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;
47 use crate::lint::builtin::{self, 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_index::vec::IndexVec;
56 use rustc_data_structures::sync::Lrc;
58 use std::collections::BTreeMap;
60 use smallvec::SmallVec;
63 use syntax::ptr::P as AstP;
66 use syntax::print::pprust;
67 use syntax::token::{self, Nonterminal, Token};
68 use syntax::tokenstream::{TokenStream, TokenTree};
69 use syntax::sess::ParseSess;
70 use syntax::source_map::{respan, ExpnData, ExpnKind, DesugaringKind, Spanned};
71 use syntax::symbol::{kw, sym, Symbol};
72 use syntax::visit::{self, Visitor};
73 use syntax_pos::hygiene::ExpnId;
76 use rustc_error_codes::*;
78 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
80 pub struct LoweringContext<'a> {
81 crate_root: Option<Symbol>,
83 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
86 resolver: &'a mut dyn Resolver,
88 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
89 /// if we don't have this function pointer. To avoid that dependency so that
90 /// librustc is independent of the parser, we use dynamic dispatch here.
91 nt_to_tokenstream: NtToTokenstream,
93 /// The items being lowered are collected here.
94 items: BTreeMap<hir::HirId, hir::Item>,
96 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
97 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
98 bodies: BTreeMap<hir::BodyId, hir::Body>,
99 exported_macros: Vec<hir::MacroDef>,
100 non_exported_macro_attrs: Vec<ast::Attribute>,
102 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
104 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
106 generator_kind: Option<hir::GeneratorKind>,
108 /// Used to get the current `fn`'s def span to point to when using `await`
109 /// outside of an `async fn`.
110 current_item: Option<Span>,
112 catch_scopes: Vec<NodeId>,
113 loop_scopes: Vec<NodeId>,
114 is_in_loop_condition: bool,
115 is_in_trait_impl: bool,
116 is_in_dyn_type: bool,
118 /// What to do when we encounter either an "anonymous lifetime
119 /// reference". The term "anonymous" is meant to encompass both
120 /// `'_` lifetimes as well as fully elided cases where nothing is
121 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
122 anonymous_lifetime_mode: AnonymousLifetimeMode,
124 /// Used to create lifetime definitions from in-band lifetime usages.
125 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
126 /// When a named lifetime is encountered in a function or impl header and
127 /// has not been defined
128 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
129 /// to this list. The results of this list are then added to the list of
130 /// lifetime definitions in the corresponding impl or function generics.
131 lifetimes_to_define: Vec<(Span, ParamName)>,
133 /// `true` if in-band lifetimes are being collected. This is used to
134 /// indicate whether or not we're in a place where new lifetimes will result
135 /// in in-band lifetime definitions, such a function or an impl header,
136 /// including implicit lifetimes from `impl_header_lifetime_elision`.
137 is_collecting_in_band_lifetimes: bool,
139 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
140 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
141 /// against this list to see if it is already in-scope, or if a definition
142 /// needs to be created for it.
144 /// We always store a `modern()` version of the param-name in this
146 in_scope_lifetimes: Vec<ParamName>,
148 current_module: hir::HirId,
150 type_def_lifetime_params: DefIdMap<usize>,
152 current_hir_id_owner: Vec<(DefIndex, u32)>,
153 item_local_id_counters: NodeMap<u32>,
154 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
156 allow_try_trait: Option<Lrc<[Symbol]>>,
157 allow_gen_future: Option<Lrc<[Symbol]>>,
161 fn cstore(&self) -> &dyn CrateStore;
163 /// Obtains resolution for a `NodeId` with a single resolution.
164 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
166 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
167 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
169 /// Obtains resolution for a label with the given `NodeId`.
170 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
172 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
173 /// This should only return `None` during testing.
174 fn definitions(&mut self) -> &mut Definitions;
176 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
177 /// resolves it based on `is_value`.
181 crate_root: Option<Symbol>,
182 components: &[Symbol],
184 ) -> (ast::Path, Res<NodeId>);
186 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
188 fn next_node_id(&mut self) -> NodeId;
191 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
193 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
194 /// and if so, what meaning it has.
196 enum ImplTraitContext<'a> {
197 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
198 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
199 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
201 /// Newly generated parameters should be inserted into the given `Vec`.
202 Universal(&'a mut Vec<hir::GenericParam>),
204 /// Treat `impl Trait` as shorthand for a new opaque type.
205 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
206 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
208 /// We optionally store a `DefId` for the parent item here so we can look up necessary
209 /// information later. It is `None` when no information about the context should be stored
210 /// (e.g., for consts and statics).
211 OpaqueTy(Option<DefId> /* fn def-ID */),
213 /// `impl Trait` is not accepted in this position.
214 Disallowed(ImplTraitPosition),
217 /// Position in which `impl Trait` is disallowed.
218 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
219 enum ImplTraitPosition {
220 /// Disallowed in `let` / `const` / `static` bindings.
223 /// All other posiitons.
227 impl<'a> ImplTraitContext<'a> {
229 fn disallowed() -> Self {
230 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
233 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
234 use self::ImplTraitContext::*;
236 Universal(params) => Universal(params),
237 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
238 Disallowed(pos) => Disallowed(*pos),
245 dep_graph: &DepGraph,
247 resolver: &mut dyn Resolver,
248 nt_to_tokenstream: NtToTokenstream,
250 // We're constructing the HIR here; we don't care what we will
251 // read, since we haven't even constructed the *input* to
253 dep_graph.assert_ignored();
255 let _prof_timer = sess.prof.generic_activity("hir_lowering");
258 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
262 items: BTreeMap::new(),
263 trait_items: BTreeMap::new(),
264 impl_items: BTreeMap::new(),
265 bodies: BTreeMap::new(),
266 trait_impls: BTreeMap::new(),
267 modules: BTreeMap::new(),
268 exported_macros: Vec::new(),
269 non_exported_macro_attrs: Vec::new(),
270 catch_scopes: Vec::new(),
271 loop_scopes: Vec::new(),
272 is_in_loop_condition: false,
273 is_in_trait_impl: false,
274 is_in_dyn_type: false,
275 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
276 type_def_lifetime_params: Default::default(),
277 current_module: hir::CRATE_HIR_ID,
278 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
279 item_local_id_counters: Default::default(),
280 node_id_to_hir_id: IndexVec::new(),
281 generator_kind: None,
283 lifetimes_to_define: Vec::new(),
284 is_collecting_in_band_lifetimes: false,
285 in_scope_lifetimes: Vec::new(),
286 allow_try_trait: Some([sym::try_trait][..].into()),
287 allow_gen_future: Some([sym::gen_future][..].into()),
291 #[derive(Copy, Clone, PartialEq)]
293 /// Any path in a type context.
295 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
297 /// The `module::Type` in `module::Type::method` in an expression.
301 enum ParenthesizedGenericArgs {
306 /// What to do when we encounter an **anonymous** lifetime
307 /// reference. Anonymous lifetime references come in two flavors. You
308 /// have implicit, or fully elided, references to lifetimes, like the
309 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
310 /// or `Ref<'_, T>`. These often behave the same, but not always:
312 /// - certain usages of implicit references are deprecated, like
313 /// `Ref<T>`, and we sometimes just give hard errors in those cases
315 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
316 /// the same as `Box<dyn Foo + '_>`.
318 /// We describe the effects of the various modes in terms of three cases:
320 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
321 /// of a `&` (e.g., the missing lifetime in something like `&T`)
322 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
323 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
324 /// elided bounds follow special rules. Note that this only covers
325 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
326 /// '_>` is a case of "modern" elision.
327 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
328 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
329 /// non-deprecated equivalent.
331 /// Currently, the handling of lifetime elision is somewhat spread out
332 /// between HIR lowering and -- as described below -- the
333 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
334 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
335 /// everything into HIR lowering.
336 #[derive(Copy, Clone, Debug)]
337 enum AnonymousLifetimeMode {
338 /// For **Modern** cases, create a new anonymous region parameter
339 /// and reference that.
341 /// For **Dyn Bound** cases, pass responsibility to
342 /// `resolve_lifetime` code.
344 /// For **Deprecated** cases, report an error.
347 /// Give a hard error when either `&` or `'_` is written. Used to
348 /// rule out things like `where T: Foo<'_>`. Does not imply an
349 /// error on default object bounds (e.g., `Box<dyn Foo>`).
352 /// Pass responsibility to `resolve_lifetime` code for all cases.
356 struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[NodeId; 1]> }
358 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
359 fn visit_ty(&mut self, ty: &'a Ty) {
365 TyKind::ImplTrait(id, _) => self.ids.push(id),
368 visit::walk_ty(self, ty);
371 fn visit_path_segment(
374 path_segment: &'v PathSegment,
376 if let Some(ref p) = path_segment.args {
377 if let GenericArgs::Parenthesized(_) = **p {
381 visit::walk_path_segment(self, path_span, path_segment)
385 impl<'a> LoweringContext<'a> {
386 fn lower_crate(mut self, c: &Crate) -> hir::Crate {
387 /// Full-crate AST visitor that inserts into a fresh
388 /// `LoweringContext` any information that may be
389 /// needed from arbitrary locations in the crate,
390 /// e.g., the number of lifetime generic parameters
391 /// declared for every type and trait definition.
