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 // Clones the resolution (if any) on 'source' and applies it
164 // to 'target'. Used when desugaring a `UseTreeKind::Nested` to
165 // multiple `UseTreeKind::Simple`s
166 fn clone_res(&mut self, source: NodeId, target: NodeId);
167 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
168 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
169 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
170 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
173 impl ResolverAstLoweringExt for ResolverAstLowering {
174 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
175 if let ExprKind::Path(None, path) = &expr.kind {
176 // Don't perform legacy const generics rewriting if the path already
177 // has generic arguments.
178 if path.segments.last().unwrap().args.is_some() {
182 if let Res::Def(DefKind::Fn, def_id) = self.partial_res_map.get(&expr.id)?.full_res()? {
183 // We only support cross-crate argument rewriting. Uses
184 // within the same crate should be updated to use the new
185 // const generics style.
186 if def_id.is_local() {
190 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
199 fn clone_res(&mut self, source: NodeId, target: NodeId) {
200 if let Some(res) = self.partial_res_map.get(&source) {
201 self.partial_res_map.insert(target, *res);
205 /// Obtains resolution for a `NodeId` with a single resolution.
206 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
207 self.partial_res_map.get(&id).copied()
210 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
211 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
212 self.import_res_map.get(&id).copied().unwrap_or_default()
215 /// Obtains resolution for a label with the given `NodeId`.
216 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
217 self.label_res_map.get(&id).copied()
220 /// Obtains resolution for a lifetime with the given `NodeId`.
221 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
222 self.lifetimes_res_map.get(&id).copied()
225 /// Obtain the list of lifetimes parameters to add to an item.
227 /// Extra lifetime parameters should only be added in places that can appear
228 /// as a `binder` in `LifetimeRes`.
230 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
231 /// should appear at the enclosing `PolyTraitRef`.
232 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
233 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
236 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
237 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
241 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
242 /// and if so, what meaning it has.
243 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
244 enum ImplTraitContext {
245 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
246 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
247 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
249 /// Newly generated parameters should be inserted into the given `Vec`.
252 /// Treat `impl Trait` as shorthand for a new opaque type.
253 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
254 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
256 ReturnPositionOpaqueTy {
257 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
258 origin: hir::OpaqueTyOrigin,
261 /// Impl trait in type aliases.
263 /// `impl Trait` is not accepted in this position.
264 Disallowed(ImplTraitPosition),
267 /// Position in which `impl Trait` is disallowed.
268 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
269 enum ImplTraitPosition {
291 impl std::fmt::Display for ImplTraitPosition {
292 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
293 let name = match self {
294 ImplTraitPosition::Path => "path",
295 ImplTraitPosition::Variable => "variable binding",
296 ImplTraitPosition::Type => "type",
297 ImplTraitPosition::Trait => "trait",
298 ImplTraitPosition::AsyncBlock => "async block",
299 ImplTraitPosition::Bound => "bound",
300 ImplTraitPosition::Generic => "generic",
301 ImplTraitPosition::ExternFnParam => "`extern fn` param",
302 ImplTraitPosition::ClosureParam => "closure param",
303 ImplTraitPosition::PointerParam => "`fn` pointer param",
304 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
305 ImplTraitPosition::TraitParam => "trait method param",
306 ImplTraitPosition::ImplParam => "`impl` method param",
307 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
308 ImplTraitPosition::ClosureReturn => "closure return",
309 ImplTraitPosition::PointerReturn => "`fn` pointer return",
310 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
311 ImplTraitPosition::TraitReturn => "trait method return",
312 ImplTraitPosition::ImplReturn => "`impl` method return",
315 write!(f, "{}", name)
319 #[derive(Debug, PartialEq, Eq)]
331 fn impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
333 FnDeclKind::Fn | FnDeclKind::Inherent => true,
334 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
335 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
340 fn async_fn_allowed(&self, tcx: TyCtxt<'_>) -> bool {
342 FnDeclKind::Fn | FnDeclKind::Inherent => true,
343 FnDeclKind::Impl if tcx.features().async_fn_in_trait => true,
344 FnDeclKind::Trait if tcx.features().async_fn_in_trait => true,
350 #[derive(Copy, Clone)]
353 Crate(&'a ast::Crate),
355 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
356 ForeignItem(&'a ast::ForeignItem),
360 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
362 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
363 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
364 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
365 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
366 visit::walk_crate(&mut indexer, krate);
367 return indexer.index;
369 struct Indexer<'s, 'a> {
370 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
371 index: IndexVec<LocalDefId, AstOwner<'a>>,
374 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
375 fn visit_attribute(&mut self, _: &'a Attribute) {
376 // We do not want to lower expressions that appear in attributes,
377 // as they are not accessible to the rest of the HIR.
380 fn visit_item(&mut self, item: &'a ast::Item) {
381 let def_id = self.node_id_to_def_id[&item.id];
382 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
383 self.index[def_id] = AstOwner::Item(item);
384 visit::walk_item(self, item)
387 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
388 let def_id = self.node_id_to_def_id[&item.id];
389 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
390 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
391 visit::walk_assoc_item(self, item, ctxt);
394 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
395 let def_id = self.node_id_to_def_id[&item.id];
396 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
397 self.index[def_id] = AstOwner::ForeignItem(item);
398 visit::walk_foreign_item(self, item);
403 /// Compute the hash for the HIR of the full crate.
404 /// This hash will then be part of the crate_hash which is stored in the metadata.
407 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
409 let mut hir_body_nodes: Vec<_> = owners
411 .filter_map(|(def_id, info)| {
412 let info = info.as_owner()?;
413 let def_path_hash = tcx.hir().def_path_hash(def_id);
414 Some((def_path_hash, info))
417 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
419 tcx.with_stable_hashing_context(|mut hcx| {
420 let mut stable_hasher = StableHasher::new();
421 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
422 stable_hasher.finish()
426 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
428 let krate = tcx.untracked_crate.steal();
429 let mut resolver = tcx.resolver_for_lowering(()).steal();
431 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
432 let mut owners = IndexVec::from_fn_n(
433 |_| hir::MaybeOwner::Phantom,
434 tcx.definitions_untracked().def_index_count(),
437 let ast_arena = Arena::default();
439 for def_id in ast_index.indices() {
442 resolver: &mut resolver,
443 ast_arena: &ast_arena,
444 ast_index: &ast_index,
450 // Drop AST to free memory
451 std::mem::drop(ast_index);
452 sess.time("drop_ast", || std::mem::drop(krate));
454 // Discard hygiene data, which isn't required after lowering to HIR.
455 if !sess.opts.unstable_opts.keep_hygiene_data {
456 rustc_span::hygiene::clear_syntax_context_map();
459 let hir_hash = compute_hir_hash(tcx, &owners);
460 hir::Crate { owners, hir_hash }
463 #[derive(Copy, Clone, PartialEq, Debug)]
465 /// Any path in a type context.
467 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
469 /// The `module::Type` in `module::Type::method` in an expression.
