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 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
79 pub struct LoweringContext<'a> {
80 crate_root: Option<Symbol>,
82 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
85 resolver: &'a mut dyn Resolver,
87 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
88 /// if we don't have this function pointer. To avoid that dependency so that
89 /// librustc is independent of the parser, we use dynamic dispatch here.
90 nt_to_tokenstream: NtToTokenstream,
92 /// The items being lowered are collected here.
93 items: BTreeMap<hir::HirId, hir::Item>,
95 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
96 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
97 bodies: BTreeMap<hir::BodyId, hir::Body>,
98 exported_macros: Vec<hir::MacroDef>,
99 non_exported_macro_attrs: Vec<ast::Attribute>,
101 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
103 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
105 generator_kind: Option<hir::GeneratorKind>,
107 /// Used to get the current `fn`'s def span to point to when using `await`
108 /// outside of an `async fn`.
109 current_item: Option<Span>,
111 catch_scopes: Vec<NodeId>,
112 loop_scopes: Vec<NodeId>,
113 is_in_loop_condition: bool,
114 is_in_trait_impl: bool,
115 is_in_dyn_type: bool,
117 /// What to do when we encounter either an "anonymous lifetime
118 /// reference". The term "anonymous" is meant to encompass both
119 /// `'_` lifetimes as well as fully elided cases where nothing is
120 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
121 anonymous_lifetime_mode: AnonymousLifetimeMode,
123 /// Used to create lifetime definitions from in-band lifetime usages.
124 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
125 /// When a named lifetime is encountered in a function or impl header and
126 /// has not been defined
127 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
128 /// to this list. The results of this list are then added to the list of
129 /// lifetime definitions in the corresponding impl or function generics.
130 lifetimes_to_define: Vec<(Span, ParamName)>,
132 /// `true` if in-band lifetimes are being collected. This is used to
133 /// indicate whether or not we're in a place where new lifetimes will result
134 /// in in-band lifetime definitions, such a function or an impl header,
135 /// including implicit lifetimes from `impl_header_lifetime_elision`.
136 is_collecting_in_band_lifetimes: bool,
138 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
139 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
140 /// against this list to see if it is already in-scope, or if a definition
141 /// needs to be created for it.
143 /// We always store a `modern()` version of the param-name in this
145 in_scope_lifetimes: Vec<ParamName>,
147 current_module: hir::HirId,
149 type_def_lifetime_params: DefIdMap<usize>,
151 current_hir_id_owner: Vec<(DefIndex, u32)>,
152 item_local_id_counters: NodeMap<u32>,
153 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
155 allow_try_trait: Option<Lrc<[Symbol]>>,
156 allow_gen_future: Option<Lrc<[Symbol]>>,
160 fn cstore(&self) -> &dyn CrateStore;
162 /// Obtains resolution for a `NodeId` with a single resolution.
163 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
165 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
166 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
168 /// Obtains resolution for a label with the given `NodeId`.
169 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
171 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
172 /// This should only return `None` during testing.
173 fn definitions(&mut self) -> &mut Definitions;
175 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
176 /// resolves it based on `is_value`.
180 crate_root: Option<Symbol>,
181 components: &[Symbol],
183 ) -> (ast::Path, Res<NodeId>);
185 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
187 fn next_node_id(&mut self) -> NodeId;
190 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
192 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
193 /// and if so, what meaning it has.
195 enum ImplTraitContext<'a> {
196 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
197 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
198 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
200 /// Newly generated parameters should be inserted into the given `Vec`.
201 Universal(&'a mut Vec<hir::GenericParam>),
203 /// Treat `impl Trait` as shorthand for a new opaque type.
204 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
205 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
207 /// We optionally store a `DefId` for the parent item here so we can look up necessary
208 /// information later. It is `None` when no information about the context should be stored
209 /// (e.g., for consts and statics).
210 OpaqueTy(Option<DefId> /* fn def-ID */),
212 /// `impl Trait` is not accepted in this position.
213 Disallowed(ImplTraitPosition),
216 /// Position in which `impl Trait` is disallowed.
217 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
218 enum ImplTraitPosition {
219 /// Disallowed in `let` / `const` / `static` bindings.
222 /// All other posiitons.
226 impl<'a> ImplTraitContext<'a> {
228 fn disallowed() -> Self {
229 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
232 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
233 use self::ImplTraitContext::*;
235 Universal(params) => Universal(params),
236 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
237 Disallowed(pos) => Disallowed(*pos),
244 dep_graph: &DepGraph,
246 resolver: &mut dyn Resolver,
247 nt_to_tokenstream: NtToTokenstream,
249 // We're constructing the HIR here; we don't care what we will
250 // read, since we haven't even constructed the *input* to
252 dep_graph.assert_ignored();
254 let _prof_timer = sess.prof.generic_activity("hir_lowering");
257 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
261 items: BTreeMap::new(),
262 trait_items: BTreeMap::new(),
263 impl_items: BTreeMap::new(),
264 bodies: BTreeMap::new(),
265 trait_impls: BTreeMap::new(),
266 modules: BTreeMap::new(),
267 exported_macros: Vec::new(),
268 non_exported_macro_attrs: Vec::new(),
269 catch_scopes: Vec::new(),
270 loop_scopes: Vec::new(),
271 is_in_loop_condition: false,
272 is_in_trait_impl: false,
273 is_in_dyn_type: false,
274 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
275 type_def_lifetime_params: Default::default(),
276 current_module: hir::CRATE_HIR_ID,
277 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
278 item_local_id_counters: Default::default(),
279 node_id_to_hir_id: IndexVec::new(),
280 generator_kind: None,
282 lifetimes_to_define: Vec::new(),
283 is_collecting_in_band_lifetimes: false,
284 in_scope_lifetimes: Vec::new(),
285 allow_try_trait: Some([sym::try_trait][..].into()),
286 allow_gen_future: Some([sym::gen_future][..].into()),
290 #[derive(Copy, Clone, PartialEq)]
292 /// Any path in a type context.
294 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
296 /// The `module::Type` in `module::Type::method` in an expression.
300 enum ParenthesizedGenericArgs {
305 /// What to do when we encounter an **anonymous** lifetime
306 /// reference. Anonymous lifetime references come in two flavors. You
307 /// have implicit, or fully elided, references to lifetimes, like the
308 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
309 /// or `Ref<'_, T>`. These often behave the same, but not always:
311 /// - certain usages of implicit references are deprecated, like
312 /// `Ref<T>`, and we sometimes just give hard errors in those cases
314 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
315 /// the same as `Box<dyn Foo + '_>`.
317 /// We describe the effects of the various modes in terms of three cases:
319 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
320 /// of a `&` (e.g., the missing lifetime in something like `&T`)
321 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
322 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
323 /// elided bounds follow special rules. Note that this only covers
324 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
325 /// '_>` is a case of "modern" elision.
326 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
327 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
328 /// non-deprecated equivalent.
330 /// Currently, the handling of lifetime elision is somewhat spread out
331 /// between HIR lowering and -- as described below -- the
332 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
333 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
334 /// everything into HIR lowering.
335 #[derive(Copy, Clone, Debug)]
336 enum AnonymousLifetimeMode {
337 /// For **Modern** cases, create a new anonymous region parameter
338 /// and reference that.
340 /// For **Dyn Bound** cases, pass responsibility to
341 /// `resolve_lifetime` code.
343 /// For **Deprecated** cases, report an error.
346 /// Give a hard error when either `&` or `'_` is written. Used to
347 /// rule out things like `where T: Foo<'_>`. Does not imply an
348 /// error on default object bounds (e.g., `Box<dyn Foo>`).
351 /// Pass responsibility to `resolve_lifetime` code for all cases.
355 struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[NodeId; 1]> }
357 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
358 fn visit_ty(&mut self, ty: &'a Ty) {
364 TyKind::ImplTrait(id, _) => self.ids.push(id),
367 visit::walk_ty(self, ty);
370 fn visit_path_segment(
373 path_segment: &'v PathSegment,
375 if let Some(ref p) = path_segment.args {
376 if let GenericArgs::Parenthesized(_) = **p {
380 visit::walk_path_segment(self, path_span, path_segment)
384 impl<'a> LoweringContext<'a> {
385 fn lower_crate(mut self, c: &Crate) -> hir::Crate {
386 /// Full-crate AST visitor that inserts into a fresh
387 /// `LoweringContext` any information that may be
388 /// needed from arbitrary locations in the crate,
389 /// e.g., the number of lifetime generic parameters
390 /// declared for every type and trait definition.
