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rust / rust / HEAD / . / compiler / rustc_hir_analysis / src / collect / resolve_bound_vars.rs
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//! 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 std::cell::RefCell;
use std::fmt;
use std::ops::ControlFlow;
use rustc_ast::visit::walk_list;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::definitions::{DefPathData, DisambiguatorState};
use rustc_hir::intravisit::{self, InferKind, Visitor, VisitorExt};
use rustc_hir::{
self as hir, AmbigArg, GenericArg, GenericParam, GenericParamKind, HirId, LifetimeKind, Node,
};
use rustc_macros::extension;
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::resolve_bound_vars::*;
use rustc_middle::query::Providers;
use rustc_middle::ty::{self, TyCtxt, TypeSuperVisitable, TypeVisitor};
use rustc_middle::{bug, span_bug};
use rustc_span::def_id::{DefId, LocalDefId};
use rustc_span::{Ident, Span, sym};
use tracing::{debug, debug_span, instrument};
use crate::errors;
#[extension(trait RegionExt)]
impl ResolvedArg {
fn early(param: &GenericParam<'_>) -> ResolvedArg {
ResolvedArg::EarlyBound(param.def_id)
}
fn late(idx: u32, param: &GenericParam<'_>) -> ResolvedArg {
ResolvedArg::LateBound(ty::INNERMOST, idx, param.def_id)
}
fn id(&self) -> Option<LocalDefId> {
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,
}
}
}
struct BoundVarContext<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
rbv: &'a mut ResolveBoundVars,
disambiguator: &'a mut DisambiguatorState,
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: 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>,
},
/// 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>,
},
/// Remap lifetimes that appear in opaque types to fresh lifetime parameters. Given:
/// `fn foo<'a>() -> impl MyTrait<'a> { ... }`
///
/// HIR tells us that `'a` refer to the lifetime bound on `foo`.
/// However, typeck and borrowck for opaques work based on using a new generic type.
/// `type MyAnonTy<'b> = impl MyTrait<'b>;`
///
/// This scope collects the mapping `'a -> 'b`.
Opaque {
/// The opaque type we are traversing.
def_id: LocalDefId,
/// Mapping from each captured lifetime `'a` to the duplicate generic parameter `'b`.
captures: &'a RefCell<FxIndexMap<ResolvedArg, LocalDefId>>,
s: ScopeRef<'a>,
},
/// Disallows capturing late-bound vars 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.
LateBoundary {
s: ScopeRef<'a>,
what: &'static str,
deny_late_regions: bool,
},
Root {
opt_parent_item: Option<LocalDefId>,
},
}
impl<'a> Scope<'a> {
// A helper for debugging scopes without printing parent scopes
fn debug_truncated(&self) -> impl fmt::Debug {
fmt::from_fn(move |f| match self {
Self::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(),
Self::Opaque { captures, def_id, s: _ } => f
.debug_struct("Opaque")
.field("def_id", def_id)
.field("captures", &captures.borrow())
.field("s", &"..")
.finish(),
Self::Body { id, s: _ } => {
f.debug_struct("Body").field("id", id).field("s", &"..").finish()
}
Self::ObjectLifetimeDefault { lifetime, s: _ } => f
.debug_struct("ObjectLifetimeDefault")
.field("lifetime", lifetime)
.field("s", &"..")
.finish(),
Self::Supertrait { bound_vars, s: _ } => f
.debug_struct("Supertrait")
.field("bound_vars", bound_vars)
.field("s", &"..")
.finish(),
Self::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
Self::LateBoundary { s: _, what, deny_late_regions } => f
.debug_struct("LateBoundary")
.field("what", what)
.field("deny_late_regions", deny_late_regions)
.finish(),
Self::Root { opt_parent_item } => {
f.debug_struct("Root").field("opt_parent_item", &opt_parent_item).finish()
}
})
}
}
#[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,
}
type ScopeRef<'a> = &'a Scope<'a>;
/// Adds query implementations to the [Providers] vtable, see [`rustc_middle::query`]
pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers {
resolve_bound_vars,
named_variable_map: |tcx, id| &tcx.resolve_bound_vars(id).defs,
is_late_bound_map,
object_lifetime_default,
late_bound_vars_map: |tcx, id| &tcx.resolve_bound_vars(id).late_bound_vars,
opaque_captured_lifetimes: |tcx, id| {
&tcx.resolve_bound_vars(tcx.local_def_id_to_hir_id(id).owner)
.opaque_captured_lifetimes
.get(&id)
.map_or(&[][..], |x| &x[..])
},
..*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`, `late_bound_vars_map`, etc.
#[instrument(level = "debug", skip(tcx))]
fn resolve_bound_vars(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveBoundVars {
let mut rbv = ResolveBoundVars::default();
let mut visitor = BoundVarContext {
tcx,
rbv: &mut rbv,
scope: &Scope::Root { opt_parent_item: None },
disambiguator: &mut DisambiguatorState::new(),
};
match tcx.hir_owner_node(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(_) => {}
hir::OwnerNode::Synthetic => unreachable!(),
}
debug!(?rbv.defs);
debug!(?rbv.late_bound_vars);
debug!(?rbv.opaque_captured_lifetimes);
rbv
}
fn late_arg_as_bound_arg<'tcx>(param: &GenericParam<'tcx>) -> ty::BoundVariableKind {
let def_id = param.def_id.to_def_id();
match param.kind {
GenericParamKind::Lifetime { .. } => {
ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(def_id))
}
GenericParamKind::Type { .. } => ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(def_id)),
GenericParamKind::Const { .. } => ty::BoundVariableKind::Const,
}
}
/// Turn a [`ty::GenericParamDef`] into a bound arg. Generally, this should only
/// be used when turning early-bound vars into late-bound vars when lowering
/// return type notation.
fn generic_param_def_as_bound_arg(param: &ty::GenericParamDef) -> ty::BoundVariableKind {
match param.kind {
ty::GenericParamDefKind::Lifetime => {
ty::BoundVariableKind::Region(ty::BoundRegionKind::Named(param.def_id))
}
ty::GenericParamDefKind::Type { .. } => {
ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(param.def_id))
}
ty::GenericParamDefKind::Const { .. } => ty::BoundVariableKind::Const,
}
}
/// Whether this opaque always captures lifetimes in scope.
