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Identify anonymous lifetimes by their DefId in HIR.
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@cjgillot
cjgillot committed Mar 12, 2022
1 parent 012720f commit d3b7ea6
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Showing 3 changed files with 104 additions and 69 deletions.
24 changes: 16 additions & 8 deletions compiler/rustc_ast_lowering/src/item.rs
View file
Expand Up @@ -95,6 +95,7 @@ impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
}

fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
debug!(in_scope_lifetimes = ?self.lctx.in_scope_lifetimes);
self.lctx.with_hir_id_owner(item.id, |lctx| match ctxt {
AssocCtxt::Trait => hir::OwnerNode::TraitItem(lctx.lower_trait_item(item)),
AssocCtxt::Impl => hir::OwnerNode::ImplItem(lctx.lower_impl_item(item)),
Expand All @@ -118,35 +119,42 @@ impl<'hir> LoweringContext<'_, 'hir> {
// This should only be used with generics that have already had their
// in-band lifetimes added. In practice, this means that this function is
// only used when lowering a child item of a trait or impl.
#[tracing::instrument(level = "debug", skip(self, f))]
fn with_parent_item_lifetime_defs<T>(
&mut self,
parent_hir_id: LocalDefId,
f: impl FnOnce(&mut Self) -> T,
) -> T {
let old_len = self.in_scope_lifetimes.len();

let parent_generics = match self.owners[parent_hir_id].unwrap().node().expect_item().kind {
hir::ItemKind::Impl(hir::Impl { ref generics, .. })
| hir::ItemKind::Trait(_, _, ref generics, ..) => generics.params,
_ => &[],
};
let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
hir::GenericParamKind::Lifetime { .. } => Some(param.name.normalize_to_macros_2_0()),
_ => None,
});
self.in_scope_lifetimes.extend(lt_def_names);
let lt_def_names = parent_generics
.iter()
.filter_map(|param| match param.kind {
hir::GenericParamKind::Lifetime { .. } => {
Some(param.name.normalize_to_macros_2_0())
}
_ => None,
})
.collect();
let old_in_scope_lifetimes = mem::replace(&mut self.in_scope_lifetimes, lt_def_names);
debug!(in_scope_lifetimes = ?self.in_scope_lifetimes);

let res = f(self);

self.in_scope_lifetimes.truncate(old_len);
self.in_scope_lifetimes = old_in_scope_lifetimes;
res
}

// Clears (and restores) the `in_scope_lifetimes` field. Used when
// visiting nested items, which never inherit in-scope lifetimes
// from their surrounding environment.
#[tracing::instrument(level = "debug", skip(self, f))]
fn without_in_scope_lifetime_defs<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
let old_in_scope_lifetimes = mem::replace(&mut self.in_scope_lifetimes, vec![]);
debug!(?old_in_scope_lifetimes);

// this vector is only used when walking over impl headers,
// input types, and the like, and should not be non-empty in
Expand Down
145 changes: 86 additions & 59 deletions compiler/rustc_ast_lowering/src/lib.rs
View file
Expand Up @@ -136,13 +136,13 @@ struct LoweringContext<'a, 'hir: 'a> {
/// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
/// to this list. The results of this list are then added to the list of
/// lifetime definitions in the corresponding impl or function generics.
lifetimes_to_define: Vec<(Span, ParamName)>,
lifetimes_to_define: Vec<(Span, NodeId)>,

/// `true` if in-band lifetimes are being collected. This is used to
/// indicate whether or not we're in a place where new lifetimes will result
/// in in-band lifetime definitions, such a function or an impl header,
/// including implicit lifetimes from `impl_header_lifetime_elision`.
is_collecting_anonymous_lifetimes: bool,
is_collecting_anonymous_lifetimes: Option<LocalDefId>,

/// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
/// We always store a `normalize_to_macros_2_0()` version of the param-name in this
Expand Down Expand Up @@ -375,7 +375,7 @@ pub fn lower_crate<'a, 'hir>(
task_context: None,
current_item: None,
lifetimes_to_define: Vec::new(),
is_collecting_anonymous_lifetimes: false,
is_collecting_anonymous_lifetimes: None,
in_scope_lifetimes: Vec::new(),
allow_try_trait: Some([sym::try_trait_v2][..].into()),
allow_gen_future: Some([sym::gen_future][..].into()),
Expand Down Expand Up @@ -720,9 +720,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
/// parameter while `f` is running (and restored afterwards).
fn collect_in_band_defs<T>(
&mut self,
parent_def_id: LocalDefId,
f: impl FnOnce(&mut Self) -> T,
) -> (Vec<(Span, ParamName)>, T) {
let was_collecting = std::mem::replace(&mut self.is_collecting_anonymous_lifetimes, true);
) -> (Vec<(Span, NodeId)>, T) {
let was_collecting =
std::mem::replace(&mut self.is_collecting_anonymous_lifetimes, Some(parent_def_id));
let len = self.lifetimes_to_define.len();

let res = f(self);
Expand All @@ -733,49 +735,41 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
}

/// Converts a lifetime into a new generic parameter.
fn lifetime_to_generic_param(
fn fresh_lifetime_to_generic_param(
&mut self,
span: Span,
hir_name: ParamName,
parent_def_id: LocalDefId,
node_id: NodeId,
) -> hir::GenericParam<'hir> {
let node_id = self.resolver.next_node_id();

// Get the name we'll use to make the def-path. Note
// that collisions are ok here and this shouldn't
// really show up for end-user.
let (str_name, kind) = match hir_name {
ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::Explicit),
ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
};

// Add a definition for the in-band lifetime def.
self.resolver.create_def(
parent_def_id,
node_id,
DefPathData::LifetimeNs(str_name),
ExpnId::root(),
span.with_parent(None),
);

let hir_id = self.lower_node_id(node_id);
let def_id = self.resolver.local_def_id(node_id);
hir::GenericParam {
hir_id: self.lower_node_id(node_id),
name: hir_name,
hir_id,
name: hir::ParamName::Fresh(def_id),
bounds: &[],
span: self.lower_span(span),
pure_wrt_drop: false,
kind: hir::GenericParamKind::Lifetime { kind },
kind: hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Elided },
}
}

/// When we have either an elided or `'_` lifetime in an impl
/// header, we convert it to an in-band lifetime.
fn collect_fresh_anonymous_lifetime(&mut self, span: Span) -> ParamName {
assert!(self.is_collecting_anonymous_lifetimes);
let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
let hir_name = ParamName::Fresh(index);
self.lifetimes_to_define.push((span, hir_name));
let Some(parent_def_id) = self.is_collecting_anonymous_lifetimes else { panic!() };

let node_id = self.resolver.next_node_id();

// Add a definition for the in-band lifetime def.
let param_def_id = self.resolver.create_def(
parent_def_id,
node_id,
DefPathData::LifetimeNs(kw::UnderscoreLifetime),
ExpnId::root(),
span.with_parent(None),
);

let hir_name = ParamName::Fresh(param_def_id);
self.lifetimes_to_define.push((span, node_id));
hir_name
}

Expand Down Expand Up @@ -817,7 +811,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
) -> (hir::Generics<'hir>, T) {
let (lifetimes_to_define, (mut lowered_generics, impl_trait_defs, res)) = self
.collect_in_band_defs(|this| {
.collect_in_band_defs(parent_def_id, |this| {
this.with_anonymous_lifetime_mode(anonymous_lifetime_mode, |this| {
this.with_in_scope_lifetime_defs(&generics.params, |this| {
let mut impl_trait_defs = Vec::new();
Expand All @@ -844,9 +838,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
lowered_generics.params.extend(
lifetimes_to_define
.into_iter()
.map(|(span, hir_name)| {
self.lifetime_to_generic_param(span, hir_name, parent_def_id)
})
.map(|(span, node_id)| self.fresh_lifetime_to_generic_param(span, node_id))
.chain(impl_trait_defs),
);

Expand Down Expand Up @@ -1763,15 +1755,53 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
.in_scope_lifetimes
.iter()
.cloned()
.map(|name| (name.ident().span, name, hir::LifetimeName::Param(name)))
.chain(
self.lifetimes_to_define
.iter()
.map(|&(span, name)| (span, name, hir::LifetimeName::Param(name))),
)
.map(|name| (name.ident().span, hir::LifetimeName::Param(name)))
.chain(self.lifetimes_to_define.iter().map(|&(span, node_id)| {
let def_id = self.resolver.local_def_id(node_id);
let name = hir::ParamName::Fresh(def_id);
(span, hir::LifetimeName::Param(name))
}))
.collect();

self.with_hir_id_owner(opaque_ty_node_id, |this| {
let mut generic_params: Vec<_> = lifetime_params
.iter()
.map(|&(span, name)| {
// We can only get lifetime names from the outside.
let hir::LifetimeName::Param(hir_name) = name else { panic!() };

let node_id = this.resolver.next_node_id();

