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(crate_visibility_modifier)]
34 #![feature(box_patterns)]
36 #![recursion_limit = "256"]
38 use rustc_ast::node_id::NodeMap;
39 use rustc_ast::token::{self, Token};
40 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
41 use rustc_ast::visit::{self, AssocCtxt, Visitor};
42 use rustc_ast::walk_list;
43 use rustc_ast::{self as ast, *};
44 use rustc_ast_pretty::pprust;
45 use rustc_data_structures::captures::Captures;
46 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
47 use rustc_data_structures::sync::Lrc;
48 use rustc_errors::{struct_span_err, Applicability};
50 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
51 use rustc_hir::def_id::{DefId, DefIdMap, DefPathHash, LocalDefId, CRATE_DEF_ID};
52 use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
53 use rustc_hir::intravisit;
54 use rustc_hir::{ConstArg, GenericArg, InferKind, ParamName};
55 use rustc_index::vec::{Idx, IndexVec};
56 use rustc_session::lint::builtin::{BARE_TRAIT_OBJECTS, MISSING_ABI};
57 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
58 use rustc_session::utils::{FlattenNonterminals, NtToTokenstream};
59 use rustc_session::Session;
60 use rustc_span::edition::Edition;
61 use rustc_span::hygiene::ExpnId;
62 use rustc_span::source_map::{respan, CachingSourceMapView, DesugaringKind};
63 use rustc_span::symbol::{kw, sym, Ident, Symbol};
64 use rustc_span::{Span, DUMMY_SP};
65 use rustc_target::spec::abi::Abi;
67 use smallvec::SmallVec;
68 use std::collections::BTreeMap;
70 use tracing::{debug, trace};
72 macro_rules! arena_vec {
73 ($this:expr; $($x:expr),*) => ({
75 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
86 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
88 rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx);
90 struct LoweringContext<'a, 'hir: 'a> {
91 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
94 resolver: &'a mut dyn ResolverAstLowering,
96 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
97 /// if we don't have this function pointer. To avoid that dependency so that
98 /// `rustc_middle` is independent of the parser, we use dynamic dispatch here.
99 nt_to_tokenstream: NtToTokenstream,
101 /// Used to allocate HIR nodes.
102 arena: &'hir Arena<'hir>,
104 /// The items being lowered are collected here.
105 owners: IndexVec<LocalDefId, Option<hir::OwnerNode<'hir>>>,
106 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
108 trait_impls: BTreeMap<DefId, Vec<LocalDefId>>,
110 modules: BTreeMap<LocalDefId, hir::ModuleItems>,
112 generator_kind: Option<hir::GeneratorKind>,
114 attrs: BTreeMap<hir::HirId, &'hir [Attribute]>,
116 /// When inside an `async` context, this is the `HirId` of the
117 /// `task_context` local bound to the resume argument of the generator.
118 task_context: Option<hir::HirId>,
120 /// Used to get the current `fn`'s def span to point to when using `await`
121 /// outside of an `async fn`.
122 current_item: Option<Span>,
124 catch_scopes: Vec<NodeId>,
125 loop_scopes: Vec<NodeId>,
126 is_in_loop_condition: bool,
127 is_in_trait_impl: bool,
128 is_in_dyn_type: bool,
130 /// What to do when we encounter an "anonymous lifetime
131 /// reference". The term "anonymous" is meant to encompass both
132 /// `'_` lifetimes as well as fully elided cases where nothing is
133 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
134 anonymous_lifetime_mode: AnonymousLifetimeMode,
136 /// Used to create lifetime definitions from in-band lifetime usages.
137 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
138 /// When a named lifetime is encountered in a function or impl header and
139 /// has not been defined
140 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
141 /// to this list. The results of this list are then added to the list of
142 /// lifetime definitions in the corresponding impl or function generics.
143 lifetimes_to_define: Vec<(Span, ParamName)>,
145 /// `true` if in-band lifetimes are being collected. This is used to
146 /// indicate whether or not we're in a place where new lifetimes will result
147 /// in in-band lifetime definitions, such a function or an impl header,
148 /// including implicit lifetimes from `impl_header_lifetime_elision`.
149 is_collecting_in_band_lifetimes: bool,
151 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
152 /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
153 /// against this list to see if it is already in-scope, or if a definition
154 /// needs to be created for it.
156 /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
158 in_scope_lifetimes: Vec<ParamName>,
160 current_module: LocalDefId,
162 type_def_lifetime_params: DefIdMap<usize>,
164 current_hir_id_owner: (LocalDefId, u32),
165 item_local_id_counters: NodeMap<u32>,
166 node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
168 allow_try_trait: Option<Lrc<[Symbol]>>,
169 allow_gen_future: Option<Lrc<[Symbol]>>,
172 pub trait ResolverAstLowering {
173 fn def_key(&mut self, id: DefId) -> DefKey;
175 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
177 fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>>;
179 /// Obtains resolution for a `NodeId` with a single resolution.
180 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
182 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
183 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
185 /// Obtains resolution for a label with the given `NodeId`.
186 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
188 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
189 /// This should only return `None` during testing.
190 fn definitions(&mut self) -> &mut Definitions;
192 fn lint_buffer(&mut self) -> &mut LintBuffer;
194 fn next_node_id(&mut self) -> NodeId;
196 fn take_trait_map(&mut self) -> NodeMap<Vec<hir::TraitCandidate>>;
198 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
200 fn local_def_id(&self, node: NodeId) -> LocalDefId;
202 fn def_path_hash(&self, def_id: DefId) -> DefPathHash;
207 node_id: ast::NodeId,
214 struct LoweringHasher<'a> {
215 source_map: CachingSourceMapView<'a>,
216 resolver: &'a dyn ResolverAstLowering,
219 impl<'a> rustc_span::HashStableContext for LoweringHasher<'a> {
221 fn hash_spans(&self) -> bool {
226 fn def_path_hash(&self, def_id: DefId) -> DefPathHash {
227 self.resolver.def_path_hash(def_id)
231 fn span_data_to_lines_and_cols(
233 span: &rustc_span::SpanData,
234 ) -> Option<(Lrc<rustc_span::SourceFile>, usize, rustc_span::BytePos, usize, rustc_span::BytePos)>
236 self.source_map.span_data_to_lines_and_cols(span)
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.
243 enum ImplTraitContext<'b, 'a> {
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`.
249 Universal(&'b mut Vec<hir::GenericParam<'a>>, LocalDefId),
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 /// `DefId` for the parent function, used to look up necessary
257 /// information later.
259 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
260 origin: hir::OpaqueTyOrigin,
262 /// Impl trait in type aliases.
263 TypeAliasesOpaqueTy {
264 /// Set of lifetimes that this opaque type can capture, if it uses
265 /// them. This includes lifetimes bound since we entered this context.
269 /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
272 /// Here the inner opaque type captures `'a` because it uses it. It doesn't
273 /// need to capture `'b` because it already inherits the lifetime
274 /// parameter from `A`.
275 // FIXME(impl_trait): but `required_region_bounds` will ICE later
277 capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
279 /// `impl Trait` is not accepted in this position.
280 Disallowed(ImplTraitPosition),
283 /// Position in which `impl Trait` is disallowed.
284 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
285 enum ImplTraitPosition {
286 /// Disallowed in `let` / `const` / `static` bindings.
289 /// All other positions.
293 impl<'a> ImplTraitContext<'_, 'a> {
295 fn disallowed() -> Self {
296 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
299 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
300 use self::ImplTraitContext::*;
302 Universal(params, parent) => Universal(params, *parent),
303 ReturnPositionOpaqueTy { fn_def_id, origin } => {
304 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
306 TypeAliasesOpaqueTy { capturable_lifetimes } => {
307 TypeAliasesOpaqueTy { capturable_lifetimes }
309 Disallowed(pos) => Disallowed(*pos),
314 pub fn lower_crate<'a, 'hir>(
317 resolver: &'a mut dyn ResolverAstLowering,
318 nt_to_tokenstream: NtToTokenstream,
319 arena: &'hir Arena<'hir>,
320 ) -> &'hir hir::Crate<'hir> {
321 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
328 owners: IndexVec::default(),
329 bodies: BTreeMap::new(),
330 trait_impls: BTreeMap::new(),
331 modules: BTreeMap::new(),
332 attrs: BTreeMap::default(),
333 catch_scopes: Vec::new(),
334 loop_scopes: Vec::new(),
335 is_in_loop_condition: false,
336 is_in_trait_impl: false,
337 is_in_dyn_type: false,
338 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
339 type_def_lifetime_params: Default::default(),
340 current_module: CRATE_DEF_ID,
341 current_hir_id_owner: (CRATE_DEF_ID, 0),
342 item_local_id_counters: Default::default(),
343 node_id_to_hir_id: IndexVec::new(),
344 generator_kind: None,
347 lifetimes_to_define: Vec::new(),
348 is_collecting_in_band_lifetimes: false,
349 in_scope_lifetimes: Vec::new(),
350 allow_try_trait: Some([sym::try_trait_v2][..].into()),
351 allow_gen_future: Some([sym::gen_future][..].into()),
356 #[derive(Copy, Clone, PartialEq)]
358 /// Any path in a type context.
