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)]
39 #![deny(rustc::untranslatable_diagnostic)]
40 #![deny(rustc::diagnostic_outside_of_impl)]
45 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait};
47 use rustc_ast::ptr::P;
49 use rustc_ast::{self as ast, *};
50 use rustc_ast_pretty::pprust;
51 use rustc_data_structures::captures::Captures;
52 use rustc_data_structures::fingerprint::Fingerprint;
53 use rustc_data_structures::fx::FxHashMap;
54 use rustc_data_structures::sorted_map::SortedMap;
55 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
56 use rustc_data_structures::sync::Lrc;
57 use rustc_errors::{DiagnosticArgFromDisplay, Handler, StashKey};
59 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
60 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
61 use rustc_hir::definitions::DefPathData;
62 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
63 use rustc_index::vec::{Idx, IndexVec};
64 use rustc_middle::span_bug;
65 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
66 use rustc_session::parse::feature_err;
67 use rustc_span::hygiene::MacroKind;
68 use rustc_span::source_map::DesugaringKind;
69 use rustc_span::symbol::{kw, sym, Ident, Symbol};
70 use rustc_span::{Span, DUMMY_SP};
72 use smallvec::SmallVec;
73 use std::collections::hash_map::Entry;
75 macro_rules! arena_vec {
76 ($this:expr; $($x:expr),*) => (
77 $this.arena.alloc_from_iter([$($x),*])
87 mod lifetime_collector;
91 struct LoweringContext<'a, 'hir> {
93 resolver: &'a mut ResolverAstLowering,
95 /// Used to allocate HIR nodes.
96 arena: &'hir hir::Arena<'hir>,
98 /// Bodies inside the owner being lowered.
99 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
100 /// Attributes inside the owner being lowered.
101 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
102 /// Collect items that were created by lowering the current owner.
103 children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
105 generator_kind: Option<hir::GeneratorKind>,
107 /// When inside an `async` context, this is the `HirId` of the
108 /// `task_context` local bound to the resume argument of the generator.
109 task_context: Option<hir::HirId>,
111 /// Used to get the current `fn`'s def span to point to when using `await`
112 /// outside of an `async fn`.
113 current_item: Option<Span>,
115 catch_scope: Option<NodeId>,
116 loop_scope: Option<NodeId>,
117 is_in_loop_condition: bool,
118 is_in_trait_impl: bool,
119 is_in_dyn_type: bool,
121 current_hir_id_owner: LocalDefId,
122 item_local_id_counter: hir::ItemLocalId,
123 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
124 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
126 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
127 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
129 /// NodeIds that are lowered inside the current HIR owner.
130 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
132 allow_try_trait: Option<Lrc<[Symbol]>>,
133 allow_gen_future: Option<Lrc<[Symbol]>>,
134 allow_into_future: Option<Lrc<[Symbol]>>,
136 /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
137 /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
138 /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
139 /// field from the original parameter 'a to the new parameter 'a1.
140 generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
143 trait ResolverAstLoweringExt {
144 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
145 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
146 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
147 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
148 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
149 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
150 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
153 impl ResolverAstLoweringExt for ResolverAstLowering {
154 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
155 if let ExprKind::Path(None, path) = &expr.kind {
156 // Don't perform legacy const generics rewriting if the path already
157 // has generic arguments.
158 if path.segments.last().unwrap().args.is_some() {
162 let partial_res = self.partial_res_map.get(&expr.id)?;
163 if partial_res.unresolved_segments() != 0 {
167 if let Res::Def(DefKind::Fn, def_id) = partial_res.base_res() {
168 // We only support cross-crate argument rewriting. Uses
169 // within the same crate should be updated to use the new
170 // const generics style.
171 if def_id.is_local() {
175 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
184 /// Obtains resolution for a `NodeId` with a single resolution.
185 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
186 self.partial_res_map.get(&id).copied()
189 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
190 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
191 self.import_res_map.get(&id).copied().unwrap_or_default()
194 /// Obtains resolution for a label with the given `NodeId`.
195 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
196 self.label_res_map.get(&id).copied()
199 /// Obtains resolution for a lifetime with the given `NodeId`.
200 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
201 self.lifetimes_res_map.get(&id).copied()
204 /// Obtain the list of lifetimes parameters to add to an item.
206 /// Extra lifetime parameters should only be added in places that can appear
207 /// as a `binder` in `LifetimeRes`.
209 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
210 /// should appear at the enclosing `PolyTraitRef`.
211 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
212 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
215 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
216 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
220 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
221 /// and if so, what meaning it has.
222 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
223 enum ImplTraitContext {
224 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
225 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
226 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
228 /// Newly generated parameters should be inserted into the given `Vec`.
231 /// Treat `impl Trait` as shorthand for a new opaque type.
232 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
233 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
235 ReturnPositionOpaqueTy {
236 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
237 origin: hir::OpaqueTyOrigin,
239 /// Impl trait in type aliases.
241 /// `impl Trait` is not accepted in this position.
242 Disallowed(ImplTraitPosition),
245 /// Position in which `impl Trait` is disallowed.
246 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
247 enum ImplTraitPosition {
269 impl std::fmt::Display for ImplTraitPosition {
270 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
271 let name = match self {
272 ImplTraitPosition::Path => "path",
273 ImplTraitPosition::Variable => "variable binding",
274 ImplTraitPosition::Type => "type",
275 ImplTraitPosition::Trait => "trait",
276 ImplTraitPosition::AsyncBlock => "async block",
277 ImplTraitPosition::Bound => "bound",
278 ImplTraitPosition::Generic => "generic",
279 ImplTraitPosition::ExternFnParam => "`extern fn` param",
280 ImplTraitPosition::ClosureParam => "closure param",
281 ImplTraitPosition::PointerParam => "`fn` pointer param",
282 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
283 ImplTraitPosition::TraitParam => "trait method param",
284 ImplTraitPosition::ImplParam => "`impl` method param",
285 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
286 ImplTraitPosition::ClosureReturn => "closure return",
287 ImplTraitPosition::PointerReturn => "`fn` pointer return",
288 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
289 ImplTraitPosition::TraitReturn => "trait method return",
290 ImplTraitPosition::ImplReturn => "`impl` method return",
293 write!(f, "{}", name)
309 fn impl_trait_return_allowed(&self) -> bool {
311 FnDeclKind::Fn | FnDeclKind::Inherent => true,
317 #[derive(Copy, Clone)]
320 Crate(&'a ast::Crate),
322 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
323 ForeignItem(&'a ast::ForeignItem),
327 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
329 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
330 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
331 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
332 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
333 visit::walk_crate(&mut indexer, krate);
334 return indexer.index;
336 struct Indexer<'s, 'a> {
337 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
338 index: IndexVec<LocalDefId, AstOwner<'a>>,
341 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
342 fn visit_attribute(&mut self, _: &'a Attribute) {
343 // We do not want to lower expressions that appear in attributes,
344 // as they are not accessible to the rest of the HIR.
