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, TraitFnAsync};
47 use rustc_arena::declare_arena;
48 use rustc_ast::ptr::P;
50 use rustc_ast::{self as ast, *};
51 use rustc_ast_pretty::pprust;
52 use rustc_data_structures::captures::Captures;
53 use rustc_data_structures::fingerprint::Fingerprint;
54 use rustc_data_structures::fx::FxHashMap;
55 use rustc_data_structures::sorted_map::SortedMap;
56 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
57 use rustc_data_structures::sync::Lrc;
58 use rustc_errors::{DiagnosticArgFromDisplay, Handler, StashKey};
60 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
61 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
62 use rustc_hir::definitions::DefPathData;
63 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
64 use rustc_index::vec::{Idx, IndexVec};
65 use rustc_middle::span_bug;
66 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
67 use rustc_session::parse::feature_err;
68 use rustc_span::hygiene::MacroKind;
69 use rustc_span::source_map::DesugaringKind;
70 use rustc_span::symbol::{kw, sym, Ident, Symbol};
71 use rustc_span::{Span, DUMMY_SP};
73 use smallvec::SmallVec;
74 use std::collections::hash_map::Entry;
76 macro_rules! arena_vec {
77 ($this:expr; $($x:expr),*) => (
78 $this.arena.alloc_from_iter([$($x),*])
88 mod lifetime_collector;
92 struct LoweringContext<'a, 'hir> {
94 resolver: &'a mut ResolverAstLowering,
96 /// Used to allocate HIR nodes.
97 arena: &'hir hir::Arena<'hir>,
99 /// Used to allocate temporary AST nodes for use during lowering.
100 /// This allows us to create "fake" AST -- these nodes can sometimes
101 /// be allocated on the stack, but other times we need them to live longer
102 /// than the current stack frame, so they can be collected into vectors
103 /// and things like that.
104 ast_arena: &'a Arena<'static>,
106 /// Bodies inside the owner being lowered.
107 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
108 /// Attributes inside the owner being lowered.
109 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
110 /// Collect items that were created by lowering the current owner.
111 children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
113 generator_kind: Option<hir::GeneratorKind>,
115 /// When inside an `async` context, this is the `HirId` of the
116 /// `task_context` local bound to the resume argument of the generator.
117 task_context: Option<hir::HirId>,
119 /// Used to get the current `fn`'s def span to point to when using `await`
120 /// outside of an `async fn`.
121 current_item: Option<Span>,
123 catch_scope: Option<NodeId>,
124 loop_scope: Option<NodeId>,
125 is_in_loop_condition: bool,
126 is_in_trait_impl: bool,
127 is_in_dyn_type: bool,
129 current_hir_id_owner: LocalDefId,
130 item_local_id_counter: hir::ItemLocalId,
131 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
132 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
134 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
135 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
137 /// NodeIds that are lowered inside the current HIR owner.
138 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
140 allow_try_trait: Option<Lrc<[Symbol]>>,
141 allow_gen_future: Option<Lrc<[Symbol]>>,
142 allow_into_future: Option<Lrc<[Symbol]>>,
144 /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
145 /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
146 /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
147 /// field from the original parameter 'a to the new parameter 'a1.
148 generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
152 [] tys: rustc_ast::Ty,
153 [] aba: rustc_ast::AngleBracketedArgs,
154 [] ptr: rustc_ast::PolyTraitRef,
155 // This _marker field is needed because `declare_arena` creates `Arena<'tcx>` and we need to
156 // use `'tcx`. If we don't have this we get a compile error.
157 [] _marker: std::marker::PhantomData<&'tcx ()>,
160 trait ResolverAstLoweringExt {
161 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
162 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
163 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
164 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
165 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
166 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
167 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
170 impl ResolverAstLoweringExt for ResolverAstLowering {
171 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
172 if let ExprKind::Path(None, path) = &expr.kind {
173 // Don't perform legacy const generics rewriting if the path already
174 // has generic arguments.
175 if path.segments.last().unwrap().args.is_some() {
179 let partial_res = self.partial_res_map.get(&expr.id)?;
180 if partial_res.unresolved_segments() != 0 {
184 if let Res::Def(DefKind::Fn, def_id) = partial_res.base_res() {
185 // We only support cross-crate argument rewriting. Uses
186 // within the same crate should be updated to use the new
187 // const generics style.
188 if def_id.is_local() {
192 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
201 /// Obtains resolution for a `NodeId` with a single resolution.
202 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
203 self.partial_res_map.get(&id).copied()
206 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
207 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
208 self.import_res_map.get(&id).copied().unwrap_or_default()
211 /// Obtains resolution for a label with the given `NodeId`.
212 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
213 self.label_res_map.get(&id).copied()
216 /// Obtains resolution for a lifetime with the given `NodeId`.
217 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
218 self.lifetimes_res_map.get(&id).copied()
221 /// Obtain the list of lifetimes parameters to add to an item.
223 /// Extra lifetime parameters should only be added in places that can appear
224 /// as a `binder` in `LifetimeRes`.
226 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
227 /// should appear at the enclosing `PolyTraitRef`.
228 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
229 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
232 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
233 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
237 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
238 /// and if so, what meaning it has.
239 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
240 enum ImplTraitContext {
241 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
242 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
243 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
245 /// Newly generated parameters should be inserted into the given `Vec`.
248 /// Treat `impl Trait` as shorthand for a new opaque type.
249 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
250 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
252 ReturnPositionOpaqueTy {
253 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
254 origin: hir::OpaqueTyOrigin,
257 /// Impl trait in type aliases.
259 /// `impl Trait` is not accepted in this position.
260 Disallowed(ImplTraitPosition),
263 /// Position in which `impl Trait` is disallowed.
264 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
265 enum ImplTraitPosition {
287 impl std::fmt::Display for ImplTraitPosition {
288 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
289 let name = match self {
290 ImplTraitPosition::Path => "path",
291 ImplTraitPosition::Variable => "variable binding",
292 ImplTraitPosition::Type => "type",
293 ImplTraitPosition::Trait => "trait",
294 ImplTraitPosition::AsyncBlock => "async block",
295 ImplTraitPosition::Bound => "bound",
296 ImplTraitPosition::Generic => "generic",
297 ImplTraitPosition::ExternFnParam => "`extern fn` param",
298 ImplTraitPosition::ClosureParam => "closure param",
299 ImplTraitPosition::PointerParam => "`fn` pointer param",
300 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
301 ImplTraitPosition::TraitParam => "trait method param",
302 ImplTraitPosition::ImplParam => "`impl` method param",
303 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
304 ImplTraitPosition::ClosureReturn => "closure return",
305 ImplTraitPosition::PointerReturn => "`fn` pointer return",
306 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
307 ImplTraitPosition::TraitReturn => "trait method return",
308 ImplTraitPosition::ImplReturn => "`impl` method return",
311 write!(f, "{}", name)
327 fn impl_trait_return_allowed(&self, tcx: TyCtxt<'_>) -> bool {
329 FnDeclKind::Fn | FnDeclKind::Inherent => true,
330 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
335 fn impl_trait_in_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
337 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
343 #[derive(Copy, Clone)]
346 Crate(&'a ast::Crate),
348 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
349 ForeignItem(&'a ast::ForeignItem),
353 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
355 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
356 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
357 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
358 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
359 visit::walk_crate(&mut indexer, krate);
360 return indexer.index;
362 struct Indexer<'s, 'a> {
363 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
364 index: IndexVec<LocalDefId, AstOwner<'a>>,
367 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
368 fn visit_attribute(&mut self, _: &'a Attribute) {
369 // We do not want to lower expressions that appear in attributes,
370 // as they are not accessible to the rest of the HIR.
