1 //! Lowers the AST to the HIR.
3 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
4 //! much like a fold. Where lowering involves a bit more work things get more
5 //! interesting and there are some invariants you should know about. These mostly
6 //! concern spans and IDs.
8 //! Spans are assigned to AST nodes during parsing and then are modified during
9 //! expansion to indicate the origin of a node and the process it went through
10 //! being expanded. IDs are assigned to AST nodes just before lowering.
12 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
13 //! expansion we do not preserve the process of lowering in the spans, so spans
14 //! should not be modified here. When creating a new node (as opposed to
15 //! "folding" an existing one), create a new ID using `next_id()`.
17 //! You must ensure that IDs are unique. That means that you should only use the
18 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
19 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
20 //! If you do, you must then set the new node's ID to a fresh one.
22 //! Spans are used for error messages and for tools to map semantics back to
23 //! source code. It is therefore not as important with spans as IDs to be strict
24 //! about use (you can't break the compiler by screwing up a span). Obviously, a
25 //! HIR node can only have a single span. But multiple nodes can have the same
26 //! span and spans don't need to be kept in order, etc. Where code is preserved
27 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
28 //! new it is probably best to give a span for the whole AST node being lowered.
29 //! All nodes should have real spans; don't use dummy spans. Tools are likely to
30 //! get confused if the spans from leaf AST nodes occur in multiple places
31 //! in the HIR, especially for multiple identifiers.
33 #![feature(box_patterns)]
34 #![feature(let_chains)]
35 #![feature(never_type)]
36 #![recursion_limit = "256"]
37 #![allow(rustc::potential_query_instability)]
38 #![deny(rustc::untranslatable_diagnostic)]
39 #![deny(rustc::diagnostic_outside_of_impl)]
44 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait, TraitFnAsync};
46 use rustc_arena::declare_arena;
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::ty::{ResolverAstLowering, TyCtxt};
65 use rustc_middle::{bug, span_bug};
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 /// Used to allocate temporary AST nodes for use during lowering.
99 /// This allows us to create "fake" AST -- these nodes can sometimes
100 /// be allocated on the stack, but other times we need them to live longer
101 /// than the current stack frame, so they can be collected into vectors
102 /// and things like that.
103 ast_arena: &'a Arena<'static>,
105 /// Bodies inside the owner being lowered.
106 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
107 /// Attributes inside the owner being lowered.
108 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
109 /// Collect items that were created by lowering the current owner.
110 children: FxHashMap<LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>>,
112 generator_kind: Option<hir::GeneratorKind>,
114 /// When inside an `async` context, this is the `HirId` of the
115 /// `task_context` local bound to the resume argument of the generator.
116 task_context: Option<hir::HirId>,
118 /// Used to get the current `fn`'s def span to point to when using `await`
119 /// outside of an `async fn`.
120 current_item: Option<Span>,
122 catch_scope: Option<NodeId>,
123 loop_scope: Option<NodeId>,
124 is_in_loop_condition: bool,
125 is_in_trait_impl: bool,
126 is_in_dyn_type: bool,
128 current_hir_id_owner: hir::OwnerId,
129 item_local_id_counter: hir::ItemLocalId,
130 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
131 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
133 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
134 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
136 /// NodeIds that are lowered inside the current HIR owner.
137 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
139 allow_try_trait: Option<Lrc<[Symbol]>>,
140 allow_gen_future: Option<Lrc<[Symbol]>>,
141 allow_into_future: Option<Lrc<[Symbol]>>,
143 /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
144 /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
145 /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
146 /// field from the original parameter 'a to the new parameter 'a1.
147 generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
151 [] tys: rustc_ast::Ty,
152 [] aba: rustc_ast::AngleBracketedArgs,
153 [] ptr: rustc_ast::PolyTraitRef,
154 // This _marker field is needed because `declare_arena` creates `Arena<'tcx>` and we need to
155 // use `'tcx`. If we don't have this we get a compile error.
156 [] _marker: std::marker::PhantomData<&'tcx ()>,
159 trait ResolverAstLoweringExt {
160 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
161 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
162 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
163 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
164 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
165 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
166 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
169 impl ResolverAstLoweringExt for ResolverAstLowering {
170 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
171 if let ExprKind::Path(None, path) = &expr.kind {
172 // Don't perform legacy const generics rewriting if the path already
173 // has generic arguments.
174 if path.segments.last().unwrap().args.is_some() {
178 let partial_res = self.partial_res_map.get(&expr.id)?;
179 if partial_res.unresolved_segments() != 0 {
183 if let Res::Def(DefKind::Fn, def_id) = partial_res.base_res() {
184 // We only support cross-crate argument rewriting. Uses
185 // within the same crate should be updated to use the new
186 // const generics style.
187 if def_id.is_local() {
191 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
200 /// Obtains resolution for a `NodeId` with a single resolution.
201 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
202 self.partial_res_map.get(&id).copied()
205 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
206 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
207 self.import_res_map.get(&id).copied().unwrap_or_default()
210 /// Obtains resolution for a label with the given `NodeId`.
211 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
212 self.label_res_map.get(&id).copied()
215 /// Obtains resolution for a lifetime with the given `NodeId`.
216 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
217 self.lifetimes_res_map.get(&id).copied()
220 /// Obtain the list of lifetimes parameters to add to an item.
222 /// Extra lifetime parameters should only be added in places that can appear
223 /// as a `binder` in `LifetimeRes`.
225 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
226 /// should appear at the enclosing `PolyTraitRef`.
227 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
228 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
231 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
232 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
236 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
237 /// and if so, what meaning it has.
238 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
239 enum ImplTraitContext {
240 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
241 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
242 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
244 /// Newly generated parameters should be inserted into the given `Vec`.
247 /// Treat `impl Trait` as shorthand for a new opaque type.
248 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
249 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
251 ReturnPositionOpaqueTy {
252 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
253 origin: hir::OpaqueTyOrigin,
256 /// Impl trait in type aliases.
258 /// `impl Trait` is not accepted in this position.
259 Disallowed(ImplTraitPosition),
262 /// Position in which `impl Trait` is disallowed.
263 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
264 enum ImplTraitPosition {
286 impl std::fmt::Display for ImplTraitPosition {
287 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
288 let name = match self {
289 ImplTraitPosition::Path => "path",
290 ImplTraitPosition::Variable => "variable binding",
291 ImplTraitPosition::Type => "type",
292 ImplTraitPosition::Trait => "trait",
293 ImplTraitPosition::AsyncBlock => "async block",
294 ImplTraitPosition::Bound => "bound",
295 ImplTraitPosition::Generic => "generic",
296 ImplTraitPosition::ExternFnParam => "`extern fn` param",
297 ImplTraitPosition::ClosureParam => "closure param",
298 ImplTraitPosition::PointerParam => "`fn` pointer param",
299 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
300 ImplTraitPosition::TraitParam => "trait method param",
301 ImplTraitPosition::ImplParam => "`impl` method param",
302 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
303 ImplTraitPosition::ClosureReturn => "closure return",
304 ImplTraitPosition::PointerReturn => "`fn` pointer return",
305 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
306 ImplTraitPosition::TraitReturn => "trait method return",
307 ImplTraitPosition::ImplReturn => "`impl` method return",
310 write!(f, "{}", name)
314 #[derive(Debug, PartialEq, Eq)]
326 fn impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
328 FnDeclKind::Fn | FnDeclKind::Inherent => true,
329 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
330 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
335 fn async_fn_allowed(&self, tcx: TyCtxt<'_>) -> bool {
337 FnDeclKind::Fn | FnDeclKind::Inherent => true,
338 FnDeclKind::Impl if tcx.features().async_fn_in_trait => true,
339 FnDeclKind::Trait if tcx.features().async_fn_in_trait => true,
345 #[derive(Copy, Clone)]
348 Crate(&'a ast::Crate),
350 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
351 ForeignItem(&'a ast::ForeignItem),
355 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
357 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
358 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
359 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
360 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
361 visit::walk_crate(&mut indexer, krate);
362 return indexer.index;
364 struct Indexer<'s, 'a> {
365 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
366 index: IndexVec<LocalDefId, AstOwner<'a>>,
369 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
370 fn visit_attribute(&mut self, _: &'a Attribute) {
371 // We do not want to lower expressions that appear in attributes,
372 // as they are not accessible to the rest of the HIR.
