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 #![deny(rustc::untranslatable_diagnostic)]
38 #![deny(rustc::diagnostic_outside_of_impl)]
43 use crate::errors::{AssocTyParentheses, AssocTyParenthesesSub, MisplacedImplTrait, TraitFnAsync};
45 use rustc_arena::declare_arena;
46 use rustc_ast::ptr::P;
48 use rustc_ast::{self as ast, *};
49 use rustc_ast_pretty::pprust;
50 use rustc_data_structures::captures::Captures;
51 use rustc_data_structures::fingerprint::Fingerprint;
52 use rustc_data_structures::fx::FxHashMap;
53 use rustc_data_structures::sorted_map::SortedMap;
54 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
55 use rustc_data_structures::sync::Lrc;
56 use rustc_errors::{DiagnosticArgFromDisplay, Handler, StashKey};
58 use rustc_hir::def::{DefKind, LifetimeRes, Namespace, PartialRes, PerNS, Res};
59 use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
60 use rustc_hir::definitions::DefPathData;
61 use rustc_hir::{ConstArg, GenericArg, ItemLocalId, ParamName, TraitCandidate};
62 use rustc_index::vec::{Idx, IndexVec};
63 use rustc_middle::span_bug;
64 use rustc_middle::ty::{ResolverAstLowering, TyCtxt};
65 use rustc_session::parse::feature_err;
66 use rustc_span::hygiene::MacroKind;
67 use rustc_span::source_map::DesugaringKind;
68 use rustc_span::symbol::{kw, sym, Ident, Symbol};
69 use rustc_span::{Span, DUMMY_SP};
71 use smallvec::SmallVec;
72 use std::collections::hash_map::Entry;
74 macro_rules! arena_vec {
75 ($this:expr; $($x:expr),*) => (
76 $this.arena.alloc_from_iter([$($x),*])
86 mod lifetime_collector;
90 struct LoweringContext<'a, 'hir> {
92 resolver: &'a mut ResolverAstLowering,
94 /// Used to allocate HIR nodes.
95 arena: &'hir hir::Arena<'hir>,
97 /// Used to allocate temporary AST nodes for use during lowering.
98 /// This allows us to create "fake" AST -- these nodes can sometimes
99 /// be allocated on the stack, but other times we need them to live longer
100 /// than the current stack frame, so they can be collected into vectors
101 /// and things like that.
102 ast_arena: &'a Arena<'static>,
104 /// Bodies inside the owner being lowered.
105 bodies: Vec<(hir::ItemLocalId, &'hir hir::Body<'hir>)>,
106 /// Attributes inside the owner being lowered.
107 attrs: SortedMap<hir::ItemLocalId, &'hir [Attribute]>,
108 /// Collect items that were created by lowering the current owner.
109 children: Vec<(LocalDefId, hir::MaybeOwner<&'hir hir::OwnerInfo<'hir>>)>,
111 generator_kind: Option<hir::GeneratorKind>,
113 /// When inside an `async` context, this is the `HirId` of the
114 /// `task_context` local bound to the resume argument of the generator.
115 task_context: Option<hir::HirId>,
117 /// Used to get the current `fn`'s def span to point to when using `await`
118 /// outside of an `async fn`.
119 current_item: Option<Span>,
121 catch_scope: Option<NodeId>,
122 loop_scope: Option<NodeId>,
123 is_in_loop_condition: bool,
124 is_in_trait_impl: bool,
125 is_in_dyn_type: bool,
127 current_hir_id_owner: hir::OwnerId,
128 item_local_id_counter: hir::ItemLocalId,
129 local_id_to_def_id: SortedMap<ItemLocalId, LocalDefId>,
130 trait_map: FxHashMap<ItemLocalId, Box<[TraitCandidate]>>,
132 impl_trait_defs: Vec<hir::GenericParam<'hir>>,
133 impl_trait_bounds: Vec<hir::WherePredicate<'hir>>,
135 /// NodeIds that are lowered inside the current HIR owner.
136 node_id_to_local_id: FxHashMap<NodeId, hir::ItemLocalId>,
138 allow_try_trait: Option<Lrc<[Symbol]>>,
139 allow_gen_future: Option<Lrc<[Symbol]>>,
140 allow_into_future: Option<Lrc<[Symbol]>>,
142 /// Mapping from generics `def_id`s to TAIT generics `def_id`s.
143 /// For each captured lifetime (e.g., 'a), we create a new lifetime parameter that is a generic
144 /// defined on the TAIT, so we have type Foo<'a1> = ... and we establish a mapping in this
145 /// field from the original parameter 'a to the new parameter 'a1.
146 generics_def_id_map: Vec<FxHashMap<LocalDefId, LocalDefId>>,
150 [] tys: rustc_ast::Ty,
151 [] aba: rustc_ast::AngleBracketedArgs,
152 [] ptr: rustc_ast::PolyTraitRef,
153 // This _marker field is needed because `declare_arena` creates `Arena<'tcx>` and we need to
154 // use `'tcx`. If we don't have this we get a compile error.
155 [] _marker: std::marker::PhantomData<&'tcx ()>,
158 trait ResolverAstLoweringExt {
159 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>>;
160 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes>;
161 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
162 // Clones the resolution (if any) on 'source' and applies it
163 // to 'target'. Used when desugaring a `UseTreeKind::Nested` to
164 // multiple `UseTreeKind::Simple`s
165 fn clone_res(&mut self, source: NodeId, target: NodeId);
166 fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
167 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
168 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
169 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind;
172 impl ResolverAstLoweringExt for ResolverAstLowering {
173 fn legacy_const_generic_args(&self, expr: &Expr) -> Option<Vec<usize>> {
174 if let ExprKind::Path(None, path) = &expr.kind {
175 // Don't perform legacy const generics rewriting if the path already
176 // has generic arguments.
177 if path.segments.last().unwrap().args.is_some() {
181 if let Res::Def(DefKind::Fn, def_id) = self.partial_res_map.get(&expr.id)?.full_res()? {
182 // We only support cross-crate argument rewriting. Uses
183 // within the same crate should be updated to use the new
184 // const generics style.
185 if def_id.is_local() {
189 if let Some(v) = self.legacy_const_generic_args.get(&def_id) {
198 fn clone_res(&mut self, source: NodeId, target: NodeId) {
199 if let Some(res) = self.partial_res_map.get(&source) {
200 self.partial_res_map.insert(target, *res);
204 /// Obtains resolution for a `NodeId` with a single resolution.
205 fn get_partial_res(&self, id: NodeId) -> Option<PartialRes> {
206 self.partial_res_map.get(&id).copied()
209 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
210 fn get_import_res(&self, id: NodeId) -> PerNS<Option<Res<NodeId>>> {
211 self.import_res_map.get(&id).copied().unwrap_or_default()
214 /// Obtains resolution for a label with the given `NodeId`.
215 fn get_label_res(&self, id: NodeId) -> Option<NodeId> {
216 self.label_res_map.get(&id).copied()
219 /// Obtains resolution for a lifetime with the given `NodeId`.
220 fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes> {
221 self.lifetimes_res_map.get(&id).copied()
224 /// Obtain the list of lifetimes parameters to add to an item.
226 /// Extra lifetime parameters should only be added in places that can appear
227 /// as a `binder` in `LifetimeRes`.
229 /// The extra lifetimes that appear from the parenthesized `Fn`-trait desugaring
230 /// should appear at the enclosing `PolyTraitRef`.
231 fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
232 self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
235 fn decl_macro_kind(&self, def_id: LocalDefId) -> MacroKind {
236 self.builtin_macro_kinds.get(&def_id).copied().unwrap_or(MacroKind::Bang)
240 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
241 /// and if so, what meaning it has.
242 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
243 enum ImplTraitContext {
244 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
245 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
246 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
248 /// Newly generated parameters should be inserted into the given `Vec`.
251 /// Treat `impl Trait` as shorthand for a new opaque type.
252 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
253 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
255 ReturnPositionOpaqueTy {
256 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
257 origin: hir::OpaqueTyOrigin,
260 /// Impl trait in type aliases.
262 /// `impl Trait` is not accepted in this position.
263 Disallowed(ImplTraitPosition),
266 /// Position in which `impl Trait` is disallowed.
