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 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
664 assert_ne!(ast_node_id, DUMMY_NODE_ID);
666 match self.node_id_to_local_id.entry(ast_node_id) {
667 Entry::Occupied(o) => {
668 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
670 Entry::Vacant(v) => {
671 // Generate a new `HirId`.
672 let owner = self.current_hir_id_owner;
673 let local_id = self.item_local_id_counter;
674 let hir_id = hir::HirId { owner, local_id };
677 self.item_local_id_counter.increment_by(1);
679 assert_ne!(local_id, hir::ItemLocalId::new(0));
680 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
681 // Do not override a `MaybeOwner::Owner` that may already here.
682 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
683 self.local_id_to_def_id.insert(local_id, def_id);
686 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
687 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
695 /// Generate a new `HirId` without a backing `NodeId`.
696 fn next_id(&mut self) -> hir::HirId {
697 let owner = self.current_hir_id_owner;
698 let local_id = self.item_local_id_counter;
699 assert_ne!(local_id, hir::ItemLocalId::new(0));
700 self.item_local_id_counter.increment_by(1);
701 hir::HirId { owner, local_id }
704 #[instrument(level = "trace", skip(self))]
705 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
706 let res: Result<Res, ()> = res.apply_id(|id| {
707 let owner = self.current_hir_id_owner;
708 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
709 Ok(hir::HirId { owner, local_id })
713 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
714 // This can happen when trying to lower the return type `x` in erroneous code like
715 // async fn foo(x: u8) -> x {}
716 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
717 // an opaque type as a synthesized HIR owner.
718 res.unwrap_or(Res::Err)
721 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
722 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
723 if pr.unresolved_segments() != 0 {
724 panic!("path not fully resolved: {:?}", pr);
730 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
731 self.resolver.get_import_res(id).present_items()
734 fn diagnostic(&self) -> &Handler {
735 self.tcx.sess.diagnostic()
738 /// Reuses the span but adds information like the kind of the desugaring and features that are
739 /// allowed inside this span.
740 fn mark_span_with_reason(
742 reason: DesugaringKind,
744 allow_internal_unstable: Option<Lrc<[Symbol]>>,
746 self.tcx.with_stable_hashing_context(|hcx| {
747 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
751 /// Intercept all spans entering HIR.
752 /// Mark a span as relative to the current owning item.
753 fn lower_span(&self, span: Span) -> Span {
754 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
755 span.with_parent(Some(self.current_hir_id_owner))
757 // Do not make spans relative when not using incremental compilation.
762 fn lower_ident(&self, ident: Ident) -> Ident {
763 Ident::new(ident.name, self.lower_span(ident.span))
766 /// Converts a lifetime into a new generic parameter.
767 #[instrument(level = "debug", skip(self))]
768 fn lifetime_res_to_generic_param(
773 ) -> Option<hir::GenericParam<'hir>> {
774 let (name, kind) = match res {
775 LifetimeRes::Param { .. } => {
776 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
778 LifetimeRes::Fresh { param, .. } => {
779 // Late resolution delegates to us the creation of the `LocalDefId`.
780 let _def_id = self.create_def(
781 self.current_hir_id_owner,
783 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
787 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
789 LifetimeRes::Static | LifetimeRes::Error => return None,
791 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
792 res, ident, ident.span
795 let hir_id = self.lower_node_id(node_id);
796 Some(hir::GenericParam {
799 span: self.lower_span(ident.span),
800 pure_wrt_drop: false,
801 kind: hir::GenericParamKind::Lifetime { kind },
806 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
807 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
808 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
809 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
810 /// parameters will be successful.
811 #[instrument(level = "debug", skip(self))]
813 fn lower_lifetime_binder(
816 generic_params: &[GenericParam],
817 ) -> &'hir [hir::GenericParam<'hir>] {
818 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
819 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
820 debug!(?extra_lifetimes);
821 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
822 self.lifetime_res_to_generic_param(ident, node_id, res)
824 let generic_params = self.arena.alloc_from_iter(generic_params);
825 debug!(?generic_params);
830 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
831 let was_in_dyn_type = self.is_in_dyn_type;
832 self.is_in_dyn_type = in_scope;
834 let result = f(self);
836 self.is_in_dyn_type = was_in_dyn_type;
841 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
842 let was_in_loop_condition = self.is_in_loop_condition;
843 self.is_in_loop_condition = false;
845 let catch_scope = self.catch_scope.take();
846 let loop_scope = self.loop_scope.take();
848 self.catch_scope = catch_scope;
849 self.loop_scope = loop_scope;
851 self.is_in_loop_condition = was_in_loop_condition;
856 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
857 if attrs.is_empty() {
860 debug_assert_eq!(id.owner, self.current_hir_id_owner);
861 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
862 debug_assert!(!ret.is_empty());
863 self.attrs.insert(id.local_id, ret);
868 fn lower_attr(&self, attr: &Attribute) -> Attribute {
869 // Note that we explicitly do not walk the path. Since we don't really
870 // lower attributes (we use the AST version) there is nowhere to keep
871 // the `HirId`s. We don't actually need HIR version of attributes anyway.
872 // Tokens are also not needed after macro expansion and parsing.
