1 //! Lowers the AST to the HIR.
3 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
4 //! much like a fold. Where lowering involves a bit more work things get more
5 //! interesting and there are some invariants you should know about. These mostly
6 //! concern spans and IDs.
8 //! Spans are assigned to AST nodes during parsing and then are modified during
9 //! expansion to indicate the origin of a node and the process it went through
10 //! being expanded. IDs are assigned to AST nodes just before lowering.
12 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
13 //! expansion we do not preserve the process of lowering in the spans, so spans
14 //! should not be modified here. When creating a new node (as opposed to
15 //! "folding" an existing one), create a new ID using `next_id()`.
17 //! You must ensure that IDs are unique. That means that you should only use the
18 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
19 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
20 //! If you do, you must then set the new node's ID to a fresh one.
22 //! Spans are used for error messages and for tools to map semantics back to
23 //! source code. It is therefore not as important with spans as IDs to be strict
24 //! about use (you can't break the compiler by screwing up a span). Obviously, a
25 //! HIR node can only have a single span. But multiple nodes can have the same
26 //! span and spans don't need to be kept in order, etc. Where code is preserved
27 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
28 //! new it is probably best to give a span for the whole AST node being lowered.
29 //! All nodes should have real spans; don't use dummy spans. Tools are likely to
30 //! get confused if the spans from leaf AST nodes occur in multiple places
31 //! in the HIR, especially for multiple identifiers.
33 #![feature(box_patterns)]
34 #![feature(let_chains)]
35 #![feature(never_type)]
36 #![recursion_limit = "256"]
37 #![deny(rustc::untranslatable_diagnostic)]
38 #![deny(rustc::diagnostic_outside_of_impl)]
43 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait, TraitFnAsync};
45 use rustc_ast::ptr::P;
47 use rustc_ast::{self as ast, *};
48 use rustc_ast_pretty::pprust;
49 use rustc_data_structures::captures::Captures;
50 use rustc_data_structures::fingerprint::Fingerprint;
51 use rustc_data_structures::fx::FxHashMap;
52 use rustc_data_structures::sorted_map::SortedMap;
53 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
54 use rustc_data_structures::sync::Lrc;
55 use rustc_errors::{DiagnosticArgFromDisplay, Handler, StashKey};
57 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
58 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
59 use rustc_hir::definitions::DefPathData;
60 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
61 use rustc_index::vec::{Idx, IndexVec};
62 use rustc_middle::span_bug;
63 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
64 use rustc_session::parse::feature_err;
65 use rustc_span::hygiene::MacroKind;
66 use rustc_span::source_map::DesugaringKind;
67 use rustc_span::symbol::{kw, sym, Ident, Symbol};
68 use rustc_span::{Span, DUMMY_SP};
70 use smallvec::SmallVec;
71 use std::collections::hash_map::Entry;
73 macro_rules! arena_vec {
74 ($this:expr; $($x:expr),*) => (
75 $this.arena.alloc_from_iter([$($x),*])
85 mod lifetime_collector;
89 struct LoweringContext<'a, 'hir> {
91 resolver: &'a mut ResolverAstLowering,
93 /// Used to allocate HIR nodes.
94 arena: &'hir hir::Arena<'hir>,
96 /// Bodies inside the owner being lowered.
97 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
98 /// Attributes inside the owner being lowered.
99 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
100 /// Collect items that were created by lowering the current owner.
101 children: Vec<(LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>)>,
103 generator_kind: Option<hir::GeneratorKind>,
105 /// When inside an `async` context, this is the `HirId` of the
106 /// `task_context` local bound to the resume argument of the generator.
107 task_context: Option<hir::HirId>,
109 /// Used to get the current `fn`'s def span to point to when using `await`
110 /// outside of an `async fn`.
111 current_item: Option<Span>,
113 catch_scope: Option<NodeId>,
114 loop_scope: Option<NodeId>,
115 is_in_loop_condition: bool,
116 is_in_trait_impl: bool,
117 is_in_dyn_type: bool,
119 current_hir_id_owner: hir::OwnerId,
120 item_local_id_counter: hir::ItemLocalId,
121 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
122 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
124 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
125 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
127 /// NodeIds that are lowered inside the current HIR owner.
128 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
130 allow_try_trait: Option<Lrc<[Symbol]>>,
131 allow_gen_future: Option<Lrc<[Symbol]>>,
132 allow_into_future: Option<Lrc<[Symbol]>>,
134 /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
135 /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
136 /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
137 /// field from the original parameter 'a to the new parameter 'a1.
138 generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
141 trait ResolverAstLoweringExt {
142 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
143 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
144 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
145 // Clones the resolution (if any) on 'source' and applies it
146 // to 'target'. Used when desugaring a `UseTreeKind::Nested` to
147 // multiple `UseTreeKind::Simple`s
148 fn clone_res(&mut self, source: NodeId, target: NodeId);
149 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
150 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
151 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
152 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
155 impl ResolverAstLoweringExt for ResolverAstLowering {
156 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
157 if let ExprKind::Path(None, path) = &expr.kind {
158 // Don't perform legacy const generics rewriting if the path already
159 // has generic arguments.
160 if path.segments.last().unwrap().args.is_some() {
164 if let Res::Def(DefKind::Fn, def_id) = self.partial_res_map.get(&expr.id)?.full_res()? {
165 // We only support cross-crate argument rewriting. Uses
166 // within the same crate should be updated to use the new
167 // const generics style.
168 if def_id.is_local() {
172 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
181 fn clone_res(&mut self, source: NodeId, target: NodeId) {
182 if let Some(res) = self.partial_res_map.get(&source) {
183 self.partial_res_map.insert(target, *res);
187 /// Obtains resolution for a `NodeId` with a single resolution.
188 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
189 self.partial_res_map.get(&id).copied()
192 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
193 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
194 self.import_res_map.get(&id).copied().unwrap_or_default()
197 /// Obtains resolution for a label with the given `NodeId`.
198 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
199 self.label_res_map.get(&id).copied()
202 /// Obtains resolution for a lifetime with the given `NodeId`.
203 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
204 self.lifetimes_res_map.get(&id).copied()
207 /// Obtain the list of lifetimes parameters to add to an item.
209 /// Extra lifetime parameters should only be added in places that can appear
210 /// as a `binder` in `LifetimeRes`.
212 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
213 /// should appear at the enclosing `PolyTraitRef`.
214 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
215 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
218 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
219 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
223 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
224 /// and if so, what meaning it has.
225 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
226 enum ImplTraitContext {
227 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
228 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
229 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
231 /// Newly generated parameters should be inserted into the given `Vec`.
234 /// Treat `impl Trait` as shorthand for a new opaque type.
235 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
236 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
238 ReturnPositionOpaqueTy {
239 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
240 origin: hir::OpaqueTyOrigin,
243 /// Impl trait in type aliases.
245 /// `impl Trait` is unstably accepted in this position.
246 FeatureGated(ImplTraitPosition, Symbol),
247 /// `impl Trait` is not accepted in this position.
248 Disallowed(ImplTraitPosition),
251 /// Position in which `impl Trait` is disallowed.
