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chromium / external / github.com / rust-lang / rust / e957ed9d10ec589bdd523b88b4b44c41b1ecf763 / . / src / librustc / middle / resolve_lifetime.rs
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//! Name resolution for lifetimes.
//!
//! Name resolution for lifetimes follows MUCH simpler rules than the
//! full resolve. For example, lifetime names are never exported or
//! used between functions, and they operate in a purely top-down
//! way. Therefore we break lifetime name resolution into a separate pass.
use crate::hir::def::Def;
use crate::hir::def_id::{CrateNum, DefId, LocalDefId, LOCAL_CRATE};
use crate::hir::map::Map;
use crate::hir::{GenericArg, GenericParam, ItemLocalId, LifetimeName, Node, ParamName};
use crate::ty::{self, DefIdTree, GenericParamDefKind, TyCtxt};
use crate::errors::{Applicability, DiagnosticBuilder};
use crate::rustc::lint;
use rustc_data_structures::sync::Lrc;
use crate::session::Session;
use std::borrow::Cow;
use std::cell::Cell;
use std::mem::replace;
use syntax::ast;
use syntax::attr;
use syntax::ptr::P;
use syntax::symbol::keywords;
use syntax_pos::Span;
use crate::util::nodemap::{DefIdMap, FxHashMap, FxHashSet, NodeMap, NodeSet};
use crate::hir::intravisit::{self, NestedVisitorMap, Visitor};
use crate::hir::{self, GenericParamKind, LifetimeParamKind};
/// The origin of a named lifetime definition.
///
/// This is used to prevent the usage of in-band lifetimes in `Fn`/`fn` syntax.
#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
pub enum LifetimeDefOrigin {
// Explicit binders like `fn foo<'a>(x: &'a u8)` or elided like `impl Foo<&u32>`
ExplicitOrElided,
// In-band declarations like `fn foo(x: &'a u8)`
InBand,
// Some kind of erroneous origin
Error,
}
impl LifetimeDefOrigin {
fn from_param(param: &GenericParam) -> Self {
match param.kind {
GenericParamKind::Lifetime { kind } => match kind {
LifetimeParamKind::InBand => LifetimeDefOrigin::InBand,
LifetimeParamKind::Explicit => LifetimeDefOrigin::ExplicitOrElided,
LifetimeParamKind::Elided => LifetimeDefOrigin::ExplicitOrElided,
LifetimeParamKind::Error => LifetimeDefOrigin::Error,
},
_ => bug!("expected a lifetime param"),
}
}
}
// This counts the no of times a lifetime is used
#[derive(Clone, Copy, Debug)]
pub enum LifetimeUseSet<'tcx> {
One(&'tcx hir::Lifetime),
Many,
}
#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
pub enum Region {
Static,
EarlyBound(
/* index */ u32,
/* lifetime decl */ DefId,
LifetimeDefOrigin,
),
LateBound(
ty::DebruijnIndex,
/* lifetime decl */ DefId,
LifetimeDefOrigin,
),
LateBoundAnon(ty::DebruijnIndex, /* anon index */ u32),
Free(DefId, /* lifetime decl */ DefId),
}
impl Region {
fn early(hir_map: &Map<'_>, index: &mut u32, param: &GenericParam) -> (ParamName, Region) {
let i = *index;
*index += 1;
let def_id = hir_map.local_def_id(param.id);
let origin = LifetimeDefOrigin::from_param(param);
debug!("Region::early: index={} def_id={:?}", i, def_id);
(param.name.modern(), Region::EarlyBound(i, def_id, origin))
}
fn late(hir_map: &Map<'_>, param: &GenericParam) -> (ParamName, Region) {
let depth = ty::INNERMOST;
let def_id = hir_map.local_def_id(param.id);
let origin = LifetimeDefOrigin::from_param(param);
debug!(
"Region::late: param={:?} depth={:?} def_id={:?} origin={:?}",
param, depth, def_id, origin,
);
(
param.name.modern(),
Region::LateBound(depth, def_id, origin),
)
}
fn late_anon(index: &Cell<u32>) -> Region {
let i = index.get();
index.set(i + 1);
let depth = ty::INNERMOST;
Region::LateBoundAnon(depth, i)
}
fn id(&self) -> Option<DefId> {
match *self {
Region::Static | Region::LateBoundAnon(..) => None,
Region::EarlyBound(_, id, _) | Region::LateBound(_, id, _) | Region::Free(_, id) => {
Some(id)
}
}
}
fn shifted(self, amount: u32) -> Region {
match self {
Region::LateBound(debruijn, id, origin) => {
Region::LateBound(debruijn.shifted_in(amount), id, origin)
}
Region::LateBoundAnon(debruijn, index) => {
Region::LateBoundAnon(debruijn.shifted_in(amount), index)
}
_ => self,
}
}
fn shifted_out_to_binder(self, binder: ty::DebruijnIndex) -> Region {
match self {
Region::LateBound(debruijn, id, origin) => {
Region::LateBound(debruijn.shifted_out_to_binder(binder), id, origin)
}
Region::LateBoundAnon(debruijn, index) => {
Region::LateBoundAnon(debruijn.shifted_out_to_binder(binder), index)
}
_ => self,
}
}
fn subst<'a, L>(self, mut params: L, map: &NamedRegionMap) -> Option<Region>
where
L: Iterator<Item = &'a hir::Lifetime>,
{
if let Region::EarlyBound(index, _, _) = self {
params
.nth(index as usize)
.and_then(|lifetime| map.defs.get(&lifetime.id).cloned())
} else {
Some(self)
}
}
}
/// A set containing, at most, one known element.
/// If two distinct values are inserted into a set, then it
/// becomes `Many`, which can be used to detect ambiguities.
#[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Debug)]
pub enum Set1<T> {
Empty,
One(T),
Many,
}
impl<T: PartialEq> Set1<T> {
pub fn insert(&mut self, value: T) {
if let Set1::Empty = *self {
*self = Set1::One(value);
return;
}
if let Set1::One(ref old) = *self {
if *old == value {
return;
}
}
*self = Set1::Many;
}
}
pub type ObjectLifetimeDefault = Set1<Region>;
/// Maps the id of each lifetime reference to the lifetime decl
/// that it corresponds to.
///
/// FIXME. This struct gets converted to a `ResolveLifetimes` for
/// actual use. It has the same data, but indexed by `DefIndex`. This
/// is silly.
#[derive(Default)]
struct NamedRegionMap {
// maps from every use of a named (not anonymous) lifetime to a
// `Region` describing how that region is bound
pub defs: NodeMap<Region>,
// the set of lifetime def ids that are late-bound; a region can
// be late-bound if (a) it does NOT appear in a where-clause and
// (b) it DOES appear in the arguments.
pub late_bound: NodeSet,
// For each type and trait definition, maps type parameters
// to the trait object lifetime defaults computed from them.
pub object_lifetime_defaults: NodeMap<Vec<ObjectLifetimeDefault>>,
}
/// See `NamedRegionMap`.
#[derive(Default)]
pub struct ResolveLifetimes {
defs: FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Region>>>,
late_bound: FxHashMap<LocalDefId, Lrc<FxHashSet<ItemLocalId>>>,
object_lifetime_defaults:
FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
}
impl_stable_hash_for!(struct crate::middle::resolve_lifetime::ResolveLifetimes {
defs,
late_bound,
object_lifetime_defaults
});
struct LifetimeContext<'a, 'tcx: 'a> {
tcx: TyCtxt<'a, 'tcx, 'tcx>,
map: &'a mut NamedRegionMap,
scope: ScopeRef<'a>,
/// Deep breath. Our representation for poly trait refs contains a single
/// binder and thus we only allow a single level of quantification. However,
/// the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
/// and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the de Bruijn indices
/// correct when representing these constraints, we should only introduce one
/// scope. However, we want to support both locations for the quantifier and
/// during lifetime resolution we want precise information (so we can't
/// desugar in an earlier phase).
///
/// SO, if we encounter a quantifier at the outer scope, we set
/// trait_ref_hack to true (and introduce a scope), and then if we encounter
/// a quantifier at the inner scope, we error. If trait_ref_hack is false,
/// then we introduce the scope at the inner quantifier.
///
/// I'm sorry.
trait_ref_hack: bool,
/// Used to disallow the use of in-band lifetimes in `fn` or `Fn` syntax.
is_in_fn_syntax: bool,
/// List of labels in the function/method currently under analysis.
labels_in_fn: Vec<ast::Ident>,
/// Cache for cross-crate per-definition object lifetime defaults.
xcrate_object_lifetime_defaults: DefIdMap<Vec<ObjectLifetimeDefault>>,
lifetime_uses: &'a mut DefIdMap<LifetimeUseSet<'tcx>>,
}
#[derive(Debug)]
enum Scope<'a> {
/// Declares lifetimes, and each can be early-bound or late-bound.
/// The `DebruijnIndex` of late-bound lifetimes starts at `1` and
/// it should be shifted by the number of `Binder`s in between the
/// declaration `Binder` and the location it's referenced from.
Binder {
lifetimes: FxHashMap<hir::ParamName, Region>,
/// if we extend this scope with another scope, what is the next index
/// we should use for an early-bound region?
next_early_index: u32,
/// Flag is set to true if, in this binder, `'_` would be
/// equivalent to a "single-use region". This is true on
/// impls, but not other kinds of items.
track_lifetime_uses: bool,
/// Whether or not this binder would serve as the parent
/// binder for abstract types introduced within. For example:
///
/// fn foo<'a>() -> impl for<'b> Trait<Item = impl Trait2<'a>>
///
/// Here, the abstract types we create for the `impl Trait`
/// and `impl Trait2` references will both have the `foo` item
/// as their parent. When we get to `impl Trait2`, we find
/// that it is nested within the `for<>` binder -- this flag
/// allows us to skip that when looking for the parent binder
/// of the resulting abstract type.
abstract_type_parent: bool,
s: ScopeRef<'a>,
},
/// Lifetimes introduced by a fn are scoped to the call-site for that fn,
/// if this is a fn body, otherwise the original definitions are used.
