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,
256 /// Impl trait in type aliases.
258 /// Return-position `impl Trait` in trait definition
260 /// `impl Trait` is not accepted in this position.
261 Disallowed(ImplTraitPosition),
264 /// Position in which `impl Trait` is disallowed.
265 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
266 enum ImplTraitPosition {
288 impl std::fmt::Display for ImplTraitPosition {
289 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
290 let name = match self {
291 ImplTraitPosition::Path => "path",
292 ImplTraitPosition::Variable => "variable binding",
293 ImplTraitPosition::Type => "type",
294 ImplTraitPosition::Trait => "trait",
295 ImplTraitPosition::AsyncBlock => "async block",
296 ImplTraitPosition::Bound => "bound",
297 ImplTraitPosition::Generic => "generic",
298 ImplTraitPosition::ExternFnParam => "`extern fn` param",
299 ImplTraitPosition::ClosureParam => "closure param",
300 ImplTraitPosition::PointerParam => "`fn` pointer param",
301 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
302 ImplTraitPosition::TraitParam => "trait method param",
303 ImplTraitPosition::ImplParam => "`impl` method param",
304 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
305 ImplTraitPosition::ClosureReturn => "closure return",
306 ImplTraitPosition::PointerReturn => "`fn` pointer return",
307 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
308 ImplTraitPosition::TraitReturn => "trait method return",
309 ImplTraitPosition::ImplReturn => "`impl` method return",
312 write!(f, "{}", name)
328 fn impl_trait_return_allowed(&self, tcx: TyCtxt<'_>) -> bool {
330 FnDeclKind::Fn | FnDeclKind::Inherent => true,
331 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
336 fn impl_trait_in_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
338 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
344 #[derive(Copy, Clone)]
347 Crate(&'a ast::Crate),
349 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
350 ForeignItem(&'a ast::ForeignItem),
354 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
356 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
357 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
358 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
359 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
360 visit::walk_crate(&mut indexer, krate);
361 return indexer.index;
363 struct Indexer<'s, 'a> {
364 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
365 index: IndexVec<LocalDefId, AstOwner<'a>>,
368 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
369 fn visit_attribute(&mut self, _: &'a Attribute) {
370 // We do not want to lower expressions that appear in attributes,
371 // as they are not accessible to the rest of the HIR.
374 fn visit_item(&mut self, item: &'a ast::Item) {
375 let def_id = self.node_id_to_def_id[&item.id];
376 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
377 self.index[def_id] = AstOwner::Item(item);
378 visit::walk_item(self, item)
381 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
382 let def_id = self.node_id_to_def_id[&item.id];
383 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
384 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
385 visit::walk_assoc_item(self, item, ctxt);
388 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
389 let def_id = self.node_id_to_def_id[&item.id];
390 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
391 self.index[def_id] = AstOwner::ForeignItem(item);
392 visit::walk_foreign_item(self, item);
397 /// Compute the hash for the HIR of the full crate.
398 /// This hash will then be part of the crate_hash which is stored in the metadata.
401 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
403 let mut hir_body_nodes: Vec<_> = owners
405 .filter_map(|(def_id, info)| {
406 let info = info.as_owner()?;
407 let def_path_hash = tcx.hir().def_path_hash(def_id);
408 Some((def_path_hash, info))
411 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
413 tcx.with_stable_hashing_context(|mut hcx| {
414 let mut stable_hasher = StableHasher::new();
415 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
416 stable_hasher.finish()
420 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
422 let krate = tcx.untracked_crate.steal();
423 let mut resolver = tcx.resolver_for_lowering(()).steal();
425 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
426 let mut owners = IndexVec::from_fn_n(
427 |_| hir::MaybeOwner::Phantom,
428 tcx.definitions_untracked().def_index_count(),
431 let ast_arena = Arena::default();
433 for def_id in ast_index.indices() {
436 resolver: &mut resolver,
437 ast_arena: &ast_arena,
438 ast_index: &ast_index,
444 // Drop AST to free memory
445 std::mem::drop(ast_index);
446 sess.time("drop_ast", || std::mem::drop(krate));
448 // Discard hygiene data, which isn't required after lowering to HIR.
449 if !sess.opts.unstable_opts.keep_hygiene_data {
450 rustc_span::hygiene::clear_syntax_context_map();
453 let hir_hash = compute_hir_hash(tcx, &owners);
454 hir::Crate { owners, hir_hash }
457 #[derive(Copy, Clone, PartialEq, Debug)]
459 /// Any path in a type context.
461 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
463 /// The `module::Type` in `module::Type::method` in an expression.
467 enum ParenthesizedGenericArgs {
472 impl<'a, 'hir> LoweringContext<'a, 'hir> {
476 node_id: ast::NodeId,
479 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
481 self.opt_local_def_id(node_id).is_none(),
482 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
485 self.tcx.hir().def_key(self.local_def_id(node_id)),
488 let def_id = self.tcx.create_def(parent, data);
490 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
491 self.resolver.node_id_to_def_id.insert(node_id, def_id);
496 fn next_node_id(&mut self) -> NodeId {
497 let start = self.resolver.next_node_id;
498 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
499 self.resolver.next_node_id = ast::NodeId::from_u32(next);
503 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
504 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
506 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
507 /// invoking with the id from the `ast::Lifetime` node found inside
508 /// the `&'a u32` type would return the `LocalDefId` of the
509 /// `'a` parameter declared on `foo`.
511 /// This function also applies remapping from `get_remapped_def_id`.
512 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
513 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
514 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
515 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
516 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
520 .map(|local_def_id| self.get_remapped_def_id(*local_def_id))
523 fn local_def_id(&self, node: NodeId) -> LocalDefId {
524 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
527 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
528 /// `generics_def_id_map` field.
529 fn get_remapped_def_id(&self, mut local_def_id: LocalDefId) -> LocalDefId {
530 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
531 // push new mappings so we need to try first the latest mappings, hence `iter().rev()`.
535 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
537 // We would end with a generics_def_id_map like:
539 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
541 // for the opaque type generated on `impl Sized + 'b`, We want the result to be:
542 // impl_sized#'b, so iterating forward is the wrong thing to do.
543 for map in self.generics_def_id_map.iter().rev() {
544 if let Some(r) = map.get(&local_def_id) {
545 debug!("def_id_remapper: remapping from `{local_def_id:?}` to `{r:?}`");
548 debug!("def_id_remapper: no remapping for `{local_def_id:?}` found in map");
555 /// Freshen the `LoweringContext` and ready it to lower a nested item.
556 /// The lowered item is registered into `self.children`.
558 /// This function sets up `HirId` lowering infrastructure,
559 /// and stashes the shared mutable state to avoid pollution by the closure.
560 #[instrument(level = "debug", skip(self, f))]
561 fn with_hir_id_owner(
564 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
566 let def_id = self.local_def_id(owner);
568 let current_attrs = std::mem::take(&mut self.attrs);
569 let current_bodies = std::mem::take(&mut self.bodies);
570 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
571 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
572 let current_trait_map = std::mem::take(&mut self.trait_map);
573 let current_owner = std::mem::replace(&mut self.current_hir_id_owner, def_id);
574 let current_local_counter =
575 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
576 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
577 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
579 // Do not reset `next_node_id` and `node_id_to_def_id`:
580 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
581 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
583 // Always allocate the first `HirId` for the owner itself.
