diff options
Diffstat (limited to 'compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs')
| -rw-r--r-- | compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs | 2042 |
1 files changed, 2042 insertions, 0 deletions
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs new file mode 100644 index 000000000..65a9052a6 --- /dev/null +++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs @@ -0,0 +1,2042 @@ +//! Resolution of early vs late bound lifetimes. +//! +//! Name resolution for lifetimes is performed on the AST and embedded into HIR. From this +//! information, typechecking needs to transform the lifetime parameters into bound lifetimes. +//! Lifetimes can be early-bound or late-bound. Construction of typechecking terms needs to visit +//! the types in HIR to identify late-bound lifetimes and assign their Debruijn indices. This file +//! is also responsible for assigning their semantics to implicit lifetimes in trait objects. + +use rustc_ast::walk_list; +use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet}; +use rustc_errors::struct_span_err; +use rustc_hir as hir; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::def_id::LocalDefId; +use rustc_hir::intravisit::{self, Visitor}; +use rustc_hir::{GenericArg, GenericParam, GenericParamKind, HirIdMap, LifetimeName, Node}; +use rustc_middle::bug; +use rustc_middle::hir::nested_filter; +use rustc_middle::middle::resolve_bound_vars::*; +use rustc_middle::ty::{self, DefIdTree, TyCtxt, TypeSuperVisitable, TypeVisitor}; +use rustc_session::lint; +use rustc_span::def_id::DefId; +use rustc_span::symbol::{sym, Ident}; +use rustc_span::Span; +use std::fmt; + +use crate::errors; + +trait RegionExt { + fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg); + + fn late(index: u32, param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg); + + fn id(&self) -> Option<DefId>; + + fn shifted(self, amount: u32) -> ResolvedArg; +} + +impl RegionExt for ResolvedArg { + fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) { + debug!("ResolvedArg::early: def_id={:?}", param.def_id); + (param.def_id, ResolvedArg::EarlyBound(param.def_id.to_def_id())) + } + + fn late(idx: u32, param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) { + let depth = ty::INNERMOST; + debug!( + "ResolvedArg::late: idx={:?}, param={:?} depth={:?} def_id={:?}", + idx, param, depth, param.def_id, + ); + (param.def_id, ResolvedArg::LateBound(depth, idx, param.def_id.to_def_id())) + } + + fn id(&self) -> Option<DefId> { + match *self { + ResolvedArg::StaticLifetime | ResolvedArg::Error(_) => None, + + ResolvedArg::EarlyBound(id) + | ResolvedArg::LateBound(_, _, id) + | ResolvedArg::Free(_, id) => Some(id), + } + } + + fn shifted(self, amount: u32) -> ResolvedArg { + match self { + ResolvedArg::LateBound(debruijn, idx, id) => { + ResolvedArg::LateBound(debruijn.shifted_in(amount), idx, id) + } + _ => self, + } + } +} + +/// Maps the id of each bound variable reference to the variable decl +/// that it corresponds to. +/// +/// FIXME. This struct gets converted to a `ResolveBoundVars` for +/// actual use. It has the same data, but indexed by `LocalDefId`. This +/// is silly. +#[derive(Debug, Default)] +struct NamedVarMap { + // maps from every use of a named (not anonymous) bound var to a + // `ResolvedArg` describing how that variable is bound + defs: HirIdMap<ResolvedArg>, + + // Maps relevant hir items to the bound vars on them. These include: + // - function defs + // - function pointers + // - closures + // - trait refs + // - bound types (like `T` in `for<'a> T<'a>: Foo`) + late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>, +} + +struct BoundVarContext<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + map: &'a mut NamedVarMap, + scope: ScopeRef<'a>, +} + +#[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 { + /// We use an IndexMap here because we want these lifetimes in order + /// for diagnostics. + bound_vars: FxIndexMap<LocalDefId, ResolvedArg>, + + scope_type: BinderScopeType, + + /// The late bound vars for a given item are stored by `HirId` to be + /// queried later. However, if we enter an elision scope, we have to + /// later append the elided bound vars to the list and need to know what + /// to append to. + hir_id: hir::HirId, + + s: ScopeRef<'a>, + + /// If this binder comes from a where clause, specify how it was created. + /// This is used to diagnose inaccessible lifetimes in APIT: + /// ```ignore (illustrative) + /// fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {} + /// ``` + where_bound_origin: Option<hir::PredicateOrigin>, + }, + + /// 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). + Elision { + 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<ResolvedArg>, + s: ScopeRef<'a>, + }, + + /// When we have nested trait refs, we concatenate late bound vars for inner + /// trait refs from outer ones. But we also need to include any HRTB + /// lifetimes encountered when identifying the trait that an associated type + /// is declared on. + Supertrait { + bound_vars: Vec<ty::BoundVariableKind>, + s: ScopeRef<'a>, + }, + + TraitRefBoundary { + s: ScopeRef<'a>, + }, + + /// Disallows capturing non-lifetime binders from parent scopes. + /// + /// This is necessary for something like `for<T> [(); { /* references T */ }]:`, + /// since we don't do something more correct like replacing any captured + /// late-bound vars with early-bound params in the const's own generics. + AnonConstBoundary { + s: ScopeRef<'a>, + }, + + Root { + opt_parent_item: Option<LocalDefId>, + }, +} + +#[derive(Copy, Clone, Debug)] +enum BinderScopeType { + /// Any non-concatenating binder scopes. + Normal, + /// Within a syntactic trait ref, there may be multiple poly trait refs that + /// are nested (under the `associated_type_bounds` feature). The binders of + /// the inner poly trait refs are extended from the outer poly trait refs + /// and don't increase the late bound depth. If you had + /// `T: for<'a> Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope + /// would be `Concatenating`. This also used in trait refs in where clauses + /// where we have two binders `for<> T: for<> Foo` (I've intentionally left + /// out any lifetimes because they aren't needed to show the two scopes). + /// The inner `for<>` has a scope of `Concatenating`. + Concatenating, +} + +// A helper struct for debugging scopes without printing parent scopes +struct TruncatedScopeDebug<'a>(&'a Scope<'a>); + +impl<'a> fmt::Debug for TruncatedScopeDebug<'a> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self.0 { + Scope::Binder { bound_vars, scope_type, hir_id, where_bound_origin, s: _ } => f + .debug_struct("Binder") + .field("bound_vars", bound_vars) + .field("scope_type", scope_type) + .field("hir_id", hir_id) + .field("where_bound_origin", where_bound_origin) + .field("s", &"..") + .finish(), + Scope::Body { id, s: _ } => { + f.debug_struct("Body").field("id", id).field("s", &"..").finish() + } + Scope::Elision { s: _ } => f.debug_struct("Elision").field("s", &"..").finish(), + Scope::ObjectLifetimeDefault { lifetime, s: _ } => f + .debug_struct("ObjectLifetimeDefault") + .field("lifetime", lifetime) + .field("s", &"..") + .finish(), + Scope::Supertrait { bound_vars, s: _ } => f + .debug_struct("Supertrait") + .field("bound_vars", bound_vars) + .field("s", &"..") + .finish(), + Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(), + Scope::AnonConstBoundary { s: _ } => f.debug_struct("AnonConstBoundary").finish(), + Scope::Root { opt_parent_item } => { + f.debug_struct("Root").field("opt_parent_item", &opt_parent_item).finish() + } + } + } +} + +type ScopeRef<'a> = &'a Scope<'a>; + +pub(crate) fn provide(providers: &mut ty::query::Providers) { + *providers = ty::query::Providers { + resolve_bound_vars, + + named_variable_map: |tcx, id| tcx.resolve_bound_vars(id).defs.get(&id), + is_late_bound_map, + object_lifetime_default, + late_bound_vars_map: |tcx, id| tcx.resolve_bound_vars(id).late_bound_vars.get(&id), + + ..*providers + }; +} + +/// Computes the `ResolveBoundVars` map that contains data for an entire `Item`. +/// You should not read the result of this query directly, but rather use +/// `named_variable_map`, `is_late_bound_map`, etc. +#[instrument(level = "debug", skip(tcx))] +fn resolve_bound_vars(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveBoundVars { + let mut named_variable_map = + NamedVarMap { defs: Default::default(), late_bound_vars: Default::default() }; + let mut visitor = BoundVarContext { + tcx, + map: &mut named_variable_map, + scope: &Scope::Root { opt_parent_item: None }, + }; + match tcx.hir().owner(local_def_id) { + hir::OwnerNode::Item(item) => visitor.visit_item(item), + hir::OwnerNode::ForeignItem(item) => visitor.visit_foreign_item(item), + hir::OwnerNode::TraitItem(item) => { + let scope = + Scope::Root { opt_parent_item: Some(tcx.local_parent(item.owner_id.def_id)) }; + visitor.scope = &scope; + visitor.visit_trait_item(item) + } + hir::OwnerNode::ImplItem(item) => { + let scope = + Scope::Root { opt_parent_item: Some(tcx.local_parent(item.owner_id.def_id)) }; + visitor.scope = &scope; + visitor.visit_impl_item(item) + } + hir::OwnerNode::Crate(_) => {} + } + + let mut rl = ResolveBoundVars::default(); + + for (hir_id, v) in named_variable_map.defs { + let map = rl.defs.entry(hir_id.owner).or_default(); + map.insert(hir_id.local_id, v); + } + for (hir_id, v) in named_variable_map.late_bound_vars { + let map = rl.late_bound_vars.entry(hir_id.owner).or_default(); + map.insert(hir_id.local_id, v); + } + + debug!(?rl.defs); + debug!(?rl.late_bound_vars); + rl +} + +fn late_arg_as_bound_arg<'tcx>( + tcx: TyCtxt<'tcx>, + arg: &ResolvedArg, + param: &GenericParam<'tcx>, +) -> ty::BoundVariableKind { + match arg { + ResolvedArg::LateBound(_, _, def_id) => { + let name = tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local())); + match param.kind { + GenericParamKind::Lifetime { .. } => { + ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name)) + } + GenericParamKind::Type { .. } => { + ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(*def_id, name)) + } + GenericParamKind::Const { .. } => ty::BoundVariableKind::Const, + } + } + _ => bug!("{:?} is not a late argument", arg), + } +} + +impl<'a, 'tcx> BoundVarContext<'a, 'tcx> { + /// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref. + fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) { + let mut scope = self.scope; + let mut supertrait_bound_vars = vec![]; + loop { + match scope { + Scope::Body { .. } | Scope::Root { .. } => { + break (vec![], BinderScopeType::Normal); + } + + Scope::Elision { s, .. } + | Scope::ObjectLifetimeDefault { s, .. } + | Scope::AnonConstBoundary { s } => { + scope = s; + } + + Scope::Supertrait { s, bound_vars } => { + supertrait_bound_vars = bound_vars.clone(); + scope = s; + } + + Scope::TraitRefBoundary { .. } => { + // We should only see super trait lifetimes if there is a `Binder` above + assert!(supertrait_bound_vars.is_empty()); + break (vec![], BinderScopeType::Normal); + } + + Scope::Binder { hir_id, .. } => { + // Nested poly trait refs have the binders concatenated + let mut full_binders = + self.map.late_bound_vars.entry(*hir_id).or_default().clone(); + full_binders.extend(supertrait_bound_vars.into_iter()); + break (full_binders, BinderScopeType::Concatenating); + } + } + } + } + + fn visit_poly_trait_ref_inner( + &mut self, + trait_ref: &'tcx hir::PolyTraitRef<'tcx>, + non_lifetime_binder_allowed: NonLifetimeBinderAllowed, + ) { + debug!("visit_poly_trait_ref(trait_ref={:?})", trait_ref); + + let (mut binders, scope_type) = self.poly_trait_ref_binder_info(); + + let initial_bound_vars = binders.len() as u32; + let mut bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = FxIndexMap::default(); + let binders_iter = + trait_ref.bound_generic_params.iter().enumerate().map(|(late_bound_idx, param)| { + let pair = ResolvedArg::late(initial_bound_vars + late_bound_idx as u32, param); + let r = late_arg_as_bound_arg(self.tcx, &pair.1, param); + bound_vars.insert(pair.0, pair.1); + r + }); + binders.extend(binders_iter); + + if let NonLifetimeBinderAllowed::Deny(where_) = non_lifetime_binder_allowed { + deny_non_region_late_bound(self.tcx, &mut bound_vars, where_); + } + + debug!(?binders); + self.record_late_bound_vars(trait_ref.trait_ref.hir_ref_id, binders); + + // Always introduce a scope here, even if this is in a where clause and + // we introduced the binders around the bounded Ty. In that case, we + // just reuse the concatenation functionality also present in nested trait + // refs. + let scope = Scope::Binder { + hir_id: trait_ref.trait_ref.hir_ref_id, + bound_vars, + s: self.scope, + scope_type, + where_bound_origin: None, + }; + self.with(scope, |this| { + walk_list!