873 let kind = match attr.kind {
874 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
876 path: normal.item.path.clone(),
877 args: self.lower_mac_args(&normal.item.args),
882 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
885 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
888 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
889 debug_assert_eq!(id.owner, self.current_hir_id_owner);
890 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
891 if let Some(&a) = self.attrs.get(&target_id.local_id) {
892 debug_assert!(!a.is_empty());
893 self.attrs.insert(id.local_id, a);
897 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
899 MacArgs::Empty => MacArgs::Empty,
900 MacArgs::Delimited(dspan, delim, ref tokens) => {
901 // This is either a non-key-value attribute, or a `macro_rules!` body.
902 // We either not have any nonterminals present (in the case of an attribute),
903 // or have tokens available for all nonterminals in the case of a nested
904 // `macro_rules`: e.g:
907 // macro_rules! outer {
909 // macro_rules! inner {
916 // In both cases, we don't want to synthesize any tokens
917 MacArgs::Delimited(dspan, delim, tokens.flattened())
919 // This is an inert key-value attribute - it will never be visible to macros
920 // after it gets lowered to HIR. Therefore, we can extract literals to handle
921 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
922 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
923 // In valid code the value always ends up as a single literal. Otherwise, a dummy
924 // literal suffices because the error is handled elsewhere.
925 let lit = if let ExprKind::Lit(lit) = &expr.kind {
929 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
934 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
936 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
937 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
942 /// Given an associated type constraint like one of these:
944 /// ```ignore (illustrative)
945 /// T: Iterator<Item: Debug>
947 /// T: Iterator<Item = Debug>
951 /// returns a `hir::TypeBinding` representing `Item`.
952 #[instrument(level = "debug", skip(self))]
953 fn lower_assoc_ty_constraint(
955 constraint: &AssocConstraint,
956 itctx: ImplTraitContext,
957 ) -> hir::TypeBinding<'hir> {
958 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
959 // lower generic arguments of identifier in constraint
960 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
961 let gen_args_ctor = match gen_args {
962 GenericArgs::AngleBracketed(ref data) => {
963 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
965 GenericArgs::Parenthesized(ref data) => {
966 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
967 self.lower_angle_bracketed_parameter_data(
968 &data.as_angle_bracketed_args(),
975 gen_args_ctor.into_generic_args(self)
977 self.arena.alloc(hir::GenericArgs::none())
980 let kind = match constraint.kind {
981 AssocConstraintKind::Equality { ref term } => {
982 let term = match term {
983 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
984 Term::Const(ref c) => self.lower_anon_const(c).into(),
986 hir::TypeBindingKind::Equality { term }
988 AssocConstraintKind::Bound { ref bounds } => {
989 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
990 let (desugar_to_impl_trait, itctx) = match itctx {
991 // We are in the return position:
993 // fn foo() -> impl Iterator<Item: Debug>
997 // fn foo() -> impl Iterator<Item = impl Debug>
998 ImplTraitContext::ReturnPositionOpaqueTy { .. }
999 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1001 // We are in the argument position, but within a dyn type:
1003 // fn foo(x: dyn Iterator<Item: Debug>)
1007 // fn foo(x: dyn Iterator<Item = impl Debug>)
1008 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1010 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1011 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1012 // "impl trait context" to permit `impl Debug` in this position (it desugars
1013 // then to an opaque type).
1015 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1016 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1017 (true, ImplTraitContext::TypeAliasesOpaqueTy)
1020 // We are in the parameter position, but not within a dyn type:
1022 // fn foo(x: impl Iterator<Item: Debug>)
1024 // so we leave it as is and this gets expanded in astconv to a bound like
1025 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1027 _ => (false, itctx),
1030 if desugar_to_impl_trait {
1031 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1032 // constructing the HIR for `impl bounds...` and then lowering that.
1034 let parent_def_id = self.current_hir_id_owner;
1035 let impl_trait_node_id = self.next_node_id();
1036 self.create_def(parent_def_id, impl_trait_node_id, DefPathData::ImplTrait);
1038 self.with_dyn_type_scope(false, |this| {
1039 let node_id = this.next_node_id();
1040 let ty = this.lower_ty(
1043 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1044 span: this.lower_span(constraint.span),
1050 hir::TypeBindingKind::Equality { term: ty.into() }
1053 // Desugar `AssocTy: Bounds` into a type binding where the
1054 // later desugars into a trait predicate.
1055 let bounds = self.lower_param_bounds(bounds, itctx);
1057 hir::TypeBindingKind::Constraint { bounds }
1063 hir_id: self.lower_node_id(constraint.id),
1064 ident: self.lower_ident(constraint.ident),
1067 span: self.lower_span(constraint.span),
1071 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1072 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1073 let sub = if data.inputs.is_empty() {
1074 let parentheses_span =
1075 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1076 AssocTyParenthesesSub::Empty { parentheses_span }
1078 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1080 // Start of parameters to the 1st argument
1081 let open_param = data.inputs_span.shrink_to_lo().to(data
1087 // End of last argument to end of parameters
1089 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1090 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1092 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1095 #[instrument(level = "debug", skip(self))]
1096 fn lower_generic_arg(
1098 arg: &ast::GenericArg,
1099 itctx: ImplTraitContext,
1100 ) -> hir::GenericArg<'hir> {
1102 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1103 ast::GenericArg::Type(ty) => {
1105 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1106 return GenericArg::Infer(hir::InferArg {
1107 hir_id: self.lower_node_id(ty.id),
1108 span: self.lower_span(ty.span),
1111 // We parse const arguments as path types as we cannot distinguish them during
1112 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1113 // type and value namespaces. If we resolved the path in the value namespace, we
1114 // transform it into a generic const argument.
