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(crate_visibility_modifier)]
34 #![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_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, 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::HirId, 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<hir::HirId>>,
113 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
115 generator_kind: Option<hir::GeneratorKind>,
117 /// When inside an `async` context, this is the `HirId` of the
118 /// `task_context` local bound to the resume argument of the generator.
119 task_context: Option<hir::HirId>,
121 /// Used to get the current `fn`'s def span to point to when using `await`
122 /// outside of an `async fn`.
123 current_item: Option<Span>,
125 catch_scopes: Vec<NodeId>,
126 loop_scopes: Vec<NodeId>,
127 is_in_loop_condition: bool,
128 is_in_trait_impl: bool,
129 is_in_dyn_type: bool,
131 /// What to do when we encounter either an "anonymous lifetime
132 /// reference". The term "anonymous" is meant to encompass both
133 /// `'_` lifetimes as well as fully elided cases where nothing is
134 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
135 anonymous_lifetime_mode: AnonymousLifetimeMode,
137 /// Used to create lifetime definitions from in-band lifetime usages.
138 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
139 /// When a named lifetime is encountered in a function or impl header and
140 /// has not been defined
141 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
142 /// to this list. The results of this list are then added to the list of
143 /// lifetime definitions in the corresponding impl or function generics.
144 lifetimes_to_define: Vec<(Span, ParamName)>,
146 /// `true` if in-band lifetimes are being collected. This is used to
147 /// indicate whether or not we're in a place where new lifetimes will result
148 /// in in-band lifetime definitions, such a function or an impl header,
149 /// including implicit lifetimes from `impl_header_lifetime_elision`.
150 is_collecting_in_band_lifetimes: bool,
152 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
153 /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
154 /// against this list to see if it is already in-scope, or if a definition
155 /// needs to be created for it.
157 /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
159 in_scope_lifetimes: Vec<ParamName>,
161 current_module: hir::HirId,
163 type_def_lifetime_params: DefIdMap<usize>,
165 current_hir_id_owner: Vec<(LocalDefId, u32)>,
166 item_local_id_counters: NodeMap<u32>,
167 node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
169 allow_try_trait: Option<Lrc<[Symbol]>>,
170 allow_gen_future: Option<Lrc<[Symbol]>>,
173 pub trait ResolverAstLowering {
174 fn def_key(&mut self, id: DefId) -> DefKey;
176 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
178 /// Obtains resolution for a `NodeId` with a single resolution.
179 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
181 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
182 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
184 /// Obtains resolution for a label with the given `NodeId`.
185 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
187 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
188 /// This should only return `None` during testing.
189 fn definitions(&mut self) -> &mut Definitions;
191 fn lint_buffer(&mut self) -> &mut LintBuffer;
193 fn next_node_id(&mut self) -> NodeId;
195 fn trait_map(&self) -> &NodeMap<Vec<hir::TraitCandidate>>;
197 fn opt_local_def_id(&self, node: NodeId) -> Option<LocalDefId>;
199 fn local_def_id(&self, node: NodeId) -> LocalDefId;
204 node_id: ast::NodeId,
211 type NtToTokenstream = fn(&Nonterminal, &ParseSess, CanSynthesizeMissingTokens) -> TokenStream;
213 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
214 /// and if so, what meaning it has.
216 enum ImplTraitContext<'b, 'a> {
217 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
218 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
219 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
221 /// Newly generated parameters should be inserted into the given `Vec`.
222 Universal(&'b mut Vec<hir::GenericParam<'a>>),
224 /// Treat `impl Trait` as shorthand for a new opaque type.
225 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
226 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
228 ReturnPositionOpaqueTy {
229 /// `DefId` for the parent function, used to look up necessary
230 /// information later.
232 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
233 origin: hir::OpaqueTyOrigin,
235 /// Impl trait in type aliases, consts and statics.
237 /// Set of lifetimes that this opaque type can capture, if it uses
238 /// them. This includes lifetimes bound since we entered this context.
241 /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
243 /// the inner opaque type captures `'a` because it uses it. It doesn't
244 /// need to capture `'b` because it already inherits the lifetime
245 /// parameter from `A`.
246 // FIXME(impl_trait): but `required_region_bounds` will ICE later
248 capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
249 /// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding,
250 origin: hir::OpaqueTyOrigin,
252 /// `impl Trait` is not accepted in this position.
253 Disallowed(ImplTraitPosition),
256 /// Position in which `impl Trait` is disallowed.
257 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
258 enum ImplTraitPosition {
259 /// Disallowed in `let` / `const` / `static` bindings.
262 /// All other positions.
266 impl<'a> ImplTraitContext<'_, 'a> {
268 fn disallowed() -> Self {
269 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
272 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
273 use self::ImplTraitContext::*;
275 Universal(params) => Universal(params),
276 ReturnPositionOpaqueTy { fn_def_id, origin } => {
277 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
279 OtherOpaqueTy { capturable_lifetimes, origin } => {
280 OtherOpaqueTy { capturable_lifetimes, origin: *origin }
282 Disallowed(pos) => Disallowed(*pos),
287 pub fn lower_crate<'a, 'hir>(
290 resolver: &'a mut dyn ResolverAstLowering,
291 nt_to_tokenstream: NtToTokenstream,
292 arena: &'hir Arena<'hir>,
293 ) -> hir::Crate<'hir> {
294 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
301 items: BTreeMap::new(),
302 trait_items: BTreeMap::new(),
303 impl_items: BTreeMap::new(),
304 foreign_items: BTreeMap::new(),
305 bodies: BTreeMap::new(),
306 trait_impls: BTreeMap::new(),
307 modules: BTreeMap::new(),
308 exported_macros: Vec::new(),
309 non_exported_macro_attrs: Vec::new(),
310 catch_scopes: Vec::new(),
311 loop_scopes: Vec::new(),
312 is_in_loop_condition: false,
313 is_in_trait_impl: false,
314 is_in_dyn_type: false,
315 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
316 type_def_lifetime_params: Default::default(),
317 current_module: hir::CRATE_HIR_ID,
318 current_hir_id_owner: vec![(LocalDefId { local_def_index: CRATE_DEF_INDEX }, 0)],
319 item_local_id_counters: Default::default(),
320 node_id_to_hir_id: IndexVec::new(),
321 generator_kind: None,
324 lifetimes_to_define: Vec::new(),
325 is_collecting_in_band_lifetimes: false,
326 in_scope_lifetimes: Vec::new(),
327 allow_try_trait: Some([sym::try_trait][..].into()),
328 allow_gen_future: Some([sym::gen_future][..].into()),
333 #[derive(Copy, Clone, PartialEq)]
335 /// Any path in a type context.
337 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
339 /// The `module::Type` in `module::Type::method` in an expression.
343 enum ParenthesizedGenericArgs {
348 /// What to do when we encounter an **anonymous** lifetime
349 /// reference. Anonymous lifetime references come in two flavors. You
350 /// have implicit, or fully elided, references to lifetimes, like the
351 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
352 /// or `Ref<'_, T>`. These often behave the same, but not always:
354 /// - certain usages of implicit references are deprecated, like
355 /// `Ref<T>`, and we sometimes just give hard errors in those cases
357 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
358 /// the same as `Box<dyn Foo + '_>`.