375 fn visit_item(&mut self, item: &'a ast::Item) {
376 let def_id = self.node_id_to_def_id[&item.id];
377 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
378 self.index[def_id] = AstOwner::Item(item);
379 visit::walk_item(self, item)
382 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
383 let def_id = self.node_id_to_def_id[&item.id];
384 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
385 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
386 visit::walk_assoc_item(self, item, ctxt);
389 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
390 let def_id = self.node_id_to_def_id[&item.id];
391 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
392 self.index[def_id] = AstOwner::ForeignItem(item);
393 visit::walk_foreign_item(self, item);
398 /// Compute the hash for the HIR of the full crate.
399 /// This hash will then be part of the crate_hash which is stored in the metadata.
402 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
404 let mut hir_body_nodes: Vec<_> = owners
406 .filter_map(|(def_id, info)| {
407 let info = info.as_owner()?;
408 let def_path_hash = tcx.hir().def_path_hash(def_id);
409 Some((def_path_hash, info))
412 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
414 tcx.with_stable_hashing_context(|mut hcx| {
415 let mut stable_hasher = StableHasher::new();
416 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
417 stable_hasher.finish()
421 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
423 let krate = tcx.untracked_crate.steal();
424 let mut resolver = tcx.resolver_for_lowering(()).steal();
426 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
427 let mut owners = IndexVec::from_fn_n(
428 |_| hir::MaybeOwner::Phantom,
429 tcx.definitions_untracked().def_index_count(),
432 let ast_arena = Arena::default();
434 for def_id in ast_index.indices() {
437 resolver: &mut resolver,
438 ast_arena: &ast_arena,
439 ast_index: &ast_index,
445 // Drop AST to free memory
446 std::mem::drop(ast_index);
447 sess.time("drop_ast", || std::mem::drop(krate));
449 // Discard hygiene data, which isn't required after lowering to HIR.
450 if !sess.opts.unstable_opts.keep_hygiene_data {
451 rustc_span::hygiene::clear_syntax_context_map();
454 let hir_hash = compute_hir_hash(tcx, &owners);
455 hir::Crate { owners, hir_hash }
458 #[derive(Copy, Clone, PartialEq, Debug)]
460 /// Any path in a type context.
462 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
464 /// The `module::Type` in `module::Type::method` in an expression.
468 enum ParenthesizedGenericArgs {
473 impl<'a, 'hir> LoweringContext<'a, 'hir> {
477 node_id: ast::NodeId,
480 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
482 self.opt_local_def_id(node_id).is_none(),
483 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
486 self.tcx.hir().def_key(self.local_def_id(node_id)),
489 let def_id = self.tcx.create_def(parent, data);
491 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
492 self.resolver.node_id_to_def_id.insert(node_id, def_id);
497 fn next_node_id(&mut self) -> NodeId {
498 let start = self.resolver.next_node_id;
499 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
500 self.resolver.next_node_id = ast::NodeId::from_u32(next);
504 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
505 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
507 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
508 /// invoking with the id from the `ast::Lifetime` node found inside
509 /// the `&'a u32` type would return the `LocalDefId` of the
510 /// `'a` parameter declared on `foo`.
512 /// This function also applies remapping from `get_remapped_def_id`.
513 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
514 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
515 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
516 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
517 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
521 .map(|local_def_id| self.get_remapped_def_id(*local_def_id))
524 fn local_def_id(&self, node: NodeId) -> LocalDefId {
525 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
528 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
529 /// `generics_def_id_map` field.
530 fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId {
531 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
532 // push new mappings so we need to try first the latest mappings, hence `iter().rev()`.
536 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
538 // We would end with a generics_def_id_map like:
540 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
542 // for the opaque type generated on `impl Sized + 'b`, We want the result to be:
543 // impl_sized#'b, so iterating forward is the wrong thing to do.
544 for map in self.generics_def_id_map.iter().rev() {
545 if let Some(r) = map.get(&local_def_id) {
546 debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`");
549 debug!("def_id_remapper: no remapping for `{local_def_id:?}` found in map");
556 /// Freshen the `LoweringContext` and ready it to lower a nested item.
557 /// The lowered item is registered into `self.children`.
559 /// This function sets up `HirId` lowering infrastructure,
560 /// and stashes the shared mutable state to avoid pollution by the closure.
561 #[instrument(level = "debug", skip(self, f))]
562 fn with_hir_id_owner(
565 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
567 let def_id = self.local_def_id(owner);
569 let current_attrs = std::mem::take(&mut self.attrs);
570 let current_bodies = std::mem::take(&mut self.bodies);
571 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
572 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
573 let current_trait_map = std::mem::take(&mut self.trait_map);
575 std::mem::replace(&mut self.current_hir_id_owner, hir::OwnerId { def_id });
576 let current_local_counter =
577 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
578 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
579 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
581 // Do not reset `next_node_id` and `node_id_to_def_id`:
582 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
583 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
585 // Always allocate the first `HirId` for the owner itself.
586 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
587 debug_assert_eq!(_old, None);
590 debug_assert_eq!(def_id, item.def_id().def_id);
591 // `f` should have consumed all the elements in these vectors when constructing `item`.
592 debug_assert!(self.impl_trait_defs.is_empty());
593 debug_assert!(self.impl_trait_bounds.is_empty());
594 let info = self.make_owner_info(item);
596 self.attrs = current_attrs;
597 self.bodies = current_bodies;
598 self.node_id_to_local_id = current_node_ids;
599 self.local_id_to_def_id = current_id_to_def_id;
600 self.trait_map = current_trait_map;
601 self.current_hir_id_owner = current_owner;
602 self.item_local_id_counter = current_local_counter;
603 self.impl_trait_defs = current_impl_trait_defs;
604 self.impl_trait_bounds = current_impl_trait_bounds;
606 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
607 debug_assert!(_old.is_none())
610 /// Installs the remapping `remap` in scope while `f` is being executed.
611 /// This causes references to the `LocalDefId` keys to be changed to
612 /// refer to the values instead.
614 /// The remapping is used when one piece of AST expands to multiple
615 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
616 /// expands to both a function definition (`foo`) and a TAIT for the return value,
617 /// both of which have a lifetime parameter `'a`. The remapping allows us to
618 /// rewrite the `'a` in the return value to refer to the
619 /// `'a` declared on the TAIT, instead of the function.