/// Unspecified lifetimes are inferred, unless an elision scope is nested,
/// e.g., `(&T, fn(&T) -> &T);` becomes `(&'_ T, for<'a> fn(&'a T) -> &'a T)`.
Body {
id: hir::BodyId,
s: ScopeRef<'a>,
},
/// A scope which either determines unspecified lifetimes or errors
/// on them (e.g., due to ambiguity). For more details, see `Elide`.
Elision {
elide: Elide,
s: ScopeRef<'a>,
},
/// Use a specific lifetime (if `Some`) or leave it unset (to be
/// inferred in a function body or potentially error outside one),
/// for the default choice of lifetime in a trait object type.
ObjectLifetimeDefault {
lifetime: Option<Region>,
s: ScopeRef<'a>,
},
Root,
}
#[derive(Clone, Debug)]
enum Elide {
/// Use a fresh anonymous late-bound lifetime each time, by
/// incrementing the counter to generate sequential indices.
FreshLateAnon(Cell<u32>),
/// Always use this one lifetime.
Exact(Region),
/// Less or more than one lifetime were found, error on unspecified.
Error(Vec<ElisionFailureInfo>),
}
#[derive(Clone, Debug)]
struct ElisionFailureInfo {
/// Where we can find the argument pattern.
parent: Option<hir::BodyId>,
/// The index of the argument in the original definition.
index: usize,
lifetime_count: usize,
have_bound_regions: bool,
}
type ScopeRef<'a> = &'a Scope<'a>;
const ROOT_SCOPE: ScopeRef<'static> = &Scope::Root;
pub fn provide(providers: &mut ty::query::Providers<'_>) {
*providers = ty::query::Providers {
resolve_lifetimes,
named_region_map: |tcx, id| {
let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id).cloned()
},
is_late_bound_map: |tcx, id| {
let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
tcx.resolve_lifetimes(LOCAL_CRATE)
.late_bound
.get(&id)
.cloned()
},
object_lifetime_defaults_map: |tcx, id| {
let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
tcx.resolve_lifetimes(LOCAL_CRATE)
.object_lifetime_defaults
.get(&id)
.cloned()
},
..*providers
};
// (*) FIXME the query should be defined to take a LocalDefId
}
/// Computes the `ResolveLifetimes` map that contains data for the
/// entire crate. You should not read the result of this query
/// directly, but rather use `named_region_map`, `is_late_bound_map`,
/// etc.
fn resolve_lifetimes<'tcx>(
tcx: TyCtxt<'_, 'tcx, 'tcx>,
for_krate: CrateNum,
) -> Lrc<ResolveLifetimes> {
assert_eq!(for_krate, LOCAL_CRATE);
let named_region_map = krate(tcx);
let mut rl = ResolveLifetimes::default();
for (k, v) in named_region_map.defs {
let hir_id = tcx.hir().node_to_hir_id(k);
let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
Lrc::get_mut(map).unwrap().insert(hir_id.local_id, v);
}
for k in named_region_map.late_bound {
let hir_id = tcx.hir().node_to_hir_id(k);
let map = rl.late_bound
.entry(hir_id.owner_local_def_id())
.or_default();
Lrc::get_mut(map).unwrap().insert(hir_id.local_id);
}
for (k, v) in named_region_map.object_lifetime_defaults {
let hir_id = tcx.hir().node_to_hir_id(k);
let map = rl.object_lifetime_defaults
.entry(hir_id.owner_local_def_id())
.or_default();
Lrc::get_mut(map)
.unwrap()
.insert(hir_id.local_id, Lrc::new(v));
}
Lrc::new(rl)
}
fn krate<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) -> NamedRegionMap {
let krate = tcx.hir().krate();
let mut map = NamedRegionMap {
defs: Default::default(),
late_bound: Default::default(),
object_lifetime_defaults: compute_object_lifetime_defaults(tcx),
};
{
let mut visitor = LifetimeContext {
tcx,
map: &mut map,
scope: ROOT_SCOPE,
trait_ref_hack: false,
is_in_fn_syntax: false,
labels_in_fn: vec![],
xcrate_object_lifetime_defaults: Default::default(),
lifetime_uses: &mut Default::default(),
};
for (_, item) in &krate.items {
visitor.visit_item(item);
}
}
map
}
/// In traits, there is an implicit `Self` type parameter which comes before the generics.
/// We have to account for this when computing the index of the other generic parameters.
/// This function returns whether there is such an implicit parameter defined on the given item.
fn sub_items_have_self_param(node: &hir::ItemKind) -> bool {
match *node {
hir::ItemKind::Trait(..) |
hir::ItemKind::TraitAlias(..) => true,
_ => false,
}
}
impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::All(&self.tcx.hir())
}
// We want to nest trait/impl items in their parent, but nothing else.
fn visit_nested_item(&mut self, _: hir::ItemId) {}
fn visit_nested_body(&mut self, body: hir::BodyId) {
// Each body has their own set of labels, save labels.
let saved = replace(&mut self.labels_in_fn, vec![]);
let body = self.tcx.hir().body(body);
extract_labels(self, body);
self.with(
Scope::Body {
id: body.id(),
s: self.scope,
},
|_, this| {
this.visit_body(body);
},
);
replace(&mut self.labels_in_fn, saved);
}
fn visit_item(&mut self, item: &'tcx hir::Item) {
match item.node {
hir::ItemKind::Fn(ref decl, _, ref generics, _) => {
self.visit_early_late(None, decl, generics, |this| {
intravisit::walk_item(this, item);
});
}
hir::ItemKind::ExternCrate(_)
| hir::ItemKind::Use(..)
| hir::ItemKind::Mod(..)
| hir::ItemKind::ForeignMod(..)
| hir::ItemKind::GlobalAsm(..) => {
// These sorts of items have no lifetime parameters at all.
intravisit::walk_item(self, item);
}
hir::ItemKind::Static(..) | hir::ItemKind::Const(..) => {
// No lifetime parameters, but implied 'static.
let scope = Scope::Elision {
elide: Elide::Exact(Region::Static),
s: ROOT_SCOPE,
};
self.with(scope, |_, this| intravisit::walk_item(this, item));
}
hir::ItemKind::Existential(hir::ExistTy {
impl_trait_fn: Some(_),
..
}) => {
// currently existential type declarations are just generated from impl Trait
// items. doing anything on this node is irrelevant, as we currently don't need
// it.
}
hir::ItemKind::Ty(_, ref generics)
| hir::ItemKind::Existential(hir::ExistTy {
impl_trait_fn: None,
ref generics,
..
})
| hir::ItemKind::Enum(_, ref generics)
| hir::ItemKind::Struct(_, ref generics)
| hir::ItemKind::Union(_, ref generics)
| hir::ItemKind::Trait(_, _, ref generics, ..)
| hir::ItemKind::TraitAlias(ref generics, ..)
| hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
// Impls permit `'_` to be used and it is equivalent to "some fresh lifetime name".
// This is not true for other kinds of items.x
let track_lifetime_uses = match item.node {
hir::ItemKind::Impl(..) => true,
_ => false,
};
// These kinds of items have only early-bound lifetime parameters.
let mut index = if sub_items_have_self_param(&item.node) {
1 // Self comes before lifetimes
} else {
0
};
let mut type_count = 0;
let lifetimes = generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::early(&self.tcx.hir(), &mut index, param))
}
GenericParamKind::Type { .. } => {
type_count += 1;
None
}
})
.collect();
let scope = Scope::Binder {
lifetimes,
next_early_index: index + type_count,
abstract_type_parent: true,
track_lifetime_uses,
s: ROOT_SCOPE,
};
self.with(scope, |old_scope, this| {
this.check_lifetime_params(old_scope, &generics.params);
intravisit::walk_item(this, item);
});
}
}
}
fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem) {
match item.node {
hir::ForeignItemKind::Fn(ref decl, _, ref generics) => {
self.visit_early_late(None, decl, generics, |this| {
intravisit::walk_foreign_item(this, item);
})
}
hir::ForeignItemKind::Static(..) => {
intravisit::walk_foreign_item(self, item);
}
hir::ForeignItemKind::Type => {
intravisit::walk_foreign_item(self, item);
}
}
}
fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
debug!("visit_ty: id={:?} ty={:?}", ty.id, ty);
match ty.node {
hir::TyKind::BareFn(ref c) => {
let next_early_index = self.next_early_index();
let was_in_fn_syntax = self.is_in_fn_syntax;
self.is_in_fn_syntax = true;
let scope = Scope::Binder {
lifetimes: c.generic_params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::late(&self.tcx.hir(), param))
}
_ => None,
})
.collect(),
s: self.scope,
next_early_index,
track_lifetime_uses: true,
abstract_type_parent: false,
};
self.with(scope, |old_scope, this| {
// a bare fn has no bounds, so everything
// contained within is scoped within its binder.
this.check_lifetime_params(old_scope, &c.generic_params);
intravisit::walk_ty(this, ty);
});
self.is_in_fn_syntax = was_in_fn_syntax;
}
hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
for bound in bounds {
self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
}
match lifetime.name {
LifetimeName::Implicit => {
// 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::Underscore => {
// 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
self.resolve_elided_lifetimes(vec![lifetime])
}
LifetimeName::Param(_) | LifetimeName::Static => {
// If the user wrote an explicit name, use that.
self.visit_lifetime(lifetime);
}
LifetimeName::Error => {}
}
}
hir::TyKind::Rptr(ref lifetime_ref, ref mt) => {
self.visit_lifetime(lifetime_ref);
let scope = Scope::ObjectLifetimeDefault {
lifetime: self.map.defs.get(&lifetime_ref.id).cloned(),
s: self.scope,
};
self.with(scope, |_, this| this.visit_ty(&mt.ty));
}
hir::TyKind::Def(item_id, ref lifetimes) => {
// Resolve the lifetimes in the bounds to the lifetime defs in the generics.
