() .attrs(parent_hir_id) .iter() .any(|attr| attr.check_name(sym::automatically_derived)) { continue; } } } self.tcx.struct_span_lint_hir( lint::builtin::SINGLE_USE_LIFETIMES, id, span, |lint| { let mut err = lint.build(&format!( "lifetime parameter `{}` only used once", name )); if span == lifetime.span { // spans are the same for in-band lifetime declarations err.span_label(span, "this lifetime is only used here"); } else { err.span_label(span, "this lifetime..."); err.span_label(lifetime.span, "...is used only here"); } self.suggest_eliding_single_use_lifetime( &mut err, def_id, lifetime, ); err.emit(); }, ); } } Some(LifetimeUseSet::Many) => { debug!("not one use lifetime"); } None => { let hir_id = self.tcx.hir().as_local_hir_id(def_id.expect_local()); if let Some((id, span, name)) = match self.tcx.hir().get(hir_id) { Node::Lifetime(hir_lifetime) => Some(( hir_lifetime.hir_id, hir_lifetime.span, hir_lifetime.name.ident(), )), Node::GenericParam(param) => { Some((param.hir_id, param.span, param.name.ident())) } _ => None, } { debug!("id ={:?} span = {:?} name = {:?}", id, span, name); self.tcx.struct_span_lint_hir( lint::builtin::UNUSED_LIFETIMES, id, span, |lint| { let mut err = lint .build(&format!("lifetime parameter `{}` never used", name)); if let Some(parent_def_id) = self.tcx.parent(def_id) { if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) { let unused_lt_span = self.lifetime_deletion_span(name, generics); if let Some(span) = unused_lt_span { err.span_suggestion( span, "elide the unused lifetime", String::new(), Applicability::MachineApplicable, ); } } } err.emit(); }, ); } } } } } /// Visits self by adding a scope and handling recursive walk over the contents with `walk`. /// /// Handles visiting fns and methods. These are a bit complicated because we must distinguish /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear /// within type bounds; those are early bound lifetimes, and the rest are late bound. /// /// For example: /// /// fn foo<'a,'b,'c,T:Trait<'b>>(...) /// /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound /// lifetimes may be interspersed together. /// /// If early bound lifetimes are present, we separate them into their own list (and likewise /// for late bound). They will be numbered sequentially, starting from the lowest index that is /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late /// bound lifetimes are resolved by name and associated with a binder ID (`binder_id`), so the /// ordering is not important there. fn visit_early_late( &mut self, parent_id: Option, decl: &'tcx hir::FnDecl<'tcx>, generics: &'tcx hir::Generics<'tcx>, walk: F, ) where F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>), { insert_late_bound_lifetimes(self.map, decl, generics); // Find the start of nested early scopes, e.g., in methods. let mut index = 0; if let Some(parent_id) = parent_id { let parent = self.tcx.hir().expect_item(parent_id); if sub_items_have_self_param(&parent.kind) { index += 1; // Self comes before lifetimes } match parent.kind { hir::ItemKind::Trait(_, _, ref generics, ..) | hir::ItemKind::Impl { ref generics, .. } => { index += generics.params.len() as u32; } _ => {} } } let mut non_lifetime_count = 0; let lifetimes = generics .params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { if self.map.late_bound.contains(¶m.hir_id) { Some(Region::late(&self.tcx.hir(), param)) } else { Some(Region::early(&self.tcx.hir(), &mut index, param)) } } GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => { non_lifetime_count += 1; None } }) .collect(); let next_early_index = index + non_lifetime_count; let scope = Scope::Binder { lifetimes, next_early_index, s: self.scope, opaque_type_parent: true, track_lifetime_uses: false, }; self.with(scope, move |old_scope, this| { this.check_lifetime_params(old_scope, &generics.params); this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)` }); } fn next_early_index_helper(&self, only_opaque_type_parent: bool) -> u32 { let mut scope = self.scope; loop { match *scope { Scope::Root => return 0, Scope::Binder { next_early_index, opaque_type_parent, .. } if (!only_opaque_type_parent || opaque_type_parent) => { return next_early_index; } Scope::Binder { s, .. } | Scope::Body { s, .. } | Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => scope = s, } } } /// Returns the next index one would use for an early-bound-region /// if extending the current scope. fn next_early_index(&self) -> u32 { self.next_early_index_helper(true) } /// Returns the next index one would use for an `impl Trait` that /// is being converted into an opaque type alias `impl Trait`. This will be the /// next early index from the enclosing item, for the most /// part. See the `opaque_type_parent` field for more info. fn next_early_index_for_opaque_type(&self) -> u32 { self.next_early_index_helper(false) } fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) { debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref); // If we've already reported an error, just ignore `lifetime_ref`. if let LifetimeName::Error = lifetime_ref.name { return; } // Walk up the scope chain, tracking the number of fn scopes // that we pass through, until we find a lifetime with the // given name or we run out of scopes. // search. let mut late_depth = 0; let mut scope = self.scope; let mut outermost_body = None; let result = loop { match *scope { Scope::Body { id, s } => { outermost_body = Some(id); scope = s; } Scope::Root => { break None; } Scope::Binder { ref lifetimes, s, .. } => { match lifetime_ref.name { LifetimeName::Param(param_name) => { if let Some(&def) = lifetimes.get(¶m_name.normalize_to_macros_2_0()) { break Some(def.shifted(late_depth)); } } _ => bug!("expected LifetimeName::Param"), } late_depth += 1; scope = s; } Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => { scope = s; } } }; if let Some(mut def) = result { if let Region::EarlyBound(..) = def { // Do not free early-bound regions, only late-bound ones. } else if let Some(body_id) = outermost_body { let fn_id = self.tcx.hir().body_owner(body_id); match self.tcx.hir().get(fn_id) { Node::Item(&hir::Item { kind: hir::ItemKind::Fn(..), .. }) | Node::TraitItem(&hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. }) | Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(..), .. }) => { let scope = self.tcx.hir().local_def_id(fn_id); def = Region::Free(scope.to_def_id(), def.id().unwrap()); } _ => {} } } // Check for fn-syntax conflicts with in-band lifetime definitions if self.is_in_fn_syntax { match def { Region::EarlyBound(_, _, LifetimeDefOrigin::InBand) | Region::LateBound(_, _, LifetimeDefOrigin::InBand) => { struct_span_err!( self.tcx.sess, lifetime_ref.span, E0687, "lifetimes used in `fn` or `Fn` syntax must be \ explicitly declared using `<...>` binders" ) .span_label(lifetime_ref.span, "in-band lifetime definition") .emit(); } Region::Static | Region::EarlyBound( _, _, LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error, ) | Region::LateBound( _, _, LifetimeDefOrigin::ExplicitOrElided | LifetimeDefOrigin::Error, ) | Region::LateBoundAnon(..) | Region::Free(..) => {} } } self.insert_lifetime(lifetime_ref, def); } else { self.emit_undeclared_lifetime_error(lifetime_ref); } } fn visit_segment_args( &mut self, res: Res, depth: usize, generic_args: &'tcx hir::GenericArgs<'tcx>, ) { debug!( "visit_segment_args(res={:?}, depth={:?}, generic_args={:?})", res, depth, generic_args, ); if generic_args.parenthesized { let was_in_fn_syntax = self.is_in_fn_syntax; self.is_in_fn_syntax = true; self.visit_fn_like_elision(generic_args.inputs(), Some(generic_args.bindings[0].ty())); self.is_in_fn_syntax = was_in_fn_syntax; return; } let mut elide_lifetimes = true; let lifetimes = generic_args .args .iter() .filter_map(|arg| match arg { hir::GenericArg::Lifetime(lt) => { if !lt.is_elided() { elide_lifetimes = false; } Some(lt) } _ => None, }) .collect(); if elide_lifetimes { self.resolve_elided_lifetimes(lifetimes); } else { lifetimes.iter().for_each(|lt| self.visit_lifetime(lt)); } // Figure out if this is a type/trait segment, // which requires object lifetime defaults. let parent_def_id = |this: &mut Self, def_id: DefId| { let def_key = this.tcx.def_key(def_id); DefId { krate: def_id.krate, index: def_key.parent.expect("missing parent") } }; let type_def_id = match res { Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(parent_def_id(self, def_id)), Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(parent_def_id(self, def_id)), Res::Def( DefKind::Struct | DefKind::Union | DefKind::Enum | DefKind::TyAlias | DefKind::Trait, def_id, ) if depth == 0 => Some(def_id), _ => None, }; debug!