1115 TyKind::Path(ref qself, ref path) => {
1116 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1117 let res = partial_res.base_res();
1118 if !res.matches_ns(Namespace::TypeNS) {
1120 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1124 // Construct an AnonConst where the expr is the "ty"'s path.
1126 let parent_def_id = self.current_hir_id_owner;
1127 let node_id = self.next_node_id();
1129 // Add a definition for the in-band const def.
1130 self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
1132 let span = self.lower_span(ty.span);
1133 let path_expr = Expr {
1135 kind: ExprKind::Path(qself.clone(), path.clone()),
1137 attrs: AttrVec::new(),
1141 let ct = self.with_new_scopes(|this| hir::AnonConst {
1142 hir_id: this.lower_node_id(node_id),
1143 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1145 return GenericArg::Const(ConstArg { value: ct, span });
1151 GenericArg::Type(self.lower_ty(&ty, itctx))
1153 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1154 value: self.lower_anon_const(&ct),
1155 span: self.lower_span(ct.value.span),
1160 #[instrument(level = "debug", skip(self))]
1161 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext) -> &'hir hir::Ty<'hir> {
1162 self.arena.alloc(self.lower_ty_direct(t, itctx))
1168 qself: &Option<QSelf>,
1170 param_mode: ParamMode,
1171 itctx: ImplTraitContext,
1172 ) -> hir::Ty<'hir> {
1173 // Check whether we should interpret this as a bare trait object.
1174 // This check mirrors the one in late resolution. We only introduce this special case in
1175 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1176 // The other cases when a qpath should be opportunistically made a trait object are handled
1179 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1180 && partial_res.unresolved_segments() == 0
1181 && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
1183 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1184 let bound = this.lower_poly_trait_ref(
1186 bound_generic_params: vec![],
1187 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1192 let bounds = this.arena.alloc_from_iter([bound]);
1193 let lifetime_bound = this.elided_dyn_bound(t.span);
1194 (bounds, lifetime_bound)
1196 let kind = hir::TyKind::TraitObject(bounds, lifetime_bound, TraitObjectSyntax::None);
1197 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1200 let id = self.lower_node_id(t.id);
1201 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1202 self.ty_path(id, t.span, qpath)
1205 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1206 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1209 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1210 self.ty(span, hir::TyKind::Tup(tys))
1213 fn lower_ty_direct(&mut self, t: &Ty, itctx: ImplTraitContext) -> hir::Ty<'hir> {
1214 let kind = match t.kind {
1215 TyKind::Infer => hir::TyKind::Infer,
1216 TyKind::Err => hir::TyKind::Err,
1217 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1218 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1219 TyKind::Rptr(ref region, ref mt) => {
1220 let region = region.unwrap_or_else(|| {
1221 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1222 self.resolver.get_lifetime_res(t.id)
1224 debug_assert_eq!(start.plus(1), end);
1229 let span = self.tcx.sess.source_map().start_point(t.span);
1230 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1232 let lifetime = self.lower_lifetime(®ion);
1233 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1235 TyKind::BareFn(ref f) => {
1236 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
1237 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
1239 unsafety: self.lower_unsafety(f.unsafety),
1240 abi: self.lower_extern(f.ext),
1241 decl: self.lower_fn_decl(&f.decl, None, FnDeclKind::Pointer, None),
1242 param_names: self.lower_fn_params_to_names(&f.decl),
1245 TyKind::Never => hir::TyKind::Never,
1246 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1247 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1249 TyKind::Paren(ref ty) => {
1250 return self.lower_ty_direct(ty, itctx);
1252 TyKind::Path(ref qself, ref path) => {
1253 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1255 TyKind::ImplicitSelf => {
1256 let hir_id = self.lower_node_id(t.id);
1257 let res = self.expect_full_res(t.id);
1258 let res = self.lower_res(res);
1259 hir::TyKind::Path(hir::QPath::Resolved(
1261 self.arena.alloc(hir::Path {
1263 segments: arena_vec![self; hir::PathSegment::new(
1264 Ident::with_dummy_span(kw::SelfUpper),
1268 span: self.lower_span(t.span),
1272 TyKind::Array(ref ty, ref length) => {
1273 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1275 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1276 TyKind::TraitObject(ref bounds, kind) => {
1277 let mut lifetime_bound = None;
1278 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1280 this.arena.alloc_from_iter(bounds.iter().filter_map(
1281 |bound| match *bound {
1282 GenericBound::Trait(
1284 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1285 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1286 // `~const ?Bound` will cause an error during AST validation
1287 // anyways, so treat it like `?Bound` as compilation proceeds.