// `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
// `abstract type MyAnonTy<'b>: MyTrait<'b>;`
// ^ ^ this gets resolved in the scope of
// the exist_ty generics
let (generics, bounds) = match self.tcx.hir().expect_item(item_id.id).node {
// named existential types are reached via TyKind::Path
// this arm is for `impl Trait` in the types of statics, constants and locals
hir::ItemKind::Existential(hir::ExistTy {
impl_trait_fn: None,
..
}) => {
intravisit::walk_ty(self, ty);
return;
}
// RPIT (return position impl trait)
hir::ItemKind::Existential(hir::ExistTy {
ref generics,
ref bounds,
..
}) => (generics, bounds),
ref i => bug!("impl Trait pointed to non-existential type?? {:#?}", i),
};
// Resolve the lifetimes that are applied to the existential type.
// These are resolved in the current scope.
// `fn foo<'a>() -> impl MyTrait<'a> { ... }` desugars to
// `fn foo<'a>() -> MyAnonTy<'a> { ... }`
// ^ ^this gets resolved in the current scope
for lifetime in lifetimes {
if let hir::GenericArg::Lifetime(lifetime) = lifetime {
self.visit_lifetime(lifetime);
// Check for predicates like `impl for<'a> Trait<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.id).cloned();
if let Some(Region::LateBound(_, def_id, _)) = def {
if let Some(node_id) = self.tcx.hir().as_local_node_id(def_id) {
// Ensure that the parent of the def is an item, not HRTB
let parent_id = self.tcx.hir().get_parent_node(node_id);
let parent_impl_id = hir::ImplItemId { node_id: parent_id };
let parent_trait_id = hir::TraitItemId { node_id: parent_id };
let krate = self.tcx.hir().forest.krate();
if !(krate.items.contains_key(&parent_id)
|| krate.impl_items.contains_key(&parent_impl_id)
|| krate.trait_items.contains_key(&parent_trait_id))
{
span_err!(
self.tcx.sess,
lifetime.span,
E0657,
"`impl Trait` can only capture lifetimes \
bound at the fn or impl level"
);
self.uninsert_lifetime_on_error(lifetime, def.unwrap());
}
}
}
}
}
// We want to start our early-bound indices at the end of the parent scope,
// not including any parent `impl Trait`s.
let mut index = self.next_early_index_for_abstract_type();
debug!("visit_ty: index = {}", index);
let mut elision = None;
let mut lifetimes = FxHashMap::default();
let mut type_count = 0;
for param in &generics.params {
match param.kind {
GenericParamKind::Lifetime { .. } => {
let (name, reg) = Region::early(&self.tcx.hir(), &mut index, &param);
if let hir::ParamName::Plain(param_name) = name {
if param_name.name == keywords::UnderscoreLifetime.name() {
// Pick the elided lifetime "definition" if one exists
// and use it to make an elision scope.
elision = Some(reg);
} else {
lifetimes.insert(name, reg);
}
} else {
lifetimes.insert(name, reg);
}
}
GenericParamKind::Type { .. } => {
type_count += 1;
}
}
}
let next_early_index = index + type_count;
if let Some(elision_region) = elision {
let scope = Scope::Elision {
elide: Elide::Exact(elision_region),
s: self.scope,
};
self.with(scope, |_old_scope, this| {
let scope = Scope::Binder {
lifetimes,
next_early_index,
s: this.scope,
track_lifetime_uses: true,
abstract_type_parent: false,
};
this.with(scope, |_old_scope, this| {
this.visit_generics(generics);
for bound in bounds {
this.visit_param_bound(bound);
}
});
});
} else {
let scope = Scope::Binder {
lifetimes,
next_early_index,
s: self.scope,
track_lifetime_uses: true,
abstract_type_parent: false,
};
self.with(scope, |_old_scope, this| {
this.visit_generics(generics);
for bound in bounds {
this.visit_param_bound(bound);
}
});
}
}
_ => intravisit::walk_ty(self, ty),
}
}
fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
use self::hir::TraitItemKind::*;
match trait_item.node {
Method(ref sig, _) => {
let tcx = self.tcx;
self.visit_early_late(
Some(tcx.hir().get_parent(trait_item.id)),
&sig.decl,
&trait_item.generics,
|this| intravisit::walk_trait_item(this, trait_item),
);
}
Type(ref bounds, ref ty) => {
let generics = &trait_item.generics;
let mut index = self.next_early_index();
debug!("visit_ty: index = {}", index);
let mut type_count = 0;
let lifetimes = generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::early(&self.tcx.hir(), &mut index, param))
}
GenericParamKind::Type { .. } => {
type_count += 1;
None
}
})
.collect();
let scope = Scope::Binder {
lifetimes,
next_early_index: index + type_count,
s: self.scope,
track_lifetime_uses: true,
abstract_type_parent: true,
};
self.with(scope, |_old_scope, this| {
this.visit_generics(generics);
for bound in bounds {
this.visit_param_bound(bound);
}
if let Some(ty) = ty {
this.visit_ty(ty);
}
});
}
Const(_, _) => {
// Only methods and types support generics.
assert!(trait_item.generics.params.is_empty());
intravisit::walk_trait_item(self, trait_item);
}
}
}
fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
use self::hir::ImplItemKind::*;
match impl_item.node {
Method(ref sig, _) => {
let tcx = self.tcx;
self.visit_early_late(
Some(tcx.hir().get_parent(impl_item.id)),
&sig.decl,
&impl_item.generics,
|this| intravisit::walk_impl_item(this, impl_item),
)
}
Type(ref ty) => {
let generics = &impl_item.generics;
let mut index = self.next_early_index();
let mut next_early_index = index;
debug!("visit_ty: index = {}", index);
let lifetimes = generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::early(&self.tcx.hir(), &mut index, param))
}
GenericParamKind::Type { .. } => {
next_early_index += 1;
None
}
})
.collect();
let scope = Scope::Binder {
lifetimes,
next_early_index,
s: self.scope,
track_lifetime_uses: true,
abstract_type_parent: true,
};
self.with(scope, |_old_scope, this| {
this.visit_generics(generics);
this.visit_ty(ty);
});
}
Existential(ref bounds) => {
let generics = &impl_item.generics;
let mut index = self.next_early_index();
let mut next_early_index = index;
debug!("visit_ty: index = {}", index);
let lifetimes = generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::early(&self.tcx.hir(), &mut index, param))
}
GenericParamKind::Type { .. } => {
next_early_index += 1;
None
}
})
.collect();
let scope = Scope::Binder {
lifetimes,
next_early_index,
s: self.scope,
track_lifetime_uses: true,
abstract_type_parent: true,
};
self.with(scope, |_old_scope, this| {
this.visit_generics(generics);
for bound in bounds {
this.visit_param_bound(bound);
}
});
}
Const(_, _) => {
// Only methods and types support generics.
assert!(impl_item.generics.params.is_empty());
intravisit::walk_impl_item(self, impl_item);
}
}
}
fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
if lifetime_ref.is_elided() {
self.resolve_elided_lifetimes(vec![lifetime_ref]);
return;
}
if lifetime_ref.is_static() {
self.insert_lifetime(lifetime_ref, Region::Static);
return;
}
self.resolve_lifetime_ref(lifetime_ref);
}
fn visit_path(&mut self, path: &'tcx hir::Path, _: hir::HirId) {
for (i, segment) in path.segments.iter().enumerate() {
let depth = path.segments.len() - i - 1;
if let Some(ref args) = segment.args {
self.visit_segment_args(path.def, depth, args);
}
}
}
fn visit_fn_decl(&mut self, fd: &'tcx hir::FnDecl) {
let output = match fd.output {
hir::DefaultReturn(_) => None,
hir::Return(ref ty) => Some(ty),
};
self.visit_fn_like_elision(&fd.inputs, output);
}
fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
check_mixed_explicit_and_in_band_defs(self.tcx, &generics.params);
for param in &generics.params {
match param.kind {
GenericParamKind::Lifetime { .. } => {}
GenericParamKind::Type { ref default, .. } => {
walk_list!(self, visit_param_bound, &param.bounds);
if let Some(ref ty) = default {
self.visit_ty(&ty);
}
}
}
}
for predicate in &generics.where_clause.predicates {
match predicate {
&hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
ref bounded_ty,
ref bounds,
ref bound_generic_params,
..
}) => {
let lifetimes: FxHashMap<_, _> = bound_generic_params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::late(&self.tcx.hir(), param))
}
_ => None,
})
.collect();
if !lifetimes.is_empty() {
self.trait_ref_hack = true;
let next_early_index = self.next_early_index();
let scope = Scope::Binder {
lifetimes,
s: self.scope,
next_early_index,
track_lifetime_uses: true,
abstract_type_parent: false,
};
let result = self.with(scope, |old_scope, this| {
this.check_lifetime_params(old_scope, &bound_generic_params);
this.visit_ty(&bounded_ty);
walk_list!(this, visit_param_bound, bounds);
});
self.trait_ref_hack = false;
result
} else {
self.visit_ty(&bounded_ty);
walk_list!(self, visit_param_bound, bounds);
}
}
&hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
ref lifetime,
ref bounds,
..
}) => {
self.visit_lifetime(lifetime);
walk_list!(self, visit_param_bound, bounds);
}
&hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
ref lhs_ty,
ref rhs_ty,
..
