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)]
36 #![feature(never_type)]
37 #![recursion_limit = "256"]
38 #![allow(rustc::potential_query_instability)]
44 use rustc_ast::{self as ast, *};
45 use rustc_ast_pretty::pprust;
46 use rustc_data_structures::captures::Captures;
47 use rustc_data_structures::fingerprint::Fingerprint;
48 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
49 use rustc_data_structures::sorted_map::SortedMap;
50 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
51 use rustc_data_structures::sync::Lrc;
52 use rustc_errors::{struct_span_err, Applicability, Handler};
54 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
55 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
56 use rustc_hir::definitions::DefPathData;
57 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
58 use rustc_index::vec::{Idx, IndexVec};
59 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
60 use rustc_session::parse::feature_err;
61 use rustc_span::hygiene::MacroKind;
62 use rustc_span::source_map::DesugaringKind;
63 use rustc_span::symbol::{kw, sym, Ident, Symbol};
64 use rustc_span::{Span, DUMMY_SP};
66 use smallvec::SmallVec;
67 use std::collections::hash_map::Entry;
69 macro_rules! arena_vec {
70 ($this:expr; $($x:expr),*) => (
71 $this.arena.alloc_from_iter([$($x),*])
83 struct LoweringContext<'a, 'hir> {
85 resolver: &'a mut ResolverAstLowering,
87 /// Used to allocate HIR nodes.
88 arena: &'hir hir::Arena<'hir>,
90 /// Bodies inside the owner being lowered.
91 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
92 /// Attributes inside the owner being lowered.
93 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
94 /// Collect items that were created by lowering the current owner.
95 children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
97 generator_kind: Option<hir::GeneratorKind>,
99 /// When inside an `async` context, this is the `HirId` of the
100 /// `task_context` local bound to the resume argument of the generator.
101 task_context: Option<hir::HirId>,
103 /// Used to get the current `fn`'s def span to point to when using `await`
104 /// outside of an `async fn`.
105 current_item: Option<Span>,
107 catch_scope: Option<NodeId>,
108 loop_scope: Option<NodeId>,
109 is_in_loop_condition: bool,
110 is_in_trait_impl: bool,
111 is_in_dyn_type: bool,
113 /// Used to handle lifetimes appearing in impl-traits.
114 captured_lifetimes: Option<LifetimeCaptureContext>,
116 current_hir_id_owner: LocalDefId,
117 item_local_id_counter: hir::ItemLocalId,
118 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
119 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
121 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
122 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
124 /// NodeIds that are lowered inside the current HIR owner.
125 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
127 allow_try_trait: Option<Lrc<[Symbol]>>,
128 allow_gen_future: Option<Lrc<[Symbol]>>,
129 allow_into_future: Option<Lrc<[Symbol]>>,
132 /// When we lower a lifetime, it is inserted in `captures`, and the resolution is modified so
133 /// to point to the lifetime parameter impl-trait will generate.
134 /// When traversing `for<...>` binders, they are inserted in `binders_to_ignore` so we know *not*
135 /// to rebind the introduced lifetimes.
137 struct LifetimeCaptureContext {
138 /// parent def_id for new definitions
139 parent_def_id: LocalDefId,
140 /// Set of lifetimes to rebind.
142 LocalDefId, // original parameter id
145 NodeId, // synthetized parameter id
146 ParamName, // parameter name
147 LifetimeRes, // original resolution
150 /// Traversed binders. The ids in this set should *not* be rebound.
151 binders_to_ignore: FxHashSet<NodeId>,
154 trait ResolverAstLoweringExt {
155 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
156 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
157 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
158 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
159 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
160 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
161 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
164 impl ResolverAstLoweringExt for ResolverAstLowering {
165 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
166 if let ExprKind::Path(None, path) = &expr.kind {
167 // Don't perform legacy const generics rewriting if the path already
168 // has generic arguments.
169 if path.segments.last().unwrap().args.is_some() {
173 let partial_res = self.partial_res_map.get(&expr.id)?;
174 if partial_res.unresolved_segments() != 0 {
178 if let Res::Def(DefKind::Fn, def_id) = partial_res.base_res() {
179 // We only support cross-crate argument rewriting. Uses
180 // within the same crate should be updated to use the new
181 // const generics style.
182 if def_id.is_local() {
186 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
195 /// Obtains resolution for a `NodeId` with a single resolution.
196 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
197 self.partial_res_map.get(&id).copied()
200 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
201 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
202 self.import_res_map.get(&id).copied().unwrap_or_default()
205 /// Obtains resolution for a label with the given `NodeId`.
206 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
207 self.label_res_map.get(&id).copied()
210 /// Obtains resolution for a lifetime with the given `NodeId`.
211 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
212 self.lifetimes_res_map.get(&id).copied()
215 /// Obtain the list of lifetimes parameters to add to an item.
217 /// Extra lifetime parameters should only be added in places that can appear
218 /// as a `binder` in `LifetimeRes`.
220 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
221 /// should appear at the enclosing `PolyTraitRef`.
222 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
223 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
226 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
227 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
231 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
232 /// and if so, what meaning it has.
233 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
234 enum ImplTraitContext {
235 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
236 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
237 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
239 /// Newly generated parameters should be inserted into the given `Vec`.
242 /// Treat `impl Trait` as shorthand for a new opaque type.
243 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
244 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
246 ReturnPositionOpaqueTy {
247 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
248 origin: hir::OpaqueTyOrigin,
250 /// Impl trait in type aliases.
252 /// `impl Trait` is not accepted in this position.
253 Disallowed(ImplTraitPosition),
256 /// Position in which `impl Trait` is disallowed.
257 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
258 enum ImplTraitPosition {
280 impl std::fmt::Display for ImplTraitPosition {
281 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
282 let name = match self {
283 ImplTraitPosition::Path => "path",
284 ImplTraitPosition::Variable => "variable binding",
285 ImplTraitPosition::Type => "type",
286 ImplTraitPosition::Trait => "trait",
287 ImplTraitPosition::AsyncBlock => "async block",
288 ImplTraitPosition::Bound => "bound",
289 ImplTraitPosition::Generic => "generic",
290 ImplTraitPosition::ExternFnParam => "`extern fn` param",
291 ImplTraitPosition::ClosureParam => "closure param",
292 ImplTraitPosition::PointerParam => "`fn` pointer param",
293 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
294 ImplTraitPosition::TraitParam => "trait method param",
295 ImplTraitPosition::ImplParam => "`impl` method param",
296 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
297 ImplTraitPosition::ClosureReturn => "closure return",
298 ImplTraitPosition::PointerReturn => "`fn` pointer return",
299 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
300 ImplTraitPosition::TraitReturn => "trait method return",
301 ImplTraitPosition::ImplReturn => "`impl` method return",
304 write!(f, "{}", name)
320 fn impl_trait_return_allowed(&self) -> bool {
322 FnDeclKind::Fn | FnDeclKind::Inherent => true,
328 #[derive(Copy, Clone)]
331 Crate(&'a ast::Crate),
333 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
334 ForeignItem(&'a ast::ForeignItem),
338 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
340 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
341 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
342 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
343 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
344 visit::walk_crate(&mut indexer, krate);
345 return indexer.index;
347 struct Indexer<'s, 'a> {
348 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
349 index: IndexVec<LocalDefId, AstOwner<'a>>,
352 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
353 fn visit_attribute(&mut self, _: &'a Attribute) {
354 // We do not want to lower expressions that appear in attributes,
355 // as they are not accessible to the rest of the HIR.
