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Remap impl-trait lifetimes on HIR instead of AST lowering.

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This commit is contained in:
Camille GILLOT
2024-08-20 00:48:43 +00:00
parent 298c7462c3
commit b6e1214ac0
35 changed files with 508 additions and 597 deletions
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255
compiler/rustc_ast_lowering/src/lib.rs
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@@ -45,16 +45,14 @@ use rustc_ast::ptr::P;
use rustc_ast::{self as ast, *};
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fingerprint::Fingerprint;
use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::sorted_map::SortedMap;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_data_structures::sync::Lrc;
use rustc_errors::{DiagArgFromDisplay, DiagCtxtHandle, StashKey};
use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId, LocalDefIdMap};
use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId};
use rustc_hir::{
self as hir, ConstArg, GenericArg, HirId, ItemLocalMap, LangItem, MissingLifetimeKind,
ParamName, TraitCandidate,
self as hir, ConstArg, GenericArg, HirId, ItemLocalMap, LangItem, ParamName, TraitCandidate,
};
use rustc_index::{Idx, IndexSlice, IndexVec};
use rustc_macros::extension;
@@ -83,7 +81,6 @@ mod expr;
mod format;
mod index;
mod item;
mod lifetime_collector;
mod pat;
mod path;
@@ -149,12 +146,6 @@ struct LoweringContext<'a, 'hir> {
allow_async_iterator: Lrc<[Symbol]>,
allow_for_await: Lrc<[Symbol]>,
allow_async_fn_traits: Lrc<[Symbol]>,
/// Mapping from generics `def_id`s to TAIT generics `def_id`s.
/// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
/// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
/// field from the original parameter 'a to the new parameter 'a1.
generics_def_id_map: Vec<LocalDefIdMap<LocalDefId>>,
}
impl<'a, 'hir> LoweringContext<'a, 'hir> {
@@ -199,7 +190,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// FIXME(gen_blocks): how does `closure_track_caller`/`async_fn_track_caller`
// interact with `gen`/`async gen` blocks
allow_async_iterator: [sym::gen_future, sym::async_iterator].into(),
generics_def_id_map: Default::default(),
}
}
@@ -528,54 +518,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
/// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
/// resolver (if any).
fn orig_opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
self.resolver.node_id_to_def_id.get(&node).copied()
}
/// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
/// resolver (if any), after applying any remapping from `get_remapped_def_id`.
///
/// For example, in a function like `fn foo<'a>(x: &'a u32)`,
/// invoking with the id from the `ast::Lifetime` node found inside
/// the `&'a u32` type would return the `LocalDefId` of the
/// `'a` parameter declared on `foo`.
///
/// This function also applies remapping from `get_remapped_def_id`.
/// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
/// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
/// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
/// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
self.orig_opt_local_def_id(node).map(|local_def_id| self.get_remapped_def_id(local_def_id))
self.resolver.node_id_to_def_id.get(&node).copied()
}
fn local_def_id(&self, node: NodeId) -> LocalDefId {
self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{node:?}`"))
}
/// Get the previously recorded `to` local def id given the `from` local def id, obtained using
/// `generics_def_id_map` field.
fn get_remapped_def_id(&self, local_def_id: LocalDefId) -> LocalDefId {
// `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
// push new mappings, so we first need to get the latest (innermost) mappings, hence `iter().rev()`.
//
// Consider:
//
// `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
//
// We would end with a generics_def_id_map like:
//
// `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
//
// for the opaque type generated on `impl Sized + 'b`, we want the result to be: impl_sized#'b.
// So, if we were trying to find first from the start (outermost) would give the wrong result, impl_trait#'b.
self.generics_def_id_map
.iter()
.rev()
.find_map(|map| map.get(&local_def_id).copied())
.unwrap_or(local_def_id)
}
/// Freshen the `LoweringContext` and ready it to lower a nested item.
/// The lowered item is registered into `self.children`.
///
@@ -647,27 +597,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
result
}
/// Installs the remapping `remap` in scope while `f` is being executed.
/// This causes references to the `LocalDefId` keys to be changed to
/// refer to the values instead.
///
/// The remapping is used when one piece of AST expands to multiple
/// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
/// expands to both a function definition (`foo`) and a TAIT for the return value,
/// both of which have a lifetime parameter `'a`. The remapping allows us to
/// rewrite the `'a` in the return value to refer to the
/// `'a` declared on the TAIT, instead of the function.
fn with_remapping<R>(
&mut self,
remap: LocalDefIdMap<LocalDefId>,
f: impl FnOnce(&mut Self) -> R,
) -> R {
self.generics_def_id_map.push(remap);
let res = f(self);
self.generics_def_id_map.pop();
res
}
fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
let attrs = std::mem::take(&mut self.attrs);
let mut bodies = std::mem::take(&mut self.bodies);
@@ -1499,27 +1428,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// frequently opened issues show.
let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
// Whether this opaque always captures lifetimes in scope.
