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), then you 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(array_value_iter)]
34 #![feature(crate_visibility_modifier)]
35 #![feature(or_patterns)]
36 #![recursion_limit = "256"]
38 use rustc_ast::node_id::NodeMap;
39 use rustc_ast::token::{self, DelimToken, Nonterminal, Token};
40 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, DelimSpan, 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::FxHashSet;
47 use rustc_data_structures::sync::Lrc;
48 use rustc_errors::struct_span_err;
50 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
51 use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX};
52 use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
53 use rustc_hir::intravisit;
54 use rustc_hir::{ConstArg, GenericArg, ParamName};
55 use rustc_index::vec::{Idx, IndexVec};
56 use rustc_session::lint::{builtin::BARE_TRAIT_OBJECTS, BuiltinLintDiagnostics, LintBuffer};
57 use rustc_session::parse::ParseSess;
58 use rustc_session::Session;
59 use rustc_span::hygiene::ExpnId;
60 use rustc_span::source_map::{respan, DesugaringKind};
61 use rustc_span::symbol::{kw, sym, Ident, Symbol};
64 use smallvec::{smallvec, SmallVec};
65 use std::collections::BTreeMap;
67 use tracing::{debug, trace};
69 macro_rules! arena_vec {
70 ($this:expr; $($x:expr),*) => ({
72 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
81 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
83 rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx);
85 struct LoweringContext<'a, 'hir: 'a> {
86 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
89 resolver: &'a mut dyn ResolverAstLowering,
91 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
92 /// if we don't have this function pointer. To avoid that dependency so that
93 /// librustc_middle is independent of the parser, we use dynamic dispatch here.
94 nt_to_tokenstream: NtToTokenstream,
96 /// Used to allocate HIR nodes
97 arena: &'hir Arena<'hir>,
99 /// The items being lowered are collected here.
100 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
102 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
103 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
104 foreign_items: BTreeMap<hir::ForeignItemId, hir::ForeignItem<'hir>>,
105 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
106 exported_macros: Vec<hir::MacroDef<'hir>>,
107 non_exported_macro_attrs: Vec<ast::Attribute>,
109 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
111 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
113 generator_kind: Option<hir::GeneratorKind>,
115 /// When inside an `async` context, this is the `HirId` of the
116 /// `task_context` local bound to the resume argument of the generator.
117 task_context: Option<hir::HirId>,
119 /// Used to get the current `fn`'s def span to point to when using `await`
120 /// outside of an `async fn`.
121 current_item: Option<Span>,
123 catch_scopes: Vec<NodeId>,
124 loop_scopes: Vec<NodeId>,
125 is_in_loop_condition: bool,
126 is_in_trait_impl: bool,
127 is_in_dyn_type: bool,
129 /// What to do when we encounter either an "anonymous lifetime
130 /// reference". The term "anonymous" is meant to encompass both
131 /// `'_` lifetimes as well as fully elided cases where nothing is
132 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
133 anonymous_lifetime_mode: AnonymousLifetimeMode,
135 /// Used to create lifetime definitions from in-band lifetime usages.
136 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
137 /// When a named lifetime is encountered in a function or impl header and
138 /// has not been defined
139 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
140 /// to this list. The results of this list are then added to the list of
141 /// lifetime definitions in the corresponding impl or function generics.
142 lifetimes_to_define: Vec<(Span, ParamName)>,
144 /// `true` if in-band lifetimes are being collected. This is used to
145 /// indicate whether or not we're in a place where new lifetimes will result
146 /// in in-band lifetime definitions, such a function or an impl header,
147 /// including implicit lifetimes from `impl_header_lifetime_elision`.
148 is_collecting_in_band_lifetimes: bool,
150 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
151 /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
152 /// against this list to see if it is already in-scope, or if a definition
153 /// needs to be created for it.
155 /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
157 in_scope_lifetimes: Vec<ParamName>,
159 current_module: hir::HirId,
161 type_def_lifetime_params: DefIdMap<usize>,
163 current_hir_id_owner: Vec<(LocalDefId, u32)>,
164 item_local_id_counters: NodeMap<u32>,
165 node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
167 allow_try_trait: Option<Lrc<[Symbol]>>,
168 allow_gen_future: Option<Lrc<[Symbol]>>,
171 pub trait ResolverAstLowering {
172 fn def_key(&mut self, id: DefId) -> DefKey;
174 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
176 /// Obtains resolution for a `NodeId` with a single resolution.
177 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
179 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
180 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
182 /// Obtains resolution for a label with the given `NodeId`.
183 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
185 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
186 /// This should only return `None` during testing.
187 fn definitions(&mut self) -> &mut Definitions;
189 fn lint_buffer(&mut self) -> &mut LintBuffer;
191 fn next_node_id(&mut self) -> NodeId;
193 fn trait_map(&self) -> &NodeMap<Vec<hir::TraitCandidate>>;
195 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
197 fn local_def_id(&self, node: NodeId) -> LocalDefId;
202 node_id: ast::NodeId,
209 type NtToTokenstream =
210 fn(&Nonterminal, &ParseSess, Span, CanSynthesizeMissingTokens) -> TokenStream;
212 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
213 /// and if so, what meaning it has.
215 enum ImplTraitContext<'b, 'a> {
216 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
217 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
218 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
220 /// Newly generated parameters should be inserted into the given `Vec`.
221 Universal(&'b mut Vec<hir::GenericParam<'a>>),
223 /// Treat `impl Trait` as shorthand for a new opaque type.
224 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
225 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
227 ReturnPositionOpaqueTy {
228 /// `DefId` for the parent function, used to look up necessary
229 /// information later.
231 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
232 origin: hir::OpaqueTyOrigin,
234 /// Impl trait in type aliases, consts and statics.
236 /// Set of lifetimes that this opaque type can capture, if it uses
237 /// them. This includes lifetimes bound since we entered this context.
240 /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
242 /// the inner opaque type captures `'a` because it uses it. It doesn't
243 /// need to capture `'b` because it already inherits the lifetime
244 /// parameter from `A`.
245 // FIXME(impl_trait): but `required_region_bounds` will ICE later
247 capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
248 /// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding,
249 origin: hir::OpaqueTyOrigin,
251 /// `impl Trait` is not accepted in this position.
252 Disallowed(ImplTraitPosition),
255 /// Position in which `impl Trait` is disallowed.
256 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
257 enum ImplTraitPosition {
258 /// Disallowed in `let` / `const` / `static` bindings.
261 /// All other positions.
265 impl<'a> ImplTraitContext<'_, 'a> {
267 fn disallowed() -> Self {
268 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
271 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
272 use self::ImplTraitContext::*;
274 Universal(params) => Universal(params),
275 ReturnPositionOpaqueTy { fn_def_id, origin } => {
276 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
278 OtherOpaqueTy { capturable_lifetimes, origin } => {
279 OtherOpaqueTy { capturable_lifetimes, origin: *origin }
281 Disallowed(pos) => Disallowed(*pos),
286 pub fn lower_crate<'a, 'hir>(
289 resolver: &'a mut dyn ResolverAstLowering,
290 nt_to_tokenstream: NtToTokenstream,
291 arena: &'hir Arena<'hir>,
292 ) -> hir::Crate<'hir> {
293 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
300 items: BTreeMap::new(),
301 trait_items: BTreeMap::new(),
302 impl_items: BTreeMap::new(),
303 foreign_items: BTreeMap::new(),
304 bodies: BTreeMap::new(),
305 trait_impls: BTreeMap::new(),
306 modules: BTreeMap::new(),
307 exported_macros: Vec::new(),
308 non_exported_macro_attrs: Vec::new(),
309 catch_scopes: Vec::new(),
310 loop_scopes: Vec::new(),
311 is_in_loop_condition: false,
312 is_in_trait_impl: false,
313 is_in_dyn_type: false,
314 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
315 type_def_lifetime_params: Default::default(),
316 current_module: hir::CRATE_HIR_ID,
317 current_hir_id_owner: vec![(LocalDefId { local_def_index: CRATE_DEF_INDEX }, 0)],
318 item_local_id_counters: Default::default(),
319 node_id_to_hir_id: IndexVec::new(),
320 generator_kind: None,
323 lifetimes_to_define: Vec::new(),
324 is_collecting_in_band_lifetimes: false,
325 in_scope_lifetimes: Vec::new(),
326 allow_try_trait: Some([sym::try_trait][..].into()),
327 allow_gen_future: Some([sym::gen_future][..].into()),
332 #[derive(Copy, Clone, PartialEq)]
334 /// Any path in a type context.