267 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
268 enum ImplTraitPosition {
290 impl std::fmt::Display for ImplTraitPosition {
291 fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
292 let name = match self {
293 ImplTraitPosition::Path => "path",
294 ImplTraitPosition::Variable => "variable binding",
295 ImplTraitPosition::Type => "type",
296 ImplTraitPosition::Trait => "trait",
297 ImplTraitPosition::AsyncBlock => "async block",
298 ImplTraitPosition::Bound => "bound",
299 ImplTraitPosition::Generic => "generic",
300 ImplTraitPosition::ExternFnParam => "`extern fn` param",
301 ImplTraitPosition::ClosureParam => "closure param",
302 ImplTraitPosition::PointerParam => "`fn` pointer param",
303 ImplTraitPosition::FnTraitParam => "`Fn` trait param",
304 ImplTraitPosition::TraitParam => "trait method param",
305 ImplTraitPosition::ImplParam => "`impl` method param",
306 ImplTraitPosition::ExternFnReturn => "`extern fn` return",
307 ImplTraitPosition::ClosureReturn => "closure return",
308 ImplTraitPosition::PointerReturn => "`fn` pointer return",
309 ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
310 ImplTraitPosition::TraitReturn => "trait method return",
311 ImplTraitPosition::ImplReturn => "`impl` method return",
314 write!(f, "{}", name)
318 #[derive(Debug, PartialEq, Eq)]
330 fn param_impl_trait_allowed(&self) -> bool {
332 FnDeclKind::Fn | FnDeclKind::Inherent | FnDeclKind::Impl | FnDeclKind::Trait => true,
337 fn return_impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
339 FnDeclKind::Fn | FnDeclKind::Inherent => true,
340 FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
341 FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
346 fn async_fn_allowed(&self, tcx: TyCtxt<'_>) -> bool {
348 FnDeclKind::Fn | FnDeclKind::Inherent => true,
349 FnDeclKind::Impl if tcx.features().async_fn_in_trait => true,
350 FnDeclKind::Trait if tcx.features().async_fn_in_trait => true,
356 #[derive(Copy, Clone)]
359 Crate(&'a ast::Crate),
361 AssocItem(&'a ast::AssocItem, visit::AssocCtxt),
362 ForeignItem(&'a ast::ForeignItem),
366 node_id_to_def_id: &FxHashMap<NodeId, LocalDefId>,
368 ) -> IndexVec<LocalDefId, AstOwner<'a>> {
369 let mut indexer = Indexer { node_id_to_def_id, index: IndexVec::new() };
370 indexer.index.ensure_contains_elem(CRATE_DEF_ID, || AstOwner::NonOwner);
371 indexer.index[CRATE_DEF_ID] = AstOwner::Crate(krate);
372 visit::walk_crate(&mut indexer, krate);
373 return indexer.index;
375 struct Indexer<'s, 'a> {
376 node_id_to_def_id: &'s FxHashMap<NodeId, LocalDefId>,
377 index: IndexVec<LocalDefId, AstOwner<'a>>,
380 impl<'a> visit::Visitor<'a> for Indexer<'_, 'a> {
381 fn visit_attribute(&mut self, _: &'a Attribute) {
382 // We do not want to lower expressions that appear in attributes,
383 // as they are not accessible to the rest of the HIR.
386 fn visit_item(&mut self, item: &'a ast::Item) {
387 let def_id = self.node_id_to_def_id[&item.id];
388 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
389 self.index[def_id] = AstOwner::Item(item);
390 visit::walk_item(self, item)
393 fn visit_assoc_item(&mut self, item: &'a ast::AssocItem, ctxt: visit::AssocCtxt) {
394 let def_id = self.node_id_to_def_id[&item.id];
395 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
396 self.index[def_id] = AstOwner::AssocItem(item, ctxt);
397 visit::walk_assoc_item(self, item, ctxt);
400 fn visit_foreign_item(&mut self, item: &'a ast::ForeignItem) {
401 let def_id = self.node_id_to_def_id[&item.id];
402 self.index.ensure_contains_elem(def_id, || AstOwner::NonOwner);
403 self.index[def_id] = AstOwner::ForeignItem(item);
404 visit::walk_foreign_item(self, item);
409 /// Compute the hash for the HIR of the full crate.
410 /// This hash will then be part of the crate_hash which is stored in the metadata.
413 owners: &IndexVec<LocalDefId, hir::MaybeOwner<&hir::OwnerInfo<'_>>>,
415 let mut hir_body_nodes: Vec<_> = owners
417 .filter_map(|(def_id, info)| {
418 let info = info.as_owner()?;
419 let def_path_hash = tcx.hir().def_path_hash(def_id);
420 Some((def_path_hash, info))
423 hir_body_nodes.sort_unstable_by_key(|bn| bn.0);
425 tcx.with_stable_hashing_context(|mut hcx| {
426 let mut stable_hasher = StableHasher::new();
427 hir_body_nodes.hash_stable(&mut hcx, &mut stable_hasher);
428 stable_hasher.finish()
432 pub fn lower_to_hir<'hir>(tcx: TyCtxt<'hir>, (): ()) -> hir::Crate<'hir> {
434 let krate = tcx.untracked_crate.steal();
435 let mut resolver = tcx.resolver_for_lowering(()).steal();
437 let ast_index = index_crate(&resolver.node_id_to_def_id, &krate);
438 let mut owners = IndexVec::from_fn_n(
439 |_| hir::MaybeOwner::Phantom,
440 tcx.definitions_untracked().def_index_count(),
443 let ast_arena = Arena::default();
445 for def_id in ast_index.indices() {
448 resolver: &mut resolver,
449 ast_arena: &ast_arena,
450 ast_index: &ast_index,
456 // Drop AST to free memory
457 std::mem::drop(ast_index);
458 sess.time("drop_ast", || std::mem::drop(krate));
460 // Discard hygiene data, which isn't required after lowering to HIR.
461 if !sess.opts.unstable_opts.keep_hygiene_data {
462 rustc_span::hygiene::clear_syntax_context_map();
465 let hir_hash = compute_hir_hash(tcx, &owners);
466 hir::Crate { owners, hir_hash }
469 #[derive(Copy, Clone, PartialEq, Debug)]
471 /// Any path in a type context.
473 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
475 /// The `module::Type` in `module::Type::method` in an expression.
479 enum ParenthesizedGenericArgs {
484 impl<'a, 'hir> LoweringContext<'a, 'hir> {
488 node_id: ast::NodeId,
491 debug_assert_ne!(node_id, ast::DUMMY_NODE_ID);
493 self.opt_local_def_id(node_id).is_none(),
494 "adding a def'n for node-id {:?} and data {:?} but a previous def'n exists: {:?}",
497 self.tcx.hir().def_key(self.local_def_id(node_id)),
500 let def_id = self.tcx.create_def(parent, data).def_id();
502 debug!("create_def: def_id_to_node_id[{:?}] <-> {:?}", def_id, node_id);
503 self.resolver.node_id_to_def_id.insert(node_id, def_id);
508 fn next_node_id(&mut self) -> NodeId {
509 let start = self.resolver.next_node_id;
510 let next = start.as_u32().checked_add(1).expect("input too large; ran out of NodeIds");
511 self.resolver.next_node_id = ast::NodeId::from_u32(next);
515 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
516 /// resolver (if any).
517 fn orig_opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
518 self.resolver.node_id_to_def_id.get(&node).map(|local_def_id| *local_def_id)
521 fn orig_local_def_id(&self, node: NodeId) -> LocalDefId {
522 self.orig_opt_local_def_id(node)
523 .unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
526 /// Given the id of some node in the AST, finds the `LocalDefId` associated with it by the name
527 /// resolver (if any), after applying any remapping from `get_remapped_def_id`.
529 /// For example, in a function like `fn foo<'a>(x: &'a u32)`,
530 /// invoking with the id from the `ast::Lifetime` node found inside
531 /// the `&'a u32` type would return the `LocalDefId` of the
532 /// `'a` parameter declared on `foo`.
534 /// This function also applies remapping from `get_remapped_def_id`.
535 /// These are used when synthesizing opaque types from `-> impl Trait` return types and so forth.
536 /// For example, in a function like `fn foo<'a>() -> impl Debug + 'a`,
537 /// we would create an opaque type `type FooReturn<'a1> = impl Debug + 'a1`.
538 /// When lowering the `Debug + 'a` bounds, we add a remapping to map `'a` to `'a1`.
539 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId> {
540 self.orig_opt_local_def_id(node).map(|local_def_id| self.get_remapped_def_id(local_def_id))
543 fn local_def_id(&self, node: NodeId) -> LocalDefId {
544 self.opt_local_def_id(node).unwrap_or_else(|| panic!("no entry for node id: `{:?}`", node))
547 /// Get the previously recorded `to` local def id given the `from` local def id, obtained using
548 /// `generics_def_id_map` field.
549 fn get_remapped_def_id(&self, local_def_id: LocalDefId) -> LocalDefId {
550 // `generics_def_id_map` is a stack of mappings. As we go deeper in impl traits nesting we
551 // push new mappings, so we first need to get the latest (innermost) mappings, hence `iter().rev()`.
555 // `fn test<'a, 'b>() -> impl Trait<&'a u8, Ty = impl Sized + 'b> {}`
557 // We would end with a generics_def_id_map like:
559 // `[[fn#'b -> impl_trait#'b], [fn#'b -> impl_sized#'b]]`
561 // for the opaque type generated on `impl Sized + 'b`, we want the result to be: impl_sized#'b.
562 // So, if we were trying to find first from the start (outermost) would give the wrong result, impl_trait#'b.
563 self.generics_def_id_map
566 .find_map(|map| map.get(&local_def_id).map(|local_def_id| *local_def_id))
567 .unwrap_or(local_def_id)
570 /// Freshen the `LoweringContext` and ready it to lower a nested item.
571 /// The lowered item is registered into `self.children`.
573 /// This function sets up `HirId` lowering infrastructure,
574 /// and stashes the shared mutable state to avoid pollution by the closure.
575 #[instrument(level = "debug", skip(self, f))]
576 fn with_hir_id_owner(
579 f: impl FnOnce(&mut Self) -> hir::OwnerNode<'hir>,
581 let def_id = self.local_def_id(owner);
583 let current_attrs = std::mem::take(&mut self.attrs);
584 let current_bodies = std::mem::take(&mut self.bodies);
585 let current_node_ids = std::mem::take(&mut self.node_id_to_local_id);
586 let current_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
587 let current_trait_map = std::mem::take(&mut self.trait_map);
589 std::mem::replace(&mut self.current_hir_id_owner, hir::OwnerId { def_id });
590 let current_local_counter =
591 std::mem::replace(&mut self.item_local_id_counter, hir::ItemLocalId::new(1));
592 let current_impl_trait_defs = std::mem::take(&mut self.impl_trait_defs);
593 let current_impl_trait_bounds = std::mem::take(&mut self.impl_trait_bounds);
595 // Do not reset `next_node_id` and `node_id_to_def_id`:
596 // we want `f` to be able to refer to the `LocalDefId`s that the caller created.
597 // and the caller to refer to some of the subdefinitions' nodes' `LocalDefId`s.
599 // Always allocate the first `HirId` for the owner itself.