584 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
585 debug_assert_eq!(_old, None);
588 debug_assert_eq!(def_id, item.def_id());
589 // `f` should have consumed all the elements in these vectors when constructing `item`.
590 debug_assert!(self.impl_trait_defs.is_empty());
591 debug_assert!(self.impl_trait_bounds.is_empty());
592 let info = self.make_owner_info(item);
594 self.attrs = current_attrs;
595 self.bodies = current_bodies;
596 self.node_id_to_local_id = current_node_ids;
597 self.local_id_to_def_id = current_id_to_def_id;
598 self.trait_map = current_trait_map;
599 self.current_hir_id_owner = current_owner;
600 self.item_local_id_counter = current_local_counter;
601 self.impl_trait_defs = current_impl_trait_defs;
602 self.impl_trait_bounds = current_impl_trait_bounds;
604 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
605 debug_assert!(_old.is_none())
608 /// Installs the remapping `remap` in scope while `f` is being executed.
609 /// This causes references to the `LocalDefId` keys to be changed to
610 /// refer to the values instead.
612 /// The remapping is used when one piece of AST expands to multiple
613 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
614 /// expands to both a function definition (`foo`) and a TAIT for the return value,
615 /// both of which have a lifetime parameter `'a`. The remapping allows us to
616 /// rewrite the `'a` in the return value to refer to the
617 /// `'a` declared on the TAIT, instead of the function.
618 fn with_remapping<R>(
620 remap: FxHashMap<LocalDefId, LocalDefId>,
621 f: impl FnOnce(&mut Self) -> R,
623 self.generics_def_id_map.push(remap);
625 self.generics_def_id_map.pop();
629 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
630 let attrs = std::mem::take(&mut self.attrs);
631 let mut bodies = std::mem::take(&mut self.bodies);
632 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
633 let trait_map = std::mem::take(&mut self.trait_map);
635 #[cfg(debug_assertions)]
636 for (id, attrs) in attrs.iter() {
637 // Verify that we do not store empty slices in the map.
638 if attrs.is_empty() {
639 panic!("Stored empty attributes for {:?}", id);
643 bodies.sort_by_key(|(k, _)| *k);
644 let bodies = SortedMap::from_presorted_elements(bodies);
645 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
646 let (nodes, parenting) =
647 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
648 let nodes = hir::OwnerNodes {
649 hash_including_bodies,
656 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
657 let mut stable_hasher = StableHasher::new();
658 attrs.hash_stable(&mut hcx, &mut stable_hasher);
659 stable_hasher.finish()
661 hir::AttributeMap { map: attrs, hash }
664 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
667 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
668 /// queries which depend on the full HIR tree and those which only depend on the item signature.
671 node: hir::OwnerNode<'hir>,
672 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
673 ) -> (Fingerprint, Fingerprint) {
674 self.tcx.with_stable_hashing_context(|mut hcx| {
675 let mut stable_hasher = StableHasher::new();
676 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
677 node.hash_stable(hcx, &mut stable_hasher)
679 let hash_including_bodies = stable_hasher.finish();
680 let mut stable_hasher = StableHasher::new();
681 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
682 let hash_without_bodies = stable_hasher.finish();
683 (hash_including_bodies, hash_without_bodies)
687 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
688 /// the `LoweringContext`'s `NodeId => HirId` map.
689 /// Take care not to call this method if the resulting `HirId` is then not
690 /// actually used in the HIR, as that would trigger an assertion in the
691 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
692 /// properly. Calling the method twice with the same `NodeId` is fine though.
693 #[instrument(level = "debug", skip(self), ret)]
694 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
695 assert_ne!(ast_node_id, DUMMY_NODE_ID);
697 match self.node_id_to_local_id.entry(ast_node_id) {
698 Entry::Occupied(o) => {
699 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
701 Entry::Vacant(v) => {
702 // Generate a new `HirId`.
703 let owner = self.current_hir_id_owner;
704 let local_id = self.item_local_id_counter;
705 let hir_id = hir::HirId { owner, local_id };
708 self.item_local_id_counter.increment_by(1);
710 assert_ne!(local_id, hir::ItemLocalId::new(0));
711 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
712 // Do not override a `MaybeOwner::Owner` that may already here.
713 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
714 self.local_id_to_def_id.insert(local_id, def_id);
717 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
718 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
726 /// Generate a new `HirId` without a backing `NodeId`.
727 #[instrument(level = "debug", skip(self), ret)]
728 fn next_id(&mut self) -> hir::HirId {
729 let owner = self.current_hir_id_owner;
730 let local_id = self.item_local_id_counter;
731 assert_ne!(local_id, hir::ItemLocalId::new(0));
732 self.item_local_id_counter.increment_by(1);
733 hir::HirId { owner, local_id }
736 #[instrument(level = "trace", skip(self))]
737 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
738 let res: Result<Res, ()> = res.apply_id(|id| {
739 let owner = self.current_hir_id_owner;
740 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
741 Ok(hir::HirId { owner, local_id })
745 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
746 // This can happen when trying to lower the return type `x` in erroneous code like
747 // async fn foo(x: u8) -> x {}
748 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
749 // an opaque type as a synthesized HIR owner.
750 res.unwrap_or(Res::Err)
753 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
754 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
755 if pr.unresolved_segments() != 0 {
756 panic!("path not fully resolved: {:?}", pr);
762 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
763 self.resolver.get_import_res(id).present_items()
766 fn diagnostic(&self) -> &Handler {
767 self.tcx.sess.diagnostic()
770 /// Reuses the span but adds information like the kind of the desugaring and features that are
771 /// allowed inside this span.
772 fn mark_span_with_reason(
774 reason: DesugaringKind,
776 allow_internal_unstable: Option<Lrc<[Symbol]>>,
778 self.tcx.with_stable_hashing_context(|hcx| {
779 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
783 /// Intercept all spans entering HIR.
784 /// Mark a span as relative to the current owning item.
785 fn lower_span(&self, span: Span) -> Span {
786 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
787 span.with_parent(Some(self.current_hir_id_owner))
789 // Do not make spans relative when not using incremental compilation.
794 fn lower_ident(&self, ident: Ident) -> Ident {
795 Ident::new(ident.name, self.lower_span(ident.span))
798 /// Converts a lifetime into a new generic parameter.
799 #[instrument(level = "debug", skip(self))]
800 fn lifetime_res_to_generic_param(
805 ) -> Option<hir::GenericParam<'hir>> {
806 let (name, kind) = match res {
807 LifetimeRes::Param { .. } => {
808 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
810 LifetimeRes::Fresh { param, .. } => {
811 // Late resolution delegates to us the creation of the `LocalDefId`.