336 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
338 /// The `module::Type` in `module::Type::method` in an expression.
342 enum ParenthesizedGenericArgs {
347 /// What to do when we encounter an **anonymous** lifetime
348 /// reference. Anonymous lifetime references come in two flavors. You
349 /// have implicit, or fully elided, references to lifetimes, like the
350 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
351 /// or `Ref<'_, T>`. These often behave the same, but not always:
353 /// - certain usages of implicit references are deprecated, like
354 /// `Ref<T>`, and we sometimes just give hard errors in those cases
356 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
357 /// the same as `Box<dyn Foo + '_>`.
359 /// We describe the effects of the various modes in terms of three cases:
361 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
362 /// of a `&` (e.g., the missing lifetime in something like `&T`)
363 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
364 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
365 /// elided bounds follow special rules. Note that this only covers
366 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
367 /// '_>` is a case of "modern" elision.
368 /// - **Deprecated** -- this covers cases like `Ref<T>`, where the lifetime
369 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
370 /// non-deprecated equivalent.
372 /// Currently, the handling of lifetime elision is somewhat spread out
373 /// between HIR lowering and -- as described below -- the
374 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
375 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
376 /// everything into HIR lowering.
377 #[derive(Copy, Clone, Debug)]
378 enum AnonymousLifetimeMode {
379 /// For **Modern** cases, create a new anonymous region parameter
380 /// and reference that.
382 /// For **Dyn Bound** cases, pass responsibility to
383 /// `resolve_lifetime` code.
385 /// For **Deprecated** cases, report an error.
388 /// Give a hard error when either `&` or `'_` is written. Used to
389 /// rule out things like `where T: Foo<'_>`. Does not imply an
390 /// error on default object bounds (e.g., `Box<dyn Foo>`).
393 /// Pass responsibility to `resolve_lifetime` code for all cases.
397 struct TokenStreamLowering<'a> {
398 parse_sess: &'a ParseSess,
399 synthesize_tokens: CanSynthesizeMissingTokens,
400 nt_to_tokenstream: NtToTokenstream,
403 impl<'a> TokenStreamLowering<'a> {
404 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
405 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
408 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
410 TokenTree::Token(token) => self.lower_token(token),
411 TokenTree::Delimited(span, delim, tts) => {
412 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
417 fn lower_token(&mut self, token: Token) -> TokenStream {
419 token::Interpolated(nt) => {
420 let tts = (self.nt_to_tokenstream)(
424 self.synthesize_tokens,
426 TokenTree::Delimited(
427 DelimSpan::from_single(token.span),
429 self.lower_token_stream(tts),
433 _ => TokenTree::Token(token).into(),
438 struct ImplTraitTypeIdVisitor<'a> {
439 ids: &'a mut SmallVec<[NodeId; 1]>,
442 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
443 fn visit_ty(&mut self, ty: &Ty) {
445 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
447 TyKind::ImplTrait(id, _) => self.ids.push(id),
450 visit::walk_ty(self, ty);
453 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
454 if let Some(ref p) = path_segment.args {
455 if let GenericArgs::Parenthesized(_) = **p {
459 visit::walk_path_segment(self, path_span, path_segment)
463 impl<'a, 'hir> LoweringContext<'a, 'hir> {
464 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
465 /// Full-crate AST visitor that inserts into a fresh
466 /// `LoweringContext` any information that may be
467 /// needed from arbitrary locations in the crate,
468 /// e.g., the number of lifetime generic parameters
469 /// declared for every type and trait definition.
470 struct MiscCollector<'tcx, 'lowering, 'hir> {
471 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
474 impl MiscCollector<'_, '_, '_> {
475 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: LocalDefId) {
477 UseTreeKind::Simple(_, id1, id2) => {
478 for &id in &[id1, id2] {
479 self.lctx.resolver.create_def(
486 self.lctx.allocate_hir_id_counter(id);
489 UseTreeKind::Glob => (),
490 UseTreeKind::Nested(ref trees) => {
491 for &(ref use_tree, id) in trees {
492 let hir_id = self.lctx.allocate_hir_id_counter(id);
493 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
500 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
501 fn visit_item(&mut self, item: &'tcx Item) {
502 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
505 ItemKind::Struct(_, ref generics)
506 | ItemKind::Union(_, ref generics)
507 | ItemKind::Enum(_, ref generics)
508 | ItemKind::TyAlias(_, ref generics, ..)
509 | ItemKind::Trait(_, _, ref generics, ..) => {
510 let def_id = self.lctx.resolver.local_def_id(item.id);
514 .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime { .. }))
516 self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
518 ItemKind::Use(ref use_tree) => {
519 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
524 visit::walk_item(self, item);
527 fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
528 self.lctx.allocate_hir_id_counter(item.id);
529 visit::walk_assoc_item(self, item, ctxt);
532 fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
533 self.lctx.allocate_hir_id_counter(item.id);
534 visit::walk_foreign_item(self, item);
537 fn visit_ty(&mut self, t: &'tcx Ty) {
539 // Mirrors the case in visit::walk_ty
540 TyKind::BareFn(ref f) => {
541 walk_list!(self, visit_generic_param, &f.generic_params);
542 // Mirrors visit::walk_fn_decl
543 for parameter in &f.decl.inputs {
544 // We don't lower the ids of argument patterns
545 self.visit_pat(¶meter.pat);
546 self.visit_ty(¶meter.ty)
548 self.visit_fn_ret_ty(&f.decl.output)
550 TyKind::ImplTrait(def_node_id, _) => {
551 self.lctx.allocate_hir_id_counter(def_node_id);
552 visit::walk_ty(self, t);
554 _ => visit::walk_ty(self, t),
559 self.lower_node_id(CRATE_NODE_ID);
560 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
562 visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
563 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
565 let module = self.lower_mod(&c.module);
566 let attrs = self.lower_attrs(&c.attrs);
567 let body_ids = body_ids(&self.bodies);
569 c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
575 .filter_map(|(&k, v)| {
576 self.node_id_to_hir_id.get(k).and_then(|id| id.as_ref()).map(|id| (*id, v.clone()))
580 let mut def_id_to_hir_id = IndexVec::default();
582 for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
583 if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
584 if def_id_to_hir_id.len() <= def_id.index() {
585 def_id_to_hir_id.resize(def_id.index() + 1, None);
587 def_id_to_hir_id[def_id] = hir_id;
591 self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
594 item: hir::CrateItem { module, attrs, span: c.span },
595 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
596 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
598 trait_items: self.trait_items,
599 impl_items: self.impl_items,
600 foreign_items: self.foreign_items,
603 trait_impls: self.trait_impls,
604 modules: self.modules,
610 fn insert_item(&mut self, item: hir::Item<'hir>) {
611 let id = item.hir_id;
612 // FIXME: Use `debug_asset-rt`.
613 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
614 self.items.insert(id, item);
615 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
618 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
619 // Set up the counter if needed.
620 self.item_local_id_counters.entry(owner).or_insert(0);
621 // Always allocate the first `HirId` for the owner itself.
622 let lowered = self.lower_node_id_with_owner(owner, owner);
623 debug_assert_eq!(lowered.local_id.as_u32(), 0);
627 fn lower_node_id_generic(
630 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
632 assert_ne!(ast_node_id, DUMMY_NODE_ID);
634 let min_size = ast_node_id.as_usize() + 1;
636 if min_size > self.node_id_to_hir_id.len() {
637 self.node_id_to_hir_id.resize(min_size, None);
640 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
643 // Generate a new `HirId`.