/// Right now, this is all RPITIT and TAITs, and when the opaque
/// is coming from a span corresponding to edition 2024.
fn opaque_captures_all_in_scope_lifetimes<'tcx>(opaque: &'tcx hir::OpaqueTy<'tcx>) -> bool {
match opaque.origin {
// if the opaque has the `use<...>` syntax, the user is telling us that they only want
// to account for those lifetimes, so do not try to be clever.
_ if opaque.bounds.iter().any(|bound| matches!(bound, hir::GenericBound::Use(..))) => false,
hir::OpaqueTyOrigin::AsyncFn { .. } | hir::OpaqueTyOrigin::TyAlias { .. } => true,
_ if opaque.span.at_least_rust_2024() => true,
hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl, .. } => in_trait_or_impl.is_some(),
}
}
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::Opaque { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::LateBoundary { 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
// though this may happen when we call `poly_trait_ref_binder_info` with
// an (erroneous, #113423) associated return type bound in an impl header.
if !supertrait_bound_vars.is_empty() {
self.tcx.dcx().delayed_bug(format!(
"found supertrait lifetimes without a binder to append \
them to: {supertrait_bound_vars:?}"
));
}
break (vec![], BinderScopeType::Normal);
}
Scope::Binder { hir_id, .. } => {
// Nested poly trait refs have the binders concatenated
let mut full_binders =
self.rbv.late_bound_vars.get_mut_or_insert_default(hir_id.local_id).clone();
full_binders.extend(supertrait_bound_vars);
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 arg = ResolvedArg::late(initial_bound_vars + late_bound_idx as u32, param);
bound_vars.insert(param.def_id, arg);
late_arg_as_bound_arg(param)
});
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 maybe_tcx(&mut self) -> Self::MaybeTyCtxt {
self.tcx
}
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> {
/// Look for `_` anywhere in the signature of a `for<> ||` closure.
/// This is currently disallowed.
struct FindInferInClosureWithBinder;
impl<'v> Visitor<'v> for FindInferInClosureWithBinder {
type Result = ControlFlow<Span>;
fn visit_infer(
&mut self,
_inf_id: HirId,
inf_span: Span,
_kind: InferKind<'v>,
) -> Self::Result {
ControlFlow::Break(inf_span)
}
}
FindInferInClosureWithBinder.visit_ty_unambig(ty).break_value()
}
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
.dcx()
.emit_err(errors::ClosureImplicitHrtb { spans: infer_spans, for_sp });
}
}
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) =
bound_generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
(
(param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
late_arg_as_bound_arg(param),
)
})
.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)
}
}
/// Resolve the lifetimes inside the opaque type, and save them into
/// `opaque_captured_lifetimes`.
///
/// This method has special handling for opaques that capture all lifetimes,
/// like async desugaring.
#[instrument(level = "debug", skip(self))]
fn visit_opaque_ty(&mut self, opaque: &'tcx rustc_hir::OpaqueTy<'tcx>) {
let captures = RefCell::new(FxIndexMap::default());
let capture_all_in_scope_lifetimes = opaque_captures_all_in_scope_lifetimes(opaque);
if capture_all_in_scope_lifetimes {
let tcx = self.tcx;
let lifetime_ident = |def_id: LocalDefId| {
let name = tcx.item_name(def_id.to_def_id());
let span = tcx.def_span(def_id);
Ident::new(name, span)
};
// We list scopes outwards, this causes us to see lifetime parameters in reverse
// declaration order. In order to make it consistent with what `generics_of` might
// give, we will reverse the IndexMap after early captures.
let mut late_depth = 0;
let mut scope = self.scope;
let mut opaque_capture_scopes = vec![(opaque.def_id, &captures)];
loop {
match *scope {
Scope::Binder { ref bound_vars, scope_type, s, .. } => {
for (&original_lifetime, &def) in bound_vars.iter().rev() {
if let DefKind::LifetimeParam = self.tcx.def_kind(original_lifetime) {
let def = def.shifted(late_depth);
let ident = lifetime_ident(original_lifetime);
self.remap_opaque_captures(&opaque_capture_scopes, def, ident);
}
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::Root { mut opt_parent_item } => {
while let Some(parent_item) = opt_parent_item {
let parent_generics = self.tcx.generics_of(parent_item);
for param in parent_generics.own_params.iter().rev() {
if let ty::GenericParamDefKind::Lifetime = param.kind {
let def = ResolvedArg::EarlyBound(param.def_id.expect_local());
let ident = lifetime_ident(param.def_id.expect_local());
self.remap_opaque_captures(&opaque_capture_scopes, def, ident);
}
}
opt_parent_item = parent_generics.parent.and_then(DefId::as_local);
}
break;
}
Scope::Opaque { captures, def_id, s } => {
opaque_capture_scopes.push((def_id, captures));
late_depth = 0;
scope = s;
}
Scope::Body { .. } => {
bug!("{:?}", scope)
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
captures.borrow_mut().reverse();
}
let scope = Scope::Opaque { captures: &captures, def_id: opaque.def_id, s: self.scope };
self.with(scope, |this| {
let scope = Scope::TraitRefBoundary { s: this.scope };
this.with(scope, |this| {
let scope = Scope::LateBoundary {
s: this.scope,
what: "nested `impl Trait`",
// We can capture late-bound regions; we just don't duplicate
// lifetime or const params, so we can't allow those.
