1 //! Lowers the AST to the HIR.
3 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
4 //! much like a fold. Where lowering involves a bit more work things get more
5 //! interesting and there are some invariants you should know about. These mostly
6 //! concern spans and IDs.
8 //! Spans are assigned to AST nodes during parsing and then are modified during
9 //! expansion to indicate the origin of a node and the process it went through
10 //! being expanded. IDs are assigned to AST nodes just before lowering.
12 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
13 //! expansion we do not preserve the process of lowering in the spans, so spans
14 //! should not be modified here. When creating a new node (as opposed to
15 //! "folding" an existing one), create a new ID using `next_id()`.
17 //! You must ensure that IDs are unique. That means that you should only use the
18 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
19 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
20 //! If you do, you must then set the new node's ID to a fresh one.
22 //! Spans are used for error messages and for tools to map semantics back to
23 //! source code. It is therefore not as important with spans as IDs to be strict
24 //! about use (you can't break the compiler by screwing up a span). Obviously, a
25 //! HIR node can only have a single span. But multiple nodes can have the same
26 //! span and spans don't need to be kept in order, etc. Where code is preserved
27 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
28 //! new it is probably best to give a span for the whole AST node being lowered.
29 //! All nodes should have real spans; don't use dummy spans. Tools are likely to
30 //! get confused if the spans from leaf AST nodes occur in multiple places
31 //! in the HIR, especially for multiple identifiers.
33 #![feature(crate_visibility_modifier)]
34 #![feature(box_patterns)]
36 #![recursion_limit = "256"]
38 use rustc_ast::node_id::NodeMap;
39 use rustc_ast::token::{self, Token};
40 use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, TokenStream, TokenTree};
41 use rustc_ast::visit::{self, AssocCtxt, Visitor};
42 use rustc_ast::walk_list;
43 use rustc_ast::{self as ast, *};
44 use rustc_ast_pretty::pprust;
45 use rustc_data_structures::captures::Captures;
46 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
47 use rustc_data_structures::sync::Lrc;
48 use rustc_errors::{struct_span_err, Applicability};
50 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
51 use rustc_hir::def_id::{DefId, DefIdMap, DefPathHash, LocalDefId, CRATE_DEF_ID};
52 use rustc_hir::definitions::{DefKey, DefPathData, Definitions};
53 use rustc_hir::intravisit;
54 use rustc_hir::{ConstArg, GenericArg, InferKind, ParamName};
55 use rustc_index::vec::{Idx, IndexVec};
56 use rustc_session::lint::builtin::{BARE_TRAIT_OBJECTS, MISSING_ABI};
57 use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
58 use rustc_session::utils::{FlattenNonterminals, NtToTokenstream};
59 use rustc_session::Session;
60 use rustc_span::edition::Edition;
61 use rustc_span::hygiene::ExpnId;
62 use rustc_span::source_map::{respan, CachingSourceMapView, DesugaringKind};
63 use rustc_span::symbol::{kw, sym, Ident, Symbol};
64 use rustc_span::{Span, DUMMY_SP};
65 use rustc_target::spec::abi::Abi;
67 use smallvec::{smallvec, SmallVec};
68 use std::collections::BTreeMap;
70 use tracing::{debug, trace};
72 macro_rules! arena_vec {
73 ($this:expr; $($x:expr),*) => ({
75 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
85 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
87 rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx);
89 struct LoweringContext<'a, 'hir: 'a> {
90 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
93 resolver: &'a mut dyn ResolverAstLowering,
95 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
96 /// if we don't have this function pointer. To avoid that dependency so that
97 /// `rustc_middle` is independent of the parser, we use dynamic dispatch here.
98 nt_to_tokenstream: NtToTokenstream,
100 /// Used to allocate HIR nodes.
101 arena: &'hir Arena<'hir>,
103 /// The items being lowered are collected here.
104 owners: IndexVec<LocalDefId, Option<hir::OwnerNode<'hir>>>,
105 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
107 trait_impls: BTreeMap<DefId, Vec<LocalDefId>>,
109 modules: BTreeMap<LocalDefId, hir::ModuleItems>,
111 generator_kind: Option<hir::GeneratorKind>,
113 attrs: BTreeMap<hir::HirId, &'hir [Attribute]>,
115 /// When inside an `async` context, this is the `HirId` of the
116 /// `task_context` local bound to the resume argument of the generator.
117 task_context: Option<hir::HirId>,
119 /// Used to get the current `fn`'s def span to point to when using `await`
120 /// outside of an `async fn`.
121 current_item: Option<Span>,
123 catch_scopes: Vec<NodeId>,
124 loop_scopes: Vec<NodeId>,
125 is_in_loop_condition: bool,
126 is_in_trait_impl: bool,
127 is_in_dyn_type: bool,
129 /// What to do when we encounter an "anonymous lifetime
130 /// reference". The term "anonymous" is meant to encompass both
131 /// `'_` lifetimes as well as fully elided cases where nothing is
132 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
133 anonymous_lifetime_mode: AnonymousLifetimeMode,
135 /// Used to create lifetime definitions from in-band lifetime usages.
136 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
137 /// When a named lifetime is encountered in a function or impl header and
138 /// has not been defined
139 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
140 /// to this list. The results of this list are then added to the list of
141 /// lifetime definitions in the corresponding impl or function generics.
142 lifetimes_to_define: Vec<(Span, ParamName)>,
144 /// `true` if in-band lifetimes are being collected. This is used to
145 /// indicate whether or not we're in a place where new lifetimes will result
146 /// in in-band lifetime definitions, such a function or an impl header,
147 /// including implicit lifetimes from `impl_header_lifetime_elision`.
148 is_collecting_in_band_lifetimes: bool,
150 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
151 /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked
152 /// against this list to see if it is already in-scope, or if a definition
153 /// needs to be created for it.
155 /// We always store a `normalize_to_macros_2_0()` version of the param-name in this
157 in_scope_lifetimes: Vec<ParamName>,
159 current_module: LocalDefId,
161 type_def_lifetime_params: DefIdMap<usize>,
163 current_hir_id_owner: (LocalDefId, u32),
164 item_local_id_counters: NodeMap<u32>,
165 node_id_to_hir_id: IndexVec<NodeId, Option<hir::HirId>>,
167 allow_try_trait: Option<Lrc<[Symbol]>>,
168 allow_gen_future: Option<Lrc<[Symbol]>>,
171 pub trait ResolverAstLowering {
172 fn def_key(&mut self, id: DefId) -> DefKey;
174 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
176 fn legacy_const_generic_args(&mut self, expr: &Expr) -> Option<Vec<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 take_trait_map(&mut 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;
201 fn def_path_hash(&self, def_id: DefId) -> DefPathHash;
206 node_id: ast::NodeId,
213 struct LoweringHasher<'a> {
214 source_map: CachingSourceMapView<'a>,
215 resolver: &'a dyn ResolverAstLowering,
218 impl<'a> rustc_span::HashStableContext for LoweringHasher<'a> {
220 fn hash_spans(&self) -> bool {
225 fn def_path_hash(&self, def_id: DefId) -> DefPathHash {
226 self.resolver.def_path_hash(def_id)
230 fn span_data_to_lines_and_cols(
232 span: &rustc_span::SpanData,
233 ) -> Option<(Lrc<rustc_span::SourceFile>, usize, rustc_span::BytePos, usize, rustc_span::BytePos)>
235 self.source_map.span_data_to_lines_and_cols(span)
239 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
240 /// and if so, what meaning it has.
242 enum ImplTraitContext<'b, 'a> {
243 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
244 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
245 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
247 /// Newly generated parameters should be inserted into the given `Vec`.
248 Universal(&'b mut Vec<hir::GenericParam<'a>>, LocalDefId),
250 /// Treat `impl Trait` as shorthand for a new opaque type.
251 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
252 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
254 ReturnPositionOpaqueTy {
255 /// `DefId` for the parent function, used to look up necessary
256 /// information later.
258 /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
259 origin: hir::OpaqueTyOrigin,
261 /// Impl trait in type aliases.
262 TypeAliasesOpaqueTy {
263 /// Set of lifetimes that this opaque type can capture, if it uses
264 /// them. This includes lifetimes bound since we entered this context.
268 /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>;
271 /// Here the inner opaque type captures `'a` because it uses it. It doesn't
272 /// need to capture `'b` because it already inherits the lifetime
273 /// parameter from `A`.
274 // FIXME(impl_trait): but `required_region_bounds` will ICE later
276 capturable_lifetimes: &'b mut FxHashSet<hir::LifetimeName>,
278 /// `impl Trait` is not accepted in this position.
279 Disallowed(ImplTraitPosition),
282 /// Position in which `impl Trait` is disallowed.
283 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
284 enum ImplTraitPosition {
285 /// Disallowed in `let` / `const` / `static` bindings.
288 /// All other positions.