644 let hir_id = alloc_hir_id(self);
645 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
651 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
653 .item_local_id_counters
654 .insert(owner, HIR_ID_COUNTER_LOCKED)
655 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
656 let def_id = self.resolver.local_def_id(owner);
657 self.current_hir_id_owner.push((def_id, counter));
659 let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap();
661 debug_assert!(def_id == new_def_id);
662 debug_assert!(new_counter >= counter);
664 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
665 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
669 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
670 /// the `LoweringContext`'s `NodeId => HirId` map.
671 /// Take care not to call this method if the resulting `HirId` is then not
672 /// actually used in the HIR, as that would trigger an assertion in the
673 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
674 /// properly. Calling the method twice with the same `NodeId` is fine though.
675 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
676 self.lower_node_id_generic(ast_node_id, |this| {
677 let &mut (owner, ref mut local_id_counter) =
678 this.current_hir_id_owner.last_mut().unwrap();
679 let local_id = *local_id_counter;
680 *local_id_counter += 1;
681 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
685 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
686 self.lower_node_id_generic(ast_node_id, |this| {
687 let local_id_counter = this
688 .item_local_id_counters
690 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
691 let local_id = *local_id_counter;
693 // We want to be sure not to modify the counter in the map while it
694 // is also on the stack. Otherwise we'll get lost updates when writing
695 // back from the stack to the map.
696 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
698 *local_id_counter += 1;
699 let owner = this.resolver.opt_local_def_id(owner).expect(
700 "you forgot to call `create_def` or are lowering node-IDs \
701 that do not belong to the current owner",
704 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
708 fn next_id(&mut self) -> hir::HirId {
709 let node_id = self.resolver.next_node_id();
710 self.lower_node_id(node_id)
713 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
715 self.lower_node_id_generic(id, |_| {
716 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
721 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
722 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
723 if pr.unresolved_segments() != 0 {
724 panic!("path not fully resolved: {:?}", pr);
730 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
731 self.resolver.get_import_res(id).present_items()
734 fn diagnostic(&self) -> &rustc_errors::Handler {
735 self.sess.diagnostic()
738 /// Reuses the span but adds information like the kind of the desugaring and features that are
739 /// allowed inside this span.
740 fn mark_span_with_reason(
742 reason: DesugaringKind,
744 allow_internal_unstable: Option<Lrc<[Symbol]>>,
746 span.mark_with_reason(allow_internal_unstable, reason, self.sess.edition())
749 fn with_anonymous_lifetime_mode<R>(
751 anonymous_lifetime_mode: AnonymousLifetimeMode,
752 op: impl FnOnce(&mut Self) -> R,
755 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
756 anonymous_lifetime_mode,
758 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
759 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
760 let result = op(self);
761 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
763 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
764 old_anonymous_lifetime_mode
769 /// Creates a new `hir::GenericParam` for every new lifetime and
770 /// type parameter encountered while evaluating `f`. Definitions
771 /// are created with the parent provided. If no `parent_id` is
772 /// provided, no definitions will be returned.
774 /// Presuming that in-band lifetimes are enabled, then
775 /// `self.anonymous_lifetime_mode` will be updated to match the
776 /// parameter while `f` is running (and restored afterwards).
777 fn collect_in_band_defs<T>(
779 parent_def_id: LocalDefId,
780 anonymous_lifetime_mode: AnonymousLifetimeMode,
781 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
782 ) -> (Vec<hir::GenericParam<'hir>>, T) {
783 assert!(!self.is_collecting_in_band_lifetimes);
784 assert!(self.lifetimes_to_define.is_empty());
785 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
787 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
788 self.is_collecting_in_band_lifetimes = true;
790 let (in_band_ty_params, res) = f(self);
792 self.is_collecting_in_band_lifetimes = false;
793 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
795 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
797 let params = lifetimes_to_define
799 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
800 .chain(in_band_ty_params.into_iter())
806 /// Converts a lifetime into a new generic parameter.
807 fn lifetime_to_generic_param(
811 parent_def_id: LocalDefId,
812 ) -> hir::GenericParam<'hir> {
813 let node_id = self.resolver.next_node_id();
815 // Get the name we'll use to make the def-path. Note
816 // that collisions are ok here and this shouldn't
817 // really show up for end-user.
818 let (str_name, kind) = match hir_name {
819 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
820 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
821 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
824 // Add a definition for the in-band lifetime def.
825 self.resolver.create_def(
828 DefPathData::LifetimeNs(str_name),
834 hir_id: self.lower_node_id(node_id),
839 pure_wrt_drop: false,
840 kind: hir::GenericParamKind::Lifetime { kind },
844 /// When there is a reference to some lifetime `'a`, and in-band
845 /// lifetimes are enabled, then we want to push that lifetime into
846 /// the vector of names to define later. In that case, it will get
847 /// added to the appropriate generics.
848 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
849 if !self.is_collecting_in_band_lifetimes {
853 if !self.sess.features_untracked().in_band_lifetimes {
857 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
861 let hir_name = ParamName::Plain(ident);
863 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
864 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
869 self.lifetimes_to_define.push((ident.span, hir_name));
872 /// When we have either an elided or `'_` lifetime in an impl
873 /// header, we convert it to an in-band lifetime.
874 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
875 assert!(self.is_collecting_in_band_lifetimes);
876 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
877 let hir_name = ParamName::Fresh(index);
878 self.lifetimes_to_define.push((span, hir_name));
882 // Evaluates `f` with the lifetimes in `params` in-scope.
883 // This is used to track which lifetimes have already been defined, and
884 // which are new in-band lifetimes that need to have a definition created
886 fn with_in_scope_lifetime_defs<T>(
888 params: &[GenericParam],
889 f: impl FnOnce(&mut Self) -> T,
891 let old_len = self.in_scope_lifetimes.len();
892 let lt_def_names = params.iter().filter_map(|param| match param.kind {
893 GenericParamKind::Lifetime { .. } => {
894 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
898 self.in_scope_lifetimes.extend(lt_def_names);
902 self.in_scope_lifetimes.truncate(old_len);
906 /// Appends in-band lifetime defs and argument-position `impl
907 /// Trait` defs to the existing set of generics.
909 /// Presuming that in-band lifetimes are enabled, then
910 /// `self.anonymous_lifetime_mode` will be updated to match the
911 /// parameter while `f` is running (and restored afterwards).
912 fn add_in_band_defs<T>(
915 parent_def_id: LocalDefId,
916 anonymous_lifetime_mode: AnonymousLifetimeMode,
917 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
918 ) -> (hir::Generics<'hir>, T) {
919 let (in_band_defs, (mut lowered_generics, res)) =
920 self.with_in_scope_lifetime_defs(&generics.params, |this| {
921 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
922 let mut params = Vec::new();
923 // Note: it is necessary to lower generics *before* calling `f`.
924 // When lowering `async fn`, there's a final step when lowering
925 // the return type that assumes that all in-scope lifetimes have
926 // already been added to either `in_scope_lifetimes` or
927 // `lifetimes_to_define`. If we swapped the order of these two,
928 // in-band-lifetimes introduced by generics or where-clauses
929 // wouldn't have been added yet.
931 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
932 let res = f(this, &mut params);
933 (params, (generics, res))
937 lowered_generics.params.extend(in_band_defs);
939 let lowered_generics = lowered_generics.into_generics(self.arena);
940 (lowered_generics, res)
943 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
944 let was_in_dyn_type = self.is_in_dyn_type;
945 self.is_in_dyn_type = in_scope;
947 let result = f(self);
949 self.is_in_dyn_type = was_in_dyn_type;
954 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
955 let was_in_loop_condition = self.is_in_loop_condition;
956 self.is_in_loop_condition = false;
958 let catch_scopes = mem::take(&mut self.catch_scopes);
959 let loop_scopes = mem::take(&mut self.loop_scopes);
961 self.catch_scopes = catch_scopes;
962 self.loop_scopes = loop_scopes;
964 self.is_in_loop_condition = was_in_loop_condition;
969 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
970 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
973 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
974 // Note that we explicitly do not walk the path. Since we don't really
975 // lower attributes (we use the AST version) there is nowhere to keep
976 // the `HirId`s. We don't actually need HIR version of attributes anyway.