("visit_segment_args: type_def_id={:?}", type_def_id); // Compute a vector of defaults, one for each type parameter, // per the rules given in RFCs 599 and 1156. Example: // // ```rust // struct Foo<'a, T: 'a, U> { } // ``` // // If you have `Foo<'x, dyn Bar, dyn Baz>`, we want to default // `dyn Bar` to `dyn Bar + 'x` (because of the `T: 'a` bound) // and `dyn Baz` to `dyn Baz + 'static` (because there is no // such bound). // // Therefore, we would compute `object_lifetime_defaults` to a // vector like `['x, 'static]`. Note that the vector only // includes type parameters. let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| { let in_body = { let mut scope = self.scope; loop { match *scope { Scope::Root => break false, Scope::Body { .. } => break true, Scope::Binder { s, .. } | Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => { scope = s; } } } }; let map = &self.map; let unsubst = if let Some(def_id) = def_id.as_local() { let id = self.tcx.hir().as_local_hir_id(def_id); &map.object_lifetime_defaults[&id] } else { let tcx = self.tcx; self.xcrate_object_lifetime_defaults.entry(def_id).or_insert_with(|| { tcx.generics_of(def_id) .params .iter() .filter_map(|param| match param.kind { GenericParamDefKind::Type { object_lifetime_default, .. } => { Some(object_lifetime_default) } GenericParamDefKind::Lifetime | GenericParamDefKind::Const => None, }) .collect() }) }; debug!("visit_segment_args: unsubst={:?}", unsubst); unsubst .iter() .map(|set| match *set { Set1::Empty => { if in_body { None } else { Some(Region::Static) } } Set1::One(r) => { let lifetimes = generic_args.args.iter().filter_map(|arg| match arg { GenericArg::Lifetime(lt) => Some(lt), _ => None, }); r.subst(lifetimes, map) } Set1::Many => None, }) .collect() }); debug!("visit_segment_args: object_lifetime_defaults={:?}", object_lifetime_defaults); let mut i = 0; for arg in generic_args.args { match arg { GenericArg::Lifetime(_) => {} GenericArg::Type(ty) => { if let Some(<) = object_lifetime_defaults.get(i) { let scope = Scope::ObjectLifetimeDefault { lifetime: lt, s: self.scope }; self.with(scope, |_, this| this.visit_ty(ty)); } else { self.visit_ty(ty); } i += 1; } GenericArg::Const(ct) => { self.visit_anon_const(&ct.value); } } } // Hack: when resolving the type `XX` in binding like `dyn // Foo<'b, Item = XX>`, the current object-lifetime default // would be to examine the trait `Foo` to check whether it has // a lifetime bound declared on `Item`. e.g., if `Foo` is // declared like so, then the default object lifetime bound in // `XX` should be `'b`: // // ```rust // trait Foo<'a> { // type Item: 'a; // } // ``` // // but if we just have `type Item;`, then it would be // `'static`. However, we don't get all of this logic correct. // // Instead, we do something hacky: if there are no lifetime parameters // to the trait, then we simply use a default object lifetime // bound of `'static`, because there is no other possibility. On the other hand, // if there ARE lifetime parameters, then we require the user to give an // explicit bound for now. // // This is intended to leave room for us to implement the // correct behavior in the future. let has_lifetime_parameter = generic_args.args.iter().any(|arg| match arg { GenericArg::Lifetime(_) => true, _ => false, }); // Resolve lifetimes found in the type `XX` from `Item = XX` bindings. for b in generic_args.bindings { let scope = Scope::ObjectLifetimeDefault { lifetime: if has_lifetime_parameter { None } else { Some(Region::Static) }, s: self.scope, }; self.with(scope, |_, this| this.visit_assoc_type_binding(b)); } } fn visit_fn_like_elision( &mut self, inputs: &'tcx [hir::Ty<'tcx>], output: Option<&'tcx hir::Ty<'tcx>>, ) { debug!