620 fn with_remapping<R>(
622 remap: FxHashMap<LocalDefId, LocalDefId>,
623 f: impl FnOnce(&mut Self) -> R,
625 self.generics_def_id_map.push(remap);
627 self.generics_def_id_map.pop();
631 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
632 let attrs = std::mem::take(&mut self.attrs);
633 let mut bodies = std::mem::take(&mut self.bodies);
634 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
635 let trait_map = std::mem::take(&mut self.trait_map);
637 #[cfg(debug_assertions)]
638 for (id, attrs) in attrs.iter() {
639 // Verify that we do not store empty slices in the map.
640 if attrs.is_empty() {
641 panic!("Stored empty attributes for {:?}", id);
645 bodies.sort_by_key(|(k, _)| *k);
646 let bodies = SortedMap::from_presorted_elements(bodies);
647 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
648 let (nodes, parenting) =
649 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
650 let nodes = hir::OwnerNodes {
651 hash_including_bodies,
658 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
659 let mut stable_hasher = StableHasher::new();
660 attrs.hash_stable(&mut hcx, &mut stable_hasher);
661 stable_hasher.finish()
663 hir::AttributeMap { map: attrs, hash }
666 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
669 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
670 /// queries which depend on the full HIR tree and those which only depend on the item signature.
673 node: hir::OwnerNode<'hir>,
674 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
675 ) -> (Fingerprint, Fingerprint) {
676 self.tcx.with_stable_hashing_context(|mut hcx| {
677 let mut stable_hasher = StableHasher::new();
678 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
679 node.hash_stable(hcx, &mut stable_hasher)
681 let hash_including_bodies = stable_hasher.finish();
682 let mut stable_hasher = StableHasher::new();
683 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
684 let hash_without_bodies = stable_hasher.finish();
685 (hash_including_bodies, hash_without_bodies)
689 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
690 /// the `LoweringContext`'s `NodeId => HirId` map.
691 /// Take care not to call this method if the resulting `HirId` is then not
692 /// actually used in the HIR, as that would trigger an assertion in the
693 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
694 /// properly. Calling the method twice with the same `NodeId` is fine though.
695 #[instrument(level = "debug", skip(self), ret)]
696 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
697 assert_ne!(ast_node_id, DUMMY_NODE_ID);
699 match self.node_id_to_local_id.entry(ast_node_id) {
700 Entry::Occupied(o) => {
701 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
703 Entry::Vacant(v) => {
704 // Generate a new `HirId`.
705 let owner = self.current_hir_id_owner;
706 let local_id = self.item_local_id_counter;
707 let hir_id = hir::HirId { owner, local_id };
710 self.item_local_id_counter.increment_by(1);
712 assert_ne!(local_id, hir::ItemLocalId::new(0));
713 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
714 // Do not override a `MaybeOwner::Owner` that may already here.
715 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
716 self.local_id_to_def_id.insert(local_id, def_id);
719 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
720 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
728 /// Generate a new `HirId` without a backing `NodeId`.
729 #[instrument(level = "debug", skip(self), ret)]
730 fn next_id(&mut self) -> hir::HirId {
731 let owner = self.current_hir_id_owner;
732 let local_id = self.item_local_id_counter;
733 assert_ne!(local_id, hir::ItemLocalId::new(0));
734 self.item_local_id_counter.increment_by(1);
735 hir::HirId { owner, local_id }
738 #[instrument(level = "trace", skip(self))]
739 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
740 let res: Result<Res, ()> = res.apply_id(|id| {
741 let owner = self.current_hir_id_owner;
742 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
743 Ok(hir::HirId { owner, local_id })
747 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
748 // This can happen when trying to lower the return type `x` in erroneous code like
749 // async fn foo(x: u8) -> x {}
750 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
751 // an opaque type as a synthesized HIR owner.
752 res.unwrap_or(Res::Err)
755 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
756 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
757 if pr.unresolved_segments() != 0 {
758 panic!("path not fully resolved: {:?}", pr);
764 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
765 self.resolver.get_import_res(id).present_items()
768 fn diagnostic(&self) -> &Handler {
769 self.tcx.sess.diagnostic()
772 /// Reuses the span but adds information like the kind of the desugaring and features that are
773 /// allowed inside this span.
774 fn mark_span_with_reason(
776 reason: DesugaringKind,
778 allow_internal_unstable: Option<Lrc<[Symbol]>>,
780 self.tcx.with_stable_hashing_context(|hcx| {
781 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
785 /// Intercept all spans entering HIR.
786 /// Mark a span as relative to the current owning item.
787 fn lower_span(&self, span: Span) -> Span {
788 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
789 span.with_parent(Some(self.current_hir_id_owner.def_id))
791 // Do not make spans relative when not using incremental compilation.
796 fn lower_ident(&self, ident: Ident) -> Ident {
797 Ident::new(ident.name, self.lower_span(ident.span))
800 /// Converts a lifetime into a new generic parameter.
801 #[instrument(level = "debug", skip(self))]
802 fn lifetime_res_to_generic_param(
807 ) -> Option<hir::GenericParam<'hir>> {
808 let (name, kind) = match res {
809 LifetimeRes::Param { .. } => {
810 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
812 LifetimeRes::Fresh { param, .. } => {
813 // Late resolution delegates to us the creation of the `LocalDefId`.
814 let _def_id = self.create_def(
815 self.current_hir_id_owner.def_id,
817 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
821 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
823 LifetimeRes::Static | LifetimeRes::Error => return None,
825 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
826 res, ident, ident.span
829 let hir_id = self.lower_node_id(node_id);
830 Some(hir::GenericParam {
833 span: self.lower_span(ident.span),
834 pure_wrt_drop: false,
835 kind: hir::GenericParamKind::Lifetime { kind },
840 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
841 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
842 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
843 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
844 /// parameters will be successful.
845 #[instrument(level = "debug", skip(self))]
847 fn lower_lifetime_binder(
850 generic_params: &[GenericParam],
851 ) -> &'hir [hir::GenericParam<'hir>] {
852 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
853 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
854 debug!(?extra_lifetimes);
855 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
856 self.lifetime_res_to_generic_param(ident, node_id, res)
858 let generic_params = self.arena.alloc_from_iter(generic_params);
859 debug!(?generic_params);
864 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
865 let was_in_dyn_type = self.is_in_dyn_type;
866 self.is_in_dyn_type = in_scope;
868 let result = f(self);
870 self.is_in_dyn_type = was_in_dyn_type;
875 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
876 let was_in_loop_condition = self.is_in_loop_condition;
877 self.is_in_loop_condition = false;
879 let catch_scope = self.catch_scope.take();
880 let loop_scope = self.loop_scope.take();
882 self.catch_scope = catch_scope;
883 self.loop_scope = loop_scope;
885 self.is_in_loop_condition = was_in_loop_condition;
890 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
891 if attrs.is_empty() {
894 debug_assert_eq!(id.owner, self.current_hir_id_owner);
895 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
896 debug_assert!(!ret.is_empty());
897 self.attrs.insert(id.local_id, ret);
902 fn lower_attr(&self, attr: &Attribute) -> Attribute {
903 // Note that we explicitly do not walk the path. Since we don't really
904 // lower attributes (we use the AST version) there is nowhere to keep
905 // the `HirId`s. We don't actually need HIR version of attributes anyway.
906 // Tokens are also not needed after macro expansion and parsing.