deny_late_regions: false,
};
this.with(scope, |this| intravisit::walk_opaque_ty(this, opaque))
})
});
let captures = captures.into_inner().into_iter().collect();
debug!(?captures);
self.rbv.opaque_captured_lifetimes.insert(opaque.def_id, captures);
}
#[instrument(level = "debug", skip(self))]
fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
if let hir::ItemKind::Impl(impl_) = item.kind
&& let Some(of_trait) = impl_.of_trait
{
self.record_late_bound_vars(of_trait.trait_ref.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::Static(..)
| hir::ItemKind::GlobalAsm { .. } => {
// These sorts of items have no lifetime parameters at all.
intravisit::walk_item(self, item);
}
hir::ItemKind::TyAlias(_, generics, _)
| hir::ItemKind::Const(_, 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.
self.visit_early(item.hir_id(), generics, |this| intravisit::walk_item(this, item));
}
}
}
fn visit_precise_capturing_arg(
&mut self,
arg: &'tcx hir::PreciseCapturingArg<'tcx>,
) -> Self::Result {
match *arg {
hir::PreciseCapturingArg::Lifetime(lt) => match lt.kind {
LifetimeKind::Param(def_id) => {
self.resolve_lifetime_ref(def_id, lt);
}
LifetimeKind::Error => {}
LifetimeKind::ImplicitObjectLifetimeDefault
| LifetimeKind::Infer
| LifetimeKind::Static => {
self.tcx.dcx().emit_err(errors::BadPreciseCapture {
span: lt.ident.span,
kind: "lifetime",
found: format!("`{}`", lt.ident.name),
});
}
},
hir::PreciseCapturingArg::Param(param) => match param.res {
Res::Def(DefKind::TyParam | DefKind::ConstParam, def_id)
| Res::SelfTyParam { trait_: def_id } => {
self.resolve_type_ref(def_id.expect_local(), param.hir_id);
}
Res::SelfTyAlias { alias_to, .. } => {
self.tcx.dcx().emit_err(errors::PreciseCaptureSelfAlias {
span: param.ident.span,
self_span: self.tcx.def_span(alias_to),
what: self.tcx.def_descr(alias_to),
});
}
res => {
self.tcx.dcx().span_delayed_bug(
param.ident.span,
format!("expected type or const param, found {res:?}"),
);
}
},
}
}
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, AmbigArg>) {
match ty.kind {
hir::TyKind::FnPtr(c) => {
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = c
.generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
(
(param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
late_arg_as_bound_arg(param),
)
})
.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 FnPtr has no bounds, so everything within is scoped within its binder
intravisit::walk_ty(this, ty);
});
}
hir::TyKind::UnsafeBinder(binder) => {
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) =
binder
.generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
(
(param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
late_arg_as_bound_arg(param),
)
})
.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| {
// everything within is scoped within its binder
intravisit::walk_ty(this, ty);
});
}
hir::TyKind::TraitObject(bounds, lifetime) => {
let lifetime = lifetime.pointer();
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.kind {
LifetimeKind::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)
}
LifetimeKind::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
}
LifetimeKind::Param(..) | LifetimeKind::Static => {
// If the user wrote an explicit name, use that.
self.visit_lifetime(&*lifetime);
}
LifetimeKind::Error => {}
}
}
hir::TyKind::Ref(lifetime_ref, ref mt) => {
self.visit_lifetime(lifetime_ref);
let scope = Scope::ObjectLifetimeDefault {
lifetime: self.rbv.defs.get(&lifetime_ref.hir_id.local_id).cloned(),
s: self.scope,
};
self.with(scope, |this| this.visit_ty_unambig(mt.ty));
}
hir::TyKind::TraitAscription(bounds) => {
let scope = Scope::TraitRefBoundary { s: self.scope };
self.with(scope, |this| {
let scope = Scope::LateBoundary {
s: this.scope,
what: "`impl Trait` in binding",
deny_late_regions: true,
};
this.with(scope, |this| {
for bound in bounds {
this.visit_param_bound(bound);
}
})
});
}
_ => intravisit::walk_ty(self, ty),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_pattern_type_pattern(&mut self, p: &'tcx hir::TyPat<'tcx>) {
intravisit::walk_ty_pat(self, p)
}
#[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) => {
self.visit_early(trait_item.hir_id(), trait_item.generics, |this| {
this.visit_generics(trait_item.generics);
for bound in bounds {
this.visit_param_bound(bound);
}
if let Some(ty) = ty {
this.visit_ty_unambig(ty);
}
})
}
Const(_, _) => self.visit_early(trait_item.hir_id(), trait_item.generics, |this| {
intravisit::walk_trait_item(this, 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) => self.visit_early(impl_item.hir_id(), impl_item.generics, |this| {
this.visit_generics(impl_item.generics);
this.visit_ty_unambig(ty);
}),
Const(_, _) => self.visit_early(impl_item.hir_id(), impl_item.generics, |this| {
intravisit::walk_impl_item(this, impl_item)
}),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
match lifetime_ref.kind {
hir::LifetimeKind::Static => {
self.insert_lifetime(lifetime_ref, ResolvedArg::StaticLifetime)
}
hir::LifetimeKind::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::LifetimeKind::Error => {}
// Those will be resolved by typechecking.
hir::LifetimeKind::ImplicitObjectLifetimeDefault | hir::LifetimeKind::Infer => {}
}
}
fn visit_path(&mut self, path: &hir::Path<'tcx>, hir_id: 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,
def_id: LocalDefId,
) {
let output = match fd.output {
hir::FnRetTy::DefaultReturn(_) => None,
hir::FnRetTy::Return(ty) => Some(ty),
};
if let Some(ty) = output
&& let hir::TyKind::InferDelegation(sig_id, _) = ty.kind
{
let bound_vars: Vec<_> =
self.tcx.fn_sig(sig_id).skip_binder().bound_vars().iter().collect();
let hir_id = self.tcx.local_def_id_to_hir_id(def_id);
self.rbv.late_bound_vars.insert(hir_id.local_id, bound_vars);
}
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| {
walk_list!(this, visit_generic_param, generics.params);
walk_list!(this, visit_where_predicate, generics.predicates);
})
}
fn visit_where_predicate(&mut self, predicate: &'tcx hir::WherePredicate<'tcx>) {
let hir_id = predicate.hir_id;
match predicate.kind {
&hir::WherePredicateKind::BoundPredicate(hir::WhereBoundPredicate {
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)| {
(
(param.def_id, ResolvedArg::late(late_bound_idx as u32, param)),
late_arg_as_bound_arg(param),
)
})
.unzip();
self.record_late_bound_vars(hir_id, binders);
// If this is an RTN type in the self type, then append those to the binder.
