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::arena::Arena;
39 use crate::dep_graph::DepGraph;
40 use crate::hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
41 use crate::hir::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
42 use crate::hir::map::{DefKey, DefPathData, Definitions};
43 use crate::hir::ptr::P;
44 use crate::hir::HirVec;
45 use crate::hir::{self, ParamName};
46 use crate::hir::{ConstArg, GenericArg};
48 use crate::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
49 use crate::middle::cstore::CrateStore;
50 use crate::session::config::nightly_options;
51 use crate::session::Session;
52 use crate::util::common::FN_OUTPUT_NAME;
53 use crate::util::nodemap::{DefIdMap, NodeMap};
54 use errors::Applicability;
55 use rustc_data_structures::fx::FxHashSet;
56 use rustc_data_structures::sync::Lrc;
57 use rustc_index::vec::IndexVec;
59 use smallvec::SmallVec;
60 use std::collections::BTreeMap;
66 use syntax::print::pprust;
67 use syntax::ptr::P as AstP;
68 use syntax::sess::ParseSess;
69 use syntax::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
70 use syntax::symbol::{kw, sym, Symbol};
71 use syntax::token::{self, Nonterminal, Token};
72 use syntax::tokenstream::{TokenStream, TokenTree};
73 use syntax::visit::{self, Visitor};
74 use syntax_pos::hygiene::ExpnId;
77 use rustc_error_codes::*;
79 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
81 pub struct LoweringContext<'a, 'hir: 'a> {
82 crate_root: Option<Symbol>,
84 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
87 resolver: &'a mut dyn Resolver,
89 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
90 /// if we don't have this function pointer. To avoid that dependency so that
91 /// librustc is independent of the parser, we use dynamic dispatch here.
92 nt_to_tokenstream: NtToTokenstream,
94 /// Used to allocate HIR nodes
95 arena: &'hir Arena<'hir>,
97 /// The items being lowered are collected here.
98 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
100 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
101 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
102 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
103 exported_macros: Vec<hir::MacroDef<'hir>>,
104 non_exported_macro_attrs: Vec<ast::Attribute>,
106 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
108 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
110 generator_kind: Option<hir::GeneratorKind>,
112 /// Used to get the current `fn`'s def span to point to when using `await`
113 /// outside of an `async fn`.
114 current_item: Option<Span>,
116 catch_scopes: Vec<NodeId>,
117 loop_scopes: Vec<NodeId>,
118 is_in_loop_condition: bool,
119 is_in_trait_impl: bool,
120 is_in_dyn_type: bool,
122 /// What to do when we encounter either an "anonymous lifetime
123 /// reference". The term "anonymous" is meant to encompass both
124 /// `'_` lifetimes as well as fully elided cases where nothing is
125 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
126 anonymous_lifetime_mode: AnonymousLifetimeMode,
128 /// Used to create lifetime definitions from in-band lifetime usages.
129 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
130 /// When a named lifetime is encountered in a function or impl header and
131 /// has not been defined
132 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
133 /// to this list. The results of this list are then added to the list of
134 /// lifetime definitions in the corresponding impl or function generics.
135 lifetimes_to_define: Vec<(Span, ParamName)>,
137 /// `true` if in-band lifetimes are being collected. This is used to
138 /// indicate whether or not we're in a place where new lifetimes will result
139 /// in in-band lifetime definitions, such a function or an impl header,
140 /// including implicit lifetimes from `impl_header_lifetime_elision`.
141 is_collecting_in_band_lifetimes: bool,
143 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
144 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
145 /// against this list to see if it is already in-scope, or if a definition
146 /// needs to be created for it.
148 /// We always store a `modern()` version of the param-name in this
150 in_scope_lifetimes: Vec<ParamName>,
152 current_module: hir::HirId,
154 type_def_lifetime_params: DefIdMap<usize>,
156 current_hir_id_owner: Vec<(DefIndex, u32)>,
157 item_local_id_counters: NodeMap<u32>,
158 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
160 allow_try_trait: Option<Lrc<[Symbol]>>,
161 allow_gen_future: Option<Lrc<[Symbol]>>,
165 fn cstore(&self) -> &dyn CrateStore;
167 /// Obtains resolution for a `NodeId` with a single resolution.