907 let kind = match attr.kind {
908 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
910 path: normal.item.path.clone(),
911 args: self.lower_mac_args(&normal.item.args),
916 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
919 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
922 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
923 debug_assert_eq!(id.owner, self.current_hir_id_owner);
924 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
925 if let Some(&a) = self.attrs.get(&target_id.local_id) {
926 debug_assert!(!a.is_empty());
927 self.attrs.insert(id.local_id, a);
931 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
933 MacArgs::Empty => MacArgs::Empty,
934 MacArgs::Delimited(dspan, delim, ref tokens) => {
935 // This is either a non-key-value attribute, or a `macro_rules!` body.
936 // We either not have any nonterminals present (in the case of an attribute),
937 // or have tokens available for all nonterminals in the case of a nested
938 // `macro_rules`: e.g:
941 // macro_rules! outer {
943 // macro_rules! inner {
950 // In both cases, we don't want to synthesize any tokens
951 MacArgs::Delimited(dspan, delim, tokens.flattened())
953 // This is an inert key-value attribute - it will never be visible to macros
954 // after it gets lowered to HIR. Therefore, we can extract literals to handle
955 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
956 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
957 // In valid code the value always ends up as a single literal. Otherwise, a dummy
958 // literal suffices because the error is handled elsewhere.
959 let lit = if let ExprKind::Lit(lit) = &expr.kind {
963 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
968 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
970 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
971 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
976 /// Given an associated type constraint like one of these:
978 /// ```ignore (illustrative)
979 /// T: Iterator<Item: Debug>
981 /// T: Iterator<Item = Debug>
985 /// returns a `hir::TypeBinding` representing `Item`.
986 #[instrument(level = "debug", skip(self))]
987 fn lower_assoc_ty_constraint(
989 constraint: &AssocConstraint,
990 itctx: &ImplTraitContext,
991 ) -> hir::TypeBinding<'hir> {
992 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
993 // lower generic arguments of identifier in constraint
994 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
995 let gen_args_ctor = match gen_args {
996 GenericArgs::AngleBracketed(ref data) => {
997 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
999 GenericArgs::Parenthesized(ref data) => {
1000 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
1001 let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
1002 self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
1005 gen_args_ctor.into_generic_args(self)
1007 self.arena.alloc(hir::GenericArgs::none())
1009 let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;
1011 let kind = match constraint.kind {
1012 AssocConstraintKind::Equality { ref term } => {
1013 let term = match term {
1014 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
1015 Term::Const(ref c) => self.lower_anon_const(c).into(),
1017 hir::TypeBindingKind::Equality { term }
1019 AssocConstraintKind::Bound { ref bounds } => {
1020 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1021 let (desugar_to_impl_trait, itctx) = match itctx {
1022 // We are in the return position:
1024 // fn foo() -> impl Iterator<Item: Debug>
1028 // fn foo() -> impl Iterator<Item = impl Debug>
1029 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1030 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1032 // We are in the argument position, but within a dyn type:
1034 // fn foo(x: dyn Iterator<Item: Debug>)
1038 // fn foo(x: dyn Iterator<Item = impl Debug>)
1039 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1041 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1042 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1043 // "impl trait context" to permit `impl Debug` in this position (it desugars
1044 // then to an opaque type).
1046 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1047 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => (true, itctx_tait),
1049 // We are in the parameter position, but not within a dyn type:
1051 // fn foo(x: impl Iterator<Item: Debug>)
1053 // so we leave it as is and this gets expanded in astconv to a bound like
1054 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1056 _ => (false, itctx),
1059 if desugar_to_impl_trait {
1060 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1061 // constructing the HIR for `impl bounds...` and then lowering that.
1063 let impl_trait_node_id = self.next_node_id();
1065 self.with_dyn_type_scope(false, |this| {
1066 let node_id = this.next_node_id();
1067 let ty = this.ast_arena.tys.alloc(Ty {
1069 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1070 span: this.lower_span(constraint.span),
1073 let ty = this.lower_ty(ty, itctx);
1075 hir::TypeBindingKind::Equality { term: ty.into() }
1078 // Desugar `AssocTy: Bounds` into a type binding where the
1079 // later desugars into a trait predicate.
1080 let bounds = self.lower_param_bounds(bounds, itctx);
1082 hir::TypeBindingKind::Constraint { bounds }
1088 hir_id: self.lower_node_id(constraint.id),
1089 ident: self.lower_ident(constraint.ident),
1092 span: self.lower_span(constraint.span),
1096 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1097 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1098 let sub = if data.inputs.is_empty() {
1099 let parentheses_span =
1100 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1101 AssocTyParenthesesSub::Empty { parentheses_span }
1103 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1105 // Start of parameters to the 1st argument
1106 let open_param = data.inputs_span.shrink_to_lo().to(data
1112 // End of last argument to end of parameters
1114 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1115 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1117 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1120 #[instrument(level = "debug", skip(self))]
1121 fn lower_generic_arg(
1123 arg: &ast::GenericArg,
1124 itctx: &ImplTraitContext,
1125 ) -> hir::GenericArg<'hir> {
1127 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1128 ast::GenericArg::Type(ty) => {
1130 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1131 return GenericArg::Infer(hir::InferArg {
1132 hir_id: self.lower_node_id(ty.id),
1133 span: self.lower_span(ty.span),
1136 // We parse const arguments as path types as we cannot distinguish them during
1137 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1138 // type and value namespaces. If we resolved the path in the value namespace, we
1139 // transform it into a generic const argument.
1140 TyKind::Path(ref qself, ref path) => {
1141 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1142 let res = partial_res.base_res();
1143 if !res.matches_ns(Namespace::TypeNS) {
1145 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1149 // Construct an AnonConst where the expr is the "ty"'s path.
1151 let parent_def_id = self.current_hir_id_owner;
1152 let node_id = self.next_node_id();
1154 // Add a definition for the in-band const def.
1156 parent_def_id.def_id,
1158 DefPathData::AnonConst,
1161 let span = self.lower_span(ty.span);
1162 let path_expr = Expr {
1164 kind: ExprKind::Path(qself.clone(), path.clone()),
1166 attrs: AttrVec::new(),
1170 let ct = self.with_new_scopes(|this| hir::AnonConst {
1171 hir_id: this.lower_node_id(node_id),
1172 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1174 return GenericArg::Const(ConstArg { value: ct, span });
1180 GenericArg::Type(self.lower_ty(&ty, itctx))
1182 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1183 value: self.lower_anon_const(&ct),
1184 span: self.lower_span(ct.value.span),
1189 #[instrument(level = "debug", skip(self))]
1190 fn lower_ty(&mut self, t: &Ty, itctx: &ImplTraitContext) -> &'hir hir::Ty<'hir> {
1191 self.arena.alloc(self.lower_ty_direct(t, itctx))
1197 qself: &Option<QSelf>,
1199 param_mode: ParamMode,
1200 itctx: &ImplTraitContext,
1201 ) -> hir::Ty<'hir> {
1202 // Check whether we should interpret this as a bare trait object.
