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::thin_vec::ThinVec;
57 use rustc_data_structures::sync::Lrc;
59 use std::collections::BTreeMap;
61 use smallvec::SmallVec;
64 use syntax::ptr::P as AstP;
67 use syntax::print::pprust;
68 use syntax::token::{self, Nonterminal, Token};
69 use syntax::tokenstream::{TokenStream, TokenTree};
70 use syntax::sess::ParseSess;
71 use syntax::source_map::{respan, ExpnData, ExpnKind, DesugaringKind, Spanned};
72 use syntax::symbol::{kw, sym, Symbol};
73 use syntax::visit::{self, Visitor};
74 use syntax_pos::hygiene::ExpnId;
77 use rustc_error_codes::*;
79 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
81 pub struct LoweringContext<'a> {
82 crate_root: Option<Symbol>,
84 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
87 resolver: &'a mut dyn Resolver,
89 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
90 /// if we don't have this function pointer. To avoid that dependency so that
91 /// librustc is independent of the parser, we use dynamic dispatch here.
92 nt_to_tokenstream: NtToTokenstream,
94 /// The items being lowered are collected here.
95 items: BTreeMap<hir::HirId, hir::Item>,
97 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
98 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
99 bodies: BTreeMap<hir::BodyId, hir::Body>,
100 exported_macros: Vec<hir::MacroDef>,
101 non_exported_macro_attrs: Vec<ast::Attribute>,
103 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
105 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
107 generator_kind: Option<hir::GeneratorKind>,
109 /// Used to get the current `fn`'s def span to point to when using `await`
110 /// outside of an `async fn`.
111 current_item: Option<Span>,
113 catch_scopes: Vec<NodeId>,
114 loop_scopes: Vec<NodeId>,
115 is_in_loop_condition: bool,
116 is_in_trait_impl: bool,
117 is_in_dyn_type: bool,
119 /// What to do when we encounter either an "anonymous lifetime
120 /// reference". The term "anonymous" is meant to encompass both
121 /// `'_` lifetimes as well as fully elided cases where nothing is
122 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
123 anonymous_lifetime_mode: AnonymousLifetimeMode,
125 /// Used to create lifetime definitions from in-band lifetime usages.
126 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
127 /// When a named lifetime is encountered in a function or impl header and
128 /// has not been defined
129 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
130 /// to this list. The results of this list are then added to the list of
131 /// lifetime definitions in the corresponding impl or function generics.
132 lifetimes_to_define: Vec<(Span, ParamName)>,
134 /// `true` if in-band lifetimes are being collected. This is used to
135 /// indicate whether or not we're in a place where new lifetimes will result
136 /// in in-band lifetime definitions, such a function or an impl header,
137 /// including implicit lifetimes from `impl_header_lifetime_elision`.
138 is_collecting_in_band_lifetimes: bool,
140 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
141 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
142 /// against this list to see if it is already in-scope, or if a definition
143 /// needs to be created for it.
145 /// We always store a `modern()` version of the param-name in this
147 in_scope_lifetimes: Vec<ParamName>,
149 current_module: hir::HirId,
151 type_def_lifetime_params: DefIdMap<usize>,
153 current_hir_id_owner: Vec<(DefIndex, u32)>,
154 item_local_id_counters: NodeMap<u32>,
155 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
157 allow_try_trait: Option<Lrc<[Symbol]>>,
158 allow_gen_future: Option<Lrc<[Symbol]>>,
162 fn cstore(&self) -> &dyn CrateStore;
164 /// Obtains resolution for a `NodeId` with a single resolution.
165 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
167 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
168 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
170 /// Obtains resolution for a label with the given `NodeId`.
171 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
173 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
174 /// This should only return `None` during testing.
175 fn definitions(&mut self) -> &mut Definitions;
177 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
178 /// resolves it based on `is_value`.
182 crate_root: Option<Symbol>,
183 components: &[Symbol],
185 ) -> (ast::Path, Res<NodeId>);
187 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
189 fn next_node_id(&mut self) -> NodeId;
192 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
194 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
195 /// and if so, what meaning it has.
197 enum ImplTraitContext<'a> {
198 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
199 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
200 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
202 /// Newly generated parameters should be inserted into the given `Vec`.
203 Universal(&'a mut Vec<hir::GenericParam>),
205 /// Treat `impl Trait` as shorthand for a new opaque type.
206 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
207 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
209 /// We optionally store a `DefId` for the parent item here so we can look up necessary
210 /// information later. It is `None` when no information about the context should be stored
211 /// (e.g., for consts and statics).
212 OpaqueTy(Option<DefId> /* fn def-ID */),
214 /// `impl Trait` is not accepted in this position.
215 Disallowed(ImplTraitPosition),
218 /// Position in which `impl Trait` is disallowed.
219 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
220 enum ImplTraitPosition {
221 /// Disallowed in `let` / `const` / `static` bindings.
224 /// All other posiitons.
228 impl<'a> ImplTraitContext<'a> {
230 fn disallowed() -> Self {
231 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
234 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
235 use self::ImplTraitContext::*;
237 Universal(params) => Universal(params),
238 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
239 Disallowed(pos) => Disallowed(*pos),
246 dep_graph: &DepGraph,
248 resolver: &mut dyn Resolver,
249 nt_to_tokenstream: NtToTokenstream,
251 // We're constructing the HIR here; we don't care what we will
252 // read, since we haven't even constructed the *input* to
254 dep_graph.assert_ignored();
256 let _prof_timer = sess.prof.generic_activity("hir_lowering");
259 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
263 items: BTreeMap::new(),
264 trait_items: BTreeMap::new(),
265 impl_items: BTreeMap::new(),
266 bodies: BTreeMap::new(),
267 trait_impls: BTreeMap::new(),
268 modules: BTreeMap::new(),
269 exported_macros: Vec::new(),
270 non_exported_macro_attrs: Vec::new(),
271 catch_scopes: Vec::new(),
272 loop_scopes: Vec::new(),
273 is_in_loop_condition: false,
274 is_in_trait_impl: false,
275 is_in_dyn_type: false,
276 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
277 type_def_lifetime_params: Default::default(),
278 current_module: hir::CRATE_HIR_ID,
279 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
280 item_local_id_counters: Default::default(),
281 node_id_to_hir_id: IndexVec::new(),
282 generator_kind: None,
284 lifetimes_to_define: Vec::new(),
285 is_collecting_in_band_lifetimes: false,
286 in_scope_lifetimes: Vec::new(),
287 allow_try_trait: Some([sym::try_trait][..].into()),
288 allow_gen_future: Some([sym::gen_future][..].into()),
292 #[derive(Copy, Clone, PartialEq)]
294 /// Any path in a type context.
296 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
298 /// The `module::Type` in `module::Type::method` in an expression.
302 enum ParenthesizedGenericArgs {
307 /// What to do when we encounter an **anonymous** lifetime
308 /// reference. Anonymous lifetime references come in two flavors. You
309 /// have implicit, or fully elided, references to lifetimes, like the
310 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
311 /// or `Ref<'_, T>`. These often behave the same, but not always:
313 /// - certain usages of implicit references are deprecated, like
314 /// `Ref<T>`, and we sometimes just give hard errors in those cases
316 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
317 /// the same as `Box<dyn Foo + '_>`.
319 /// We describe the effects of the various modes in terms of three cases:
321 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
322 /// of a `&` (e.g., the missing lifetime in something like `&T`)
323 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
324 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
325 /// elided bounds follow special rules. Note that this only covers
326 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
327 /// '_>` is a case of "modern" elision.
328 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
329 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
330 /// non-deprecated equivalent.
332 /// Currently, the handling of lifetime elision is somewhat spread out
333 /// between HIR lowering and -- as described below -- the
334 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
335 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
336 /// everything into HIR lowering.
337 #[derive(Copy, Clone, Debug)]
338 enum AnonymousLifetimeMode {
339 /// For **Modern** cases, create a new anonymous region parameter
340 /// and reference that.
342 /// For **Dyn Bound** cases, pass responsibility to
343 /// `resolve_lifetime` code.
345 /// For **Deprecated** cases, report an error.
348 /// Give a hard error when either `&` or `'_` is written. Used to
349 /// rule out things like `where T: Foo<'_>`. Does not imply an
350 /// error on default object bounds (e.g., `Box<dyn Foo>`).
353 /// Pass responsibility to `resolve_lifetime` code for all cases.
357 struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[NodeId; 1]> }
359 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
360 fn visit_ty(&mut self, ty: &'a Ty) {
366 TyKind::ImplTrait(id, _) => self.ids.push(id),
369 visit::walk_ty(self, ty);
372 fn visit_path_segment(
375 path_segment: &'v PathSegment,
377 if let Some(ref p) = path_segment.args {
378 if let GenericArgs::Parenthesized(_) = **p {
382 visit::walk_path_segment(self, path_span, path_segment)
386 impl<'a> LoweringContext<'a> {
387 fn lower_crate(mut self, c: &Crate) -> hir::Crate {
388 /// Full-crate AST visitor that inserts into a fresh
389 /// `LoweringContext` any information that may be
390 /// needed from arbitrary locations in the crate,
391 /// e.g., the number of lifetime generic parameters
392 /// declared for every type and trait definition.
