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 #![cfg_attr(bootstrap, feature(or_patterns))]
35 #![feature(box_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_ID};
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, MISSING_ABI};
57 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
58 use rustc_session::parse::ParseSess;
59 use rustc_session::Session;
60 use rustc_span::hygiene::ExpnId;
61 use rustc_span::source_map::{respan, DesugaringKind};
62 use rustc_span::symbol::{kw, sym, Ident, Symbol};
64 use rustc_target::spec::abi::Abi;
66 use smallvec::{smallvec, SmallVec};
67 use std::collections::BTreeMap;
69 use tracing::{debug, trace};
71 macro_rules! arena_vec {
72 ($this:expr; $($x:expr),*) => ({
74 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
83 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
85 rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx);
87 struct LoweringContext<'a, 'hir: 'a> {
88 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
91 resolver: &'a mut dyn ResolverAstLowering,
93 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
94 /// if we don't have this function pointer. To avoid that dependency so that
95 /// librustc_middle is independent of the parser, we use dynamic dispatch here.
96 nt_to_tokenstream: NtToTokenstream,
98 /// Used to allocate HIR nodes.
99 arena: &'hir Arena<'hir>,
101 /// The items being lowered are collected here.
102 items: BTreeMap<hir::ItemId, hir::Item<'hir>>,
104 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
105 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
106 foreign_items: BTreeMap<hir::ForeignItemId, hir::ForeignItem<'hir>>,
107 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
108 exported_macros: Vec<hir::MacroDef<'hir>>,
109 non_exported_macro_attrs: Vec<ast::Attribute>,
111 trait_impls: BTreeMap<DefId, Vec<LocalDefId>>,
113 modules: BTreeMap<LocalDefId, hir::ModuleItems>,
115 generator_kind: Option<hir::GeneratorKind>,
117 attrs: BTreeMap<hir::HirId, &'hir [Attribute]>,
119 /// When inside an `async` context, this is the `HirId` of the
120 /// `task_context` local bound to the resume argument of the generator.
121 task_context: Option<hir::HirId>,
123 /// Used to get the current `fn`'s def span to point to when using `await`
124 /// outside of an `async fn`.
125 current_item: Option<Span>,
127 catch_scopes: Vec<NodeId>,
128 loop_scopes: Vec<NodeId>,
129 is_in_loop_condition: bool,
130 is_in_trait_impl: bool,
131 is_in_dyn_type: bool,
133 /// What to do when we encounter an "anonymous lifetime
134 /// reference". The term "anonymous" is meant to encompass both
135 /// `'_` lifetimes as well as fully elided cases where nothing is
136 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
137 anonymous_lifetime_mode: AnonymousLifetimeMode,
139 /// Used to create lifetime definitions from in-band lifetime usages.
140 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
141 /// When a named lifetime is encountered in a function or impl header and
142 /// has not been defined
143 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
144 /// to this list. The results of this list are then added to the list of
145 /// lifetime definitions in the corresponding impl or function generics.
146 lifetimes_to_define: Vec<(Span, ParamName)>,
148 /// `true` if in-band lifetimes are being collected. This is used to
149 /// indicate whether or not we're in a place where new lifetimes will result
150 /// in in-band lifetime definitions, such a function or an impl header,
151 /// including implicit lifetimes from `impl_header_lifetime_elision`.
152 is_collecting_in_band_lifetimes: bool,
154 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
155 /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
156 /// against this list to see if it is already in-scope, or if a definition
157 /// needs to be created for it.
159 /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
161 in_scope_lifetimes: Vec<ParamName>,
163 current_module: LocalDefId,
165 type_def_lifetime_params: DefIdMap<usize>,
167 current_hir_id_owner: Vec<(LocalDefId, u32)>,
168 item_local_id_counters: NodeMap<u32>,
169 node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
171 allow_try_trait: Option<Lrc<[Symbol]>>,
172 allow_gen_future: Option<Lrc<[Symbol]>>,
175 pub trait ResolverAstLowering {
176 fn def_key(&mut self, id: DefId) -> DefKey;
178 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
180 fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<usize>>;
182 /// Obtains resolution for a `NodeId` with a single resolution.
183 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
185 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
186 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
188 /// Obtains resolution for a label with the given `NodeId`.
189 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
191 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
192 /// This should only return `None` during testing.
193 fn definitions(&mut self) -> &mut Definitions;
195 fn lint_buffer(&mut self) -> &mut LintBuffer;
197 fn next_node_id(&mut self) -> NodeId;
199 fn trait_map(&self) -> &NodeMap<Vec<hir::TraitCandidate>>;
201 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
203 fn local_def_id(&self, node: NodeId) -> LocalDefId;
208 node_id: ast::NodeId,
215 type NtToTokenstream = fn(&Nonterminal, &ParseSess, CanSynthesizeMissingTokens) -> TokenStream;
217 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
218 /// and if so, what meaning it has.
220 enum ImplTraitContext<'b, 'a> {
221 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
222 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
223 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
225 /// Newly generated parameters should be inserted into the given `Vec`.
226 Universal(&'b mut Vec<hir::GenericParam<'a>>, LocalDefId),
228 /// Treat `impl Trait` as shorthand for a new opaque type.
229 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
230 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
232 ReturnPositionOpaqueTy {
233 /// `DefId` for the parent function, used to look up necessary
234 /// information later.
236 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
237 origin: hir::OpaqueTyOrigin,
239 /// Impl trait in type aliases, consts and statics.
241 /// Set of lifetimes that this opaque type can capture, if it uses
242 /// them. This includes lifetimes bound since we entered this context.
246 /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
249 /// Here the inner opaque type captures `'a` because it uses it. It doesn't
250 /// need to capture `'b` because it already inherits the lifetime
251 /// parameter from `A`.
252 // FIXME(impl_trait): but `required_region_bounds` will ICE later
254 capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
255 /// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding,
256 origin: hir::OpaqueTyOrigin,
258 /// `impl Trait` is not accepted in this position.
259 Disallowed(ImplTraitPosition),
262 /// Position in which `impl Trait` is disallowed.
263 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
264 enum ImplTraitPosition {
265 /// Disallowed in `let` / `const` / `static` bindings.
268 /// All other positions.
272 impl<'a> ImplTraitContext<'_, 'a> {
274 fn disallowed() -> Self {
275 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
278 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
279 use self::ImplTraitContext::*;
281 Universal(params, parent) => Universal(params, *parent),
282 ReturnPositionOpaqueTy { fn_def_id, origin } => {
283 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
285 OtherOpaqueTy { capturable_lifetimes, origin } => {
286 OtherOpaqueTy { capturable_lifetimes, origin: *origin }
288 Disallowed(pos) => Disallowed(*pos),
293 pub fn lower_crate<'a, 'hir>(
296 resolver: &'a mut dyn ResolverAstLowering,
297 nt_to_tokenstream: NtToTokenstream,
298 arena: &'hir Arena<'hir>,
299 ) -> hir::Crate<'hir> {
300 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
307 items: BTreeMap::new(),
308 trait_items: BTreeMap::new(),
309 impl_items: BTreeMap::new(),
310 foreign_items: BTreeMap::new(),
311 bodies: BTreeMap::new(),
312 trait_impls: BTreeMap::new(),
313 modules: BTreeMap::new(),
314 attrs: BTreeMap::default(),
315 exported_macros: Vec::new(),
316 non_exported_macro_attrs: Vec::new(),
317 catch_scopes: Vec::new(),
318 loop_scopes: Vec::new(),
319 is_in_loop_condition: false,
320 is_in_trait_impl: false,
321 is_in_dyn_type: false,
322 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
323 type_def_lifetime_params: Default::default(),
324 current_module: CRATE_DEF_ID,
325 current_hir_id_owner: vec![(CRATE_DEF_ID, 0)],
326 item_local_id_counters: Default::default(),
327 node_id_to_hir_id: IndexVec::new(),
328 generator_kind: None,
331 lifetimes_to_define: Vec::new(),
332 is_collecting_in_band_lifetimes: false,
333 in_scope_lifetimes: Vec::new(),
334 allow_try_trait: Some([sym::try_trait][..].into()),
335 allow_gen_future: Some([sym::gen_future][..].into()),
340 #[derive(Copy, Clone, PartialEq)]
342 /// Any path in a type context.
344 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
346 /// The `module::Type` in `module::Type::method` in an expression.