360 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
362 /// The `module::Type` in `module::Type::method` in an expression.
366 enum ParenthesizedGenericArgs {
371 /// What to do when we encounter an **anonymous** lifetime
372 /// reference. Anonymous lifetime references come in two flavors. You
373 /// have implicit, or fully elided, references to lifetimes, like the
374 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
375 /// or `Ref<'_, T>`. These often behave the same, but not always:
377 /// - certain usages of implicit references are deprecated, like
378 /// `Ref<T>`, and we sometimes just give hard errors in those cases
380 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
381 /// the same as `Box<dyn Foo + '_>`.
383 /// We describe the effects of the various modes in terms of three cases:
385 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
386 /// of a `&` (e.g., the missing lifetime in something like `&T`)
387 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
388 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
389 /// elided bounds follow special rules. Note that this only covers
390 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
391 /// '_>` is a case of "modern" elision.
392 /// - **Deprecated** -- this covers cases like `Ref<T>`, where the lifetime
393 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
394 /// non-deprecated equivalent.
396 /// Currently, the handling of lifetime elision is somewhat spread out
397 /// between HIR lowering and -- as described below -- the
398 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
399 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
400 /// everything into HIR lowering.
401 #[derive(Copy, Clone, Debug)]
402 enum AnonymousLifetimeMode {
403 /// For **Modern** cases, create a new anonymous region parameter
404 /// and reference that.
406 /// For **Dyn Bound** cases, pass responsibility to
407 /// `resolve_lifetime` code.
409 /// For **Deprecated** cases, report an error.
412 /// Give a hard error when either `&` or `'_` is written. Used to
413 /// rule out things like `where T: Foo<'_>`. Does not imply an
414 /// error on default object bounds (e.g., `Box<dyn Foo>`).
417 /// Pass responsibility to `resolve_lifetime` code for all cases.
421 impl<'a, 'hir> LoweringContext<'a, 'hir> {
422 fn lower_crate(mut self, c: &Crate) -> &'hir hir::Crate<'hir> {
423 /// Full-crate AST visitor that inserts into a fresh
424 /// `LoweringContext` any information that may be
425 /// needed from arbitrary locations in the crate,
426 /// e.g., the number of lifetime generic parameters
427 /// declared for every type and trait definition.
428 struct MiscCollector<'tcx, 'lowering, 'hir> {
429 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
432 impl MiscCollector<'_, '_, '_> {
433 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
435 UseTreeKind::Simple(_, id1, id2) => {
436 for id in [id1, id2] {
437 self.lctx.allocate_hir_id_counter(id);
440 UseTreeKind::Glob => (),
441 UseTreeKind::Nested(ref trees) => {
442 for &(ref use_tree, id) in trees {
443 self.lctx.allocate_hir_id_counter(id);
444 self.allocate_use_tree_hir_id_counters(use_tree);
451 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
452 fn visit_item(&mut self, item: &'tcx Item) {
453 self.lctx.allocate_hir_id_counter(item.id);
456 ItemKind::Struct(_, ref generics)
457 | ItemKind::Union(_, ref generics)
458 | ItemKind::Enum(_, ref generics)
459 | ItemKind::TyAlias(box TyAliasKind(_, ref generics, ..))
460 | ItemKind::Trait(box TraitKind(_, _, ref generics, ..)) => {
461 let def_id = self.lctx.resolver.local_def_id(item.id);
466 matches!(param.kind, ast::GenericParamKind::Lifetime { .. })
469 self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
471 ItemKind::Use(ref use_tree) => {
472 self.allocate_use_tree_hir_id_counters(use_tree);
477 visit::walk_item(self, item);
480 fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
481 self.lctx.allocate_hir_id_counter(item.id);
482 visit::walk_assoc_item(self, item, ctxt);
485 fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
486 self.lctx.allocate_hir_id_counter(item.id);
487 visit::walk_foreign_item(self, item);
490 fn visit_ty(&mut self, t: &'tcx Ty) {
492 // Mirrors the case in visit::walk_ty
493 TyKind::BareFn(ref f) => {
494 walk_list!(self, visit_generic_param, &f.generic_params);
495 // Mirrors visit::walk_fn_decl
496 for parameter in &f.decl.inputs {
497 // We don't lower the ids of argument patterns
498 self.visit_pat(¶meter.pat);
499 self.visit_ty(¶meter.ty)
501 self.visit_fn_ret_ty(&f.decl.output)
503 _ => visit::walk_ty(self, t),
508 self.lower_node_id(CRATE_NODE_ID);
509 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
511 visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
512 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
514 let module = self.arena.alloc(self.lower_mod(&c.items, c.span));
515 self.lower_attrs(hir::CRATE_HIR_ID, &c.attrs);
516 self.owners.ensure_contains_elem(CRATE_DEF_ID, || None);
517 self.owners[CRATE_DEF_ID] = Some(hir::OwnerNode::Crate(module));
519 let body_ids = body_ids(&self.bodies);
521 c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
523 let mut trait_map: FxHashMap<_, FxHashMap<_, _>> = FxHashMap::default();
524 for (k, v) in self.resolver.take_trait_map().into_iter() {
525 if let Some(Some(hir_id)) = self.node_id_to_hir_id.get(k) {
526 let map = trait_map.entry(hir_id.owner).or_default();
527 map.insert(hir_id.local_id, v.into_boxed_slice());
531 let mut def_id_to_hir_id = IndexVec::default();
533 for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
534 if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
535 if def_id_to_hir_id.len() <= def_id.index() {
536 def_id_to_hir_id.resize(def_id.index() + 1, None);
538 def_id_to_hir_id[def_id] = hir_id;
542 self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
544 #[cfg(debug_assertions)]
545 for (&id, attrs) in self.attrs.iter() {
546 // Verify that we do not store empty slices in the map.
547 if attrs.is_empty() {
548 panic!("Stored empty attributes for {:?}", id);
552 let krate = hir::Crate {
556 trait_impls: self.trait_impls,
557 modules: self.modules,
562 self.arena.alloc(krate)
565 fn insert_item(&mut self, item: hir::Item<'hir>) -> hir::ItemId {
566 let id = item.item_id();
567 let item = self.arena.alloc(item);
568 self.owners.ensure_contains_elem(id.def_id, || None);
569 self.owners[id.def_id] = Some(hir::OwnerNode::Item(item));
570 self.modules.entry(self.current_module).or_default().items.insert(id);
574 fn insert_foreign_item(&mut self, item: hir::ForeignItem<'hir>) -> hir::ForeignItemId {
575 let id = item.foreign_item_id();
576 let item = self.arena.alloc(item);
577 self.owners.ensure_contains_elem(id.def_id, || None);
578 self.owners[id.def_id] = Some(hir::OwnerNode::ForeignItem(item));
579 self.modules.entry(self.current_module).or_default().foreign_items.insert(id);
583 fn insert_impl_item(&mut self, item: hir::ImplItem<'hir>) -> hir::ImplItemId {
584 let id = item.impl_item_id();
585 let item = self.arena.alloc(item);
586 self.owners.ensure_contains_elem(id.def_id, || None);
587 self.owners[id.def_id] = Some(hir::OwnerNode::ImplItem(item));
588 self.modules.entry(self.current_module).or_default().impl_items.insert(id);
592 fn insert_trait_item(&mut self, item: hir::TraitItem<'hir>) -> hir::TraitItemId {
593 let id = item.trait_item_id();
594 let item = self.arena.alloc(item);
595 self.owners.ensure_contains_elem(id.def_id, || None);
596 self.owners[id.def_id] = Some(hir::OwnerNode::TraitItem(item));
597 self.modules.entry(self.current_module).or_default().trait_items.insert(id);
601 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
602 // Set up the counter if needed.
603 self.item_local_id_counters.entry(owner).or_insert(0);
604 // Always allocate the first `HirId` for the owner itself.