473 enum ParenthesizedGenericArgs {
478 impl<'a, 'hir> LoweringContext<'a, 'hir> {
482 node_id: ast::NodeId,
485 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
487 self.opt_local_def_id(node_id).is_none(),
488 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
491 self.tcx.hir().def_key(self.local_def_id(node_id)),
494 let def_id = self.tcx.create_def(parent, data);
496 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
497 self.resolver.node_id_to_def_id.insert(node_id, def_id);
502 fn next_node_id(&mut self) -> NodeId {
503 let start = self.resolver.next_node_id;
504 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
505 self.resolver.next_node_id = ast::NodeId::from_u32(next);
509 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
510 /// resolver (if any).
511 fn orig_opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
512 self.resolver.node_id_to_def_id.get(&node).map(|local_def_id| *local_def_id)
515 fn orig_local_def_id(&self, node: NodeId) -> LocalDefId {
516 self.orig_opt_local_def_id(node)
517 .unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
520 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
521 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
523 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
524 /// invoking with the id from the `ast::Lifetime` node found inside
525 /// the `&'a u32` type would return the `LocalDefId` of the
526 /// `'a` parameter declared on `foo`.
528 /// This function also applies remapping from `get_remapped_def_id`.
529 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
530 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
531 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
532 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
533 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
534 self.orig_opt_local_def_id(node).map(|local_def_id| self.get_remapped_def_id(local_def_id))
537 fn local_def_id(&self, node: NodeId) -> LocalDefId {
538 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
541 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
542 /// `generics_def_id_map` field.
543 fn get_remapped_def_id(&self, local_def_id: LocalDefId) -> LocalDefId {
544 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
545 // push new mappings, so we first need to get the latest (innermost) mappings, hence `iter().rev()`.
549 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
551 // We would end with a generics_def_id_map like:
553 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
555 // for the opaque type generated on `impl Sized + 'b`, we want the result to be: impl_sized#'b.
556 // So, if we were trying to find first from the start (outermost) would give the wrong result, impl_trait#'b.
557 self.generics_def_id_map
560 .find_map(|map| map.get(&local_def_id).map(|local_def_id| *local_def_id))
561 .unwrap_or(local_def_id)
564 /// Freshen the `LoweringContext` and ready it to lower a nested item.
565 /// The lowered item is registered into `self.children`.
567 /// This function sets up `HirId` lowering infrastructure,
568 /// and stashes the shared mutable state to avoid pollution by the closure.
569 #[instrument(level = "debug", skip(self, f))]
570 fn with_hir_id_owner(
573 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
575 let def_id = self.local_def_id(owner);
577 let current_attrs = std::mem::take(&mut self.attrs);
578 let current_bodies = std::mem::take(&mut self.bodies);
579 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
580 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
581 let current_trait_map = std::mem::take(&mut self.trait_map);
583 std::mem::replace(&mut self.current_hir_id_owner, hir::OwnerId { def_id });
584 let current_local_counter =
585 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
586 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
587 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
589 // Do not reset `next_node_id` and `node_id_to_def_id`:
590 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
591 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
593 // Always allocate the first `HirId` for the owner itself.
594 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
595 debug_assert_eq!(_old, None);
598 debug_assert_eq!(def_id, item.def_id().def_id);
599 // `f` should have consumed all the elements in these vectors when constructing `item`.
600 debug_assert!(self.impl_trait_defs.is_empty());
601 debug_assert!(self.impl_trait_bounds.is_empty());
602 let info = self.make_owner_info(item);
604 self.attrs = current_attrs;
605 self.bodies = current_bodies;
606 self.node_id_to_local_id = current_node_ids;
607 self.local_id_to_def_id = current_id_to_def_id;
608 self.trait_map = current_trait_map;
609 self.current_hir_id_owner = current_owner;
610 self.item_local_id_counter = current_local_counter;
611 self.impl_trait_defs = current_impl_trait_defs;
612 self.impl_trait_bounds = current_impl_trait_bounds;
614 let _old = self.children.insert(def_id, hir::MaybeOwner::Owner(info));
615 debug_assert!(_old.is_none())
618 /// Installs the remapping `remap` in scope while `f` is being executed.
619 /// This causes references to the `LocalDefId` keys to be changed to
620 /// refer to the values instead.
622 /// The remapping is used when one piece of AST expands to multiple
623 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
624 /// expands to both a function definition (`foo`) and a TAIT for the return value,
625 /// both of which have a lifetime parameter `'a`. The remapping allows us to
626 /// rewrite the `'a` in the return value to refer to the
627 /// `'a` declared on the TAIT, instead of the function.
628 fn with_remapping<R>(
630 remap: FxHashMap<LocalDefId, LocalDefId>,
631 f: impl FnOnce(&mut Self) -> R,
633 self.generics_def_id_map.push(remap);
635 self.generics_def_id_map.pop();
639 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
640 let attrs = std::mem::take(&mut self.attrs);
641 let mut bodies = std::mem::take(&mut self.bodies);
642 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
643 let trait_map = std::mem::take(&mut self.trait_map);
645 #[cfg(debug_assertions)]
646 for (id, attrs) in attrs.iter() {
647 // Verify that we do not store empty slices in the map.
648 if attrs.is_empty() {
649 panic!("Stored empty attributes for {:?}", id);
653 bodies.sort_by_key(|(k, _)| *k);
654 let bodies = SortedMap::from_presorted_elements(bodies);
655 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
656 let (nodes, parenting) =
657 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
658 let nodes = hir::OwnerNodes {
659 hash_including_bodies,
666 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
667 let mut stable_hasher = StableHasher::new();
668 attrs.hash_stable(&mut hcx, &mut stable_hasher);
669 stable_hasher.finish()
671 hir::AttributeMap { map: attrs, hash }
674 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
677 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
678 /// queries which depend on the full HIR tree and those which only depend on the item signature.
681 node: hir::OwnerNode<'hir>,
682 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
683 ) -> (Fingerprint, Fingerprint) {
684 self.tcx.with_stable_hashing_context(|mut hcx| {
685 let mut stable_hasher = StableHasher::new();
686 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
687 node.hash_stable(hcx, &mut stable_hasher)
689 let hash_including_bodies = stable_hasher.finish();
690 let mut stable_hasher = StableHasher::new();
691 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
692 let hash_without_bodies = stable_hasher.finish();
693 (hash_including_bodies, hash_without_bodies)
697 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
698 /// the `LoweringContext`'s `NodeId => HirId` map.
699 /// Take care not to call this method if the resulting `HirId` is then not
700 /// actually used in the HIR, as that would trigger an assertion in the
701 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
702 /// properly. Calling the method twice with the same `NodeId` is fine though.
703 #[instrument(level = "debug", skip(self), ret)]
704 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
705 assert_ne!(ast_node_id, DUMMY_NODE_ID);
707 match self.node_id_to_local_id.entry(ast_node_id) {
708 Entry::Occupied(o) => {
709 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
711 Entry::Vacant(v) => {
712 // Generate a new `HirId`.