(this, visit_generic_param, trait_ref.bound_generic_params); + this.visit_trait_ref(&trait_ref.trait_ref); + }); + } +} + +enum NonLifetimeBinderAllowed { + Deny(&'static str), + Allow, +} + +impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> { + type NestedFilter = nested_filter::OnlyBodies; + + fn nested_visit_map(&mut self) -> Self::Map { + self.tcx.hir() + } + + fn visit_nested_body(&mut self, body: hir::BodyId) { + let body = self.tcx.hir().body(body); + self.with(Scope::Body { id: body.id(), s: self.scope }, |this| { + this.visit_body(body); + }); + } + + fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) { + if let hir::ExprKind::Closure(hir::Closure { + binder, bound_generic_params, fn_decl, .. + }) = e.kind + { + if let &hir::ClosureBinder::For { span: for_sp, .. } = binder { + fn span_of_infer(ty: &hir::Ty<'_>) -> Option<Span> { + struct V(Option<Span>); + + impl<'v> Visitor<'v> for V { + fn visit_ty(&mut self, t: &'v hir::Ty<'v>) { + match t.kind { + _ if self.0.is_some() => (), + hir::TyKind::Infer => { + self.0 = Some(t.span); + } + _ => intravisit::walk_ty(self, t), + } + } + } + + let mut v = V(None); + v.visit_ty(ty); + v.0 + } + + let infer_in_rt_sp = match fn_decl.output { + hir::FnRetTy::DefaultReturn(sp) => Some(sp), + hir::FnRetTy::Return(ty) => span_of_infer(ty), + }; + + let infer_spans = fn_decl + .inputs + .into_iter() + .filter_map(span_of_infer) + .chain(infer_in_rt_sp) + .collect::<Vec<_>>(); + + if !infer_spans.is_empty() { + self.tcx.sess + .struct_span_err( + infer_spans, + "implicit types in closure signatures are forbidden when `for<...>` is present", + ) + .span_label(for_sp, "`for<...>` is here") + .emit(); + } + } + + let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = + bound_generic_params + .iter() + .enumerate() + .map(|(late_bound_idx, param)| { + let pair = ResolvedArg::late(late_bound_idx as u32, param); + let r = late_arg_as_bound_arg(self.tcx, &pair.1, param); + (pair, r) + }) + .unzip(); + + deny_non_region_late_bound(self.tcx, &mut bound_vars, "closures"); + + self.record_late_bound_vars(e.hir_id, binders); + let scope = Scope::Binder { + hir_id: e.hir_id, + bound_vars, + s: self.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + + self.with(scope, |this| { + // a closure has no bounds, so everything + // contained within is scoped within its binder. + intravisit::walk_expr(this, e) + }); + } else { + intravisit::walk_expr(self, e) + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) { + match &item.kind { + hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => { + if let Some(of_trait) = of_trait { + self.record_late_bound_vars(of_trait.hir_ref_id, Vec::default()); + } + } + _ => {} + } + match item.kind { + hir::ItemKind::Fn(_, generics, _) => { + self.visit_early_late(item.hir_id(), generics, |this| { + intravisit::walk_item(this, item); + }); + } + + hir::ItemKind::ExternCrate(_) + | hir::ItemKind::Use(..) + | hir::ItemKind::Macro(..) + | 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. + self.with(Scope::Elision { s: self.scope }, |this| { + intravisit::walk_item(this, item) + }); + } + hir::ItemKind::OpaqueTy(hir::OpaqueTy { + origin: hir::OpaqueTyOrigin::TyAlias, .. + }) => { + // Opaque types are visited when we visit the + // `TyKind::OpaqueDef`, so that they have the lifetimes from + // their parent opaque_ty in scope. + // + // The core idea here is that since OpaqueTys are generated with the impl Trait as + // their owner, we can keep going until we find the Item that owns that. We then + // conservatively add all resolved lifetimes. Otherwise we run into problems in + // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`. + let parent_item = self.tcx.hir().get_parent_item(item.hir_id()); + let resolved_lifetimes: &ResolveBoundVars = + self.tcx.resolve_bound_vars(parent_item); + // We need to add *all* deps, since opaque tys may want them from *us* + for (&owner, defs) in resolved_lifetimes.defs.iter() { + defs.iter().for_each(|(&local_id, region)| { + self.map.defs.insert(hir::HirId { owner, local_id }, *region); + }); + } + for (&owner, late_bound_vars) in resolved_lifetimes.late_bound_vars.iter() { + late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| { + self.record_late_bound_vars( + hir::HirId { owner, local_id }, + late_bound_vars.clone(), + ); + }); + } + } + hir::ItemKind::OpaqueTy(hir::OpaqueTy { + origin: hir::OpaqueTyOrigin::FnReturn(parent) | hir::OpaqueTyOrigin::AsyncFn(parent), + generics, + .. + }) => { + // We want to start our early-bound indices at the end of the parent scope, + // not including any parent `impl Trait`s. + let mut bound_vars = FxIndexMap::default(); + debug!(?generics.params); + for param in generics.params { + let (def_id, reg) = ResolvedArg::early(¶m); + bound_vars.insert(def_id, reg); + } + + let scope = Scope::Root { opt_parent_item: Some(parent) }; + self.with(scope, |this| { + let scope = Scope::Binder { + hir_id: item.hir_id(), + bound_vars, + s: this.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + this.with(scope, |this| { + let scope = Scope::TraitRefBoundary { s: this.scope }; + this.with(scope, |this| intravisit::walk_item(this, item)) + }); + }) + } + hir::ItemKind::TyAlias(_, generics) + | hir::ItemKind::Enum(_, generics) + | hir::ItemKind::Struct(_, generics) + | hir::ItemKind::Union(_, generics) + | hir::ItemKind::Trait(_, _, generics, ..) + | hir::ItemKind::TraitAlias(generics, ..) + | hir::ItemKind::Impl(&hir::Impl { generics, .. }) => { + // These kinds of items have only early-bound lifetime parameters. + let bound_vars = generics.params.iter().map(ResolvedArg::early).collect(); + self.record_late_bound_vars(item.hir_id(), vec![]); + let scope = Scope::Binder { + hir_id: item.hir_id(), + bound_vars, + scope_type: BinderScopeType::Normal, + s: self.scope, + where_bound_origin: None, + }; + self.with(scope, |this| { + let scope = Scope::TraitRefBoundary { s: this.scope }; + this.with(scope, |this| { + intravisit::walk_item(this, item); + }); + }); + } + } + } + + fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) { + match item.kind { + hir::ForeignItemKind::Fn(_, _, generics) => { + self.visit_early_late(item.hir_id(), 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); + } + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) { + match ty.kind { + hir::TyKind::BareFn(c) => { + let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = c + .generic_params + .iter() + .enumerate() + .map(|(late_bound_idx, param)| { + let pair = ResolvedArg::late(late_bound_idx as u32, param); + let r = late_arg_as_bound_arg(self.tcx, &pair.1, param); + (pair, r) + }) + .unzip(); + + deny_non_region_late_bound(self.tcx, &mut bound_vars, "function pointer types"); + + self.record_late_bound_vars(ty.hir_id, binders); + let scope = Scope::Binder { + hir_id: ty.hir_id, + bound_vars, + s: self.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + self.with(scope, |this| { + // a bare fn has no bounds, so everything + // contained within is scoped within its binder. + intravisit::walk_ty(this, ty); + }); + } + hir::TyKind::TraitObject(bounds, lifetime, _) => { + debug!