605 let lowered = self.lower_node_id_with_owner(owner, owner);
606 debug_assert_eq!(lowered.local_id.as_u32(), 0);
610 fn create_stable_hashing_context(&self) -> LoweringHasher<'_> {
612 source_map: CachingSourceMapView::new(self.sess.source_map()),
613 resolver: self.resolver,
617 fn lower_node_id_generic(
620 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
622 assert_ne!(ast_node_id, DUMMY_NODE_ID);
624 let min_size = ast_node_id.as_usize() + 1;
626 if min_size > self.node_id_to_hir_id.len() {
627 self.node_id_to_hir_id.resize(min_size, None);
630 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
633 // Generate a new `HirId`.
634 let hir_id = alloc_hir_id(self);
635 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
641 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
643 .item_local_id_counters
644 .insert(owner, HIR_ID_COUNTER_LOCKED)
645 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
646 let def_id = self.resolver.local_def_id(owner);
647 let old_owner = std::mem::replace(&mut self.current_hir_id_owner, (def_id, counter));
649 let (new_def_id, new_counter) =
650 std::mem::replace(&mut self.current_hir_id_owner, old_owner);
652 debug_assert!(def_id == new_def_id);
653 debug_assert!(new_counter >= counter);
655 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
656 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
660 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
661 /// the `LoweringContext`'s `NodeId => HirId` map.
662 /// Take care not to call this method if the resulting `HirId` is then not
663 /// actually used in the HIR, as that would trigger an assertion in the
664 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
665 /// properly. Calling the method twice with the same `NodeId` is fine though.
666 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
667 self.lower_node_id_generic(ast_node_id, |this| {
668 let &mut (owner, ref mut local_id_counter) = &mut this.current_hir_id_owner;
669 let local_id = *local_id_counter;
670 *local_id_counter += 1;
671 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
675 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
676 self.lower_node_id_generic(ast_node_id, |this| {
677 let local_id_counter = this
678 .item_local_id_counters
680 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
681 let local_id = *local_id_counter;
683 // We want to be sure not to modify the counter in the map while it
684 // is also on the stack. Otherwise we'll get lost updates when writing
685 // back from the stack to the map.
686 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
688 *local_id_counter += 1;
689 let owner = this.resolver.opt_local_def_id(owner).expect(
690 "you forgot to call `create_def` or are lowering node-IDs \
691 that do not belong to the current owner",
694 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
698 fn next_id(&mut self) -> hir::HirId {
699 let node_id = self.resolver.next_node_id();
700 self.lower_node_id(node_id)
703 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
705 self.lower_node_id_generic(id, |_| {
706 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
711 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
712 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
713 if pr.unresolved_segments() != 0 {
714 panic!("path not fully resolved: {:?}", pr);
720 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
721 self.resolver.get_import_res(id).present_items()
724 fn diagnostic(&self) -> &rustc_errors::Handler {
725 self.sess.diagnostic()
728 /// Reuses the span but adds information like the kind of the desugaring and features that are
729 /// allowed inside this span.
730 fn mark_span_with_reason(
732 reason: DesugaringKind,
734 allow_internal_unstable: Option<Lrc<[Symbol]>>,
736 span.mark_with_reason(
737 allow_internal_unstable,
740 self.create_stable_hashing_context(),
744 fn with_anonymous_lifetime_mode<R>(
746 anonymous_lifetime_mode: AnonymousLifetimeMode,
747 op: impl FnOnce(&mut Self) -> R,
750 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
751 anonymous_lifetime_mode,
753 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
754 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
755 let result = op(self);
756 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
758 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
759 old_anonymous_lifetime_mode
764 /// Intercept all spans entering HIR.
765 /// For now we are not doing anything with the intercepted spans.
766 fn lower_span(&self, span: Span) -> Span {
770 fn lower_ident(&self, ident: Ident) -> Ident {
771 Ident::new(ident.name, self.lower_span(ident.span))
774 /// Creates a new `hir::GenericParam` for every new lifetime and
775 /// type parameter encountered while evaluating `f`. Definitions
776 /// are created with the parent provided. If no `parent_id` is
777 /// provided, no definitions will be returned.
779 /// Presuming that in-band lifetimes are enabled, then
780 /// `self.anonymous_lifetime_mode` will be updated to match the
781 /// parameter while `f` is running (and restored afterwards).
782 fn collect_in_band_defs<T>(
784 parent_def_id: LocalDefId,
785 anonymous_lifetime_mode: AnonymousLifetimeMode,
786 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
787 ) -> (Vec<hir::GenericParam<'hir>>, T) {
788 assert!(!self.is_collecting_in_band_lifetimes);
789 assert!(self.lifetimes_to_define.is_empty());
790 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
792 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
793 self.is_collecting_in_band_lifetimes = true;
795 let (in_band_ty_params, res) = f(self);
797 self.is_collecting_in_band_lifetimes = false;
798 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
800 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
802 let params = lifetimes_to_define
804 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
805 .chain(in_band_ty_params.into_iter())
811 /// Converts a lifetime into a new generic parameter.
812 fn lifetime_to_generic_param(
816 parent_def_id: LocalDefId,
817 ) -> hir::GenericParam<'hir> {
818 let node_id = self.resolver.next_node_id();
820 // Get the name we'll use to make the def-path. Note
821 // that collisions are ok here and this shouldn't
822 // really show up for end-user.
823 let (str_name, kind) = match hir_name {
824 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
825 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
826 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
829 // Add a definition for the in-band lifetime def.
830 self.resolver.create_def(
833 DefPathData::LifetimeNs(str_name),
839 hir_id: self.lower_node_id(node_id),
842 span: self.lower_span(span),
843 pure_wrt_drop: false,
844 kind: hir::GenericParamKind::Lifetime { kind },
848 /// When there is a reference to some lifetime `'a`, and in-band
849 /// lifetimes are enabled, then we want to push that lifetime into
850 /// the vector of names to define later. In that case, it will get
851 /// added to the appropriate generics.
852 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
853 if !self.is_collecting_in_band_lifetimes {
857 if !self.sess.features_untracked().in_band_lifetimes {
861 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
865 let hir_name = ParamName::Plain(ident);
867 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
868 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
873 self.lifetimes_to_define.push((ident.span, hir_name));
876 /// When we have either an elided or `'_` lifetime in an impl
877 /// header, we convert it to an in-band lifetime.
878 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
879 assert!(self.is_collecting_in_band_lifetimes);
880 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
881 let hir_name = ParamName::Fresh(index);
882 self.lifetimes_to_define.push((span, hir_name));
886 // Evaluates `f` with the lifetimes in `params` in-scope.
887 // This is used to track which lifetimes have already been defined, and
888 // which are new in-band lifetimes that need to have a definition created
890 fn with_in_scope_lifetime_defs<T>(
892 params: &[GenericParam],
893 f: impl FnOnce(&mut Self) -> T,
895 let old_len = self.in_scope_lifetimes.len();
896 let lt_def_names = params.iter().filter_map(|param| match param.kind {
897 GenericParamKind::Lifetime { .. } => {
898 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
902 self.in_scope_lifetimes.extend(lt_def_names);
906 self.in_scope_lifetimes.truncate(old_len);
910 /// Appends in-band lifetime defs and argument-position `impl
911 /// Trait` defs to the existing set of generics.
913 /// Presuming that in-band lifetimes are enabled, then
914 /// `self.anonymous_lifetime_mode` will be updated to match the
915 /// parameter while `f` is running (and restored afterwards).
916 fn add_in_band_defs<T>(
919 parent_def_id: LocalDefId,
920 anonymous_lifetime_mode: AnonymousLifetimeMode,
921 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
922 ) -> (hir::Generics<'hir>, T) {
923 let (in_band_defs, (mut lowered_generics, res)) =
924 self.with_in_scope_lifetime_defs(&generics.params, |this| {
925 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
926 let mut params = Vec::new();
927 // Note: it is necessary to lower generics *before* calling `f`.
928 // When lowering `async fn`, there's a final step when lowering
929 // the return type that assumes that all in-scope lifetimes have
930 // already been added to either `in_scope_lifetimes` or
931 // `lifetimes_to_define`. If we swapped the order of these two,
932 // in-band-lifetimes introduced by generics or where-clauses
933 // wouldn't have been added yet.