373 fn visit_item(&mut self, item: &'a ast::Item) {
374 let def_id = self.node_id_to_def_id[&item.id];
375 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
376 self.index[def_id] = AstOwner::Item(item);
377 visit::walk_item(self, item)
380 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
381 let def_id = self.node_id_to_def_id[&item.id];
382 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
383 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
384 visit::walk_assoc_item(self, item, ctxt);
387 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
388 let def_id = self.node_id_to_def_id[&item.id];
389 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
390 self.index[def_id] = AstOwner::ForeignItem(item);
391 visit::walk_foreign_item(self, item);
396 /// Compute the hash for the HIR of the full crate.
397 /// This hash will then be part of the crate_hash which is stored in the metadata.
400 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
402 let mut hir_body_nodes: Vec<_> = owners
404 .filter_map(|(def_id, info)| {
405 let info = info.as_owner()?;
406 let def_path_hash = tcx.hir().def_path_hash(def_id);
407 Some((def_path_hash, info))
410 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
412 tcx.with_stable_hashing_context(|mut hcx| {
413 let mut stable_hasher = StableHasher::new();
414 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
415 stable_hasher.finish()
419 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
421 let krate = tcx.untracked_crate.steal();
422 let mut resolver = tcx.resolver_for_lowering(()).steal();
424 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
425 let mut owners = IndexVec::from_fn_n(
426 |_| hir::MaybeOwner::Phantom,
427 tcx.definitions_untracked().def_index_count(),
430 let ast_arena = Arena::default();
432 for def_id in ast_index.indices() {
435 resolver: &mut resolver,
436 ast_arena: &ast_arena,
437 ast_index: &ast_index,
443 // Drop AST to free memory
444 std::mem::drop(ast_index);
445 sess.time("drop_ast", || std::mem::drop(krate));
447 // Discard hygiene data, which isn't required after lowering to HIR.
448 if !sess.opts.unstable_opts.keep_hygiene_data {
449 rustc_span::hygiene::clear_syntax_context_map();
452 let hir_hash = compute_hir_hash(tcx, &owners);
453 hir::Crate { owners, hir_hash }
456 #[derive(Copy, Clone, PartialEq, Debug)]
458 /// Any path in a type context.
460 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
462 /// The `module::Type` in `module::Type::method` in an expression.
466 enum ParenthesizedGenericArgs {
471 impl<'a, 'hir> LoweringContext<'a, 'hir> {
475 node_id: ast::NodeId,
478 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
480 self.opt_local_def_id(node_id).is_none(),
481 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
484 self.tcx.hir().def_key(self.local_def_id(node_id)),
487 let def_id = self.tcx.create_def(parent, data);
489 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
490 self.resolver.node_id_to_def_id.insert(node_id, def_id);
495 fn next_node_id(&mut self) -> NodeId {
496 let start = self.resolver.next_node_id;
497 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
498 self.resolver.next_node_id = ast::NodeId::from_u32(next);
502 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
503 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
505 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
506 /// invoking with the id from the `ast::Lifetime` node found inside
507 /// the `&'a u32` type would return the `LocalDefId` of the
508 /// `'a` parameter declared on `foo`.
510 /// This function also applies remapping from `get_remapped_def_id`.
511 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
512 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
513 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
514 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
515 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
519 .map(|local_def_id| self.get_remapped_def_id(*local_def_id))
522 fn local_def_id(&self, node: NodeId) -> LocalDefId {
523 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
526 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
527 /// `generics_def_id_map` field.
528 fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId {
529 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
530 // push new mappings so we need to try first the latest mappings, hence `iter().rev()`.
534 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
536 // We would end with a generics_def_id_map like:
538 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
540 // for the opaque type generated on `impl Sized + 'b`, We want the result to be:
541 // impl_sized#'b, so iterating forward is the wrong thing to do.
542 for map in self.generics_def_id_map.iter().rev() {
543 if let Some(r) = map.get(&local_def_id) {
544 debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`");
547 debug!("def_id_remapper: no remapping for `{local_def_id:?}` found in map");
554 /// Freshen the `LoweringContext` and ready it to lower a nested item.
555 /// The lowered item is registered into `self.children`.
557 /// This function sets up `HirId` lowering infrastructure,
558 /// and stashes the shared mutable state to avoid pollution by the closure.
559 #[instrument(level = "debug", skip(self, f))]
560 fn with_hir_id_owner(
563 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
565 let def_id = self.local_def_id(owner);
567 let current_attrs = std::mem::take(&mut self.attrs);
568 let current_bodies = std::mem::take(&mut self.bodies);
569 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
570 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
571 let current_trait_map = std::mem::take(&mut self.trait_map);
572 let current_owner = std::mem::replace(&mut self.current_hir_id_owner, def_id);
573 let current_local_counter =
574 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
575 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
576 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
578 // Do not reset `next_node_id` and `node_id_to_def_id`:
579 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
580 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
582 // Always allocate the first `HirId` for the owner itself.
583 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
584 debug_assert_eq!(_old, None);
587 debug_assert_eq!(def_id, item.def_id());
588 // `f` should have consumed all the elements in these vectors when constructing `item`.
589 debug_assert!(self.impl_trait_defs.is_empty());
590 debug_assert!(self.impl_trait_bounds.is_empty());
591 let info = self.make_owner_info(item);
593 self.attrs = current_attrs;
594 self.bodies = current_bodies;
595 self.node_id_to_local_id = current_node_ids;
596 self.local_id_to_def_id = current_id_to_def_id;
597 self.trait_map = current_trait_map;
598 self.current_hir_id_owner = current_owner;
599 self.item_local_id_counter = current_local_counter;
600 self.impl_trait_defs = current_impl_trait_defs;
601 self.impl_trait_bounds = current_impl_trait_bounds;
603 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
604 debug_assert!(_old.is_none())
607 /// Installs the remapping `remap` in scope while `f` is being executed.
608 /// This causes references to the `LocalDefId` keys to be changed to
609 /// refer to the values instead.
611 /// The remapping is used when one piece of AST expands to multiple
612 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
613 /// expands to both a function definition (`foo`) and a TAIT for the return value,
614 /// both of which have a lifetime parameter `'a`. The remapping allows us to
615 /// rewrite the `'a` in the return value to refer to the
616 /// `'a` declared on the TAIT, instead of the function.
617 fn with_remapping<R>(
619 remap: FxHashMap<LocalDefId, LocalDefId>,
620 f: impl FnOnce(&mut Self) -> R,
622 self.generics_def_id_map.push(remap);
624 self.generics_def_id_map.pop();
628 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
629 let attrs = std::mem::take(&mut self.attrs);
630 let mut bodies = std::mem::take(&mut self.bodies);
631 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
632 let trait_map = std::mem::take(&mut self.trait_map);
634 #[cfg(debug_assertions)]
635 for (id, attrs) in attrs.iter() {
636 // Verify that we do not store empty slices in the map.