713 let owner = self.current_hir_id_owner;
714 let local_id = self.item_local_id_counter;
715 let hir_id = hir::HirId { owner, local_id };
718 self.item_local_id_counter.increment_by(1);
720 assert_ne!(local_id, hir::ItemLocalId::new(0));
721 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
722 // Do not override a `MaybeOwner::Owner` that may already here.
723 self.children.entry(def_id).or_insert(hir::MaybeOwner::NonOwner(hir_id));
724 self.local_id_to_def_id.insert(local_id, def_id);
727 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
728 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
736 /// Generate a new `HirId` without a backing `NodeId`.
737 #[instrument(level = "debug", skip(self), ret)]
738 fn next_id(&mut self) -> hir::HirId {
739 let owner = self.current_hir_id_owner;
740 let local_id = self.item_local_id_counter;
741 assert_ne!(local_id, hir::ItemLocalId::new(0));
742 self.item_local_id_counter.increment_by(1);
743 hir::HirId { owner, local_id }
746 #[instrument(level = "trace", skip(self))]
747 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
748 let res: Result<Res, ()> = res.apply_id(|id| {
749 let owner = self.current_hir_id_owner;
750 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
751 Ok(hir::HirId { owner, local_id })
755 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
756 // This can happen when trying to lower the return type `x` in erroneous code like
757 // async fn foo(x: u8) -> x {}
758 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
759 // an opaque type as a synthesized HIR owner.
760 res.unwrap_or(Res::Err)
763 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
764 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| pr.expect_full_res())
767 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
768 self.resolver.get_import_res(id).present_items()
771 fn diagnostic(&self) -> &Handler {
772 self.tcx.sess.diagnostic()
775 /// Reuses the span but adds information like the kind of the desugaring and features that are
776 /// allowed inside this span.
777 fn mark_span_with_reason(
779 reason: DesugaringKind,
781 allow_internal_unstable: Option<Lrc<[Symbol]>>,
783 self.tcx.with_stable_hashing_context(|hcx| {
784 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
788 /// Intercept all spans entering HIR.
789 /// Mark a span as relative to the current owning item.
790 fn lower_span(&self, span: Span) -> Span {
791 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
792 span.with_parent(Some(self.current_hir_id_owner.def_id))
794 // Do not make spans relative when not using incremental compilation.
799 fn lower_ident(&self, ident: Ident) -> Ident {
800 Ident::new(ident.name, self.lower_span(ident.span))
803 /// Converts a lifetime into a new generic parameter.
804 #[instrument(level = "debug", skip(self))]
805 fn lifetime_res_to_generic_param(
810 ) -> Option<hir::GenericParam<'hir>> {
811 let (name, kind) = match res {
812 LifetimeRes::Param { .. } => {
813 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
815 LifetimeRes::Fresh { param, .. } => {
816 // Late resolution delegates to us the creation of the `LocalDefId`.
817 let _def_id = self.create_def(
818 self.current_hir_id_owner.def_id,
820 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
824 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
826 LifetimeRes::Static | LifetimeRes::Error => return None,
828 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
829 res, ident, ident.span
832 let hir_id = self.lower_node_id(node_id);
833 Some(hir::GenericParam {
836 span: self.lower_span(ident.span),
837 pure_wrt_drop: false,
838 kind: hir::GenericParamKind::Lifetime { kind },
843 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
844 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
845 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
846 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
847 /// parameters will be successful.
848 #[instrument(level = "debug", skip(self))]
850 fn lower_lifetime_binder(
853 generic_params: &[GenericParam],
854 ) -> &'hir [hir::GenericParam<'hir>] {
855 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
856 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
857 debug!(?extra_lifetimes);
858 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
859 self.lifetime_res_to_generic_param(ident, node_id, res)
861 let generic_params = self.arena.alloc_from_iter(generic_params);
862 debug!(?generic_params);
867 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
868 let was_in_dyn_type = self.is_in_dyn_type;
869 self.is_in_dyn_type = in_scope;
871 let result = f(self);
873 self.is_in_dyn_type = was_in_dyn_type;
878 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
879 let was_in_loop_condition = self.is_in_loop_condition;
880 self.is_in_loop_condition = false;
882 let catch_scope = self.catch_scope.take();
883 let loop_scope = self.loop_scope.take();
885 self.catch_scope = catch_scope;
886 self.loop_scope = loop_scope;
888 self.is_in_loop_condition = was_in_loop_condition;
893 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
894 if attrs.is_empty() {
897 debug_assert_eq!(id.owner, self.current_hir_id_owner);
898 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
899 debug_assert!(!ret.is_empty());
900 self.attrs.insert(id.local_id, ret);
905 fn lower_attr(&self, attr: &Attribute) -> Attribute {
906 // Note that we explicitly do not walk the path. Since we don't really
907 // lower attributes (we use the AST version) there is nowhere to keep
908 // the `HirId`s. We don't actually need HIR version of attributes anyway.
909 // Tokens are also not needed after macro expansion and parsing.
910 let kind = match attr.kind {
911 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
913 path: normal.item.path.clone(),
914 args: self.lower_mac_args(&normal.item.args),
919 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
922 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
925 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
926 debug_assert_eq!(id.owner, self.current_hir_id_owner);
927 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
928 if let Some(&a) = self.attrs.get(&target_id.local_id) {
929 debug_assert!(!a.is_empty());
930 self.attrs.insert(id.local_id, a);
934 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
936 MacArgs::Empty => MacArgs::Empty,
937 MacArgs::Delimited(dspan, delim, ref tokens) => {
938 // This is either a non-key-value attribute, or a `macro_rules!` body.
939 // We either not have any nonterminals present (in the case of an attribute),
940 // or have tokens available for all nonterminals in the case of a nested
941 // `macro_rules`: e.g:
944 // macro_rules! outer {
946 // macro_rules! inner {
953 // In both cases, we don't want to synthesize any tokens
954 MacArgs::Delimited(dspan, delim, tokens.flattened())
956 // This is an inert key-value attribute - it will never be visible to macros
957 // after it gets lowered to HIR. Therefore, we can extract literals to handle
958 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
959 MacArgs::Eq(eq_span, MacArgsEq::Ast(ref expr)) => {
960 // In valid code the value always ends up as a single literal. Otherwise, a dummy
961 // literal suffices because the error is handled elsewhere.
962 let lit = if let ExprKind::Lit(token_lit) = expr.kind {
963 match Lit::from_token_lit(token_lit, expr.span) {
966 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
973 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
978 MacArgs::Eq(eq_span, MacArgsEq::Hir(lit))
980 MacArgs::Eq(_, MacArgsEq::Hir(ref lit)) => {
981 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
986 /// Given an associated type constraint like one of these:
988 /// ```ignore (illustrative)
989 /// T: Iterator<Item: Debug>
991 /// T: Iterator<Item = Debug>
995 /// returns a `hir::TypeBinding` representing `Item`.