934 let generics = this.lower_generics_mut(
936 ImplTraitContext::Universal(&mut params, this.current_hir_id_owner.0),
938 let res = f(this, &mut params);
939 (params, (generics, res))
943 lowered_generics.params.extend(in_band_defs);
945 let lowered_generics = lowered_generics.into_generics(self.arena);
946 (lowered_generics, res)
949 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
950 let was_in_dyn_type = self.is_in_dyn_type;
951 self.is_in_dyn_type = in_scope;
953 let result = f(self);
955 self.is_in_dyn_type = was_in_dyn_type;
960 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
961 let was_in_loop_condition = self.is_in_loop_condition;
962 self.is_in_loop_condition = false;
964 let catch_scopes = mem::take(&mut self.catch_scopes);
965 let loop_scopes = mem::take(&mut self.loop_scopes);
967 self.catch_scopes = catch_scopes;
968 self.loop_scopes = loop_scopes;
970 self.is_in_loop_condition = was_in_loop_condition;
975 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
976 if attrs.is_empty() {
979 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
980 debug_assert!(!ret.is_empty());
981 self.attrs.insert(id, ret);
986 fn lower_attr(&self, attr: &Attribute) -> Attribute {
987 // Note that we explicitly do not walk the path. Since we don't really
988 // lower attributes (we use the AST version) there is nowhere to keep
989 // the `HirId`s. We don't actually need HIR version of attributes anyway.
990 // Tokens are also not needed after macro expansion and parsing.
991 let kind = match attr.kind {
992 AttrKind::Normal(ref item, _) => AttrKind::Normal(
994 path: item.path.clone(),
995 args: self.lower_mac_args(&item.args),
1000 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
1003 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
1006 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
1007 if let Some(&a) = self.attrs.get(&target_id) {
1008 debug_assert!(!a.is_empty());
1009 self.attrs.insert(id, a);
1013 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
1015 MacArgs::Empty => MacArgs::Empty,
1016 MacArgs::Delimited(dspan, delim, ref tokens) => {
1017 // This is either a non-key-value attribute, or a `macro_rules!` body.
1018 // We either not have any nonterminals present (in the case of an attribute),
1019 // or have tokens available for all nonterminals in the case of a nested
1020 // `macro_rules`: e.g:
1023 // macro_rules! outer {
1025 // macro_rules! inner {
1032 // In both cases, we don't want to synthesize any tokens
1036 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1039 // This is an inert key-value attribute - it will never be visible to macros
1040 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1041 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1042 MacArgs::Eq(eq_span, ref token) => {
1043 // In valid code the value is always representable as a single literal token.
1044 fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
1045 if tokens.len() != 1 {
1047 .delay_span_bug(span, "multiple tokens in key-value attribute's value");
1049 match tokens.into_trees().next() {
1050 Some(TokenTree::Token(token)) => token,
1051 Some(TokenTree::Delimited(_, delim, tokens)) => {
1052 if delim != token::NoDelim {
1053 sess.diagnostic().delay_span_bug(
1055 "unexpected delimiter in key-value attribute's value",
1058 unwrap_single_token(sess, tokens, span)
1060 None => Token::dummy(),
1064 let tokens = FlattenNonterminals {
1065 parse_sess: &self.sess.parse_sess,
1066 synthesize_tokens: CanSynthesizeMissingTokens::Yes,
1067 nt_to_tokenstream: self.nt_to_tokenstream,
1069 .process_token(token.clone());
1070 MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
1075 fn lower_token_stream(
1077 tokens: TokenStream,
1078 synthesize_tokens: CanSynthesizeMissingTokens,
1080 FlattenNonterminals {
1081 parse_sess: &self.sess.parse_sess,
1083 nt_to_tokenstream: self.nt_to_tokenstream,
1085 .process_token_stream(tokens)
1088 /// Given an associated type constraint like one of these:
1091 /// T: Iterator<Item: Debug>
1093 /// T: Iterator<Item = Debug>
1097 /// returns a `hir::TypeBinding` representing `Item`.
1098 fn lower_assoc_ty_constraint(
1100 constraint: &AssocTyConstraint,
1101 mut itctx: ImplTraitContext<'_, 'hir>,
1102 ) -> hir::TypeBinding<'hir> {
1103 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1105 // lower generic arguments of identifier in constraint
1106 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1107 let gen_args_ctor = match gen_args {
1108 GenericArgs::AngleBracketed(ref data) => {
1109 self.lower_angle_bracketed_parameter_data(
1111 ParamMode::Explicit,
1116 GenericArgs::Parenthesized(ref data) => {
1117 let mut err = self.sess.struct_span_err(
1119 "parenthesized generic arguments cannot be used in associated type constraints"
1121 // FIXME: try to write a suggestion here
1123 self.lower_angle_bracketed_parameter_data(
1124 &data.as_angle_bracketed_args(),
1125 ParamMode::Explicit,
1131 gen_args_ctor.into_generic_args(self)
1133 self.arena.alloc(hir::GenericArgs::none())
1136 let kind = match constraint.kind {
1137 AssocTyConstraintKind::Equality { ref ty } => {
1138 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1140 AssocTyConstraintKind::Bound { ref bounds } => {
1141 let mut capturable_lifetimes;
1142 let mut parent_def_id = self.current_hir_id_owner.0;
1143 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1144 let (desugar_to_impl_trait, itctx) = match itctx {
1145 // We are in the return position:
1147 // fn foo() -> impl Iterator<Item: Debug>
1151 // fn foo() -> impl Iterator<Item = impl Debug>
1152 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1153 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1155 // We are in the argument position, but within a dyn type:
1157 // fn foo(x: dyn Iterator<Item: Debug>)
1161 // fn foo(x: dyn Iterator<Item = impl Debug>)
1162 ImplTraitContext::Universal(_, parent) if self.is_in_dyn_type => {
1163 parent_def_id = parent;
1167 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1168 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1169 // "impl trait context" to permit `impl Debug` in this position (it desugars
1170 // then to an opaque type).
1172 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1173 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1174 capturable_lifetimes = FxHashSet::default();
1177 ImplTraitContext::TypeAliasesOpaqueTy {
1178 capturable_lifetimes: &mut capturable_lifetimes,
1183 // We are in the parameter position, but not within a dyn type:
1185 // fn foo(x: impl Iterator<Item: Debug>)
1187 // so we leave it as is and this gets expanded in astconv to a bound like
1188 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1190 _ => (false, itctx),
1193 if desugar_to_impl_trait {
1194 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1195 // constructing the HIR for `impl bounds...` and then lowering that.
1197 let impl_trait_node_id = self.resolver.next_node_id();
1198 self.resolver.create_def(
1201 DefPathData::ImplTrait,
1206 self.with_dyn_type_scope(false, |this| {
1207 let node_id = this.resolver.next_node_id();
1208 let ty = this.lower_ty(
1211 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1212 span: this.lower_span(constraint.span),
1218 hir::TypeBindingKind::Equality { ty }
1221 // Desugar `AssocTy: Bounds` into a type binding where the
1222 // later desugars into a trait predicate.
1223 let bounds = self.lower_param_bounds(bounds, itctx);
1225 hir::TypeBindingKind::Constraint { bounds }
1231 hir_id: self.lower_node_id(constraint.id),
1232 ident: self.lower_ident(constraint.ident),
1235 span: self.lower_span(constraint.span),
1239 fn lower_generic_arg(
1241 arg: &ast::GenericArg,
1242 itctx: ImplTraitContext<'_, 'hir>,
1243 ) -> hir::GenericArg<'hir> {
1245 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1246 ast::GenericArg::Type(ty) => {
1248 TyKind::Infer if self.sess.features_untracked().generic_arg_infer => {
1249 return GenericArg::Infer(hir::InferArg {
1250 hir_id: self.lower_node_id(ty.id),
1251 span: self.lower_span(ty.span),
1252 kind: InferKind::Type,
1255 // We parse const arguments as path types as we cannot distinguish them during
1256 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1257 // type and value namespaces. If we resolved the path in the value namespace, we
1258 // transform it into a generic const argument.
1259 TyKind::Path(ref qself, ref path) => {
1260 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1261 let res = partial_res.base_res();
1262 if !res.matches_ns(Namespace::TypeNS) {
1264 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1268 // Construct an AnonConst where the expr is the "ty"'s path.
1270 let parent_def_id = self.current_hir_id_owner.0;
1271 let node_id = self.resolver.next_node_id();
1273 // Add a definition for the in-band const def.
