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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 core::ops::ControlFlow;
use rustc_ast::visit::walk_list;
use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
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, HirId, HirIdMap, LifetimeName, 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;
use rustc_span::symbol::{sym, Ident};
use rustc_span::Span;
use std::fmt;
use crate::errors;
#[extension(trait RegionExt)]
impl ResolvedArg {
fn early(param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) {
debug!("ResolvedArg::early: def_id={:?}", param.def_id);
(param.def_id, ResolvedArg::EarlyBound(param.def_id.to_def_id()))
}
fn late(idx: u32, param: &GenericParam<'_>) -> (LocalDefId, ResolvedArg) {
let depth = ty::INNERMOST;
debug!(
"ResolvedArg::late: idx={:?}, param={:?} depth={:?} def_id={:?}",
idx, param, depth, param.def_id,
);
(param.def_id, ResolvedArg::LateBound(depth, idx, param.def_id.to_def_id()))
}
fn id(&self) -> Option<DefId> {
match *self {
ResolvedArg::StaticLifetime | ResolvedArg::Error(_) => None,
ResolvedArg::EarlyBound(id)
| ResolvedArg::LateBound(_, _, id)
| ResolvedArg::Free(_, id) => Some(id),
}
}
fn shifted(self, amount: u32) -> ResolvedArg {
match self {
ResolvedArg::LateBound(debruijn, idx, id) => {
ResolvedArg::LateBound(debruijn.shifted_in(amount), idx, id)
}
_ => self,
}
}
}
/// Maps the id of each bound variable reference to the variable decl
/// that it corresponds to.
///
/// FIXME. This struct gets converted to a `ResolveBoundVars` for
/// actual use. It has the same data, but indexed by `LocalDefId`. This
/// is silly.
#[derive(Debug, Default)]
struct NamedVarMap {
// maps from every use of a named (not anonymous) bound var to a
// `ResolvedArg` describing how that variable is bound
defs: HirIdMap<ResolvedArg>,
// Maps relevant hir items to the bound vars on them. These include:
// - function defs
// - function pointers
// - closures
// - trait refs
// - bound types (like `T` in `for<'a> T<'a>: Foo`)
late_bound_vars: HirIdMap<Vec<ty::BoundVariableKind>>,
}
struct BoundVarContext<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
map: &'a mut NamedVarMap,
scope: ScopeRef<'a>,
}
#[derive(Debug)]
enum Scope<'a> {
/// Declares lifetimes, and each can be early-bound or late-bound.
/// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
/// it should be shifted by the number of `Binder`s in between the
/// declaration `Binder` and the location it's referenced from.
Binder {
/// We use an IndexMap here because we want these lifetimes in order
/// for diagnostics.
bound_vars: FxIndexMap<LocalDefId, ResolvedArg>,
scope_type: BinderScopeType,
/// The late bound vars for a given item are stored by `HirId` to be
/// queried later. However, if we enter an elision scope, we have to
/// later append the elided bound vars to the list and need to know what
/// to append to.
hir_id: 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>,
},
/// 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,
},
Root {
opt_parent_item: Option<LocalDefId>,
},
}
#[derive(Copy, Clone, Debug)]
enum BinderScopeType {
/// Any non-concatenating binder scopes.
Normal,
/// Within a syntactic trait ref, there may be multiple poly trait refs that
/// are nested (under the `associated_type_bounds` feature). The binders of
/// the inner poly trait refs are extended from the outer poly trait refs
/// and don't increase the late bound depth. If you had
/// `T: for<'a> Foo<Bar: for<'b> Baz<'a, 'b>>`, then the `for<'b>` scope
/// would be `Concatenating`. This also used in trait refs in where clauses
/// where we have two binders `for<> T: for<> Foo` (I've intentionally left
/// out any lifetimes because they aren't needed to show the two scopes).
/// The inner `for<>` has a scope of `Concatenating`.