391 struct MiscCollector<'tcx, 'interner> {
392 lctx: &'tcx mut LoweringContext<'interner>,
393 hir_id_owner: Option<NodeId>,
396 impl MiscCollector<'_, '_> {
397 fn allocate_use_tree_hir_id_counters(
403 UseTreeKind::Simple(_, id1, id2) => {
404 for &id in &[id1, id2] {
405 self.lctx.resolver.definitions().create_def_with_parent(
412 self.lctx.allocate_hir_id_counter(id);
415 UseTreeKind::Glob => (),
416 UseTreeKind::Nested(ref trees) => {
417 for &(ref use_tree, id) in trees {
418 let hir_id = self.lctx.allocate_hir_id_counter(id);
419 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
425 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
427 F: FnOnce(&mut Self) -> T,
429 let old = mem::replace(&mut self.hir_id_owner, owner);
431 self.hir_id_owner = old;
436 impl<'tcx, 'interner> Visitor<'tcx> for MiscCollector<'tcx, 'interner> {
437 fn visit_pat(&mut self, p: &'tcx Pat) {
438 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
439 // Doesn't generate a HIR node
440 } else if let Some(owner) = self.hir_id_owner {
441 self.lctx.lower_node_id_with_owner(p.id, owner);
444 visit::walk_pat(self, p)
447 fn visit_item(&mut self, item: &'tcx Item) {
448 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
451 ItemKind::Struct(_, ref generics)
452 | ItemKind::Union(_, ref generics)
453 | ItemKind::Enum(_, ref generics)
454 | ItemKind::TyAlias(_, ref generics)
455 | ItemKind::OpaqueTy(_, ref generics)
456 | ItemKind::Trait(_, _, ref generics, ..) => {
457 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
461 .filter(|param| match param.kind {
462 ast::GenericParamKind::Lifetime { .. } => true,
466 self.lctx.type_def_lifetime_params.insert(def_id, count);
468 ItemKind::Use(ref use_tree) => {
469 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
474 self.with_hir_id_owner(Some(item.id), |this| {
475 visit::walk_item(this, item);
479 fn visit_trait_item(&mut self, item: &'tcx TraitItem) {
480 self.lctx.allocate_hir_id_counter(item.id);
483 TraitItemKind::Method(_, None) => {
484 // Ignore patterns in trait methods without bodies
485 self.with_hir_id_owner(None, |this| {
486 visit::walk_trait_item(this, item)
489 _ => self.with_hir_id_owner(Some(item.id), |this| {
490 visit::walk_trait_item(this, item);
495 fn visit_impl_item(&mut self, item: &'tcx ImplItem) {
496 self.lctx.allocate_hir_id_counter(item.id);
497 self.with_hir_id_owner(Some(item.id), |this| {
498 visit::walk_impl_item(this, item);
502 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
503 // Ignore patterns in foreign items
504 self.with_hir_id_owner(None, |this| {
505 visit::walk_foreign_item(this, i)
509 fn visit_ty(&mut self, t: &'tcx Ty) {
511 // Mirrors the case in visit::walk_ty
512 TyKind::BareFn(ref f) => {
518 // Mirrors visit::walk_fn_decl
519 for parameter in &f.decl.inputs {
520 // We don't lower the ids of argument patterns
521 self.with_hir_id_owner(None, |this| {
522 this.visit_pat(¶meter.pat);
524 self.visit_ty(¶meter.ty)
526 self.visit_fn_ret_ty(&f.decl.output)
528 _ => visit::walk_ty(self, t),
533 self.lower_node_id(CRATE_NODE_ID);
534 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
536 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
537 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
539 let module = self.lower_mod(&c.module);
540 let attrs = self.lower_attrs(&c.attrs);
541 let body_ids = body_ids(&self.bodies);
545 .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
551 exported_macros: hir::HirVec::from(self.exported_macros),
552 non_exported_macro_attrs: hir::HirVec::from(self.non_exported_macro_attrs),
554 trait_items: self.trait_items,
555 impl_items: self.impl_items,
558 trait_impls: self.trait_impls,
559 modules: self.modules,
563 fn insert_item(&mut self, item: hir::Item) {
564 let id = item.hir_id;
565 // FIXME: Use `debug_asset-rt`.
566 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
567 self.items.insert(id, item);
568 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
571 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
572 // Set up the counter if needed.
573 self.item_local_id_counters.entry(owner).or_insert(0);
574 // Always allocate the first `HirId` for the owner itself.
575 let lowered = self.lower_node_id_with_owner(owner, owner);
576 debug_assert_eq!(lowered.local_id.as_u32(), 0);
580 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
582 F: FnOnce(&mut Self) -> hir::HirId,
584 if ast_node_id == DUMMY_NODE_ID {
585 return hir::DUMMY_HIR_ID;
588 let min_size = ast_node_id.as_usize() + 1;
590 if min_size > self.node_id_to_hir_id.len() {
591 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
594 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
596 if existing_hir_id == hir::DUMMY_HIR_ID {
597 // Generate a new `HirId`.
598 let hir_id = alloc_hir_id(self);
599 self.node_id_to_hir_id[ast_node_id] = hir_id;
607 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
609 F: FnOnce(&mut Self) -> T,
611 let counter = self.item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters
623 .insert(owner, new_counter)
625 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
629 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
630 /// the `LoweringContext`'s `NodeId => HirId` map.
631 /// Take care not to call this method if the resulting `HirId` is then not
632 /// actually used in the HIR, as that would trigger an assertion in the
633 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
634 /// properly. Calling the method twice with the same `NodeId` is fine though.
635 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
636 self.lower_node_id_generic(ast_node_id, |this| {
637 let &mut (def_index, ref mut local_id_counter) =
638 this.current_hir_id_owner.last_mut().unwrap();
639 let local_id = *local_id_counter;
640 *local_id_counter += 1;
643 local_id: hir::ItemLocalId::from_u32(local_id),
648 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
649 self.lower_node_id_generic(ast_node_id, |this| {
650 let local_id_counter = this
651 .item_local_id_counters
653 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
654 let local_id = *local_id_counter;
656 // We want to be sure not to modify the counter in the map while it
657 // is also on the stack. Otherwise we'll get lost updates when writing
658 // back from the stack to the map.
659 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
661 *local_id_counter += 1;
665 .opt_def_index(owner)
666 .expect("you forgot to call `create_def_with_parent` or are lowering node-IDs \
667 that do not belong to the current owner");
671 local_id: hir::ItemLocalId::from_u32(local_id),
676 fn next_id(&mut self) -> hir::HirId {
677 let node_id = self.resolver.next_node_id();
678 self.lower_node_id(node_id)
681 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
683 self.lower_node_id_generic(id, |_| {
684 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
689 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
690 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
691 if pr.unresolved_segments() != 0 {
692 bug!("path not fully resolved: {:?}", pr);
698 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
699 self.resolver.get_import_res(id).present_items()
702 fn diagnostic(&self) -> &errors::Handler {
703 self.sess.diagnostic()
706 /// Reuses the span but adds information like the kind of the desugaring and features that are
707 /// allowed inside this span.
708 fn mark_span_with_reason(
710 reason: DesugaringKind,
712 allow_internal_unstable: Option<Lrc<[Symbol]>>,
714 span.fresh_expansion(ExpnData {
715 allow_internal_unstable,
716 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
720 fn with_anonymous_lifetime_mode<R>(
722 anonymous_lifetime_mode: AnonymousLifetimeMode,
723 op: impl FnOnce(&mut Self) -> R,
726 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
727 anonymous_lifetime_mode,
729 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
730 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
731 let result = op(self);
732 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
733 debug!("with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
734 old_anonymous_lifetime_mode);
738 /// Creates a new `hir::GenericParam` for every new lifetime and
739 /// type parameter encountered while evaluating `f`. Definitions
740 /// are created with the parent provided. If no `parent_id` is
741 /// provided, no definitions will be returned.
743 /// Presuming that in-band lifetimes are enabled, then
744 /// `self.anonymous_lifetime_mode` will be updated to match the
745 /// parameter while `f` is running (and restored afterwards).
746 fn collect_in_band_defs<T, F>(
749 anonymous_lifetime_mode: AnonymousLifetimeMode,
751 ) -> (Vec<hir::GenericParam>, T)
753 F: FnOnce(&mut LoweringContext<'_>) -> (Vec<hir::GenericParam>, T),
755 assert!(!self.is_collecting_in_band_lifetimes);
756 assert!(self.lifetimes_to_define.is_empty());
757 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
759 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
760 self.is_collecting_in_band_lifetimes = true;
762 let (in_band_ty_params, res) = f(self);
764 self.is_collecting_in_band_lifetimes = false;
765 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
767 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
769 let params = lifetimes_to_define
771 .map(|(span, hir_name)| self.lifetime_to_generic_param(
772 span, hir_name, parent_id.index,
774 .chain(in_band_ty_params.into_iter())
780 /// Converts a lifetime into a new generic parameter.
781 fn lifetime_to_generic_param(
785 parent_index: DefIndex,
786 ) -> hir::GenericParam {
787 let node_id = self.resolver.next_node_id();
789 // Get the name we'll use to make the def-path. Note
790 // that collisions are ok here and this shouldn't
791 // really show up for end-user.
792 let (str_name, kind) = match hir_name {
793 ParamName::Plain(ident) => (
795 hir::LifetimeParamKind::InBand,
797 ParamName::Fresh(_) => (
798 kw::UnderscoreLifetime,
799 hir::LifetimeParamKind::Elided,
801 ParamName::Error => (
802 kw::UnderscoreLifetime,
803 hir::LifetimeParamKind::Error,
807 // Add a definition for the in-band lifetime def.
808 self.resolver.definitions().create_def_with_parent(
811 DefPathData::LifetimeNs(str_name),
817 hir_id: self.lower_node_id(node_id),
822 pure_wrt_drop: false,
823 kind: hir::GenericParamKind::Lifetime { kind }
827 /// When there is a reference to some lifetime `'a`, and in-band
828 /// lifetimes are enabled, then we want to push that lifetime into
829 /// the vector of names to define later. In that case, it will get
830 /// added to the appropriate generics.
831 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
832 if !self.is_collecting_in_band_lifetimes {
836 if !self.sess.features_untracked().in_band_lifetimes {
840 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
844 let hir_name = ParamName::Plain(ident);
846 if self.lifetimes_to_define.iter()
847 .any(|(_, lt_name)| lt_name.modern() == hir_name.modern()) {
851 self.lifetimes_to_define.push((ident.span, hir_name));
854 /// When we have either an elided or `'_` lifetime in an impl
855 /// header, we convert it to an in-band lifetime.
856 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
857 assert!(self.is_collecting_in_band_lifetimes);
858 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
859 let hir_name = ParamName::Fresh(index);
860 self.lifetimes_to_define.push((span, hir_name));
864 // Evaluates `f` with the lifetimes in `params` in-scope.
865 // This is used to track which lifetimes have already been defined, and
866 // which are new in-band lifetimes that need to have a definition created
868 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
870 F: FnOnce(&mut LoweringContext<'_>) -> T,
872 let old_len = self.in_scope_lifetimes.len();
873 let lt_def_names = params.iter().filter_map(|param| match param.kind {
874 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
877 self.in_scope_lifetimes.extend(lt_def_names);
881 self.in_scope_lifetimes.truncate(old_len);
885 /// Appends in-band lifetime defs and argument-position `impl
886 /// Trait` defs to the existing set of generics.
