1 // ignore-tidy-filelength
3 //! Lowers the AST to the HIR.
5 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
6 //! much like a fold. Where lowering involves a bit more work things get more
7 //! interesting and there are some invariants you should know about. These mostly
8 //! concern spans and IDs.
10 //! Spans are assigned to AST nodes during parsing and then are modified during
11 //! expansion to indicate the origin of a node and the process it went through
12 //! being expanded. IDs are assigned to AST nodes just before lowering.
14 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
15 //! expansion we do not preserve the process of lowering in the spans, so spans
16 //! should not be modified here. When creating a new node (as opposed to
17 //! 'folding' an existing one), then you create a new ID using `next_id()`.
19 //! You must ensure that IDs are unique. That means that you should only use the
20 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
21 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
22 //! If you do, you must then set the new node's ID to a fresh one.
24 //! Spans are used for error messages and for tools to map semantics back to
25 //! source code. It is therefore not as important with spans as IDs to be strict
26 //! about use (you can't break the compiler by screwing up a span). Obviously, a
27 //! HIR node can only have a single span. But multiple nodes can have the same
28 //! span and spans don't need to be kept in order, etc. Where code is preserved
29 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
30 //! new it is probably best to give a span for the whole AST node being lowered.
31 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
32 //! get confused if the spans from leaf AST nodes occur in multiple places
33 //! in the HIR, especially for multiple identifiers.
38 use crate::dep_graph::DepGraph;
39 use crate::hir::{self, ParamName};
40 use crate::hir::HirVec;
41 use crate::hir::map::{DefKey, DefPathData, Definitions};
42 use crate::hir::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
43 use crate::hir::def::{Namespace, Res, DefKind, PartialRes, PerNS};
44 use crate::hir::{GenericArg, ConstArg};
45 use crate::hir::ptr::P;
46 use crate::lint::builtin::{self, PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
47 ELIDED_LIFETIMES_IN_PATHS};
48 use crate::middle::cstore::CrateStore;
49 use crate::session::Session;
50 use crate::session::config::nightly_options;
51 use crate::util::common::FN_OUTPUT_NAME;
52 use crate::util::nodemap::{DefIdMap, NodeMap};
53 use errors::Applicability;
54 use rustc_data_structures::fx::FxHashSet;
55 use rustc_data_structures::indexed_vec::IndexVec;
56 use rustc_data_structures::thin_vec::ThinVec;
57 use rustc_data_structures::sync::Lrc;
59 use std::collections::BTreeMap;
61 use smallvec::SmallVec;
64 use syntax::ptr::P as AstP;
67 use syntax::ext::base::SpecialDerives;
68 use syntax::ext::hygiene::ExpnId;
69 use syntax::print::pprust;
70 use syntax::source_map::{respan, ExpnData, ExpnKind, DesugaringKind, Spanned};
71 use syntax::symbol::{kw, sym, Symbol};
72 use syntax::tokenstream::{TokenStream, TokenTree};
73 use syntax::parse::token::{self, Token};
74 use syntax::visit::{self, Visitor};
77 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
79 pub struct LoweringContext<'a> {
80 crate_root: Option<Symbol>,
82 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
85 cstore: &'a dyn CrateStore,
87 resolver: &'a mut dyn Resolver,
89 /// The items being lowered are collected here.
90 items: BTreeMap<hir::HirId, hir::Item>,
92 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
93 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
94 bodies: BTreeMap<hir::BodyId, hir::Body>,
95 exported_macros: Vec<hir::MacroDef>,
96 non_exported_macro_attrs: Vec<ast::Attribute>,
98 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
100 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
102 generator_kind: Option<hir::GeneratorKind>,
104 /// Used to get the current `fn`'s def span to point to when using `await`
105 /// outside of an `async fn`.
106 current_item: Option<Span>,
108 catch_scopes: Vec<NodeId>,
109 loop_scopes: Vec<NodeId>,
110 is_in_loop_condition: bool,
111 is_in_trait_impl: bool,
112 is_in_dyn_type: bool,
114 /// What to do when we encounter either an "anonymous lifetime
115 /// reference". The term "anonymous" is meant to encompass both
116 /// `'_` lifetimes as well as fully elided cases where nothing is
117 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
118 anonymous_lifetime_mode: AnonymousLifetimeMode,
120 /// Used to create lifetime definitions from in-band lifetime usages.
121 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
122 /// When a named lifetime is encountered in a function or impl header and
123 /// has not been defined
124 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
125 /// to this list. The results of this list are then added to the list of
126 /// lifetime definitions in the corresponding impl or function generics.
127 lifetimes_to_define: Vec<(Span, ParamName)>,
129 /// `true` if in-band lifetimes are being collected. This is used to
130 /// indicate whether or not we're in a place where new lifetimes will result
131 /// in in-band lifetime definitions, such a function or an impl header,
132 /// including implicit lifetimes from `impl_header_lifetime_elision`.
133 is_collecting_in_band_lifetimes: bool,
135 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
136 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
137 /// against this list to see if it is already in-scope, or if a definition
138 /// needs to be created for it.
140 /// We always store a `modern()` version of the param-name in this
142 in_scope_lifetimes: Vec<ParamName>,
144 current_module: hir::HirId,
146 type_def_lifetime_params: DefIdMap<usize>,
148 current_hir_id_owner: Vec<(DefIndex, u32)>,
149 item_local_id_counters: NodeMap<u32>,
150 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
152 allow_try_trait: Option<Lrc<[Symbol]>>,
153 allow_gen_future: Option<Lrc<[Symbol]>>,
157 /// Obtains resolution for a `NodeId` with a single resolution.
158 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
160 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
161 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
163 /// Obtains resolution for a label with the given `NodeId`.
164 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
166 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
167 /// This should only return `None` during testing.
168 fn definitions(&mut self) -> &mut Definitions;
170 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
171 /// resolves it based on `is_value`.
175 crate_root: Option<Symbol>,
176 components: &[Symbol],
178 ) -> (ast::Path, Res<NodeId>);
180 fn has_derives(&self, node_id: NodeId, derives: SpecialDerives) -> bool;
183 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
184 /// and if so, what meaning it has.
186 enum ImplTraitContext<'a> {
187 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
188 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
189 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
191 /// Newly generated parameters should be inserted into the given `Vec`.
192 Universal(&'a mut Vec<hir::GenericParam>),
194 /// Treat `impl Trait` as shorthand for a new opaque type.
195 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
196 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
198 /// We optionally store a `DefId` for the parent item here so we can look up necessary
199 /// information later. It is `None` when no information about the context should be stored
200 /// (e.g., for consts and statics).
201 OpaqueTy(Option<DefId> /* fn def-ID */),
203 /// `impl Trait` is not accepted in this position.
204 Disallowed(ImplTraitPosition),
207 /// Position in which `impl Trait` is disallowed.
208 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
209 enum ImplTraitPosition {
210 /// Disallowed in `let` / `const` / `static` bindings.
213 /// All other posiitons.
217 impl<'a> ImplTraitContext<'a> {
219 fn disallowed() -> Self {
220 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
223 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
224 use self::ImplTraitContext::*;
226 Universal(params) => Universal(params),
227 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
228 Disallowed(pos) => Disallowed(*pos),
235 cstore: &dyn CrateStore,
236 dep_graph: &DepGraph,
238 resolver: &mut dyn Resolver,
240 // We're constructing the HIR here; we don't care what we will
241 // read, since we haven't even constructed the *input* to
243 dep_graph.assert_ignored();
246 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
250 items: BTreeMap::new(),
251 trait_items: BTreeMap::new(),
252 impl_items: BTreeMap::new(),
253 bodies: BTreeMap::new(),
254 trait_impls: BTreeMap::new(),
255 modules: BTreeMap::new(),
256 exported_macros: Vec::new(),
257 non_exported_macro_attrs: Vec::new(),
258 catch_scopes: Vec::new(),
259 loop_scopes: Vec::new(),
260 is_in_loop_condition: false,
261 is_in_trait_impl: false,
262 is_in_dyn_type: false,
263 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
264 type_def_lifetime_params: Default::default(),
265 current_module: hir::CRATE_HIR_ID,
266 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
267 item_local_id_counters: Default::default(),
268 node_id_to_hir_id: IndexVec::new(),
269 generator_kind: None,
271 lifetimes_to_define: Vec::new(),
272 is_collecting_in_band_lifetimes: false,
273 in_scope_lifetimes: Vec::new(),
274 allow_try_trait: Some([sym::try_trait][..].into()),
275 allow_gen_future: Some([sym::gen_future][..].into()),
279 #[derive(Copy, Clone, PartialEq)]
281 /// Any path in a type context.
283 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
285 /// The `module::Type` in `module::Type::method` in an expression.
289 enum ParenthesizedGenericArgs {
295 /// What to do when we encounter an **anonymous** lifetime
296 /// reference. Anonymous lifetime references come in two flavors. You
297 /// have implicit, or fully elided, references to lifetimes, like the
298 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
299 /// or `Ref<'_, T>`. These often behave the same, but not always:
301 /// - certain usages of implicit references are deprecated, like
302 /// `Ref<T>`, and we sometimes just give hard errors in those cases
304 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
305 /// the same as `Box<dyn Foo + '_>`.
307 /// We describe the effects of the various modes in terms of three cases:
309 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
310 /// of a `&` (e.g., the missing lifetime in something like `&T`)
311 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
312 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
313 /// elided bounds follow special rules. Note that this only covers
314 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
315 /// '_>` is a case of "modern" elision.
316 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
317 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
318 /// non-deprecated equivalent.
320 /// Currently, the handling of lifetime elision is somewhat spread out
321 /// between HIR lowering and -- as described below -- the
322 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
323 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
324 /// everything into HIR lowering.
325 #[derive(Copy, Clone, Debug)]
326 enum AnonymousLifetimeMode {
327 /// For **Modern** cases, create a new anonymous region parameter
328 /// and reference that.
330 /// For **Dyn Bound** cases, pass responsibility to
331 /// `resolve_lifetime` code.
333 /// For **Deprecated** cases, report an error.
336 /// Give a hard error when either `&` or `'_` is written. Used to
337 /// rule out things like `where T: Foo<'_>`. Does not imply an
338 /// error on default object bounds (e.g., `Box<dyn Foo>`).