Concatenating,
}
// A helper struct for debugging scopes without printing parent scopes
struct TruncatedScopeDebug<'a>(&'a Scope<'a>);
impl<'a> fmt::Debug for TruncatedScopeDebug<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.0 {
Scope::Binder { bound_vars, scope_type, hir_id, where_bound_origin, s: _ } => f
.debug_struct("Binder")
.field("bound_vars", bound_vars)
.field("scope_type", scope_type)
.field("hir_id", hir_id)
.field("where_bound_origin", where_bound_origin)
.field("s", &"..")
.finish(),
Scope::Body { id, s: _ } => {
f.debug_struct("Body").field("id", id).field("s", &"..").finish()
}
Scope::ObjectLifetimeDefault { lifetime, s: _ } => f
.debug_struct("ObjectLifetimeDefault")
.field("lifetime", lifetime)
.field("s", &"..")
.finish(),
Scope::Supertrait { bound_vars, s: _ } => f
.debug_struct("Supertrait")
.field("bound_vars", bound_vars)
.field("s", &"..")
.finish(),
Scope::TraitRefBoundary { s: _ } => f.debug_struct("TraitRefBoundary").finish(),
Scope::LateBoundary { s: _, what } => {
f.debug_struct("LateBoundary").field("what", what).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 Providers) {
*providers = Providers {
resolve_bound_vars,
named_variable_map: |tcx, id| tcx.resolve_bound_vars(id).defs.get(&id),
is_late_bound_map,
object_lifetime_default,
late_bound_vars_map: |tcx, id| tcx.resolve_bound_vars(id).late_bound_vars.get(&id),
..*providers
};
}
/// Computes the `ResolveBoundVars` map that contains data for an entire `Item`.
/// You should not read the result of this query directly, but rather use
/// `named_variable_map`, `is_late_bound_map`, etc.
#[instrument(level = "debug", skip(tcx))]
fn resolve_bound_vars(tcx: TyCtxt<'_>, local_def_id: hir::OwnerId) -> ResolveBoundVars {
let mut named_variable_map =
NamedVarMap { defs: Default::default(), late_bound_vars: Default::default() };
let mut visitor = BoundVarContext {
tcx,
map: &mut named_variable_map,
scope: &Scope::Root { opt_parent_item: None },
};
match tcx.hir_owner_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!(),
}
let mut rl = ResolveBoundVars::default();
for (hir_id, v) in named_variable_map.defs {
let map = rl.defs.entry(hir_id.owner).or_default();
map.insert(hir_id.local_id, v);
}
for (hir_id, v) in named_variable_map.late_bound_vars {
let map = rl.late_bound_vars.entry(hir_id.owner).or_default();
map.insert(hir_id.local_id, v);
}
debug!(?rl.defs);
debug!(?rl.late_bound_vars);
rl
}
fn late_arg_as_bound_arg<'tcx>(
tcx: TyCtxt<'tcx>,
arg: &ResolvedArg,
param: &GenericParam<'tcx>,
) -> ty::BoundVariableKind {
match arg {
ResolvedArg::LateBound(_, _, def_id) => {
let name = tcx.hir().name(tcx.local_def_id_to_hir_id(def_id.expect_local()));
match param.kind {
GenericParamKind::Lifetime { .. } => {
ty::BoundVariableKind::Region(ty::BrNamed(*def_id, name))
}
GenericParamKind::Type { .. } => {
ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(*def_id, name))
}
GenericParamKind::Const { .. } => ty::BoundVariableKind::Const,
}
}
_ => bug!("{:?} is not a late argument", arg),
}
}
impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
/// Returns the binders in scope and the type of `Binder` that should be created for a poly trait ref.
