1 //! Lowers the AST to the HIR.
3 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
4 //! much like a fold. Where lowering involves a bit more work things get more
5 //! interesting and there are some invariants you should know about. These mostly
6 //! concern spans and IDs.
8 //! Spans are assigned to AST nodes during parsing and then are modified during
9 //! expansion to indicate the origin of a node and the process it went through
10 //! being expanded. IDs are assigned to AST nodes just before lowering.
12 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
13 //! expansion we do not preserve the process of lowering in the spans, so spans
14 //! should not be modified here. When creating a new node (as opposed to
15 //! "folding" an existing one), create a new ID using `next_id()`.
17 //! You must ensure that IDs are unique. That means that you should only use the
18 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
19 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
20 //! If you do, you must then set the new node's ID to a fresh one.
22 //! Spans are used for error messages and for tools to map semantics back to
23 //! source code. It is therefore not as important with spans as IDs to be strict
24 //! about use (you can't break the compiler by screwing up a span). Obviously, a
25 //! HIR node can only have a single span. But multiple nodes can have the same
26 //! span and spans don't need to be kept in order, etc. Where code is preserved
27 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
28 //! new it is probably best to give a span for the whole AST node being lowered.
29 //! All nodes should have real spans; don't use dummy spans. Tools are likely to
30 //! get confused if the spans from leaf AST nodes occur in multiple places
31 //! in the HIR, especially for multiple identifiers.
33 #![feature(crate_visibility_modifier)]
34 #![feature(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 struct ImplTraitTypeIdVisitor<'a> {
442 ids: &'a mut SmallVec<[NodeId; 1]>,
445 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
446 fn visit_ty(&mut self, ty: &Ty) {
448 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
450 TyKind::ImplTrait(id, _) => self.ids.push(id),
453 visit::walk_ty(self, ty);
456 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
457 if let Some(ref p) = path_segment.args {
458 if let GenericArgs::Parenthesized(_) = **p {
462 visit::walk_path_segment(self, path_span, path_segment)
466 impl<'a, 'hir> LoweringContext<'a, 'hir> {
467 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
468 /// Full-crate AST visitor that inserts into a fresh
469 /// `LoweringContext` any information that may be
470 /// needed from arbitrary locations in the crate,
471 /// e.g., the number of lifetime generic parameters
472 /// declared for every type and trait definition.
473 struct MiscCollector<'tcx, 'lowering, 'hir> {
474 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
477 impl MiscCollector<'_, '_, '_> {
478 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
480 UseTreeKind::Simple(_, id1, id2) => {
481 for &id in &[id1, id2] {
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 self.lctx.allocate_hir_id_counter(id);
489 self.allocate_use_tree_hir_id_counters(use_tree);
496 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
497 fn visit_item(&mut self, item: &'tcx Item) {
498 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);
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.items, c.span);
564 self.lower_attrs(hir::CRATE_HIR_ID, &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);
591 #[cfg(debug_assertions)]
592 for (&id, attrs) in self.attrs.iter() {
593 // Verify that we do not store empty slices in the map.
594 if attrs.is_empty() {
595 panic!("Stored empty attributes for {:?}", id);
600 item: hir::CrateItem { module, span: c.span },
601 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
602 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
604 trait_items: self.trait_items,
605 impl_items: self.impl_items,
606 foreign_items: self.foreign_items,
609 trait_impls: self.trait_impls,
610 modules: self.modules,
617 fn insert_item(&mut self, item: hir::Item<'hir>) -> hir::ItemId {
618 let id = hir::ItemId { def_id: item.def_id };
619 self.items.insert(id, item);
620 self.modules.entry(self.current_module).or_default().items.insert(id);
624 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
625 // Set up the counter if needed.
626 self.item_local_id_counters.entry(owner).or_insert(0);
627 // Always allocate the first `HirId` for the owner itself.
628 let lowered = self.lower_node_id_with_owner(owner, owner);
629 debug_assert_eq!(lowered.local_id.as_u32(), 0);
633 fn lower_node_id_generic(
636 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
638 assert_ne!(ast_node_id, DUMMY_NODE_ID);
640 let min_size = ast_node_id.as_usize() + 1;
642 if min_size > self.node_id_to_hir_id.len() {
643 self.node_id_to_hir_id.resize(min_size, None);
646 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
649 // Generate a new `HirId`.
650 let hir_id = alloc_hir_id(self);
651 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
657 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
659 .item_local_id_counters
660 .insert(owner, HIR_ID_COUNTER_LOCKED)
661 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
662 let def_id = self.resolver.local_def_id(owner);
663 self.current_hir_id_owner.push((def_id, counter));
665 let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap();
667 debug_assert!(def_id == new_def_id);
668 debug_assert!(new_counter >= counter);
670 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
671 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
675 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
676 /// the `LoweringContext`'s `NodeId => HirId` map.
677 /// Take care not to call this method if the resulting `HirId` is then not
678 /// actually used in the HIR, as that would trigger an assertion in the
679 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
680 /// properly. Calling the method twice with the same `NodeId` is fine though.
681 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
682 self.lower_node_id_generic(ast_node_id, |this| {
683 let &mut (owner, ref mut local_id_counter) =
684 this.current_hir_id_owner.last_mut().unwrap();
685 let local_id = *local_id_counter;
686 *local_id_counter += 1;
687 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
691 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
692 self.lower_node_id_generic(ast_node_id, |this| {
693 let local_id_counter = this
694 .item_local_id_counters
696 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
697 let local_id = *local_id_counter;
699 // We want to be sure not to modify the counter in the map while it
700 // is also on the stack. Otherwise we'll get lost updates when writing
701 // back from the stack to the map.
702 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
704 *local_id_counter += 1;
705 let owner = this.resolver.opt_local_def_id(owner).expect(
706 "you forgot to call `create_def` or are lowering node-IDs \
707 that do not belong to the current owner",
710 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
714 fn next_id(&mut self) -> hir::HirId {
715 let node_id = self.resolver.next_node_id();
716 self.lower_node_id(node_id)
719 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
721 self.lower_node_id_generic(id, |_| {
722 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
727 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
728 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
729 if pr.unresolved_segments() != 0 {
730 panic!("path not fully resolved: {:?}", pr);
736 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
737 self.resolver.get_import_res(id).present_items()
740 fn diagnostic(&self) -> &rustc_errors::Handler {
741 self.sess.diagnostic()
744 /// Reuses the span but adds information like the kind of the desugaring and features that are
745 /// allowed inside this span.
746 fn mark_span_with_reason(
748 reason: DesugaringKind,
750 allow_internal_unstable: Option<Lrc<[Symbol]>>,
752 span.mark_with_reason(allow_internal_unstable, reason, self.sess.edition())
755 fn with_anonymous_lifetime_mode<R>(
757 anonymous_lifetime_mode: AnonymousLifetimeMode,
758 op: impl FnOnce(&mut Self) -> R,
761 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
762 anonymous_lifetime_mode,
764 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
765 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
766 let result = op(self);
767 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
769 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
770 old_anonymous_lifetime_mode
775 /// Creates a new `hir::GenericParam` for every new lifetime and
776 /// type parameter encountered while evaluating `f`. Definitions
777 /// are created with the parent provided. If no `parent_id` is
778 /// provided, no definitions will be returned.