347 fn visit_item(&mut self, item: &'a ast::Item) {
348 let def_id = self.node_id_to_def_id[&item.id];
349 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
350 self.index[def_id] = AstOwner::Item(item);
351 visit::walk_item(self, item)
354 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
355 let def_id = self.node_id_to_def_id[&item.id];
356 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
357 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
358 visit::walk_assoc_item(self, item, ctxt);
361 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
362 let def_id = self.node_id_to_def_id[&item.id];
363 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
364 self.index[def_id] = AstOwner::ForeignItem(item);
365 visit::walk_foreign_item(self, item);
370 /// Compute the hash for the HIR of the full crate.
371 /// This hash will then be part of the crate_hash which is stored in the metadata.
374 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
376 let mut hir_body_nodes: Vec<_> = owners
378 .filter_map(|(def_id, info)| {
379 let info = info.as_owner()?;
380 let def_path_hash = tcx.hir().def_path_hash(def_id);
381 Some((def_path_hash, info))
384 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
386 tcx.with_stable_hashing_context(|mut hcx| {
387 let mut stable_hasher = StableHasher::new();
388 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
389 stable_hasher.finish()
393 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
395 let krate = tcx.untracked_crate.steal();
396 let mut resolver = tcx.resolver_for_lowering(()).steal();
398 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
399 let mut owners = IndexVec::from_fn_n(
400 |_| hir::MaybeOwner::Phantom,
401 tcx.definitions_untracked().def_index_count(),
404 for def_id in ast_index.indices() {
407 resolver: &mut resolver,
408 ast_index: &ast_index,
414 // Drop AST to free memory
415 std::mem::drop(ast_index);
416 sess.time("drop_ast", || std::mem::drop(krate));
418 // Discard hygiene data, which isn't required after lowering to HIR.
419 if !sess.opts.unstable_opts.keep_hygiene_data {
420 rustc_span::hygiene::clear_syntax_context_map();
423 let hir_hash = compute_hir_hash(tcx, &owners);
424 hir::Crate { owners, hir_hash }
427 #[derive(Copy, Clone, PartialEq, Debug)]
429 /// Any path in a type context.
431 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
433 /// The `module::Type` in `module::Type::method` in an expression.
437 enum ParenthesizedGenericArgs {
442 impl<'a, 'hir> LoweringContext<'a, 'hir> {
446 node_id: ast::NodeId,
449 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
451 self.opt_local_def_id(node_id).is_none(),
452 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
455 self.tcx.hir().def_key(self.local_def_id(node_id)),
458 let def_id = self.tcx.create_def(parent, data);
460 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
461 self.resolver.node_id_to_def_id.insert(node_id, def_id);
466 fn next_node_id(&mut self) -> NodeId {
467 let start = self.resolver.next_node_id;
468 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
469 self.resolver.next_node_id = ast::NodeId::from_u32(next);
473 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
474 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
476 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
477 /// invoking with the id from the `ast::Lifetime` node found inside
478 /// the `&'a u32` type would return the `LocalDefId` of the
479 /// `'a` parameter declared on `foo`.
481 /// This function also applies remapping from `get_remapped_def_id`.
482 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
483 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
484 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
485 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
486 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
490 .map(|local_def_id| self.get_remapped_def_id(*local_def_id))
493 fn local_def_id(&self, node: NodeId) -> LocalDefId {
494 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
497 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
498 /// `generics_def_id_map` field.
499 fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId {
500 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
501 // push new mappings so we need to try first the latest mappings, hence `iter().rev()`.
505 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
507 // We would end with a generics_def_id_map like:
509 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
511 // for the opaque type generated on `impl Sized + 'b`, We want the result to be:
512 // impl_sized#'b, so iterating forward is the wrong thing to do.
513 for map in self.generics_def_id_map.iter().rev() {
514 if let Some(r) = map.get(&local_def_id) {
515 debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`");
518 debug!("def_id_remapper: no remapping for `{local_def_id:?}` found in map");
525 /// Freshen the `LoweringContext` and ready it to lower a nested item.
526 /// The lowered item is registered into `self.children`.
528 /// This function sets up `HirId` lowering infrastructure,
529 /// and stashes the shared mutable state to avoid pollution by the closure.
530 #[instrument(level = "debug", skip(self, f))]
531 fn with_hir_id_owner(
534 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
536 let def_id = self.local_def_id(owner);
538 let current_attrs = std::mem::take(&mut self.attrs);
539 let current_bodies = std::mem::take(&mut self.bodies);
540 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
541 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
542 let current_trait_map = std::mem::take(&mut self.trait_map);
543 let current_owner = std::mem::replace(&mut self.current_hir_id_owner, def_id);
544 let current_local_counter =
545 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
546 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
547 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
549 // Do not reset `next_node_id` and `node_id_to_def_id`:
550 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
551 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
553 // Always allocate the first `HirId` for the owner itself.
554 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
555 debug_assert_eq!(_old, None);
558 debug_assert_eq!(def_id, item.def_id());
559 // `f` should have consumed all the elements in these vectors when constructing `item`.
560 debug_assert!(self.impl_trait_defs.is_empty());
561 debug_assert!(self.impl_trait_bounds.is_empty());
562 let info = self.make_owner_info(item);
564 self.attrs = current_attrs;
565 self.bodies = current_bodies;
566 self.node_id_to_local_id = current_node_ids;
567 self.local_id_to_def_id = current_id_to_def_id;
568 self.trait_map = current_trait_map;
569 self.current_hir_id_owner = current_owner;
570 self.item_local_id_counter = current_local_counter;
571 self.impl_trait_defs = current_impl_trait_defs;
572 self.impl_trait_bounds = current_impl_trait_bounds;
574 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
575 debug_assert!(_old.is_none())
578 /// Installs the remapping `remap` in scope while `f` is being executed.
579 /// This causes references to the `LocalDefId` keys to be changed to
580 /// refer to the values instead.
582 /// The remapping is used when one piece of AST expands to multiple
583 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
584 /// expands to both a function definition (`foo`) and a TAIT for the return value,
585 /// both of which have a lifetime parameter `'a`. The remapping allows us to
586 /// rewrite the `'a` in the return value to refer to the
587 /// `'a` declared on the TAIT, instead of the function.
588 fn with_remapping<R>(
590 remap: FxHashMap<LocalDefId, LocalDefId>,
591 f: impl FnOnce(&mut Self) -> R,
593 self.generics_def_id_map.push(remap);
595 self.generics_def_id_map.pop();
599 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
600 let attrs = std::mem::take(&mut self.attrs);
601 let mut bodies = std::mem::take(&mut self.bodies);
602 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
603 let trait_map = std::mem::take(&mut self.trait_map);
605 #[cfg(debug_assertions)]
606 for (id, attrs) in attrs.iter() {
607 // Verify that we do not store empty slices in the map.
608 if attrs.is_empty() {
609 panic!("Stored empty attributes for {:?}", id);
613 bodies.sort_by_key(|(k, _)| *k);
614 let bodies = SortedMap::from_presorted_elements(bodies);
615 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
616 let (nodes, parenting) =
617 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
618 let nodes = hir::OwnerNodes {
619 hash_including_bodies,
626 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
627 let mut stable_hasher = StableHasher::new();
628 attrs.hash_stable(&mut hcx, &mut stable_hasher);
629 stable_hasher.finish()
631 hir::AttributeMap { map: attrs, hash }
634 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
637 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
638 /// queries which depend on the full HIR tree and those which only depend on the item signature.