1203 // This check mirrors the one in late resolution. We only introduce this special case in
1204 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1205 // The other cases when a qpath should be opportunistically made a trait object are handled
1208 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1209 && partial_res.unresolved_segments() == 0
1210 && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
1212 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1213 let poly_trait_ref = this.ast_arena.ptr.alloc(PolyTraitRef {
1214 bound_generic_params: vec![],
1215 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1218 let bound = this.lower_poly_trait_ref(
1222 let bounds = this.arena.alloc_from_iter([bound]);
1223 let lifetime_bound = this.elided_dyn_bound(t.span);
1224 (bounds, lifetime_bound)
1226 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1227 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1230 let id = self.lower_node_id(t.id);
1231 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1232 self.ty_path(id, t.span, qpath)
1235 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1236 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1239 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1240 self.ty(span, hir::TyKind::Tup(tys))
1243 fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir> {
1244 let kind = match t.kind {
1245 TyKind::Infer => hir::TyKind::Infer,
1246 TyKind::Err => hir::TyKind::Err,
1247 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1248 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1249 TyKind::Rptr(ref region, ref mt) => {
1250 let region = region.unwrap_or_else(|| {
1251 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1252 self.resolver.get_lifetime_res(t.id)
1254 debug_assert_eq!(start.plus(1), end);
1259 let span = self.tcx.sess.source_map().start_point(t.span);
1260 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1262 let lifetime = self.lower_lifetime(®ion);
1263 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1265 TyKind::BareFn(ref f) => {
1266 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
1267 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
1269 unsafety: self.lower_unsafety(f.unsafety),
1270 abi: self.lower_extern(f.ext),
1271 decl: self.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
1272 param_names: self.lower_fn_params_to_names(&f.decl),
1275 TyKind::Never => hir::TyKind::Never,
1276 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1277 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1279 TyKind::Paren(ref ty) => {
1280 return self.lower_ty_direct(ty, itctx);
1282 TyKind::Path(ref qself, ref path) => {
1283 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1285 TyKind::ImplicitSelf => {
1286 let hir_id = self.next_id();
1287 let res = self.expect_full_res(t.id);
1288 let res = self.lower_res(res);
1289 hir::TyKind::Path(hir::QPath::Resolved(
1291 self.arena.alloc(hir::Path {
1293 segments: arena_vec![self; hir::PathSegment::new(
1294 Ident::with_dummy_span(kw::SelfUpper),
1298 span: self.lower_span(t.span),
1302 TyKind::Array(ref ty, ref length) => {
1303 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1305 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1306 TyKind::TraitObject(ref bounds, kind) => {
1307 let mut lifetime_bound = None;
1308 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1310 this.arena.alloc_from_iter(bounds.iter().filter_map(
1311 |bound| match *bound {
1312 GenericBound::Trait(
1314 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1315 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1316 // `~const ?Bound` will cause an error during AST validation
1317 // anyways, so treat it like `?Bound` as compilation proceeds.
1318 GenericBound::Trait(
1320 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1322 GenericBound::Outlives(ref lifetime) => {
1323 if lifetime_bound.is_none() {
1324 lifetime_bound = Some(this.lower_lifetime(lifetime));
1330 let lifetime_bound =
1331 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1332 (bounds, lifetime_bound)
1334 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1336 TyKind::ImplTrait(def_node_id, ref bounds) => {
1339 ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
1340 .lower_opaque_impl_trait(
1348 ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
1350 hir::OpaqueTyOrigin::TyAlias,
1356 ImplTraitContext::Universal => {
1358 self.current_hir_id_owner.def_id,
1360 DefPathData::ImplTrait,
1363 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1364 let (param, bounds, path) =
1365 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1366 self.impl_trait_defs.push(param);
1367 if let Some(bounds) = bounds {
1368 self.impl_trait_bounds.push(bounds);
1372 ImplTraitContext::Disallowed(
1373 position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
1377 .create_feature_err(
1378 MisplacedImplTrait {
1380 position: DiagnosticArgFromDisplay(&position),
1382 sym::return_position_impl_trait_in_trait,
1387 ImplTraitContext::Disallowed(position) => {
1388 self.tcx.sess.emit_err(MisplacedImplTrait {
1390 position: DiagnosticArgFromDisplay(&position),
1396 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1397 TyKind::CVarArgs => {
1398 self.tcx.sess.delay_span_bug(
1400 "`TyKind::CVarArgs` should have been handled elsewhere",
1406 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1409 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1410 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1411 /// HIR type that references the TAIT.
1413 /// Given a function definition like:
1416 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1421 /// we will create a TAIT definition in the HIR like
1424 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1427 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1430 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1433 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1434 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1435 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1436 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1437 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1438 #[instrument(level = "debug", skip(self), ret)]
1439 fn lower_opaque_impl_trait(
1442 origin: hir::OpaqueTyOrigin,
1443 opaque_ty_node_id: NodeId,
1444 bounds: &GenericBounds,
1446 itctx: &ImplTraitContext,
1447 ) -> hir::TyKind<'hir> {
1448 // Make sure we know that some funky desugaring has been going on here.
1449 // This is a first: there is code in other places like for loop
1450 // desugaring that explicitly states that we don't want to track that.
1451 // Not tracking it makes lints in rustc and clippy very fragile, as
1452 // frequently opened issues show.
1453 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1455 let opaque_ty_def_id = match origin {
1456 hir::OpaqueTyOrigin::TyAlias => self.create_def(
1457 self.current_hir_id_owner.def_id,
1459 DefPathData::ImplTrait,
1461 hir::OpaqueTyOrigin::FnReturn(fn_def_id) => {
1462 self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait)
1464 hir::OpaqueTyOrigin::AsyncFn(..) => bug!("unreachable"),
1466 debug!(?opaque_ty_def_id);
1468 // Contains the new lifetime definitions created for the TAIT (if any).
1469 let mut collected_lifetimes = Vec::new();
1471 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1472 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1473 // exactly which ones those are.
1474 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1475 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1478 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1479 // we only keep the lifetimes that appear in the `impl Debug` itself:
1480 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1482 debug!(?lifetimes_to_remap);
1484 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1485 let mut new_remapping = FxHashMap::default();
1487 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1488 // in bounds), then create the new lifetime parameters required and create a mapping
1489 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1490 collected_lifetimes = lctx.create_lifetime_defs(
1492 &lifetimes_to_remap,
1495 debug!(?collected_lifetimes);
1496 debug!(?new_remapping);
1498 // Install the remapping from old to new (if any):
1499 lctx.with_remapping(new_remapping, |lctx| {
1500 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1501 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1502 // containing `&['x]`.
1503 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1504 |&(new_node_id, lifetime)| {
1505 let hir_id = lctx.lower_node_id(new_node_id);
1506 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1508 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1509 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1512 hir::ParamName::Plain(lifetime.ident),
1513 hir::LifetimeParamKind::Explicit,
1520 span: lifetime.ident.span,
1521 pure_wrt_drop: false,
1522 kind: hir::GenericParamKind::Lifetime { kind },
1527 debug!(?lifetime_defs);
1529 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1530 // get back Debug + 'a1, which is suitable for use on the TAIT.
1531 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1532 debug!(?hir_bounds);
1534 let opaque_ty_item = hir::OpaqueTy {
1535 generics: self.arena.alloc(hir::Generics {
1536 params: lifetime_defs,
1538 has_where_clause_predicates: false,
1539 where_clause_span: lctx.lower_span(span),
1540 span: lctx.lower_span(span),
1546 debug!(?opaque_ty_item);
1548 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1552 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1553 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1555 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1556 let id = self.next_node_id();
1557 let span = lifetime.ident.span;
1559 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1560 Ident::with_dummy_span(kw::UnderscoreLifetime)
1565 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1566 hir::GenericArg::Lifetime(l)
1570 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1571 hir::TyKind::OpaqueDef(
1572 hir::ItemId { def_id: hir::OwnerId { def_id: opaque_ty_def_id } },
1578 /// Registers a new opaque type with the proper `NodeId`s and
1579 /// returns the lowered node-ID for the opaque type.