1274 self.resolver.create_def(
1277 DefPathData::AnonConst,
1282 let span = self.lower_span(ty.span);
1283 let path_expr = Expr {
1285 kind: ExprKind::Path(qself.clone(), path.clone()),
1287 attrs: AttrVec::new(),
1291 let ct = self.with_new_scopes(|this| hir::AnonConst {
1292 hir_id: this.lower_node_id(node_id),
1293 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1295 return GenericArg::Const(ConstArg { value: ct, span });
1301 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1303 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1304 value: self.lower_anon_const(&ct),
1305 span: self.lower_span(ct.value.span),
1310 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1311 self.arena.alloc(self.lower_ty_direct(t, itctx))
1317 qself: &Option<QSelf>,
1319 param_mode: ParamMode,
1320 itctx: ImplTraitContext<'_, 'hir>,
1321 ) -> hir::Ty<'hir> {
1322 let id = self.lower_node_id(t.id);
1323 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1324 let ty = self.ty_path(id, t.span, qpath);
1325 if let hir::TyKind::TraitObject(..) = ty.kind {
1326 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1331 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1332 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1335 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1336 self.ty(span, hir::TyKind::Tup(tys))
1339 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1340 let kind = match t.kind {
1341 TyKind::Infer => hir::TyKind::Infer,
1342 TyKind::Err => hir::TyKind::Err,
1343 // FIXME(unnamed_fields): IMPLEMENTATION IN PROGRESS
1344 TyKind::AnonymousStruct(ref _fields, _recovered) => {
1345 self.sess.struct_span_err(t.span, "anonymous structs are unimplemented").emit();
1348 TyKind::AnonymousUnion(ref _fields, _recovered) => {
1349 self.sess.struct_span_err(t.span, "anonymous unions are unimplemented").emit();
1352 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1353 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1354 TyKind::Rptr(ref region, ref mt) => {
1355 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1356 let lifetime = match *region {
1357 Some(ref lt) => self.lower_lifetime(lt),
1358 None => self.elided_ref_lifetime(span),
1360 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1362 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1363 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1364 let span = this.sess.source_map().next_point(t.span.shrink_to_lo());
1365 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1366 generic_params: this.lower_generic_params(
1368 &NodeMap::default(),
1369 ImplTraitContext::disallowed(),
1371 unsafety: this.lower_unsafety(f.unsafety),
1372 abi: this.lower_extern(f.ext, span, t.id),
1373 decl: this.lower_fn_decl(&f.decl, None, false, None),
1374 param_names: this.lower_fn_params_to_names(&f.decl),
1378 TyKind::Never => hir::TyKind::Never,
1379 TyKind::Tup(ref tys) => {
1380 hir::TyKind::Tup(self.arena.alloc_from_iter(
1381 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1384 TyKind::Paren(ref ty) => {
1385 return self.lower_ty_direct(ty, itctx);
1387 TyKind::Path(ref qself, ref path) => {
1388 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1390 TyKind::ImplicitSelf => {
1391 let res = self.expect_full_res(t.id);
1392 let res = self.lower_res(res);
1393 hir::TyKind::Path(hir::QPath::Resolved(
1395 self.arena.alloc(hir::Path {
1397 segments: arena_vec![self; hir::PathSegment::from_ident(
1398 Ident::with_dummy_span(kw::SelfUpper)
1400 span: self.lower_span(t.span),
1404 TyKind::Array(ref ty, ref length) => {
1405 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1407 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1408 TyKind::TraitObject(ref bounds, kind) => {
1409 let mut lifetime_bound = None;
1410 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1412 this.arena.alloc_from_iter(bounds.iter().filter_map(
1413 |bound| match *bound {
1414 GenericBound::Trait(
1416 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1417 ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
1418 // `~const ?Bound` will cause an error during AST validation
1419 // anyways, so treat it like `?Bound` as compilation proceeds.
1420 GenericBound::Trait(
1422 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1424 GenericBound::Outlives(ref lifetime) => {
1425 if lifetime_bound.is_none() {
1426 lifetime_bound = Some(this.lower_lifetime(lifetime));
1432 let lifetime_bound =
1433 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1434 (bounds, lifetime_bound)
1436 if kind != TraitObjectSyntax::Dyn {
1437 self.maybe_lint_bare_trait(t.span, t.id, false);
1439 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1441 TyKind::ImplTrait(def_node_id, ref bounds) => {
1444 ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
1445 .lower_opaque_impl_trait(
1451 |this| this.lower_param_bounds(bounds, itctx),
1453 ImplTraitContext::TypeAliasesOpaqueTy { ref capturable_lifetimes } => {
1454 // Reset capturable lifetimes, any nested impl trait
1455 // types will inherit lifetimes from this opaque type,
1456 // so don't need to capture them again.
1457 let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy {
1458 capturable_lifetimes: &mut FxHashSet::default(),
1460 self.lower_opaque_impl_trait(
1463 hir::OpaqueTyOrigin::TyAlias,
1465 Some(capturable_lifetimes),
1466 |this| this.lower_param_bounds(bounds, nested_itctx),
1469 ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
1470 // Add a definition for the in-band `Param`.
1471 let def_id = self.resolver.local_def_id(def_node_id);
1473 let hir_bounds = self.lower_param_bounds(
1475 ImplTraitContext::Universal(in_band_ty_params, parent_def_id),
1477 // Set the name to `impl Bound1 + Bound2`.
1478 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1479 in_band_ty_params.push(hir::GenericParam {
1480 hir_id: self.lower_node_id(def_node_id),
1481 name: ParamName::Plain(self.lower_ident(ident)),
1482 pure_wrt_drop: false,
1484 span: self.lower_span(span),
1485 kind: hir::GenericParamKind::Type {
1487 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1491 hir::TyKind::Path(hir::QPath::Resolved(
1493 self.arena.alloc(hir::Path {
1494 span: self.lower_span(span),
1495 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1496 segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
1500 ImplTraitContext::Disallowed(_) => {
1501 let mut err = struct_span_err!(
1505 "`impl Trait` not allowed outside of {}",
1506 "function and method return types",
1513 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1514 TyKind::CVarArgs => {
1515 self.sess.delay_span_bug(
1517 "`TyKind::CVarArgs` should have been handled elsewhere",
1523 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1526 fn lower_opaque_impl_trait(
1529 fn_def_id: Option<DefId>,
1530 origin: hir::OpaqueTyOrigin,
1531 opaque_ty_node_id: NodeId,
1532 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1533 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1534 ) -> hir::TyKind<'hir> {
1536 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1537 fn_def_id, opaque_ty_node_id, span,
1540 // Make sure we know that some funky desugaring has been going on here.
1541 // This is a first: there is code in other places like for loop
1542 // desugaring that explicitly states that we don't want to track that.
1543 // Not tracking it makes lints in rustc and clippy very fragile, as
1544 // frequently opened issues show.
1545 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1547 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1549 self.allocate_hir_id_counter(opaque_ty_node_id);
1551 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1553 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1557 capturable_lifetimes,
1560 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1562 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1564 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1565 let opaque_ty_item = hir::OpaqueTy {
1566 generics: hir::Generics {
1567 params: lifetime_defs,
1568 where_clause: hir::WhereClause { predicates: &[], span: lctx.lower_span(span) },
1569 span: lctx.lower_span(span),
1572 impl_trait_fn: fn_def_id,
1576 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1577 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
1579 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1580 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1584 /// Registers a new opaque type with the proper `NodeId`s and
1585 /// returns the lowered node-ID for the opaque type.
1586 fn generate_opaque_type(
1588 opaque_ty_id: LocalDefId,
1589 opaque_ty_item: hir::OpaqueTy<'hir>,
1591 opaque_ty_span: Span,
1593 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1594 // Generate an `type Foo = impl Trait;` declaration.
1595 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1596 let opaque_ty_item = hir::Item {
1597 def_id: opaque_ty_id,
1598 ident: Ident::invalid(),
1599 kind: opaque_ty_item_kind,
1600 vis: respan(self.lower_span(span.shrink_to_lo()), hir::VisibilityKind::Inherited),
1601 span: self.lower_span(opaque_ty_span),
1604 // Insert the item into the global item list. This usually happens
1605 // automatically for all AST items. But this opaque type item
1606 // does not actually exist in the AST.
1607 self.insert_item(opaque_ty_item);
1610 fn lifetimes_from_impl_trait_bounds(
1612 opaque_ty_id: NodeId,
1613 parent_def_id: LocalDefId,
1614 bounds: hir::GenericBounds<'hir>,
1615 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1616 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1618 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1619 parent_def_id={:?}, \
1621 opaque_ty_id, parent_def_id, bounds,
1624 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1625 // appear in the bounds, excluding lifetimes that are created within the bounds.
1626 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1627 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1628 context: &'r mut LoweringContext<'a, 'hir>,
1630 opaque_ty_id: NodeId,
1631 collect_elided_lifetimes: bool,
1632 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1633 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1634 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1635 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1636 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1639 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1640 type Map = intravisit::ErasedMap<'v>;
1642 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1643 intravisit::NestedVisitorMap::None
1646 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1647 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1648 if parameters.parenthesized {
1649 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1650 self.collect_elided_lifetimes = false;
1651 intravisit::walk_generic_args(self, span, parameters);
1652 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1654 intravisit::walk_generic_args(self, span, parameters);
1658 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1659 // Don't collect elided lifetimes used inside of `fn()` syntax.