360 /// We describe the effects of the various modes in terms of three cases:
362 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
363 /// of a `&` (e.g., the missing lifetime in something like `&T`)
364 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
365 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
366 /// elided bounds follow special rules. Note that this only covers
367 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
368 /// '_>` is a case of "modern" elision.
369 /// - **Deprecated** -- this covers cases like `Ref<T>`, where the lifetime
370 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
371 /// non-deprecated equivalent.
373 /// Currently, the handling of lifetime elision is somewhat spread out
374 /// between HIR lowering and -- as described below -- the
375 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
376 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
377 /// everything into HIR lowering.
378 #[derive(Copy, Clone, Debug)]
379 enum AnonymousLifetimeMode {
380 /// For **Modern** cases, create a new anonymous region parameter
381 /// and reference that.
383 /// For **Dyn Bound** cases, pass responsibility to
384 /// `resolve_lifetime` code.
386 /// For **Deprecated** cases, report an error.
389 /// Give a hard error when either `&` or `'_` is written. Used to
390 /// rule out things like `where T: Foo<'_>`. Does not imply an
391 /// error on default object bounds (e.g., `Box<dyn Foo>`).
394 /// Pass responsibility to `resolve_lifetime` code for all cases.
398 struct TokenStreamLowering<'a> {
399 parse_sess: &'a ParseSess,
400 synthesize_tokens: CanSynthesizeMissingTokens,
401 nt_to_tokenstream: NtToTokenstream,
404 impl<'a> TokenStreamLowering<'a> {
405 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
406 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
409 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
411 TokenTree::Token(token) => self.lower_token(token),
412 TokenTree::Delimited(span, delim, tts) => {
413 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
418 fn lower_token(&mut self, token: Token) -> TokenStream {
420 token::Interpolated(nt) => {
421 let tts = (self.nt_to_tokenstream)(&nt, self.parse_sess, self.synthesize_tokens);
422 TokenTree::Delimited(
423 DelimSpan::from_single(token.span),
425 self.lower_token_stream(tts),
429 _ => TokenTree::Token(token).into(),
434 struct ImplTraitTypeIdVisitor<'a> {
435 ids: &'a mut SmallVec<[NodeId; 1]>,
438 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
439 fn visit_ty(&mut self, ty: &Ty) {
441 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
443 TyKind::ImplTrait(id, _) => self.ids.push(id),
446 visit::walk_ty(self, ty);
449 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
450 if let Some(ref p) = path_segment.args {
451 if let GenericArgs::Parenthesized(_) = **p {
455 visit::walk_path_segment(self, path_span, path_segment)
459 impl<'a, 'hir> LoweringContext<'a, 'hir> {
460 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
461 /// Full-crate AST visitor that inserts into a fresh
462 /// `LoweringContext` any information that may be
463 /// needed from arbitrary locations in the crate,
464 /// e.g., the number of lifetime generic parameters
465 /// declared for every type and trait definition.
466 struct MiscCollector<'tcx, 'lowering, 'hir> {
467 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
470 impl MiscCollector<'_, '_, '_> {
471 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: LocalDefId) {
473 UseTreeKind::Simple(_, id1, id2) => {
474 for &id in &[id1, id2] {
475 self.lctx.resolver.create_def(
482 self.lctx.allocate_hir_id_counter(id);
485 UseTreeKind::Glob => (),
486 UseTreeKind::Nested(ref trees) => {
487 for &(ref use_tree, id) in trees {
488 let hir_id = self.lctx.allocate_hir_id_counter(id);
489 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
496 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
497 fn visit_item(&mut self, item: &'tcx Item) {
498 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
501 ItemKind::Struct(_, ref generics)
502 | ItemKind::Union(_, ref generics)
503 | ItemKind::Enum(_, ref generics)
504 | ItemKind::TyAlias(box TyAliasKind(_, ref generics, ..))
505 | ItemKind::Trait(box TraitKind(_, _, ref generics, ..)) => {
506 let def_id = self.lctx.resolver.local_def_id(item.id);
511 matches!(param.kind, ast::GenericParamKind::Lifetime { .. })
514 self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
516 ItemKind::Use(ref use_tree) => {
517 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
522 visit::walk_item(self, item);
525 fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
526 self.lctx.allocate_hir_id_counter(item.id);
527 visit::walk_assoc_item(self, item, ctxt);
530 fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
531 self.lctx.allocate_hir_id_counter(item.id);
532 visit::walk_foreign_item(self, item);
535 fn visit_ty(&mut self, t: &'tcx Ty) {
537 // Mirrors the case in visit::walk_ty
538 TyKind::BareFn(ref f) => {
539 walk_list!(self, visit_generic_param, &f.generic_params);
540 // Mirrors visit::walk_fn_decl
541 for parameter in &f.decl.inputs {
542 // We don't lower the ids of argument patterns
543 self.visit_pat(¶meter.pat);
544 self.visit_ty(¶meter.ty)
546 self.visit_fn_ret_ty(&f.decl.output)
548 TyKind::ImplTrait(def_node_id, _) => {
549 self.lctx.allocate_hir_id_counter(def_node_id);
550 visit::walk_ty(self, t);
552 _ => visit::walk_ty(self, t),
557 self.lower_node_id(CRATE_NODE_ID);
558 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
560 visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
561 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
563 let module = self.lower_mod(&c.module);
564 let attrs = self.lower_attrs(&c.attrs);
565 let body_ids = body_ids(&self.bodies);
567 c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
573 .filter_map(|(&k, v)| {
574 self.node_id_to_hir_id.get(k).and_then(|id| id.as_ref()).map(|id| (*id, v.clone()))
578 let mut def_id_to_hir_id = IndexVec::default();
580 for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
581 if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
582 if def_id_to_hir_id.len() <= def_id.index() {
583 def_id_to_hir_id.resize(def_id.index() + 1, None);
585 def_id_to_hir_id[def_id] = hir_id;
589 self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
592 item: hir::CrateItem { module, attrs, span: c.span },
593 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
594 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
596 trait_items: self.trait_items,
597 impl_items: self.impl_items,
598 foreign_items: self.foreign_items,
601 trait_impls: self.trait_impls,
602 modules: self.modules,
608 fn insert_item(&mut self, item: hir::Item<'hir>) {
609 let id = item.hir_id;
610 // FIXME: Use `debug_asset-rt`.
611 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
612 self.items.insert(id, item);
613 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
616 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
617 // Set up the counter if needed.
618 self.item_local_id_counters.entry(owner).or_insert(0);
619 // Always allocate the first `HirId` for the owner itself.
620 let lowered = self.lower_node_id_with_owner(owner, owner);
621 debug_assert_eq!(lowered.local_id.as_u32(), 0);
625 fn lower_node_id_generic(
628 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
630 assert_ne!(ast_node_id, DUMMY_NODE_ID);
632 let min_size = ast_node_id.as_usize() + 1;
634 if min_size > self.node_id_to_hir_id.len() {
635 self.node_id_to_hir_id.resize(min_size, None);
638 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
641 // Generate a new `HirId`.
642 let hir_id = alloc_hir_id(self);
643 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
649 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
651 .item_local_id_counters
652 .insert(owner, HIR_ID_COUNTER_LOCKED)
653 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
654 let def_id = self.resolver.local_def_id(owner);
655 self.current_hir_id_owner.push((def_id, counter));
657 let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap();
659 debug_assert!(def_id == new_def_id);
660 debug_assert!(new_counter >= counter);
662 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
663 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
667 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
668 /// the `LoweringContext`'s `NodeId => HirId` map.