(?bounds, ?lifetime, "TraitObject"); + let scope = Scope::TraitRefBoundary { s: self.scope }; + self.with(scope, |this| { + for bound in bounds { + this.visit_poly_trait_ref_inner( + bound, + NonLifetimeBinderAllowed::Deny("trait object types"), + ); + } + }); + match lifetime.res { + LifetimeName::ImplicitObjectLifetimeDefault => { + // If the user does not write *anything*, we + // use the object lifetime defaulting + // rules. So e.g., `Box<dyn Debug>` becomes + // `Box<dyn Debug + 'static>`. + self.resolve_object_lifetime_default(lifetime) + } + LifetimeName::Infer => { + // If the user writes `'_`, we use the *ordinary* elision + // rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be + // resolved the same as the `'_` in `&'_ Foo`. + // + // cc #48468 + } + LifetimeName::Param(..) | LifetimeName::Static => { + // If the user wrote an explicit name, use that. + self.visit_lifetime(lifetime); + } + LifetimeName::Error => {} + } + } + hir::TyKind::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::OpaqueDef(item_id, lifetimes, _in_trait) => { + // 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 opaque_ty = self.tcx.hir().item(item_id); + match &opaque_ty.kind { + hir::ItemKind::OpaqueTy(hir::OpaqueTy { + origin: hir::OpaqueTyOrigin::TyAlias, + .. + }) => { + intravisit::walk_ty(self, ty); + + // Elided lifetimes are not allowed in non-return + // position impl Trait + let scope = Scope::TraitRefBoundary { s: self.scope }; + self.with(scope, |this| { + let scope = Scope::Elision { s: this.scope }; + this.with(scope, |this| { + intravisit::walk_item(this, opaque_ty); + }) + }); + + return; + } + hir::ItemKind::OpaqueTy(hir::OpaqueTy { + origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..), + .. + }) => {} + 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 { + let hir::GenericArg::Lifetime(lifetime) = lifetime else { + continue + }; + self.visit_lifetime(lifetime); + + // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>` + // 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(); + let Some(ResolvedArg::LateBound(_, _, def_id)) = def else { + continue + }; + let Some(def_id) = def_id.as_local() else { + continue + }; + let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id); + // Ensure that the parent of the def is an item, not HRTB + let parent_id = self.tcx.hir().parent_id(hir_id); + if !parent_id.is_owner() { + struct_span_err!( + self.tcx.sess, + lifetime.ident.span, + E0657, + "`impl Trait` can only capture lifetimes bound at the fn or impl level" + ) + .emit(); + self.uninsert_lifetime_on_error(lifetime, def.unwrap()); + } + if let hir::Node::Item(hir::Item { + kind: hir::ItemKind::OpaqueTy { .. }, .. + }) = self.tcx.hir().get(parent_id) + { + let mut err = self.tcx.sess.struct_span_err( + lifetime.ident.span, + "higher kinded lifetime bounds on nested opaque types are not supported yet", + ); + err.span_note(self.tcx.def_span(def_id), "lifetime declared here"); + err.emit(); + self.uninsert_lifetime_on_error(lifetime, def.unwrap()); + } + } + } + _ => intravisit::walk_ty(self, ty), + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem<'tcx>) { + use self::hir::TraitItemKind::*; + match trait_item.kind { + Fn(_, _) => { + self.visit_early_late(trait_item.hir_id(), &trait_item.generics, |this| { + intravisit::walk_trait_item(this, trait_item) + }); + } + Type(bounds, ty) => { + let generics = &trait_item.generics; + let bound_vars = generics.params.iter().map(ResolvedArg::early).collect(); + self.record_late_bound_vars(trait_item.hir_id(), vec![]); + let scope = Scope::Binder { + hir_id: trait_item.hir_id(), + bound_vars, + s: self.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + self.with(scope, |this| { + let scope = Scope::TraitRefBoundary { s: this.scope }; + this.with(scope, |this| { + 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); + } + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem<'tcx>) { + use self::hir::ImplItemKind::*; + match impl_item.kind { + Fn(..) => self.visit_early_late(impl_item.hir_id(), &impl_item.generics, |this| { + intravisit::walk_impl_item(this, impl_item) + }), + Type(ty) => { + let generics = &impl_item.generics; + let bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = + generics.params.iter().map(ResolvedArg::early).collect(); + self.record_late_bound_vars(impl_item.hir_id(), vec![]); + let scope = Scope::Binder { + hir_id: impl_item.hir_id(), + bound_vars, + s: self.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + self.with(scope, |this| { + let scope = Scope::TraitRefBoundary { s: this.scope }; + this.with(scope, |this| { + this.visit_generics(generics); + this.visit_ty(ty); + }) + }); + } + Const(_, _) => { + // Only methods and types support generics. + assert!(impl_item.generics.params.is_empty()); + intravisit::walk_impl_item(self, impl_item); + } + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) { + match lifetime_ref.res { + hir::LifetimeName::Static => { + self.insert_lifetime(lifetime_ref, ResolvedArg::StaticLifetime) + } + hir::LifetimeName::Param(param_def_id) => { + self.resolve_lifetime_ref(param_def_id, lifetime_ref) + } + // If we've already reported an error, just ignore `lifetime_ref`. + hir::LifetimeName::Error => {} + // Those will be resolved by typechecking. + hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {} + } + } + + fn visit_path(&mut self, path: &hir::Path<'tcx>, hir_id: hir::HirId) { + for (i, segment) in path.segments.iter().enumerate() { + let depth = path.segments.len() - i - 1; + if let Some(args) = segment.args { + self.visit_segment_args(path.res, depth, args); + } + } + if let Res::Def(DefKind::TyParam | DefKind::ConstParam, param_def_id) = path.res { + self.resolve_type_ref(param_def_id.expect_local(), hir_id); + } + } + + fn visit_fn( + &mut self, + fk: intravisit::FnKind<'tcx>, + fd: &'tcx hir::FnDecl<'tcx>, + body_id: hir::BodyId, + _: Span, + _: LocalDefId, + ) { + let output = match fd.output { + hir::FnRetTy::DefaultReturn(_) => None, + hir::FnRetTy::Return(ty) => Some(ty), + }; + self.visit_fn_like_elision(&fd.inputs, output, matches!(fk, intravisit::FnKind::Closure)); + intravisit::walk_fn_kind(self, fk); + self.visit_nested_body(body_id) + } + + fn visit_generics(&mut self, generics: &'tcx hir::Generics<'tcx>) { + let scope = Scope::TraitRefBoundary { s: self.scope }; + self.with(scope, |this| { + for param in generics.params { + match param.kind { + GenericParamKind::Lifetime { .. } => {} + GenericParamKind::Type { default, .. } => { + if let Some(ty) = default { + this.visit_ty(ty); + } + } + GenericParamKind::Const { ty, default } => { + this.visit_ty(ty); + if let Some(default) = default { + this.visit_body(this.tcx.hir().body(default.body)); + } + } + } + } + for predicate in generics.predicates { + match predicate { + &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate { + hir_id, + bounded_ty, + bounds, + bound_generic_params, + origin, + .. + }) => { + let (bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = + bound_generic_params + .iter() + .enumerate() + .map(|(late_bound_idx, param)| { + let pair = ResolvedArg::late(late_bound_idx as u32, param); + let r = late_arg_as_bound_arg(this.tcx, &pair.1, param); + (pair, r) + }) + .unzip(); + this.record_late_bound_vars(hir_id, binders.clone()); + // Even if there are no lifetimes defined here, we still wrap it in a binder + // scope. If there happens to be a nested poly trait ref (an error), that + // will be `Concatenating` anyways, so we don't have to worry about the depth + // being wrong. + let scope = Scope::Binder { + hir_id, + bound_vars, + s: this.