fn poly_trait_ref_binder_info(&mut self) -> (Vec<ty::BoundVariableKind>, BinderScopeType) {
let mut scope = self.scope;
let mut supertrait_bound_vars = vec![];
loop {
match scope {
Scope::Body { .. } | Scope::Root { .. } => {
break (vec![], BinderScopeType::Normal);
}
Scope::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.map.late_bound_vars.entry(*hir_id).or_default().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 pair = ResolvedArg::late(initial_bound_vars + late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
bound_vars.insert(pair.0, pair.1);
r
});
binders.extend(binders_iter);
if let NonLifetimeBinderAllowed::Deny(where_) = non_lifetime_binder_allowed {
deny_non_region_late_bound(self.tcx, &mut bound_vars, where_);
}
debug!(?binders);
self.record_late_bound_vars(trait_ref.trait_ref.hir_ref_id, binders);
// Always introduce a scope here, even if this is in a where clause and
// we introduced the binders around the bounded Ty. In that case, we
// just reuse the concatenation functionality also present in nested trait
// refs.
let scope = Scope::Binder {
hir_id: trait_ref.trait_ref.hir_ref_id,
bound_vars,
s: self.scope,
scope_type,
where_bound_origin: None,
};
self.with(scope, |this| {
walk_list!(this, visit_generic_param, trait_ref.bound_generic_params);
this.visit_trait_ref(&trait_ref.trait_ref);
});
}
}
enum NonLifetimeBinderAllowed {
Deny(&'static str),
Allow,
}
impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
type NestedFilter = nested_filter::OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.tcx.hir()
}
fn visit_nested_body(&mut self, body: hir::BodyId) {
let body = self.tcx.hir().body(body);
self.with(Scope::Body { id: body.id(), s: self.scope }, |this| {
this.visit_body(body);
});
}
fn visit_expr(&mut self, e: &'tcx hir::Expr<'tcx>) {
if let hir::ExprKind::Closure(hir::Closure {
binder, bound_generic_params, fn_decl, ..
}) = e.kind
{
if let &hir::ClosureBinder::For { span: for_sp, .. } = binder {
fn span_of_infer(ty: &hir::Ty<'_>) -> Option<Span> {
/// 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_ty(&mut self, t: &'v hir::Ty<'v>) -> Self::Result {
if matches!(t.kind, hir::TyKind::Infer) {
ControlFlow::Break(t.span)
} else {
intravisit::walk_ty(self, t)
}
}
}
FindInferInClosureWithBinder.visit_ty(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)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
deny_non_region_late_bound(self.tcx, &mut bound_vars, "closures");
self.record_late_bound_vars(e.hir_id, binders);
let scope = Scope::Binder {
hir_id: e.hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, |this| {
// a closure has no bounds, so everything
// contained within is scoped within its binder.
intravisit::walk_expr(this, e)
});
} else {
intravisit::walk_expr(self, e)
}
}
#[instrument(level = "debug", skip(self))]
fn visit_item(&mut self, item: &'tcx hir::Item<'tcx>) {
match &item.kind {
hir::ItemKind::Impl(hir::Impl { of_trait, .. }) => {
if let Some(of_trait) = of_trait {
self.record_late_bound_vars(of_trait.hir_ref_id, Vec::default());
}
}
_ => {}
}
match item.kind {
hir::ItemKind::Fn(_, generics, _) => {
self.visit_early_late(item.hir_id(), generics, |this| {
intravisit::walk_item(this, item);
});
}
hir::ItemKind::ExternCrate(_)
| hir::ItemKind::Use(..)
| hir::ItemKind::Macro(..)
| hir::ItemKind::Mod(..)
| hir::ItemKind::ForeignMod { .. }
| hir::ItemKind::Static(..)
| hir::ItemKind::GlobalAsm(..) => {
// These sorts of items have no lifetime parameters at all.
intravisit::walk_item(self, item);
}
hir::ItemKind::OpaqueTy(&hir::OpaqueTy {
origin:
hir::OpaqueTyOrigin::FnReturn(parent)
| hir::OpaqueTyOrigin::AsyncFn(parent)
| hir::OpaqueTyOrigin::TyAlias { parent, .. },
generics,
..