780 /// Presuming that in-band lifetimes are enabled, then
781 /// `self.anonymous_lifetime_mode` will be updated to match the
782 /// parameter while `f` is running (and restored afterwards).
783 fn collect_in_band_defs<T>(
785 parent_def_id: LocalDefId,
786 anonymous_lifetime_mode: AnonymousLifetimeMode,
787 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
788 ) -> (Vec<hir::GenericParam<'hir>>, T) {
789 assert!(!self.is_collecting_in_band_lifetimes);
790 assert!(self.lifetimes_to_define.is_empty());
791 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
793 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
794 self.is_collecting_in_band_lifetimes = true;
796 let (in_band_ty_params, res) = f(self);
798 self.is_collecting_in_band_lifetimes = false;
799 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
801 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
803 let params = lifetimes_to_define
805 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
806 .chain(in_band_ty_params.into_iter())
812 /// Converts a lifetime into a new generic parameter.
813 fn lifetime_to_generic_param(
817 parent_def_id: LocalDefId,
818 ) -> hir::GenericParam<'hir> {
819 let node_id = self.resolver.next_node_id();
821 // Get the name we'll use to make the def-path. Note
822 // that collisions are ok here and this shouldn't
823 // really show up for end-user.
824 let (str_name, kind) = match hir_name {
825 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
826 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
827 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
830 // Add a definition for the in-band lifetime def.
831 self.resolver.create_def(
834 DefPathData::LifetimeNs(str_name),
840 hir_id: self.lower_node_id(node_id),
844 pure_wrt_drop: false,
845 kind: hir::GenericParamKind::Lifetime { kind },
849 /// When there is a reference to some lifetime `'a`, and in-band
850 /// lifetimes are enabled, then we want to push that lifetime into
851 /// the vector of names to define later. In that case, it will get
852 /// added to the appropriate generics.
853 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
854 if !self.is_collecting_in_band_lifetimes {
858 if !self.sess.features_untracked().in_band_lifetimes {
862 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
866 let hir_name = ParamName::Plain(ident);
868 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
869 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
874 self.lifetimes_to_define.push((ident.span, hir_name));
877 /// When we have either an elided or `'_` lifetime in an impl
878 /// header, we convert it to an in-band lifetime.
879 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
880 assert!(self.is_collecting_in_band_lifetimes);
881 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
882 let hir_name = ParamName::Fresh(index);
883 self.lifetimes_to_define.push((span, hir_name));
887 // Evaluates `f` with the lifetimes in `params` in-scope.
888 // This is used to track which lifetimes have already been defined, and
889 // which are new in-band lifetimes that need to have a definition created
891 fn with_in_scope_lifetime_defs<T>(
893 params: &[GenericParam],
894 f: impl FnOnce(&mut Self) -> T,
896 let old_len = self.in_scope_lifetimes.len();
897 let lt_def_names = params.iter().filter_map(|param| match param.kind {
898 GenericParamKind::Lifetime { .. } => {
899 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
903 self.in_scope_lifetimes.extend(lt_def_names);
907 self.in_scope_lifetimes.truncate(old_len);
911 /// Appends in-band lifetime defs and argument-position `impl
912 /// Trait` defs to the existing set of generics.
914 /// Presuming that in-band lifetimes are enabled, then
915 /// `self.anonymous_lifetime_mode` will be updated to match the
916 /// parameter while `f` is running (and restored afterwards).
917 fn add_in_band_defs<T>(
920 parent_def_id: LocalDefId,
921 anonymous_lifetime_mode: AnonymousLifetimeMode,
922 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
923 ) -> (hir::Generics<'hir>, T) {
924 let (in_band_defs, (mut lowered_generics, res)) =
925 self.with_in_scope_lifetime_defs(&generics.params, |this| {
926 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
927 let mut params = Vec::new();
928 // Note: it is necessary to lower generics *before* calling `f`.
929 // When lowering `async fn`, there's a final step when lowering
930 // the return type that assumes that all in-scope lifetimes have
931 // already been added to either `in_scope_lifetimes` or
932 // `lifetimes_to_define`. If we swapped the order of these two,
933 // in-band-lifetimes introduced by generics or where-clauses
934 // wouldn't have been added yet.
935 let generics = this.lower_generics_mut(
937 ImplTraitContext::Universal(
939 this.current_hir_id_owner.last().unwrap().0,
942 let res = f(this, &mut params);
943 (params, (generics, res))
947 lowered_generics.params.extend(in_band_defs);
949 let lowered_generics = lowered_generics.into_generics(self.arena);
950 (lowered_generics, res)
953 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
954 let was_in_dyn_type = self.is_in_dyn_type;
955 self.is_in_dyn_type = in_scope;
957 let result = f(self);
959 self.is_in_dyn_type = was_in_dyn_type;
964 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
965 let was_in_loop_condition = self.is_in_loop_condition;
966 self.is_in_loop_condition = false;
968 let catch_scopes = mem::take(&mut self.catch_scopes);
969 let loop_scopes = mem::take(&mut self.loop_scopes);
971 self.catch_scopes = catch_scopes;
972 self.loop_scopes = loop_scopes;
974 self.is_in_loop_condition = was_in_loop_condition;
979 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
980 if attrs.is_empty() {
983 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
984 debug_assert!(!ret.is_empty());
985 self.attrs.insert(id, ret);
990 fn lower_attr(&self, attr: &Attribute) -> Attribute {
991 // Note that we explicitly do not walk the path. Since we don't really
992 // lower attributes (we use the AST version) there is nowhere to keep
993 // the `HirId`s. We don't actually need HIR version of attributes anyway.
994 // Tokens are also not needed after macro expansion and parsing.
995 let kind = match attr.kind {
996 AttrKind::Normal(ref item, _) => AttrKind::Normal(
998 path: item.path.clone(),
999 args: self.lower_mac_args(&item.args),
1004 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
1007 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
1010 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
1011 if let Some(&a) = self.attrs.get(&target_id) {
1012 debug_assert!(!a.is_empty());
1013 self.attrs.insert(id, a);
1017 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
1019 MacArgs::Empty => MacArgs::Empty,
1020 MacArgs::Delimited(dspan, delim, ref tokens) => {
1021 // This is either a non-key-value attribute, or a `macro_rules!` body.
1022 // We either not have any nonterminals present (in the case of an attribute),
1023 // or have tokens available for all nonterminals in the case of a nested
1024 // `macro_rules`: e.g:
1027 // macro_rules! outer {
1029 // macro_rules! inner {
1036 // In both cases, we don't want to synthesize any tokens
1040 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1043 // This is an inert key-value attribute - it will never be visible to macros
1044 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1045 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1046 MacArgs::Eq(eq_span, ref token) => {
1047 // In valid code the value is always representable as a single literal token.