252 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
253 enum ImplTraitPosition {
275 impl std::fmt::Display for ImplTraitPosition {
276 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
277 let name = match self {
278 ImplTraitPosition::Path => "path",
279 ImplTraitPosition::Variable => "variable binding",
280 ImplTraitPosition::Type => "type",
281 ImplTraitPosition::Trait => "trait",
282 ImplTraitPosition::AsyncBlock => "async block",
283 ImplTraitPosition::Bound => "bound",
284 ImplTraitPosition::Generic => "generic",
285 ImplTraitPosition::ExternFnParam => "`extern fn` param",
286 ImplTraitPosition::ClosureParam => "closure param",
287 ImplTraitPosition::PointerParam => "`fn` pointer param",
288 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
289 ImplTraitPosition::TraitParam => "trait method param",
290 ImplTraitPosition::ImplParam => "`impl` method param",
291 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
292 ImplTraitPosition::ClosureReturn => "closure return",
293 ImplTraitPosition::PointerReturn => "`fn` pointer return",
294 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
295 ImplTraitPosition::TraitReturn => "trait method return",
296 ImplTraitPosition::ImplReturn => "`impl` method return",
299 write!(f, "{}", name)
303 #[derive(Debug, PartialEq, Eq)]
315 fn param_impl_trait_allowed(&self) -> bool {
317 FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
322 fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
324 FnDeclKind::Fn | FnDeclKind::Inherent => true,
325 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
326 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
331 fn async_fn_allowed(&self, tcx: TyCtxt<'_>) -> bool {
333 FnDeclKind::Fn | FnDeclKind::Inherent => true,
334 FnDeclKind::Impl if tcx.features().async_fn_in_trait => true,
335 FnDeclKind::Trait if tcx.features().async_fn_in_trait => true,
341 #[derive(Copy, Clone)]
344 Crate(&'a ast::Crate),
346 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
347 ForeignItem(&'a ast::ForeignItem),
351 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
353 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
354 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
355 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
356 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
357 visit::walk_crate(&mut indexer, krate);
358 return indexer.index;
360 struct Indexer<'s, 'a> {
361 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
362 index: IndexVec<LocalDefId, AstOwner<'a>>,
365 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
366 fn visit_attribute(&mut self, _: &'a Attribute) {
367 // We do not want to lower expressions that appear in attributes,
368 // as they are not accessible to the rest of the HIR.
371 fn visit_item(&mut self, item: &'a ast::Item) {
372 let def_id = self.node_id_to_def_id[&item.id];
373 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
374 self.index[def_id] = AstOwner::Item(item);
375 visit::walk_item(self, item)
378 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
379 let def_id = self.node_id_to_def_id[&item.id];
380 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
381 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
382 visit::walk_assoc_item(self, item, ctxt);
385 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
386 let def_id = self.node_id_to_def_id[&item.id];
387 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
388 self.index[def_id] = AstOwner::ForeignItem(item);
389 visit::walk_foreign_item(self, item);
394 /// Compute the hash for the HIR of the full crate.
395 /// This hash will then be part of the crate_hash which is stored in the metadata.
398 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
400 let mut hir_body_nodes: Vec<_> = owners
402 .filter_map(|(def_id, info)| {
403 let info = info.as_owner()?;
404 let def_path_hash = tcx.hir().def_path_hash(def_id);
405 Some((def_path_hash, info))
408 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
410 tcx.with_stable_hashing_context(|mut hcx| {
411 let mut stable_hasher = StableHasher::new();
412 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
413 stable_hasher.finish()
417 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
419 let krate = tcx.untracked_crate.steal();
420 let mut resolver = tcx.resolver_for_lowering(()).steal();
422 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
423 let mut owners = IndexVec::from_fn_n(
424 |_| hir::MaybeOwner::Phantom,
425 tcx.definitions_untracked().def_index_count(),
428 for def_id in ast_index.indices() {
431 resolver: &mut resolver,
432 ast_index: &ast_index,
438 // Drop AST to free memory
440 sess.time("drop_ast", || drop(krate));
442 // Discard hygiene data, which isn't required after lowering to HIR.
443 if !sess.opts.unstable_opts.keep_hygiene_data {
444 rustc_span::hygiene::clear_syntax_context_map();
447 let hir_hash = compute_hir_hash(tcx, &owners);
448 hir::Crate { owners, hir_hash }
451 #[derive(Copy, Clone, PartialEq, Debug)]
453 /// Any path in a type context.
455 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
457 /// The `module::Type` in `module::Type::method` in an expression.
461 enum ParenthesizedGenericArgs {
466 impl<'a, 'hir> LoweringContext<'a, 'hir> {
470 node_id: ast::NodeId,
474 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
476 self.opt_local_def_id(node_id).is_none(),
477 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
480 self.tcx.hir().def_key(self.local_def_id(node_id)),
483 let def_id = self.tcx.at(span).create_def(parent, data).def_id();
485 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
486 self.resolver.node_id_to_def_id.insert(node_id, def_id);
491 fn next_node_id(&mut self) -> NodeId {
492 let start = self.resolver.next_node_id;
493 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
494 self.resolver.next_node_id = ast::NodeId::from_u32(next);
498 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
499 /// resolver (if any).
500 fn orig_opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
501 self.resolver.node_id_to_def_id.get(&node).map(|local_def_id| *local_def_id)
504 fn orig_local_def_id(&self, node: NodeId) -> LocalDefId {
505 self.orig_opt_local_def_id(node)
506 .unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
509 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
510 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
512 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
513 /// invoking with the id from the `ast::Lifetime` node found inside
514 /// the `&'a u32` type would return the `LocalDefId` of the
515 /// `'a` parameter declared on `foo`.
517 /// This function also applies remapping from `get_remapped_def_id`.
518 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
519 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
520 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
521 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
522 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
523 self.orig_opt_local_def_id(node).map(|local_def_id| self.get_remapped_def_id(local_def_id))
526 fn local_def_id(&self, node: NodeId) -> LocalDefId {
527 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
530 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
531 /// `generics_def_id_map` field.
532 fn get_remapped_def_id(&self, local_def_id: LocalDefId) -> LocalDefId {
533 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
534 // push new mappings, so we first need to get the latest (innermost) mappings, hence `iter().rev()`.
538 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
540 // We would end with a generics_def_id_map like:
542 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
544 // for the opaque type generated on `impl Sized + 'b`, we want the result to be: impl_sized#'b.
545 // So, if we were trying to find first from the start (outermost) would give the wrong result, impl_trait#'b.
546 self.generics_def_id_map
549 .find_map(|map| map.get(&local_def_id).map(|local_def_id| *local_def_id))
550 .unwrap_or(local_def_id)
553 /// Freshen the `LoweringContext` and ready it to lower a nested item.
554 /// The lowered item is registered into `self.children`.
556 /// This function sets up `HirId` lowering infrastructure,
557 /// and stashes the shared mutable state to avoid pollution by the closure.
558 #[instrument(level = "debug", skip(self, f))]
559 fn with_hir_id_owner(
562 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
564 let def_id = self.local_def_id(owner);
566 let current_attrs = std::mem::take(&mut self.attrs);
567 let current_bodies = std::mem::take(&mut self.bodies);
568 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
569 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
570 let current_trait_map = std::mem::take(&mut self.trait_map);
572 std::mem::replace(&mut self.current_hir_id_owner, hir::OwnerId { def_id });
573 let current_local_counter =
574 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
575 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
576 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
578 // Do not reset `next_node_id` and `node_id_to_def_id`:
579 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
580 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
582 // Always allocate the first `HirId` for the owner itself.
583 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
584 debug_assert_eq!(_old, None);
587 debug_assert_eq!(def_id, item.def_id().def_id);
588 // `f` should have consumed all the elements in these vectors when constructing `item`.
589 debug_assert!(self.impl_trait_defs.is_empty());
590 debug_assert!(self.impl_trait_bounds.is_empty());
591 let info = self.make_owner_info(item);
593 self.attrs = current_attrs;
594 self.bodies = current_bodies;
595 self.node_id_to_local_id = current_node_ids;
596 self.local_id_to_def_id = current_id_to_def_id;
597 self.trait_map = current_trait_map;
598 self.current_hir_id_owner = current_owner;
599 self.item_local_id_counter = current_local_counter;
600 self.impl_trait_defs = current_impl_trait_defs;
601 self.impl_trait_bounds = current_impl_trait_bounds;
603 debug_assert!(!self.children.iter().any(|(id, _)| id == &def_id));
604 self.children.push((def_id, hir::MaybeOwner::Owner(info)));
607 /// Installs the remapping `remap` in scope while `f` is being executed.