888 /// Presuming that in-band lifetimes are enabled, then
889 /// `self.anonymous_lifetime_mode` will be updated to match the
890 /// parameter while `f` is running (and restored afterwards).
891 fn add_in_band_defs<F, T>(
895 anonymous_lifetime_mode: AnonymousLifetimeMode,
897 ) -> (hir::Generics, T)
899 F: FnOnce(&mut LoweringContext<'_>, &mut Vec<hir::GenericParam>) -> T,
901 let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
904 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
905 let mut params = Vec::new();
906 // Note: it is necessary to lower generics *before* calling `f`.
907 // When lowering `async fn`, there's a final step when lowering
908 // the return type that assumes that all in-scope lifetimes have
909 // already been added to either `in_scope_lifetimes` or
910 // `lifetimes_to_define`. If we swapped the order of these two,
911 // in-band-lifetimes introduced by generics or where-clauses
912 // wouldn't have been added yet.
913 let generics = this.lower_generics(
915 ImplTraitContext::Universal(&mut params),
917 let res = f(this, &mut params);
918 (params, (generics, res))
923 let mut lowered_params: Vec<_> = lowered_generics
929 // FIXME(const_generics): the compiler doesn't always cope with
930 // unsorted generic parameters at the moment, so we make sure
931 // that they're ordered correctly here for now. (When we chain
932 // the `in_band_defs`, we might make the order unsorted.)
933 lowered_params.sort_by_key(|param| {
935 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
936 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
937 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
941 lowered_generics.params = lowered_params.into();
943 (lowered_generics, res)
946 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
948 F: FnOnce(&mut LoweringContext<'_>) -> T,
950 let was_in_dyn_type = self.is_in_dyn_type;
951 self.is_in_dyn_type = in_scope;
953 let result = f(self);
955 self.is_in_dyn_type = was_in_dyn_type;
960 fn with_new_scopes<T, F>(&mut self, f: F) -> T
962 F: FnOnce(&mut LoweringContext<'_>) -> T,
964 let was_in_loop_condition = self.is_in_loop_condition;
965 self.is_in_loop_condition = false;
967 let catch_scopes = mem::take(&mut self.catch_scopes);
968 let loop_scopes = mem::take(&mut self.loop_scopes);
970 self.catch_scopes = catch_scopes;
971 self.loop_scopes = loop_scopes;
973 self.is_in_loop_condition = was_in_loop_condition;
978 fn def_key(&mut self, id: DefId) -> DefKey {
980 self.resolver.definitions().def_key(id.index)
982 self.resolver.cstore().def_key(id)
986 fn lower_attrs_extendable(&mut self, attrs: &[Attribute]) -> Vec<Attribute> {
989 .map(|a| self.lower_attr(a))
993 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
994 self.lower_attrs_extendable(attrs).into()
997 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
998 // Note that we explicitly do not walk the path. Since we don't really
999 // lower attributes (we use the AST version) there is nowhere to keep
1000 // the `HirId`s. We don't actually need HIR version of attributes anyway.
1001 let kind = match attr.kind {
1002 AttrKind::Normal(ref item) => {
1003 AttrKind::Normal(AttrItem {
1004 path: item.path.clone(),
1005 tokens: self.lower_token_stream(item.tokens.clone()),
1008 AttrKind::DocComment(comment) => AttrKind::DocComment(comment)
1019 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
1022 .flat_map(|tree| self.lower_token_tree(tree).into_trees())
1026 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
1028 TokenTree::Token(token) => self.lower_token(token),
1029 TokenTree::Delimited(span, delim, tts) => TokenTree::Delimited(
1032 self.lower_token_stream(tts),
1037 fn lower_token(&mut self, token: Token) -> TokenStream {
1039 token::Interpolated(nt) => {
1040 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1041 self.lower_token_stream(tts)
1043 _ => TokenTree::Token(token).into(),
1047 /// Given an associated type constraint like one of these:
1050 /// T: Iterator<Item: Debug>
1052 /// T: Iterator<Item = Debug>
1056 /// returns a `hir::TypeBinding` representing `Item`.
1057 fn lower_assoc_ty_constraint(
1059 constraint: &AssocTyConstraint,
1060 itctx: ImplTraitContext<'_>,
1061 ) -> hir::TypeBinding {
1062 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1064 let kind = match constraint.kind {
1065 AssocTyConstraintKind::Equality { ref ty } => hir::TypeBindingKind::Equality {
1066 ty: self.lower_ty(ty, itctx)
1068 AssocTyConstraintKind::Bound { ref bounds } => {
1069 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1070 let (desugar_to_impl_trait, itctx) = match itctx {
1071 // We are in the return position:
1073 // fn foo() -> impl Iterator<Item: Debug>
1077 // fn foo() -> impl Iterator<Item = impl Debug>
1078 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1080 // We are in the argument position, but within a dyn type:
1082 // fn foo(x: dyn Iterator<Item: Debug>)
1086 // fn foo(x: dyn Iterator<Item = impl Debug>)
1087 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1089 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1090 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1091 // "impl trait context" to permit `impl Debug` in this position (it desugars
1092 // then to an opaque type).
1094 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1095 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type =>
1096 (true, ImplTraitContext::OpaqueTy(None)),
1098 // We are in the parameter position, but not within a dyn type:
1100 // fn foo(x: impl Iterator<Item: Debug>)
1102 // so we leave it as is and this gets expanded in astconv to a bound like
1103 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1105 _ => (false, itctx),
1108 if desugar_to_impl_trait {
1109 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1110 // constructing the HIR for `impl bounds...` and then lowering that.
1112 let impl_trait_node_id = self.resolver.next_node_id();
1113 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1114 self.resolver.definitions().create_def_with_parent(
1117 DefPathData::ImplTrait,
1122 self.with_dyn_type_scope(false, |this| {
1123 let node_id = this.resolver.next_node_id();
1124 let ty = this.lower_ty(
1127 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1128 span: constraint.span,
1133 hir::TypeBindingKind::Equality {
1138 // Desugar `AssocTy: Bounds` into a type binding where the
1139 // later desugars into a trait predicate.
1140 let bounds = self.lower_param_bounds(bounds, itctx);
1142 hir::TypeBindingKind::Constraint {
1150 hir_id: self.lower_node_id(constraint.id),
1151 ident: constraint.ident,
1153 span: constraint.span,
1157 fn lower_generic_arg(&mut self,
1158 arg: &ast::GenericArg,
1159 itctx: ImplTraitContext<'_>)
1160 -> hir::GenericArg {
1162 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1163 ast::GenericArg::Type(ty) => GenericArg::Type(self.lower_ty_direct(&ty, itctx)),
1164 ast::GenericArg::Const(ct) => {
1165 GenericArg::Const(ConstArg {
1166 value: self.lower_anon_const(&ct),
1167 span: ct.value.span,
1173 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1174 P(self.lower_ty_direct(t, itctx))
1180 qself: &Option<QSelf>,
1182 param_mode: ParamMode,
1183 itctx: ImplTraitContext<'_>
1185 let id = self.lower_node_id(t.id);
1186 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1187 let ty = self.ty_path(id, t.span, qpath);
1188 if let hir::TyKind::TraitObject(..) = ty.kind {
1189 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1194 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1195 let kind = match t.kind {
1196 TyKind::Infer => hir::TyKind::Infer,
1197 TyKind::Err => hir::TyKind::Err,
1198 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1199 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1200 TyKind::Rptr(ref region, ref mt) => {
1201 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1202 let lifetime = match *region {
1203 Some(ref lt) => self.lower_lifetime(lt),
1204 None => self.elided_ref_lifetime(span),
1206 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1208 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1211 this.with_anonymous_lifetime_mode(
1212 AnonymousLifetimeMode::PassThrough,
1214 hir::TyKind::BareFn(P(hir::BareFnTy {
1215 generic_params: this.lower_generic_params(
1217 &NodeMap::default(),
1218 ImplTraitContext::disallowed(),
1220 unsafety: this.lower_unsafety(f.unsafety),
1221 abi: this.lower_abi(f.abi),
1222 decl: this.lower_fn_decl(&f.decl, None, false, None),
1223 param_names: this.lower_fn_params_to_names(&f.decl),
1229 TyKind::Never => hir::TyKind::Never,
1230 TyKind::Tup(ref tys) => {
1231 hir::TyKind::Tup(tys.iter().map(|ty| {
1232 self.lower_ty_direct(ty, itctx.reborrow())
1235 TyKind::Paren(ref ty) => {
1236 return self.lower_ty_direct(ty, itctx);
1238 TyKind::Path(ref qself, ref path) => {
1239 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1241 TyKind::ImplicitSelf => {
1242 let res = self.expect_full_res(t.id);
1243 let res = self.lower_res(res);
1244 hir::TyKind::Path(hir::QPath::Resolved(
1248 segments: hir_vec![hir::PathSegment::from_ident(
1249 Ident::with_dummy_span(kw::SelfUpper)
1255 TyKind::Array(ref ty, ref length) => {
1256 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1258 TyKind::Typeof(ref expr) => {
1259 hir::TyKind::Typeof(self.lower_anon_const(expr))
1261 TyKind::TraitObject(ref bounds, kind) => {
1262 let mut lifetime_bound = None;
1263 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1266 .filter_map(|bound| match *bound {
1267 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1268 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1270 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1271 GenericBound::Outlives(ref lifetime) => {
1272 if lifetime_bound.is_none() {
1273 lifetime_bound = Some(this.lower_lifetime(lifetime));
1279 let lifetime_bound =
1280 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1281 (bounds, lifetime_bound)
1283 if kind != TraitObjectSyntax::Dyn {
1284 self.maybe_lint_bare_trait(t.span, t.id, false);
1286 hir::TyKind::TraitObject(bounds, lifetime_bound)
1288 TyKind::ImplTrait(def_node_id, ref bounds) => {
1291 ImplTraitContext::OpaqueTy(fn_def_id) => {
1292 self.lower_opaque_impl_trait(
1293 span, fn_def_id, def_node_id,
1294 |this| this.lower_param_bounds(bounds, itctx),
1297 ImplTraitContext::Universal(in_band_ty_params) => {
1298 // Add a definition for the in-band `Param`.