}) => {
self.visit_ty(lhs_ty);
self.visit_ty(rhs_ty);
}
}
}
}
fn visit_poly_trait_ref(
&mut self,
trait_ref: &'tcx hir::PolyTraitRef,
_modifier: hir::TraitBoundModifier,
) {
debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
if !self.trait_ref_hack || trait_ref.bound_generic_params.iter().any(|param| {
match param.kind {
GenericParamKind::Lifetime { .. } => true,
_ => false,
}
}) {
if self.trait_ref_hack {
span_err!(
self.tcx.sess,
trait_ref.span,
E0316,
"nested quantification of lifetimes"
);
}
let next_early_index = self.next_early_index();
let scope = Scope::Binder {
lifetimes: trait_ref
.bound_generic_params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
Some(Region::late(&self.tcx.hir(), param))
}
_ => None,
})
.collect(),
s: self.scope,
next_early_index,
track_lifetime_uses: true,
abstract_type_parent: false,
};
self.with(scope, |old_scope, this| {
this.check_lifetime_params(old_scope, &trait_ref.bound_generic_params);
walk_list!(this, visit_generic_param, &trait_ref.bound_generic_params);
this.visit_trait_ref(&trait_ref.trait_ref)
})
} else {
self.visit_trait_ref(&trait_ref.trait_ref)
}
}
}
#[derive(Copy, Clone, PartialEq)]
enum ShadowKind {
Label,
Lifetime,
}
struct Original {
kind: ShadowKind,
span: Span,
}
struct Shadower {
kind: ShadowKind,
span: Span,
}
fn original_label(span: Span) -> Original {
Original {
kind: ShadowKind::Label,
span: span,
}
}
fn shadower_label(span: Span) -> Shadower {
Shadower {
kind: ShadowKind::Label,
span: span,
}
}
fn original_lifetime(span: Span) -> Original {
Original {
kind: ShadowKind::Lifetime,
span: span,
}
}
fn shadower_lifetime(param: &hir::GenericParam) -> Shadower {
Shadower {
kind: ShadowKind::Lifetime,
span: param.span,
}
}
impl ShadowKind {
fn desc(&self) -> &'static str {
match *self {
ShadowKind::Label => "label",
ShadowKind::Lifetime => "lifetime",
}
}
}
fn check_mixed_explicit_and_in_band_defs(tcx: TyCtxt<'_, '_, '_>, params: &P<[hir::GenericParam]>) {
let lifetime_params: Vec<_> = params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { kind, .. } => Some((kind, param.span)),
_ => None,
})
.collect();
let explicit = lifetime_params
.iter()
.find(|(kind, _)| *kind == LifetimeParamKind::Explicit);
let in_band = lifetime_params
.iter()
.find(|(kind, _)| *kind == LifetimeParamKind::InBand);
if let (Some((_, explicit_span)), Some((_, in_band_span))) = (explicit, in_band) {
struct_span_err!(
tcx.sess,
*in_band_span,
E0688,
"cannot mix in-band and explicit lifetime definitions"
).span_label(*in_band_span, "in-band lifetime definition here")
.span_label(*explicit_span, "explicit lifetime definition here")
.emit();
}
}
fn signal_shadowing_problem(
tcx: TyCtxt<'_, '_, '_>,
name: ast::Name,
orig: Original,
shadower: Shadower,
) {
let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
// lifetime/lifetime shadowing is an error
struct_span_err!(
tcx.sess,
shadower.span,
E0496,
"{} name `{}` shadows a \
{} name that is already in scope",
shadower.kind.desc(),
name,
orig.kind.desc()
)
} else {
// shadowing involving a label is only a warning, due to issues with
// labels and lifetimes not being macro-hygienic.
tcx.sess.struct_span_warn(
shadower.span,
&format!(
"{} name `{}` shadows a \
{} name that is already in scope",
shadower.kind.desc(),
name,
orig.kind.desc()
),
)
};
err.span_label(orig.span, "first declared here");
err.span_label(shadower.span, format!("lifetime {} already in scope", name));
err.emit();
}
// Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
// if one of the label shadows a lifetime or another label.
fn extract_labels(ctxt: &mut LifetimeContext<'_, '_>, body: &hir::Body) {
struct GatherLabels<'a, 'tcx: 'a> {
tcx: TyCtxt<'a, 'tcx, 'tcx>,
scope: ScopeRef<'a>,
labels_in_fn: &'a mut Vec<ast::Ident>,
}
let mut gather = GatherLabels {
tcx: ctxt.tcx,
scope: ctxt.scope,
labels_in_fn: &mut ctxt.labels_in_fn,
};
gather.visit_body(body);
impl<'v, 'a, 'tcx> Visitor<'v> for GatherLabels<'a, 'tcx> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
NestedVisitorMap::None
}
fn visit_expr(&mut self, ex: &hir::Expr) {
if let Some(label) = expression_label(ex) {
for prior_label in &self.labels_in_fn[..] {
// FIXME (#24278): non-hygienic comparison
if label.name == prior_label.name {
signal_shadowing_problem(
self.tcx,
label.name,
original_label(prior_label.span),
shadower_label(label.span),
);
}
}
check_if_label_shadows_lifetime(self.tcx, self.scope, label);
self.labels_in_fn.push(label);
}
intravisit::walk_expr(self, ex)
}
}
fn expression_label(ex: &hir::Expr) -> Option<ast::Ident> {
match ex.node {
hir::ExprKind::While(.., Some(label)) | hir::ExprKind::Loop(_, Some(label), _) => {
Some(label.ident)
}
_ => None,
}
}
fn check_if_label_shadows_lifetime(
tcx: TyCtxt<'_, '_, '_>,
mut scope: ScopeRef<'_>,
label: ast::Ident,
) {
loop {
match *scope {
Scope::Body { s, .. }
| Scope::Elision { s, .. }
| Scope::ObjectLifetimeDefault { s, .. } => {
scope = s;
}
Scope::Root => {
return;
}
Scope::Binder {
ref lifetimes, s, ..
} => {
// FIXME (#24278): non-hygienic comparison
if let Some(def) = lifetimes.get(&hir::ParamName::Plain(label.modern())) {
let node_id = tcx.hir().as_local_node_id(def.id().unwrap()).unwrap();
signal_shadowing_problem(
tcx,
label.name,
original_lifetime(tcx.hir().span(node_id)),
shadower_label(label.span),
);
return;
}
scope = s;
}
}
}
}
}
fn compute_object_lifetime_defaults(
tcx: TyCtxt<'_, '_, '_>,
) -> NodeMap<Vec<ObjectLifetimeDefault>> {
let mut map = NodeMap::default();
for item in tcx.hir().krate().items.values() {
match item.node {
hir::ItemKind::Struct(_, ref generics)
| hir::ItemKind::Union(_, ref generics)
| hir::ItemKind::Enum(_, ref generics)
| hir::ItemKind::Existential(hir::ExistTy {
ref generics,
impl_trait_fn: None,
..
})
| hir::ItemKind::Ty(_, ref generics)
| hir::ItemKind::Trait(_, _, ref generics, ..) => {
let result = object_lifetime_defaults_for_item(tcx, generics);
// Debugging aid.
if attr::contains_name(&item.attrs, "rustc_object_lifetime_default") {
let object_lifetime_default_reprs: String = result
.iter()
.map(|set| match *set {
Set1::Empty => "BaseDefault".into(),
Set1::One(Region::Static) => "'static".into(),
Set1::One(Region::EarlyBound(mut i, _, _)) => generics
.params
.iter()
.find_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
if i == 0 {
return Some(param.name.ident().to_string().into());
}
i -= 1;
None
}
_ => None,
})
.unwrap(),
Set1::One(_) => bug!(),
Set1::Many => "Ambiguous".into(),
})
.collect::<Vec<Cow<'static, str>>>()
.join(",");
tcx.sess.span_err(item.span, &object_lifetime_default_reprs);
}
map.insert(item.id, result);
}
_ => {}
}
}
map
}
/// Scan the bounds and where-clauses on parameters to extract bounds
/// of the form `T:'a` so as to determine the `ObjectLifetimeDefault`
/// for each type parameter.
fn object_lifetime_defaults_for_item(
tcx: TyCtxt<'_, '_, '_>,
generics: &hir::Generics,
) -> Vec<ObjectLifetimeDefault> {
fn add_bounds(set: &mut Set1<hir::LifetimeName>, bounds: &[hir::GenericBound]) {
for bound in bounds {
if let hir::GenericBound::Outlives(ref lifetime) = *bound {
set.insert(lifetime.name.modern());
}
}
}
generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => None,
GenericParamKind::Type { .. } => {
let mut set = Set1::Empty;
add_bounds(&mut set, &param.bounds);
let param_def_id = tcx.hir().local_def_id(param.id);
for predicate in &generics.where_clause.predicates {
// Look for `type: ...` where clauses.
let data = match *predicate {
hir::WherePredicate::BoundPredicate(ref data) => data,
_ => continue,
};
// Ignore `for<'a> type: ...` as they can change what
// lifetimes mean (although we could "just" handle it).
if !data.bound_generic_params.is_empty() {
continue;
}
let def = match data.bounded_ty.node {
hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => path.def,
_ => continue,
};
if def == Def::TyParam(param_def_id) {
add_bounds(&mut set, &data.bounds);
}
}
Some(match set {
Set1::Empty => Set1::Empty,
Set1::One(name) => {
if name == hir::LifetimeName::Static {
Set1::One(Region::Static)
} else {
generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => Some((
param.id,
hir::LifetimeName::Param(param.name),
LifetimeDefOrigin::from_param(param),
)),
_ => None,
})
.enumerate()
.find(|&(_, (_, lt_name, _))| lt_name == name)
.map_or(Set1::Many, |(i, (id, _, origin))| {
let def_id = tcx.hir().local_def_id(id);
Set1::One(Region::EarlyBound(i as u32, def_id, origin))
})
}
}
Set1::Many => Set1::Many,
})
}
})
.collect()
}
impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
// FIXME(#37666) this works around a limitation in the region inferencer
fn hack<F>(&mut self, f: F)
where
F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
{
f(self)
}
fn with<F>(&mut self, wrap_scope: Scope<'_>, f: F)
where
F: for<'b> FnOnce(ScopeRef<'_>, &mut LifetimeContext<'b, 'tcx>),
{
let LifetimeContext {
tcx,
map,
lifetime_uses,
..