1048 fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
1049 if tokens.len() != 1 {
1051 .delay_span_bug(span, "multiple tokens in key-value attribute's value");
1053 match tokens.into_trees().next() {
1054 Some(TokenTree::Token(token)) => token,
1055 Some(TokenTree::Delimited(_, delim, tokens)) => {
1056 if delim != token::NoDelim {
1057 sess.diagnostic().delay_span_bug(
1059 "unexpected delimiter in key-value attribute's value",
1062 unwrap_single_token(sess, tokens, span)
1064 None => Token::dummy(),
1068 let tokens = TokenStreamLowering {
1069 parse_sess: &self.sess.parse_sess,
1070 synthesize_tokens: CanSynthesizeMissingTokens::Yes,
1071 nt_to_tokenstream: self.nt_to_tokenstream,
1073 .lower_token(token.clone());
1074 MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
1079 fn lower_token_stream(
1081 tokens: TokenStream,
1082 synthesize_tokens: CanSynthesizeMissingTokens,
1084 TokenStreamLowering {
1085 parse_sess: &self.sess.parse_sess,
1087 nt_to_tokenstream: self.nt_to_tokenstream,
1089 .lower_token_stream(tokens)
1092 /// Given an associated type constraint like one of these:
1095 /// T: Iterator<Item: Debug>
1097 /// T: Iterator<Item = Debug>
1101 /// returns a `hir::TypeBinding` representing `Item`.
1102 fn lower_assoc_ty_constraint(
1104 constraint: &AssocTyConstraint,
1105 mut itctx: ImplTraitContext<'_, 'hir>,
1106 ) -> hir::TypeBinding<'hir> {
1107 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1109 // lower generic arguments of identifier in constraint
1110 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1111 let gen_args_ctor = match gen_args {
1112 GenericArgs::AngleBracketed(ref data) => {
1113 self.lower_angle_bracketed_parameter_data(
1115 ParamMode::Explicit,
1120 GenericArgs::Parenthesized(ref data) => {
1121 let mut err = self.sess.struct_span_err(
1123 "parenthesized generic arguments cannot be used in associated type constraints"
1125 // FIXME: try to write a suggestion here
1127 self.lower_angle_bracketed_parameter_data(
1128 &data.as_angle_bracketed_args(),
1129 ParamMode::Explicit,
1135 self.arena.alloc(gen_args_ctor.into_generic_args(&self.arena))
1137 self.arena.alloc(hir::GenericArgs::none())
1140 let kind = match constraint.kind {
1141 AssocTyConstraintKind::Equality { ref ty } => {
1142 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1144 AssocTyConstraintKind::Bound { ref bounds } => {
1145 let mut capturable_lifetimes;
1146 let mut parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1147 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1148 let (desugar_to_impl_trait, itctx) = match itctx {
1149 // We are in the return position:
1151 // fn foo() -> impl Iterator<Item: Debug>
1155 // fn foo() -> impl Iterator<Item = impl Debug>
1156 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1157 | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx),
1159 // We are in the argument position, but within a dyn type:
1161 // fn foo(x: dyn Iterator<Item: Debug>)
1165 // fn foo(x: dyn Iterator<Item = impl Debug>)
1166 ImplTraitContext::Universal(_, parent) if self.is_in_dyn_type => {
1167 parent_def_id = parent;
1171 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1172 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1173 // "impl trait context" to permit `impl Debug` in this position (it desugars
1174 // then to an opaque type).
1176 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1177 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1178 capturable_lifetimes = FxHashSet::default();
1181 ImplTraitContext::OtherOpaqueTy {
1182 capturable_lifetimes: &mut capturable_lifetimes,
1183 origin: hir::OpaqueTyOrigin::Misc,
1188 // We are in the parameter position, but not within a dyn type:
1190 // fn foo(x: impl Iterator<Item: Debug>)
1192 // so we leave it as is and this gets expanded in astconv to a bound like
1193 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1195 _ => (false, itctx),
1198 if desugar_to_impl_trait {
1199 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1200 // constructing the HIR for `impl bounds...` and then lowering that.
1202 let impl_trait_node_id = self.resolver.next_node_id();
1203 self.resolver.create_def(
1206 DefPathData::ImplTrait,
1211 self.with_dyn_type_scope(false, |this| {
1212 let node_id = this.resolver.next_node_id();
1213 let ty = this.lower_ty(
1216 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1217 span: constraint.span,
1223 hir::TypeBindingKind::Equality { ty }
1226 // Desugar `AssocTy: Bounds` into a type binding where the
1227 // later desugars into a trait predicate.
1228 let bounds = self.lower_param_bounds(bounds, itctx);
1230 hir::TypeBindingKind::Constraint { bounds }
1236 hir_id: self.lower_node_id(constraint.id),
1237 ident: constraint.ident,
1240 span: constraint.span,
1244 fn lower_generic_arg(
1246 arg: &ast::GenericArg,
1247 itctx: ImplTraitContext<'_, 'hir>,
1248 ) -> hir::GenericArg<'hir> {
1250 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1251 ast::GenericArg::Type(ty) => {
1252 // We parse const arguments as path types as we cannot distinguish them during
1253 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1254 // type and value namespaces. If we resolved the path in the value namespace, we
1255 // transform it into a generic const argument.
1256 if let TyKind::Path(ref qself, ref path) = ty.kind {
1257 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1258 let res = partial_res.base_res();
1259 if !res.matches_ns(Namespace::TypeNS) {
1261 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1265 // Construct a AnonConst where the expr is the "ty"'s path.
1267 let parent_def_id = self.current_hir_id_owner.last().unwrap().0;
1268 let node_id = self.resolver.next_node_id();
1270 // Add a definition for the in-band const def.