// Add a definition for the in-band lifetime def.
let def_id = this.resolver.create_def(
opaque_ty_def_id,
node_id,
DefPathData::LifetimeNs(hir_name.ident().name),
ExpnId::root(),
span.with_parent(None),
);

let (kind, name) = match hir_name {
ParamName::Plain(ident) => {
(hir::LifetimeParamKind::Explicit, hir::ParamName::Plain(ident))
}
ParamName::Fresh(_) => {
(hir::LifetimeParamKind::Elided, hir::ParamName::Fresh(def_id))
}
ParamName::Error => (hir::LifetimeParamKind::Error, hir::ParamName::Error),
};

hir::GenericParam {
hir_id: this.lower_node_id(node_id),
name,
bounds: &[],
span: this.lower_span(span),
pure_wrt_drop: false,
kind: hir::GenericParamKind::Lifetime { kind },
}
})
.collect();

// We have to be careful to get elision right here. The
// idea is that we create a lifetime parameter for each
// lifetime in the return type. So, given a return type
Expand All @@ -1782,25 +1812,22 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// hence the elision takes place at the fn site.
let (lifetimes_to_define, future_bound) =
this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
this.collect_in_band_defs(|this| {
this.collect_in_band_defs(opaque_ty_def_id, |this| {
this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
})
});
debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", lifetimes_to_define);

lifetime_params.extend(
// Output lifetime like `'_`:
lifetimes_to_define
.into_iter()
.map(|(span, name)| (span, name, hir::LifetimeName::Implicit(false))),
);
// Output lifetime like `'_`:
for (span, node_id) in lifetimes_to_define {
let param = this.fresh_lifetime_to_generic_param(span, node_id);
lifetime_params.push((span, hir::LifetimeName::Implicit(false)));
generic_params.push(param);
}
let generic_params = this.arena.alloc_from_iter(generic_params);
debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);

let generic_params =
this.arena.alloc_from_iter(lifetime_params.iter().map(|&(span, hir_name, _)| {
this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_id)
}));
debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);

let opaque_ty_item = hir::OpaqueTy {
generics: hir::Generics {
Expand Down Expand Up @@ -1833,7 +1860,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// For the "output" lifetime parameters, we just want to
// generate `'_`.
let generic_args =
self.arena.alloc_from_iter(lifetime_params.into_iter().map(|(span, _, name)| {
self.arena.alloc_from_iter(lifetime_params.into_iter().map(|(span, name)| {
GenericArg::Lifetime(hir::Lifetime {
hir_id: self.next_id(),
span: self.lower_span(span),
Expand Down Expand Up @@ -1969,7 +1996,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let (name, kind) = match param.kind {
GenericParamKind::Lifetime => {
let was_collecting_in_band = self.is_collecting_anonymous_lifetimes;
self.is_collecting_anonymous_lifetimes = false;
self.is_collecting_anonymous_lifetimes = None;

let lt = self
.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
Expand Down
4 changes: 2 additions & 2 deletions compiler/rustc_hir/src/hir.rs
View file
Expand Up @@ -59,7 +59,7 @@ pub enum ParamName {
///
/// where `'f` is something like `Fresh(0)`. The indices are
/// unique per impl, but not necessarily continuous.
Fresh(usize),
Fresh(LocalDefId),

/// Indicates an illegal name was given and an error has been
/// reported (so we should squelch other derived errors). Occurs
Expand Down Expand Up @@ -3303,7 +3303,7 @@ mod size_asserts {
rustc_data_structures::static_assert_size!(super::Expr<'static>, 56);
rustc_data_structures::static_assert_size!(super::Pat<'static>, 88);
rustc_data_structures::static_assert_size!(super::QPath<'static>, 24);
rustc_data_structures::static_assert_size!(super::Ty<'static>, 80);
rustc_data_structures::static_assert_size!(super::Ty<'static>, 72);

rustc_data_structures::static_assert_size!(super::Item<'static>, 184);
rustc_data_structures::static_assert_size!(super::TraitItem<'static>, 128);
Expand Down

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