812 let _def_id = self.create_def(
813 self.current_hir_id_owner,
815 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
819 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
821 LifetimeRes::Static | LifetimeRes::Error => return None,
823 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
824 res, ident, ident.span
827 let hir_id = self.lower_node_id(node_id);
828 Some(hir::GenericParam {
831 span: self.lower_span(ident.span),
832 pure_wrt_drop: false,
833 kind: hir::GenericParamKind::Lifetime { kind },
838 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
839 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
840 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
841 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
842 /// parameters will be successful.
843 #[instrument(level = "debug", skip(self, in_binder))]
845 fn lower_lifetime_binder<R>(
848 generic_params: &[GenericParam],
849 in_binder: impl FnOnce(&mut Self, &'hir [hir::GenericParam<'hir>]) -> R,
851 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
852 debug!(?extra_lifetimes);
853 let extra_lifetimes: Vec<_> = extra_lifetimes
855 .filter_map(|(ident, node_id, res)| {
856 self.lifetime_res_to_generic_param(ident, node_id, res)
860 let generic_params: Vec<_> = self
861 .lower_generic_params_mut(generic_params)
862 .chain(extra_lifetimes.into_iter())
864 let generic_params = self.arena.alloc_from_iter(generic_params);
865 debug!(?generic_params);
867 in_binder(self, generic_params)
870 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
871 let was_in_dyn_type = self.is_in_dyn_type;
872 self.is_in_dyn_type = in_scope;
874 let result = f(self);
876 self.is_in_dyn_type = was_in_dyn_type;
881 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
882 let was_in_loop_condition = self.is_in_loop_condition;
883 self.is_in_loop_condition = false;
885 let catch_scope = self.catch_scope.take();
886 let loop_scope = self.loop_scope.take();
888 self.catch_scope = catch_scope;
889 self.loop_scope = loop_scope;
891 self.is_in_loop_condition = was_in_loop_condition;
896 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
897 if attrs.is_empty() {
900 debug_assert_eq!(id.owner, self.current_hir_id_owner);
901 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
902 debug_assert!(!ret.is_empty());
903 self.attrs.insert(id.local_id, ret);
908 fn lower_attr(&self, attr: &Attribute) -> Attribute {
909 // Note that we explicitly do not walk the path. Since we don't really
910 // lower attributes (we use the AST version) there is nowhere to keep
911 // the `HirId`s. We don't actually need HIR version of attributes anyway.
912 // Tokens are also not needed after macro expansion and parsing.
913 let kind = match attr.kind {
914 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
916 path: normal.item.path.clone(),
917 args: self.lower_mac_args(&normal.item.args),
922 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
925 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
928 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
929 debug_assert_eq!(id.owner, self.current_hir_id_owner);
930 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
931 if let Some(&a) = self.attrs.get(&target_id.local_id) {
932 debug_assert!(!a.is_empty());
933 self.attrs.insert(id.local_id, a);
937 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
939 MacArgs::Empty => MacArgs::Empty,
940 MacArgs::Delimited(dspan, delim, ref tokens) => {
941 // This is either a non-key-value attribute, or a `macro_rules!` body.
942 // We either not have any nonterminals present (in the case of an attribute),
943 // or have tokens available for all nonterminals in the case of a nested
944 // `macro_rules`: e.g:
947 // macro_rules! outer {
949 // macro_rules! inner {
956 // In both cases, we don't want to synthesize any tokens
957 MacArgs::Delimited(dspan, delim, tokens.flattened())
959 // This is an inert key-value attribute - it will never be visible to macros
960 // after it gets lowered to HIR. Therefore, we can extract literals to handle
961 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
962 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
963 // In valid code the value always ends up as a single literal. Otherwise, a dummy
964 // literal suffices because the error is handled elsewhere.
965 let lit = if let ExprKind::Lit(lit) = &expr.kind {
969 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
974 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
976 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
977 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
982 /// Given an associated type constraint like one of these:
984 /// ```ignore (illustrative)
985 /// T: Iterator<Item: Debug>
987 /// T: Iterator<Item = Debug>
991 /// returns a `hir::TypeBinding` representing `Item`.
992 #[instrument(level = "debug", skip(self))]
993 fn lower_assoc_ty_constraint(
995 constraint: &AssocConstraint,
996 itctx: &mut ImplTraitContext,
997 ) -> hir::TypeBinding<'hir> {
998 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
999 // lower generic arguments of identifier in constraint
1000 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1001 let gen_args_ctor = match gen_args {
1002 GenericArgs::AngleBracketed(ref data) => {
1003 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
1005 GenericArgs::Parenthesized(ref data) => {
1006 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
1007 let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
1008 self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
1011 gen_args_ctor.into_generic_args(self)
1013 self.arena.alloc(hir::GenericArgs::none())
1015 let mut itctx_tait = ImplTraitContext::TypeAliasesOpaqueTy;
1017 let kind = match constraint.kind {
1018 AssocConstraintKind::Equality { ref term } => {
1019 let term = match term {
1020 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
1021 Term::Const(ref c) => self.lower_anon_const(c).into(),
1023 hir::TypeBindingKind::Equality { term }
1025 AssocConstraintKind::Bound { ref bounds } => {
1026 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1027 let (desugar_to_impl_trait, itctx) = match itctx {
1028 // We are in the return position:
1030 // fn foo() -> impl Iterator<Item: Debug>
1034 // fn foo() -> impl Iterator<Item = impl Debug>
1035 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1036 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1038 // We are in the argument position, but within a dyn type:
1040 // fn foo(x: dyn Iterator<Item: Debug>)
1044 // fn foo(x: dyn Iterator<Item = impl Debug>)
1045 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1047 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1048 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1049 // "impl trait context" to permit `impl Debug` in this position (it desugars
1050 // then to an opaque type).
1052 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1053 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1054 (true, &mut itctx_tait)
1057 // We are in the parameter position, but not within a dyn type:
1059 // fn foo(x: impl Iterator<Item: Debug>)
1061 // so we leave it as is and this gets expanded in astconv to a bound like
1062 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1064 _ => (false, itctx),
1067 if desugar_to_impl_trait {
1068 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1069 // constructing the HIR for `impl bounds...` and then lowering that.
1071 let parent_def_id = self.current_hir_id_owner;
1072 let impl_trait_node_id = self.next_node_id();
1073 self.create_def(parent_def_id, impl_trait_node_id, DefPathData::ImplTrait);
1075 self.with_dyn_type_scope(false, |this| {
1076 let node_id = this.next_node_id();
1077 let ty = this.ast_arena.tys.alloc(Ty {
1079 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1080 span: this.lower_span(constraint.span),
1083 let ty = this.lower_ty(ty, itctx);
1085 hir::TypeBindingKind::Equality { term: ty.into() }
1088 // Desugar `AssocTy: Bounds` into a type binding where the
1089 // later desugars into a trait predicate.