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: Some(origin), + }; + this.with(scope, |this| { + this.visit_ty(&bounded_ty); + walk_list!(this, visit_param_bound, bounds); + }) + } + &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate { + lifetime, + bounds, + .. + }) => { + this.visit_lifetime(lifetime); + walk_list!(this, visit_param_bound, bounds); + + if lifetime.res != hir::LifetimeName::Static { + for bound in bounds { + let hir::GenericBound::Outlives(lt) = bound else { + continue; + }; + if lt.res != hir::LifetimeName::Static { + continue; + } + this.insert_lifetime(lt, ResolvedArg::StaticLifetime); + this.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_LIFETIMES, + lifetime.hir_id, + lifetime.ident.span, + format!( + "unnecessary lifetime parameter `{}`", + lifetime.ident + ), + |lint| { + let help = &format!( + "you can use the `'static` lifetime directly, in place of `{}`", + lifetime.ident, + ); + lint.help(help) + }, + ); + } + } + } + &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate { + lhs_ty, + rhs_ty, + .. + }) => { + this.visit_ty(lhs_ty); + this.visit_ty(rhs_ty); + } + } + } + }) + } + + fn visit_param_bound(&mut self, bound: &'tcx hir::GenericBound<'tcx>) { + match bound { + hir::GenericBound::LangItemTrait(_, _, hir_id, _) => { + // FIXME(jackh726): This is pretty weird. `LangItemTrait` doesn't go + // through the regular poly trait ref code, so we don't get another + // chance to introduce a binder. For now, I'm keeping the existing logic + // of "if there isn't a Binder scope above us, add one", but I + // imagine there's a better way to go about this. + let (binders, scope_type) = self.poly_trait_ref_binder_info(); + + self.record_late_bound_vars(*hir_id, binders); + let scope = Scope::Binder { + hir_id: *hir_id, + bound_vars: FxIndexMap::default(), + s: self.scope, + scope_type, + where_bound_origin: None, + }; + self.with(scope, |this| { + intravisit::walk_param_bound(this, bound); + }); + } + _ => intravisit::walk_param_bound(self, bound), + } + } + + fn visit_poly_trait_ref(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) { + self.visit_poly_trait_ref_inner(trait_ref, NonLifetimeBinderAllowed::Allow); + } + + fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) { + self.with(Scope::AnonConstBoundary { s: self.scope }, |this| { + intravisit::walk_anon_const(this, c); + }); + } +} + +fn object_lifetime_default(tcx: TyCtxt<'_>, param_def_id: DefId) -> ObjectLifetimeDefault { + debug_assert_eq!(tcx.def_kind(param_def_id), DefKind::TyParam); + let param_def_id = param_def_id.expect_local(); + let hir::Node::GenericParam(param) = tcx.hir().get_by_def_id(param_def_id) else { + bug!("expected GenericParam for object_lifetime_default"); + }; + match param.source { + hir::GenericParamSource::Generics => { + let parent_def_id = tcx.local_parent(param_def_id); + let generics = tcx.hir().get_generics(parent_def_id).unwrap(); + let param_hir_id = tcx.local_def_id_to_hir_id(param_def_id); + let param = generics.params.iter().find(|p| p.hir_id == param_hir_id).unwrap(); + + // 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. + match param.kind { + GenericParamKind::Type { .. } => { + let mut set = Set1::Empty; + + // Look for `type: ...` where clauses. + for bound in generics.bounds_for_param(param_def_id) { + // Ignore `for<'a> type: ...` as they can change what + // lifetimes mean (although we could "just" handle it). + if !bound.bound_generic_params.is_empty() { + continue; + } + + for bound in bound.bounds { + if let hir::GenericBound::Outlives(lifetime) = bound { + set.insert(lifetime.res); + } + } + } + + match set { + Set1::Empty => ObjectLifetimeDefault::Empty, + Set1::One(hir::LifetimeName::Static) => ObjectLifetimeDefault::Static, + Set1::One(hir::LifetimeName::Param(param_def_id)) => { + ObjectLifetimeDefault::Param(param_def_id.to_def_id()) + } + _ => ObjectLifetimeDefault::Ambiguous, + } + } + _ => { + bug!("object_lifetime_default_raw must only be called on a type parameter") + } + } + } + hir::GenericParamSource::Binder => ObjectLifetimeDefault::Empty, + } +} + +impl<'a, 'tcx> BoundVarContext<'a, 'tcx> { + fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F) + where + F: for<'b> FnOnce(&mut BoundVarContext<'b, 'tcx>), + { + let BoundVarContext { tcx, map, .. } = self; + let mut this = BoundVarContext { tcx: *tcx, map, scope: &wrap_scope }; + let span = debug_span!("scope", scope = ?TruncatedScopeDebug(&this.scope)); + { + let _enter = span.enter(); + f(&mut this); + } + } + + fn record_late_bound_vars(&mut self, hir_id: hir::HirId, binder: Vec<ty::BoundVariableKind>) { + if let Some(old) = self.map.late_bound_vars.insert(hir_id, binder) { + bug!( + "overwrote bound vars for {hir_id:?}:\nold={old:?}\nnew={:?}", + self.map.late_bound_vars[&hir_id] + ) + } + } + + /// 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<F>( + &mut self, + hir_id: hir::HirId, + generics: &'tcx hir::Generics<'tcx>, + walk: F, + ) where + F: for<'b, 'c> FnOnce(&'b mut BoundVarContext<'c, 'tcx>), + { + let mut named_late_bound_vars = 0; + let bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = generics + .params + .iter() + .map(|param| match param.kind { + GenericParamKind::Lifetime { .. } => { + if self.tcx.is_late_bound(param.hir_id) { + let late_bound_idx = named_late_bound_vars; + named_late_bound_vars += 1; + ResolvedArg::late(late_bound_idx, param) + } else { + ResolvedArg::early(param) + } + } + GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => { + ResolvedArg::early(param) + } + }) + .collect(); + + let binders: Vec<_> = generics + .params + .iter() + .filter(|param| { + matches!