} = self;
let labels_in_fn = replace(&mut self.labels_in_fn, vec![]);
let xcrate_object_lifetime_defaults =
replace(&mut self.xcrate_object_lifetime_defaults, DefIdMap::default());
let mut this = LifetimeContext {
tcx: *tcx,
map: map,
scope: &wrap_scope,
trait_ref_hack: self.trait_ref_hack,
is_in_fn_syntax: self.is_in_fn_syntax,
labels_in_fn,
xcrate_object_lifetime_defaults,
lifetime_uses: lifetime_uses,
};
debug!("entering scope {:?}", this.scope);
f(self.scope, &mut this);
this.check_uses_for_lifetimes_defined_by_scope();
debug!("exiting scope {:?}", this.scope);
self.labels_in_fn = this.labels_in_fn;
self.xcrate_object_lifetime_defaults = this.xcrate_object_lifetime_defaults;
}
/// helper method to determine the span to remove when suggesting the
/// deletion of a lifetime
fn lifetime_deletion_span(&self, name: ast::Ident, generics: &hir::Generics) -> Option<Span> {
generics.params.iter().enumerate().find_map(|(i, param)| {
if param.name.ident() == name {
let mut in_band = false;
if let hir::GenericParamKind::Lifetime { kind } = param.kind {
if let hir::LifetimeParamKind::InBand = kind {
in_band = true;
}
}
if in_band {
Some(param.span)
} else {
if generics.params.len() == 1 {
// if sole lifetime, remove the entire `<>` brackets
Some(generics.span)
} else {
// if removing within `<>` brackets, we also want to
// delete a leading or trailing comma as appropriate
if i >= generics.params.len() - 1 {
Some(generics.params[i - 1].span.shrink_to_hi().to(param.span))
} else {
Some(param.span.to(generics.params[i + 1].span.shrink_to_lo()))
}
}
}
} else {
None
}
})
}
// helper method to issue suggestions from `fn rah<'a>(&'a T)` to `fn rah(&T)`
fn suggest_eliding_single_use_lifetime(
&self, err: &mut DiagnosticBuilder<'_>, def_id: DefId, lifetime: &hir::Lifetime
) {
// FIXME: future work: also suggest `impl Foo<'_>` for `impl<'a> Foo<'a>`
let name = lifetime.name.ident();
let mut remove_decl = None;
if let Some(parent_def_id) = self.tcx.parent(def_id) {
if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
remove_decl = self.lifetime_deletion_span(name, generics);
}
}
let mut remove_use = None;
let mut find_arg_use_span = |inputs: &hir::HirVec<hir::Ty>| {
for input in inputs {
if let hir::TyKind::Rptr(lt, _) = input.node {
if lt.name.ident() == name {
// include the trailing whitespace between the ampersand and the type name
let lt_through_ty_span = lifetime.span.to(input.span.shrink_to_hi());
remove_use = Some(
self.tcx.sess.source_map()
.span_until_non_whitespace(lt_through_ty_span)
);
break;
}
}
}
};
if let Node::Lifetime(hir_lifetime) = self.tcx.hir().get(lifetime.id) {
if let Some(parent) = self.tcx.hir().find(self.tcx.hir().get_parent(hir_lifetime.id)) {
match parent {
Node::Item(item) => {
if let hir::ItemKind::Fn(decl, _, _, _) = &item.node {
find_arg_use_span(&decl.inputs);
}
},
Node::ImplItem(impl_item) => {
if let hir::ImplItemKind::Method(sig, _) = &impl_item.node {
find_arg_use_span(&sig.decl.inputs);
}
}
_ => {}
}
}
}
if let (Some(decl_span), Some(use_span)) = (remove_decl, remove_use) {
// if both declaration and use deletion spans start at the same
// place ("start at" because the latter includes trailing
// whitespace), then this is an in-band lifetime
if decl_span.shrink_to_lo() == use_span.shrink_to_lo() {
err.span_suggestion(
use_span,
"elide the single-use lifetime",
String::new(),
Applicability::MachineApplicable,
);
} else {
err.multipart_suggestion(
"elide the single-use lifetime",
vec![(decl_span, String::new()), (use_span, String::new())],
Applicability::MachineApplicable,
);
}
}
}
fn check_uses_for_lifetimes_defined_by_scope(&mut self) {
let defined_by = match self.scope {
Scope::Binder { lifetimes, .. } => lifetimes,
_ => {
debug!("check_uses_for_lifetimes_defined_by_scope: not in a binder scope");
return;
}
};
let mut def_ids: Vec<_> = defined_by
.values()
.flat_map(|region| match region {
Region::EarlyBound(_, def_id, _)
| Region::LateBound(_, def_id, _)
| Region::Free(_, def_id) => Some(*def_id),
Region::LateBoundAnon(..) | Region::Static => None,
})
.collect();
// ensure that we issue lints in a repeatable order
def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
for def_id in def_ids {
debug!(
"check_uses_for_lifetimes_defined_by_scope: def_id = {:?}",
def_id
);
let lifetimeuseset = self.lifetime_uses.remove(&def_id);
debug!(
"check_uses_for_lifetimes_defined_by_scope: lifetimeuseset = {:?}",
lifetimeuseset
);
match lifetimeuseset {
Some(LifetimeUseSet::One(lifetime)) => {
let node_id = self.tcx.hir().as_local_node_id(def_id).unwrap();
debug!("node id first={:?}", node_id);
if let Some((id, span, name)) = match self.tcx.hir().get(node_id) {
Node::Lifetime(hir_lifetime) => Some((
hir_lifetime.id,
hir_lifetime.span,
hir_lifetime.name.ident(),
)),
Node::GenericParam(param) => {
Some((param.id, param.span, param.name.ident()))
}
_ => None,
} {
debug!("id = {:?} span = {:?} name = {:?}", node_id, span, name);
if name == keywords::UnderscoreLifetime.ident() {
continue;
}
let mut err = self.tcx.struct_span_lint_node(
lint::builtin::SINGLE_USE_LIFETIMES,
id,
span,
&format!("lifetime parameter `{}` only used once", name),
);
if span == lifetime.span {
// spans are the same for in-band lifetime declarations
err.span_label(span, "this lifetime is only used here");
} else {
err.span_label(span, "this lifetime...");
err.span_label(lifetime.span, "...is used only here");
}
self.suggest_eliding_single_use_lifetime(&mut err, def_id, lifetime);
err.emit();
}
}
Some(LifetimeUseSet::Many) => {
debug!("Not one use lifetime");
}
None => {
let node_id = self.tcx.hir().as_local_node_id(def_id).unwrap();
if let Some((id, span, name)) = match self.tcx.hir().get(node_id) {
Node::Lifetime(hir_lifetime) => Some((
hir_lifetime.id,
hir_lifetime.span,
hir_lifetime.name.ident(),
)),
Node::GenericParam(param) => {
Some((param.id, param.span, param.name.ident()))
}
_ => None,
} {
debug!("id ={:?} span = {:?} name = {:?}", node_id, span, name);
let mut err = self.tcx.struct_span_lint_node(
lint::builtin::UNUSED_LIFETIMES,
id,
span,
&format!("lifetime parameter `{}` never used", name),
);
if let Some(parent_def_id) = self.tcx.parent(def_id) {
if let Some(generics) = self.tcx.hir().get_generics(parent_def_id) {
let unused_lt_span = self.lifetime_deletion_span(name, generics);
if let Some(span) = unused_lt_span {
err.span_suggestion(
span,
"elide the unused lifetime",
String::new(),
Applicability::MachineApplicable,
);
}
}
}
err.emit();
}
}
}
}
}
/// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
///
/// Handles visiting fns and methods. These are a bit complicated because we must distinguish
/// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
/// within type bounds; those are early bound lifetimes, and the rest are late bound.
///
/// For example:
///
/// fn foo<'a,'b,'c,T:Trait<'b>>(...)
///
/// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
/// lifetimes may be interspersed together.
///
/// If early bound lifetimes are present, we separate them into their own list (and likewise
/// for late bound). They will be numbered sequentially, starting from the lowest index that is
/// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
/// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
/// ordering is not important there.
fn visit_early_late<F>(
&mut self,
parent_id: Option<ast::NodeId>,
decl: &'tcx hir::FnDecl,
generics: &'tcx hir::Generics,
walk: F,
) where
F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
{
insert_late_bound_lifetimes(self.map, decl, generics);
// Find the start of nested early scopes, e.g., in methods.
let mut index = 0;
if let Some(parent_id) = parent_id {
let parent = self.tcx.hir().expect_item(parent_id);
if sub_items_have_self_param(&parent.node) {
index += 1; // Self comes before lifetimes
}
match parent.node {
hir::ItemKind::Trait(_, _, ref generics, ..)
| hir::ItemKind::Impl(_, _, _, ref generics, ..) => {
index += generics.params.len() as u32;
}
_ => {}
}
}
let mut type_count = 0;
let lifetimes = generics
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => {
if self.map.late_bound.contains(&param.id) {
Some(Region::late(&self.tcx.hir(), param))
} else {
Some(Region::early(&self.tcx.hir(), &mut index, param))
}
}
GenericParamKind::Type { .. } => {
type_count += 1;
None
}
})
.collect();
let next_early_index = index + type_count;
let scope = Scope::Binder {
lifetimes,
next_early_index,
s: self.scope,
abstract_type_parent: true,
track_lifetime_uses: false,
};
self.with(scope, move |old_scope, this| {
this.check_lifetime_params(old_scope, &generics.params);
this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
});
}
fn next_early_index_helper(&self, only_abstract_type_parent: bool) -> u32 {
let mut scope = self.scope;
loop {
match *scope {
Scope::Root => return 0,
Scope::Binder {
next_early_index,
abstract_type_parent,
..