641 node: hir::OwnerNode<'hir>,
642 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
643 ) -> (Fingerprint, Fingerprint) {
644 self.tcx.with_stable_hashing_context(|mut hcx| {
645 let mut stable_hasher = StableHasher::new();
646 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
647 node.hash_stable(hcx, &mut stable_hasher)
649 let hash_including_bodies = stable_hasher.finish();
650 let mut stable_hasher = StableHasher::new();
651 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
652 let hash_without_bodies = stable_hasher.finish();
653 (hash_including_bodies, hash_without_bodies)
657 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
658 /// the `LoweringContext`'s `NodeId => HirId` map.
659 /// Take care not to call this method if the resulting `HirId` is then not
660 /// actually used in the HIR, as that would trigger an assertion in the
661 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
662 /// properly. Calling the method twice with the same `NodeId` is fine though.
663 #[instrument(level = "debug", skip(self), ret)]
664 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
665 assert_ne!(ast_node_id, DUMMY_NODE_ID);
667 match self.node_id_to_local_id.entry(ast_node_id) {
668 Entry::Occupied(o) => {
669 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
671 Entry::Vacant(v) => {
672 // Generate a new `HirId`.
673 let owner = self.current_hir_id_owner;
674 let local_id = self.item_local_id_counter;
675 let hir_id = hir::HirId { owner, local_id };
678 self.item_local_id_counter.increment_by(1);
680 assert_ne!(local_id, hir::ItemLocalId::new(0));
681 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
682 // Do not override a `MaybeOwner::Owner` that may already here.
683 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
684 self.local_id_to_def_id.insert(local_id, def_id);
687 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
688 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
696 /// Generate a new `HirId` without a backing `NodeId`.
697 #[instrument(level = "debug", skip(self), ret)]
698 fn next_id(&mut self) -> hir::HirId {
699 let owner = self.current_hir_id_owner;
700 let local_id = self.item_local_id_counter;
701 assert_ne!(local_id, hir::ItemLocalId::new(0));
702 self.item_local_id_counter.increment_by(1);
703 hir::HirId { owner, local_id }
706 #[instrument(level = "trace", skip(self))]
707 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
708 let res: Result<Res, ()> = res.apply_id(|id| {
709 let owner = self.current_hir_id_owner;
710 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
711 Ok(hir::HirId { owner, local_id })
715 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
716 // This can happen when trying to lower the return type `x` in erroneous code like
717 // async fn foo(x: u8) -> x {}
718 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
719 // an opaque type as a synthesized HIR owner.
720 res.unwrap_or(Res::Err)
723 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
724 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
725 if pr.unresolved_segments() != 0 {
726 panic!("path not fully resolved: {:?}", pr);
732 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
733 self.resolver.get_import_res(id).present_items()
736 fn diagnostic(&self) -> &Handler {
737 self.tcx.sess.diagnostic()
740 /// Reuses the span but adds information like the kind of the desugaring and features that are
741 /// allowed inside this span.
742 fn mark_span_with_reason(
744 reason: DesugaringKind,
746 allow_internal_unstable: Option<Lrc<[Symbol]>>,
748 self.tcx.with_stable_hashing_context(|hcx| {
749 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
753 /// Intercept all spans entering HIR.
754 /// Mark a span as relative to the current owning item.
755 fn lower_span(&self, span: Span) -> Span {
756 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
757 span.with_parent(Some(self.current_hir_id_owner))
759 // Do not make spans relative when not using incremental compilation.
764 fn lower_ident(&self, ident: Ident) -> Ident {
765 Ident::new(ident.name, self.lower_span(ident.span))
768 /// Converts a lifetime into a new generic parameter.
769 #[instrument(level = "debug", skip(self))]
770 fn lifetime_res_to_generic_param(
775 ) -> Option<hir::GenericParam<'hir>> {
776 let (name, kind) = match res {
777 LifetimeRes::Param { .. } => {
778 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
780 LifetimeRes::Fresh { param, .. } => {
781 // Late resolution delegates to us the creation of the `LocalDefId`.
782 let _def_id = self.create_def(
783 self.current_hir_id_owner,
785 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
789 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
791 LifetimeRes::Static | LifetimeRes::Error => return None,
793 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
794 res, ident, ident.span
797 let hir_id = self.lower_node_id(node_id);
798 Some(hir::GenericParam {
801 span: self.lower_span(ident.span),
802 pure_wrt_drop: false,
803 kind: hir::GenericParamKind::Lifetime { kind },
808 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
809 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
810 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
811 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
812 /// parameters will be successful.
813 #[instrument(level = "debug", skip(self, in_binder))]
815 fn lower_lifetime_binder<R>(
818 generic_params: &[GenericParam],
819 in_binder: impl FnOnce(&mut Self, &'hir [hir::GenericParam<'hir>]) -> R,
821 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
822 debug!(?extra_lifetimes);
823 let extra_lifetimes: Vec<_> = extra_lifetimes
825 .filter_map(|(ident, node_id, res)| {
826 self.lifetime_res_to_generic_param(ident, node_id, res)
830 let generic_params: Vec<_> = self
831 .lower_generic_params_mut(generic_params)
832 .chain(extra_lifetimes.into_iter())
834 let generic_params = self.arena.alloc_from_iter(generic_params);
835 debug!(?generic_params);
837 in_binder(self, generic_params)
840 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
841 let was_in_dyn_type = self.is_in_dyn_type;
842 self.is_in_dyn_type = in_scope;
844 let result = f(self);
846 self.is_in_dyn_type = was_in_dyn_type;
851 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
852 let was_in_loop_condition = self.is_in_loop_condition;
853 self.is_in_loop_condition = false;
855 let catch_scope = self.catch_scope.take();
856 let loop_scope = self.loop_scope.take();
858 self.catch_scope = catch_scope;
859 self.loop_scope = loop_scope;
861 self.is_in_loop_condition = was_in_loop_condition;
866 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
867 if attrs.is_empty() {
870 debug_assert_eq!(id.owner, self.current_hir_id_owner);
871 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
872 debug_assert!(!ret.is_empty());
873 self.attrs.insert(id.local_id, ret);
878 fn lower_attr(&self, attr: &Attribute) -> Attribute {
879 // Note that we explicitly do not walk the path. Since we don't really
880 // lower attributes (we use the AST version) there is nowhere to keep
881 // the `HirId`s. We don't actually need HIR version of attributes anyway.
882 // Tokens are also not needed after macro expansion and parsing.
883 let kind = match attr.kind {
884 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
886 path: normal.item.path.clone(),
887 args: self.lower_mac_args(&normal.item.args),
892 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
895 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
898 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
899 debug_assert_eq!(id.owner, self.current_hir_id_owner);
900 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
901 if let Some(&a) = self.attrs.get(&target_id.local_id) {
902 debug_assert!(!a.is_empty());
903 self.attrs.insert(id.local_id, a);
907 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
909 MacArgs::Empty => MacArgs::Empty,
910 MacArgs::Delimited(dspan, delim, ref tokens) => {
911 // This is either a non-key-value attribute, or a `macro_rules!` body.