168 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
170 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
171 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
173 /// Obtains resolution for a label with the given `NodeId`.
174 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
176 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
177 /// This should only return `None` during testing.
178 fn definitions(&mut self) -> &mut Definitions;
180 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
181 /// resolves it based on `is_value`.
185 crate_root: Option<Symbol>,
186 components: &[Symbol],
188 ) -> (ast::Path, Res<NodeId>);
190 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
192 fn next_node_id(&mut self) -> NodeId;
195 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
197 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
198 /// and if so, what meaning it has.
200 enum ImplTraitContext<'a> {
201 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
202 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
203 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
205 /// Newly generated parameters should be inserted into the given `Vec`.
206 Universal(&'a mut Vec<hir::GenericParam>),
208 /// Treat `impl Trait` as shorthand for a new opaque type.
209 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
210 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
212 /// We optionally store a `DefId` for the parent item here so we can look up necessary
213 /// information later. It is `None` when no information about the context should be stored
214 /// (e.g., for consts and statics).
215 OpaqueTy(Option<DefId> /* fn def-ID */),
217 /// `impl Trait` is not accepted in this position.
218 Disallowed(ImplTraitPosition),
221 /// Position in which `impl Trait` is disallowed.
222 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
223 enum ImplTraitPosition {
224 /// Disallowed in `let` / `const` / `static` bindings.
227 /// All other posiitons.
231 impl<'a> ImplTraitContext<'a> {
233 fn disallowed() -> Self {
234 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
237 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
238 use self::ImplTraitContext::*;
240 Universal(params) => Universal(params),
241 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
242 Disallowed(pos) => Disallowed(*pos),
247 pub fn lower_crate<'a, 'hir>(
249 dep_graph: &'a DepGraph,
251 resolver: &'a mut dyn Resolver,
252 nt_to_tokenstream: NtToTokenstream,
253 arena: &'hir Arena<'hir>,
254 ) -> hir::Crate<'hir> {
255 // We're constructing the HIR here; we don't care what we will
256 // read, since we haven't even constructed the *input* to
258 dep_graph.assert_ignored();
260 let _prof_timer = sess.prof.generic_activity("hir_lowering");
263 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
268 items: BTreeMap::new(),
269 trait_items: BTreeMap::new(),
270 impl_items: BTreeMap::new(),
271 bodies: BTreeMap::new(),
272 trait_impls: BTreeMap::new(),
273 modules: BTreeMap::new(),
274 exported_macros: Vec::new(),
275 non_exported_macro_attrs: Vec::new(),
276 catch_scopes: Vec::new(),
277 loop_scopes: Vec::new(),
278 is_in_loop_condition: false,
279 is_in_trait_impl: false,
280 is_in_dyn_type: false,
281 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
282 type_def_lifetime_params: Default::default(),
283 current_module: hir::CRATE_HIR_ID,
284 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
285 item_local_id_counters: Default::default(),
286 node_id_to_hir_id: IndexVec::new(),
287 generator_kind: None,
289 lifetimes_to_define: Vec::new(),
290 is_collecting_in_band_lifetimes: false,
291 in_scope_lifetimes: Vec::new(),
292 allow_try_trait: Some([sym::try_trait][..].into()),
293 allow_gen_future: Some([sym::gen_future][..].into()),
298 #[derive(Copy, Clone, PartialEq)]
300 /// Any path in a type context.
302 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
304 /// The `module::Type` in `module::Type::method` in an expression.
308 enum ParenthesizedGenericArgs {
313 /// What to do when we encounter an **anonymous** lifetime
314 /// reference. Anonymous lifetime references come in two flavors. You
315 /// have implicit, or fully elided, references to lifetimes, like the
316 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
317 /// or `Ref<'_, T>`. These often behave the same, but not always:
319 /// - certain usages of implicit references are deprecated, like
320 /// `Ref<T>`, and we sometimes just give hard errors in those cases
322 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
323 /// the same as `Box<dyn Foo + '_>`.
325 /// We describe the effects of the various modes in terms of three cases:
327 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
328 /// of a `&` (e.g., the missing lifetime in something like `&T`)
329 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
330 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
331 /// elided bounds follow special rules. Note that this only covers
332 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
333 /// '_>` is a case of "modern" elision.