1288 GenericBound::Trait(
1290 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1292 GenericBound::Outlives(ref lifetime) => {
1293 if lifetime_bound.is_none() {
1294 lifetime_bound = Some(this.lower_lifetime(lifetime));
1300 let lifetime_bound =
1301 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1302 (bounds, lifetime_bound)
1304 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1306 TyKind::ImplTrait(def_node_id, ref bounds) => {
1309 ImplTraitContext::ReturnPositionOpaqueTy { origin } => {
1310 self.lower_opaque_impl_trait(span, origin, def_node_id, bounds, itctx)
1312 ImplTraitContext::TypeAliasesOpaqueTy => {
1313 let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
1314 self.lower_opaque_impl_trait(
1316 hir::OpaqueTyOrigin::TyAlias,
1322 ImplTraitContext::Universal => {
1324 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1325 let (param, bounds, path) =
1326 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1327 self.impl_trait_defs.push(param);
1328 if let Some(bounds) = bounds {
1329 self.impl_trait_bounds.push(bounds);
1333 ImplTraitContext::Disallowed(position) => {
1334 self.tcx.sess.emit_err(MisplacedImplTrait {
1336 position: DiagnosticArgFromDisplay(&position),
1342 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1343 TyKind::CVarArgs => {
1344 self.tcx.sess.delay_span_bug(
1346 "`TyKind::CVarArgs` should have been handled elsewhere",
1352 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1355 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1356 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1357 /// HIR type that references the TAIT.
1359 /// Given a function definition like:
1362 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1367 /// we will create a TAIT definition in the HIR like
1370 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1373 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1376 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1379 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1380 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1381 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1382 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1383 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1384 #[instrument(level = "debug", skip(self))]
1385 fn lower_opaque_impl_trait(
1388 origin: hir::OpaqueTyOrigin,
1389 opaque_ty_node_id: NodeId,
1390 bounds: &GenericBounds,
1391 itctx: ImplTraitContext,
1392 ) -> hir::TyKind<'hir> {
1393 // Make sure we know that some funky desugaring has been going on here.
1394 // This is a first: there is code in other places like for loop
1395 // desugaring that explicitly states that we don't want to track that.
1396 // Not tracking it makes lints in rustc and clippy very fragile, as
1397 // frequently opened issues show.
1398 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1400 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1401 debug!(?opaque_ty_def_id);
1403 // Contains the new lifetime definitions created for the TAIT (if any).
1404 let mut collected_lifetimes = Vec::new();
1406 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1407 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1408 // exactly which ones those are.
1409 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1410 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1413 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1414 // we only keep the lifetimes that appear in the `impl Debug` itself:
1415 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1417 debug!(?lifetimes_to_remap);
1419 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1420 let mut new_remapping = FxHashMap::default();
1422 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1423 // in bounds), then create the new lifetime parameters required and create a mapping
1424 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1425 collected_lifetimes = lctx.create_lifetime_defs(
1427 &lifetimes_to_remap,
1430 debug!(?collected_lifetimes);
1431 debug!(?new_remapping);
1433 // Install the remapping from old to new (if any):
1434 lctx.with_remapping(new_remapping, |lctx| {
1435 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1436 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1437 // containing `&['x]`.
1438 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1439 |&(new_node_id, lifetime)| {
1440 let hir_id = lctx.lower_node_id(new_node_id);
1441 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1443 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1444 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1447 hir::ParamName::Plain(lifetime.ident),
1448 hir::LifetimeParamKind::Explicit,
1455 span: lifetime.ident.span,
1456 pure_wrt_drop: false,
1457 kind: hir::GenericParamKind::Lifetime { kind },
1462 debug!(?lifetime_defs);
1464 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1465 // get back Debug + 'a1, which is suitable for use on the TAIT.
1466 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1467 debug!(?hir_bounds);
1469 let opaque_ty_item = hir::OpaqueTy {
1470 generics: self.arena.alloc(hir::Generics {
1471 params: lifetime_defs,
1473 has_where_clause_predicates: false,
1474 where_clause_span: lctx.lower_span(span),
1475 span: lctx.lower_span(span),
1480 debug!(?opaque_ty_item);
1482 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1486 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1487 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1489 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1490 let id = self.next_node_id();
1491 let span = lifetime.ident.span;
1493 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1494 Ident::with_dummy_span(kw::UnderscoreLifetime)
1499 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1500 hir::GenericArg::Lifetime(l)
1504 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1505 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1508 /// Registers a new opaque type with the proper `NodeId`s and
1509 /// returns the lowered node-ID for the opaque type.
1510 fn generate_opaque_type(
1512 opaque_ty_id: LocalDefId,
1513 opaque_ty_item: hir::OpaqueTy<'hir>,
1515 opaque_ty_span: Span,
1516 ) -> hir::OwnerNode<'hir> {
1517 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1518 // Generate an `type Foo = impl Trait;` declaration.
1519 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1520 let opaque_ty_item = hir::Item {
1521 def_id: opaque_ty_id,
1522 ident: Ident::empty(),
1523 kind: opaque_ty_item_kind,
1524 vis_span: self.lower_span(span.shrink_to_lo()),
1525 span: self.lower_span(opaque_ty_span),
1527 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1530 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1531 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1532 /// new definition, adds it to the remapping with the definition of the given lifetime and
1533 /// returns a list of lifetimes to be lowered afterwards.