}) => {
// We want to start our early-bound indices at the end of the parent scope,
// not including any parent `impl Trait`s.
let mut bound_vars = FxIndexMap::default();
debug!(?generics.params);
for param in generics.params {
let (def_id, reg) = ResolvedArg::early(param);
bound_vars.insert(def_id, reg);
}
let scope = Scope::Root { opt_parent_item: Some(parent) };
self.with(scope, |this| {
let scope = Scope::Binder {
hir_id: item.hir_id(),
bound_vars,
s: this.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
this.with(scope, |this| {
let scope = Scope::TraitRefBoundary { s: this.scope };
this.with(scope, |this| intravisit::walk_item(this, item))
});
})
}
hir::ItemKind::TyAlias(_, generics)
| hir::ItemKind::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.res {
LifetimeName::Param(def_id) => {
self.resolve_lifetime_ref(def_id, lt);
}
LifetimeName::Error => {}
LifetimeName::ImplicitObjectLifetimeDefault
| LifetimeName::Infer
| LifetimeName::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::Err => {}
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().emit_err(errors::BadPreciseCapture {
span: param.ident.span,
kind: "type or const",
found: res.descr().to_string(),
});
}
},
}
}
fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem<'tcx>) {
match item.kind {
hir::ForeignItemKind::Fn(_, _, generics, _) => {
self.visit_early_late(item.hir_id(), generics, |this| {
intravisit::walk_foreign_item(this, item);
})
}
hir::ForeignItemKind::Static(..) => {
intravisit::walk_foreign_item(self, item);
}
hir::ForeignItemKind::Type => {
intravisit::walk_foreign_item(self, item);
}
}
}
#[instrument(level = "debug", skip(self))]
fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
match ty.kind {
hir::TyKind::BareFn(c) => {
let (mut bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) = c
.generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
deny_non_region_late_bound(self.tcx, &mut bound_vars, "function pointer types");
self.record_late_bound_vars(ty.hir_id, binders);
let scope = Scope::Binder {
hir_id: ty.hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, |this| {
// a bare fn has no bounds, so everything
// contained within is scoped within its binder.
intravisit::walk_ty(this, ty);
});
}
hir::TyKind::TraitObject(bounds, lifetime, _) => {
debug!(?bounds, ?lifetime, "TraitObject");
let scope = Scope::TraitRefBoundary { s: self.scope };
self.with(scope, |this| {
for bound in bounds {
this.visit_poly_trait_ref_inner(
bound,
NonLifetimeBinderAllowed::Deny("trait object types"),
);
}
});
match lifetime.res {
LifetimeName::ImplicitObjectLifetimeDefault => {
// If the user does not write *anything*, we
// use the object lifetime defaulting
// rules. So e.g., `Box<dyn Debug>` becomes
// `Box<dyn Debug + 'static>`.
self.resolve_object_lifetime_default(lifetime)
}
LifetimeName::Infer => {
// If the user writes `'_`, we use the *ordinary* elision
// rules. So the `'_` in e.g., `Box<dyn Debug + '_>` will be
// resolved the same as the `'_` in `&'_ Foo`.
//
// cc #48468
}
LifetimeName::Param(..) | LifetimeName::Static => {
// If the user wrote an explicit name, use that.
self.visit_lifetime(lifetime);
}
LifetimeName::Error => {}
}
}
hir::TyKind::Ref(lifetime_ref, ref mt) => {
self.visit_lifetime(lifetime_ref);
let scope = Scope::ObjectLifetimeDefault {
lifetime: self.map.defs.get(&lifetime_ref.hir_id).cloned(),
s: self.scope,
};
self.with(scope, |this| this.visit_ty(mt.ty));
}
hir::TyKind::OpaqueDef(item_id, lifetimes, _in_trait) => {
// Resolve the lifetimes in the bounds to the lifetime defs in the generics.