977 // Tokens are also not needed after macro expansion and parsing.
978 let kind = match attr.kind {
979 AttrKind::Normal(ref item, _) => AttrKind::Normal(
981 path: item.path.clone(),
982 args: self.lower_mac_args(&item.args),
987 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
990 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
993 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
995 MacArgs::Empty => MacArgs::Empty,
996 MacArgs::Delimited(dspan, delim, ref tokens) => {
997 // This is either a non-key-value attribute, or a `macro_rules!` body.
998 // We either not have any nonterminals present (in the case of an attribute),
999 // or have tokens available for all nonterminals in the case of a nested
1000 // `macro_rules`: e.g:
1003 // macro_rules! outer {
1005 // macro_rules! inner {
1012 // In both cases, we don't want to synthesize any tokens
1016 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1019 // This is an inert key-value attribute - it will never be visible to macros
1020 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1021 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1022 MacArgs::Eq(eq_span, ref tokens) => MacArgs::Eq(
1024 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::Yes),
1029 fn lower_token_stream(
1031 tokens: TokenStream,
1032 synthesize_tokens: CanSynthesizeMissingTokens,
1034 TokenStreamLowering {
1035 parse_sess: &self.sess.parse_sess,
1037 nt_to_tokenstream: self.nt_to_tokenstream,
1039 .lower_token_stream(tokens)
1042 /// Given an associated type constraint like one of these:
1045 /// T: Iterator<Item: Debug>
1047 /// T: Iterator<Item = Debug>
1051 /// returns a `hir::TypeBinding` representing `Item`.
1052 fn lower_assoc_ty_constraint(
1054 constraint: &AssocTyConstraint,
1055 itctx: ImplTraitContext<'_, 'hir>,
1056 ) -> hir::TypeBinding<'hir> {
1057 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1059 if let Some(ref gen_args) = constraint.gen_args {
1060 self.sess.span_fatal(
1062 "generic associated types in trait paths are currently not implemented",
1066 let kind = match constraint.kind {
1067 AssocTyConstraintKind::Equality { ref ty } => {
1068 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1070 AssocTyConstraintKind::Bound { ref bounds } => {
1071 let mut capturable_lifetimes;
1072 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1073 let (desugar_to_impl_trait, itctx) = match itctx {
1074 // We are in the return position:
1076 // fn foo() -> impl Iterator<Item: Debug>
1080 // fn foo() -> impl Iterator<Item = impl Debug>
1081 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1082 | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
1084 // We are in the argument position, but within a dyn type:
1086 // fn foo(x: dyn Iterator<Item: Debug>)
1090 // fn foo(x: dyn Iterator<Item = impl Debug>)
1091 ImplTraitContext::Universal(..) if self.is_in_dyn_type => (true, itctx),
1093 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1094 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1095 // "impl trait context" to permit `impl Debug` in this position (it desugars
1096 // then to an opaque type).
1098 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1099 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1100 capturable_lifetimes = FxHashSet::default();
1103 ImplTraitContext::OtherOpaqueTy {
1104 capturable_lifetimes: &mut capturable_lifetimes,
1105 origin: hir::OpaqueTyOrigin::Misc,
1110 // We are in the parameter position, but not within a dyn type:
1112 // fn foo(x: impl Iterator<Item: Debug>)
1114 // so we leave it as is and this gets expanded in astconv to a bound like
1115 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1117 _ => (false, itctx),
1120 if desugar_to_impl_trait {
1121 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1122 // constructing the HIR for `impl bounds...` and then lowering that.
1124 let impl_trait_node_id = self.resolver.next_node_id();
1125 let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1126 self.resolver.create_def(
1129 DefPathData::ImplTrait,
1134 self.with_dyn_type_scope(false, |this| {
1135 let node_id = this.resolver.next_node_id();
1136 let ty = this.lower_ty(
1139 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1140 span: constraint.span,
1146 hir::TypeBindingKind::Equality { ty }
1149 // Desugar `AssocTy: Bounds` into a type binding where the
1150 // later desugars into a trait predicate.
1151 let bounds = self.lower_param_bounds(bounds, itctx);
1153 hir::TypeBindingKind::Constraint { bounds }
1159 hir_id: self.lower_node_id(constraint.id),
1160 ident: constraint.ident,
1162 span: constraint.span,
1166 fn lower_generic_arg(
1168 arg: &ast::GenericArg,
1169 itctx: ImplTraitContext<'_, 'hir>,
1170 ) -> hir::GenericArg<'hir> {
1172 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1173 ast::GenericArg::Type(ty) => {
1174 // We parse const arguments as path types as we cannot distinguish them during
1175 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1176 // type and value namespaces. If we resolved the path in the value namespace, we
1177 // transform it into a generic const argument.
1178 if let TyKind::Path(ref qself, ref path) = ty.kind {
1179 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1180 let res = partial_res.base_res();
1181 if !res.matches_ns(Namespace::TypeNS) {
1183 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1187 // Construct a AnonConst where the expr is the "ty"'s path.
1189 let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1190 let node_id = self.resolver.next_node_id();
1192 // Add a definition for the in-band const def.
1193 self.resolver.create_def(
1196 DefPathData::AnonConst,
1201 let path_expr = Expr {
1203 kind: ExprKind::Path(qself.clone(), path.clone()),
1205 attrs: AttrVec::new(),
1209 let ct = self.with_new_scopes(|this| hir::AnonConst {
1210 hir_id: this.lower_node_id(node_id),
1211 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1213 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1217 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1219 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1220 value: self.lower_anon_const(&ct),
1221 span: ct.value.span,
1226 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1227 self.arena.alloc(self.lower_ty_direct(t, itctx))
1233 qself: &Option<QSelf>,
1235 param_mode: ParamMode,
1236 itctx: ImplTraitContext<'_, 'hir>,
1237 ) -> hir::Ty<'hir> {
1238 let id = self.lower_node_id(t.id);
1239 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1240 let ty = self.ty_path(id, t.span, qpath);
1241 if let hir::TyKind::TraitObject(..) = ty.kind {
1242 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1247 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1248 hir::Ty { hir_id: self.next_id(), kind, span }
1251 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1252 self.ty(span, hir::TyKind::Tup(tys))
1255 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1256 let kind = match t.kind {
1257 TyKind::Infer => hir::TyKind::Infer,
1258 TyKind::Err => hir::TyKind::Err,
1259 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1260 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1261 TyKind::Rptr(ref region, ref mt) => {
1262 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1263 let lifetime = match *region {
1264 Some(ref lt) => self.lower_lifetime(lt),
1265 None => self.elided_ref_lifetime(span),
1267 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1269 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1270 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1271 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1272 generic_params: this.lower_generic_params(
1274 &NodeMap::default(),
1275 ImplTraitContext::disallowed(),
1277 unsafety: this.lower_unsafety(f.unsafety),
1278 abi: this.lower_extern(f.ext),
1279 decl: this.lower_fn_decl(&f.decl, None, false, None),
1280 param_names: this.lower_fn_params_to_names(&f.decl),
1284 TyKind::Never => hir::TyKind::Never,
1285 TyKind::Tup(ref tys) => {
1286 hir::TyKind::Tup(self.arena.alloc_from_iter(
1287 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1290 TyKind::Paren(ref ty) => {
1291 return self.lower_ty_direct(ty, itctx);
1293 TyKind::Path(ref qself, ref path) => {
1294 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1296 TyKind::ImplicitSelf => {
1297 let res = self.expect_full_res(t.id);
1298 let res = self.lower_res(res);
1299 hir::TyKind::Path(hir::QPath::Resolved(
1301 self.arena.alloc(hir::Path {
1303 segments: arena_vec![self; hir::PathSegment::from_ident(
1304 Ident::with_dummy_span(kw::SelfUpper)
1310 TyKind::Array(ref ty, ref length) => {
1311 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1313 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1314 TyKind::TraitObject(ref bounds, kind) => {
1315 let mut lifetime_bound = None;
1316 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1318 this.arena.alloc_from_iter(bounds.iter().filter_map(
1319 |bound| match *bound {
1320 GenericBound::Trait(
1322 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1323 ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
1324 // `?const ?Bound` will cause an error during AST validation
1325 // anyways, so treat it like `?Bound` as compilation proceeds.