393 struct MiscCollector<'tcx, 'interner> {
394 lctx: &'tcx mut LoweringContext<'interner>,
395 hir_id_owner: Option<NodeId>,
398 impl MiscCollector<'_, '_> {
399 fn allocate_use_tree_hir_id_counters(
405 UseTreeKind::Simple(_, id1, id2) => {
406 for &id in &[id1, id2] {
407 self.lctx.resolver.definitions().create_def_with_parent(
414 self.lctx.allocate_hir_id_counter(id);
417 UseTreeKind::Glob => (),
418 UseTreeKind::Nested(ref trees) => {
419 for &(ref use_tree, id) in trees {
420 let hir_id = self.lctx.allocate_hir_id_counter(id);
421 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
427 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
429 F: FnOnce(&mut Self) -> T,
431 let old = mem::replace(&mut self.hir_id_owner, owner);
433 self.hir_id_owner = old;
438 impl<'tcx, 'interner> Visitor<'tcx> for MiscCollector<'tcx, 'interner> {
439 fn visit_pat(&mut self, p: &'tcx Pat) {
440 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
441 // Doesn't generate a HIR node
442 } else if let Some(owner) = self.hir_id_owner {
443 self.lctx.lower_node_id_with_owner(p.id, owner);
446 visit::walk_pat(self, p)
449 fn visit_item(&mut self, item: &'tcx Item) {
450 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
453 ItemKind::Struct(_, ref generics)
454 | ItemKind::Union(_, ref generics)
455 | ItemKind::Enum(_, ref generics)
456 | ItemKind::TyAlias(_, ref generics)
457 | ItemKind::Trait(_, _, ref generics, ..) => {
458 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
462 .filter(|param| match param.kind {
463 ast::GenericParamKind::Lifetime { .. } => true,
467 self.lctx.type_def_lifetime_params.insert(def_id, count);
469 ItemKind::Use(ref use_tree) => {
470 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
475 self.with_hir_id_owner(Some(item.id), |this| {
476 visit::walk_item(this, item);
480 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
481 self.lctx.allocate_hir_id_counter(item.id);
484 AssocItemKind::Fn(_, None) => {
485 // Ignore patterns in trait methods without bodies
486 self.with_hir_id_owner(None, |this| {
487 visit::walk_trait_item(this, item)
490 _ => self.with_hir_id_owner(Some(item.id), |this| {
491 visit::walk_trait_item(this, item);
496 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
497 self.lctx.allocate_hir_id_counter(item.id);
498 self.with_hir_id_owner(Some(item.id), |this| {
499 visit::walk_impl_item(this, item);
503 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
504 // Ignore patterns in foreign items
505 self.with_hir_id_owner(None, |this| {
506 visit::walk_foreign_item(this, i)
510 fn visit_ty(&mut self, t: &'tcx Ty) {
512 // Mirrors the case in visit::walk_ty
513 TyKind::BareFn(ref f) => {
519 // Mirrors visit::walk_fn_decl
520 for parameter in &f.decl.inputs {
521 // We don't lower the ids of argument patterns
522 self.with_hir_id_owner(None, |this| {
523 this.visit_pat(¶meter.pat);
525 self.visit_ty(¶meter.ty)
527 self.visit_fn_ret_ty(&f.decl.output)
529 _ => visit::walk_ty(self, t),
534 self.lower_node_id(CRATE_NODE_ID);
535 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
537 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
538 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
540 let module = self.lower_mod(&c.module);
541 let attrs = self.lower_attrs(&c.attrs);
542 let body_ids = body_ids(&self.bodies);
546 .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
552 exported_macros: hir::HirVec::from(self.exported_macros),
553 non_exported_macro_attrs: hir::HirVec::from(self.non_exported_macro_attrs),
555 trait_items: self.trait_items,
556 impl_items: self.impl_items,
559 trait_impls: self.trait_impls,
560 modules: self.modules,
564 fn insert_item(&mut self, item: hir::Item) {
565 let id = item.hir_id;
566 // FIXME: Use `debug_asset-rt`.
567 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
568 self.items.insert(id, item);
569 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
572 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
573 // Set up the counter if needed.
574 self.item_local_id_counters.entry(owner).or_insert(0);
575 // Always allocate the first `HirId` for the owner itself.
576 let lowered = self.lower_node_id_with_owner(owner, owner);
577 debug_assert_eq!(lowered.local_id.as_u32(), 0);
581 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
583 F: FnOnce(&mut Self) -> hir::HirId,
585 if ast_node_id == DUMMY_NODE_ID {
586 return hir::DUMMY_HIR_ID;
589 let min_size = ast_node_id.as_usize() + 1;
591 if min_size > self.node_id_to_hir_id.len() {
592 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
595 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
597 if existing_hir_id == hir::DUMMY_HIR_ID {
598 // Generate a new `HirId`.
599 let hir_id = alloc_hir_id(self);
600 self.node_id_to_hir_id[ast_node_id] = hir_id;
608 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
610 F: FnOnce(&mut Self) -> T,
612 let counter = self.item_local_id_counters
613 .insert(owner, HIR_ID_COUNTER_LOCKED)
614 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
615 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
616 self.current_hir_id_owner.push((def_index, counter));
618 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
620 debug_assert!(def_index == new_def_index);
621 debug_assert!(new_counter >= counter);
623 let prev = self.item_local_id_counters
624 .insert(owner, new_counter)
626 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
630 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
631 /// the `LoweringContext`'s `NodeId => HirId` map.
632 /// Take care not to call this method if the resulting `HirId` is then not
633 /// actually used in the HIR, as that would trigger an assertion in the
634 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
635 /// properly. Calling the method twice with the same `NodeId` is fine though.
636 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
637 self.lower_node_id_generic(ast_node_id, |this| {
638 let &mut (def_index, ref mut local_id_counter) =
639 this.current_hir_id_owner.last_mut().unwrap();
640 let local_id = *local_id_counter;
641 *local_id_counter += 1;
644 local_id: hir::ItemLocalId::from_u32(local_id),
649 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
650 self.lower_node_id_generic(ast_node_id, |this| {
651 let local_id_counter = this
652 .item_local_id_counters
654 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
655 let local_id = *local_id_counter;
657 // We want to be sure not to modify the counter in the map while it
658 // is also on the stack. Otherwise we'll get lost updates when writing
659 // back from the stack to the map.
660 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
662 *local_id_counter += 1;
666 .opt_def_index(owner)
667 .expect("you forgot to call `create_def_with_parent` or are lowering node-IDs \
668 that do not belong to the current owner");
672 local_id: hir::ItemLocalId::from_u32(local_id),
677 fn next_id(&mut self) -> hir::HirId {
678 let node_id = self.resolver.next_node_id();
679 self.lower_node_id(node_id)
682 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
684 self.lower_node_id_generic(id, |_| {
685 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
690 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
691 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
692 if pr.unresolved_segments() != 0 {
693 bug!("path not fully resolved: {:?}", pr);
699 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
700 self.resolver.get_import_res(id).present_items()
703 fn diagnostic(&self) -> &errors::Handler {
704 self.sess.diagnostic()
707 /// Reuses the span but adds information like the kind of the desugaring and features that are
708 /// allowed inside this span.
709 fn mark_span_with_reason(
711 reason: DesugaringKind,
713 allow_internal_unstable: Option<Lrc<[Symbol]>>,
715 span.fresh_expansion(ExpnData {
716 allow_internal_unstable,
717 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
721 fn with_anonymous_lifetime_mode<R>(
723 anonymous_lifetime_mode: AnonymousLifetimeMode,
724 op: impl FnOnce(&mut Self) -> R,
727 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
728 anonymous_lifetime_mode,
730 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
731 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
732 let result = op(self);
733 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
734 debug!("with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
735 old_anonymous_lifetime_mode);
739 /// Creates a new `hir::GenericParam` for every new lifetime and
740 /// type parameter encountered while evaluating `f`. Definitions
741 /// are created with the parent provided. If no `parent_id` is
742 /// provided, no definitions will be returned.
744 /// Presuming that in-band lifetimes are enabled, then
745 /// `self.anonymous_lifetime_mode` will be updated to match the
746 /// parameter while `f` is running (and restored afterwards).
747 fn collect_in_band_defs<T, F>(
750 anonymous_lifetime_mode: AnonymousLifetimeMode,
752 ) -> (Vec<hir::GenericParam>, T)
754 F: FnOnce(&mut LoweringContext<'_>) -> (Vec<hir::GenericParam>, T),
756 assert!(!self.is_collecting_in_band_lifetimes);
757 assert!(self.lifetimes_to_define.is_empty());
758 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
760 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
761 self.is_collecting_in_band_lifetimes = true;
763 let (in_band_ty_params, res) = f(self);
765 self.is_collecting_in_band_lifetimes = false;
766 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
768 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
770 let params = lifetimes_to_define
772 .map(|(span, hir_name)| self.lifetime_to_generic_param(
773 span, hir_name, parent_id.index,
775 .chain(in_band_ty_params.into_iter())
781 /// Converts a lifetime into a new generic parameter.
782 fn lifetime_to_generic_param(
786 parent_index: DefIndex,
787 ) -> hir::GenericParam {
788 let node_id = self.resolver.next_node_id();
790 // Get the name we'll use to make the def-path. Note
791 // that collisions are ok here and this shouldn't
792 // really show up for end-user.
793 let (str_name, kind) = match hir_name {
794 ParamName::Plain(ident) => (
796 hir::LifetimeParamKind::InBand,
798 ParamName::Fresh(_) => (
799 kw::UnderscoreLifetime,
800 hir::LifetimeParamKind::Elided,
802 ParamName::Error => (
803 kw::UnderscoreLifetime,
804 hir::LifetimeParamKind::Error,
808 // Add a definition for the in-band lifetime def.
809 self.resolver.definitions().create_def_with_parent(
812 DefPathData::LifetimeNs(str_name),
818 hir_id: self.lower_node_id(node_id),
823 pure_wrt_drop: false,
824 kind: hir::GenericParamKind::Lifetime { kind }
828 /// When there is a reference to some lifetime `'a`, and in-band
829 /// lifetimes are enabled, then we want to push that lifetime into
830 /// the vector of names to define later. In that case, it will get
831 /// added to the appropriate generics.
832 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
833 if !self.is_collecting_in_band_lifetimes {
837 if !self.sess.features_untracked().in_band_lifetimes {
841 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
845 let hir_name = ParamName::Plain(ident);
847 if self.lifetimes_to_define.iter()
848 .any(|(_, lt_name)| lt_name.modern() == hir_name.modern()) {
852 self.lifetimes_to_define.push((ident.span, hir_name));
855 /// When we have either an elided or `'_` lifetime in an impl
856 /// header, we convert it to an in-band lifetime.
857 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
858 assert!(self.is_collecting_in_band_lifetimes);
859 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
860 let hir_name = ParamName::Fresh(index);
861 self.lifetimes_to_define.push((span, hir_name));
865 // Evaluates `f` with the lifetimes in `params` in-scope.