637 if attrs.is_empty() {
638 panic!("Stored empty attributes for {:?}", id);
642 bodies.sort_by_key(|(k, _)| *k);
643 let bodies = SortedMap::from_presorted_elements(bodies);
644 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
645 let (nodes, parenting) =
646 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
647 let nodes = hir::OwnerNodes {
648 hash_including_bodies,
655 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
656 let mut stable_hasher = StableHasher::new();
657 attrs.hash_stable(&mut hcx, &mut stable_hasher);
658 stable_hasher.finish()
660 hir::AttributeMap { map: attrs, hash }
663 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
666 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
667 /// queries which depend on the full HIR tree and those which only depend on the item signature.
670 node: hir::OwnerNode<'hir>,
671 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
672 ) -> (Fingerprint, Fingerprint) {
673 self.tcx.with_stable_hashing_context(|mut hcx| {
674 let mut stable_hasher = StableHasher::new();
675 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
676 node.hash_stable(hcx, &mut stable_hasher)
678 let hash_including_bodies = stable_hasher.finish();
679 let mut stable_hasher = StableHasher::new();
680 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
681 let hash_without_bodies = stable_hasher.finish();
682 (hash_including_bodies, hash_without_bodies)
686 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
687 /// the `LoweringContext`'s `NodeId => HirId` map.
688 /// Take care not to call this method if the resulting `HirId` is then not
689 /// actually used in the HIR, as that would trigger an assertion in the
690 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
691 /// properly. Calling the method twice with the same `NodeId` is fine though.
692 #[instrument(level = "debug", skip(self), ret)]
693 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
694 assert_ne!(ast_node_id, DUMMY_NODE_ID);
696 match self.node_id_to_local_id.entry(ast_node_id) {
697 Entry::Occupied(o) => {
698 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
700 Entry::Vacant(v) => {
701 // Generate a new `HirId`.
702 let owner = self.current_hir_id_owner;
703 let local_id = self.item_local_id_counter;
704 let hir_id = hir::HirId { owner, local_id };
707 self.item_local_id_counter.increment_by(1);
709 assert_ne!(local_id, hir::ItemLocalId::new(0));
710 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
711 // Do not override a `MaybeOwner::Owner` that may already here.
712 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
713 self.local_id_to_def_id.insert(local_id, def_id);
716 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
717 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
725 /// Generate a new `HirId` without a backing `NodeId`.
726 #[instrument(level = "debug", skip(self), ret)]
727 fn next_id(&mut self) -> hir::HirId {
728 let owner = self.current_hir_id_owner;
729 let local_id = self.item_local_id_counter;
730 assert_ne!(local_id, hir::ItemLocalId::new(0));
731 self.item_local_id_counter.increment_by(1);
732 hir::HirId { owner, local_id }
735 #[instrument(level = "trace", skip(self))]
736 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
737 let res: Result<Res, ()> = res.apply_id(|id| {
738 let owner = self.current_hir_id_owner;
739 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
740 Ok(hir::HirId { owner, local_id })
744 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
745 // This can happen when trying to lower the return type `x` in erroneous code like
746 // async fn foo(x: u8) -> x {}
747 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
748 // an opaque type as a synthesized HIR owner.
749 res.unwrap_or(Res::Err)
752 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
753 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
754 if pr.unresolved_segments() != 0 {
755 panic!("path not fully resolved: {:?}", pr);
761 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
762 self.resolver.get_import_res(id).present_items()
765 fn diagnostic(&self) -> &Handler {
766 self.tcx.sess.diagnostic()
769 /// Reuses the span but adds information like the kind of the desugaring and features that are
770 /// allowed inside this span.
771 fn mark_span_with_reason(
773 reason: DesugaringKind,
775 allow_internal_unstable: Option<Lrc<[Symbol]>>,
777 self.tcx.with_stable_hashing_context(|hcx| {
778 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
782 /// Intercept all spans entering HIR.
783 /// Mark a span as relative to the current owning item.
784 fn lower_span(&self, span: Span) -> Span {
785 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
786 span.with_parent(Some(self.current_hir_id_owner))
788 // Do not make spans relative when not using incremental compilation.
793 fn lower_ident(&self, ident: Ident) -> Ident {
794 Ident::new(ident.name, self.lower_span(ident.span))
797 /// Converts a lifetime into a new generic parameter.
798 #[instrument(level = "debug", skip(self))]
799 fn lifetime_res_to_generic_param(
804 ) -> Option<hir::GenericParam<'hir>> {
805 let (name, kind) = match res {
806 LifetimeRes::Param { .. } => {
807 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
809 LifetimeRes::Fresh { param, .. } => {
810 // Late resolution delegates to us the creation of the `LocalDefId`.
811 let _def_id = self.create_def(
812 self.current_hir_id_owner,
814 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
818 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
820 LifetimeRes::Static | LifetimeRes::Error => return None,
822 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
823 res, ident, ident.span
826 let hir_id = self.lower_node_id(node_id);
827 Some(hir::GenericParam {
830 span: self.lower_span(ident.span),
831 pure_wrt_drop: false,
832 kind: hir::GenericParamKind::Lifetime { kind },
837 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
838 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
839 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
840 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
841 /// parameters will be successful.
842 #[instrument(level = "debug", skip(self, in_binder))]
844 fn lower_lifetime_binder<R>(
847 generic_params: &[GenericParam],
848 in_binder: impl FnOnce(&mut Self, &'hir [hir::GenericParam<'hir>]) -> R,
850 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
851 debug!(?extra_lifetimes);
852 let extra_lifetimes: Vec<_> = extra_lifetimes
854 .filter_map(|(ident, node_id, res)| {
855 self.lifetime_res_to_generic_param(ident, node_id, res)
859 let generic_params: Vec<_> = self
860 .lower_generic_params_mut(generic_params)
861 .chain(extra_lifetimes.into_iter())
863 let generic_params = self.arena.alloc_from_iter(generic_params);
864 debug!(?generic_params);
866 in_binder(self, generic_params)
869 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
870 let was_in_dyn_type = self.is_in_dyn_type;
871 self.is_in_dyn_type = in_scope;
873 let result = f(self);
875 self.is_in_dyn_type = was_in_dyn_type;
880 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
881 let was_in_loop_condition = self.is_in_loop_condition;
882 self.is_in_loop_condition = false;
884 let catch_scope = self.catch_scope.take();
885 let loop_scope = self.loop_scope.take();
887 self.catch_scope = catch_scope;
888 self.loop_scope = loop_scope;
890 self.is_in_loop_condition = was_in_loop_condition;
895 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
896 if attrs.is_empty() {
899 debug_assert_eq!(id.owner, self.current_hir_id_owner);
900 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
901 debug_assert!(!ret.is_empty());
902 self.attrs.insert(id.local_id, ret);
907 fn lower_attr(&self, attr: &Attribute) -> Attribute {
908 // Note that we explicitly do not walk the path. Since we don't really
909 // lower attributes (we use the AST version) there is nowhere to keep
910 // the `HirId`s. We don't actually need HIR version of attributes anyway.
911 // Tokens are also not needed after macro expansion and parsing.
912 let kind = match attr.kind {
913 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
915 path: normal.item.path.clone(),
916 args: self.lower_mac_args(&normal.item.args),
921 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
924 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
927 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
928 debug_assert_eq!(id.owner, self.current_hir_id_owner);
929 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
930 if let Some(&a) = self.attrs.get(&target_id.local_id) {
931 debug_assert!(!a.is_empty());
932 self.attrs.insert(id.local_id, a);
936 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
938 MacArgs::Empty => MacArgs::Empty,
939 MacArgs::Delimited(dspan, delim, ref tokens) => {
940 // This is either a non-key-value attribute, or a `macro_rules!` body.