1534 fn create_lifetime_defs(
1536 parent_def_id: LocalDefId,
1537 lifetimes_in_bounds: &[Lifetime],
1538 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1539 ) -> Vec<(NodeId, Lifetime)> {
1540 let mut result = Vec::new();
1542 for lifetime in lifetimes_in_bounds {
1543 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1547 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1548 if remapping.get(&old_def_id).is_none() {
1549 let node_id = self.next_node_id();
1551 let new_def_id = self.create_def(
1554 DefPathData::LifetimeNs(lifetime.ident.name),
1556 remapping.insert(old_def_id, new_def_id);
1558 result.push((node_id, *lifetime));
1562 LifetimeRes::Fresh { param, binder: _ } => {
1563 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1564 let old_def_id = self.local_def_id(param);
1565 if remapping.get(&old_def_id).is_none() {
1566 let node_id = self.next_node_id();
1568 let new_def_id = self.create_def(
1571 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1573 remapping.insert(old_def_id, new_def_id);
1575 result.push((node_id, *lifetime));
1579 LifetimeRes::Static | LifetimeRes::Error => {}
1582 let bug_msg = format!(
1583 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1584 res, lifetime.ident, lifetime.ident.span
1586 span_bug!(lifetime.ident.span, "{}", bug_msg);
1594 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1595 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1596 // as they are not explicit in HIR/Ty function signatures.
1597 // (instead, the `c_variadic` flag is set to `true`)
1598 let mut inputs = &decl.inputs[..];
1599 if decl.c_variadic() {
1600 inputs = &inputs[..inputs.len() - 1];
1602 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1603 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1604 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1608 // Lowers a function declaration.
1610 // `decl`: the unlowered (AST) function declaration.
1611 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1612 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1613 // `make_ret_async` is also `Some`.
1614 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1615 // This guards against trait declarations and implementations where `impl Trait` is
1617 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1618 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1619 // return type `impl Trait` item.
1620 #[instrument(level = "debug", skip(self))]
1624 fn_node_id: Option<NodeId>,
1626 make_ret_async: Option<NodeId>,
1627 ) -> &'hir hir::FnDecl<'hir> {
1628 let c_variadic = decl.c_variadic();
1630 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1631 // as they are not explicit in HIR/Ty function signatures.
1632 // (instead, the `c_variadic` flag is set to `true`)
1633 let mut inputs = &decl.inputs[..];
1635 inputs = &inputs[..inputs.len() - 1];
1637 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1638 if fn_node_id.is_some() {
1639 self.lower_ty_direct(¶m.ty, ImplTraitContext::Universal)
1641 self.lower_ty_direct(
1643 ImplTraitContext::Disallowed(match kind {
1644 FnDeclKind::Fn | FnDeclKind::Inherent => {
1645 unreachable!("fn should allow in-band lifetimes")
1647 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1648 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1649 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1650 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1651 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1657 let output = if let Some(ret_id) = make_ret_async {
1658 self.lower_async_fn_ret_ty(
1660 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1665 FnRetTy::Ty(ref ty) => {
1666 let context = match fn_node_id {
1667 Some(fn_node_id) if kind.impl_trait_return_allowed() => {
1668 let fn_def_id = self.local_def_id(fn_node_id);
1669 ImplTraitContext::ReturnPositionOpaqueTy {
1670 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1673 _ => ImplTraitContext::Disallowed(match kind {
1674 FnDeclKind::Fn | FnDeclKind::Inherent => {
1675 unreachable!("fn should allow in-band lifetimes")
1677 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1678 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1679 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1680 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1681 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1684 hir::FnRetTy::Return(self.lower_ty(ty, context))
1686 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1690 self.arena.alloc(hir::FnDecl {
1694 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1695 let is_mutable_pat = matches!(
1697 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1701 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1702 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1703 // Given we are only considering `ImplicitSelf` types, we needn't consider
1704 // the case where we have a mutable pattern to a reference as that would
1705 // no longer be an `ImplicitSelf`.
1706 TyKind::Rptr(_, ref mt)
1707 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1709 hir::ImplicitSelfKind::MutRef
1711 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1712 hir::ImplicitSelfKind::ImmRef
1714 _ => hir::ImplicitSelfKind::None,
1720 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1721 // combined with the following definition of `OpaqueTy`:
1723 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1725 // `output`: unlowered output type (`T` in `-> T`)
1726 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1727 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1728 #[instrument(level = "debug", skip(self))]
1729 fn lower_async_fn_ret_ty(
1733 opaque_ty_node_id: NodeId,
1734 ) -> hir::FnRetTy<'hir> {
1735 let span = output.span();
1737 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1739 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1740 let fn_def_id = self.local_def_id(fn_node_id);
1742 // When we create the opaque type for this async fn, it is going to have
1743 // to capture all the lifetimes involved in the signature (including in the
1744 // return type). This is done by introducing lifetime parameters for:
1746 // - all the explicitly declared lifetimes from the impl and function itself;
1747 // - all the elided lifetimes in the fn arguments;
1748 // - all the elided lifetimes in the return type.