} if (!only_abstract_type_parent || abstract_type_parent) =>
{
return next_early_index
}
Scope::Binder { s, .. }
| Scope::Body { s, .. }
| Scope::Elision { s, .. }
| Scope::ObjectLifetimeDefault { s, .. } => scope = s,
}
}
}
/// Returns the next index one would use for an early-bound-region
/// if extending the current scope.
fn next_early_index(&self) -> u32 {
self.next_early_index_helper(true)
}
/// Returns the next index one would use for an `impl Trait` that
/// is being converted into an `abstract type`. This will be the
/// next early index from the enclosing item, for the most
/// part. See the `abstract_type_parent` field for more info.
fn next_early_index_for_abstract_type(&self) -> u32 {
self.next_early_index_helper(false)
}
fn resolve_lifetime_ref(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
debug!("resolve_lifetime_ref(lifetime_ref={:?})", lifetime_ref);
// If we've already reported an error, just ignore `lifetime_ref`.
if let LifetimeName::Error = lifetime_ref.name {
return;
}
// Walk up the scope chain, tracking the number of fn scopes
// that we pass through, until we find a lifetime with the
// given name or we run out of scopes.
// search.
let mut late_depth = 0;
let mut scope = self.scope;
let mut outermost_body = None;
let result = loop {
match *scope {
Scope::Body { id, s } => {
outermost_body = Some(id);
scope = s;
}
Scope::Root => {
break None;
}
Scope::Binder {
ref lifetimes, s, ..
} => {
match lifetime_ref.name {
LifetimeName::Param(param_name) => {
if let Some(&def) = lifetimes.get(&param_name.modern()) {
break Some(def.shifted(late_depth));
}
}
_ => bug!("expected LifetimeName::Param"),
}
late_depth += 1;
scope = s;
}
Scope::Elision { s, .. } | Scope::ObjectLifetimeDefault { s, .. } => {
scope = s;
}
}
};
if let Some(mut def) = result {
if let Region::EarlyBound(..) = def {
// Do not free early-bound regions, only late-bound ones.
} else if let Some(body_id) = outermost_body {
let fn_id = self.tcx.hir().body_owner(body_id);
match self.tcx.hir().get(fn_id) {
Node::Item(&hir::Item {
node: hir::ItemKind::Fn(..),
..
})
| Node::TraitItem(&hir::TraitItem {
node: hir::TraitItemKind::Method(..),
..
})
| Node::ImplItem(&hir::ImplItem {
node: hir::ImplItemKind::Method(..),
..
}) => {
let scope = self.tcx.hir().local_def_id(fn_id);
def = Region::Free(scope, def.id().unwrap());
}
_ => {}
}
}
// Check for fn-syntax conflicts with in-band lifetime definitions
if self.is_in_fn_syntax {
match def {
Region::EarlyBound(_, _, LifetimeDefOrigin::InBand)
| Region::LateBound(_, _, LifetimeDefOrigin::InBand) => {
struct_span_err!(
self.tcx.sess,
lifetime_ref.span,
E0687,
"lifetimes used in `fn` or `Fn` syntax must be \
explicitly declared using `<...>` binders"
).span_label(lifetime_ref.span, "in-band lifetime definition")
.emit();
}
Region::Static
| Region::EarlyBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
| Region::LateBound(_, _, LifetimeDefOrigin::ExplicitOrElided)
| Region::EarlyBound(_, _, LifetimeDefOrigin::Error)
| Region::LateBound(_, _, LifetimeDefOrigin::Error)
| Region::LateBoundAnon(..)
| Region::Free(..) => {}
}
}
self.insert_lifetime(lifetime_ref, def);
} else {
struct_span_err!(
self.tcx.sess,
lifetime_ref.span,
E0261,
"use of undeclared lifetime name `{}`",
lifetime_ref
).span_label(lifetime_ref.span, "undeclared lifetime")
.emit();
}
}
fn visit_segment_args(&mut self, def: Def, depth: usize, generic_args: &'tcx hir::GenericArgs) {
if generic_args.parenthesized {
let was_in_fn_syntax = self.is_in_fn_syntax;
self.is_in_fn_syntax = true;
self.visit_fn_like_elision(generic_args.inputs(), Some(&generic_args.bindings[0].ty));
self.is_in_fn_syntax = was_in_fn_syntax;
return;
}
let mut elide_lifetimes = true;
let lifetimes = generic_args
.args
.iter()
.filter_map(|arg| match arg {
hir::GenericArg::Lifetime(lt) => {
if !lt.is_elided() {
elide_lifetimes = false;
}
Some(lt)
}
_ => None,
})
.collect();
if elide_lifetimes {
self.resolve_elided_lifetimes(lifetimes);
} else {
lifetimes.iter().for_each(|lt| self.visit_lifetime(lt));
}
// Figure out if this is a type/trait segment,
// which requires object lifetime defaults.
let parent_def_id = |this: &mut Self, def_id: DefId| {
let def_key = this.tcx.def_key(def_id);
DefId {
krate: def_id.krate,
index: def_key.parent.expect("missing parent"),
}
};
let type_def_id = match def {
Def::AssociatedTy(def_id) if depth == 1 => Some(parent_def_id(self, def_id)),
Def::Variant(def_id) if depth == 0 => Some(parent_def_id(self, def_id)),
Def::Struct(def_id)
| Def::Union(def_id)
| Def::Enum(def_id)
| Def::TyAlias(def_id)
| Def::Trait(def_id) if depth == 0 =>
{
Some(def_id)
}
_ => None,
};
let object_lifetime_defaults = type_def_id.map_or(vec![], |def_id| {
let in_body = {
let mut scope = self.scope;
loop {
match *scope {
Scope::Root => break false,
Scope::Body { .. } => break true,
Scope::Binder { s, .. }
| Scope::Elision { s, .. }
| Scope::ObjectLifetimeDefault { s, .. } => {
scope = s;
}
}
}
};
let map = &self.map;
let unsubst = if let Some(id) = self.tcx.hir().as_local_node_id(def_id) {
&map.object_lifetime_defaults[&id]
} else {
let tcx = self.tcx;
self.xcrate_object_lifetime_defaults
.entry(def_id)
.or_insert_with(|| {
tcx.generics_of(def_id)
.params
.iter()
.filter_map(|param| match param.kind {
GenericParamDefKind::Type {
object_lifetime_default,
..
} => Some(object_lifetime_default),
GenericParamDefKind::Lifetime => None,
})
.collect()
})
};
unsubst
.iter()
.map(|set| match *set {
Set1::Empty => if in_body {
None
} else {
Some(Region::Static)
},
Set1::One(r) => {
let lifetimes = generic_args.args.iter().filter_map(|arg| match arg {
GenericArg::Lifetime(lt) => Some(lt),
_ => None,
});
r.subst(lifetimes, map)
}
Set1::Many => None,
})
.collect()
});
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;
}
}
}
for b in &generic_args.bindings {
self.visit_assoc_type_binding(b);
}
}
fn visit_fn_like_elision(&mut self, inputs: &'tcx [hir::Ty], output: Option<&'tcx P<hir::Ty>>) {
debug!("visit_fn_like_elision: enter");
let mut arg_elide = Elide::FreshLateAnon(Cell::new(0));
let arg_scope = Scope::Elision {
elide: arg_elide.clone(),
s: self.scope,
};
self.with(arg_scope, |_, this| {
for input in inputs {
this.visit_ty(input);
}
match *this.scope {
Scope::Elision { ref elide, .. } => {
arg_elide = elide.clone();
}
_ => bug!(),
}
});
let output = match output {
Some(ty) => ty,
None => return,
};
debug!("visit_fn_like_elision: determine output");
// Figure out if there's a body we can get argument names from,
// and whether there's a `self` argument (treated specially).
let mut assoc_item_kind = None;
let mut impl_self = None;
let parent = self.tcx.hir().get_parent_node(output.id);
let body = match self.tcx.hir().get(parent) {
// `fn` definitions and methods.
Node::Item(&hir::Item {
node: hir::ItemKind::Fn(.., body),
..
}) => Some(body),
Node::TraitItem(&hir::TraitItem {
node: hir::TraitItemKind::Method(_, ref m),
..
}) => {
if let hir::ItemKind::Trait(.., ref trait_items) = self.tcx
.hir()
.expect_item(self.tcx.hir().get_parent(parent))
.node
{
assoc_item_kind = trait_items
.iter()
.find(|ti| ti.id.node_id == parent)
.map(|ti| ti.kind);
}
match *m {
hir::TraitMethod::Required(_) => None,
hir::TraitMethod::Provided(body) => Some(body),
}
}
Node::ImplItem(&hir::ImplItem {
node: hir::ImplItemKind::Method(_, body),
..
}) => {
if let hir::ItemKind::Impl(.., ref self_ty, ref impl_items) = self.tcx
.hir()
.expect_item(self.tcx.hir().get_parent(parent))
.node
{
impl_self = Some(self_ty);
assoc_item_kind = impl_items
.iter()
.find(|ii| ii.id.node_id == parent)
.map(|ii| ii.kind);
}
Some(body)
}
// Foreign functions, `fn(...) -> R` and `Trait(...) -> R` (both types and bounds).
Node::ForeignItem(_) | Node::Ty(_) | Node::TraitRef(_) => None,
// Everything else (only closures?) doesn't
// actually enjoy elision in return types.
_ => {
self.visit_ty(output);
return;
}
};
let has_self = match assoc_item_kind {
Some(hir::AssociatedItemKind::Method { has_self }) => has_self,
_ => false,
};
// In accordance with the rules for lifetime elision, we can determine
// what region to use for elision in the output type in two ways.