("visit_fn_like_elision: enter"); let mut arg_elide = Elide::FreshLateAnon(Cell::new(0)); let arg_scope = Scope::Elision { elide: arg_elide.clone(), s: self.scope }; self.with(arg_scope, |_, this| { for input in inputs { this.visit_ty(input); } match *this.scope { Scope::Elision { ref elide, .. } => { arg_elide = elide.clone(); } _ => bug!(), } }); let output = match output { Some(ty) => ty, None => return, }; debug!("visit_fn_like_elision: determine output"); // Figure out if there's a body we can get argument names from, // and whether there's a `self` argument (treated specially). let mut assoc_item_kind = None; let mut impl_self = None; let parent = self.tcx.hir().get_parent_node(output.hir_id); let body = match self.tcx.hir().get(parent) { // `fn` definitions and methods. Node::Item(&hir::Item { kind: hir::ItemKind::Fn(.., body), .. }) => Some(body), Node::TraitItem(&hir::TraitItem { kind: hir::TraitItemKind::Fn(_, ref m), .. }) => { if let hir::ItemKind::Trait(.., ref trait_items) = self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind { assoc_item_kind = trait_items.iter().find(|ti| ti.id.hir_id == parent).map(|ti| ti.kind); } match *m { hir::TraitFn::Required(_) => None, hir::TraitFn::Provided(body) => Some(body), } } Node::ImplItem(&hir::ImplItem { kind: hir::ImplItemKind::Fn(_, body), .. }) => { if let hir::ItemKind::Impl { ref self_ty, ref items, .. } = self.tcx.hir().expect_item(self.tcx.hir().get_parent_item(parent)).kind { impl_self = Some(self_ty); assoc_item_kind = items.iter().find(|ii| ii.id.hir_id == parent).map(|ii| ii.kind); } Some(body) } // Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds). Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None, // Everything else (only closures?) doesn't // actually enjoy elision in return types. _ => { self.visit_ty(output); return; } }; let has_self = match assoc_item_kind { Some(hir::AssocItemKind::Fn { has_self }) => has_self, _ => false, }; // In accordance with the rules for lifetime elision, we can determine // what region to use for elision in the output type in two ways. // First (determined here), if `self` is by-reference, then the // implied output region is the region of the self parameter. if has_self { struct SelfVisitor<'a> { map: &'a NamedRegionMap, impl_self: Option<&'a hir::TyKind<'a>>, lifetime: Set1, } impl SelfVisitor<'_> { // Look for `self: &'a Self` - also desugared from `&'a self`, // and if that matches, use it for elision and return early. fn is_self_ty(&self, res: Res) -> bool { if let Res::SelfTy(..) = res { return true; } // Can't always rely on literal (or implied) `Self` due // to the way elision rules were originally specified. if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) = self.impl_self { match path.res { // Whitelist the types that unambiguously always // result in the same type constructor being used // (it can't differ between `Self` and `self`). Res::Def(DefKind::Struct | DefKind::Union | DefKind::Enum, _) | Res::PrimTy(_) => return res == path.res, _ => {} } } false } } impl<'a> Visitor<'a> for SelfVisitor<'a> { type Map = intravisit::ErasedMap<'a>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } fn visit_ty(&mut self, ty: &'a hir::Ty<'a>) { if let hir::TyKind::Rptr(lifetime_ref, ref mt) = ty.kind { if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.kind { if self.is_self_ty(path.res) { if let Some(lifetime) = self.map.defs.get(&lifetime_ref.hir_id) { self.lifetime.insert(*lifetime); } } } } intravisit::walk_ty(self, ty) } } let mut visitor = SelfVisitor { map: self.map, impl_self: impl_self.map(|ty| &ty.kind), lifetime: Set1::Empty, }; visitor.visit_ty(&inputs[0]); if let Set1::One(lifetime) = visitor.lifetime { let scope = Scope::Elision { elide: Elide::Exact(lifetime), s: self.scope }; self.with(scope, |_, this| this.visit_ty(output)); return; } } // Second, if there was exactly one lifetime (either a substitution or