(param.kind, GenericParamKind::Lifetime { .. }) + && self.tcx.is_late_bound(param.hir_id) + }) + .enumerate() + .map(|(late_bound_idx, param)| { + let pair = ResolvedArg::late(late_bound_idx as u32, param); + late_arg_as_bound_arg(self.tcx, &pair.1, param) + }) + .collect(); + self.record_late_bound_vars(hir_id, binders); + let scope = Scope::Binder { + hir_id, + bound_vars, + s: self.scope, + scope_type: BinderScopeType::Normal, + where_bound_origin: None, + }; + self.with(scope, walk); + } + + #[instrument(level = "debug", skip(self))] + fn resolve_lifetime_ref( + &mut self, + region_def_id: LocalDefId, + lifetime_ref: &'tcx hir::Lifetime, + ) { + // 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 { opt_parent_item } => { + if let Some(parent_item) = opt_parent_item + && let parent_generics = self.tcx.generics_of(parent_item) + && parent_generics.param_def_id_to_index(self.tcx, region_def_id.to_def_id()).is_some() + { + break Some(ResolvedArg::EarlyBound(region_def_id.to_def_id())); + } + break None; + } + + Scope::Binder { ref bound_vars, scope_type, s, where_bound_origin, .. } => { + if let Some(&def) = bound_vars.get(®ion_def_id) { + break Some(def.shifted(late_depth)); + } + match scope_type { + BinderScopeType::Normal => late_depth += 1, + BinderScopeType::Concatenating => {} + } + // Fresh lifetimes in APIT used to be allowed in async fns and forbidden in + // regular fns. + if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin + && let hir::LifetimeName::Param(param_id) = lifetime_ref.res + && let Some(generics) = self.tcx.hir().get_generics(self.tcx.local_parent(param_id)) + && let Some(param) = generics.params.iter().find(|p| p.def_id == param_id) + && param.is_elided_lifetime() + && let hir::IsAsync::NotAsync = self.tcx.asyncness(lifetime_ref.hir_id.owner.def_id) + && !self.tcx.features().anonymous_lifetime_in_impl_trait + { + let mut diag = rustc_session::parse::feature_err( + &self.tcx.sess.parse_sess, + sym::anonymous_lifetime_in_impl_trait, + lifetime_ref.ident.span, + "anonymous lifetimes in `impl Trait` are unstable", + ); + + if let Some(generics) = + self.tcx.hir().get_generics(lifetime_ref.hir_id.owner.def_id) + { + let new_param_sugg = if let Some(span) = + generics.span_for_lifetime_suggestion() + { + (span, "'a, ".to_owned()) + } else { + (generics.span, "<'a>".to_owned()) + }; + + let lifetime_sugg = match lifetime_ref.suggestion_position() { + (hir::LifetimeSuggestionPosition::Normal, span) => (span, "'a".to_owned()), + (hir::LifetimeSuggestionPosition::Ampersand, span) => (span, "'a ".to_owned()), + (hir::LifetimeSuggestionPosition::ElidedPath, span) => (span, "<'a>".to_owned()), + (hir::LifetimeSuggestionPosition::ElidedPathArgument, span) => (span, "'a, ".to_owned()), + (hir::LifetimeSuggestionPosition::ObjectDefault, span) => (span, "+ 'a".to_owned()), + }; + let suggestions = vec![ + lifetime_sugg, + new_param_sugg, + ]; + + diag.span_label( + lifetime_ref.ident.span, + "expected named lifetime parameter", + ); + diag.multipart_suggestion( + "consider introducing a named lifetime parameter", + suggestions, + rustc_errors::Applicability::MaybeIncorrect, + ); + } + + diag.emit(); + return; + } + scope = s; + } + + Scope::Elision { s, .. } + | Scope::ObjectLifetimeDefault { s, .. } + | Scope::Supertrait { s, .. } + | Scope::TraitRefBoundary { s, .. } + | Scope::AnonConstBoundary { s } => { + scope = s; + } + } + }; + + if let Some(mut def) = result { + if let ResolvedArg::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 { owner_id, kind: hir::ItemKind::Fn(..), .. }) + | Node::TraitItem(hir::TraitItem { + owner_id, + kind: hir::TraitItemKind::Fn(..), + .. + }) + | Node::ImplItem(hir::ImplItem { + owner_id, + kind: hir::ImplItemKind::Fn(..), + .. + }) => { + def = ResolvedArg::Free(owner_id.to_def_id(), def.id().unwrap()); + } + Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(closure), .. }) => { + def = ResolvedArg::Free(closure.def_id.to_def_id(), def.id().unwrap()); + } + _ => {} + } + } + + self.insert_lifetime(lifetime_ref, def); + return; + } + + // We may fail to resolve higher-ranked lifetimes that are mentioned by APIT. + // AST-based resolution does not care for impl-trait desugaring, which are the + // responibility of lowering. This may create a mismatch between the resolution + // AST found (`region_def_id`) which points to HRTB, and what HIR allows. + // ``` + // fn foo(x: impl for<'a> Trait<'a, Assoc = impl Copy + 'a>) {} + // ``` + // + // In such case, walk back the binders to diagnose it properly. + let mut scope = self.scope; + loop { + match *scope { + Scope::Binder { + where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), .. + } => { + let mut err = self.tcx.sess.struct_span_err( + lifetime_ref.ident.span, + "`impl Trait` can only mention lifetimes bound at the fn or impl level", + ); + err.span_note(self.tcx.def_span(region_def_id), "lifetime declared here"); + err.emit(); + return; + } + Scope::Root { .. } => break, + Scope::Binder { s, .. } + | Scope::Body { s, .. } + | Scope::Elision { s, .. } + | Scope::ObjectLifetimeDefault { s, .. } + | Scope::Supertrait { s, .. } + | Scope::TraitRefBoundary { s, .. } + | Scope::AnonConstBoundary { s } => { + scope = s; + } + } + } + + self.tcx.sess.delay_span_bug( + lifetime_ref.ident.span, + &format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,), + ); + } + + fn resolve_type_ref(&mut self, param_def_id: LocalDefId, hir_id: hir::HirId) { + // 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 crossed_anon_const = false; + let result = loop { + match *scope { + Scope::Body { s, .. } => { + scope = s; + } + + Scope::Root { opt_parent_item } => { + if let Some(parent_item) = opt_parent_item + && let parent_generics = self.tcx.generics_of(parent_item) + && parent_generics.param_def_id_to_index(self.tcx, param_def_id.to_def_id()).is_some() + { + break Some(ResolvedArg::EarlyBound(param_def_id.to_def_id())); + } + break None; + } + + Scope::Binder { ref bound_vars, scope_type, s, .. } => { + if let Some(&def) = bound_vars.get(¶m_def_id) { + break Some(def.shifted(late_depth)); + } + match scope_type { + BinderScopeType::Normal => late_depth += 1, + BinderScopeType::Concatenating => {} + } + scope = s; + } + + Scope::Elision { s, .. } + | Scope::ObjectLifetimeDefault { s, .. } + | Scope::Supertrait { s, .. } + | Scope::TraitRefBoundary { s, .. } => { + scope = s; + } + + Scope::AnonConstBoundary { s } => { + crossed_anon_const = true; + scope = s; + } + } + }; + + if let Some(def) = result { + if let ResolvedArg::LateBound(..) = def && crossed_anon_const { + let use_span = self.tcx.hir().span(hir_id); + let def_span = self.tcx.def_span(param_def_id); + match self.tcx.def_kind(param_def_id) { + DefKind::ConstParam => { + self.tcx.sess.emit_err(errors::CannotCaptureLateBoundInAnonConst::Const { + use_span, + def_span, + }); + } + DefKind::TyParam => { + self.tcx.sess.emit_err(errors::CannotCaptureLateBoundInAnonConst::Type { + use_span, + def_span, + }); + } + _ => unreachable!(), + } + return; + } + + self.map.defs.insert(hir_id, def); + return; + } + + self.tcx.sess.delay_span_bug( + self.tcx.hir().span(hir_id), + format!