669 /// Take care not to call this method if the resulting `HirId` is then not
670 /// actually used in the HIR, as that would trigger an assertion in the
671 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
672 /// properly. Calling the method twice with the same `NodeId` is fine though.
673 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
674 self.lower_node_id_generic(ast_node_id, |this| {
675 let &mut (owner, ref mut local_id_counter) =
676 this.current_hir_id_owner.last_mut().unwrap();
677 let local_id = *local_id_counter;
678 *local_id_counter += 1;
679 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
683 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
684 self.lower_node_id_generic(ast_node_id, |this| {
685 let local_id_counter = this
686 .item_local_id_counters
688 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
689 let local_id = *local_id_counter;
691 // We want to be sure not to modify the counter in the map while it
692 // is also on the stack. Otherwise we'll get lost updates when writing
693 // back from the stack to the map.
694 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
696 *local_id_counter += 1;
697 let owner = this.resolver.opt_local_def_id(owner).expect(
698 "you forgot to call `create_def` or are lowering node-IDs \
699 that do not belong to the current owner",
702 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
706 fn next_id(&mut self) -> hir::HirId {
707 let node_id = self.resolver.next_node_id();
708 self.lower_node_id(node_id)
711 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
713 self.lower_node_id_generic(id, |_| {
714 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
719 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
720 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
721 if pr.unresolved_segments() != 0 {
722 panic!("path not fully resolved: {:?}", pr);
728 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
729 self.resolver.get_import_res(id).present_items()
732 fn diagnostic(&self) -> &rustc_errors::Handler {
733 self.sess.diagnostic()
736 /// Reuses the span but adds information like the kind of the desugaring and features that are
737 /// allowed inside this span.
738 fn mark_span_with_reason(
740 reason: DesugaringKind,
742 allow_internal_unstable: Option<Lrc<[Symbol]>>,
744 span.mark_with_reason(allow_internal_unstable, reason, self.sess.edition())
747 fn with_anonymous_lifetime_mode<R>(
749 anonymous_lifetime_mode: AnonymousLifetimeMode,
750 op: impl FnOnce(&mut Self) -> R,
753 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
754 anonymous_lifetime_mode,
756 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
757 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
758 let result = op(self);
759 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
761 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
762 old_anonymous_lifetime_mode
767 /// Creates a new `hir::GenericParam` for every new lifetime and
768 /// type parameter encountered while evaluating `f`. Definitions
769 /// are created with the parent provided. If no `parent_id` is
770 /// provided, no definitions will be returned.
772 /// Presuming that in-band lifetimes are enabled, then
773 /// `self.anonymous_lifetime_mode` will be updated to match the
774 /// parameter while `f` is running (and restored afterwards).
775 fn collect_in_band_defs<T>(
777 parent_def_id: LocalDefId,
778 anonymous_lifetime_mode: AnonymousLifetimeMode,
779 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
780 ) -> (Vec<hir::GenericParam<'hir>>, T) {
781 assert!(!self.is_collecting_in_band_lifetimes);
782 assert!(self.lifetimes_to_define.is_empty());
783 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
785 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
786 self.is_collecting_in_band_lifetimes = true;
788 let (in_band_ty_params, res) = f(self);
790 self.is_collecting_in_band_lifetimes = false;
791 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
793 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
795 let params = lifetimes_to_define
797 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
798 .chain(in_band_ty_params.into_iter())
804 /// Converts a lifetime into a new generic parameter.
805 fn lifetime_to_generic_param(
809 parent_def_id: LocalDefId,
810 ) -> hir::GenericParam<'hir> {
811 let node_id = self.resolver.next_node_id();
813 // Get the name we'll use to make the def-path. Note
814 // that collisions are ok here and this shouldn't
815 // really show up for end-user.
816 let (str_name, kind) = match hir_name {
817 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
818 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
819 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
822 // Add a definition for the in-band lifetime def.
823 self.resolver.create_def(
826 DefPathData::LifetimeNs(str_name),
832 hir_id: self.lower_node_id(node_id),
837 pure_wrt_drop: false,
838 kind: hir::GenericParamKind::Lifetime { kind },
842 /// When there is a reference to some lifetime `'a`, and in-band
843 /// lifetimes are enabled, then we want to push that lifetime into
844 /// the vector of names to define later. In that case, it will get
845 /// added to the appropriate generics.
846 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
847 if !self.is_collecting_in_band_lifetimes {
851 if !self.sess.features_untracked().in_band_lifetimes {
855 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
859 let hir_name = ParamName::Plain(ident);
861 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
862 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
867 self.lifetimes_to_define.push((ident.span, hir_name));
870 /// When we have either an elided or `'_` lifetime in an impl
871 /// header, we convert it to an in-band lifetime.
872 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
873 assert!(self.is_collecting_in_band_lifetimes);
874 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
875 let hir_name = ParamName::Fresh(index);
876 self.lifetimes_to_define.push((span, hir_name));
880 // Evaluates `f` with the lifetimes in `params` in-scope.
881 // This is used to track which lifetimes have already been defined, and
882 // which are new in-band lifetimes that need to have a definition created
884 fn with_in_scope_lifetime_defs<T>(
886 params: &[GenericParam],
887 f: impl FnOnce(&mut Self) -> T,
889 let old_len = self.in_scope_lifetimes.len();
890 let lt_def_names = params.iter().filter_map(|param| match param.kind {
891 GenericParamKind::Lifetime { .. } => {
892 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
896 self.in_scope_lifetimes.extend(lt_def_names);
900 self.in_scope_lifetimes.truncate(old_len);
904 /// Appends in-band lifetime defs and argument-position `impl
905 /// Trait` defs to the existing set of generics.
907 /// Presuming that in-band lifetimes are enabled, then
908 /// `self.anonymous_lifetime_mode` will be updated to match the
909 /// parameter while `f` is running (and restored afterwards).
910 fn add_in_band_defs<T>(
913 parent_def_id: LocalDefId,
914 anonymous_lifetime_mode: AnonymousLifetimeMode,
915 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
916 ) -> (hir::Generics<'hir>, T) {
917 let (in_band_defs, (mut lowered_generics, res)) =
918 self.with_in_scope_lifetime_defs(&generics.params, |this| {
919 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
920 let mut params = Vec::new();
921 // Note: it is necessary to lower generics *before* calling `f`.
922 // When lowering `async fn`, there's a final step when lowering
923 // the return type that assumes that all in-scope lifetimes have
924 // already been added to either `in_scope_lifetimes` or
925 // `lifetimes_to_define`. If we swapped the order of these two,
926 // in-band-lifetimes introduced by generics or where-clauses
927 // wouldn't have been added yet.