292 impl<'a> ImplTraitContext<'_, 'a> {
294 fn disallowed() -> Self {
295 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
298 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
299 use self::ImplTraitContext::*;
301 Universal(params, parent) => Universal(params, *parent),
302 ReturnPositionOpaqueTy { fn_def_id, origin } => {
303 ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin }
305 TypeAliasesOpaqueTy { capturable_lifetimes } => {
306 TypeAliasesOpaqueTy { capturable_lifetimes }
308 Disallowed(pos) => Disallowed(*pos),
313 pub fn lower_crate<'a, 'hir>(
316 resolver: &'a mut dyn ResolverAstLowering,
317 nt_to_tokenstream: NtToTokenstream,
318 arena: &'hir Arena<'hir>,
319 ) -> &'hir hir::Crate<'hir> {
320 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
327 owners: IndexVec::default(),
328 bodies: BTreeMap::new(),
329 trait_impls: BTreeMap::new(),
330 modules: BTreeMap::new(),
331 attrs: BTreeMap::default(),
332 catch_scopes: Vec::new(),
333 loop_scopes: Vec::new(),
334 is_in_loop_condition: false,
335 is_in_trait_impl: false,
336 is_in_dyn_type: false,
337 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
338 type_def_lifetime_params: Default::default(),
339 current_module: CRATE_DEF_ID,
340 current_hir_id_owner: (CRATE_DEF_ID, 0),
341 item_local_id_counters: Default::default(),
342 node_id_to_hir_id: IndexVec::new(),
343 generator_kind: None,
346 lifetimes_to_define: Vec::new(),
347 is_collecting_in_band_lifetimes: false,
348 in_scope_lifetimes: Vec::new(),
349 allow_try_trait: Some([sym::try_trait_v2][..].into()),
350 allow_gen_future: Some([sym::gen_future][..].into()),
355 #[derive(Copy, Clone, PartialEq)]
357 /// Any path in a type context.
359 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
361 /// The `module::Type` in `module::Type::method` in an expression.
365 enum ParenthesizedGenericArgs {
370 /// What to do when we encounter an **anonymous** lifetime
371 /// reference. Anonymous lifetime references come in two flavors. You
372 /// have implicit, or fully elided, references to lifetimes, like the
373 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
374 /// or `Ref<'_, T>`. These often behave the same, but not always:
376 /// - certain usages of implicit references are deprecated, like
377 /// `Ref<T>`, and we sometimes just give hard errors in those cases
379 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
380 /// the same as `Box<dyn Foo + '_>`.
382 /// We describe the effects of the various modes in terms of three cases:
384 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
385 /// of a `&` (e.g., the missing lifetime in something like `&T`)
386 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
387 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
388 /// elided bounds follow special rules. Note that this only covers
389 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
390 /// '_>` is a case of "modern" elision.
391 /// - **Deprecated** -- this covers cases like `Ref<T>`, where the lifetime
392 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
393 /// non-deprecated equivalent.
395 /// Currently, the handling of lifetime elision is somewhat spread out
396 /// between HIR lowering and -- as described below -- the
397 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
398 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
399 /// everything into HIR lowering.
400 #[derive(Copy, Clone, Debug)]
401 enum AnonymousLifetimeMode {
402 /// For **Modern** cases, create a new anonymous region parameter
403 /// and reference that.
405 /// For **Dyn Bound** cases, pass responsibility to
406 /// `resolve_lifetime` code.
408 /// For **Deprecated** cases, report an error.
411 /// Give a hard error when either `&` or `'_` is written. Used to
412 /// rule out things like `where T: Foo<'_>`. Does not imply an
413 /// error on default object bounds (e.g., `Box<dyn Foo>`).
416 /// Pass responsibility to `resolve_lifetime` code for all cases.
420 impl<'a, 'hir> LoweringContext<'a, 'hir> {
421 fn lower_crate(mut self, c: &Crate) -> &'hir hir::Crate<'hir> {
422 /// Full-crate AST visitor that inserts into a fresh
423 /// `LoweringContext` any information that may be
424 /// needed from arbitrary locations in the crate,
425 /// e.g., the number of lifetime generic parameters
426 /// declared for every type and trait definition.
427 struct MiscCollector<'tcx, 'lowering, 'hir> {
428 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
431 impl MiscCollector<'_, '_, '_> {
432 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree) {
434 UseTreeKind::Simple(_, id1, id2) => {
435 for id in [id1, id2] {
436 self.lctx.allocate_hir_id_counter(id);
439 UseTreeKind::Glob => (),
440 UseTreeKind::Nested(ref trees) => {
441 for &(ref use_tree, id) in trees {
442 self.lctx.allocate_hir_id_counter(id);
443 self.allocate_use_tree_hir_id_counters(use_tree);
450 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
451 fn visit_item(&mut self, item: &'tcx Item) {
452 self.lctx.allocate_hir_id_counter(item.id);
455 ItemKind::Struct(_, ref generics)
456 | ItemKind::Union(_, ref generics)
457 | ItemKind::Enum(_, ref generics)
458 | ItemKind::TyAlias(box TyAliasKind(_, ref generics, ..))
459 | ItemKind::Trait(box TraitKind(_, _, ref generics, ..)) => {
460 let def_id = self.lctx.resolver.local_def_id(item.id);
465 matches!(param.kind, ast::GenericParamKind::Lifetime { .. })
468 self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count);
470 ItemKind::Use(ref use_tree) => {
471 self.allocate_use_tree_hir_id_counters(use_tree);
476 visit::walk_item(self, item);
479 fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
480 self.lctx.allocate_hir_id_counter(item.id);
481 visit::walk_assoc_item(self, item, ctxt);
484 fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) {
485 self.lctx.allocate_hir_id_counter(item.id);
486 visit::walk_foreign_item(self, item);
489 fn visit_ty(&mut self, t: &'tcx Ty) {
491 // Mirrors the case in visit::walk_ty
492 TyKind::BareFn(ref f) => {
493 walk_list!(self, visit_generic_param, &f.generic_params);
494 // Mirrors visit::walk_fn_decl
495 for parameter in &f.decl.inputs {
496 // We don't lower the ids of argument patterns
497 self.visit_pat(¶meter.pat);
498 self.visit_ty(¶meter.ty)
500 self.visit_fn_ret_ty(&f.decl.output)
502 _ => visit::walk_ty(self, t),
507 self.lower_node_id(CRATE_NODE_ID);
508 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID));
510 visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
511 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
513 let module = self.arena.alloc(self.lower_mod(&c.items, c.span));
514 self.lower_attrs(hir::CRATE_HIR_ID, &c.attrs);
515 self.owners.ensure_contains_elem(CRATE_DEF_ID, || None);
516 self.owners[CRATE_DEF_ID] = Some(hir::OwnerNode::Crate(module));
518 let body_ids = body_ids(&self.bodies);
520 c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect();
522 let mut trait_map: FxHashMap<_, FxHashMap<_, _>> = FxHashMap::default();
523 for (k, v) in self.resolver.take_trait_map().into_iter() {
524 if let Some(Some(hir_id)) = self.node_id_to_hir_id.get(k) {
525 let map = trait_map.entry(hir_id.owner).or_default();
526 map.insert(hir_id.local_id, v.into_boxed_slice());
530 let mut def_id_to_hir_id = IndexVec::default();
532 for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() {
533 if let Some(def_id) = self.resolver.opt_local_def_id(node_id) {
534 if def_id_to_hir_id.len() <= def_id.index() {
535 def_id_to_hir_id.resize(def_id.index() + 1, None);
537 def_id_to_hir_id[def_id] = hir_id;
541 self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id);
543 #[cfg(debug_assertions)]
544 for (&id, attrs) in self.attrs.iter() {
545 // Verify that we do not store empty slices in the map.
546 if attrs.is_empty() {
547 panic!("Stored empty attributes for {:?}", id);
551 let krate = hir::Crate {
555 trait_impls: self.trait_impls,
556 modules: self.modules,
561 self.arena.alloc(krate)
564 fn insert_item(&mut self, item: hir::Item<'hir>) -> hir::ItemId {
565 let id = item.item_id();
566 let item = self.arena.alloc(item);
567 self.owners.ensure_contains_elem(id.def_id, || None);
568 self.owners[id.def_id] = Some(hir::OwnerNode::Item(item));
569 self.modules.entry(self.current_module).or_default().items.insert(id);
573 fn insert_foreign_item(&mut self, item: hir::ForeignItem<'hir>) -> hir::ForeignItemId {
574 let id = item.foreign_item_id();
575 let item = self.arena.alloc(item);
576 self.owners.ensure_contains_elem(id.def_id, || None);
577 self.owners[id.def_id] = Some(hir::OwnerNode::ForeignItem(item));
578 self.modules.entry(self.current_module).or_default().foreign_items.insert(id);
582 fn insert_impl_item(&mut self, item: hir::ImplItem<'hir>) -> hir::ImplItemId {
583 let id = item.impl_item_id();
584 let item = self.arena.alloc(item);
585 self.owners.ensure_contains_elem(id.def_id, || None);
586 self.owners[id.def_id] = Some(hir::OwnerNode::ImplItem(item));
587 self.modules.entry(self.current_module).or_default().impl_items.insert(id);
591 fn insert_trait_item(&mut self, item: hir::TraitItem<'hir>) -> hir::TraitItemId {
592 let id = item.trait_item_id();
593 let item = self.arena.alloc(item);
594 self.owners.ensure_contains_elem(id.def_id, || None);
595 self.owners[id.def_id] = Some(hir::OwnerNode::TraitItem(item));
596 self.modules.entry(self.current_module).or_default().trait_items.insert(id);
600 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
601 // Set up the counter if needed.
602 self.item_local_id_counters.entry(owner).or_insert(0);
603 // Always allocate the first `HirId` for the owner itself.
604 let lowered = self.lower_node_id_with_owner(owner, owner);
605 debug_assert_eq!(lowered.local_id.as_u32(), 0);
609 fn create_stable_hashing_context(&self) -> LoweringHasher<'_> {
611 source_map: CachingSourceMapView::new(self.sess.source_map()),
612 resolver: self.resolver,
616 fn lower_node_id_generic(
619 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
621 assert_ne!(ast_node_id, DUMMY_NODE_ID);
623 let min_size = ast_node_id.as_usize() + 1;
625 if min_size > self.node_id_to_hir_id.len() {
626 self.node_id_to_hir_id.resize(min_size, None);
629 if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] {
632 // Generate a new `HirId`.