// First (determined here), if `self` is by-reference, then the
// implied output region is the region of the self parameter.
if has_self {
// Look for `self: &'a Self` - also desugared from `&'a self`,
// and if that matches, use it for elision and return early.
let is_self_ty = |def: Def| {
if let Def::SelfTy(..) = def {
return true;
}
// Can't always rely on literal (or implied) `Self` due
// to the way elision rules were originally specified.
let impl_self = impl_self.map(|ty| &ty.node);
if let Some(&hir::TyKind::Path(hir::QPath::Resolved(None, ref path))) = impl_self {
match path.def {
// Whitelist the types that unambiguously always
// result in the same type constructor being used
// (it can't differ between `Self` and `self`).
Def::Struct(_) | Def::Union(_) | Def::Enum(_) | Def::PrimTy(_) => {
return def == path.def
}
_ => {}
}
}
false
};
if let hir::TyKind::Rptr(lifetime_ref, ref mt) = inputs[0].node {
if let hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) = mt.ty.node {
if is_self_ty(path.def) {
if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
let scope = Scope::Elision {
elide: Elide::Exact(lifetime),
s: self.scope,
};
self.with(scope, |_, this| this.visit_ty(output));
return;
}
}
}
}
}
// Second, if there was exactly one lifetime (either a substitution or a
// reference) in the arguments, then any anonymous regions in the output
// have that lifetime.
let mut possible_implied_output_region = None;
let mut lifetime_count = 0;
let arg_lifetimes = inputs
.iter()
.enumerate()
.skip(has_self as usize)
.map(|(i, input)| {
let mut gather = GatherLifetimes {
map: self.map,
outer_index: ty::INNERMOST,
have_bound_regions: false,
lifetimes: Default::default(),
};
gather.visit_ty(input);
lifetime_count += gather.lifetimes.len();
if lifetime_count == 1 && gather.lifetimes.len() == 1 {
// there's a chance that the unique lifetime of this
// iteration will be the appropriate lifetime for output
// parameters, so lets store it.
possible_implied_output_region = gather.lifetimes.iter().cloned().next();
}
ElisionFailureInfo {
parent: body,
index: i,
lifetime_count: gather.lifetimes.len(),
have_bound_regions: gather.have_bound_regions,
}
})
.collect();
let elide = if lifetime_count == 1 {
Elide::Exact(possible_implied_output_region.unwrap())
} else {
Elide::Error(arg_lifetimes)
};
debug!("visit_fn_like_elision: elide={:?}", elide);
let scope = Scope::Elision {
elide,
s: self.scope,
};
self.with(scope, |_, this| this.visit_ty(output));
debug!("visit_fn_like_elision: exit");
struct GatherLifetimes<'a> {
map: &'a NamedRegionMap,
outer_index: ty::DebruijnIndex,
have_bound_regions: bool,
lifetimes: FxHashSet<Region>,
}
impl<'v, 'a> Visitor<'v> for GatherLifetimes<'a> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
NestedVisitorMap::None
}
fn visit_ty(&mut self, ty: &hir::Ty) {
if let hir::TyKind::BareFn(_) = ty.node {
self.outer_index.shift_in(1);
}
if let hir::TyKind::TraitObject(ref bounds, ref lifetime) = ty.node {
for bound in bounds {
self.visit_poly_trait_ref(bound, hir::TraitBoundModifier::None);
}
// Stay on the safe side and don't include the object
// lifetime default (which may not end up being used).
if !lifetime.is_elided() {
self.visit_lifetime(lifetime);
}
} else {
intravisit::walk_ty(self, ty);
}
if let hir::TyKind::BareFn(_) = ty.node {
self.outer_index.shift_out(1);
}
}
fn visit_generic_param(&mut self, param: &hir::GenericParam) {
if let hir::GenericParamKind::Lifetime { .. } = param.kind {
// FIXME(eddyb) Do we want this? It only makes a difference
// if this `for<'a>` lifetime parameter is never used.
self.have_bound_regions = true;
}
intravisit::walk_generic_param(self, param);
}
fn visit_poly_trait_ref(
&mut self,
trait_ref: &hir::PolyTraitRef,
modifier: hir::TraitBoundModifier,
) {
self.outer_index.shift_in(1);
intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
self.outer_index.shift_out(1);
}
fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
if let Some(&lifetime) = self.map.defs.get(&lifetime_ref.id) {
match lifetime {
Region::LateBound(debruijn, _, _) | Region::LateBoundAnon(debruijn, _)
if debruijn < self.outer_index =>
{
self.have_bound_regions = true;
}
_ => {
self.lifetimes
.insert(lifetime.shifted_out_to_binder(self.outer_index));
}
}
}
}
}
}
fn resolve_elided_lifetimes(&mut self, lifetime_refs: Vec<&'tcx hir::Lifetime>) {
if lifetime_refs.is_empty() {
return;
}
let span = lifetime_refs[0].span;
let mut late_depth = 0;
let mut scope = self.scope;
let error = loop {
match *scope {
// Do not assign any resolution, it will be inferred.
Scope::Body { .. } => return,
Scope::Root => break None,
Scope::Binder { s, .. } => {
late_depth += 1;
scope = s;
}
Scope::Elision { ref elide, .. } => {
let lifetime = match *elide {
Elide::FreshLateAnon(ref counter) => {
for lifetime_ref in lifetime_refs {
let lifetime = Region::late_anon(counter).shifted(late_depth);
self.insert_lifetime(lifetime_ref, lifetime);
}
return;
}
Elide::Exact(l) => l.shifted(late_depth),
Elide::Error(ref e) => break Some(e),
};
for lifetime_ref in lifetime_refs {
self.insert_lifetime(lifetime_ref, lifetime);
}
return;
}
Scope::ObjectLifetimeDefault { s, .. } => {
scope = s;
}
}
};
let mut err = report_missing_lifetime_specifiers(self.tcx.sess, span, lifetime_refs.len());
let mut add_label = true;
if let Some(params) = error {
if lifetime_refs.len() == 1 {
add_label = add_label && self.report_elision_failure(&mut err, params, span);
}
}
if add_label {
add_missing_lifetime_specifiers_label(&mut err, span, lifetime_refs.len());
}
err.emit();
}
fn suggest_lifetime(&self, db: &mut DiagnosticBuilder<'_>, span: Span, msg: &str) -> bool {
match self.tcx.sess.source_map().span_to_snippet(span) {
Ok(ref snippet) => {
let (sugg, applicability) = if snippet == "&" {
("&'static ".to_owned(), Applicability::MachineApplicable)
} else if snippet == "'_" {
("'static".to_owned(), Applicability::MachineApplicable)
} else {
(format!("{} + 'static", snippet), Applicability::MaybeIncorrect)
};
db.span_suggestion(span, msg, sugg, applicability);
false
}
Err(_) => {
db.help(msg);
true
}
}
}
fn report_elision_failure(
&mut self,
db: &mut DiagnosticBuilder<'_>,
params: &[ElisionFailureInfo],
span: Span,
) -> bool {
let mut m = String::new();
let len = params.len();
let elided_params: Vec<_> = params
.iter()
.cloned()
.filter(|info| info.lifetime_count > 0)
.collect();
let elided_len = elided_params.len();
for (i, info) in elided_params.into_iter().enumerate() {
let ElisionFailureInfo {
parent,
index,
lifetime_count: n,
have_bound_regions,
} = info;
let help_name = if let Some(body) = parent {
let arg = &self.tcx.hir().body(body).arguments[index];
format!("`{}`", self.tcx.hir().node_to_pretty_string(arg.pat.id))
} else {
format!("argument {}", index + 1)
};
m.push_str(
&(if n == 1 {
help_name
} else {
format!(
"one of {}'s {} {}lifetimes",
help_name,
n,
if have_bound_regions { "free " } else { "" }
)
})[..],
);
if elided_len == 2 && i == 0 {
m.push_str(" or ");
} else if i + 2 == elided_len {
m.push_str(", or ");
} else if i != elided_len - 1 {
m.push_str(", ");
}
}
if len == 0 {
help!(
db,
"this function's return type contains a borrowed value, but \
there is no value for it to be borrowed from"
);
self.suggest_lifetime(db, span, "consider giving it a 'static lifetime")
} else if elided_len == 0 {
help!(
db,
"this function's return type contains a borrowed value with \
an elided lifetime, but the lifetime cannot be derived from \
the arguments"
);
let msg = "consider giving it an explicit bounded or 'static lifetime";
self.suggest_lifetime(db, span, msg)
} else if elided_len == 1 {
help!(
db,
"this function's return type contains a borrowed value, but \
the signature does not say which {} it is borrowed from",
m
);
true
} else {
help!(
db,
"this function's return type contains a borrowed value, but \
the signature does not say whether it is borrowed from {}",
m
);
true
}
}
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, .. } => {
late_depth += 1;
scope = s;
}
Scope::Root | Scope::Elision { .. } => break Region::Static,
Scope::Body { .. } | Scope::ObjectLifetimeDefault { lifetime: None, .. } => return,
Scope::ObjectLifetimeDefault {
lifetime: Some(l), ..