358 fn visit_item(&mut self, item: &'a ast::Item) {
359 let def_id = self.node_id_to_def_id[&item.id];
360 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
361 self.index[def_id] = AstOwner::Item(item);
362 visit::walk_item(self, item)
365 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
366 let def_id = self.node_id_to_def_id[&item.id];
367 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
368 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
369 visit::walk_assoc_item(self, item, ctxt);
372 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
373 let def_id = self.node_id_to_def_id[&item.id];
374 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
375 self.index[def_id] = AstOwner::ForeignItem(item);
376 visit::walk_foreign_item(self, item);
381 /// Compute the hash for the HIR of the full crate.
382 /// This hash will then be part of the crate_hash which is stored in the metadata.
385 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
387 let mut hir_body_nodes: Vec<_> = owners
389 .filter_map(|(def_id, info)| {
390 let info = info.as_owner()?;
391 let def_path_hash = tcx.hir().def_path_hash(def_id);
392 Some((def_path_hash, info))
395 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
397 tcx.with_stable_hashing_context(|mut hcx| {
398 let mut stable_hasher = StableHasher::new();
399 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
400 stable_hasher.finish()
404 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
406 let krate = tcx.untracked_crate.steal();
407 let mut resolver = tcx.resolver_for_lowering(()).steal();
409 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
410 let mut owners = IndexVec::from_fn_n(
411 |_| hir::MaybeOwner::Phantom,
412 tcx.definitions_untracked().def_index_count(),
415 for def_id in ast_index.indices() {
418 resolver: &mut resolver,
419 ast_index: &ast_index,
425 // Drop AST to free memory
426 std::mem::drop(ast_index);
427 sess.time("drop_ast", || std::mem::drop(krate));
429 // Discard hygiene data, which isn't required after lowering to HIR.
430 if !sess.opts.debugging_opts.keep_hygiene_data {
431 rustc_span::hygiene::clear_syntax_context_map();
434 let hir_hash = compute_hir_hash(tcx, &owners);
435 hir::Crate { owners, hir_hash }
438 #[derive(Copy, Clone, PartialEq, Debug)]
440 /// Any path in a type context.
442 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
444 /// The `module::Type` in `module::Type::method` in an expression.
448 enum ParenthesizedGenericArgs {
453 impl<'a, 'hir> LoweringContext<'a, 'hir> {
457 node_id: ast::NodeId,
460 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
462 self.opt_local_def_id(node_id).is_none(),
463 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
466 self.tcx.hir().def_key(self.local_def_id(node_id)),
469 let def_id = self.tcx.create_def(parent, data);
471 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
472 self.resolver.node_id_to_def_id.insert(node_id, def_id);
477 fn next_node_id(&mut self) -> NodeId {
478 let start = self.resolver.next_node_id;
479 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
480 self.resolver.next_node_id = ast::NodeId::from_u32(next);
484 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
485 self.resolver.node_id_to_def_id.get(&node).copied()
488 fn local_def_id(&self, node: NodeId) -> LocalDefId {
489 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
492 /// Freshen the `LoweringContext` and ready it to lower a nested item.
493 /// The lowered item is registered into `self.children`.
495 /// This function sets up `HirId` lowering infrastructure,
496 /// and stashes the shared mutable state to avoid pollution by the closure.
497 #[instrument(level = "debug", skip(self, f))]
498 fn with_hir_id_owner(
501 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
503 let def_id = self.local_def_id(owner);
505 let current_attrs = std::mem::take(&mut self.attrs);
506 let current_bodies = std::mem::take(&mut self.bodies);
507 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
508 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
509 let current_trait_map = std::mem::take(&mut self.trait_map);
510 let current_owner = std::mem::replace(&mut self.current_hir_id_owner, def_id);
511 let current_local_counter =
512 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
513 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
514 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
516 // Do not reset `next_node_id` and `node_id_to_def_id`:
517 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
518 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
520 // Always allocate the first `HirId` for the owner itself.
521 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
522 debug_assert_eq!(_old, None);
525 debug_assert_eq!(def_id, item.def_id());
526 // `f` should have consumed all the elements in these vectors when constructing `item`.
527 debug_assert!(self.impl_trait_defs.is_empty());
528 debug_assert!(self.impl_trait_bounds.is_empty());
529 let info = self.make_owner_info(item);
531 self.attrs = current_attrs;
532 self.bodies = current_bodies;
533 self.node_id_to_local_id = current_node_ids;
534 self.local_id_to_def_id = current_id_to_def_id;
535 self.trait_map = current_trait_map;
536 self.current_hir_id_owner = current_owner;
537 self.item_local_id_counter = current_local_counter;
538 self.impl_trait_defs = current_impl_trait_defs;
539 self.impl_trait_bounds = current_impl_trait_bounds;
541 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
542 debug_assert!(_old.is_none())
545 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
546 let attrs = std::mem::take(&mut self.attrs);
547 let mut bodies = std::mem::take(&mut self.bodies);
548 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
549 let trait_map = std::mem::take(&mut self.trait_map);
551 #[cfg(debug_assertions)]
552 for (id, attrs) in attrs.iter() {
553 // Verify that we do not store empty slices in the map.
554 if attrs.is_empty() {
555 panic!("Stored empty attributes for {:?}", id);
559 bodies.sort_by_key(|(k, _)| *k);
560 let bodies = SortedMap::from_presorted_elements(bodies);
561 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
562 let (nodes, parenting) =
563 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
564 let nodes = hir::OwnerNodes {
565 hash_including_bodies,
572 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
573 let mut stable_hasher = StableHasher::new();
574 attrs.hash_stable(&mut hcx, &mut stable_hasher);
575 stable_hasher.finish()
577 hir::AttributeMap { map: attrs, hash }
580 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
583 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
584 /// queries which depend on the full HIR tree and those which only depend on the item signature.
587 node: hir::OwnerNode<'hir>,
588 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
589 ) -> (Fingerprint, Fingerprint) {
590 self.tcx.with_stable_hashing_context(|mut hcx| {
591 let mut stable_hasher = StableHasher::new();
592 hcx.with_hir_bodies(true, node.def_id(), bodies, |hcx| {
593 node.hash_stable(hcx, &mut stable_hasher)
595 let hash_including_bodies = stable_hasher.finish();
596 let mut stable_hasher = StableHasher::new();
597 hcx.with_hir_bodies(false, node.def_id(), bodies, |hcx| {
598 node.hash_stable(hcx, &mut stable_hasher)
600 let hash_without_bodies = stable_hasher.finish();
601 (hash_including_bodies, hash_without_bodies)
605 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
606 /// the `LoweringContext`'s `NodeId => HirId` map.