633 let hir_id = alloc_hir_id(self);
634 self.node_id_to_hir_id[ast_node_id] = Some(hir_id);
640 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
642 .item_local_id_counters
643 .insert(owner, HIR_ID_COUNTER_LOCKED)
644 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
645 let def_id = self.resolver.local_def_id(owner);
646 let old_owner = std::mem::replace(&mut self.current_hir_id_owner, (def_id, counter));
648 let (new_def_id, new_counter) =
649 std::mem::replace(&mut self.current_hir_id_owner, old_owner);
651 debug_assert!(def_id == new_def_id);
652 debug_assert!(new_counter >= counter);
654 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
655 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
659 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
660 /// the `LoweringContext`'s `NodeId => HirId` map.
661 /// Take care not to call this method if the resulting `HirId` is then not
662 /// actually used in the HIR, as that would trigger an assertion in the
663 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
664 /// properly. Calling the method twice with the same `NodeId` is fine though.
665 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
666 self.lower_node_id_generic(ast_node_id, |this| {
667 let &mut (owner, ref mut local_id_counter) = &mut this.current_hir_id_owner;
668 let local_id = *local_id_counter;
669 *local_id_counter += 1;
670 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
674 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
675 self.lower_node_id_generic(ast_node_id, |this| {
676 let local_id_counter = this
677 .item_local_id_counters
679 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
680 let local_id = *local_id_counter;
682 // We want to be sure not to modify the counter in the map while it
683 // is also on the stack. Otherwise we'll get lost updates when writing
684 // back from the stack to the map.
685 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
687 *local_id_counter += 1;
688 let owner = this.resolver.opt_local_def_id(owner).expect(
689 "you forgot to call `create_def` or are lowering node-IDs \
690 that do not belong to the current owner",
693 hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) }
697 fn next_id(&mut self) -> hir::HirId {
698 let node_id = self.resolver.next_node_id();
699 self.lower_node_id(node_id)
702 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
704 self.lower_node_id_generic(id, |_| {
705 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
710 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
711 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
712 if pr.unresolved_segments() != 0 {
713 panic!("path not fully resolved: {:?}", pr);
719 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
720 self.resolver.get_import_res(id).present_items()
723 fn diagnostic(&self) -> &rustc_errors::Handler {
724 self.sess.diagnostic()
727 /// Reuses the span but adds information like the kind of the desugaring and features that are
728 /// allowed inside this span.
729 fn mark_span_with_reason(
731 reason: DesugaringKind,
733 allow_internal_unstable: Option<Lrc<[Symbol]>>,
735 span.mark_with_reason(
736 allow_internal_unstable,
739 self.create_stable_hashing_context(),
743 fn with_anonymous_lifetime_mode<R>(
745 anonymous_lifetime_mode: AnonymousLifetimeMode,
746 op: impl FnOnce(&mut Self) -> R,
749 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
750 anonymous_lifetime_mode,
752 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
753 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
754 let result = op(self);
755 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
757 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
758 old_anonymous_lifetime_mode
763 /// Intercept all spans entering HIR.
764 /// For now we are not doing anything with the intercepted spans.
765 fn lower_span(&self, span: Span) -> Span {
769 fn lower_ident(&self, ident: Ident) -> Ident {
770 Ident::new(ident.name, self.lower_span(ident.span))
773 /// Creates a new `hir::GenericParam` for every new lifetime and
774 /// type parameter encountered while evaluating `f`. Definitions
775 /// are created with the parent provided. If no `parent_id` is
776 /// provided, no definitions will be returned.
778 /// Presuming that in-band lifetimes are enabled, then
779 /// `self.anonymous_lifetime_mode` will be updated to match the
780 /// parameter while `f` is running (and restored afterwards).
781 fn collect_in_band_defs<T>(
783 parent_def_id: LocalDefId,
784 anonymous_lifetime_mode: AnonymousLifetimeMode,
785 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
786 ) -> (Vec<hir::GenericParam<'hir>>, T) {
787 assert!(!self.is_collecting_in_band_lifetimes);
788 assert!(self.lifetimes_to_define.is_empty());
789 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
791 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
792 self.is_collecting_in_band_lifetimes = true;
794 let (in_band_ty_params, res) = f(self);
796 self.is_collecting_in_band_lifetimes = false;
797 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
799 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
801 let params = lifetimes_to_define
803 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id))
804 .chain(in_band_ty_params.into_iter())
810 /// Converts a lifetime into a new generic parameter.
811 fn lifetime_to_generic_param(
815 parent_def_id: LocalDefId,
816 ) -> hir::GenericParam<'hir> {
817 let node_id = self.resolver.next_node_id();
819 // Get the name we'll use to make the def-path. Note
820 // that collisions are ok here and this shouldn't
821 // really show up for end-user.
822 let (str_name, kind) = match hir_name {
823 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
824 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
825 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
828 // Add a definition for the in-band lifetime def.
829 self.resolver.create_def(
832 DefPathData::LifetimeNs(str_name),
838 hir_id: self.lower_node_id(node_id),
841 span: self.lower_span(span),
842 pure_wrt_drop: false,
843 kind: hir::GenericParamKind::Lifetime { kind },
847 /// When there is a reference to some lifetime `'a`, and in-band
848 /// lifetimes are enabled, then we want to push that lifetime into
849 /// the vector of names to define later. In that case, it will get
850 /// added to the appropriate generics.
851 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
852 if !self.is_collecting_in_band_lifetimes {
856 if !self.sess.features_untracked().in_band_lifetimes {
860 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) {
864 let hir_name = ParamName::Plain(ident);
866 if self.lifetimes_to_define.iter().any(|(_, lt_name)| {
867 lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0()
872 self.lifetimes_to_define.push((ident.span, hir_name));
875 /// When we have either an elided or `'_` lifetime in an impl
876 /// header, we convert it to an in-band lifetime.
877 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
878 assert!(self.is_collecting_in_band_lifetimes);
879 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
880 let hir_name = ParamName::Fresh(index);
881 self.lifetimes_to_define.push((span, hir_name));
885 // Evaluates `f` with the lifetimes in `params` in-scope.
886 // This is used to track which lifetimes have already been defined, and
887 // which are new in-band lifetimes that need to have a definition created
889 fn with_in_scope_lifetime_defs<T>(
891 params: &[GenericParam],
892 f: impl FnOnce(&mut Self) -> T,
894 let old_len = self.in_scope_lifetimes.len();
895 let lt_def_names = params.iter().filter_map(|param| match param.kind {
896 GenericParamKind::Lifetime { .. } => {
897 Some(ParamName::Plain(param.ident.normalize_to_macros_2_0()))
901 self.in_scope_lifetimes.extend(lt_def_names);
905 self.in_scope_lifetimes.truncate(old_len);
909 /// Appends in-band lifetime defs and argument-position `impl
910 /// Trait` defs to the existing set of generics.
912 /// Presuming that in-band lifetimes are enabled, then
913 /// `self.anonymous_lifetime_mode` will be updated to match the
914 /// parameter while `f` is running (and restored afterwards).
915 fn add_in_band_defs<T>(
918 parent_def_id: LocalDefId,
919 anonymous_lifetime_mode: AnonymousLifetimeMode,
920 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
921 ) -> (hir::Generics<'hir>, T) {
922 let (in_band_defs, (mut lowered_generics, res)) =
923 self.with_in_scope_lifetime_defs(&generics.params, |this| {
924 this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| {
925 let mut params = Vec::new();
926 // Note: it is necessary to lower generics *before* calling `f`.
927 // When lowering `async fn`, there's a final step when lowering
928 // the return type that assumes that all in-scope lifetimes have
929 // already been added to either `in_scope_lifetimes` or
930 // `lifetimes_to_define`. If we swapped the order of these two,
931 // in-band-lifetimes introduced by generics or where-clauses
932 // wouldn't have been added yet.
933 let generics = this.lower_generics_mut(
935 ImplTraitContext::Universal(&mut params, this.current_hir_id_owner.0),
937 let res = f(this, &mut params);
938 (params, (generics, res))
942 lowered_generics.params.extend(in_band_defs);
944 let lowered_generics = lowered_generics.into_generics(self.arena);
945 (lowered_generics, res)
948 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
949 let was_in_dyn_type = self.is_in_dyn_type;
950 self.is_in_dyn_type = in_scope;
952 let result = f(self);
954 self.is_in_dyn_type = was_in_dyn_type;
959 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
960 let was_in_loop_condition = self.is_in_loop_condition;
961 self.is_in_loop_condition = false;
963 let catch_scopes = mem::take(&mut self.catch_scopes);
964 let loop_scopes = mem::take(&mut self.loop_scopes);
966 self.catch_scopes = catch_scopes;
967 self.loop_scopes = loop_scopes;
969 self.is_in_loop_condition = was_in_loop_condition;
974 fn lower_attrs(&mut self, id: hir::HirId, attrs: &[Attribute]) -> Option<&'hir [Attribute]> {
975 if attrs.is_empty() {
978 let ret = self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)));
979 debug_assert!(!ret.is_empty());
980 self.attrs.insert(id, ret);
985 fn lower_attr(&self, attr: &Attribute) -> Attribute {
986 // Note that we explicitly do not walk the path. Since we don't really
987 // lower attributes (we use the AST version) there is nowhere to keep
988 // the `HirId`s. We don't actually need HIR version of attributes anyway.
989 // Tokens are also not needed after macro expansion and parsing.