608 /// This causes references to the `LocalDefId` keys to be changed to
609 /// refer to the values instead.
611 /// The remapping is used when one piece of AST expands to multiple
612 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
613 /// expands to both a function definition (`foo`) and a TAIT for the return value,
614 /// both of which have a lifetime parameter `'a`. The remapping allows us to
615 /// rewrite the `'a` in the return value to refer to the
616 /// `'a` declared on the TAIT, instead of the function.
617 fn with_remapping<R>(
619 remap: FxHashMap<LocalDefId, LocalDefId>,
620 f: impl FnOnce(&mut Self) -> R,
622 self.generics_def_id_map.push(remap);
624 self.generics_def_id_map.pop();
628 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
629 let attrs = std::mem::take(&mut self.attrs);
630 let mut bodies = std::mem::take(&mut self.bodies);
631 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
632 let trait_map = std::mem::take(&mut self.trait_map);
634 #[cfg(debug_assertions)]
635 for (id, attrs) in attrs.iter() {
636 // Verify that we do not store empty slices in the map.
637 if attrs.is_empty() {
638 panic!("Stored empty attributes for {:?}", id);
642 bodies.sort_by_key(|(k, _)| *k);
643 let bodies = SortedMap::from_presorted_elements(bodies);
644 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
645 let (nodes, parenting) =
646 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
647 let nodes = hir::OwnerNodes {
648 hash_including_bodies,
655 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
656 let mut stable_hasher = StableHasher::new();
657 attrs.hash_stable(&mut hcx, &mut stable_hasher);
658 stable_hasher.finish()
660 hir::AttributeMap { map: attrs, hash }
663 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
666 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
667 /// queries which depend on the full HIR tree and those which only depend on the item signature.
670 node: hir::OwnerNode<'hir>,
671 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
672 ) -> (Fingerprint, Fingerprint) {
673 self.tcx.with_stable_hashing_context(|mut hcx| {
674 let mut stable_hasher = StableHasher::new();
675 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
676 node.hash_stable(hcx, &mut stable_hasher)
678 let hash_including_bodies = stable_hasher.finish();
679 let mut stable_hasher = StableHasher::new();
680 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
681 let hash_without_bodies = stable_hasher.finish();
682 (hash_including_bodies, hash_without_bodies)
686 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
687 /// the `LoweringContext`'s `NodeId => HirId` map.
688 /// Take care not to call this method if the resulting `HirId` is then not
689 /// actually used in the HIR, as that would trigger an assertion in the
690 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
691 /// properly. Calling the method twice with the same `NodeId` is fine though.
692 #[instrument(level = "debug", skip(self), ret)]
693 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
694 assert_ne!(ast_node_id, DUMMY_NODE_ID);
696 match self.node_id_to_local_id.entry(ast_node_id) {
697 Entry::Occupied(o) => {
698 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
700 Entry::Vacant(v) => {
701 // Generate a new `HirId`.
702 let owner = self.current_hir_id_owner;
703 let local_id = self.item_local_id_counter;
704 let hir_id = hir::HirId { owner, local_id };
707 self.item_local_id_counter.increment_by(1);
709 assert_ne!(local_id, hir::ItemLocalId::new(0));
710 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
711 self.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
712 self.local_id_to_def_id.insert(local_id, def_id);
715 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
716 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
724 /// Generate a new `HirId` without a backing `NodeId`.
725 #[instrument(level = "debug", skip(self), ret)]
726 fn next_id(&mut self) -> hir::HirId {
727 let owner = self.current_hir_id_owner;
728 let local_id = self.item_local_id_counter;
729 assert_ne!(local_id, hir::ItemLocalId::new(0));
730 self.item_local_id_counter.increment_by(1);
731 hir::HirId { owner, local_id }
734 #[instrument(level = "trace", skip(self))]
735 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
736 let res: Result<Res, ()> = res.apply_id(|id| {
737 let owner = self.current_hir_id_owner;
738 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
739 Ok(hir::HirId { owner, local_id })
743 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
744 // This can happen when trying to lower the return type `x` in erroneous code like
745 // async fn foo(x: u8) -> x {}
746 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
747 // an opaque type as a synthesized HIR owner.
748 res.unwrap_or(Res::Err)
751 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
752 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| pr.expect_full_res())
755 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
756 self.resolver.get_import_res(id).present_items()
759 fn diagnostic(&self) -> &Handler {
760 self.tcx.sess.diagnostic()
763 /// Reuses the span but adds information like the kind of the desugaring and features that are
764 /// allowed inside this span.
765 fn mark_span_with_reason(
767 reason: DesugaringKind,
769 allow_internal_unstable: Option<Lrc<[Symbol]>>,
771 self.tcx.with_stable_hashing_context(|hcx| {
772 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
776 /// Intercept all spans entering HIR.
777 /// Mark a span as relative to the current owning item.
778 fn lower_span(&self, span: Span) -> Span {
779 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
780 span.with_parent(Some(self.current_hir_id_owner.def_id))
782 // Do not make spans relative when not using incremental compilation.
787 fn lower_ident(&self, ident: Ident) -> Ident {
788 Ident::new(ident.name, self.lower_span(ident.span))
791 /// Converts a lifetime into a new generic parameter.
792 #[instrument(level = "debug", skip(self))]
793 fn lifetime_res_to_generic_param(
798 ) -> Option<hir::GenericParam<'hir>> {
799 let (name, kind) = match res {
800 LifetimeRes::Param { .. } => {
801 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
803 LifetimeRes::Fresh { param, .. } => {
804 // Late resolution delegates to us the creation of the `LocalDefId`.
805 let _def_id = self.create_def(
806 self.current_hir_id_owner.def_id,
808 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
813 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
815 LifetimeRes::Static | LifetimeRes::Error => return None,
817 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
818 res, ident, ident.span
821 let hir_id = self.lower_node_id(node_id);
822 let def_id = self.local_def_id(node_id);
823 Some(hir::GenericParam {
827 span: self.lower_span(ident.span),
828 pure_wrt_drop: false,
829 kind: hir::GenericParamKind::Lifetime { kind },
834 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
835 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
836 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
837 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
838 /// parameters will be successful.
839 #[instrument(level = "debug", skip(self))]
841 fn lower_lifetime_binder(
844 generic_params: &[GenericParam],
845 ) -> &'hir [hir::GenericParam<'hir>] {
846 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
847 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
848 debug!(?extra_lifetimes);
849 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
850 self.lifetime_res_to_generic_param(ident, node_id, res)
852 let generic_params = self.arena.alloc_from_iter(generic_params);
853 debug!(?generic_params);
858 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
859 let was_in_dyn_type = self.is_in_dyn_type;
860 self.is_in_dyn_type = in_scope;
862 let result = f(self);
864 self.is_in_dyn_type = was_in_dyn_type;
869 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
870 let was_in_loop_condition = self.is_in_loop_condition;
871 self.is_in_loop_condition = false;
873 let catch_scope = self.catch_scope.take();
874 let loop_scope = self.loop_scope.take();
876 self.catch_scope = catch_scope;
877 self.loop_scope = loop_scope;
879 self.is_in_loop_condition = was_in_loop_condition;
884 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
885 if attrs.is_empty() {
888 debug_assert_eq!(id.owner, self.current_hir_id_owner);
889 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
890 debug_assert!(!ret.is_empty());
891 self.attrs.insert(id.local_id, ret);
896 fn lower_attr(&self, attr: &Attribute) -> Attribute {
897 // Note that we explicitly do not walk the path. Since we don't really
898 // lower attributes (we use the AST version) there is nowhere to keep
899 // the `HirId`s. We don't actually need HIR version of attributes anyway.