929 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
930 let res = f(this, &mut params);
931 (params, (generics, res))
935 lowered_generics.params.extend(in_band_defs);
937 let lowered_generics = lowered_generics.into_generics(self.arena);
938 (lowered_generics, res)
941 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
942 let was_in_dyn_type = self.is_in_dyn_type;
943 self.is_in_dyn_type = in_scope;
945 let result = f(self);
947 self.is_in_dyn_type = was_in_dyn_type;
952 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
953 let was_in_loop_condition = self.is_in_loop_condition;
954 self.is_in_loop_condition = false;
956 let catch_scopes = mem::take(&mut self.catch_scopes);
957 let loop_scopes = mem::take(&mut self.loop_scopes);
959 self.catch_scopes = catch_scopes;
960 self.loop_scopes = loop_scopes;
962 self.is_in_loop_condition = was_in_loop_condition;
967 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
968 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
971 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
972 // Note that we explicitly do not walk the path. Since we don't really
973 // lower attributes (we use the AST version) there is nowhere to keep
974 // the `HirId`s. We don't actually need HIR version of attributes anyway.
975 // Tokens are also not needed after macro expansion and parsing.
976 let kind = match attr.kind {
977 AttrKind::Normal(ref item, _) => AttrKind::Normal(
979 path: item.path.clone(),
980 args: self.lower_mac_args(&item.args),
985 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
988 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
991 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
993 MacArgs::Empty => MacArgs::Empty,
994 MacArgs::Delimited(dspan, delim, ref tokens) => {
995 // This is either a non-key-value attribute, or a `macro_rules!` body.
996 // We either not have any nonterminals present (in the case of an attribute),
997 // or have tokens available for all nonterminals in the case of a nested
998 // `macro_rules`: e.g:
1001 // macro_rules! outer {
1003 // macro_rules! inner {
1010 // In both cases, we don't want to synthesize any tokens
1014 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1017 // This is an inert key-value attribute - it will never be visible to macros
1018 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1019 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1020 MacArgs::Eq(eq_span, ref token) => {
1021 // In valid code the value is always representable as a single literal token.
1022 fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
1023 if tokens.len() != 1 {
1025 .delay_span_bug(span, "multiple tokens in key-value attribute's value");
1027 match tokens.into_trees().next() {
1028 Some(TokenTree::Token(token)) => token,
1029 Some(TokenTree::Delimited(_, delim, tokens)) => {
1030 if delim != token::NoDelim {
1031 sess.diagnostic().delay_span_bug(
1033 "unexpected delimiter in key-value attribute's value",
1036 unwrap_single_token(sess, tokens, span)
1038 None => Token::dummy(),
1042 let tokens = TokenStreamLowering {
1043 parse_sess: &self.sess.parse_sess,
1044 synthesize_tokens: CanSynthesizeMissingTokens::Yes,
1045 nt_to_tokenstream: self.nt_to_tokenstream,
1047 .lower_token(token.clone());
1048 MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
1053 fn lower_token_stream(
1055 tokens: TokenStream,
1056 synthesize_tokens: CanSynthesizeMissingTokens,
1058 TokenStreamLowering {
1059 parse_sess: &self.sess.parse_sess,
1061 nt_to_tokenstream: self.nt_to_tokenstream,
1063 .lower_token_stream(tokens)
1066 /// Given an associated type constraint like one of these:
1069 /// T: Iterator<Item: Debug>
1071 /// T: Iterator<Item = Debug>
1075 /// returns a `hir::TypeBinding` representing `Item`.
1076 fn lower_assoc_ty_constraint(
1078 constraint: &AssocTyConstraint,
1079 mut itctx: ImplTraitContext<'_, 'hir>,
1080 ) -> hir::TypeBinding<'hir> {
1081 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1083 // lower generic arguments of identifier in constraint
1084 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1085 let gen_args_ctor = match gen_args {
1086 GenericArgs::AngleBracketed(ref data) => {
1087 self.lower_angle_bracketed_parameter_data(
1089 ParamMode::Explicit,
1094 GenericArgs::Parenthesized(ref data) => {
1095 let mut err = self.sess.struct_span_err(
1097 "parenthesized generic arguments cannot be used in associated type constraints"
1099 // FIXME: try to write a suggestion here
1101 self.lower_angle_bracketed_parameter_data(
1102 &data.as_angle_bracketed_args(),
1103 ParamMode::Explicit,
1109 self.arena.alloc(gen_args_ctor.into_generic_args(&self.arena))
1111 self.arena.alloc(hir::GenericArgs::none())
1114 let kind = match constraint.kind {
1115 AssocTyConstraintKind::Equality { ref ty } => {
1116 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1118 AssocTyConstraintKind::Bound { ref bounds } => {
1119 let mut capturable_lifetimes;
1120 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1121 let (desugar_to_impl_trait, itctx) = match itctx {
1122 // We are in the return position:
1124 // fn foo() -> impl Iterator<Item: Debug>
1128 // fn foo() -> impl Iterator<Item = impl Debug>
1129 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1130 | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
1132 // We are in the argument position, but within a dyn type:
1134 // fn foo(x: dyn Iterator<Item: Debug>)
1138 // fn foo(x: dyn Iterator<Item = impl Debug>)
1139 ImplTraitContext::Universal(..) if self.is_in_dyn_type => (true, itctx),
1141 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1142 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1143 // "impl trait context" to permit `impl Debug` in this position (it desugars
1144 // then to an opaque type).
1146 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1147 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1148 capturable_lifetimes = FxHashSet::default();
1151 ImplTraitContext::OtherOpaqueTy {
1152 capturable_lifetimes: &mut capturable_lifetimes,
1153 origin: hir::OpaqueTyOrigin::Misc,
1158 // We are in the parameter position, but not within a dyn type:
1160 // fn foo(x: impl Iterator<Item: Debug>)
1162 // so we leave it as is and this gets expanded in astconv to a bound like
1163 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1165 _ => (false, itctx),
1168 if desugar_to_impl_trait {
1169 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1170 // constructing the HIR for `impl bounds...` and then lowering that.
1172 let impl_trait_node_id = self.resolver.next_node_id();
1173 let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
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)
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) => {
1427 // Add a definition for the in-band `Param`.
1428 let def_id = self.resolver.local_def_id(def_node_id);
1430 self.allocate_hir_id_counter(def_node_id);
1432 let hir_bounds = self.with_hir_id_owner(def_node_id, |this| {
1433 this.lower_param_bounds(
1435 ImplTraitContext::Universal(in_band_ty_params),
1438 // Set the name to `impl Bound1 + Bound2`.
1439 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1440 in_band_ty_params.push(hir::GenericParam {
1441 hir_id: self.lower_node_id(def_node_id),
1442 name: ParamName::Plain(ident),
1443 pure_wrt_drop: false,
1447 kind: hir::GenericParamKind::Type {
1449 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1453 hir::TyKind::Path(hir::QPath::Resolved(
1455 self.arena.alloc(hir::Path {
1457 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1458 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1462 ImplTraitContext::Disallowed(pos) => {
1463 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1464 "bindings or function and inherent method return types"
1466 "function and inherent method return types"
1468 let mut err = struct_span_err!(
1472 "`impl Trait` not allowed outside of {}",
1475 if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() {
1477 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1478 attributes to enable",
1486 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1487 TyKind::CVarArgs => {
1488 self.sess.delay_span_bug(
1490 "`TyKind::CVarArgs` should have been handled elsewhere",
1496 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1499 fn lower_opaque_impl_trait(
1502 fn_def_id: Option<DefId>,
1503 origin: hir::OpaqueTyOrigin,
1504 opaque_ty_node_id: NodeId,
1505 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1506 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1507 ) -> hir::TyKind<'hir> {
1509 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1510 fn_def_id, opaque_ty_node_id, span,
1513 // Make sure we know that some funky desugaring has been going on here.