1326 GenericBound::Trait(
1328 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1330 GenericBound::Outlives(ref lifetime) => {
1331 if lifetime_bound.is_none() {
1332 lifetime_bound = Some(this.lower_lifetime(lifetime));
1338 let lifetime_bound =
1339 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1340 (bounds, lifetime_bound)
1342 if kind != TraitObjectSyntax::Dyn {
1343 self.maybe_lint_bare_trait(t.span, t.id, false);
1345 hir::TyKind::TraitObject(bounds, lifetime_bound)
1347 TyKind::ImplTrait(def_node_id, ref bounds) => {
1350 ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
1351 .lower_opaque_impl_trait(
1357 |this| this.lower_param_bounds(bounds, itctx),
1359 ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => {
1360 // Reset capturable lifetimes, any nested impl trait
1361 // types will inherit lifetimes from this opaque type,
1362 // so don't need to capture them again.
1363 let nested_itctx = ImplTraitContext::OtherOpaqueTy {
1364 capturable_lifetimes: &mut FxHashSet::default(),
1367 self.lower_opaque_impl_trait(
1372 Some(capturable_lifetimes),
1373 |this| this.lower_param_bounds(bounds, nested_itctx),
1376 ImplTraitContext::Universal(in_band_ty_params) => {
1377 // Add a definition for the in-band `Param`.
1378 let def_id = self.resolver.local_def_id(def_node_id);
1380 self.allocate_hir_id_counter(def_node_id);
1382 let hir_bounds = self.with_hir_id_owner(def_node_id, |this| {
1383 this.lower_param_bounds(
1385 ImplTraitContext::Universal(in_band_ty_params),
1388 // Set the name to `impl Bound1 + Bound2`.
1389 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1390 in_band_ty_params.push(hir::GenericParam {
1391 hir_id: self.lower_node_id(def_node_id),
1392 name: ParamName::Plain(ident),
1393 pure_wrt_drop: false,
1397 kind: hir::GenericParamKind::Type {
1399 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1403 hir::TyKind::Path(hir::QPath::Resolved(
1405 self.arena.alloc(hir::Path {
1407 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1408 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1412 ImplTraitContext::Disallowed(pos) => {
1413 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1414 "bindings or function and inherent method return types"
1416 "function and inherent method return types"
1418 let mut err = struct_span_err!(
1422 "`impl Trait` not allowed outside of {}",
1425 if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() {
1427 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1428 attributes to enable",
1436 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1437 TyKind::CVarArgs => {
1438 self.sess.delay_span_bug(
1440 "`TyKind::CVarArgs` should have been handled elsewhere",
1446 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1449 fn lower_opaque_impl_trait(
1452 fn_def_id: Option<DefId>,
1453 origin: hir::OpaqueTyOrigin,
1454 opaque_ty_node_id: NodeId,
1455 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1456 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1457 ) -> hir::TyKind<'hir> {
1459 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1460 fn_def_id, opaque_ty_node_id, span,
1463 // Make sure we know that some funky desugaring has been going on here.
1464 // This is a first: there is code in other places like for loop
1465 // desugaring that explicitly states that we don't want to track that.
1466 // Not tracking it makes lints in rustc and clippy very fragile, as
1467 // frequently opened issues show.
1468 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1470 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1472 self.allocate_hir_id_counter(opaque_ty_node_id);
1474 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1476 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1480 capturable_lifetimes,
1483 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1485 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1487 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1488 let opaque_ty_item = hir::OpaqueTy {
1489 generics: hir::Generics {
1490 params: lifetime_defs,
1491 where_clause: hir::WhereClause { predicates: &[], span },
1495 impl_trait_fn: fn_def_id,
1499 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1501 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1503 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1504 hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, lifetimes)
1508 /// Registers a new opaque type with the proper `NodeId`s and
1509 /// returns the lowered node-ID for the opaque type.
1510 fn generate_opaque_type(
1512 opaque_ty_node_id: NodeId,
1513 opaque_ty_item: hir::OpaqueTy<'hir>,
1515 opaque_ty_span: Span,
1517 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1518 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1519 // Generate an `type Foo = impl Trait;` declaration.
1520 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1521 let opaque_ty_item = hir::Item {
1522 hir_id: opaque_ty_id,
1523 ident: Ident::invalid(),
1524 attrs: Default::default(),
1525 kind: opaque_ty_item_kind,
1526 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1527 span: opaque_ty_span,
1530 // Insert the item into the global item list. This usually happens
1531 // automatically for all AST items. But this opaque type item
1532 // does not actually exist in the AST.
1533 self.insert_item(opaque_ty_item);
1537 fn lifetimes_from_impl_trait_bounds(
1539 opaque_ty_id: NodeId,
1540 parent_def_id: LocalDefId,
1541 bounds: hir::GenericBounds<'hir>,
1542 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1543 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1545 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1546 parent_def_id={:?}, \
1548 opaque_ty_id, parent_def_id, bounds,
1551 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1552 // appear in the bounds, excluding lifetimes that are created within the bounds.
1553 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1554 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1555 context: &'r mut LoweringContext<'a, 'hir>,
1557 opaque_ty_id: NodeId,
1558 collect_elided_lifetimes: bool,
1559 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1560 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1561 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1562 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1563 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1566 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1567 type Map = intravisit::ErasedMap<'v>;
1569 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1570 intravisit::NestedVisitorMap::None
1573 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1574 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1575 if parameters.parenthesized {
1576 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1577 self.collect_elided_lifetimes = false;
1578 intravisit::walk_generic_args(self, span, parameters);
1579 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1581 intravisit::walk_generic_args(self, span, parameters);
1585 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1586 // Don't collect elided lifetimes used inside of `fn()` syntax.
1587 if let hir::TyKind::BareFn(_) = t.kind {
1588 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1589 self.collect_elided_lifetimes = false;
1591 // Record the "stack height" of `for<'a>` lifetime bindings
1592 // to be able to later fully undo their introduction.
1593 let old_len = self.currently_bound_lifetimes.len();
1594 intravisit::walk_ty(self, t);
1595 self.currently_bound_lifetimes.truncate(old_len);
1597 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1599 intravisit::walk_ty(self, t)
1603 fn visit_poly_trait_ref(
1605 trait_ref: &'v hir::PolyTraitRef<'v>,
1606 modifier: hir::TraitBoundModifier,
1608 // Record the "stack height" of `for<'a>` lifetime bindings
1609 // to be able to later fully undo their introduction.
1610 let old_len = self.currently_bound_lifetimes.len();
1611 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1612 self.currently_bound_lifetimes.truncate(old_len);
1615 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1616 // Record the introduction of 'a in `for<'a> ...`.
1617 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1618 // Introduce lifetimes one at a time so that we can handle
1619 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1620 let lt_name = hir::LifetimeName::Param(param.name);
1621 self.currently_bound_lifetimes.push(lt_name);
1624 intravisit::walk_generic_param(self, param);
1627 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1628 let name = match lifetime.name {
1629 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1630 if self.collect_elided_lifetimes {
1631 // Use `'_` for both implicit and underscore lifetimes in
1632 // `type Foo<'_> = impl SomeTrait<'_>;`.
1633 hir::LifetimeName::Underscore
1638 hir::LifetimeName::Param(_) => lifetime.name,
1640 // Refers to some other lifetime that is "in
1641 // scope" within the type.