self.try_append_return_type_notation_params(hir_id, bounded_ty);
// 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: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: Some(origin),
};
self.with(scope, |this| {
walk_list!(this, visit_generic_param, bound_generic_params);
this.visit_ty_unambig(bounded_ty);
walk_list!(this, visit_param_bound, bounds);
})
}
&hir::WherePredicateKind::RegionPredicate(hir::WhereRegionPredicate {
lifetime,
bounds,
..
}) => {
self.visit_lifetime(lifetime);
walk_list!(self, visit_param_bound, bounds);
}
&hir::WherePredicateKind::EqPredicate(hir::WhereEqPredicate {
lhs_ty, rhs_ty, ..
}) => {
self.visit_ty_unambig(lhs_ty);
self.visit_ty_unambig(rhs_ty);
}
}
}
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::LateBoundary { s: self.scope, what: "constant", deny_late_regions: true },
|this| {
intravisit::walk_anon_const(this, c);
},
);
}
fn visit_generic_param(&mut self, p: &'tcx GenericParam<'tcx>) {
match p.kind {
GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
self.resolve_type_ref(p.def_id, p.hir_id);
}
GenericParamKind::Lifetime { .. } => {
// No need to resolve lifetime params, we don't use them for things
// like implicit `?Sized` or const-param-has-ty predicates.
}
}
match p.kind {
GenericParamKind::Lifetime { .. } => {}
GenericParamKind::Type { default, .. } => {
if let Some(ty) = default {
self.visit_ty_unambig(ty);
}
}
GenericParamKind::Const { ty, default, .. } => {
self.visit_ty_unambig(ty);
if let Some(default) = default {
self.visit_const_arg_unambig(default);
}
}
}
}
}
fn object_lifetime_default(tcx: TyCtxt<'_>, param_def_id: LocalDefId) -> ObjectLifetimeDefault {
debug_assert_eq!(tcx.def_kind(param_def_id), DefKind::TyParam);
let hir::Node::GenericParam(param) = tcx.hir_node_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.kind);
}
}
}
match set {
Set1::Empty => ObjectLifetimeDefault::Empty,
Set1::One(hir::LifetimeKind::Static) => ObjectLifetimeDefault::Static,
Set1::One(hir::LifetimeKind::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, rbv, disambiguator, .. } = self;
let mut this = BoundVarContext { tcx: *tcx, rbv, disambiguator, scope: &wrap_scope };
let span = debug_span!("scope", scope = ?this.scope.debug_truncated());
{
let _enter = span.enter();
f(&mut this);
}
}
fn record_late_bound_vars(&mut self, hir_id: HirId, binder: Vec<ty::BoundVariableKind>) {
if let Some(old) = self.rbv.late_bound_vars.insert(hir_id.local_id, binder) {
bug!(
"overwrote bound vars for {hir_id:?}:\nold={old:?}\nnew={:?}",
self.rbv.late_bound_vars[&hir_id.local_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: 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| {
(
param.def_id,
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)
})
.map(|param| late_arg_as_bound_arg(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);
}
fn visit_early<F>(&mut self, hir_id: HirId, generics: &'tcx hir::Generics<'tcx>, walk: F)
where
F: for<'b, 'c> FnOnce(&'b mut BoundVarContext<'c, 'tcx>),
{
let bound_vars =
generics.params.iter().map(|param| (param.def_id, ResolvedArg::early(param))).collect();
self.record_late_bound_vars(hir_id, vec![]);
let scope = Scope::Binder {
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, 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 mut crossed_late_boundary = None;
let mut opaque_capture_scopes = vec![];
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));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, where_bound_origin, .. } => {
if let Some(&def) = bound_vars.get(&region_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::LifetimeKind::Param(param_id) = lifetime_ref.kind
&& 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()
&& !self.tcx.asyncness(lifetime_ref.hir_id.owner.def_id).is_async()
&& !self.tcx.features().anonymous_lifetime_in_impl_trait()
{
let mut diag: rustc_errors::Diag<'_> = rustc_session::parse::feature_err(
&self.tcx.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 = lifetime_ref.suggestion("'a");
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::Opaque { captures, def_id, s } => {
opaque_capture_scopes.push((def_id, captures));
late_depth = 0;
scope = s;
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what, deny_late_regions } => {
if deny_late_regions {
crossed_late_boundary = Some(what);
}
scope = s;
}
}
};
if let Some(mut def) = result {
def = self.remap_opaque_captures(&opaque_capture_scopes, def, lifetime_ref.ident);
if let ResolvedArg::EarlyBound(..) = def {
// Do not free early-bound regions, only late-bound ones.
} else if let ResolvedArg::LateBound(_, _, param_def_id) = def
&& let Some(what) = crossed_late_boundary
{
let use_span = lifetime_ref.ident.span;
let def_span = self.tcx.def_span(param_def_id);
let guar = match self.tcx.def_kind(param_def_id) {
DefKind::LifetimeParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Lifetime {
use_span,
def_span,
what,
})
}
kind => span_bug!(
use_span,
"did not expect to resolve lifetime to {}",
kind.descr(param_def_id.to_def_id())
),
};
def = ResolvedArg::Error(guar);
} else if let Some(body_id) = outermost_body {
let fn_id = self.tcx.hir_body_owner(body_id);
match self.tcx.hir_node(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.def_id, def.id().unwrap());
}
Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(closure), .. }) => {
def = ResolvedArg::Free(closure.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
// responsibility 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), ..