600 let _old = self.node_id_to_local_id.insert(owner, hir::ItemLocalId::new(0));
601 debug_assert_eq!(_old, None);
604 debug_assert_eq!(def_id, item.def_id().def_id);
605 // `f` should have consumed all the elements in these vectors when constructing `item`.
606 debug_assert!(self.impl_trait_defs.is_empty());
607 debug_assert!(self.impl_trait_bounds.is_empty());
608 let info = self.make_owner_info(item);
610 self.attrs = current_attrs;
611 self.bodies = current_bodies;
612 self.node_id_to_local_id = current_node_ids;
613 self.local_id_to_def_id = current_id_to_def_id;
614 self.trait_map = current_trait_map;
615 self.current_hir_id_owner = current_owner;
616 self.item_local_id_counter = current_local_counter;
617 self.impl_trait_defs = current_impl_trait_defs;
618 self.impl_trait_bounds = current_impl_trait_bounds;
620 debug_assert!(self.children.iter().find(|(id, _)| id == &def_id).is_none());
621 self.children.push((def_id, hir::MaybeOwner::Owner(info)));
624 /// Installs the remapping `remap` in scope while `f` is being executed.
625 /// This causes references to the `LocalDefId` keys to be changed to
626 /// refer to the values instead.
628 /// The remapping is used when one piece of AST expands to multiple
629 /// pieces of HIR. For example, the function `fn foo<'a>(...) -> impl Debug + 'a`,
630 /// expands to both a function definition (`foo`) and a TAIT for the return value,
631 /// both of which have a lifetime parameter `'a`. The remapping allows us to
632 /// rewrite the `'a` in the return value to refer to the
633 /// `'a` declared on the TAIT, instead of the function.
634 fn with_remapping<R>(
636 remap: FxHashMap<LocalDefId, LocalDefId>,
637 f: impl FnOnce(&mut Self) -> R,
639 self.generics_def_id_map.push(remap);
641 self.generics_def_id_map.pop();
645 fn make_owner_info(&mut self, node: hir::OwnerNode<'hir>) -> &'hir hir::OwnerInfo<'hir> {
646 let attrs = std::mem::take(&mut self.attrs);
647 let mut bodies = std::mem::take(&mut self.bodies);
648 let local_id_to_def_id = std::mem::take(&mut self.local_id_to_def_id);
649 let trait_map = std::mem::take(&mut self.trait_map);
651 #[cfg(debug_assertions)]
652 for (id, attrs) in attrs.iter() {
653 // Verify that we do not store empty slices in the map.
654 if attrs.is_empty() {
655 panic!("Stored empty attributes for {:?}", id);
659 bodies.sort_by_key(|(k, _)| *k);
660 let bodies = SortedMap::from_presorted_elements(bodies);
661 let (hash_including_bodies, hash_without_bodies) = self.hash_owner(node, &bodies);
662 let (nodes, parenting) =
663 index::index_hir(self.tcx.sess, &*self.tcx.definitions_untracked(), node, &bodies);
664 let nodes = hir::OwnerNodes {
665 hash_including_bodies,
672 let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
673 let mut stable_hasher = StableHasher::new();
674 attrs.hash_stable(&mut hcx, &mut stable_hasher);
675 stable_hasher.finish()
677 hir::AttributeMap { map: attrs, hash }
680 self.arena.alloc(hir::OwnerInfo { nodes, parenting, attrs, trait_map })
683 /// Hash the HIR node twice, one deep and one shallow hash. This allows to differentiate
684 /// queries which depend on the full HIR tree and those which only depend on the item signature.
687 node: hir::OwnerNode<'hir>,
688 bodies: &SortedMap<hir::ItemLocalId, &'hir hir::Body<'hir>>,
689 ) -> (Fingerprint, Fingerprint) {
690 self.tcx.with_stable_hashing_context(|mut hcx| {
691 let mut stable_hasher = StableHasher::new();
692 hcx.with_hir_bodies(node.def_id(), bodies, |hcx| {
693 node.hash_stable(hcx, &mut stable_hasher)
695 let hash_including_bodies = stable_hasher.finish();
696 let mut stable_hasher = StableHasher::new();
697 hcx.without_hir_bodies(|hcx| node.hash_stable(hcx, &mut stable_hasher));
698 let hash_without_bodies = stable_hasher.finish();
699 (hash_including_bodies, hash_without_bodies)
703 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
704 /// the `LoweringContext`'s `NodeId => HirId` map.
705 /// Take care not to call this method if the resulting `HirId` is then not
706 /// actually used in the HIR, as that would trigger an assertion in the
707 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
708 /// properly. Calling the method twice with the same `NodeId` is fine though.
709 #[instrument(level = "debug", skip(self), ret)]
710 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
711 assert_ne!(ast_node_id, DUMMY_NODE_ID);
713 match self.node_id_to_local_id.entry(ast_node_id) {
714 Entry::Occupied(o) => {
715 hir::HirId { owner: self.current_hir_id_owner, local_id: *o.get() }
717 Entry::Vacant(v) => {
718 // Generate a new `HirId`.
719 let owner = self.current_hir_id_owner;
720 let local_id = self.item_local_id_counter;
721 let hir_id = hir::HirId { owner, local_id };
724 self.item_local_id_counter.increment_by(1);
726 assert_ne!(local_id, hir::ItemLocalId::new(0));
727 if let Some(def_id) = self.opt_local_def_id(ast_node_id) {
728 self.children.push((def_id, hir::MaybeOwner::NonOwner(hir_id)));
729 self.local_id_to_def_id.insert(local_id, def_id);
732 if let Some(traits) = self.resolver.trait_map.remove(&ast_node_id) {
733 self.trait_map.insert(hir_id.local_id, traits.into_boxed_slice());
741 /// Generate a new `HirId` without a backing `NodeId`.
742 #[instrument(level = "debug", skip(self), ret)]
743 fn next_id(&mut self) -> hir::HirId {
744 let owner = self.current_hir_id_owner;
745 let local_id = self.item_local_id_counter;
746 assert_ne!(local_id, hir::ItemLocalId::new(0));
747 self.item_local_id_counter.increment_by(1);
748 hir::HirId { owner, local_id }
751 #[instrument(level = "trace", skip(self))]
752 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
753 let res: Result<Res, ()> = res.apply_id(|id| {
754 let owner = self.current_hir_id_owner;
755 let local_id = self.node_id_to_local_id.get(&id).copied().ok_or(())?;
756 Ok(hir::HirId { owner, local_id })
760 // We may fail to find a HirId when the Res points to a Local from an enclosing HIR owner.
761 // This can happen when trying to lower the return type `x` in erroneous code like
762 // async fn foo(x: u8) -> x {}
763 // In that case, `x` is lowered as a function parameter, and the return type is lowered as
764 // an opaque type as a synthesized HIR owner.
765 res.unwrap_or(Res::Err)
768 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
769 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| pr.expect_full_res())
772 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
773 self.resolver.get_import_res(id).present_items()
776 fn diagnostic(&self) -> &Handler {
777 self.tcx.sess.diagnostic()
780 /// Reuses the span but adds information like the kind of the desugaring and features that are
781 /// allowed inside this span.
782 fn mark_span_with_reason(
784 reason: DesugaringKind,
786 allow_internal_unstable: Option<Lrc<[Symbol]>>,
788 self.tcx.with_stable_hashing_context(|hcx| {
789 span.mark_with_reason(allow_internal_unstable, reason, self.tcx.sess.edition(), hcx)
793 /// Intercept all spans entering HIR.
794 /// Mark a span as relative to the current owning item.
795 fn lower_span(&self, span: Span) -> Span {
796 if self.tcx.sess.opts.unstable_opts.incremental_relative_spans {
797 span.with_parent(Some(self.current_hir_id_owner.def_id))
799 // Do not make spans relative when not using incremental compilation.
804 fn lower_ident(&self, ident: Ident) -> Ident {
805 Ident::new(ident.name, self.lower_span(ident.span))
808 /// Converts a lifetime into a new generic parameter.
809 #[instrument(level = "debug", skip(self))]
810 fn lifetime_res_to_generic_param(
815 ) -> Option<hir::GenericParam<'hir>> {
816 let (name, kind) = match res {
817 LifetimeRes::Param { .. } => {
818 (hir::ParamName::Plain(ident), hir::LifetimeParamKind::Explicit)
820 LifetimeRes::Fresh { param, .. } => {
821 // Late resolution delegates to us the creation of the `LocalDefId`.
822 let _def_id = self.create_def(
823 self.current_hir_id_owner.def_id,
825 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
829 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
831 LifetimeRes::Static | LifetimeRes::Error => return None,
833 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
834 res, ident, ident.span
837 let hir_id = self.lower_node_id(node_id);
838 let def_id = self.local_def_id(node_id);
839 Some(hir::GenericParam {
843 span: self.lower_span(ident.span),
844 pure_wrt_drop: false,
845 kind: hir::GenericParamKind::Lifetime { kind },
850 /// Lowers a lifetime binder that defines `generic_params`, returning the corresponding HIR
851 /// nodes. The returned list includes any "extra" lifetime parameters that were added by the
852 /// name resolver owing to lifetime elision; this also populates the resolver's node-id->def-id
853 /// map, so that later calls to `opt_node_id_to_def_id` that refer to these extra lifetime
854 /// parameters will be successful.