1642 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1644 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1647 if !self.currently_bound_lifetimes.contains(&name)
1648 && !self.already_defined_lifetimes.contains(&name)
1649 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1651 self.already_defined_lifetimes.insert(name);
1653 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1654 hir_id: self.context.next_id(),
1655 span: lifetime.span,
1659 let def_node_id = self.context.resolver.next_node_id();
1661 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1662 self.context.resolver.create_def(
1665 DefPathData::LifetimeNs(name.ident().name),
1670 let (name, kind) = match name {
1671 hir::LifetimeName::Underscore => (
1672 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1673 hir::LifetimeParamKind::Elided,
1675 hir::LifetimeName::Param(param_name) => {
1676 (param_name, hir::LifetimeParamKind::Explicit)
1678 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1681 self.output_lifetime_params.push(hir::GenericParam {
1684 span: lifetime.span,
1685 pure_wrt_drop: false,
1688 kind: hir::GenericParamKind::Lifetime { kind },
1694 let mut lifetime_collector = ImplTraitLifetimeCollector {
1696 parent: parent_def_id,
1698 collect_elided_lifetimes: true,
1699 currently_bound_lifetimes: Vec::new(),
1700 already_defined_lifetimes: FxHashSet::default(),
1701 output_lifetimes: Vec::new(),
1702 output_lifetime_params: Vec::new(),
1703 lifetimes_to_include,
1706 for bound in bounds {
1707 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1710 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1714 self.arena.alloc_from_iter(output_lifetimes),
1715 self.arena.alloc_from_iter(output_lifetime_params),
1719 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1720 let mut ids = SmallVec::<[NodeId; 1]>::new();
1721 if self.sess.features_untracked().impl_trait_in_bindings {
1722 if let Some(ref ty) = l.ty {
1723 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1724 visitor.visit_ty(ty);
1727 let ty = l.ty.as_ref().map(|t| {
1728 let mut capturable_lifetimes;
1731 if self.sess.features_untracked().impl_trait_in_bindings {
1732 capturable_lifetimes = FxHashSet::default();
1733 ImplTraitContext::OtherOpaqueTy {
1734 capturable_lifetimes: &mut capturable_lifetimes,
1735 origin: hir::OpaqueTyOrigin::Binding,
1738 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1742 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1745 hir_id: self.lower_node_id(l.id),
1747 pat: self.lower_pat(&l.pat),
1750 attrs: l.attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into(),
1751 source: hir::LocalSource::Normal,
1757 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1758 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1759 // as they are not explicit in HIR/Ty function signatures.
1760 // (instead, the `c_variadic` flag is set to `true`)
1761 let mut inputs = &decl.inputs[..];
1762 if decl.c_variadic() {
1763 inputs = &inputs[..inputs.len() - 1];
1765 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1766 PatKind::Ident(_, ident, _) => ident,
1767 _ => Ident::new(kw::Empty, param.pat.span),
1771 // Lowers a function declaration.
1773 // `decl`: the unlowered (AST) function declaration.
1774 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1775 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1776 // `make_ret_async` is also `Some`.
1777 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1778 // This guards against trait declarations and implementations where `impl Trait` is
1780 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1781 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1782 // return type `impl Trait` item.
1786 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1787 impl_trait_return_allow: bool,
1788 make_ret_async: Option<NodeId>,
1789 ) -> &'hir hir::FnDecl<'hir> {
1793 in_band_ty_params: {:?}, \
1794 impl_trait_return_allow: {}, \
1795 make_ret_async: {:?})",
1796 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1798 let lt_mode = if make_ret_async.is_some() {
1799 // In `async fn`, argument-position elided lifetimes
1800 // must be transformed into fresh generic parameters so that
1801 // they can be applied to the opaque `impl Trait` return type.
1802 AnonymousLifetimeMode::CreateParameter
1804 self.anonymous_lifetime_mode
1807 let c_variadic = decl.c_variadic();
1809 // Remember how many lifetimes were already around so that we can
1810 // only look at the lifetime parameters introduced by the arguments.
1811 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1812 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1813 // as they are not explicit in HIR/Ty function signatures.
1814 // (instead, the `c_variadic` flag is set to `true`)
1815 let mut inputs = &decl.inputs[..];
1817 inputs = &inputs[..inputs.len() - 1];
1819 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1820 if let Some((_, ibty)) = &mut in_band_ty_params {
1821 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1823 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1828 let output = if let Some(ret_id) = make_ret_async {
1829 self.lower_async_fn_ret_ty(
1831 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1836 FnRetTy::Ty(ref ty) => {
1837 let context = match in_band_ty_params {
1838 Some((def_id, _)) if impl_trait_return_allow => {
1839 ImplTraitContext::ReturnPositionOpaqueTy {
1841 origin: hir::OpaqueTyOrigin::FnReturn,
1844 _ => ImplTraitContext::disallowed(),
1846 hir::FnRetTy::Return(self.lower_ty(ty, context))
1848 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
1852 self.arena.alloc(hir::FnDecl {
1856 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1857 use BindingMode::{ByRef, ByValue};
1858 let is_mutable_pat = matches!(
1860 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1864 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1865 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1866 // Given we are only considering `ImplicitSelf` types, we needn't consider
1867 // the case where we have a mutable pattern to a reference as that would
1868 // no longer be an `ImplicitSelf`.
1869 TyKind::Rptr(_, ref mt)
1870 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1872 hir::ImplicitSelfKind::MutRef
1874 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1875 hir::ImplicitSelfKind::ImmRef
1877 _ => hir::ImplicitSelfKind::None,
1883 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1884 // combined with the following definition of `OpaqueTy`:
1886 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1888 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1889 // `output`: unlowered output type (`T` in `-> T`)
1890 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1891 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1892 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1893 fn lower_async_fn_ret_ty(
1897 opaque_ty_node_id: NodeId,
1898 ) -> hir::FnRetTy<'hir> {
1900 "lower_async_fn_ret_ty(\
1903 opaque_ty_node_id={:?})",
1904 output, fn_def_id, opaque_ty_node_id,
1907 let span = output.span();
1909 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1911 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1913 self.allocate_hir_id_counter(opaque_ty_node_id);
1915 // When we create the opaque type for this async fn, it is going to have
1916 // to capture all the lifetimes involved in the signature (including in the
1917 // return type). This is done by introducing lifetime parameters for:
1919 // - all the explicitly declared lifetimes from the impl and function itself;
1920 // - all the elided lifetimes in the fn arguments;
1921 // - all the elided lifetimes in the return type.
1923 // So for example in this snippet:
1926 // impl<'a> Foo<'a> {
1927 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1928 // // ^ '0 ^ '1 ^ '2
1929 // // elided lifetimes used below
1934 // we would create an opaque type like:
1937 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1940 // and we would then desugar `bar` to the equivalent of:
1943 // impl<'a> Foo<'a> {
1944 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1948 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1949 // this is because the elided lifetimes from the return type
1950 // should be figured out using the ordinary elision rules, and
1951 // this desugaring achieves that.
1953 // The variable `input_lifetimes_count` tracks the number of
1954 // lifetime parameters to the opaque type *not counting* those
1955 // lifetimes elided in the return type. This includes those
1956 // that are explicitly declared (`in_scope_lifetimes`) and
1957 // those elided lifetimes we found in the arguments (current
1958 // content of `lifetimes_to_define`). Next, we will process
1959 // the return type, which will cause `lifetimes_to_define` to
1961 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
1963 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
1964 // We have to be careful to get elision right here. The
1965 // idea is that we create a lifetime parameter for each
1966 // lifetime in the return type. So, given a return type
1967 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1968 // Future<Output = &'1 [ &'2 u32 ]>`.
1970 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1971 // hence the elision takes place at the fn site.
1972 let future_bound = this
1973 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
1974 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1977 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1979 // Calculate all the lifetimes that should be captured
1980 // by the opaque type. This should include all in-scope
1981 // lifetime parameters, including those defined in-band.
1983 // Note: this must be done after lowering the output type,
1984 // as the output type may introduce new in-band lifetimes.