// Right now, this is all RPITIT and TAITs, and when `lifetime_capture_rules_2024`
// is enabled. We don't check the span of the edition, since this is done
// on a per-opaque basis to account for nested opaques.
let always_capture_in_scope = match origin {
_ if self.tcx.features().lifetime_capture_rules_2024() => true,
hir::OpaqueTyOrigin::TyAlias { .. } => true,
hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl, .. } => in_trait_or_impl.is_some(),
hir::OpaqueTyOrigin::AsyncFn { .. } => {
unreachable!("should be using `lower_coroutine_fn_ret_ty`")
}
};
let captured_lifetimes_to_duplicate = lifetime_collector::lifetimes_for_opaque(
self.resolver,
always_capture_in_scope,
opaque_ty_node_id,
bounds,
span,
);
debug!(?captured_lifetimes_to_duplicate);
// Feature gate for RPITIT + use<..>
match origin {
rustc_hir::OpaqueTyOrigin::FnReturn { in_trait_or_impl: Some(_), .. } => {
@@ -1542,22 +1450,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
_ => {}
}
self.lower_opaque_inner(
opaque_ty_node_id,
origin,
captured_lifetimes_to_duplicate,
span,
opaque_ty_span,
|this| this.lower_param_bounds(bounds, itctx),
)
self.lower_opaque_inner(opaque_ty_node_id, origin, opaque_ty_span, |this| {
this.lower_param_bounds(bounds, itctx)
})
}
fn lower_opaque_inner(
&mut self,
opaque_ty_node_id: NodeId,
origin: hir::OpaqueTyOrigin,
captured_lifetimes_to_duplicate: FxIndexSet<Lifetime>,
span: Span,
opaque_ty_span: Span,
lower_item_bounds: impl FnOnce(&mut Self) -> &'hir [hir::GenericBound<'hir>],
) -> hir::TyKind<'hir> {
@@ -1565,145 +1466,19 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let opaque_ty_hir_id = self.lower_node_id(opaque_ty_node_id);
debug!(?opaque_ty_def_id, ?opaque_ty_hir_id);
// Map from captured (old) lifetime to synthetic (new) lifetime.
// Used to resolve lifetimes in the bounds of the opaque.
let mut captured_to_synthesized_mapping = LocalDefIdMap::default();
// List of (early-bound) synthetic lifetimes that are owned by the opaque.
// This is used to create the `hir::Generics` owned by the opaque.
let mut synthesized_lifetime_definitions = vec![];
// Pairs of lifetime arg (that resolves to the captured lifetime)
// and the def-id of the (early-bound) synthetic lifetime definition.
// This is used both to create generics for the `TyKind::OpaqueDef` that
// we return, and also as a captured lifetime mapping for RPITITs.
let mut synthesized_lifetime_args = vec![];
for lifetime in captured_lifetimes_to_duplicate {
let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
let (old_def_id, missing_kind) = match res {
LifetimeRes::Param { param: old_def_id, binder: _ } => (old_def_id, None),
LifetimeRes::Fresh { param, kind, .. } => {
debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
if let Some(old_def_id) = self.orig_opt_local_def_id(param) {
(old_def_id, Some(kind))
} else {
self.dcx()
.span_delayed_bug(lifetime.ident.span, "no def-id for fresh lifetime");
continue;
}
}
// Opaques do not capture `'static`
LifetimeRes::Static { .. } | LifetimeRes::Error => {
continue;
}
res => {
let bug_msg = format!(
"Unexpected lifetime resolution {:?} for {:?} at {:?}",
res, lifetime.ident, lifetime.ident.span
);
span_bug!(lifetime.ident.span, "{}", bug_msg);
}
};
if captured_to_synthesized_mapping.get(&old_def_id).is_none() {
// Create a new lifetime parameter local to the opaque.
let duplicated_lifetime_node_id = self.next_node_id();
let duplicated_lifetime_def_id = self.create_def(
opaque_ty_def_id,
duplicated_lifetime_node_id,
lifetime.ident.name,
DefKind::LifetimeParam,
self.lower_span(lifetime.ident.span),
);
captured_to_synthesized_mapping.insert(old_def_id, duplicated_lifetime_def_id);
// FIXME: Instead of doing this, we could move this whole loop
// into the `with_hir_id_owner`, then just directly construct
// the `hir::GenericParam` here.