1660 if let hir::TyKind::BareFn(_) = t.kind {
1661 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1662 self.collect_elided_lifetimes = false;
1664 // Record the "stack height" of `for<'a>` lifetime bindings
1665 // to be able to later fully undo their introduction.
1666 let old_len = self.currently_bound_lifetimes.len();
1667 intravisit::walk_ty(self, t);
1668 self.currently_bound_lifetimes.truncate(old_len);
1670 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1672 intravisit::walk_ty(self, t)
1676 fn visit_poly_trait_ref(
1678 trait_ref: &'v hir::PolyTraitRef<'v>,
1679 modifier: hir::TraitBoundModifier,
1681 // Record the "stack height" of `for<'a>` lifetime bindings
1682 // to be able to later fully undo their introduction.
1683 let old_len = self.currently_bound_lifetimes.len();
1684 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1685 self.currently_bound_lifetimes.truncate(old_len);
1688 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1689 // Record the introduction of 'a in `for<'a> ...`.
1690 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1691 // Introduce lifetimes one at a time so that we can handle
1692 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1693 let lt_name = hir::LifetimeName::Param(param.name);
1694 self.currently_bound_lifetimes.push(lt_name);
1697 intravisit::walk_generic_param(self, param);
1700 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1701 let name = match lifetime.name {
1702 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1703 if self.collect_elided_lifetimes {
1704 // Use `'_` for both implicit and underscore lifetimes in
1705 // `type Foo<'_> = impl SomeTrait<'_>;`.
1706 hir::LifetimeName::Underscore
1711 hir::LifetimeName::Param(_) => lifetime.name,
1713 // Refers to some other lifetime that is "in
1714 // scope" within the type.
1715 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1717 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1720 if !self.currently_bound_lifetimes.contains(&name)
1721 && !self.already_defined_lifetimes.contains(&name)
1722 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1724 self.already_defined_lifetimes.insert(name);
1726 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1727 hir_id: self.context.next_id(),
1728 span: self.context.lower_span(lifetime.span),
1732 let def_node_id = self.context.resolver.next_node_id();
1734 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1735 self.context.resolver.create_def(
1738 DefPathData::LifetimeNs(name.ident().name),
1743 let (name, kind) = match name {
1744 hir::LifetimeName::Underscore => (
1745 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1746 hir::LifetimeParamKind::Elided,
1748 hir::LifetimeName::Param(param_name) => {
1749 (param_name, hir::LifetimeParamKind::Explicit)
1751 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1753 let name = match name {
1754 hir::ParamName::Plain(ident) => {
1755 hir::ParamName::Plain(self.context.lower_ident(ident))
1760 self.output_lifetime_params.push(hir::GenericParam {
1763 span: self.context.lower_span(lifetime.span),
1764 pure_wrt_drop: false,
1766 kind: hir::GenericParamKind::Lifetime { kind },
1772 let mut lifetime_collector = ImplTraitLifetimeCollector {
1774 parent: parent_def_id,
1776 collect_elided_lifetimes: true,
1777 currently_bound_lifetimes: Vec::new(),
1778 already_defined_lifetimes: FxHashSet::default(),
1779 output_lifetimes: Vec::new(),
1780 output_lifetime_params: Vec::new(),
1781 lifetimes_to_include,
1784 for bound in bounds {
1785 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1788 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1792 self.arena.alloc_from_iter(output_lifetimes),
1793 self.arena.alloc_from_iter(output_lifetime_params),
1797 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1798 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1799 // as they are not explicit in HIR/Ty function signatures.
1800 // (instead, the `c_variadic` flag is set to `true`)
1801 let mut inputs = &decl.inputs[..];
1802 if decl.c_variadic() {
1803 inputs = &inputs[..inputs.len() - 1];
1805 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1806 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1807 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1811 // Lowers a function declaration.
1813 // `decl`: the unlowered (AST) function declaration.
1814 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1815 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1816 // `make_ret_async` is also `Some`.
1817 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1818 // This guards against trait declarations and implementations where `impl Trait` is
1820 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1821 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1822 // return type `impl Trait` item.
1826 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1827 impl_trait_return_allow: bool,
1828 make_ret_async: Option<NodeId>,
1829 ) -> &'hir hir::FnDecl<'hir> {
1833 in_band_ty_params: {:?}, \
1834 impl_trait_return_allow: {}, \
1835 make_ret_async: {:?})",
1836 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1838 let lt_mode = if make_ret_async.is_some() {
1839 // In `async fn`, argument-position elided lifetimes
1840 // must be transformed into fresh generic parameters so that
1841 // they can be applied to the opaque `impl Trait` return type.
1842 AnonymousLifetimeMode::CreateParameter
1844 self.anonymous_lifetime_mode
1847 let c_variadic = decl.c_variadic();
1849 // Remember how many lifetimes were already around so that we can
1850 // only look at the lifetime parameters introduced by the arguments.
1851 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1852 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1853 // as they are not explicit in HIR/Ty function signatures.
1854 // (instead, the `c_variadic` flag is set to `true`)
1855 let mut inputs = &decl.inputs[..];
1857 inputs = &inputs[..inputs.len() - 1];
1859 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1860 if let Some((_, ibty)) = &mut in_band_ty_params {
1861 this.lower_ty_direct(
1863 ImplTraitContext::Universal(ibty, this.current_hir_id_owner.0),
1866 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1871 let output = if let Some(ret_id) = make_ret_async {
1872 self.lower_async_fn_ret_ty(
1874 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1879 FnRetTy::Ty(ref ty) => {
1880 let context = match in_band_ty_params {
1881 Some((def_id, _)) if impl_trait_return_allow => {
1882 ImplTraitContext::ReturnPositionOpaqueTy {
1884 origin: hir::OpaqueTyOrigin::FnReturn,
1887 _ => ImplTraitContext::disallowed(),
1889 hir::FnRetTy::Return(self.lower_ty(ty, context))
1891 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1895 self.arena.alloc(hir::FnDecl {
1899 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1900 use BindingMode::{ByRef, ByValue};
1901 let is_mutable_pat = matches!(
1903 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1907 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1908 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1909 // Given we are only considering `ImplicitSelf` types, we needn't consider
1910 // the case where we have a mutable pattern to a reference as that would
1911 // no longer be an `ImplicitSelf`.
1912 TyKind::Rptr(_, ref mt)
1913 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1915 hir::ImplicitSelfKind::MutRef
1917 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1918 hir::ImplicitSelfKind::ImmRef
1920 _ => hir::ImplicitSelfKind::None,
1926 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1927 // combined with the following definition of `OpaqueTy`:
1929 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1931 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1932 // `output`: unlowered output type (`T` in `-> T`)
1933 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1934 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1935 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1936 fn lower_async_fn_ret_ty(
1940 opaque_ty_node_id: NodeId,
1941 ) -> hir::FnRetTy<'hir> {
1943 "lower_async_fn_ret_ty(\
1946 opaque_ty_node_id={:?})",
1947 output, fn_def_id, opaque_ty_node_id,
1950 let span = output.span();
1952 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1954 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1956 self.allocate_hir_id_counter(opaque_ty_node_id);
1958 // When we create the opaque type for this async fn, it is going to have
1959 // to capture all the lifetimes involved in the signature (including in the
1960 // return type). This is done by introducing lifetime parameters for:
1962 // - all the explicitly declared lifetimes from the impl and function itself;
1963 // - all the elided lifetimes in the fn arguments;
1964 // - all the elided lifetimes in the return type.
1966 // So for example in this snippet:
1969 // impl<'a> Foo<'a> {
1970 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1971 // // ^ '0 ^ '1 ^ '2
1972 // // elided lifetimes used below
1977 // we would create an opaque type like:
1980 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1983 // and we would then desugar `bar` to the equivalent of:
1986 // impl<'a> Foo<'a> {
1987 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1991 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1992 // this is because the elided lifetimes from the return type
1993 // should be figured out using the ordinary elision rules, and
1994 // this desugaring achieves that.
1996 // The variable `input_lifetimes_count` tracks the number of
1997 // lifetime parameters to the opaque type *not counting* those
1998 // lifetimes elided in the return type. This includes those
1999 // that are explicitly declared (`in_scope_lifetimes`) and
2000 // those elided lifetimes we found in the arguments (current
2001 // content of `lifetimes_to_define`). Next, we will process
2002 // the return type, which will cause `lifetimes_to_define` to
2004 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2006 let lifetime_params = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2007 // We have to be careful to get elision right here. The
2008 // idea is that we create a lifetime parameter for each
2009 // lifetime in the return type. So, given a return type
2010 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2011 // Future<Output = &'1 [ &'2 u32 ]>`.