1985 let lifetime_params: Vec<(Span, ParamName)> = this
1989 .map(|name| (name.ident().span, name))
1990 .chain(this.lifetimes_to_define.iter().cloned())
1993 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
1994 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
1995 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
1997 let generic_params =
1998 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
1999 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2002 let opaque_ty_item = hir::OpaqueTy {
2003 generics: hir::Generics {
2004 params: generic_params,
2005 where_clause: hir::WhereClause { predicates: &[], span },
2008 bounds: arena_vec![this; future_bound],
2009 impl_trait_fn: Some(fn_def_id),
2010 origin: hir::OpaqueTyOrigin::AsyncFn,
2013 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2015 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2017 (opaque_ty_id, lifetime_params)
2020 // As documented above on the variable
2021 // `input_lifetimes_count`, we need to create the lifetime
2022 // arguments to our opaque type. Continuing with our example,
2023 // we're creating the type arguments for the return type:
2026 // Bar<'a, 'b, '0, '1, '_>
2029 // For the "input" lifetime parameters, we wish to create
2030 // references to the parameters themselves, including the
2031 // "implicit" ones created from parameter types (`'a`, `'b`,
2034 // For the "output" lifetime parameters, we just want to
2036 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2037 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2038 |&(span, hir_name)| {
2039 // Input lifetime like `'a` or `'1`:
2040 GenericArg::Lifetime(hir::Lifetime {
2041 hir_id: self.next_id(),
2043 name: hir::LifetimeName::Param(hir_name),
2047 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2048 // Output lifetime like `'_`.
2049 GenericArg::Lifetime(hir::Lifetime {
2050 hir_id: self.next_id(),
2052 name: hir::LifetimeName::Implicit,
2054 let generic_args = self.arena.alloc_from_iter(generic_args);
2056 // Create the `Foo<...>` reference itself. Note that the `type
2057 // Foo = impl Trait` is, internally, created as a child of the
2058 // async fn, so the *type parameters* are inherited. It's
2059 // only the lifetime parameters that we must supply.
2060 let opaque_ty_ref = hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, generic_args);
2061 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2062 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2065 /// Transforms `-> T` into `Future<Output = T>`
2066 fn lower_async_fn_output_type_to_future_bound(
2071 ) -> hir::GenericBound<'hir> {
2072 // Compute the `T` in `Future<Output = T>` from the return type.
2073 let output_ty = match output {
2074 FnRetTy::Ty(ty) => {
2075 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2076 // `impl Future` opaque type that `async fn` implicitly
2078 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2080 origin: hir::OpaqueTyOrigin::FnReturn,
2082 self.lower_ty(ty, context)
2084 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2088 let future_args = self.arena.alloc(hir::GenericArgs {
2090 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2091 parenthesized: false,
2094 hir::GenericBound::LangItemTrait(
2095 // ::std::future::Future<future_params>
2096 hir::LangItem::Future,
2103 fn lower_param_bound(
2106 itctx: ImplTraitContext<'_, 'hir>,
2107 ) -> hir::GenericBound<'hir> {
2109 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2110 self.lower_poly_trait_ref(ty, itctx),
2111 self.lower_trait_bound_modifier(modifier),
2113 GenericBound::Outlives(ref lifetime) => {
2114 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2119 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2120 let span = l.ident.span;
2122 ident if ident.name == kw::StaticLifetime => {
2123 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2125 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2126 AnonymousLifetimeMode::CreateParameter => {
2127 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2128 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2131 AnonymousLifetimeMode::PassThrough => {
2132 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2135 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2138 self.maybe_collect_in_band_lifetime(ident);
2139 let param_name = ParamName::Plain(ident);
2140 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2145 fn new_named_lifetime(
2149 name: hir::LifetimeName,
2150 ) -> hir::Lifetime {
2151 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2154 fn lower_generic_params_mut<'s>(
2156 params: &'s [GenericParam],
2157 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2158 mut itctx: ImplTraitContext<'s, 'hir>,
2159 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2162 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2165 fn lower_generic_params(
2167 params: &[GenericParam],
2168 add_bounds: &NodeMap<Vec<GenericBound>>,
2169 itctx: ImplTraitContext<'_, 'hir>,
2170 ) -> &'hir [hir::GenericParam<'hir>] {
2171 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2174 fn lower_generic_param(
2176 param: &GenericParam,
2177 add_bounds: &NodeMap<Vec<GenericBound>>,
2178 mut itctx: ImplTraitContext<'_, 'hir>,
2179 ) -> hir::GenericParam<'hir> {
2180 let mut bounds: Vec<_> = self
2181 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2182 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2185 let (name, kind) = match param.kind {
2186 GenericParamKind::Lifetime => {
2187 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2188 self.is_collecting_in_band_lifetimes = false;
2191 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2192 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2194 let param_name = match lt.name {
2195 hir::LifetimeName::Param(param_name) => param_name,
2196 hir::LifetimeName::Implicit
2197 | hir::LifetimeName::Underscore
2198 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2199 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2200 self.sess.diagnostic().span_bug(
2202 "object-lifetime-default should not occur here",
2205 hir::LifetimeName::Error => ParamName::Error,
2209 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2211 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2215 GenericParamKind::Type { ref default, .. } => {
2216 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2217 if !add_bounds.is_empty() {
2218 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2219 bounds.extend(params);
2222 let kind = hir::GenericParamKind::Type {
2223 default: default.as_ref().map(|x| {
2226 ImplTraitContext::OtherOpaqueTy {
2227 capturable_lifetimes: &mut FxHashSet::default(),
2228 origin: hir::OpaqueTyOrigin::Misc,
2235 .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic))
2236 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2240 (hir::ParamName::Plain(param.ident), kind)
2242 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2244 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2245 this.lower_ty(&ty, ImplTraitContext::disallowed())
2247 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2249 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty, default })
2254 hir_id: self.lower_node_id(param.id),
2256 span: param.ident.span,
2257 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2258 attrs: self.lower_attrs(¶m.attrs),
2259 bounds: self.arena.alloc_from_iter(bounds),
2267 itctx: ImplTraitContext<'_, 'hir>,
2268 ) -> hir::TraitRef<'hir> {
2269 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2270 hir::QPath::Resolved(None, path) => path,
2271 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2273 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2276 fn lower_poly_trait_ref(
2279 mut itctx: ImplTraitContext<'_, 'hir>,
2280 ) -> hir::PolyTraitRef<'hir> {
2281 let bound_generic_params = self.lower_generic_params(
2282 &p.bound_generic_params,
2283 &NodeMap::default(),
2287 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2288 // Any impl Trait types defined within this scope can capture
2289 // lifetimes bound on this predicate.
2290 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2291 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2292 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2296 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2297 capturable_lifetimes.extend(lt_def_names.clone());
2300 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2302 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2303 for param in lt_def_names {
2304 capturable_lifetimes.remove(¶m);
2310 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2313 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2314 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2317 fn lower_param_bounds(
2319 bounds: &[GenericBound],
2320 itctx: ImplTraitContext<'_, 'hir>,
2321 ) -> hir::GenericBounds<'hir> {
2322 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2325 fn lower_param_bounds_mut<'s>(
2327 bounds: &'s [GenericBound],
2328 mut itctx: ImplTraitContext<'s, 'hir>,
2329 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2330 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2333 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2334 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2337 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2338 let mut expr: Option<&'hir _> = None;
2340 let stmts = self.arena.alloc_from_iter(
2344 .filter_map(|(index, stmt)| {
2345 if index == b.stmts.len() - 1 {
2346 if let StmtKind::Expr(ref e) = stmt.kind {
2347 expr = Some(self.lower_expr(e));
2350 Some(self.lower_stmt(stmt))
2353 Some(self.lower_stmt(stmt))
2358 let rules = self.lower_block_check_mode(&b.rules);
2359 let hir_id = self.lower_node_id(b.id);
2361 hir::Block { hir_id, stmts, expr, rules, span: b.span, targeted_by_break }
2364 /// Lowers a block directly to an expression, presuming that it
2365 /// has no attributes and is not targeted by a `break`.