334 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
335 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
336 /// non-deprecated equivalent.
338 /// Currently, the handling of lifetime elision is somewhat spread out
339 /// between HIR lowering and -- as described below -- the
340 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
341 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
342 /// everything into HIR lowering.
343 #[derive(Copy, Clone, Debug)]
344 enum AnonymousLifetimeMode {
345 /// For **Modern** cases, create a new anonymous region parameter
346 /// and reference that.
348 /// For **Dyn Bound** cases, pass responsibility to
349 /// `resolve_lifetime` code.
351 /// For **Deprecated** cases, report an error.
354 /// Give a hard error when either `&` or `'_` is written. Used to
355 /// rule out things like `where T: Foo<'_>`. Does not imply an
356 /// error on default object bounds (e.g., `Box<dyn Foo>`).
359 /// Pass responsibility to `resolve_lifetime` code for all cases.
363 struct ImplTraitTypeIdVisitor<'a> {
364 ids: &'a mut SmallVec<[NodeId; 1]>,
367 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
368 fn visit_ty(&mut self, ty: &'a Ty) {
370 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
372 TyKind::ImplTrait(id, _) => self.ids.push(id),
375 visit::walk_ty(self, ty);
378 fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment) {
379 if let Some(ref p) = path_segment.args {
380 if let GenericArgs::Parenthesized(_) = **p {
384 visit::walk_path_segment(self, path_span, path_segment)
388 impl<'a, 'hir> LoweringContext<'a, 'hir> {
389 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
390 /// Full-crate AST visitor that inserts into a fresh
391 /// `LoweringContext` any information that may be
392 /// needed from arbitrary locations in the crate,
393 /// e.g., the number of lifetime generic parameters
394 /// declared for every type and trait definition.
395 struct MiscCollector<'tcx, 'lowering, 'hir> {
396 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
397 hir_id_owner: Option<NodeId>,
400 impl MiscCollector<'_, '_, '_> {
401 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
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, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
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::Trait(_, _, ref generics, ..) => {
456 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
460 .filter(|param| match param.kind {
461 ast::GenericParamKind::Lifetime { .. } => true,
465 self.lctx.type_def_lifetime_params.insert(def_id, count);
467 ItemKind::Use(ref use_tree) => {
468 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
473 self.with_hir_id_owner(Some(item.id), |this| {
474 visit::walk_item(this, item);
478 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
479 self.lctx.allocate_hir_id_counter(item.id);
482 AssocItemKind::Fn(_, None) => {
483 // Ignore patterns in trait methods without bodies
484 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
486 _ => self.with_hir_id_owner(Some(item.id), |this| {
487 visit::walk_trait_item(this, item);
492 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
493 self.lctx.allocate_hir_id_counter(item.id);
494 self.with_hir_id_owner(Some(item.id), |this| {
495 visit::walk_impl_item(this, item);
499 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
500 // Ignore patterns in foreign items
501 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
504 fn visit_ty(&mut self, t: &'tcx Ty) {
506 // Mirrors the case in visit::walk_ty
507 TyKind::BareFn(ref f) => {
508 walk_list!(self, visit_generic_param, &f.generic_params);
509 // Mirrors visit::walk_fn_decl
510 for parameter in &f.decl.inputs {
511 // We don't lower the ids of argument patterns
512 self.with_hir_id_owner(None, |this| {
513 this.visit_pat(¶meter.pat);
515 self.visit_ty(¶meter.ty)
517 self.visit_fn_ret_ty(&f.decl.output)
519 _ => visit::walk_ty(self, t),
524 self.lower_node_id(CRATE_NODE_ID);
525 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
527 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
528 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
530 let module = self.lower_mod(&c.module);
531 let attrs = self.arena.alloc_from_iter(self.lower_attrs(&c.attrs).into_iter());
532 let body_ids = body_ids(&self.bodies);
534 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
540 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
541 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
543 trait_items: self.trait_items,
544 impl_items: self.impl_items,
547 trait_impls: self.trait_impls,
548 modules: self.modules,
552 fn insert_item(&mut self, item: hir::Item<'hir>) {
553 let id = item.hir_id;
554 // FIXME: Use `debug_asset-rt`.