1580 fn generate_opaque_type(
1582 opaque_ty_id: LocalDefId,
1583 opaque_ty_item: hir::OpaqueTy<'hir>,
1585 opaque_ty_span: Span,
1586 ) -> hir::OwnerNode<'hir> {
1587 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1588 // Generate an `type Foo = impl Trait;` declaration.
1589 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1590 let opaque_ty_item = hir::Item {
1591 def_id: hir::OwnerId { def_id: opaque_ty_id },
1592 ident: Ident::empty(),
1593 kind: opaque_ty_item_kind,
1594 vis_span: self.lower_span(span.shrink_to_lo()),
1595 span: self.lower_span(opaque_ty_span),
1597 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1600 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1601 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1602 /// new definition, adds it to the remapping with the definition of the given lifetime and
1603 /// returns a list of lifetimes to be lowered afterwards.
1604 fn create_lifetime_defs(
1606 parent_def_id: LocalDefId,
1607 lifetimes_in_bounds: &[Lifetime],
1608 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1609 ) -> Vec<(NodeId, Lifetime)> {
1610 let mut result = Vec::new();
1612 for lifetime in lifetimes_in_bounds {
1613 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1617 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1618 if remapping.get(&old_def_id).is_none() {
1619 let node_id = self.next_node_id();
1621 let new_def_id = self.create_def(
1624 DefPathData::LifetimeNs(lifetime.ident.name),
1626 remapping.insert(old_def_id, new_def_id);
1628 result.push((node_id, *lifetime));
1632 LifetimeRes::Fresh { param, binder: _ } => {
1633 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1634 if let Some(old_def_id) = self.opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1635 let node_id = self.next_node_id();
1637 let new_def_id = self.create_def(
1640 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1642 remapping.insert(old_def_id, new_def_id);
1644 result.push((node_id, *lifetime));
1648 LifetimeRes::Static | LifetimeRes::Error => {}
1651 let bug_msg = format!(
1652 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1653 res, lifetime.ident, lifetime.ident.span
1655 span_bug!(lifetime.ident.span, "{}", bug_msg);
1663 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1664 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1665 // as they are not explicit in HIR/Ty function signatures.
1666 // (instead, the `c_variadic` flag is set to `true`)
1667 let mut inputs = &decl.inputs[..];
1668 if decl.c_variadic() {
1669 inputs = &inputs[..inputs.len() - 1];
1671 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1672 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1673 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1677 // Lowers a function declaration.
1679 // `decl`: the unlowered (AST) function declaration.
1680 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1681 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1682 // `make_ret_async` is also `Some`.
1683 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1684 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1685 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1686 #[instrument(level = "debug", skip(self))]
1690 fn_node_id: Option<NodeId>,
1693 make_ret_async: Option<(NodeId, Span)>,
1694 ) -> &'hir hir::FnDecl<'hir> {
1695 let c_variadic = decl.c_variadic();
1697 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1698 // as they are not explicit in HIR/Ty function signatures.
1699 // (instead, the `c_variadic` flag is set to `true`)
1700 let mut inputs = &decl.inputs[..];
1702 inputs = &inputs[..inputs.len() - 1];
1704 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1705 if fn_node_id.is_some() {
1706 self.lower_ty_direct(¶m.ty, &ImplTraitContext::Universal)
1708 self.lower_ty_direct(
1710 &ImplTraitContext::Disallowed(match kind {
1711 FnDeclKind::Fn | FnDeclKind::Inherent => {
1712 unreachable!("fn should allow in-band lifetimes")
1714 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1715 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1716 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1717 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1718 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1724 let output = if let Some((ret_id, span)) = make_ret_async {
1725 if !kind.async_fn_allowed(self.tcx) {
1727 FnDeclKind::Trait | FnDeclKind::Impl => {
1730 .create_feature_err(
1731 TraitFnAsync { fn_span, span },
1732 sym::async_fn_in_trait,
1737 self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
1742 self.lower_async_fn_ret_ty(
1744 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1746 matches!(kind, FnDeclKind::Trait),
1750 FnRetTy::Ty(ref ty) => {
1751 let mut context = match fn_node_id {
1752 Some(fn_node_id) if kind.impl_trait_allowed(self.tcx) => {
1753 let fn_def_id = self.local_def_id(fn_node_id);
1754 ImplTraitContext::ReturnPositionOpaqueTy {
1755 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1756 in_trait: matches!(kind, FnDeclKind::Trait),
1759 _ => ImplTraitContext::Disallowed(match kind {
1760 FnDeclKind::Fn | FnDeclKind::Inherent => {
1761 unreachable!("fn should allow in-band lifetimes")
1763 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1764 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1765 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1766 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1767 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1770 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1772 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1776 self.arena.alloc(hir::FnDecl {
1780 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1781 let is_mutable_pat = matches!(
1783 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1787 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1788 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1789 // Given we are only considering `ImplicitSelf` types, we needn't consider
1790 // the case where we have a mutable pattern to a reference as that would
1791 // no longer be an `ImplicitSelf`.
1792 TyKind::Rptr(_, ref mt)
1793 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1795 hir::ImplicitSelfKind::MutRef
1797 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1798 hir::ImplicitSelfKind::ImmRef
1800 _ => hir::ImplicitSelfKind::None,
1806 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1807 // combined with the following definition of `OpaqueTy`:
1809 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1811 // `output`: unlowered output type (`T` in `-> T`)
1812 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1813 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1814 #[instrument(level = "debug", skip(self))]
1815 fn lower_async_fn_ret_ty(
1819 opaque_ty_node_id: NodeId,
1821 ) -> hir::FnRetTy<'hir> {
1822 let span = output.span();
1824 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1826 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1827 let fn_def_id = self.local_def_id(fn_node_id);
1829 // When we create the opaque type for this async fn, it is going to have
1830 // to capture all the lifetimes involved in the signature (including in the
1831 // return type). This is done by introducing lifetime parameters for:
1833 // - all the explicitly declared lifetimes from the impl and function itself;
1834 // - all the elided lifetimes in the fn arguments;
1835 // - all the elided lifetimes in the return type.
1837 // So for example in this snippet:
1840 // impl<'a> Foo<'a> {
1841 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1842 // // ^ '0 ^ '1 ^ '2
1843 // // elided lifetimes used below
1848 // we would create an opaque type like:
1851 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1854 // and we would then desugar `bar` to the equivalent of:
1857 // impl<'a> Foo<'a> {
1858 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1862 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1863 // this is because the elided lifetimes from the return type
1864 // should be figured out using the ordinary elision rules, and
1865 // this desugaring achieves that.
1867 // Calculate all the lifetimes that should be captured
1868 // by the opaque type. This should include all in-scope
1869 // lifetime parameters, including those defined in-band.
1871 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1873 let mut collected_lifetimes = Vec::new();
1874 let mut new_remapping = FxHashMap::default();
1876 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1877 debug!(?extra_lifetime_params);
1878 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1879 let outer_def_id = self.local_def_id(outer_node_id);
1880 let inner_node_id = self.next_node_id();
1882 // Add a definition for the in scope lifetime def.