1090 let bounds = self.lower_param_bounds(bounds, itctx);
1092 hir::TypeBindingKind::Constraint { bounds }
1098 hir_id: self.lower_node_id(constraint.id),
1099 ident: self.lower_ident(constraint.ident),
1102 span: self.lower_span(constraint.span),
1106 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1107 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1108 let sub = if data.inputs.is_empty() {
1109 let parentheses_span =
1110 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1111 AssocTyParenthesesSub::Empty { parentheses_span }
1113 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1115 // Start of parameters to the 1st argument
1116 let open_param = data.inputs_span.shrink_to_lo().to(data
1122 // End of last argument to end of parameters
1124 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1125 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1127 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1130 #[instrument(level = "debug", skip(self))]
1131 fn lower_generic_arg(
1133 arg: &ast::GenericArg,
1134 itctx: &mut ImplTraitContext,
1135 ) -> hir::GenericArg<'hir> {
1137 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1138 ast::GenericArg::Type(ty) => {
1140 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1141 return GenericArg::Infer(hir::InferArg {
1142 hir_id: self.lower_node_id(ty.id),
1143 span: self.lower_span(ty.span),
1146 // We parse const arguments as path types as we cannot distinguish them during
1147 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1148 // type and value namespaces. If we resolved the path in the value namespace, we
1149 // transform it into a generic const argument.
1150 TyKind::Path(ref qself, ref path) => {
1151 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1152 let res = partial_res.base_res();
1153 if !res.matches_ns(Namespace::TypeNS) {
1155 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1159 // Construct an AnonConst where the expr is the "ty"'s path.
1161 let parent_def_id = self.current_hir_id_owner;
1162 let node_id = self.next_node_id();
1164 // Add a definition for the in-band const def.
1165 self.create_def(parent_def_id, node_id, DefPathData::AnonConst);
1167 let span = self.lower_span(ty.span);
1168 let path_expr = Expr {
1170 kind: ExprKind::Path(qself.clone(), path.clone()),
1172 attrs: AttrVec::new(),
1176 let ct = self.with_new_scopes(|this| hir::AnonConst {
1177 hir_id: this.lower_node_id(node_id),
1178 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1180 return GenericArg::Const(ConstArg { value: ct, span });
1186 GenericArg::Type(self.lower_ty(&ty, itctx))
1188 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1189 value: self.lower_anon_const(&ct),
1190 span: self.lower_span(ct.value.span),
1195 #[instrument(level = "debug", skip(self))]
1196 fn lower_ty(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> &'hir hir::Ty<'hir> {
1197 self.arena.alloc(self.lower_ty_direct(t, itctx))
1203 qself: &Option<QSelf>,
1205 param_mode: ParamMode,
1206 itctx: &mut ImplTraitContext,
1207 ) -> hir::Ty<'hir> {
1208 // Check whether we should interpret this as a bare trait object.
1209 // This check mirrors the one in late resolution. We only introduce this special case in
1210 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1211 // The other cases when a qpath should be opportunistically made a trait object are handled
1214 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1215 && partial_res.unresolved_segments() == 0
1216 && let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
1218 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1219 let poly_trait_ref = this.ast_arena.ptr.alloc(PolyTraitRef {
1220 bound_generic_params: vec![],
1221 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1224 let bound = this.lower_poly_trait_ref(
1228 let bounds = this.arena.alloc_from_iter([bound]);
1229 let lifetime_bound = this.elided_dyn_bound(t.span);
1230 (bounds, lifetime_bound)
1232 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1233 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1236 let id = self.lower_node_id(t.id);
1237 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1238 self.ty_path(id, t.span, qpath)
1241 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1242 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1245 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1246 self.ty(span, hir::TyKind::Tup(tys))
1249 fn lower_ty_direct(&mut self, t: &Ty, itctx: &mut ImplTraitContext) -> hir::Ty<'hir> {
1250 let kind = match t.kind {
1251 TyKind::Infer => hir::TyKind::Infer,
1252 TyKind::Err => hir::TyKind::Err,
1253 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1254 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1255 TyKind::Rptr(ref region, ref mt) => {
1256 let region = region.unwrap_or_else(|| {
1257 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1258 self.resolver.get_lifetime_res(t.id)
1260 debug_assert_eq!(start.plus(1), end);
1265 let span = self.tcx.sess.source_map().start_point(t.span);
1266 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1268 let lifetime = self.lower_lifetime(®ion);
1269 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1271 TyKind::BareFn(ref f) => {
1272 self.lower_lifetime_binder(t.id, &f.generic_params, |lctx, generic_params| {
1273 hir::TyKind::BareFn(lctx.arena.alloc(hir::BareFnTy {
1275 unsafety: lctx.lower_unsafety(f.unsafety),
1276 abi: lctx.lower_extern(f.ext),
1277 decl: lctx.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
1278 param_names: lctx.lower_fn_params_to_names(&f.decl),
1282 TyKind::Never => hir::TyKind::Never,
1283 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1284 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1286 TyKind::Paren(ref ty) => {
1287 return self.lower_ty_direct(ty, itctx);
1289 TyKind::Path(ref qself, ref path) => {
1290 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1292 TyKind::ImplicitSelf => {
1293 let hir_id = self.lower_node_id(t.id);
1294 let res = self.expect_full_res(t.id);
1295 let res = self.lower_res(res);
1296 hir::TyKind::Path(hir::QPath::Resolved(
1298 self.arena.alloc(hir::Path {
1300 segments: arena_vec![self; hir::PathSegment::new(
1301 Ident::with_dummy_span(kw::SelfUpper),
1305 span: self.lower_span(t.span),
1309 TyKind::Array(ref ty, ref length) => {
1310 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1312 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1313 TyKind::TraitObject(ref bounds, kind) => {
1314 let mut lifetime_bound = None;
1315 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1317 this.arena.alloc_from_iter(bounds.iter().filter_map(
1318 |bound| match *bound {
1319 GenericBound::Trait(
1321 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1322 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1323 // `~const ?Bound` will cause an error during AST validation
1324 // anyways, so treat it like `?Bound` as compilation proceeds.
1325 GenericBound::Trait(
1327 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1329 GenericBound::Outlives(ref lifetime) => {
1330 if lifetime_bound.is_none() {
1331 lifetime_bound = Some(this.lower_lifetime(lifetime));
1337 let lifetime_bound =
1338 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1339 (bounds, lifetime_bound)
1341 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1343 TyKind::ImplTrait(def_node_id, ref bounds) => {
1346 ImplTraitContext::ReturnPositionOpaqueTy { origin } => {
1347 self.lower_opaque_impl_trait(span, *origin, def_node_id, bounds, itctx)
1349 ImplTraitContext::TypeAliasesOpaqueTy => {
1350 let mut nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy;
1351 self.lower_opaque_impl_trait(
1353 hir::OpaqueTyOrigin::TyAlias,
1359 ImplTraitContext::InTrait => {
1360 // FIXME(RPITIT): Should we use def_node_id here?