350 enum ParenthesizedGenericArgs {
355 /// What to do when we encounter an **anonymous** lifetime
356 /// reference. Anonymous lifetime references come in two flavors. You
357 /// have implicit, or fully elided, references to lifetimes, like the
358 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
359 /// or `Ref<'_, T>`. These often behave the same, but not always:
361 /// - certain usages of implicit references are deprecated, like
362 /// `Ref<T>`, and we sometimes just give hard errors in those cases
364 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
365 /// the same as `Box<dyn Foo + '_>`.
367 /// We describe the effects of the various modes in terms of three cases:
369 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
370 /// of a `&` (e.g., the missing lifetime in something like `&T`)
371 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
372 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
373 /// elided bounds follow special rules. Note that this only covers
374 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
375 /// '_>` is a case of "modern" elision.
376 /// - **Deprecated** -- this covers cases like `Ref<T>`, where the lifetime
377 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
378 /// non-deprecated equivalent.
380 /// Currently, the handling of lifetime elision is somewhat spread out
381 /// between HIR lowering and -- as described below -- the
382 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
383 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
384 /// everything into HIR lowering.
385 #[derive(Copy, Clone, Debug)]
386 enum AnonymousLifetimeMode {
387 /// For **Modern** cases, create a new anonymous region parameter
388 /// and reference that.
390 /// For **Dyn Bound** cases, pass responsibility to
391 /// `resolve_lifetime` code.
393 /// For **Deprecated** cases, report an error.
396 /// Give a hard error when either `&` or `'_` is written. Used to
397 /// rule out things like `where T: Foo<'_>`. Does not imply an
398 /// error on default object bounds (e.g., `Box<dyn Foo>`).
401 /// Pass responsibility to `resolve_lifetime` code for all cases.
405 struct TokenStreamLowering<'a> {
406 parse_sess: &'a ParseSess,
407 synthesize_tokens: CanSynthesizeMissingTokens,
408 nt_to_tokenstream: NtToTokenstream,
411 impl<'a> TokenStreamLowering<'a> {
412 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
413 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
416 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
418 TokenTree::Token(token) => self.lower_token(token),
419 TokenTree::Delimited(span, delim, tts) => {
420 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
425 fn lower_token(&mut self, token: Token) -> TokenStream {
427 token::Interpolated(nt) => {
428 let tts = (self.nt_to_tokenstream)(&nt, self.parse_sess, self.synthesize_tokens);
429 TokenTree::Delimited(
430 DelimSpan::from_single(token.span),
432 self.lower_token_stream(tts),
436 _ => TokenTree::Token(token).into(),
441 impl<'a, 'hir> LoweringContext<'a, 'hir> {
442 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
443 /// Full-crate AST visitor that inserts into a fresh
444 /// `LoweringContext` any information that may be
445 /// needed from arbitrary locations in the crate,
446 /// e.g., the number of lifetime generic parameters
447 /// declared for every type and trait definition.
448 struct MiscCollector<'tcx, 'lowering, 'hir> {
449 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
452 impl MiscCollector<'_, '_, '_> {
453 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
455 UseTreeKind::Simple(_, id1, id2) => {
456 for &id in &[id1, id2] {
457 self.lctx.allocate_hir_id_counter(id);
460 UseTreeKind::Glob => (),
461 UseTreeKind::Nested(ref trees) => {
462 for &(ref use_tree, id) in trees {
463 self.lctx.allocate_hir_id_counter(id);
464 self.allocate_use_tree_hir_id_counters(use_tree);
471 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
472 fn visit_item(&mut self, item: &'tcx Item) {
473 self.lctx.allocate_hir_id_counter(item.id);
476 ItemKind::Struct(_, ref generics)
477 | ItemKind::Union(_, ref generics)
478 | ItemKind::Enum(_, ref generics)
479 | ItemKind::TyAlias(box TyAliasKind(_, ref generics, ..))
480 | ItemKind::Trait(box TraitKind(_, _, ref generics, ..)) => {
481 let def_id = self.lctx.resolver.local_def_id(item.id);
486 matches!(param.kind, ast::GenericParamKind::Lifetime { .. })
489 self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
491 ItemKind::Use(ref use_tree) => {
492 self.allocate_use_tree_hir_id_counters(use_tree);
497 visit::walk_item(self, item);
500 fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
501 self.lctx.allocate_hir_id_counter(item.id);
502 visit::walk_assoc_item(self, item, ctxt);
505 fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
506 self.lctx.allocate_hir_id_counter(item.id);
507 visit::walk_foreign_item(self, item);
510 fn visit_ty(&mut self, t: &'tcx Ty) {
512 // Mirrors the case in visit::walk_ty
513 TyKind::BareFn(ref f) => {
514 walk_list!(self, visit_generic_param, &f.generic_params);
515 // Mirrors visit::walk_fn_decl
516 for parameter in &f.decl.inputs {
517 // We don't lower the ids of argument patterns
518 self.visit_pat(¶meter.pat);
519 self.visit_ty(¶meter.ty)
521 self.visit_fn_ret_ty(&f.decl.output)
523 _ => visit::walk_ty(self, t),
528 self.lower_node_id(CRATE_NODE_ID);
529 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
531 visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
532 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
534 let module = self.lower_mod(&c.items, c.span);
535 self.lower_attrs(hir::CRATE_HIR_ID, &c.attrs);
536 let body_ids = body_ids(&self.bodies);
538 c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
544 .filter_map(|(&k, v)| {
545 self.node_id_to_hir_id.get(k).and_then(|id| id.as_ref()).map(|id| (*id, v.clone()))
549 let mut def_id_to_hir_id = IndexVec::default();
551 for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
552 if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
553 if def_id_to_hir_id.len() <= def_id.index() {
554 def_id_to_hir_id.resize(def_id.index() + 1, None);
556 def_id_to_hir_id[def_id] = hir_id;
560 self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
562 #[cfg(debug_assertions)]
563 for (&id, attrs) in self.attrs.iter() {
564 // Verify that we do not store empty slices in the map.
565 if attrs.is_empty() {
566 panic!("Stored empty attributes for {:?}", id);
571 item: hir::CrateItem { module, span: c.span },
572 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
573 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
575 trait_items: self.trait_items,
576 impl_items: self.impl_items,
577 foreign_items: self.foreign_items,
580 trait_impls: self.trait_impls,
581 modules: self.modules,
588 fn insert_item(&mut self, item: hir::Item<'hir>) -> hir::ItemId {
589 let id = hir::ItemId { def_id: item.def_id };
590 self.items.insert(id, item);
591 self.modules.entry(self.current_module).or_default().items.insert(id);
595 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
596 // Set up the counter if needed.
597 self.item_local_id_counters.entry(owner).or_insert(0);
598 // Always allocate the first `HirId` for the owner itself.
599 let lowered = self.lower_node_id_with_owner(owner, owner);
600 debug_assert_eq!(lowered.local_id.as_u32(), 0);
604 fn lower_node_id_generic(
607 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
609 assert_ne!(ast_node_id, DUMMY_NODE_ID);
611 let min_size = ast_node_id.as_usize() + 1;
613 if min_size > self.node_id_to_hir_id.len() {
614 self.node_id_to_hir_id.resize(min_size, None);
617 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
620 // Generate a new `HirId`.
621 let hir_id = alloc_hir_id(self);
622 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
628 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
630 .item_local_id_counters
631 .insert(owner, HIR_ID_COUNTER_LOCKED)
632 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
633 let def_id = self.resolver.local_def_id(owner);
634 self.current_hir_id_owner.push((def_id, counter));
636 let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap();
638 debug_assert!(def_id == new_def_id);
639 debug_assert!(new_counter >= counter);
641 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
642 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
646 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
647 /// the `LoweringContext`'s `NodeId => HirId` map.
648 /// Take care not to call this method if the resulting `HirId` is then not
649 /// actually used in the HIR, as that would trigger an assertion in the
650 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
651 /// properly. Calling the method twice with the same `NodeId` is fine though.
652 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
653 self.lower_node_id_generic(ast_node_id, |this| {
654 let &mut (owner, ref mut local_id_counter) =
655 this.current_hir_id_owner.last_mut().unwrap();
656 let local_id = *local_id_counter;
657 *local_id_counter += 1;
658 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
662 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
663 self.lower_node_id_generic(ast_node_id, |this| {
664 let local_id_counter = this
665 .item_local_id_counters
667 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
668 let local_id = *local_id_counter;
670 // We want to be sure not to modify the counter in the map while it
671 // is also on the stack. Otherwise we'll get lost updates when writing
672 // back from the stack to the map.