1750 // So for example in this snippet:
1753 // impl<'a> Foo<'a> {
1754 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1755 // // ^ '0 ^ '1 ^ '2
1756 // // elided lifetimes used below
1761 // we would create an opaque type like:
1764 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1767 // and we would then desugar `bar` to the equivalent of:
1770 // impl<'a> Foo<'a> {
1771 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1775 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1776 // this is because the elided lifetimes from the return type
1777 // should be figured out using the ordinary elision rules, and
1778 // this desugaring achieves that.
1780 // Calculate all the lifetimes that should be captured
1781 // by the opaque type. This should include all in-scope
1782 // lifetime parameters, including those defined in-band.
1784 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1786 let mut collected_lifetimes = Vec::new();
1787 let mut new_remapping = FxHashMap::default();
1789 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1790 debug!(?extra_lifetime_params);
1791 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1792 let outer_def_id = self.local_def_id(outer_node_id);
1793 let inner_node_id = self.next_node_id();
1795 // Add a definition for the in scope lifetime def.
1796 let inner_def_id = self.create_def(
1799 DefPathData::LifetimeNs(ident.name),
1801 new_remapping.insert(outer_def_id, inner_def_id);
1803 let inner_res = match outer_res {
1804 // Input lifetime like `'a`:
1805 LifetimeRes::Param { param, .. } => {
1806 LifetimeRes::Param { param, binder: fn_node_id }
1808 // Input lifetime like `'1`:
1809 LifetimeRes::Fresh { param, .. } => {
1810 LifetimeRes::Fresh { param, binder: fn_node_id }
1812 LifetimeRes::Static | LifetimeRes::Error => continue,
1815 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1816 res, ident, ident.span
1821 let lifetime = Lifetime { id: outer_node_id, ident };
1822 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1825 debug!(?collected_lifetimes);
1827 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1828 // find out exactly which ones those are.
1829 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1830 // we only keep the lifetimes that appear in the `impl Debug` itself:
1831 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1832 debug!(?lifetimes_to_remap);
1834 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1835 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1836 // in bounds), then create the new lifetime parameters required and create a mapping
1837 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1838 collected_lifetimes.extend(
1839 this.create_lifetime_defs(
1841 &lifetimes_to_remap,
1845 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1847 debug!(?collected_lifetimes);
1848 debug!(?new_remapping);
1850 // Install the remapping from old to new (if any):
1851 this.with_remapping(new_remapping, |this| {
1852 // We have to be careful to get elision right here. The
1853 // idea is that we create a lifetime parameter for each
1854 // lifetime in the return type. So, given a return type
1855 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1856 // Future<Output = &'1 [ &'2 u32 ]>`.
1858 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1859 // hence the elision takes place at the fn site.
1861 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span);
1863 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1864 |&(new_node_id, lifetime, _)| {
1865 let hir_id = this.lower_node_id(new_node_id);
1866 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1868 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1869 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1872 hir::ParamName::Plain(lifetime.ident),
1873 hir::LifetimeParamKind::Explicit,
1880 span: lifetime.ident.span,
1881 pure_wrt_drop: false,
1882 kind: hir::GenericParamKind::Lifetime { kind },
1887 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1889 let opaque_ty_item = hir::OpaqueTy {
1890 generics: this.arena.alloc(hir::Generics {
1891 params: generic_params,
1893 has_where_clause_predicates: false,
1894 where_clause_span: this.lower_span(span),
1895 span: this.lower_span(span),
1897 bounds: arena_vec![this; future_bound],
1898 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1901 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1902 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1906 // As documented above, we need to create the lifetime
1907 // arguments to our opaque type. Continuing with our example,
1908 // we're creating the type arguments for the return type:
1911 // Bar<'a, 'b, '0, '1, '_>
1914 // For the "input" lifetime parameters, we wish to create
1915 // references to the parameters themselves, including the
1916 // "implicit" ones created from parameter types (`'a`, `'b`,
1919 // For the "output" lifetime parameters, we just want to
1921 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
1922 |(_, lifetime, res)| {
1923 let id = self.next_node_id();
1924 let span = lifetime.ident.span;
1926 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1927 Ident::with_dummy_span(kw::UnderscoreLifetime)
1932 let res = res.unwrap_or(
1933 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
1935 let l = self.new_named_lifetime_with_res(id, span, ident, res);
1936 hir::GenericArg::Lifetime(l)
1940 // Create the `Foo<...>` reference itself. Note that the `type
1941 // Foo = impl Trait` is, internally, created as a child of the
1942 // async fn, so the *type parameters* are inherited. It's
1943 // only the lifetime parameters that we must supply.
1945 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
1946 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1947 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
1950 /// Transforms `-> T` into `Future<Output = T>`.
1951 fn lower_async_fn_output_type_to_future_bound(
1954 fn_def_id: LocalDefId,
1956 ) -> hir::GenericBound<'hir> {
1957 // Compute the `T` in `Future<Output = T>` from the return type.