855 #[instrument(level = "debug", skip(self))]
857 fn lower_lifetime_binder(
860 generic_params: &[GenericParam],
861 ) -> &'hir [hir::GenericParam<'hir>] {
862 let mut generic_params: Vec<_> = self.lower_generic_params_mut(generic_params).collect();
863 let extra_lifetimes = self.resolver.take_extra_lifetime_params(binder);
864 debug!(?extra_lifetimes);
865 generic_params.extend(extra_lifetimes.into_iter().filter_map(|(ident, node_id, res)| {
866 self.lifetime_res_to_generic_param(ident, node_id, res)
868 let generic_params = self.arena.alloc_from_iter(generic_params);
869 debug!(?generic_params);
874 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
875 let was_in_dyn_type = self.is_in_dyn_type;
876 self.is_in_dyn_type = in_scope;
878 let result = f(self);
880 self.is_in_dyn_type = was_in_dyn_type;
885 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
886 let was_in_loop_condition = self.is_in_loop_condition;
887 self.is_in_loop_condition = false;
889 let catch_scope = self.catch_scope.take();
890 let loop_scope = self.loop_scope.take();
892 self.catch_scope = catch_scope;
893 self.loop_scope = loop_scope;
895 self.is_in_loop_condition = was_in_loop_condition;
900 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
901 if attrs.is_empty() {
904 debug_assert_eq!(id.owner, self.current_hir_id_owner);
905 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
906 debug_assert!(!ret.is_empty());
907 self.attrs.insert(id.local_id, ret);
912 fn lower_attr(&self, attr: &Attribute) -> Attribute {
913 // Note that we explicitly do not walk the path. Since we don't really
914 // lower attributes (we use the AST version) there is nowhere to keep
915 // the `HirId`s. We don't actually need HIR version of attributes anyway.
916 // Tokens are also not needed after macro expansion and parsing.
917 let kind = match attr.kind {
918 AttrKind::Normal(ref normal) => AttrKind::Normal(P(NormalAttr {
920 path: normal.item.path.clone(),
921 args: self.lower_attr_args(&normal.item.args),
926 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
929 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
932 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
933 debug_assert_eq!(id.owner, self.current_hir_id_owner);
934 debug_assert_eq!(target_id.owner, self.current_hir_id_owner);
935 if let Some(&a) = self.attrs.get(&target_id.local_id) {
936 debug_assert!(!a.is_empty());
937 self.attrs.insert(id.local_id, a);
941 fn lower_attr_args(&self, args: &AttrArgs) -> AttrArgs {
943 AttrArgs::Empty => AttrArgs::Empty,
944 AttrArgs::Delimited(args) => AttrArgs::Delimited(self.lower_delim_args(args)),
945 // This is an inert key-value attribute - it will never be visible to macros
946 // after it gets lowered to HIR. Therefore, we can extract literals to handle
947 // nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
948 AttrArgs::Eq(eq_span, AttrArgsEq::Ast(expr)) => {
949 // In valid code the value always ends up as a single literal. Otherwise, a dummy
950 // literal suffices because the error is handled elsewhere.
951 let lit = if let ExprKind::Lit(token_lit) = expr.kind
952 && let Ok(lit) = MetaItemLit::from_token_lit(token_lit, expr.span)
957 token_lit: token::Lit::new(token::LitKind::Err, kw::Empty, None),
962 AttrArgs::Eq(*eq_span, AttrArgsEq::Hir(lit))
964 AttrArgs::Eq(_, AttrArgsEq::Hir(lit)) => {
965 unreachable!("in literal form when lowering mac args eq: {:?}", lit)
970 fn lower_delim_args(&self, args: &DelimArgs) -> DelimArgs {
971 DelimArgs { dspan: args.dspan, delim: args.delim, tokens: args.tokens.flattened() }
974 /// Given an associated type constraint like one of these:
976 /// ```ignore (illustrative)
977 /// T: Iterator<Item: Debug>
979 /// T: Iterator<Item = Debug>
983 /// returns a `hir::TypeBinding` representing `Item`.
984 #[instrument(level = "debug", skip(self))]
985 fn lower_assoc_ty_constraint(
987 constraint: &AssocConstraint,
988 itctx: &ImplTraitContext,
989 ) -> hir::TypeBinding<'hir> {
990 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
991 // lower generic arguments of identifier in constraint
992 let gen_args = if let Some(gen_args) = &constraint.gen_args {
993 let gen_args_ctor = match gen_args {
994 GenericArgs::AngleBracketed(data) => {
995 self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
997 GenericArgs::Parenthesized(data) => {
998 self.emit_bad_parenthesized_trait_in_assoc_ty(data);
999 let aba = self.ast_arena.aba.alloc(data.as_angle_bracketed_args());
1000 self.lower_angle_bracketed_parameter_data(aba, ParamMode::Explicit, itctx).0
1003 gen_args_ctor.into_generic_args(self)
1005 self.arena.alloc(hir::GenericArgs::none())
1007 let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;
1009 let kind = match &constraint.kind {
1010 AssocConstraintKind::Equality { term } => {
1011 let term = match term {
1012 Term::Ty(ty) => self.lower_ty(ty, itctx).into(),
1013 Term::Const(c) => self.lower_anon_const(c).into(),
1015 hir::TypeBindingKind::Equality { term }
1017 AssocConstraintKind::Bound { bounds } => {
1018 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1019 let (desugar_to_impl_trait, itctx) = match itctx {
1020 // We are in the return position:
1022 // fn foo() -> impl Iterator<Item: Debug>
1026 // fn foo() -> impl Iterator<Item = impl Debug>
1027 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1028 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1030 // We are in the argument position, but within a dyn type:
1032 // fn foo(x: dyn Iterator<Item: Debug>)
1036 // fn foo(x: dyn Iterator<Item = impl Debug>)
1037 ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
1039 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1040 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1041 // "impl trait context" to permit `impl Debug` in this position (it desugars
1042 // then to an opaque type).
1044 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1045 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => (true, itctx_tait),
1047 // We are in the parameter position, but not within a dyn type:
1049 // fn foo(x: impl Iterator<Item: Debug>)
1051 // so we leave it as is and this gets expanded in astconv to a bound like
1052 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1054 _ => (false, itctx),
1057 if desugar_to_impl_trait {
1058 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1059 // constructing the HIR for `impl bounds...` and then lowering that.
1061 let impl_trait_node_id = self.next_node_id();
1063 self.with_dyn_type_scope(false, |this| {
1064 let node_id = this.next_node_id();
1065 let ty = this.ast_arena.tys.alloc(Ty {
1067 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1068 span: this.lower_span(constraint.span),
1071 let ty = this.lower_ty(ty, itctx);
1073 hir::TypeBindingKind::Equality { term: ty.into() }
1076 // Desugar `AssocTy: Bounds` into a type binding where the
1077 // later desugars into a trait predicate.
1078 let bounds = self.lower_param_bounds(bounds, itctx);
1080 hir::TypeBindingKind::Constraint { bounds }
1086 hir_id: self.lower_node_id(constraint.id),
1087 ident: self.lower_ident(constraint.ident),
1090 span: self.lower_span(constraint.span),
1094 fn emit_bad_parenthesized_trait_in_assoc_ty(&self, data: &ParenthesizedArgs) {
1095 // Suggest removing empty parentheses: "Trait()" -> "Trait"
1096 let sub = if data.inputs.is_empty() {
1097 let parentheses_span =
1098 data.inputs_span.shrink_to_lo().to(data.inputs_span.shrink_to_hi());
1099 AssocTyParenthesesSub::Empty { parentheses_span }
1101 // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
1103 // Start of parameters to the 1st argument
1104 let open_param = data.inputs_span.shrink_to_lo().to(data
1110 // End of last argument to end of parameters
1112 data.inputs.last().unwrap().span.shrink_to_hi().to(data.inputs_span.shrink_to_hi());
1113 AssocTyParenthesesSub::NotEmpty { open_param, close_param }
1115 self.tcx.sess.emit_err(AssocTyParentheses { span: data.span, sub });
1118 #[instrument(level = "debug", skip(self))]
1119 fn lower_generic_arg(
1121 arg: &ast::GenericArg,
1122 itctx: &ImplTraitContext,
1123 ) -> hir::GenericArg<'hir> {
1125 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1126 ast::GenericArg::Type(ty) => {
1128 TyKind::Infer if self.tcx.features().generic_arg_infer => {
1129 return GenericArg::Infer(hir::InferArg {
1130 hir_id: self.lower_node_id(ty.id),
1131 span: self.lower_span(ty.span),
1134 // We parse const arguments as path types as we cannot distinguish them during
1135 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1136 // type and value namespaces. If we resolved the path in the value namespace, we
1137 // transform it into a generic const argument.
1138 TyKind::Path(qself, path) => {
1139 if let Some(res) = self
1141 .get_partial_res(ty.id)
1142 .and_then(|partial_res| partial_res.full_res())
1144 if !res.matches_ns(Namespace::TypeNS) {
1146 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1150 // Construct an AnonConst where the expr is the "ty"'s path.
1152 let parent_def_id = self.current_hir_id_owner;
1153 let node_id = self.next_node_id();
1155 // Add a definition for the in-band const def.
1156 let def_id = self.create_def(
1157 parent_def_id.def_id,
1159 DefPathData::AnonConst,
1162 let span = self.lower_span(ty.span);
1163 let path_expr = Expr {
1165 kind: ExprKind::Path(qself.clone(), path.clone()),
1167 attrs: AttrVec::new(),
1171 let ct = self.with_new_scopes(|this| hir::AnonConst {
1173 hir_id: this.lower_node_id(node_id),
1174 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1176 return GenericArg::Const(ConstArg { value: ct, span });
1182 GenericArg::Type(self.lower_ty(&ty, itctx))
1184 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1185 value: self.lower_anon_const(&ct),
1186 span: self.lower_span(ct.value.span),
1191 #[instrument(level = "debug", skip(self))]
1192 fn lower_ty(&mut self, t: &Ty, itctx: &ImplTraitContext) -> &'hir hir::Ty<'hir> {
1193 self.arena.alloc(self.lower_ty_direct(t, itctx))
1199 qself: &Option<ptr::P<QSelf>>,
1201 param_mode: ParamMode,
1202 itctx: &ImplTraitContext,
1203 ) -> hir::Ty<'hir> {
1204 // Check whether we should interpret this as a bare trait object.