996 #[instrument(level = "debug", skip(self))]
997 fn lower_assoc_ty_constraint(
999 constraint: &AssocConstraint,
1000 itctx: &ImplTraitContext,
1001 ) -> hir::TypeBinding<'hir> {
1002 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1003 // lower generic arguments of identifier in constraint
1004 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1005 let gen_args_ctor = match gen_args {
1006 GenericArgs::AngleBracketed(ref data) => {
1007 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
1009 GenericArgs::Parenthesized(ref data) => {
1010 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
1011 let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
1012 self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
1015 gen_args_ctor.into_generic_args(self)
1017 self.arena.alloc(hir::GenericArgs::none())
1019 let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;
1021 let kind = match constraint.kind {
1022 AssocConstraintKind::Equality { ref term } => {
1023 let term = match term {
1024 Term::Ty(ref ty) => self.lower_ty(ty, itctx).into(),
1025 Term::Const(ref c) => self.lower_anon_const(c).into(),
1027 hir::TypeBindingKind::Equality { term }
1029 AssocConstraintKind::Bound { ref bounds } => {
1030 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1031 let (desugar_to_impl_trait, itctx) = match itctx {
1032 // We are in the return position:
1034 // fn foo() -> impl Iterator<Item: Debug>
1038 // fn foo() -> impl Iterator<Item = impl Debug>
1039 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1040 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1042 // We are in the argument position, but within a dyn type:
1044 // fn foo(x: dyn Iterator<Item: Debug>)
1048 // fn foo(x: dyn Iterator<Item = impl Debug>)
1049 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1051 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1052 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1053 // "impl trait context" to permit `impl Debug` in this position (it desugars
1054 // then to an opaque type).
1056 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1057 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => (true, itctx_tait),
1059 // We are in the parameter position, but not within a dyn type:
1061 // fn foo(x: impl Iterator<Item: Debug>)
1063 // so we leave it as is and this gets expanded in astconv to a bound like
1064 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1066 _ => (false, itctx),
1069 if desugar_to_impl_trait {
1070 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1071 // constructing the HIR for `impl bounds...` and then lowering that.
1073 let impl_trait_node_id = self.next_node_id();
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: &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(res) = self
1153 .get_partial_res(ty.id)
1154 .and_then(|partial_res| partial_res.full_res())
1156 if !res.matches_ns(Namespace::TypeNS) {
1158 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1162 // Construct an AnonConst where the expr is the "ty"'s path.
1164 let parent_def_id = self.current_hir_id_owner;
1165 let node_id = self.next_node_id();
1167 // Add a definition for the in-band const def.
1169 parent_def_id.def_id,
1171 DefPathData::AnonConst,
1174 let span = self.lower_span(ty.span);
1175 let path_expr = Expr {
1177 kind: ExprKind::Path(qself.clone(), path.clone()),
1179 attrs: AttrVec::new(),
1183 let ct = self.with_new_scopes(|this| hir::AnonConst {
1184 hir_id: this.lower_node_id(node_id),
1185 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1187 return GenericArg::Const(ConstArg { value: ct, span });
1193 GenericArg::Type(self.lower_ty(&ty, itctx))
1195 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1196 value: self.lower_anon_const(&ct),
1197 span: self.lower_span(ct.value.span),
1202 #[instrument(level = "debug", skip(self))]
1203 fn lower_ty(&mut self, t: &Ty, itctx: &ImplTraitContext) -> &'hir hir::Ty<'hir> {
1204 self.arena.alloc(self.lower_ty_direct(t, itctx))
1210 qself: &Option<ptr::P<QSelf>>,
1212 param_mode: ParamMode,
1213 itctx: &ImplTraitContext,
1214 ) -> hir::Ty<'hir> {
1215 // Check whether we should interpret this as a bare trait object.
1216 // This check mirrors the one in late resolution. We only introduce this special case in
1217 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1218 // The other cases when a qpath should be opportunistically made a trait object are handled
1221 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1222 && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) = partial_res.full_res()
1224 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1225 let poly_trait_ref = this.ast_arena.ptr.alloc(PolyTraitRef {
1226 bound_generic_params: vec![],
1227 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1230 let bound = this.lower_poly_trait_ref(
1234 let bounds = this.arena.alloc_from_iter([bound]);
1235 let lifetime_bound = this.elided_dyn_bound(t.span);
1236 (bounds, lifetime_bound)
1238 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1239 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1242 let id = self.lower_node_id(t.id);
1243 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1244 self.ty_path(id, t.span, qpath)
1247 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1248 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1251 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1252 self.ty(span, hir::TyKind::Tup(tys))
1255 fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir> {
1256 let kind = match t.kind {
1257 TyKind::Infer => hir::TyKind::Infer,
1258 TyKind::Err => hir::TyKind::Err,
1259 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1260 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1261 TyKind::Rptr(ref region, ref mt) => {
1262 let region = region.unwrap_or_else(|| {
1263 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1264 self.resolver.get_lifetime_res(t.id)
1266 debug_assert_eq!(start.plus(1), end);
1271 let span = self.tcx.sess.source_map().start_point(t.span);
1272 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1274 let lifetime = self.lower_lifetime(®ion);
1275 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1277 TyKind::BareFn(ref f) => {
1278 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
1279 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
1281 unsafety: self.lower_unsafety(f.unsafety),
1282 abi: self.lower_extern(f.ext),
1283 decl: self.lower_fn_decl(&f.decl, None, t.span, FnDeclKind::Pointer, None),
1284 param_names: self.lower_fn_params_to_names(&f.decl),
1287 TyKind::Never => hir::TyKind::Never,
1288 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1289 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1291 TyKind::Paren(ref ty) => {
1292 return self.lower_ty_direct(ty, itctx);
1294 TyKind::Path(ref qself, ref path) => {
1295 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1297 TyKind::ImplicitSelf => {
1298 let hir_id = self.next_id();
1299 let res = self.expect_full_res(t.id);
1300 let res = self.lower_res(res);
1301 hir::TyKind::Path(hir::QPath::Resolved(
1303 self.arena.alloc(hir::Path {
1305 segments: arena_vec![self; hir::PathSegment::new(
1306 Ident::with_dummy_span(kw::SelfUpper),
1310 span: self.lower_span(t.span),
1314 TyKind::Array(ref ty, ref length) => {
1315 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1317 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1318 TyKind::TraitObject(ref bounds, kind) => {
1319 let mut lifetime_bound = None;
1320 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1322 this.arena.alloc_from_iter(bounds.iter().filter_map(
1323 |bound| match *bound {
1324 GenericBound::Trait(
1326 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1327 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1328 // `~const ?Bound` will cause an error during AST validation
1329 // anyways, so treat it like `?Bound` as compilation proceeds.