// `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
// `type MyAnonTy<'b> = impl MyTrait<'b>;`
// ^ ^ this gets resolved in the scope of
// the opaque_ty generics
let opaque_ty = self.tcx.hir().item(item_id);
match &opaque_ty.kind {
hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin: _, .. }) => {}
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).copied();
let Some(ResolvedArg::LateBound(_, _, lifetime_def_id)) = def else { continue };
let Some(lifetime_def_id) = lifetime_def_id.as_local() else { continue };
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::Item(hir::Item {
kind: hir::ItemKind::OpaqueTy { .. }, ..
}) => "higher-ranked lifetime from outer `impl Trait`",
// Other items are fine.
hir::Node::Item(_) | hir::Node::TraitItem(_) | hir::Node::ImplItem(_) => {
continue;
}
hir::Node::Ty(hir::Ty { kind: hir::TyKind::BareFn(_), .. }) => {
"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 (span, label) = if lifetime.ident.span == self.tcx.def_span(lifetime_def_id)
{
let opaque_span = self.tcx.def_span(item_id.owner_id);
(opaque_span, Some(opaque_span))
} else {
(lifetime.ident.span, None)
};
// Ensure that the parent of the def is an item, not HRTB
self.tcx.dcx().emit_err(errors::OpaqueCapturesHigherRankedLifetime {
span,
label,
decl_span: self.tcx.def_span(lifetime_def_id),
bad_place,
});
self.uninsert_lifetime_on_error(lifetime, def.unwrap());
}
}
_ => intravisit::walk_ty(self, ty),
}
}
#[instrument(level = "debug", skip(self))]
fn visit_pattern_type_pattern(&mut self, p: &'tcx hir::Pat<'tcx>) {
intravisit::walk_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(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(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.res {
hir::LifetimeName::Static => {
self.insert_lifetime(lifetime_ref, ResolvedArg::StaticLifetime)
}
hir::LifetimeName::Param(param_def_id) => {
self.resolve_lifetime_ref(param_def_id, lifetime_ref)
}
// If we've already reported an error, just ignore `lifetime_ref`.
hir::LifetimeName::Error => {}
// Those will be resolved by typechecking.
hir::LifetimeName::ImplicitObjectLifetimeDefault | hir::LifetimeName::Infer => {}
}
}
fn visit_path(&mut self, path: &hir::Path<'tcx>, hir_id: 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.map.late_bound_vars.insert(hir_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>) {
match predicate {
&hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
hir_id,
bounded_ty,
bounds,
bound_generic_params,
origin,
..
}) => {
let (bound_vars, binders): (FxIndexMap<LocalDefId, ResolvedArg>, Vec<_>) =
bound_generic_params
.iter()
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
let r = late_arg_as_bound_arg(self.tcx, &pair.1, param);
(pair, r)
})
.unzip();
self.record_late_bound_vars(hir_id, binders);
// 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(bounded_ty);
walk_list!(this, visit_param_bound, bounds);
})
}
&hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
lifetime,
bounds,
..