1205 // This check mirrors the one in late resolution. We only introduce this special case in
1206 // the rare occurrence we need to lower `Fresh` anonymous lifetimes.
1207 // The other cases when a qpath should be opportunistically made a trait object are handled
1210 && let Some(partial_res) = self.resolver.get_partial_res(t.id)
1211 && let Some(Res::Def(DefKind::Trait | DefKind::TraitAlias, _)) = partial_res.full_res()
1213 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1214 let poly_trait_ref = this.ast_arena.ptr.alloc(PolyTraitRef {
1215 bound_generic_params: vec![],
1216 trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
1219 let bound = this.lower_poly_trait_ref(
1223 let bounds = this.arena.alloc_from_iter([bound]);
1224 let lifetime_bound = this.elided_dyn_bound(t.span);
1225 (bounds, lifetime_bound)
1227 let kind = hir::TyKind::TraitObject(bounds, &lifetime_bound, TraitObjectSyntax::None);
1228 return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
1231 let id = self.lower_node_id(t.id);
1232 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1233 self.ty_path(id, t.span, qpath)
1236 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1237 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1240 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1241 self.ty(span, hir::TyKind::Tup(tys))
1244 fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir> {
1245 let kind = match &t.kind {
1246 TyKind::Infer => hir::TyKind::Infer,
1247 TyKind::Err => hir::TyKind::Err,
1248 TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1249 TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1250 TyKind::Rptr(region, mt) => {
1251 let region = region.unwrap_or_else(|| {
1252 let id = if let Some(LifetimeRes::ElidedAnchor { start, end }) =
1253 self.resolver.get_lifetime_res(t.id)
1255 debug_assert_eq!(start.plus(1), end);
1260 let span = self.tcx.sess.source_map().start_point(t.span).shrink_to_hi();
1261 Lifetime { ident: Ident::new(kw::UnderscoreLifetime, span), id }
1263 let lifetime = self.lower_lifetime(®ion);
1264 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1266 TyKind::BareFn(f) => {
1267 let generic_params = self.lower_lifetime_binder(t.id, &f.generic_params);
1268 hir::TyKind::BareFn(self.arena.alloc(hir::BareFnTy {
1270 unsafety: self.lower_unsafety(f.unsafety),
1271 abi: self.lower_extern(f.ext),
1272 decl: self.lower_fn_decl(&f.decl, t.id, t.span, FnDeclKind::Pointer, None),
1273 param_names: self.lower_fn_params_to_names(&f.decl),
1276 TyKind::Never => hir::TyKind::Never,
1277 TyKind::Tup(tys) => hir::TyKind::Tup(
1278 self.arena.alloc_from_iter(tys.iter().map(|ty| self.lower_ty_direct(ty, itctx))),
1280 TyKind::Paren(ty) => {
1281 return self.lower_ty_direct(ty, itctx);
1283 TyKind::Path(qself, path) => {
1284 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1286 TyKind::ImplicitSelf => {
1287 let hir_id = self.next_id();
1288 let res = self.expect_full_res(t.id);
1289 let res = self.lower_res(res);
1290 hir::TyKind::Path(hir::QPath::Resolved(
1292 self.arena.alloc(hir::Path {
1294 segments: arena_vec![self; hir::PathSegment::new(
1295 Ident::with_dummy_span(kw::SelfUpper),
1299 span: self.lower_span(t.span),
1303 TyKind::Array(ty, length) => {
1304 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_array_length(length))
1306 TyKind::Typeof(expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1307 TyKind::TraitObject(bounds, kind) => {
1308 let mut lifetime_bound = None;
1309 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1311 this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| match bound {
1312 GenericBound::Trait(
1314 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1315 ) => Some(this.lower_poly_trait_ref(ty, itctx)),
1316 // `~const ?Bound` will cause an error during AST validation
1317 // anyways, so treat it like `?Bound` as compilation proceeds.
1318 GenericBound::Trait(
1320 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1322 GenericBound::Outlives(lifetime) => {
1323 if lifetime_bound.is_none() {
1324 lifetime_bound = Some(this.lower_lifetime(lifetime));
1329 let lifetime_bound =
1330 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1331 (bounds, lifetime_bound)
1333 hir::TyKind::TraitObject(bounds, lifetime_bound, *kind)
1335 TyKind::ImplTrait(def_node_id, bounds) => {
1338 ImplTraitContext::ReturnPositionOpaqueTy { origin, in_trait } => self
1339 .lower_opaque_impl_trait(
1347 ImplTraitContext::TypeAliasesOpaqueTy => self.lower_opaque_impl_trait(
1349 hir::OpaqueTyOrigin::TyAlias,
1355 ImplTraitContext::Universal => {
1357 self.current_hir_id_owner.def_id,
1359 DefPathData::ImplTrait,
1362 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1363 let (param, bounds, path) =
1364 self.lower_generic_and_bounds(*def_node_id, span, ident, bounds);
1365 self.impl_trait_defs.push(param);
1366 if let Some(bounds) = bounds {
1367 self.impl_trait_bounds.push(bounds);
1371 ImplTraitContext::Disallowed(
1372 position @ (ImplTraitPosition::TraitReturn | ImplTraitPosition::ImplReturn),
1376 .create_feature_err(
1377 MisplacedImplTrait {
1379 position: DiagnosticArgFromDisplay(&position),
1381 sym::return_position_impl_trait_in_trait,
1386 ImplTraitContext::Disallowed(position) => {
1387 self.tcx.sess.emit_err(MisplacedImplTrait {
1389 position: DiagnosticArgFromDisplay(&position),
1395 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1396 TyKind::CVarArgs => {
1397 self.tcx.sess.delay_span_bug(
1399 "`TyKind::CVarArgs` should have been handled elsewhere",
1405 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1408 /// Lowers a `ReturnPositionOpaqueTy` (`-> impl Trait`) or a `TypeAliasesOpaqueTy` (`type F =
1409 /// impl Trait`): this creates the associated Opaque Type (TAIT) definition and then returns a
1410 /// HIR type that references the TAIT.
1412 /// Given a function definition like:
1415 /// fn test<'a, T: Debug>(x: &'a T) -> impl Debug + 'a {
1420 /// we will create a TAIT definition in the HIR like
1423 /// type TestReturn<'a, T, 'x> = impl Debug + 'x
1426 /// and return a type like `TestReturn<'static, T, 'a>`, so that the function looks like:
1429 /// fn test<'a, T: Debug>(x: &'a T) -> TestReturn<'static, T, 'a>
1432 /// Note the subtlety around type parameters! The new TAIT, `TestReturn`, inherits all the
1433 /// type parameters from the function `test` (this is implemented in the query layer, they aren't
1434 /// added explicitly in the HIR). But this includes all the lifetimes, and we only want to
1435 /// capture the lifetimes that are referenced in the bounds. Therefore, we add *extra* lifetime parameters
1436 /// for the lifetimes that get captured (`'x`, in our example above) and reference those.
1437 #[instrument(level = "debug", skip(self), ret)]
1438 fn lower_opaque_impl_trait(
1441 origin: hir::OpaqueTyOrigin,
1442 opaque_ty_node_id: NodeId,
1443 bounds: &GenericBounds,
1445 itctx: &ImplTraitContext,
1446 ) -> hir::TyKind<'hir> {
1447 // Make sure we know that some funky desugaring has been going on here.
1448 // This is a first: there is code in other places like for loop
1449 // desugaring that explicitly states that we don't want to track that.
1450 // Not tracking it makes lints in rustc and clippy very fragile, as
1451 // frequently opened issues show.
1452 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1454 let opaque_ty_def_id = self.create_def(
1455 self.current_hir_id_owner.def_id,
1457 DefPathData::ImplTrait,
1459 debug!(?opaque_ty_def_id);
1461 // Contains the new lifetime definitions created for the TAIT (if any).
1462 let mut collected_lifetimes = Vec::new();
1464 // If this came from a TAIT (as opposed to a function that returns an RPIT), we only want
1465 // to capture the lifetimes that appear in the bounds. So visit the bounds to find out
1466 // exactly which ones those are.
1467 let lifetimes_to_remap = if origin == hir::OpaqueTyOrigin::TyAlias {
1468 // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't keep all the lifetime parameters
1471 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1472 // we only keep the lifetimes that appear in the `impl Debug` itself:
1473 lifetime_collector::lifetimes_in_bounds(&self.resolver, bounds)
1475 debug!(?lifetimes_to_remap);
1477 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1478 let mut new_remapping = FxHashMap::default();
1480 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1481 // in bounds), then create the new lifetime parameters required and create a mapping
1482 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1483 collected_lifetimes = lctx.create_lifetime_defs(
1485 &lifetimes_to_remap,
1488 debug!(?collected_lifetimes);
1489 debug!(?new_remapping);
1491 // Install the remapping from old to new (if any):
1492 lctx.with_remapping(new_remapping, |lctx| {
1493 // This creates HIR lifetime definitions as `hir::GenericParam`, in the given
1494 // example `type TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection
1495 // containing `&['x]`.