1271 self.resolver.create_def(
1274 DefPathData::AnonConst,
1279 let path_expr = Expr {
1281 kind: ExprKind::Path(qself.clone(), path.clone()),
1283 attrs: AttrVec::new(),
1287 let ct = self.with_new_scopes(|this| hir::AnonConst {
1288 hir_id: this.lower_node_id(node_id),
1289 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1291 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1295 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1297 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1298 value: self.lower_anon_const(&ct),
1299 span: ct.value.span,
1304 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1305 self.arena.alloc(self.lower_ty_direct(t, itctx))
1311 qself: &Option<QSelf>,
1313 param_mode: ParamMode,
1314 itctx: ImplTraitContext<'_, 'hir>,
1315 ) -> hir::Ty<'hir> {
1316 let id = self.lower_node_id(t.id);
1317 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1318 let ty = self.ty_path(id, t.span, qpath);
1319 if let hir::TyKind::TraitObject(..) = ty.kind {
1320 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1325 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1326 hir::Ty { hir_id: self.next_id(), kind, span }
1329 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1330 self.ty(span, hir::TyKind::Tup(tys))
1333 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1334 let kind = match t.kind {
1335 TyKind::Infer => hir::TyKind::Infer,
1336 TyKind::Err => hir::TyKind::Err,
1337 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1338 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1339 TyKind::Rptr(ref region, ref mt) => {
1340 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1341 let lifetime = match *region {
1342 Some(ref lt) => self.lower_lifetime(lt),
1343 None => self.elided_ref_lifetime(span),
1345 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1347 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1348 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1349 let span = this.sess.source_map().next_point(t.span.shrink_to_lo());
1350 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1351 generic_params: this.lower_generic_params(
1353 &NodeMap::default(),
1354 ImplTraitContext::disallowed(),
1356 unsafety: this.lower_unsafety(f.unsafety),
1357 abi: this.lower_extern(f.ext, span, t.id),
1358 decl: this.lower_fn_decl(&f.decl, None, false, None),
1359 param_names: this.lower_fn_params_to_names(&f.decl),
1363 TyKind::Never => hir::TyKind::Never,
1364 TyKind::Tup(ref tys) => {
1365 hir::TyKind::Tup(self.arena.alloc_from_iter(
1366 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1369 TyKind::Paren(ref ty) => {
1370 return self.lower_ty_direct(ty, itctx);
1372 TyKind::Path(ref qself, ref path) => {
1373 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1375 TyKind::ImplicitSelf => {
1376 let res = self.expect_full_res(t.id);
1377 let res = self.lower_res(res);
1378 hir::TyKind::Path(hir::QPath::Resolved(
1380 self.arena.alloc(hir::Path {
1382 segments: arena_vec![self; hir::PathSegment::from_ident(
1383 Ident::with_dummy_span(kw::SelfUpper)
1389 TyKind::Array(ref ty, ref length) => {
1390 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1392 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1393 TyKind::TraitObject(ref bounds, kind) => {
1394 let mut lifetime_bound = None;
1395 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1397 this.arena.alloc_from_iter(bounds.iter().filter_map(
1398 |bound| match *bound {
1399 GenericBound::Trait(
1401 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1402 ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
1403 // `?const ?Bound` will cause an error during AST validation
1404 // anyways, so treat it like `?Bound` as compilation proceeds.
1405 GenericBound::Trait(
1407 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1409 GenericBound::Outlives(ref lifetime) => {
1410 if lifetime_bound.is_none() {
1411 lifetime_bound = Some(this.lower_lifetime(lifetime));
1417 let lifetime_bound =
1418 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1419 (bounds, lifetime_bound)
1421 if kind != TraitObjectSyntax::Dyn {
1422 self.maybe_lint_bare_trait(t.span, t.id, false);
1424 hir::TyKind::TraitObject(bounds, lifetime_bound)
1426 TyKind::ImplTrait(def_node_id, ref bounds) => {
1429 ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
1430 .lower_opaque_impl_trait(
1436 |this| this.lower_param_bounds(bounds, itctx),
1438 ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => {
1439 // Reset capturable lifetimes, any nested impl trait
1440 // types will inherit lifetimes from this opaque type,
1441 // so don't need to capture them again.
1442 let nested_itctx = ImplTraitContext::OtherOpaqueTy {
1443 capturable_lifetimes: &mut FxHashSet::default(),
1446 self.lower_opaque_impl_trait(
1451 Some(capturable_lifetimes),
1452 |this| this.lower_param_bounds(bounds, nested_itctx),
1455 ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
1456 // Add a definition for the in-band `Param`.
1457 let def_id = self.resolver.local_def_id(def_node_id);
1459 self.allocate_hir_id_counter(def_node_id);
1461 let hir_bounds = self.with_hir_id_owner(def_node_id, |this| {
1462 this.lower_param_bounds(
1464 ImplTraitContext::Universal(in_band_ty_params, parent_def_id),
1467 // Set the name to `impl Bound1 + Bound2`.
1468 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1469 in_band_ty_params.push(hir::GenericParam {
1470 hir_id: self.lower_node_id(def_node_id),
1471 name: ParamName::Plain(ident),
1472 pure_wrt_drop: false,
1475 kind: hir::GenericParamKind::Type {
1477 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1481 hir::TyKind::Path(hir::QPath::Resolved(
1483 self.arena.alloc(hir::Path {
1485 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1486 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1490 ImplTraitContext::Disallowed(pos) => {
1491 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1492 "bindings or function and inherent method return types"
1494 "function and inherent method return types"
1496 let mut err = struct_span_err!(
1500 "`impl Trait` not allowed outside of {}",
1503 if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() {
1505 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1506 attributes to enable",
1514 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1515 TyKind::CVarArgs => {
1516 self.sess.delay_span_bug(
1518 "`TyKind::CVarArgs` should have been handled elsewhere",
1524 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1527 fn lower_opaque_impl_trait(
1530 fn_def_id: Option<DefId>,
1531 origin: hir::OpaqueTyOrigin,
1532 opaque_ty_node_id: NodeId,
1533 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1534 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1535 ) -> hir::TyKind<'hir> {
1537 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1538 fn_def_id, opaque_ty_node_id, span,
1541 // Make sure we know that some funky desugaring has been going on here.
1542 // This is a first: there is code in other places like for loop
1543 // desugaring that explicitly states that we don't want to track that.
1544 // Not tracking it makes lints in rustc and clippy very fragile, as
1545 // frequently opened issues show.
1546 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1548 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1550 self.allocate_hir_id_counter(opaque_ty_node_id);
1552 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1554 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1558 capturable_lifetimes,
1561 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1563 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1565 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1566 let opaque_ty_item = hir::OpaqueTy {
1567 generics: hir::Generics {
1568 params: lifetime_defs,
1569 where_clause: hir::WhereClause { predicates: &[], span },
1573 impl_trait_fn: fn_def_id,
1577 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1578 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
1580 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1581 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1585 /// Registers a new opaque type with the proper `NodeId`s and
1586 /// returns the lowered node-ID for the opaque type.
1587 fn generate_opaque_type(
1589 opaque_ty_id: LocalDefId,
1590 opaque_ty_item: hir::OpaqueTy<'hir>,
1592 opaque_ty_span: Span,
1594 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1595 // Generate an `type Foo = impl Trait;` declaration.
1596 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1597 let opaque_ty_item = hir::Item {
1598 def_id: opaque_ty_id,
1599 ident: Ident::invalid(),
1600 kind: opaque_ty_item_kind,
1601 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1602 span: opaque_ty_span,
1605 // Insert the item into the global item list. This usually happens
1606 // automatically for all AST items. But this opaque type item
1607 // does not actually exist in the AST.
1608 self.insert_item(opaque_ty_item);
1611 fn lifetimes_from_impl_trait_bounds(
1613 opaque_ty_id: NodeId,
1614 parent_def_id: LocalDefId,
1615 bounds: hir::GenericBounds<'hir>,
1616 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1617 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1619 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1620 parent_def_id={:?}, \
1622 opaque_ty_id, parent_def_id, bounds,
1625 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1626 // appear in the bounds, excluding lifetimes that are created within the bounds.