392 struct MiscCollector<'tcx, 'interner> {
393 lctx: &'tcx mut LoweringContext<'interner>,
394 hir_id_owner: Option<NodeId>,
397 impl MiscCollector<'_, '_> {
398 fn allocate_use_tree_hir_id_counters(
404 UseTreeKind::Simple(_, id1, id2) => {
405 for &id in &[id1, id2] {
406 self.lctx.resolver.definitions().create_def_with_parent(
413 self.lctx.allocate_hir_id_counter(id);
416 UseTreeKind::Glob => (),
417 UseTreeKind::Nested(ref trees) => {
418 for &(ref use_tree, id) in trees {
419 let hir_id = self.lctx.allocate_hir_id_counter(id);
420 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
426 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
428 F: FnOnce(&mut Self) -> T,
430 let old = mem::replace(&mut self.hir_id_owner, owner);
432 self.hir_id_owner = old;
437 impl<'tcx, 'interner> Visitor<'tcx> for MiscCollector<'tcx, 'interner> {
438 fn visit_pat(&mut self, p: &'tcx Pat) {
439 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
440 // Doesn't generate a HIR node
441 } else if let Some(owner) = self.hir_id_owner {
442 self.lctx.lower_node_id_with_owner(p.id, owner);
445 visit::walk_pat(self, p)
448 fn visit_item(&mut self, item: &'tcx Item) {
449 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
452 ItemKind::Struct(_, ref generics)
453 | ItemKind::Union(_, ref generics)
454 | ItemKind::Enum(_, ref generics)
455 | ItemKind::TyAlias(_, ref generics)
456 | ItemKind::Trait(_, _, ref generics, ..) => {
457 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
461 .filter(|param| match param.kind {
462 ast::GenericParamKind::Lifetime { .. } => true,
466 self.lctx.type_def_lifetime_params.insert(def_id, count);
468 ItemKind::Use(ref use_tree) => {
469 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
474 self.with_hir_id_owner(Some(item.id), |this| {
475 visit::walk_item(this, item);
479 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
480 self.lctx.allocate_hir_id_counter(item.id);
483 AssocItemKind::Fn(_, None) => {
484 // Ignore patterns in trait methods without bodies
485 self.with_hir_id_owner(None, |this| {
486 visit::walk_trait_item(this, item)
489 _ => self.with_hir_id_owner(Some(item.id), |this| {
490 visit::walk_trait_item(this, item);
495 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
496 self.lctx.allocate_hir_id_counter(item.id);
497 self.with_hir_id_owner(Some(item.id), |this| {
498 visit::walk_impl_item(this, item);
502 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
503 // Ignore patterns in foreign items
504 self.with_hir_id_owner(None, |this| {
505 visit::walk_foreign_item(this, i)
509 fn visit_ty(&mut self, t: &'tcx Ty) {
511 // Mirrors the case in visit::walk_ty
512 TyKind::BareFn(ref f) => {
518 // Mirrors visit::walk_fn_decl
519 for parameter in &f.decl.inputs {
520 // We don't lower the ids of argument patterns
521 self.with_hir_id_owner(None, |this| {
522 this.visit_pat(¶meter.pat);
524 self.visit_ty(¶meter.ty)
526 self.visit_fn_ret_ty(&f.decl.output)
528 _ => visit::walk_ty(self, t),
533 self.lower_node_id(CRATE_NODE_ID);
534 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
536 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
537 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
539 let module = self.lower_mod(&c.module);
540 let attrs = self.lower_attrs(&c.attrs);
541 let body_ids = body_ids(&self.bodies);
545 .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
551 exported_macros: hir::HirVec::from(self.exported_macros),
552 non_exported_macro_attrs: hir::HirVec::from(self.non_exported_macro_attrs),
554 trait_items: self.trait_items,
555 impl_items: self.impl_items,
558 trait_impls: self.trait_impls,
559 modules: self.modules,
563 fn insert_item(&mut self, item: hir::Item) {
564 let id = item.hir_id;
565 // FIXME: Use `debug_asset-rt`.
566 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
567 self.items.insert(id, item);
568 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
571 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
572 // Set up the counter if needed.
573 self.item_local_id_counters.entry(owner).or_insert(0);
574 // Always allocate the first `HirId` for the owner itself.
575 let lowered = self.lower_node_id_with_owner(owner, owner);
576 debug_assert_eq!(lowered.local_id.as_u32(), 0);
580 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
582 F: FnOnce(&mut Self) -> hir::HirId,
584 if ast_node_id == DUMMY_NODE_ID {
585 return hir::DUMMY_HIR_ID;
588 let min_size = ast_node_id.as_usize() + 1;
590 if min_size > self.node_id_to_hir_id.len() {
591 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
594 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
596 if existing_hir_id == hir::DUMMY_HIR_ID {
597 // Generate a new `HirId`.
598 let hir_id = alloc_hir_id(self);
599 self.node_id_to_hir_id[ast_node_id] = hir_id;
607 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
609 F: FnOnce(&mut Self) -> T,
611 let counter = self.item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters
623 .insert(owner, new_counter)
625 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
629 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
630 /// the `LoweringContext`'s `NodeId => HirId` map.
631 /// Take care not to call this method if the resulting `HirId` is then not
632 /// actually used in the HIR, as that would trigger an assertion in the
633 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
634 /// properly. Calling the method twice with the same `NodeId` is fine though.
635 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
636 self.lower_node_id_generic(ast_node_id, |this| {
637 let &mut (def_index, ref mut local_id_counter) =
638 this.current_hir_id_owner.last_mut().unwrap();
639 let local_id = *local_id_counter;
640 *local_id_counter += 1;
643 local_id: hir::ItemLocalId::from_u32(local_id),
648 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
649 self.lower_node_id_generic(ast_node_id, |this| {
650 let local_id_counter = this
651 .item_local_id_counters
653 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
654 let local_id = *local_id_counter;
656 // We want to be sure not to modify the counter in the map while it
657 // is also on the stack. Otherwise we'll get lost updates when writing
658 // back from the stack to the map.
659 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
661 *local_id_counter += 1;
665 .opt_def_index(owner)
666 .expect("you forgot to call `create_def_with_parent` or are lowering node-IDs \
667 that do not belong to the current owner");
671 local_id: hir::ItemLocalId::from_u32(local_id),
676 fn next_id(&mut self) -> hir::HirId {
677 let node_id = self.resolver.next_node_id();
678 self.lower_node_id(node_id)
681 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
683 self.lower_node_id_generic(id, |_| {
684 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
689 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
690 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
691 if pr.unresolved_segments() != 0 {
692 bug!("path not fully resolved: {:?}", pr);
698 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
699 self.resolver.get_import_res(id).present_items()
702 fn diagnostic(&self) -> &errors::Handler {
703 self.sess.diagnostic()
706 /// Reuses the span but adds information like the kind of the desugaring and features that are
707 /// allowed inside this span.
708 fn mark_span_with_reason(
710 reason: DesugaringKind,
712 allow_internal_unstable: Option<Lrc<[Symbol]>>,
714 span.fresh_expansion(ExpnData {
715 allow_internal_unstable,
716 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
720 fn with_anonymous_lifetime_mode<R>(
722 anonymous_lifetime_mode: AnonymousLifetimeMode,
723 op: impl FnOnce(&mut Self) -> R,
726 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
727 anonymous_lifetime_mode,
729 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
730 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
731 let result = op(self);
732 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
733 debug!("with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
734 old_anonymous_lifetime_mode);
738 /// Creates a new `hir::GenericParam` for every new lifetime and
739 /// type parameter encountered while evaluating `f`. Definitions
740 /// are created with the parent provided. If no `parent_id` is
741 /// provided, no definitions will be returned.
743 /// Presuming that in-band lifetimes are enabled, then
744 /// `self.anonymous_lifetime_mode` will be updated to match the
745 /// parameter while `f` is running (and restored afterwards).
746 fn collect_in_band_defs<T, F>(
749 anonymous_lifetime_mode: AnonymousLifetimeMode,
751 ) -> (Vec<hir::GenericParam>, T)
753 F: FnOnce(&mut LoweringContext<'_>) -> (Vec<hir::GenericParam>, T),
755 assert!(!self.is_collecting_in_band_lifetimes);
756 assert!(self.lifetimes_to_define.is_empty());
757 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
759 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
760 self.is_collecting_in_band_lifetimes = true;
762 let (in_band_ty_params, res) = f(self);
764 self.is_collecting_in_band_lifetimes = false;
765 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
767 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
769 let params = lifetimes_to_define
771 .map(|(span, hir_name)| self.lifetime_to_generic_param(
772 span, hir_name, parent_id.index,
774 .chain(in_band_ty_params.into_iter())
780 /// Converts a lifetime into a new generic parameter.
781 fn lifetime_to_generic_param(
785 parent_index: DefIndex,
786 ) -> hir::GenericParam {
787 let node_id = self.resolver.next_node_id();
789 // Get the name we'll use to make the def-path. Note
790 // that collisions are ok here and this shouldn't
791 // really show up for end-user.
792 let (str_name, kind) = match hir_name {
793 ParamName::Plain(ident) => (
795 hir::LifetimeParamKind::InBand,
797 ParamName::Fresh(_) => (
798 kw::UnderscoreLifetime,
799 hir::LifetimeParamKind::Elided,
801 ParamName::Error => (
802 kw::UnderscoreLifetime,
803 hir::LifetimeParamKind::Error,
807 // Add a definition for the in-band lifetime def.
808 self.resolver.definitions().create_def_with_parent(
811 DefPathData::LifetimeNs(str_name),
817 hir_id: self.lower_node_id(node_id),
822 pure_wrt_drop: false,
823 kind: hir::GenericParamKind::Lifetime { kind }
827 /// When there is a reference to some lifetime `'a`, and in-band
828 /// lifetimes are enabled, then we want to push that lifetime into
829 /// the vector of names to define later. In that case, it will get
830 /// added to the appropriate generics.
831 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
832 if !self.is_collecting_in_band_lifetimes {
836 if !self.sess.features_untracked().in_band_lifetimes {
840 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
844 let hir_name = ParamName::Plain(ident);
846 if self.lifetimes_to_define.iter()
847 .any(|(_, lt_name)| lt_name.modern() == hir_name.modern()) {
851 self.lifetimes_to_define.push((ident.span, hir_name));
854 /// When we have either an elided or `'_` lifetime in an impl
855 /// header, we convert it to an in-band lifetime.
856 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
857 assert!(self.is_collecting_in_band_lifetimes);
858 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
859 let hir_name = ParamName::Fresh(index);
860 self.lifetimes_to_define.push((span, hir_name));
864 // Evaluates `f` with the lifetimes in `params` in-scope.