}) => {
self.visit_lifetime(lifetime);
walk_list!(self, visit_param_bound, bounds);
}
&hir::WherePredicate::EqPredicate(hir::WhereEqPredicate { lhs_ty, rhs_ty, .. }) => {
self.visit_ty(lhs_ty);
self.visit_ty(rhs_ty);
}
}
}
fn visit_poly_trait_ref(&mut self, trait_ref: &'tcx hir::PolyTraitRef<'tcx>) {
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" }, |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(ty);
}
}
GenericParamKind::Const { ty, default, .. } => {
self.visit_ty(ty);
if let Some(default) = default {
self.visit_const_arg(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.res);
}
}
}
match set {
Set1::Empty => ObjectLifetimeDefault::Empty,
Set1::One(hir::LifetimeName::Static) => ObjectLifetimeDefault::Static,
Set1::One(hir::LifetimeName::Param(param_def_id)) => {
ObjectLifetimeDefault::Param(param_def_id.to_def_id())
}
_ => ObjectLifetimeDefault::Ambiguous,
}
}
_ => {
bug!("object_lifetime_default_raw must only be called on a type parameter")
}
}
}
hir::GenericParamSource::Binder => ObjectLifetimeDefault::Empty,
}
}
impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
where
F: for<'b> FnOnce(&mut BoundVarContext<'b, 'tcx>),
{
let BoundVarContext { tcx, map, .. } = self;
let mut this = BoundVarContext { tcx: *tcx, map, scope: &wrap_scope };
let span = debug_span!("scope", scope = ?TruncatedScopeDebug(this.scope));
{
let _enter = span.enter();
f(&mut this);
}
}
fn record_late_bound_vars(&mut self, hir_id: 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: HirId, generics: &'tcx hir::Generics<'tcx>, walk: F)
where
F: for<'b, 'c> FnOnce(&'b mut BoundVarContext<'c, 'tcx>),
{
let mut named_late_bound_vars = 0;
let bound_vars: FxIndexMap<LocalDefId, ResolvedArg> = generics
.params
.iter()
.map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
if self.tcx.is_late_bound(param.hir_id) {
let late_bound_idx = named_late_bound_vars;
named_late_bound_vars += 1;
ResolvedArg::late(late_bound_idx, param)
} else {
ResolvedArg::early(param)
}
}
GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
ResolvedArg::early(param)
}
})
.collect();
let binders: Vec<_> = generics
.params
.iter()
.filter(|param| {
matches!(param.kind, GenericParamKind::Lifetime { .. })
&& self.tcx.is_late_bound(param.hir_id)
})
.enumerate()
.map(|(late_bound_idx, param)| {
let pair = ResolvedArg::late(late_bound_idx as u32, param);
late_arg_as_bound_arg(self.tcx, &pair.1, param)
})
.collect();
self.record_late_bound_vars(hir_id, binders);
let scope = Scope::Binder {
hir_id,
bound_vars,
s: self.scope,
scope_type: BinderScopeType::Normal,
where_bound_origin: None,
};
self.with(scope, walk);
}
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(ResolvedArg::early).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 result = loop {
match *scope {
Scope::Body { id, s } => {
outermost_body = Some(id);
scope = s;
}
Scope::Root { opt_parent_item } => {
if let Some(parent_item) = opt_parent_item
&& let parent_generics = self.tcx.generics_of(parent_item)
&& parent_generics
.param_def_id_to_index(self.tcx, region_def_id.to_def_id())
.is_some()
{
break Some(ResolvedArg::EarlyBound(region_def_id.to_def_id()));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, where_bound_origin, .. } => {
if let Some(&def) = bound_vars.get(®ion_def_id) {
break Some(def.shifted(late_depth));
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
// Fresh lifetimes in APIT used to be allowed in async fns and forbidden in
// regular fns.
if let Some(hir::PredicateOrigin::ImplTrait) = where_bound_origin
&& let hir::LifetimeName::Param(param_id) = lifetime_ref.res
&& let Some(generics) =
self.tcx.hir().get_generics(self.tcx.local_parent(param_id))
&& let Some(param) = generics.params.iter().find(|p| p.def_id == param_id)
&& param.is_elided_lifetime()
&& !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 = 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::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what } => {
crossed_late_boundary = Some(what);
scope = s;
}
}
};
if let Some(mut def) = result {
if let ResolvedArg::EarlyBound(..) = def {
// Do not free early-bound regions, only late-bound ones.