941 // We either not have any nonterminals present (in the case of an attribute),
942 // or have tokens available for all nonterminals in the case of a nested
943 // `macro_rules`: e.g:
946 // macro_rules! outer {
948 // macro_rules! inner {
955 // In both cases, we don't want to synthesize any tokens
956 MacArgs::Delimited(dspan, delim, tokens.flattened())
958 // This is an inert key-value attribute - it will never be visible to macros
959 // after it gets lowered to HIR. Therefore, we can extract literals to handle
960 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
961 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
962 // In valid code the value always ends up as a single literal. Otherwise, a dummy
963 // literal suffices because the error is handled elsewhere.
964 let lit = if let ExprKind::Lit(lit) = &expr.kind {
968 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
973 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
975 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
976 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
981 /// Given an associated type constraint like one of these:
983 /// ```ignore (illustrative)
984 /// T: Iterator<Item: Debug>
986 /// T: Iterator<Item = Debug>
990 /// returns a `hir::TypeBinding` representing `Item`.
991 #[instrument(level = "debug", skip(self))]
992 fn lower_assoc_ty_constraint(
994 constraint: &AssocConstraint,
995 itctx: &mut ImplTraitContext,
996 ) -> hir::TypeBinding<'hir> {
997 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
998 // lower generic arguments of identifier in constraint
999 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1000 let gen_args_ctor = match gen_args {
1001 GenericArgs::AngleBracketed(ref data) => {
1002 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
1004 GenericArgs::Parenthesized(ref data) => {
1005 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
1006 let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
1007 self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
1010 gen_args_ctor.into_generic_args(self)
1012 self.arena.alloc(hir::GenericArgs::none())
1014 let mut itctx_tait = ImplTraitContext::TypeAliasesOpaqueTy;
1016 let kind = match constraint.kind {
1017 AssocConstraintKind::Equality { ref term } => {
1018 let term = match term {
1019 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
1020 Term::Const(ref c) => self.lower_anon_const(c).into(),
1022 hir::TypeBindingKind::Equality { term }
1024 AssocConstraintKind::Bound { ref bounds } => {
1025 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1026 let (desugar_to_impl_trait, itctx) = match itctx {
1027 // We are in the return position:
1029 // fn foo() -> impl Iterator<Item: Debug>
1033 // fn foo() -> impl Iterator<Item = impl Debug>
1034 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1035 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1037 // We are in the argument position, but within a dyn type:
1039 // fn foo(x: dyn Iterator<Item: Debug>)
1043 // fn foo(x: dyn Iterator<Item = impl Debug>)
1044 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1046 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1047 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1048 // "impl trait context" to permit `impl Debug` in this position (it desugars
1049 // then to an opaque type).
1051 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1052 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1053 (true, &mut itctx_tait)
1056 // We are in the parameter position, but not within a dyn type:
1058 // fn foo(x: impl Iterator<Item: Debug>)
1060 // so we leave it as is and this gets expanded in astconv to a bound like
1061 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1063 _ => (false, itctx),
1066 if desugar_to_impl_trait {
1067 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1068 // constructing the HIR for `impl bounds...` and then lowering that.
1070 let parent_def_id = self.current_hir_id_owner;
1071 let impl_trait_node_id = self.next_node_id();
1072 self.create_def(parent_def_id, impl_trait_node_id, DefPathData::ImplTrait);
1074 self.with_dyn_type_scope(false, |this| {
1075 let node_id = this.next_node_id();
1076 let ty = this.ast_arena.tys.alloc(Ty {
1078 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1079 span: this.lower_span(constraint.span),
1082 let ty = this.lower_ty(ty, itctx);
1084 hir::TypeBindingKind::Equality { term: ty.into() }
1087 // Desugar `AssocTy: Bounds` into a type binding where the
1088 // later desugars into a trait predicate.
1089 let bounds = self.lower_param_bounds(bounds, itctx);
1091 hir::TypeBindingKind::Constraint { bounds }
1097 hir_id: self.lower_node_id(constraint.id),
1098 ident: self.lower_ident(constraint.ident),
1101 span: self.lower_span(constraint.span),
1105 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1106 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1107 let sub = if data.inputs.is_empty() {
1108 let parentheses_span =
1109 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1110 AssocTyParenthesesSub::Empty { parentheses_span }
1112 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1114 // Start of parameters to the 1st argument
1115 let open_param = data.inputs_span.shrink_to_lo().to(data
1121 // End of last argument to end of parameters
1123 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1124 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1126 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1129 #[instrument(level = "debug", skip(self))]
1130 fn lower_generic_arg(
1132 arg: &ast::GenericArg,
1133 itctx: &mut ImplTraitContext,
1134 ) -> hir::GenericArg<'hir> {
1136 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1137 ast::GenericArg::Type(ty) => {
1139 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1140 return GenericArg::Infer(hir::InferArg {
1141 hir_id: self.lower_node_id(ty.id),
1142 span: self.lower_span(ty.span),
1145 // We parse const arguments as path types as we cannot distinguish them during
1146 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1147 // type and value namespaces. If we resolved the path in the value namespace, we
1148 // transform it into a generic const argument.
1149 TyKind::Path(ref qself, ref path) => {
1150 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1151 let res = partial_res.base_res();
1152 if !res.matches_ns(Namespace::TypeNS) {
1154 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1158 // Construct an AnonConst where the expr is the "ty"'s path.
1160 let parent_def_id = self.current_hir_id_owner;
1161 let node_id = self.next_node_id();
1163 // Add a definition for the in-band const def.
1164 self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
1166 let span = self.lower_span(ty.span);
1167 let path_expr = Expr {
1169 kind: ExprKind::Path(qself.clone(), path.clone()),
1171 attrs: AttrVec::new(),
1175 let ct = self.with_new_scopes(|this| hir::AnonConst {
1176 hir_id: this.lower_node_id(node_id),
1177 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1179 return GenericArg::Const(ConstArg { value: ct, span });
1185 GenericArg::Type(self.lower_ty(&ty, itctx))
1187 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1188 value: self.lower_anon_const(&ct),
1189 span: self.lower_span(ct.value.span),
1194 #[instrument(level = "debug", skip(self))]
1195 fn lower_ty(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> &'hir hir::Ty<'hir> {
1196 self.arena.alloc(self.lower_ty_direct(t, itctx))
1202 qself: &Option<QSelf>,
1204 param_mode: ParamMode,
1205 itctx: &mut ImplTraitContext,
1206 ) -> hir::Ty<'hir> {
1207 // Check whether we should interpret this as a bare trait object.