1330 GenericBound::Trait(
1332 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1334 GenericBound::Outlives(ref lifetime) => {
1335 if lifetime_bound.is_none() {
1336 lifetime_bound = Some(this.lower_lifetime(lifetime));
1342 let lifetime_bound =
1343 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1344 (bounds, lifetime_bound)
1346 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1348 TyKind::ImplTrait(def_node_id, ref bounds) => {
1351 ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
1352 .lower_opaque_impl_trait(
1360 ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
1362 hir::OpaqueTyOrigin::TyAlias,
1368 ImplTraitContext::Universal => {
1370 self.current_hir_id_owner.def_id,
1372 DefPathData::ImplTrait,
1375 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1376 let (param, bounds, path) =
1377 self.lower_generic_and_bounds(def_node_id, span, ident, bounds);
1378 self.impl_trait_defs.push(param);
1379 if let Some(bounds) = bounds {
1380 self.impl_trait_bounds.push(bounds);
1384 ImplTraitContext::Disallowed(
1385 position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
1389 .create_feature_err(
1390 MisplacedImplTrait {
1392 position: DiagnosticArgFromDisplay(&position),
1394 sym::return_position_impl_trait_in_trait,
1399 ImplTraitContext::Disallowed(position) => {
1400 self.tcx.sess.emit_err(MisplacedImplTrait {
1402 position: DiagnosticArgFromDisplay(&position),
1408 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1409 TyKind::CVarArgs => {
1410 self.tcx.sess.delay_span_bug(
1412 "`TyKind::CVarArgs` should have been handled elsewhere",
1418 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1421 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1422 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1423 /// HIR type that references the TAIT.
1425 /// Given a function definition like:
1428 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1433 /// we will create a TAIT definition in the HIR like
1436 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1439 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1442 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1445 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1446 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1447 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1448 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1449 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1450 #[instrument(level = "debug", skip(self), ret)]
1451 fn lower_opaque_impl_trait(
1454 origin: hir::OpaqueTyOrigin,
1455 opaque_ty_node_id: NodeId,
1456 bounds: &GenericBounds,
1458 itctx: &ImplTraitContext,
1459 ) -> hir::TyKind<'hir> {
1460 // Make sure we know that some funky desugaring has been going on here.
1461 // This is a first: there is code in other places like for loop
1462 // desugaring that explicitly states that we don't want to track that.
1463 // Not tracking it makes lints in rustc and clippy very fragile, as
1464 // frequently opened issues show.
1465 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1467 let opaque_ty_def_id = match origin {
1468 hir::OpaqueTyOrigin::TyAlias => self.create_def(
1469 self.current_hir_id_owner.def_id,
1471 DefPathData::ImplTrait,
1473 hir::OpaqueTyOrigin::FnReturn(fn_def_id) => {
1474 self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait)
1476 hir::OpaqueTyOrigin::AsyncFn(..) => bug!("unreachable"),
1478 debug!(?opaque_ty_def_id);
1480 // Contains the new lifetime definitions created for the TAIT (if any).
1481 let mut collected_lifetimes = Vec::new();
1483 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1484 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1485 // exactly which ones those are.
1486 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1487 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1490 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1491 // we only keep the lifetimes that appear in the `impl Debug` itself:
1492 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1494 debug!(?lifetimes_to_remap);
1496 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1497 let mut new_remapping = FxHashMap::default();
1499 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1500 // in bounds), then create the new lifetime parameters required and create a mapping
1501 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1502 collected_lifetimes = lctx.create_lifetime_defs(
1504 &lifetimes_to_remap,
1507 debug!(?collected_lifetimes);
1508 debug!(?new_remapping);
1510 // Install the remapping from old to new (if any):
1511 lctx.with_remapping(new_remapping, |lctx| {
1512 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1513 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1514 // containing `&['x]`.
1515 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1516 |&(new_node_id, lifetime)| {
1517 let hir_id = lctx.lower_node_id(new_node_id);
1518 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1520 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1521 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1524 hir::ParamName::Plain(lifetime.ident),
1525 hir::LifetimeParamKind::Explicit,
1532 span: lifetime.ident.span,
1533 pure_wrt_drop: false,
1534 kind: hir::GenericParamKind::Lifetime { kind },
1539 debug!(?lifetime_defs);
1541 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1542 // get back Debug + 'a1, which is suitable for use on the TAIT.
1543 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1544 debug!(?hir_bounds);
1546 let opaque_ty_item = hir::OpaqueTy {
1547 generics: self.arena.alloc(hir::Generics {
1548 params: lifetime_defs,
1550 has_where_clause_predicates: false,
1551 where_clause_span: lctx.lower_span(span),
1552 span: lctx.lower_span(span),
1558 debug!(?opaque_ty_item);
1560 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1564 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1565 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1567 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1568 let id = self.next_node_id();
1569 let span = lifetime.ident.span;
1571 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
1572 Ident::with_dummy_span(kw::UnderscoreLifetime)
1577 let l = self.new_named_lifetime(lifetime.id, id, span, ident);
1578 hir::GenericArg::Lifetime(l)
1582 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1583 hir::TyKind::OpaqueDef(
1584 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
1590 /// Registers a new opaque type with the proper `NodeId`s and
1591 /// returns the lowered node-ID for the opaque type.
1592 fn generate_opaque_type(
1594 opaque_ty_id: LocalDefId,
1595 opaque_ty_item: hir::OpaqueTy<'hir>,
1597 opaque_ty_span: Span,
1598 ) -> hir::OwnerNode<'hir> {
1599 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1600 // Generate an `type Foo = impl Trait;` declaration.
1601 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1602 let opaque_ty_item = hir::Item {
1603 owner_id: hir::OwnerId { def_id: opaque_ty_id },
1604 ident: Ident::empty(),
1605 kind: opaque_ty_item_kind,
1606 vis_span: self.lower_span(span.shrink_to_lo()),
1607 span: self.lower_span(opaque_ty_span),
1609 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1612 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1613 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1614 /// new definition, adds it to the remapping with the definition of the given lifetime and
1615 /// returns a list of lifetimes to be lowered afterwards.
1616 fn create_lifetime_defs(
1618 parent_def_id: LocalDefId,
1619 lifetimes_in_bounds: &[Lifetime],
1620 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1621 ) -> Vec<(NodeId, Lifetime)> {
1622 let mut result = Vec::new();
1624 for lifetime in lifetimes_in_bounds {
1625 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1629 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1630 if remapping.get(&old_def_id).is_none() {
1631 let node_id = self.next_node_id();
1633 let new_def_id = self.create_def(
1636 DefPathData::LifetimeNs(lifetime.ident.name),
1638 remapping.insert(old_def_id, new_def_id);
1640 result.push((node_id, *lifetime));
1644 LifetimeRes::Fresh { param, binder: _ } => {
1645 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1646 if let Some(old_def_id) = self.orig_opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1647 let node_id = self.next_node_id();
1649 let new_def_id = self.create_def(
1652 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1654 remapping.insert(old_def_id, new_def_id);
1656 result.push((node_id, *lifetime));
1660 LifetimeRes::Static | LifetimeRes::Error => {}
1663 let bug_msg = format!(
1664 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1665 res, lifetime.ident, lifetime.ident.span
1667 span_bug!(lifetime.ident.span, "{}", bug_msg);
1675 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1676 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1677 // as they are not explicit in HIR/Ty function signatures.