866 // This is used to track which lifetimes have already been defined, and
867 // which are new in-band lifetimes that need to have a definition created
869 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
871 F: FnOnce(&mut LoweringContext<'_>) -> T,
873 let old_len = self.in_scope_lifetimes.len();
874 let lt_def_names = params.iter().filter_map(|param| match param.kind {
875 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
878 self.in_scope_lifetimes.extend(lt_def_names);
882 self.in_scope_lifetimes.truncate(old_len);
886 /// Appends in-band lifetime defs and argument-position `impl
887 /// Trait` defs to the existing set of generics.
889 /// Presuming that in-band lifetimes are enabled, then
890 /// `self.anonymous_lifetime_mode` will be updated to match the
891 /// parameter while `f` is running (and restored afterwards).
892 fn add_in_band_defs<F, T>(
896 anonymous_lifetime_mode: AnonymousLifetimeMode,
898 ) -> (hir::Generics, T)
900 F: FnOnce(&mut LoweringContext<'_>, &mut Vec<hir::GenericParam>) -> T,
902 let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
905 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
906 let mut params = Vec::new();
907 // Note: it is necessary to lower generics *before* calling `f`.
908 // When lowering `async fn`, there's a final step when lowering
909 // the return type that assumes that all in-scope lifetimes have
910 // already been added to either `in_scope_lifetimes` or
911 // `lifetimes_to_define`. If we swapped the order of these two,
912 // in-band-lifetimes introduced by generics or where-clauses
913 // wouldn't have been added yet.
914 let generics = this.lower_generics(
916 ImplTraitContext::Universal(&mut params),
918 let res = f(this, &mut params);
919 (params, (generics, res))
924 let mut lowered_params: Vec<_> = lowered_generics
930 // FIXME(const_generics): the compiler doesn't always cope with
931 // unsorted generic parameters at the moment, so we make sure
932 // that they're ordered correctly here for now. (When we chain
933 // the `in_band_defs`, we might make the order unsorted.)
934 lowered_params.sort_by_key(|param| {
936 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
937 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
938 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
942 lowered_generics.params = lowered_params.into();
944 (lowered_generics, res)
947 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
949 F: FnOnce(&mut LoweringContext<'_>) -> T,
951 let was_in_dyn_type = self.is_in_dyn_type;
952 self.is_in_dyn_type = in_scope;
954 let result = f(self);
956 self.is_in_dyn_type = was_in_dyn_type;
961 fn with_new_scopes<T, F>(&mut self, f: F) -> T
963 F: FnOnce(&mut LoweringContext<'_>) -> T,
965 let was_in_loop_condition = self.is_in_loop_condition;
966 self.is_in_loop_condition = false;
968 let catch_scopes = mem::take(&mut self.catch_scopes);
969 let loop_scopes = mem::take(&mut self.loop_scopes);
971 self.catch_scopes = catch_scopes;
972 self.loop_scopes = loop_scopes;
974 self.is_in_loop_condition = was_in_loop_condition;
979 fn def_key(&mut self, id: DefId) -> DefKey {
981 self.resolver.definitions().def_key(id.index)
983 self.resolver.cstore().def_key(id)
987 fn lower_attrs_extendable(&mut self, attrs: &[Attribute]) -> Vec<Attribute> {
990 .map(|a| self.lower_attr(a))
994 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
995 self.lower_attrs_extendable(attrs).into()
998 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
999 // Note that we explicitly do not walk the path. Since we don't really
1000 // lower attributes (we use the AST version) there is nowhere to keep
1001 // the `HirId`s. We don't actually need HIR version of attributes anyway.
1002 let kind = match attr.kind {
1003 AttrKind::Normal(ref item) => {
1004 AttrKind::Normal(AttrItem {
1005 path: item.path.clone(),
1006 args: self.lower_mac_args(&item.args),
1009 AttrKind::DocComment(comment) => AttrKind::DocComment(comment)
1020 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
1022 MacArgs::Empty => MacArgs::Empty,
1023 MacArgs::Delimited(dspan, delim, ref tokens) =>
1024 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone())),
1025 MacArgs::Eq(eq_span, ref tokens) =>
1026 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone())),
1030 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
1033 .flat_map(|tree| self.lower_token_tree(tree).into_trees())
1037 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
1039 TokenTree::Token(token) => self.lower_token(token),
1040 TokenTree::Delimited(span, delim, tts) => TokenTree::Delimited(
1043 self.lower_token_stream(tts),
1048 fn lower_token(&mut self, token: Token) -> TokenStream {
1050 token::Interpolated(nt) => {
1051 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1052 self.lower_token_stream(tts)
1054 _ => TokenTree::Token(token).into(),
1058 /// Given an associated type constraint like one of these:
1061 /// T: Iterator<Item: Debug>
1063 /// T: Iterator<Item = Debug>
1067 /// returns a `hir::TypeBinding` representing `Item`.
1068 fn lower_assoc_ty_constraint(
1070 constraint: &AssocTyConstraint,
1071 itctx: ImplTraitContext<'_>,
1072 ) -> hir::TypeBinding {
1073 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1075 let kind = match constraint.kind {
1076 AssocTyConstraintKind::Equality { ref ty } => hir::TypeBindingKind::Equality {
1077 ty: self.lower_ty(ty, itctx)
1079 AssocTyConstraintKind::Bound { ref bounds } => {
1080 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1081 let (desugar_to_impl_trait, itctx) = match itctx {
1082 // We are in the return position:
1084 // fn foo() -> impl Iterator<Item: Debug>
1088 // fn foo() -> impl Iterator<Item = impl Debug>
1089 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1091 // We are in the argument position, but within a dyn type:
1093 // fn foo(x: dyn Iterator<Item: Debug>)
1097 // fn foo(x: dyn Iterator<Item = impl Debug>)
1098 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1100 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1101 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1102 // "impl trait context" to permit `impl Debug` in this position (it desugars
1103 // then to an opaque type).
1105 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1106 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type =>
1107 (true, ImplTraitContext::OpaqueTy(None)),
1109 // We are in the parameter position, but not within a dyn type:
1111 // fn foo(x: impl Iterator<Item: Debug>)
1113 // so we leave it as is and this gets expanded in astconv to a bound like
1114 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1116 _ => (false, itctx),
1119 if desugar_to_impl_trait {
1120 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1121 // constructing the HIR for `impl bounds...` and then lowering that.
1123 let impl_trait_node_id = self.resolver.next_node_id();
1124 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1125 self.resolver.definitions().create_def_with_parent(
1128 DefPathData::ImplTrait,
1133 self.with_dyn_type_scope(false, |this| {
1134 let node_id = this.resolver.next_node_id();
1135 let ty = this.lower_ty(
1138 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1139 span: constraint.span,
1144 hir::TypeBindingKind::Equality {
1149 // Desugar `AssocTy: Bounds` into a type binding where the
1150 // later desugars into a trait predicate.
1151 let bounds = self.lower_param_bounds(bounds, itctx);
1153 hir::TypeBindingKind::Constraint {
1161 hir_id: self.lower_node_id(constraint.id),
1162 ident: constraint.ident,
1164 span: constraint.span,
1168 fn lower_generic_arg(
1170 arg: &ast::GenericArg,
1171 itctx: ImplTraitContext<'_>
1172 ) -> hir::GenericArg {
1174 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1175 ast::GenericArg::Type(ty) => {
1176 // We parse const arguments as path types as we cannot distiguish them durring
1177 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1178 // type and value namespaces. If we resolved the path in the value namespace, we
1179 // transform it into a generic const argument.
1180 if let TyKind::Path(ref qself, ref path) = ty.kind {
1181 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1182 let res = partial_res.base_res();
1183 if !res.matches_ns(Namespace::TypeNS) {
1185 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1189 // Construct a AnonConst where the expr is the "ty"'s path.
1191 let parent_def_index =
1192 self.current_hir_id_owner.last().unwrap().0;
1193 let node_id = self.resolver.next_node_id();
1195 // Add a definition for the in-band const def.
1196 self.resolver.definitions().create_def_with_parent(
1199 DefPathData::AnonConst,
1204 let path_expr = Expr {
1206 kind: ExprKind::Path(qself.clone(), path.clone()),
1208 attrs: ThinVec::new(),
1211 let ct = self.with_new_scopes(|this| {
1213 hir_id: this.lower_node_id(node_id),
1214 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1217 return GenericArg::Const(ConstArg {
1224 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1226 ast::GenericArg::Const(ct) => {
1227 GenericArg::Const(ConstArg {
1228 value: self.lower_anon_const(&ct),
1229 span: ct.value.span,
1235 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1236 P(self.lower_ty_direct(t, itctx))
1242 qself: &Option<QSelf>,
1244 param_mode: ParamMode,
1245 itctx: ImplTraitContext<'_>
1247 let id = self.lower_node_id(t.id);
1248 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1249 let ty = self.ty_path(id, t.span, qpath);
1250 if let hir::TyKind::TraitObject(..) = ty.kind {
1251 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1256 fn ty(&mut self, span: Span, kind: hir::TyKind) -> hir::Ty {
1257 hir::Ty { hir_id: self.next_id(), kind, span }
1260 fn ty_tup(&mut self, span: Span, tys: HirVec<hir::Ty>) -> hir::Ty {
1261 self.ty(span, hir::TyKind::Tup(tys))
1264 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1265 let kind = match t.kind {
1266 TyKind::Infer => hir::TyKind::Infer,
1267 TyKind::Err => hir::TyKind::Err,
1268 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1269 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1270 TyKind::Rptr(ref region, ref mt) => {
1271 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1272 let lifetime = match *region {
1273 Some(ref lt) => self.lower_lifetime(lt),
1274 None => self.elided_ref_lifetime(span),
1276 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1278 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1281 this.with_anonymous_lifetime_mode(
1282 AnonymousLifetimeMode::PassThrough,
1284 hir::TyKind::BareFn(P(hir::BareFnTy {
1285 generic_params: this.lower_generic_params(
1287 &NodeMap::default(),
1288 ImplTraitContext::disallowed(),
1290 unsafety: f.unsafety,
1291 abi: this.lower_extern(f.ext),
1292 decl: this.lower_fn_decl(&f.decl, None, false, None),
1293 param_names: this.lower_fn_params_to_names(&f.decl),
1299 TyKind::Never => hir::TyKind::Never,
1300 TyKind::Tup(ref tys) => {
1301 hir::TyKind::Tup(tys.iter().map(|ty| {
1302 self.lower_ty_direct(ty, itctx.reborrow())
1305 TyKind::Paren(ref ty) => {
1306 return self.lower_ty_direct(ty, itctx);
1308 TyKind::Path(ref qself, ref path) => {
1309 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1311 TyKind::ImplicitSelf => {
1312 let res = self.expect_full_res(t.id);
1313 let res = self.lower_res(res);
1314 hir::TyKind::Path(hir::QPath::Resolved(
1318 segments: hir_vec![hir::PathSegment::from_ident(
1319 Ident::with_dummy_span(kw::SelfUpper)
1325 TyKind::Array(ref ty, ref length) => {
1326 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1328 TyKind::Typeof(ref expr) => {
1329 hir::TyKind::Typeof(self.lower_anon_const(expr))
1331 TyKind::TraitObject(ref bounds, kind) => {
1332 let mut lifetime_bound = None;
1333 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1336 .filter_map(|bound| match *bound {
1337 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1338 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1340 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1341 GenericBound::Outlives(ref lifetime) => {
1342 if lifetime_bound.is_none() {
1343 lifetime_bound = Some(this.lower_lifetime(lifetime));
1349 let lifetime_bound =
1350 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1351 (bounds, lifetime_bound)
1353 if kind != TraitObjectSyntax::Dyn {
1354 self.maybe_lint_bare_trait(t.span, t.id, false);
1356 hir::TyKind::TraitObject(bounds, lifetime_bound)
1358 TyKind::ImplTrait(def_node_id, ref bounds) => {
1361 ImplTraitContext::OpaqueTy(fn_def_id) => {
1362 self.lower_opaque_impl_trait(
1363 span, fn_def_id, def_node_id,
1364 |this| this.lower_param_bounds(bounds, itctx),
1367 ImplTraitContext::Universal(in_band_ty_params) => {
1368 // Add a definition for the in-band `Param`.
