+++ /dev/null
-//! 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_lifetime::*;
-use rustc_middle::ty::{self, DefIdTree, TyCtxt, TypeSuperVisitable, TypeVisitor};
-use rustc_span::def_id::DefId;
-use rustc_span::symbol::{sym, Ident};
-use rustc_span::Span;
-use std::fmt;
-
-trait RegionExt {
- fn early(param: &GenericParam<'_>) -> (LocalDefId, Region);
-
- fn late(index: u32, param: &GenericParam<'_>) -> (LocalDefId, Region);
-
- fn id(&self) -> Option<DefId>;
-
- fn shifted(self, amount: u32) -> Region;
-}
-
-impl RegionExt for Region {
- fn early(param: &GenericParam<'_>) -> (LocalDefId, Region) {
- debug!("Region::early: def_id={:?}", param.def_id);
- (param.def_id, Region::EarlyBound(param.def_id.to_def_id()))
- }
-
- fn late(idx: u32, param: &GenericParam<'_>) -> (LocalDefId, Region) {
- let depth = ty::INNERMOST;
- debug!(
- "Region::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
- idx, param, depth, param.def_id,
- );
- (param.def_id, Region::LateBound(depth, idx, param.def_id.to_def_id()))
- }
-
- fn id(&self) -> Option<DefId> {
- match *self {
- Region::Static => None,
-
- Region::EarlyBound(id) | Region::LateBound(_, _, id) | Region::Free(_, id) => Some(id),
- }
- }
-
- fn shifted(self, amount: u32) -> Region {
- match self {
- Region::LateBound(debruijn, idx, id) => {
- Region::LateBound(debruijn.shifted_in(amount), idx, id)
- }
- _ => 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(Debug, Default)]
-struct NamedRegionMap {
- // maps from every use of a named (not anonymous) lifetime to a
- // `Region` describing how that region is bound
- defs: HirIdMap<Region>,
-
- // 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 LifetimeContext<'a, 'tcx> {
- tcx: TyCtxt<'tcx>,
- map: &'a mut NamedRegionMap,
- 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.
- lifetimes: FxIndexMap<LocalDefId, Region>,
-
- 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<Region>,
- 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 {
- lifetimes: Vec<ty::BoundVariableKind>,
- s: ScopeRef<'a>,
- },
-
- TraitRefBoundary {
- 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 { lifetimes, scope_type, hir_id, where_bound_origin, s: _ } => f
- .debug_struct("Binder")
- .field("lifetimes", lifetimes)
- .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 { lifetimes, s: _ } => f
- .debug_struct("Supertrait")
- .field("lifetimes", lifetimes)
- .field("s", &"..")
- .finish(),
- Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").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_lifetimes,
-
- named_region_map: |tcx, id| tcx.resolve_lifetimes(id).defs.get(&id),
- is_late_bound_map,
- object_lifetime_default,
- late_bound_vars_map: |tcx, id| tcx.resolve_lifetimes(id).late_bound_vars.get(&id),
-
- ..*providers
- };
-}
-
-/// Computes the `ResolveLifetimes` map that contains data for an entire `Item`.
-/// You should not read the result of this query directly, but rather use
-/// `named_region_map`, `is_late_bound_map`, etc.