1208 // This check mirrors the one in late resolution. We only introduce this special case in
1209 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1210 // The other cases when a qpath should be opportunistically made a trait object are handled
1213 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1214 && partial_res.unresolved_segments() == 0
1215 && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
1217 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1218 let poly_trait_ref = this.ast_arena.ptr.alloc(PolyTraitRef {
1219 bound_generic_params: vec![],
1220 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1223 let bound = this.lower_poly_trait_ref(
1227 let bounds = this.arena.alloc_from_iter([bound]);
1228 let lifetime_bound = this.elided_dyn_bound(t.span);
1229 (bounds, lifetime_bound)
1231 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1232 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1235 let id = self.lower_node_id(t.id);
1236 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1237 self.ty_path(id, t.span, qpath)
1240 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1241 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1244 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1245 self.ty(span, hir::TyKind::Tup(tys))
1248 fn lower_ty_direct(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> hir::Ty<'hir> {
1249 let kind = match t.kind {
1250 TyKind::Infer => hir::TyKind::Infer,
1251 TyKind::Err => hir::TyKind::Err,
1252 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1253 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1254 TyKind::Rptr(ref region, ref mt) => {
1255 let region = region.unwrap_or_else(|| {
1256 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1257 self.resolver.get_lifetime_res(t.id)
1259 debug_assert_eq!(start.plus(1), end);
1264 let span = self.tcx.sess.source_map().start_point(t.span);
1265 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1267 let lifetime = self.lower_lifetime(®ion);
1268 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1270 TyKind::BareFn(ref f) => {
1271 self.lower_lifetime_binder(t.id, &f.generic_params, |lctx, generic_params| {
1272 hir::TyKind::BareFn(lctx.arena.alloc(hir::BareFnTy {
1274 unsafety: lctx.lower_unsafety(f.unsafety),
1275 abi: lctx.lower_extern(f.ext),
1276 decl: lctx.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
1277 param_names: lctx.lower_fn_params_to_names(&f.decl),
1281 TyKind::Never => hir::TyKind::Never,
1282 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1283 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1285 TyKind::Paren(ref ty) => {
1286 return self.lower_ty_direct(ty, itctx);
1288 TyKind::Path(ref qself, ref path) => {
1289 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1291 TyKind::ImplicitSelf => {
1292 let hir_id = self.lower_node_id(t.id);
1293 let res = self.expect_full_res(t.id);
1294 let res = self.lower_res(res);
1295 hir::TyKind::Path(hir::QPath::Resolved(
1297 self.arena.alloc(hir::Path {
1299 segments: arena_vec![self; hir::PathSegment::new(
1300 Ident::with_dummy_span(kw::SelfUpper),
1304 span: self.lower_span(t.span),
1308 TyKind::Array(ref ty, ref length) => {
1309 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1311 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1312 TyKind::TraitObject(ref bounds, kind) => {
1313 let mut lifetime_bound = None;
1314 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1316 this.arena.alloc_from_iter(bounds.iter().filter_map(
1317 |bound| match *bound {
1318 GenericBound::Trait(
1320 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1321 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1322 // `~const ?Bound` will cause an error during AST validation
1323 // anyways, so treat it like `?Bound` as compilation proceeds.
1324 GenericBound::Trait(
1326 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1328 GenericBound::Outlives(ref lifetime) => {
1329 if lifetime_bound.is_none() {
1330 lifetime_bound = Some(this.lower_lifetime(lifetime));
1336 let lifetime_bound =
1337 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1338 (bounds, lifetime_bound)
1340 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1342 TyKind::ImplTrait(def_node_id, ref bounds) => {
1345 ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
1346 .lower_opaque_impl_trait(
1354 ImplTraitContext::TypeAliasesOpaqueTy => {
1355 let mut nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
1356 self.lower_opaque_impl_trait(
1358 hir::OpaqueTyOrigin::TyAlias,
1365 ImplTraitContext::Universal => {
1367 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1368 let (param, bounds, path) =
1369 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1370 self.impl_trait_defs.push(param);
1371 if let Some(bounds) = bounds {
1372 self.impl_trait_bounds.push(bounds);
1376 ImplTraitContext::Disallowed(position) => {
1377 self.tcx.sess.emit_err(MisplacedImplTrait {
1379 position: DiagnosticArgFromDisplay(&position),
1385 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1386 TyKind::CVarArgs => {
1387 self.tcx.sess.delay_span_bug(
1389 "`TyKind::CVarArgs` should have been handled elsewhere",
1395 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1398 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1399 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1400 /// HIR type that references the TAIT.
1402 /// Given a function definition like:
1405 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1410 /// we will create a TAIT definition in the HIR like
1413 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1416 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1419 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1422 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1423 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1424 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1425 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1426 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1427 #[instrument(level = "debug", skip(self), ret)]
1428 fn lower_opaque_impl_trait(
1431 origin: hir::OpaqueTyOrigin,
1432 opaque_ty_node_id: NodeId,
1433 bounds: &GenericBounds,
1435 itctx: &mut ImplTraitContext,
1436 ) -> hir::TyKind<'hir> {
1437 // Make sure we know that some funky desugaring has been going on here.
1438 // This is a first: there is code in other places like for loop
1439 // desugaring that explicitly states that we don't want to track that.
1440 // Not tracking it makes lints in rustc and clippy very fragile, as
1441 // frequently opened issues show.
1442 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1444 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1445 debug!(?opaque_ty_def_id);
1447 // Contains the new lifetime definitions created for the TAIT (if any).
1448 let mut collected_lifetimes = Vec::new();
1450 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1451 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1452 // exactly which ones those are.
1453 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1454 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1457 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1458 // we only keep the lifetimes that appear in the `impl Debug` itself:
1459 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1461 debug!(?lifetimes_to_remap);
1463 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1464 let mut new_remapping = FxHashMap::default();
1466 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1467 // in bounds), then create the new lifetime parameters required and create a mapping
1468 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1469 collected_lifetimes = lctx.create_lifetime_defs(
1471 &lifetimes_to_remap,
1474 debug!(?collected_lifetimes);
1475 debug!(?new_remapping);
1477 // Install the remapping from old to new (if any):
1478 lctx.with_remapping(new_remapping, |lctx| {
1479 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1480 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1481 // containing `&['x]`.
1482 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1483 |&(new_node_id, lifetime)| {
1484 let hir_id = lctx.lower_node_id(new_node_id);
1485 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1487 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1488 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1491 hir::ParamName::Plain(lifetime.ident),
1492 hir::LifetimeParamKind::Explicit,
1499 span: lifetime.ident.span,
1500 pure_wrt_drop: false,
1501 kind: hir::GenericParamKind::Lifetime { kind },
1506 debug!(?lifetime_defs);
1508 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1509 // get back Debug + 'a1, which is suitable for use on the TAIT.
1510 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1511 debug!(?hir_bounds);
1513 let opaque_ty_item = hir::OpaqueTy {
1514 generics: self.arena.alloc(hir::Generics {
1515 params: lifetime_defs,
1517 has_where_clause_predicates: false,
1518 where_clause_span: lctx.lower_span(span),
1519 span: lctx.lower_span(span),
1525 debug!(?opaque_ty_item);
1527 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1531 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1532 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1534 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1535 let id = self.next_node_id();
1536 let span = lifetime.ident.span;
1538 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1539 Ident::with_dummy_span(kw::UnderscoreLifetime)
1544 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1545 hir::GenericArg::Lifetime(l)
1549 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1550 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes, in_trait)
1553 /// Registers a new opaque type with the proper `NodeId`s and
1554 /// returns the lowered node-ID for the opaque type.
1555 fn generate_opaque_type(
1557 opaque_ty_id: LocalDefId,
1558 opaque_ty_item: hir::OpaqueTy<'hir>,
1560 opaque_ty_span: Span,
1561 ) -> hir::OwnerNode<'hir> {
1562 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1563 // Generate an `type Foo = impl Trait;` declaration.
1564 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1565 let opaque_ty_item = hir::Item {
1566 def_id: opaque_ty_id,
1567 ident: Ident::empty(),
1568 kind: opaque_ty_item_kind,
1569 vis_span: self.lower_span(span.shrink_to_lo()),
1570 span: self.lower_span(opaque_ty_span),
1572 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1575 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1576 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1577 /// new definition, adds it to the remapping with the definition of the given lifetime and
1578 /// returns a list of lifetimes to be lowered afterwards.