673 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
675 *local_id_counter += 1;
676 let owner = this.resolver.opt_local_def_id(owner).expect(
677 "you forgot to call `create_def` or are lowering node-IDs \
678 that do not belong to the current owner",
681 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
685 fn next_id(&mut self) -> hir::HirId {
686 let node_id = self.resolver.next_node_id();
687 self.lower_node_id(node_id)
690 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
692 self.lower_node_id_generic(id, |_| {
693 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
698 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
699 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
700 if pr.unresolved_segments() != 0 {
701 panic!("path not fully resolved: {:?}", pr);
707 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
708 self.resolver.get_import_res(id).present_items()
711 fn diagnostic(&self) -> &rustc_errors::Handler {
712 self.sess.diagnostic()
715 /// Reuses the span but adds information like the kind of the desugaring and features that are
716 /// allowed inside this span.
717 fn mark_span_with_reason(
719 reason: DesugaringKind,
721 allow_internal_unstable: Option<Lrc<[Symbol]>>,
723 span.mark_with_reason(allow_internal_unstable, reason, self.sess.edition())
726 fn with_anonymous_lifetime_mode<R>(
728 anonymous_lifetime_mode: AnonymousLifetimeMode,
729 op: impl FnOnce(&mut Self) -> R,
732 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
733 anonymous_lifetime_mode,
735 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
736 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
737 let result = op(self);
738 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
740 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
741 old_anonymous_lifetime_mode
746 /// Creates a new `hir::GenericParam` for every new lifetime and
747 /// type parameter encountered while evaluating `f`. Definitions
748 /// are created with the parent provided. If no `parent_id` is
749 /// provided, no definitions will be returned.
751 /// Presuming that in-band lifetimes are enabled, then
752 /// `self.anonymous_lifetime_mode` will be updated to match the
753 /// parameter while `f` is running (and restored afterwards).
754 fn collect_in_band_defs<T>(
756 parent_def_id: LocalDefId,
757 anonymous_lifetime_mode: AnonymousLifetimeMode,
758 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
759 ) -> (Vec<hir::GenericParam<'hir>>, T) {
760 assert!(!self.is_collecting_in_band_lifetimes);
761 assert!(self.lifetimes_to_define.is_empty());
762 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
764 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
765 self.is_collecting_in_band_lifetimes = true;
767 let (in_band_ty_params, res) = f(self);
769 self.is_collecting_in_band_lifetimes = false;
770 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
772 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
774 let params = lifetimes_to_define
776 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
777 .chain(in_band_ty_params.into_iter())
783 /// Converts a lifetime into a new generic parameter.
784 fn lifetime_to_generic_param(
788 parent_def_id: LocalDefId,
789 ) -> hir::GenericParam<'hir> {
790 let node_id = self.resolver.next_node_id();
792 // Get the name we'll use to make the def-path. Note
793 // that collisions are ok here and this shouldn't
794 // really show up for end-user.
795 let (str_name, kind) = match hir_name {
796 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
797 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
798 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
801 // Add a definition for the in-band lifetime def.
802 self.resolver.create_def(
805 DefPathData::LifetimeNs(str_name),
811 hir_id: self.lower_node_id(node_id),
815 pure_wrt_drop: false,
816 kind: hir::GenericParamKind::Lifetime { kind },
820 /// When there is a reference to some lifetime `'a`, and in-band
821 /// lifetimes are enabled, then we want to push that lifetime into
822 /// the vector of names to define later. In that case, it will get
823 /// added to the appropriate generics.
824 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
825 if !self.is_collecting_in_band_lifetimes {
829 if !self.sess.features_untracked().in_band_lifetimes {
833 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
837 let hir_name = ParamName::Plain(ident);
839 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
840 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
845 self.lifetimes_to_define.push((ident.span, hir_name));
848 /// When we have either an elided or `'_` lifetime in an impl
849 /// header, we convert it to an in-band lifetime.
850 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
851 assert!(self.is_collecting_in_band_lifetimes);
852 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
853 let hir_name = ParamName::Fresh(index);
854 self.lifetimes_to_define.push((span, hir_name));
858 // Evaluates `f` with the lifetimes in `params` in-scope.
859 // This is used to track which lifetimes have already been defined, and
860 // which are new in-band lifetimes that need to have a definition created
862 fn with_in_scope_lifetime_defs<T>(
864 params: &[GenericParam],
865 f: impl FnOnce(&mut Self) -> T,
867 let old_len = self.in_scope_lifetimes.len();
868 let lt_def_names = params.iter().filter_map(|param| match param.kind {
869 GenericParamKind::Lifetime { .. } => {
870 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
874 self.in_scope_lifetimes.extend(lt_def_names);
878 self.in_scope_lifetimes.truncate(old_len);
882 /// Appends in-band lifetime defs and argument-position `impl
883 /// Trait` defs to the existing set of generics.
885 /// Presuming that in-band lifetimes are enabled, then
886 /// `self.anonymous_lifetime_mode` will be updated to match the
887 /// parameter while `f` is running (and restored afterwards).
888 fn add_in_band_defs<T>(
891 parent_def_id: LocalDefId,
892 anonymous_lifetime_mode: AnonymousLifetimeMode,
893 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
894 ) -> (hir::Generics<'hir>, T) {
895 let (in_band_defs, (mut lowered_generics, res)) =
896 self.with_in_scope_lifetime_defs(&generics.params, |this| {
897 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
898 let mut params = Vec::new();
899 // Note: it is necessary to lower generics *before* calling `f`.
900 // When lowering `async fn`, there's a final step when lowering
901 // the return type that assumes that all in-scope lifetimes have
902 // already been added to either `in_scope_lifetimes` or
903 // `lifetimes_to_define`. If we swapped the order of these two,
904 // in-band-lifetimes introduced by generics or where-clauses
905 // wouldn't have been added yet.
906 let generics = this.lower_generics_mut(
908 ImplTraitContext::Universal(
910 this.current_hir_id_owner.last().unwrap().0,
913 let res = f(this, &mut params);
914 (params, (generics, res))
918 lowered_generics.params.extend(in_band_defs);
920 let lowered_generics = lowered_generics.into_generics(self.arena);
921 (lowered_generics, res)
924 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
925 let was_in_dyn_type = self.is_in_dyn_type;
926 self.is_in_dyn_type = in_scope;
928 let result = f(self);
930 self.is_in_dyn_type = was_in_dyn_type;
935 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
936 let was_in_loop_condition = self.is_in_loop_condition;
937 self.is_in_loop_condition = false;
939 let catch_scopes = mem::take(&mut self.catch_scopes);
940 let loop_scopes = mem::take(&mut self.loop_scopes);
942 self.catch_scopes = catch_scopes;
943 self.loop_scopes = loop_scopes;
945 self.is_in_loop_condition = was_in_loop_condition;
950 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
951 if attrs.is_empty() {
954 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
955 debug_assert!(!ret.is_empty());
956 self.attrs.insert(id, ret);
961 fn lower_attr(&self, attr: &Attribute) -> Attribute {
962 // Note that we explicitly do not walk the path. Since we don't really
963 // lower attributes (we use the AST version) there is nowhere to keep
964 // the `HirId`s. We don't actually need HIR version of attributes anyway.
965 // Tokens are also not needed after macro expansion and parsing.
966 let kind = match attr.kind {
967 AttrKind::Normal(ref item, _) => AttrKind::Normal(
969 path: item.path.clone(),
970 args: self.lower_mac_args(&item.args),
975 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
978 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
981 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
982 if let Some(&a) = self.attrs.get(&target_id) {
983 debug_assert!(!a.is_empty());
984 self.attrs.insert(id, a);
988 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
990 MacArgs::Empty => MacArgs::Empty,
991 MacArgs::Delimited(dspan, delim, ref tokens) => {
992 // This is either a non-key-value attribute, or a `macro_rules!` body.
993 // We either not have any nonterminals present (in the case of an attribute),
994 // or have tokens available for all nonterminals in the case of a nested
995 // `macro_rules`: e.g:
998 // macro_rules! outer {
1000 // macro_rules! inner {
1007 // In both cases, we don't want to synthesize any tokens
1011 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1014 // This is an inert key-value attribute - it will never be visible to macros
1015 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1016 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1017 MacArgs::Eq(eq_span, ref token) => {
1018 // In valid code the value is always representable as a single literal token.