341 /// Pass responsibility to `resolve_lifetime` code for all cases.
345 struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[NodeId; 1]> }
347 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
348 fn visit_ty(&mut self, ty: &'a Ty) {
354 TyKind::ImplTrait(id, _) => self.ids.push(id),
357 visit::walk_ty(self, ty);
360 fn visit_path_segment(
363 path_segment: &'v PathSegment,
365 if let Some(ref p) = path_segment.args {
366 if let GenericArgs::Parenthesized(_) = **p {
370 visit::walk_path_segment(self, path_span, path_segment)
374 impl<'a> LoweringContext<'a> {
375 fn lower_crate(mut self, c: &Crate) -> hir::Crate {
376 /// Full-crate AST visitor that inserts into a fresh
377 /// `LoweringContext` any information that may be
378 /// needed from arbitrary locations in the crate,
379 /// e.g., the number of lifetime generic parameters
380 /// declared for every type and trait definition.
381 struct MiscCollector<'tcx, 'interner> {
382 lctx: &'tcx mut LoweringContext<'interner>,
383 hir_id_owner: Option<NodeId>,
386 impl MiscCollector<'_, '_> {
387 fn allocate_use_tree_hir_id_counters(
393 UseTreeKind::Simple(_, id1, id2) => {
394 for &id in &[id1, id2] {
395 self.lctx.resolver.definitions().create_def_with_parent(
402 self.lctx.allocate_hir_id_counter(id);
405 UseTreeKind::Glob => (),
406 UseTreeKind::Nested(ref trees) => {
407 for &(ref use_tree, id) in trees {
408 let hir_id = self.lctx.allocate_hir_id_counter(id);
409 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
415 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
417 F: FnOnce(&mut Self) -> T,
419 let old = mem::replace(&mut self.hir_id_owner, owner);
421 self.hir_id_owner = old;
426 impl<'tcx, 'interner> Visitor<'tcx> for MiscCollector<'tcx, 'interner> {
427 fn visit_pat(&mut self, p: &'tcx Pat) {
428 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
429 // Doesn't generate a HIR node
430 } else if let Some(owner) = self.hir_id_owner {
431 self.lctx.lower_node_id_with_owner(p.id, owner);
434 visit::walk_pat(self, p)
437 fn visit_item(&mut self, item: &'tcx Item) {
438 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
441 ItemKind::Struct(_, ref generics)
442 | ItemKind::Union(_, ref generics)
443 | ItemKind::Enum(_, ref generics)
444 | ItemKind::TyAlias(_, ref generics)
445 | ItemKind::OpaqueTy(_, ref generics)
446 | ItemKind::Trait(_, _, ref generics, ..) => {
447 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
451 .filter(|param| match param.kind {
452 ast::GenericParamKind::Lifetime { .. } => true,
456 self.lctx.type_def_lifetime_params.insert(def_id, count);
458 ItemKind::Use(ref use_tree) => {
459 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
464 self.with_hir_id_owner(Some(item.id), |this| {
465 visit::walk_item(this, item);
469 fn visit_trait_item(&mut self, item: &'tcx TraitItem) {
470 self.lctx.allocate_hir_id_counter(item.id);
473 TraitItemKind::Method(_, None) => {
474 // Ignore patterns in trait methods without bodies
475 self.with_hir_id_owner(None, |this| {
476 visit::walk_trait_item(this, item)
479 _ => self.with_hir_id_owner(Some(item.id), |this| {
480 visit::walk_trait_item(this, item);
485 fn visit_impl_item(&mut self, item: &'tcx ImplItem) {
486 self.lctx.allocate_hir_id_counter(item.id);
487 self.with_hir_id_owner(Some(item.id), |this| {
488 visit::walk_impl_item(this, item);
492 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
493 // Ignore patterns in foreign items
494 self.with_hir_id_owner(None, |this| {
495 visit::walk_foreign_item(this, i)
499 fn visit_ty(&mut self, t: &'tcx Ty) {
501 // Mirrors the case in visit::walk_ty
502 TyKind::BareFn(ref f) => {
508 // Mirrors visit::walk_fn_decl
509 for parameter in &f.decl.inputs {
510 // We don't lower the ids of argument patterns
511 self.with_hir_id_owner(None, |this| {
512 this.visit_pat(¶meter.pat);
514 self.visit_ty(¶meter.ty)
516 self.visit_fn_ret_ty(&f.decl.output)
518 _ => visit::walk_ty(self, t),
523 self.lower_node_id(CRATE_NODE_ID);
524 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
526 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
527 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
529 let module = self.lower_mod(&c.module);
530 let attrs = self.lower_attrs(&c.attrs);
531 let body_ids = body_ids(&self.bodies);
535 .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
541 exported_macros: hir::HirVec::from(self.exported_macros),
542 non_exported_macro_attrs: hir::HirVec::from(self.non_exported_macro_attrs),
544 trait_items: self.trait_items,
545 impl_items: self.impl_items,
548 trait_impls: self.trait_impls,
549 modules: self.modules,
553 fn insert_item(&mut self, item: hir::Item) {
554 let id = item.hir_id;
555 // FIXME: Use `debug_asset-rt`.
556 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
557 self.items.insert(id, item);
558 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
561 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
562 // Set up the counter if needed.
563 self.item_local_id_counters.entry(owner).or_insert(0);
564 // Always allocate the first `HirId` for the owner itself.
565 let lowered = self.lower_node_id_with_owner(owner, owner);
566 debug_assert_eq!(lowered.local_id.as_u32(), 0);
570 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
572 F: FnOnce(&mut Self) -> hir::HirId,
574 if ast_node_id == DUMMY_NODE_ID {
575 return hir::DUMMY_HIR_ID;
578 let min_size = ast_node_id.as_usize() + 1;
580 if min_size > self.node_id_to_hir_id.len() {
581 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
584 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
586 if existing_hir_id == hir::DUMMY_HIR_ID {
587 // Generate a new `HirId`.
588 let hir_id = alloc_hir_id(self);
589 self.node_id_to_hir_id[ast_node_id] = hir_id;
597 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
599 F: FnOnce(&mut Self) -> T,
601 let counter = self.item_local_id_counters
602 .insert(owner, HIR_ID_COUNTER_LOCKED)
603 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
604 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
605 self.current_hir_id_owner.push((def_index, counter));
607 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
609 debug_assert!(def_index == new_def_index);
610 debug_assert!(new_counter >= counter);
612 let prev = self.item_local_id_counters
613 .insert(owner, new_counter)
615 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
619 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
620 /// the `LoweringContext`'s `NodeId => HirId` map.
621 /// Take care not to call this method if the resulting `HirId` is then not
622 /// actually used in the HIR, as that would trigger an assertion in the
623 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
624 /// properly. Calling the method twice with the same `NodeId` is fine though.
625 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
626 self.lower_node_id_generic(ast_node_id, |this| {
627 let &mut (def_index, ref mut local_id_counter) =
628 this.current_hir_id_owner.last_mut().unwrap();
629 let local_id = *local_id_counter;
630 *local_id_counter += 1;
633 local_id: hir::ItemLocalId::from_u32(local_id),
638 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
639 self.lower_node_id_generic(ast_node_id, |this| {
640 let local_id_counter = this
641 .item_local_id_counters
643 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
644 let local_id = *local_id_counter;
646 // We want to be sure not to modify the counter in the map while it
647 // is also on the stack. Otherwise we'll get lost updates when writing
648 // back from the stack to the map.
649 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
651 *local_id_counter += 1;
655 .opt_def_index(owner)
656 .expect("you forgot to call `create_def_with_parent` or are lowering node-IDs \
657 that do not belong to the current owner");
661 local_id: hir::ItemLocalId::from_u32(local_id),
666 fn next_id(&mut self) -> hir::HirId {
667 self.lower_node_id(self.sess.next_node_id())
670 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
672 self.lower_node_id_generic(id, |_| {
673 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
678 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
679 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
680 if pr.unresolved_segments() != 0 {
681 bug!("path not fully resolved: {:?}", pr);
687 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
688 self.resolver.get_import_res(id).present_items()
691 fn diagnostic(&self) -> &errors::Handler {
692 self.sess.diagnostic()
695 /// Reuses the span but adds information like the kind of the desugaring and features that are
696 /// allowed inside this span.
697 fn mark_span_with_reason(
699 reason: DesugaringKind,
701 allow_internal_unstable: Option<Lrc<[Symbol]>>,
703 span.fresh_expansion(ExpnData {
704 allow_internal_unstable,
705 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
709 fn with_anonymous_lifetime_mode<R>(
711 anonymous_lifetime_mode: AnonymousLifetimeMode,
712 op: impl FnOnce(&mut Self) -> R,
715 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
716 anonymous_lifetime_mode,
718 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
719 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
720 let result = op(self);
721 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
722 debug!("with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
723 old_anonymous_lifetime_mode);
727 /// Creates a new `hir::GenericParam` for every new lifetime and
728 /// type parameter encountered while evaluating `f`. Definitions
729 /// are created with the parent provided. If no `parent_id` is
730 /// provided, no definitions will be returned.
732 /// Presuming that in-band lifetimes are enabled, then
733 /// `self.anonymous_lifetime_mode` will be updated to match the
734 /// parameter while `f` is running (and restored afterwards).
735 fn collect_in_band_defs<T, F>(
738 anonymous_lifetime_mode: AnonymousLifetimeMode,
740 ) -> (Vec<hir::GenericParam>, T)
742 F: FnOnce(&mut LoweringContext<'_>) -> (Vec<hir::GenericParam>, T),
744 assert!(!self.is_collecting_in_band_lifetimes);
745 assert!(self.lifetimes_to_define.is_empty());
746 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
748 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
749 self.is_collecting_in_band_lifetimes = true;
751 let (in_band_ty_params, res) = f(self);
753 self.is_collecting_in_band_lifetimes = false;
754 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
756 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
758 let params = lifetimes_to_define
760 .map(|(span, hir_name)| self.lifetime_to_generic_param(
761 span, hir_name, parent_id.index,
763 .chain(in_band_ty_params.into_iter())
769 /// Converts a lifetime into a new generic parameter.