1958 let output_ty = match output {
1959 FnRetTy::Ty(ty) => {
1960 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
1961 // `impl Future` opaque type that `async fn` implicitly
1963 let context = ImplTraitContext::ReturnPositionOpaqueTy {
1964 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1966 self.lower_ty(ty, context)
1968 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1972 let future_args = self.arena.alloc(hir::GenericArgs {
1974 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1975 parenthesized: false,
1979 hir::GenericBound::LangItemTrait(
1980 // ::std::future::Future<future_params>
1981 hir::LangItem::Future,
1982 self.lower_span(span),
1988 #[instrument(level = "trace", skip(self))]
1989 fn lower_param_bound(
1992 itctx: ImplTraitContext,
1993 ) -> hir::GenericBound<'hir> {
1995 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
1996 self.lower_poly_trait_ref(p, itctx),
1997 self.lower_trait_bound_modifier(*modifier),
1999 GenericBound::Outlives(lifetime) => {
2000 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2005 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2006 let span = self.lower_span(l.ident.span);
2007 let ident = self.lower_ident(l.ident);
2008 self.new_named_lifetime(l.id, l.id, span, ident)
2011 #[instrument(level = "debug", skip(self))]
2012 fn new_named_lifetime_with_res(
2018 ) -> hir::Lifetime {
2019 let name = match res {
2020 LifetimeRes::Param { param, .. } => {
2021 let p_name = ParamName::Plain(ident);
2022 let param = self.get_remapped_def_id(param);
2024 hir::LifetimeName::Param(param, p_name)
2026 LifetimeRes::Fresh { param, .. } => {
2027 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2028 let param = self.local_def_id(param);
2030 hir::LifetimeName::Param(param, ParamName::Fresh)
2032 LifetimeRes::Infer => hir::LifetimeName::Infer,
2033 LifetimeRes::Static => hir::LifetimeName::Static,
2034 LifetimeRes::Error => hir::LifetimeName::Error,
2035 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2039 hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
2042 #[instrument(level = "debug", skip(self))]
2043 fn new_named_lifetime(
2049 ) -> hir::Lifetime {
2050 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2051 self.new_named_lifetime_with_res(new_id, span, ident, res)
2054 fn lower_generic_params_mut<'s>(
2056 params: &'s [GenericParam],
2057 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2058 params.iter().map(move |param| self.lower_generic_param(param))
2061 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2062 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2065 #[instrument(level = "trace", skip(self))]
2066 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2067 let (name, kind) = self.lower_generic_param_kind(param);
2069 let hir_id = self.lower_node_id(param.id);
2070 self.lower_attrs(hir_id, ¶m.attrs);
2074 span: self.lower_span(param.span()),
2075 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2077 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2081 fn lower_generic_param_kind(
2083 param: &GenericParam,
2084 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2086 GenericParamKind::Lifetime => {
2087 // AST resolution emitted an error on those parameters, so we lower them using
2088 // `ParamName::Error`.
2090 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2093 let ident = self.lower_ident(param.ident);
2094 ParamName::Plain(ident)
2097 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2101 GenericParamKind::Type { ref default, .. } => {
2102 let kind = hir::GenericParamKind::Type {
2103 default: default.as_ref().map(|x| {
2104 self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2109 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2111 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2112 let ty = self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2113 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2115 hir::ParamName::Plain(self.lower_ident(param.ident)),
2116 hir::GenericParamKind::Const { ty, default },
2122 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext) -> hir::TraitRef<'hir> {
2123 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2124 hir::QPath::Resolved(None, path) => path,
2125 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2127 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2130 #[instrument(level = "debug", skip(self))]
2131 fn lower_poly_trait_ref(
2134 itctx: ImplTraitContext,
2135 ) -> hir::PolyTraitRef<'hir> {
2136 let bound_generic_params =
2137 self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
2138 let trait_ref = self.lower_trait_ref(&p.trait_ref, itctx);
2139 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2142 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy<'hir> {
2143 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2146 fn lower_param_bounds(
2148 bounds: &[GenericBound],
2149 itctx: ImplTraitContext,
2150 ) -> hir::GenericBounds<'hir> {
2151 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2154 fn lower_param_bounds_mut<'s>(
2156 bounds: &'s [GenericBound],
2157 itctx: ImplTraitContext,
2158 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2159 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2162 fn lower_generic_and_bounds(
2167 bounds: &[GenericBound],
2168 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2169 // Add a definition for the in-band `Param`.
2170 let def_id = self.local_def_id(node_id);
2172 // Set the name to `impl Bound1 + Bound2`.
2173 let param = hir::GenericParam {
2174 hir_id: self.lower_node_id(node_id),
2175 name: ParamName::Plain(self.lower_ident(ident)),
2176 pure_wrt_drop: false,
2177 span: self.lower_span(span),
2178 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2182 let preds = self.lower_generic_bound_predicate(
2185 &GenericParamKind::Type { default: None },
2187 ImplTraitContext::Universal,
2188 hir::PredicateOrigin::ImplTrait,
2191 let hir_id = self.next_id();
2192 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2193 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2195 self.arena.alloc(hir::Path {
2196 span: self.lower_span(span),
2199 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2206 /// Lowers a block directly to an expression, presuming that it
2207 /// has no attributes and is not targeted by a `break`.