} else if let 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)
),
};
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.to_def_id(), def.id().unwrap());
}
Node::Expr(hir::Expr { kind: hir::ExprKind::Closure(closure), .. }) => {
def = ResolvedArg::Free(closure.def_id.to_def_id(), def.id().unwrap());
}
_ => {}
}
}
self.insert_lifetime(lifetime_ref, def);
return;
}
// We may fail to resolve higher-ranked lifetimes that are mentioned by APIT.
// AST-based resolution does not care for impl-trait desugaring, which are the
// 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::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,),
);
}
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.to_def_id()));
}
break None;
}
Scope::Binder { ref bound_vars, scope_type, s, .. } => {
if let Some(&def) = bound_vars.get(¶m_def_id) {
break Some(def.shifted(late_depth));
}
match scope_type {
BinderScopeType::Normal => late_depth += 1,
BinderScopeType::Concatenating => {}
}
scope = s;
}
Scope::ObjectLifetimeDefault { s, .. }
| Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. } => {
scope = s;
}
Scope::LateBoundary { s, what } => {
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.map.defs.insert(hir_id, ResolvedArg::Error(guar));
} else {
self.map.defs.insert(hir_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.map.defs.insert(hir_id, ResolvedArg::Error(guar));
return;
}
Scope::Root { .. } => break,
Scope::Binder { s, .. }
| Scope::Body { 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::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
}
};
let map = &self.map;
let generics = self.tcx.generics_of(def_id);
// `type_def_id` points to an item, so there is nothing to inherit generics from.
debug_assert_eq!(generics.parent_count, 0);
let set_to_region = |set: ObjectLifetimeDefault| match set {
ObjectLifetimeDefault::Empty => {
if in_body {
None
} else {
Some(ResolvedArg::StaticLifetime)
}
}
ObjectLifetimeDefault::Static => Some(ResolvedArg::StaticLifetime),
ObjectLifetimeDefault::Param(param_def_id) => {
// This index can be used with `generic_args` since `parent_count == 0`.
let index = generics.param_def_id_to_index[¶m_def_id] as usize;
generic_args.args.get(index).and_then(|arg| match arg {
GenericArg::Lifetime(lt) => map.defs.get(<.hir_id).copied(),
_ => None,
})
}
ObjectLifetimeDefault::Ambiguous => None,
};
generics
.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(<) = 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> <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::AssocKind::Fn,
) {
bound_vars.extend(self.tcx.generics_of(assoc_fn.def_id).own_params.iter().map(
|param| match param.kind {
ty::GenericParamDefKind::Lifetime => ty::BoundVariableKind::Region(
ty::BoundRegionKind::BrNamed(param.def_id, param.name),
),
ty::GenericParamDefKind::Type { .. } => ty::BoundVariableKind::Ty(
ty::BoundTyKind::Param(param.def_id, param.name),
),
ty::GenericParamDefKind::Const { .. } => ty::BoundVariableKind::Const,
},
));
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::AssocKind::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_name: Ident,
assoc_kind: ty::AssocKind,
) -> 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_name_and_kind(
tcx,
assoc_name,
assoc_kind,
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_name));
let obligations = predicates.predicates.iter().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(input);
}
if !in_closure && let Some(output) = output {
this.visit_ty(output);
}
},
);
if in_closure && let Some(output) = output {
self.visit_ty(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 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,
Scope::Supertrait { s, .. }
| Scope::TraitRefBoundary { s, .. }
| Scope::LateBoundary { s, .. } => {
scope = s;
}
}
};
self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
}
#[instrument(level = "debug", skip(self))]
fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: ResolvedArg) {
debug!(span = ?lifetime_ref.ident.span);
self.map.defs.insert(lifetime_ref.hir_id, def);
}
/// Sometimes we resolve a lifetime, but later find that it is an
/// error (esp. around impl trait). In that case, we remove the
/// entry into `map.defs` so as not to confuse later code.
fn uninsert_lifetime_on_error(
&mut self,
lifetime_ref: &'tcx hir::Lifetime,
bad_def: ResolvedArg,
) {
// FIXME(#120456) - is `swap_remove` correct?
let old_value = self.map.defs.swap_remove(&lifetime_ref.hir_id);
assert_eq!(old_value, Some(bad_def));
}
}
/// Detects late-bound lifetimes and inserts them into
/// `late_bound`.