865 // This is used to track which lifetimes have already been defined, and
866 // which are new in-band lifetimes that need to have a definition created
868 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
870 F: FnOnce(&mut LoweringContext<'_>) -> T,
872 let old_len = self.in_scope_lifetimes.len();
873 let lt_def_names = params.iter().filter_map(|param| match param.kind {
874 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
877 self.in_scope_lifetimes.extend(lt_def_names);
881 self.in_scope_lifetimes.truncate(old_len);
885 /// Appends in-band lifetime defs and argument-position `impl
886 /// Trait` defs to the existing set of generics.
888 /// Presuming that in-band lifetimes are enabled, then
889 /// `self.anonymous_lifetime_mode` will be updated to match the
890 /// parameter while `f` is running (and restored afterwards).
891 fn add_in_band_defs<F, T>(
895 anonymous_lifetime_mode: AnonymousLifetimeMode,
897 ) -> (hir::Generics, T)
899 F: FnOnce(&mut LoweringContext<'_>, &mut Vec<hir::GenericParam>) -> T,
901 let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
904 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
905 let mut params = Vec::new();
906 // Note: it is necessary to lower generics *before* calling `f`.
907 // When lowering `async fn`, there's a final step when lowering
908 // the return type that assumes that all in-scope lifetimes have
909 // already been added to either `in_scope_lifetimes` or
910 // `lifetimes_to_define`. If we swapped the order of these two,
911 // in-band-lifetimes introduced by generics or where-clauses
912 // wouldn't have been added yet.
913 let generics = this.lower_generics(
915 ImplTraitContext::Universal(&mut params),
917 let res = f(this, &mut params);
918 (params, (generics, res))
923 let mut lowered_params: Vec<_> = lowered_generics
929 // FIXME(const_generics): the compiler doesn't always cope with
930 // unsorted generic parameters at the moment, so we make sure
931 // that they're ordered correctly here for now. (When we chain
932 // the `in_band_defs`, we might make the order unsorted.)
933 lowered_params.sort_by_key(|param| {
935 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
936 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
937 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
941 lowered_generics.params = lowered_params.into();
943 (lowered_generics, res)
946 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
948 F: FnOnce(&mut LoweringContext<'_>) -> T,
950 let was_in_dyn_type = self.is_in_dyn_type;
951 self.is_in_dyn_type = in_scope;
953 let result = f(self);
955 self.is_in_dyn_type = was_in_dyn_type;
960 fn with_new_scopes<T, F>(&mut self, f: F) -> T
962 F: FnOnce(&mut LoweringContext<'_>) -> T,
964 let was_in_loop_condition = self.is_in_loop_condition;
965 self.is_in_loop_condition = false;
967 let catch_scopes = mem::take(&mut self.catch_scopes);
968 let loop_scopes = mem::take(&mut self.loop_scopes);
970 self.catch_scopes = catch_scopes;
971 self.loop_scopes = loop_scopes;
973 self.is_in_loop_condition = was_in_loop_condition;
978 fn def_key(&mut self, id: DefId) -> DefKey {
980 self.resolver.definitions().def_key(id.index)
982 self.resolver.cstore().def_key(id)
986 fn lower_attrs_extendable(&mut self, attrs: &[Attribute]) -> Vec<Attribute> {
989 .map(|a| self.lower_attr(a))
993 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
994 self.lower_attrs_extendable(attrs).into()
997 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
998 // Note that we explicitly do not walk the path. Since we don't really
999 // lower attributes (we use the AST version) there is nowhere to keep
1000 // the `HirId`s. We don't actually need HIR version of attributes anyway.
1001 let kind = match attr.kind {
1002 AttrKind::Normal(ref item) => {
1003 AttrKind::Normal(AttrItem {
1004 path: item.path.clone(),
1005 args: self.lower_mac_args(&item.args),
1008 AttrKind::DocComment(comment) => AttrKind::DocComment(comment)
1019 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
1021 MacArgs::Empty => MacArgs::Empty,
1022 MacArgs::Delimited(dspan, delim, ref tokens) =>
1023 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone())),
1024 MacArgs::Eq(eq_span, ref tokens) =>
1025 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone())),
1029 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
1032 .flat_map(|tree| self.lower_token_tree(tree).into_trees())
1036 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
1038 TokenTree::Token(token) => self.lower_token(token),
1039 TokenTree::Delimited(span, delim, tts) => TokenTree::Delimited(
1042 self.lower_token_stream(tts),
1047 fn lower_token(&mut self, token: Token) -> TokenStream {
1049 token::Interpolated(nt) => {
1050 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1051 self.lower_token_stream(tts)
1053 _ => TokenTree::Token(token).into(),
1057 /// Given an associated type constraint like one of these:
1060 /// T: Iterator<Item: Debug>
1062 /// T: Iterator<Item = Debug>
1066 /// returns a `hir::TypeBinding` representing `Item`.
1067 fn lower_assoc_ty_constraint(
1069 constraint: &AssocTyConstraint,
1070 itctx: ImplTraitContext<'_>,
1071 ) -> hir::TypeBinding {
1072 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1074 let kind = match constraint.kind {
1075 AssocTyConstraintKind::Equality { ref ty } => hir::TypeBindingKind::Equality {
1076 ty: self.lower_ty(ty, itctx)
1078 AssocTyConstraintKind::Bound { ref bounds } => {
1079 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1080 let (desugar_to_impl_trait, itctx) = match itctx {
1081 // We are in the return position:
1083 // fn foo() -> impl Iterator<Item: Debug>
1087 // fn foo() -> impl Iterator<Item = impl Debug>
1088 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1090 // We are in the argument position, but within a dyn type:
1092 // fn foo(x: dyn Iterator<Item: Debug>)
1096 // fn foo(x: dyn Iterator<Item = impl Debug>)
1097 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1099 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1100 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1101 // "impl trait context" to permit `impl Debug` in this position (it desugars
1102 // then to an opaque type).
1104 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1105 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type =>
1106 (true, ImplTraitContext::OpaqueTy(None)),
1108 // We are in the parameter position, but not within a dyn type:
1110 // fn foo(x: impl Iterator<Item: Debug>)
1112 // so we leave it as is and this gets expanded in astconv to a bound like
1113 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1115 _ => (false, itctx),
1118 if desugar_to_impl_trait {
1119 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1120 // constructing the HIR for `impl bounds...` and then lowering that.
1122 let impl_trait_node_id = self.resolver.next_node_id();
1123 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1124 self.resolver.definitions().create_def_with_parent(
1127 DefPathData::ImplTrait,
1132 self.with_dyn_type_scope(false, |this| {
1133 let node_id = this.resolver.next_node_id();
1134 let ty = this.lower_ty(
1137 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1138 span: constraint.span,
1143 hir::TypeBindingKind::Equality {
1148 // Desugar `AssocTy: Bounds` into a type binding where the
1149 // later desugars into a trait predicate.
1150 let bounds = self.lower_param_bounds(bounds, itctx);
1152 hir::TypeBindingKind::Constraint {
1160 hir_id: self.lower_node_id(constraint.id),
1161 ident: constraint.ident,
1163 span: constraint.span,
1167 fn lower_generic_arg(
1169 arg: &ast::GenericArg,
1170 itctx: ImplTraitContext<'_>
1171 ) -> hir::GenericArg {
1173 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1174 ast::GenericArg::Type(ty) => {
1175 // We parse const arguments as path types as we cannot distiguish them durring
1176 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1177 // type and value namespaces. If we resolved the path in the value namespace, we
1178 // transform it into a generic const argument.
1179 if let TyKind::Path(ref qself, ref path) = ty.kind {
1180 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1181 let res = partial_res.base_res();
1182 if !res.matches_ns(Namespace::TypeNS) {
1184 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1188 // Construct a AnonConst where the expr is the "ty"'s path.
1190 let parent_def_index =
1191 self.current_hir_id_owner.last().unwrap().0;
1192 let node_id = self.resolver.next_node_id();
1194 // Add a definition for the in-band const def.
1195 self.resolver.definitions().create_def_with_parent(
1198 DefPathData::AnonConst,
1203 let path_expr = Expr {
1205 kind: ExprKind::Path(qself.clone(), path.clone()),
1207 attrs: AttrVec::new(),
1210 let ct = self.with_new_scopes(|this| {
1212 hir_id: this.lower_node_id(node_id),
1213 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1216 return GenericArg::Const(ConstArg {
1223 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1225 ast::GenericArg::Const(ct) => {
1226 GenericArg::Const(ConstArg {
1227 value: self.lower_anon_const(&ct),
1228 span: ct.value.span,
1234 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1235 P(self.lower_ty_direct(t, itctx))
1241 qself: &Option<QSelf>,
1243 param_mode: ParamMode,
1244 itctx: ImplTraitContext<'_>
1246 let id = self.lower_node_id(t.id);
1247 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1248 let ty = self.ty_path(id, t.span, qpath);
1249 if let hir::TyKind::TraitObject(..) = ty.kind {
1250 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1255 fn ty(&mut self, span: Span, kind: hir::TyKind) -> hir::Ty {
1256 hir::Ty { hir_id: self.next_id(), kind, span }
1259 fn ty_tup(&mut self, span: Span, tys: HirVec<hir::Ty>) -> hir::Ty {
1260 self.ty(span, hir::TyKind::Tup(tys))
1263 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1264 let kind = match t.kind {
1265 TyKind::Infer => hir::TyKind::Infer,
1266 TyKind::Err => hir::TyKind::Err,
1267 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1268 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1269 TyKind::Rptr(ref region, ref mt) => {
1270 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1271 let lifetime = match *region {
1272 Some(ref lt) => self.lower_lifetime(lt),
1273 None => self.elided_ref_lifetime(span),
1275 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1277 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1280 this.with_anonymous_lifetime_mode(
1281 AnonymousLifetimeMode::PassThrough,
1283 hir::TyKind::BareFn(P(hir::BareFnTy {
1284 generic_params: this.lower_generic_params(
1286 &NodeMap::default(),
1287 ImplTraitContext::disallowed(),
1289 unsafety: f.unsafety,
1290 abi: this.lower_extern(f.ext),
1291 decl: this.lower_fn_decl(&f.decl, None, false, None),
1292 param_names: this.lower_fn_params_to_names(&f.decl),
1298 TyKind::Never => hir::TyKind::Never,
1299 TyKind::Tup(ref tys) => {
1300 hir::TyKind::Tup(tys.iter().map(|ty| {
1301 self.lower_ty_direct(ty, itctx.reborrow())
1304 TyKind::Paren(ref ty) => {
1305 return self.lower_ty_direct(ty, itctx);
1307 TyKind::Path(ref qself, ref path) => {
1308 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1310 TyKind::ImplicitSelf => {
1311 let res = self.expect_full_res(t.id);
1312 let res = self.lower_res(res);
1313 hir::TyKind::Path(hir::QPath::Resolved(
1317 segments: hir_vec![hir::PathSegment::from_ident(
1318 Ident::with_dummy_span(kw::SelfUpper)
1324 TyKind::Array(ref ty, ref length) => {
1325 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1327 TyKind::Typeof(ref expr) => {
1328 hir::TyKind::Typeof(self.lower_anon_const(expr))
1330 TyKind::TraitObject(ref bounds, kind) => {
1331 let mut lifetime_bound = None;
1332 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1335 .filter_map(|bound| match *bound {
1336 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1337 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1339 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1340 GenericBound::Outlives(ref lifetime) => {
1341 if lifetime_bound.is_none() {
1342 lifetime_bound = Some(this.lower_lifetime(lifetime));
1348 let lifetime_bound =
1349 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1350 (bounds, lifetime_bound)
1352 if kind != TraitObjectSyntax::Dyn {
1353 self.maybe_lint_bare_trait(t.span, t.id, false);
1355 hir::TyKind::TraitObject(bounds, lifetime_bound)
1357 TyKind::ImplTrait(def_node_id, ref bounds) => {
1360 ImplTraitContext::OpaqueTy(fn_def_id) => {
1361 self.lower_opaque_impl_trait(
1362 span, fn_def_id, def_node_id,
1363 |this| this.lower_param_bounds(bounds, itctx),
1366 ImplTraitContext::Universal(in_band_ty_params) => {
1367 // Add a definition for the in-band `Param`.