1514 // This is a first: there is code in other places like for loop
1515 // desugaring that explicitly states that we don't want to track that.
1516 // Not tracking it makes lints in rustc and clippy very fragile, as
1517 // frequently opened issues show.
1518 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1520 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1522 self.allocate_hir_id_counter(opaque_ty_node_id);
1524 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1526 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1530 capturable_lifetimes,
1533 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1535 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1537 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1538 let opaque_ty_item = hir::OpaqueTy {
1539 generics: hir::Generics {
1540 params: lifetime_defs,
1541 where_clause: hir::WhereClause { predicates: &[], span },
1545 impl_trait_fn: fn_def_id,
1549 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1551 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1553 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1554 hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, lifetimes)
1558 /// Registers a new opaque type with the proper `NodeId`s and
1559 /// returns the lowered node-ID for the opaque type.
1560 fn generate_opaque_type(
1562 opaque_ty_node_id: NodeId,
1563 opaque_ty_item: hir::OpaqueTy<'hir>,
1565 opaque_ty_span: Span,
1567 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1568 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1569 // Generate an `type Foo = impl Trait;` declaration.
1570 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1571 let opaque_ty_item = hir::Item {
1572 hir_id: opaque_ty_id,
1573 ident: Ident::invalid(),
1574 attrs: Default::default(),
1575 kind: opaque_ty_item_kind,
1576 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1577 span: opaque_ty_span,
1580 // Insert the item into the global item list. This usually happens
1581 // automatically for all AST items. But this opaque type item
1582 // does not actually exist in the AST.
1583 self.insert_item(opaque_ty_item);
1587 fn lifetimes_from_impl_trait_bounds(
1589 opaque_ty_id: NodeId,
1590 parent_def_id: LocalDefId,
1591 bounds: hir::GenericBounds<'hir>,
1592 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1593 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1595 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1596 parent_def_id={:?}, \
1598 opaque_ty_id, parent_def_id, bounds,
1601 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1602 // appear in the bounds, excluding lifetimes that are created within the bounds.
1603 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1604 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1605 context: &'r mut LoweringContext<'a, 'hir>,
1607 opaque_ty_id: NodeId,
1608 collect_elided_lifetimes: bool,
1609 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1610 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1611 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1612 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1613 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1616 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1617 type Map = intravisit::ErasedMap<'v>;
1619 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1620 intravisit::NestedVisitorMap::None
1623 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1624 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1625 if parameters.parenthesized {
1626 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1627 self.collect_elided_lifetimes = false;
1628 intravisit::walk_generic_args(self, span, parameters);
1629 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1631 intravisit::walk_generic_args(self, span, parameters);
1635 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1636 // Don't collect elided lifetimes used inside of `fn()` syntax.
1637 if let hir::TyKind::BareFn(_) = t.kind {
1638 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1639 self.collect_elided_lifetimes = false;
1641 // Record the "stack height" of `for<'a>` lifetime bindings
1642 // to be able to later fully undo their introduction.
1643 let old_len = self.currently_bound_lifetimes.len();
1644 intravisit::walk_ty(self, t);
1645 self.currently_bound_lifetimes.truncate(old_len);
1647 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1649 intravisit::walk_ty(self, t)
1653 fn visit_poly_trait_ref(
1655 trait_ref: &'v hir::PolyTraitRef<'v>,
1656 modifier: hir::TraitBoundModifier,
1658 // Record the "stack height" of `for<'a>` lifetime bindings
1659 // to be able to later fully undo their introduction.
1660 let old_len = self.currently_bound_lifetimes.len();
1661 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1662 self.currently_bound_lifetimes.truncate(old_len);
1665 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1666 // Record the introduction of 'a in `for<'a> ...`.
1667 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1668 // Introduce lifetimes one at a time so that we can handle
1669 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1670 let lt_name = hir::LifetimeName::Param(param.name);
1671 self.currently_bound_lifetimes.push(lt_name);
1674 intravisit::walk_generic_param(self, param);
1677 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1678 let name = match lifetime.name {
1679 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1680 if self.collect_elided_lifetimes {
1681 // Use `'_` for both implicit and underscore lifetimes in
1682 // `type Foo<'_> = impl SomeTrait<'_>;`.
1683 hir::LifetimeName::Underscore
1688 hir::LifetimeName::Param(_) => lifetime.name,
1690 // Refers to some other lifetime that is "in
1691 // scope" within the type.
1692 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1694 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1697 if !self.currently_bound_lifetimes.contains(&name)
1698 && !self.already_defined_lifetimes.contains(&name)
1699 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1701 self.already_defined_lifetimes.insert(name);
1703 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1704 hir_id: self.context.next_id(),
1705 span: lifetime.span,
1709 let def_node_id = self.context.resolver.next_node_id();
1711 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1712 self.context.resolver.create_def(
1715 DefPathData::LifetimeNs(name.ident().name),
1720 let (name, kind) = match name {
1721 hir::LifetimeName::Underscore => (
1722 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1723 hir::LifetimeParamKind::Elided,
1725 hir::LifetimeName::Param(param_name) => {
1726 (param_name, hir::LifetimeParamKind::Explicit)
1728 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1731 self.output_lifetime_params.push(hir::GenericParam {
1734 span: lifetime.span,
1735 pure_wrt_drop: false,
1738 kind: hir::GenericParamKind::Lifetime { kind },
1744 let mut lifetime_collector = ImplTraitLifetimeCollector {
1746 parent: parent_def_id,
1748 collect_elided_lifetimes: true,
1749 currently_bound_lifetimes: Vec::new(),
1750 already_defined_lifetimes: FxHashSet::default(),
1751 output_lifetimes: Vec::new(),
1752 output_lifetime_params: Vec::new(),
1753 lifetimes_to_include,
1756 for bound in bounds {
1757 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1760 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1764 self.arena.alloc_from_iter(output_lifetimes),
1765 self.arena.alloc_from_iter(output_lifetime_params),
1769 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1770 let mut ids = SmallVec::<[NodeId; 1]>::new();
1771 if self.sess.features_untracked().impl_trait_in_bindings {
1772 if let Some(ref ty) = l.ty {
1773 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1774 visitor.visit_ty(ty);
1777 let ty = l.ty.as_ref().map(|t| {
1778 let mut capturable_lifetimes;
1781 if self.sess.features_untracked().impl_trait_in_bindings {
1782 capturable_lifetimes = FxHashSet::default();
1783 ImplTraitContext::OtherOpaqueTy {
1784 capturable_lifetimes: &mut capturable_lifetimes,
1785 origin: hir::OpaqueTyOrigin::Binding,
1788 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1792 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1795 hir_id: self.lower_node_id(l.id),
1797 pat: self.lower_pat(&l.pat),
1800 attrs: l.attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into(),
1801 source: hir::LocalSource::Normal,
1807 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1808 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1809 // as they are not explicit in HIR/Ty function signatures.
1810 // (instead, the `c_variadic` flag is set to `true`)
1811 let mut inputs = &decl.inputs[..];
1812 if decl.c_variadic() {
1813 inputs = &inputs[..inputs.len() - 1];
1815 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1816 PatKind::Ident(_, ident, _) => ident,
1817 _ => Ident::new(kw::Empty, param.pat.span),
1821 // Lowers a function declaration.
1823 // `decl`: the unlowered (AST) function declaration.