-#[instrument(level = "debug", skip(tcx))]
-fn resolve_lifetimes(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveLifetimes {
- let mut named_region_map =
- NamedRegionMap { defs: Default::default(), late_bound_vars: Default::default() };
- let mut visitor = LifetimeContext {
- tcx,
- map: &mut named_region_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 = 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, v) in named_region_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_region_as_bound_region(tcx: TyCtxt<'_>, region: &Region) -> ty::BoundVariableKind {
- match region {
- Region::LateBound(_, _, def_id) => {
- let name = tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id.expect_local()));
- ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
- }
- _ => bug!("{:?} is not a late region", region),
- }
-}
-
-impl<'a, 'tcx> LifetimeContext<'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_lifetimes = vec![];
- loop {
- match scope {
- Scope::Body { .. } | Scope::Root { .. } => {
- break (vec![], BinderScopeType::Normal);
- }
-
- Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
- scope = s;
- }
-
- Scope::Supertrait { s, lifetimes } => {
- supertrait_lifetimes = lifetimes.clone();
- scope = s;
- }
-
- Scope::TraitRefBoundary { .. } => {
- // We should only see super trait lifetimes if there is a `Binder` above
- assert!(supertrait_lifetimes.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_lifetimes.into_iter());
- break (full_binders, BinderScopeType::Concatenating);
- }
- }
- }
- }
-}
-impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'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 (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) =
- bound_generic_params
- .iter()
- .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
- .enumerate()
- .map(|(late_bound_idx, param)| {
- let pair = Region::late(late_bound_idx as u32, param);
- let r = late_region_as_bound_region(self.tcx, &pair.1);
- (pair, r)
- })
- .unzip();
-
- self.record_late_bound_vars(e.hir_id, binders);
- let scope = Scope::Binder {
- hir_id: e.hir_id,
- lifetimes,
- 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: &ResolveLifetimes = self.tcx.resolve_lifetimes(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(_) | hir::OpaqueTyOrigin::AsyncFn(_),
- 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 lifetimes = FxIndexMap::default();
- debug!(?generics.params);
- for param in generics.params {
- match param.kind {
- GenericParamKind::Lifetime { .. } => {
- let (def_id, reg) = Region::early(¶m);
- lifetimes.insert(def_id, reg);
- }
- GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {}
- }
- }
-
- let scope = Scope::Binder {
- hir_id: item.hir_id(),
- lifetimes,
- 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| 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 lifetimes = generics
- .params
- .iter()
- .filter_map(|param| match param.kind {
- GenericParamKind::Lifetime { .. } => Some(Region::early(param)),
- GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
- })
- .collect();
- self.record_late_bound_vars(item.hir_id(), vec![]);
- let scope = Scope::Binder {
- hir_id: item.hir_id(),
- lifetimes,
- 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 (lifetimes, binders): (FxIndexMap<LocalDefId, Region>, Vec<_>) = c
- .generic_params
- .iter()
- .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
- .enumerate()
- .map(|(late_bound_idx, param)| {
- let pair = Region::late(late_bound_idx as u32, param);
- let r = late_region_as_bound_region(self.tcx, &pair.1);
- (pair, r)
- })
- .unzip();
- self.record_late_bound_vars(ty.hir_id, binders);
- let scope = Scope::Binder {
- hir_id: ty.hir_id,
- lifetimes,
- 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(bound);
- }
- });
- 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(Region::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 lifetimes = generics
- .params
- .iter()
- .filter_map(|param| match param.kind {
- GenericParamKind::Lifetime { .. } => Some(Region::early(param)),
- GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
- })
- .collect();
- self.record_late_bound_vars(trait_item.hir_id(), vec![]);
- let scope = Scope::Binder {
- hir_id: trait_item.hir_id(),
- lifetimes,
- 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 lifetimes: FxIndexMap<LocalDefId, Region> = generics
- .params
- .iter()
- .filter_map(|param| match param.kind {
- GenericParamKind::Lifetime { .. } => Some(Region::early(param)),
- GenericParamKind::Const { .. } | GenericParamKind::Type { .. } => None,
- })
- .collect();
- self.record_late_bound_vars(impl_item.hir_id(), vec![]);
- let scope = Scope::Binder {
- hir_id: impl_item.hir_id(),
- lifetimes,
- 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, Region::Static),
- 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::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);
- }
- }
- }
-
- fn visit_fn(
- &mut self,
- fk: intravisit::FnKind<'tcx>,
- fd: &'tcx hir::FnDecl<'tcx>,
- body_id: hir::BodyId,
- _: Span,
- _: hir::HirId,
- ) {
- 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 lifetimes: FxIndexMap<LocalDefId, Region> =
- bound_generic_params
- .iter()
- .filter(|param| {