770 fn lifetime_to_generic_param(
774 parent_index: DefIndex,
775 ) -> hir::GenericParam {
776 let node_id = self.sess.next_node_id();
778 // Get the name we'll use to make the def-path. Note
779 // that collisions are ok here and this shouldn't
780 // really show up for end-user.
781 let (str_name, kind) = match hir_name {
782 ParamName::Plain(ident) => (
783 ident.as_interned_str(),
784 hir::LifetimeParamKind::InBand,
786 ParamName::Fresh(_) => (
787 kw::UnderscoreLifetime.as_interned_str(),
788 hir::LifetimeParamKind::Elided,
790 ParamName::Error => (
791 kw::UnderscoreLifetime.as_interned_str(),
792 hir::LifetimeParamKind::Error,
796 // Add a definition for the in-band lifetime def.
797 self.resolver.definitions().create_def_with_parent(
800 DefPathData::LifetimeNs(str_name),
806 hir_id: self.lower_node_id(node_id),
811 pure_wrt_drop: false,
812 kind: hir::GenericParamKind::Lifetime { kind }
816 /// When there is a reference to some lifetime `'a`, and in-band
817 /// lifetimes are enabled, then we want to push that lifetime into
818 /// the vector of names to define later. In that case, it will get
819 /// added to the appropriate generics.
820 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
821 if !self.is_collecting_in_band_lifetimes {
825 if !self.sess.features_untracked().in_band_lifetimes {
829 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
833 let hir_name = ParamName::Plain(ident);
835 if self.lifetimes_to_define.iter()
836 .any(|(_, lt_name)| lt_name.modern() == hir_name.modern()) {
840 self.lifetimes_to_define.push((ident.span, hir_name));
843 /// When we have either an elided or `'_` lifetime in an impl
844 /// header, we convert it to an in-band lifetime.
845 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
846 assert!(self.is_collecting_in_band_lifetimes);
847 let index = self.lifetimes_to_define.len();
848 let hir_name = ParamName::Fresh(index);
849 self.lifetimes_to_define.push((span, hir_name));
853 // Evaluates `f` with the lifetimes in `params` in-scope.
854 // This is used to track which lifetimes have already been defined, and
855 // which are new in-band lifetimes that need to have a definition created
857 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
859 F: FnOnce(&mut LoweringContext<'_>) -> T,
861 let old_len = self.in_scope_lifetimes.len();
862 let lt_def_names = params.iter().filter_map(|param| match param.kind {
863 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
866 self.in_scope_lifetimes.extend(lt_def_names);
870 self.in_scope_lifetimes.truncate(old_len);
874 /// Appends in-band lifetime defs and argument-position `impl
875 /// Trait` defs to the existing set of generics.
877 /// Presuming that in-band lifetimes are enabled, then
878 /// `self.anonymous_lifetime_mode` will be updated to match the
879 /// parameter while `f` is running (and restored afterwards).
880 fn add_in_band_defs<F, T>(
884 anonymous_lifetime_mode: AnonymousLifetimeMode,
886 ) -> (hir::Generics, T)
888 F: FnOnce(&mut LoweringContext<'_>, &mut Vec<hir::GenericParam>) -> T,
890 let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
893 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
894 let mut params = Vec::new();
895 // Note: it is necessary to lower generics *before* calling `f`.
896 // When lowering `async fn`, there's a final step when lowering
897 // the return type that assumes that all in-scope lifetimes have
898 // already been added to either `in_scope_lifetimes` or
899 // `lifetimes_to_define`. If we swapped the order of these two,
900 // in-band-lifetimes introduced by generics or where-clauses
901 // wouldn't have been added yet.
902 let generics = this.lower_generics(
904 ImplTraitContext::Universal(&mut params),
906 let res = f(this, &mut params);
907 (params, (generics, res))
912 let mut lowered_params: Vec<_> = lowered_generics
918 // FIXME(const_generics): the compiler doesn't always cope with
919 // unsorted generic parameters at the moment, so we make sure
920 // that they're ordered correctly here for now. (When we chain
921 // the `in_band_defs`, we might make the order unsorted.)
922 lowered_params.sort_by_key(|param| {
924 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
925 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
926 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
930 lowered_generics.params = lowered_params.into();
932 (lowered_generics, res)
935 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
937 F: FnOnce(&mut LoweringContext<'_>) -> T,
939 let was_in_dyn_type = self.is_in_dyn_type;
940 self.is_in_dyn_type = in_scope;
942 let result = f(self);
944 self.is_in_dyn_type = was_in_dyn_type;
949 fn with_new_scopes<T, F>(&mut self, f: F) -> T
951 F: FnOnce(&mut LoweringContext<'_>) -> T,
953 let was_in_loop_condition = self.is_in_loop_condition;
954 self.is_in_loop_condition = false;
956 let catch_scopes = mem::take(&mut self.catch_scopes);
957 let loop_scopes = mem::take(&mut self.loop_scopes);
959 self.catch_scopes = catch_scopes;
960 self.loop_scopes = loop_scopes;
962 self.is_in_loop_condition = was_in_loop_condition;
967 fn def_key(&mut self, id: DefId) -> DefKey {
969 self.resolver.definitions().def_key(id.index)
971 self.cstore.def_key(id)
975 fn lower_attrs_extendable(&mut self, attrs: &[Attribute]) -> Vec<Attribute> {
978 .map(|a| self.lower_attr(a))
982 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
983 self.lower_attrs_extendable(attrs).into()
986 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
987 // Note that we explicitly do not walk the path. Since we don't really
988 // lower attributes (we use the AST version) there is nowhere to keep
989 // the `HirId`s. We don't actually need HIR version of attributes anyway.
993 path: attr.path.clone(),
994 tokens: self.lower_token_stream(attr.tokens.clone()),
995 is_sugared_doc: attr.is_sugared_doc,
1000 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
1003 .flat_map(|tree| self.lower_token_tree(tree).into_trees())
1007 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
1009 TokenTree::Token(token) => self.lower_token(token),
1010 TokenTree::Delimited(span, delim, tts) => TokenTree::Delimited(
1013 self.lower_token_stream(tts),
1018 fn lower_token(&mut self, token: Token) -> TokenStream {
1020 token::Interpolated(nt) => {
1021 let tts = nt.to_tokenstream(&self.sess.parse_sess, token.span);
1022 self.lower_token_stream(tts)
1024 _ => TokenTree::Token(token).into(),
1028 /// Given an associated type constraint like one of these:
1031 /// T: Iterator<Item: Debug>
1033 /// T: Iterator<Item = Debug>
1037 /// returns a `hir::TypeBinding` representing `Item`.
1038 fn lower_assoc_ty_constraint(
1040 constraint: &AssocTyConstraint,
1041 itctx: ImplTraitContext<'_>,
1042 ) -> hir::TypeBinding {
1043 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1045 let kind = match constraint.kind {
1046 AssocTyConstraintKind::Equality { ref ty } => hir::TypeBindingKind::Equality {
1047 ty: self.lower_ty(ty, itctx)
1049 AssocTyConstraintKind::Bound { ref bounds } => {
1050 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1051 let (desugar_to_impl_trait, itctx) = match itctx {
1052 // We are in the return position:
1054 // fn foo() -> impl Iterator<Item: Debug>
1058 // fn foo() -> impl Iterator<Item = impl Debug>
1059 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1061 // We are in the argument position, but within a dyn type:
1063 // fn foo(x: dyn Iterator<Item: Debug>)
1067 // fn foo(x: dyn Iterator<Item = impl Debug>)
1068 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1070 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1071 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1072 // "impl trait context" to permit `impl Debug` in this position (it desugars
1073 // then to an opaque type).
1075 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1076 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type =>
1077 (true, ImplTraitContext::OpaqueTy(None)),
1079 // We are in the parameter position, but not within a dyn type:
1081 // fn foo(x: impl Iterator<Item: Debug>)
1083 // so we leave it as is and this gets expanded in astconv to a bound like
1084 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1086 _ => (false, itctx),
1089 if desugar_to_impl_trait {
1090 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1091 // constructing the HIR for `impl bounds...` and then lowering that.
1093 let impl_trait_node_id = self.sess.next_node_id();
1094 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1095 self.resolver.definitions().create_def_with_parent(
1098 DefPathData::ImplTrait,
1103 self.with_dyn_type_scope(false, |this| {
1104 let ty = this.lower_ty(
1106 id: this.sess.next_node_id(),
1107 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1108 span: constraint.span,
1113 hir::TypeBindingKind::Equality {
1118 // Desugar `AssocTy: Bounds` into a type binding where the
1119 // later desugars into a trait predicate.