990 let kind = match attr.kind {
991 AttrKind::Normal(ref item, _) => AttrKind::Normal(
993 path: item.path.clone(),
994 args: self.lower_mac_args(&item.args),
999 AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data),
1002 Attribute { kind, id: attr.id, style: attr.style, span: self.lower_span(attr.span) }
1005 fn alias_attrs(&mut self, id: hir::HirId, target_id: hir::HirId) {
1006 if let Some(&a) = self.attrs.get(&target_id) {
1007 debug_assert!(!a.is_empty());
1008 self.attrs.insert(id, a);
1012 fn lower_mac_args(&self, args: &MacArgs) -> MacArgs {
1014 MacArgs::Empty => MacArgs::Empty,
1015 MacArgs::Delimited(dspan, delim, ref tokens) => {
1016 // This is either a non-key-value attribute, or a `macro_rules!` body.
1017 // We either not have any nonterminals present (in the case of an attribute),
1018 // or have tokens available for all nonterminals in the case of a nested
1019 // `macro_rules`: e.g:
1022 // macro_rules! outer {
1024 // macro_rules! inner {
1031 // In both cases, we don't want to synthesize any tokens
1035 self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No),
1038 // This is an inert key-value attribute - it will never be visible to macros
1039 // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake
1040 // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`).
1041 MacArgs::Eq(eq_span, ref token) => {
1042 // In valid code the value is always representable as a single literal token.
1043 fn unwrap_single_token(sess: &Session, tokens: TokenStream, span: Span) -> Token {
1044 if tokens.len() != 1 {
1046 .delay_span_bug(span, "multiple tokens in key-value attribute's value");
1048 match tokens.into_trees().next() {
1049 Some(TokenTree::Token(token)) => token,
1050 Some(TokenTree::Delimited(_, delim, tokens)) => {
1051 if delim != token::NoDelim {
1052 sess.diagnostic().delay_span_bug(
1054 "unexpected delimiter in key-value attribute's value",
1057 unwrap_single_token(sess, tokens, span)
1059 None => Token::dummy(),
1063 let tokens = FlattenNonterminals {
1064 parse_sess: &self.sess.parse_sess,
1065 synthesize_tokens: CanSynthesizeMissingTokens::Yes,
1066 nt_to_tokenstream: self.nt_to_tokenstream,
1068 .process_token(token.clone());
1069 MacArgs::Eq(eq_span, unwrap_single_token(self.sess, tokens, token.span))
1074 fn lower_token_stream(
1076 tokens: TokenStream,
1077 synthesize_tokens: CanSynthesizeMissingTokens,
1079 FlattenNonterminals {
1080 parse_sess: &self.sess.parse_sess,
1082 nt_to_tokenstream: self.nt_to_tokenstream,
1084 .process_token_stream(tokens)
1087 /// Given an associated type constraint like one of these:
1090 /// T: Iterator<Item: Debug>
1092 /// T: Iterator<Item = Debug>
1096 /// returns a `hir::TypeBinding` representing `Item`.
1097 fn lower_assoc_ty_constraint(
1099 constraint: &AssocTyConstraint,
1100 mut itctx: ImplTraitContext<'_, 'hir>,
1101 ) -> hir::TypeBinding<'hir> {
1102 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1104 // lower generic arguments of identifier in constraint
1105 let gen_args = if let Some(ref gen_args) = constraint.gen_args {
1106 let gen_args_ctor = match gen_args {
1107 GenericArgs::AngleBracketed(ref data) => {
1108 self.lower_angle_bracketed_parameter_data(
1110 ParamMode::Explicit,
1115 GenericArgs::Parenthesized(ref data) => {
1116 let mut err = self.sess.struct_span_err(
1118 "parenthesized generic arguments cannot be used in associated type constraints"
1120 // FIXME: try to write a suggestion here
1122 self.lower_angle_bracketed_parameter_data(
1123 &data.as_angle_bracketed_args(),
1124 ParamMode::Explicit,
1130 gen_args_ctor.into_generic_args(self)
1132 self.arena.alloc(hir::GenericArgs::none())
1135 let kind = match constraint.kind {
1136 AssocTyConstraintKind::Equality { ref ty } => {
1137 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1139 AssocTyConstraintKind::Bound { ref bounds } => {
1140 let mut capturable_lifetimes;
1141 let mut parent_def_id = self.current_hir_id_owner.0;
1142 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1143 let (desugar_to_impl_trait, itctx) = match itctx {
1144 // We are in the return position:
1146 // fn foo() -> impl Iterator<Item: Debug>
1150 // fn foo() -> impl Iterator<Item = impl Debug>
1151 ImplTraitContext::ReturnPositionOpaqueTy { .. }
1152 | ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
1154 // We are in the argument position, but within a dyn type:
1156 // fn foo(x: dyn Iterator<Item: Debug>)
1160 // fn foo(x: dyn Iterator<Item = impl Debug>)
1161 ImplTraitContext::Universal(_, parent) if self.is_in_dyn_type => {
1162 parent_def_id = parent;
1166 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1167 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1168 // "impl trait context" to permit `impl Debug` in this position (it desugars
1169 // then to an opaque type).
1171 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1172 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1173 capturable_lifetimes = FxHashSet::default();
1176 ImplTraitContext::TypeAliasesOpaqueTy {
1177 capturable_lifetimes: &mut capturable_lifetimes,
1182 // We are in the parameter position, but not within a dyn type:
1184 // fn foo(x: impl Iterator<Item: Debug>)
1186 // so we leave it as is and this gets expanded in astconv to a bound like
1187 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1189 _ => (false, itctx),
1192 if desugar_to_impl_trait {
1193 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1194 // constructing the HIR for `impl bounds...` and then lowering that.
1196 let impl_trait_node_id = self.resolver.next_node_id();
1197 self.resolver.create_def(
1200 DefPathData::ImplTrait,
1205 self.with_dyn_type_scope(false, |this| {
1206 let node_id = this.resolver.next_node_id();
1207 let ty = this.lower_ty(
1210 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1211 span: this.lower_span(constraint.span),
1217 hir::TypeBindingKind::Equality { ty }
1220 // Desugar `AssocTy: Bounds` into a type binding where the
1221 // later desugars into a trait predicate.
1222 let bounds = self.lower_param_bounds(bounds, itctx);
1224 hir::TypeBindingKind::Constraint { bounds }
1230 hir_id: self.lower_node_id(constraint.id),
1231 ident: self.lower_ident(constraint.ident),
1234 span: self.lower_span(constraint.span),
1238 fn lower_generic_arg(
1240 arg: &ast::GenericArg,
1241 itctx: ImplTraitContext<'_, 'hir>,
1242 ) -> hir::GenericArg<'hir> {
1244 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1245 ast::GenericArg::Type(ty) => {
1247 TyKind::Infer if self.sess.features_untracked().generic_arg_infer => {
1248 return GenericArg::Infer(hir::InferArg {
1249 hir_id: self.lower_node_id(ty.id),
1250 span: self.lower_span(ty.span),
1251 kind: InferKind::Type,
1254 // We parse const arguments as path types as we cannot distinguish them during
1255 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1256 // type and value namespaces. If we resolved the path in the value namespace, we
1257 // transform it into a generic const argument.
1258 TyKind::Path(ref qself, ref path) => {
1259 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1260 let res = partial_res.base_res();
1261 if !res.matches_ns(Namespace::TypeNS) {
1263 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1267 // Construct an AnonConst where the expr is the "ty"'s path.
1269 let parent_def_id = self.current_hir_id_owner.0;
1270 let node_id = self.resolver.next_node_id();
1272 // Add a definition for the in-band const def.
1273 self.resolver.create_def(
1276 DefPathData::AnonConst,
1281 let span = self.lower_span(ty.span);
1282 let path_expr = Expr {
1284 kind: ExprKind::Path(qself.clone(), path.clone()),
1286 attrs: AttrVec::new(),
1290 let ct = self.with_new_scopes(|this| hir::AnonConst {
1291 hir_id: this.lower_node_id(node_id),
1292 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1294 return GenericArg::Const(ConstArg { value: ct, span });
1300 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1302 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1303 value: self.lower_anon_const(&ct),
1304 span: self.lower_span(ct.value.span),
1309 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1310 self.arena.alloc(self.lower_ty_direct(t, itctx))
1316 qself: &Option<QSelf>,
1318 param_mode: ParamMode,
1319 itctx: ImplTraitContext<'_, 'hir>,
1320 ) -> hir::Ty<'hir> {
1321 let id = self.lower_node_id(t.id);
1322 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1323 let ty = self.ty_path(id, t.span, qpath);
1324 if let hir::TyKind::TraitObject(..) = ty.kind {
1325 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1330 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1331 hir::Ty { hir_id: self.next_id(), kind, span: self.lower_span(span) }
1334 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1335 self.ty(span, hir::TyKind::Tup(tys))
1338 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1339 let kind = match t.kind {
1340 TyKind::Infer => hir::TyKind::Infer,
1341 TyKind::Err => hir::TyKind::Err,
1342 // FIXME(unnamed_fields): IMPLEMENTATION IN PROGRESS
1343 TyKind::AnonymousStruct(ref _fields, _recovered) => {
1344 self.sess.struct_span_err(t.span, "anonymous structs are unimplemented").emit();
1347 TyKind::AnonymousUnion(ref _fields, _recovered) => {
1348 self.sess.struct_span_err(t.span, "anonymous unions are unimplemented").emit();
1351 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1352 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1353 TyKind::Rptr(ref region, ref mt) => {
1354 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1355 let lifetime = match *region {
1356 Some(ref lt) => self.lower_lifetime(lt),
1357 None => self.elided_ref_lifetime(span),
1359 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1361 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1362 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1363 let span = this.sess.source_map().next_point(t.span.shrink_to_lo());
1364 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1365 generic_params: this.lower_generic_params(
1367 &NodeMap::default(),
1368 ImplTraitContext::disallowed(),
1370 unsafety: this.lower_unsafety(f.unsafety),
1371 abi: this.lower_extern(f.ext, span, t.id),
1372 decl: this.lower_fn_decl(&f.decl, None, false, None),
1373 param_names: this.lower_fn_params_to_names(&f.decl),
1377 TyKind::Never => hir::TyKind::Never,
1378 TyKind::Tup(ref tys) => {
1379 hir::TyKind::Tup(self.arena.alloc_from_iter(
1380 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1383 TyKind::Paren(ref ty) => {
1384 return self.lower_ty_direct(ty, itctx);
1386 TyKind::Path(ref qself, ref path) => {
1387 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1389 TyKind::ImplicitSelf => {
1390 let res = self.expect_full_res(t.id);
1391 let res = self.lower_res(res);
1392 hir::TyKind::Path(hir::QPath::Resolved(
1394 self.arena.alloc(hir::Path {
1396 segments: arena_vec![self; hir::PathSegment::from_ident(
1397 Ident::with_dummy_span(kw::SelfUpper)
1399 span: self.lower_span(t.span),
1403 TyKind::Array(ref ty, ref length) => {
1404 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1406 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1407 TyKind::TraitObject(ref bounds, kind) => {
1408 let mut lifetime_bound = None;
1409 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1411 this.arena.alloc_from_iter(bounds.iter().filter_map(
1412 |bound| match *bound {
1413 GenericBound::Trait(
1415 TraitBoundModifier::None | TraitBoundModifier::MaybeConst,
1416 ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())),
1417 // `~const ?Bound` will cause an error during AST validation
1418 // anyways, so treat it like `?Bound` as compilation proceeds.