1368 let def_index = self
1371 .opt_def_index(def_node_id)
1374 let hir_bounds = self.lower_param_bounds(
1376 ImplTraitContext::Universal(in_band_ty_params),
1378 // Set the name to `impl Bound1 + Bound2`.
1379 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1380 in_band_ty_params.push(hir::GenericParam {
1381 hir_id: self.lower_node_id(def_node_id),
1382 name: ParamName::Plain(ident),
1383 pure_wrt_drop: false,
1387 kind: hir::GenericParamKind::Type {
1389 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1393 hir::TyKind::Path(hir::QPath::Resolved(
1397 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1398 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1402 ImplTraitContext::Disallowed(pos) => {
1403 let allowed_in = if self.sess.features_untracked()
1404 .impl_trait_in_bindings {
1405 "bindings or function and inherent method return types"
1407 "function and inherent method return types"
1409 let mut err = struct_span_err!(
1413 "`impl Trait` not allowed outside of {}",
1416 if pos == ImplTraitPosition::Binding &&
1417 nightly_options::is_nightly_build() {
1419 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1420 attributes to enable");
1427 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1428 TyKind::CVarArgs => {
1429 self.sess.delay_span_bug(
1431 "`TyKind::CVarArgs` should have been handled elsewhere",
1440 hir_id: self.lower_node_id(t.id),
1444 fn lower_opaque_impl_trait(
1447 fn_def_id: Option<DefId>,
1448 opaque_ty_node_id: NodeId,
1449 lower_bounds: impl FnOnce(&mut LoweringContext<'_>) -> hir::GenericBounds,
1452 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1458 // Make sure we know that some funky desugaring has been going on here.
1459 // This is a first: there is code in other places like for loop
1460 // desugaring that explicitly states that we don't want to track that.
1461 // Not tracking it makes lints in rustc and clippy very fragile, as
1462 // frequently opened issues show.
1463 let opaque_ty_span = self.mark_span_with_reason(
1464 DesugaringKind::OpaqueTy,
1469 let opaque_ty_def_index = self
1472 .opt_def_index(opaque_ty_node_id)
1475 self.allocate_hir_id_counter(opaque_ty_node_id);
1477 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1479 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1481 opaque_ty_def_index,
1486 "lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,
1490 "lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,
1493 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1494 let opaque_ty_item = hir::OpaqueTy {
1495 generics: hir::Generics {
1496 params: lifetime_defs,
1497 where_clause: hir::WhereClause {
1498 predicates: hir_vec![],
1504 impl_trait_fn: fn_def_id,
1505 origin: hir::OpaqueTyOrigin::FnReturn,
1508 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1509 let opaque_ty_id = lctx.generate_opaque_type(
1516 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1517 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1521 /// Registers a new opaque type with the proper `NodeId`s and
1522 /// returns the lowered node-ID for the opaque type.
1523 fn generate_opaque_type(
1525 opaque_ty_node_id: NodeId,
1526 opaque_ty_item: hir::OpaqueTy,
1528 opaque_ty_span: Span,
1530 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1531 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1532 // Generate an `type Foo = impl Trait;` declaration.
1533 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1534 let opaque_ty_item = hir::Item {
1535 hir_id: opaque_ty_id,
1536 ident: Ident::invalid(),
1537 attrs: Default::default(),
1538 kind: opaque_ty_item_kind,
1539 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1540 span: opaque_ty_span,
1543 // Insert the item into the global item list. This usually happens
1544 // automatically for all AST items. But this opaque type item
1545 // does not actually exist in the AST.
1546 self.insert_item(opaque_ty_item);
1550 fn lifetimes_from_impl_trait_bounds(
1552 opaque_ty_id: NodeId,
1553 parent_index: DefIndex,
1554 bounds: &hir::GenericBounds,
1555 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1557 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1558 parent_index={:?}, \
1560 opaque_ty_id, parent_index, bounds,
1563 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1564 // appear in the bounds, excluding lifetimes that are created within the bounds.
1565 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1566 struct ImplTraitLifetimeCollector<'r, 'a> {
1567 context: &'r mut LoweringContext<'a>,
1569 opaque_ty_id: NodeId,
1570 collect_elided_lifetimes: bool,
1571 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1572 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1573 output_lifetimes: Vec<hir::GenericArg>,
1574 output_lifetime_params: Vec<hir::GenericParam>,
1577 impl<'r, 'a, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1578 fn nested_visit_map<'this>(
1580 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1581 hir::intravisit::NestedVisitorMap::None
1584 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1585 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1586 if parameters.parenthesized {
1587 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1588 self.collect_elided_lifetimes = false;
1589 hir::intravisit::walk_generic_args(self, span, parameters);
1590 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1592 hir::intravisit::walk_generic_args(self, span, parameters);
1596 fn visit_ty(&mut self, t: &'v hir::Ty) {
1597 // Don't collect elided lifetimes used inside of `fn()` syntax.
1598 if let hir::TyKind::BareFn(_) = t.kind {
1599 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1600 self.collect_elided_lifetimes = false;
1602 // Record the "stack height" of `for<'a>` lifetime bindings
1603 // to be able to later fully undo their introduction.
1604 let old_len = self.currently_bound_lifetimes.len();
1605 hir::intravisit::walk_ty(self, t);
1606 self.currently_bound_lifetimes.truncate(old_len);
1608 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1610 hir::intravisit::walk_ty(self, t)
1614 fn visit_poly_trait_ref(
1616 trait_ref: &'v hir::PolyTraitRef,
1617 modifier: hir::TraitBoundModifier,
1619 // Record the "stack height" of `for<'a>` lifetime bindings
1620 // to be able to later fully undo their introduction.
1621 let old_len = self.currently_bound_lifetimes.len();
1622 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1623 self.currently_bound_lifetimes.truncate(old_len);
1626 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1627 // Record the introduction of 'a in `for<'a> ...`.
1628 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1629 // Introduce lifetimes one at a time so that we can handle
1630 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1631 let lt_name = hir::LifetimeName::Param(param.name);
1632 self.currently_bound_lifetimes.push(lt_name);
1635 hir::intravisit::walk_generic_param(self, param);
1638 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1639 let name = match lifetime.name {
1640 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1641 if self.collect_elided_lifetimes {
1642 // Use `'_` for both implicit and underscore lifetimes in
1643 // `type Foo<'_> = impl SomeTrait<'_>;`.
1644 hir::LifetimeName::Underscore
1649 hir::LifetimeName::Param(_) => lifetime.name,
1651 // Refers to some other lifetime that is "in
1652 // scope" within the type.
1653 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1655 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1658 if !self.currently_bound_lifetimes.contains(&name)
1659 && !self.already_defined_lifetimes.contains(&name) {
1660 self.already_defined_lifetimes.insert(name);
1662 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1663 hir_id: self.context.next_id(),
1664 span: lifetime.span,
1668 let def_node_id = self.context.resolver.next_node_id();
1670 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1671 self.context.resolver.definitions().create_def_with_parent(
1674 DefPathData::LifetimeNs(name.ident().name),
1678 let (name, kind) = match name {
1679 hir::LifetimeName::Underscore => (
1680 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1681 hir::LifetimeParamKind::Elided,
1683 hir::LifetimeName::Param(param_name) => (
1685 hir::LifetimeParamKind::Explicit,
1687 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1690 self.output_lifetime_params.push(hir::GenericParam {
1693 span: lifetime.span,
1694 pure_wrt_drop: false,
1697 kind: hir::GenericParamKind::Lifetime { kind }
1703 let mut lifetime_collector = ImplTraitLifetimeCollector {
1705 parent: parent_index,
1707 collect_elided_lifetimes: true,
1708 currently_bound_lifetimes: Vec::new(),
1709 already_defined_lifetimes: FxHashSet::default(),
1710 output_lifetimes: Vec::new(),
1711 output_lifetime_params: Vec::new(),
1714 for bound in bounds {
1715 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1719 lifetime_collector.output_lifetimes.into(),
1720 lifetime_collector.output_lifetime_params.into(),
1727 qself: &Option<QSelf>,
1729 param_mode: ParamMode,
1730 mut itctx: ImplTraitContext<'_>,
1732 let qself_position = qself.as_ref().map(|q| q.position);
1733 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1735 let partial_res = self.resolver
1736 .get_partial_res(id)
1737 .unwrap_or_else(|| PartialRes::new(Res::Err));
1739 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1740 let path = P(hir::Path {
1741 res: self.lower_res(partial_res.base_res()),
1742 segments: p.segments[..proj_start]
1745 .map(|(i, segment)| {
1746 let param_mode = match (qself_position, param_mode) {
1747 (Some(j), ParamMode::Optional) if i < j => {
1748 // This segment is part of the trait path in a
1749 // qualified path - one of `a`, `b` or `Trait`
1750 // in `<X as a::b::Trait>::T::U::method`.