1120 let bounds = self.lower_param_bounds(bounds, itctx);
1122 hir::TypeBindingKind::Constraint {
1130 hir_id: self.lower_node_id(constraint.id),
1131 ident: constraint.ident,
1133 span: constraint.span,
1137 fn lower_generic_arg(&mut self,
1138 arg: &ast::GenericArg,
1139 itctx: ImplTraitContext<'_>)
1140 -> hir::GenericArg {
1142 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1143 ast::GenericArg::Type(ty) => GenericArg::Type(self.lower_ty_direct(&ty, itctx)),
1144 ast::GenericArg::Const(ct) => {
1145 GenericArg::Const(ConstArg {
1146 value: self.lower_anon_const(&ct),
1147 span: ct.value.span,
1153 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1154 P(self.lower_ty_direct(t, itctx))
1160 qself: &Option<QSelf>,
1162 param_mode: ParamMode,
1163 itctx: ImplTraitContext<'_>
1165 let id = self.lower_node_id(t.id);
1166 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1167 let ty = self.ty_path(id, t.span, qpath);
1168 if let hir::TyKind::TraitObject(..) = ty.kind {
1169 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1174 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1175 let kind = match t.kind {
1176 TyKind::Infer => hir::TyKind::Infer,
1177 TyKind::Err => hir::TyKind::Err,
1178 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1179 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1180 TyKind::Rptr(ref region, ref mt) => {
1181 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1182 let lifetime = match *region {
1183 Some(ref lt) => self.lower_lifetime(lt),
1184 None => self.elided_ref_lifetime(span),
1186 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1188 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1191 this.with_anonymous_lifetime_mode(
1192 AnonymousLifetimeMode::PassThrough,
1194 hir::TyKind::BareFn(P(hir::BareFnTy {
1195 generic_params: this.lower_generic_params(
1197 &NodeMap::default(),
1198 ImplTraitContext::disallowed(),
1200 unsafety: this.lower_unsafety(f.unsafety),
1202 decl: this.lower_fn_decl(&f.decl, None, false, None),
1203 param_names: this.lower_fn_params_to_names(&f.decl),
1209 TyKind::Never => hir::TyKind::Never,
1210 TyKind::Tup(ref tys) => {
1211 hir::TyKind::Tup(tys.iter().map(|ty| {
1212 self.lower_ty_direct(ty, itctx.reborrow())
1215 TyKind::Paren(ref ty) => {
1216 return self.lower_ty_direct(ty, itctx);
1218 TyKind::Path(ref qself, ref path) => {
1219 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1221 TyKind::ImplicitSelf => {
1222 let res = self.expect_full_res(t.id);
1223 let res = self.lower_res(res);
1224 hir::TyKind::Path(hir::QPath::Resolved(
1228 segments: hir_vec![hir::PathSegment::from_ident(
1229 Ident::with_dummy_span(kw::SelfUpper)
1235 TyKind::Array(ref ty, ref length) => {
1236 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1238 TyKind::Typeof(ref expr) => {
1239 hir::TyKind::Typeof(self.lower_anon_const(expr))
1241 TyKind::TraitObject(ref bounds, kind) => {
1242 let mut lifetime_bound = None;
1243 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1246 .filter_map(|bound| match *bound {
1247 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1248 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1250 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1251 GenericBound::Outlives(ref lifetime) => {
1252 if lifetime_bound.is_none() {
1253 lifetime_bound = Some(this.lower_lifetime(lifetime));
1259 let lifetime_bound =
1260 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1261 (bounds, lifetime_bound)
1263 if kind != TraitObjectSyntax::Dyn {
1264 self.maybe_lint_bare_trait(t.span, t.id, false);
1266 hir::TyKind::TraitObject(bounds, lifetime_bound)
1268 TyKind::ImplTrait(def_node_id, ref bounds) => {
1271 ImplTraitContext::OpaqueTy(fn_def_id) => {
1272 self.lower_opaque_impl_trait(
1273 span, fn_def_id, def_node_id,
1274 |this| this.lower_param_bounds(bounds, itctx),
1277 ImplTraitContext::Universal(in_band_ty_params) => {
1278 // Add a definition for the in-band `Param`.
1279 let def_index = self
1282 .opt_def_index(def_node_id)
1285 let hir_bounds = self.lower_param_bounds(
1287 ImplTraitContext::Universal(in_band_ty_params),
1289 // Set the name to `impl Bound1 + Bound2`.
1290 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1291 in_band_ty_params.push(hir::GenericParam {
1292 hir_id: self.lower_node_id(def_node_id),
1293 name: ParamName::Plain(ident),
1294 pure_wrt_drop: false,
1298 kind: hir::GenericParamKind::Type {
1300 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1304 hir::TyKind::Path(hir::QPath::Resolved(
1308 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1309 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1313 ImplTraitContext::Disallowed(pos) => {
1314 let allowed_in = if self.sess.features_untracked()
1315 .impl_trait_in_bindings {
1316 "bindings or function and inherent method return types"
1318 "function and inherent method return types"
1320 let mut err = struct_span_err!(
1324 "`impl Trait` not allowed outside of {}",
1327 if pos == ImplTraitPosition::Binding &&
1328 nightly_options::is_nightly_build() {
1330 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1331 attributes to enable");
1338 TyKind::Mac(_) => bug!("`TyMac` should have been expanded by now"),
1339 TyKind::CVarArgs => {
1340 // Create the implicit lifetime of the "spoofed" `VaListImpl`.
1341 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1342 let lt = self.new_implicit_lifetime(span);
1343 hir::TyKind::CVarArgs(lt)
1350 hir_id: self.lower_node_id(t.id),
1354 fn lower_opaque_impl_trait(
1357 fn_def_id: Option<DefId>,
1358 opaque_ty_node_id: NodeId,
1359 lower_bounds: impl FnOnce(&mut LoweringContext<'_>) -> hir::GenericBounds,
1362 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1368 // Make sure we know that some funky desugaring has been going on here.
1369 // This is a first: there is code in other places like for loop
1370 // desugaring that explicitly states that we don't want to track that.
1371 // Not tracking it makes lints in rustc and clippy very fragile, as
1372 // frequently opened issues show.
1373 let opaque_ty_span = self.mark_span_with_reason(
1374 DesugaringKind::OpaqueTy,
1379 let opaque_ty_def_index = self
1382 .opt_def_index(opaque_ty_node_id)
1385 self.allocate_hir_id_counter(opaque_ty_node_id);
1387 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1389 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1391 opaque_ty_def_index,
1396 "lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,
1400 "lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,
1403 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1404 let opaque_ty_item = hir::OpaqueTy {
1405 generics: hir::Generics {
1406 params: lifetime_defs,
1407 where_clause: hir::WhereClause {
1408 predicates: hir_vec![],
1414 impl_trait_fn: fn_def_id,
1415 origin: hir::OpaqueTyOrigin::FnReturn,
1418 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1419 let opaque_ty_id = lctx.generate_opaque_type(
1426 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1427 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1431 /// Registers a new opaque type with the proper `NodeId`s and
1432 /// returns the lowered node-ID for the opaque type.
1433 fn generate_opaque_type(
1435 opaque_ty_node_id: NodeId,
1436 opaque_ty_item: hir::OpaqueTy,
1438 opaque_ty_span: Span,
1440 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1441 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1442 // Generate an `type Foo = impl Trait;` declaration.
1443 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1444 let opaque_ty_item = hir::Item {
1445 hir_id: opaque_ty_id,
1446 ident: Ident::invalid(),
1447 attrs: Default::default(),
1448 node: opaque_ty_item_kind,
1449 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1450 span: opaque_ty_span,
1453 // Insert the item into the global item list. This usually happens
1454 // automatically for all AST items. But this opaque type item
1455 // does not actually exist in the AST.
1456 self.insert_item(opaque_ty_item);
1460 fn lifetimes_from_impl_trait_bounds(
1462 opaque_ty_id: NodeId,
1463 parent_index: DefIndex,
1464 bounds: &hir::GenericBounds,
1465 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1467 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1468 parent_index={:?}, \
1470 opaque_ty_id, parent_index, bounds,
1473 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1474 // appear in the bounds, excluding lifetimes that are created within the bounds.
1475 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1476 struct ImplTraitLifetimeCollector<'r, 'a> {
1477 context: &'r mut LoweringContext<'a>,
1479 opaque_ty_id: NodeId,
1480 collect_elided_lifetimes: bool,
1481 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1482 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1483 output_lifetimes: Vec<hir::GenericArg>,
1484 output_lifetime_params: Vec<hir::GenericParam>,
1487 impl<'r, 'a, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1488 fn nested_visit_map<'this>(
1490 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1491 hir::intravisit::NestedVisitorMap::None
1494 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1495 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1496 if parameters.parenthesized {
1497 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1498 self.collect_elided_lifetimes = false;
1499 hir::intravisit::walk_generic_args(self, span, parameters);
1500 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1502 hir::intravisit::walk_generic_args(self, span, parameters);
1506 fn visit_ty(&mut self, t: &'v hir::Ty) {
1507 // Don't collect elided lifetimes used inside of `fn()` syntax.
1508 if let hir::TyKind::BareFn(_) = t.kind {
1509 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1510 self.collect_elided_lifetimes = false;
1512 // Record the "stack height" of `for<'a>` lifetime bindings
1513 // to be able to later fully undo their introduction.
1514 let old_len = self.currently_bound_lifetimes.len();
1515 hir::intravisit::walk_ty(self, t);
1516 self.currently_bound_lifetimes.truncate(old_len);
1518 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1520 hir::intravisit::walk_ty(self, t)
1524 fn visit_poly_trait_ref(
1526 trait_ref: &'v hir::PolyTraitRef,
1527 modifier: hir::TraitBoundModifier,
1529 // Record the "stack height" of `for<'a>` lifetime bindings
1530 // to be able to later fully undo their introduction.
1531 let old_len = self.currently_bound_lifetimes.len();
1532 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1533 self.currently_bound_lifetimes.truncate(old_len);
1536 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1537 // Record the introduction of 'a in `for<'a> ...`.
1538 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1539 // Introduce lifetimes one at a time so that we can handle
1540 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1541 let lt_name = hir::LifetimeName::Param(param.name);
1542 self.currently_bound_lifetimes.push(lt_name);
1545 hir::intravisit::walk_generic_param(self, param);
1548 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1549 let name = match lifetime.name {
1550 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1551 if self.collect_elided_lifetimes {
1552 // Use `'_` for both implicit and underscore lifetimes in
1553 // `type Foo<'_> = impl SomeTrait<'_>;`.
1554 hir::LifetimeName::Underscore
1559 hir::LifetimeName::Param(_) => lifetime.name,
1561 // Refers to some other lifetime that is "in
1562 // scope" within the type.