1579 fn create_lifetime_defs(
1581 parent_def_id: LocalDefId,
1582 lifetimes_in_bounds: &[Lifetime],
1583 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1584 ) -> Vec<(NodeId, Lifetime)> {
1585 let mut result = Vec::new();
1587 for lifetime in lifetimes_in_bounds {
1588 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1592 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1593 if remapping.get(&old_def_id).is_none() {
1594 let node_id = self.next_node_id();
1596 let new_def_id = self.create_def(
1599 DefPathData::LifetimeNs(lifetime.ident.name),
1601 remapping.insert(old_def_id, new_def_id);
1603 result.push((node_id, *lifetime));
1607 LifetimeRes::Fresh { param, binder: _ } => {
1608 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1609 if let Some(old_def_id) = self.opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1610 let node_id = self.next_node_id();
1612 let new_def_id = self.create_def(
1615 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1617 remapping.insert(old_def_id, new_def_id);
1619 result.push((node_id, *lifetime));
1623 LifetimeRes::Static | LifetimeRes::Error => {}
1626 let bug_msg = format!(
1627 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1628 res, lifetime.ident, lifetime.ident.span
1630 span_bug!(lifetime.ident.span, "{}", bug_msg);
1638 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1639 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1640 // as they are not explicit in HIR/Ty function signatures.
1641 // (instead, the `c_variadic` flag is set to `true`)
1642 let mut inputs = &decl.inputs[..];
1643 if decl.c_variadic() {
1644 inputs = &inputs[..inputs.len() - 1];
1646 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1647 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1648 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1652 // Lowers a function declaration.
1654 // `decl`: the unlowered (AST) function declaration.
1655 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1656 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1657 // `make_ret_async` is also `Some`.
1658 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1659 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1660 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1661 #[instrument(level = "debug", skip(self))]
1665 fn_node_id: Option<NodeId>,
1668 make_ret_async: Option<(NodeId, Span)>,
1669 ) -> &'hir hir::FnDecl<'hir> {
1670 let c_variadic = decl.c_variadic();
1672 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1673 // as they are not explicit in HIR/Ty function signatures.
1674 // (instead, the `c_variadic` flag is set to `true`)
1675 let mut inputs = &decl.inputs[..];
1677 inputs = &inputs[..inputs.len() - 1];
1679 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1680 if fn_node_id.is_some() {
1681 self.lower_ty_direct(¶m.ty, &mut ImplTraitContext::Universal)
1683 self.lower_ty_direct(
1685 &mut ImplTraitContext::Disallowed(match kind {
1686 FnDeclKind::Fn | FnDeclKind::Inherent => {
1687 unreachable!("fn should allow in-band lifetimes")
1689 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1690 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1691 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1692 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1693 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1699 let output = if let Some((ret_id, span)) = make_ret_async {
1701 FnDeclKind::Trait => {
1702 if !kind.impl_trait_in_trait_allowed(self.tcx) {
1705 .create_feature_err(
1706 TraitFnAsync { fn_span, span },
1707 sym::return_position_impl_trait_in_trait,
1711 self.lower_async_fn_ret_ty(
1713 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1719 if !kind.impl_trait_return_allowed(self.tcx) {
1722 .create_feature_err(
1723 TraitFnAsync { fn_span, span },
1724 sym::return_position_impl_trait_in_trait,
1728 self.lower_async_fn_ret_ty(
1730 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1738 FnRetTy::Ty(ref ty) => {
1739 let mut context = match fn_node_id {
1740 Some(fn_node_id) if kind.impl_trait_return_allowed(self.tcx) => {
1741 let fn_def_id = self.local_def_id(fn_node_id);
1742 ImplTraitContext::ReturnPositionOpaqueTy {
1743 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1747 Some(fn_node_id) if kind.impl_trait_in_trait_allowed(self.tcx) => {
1748 let fn_def_id = self.local_def_id(fn_node_id);
1749 ImplTraitContext::ReturnPositionOpaqueTy {
1750 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1754 _ => ImplTraitContext::Disallowed(match kind {
1755 FnDeclKind::Fn | FnDeclKind::Inherent => {
1756 unreachable!("fn should allow in-band lifetimes")
1758 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1759 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1760 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1761 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1762 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1765 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1767 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1771 self.arena.alloc(hir::FnDecl {
1775 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1776 let is_mutable_pat = matches!(
1778 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1782 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1783 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1784 // Given we are only considering `ImplicitSelf` types, we needn't consider
1785 // the case where we have a mutable pattern to a reference as that would
1786 // no longer be an `ImplicitSelf`.
1787 TyKind::Rptr(_, ref mt)
1788 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1790 hir::ImplicitSelfKind::MutRef
1792 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1793 hir::ImplicitSelfKind::ImmRef
1795 _ => hir::ImplicitSelfKind::None,
1801 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1802 // combined with the following definition of `OpaqueTy`:
1804 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1806 // `output`: unlowered output type (`T` in `-> T`)
1807 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1808 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1809 #[instrument(level = "debug", skip(self))]
1810 fn lower_async_fn_ret_ty(
1814 opaque_ty_node_id: NodeId,
1816 ) -> hir::FnRetTy<'hir> {
1817 let span = output.span();
1819 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1821 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1822 let fn_def_id = self.local_def_id(fn_node_id);
1824 // When we create the opaque type for this async fn, it is going to have
1825 // to capture all the lifetimes involved in the signature (including in the
1826 // return type). This is done by introducing lifetime parameters for:
1828 // - all the explicitly declared lifetimes from the impl and function itself;
1829 // - all the elided lifetimes in the fn arguments;
1830 // - all the elided lifetimes in the return type.
1832 // So for example in this snippet:
1835 // impl<'a> Foo<'a> {
1836 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1837 // // ^ '0 ^ '1 ^ '2
1838 // // elided lifetimes used below
1843 // we would create an opaque type like:
1846 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1849 // and we would then desugar `bar` to the equivalent of:
1852 // impl<'a> Foo<'a> {
1853 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1857 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1858 // this is because the elided lifetimes from the return type
1859 // should be figured out using the ordinary elision rules, and
1860 // this desugaring achieves that.
1862 // Calculate all the lifetimes that should be captured
1863 // by the opaque type. This should include all in-scope
1864 // lifetime parameters, including those defined in-band.
1866 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1868 let mut collected_lifetimes = Vec::new();
1869 let mut new_remapping = FxHashMap::default();
1871 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1872 debug!(?extra_lifetime_params);
1873 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1874 let outer_def_id = self.local_def_id(outer_node_id);
1875 let inner_node_id = self.next_node_id();
1877 // Add a definition for the in scope lifetime def.
1878 let inner_def_id = self.create_def(
1881 DefPathData::LifetimeNs(ident.name),
1883 new_remapping.insert(outer_def_id, inner_def_id);
1885 let inner_res = match outer_res {
1886 // Input lifetime like `'a`:
1887 LifetimeRes::Param { param, .. } => {
1888 LifetimeRes::Param { param, binder: fn_node_id }
1890 // Input lifetime like `'1`:
1891 LifetimeRes::Fresh { param, .. } => {
1892 LifetimeRes::Fresh { param, binder: fn_node_id }
1894 LifetimeRes::Static | LifetimeRes::Error => continue,
1897 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1898 res, ident, ident.span
1903 let lifetime = Lifetime { id: outer_node_id, ident };
1904 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1907 debug!(?collected_lifetimes);
1909 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1910 // find out exactly which ones those are.