607 /// Take care not to call this method if the resulting `HirId` is then not
608 /// actually used in the HIR, as that would trigger an assertion in the
609 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
610 /// properly. Calling the method twice with the same `NodeId` is fine though.
611 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
612 assert_ne!(ast_node_id, DUMMY_NODE_ID);
614 match self.node_id_to_local_id.entry(ast_node_id) {
615 Entry::Occupied(o) => {
616 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
618 Entry::Vacant(v) => {
619 // Generate a new `HirId`.
620 let owner = self.current_hir_id_owner;
621 let local_id = self.item_local_id_counter;
622 let hir_id = hir::HirId { owner, local_id };
625 self.item_local_id_counter.increment_by(1);
627 assert_ne!(local_id, hir::ItemLocalId::new(0));
628 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
629 // Do not override a `MaybeOwner::Owner` that may already here.
630 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
631 self.local_id_to_def_id.insert(local_id, def_id);
634 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
635 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
643 /// Generate a new `HirId` without a backing `NodeId`.
644 fn next_id(&mut self) -> hir::HirId {
645 let owner = self.current_hir_id_owner;
646 let local_id = self.item_local_id_counter;
647 assert_ne!(local_id, hir::ItemLocalId::new(0));
648 self.item_local_id_counter.increment_by(1);
649 hir::HirId { owner, local_id }
652 #[instrument(level = "trace", skip(self))]
653 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
654 let res: Result<Res, ()> = res.apply_id(|id| {
655 let owner = self.current_hir_id_owner;
656 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
657 Ok(hir::HirId { owner, local_id })
661 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
662 // This can happen when trying to lower the return type `x` in erroneous code like
663 // async fn foo(x: u8) -> x {}
664 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
665 // an opaque type as a synthesized HIR owner.
666 res.unwrap_or(Res::Err)
669 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
670 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
671 if pr.unresolved_segments() != 0 {
672 panic!("path not fully resolved: {:?}", pr);
678 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
679 self.resolver.get_import_res(id).present_items()
682 fn diagnostic(&self) -> &Handler {
683 self.tcx.sess.diagnostic()
686 /// Reuses the span but adds information like the kind of the desugaring and features that are
687 /// allowed inside this span.
688 fn mark_span_with_reason(
690 reason: DesugaringKind,
692 allow_internal_unstable: Option<Lrc<[Symbol]>>,
694 self.tcx.with_stable_hashing_context(|hcx| {
695 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
699 /// Intercept all spans entering HIR.
700 /// Mark a span as relative to the current owning item.
701 fn lower_span(&self, span: Span) -> Span {
702 if self.tcx.sess.opts.debugging_opts.incremental_relative_spans {
703 span.with_parent(Some(self.current_hir_id_owner))
705 // Do not make spans relative when not using incremental compilation.
710 fn lower_ident(&self, ident: Ident) -> Ident {
711 Ident::new(ident.name, self.lower_span(ident.span))
714 /// Converts a lifetime into a new generic parameter.
715 #[tracing::instrument(level = "debug", skip(self))]
716 fn lifetime_res_to_generic_param(
721 ) -> Option<hir::GenericParam<'hir>> {
722 let (name, kind) = match res {
723 LifetimeRes::Param { .. } => {
724 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
726 LifetimeRes::Fresh { param, .. } => {
727 // Late resolution delegates to us the creation of the `LocalDefId`.
728 let _def_id = self.create_def(
729 self.current_hir_id_owner,
731 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
735 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
737 LifetimeRes::Static | LifetimeRes::Error => return None,
739 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
740 res, ident, ident.span
743 let hir_id = self.lower_node_id(node_id);
744 Some(hir::GenericParam {
747 span: self.lower_span(ident.span),
748 pure_wrt_drop: false,
749 kind: hir::GenericParamKind::Lifetime { kind },
754 /// Setup lifetime capture for and impl-trait.
755 /// The captures will be added to `captures`.
756 fn while_capturing_lifetimes<T>(
758 parent_def_id: LocalDefId,
759 captures: &mut FxHashMap<LocalDefId, (Span, NodeId, ParamName, LifetimeRes)>,
760 f: impl FnOnce(&mut Self) -> T,
762 let lifetime_stash = std::mem::replace(
763 &mut self.captured_lifetimes,
764 Some(LifetimeCaptureContext {
766 captures: std::mem::take(captures),
767 binders_to_ignore: Default::default(),
773 let ctxt = std::mem::replace(&mut self.captured_lifetimes, lifetime_stash).unwrap();
774 *captures = ctxt.captures;
779 /// Register a binder to be ignored for lifetime capture.
780 #[tracing::instrument(level = "debug", skip(self, f))]
782 fn with_lifetime_binder<T>(
785 generic_params: &[GenericParam],
786 f: impl FnOnce(&mut Self, &'hir [hir::GenericParam<'hir>]) -> T,
788 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
789 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
790 debug!(?extra_lifetimes);
791 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
792 self.lifetime_res_to_generic_param(ident, node_id, res)
794 let generic_params = self.arena.alloc_from_iter(generic_params);
795 debug!(?generic_params);
797 if let Some(ctxt) = &mut self.captured_lifetimes {
798 ctxt.binders_to_ignore.insert(binder);
800 let ret = f(self, generic_params);
801 if let Some(ctxt) = &mut self.captured_lifetimes {
802 ctxt.binders_to_ignore.remove(&binder);
807 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
808 let was_in_dyn_type = self.is_in_dyn_type;
809 self.is_in_dyn_type = in_scope;
811 let result = f(self);
813 self.is_in_dyn_type = was_in_dyn_type;
818 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
819 let was_in_loop_condition = self.is_in_loop_condition;
820 self.is_in_loop_condition = false;
822 let catch_scope = self.catch_scope.take();
823 let loop_scope = self.loop_scope.take();
825 self.catch_scope = catch_scope;
826 self.loop_scope = loop_scope;
828 self.is_in_loop_condition = was_in_loop_condition;
833 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
834 if attrs.is_empty() {
837 debug_assert_eq!(id.owner, self.current_hir_id_owner);
838 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
839 debug_assert!(!ret.is_empty());
840 self.attrs.insert(id.local_id, ret);
845 fn lower_attr(&self, attr: &Attribute) -> Attribute {
846 // Note that we explicitly do not walk the path. Since we don't really
847 // lower attributes (we use the AST version) there is nowhere to keep
848 // the `HirId`s. We don't actually need HIR version of attributes anyway.
849 // Tokens are also not needed after macro expansion and parsing.
850 let kind = match attr.kind {
851 AttrKind::Normal(ref item, _) => AttrKind::Normal(
853 path: item.path.clone(),
854 args: self.lower_mac_args(&item.args),
859 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
862 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
865 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
866 debug_assert_eq!(id.owner, self.current_hir_id_owner);
867 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
868 if let Some(&a) = self.attrs.get(&target_id.local_id) {
869 debug_assert!(!a.is_empty());
870 self.attrs.insert(id.local_id, a);
874 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
876 MacArgs::Empty => MacArgs::Empty,
877 MacArgs::Delimited(dspan, delim, ref tokens) => {
878 // This is either a non-key-value attribute, or a `macro_rules!` body.