912 // We either not have any nonterminals present (in the case of an attribute),
913 // or have tokens available for all nonterminals in the case of a nested
914 // `macro_rules`: e.g:
917 // macro_rules! outer {
919 // macro_rules! inner {
926 // In both cases, we don't want to synthesize any tokens
927 MacArgs::Delimited(dspan, delim, tokens.flattened())
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 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref 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(lit) = &expr.kind {
939 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
944 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
946 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
947 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
952 /// Given an associated type constraint like one of these:
954 /// ```ignore (illustrative)
955 /// T: Iterator<Item: Debug>
957 /// T: Iterator<Item = Debug>
961 /// returns a `hir::TypeBinding` representing `Item`.
962 #[instrument(level = "debug", skip(self))]
963 fn lower_assoc_ty_constraint(
965 constraint: &AssocConstraint,
966 itctx: &mut ImplTraitContext,
967 ) -> hir::TypeBinding<'hir> {
968 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
969 // lower generic arguments of identifier in constraint
970 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
971 let gen_args_ctor = match gen_args {
972 GenericArgs::AngleBracketed(ref data) => {
973 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
975 GenericArgs::Parenthesized(ref data) => {
976 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
977 self.lower_angle_bracketed_parameter_data(
978 &data.as_angle_bracketed_args(),
985 gen_args_ctor.into_generic_args(self)
987 self.arena.alloc(hir::GenericArgs::none())
989 let mut itctx_tait = ImplTraitContext::TypeAliasesOpaqueTy;
991 let kind = match constraint.kind {
992 AssocConstraintKind::Equality { ref term } => {
993 let term = match term {
994 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
995 Term::Const(ref c) => self.lower_anon_const(c).into(),
997 hir::TypeBindingKind::Equality { term }
999 AssocConstraintKind::Bound { ref bounds } => {
1000 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1001 let (desugar_to_impl_trait, itctx) = match itctx {
1002 // We are in the return position:
1004 // fn foo() -> impl Iterator<Item: Debug>
1008 // fn foo() -> impl Iterator<Item = impl Debug>
1009 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1010 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1012 // We are in the argument position, but within a dyn type:
1014 // fn foo(x: dyn Iterator<Item: Debug>)
1018 // fn foo(x: dyn Iterator<Item = impl Debug>)
1019 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1021 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1022 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1023 // "impl trait context" to permit `impl Debug` in this position (it desugars
1024 // then to an opaque type).
1026 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1027 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1028 (true, &mut itctx_tait)
1031 // We are in the parameter position, but not within a dyn type:
1033 // fn foo(x: impl Iterator<Item: Debug>)
1035 // so we leave it as is and this gets expanded in astconv to a bound like
1036 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1038 _ => (false, itctx),
1041 if desugar_to_impl_trait {
1042 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1043 // constructing the HIR for `impl bounds...` and then lowering that.
1045 let parent_def_id = self.current_hir_id_owner;
1046 let impl_trait_node_id = self.next_node_id();
1047 self.create_def(parent_def_id, impl_trait_node_id, DefPathData::ImplTrait);
1049 self.with_dyn_type_scope(false, |this| {
1050 let node_id = this.next_node_id();
1051 let ty = this.lower_ty(
1054 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1055 span: this.lower_span(constraint.span),
1061 hir::TypeBindingKind::Equality { term: ty.into() }
1064 // Desugar `AssocTy: Bounds` into a type binding where the
1065 // later desugars into a trait predicate.
1066 let bounds = self.lower_param_bounds(bounds, itctx);
1068 hir::TypeBindingKind::Constraint { bounds }
1074 hir_id: self.lower_node_id(constraint.id),
1075 ident: self.lower_ident(constraint.ident),
1078 span: self.lower_span(constraint.span),
1082 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1083 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1084 let sub = if data.inputs.is_empty() {
1085 let parentheses_span =
1086 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1087 AssocTyParenthesesSub::Empty { parentheses_span }
1089 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1091 // Start of parameters to the 1st argument
1092 let open_param = data.inputs_span.shrink_to_lo().to(data
1098 // End of last argument to end of parameters
1100 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1101 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1103 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1106 #[instrument(level = "debug", skip(self))]
1107 fn lower_generic_arg(
1109 arg: &ast::GenericArg,
1110 itctx: &mut ImplTraitContext,
1111 ) -> hir::GenericArg<'hir> {
1113 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1114 ast::GenericArg::Type(ty) => {
1116 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1117 return GenericArg::Infer(hir::InferArg {
1118 hir_id: self.lower_node_id(ty.id),
1119 span: self.lower_span(ty.span),
1122 // We parse const arguments as path types as we cannot distinguish them during
1123 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1124 // type and value namespaces. If we resolved the path in the value namespace, we
1125 // transform it into a generic const argument.
1126 TyKind::Path(ref qself, ref path) => {
1127 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1128 let res = partial_res.base_res();
1129 if !res.matches_ns(Namespace::TypeNS) {
1131 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1135 // Construct an AnonConst where the expr is the "ty"'s path.
1137 let parent_def_id = self.current_hir_id_owner;
1138 let node_id = self.next_node_id();
1140 // Add a definition for the in-band const def.
1141 self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
1143 let span = self.lower_span(ty.span);
1144 let path_expr = Expr {
1146 kind: ExprKind::Path(qself.clone(), path.clone()),
1148 attrs: AttrVec::new(),
1152 let ct = self.with_new_scopes(|this| hir::AnonConst {
1153 hir_id: this.lower_node_id(node_id),
1154 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1156 return GenericArg::Const(ConstArg { value: ct, span });
1162 GenericArg::Type(self.lower_ty(&ty, itctx))
1164 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1165 value: self.lower_anon_const(&ct),
1166 span: self.lower_span(ct.value.span),
1171 #[instrument(level = "debug", skip(self))]
1172 fn lower_ty(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> &'hir hir::Ty<'hir> {
1173 self.arena.alloc(self.lower_ty_direct(t, itctx))
1179 qself: &Option<QSelf>,
1181 param_mode: ParamMode,
1182 itctx: &mut ImplTraitContext,
1183 ) -> hir::Ty<'hir> {
1184 // Check whether we should interpret this as a bare trait object.