1369 let def_index = self
1372 .opt_def_index(def_node_id)
1375 let hir_bounds = self.lower_param_bounds(
1377 ImplTraitContext::Universal(in_band_ty_params),
1379 // Set the name to `impl Bound1 + Bound2`.
1380 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1381 in_band_ty_params.push(hir::GenericParam {
1382 hir_id: self.lower_node_id(def_node_id),
1383 name: ParamName::Plain(ident),
1384 pure_wrt_drop: false,
1388 kind: hir::GenericParamKind::Type {
1390 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1394 hir::TyKind::Path(hir::QPath::Resolved(
1398 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1399 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1403 ImplTraitContext::Disallowed(pos) => {
1404 let allowed_in = if self.sess.features_untracked()
1405 .impl_trait_in_bindings {
1406 "bindings or function and inherent method return types"
1408 "function and inherent method return types"
1410 let mut err = struct_span_err!(
1414 "`impl Trait` not allowed outside of {}",
1417 if pos == ImplTraitPosition::Binding &&
1418 nightly_options::is_nightly_build() {
1420 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1421 attributes to enable");
1428 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1429 TyKind::CVarArgs => {
1430 self.sess.delay_span_bug(
1432 "`TyKind::CVarArgs` should have been handled elsewhere",
1441 hir_id: self.lower_node_id(t.id),
1445 fn lower_opaque_impl_trait(
1448 fn_def_id: Option<DefId>,
1449 opaque_ty_node_id: NodeId,
1450 lower_bounds: impl FnOnce(&mut LoweringContext<'_>) -> hir::GenericBounds,
1453 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1459 // Make sure we know that some funky desugaring has been going on here.
1460 // This is a first: there is code in other places like for loop
1461 // desugaring that explicitly states that we don't want to track that.
1462 // Not tracking it makes lints in rustc and clippy very fragile, as
1463 // frequently opened issues show.
1464 let opaque_ty_span = self.mark_span_with_reason(
1465 DesugaringKind::OpaqueTy,
1470 let opaque_ty_def_index = self
1473 .opt_def_index(opaque_ty_node_id)
1476 self.allocate_hir_id_counter(opaque_ty_node_id);
1478 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1480 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1482 opaque_ty_def_index,
1487 "lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,
1491 "lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,
1494 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1495 let opaque_ty_item = hir::OpaqueTy {
1496 generics: hir::Generics {
1497 params: lifetime_defs,
1498 where_clause: hir::WhereClause {
1499 predicates: hir_vec![],
1505 impl_trait_fn: fn_def_id,
1506 origin: hir::OpaqueTyOrigin::FnReturn,
1509 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1510 let opaque_ty_id = lctx.generate_opaque_type(
1517 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1518 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1522 /// Registers a new opaque type with the proper `NodeId`s and
1523 /// returns the lowered node-ID for the opaque type.
1524 fn generate_opaque_type(
1526 opaque_ty_node_id: NodeId,
1527 opaque_ty_item: hir::OpaqueTy,
1529 opaque_ty_span: Span,
1531 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1532 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1533 // Generate an `type Foo = impl Trait;` declaration.
1534 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1535 let opaque_ty_item = hir::Item {
1536 hir_id: opaque_ty_id,
1537 ident: Ident::invalid(),
1538 attrs: Default::default(),
1539 kind: opaque_ty_item_kind,
1540 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1541 span: opaque_ty_span,
1544 // Insert the item into the global item list. This usually happens
1545 // automatically for all AST items. But this opaque type item
1546 // does not actually exist in the AST.
1547 self.insert_item(opaque_ty_item);
1551 fn lifetimes_from_impl_trait_bounds(
1553 opaque_ty_id: NodeId,
1554 parent_index: DefIndex,
1555 bounds: &hir::GenericBounds,
1556 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1558 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1559 parent_index={:?}, \
1561 opaque_ty_id, parent_index, bounds,
1564 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1565 // appear in the bounds, excluding lifetimes that are created within the bounds.
1566 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1567 struct ImplTraitLifetimeCollector<'r, 'a> {
1568 context: &'r mut LoweringContext<'a>,
1570 opaque_ty_id: NodeId,
1571 collect_elided_lifetimes: bool,
1572 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1573 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1574 output_lifetimes: Vec<hir::GenericArg>,
1575 output_lifetime_params: Vec<hir::GenericParam>,
1578 impl<'r, 'a, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1579 fn nested_visit_map<'this>(
1581 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1582 hir::intravisit::NestedVisitorMap::None
1585 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1586 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1587 if parameters.parenthesized {
1588 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1589 self.collect_elided_lifetimes = false;
1590 hir::intravisit::walk_generic_args(self, span, parameters);
1591 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1593 hir::intravisit::walk_generic_args(self, span, parameters);
1597 fn visit_ty(&mut self, t: &'v hir::Ty) {
1598 // Don't collect elided lifetimes used inside of `fn()` syntax.
1599 if let hir::TyKind::BareFn(_) = t.kind {
1600 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1601 self.collect_elided_lifetimes = false;
1603 // Record the "stack height" of `for<'a>` lifetime bindings
1604 // to be able to later fully undo their introduction.
1605 let old_len = self.currently_bound_lifetimes.len();
1606 hir::intravisit::walk_ty(self, t);
1607 self.currently_bound_lifetimes.truncate(old_len);
1609 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1611 hir::intravisit::walk_ty(self, t)
1615 fn visit_poly_trait_ref(
1617 trait_ref: &'v hir::PolyTraitRef,
1618 modifier: hir::TraitBoundModifier,
1620 // Record the "stack height" of `for<'a>` lifetime bindings
1621 // to be able to later fully undo their introduction.
1622 let old_len = self.currently_bound_lifetimes.len();
1623 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1624 self.currently_bound_lifetimes.truncate(old_len);
1627 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1628 // Record the introduction of 'a in `for<'a> ...`.
1629 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1630 // Introduce lifetimes one at a time so that we can handle
1631 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1632 let lt_name = hir::LifetimeName::Param(param.name);
1633 self.currently_bound_lifetimes.push(lt_name);
1636 hir::intravisit::walk_generic_param(self, param);
1639 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1640 let name = match lifetime.name {
1641 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1642 if self.collect_elided_lifetimes {
1643 // Use `'_` for both implicit and underscore lifetimes in
1644 // `type Foo<'_> = impl SomeTrait<'_>;`.
1645 hir::LifetimeName::Underscore
1650 hir::LifetimeName::Param(_) => lifetime.name,
1652 // Refers to some other lifetime that is "in
1653 // scope" within the type.
1654 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1656 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1659 if !self.currently_bound_lifetimes.contains(&name)
1660 && !self.already_defined_lifetimes.contains(&name) {
1661 self.already_defined_lifetimes.insert(name);
1663 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1664 hir_id: self.context.next_id(),
1665 span: lifetime.span,
1669 let def_node_id = self.context.resolver.next_node_id();
1671 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1672 self.context.resolver.definitions().create_def_with_parent(
1675 DefPathData::LifetimeNs(name.ident().name),
1679 let (name, kind) = match name {
1680 hir::LifetimeName::Underscore => (
1681 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1682 hir::LifetimeParamKind::Elided,
1684 hir::LifetimeName::Param(param_name) => (
1686 hir::LifetimeParamKind::Explicit,
1688 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1691 self.output_lifetime_params.push(hir::GenericParam {
1694 span: lifetime.span,
1695 pure_wrt_drop: false,
1698 kind: hir::GenericParamKind::Lifetime { kind }
1704 let mut lifetime_collector = ImplTraitLifetimeCollector {
1706 parent: parent_index,
1708 collect_elided_lifetimes: true,
1709 currently_bound_lifetimes: Vec::new(),
1710 already_defined_lifetimes: FxHashSet::default(),
1711 output_lifetimes: Vec::new(),
1712 output_lifetime_params: Vec::new(),
1715 for bound in bounds {
1716 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1720 lifetime_collector.output_lifetimes.into(),
1721 lifetime_collector.output_lifetime_params.into(),
1728 qself: &Option<QSelf>,
1730 param_mode: ParamMode,
1731 mut itctx: ImplTraitContext<'_>,
1733 let qself_position = qself.as_ref().map(|q| q.position);
1734 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1736 let partial_res = self.resolver
1737 .get_partial_res(id)
1738 .unwrap_or_else(|| PartialRes::new(Res::Err));
1740 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1741 let path = P(hir::Path {
1742 res: self.lower_res(partial_res.base_res()),
1743 segments: p.segments[..proj_start]
1746 .map(|(i, segment)| {
1747 let param_mode = match (qself_position, param_mode) {
1748 (Some(j), ParamMode::Optional) if i < j => {
1749 // This segment is part of the trait path in a
1750 // qualified path - one of `a`, `b` or `Trait`
1751 // in `<X as a::b::Trait>::T::U::method`.