555 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
556 self.items.insert(id, item);
557 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
560 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
561 // Set up the counter if needed.
562 self.item_local_id_counters.entry(owner).or_insert(0);
563 // Always allocate the first `HirId` for the owner itself.
564 let lowered = self.lower_node_id_with_owner(owner, owner);
565 debug_assert_eq!(lowered.local_id.as_u32(), 0);
569 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
571 F: FnOnce(&mut Self) -> hir::HirId,
573 if ast_node_id == DUMMY_NODE_ID {
574 return hir::DUMMY_HIR_ID;
577 let min_size = ast_node_id.as_usize() + 1;
579 if min_size > self.node_id_to_hir_id.len() {
580 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
583 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
585 if existing_hir_id == hir::DUMMY_HIR_ID {
586 // Generate a new `HirId`.
587 let hir_id = alloc_hir_id(self);
588 self.node_id_to_hir_id[ast_node_id] = hir_id;
596 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
598 F: FnOnce(&mut Self) -> T,
601 .item_local_id_counters
602 .insert(owner, HIR_ID_COUNTER_LOCKED)
603 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
604 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
605 self.current_hir_id_owner.push((def_index, counter));
607 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
609 debug_assert!(def_index == new_def_index);
610 debug_assert!(new_counter >= counter);
612 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
613 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
617 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
618 /// the `LoweringContext`'s `NodeId => HirId` map.
619 /// Take care not to call this method if the resulting `HirId` is then not
620 /// actually used in the HIR, as that would trigger an assertion in the
621 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
622 /// properly. Calling the method twice with the same `NodeId` is fine though.
623 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
624 self.lower_node_id_generic(ast_node_id, |this| {
625 let &mut (def_index, ref mut local_id_counter) =
626 this.current_hir_id_owner.last_mut().unwrap();
627 let local_id = *local_id_counter;
628 *local_id_counter += 1;
629 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
633 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let local_id_counter = this
636 .item_local_id_counters
638 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
639 let local_id = *local_id_counter;
641 // We want to be sure not to modify the counter in the map while it
642 // is also on the stack. Otherwise we'll get lost updates when writing
643 // back from the stack to the map.
644 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
646 *local_id_counter += 1;
647 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
648 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
649 that do not belong to the current owner",
652 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
656 fn next_id(&mut self) -> hir::HirId {
657 let node_id = self.resolver.next_node_id();
658 self.lower_node_id(node_id)
661 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
663 self.lower_node_id_generic(id, |_| {
664 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
669 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
670 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
671 if pr.unresolved_segments() != 0 {
672 bug!("path not fully resolved: {:?}", pr);
678 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
679 self.resolver.get_import_res(id).present_items()
682 fn diagnostic(&self) -> &errors::Handler {
683 self.sess.diagnostic()
686 /// Reuses the span but adds information like the kind of the desugaring and features that are
687 /// allowed inside this span.
688 fn mark_span_with_reason(
690 reason: DesugaringKind,
692 allow_internal_unstable: Option<Lrc<[Symbol]>>,
694 span.fresh_expansion(ExpnData {
695 allow_internal_unstable,
696 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
700 fn with_anonymous_lifetime_mode<R>(
702 anonymous_lifetime_mode: AnonymousLifetimeMode,
703 op: impl FnOnce(&mut Self) -> R,
706 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
707 anonymous_lifetime_mode,
709 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
710 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
711 let result = op(self);
712 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
714 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
715 old_anonymous_lifetime_mode
720 /// Creates a new `hir::GenericParam` for every new lifetime and
721 /// type parameter encountered while evaluating `f`. Definitions
722 /// are created with the parent provided. If no `parent_id` is
723 /// provided, no definitions will be returned.
725 /// Presuming that in-band lifetimes are enabled, then
726 /// `self.anonymous_lifetime_mode` will be updated to match the
727 /// parameter while `f` is running (and restored afterwards).