2013 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2014 // hence the elision takes place at the fn site.
2015 let future_bound = this
2016 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2017 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2020 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2022 // Calculate all the lifetimes that should be captured
2023 // by the opaque type. This should include all in-scope
2024 // lifetime parameters, including those defined in-band.
2026 // Note: this must be done after lowering the output type,
2027 // as the output type may introduce new in-band lifetimes.
2028 let lifetime_params: Vec<(Span, ParamName)> = this
2032 .map(|name| (name.ident().span, name))
2033 .chain(this.lifetimes_to_define.iter().cloned())
2036 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2037 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2038 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2040 let generic_params =
2041 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2042 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2045 let opaque_ty_item = hir::OpaqueTy {
2046 generics: hir::Generics {
2047 params: generic_params,
2048 where_clause: hir::WhereClause { predicates: &[], span: this.lower_span(span) },
2049 span: this.lower_span(span),
2051 bounds: arena_vec![this; future_bound],
2052 impl_trait_fn: Some(fn_def_id),
2053 origin: hir::OpaqueTyOrigin::AsyncFn,
2056 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2057 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
2062 // As documented above on the variable
2063 // `input_lifetimes_count`, we need to create the lifetime
2064 // arguments to our opaque type. Continuing with our example,
2065 // we're creating the type arguments for the return type:
2068 // Bar<'a, 'b, '0, '1, '_>
2071 // For the "input" lifetime parameters, we wish to create
2072 // references to the parameters themselves, including the
2073 // "implicit" ones created from parameter types (`'a`, `'b`,
2076 // For the "output" lifetime parameters, we just want to
2078 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2079 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2080 |&(span, hir_name)| {
2081 // Input lifetime like `'a` or `'1`:
2082 GenericArg::Lifetime(hir::Lifetime {
2083 hir_id: self.next_id(),
2084 span: self.lower_span(span),
2085 name: hir::LifetimeName::Param(hir_name),
2089 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2090 // Output lifetime like `'_`.
2091 GenericArg::Lifetime(hir::Lifetime {
2092 hir_id: self.next_id(),
2093 span: self.lower_span(span),
2094 name: hir::LifetimeName::Implicit,
2096 let generic_args = self.arena.alloc_from_iter(generic_args);
2098 // Create the `Foo<...>` reference itself. Note that the `type
2099 // Foo = impl Trait` is, internally, created as a child of the
2100 // async fn, so the *type parameters* are inherited. It's
2101 // only the lifetime parameters that we must supply.
2103 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
2104 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2105 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2108 /// Transforms `-> T` into `Future<Output = T>`.
2109 fn lower_async_fn_output_type_to_future_bound(
2114 ) -> hir::GenericBound<'hir> {
2115 // Compute the `T` in `Future<Output = T>` from the return type.
2116 let output_ty = match output {
2117 FnRetTy::Ty(ty) => {
2118 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2119 // `impl Future` opaque type that `async fn` implicitly
2121 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2123 origin: hir::OpaqueTyOrigin::FnReturn,
2125 self.lower_ty(ty, context)
2127 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2131 let future_args = self.arena.alloc(hir::GenericArgs {
2133 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2134 parenthesized: false,
2138 hir::GenericBound::LangItemTrait(
2139 // ::std::future::Future<future_params>
2140 hir::LangItem::Future,
2141 self.lower_span(span),
2147 fn lower_param_bound(
2150 itctx: ImplTraitContext<'_, 'hir>,
2151 ) -> hir::GenericBound<'hir> {
2153 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2154 self.lower_poly_trait_ref(p, itctx),
2155 self.lower_trait_bound_modifier(*modifier),
2157 GenericBound::Outlives(lifetime) => {
2158 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2163 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2164 let span = self.lower_span(l.ident.span);
2166 ident if ident.name == kw::StaticLifetime => {
2167 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2169 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2170 AnonymousLifetimeMode::CreateParameter => {
2171 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2172 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2175 AnonymousLifetimeMode::PassThrough => {
2176 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2179 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2182 self.maybe_collect_in_band_lifetime(ident);
2183 let param_name = ParamName::Plain(self.lower_ident(ident));
2184 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2189 fn new_named_lifetime(
2193 name: hir::LifetimeName,
2194 ) -> hir::Lifetime {
2195 hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
2198 fn lower_generic_params_mut<'s>(
2200 params: &'s [GenericParam],
2201 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2202 mut itctx: ImplTraitContext<'s, 'hir>,
2203 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2206 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2209 fn lower_generic_params(
2211 params: &[GenericParam],
2212 add_bounds: &NodeMap<Vec<GenericBound>>,
2213 itctx: ImplTraitContext<'_, 'hir>,
2214 ) -> &'hir [hir::GenericParam<'hir>] {
2215 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2218 fn lower_generic_param(
2220 param: &GenericParam,
2221 add_bounds: &NodeMap<Vec<GenericBound>>,
2222 mut itctx: ImplTraitContext<'_, 'hir>,
2223 ) -> hir::GenericParam<'hir> {
2224 let mut bounds: Vec<_> = self
2225 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2226 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2229 let (name, kind) = match param.kind {
2230 GenericParamKind::Lifetime => {
2231 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2232 self.is_collecting_in_band_lifetimes = false;
2235 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2236 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2238 let param_name = match lt.name {
2239 hir::LifetimeName::Param(param_name) => param_name,
2240 hir::LifetimeName::Implicit
2241 | hir::LifetimeName::Underscore
2242 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2243 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2244 self.sess.diagnostic().span_bug(
2246 "object-lifetime-default should not occur here",
2249 hir::LifetimeName::Error => ParamName::Error,
2253 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2255 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2259 GenericParamKind::Type { ref default, .. } => {
2260 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2261 if !add_bounds.is_empty() {
2262 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2263 bounds.extend(params);
2266 let kind = hir::GenericParamKind::Type {
2267 default: default.as_ref().map(|x| {
2268 self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Other))
2273 .filter(|attr| attr.has_name(sym::rustc_synthetic))
2274 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2278 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2280 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2282 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2283 this.lower_ty(&ty, ImplTraitContext::disallowed())
2285 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2287 hir::ParamName::Plain(self.lower_ident(param.ident)),
2288 hir::GenericParamKind::Const { ty, default },
2292 let name = match name {
2293 hir::ParamName::Plain(ident) => hir::ParamName::Plain(self.lower_ident(ident)),
2297 let hir_id = self.lower_node_id(param.id);
2298 self.lower_attrs(hir_id, ¶m.attrs);
2302 span: self.lower_span(param.ident.span),
2303 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2304 bounds: self.arena.alloc_from_iter(bounds),
2312 itctx: ImplTraitContext<'_, 'hir>,
2313 ) -> hir::TraitRef<'hir> {
2314 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2315 hir::QPath::Resolved(None, path) => path,
2316 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2318 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2321 fn lower_poly_trait_ref(
2324 mut itctx: ImplTraitContext<'_, 'hir>,
2325 ) -> hir::PolyTraitRef<'hir> {
2326 let bound_generic_params = self.lower_generic_params(
2327 &p.bound_generic_params,
2328 &NodeMap::default(),
2332 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2333 // Any impl Trait types defined within this scope can capture
2334 // lifetimes bound on this predicate.
2335 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2336 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2337 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2341 if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
2344 capturable_lifetimes.extend(lt_def_names.clone());
2347 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2349 if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
2352 for param in lt_def_names {
2353 capturable_lifetimes.remove(¶m);
2359 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2362 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2363 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2366 fn lower_param_bounds(
2368 bounds: &[GenericBound],
2369 itctx: ImplTraitContext<'_, 'hir>,
2370 ) -> hir::GenericBounds<'hir> {
2371 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2374 fn lower_param_bounds_mut<'s>(
2376 bounds: &'s [GenericBound],
2377 mut itctx: ImplTraitContext<'s, 'hir>,
2378 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2379 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2382 /// Lowers a block directly to an expression, presuming that it
2383 /// has no attributes and is not targeted by a `break`.
2384 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2385 let block = self.lower_block(b, false);
2386 self.expr_block(block, AttrVec::new())
2389 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2390 self.with_new_scopes(|this| hir::AnonConst {
2391 hir_id: this.lower_node_id(c.id),
2392 body: this.lower_const_body(c.value.span, Some(&c.value)),
2396 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2398 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2399 UserProvided => hir::UnsafeSource::UserProvided,
2403 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2405 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2406 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2408 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2409 // placeholder for compilation to proceed.