1756 // Figure out if this is a type/trait segment,
1757 // which may need lifetime elision performed.
1758 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1759 krate: def_id.krate,
1760 index: this.def_key(def_id).parent.expect("missing parent"),
1762 let type_def_id = match partial_res.base_res() {
1763 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1764 Some(parent_def_id(self, def_id))
1766 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1767 Some(parent_def_id(self, def_id))
1769 Res::Def(DefKind::Struct, def_id)
1770 | Res::Def(DefKind::Union, def_id)
1771 | Res::Def(DefKind::Enum, def_id)
1772 | Res::Def(DefKind::TyAlias, def_id)
1773 | Res::Def(DefKind::Trait, def_id) if i + 1 == proj_start =>
1779 let parenthesized_generic_args = match partial_res.base_res() {
1780 // `a::b::Trait(Args)`
1781 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1782 ParenthesizedGenericArgs::Ok
1784 // `a::b::Trait(Args)::TraitItem`
1785 Res::Def(DefKind::Method, _) |
1786 Res::Def(DefKind::AssocConst, _) |
1787 Res::Def(DefKind::AssocTy, _) if i + 2 == proj_start => {
1788 ParenthesizedGenericArgs::Ok
1790 // Avoid duplicated errors.
1791 Res::Err => ParenthesizedGenericArgs::Ok,
1793 _ => ParenthesizedGenericArgs::Err,
1796 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1797 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1800 assert!(!def_id.is_local());
1801 let item_generics = self.resolver.cstore()
1802 .item_generics_cloned_untracked(def_id, self.sess);
1803 let n = item_generics.own_counts().lifetimes;
1804 self.type_def_lifetime_params.insert(def_id, n);
1807 self.lower_path_segment(
1812 parenthesized_generic_args,
1821 // Simple case, either no projections, or only fully-qualified.
1822 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1823 if partial_res.unresolved_segments() == 0 {
1824 return hir::QPath::Resolved(qself, path);
1827 // Create the innermost type that we're projecting from.
1828 let mut ty = if path.segments.is_empty() {
1829 // If the base path is empty that means there exists a
1830 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1831 qself.expect("missing QSelf for <T>::...")
1833 // Otherwise, the base path is an implicit `Self` type path,
1834 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1835 // `<I as Iterator>::Item::default`.
1836 let new_id = self.next_id();
1837 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1840 // Anything after the base path are associated "extensions",
1841 // out of which all but the last one are associated types,
1842 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1843 // * base path is `std::vec::Vec<T>`
1844 // * "extensions" are `IntoIter`, `Item` and `clone`
1845 // * type nodes are:
1846 // 1. `std::vec::Vec<T>` (created above)
1847 // 2. `<std::vec::Vec<T>>::IntoIter`
1848 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1849 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1850 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1851 let segment = P(self.lower_path_segment(
1856 ParenthesizedGenericArgs::Err,
1860 let qpath = hir::QPath::TypeRelative(ty, segment);
1862 // It's finished, return the extension of the right node type.
1863 if i == p.segments.len() - 1 {
1867 // Wrap the associated extension in another type node.
1868 let new_id = self.next_id();
1869 ty = P(self.ty_path(new_id, p.span, qpath));
1872 // We should've returned in the for loop above.
1875 "lower_qpath: no final extension segment in {}..{}",
1881 fn lower_path_extra(
1885 param_mode: ParamMode,
1886 explicit_owner: Option<NodeId>,
1890 segments: p.segments
1893 self.lower_path_segment(
1898 ParenthesizedGenericArgs::Err,
1899 ImplTraitContext::disallowed(),
1908 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1909 let res = self.expect_full_res(id);
1910 let res = self.lower_res(res);
1911 self.lower_path_extra(res, p, param_mode, None)
1914 fn lower_path_segment(
1917 segment: &PathSegment,
1918 param_mode: ParamMode,
1919 expected_lifetimes: usize,
1920 parenthesized_generic_args: ParenthesizedGenericArgs,
1921 itctx: ImplTraitContext<'_>,
1922 explicit_owner: Option<NodeId>,
1923 ) -> hir::PathSegment {
1924 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1925 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1926 match **generic_args {
1927 GenericArgs::AngleBracketed(ref data) => {
1928 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1930 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1931 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1932 ParenthesizedGenericArgs::Err => {
1933 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1934 err.span_label(data.span, "only `Fn` traits may use parentheses");
1935 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1936 // Do not suggest going from `Trait()` to `Trait<>`
1937 if data.inputs.len() > 0 {
1938 if let Some(split) = snippet.find('(') {
1939 let trait_name = &snippet[0..split];
1940 let args = &snippet[split + 1 .. snippet.len() - 1];
1941 err.span_suggestion(
1943 "use angle brackets instead",
1944 format!("{}<{}>", trait_name, args),
1945 Applicability::MaybeIncorrect,
1952 self.lower_angle_bracketed_parameter_data(
1953 &data.as_angle_bracketed_args(),
1963 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1966 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1967 GenericArg::Lifetime(_) => true,
1970 let first_generic_span = generic_args.args.iter().map(|a| a.span())
1971 .chain(generic_args.bindings.iter().map(|b| b.span)).next();
1972 if !generic_args.parenthesized && !has_lifetimes {
1974 self.elided_path_lifetimes(path_span, expected_lifetimes)
1976 .map(|lt| GenericArg::Lifetime(lt))
1977 .chain(generic_args.args.into_iter())
1979 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1980 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1981 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1982 let no_bindings = generic_args.bindings.is_empty();
1983 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1984 // If there are no (non-implicit) generic args or associated type
1985 // bindings, our suggestion includes the angle brackets.
1986 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1988 // Otherwise (sorry, this is kind of gross) we need to infer the
1989 // place to splice in the `'_, ` from the generics that do exist.
1990 let first_generic_span = first_generic_span
1991 .expect("already checked that non-lifetime args or bindings exist");
1992 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1994 match self.anonymous_lifetime_mode {
1995 // In create-parameter mode we error here because we don't want to support
1996 // deprecated impl elision in new features like impl elision and `async fn`,
1997 // both of which work using the `CreateParameter` mode:
1999 // impl Foo for std::cell::Ref<u32> // note lack of '_
2000 // async fn foo(_: std::cell::Ref<u32>) { ... }
2001 AnonymousLifetimeMode::CreateParameter => {
2002 let mut err = struct_span_err!(
2006 "implicit elided lifetime not allowed here"
2008 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
2019 AnonymousLifetimeMode::PassThrough |
2020 AnonymousLifetimeMode::ReportError => {
2021 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2022 ELIDED_LIFETIMES_IN_PATHS,
2025 "hidden lifetime parameters in types are deprecated",
2026 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
2039 let res = self.expect_full_res(segment.id);
2040 let id = if let Some(owner) = explicit_owner {
2041 self.lower_node_id_with_owner(segment.id, owner)
2043 self.lower_node_id(segment.id)
2046 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
2047 segment.ident, segment.id, id,
2050 hir::PathSegment::new(
2053 Some(self.lower_res(res)),
2059 fn lower_angle_bracketed_parameter_data(
2061 data: &AngleBracketedArgs,
2062 param_mode: ParamMode,
2063 mut itctx: ImplTraitContext<'_>,
2064 ) -> (hir::GenericArgs, bool) {
2065 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
2066 let has_non_lt_args = args.iter().any(|arg| match arg {
2067 ast::GenericArg::Lifetime(_) => false,
2068 ast::GenericArg::Type(_) => true,
2069 ast::GenericArg::Const(_) => true,
2073 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
2074 bindings: constraints.iter()
2075 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
2077 parenthesized: false,
2079 !has_non_lt_args && param_mode == ParamMode::Optional
2083 fn lower_parenthesized_parameter_data(
2085 data: &ParenthesizedArgs,
2086 ) -> (hir::GenericArgs, bool) {
2087 // Switch to `PassThrough` mode for anonymous lifetimes; this
2088 // means that we permit things like `&Ref<T>`, where `Ref` has
2089 // a hidden lifetime parameter. This is needed for backwards
2090 // compatibility, even in contexts like an impl header where
2091 // we generally don't permit such things (see #51008).
2092 self.with_anonymous_lifetime_mode(
2093 AnonymousLifetimeMode::PassThrough,
2095 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2098 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2100 let output_ty = match output {
2101 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2102 FunctionRetTy::Default(_) => P(this.ty_tup(span, hir::HirVec::new())),
2104 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2105 let binding = hir::TypeBinding {
2106 hir_id: this.next_id(),
2107 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2108 span: output_ty.span,
2109 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2112 hir::GenericArgs { args, bindings: hir_vec![binding], parenthesized: true },
2119 fn lower_local(&mut self, l: &Local) -> (hir::Local, SmallVec<[NodeId; 1]>) {
2120 let mut ids = SmallVec::<[NodeId; 1]>::new();
2121 if self.sess.features_untracked().impl_trait_in_bindings {
2122 if let Some(ref ty) = l.ty {
2123 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2124 visitor.visit_ty(ty);
2127 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2129 hir_id: self.lower_node_id(l.id),
2132 .map(|t| self.lower_ty(t,
2133 if self.sess.features_untracked().impl_trait_in_bindings {
2134 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2136 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2139 pat: self.lower_pat(&l.pat),
2140 init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
2142 attrs: l.attrs.clone(),
2143 source: hir::LocalSource::Normal,
2147 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2148 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2149 // as they are not explicit in HIR/Ty function signatures.