("could not resolve {param_def_id:?}"), + ); + } + + #[instrument(level = "debug", skip(self))] + fn visit_segment_args( + &mut self, + res: Res, + depth: usize, + generic_args: &'tcx hir::GenericArgs<'tcx>, + ) { + if generic_args.parenthesized { + self.visit_fn_like_elision( + generic_args.inputs(), + Some(generic_args.bindings[0].ty()), + false, + ); + return; + } + + for arg in generic_args.args { + if let hir::GenericArg::Lifetime(lt) = arg { + self.visit_lifetime(lt); + } + } + + // Figure out if this is a type/trait segment, + // which requires object lifetime defaults. + let type_def_id = match res { + Res::Def(DefKind::AssocTy, def_id) if depth == 1 => Some(self.tcx.parent(def_id)), + Res::Def(DefKind::Variant, def_id) if depth == 0 => Some(self.tcx.parent(def_id)), + Res::Def( + DefKind::Struct + | DefKind::Union + | DefKind::Enum + | DefKind::TyAlias + | DefKind::Trait, + def_id, + ) if depth == 0 => Some(def_id), + _ => None, + }; + + debug!(?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_else(Vec::new, |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::Supertrait { s, .. } + | Scope::TraitRefBoundary { s, .. } + | Scope::AnonConstBoundary { s } => { + scope = s; + } + } + } + }; + + let map = &self.map; + let generics = self.tcx.generics_of(def_id); + + // `type_def_id` points to an item, so there is nothing to inherit generics from. + debug_assert_eq!(generics.parent_count, 0); + + let set_to_region = |set: ObjectLifetimeDefault| match set { + ObjectLifetimeDefault::Empty => { + if in_body { + None + } else { + Some(ResolvedArg::StaticLifetime) + } + } + ObjectLifetimeDefault::Static => Some(ResolvedArg::StaticLifetime), + ObjectLifetimeDefault::Param(param_def_id) => { + // This index can be used with `generic_args` since `parent_count == 0`. + let index = generics.param_def_id_to_index[¶m_def_id] as usize; + generic_args.args.get(index).and_then(|arg| match arg { + GenericArg::Lifetime(lt) => map.defs.get(<.hir_id).copied(), + _ => None, + }) + } + ObjectLifetimeDefault::Ambiguous => None, + }; + generics + .params + .iter() + .filter_map(|param| { + match self.tcx.def_kind(param.def_id) { + // Generic consts don't impose any constraints. + // + // We still store a dummy value here to allow generic parameters + // in an arbitrary order. + DefKind::ConstParam => Some(ObjectLifetimeDefault::Empty), + DefKind::TyParam => Some(self.tcx.object_lifetime_default(param.def_id)), + // We may also get a `Trait` or `TraitAlias` because of how generics `Self` parameter + // works. Ignore it because it can't have a meaningful lifetime default. + DefKind::LifetimeParam | DefKind::Trait | DefKind::TraitAlias => None, + dk => bug!("unexpected def_kind {:?}", dk), + } + }) + .map(set_to_region) + .collect() + }); + + debug!(?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); + i += 1; + } + GenericArg::Infer(inf) => { + self.visit_id(inf.hir_id); + i += 1; + } + } + } + + // 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| matches!(arg, GenericArg::Lifetime(_))); + + // Resolve lifetimes found in the bindings, so either in the type `XX` in `Item = XX` or + // in the trait ref `YY<...>` in `Item: YY<...>`. + for binding in generic_args.bindings { + let scope = Scope::ObjectLifetimeDefault { + lifetime: if has_lifetime_parameter { + None + } else { + Some(ResolvedArg::StaticLifetime) + }, + s: self.scope, + }; + if let Some(type_def_id) = type_def_id { + let bound_vars = + BoundVarContext::supertrait_hrtb_vars(self.tcx, type_def_id, binding.ident); + self.with(scope, |this| { + let scope = Scope::Supertrait { + bound_vars: bound_vars.unwrap_or_default(), + s: this.scope, + }; + this.with(scope, |this| this.visit_assoc_type_binding(binding)); + }); + } else { + self.with(scope, |this| this.visit_assoc_type_binding(binding)); + } + } + } + + /// Returns all the late-bound vars that come into scope from supertrait HRTBs, based on the + /// associated type name and starting trait. + /// For example, imagine we have + /// ```ignore (illustrative) + /// trait Foo<'a, 'b> { + /// type As; + /// } + /// trait Bar<'b>: for<'a> Foo<'a, 'b> {} + /// trait Bar: for<'b> Bar<'b> {} + /// ``` + /// In this case, if we wanted to the supertrait HRTB lifetimes for `As` on + /// the starting trait `Bar`, we would return `Some(['b, 'a])`. + fn supertrait_hrtb_vars( + tcx: TyCtxt<'tcx>, + def_id: DefId, + assoc_name: Ident, + ) -> Option<Vec<ty::BoundVariableKind>> { + let trait_defines_associated_type_named = |trait_def_id: DefId| { + tcx.associated_items(trait_def_id) + .find_by_name_and_kind(tcx, assoc_name, ty::AssocKind::Type, trait_def_id) + .is_some() + }; + + use smallvec::{smallvec, SmallVec}; + let mut stack: SmallVec<[(DefId, SmallVec<[ty::BoundVariableKind; 8]>); 8]> = + smallvec![(def_id, smallvec![])]; + let mut visited: FxHashSet<DefId> = FxHashSet::default(); + loop { + let Some((def_id, bound_vars)) = stack.pop() else { + break None; + }; + // See issue #83753. If someone writes an associated type on a non-trait, just treat it as + // there being no supertrait HRTBs. + match tcx.def_kind(def_id) { + DefKind::Trait | DefKind::TraitAlias | DefKind::Impl { .. } => {} + _ => break None, + } + + if trait_defines_associated_type_named(def_id) { + break Some(bound_vars.into_iter().collect()); + } + let predicates = + tcx.super_predicates_that_define_assoc_type((def_id, Some(assoc_name))); + let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| { + let bound_predicate = pred.kind(); + match bound_predicate.skip_binder() { + ty::PredicateKind::Clause(ty::Clause::Trait(data)) => { + // The order here needs to match what we would get from `subst_supertrait` + let pred_bound_vars = bound_predicate.bound_vars(); + let mut all_bound_vars = bound_vars.clone(); + all_bound_vars.extend(pred_bound_vars.iter()); + let super_def_id = data.trait_ref.def_id; + Some((super_def_id, all_bound_vars)) + } + _ => None, + } + }); + + let obligations = obligations.filter(|o| visited.insert(o.0)); + stack.extend(obligations); + } + } + + #[instrument(level = "debug", skip(self))] + fn visit_fn_like_elision( + &mut self, + inputs: &'tcx [hir::Ty<'tcx>], + output: Option<&'tcx hir::Ty<'tcx>>, + in_closure: bool, + ) { + self.with(Scope::Elision { s: self.scope }, |this| { + for input in inputs { + this.visit_ty(input); + } + if !in_closure && let Some(output) = output { + this.visit_ty(output); + } + }); + if in_closure && let Some(output) = output { + self.visit_ty(output); + } + } + + 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, scope_type, .. } => { + match scope_type { + BinderScopeType::Normal => late_depth += 1, + BinderScopeType::Concatenating => {} + } + scope = s; + } + + Scope::Root { .. } | Scope::Elision { .. } => break ResolvedArg::StaticLifetime, + + Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return, + + Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l, + + Scope::Supertrait { s, .. } + | Scope::TraitRefBoundary { s, .. } + | Scope::AnonConstBoundary { s } => { + scope = s; + } + } + }; + self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth)); + } + + #[instrument(level = "debug", skip(self))] + fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: ResolvedArg) { + debug!