1361 self.lower_impl_trait_in_trait(span, def_node_id, |lctx| {
1362 lctx.lower_param_bounds(
1364 ImplTraitContext::Disallowed(ImplTraitPosition::Trait),
1368 ImplTraitContext::Universal => {
1370 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1371 let (param, bounds, path) =
1372 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1373 self.impl_trait_defs.push(param);
1374 if let Some(bounds) = bounds {
1375 self.impl_trait_bounds.push(bounds);
1379 ImplTraitContext::Disallowed(position) => {
1380 self.tcx.sess.emit_err(MisplacedImplTrait {
1382 position: DiagnosticArgFromDisplay(&position),
1388 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1389 TyKind::CVarArgs => {
1390 self.tcx.sess.delay_span_bug(
1392 "`TyKind::CVarArgs` should have been handled elsewhere",
1398 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1401 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1402 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1403 /// HIR type that references the TAIT.
1405 /// Given a function definition like:
1408 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1413 /// we will create a TAIT definition in the HIR like
1416 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1419 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1422 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1425 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1426 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1427 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1428 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1429 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1430 #[instrument(level = "debug", skip(self), ret)]
1431 fn lower_opaque_impl_trait(
1434 origin: hir::OpaqueTyOrigin,
1435 opaque_ty_node_id: NodeId,
1436 bounds: &GenericBounds,
1437 itctx: &mut ImplTraitContext,
1438 ) -> hir::TyKind<'hir> {
1439 // Make sure we know that some funky desugaring has been going on here.
1440 // This is a first: there is code in other places like for loop
1441 // desugaring that explicitly states that we don't want to track that.
1442 // Not tracking it makes lints in rustc and clippy very fragile, as
1443 // frequently opened issues show.
1444 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1446 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1447 debug!(?opaque_ty_def_id);
1449 // Contains the new lifetime definitions created for the TAIT (if any).
1450 let mut collected_lifetimes = Vec::new();
1452 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1453 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1454 // exactly which ones those are.
1455 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1456 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1459 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1460 // we only keep the lifetimes that appear in the `impl Debug` itself:
1461 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1463 debug!(?lifetimes_to_remap);
1465 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1466 let mut new_remapping = FxHashMap::default();
1468 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1469 // in bounds), then create the new lifetime parameters required and create a mapping
1470 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1471 collected_lifetimes = lctx.create_lifetime_defs(
1473 &lifetimes_to_remap,
1476 debug!(?collected_lifetimes);
1477 debug!(?new_remapping);
1479 // Install the remapping from old to new (if any):
1480 lctx.with_remapping(new_remapping, |lctx| {
1481 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1482 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1483 // containing `&['x]`.
1484 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1485 |&(new_node_id, lifetime)| {
1486 let hir_id = lctx.lower_node_id(new_node_id);
1487 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1489 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1490 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1493 hir::ParamName::Plain(lifetime.ident),
1494 hir::LifetimeParamKind::Explicit,
1501 span: lifetime.ident.span,
1502 pure_wrt_drop: false,
1503 kind: hir::GenericParamKind::Lifetime { kind },
1508 debug!(?lifetime_defs);
1510 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1511 // get back Debug + 'a1, which is suitable for use on the TAIT.
1512 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1513 debug!(?hir_bounds);
1515 let opaque_ty_item = hir::OpaqueTy {
1516 generics: self.arena.alloc(hir::Generics {
1517 params: lifetime_defs,
1519 has_where_clause_predicates: false,
1520 where_clause_span: lctx.lower_span(span),
1521 span: lctx.lower_span(span),
1526 debug!(?opaque_ty_item);
1528 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1532 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1533 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1535 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1536 let id = self.next_node_id();
1537 let span = lifetime.ident.span;
1539 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1540 Ident::with_dummy_span(kw::UnderscoreLifetime)
1545 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1546 hir::GenericArg::Lifetime(l)
1550 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1551 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1554 #[instrument(level = "debug", skip(self, lower_bounds))]
1555 fn lower_impl_trait_in_trait(
1558 opaque_ty_node_id: NodeId,
1559 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1560 ) -> hir::TyKind<'hir> {
1561 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1562 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1563 // FIXME(RPITIT): This should be a more descriptive ImplTraitPosition, i.e. nested RPITIT
1564 // FIXME(RPITIT): We _also_ should support this eventually
1565 let hir_bounds = lower_bounds(lctx);
1566 let rpitit_placeholder = hir::ImplTraitPlaceholder { bounds: hir_bounds };
1567 let rpitit_item = hir::Item {
1568 def_id: opaque_ty_def_id,
1569 ident: Ident::empty(),
1570 kind: hir::ItemKind::ImplTraitPlaceholder(rpitit_placeholder),
1571 span: lctx.lower_span(span),
1572 vis_span: lctx.lower_span(span.shrink_to_lo()),
1574 hir::OwnerNode::Item(lctx.arena.alloc(rpitit_item))
1576 hir::TyKind::ImplTraitInTrait(hir::ItemId { def_id: opaque_ty_def_id })
1579 /// Registers a new opaque type with the proper `NodeId`s and
1580 /// returns the lowered node-ID for the opaque type.
1581 fn generate_opaque_type(
1583 opaque_ty_id: LocalDefId,
1584 opaque_ty_item: hir::OpaqueTy<'hir>,
1586 opaque_ty_span: Span,
1587 ) -> hir::OwnerNode<'hir> {
1588 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1589 // Generate an `type Foo = impl Trait;` declaration.
1590 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1591 let opaque_ty_item = hir::Item {
1592 def_id: opaque_ty_id,
1593 ident: Ident::empty(),
1594 kind: opaque_ty_item_kind,
1595 vis_span: self.lower_span(span.shrink_to_lo()),
1596 span: self.lower_span(opaque_ty_span),
1598 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1601 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1602 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1603 /// new definition, adds it to the remapping with the definition of the given lifetime and
1604 /// returns a list of lifetimes to be lowered afterwards.
1605 fn create_lifetime_defs(
1607 parent_def_id: LocalDefId,
1608 lifetimes_in_bounds: &[Lifetime],
1609 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1610 ) -> Vec<(NodeId, Lifetime)> {
1611 let mut result = Vec::new();
1613 for lifetime in lifetimes_in_bounds {
1614 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1618 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1619 if remapping.get(&old_def_id).is_none() {
1620 let node_id = self.next_node_id();
1622 let new_def_id = self.create_def(
1625 DefPathData::LifetimeNs(lifetime.ident.name),
1627 remapping.insert(old_def_id, new_def_id);
1629 result.push((node_id, *lifetime));
1633 LifetimeRes::Fresh { param, binder: _ } => {
1634 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1635 if let Some(old_def_id) = self.opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1636 let node_id = self.next_node_id();
1638 let new_def_id = self.create_def(
1641 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1643 remapping.insert(old_def_id, new_def_id);
1645 result.push((node_id, *lifetime));
1649 LifetimeRes::Static | LifetimeRes::Error => {}
1652 let bug_msg = format!(
1653 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1654 res, lifetime.ident, lifetime.ident.span
1656 span_bug!(lifetime.ident.span, "{}", bug_msg);
1664 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1665 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1666 // as they are not explicit in HIR/Ty function signatures.
1667 // (instead, the `c_variadic` flag is set to `true`)
1668 let mut inputs = &decl.inputs[..];
1669 if decl.c_variadic() {
1670 inputs = &inputs[..inputs.len() - 1];
1672 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1673 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1674 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1678 // Lowers a function declaration.