1757 // Figure out if this is a type/trait segment,
1758 // which may need lifetime elision performed.
1759 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1760 krate: def_id.krate,
1761 index: this.def_key(def_id).parent.expect("missing parent"),
1763 let type_def_id = match partial_res.base_res() {
1764 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1765 Some(parent_def_id(self, def_id))
1767 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1768 Some(parent_def_id(self, def_id))
1770 Res::Def(DefKind::Struct, def_id)
1771 | Res::Def(DefKind::Union, def_id)
1772 | Res::Def(DefKind::Enum, def_id)
1773 | Res::Def(DefKind::TyAlias, def_id)
1774 | Res::Def(DefKind::Trait, def_id) if i + 1 == proj_start =>
1780 let parenthesized_generic_args = match partial_res.base_res() {
1781 // `a::b::Trait(Args)`
1782 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1783 ParenthesizedGenericArgs::Ok
1785 // `a::b::Trait(Args)::TraitItem`
1786 Res::Def(DefKind::Method, _) |
1787 Res::Def(DefKind::AssocConst, _) |
1788 Res::Def(DefKind::AssocTy, _) if i + 2 == proj_start => {
1789 ParenthesizedGenericArgs::Ok
1791 // Avoid duplicated errors.
1792 Res::Err => ParenthesizedGenericArgs::Ok,
1794 _ => ParenthesizedGenericArgs::Err,
1797 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1798 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1801 assert!(!def_id.is_local());
1802 let item_generics = self.resolver.cstore()
1803 .item_generics_cloned_untracked(def_id, self.sess);
1804 let n = item_generics.own_counts().lifetimes;
1805 self.type_def_lifetime_params.insert(def_id, n);
1808 self.lower_path_segment(
1813 parenthesized_generic_args,
1822 // Simple case, either no projections, or only fully-qualified.
1823 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1824 if partial_res.unresolved_segments() == 0 {
1825 return hir::QPath::Resolved(qself, path);
1828 // Create the innermost type that we're projecting from.
1829 let mut ty = if path.segments.is_empty() {
1830 // If the base path is empty that means there exists a
1831 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1832 qself.expect("missing QSelf for <T>::...")
1834 // Otherwise, the base path is an implicit `Self` type path,
1835 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1836 // `<I as Iterator>::Item::default`.
1837 let new_id = self.next_id();
1838 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1841 // Anything after the base path are associated "extensions",
1842 // out of which all but the last one are associated types,
1843 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1844 // * base path is `std::vec::Vec<T>`
1845 // * "extensions" are `IntoIter`, `Item` and `clone`
1846 // * type nodes are:
1847 // 1. `std::vec::Vec<T>` (created above)
1848 // 2. `<std::vec::Vec<T>>::IntoIter`
1849 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1850 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1851 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1852 let segment = P(self.lower_path_segment(
1857 ParenthesizedGenericArgs::Err,
1861 let qpath = hir::QPath::TypeRelative(ty, segment);
1863 // It's finished, return the extension of the right node type.
1864 if i == p.segments.len() - 1 {
1868 // Wrap the associated extension in another type node.
1869 let new_id = self.next_id();
1870 ty = P(self.ty_path(new_id, p.span, qpath));
1873 // We should've returned in the for loop above.
1876 "lower_qpath: no final extension segment in {}..{}",
1882 fn lower_path_extra(
1886 param_mode: ParamMode,
1887 explicit_owner: Option<NodeId>,
1891 segments: p.segments
1894 self.lower_path_segment(
1899 ParenthesizedGenericArgs::Err,
1900 ImplTraitContext::disallowed(),
1909 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1910 let res = self.expect_full_res(id);
1911 let res = self.lower_res(res);
1912 self.lower_path_extra(res, p, param_mode, None)
1915 fn lower_path_segment(
1918 segment: &PathSegment,
1919 param_mode: ParamMode,
1920 expected_lifetimes: usize,
1921 parenthesized_generic_args: ParenthesizedGenericArgs,
1922 itctx: ImplTraitContext<'_>,
1923 explicit_owner: Option<NodeId>,
1924 ) -> hir::PathSegment {
1925 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1926 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1927 match **generic_args {
1928 GenericArgs::AngleBracketed(ref data) => {
1929 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1931 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1932 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1933 ParenthesizedGenericArgs::Err => {
1934 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1935 err.span_label(data.span, "only `Fn` traits may use parentheses");
1936 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1937 // Do not suggest going from `Trait()` to `Trait<>`
1938 if data.inputs.len() > 0 {
1939 if let Some(split) = snippet.find('(') {
1940 let trait_name = &snippet[0..split];
1941 let args = &snippet[split + 1 .. snippet.len() - 1];
1942 err.span_suggestion(
1944 "use angle brackets instead",
1945 format!("{}<{}>", trait_name, args),
1946 Applicability::MaybeIncorrect,
1953 self.lower_angle_bracketed_parameter_data(
1954 &data.as_angle_bracketed_args(),
1964 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1967 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1968 GenericArg::Lifetime(_) => true,
1971 let first_generic_span = generic_args.args.iter().map(|a| a.span())
1972 .chain(generic_args.bindings.iter().map(|b| b.span)).next();
1973 if !generic_args.parenthesized && !has_lifetimes {
1975 self.elided_path_lifetimes(path_span, expected_lifetimes)
1977 .map(|lt| GenericArg::Lifetime(lt))
1978 .chain(generic_args.args.into_iter())
1980 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1981 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1982 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1983 let no_bindings = generic_args.bindings.is_empty();
1984 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1985 // If there are no (non-implicit) generic args or associated type
1986 // bindings, our suggestion includes the angle brackets.
1987 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1989 // Otherwise (sorry, this is kind of gross) we need to infer the
1990 // place to splice in the `'_, ` from the generics that do exist.
1991 let first_generic_span = first_generic_span
1992 .expect("already checked that non-lifetime args or bindings exist");
1993 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1995 match self.anonymous_lifetime_mode {
1996 // In create-parameter mode we error here because we don't want to support
1997 // deprecated impl elision in new features like impl elision and `async fn`,
1998 // both of which work using the `CreateParameter` mode:
2000 // impl Foo for std::cell::Ref<u32> // note lack of '_
2001 // async fn foo(_: std::cell::Ref<u32>) { ... }
2002 AnonymousLifetimeMode::CreateParameter => {
2003 let mut err = struct_span_err!(
2007 "implicit elided lifetime not allowed here"
2009 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
2020 AnonymousLifetimeMode::PassThrough |
2021 AnonymousLifetimeMode::ReportError => {
2022 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2023 ELIDED_LIFETIMES_IN_PATHS,
2026 "hidden lifetime parameters in types are deprecated",
2027 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
2040 let res = self.expect_full_res(segment.id);
2041 let id = if let Some(owner) = explicit_owner {
2042 self.lower_node_id_with_owner(segment.id, owner)
2044 self.lower_node_id(segment.id)
2047 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
2048 segment.ident, segment.id, id,
2051 hir::PathSegment::new(
2054 Some(self.lower_res(res)),
2060 fn lower_angle_bracketed_parameter_data(
2062 data: &AngleBracketedArgs,
2063 param_mode: ParamMode,
2064 mut itctx: ImplTraitContext<'_>,
2065 ) -> (hir::GenericArgs, bool) {
2066 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
2067 let has_non_lt_args = args.iter().any(|arg| match arg {
2068 ast::GenericArg::Lifetime(_) => false,
2069 ast::GenericArg::Type(_) => true,
2070 ast::GenericArg::Const(_) => true,
2074 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
2075 bindings: constraints.iter()
2076 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
2078 parenthesized: false,
2080 !has_non_lt_args && param_mode == ParamMode::Optional
2084 fn lower_parenthesized_parameter_data(
2086 data: &ParenthesizedArgs,
2087 ) -> (hir::GenericArgs, bool) {
2088 // Switch to `PassThrough` mode for anonymous lifetimes; this
2089 // means that we permit things like `&Ref<T>`, where `Ref` has
2090 // a hidden lifetime parameter. This is needed for backwards
2091 // compatibility, even in contexts like an impl header where
2092 // we generally don't permit such things (see #51008).
2093 self.with_anonymous_lifetime_mode(
2094 AnonymousLifetimeMode::PassThrough,
2096 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2099 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2101 let output_ty = match output {
2102 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2103 FunctionRetTy::Default(_) => P(this.ty_tup(span, hir::HirVec::new())),
2105 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2106 let binding = hir::TypeBinding {
2107 hir_id: this.next_id(),
2108 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2109 span: output_ty.span,
2110 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2113 hir::GenericArgs { args, bindings: hir_vec![binding], parenthesized: true },
2120 fn lower_local(&mut self, l: &Local) -> (hir::Local, SmallVec<[NodeId; 1]>) {
2121 let mut ids = SmallVec::<[NodeId; 1]>::new();
2122 if self.sess.features_untracked().impl_trait_in_bindings {
2123 if let Some(ref ty) = l.ty {
2124 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2125 visitor.visit_ty(ty);
2128 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2130 hir_id: self.lower_node_id(l.id),
2133 .map(|t| self.lower_ty(t,
2134 if self.sess.features_untracked().impl_trait_in_bindings {
2135 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2137 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2140 pat: self.lower_pat(&l.pat),
2141 init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
2143 attrs: l.attrs.clone(),
2144 source: hir::LocalSource::Normal,
2148 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2149 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2150 // as they are not explicit in HIR/Ty function signatures.