} => {
self.tcx.dcx().emit_err(errors::LateBoundInApit::Lifetime {
span: lifetime_ref.ident.span,
param_span: self.tcx.def_span(region_def_id),
});
return;
}
Scope::Root { .. } => break,
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::Opaque { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
self.tcx.dcx().span_delayed_bug(
lifetime_ref.ident.span,
format!("Could not resolve {:?} in scope {:#?}", lifetime_ref, self.scope,),
);
}
/// 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.
fn check_lifetime_is_capturable(
&self,
opaque_def_id: LocalDefId,
lifetime: ResolvedArg,
capture_span: Span,
) -> Result<(), ErrorGuaranteed> {
let ResolvedArg::LateBound(_, _, lifetime_def_id) = lifetime else { return Ok(()) };
let lifetime_hir_id = self.tcx.local_def_id_to_hir_id(lifetime_def_id);
let bad_place = match self.tcx.hir_node(self.tcx.parent_hir_id(lifetime_hir_id)) {
// Opaques do not declare their own lifetimes, so if a lifetime comes from an opaque
// it must be a reified late-bound lifetime from a trait goal.
hir::Node::OpaqueTy(_) => "higher-ranked lifetime from outer `impl Trait`",
// Other items are fine.
hir::Node::Item(_) | hir::Node::TraitItem(_) | hir::Node::ImplItem(_) => return Ok(()),
hir::Node::Ty(hir::Ty { kind: hir::TyKind::FnPtr(_), .. }) => {
"higher-ranked lifetime from function pointer"
}
hir::Node::Ty(hir::Ty { kind: hir::TyKind::TraitObject(..), .. }) => {
"higher-ranked lifetime from `dyn` type"
}
_ => "higher-ranked lifetime",
};
let decl_span = self.tcx.def_span(lifetime_def_id);
let (span, label) = if capture_span != decl_span {
(capture_span, None)
} else {
let opaque_span = self.tcx.def_span(opaque_def_id);
(opaque_span, Some(opaque_span))
};
// Ensure that the parent of the def is an item, not HRTB
let guar = self.tcx.dcx().emit_err(errors::OpaqueCapturesHigherRankedLifetime {
span,
label,
decl_span,
bad_place,
});
Err(guar)
}
#[instrument(level = "trace", skip(self, opaque_capture_scopes), ret)]
fn remap_opaque_captures(
&mut self,
opaque_capture_scopes: &Vec<(LocalDefId, &RefCell<FxIndexMap<ResolvedArg, LocalDefId>>)>,
mut lifetime: ResolvedArg,
ident: Ident,
) -> ResolvedArg {
if let Some(&(opaque_def_id, _)) = opaque_capture_scopes.last() {
if let Err(guar) =
self.check_lifetime_is_capturable(opaque_def_id, lifetime, ident.span)
{
lifetime = ResolvedArg::Error(guar);
}
}
for &(opaque_def_id, captures) in opaque_capture_scopes.iter().rev() {
let mut captures = captures.borrow_mut();
let remapped = *captures.entry(lifetime).or_insert_with(|| {
// `opaque_def_id` is unique to the `BoundVarContext` pass which is executed once
// per `resolve_bound_vars` query. This is the only location that creates
// `OpaqueLifetime` paths. `<opaque_def_id>::OpaqueLifetime(..)` is thus unique
// to this query and duplicates within the query are handled by `self.disambiguator`.
let feed = self.tcx.create_def(
opaque_def_id,
None,
DefKind::LifetimeParam,
Some(DefPathData::OpaqueLifetime(ident.name)),
&mut self.disambiguator,
);
feed.def_span(ident.span);
feed.def_ident_span(Some(ident.span));
feed.def_id()
});
lifetime = ResolvedArg::EarlyBound(remapped);
}
lifetime
}
fn resolve_type_ref(&mut self, param_def_id: LocalDefId, hir_id: 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_late_boundary = None;
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));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, .. } => {
if let Some(&def) = bound_vars.get(&param_def_id) {
break Some(def.shifted(late_depth));
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Opaque { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what, deny_late_regions: _ } => {
crossed_late_boundary = Some(what);
scope = s;
}
}
};
if let Some(def) = result {
if let ResolvedArg::LateBound(..) = def
&& let Some(what) = crossed_late_boundary
{
let use_span = self.tcx.hir_span(hir_id);
let def_span = self.tcx.def_span(param_def_id);
let guar = match self.tcx.def_kind(param_def_id) {
DefKind::ConstParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Const {
use_span,
def_span,
what,
})
}
DefKind::TyParam => {
self.tcx.dcx().emit_err(errors::CannotCaptureLateBound::Type {
use_span,
def_span,
what,
})
}
kind => span_bug!(
use_span,
"did not expect to resolve non-lifetime param to {}",
kind.descr(param_def_id.to_def_id())
),
};
self.rbv.defs.insert(hir_id.local_id, ResolvedArg::Error(guar));
} else {
self.rbv.defs.insert(hir_id.local_id, def);
}
return;
}
// We may fail to resolve higher-ranked ty/const vars that are mentioned by APIT.
// AST-based resolution does not care for impl-trait desugaring, which are the
// responsibility of lowering. This may create a mismatch between the resolution
// AST found (`param_def_id`) which points to HRTB, and what HIR allows.