1299 let def_index = self
1302 .opt_def_index(def_node_id)
1305 let hir_bounds = self.lower_param_bounds(
1307 ImplTraitContext::Universal(in_band_ty_params),
1309 // Set the name to `impl Bound1 + Bound2`.
1310 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1311 in_band_ty_params.push(hir::GenericParam {
1312 hir_id: self.lower_node_id(def_node_id),
1313 name: ParamName::Plain(ident),
1314 pure_wrt_drop: false,
1318 kind: hir::GenericParamKind::Type {
1320 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1324 hir::TyKind::Path(hir::QPath::Resolved(
1328 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1329 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1333 ImplTraitContext::Disallowed(pos) => {
1334 let allowed_in = if self.sess.features_untracked()
1335 .impl_trait_in_bindings {
1336 "bindings or function and inherent method return types"
1338 "function and inherent method return types"
1340 let mut err = struct_span_err!(
1344 "`impl Trait` not allowed outside of {}",
1347 if pos == ImplTraitPosition::Binding &&
1348 nightly_options::is_nightly_build() {
1350 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1351 attributes to enable");
1358 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1359 TyKind::CVarArgs => bug!("`TyKind::CVarArgs` should have been handled elsewhere"),
1365 hir_id: self.lower_node_id(t.id),
1369 fn lower_opaque_impl_trait(
1372 fn_def_id: Option<DefId>,
1373 opaque_ty_node_id: NodeId,
1374 lower_bounds: impl FnOnce(&mut LoweringContext<'_>) -> hir::GenericBounds,
1377 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1383 // Make sure we know that some funky desugaring has been going on here.
1384 // This is a first: there is code in other places like for loop
1385 // desugaring that explicitly states that we don't want to track that.
1386 // Not tracking it makes lints in rustc and clippy very fragile, as
1387 // frequently opened issues show.
1388 let opaque_ty_span = self.mark_span_with_reason(
1389 DesugaringKind::OpaqueTy,
1394 let opaque_ty_def_index = self
1397 .opt_def_index(opaque_ty_node_id)
1400 self.allocate_hir_id_counter(opaque_ty_node_id);
1402 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1404 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1406 opaque_ty_def_index,
1411 "lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,
1415 "lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,
1418 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1419 let opaque_ty_item = hir::OpaqueTy {
1420 generics: hir::Generics {
1421 params: lifetime_defs,
1422 where_clause: hir::WhereClause {
1423 predicates: hir_vec![],
1429 impl_trait_fn: fn_def_id,
1430 origin: hir::OpaqueTyOrigin::FnReturn,
1433 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1434 let opaque_ty_id = lctx.generate_opaque_type(
1441 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1442 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1446 /// Registers a new opaque type with the proper `NodeId`s and
1447 /// returns the lowered node-ID for the opaque type.
1448 fn generate_opaque_type(
1450 opaque_ty_node_id: NodeId,
1451 opaque_ty_item: hir::OpaqueTy,
1453 opaque_ty_span: Span,
1455 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1456 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1457 // Generate an `type Foo = impl Trait;` declaration.
1458 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1459 let opaque_ty_item = hir::Item {
1460 hir_id: opaque_ty_id,
1461 ident: Ident::invalid(),
1462 attrs: Default::default(),
1463 kind: opaque_ty_item_kind,
1464 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1465 span: opaque_ty_span,
1468 // Insert the item into the global item list. This usually happens
1469 // automatically for all AST items. But this opaque type item
1470 // does not actually exist in the AST.
1471 self.insert_item(opaque_ty_item);
1475 fn lifetimes_from_impl_trait_bounds(
1477 opaque_ty_id: NodeId,
1478 parent_index: DefIndex,
1479 bounds: &hir::GenericBounds,
1480 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1482 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1483 parent_index={:?}, \
1485 opaque_ty_id, parent_index, bounds,
1488 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1489 // appear in the bounds, excluding lifetimes that are created within the bounds.
1490 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1491 struct ImplTraitLifetimeCollector<'r, 'a> {
1492 context: &'r mut LoweringContext<'a>,
1494 opaque_ty_id: NodeId,
1495 collect_elided_lifetimes: bool,
1496 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1497 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1498 output_lifetimes: Vec<hir::GenericArg>,
1499 output_lifetime_params: Vec<hir::GenericParam>,
1502 impl<'r, 'a, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1503 fn nested_visit_map<'this>(
1505 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1506 hir::intravisit::NestedVisitorMap::None
1509 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1510 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1511 if parameters.parenthesized {
1512 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1513 self.collect_elided_lifetimes = false;
1514 hir::intravisit::walk_generic_args(self, span, parameters);
1515 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1517 hir::intravisit::walk_generic_args(self, span, parameters);
1521 fn visit_ty(&mut self, t: &'v hir::Ty) {
1522 // Don't collect elided lifetimes used inside of `fn()` syntax.
1523 if let hir::TyKind::BareFn(_) = t.kind {
1524 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1525 self.collect_elided_lifetimes = false;
1527 // Record the "stack height" of `for<'a>` lifetime bindings
1528 // to be able to later fully undo their introduction.
1529 let old_len = self.currently_bound_lifetimes.len();
1530 hir::intravisit::walk_ty(self, t);
1531 self.currently_bound_lifetimes.truncate(old_len);
1533 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1535 hir::intravisit::walk_ty(self, t)
1539 fn visit_poly_trait_ref(
1541 trait_ref: &'v hir::PolyTraitRef,
1542 modifier: hir::TraitBoundModifier,
1544 // Record the "stack height" of `for<'a>` lifetime bindings
1545 // to be able to later fully undo their introduction.
1546 let old_len = self.currently_bound_lifetimes.len();
1547 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1548 self.currently_bound_lifetimes.truncate(old_len);
1551 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1552 // Record the introduction of 'a in `for<'a> ...`.
1553 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1554 // Introduce lifetimes one at a time so that we can handle
1555 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1556 let lt_name = hir::LifetimeName::Param(param.name);
1557 self.currently_bound_lifetimes.push(lt_name);
1560 hir::intravisit::walk_generic_param(self, param);
1563 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1564 let name = match lifetime.name {
1565 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1566 if self.collect_elided_lifetimes {
1567 // Use `'_` for both implicit and underscore lifetimes in
1568 // `type Foo<'_> = impl SomeTrait<'_>;`.
1569 hir::LifetimeName::Underscore
1574 hir::LifetimeName::Param(_) => lifetime.name,
1576 // Refers to some other lifetime that is "in
1577 // scope" within the type.
1578 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1580 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1583 if !self.currently_bound_lifetimes.contains(&name)
1584 && !self.already_defined_lifetimes.contains(&name) {
1585 self.already_defined_lifetimes.insert(name);
1587 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1588 hir_id: self.context.next_id(),
1589 span: lifetime.span,
1593 let def_node_id = self.context.resolver.next_node_id();
1595 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1596 self.context.resolver.definitions().create_def_with_parent(
1599 DefPathData::LifetimeNs(name.ident().name),
1603 let (name, kind) = match name {
1604 hir::LifetimeName::Underscore => (
1605 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1606 hir::LifetimeParamKind::Elided,
1608 hir::LifetimeName::Param(param_name) => (
1610 hir::LifetimeParamKind::Explicit,
1612 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1615 self.output_lifetime_params.push(hir::GenericParam {
1618 span: lifetime.span,
1619 pure_wrt_drop: false,
1622 kind: hir::GenericParamKind::Lifetime { kind }
1628 let mut lifetime_collector = ImplTraitLifetimeCollector {
1630 parent: parent_index,
1632 collect_elided_lifetimes: true,
1633 currently_bound_lifetimes: Vec::new(),
1634 already_defined_lifetimes: FxHashSet::default(),
1635 output_lifetimes: Vec::new(),
1636 output_lifetime_params: Vec::new(),
1639 for bound in bounds {
1640 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1644 lifetime_collector.output_lifetimes.into(),
1645 lifetime_collector.output_lifetime_params.into(),
1652 qself: &Option<QSelf>,
1654 param_mode: ParamMode,
1655 mut itctx: ImplTraitContext<'_>,
1657 let qself_position = qself.as_ref().map(|q| q.position);
1658 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1660 let partial_res = self.resolver
1661 .get_partial_res(id)
1662 .unwrap_or_else(|| PartialRes::new(Res::Err));
1664 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1665 let path = P(hir::Path {
1666 res: self.lower_res(partial_res.base_res()),
1667 segments: p.segments[..proj_start]
1670 .map(|(i, segment)| {
1671 let param_mode = match (qself_position, param_mode) {
1672 (Some(j), ParamMode::Optional) if i < j => {
1673 // This segment is part of the trait path in a
1674 // qualified path - one of `a`, `b` or `Trait`
1675 // in `<X as a::b::Trait>::T::U::method`.
1681 // Figure out if this is a type/trait segment,
1682 // which may need lifetime elision performed.