1678 // (instead, the `c_variadic` flag is set to `true`)
1679 let mut inputs = &decl.inputs[..];
1680 if decl.c_variadic() {
1681 inputs = &inputs[..inputs.len() - 1];
1683 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1684 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1685 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1689 // Lowers a function declaration.
1691 // `decl`: the unlowered (AST) function declaration.
1692 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1693 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1694 // `make_ret_async` is also `Some`.
1695 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1696 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1697 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1698 #[instrument(level = "debug", skip(self))]
1702 fn_node_id: Option<NodeId>,
1705 make_ret_async: Option<(NodeId, Span)>,
1706 ) -> &'hir hir::FnDecl<'hir> {
1707 let c_variadic = decl.c_variadic();
1709 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1710 // as they are not explicit in HIR/Ty function signatures.
1711 // (instead, the `c_variadic` flag is set to `true`)
1712 let mut inputs = &decl.inputs[..];
1714 inputs = &inputs[..inputs.len() - 1];
1716 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1717 if fn_node_id.is_some() {
1718 self.lower_ty_direct(¶m.ty, &ImplTraitContext::Universal)
1720 self.lower_ty_direct(
1722 &ImplTraitContext::Disallowed(match kind {
1723 FnDeclKind::Fn | FnDeclKind::Inherent => {
1724 unreachable!("fn should allow in-band lifetimes")
1726 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1727 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1728 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1729 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1730 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1736 let output = if let Some((ret_id, span)) = make_ret_async {
1737 if !kind.async_fn_allowed(self.tcx) {
1739 FnDeclKind::Trait | FnDeclKind::Impl => {
1742 .create_feature_err(
1743 TraitFnAsync { fn_span, span },
1744 sym::async_fn_in_trait,
1749 self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
1754 self.lower_async_fn_ret_ty(
1756 fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
1758 matches!(kind, FnDeclKind::Trait),
1762 FnRetTy::Ty(ref ty) => {
1763 let mut context = match fn_node_id {
1764 Some(fn_node_id) if kind.impl_trait_allowed(self.tcx) => {
1765 let fn_def_id = self.local_def_id(fn_node_id);
1766 ImplTraitContext::ReturnPositionOpaqueTy {
1767 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1768 in_trait: matches!(kind, FnDeclKind::Trait),
1771 _ => ImplTraitContext::Disallowed(match kind {
1772 FnDeclKind::Fn | FnDeclKind::Inherent => {
1773 unreachable!("fn should allow in-band lifetimes")
1775 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1776 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1777 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1778 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1779 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1782 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1784 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1788 self.arena.alloc(hir::FnDecl {
1792 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1793 let is_mutable_pat = matches!(
1795 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1799 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1800 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1801 // Given we are only considering `ImplicitSelf` types, we needn't consider
1802 // the case where we have a mutable pattern to a reference as that would
1803 // no longer be an `ImplicitSelf`.
1804 TyKind::Rptr(_, ref mt)
1805 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1807 hir::ImplicitSelfKind::MutRef
1809 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1810 hir::ImplicitSelfKind::ImmRef
1812 _ => hir::ImplicitSelfKind::None,
1818 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1819 // combined with the following definition of `OpaqueTy`:
1821 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1823 // `output`: unlowered output type (`T` in `-> T`)
1824 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1825 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1826 #[instrument(level = "debug", skip(self))]
1827 fn lower_async_fn_ret_ty(
1831 opaque_ty_node_id: NodeId,
1833 ) -> hir::FnRetTy<'hir> {
1834 let span = output.span();
1836 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1838 let opaque_ty_def_id = self.local_def_id(opaque_ty_node_id);
1839 let fn_def_id = self.local_def_id(fn_node_id);
1841 // When we create the opaque type for this async fn, it is going to have
1842 // to capture all the lifetimes involved in the signature (including in the
1843 // return type). This is done by introducing lifetime parameters for:
1845 // - all the explicitly declared lifetimes from the impl and function itself;
1846 // - all the elided lifetimes in the fn arguments;
1847 // - all the elided lifetimes in the return type.
1849 // So for example in this snippet:
1852 // impl<'a> Foo<'a> {
1853 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1854 // // ^ '0 ^ '1 ^ '2
1855 // // elided lifetimes used below
1860 // we would create an opaque type like:
1863 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1866 // and we would then desugar `bar` to the equivalent of:
1869 // impl<'a> Foo<'a> {
1870 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1874 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1875 // this is because the elided lifetimes from the return type
1876 // should be figured out using the ordinary elision rules, and
1877 // this desugaring achieves that.
1879 // Calculate all the lifetimes that should be captured
1880 // by the opaque type. This should include all in-scope
1881 // lifetime parameters, including those defined in-band.
1883 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1885 let mut collected_lifetimes = Vec::new();
1886 let mut new_remapping = FxHashMap::default();
1888 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1889 debug!(?extra_lifetime_params);
1890 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1891 let outer_def_id = self.orig_local_def_id(outer_node_id);
1892 let inner_node_id = self.next_node_id();
1894 // Add a definition for the in scope lifetime def.
1895 let inner_def_id = self.create_def(
1898 DefPathData::LifetimeNs(ident.name),
1900 new_remapping.insert(outer_def_id, inner_def_id);
1902 let inner_res = match outer_res {
1903 // Input lifetime like `'a`:
1904 LifetimeRes::Param { param, .. } => {
1905 LifetimeRes::Param { param, binder: fn_node_id }
1907 // Input lifetime like `'1`:
1908 LifetimeRes::Fresh { param, .. } => {
1909 LifetimeRes::Fresh { param, binder: fn_node_id }
1911 LifetimeRes::Static | LifetimeRes::Error => continue,
1914 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1915 res, ident, ident.span
1920 let lifetime = Lifetime { id: outer_node_id, ident };
1921 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1924 debug!(?collected_lifetimes);
1926 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1927 // find out exactly which ones those are.
1928 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1929 // we only keep the lifetimes that appear in the `impl Debug` itself:
1930 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1931 debug!(?lifetimes_to_remap);
1933 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1934 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1935 // in bounds), then create the new lifetime parameters required and create a mapping
1936 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1937 collected_lifetimes.extend(
1938 this.create_lifetime_defs(
1940 &lifetimes_to_remap,
1944 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1946 debug!(?collected_lifetimes);
1947 debug!(?new_remapping);
1949 // Install the remapping from old to new (if any):
1950 this.with_remapping(new_remapping, |this| {
1951 // We have to be careful to get elision right here. The
1952 // idea is that we create a lifetime parameter for each
1953 // lifetime in the return type. So, given a return type
1954 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1955 // Future<Output = &'1 [ &'2 u32 ]>`.
1957 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1958 // hence the elision takes place at the fn site.