// ```
// fn foo(x: impl for<T> Trait<Assoc = impl Trait2<T>>) {}
// ```
//
// 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 guar = self.tcx.dcx().emit_err(match self.tcx.def_kind(param_def_id) {
DefKind::TyParam => errors::LateBoundInApit::Type {
span: self.tcx.hir_span(hir_id),
param_span: self.tcx.def_span(param_def_id),
},
DefKind::ConstParam => errors::LateBoundInApit::Const {
span: self.tcx.hir_span(hir_id),
param_span: self.tcx.def_span(param_def_id),
},
kind => {
bug!("unexpected def-kind: {}", kind.descr(param_def_id.to_def_id()))
}
});
self.rbv.defs.insert(hir_id.local_id, ResolvedArg::Error(guar));
return;
}
Scope::Root { .. } => break,
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::Opaque { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
self.tcx
.dcx()
.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 let Some((inputs, output)) = generic_args.paren_sugar_inputs_output() {
self.visit_fn_like_elision(inputs, Some(output), 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::ObjectLifetimeDefault { s, .. }
| Scope::Opaque { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
};
let rbv = &self.rbv;
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[&param_def_id] as usize;
generic_args.args.get(index).and_then(|arg| match arg {
GenericArg::Lifetime(lt) => rbv.defs.get(&lt.hir_id.local_id).copied(),
_ => None,
})
}
ObjectLifetimeDefault::Ambiguous => None,
};
generics
.own_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(&lt) = 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_const_arg(ct);
i += 1;
}
GenericArg::Infer(inf) => {
self.visit_id(inf.hir_id);
i += 1;
}
}
}
// Hack: When resolving the type `XX` in an assoc ty 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 constraint in generic_args.constraints {
let scope = Scope::ObjectLifetimeDefault {
lifetime: if has_lifetime_parameter {
None
} else {
Some(ResolvedArg::StaticLifetime)
},
s: self.scope,
};
// If the args are parenthesized, then this must be `feature(return_type_notation)`.
// In that case, introduce a binder over all of the function's early and late bound vars.
//
// For example, given
// ```
// trait Foo {
// async fn x<'r, T>();
// }
// ```
// and a bound that looks like:
// `for<'a> T::Trait<'a, x(..): for<'b> Other<'b>>`
// this is going to expand to something like:
// `for<'a> for<'r> <T as Trait<'a>>::x::<'r, T>::{opaque#0}: for<'b> Other<'b>`.
if constraint.gen_args.parenthesized == hir::GenericArgsParentheses::ReturnTypeNotation
{
let bound_vars = if let Some(type_def_id) = type_def_id
&& self.tcx.def_kind(type_def_id) == DefKind::Trait
&& let Some((mut bound_vars, assoc_fn)) = BoundVarContext::supertrait_hrtb_vars(
self.tcx,
type_def_id,
constraint.ident,
ty::AssocTag::Fn,
) {
bound_vars.extend(
self.tcx
.generics_of(assoc_fn.def_id)
.own_params
.iter()
.map(|param| generic_param_def_as_bound_arg(param)),
);
bound_vars.extend(
self.tcx.fn_sig(assoc_fn.def_id).instantiate_identity().bound_vars(),
);
bound_vars
} else {
self.tcx
.dcx()
.span_delayed_bug(constraint.ident.span, "bad return type notation here");
vec![]
};
self.with(scope, |this| {
let scope = Scope::Supertrait { bound_vars, s: this.scope };
this.with(scope, |this| {
let (bound_vars, _) = this.poly_trait_ref_binder_info();
this.record_late_bound_vars(constraint.hir_id, bound_vars);
this.visit_assoc_item_constraint(constraint)
});
});
} else if let Some(type_def_id) = type_def_id {
let bound_vars = BoundVarContext::supertrait_hrtb_vars(
self.tcx,
type_def_id,
constraint.ident,
ty::AssocTag::Type,
)
.map(|(bound_vars, _)| bound_vars);
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_item_constraint(constraint));
});
} else {
self.with(scope, |this| this.visit_assoc_item_constraint(constraint));
}
}
}
/// 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_ident: Ident,
assoc_tag: ty::AssocTag,
) -> Option<(Vec<ty::BoundVariableKind>, &'tcx ty::AssocItem)> {
let trait_defines_associated_item_named = |trait_def_id: DefId| {
tcx.associated_items(trait_def_id).find_by_ident_and_kind(
tcx,
assoc_ident,
assoc_tag,
trait_def_id,
)
};
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 let Some(assoc_item) = trait_defines_associated_item_named(def_id) {
break Some((bound_vars.into_iter().collect(), assoc_item));
}
let predicates = tcx.explicit_supertraits_containing_assoc_item((def_id, assoc_ident));
let obligations = predicates.iter_identity_copied().filter_map(|(pred, _)| {
let bound_predicate = pred.kind();
match bound_predicate.skip_binder() {
ty::ClauseKind::Trait(data) => {
// The order here needs to match what we would get from
// `rustc_middle::ty::predicate::Clause::instantiate_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::ObjectLifetimeDefault {
lifetime: Some(ResolvedArg::StaticLifetime),
s: self.scope,
},
|this| {
for input in inputs {
this.visit_ty_unambig(input);
}
if !in_closure && let Some(output) = output {
this.visit_ty_unambig(output);
}
},
);
if in_closure && let Some(output) = output {
self.visit_ty_unambig(output);
}
}
#[instrument(level = "debug", skip(self))]
fn resolve_object_lifetime_default(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
let mut late_depth = 0;
let mut scope = self.scope;
let mut opaque_capture_scopes = vec![];
let mut lifetime = loop {
match *scope {
Scope::Binder { s, scope_type, .. } => {
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::Root { .. } => break ResolvedArg::StaticLifetime,
Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
Scope::ObjectLifetimeDefault { lifetime: Some(l), .. } => {
break l.shifted(late_depth);
}
Scope::Opaque { captures, def_id, s } => {
opaque_capture_scopes.push((def_id, captures));
late_depth = 0;
scope = s;
}
Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
};
lifetime = self.remap_opaque_captures(&opaque_capture_scopes, lifetime, lifetime_ref.ident);
self.insert_lifetime(lifetime_ref, lifetime);
}
#[instrument(level = "debug", skip(self))]
fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: ResolvedArg) {
debug!(span = ?lifetime_ref.ident.span);
self.rbv.defs.insert(lifetime_ref.hir_id.local_id, def);
}
// When we have a return type notation type in a where clause, like
// `where <T as Trait>::method(..): Send`, we need to introduce new bound
// vars to the existing where clause's binder, to represent the lifetimes
// elided by the return-type-notation syntax.