900 // Tokens are also not needed after macro expansion and parsing.
901 let kind = match attr.kind {
902 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
904 path: normal.item.path.clone(),
905 args: self.lower_attr_args(&normal.item.args),
910 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
913 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
916 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
917 debug_assert_eq!(id.owner, self.current_hir_id_owner);
918 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
919 if let Some(&a) = self.attrs.get(&target_id.local_id) {
920 debug_assert!(!a.is_empty());
921 self.attrs.insert(id.local_id, a);
925 fn lower_attr_args(&self, args: &AttrArgs) -> AttrArgs {
927 AttrArgs::Empty => AttrArgs::Empty,
928 AttrArgs::Delimited(args) => AttrArgs::Delimited(self.lower_delim_args(args)),
929 // This is an inert key-value attribute - it will never be visible to macros
930 // after it gets lowered to HIR. Therefore, we can extract literals to handle
931 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
932 AttrArgs::Eq(eq_span, AttrArgsEq::Ast(expr)) => {
933 // In valid code the value always ends up as a single literal. Otherwise, a dummy
934 // literal suffices because the error is handled elsewhere.
935 let lit = if let ExprKind::Lit(token_lit) = expr.kind
936 && let Ok(lit) = MetaItemLit::from_token_lit(token_lit, expr.span)
947 AttrArgs::Eq(*eq_span, AttrArgsEq::Hir(lit))
949 AttrArgs::Eq(_, AttrArgsEq::Hir(lit)) => {
950 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
955 fn lower_delim_args(&self, args: &DelimArgs) -> DelimArgs {
956 DelimArgs { dspan: args.dspan, delim: args.delim, tokens: args.tokens.flattened() }
959 /// Given an associated type constraint like one of these:
961 /// ```ignore (illustrative)
962 /// T: Iterator<Item: Debug>
964 /// T: Iterator<Item = Debug>
968 /// returns a `hir::TypeBinding` representing `Item`.
969 #[instrument(level = "debug", skip(self))]
970 fn lower_assoc_ty_constraint(
972 constraint: &AssocConstraint,
973 itctx: &ImplTraitContext,
974 ) -> hir::TypeBinding<'hir> {
975 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
976 // lower generic arguments of identifier in constraint
977 let gen_args = if let Some(gen_args) = &constraint.gen_args {
978 let gen_args_ctor = match gen_args {
979 GenericArgs::AngleBracketed(data) => {
980 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
982 GenericArgs::Parenthesized(data) => {
983 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
984 self.lower_angle_bracketed_parameter_data(
985 &data.as_angle_bracketed_args(),
992 gen_args_ctor.into_generic_args(self)
994 self.arena.alloc(hir::GenericArgs::none())
996 let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;
998 let kind = match &constraint.kind {
999 AssocConstraintKind::Equality { term } => {
1000 let term = match term {
1001 Term::Ty(ty) => self.lower_ty(ty, itctx).into(),
1002 Term::Const(c) => self.lower_anon_const(c).into(),
1004 hir::TypeBindingKind::Equality { term }
1006 AssocConstraintKind::Bound { bounds } => {
1007 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1008 let (desugar_to_impl_trait, itctx) = match itctx {
1009 // We are in the return position:
1011 // fn foo() -> impl Iterator<Item: Debug>
1015 // fn foo() -> impl Iterator<Item = impl Debug>
1016 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1017 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1019 // We are in the argument position, but within a dyn type:
1021 // fn foo(x: dyn Iterator<Item: Debug>)
1025 // fn foo(x: dyn Iterator<Item = impl Debug>)
1026 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1028 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1029 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1030 // "impl trait context" to permit `impl Debug` in this position (it desugars
1031 // then to an opaque type).
1033 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1034 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => (true, itctx_tait),
1036 // We are in the parameter position, but not within a dyn type:
1038 // fn foo(x: impl Iterator<Item: Debug>)
1040 // so we leave it as is and this gets expanded in astconv to a bound like
1041 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1043 _ => (false, itctx),
1046 if desugar_to_impl_trait {
1047 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1048 // constructing the HIR for `impl bounds...` and then lowering that.
1050 let impl_trait_node_id = self.next_node_id();
1052 self.with_dyn_type_scope(false, |this| {
1053 let node_id = this.next_node_id();
1054 let ty = this.lower_ty(
1057 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1058 span: this.lower_span(constraint.span),
1064 hir::TypeBindingKind::Equality { term: ty.into() }
1067 // Desugar `AssocTy: Bounds` into a type binding where the
1068 // later desugars into a trait predicate.
1069 let bounds = self.lower_param_bounds(bounds, itctx);
1071 hir::TypeBindingKind::Constraint { bounds }
1077 hir_id: self.lower_node_id(constraint.id),
1078 ident: self.lower_ident(constraint.ident),
1081 span: self.lower_span(constraint.span),
1085 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1086 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1087 let sub = if data.inputs.is_empty() {
1088 let parentheses_span =
1089 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1090 AssocTyParenthesesSub::Empty { parentheses_span }
1092 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1094 // Start of parameters to the 1st argument
1095 let open_param = data.inputs_span.shrink_to_lo().to(data
1101 // End of last argument to end of parameters
1103 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1104 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1106 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1109 #[instrument(level = "debug", skip(self))]
1110 fn lower_generic_arg(
1112 arg: &ast::GenericArg,
1113 itctx: &ImplTraitContext,
1114 ) -> hir::GenericArg<'hir> {
1116 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1117 ast::GenericArg::Type(ty) => {
1119 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1120 return GenericArg::Infer(hir::InferArg {
1121 hir_id: self.lower_node_id(ty.id),
1122 span: self.lower_span(ty.span),
1125 // We parse const arguments as path types as we cannot distinguish them during
1126 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1127 // type and value namespaces. If we resolved the path in the value namespace, we
1128 // transform it into a generic const argument.
1129 TyKind::Path(qself, path) => {
1130 if let Some(res) = self
1132 .get_partial_res(ty.id)
1133 .and_then(|partial_res| partial_res.full_res())
1135 if !res.matches_ns(Namespace::TypeNS) {
1137 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1141 // Construct an AnonConst where the expr is the "ty"'s path.
1143 let parent_def_id = self.current_hir_id_owner;
1144 let node_id = self.next_node_id();
1145 let span = self.lower_span(ty.span);
1147 // Add a definition for the in-band const def.
1148 let def_id = self.create_def(
1149 parent_def_id.def_id,
1151 DefPathData::AnonConst,
1155 let path_expr = Expr {
1157 kind: ExprKind::Path(qself.clone(), path.clone()),
1159 attrs: AttrVec::new(),
1163 let ct = self.with_new_scopes(|this| hir::AnonConst {
1165 hir_id: this.lower_node_id(node_id),
1166 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1168 return GenericArg::Const(ConstArg { value: ct, span });
1174 GenericArg::Type(self.lower_ty(&ty, itctx))
1176 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1177 value: self.lower_anon_const(&ct),
1178 span: self.lower_span(ct.value.span),
1183 #[instrument(level = "debug", skip(self))]
1184 fn lower_ty(&mut self, t: &Ty, itctx: &ImplTraitContext) -> &'hir hir::Ty<'hir> {
1185 self.arena.alloc(self.lower_ty_direct(t, itctx))
1191 qself: &Option<ptr::P<QSelf>>,
1193 param_mode: ParamMode,
1194 itctx: &ImplTraitContext,
1195 ) -> hir::Ty<'hir> {
1196 // Check whether we should interpret this as a bare trait object.