2366 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2367 let block = self.lower_block(b, false);
2368 self.expr_block(block, AttrVec::new())
2371 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2372 self.with_new_scopes(|this| hir::AnonConst {
2373 hir_id: this.lower_node_id(c.id),
2374 body: this.lower_const_body(c.value.span, Some(&c.value)),
2378 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2379 let kind = match s.kind {
2380 StmtKind::Local(ref l) => {
2381 let (l, item_ids) = self.lower_local(l);
2382 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2385 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2386 self.stmt(s.span, hir::StmtKind::Item(item_id))
2391 hir_id: self.lower_node_id(s.id),
2392 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2398 StmtKind::Item(ref it) => {
2399 // Can only use the ID once.
2400 let mut id = Some(s.id);
2407 .map(|id| self.lower_node_id(id))
2408 .unwrap_or_else(|| self.next_id());
2410 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2414 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2415 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2416 StmtKind::Empty => return smallvec![],
2417 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
2419 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2422 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2424 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2425 BlockCheckMode::Unsafe(u) => {
2426 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2431 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2433 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2434 UserProvided => hir::UnsafeSource::UserProvided,
2438 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2440 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2441 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2443 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2444 // placeholder for compilation to proceed.
2445 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2446 hir::TraitBoundModifier::Maybe
2451 // Helper methods for building HIR.
2453 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2454 hir::Stmt { span, kind, hir_id: self.next_id() }
2457 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2458 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2465 init: Option<&'hir hir::Expr<'hir>>,
2466 pat: &'hir hir::Pat<'hir>,
2467 source: hir::LocalSource,
2468 ) -> hir::Stmt<'hir> {
2469 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2470 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2473 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2474 self.block_all(expr.span, &[], Some(expr))
2480 stmts: &'hir [hir::Stmt<'hir>],
2481 expr: Option<&'hir hir::Expr<'hir>>,
2482 ) -> &'hir hir::Block<'hir> {
2483 let blk = hir::Block {
2486 hir_id: self.next_id(),
2487 rules: hir::BlockCheckMode::DefaultBlock,
2489 targeted_by_break: false,
2491 self.arena.alloc(blk)
2494 /// Constructs a `true` or `false` literal pattern.
2495 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2496 let expr = self.expr_bool(span, val);
2497 self.pat(span, hir::PatKind::Lit(expr))
2500 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2501 let field = self.single_pat_field(span, pat);
2502 self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
2505 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2506 let field = self.single_pat_field(span, pat);
2507 self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field)
2510 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2511 let field = self.single_pat_field(span, pat);
2512 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2515 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2516 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2519 fn single_pat_field(
2522 pat: &'hir hir::Pat<'hir>,
2523 ) -> &'hir [hir::FieldPat<'hir>] {
2524 let field = hir::FieldPat {
2525 hir_id: self.next_id(),
2526 ident: Ident::new(sym::integer(0), span),
2527 is_shorthand: false,
2531 arena_vec![self; field]
2534 fn pat_lang_item_variant(
2537 lang_item: hir::LangItem,
2538 fields: &'hir [hir::FieldPat<'hir>],
2539 ) -> &'hir hir::Pat<'hir> {
2540 let qpath = hir::QPath::LangItem(lang_item, span);
2541 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2544 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2545 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2548 fn pat_ident_binding_mode(
2552 bm: hir::BindingAnnotation,
2553 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2554 let hir_id = self.next_id();
2557 self.arena.alloc(hir::Pat {
2559 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2561 default_binding_modes: true,
2567 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2568 self.pat(span, hir::PatKind::Wild)
2571 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2572 self.arena.alloc(hir::Pat {
2573 hir_id: self.next_id(),
2576 default_binding_modes: true,
2580 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2581 self.arena.alloc(hir::Pat {
2582 hir_id: self.next_id(),
2585 default_binding_modes: false,
2591 mut hir_id: hir::HirId,
2593 qpath: hir::QPath<'hir>,
2594 ) -> hir::Ty<'hir> {
2595 let kind = match qpath {
2596 hir::QPath::Resolved(None, path) => {
2597 // Turn trait object paths into `TyKind::TraitObject` instead.
2599 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2600 let principal = hir::PolyTraitRef {
2601 bound_generic_params: &[],
2602 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2606 // The original ID is taken by the `PolyTraitRef`,
2607 // so the `Ty` itself needs a different one.
2608 hir_id = self.next_id();
2609 hir::TyKind::TraitObject(
2610 arena_vec![self; principal],
2611 self.elided_dyn_bound(span),
2614 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2617 _ => hir::TyKind::Path(qpath),
2620 hir::Ty { hir_id, kind, span }
2623 /// Invoked to create the lifetime argument for a type `&T`
2624 /// with no explicit lifetime.
2625 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2626 match self.anonymous_lifetime_mode {
2627 // Intercept when we are in an impl header or async fn and introduce an in-band
2629 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2631 AnonymousLifetimeMode::CreateParameter => {
2632 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2634 hir_id: self.next_id(),
2636 name: hir::LifetimeName::Param(fresh_name),
2640 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2642 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2646 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2647 /// return a "error lifetime".
2648 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2649 let (id, msg, label) = match id {
2650 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2653 self.resolver.next_node_id(),
2654 "`&` without an explicit lifetime name cannot be used here",
2655 "explicit lifetime name needed here",
2659 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2660 err.span_label(span, label);
2663 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2666 /// Invoked to create the lifetime argument(s) for a path like
2667 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2668 /// sorts of cases are deprecated. This may therefore report a warning or an
2669 /// error, depending on the mode.
2670 fn elided_path_lifetimes<'s>(
2674 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2675 (0..count).map(move |_| self.elided_path_lifetime(span))
2678 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2679 match self.anonymous_lifetime_mode {
2680 AnonymousLifetimeMode::CreateParameter => {
2681 // We should have emitted E0726 when processing this path above
2683 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2684 let id = self.resolver.next_node_id();
2685 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2687 // `PassThrough` is the normal case.
2688 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2689 // is unsuitable here, as these can occur from missing lifetime parameters in a
2690 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2691 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2692 // later, at which point a suitable error will be emitted.
2693 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2694 self.new_implicit_lifetime(span)
2699 /// Invoked to create the lifetime argument(s) for an elided trait object
2700 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2701 /// when the bound is written, even if it is written with `'_` like in
2702 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2703 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2704 match self.anonymous_lifetime_mode {
2705 // NB. We intentionally ignore the create-parameter mode here.
2706 // and instead "pass through" to resolve-lifetimes, which will apply
2707 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2708 // do not act like other elided lifetimes. In other words, given this:
2710 // impl Foo for Box<dyn Debug>
2712 // we do not introduce a fresh `'_` to serve as the bound, but instead
2713 // ultimately translate to the equivalent of:
2715 // impl Foo for Box<dyn Debug + 'static>
2717 // `resolve_lifetime` has the code to make that happen.
2718 AnonymousLifetimeMode::CreateParameter => {}
2720 AnonymousLifetimeMode::ReportError => {
2721 // ReportError applies to explicit use of `'_`.
2724 // This is the normal case.
2725 AnonymousLifetimeMode::PassThrough => {}
2728 let r = hir::Lifetime {
2729 hir_id: self.next_id(),
2731 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2733 debug!("elided_dyn_bound: r={:?}", r);
2737 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2738 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2741 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2742 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2743 // call site which do not have a macro backtrace. See #61963.
2744 let is_macro_callsite = self
2747 .span_to_snippet(span)
2748 .map(|snippet| snippet.starts_with("#["))
2750 if !is_macro_callsite {
2751 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2755 "trait objects without an explicit `dyn` are deprecated",
2756 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2762 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2763 // Sorting by span ensures that we get things in order within a
2764 // file, and also puts the files in a sensible order.
2765 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2766 body_ids.sort_by_key(|b| bodies[b].value.span);
2770 /// Helper struct for delayed construction of GenericArgs.
2771 struct GenericArgsCtor<'hir> {
2772 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2773 bindings: &'hir [hir::TypeBinding<'hir>],
2774 parenthesized: bool,
2777 impl<'hir> GenericArgsCtor<'hir> {
2778 fn is_empty(&self) -> bool {
2779 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2782 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2784 args: arena.alloc_from_iter(self.args),
2785 bindings: self.bindings,
2786 parenthesized: self.parenthesized,