1683 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1684 krate: def_id.krate,
1685 index: this.def_key(def_id).parent.expect("missing parent"),
1687 let type_def_id = match partial_res.base_res() {
1688 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1689 Some(parent_def_id(self, def_id))
1691 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1692 Some(parent_def_id(self, def_id))
1694 Res::Def(DefKind::Struct, def_id)
1695 | Res::Def(DefKind::Union, def_id)
1696 | Res::Def(DefKind::Enum, def_id)
1697 | Res::Def(DefKind::TyAlias, def_id)
1698 | Res::Def(DefKind::Trait, def_id) if i + 1 == proj_start =>
1704 let parenthesized_generic_args = match partial_res.base_res() {
1705 // `a::b::Trait(Args)`
1706 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1707 ParenthesizedGenericArgs::Ok
1709 // `a::b::Trait(Args)::TraitItem`
1710 Res::Def(DefKind::Method, _) |
1711 Res::Def(DefKind::AssocConst, _) |
1712 Res::Def(DefKind::AssocTy, _) if i + 2 == proj_start => {
1713 ParenthesizedGenericArgs::Ok
1715 // Avoid duplicated errors.
1716 Res::Err => ParenthesizedGenericArgs::Ok,
1718 _ => ParenthesizedGenericArgs::Err,
1721 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1722 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1725 assert!(!def_id.is_local());
1726 let item_generics = self.resolver.cstore()
1727 .item_generics_cloned_untracked(def_id, self.sess);
1728 let n = item_generics.own_counts().lifetimes;
1729 self.type_def_lifetime_params.insert(def_id, n);
1732 self.lower_path_segment(
1737 parenthesized_generic_args,
1746 // Simple case, either no projections, or only fully-qualified.
1747 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1748 if partial_res.unresolved_segments() == 0 {
1749 return hir::QPath::Resolved(qself, path);
1752 // Create the innermost type that we're projecting from.
1753 let mut ty = if path.segments.is_empty() {
1754 // If the base path is empty that means there exists a
1755 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1756 qself.expect("missing QSelf for <T>::...")
1758 // Otherwise, the base path is an implicit `Self` type path,
1759 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1760 // `<I as Iterator>::Item::default`.
1761 let new_id = self.next_id();
1762 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1765 // Anything after the base path are associated "extensions",
1766 // out of which all but the last one are associated types,
1767 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1768 // * base path is `std::vec::Vec<T>`
1769 // * "extensions" are `IntoIter`, `Item` and `clone`
1770 // * type nodes are:
1771 // 1. `std::vec::Vec<T>` (created above)
1772 // 2. `<std::vec::Vec<T>>::IntoIter`
1773 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1774 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1775 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1776 let segment = P(self.lower_path_segment(
1781 ParenthesizedGenericArgs::Err,
1785 let qpath = hir::QPath::TypeRelative(ty, segment);
1787 // It's finished, return the extension of the right node type.
1788 if i == p.segments.len() - 1 {
1792 // Wrap the associated extension in another type node.
1793 let new_id = self.next_id();
1794 ty = P(self.ty_path(new_id, p.span, qpath));
1797 // We should've returned in the for loop above.
1800 "lower_qpath: no final extension segment in {}..{}",
1806 fn lower_path_extra(
1810 param_mode: ParamMode,
1811 explicit_owner: Option<NodeId>,
1815 segments: p.segments
1818 self.lower_path_segment(
1823 ParenthesizedGenericArgs::Err,
1824 ImplTraitContext::disallowed(),
1833 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1834 let res = self.expect_full_res(id);
1835 let res = self.lower_res(res);
1836 self.lower_path_extra(res, p, param_mode, None)
1839 fn lower_path_segment(
1842 segment: &PathSegment,
1843 param_mode: ParamMode,
1844 expected_lifetimes: usize,
1845 parenthesized_generic_args: ParenthesizedGenericArgs,
1846 itctx: ImplTraitContext<'_>,
1847 explicit_owner: Option<NodeId>,
1848 ) -> hir::PathSegment {
1849 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1850 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1851 match **generic_args {
1852 GenericArgs::AngleBracketed(ref data) => {
1853 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1855 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1856 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1857 ParenthesizedGenericArgs::Err => {
1858 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1859 err.span_label(data.span, "only `Fn` traits may use parentheses");
1860 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1861 // Do not suggest going from `Trait()` to `Trait<>`
1862 if data.inputs.len() > 0 {
1863 let split = snippet.find('(').unwrap();
1864 let trait_name = &snippet[0..split];
1865 let args = &snippet[split + 1 .. snippet.len() - 1];
1866 err.span_suggestion(
1868 "use angle brackets instead",
1869 format!("{}<{}>", trait_name, args),
1870 Applicability::MaybeIncorrect,
1876 self.lower_angle_bracketed_parameter_data(
1877 &data.as_angle_bracketed_args(),
1887 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1890 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1891 GenericArg::Lifetime(_) => true,
1894 let first_generic_span = generic_args.args.iter().map(|a| a.span())
1895 .chain(generic_args.bindings.iter().map(|b| b.span)).next();
1896 if !generic_args.parenthesized && !has_lifetimes {
1898 self.elided_path_lifetimes(path_span, expected_lifetimes)
1900 .map(|lt| GenericArg::Lifetime(lt))
1901 .chain(generic_args.args.into_iter())
1903 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1904 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1905 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1906 let no_bindings = generic_args.bindings.is_empty();
1907 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1908 // If there are no (non-implicit) generic args or associated type
1909 // bindings, our suggestion includes the angle brackets.
1910 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1912 // Otherwise (sorry, this is kind of gross) we need to infer the
1913 // place to splice in the `'_, ` from the generics that do exist.
1914 let first_generic_span = first_generic_span
1915 .expect("already checked that non-lifetime args or bindings exist");
1916 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1918 match self.anonymous_lifetime_mode {
1919 // In create-parameter mode we error here because we don't want to support
1920 // deprecated impl elision in new features like impl elision and `async fn`,
1921 // both of which work using the `CreateParameter` mode:
1923 // impl Foo for std::cell::Ref<u32> // note lack of '_
1924 // async fn foo(_: std::cell::Ref<u32>) { ... }
1925 AnonymousLifetimeMode::CreateParameter => {
1926 let mut err = struct_span_err!(
1930 "implicit elided lifetime not allowed here"
1932 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1943 AnonymousLifetimeMode::PassThrough |
1944 AnonymousLifetimeMode::ReportError => {
1945 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1946 ELIDED_LIFETIMES_IN_PATHS,
1949 "hidden lifetime parameters in types are deprecated",
1950 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1963 let res = self.expect_full_res(segment.id);
1964 let id = if let Some(owner) = explicit_owner {
1965 self.lower_node_id_with_owner(segment.id, owner)
1967 self.lower_node_id(segment.id)
1970 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1971 segment.ident, segment.id, id,
1974 hir::PathSegment::new(
1977 Some(self.lower_res(res)),
1983 fn lower_angle_bracketed_parameter_data(
1985 data: &AngleBracketedArgs,
1986 param_mode: ParamMode,
1987 mut itctx: ImplTraitContext<'_>,
1988 ) -> (hir::GenericArgs, bool) {
1989 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1990 let has_non_lt_args = args.iter().any(|arg| match arg {
1991 ast::GenericArg::Lifetime(_) => false,
1992 ast::GenericArg::Type(_) => true,
1993 ast::GenericArg::Const(_) => true,
1997 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1998 bindings: constraints.iter()
1999 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
2001 parenthesized: false,
2003 !has_non_lt_args && param_mode == ParamMode::Optional
2007 fn lower_parenthesized_parameter_data(
2009 data: &ParenthesizedArgs,
2010 ) -> (hir::GenericArgs, bool) {
2011 // Switch to `PassThrough` mode for anonymous lifetimes; this
2012 // means that we permit things like `&Ref<T>`, where `Ref` has
2013 // a hidden lifetime parameter. This is needed for backwards
2014 // compatibility, even in contexts like an impl header where
2015 // we generally don't permit such things (see #51008).
2016 self.with_anonymous_lifetime_mode(
2017 AnonymousLifetimeMode::PassThrough,
2019 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2022 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2024 let mk_tup = |this: &mut Self, tys, span| {
2025 hir::Ty { kind: hir::TyKind::Tup(tys), hir_id: this.next_id(), span }
2029 args: hir_vec![GenericArg::Type(mk_tup(this, inputs, span))],
2032 hir_id: this.next_id(),
2033 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2034 kind: hir::TypeBindingKind::Equality {
2037 .map(|ty| this.lower_ty(
2039 ImplTraitContext::disallowed()
2042 P(mk_tup(this, hir::HirVec::new(), span))
2045 span: output.as_ref().map_or(span, |ty| ty.span),
2048 parenthesized: true,
2056 fn lower_local(&mut self, l: &Local) -> (hir::Local, SmallVec<[NodeId; 1]>) {
2057 let mut ids = SmallVec::<[NodeId; 1]>::new();
2058 if self.sess.features_untracked().impl_trait_in_bindings {
2059 if let Some(ref ty) = l.ty {
2060 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2061 visitor.visit_ty(ty);
2064 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2066 hir_id: self.lower_node_id(l.id),
2069 .map(|t| self.lower_ty(t,
2070 if self.sess.features_untracked().impl_trait_in_bindings {
2071 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2073 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2076 pat: self.lower_pat(&l.pat),
2077 init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
2079 attrs: l.attrs.clone(),
2080 source: hir::LocalSource::Normal,
2084 fn lower_mutability(&mut self, m: Mutability) -> hir::Mutability {
2086 Mutability::Mutable => hir::MutMutable,
2087 Mutability::Immutable => hir::MutImmutable,
2091 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2092 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2093 // as they are not explicit in HIR/Ty function signatures.
2094 // (instead, the `c_variadic` flag is set to `true`)
2095 let mut inputs = &decl.inputs[..];
2096 if decl.c_variadic() {
2097 inputs = &inputs[..inputs.len() - 1];
2101 .map(|param| match param.pat.kind {
2102 PatKind::Ident(_, ident, _) => ident,
2103 _ => Ident::new(kw::Invalid, param.pat.span),
2108 // Lowers a function declaration.
2110 // `decl`: the unlowered (AST) function declaration.
2111 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2112 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2113 // `make_ret_async` is also `Some`.
2114 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2115 // This guards against trait declarations and implementations where `impl Trait` is
2117 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2118 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2119 // return type `impl Trait` item.