1197 // This check mirrors the one in late resolution. We only introduce this special case in
1198 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1199 // The other cases when a qpath should be opportunistically made a trait object are handled
1202 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1203 && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) = partial_res.full_res()
1205 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1206 let bound = this.lower_poly_trait_ref(
1208 bound_generic_params: vec![],
1209 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1214 let bounds = this.arena.alloc_from_iter([bound]);
1215 let lifetime_bound = this.elided_dyn_bound(t.span);
1216 (bounds, lifetime_bound)
1218 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1219 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1222 let id = self.lower_node_id(t.id);
1223 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1224 self.ty_path(id, t.span, qpath)
1227 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1228 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1231 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1232 self.ty(span, hir::TyKind::Tup(tys))
1235 fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir> {
1236 let kind = match &t.kind {
1237 TyKind::Infer => hir::TyKind::Infer,
1238 TyKind::Err => hir::TyKind::Err,
1239 TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1240 TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1241 TyKind::Rptr(region, mt) => {
1242 let region = region.unwrap_or_else(|| {
1243 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1244 self.resolver.get_lifetime_res(t.id)
1246 debug_assert_eq!(start.plus(1), end);
1251 let span = self.tcx.sess.source_map().start_point(t.span).shrink_to_hi();
1252 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1254 let lifetime = self.lower_lifetime(®ion);
1255 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1257 TyKind::BareFn(f) => {
1258 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
1259 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
1261 unsafety: self.lower_unsafety(f.unsafety),
1262 abi: self.lower_extern(f.ext),
1263 decl: self.lower_fn_decl(&f.decl, t.id, t.span, FnDeclKind::Pointer, None),
1264 param_names: self.lower_fn_params_to_names(&f.decl),
1267 TyKind::Never => hir::TyKind::Never,
1268 TyKind::Tup(tys) => hir::TyKind::Tup(
1269 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1271 TyKind::Paren(ty) => {
1272 return self.lower_ty_direct(ty, itctx);
1274 TyKind::Path(qself, path) => {
1275 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1277 TyKind::ImplicitSelf => {
1278 let hir_id = self.next_id();
1279 let res = self.expect_full_res(t.id);
1280 let res = self.lower_res(res);
1281 hir::TyKind::Path(hir::QPath::Resolved(
1283 self.arena.alloc(hir::Path {
1285 segments: arena_vec![self; hir::PathSegment::new(
1286 Ident::with_dummy_span(kw::SelfUpper),
1290 span: self.lower_span(t.span),
1294 TyKind::Array(ty, length) => {
1295 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1297 TyKind::Typeof(expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1298 TyKind::TraitObject(bounds, kind) => {
1299 let mut lifetime_bound = None;
1300 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1302 this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| match bound {
1303 GenericBound::Trait(
1305 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1306 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1307 // `~const ?Bound` will cause an error during AST validation
1308 // anyways, so treat it like `?Bound` as compilation proceeds.
1309 GenericBound::Trait(
1311 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1313 GenericBound::Outlives(lifetime) => {
1314 if lifetime_bound.is_none() {
1315 lifetime_bound = Some(this.lower_lifetime(lifetime));
1320 let lifetime_bound =
1321 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1322 (bounds, lifetime_bound)
1324 hir::TyKind::TraitObject(bounds, lifetime_bound, *kind)
1326 TyKind::ImplTrait(def_node_id, bounds) => {
1329 ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
1330 .lower_opaque_impl_trait(
1338 ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
1340 hir::OpaqueTyOrigin::TyAlias,
1346 ImplTraitContext::Universal => {
1349 self.current_hir_id_owner.def_id,
1351 DefPathData::ImplTrait,
1354 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1355 let (param, bounds, path) =
1356 self.lower_generic_and_bounds(*def_node_id, span, ident, bounds);
1357 self.impl_trait_defs.push(param);
1358 if let Some(bounds) = bounds {
1359 self.impl_trait_bounds.push(bounds);
1363 ImplTraitContext::FeatureGated(position, feature) => {
1366 .create_feature_err(
1367 MisplacedImplTrait {
1369 position: DiagnosticArgFromDisplay(position),
1376 ImplTraitContext::Disallowed(position) => {
1377 self.tcx.sess.emit_err(MisplacedImplTrait {
1379 position: DiagnosticArgFromDisplay(position),
1385 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1386 TyKind::CVarArgs => {
1387 self.tcx.sess.delay_span_bug(
1389 "`TyKind::CVarArgs` should have been handled elsewhere",
1395 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1398 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1399 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1400 /// HIR type that references the TAIT.
1402 /// Given a function definition like:
1405 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1410 /// we will create a TAIT definition in the HIR like
1413 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1416 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1419 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1422 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1423 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1424 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1425 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1426 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1427 #[instrument(level = "debug", skip(self), ret)]
1428 fn lower_opaque_impl_trait(
1431 origin: hir::OpaqueTyOrigin,
1432 opaque_ty_node_id: NodeId,
1433 bounds: &GenericBounds,
1435 itctx: &ImplTraitContext,
1436 ) -> hir::TyKind<'hir> {
1437 // Make sure we know that some funky desugaring has been going on here.
1438 // This is a first: there is code in other places like for loop
1439 // desugaring that explicitly states that we don't want to track that.
1440 // Not tracking it makes lints in rustc and clippy very fragile, as
1441 // frequently opened issues show.
1442 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1444 let opaque_ty_def_id = self.create_def(
1445 self.current_hir_id_owner.def_id,
1447 DefPathData::ImplTrait,
1450 debug!(?opaque_ty_def_id);
1452 // Contains the new lifetime definitions created for the TAIT (if any).
1453 let mut collected_lifetimes = Vec::new();
1455 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1456 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1457 // exactly which ones those are.
1458 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1459 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1462 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1463 // we only keep the lifetimes that appear in the `impl Debug` itself:
1464 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1466 debug!(?lifetimes_to_remap);
1468 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1469 let mut new_remapping = FxHashMap::default();
1471 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1472 // in bounds), then create the new lifetime parameters required and create a mapping
1473 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1474 collected_lifetimes = lctx.create_lifetime_defs(
1476 &lifetimes_to_remap,
1479 debug!(?collected_lifetimes);
1480 debug!(?new_remapping);
1482 // Install the remapping from old to new (if any):
1483 lctx.with_remapping(new_remapping, |lctx| {
1484 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1485 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1486 // containing `&['x]`.
1487 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1488 |&(new_node_id, lifetime)| {
1489 let hir_id = lctx.lower_node_id(new_node_id);
1490 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1492 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1493 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1496 hir::ParamName::Plain(lifetime.ident),
1497 hir::LifetimeParamKind::Explicit,
1503 def_id: lctx.local_def_id(new_node_id),
1505 span: lifetime.ident.span,
1506 pure_wrt_drop: false,
1507 kind: hir::GenericParamKind::Lifetime { kind },
1512 debug!(?lifetime_defs);
1514 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1515 // get back Debug + 'a1, which is suitable for use on the TAIT.
1516 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1517 debug!(?hir_bounds);
1519 let opaque_ty_item = hir::OpaqueTy {
1520 generics: self.arena.alloc(hir::Generics {
1521 params: lifetime_defs,
1523 has_where_clause_predicates: false,
1524 where_clause_span: lctx.lower_span(span),
1525 span: lctx.lower_span(span),
1531 debug!(?opaque_ty_item);
1533 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1537 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1538 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1540 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1541 let id = self.next_node_id();
1542 let l = self.new_named_lifetime(lifetime.id, id, lifetime.ident);
1543 hir::GenericArg::Lifetime(l)
1547 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1548 hir::TyKind::OpaqueDef(
1549 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
1555 /// Registers a new opaque type with the proper `NodeId`s and
1556 /// returns the lowered node-ID for the opaque type.