1563 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1565 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1568 if !self.currently_bound_lifetimes.contains(&name)
1569 && !self.already_defined_lifetimes.contains(&name) {
1570 self.already_defined_lifetimes.insert(name);
1572 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1573 hir_id: self.context.next_id(),
1574 span: lifetime.span,
1578 let def_node_id = self.context.sess.next_node_id();
1580 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1581 self.context.resolver.definitions().create_def_with_parent(
1584 DefPathData::LifetimeNs(name.ident().as_interned_str()),
1588 let (name, kind) = match name {
1589 hir::LifetimeName::Underscore => (
1590 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1591 hir::LifetimeParamKind::Elided,
1593 hir::LifetimeName::Param(param_name) => (
1595 hir::LifetimeParamKind::Explicit,
1597 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1600 self.output_lifetime_params.push(hir::GenericParam {
1603 span: lifetime.span,
1604 pure_wrt_drop: false,
1607 kind: hir::GenericParamKind::Lifetime { kind }
1613 let mut lifetime_collector = ImplTraitLifetimeCollector {
1615 parent: parent_index,
1617 collect_elided_lifetimes: true,
1618 currently_bound_lifetimes: Vec::new(),
1619 already_defined_lifetimes: FxHashSet::default(),
1620 output_lifetimes: Vec::new(),
1621 output_lifetime_params: Vec::new(),
1624 for bound in bounds {
1625 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1629 lifetime_collector.output_lifetimes.into(),
1630 lifetime_collector.output_lifetime_params.into(),
1637 qself: &Option<QSelf>,
1639 param_mode: ParamMode,
1640 mut itctx: ImplTraitContext<'_>,
1642 let qself_position = qself.as_ref().map(|q| q.position);
1643 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1645 let partial_res = self.resolver
1646 .get_partial_res(id)
1647 .unwrap_or_else(|| PartialRes::new(Res::Err));
1649 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1650 let path = P(hir::Path {
1651 res: self.lower_res(partial_res.base_res()),
1652 segments: p.segments[..proj_start]
1655 .map(|(i, segment)| {
1656 let param_mode = match (qself_position, param_mode) {
1657 (Some(j), ParamMode::Optional) if i < j => {
1658 // This segment is part of the trait path in a
1659 // qualified path - one of `a`, `b` or `Trait`
1660 // in `<X as a::b::Trait>::T::U::method`.
1666 // Figure out if this is a type/trait segment,
1667 // which may need lifetime elision performed.
1668 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1669 krate: def_id.krate,
1670 index: this.def_key(def_id).parent.expect("missing parent"),
1672 let type_def_id = match partial_res.base_res() {
1673 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1674 Some(parent_def_id(self, def_id))
1676 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1677 Some(parent_def_id(self, def_id))
1679 Res::Def(DefKind::Struct, def_id)
1680 | Res::Def(DefKind::Union, def_id)
1681 | Res::Def(DefKind::Enum, def_id)
1682 | Res::Def(DefKind::TyAlias, def_id)
1683 | Res::Def(DefKind::Trait, def_id) if i + 1 == proj_start =>
1689 let parenthesized_generic_args = match partial_res.base_res() {
1690 // `a::b::Trait(Args)`
1691 Res::Def(DefKind::Trait, _)
1692 if i + 1 == proj_start => ParenthesizedGenericArgs::Ok,
1693 // `a::b::Trait(Args)::TraitItem`
1694 Res::Def(DefKind::Method, _)
1695 | Res::Def(DefKind::AssocConst, _)
1696 | Res::Def(DefKind::AssocTy, _)
1697 if i + 2 == proj_start =>
1699 ParenthesizedGenericArgs::Ok
1701 // Avoid duplicated errors.
1702 Res::Err => ParenthesizedGenericArgs::Ok,
1704 Res::Def(DefKind::Struct, _)
1705 | Res::Def(DefKind::Enum, _)
1706 | Res::Def(DefKind::Union, _)
1707 | Res::Def(DefKind::TyAlias, _)
1708 | Res::Def(DefKind::Variant, _) if i + 1 == proj_start =>
1710 ParenthesizedGenericArgs::Err
1712 // A warning for now, for compatibility reasons.
1713 _ => ParenthesizedGenericArgs::Warn,
1716 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1717 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1720 assert!(!def_id.is_local());
1722 self.cstore.item_generics_cloned_untracked(def_id, self.sess);
1723 let n = item_generics.own_counts().lifetimes;
1724 self.type_def_lifetime_params.insert(def_id, n);
1727 self.lower_path_segment(
1732 parenthesized_generic_args,
1741 // Simple case, either no projections, or only fully-qualified.
1742 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1743 if partial_res.unresolved_segments() == 0 {
1744 return hir::QPath::Resolved(qself, path);
1747 // Create the innermost type that we're projecting from.
1748 let mut ty = if path.segments.is_empty() {
1749 // If the base path is empty that means there exists a
1750 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1751 qself.expect("missing QSelf for <T>::...")
1753 // Otherwise, the base path is an implicit `Self` type path,
1754 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1755 // `<I as Iterator>::Item::default`.
1756 let new_id = self.next_id();
1757 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1760 // Anything after the base path are associated "extensions",
1761 // out of which all but the last one are associated types,
1762 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1763 // * base path is `std::vec::Vec<T>`
1764 // * "extensions" are `IntoIter`, `Item` and `clone`
1765 // * type nodes are:
1766 // 1. `std::vec::Vec<T>` (created above)
1767 // 2. `<std::vec::Vec<T>>::IntoIter`
1768 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1769 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1770 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1771 let segment = P(self.lower_path_segment(
1776 ParenthesizedGenericArgs::Warn,
1780 let qpath = hir::QPath::TypeRelative(ty, segment);
1782 // It's finished, return the extension of the right node type.
1783 if i == p.segments.len() - 1 {
1787 // Wrap the associated extension in another type node.
1788 let new_id = self.next_id();
1789 ty = P(self.ty_path(new_id, p.span, qpath));
1792 // We should've returned in the for loop above.
1795 "lower_qpath: no final extension segment in {}..{}",
1801 fn lower_path_extra(
1805 param_mode: ParamMode,
1806 explicit_owner: Option<NodeId>,
1810 segments: p.segments
1813 self.lower_path_segment(
1818 ParenthesizedGenericArgs::Err,
1819 ImplTraitContext::disallowed(),
1828 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1829 let res = self.expect_full_res(id);
1830 let res = self.lower_res(res);
1831 self.lower_path_extra(res, p, param_mode, None)
1834 fn lower_path_segment(
1837 segment: &PathSegment,
1838 param_mode: ParamMode,
1839 expected_lifetimes: usize,
1840 parenthesized_generic_args: ParenthesizedGenericArgs,
1841 itctx: ImplTraitContext<'_>,
1842 explicit_owner: Option<NodeId>,
1843 ) -> hir::PathSegment {
1844 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1845 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1846 match **generic_args {
1847 GenericArgs::AngleBracketed(ref data) => {
1848 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1850 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1851 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1852 ParenthesizedGenericArgs::Warn => {
1853 self.sess.buffer_lint(
1854 PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
1859 (hir::GenericArgs::none(), true)
1861 ParenthesizedGenericArgs::Err => {
1862 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1863 err.span_label(data.span, "only `Fn` traits may use parentheses");
1864 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1865 // Do not suggest going from `Trait()` to `Trait<>`
1866 if data.inputs.len() > 0 {
1867 let split = snippet.find('(').unwrap();
1868 let trait_name = &snippet[0..split];
1869 let args = &snippet[split + 1 .. snippet.len() - 1];
1870 err.span_suggestion(
1872 "use angle brackets instead",
1873 format!("{}<{}>", trait_name, args),
1874 Applicability::MaybeIncorrect,
1880 self.lower_angle_bracketed_parameter_data(
1881 &data.as_angle_bracketed_args(),
1891 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1894 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1895 GenericArg::Lifetime(_) => true,
1898 let first_generic_span = generic_args.args.iter().map(|a| a.span())
1899 .chain(generic_args.bindings.iter().map(|b| b.span)).next();
1900 if !generic_args.parenthesized && !has_lifetimes {
1902 self.elided_path_lifetimes(path_span, expected_lifetimes)
1904 .map(|lt| GenericArg::Lifetime(lt))
1905 .chain(generic_args.args.into_iter())
1907 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1908 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1909 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1910 let no_bindings = generic_args.bindings.is_empty();
1911 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1912 // If there are no (non-implicit) generic args or associated type
1913 // bindings, our suggestion includes the angle brackets.
1914 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1916 // Otherwise (sorry, this is kind of gross) we need to infer the
1917 // place to splice in the `'_, ` from the generics that do exist.
1918 let first_generic_span = first_generic_span
1919 .expect("already checked that non-lifetime args or bindings exist");
1920 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1922 match self.anonymous_lifetime_mode {
1923 // In create-parameter mode we error here because we don't want to support
1924 // deprecated impl elision in new features like impl elision and `async fn`,
1925 // both of which work using the `CreateParameter` mode:
1927 // impl Foo for std::cell::Ref<u32> // note lack of '_
1928 // async fn foo(_: std::cell::Ref<u32>) { ... }
1929 AnonymousLifetimeMode::CreateParameter => {
1930 let mut err = struct_span_err!(
1934 "implicit elided lifetime not allowed here"
1936 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1947 AnonymousLifetimeMode::PassThrough |
1948 AnonymousLifetimeMode::ReportError => {
1949 self.sess.buffer_lint_with_diagnostic(
1950 ELIDED_LIFETIMES_IN_PATHS,
1953 "hidden lifetime parameters in types are deprecated",
1954 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1967 let res = self.expect_full_res(segment.id);
1968 let id = if let Some(owner) = explicit_owner {
1969 self.lower_node_id_with_owner(segment.id, owner)
1971 self.lower_node_id(segment.id)
1974 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1975 segment.ident, segment.id, id,
1978 hir::PathSegment::new(
1981 Some(self.lower_res(res)),
1987 fn lower_angle_bracketed_parameter_data(
1989 data: &AngleBracketedArgs,
1990 param_mode: ParamMode,
1991 mut itctx: ImplTraitContext<'_>,
1992 ) -> (hir::GenericArgs, bool) {
1993 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1994 let has_non_lt_args = args.iter().any(|arg| match arg {
1995 ast::GenericArg::Lifetime(_) => false,
1996 ast::GenericArg::Type(_) => true,
1997 ast::GenericArg::Const(_) => true,
2001 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
2002 bindings: constraints.iter()
2003 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
2005 parenthesized: false,
2007 !has_non_lt_args && param_mode == ParamMode::Optional
2011 fn lower_parenthesized_parameter_data(
2013 data: &ParenthesizedArgs,
2014 ) -> (hir::GenericArgs, bool) {
2015 // Switch to `PassThrough` mode for anonymous lifetimes; this
2016 // means that we permit things like `&Ref<T>`, where `Ref` has
2017 // a hidden lifetime parameter. This is needed for backwards
2018 // compatibility, even in contexts like an impl header where
2019 // we generally don't permit such things (see #51008).