1185 // This check mirrors the one in late resolution. We only introduce this special case in
1186 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1187 // The other cases when a qpath should be opportunistically made a trait object are handled
1190 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1191 && partial_res.unresolved_segments() == 0
1192 && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
1194 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1195 let bound = this.lower_poly_trait_ref(
1197 bound_generic_params: vec![],
1198 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1203 let bounds = this.arena.alloc_from_iter([bound]);
1204 let lifetime_bound = this.elided_dyn_bound(t.span);
1205 (bounds, lifetime_bound)
1207 let kind = hir::TyKind::TraitObject(bounds, lifetime_bound, TraitObjectSyntax::None);
1208 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1211 let id = self.lower_node_id(t.id);
1212 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1213 self.ty_path(id, t.span, qpath)
1216 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1217 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1220 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1221 self.ty(span, hir::TyKind::Tup(tys))
1224 fn lower_ty_direct(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> hir::Ty<'hir> {
1225 let kind = match t.kind {
1226 TyKind::Infer => hir::TyKind::Infer,
1227 TyKind::Err => hir::TyKind::Err,
1228 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1229 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1230 TyKind::Rptr(ref region, ref mt) => {
1231 let region = region.unwrap_or_else(|| {
1232 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1233 self.resolver.get_lifetime_res(t.id)
1235 debug_assert_eq!(start.plus(1), end);
1240 let span = self.tcx.sess.source_map().start_point(t.span);
1241 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1243 let lifetime = self.lower_lifetime(®ion);
1244 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1246 TyKind::BareFn(ref f) => {
1247 self.lower_lifetime_binder(t.id, &f.generic_params, |lctx, generic_params| {
1248 hir::TyKind::BareFn(lctx.arena.alloc(hir::BareFnTy {
1250 unsafety: lctx.lower_unsafety(f.unsafety),
1251 abi: lctx.lower_extern(f.ext),
1252 decl: lctx.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
1253 param_names: lctx.lower_fn_params_to_names(&f.decl),
1257 TyKind::Never => hir::TyKind::Never,
1258 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1259 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1261 TyKind::Paren(ref ty) => {
1262 return self.lower_ty_direct(ty, itctx);
1264 TyKind::Path(ref qself, ref path) => {
1265 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1267 TyKind::ImplicitSelf => {
1268 let hir_id = self.lower_node_id(t.id);
1269 let res = self.expect_full_res(t.id);
1270 let res = self.lower_res(res);
1271 hir::TyKind::Path(hir::QPath::Resolved(
1273 self.arena.alloc(hir::Path {
1275 segments: arena_vec![self; hir::PathSegment::new(
1276 Ident::with_dummy_span(kw::SelfUpper),
1280 span: self.lower_span(t.span),
1284 TyKind::Array(ref ty, ref length) => {
1285 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1287 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1288 TyKind::TraitObject(ref bounds, kind) => {
1289 let mut lifetime_bound = None;
1290 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1292 this.arena.alloc_from_iter(bounds.iter().filter_map(
1293 |bound| match *bound {
1294 GenericBound::Trait(
1296 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1297 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1298 // `~const ?Bound` will cause an error during AST validation
1299 // anyways, so treat it like `?Bound` as compilation proceeds.
1300 GenericBound::Trait(
1302 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1304 GenericBound::Outlives(ref lifetime) => {
1305 if lifetime_bound.is_none() {
1306 lifetime_bound = Some(this.lower_lifetime(lifetime));
1312 let lifetime_bound =
1313 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1314 (bounds, lifetime_bound)
1316 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1318 TyKind::ImplTrait(def_node_id, ref bounds) => {
1321 ImplTraitContext::ReturnPositionOpaqueTy { origin } => {
1322 self.lower_opaque_impl_trait(span, *origin, def_node_id, bounds, itctx)
1324 ImplTraitContext::TypeAliasesOpaqueTy => {
1325 let mut nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
1326 self.lower_opaque_impl_trait(
1328 hir::OpaqueTyOrigin::TyAlias,
1334 ImplTraitContext::Universal => {
1336 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1337 let (param, bounds, path) =
1338 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1339 self.impl_trait_defs.push(param);
1340 if let Some(bounds) = bounds {
1341 self.impl_trait_bounds.push(bounds);
1345 ImplTraitContext::Disallowed(position) => {
1346 self.tcx.sess.emit_err(MisplacedImplTrait {
1348 position: DiagnosticArgFromDisplay(&position),
1354 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1355 TyKind::CVarArgs => {
1356 self.tcx.sess.delay_span_bug(
1358 "`TyKind::CVarArgs` should have been handled elsewhere",
1364 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1367 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1368 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1369 /// HIR type that references the TAIT.
1371 /// Given a function definition like:
1374 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1379 /// we will create a TAIT definition in the HIR like
1382 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1385 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1388 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1391 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1392 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1393 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1394 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1395 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1396 #[instrument(level = "debug", skip(self), ret)]
1397 fn lower_opaque_impl_trait(
1400 origin: hir::OpaqueTyOrigin,
1401 opaque_ty_node_id: NodeId,
1402 bounds: &GenericBounds,
1403 itctx: &mut ImplTraitContext,
1404 ) -> hir::TyKind<'hir> {
1405 // Make sure we know that some funky desugaring has been going on here.
1406 // This is a first: there is code in other places like for loop
1407 // desugaring that explicitly states that we don't want to track that.
1408 // Not tracking it makes lints in rustc and clippy very fragile, as
1409 // frequently opened issues show.
1410 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1412 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1413 debug!(?opaque_ty_def_id);
1415 // Contains the new lifetime definitions created for the TAIT (if any).
1416 let mut collected_lifetimes = Vec::new();
1418 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1419 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1420 // exactly which ones those are.
1421 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1422 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1425 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1426 // we only keep the lifetimes that appear in the `impl Debug` itself:
1427 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1429 debug!(?lifetimes_to_remap);
1431 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1432 let mut new_remapping = FxHashMap::default();
1434 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1435 // in bounds), then create the new lifetime parameters required and create a mapping
1436 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1437 collected_lifetimes = lctx.create_lifetime_defs(
1439 &lifetimes_to_remap,
1442 debug!(?collected_lifetimes);
1443 debug!(?new_remapping);
1445 // Install the remapping from old to new (if any):
1446 lctx.with_remapping(new_remapping, |lctx| {
1447 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1448 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1449 // containing `&['x]`.
1450 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1451 |&(new_node_id, lifetime)| {
1452 let hir_id = lctx.lower_node_id(new_node_id);
1453 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1455 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1456 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1459 hir::ParamName::Plain(lifetime.ident),
1460 hir::LifetimeParamKind::Explicit,
1467 span: lifetime.ident.span,
1468 pure_wrt_drop: false,
1469 kind: hir::GenericParamKind::Lifetime { kind },
1474 debug!(?lifetime_defs);
1476 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1477 // get back Debug + 'a1, which is suitable for use on the TAIT.
1478 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1479 debug!(?hir_bounds);
1481 let opaque_ty_item = hir::OpaqueTy {
1482 generics: self.arena.alloc(hir::Generics {
1483 params: lifetime_defs,
1485 has_where_clause_predicates: false,
1486 where_clause_span: lctx.lower_span(span),
1487 span: lctx.lower_span(span),
1492 debug!(?opaque_ty_item);
1494 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1498 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1499 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1501 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1502 let id = self.next_node_id();
1503 let span = lifetime.ident.span;
1505 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1506 Ident::with_dummy_span(kw::UnderscoreLifetime)
1511 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1512 hir::GenericArg::Lifetime(l)
1516 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1517 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1520 /// Registers a new opaque type with the proper `NodeId`s and
1521 /// returns the lowered node-ID for the opaque type.
1522 fn generate_opaque_type(
1524 opaque_ty_id: LocalDefId,
1525 opaque_ty_item: hir::OpaqueTy<'hir>,
1527 opaque_ty_span: Span,
1528 ) -> hir::OwnerNode<'hir> {
1529 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1530 // Generate an `type Foo = impl Trait;` declaration.