//
// For example, given
// ```
// trait Foo {
// async fn x<'r>();
// }
// ```
// and a bound that looks like:
// `for<'a, 'b> <T as Trait<'a>>::x(): Other<'b>`
// this is going to expand to something like:
// `for<'a, 'b, 'r> <T as Trait<'a>>::x::<'r, T>::{opaque#0}: Other<'b>`.
//
// We handle this similarly for associated-type-bound style return-type-notation
// in `visit_segment_args`.
fn try_append_return_type_notation_params(
&mut self,
hir_id: HirId,
hir_ty: &'tcx hir::Ty<'tcx>,
) {
let hir::TyKind::Path(qpath) = hir_ty.kind else {
// We only care about path types here. All other self types
// (including nesting the RTN type in another type) don't do
// anything.
return;
};
let (mut bound_vars, item_def_id, item_segment) = match qpath {
// If we have a fully qualified method, then we don't need to do any special lookup.
hir::QPath::Resolved(_, path)
if let [.., item_segment] = &path.segments[..]
&& item_segment.args.is_some_and(|args| {
matches!(
args.parenthesized,
hir::GenericArgsParentheses::ReturnTypeNotation
)
}) =>
{
match path.res {
Res::Err => return,
Res::Def(DefKind::AssocFn, item_def_id) => (vec![], item_def_id, item_segment),
_ => bug!("only expected method resolution for fully qualified RTN"),
}
}
// If we have a type-dependent path, then we do need to do some lookup.
hir::QPath::TypeRelative(qself, item_segment)
if item_segment.args.is_some_and(|args| {
matches!(args.parenthesized, hir::GenericArgsParentheses::ReturnTypeNotation)
}) =>
{
// First, ignore a qself that isn't a type or `Self` param. Those are the
// only ones that support `T::Assoc` anyways in HIR lowering.
let hir::TyKind::Path(hir::QPath::Resolved(None, path)) = qself.kind else {
return;
};
match path.res {
Res::Def(DefKind::TyParam, _) | Res::SelfTyParam { trait_: _ } => {
let mut bounds =
self.for_each_trait_bound_on_res(path.res).filter_map(|trait_def_id| {
BoundVarContext::supertrait_hrtb_vars(
self.tcx,
trait_def_id,
item_segment.ident,
ty::AssocTag::Fn,
)
});
let Some((bound_vars, assoc_item)) = bounds.next() else {
// This will error in HIR lowering.
self.tcx
.dcx()
.span_delayed_bug(path.span, "no resolution for RTN path");
return;
};
// Don't bail if we have identical bounds, which may be collected from
// something like `T: Bound + Bound`, or via elaborating supertraits.
for (second_vars, second_assoc_item) in bounds {
if second_vars != bound_vars || second_assoc_item != assoc_item {
// This will error in HIR lowering.
self.tcx.dcx().span_delayed_bug(
path.span,
"ambiguous resolution for RTN path",
);
return;
}
}
(bound_vars, assoc_item.def_id, item_segment)
}
// If we have a self type alias (in an impl), try to resolve an
// associated item from one of the supertraits of the impl's trait.
Res::SelfTyAlias { alias_to: impl_def_id, is_trait_impl: true, .. } => {
let hir::ItemKind::Impl(hir::Impl { of_trait: Some(of_trait), .. }) = self
.tcx
.hir_node_by_def_id(impl_def_id.expect_local())
.expect_item()
.kind
else {
return;
};
let Some(trait_def_id) = of_trait.trait_ref.trait_def_id() else {
return;
};
let Some((bound_vars, assoc_item)) = BoundVarContext::supertrait_hrtb_vars(
self.tcx,
trait_def_id,
item_segment.ident,
ty::AssocTag::Fn,
) else {
return;
};
(bound_vars, assoc_item.def_id, item_segment)
}
_ => return,
}
}
_ => return,
};
// Append the early-bound vars on the function, and then the late-bound ones.
// We actually turn type parameters into higher-ranked types here, but we
// deny them later in HIR lowering.
bound_vars.extend(
self.tcx
.generics_of(item_def_id)
.own_params
.iter()
.map(|param| generic_param_def_as_bound_arg(param)),
);
bound_vars.extend(self.tcx.fn_sig(item_def_id).instantiate_identity().bound_vars());
// SUBTLE: Stash the old bound vars onto the *item segment* before appending
// the new bound vars. We do this because we need to know how many bound vars
// are present on the binder explicitly (i.e. not return-type-notation vars)
// to do bound var shifting correctly in HIR lowering.
//
// For example, in `where for<'a> <T as Trait<'a>>::method(..): Other`,
// the `late_bound_vars` of the where clause predicate (i.e. this HIR ty's
// parent) will include `'a` AND all the early- and late-bound vars of the
// method. But when lowering the RTN type, we just want the list of vars
// we used to resolve the trait ref. We explicitly stored those back onto
// the item segment, since there's no other good place to put them.
//
// See where these vars are used in `HirTyLowerer::lower_ty_maybe_return_type_notation`.