1627 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1628 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1629 context: &'r mut LoweringContext<'a, 'hir>,
1631 opaque_ty_id: NodeId,
1632 collect_elided_lifetimes: bool,
1633 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1634 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1635 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1636 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1637 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1640 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1641 type Map = intravisit::ErasedMap<'v>;
1643 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1644 intravisit::NestedVisitorMap::None
1647 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1648 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1649 if parameters.parenthesized {
1650 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1651 self.collect_elided_lifetimes = false;
1652 intravisit::walk_generic_args(self, span, parameters);
1653 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1655 intravisit::walk_generic_args(self, span, parameters);
1659 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1660 // Don't collect elided lifetimes used inside of `fn()` syntax.
1661 if let hir::TyKind::BareFn(_) = t.kind {
1662 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1663 self.collect_elided_lifetimes = false;
1665 // Record the "stack height" of `for<'a>` lifetime bindings
1666 // to be able to later fully undo their introduction.
1667 let old_len = self.currently_bound_lifetimes.len();
1668 intravisit::walk_ty(self, t);
1669 self.currently_bound_lifetimes.truncate(old_len);
1671 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1673 intravisit::walk_ty(self, t)
1677 fn visit_poly_trait_ref(
1679 trait_ref: &'v hir::PolyTraitRef<'v>,
1680 modifier: hir::TraitBoundModifier,
1682 // Record the "stack height" of `for<'a>` lifetime bindings
1683 // to be able to later fully undo their introduction.
1684 let old_len = self.currently_bound_lifetimes.len();
1685 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1686 self.currently_bound_lifetimes.truncate(old_len);
1689 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1690 // Record the introduction of 'a in `for<'a> ...`.
1691 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1692 // Introduce lifetimes one at a time so that we can handle
1693 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1694 let lt_name = hir::LifetimeName::Param(param.name);
1695 self.currently_bound_lifetimes.push(lt_name);
1698 intravisit::walk_generic_param(self, param);
1701 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1702 let name = match lifetime.name {
1703 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1704 if self.collect_elided_lifetimes {
1705 // Use `'_` for both implicit and underscore lifetimes in
1706 // `type Foo<'_> = impl SomeTrait<'_>;`.
1707 hir::LifetimeName::Underscore
1712 hir::LifetimeName::Param(_) => lifetime.name,
1714 // Refers to some other lifetime that is "in
1715 // scope" within the type.
1716 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1718 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1721 if !self.currently_bound_lifetimes.contains(&name)
1722 && !self.already_defined_lifetimes.contains(&name)
1723 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1725 self.already_defined_lifetimes.insert(name);
1727 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1728 hir_id: self.context.next_id(),
1729 span: lifetime.span,
1733 let def_node_id = self.context.resolver.next_node_id();
1735 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1736 self.context.resolver.create_def(
1739 DefPathData::LifetimeNs(name.ident().name),
1744 let (name, kind) = match name {
1745 hir::LifetimeName::Underscore => (
1746 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1747 hir::LifetimeParamKind::Elided,
1749 hir::LifetimeName::Param(param_name) => {
1750 (param_name, hir::LifetimeParamKind::Explicit)
1752 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1755 self.output_lifetime_params.push(hir::GenericParam {
1758 span: lifetime.span,
1759 pure_wrt_drop: false,
1761 kind: hir::GenericParamKind::Lifetime { kind },
1767 let mut lifetime_collector = ImplTraitLifetimeCollector {
1769 parent: parent_def_id,
1771 collect_elided_lifetimes: true,
1772 currently_bound_lifetimes: Vec::new(),
1773 already_defined_lifetimes: FxHashSet::default(),
1774 output_lifetimes: Vec::new(),
1775 output_lifetime_params: Vec::new(),
1776 lifetimes_to_include,
1779 for bound in bounds {
1780 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1783 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1787 self.arena.alloc_from_iter(output_lifetimes),
1788 self.arena.alloc_from_iter(output_lifetime_params),
1792 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1793 let mut ids = SmallVec::<[NodeId; 1]>::new();
1794 if self.sess.features_untracked().impl_trait_in_bindings {
1795 if let Some(ref ty) = l.ty {
1796 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1797 visitor.visit_ty(ty);
1800 let ty = l.ty.as_ref().map(|t| {
1801 let mut capturable_lifetimes;
1804 if self.sess.features_untracked().impl_trait_in_bindings {
1805 capturable_lifetimes = FxHashSet::default();
1806 ImplTraitContext::OtherOpaqueTy {
1807 capturable_lifetimes: &mut capturable_lifetimes,
1808 origin: hir::OpaqueTyOrigin::Binding,
1811 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1815 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1816 let hir_id = self.lower_node_id(l.id);
1817 self.lower_attrs(hir_id, &l.attrs);
1822 pat: self.lower_pat(&l.pat),
1825 source: hir::LocalSource::Normal,
1831 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1832 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1833 // as they are not explicit in HIR/Ty function signatures.
1834 // (instead, the `c_variadic` flag is set to `true`)
1835 let mut inputs = &decl.inputs[..];
1836 if decl.c_variadic() {
1837 inputs = &inputs[..inputs.len() - 1];
1839 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1840 PatKind::Ident(_, ident, _) => ident,
1841 _ => Ident::new(kw::Empty, param.pat.span),
1845 // Lowers a function declaration.
1847 // `decl`: the unlowered (AST) function declaration.
1848 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1849 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1850 // `make_ret_async` is also `Some`.
1851 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1852 // This guards against trait declarations and implementations where `impl Trait` is
1854 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1855 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1856 // return type `impl Trait` item.
1860 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1861 impl_trait_return_allow: bool,
1862 make_ret_async: Option<NodeId>,
1863 ) -> &'hir hir::FnDecl<'hir> {
1867 in_band_ty_params: {:?}, \
1868 impl_trait_return_allow: {}, \
1869 make_ret_async: {:?})",
1870 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1872 let lt_mode = if make_ret_async.is_some() {
1873 // In `async fn`, argument-position elided lifetimes
1874 // must be transformed into fresh generic parameters so that
1875 // they can be applied to the opaque `impl Trait` return type.
1876 AnonymousLifetimeMode::CreateParameter
1878 self.anonymous_lifetime_mode
1881 let c_variadic = decl.c_variadic();
1883 // Remember how many lifetimes were already around so that we can
1884 // only look at the lifetime parameters introduced by the arguments.
1885 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1886 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1887 // as they are not explicit in HIR/Ty function signatures.
1888 // (instead, the `c_variadic` flag is set to `true`)
1889 let mut inputs = &decl.inputs[..];
1891 inputs = &inputs[..inputs.len() - 1];
1893 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1894 if let Some((_, ibty)) = &mut in_band_ty_params {
1895 this.lower_ty_direct(
1897 ImplTraitContext::Universal(
1899 this.current_hir_id_owner.last().unwrap().0,
1903 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1908 let output = if let Some(ret_id) = make_ret_async {
1909 self.lower_async_fn_ret_ty(
1911 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1916 FnRetTy::Ty(ref ty) => {
1917 let context = match in_band_ty_params {
1918 Some((def_id, _)) if impl_trait_return_allow => {
1919 ImplTraitContext::ReturnPositionOpaqueTy {
1921 origin: hir::OpaqueTyOrigin::FnReturn,
1924 _ => ImplTraitContext::disallowed(),
1926 hir::FnRetTy::Return(self.lower_ty(ty, context))
1928 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
1932 self.arena.alloc(hir::FnDecl {
1936 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1937 use BindingMode::{ByRef, ByValue};
1938 let is_mutable_pat = matches!(
1940 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1944 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1945 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1946 // Given we are only considering `ImplicitSelf` types, we needn't consider
1947 // the case where we have a mutable pattern to a reference as that would
1948 // no longer be an `ImplicitSelf`.