1959 let future_bound = this.lower_async_fn_output_type_to_future_bound(
1962 if in_trait && !this.tcx.features().return_position_impl_trait_in_trait {
1963 ImplTraitContext::Disallowed(ImplTraitPosition::TraitReturn)
1965 ImplTraitContext::ReturnPositionOpaqueTy {
1966 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1972 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1973 |&(new_node_id, lifetime, _)| {
1974 let hir_id = this.lower_node_id(new_node_id);
1975 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1977 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1978 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1981 hir::ParamName::Plain(lifetime.ident),
1982 hir::LifetimeParamKind::Explicit,
1989 span: lifetime.ident.span,
1990 pure_wrt_drop: false,
1991 kind: hir::GenericParamKind::Lifetime { kind },
1996 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1998 let opaque_ty_item = hir::OpaqueTy {
1999 generics: this.arena.alloc(hir::Generics {
2000 params: generic_params,
2002 has_where_clause_predicates: false,
2003 where_clause_span: this.lower_span(span),
2004 span: this.lower_span(span),
2006 bounds: arena_vec![this; future_bound],
2007 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
2011 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2012 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
2016 // As documented above, we need to create the lifetime
2017 // arguments to our opaque type. Continuing with our example,
2018 // we're creating the type arguments for the return type:
2021 // Bar<'a, 'b, '0, '1, '_>
2024 // For the "input" lifetime parameters, we wish to create
2025 // references to the parameters themselves, including the
2026 // "implicit" ones created from parameter types (`'a`, `'b`,
2029 // For the "output" lifetime parameters, we just want to
2031 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2032 |(_, lifetime, res)| {
2033 let id = self.next_node_id();
2034 let span = lifetime.ident.span;
2036 let ident = if lifetime.ident.name == kw::UnderscoreLifetime {
2037 Ident::with_dummy_span(kw::UnderscoreLifetime)
2042 let res = res.unwrap_or(
2043 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2045 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, span, ident, res))
2049 // Create the `Foo<...>` reference itself. Note that the `type
2050 // Foo = impl Trait` is, internally, created as a child of the
2051 // async fn, so the *type parameters* are inherited. It's
2052 // only the lifetime parameters that we must supply.
2053 let opaque_ty_ref = hir::TyKind::OpaqueDef(
2054 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
2058 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2059 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2062 /// Transforms `-> T` into `Future<Output = T>`.
2063 fn lower_async_fn_output_type_to_future_bound(
2067 mut nested_impl_trait_context: ImplTraitContext,
2068 ) -> hir::GenericBound<'hir> {
2069 // Compute the `T` in `Future<Output = T>` from the return type.
2070 let output_ty = match output {
2071 FnRetTy::Ty(ty) => {
2072 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2073 // `impl Future` opaque type that `async fn` implicitly
2075 self.lower_ty(ty, &mut nested_impl_trait_context)
2077 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2081 let future_args = self.arena.alloc(hir::GenericArgs {
2083 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2084 parenthesized: false,
2088 hir::GenericBound::LangItemTrait(
2089 // ::std::future::Future<future_params>
2090 hir::LangItem::Future,
2091 self.lower_span(span),
2097 #[instrument(level = "trace", skip(self))]
2098 fn lower_param_bound(
2101 itctx: &ImplTraitContext,
2102 ) -> hir::GenericBound<'hir> {
2104 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2105 self.lower_poly_trait_ref(p, itctx),
2106 self.lower_trait_bound_modifier(*modifier),
2108 GenericBound::Outlives(lifetime) => {
2109 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2114 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2115 let span = self.lower_span(l.ident.span);
2116 let ident = self.lower_ident(l.ident);
2117 self.new_named_lifetime(l.id, l.id, span, ident)
2120 #[instrument(level = "debug", skip(self))]
2121 fn new_named_lifetime_with_res(
2127 ) -> &'hir hir::Lifetime {
2128 let name = match res {
2129 LifetimeRes::Param { param, .. } => {
2130 let p_name = ParamName::Plain(ident);
2131 let param = self.get_remapped_def_id(param);
2133 hir::LifetimeName::Param(param, p_name)
2135 LifetimeRes::Fresh { param, .. } => {
2136 debug_assert_eq!(ident.name, kw::UnderscoreLifetime);
2137 let param = self.local_def_id(param);
2139 hir::LifetimeName::Param(param, ParamName::Fresh)
2141 LifetimeRes::Infer => hir::LifetimeName::Infer,
2142 LifetimeRes::Static => hir::LifetimeName::Static,
2143 LifetimeRes::Error => hir::LifetimeName::Error,
2144 res => panic!("Unexpected lifetime resolution {:?} for {:?} at {:?}", res, ident, span),
2148 self.arena.alloc(hir::Lifetime {
2149 hir_id: self.lower_node_id(id),
2150 span: self.lower_span(span),
2155 #[instrument(level = "debug", skip(self))]
2156 fn new_named_lifetime(
2162 ) -> &'hir hir::Lifetime {
2163 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2164 self.new_named_lifetime_with_res(new_id, span, ident, res)
2167 fn lower_generic_params_mut<'s>(
2169 params: &'s [GenericParam],
2170 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2171 params.iter().map(move |param| self.lower_generic_param(param))
2174 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2175 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2178 #[instrument(level = "trace", skip(self))]
2179 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2180 let (name, kind) = self.lower_generic_param_kind(param);
2182 let hir_id = self.lower_node_id(param.id);
2183 self.lower_attrs(hir_id, ¶m.attrs);
2187 span: self.lower_span(param.span()),
2188 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2190 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2194 fn lower_generic_param_kind(
2196 param: &GenericParam,
2197 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2199 GenericParamKind::Lifetime => {
2200 // AST resolution emitted an error on those parameters, so we lower them using
2201 // `ParamName::Error`.
2203 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2206 let ident = self.lower_ident(param.ident);
2207 ParamName::Plain(ident)
2210 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2214 GenericParamKind::Type { ref default, .. } => {
2215 let kind = hir::GenericParamKind::Type {
2216 default: default.as_ref().map(|x| {
2217 self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2222 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2224 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2225 let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2226 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2228 hir::ParamName::Plain(self.lower_ident(param.ident)),
2229 hir::GenericParamKind::Const { ty, default },
2235 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: &ImplTraitContext) -> hir::TraitRef<'hir> {
2236 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2237 hir::QPath::Resolved(None, path) => path,
2238 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2240 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2243 #[instrument(level = "debug", skip(self))]
2244 fn lower_poly_trait_ref(
2247 itctx: &ImplTraitContext,
2248 ) -> hir::PolyTraitRef<'hir> {
2249 let bound_generic_params =
2250 self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
2251 let trait_ref = self.lower_trait_ref(&p.trait_ref, itctx);
2252 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2255 fn lower_mt(&mut self, mt: &MutTy, itctx: &ImplTraitContext) -> hir::MutTy<'hir> {
2256 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2259 #[instrument(level = "debug", skip(self), ret)]
2260 fn lower_param_bounds(
2262 bounds: &[GenericBound],
2263 itctx: &ImplTraitContext,
2264 ) -> hir::GenericBounds<'hir> {
2265 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2268 fn lower_param_bounds_mut<'s>(
2270 bounds: &'s [GenericBound],
2271 itctx: &'s ImplTraitContext,
2272 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2273 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2276 #[instrument(level = "debug", skip(self), ret)]
2277 fn lower_generic_and_bounds(
2282 bounds: &[GenericBound],
2283 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2284 // Add a definition for the in-band `Param`.