1557 fn generate_opaque_type(
1559 opaque_ty_id: LocalDefId,
1560 opaque_ty_item: hir::OpaqueTy<'hir>,
1562 opaque_ty_span: Span,
1563 ) -> hir::OwnerNode<'hir> {
1564 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1565 // Generate an `type Foo = impl Trait;` declaration.
1566 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1567 let opaque_ty_item = hir::Item {
1568 owner_id: hir::OwnerId { def_id: opaque_ty_id },
1569 ident: Ident::empty(),
1570 kind: opaque_ty_item_kind,
1571 vis_span: self.lower_span(span.shrink_to_lo()),
1572 span: self.lower_span(opaque_ty_span),
1574 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1577 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1578 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1579 /// new definition, adds it to the remapping with the definition of the given lifetime and
1580 /// returns a list of lifetimes to be lowered afterwards.
1581 fn create_lifetime_defs(
1583 parent_def_id: LocalDefId,
1584 lifetimes_in_bounds: &[Lifetime],
1585 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1586 ) -> Vec<(NodeId, Lifetime)> {
1587 let mut result = Vec::new();
1589 for lifetime in lifetimes_in_bounds {
1590 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1594 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1595 if remapping.get(&old_def_id).is_none() {
1596 let node_id = self.next_node_id();
1598 let new_def_id = self.create_def(
1601 DefPathData::LifetimeNs(lifetime.ident.name),
1602 lifetime.ident.span,
1604 remapping.insert(old_def_id, new_def_id);
1606 result.push((node_id, *lifetime));
1610 LifetimeRes::Fresh { param, binder: _ } => {
1611 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1612 if let Some(old_def_id) = self.orig_opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1613 let node_id = self.next_node_id();
1615 let new_def_id = self.create_def(
1618 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1619 lifetime.ident.span,
1621 remapping.insert(old_def_id, new_def_id);
1623 result.push((node_id, *lifetime));
1627 LifetimeRes::Static | LifetimeRes::Error => {}
1630 let bug_msg = format!(
1631 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1632 res, lifetime.ident, lifetime.ident.span
1634 span_bug!(lifetime.ident.span, "{}", bug_msg);
1642 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1643 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1644 // as they are not explicit in HIR/Ty function signatures.
1645 // (instead, the `c_variadic` flag is set to `true`)
1646 let mut inputs = &decl.inputs[..];
1647 if decl.c_variadic() {
1648 inputs = &inputs[..inputs.len() - 1];
1650 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1651 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1652 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1656 // Lowers a function declaration.
1658 // `decl`: the unlowered (AST) function declaration.
1659 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1660 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1661 // `make_ret_async` is also `Some`.
1662 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1663 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1664 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1665 #[instrument(level = "debug", skip(self))]
1672 make_ret_async: Option<(NodeId, Span)>,
1673 ) -> &'hir hir::FnDecl<'hir> {
1674 let c_variadic = decl.c_variadic();
1676 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1677 // as they are not explicit in HIR/Ty function signatures.
1678 // (instead, the `c_variadic` flag is set to `true`)
1679 let mut inputs = &decl.inputs[..];
1681 inputs = &inputs[..inputs.len() - 1];
1683 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1684 let itctx = if kind.param_impl_trait_allowed() {
1685 ImplTraitContext::Universal
1687 ImplTraitContext::Disallowed(match kind {
1688 FnDeclKind::Fn | FnDeclKind::Inherent => {
1689 unreachable!("fn should allow APIT")
1691 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1692 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1693 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1694 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1695 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1698 self.lower_ty_direct(¶m.ty, &itctx)
1701 let output = if let Some((ret_id, span)) = make_ret_async {
1702 if !kind.async_fn_allowed(self.tcx) {
1704 FnDeclKind::Trait | FnDeclKind::Impl => {
1707 .create_feature_err(
1708 TraitFnAsync { fn_span, span },
1709 sym::async_fn_in_trait,
1714 self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
1719 self.lower_async_fn_ret_ty(
1723 matches!(kind, FnDeclKind::Trait),
1726 match &decl.output {
1727 FnRetTy::Ty(ty) => {
1728 let context = if kind.return_impl_trait_allowed(self.tcx) {
1729 let fn_def_id = self.local_def_id(fn_node_id);
1730 ImplTraitContext::ReturnPositionOpaqueTy {
1731 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1732 in_trait: matches!(kind, FnDeclKind::Trait),
1735 let position = match kind {
1736 FnDeclKind::Fn | FnDeclKind::Inherent => {
1737 unreachable!("fn should allow in-band lifetimes")
1739 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1740 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1741 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1742 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1743 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1746 FnDeclKind::Trait | FnDeclKind::Impl => ImplTraitContext::FeatureGated(
1748 sym::return_position_impl_trait_in_trait,
1750 _ => ImplTraitContext::Disallowed(position),
1753 hir::FnRetTy::Return(self.lower_ty(ty, &context))
1755 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(*span)),
1759 self.arena.alloc(hir::FnDecl {
1763 lifetime_elision_allowed: self.resolver.lifetime_elision_allowed.contains(&fn_node_id),
1764 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1765 let is_mutable_pat = matches!(
1767 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1770 match &arg.ty.kind {
1771 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1772 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1773 // Given we are only considering `ImplicitSelf` types, we needn't consider
1774 // the case where we have a mutable pattern to a reference as that would
1775 // no longer be an `ImplicitSelf`.
1776 TyKind::Rptr(_, mt) if mt.ty.kind.is_implicit_self() => match mt.mutbl {
1777 hir::Mutability::Not => hir::ImplicitSelfKind::ImmRef,
1778 hir::Mutability::Mut => hir::ImplicitSelfKind::MutRef,
1780 _ => hir::ImplicitSelfKind::None,
1786 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1787 // combined with the following definition of `OpaqueTy`:
1789 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1791 // `output`: unlowered output type (`T` in `-> T`)
1792 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1793 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1794 #[instrument(level = "debug", skip(self))]
1795 fn lower_async_fn_ret_ty(
1799 opaque_ty_node_id: NodeId,
1801 ) -> hir::FnRetTy<'hir> {
1802 let span = output.span();
1804 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1806 let fn_def_id = self.local_def_id(fn_node_id);
1808 let opaque_ty_def_id =
1809 self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait, opaque_ty_span);
1811 // When we create the opaque type for this async fn, it is going to have
1812 // to capture all the lifetimes involved in the signature (including in the
1813 // return type). This is done by introducing lifetime parameters for:
1815 // - all the explicitly declared lifetimes from the impl and function itself;
1816 // - all the elided lifetimes in the fn arguments;
1817 // - all the elided lifetimes in the return type.
1819 // So for example in this snippet:
1822 // impl<'a> Foo<'a> {
1823 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1824 // // ^ '0 ^ '1 ^ '2
1825 // // elided lifetimes used below
1830 // we would create an opaque type like:
1833 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1836 // and we would then desugar `bar` to the equivalent of:
1839 // impl<'a> Foo<'a> {
1840 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1844 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1845 // this is because the elided lifetimes from the return type
1846 // should be figured out using the ordinary elision rules, and
1847 // this desugaring achieves that.
1849 // Calculate all the lifetimes that should be captured
1850 // by the opaque type. This should include all in-scope
1851 // lifetime parameters, including those defined in-band.
1853 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1855 let mut collected_lifetimes = Vec::new();
1856 let mut new_remapping = FxHashMap::default();
1858 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1859 debug!(?extra_lifetime_params);
1860 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1861 let outer_def_id = self.orig_local_def_id(outer_node_id);
1862 let inner_node_id = self.next_node_id();
1864 // Add a definition for the in scope lifetime def.