1824 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1825 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1826 // `make_ret_async` is also `Some`.
1827 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1828 // This guards against trait declarations and implementations where `impl Trait` is
1830 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1831 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1832 // return type `impl Trait` item.
1836 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1837 impl_trait_return_allow: bool,
1838 make_ret_async: Option<NodeId>,
1839 ) -> &'hir hir::FnDecl<'hir> {
1843 in_band_ty_params: {:?}, \
1844 impl_trait_return_allow: {}, \
1845 make_ret_async: {:?})",
1846 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1848 let lt_mode = if make_ret_async.is_some() {
1849 // In `async fn`, argument-position elided lifetimes
1850 // must be transformed into fresh generic parameters so that
1851 // they can be applied to the opaque `impl Trait` return type.
1852 AnonymousLifetimeMode::CreateParameter
1854 self.anonymous_lifetime_mode
1857 let c_variadic = decl.c_variadic();
1859 // Remember how many lifetimes were already around so that we can
1860 // only look at the lifetime parameters introduced by the arguments.
1861 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1862 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1863 // as they are not explicit in HIR/Ty function signatures.
1864 // (instead, the `c_variadic` flag is set to `true`)
1865 let mut inputs = &decl.inputs[..];
1867 inputs = &inputs[..inputs.len() - 1];
1869 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1870 if let Some((_, ibty)) = &mut in_band_ty_params {
1871 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1873 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1878 let output = if let Some(ret_id) = make_ret_async {
1879 self.lower_async_fn_ret_ty(
1881 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1886 FnRetTy::Ty(ref ty) => {
1887 let context = match in_band_ty_params {
1888 Some((def_id, _)) if impl_trait_return_allow => {
1889 ImplTraitContext::ReturnPositionOpaqueTy {
1891 origin: hir::OpaqueTyOrigin::FnReturn,
1894 _ => ImplTraitContext::disallowed(),
1896 hir::FnRetTy::Return(self.lower_ty(ty, context))
1898 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
1902 self.arena.alloc(hir::FnDecl {
1906 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1907 use BindingMode::{ByRef, ByValue};
1908 let is_mutable_pat = matches!(
1910 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1914 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1915 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1916 // Given we are only considering `ImplicitSelf` types, we needn't consider
1917 // the case where we have a mutable pattern to a reference as that would
1918 // no longer be an `ImplicitSelf`.
1919 TyKind::Rptr(_, ref mt)
1920 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1922 hir::ImplicitSelfKind::MutRef
1924 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1925 hir::ImplicitSelfKind::ImmRef
1927 _ => hir::ImplicitSelfKind::None,
1933 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1934 // combined with the following definition of `OpaqueTy`:
1936 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1938 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1939 // `output`: unlowered output type (`T` in `-> T`)
1940 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1941 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1942 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1943 fn lower_async_fn_ret_ty(
1947 opaque_ty_node_id: NodeId,
1948 ) -> hir::FnRetTy<'hir> {
1950 "lower_async_fn_ret_ty(\
1953 opaque_ty_node_id={:?})",
1954 output, fn_def_id, opaque_ty_node_id,
1957 let span = output.span();
1959 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1961 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1963 self.allocate_hir_id_counter(opaque_ty_node_id);
1965 // When we create the opaque type for this async fn, it is going to have
1966 // to capture all the lifetimes involved in the signature (including in the
1967 // return type). This is done by introducing lifetime parameters for:
1969 // - all the explicitly declared lifetimes from the impl and function itself;
1970 // - all the elided lifetimes in the fn arguments;
1971 // - all the elided lifetimes in the return type.
1973 // So for example in this snippet:
1976 // impl<'a> Foo<'a> {
1977 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1978 // // ^ '0 ^ '1 ^ '2
1979 // // elided lifetimes used below
1984 // we would create an opaque type like:
1987 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1990 // and we would then desugar `bar` to the equivalent of:
1993 // impl<'a> Foo<'a> {
1994 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1998 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1999 // this is because the elided lifetimes from the return type
2000 // should be figured out using the ordinary elision rules, and
2001 // this desugaring achieves that.
2003 // The variable `input_lifetimes_count` tracks the number of
2004 // lifetime parameters to the opaque type *not counting* those
2005 // lifetimes elided in the return type. This includes those
2006 // that are explicitly declared (`in_scope_lifetimes`) and
2007 // those elided lifetimes we found in the arguments (current
2008 // content of `lifetimes_to_define`). Next, we will process
2009 // the return type, which will cause `lifetimes_to_define` to
2011 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2013 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2014 // We have to be careful to get elision right here. The
2015 // idea is that we create a lifetime parameter for each
2016 // lifetime in the return type. So, given a return type
2017 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2018 // Future<Output = &'1 [ &'2 u32 ]>`.
2020 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2021 // hence the elision takes place at the fn site.
2022 let future_bound = this
2023 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2024 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2027 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2029 // Calculate all the lifetimes that should be captured
2030 // by the opaque type. This should include all in-scope
2031 // lifetime parameters, including those defined in-band.
2033 // Note: this must be done after lowering the output type,
2034 // as the output type may introduce new in-band lifetimes.
2035 let lifetime_params: Vec<(Span, ParamName)> = this
2039 .map(|name| (name.ident().span, name))
2040 .chain(this.lifetimes_to_define.iter().cloned())
2043 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2044 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2045 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2047 let generic_params =
2048 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2049 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2052 let opaque_ty_item = hir::OpaqueTy {
2053 generics: hir::Generics {
2054 params: generic_params,
2055 where_clause: hir::WhereClause { predicates: &[], span },
2058 bounds: arena_vec![this; future_bound],
2059 impl_trait_fn: Some(fn_def_id),
2060 origin: hir::OpaqueTyOrigin::AsyncFn,
2063 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2065 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2067 (opaque_ty_id, lifetime_params)
2070 // As documented above on the variable
2071 // `input_lifetimes_count`, we need to create the lifetime
2072 // arguments to our opaque type. Continuing with our example,
2073 // we're creating the type arguments for the return type:
2076 // Bar<'a, 'b, '0, '1, '_>
2079 // For the "input" lifetime parameters, we wish to create
2080 // references to the parameters themselves, including the
2081 // "implicit" ones created from parameter types (`'a`, `'b`,
2084 // For the "output" lifetime parameters, we just want to
2086 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2087 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2088 |&(span, hir_name)| {
2089 // Input lifetime like `'a` or `'1`:
2090 GenericArg::Lifetime(hir::Lifetime {
2091 hir_id: self.next_id(),
2093 name: hir::LifetimeName::Param(hir_name),
2097 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2098 // Output lifetime like `'_`.
2099 GenericArg::Lifetime(hir::Lifetime {
2100 hir_id: self.next_id(),
2102 name: hir::LifetimeName::Implicit,
2104 let generic_args = self.arena.alloc_from_iter(generic_args);
2106 // Create the `Foo<...>` reference itself. Note that the `type
2107 // Foo = impl Trait` is, internally, created as a child of the
2108 // async fn, so the *type parameters* are inherited. It's
2109 // only the lifetime parameters that we must supply.
2110 let opaque_ty_ref = hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, generic_args);
2111 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2112 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2115 /// Transforms `-> T` into `Future<Output = T>`
2116 fn lower_async_fn_output_type_to_future_bound(
2121 ) -> hir::GenericBound<'hir> {
2122 // Compute the `T` in `Future<Output = T>` from the return type.