879 // We either not have any nonterminals present (in the case of an attribute),
880 // or have tokens available for all nonterminals in the case of a nested
881 // `macro_rules`: e.g:
884 // macro_rules! outer {
886 // macro_rules! inner {
893 // In both cases, we don't want to synthesize any tokens
894 MacArgs::Delimited(dspan, delim, tokens.flattened())
896 // This is an inert key-value attribute - it will never be visible to macros
897 // after it gets lowered to HIR. Therefore, we can extract literals to handle
898 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
899 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
900 // In valid code the value always ends up as a single literal. Otherwise, a dummy
901 // literal suffices because the error is handled elsewhere.
902 let lit = if let ExprKind::Lit(lit) = &expr.kind {
906 token: token::Lit::new(token::LitKind::Err, kw::Empty, None),
907 kind: LitKind::Err(kw::Empty),
911 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
913 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
914 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
919 /// Given an associated type constraint like one of these:
921 /// ```ignore (illustrative)
922 /// T: Iterator<Item: Debug>
924 /// T: Iterator<Item = Debug>
928 /// returns a `hir::TypeBinding` representing `Item`.
929 #[instrument(level = "debug", skip(self))]
930 fn lower_assoc_ty_constraint(
932 constraint: &AssocConstraint,
933 itctx: ImplTraitContext,
934 ) -> hir::TypeBinding<'hir> {
935 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
936 // lower generic arguments of identifier in constraint
937 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
938 let gen_args_ctor = match gen_args {
939 GenericArgs::AngleBracketed(ref data) => {
940 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
942 GenericArgs::Parenthesized(ref data) => {
943 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
944 self.lower_angle_bracketed_parameter_data(
945 &data.as_angle_bracketed_args(),
952 gen_args_ctor.into_generic_args(self)
954 self.arena.alloc(hir::GenericArgs::none())
957 let kind = match constraint.kind {
958 AssocConstraintKind::Equality { ref term } => {
959 let term = match term {
960 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
961 Term::Const(ref c) => self.lower_anon_const(c).into(),
963 hir::TypeBindingKind::Equality { term }
965 AssocConstraintKind::Bound { ref bounds } => {
966 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
967 let (desugar_to_impl_trait, itctx) = match itctx {
968 // We are in the return position:
970 // fn foo() -> impl Iterator<Item: Debug>
974 // fn foo() -> impl Iterator<Item = impl Debug>
975 ImplTraitContext::ReturnPositionOpaqueTy { .. }
976 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
978 // We are in the argument position, but within a dyn type:
980 // fn foo(x: dyn Iterator<Item: Debug>)
984 // fn foo(x: dyn Iterator<Item = impl Debug>)
985 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
987 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
988 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
989 // "impl trait context" to permit `impl Debug` in this position (it desugars
990 // then to an opaque type).
992 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
993 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
994 (true, ImplTraitContext::TypeAliasesOpaqueTy)
997 // We are in the parameter position, but not within a dyn type:
999 // fn foo(x: impl Iterator<Item: Debug>)
1001 // so we leave it as is and this gets expanded in astconv to a bound like
1002 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1004 _ => (false, itctx),
1007 if desugar_to_impl_trait {
1008 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1009 // constructing the HIR for `impl bounds...` and then lowering that.
1011 let parent_def_id = self.current_hir_id_owner;
1012 let impl_trait_node_id = self.next_node_id();
1013 self.create_def(parent_def_id, impl_trait_node_id, DefPathData::ImplTrait);
1015 self.with_dyn_type_scope(false, |this| {
1016 let node_id = this.next_node_id();
1017 let ty = this.lower_ty(
1020 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1021 span: this.lower_span(constraint.span),
1027 hir::TypeBindingKind::Equality { term: ty.into() }
1030 // Desugar `AssocTy: Bounds` into a type binding where the
1031 // later desugars into a trait predicate.
1032 let bounds = self.lower_param_bounds(bounds, itctx);
1034 hir::TypeBindingKind::Constraint { bounds }
1040 hir_id: self.lower_node_id(constraint.id),
1041 ident: self.lower_ident(constraint.ident),
1044 span: self.lower_span(constraint.span),
1048 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1049 let mut err = self.tcx.sess.struct_span_err(
1051 "parenthesized generic arguments cannot be used in associated type constraints",
1053 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1054 if data.inputs.is_empty() {
1055 let parentheses_span =
1056 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1057 err.multipart_suggestion(
1058 "remove these parentheses",
1059 vec![(parentheses_span, String::new())],
1060 Applicability::MaybeIncorrect,
1063 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1065 // Start of parameters to the 1st argument
1066 let open_param = data.inputs_span.shrink_to_lo().to(data
1072 // End of last argument to end of parameters
1074 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1075 err.multipart_suggestion(
1076 &format!("use angle brackets instead",),
1077 vec![(open_param, String::from("<")), (close_param, String::from(">"))],
1078 Applicability::MaybeIncorrect,
1084 #[instrument(level = "debug", skip(self))]
1085 fn lower_generic_arg(
1087 arg: &ast::GenericArg,
1088 itctx: ImplTraitContext,
1089 ) -> hir::GenericArg<'hir> {
1091 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1092 ast::GenericArg::Type(ty) => {
1094 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1095 return GenericArg::Infer(hir::InferArg {
1096 hir_id: self.lower_node_id(ty.id),
1097 span: self.lower_span(ty.span),
1100 // We parse const arguments as path types as we cannot distinguish them during
1101 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1102 // type and value namespaces. If we resolved the path in the value namespace, we
1103 // transform it into a generic const argument.
1104 TyKind::Path(ref qself, ref path) => {
1105 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1106 let res = partial_res.base_res();
1107 if !res.matches_ns(Namespace::TypeNS) {
1109 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1113 // Construct an AnonConst where the expr is the "ty"'s path.
1115 let parent_def_id = self.current_hir_id_owner;
1116 let node_id = self.next_node_id();
1118 // Add a definition for the in-band const def.