1019 fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
1020 if tokens.len() != 1 {
1022 .delay_span_bug(span, "multiple tokens in key-value attribute's value");
1024 match tokens.into_trees().next() {
1025 Some(TokenTree::Token(token)) => token,
1026 Some(TokenTree::Delimited(_, delim, tokens)) => {
1027 if delim != token::NoDelim {
1028 sess.diagnostic().delay_span_bug(
1030 "unexpected delimiter in key-value attribute's value",
1033 unwrap_single_token(sess, tokens, span)
1035 None => Token::dummy(),
1039 let tokens = TokenStreamLowering {
1040 parse_sess: &self.sess.parse_sess,
1041 synthesize_tokens: CanSynthesizeMissingTokens::Yes,
1042 nt_to_tokenstream: self.nt_to_tokenstream,
1044 .lower_token(token.clone());
1045 MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
1050 fn lower_token_stream(
1052 tokens: TokenStream,
1053 synthesize_tokens: CanSynthesizeMissingTokens,
1055 TokenStreamLowering {
1056 parse_sess: &self.sess.parse_sess,
1058 nt_to_tokenstream: self.nt_to_tokenstream,
1060 .lower_token_stream(tokens)
1063 /// Given an associated type constraint like one of these:
1066 /// T: Iterator<Item: Debug>
1068 /// T: Iterator<Item = Debug>
1072 /// returns a `hir::TypeBinding` representing `Item`.
1073 fn lower_assoc_ty_constraint(
1075 constraint: &AssocTyConstraint,
1076 mut itctx: ImplTraitContext<'_, 'hir>,
1077 ) -> hir::TypeBinding<'hir> {
1078 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1080 // lower generic arguments of identifier in constraint
1081 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1082 let gen_args_ctor = match gen_args {
1083 GenericArgs::AngleBracketed(ref data) => {
1084 self.lower_angle_bracketed_parameter_data(
1086 ParamMode::Explicit,
1091 GenericArgs::Parenthesized(ref data) => {
1092 let mut err = self.sess.struct_span_err(
1094 "parenthesized generic arguments cannot be used in associated type constraints"
1096 // FIXME: try to write a suggestion here
1098 self.lower_angle_bracketed_parameter_data(
1099 &data.as_angle_bracketed_args(),
1100 ParamMode::Explicit,
1106 self.arena.alloc(gen_args_ctor.into_generic_args(&self.arena))
1108 self.arena.alloc(hir::GenericArgs::none())
1111 let kind = match constraint.kind {
1112 AssocTyConstraintKind::Equality { ref ty } => {
1113 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1115 AssocTyConstraintKind::Bound { ref bounds } => {
1116 let mut capturable_lifetimes;
1117 let mut parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1118 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1119 let (desugar_to_impl_trait, itctx) = match itctx {
1120 // We are in the return position:
1122 // fn foo() -> impl Iterator<Item: Debug>
1126 // fn foo() -> impl Iterator<Item = impl Debug>
1127 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1128 | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
1130 // We are in the argument position, but within a dyn type:
1132 // fn foo(x: dyn Iterator<Item: Debug>)
1136 // fn foo(x: dyn Iterator<Item = impl Debug>)
1137 ImplTraitContext::Universal(_, parent) if self.is_in_dyn_type => {
1138 parent_def_id = parent;
1142 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1143 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1144 // "impl trait context" to permit `impl Debug` in this position (it desugars
1145 // then to an opaque type).
1147 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1148 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1149 capturable_lifetimes = FxHashSet::default();
1152 ImplTraitContext::OtherOpaqueTy {
1153 capturable_lifetimes: &mut capturable_lifetimes,
1154 origin: hir::OpaqueTyOrigin::Misc,
1159 // We are in the parameter position, but not within a dyn type:
1161 // fn foo(x: impl Iterator<Item: Debug>)
1163 // so we leave it as is and this gets expanded in astconv to a bound like
1164 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1166 _ => (false, itctx),
1169 if desugar_to_impl_trait {
1170 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1171 // constructing the HIR for `impl bounds...` and then lowering that.
1173 let impl_trait_node_id = self.resolver.next_node_id();
1174 self.resolver.create_def(
1177 DefPathData::ImplTrait,
1182 self.with_dyn_type_scope(false, |this| {
1183 let node_id = this.resolver.next_node_id();
1184 let ty = this.lower_ty(
1187 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1188 span: constraint.span,
1194 hir::TypeBindingKind::Equality { ty }
1197 // Desugar `AssocTy: Bounds` into a type binding where the
1198 // later desugars into a trait predicate.
1199 let bounds = self.lower_param_bounds(bounds, itctx);
1201 hir::TypeBindingKind::Constraint { bounds }
1207 hir_id: self.lower_node_id(constraint.id),
1208 ident: constraint.ident,
1211 span: constraint.span,
1215 fn lower_generic_arg(
1217 arg: &ast::GenericArg,
1218 itctx: ImplTraitContext<'_, 'hir>,
1219 ) -> hir::GenericArg<'hir> {
1221 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1222 ast::GenericArg::Type(ty) => {
1223 // We parse const arguments as path types as we cannot distinguish them during
1224 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1225 // type and value namespaces. If we resolved the path in the value namespace, we
1226 // transform it into a generic const argument.
1227 if let TyKind::Path(ref qself, ref path) = ty.kind {
1228 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1229 let res = partial_res.base_res();
1230 if !res.matches_ns(Namespace::TypeNS) {
1232 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1236 // Construct a AnonConst where the expr is the "ty"'s path.
1238 let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1239 let node_id = self.resolver.next_node_id();
1241 // Add a definition for the in-band const def.
1242 self.resolver.create_def(
1245 DefPathData::AnonConst,
1250 let path_expr = Expr {
1252 kind: ExprKind::Path(qself.clone(), path.clone()),
1254 attrs: AttrVec::new(),
1258 let ct = self.with_new_scopes(|this| hir::AnonConst {
1259 hir_id: this.lower_node_id(node_id),
1260 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1262 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1266 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1268 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1269 value: self.lower_anon_const(&ct),
1270 span: ct.value.span,
1275 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1276 self.arena.alloc(self.lower_ty_direct(t, itctx))
1282 qself: &Option<QSelf>,
1284 param_mode: ParamMode,
1285 itctx: ImplTraitContext<'_, 'hir>,
1286 ) -> hir::Ty<'hir> {
1287 let id = self.lower_node_id(t.id);
1288 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1289 let ty = self.ty_path(id, t.span, qpath);
1290 if let hir::TyKind::TraitObject(..) = ty.kind {
1291 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1296 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1297 hir::Ty { hir_id: self.next_id(), kind, span }
1300 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1301 self.ty(span, hir::TyKind::Tup(tys))
1304 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1305 let kind = match t.kind {
1306 TyKind::Infer => hir::TyKind::Infer,
1307 TyKind::Err => hir::TyKind::Err,
1308 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1309 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1310 TyKind::Rptr(ref region, ref mt) => {
1311 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1312 let lifetime = match *region {
1313 Some(ref lt) => self.lower_lifetime(lt),
1314 None => self.elided_ref_lifetime(span),
1316 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1318 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1319 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1320 let span = this.sess.source_map().next_point(t.span.shrink_to_lo());
1321 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1322 generic_params: this.lower_generic_params(
1324 &NodeMap::default(),
1325 ImplTraitContext::disallowed(),
1327 unsafety: this.lower_unsafety(f.unsafety),
1328 abi: this.lower_extern(f.ext, span, t.id),
1329 decl: this.lower_fn_decl(&f.decl, None, false, None),
1330 param_names: this.lower_fn_params_to_names(&f.decl),
1334 TyKind::Never => hir::TyKind::Never,
1335 TyKind::Tup(ref tys) => {
1336 hir::TyKind::Tup(self.arena.alloc_from_iter(
1337 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1340 TyKind::Paren(ref ty) => {
1341 return self.lower_ty_direct(ty, itctx);
1343 TyKind::Path(ref qself, ref path) => {
1344 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1346 TyKind::ImplicitSelf => {
1347 let res = self.expect_full_res(t.id);
1348 let res = self.lower_res(res);
1349 hir::TyKind::Path(hir::QPath::Resolved(
1351 self.arena.alloc(hir::Path {
1353 segments: arena_vec![self; hir::PathSegment::from_ident(
1354 Ident::with_dummy_span(kw::SelfUpper)
1360 TyKind::Array(ref ty, ref length) => {
1361 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1363 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1364 TyKind::TraitObject(ref bounds, kind) => {
1365 let mut lifetime_bound = None;
1366 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1368 this.arena.alloc_from_iter(bounds.iter().filter_map(
1369 |bound| match *bound {
1370 GenericBound::Trait(
1372 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1373 ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
1374 // `?const ?Bound` will cause an error during AST validation
1375 // anyways, so treat it like `?Bound` as compilation proceeds.