2208 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2209 let block = self.lower_block(b, false);
2210 self.expr_block(block, AttrVec::new())
2213 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2214 match c.value.kind {
2215 ExprKind::Underscore => {
2216 if self.tcx.features().generic_arg_infer {
2217 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2220 &self.tcx.sess.parse_sess,
2221 sym::generic_arg_infer,
2223 "using `_` for array lengths is unstable",
2225 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2226 hir::ArrayLen::Body(self.lower_anon_const(c))
2229 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2233 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2234 self.with_new_scopes(|this| hir::AnonConst {
2235 hir_id: this.lower_node_id(c.id),
2236 body: this.lower_const_body(c.value.span, Some(&c.value)),
2240 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2242 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2243 UserProvided => hir::UnsafeSource::UserProvided,
2247 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2249 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2250 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2252 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2253 // placeholder for compilation to proceed.
2254 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2255 hir::TraitBoundModifier::Maybe
2260 // Helper methods for building HIR.
2262 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2263 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2266 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2267 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2272 attrs: Option<&'hir [Attribute]>,
2274 init: Option<&'hir hir::Expr<'hir>>,
2275 pat: &'hir hir::Pat<'hir>,
2276 source: hir::LocalSource,
2277 ) -> hir::Stmt<'hir> {
2278 let hir_id = self.next_id();
2279 if let Some(a) = attrs {
2280 debug_assert!(!a.is_empty());
2281 self.attrs.insert(hir_id.local_id, a);
2283 let local = hir::Local {
2289 span: self.lower_span(span),
2292 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2295 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2296 self.block_all(expr.span, &[], Some(expr))
2302 stmts: &'hir [hir::Stmt<'hir>],
2303 expr: Option<&'hir hir::Expr<'hir>>,
2304 ) -> &'hir hir::Block<'hir> {
2305 let blk = hir::Block {
2308 hir_id: self.next_id(),
2309 rules: hir::BlockCheckMode::DefaultBlock,
2310 span: self.lower_span(span),
2311 targeted_by_break: false,
2313 self.arena.alloc(blk)
2316 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2317 let field = self.single_pat_field(span, pat);
2318 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2321 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2322 let field = self.single_pat_field(span, pat);
2323 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2326 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2327 let field = self.single_pat_field(span, pat);
2328 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2331 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2332 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2335 fn single_pat_field(
2338 pat: &'hir hir::Pat<'hir>,
2339 ) -> &'hir [hir::PatField<'hir>] {
2340 let field = hir::PatField {
2341 hir_id: self.next_id(),
2342 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2343 is_shorthand: false,
2345 span: self.lower_span(span),
2347 arena_vec![self; field]
2350 fn pat_lang_item_variant(
2353 lang_item: hir::LangItem,
2354 fields: &'hir [hir::PatField<'hir>],
2355 hir_id: Option<hir::HirId>,
2356 ) -> &'hir hir::Pat<'hir> {
2357 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2358 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2361 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2362 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2365 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2366 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2369 fn pat_ident_binding_mode(
2373 bm: hir::BindingAnnotation,
2374 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2375 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2376 (self.arena.alloc(pat), hir_id)
2379 fn pat_ident_binding_mode_mut(
2383 bm: hir::BindingAnnotation,
2384 ) -> (hir::Pat<'hir>, hir::HirId) {
2385 let hir_id = self.next_id();
2390 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2391 span: self.lower_span(span),
2392 default_binding_modes: true,
2398 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2399 self.arena.alloc(hir::Pat {
2400 hir_id: self.next_id(),
2402 span: self.lower_span(span),
2403 default_binding_modes: true,
2407 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2409 hir_id: self.next_id(),
2411 span: self.lower_span(span),
2412 default_binding_modes: false,
2418 mut hir_id: hir::HirId,
2420 qpath: hir::QPath<'hir>,
2421 ) -> hir::Ty<'hir> {
2422 let kind = match qpath {
2423 hir::QPath::Resolved(None, path) => {
2424 // Turn trait object paths into `TyKind::TraitObject` instead.
2426 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2427 let principal = hir::PolyTraitRef {
2428 bound_generic_params: &[],
2429 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2430 span: self.lower_span(span),
2433 // The original ID is taken by the `PolyTraitRef`,
2434 // so the `Ty` itself needs a different one.
2435 hir_id = self.next_id();
2436 hir::TyKind::TraitObject(
2437 arena_vec![self; principal],
2438 self.elided_dyn_bound(span),
2439 TraitObjectSyntax::None,
2442 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2445 _ => hir::TyKind::Path(qpath),
2448 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2451 /// Invoked to create the lifetime argument(s) for an elided trait object
2452 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2453 /// when the bound is written, even if it is written with `'_` like in
2454 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2455 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2456 let r = hir::Lifetime {
2457 hir_id: self.next_id(),
2458 span: self.lower_span(span),
2459 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2461 debug!("elided_dyn_bound: r={:?}", r);
2466 /// Helper struct for delayed construction of GenericArgs.
2467 struct GenericArgsCtor<'hir> {
2468 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2469 bindings: &'hir [hir::TypeBinding<'hir>],
2470 parenthesized: bool,
2474 impl<'hir> GenericArgsCtor<'hir> {
2475 fn is_empty(&self) -> bool {
2476 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2479 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2480 let ga = hir::GenericArgs {
2481 args: this.arena.alloc_from_iter(self.args),
2482 bindings: self.bindings,
2483 parenthesized: self.parenthesized,
2484 span_ext: this.lower_span(self.span),
2486 this.arena.alloc(ga)