1419 GenericBound::Trait(
1421 TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe,
1423 GenericBound::Outlives(ref lifetime) => {
1424 if lifetime_bound.is_none() {
1425 lifetime_bound = Some(this.lower_lifetime(lifetime));
1431 let lifetime_bound =
1432 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1433 (bounds, lifetime_bound)
1435 if kind != TraitObjectSyntax::Dyn {
1436 self.maybe_lint_bare_trait(t.span, t.id, false);
1438 hir::TyKind::TraitObject(bounds, lifetime_bound, kind)
1440 TyKind::ImplTrait(def_node_id, ref bounds) => {
1443 ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self
1444 .lower_opaque_impl_trait(
1450 |this| this.lower_param_bounds(bounds, itctx),
1452 ImplTraitContext::TypeAliasesOpaqueTy { ref capturable_lifetimes } => {
1453 // Reset capturable lifetimes, any nested impl trait
1454 // types will inherit lifetimes from this opaque type,
1455 // so don't need to capture them again.
1456 let nested_itctx = ImplTraitContext::TypeAliasesOpaqueTy {
1457 capturable_lifetimes: &mut FxHashSet::default(),
1459 self.lower_opaque_impl_trait(
1462 hir::OpaqueTyOrigin::TyAlias,
1464 Some(capturable_lifetimes),
1465 |this| this.lower_param_bounds(bounds, nested_itctx),
1468 ImplTraitContext::Universal(in_band_ty_params, parent_def_id) => {
1469 // Add a definition for the in-band `Param`.
1470 let def_id = self.resolver.local_def_id(def_node_id);
1472 let hir_bounds = self.lower_param_bounds(
1474 ImplTraitContext::Universal(in_band_ty_params, parent_def_id),
1476 // Set the name to `impl Bound1 + Bound2`.
1477 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1478 in_band_ty_params.push(hir::GenericParam {
1479 hir_id: self.lower_node_id(def_node_id),
1480 name: ParamName::Plain(self.lower_ident(ident)),
1481 pure_wrt_drop: false,
1483 span: self.lower_span(span),
1484 kind: hir::GenericParamKind::Type {
1486 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1490 hir::TyKind::Path(hir::QPath::Resolved(
1492 self.arena.alloc(hir::Path {
1493 span: self.lower_span(span),
1494 res: Res::Def(DefKind::TyParam, def_id.to_def_id()),
1495 segments: arena_vec![self; hir::PathSegment::from_ident(self.lower_ident(ident))],
1499 ImplTraitContext::Disallowed(_) => {
1500 let mut err = struct_span_err!(
1504 "`impl Trait` not allowed outside of {}",
1505 "function and method return types",
1512 TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"),
1513 TyKind::CVarArgs => {
1514 self.sess.delay_span_bug(
1516 "`TyKind::CVarArgs` should have been handled elsewhere",
1522 hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }
1525 fn lower_opaque_impl_trait(
1528 fn_def_id: Option<DefId>,
1529 origin: hir::OpaqueTyOrigin,
1530 opaque_ty_node_id: NodeId,
1531 capturable_lifetimes: Option<&FxHashSet<hir::LifetimeName>>,
1532 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1533 ) -> hir::TyKind<'hir> {
1535 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1536 fn_def_id, opaque_ty_node_id, span,
1539 // Make sure we know that some funky desugaring has been going on here.
1540 // This is a first: there is code in other places like for loop
1541 // desugaring that explicitly states that we don't want to track that.
1542 // Not tracking it makes lints in rustc and clippy very fragile, as
1543 // frequently opened issues show.
1544 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1546 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1548 self.allocate_hir_id_counter(opaque_ty_node_id);
1550 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1552 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1556 capturable_lifetimes,
1559 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes);
1561 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs);
1563 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1564 let opaque_ty_item = hir::OpaqueTy {
1565 generics: hir::Generics {
1566 params: lifetime_defs,
1567 where_clause: hir::WhereClause { predicates: &[], span: lctx.lower_span(span) },
1568 span: lctx.lower_span(span),
1571 impl_trait_fn: fn_def_id,
1575 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id);
1576 lctx.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
1578 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1579 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, lifetimes)
1583 /// Registers a new opaque type with the proper `NodeId`s and
1584 /// returns the lowered node-ID for the opaque type.
1585 fn generate_opaque_type(
1587 opaque_ty_id: LocalDefId,
1588 opaque_ty_item: hir::OpaqueTy<'hir>,
1590 opaque_ty_span: Span,
1592 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1593 // Generate an `type Foo = impl Trait;` declaration.
1594 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1595 let opaque_ty_item = hir::Item {
1596 def_id: opaque_ty_id,
1597 ident: Ident::invalid(),
1598 kind: opaque_ty_item_kind,
1599 vis: respan(self.lower_span(span.shrink_to_lo()), hir::VisibilityKind::Inherited),
1600 span: self.lower_span(opaque_ty_span),
1603 // Insert the item into the global item list. This usually happens
1604 // automatically for all AST items. But this opaque type item
1605 // does not actually exist in the AST.
1606 self.insert_item(opaque_ty_item);
1609 fn lifetimes_from_impl_trait_bounds(
1611 opaque_ty_id: NodeId,
1612 parent_def_id: LocalDefId,
1613 bounds: hir::GenericBounds<'hir>,
1614 lifetimes_to_include: Option<&FxHashSet<hir::LifetimeName>>,
1615 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1617 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1618 parent_def_id={:?}, \
1620 opaque_ty_id, parent_def_id, bounds,
1623 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1624 // appear in the bounds, excluding lifetimes that are created within the bounds.
1625 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1626 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1627 context: &'r mut LoweringContext<'a, 'hir>,
1629 opaque_ty_id: NodeId,
1630 collect_elided_lifetimes: bool,
1631 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1632 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1633 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1634 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1635 lifetimes_to_include: Option<&'r FxHashSet<hir::LifetimeName>>,
1638 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1639 type Map = intravisit::ErasedMap<'v>;
1641 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1642 intravisit::NestedVisitorMap::None
1645 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1646 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1647 if parameters.parenthesized {
1648 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1649 self.collect_elided_lifetimes = false;
1650 intravisit::walk_generic_args(self, span, parameters);
1651 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1653 intravisit::walk_generic_args(self, span, parameters);
1657 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1658 // Don't collect elided lifetimes used inside of `fn()` syntax.
1659 if let hir::TyKind::BareFn(_) = t.kind {
1660 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1661 self.collect_elided_lifetimes = false;
1663 // Record the "stack height" of `for<'a>` lifetime bindings
1664 // to be able to later fully undo their introduction.
1665 let old_len = self.currently_bound_lifetimes.len();
1666 intravisit::walk_ty(self, t);
1667 self.currently_bound_lifetimes.truncate(old_len);
1669 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1671 intravisit::walk_ty(self, t)
1675 fn visit_poly_trait_ref(
1677 trait_ref: &'v hir::PolyTraitRef<'v>,
1678 modifier: hir::TraitBoundModifier,
1680 // Record the "stack height" of `for<'a>` lifetime bindings
1681 // to be able to later fully undo their introduction.
1682 let old_len = self.currently_bound_lifetimes.len();
1683 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1684 self.currently_bound_lifetimes.truncate(old_len);
1687 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1688 // Record the introduction of 'a in `for<'a> ...`.
1689 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1690 // Introduce lifetimes one at a time so that we can handle
1691 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1692 let lt_name = hir::LifetimeName::Param(param.name);
1693 self.currently_bound_lifetimes.push(lt_name);
1696 intravisit::walk_generic_param(self, param);
1699 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1700 let name = match lifetime.name {
1701 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1702 if self.collect_elided_lifetimes {
1703 // Use `'_` for both implicit and underscore lifetimes in
1704 // `type Foo<'_> = impl SomeTrait<'_>;`.
1705 hir::LifetimeName::Underscore
1710 hir::LifetimeName::Param(_) => lifetime.name,
1712 // Refers to some other lifetime that is "in
1713 // scope" within the type.