1376 GenericBound::Trait(
1378 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1380 GenericBound::Outlives(ref lifetime) => {
1381 if lifetime_bound.is_none() {
1382 lifetime_bound = Some(this.lower_lifetime(lifetime));
1388 let lifetime_bound =
1389 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1390 (bounds, lifetime_bound)
1392 if kind != TraitObjectSyntax::Dyn {
1393 self.maybe_lint_bare_trait(t.span, t.id, false);
1395 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1397 TyKind::ImplTrait(def_node_id, ref bounds) => {
1400 ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
1401 .lower_opaque_impl_trait(
1407 |this| this.lower_param_bounds(bounds, itctx),
1409 ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => {
1410 // Reset capturable lifetimes, any nested impl trait
1411 // types will inherit lifetimes from this opaque type,
1412 // so don't need to capture them again.
1413 let nested_itctx = ImplTraitContext::OtherOpaqueTy {
1414 capturable_lifetimes: &mut FxHashSet::default(),
1417 self.lower_opaque_impl_trait(
1422 Some(capturable_lifetimes),
1423 |this| this.lower_param_bounds(bounds, nested_itctx),
1426 ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
1427 // Add a definition for the in-band `Param`.
1428 let def_id = self.resolver.local_def_id(def_node_id);
1430 let hir_bounds = self.lower_param_bounds(
1432 ImplTraitContext::Universal(in_band_ty_params, parent_def_id),
1434 // Set the name to `impl Bound1 + Bound2`.
1435 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1436 in_band_ty_params.push(hir::GenericParam {
1437 hir_id: self.lower_node_id(def_node_id),
1438 name: ParamName::Plain(ident),
1439 pure_wrt_drop: false,
1442 kind: hir::GenericParamKind::Type {
1444 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1448 hir::TyKind::Path(hir::QPath::Resolved(
1450 self.arena.alloc(hir::Path {
1452 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1453 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1457 ImplTraitContext::Disallowed(pos) => {
1458 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1459 "bindings or function and inherent method return types"
1461 "function and inherent method return types"
1463 let mut err = struct_span_err!(
1467 "`impl Trait` not allowed outside of {}",
1470 if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() {
1472 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1473 attributes to enable",
1481 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1482 TyKind::CVarArgs => {
1483 self.sess.delay_span_bug(
1485 "`TyKind::CVarArgs` should have been handled elsewhere",
1491 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1494 fn lower_opaque_impl_trait(
1497 fn_def_id: Option<DefId>,
1498 origin: hir::OpaqueTyOrigin,
1499 opaque_ty_node_id: NodeId,
1500 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1501 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1502 ) -> hir::TyKind<'hir> {
1504 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1505 fn_def_id, opaque_ty_node_id, span,
1508 // Make sure we know that some funky desugaring has been going on here.
1509 // This is a first: there is code in other places like for loop
1510 // desugaring that explicitly states that we don't want to track that.
1511 // Not tracking it makes lints in rustc and clippy very fragile, as
1512 // frequently opened issues show.
1513 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1515 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1517 self.allocate_hir_id_counter(opaque_ty_node_id);
1519 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1521 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1525 capturable_lifetimes,
1528 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1530 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1532 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1533 let opaque_ty_item = hir::OpaqueTy {
1534 generics: hir::Generics {
1535 params: lifetime_defs,
1536 where_clause: hir::WhereClause { predicates: &[], span },
1540 impl_trait_fn: fn_def_id,
1544 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1545 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
1547 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1548 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1552 /// Registers a new opaque type with the proper `NodeId`s and
1553 /// returns the lowered node-ID for the opaque type.
1554 fn generate_opaque_type(
1556 opaque_ty_id: LocalDefId,
1557 opaque_ty_item: hir::OpaqueTy<'hir>,
1559 opaque_ty_span: Span,
1561 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1562 // Generate an `type Foo = impl Trait;` declaration.
1563 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1564 let opaque_ty_item = hir::Item {
1565 def_id: opaque_ty_id,
1566 ident: Ident::invalid(),
1567 kind: opaque_ty_item_kind,
1568 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1569 span: opaque_ty_span,
1572 // Insert the item into the global item list. This usually happens
1573 // automatically for all AST items. But this opaque type item
1574 // does not actually exist in the AST.
1575 self.insert_item(opaque_ty_item);
1578 fn lifetimes_from_impl_trait_bounds(
1580 opaque_ty_id: NodeId,
1581 parent_def_id: LocalDefId,
1582 bounds: hir::GenericBounds<'hir>,
1583 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1584 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1586 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1587 parent_def_id={:?}, \
1589 opaque_ty_id, parent_def_id, bounds,
1592 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1593 // appear in the bounds, excluding lifetimes that are created within the bounds.
1594 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1595 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1596 context: &'r mut LoweringContext<'a, 'hir>,
1598 opaque_ty_id: NodeId,
1599 collect_elided_lifetimes: bool,
1600 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1601 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1602 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1603 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1604 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1607 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1608 type Map = intravisit::ErasedMap<'v>;
1610 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1611 intravisit::NestedVisitorMap::None
1614 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1615 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1616 if parameters.parenthesized {
1617 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1618 self.collect_elided_lifetimes = false;
1619 intravisit::walk_generic_args(self, span, parameters);
1620 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1622 intravisit::walk_generic_args(self, span, parameters);
1626 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1627 // Don't collect elided lifetimes used inside of `fn()` syntax.
1628 if let hir::TyKind::BareFn(_) = t.kind {
1629 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1630 self.collect_elided_lifetimes = false;
1632 // Record the "stack height" of `for<'a>` lifetime bindings
1633 // to be able to later fully undo their introduction.
1634 let old_len = self.currently_bound_lifetimes.len();
1635 intravisit::walk_ty(self, t);
1636 self.currently_bound_lifetimes.truncate(old_len);
1638 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1640 intravisit::walk_ty(self, t)
1644 fn visit_poly_trait_ref(
1646 trait_ref: &'v hir::PolyTraitRef<'v>,
1647 modifier: hir::TraitBoundModifier,
1649 // Record the "stack height" of `for<'a>` lifetime bindings
1650 // to be able to later fully undo their introduction.
1651 let old_len = self.currently_bound_lifetimes.len();
1652 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1653 self.currently_bound_lifetimes.truncate(old_len);
1656 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1657 // Record the introduction of 'a in `for<'a> ...`.
1658 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1659 // Introduce lifetimes one at a time so that we can handle
1660 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1661 let lt_name = hir::LifetimeName::Param(param.name);
1662 self.currently_bound_lifetimes.push(lt_name);
1665 intravisit::walk_generic_param(self, param);
1668 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1669 let name = match lifetime.name {
1670 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1671 if self.collect_elided_lifetimes {
1672 // Use `'_` for both implicit and underscore lifetimes in
1673 // `type Foo<'_> = impl SomeTrait<'_>;`.
1674 hir::LifetimeName::Underscore
1679 hir::LifetimeName::Param(_) => lifetime.name,
1681 // Refers to some other lifetime that is "in
1682 // scope" within the type.