1119 self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
1121 let span = self.lower_span(ty.span);
1122 let path_expr = Expr {
1124 kind: ExprKind::Path(qself.clone(), path.clone()),
1126 attrs: AttrVec::new(),
1130 let ct = self.with_new_scopes(|this| hir::AnonConst {
1131 hir_id: this.lower_node_id(node_id),
1132 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1134 return GenericArg::Const(ConstArg { value: ct, span });
1140 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1142 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1143 value: self.lower_anon_const(&ct),
1144 span: self.lower_span(ct.value.span),
1149 #[instrument(level = "debug", skip(self))]
1150 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext) -> &'hir hir::Ty<'hir> {
1151 self.arena.alloc(self.lower_ty_direct(t, itctx))
1157 qself: &Option<QSelf>,
1159 param_mode: ParamMode,
1160 itctx: ImplTraitContext,
1161 ) -> hir::Ty<'hir> {
1162 let id = self.lower_node_id(t.id);
1163 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1164 self.ty_path(id, t.span, qpath)
1167 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1168 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1171 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1172 self.ty(span, hir::TyKind::Tup(tys))
1175 fn lower_ty_direct(&mut self, t: &Ty, itctx: ImplTraitContext) -> hir::Ty<'hir> {
1176 let kind = match t.kind {
1177 TyKind::Infer => hir::TyKind::Infer,
1178 TyKind::Err => hir::TyKind::Err,
1179 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1180 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1181 TyKind::Rptr(ref region, ref mt) => {
1182 let region = region.unwrap_or_else(|| {
1183 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1184 self.resolver.get_lifetime_res(t.id)
1186 debug_assert_eq!(start.plus(1), end);
1191 let span = self.tcx.sess.source_map().next_point(t.span.shrink_to_lo());
1192 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1194 let lifetime = self.lower_lifetime(®ion);
1195 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1197 TyKind::BareFn(ref f) => {
1198 self.with_lifetime_binder(t.id, &f.generic_params, |this, generic_params| {
1199 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1201 unsafety: this.lower_unsafety(f.unsafety),
1202 abi: this.lower_extern(f.ext),
1203 decl: this.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
1204 param_names: this.lower_fn_params_to_names(&f.decl),
1208 TyKind::Never => hir::TyKind::Never,
1209 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1210 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1212 TyKind::Paren(ref ty) => {
1213 return self.lower_ty_direct(ty, itctx);
1215 TyKind::Path(ref qself, ref path) => {
1216 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1218 TyKind::ImplicitSelf => {
1219 let res = self.expect_full_res(t.id);
1220 let res = self.lower_res(res);
1221 hir::TyKind::Path(hir::QPath::Resolved(
1223 self.arena.alloc(hir::Path {
1225 segments: arena_vec![self; hir::PathSegment::from_ident(
1226 Ident::with_dummy_span(kw::SelfUpper)
1228 span: self.lower_span(t.span),
1232 TyKind::Array(ref ty, ref length) => {
1233 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1235 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1236 TyKind::TraitObject(ref bounds, kind) => {
1237 let mut lifetime_bound = None;
1238 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1240 this.arena.alloc_from_iter(bounds.iter().filter_map(
1241 |bound| match *bound {
1242 GenericBound::Trait(
1244 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1245 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1246 // `~const ?Bound` will cause an error during AST validation
1247 // anyways, so treat it like `?Bound` as compilation proceeds.
1248 GenericBound::Trait(
1250 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1252 GenericBound::Outlives(ref lifetime) => {
1253 if lifetime_bound.is_none() {
1254 lifetime_bound = Some(this.lower_lifetime(lifetime));
1260 let lifetime_bound =
1261 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1262 (bounds, lifetime_bound)
1264 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1266 TyKind::ImplTrait(def_node_id, ref bounds) => {
1269 ImplTraitContext::ReturnPositionOpaqueTy { origin } => self
1270 .lower_opaque_impl_trait(span, origin, def_node_id, |this| {
1271 this.lower_param_bounds(bounds, itctx)
1273 ImplTraitContext::TypeAliasesOpaqueTy => {
1274 let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
1275 self.lower_opaque_impl_trait(
1277 hir::OpaqueTyOrigin::TyAlias,
1279 |this| this.lower_param_bounds(bounds, nested_itctx),
1282 ImplTraitContext::Universal => {
1284 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1285 let (param, bounds, path) =
1286 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1287 self.impl_trait_defs.push(param);
1288 if let Some(bounds) = bounds {
1289 self.impl_trait_bounds.push(bounds);
1293 ImplTraitContext::Disallowed(position) => {
1294 let mut err = struct_span_err!(
1298 "`impl Trait` only allowed in function and inherent method return types, not in {}",
1306 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1307 TyKind::CVarArgs => {
1308 self.tcx.sess.delay_span_bug(
1310 "`TyKind::CVarArgs` should have been handled elsewhere",
1316 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1319 #[tracing::instrument(level = "debug", skip(self, lower_bounds))]
1320 fn lower_opaque_impl_trait(
1323 origin: hir::OpaqueTyOrigin,
1324 opaque_ty_node_id: NodeId,
1325 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1326 ) -> hir::TyKind<'hir> {
1327 // Make sure we know that some funky desugaring has been going on here.
1328 // This is a first: there is code in other places like for loop
1329 // desugaring that explicitly states that we don't want to track that.
1330 // Not tracking it makes lints in rustc and clippy very fragile, as
1331 // frequently opened issues show.
1332 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1334 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1336 let mut collected_lifetimes = FxHashMap::default();
1337 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1338 let hir_bounds = if origin == hir::OpaqueTyOrigin::TyAlias {
1341 lctx.while_capturing_lifetimes(
1343 &mut collected_lifetimes,
1347 debug!(?collected_lifetimes);
1349 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1350 |(_, &(span, p_id, p_name, _))| {
1351 let hir_id = lctx.lower_node_id(p_id);
1352 debug_assert_ne!(lctx.opt_local_def_id(p_id), None);
1354 let kind = if p_name.ident().name == kw::UnderscoreLifetime {
1355 hir::LifetimeParamKind::Elided
1357 hir::LifetimeParamKind::Explicit
1364 pure_wrt_drop: false,
1365 kind: hir::GenericParamKind::Lifetime { kind },
1371 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1373 let opaque_ty_item = hir::OpaqueTy {
1374 generics: self.arena.alloc(hir::Generics {
1375 params: lifetime_defs,
1377 has_where_clause_predicates: false,
1378 where_clause_span: lctx.lower_span(span),
1379 span: lctx.lower_span(span),
1385 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1386 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1389 let lifetimes = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
1390 |(_, (span, _, p_name, res))| {
1391 let id = self.next_node_id();
1392 let ident = Ident::new(p_name.ident().name, span);
1393 let l = self.new_named_lifetime_with_res(id, span, ident, res);
1394 hir::GenericArg::Lifetime(l)
1398 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1400 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1401 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1404 /// Registers a new opaque type with the proper `NodeId`s and
1405 /// returns the lowered node-ID for the opaque type.
1406 fn generate_opaque_type(
1408 opaque_ty_id: LocalDefId,
1409 opaque_ty_item: hir::OpaqueTy<'hir>,
1411 opaque_ty_span: Span,
1412 ) -> hir::OwnerNode<'hir> {
1413 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1414 // Generate an `type Foo = impl Trait;` declaration.
1415 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1416 let opaque_ty_item = hir::Item {
1417 def_id: opaque_ty_id,
1418 ident: Ident::empty(),
1419 kind: opaque_ty_item_kind,
1420 vis_span: self.lower_span(span.shrink_to_lo()),
1421 span: self.lower_span(opaque_ty_span),
1423 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1426 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1427 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1428 // as they are not explicit in HIR/Ty function signatures.
1429 // (instead, the `c_variadic` flag is set to `true`)
1430 let mut inputs = &decl.inputs[..];
1431 if decl.c_variadic() {
1432 inputs = &inputs[..inputs.len() - 1];
1434 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1435 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1436 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1440 // Lowers a function declaration.