a // reference) in the arguments, then any anonymous regions in the output // have that lifetime. let mut possible_implied_output_region = None; let mut lifetime_count = 0; let arg_lifetimes = inputs .iter() .enumerate() .skip(has_self as usize) .map(|(i, input)| { let mut gather = GatherLifetimes { map: self.map, outer_index: ty::INNERMOST, have_bound_regions: false, lifetimes: Default::default(), }; gather.visit_ty(input); lifetime_count += gather.lifetimes.len(); if lifetime_count == 1 && gather.lifetimes.len() == 1 { // there's a chance that the unique lifetime of this // iteration will be the appropriate lifetime for output // parameters, so lets store it. possible_implied_output_region = gather.lifetimes.iter().cloned().next(); } ElisionFailureInfo { parent: body, index: i, lifetime_count: gather.lifetimes.len(), have_bound_regions: gather.have_bound_regions, span: input.span, } }) .collect(); let elide = if lifetime_count == 1 { Elide::Exact(possible_implied_output_region.unwrap()) } else { Elide::Error(arg_lifetimes) }; debug!("visit_fn_like_elision: elide={:?}", elide); let scope = Scope::Elision { elide, s: self.scope }; self.with(scope, |_, this| this.visit_ty(output)); debug!("visit_fn_like_elision: exit"); struct GatherLifetimes<'a> { map: &'a NamedRegionMap, outer_index: ty::DebruijnIndex, have_bound_regions: bool, lifetimes: FxHashSet, } impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> { type Map = intravisit::ErasedMap<'v>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } fn visit_ty(&mut self, ty: &hir::Ty<'_>) { if let hir::TyKind::BareFn(_) = ty.kind { self.outer_index.shift_in(1); } match ty.kind { hir::TyKind::TraitObject(bounds, ref lifetime) => { for bound in bounds { self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None); } // Stay on the safe side and don't include the object // lifetime default (which may not end up being used). if !lifetime.is_elided() { self.visit_lifetime(lifetime); } } _ => { intravisit::walk_ty(self, ty); } } if let hir::TyKind::BareFn(_) = ty.kind { self.outer_index.shift_out(1); } } fn visit_generic_param(&mut self, param: &hir::GenericParam<'_>) { if let hir::GenericParamKind::Lifetime { .. } = param.kind { // FIXME(eddyb) Do we want this? It only makes a difference // if this `for<'a>` lifetime parameter is never used. self.have_bound_regions = true; } intravisit::walk_generic_param(self, param); } fn visit_poly_trait_ref( &mut self, trait_ref: &hir::PolyTraitRef<'_>, modifier: hir::TraitBoundModifier, ) { self.outer_index.shift_in(1); intravisit::walk_poly_trait_ref(self, trait_ref, modifier); self.outer_index.shift_out(1); } fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) { if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.hir_id) { match lifetime { Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _) if debruijn < self.outer_index => { self.have_bound_regions = true; } _ => { self.lifetimes.insert(lifetime.shifted_out_to_binder(self.outer_index)); } } } } } } fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) { debug!("resolve_elided_lifetimes(lifetime_refs={:?})", lifetime_refs); if lifetime_refs.is_empty() { return; } let span = lifetime_refs[0].span; let mut late_depth = 0; let mut scope = self.scope; let mut lifetime_names = FxHashSet::default(); let error = loop { match *scope { // Do not assign any resolution, it will be inferred. Scope::Body { .. } => return, Scope::Root => break None, Scope::Binder { s, ref lifetimes, .. } => { // collect named lifetimes for suggestions for name in lifetimes.keys() { if let hir::ParamName::Plain(name) = name { lifetime_names.insert(*name); } } late_depth += 1; scope = s; } Scope::Elision { ref elide, ref s, .. } => { let lifetime = match *elide { Elide::FreshLateAnon(ref counter) => { for lifetime_ref in lifetime_refs { let lifetime = Region::late_anon(counter).shifted(late_depth); self.insert_lifetime(lifetime_ref, lifetime); } return; } Elide::Exact(l) => l.shifted(late_depth), Elide::Error(ref e) => { if let Scope::Binder { ref lifetimes, .. } = s { // collect named