1683 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1685 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1688 if !self.currently_bound_lifetimes.contains(&name)
1689 && !self.already_defined_lifetimes.contains(&name)
1690 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1692 self.already_defined_lifetimes.insert(name);
1694 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1695 hir_id: self.context.next_id(),
1696 span: lifetime.span,
1700 let def_node_id = self.context.resolver.next_node_id();
1702 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1703 self.context.resolver.create_def(
1706 DefPathData::LifetimeNs(name.ident().name),
1711 let (name, kind) = match name {
1712 hir::LifetimeName::Underscore => (
1713 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1714 hir::LifetimeParamKind::Elided,
1716 hir::LifetimeName::Param(param_name) => {
1717 (param_name, hir::LifetimeParamKind::Explicit)
1719 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1722 self.output_lifetime_params.push(hir::GenericParam {
1725 span: lifetime.span,
1726 pure_wrt_drop: false,
1728 kind: hir::GenericParamKind::Lifetime { kind },
1734 let mut lifetime_collector = ImplTraitLifetimeCollector {
1736 parent: parent_def_id,
1738 collect_elided_lifetimes: true,
1739 currently_bound_lifetimes: Vec::new(),
1740 already_defined_lifetimes: FxHashSet::default(),
1741 output_lifetimes: Vec::new(),
1742 output_lifetime_params: Vec::new(),
1743 lifetimes_to_include,
1746 for bound in bounds {
1747 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1750 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1754 self.arena.alloc_from_iter(output_lifetimes),
1755 self.arena.alloc_from_iter(output_lifetime_params),
1759 fn lower_local(&mut self, l: &Local) -> hir::Local<'hir> {
1760 let ty = l.ty.as_ref().map(|t| {
1761 let mut capturable_lifetimes;
1764 if self.sess.features_untracked().impl_trait_in_bindings {
1765 capturable_lifetimes = FxHashSet::default();
1766 ImplTraitContext::OtherOpaqueTy {
1767 capturable_lifetimes: &mut capturable_lifetimes,
1768 origin: hir::OpaqueTyOrigin::Binding,
1771 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1775 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1776 let hir_id = self.lower_node_id(l.id);
1777 self.lower_attrs(hir_id, &l.attrs);
1781 pat: self.lower_pat(&l.pat),
1784 source: hir::LocalSource::Normal,
1788 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1789 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1790 // as they are not explicit in HIR/Ty function signatures.
1791 // (instead, the `c_variadic` flag is set to `true`)
1792 let mut inputs = &decl.inputs[..];
1793 if decl.c_variadic() {
1794 inputs = &inputs[..inputs.len() - 1];
1796 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1797 PatKind::Ident(_, ident, _) => ident,
1798 _ => Ident::new(kw::Empty, param.pat.span),
1802 // Lowers a function declaration.
1804 // `decl`: the unlowered (AST) function declaration.
1805 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1806 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1807 // `make_ret_async` is also `Some`.
1808 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1809 // This guards against trait declarations and implementations where `impl Trait` is
1811 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1812 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1813 // return type `impl Trait` item.
1817 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1818 impl_trait_return_allow: bool,
1819 make_ret_async: Option<NodeId>,
1820 ) -> &'hir hir::FnDecl<'hir> {
1824 in_band_ty_params: {:?}, \
1825 impl_trait_return_allow: {}, \
1826 make_ret_async: {:?})",
1827 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1829 let lt_mode = if make_ret_async.is_some() {
1830 // In `async fn`, argument-position elided lifetimes
1831 // must be transformed into fresh generic parameters so that
1832 // they can be applied to the opaque `impl Trait` return type.
1833 AnonymousLifetimeMode::CreateParameter
1835 self.anonymous_lifetime_mode
1838 let c_variadic = decl.c_variadic();
1840 // Remember how many lifetimes were already around so that we can
1841 // only look at the lifetime parameters introduced by the arguments.
1842 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1843 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1844 // as they are not explicit in HIR/Ty function signatures.
1845 // (instead, the `c_variadic` flag is set to `true`)
1846 let mut inputs = &decl.inputs[..];
1848 inputs = &inputs[..inputs.len() - 1];
1850 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1851 if let Some((_, ibty)) = &mut in_band_ty_params {
1852 this.lower_ty_direct(
1854 ImplTraitContext::Universal(
1856 this.current_hir_id_owner.last().unwrap().0,
1860 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1865 let output = if let Some(ret_id) = make_ret_async {
1866 self.lower_async_fn_ret_ty(
1868 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1873 FnRetTy::Ty(ref ty) => {
1874 let context = match in_band_ty_params {
1875 Some((def_id, _)) if impl_trait_return_allow => {
1876 ImplTraitContext::ReturnPositionOpaqueTy {
1878 origin: hir::OpaqueTyOrigin::FnReturn,
1881 _ => ImplTraitContext::disallowed(),
1883 hir::FnRetTy::Return(self.lower_ty(ty, context))
1885 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
1889 self.arena.alloc(hir::FnDecl {
1893 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1894 use BindingMode::{ByRef, ByValue};
1895 let is_mutable_pat = matches!(
1897 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1901 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1902 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1903 // Given we are only considering `ImplicitSelf` types, we needn't consider
1904 // the case where we have a mutable pattern to a reference as that would
1905 // no longer be an `ImplicitSelf`.
1906 TyKind::Rptr(_, ref mt)
1907 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1909 hir::ImplicitSelfKind::MutRef
1911 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1912 hir::ImplicitSelfKind::ImmRef
1914 _ => hir::ImplicitSelfKind::None,
1920 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1921 // combined with the following definition of `OpaqueTy`:
1923 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1925 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1926 // `output`: unlowered output type (`T` in `-> T`)
1927 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1928 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1929 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1930 fn lower_async_fn_ret_ty(
1934 opaque_ty_node_id: NodeId,
1935 ) -> hir::FnRetTy<'hir> {
1937 "lower_async_fn_ret_ty(\
1940 opaque_ty_node_id={:?})",
1941 output, fn_def_id, opaque_ty_node_id,
1944 let span = output.span();
1946 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1948 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1950 self.allocate_hir_id_counter(opaque_ty_node_id);
1952 // When we create the opaque type for this async fn, it is going to have
1953 // to capture all the lifetimes involved in the signature (including in the
1954 // return type). This is done by introducing lifetime parameters for:
1956 // - all the explicitly declared lifetimes from the impl and function itself;
1957 // - all the elided lifetimes in the fn arguments;
1958 // - all the elided lifetimes in the return type.
1960 // So for example in this snippet:
1963 // impl<'a> Foo<'a> {
1964 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1965 // // ^ '0 ^ '1 ^ '2
1966 // // elided lifetimes used below
1971 // we would create an opaque type like:
1974 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1977 // and we would then desugar `bar` to the equivalent of:
1980 // impl<'a> Foo<'a> {
1981 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1985 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1986 // this is because the elided lifetimes from the return type
1987 // should be figured out using the ordinary elision rules, and
1988 // this desugaring achieves that.
1990 // The variable `input_lifetimes_count` tracks the number of
1991 // lifetime parameters to the opaque type *not counting* those
1992 // lifetimes elided in the return type. This includes those
1993 // that are explicitly declared (`in_scope_lifetimes`) and
1994 // those elided lifetimes we found in the arguments (current
1995 // content of `lifetimes_to_define`). Next, we will process
1996 // the return type, which will cause `lifetimes_to_define` to
1998 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2000 let lifetime_params = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2001 // We have to be careful to get elision right here. The
2002 // idea is that we create a lifetime parameter for each
2003 // lifetime in the return type. So, given a return type
2004 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2005 // Future<Output = &'1 [ &'2 u32 ]>`.
2007 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2008 // hence the elision takes place at the fn site.
2009 let future_bound = this
2010 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2011 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2014 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2016 // Calculate all the lifetimes that should be captured
2017 // by the opaque type. This should include all in-scope
2018 // lifetime parameters, including those defined in-band.
2020 // Note: this must be done after lowering the output type,
2021 // as the output type may introduce new in-band lifetimes.
2022 let lifetime_params: Vec<(Span, ParamName)> = this
2026 .map(|name| (name.ident().span, name))
2027 .chain(this.lifetimes_to_define.iter().cloned())
2030 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2031 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2032 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2034 let generic_params =
2035 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2036 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2039 let opaque_ty_item = hir::OpaqueTy {
2040 generics: hir::Generics {
2041 params: generic_params,
2042 where_clause: hir::WhereClause { predicates: &[], span },
2045 bounds: arena_vec![this; future_bound],
2046 impl_trait_fn: Some(fn_def_id),
2047 origin: hir::OpaqueTyOrigin::AsyncFn,
2050 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2051 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
2056 // As documented above on the variable
2057 // `input_lifetimes_count`, we need to create the lifetime
2058 // arguments to our opaque type. Continuing with our example,
2059 // we're creating the type arguments for the return type:
2062 // Bar<'a, 'b, '0, '1, '_>
2065 // For the "input" lifetime parameters, we wish to create
2066 // references to the parameters themselves, including the
2067 // "implicit" ones created from parameter types (`'a`, `'b`,
2070 // For the "output" lifetime parameters, we just want to
2072 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2073 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2074 |&(span, hir_name)| {
2075 // Input lifetime like `'a` or `'1`:
2076 GenericArg::Lifetime(hir::Lifetime {
2077 hir_id: self.next_id(),
2079 name: hir::LifetimeName::Param(hir_name),
2083 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2084 // Output lifetime like `'_`.