2151 // (instead, the `c_variadic` flag is set to `true`)
2152 let mut inputs = &decl.inputs[..];
2153 if decl.c_variadic() {
2154 inputs = &inputs[..inputs.len() - 1];
2158 .map(|param| match param.pat.kind {
2159 PatKind::Ident(_, ident, _) => ident,
2160 _ => Ident::new(kw::Invalid, param.pat.span),
2165 // Lowers a function declaration.
2167 // `decl`: the unlowered (AST) function declaration.
2168 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2169 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2170 // `make_ret_async` is also `Some`.
2171 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2172 // This guards against trait declarations and implementations where `impl Trait` is
2174 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2175 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2176 // return type `impl Trait` item.
2180 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2181 impl_trait_return_allow: bool,
2182 make_ret_async: Option<NodeId>,
2183 ) -> P<hir::FnDecl> {
2184 debug!("lower_fn_decl(\
2186 in_band_ty_params: {:?}, \
2187 impl_trait_return_allow: {}, \
2188 make_ret_async: {:?})",
2191 impl_trait_return_allow,
2194 let lt_mode = if make_ret_async.is_some() {
2195 // In `async fn`, argument-position elided lifetimes
2196 // must be transformed into fresh generic parameters so that
2197 // they can be applied to the opaque `impl Trait` return type.
2198 AnonymousLifetimeMode::CreateParameter
2200 self.anonymous_lifetime_mode
2203 let c_variadic = decl.c_variadic();
2205 // Remember how many lifetimes were already around so that we can
2206 // only look at the lifetime parameters introduced by the arguments.
2207 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2208 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2209 // as they are not explicit in HIR/Ty function signatures.
2210 // (instead, the `c_variadic` flag is set to `true`)
2211 let mut inputs = &decl.inputs[..];
2213 inputs = &inputs[..inputs.len() - 1];
2218 if let Some((_, ibty)) = &mut in_band_ty_params {
2219 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2221 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2224 .collect::<HirVec<_>>()
2227 let output = if let Some(ret_id) = make_ret_async {
2228 self.lower_async_fn_ret_ty(
2230 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2235 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2236 Some((def_id, _)) if impl_trait_return_allow => {
2237 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2240 hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed()))
2243 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2251 implicit_self: decl.inputs.get(0).map_or(
2252 hir::ImplicitSelfKind::None,
2254 let is_mutable_pat = match arg.pat.kind {
2255 PatKind::Ident(BindingMode::ByValue(mt), _, _) |
2256 PatKind::Ident(BindingMode::ByRef(mt), _, _) =>
2257 mt == Mutability::Mutable,
2262 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2263 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2264 // Given we are only considering `ImplicitSelf` types, we needn't consider
2265 // the case where we have a mutable pattern to a reference as that would
2266 // no longer be an `ImplicitSelf`.
2267 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() &&
2268 mt.mutbl == ast::Mutability::Mutable =>
2269 hir::ImplicitSelfKind::MutRef,
2270 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() =>
2271 hir::ImplicitSelfKind::ImmRef,
2272 _ => hir::ImplicitSelfKind::None,
2279 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2280 // combined with the following definition of `OpaqueTy`:
2282 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2284 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2285 // `output`: unlowered output type (`T` in `-> T`)
2286 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2287 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2288 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2289 fn lower_async_fn_ret_ty(
2291 output: &FunctionRetTy,
2293 opaque_ty_node_id: NodeId,
2294 ) -> hir::FunctionRetTy {
2296 "lower_async_fn_ret_ty(\
2299 opaque_ty_node_id={:?})",
2300 output, fn_def_id, opaque_ty_node_id,
2303 let span = output.span();
2305 let opaque_ty_span = self.mark_span_with_reason(
2306 DesugaringKind::Async,
2311 let opaque_ty_def_index = self
2314 .opt_def_index(opaque_ty_node_id)
2317 self.allocate_hir_id_counter(opaque_ty_node_id);
2319 // When we create the opaque type for this async fn, it is going to have
2320 // to capture all the lifetimes involved in the signature (including in the
2321 // return type). This is done by introducing lifetime parameters for:
2323 // - all the explicitly declared lifetimes from the impl and function itself;
2324 // - all the elided lifetimes in the fn arguments;
2325 // - all the elided lifetimes in the return type.
2327 // So for example in this snippet:
2330 // impl<'a> Foo<'a> {
2331 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2332 // // ^ '0 ^ '1 ^ '2
2333 // // elided lifetimes used below
2338 // we would create an opaque type like:
2341 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2344 // and we would then desugar `bar` to the equivalent of:
2347 // impl<'a> Foo<'a> {
2348 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2352 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2353 // this is because the elided lifetimes from the return type
2354 // should be figured out using the ordinary elision rules, and
2355 // this desugaring achieves that.
2357 // The variable `input_lifetimes_count` tracks the number of
2358 // lifetime parameters to the opaque type *not counting* those
2359 // lifetimes elided in the return type. This includes those
2360 // that are explicitly declared (`in_scope_lifetimes`) and
2361 // those elided lifetimes we found in the arguments (current
2362 // content of `lifetimes_to_define`). Next, we will process
2363 // the return type, which will cause `lifetimes_to_define` to
2365 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2367 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2368 // We have to be careful to get elision right here. The
2369 // idea is that we create a lifetime parameter for each
2370 // lifetime in the return type. So, given a return type
2371 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2372 // Future<Output = &'1 [ &'2 u32 ]>`.
2374 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2375 // hence the elision takes place at the fn site.
2376 let future_bound = this.with_anonymous_lifetime_mode(
2377 AnonymousLifetimeMode::CreateParameter,
2378 |this| this.lower_async_fn_output_type_to_future_bound(
2385 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2387 // Calculate all the lifetimes that should be captured
2388 // by the opaque type. This should include all in-scope
2389 // lifetime parameters, including those defined in-band.
2391 // Note: this must be done after lowering the output type,
2392 // as the output type may introduce new in-band lifetimes.
2393 let lifetime_params: Vec<(Span, ParamName)> =
2394 this.in_scope_lifetimes
2396 .map(|name| (name.ident().span, name))
2397 .chain(this.lifetimes_to_define.iter().cloned())
2400 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2401 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2402 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2404 let generic_params =
2407 .map(|(span, hir_name)| {
2408 this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_index)
2412 let opaque_ty_item = hir::OpaqueTy {
2413 generics: hir::Generics {
2414 params: generic_params,
2415 where_clause: hir::WhereClause {
2416 predicates: hir_vec![],
2421 bounds: hir_vec![future_bound],
2422 impl_trait_fn: Some(fn_def_id),
2423 origin: hir::OpaqueTyOrigin::AsyncFn,
2426 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2427 let opaque_ty_id = this.generate_opaque_type(
2434 (opaque_ty_id, lifetime_params)
2437 // As documented above on the variable
2438 // `input_lifetimes_count`, we need to create the lifetime
2439 // arguments to our opaque type. Continuing with our example,
2440 // we're creating the type arguments for the return type:
2443 // Bar<'a, 'b, '0, '1, '_>
2446 // For the "input" lifetime parameters, we wish to create
2447 // references to the parameters themselves, including the
2448 // "implicit" ones created from parameter types (`'a`, `'b`,
2451 // For the "output" lifetime parameters, we just want to
2453 let mut generic_args: Vec<_> =
2454 lifetime_params[..input_lifetimes_count]
2456 .map(|&(span, hir_name)| {
2457 // Input lifetime like `'a` or `'1`:
2458 GenericArg::Lifetime(hir::Lifetime {
2459 hir_id: self.next_id(),
2461 name: hir::LifetimeName::Param(hir_name),
2465 generic_args.extend(
2466 lifetime_params[input_lifetimes_count..]
2469 // Output lifetime like `'_`.
2470 GenericArg::Lifetime(hir::Lifetime {
2471 hir_id: self.next_id(),
2473 name: hir::LifetimeName::Implicit,
2478 // Create the `Foo<...>` reference itself. Note that the `type
2479 // Foo = impl Trait` is, internally, created as a child of the
2480 // async fn, so the *type parameters* are inherited. It's
2481 // only the lifetime parameters that we must supply.
2482 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args.into());
2483 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2484 hir::FunctionRetTy::Return(P(opaque_ty))
2487 /// Transforms `-> T` into `Future<Output = T>`
2488 fn lower_async_fn_output_type_to_future_bound(
2490 output: &FunctionRetTy,
2493 ) -> hir::GenericBound {
2494 // Compute the `T` in `Future<Output = T>` from the return type.