1496 let lifetime_defs = lctx.arena.alloc_from_iter(collected_lifetimes.iter().map(
1497 |&(new_node_id, lifetime)| {
1498 let hir_id = lctx.lower_node_id(new_node_id);
1499 debug_assert_ne!(lctx.opt_local_def_id(new_node_id), None);
1501 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1502 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1505 hir::ParamName::Plain(lifetime.ident),
1506 hir::LifetimeParamKind::Explicit,
1512 def_id: lctx.local_def_id(new_node_id),
1514 span: lifetime.ident.span,
1515 pure_wrt_drop: false,
1516 kind: hir::GenericParamKind::Lifetime { kind },
1521 debug!(?lifetime_defs);
1523 // Then when we lower the param bounds, references to 'a are remapped to 'a1, so we
1524 // get back Debug + 'a1, which is suitable for use on the TAIT.
1525 let hir_bounds = lctx.lower_param_bounds(bounds, itctx);
1526 debug!(?hir_bounds);
1528 let opaque_ty_item = hir::OpaqueTy {
1529 generics: self.arena.alloc(hir::Generics {
1530 params: lifetime_defs,
1532 has_where_clause_predicates: false,
1533 where_clause_span: lctx.lower_span(span),
1534 span: lctx.lower_span(span),
1540 debug!(?opaque_ty_item);
1542 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1546 // This creates HIR lifetime arguments as `hir::GenericArg`, in the given example `type
1547 // TestReturn<'a, T, 'x> = impl Debug + 'x`, it creates a collection containing `&['x]`.
1549 self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(|(_, lifetime)| {
1550 let id = self.next_node_id();
1551 let l = self.new_named_lifetime(lifetime.id, id, lifetime.ident);
1552 hir::GenericArg::Lifetime(l)
1556 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1557 hir::TyKind::OpaqueDef(
1558 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
1564 /// Registers a new opaque type with the proper `NodeId`s and
1565 /// returns the lowered node-ID for the opaque type.
1566 fn generate_opaque_type(
1568 opaque_ty_id: LocalDefId,
1569 opaque_ty_item: hir::OpaqueTy<'hir>,
1571 opaque_ty_span: Span,
1572 ) -> hir::OwnerNode<'hir> {
1573 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1574 // Generate an `type Foo = impl Trait;` declaration.
1575 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1576 let opaque_ty_item = hir::Item {
1577 owner_id: hir::OwnerId { def_id: opaque_ty_id },
1578 ident: Ident::empty(),
1579 kind: opaque_ty_item_kind,
1580 vis_span: self.lower_span(span.shrink_to_lo()),
1581 span: self.lower_span(opaque_ty_span),
1583 hir::OwnerNode::Item(self.arena.alloc(opaque_ty_item))
1586 /// Given a `parent_def_id`, a list of `lifetimes_in_bounds and a `remapping` hash to be
1587 /// filled, this function creates new definitions for `Param` and `Fresh` lifetimes, inserts the
1588 /// new definition, adds it to the remapping with the definition of the given lifetime and
1589 /// returns a list of lifetimes to be lowered afterwards.
1590 fn create_lifetime_defs(
1592 parent_def_id: LocalDefId,
1593 lifetimes_in_bounds: &[Lifetime],
1594 remapping: &mut FxHashMap<LocalDefId, LocalDefId>,
1595 ) -> Vec<(NodeId, Lifetime)> {
1596 let mut result = Vec::new();
1598 for lifetime in lifetimes_in_bounds {
1599 let res = self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error);
1603 LifetimeRes::Param { param: old_def_id, binder: _ } => {
1604 if remapping.get(&old_def_id).is_none() {
1605 let node_id = self.next_node_id();
1607 let new_def_id = self.create_def(
1610 DefPathData::LifetimeNs(lifetime.ident.name),
1612 remapping.insert(old_def_id, new_def_id);
1614 result.push((node_id, *lifetime));
1618 LifetimeRes::Fresh { param, binder: _ } => {
1619 debug_assert_eq!(lifetime.ident.name, kw::UnderscoreLifetime);
1620 if let Some(old_def_id) = self.orig_opt_local_def_id(param) && remapping.get(&old_def_id).is_none() {
1621 let node_id = self.next_node_id();
1623 let new_def_id = self.create_def(
1626 DefPathData::LifetimeNs(kw::UnderscoreLifetime),
1628 remapping.insert(old_def_id, new_def_id);
1630 result.push((node_id, *lifetime));
1634 LifetimeRes::Static | LifetimeRes::Error => {}
1637 let bug_msg = format!(
1638 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1639 res, lifetime.ident, lifetime.ident.span
1641 span_bug!(lifetime.ident.span, "{}", bug_msg);
1649 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1650 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1651 // as they are not explicit in HIR/Ty function signatures.
1652 // (instead, the `c_variadic` flag is set to `true`)
1653 let mut inputs = &decl.inputs[..];
1654 if decl.c_variadic() {
1655 inputs = &inputs[..inputs.len() - 1];
1657 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1658 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1659 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1663 // Lowers a function declaration.
1665 // `decl`: the unlowered (AST) function declaration.
1666 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1667 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1668 // `make_ret_async` is also `Some`.
1669 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1670 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1671 // return type `impl Trait` item, and the `Span` points to the `async` keyword.
1672 #[instrument(level = "debug", skip(self))]
1679 make_ret_async: Option<(NodeId, Span)>,
1680 ) -> &'hir hir::FnDecl<'hir> {
1681 let c_variadic = decl.c_variadic();
1683 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1684 // as they are not explicit in HIR/Ty function signatures.
1685 // (instead, the `c_variadic` flag is set to `true`)
1686 let mut inputs = &decl.inputs[..];
1688 inputs = &inputs[..inputs.len() - 1];
1690 let inputs = self.arena.alloc_from_iter(inputs.iter().map(|param| {
1691 let itctx = if kind.param_impl_trait_allowed() {
1692 ImplTraitContext::Universal
1694 ImplTraitContext::Disallowed(match kind {
1695 FnDeclKind::Fn | FnDeclKind::Inherent => {
1696 unreachable!("fn should allow APIT")
1698 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnParam,
1699 FnDeclKind::Closure => ImplTraitPosition::ClosureParam,
1700 FnDeclKind::Pointer => ImplTraitPosition::PointerParam,
1701 FnDeclKind::Trait => ImplTraitPosition::TraitParam,
1702 FnDeclKind::Impl => ImplTraitPosition::ImplParam,
1705 self.lower_ty_direct(¶m.ty, &itctx)
1708 let output = if let Some((ret_id, span)) = make_ret_async {
1709 if !kind.async_fn_allowed(self.tcx) {
1711 FnDeclKind::Trait | FnDeclKind::Impl => {
1714 .create_feature_err(
1715 TraitFnAsync { fn_span, span },
1716 sym::async_fn_in_trait,
1721 self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
1726 self.lower_async_fn_ret_ty(
1730 matches!(kind, FnDeclKind::Trait),
1733 match &decl.output {
1734 FnRetTy::Ty(ty) => {
1735 let mut context = if kind.return_impl_trait_allowed(self.tcx) {
1736 let fn_def_id = self.local_def_id(fn_node_id);
1737 ImplTraitContext::ReturnPositionOpaqueTy {
1738 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1739 in_trait: matches!(kind, FnDeclKind::Trait),
1742 ImplTraitContext::Disallowed(match kind {
1743 FnDeclKind::Fn | FnDeclKind::Inherent => {
1744 unreachable!("fn should allow in-band lifetimes")
1746 FnDeclKind::ExternFn => ImplTraitPosition::ExternFnReturn,
1747 FnDeclKind::Closure => ImplTraitPosition::ClosureReturn,
1748 FnDeclKind::Pointer => ImplTraitPosition::PointerReturn,
1749 FnDeclKind::Trait => ImplTraitPosition::TraitReturn,
1750 FnDeclKind::Impl => ImplTraitPosition::ImplReturn,
1753 hir::FnRetTy::Return(self.lower_ty(ty, &mut context))
1755 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(*span)),
1759 self.arena.alloc(hir::FnDecl {
1763 lifetime_elision_allowed: self.resolver.lifetime_elision_allowed.contains(&fn_node_id),
1764 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1765 let is_mutable_pat = matches!(
1767 PatKind::Ident(hir::BindingAnnotation(_, Mutability::Mut), ..)
1770 match &arg.ty.kind {
1771 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1772 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1773 // Given we are only considering `ImplicitSelf` types, we needn't consider
1774 // the case where we have a mutable pattern to a reference as that would
1775 // no longer be an `ImplicitSelf`.
1776 TyKind::Rptr(_, mt) if mt.ty.kind.is_implicit_self() => match mt.mutbl {
1777 hir::Mutability::Not => hir::ImplicitSelfKind::ImmRef,
1778 hir::Mutability::Mut => hir::ImplicitSelfKind::MutRef,
1780 _ => hir::ImplicitSelfKind::None,
1786 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1787 // combined with the following definition of `OpaqueTy`:
1789 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1791 // `output`: unlowered output type (`T` in `-> T`)
1792 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1793 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1794 #[instrument(level = "debug", skip(self))]
1795 fn lower_async_fn_ret_ty(
1799 opaque_ty_node_id: NodeId,
1801 ) -> hir::FnRetTy<'hir> {
1802 let span = output.span();
1804 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1806 let fn_def_id = self.local_def_id(fn_node_id);
1808 let opaque_ty_def_id =
1809 self.create_def(fn_def_id, opaque_ty_node_id, DefPathData::ImplTrait);
1811 // When we create the opaque type for this async fn, it is going to have
1812 // to capture all the lifetimes involved in the signature (including in the
1813 // return type). This is done by introducing lifetime parameters for:
1815 // - all the explicitly declared lifetimes from the impl and function itself;
1816 // - all the elided lifetimes in the fn arguments;
1817 // - all the elided lifetimes in the return type.