1531 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1532 let opaque_ty_item = hir::Item {
1533 def_id: opaque_ty_id,
1534 ident: Ident::empty(),
1535 kind: opaque_ty_item_kind,
1536 vis_span: self.lower_span(span.shrink_to_lo()),
1537 span: self.lower_span(opaque_ty_span),
1539 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1542 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1543 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1544 /// new definition, adds it to the remapping with the definition of the given lifetime and
1545 /// returns a list of lifetimes to be lowered afterwards.
1546 fn create_lifetime_defs(
1548 parent_def_id: LocalDefId,
1549 lifetimes_in_bounds: &[Lifetime],
1550 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1551 ) -> Vec<(NodeId, Lifetime)> {
1552 let mut result = Vec::new();
1554 for lifetime in lifetimes_in_bounds {
1555 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1559 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1560 if remapping.get(&old_def_id).is_none() {
1561 let node_id = self.next_node_id();
1563 let new_def_id = self.create_def(
1566 DefPathData::LifetimeNs(lifetime.ident.name),
1568 remapping.insert(old_def_id, new_def_id);
1570 result.push((node_id, *lifetime));
1574 LifetimeRes::Fresh { param, binder: _ } => {
1575 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1576 if let Some(old_def_id) = self.opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1577 let node_id = self.next_node_id();
1579 let new_def_id = self.create_def(
1582 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1584 remapping.insert(old_def_id, new_def_id);
1586 result.push((node_id, *lifetime));
1590 LifetimeRes::Static | LifetimeRes::Error => {}
1593 let bug_msg = format!(
1594 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1595 res, lifetime.ident, lifetime.ident.span
1597 span_bug!(lifetime.ident.span, "{}", bug_msg);
1605 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1606 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1607 // as they are not explicit in HIR/Ty function signatures.
1608 // (instead, the `c_variadic` flag is set to `true`)
1609 let mut inputs = &decl.inputs[..];
1610 if decl.c_variadic() {
1611 inputs = &inputs[..inputs.len() - 1];
1613 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1614 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1615 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1619 // Lowers a function declaration.
1621 // `decl`: the unlowered (AST) function declaration.
1622 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1623 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1624 // `make_ret_async` is also `Some`.
1625 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1626 // This guards against trait declarations and implementations where `impl Trait` is
1628 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1629 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1630 // return type `impl Trait` item.
1631 #[instrument(level = "debug", skip(self))]
1635 fn_node_id: Option<NodeId>,
1637 make_ret_async: Option<NodeId>,
1638 ) -> &'hir hir::FnDecl<'hir> {
1639 let c_variadic = decl.c_variadic();
1641 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1642 // as they are not explicit in HIR/Ty function signatures.
1643 // (instead, the `c_variadic` flag is set to `true`)
1644 let mut inputs = &decl.inputs[..];
1646 inputs = &inputs[..inputs.len() - 1];
1648 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1649 if fn_node_id.is_some() {
1650 self.lower_ty_direct(¶m.ty, &mut ImplTraitContext::Universal)
1652 self.lower_ty_direct(
1654 &mut ImplTraitContext::Disallowed(match kind {
1655 FnDeclKind::Fn | FnDeclKind::Inherent => {
1656 unreachable!("fn should allow in-band lifetimes")
1658 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1659 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1660 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1661 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1662 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1668 let output = if let Some(ret_id) = make_ret_async {
1669 self.lower_async_fn_ret_ty(
1671 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1676 FnRetTy::Ty(ref ty) => {
1677 let mut context = match fn_node_id {
1678 Some(fn_node_id) if kind.impl_trait_return_allowed() => {
1679 let fn_def_id = self.local_def_id(fn_node_id);
1680 ImplTraitContext::ReturnPositionOpaqueTy {
1681 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1684 _ => ImplTraitContext::Disallowed(match kind {
1685 FnDeclKind::Fn | FnDeclKind::Inherent => {
1686 unreachable!("fn should allow in-band lifetimes")
1688 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1689 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1690 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1691 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1692 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1695 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1697 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1701 self.arena.alloc(hir::FnDecl {
1705 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1706 let is_mutable_pat = matches!(
1708 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1712 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1713 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1714 // Given we are only considering `ImplicitSelf` types, we needn't consider
1715 // the case where we have a mutable pattern to a reference as that would
1716 // no longer be an `ImplicitSelf`.
1717 TyKind::Rptr(_, ref mt)
1718 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1720 hir::ImplicitSelfKind::MutRef
1722 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1723 hir::ImplicitSelfKind::ImmRef
1725 _ => hir::ImplicitSelfKind::None,
1731 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1732 // combined with the following definition of `OpaqueTy`:
1734 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1736 // `output`: unlowered output type (`T` in `-> T`)
1737 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1738 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1739 #[instrument(level = "debug", skip(self))]
1740 fn lower_async_fn_ret_ty(
1744 opaque_ty_node_id: NodeId,
1745 ) -> hir::FnRetTy<'hir> {
1746 let span = output.span();
1748 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1750 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1751 let fn_def_id = self.local_def_id(fn_node_id);
1753 // When we create the opaque type for this async fn, it is going to have
1754 // to capture all the lifetimes involved in the signature (including in the
1755 // return type). This is done by introducing lifetime parameters for:
1757 // - all the explicitly declared lifetimes from the impl and function itself;
1758 // - all the elided lifetimes in the fn arguments;
1759 // - all the elided lifetimes in the return type.
1761 // So for example in this snippet:
1764 // impl<'a> Foo<'a> {
1765 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1766 // // ^ '0 ^ '1 ^ '2
1767 // // elided lifetimes used below
1772 // we would create an opaque type like:
1775 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1778 // and we would then desugar `bar` to the equivalent of:
1781 // impl<'a> Foo<'a> {
1782 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1786 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1787 // this is because the elided lifetimes from the return type
1788 // should be figured out using the ordinary elision rules, and
1789 // this desugaring achieves that.
1791 // Calculate all the lifetimes that should be captured
1792 // by the opaque type. This should include all in-scope
1793 // lifetime parameters, including those defined in-band.
1795 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1797 let mut collected_lifetimes = Vec::new();
1798 let mut new_remapping = FxHashMap::default();
1800 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1801 debug!(?extra_lifetime_params);
1802 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1803 let outer_def_id = self.local_def_id(outer_node_id);
1804 let inner_node_id = self.next_node_id();
1806 // Add a definition for the in scope lifetime def.
1807 let inner_def_id = self.create_def(
1810 DefPathData::LifetimeNs(ident.name),
1812 new_remapping.insert(outer_def_id, inner_def_id);
1814 let inner_res = match outer_res {
1815 // Input lifetime like `'a`:
1816 LifetimeRes::Param { param, .. } => {
1817 LifetimeRes::Param { param, binder: fn_node_id }
1819 // Input lifetime like `'1`:
1820 LifetimeRes::Fresh { param, .. } => {
1821 LifetimeRes::Fresh { param, binder: fn_node_id }
1823 LifetimeRes::Static | LifetimeRes::Error => continue,
1826 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1827 res, ident, ident.span
1832 let lifetime = Lifetime { id: outer_node_id, ident };
1833 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1836 debug!(?collected_lifetimes);
1838 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1839 // find out exactly which ones those are.