2150 // (instead, the `c_variadic` flag is set to `true`)
2151 let mut inputs = &decl.inputs[..];
2152 if decl.c_variadic() {
2153 inputs = &inputs[..inputs.len() - 1];
2157 .map(|param| match param.pat.kind {
2158 PatKind::Ident(_, ident, _) => ident,
2159 _ => Ident::new(kw::Invalid, param.pat.span),
2164 // Lowers a function declaration.
2166 // `decl`: the unlowered (AST) function declaration.
2167 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2168 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2169 // `make_ret_async` is also `Some`.
2170 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2171 // This guards against trait declarations and implementations where `impl Trait` is
2173 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2174 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2175 // return type `impl Trait` item.
2179 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2180 impl_trait_return_allow: bool,
2181 make_ret_async: Option<NodeId>,
2182 ) -> P<hir::FnDecl> {
2183 debug!("lower_fn_decl(\
2185 in_band_ty_params: {:?}, \
2186 impl_trait_return_allow: {}, \
2187 make_ret_async: {:?})",
2190 impl_trait_return_allow,
2193 let lt_mode = if make_ret_async.is_some() {
2194 // In `async fn`, argument-position elided lifetimes
2195 // must be transformed into fresh generic parameters so that
2196 // they can be applied to the opaque `impl Trait` return type.
2197 AnonymousLifetimeMode::CreateParameter
2199 self.anonymous_lifetime_mode
2202 let c_variadic = decl.c_variadic();
2204 // Remember how many lifetimes were already around so that we can
2205 // only look at the lifetime parameters introduced by the arguments.
2206 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2207 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2208 // as they are not explicit in HIR/Ty function signatures.
2209 // (instead, the `c_variadic` flag is set to `true`)
2210 let mut inputs = &decl.inputs[..];
2212 inputs = &inputs[..inputs.len() - 1];
2217 if let Some((_, ibty)) = &mut in_band_ty_params {
2218 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2220 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2223 .collect::<HirVec<_>>()
2226 let output = if let Some(ret_id) = make_ret_async {
2227 self.lower_async_fn_ret_ty(
2229 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2234 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2235 Some((def_id, _)) if impl_trait_return_allow => {
2236 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2239 hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed()))
2242 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2250 implicit_self: decl.inputs.get(0).map_or(
2251 hir::ImplicitSelfKind::None,
2253 let is_mutable_pat = match arg.pat.kind {
2254 PatKind::Ident(BindingMode::ByValue(mt), _, _) |
2255 PatKind::Ident(BindingMode::ByRef(mt), _, _) =>
2256 mt == Mutability::Mut,
2261 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2262 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2263 // Given we are only considering `ImplicitSelf` types, we needn't consider
2264 // the case where we have a mutable pattern to a reference as that would
2265 // no longer be an `ImplicitSelf`.
2266 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() &&
2267 mt.mutbl == ast::Mutability::Mut =>
2268 hir::ImplicitSelfKind::MutRef,
2269 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() =>
2270 hir::ImplicitSelfKind::ImmRef,
2271 _ => hir::ImplicitSelfKind::None,
2278 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2279 // combined with the following definition of `OpaqueTy`:
2281 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2283 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2284 // `output`: unlowered output type (`T` in `-> T`)
2285 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2286 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2287 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2288 fn lower_async_fn_ret_ty(
2290 output: &FunctionRetTy,
2292 opaque_ty_node_id: NodeId,
2293 ) -> hir::FunctionRetTy {
2295 "lower_async_fn_ret_ty(\
2298 opaque_ty_node_id={:?})",
2299 output, fn_def_id, opaque_ty_node_id,
2302 let span = output.span();
2304 let opaque_ty_span = self.mark_span_with_reason(
2305 DesugaringKind::Async,
2310 let opaque_ty_def_index = self
2313 .opt_def_index(opaque_ty_node_id)
2316 self.allocate_hir_id_counter(opaque_ty_node_id);
2318 // When we create the opaque type for this async fn, it is going to have
2319 // to capture all the lifetimes involved in the signature (including in the
2320 // return type). This is done by introducing lifetime parameters for:
2322 // - all the explicitly declared lifetimes from the impl and function itself;
2323 // - all the elided lifetimes in the fn arguments;
2324 // - all the elided lifetimes in the return type.
2326 // So for example in this snippet:
2329 // impl<'a> Foo<'a> {
2330 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2331 // // ^ '0 ^ '1 ^ '2
2332 // // elided lifetimes used below
2337 // we would create an opaque type like:
2340 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2343 // and we would then desugar `bar` to the equivalent of:
2346 // impl<'a> Foo<'a> {
2347 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2351 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2352 // this is because the elided lifetimes from the return type
2353 // should be figured out using the ordinary elision rules, and
2354 // this desugaring achieves that.
2356 // The variable `input_lifetimes_count` tracks the number of
2357 // lifetime parameters to the opaque type *not counting* those
2358 // lifetimes elided in the return type. This includes those
2359 // that are explicitly declared (`in_scope_lifetimes`) and
2360 // those elided lifetimes we found in the arguments (current
2361 // content of `lifetimes_to_define`). Next, we will process
2362 // the return type, which will cause `lifetimes_to_define` to
2364 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2366 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2367 // We have to be careful to get elision right here. The
2368 // idea is that we create a lifetime parameter for each
2369 // lifetime in the return type. So, given a return type
2370 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2371 // Future<Output = &'1 [ &'2 u32 ]>`.
2373 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2374 // hence the elision takes place at the fn site.
2375 let future_bound = this.with_anonymous_lifetime_mode(
2376 AnonymousLifetimeMode::CreateParameter,
2377 |this| this.lower_async_fn_output_type_to_future_bound(
2384 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2386 // Calculate all the lifetimes that should be captured
2387 // by the opaque type. This should include all in-scope
2388 // lifetime parameters, including those defined in-band.
2390 // Note: this must be done after lowering the output type,
2391 // as the output type may introduce new in-band lifetimes.
2392 let lifetime_params: Vec<(Span, ParamName)> =
2393 this.in_scope_lifetimes
2395 .map(|name| (name.ident().span, name))
2396 .chain(this.lifetimes_to_define.iter().cloned())
2399 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2400 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2401 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2403 let generic_params =
2406 .map(|(span, hir_name)| {
2407 this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_index)
2411 let opaque_ty_item = hir::OpaqueTy {
2412 generics: hir::Generics {
2413 params: generic_params,
2414 where_clause: hir::WhereClause {
2415 predicates: hir_vec![],
2420 bounds: hir_vec![future_bound],
2421 impl_trait_fn: Some(fn_def_id),
2422 origin: hir::OpaqueTyOrigin::AsyncFn,
2425 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2426 let opaque_ty_id = this.generate_opaque_type(
2433 (opaque_ty_id, lifetime_params)
2436 // As documented above on the variable
2437 // `input_lifetimes_count`, we need to create the lifetime
2438 // arguments to our opaque type. Continuing with our example,
2439 // we're creating the type arguments for the return type:
2442 // Bar<'a, 'b, '0, '1, '_>
2445 // For the "input" lifetime parameters, we wish to create
2446 // references to the parameters themselves, including the
2447 // "implicit" ones created from parameter types (`'a`, `'b`,
2450 // For the "output" lifetime parameters, we just want to
2452 let mut generic_args: Vec<_> =
2453 lifetime_params[..input_lifetimes_count]
2455 .map(|&(span, hir_name)| {
2456 // Input lifetime like `'a` or `'1`:
2457 GenericArg::Lifetime(hir::Lifetime {
2458 hir_id: self.next_id(),
2460 name: hir::LifetimeName::Param(hir_name),
2464 generic_args.extend(
2465 lifetime_params[input_lifetimes_count..]
2468 // Output lifetime like `'_`.
2469 GenericArg::Lifetime(hir::Lifetime {
2470 hir_id: self.next_id(),
2472 name: hir::LifetimeName::Implicit,
2477 // Create the `Foo<...>` reference itself. Note that the `type
2478 // Foo = impl Trait` is, internally, created as a child of the
2479 // async fn, so the *type parameters* are inherited. It's
2480 // only the lifetime parameters that we must supply.
2481 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args.into());
2482 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2483 hir::FunctionRetTy::Return(P(opaque_ty))
2486 /// Transforms `-> T` into `Future<Output = T>`
2487 fn lower_async_fn_output_type_to_future_bound(
2489 output: &FunctionRetTy,
2492 ) -> hir::GenericBound {
2493 // Compute the `T` in `Future<Output = T>` from the return type.