1442 // `decl`: the unlowered (AST) function declaration.
1443 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1444 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1445 // `make_ret_async` is also `Some`.
1446 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1447 // This guards against trait declarations and implementations where `impl Trait` is
1449 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1450 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1451 // return type `impl Trait` item.
1452 #[tracing::instrument(level = "debug", skip(self))]
1456 fn_node_id: Option<NodeId>,
1458 make_ret_async: Option<NodeId>,
1459 ) -> &'hir hir::FnDecl<'hir> {
1460 let c_variadic = decl.c_variadic();
1462 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1463 // as they are not explicit in HIR/Ty function signatures.
1464 // (instead, the `c_variadic` flag is set to `true`)
1465 let mut inputs = &decl.inputs[..];
1467 inputs = &inputs[..inputs.len() - 1];
1469 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1470 if fn_node_id.is_some() {
1471 self.lower_ty_direct(¶m.ty, ImplTraitContext::Universal)
1473 self.lower_ty_direct(
1475 ImplTraitContext::Disallowed(match kind {
1476 FnDeclKind::Fn | FnDeclKind::Inherent => {
1477 unreachable!("fn should allow in-band lifetimes")
1479 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1480 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1481 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1482 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1483 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1489 let output = if let Some(ret_id) = make_ret_async {
1490 self.lower_async_fn_ret_ty(
1492 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1497 FnRetTy::Ty(ref ty) => {
1498 let context = match fn_node_id {
1499 Some(fn_node_id) if kind.impl_trait_return_allowed() => {
1500 let fn_def_id = self.local_def_id(fn_node_id);
1501 ImplTraitContext::ReturnPositionOpaqueTy {
1502 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1505 _ => ImplTraitContext::Disallowed(match kind {
1506 FnDeclKind::Fn | FnDeclKind::Inherent => {
1507 unreachable!("fn should allow in-band lifetimes")
1509 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1510 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1511 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1512 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1513 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1516 hir::FnRetTy::Return(self.lower_ty(ty, context))
1518 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1522 self.arena.alloc(hir::FnDecl {
1526 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1527 use BindingMode::{ByRef, ByValue};
1528 let is_mutable_pat = matches!(
1530 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1534 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1535 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1536 // Given we are only considering `ImplicitSelf` types, we needn't consider
1537 // the case where we have a mutable pattern to a reference as that would
1538 // no longer be an `ImplicitSelf`.
1539 TyKind::Rptr(_, ref mt)
1540 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1542 hir::ImplicitSelfKind::MutRef
1544 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1545 hir::ImplicitSelfKind::ImmRef
1547 _ => hir::ImplicitSelfKind::None,
1553 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1554 // combined with the following definition of `OpaqueTy`:
1556 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1558 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1559 // `output`: unlowered output type (`T` in `-> T`)
1560 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1561 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1562 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1563 #[tracing::instrument(level = "debug", skip(self))]
1564 fn lower_async_fn_ret_ty(
1568 opaque_ty_node_id: NodeId,
1569 ) -> hir::FnRetTy<'hir> {
1570 let span = output.span();
1572 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1574 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1575 let fn_def_id = self.local_def_id(fn_node_id);
1577 // When we create the opaque type for this async fn, it is going to have
1578 // to capture all the lifetimes involved in the signature (including in the
1579 // return type). This is done by introducing lifetime parameters for:
1581 // - all the explicitly declared lifetimes from the impl and function itself;
1582 // - all the elided lifetimes in the fn arguments;
1583 // - all the elided lifetimes in the return type.
1585 // So for example in this snippet:
1588 // impl<'a> Foo<'a> {
1589 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1590 // // ^ '0 ^ '1 ^ '2
1591 // // elided lifetimes used below
1596 // we would create an opaque type like:
1599 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1602 // and we would then desugar `bar` to the equivalent of:
1605 // impl<'a> Foo<'a> {
1606 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1610 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1611 // this is because the elided lifetimes from the return type
1612 // should be figured out using the ordinary elision rules, and
1613 // this desugaring achieves that.
1615 // Calculate all the lifetimes that should be captured
1616 // by the opaque type. This should include all in-scope
1617 // lifetime parameters, including those defined in-band.
1619 let mut captures = FxHashMap::default();
1621 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1622 debug!(?extra_lifetime_params);
1623 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1624 let Ident { name, span } = ident;
1625 let outer_def_id = self.local_def_id(outer_node_id);
1626 let inner_node_id = self.next_node_id();
1628 // Add a definition for the in scope lifetime def.
1629 self.create_def(opaque_ty_def_id, inner_node_id, DefPathData::LifetimeNs(name));
1631 let (p_name, inner_res) = match outer_res {
1632 // Input lifetime like `'a`:
1633 LifetimeRes::Param { param, .. } => {
1634 (hir::ParamName::Plain(ident), LifetimeRes::Param { param, binder: fn_node_id })
1636 // Input lifetime like `'1`:
1637 LifetimeRes::Fresh { param, .. } => {
1638 (hir::ParamName::Fresh, LifetimeRes::Fresh { param, binder: fn_node_id })
1640 LifetimeRes::Static | LifetimeRes::Error => continue,
1642 panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span)
1646 captures.insert(outer_def_id, (span, inner_node_id, p_name, inner_res));
1651 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1653 this.while_capturing_lifetimes(opaque_ty_def_id, &mut captures, |this| {
1654 // We have to be careful to get elision right here. The
1655 // idea is that we create a lifetime parameter for each
1656 // lifetime in the return type. So, given a return type
1657 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1658 // Future<Output = &'1 [ &'2 u32 ]>`.
1660 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1661 // hence the elision takes place at the fn site.
1662 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1664 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1665 debug!("lower_async_fn_ret_ty: captures={:#?}", captures);
1667 let generic_params =
1668 this.arena.alloc_from_iter(captures.iter().map(|(_, &(span, p_id, p_name, _))| {
1669 let hir_id = this.lower_node_id(p_id);
1670 debug_assert_ne!(this.opt_local_def_id(p_id), None);
1672 let kind = if p_name.ident().name == kw::UnderscoreLifetime {
1673 hir::LifetimeParamKind::Elided
1675 hir::LifetimeParamKind::Explicit
1682 pure_wrt_drop: false,
1683 kind: hir::GenericParamKind::Lifetime { kind },
1687 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1689 let opaque_ty_item = hir::OpaqueTy {
1690 generics: this.arena.alloc(hir::Generics {
1691 params: generic_params,
1693 has_where_clause_predicates: false,
1694 where_clause_span: this.lower_span(span),
1695 span: this.lower_span(span),
1697 bounds: arena_vec![this; future_bound],
1698 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1701 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1702 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1705 // As documented above, we need to create the lifetime
1706 // arguments to our opaque type. Continuing with our example,
1707 // we're creating the type arguments for the return type:
1710 // Bar<'a, 'b, '0, '1, '_>
1713 // For the "input" lifetime parameters, we wish to create
1714 // references to the parameters themselves, including the
1715 // "implicit" ones created from parameter types (`'a`, `'b`,
1718 // For the "output" lifetime parameters, we just want to
1721 self.arena.alloc_from_iter(captures.into_iter().map(|(_, (span, _, p_name, res))| {
1722 let id = self.next_node_id();
1723 let ident = Ident::new(p_name.ident().name, span);
1724 let l = self.new_named_lifetime_with_res(id, span, ident, res);
1725 hir::GenericArg::Lifetime(l)
1728 // Create the `Foo<...>` reference itself. Note that the `type
1729 // Foo = impl Trait` is, internally, created as a child of the
1730 // async fn, so the *type parameters* are inherited. It's
1731 // only the lifetime parameters that we must supply.