1714 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1716 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1719 if !self.currently_bound_lifetimes.contains(&name)
1720 && !self.already_defined_lifetimes.contains(&name)
1721 && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name))
1723 self.already_defined_lifetimes.insert(name);
1725 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1726 hir_id: self.context.next_id(),
1727 span: self.context.lower_span(lifetime.span),
1731 let def_node_id = self.context.resolver.next_node_id();
1733 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1734 self.context.resolver.create_def(
1737 DefPathData::LifetimeNs(name.ident().name),
1742 let (name, kind) = match name {
1743 hir::LifetimeName::Underscore => (
1744 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1745 hir::LifetimeParamKind::Elided,
1747 hir::LifetimeName::Param(param_name) => {
1748 (param_name, hir::LifetimeParamKind::Explicit)
1750 _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1752 let name = match name {
1753 hir::ParamName::Plain(ident) => {
1754 hir::ParamName::Plain(self.context.lower_ident(ident))
1759 self.output_lifetime_params.push(hir::GenericParam {
1762 span: self.context.lower_span(lifetime.span),
1763 pure_wrt_drop: false,
1765 kind: hir::GenericParamKind::Lifetime { kind },
1771 let mut lifetime_collector = ImplTraitLifetimeCollector {
1773 parent: parent_def_id,
1775 collect_elided_lifetimes: true,
1776 currently_bound_lifetimes: Vec::new(),
1777 already_defined_lifetimes: FxHashSet::default(),
1778 output_lifetimes: Vec::new(),
1779 output_lifetime_params: Vec::new(),
1780 lifetimes_to_include,
1783 for bound in bounds {
1784 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1787 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1791 self.arena.alloc_from_iter(output_lifetimes),
1792 self.arena.alloc_from_iter(output_lifetime_params),
1796 fn lower_local(&mut self, l: &Local) -> hir::Local<'hir> {
1800 .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed(ImplTraitPosition::Binding)));
1801 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1802 let hir_id = self.lower_node_id(l.id);
1803 self.lower_attrs(hir_id, &l.attrs);
1807 pat: self.lower_pat(&l.pat),
1809 span: self.lower_span(l.span),
1810 source: hir::LocalSource::Normal,
1814 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1815 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1816 // as they are not explicit in HIR/Ty function signatures.
1817 // (instead, the `c_variadic` flag is set to `true`)
1818 let mut inputs = &decl.inputs[..];
1819 if decl.c_variadic() {
1820 inputs = &inputs[..inputs.len() - 1];
1822 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1823 PatKind::Ident(_, ident, _) => self.lower_ident(ident),
1824 _ => Ident::new(kw::Empty, self.lower_span(param.pat.span)),
1828 // Lowers a function declaration.
1830 // `decl`: the unlowered (AST) function declaration.
1831 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1832 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1833 // `make_ret_async` is also `Some`.
1834 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1835 // This guards against trait declarations and implementations where `impl Trait` is
1837 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1838 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1839 // return type `impl Trait` item.
1843 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1844 impl_trait_return_allow: bool,
1845 make_ret_async: Option<NodeId>,
1846 ) -> &'hir hir::FnDecl<'hir> {
1850 in_band_ty_params: {:?}, \
1851 impl_trait_return_allow: {}, \
1852 make_ret_async: {:?})",
1853 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1855 let lt_mode = if make_ret_async.is_some() {
1856 // In `async fn`, argument-position elided lifetimes
1857 // must be transformed into fresh generic parameters so that
1858 // they can be applied to the opaque `impl Trait` return type.
1859 AnonymousLifetimeMode::CreateParameter
1861 self.anonymous_lifetime_mode
1864 let c_variadic = decl.c_variadic();
1866 // Remember how many lifetimes were already around so that we can
1867 // only look at the lifetime parameters introduced by the arguments.
1868 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1869 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1870 // as they are not explicit in HIR/Ty function signatures.
1871 // (instead, the `c_variadic` flag is set to `true`)
1872 let mut inputs = &decl.inputs[..];
1874 inputs = &inputs[..inputs.len() - 1];
1876 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1877 if let Some((_, ibty)) = &mut in_band_ty_params {
1878 this.lower_ty_direct(
1880 ImplTraitContext::Universal(ibty, this.current_hir_id_owner.0),
1883 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1888 let output = if let Some(ret_id) = make_ret_async {
1889 self.lower_async_fn_ret_ty(
1891 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1896 FnRetTy::Ty(ref ty) => {
1897 let context = match in_band_ty_params {
1898 Some((def_id, _)) if impl_trait_return_allow => {
1899 ImplTraitContext::ReturnPositionOpaqueTy {
1901 origin: hir::OpaqueTyOrigin::FnReturn,
1904 _ => ImplTraitContext::disallowed(),
1906 hir::FnRetTy::Return(self.lower_ty(ty, context))
1908 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(self.lower_span(span)),
1912 self.arena.alloc(hir::FnDecl {
1916 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1917 use BindingMode::{ByRef, ByValue};
1918 let is_mutable_pat = matches!(
1920 PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..)
1924 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1925 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1926 // Given we are only considering `ImplicitSelf` types, we needn't consider
1927 // the case where we have a mutable pattern to a reference as that would
1928 // no longer be an `ImplicitSelf`.
1929 TyKind::Rptr(_, ref mt)
1930 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1932 hir::ImplicitSelfKind::MutRef
1934 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1935 hir::ImplicitSelfKind::ImmRef
1937 _ => hir::ImplicitSelfKind::None,
1943 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1944 // combined with the following definition of `OpaqueTy`:
1946 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1948 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1949 // `output`: unlowered output type (`T` in `-> T`)
1950 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1951 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1952 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1953 fn lower_async_fn_ret_ty(
1957 opaque_ty_node_id: NodeId,
1958 ) -> hir::FnRetTy<'hir> {
1960 "lower_async_fn_ret_ty(\
1963 opaque_ty_node_id={:?})",
1964 output, fn_def_id, opaque_ty_node_id,
1967 let span = output.span();
1969 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1971 let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id);
1973 self.allocate_hir_id_counter(opaque_ty_node_id);
1975 // When we create the opaque type for this async fn, it is going to have
1976 // to capture all the lifetimes involved in the signature (including in the
1977 // return type). This is done by introducing lifetime parameters for:
1979 // - all the explicitly declared lifetimes from the impl and function itself;
1980 // - all the elided lifetimes in the fn arguments;
1981 // - all the elided lifetimes in the return type.
1983 // So for example in this snippet:
1986 // impl<'a> Foo<'a> {
1987 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1988 // // ^ '0 ^ '1 ^ '2
1989 // // elided lifetimes used below
1994 // we would create an opaque type like:
1997 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2000 // and we would then desugar `bar` to the equivalent of:
2003 // impl<'a> Foo<'a> {
2004 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2008 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2009 // this is because the elided lifetimes from the return type
2010 // should be figured out using the ordinary elision rules, and
2011 // this desugaring achieves that.
2013 // The variable `input_lifetimes_count` tracks the number of
2014 // lifetime parameters to the opaque type *not counting* those
2015 // lifetimes elided in the return type. This includes those
2016 // that are explicitly declared (`in_scope_lifetimes`) and
2017 // those elided lifetimes we found in the arguments (current
2018 // content of `lifetimes_to_define`). Next, we will process
2019 // the return type, which will cause `lifetimes_to_define` to
2021 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2023 let lifetime_params = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2024 // We have to be careful to get elision right here. The
2025 // idea is that we create a lifetime parameter for each
2026 // lifetime in the return type. So, given a return type
2027 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2028 // Future<Output = &'1 [ &'2 u32 ]>`.
2030 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2031 // hence the elision takes place at the fn site.
2032 let future_bound = this
2033 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2034 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2037 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2039 // Calculate all the lifetimes that should be captured
2040 // by the opaque type. This should include all in-scope
2041 // lifetime parameters, including those defined in-band.
2043 // Note: this must be done after lowering the output type,
2044 // as the output type may introduce new in-band lifetimes.
2045 let lifetime_params: Vec<(Span, ParamName)> = this
2049 .map(|name| (name.ident().span, name))
2050 .chain(this.lifetimes_to_define.iter().cloned())
2053 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2054 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2055 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2057 let generic_params =
2058 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2059 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id)
2062 let opaque_ty_item = hir::OpaqueTy {
2063 generics: hir::Generics {
2064 params: generic_params,
2065 where_clause: hir::WhereClause { predicates: &[], span: this.lower_span(span) },
2066 span: this.lower_span(span),
2068 bounds: arena_vec![this; future_bound],
2069 impl_trait_fn: Some(fn_def_id),
2070 origin: hir::OpaqueTyOrigin::AsyncFn,
2073 trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id);
2074 this.generate_opaque_type(opaque_ty_def_id, opaque_ty_item, span, opaque_ty_span);
2079 // As documented above on the variable
2080 // `input_lifetimes_count`, we need to create the lifetime
2081 // arguments to our opaque type. Continuing with our example,
2082 // we're creating the type arguments for the return type:
2085 // Bar<'a, 'b, '0, '1, '_>
2088 // For the "input" lifetime parameters, we wish to create
2089 // references to the parameters themselves, including the
2090 // "implicit" ones created from parameter types (`'a`, `'b`,
2093 // For the "output" lifetime parameters, we just want to
2095 let mut generic_args = Vec::with_capacity(lifetime_params.len());
2096 generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map(
2097 |&(span, hir_name)| {
2098 // Input lifetime like `'a` or `'1`:
2099 GenericArg::Lifetime(hir::Lifetime {
2100 hir_id: self.next_id(),
2101 span: self.lower_span(span),
2102 name: hir::LifetimeName::Param(hir_name),
2106 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2107 // Output lifetime like `'_`.