1819 // So for example in this snippet:
1822 // impl<'a> Foo<'a> {
1823 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1824 // // ^ '0 ^ '1 ^ '2
1825 // // elided lifetimes used below
1830 // we would create an opaque type like:
1833 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1836 // and we would then desugar `bar` to the equivalent of:
1839 // impl<'a> Foo<'a> {
1840 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1844 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1845 // this is because the elided lifetimes from the return type
1846 // should be figured out using the ordinary elision rules, and
1847 // this desugaring achieves that.
1849 // Calculate all the lifetimes that should be captured
1850 // by the opaque type. This should include all in-scope
1851 // lifetime parameters, including those defined in-band.
1853 // Contains the new lifetime definitions created for the TAIT (if any) generated for the
1855 let mut collected_lifetimes = Vec::new();
1856 let mut new_remapping = FxHashMap::default();
1858 let extra_lifetime_params = self.resolver.take_extra_lifetime_params(opaque_ty_node_id);
1859 debug!(?extra_lifetime_params);
1860 for (ident, outer_node_id, outer_res) in extra_lifetime_params {
1861 let outer_def_id = self.orig_local_def_id(outer_node_id);
1862 let inner_node_id = self.next_node_id();
1864 // Add a definition for the in scope lifetime def.
1865 let inner_def_id = self.create_def(
1868 DefPathData::LifetimeNs(ident.name),
1870 new_remapping.insert(outer_def_id, inner_def_id);
1872 let inner_res = match outer_res {
1873 // Input lifetime like `'a`:
1874 LifetimeRes::Param { param, .. } => {
1875 LifetimeRes::Param { param, binder: fn_node_id }
1877 // Input lifetime like `'1`:
1878 LifetimeRes::Fresh { param, .. } => {
1879 LifetimeRes::Fresh { param, binder: fn_node_id }
1881 LifetimeRes::Static | LifetimeRes::Error => continue,
1884 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
1885 res, ident, ident.span
1890 let lifetime = Lifetime { id: outer_node_id, ident };
1891 collected_lifetimes.push((inner_node_id, lifetime, Some(inner_res)));
1894 debug!(?collected_lifetimes);
1896 // We only want to capture the lifetimes that appear in the bounds. So visit the bounds to
1897 // find out exactly which ones those are.
1898 // in fn return position, like the `fn test<'a>() -> impl Debug + 'a` example,
1899 // we only keep the lifetimes that appear in the `impl Debug` itself:
1900 let lifetimes_to_remap = lifetime_collector::lifetimes_in_ret_ty(&self.resolver, output);
1901 debug!(?lifetimes_to_remap);
1903 self.with_hir_id_owner(opaque_ty_node_id, |this| {
1904 // If this opaque type is only capturing a subset of the lifetimes (those that appear
1905 // in bounds), then create the new lifetime parameters required and create a mapping
1906 // from the old `'a` (on the function) to the new `'a` (on the opaque type).
1907 collected_lifetimes.extend(
1908 this.create_lifetime_defs(
1910 &lifetimes_to_remap,
1914 .map(|(new_node_id, lifetime)| (new_node_id, lifetime, None)),
1916 debug!(?collected_lifetimes);
1917 debug!(?new_remapping);
1919 // Install the remapping from old to new (if any):
1920 this.with_remapping(new_remapping, |this| {
1921 // We have to be careful to get elision right here. The
1922 // idea is that we create a lifetime parameter for each
1923 // lifetime in the return type. So, given a return type
1924 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1925 // Future<Output = &'1 [ &'2 u32 ]>`.
1927 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1928 // hence the elision takes place at the fn site.
1929 let future_bound = this.lower_async_fn_output_type_to_future_bound(
1932 if in_trait && !this.tcx.features().return_position_impl_trait_in_trait {
1933 ImplTraitContext::Disallowed(ImplTraitPosition::TraitReturn)
1935 ImplTraitContext::ReturnPositionOpaqueTy {
1936 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
1942 let generic_params = this.arena.alloc_from_iter(collected_lifetimes.iter().map(
1943 |&(new_node_id, lifetime, _)| {
1944 let hir_id = this.lower_node_id(new_node_id);
1945 debug_assert_ne!(this.opt_local_def_id(new_node_id), None);
1947 let (name, kind) = if lifetime.ident.name == kw::UnderscoreLifetime {
1948 (hir::ParamName::Fresh, hir::LifetimeParamKind::Elided)
1951 hir::ParamName::Plain(lifetime.ident),
1952 hir::LifetimeParamKind::Explicit,
1958 def_id: this.local_def_id(new_node_id),
1960 span: lifetime.ident.span,
1961 pure_wrt_drop: false,
1962 kind: hir::GenericParamKind::Lifetime { kind },
1967 debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
1969 let opaque_ty_item = hir::OpaqueTy {
1970 generics: this.arena.alloc(hir::Generics {
1971 params: generic_params,
1973 has_where_clause_predicates: false,
1974 where_clause_span: this.lower_span(span),
1975 span: this.lower_span(span),
1977 bounds: arena_vec![this; future_bound],
1978 origin: hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
1982 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
1983 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span)
1987 // As documented above, we need to create the lifetime
1988 // arguments to our opaque type. Continuing with our example,
1989 // we're creating the type arguments for the return type:
1992 // Bar<'a, 'b, '0, '1, '_>
1995 // For the "input" lifetime parameters, we wish to create
1996 // references to the parameters themselves, including the
1997 // "implicit" ones created from parameter types (`'a`, `'b`,
2000 // For the "output" lifetime parameters, we just want to
2002 let generic_args = self.arena.alloc_from_iter(collected_lifetimes.into_iter().map(
2003 |(_, lifetime, res)| {
2004 let id = self.next_node_id();
2005 let res = res.unwrap_or(
2006 self.resolver.get_lifetime_res(lifetime.id).unwrap_or(LifetimeRes::Error),
2008 hir::GenericArg::Lifetime(self.new_named_lifetime_with_res(id, lifetime.ident, res))
2012 // Create the `Foo<...>` reference itself. Note that the `type
2013 // Foo = impl Trait` is, internally, created as a child of the
2014 // async fn, so the *type parameters* are inherited. It's
2015 // only the lifetime parameters that we must supply.
2016 let opaque_ty_ref = hir::TyKind::OpaqueDef(
2017 hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
2021 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2022 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2025 /// Transforms `-> T` into `Future<Output = T>`.
2026 fn lower_async_fn_output_type_to_future_bound(
2030 mut nested_impl_trait_context: ImplTraitContext,
2031 ) -> hir::GenericBound<'hir> {
2032 // Compute the `T` in `Future<Output = T>` from the return type.
2033 let output_ty = match output {
2034 FnRetTy::Ty(ty) => {
2035 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2036 // `impl Future` opaque type that `async fn` implicitly
2038 self.lower_ty(ty, &mut nested_impl_trait_context)
2040 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2044 let future_args = self.arena.alloc(hir::GenericArgs {
2046 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2047 parenthesized: false,
2051 hir::GenericBound::LangItemTrait(
2052 // ::std::future::Future<future_params>
2053 hir::LangItem::Future,
2054 self.lower_span(span),
2060 #[instrument(level = "trace", skip(self))]
2061 fn lower_param_bound(
2064 itctx: &ImplTraitContext,
2065 ) -> hir::GenericBound<'hir> {
2067 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2068 self.lower_poly_trait_ref(p, itctx),
2069 self.lower_trait_bound_modifier(*modifier),
2071 GenericBound::Outlives(lifetime) => {
2072 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2077 fn lower_lifetime(&mut self, l: &Lifetime) -> &'hir hir::Lifetime {
2078 let ident = self.lower_ident(l.ident);
2079 self.new_named_lifetime(l.id, l.id, ident)
2082 #[instrument(level = "debug", skip(self))]
2083 fn new_named_lifetime_with_res(
2088 ) -> &'hir hir::Lifetime {
2089 let res = match res {
2090 LifetimeRes::Param { param, .. } => {
2091 let param = self.get_remapped_def_id(param);
2092 hir::LifetimeName::Param(param)
2094 LifetimeRes::Fresh { param, .. } => {
2095 let param = self.local_def_id(param);
2096 hir::LifetimeName::Param(param)
2098 LifetimeRes::Infer => hir::LifetimeName::Infer,
2099 LifetimeRes::Static => hir::LifetimeName::Static,
2100 LifetimeRes::Error => hir::LifetimeName::Error,
2102 "Unexpected lifetime resolution {:?} for {:?} at {:?}",
2103 res, ident, ident.span
2108 self.arena.alloc(hir::Lifetime {
2109 hir_id: self.lower_node_id(id),
2110 ident: self.lower_ident(ident),
2115 #[instrument(level = "debug", skip(self))]
2116 fn new_named_lifetime(
2121 ) -> &'hir hir::Lifetime {
2122 let res = self.resolver.get_lifetime_res(id).unwrap_or(LifetimeRes::Error);
2123 self.new_named_lifetime_with_res(new_id, ident, res)
2126 fn lower_generic_params_mut<'s>(
2128 params: &'s [GenericParam],
2129 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2130 params.iter().map(move |param| self.lower_generic_param(param))
2133 fn lower_generic_params(&mut self, params: &[GenericParam]) -> &'hir [hir::GenericParam<'hir>] {
2134 self.arena.alloc_from_iter(self.lower_generic_params_mut(params))
2137 #[instrument(level = "trace", skip(self))]
2138 fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
2139 let (name, kind) = self.lower_generic_param_kind(param);
2141 let hir_id = self.lower_node_id(param.id);
2142 self.lower_attrs(hir_id, ¶m.attrs);
2145 def_id: self.local_def_id(param.id),
2147 span: self.lower_span(param.span()),
2148 pure_wrt_drop: self.tcx.sess.contains_name(¶m.attrs, sym::may_dangle),
2150 colon_span: param.colon_span.map(|s| self.lower_span(s)),
2154 fn lower_generic_param_kind(
2156 param: &GenericParam,
2157 ) -> (hir::ParamName, hir::GenericParamKind<'hir>) {
2159 GenericParamKind::Lifetime => {
2160 // AST resolution emitted an error on those parameters, so we lower them using
2161 // `ParamName::Error`.