1733 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
1734 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1735 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
1738 /// Transforms `-> T` into `Future<Output = T>`.
1739 fn lower_async_fn_output_type_to_future_bound(
1742 fn_def_id: LocalDefId,
1744 ) -> hir::GenericBound<'hir> {
1745 // Compute the `T` in `Future<Output = T>` from the return type.
1746 let output_ty = match output {
1747 FnRetTy::Ty(ty) => {
1748 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
1749 // `impl Future` opaque type that `async fn` implicitly
1751 let context = ImplTraitContext::ReturnPositionOpaqueTy {
1752 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1754 self.lower_ty(ty, context)
1756 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1760 let future_args = self.arena.alloc(hir::GenericArgs {
1762 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1763 parenthesized: false,
1767 hir::GenericBound::LangItemTrait(
1768 // ::std::future::Future<future_params>
1769 hir::LangItem::Future,
1770 self.lower_span(span),
1776 #[instrument(level = "trace", skip(self))]
1777 fn lower_param_bound(
1780 itctx: ImplTraitContext,
1781 ) -> hir::GenericBound<'hir> {
1783 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
1784 self.lower_poly_trait_ref(p, itctx),
1785 self.lower_trait_bound_modifier(*modifier),
1787 GenericBound::Outlives(lifetime) => {
1788 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
1793 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
1794 let span = self.lower_span(l.ident.span);
1795 let ident = self.lower_ident(l.ident);
1796 let res = self.resolver.get_lifetime_res(l.id).unwrap_or(LifetimeRes::Error);
1797 self.new_named_lifetime_with_res(l.id, span, ident, res)
1800 #[tracing::instrument(level = "debug", skip(self))]
1801 fn new_named_lifetime_with_res(
1807 ) -> hir::Lifetime {
1808 debug!(?self.captured_lifetimes);
1809 let name = match res {
1810 LifetimeRes::Param { mut param, binder } => {
1811 debug_assert_ne!(ident.name, kw::UnderscoreLifetime);
1812 let p_name = ParamName::Plain(ident);
1813 if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
1814 if !captured_lifetimes.binders_to_ignore.contains(&binder) {
1815 match captured_lifetimes.captures.entry(param) {
1816 Entry::Occupied(o) => param = self.local_def_id(o.get().1),
1817 Entry::Vacant(v) => {
1818 let p_id = self.next_node_id();
1819 let p_def_id = self.create_def(
1820 captured_lifetimes.parent_def_id,
1822 DefPathData::LifetimeNs(p_name.ident().name),
1825 v.insert((span, p_id, p_name, res));
1831 self.captured_lifetimes = Some(captured_lifetimes);
1833 hir::LifetimeName::Param(param, p_name)
1835 LifetimeRes::Fresh { param, binder } => {
1836 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
1837 let mut param = self.local_def_id(param);
1838 if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
1839 if !captured_lifetimes.binders_to_ignore.contains(&binder) {
1840 match captured_lifetimes.captures.entry(param) {
1841 Entry::Occupied(o) => param = self.local_def_id(o.get().1),
1842 Entry::Vacant(v) => {
1843 let p_id = self.next_node_id();
1844 let p_def_id = self.create_def(
1845 captured_lifetimes.parent_def_id,
1847 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1850 v.insert((span, p_id, ParamName::Fresh, res));
1856 self.captured_lifetimes = Some(captured_lifetimes);
1858 hir::LifetimeName::Param(param, ParamName::Fresh)
1860 LifetimeRes::Anonymous { binder, elided } => {
1861 let mut l_name = None;
1862 if let Some(mut captured_lifetimes) = self.captured_lifetimes.take() {
1863 if !captured_lifetimes.binders_to_ignore.contains(&binder) {
1864 let p_id = self.next_node_id();
1865 let p_def_id = self.create_def(
1866 captured_lifetimes.parent_def_id,
1868 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1872 .insert(p_def_id, (span, p_id, ParamName::Fresh, res));
1873 l_name = Some(hir::LifetimeName::Param(p_def_id, ParamName::Fresh));
1875 self.captured_lifetimes = Some(captured_lifetimes);
1877 l_name.unwrap_or(if elided {
1878 hir::LifetimeName::Implicit
1880 hir::LifetimeName::Underscore
1883 LifetimeRes::Static => hir::LifetimeName::Static,
1884 LifetimeRes::Error => hir::LifetimeName::Error,
1885 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
1887 debug!(?self.captured_lifetimes);
1889 hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
1892 fn lower_generic_params_mut<'s>(
1894 params: &'s [GenericParam],
1895 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
1896 params.iter().map(move |param| self.lower_generic_param(param))
1899 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
1900 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
1903 #[instrument(level = "trace", skip(self))]
1904 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
1905 let (name, kind) = self.lower_generic_param_kind(param);
1907 let hir_id = self.lower_node_id(param.id);
1908 self.lower_attrs(hir_id, ¶m.attrs);
1912 span: self.lower_span(param.span()),
1913 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
1915 colon_span: param.colon_span.map(|s| self.lower_span(s)),
1919 fn lower_generic_param_kind(
1921 param: &GenericParam,
1922 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
1924 GenericParamKind::Lifetime => {
1925 // AST resolution emitted an error on those parameters, so we lower them using
1926 // `ParamName::Error`.
1928 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
1931 let ident = self.lower_ident(param.ident);
1932 ParamName::Plain(ident)
1935 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
1939 GenericParamKind::Type { ref default, .. } => {
1940 let kind = hir::GenericParamKind::Type {
1941 default: default.as_ref().map(|x| {
1942 self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Type))
1947 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
1949 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
1950 let ty = self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type));
1951 let default = default.as_ref().map(|def| self.lower_anon_const(def));
1953 hir::ParamName::Plain(self.lower_ident(param.ident)),
1954 hir::GenericParamKind::Const { ty, default },
1960 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext) -> hir::TraitRef<'hir> {
1961 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
1962 hir::QPath::Resolved(None, path) => path,
1963 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
1965 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
1968 #[tracing::instrument(level = "debug", skip(self))]
1969 fn lower_poly_trait_ref(
1972 itctx: ImplTraitContext,
1973 ) -> hir::PolyTraitRef<'hir> {
1974 self.with_lifetime_binder(
1976 &p.bound_generic_params,
1977 |this, bound_generic_params| {
1978 let trait_ref = this.lower_trait_ref(&p.trait_ref, itctx);
1979 hir::PolyTraitRef { bound_generic_params, trait_ref, span: this.lower_span(p.span) }
1984 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy<'hir> {
1985 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
1988 fn lower_param_bounds(
1990 bounds: &[GenericBound],
1991 itctx: ImplTraitContext,
1992 ) -> hir::GenericBounds<'hir> {
1993 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
1996 fn lower_param_bounds_mut<'s>(
1998 bounds: &'s [GenericBound],
1999 itctx: ImplTraitContext,
2000 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2001 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2004 fn lower_generic_and_bounds(
2009 bounds: &[GenericBound],
2010 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2011 // Add a definition for the in-band `Param`.