///
/// A region declared on a fn is **late-bound** if:
/// - it is constrained by an argument type;
/// - it does not appear in a where-clause.
///
/// "Constrained" basically means that it appears in any type but
/// not amongst the inputs to a projection. In other words, `<&'a
/// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
fn is_late_bound_map(
tcx: TyCtxt<'_>,
owner_id: hir::OwnerId,
) -> Option<&FxIndexSet<hir::ItemLocalId>> {
let decl = tcx.hir().fn_decl_by_hir_id(owner_id.into())?;
let generics = tcx.hir().get_generics(owner_id.def_id)?;
let mut late_bound = FxIndexSet::default();
let mut constrained_by_input = ConstrainedCollector { regions: Default::default(), tcx };
for arg_ty in decl.inputs {
constrained_by_input.visit_ty(arg_ty);
}
let mut appears_in_output = AllCollector::default();
intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
debug!(?constrained_by_input.regions);
// Walk the lifetimes that appear in where clauses.
//
// Subtle point: because we disallow nested bindings, we can just
// ignore binders here and scrape up all names we see.
let mut appears_in_where_clause = AllCollector::default();
appears_in_where_clause.visit_generics(generics);
debug!(?appears_in_where_clause.regions);
// Late bound regions are those that:
// - appear in the inputs
// - do not appear in the where-clauses
// - are not implicitly captured by `impl Trait`
for param in generics.params {
match param.kind {
hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
// Neither types nor consts are late-bound.
hir::GenericParamKind::Type { .. } | hir::GenericParamKind::Const { .. } => continue,
}
// appears in the where clauses? early-bound.
if appears_in_where_clause.regions.contains(¶m.def_id) {
continue;
}
// does not appear in the inputs, but appears in the return type? early-bound.
if !constrained_by_input.regions.contains(¶m.def_id)
&& appears_in_output.regions.contains(¶m.def_id)
{
continue;
}
debug!("lifetime {:?} with id {:?} is late-bound", param.name.ident(), param.def_id);
let inserted = late_bound.insert(param.hir_id.local_id);
assert!(inserted, "visited lifetime {:?} twice", param.def_id);
}
debug!(?late_bound);
return Some(tcx.arena.alloc(late_bound));
/// Visits a `ty::Ty` collecting information about what generic parameters are constrained.
///
/// The visitor does not operate on `hir::Ty` so that it can be called on the rhs of a `type Alias<...> = ...;`
/// which may live in a separate crate so there would not be any hir available. Instead we use the `type_of`
/// query to obtain a `ty::Ty` which will be present even in cross crate scenarios. It also naturally
/// handles cycle detection as we go through the query system.
///
/// This is necessary in the first place for the following case:
/// ```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>) {
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::LifetimeName::Param(def_id) = lifetime_ref.res {
self.regions.insert(def_id);
}
}
}
#[derive(Default)]
struct AllCollector {
regions: FxHashSet<LocalDefId>,
}
impl<'v> Visitor<'v> for AllCollector {
fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
if let hir::LifetimeName::Param(def_id) = lifetime_ref.res {
self.regions.insert(def_id);
}
}
}
}
pub fn deny_non_region_late_bound(
tcx: TyCtxt<'_>,
bound_vars: &mut FxIndexMap<LocalDefId, ResolvedArg>,
where_: &str,
) {
let mut first = true;
for (var, arg) in bound_vars {
let Node::GenericParam(param) = tcx.hir_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(!tcx.features().non_lifetime_binders || !first);
first = false;
*arg = ResolvedArg::Error(guar);
}
}