2410 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2411 hir::TraitBoundModifier::Maybe
2416 // Helper methods for building HIR.
2418 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2419 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2422 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2423 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2428 attrs: Option<&'hir [Attribute]>,
2430 init: Option<&'hir hir::Expr<'hir>>,
2431 pat: &'hir hir::Pat<'hir>,
2432 source: hir::LocalSource,
2433 ) -> hir::Stmt<'hir> {
2434 let hir_id = self.next_id();
2435 if let Some(a) = attrs {
2436 debug_assert!(!a.is_empty());
2437 self.attrs.insert(hir_id, a);
2439 let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
2440 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2443 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2444 self.block_all(expr.span, &[], Some(expr))
2450 stmts: &'hir [hir::Stmt<'hir>],
2451 expr: Option<&'hir hir::Expr<'hir>>,
2452 ) -> &'hir hir::Block<'hir> {
2453 let blk = hir::Block {
2456 hir_id: self.next_id(),
2457 rules: hir::BlockCheckMode::DefaultBlock,
2458 span: self.lower_span(span),
2459 targeted_by_break: false,
2461 self.arena.alloc(blk)
2464 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2465 let field = self.single_pat_field(span, pat);
2466 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field)
2469 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2470 let field = self.single_pat_field(span, pat);
2471 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field)
2474 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2475 let field = self.single_pat_field(span, pat);
2476 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2479 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2480 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2483 fn single_pat_field(
2486 pat: &'hir hir::Pat<'hir>,
2487 ) -> &'hir [hir::PatField<'hir>] {
2488 let field = hir::PatField {
2489 hir_id: self.next_id(),
2490 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2491 is_shorthand: false,
2493 span: self.lower_span(span),
2495 arena_vec![self; field]
2498 fn pat_lang_item_variant(
2501 lang_item: hir::LangItem,
2502 fields: &'hir [hir::PatField<'hir>],
2503 ) -> &'hir hir::Pat<'hir> {
2504 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span));
2505 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2508 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2509 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2512 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2513 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::Unannotated)
2516 fn pat_ident_binding_mode(
2520 bm: hir::BindingAnnotation,
2521 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2522 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2523 (self.arena.alloc(pat), hir_id)
2526 fn pat_ident_binding_mode_mut(
2530 bm: hir::BindingAnnotation,
2531 ) -> (hir::Pat<'hir>, hir::HirId) {
2532 let hir_id = self.next_id();
2537 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2538 span: self.lower_span(span),
2539 default_binding_modes: true,
2545 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2546 self.arena.alloc(hir::Pat {
2547 hir_id: self.next_id(),
2549 span: self.lower_span(span),
2550 default_binding_modes: true,
2554 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2556 hir_id: self.next_id(),
2558 span: self.lower_span(span),
2559 default_binding_modes: false,
2565 mut hir_id: hir::HirId,
2567 qpath: hir::QPath<'hir>,
2568 ) -> hir::Ty<'hir> {
2569 let kind = match qpath {
2570 hir::QPath::Resolved(None, path) => {
2571 // Turn trait object paths into `TyKind::TraitObject` instead.
2573 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2574 let principal = hir::PolyTraitRef {
2575 bound_generic_params: &[],
2576 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2577 span: self.lower_span(span),
2580 // The original ID is taken by the `PolyTraitRef`,
2581 // so the `Ty` itself needs a different one.
2582 hir_id = self.next_id();
2583 hir::TyKind::TraitObject(
2584 arena_vec![self; principal],
2585 self.elided_dyn_bound(span),
2586 TraitObjectSyntax::None,
2589 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2592 _ => hir::TyKind::Path(qpath),
2595 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2598 /// Invoked to create the lifetime argument for a type `&T`
2599 /// with no explicit lifetime.
2600 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2601 match self.anonymous_lifetime_mode {
2602 // Intercept when we are in an impl header or async fn and introduce an in-band
2604 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2606 AnonymousLifetimeMode::CreateParameter => {
2607 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2609 hir_id: self.next_id(),
2610 span: self.lower_span(span),
2611 name: hir::LifetimeName::Param(fresh_name),
2615 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2617 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2621 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2622 /// return an "error lifetime".
2623 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2624 let (id, msg, label) = match id {
2625 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2628 self.resolver.next_node_id(),
2629 "`&` without an explicit lifetime name cannot be used here",
2630 "explicit lifetime name needed here",
2634 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2635 err.span_label(span, label);
2638 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2641 /// Invoked to create the lifetime argument(s) for a path like
2642 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2643 /// sorts of cases are deprecated. This may therefore report a warning or an
2644 /// error, depending on the mode.
2645 fn elided_path_lifetimes<'s>(
2649 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2650 (0..count).map(move |_| self.elided_path_lifetime(span))
2653 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2654 match self.anonymous_lifetime_mode {
2655 AnonymousLifetimeMode::CreateParameter => {
2656 // We should have emitted E0726 when processing this path above
2658 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2659 let id = self.resolver.next_node_id();
2660 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2662 // `PassThrough` is the normal case.
2663 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2664 // is unsuitable here, as these can occur from missing lifetime parameters in a
2665 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2666 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2667 // later, at which point a suitable error will be emitted.
2668 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2669 self.new_implicit_lifetime(span)
2674 /// Invoked to create the lifetime argument(s) for an elided trait object
2675 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2676 /// when the bound is written, even if it is written with `'_` like in
2677 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2678 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2679 match self.anonymous_lifetime_mode {
2680 // NB. We intentionally ignore the create-parameter mode here.
2681 // and instead "pass through" to resolve-lifetimes, which will apply
2682 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2683 // do not act like other elided lifetimes. In other words, given this:
2685 // impl Foo for Box<dyn Debug>
2687 // we do not introduce a fresh `'_` to serve as the bound, but instead
2688 // ultimately translate to the equivalent of:
2690 // impl Foo for Box<dyn Debug + 'static>
2692 // `resolve_lifetime` has the code to make that happen.
2693 AnonymousLifetimeMode::CreateParameter => {}
2695 AnonymousLifetimeMode::ReportError => {
2696 // ReportError applies to explicit use of `'_`.
2699 // This is the normal case.
2700 AnonymousLifetimeMode::PassThrough => {}
2703 let r = hir::Lifetime {
2704 hir_id: self.next_id(),
2705 span: self.lower_span(span),
2706 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2708 debug!("elided_dyn_bound: r={:?}", r);
2712 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2714 hir_id: self.next_id(),
2715 span: self.lower_span(span),
2716 name: hir::LifetimeName::Implicit,
2720 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2721 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2722 // call site which do not have a macro backtrace. See #61963.
2723 let is_macro_callsite = self
2726 .span_to_snippet(span)
2727 .map(|snippet| snippet.starts_with("#["))
2729 if !is_macro_callsite {
2730 if span.edition() < Edition::Edition2021 {
2731 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2735 "trait objects without an explicit `dyn` are deprecated",
2736 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2739 let msg = "trait objects must include the `dyn` keyword";
2740 let label = "add `dyn` keyword before this trait";
2741 let mut err = struct_span_err!(self.sess, span, E0782, "{}", msg,);
2742 err.span_suggestion_verbose(
2743 span.shrink_to_lo(),
2745 String::from("dyn "),
2746 Applicability::MachineApplicable,
2753 fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId, default: Abi) {
2754 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2755 // call site which do not have a macro backtrace. See #61963.
2756 let is_macro_callsite = self
2759 .span_to_snippet(span)
2760 .map(|snippet| snippet.starts_with("#["))
2762 if !is_macro_callsite {
2763 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2767 "extern declarations without an explicit ABI are deprecated",
2768 BuiltinLintDiagnostics::MissingAbi(span, default),
2774 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2775 // Sorting by span ensures that we get things in order within a
2776 // file, and also puts the files in a sensible order.
2777 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2778 body_ids.sort_by_key(|b| bodies[b].value.span);
2782 /// Helper struct for delayed construction of GenericArgs.
2783 struct GenericArgsCtor<'hir> {
2784 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2785 bindings: &'hir [hir::TypeBinding<'hir>],
2786 parenthesized: bool,
2790 impl<'hir> GenericArgsCtor<'hir> {
2791 fn is_empty(&self) -> bool {
2792 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2795 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2796 let ga = hir::GenericArgs {
2797 args: this.arena.alloc_from_iter(self.args),
2798 bindings: self.bindings,
2799 parenthesized: self.parenthesized,
2800 span_ext: this.lower_span(self.span),
2802 this.arena.alloc(ga)