2123 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2124 impl_trait_return_allow: bool,
2125 make_ret_async: Option<NodeId>,
2126 ) -> P<hir::FnDecl> {
2127 let lt_mode = if make_ret_async.is_some() {
2128 // In `async fn`, argument-position elided lifetimes
2129 // must be transformed into fresh generic parameters so that
2130 // they can be applied to the opaque `impl Trait` return type.
2131 AnonymousLifetimeMode::CreateParameter
2133 self.anonymous_lifetime_mode
2136 let c_variadic = decl.c_variadic();
2138 // Remember how many lifetimes were already around so that we can
2139 // only look at the lifetime parameters introduced by the arguments.
2140 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2141 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2142 // as they are not explicit in HIR/Ty function signatures.
2143 // (instead, the `c_variadic` flag is set to `true`)
2144 let mut inputs = &decl.inputs[..];
2146 inputs = &inputs[..inputs.len() - 1];
2151 if let Some((_, ibty)) = &mut in_band_ty_params {
2152 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2154 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2157 .collect::<HirVec<_>>()
2160 let output = if let Some(ret_id) = make_ret_async {
2161 self.lower_async_fn_ret_ty(
2163 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2168 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2169 Some((def_id, _)) if impl_trait_return_allow => {
2170 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2173 hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed()))
2176 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2184 implicit_self: decl.inputs.get(0).map_or(
2185 hir::ImplicitSelfKind::None,
2187 let is_mutable_pat = match arg.pat.kind {
2188 PatKind::Ident(BindingMode::ByValue(mt), _, _) |
2189 PatKind::Ident(BindingMode::ByRef(mt), _, _) =>
2190 mt == Mutability::Mutable,
2195 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2196 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2197 // Given we are only considering `ImplicitSelf` types, we needn't consider
2198 // the case where we have a mutable pattern to a reference as that would
2199 // no longer be an `ImplicitSelf`.
2200 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() &&
2201 mt.mutbl == ast::Mutability::Mutable =>
2202 hir::ImplicitSelfKind::MutRef,
2203 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() =>
2204 hir::ImplicitSelfKind::ImmRef,
2205 _ => hir::ImplicitSelfKind::None,
2212 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2213 // combined with the following definition of `OpaqueTy`:
2215 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2217 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2218 // `output`: unlowered output type (`T` in `-> T`)
2219 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2220 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2221 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2222 fn lower_async_fn_ret_ty(
2224 output: &FunctionRetTy,
2226 opaque_ty_node_id: NodeId,
2227 ) -> hir::FunctionRetTy {
2229 "lower_async_fn_ret_ty(\
2232 opaque_ty_node_id={:?})",
2233 output, fn_def_id, opaque_ty_node_id,
2236 let span = output.span();
2238 let opaque_ty_span = self.mark_span_with_reason(
2239 DesugaringKind::Async,
2244 let opaque_ty_def_index = self
2247 .opt_def_index(opaque_ty_node_id)
2250 self.allocate_hir_id_counter(opaque_ty_node_id);
2252 // When we create the opaque type for this async fn, it is going to have
2253 // to capture all the lifetimes involved in the signature (including in the
2254 // return type). This is done by introducing lifetime parameters for:
2256 // - all the explicitly declared lifetimes from the impl and function itself;
2257 // - all the elided lifetimes in the fn arguments;
2258 // - all the elided lifetimes in the return type.
2260 // So for example in this snippet:
2263 // impl<'a> Foo<'a> {
2264 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2265 // // ^ '0 ^ '1 ^ '2
2266 // // elided lifetimes used below
2271 // we would create an opaque type like:
2274 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2277 // and we would then desugar `bar` to the equivalent of:
2280 // impl<'a> Foo<'a> {
2281 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2285 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2286 // this is because the elided lifetimes from the return type
2287 // should be figured out using the ordinary elision rules, and
2288 // this desugaring achieves that.
2290 // The variable `input_lifetimes_count` tracks the number of
2291 // lifetime parameters to the opaque type *not counting* those
2292 // lifetimes elided in the return type. This includes those
2293 // that are explicitly declared (`in_scope_lifetimes`) and
2294 // those elided lifetimes we found in the arguments (current
2295 // content of `lifetimes_to_define`). Next, we will process
2296 // the return type, which will cause `lifetimes_to_define` to
2298 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2300 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2301 // We have to be careful to get elision right here. The
2302 // idea is that we create a lifetime parameter for each
2303 // lifetime in the return type. So, given a return type
2304 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2305 // Future<Output = &'1 [ &'2 u32 ]>`.
2307 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2308 // hence the elision takes place at the fn site.
2309 let future_bound = this.with_anonymous_lifetime_mode(
2310 AnonymousLifetimeMode::CreateParameter,
2311 |this| this.lower_async_fn_output_type_to_future_bound(
2318 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2320 // Calculate all the lifetimes that should be captured
2321 // by the opaque type. This should include all in-scope
2322 // lifetime parameters, including those defined in-band.
2324 // Note: this must be done after lowering the output type,
2325 // as the output type may introduce new in-band lifetimes.
2326 let lifetime_params: Vec<(Span, ParamName)> =
2327 this.in_scope_lifetimes
2329 .map(|name| (name.ident().span, name))
2330 .chain(this.lifetimes_to_define.iter().cloned())
2333 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2334 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2335 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2337 let generic_params =
2340 .map(|(span, hir_name)| {
2341 this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_index)
2345 let opaque_ty_item = hir::OpaqueTy {
2346 generics: hir::Generics {
2347 params: generic_params,
2348 where_clause: hir::WhereClause {
2349 predicates: hir_vec![],
2354 bounds: hir_vec![future_bound],
2355 impl_trait_fn: Some(fn_def_id),
2356 origin: hir::OpaqueTyOrigin::AsyncFn,
2359 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2360 let opaque_ty_id = this.generate_opaque_type(
2367 (opaque_ty_id, lifetime_params)
2370 // As documented above on the variable
2371 // `input_lifetimes_count`, we need to create the lifetime
2372 // arguments to our opaque type. Continuing with our example,
2373 // we're creating the type arguments for the return type:
2376 // Bar<'a, 'b, '0, '1, '_>
2379 // For the "input" lifetime parameters, we wish to create
2380 // references to the parameters themselves, including the
2381 // "implicit" ones created from parameter types (`'a`, `'b`,
2384 // For the "output" lifetime parameters, we just want to
2386 let mut generic_args: Vec<_> =
2387 lifetime_params[..input_lifetimes_count]
2389 .map(|&(span, hir_name)| {
2390 // Input lifetime like `'a` or `'1`:
2391 GenericArg::Lifetime(hir::Lifetime {
2392 hir_id: self.next_id(),
2394 name: hir::LifetimeName::Param(hir_name),
2398 generic_args.extend(
2399 lifetime_params[input_lifetimes_count..]
2402 // Output lifetime like `'_`.
2403 GenericArg::Lifetime(hir::Lifetime {
2404 hir_id: self.next_id(),
2406 name: hir::LifetimeName::Implicit,
2411 // Create the `Foo<...>` refernece itself. Note that the `type
2412 // Foo = impl Trait` is, internally, created as a child of the
2413 // async fn, so the *type parameters* are inherited. It's
2414 // only the lifetime parameters that we must supply.
2415 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args.into());
2417 hir::FunctionRetTy::Return(P(hir::Ty {
2418 kind: opaque_ty_ref,
2420 hir_id: self.next_id(),
2424 /// Transforms `-> T` into `Future<Output = T>`
2425 fn lower_async_fn_output_type_to_future_bound(
2427 output: &FunctionRetTy,
2430 ) -> hir::GenericBound {
2431 // Compute the `T` in `Future<Output = T>` from the return type.