2285 let def_id = self.local_def_id(node_id);
2287 // Set the name to `impl Bound1 + Bound2`.
2288 let param = hir::GenericParam {
2289 hir_id: self.lower_node_id(node_id),
2290 name: ParamName::Plain(self.lower_ident(ident)),
2291 pure_wrt_drop: false,
2292 span: self.lower_span(span),
2293 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2297 let preds = self.lower_generic_bound_predicate(
2300 &GenericParamKind::Type { default: None },
2302 &ImplTraitContext::Universal,
2303 hir::PredicateOrigin::ImplTrait,
2306 let hir_id = self.next_id();
2307 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2308 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2310 self.arena.alloc(hir::Path {
2311 span: self.lower_span(span),
2314 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2321 /// Lowers a block directly to an expression, presuming that it
2322 /// has no attributes and is not targeted by a `break`.
2323 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2324 let block = self.lower_block(b, false);
2325 self.expr_block(block, AttrVec::new())
2328 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2329 match c.value.kind {
2330 ExprKind::Underscore => {
2331 if self.tcx.features().generic_arg_infer {
2332 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2335 &self.tcx.sess.parse_sess,
2336 sym::generic_arg_infer,
2338 "using `_` for array lengths is unstable",
2340 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2341 hir::ArrayLen::Body(self.lower_anon_const(c))
2344 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2348 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2349 self.with_new_scopes(|this| hir::AnonConst {
2350 hir_id: this.lower_node_id(c.id),
2351 body: this.lower_const_body(c.value.span, Some(&c.value)),
2355 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2357 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2358 UserProvided => hir::UnsafeSource::UserProvided,
2362 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2364 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2365 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2367 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2368 // placeholder for compilation to proceed.
2369 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2370 hir::TraitBoundModifier::Maybe
2375 // Helper methods for building HIR.
2377 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2378 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2381 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2382 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2387 attrs: Option<&'hir [Attribute]>,
2389 init: Option<&'hir hir::Expr<'hir>>,
2390 pat: &'hir hir::Pat<'hir>,
2391 source: hir::LocalSource,
2392 ) -> hir::Stmt<'hir> {
2393 let hir_id = self.next_id();
2394 if let Some(a) = attrs {
2395 debug_assert!(!a.is_empty());
2396 self.attrs.insert(hir_id.local_id, a);
2398 let local = hir::Local {
2404 span: self.lower_span(span),
2407 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2410 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2411 self.block_all(expr.span, &[], Some(expr))
2417 stmts: &'hir [hir::Stmt<'hir>],
2418 expr: Option<&'hir hir::Expr<'hir>>,
2419 ) -> &'hir hir::Block<'hir> {
2420 let blk = hir::Block {
2423 hir_id: self.next_id(),
2424 rules: hir::BlockCheckMode::DefaultBlock,
2425 span: self.lower_span(span),
2426 targeted_by_break: false,
2428 self.arena.alloc(blk)
2431 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2432 let field = self.single_pat_field(span, pat);
2433 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2436 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2437 let field = self.single_pat_field(span, pat);
2438 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2441 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2442 let field = self.single_pat_field(span, pat);
2443 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2446 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2447 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2450 fn single_pat_field(
2453 pat: &'hir hir::Pat<'hir>,
2454 ) -> &'hir [hir::PatField<'hir>] {
2455 let field = hir::PatField {
2456 hir_id: self.next_id(),
2457 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2458 is_shorthand: false,
2460 span: self.lower_span(span),
2462 arena_vec![self; field]
2465 fn pat_lang_item_variant(
2468 lang_item: hir::LangItem,
2469 fields: &'hir [hir::PatField<'hir>],
2470 hir_id: Option<hir::HirId>,
2471 ) -> &'hir hir::Pat<'hir> {
2472 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2473 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2476 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2477 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2480 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2481 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2484 fn pat_ident_binding_mode(
2488 bm: hir::BindingAnnotation,
2489 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2490 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2491 (self.arena.alloc(pat), hir_id)
2494 fn pat_ident_binding_mode_mut(
2498 bm: hir::BindingAnnotation,
2499 ) -> (hir::Pat<'hir>, hir::HirId) {
2500 let hir_id = self.next_id();
2505 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2506 span: self.lower_span(span),
2507 default_binding_modes: true,
2513 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2514 self.arena.alloc(hir::Pat {
2515 hir_id: self.next_id(),
2517 span: self.lower_span(span),
2518 default_binding_modes: true,
2522 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2524 hir_id: self.next_id(),
2526 span: self.lower_span(span),
2527 default_binding_modes: false,
2533 mut hir_id: hir::HirId,
2535 qpath: hir::QPath<'hir>,
2536 ) -> hir::Ty<'hir> {
2537 let kind = match qpath {
2538 hir::QPath::Resolved(None, path) => {
2539 // Turn trait object paths into `TyKind::TraitObject` instead.
2541 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2542 let principal = hir::PolyTraitRef {
2543 bound_generic_params: &[],
2544 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2545 span: self.lower_span(span),
2548 // The original ID is taken by the `PolyTraitRef`,
2549 // so the `Ty` itself needs a different one.
2550 hir_id = self.next_id();
2551 hir::TyKind::TraitObject(
2552 arena_vec![self; principal],
2553 self.elided_dyn_bound(span),
2554 TraitObjectSyntax::None,
2557 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2560 _ => hir::TyKind::Path(qpath),
2563 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2566 /// Invoked to create the lifetime argument(s) for an elided trait object
2567 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2568 /// when the bound is written, even if it is written with `'_` like in
2569 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2570 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2571 let r = hir::Lifetime {
2572 hir_id: self.next_id(),
2573 span: self.lower_span(span),
2574 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2576 debug!("elided_dyn_bound: r={:?}", r);
2581 /// Helper struct for delayed construction of GenericArgs.
2582 struct GenericArgsCtor<'hir> {
2583 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2584 bindings: &'hir [hir::TypeBinding<'hir>],
2585 parenthesized: bool,
2589 impl<'hir> GenericArgsCtor<'hir> {
2590 fn is_empty(&self) -> bool {
2591 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2594 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2595 let ga = hir::GenericArgs {
2596 args: this.arena.alloc_from_iter(self.args),
2597 bindings: self.bindings,
2598 parenthesized: self.parenthesized,
2599 span_ext: this.lower_span(self.span),
2601 this.arena.alloc(ga)