1911 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1912 // we only keep the lifetimes that appear in the `impl Debug` itself:
1913 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1914 debug!(?lifetimes_to_remap);
1916 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1917 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1918 // in bounds), then create the new lifetime parameters required and create a mapping
1919 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1920 collected_lifetimes.extend(
1921 this.create_lifetime_defs(
1923 &lifetimes_to_remap,
1927 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1929 debug!(?collected_lifetimes);
1930 debug!(?new_remapping);
1932 // Install the remapping from old to new (if any):
1933 this.with_remapping(new_remapping, |this| {
1934 // We have to be careful to get elision right here. The
1935 // idea is that we create a lifetime parameter for each
1936 // lifetime in the return type. So, given a return type
1937 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1938 // Future<Output = &'1 [ &'2 u32 ]>`.
1940 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1941 // hence the elision takes place at the fn site.
1942 let future_bound = this.lower_async_fn_output_type_to_future_bound(
1945 ImplTraitContext::ReturnPositionOpaqueTy {
1946 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1951 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1952 |&(new_node_id, lifetime, _)| {
1953 let hir_id = this.lower_node_id(new_node_id);
1954 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1956 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1957 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1960 hir::ParamName::Plain(lifetime.ident),
1961 hir::LifetimeParamKind::Explicit,
1968 span: lifetime.ident.span,
1969 pure_wrt_drop: false,
1970 kind: hir::GenericParamKind::Lifetime { kind },
1975 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1977 let opaque_ty_item = hir::OpaqueTy {
1978 generics: this.arena.alloc(hir::Generics {
1979 params: generic_params,
1981 has_where_clause_predicates: false,
1982 where_clause_span: this.lower_span(span),
1983 span: this.lower_span(span),
1985 bounds: arena_vec![this; future_bound],
1986 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1990 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1991 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1995 // As documented above, we need to create the lifetime
1996 // arguments to our opaque type. Continuing with our example,
1997 // we're creating the type arguments for the return type:
2000 // Bar<'a, 'b, '0, '1, '_>
2003 // For the "input" lifetime parameters, we wish to create
2004 // references to the parameters themselves, including the
2005 // "implicit" ones created from parameter types (`'a`, `'b`,
2008 // For the "output" lifetime parameters, we just want to
2010 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2011 |(_, lifetime, res)| {
2012 let id = self.next_node_id();
2013 let span = lifetime.ident.span;
2015 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
2016 Ident::with_dummy_span(kw::UnderscoreLifetime)
2021 let res = res.unwrap_or(
2022 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2024 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
2028 // Create the `Foo<...>` reference itself. Note that the `type
2029 // Foo = impl Trait` is, internally, created as a child of the
2030 // async fn, so the *type parameters* are inherited. It's
2031 // only the lifetime parameters that we must supply.
2032 let opaque_ty_ref = hir::TyKind::OpaqueDef(
2033 hir::ItemId { def_id: opaque_ty_def_id },
2037 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2038 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2041 /// Transforms `-> T` into `Future<Output = T>`.
2042 fn lower_async_fn_output_type_to_future_bound(
2046 mut nested_impl_trait_context: ImplTraitContext,
2047 ) -> hir::GenericBound<'hir> {
2048 // Compute the `T` in `Future<Output = T>` from the return type.
2049 let output_ty = match output {
2050 FnRetTy::Ty(ty) => {
2051 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2052 // `impl Future` opaque type that `async fn` implicitly
2054 self.lower_ty(ty, &mut nested_impl_trait_context)
2056 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2060 let future_args = self.arena.alloc(hir::GenericArgs {
2062 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2063 parenthesized: false,
2067 hir::GenericBound::LangItemTrait(
2068 // ::std::future::Future<future_params>
2069 hir::LangItem::Future,
2070 self.lower_span(span),
2076 #[instrument(level = "trace", skip(self))]
2077 fn lower_param_bound(
2080 itctx: &mut ImplTraitContext,
2081 ) -> hir::GenericBound<'hir> {
2083 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2084 self.lower_poly_trait_ref(p, itctx),
2085 self.lower_trait_bound_modifier(*modifier),
2087 GenericBound::Outlives(lifetime) => {
2088 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2093 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2094 let span = self.lower_span(l.ident.span);
2095 let ident = self.lower_ident(l.ident);
2096 self.new_named_lifetime(l.id, l.id, span, ident)
2099 #[instrument(level = "debug", skip(self))]
2100 fn new_named_lifetime_with_res(
2106 ) -> &'hir hir::Lifetime {
2107 let name = match res {
2108 LifetimeRes::Param { param, .. } => {
2109 let p_name = ParamName::Plain(ident);
2110 let param = self.get_remapped_def_id(param);
2112 hir::LifetimeName::Param(param, p_name)
2114 LifetimeRes::Fresh { param, .. } => {
2115 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2116 let param = self.local_def_id(param);
2118 hir::LifetimeName::Param(param, ParamName::Fresh)
2120 LifetimeRes::Infer => hir::LifetimeName::Infer,
2121 LifetimeRes::Static => hir::LifetimeName::Static,
2122 LifetimeRes::Error => hir::LifetimeName::Error,
2123 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2127 self.arena.alloc(hir::Lifetime {
2128 hir_id: self.lower_node_id(id),
2129 span: self.lower_span(span),
2134 #[instrument(level = "debug", skip(self))]
2135 fn new_named_lifetime(
2141 ) -> &'hir hir::Lifetime {
2142 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2143 self.new_named_lifetime_with_res(new_id, span, ident, res)
2146 fn lower_generic_params_mut<'s>(
2148 params: &'s [GenericParam],
2149 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2150 params.iter().map(move |param| self.lower_generic_param(param))
2153 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2154 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2157 #[instrument(level = "trace", skip(self))]
2158 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2159 let (name, kind) = self.lower_generic_param_kind(param);
2161 let hir_id = self.lower_node_id(param.id);
2162 self.lower_attrs(hir_id, ¶m.attrs);
2166 span: self.lower_span(param.span()),
2167 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2169 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2173 fn lower_generic_param_kind(
2175 param: &GenericParam,
2176 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2178 GenericParamKind::Lifetime => {
2179 // AST resolution emitted an error on those parameters, so we lower them using
2180 // `ParamName::Error`.