1883 let inner_def_id = self.create_def(
1886 DefPathData::LifetimeNs(ident.name),
1888 new_remapping.insert(outer_def_id, inner_def_id);
1890 let inner_res = match outer_res {
1891 // Input lifetime like `'a`:
1892 LifetimeRes::Param { param, .. } => {
1893 LifetimeRes::Param { param, binder: fn_node_id }
1895 // Input lifetime like `'1`:
1896 LifetimeRes::Fresh { param, .. } => {
1897 LifetimeRes::Fresh { param, binder: fn_node_id }
1899 LifetimeRes::Static | LifetimeRes::Error => continue,
1902 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1903 res, ident, ident.span
1908 let lifetime = Lifetime { id: outer_node_id, ident };
1909 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1912 debug!(?collected_lifetimes);
1914 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1915 // find out exactly which ones those are.
1916 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1917 // we only keep the lifetimes that appear in the `impl Debug` itself:
1918 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1919 debug!(?lifetimes_to_remap);
1921 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1922 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1923 // in bounds), then create the new lifetime parameters required and create a mapping
1924 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1925 collected_lifetimes.extend(
1926 this.create_lifetime_defs(
1928 &lifetimes_to_remap,
1932 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1934 debug!(?collected_lifetimes);
1935 debug!(?new_remapping);
1937 // Install the remapping from old to new (if any):
1938 this.with_remapping(new_remapping, |this| {
1939 // We have to be careful to get elision right here. The
1940 // idea is that we create a lifetime parameter for each
1941 // lifetime in the return type. So, given a return type
1942 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1943 // Future<Output = &'1 [ &'2 u32 ]>`.
1945 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1946 // hence the elision takes place at the fn site.
1947 let future_bound = this.lower_async_fn_output_type_to_future_bound(
1950 if in_trait && !this.tcx.features().return_position_impl_trait_in_trait {
1951 ImplTraitContext::Disallowed(ImplTraitPosition::TraitReturn)
1953 ImplTraitContext::ReturnPositionOpaqueTy {
1954 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1960 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1961 |&(new_node_id, lifetime, _)| {
1962 let hir_id = this.lower_node_id(new_node_id);
1963 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1965 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1966 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1969 hir::ParamName::Plain(lifetime.ident),
1970 hir::LifetimeParamKind::Explicit,
1977 span: lifetime.ident.span,
1978 pure_wrt_drop: false,
1979 kind: hir::GenericParamKind::Lifetime { kind },
1984 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1986 let opaque_ty_item = hir::OpaqueTy {
1987 generics: this.arena.alloc(hir::Generics {
1988 params: generic_params,
1990 has_where_clause_predicates: false,
1991 where_clause_span: this.lower_span(span),
1992 span: this.lower_span(span),
1994 bounds: arena_vec![this; future_bound],
1995 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1999 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2000 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
2004 // As documented above, we need to create the lifetime
2005 // arguments to our opaque type. Continuing with our example,
2006 // we're creating the type arguments for the return type:
2009 // Bar<'a, 'b, '0, '1, '_>
2012 // For the "input" lifetime parameters, we wish to create
2013 // references to the parameters themselves, including the
2014 // "implicit" ones created from parameter types (`'a`, `'b`,
2017 // For the "output" lifetime parameters, we just want to
2019 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2020 |(_, lifetime, res)| {
2021 let id = self.next_node_id();
2022 let span = lifetime.ident.span;
2024 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
2025 Ident::with_dummy_span(kw::UnderscoreLifetime)
2030 let res = res.unwrap_or(
2031 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2033 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
2037 // Create the `Foo<...>` reference itself. Note that the `type
2038 // Foo = impl Trait` is, internally, created as a child of the
2039 // async fn, so the *type parameters* are inherited. It's
2040 // only the lifetime parameters that we must supply.
2041 let opaque_ty_ref = hir::TyKind::OpaqueDef(
2042 hir::ItemId { def_id: hir::OwnerId { def_id: opaque_ty_def_id } },
2046 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2047 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2050 /// Transforms `-> T` into `Future<Output = T>`.
2051 fn lower_async_fn_output_type_to_future_bound(
2055 mut nested_impl_trait_context: ImplTraitContext,
2056 ) -> hir::GenericBound<'hir> {
2057 // Compute the `T` in `Future<Output = T>` from the return type.
2058 let output_ty = match output {
2059 FnRetTy::Ty(ty) => {
2060 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2061 // `impl Future` opaque type that `async fn` implicitly
2063 self.lower_ty(ty, &mut nested_impl_trait_context)
2065 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2069 let future_args = self.arena.alloc(hir::GenericArgs {
2071 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2072 parenthesized: false,
2076 hir::GenericBound::LangItemTrait(
2077 // ::std::future::Future<future_params>
2078 hir::LangItem::Future,
2079 self.lower_span(span),
2085 #[instrument(level = "trace", skip(self))]
2086 fn lower_param_bound(
2089 itctx: &ImplTraitContext,
2090 ) -> hir::GenericBound<'hir> {
2092 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2093 self.lower_poly_trait_ref(p, itctx),
2094 self.lower_trait_bound_modifier(*modifier),
2096 GenericBound::Outlives(lifetime) => {
2097 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2102 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2103 let span = self.lower_span(l.ident.span);
2104 let ident = self.lower_ident(l.ident);
2105 self.new_named_lifetime(l.id, l.id, span, ident)
2108 #[instrument(level = "debug", skip(self))]
2109 fn new_named_lifetime_with_res(
2115 ) -> &'hir hir::Lifetime {
2116 let name = match res {
2117 LifetimeRes::Param { param, .. } => {
2118 let p_name = ParamName::Plain(ident);
2119 let param = self.get_remapped_def_id(param);
2121 hir::LifetimeName::Param(param, p_name)
2123 LifetimeRes::Fresh { param, .. } => {
2124 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2125 let param = self.local_def_id(param);
2127 hir::LifetimeName::Param(param, ParamName::Fresh)
2129 LifetimeRes::Infer => hir::LifetimeName::Infer,
2130 LifetimeRes::Static => hir::LifetimeName::Static,
2131 LifetimeRes::Error => hir::LifetimeName::Error,
2132 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2136 self.arena.alloc(hir::Lifetime {
2137 hir_id: self.lower_node_id(id),
2138 span: self.lower_span(span),
2143 #[instrument(level = "debug", skip(self))]
2144 fn new_named_lifetime(
2150 ) -> &'hir hir::Lifetime {
2151 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2152 self.new_named_lifetime_with_res(new_id, span, ident, res)
2155 fn lower_generic_params_mut<'s>(
2157 params: &'s [GenericParam],
2158 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2159 params.iter().map(move |param| self.lower_generic_param(param))
2162 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2163 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2166 #[instrument(level = "trace", skip(self))]
2167 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2168 let (name, kind) = self.lower_generic_param_kind(param);
2170 let hir_id = self.lower_node_id(param.id);
2171 self.lower_attrs(hir_id, ¶m.attrs);
2175 span: self.lower_span(param.span()),
2176 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2178 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2182 fn lower_generic_param_kind(
2184 param: &GenericParam,
2185 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2187 GenericParamKind::Lifetime => {
2188 // AST resolution emitted an error on those parameters, so we lower them using
2189 // `ParamName::Error`.