lifetimes for suggestions for name in lifetimes.keys() { if let hir::ParamName::Plain(name) = name { lifetime_names.insert(*name); } } } break Some(e); } }; for lifetime_ref in lifetime_refs { self.insert_lifetime(lifetime_ref, lifetime); } return; } Scope::ObjectLifetimeDefault { s, .. } => { scope = s; } } }; let mut err = self.report_missing_lifetime_specifiers(span, lifetime_refs.len()); if let Some(params) = error { // If there's no lifetime available, suggest `'static`. if self.report_elision_failure(&mut err, params) && lifetime_names.is_empty() { lifetime_names.insert(ast::Ident::from_str("'static")); } } self.add_missing_lifetime_specifiers_label( &mut err, span, lifetime_refs.len(), &lifetime_names, error.map(|p| &p[..]).unwrap_or(&[]), ); err.emit(); } fn report_elision_failure( &mut self, db: &mut DiagnosticBuilder<'_>, params: &[ElisionFailureInfo], ) -> bool /* add `'static` lifetime to lifetime list */ { let mut m = String::new(); let len = params.len(); let elided_params: Vec<_> = params.iter().cloned().filter(|info| info.lifetime_count > 0).collect(); let elided_len = elided_params.len(); for (i, info) in elided_params.into_iter().enumerate() { let ElisionFailureInfo { parent, index, lifetime_count: n, have_bound_regions, span } = info; db.span_label(span, ""); let help_name = if let Some(ident) = parent.and_then(|body| self.tcx.hir().body(body).params[index].pat.simple_ident()) { format!("`{}`", ident) } else { format!("argument {}", index + 1) }; m.push_str( &(if n == 1 { help_name } else { format!( "one of {}'s {} {}lifetimes", help_name, n, if have_bound_regions { "free " } else { "" } ) })[..], ); if elided_len == 2 && i == 0 { m.push_str(" or "); } else if i + 2 == elided_len { m.push_str(", or "); } else if i != elided_len - 1 { m.push_str(", "); } } if len == 0 { db.help( "this function's return type contains a borrowed value, \ but there is no value for it to be borrowed from", ); true } else if elided_len == 0 { db.help( "this function's return type contains a borrowed value with \ an elided lifetime, but the lifetime cannot be derived from \ the arguments", ); true } else if elided_len == 1 { db.help(&format!( "this function's return type contains a borrowed value, \ but the signature does not say which {} it is borrowed from", m )); false } else { db.help(&format!( "this function's return type contains a borrowed value, \ but the signature does not say whether it is borrowed from {}", m )); false } } fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) { debug!("resolve_object_lifetime_default(lifetime_ref={:?})", lifetime_ref); let mut late_depth = 0; let mut scope = self.scope; let lifetime = loop { match *scope { Scope::Binder { s, .. } => { late_depth += 1; scope = s; } Scope::Root | Scope::Elision { .. } => break Region::Static, Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return, Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l, } }; self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth)); } fn check_lifetime_params( &mut self, old_scope: ScopeRef<'_>, params: &'tcx [hir::GenericParam<'tcx>], ) { let lifetimes: Vec<_> = params .iter() .filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some((param, param.name.normalize_to_macros_2_0())) } _ => None, }) .collect(); for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() { if let hir::ParamName::Plain(_) = lifetime_i_name { let name = lifetime_i_name.ident().name; if name == kw::UnderscoreLifetime || name == kw::StaticLifetime { let mut err = struct_span_err!( self.tcx.sess, lifetime_i.span, E0262, "invalid lifetime parameter name: `{}`", lifetime_i.name.ident(), ); err.span_label( lifetime_i.span, format!("{} is a reserved lifetime name", name), ); err.emit(); } } // It is a hard error to shadow a lifetime within the same scope. for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) { if lifetime_i_name == lifetime_j_name { struct_span_err!