2182 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2185 let ident = self.lower_ident(param.ident);
2186 ParamName::Plain(ident)
2189 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2193 GenericParamKind::Type { ref default, .. } => {
2194 let kind = hir::GenericParamKind::Type {
2195 default: default.as_ref().map(|x| {
2196 self.lower_ty(x, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2201 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2203 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2205 self.lower_ty(&ty, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2206 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2208 hir::ParamName::Plain(self.lower_ident(param.ident)),
2209 hir::GenericParamKind::Const { ty, default },
2218 itctx: &mut ImplTraitContext,
2219 ) -> hir::TraitRef<'hir> {
2220 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2221 hir::QPath::Resolved(None, path) => path,
2222 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2224 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2227 #[instrument(level = "debug", skip(self))]
2228 fn lower_poly_trait_ref(
2231 itctx: &mut ImplTraitContext,
2232 ) -> hir::PolyTraitRef<'hir> {
2233 self.lower_lifetime_binder(
2235 &p.bound_generic_params,
2236 |lctx, bound_generic_params| {
2237 let trait_ref = lctx.lower_trait_ref(&p.trait_ref, itctx);
2238 hir::PolyTraitRef { bound_generic_params, trait_ref, span: lctx.lower_span(p.span) }
2243 fn lower_mt(&mut self, mt: &MutTy, itctx: &mut ImplTraitContext) -> hir::MutTy<'hir> {
2244 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2247 #[instrument(level = "debug", skip(self), ret)]
2248 fn lower_param_bounds(
2250 bounds: &[GenericBound],
2251 itctx: &mut ImplTraitContext,
2252 ) -> hir::GenericBounds<'hir> {
2253 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2256 fn lower_param_bounds_mut<'s, 'b>(
2258 bounds: &'s [GenericBound],
2259 itctx: &'b mut ImplTraitContext,
2260 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> + Captures<'b>
2262 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2265 #[instrument(level = "debug", skip(self), ret)]
2266 fn lower_generic_and_bounds(
2271 bounds: &[GenericBound],
2272 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2273 // Add a definition for the in-band `Param`.
2274 let def_id = self.local_def_id(node_id);
2276 // Set the name to `impl Bound1 + Bound2`.
2277 let param = hir::GenericParam {
2278 hir_id: self.lower_node_id(node_id),
2279 name: ParamName::Plain(self.lower_ident(ident)),
2280 pure_wrt_drop: false,
2281 span: self.lower_span(span),
2282 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2286 let preds = self.lower_generic_bound_predicate(
2289 &GenericParamKind::Type { default: None },
2291 &mut ImplTraitContext::Universal,
2292 hir::PredicateOrigin::ImplTrait,
2295 let hir_id = self.next_id();
2296 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2297 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2299 self.arena.alloc(hir::Path {
2300 span: self.lower_span(span),
2303 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2310 /// Lowers a block directly to an expression, presuming that it
2311 /// has no attributes and is not targeted by a `break`.
2312 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2313 let block = self.lower_block(b, false);
2314 self.expr_block(block, AttrVec::new())
2317 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2318 match c.value.kind {
2319 ExprKind::Underscore => {
2320 if self.tcx.features().generic_arg_infer {
2321 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2324 &self.tcx.sess.parse_sess,
2325 sym::generic_arg_infer,
2327 "using `_` for array lengths is unstable",
2329 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2330 hir::ArrayLen::Body(self.lower_anon_const(c))
2333 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2337 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2338 self.with_new_scopes(|this| hir::AnonConst {
2339 hir_id: this.lower_node_id(c.id),
2340 body: this.lower_const_body(c.value.span, Some(&c.value)),
2344 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2346 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2347 UserProvided => hir::UnsafeSource::UserProvided,
2351 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2353 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2354 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2356 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2357 // placeholder for compilation to proceed.
2358 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2359 hir::TraitBoundModifier::Maybe
2364 // Helper methods for building HIR.
2366 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2367 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2370 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2371 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2376 attrs: Option<&'hir [Attribute]>,
2378 init: Option<&'hir hir::Expr<'hir>>,
2379 pat: &'hir hir::Pat<'hir>,
2380 source: hir::LocalSource,
2381 ) -> hir::Stmt<'hir> {
2382 let hir_id = self.next_id();
2383 if let Some(a) = attrs {
2384 debug_assert!(!a.is_empty());
2385 self.attrs.insert(hir_id.local_id, a);
2387 let local = hir::Local {
2393 span: self.lower_span(span),
2396 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2399 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2400 self.block_all(expr.span, &[], Some(expr))
2406 stmts: &'hir [hir::Stmt<'hir>],
2407 expr: Option<&'hir hir::Expr<'hir>>,
2408 ) -> &'hir hir::Block<'hir> {
2409 let blk = hir::Block {
2412 hir_id: self.next_id(),
2413 rules: hir::BlockCheckMode::DefaultBlock,
2414 span: self.lower_span(span),
2415 targeted_by_break: false,
2417 self.arena.alloc(blk)
2420 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2421 let field = self.single_pat_field(span, pat);
2422 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2425 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2426 let field = self.single_pat_field(span, pat);
2427 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2430 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2431 let field = self.single_pat_field(span, pat);
2432 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2435 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2436 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2439 fn single_pat_field(
2442 pat: &'hir hir::Pat<'hir>,
2443 ) -> &'hir [hir::PatField<'hir>] {
2444 let field = hir::PatField {
2445 hir_id: self.next_id(),
2446 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2447 is_shorthand: false,
2449 span: self.lower_span(span),
2451 arena_vec![self; field]
2454 fn pat_lang_item_variant(
2457 lang_item: hir::LangItem,
2458 fields: &'hir [hir::PatField<'hir>],
2459 hir_id: Option<hir::HirId>,
2460 ) -> &'hir hir::Pat<'hir> {
2461 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2462 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2465 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2466 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2469 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2470 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2473 fn pat_ident_binding_mode(
2477 bm: hir::BindingAnnotation,
2478 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2479 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2480 (self.arena.alloc(pat), hir_id)
2483 fn pat_ident_binding_mode_mut(
2487 bm: hir::BindingAnnotation,
2488 ) -> (hir::Pat<'hir>, hir::HirId) {
2489 let hir_id = self.next_id();
2494 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2495 span: self.lower_span(span),
2496 default_binding_modes: true,
2502 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2503 self.arena.alloc(hir::Pat {
2504 hir_id: self.next_id(),
2506 span: self.lower_span(span),
2507 default_binding_modes: true,
2511 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2513 hir_id: self.next_id(),
2515 span: self.lower_span(span),
2516 default_binding_modes: false,
2522 mut hir_id: hir::HirId,
2524 qpath: hir::QPath<'hir>,
2525 ) -> hir::Ty<'hir> {
2526 let kind = match qpath {
2527 hir::QPath::Resolved(None, path) => {
2528 // Turn trait object paths into `TyKind::TraitObject` instead.
2530 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2531 let principal = hir::PolyTraitRef {
2532 bound_generic_params: &[],
2533 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2534 span: self.lower_span(span),
2537 // The original ID is taken by the `PolyTraitRef`,
2538 // so the `Ty` itself needs a different one.
2539 hir_id = self.next_id();
2540 hir::TyKind::TraitObject(
2541 arena_vec![self; principal],
2542 self.elided_dyn_bound(span),
2543 TraitObjectSyntax::None,
2546 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2549 _ => hir::TyKind::Path(qpath),
2552 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2555 /// Invoked to create the lifetime argument(s) for an elided trait object
2556 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2557 /// when the bound is written, even if it is written with `'_` like in
2558 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2559 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2560 let r = hir::Lifetime {
2561 hir_id: self.next_id(),
2562 span: self.lower_span(span),
2563 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2565 debug!("elided_dyn_bound: r={:?}", r);
2570 /// Helper struct for delayed construction of GenericArgs.
2571 struct GenericArgsCtor<'hir> {
2572 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2573 bindings: &'hir [hir::TypeBinding<'hir>],
2574 parenthesized: bool,
2578 impl<'hir> GenericArgsCtor<'hir> {
2579 fn is_empty(&self) -> bool {
2580 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2583 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2584 let ga = hir::GenericArgs {
2585 args: this.arena.alloc_from_iter(self.args),
2586 bindings: self.bindings,
2587 parenthesized: self.parenthesized,
2588 span_ext: this.lower_span(self.span),
2590 this.arena.alloc(ga)