1949 TyKind::Rptr(_, ref mt)
1950 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1952 hir::ImplicitSelfKind::MutRef
1954 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1955 hir::ImplicitSelfKind::ImmRef
1957 _ => hir::ImplicitSelfKind::None,
1963 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1964 // combined with the following definition of `OpaqueTy`:
1966 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1968 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1969 // `output`: unlowered output type (`T` in `-> T`)
1970 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1971 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1972 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1973 fn lower_async_fn_ret_ty(
1977 opaque_ty_node_id: NodeId,
1978 ) -> hir::FnRetTy<'hir> {
1980 "lower_async_fn_ret_ty(\
1983 opaque_ty_node_id={:?})",
1984 output, fn_def_id, opaque_ty_node_id,
1987 let span = output.span();
1989 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1991 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1993 self.allocate_hir_id_counter(opaque_ty_node_id);
1995 // When we create the opaque type for this async fn, it is going to have
1996 // to capture all the lifetimes involved in the signature (including in the
1997 // return type). This is done by introducing lifetime parameters for:
1999 // - all the explicitly declared lifetimes from the impl and function itself;
2000 // - all the elided lifetimes in the fn arguments;
2001 // - all the elided lifetimes in the return type.
2003 // So for example in this snippet:
2006 // impl<'a> Foo<'a> {
2007 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2008 // // ^ '0 ^ '1 ^ '2
2009 // // elided lifetimes used below
2014 // we would create an opaque type like:
2017 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2020 // and we would then desugar `bar` to the equivalent of:
2023 // impl<'a> Foo<'a> {
2024 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2028 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2029 // this is because the elided lifetimes from the return type
2030 // should be figured out using the ordinary elision rules, and
2031 // this desugaring achieves that.
2033 // The variable `input_lifetimes_count` tracks the number of
2034 // lifetime parameters to the opaque type *not counting* those
2035 // lifetimes elided in the return type. This includes those
2036 // that are explicitly declared (`in_scope_lifetimes`) and
2037 // those elided lifetimes we found in the arguments (current
2038 // content of `lifetimes_to_define`). Next, we will process
2039 // the return type, which will cause `lifetimes_to_define` to
2041 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2043 let lifetime_params = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2044 // We have to be careful to get elision right here. The
2045 // idea is that we create a lifetime parameter for each
2046 // lifetime in the return type. So, given a return type
2047 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2048 // Future<Output = &'1 [ &'2 u32 ]>`.
2050 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2051 // hence the elision takes place at the fn site.
2052 let future_bound = this
2053 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2054 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2057 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2059 // Calculate all the lifetimes that should be captured
2060 // by the opaque type. This should include all in-scope
2061 // lifetime parameters, including those defined in-band.
2063 // Note: this must be done after lowering the output type,
2064 // as the output type may introduce new in-band lifetimes.
2065 let lifetime_params: Vec<(Span, ParamName)> = this
2069 .map(|name| (name.ident().span, name))
2070 .chain(this.lifetimes_to_define.iter().cloned())
2073 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2074 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2075 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2077 let generic_params =
2078 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2079 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2082 let opaque_ty_item = hir::OpaqueTy {
2083 generics: hir::Generics {
2084 params: generic_params,
2085 where_clause: hir::WhereClause { predicates: &[], span },
2088 bounds: arena_vec![this; future_bound],
2089 impl_trait_fn: Some(fn_def_id),
2090 origin: hir::OpaqueTyOrigin::AsyncFn,
2093 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2094 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
2099 // As documented above on the variable
2100 // `input_lifetimes_count`, we need to create the lifetime
2101 // arguments to our opaque type. Continuing with our example,
2102 // we're creating the type arguments for the return type:
2105 // Bar<'a, 'b, '0, '1, '_>
2108 // For the "input" lifetime parameters, we wish to create
2109 // references to the parameters themselves, including the
2110 // "implicit" ones created from parameter types (`'a`, `'b`,
2113 // For the "output" lifetime parameters, we just want to
2115 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2116 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2117 |&(span, hir_name)| {
2118 // Input lifetime like `'a` or `'1`:
2119 GenericArg::Lifetime(hir::Lifetime {
2120 hir_id: self.next_id(),
2122 name: hir::LifetimeName::Param(hir_name),
2126 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2127 // Output lifetime like `'_`.
2128 GenericArg::Lifetime(hir::Lifetime {
2129 hir_id: self.next_id(),
2131 name: hir::LifetimeName::Implicit,
2133 let generic_args = self.arena.alloc_from_iter(generic_args);
2135 // Create the `Foo<...>` reference itself. Note that the `type
2136 // Foo = impl Trait` is, internally, created as a child of the
2137 // async fn, so the *type parameters* are inherited. It's
2138 // only the lifetime parameters that we must supply.
2140 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
2141 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2142 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2145 /// Transforms `-> T` into `Future<Output = T>`.
2146 fn lower_async_fn_output_type_to_future_bound(
2151 ) -> hir::GenericBound<'hir> {
2152 // Compute the `T` in `Future<Output = T>` from the return type.