2108 GenericArg::Lifetime(hir::Lifetime {
2109 hir_id: self.next_id(),
2110 span: self.lower_span(span),
2111 name: hir::LifetimeName::Implicit,
2113 let generic_args = self.arena.alloc_from_iter(generic_args);
2115 // Create the `Foo<...>` reference itself. Note that the `type
2116 // Foo = impl Trait` is, internally, created as a child of the
2117 // async fn, so the *type parameters* are inherited. It's
2118 // only the lifetime parameters that we must supply.
2120 hir::TyKind::OpaqueDef(hir::ItemId { def_id: opaque_ty_def_id }, generic_args);
2121 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2122 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
2125 /// Transforms `-> T` into `Future<Output = T>`.
2126 fn lower_async_fn_output_type_to_future_bound(
2131 ) -> hir::GenericBound<'hir> {
2132 // Compute the `T` in `Future<Output = T>` from the return type.
2133 let output_ty = match output {
2134 FnRetTy::Ty(ty) => {
2135 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
2136 // `impl Future` opaque type that `async fn` implicitly
2138 let context = ImplTraitContext::ReturnPositionOpaqueTy {
2140 origin: hir::OpaqueTyOrigin::FnReturn,
2142 self.lower_ty(ty, context)
2144 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2148 let future_args = self.arena.alloc(hir::GenericArgs {
2150 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
2151 parenthesized: false,
2155 hir::GenericBound::LangItemTrait(
2156 // ::std::future::Future<future_params>
2157 hir::LangItem::Future,
2158 self.lower_span(span),
2164 fn lower_param_bound(
2167 itctx: ImplTraitContext<'_, 'hir>,
2168 ) -> hir::GenericBound<'hir> {
2170 GenericBound::Trait(p, modifier) => hir::GenericBound::Trait(
2171 self.lower_poly_trait_ref(p, itctx),
2172 self.lower_trait_bound_modifier(*modifier),
2174 GenericBound::Outlives(lifetime) => {
2175 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2180 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2181 let span = self.lower_span(l.ident.span);
2183 ident if ident.name == kw::StaticLifetime => {
2184 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2186 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2187 AnonymousLifetimeMode::CreateParameter => {
2188 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2189 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2192 AnonymousLifetimeMode::PassThrough => {
2193 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2196 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2199 self.maybe_collect_in_band_lifetime(ident);
2200 let param_name = ParamName::Plain(self.lower_ident(ident));
2201 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2206 fn new_named_lifetime(
2210 name: hir::LifetimeName,
2211 ) -> hir::Lifetime {
2212 hir::Lifetime { hir_id: self.lower_node_id(id), span: self.lower_span(span), name }
2215 fn lower_generic_params_mut<'s>(
2217 params: &'s [GenericParam],
2218 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2219 mut itctx: ImplTraitContext<'s, 'hir>,
2220 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2223 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2226 fn lower_generic_params(
2228 params: &[GenericParam],
2229 add_bounds: &NodeMap<Vec<GenericBound>>,
2230 itctx: ImplTraitContext<'_, 'hir>,
2231 ) -> &'hir [hir::GenericParam<'hir>] {
2232 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2235 fn lower_generic_param(
2237 param: &GenericParam,
2238 add_bounds: &NodeMap<Vec<GenericBound>>,
2239 mut itctx: ImplTraitContext<'_, 'hir>,
2240 ) -> hir::GenericParam<'hir> {
2241 let mut bounds: Vec<_> = self
2242 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2243 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2246 let (name, kind) = match param.kind {
2247 GenericParamKind::Lifetime => {
2248 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2249 self.is_collecting_in_band_lifetimes = false;
2252 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2253 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2255 let param_name = match lt.name {
2256 hir::LifetimeName::Param(param_name) => param_name,
2257 hir::LifetimeName::Implicit
2258 | hir::LifetimeName::Underscore
2259 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2260 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2261 self.sess.diagnostic().span_bug(
2263 "object-lifetime-default should not occur here",
2266 hir::LifetimeName::Error => ParamName::Error,
2270 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2272 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2276 GenericParamKind::Type { ref default, .. } => {
2277 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2278 if !add_bounds.is_empty() {
2279 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2280 bounds.extend(params);
2283 let kind = hir::GenericParamKind::Type {
2284 default: default.as_ref().map(|x| {
2285 self.lower_ty(x, ImplTraitContext::Disallowed(ImplTraitPosition::Other))
2290 .filter(|attr| attr.has_name(sym::rustc_synthetic))
2291 .map(|_| hir::SyntheticTyParamKind::FromAttr)
2295 (hir::ParamName::Plain(self.lower_ident(param.ident)), kind)
2297 GenericParamKind::Const { ref ty, kw_span: _, ref default } => {
2299 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2300 this.lower_ty(&ty, ImplTraitContext::disallowed())
2302 let default = default.as_ref().map(|def| self.lower_anon_const(def));
2304 hir::ParamName::Plain(self.lower_ident(param.ident)),
2305 hir::GenericParamKind::Const { ty, default },
2309 let name = match name {
2310 hir::ParamName::Plain(ident) => hir::ParamName::Plain(self.lower_ident(ident)),
2314 let hir_id = self.lower_node_id(param.id);
2315 self.lower_attrs(hir_id, ¶m.attrs);
2319 span: self.lower_span(param.ident.span),
2320 pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle),
2321 bounds: self.arena.alloc_from_iter(bounds),
2329 itctx: ImplTraitContext<'_, 'hir>,
2330 ) -> hir::TraitRef<'hir> {
2331 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2332 hir::QPath::Resolved(None, path) => path,
2333 qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2335 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2338 fn lower_poly_trait_ref(
2341 mut itctx: ImplTraitContext<'_, 'hir>,
2342 ) -> hir::PolyTraitRef<'hir> {
2343 let bound_generic_params = self.lower_generic_params(
2344 &p.bound_generic_params,
2345 &NodeMap::default(),
2349 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2350 // Any impl Trait types defined within this scope can capture
2351 // lifetimes bound on this predicate.
2352 let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind {
2353 GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param(
2354 ParamName::Plain(param.ident.normalize_to_macros_2_0()),
2358 if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
2361 capturable_lifetimes.extend(lt_def_names.clone());
2364 let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow());
2366 if let ImplTraitContext::TypeAliasesOpaqueTy { ref mut capturable_lifetimes, .. } =
2369 for param in lt_def_names {
2370 capturable_lifetimes.remove(¶m);
2376 hir::PolyTraitRef { bound_generic_params, trait_ref, span: self.lower_span(p.span) }
2379 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2380 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2383 fn lower_param_bounds(
2385 bounds: &[GenericBound],
2386 itctx: ImplTraitContext<'_, 'hir>,
2387 ) -> hir::GenericBounds<'hir> {
2388 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2391 fn lower_param_bounds_mut<'s>(
2393 bounds: &'s [GenericBound],
2394 mut itctx: ImplTraitContext<'s, 'hir>,
2395 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2396 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2399 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2400 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2403 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2404 let (stmts, expr) = match &*b.stmts {
2405 [stmts @ .., Stmt { kind: StmtKind::Expr(e), .. }] => (stmts, Some(&*e)),
2406 stmts => (stmts, None),
2408 let stmts = self.arena.alloc_from_iter(stmts.iter().flat_map(|stmt| self.lower_stmt(stmt)));
2409 let expr = expr.map(|e| self.lower_expr(e));
2410 let rules = self.lower_block_check_mode(&b.rules);
2411 let hir_id = self.lower_node_id(b.id);
2413 hir::Block { hir_id, stmts, expr, rules, span: self.lower_span(b.span), targeted_by_break }
2416 /// Lowers a block directly to an expression, presuming that it
2417 /// has no attributes and is not targeted by a `break`.
2418 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2419 let block = self.lower_block(b, false);
2420 self.expr_block(block, AttrVec::new())
2423 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2424 self.with_new_scopes(|this| hir::AnonConst {
2425 hir_id: this.lower_node_id(c.id),
2426 body: this.lower_const_body(c.value.span, Some(&c.value)),
2430 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2431 let (hir_id, kind) = match s.kind {
2432 StmtKind::Local(ref l) => {
2433 let l = self.lower_local(l);
2434 let hir_id = self.lower_node_id(s.id);
2435 self.alias_attrs(hir_id, l.hir_id);
2436 return smallvec![hir::Stmt {
2438 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2439 span: self.lower_span(s.span),
2442 StmtKind::Item(ref it) => {
2443 // Can only use the ID once.
2444 let mut id = Some(s.id);
2451 .map(|id| self.lower_node_id(id))
2452 .unwrap_or_else(|| self.next_id());
2456 kind: hir::StmtKind::Item(item_id),
2457 span: self.lower_span(s.span),
2462 StmtKind::Expr(ref e) => {
2463 let e = self.lower_expr(e);
2464 let hir_id = self.lower_node_id(s.id);
2465 self.alias_attrs(hir_id, e.hir_id);
2466 (hir_id, hir::StmtKind::Expr(e))
2468 StmtKind::Semi(ref e) => {
2469 let e = self.lower_expr(e);
2470 let hir_id = self.lower_node_id(s.id);
2471 self.alias_attrs(hir_id, e.hir_id);
2472 (hir_id, hir::StmtKind::Semi(e))
2474 StmtKind::Empty => return smallvec![],
2475 StmtKind::MacCall(..) => panic!("shouldn't exist here"),
2477 smallvec![hir::Stmt { hir_id, kind, span: self.lower_span(s.span) }]
2480 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2482 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2483 BlockCheckMode::Unsafe(u) => {
2484 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2489 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2491 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2492 UserProvided => hir::UnsafeSource::UserProvided,
2496 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2498 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2499 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2501 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2502 // placeholder for compilation to proceed.