synthesized_lifetime_definitions.push((
duplicated_lifetime_node_id,
duplicated_lifetime_def_id,
self.lower_ident(lifetime.ident),
missing_kind,
));
// Now make an arg that we can use for the generic params of the opaque tykind.
let id = self.next_node_id();
let lifetime_arg = self.new_named_lifetime_with_res(id, lifetime.ident, res);
let duplicated_lifetime_def_id = self.local_def_id(duplicated_lifetime_node_id);
synthesized_lifetime_args.push((lifetime_arg, duplicated_lifetime_def_id))
}
}
let opaque_ty_def = self.with_def_id_parent(opaque_ty_def_id, |this| {
// Install the remapping from old to new (if any). This makes sure that
// any lifetimes that would have resolved to the def-id of captured
// lifetimes are remapped to the new *synthetic* lifetimes of the opaque.
let bounds = this
.with_remapping(captured_to_synthesized_mapping, |this| lower_item_bounds(this));
let generic_params =
this.arena.alloc_from_iter(synthesized_lifetime_definitions.iter().map(
|&(new_node_id, new_def_id, ident, missing_kind)| {
let hir_id = this.lower_node_id(new_node_id);
let (name, kind) = if ident.name == kw::UnderscoreLifetime {
(
hir::ParamName::Fresh,
hir::LifetimeParamKind::Elided(
missing_kind.unwrap_or(MissingLifetimeKind::Underscore),
),
)
} else {
(hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
};
hir::GenericParam {
hir_id,
def_id: new_def_id,
name,
span: ident.span,
pure_wrt_drop: false,
kind: hir::GenericParamKind::Lifetime { kind },
colon_span: None,
source: hir::GenericParamSource::Generics,
}
},
));
debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
let lifetime_mapping = self.arena.alloc_slice(&synthesized_lifetime_args);
trace!("registering opaque type with id {:#?}", opaque_ty_def_id);
let bounds = lower_item_bounds(this);
let opaque_ty_def = hir::OpaqueTy {
hir_id: opaque_ty_hir_id,
def_id: opaque_ty_def_id,
generics: this.arena.alloc(hir::Generics {
params: generic_params,
predicates: &[],
has_where_clause_predicates: false,
where_clause_span: this.lower_span(span),
span: this.lower_span(span),
}),
bounds,
origin,
lifetime_mapping,
span: this.lower_span(opaque_ty_span),
};
this.arena.alloc(opaque_ty_def)
});
let generic_args = self.arena.alloc_from_iter(
synthesized_lifetime_args
.iter()
.map(|(lifetime, _)| hir::GenericArg::Lifetime(*lifetime)),
);
// Create the `Foo<...>` reference itself. Note that the `type
// Foo = impl Trait` is, internally, created as a child of the
// async fn, so the *type parameters* are inherited. It's
// only the lifetime parameters that we must supply.
hir::TyKind::OpaqueDef(opaque_ty_def, generic_args)
hir::TyKind::OpaqueDef(opaque_ty_def)
}
fn lower_precise_capturing_args(
@@ -1885,13 +1660,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let opaque_ty_span =
self.mark_span_with_reason(DesugaringKind::Async, span, allowed_features);
let captured_lifetimes = self
.resolver
.extra_lifetime_params(opaque_ty_node_id)
.into_iter()
.map(|(ident, id, _)| Lifetime { id, ident })
.collect();
let in_trait_or_impl = match fn_kind {
FnDeclKind::Trait => Some(hir::RpitContext::Trait),
FnDeclKind::Impl => Some(hir::RpitContext::TraitImpl),
@@ -1902,8 +1670,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
let opaque_ty_ref = self.lower_opaque_inner(
opaque_ty_node_id,
hir::OpaqueTyOrigin::AsyncFn { parent: fn_def_id, in_trait_or_impl },
captured_lifetimes,
span,
opaque_ty_span,
|this| {
let bound = this.lower_coroutine_fn_output_type_to_bound(
@@ -2000,10 +1766,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
res: LifetimeRes,
) -> &'hir hir::Lifetime {
let res = match res {
LifetimeRes::Param { param, .. } => {
let param = self.get_remapped_def_id(param);
hir::LifetimeName::Param(param)
}
LifetimeRes::Param { param, .. } => hir::LifetimeName::Param(param),
LifetimeRes::Fresh { param, .. } => {
let param = self.local_def_id(param);
hir::LifetimeName::Param(param)