2085 GenericArg::Lifetime(hir::Lifetime {
2086 hir_id: self.next_id(),
2088 name: hir::LifetimeName::Implicit,
2090 let generic_args = self.arena.alloc_from_iter(generic_args);
2092 // Create the `Foo<...>` reference itself. Note that the `type
2093 // Foo = impl Trait` is, internally, created as a child of the
2094 // async fn, so the *type parameters* are inherited. It's
2095 // only the lifetime parameters that we must supply.
2097 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
2098 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2099 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2102 /// Transforms `-> T` into `Future<Output = T>`.
2103 fn lower_async_fn_output_type_to_future_bound(
2108 ) -> hir::GenericBound<'hir> {
2109 // Compute the `T` in `Future<Output = T>` from the return type.
2110 let output_ty = match output {
2111 FnRetTy::Ty(ty) => {
2112 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2113 // `impl Future` opaque type that `async fn` implicitly
2115 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2117 origin: hir::OpaqueTyOrigin::FnReturn,
2119 self.lower_ty(ty, context)
2121 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2125 let future_args = self.arena.alloc(hir::GenericArgs {
2127 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2128 parenthesized: false,
2131 hir::GenericBound::LangItemTrait(
2132 // ::std::future::Future<future_params>
2133 hir::LangItem::Future,
2140 fn lower_param_bound(
2143 itctx: ImplTraitContext<'_, 'hir>,
2144 ) -> hir::GenericBound<'hir> {
2146 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2147 self.lower_poly_trait_ref(ty, itctx),
2148 self.lower_trait_bound_modifier(modifier),
2150 GenericBound::Outlives(ref lifetime) => {
2151 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2156 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2157 let span = l.ident.span;
2159 ident if ident.name == kw::StaticLifetime => {
2160 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2162 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2163 AnonymousLifetimeMode::CreateParameter => {
2164 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2165 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2168 AnonymousLifetimeMode::PassThrough => {
2169 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2172 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2175 self.maybe_collect_in_band_lifetime(ident);
2176 let param_name = ParamName::Plain(ident);
2177 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2182 fn new_named_lifetime(
2186 name: hir::LifetimeName,
2187 ) -> hir::Lifetime {
2188 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2191 fn lower_generic_params_mut<'s>(
2193 params: &'s [GenericParam],
2194 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2195 mut itctx: ImplTraitContext<'s, 'hir>,
2196 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2199 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2202 fn lower_generic_params(
2204 params: &[GenericParam],
2205 add_bounds: &NodeMap<Vec<GenericBound>>,
2206 itctx: ImplTraitContext<'_, 'hir>,
2207 ) -> &'hir [hir::GenericParam<'hir>] {
2208 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2211 fn lower_generic_param(
2213 param: &GenericParam,
2214 add_bounds: &NodeMap<Vec<GenericBound>>,
2215 mut itctx: ImplTraitContext<'_, 'hir>,
2216 ) -> hir::GenericParam<'hir> {
2217 let mut bounds: Vec<_> = self
2218 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2219 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2222 let (name, kind) = match param.kind {
2223 GenericParamKind::Lifetime => {
2224 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2225 self.is_collecting_in_band_lifetimes = false;
2228 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2229 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2231 let param_name = match lt.name {
2232 hir::LifetimeName::Param(param_name) => param_name,
2233 hir::LifetimeName::Implicit
2234 | hir::LifetimeName::Underscore
2235 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2236 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2237 self.sess.diagnostic().span_bug(
2239 "object-lifetime-default should not occur here",
2242 hir::LifetimeName::Error => ParamName::Error,
2246 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2248 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2252 GenericParamKind::Type { ref default, .. } => {
2253 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2254 if !add_bounds.is_empty() {
2255 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2256 bounds.extend(params);
2259 let kind = hir::GenericParamKind::Type {
2260 default: default.as_ref().map(|x| {
2263 ImplTraitContext::OtherOpaqueTy {
2264 capturable_lifetimes: &mut FxHashSet::default(),
2265 origin: hir::OpaqueTyOrigin::Misc,
2272 .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic))
2273 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2277 (hir::ParamName::Plain(param.ident), kind)
2279 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2281 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2282 this.lower_ty(&ty, ImplTraitContext::disallowed())
2284 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2285 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty, default })
2289 let hir_id = self.lower_node_id(param.id);
2290 self.lower_attrs(hir_id, ¶m.attrs);
2294 span: param.ident.span,
2295 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2296 bounds: self.arena.alloc_from_iter(bounds),
2304 itctx: ImplTraitContext<'_, 'hir>,
2305 ) -> hir::TraitRef<'hir> {
2306 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2307 hir::QPath::Resolved(None, path) => path,
2308 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2310 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2313 fn lower_poly_trait_ref(
2316 mut itctx: ImplTraitContext<'_, 'hir>,
2317 ) -> hir::PolyTraitRef<'hir> {
2318 let bound_generic_params = self.lower_generic_params(
2319 &p.bound_generic_params,
2320 &NodeMap::default(),
2324 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2325 // Any impl Trait types defined within this scope can capture
2326 // lifetimes bound on this predicate.
2327 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2328 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2329 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2333 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2334 capturable_lifetimes.extend(lt_def_names.clone());
2337 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2339 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2340 for param in lt_def_names {
2341 capturable_lifetimes.remove(¶m);
2347 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2350 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2351 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2354 fn lower_param_bounds(
2356 bounds: &[GenericBound],
2357 itctx: ImplTraitContext<'_, 'hir>,
2358 ) -> hir::GenericBounds<'hir> {
2359 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2362 fn lower_param_bounds_mut<'s>(
2364 bounds: &'s [GenericBound],
2365 mut itctx: ImplTraitContext<'s, 'hir>,
2366 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2367 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2370 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2371 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2374 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2375 let (stmts, expr) = match &*b.stmts {
2376 [stmts @ .., Stmt { kind: StmtKind::Expr(e), .. }] => (stmts, Some(&*e)),
2377 stmts => (stmts, None),
2379 let stmts = self.arena.alloc_from_iter(stmts.iter().flat_map(|stmt| self.lower_stmt(stmt)));
2380 let expr = expr.map(|e| self.lower_expr(e));
2381 let rules = self.lower_block_check_mode(&b.rules);
2382 let hir_id = self.lower_node_id(b.id);
2384 hir::Block { hir_id, stmts, expr, rules, span: b.span, targeted_by_break }
2387 /// Lowers a block directly to an expression, presuming that it
2388 /// has no attributes and is not targeted by a `break`.
2389 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2390 let block = self.lower_block(b, false);
2391 self.expr_block(block, AttrVec::new())
2394 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2395 self.with_new_scopes(|this| hir::AnonConst {
2396 hir_id: this.lower_node_id(c.id),
2397 body: this.lower_const_body(c.value.span, Some(&c.value)),
2401 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2402 let (hir_id, kind) = match s.kind {
2403 StmtKind::Local(ref l) => {
2404 let l = self.lower_local(l);
2405 let hir_id = self.lower_node_id(s.id);
2406 self.alias_attrs(hir_id, l.hir_id);
2407 return smallvec![hir::Stmt {
2409 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2413 StmtKind::Item(ref it) => {
2414 // Can only use the ID once.
2415 let mut id = Some(s.id);
2422 .map(|id| self.lower_node_id(id))
2423 .unwrap_or_else(|| self.next_id());
2425 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2429 StmtKind::Expr(ref e) => {
2430 let e = self.lower_expr(e);
2431 let hir_id = self.lower_node_id(s.id);
2432 self.alias_attrs(hir_id, e.hir_id);
2433 (hir_id, hir::StmtKind::Expr(e))
2435 StmtKind::Semi(ref e) => {
2436 let e = self.lower_expr(e);
2437 let hir_id = self.lower_node_id(s.id);
2438 self.alias_attrs(hir_id, e.hir_id);
2439 (hir_id, hir::StmtKind::Semi(e))
2441 StmtKind::Empty => return smallvec![],
2442 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
2444 smallvec![hir::Stmt { hir_id, kind, span: s.span }]
2447 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2449 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2450 BlockCheckMode::Unsafe(u) => {
2451 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2456 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2458 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2459 UserProvided => hir::UnsafeSource::UserProvided,
2463 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2465 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2466 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2468 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2469 // placeholder for compilation to proceed.