2503 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2504 hir::TraitBoundModifier::Maybe
2509 // Helper methods for building HIR.
2511 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2512 hir::Stmt { span: self.lower_span(span), kind, hir_id: self.next_id() }
2515 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2516 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2521 attrs: Option<&'hir [Attribute]>,
2523 init: Option<&'hir hir::Expr<'hir>>,
2524 pat: &'hir hir::Pat<'hir>,
2525 source: hir::LocalSource,
2526 ) -> hir::Stmt<'hir> {
2527 let hir_id = self.next_id();
2528 if let Some(a) = attrs {
2529 debug_assert!(!a.is_empty());
2530 self.attrs.insert(hir_id, a);
2532 let local = hir::Local { hir_id, init, pat, source, span: self.lower_span(span), ty: None };
2533 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2536 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2537 self.block_all(expr.span, &[], Some(expr))
2543 stmts: &'hir [hir::Stmt<'hir>],
2544 expr: Option<&'hir hir::Expr<'hir>>,
2545 ) -> &'hir hir::Block<'hir> {
2546 let blk = hir::Block {
2549 hir_id: self.next_id(),
2550 rules: hir::BlockCheckMode::DefaultBlock,
2551 span: self.lower_span(span),
2552 targeted_by_break: false,
2554 self.arena.alloc(blk)
2557 fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2558 let field = self.single_pat_field(span, pat);
2559 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field)
2562 fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2563 let field = self.single_pat_field(span, pat);
2564 self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field)
2567 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2568 let field = self.single_pat_field(span, pat);
2569 self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field)
2572 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2573 self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
2576 fn single_pat_field(
2579 pat: &'hir hir::Pat<'hir>,
2580 ) -> &'hir [hir::PatField<'hir>] {
2581 let field = hir::PatField {
2582 hir_id: self.next_id(),
2583 ident: Ident::new(sym::integer(0), self.lower_span(span)),
2584 is_shorthand: false,
2586 span: self.lower_span(span),
2588 arena_vec![self; field]
2591 fn pat_lang_item_variant(
2594 lang_item: hir::LangItem,
2595 fields: &'hir [hir::PatField<'hir>],
2596 ) -> &'hir hir::Pat<'hir> {
2597 let qpath = hir::QPath::LangItem(lang_item, self.lower_span(span));
2598 self.pat(span, hir::PatKind::Struct(qpath, fields, false))
2601 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2602 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2605 fn pat_ident_mut(&mut self, span: Span, ident: Ident) -> (hir::Pat<'hir>, hir::HirId) {
2606 self.pat_ident_binding_mode_mut(span, ident, hir::BindingAnnotation::Unannotated)
2609 fn pat_ident_binding_mode(
2613 bm: hir::BindingAnnotation,
2614 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2615 let (pat, hir_id) = self.pat_ident_binding_mode_mut(span, ident, bm);
2616 (self.arena.alloc(pat), hir_id)
2619 fn pat_ident_binding_mode_mut(
2623 bm: hir::BindingAnnotation,
2624 ) -> (hir::Pat<'hir>, hir::HirId) {
2625 let hir_id = self.next_id();
2630 kind: hir::PatKind::Binding(bm, hir_id, self.lower_ident(ident), None),
2631 span: self.lower_span(span),
2632 default_binding_modes: true,
2638 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2639 self.arena.alloc(hir::Pat {
2640 hir_id: self.next_id(),
2642 span: self.lower_span(span),
2643 default_binding_modes: true,
2647 fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> hir::Pat<'hir> {
2649 hir_id: self.next_id(),
2651 span: self.lower_span(span),
2652 default_binding_modes: false,
2658 mut hir_id: hir::HirId,
2660 qpath: hir::QPath<'hir>,
2661 ) -> hir::Ty<'hir> {
2662 let kind = match qpath {
2663 hir::QPath::Resolved(None, path) => {
2664 // Turn trait object paths into `TyKind::TraitObject` instead.
2666 Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
2667 let principal = hir::PolyTraitRef {
2668 bound_generic_params: &[],
2669 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2670 span: self.lower_span(span),
2673 // The original ID is taken by the `PolyTraitRef`,
2674 // so the `Ty` itself needs a different one.
2675 hir_id = self.next_id();
2676 hir::TyKind::TraitObject(
2677 arena_vec![self; principal],
2678 self.elided_dyn_bound(span),
2679 TraitObjectSyntax::None,
2682 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2685 _ => hir::TyKind::Path(qpath),
2688 hir::Ty { hir_id, kind, span: self.lower_span(span) }
2691 /// Invoked to create the lifetime argument for a type `&T`
2692 /// with no explicit lifetime.
2693 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2694 match self.anonymous_lifetime_mode {
2695 // Intercept when we are in an impl header or async fn and introduce an in-band
2697 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2699 AnonymousLifetimeMode::CreateParameter => {
2700 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2702 hir_id: self.next_id(),
2703 span: self.lower_span(span),
2704 name: hir::LifetimeName::Param(fresh_name),
2708 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2710 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2714 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2715 /// return an "error lifetime".
2716 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2717 let (id, msg, label) = match id {
2718 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2721 self.resolver.next_node_id(),
2722 "`&` without an explicit lifetime name cannot be used here",
2723 "explicit lifetime name needed here",
2727 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2728 err.span_label(span, label);
2731 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2734 /// Invoked to create the lifetime argument(s) for a path like
2735 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2736 /// sorts of cases are deprecated. This may therefore report a warning or an
2737 /// error, depending on the mode.
2738 fn elided_path_lifetimes<'s>(
2742 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2743 (0..count).map(move |_| self.elided_path_lifetime(span))
2746 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2747 match self.anonymous_lifetime_mode {
2748 AnonymousLifetimeMode::CreateParameter => {
2749 // We should have emitted E0726 when processing this path above
2751 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2752 let id = self.resolver.next_node_id();
2753 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2755 // `PassThrough` is the normal case.
2756 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2757 // is unsuitable here, as these can occur from missing lifetime parameters in a
2758 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2759 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2760 // later, at which point a suitable error will be emitted.
2761 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2762 self.new_implicit_lifetime(span)
2767 /// Invoked to create the lifetime argument(s) for an elided trait object
2768 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2769 /// when the bound is written, even if it is written with `'_` like in
2770 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2771 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2772 match self.anonymous_lifetime_mode {
2773 // NB. We intentionally ignore the create-parameter mode here.
2774 // and instead "pass through" to resolve-lifetimes, which will apply
2775 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2776 // do not act like other elided lifetimes. In other words, given this:
2778 // impl Foo for Box<dyn Debug>
2780 // we do not introduce a fresh `'_` to serve as the bound, but instead
2781 // ultimately translate to the equivalent of:
2783 // impl Foo for Box<dyn Debug + 'static>
2785 // `resolve_lifetime` has the code to make that happen.
2786 AnonymousLifetimeMode::CreateParameter => {}
2788 AnonymousLifetimeMode::ReportError => {
2789 // ReportError applies to explicit use of `'_`.
2792 // This is the normal case.
2793 AnonymousLifetimeMode::PassThrough => {}
2796 let r = hir::Lifetime {
2797 hir_id: self.next_id(),
2798 span: self.lower_span(span),
2799 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2801 debug!("elided_dyn_bound: r={:?}", r);
2805 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2807 hir_id: self.next_id(),
2808 span: self.lower_span(span),
2809 name: hir::LifetimeName::Implicit,
2813 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2814 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2815 // call site which do not have a macro backtrace. See #61963.
2816 let is_macro_callsite = self
2819 .span_to_snippet(span)
2820 .map(|snippet| snippet.starts_with("#["))
2822 if !is_macro_callsite {
2823 if span.edition() < Edition::Edition2021 {
2824 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2828 "trait objects without an explicit `dyn` are deprecated",
2829 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2832 let msg = "trait objects must include the `dyn` keyword";
2833 let label = "add `dyn` keyword before this trait";
2834 let mut err = struct_span_err!(self.sess, span, E0782, "{}", msg,);
2835 err.span_suggestion_verbose(
2836 span.shrink_to_lo(),
2838 String::from("dyn "),
2839 Applicability::MachineApplicable,
2846 fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId, default: Abi) {
2847 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2848 // call site which do not have a macro backtrace. See #61963.
2849 let is_macro_callsite = self
2852 .span_to_snippet(span)
2853 .map(|snippet| snippet.starts_with("#["))
2855 if !is_macro_callsite {
2856 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2860 "extern declarations without an explicit ABI are deprecated",
2861 BuiltinLintDiagnostics::MissingAbi(span, default),
2867 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2868 // Sorting by span ensures that we get things in order within a
2869 // file, and also puts the files in a sensible order.
2870 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2871 body_ids.sort_by_key(|b| bodies[b].value.span);
2875 /// Helper struct for delayed construction of GenericArgs.
2876 struct GenericArgsCtor<'hir> {
2877 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2878 bindings: &'hir [hir::TypeBinding<'hir>],
2879 parenthesized: bool,
2883 impl<'hir> GenericArgsCtor<'hir> {
2884 fn is_empty(&self) -> bool {
2885 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2888 fn into_generic_args(self, this: &LoweringContext<'_, 'hir>) -> &'hir hir::GenericArgs<'hir> {
2889 let ga = hir::GenericArgs {
2890 args: this.arena.alloc_from_iter(self.args),
2891 bindings: self.bindings,
2892 parenthesized: self.parenthesized,
2893 span_ext: this.lower_span(self.span),
2895 this.arena.alloc(ga)