2432 let output_ty = match output {
2433 FunctionRetTy::Ty(ty) => {
2434 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id)))
2436 FunctionRetTy::Default(ret_ty_span) => {
2438 hir_id: self.next_id(),
2439 kind: hir::TyKind::Tup(hir_vec![]),
2446 let future_params = P(hir::GenericArgs {
2448 bindings: hir_vec![hir::TypeBinding {
2449 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2450 kind: hir::TypeBindingKind::Equality {
2453 hir_id: self.next_id(),
2456 parenthesized: false,
2459 // ::std::future::Future<future_params>
2461 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2463 hir::GenericBound::Trait(
2465 trait_ref: hir::TraitRef {
2467 hir_ref_id: self.next_id(),
2469 bound_generic_params: hir_vec![],
2472 hir::TraitBoundModifier::None,
2476 fn lower_param_bound(
2479 itctx: ImplTraitContext<'_>,
2480 ) -> hir::GenericBound {
2482 GenericBound::Trait(ref ty, modifier) => {
2483 hir::GenericBound::Trait(
2484 self.lower_poly_trait_ref(ty, itctx),
2485 self.lower_trait_bound_modifier(modifier),
2488 GenericBound::Outlives(ref lifetime) => {
2489 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2494 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2495 let span = l.ident.span;
2497 ident if ident.name == kw::StaticLifetime =>
2498 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
2499 ident if ident.name == kw::UnderscoreLifetime =>
2500 match self.anonymous_lifetime_mode {
2501 AnonymousLifetimeMode::CreateParameter => {
2502 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2503 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2506 AnonymousLifetimeMode::PassThrough => {
2507 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2510 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2513 self.maybe_collect_in_band_lifetime(ident);
2514 let param_name = ParamName::Plain(ident);
2515 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2520 fn new_named_lifetime(
2524 name: hir::LifetimeName,
2525 ) -> hir::Lifetime {
2527 hir_id: self.lower_node_id(id),
2533 fn lower_generic_params(
2535 params: &[GenericParam],
2536 add_bounds: &NodeMap<Vec<GenericBound>>,
2537 mut itctx: ImplTraitContext<'_>,
2538 ) -> hir::HirVec<hir::GenericParam> {
2539 params.iter().map(|param| {
2540 self.lower_generic_param(param, add_bounds, itctx.reborrow())
2544 fn lower_generic_param(&mut self,
2545 param: &GenericParam,
2546 add_bounds: &NodeMap<Vec<GenericBound>>,
2547 mut itctx: ImplTraitContext<'_>)
2548 -> hir::GenericParam {
2549 let mut bounds = self.with_anonymous_lifetime_mode(
2550 AnonymousLifetimeMode::ReportError,
2551 |this| this.lower_param_bounds(¶m.bounds, itctx.reborrow()),
2554 let (name, kind) = match param.kind {
2555 GenericParamKind::Lifetime => {
2556 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2557 self.is_collecting_in_band_lifetimes = false;
2559 let lt = self.with_anonymous_lifetime_mode(
2560 AnonymousLifetimeMode::ReportError,
2561 |this| this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }),
2563 let param_name = match lt.name {
2564 hir::LifetimeName::Param(param_name) => param_name,
2565 hir::LifetimeName::Implicit
2566 | hir::LifetimeName::Underscore
2567 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2568 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2571 "object-lifetime-default should not occur here",
2574 hir::LifetimeName::Error => ParamName::Error,
2577 let kind = hir::GenericParamKind::Lifetime {
2578 kind: hir::LifetimeParamKind::Explicit
2581 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2585 GenericParamKind::Type { ref default, .. } => {
2586 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2587 if !add_bounds.is_empty() {
2588 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2589 bounds = bounds.into_iter()
2594 let kind = hir::GenericParamKind::Type {
2595 default: default.as_ref().map(|x| {
2596 self.lower_ty(x, ImplTraitContext::OpaqueTy(None))
2598 synthetic: param.attrs.iter()
2599 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2600 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2604 (hir::ParamName::Plain(param.ident), kind)
2606 GenericParamKind::Const { ref ty } => {
2607 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const {
2608 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2614 hir_id: self.lower_node_id(param.id),
2616 span: param.ident.span,
2617 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2618 attrs: self.lower_attrs(¶m.attrs),
2624 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2625 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2626 hir::QPath::Resolved(None, path) => path,
2627 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2631 hir_ref_id: self.lower_node_id(p.ref_id),
2635 fn lower_poly_trait_ref(
2638 mut itctx: ImplTraitContext<'_>,
2639 ) -> hir::PolyTraitRef {
2640 let bound_generic_params = self.lower_generic_params(
2641 &p.bound_generic_params,
2642 &NodeMap::default(),
2645 let trait_ref = self.with_in_scope_lifetime_defs(
2646 &p.bound_generic_params,
2647 |this| this.lower_trait_ref(&p.trait_ref, itctx),
2651 bound_generic_params,
2657 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2659 ty: self.lower_ty(&mt.ty, itctx),
2660 mutbl: self.lower_mutability(mt.mutbl),
2664 fn lower_param_bounds(&mut self, bounds: &[GenericBound], mut itctx: ImplTraitContext<'_>)
2665 -> hir::GenericBounds {
2666 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2669 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2670 let mut stmts = vec![];
2671 let mut expr = None;
2673 for (index, stmt) in b.stmts.iter().enumerate() {
2674 if index == b.stmts.len() - 1 {
2675 if let StmtKind::Expr(ref e) = stmt.kind {
2676 expr = Some(P(self.lower_expr(e)));
2678 stmts.extend(self.lower_stmt(stmt));
2681 stmts.extend(self.lower_stmt(stmt));
2686 hir_id: self.lower_node_id(b.id),
2687 stmts: stmts.into(),
2689 rules: self.lower_block_check_mode(&b.rules),
2695 /// Lowers a block directly to an expression, presuming that it
2696 /// has no attributes and is not targeted by a `break`.
2697 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr {
2698 let block = self.lower_block(b, false);
2699 self.expr_block(block, ThinVec::new())
2702 fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2703 let node = match p.kind {
2704 PatKind::Wild => hir::PatKind::Wild,
2705 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2706 let lower_sub = |this: &mut Self| sub.as_ref().map(|x| this.lower_pat(x));
2707 self.lower_pat_ident(p, binding_mode, ident, lower_sub)
2709 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2710 PatKind::TupleStruct(ref path, ref pats) => {
2711 let qpath = self.lower_qpath(
2715 ParamMode::Optional,
2716 ImplTraitContext::disallowed(),
2718 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2719 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2721 PatKind::Or(ref pats) => {
2722 hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
2724 PatKind::Path(ref qself, ref path) => {
2725 let qpath = self.lower_qpath(
2729 ParamMode::Optional,
2730 ImplTraitContext::disallowed(),
2732 hir::PatKind::Path(qpath)
2734 PatKind::Struct(ref path, ref fields, etc) => {
2735 let qpath = self.lower_qpath(
2739 ParamMode::Optional,
2740 ImplTraitContext::disallowed(),
2745 .map(|f| hir::FieldPat {
2746 hir_id: self.next_id(),
2748 pat: self.lower_pat(&f.pat),
2749 is_shorthand: f.is_shorthand,
2753 hir::PatKind::Struct(qpath, fs, etc)
2755 PatKind::Tuple(ref pats) => {
2756 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2757 hir::PatKind::Tuple(pats, ddpos)
2759 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2760 PatKind::Ref(ref inner, mutbl) => {
2761 hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
2763 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2764 P(self.lower_expr(e1)),
2765 P(self.lower_expr(e2)),
2766 self.lower_range_end(end),
2768 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2770 // If we reach here the `..` pattern is not semantically allowed.
2771 self.ban_illegal_rest_pat(p.span)
2773 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2774 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2777 self.pat_with_node_id_of(p, node)
2784 ) -> (HirVec<P<hir::Pat>>, Option<usize>) {
2785 let mut elems = Vec::with_capacity(pats.len());
2786 let mut rest = None;
2788 let mut iter = pats.iter().enumerate();
2789 while let Some((idx, pat)) = iter.next() {
2790 // Interpret the first `..` pattern as a subtuple pattern.
2792 rest = Some((idx, pat.span));
2795 // It was not a subslice pattern so lower it normally.
2796 elems.push(self.lower_pat(pat));
2799 while let Some((_, pat)) = iter.next() {
2800 // There was a previous subtuple pattern; make sure we don't allow more.
2802 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2804 elems.push(self.lower_pat(pat));
2808 (elems.into(), rest.map(|(ddpos, _)| ddpos))
2811 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind {
2812 let mut before = Vec::new();
2813 let mut after = Vec::new();
2814 let mut slice = None;
2815 let mut prev_rest_span = None;
2817 let mut iter = pats.iter();
2818 while let Some(pat) = iter.next() {
2819 // Interpret the first `((ref mut?)? x @)? ..` pattern as a subslice pattern.
2822 prev_rest_span = Some(pat.span);
2823 slice = Some(self.pat_wild_with_node_id_of(pat));
2826 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2827 prev_rest_span = Some(sub.span);
2828 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2829 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2830 slice = Some(self.pat_with_node_id_of(pat, node));
2836 // It was not a subslice pattern so lower it normally.
2837 before.push(self.lower_pat(pat));
2840 while let Some(pat) = iter.next() {
2841 // There was a previous subslice pattern; make sure we don't allow more.
2842 let rest_span = match pat.kind {
2843 PatKind::Rest => Some(pat.span),
2844 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2845 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2846 after.push(self.pat_wild_with_node_id_of(pat));
2851 if let Some(rest_span) = rest_span {
2852 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2854 after.push(self.lower_pat(pat));
2858 hir::PatKind::Slice(before.into(), slice, after.into())
2864 binding_mode: &BindingMode,
2866 lower_sub: impl FnOnce(&mut Self) -> Option<P<hir::Pat>>,
2868 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2869 // `None` can occur in body-less function signatures
2870 res @ None | res @ Some(Res::Local(_)) => {
2871 let canonical_id = match res {
2872 Some(Res::Local(id)) => id,
2876 hir::PatKind::Binding(
2877 self.lower_binding_mode(binding_mode),
2878 self.lower_node_id(canonical_id),
2883 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2887 res: self.lower_res(res),
2888 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2894 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> P<hir::Pat> {
2895 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2898 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2899 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind) -> P<hir::Pat> {
2901 hir_id: self.lower_node_id(p.id),
2907 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2908 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2910 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2911 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2912 .span_label(prev_sp, "previously used here")
2916 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2917 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind {
2919 .struct_span_err(sp, "`..` patterns are not allowed here")
2920 .note("only allowed in tuple, tuple struct, and slice patterns")
2923 // We're not in a list context so `..` can be reasonably treated
2924 // as `_` because it should always be valid and roughly matches the
2925 // intent of `..` (notice that the rest of a single slot is that slot).
2929 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2931 RangeEnd::Included(_) => hir::RangeEnd::Included,
2932 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2936 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2937 self.with_new_scopes(|this| {
2939 hir_id: this.lower_node_id(c.id),
2940 body: this.lower_const_body(&c.value),
2945 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt; 1]> {
2946 let kind = match s.kind {
2947 StmtKind::Local(ref l) => {
2948 let (l, item_ids) = self.lower_local(l);
2949 let mut ids: SmallVec<[hir::Stmt; 1]> = item_ids
2952 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2953 self.stmt(s.span, hir::StmtKind::Item(item_id))
2958 hir_id: self.lower_node_id(s.id),
2959 kind: hir::StmtKind::Local(P(l)),
2965 StmtKind::Item(ref it) => {
2966 // Can only use the ID once.