1680 // `decl`: the unlowered (AST) function declaration.
1681 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1682 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1683 // `make_ret_async` is also `Some`.
1684 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1685 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1686 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1687 #[instrument(level = "debug", skip(self))]
1691 fn_node_id: Option<NodeId>,
1694 make_ret_async: Option<(NodeId, Span)>,
1695 ) -> &'hir hir::FnDecl<'hir> {
1696 let c_variadic = decl.c_variadic();
1698 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1699 // as they are not explicit in HIR/Ty function signatures.
1700 // (instead, the `c_variadic` flag is set to `true`)
1701 let mut inputs = &decl.inputs[..];
1703 inputs = &inputs[..inputs.len() - 1];
1705 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1706 if fn_node_id.is_some() {
1707 self.lower_ty_direct(¶m.ty, &mut ImplTraitContext::Universal)
1709 self.lower_ty_direct(
1711 &mut ImplTraitContext::Disallowed(match kind {
1712 FnDeclKind::Fn | FnDeclKind::Inherent => {
1713 unreachable!("fn should allow in-band lifetimes")
1715 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1716 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1717 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1718 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1719 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1725 let output = if let Some((ret_id, span)) = make_ret_async {
1727 FnDeclKind::Trait => {
1728 if !kind.impl_trait_in_trait_allowed(self.tcx) {
1731 .create_feature_err(
1732 TraitFnAsync { fn_span, span },
1733 sym::return_position_impl_trait_in_trait,
1737 self.lower_async_fn_ret_ty_in_trait(
1739 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1744 if !kind.impl_trait_return_allowed(self.tcx) {
1745 if kind == FnDeclKind::Impl {
1748 .create_feature_err(
1749 TraitFnAsync { fn_span, span },
1750 sym::return_position_impl_trait_in_trait,
1754 self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
1757 self.lower_async_fn_ret_ty(
1759 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1766 FnRetTy::Ty(ref ty) => {
1767 let mut context = match fn_node_id {
1768 Some(fn_node_id) if kind.impl_trait_return_allowed(self.tcx) => {
1769 let fn_def_id = self.local_def_id(fn_node_id);
1770 ImplTraitContext::ReturnPositionOpaqueTy {
1771 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1774 Some(_) if kind.impl_trait_in_trait_allowed(self.tcx) => {
1775 ImplTraitContext::InTrait
1777 _ => ImplTraitContext::Disallowed(match kind {
1778 FnDeclKind::Fn | FnDeclKind::Inherent => {
1779 unreachable!("fn should allow in-band lifetimes")
1781 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1782 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1783 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1784 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1785 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1788 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1790 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1794 self.arena.alloc(hir::FnDecl {
1798 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1799 let is_mutable_pat = matches!(
1801 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1805 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1806 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1807 // Given we are only considering `ImplicitSelf` types, we needn't consider
1808 // the case where we have a mutable pattern to a reference as that would
1809 // no longer be an `ImplicitSelf`.
1810 TyKind::Rptr(_, ref mt)
1811 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1813 hir::ImplicitSelfKind::MutRef
1815 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1816 hir::ImplicitSelfKind::ImmRef
1818 _ => hir::ImplicitSelfKind::None,
1824 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1825 // combined with the following definition of `OpaqueTy`:
1827 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1829 // `output`: unlowered output type (`T` in `-> T`)
1830 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1831 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1832 #[instrument(level = "debug", skip(self))]
1833 fn lower_async_fn_ret_ty(
1837 opaque_ty_node_id: NodeId,
1838 ) -> hir::FnRetTy<'hir> {
1839 let span = output.span();
1841 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1843 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1844 let fn_def_id = self.local_def_id(fn_node_id);
1846 // When we create the opaque type for this async fn, it is going to have
1847 // to capture all the lifetimes involved in the signature (including in the
1848 // return type). This is done by introducing lifetime parameters for:
1850 // - all the explicitly declared lifetimes from the impl and function itself;
1851 // - all the elided lifetimes in the fn arguments;
1852 // - all the elided lifetimes in the return type.
1854 // So for example in this snippet:
1857 // impl<'a> Foo<'a> {
1858 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1859 // // ^ '0 ^ '1 ^ '2
1860 // // elided lifetimes used below
1865 // we would create an opaque type like:
1868 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1871 // and we would then desugar `bar` to the equivalent of:
1874 // impl<'a> Foo<'a> {
1875 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1879 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1880 // this is because the elided lifetimes from the return type
1881 // should be figured out using the ordinary elision rules, and
1882 // this desugaring achieves that.
1884 // Calculate all the lifetimes that should be captured
1885 // by the opaque type. This should include all in-scope
1886 // lifetime parameters, including those defined in-band.
1888 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1890 let mut collected_lifetimes = Vec::new();
1891 let mut new_remapping = FxHashMap::default();
1893 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1894 debug!(?extra_lifetime_params);
1895 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1896 let outer_def_id = self.local_def_id(outer_node_id);
1897 let inner_node_id = self.next_node_id();
1899 // Add a definition for the in scope lifetime def.
1900 let inner_def_id = self.create_def(
1903 DefPathData::LifetimeNs(ident.name),
1905 new_remapping.insert(outer_def_id, inner_def_id);
1907 let inner_res = match outer_res {
1908 // Input lifetime like `'a`:
1909 LifetimeRes::Param { param, .. } => {
1910 LifetimeRes::Param { param, binder: fn_node_id }
1912 // Input lifetime like `'1`:
1913 LifetimeRes::Fresh { param, .. } => {
1914 LifetimeRes::Fresh { param, binder: fn_node_id }
1916 LifetimeRes::Static | LifetimeRes::Error => continue,
1919 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1920 res, ident, ident.span
1925 let lifetime = Lifetime { id: outer_node_id, ident };
1926 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1929 debug!(?collected_lifetimes);
1931 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1932 // find out exactly which ones those are.
1933 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1934 // we only keep the lifetimes that appear in the `impl Debug` itself:
1935 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1936 debug!(?lifetimes_to_remap);
1938 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1939 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1940 // in bounds), then create the new lifetime parameters required and create a mapping
1941 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1942 collected_lifetimes.extend(
1943 this.create_lifetime_defs(
1945 &lifetimes_to_remap,
1949 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1951 debug!(?collected_lifetimes);
1952 debug!(?new_remapping);
1954 // Install the remapping from old to new (if any):
1955 this.with_remapping(new_remapping, |this| {
1956 // We have to be careful to get elision right here. The
1957 // idea is that we create a lifetime parameter for each
1958 // lifetime in the return type. So, given a return type
1959 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1960 // Future<Output = &'1 [ &'2 u32 ]>`.
1962 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1963 // hence the elision takes place at the fn site.