(span = ?lifetime_ref.ident.span); + self.map.defs.insert(lifetime_ref.hir_id, def); + } + + /// 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: ResolvedArg, + ) { + 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 +/// `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 is_late_bound_map( + tcx: TyCtxt<'_>, + owner_id: hir::OwnerId, +) -> Option<&FxIndexSet<hir::ItemLocalId>> { + let decl = tcx.hir().fn_decl_by_hir_id(owner_id.into())?; + let generics = tcx.hir().get_generics(owner_id.def_id)?; + + let mut late_bound = FxIndexSet::default(); + + let mut constrained_by_input = ConstrainedCollector { regions: Default::default(), tcx }; + 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!(?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); + debug!(?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, + } + + // appears in the where clauses? early-bound. + if appears_in_where_clause.regions.contains(¶m.def_id) { + continue; + } + + // does not appear in the inputs, but appears in the return type? early-bound. + if !constrained_by_input.regions.contains(¶m.def_id) + && appears_in_output.regions.contains(¶m.def_id) + { + continue; + } + + debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.def_id); + + let inserted = late_bound.insert(param.hir_id.local_id); + assert!(inserted, "visited lifetime {:?} twice", param.def_id); + } + + debug!(?late_bound); + return Some(tcx.arena.alloc(late_bound)); + + /// Visits a `ty::Ty` collecting information about what generic parameters are constrained. + /// + /// The visitor does not operate on `hir::Ty` so that it can be called on the rhs of a `type Alias<...> = ...;` + /// which may live in a separate crate so there would not be any hir available. Instead we use the `type_of` + /// query to obtain a `ty::Ty` which will be present even in cross crate scenarios. It also naturally + /// handles cycle detection as we go through the query system. + /// + /// This is necessary in the first place for the following case: + /// ``` + /// type Alias<'a, T> = <T as Trait<'a>>::Assoc; + /// fn foo<'a>(_: Alias<'a, ()>) -> Alias<'a, ()> { ... } + /// ``` + /// + /// If we conservatively considered `'a` unconstrained then we could break users who had written code before + /// we started correctly handling aliases. If we considered `'a` constrained then it would become late bound + /// causing an error during astconv as the `'a` is not constrained by the input type `<() as Trait<'a>>::Assoc` + /// but appears in the output type `<() as Trait<'a>>::Assoc`. + /// + /// We must therefore "look into" the `Alias` to see whether we should consider `'a` constrained or not. + /// + /// See #100508 #85533 #47511 for additional context + struct ConstrainedCollectorPostAstConv { + arg_is_constrained: Box<[bool]>, + } + + use std::ops::ControlFlow; + use ty::Ty; + impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ConstrainedCollectorPostAstConv { + fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<!> { + match t.kind() { + ty::Param(param_ty) => { + self.arg_is_constrained[param_ty.index as usize] = true; + } + ty::Alias(ty::Projection, _) => return ControlFlow::Continue(()), + _ => (), + } + t.super_visit_with(self) + } + + fn visit_const(&mut self, _: ty::Const<'tcx>) -> ControlFlow<!> { + ControlFlow::Continue(()) + } + + fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<!> { + debug!("r={:?}", r.kind()); + if let ty::RegionKind::ReEarlyBound(region) = r.kind() { + self.arg_is_constrained[region.index as usize] = true; + } + + ControlFlow::Continue(()) + } + } + + struct ConstrainedCollector<'tcx> { + tcx: TyCtxt<'tcx>, + regions: FxHashSet<LocalDefId>, + } + + impl<'v> Visitor<'v> for ConstrainedCollector<'_> { + 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, + hir::Path { res: Res::Def(DefKind::TyAlias, alias_def), segments, span }, + )) => { + // See comments on `ConstrainedCollectorPostAstConv` for why this arm does not just consider + // substs to be unconstrained. + let generics = self.tcx.generics_of(alias_def); + let mut walker = ConstrainedCollectorPostAstConv { + arg_is_constrained: vec![false; generics.params.len()].into_boxed_slice(), + }; + walker.visit_ty(self.tcx.type_of(alias_def).subst_identity()); + + match segments.last() { + Some(hir::PathSegment { args: Some(args), .. }) => { + let tcx = self.tcx; + for constrained_arg in + args.args.iter().enumerate().flat_map(|(n, arg)| { + match walker.arg_is_constrained.get(n) { + Some(true) => Some(arg), + Some(false) => None, + None => { + tcx.sess.delay_span_bug( + *span, + format!( + "Incorrect generic arg count for alias {:?}", + alias_def + ), + ); + None + } + } + }) + { + self.visit_generic_arg(constrained_arg); + } + } + Some(_) => (), + None => bug!("Path with no segments or self type"), + } + } + + hir::TyKind::Path(hir::QPath::Resolved(None, 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(last_segment); + } + } + + _ => { + intravisit::walk_ty(self, ty); + } + } + } + + fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) { + if let hir::LifetimeName::Param(def_id) = lifetime_ref.res { + self.regions.insert(def_id); + } + } + } + + #[derive(Default)] + struct AllCollector { + regions: FxHashSet<LocalDefId>, + } + + impl<'v> Visitor<'v> for AllCollector { + fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) { + if let hir::LifetimeName::Param(def_id) = lifetime_ref.res { + self.regions.insert(def_id); + } + } + } +} + +pub fn deny_non_region_late_bound( + tcx: TyCtxt<'_>, + bound_vars: &mut FxIndexMap<LocalDefId, ResolvedArg>, + where_: &str, +) { + let mut first = true; + + for (var, arg) in bound_vars { + let Node::GenericParam(param) = tcx.hir().get_by_def_id(*var) else { + bug!(); + }; + + let what = match param.kind { + hir::GenericParamKind::Type { .. } => "type", + hir::GenericParamKind::Const { .. } => "const", + hir::GenericParamKind::Lifetime { .. } => continue, + }; + + let mut diag = tcx.sess.struct_span_err( + param.span, + format!("late-bound {what} parameter not allowed on {where_}"), + ); + + let guar = if tcx.features().non_lifetime_binders && first { + diag.emit() + } else { + diag.delay_as_bug() + }; + + first = false; + *arg = ResolvedArg::Error(guar); + } +} |