2967 let mut id = Some(s.id);
2968 return self.lower_item_id(it)
2971 let hir_id = id.take()
2972 .map(|id| self.lower_node_id(id))
2973 .unwrap_or_else(|| self.next_id());
2977 kind: hir::StmtKind::Item(item_id),
2983 StmtKind::Expr(ref e) => hir::StmtKind::Expr(P(self.lower_expr(e))),
2984 StmtKind::Semi(ref e) => hir::StmtKind::Semi(P(self.lower_expr(e))),
2985 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2987 smallvec![hir::Stmt {
2988 hir_id: self.lower_node_id(s.id),
2994 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2996 BlockCheckMode::Default => hir::DefaultBlock,
2997 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
3001 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
3003 BindingMode::ByValue(Mutability::Immutable) => hir::BindingAnnotation::Unannotated,
3004 BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
3005 BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
3006 BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
3010 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3012 CompilerGenerated => hir::CompilerGenerated,
3013 UserProvided => hir::UserProvided,
3017 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3019 TraitBoundModifier::None => hir::TraitBoundModifier::None,
3020 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3024 // Helper methods for building HIR.
3026 fn stmt(&mut self, span: Span, kind: hir::StmtKind) -> hir::Stmt {
3027 hir::Stmt { span, kind, hir_id: self.next_id() }
3030 fn stmt_expr(&mut self, span: Span, expr: hir::Expr) -> hir::Stmt {
3031 self.stmt(span, hir::StmtKind::Expr(P(expr)))
3036 attrs: ThinVec<Attribute>,
3038 init: Option<P<hir::Expr>>,
3040 source: hir::LocalSource,
3042 let local = hir::Local {
3044 hir_id: self.next_id(),
3051 self.stmt(span, hir::StmtKind::Local(P(local)))
3054 fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
3055 self.block_all(expr.span, hir::HirVec::new(), Some(expr))
3061 stmts: hir::HirVec<hir::Stmt>,
3062 expr: Option<P<hir::Expr>>,
3067 hir_id: self.next_id(),
3068 rules: hir::DefaultBlock,
3070 targeted_by_break: false,
3074 /// Constructs a `true` or `false` literal pattern.
3075 fn pat_bool(&mut self, span: Span, val: bool) -> P<hir::Pat> {
3076 let expr = self.expr_bool(span, val);
3077 self.pat(span, hir::PatKind::Lit(P(expr)))
3080 fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3081 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], hir_vec![pat])
3084 fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3085 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], hir_vec![pat])
3088 fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3089 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], hir_vec![pat])
3092 fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
3093 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], hir_vec![])
3099 components: &[Symbol],
3100 subpats: hir::HirVec<P<hir::Pat>>,
3102 let path = self.std_path(span, components, None, true);
3103 let qpath = hir::QPath::Resolved(None, P(path));
3104 let pt = if subpats.is_empty() {
3105 hir::PatKind::Path(qpath)
3107 hir::PatKind::TupleStruct(qpath, subpats, None)
3112 fn pat_ident(&mut self, span: Span, ident: Ident) -> (P<hir::Pat>, hir::HirId) {
3113 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3116 fn pat_ident_binding_mode(
3120 bm: hir::BindingAnnotation,
3121 ) -> (P<hir::Pat>, hir::HirId) {
3122 let hir_id = self.next_id();
3127 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3134 fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
3135 self.pat(span, hir::PatKind::Wild)
3138 fn pat(&mut self, span: Span, kind: hir::PatKind) -> P<hir::Pat> {
3140 hir_id: self.next_id(),
3146 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3147 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3148 /// The path is also resolved according to `is_value`.
3152 components: &[Symbol],
3153 params: Option<P<hir::GenericArgs>>,
3156 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3157 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3159 let mut segments: Vec<_> = path.segments.iter().map(|segment| {
3160 let res = self.expect_full_res(segment.id);
3162 ident: segment.ident,
3163 hir_id: Some(self.lower_node_id(segment.id)),
3164 res: Some(self.lower_res(res)),
3169 segments.last_mut().unwrap().args = params;
3173 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3174 segments: segments.into(),
3178 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3179 let kind = match qpath {
3180 hir::QPath::Resolved(None, path) => {
3181 // Turn trait object paths into `TyKind::TraitObject` instead.
3183 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3184 let principal = hir::PolyTraitRef {
3185 bound_generic_params: hir::HirVec::new(),
3186 trait_ref: hir::TraitRef {
3193 // The original ID is taken by the `PolyTraitRef`,
3194 // so the `Ty` itself needs a different one.
3195 hir_id = self.next_id();
3196 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3198 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3201 _ => hir::TyKind::Path(qpath),
3211 /// Invoked to create the lifetime argument for a type `&T`
3212 /// with no explicit lifetime.
3213 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3214 match self.anonymous_lifetime_mode {
3215 // Intercept when we are in an impl header or async fn and introduce an in-band
3217 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3219 AnonymousLifetimeMode::CreateParameter => {
3220 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3222 hir_id: self.next_id(),
3224 name: hir::LifetimeName::Param(fresh_name),
3228 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3230 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3234 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3235 /// return a "error lifetime".
3236 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3237 let (id, msg, label) = match id {
3238 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3241 self.resolver.next_node_id(),
3242 "`&` without an explicit lifetime name cannot be used here",
3243 "explicit lifetime name needed here",
3247 let mut err = struct_span_err!(
3254 err.span_label(span, label);
3257 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3260 /// Invoked to create the lifetime argument(s) for a path like
3261 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3262 /// sorts of cases are deprecated. This may therefore report a warning or an
3263 /// error, depending on the mode.
3264 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3266 .map(|_| self.elided_path_lifetime(span))
3270 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3271 match self.anonymous_lifetime_mode {
3272 AnonymousLifetimeMode::CreateParameter => {
3273 // We should have emitted E0726 when processing this path above
3274 self.sess.delay_span_bug(
3276 "expected 'implicit elided lifetime not allowed' error",
3278 let id = self.resolver.next_node_id();
3279 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3281 // `PassThrough` is the normal case.
3282 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3283 // is unsuitable here, as these can occur from missing lifetime parameters in a
3284 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3285 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3286 // later, at which point a suitable error will be emitted.
3287 | AnonymousLifetimeMode::PassThrough
3288 | AnonymousLifetimeMode::ReportError => self.new_implicit_lifetime(span),
3292 /// Invoked to create the lifetime argument(s) for an elided trait object
3293 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3294 /// when the bound is written, even if it is written with `'_` like in
3295 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3296 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3297 match self.anonymous_lifetime_mode {
3298 // NB. We intentionally ignore the create-parameter mode here.
3299 // and instead "pass through" to resolve-lifetimes, which will apply
3300 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3301 // do not act like other elided lifetimes. In other words, given this:
3303 // impl Foo for Box<dyn Debug>
3305 // we do not introduce a fresh `'_` to serve as the bound, but instead
3306 // ultimately translate to the equivalent of:
3308 // impl Foo for Box<dyn Debug + 'static>
3310 // `resolve_lifetime` has the code to make that happen.
3311 AnonymousLifetimeMode::CreateParameter => {}
3313 AnonymousLifetimeMode::ReportError => {
3314 // ReportError applies to explicit use of `'_`.
3317 // This is the normal case.
3318 AnonymousLifetimeMode::PassThrough => {}
3321 let r = hir::Lifetime {
3322 hir_id: self.next_id(),
3324 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3326 debug!("elided_dyn_bound: r={:?}", r);
3330 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3332 hir_id: self.next_id(),
3334 name: hir::LifetimeName::Implicit,
3338 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3339 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3340 // call site which do not have a macro backtrace. See #61963.
3341 let is_macro_callsite = self.sess.source_map()
3342 .span_to_snippet(span)
3343 .map(|snippet| snippet.starts_with("#["))
3345 if !is_macro_callsite {
3346 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3347 builtin::BARE_TRAIT_OBJECTS,
3350 "trait objects without an explicit `dyn` are deprecated",
3351 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3357 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
3358 // Sorting by span ensures that we get things in order within a
3359 // file, and also puts the files in a sensible order.
3360 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3361 body_ids.sort_by_key(|b| bodies[b].value.span);
3365 /// Checks if the specified expression is a built-in range literal.
3366 /// (See: `LoweringContext::lower_expr()`).
3367 pub fn is_range_literal(sess: &Session, expr: &hir::Expr) -> bool {
3368 use hir::{Path, QPath, ExprKind, TyKind};
3370 // Returns whether the given path represents a (desugared) range,
3371 // either in std or core, i.e. has either a `::std::ops::Range` or
3372 // `::core::ops::Range` prefix.
3373 fn is_range_path(path: &Path) -> bool {
3374 let segs: Vec<_> = path.segments.iter().map(|seg| seg.ident.to_string()).collect();
3375 let segs: Vec<_> = segs.iter().map(|seg| &**seg).collect();
3377 // "{{root}}" is the equivalent of `::` prefix in `Path`.
3378 if let ["{{root}}", std_core, "ops", range] = segs.as_slice() {
3379 (*std_core == "std" || *std_core == "core") && range.starts_with("Range")
3385 // Check whether a span corresponding to a range expression is a
3386 // range literal, rather than an explicit struct or `new()` call.
3387 fn is_lit(sess: &Session, span: &Span) -> bool {
3388 let source_map = sess.source_map();
3389 let end_point = source_map.end_point(*span);
3391 if let Ok(end_string) = source_map.span_to_snippet(end_point) {
3392 !(end_string.ends_with("}") || end_string.ends_with(")"))
3399 // All built-in range literals but `..=` and `..` desugar to `Struct`s.
3400 ExprKind::Struct(ref qpath, _, _) => {
3401 if let QPath::Resolved(None, ref path) = **qpath {
3402 return is_range_path(&path) && is_lit(sess, &expr.span);
3406 // `..` desugars to its struct path.
3407 ExprKind::Path(QPath::Resolved(None, ref path)) => {
3408 return is_range_path(&path) && is_lit(sess, &expr.span);
3411 // `..=` desugars into `::std::ops::RangeInclusive::new(...)`.
3412 ExprKind::Call(ref func, _) => {
3413 if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.kind {
3414 if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.kind {
3415 let new_call = segment.ident.name == sym::new;
3416 return is_range_path(&path) && is_lit(sess, &expr.span) && new_call;