1840 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1841 // we only keep the lifetimes that appear in the `impl Debug` itself:
1842 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1843 debug!(?lifetimes_to_remap);
1845 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1846 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1847 // in bounds), then create the new lifetime parameters required and create a mapping
1848 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1849 collected_lifetimes.extend(
1850 this.create_lifetime_defs(
1852 &lifetimes_to_remap,
1856 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1858 debug!(?collected_lifetimes);
1859 debug!(?new_remapping);
1861 // Install the remapping from old to new (if any):
1862 this.with_remapping(new_remapping, |this| {
1863 // We have to be careful to get elision right here. The
1864 // idea is that we create a lifetime parameter for each
1865 // lifetime in the return type. So, given a return type
1866 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1867 // Future<Output = &'1 [ &'2 u32 ]>`.
1869 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1870 // hence the elision takes place at the fn site.
1872 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span);
1874 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1875 |&(new_node_id, lifetime, _)| {
1876 let hir_id = this.lower_node_id(new_node_id);
1877 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1879 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1880 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1883 hir::ParamName::Plain(lifetime.ident),
1884 hir::LifetimeParamKind::Explicit,
1891 span: lifetime.ident.span,
1892 pure_wrt_drop: false,
1893 kind: hir::GenericParamKind::Lifetime { kind },
1898 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1900 let opaque_ty_item = hir::OpaqueTy {
1901 generics: this.arena.alloc(hir::Generics {
1902 params: generic_params,
1904 has_where_clause_predicates: false,
1905 where_clause_span: this.lower_span(span),
1906 span: this.lower_span(span),
1908 bounds: arena_vec![this; future_bound],
1909 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1912 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1913 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1917 // As documented above, we need to create the lifetime
1918 // arguments to our opaque type. Continuing with our example,
1919 // we're creating the type arguments for the return type:
1922 // Bar<'a, 'b, '0, '1, '_>
1925 // For the "input" lifetime parameters, we wish to create
1926 // references to the parameters themselves, including the
1927 // "implicit" ones created from parameter types (`'a`, `'b`,
1930 // For the "output" lifetime parameters, we just want to
1932 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
1933 |(_, lifetime, res)| {
1934 let id = self.next_node_id();
1935 let span = lifetime.ident.span;
1937 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1938 Ident::with_dummy_span(kw::UnderscoreLifetime)
1943 let res = res.unwrap_or(
1944 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
1946 let l = self.new_named_lifetime_with_res(id, span, ident, res);
1947 hir::GenericArg::Lifetime(l)
1951 // Create the `Foo<...>` reference itself. Note that the `type
1952 // Foo = impl Trait` is, internally, created as a child of the
1953 // async fn, so the *type parameters* are inherited. It's
1954 // only the lifetime parameters that we must supply.
1956 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
1957 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1958 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
1961 /// Transforms `-> T` into `Future<Output = T>`.
1962 fn lower_async_fn_output_type_to_future_bound(
1965 fn_def_id: LocalDefId,
1967 ) -> hir::GenericBound<'hir> {
1968 // Compute the `T` in `Future<Output = T>` from the return type.
1969 let output_ty = match output {
1970 FnRetTy::Ty(ty) => {
1971 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
1972 // `impl Future` opaque type that `async fn` implicitly
1974 let mut context = ImplTraitContext::ReturnPositionOpaqueTy {
1975 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1977 self.lower_ty(ty, &mut context)
1979 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1983 let future_args = self.arena.alloc(hir::GenericArgs {
1985 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1986 parenthesized: false,
1990 hir::GenericBound::LangItemTrait(
1991 // ::std::future::Future<future_params>
1992 hir::LangItem::Future,
1993 self.lower_span(span),
1999 #[instrument(level = "trace", skip(self))]
2000 fn lower_param_bound(
2003 itctx: &mut ImplTraitContext,
2004 ) -> hir::GenericBound<'hir> {
2006 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2007 self.lower_poly_trait_ref(p, itctx),
2008 self.lower_trait_bound_modifier(*modifier),
2010 GenericBound::Outlives(lifetime) => {
2011 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2016 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2017 let span = self.lower_span(l.ident.span);
2018 let ident = self.lower_ident(l.ident);
2019 self.new_named_lifetime(l.id, l.id, span, ident)
2022 #[instrument(level = "debug", skip(self))]
2023 fn new_named_lifetime_with_res(
2029 ) -> hir::Lifetime {
2030 let name = match res {
2031 LifetimeRes::Param { param, .. } => {
2032 let p_name = ParamName::Plain(ident);
2033 let param = self.get_remapped_def_id(param);
2035 hir::LifetimeName::Param(param, p_name)
2037 LifetimeRes::Fresh { param, .. } => {
2038 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2039 let param = self.local_def_id(param);
2041 hir::LifetimeName::Param(param, ParamName::Fresh)
2043 LifetimeRes::Infer => hir::LifetimeName::Infer,
2044 LifetimeRes::Static => hir::LifetimeName::Static,
2045 LifetimeRes::Error => hir::LifetimeName::Error,
2046 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2050 hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
2053 #[instrument(level = "debug", skip(self))]
2054 fn new_named_lifetime(
2060 ) -> hir::Lifetime {
2061 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2062 self.new_named_lifetime_with_res(new_id, span, ident, res)
2065 fn lower_generic_params_mut<'s>(
2067 params: &'s [GenericParam],
2068 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2069 params.iter().map(move |param| self.lower_generic_param(param))
2072 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2073 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2076 #[instrument(level = "trace", skip(self))]
2077 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2078 let (name, kind) = self.lower_generic_param_kind(param);
2080 let hir_id = self.lower_node_id(param.id);
2081 self.lower_attrs(hir_id, ¶m.attrs);
2085 span: self.lower_span(param.span()),
2086 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2088 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2092 fn lower_generic_param_kind(
2094 param: &GenericParam,
2095 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2097 GenericParamKind::Lifetime => {
2098 // AST resolution emitted an error on those parameters, so we lower them using
2099 // `ParamName::Error`.
2101 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2104 let ident = self.lower_ident(param.ident);
2105 ParamName::Plain(ident)
2108 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2112 GenericParamKind::Type { ref default, .. } => {
2113 let kind = hir::GenericParamKind::Type {
2114 default: default.as_ref().map(|x| {
2115 self.lower_ty(x, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2120 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2122 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2124 self.lower_ty(&ty, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2125 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2127 hir::ParamName::Plain(self.lower_ident(param.ident)),
2128 hir::GenericParamKind::Const { ty, default },
2137 itctx: &mut ImplTraitContext,
2138 ) -> hir::TraitRef<'hir> {
2139 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2140 hir::QPath::Resolved(None, path) => path,
2141 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2143 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2146 #[instrument(level = "debug", skip(self))]
2147 fn lower_poly_trait_ref(
2150 itctx: &mut ImplTraitContext,
2151 ) -> hir::PolyTraitRef<'hir> {
2152 self.lower_lifetime_binder(
2154 &p.bound_generic_params,
2155 |lctx, bound_generic_params| {
2156 let trait_ref = lctx.lower_trait_ref(&p.trait_ref, itctx);
2157 hir::PolyTraitRef { bound_generic_params, trait_ref, span: lctx.lower_span(p.span) }
2162 fn lower_mt(&mut self, mt: &MutTy, itctx: &mut ImplTraitContext) -> hir::MutTy<'hir> {
2163 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2166 #[instrument(level = "debug", skip(self), ret)]
2167 fn lower_param_bounds(
2169 bounds: &[GenericBound],
2170 itctx: &mut ImplTraitContext,
2171 ) -> hir::GenericBounds<'hir> {
2172 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2175 fn lower_param_bounds_mut<'s, 'b>(
2177 bounds: &'s [GenericBound],
2178 itctx: &'b mut ImplTraitContext,
2179 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> + Captures<'b>
2181 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2184 #[instrument(level = "debug", skip(self), ret)]
2185 fn lower_generic_and_bounds(
2190 bounds: &[GenericBound],
2191 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2192 // Add a definition for the in-band `Param`.