1965 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span);
1967 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1968 |&(new_node_id, lifetime, _)| {
1969 let hir_id = this.lower_node_id(new_node_id);
1970 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1972 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1973 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1976 hir::ParamName::Plain(lifetime.ident),
1977 hir::LifetimeParamKind::Explicit,
1984 span: lifetime.ident.span,
1985 pure_wrt_drop: false,
1986 kind: hir::GenericParamKind::Lifetime { kind },
1991 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1993 let opaque_ty_item = hir::OpaqueTy {
1994 generics: this.arena.alloc(hir::Generics {
1995 params: generic_params,
1997 has_where_clause_predicates: false,
1998 where_clause_span: this.lower_span(span),
1999 span: this.lower_span(span),
2001 bounds: arena_vec![this; future_bound],
2002 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
2005 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2006 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
2010 // As documented above, we need to create the lifetime
2011 // arguments to our opaque type. Continuing with our example,
2012 // we're creating the type arguments for the return type:
2015 // Bar<'a, 'b, '0, '1, '_>
2018 // For the "input" lifetime parameters, we wish to create
2019 // references to the parameters themselves, including the
2020 // "implicit" ones created from parameter types (`'a`, `'b`,
2023 // For the "output" lifetime parameters, we just want to
2025 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2026 |(_, lifetime, res)| {
2027 let id = self.next_node_id();
2028 let span = lifetime.ident.span;
2030 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
2031 Ident::with_dummy_span(kw::UnderscoreLifetime)
2036 let res = res.unwrap_or(
2037 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2039 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
2043 // Create the `Foo<...>` reference itself. Note that the `type
2044 // Foo = impl Trait` is, internally, created as a child of the
2045 // async fn, so the *type parameters* are inherited. It's
2046 // only the lifetime parameters that we must supply.
2048 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
2049 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2050 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2053 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2054 // combined with the following definition of `OpaqueTy`:
2056 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2058 // `output`: unlowered output type (`T` in `-> T`)
2059 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2060 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2061 #[instrument(level = "debug", skip(self))]
2062 fn lower_async_fn_ret_ty_in_trait(
2066 opaque_ty_node_id: NodeId,
2067 ) -> hir::FnRetTy<'hir> {
2068 let span = output.span();
2070 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2072 let fn_def_id = self.local_def_id(fn_node_id);
2074 let kind = self.lower_impl_trait_in_trait(output.span(), opaque_ty_node_id, |lctx| {
2076 lctx.lower_async_fn_output_type_to_future_bound(output, fn_def_id, output.span());
2077 arena_vec![lctx; bound]
2079 let opaque_ty = self.ty(opaque_ty_span, kind);
2080 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2083 /// Transforms `-> T` into `Future<Output = T>`.
2084 fn lower_async_fn_output_type_to_future_bound(
2087 fn_def_id: LocalDefId,
2089 ) -> hir::GenericBound<'hir> {
2090 // Compute the `T` in `Future<Output = T>` from the return type.
2091 let output_ty = match output {
2092 FnRetTy::Ty(ty) => {
2093 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2094 // `impl Future` opaque type that `async fn` implicitly
2096 let mut context = ImplTraitContext::ReturnPositionOpaqueTy {
2097 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
2099 self.lower_ty(ty, &mut context)
2101 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2105 let future_args = self.arena.alloc(hir::GenericArgs {
2107 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2108 parenthesized: false,
2112 hir::GenericBound::LangItemTrait(
2113 // ::std::future::Future<future_params>
2114 hir::LangItem::Future,
2115 self.lower_span(span),
2121 #[instrument(level = "trace", skip(self))]
2122 fn lower_param_bound(
2125 itctx: &mut ImplTraitContext,
2126 ) -> hir::GenericBound<'hir> {
2128 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2129 self.lower_poly_trait_ref(p, itctx),
2130 self.lower_trait_bound_modifier(*modifier),
2132 GenericBound::Outlives(lifetime) => {
2133 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2138 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2139 let span = self.lower_span(l.ident.span);
2140 let ident = self.lower_ident(l.ident);
2141 self.new_named_lifetime(l.id, l.id, span, ident)
2144 #[instrument(level = "debug", skip(self))]
2145 fn new_named_lifetime_with_res(
2151 ) -> &'hir hir::Lifetime {
2152 let name = match res {
2153 LifetimeRes::Param { param, .. } => {
2154 let p_name = ParamName::Plain(ident);
2155 let param = self.get_remapped_def_id(param);
2157 hir::LifetimeName::Param(param, p_name)
2159 LifetimeRes::Fresh { param, .. } => {
2160 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2161 let param = self.local_def_id(param);
2163 hir::LifetimeName::Param(param, ParamName::Fresh)
2165 LifetimeRes::Infer => hir::LifetimeName::Infer,
2166 LifetimeRes::Static => hir::LifetimeName::Static,
2167 LifetimeRes::Error => hir::LifetimeName::Error,
2168 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2172 self.arena.alloc(hir::Lifetime {
2173 hir_id: self.lower_node_id(id),
2174 span: self.lower_span(span),
2179 #[instrument(level = "debug", skip(self))]
2180 fn new_named_lifetime(
2186 ) -> &'hir hir::Lifetime {
2187 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2188 self.new_named_lifetime_with_res(new_id, span, ident, res)
2191 fn lower_generic_params_mut<'s>(
2193 params: &'s [GenericParam],
2194 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2195 params.iter().map(move |param| self.lower_generic_param(param))
2198 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2199 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2202 #[instrument(level = "trace", skip(self))]
2203 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2204 let (name, kind) = self.lower_generic_param_kind(param);
2206 let hir_id = self.lower_node_id(param.id);
2207 self.lower_attrs(hir_id, ¶m.attrs);
2211 span: self.lower_span(param.span()),
2212 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2214 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2218 fn lower_generic_param_kind(
2220 param: &GenericParam,
2221 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2223 GenericParamKind::Lifetime => {
2224 // AST resolution emitted an error on those parameters, so we lower them using
2225 // `ParamName::Error`.
2227 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2230 let ident = self.lower_ident(param.ident);
2231 ParamName::Plain(ident)
2234 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2238 GenericParamKind::Type { ref default, .. } => {
2239 let kind = hir::GenericParamKind::Type {
2240 default: default.as_ref().map(|x| {
2241 self.lower_ty(x, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2246 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2248 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2250 self.lower_ty(&ty, &mut ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2251 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2253 hir::ParamName::Plain(self.lower_ident(param.ident)),
2254 hir::GenericParamKind::Const { ty, default },
2263 itctx: &mut ImplTraitContext,
2264 ) -> hir::TraitRef<'hir> {
2265 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2266 hir::QPath::Resolved(None, path) => path,
2267 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2269 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2272 #[instrument(level = "debug", skip(self))]
2273 fn lower_poly_trait_ref(
2276 itctx: &mut ImplTraitContext,
2277 ) -> hir::PolyTraitRef<'hir> {
2278 self.lower_lifetime_binder(
2280 &p.bound_generic_params,
2281 |lctx, bound_generic_params| {
2282 let trait_ref = lctx.lower_trait_ref(&p.trait_ref, itctx);
2283 hir::PolyTraitRef { bound_generic_params, trait_ref, span: lctx.lower_span(p.span) }
2288 fn lower_mt(&mut self, mt: &MutTy, itctx: &mut ImplTraitContext) -> hir::MutTy<'hir> {
2289 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2292 #[instrument(level = "debug", skip(self), ret)]
2293 fn lower_param_bounds(
2295 bounds: &[GenericBound],
2296 itctx: &mut ImplTraitContext,
2297 ) -> hir::GenericBounds<'hir> {
2298 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2301 fn lower_param_bounds_mut<'s, 'b>(
2303 bounds: &'s [GenericBound],
2304 itctx: &'b mut ImplTraitContext,
2305 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> + Captures<'b>
2307 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2310 #[instrument(level = "debug", skip(self), ret)]
2311 fn lower_generic_and_bounds(
2316 bounds: &[GenericBound],
2317 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2318 // Add a definition for the in-band `Param`.