2470 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2471 hir::TraitBoundModifier::Maybe
2476 // Helper methods for building HIR.
2478 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2479 hir::Stmt { span, kind, hir_id: self.next_id() }
2482 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2483 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2488 attrs: Option<&'hir [Attribute]>,
2490 init: Option<&'hir hir::Expr<'hir>>,
2491 pat: &'hir hir::Pat<'hir>,
2492 source: hir::LocalSource,
2493 ) -> hir::Stmt<'hir> {
2494 let hir_id = self.next_id();
2495 if let Some(a) = attrs {
2496 debug_assert!(!a.is_empty());
2497 self.attrs.insert(hir_id, a);
2499 let local = hir::Local { hir_id, init, pat, source, span, ty: None };
2500 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2503 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2504 self.block_all(expr.span, &[], Some(expr))
2510 stmts: &'hir [hir::Stmt<'hir>],
2511 expr: Option<&'hir hir::Expr<'hir>>,
2512 ) -> &'hir hir::Block<'hir> {
2513 let blk = hir::Block {
2516 hir_id: self.next_id(),
2517 rules: hir::BlockCheckMode::DefaultBlock,
2519 targeted_by_break: false,
2521 self.arena.alloc(blk)
2524 /// Constructs a `true` or `false` literal pattern.
2525 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2526 let expr = self.expr_bool(span, val);
2527 self.pat(span, hir::PatKind::Lit(expr))
2530 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2531 let field = self.single_pat_field(span, pat);
2532 self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
2535 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2536 let field = self.single_pat_field(span, pat);
2537 self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field)
2540 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2541 let field = self.single_pat_field(span, pat);
2542 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2545 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2546 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2549 fn single_pat_field(
2552 pat: &'hir hir::Pat<'hir>,
2553 ) -> &'hir [hir::PatField<'hir>] {
2554 let field = hir::PatField {
2555 hir_id: self.next_id(),
2556 ident: Ident::new(sym::integer(0), span),
2557 is_shorthand: false,
2561 arena_vec![self; field]
2564 fn pat_lang_item_variant(
2567 lang_item: hir::LangItem,
2568 fields: &'hir [hir::PatField<'hir>],
2569 ) -> &'hir hir::Pat<'hir> {
2570 let qpath = hir::QPath::LangItem(lang_item, span);
2571 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2574 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2575 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2578 fn pat_ident_binding_mode(
2582 bm: hir::BindingAnnotation,
2583 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2584 let hir_id = self.next_id();
2587 self.arena.alloc(hir::Pat {
2589 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2591 default_binding_modes: true,
2597 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2598 self.pat(span, hir::PatKind::Wild)
2601 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2602 self.arena.alloc(hir::Pat {
2603 hir_id: self.next_id(),
2606 default_binding_modes: true,
2610 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2611 self.arena.alloc(hir::Pat {
2612 hir_id: self.next_id(),
2615 default_binding_modes: false,
2621 mut hir_id: hir::HirId,
2623 qpath: hir::QPath<'hir>,
2624 ) -> hir::Ty<'hir> {
2625 let kind = match qpath {
2626 hir::QPath::Resolved(None, path) => {
2627 // Turn trait object paths into `TyKind::TraitObject` instead.
2629 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2630 let principal = hir::PolyTraitRef {
2631 bound_generic_params: &[],
2632 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2636 // The original ID is taken by the `PolyTraitRef`,
2637 // so the `Ty` itself needs a different one.
2638 hir_id = self.next_id();
2639 hir::TyKind::TraitObject(
2640 arena_vec![self; principal],
2641 self.elided_dyn_bound(span),
2642 TraitObjectSyntax::None,
2645 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2648 _ => hir::TyKind::Path(qpath),
2651 hir::Ty { hir_id, kind, span }
2654 /// Invoked to create the lifetime argument for a type `&T`
2655 /// with no explicit lifetime.
2656 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2657 match self.anonymous_lifetime_mode {
2658 // Intercept when we are in an impl header or async fn and introduce an in-band
2660 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2662 AnonymousLifetimeMode::CreateParameter => {
2663 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2665 hir_id: self.next_id(),
2667 name: hir::LifetimeName::Param(fresh_name),
2671 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2673 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2677 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2678 /// return a "error lifetime".
2679 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2680 let (id, msg, label) = match id {
2681 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2684 self.resolver.next_node_id(),
2685 "`&` without an explicit lifetime name cannot be used here",
2686 "explicit lifetime name needed here",
2690 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2691 err.span_label(span, label);
2694 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2697 /// Invoked to create the lifetime argument(s) for a path like
2698 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2699 /// sorts of cases are deprecated. This may therefore report a warning or an
2700 /// error, depending on the mode.
2701 fn elided_path_lifetimes<'s>(
2705 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2706 (0..count).map(move |_| self.elided_path_lifetime(span))
2709 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2710 match self.anonymous_lifetime_mode {
2711 AnonymousLifetimeMode::CreateParameter => {
2712 // We should have emitted E0726 when processing this path above
2714 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2715 let id = self.resolver.next_node_id();
2716 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2718 // `PassThrough` is the normal case.
2719 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2720 // is unsuitable here, as these can occur from missing lifetime parameters in a
2721 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2722 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2723 // later, at which point a suitable error will be emitted.
2724 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2725 self.new_implicit_lifetime(span)
2730 /// Invoked to create the lifetime argument(s) for an elided trait object
2731 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2732 /// when the bound is written, even if it is written with `'_` like in
2733 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2734 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2735 match self.anonymous_lifetime_mode {
2736 // NB. We intentionally ignore the create-parameter mode here.
2737 // and instead "pass through" to resolve-lifetimes, which will apply
2738 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2739 // do not act like other elided lifetimes. In other words, given this:
2741 // impl Foo for Box<dyn Debug>
2743 // we do not introduce a fresh `'_` to serve as the bound, but instead
2744 // ultimately translate to the equivalent of:
2746 // impl Foo for Box<dyn Debug + 'static>
2748 // `resolve_lifetime` has the code to make that happen.
2749 AnonymousLifetimeMode::CreateParameter => {}
2751 AnonymousLifetimeMode::ReportError => {
2752 // ReportError applies to explicit use of `'_`.
2755 // This is the normal case.
2756 AnonymousLifetimeMode::PassThrough => {}
2759 let r = hir::Lifetime {
2760 hir_id: self.next_id(),
2762 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2764 debug!("elided_dyn_bound: r={:?}", r);
2768 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2769 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2772 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2773 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2774 // call site which do not have a macro backtrace. See #61963.
2775 let is_macro_callsite = self
2778 .span_to_snippet(span)
2779 .map(|snippet| snippet.starts_with("#["))
2781 if !is_macro_callsite {
2782 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2786 "trait objects without an explicit `dyn` are deprecated",
2787 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2792 fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId, default: Abi) {
2793 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2794 // call site which do not have a macro backtrace. See #61963.
2795 let is_macro_callsite = self
2798 .span_to_snippet(span)
2799 .map(|snippet| snippet.starts_with("#["))
2801 if !is_macro_callsite {
2802 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2806 "extern declarations without an explicit ABI are deprecated",
2807 BuiltinLintDiagnostics::MissingAbi(span, default),
2813 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2814 // Sorting by span ensures that we get things in order within a
2815 // file, and also puts the files in a sensible order.
2816 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2817 body_ids.sort_by_key(|b| bodies[b].value.span);
2821 /// Helper struct for delayed construction of GenericArgs.
2822 struct GenericArgsCtor<'hir> {
2823 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2824 bindings: &'hir [hir::TypeBinding<'hir>],
2825 parenthesized: bool,
2828 impl<'hir> GenericArgsCtor<'hir> {
2829 fn is_empty(&self) -> bool {
2830 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2833 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2835 args: arena.alloc_from_iter(self.args),
2836 bindings: self.bindings,
2837 parenthesized: self.parenthesized,