1865 let inner_def_id = self.create_def(
1868 DefPathData::LifetimeNs(ident.name),
1871 new_remapping.insert(outer_def_id, inner_def_id);
1873 let inner_res = match outer_res {
1874 // Input lifetime like `'a`:
1875 LifetimeRes::Param { param, .. } => {
1876 LifetimeRes::Param { param, binder: fn_node_id }
1878 // Input lifetime like `'1`:
1879 LifetimeRes::Fresh { param, .. } => {
1880 LifetimeRes::Fresh { param, binder: fn_node_id }
1882 LifetimeRes::Static | LifetimeRes::Error => continue,
1885 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1886 res, ident, ident.span
1891 let lifetime = Lifetime { id: outer_node_id, ident };
1892 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1895 debug!(?collected_lifetimes);
1897 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1898 // find out exactly which ones those are.
1899 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1900 // we only keep the lifetimes that appear in the `impl Debug` itself:
1901 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1902 debug!(?lifetimes_to_remap);
1904 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1905 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1906 // in bounds), then create the new lifetime parameters required and create a mapping
1907 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1908 collected_lifetimes.extend(
1909 this.create_lifetime_defs(
1911 &lifetimes_to_remap,
1915 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1917 debug!(?collected_lifetimes);
1918 debug!(?new_remapping);
1920 // Install the remapping from old to new (if any):
1921 this.with_remapping(new_remapping, |this| {
1922 // We have to be careful to get elision right here. The
1923 // idea is that we create a lifetime parameter for each
1924 // lifetime in the return type. So, given a return type
1925 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1926 // Future<Output = &'1 [ &'2 u32 ]>`.
1928 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1929 // hence the elision takes place at the fn site.
1930 let future_bound = this.lower_async_fn_output_type_to_future_bound(
1933 if in_trait && !this.tcx.features().return_position_impl_trait_in_trait {
1934 ImplTraitContext::FeatureGated(
1935 ImplTraitPosition::TraitReturn,
1936 sym::return_position_impl_trait_in_trait,
1939 ImplTraitContext::ReturnPositionOpaqueTy {
1940 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1946 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1947 |&(new_node_id, lifetime, _)| {
1948 let hir_id = this.lower_node_id(new_node_id);
1949 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1951 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1952 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1955 hir::ParamName::Plain(lifetime.ident),
1956 hir::LifetimeParamKind::Explicit,
1962 def_id: this.local_def_id(new_node_id),
1964 span: lifetime.ident.span,
1965 pure_wrt_drop: false,
1966 kind: hir::GenericParamKind::Lifetime { kind },
1971 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1973 let opaque_ty_item = hir::OpaqueTy {
1974 generics: this.arena.alloc(hir::Generics {
1975 params: generic_params,
1977 has_where_clause_predicates: false,
1978 where_clause_span: this.lower_span(span),
1979 span: this.lower_span(span),
1981 bounds: arena_vec![this; future_bound],
1982 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1986 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1987 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1991 // As documented above, we need to create the lifetime
1992 // arguments to our opaque type. Continuing with our example,
1993 // we're creating the type arguments for the return type:
1996 // Bar<'a, 'b, '0, '1, '_>
1999 // For the "input" lifetime parameters, we wish to create
2000 // references to the parameters themselves, including the
2001 // "implicit" ones created from parameter types (`'a`, `'b`,
2004 // For the "output" lifetime parameters, we just want to
2006 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2007 |(_, lifetime, res)| {
2008 let id = self.next_node_id();
2009 let res = res.unwrap_or(
2010 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2012 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, lifetime.ident, res))
2016 // Create the `Foo<...>` reference itself. Note that the `type
2017 // Foo = impl Trait` is, internally, created as a child of the
2018 // async fn, so the *type parameters* are inherited. It's
2019 // only the lifetime parameters that we must supply.
2020 let opaque_ty_ref = hir::TyKind::OpaqueDef(
2021 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
2025 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2026 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2029 /// Transforms `-> T` into `Future<Output = T>`.
2030 fn lower_async_fn_output_type_to_future_bound(
2034 mut nested_impl_trait_context: ImplTraitContext,
2035 ) -> hir::GenericBound<'hir> {
2036 // Compute the `T` in `Future<Output = T>` from the return type.
2037 let output_ty = match output {
2038 FnRetTy::Ty(ty) => {
2039 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2040 // `impl Future` opaque type that `async fn` implicitly
2042 self.lower_ty(ty, &mut nested_impl_trait_context)
2044 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2048 let future_args = self.arena.alloc(hir::GenericArgs {
2050 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2051 parenthesized: false,
2055 hir::GenericBound::LangItemTrait(
2056 // ::std::future::Future<future_params>
2057 hir::LangItem::Future,
2058 self.lower_span(span),
2064 #[instrument(level = "trace", skip(self))]
2065 fn lower_param_bound(
2068 itctx: &ImplTraitContext,
2069 ) -> hir::GenericBound<'hir> {
2071 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2072 self.lower_poly_trait_ref(p, itctx),
2073 self.lower_trait_bound_modifier(*modifier),
2075 GenericBound::Outlives(lifetime) => {
2076 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2081 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2082 let ident = self.lower_ident(l.ident);
2083 self.new_named_lifetime(l.id, l.id, ident)
2086 #[instrument(level = "debug", skip(self))]
2087 fn new_named_lifetime_with_res(
2092 ) -> &'hir hir::Lifetime {
2093 let res = match res {
2094 LifetimeRes::Param { param, .. } => {
2095 let param = self.get_remapped_def_id(param);
2096 hir::LifetimeName::Param(param)
2098 LifetimeRes::Fresh { param, .. } => {
2099 let param = self.local_def_id(param);
2100 hir::LifetimeName::Param(param)
2102 LifetimeRes::Infer => hir::LifetimeName::Infer,
2103 LifetimeRes::Static => hir::LifetimeName::Static,
2104 LifetimeRes::Error => hir::LifetimeName::Error,
2106 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
2107 res, ident, ident.span
2112 self.arena.alloc(hir::Lifetime {
2113 hir_id: self.lower_node_id(id),
2114 ident: self.lower_ident(ident),
2119 #[instrument(level = "debug", skip(self))]
2120 fn new_named_lifetime(
2125 ) -> &'hir hir::Lifetime {
2126 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2127 self.new_named_lifetime_with_res(new_id, ident, res)
2130 fn lower_generic_params_mut<'s>(
2132 params: &'s [GenericParam],
2133 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2134 params.iter().map(move |param| self.lower_generic_param(param))
2137 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2138 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2141 #[instrument(level = "trace", skip(self))]
2142 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2143 let (name, kind) = self.lower_generic_param_kind(param);
2145 let hir_id = self.lower_node_id(param.id);
2146 self.lower_attrs(hir_id, ¶m.attrs);
2149 def_id: self.local_def_id(param.id),
2151 span: self.lower_span(param.span()),
2152 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2154 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2158 fn lower_generic_param_kind(
2160 param: &GenericParam,
2161 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2163 GenericParamKind::Lifetime => {
2164 // AST resolution emitted an error on those parameters, so we lower them using
2165 // `ParamName::Error`.