2191 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2194 let ident = self.lower_ident(param.ident);
2195 ParamName::Plain(ident)
2198 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2202 GenericParamKind::Type { ref default, .. } => {
2203 let kind = hir::GenericParamKind::Type {
2204 default: default.as_ref().map(|x| {
2205 self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2210 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2212 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2213 let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2214 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2216 hir::ParamName::Plain(self.lower_ident(param.ident)),
2217 hir::GenericParamKind::Const { ty, default },
2223 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: &ImplTraitContext) -> hir::TraitRef<'hir> {
2224 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2225 hir::QPath::Resolved(None, path) => path,
2226 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2228 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2231 #[instrument(level = "debug", skip(self))]
2232 fn lower_poly_trait_ref(
2235 itctx: &ImplTraitContext,
2236 ) -> hir::PolyTraitRef<'hir> {
2237 let bound_generic_params =
2238 self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
2239 let trait_ref = self.lower_trait_ref(&p.trait_ref, itctx);
2240 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2243 fn lower_mt(&mut self, mt: &MutTy, itctx: &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: &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>(
2258 bounds: &'s [GenericBound],
2259 itctx: &'s ImplTraitContext,
2260 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2261 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2264 #[instrument(level = "debug", skip(self), ret)]
2265 fn lower_generic_and_bounds(
2270 bounds: &[GenericBound],
2271 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2272 // Add a definition for the in-band `Param`.
2273 let def_id = self.local_def_id(node_id);
2275 // Set the name to `impl Bound1 + Bound2`.
2276 let param = hir::GenericParam {
2277 hir_id: self.lower_node_id(node_id),
2278 name: ParamName::Plain(self.lower_ident(ident)),
2279 pure_wrt_drop: false,
2280 span: self.lower_span(span),
2281 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2285 let preds = self.lower_generic_bound_predicate(
2288 &GenericParamKind::Type { default: None },
2290 &ImplTraitContext::Universal,
2291 hir::PredicateOrigin::ImplTrait,
2294 let hir_id = self.next_id();
2295 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2296 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2298 self.arena.alloc(hir::Path {
2299 span: self.lower_span(span),
2302 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2309 /// Lowers a block directly to an expression, presuming that it
2310 /// has no attributes and is not targeted by a `break`.
2311 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2312 let block = self.lower_block(b, false);
2313 self.expr_block(block, AttrVec::new())
2316 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2317 match c.value.kind {
2318 ExprKind::Underscore => {
2319 if self.tcx.features().generic_arg_infer {
2320 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2323 &self.tcx.sess.parse_sess,
2324 sym::generic_arg_infer,
2326 "using `_` for array lengths is unstable",
2328 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2329 hir::ArrayLen::Body(self.lower_anon_const(c))
2332 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2336 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2337 self.with_new_scopes(|this| hir::AnonConst {
2338 hir_id: this.lower_node_id(c.id),
2339 body: this.lower_const_body(c.value.span, Some(&c.value)),
2343 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2345 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2346 UserProvided => hir::UnsafeSource::UserProvided,
2350 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2352 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2353 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2355 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2356 // placeholder for compilation to proceed.
2357 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2358 hir::TraitBoundModifier::Maybe
2363 // Helper methods for building HIR.
2365 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2366 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2369 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2370 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2375 attrs: Option<&'hir [Attribute]>,
2377 init: Option<&'hir hir::Expr<'hir>>,
2378 pat: &'hir hir::Pat<'hir>,
2379 source: hir::LocalSource,
2380 ) -> hir::Stmt<'hir> {
2381 let hir_id = self.next_id();
2382 if let Some(a) = attrs {
2383 debug_assert!(!a.is_empty());
2384 self.attrs.insert(hir_id.local_id, a);
2386 let local = hir::Local {
2392 span: self.lower_span(span),
2395 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2398 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2399 self.block_all(expr.span, &[], Some(expr))
2405 stmts: &'hir [hir::Stmt<'hir>],
2406 expr: Option<&'hir hir::Expr<'hir>>,
2407 ) -> &'hir hir::Block<'hir> {
2408 let blk = hir::Block {
2411 hir_id: self.next_id(),
2412 rules: hir::BlockCheckMode::DefaultBlock,
2413 span: self.lower_span(span),
2414 targeted_by_break: false,
2416 self.arena.alloc(blk)
2419 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2420 let field = self.single_pat_field(span, pat);
2421 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2424 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2425 let field = self.single_pat_field(span, pat);
2426 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2429 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2430 let field = self.single_pat_field(span, pat);
2431 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2434 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2435 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2438 fn single_pat_field(
2441 pat: &'hir hir::Pat<'hir>,
2442 ) -> &'hir [hir::PatField<'hir>] {
2443 let field = hir::PatField {
2444 hir_id: self.next_id(),
2445 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2446 is_shorthand: false,
2448 span: self.lower_span(span),
2450 arena_vec![self; field]
2453 fn pat_lang_item_variant(
2456 lang_item: hir::LangItem,
2457 fields: &'hir [hir::PatField<'hir>],
2458 hir_id: Option<hir::HirId>,
2459 ) -> &'hir hir::Pat<'hir> {
2460 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2461 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2464 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2465 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2468 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2469 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2472 fn pat_ident_binding_mode(
2476 bm: hir::BindingAnnotation,
2477 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2478 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2479 (self.arena.alloc(pat), hir_id)
2482 fn pat_ident_binding_mode_mut(
2486 bm: hir::BindingAnnotation,
2487 ) -> (hir::Pat<'hir>, hir::HirId) {
2488 let hir_id = self.next_id();
2493 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2494 span: self.lower_span(span),
2495 default_binding_modes: true,
2501 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2502 self.arena.alloc(hir::Pat {
2503 hir_id: self.next_id(),
2505 span: self.lower_span(span),
2506 default_binding_modes: true,
2510 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2512 hir_id: self.next_id(),
2514 span: self.lower_span(span),
2515 default_binding_modes: false,
2521 mut hir_id: hir::HirId,
2523 qpath: hir::QPath<'hir>,
2524 ) -> hir::Ty<'hir> {
2525 let kind = match qpath {
2526 hir::QPath::Resolved(None, path) => {
2527 // Turn trait object paths into `TyKind::TraitObject` instead.
2529 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2530 let principal = hir::PolyTraitRef {
2531 bound_generic_params: &[],
2532 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2533 span: self.lower_span(span),
2536 // The original ID is taken by the `PolyTraitRef`,
2537 // so the `Ty` itself needs a different one.
2538 hir_id = self.next_id();
2539 hir::TyKind::TraitObject(
2540 arena_vec![self; principal],
2541 self.elided_dyn_bound(span),
2542 TraitObjectSyntax::None,
2545 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2548 _ => hir::TyKind::Path(qpath),
2551 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2554 /// Invoked to create the lifetime argument(s) for an elided trait object
2555 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2556 /// when the bound is written, even if it is written with `'_` like in
2557 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2558 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2559 let r = hir::Lifetime {
2560 hir_id: self.next_id(),
2561 span: self.lower_span(span),
2562 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2564 debug!("elided_dyn_bound: r={:?}", r);
2569 /// Helper struct for delayed construction of GenericArgs.
2570 struct GenericArgsCtor<'hir> {
2571 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2572 bindings: &'hir [hir::TypeBinding<'hir>],
2573 parenthesized: bool,
2577 impl<'hir> GenericArgsCtor<'hir> {
2578 fn is_empty(&self) -> bool {
2579 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2582 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2583 let ga = hir::GenericArgs {
2584 args: this.arena.alloc_from_iter(self.args),
2585 bindings: self.bindings,
2586 parenthesized: self.parenthesized,
2587 span_ext: this.lower_span(self.span),
2589 this.arena.alloc(ga)