( self.tcx.sess, lifetime_j.span, E0263, "lifetime name `{}` declared twice in the same scope", lifetime_j.name.ident() ) .span_label(lifetime_j.span, "declared twice") .span_label(lifetime_i.span, "previous declaration here") .emit(); } } // It is a soft error to shadow a lifetime within a parent scope. self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i); for bound in lifetime_i.bounds { match bound { hir::GenericBound::Outlives(ref lt) => match lt.name { hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug( lt.span, "use of `'_` in illegal place, but not caught by lowering", ), hir::LifetimeName::Static => { self.insert_lifetime(lt, Region::Static); self.tcx .sess .struct_span_warn( lifetime_i.span.to(lt.span), &format!( "unnecessary lifetime parameter `{}`", lifetime_i.name.ident(), ), ) .help(&format!( "you can use the `'static` lifetime directly, in place of `{}`", lifetime_i.name.ident(), )) .emit(); } hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => { self.resolve_lifetime_ref(lt); } hir::LifetimeName::ImplicitObjectLifetimeDefault => { self.tcx.sess.delay_span_bug( lt.span, "lowering generated `ImplicitObjectLifetimeDefault` \ outside of an object type", ) } hir::LifetimeName::Error => { // No need to do anything, error already reported. } }, _ => bug!(), } } } } fn check_lifetime_param_for_shadowing( &self, mut old_scope: ScopeRef<'_>, param: &'tcx hir::GenericParam<'tcx>, ) { for label in &self.labels_in_fn { // FIXME (#24278): non-hygienic comparison if param.name.ident().name == label.name { signal_shadowing_problem( self.tcx, label.name, original_label(label.span), shadower_lifetime(¶m), ); return; } } loop { match *old_scope { Scope::Body { s, .. } | Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => { old_scope = s; } Scope::Root => { return; } Scope::Binder { ref lifetimes, s, .. } => { if let Some(&def) = lifetimes.get(¶m.name.normalize_to_macros_2_0()) { let hir_id = self.tcx.hir().as_local_hir_id(def.id().unwrap().expect_local()); signal_shadowing_problem( self.tcx, param.name.ident().name, original_lifetime(self.tcx.hir().span(hir_id)), shadower_lifetime(¶m), ); return; } old_scope = s; } } } } /// Returns `true` if, in the current scope, replacing `'_` would be /// equivalent to a single-use lifetime. fn track_lifetime_uses(&self) -> bool { let mut scope = self.scope; loop { match *scope { Scope::Root => break false, // Inside of items, it depends on the kind of item. Scope::Binder { track_lifetime_uses, .. } => break track_lifetime_uses, // Inside a body, `'_` will use an inference variable, // should be fine. Scope::Body { .. } => break true, // A lifetime only used in a fn argument could as well // be replaced with `'_`, as that would generate a // fresh name, too. Scope::Elision { elide: Elide::FreshLateAnon(_), .. } => break true, // In the return type or other such place, `'_` is not // going to make a fresh name, so we cannot // necessarily replace a single-use lifetime with // `'_`. Scope::Elision { elide: Elide::Exact(_), .. } => break false, Scope::Elision { elide: Elide::Error(_), .. } => break false, Scope::ObjectLifetimeDefault { s, .. } => scope = s, } } } fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) { debug!( "insert_lifetime: {} resolved to {:?} span={:?}", self.tcx.hir().node_to_string(lifetime_ref.hir_id), def, self.tcx.sess.source_map().span_to_string(lifetime_ref.span) ); self.map.defs.insert(lifetime_ref.hir_id, def); match def { Region::LateBoundAnon(..) | Region::Static => { // These are anonymous lifetimes or lifetimes that are not declared. } Region::Free(_, def_id) | Region::LateBound(_, def_id, _) | Region::EarlyBound(_, def_id, _) => { // A lifetime declared by the user. let track_lifetime_uses = self.track_lifetime_uses(); debug!("insert_lifetime: track_lifetime_uses={}", track_lifetime_uses); if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) { debug!("insert_lifetime: first use of {:?}", def_id); self.lifetime_uses.insert(def_id, LifetimeUseSet::One(lifetime_ref)); } else { debug!("insert_lifetime: many uses of {:?