2319 let def_id = self.local_def_id(node_id);
2321 // Set the name to `impl Bound1 + Bound2`.
2322 let param = hir::GenericParam {
2323 hir_id: self.lower_node_id(node_id),
2324 name: ParamName::Plain(self.lower_ident(ident)),
2325 pure_wrt_drop: false,
2326 span: self.lower_span(span),
2327 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2331 let preds = self.lower_generic_bound_predicate(
2334 &GenericParamKind::Type { default: None },
2336 &mut ImplTraitContext::Universal,
2337 hir::PredicateOrigin::ImplTrait,
2340 let hir_id = self.next_id();
2341 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2342 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2344 self.arena.alloc(hir::Path {
2345 span: self.lower_span(span),
2348 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2355 /// Lowers a block directly to an expression, presuming that it
2356 /// has no attributes and is not targeted by a `break`.
2357 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2358 let block = self.lower_block(b, false);
2359 self.expr_block(block, AttrVec::new())
2362 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2363 match c.value.kind {
2364 ExprKind::Underscore => {
2365 if self.tcx.features().generic_arg_infer {
2366 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2369 &self.tcx.sess.parse_sess,
2370 sym::generic_arg_infer,
2372 "using `_` for array lengths is unstable",
2374 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2375 hir::ArrayLen::Body(self.lower_anon_const(c))
2378 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2382 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2383 self.with_new_scopes(|this| hir::AnonConst {
2384 hir_id: this.lower_node_id(c.id),
2385 body: this.lower_const_body(c.value.span, Some(&c.value)),
2389 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2391 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2392 UserProvided => hir::UnsafeSource::UserProvided,
2396 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2398 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2399 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2401 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2402 // placeholder for compilation to proceed.
2403 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2404 hir::TraitBoundModifier::Maybe
2409 // Helper methods for building HIR.
2411 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2412 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2415 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2416 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2421 attrs: Option<&'hir [Attribute]>,
2423 init: Option<&'hir hir::Expr<'hir>>,
2424 pat: &'hir hir::Pat<'hir>,
2425 source: hir::LocalSource,
2426 ) -> hir::Stmt<'hir> {
2427 let hir_id = self.next_id();
2428 if let Some(a) = attrs {
2429 debug_assert!(!a.is_empty());
2430 self.attrs.insert(hir_id.local_id, a);
2432 let local = hir::Local {
2438 span: self.lower_span(span),
2441 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2444 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2445 self.block_all(expr.span, &[], Some(expr))
2451 stmts: &'hir [hir::Stmt<'hir>],
2452 expr: Option<&'hir hir::Expr<'hir>>,
2453 ) -> &'hir hir::Block<'hir> {
2454 let blk = hir::Block {
2457 hir_id: self.next_id(),
2458 rules: hir::BlockCheckMode::DefaultBlock,
2459 span: self.lower_span(span),
2460 targeted_by_break: false,
2462 self.arena.alloc(blk)
2465 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2466 let field = self.single_pat_field(span, pat);
2467 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2470 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2471 let field = self.single_pat_field(span, pat);
2472 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2475 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2476 let field = self.single_pat_field(span, pat);
2477 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2480 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2481 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2484 fn single_pat_field(
2487 pat: &'hir hir::Pat<'hir>,
2488 ) -> &'hir [hir::PatField<'hir>] {
2489 let field = hir::PatField {
2490 hir_id: self.next_id(),
2491 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2492 is_shorthand: false,
2494 span: self.lower_span(span),
2496 arena_vec![self; field]
2499 fn pat_lang_item_variant(
2502 lang_item: hir::LangItem,
2503 fields: &'hir [hir::PatField<'hir>],
2504 hir_id: Option<hir::HirId>,
2505 ) -> &'hir hir::Pat<'hir> {
2506 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2507 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2510 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2511 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2514 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2515 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2518 fn pat_ident_binding_mode(
2522 bm: hir::BindingAnnotation,
2523 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2524 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2525 (self.arena.alloc(pat), hir_id)
2528 fn pat_ident_binding_mode_mut(
2532 bm: hir::BindingAnnotation,
2533 ) -> (hir::Pat<'hir>, hir::HirId) {
2534 let hir_id = self.next_id();
2539 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2540 span: self.lower_span(span),
2541 default_binding_modes: true,
2547 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2548 self.arena.alloc(hir::Pat {
2549 hir_id: self.next_id(),
2551 span: self.lower_span(span),
2552 default_binding_modes: true,
2556 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2558 hir_id: self.next_id(),
2560 span: self.lower_span(span),
2561 default_binding_modes: false,
2567 mut hir_id: hir::HirId,
2569 qpath: hir::QPath<'hir>,
2570 ) -> hir::Ty<'hir> {
2571 let kind = match qpath {
2572 hir::QPath::Resolved(None, path) => {
2573 // Turn trait object paths into `TyKind::TraitObject` instead.
2575 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2576 let principal = hir::PolyTraitRef {
2577 bound_generic_params: &[],
2578 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2579 span: self.lower_span(span),
2582 // The original ID is taken by the `PolyTraitRef`,
2583 // so the `Ty` itself needs a different one.
2584 hir_id = self.next_id();
2585 hir::TyKind::TraitObject(
2586 arena_vec![self; principal],
2587 self.elided_dyn_bound(span),
2588 TraitObjectSyntax::None,
2591 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2594 _ => hir::TyKind::Path(qpath),
2597 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2600 /// Invoked to create the lifetime argument(s) for an elided trait object
2601 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2602 /// when the bound is written, even if it is written with `'_` like in
2603 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2604 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2605 let r = hir::Lifetime {
2606 hir_id: self.next_id(),
2607 span: self.lower_span(span),
2608 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2610 debug!("elided_dyn_bound: r={:?}", r);
2615 /// Helper struct for delayed construction of GenericArgs.
2616 struct GenericArgsCtor<'hir> {
2617 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2618 bindings: &'hir [hir::TypeBinding<'hir>],
2619 parenthesized: bool,
2623 impl<'hir> GenericArgsCtor<'hir> {
2624 fn is_empty(&self) -> bool {
2625 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2628 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2629 let ga = hir::GenericArgs {
2630 args: this.arena.alloc_from_iter(self.args),
2631 bindings: self.bindings,
2632 parenthesized: self.parenthesized,
2633 span_ext: this.lower_span(self.span),
2635 this.arena.alloc(ga)