2495 let output_ty = match output {
2496 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2497 FunctionRetTy::Default(ret_ty_span) => P(self.ty_tup(*ret_ty_span, hir_vec![])),
2501 let future_params = P(hir::GenericArgs {
2503 bindings: hir_vec![hir::TypeBinding {
2504 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2505 kind: hir::TypeBindingKind::Equality {
2508 hir_id: self.next_id(),
2511 parenthesized: false,
2514 // ::std::future::Future<future_params>
2516 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2518 hir::GenericBound::Trait(
2520 trait_ref: hir::TraitRef {
2522 hir_ref_id: self.next_id(),
2524 bound_generic_params: hir_vec![],
2527 hir::TraitBoundModifier::None,
2531 fn lower_param_bound(
2534 itctx: ImplTraitContext<'_>,
2535 ) -> hir::GenericBound {
2537 GenericBound::Trait(ref ty, modifier) => {
2538 hir::GenericBound::Trait(
2539 self.lower_poly_trait_ref(ty, itctx),
2540 self.lower_trait_bound_modifier(modifier),
2543 GenericBound::Outlives(ref lifetime) => {
2544 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2549 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2550 let span = l.ident.span;
2552 ident if ident.name == kw::StaticLifetime =>
2553 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
2554 ident if ident.name == kw::UnderscoreLifetime =>
2555 match self.anonymous_lifetime_mode {
2556 AnonymousLifetimeMode::CreateParameter => {
2557 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2558 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2561 AnonymousLifetimeMode::PassThrough => {
2562 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2565 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2568 self.maybe_collect_in_band_lifetime(ident);
2569 let param_name = ParamName::Plain(ident);
2570 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2575 fn new_named_lifetime(
2579 name: hir::LifetimeName,
2580 ) -> hir::Lifetime {
2582 hir_id: self.lower_node_id(id),
2588 fn lower_generic_params(
2590 params: &[GenericParam],
2591 add_bounds: &NodeMap<Vec<GenericBound>>,
2592 mut itctx: ImplTraitContext<'_>,
2593 ) -> hir::HirVec<hir::GenericParam> {
2594 params.iter().map(|param| {
2595 self.lower_generic_param(param, add_bounds, itctx.reborrow())
2599 fn lower_generic_param(&mut self,
2600 param: &GenericParam,
2601 add_bounds: &NodeMap<Vec<GenericBound>>,
2602 mut itctx: ImplTraitContext<'_>)
2603 -> hir::GenericParam {
2604 let mut bounds = self.with_anonymous_lifetime_mode(
2605 AnonymousLifetimeMode::ReportError,
2606 |this| this.lower_param_bounds(¶m.bounds, itctx.reborrow()),
2609 let (name, kind) = match param.kind {
2610 GenericParamKind::Lifetime => {
2611 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2612 self.is_collecting_in_band_lifetimes = false;
2614 let lt = self.with_anonymous_lifetime_mode(
2615 AnonymousLifetimeMode::ReportError,
2616 |this| this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }),
2618 let param_name = match lt.name {
2619 hir::LifetimeName::Param(param_name) => param_name,
2620 hir::LifetimeName::Implicit
2621 | hir::LifetimeName::Underscore
2622 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2623 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2626 "object-lifetime-default should not occur here",
2629 hir::LifetimeName::Error => ParamName::Error,
2632 let kind = hir::GenericParamKind::Lifetime {
2633 kind: hir::LifetimeParamKind::Explicit
2636 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2640 GenericParamKind::Type { ref default, .. } => {
2641 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2642 if !add_bounds.is_empty() {
2643 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2644 bounds = bounds.into_iter()
2649 let kind = hir::GenericParamKind::Type {
2650 default: default.as_ref().map(|x| {
2651 self.lower_ty(x, ImplTraitContext::OpaqueTy(None))
2653 synthetic: param.attrs.iter()
2654 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2655 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2659 (hir::ParamName::Plain(param.ident), kind)
2661 GenericParamKind::Const { ref ty } => {
2662 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const {
2663 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2669 hir_id: self.lower_node_id(param.id),
2671 span: param.ident.span,
2672 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2673 attrs: self.lower_attrs(¶m.attrs),
2679 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2680 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2681 hir::QPath::Resolved(None, path) => path,
2682 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2686 hir_ref_id: self.lower_node_id(p.ref_id),
2690 fn lower_poly_trait_ref(
2693 mut itctx: ImplTraitContext<'_>,
2694 ) -> hir::PolyTraitRef {
2695 let bound_generic_params = self.lower_generic_params(
2696 &p.bound_generic_params,
2697 &NodeMap::default(),
2700 let trait_ref = self.with_in_scope_lifetime_defs(
2701 &p.bound_generic_params,
2702 |this| this.lower_trait_ref(&p.trait_ref, itctx),
2706 bound_generic_params,
2712 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2714 ty: self.lower_ty(&mt.ty, itctx),
2719 fn lower_param_bounds(&mut self, bounds: &[GenericBound], mut itctx: ImplTraitContext<'_>)
2720 -> hir::GenericBounds {
2721 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2724 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2725 let mut stmts = vec![];
2726 let mut expr = None;
2728 for (index, stmt) in b.stmts.iter().enumerate() {
2729 if index == b.stmts.len() - 1 {
2730 if let StmtKind::Expr(ref e) = stmt.kind {
2731 expr = Some(P(self.lower_expr(e)));
2733 stmts.extend(self.lower_stmt(stmt));
2736 stmts.extend(self.lower_stmt(stmt));
2741 hir_id: self.lower_node_id(b.id),
2742 stmts: stmts.into(),
2744 rules: self.lower_block_check_mode(&b.rules),
2750 /// Lowers a block directly to an expression, presuming that it
2751 /// has no attributes and is not targeted by a `break`.
2752 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr {
2753 let block = self.lower_block(b, false);
2754 self.expr_block(block, ThinVec::new())
2757 fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2758 let node = match p.kind {
2759 PatKind::Wild => hir::PatKind::Wild,
2760 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2761 let lower_sub = |this: &mut Self| sub.as_ref().map(|x| this.lower_pat(x));
2762 self.lower_pat_ident(p, binding_mode, ident, lower_sub)
2764 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2765 PatKind::TupleStruct(ref path, ref pats) => {
2766 let qpath = self.lower_qpath(
2770 ParamMode::Optional,
2771 ImplTraitContext::disallowed(),
2773 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2774 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2776 PatKind::Or(ref pats) => {
2777 hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
2779 PatKind::Path(ref qself, ref path) => {
2780 let qpath = self.lower_qpath(
2784 ParamMode::Optional,
2785 ImplTraitContext::disallowed(),
2787 hir::PatKind::Path(qpath)
2789 PatKind::Struct(ref path, ref fields, etc) => {
2790 let qpath = self.lower_qpath(
2794 ParamMode::Optional,
2795 ImplTraitContext::disallowed(),
2800 .map(|f| hir::FieldPat {
2801 hir_id: self.next_id(),
2803 pat: self.lower_pat(&f.pat),
2804 is_shorthand: f.is_shorthand,
2808 hir::PatKind::Struct(qpath, fs, etc)
2810 PatKind::Tuple(ref pats) => {
2811 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2812 hir::PatKind::Tuple(pats, ddpos)
2814 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2815 PatKind::Ref(ref inner, mutbl) => {
2816 hir::PatKind::Ref(self.lower_pat(inner), mutbl)
2818 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2819 P(self.lower_expr(e1)),
2820 P(self.lower_expr(e2)),
2821 self.lower_range_end(end),
2823 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2825 // If we reach here the `..` pattern is not semantically allowed.
2826 self.ban_illegal_rest_pat(p.span)
2828 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2829 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2832 self.pat_with_node_id_of(p, node)
2839 ) -> (HirVec<P<hir::Pat>>, Option<usize>) {
2840 let mut elems = Vec::with_capacity(pats.len());
2841 let mut rest = None;
2843 let mut iter = pats.iter().enumerate();
2844 for (idx, pat) in iter.by_ref() {
2845 // Interpret the first `..` pattern as a sub-tuple pattern.
2846 // Note that unlike for slice patterns,
2847 // where `xs @ ..` is a legal sub-slice pattern,
2848 // it is not a legal sub-tuple pattern.
2850 rest = Some((idx, pat.span));
2853 // It was not a sub-tuple pattern so lower it normally.
2854 elems.push(self.lower_pat(pat));
2857 for (_, pat) in iter {
2858 // There was a previous sub-tuple pattern; make sure we don't allow more...
2860 // ...but there was one again, so error.
2861 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2863 elems.push(self.lower_pat(pat));
2867 (elems.into(), rest.map(|(ddpos, _)| ddpos))
2870 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2871 /// `hir::PatKind::Slice(before, slice, after)`.
2873 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2874 /// this is interpreted as a sub-slice pattern semantically.
2875 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2876 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind {
2877 let mut before = Vec::new();
2878 let mut after = Vec::new();
2879 let mut slice = None;
2880 let mut prev_rest_span = None;
2882 let mut iter = pats.iter();
2883 // Lower all the patterns until the first occurence of a sub-slice pattern.
2884 for pat in iter.by_ref() {
2886 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2888 prev_rest_span = Some(pat.span);
2889 slice = Some(self.pat_wild_with_node_id_of(pat));
2892 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2893 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2894 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2895 prev_rest_span = Some(sub.span);
2896 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2897 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2898 slice = Some(self.pat_with_node_id_of(pat, node));
2901 // It was not a subslice pattern so lower it normally.
2902 _ => before.push(self.lower_pat(pat)),
2906 // Lower all the patterns after the first sub-slice pattern.
2908 // There was a previous subslice pattern; make sure we don't allow more.
2909 let rest_span = match pat.kind {
2910 PatKind::Rest => Some(pat.span),
2911 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2912 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2913 after.push(self.pat_wild_with_node_id_of(pat));
2918 if let Some(rest_span) = rest_span {
2919 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2920 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2922 // Lower the pattern normally.
2923 after.push(self.lower_pat(pat));
2927 hir::PatKind::Slice(before.into(), slice, after.into())
2933 binding_mode: &BindingMode,
2935 lower_sub: impl FnOnce(&mut Self) -> Option<P<hir::Pat>>,
2937 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2938 // `None` can occur in body-less function signatures
2939 res @ None | res @ Some(Res::Local(_)) => {
2940 let canonical_id = match res {
2941 Some(Res::Local(id)) => id,
2945 hir::PatKind::Binding(
2946 self.lower_binding_mode(binding_mode),
2947 self.lower_node_id(canonical_id),
2952 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2956 res: self.lower_res(res),
2957 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2963 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> P<hir::Pat> {
2964 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2967 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2968 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind) -> P<hir::Pat> {
2970 hir_id: self.lower_node_id(p.id),
2976 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2977 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2979 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2980 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2981 .span_label(prev_sp, "previously used here")
2985 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2986 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind {
2988 .struct_span_err(sp, "`..` patterns are not allowed here")
2989 .note("only allowed in tuple, tuple struct, and slice patterns")
2992 // We're not in a list context so `..` can be reasonably treated
2993 // as `_` because it should always be valid and roughly matches the
2994 // intent of `..` (notice that the rest of a single slot is that slot).
2998 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
3000 RangeEnd::Included(_) => hir::RangeEnd::Included,
3001 RangeEnd::Excluded => hir::RangeEnd::Excluded,
3005 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
3006 self.with_new_scopes(|this| {
3008 hir_id: this.lower_node_id(c.id),
3009 body: this.lower_const_body(c.value.span, Some(&c.value)),
3014 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt; 1]> {
3015 let kind = match s.kind {
3016 StmtKind::Local(ref l) => {
3017 let (l, item_ids) = self.lower_local(l);
3018 let mut ids: SmallVec<[hir::Stmt; 1]> = item_ids
3021 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
3022 self.stmt(s.span, hir::StmtKind::Item(item_id))
3027 hir_id: self.lower_node_id(s.id),
3028 kind: hir::StmtKind::Local(P(l)),
3034 StmtKind::Item(ref it) => {
3035 // Can only use the ID once.