2193 let def_id = self.local_def_id(node_id);
2195 // Set the name to `impl Bound1 + Bound2`.
2196 let param = hir::GenericParam {
2197 hir_id: self.lower_node_id(node_id),
2198 name: ParamName::Plain(self.lower_ident(ident)),
2199 pure_wrt_drop: false,
2200 span: self.lower_span(span),
2201 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2205 let preds = self.lower_generic_bound_predicate(
2208 &GenericParamKind::Type { default: None },
2210 &mut ImplTraitContext::Universal,
2211 hir::PredicateOrigin::ImplTrait,
2214 let hir_id = self.next_id();
2215 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2216 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2218 self.arena.alloc(hir::Path {
2219 span: self.lower_span(span),
2222 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2229 /// Lowers a block directly to an expression, presuming that it
2230 /// has no attributes and is not targeted by a `break`.
2231 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2232 let block = self.lower_block(b, false);
2233 self.expr_block(block, AttrVec::new())
2236 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2237 match c.value.kind {
2238 ExprKind::Underscore => {
2239 if self.tcx.features().generic_arg_infer {
2240 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2243 &self.tcx.sess.parse_sess,
2244 sym::generic_arg_infer,
2246 "using `_` for array lengths is unstable",
2248 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2249 hir::ArrayLen::Body(self.lower_anon_const(c))
2252 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2256 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2257 self.with_new_scopes(|this| hir::AnonConst {
2258 hir_id: this.lower_node_id(c.id),
2259 body: this.lower_const_body(c.value.span, Some(&c.value)),
2263 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2265 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2266 UserProvided => hir::UnsafeSource::UserProvided,
2270 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2272 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2273 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2275 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2276 // placeholder for compilation to proceed.
2277 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2278 hir::TraitBoundModifier::Maybe
2283 // Helper methods for building HIR.
2285 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2286 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2289 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2290 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2295 attrs: Option<&'hir [Attribute]>,
2297 init: Option<&'hir hir::Expr<'hir>>,
2298 pat: &'hir hir::Pat<'hir>,
2299 source: hir::LocalSource,
2300 ) -> hir::Stmt<'hir> {
2301 let hir_id = self.next_id();
2302 if let Some(a) = attrs {
2303 debug_assert!(!a.is_empty());
2304 self.attrs.insert(hir_id.local_id, a);
2306 let local = hir::Local {
2312 span: self.lower_span(span),
2315 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2318 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2319 self.block_all(expr.span, &[], Some(expr))
2325 stmts: &'hir [hir::Stmt<'hir>],
2326 expr: Option<&'hir hir::Expr<'hir>>,
2327 ) -> &'hir hir::Block<'hir> {
2328 let blk = hir::Block {
2331 hir_id: self.next_id(),
2332 rules: hir::BlockCheckMode::DefaultBlock,
2333 span: self.lower_span(span),
2334 targeted_by_break: false,
2336 self.arena.alloc(blk)
2339 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2340 let field = self.single_pat_field(span, pat);
2341 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2344 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2345 let field = self.single_pat_field(span, pat);
2346 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2349 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2350 let field = self.single_pat_field(span, pat);
2351 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2354 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2355 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2358 fn single_pat_field(
2361 pat: &'hir hir::Pat<'hir>,
2362 ) -> &'hir [hir::PatField<'hir>] {
2363 let field = hir::PatField {
2364 hir_id: self.next_id(),
2365 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2366 is_shorthand: false,
2368 span: self.lower_span(span),
2370 arena_vec![self; field]
2373 fn pat_lang_item_variant(
2376 lang_item: hir::LangItem,
2377 fields: &'hir [hir::PatField<'hir>],
2378 hir_id: Option<hir::HirId>,
2379 ) -> &'hir hir::Pat<'hir> {
2380 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2381 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2384 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2385 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2388 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2389 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2392 fn pat_ident_binding_mode(
2396 bm: hir::BindingAnnotation,
2397 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2398 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2399 (self.arena.alloc(pat), hir_id)
2402 fn pat_ident_binding_mode_mut(
2406 bm: hir::BindingAnnotation,
2407 ) -> (hir::Pat<'hir>, hir::HirId) {
2408 let hir_id = self.next_id();
2413 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2414 span: self.lower_span(span),
2415 default_binding_modes: true,
2421 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2422 self.arena.alloc(hir::Pat {
2423 hir_id: self.next_id(),
2425 span: self.lower_span(span),
2426 default_binding_modes: true,
2430 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2432 hir_id: self.next_id(),
2434 span: self.lower_span(span),
2435 default_binding_modes: false,
2441 mut hir_id: hir::HirId,
2443 qpath: hir::QPath<'hir>,
2444 ) -> hir::Ty<'hir> {
2445 let kind = match qpath {
2446 hir::QPath::Resolved(None, path) => {
2447 // Turn trait object paths into `TyKind::TraitObject` instead.
2449 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2450 let principal = hir::PolyTraitRef {
2451 bound_generic_params: &[],
2452 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2453 span: self.lower_span(span),
2456 // The original ID is taken by the `PolyTraitRef`,
2457 // so the `Ty` itself needs a different one.
2458 hir_id = self.next_id();
2459 hir::TyKind::TraitObject(
2460 arena_vec![self; principal],
2461 self.elided_dyn_bound(span),
2462 TraitObjectSyntax::None,
2465 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2468 _ => hir::TyKind::Path(qpath),
2471 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2474 /// Invoked to create the lifetime argument(s) for an elided trait object
2475 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2476 /// when the bound is written, even if it is written with `'_` like in
2477 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2478 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2479 let r = hir::Lifetime {
2480 hir_id: self.next_id(),
2481 span: self.lower_span(span),
2482 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2484 debug!("elided_dyn_bound: r={:?}", r);
2489 /// Helper struct for delayed construction of GenericArgs.
2490 struct GenericArgsCtor<'hir> {
2491 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2492 bindings: &'hir [hir::TypeBinding<'hir>],
2493 parenthesized: bool,
2497 impl<'hir> GenericArgsCtor<'hir> {
2498 fn is_empty(&self) -> bool {
2499 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2502 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2503 let ga = hir::GenericArgs {
2504 args: this.arena.alloc_from_iter(self.args),
2505 bindings: self.bindings,
2506 parenthesized: self.parenthesized,
2507 span_ext: this.lower_span(self.span),
2509 this.arena.alloc(ga)