}", def_id); self.lifetime_uses.insert(def_id, LifetimeUseSet::Many); } } } } /// Sometimes we resolve a lifetime, but later find that it is an /// error (esp. around impl trait). In that case, we remove the /// entry into `map.defs` so as not to confuse later code. fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) { let old_value = self.map.defs.remove(&lifetime_ref.hir_id); assert_eq!(old_value, Some(bad_def)); } } /// Detects late-bound lifetimes and inserts them into /// `map.late_bound`. /// /// A region declared on a fn is **late-bound** if: /// - it is constrained by an argument type; /// - it does not appear in a where-clause. /// /// "Constrained" basically means that it appears in any type but /// not amongst the inputs to a projection. In other words, `<&'a /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`. fn insert_late_bound_lifetimes( map: &mut NamedRegionMap, decl: &hir::FnDecl<'_>, generics: &hir::Generics<'_>, ) { debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics); let mut constrained_by_input = ConstrainedCollector::default(); for arg_ty in decl.inputs { constrained_by_input.visit_ty(arg_ty); } let mut appears_in_output = AllCollector::default(); intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output); debug!("insert_late_bound_lifetimes: constrained_by_input={:?}", constrained_by_input.regions); // Walk the lifetimes that appear in where clauses. // // Subtle point: because we disallow nested bindings, we can just // ignore binders here and scrape up all names we see. let mut appears_in_where_clause = AllCollector::default(); appears_in_where_clause.visit_generics(generics); for param in generics.params { if let hir::GenericParamKind::Lifetime { .. } = param.kind { if !param.bounds.is_empty() { // `'a: 'b` means both `'a` and `'b` are referenced appears_in_where_clause .regions .insert(hir::LifetimeName::Param(param.name.normalize_to_macros_2_0())); } } } debug!( "insert_late_bound_lifetimes: appears_in_where_clause={:?}", appears_in_where_clause.regions ); // Late bound regions are those that: // - appear in the inputs // - do not appear in the where-clauses // - are not implicitly captured by `impl Trait` for param in generics.params { match param.kind { hir::GenericParamKind::Lifetime { .. } => { /* fall through */ } // Neither types nor consts are late-bound. hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue, } let lt_name = hir::LifetimeName::Param(param.name.normalize_to_macros_2_0()); // appears in the where clauses? early-bound. if appears_in_where_clause.regions.contains(<_name) { continue; } // does not appear in the inputs, but appears in the return type? early-bound. if !constrained_by_input.regions.contains(<_name) && appears_in_output.regions.contains(<_name) { continue; } debug!( "insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.hir_id ); let inserted = map.late_bound.insert(param.hir_id); assert!(inserted, "visited lifetime {:?} twice", param.hir_id); } return; #[derive(Default)] struct ConstrainedCollector { regions: FxHashSet, } impl<'v> Visitor<'v> for ConstrainedCollector { type Map = intravisit::ErasedMap<'v>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) { match ty.kind { hir::TyKind::Path( hir::QPath::Resolved(Some(_), _) | hir::QPath::TypeRelative(..), ) => { // ignore lifetimes appearing in associated type // projections, as they are not *constrained* // (defined above) } hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => { // consider only the lifetimes on the final // segment; I am not sure it's even currently // valid to have them elsewhere, but even if it // is, those would be potentially inputs to // projections if let Some(last_segment) = path.segments.last() { self.visit_path_segment(path.span, last_segment); } } _ => { intravisit::walk_ty(self, ty); } } } fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) { self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0()); } } #[derive(Default)] struct AllCollector { regions: FxHashSet, } impl<'v> Visitor<'v> for AllCollector { type Map = intravisit::ErasedMap<'v>; fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) { self.regions.insert(lifetime_ref.name.normalize_to_macros_2_0()); } } }