2494 let output_ty = match output {
2495 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2496 FunctionRetTy::Default(ret_ty_span) => P(self.ty_tup(*ret_ty_span, hir_vec![])),
2500 let future_params = P(hir::GenericArgs {
2502 bindings: hir_vec![hir::TypeBinding {
2503 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2504 kind: hir::TypeBindingKind::Equality {
2507 hir_id: self.next_id(),
2510 parenthesized: false,
2513 // ::std::future::Future<future_params>
2515 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2517 hir::GenericBound::Trait(
2519 trait_ref: hir::TraitRef {
2521 hir_ref_id: self.next_id(),
2523 bound_generic_params: hir_vec![],
2526 hir::TraitBoundModifier::None,
2530 fn lower_param_bound(
2533 itctx: ImplTraitContext<'_>,
2534 ) -> hir::GenericBound {
2536 GenericBound::Trait(ref ty, modifier) => {
2537 hir::GenericBound::Trait(
2538 self.lower_poly_trait_ref(ty, itctx),
2539 self.lower_trait_bound_modifier(modifier),
2542 GenericBound::Outlives(ref lifetime) => {
2543 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2548 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2549 let span = l.ident.span;
2551 ident if ident.name == kw::StaticLifetime =>
2552 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
2553 ident if ident.name == kw::UnderscoreLifetime =>
2554 match self.anonymous_lifetime_mode {
2555 AnonymousLifetimeMode::CreateParameter => {
2556 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2557 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2560 AnonymousLifetimeMode::PassThrough => {
2561 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2564 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2567 self.maybe_collect_in_band_lifetime(ident);
2568 let param_name = ParamName::Plain(ident);
2569 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2574 fn new_named_lifetime(
2578 name: hir::LifetimeName,
2579 ) -> hir::Lifetime {
2581 hir_id: self.lower_node_id(id),
2587 fn lower_generic_params(
2589 params: &[GenericParam],
2590 add_bounds: &NodeMap<Vec<GenericBound>>,
2591 mut itctx: ImplTraitContext<'_>,
2592 ) -> hir::HirVec<hir::GenericParam> {
2593 params.iter().map(|param| {
2594 self.lower_generic_param(param, add_bounds, itctx.reborrow())
2598 fn lower_generic_param(&mut self,
2599 param: &GenericParam,
2600 add_bounds: &NodeMap<Vec<GenericBound>>,
2601 mut itctx: ImplTraitContext<'_>)
2602 -> hir::GenericParam {
2603 let mut bounds = self.with_anonymous_lifetime_mode(
2604 AnonymousLifetimeMode::ReportError,
2605 |this| this.lower_param_bounds(¶m.bounds, itctx.reborrow()),
2608 let (name, kind) = match param.kind {
2609 GenericParamKind::Lifetime => {
2610 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2611 self.is_collecting_in_band_lifetimes = false;
2613 let lt = self.with_anonymous_lifetime_mode(
2614 AnonymousLifetimeMode::ReportError,
2615 |this| this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }),
2617 let param_name = match lt.name {
2618 hir::LifetimeName::Param(param_name) => param_name,
2619 hir::LifetimeName::Implicit
2620 | hir::LifetimeName::Underscore
2621 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2622 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2625 "object-lifetime-default should not occur here",
2628 hir::LifetimeName::Error => ParamName::Error,
2631 let kind = hir::GenericParamKind::Lifetime {
2632 kind: hir::LifetimeParamKind::Explicit
2635 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2639 GenericParamKind::Type { ref default, .. } => {
2640 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2641 if !add_bounds.is_empty() {
2642 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2643 bounds = bounds.into_iter()
2648 let kind = hir::GenericParamKind::Type {
2649 default: default.as_ref().map(|x| {
2650 self.lower_ty(x, ImplTraitContext::OpaqueTy(None))
2652 synthetic: param.attrs.iter()
2653 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2654 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2658 (hir::ParamName::Plain(param.ident), kind)
2660 GenericParamKind::Const { ref ty } => {
2661 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const {
2662 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2668 hir_id: self.lower_node_id(param.id),
2670 span: param.ident.span,
2671 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2672 attrs: self.lower_attrs(¶m.attrs),
2678 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2679 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2680 hir::QPath::Resolved(None, path) => path,
2681 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2685 hir_ref_id: self.lower_node_id(p.ref_id),
2689 fn lower_poly_trait_ref(
2692 mut itctx: ImplTraitContext<'_>,
2693 ) -> hir::PolyTraitRef {
2694 let bound_generic_params = self.lower_generic_params(
2695 &p.bound_generic_params,
2696 &NodeMap::default(),
2699 let trait_ref = self.with_in_scope_lifetime_defs(
2700 &p.bound_generic_params,
2701 |this| this.lower_trait_ref(&p.trait_ref, itctx),
2705 bound_generic_params,
2711 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2713 ty: self.lower_ty(&mt.ty, itctx),
2718 fn lower_param_bounds(&mut self, bounds: &[GenericBound], mut itctx: ImplTraitContext<'_>)
2719 -> hir::GenericBounds {
2720 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2723 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2724 let mut stmts = vec![];
2725 let mut expr = None;
2727 for (index, stmt) in b.stmts.iter().enumerate() {
2728 if index == b.stmts.len() - 1 {
2729 if let StmtKind::Expr(ref e) = stmt.kind {
2730 expr = Some(P(self.lower_expr(e)));
2732 stmts.extend(self.lower_stmt(stmt));
2735 stmts.extend(self.lower_stmt(stmt));
2740 hir_id: self.lower_node_id(b.id),
2741 stmts: stmts.into(),
2743 rules: self.lower_block_check_mode(&b.rules),
2749 /// Lowers a block directly to an expression, presuming that it
2750 /// has no attributes and is not targeted by a `break`.
2751 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr {
2752 let block = self.lower_block(b, false);
2753 self.expr_block(block, AttrVec::new())
2756 fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2757 let node = match p.kind {
2758 PatKind::Wild => hir::PatKind::Wild,
2759 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2760 let lower_sub = |this: &mut Self| sub.as_ref().map(|x| this.lower_pat(x));
2761 self.lower_pat_ident(p, binding_mode, ident, lower_sub)
2763 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2764 PatKind::TupleStruct(ref path, ref pats) => {
2765 let qpath = self.lower_qpath(
2769 ParamMode::Optional,
2770 ImplTraitContext::disallowed(),
2772 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2773 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2775 PatKind::Or(ref pats) => {
2776 hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
2778 PatKind::Path(ref qself, ref path) => {
2779 let qpath = self.lower_qpath(
2783 ParamMode::Optional,
2784 ImplTraitContext::disallowed(),
2786 hir::PatKind::Path(qpath)
2788 PatKind::Struct(ref path, ref fields, etc) => {
2789 let qpath = self.lower_qpath(
2793 ParamMode::Optional,
2794 ImplTraitContext::disallowed(),
2799 .map(|f| hir::FieldPat {
2800 hir_id: self.next_id(),
2802 pat: self.lower_pat(&f.pat),
2803 is_shorthand: f.is_shorthand,
2807 hir::PatKind::Struct(qpath, fs, etc)
2809 PatKind::Tuple(ref pats) => {
2810 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2811 hir::PatKind::Tuple(pats, ddpos)
2813 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2814 PatKind::Ref(ref inner, mutbl) => {
2815 hir::PatKind::Ref(self.lower_pat(inner), mutbl)
2817 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2818 P(self.lower_expr(e1)),
2819 P(self.lower_expr(e2)),
2820 self.lower_range_end(end),
2822 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2824 // If we reach here the `..` pattern is not semantically allowed.
2825 self.ban_illegal_rest_pat(p.span)
2827 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2828 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2831 self.pat_with_node_id_of(p, node)
2838 ) -> (HirVec<P<hir::Pat>>, Option<usize>) {
2839 let mut elems = Vec::with_capacity(pats.len());
2840 let mut rest = None;
2842 let mut iter = pats.iter().enumerate();
2843 for (idx, pat) in iter.by_ref() {
2844 // Interpret the first `..` pattern as a sub-tuple pattern.
2845 // Note that unlike for slice patterns,
2846 // where `xs @ ..` is a legal sub-slice pattern,
2847 // it is not a legal sub-tuple pattern.
2849 rest = Some((idx, pat.span));
2852 // It was not a sub-tuple pattern so lower it normally.
2853 elems.push(self.lower_pat(pat));
2856 for (_, pat) in iter {
2857 // There was a previous sub-tuple pattern; make sure we don't allow more...
2859 // ...but there was one again, so error.
2860 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2862 elems.push(self.lower_pat(pat));
2866 (elems.into(), rest.map(|(ddpos, _)| ddpos))
2869 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2870 /// `hir::PatKind::Slice(before, slice, after)`.
2872 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2873 /// this is interpreted as a sub-slice pattern semantically.
2874 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2875 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind {
2876 let mut before = Vec::new();
2877 let mut after = Vec::new();
2878 let mut slice = None;
2879 let mut prev_rest_span = None;
2881 let mut iter = pats.iter();
2882 // Lower all the patterns until the first occurence of a sub-slice pattern.
2883 for pat in iter.by_ref() {
2885 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2887 prev_rest_span = Some(pat.span);
2888 slice = Some(self.pat_wild_with_node_id_of(pat));
2891 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2892 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2893 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2894 prev_rest_span = Some(sub.span);
2895 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2896 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2897 slice = Some(self.pat_with_node_id_of(pat, node));
2900 // It was not a subslice pattern so lower it normally.
2901 _ => before.push(self.lower_pat(pat)),
2905 // Lower all the patterns after the first sub-slice pattern.
2907 // There was a previous subslice pattern; make sure we don't allow more.
2908 let rest_span = match pat.kind {
2909 PatKind::Rest => Some(pat.span),
2910 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2911 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2912 after.push(self.pat_wild_with_node_id_of(pat));
2917 if let Some(rest_span) = rest_span {
2918 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2919 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2921 // Lower the pattern normally.
2922 after.push(self.lower_pat(pat));
2926 hir::PatKind::Slice(before.into(), slice, after.into())
2932 binding_mode: &BindingMode,
2934 lower_sub: impl FnOnce(&mut Self) -> Option<P<hir::Pat>>,
2936 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2937 // `None` can occur in body-less function signatures
2938 res @ None | res @ Some(Res::Local(_)) => {
2939 let canonical_id = match res {
2940 Some(Res::Local(id)) => id,
2944 hir::PatKind::Binding(
2945 self.lower_binding_mode(binding_mode),
2946 self.lower_node_id(canonical_id),
2951 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2955 res: self.lower_res(res),
2956 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2962 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> P<hir::Pat> {
2963 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2966 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2967 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind) -> P<hir::Pat> {
2969 hir_id: self.lower_node_id(p.id),
2975 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2976 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2978 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2979 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2980 .span_label(prev_sp, "previously used here")
2984 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2985 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind {
2987 .struct_span_err(sp, "`..` patterns are not allowed here")
2988 .note("only allowed in tuple, tuple struct, and slice patterns")
2991 // We're not in a list context so `..` can be reasonably treated
2992 // as `_` because it should always be valid and roughly matches the
2993 // intent of `..` (notice that the rest of a single slot is that slot).
2997 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2999 RangeEnd::Included(_) => hir::RangeEnd::Included,
3000 RangeEnd::Excluded => hir::RangeEnd::Excluded,
3004 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
3005 self.with_new_scopes(|this| {
3007 hir_id: this.lower_node_id(c.id),
3008 body: this.lower_const_body(c.value.span, Some(&c.value)),
3013 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt; 1]> {
3014 let kind = match s.kind {
3015 StmtKind::Local(ref l) => {
3016 let (l, item_ids) = self.lower_local(l);
3017 let mut ids: SmallVec<[hir::Stmt; 1]> = item_ids
3020 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
3021 self.stmt(s.span, hir::StmtKind::Item(item_id))
3026 hir_id: self.lower_node_id(s.id),
3027 kind: hir::StmtKind::Local(P(l)),
3033 StmtKind::Item(ref it) => {
3034 // Can only use the ID once.