2020 self.with_anonymous_lifetime_mode(
2021 AnonymousLifetimeMode::PassThrough,
2023 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2026 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2028 let mk_tup = |this: &mut Self, tys, span| {
2029 hir::Ty { kind: hir::TyKind::Tup(tys), hir_id: this.next_id(), span }
2033 args: hir_vec![GenericArg::Type(mk_tup(this, inputs, span))],
2036 hir_id: this.next_id(),
2037 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2038 kind: hir::TypeBindingKind::Equality {
2041 .map(|ty| this.lower_ty(
2043 ImplTraitContext::disallowed()
2046 P(mk_tup(this, hir::HirVec::new(), span))
2049 span: output.as_ref().map_or(span, |ty| ty.span),
2052 parenthesized: true,
2060 fn lower_local(&mut self, l: &Local) -> (hir::Local, SmallVec<[NodeId; 1]>) {
2061 let mut ids = SmallVec::<[NodeId; 1]>::new();
2062 if self.sess.features_untracked().impl_trait_in_bindings {
2063 if let Some(ref ty) = l.ty {
2064 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2065 visitor.visit_ty(ty);
2068 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2070 hir_id: self.lower_node_id(l.id),
2073 .map(|t| self.lower_ty(t,
2074 if self.sess.features_untracked().impl_trait_in_bindings {
2075 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2077 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2080 pat: self.lower_pat(&l.pat),
2081 init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
2083 attrs: l.attrs.clone(),
2084 source: hir::LocalSource::Normal,
2088 fn lower_mutability(&mut self, m: Mutability) -> hir::Mutability {
2090 Mutability::Mutable => hir::MutMutable,
2091 Mutability::Immutable => hir::MutImmutable,
2095 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2098 .map(|param| match param.pat.kind {
2099 PatKind::Ident(_, ident, _) => ident,
2100 _ => Ident::new(kw::Invalid, param.pat.span),
2105 // Lowers a function declaration.
2107 // `decl`: the unlowered (AST) function declaration.
2108 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2109 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2110 // `make_ret_async` is also `Some`.
2111 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2112 // This guards against trait declarations and implementations where `impl Trait` is
2114 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2115 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2116 // return type `impl Trait` item.
2120 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2121 impl_trait_return_allow: bool,
2122 make_ret_async: Option<NodeId>,
2123 ) -> P<hir::FnDecl> {
2124 let lt_mode = if make_ret_async.is_some() {
2125 // In `async fn`, argument-position elided lifetimes
2126 // must be transformed into fresh generic parameters so that
2127 // they can be applied to the opaque `impl Trait` return type.
2128 AnonymousLifetimeMode::CreateParameter
2130 self.anonymous_lifetime_mode
2133 // Remember how many lifetimes were already around so that we can
2134 // only look at the lifetime parameters introduced by the arguments.
2135 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2139 if let Some((_, ibty)) = &mut in_band_ty_params {
2140 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2142 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2145 .collect::<HirVec<_>>()
2148 let output = if let Some(ret_id) = make_ret_async {
2149 self.lower_async_fn_ret_ty(
2151 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2156 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2157 Some((def_id, _)) if impl_trait_return_allow => {
2158 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2161 hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed()))
2164 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2171 c_variadic: decl.c_variadic,
2172 implicit_self: decl.inputs.get(0).map_or(
2173 hir::ImplicitSelfKind::None,
2175 let is_mutable_pat = match arg.pat.kind {
2176 PatKind::Ident(BindingMode::ByValue(mt), _, _) |
2177 PatKind::Ident(BindingMode::ByRef(mt), _, _) =>
2178 mt == Mutability::Mutable,
2183 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2184 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2185 // Given we are only considering `ImplicitSelf` types, we needn't consider
2186 // the case where we have a mutable pattern to a reference as that would
2187 // no longer be an `ImplicitSelf`.
2188 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() &&
2189 mt.mutbl == ast::Mutability::Mutable =>
2190 hir::ImplicitSelfKind::MutRef,
2191 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() =>
2192 hir::ImplicitSelfKind::ImmRef,
2193 _ => hir::ImplicitSelfKind::None,
2200 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2201 // combined with the following definition of `OpaqueTy`:
2203 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2205 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2206 // `output`: unlowered output type (`T` in `-> T`)
2207 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2208 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2209 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2210 fn lower_async_fn_ret_ty(
2212 output: &FunctionRetTy,
2214 opaque_ty_node_id: NodeId,
2215 ) -> hir::FunctionRetTy {
2217 "lower_async_fn_ret_ty(\
2220 opaque_ty_node_id={:?})",
2221 output, fn_def_id, opaque_ty_node_id,
2224 let span = output.span();
2226 let opaque_ty_span = self.mark_span_with_reason(
2227 DesugaringKind::Async,
2232 let opaque_ty_def_index = self
2235 .opt_def_index(opaque_ty_node_id)
2238 self.allocate_hir_id_counter(opaque_ty_node_id);
2240 // When we create the opaque type for this async fn, it is going to have
2241 // to capture all the lifetimes involved in the signature (including in the
2242 // return type). This is done by introducing lifetime parameters for:
2244 // - all the explicitly declared lifetimes from the impl and function itself;
2245 // - all the elided lifetimes in the fn arguments;
2246 // - all the elided lifetimes in the return type.
2248 // So for example in this snippet:
2251 // impl<'a> Foo<'a> {
2252 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2253 // // ^ '0 ^ '1 ^ '2
2254 // // elided lifetimes used below
2259 // we would create an opaque type like:
2262 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2265 // and we would then desugar `bar` to the equivalent of:
2268 // impl<'a> Foo<'a> {
2269 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2273 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2274 // this is because the elided lifetimes from the return type
2275 // should be figured out using the ordinary elision rules, and
2276 // this desugaring achieves that.
2278 // The variable `input_lifetimes_count` tracks the number of
2279 // lifetime parameters to the opaque type *not counting* those
2280 // lifetimes elided in the return type. This includes those
2281 // that are explicitly declared (`in_scope_lifetimes`) and
2282 // those elided lifetimes we found in the arguments (current
2283 // content of `lifetimes_to_define`). Next, we will process
2284 // the return type, which will cause `lifetimes_to_define` to
2286 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2288 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2289 // We have to be careful to get elision right here. The
2290 // idea is that we create a lifetime parameter for each
2291 // lifetime in the return type. So, given a return type
2292 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2293 // Future<Output = &'1 [ &'2 u32 ]>`.
2295 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2296 // hence the elision takes place at the fn site.
2297 let future_bound = this.with_anonymous_lifetime_mode(
2298 AnonymousLifetimeMode::CreateParameter,
2299 |this| this.lower_async_fn_output_type_to_future_bound(
2306 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2308 // Calculate all the lifetimes that should be captured
2309 // by the opaque type. This should include all in-scope
2310 // lifetime parameters, including those defined in-band.
2312 // Note: this must be done after lowering the output type,
2313 // as the output type may introduce new in-band lifetimes.
2314 let lifetime_params: Vec<(Span, ParamName)> =
2315 this.in_scope_lifetimes
2317 .map(|name| (name.ident().span, name))
2318 .chain(this.lifetimes_to_define.iter().cloned())
2321 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2322 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2323 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2325 let generic_params =
2328 .map(|(span, hir_name)| {
2329 this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_index)
2333 let opaque_ty_item = hir::OpaqueTy {
2334 generics: hir::Generics {
2335 params: generic_params,
2336 where_clause: hir::WhereClause {
2337 predicates: hir_vec![],
2342 bounds: hir_vec![future_bound],
2343 impl_trait_fn: Some(fn_def_id),
2344 origin: hir::OpaqueTyOrigin::AsyncFn,
2347 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2348 let opaque_ty_id = this.generate_opaque_type(
2355 (opaque_ty_id, lifetime_params)
2358 // As documented above on the variable
2359 // `input_lifetimes_count`, we need to create the lifetime
2360 // arguments to our opaque type. Continuing with our example,
2361 // we're creating the type arguments for the return type:
2364 // Bar<'a, 'b, '0, '1, '_>
2367 // For the "input" lifetime parameters, we wish to create
2368 // references to the parameters themselves, including the
2369 // "implicit" ones created from parameter types (`'a`, `'b`,
2372 // For the "output" lifetime parameters, we just want to
2374 let mut generic_args: Vec<_> =
2375 lifetime_params[..input_lifetimes_count]
2377 .map(|&(span, hir_name)| {
2378 // Input lifetime like `'a` or `'1`:
2379 GenericArg::Lifetime(hir::Lifetime {
2380 hir_id: self.next_id(),
2382 name: hir::LifetimeName::Param(hir_name),
2386 generic_args.extend(
2387 lifetime_params[input_lifetimes_count..]
2390 // Output lifetime like `'_`.
2391 GenericArg::Lifetime(hir::Lifetime {
2392 hir_id: self.next_id(),
2394 name: hir::LifetimeName::Implicit,
2399 // Create the `Foo<...>` refernece itself. Note that the `type
2400 // Foo = impl Trait` is, internally, created as a child of the
2401 // async fn, so the *type parameters* are inherited. It's
2402 // only the lifetime parameters that we must supply.
2403 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args.into());
2405 hir::FunctionRetTy::Return(P(hir::Ty {
2406 kind: opaque_ty_ref,
2408 hir_id: self.next_id(),
2412 /// Transforms `-> T` into `Future<Output = T>`
2413 fn lower_async_fn_output_type_to_future_bound(
2415 output: &FunctionRetTy,
2418 ) -> hir::GenericBound {
2419 // Compute the `T` in `Future<Output = T>` from the return type.