2123 let output_ty = match output {
2124 FnRetTy::Ty(ty) => {
2125 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2126 // `impl Future` opaque type that `async fn` implicitly
2128 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2130 origin: hir::OpaqueTyOrigin::FnReturn,
2132 self.lower_ty(ty, context)
2134 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2138 let future_args = self.arena.alloc(hir::GenericArgs {
2140 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2141 parenthesized: false,
2144 hir::GenericBound::LangItemTrait(
2145 // ::std::future::Future<future_params>
2146 hir::LangItem::Future,
2153 fn lower_param_bound(
2156 itctx: ImplTraitContext<'_, 'hir>,
2157 ) -> hir::GenericBound<'hir> {
2159 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2160 self.lower_poly_trait_ref(ty, itctx),
2161 self.lower_trait_bound_modifier(modifier),
2163 GenericBound::Outlives(ref lifetime) => {
2164 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2169 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2170 let span = l.ident.span;
2172 ident if ident.name == kw::StaticLifetime => {
2173 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2175 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2176 AnonymousLifetimeMode::CreateParameter => {
2177 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2178 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2181 AnonymousLifetimeMode::PassThrough => {
2182 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2185 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2188 self.maybe_collect_in_band_lifetime(ident);
2189 let param_name = ParamName::Plain(ident);
2190 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2195 fn new_named_lifetime(
2199 name: hir::LifetimeName,
2200 ) -> hir::Lifetime {
2201 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2204 fn lower_generic_params_mut<'s>(
2206 params: &'s [GenericParam],
2207 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2208 mut itctx: ImplTraitContext<'s, 'hir>,
2209 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2212 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2215 fn lower_generic_params(
2217 params: &[GenericParam],
2218 add_bounds: &NodeMap<Vec<GenericBound>>,
2219 itctx: ImplTraitContext<'_, 'hir>,
2220 ) -> &'hir [hir::GenericParam<'hir>] {
2221 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2224 fn lower_generic_param(
2226 param: &GenericParam,
2227 add_bounds: &NodeMap<Vec<GenericBound>>,
2228 mut itctx: ImplTraitContext<'_, 'hir>,
2229 ) -> hir::GenericParam<'hir> {
2230 let mut bounds: Vec<_> = self
2231 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2232 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2235 let (name, kind) = match param.kind {
2236 GenericParamKind::Lifetime => {
2237 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2238 self.is_collecting_in_band_lifetimes = false;
2241 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2242 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2244 let param_name = match lt.name {
2245 hir::LifetimeName::Param(param_name) => param_name,
2246 hir::LifetimeName::Implicit
2247 | hir::LifetimeName::Underscore
2248 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2249 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2250 self.sess.diagnostic().span_bug(
2252 "object-lifetime-default should not occur here",
2255 hir::LifetimeName::Error => ParamName::Error,
2259 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2261 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2265 GenericParamKind::Type { ref default, .. } => {
2266 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2267 if !add_bounds.is_empty() {
2268 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2269 bounds.extend(params);
2272 let kind = hir::GenericParamKind::Type {
2273 default: default.as_ref().map(|x| {
2276 ImplTraitContext::OtherOpaqueTy {
2277 capturable_lifetimes: &mut FxHashSet::default(),
2278 origin: hir::OpaqueTyOrigin::Misc,
2285 .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic))
2286 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2290 (hir::ParamName::Plain(param.ident), kind)
2292 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2294 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2295 this.lower_ty(&ty, ImplTraitContext::disallowed())
2297 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2299 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty, default })
2304 hir_id: self.lower_node_id(param.id),
2306 span: param.ident.span,
2307 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2308 attrs: self.lower_attrs(¶m.attrs),
2309 bounds: self.arena.alloc_from_iter(bounds),
2317 itctx: ImplTraitContext<'_, 'hir>,
2318 ) -> hir::TraitRef<'hir> {
2319 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2320 hir::QPath::Resolved(None, path) => path,
2321 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2323 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2326 fn lower_poly_trait_ref(
2329 mut itctx: ImplTraitContext<'_, 'hir>,
2330 ) -> hir::PolyTraitRef<'hir> {
2331 let bound_generic_params = self.lower_generic_params(
2332 &p.bound_generic_params,
2333 &NodeMap::default(),
2337 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2338 // Any impl Trait types defined within this scope can capture
2339 // lifetimes bound on this predicate.
2340 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2341 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2342 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2346 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2347 capturable_lifetimes.extend(lt_def_names.clone());
2350 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2352 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2353 for param in lt_def_names {
2354 capturable_lifetimes.remove(¶m);
2360 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2363 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2364 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2367 fn lower_param_bounds(
2369 bounds: &[GenericBound],
2370 itctx: ImplTraitContext<'_, 'hir>,
2371 ) -> hir::GenericBounds<'hir> {
2372 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2375 fn lower_param_bounds_mut<'s>(
2377 bounds: &'s [GenericBound],
2378 mut itctx: ImplTraitContext<'s, 'hir>,
2379 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2380 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2383 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2384 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2387 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2388 let mut expr: Option<&'hir _> = None;
2390 let stmts = self.arena.alloc_from_iter(
2394 .filter_map(|(index, stmt)| {
2395 if index == b.stmts.len() - 1 {
2396 if let StmtKind::Expr(ref e) = stmt.kind {
2397 expr = Some(self.lower_expr(e));
2400 Some(self.lower_stmt(stmt))
2403 Some(self.lower_stmt(stmt))
2408 let rules = self.lower_block_check_mode(&b.rules);
2409 let hir_id = self.lower_node_id(b.id);
2411 hir::Block { hir_id, stmts, expr, rules, span: b.span, targeted_by_break }
2414 /// Lowers a block directly to an expression, presuming that it
2415 /// has no attributes and is not targeted by a `break`.
2416 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2417 let block = self.lower_block(b, false);
2418 self.expr_block(block, AttrVec::new())
2421 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2422 self.with_new_scopes(|this| hir::AnonConst {
2423 hir_id: this.lower_node_id(c.id),
2424 body: this.lower_const_body(c.value.span, Some(&c.value)),
2428 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2429 let kind = match s.kind {
2430 StmtKind::Local(ref l) => {
2431 let (l, item_ids) = self.lower_local(l);
2432 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2435 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2436 self.stmt(s.span, hir::StmtKind::Item(item_id))
2441 hir_id: self.lower_node_id(s.id),
2442 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2448 StmtKind::Item(ref it) => {
2449 // Can only use the ID once.
2450 let mut id = Some(s.id);
2457 .map(|id| self.lower_node_id(id))
2458 .unwrap_or_else(|| self.next_id());
2460 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2464 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2465 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2466 StmtKind::Empty => return smallvec![],
2467 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
2469 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2472 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2474 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2475 BlockCheckMode::Unsafe(u) => {
2476 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2481 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2483 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2484 UserProvided => hir::UnsafeSource::UserProvided,
2488 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2490 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2491 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2493 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2494 // placeholder for compilation to proceed.
2495 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2496 hir::TraitBoundModifier::Maybe
2501 // Helper methods for building HIR.