// And this is exercised in:
// `tests/ui/associated-type-bounds/return-type-notation/higher-ranked-bound-works.rs`.
let existing_bound_vars = self.rbv.late_bound_vars.get_mut(&hir_id.local_id).unwrap();
let existing_bound_vars_saved = existing_bound_vars.clone();
existing_bound_vars.extend(bound_vars);
self.record_late_bound_vars(item_segment.hir_id, existing_bound_vars_saved);
}
/// Walk the generics of the item for a trait bound whose self type
/// corresponds to the expected res, and return the trait def id.
fn for_each_trait_bound_on_res(&self, expected_res: Res) -> impl Iterator<Item = DefId> {
gen move {
let mut scope = self.scope;
loop {
let hir_id = match *scope {
Scope::Binder { hir_id, .. } => Some(hir_id),
Scope::Root { opt_parent_item: Some(parent_def_id) } => {
Some(self.tcx.local_def_id_to_hir_id(parent_def_id))
}
Scope::Body { .. }
| Scope::ObjectLifetimeDefault { .. }
| Scope::Supertrait { .. }
| Scope::TraitRefBoundary { .. }
| Scope::LateBoundary { .. }
| Scope::Opaque { .. }
| Scope::Root { opt_parent_item: None } => None,
};
if let Some(hir_id) = hir_id {
let node = self.tcx.hir_node(hir_id);
// If this is a `Self` bound in a trait, yield the trait itself.
// Specifically, we don't need to look at any supertraits since
// we already do that in `BoundVarContext::supertrait_hrtb_vars`.
if let Res::SelfTyParam { trait_: _ } = expected_res
&& let hir::Node::Item(item) = node
&& let hir::ItemKind::Trait(..) = item.kind
{
// Yield the trait's def id. Supertraits will be
// elaborated from that.
yield item.owner_id.def_id.to_def_id();
} else if let Some(generics) = node.generics() {
for pred in generics.predicates {
let hir::WherePredicateKind::BoundPredicate(pred) = pred.kind else {
continue;
};
let hir::TyKind::Path(hir::QPath::Resolved(None, bounded_path)) =
pred.bounded_ty.kind
else {
continue;
};
// Match the expected res.
if bounded_path.res != expected_res {
continue;
}
for pred in pred.bounds {
match pred {
hir::GenericBound::Trait(poly_trait_ref) => {
if let Some(def_id) =
poly_trait_ref.trait_ref.trait_def_id()
{
yield def_id;
}
}
hir::GenericBound::Outlives(_)
| hir::GenericBound::Use(_, _) => {}
}
}
}
}
}
match *scope {
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s }
| Scope::LateBoundary { s, .. }
| Scope::Opaque { s, .. } => {
scope = s;
}
Scope::Root { .. } => break,
}
}
}
}
}
/// 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 sig = tcx.hir_fn_sig_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 sig.decl.inputs {
constrained_by_input.visit_ty_unambig(arg_ty);
}
let mut appears_in_output =
AllCollector { has_fully_capturing_opaque: false, regions: Default::default() };
intravisit::walk_fn_ret_ty(&mut appears_in_output, &sig.decl.output);
if appears_in_output.has_fully_capturing_opaque {
appears_in_output.regions.extend(generics.params.iter().map(|param| param.def_id));
}
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 { has_fully_capturing_opaque: true, regions: Default::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(&param.def_id) {
continue;
}
// does not appear in the inputs, but appears in the return type? early-bound.
if !constrained_by_input.regions.contains(&param.def_id)
&& appears_in_output.regions.contains(&param.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:
/// ```rust,ignore (pseudo-Rust)
/// 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 HIR ty lowering 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 ConstrainedCollectorPostHirTyLowering {
arg_is_constrained: Box<[bool]>,
}
use ty::Ty;
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ConstrainedCollectorPostHirTyLowering {
fn visit_ty(&mut self, t: Ty<'tcx>) {
match t.kind() {
ty::Param(param_ty) => {
self.arg_is_constrained[param_ty.index as usize] = true;
}
ty::Alias(ty::Projection | ty::Inherent, _) => return,
_ => (),
}
t.super_visit_with(self)
}
fn visit_const(&mut self, _: ty::Const<'tcx>) {}
fn visit_region(&mut self, r: ty::Region<'tcx>) {
debug!("r={:?}", r.kind());
if let ty::RegionKind::ReEarlyParam(region) = r.kind() {
self.arg_is_constrained[region.index as usize] = true;
}
}
}
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, AmbigArg>) {
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 `ConstrainedCollectorPostHirTyLowering` for why this arm does not
// just consider args to be unconstrained.
let generics = self.tcx.generics_of(alias_def);
let mut walker = ConstrainedCollectorPostHirTyLowering {
arg_is_constrained: vec![false; generics.own_params.len()]
.into_boxed_slice(),
};
walker.visit_ty(self.tcx.type_of(alias_def).instantiate_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.dcx().span_delayed_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::LifetimeKind::Param(def_id) = lifetime_ref.kind {
self.regions.insert(def_id);
}
}
}
struct AllCollector {
has_fully_capturing_opaque: bool,
regions: FxHashSet<LocalDefId>,
}
impl<'tcx> Visitor<'tcx> for AllCollector {
fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
if let hir::LifetimeKind::Param(def_id) = lifetime_ref.kind {
self.regions.insert(def_id);
}
}
fn visit_opaque_ty(&mut self, opaque: &'tcx hir::OpaqueTy<'tcx>) {
if !self.has_fully_capturing_opaque {
self.has_fully_capturing_opaque = opaque_captures_all_in_scope_lifetimes(opaque);
}
intravisit::walk_opaque_ty(self, opaque);
}
}
}
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_node_by_def_id(*var) else {
span_bug!(tcx.def_span(*var), "expected bound-var def-id to resolve to param");
};
let what = match param.kind {
hir::GenericParamKind::Type { .. } => "type",
hir::GenericParamKind::Const { .. } => "const",
hir::GenericParamKind::Lifetime { .. } => continue,
};
let diag = tcx.dcx().struct_span_err(
param.span,
format!("late-bound {what} parameter not allowed on {where_}"),
);
let guar = diag.emit_unless_delay(!tcx.features().non_lifetime_binders() || !first);
first = false;
*arg = ResolvedArg::Error(guar);
}
}