} => break l,
}
};
self.insert_lifetime(lifetime_ref, lifetime.shifted(late_depth));
}
fn check_lifetime_params(
&mut self,
old_scope: ScopeRef<'_>,
params: &'tcx [hir::GenericParam],
) {
let lifetimes: Vec<_> = params
.iter()
.filter_map(|param| match param.kind {
GenericParamKind::Lifetime { .. } => Some((param, param.name)),
_ => None,
})
.collect();
for (i, (lifetime_i, lifetime_i_name)) in lifetimes.iter().enumerate() {
if let hir::ParamName::Plain(_) = lifetime_i_name {
let name = lifetime_i_name.ident().name;
if name == keywords::UnderscoreLifetime.name()
|| name == keywords::StaticLifetime.name()
{
let mut err = struct_span_err!(
self.tcx.sess,
lifetime_i.span,
E0262,
"invalid lifetime parameter name: `{}`",
lifetime_i.name.ident(),
);
err.span_label(
lifetime_i.span,
format!("{} is a reserved lifetime name", name),
);
err.emit();
}
}
// It is a hard error to shadow a lifetime within the same scope.
for (lifetime_j, lifetime_j_name) in lifetimes.iter().skip(i + 1) {
if lifetime_i_name == lifetime_j_name {
struct_span_err!(
self.tcx.sess,
lifetime_j.span,
E0263,
"lifetime name `{}` declared twice in the same scope",
lifetime_j.name.ident()
).span_label(lifetime_j.span, "declared twice")
.span_label(lifetime_i.span, "previous declaration here")
.emit();
}
}
// It is a soft error to shadow a lifetime within a parent scope.
self.check_lifetime_param_for_shadowing(old_scope, &lifetime_i);
for bound in &lifetime_i.bounds {
match bound {
hir::GenericBound::Outlives(lt) => match lt.name {
hir::LifetimeName::Underscore => self.tcx.sess.delay_span_bug(
lt.span,
"use of `'_` in illegal place, but not caught by lowering",
),
hir::LifetimeName::Static => {
self.insert_lifetime(lt, Region::Static);
self.tcx
.sess
.struct_span_warn(
lifetime_i.span.to(lt.span),
&format!(
"unnecessary lifetime parameter `{}`",
lifetime_i.name.ident(),
),
)
.help(&format!(
"you can use the `'static` lifetime directly, in place of `{}`",
lifetime_i.name.ident(),
))
.emit();
}
hir::LifetimeName::Param(_) | hir::LifetimeName::Implicit => {
self.resolve_lifetime_ref(lt);
}
hir::LifetimeName::Error => {
// No need to do anything, error already reported.
}
},
_ => bug!(),
}
}
}
}
fn check_lifetime_param_for_shadowing(
&self,
mut old_scope: ScopeRef<'_>,
param: &'tcx hir::GenericParam,
) {
for label in &self.labels_in_fn {
// FIXME (#24278): non-hygienic comparison
if param.name.ident().name == label.name {
signal_shadowing_problem(
self.tcx,
label.name,
original_label(label.span),
shadower_lifetime(&param),
);
return;
}
}
loop {
match *old_scope {
Scope::Body { s, .. }
| Scope::Elision { s, .. }
| Scope::ObjectLifetimeDefault { s, .. } => {
old_scope = s;
}
Scope::Root => {
return;
}
Scope::Binder {
ref lifetimes, s, ..
} => {
if let Some(&def) = lifetimes.get(&param.name.modern()) {
let node_id = self.tcx.hir().as_local_node_id(def.id().unwrap()).unwrap();
signal_shadowing_problem(
self.tcx,
param.name.ident().name,
original_lifetime(self.tcx.hir().span(node_id)),
shadower_lifetime(&param),
);
return;
}
old_scope = s;
}
}
}
}
/// Returns true if, in the current scope, replacing `'_` would be
/// equivalent to a single-use lifetime.
fn track_lifetime_uses(&self) -> bool {
let mut scope = self.scope;
loop {
match *scope {
Scope::Root => break false,
// Inside of items, it depends on the kind of item.
Scope::Binder {
track_lifetime_uses,
..
} => break track_lifetime_uses,
// Inside a body, `'_` will use an inference variable,
// should be fine.
Scope::Body { .. } => break true,
// A lifetime only used in a fn argument could as well
// be replaced with `'_`, as that would generate a
// fresh name, too.
Scope::Elision {
elide: Elide::FreshLateAnon(_),
..
} => break true,
// In the return type or other such place, `'_` is not
// going to make a fresh name, so we cannot
// necessarily replace a single-use lifetime with
// `'_`.
Scope::Elision {
elide: Elide::Exact(_),
..
} => break false,
Scope::Elision {
elide: Elide::Error(_),
..
} => break false,
Scope::ObjectLifetimeDefault { s, .. } => scope = s,
}
}
}
fn insert_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime, def: Region) {
if lifetime_ref.id == ast::DUMMY_NODE_ID {
span_bug!(
lifetime_ref.span,
"lifetime reference not renumbered, \
probably a bug in syntax::fold"
);
}
debug!(
"insert_lifetime: {} resolved to {:?} span={:?}",
self.tcx.hir().node_to_string(lifetime_ref.id),
def,
self.tcx.sess.source_map().span_to_string(lifetime_ref.span)
);
self.map.defs.insert(lifetime_ref.id, def);
match def {
Region::LateBoundAnon(..) | Region::Static => {
// These are anonymous lifetimes or lifetimes that are not declared.
}
Region::Free(_, def_id)
| Region::LateBound(_, def_id, _)
| Region::EarlyBound(_, def_id, _) => {
// A lifetime declared by the user.
let track_lifetime_uses = self.track_lifetime_uses();
debug!(
"insert_lifetime: track_lifetime_uses={}",
track_lifetime_uses
);
if track_lifetime_uses && !self.lifetime_uses.contains_key(&def_id) {
debug!("insert_lifetime: first use of {:?}", def_id);
self.lifetime_uses
.insert(def_id, LifetimeUseSet::One(lifetime_ref));
} else {
debug!("insert_lifetime: many uses of {:?}", def_id);
self.lifetime_uses.insert(def_id, LifetimeUseSet::Many);
}
}
}
}
/// Sometimes we resolve a lifetime, but later find that it is an
/// error (esp. around impl trait). In that case, we remove the
/// entry into `map.defs` so as not to confuse later code.
fn uninsert_lifetime_on_error(&mut self, lifetime_ref: &'tcx hir::Lifetime, bad_def: Region) {
let old_value = self.map.defs.remove(&lifetime_ref.id);
assert_eq!(old_value, Some(bad_def));
}
}
/// Detects late-bound lifetimes and inserts them into
/// `map.late_bound`.
///
/// A region declared on a fn is **late-bound** if:
/// - it is constrained by an argument type;
/// - it does not appear in a where-clause.
///
/// "Constrained" basically means that it appears in any type but
/// not amongst the inputs to a projection. In other words, `<&'a
/// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
fn insert_late_bound_lifetimes(
map: &mut NamedRegionMap,
decl: &hir::FnDecl,
generics: &hir::Generics,
) {
debug!(
"insert_late_bound_lifetimes(decl={:?}, generics={:?})",
decl, generics
);
let mut constrained_by_input = ConstrainedCollector::default();
for arg_ty in &decl.inputs {
constrained_by_input.visit_ty(arg_ty);
}
let mut appears_in_output = AllCollector::default();
intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
debug!(
"insert_late_bound_lifetimes: constrained_by_input={:?}",
constrained_by_input.regions
);
// Walk the lifetimes that appear in where clauses.
//
// Subtle point: because we disallow nested bindings, we can just
// ignore binders here and scrape up all names we see.
let mut appears_in_where_clause = AllCollector::default();
appears_in_where_clause.visit_generics(generics);
for param in &generics.params {
if let hir::GenericParamKind::Lifetime { .. } = param.kind {
if !param.bounds.is_empty() {
// `'a: 'b` means both `'a` and `'b` are referenced
appears_in_where_clause
.regions
.insert(hir::LifetimeName::Param(param.name.modern()));
}
}
}
debug!(
"insert_late_bound_lifetimes: appears_in_where_clause={:?}",
appears_in_where_clause.regions
);
// Late bound regions are those that:
// - appear in the inputs
// - do not appear in the where-clauses
// - are not implicitly captured by `impl Trait`
for param in &generics.params {
match param.kind {
hir::GenericParamKind::Lifetime { .. } => { /* fall through */ }
// Types are not late-bound.
hir::GenericParamKind::Type { .. } => continue,
}
let lt_name = hir::LifetimeName::Param(param.name.modern());
// appears in the where clauses? early-bound.
if appears_in_where_clause.regions.contains(&lt_name) {
continue;
}
// does not appear in the inputs, but appears in the return type? early-bound.
if !constrained_by_input.regions.contains(&lt_name)
&& appears_in_output.regions.contains(&lt_name)
{
continue;
}
debug!(
"insert_late_bound_lifetimes: lifetime {:?} with id {:?} is late-bound",
param.name.ident(),
param.id
);
let inserted = map.late_bound.insert(param.id);
assert!(inserted, "visited lifetime {:?} twice", param.id);
}
return;
#[derive(Default)]
struct ConstrainedCollector {
regions: FxHashSet<hir::LifetimeName>,
}
impl<'v> Visitor<'v> for ConstrainedCollector {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
NestedVisitorMap::None
}
fn visit_ty(&mut self, ty: &'v hir::Ty) {
match ty.node {
hir::TyKind::Path(hir::QPath::Resolved(Some(_), _))
| hir::TyKind::Path(hir::QPath::TypeRelative(..)) => {
// ignore lifetimes appearing in associated type
// projections, as they are not *constrained*
// (defined above)
}
hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
// consider only the lifetimes on the final
// segment; I am not sure it's even currently
// valid to have them elsewhere, but even if it
// is, those would be potentially inputs to
// projections
if let Some(last_segment) = path.segments.last() {
self.visit_path_segment(path.span, last_segment);
}
}
_ => {
intravisit::walk_ty(self, ty);
}
}
}
fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
self.regions.insert(lifetime_ref.name.modern());
}
}
#[derive(Default)]
struct AllCollector {
regions: FxHashSet<hir::LifetimeName>,
}
impl<'v> Visitor<'v> for AllCollector {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
NestedVisitorMap::None
}
fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
self.regions.insert(lifetime_ref.name.modern());
}
}
}
fn report_missing_lifetime_specifiers(
sess: &Session,
span: Span,
count: usize,
) -> DiagnosticBuilder<'_> {
struct_span_err!(
sess,
span,
E0106,
"missing lifetime specifier{}",
if count > 1 { "s" } else { "" }
)
}
fn add_missing_lifetime_specifiers_label(
err: &mut DiagnosticBuilder<'_>,
span: Span,
count: usize,
) {
if count > 1 {
err.span_label(span, format!("expected {} lifetime parameters", count));
} else {
err.span_label(span, "expected lifetime parameter");
};
}