2420 let output_ty = match output {
2421 FunctionRetTy::Ty(ty) => {
2422 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id)))
2424 FunctionRetTy::Default(ret_ty_span) => {
2426 hir_id: self.next_id(),
2427 kind: hir::TyKind::Tup(hir_vec![]),
2434 let future_params = P(hir::GenericArgs {
2436 bindings: hir_vec![hir::TypeBinding {
2437 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2438 kind: hir::TypeBindingKind::Equality {
2441 hir_id: self.next_id(),
2444 parenthesized: false,
2447 // ::std::future::Future<future_params>
2449 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2451 hir::GenericBound::Trait(
2453 trait_ref: hir::TraitRef {
2455 hir_ref_id: self.next_id(),
2457 bound_generic_params: hir_vec![],
2460 hir::TraitBoundModifier::None,
2464 fn lower_param_bound(
2467 itctx: ImplTraitContext<'_>,
2468 ) -> hir::GenericBound {
2470 GenericBound::Trait(ref ty, modifier) => {
2471 hir::GenericBound::Trait(
2472 self.lower_poly_trait_ref(ty, itctx),
2473 self.lower_trait_bound_modifier(modifier),
2476 GenericBound::Outlives(ref lifetime) => {
2477 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2482 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2483 let span = l.ident.span;
2485 ident if ident.name == kw::StaticLifetime =>
2486 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
2487 ident if ident.name == kw::UnderscoreLifetime =>
2488 match self.anonymous_lifetime_mode {
2489 AnonymousLifetimeMode::CreateParameter => {
2490 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2491 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2494 AnonymousLifetimeMode::PassThrough => {
2495 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2498 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2501 self.maybe_collect_in_band_lifetime(ident);
2502 let param_name = ParamName::Plain(ident);
2503 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2508 fn new_named_lifetime(
2512 name: hir::LifetimeName,
2513 ) -> hir::Lifetime {
2515 hir_id: self.lower_node_id(id),
2521 fn lower_generic_params(
2523 params: &[GenericParam],
2524 add_bounds: &NodeMap<Vec<GenericBound>>,
2525 mut itctx: ImplTraitContext<'_>,
2526 ) -> hir::HirVec<hir::GenericParam> {
2527 params.iter().map(|param| {
2528 self.lower_generic_param(param, add_bounds, itctx.reborrow())
2532 fn lower_generic_param(&mut self,
2533 param: &GenericParam,
2534 add_bounds: &NodeMap<Vec<GenericBound>>,
2535 mut itctx: ImplTraitContext<'_>)
2536 -> hir::GenericParam {
2537 let mut bounds = self.with_anonymous_lifetime_mode(
2538 AnonymousLifetimeMode::ReportError,
2539 |this| this.lower_param_bounds(¶m.bounds, itctx.reborrow()),
2542 let (name, kind) = match param.kind {
2543 GenericParamKind::Lifetime => {
2544 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2545 self.is_collecting_in_band_lifetimes = false;
2547 let lt = self.with_anonymous_lifetime_mode(
2548 AnonymousLifetimeMode::ReportError,
2549 |this| this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }),
2551 let param_name = match lt.name {
2552 hir::LifetimeName::Param(param_name) => param_name,
2553 hir::LifetimeName::Implicit
2554 | hir::LifetimeName::Underscore
2555 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2556 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2559 "object-lifetime-default should not occur here",
2562 hir::LifetimeName::Error => ParamName::Error,
2565 let kind = hir::GenericParamKind::Lifetime {
2566 kind: hir::LifetimeParamKind::Explicit
2569 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2573 GenericParamKind::Type { ref default, .. } => {
2574 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2575 if !add_bounds.is_empty() {
2576 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2577 bounds = bounds.into_iter()
2582 let kind = hir::GenericParamKind::Type {
2583 default: default.as_ref().map(|x| {
2584 self.lower_ty(x, ImplTraitContext::OpaqueTy(None))
2586 synthetic: param.attrs.iter()
2587 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2588 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2592 (hir::ParamName::Plain(param.ident), kind)
2594 GenericParamKind::Const { ref ty } => {
2595 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const {
2596 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2602 hir_id: self.lower_node_id(param.id),
2604 span: param.ident.span,
2605 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2606 attrs: self.lower_attrs(¶m.attrs),
2612 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2613 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2614 hir::QPath::Resolved(None, path) => path,
2615 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2619 hir_ref_id: self.lower_node_id(p.ref_id),
2623 fn lower_poly_trait_ref(
2626 mut itctx: ImplTraitContext<'_>,
2627 ) -> hir::PolyTraitRef {
2628 let bound_generic_params = self.lower_generic_params(
2629 &p.bound_generic_params,
2630 &NodeMap::default(),
2633 let trait_ref = self.with_in_scope_lifetime_defs(
2634 &p.bound_generic_params,
2635 |this| this.lower_trait_ref(&p.trait_ref, itctx),
2639 bound_generic_params,
2645 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2647 ty: self.lower_ty(&mt.ty, itctx),
2648 mutbl: self.lower_mutability(mt.mutbl),
2652 fn lower_param_bounds(&mut self, bounds: &[GenericBound], mut itctx: ImplTraitContext<'_>)
2653 -> hir::GenericBounds {
2654 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2657 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2658 let mut stmts = vec![];
2659 let mut expr = None;
2661 for (index, stmt) in b.stmts.iter().enumerate() {
2662 if index == b.stmts.len() - 1 {
2663 if let StmtKind::Expr(ref e) = stmt.kind {
2664 expr = Some(P(self.lower_expr(e)));
2666 stmts.extend(self.lower_stmt(stmt));
2669 stmts.extend(self.lower_stmt(stmt));
2674 hir_id: self.lower_node_id(b.id),
2675 stmts: stmts.into(),
2677 rules: self.lower_block_check_mode(&b.rules),
2683 /// Lowers a block directly to an expression, presuming that it
2684 /// has no attributes and is not targeted by a `break`.
2685 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr {
2686 let block = self.lower_block(b, false);
2687 self.expr_block(block, ThinVec::new())
2690 fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2691 let node = match p.kind {
2692 PatKind::Wild => hir::PatKind::Wild,
2693 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2694 let lower_sub = |this: &mut Self| sub.as_ref().map(|x| this.lower_pat(x));
2695 self.lower_pat_ident(p, binding_mode, ident, lower_sub)
2697 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2698 PatKind::TupleStruct(ref path, ref pats) => {
2699 let qpath = self.lower_qpath(
2703 ParamMode::Optional,
2704 ImplTraitContext::disallowed(),
2706 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2707 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2709 PatKind::Or(ref pats) => {
2710 hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
2712 PatKind::Path(ref qself, ref path) => {
2713 let qpath = self.lower_qpath(
2717 ParamMode::Optional,
2718 ImplTraitContext::disallowed(),
2720 hir::PatKind::Path(qpath)
2722 PatKind::Struct(ref path, ref fields, etc) => {
2723 let qpath = self.lower_qpath(
2727 ParamMode::Optional,
2728 ImplTraitContext::disallowed(),
2733 .map(|f| hir::FieldPat {
2734 hir_id: self.next_id(),
2736 pat: self.lower_pat(&f.pat),
2737 is_shorthand: f.is_shorthand,
2741 hir::PatKind::Struct(qpath, fs, etc)
2743 PatKind::Tuple(ref pats) => {
2744 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2745 hir::PatKind::Tuple(pats, ddpos)
2747 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2748 PatKind::Ref(ref inner, mutbl) => {
2749 hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
2751 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2752 P(self.lower_expr(e1)),
2753 P(self.lower_expr(e2)),
2754 self.lower_range_end(end),
2756 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2758 // If we reach here the `..` pattern is not semantically allowed.
2759 self.ban_illegal_rest_pat(p.span)
2761 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2762 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2765 self.pat_with_node_id_of(p, node)
2772 ) -> (HirVec<P<hir::Pat>>, Option<usize>) {
2773 let mut elems = Vec::with_capacity(pats.len());
2774 let mut rest = None;
2776 let mut iter = pats.iter().enumerate();
2777 while let Some((idx, pat)) = iter.next() {
2778 // Interpret the first `..` pattern as a subtuple pattern.
2780 rest = Some((idx, pat.span));
2783 // It was not a subslice pattern so lower it normally.
2784 elems.push(self.lower_pat(pat));
2787 while let Some((_, pat)) = iter.next() {
2788 // There was a previous subtuple pattern; make sure we don't allow more.
2790 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2792 elems.push(self.lower_pat(pat));
2796 (elems.into(), rest.map(|(ddpos, _)| ddpos))
2799 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind {
2800 let mut before = Vec::new();
2801 let mut after = Vec::new();
2802 let mut slice = None;
2803 let mut prev_rest_span = None;
2805 let mut iter = pats.iter();
2806 while let Some(pat) = iter.next() {
2807 // Interpret the first `((ref mut?)? x @)? ..` pattern as a subslice pattern.
2810 prev_rest_span = Some(pat.span);
2811 slice = Some(self.pat_wild_with_node_id_of(pat));
2814 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2815 prev_rest_span = Some(sub.span);
2816 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2817 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2818 slice = Some(self.pat_with_node_id_of(pat, node));
2824 // It was not a subslice pattern so lower it normally.
2825 before.push(self.lower_pat(pat));
2828 while let Some(pat) = iter.next() {
2829 // There was a previous subslice pattern; make sure we don't allow more.
2830 let rest_span = match pat.kind {
2831 PatKind::Rest => Some(pat.span),
2832 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2833 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2834 after.push(self.pat_wild_with_node_id_of(pat));
2839 if let Some(rest_span) = rest_span {
2840 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2842 after.push(self.lower_pat(pat));
2846 hir::PatKind::Slice(before.into(), slice, after.into())
2852 binding_mode: &BindingMode,
2854 lower_sub: impl FnOnce(&mut Self) -> Option<P<hir::Pat>>,
2856 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2857 // `None` can occur in body-less function signatures
2858 res @ None | res @ Some(Res::Local(_)) => {
2859 let canonical_id = match res {
2860 Some(Res::Local(id)) => id,
2864 hir::PatKind::Binding(
2865 self.lower_binding_mode(binding_mode),
2866 self.lower_node_id(canonical_id),
2871 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2875 res: self.lower_res(res),
2876 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2882 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> P<hir::Pat> {
2883 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2886 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2887 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind) -> P<hir::Pat> {
2889 hir_id: self.lower_node_id(p.id),
2895 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2896 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2898 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2899 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2900 .span_label(prev_sp, "previously used here")
2904 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2905 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind {
2907 .struct_span_err(sp, "`..` patterns are not allowed here")
2908 .note("only allowed in tuple, tuple struct, and slice patterns")
2911 // We're not in a list context so `..` can be reasonably treated
2912 // as `_` because it should always be valid and roughly matches the
2913 // intent of `..` (notice that the rest of a single slot is that slot).