2163 if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
2166 let ident = self.lower_ident(param.ident);
2167 ParamName::Plain(ident)
2170 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2174 GenericParamKind::Type { default, .. } => {
2175 let kind = hir::GenericParamKind::Type {
2176 default: default.as_ref().map(|x| {
2177 self.lower_ty(x, &ImplTraitContext::Disallowed(ImplTraitPosition::Type))
2182 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2184 GenericParamKind::Const { ty, kw_span: _, default } => {
2185 let ty = self.lower_ty(&ty, &ImplTraitContext::Disallowed(ImplTraitPosition::Type));
2186 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2188 hir::ParamName::Plain(self.lower_ident(param.ident)),
2189 hir::GenericParamKind::Const { ty, default },
2195 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: &ImplTraitContext) -> hir::TraitRef<'hir> {
2196 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2197 hir::QPath::Resolved(None, path) => path,
2198 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2200 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2203 #[instrument(level = "debug", skip(self))]
2204 fn lower_poly_trait_ref(
2207 itctx: &ImplTraitContext,
2208 ) -> hir::PolyTraitRef<'hir> {
2209 let bound_generic_params =
2210 self.lower_lifetime_binder(p.trait_ref.ref_id, &p.bound_generic_params);
2211 let trait_ref = self.lower_trait_ref(&p.trait_ref, itctx);
2212 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2215 fn lower_mt(&mut self, mt: &MutTy, itctx: &ImplTraitContext) -> hir::MutTy<'hir> {
2216 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2219 #[instrument(level = "debug", skip(self), ret)]
2220 fn lower_param_bounds(
2222 bounds: &[GenericBound],
2223 itctx: &ImplTraitContext,
2224 ) -> hir::GenericBounds<'hir> {
2225 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2228 fn lower_param_bounds_mut<'s>(
2230 bounds: &'s [GenericBound],
2231 itctx: &'s ImplTraitContext,
2232 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2233 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx))
2236 #[instrument(level = "debug", skip(self), ret)]
2237 fn lower_generic_and_bounds(
2242 bounds: &[GenericBound],
2243 ) -> (hir::GenericParam<'hir>, Option<hir::WherePredicate<'hir>>, hir::TyKind<'hir>) {
2244 // Add a definition for the in-band `Param`.
2245 let def_id = self.local_def_id(node_id);
2247 // Set the name to `impl Bound1 + Bound2`.
2248 let param = hir::GenericParam {
2249 hir_id: self.lower_node_id(node_id),
2251 name: ParamName::Plain(self.lower_ident(ident)),
2252 pure_wrt_drop: false,
2253 span: self.lower_span(span),
2254 kind: hir::GenericParamKind::Type { default: None, synthetic: true },
2258 let preds = self.lower_generic_bound_predicate(
2261 &GenericParamKind::Type { default: None },
2263 &ImplTraitContext::Universal,
2264 hir::PredicateOrigin::ImplTrait,
2267 let hir_id = self.next_id();
2268 let res = Res::Def(DefKind::TyParam, def_id.to_def_id());
2269 let ty = hir::TyKind::Path(hir::QPath::Resolved(
2271 self.arena.alloc(hir::Path {
2272 span: self.lower_span(span),
2275 arena_vec![self; hir::PathSegment::new(self.lower_ident(ident), hir_id, res)],
2282 /// Lowers a block directly to an expression, presuming that it
2283 /// has no attributes and is not targeted by a `break`.
2284 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2285 let block = self.lower_block(b, false);
2286 self.expr_block(block, AttrVec::new())
2289 fn lower_array_length(&mut self, c: &AnonConst) -> hir::ArrayLen {
2290 match c.value.kind {
2291 ExprKind::Underscore => {
2292 if self.tcx.features().generic_arg_infer {
2293 hir::ArrayLen::Infer(self.lower_node_id(c.id), c.value.span)
2296 &self.tcx.sess.parse_sess,
2297 sym::generic_arg_infer,
2299 "using `_` for array lengths is unstable",
2301 .stash(c.value.span, StashKey::UnderscoreForArrayLengths);
2302 hir::ArrayLen::Body(self.lower_anon_const(c))
2305 _ => hir::ArrayLen::Body(self.lower_anon_const(c)),
2309 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2310 self.with_new_scopes(|this| hir::AnonConst {
2311 def_id: this.local_def_id(c.id),
2312 hir_id: this.lower_node_id(c.id),
2313 body: this.lower_const_body(c.value.span, Some(&c.value)),
2317 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2319 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2320 UserProvided => hir::UnsafeSource::UserProvided,
2324 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2326 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2327 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2329 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2330 // placeholder for compilation to proceed.
2331 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2332 hir::TraitBoundModifier::Maybe
2337 // Helper methods for building HIR.
2339 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2340 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2343 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2344 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2349 attrs: Option<&'hir [Attribute]>,
2351 init: Option<&'hir hir::Expr<'hir>>,
2352 pat: &'hir hir::Pat<'hir>,
2353 source: hir::LocalSource,
2354 ) -> hir::Stmt<'hir> {
2355 let hir_id = self.next_id();
2356 if let Some(a) = attrs {
2357 debug_assert!(!a.is_empty());
2358 self.attrs.insert(hir_id.local_id, a);
2360 let local = hir::Local {
2366 span: self.lower_span(span),
2369 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2372 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2373 self.block_all(expr.span, &[], Some(expr))
2379 stmts: &'hir [hir::Stmt<'hir>],
2380 expr: Option<&'hir hir::Expr<'hir>>,
2381 ) -> &'hir hir::Block<'hir> {
2382 let blk = hir::Block {
2385 hir_id: self.next_id(),
2386 rules: hir::BlockCheckMode::DefaultBlock,
2387 span: self.lower_span(span),
2388 targeted_by_break: false,
2390 self.arena.alloc(blk)
2393 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2394 let field = self.single_pat_field(span, pat);
2395 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field, None)
2398 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2399 let field = self.single_pat_field(span, pat);
2400 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field, None)
2403 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2404 let field = self.single_pat_field(span, pat);
2405 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field, None)
2408 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2409 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[], None)
2412 fn single_pat_field(
2415 pat: &'hir hir::Pat<'hir>,
2416 ) -> &'hir [hir::PatField<'hir>] {
2417 let field = hir::PatField {
2418 hir_id: self.next_id(),
2419 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2420 is_shorthand: false,
2422 span: self.lower_span(span),
2424 arena_vec![self; field]
2427 fn pat_lang_item_variant(
2430 lang_item: hir::LangItem,
2431 fields: &'hir [hir::PatField<'hir>],
2432 hir_id: Option<hir::HirId>,
2433 ) -> &'hir hir::Pat<'hir> {
2434 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span), hir_id);
2435 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2438 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2439 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::NONE)
2442 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2443 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::NONE)
2446 fn pat_ident_binding_mode(
2450 bm: hir::BindingAnnotation,
2451 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2452 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2453 (self.arena.alloc(pat), hir_id)
2456 fn pat_ident_binding_mode_mut(
2460 bm: hir::BindingAnnotation,
2461 ) -> (hir::Pat<'hir>, hir::HirId) {
2462 let hir_id = self.next_id();
2467 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2468 span: self.lower_span(span),
2469 default_binding_modes: true,
2475 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2476 self.arena.alloc(hir::Pat {
2477 hir_id: self.next_id(),
2479 span: self.lower_span(span),
2480 default_binding_modes: true,
2484 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2486 hir_id: self.next_id(),
2488 span: self.lower_span(span),
2489 default_binding_modes: false,
2495 mut hir_id: hir::HirId,
2497 qpath: hir::QPath<'hir>,
2498 ) -> hir::Ty<'hir> {
2499 let kind = match qpath {
2500 hir::QPath::Resolved(None, path) => {
2501 // Turn trait object paths into `TyKind::TraitObject` instead.
2503 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2504 let principal = hir::PolyTraitRef {
2505 bound_generic_params: &[],
2506 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2507 span: self.lower_span(span),
2510 // The original ID is taken by the `PolyTraitRef`,
2511 // so the `Ty` itself needs a different one.
2512 hir_id = self.next_id();
2513 hir::TyKind::TraitObject(
2514 arena_vec![self; principal],
2515 self.elided_dyn_bound(span),
2516 TraitObjectSyntax::None,
2519 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2522 _ => hir::TyKind::Path(qpath),
2525 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2528 /// Invoked to create the lifetime argument(s) for an elided trait object
2529 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2530 /// when the bound is written, even if it is written with `'_` like in
2531 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2532 fn elided_dyn_bound(&mut self, span: Span) -> &'hir hir::Lifetime {
2533 let r = hir::Lifetime {
2534 hir_id: self.next_id(),
2535 ident: Ident::new(kw::Empty, self.lower_span(span)),
2536 res: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2538 debug!("elided_dyn_bound: r={:?}", r);
2543 /// Helper struct for delayed construction of GenericArgs.
2544 struct GenericArgsCtor<'hir> {
2545 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2546 bindings: &'hir [hir::TypeBinding<'hir>],
2547 parenthesized: bool,
2551 impl<'hir> GenericArgsCtor<'hir> {
2552 fn is_empty(&self) -> bool {
2553 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2556 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2557 let ga = hir::GenericArgs {
2558 args: this.arena.alloc_from_iter(self.args),
2559 bindings: self.bindings,
2560 parenthesized: self.parenthesized,
2561 span_ext: this.lower_span(self.span),
2563 this.arena.alloc(ga)