2153 let output_ty = match output {
2154 FnRetTy::Ty(ty) => {
2155 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2156 // `impl Future` opaque type that `async fn` implicitly
2158 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2160 origin: hir::OpaqueTyOrigin::FnReturn,
2162 self.lower_ty(ty, context)
2164 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2168 let future_args = self.arena.alloc(hir::GenericArgs {
2170 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2171 parenthesized: false,
2174 hir::GenericBound::LangItemTrait(
2175 // ::std::future::Future<future_params>
2176 hir::LangItem::Future,
2183 fn lower_param_bound(
2186 itctx: ImplTraitContext<'_, 'hir>,
2187 ) -> hir::GenericBound<'hir> {
2189 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2190 self.lower_poly_trait_ref(ty, itctx),
2191 self.lower_trait_bound_modifier(modifier),
2193 GenericBound::Outlives(ref lifetime) => {
2194 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2199 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2200 let span = l.ident.span;
2202 ident if ident.name == kw::StaticLifetime => {
2203 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2205 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2206 AnonymousLifetimeMode::CreateParameter => {
2207 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2208 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2211 AnonymousLifetimeMode::PassThrough => {
2212 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2215 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2218 self.maybe_collect_in_band_lifetime(ident);
2219 let param_name = ParamName::Plain(ident);
2220 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2225 fn new_named_lifetime(
2229 name: hir::LifetimeName,
2230 ) -> hir::Lifetime {
2231 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2234 fn lower_generic_params_mut<'s>(
2236 params: &'s [GenericParam],
2237 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2238 mut itctx: ImplTraitContext<'s, 'hir>,
2239 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2242 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2245 fn lower_generic_params(
2247 params: &[GenericParam],
2248 add_bounds: &NodeMap<Vec<GenericBound>>,
2249 itctx: ImplTraitContext<'_, 'hir>,
2250 ) -> &'hir [hir::GenericParam<'hir>] {
2251 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2254 fn lower_generic_param(
2256 param: &GenericParam,
2257 add_bounds: &NodeMap<Vec<GenericBound>>,
2258 mut itctx: ImplTraitContext<'_, 'hir>,
2259 ) -> hir::GenericParam<'hir> {
2260 let mut bounds: Vec<_> = self
2261 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2262 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2265 let (name, kind) = match param.kind {
2266 GenericParamKind::Lifetime => {
2267 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2268 self.is_collecting_in_band_lifetimes = false;
2271 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2272 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2274 let param_name = match lt.name {
2275 hir::LifetimeName::Param(param_name) => param_name,
2276 hir::LifetimeName::Implicit
2277 | hir::LifetimeName::Underscore
2278 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2279 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2280 self.sess.diagnostic().span_bug(
2282 "object-lifetime-default should not occur here",
2285 hir::LifetimeName::Error => ParamName::Error,
2289 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2291 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2295 GenericParamKind::Type { ref default, .. } => {
2296 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2297 if !add_bounds.is_empty() {
2298 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2299 bounds.extend(params);
2302 let kind = hir::GenericParamKind::Type {
2303 default: default.as_ref().map(|x| {
2306 ImplTraitContext::OtherOpaqueTy {
2307 capturable_lifetimes: &mut FxHashSet::default(),
2308 origin: hir::OpaqueTyOrigin::Misc,
2315 .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic))
2316 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2320 (hir::ParamName::Plain(param.ident), kind)
2322 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2324 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2325 this.lower_ty(&ty, ImplTraitContext::disallowed())
2327 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2329 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty, default })
2333 let hir_id = self.lower_node_id(param.id);
2334 self.lower_attrs(hir_id, ¶m.attrs);
2338 span: param.ident.span,
2339 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2340 bounds: self.arena.alloc_from_iter(bounds),
2348 itctx: ImplTraitContext<'_, 'hir>,
2349 ) -> hir::TraitRef<'hir> {
2350 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2351 hir::QPath::Resolved(None, path) => path,
2352 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2354 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2357 fn lower_poly_trait_ref(
2360 mut itctx: ImplTraitContext<'_, 'hir>,
2361 ) -> hir::PolyTraitRef<'hir> {
2362 let bound_generic_params = self.lower_generic_params(
2363 &p.bound_generic_params,
2364 &NodeMap::default(),
2368 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2369 // Any impl Trait types defined within this scope can capture
2370 // lifetimes bound on this predicate.
2371 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2372 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2373 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2377 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2378 capturable_lifetimes.extend(lt_def_names.clone());
2381 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2383 if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx {
2384 for param in lt_def_names {
2385 capturable_lifetimes.remove(¶m);
2391 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2394 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2395 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2398 fn lower_param_bounds(
2400 bounds: &[GenericBound],
2401 itctx: ImplTraitContext<'_, 'hir>,
2402 ) -> hir::GenericBounds<'hir> {
2403 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2406 fn lower_param_bounds_mut<'s>(
2408 bounds: &'s [GenericBound],
2409 mut itctx: ImplTraitContext<'s, 'hir>,
2410 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2411 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2414 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2415 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2418 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2419 let (stmts, expr) = match &*b.stmts {
2420 [stmts @ .., Stmt { kind: StmtKind::Expr(e), .. }] => (stmts, Some(&*e)),
2421 stmts => (stmts, None),
2423 let stmts = self.arena.alloc_from_iter(stmts.iter().flat_map(|stmt| self.lower_stmt(stmt)));
2424 let expr = expr.map(|e| self.lower_expr(e));
2425 let rules = self.lower_block_check_mode(&b.rules);
2426 let hir_id = self.lower_node_id(b.id);
2428 hir::Block { hir_id, stmts, expr, rules, span: b.span, targeted_by_break }
2431 /// Lowers a block directly to an expression, presuming that it
2432 /// has no attributes and is not targeted by a `break`.
2433 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2434 let block = self.lower_block(b, false);
2435 self.expr_block(block, AttrVec::new())
2438 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2439 self.with_new_scopes(|this| hir::AnonConst {
2440 hir_id: this.lower_node_id(c.id),
2441 body: this.lower_const_body(c.value.span, Some(&c.value)),
2445 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2446 let (hir_id, kind) = match s.kind {
2447 StmtKind::Local(ref l) => {
2448 let (l, item_ids) = self.lower_local(l);
2449 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2452 let item_id = hir::ItemId {
2453 // All the items that `lower_local` finds are `impl Trait` types.
2454 def_id: self.lower_node_id(item_id).expect_owner(),
2456 self.stmt(s.span, hir::StmtKind::Item(item_id))
2459 let hir_id = self.lower_node_id(s.id);
2460 self.alias_attrs(hir_id, l.hir_id);
2464 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2470 StmtKind::Item(ref it) => {
2471 // Can only use the ID once.
2472 let mut id = Some(s.id);
2479 .map(|id| self.lower_node_id(id))
2480 .unwrap_or_else(|| self.next_id());
2482 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2486 StmtKind::Expr(ref e) => {
2487 let e = self.lower_expr(e);
2488 let hir_id = self.lower_node_id(s.id);
2489 self.alias_attrs(hir_id, e.hir_id);
2490 (hir_id, hir::StmtKind::Expr(e))
2492 StmtKind::Semi(ref e) => {
2493 let e = self.lower_expr(e);
2494 let hir_id = self.lower_node_id(s.id);
2495 self.alias_attrs(hir_id, e.hir_id);
2496 (hir_id, hir::StmtKind::Semi(e))
2498 StmtKind::Empty => return smallvec![],
2499 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
2501 smallvec![hir::Stmt { hir_id, kind, span: s.span }]
2504 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2506 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2507 BlockCheckMode::Unsafe(u) => {
2508 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2513 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2515 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2516 UserProvided => hir::UnsafeSource::UserProvided,
2520 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2522 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2523 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2525 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2526 // placeholder for compilation to proceed.
2527 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2528 hir::TraitBoundModifier::Maybe
2533 // Helper methods for building HIR.
2535 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2536 hir::Stmt { span, kind, hir_id: self.next_id() }
2539 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2540 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2545 attrs: Option<&'hir [Attribute]>,
2547 init: Option<&'hir hir::Expr<'hir>>,
2548 pat: &'hir hir::Pat<'hir>,
2549 source: hir::LocalSource,
2550 ) -> hir::Stmt<'hir> {
2551 let hir_id = self.next_id();
2552 if let Some(a) = attrs {
2553 debug_assert!(!a.is_empty());
2554 self.attrs.insert(hir_id, a);
2556 let local = hir::Local { hir_id, init, pat, source, span, ty: None };
2557 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2560 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2561 self.block_all(expr.span, &[], Some(expr))
2567 stmts: &'hir [hir::Stmt<'hir>],
2568 expr: Option<&'hir hir::Expr<'hir>>,
2569 ) -> &'hir hir::Block<'hir> {
2570 let blk = hir::Block {
2573 hir_id: self.next_id(),
2574 rules: hir::BlockCheckMode::DefaultBlock,
2576 targeted_by_break: false,
2578 self.arena.alloc(blk)
2581 /// Constructs a `true` or `false` literal pattern.