- matches!(param.kind, GenericParamKind::Lifetime { .. })
- })
- .enumerate()
- .map(|(late_bound_idx, param)| {
- Region::late(late_bound_idx as u32, param)
- })
- .collect();
- let binders: Vec<_> =
- lifetimes
- .iter()
- .map(|(_, region)| {
- late_region_as_bound_region(this.tcx, region)
- })
- .collect();
- 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,
- lifetimes,
- 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, Region::Static);
- this.tcx
- .sess
- .struct_span_warn(
- lifetime.ident.span,
- &format!(
- "unnecessary lifetime parameter `{}`",
- lifetime.ident,
- ),
- )
- .help(&format!(
- "you can use the `'static` lifetime directly, in place of `{}`",
- lifetime.ident,
- ))
- .emit();
- }
- }
- }
- &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,
- lifetimes: 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>) {
- 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 lifetimes: FxIndexMap<LocalDefId, Region> = FxIndexMap::default();
- let binders_iter = trait_ref
- .bound_generic_params
- .iter()
- .filter(|param| matches!(param.kind, GenericParamKind::Lifetime { .. }))
- .enumerate()
- .map(|(late_bound_idx, param)| {
- let pair = Region::late(initial_bound_vars + late_bound_idx as u32, param);
- let r = late_region_as_bound_region(self.tcx, &pair.1);
- lifetimes.insert(pair.0, pair.1);
- r
- });
- binders.extend(binders_iter);
-
- 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,
- lifetimes,
- 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);
- });
- }
-}
-
-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 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")
- }
- }
-}
-
-impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
- fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
- where
- F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
- {
- let LifetimeContext { tcx, map, .. } = self;
- let mut this = LifetimeContext { 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 LifetimeContext<'c, 'tcx>),
- {
- let mut named_late_bound_vars = 0;
- let lifetimes: FxIndexMap<LocalDefId, Region> = generics
- .params
- .iter()
- .filter_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;
- Some(Region::late(late_bound_idx, param))
- } else {
- Some(Region::early(param))
- }
- }
- GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => None,
- })
- .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 = Region::late(late_bound_idx as u32, param);
- late_region_as_bound_region(self.tcx, &pair.1)
- })
- .collect();
- self.record_late_bound_vars(hir_id, binders);
- let scope = Scope::Binder {
- hir_id,
- lifetimes,
- 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.contains_key(®ion_def_id.to_def_id())
- {
- break Some(Region::EarlyBound(region_def_id.to_def_id()));
- }
- break None;
- }
-
- Scope::Binder { ref lifetimes, scope_type, s, where_bound_origin, .. } => {
- if let Some(&def) = lifetimes.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 = 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(..), .. })
- | Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(..), .. }) => {
- let scope = self.tcx.hir().local_def_id(fn_id);
- def = Region::Free(scope.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 = s;
- }
- }
- }
-
- self.tcx.sess.delay_span_bug(
- lifetime_ref.ident.span,
- &format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,),
- );
- }
-
- #[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 = 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(Region::Static)
- }
- }
- ObjectLifetimeDefault::Static => Some(Region::Static),
- 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(Region::Static) },
- s: self.scope,
- };
- if let Some(type_def_id) = type_def_id {
- let lifetimes = LifetimeContext::supertrait_hrtb_lifetimes(
- self.tcx,
- type_def_id,
- binding.ident,
- );
- self.with(scope, |this| {
- let scope = Scope::Supertrait {
- lifetimes: lifetimes.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_lifetimes(
- 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 Region::Static,
-
- Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
-
- Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => break l,
-
- Scope::Supertrait { s, .. } | Scope::TraitRefBoundary { 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: Region) {
- 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: 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
-/// `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<'_>, def_id: LocalDefId) -> Option<&FxIndexSet<LocalDefId>> {
- let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
- let decl = tcx.hir().fn_decl_by_hir_id(hir_id)?;
- let generics = tcx.hir().get_generics(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,
- }
-
- let param_def_id = tcx.hir().local_def_id(param.hir_id);
-
- // 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.hir_id);
-
- let inserted = late_bound.insert(param_def_id);
- assert!(inserted, "visited lifetime {:?} twice", param.hir_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<'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));
-
- 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);
- }
- }
- }
-}
projects / rustc.git / blobdiff