2167 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2170 let ident = self.lower_ident(param.ident);
2171 ParamName::Plain(ident)
2174 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2178 GenericParamKind::Type { default, .. } => {
2179 let kind = hir::GenericParamKind::Type {
2180 default: default.as_ref().map(|x| {
2181 self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2186 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2188 GenericParamKind::Const { ty, kw_span: _, default } => {
2189 let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2190 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2192 hir::ParamName::Plain(self.lower_ident(param.ident)),
2193 hir::GenericParamKind::Const { ty, default },
2199 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: &ImplTraitContext) -> hir::TraitRef<'hir> {
2200 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2201 hir::QPath::Resolved(None, path) => path,
2202 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2204 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2207 #[instrument(level = "debug", skip(self))]
2208 fn lower_poly_trait_ref(
2211 itctx: &ImplTraitContext,
2212 ) -> hir::PolyTraitRef<'hir> {
2213 let bound_generic_params =
2214 self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
2215 let trait_ref = self.lower_trait_ref(&p.trait_ref, itctx);
2216 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2219 fn lower_mt(&mut self, mt: &MutTy, itctx: &ImplTraitContext) -> hir::MutTy<'hir> {
2220 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2223 #[instrument(level = "debug", skip(self), ret)]
2224 fn lower_param_bounds(
2226 bounds: &[GenericBound],
2227 itctx: &ImplTraitContext,
2228 ) -> hir::GenericBounds<'hir> {
2229 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2232 fn lower_param_bounds_mut<'s>(
2234 bounds: &'s [GenericBound],
2235 itctx: &'s ImplTraitContext,
2236 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2237 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2240 #[instrument(level = "debug", skip(self), ret)]
2241 fn lower_generic_and_bounds(
2246 bounds: &[GenericBound],
2247 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2248 // Add a definition for the in-band `Param`.
2249 let def_id = self.local_def_id(node_id);
2251 // Set the name to `impl Bound1 + Bound2`.
2252 let param = hir::GenericParam {
2253 hir_id: self.lower_node_id(node_id),
2255 name: ParamName::Plain(self.lower_ident(ident)),
2256 pure_wrt_drop: false,
2257 span: self.lower_span(span),
2258 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2262 let preds = self.lower_generic_bound_predicate(
2265 &GenericParamKind::Type { default: None },
2267 &ImplTraitContext::Universal,
2268 hir::PredicateOrigin::ImplTrait,
2271 let hir_id = self.next_id();
2272 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2273 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2275 self.arena.alloc(hir::Path {
2276 span: self.lower_span(span),
2279 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2286 /// Lowers a block directly to an expression, presuming that it
2287 /// has no attributes and is not targeted by a `break`.
2288 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2289 let block = self.lower_block(b, false);
2290 self.expr_block(block)
2293 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2294 match c.value.kind {
2295 ExprKind::Underscore => {
2296 if self.tcx.features().generic_arg_infer {
2297 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2300 &self.tcx.sess.parse_sess,
2301 sym::generic_arg_infer,
2303 "using `_` for array lengths is unstable",
2305 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2306 hir::ArrayLen::Body(self.lower_anon_const(c))
2309 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2313 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2314 self.with_new_scopes(|this| hir::AnonConst {
2315 def_id: this.local_def_id(c.id),
2316 hir_id: this.lower_node_id(c.id),
2317 body: this.lower_const_body(c.value.span, Some(&c.value)),
2321 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2323 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2324 UserProvided => hir::UnsafeSource::UserProvided,
2328 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2330 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2331 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2333 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2334 // placeholder for compilation to proceed.
2335 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2336 hir::TraitBoundModifier::Maybe
2341 // Helper methods for building HIR.
2343 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2344 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2347 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2348 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2353 attrs: Option<&'hir [Attribute]>,
2355 init: Option<&'hir hir::Expr<'hir>>,
2356 pat: &'hir hir::Pat<'hir>,
2357 source: hir::LocalSource,
2358 ) -> hir::Stmt<'hir> {
2359 let hir_id = self.next_id();
2360 if let Some(a) = attrs {
2361 debug_assert!(!a.is_empty());
2362 self.attrs.insert(hir_id.local_id, a);
2364 let local = hir::Local {
2370 span: self.lower_span(span),
2373 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2376 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2377 self.block_all(expr.span, &[], Some(expr))
2383 stmts: &'hir [hir::Stmt<'hir>],
2384 expr: Option<&'hir hir::Expr<'hir>>,
2385 ) -> &'hir hir::Block<'hir> {
2386 let blk = hir::Block {
2389 hir_id: self.next_id(),
2390 rules: hir::BlockCheckMode::DefaultBlock,
2391 span: self.lower_span(span),
2392 targeted_by_break: false,
2394 self.arena.alloc(blk)
2397 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2398 let field = self.single_pat_field(span, pat);
2399 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2402 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2403 let field = self.single_pat_field(span, pat);
2404 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2407 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2408 let field = self.single_pat_field(span, pat);
2409 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2412 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2413 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2416 fn single_pat_field(
2419 pat: &'hir hir::Pat<'hir>,
2420 ) -> &'hir [hir::PatField<'hir>] {
2421 let field = hir::PatField {
2422 hir_id: self.next_id(),
2423 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2424 is_shorthand: false,
2426 span: self.lower_span(span),
2428 arena_vec![self; field]
2431 fn pat_lang_item_variant(
2434 lang_item: hir::LangItem,
2435 fields: &'hir [hir::PatField<'hir>],
2436 hir_id: Option<hir::HirId>,
2437 ) -> &'hir hir::Pat<'hir> {
2438 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2439 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2442 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2443 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2446 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2447 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2450 fn pat_ident_binding_mode(
2454 bm: hir::BindingAnnotation,
2455 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2456 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2457 (self.arena.alloc(pat), hir_id)
2460 fn pat_ident_binding_mode_mut(
2464 bm: hir::BindingAnnotation,
2465 ) -> (hir::Pat<'hir>, hir::HirId) {
2466 let hir_id = self.next_id();
2471 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2472 span: self.lower_span(span),
2473 default_binding_modes: true,
2479 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2480 self.arena.alloc(hir::Pat {
2481 hir_id: self.next_id(),
2483 span: self.lower_span(span),
2484 default_binding_modes: true,
2488 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2490 hir_id: self.next_id(),
2492 span: self.lower_span(span),
2493 default_binding_modes: false,
2499 mut hir_id: hir::HirId,
2501 qpath: hir::QPath<'hir>,
2502 ) -> hir::Ty<'hir> {
2503 let kind = match qpath {
2504 hir::QPath::Resolved(None, path) => {
2505 // Turn trait object paths into `TyKind::TraitObject` instead.
2507 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2508 let principal = hir::PolyTraitRef {
2509 bound_generic_params: &[],
2510 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2511 span: self.lower_span(span),
2514 // The original ID is taken by the `PolyTraitRef`,
2515 // so the `Ty` itself needs a different one.
2516 hir_id = self.next_id();
2517 hir::TyKind::TraitObject(
2518 arena_vec![self; principal],
2519 self.elided_dyn_bound(span),
2520 TraitObjectSyntax::None,
2523 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2526 _ => hir::TyKind::Path(qpath),
2529 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2532 /// Invoked to create the lifetime argument(s) for an elided trait object
2533 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2534 /// when the bound is written, even if it is written with `'_` like in
2535 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2536 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2537 let r = hir::Lifetime {
2538 hir_id: self.next_id(),
2539 ident: Ident::new(kw::Empty, self.lower_span(span)),
2540 res: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2542 debug!("elided_dyn_bound: r={:?}", r);
2547 /// Helper struct for delayed construction of GenericArgs.
2548 struct GenericArgsCtor<'hir> {
2549 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2550 bindings: &'hir [hir::TypeBinding<'hir>],
2551 parenthesized: bool,
2555 impl<'hir> GenericArgsCtor<'hir> {
2556 fn is_empty(&self) -> bool {
2557 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2560 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2561 let ga = hir::GenericArgs {
2562 args: this.arena.alloc_from_iter(self.args),
2563 bindings: self.bindings,
2564 parenthesized: self.parenthesized,
2565 span_ext: this.lower_span(self.span),
2567 this.arena.alloc(ga)