2582 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2583 let expr = self.expr_bool(span, val);
2584 self.pat(span, hir::PatKind::Lit(expr))
2587 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2588 let field = self.single_pat_field(span, pat);
2589 self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
2592 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2593 let field = self.single_pat_field(span, pat);
2594 self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field)
2597 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2598 let field = self.single_pat_field(span, pat);
2599 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2602 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2603 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2606 fn single_pat_field(
2609 pat: &'hir hir::Pat<'hir>,
2610 ) -> &'hir [hir::FieldPat<'hir>] {
2611 let field = hir::FieldPat {
2612 hir_id: self.next_id(),
2613 ident: Ident::new(sym::integer(0), span),
2614 is_shorthand: false,
2618 arena_vec![self; field]
2621 fn pat_lang_item_variant(
2624 lang_item: hir::LangItem,
2625 fields: &'hir [hir::FieldPat<'hir>],
2626 ) -> &'hir hir::Pat<'hir> {
2627 let qpath = hir::QPath::LangItem(lang_item, span);
2628 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2631 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2632 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2635 fn pat_ident_binding_mode(
2639 bm: hir::BindingAnnotation,
2640 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2641 let hir_id = self.next_id();
2644 self.arena.alloc(hir::Pat {
2646 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2648 default_binding_modes: true,
2654 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2655 self.pat(span, hir::PatKind::Wild)
2658 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2659 self.arena.alloc(hir::Pat {
2660 hir_id: self.next_id(),
2663 default_binding_modes: true,
2667 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2668 self.arena.alloc(hir::Pat {
2669 hir_id: self.next_id(),
2672 default_binding_modes: false,
2678 mut hir_id: hir::HirId,
2680 qpath: hir::QPath<'hir>,
2681 ) -> hir::Ty<'hir> {
2682 let kind = match qpath {
2683 hir::QPath::Resolved(None, path) => {
2684 // Turn trait object paths into `TyKind::TraitObject` instead.
2686 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2687 let principal = hir::PolyTraitRef {
2688 bound_generic_params: &[],
2689 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2693 // The original ID is taken by the `PolyTraitRef`,
2694 // so the `Ty` itself needs a different one.
2695 hir_id = self.next_id();
2696 hir::TyKind::TraitObject(
2697 arena_vec![self; principal],
2698 self.elided_dyn_bound(span),
2701 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2704 _ => hir::TyKind::Path(qpath),
2707 hir::Ty { hir_id, kind, span }
2710 /// Invoked to create the lifetime argument for a type `&T`
2711 /// with no explicit lifetime.
2712 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2713 match self.anonymous_lifetime_mode {
2714 // Intercept when we are in an impl header or async fn and introduce an in-band
2716 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2718 AnonymousLifetimeMode::CreateParameter => {
2719 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2721 hir_id: self.next_id(),
2723 name: hir::LifetimeName::Param(fresh_name),
2727 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2729 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2733 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2734 /// return a "error lifetime".
2735 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2736 let (id, msg, label) = match id {
2737 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2740 self.resolver.next_node_id(),
2741 "`&` without an explicit lifetime name cannot be used here",
2742 "explicit lifetime name needed here",
2746 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2747 err.span_label(span, label);
2750 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2753 /// Invoked to create the lifetime argument(s) for a path like
2754 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2755 /// sorts of cases are deprecated. This may therefore report a warning or an
2756 /// error, depending on the mode.
2757 fn elided_path_lifetimes<'s>(
2761 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2762 (0..count).map(move |_| self.elided_path_lifetime(span))
2765 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2766 match self.anonymous_lifetime_mode {
2767 AnonymousLifetimeMode::CreateParameter => {
2768 // We should have emitted E0726 when processing this path above
2770 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2771 let id = self.resolver.next_node_id();
2772 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2774 // `PassThrough` is the normal case.
2775 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2776 // is unsuitable here, as these can occur from missing lifetime parameters in a
2777 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2778 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2779 // later, at which point a suitable error will be emitted.
2780 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2781 self.new_implicit_lifetime(span)
2786 /// Invoked to create the lifetime argument(s) for an elided trait object
2787 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2788 /// when the bound is written, even if it is written with `'_` like in
2789 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2790 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2791 match self.anonymous_lifetime_mode {
2792 // NB. We intentionally ignore the create-parameter mode here.
2793 // and instead "pass through" to resolve-lifetimes, which will apply
2794 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2795 // do not act like other elided lifetimes. In other words, given this:
2797 // impl Foo for Box<dyn Debug>
2799 // we do not introduce a fresh `'_` to serve as the bound, but instead
2800 // ultimately translate to the equivalent of:
2802 // impl Foo for Box<dyn Debug + 'static>
2804 // `resolve_lifetime` has the code to make that happen.
2805 AnonymousLifetimeMode::CreateParameter => {}
2807 AnonymousLifetimeMode::ReportError => {
2808 // ReportError applies to explicit use of `'_`.
2811 // This is the normal case.
2812 AnonymousLifetimeMode::PassThrough => {}
2815 let r = hir::Lifetime {
2816 hir_id: self.next_id(),
2818 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2820 debug!("elided_dyn_bound: r={:?}", r);
2824 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2825 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2828 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2829 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2830 // call site which do not have a macro backtrace. See #61963.
2831 let is_macro_callsite = self
2834 .span_to_snippet(span)
2835 .map(|snippet| snippet.starts_with("#["))
2837 if !is_macro_callsite {
2838 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2842 "trait objects without an explicit `dyn` are deprecated",
2843 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2848 fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId, default: Abi) {
2849 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2850 // call site which do not have a macro backtrace. See #61963.
2851 let is_macro_callsite = self
2854 .span_to_snippet(span)
2855 .map(|snippet| snippet.starts_with("#["))
2857 if !is_macro_callsite {
2858 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2862 "extern declarations without an explicit ABI are deprecated",
2863 BuiltinLintDiagnostics::MissingAbi(span, default),
2869 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2870 // Sorting by span ensures that we get things in order within a
2871 // file, and also puts the files in a sensible order.
2872 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2873 body_ids.sort_by_key(|b| bodies[b].value.span);
2877 /// Helper struct for delayed construction of GenericArgs.
2878 struct GenericArgsCtor<'hir> {
2879 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2880 bindings: &'hir [hir::TypeBinding<'hir>],
2881 parenthesized: bool,
2884 impl<'hir> GenericArgsCtor<'hir> {
2885 fn is_empty(&self) -> bool {
2886 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2889 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2891 args: arena.alloc_from_iter(self.args),
2892 bindings: self.bindings,
2893 parenthesized: self.parenthesized,