3035 let mut id = Some(s.id);
3036 return self.lower_item_id(it)
3039 let hir_id = id.take()
3040 .map(|id| self.lower_node_id(id))
3041 .unwrap_or_else(|| self.next_id());
3045 kind: hir::StmtKind::Item(item_id),
3051 StmtKind::Expr(ref e) => hir::StmtKind::Expr(P(self.lower_expr(e))),
3052 StmtKind::Semi(ref e) => hir::StmtKind::Semi(P(self.lower_expr(e))),
3053 StmtKind::Mac(..) => panic!("shouldn't exist here"),
3055 smallvec![hir::Stmt {
3056 hir_id: self.lower_node_id(s.id),
3062 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
3064 BlockCheckMode::Default => hir::DefaultBlock,
3065 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
3069 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
3071 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
3072 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
3073 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
3074 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
3078 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3080 CompilerGenerated => hir::CompilerGenerated,
3081 UserProvided => hir::UserProvided,
3085 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3087 TraitBoundModifier::None => hir::TraitBoundModifier::None,
3088 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3092 // Helper methods for building HIR.
3094 fn stmt(&mut self, span: Span, kind: hir::StmtKind) -> hir::Stmt {
3095 hir::Stmt { span, kind, hir_id: self.next_id() }
3098 fn stmt_expr(&mut self, span: Span, expr: hir::Expr) -> hir::Stmt {
3099 self.stmt(span, hir::StmtKind::Expr(P(expr)))
3106 init: Option<P<hir::Expr>>,
3108 source: hir::LocalSource,
3110 let local = hir::Local {
3112 hir_id: self.next_id(),
3119 self.stmt(span, hir::StmtKind::Local(P(local)))
3122 fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
3123 self.block_all(expr.span, hir::HirVec::new(), Some(expr))
3129 stmts: hir::HirVec<hir::Stmt>,
3130 expr: Option<P<hir::Expr>>,
3135 hir_id: self.next_id(),
3136 rules: hir::DefaultBlock,
3138 targeted_by_break: false,
3142 /// Constructs a `true` or `false` literal pattern.
3143 fn pat_bool(&mut self, span: Span, val: bool) -> P<hir::Pat> {
3144 let expr = self.expr_bool(span, val);
3145 self.pat(span, hir::PatKind::Lit(P(expr)))
3148 fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3149 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], hir_vec![pat])
3152 fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3153 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], hir_vec![pat])
3156 fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3157 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], hir_vec![pat])
3160 fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
3161 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], hir_vec![])
3167 components: &[Symbol],
3168 subpats: hir::HirVec<P<hir::Pat>>,
3170 let path = self.std_path(span, components, None, true);
3171 let qpath = hir::QPath::Resolved(None, P(path));
3172 let pt = if subpats.is_empty() {
3173 hir::PatKind::Path(qpath)
3175 hir::PatKind::TupleStruct(qpath, subpats, None)
3180 fn pat_ident(&mut self, span: Span, ident: Ident) -> (P<hir::Pat>, hir::HirId) {
3181 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3184 fn pat_ident_binding_mode(
3188 bm: hir::BindingAnnotation,
3189 ) -> (P<hir::Pat>, hir::HirId) {
3190 let hir_id = self.next_id();
3195 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3202 fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
3203 self.pat(span, hir::PatKind::Wild)
3206 fn pat(&mut self, span: Span, kind: hir::PatKind) -> P<hir::Pat> {
3208 hir_id: self.next_id(),
3214 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3215 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3216 /// The path is also resolved according to `is_value`.
3220 components: &[Symbol],
3221 params: Option<P<hir::GenericArgs>>,
3224 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3225 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3227 let mut segments: Vec<_> = path.segments.iter().map(|segment| {
3228 let res = self.expect_full_res(segment.id);
3230 ident: segment.ident,
3231 hir_id: Some(self.lower_node_id(segment.id)),
3232 res: Some(self.lower_res(res)),
3237 segments.last_mut().unwrap().args = params;
3241 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3242 segments: segments.into(),
3246 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3247 let kind = match qpath {
3248 hir::QPath::Resolved(None, path) => {
3249 // Turn trait object paths into `TyKind::TraitObject` instead.
3251 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3252 let principal = hir::PolyTraitRef {
3253 bound_generic_params: hir::HirVec::new(),
3254 trait_ref: hir::TraitRef {
3261 // The original ID is taken by the `PolyTraitRef`,
3262 // so the `Ty` itself needs a different one.
3263 hir_id = self.next_id();
3264 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3266 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3269 _ => hir::TyKind::Path(qpath),
3279 /// Invoked to create the lifetime argument for a type `&T`
3280 /// with no explicit lifetime.
3281 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3282 match self.anonymous_lifetime_mode {
3283 // Intercept when we are in an impl header or async fn and introduce an in-band
3285 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3287 AnonymousLifetimeMode::CreateParameter => {
3288 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3290 hir_id: self.next_id(),
3292 name: hir::LifetimeName::Param(fresh_name),
3296 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3298 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3302 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3303 /// return a "error lifetime".
3304 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3305 let (id, msg, label) = match id {
3306 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3309 self.resolver.next_node_id(),
3310 "`&` without an explicit lifetime name cannot be used here",
3311 "explicit lifetime name needed here",
3315 let mut err = struct_span_err!(
3322 err.span_label(span, label);
3325 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3328 /// Invoked to create the lifetime argument(s) for a path like
3329 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3330 /// sorts of cases are deprecated. This may therefore report a warning or an
3331 /// error, depending on the mode.
3332 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3334 .map(|_| self.elided_path_lifetime(span))
3338 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3339 match self.anonymous_lifetime_mode {
3340 AnonymousLifetimeMode::CreateParameter => {
3341 // We should have emitted E0726 when processing this path above
3342 self.sess.delay_span_bug(
3344 "expected 'implicit elided lifetime not allowed' error",
3346 let id = self.resolver.next_node_id();
3347 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3349 // `PassThrough` is the normal case.
3350 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3351 // is unsuitable here, as these can occur from missing lifetime parameters in a
3352 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3353 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3354 // later, at which point a suitable error will be emitted.
3355 | AnonymousLifetimeMode::PassThrough
3356 | AnonymousLifetimeMode::ReportError => self.new_implicit_lifetime(span),
3360 /// Invoked to create the lifetime argument(s) for an elided trait object
3361 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3362 /// when the bound is written, even if it is written with `'_` like in
3363 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3364 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3365 match self.anonymous_lifetime_mode {
3366 // NB. We intentionally ignore the create-parameter mode here.
3367 // and instead "pass through" to resolve-lifetimes, which will apply
3368 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3369 // do not act like other elided lifetimes. In other words, given this:
3371 // impl Foo for Box<dyn Debug>
3373 // we do not introduce a fresh `'_` to serve as the bound, but instead
3374 // ultimately translate to the equivalent of:
3376 // impl Foo for Box<dyn Debug + 'static>
3378 // `resolve_lifetime` has the code to make that happen.
3379 AnonymousLifetimeMode::CreateParameter => {}
3381 AnonymousLifetimeMode::ReportError => {
3382 // ReportError applies to explicit use of `'_`.
3385 // This is the normal case.
3386 AnonymousLifetimeMode::PassThrough => {}
3389 let r = hir::Lifetime {
3390 hir_id: self.next_id(),
3392 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3394 debug!("elided_dyn_bound: r={:?}", r);
3398 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3400 hir_id: self.next_id(),
3402 name: hir::LifetimeName::Implicit,
3406 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3407 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3408 // call site which do not have a macro backtrace. See #61963.
3409 let is_macro_callsite = self.sess.source_map()
3410 .span_to_snippet(span)
3411 .map(|snippet| snippet.starts_with("#["))
3413 if !is_macro_callsite {
3414 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3415 builtin::BARE_TRAIT_OBJECTS,
3418 "trait objects without an explicit `dyn` are deprecated",
3419 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3425 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
3426 // Sorting by span ensures that we get things in order within a
3427 // file, and also puts the files in a sensible order.
3428 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3429 body_ids.sort_by_key(|b| bodies[b].value.span);
3433 /// Checks if the specified expression is a built-in range literal.
3434 /// (See: `LoweringContext::lower_expr()`).
3435 pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
3436 use hir::{Path, QPath, ExprKind, TyKind};
3438 // Returns whether the given path represents a (desugared) range,
3439 // either in std or core, i.e. has either a `::std::ops::Range` or
3440 // `::core::ops::Range` prefix.
3441 fn is_range_path(path: &Path) -> bool {
3442 let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.to_string()).collect();
3443 let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
3445 // "{{root}}" is the equivalent of `::` prefix in `Path`.
3446 if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
3447 (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
3453 // Check whether a span corresponding to a range expression is a
3454 // range literal, rather than an explicit struct or `new()` call.
3455 fn is_lit(sess: &Session, span: &Span) -> bool {
3456 let source_map = sess.source_map();
3457 let end_point = source_map.end_point(*span);
3459 if let Ok(end_string) = source_map.span_to_snippet(end_point) {
3460 !(end_string.ends_with("}") || end_string.ends_with(")"))
3467 // All built-in range literals but `..=` and `..` desugar to `Struct`s.
3468 ExprKind::Struct(ref qpath, _, _) => {
3469 if let QPath::Resolved(None, ref path) = **qpath {
3470 return is_range_path(&path) && is_lit(sess, &expr.span);
3474 // `..` desugars to its struct path.
3475 ExprKind::Path(QPath::Resolved(None, ref path)) => {
3476 return is_range_path(&path) && is_lit(sess, &expr.span);
3479 // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
3480 ExprKind::Call(ref func, _) => {
3481 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
3482 if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
3483 let new_call = segment.ident.name == sym::new;
3484 return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;