2503 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2504 hir::Stmt { span, kind, hir_id: self.next_id() }
2507 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2508 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2515 init: Option<&'hir hir::Expr<'hir>>,
2516 pat: &'hir hir::Pat<'hir>,
2517 source: hir::LocalSource,
2518 ) -> hir::Stmt<'hir> {
2519 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2520 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2523 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2524 self.block_all(expr.span, &[], Some(expr))
2530 stmts: &'hir [hir::Stmt<'hir>],
2531 expr: Option<&'hir hir::Expr<'hir>>,
2532 ) -> &'hir hir::Block<'hir> {
2533 let blk = hir::Block {
2536 hir_id: self.next_id(),
2537 rules: hir::BlockCheckMode::DefaultBlock,
2539 targeted_by_break: false,
2541 self.arena.alloc(blk)
2544 /// Constructs a `true` or `false` literal pattern.
2545 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2546 let expr = self.expr_bool(span, val);
2547 self.pat(span, hir::PatKind::Lit(expr))
2550 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2551 let field = self.single_pat_field(span, pat);
2552 self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
2555 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2556 let field = self.single_pat_field(span, pat);
2557 self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field)
2560 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2561 let field = self.single_pat_field(span, pat);
2562 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2565 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2566 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2569 fn single_pat_field(
2572 pat: &'hir hir::Pat<'hir>,
2573 ) -> &'hir [hir::FieldPat<'hir>] {
2574 let field = hir::FieldPat {
2575 hir_id: self.next_id(),
2576 ident: Ident::new(sym::integer(0), span),
2577 is_shorthand: false,
2581 arena_vec![self; field]
2584 fn pat_lang_item_variant(
2587 lang_item: hir::LangItem,
2588 fields: &'hir [hir::FieldPat<'hir>],
2589 ) -> &'hir hir::Pat<'hir> {
2590 let qpath = hir::QPath::LangItem(lang_item, span);
2591 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2594 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2595 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2598 fn pat_ident_binding_mode(
2602 bm: hir::BindingAnnotation,
2603 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2604 let hir_id = self.next_id();
2607 self.arena.alloc(hir::Pat {
2609 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2611 default_binding_modes: true,
2617 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2618 self.pat(span, hir::PatKind::Wild)
2621 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2622 self.arena.alloc(hir::Pat {
2623 hir_id: self.next_id(),
2626 default_binding_modes: true,
2630 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2631 self.arena.alloc(hir::Pat {
2632 hir_id: self.next_id(),
2635 default_binding_modes: false,
2641 mut hir_id: hir::HirId,
2643 qpath: hir::QPath<'hir>,
2644 ) -> hir::Ty<'hir> {
2645 let kind = match qpath {
2646 hir::QPath::Resolved(None, path) => {
2647 // Turn trait object paths into `TyKind::TraitObject` instead.
2649 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2650 let principal = hir::PolyTraitRef {
2651 bound_generic_params: &[],
2652 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2656 // The original ID is taken by the `PolyTraitRef`,
2657 // so the `Ty` itself needs a different one.
2658 hir_id = self.next_id();
2659 hir::TyKind::TraitObject(
2660 arena_vec![self; principal],
2661 self.elided_dyn_bound(span),
2664 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2667 _ => hir::TyKind::Path(qpath),
2670 hir::Ty { hir_id, kind, span }
2673 /// Invoked to create the lifetime argument for a type `&T`
2674 /// with no explicit lifetime.
2675 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2676 match self.anonymous_lifetime_mode {
2677 // Intercept when we are in an impl header or async fn and introduce an in-band
2679 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2681 AnonymousLifetimeMode::CreateParameter => {
2682 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2684 hir_id: self.next_id(),
2686 name: hir::LifetimeName::Param(fresh_name),
2690 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2692 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2696 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2697 /// return a "error lifetime".
2698 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2699 let (id, msg, label) = match id {
2700 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2703 self.resolver.next_node_id(),
2704 "`&` without an explicit lifetime name cannot be used here",
2705 "explicit lifetime name needed here",
2709 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2710 err.span_label(span, label);
2713 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2716 /// Invoked to create the lifetime argument(s) for a path like
2717 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2718 /// sorts of cases are deprecated. This may therefore report a warning or an
2719 /// error, depending on the mode.
2720 fn elided_path_lifetimes<'s>(
2724 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2725 (0..count).map(move |_| self.elided_path_lifetime(span))
2728 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2729 match self.anonymous_lifetime_mode {
2730 AnonymousLifetimeMode::CreateParameter => {
2731 // We should have emitted E0726 when processing this path above
2733 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2734 let id = self.resolver.next_node_id();
2735 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2737 // `PassThrough` is the normal case.
2738 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2739 // is unsuitable here, as these can occur from missing lifetime parameters in a
2740 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2741 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2742 // later, at which point a suitable error will be emitted.
2743 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2744 self.new_implicit_lifetime(span)
2749 /// Invoked to create the lifetime argument(s) for an elided trait object
2750 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2751 /// when the bound is written, even if it is written with `'_` like in
2752 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2753 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2754 match self.anonymous_lifetime_mode {
2755 // NB. We intentionally ignore the create-parameter mode here.
2756 // and instead "pass through" to resolve-lifetimes, which will apply
2757 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2758 // do not act like other elided lifetimes. In other words, given this:
2760 // impl Foo for Box<dyn Debug>
2762 // we do not introduce a fresh `'_` to serve as the bound, but instead
2763 // ultimately translate to the equivalent of:
2765 // impl Foo for Box<dyn Debug + 'static>
2767 // `resolve_lifetime` has the code to make that happen.
2768 AnonymousLifetimeMode::CreateParameter => {}
2770 AnonymousLifetimeMode::ReportError => {
2771 // ReportError applies to explicit use of `'_`.
2774 // This is the normal case.
2775 AnonymousLifetimeMode::PassThrough => {}
2778 let r = hir::Lifetime {
2779 hir_id: self.next_id(),
2781 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2783 debug!("elided_dyn_bound: r={:?}", r);
2787 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2788 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2791 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2792 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2793 // call site which do not have a macro backtrace. See #61963.
2794 let is_macro_callsite = self
2797 .span_to_snippet(span)
2798 .map(|snippet| snippet.starts_with("#["))
2800 if !is_macro_callsite {
2801 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2805 "trait objects without an explicit `dyn` are deprecated",
2806 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2811 fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId, default: Abi) {
2812 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2813 // call site which do not have a macro backtrace. See #61963.
2814 let is_macro_callsite = self
2817 .span_to_snippet(span)
2818 .map(|snippet| snippet.starts_with("#["))
2820 if !is_macro_callsite {
2821 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2825 "extern declarations without an explicit ABI are deprecated",
2826 BuiltinLintDiagnostics::MissingAbi(span, default),
2832 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2833 // Sorting by span ensures that we get things in order within a
2834 // file, and also puts the files in a sensible order.
2835 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2836 body_ids.sort_by_key(|b| bodies[b].value.span);
2840 /// Helper struct for delayed construction of GenericArgs.
2841 struct GenericArgsCtor<'hir> {
2842 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2843 bindings: &'hir [hir::TypeBinding<'hir>],
2844 parenthesized: bool,
2847 impl<'hir> GenericArgsCtor<'hir> {
2848 fn is_empty(&self) -> bool {
2849 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2852 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2854 args: arena.alloc_from_iter(self.args),
2855 bindings: self.bindings,
2856 parenthesized: self.parenthesized,