3036 let mut id = Some(s.id);
3037 return self.lower_item_id(it)
3040 let hir_id = id.take()
3041 .map(|id| self.lower_node_id(id))
3042 .unwrap_or_else(|| self.next_id());
3046 kind: hir::StmtKind::Item(item_id),
3052 StmtKind::Expr(ref e) => hir::StmtKind::Expr(P(self.lower_expr(e))),
3053 StmtKind::Semi(ref e) => hir::StmtKind::Semi(P(self.lower_expr(e))),
3054 StmtKind::Mac(..) => panic!("shouldn't exist here"),
3056 smallvec![hir::Stmt {
3057 hir_id: self.lower_node_id(s.id),
3063 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
3065 BlockCheckMode::Default => hir::DefaultBlock,
3066 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
3070 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
3072 BindingMode::ByValue(Mutability::Immutable) => hir::BindingAnnotation::Unannotated,
3073 BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
3074 BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
3075 BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
3079 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3081 CompilerGenerated => hir::CompilerGenerated,
3082 UserProvided => hir::UserProvided,
3086 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3088 TraitBoundModifier::None => hir::TraitBoundModifier::None,
3089 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3093 // Helper methods for building HIR.
3095 fn stmt(&mut self, span: Span, kind: hir::StmtKind) -> hir::Stmt {
3096 hir::Stmt { span, kind, hir_id: self.next_id() }
3099 fn stmt_expr(&mut self, span: Span, expr: hir::Expr) -> hir::Stmt {
3100 self.stmt(span, hir::StmtKind::Expr(P(expr)))
3105 attrs: ThinVec<Attribute>,
3107 init: Option<P<hir::Expr>>,
3109 source: hir::LocalSource,
3111 let local = hir::Local {
3113 hir_id: self.next_id(),
3120 self.stmt(span, hir::StmtKind::Local(P(local)))
3123 fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
3124 self.block_all(expr.span, hir::HirVec::new(), Some(expr))
3130 stmts: hir::HirVec<hir::Stmt>,
3131 expr: Option<P<hir::Expr>>,
3136 hir_id: self.next_id(),
3137 rules: hir::DefaultBlock,
3139 targeted_by_break: false,
3143 /// Constructs a `true` or `false` literal pattern.
3144 fn pat_bool(&mut self, span: Span, val: bool) -> P<hir::Pat> {
3145 let expr = self.expr_bool(span, val);
3146 self.pat(span, hir::PatKind::Lit(P(expr)))
3149 fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3150 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], hir_vec![pat])
3153 fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3154 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], hir_vec![pat])
3157 fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3158 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], hir_vec![pat])
3161 fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
3162 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], hir_vec![])
3168 components: &[Symbol],
3169 subpats: hir::HirVec<P<hir::Pat>>,
3171 let path = self.std_path(span, components, None, true);
3172 let qpath = hir::QPath::Resolved(None, P(path));
3173 let pt = if subpats.is_empty() {
3174 hir::PatKind::Path(qpath)
3176 hir::PatKind::TupleStruct(qpath, subpats, None)
3181 fn pat_ident(&mut self, span: Span, ident: Ident) -> (P<hir::Pat>, hir::HirId) {
3182 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3185 fn pat_ident_binding_mode(
3189 bm: hir::BindingAnnotation,
3190 ) -> (P<hir::Pat>, hir::HirId) {
3191 let hir_id = self.next_id();
3196 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3203 fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
3204 self.pat(span, hir::PatKind::Wild)
3207 fn pat(&mut self, span: Span, kind: hir::PatKind) -> P<hir::Pat> {
3209 hir_id: self.next_id(),
3215 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3216 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3217 /// The path is also resolved according to `is_value`.
3221 components: &[Symbol],
3222 params: Option<P<hir::GenericArgs>>,
3225 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3226 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3228 let mut segments: Vec<_> = path.segments.iter().map(|segment| {
3229 let res = self.expect_full_res(segment.id);
3231 ident: segment.ident,
3232 hir_id: Some(self.lower_node_id(segment.id)),
3233 res: Some(self.lower_res(res)),
3238 segments.last_mut().unwrap().args = params;
3242 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3243 segments: segments.into(),
3247 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3248 let kind = match qpath {
3249 hir::QPath::Resolved(None, path) => {
3250 // Turn trait object paths into `TyKind::TraitObject` instead.
3252 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3253 let principal = hir::PolyTraitRef {
3254 bound_generic_params: hir::HirVec::new(),
3255 trait_ref: hir::TraitRef {
3262 // The original ID is taken by the `PolyTraitRef`,
3263 // so the `Ty` itself needs a different one.
3264 hir_id = self.next_id();
3265 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3267 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3270 _ => hir::TyKind::Path(qpath),
3280 /// Invoked to create the lifetime argument for a type `&T`
3281 /// with no explicit lifetime.
3282 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3283 match self.anonymous_lifetime_mode {
3284 // Intercept when we are in an impl header or async fn and introduce an in-band
3286 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3288 AnonymousLifetimeMode::CreateParameter => {
3289 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3291 hir_id: self.next_id(),
3293 name: hir::LifetimeName::Param(fresh_name),
3297 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3299 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3303 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3304 /// return a "error lifetime".
3305 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3306 let (id, msg, label) = match id {
3307 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3310 self.resolver.next_node_id(),
3311 "`&` without an explicit lifetime name cannot be used here",
3312 "explicit lifetime name needed here",
3316 let mut err = struct_span_err!(
3323 err.span_label(span, label);
3326 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3329 /// Invoked to create the lifetime argument(s) for a path like
3330 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3331 /// sorts of cases are deprecated. This may therefore report a warning or an
3332 /// error, depending on the mode.
3333 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3335 .map(|_| self.elided_path_lifetime(span))
3339 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3340 match self.anonymous_lifetime_mode {
3341 AnonymousLifetimeMode::CreateParameter => {
3342 // We should have emitted E0726 when processing this path above
3343 self.sess.delay_span_bug(
3345 "expected 'implicit elided lifetime not allowed' error",
3347 let id = self.resolver.next_node_id();
3348 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3350 // `PassThrough` is the normal case.
3351 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3352 // is unsuitable here, as these can occur from missing lifetime parameters in a
3353 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3354 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3355 // later, at which point a suitable error will be emitted.
3356 | AnonymousLifetimeMode::PassThrough
3357 | AnonymousLifetimeMode::ReportError => self.new_implicit_lifetime(span),
3361 /// Invoked to create the lifetime argument(s) for an elided trait object
3362 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3363 /// when the bound is written, even if it is written with `'_` like in
3364 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3365 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3366 match self.anonymous_lifetime_mode {
3367 // NB. We intentionally ignore the create-parameter mode here.
3368 // and instead "pass through" to resolve-lifetimes, which will apply
3369 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3370 // do not act like other elided lifetimes. In other words, given this:
3372 // impl Foo for Box<dyn Debug>
3374 // we do not introduce a fresh `'_` to serve as the bound, but instead
3375 // ultimately translate to the equivalent of:
3377 // impl Foo for Box<dyn Debug + 'static>
3379 // `resolve_lifetime` has the code to make that happen.
3380 AnonymousLifetimeMode::CreateParameter => {}
3382 AnonymousLifetimeMode::ReportError => {
3383 // ReportError applies to explicit use of `'_`.
3386 // This is the normal case.
3387 AnonymousLifetimeMode::PassThrough => {}
3390 let r = hir::Lifetime {
3391 hir_id: self.next_id(),
3393 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3395 debug!("elided_dyn_bound: r={:?}", r);
3399 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3401 hir_id: self.next_id(),
3403 name: hir::LifetimeName::Implicit,
3407 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3408 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3409 // call site which do not have a macro backtrace. See #61963.
3410 let is_macro_callsite = self.sess.source_map()
3411 .span_to_snippet(span)
3412 .map(|snippet| snippet.starts_with("#["))
3414 if !is_macro_callsite {
3415 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3416 builtin::BARE_TRAIT_OBJECTS,
3419 "trait objects without an explicit `dyn` are deprecated",
3420 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3426 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
3427 // Sorting by span ensures that we get things in order within a
3428 // file, and also puts the files in a sensible order.
3429 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3430 body_ids.sort_by_key(|b| bodies[b].value.span);
3434 /// Checks if the specified expression is a built-in range literal.
3435 /// (See: `LoweringContext::lower_expr()`).
3436 pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
3437 use hir::{Path, QPath, ExprKind, TyKind};
3439 // Returns whether the given path represents a (desugared) range,
3440 // either in std or core, i.e. has either a `::std::ops::Range` or
3441 // `::core::ops::Range` prefix.
3442 fn is_range_path(path: &Path) -> bool {
3443 let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.to_string()).collect();
3444 let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
3446 // "{{root}}" is the equivalent of `::` prefix in `Path`.
3447 if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
3448 (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
3454 // Check whether a span corresponding to a range expression is a
3455 // range literal, rather than an explicit struct or `new()` call.
3456 fn is_lit(sess: &Session, span: &Span) -> bool {
3457 let source_map = sess.source_map();
3458 let end_point = source_map.end_point(*span);
3460 if let Ok(end_string) = source_map.span_to_snippet(end_point) {
3461 !(end_string.ends_with("}") || end_string.ends_with(")"))
3468 // All built-in range literals but `..=` and `..` desugar to `Struct`s.
3469 ExprKind::Struct(ref qpath, _, _) => {
3470 if let QPath::Resolved(None, ref path) = **qpath {
3471 return is_range_path(&path) && is_lit(sess, &expr.span);
3475 // `..` desugars to its struct path.
3476 ExprKind::Path(QPath::Resolved(None, ref path)) => {
3477 return is_range_path(&path) && is_lit(sess, &expr.span);
3480 // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
3481 ExprKind::Call(ref func, _) => {
3482 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
3483 if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
3484 let new_call = segment.ident.name == sym::new;
3485 return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;