2012 let def_id = self.local_def_id(node_id);
2014 let hir_bounds = self.lower_param_bounds(bounds, ImplTraitContext::Universal);
2015 // Set the name to `impl Bound1 + Bound2`.
2016 let param = hir::GenericParam {
2017 hir_id: self.lower_node_id(node_id),
2018 name: ParamName::Plain(self.lower_ident(ident)),
2019 pure_wrt_drop: false,
2020 span: self.lower_span(span),
2021 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2025 let preds = self.lower_generic_bound_predicate(
2028 &GenericParamKind::Type { default: None },
2030 hir::PredicateOrigin::ImplTrait,
2033 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2035 self.arena.alloc(hir::Path {
2036 span: self.lower_span(span),
2037 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
2038 segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
2045 /// Lowers a block directly to an expression, presuming that it
2046 /// has no attributes and is not targeted by a `break`.
2047 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2048 let block = self.lower_block(b, false);
2049 self.expr_block(block, AttrVec::new())
2052 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2053 match c.value.kind {
2054 ExprKind::Underscore => {
2055 if self.tcx.features().generic_arg_infer {
2056 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2059 &self.tcx.sess.parse_sess,
2060 sym::generic_arg_infer,
2062 "using `_` for array lengths is unstable",
2065 hir::ArrayLen::Body(self.lower_anon_const(c))
2068 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2072 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2073 self.with_new_scopes(|this| hir::AnonConst {
2074 hir_id: this.lower_node_id(c.id),
2075 body: this.lower_const_body(c.value.span, Some(&c.value)),
2079 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2081 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2082 UserProvided => hir::UnsafeSource::UserProvided,
2086 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2088 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2089 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2091 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2092 // placeholder for compilation to proceed.
2093 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2094 hir::TraitBoundModifier::Maybe
2099 // Helper methods for building HIR.
2101 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2102 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2105 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2106 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2111 attrs: Option<&'hir [Attribute]>,
2113 init: Option<&'hir hir::Expr<'hir>>,
2114 pat: &'hir hir::Pat<'hir>,
2115 source: hir::LocalSource,
2116 ) -> hir::Stmt<'hir> {
2117 let hir_id = self.next_id();
2118 if let Some(a) = attrs {
2119 debug_assert!(!a.is_empty());
2120 self.attrs.insert(hir_id.local_id, a);
2122 let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
2123 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2126 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2127 self.block_all(expr.span, &[], Some(expr))
2133 stmts: &'hir [hir::Stmt<'hir>],
2134 expr: Option<&'hir hir::Expr<'hir>>,
2135 ) -> &'hir hir::Block<'hir> {
2136 let blk = hir::Block {
2139 hir_id: self.next_id(),
2140 rules: hir::BlockCheckMode::DefaultBlock,
2141 span: self.lower_span(span),
2142 targeted_by_break: false,
2144 self.arena.alloc(blk)
2147 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2148 let field = self.single_pat_field(span, pat);
2149 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2152 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2153 let field = self.single_pat_field(span, pat);
2154 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2157 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2158 let field = self.single_pat_field(span, pat);
2159 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2162 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2163 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2166 fn single_pat_field(
2169 pat: &'hir hir::Pat<'hir>,
2170 ) -> &'hir [hir::PatField<'hir>] {
2171 let field = hir::PatField {
2172 hir_id: self.next_id(),
2173 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2174 is_shorthand: false,
2176 span: self.lower_span(span),
2178 arena_vec![self; field]
2181 fn pat_lang_item_variant(
2184 lang_item: hir::LangItem,
2185 fields: &'hir [hir::PatField<'hir>],
2186 hir_id: Option<hir::HirId>,
2187 ) -> &'hir hir::Pat<'hir> {
2188 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2189 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2192 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2193 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2196 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2197 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::Unannotated)
2200 fn pat_ident_binding_mode(
2204 bm: hir::BindingAnnotation,
2205 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2206 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2207 (self.arena.alloc(pat), hir_id)
2210 fn pat_ident_binding_mode_mut(
2214 bm: hir::BindingAnnotation,
2215 ) -> (hir::Pat<'hir>, hir::HirId) {
2216 let hir_id = self.next_id();
2221 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2222 span: self.lower_span(span),
2223 default_binding_modes: true,
2229 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2230 self.arena.alloc(hir::Pat {
2231 hir_id: self.next_id(),
2233 span: self.lower_span(span),
2234 default_binding_modes: true,
2238 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2240 hir_id: self.next_id(),
2242 span: self.lower_span(span),
2243 default_binding_modes: false,
2249 mut hir_id: hir::HirId,
2251 qpath: hir::QPath<'hir>,
2252 ) -> hir::Ty<'hir> {
2253 let kind = match qpath {
2254 hir::QPath::Resolved(None, path) => {
2255 // Turn trait object paths into `TyKind::TraitObject` instead.
2257 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2258 let principal = hir::PolyTraitRef {
2259 bound_generic_params: &[],
2260 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2261 span: self.lower_span(span),
2264 // The original ID is taken by the `PolyTraitRef`,
2265 // so the `Ty` itself needs a different one.
2266 hir_id = self.next_id();
2267 hir::TyKind::TraitObject(
2268 arena_vec![self; principal],
2269 self.elided_dyn_bound(span),
2270 TraitObjectSyntax::None,
2273 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2276 _ => hir::TyKind::Path(qpath),
2279 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2282 /// Invoked to create the lifetime argument(s) for an elided trait object
2283 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2284 /// when the bound is written, even if it is written with `'_` like in
2285 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2286 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2287 let r = hir::Lifetime {
2288 hir_id: self.next_id(),
2289 span: self.lower_span(span),
2290 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2292 debug!("elided_dyn_bound: r={:?}", r);
2297 /// Helper struct for delayed construction of GenericArgs.
2298 struct GenericArgsCtor<'hir> {
2299 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2300 bindings: &'hir [hir::TypeBinding<'hir>],
2301 parenthesized: bool,
2305 impl<'hir> GenericArgsCtor<'hir> {
2306 fn is_empty(&self) -> bool {
2307 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2310 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2311 let ga = hir::GenericArgs {
2312 args: this.arena.alloc_from_iter(self.args),
2313 bindings: self.bindings,
2314 parenthesized: self.parenthesized,
2315 span_ext: this.lower_span(self.span),
2317 this.arena.alloc(ga)