2917 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2919 RangeEnd::Included(_) => hir::RangeEnd::Included,
2920 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2924 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2925 self.with_new_scopes(|this| {
2927 hir_id: this.lower_node_id(c.id),
2928 body: this.lower_const_body(&c.value),
2933 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt; 1]> {
2934 let kind = match s.kind {
2935 StmtKind::Local(ref l) => {
2936 let (l, item_ids) = self.lower_local(l);
2937 let mut ids: SmallVec<[hir::Stmt; 1]> = item_ids
2940 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2941 self.stmt(s.span, hir::StmtKind::Item(item_id))
2946 hir_id: self.lower_node_id(s.id),
2947 kind: hir::StmtKind::Local(P(l)),
2953 StmtKind::Item(ref it) => {
2954 // Can only use the ID once.
2955 let mut id = Some(s.id);
2956 return self.lower_item_id(it)
2959 let hir_id = id.take()
2960 .map(|id| self.lower_node_id(id))
2961 .unwrap_or_else(|| self.next_id());
2965 kind: hir::StmtKind::Item(item_id),
2971 StmtKind::Expr(ref e) => hir::StmtKind::Expr(P(self.lower_expr(e))),
2972 StmtKind::Semi(ref e) => hir::StmtKind::Semi(P(self.lower_expr(e))),
2973 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2975 smallvec![hir::Stmt {
2976 hir_id: self.lower_node_id(s.id),
2982 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2984 BlockCheckMode::Default => hir::DefaultBlock,
2985 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2989 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2991 BindingMode::ByValue(Mutability::Immutable) => hir::BindingAnnotation::Unannotated,
2992 BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
2993 BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
2994 BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
2998 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3000 CompilerGenerated => hir::CompilerGenerated,
3001 UserProvided => hir::UserProvided,
3005 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3007 TraitBoundModifier::None => hir::TraitBoundModifier::None,
3008 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3012 // Helper methods for building HIR.
3014 fn stmt(&mut self, span: Span, kind: hir::StmtKind) -> hir::Stmt {
3015 hir::Stmt { span, kind, hir_id: self.next_id() }
3018 fn stmt_expr(&mut self, span: Span, expr: hir::Expr) -> hir::Stmt {
3019 self.stmt(span, hir::StmtKind::Expr(P(expr)))
3024 attrs: ThinVec<Attribute>,
3026 init: Option<P<hir::Expr>>,
3028 source: hir::LocalSource,
3030 let local = hir::Local {
3032 hir_id: self.next_id(),
3039 self.stmt(span, hir::StmtKind::Local(P(local)))
3042 fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
3043 self.block_all(expr.span, hir::HirVec::new(), Some(expr))
3049 stmts: hir::HirVec<hir::Stmt>,
3050 expr: Option<P<hir::Expr>>,
3055 hir_id: self.next_id(),
3056 rules: hir::DefaultBlock,
3058 targeted_by_break: false,
3062 /// Constructs a `true` or `false` literal pattern.
3063 fn pat_bool(&mut self, span: Span, val: bool) -> P<hir::Pat> {
3064 let expr = self.expr_bool(span, val);
3065 self.pat(span, hir::PatKind::Lit(P(expr)))
3068 fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3069 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], hir_vec![pat])
3072 fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3073 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], hir_vec![pat])
3076 fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3077 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], hir_vec![pat])
3080 fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
3081 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], hir_vec![])
3087 components: &[Symbol],
3088 subpats: hir::HirVec<P<hir::Pat>>,
3090 let path = self.std_path(span, components, None, true);
3091 let qpath = hir::QPath::Resolved(None, P(path));
3092 let pt = if subpats.is_empty() {
3093 hir::PatKind::Path(qpath)
3095 hir::PatKind::TupleStruct(qpath, subpats, None)
3100 fn pat_ident(&mut self, span: Span, ident: Ident) -> (P<hir::Pat>, hir::HirId) {
3101 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3104 fn pat_ident_binding_mode(
3108 bm: hir::BindingAnnotation,
3109 ) -> (P<hir::Pat>, hir::HirId) {
3110 let hir_id = self.next_id();
3115 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3122 fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
3123 self.pat(span, hir::PatKind::Wild)
3126 fn pat(&mut self, span: Span, kind: hir::PatKind) -> P<hir::Pat> {
3128 hir_id: self.next_id(),
3134 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3135 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3136 /// The path is also resolved according to `is_value`.
3140 components: &[Symbol],
3141 params: Option<P<hir::GenericArgs>>,
3144 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3145 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3147 let mut segments: Vec<_> = path.segments.iter().map(|segment| {
3148 let res = self.expect_full_res(segment.id);
3150 ident: segment.ident,
3151 hir_id: Some(self.lower_node_id(segment.id)),
3152 res: Some(self.lower_res(res)),
3157 segments.last_mut().unwrap().args = params;
3161 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3162 segments: segments.into(),
3166 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3167 let kind = match qpath {
3168 hir::QPath::Resolved(None, path) => {
3169 // Turn trait object paths into `TyKind::TraitObject` instead.
3171 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3172 let principal = hir::PolyTraitRef {
3173 bound_generic_params: hir::HirVec::new(),
3174 trait_ref: hir::TraitRef {
3181 // The original ID is taken by the `PolyTraitRef`,
3182 // so the `Ty` itself needs a different one.
3183 hir_id = self.next_id();
3184 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3186 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3189 _ => hir::TyKind::Path(qpath),
3199 /// Invoked to create the lifetime argument for a type `&T`
3200 /// with no explicit lifetime.
3201 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3202 match self.anonymous_lifetime_mode {
3203 // Intercept when we are in an impl header or async fn and introduce an in-band
3205 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3207 AnonymousLifetimeMode::CreateParameter => {
3208 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3210 hir_id: self.next_id(),
3212 name: hir::LifetimeName::Param(fresh_name),
3216 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3218 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3222 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3223 /// return a "error lifetime".
3224 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3225 let (id, msg, label) = match id {
3226 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3229 self.sess.next_node_id(),
3230 "`&` without an explicit lifetime name cannot be used here",
3231 "explicit lifetime name needed here",
3235 let mut err = struct_span_err!(
3242 err.span_label(span, label);
3245 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3248 /// Invoked to create the lifetime argument(s) for a path like
3249 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3250 /// sorts of cases are deprecated. This may therefore report a warning or an
3251 /// error, depending on the mode.
3252 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3254 .map(|_| self.elided_path_lifetime(span))
3258 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3259 match self.anonymous_lifetime_mode {
3260 AnonymousLifetimeMode::CreateParameter => {
3261 // We should have emitted E0726 when processing this path above
3262 self.sess.delay_span_bug(
3264 "expected 'implicit elided lifetime not allowed' error",
3266 let id = self.sess.next_node_id();
3267 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3269 // This is the normal case.
3270 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3272 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3276 /// Invoked to create the lifetime argument(s) for an elided trait object
3277 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3278 /// when the bound is written, even if it is written with `'_` like in
3279 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3280 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3281 match self.anonymous_lifetime_mode {
3282 // NB. We intentionally ignore the create-parameter mode here.
3283 // and instead "pass through" to resolve-lifetimes, which will apply
3284 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3285 // do not act like other elided lifetimes. In other words, given this:
3287 // impl Foo for Box<dyn Debug>
3289 // we do not introduce a fresh `'_` to serve as the bound, but instead
3290 // ultimately translate to the equivalent of:
3292 // impl Foo for Box<dyn Debug + 'static>
3294 // `resolve_lifetime` has the code to make that happen.
3295 AnonymousLifetimeMode::CreateParameter => {}
3297 AnonymousLifetimeMode::ReportError => {
3298 // ReportError applies to explicit use of `'_`.
3301 // This is the normal case.
3302 AnonymousLifetimeMode::PassThrough => {}
3305 let r = hir::Lifetime {
3306 hir_id: self.next_id(),
3308 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3310 debug!("elided_dyn_bound: r={:?}", r);
3314 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3316 hir_id: self.next_id(),
3318 name: hir::LifetimeName::Implicit,
3322 fn maybe_lint_bare_trait(&self, span: Span, id: NodeId, is_global: bool) {
3323 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3324 // call site which do not have a macro backtrace. See #61963.
3325 let is_macro_callsite = self.sess.source_map()
3326 .span_to_snippet(span)
3327 .map(|snippet| snippet.starts_with("#["))
3329 if !is_macro_callsite {
3330 self.sess.buffer_lint_with_diagnostic(
3331 builtin::BARE_TRAIT_OBJECTS,
3334 "trait objects without an explicit `dyn` are deprecated",
3335 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3341 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
3342 // Sorting by span ensures that we get things in order within a
3343 // file, and also puts the files in a sensible order.
3344 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3345 body_ids.sort_by_key(|b| bodies[b].value.span);
3349 /// Checks if the specified expression is a built-in range literal.
3350 /// (See: `LoweringContext::lower_expr()`).
3351 pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
3352 use hir::{Path, QPath, ExprKind, TyKind};
3354 // Returns whether the given path represents a (desugared) range,
3355 // either in std or core, i.e. has either a `::std::ops::Range` or
3356 // `::core::ops::Range` prefix.
3357 fn is_range_path(path: &Path) -> bool {
3358 let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.as_str().to_string()).collect();
3359 let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
3361 // "{{root}}" is the equivalent of `::` prefix in `Path`.
3362 if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
3363 (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
3369 // Check whether a span corresponding to a range expression is a
3370 // range literal, rather than an explicit struct or `new()` call.
3371 fn is_lit(sess: &Session, span: &Span) -> bool {
3372 let source_map = sess.source_map();
3373 let end_point = source_map.end_point(*span);
3375 if let Ok(end_string) = source_map.span_to_snippet(end_point) {
3376 !(end_string.ends_with("}") || end_string.ends_with(")"))
3383 // All built-in range literals but `..=` and `..` desugar to `Struct`s.
3384 ExprKind::Struct(ref qpath, _, _) => {
3385 if let QPath::Resolved(None, ref path) = **qpath {
3386 return is_range_path(&path) && is_lit(sess, &expr.span);
3390 // `..` desugars to its struct path.
3391 ExprKind::Path(QPath::Resolved(None, ref path)) => {
3392 return is_range_path(&path) && is_lit(sess, &expr.span);
3395 // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
3396 ExprKind::Call(ref func, _) => {
3397 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
3398 if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
3399 let new_call = segment.ident.as_str() == "new";
3400 return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;