728 fn collect_in_band_defs<T, F>(
731 anonymous_lifetime_mode: AnonymousLifetimeMode,
733 ) -> (Vec<hir::GenericParam>, T)
735 F: FnOnce(&mut LoweringContext<'_, '_>) -> (Vec<hir::GenericParam>, T),
737 assert!(!self.is_collecting_in_band_lifetimes);
738 assert!(self.lifetimes_to_define.is_empty());
739 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
741 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
742 self.is_collecting_in_band_lifetimes = true;
744 let (in_band_ty_params, res) = f(self);
746 self.is_collecting_in_band_lifetimes = false;
747 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
749 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
751 let params = lifetimes_to_define
753 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
754 .chain(in_band_ty_params.into_iter())
760 /// Converts a lifetime into a new generic parameter.
761 fn lifetime_to_generic_param(
765 parent_index: DefIndex,
766 ) -> hir::GenericParam {
767 let node_id = self.resolver.next_node_id();
769 // Get the name we'll use to make the def-path. Note
770 // that collisions are ok here and this shouldn't
771 // really show up for end-user.
772 let (str_name, kind) = match hir_name {
773 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
774 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
775 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
778 // Add a definition for the in-band lifetime def.
779 self.resolver.definitions().create_def_with_parent(
782 DefPathData::LifetimeNs(str_name),
788 hir_id: self.lower_node_id(node_id),
793 pure_wrt_drop: false,
794 kind: hir::GenericParamKind::Lifetime { kind },
798 /// When there is a reference to some lifetime `'a`, and in-band
799 /// lifetimes are enabled, then we want to push that lifetime into
800 /// the vector of names to define later. In that case, it will get
801 /// added to the appropriate generics.
802 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
803 if !self.is_collecting_in_band_lifetimes {
807 if !self.sess.features_untracked().in_band_lifetimes {
811 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
815 let hir_name = ParamName::Plain(ident);
817 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
822 self.lifetimes_to_define.push((ident.span, hir_name));
825 /// When we have either an elided or `'_` lifetime in an impl
826 /// header, we convert it to an in-band lifetime.
827 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
828 assert!(self.is_collecting_in_band_lifetimes);
829 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
830 let hir_name = ParamName::Fresh(index);
831 self.lifetimes_to_define.push((span, hir_name));
835 // Evaluates `f` with the lifetimes in `params` in-scope.
836 // This is used to track which lifetimes have already been defined, and
837 // which are new in-band lifetimes that need to have a definition created
839 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
841 F: FnOnce(&mut LoweringContext<'_, 'hir>) -> T,
843 let old_len = self.in_scope_lifetimes.len();
844 let lt_def_names = params.iter().filter_map(|param| match param.kind {
845 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
848 self.in_scope_lifetimes.extend(lt_def_names);
852 self.in_scope_lifetimes.truncate(old_len);
856 /// Appends in-band lifetime defs and argument-position `impl
857 /// Trait` defs to the existing set of generics.
859 /// Presuming that in-band lifetimes are enabled, then
860 /// `self.anonymous_lifetime_mode` will be updated to match the
861 /// parameter while `f` is running (and restored afterwards).
862 fn add_in_band_defs<F, T>(
866 anonymous_lifetime_mode: AnonymousLifetimeMode,
868 ) -> (hir::Generics, T)
870 F: FnOnce(&mut LoweringContext<'_, '_>, &mut Vec<hir::GenericParam>) -> T,
872 let (in_band_defs, (mut lowered_generics, res)) =
873 self.with_in_scope_lifetime_defs(&generics.params, |this| {
874 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
875 let mut params = Vec::new();
876 // Note: it is necessary to lower generics *before* calling `f`.
877 // When lowering `async fn`, there's a final step when lowering
878 // the return type that assumes that all in-scope lifetimes have
879 // already been added to either `in_scope_lifetimes` or
880 // `lifetimes_to_define`. If we swapped the order of these two,
881 // in-band-lifetimes introduced by generics or where-clauses
882 // wouldn't have been added yet.
884 this.lower_generics(generics, ImplTraitContext::Universal(&mut params));
885 let res = f(this, &mut params);
886 (params, (generics, res))
890 let mut lowered_params: Vec<_> =
891 lowered_generics.params.into_iter().chain(in_band_defs).collect();
893 // FIXME(const_generics): the compiler doesn't always cope with
894 // unsorted generic parameters at the moment, so we make sure
895 // that they're ordered correctly here for now. (When we chain
896 // the `in_band_defs`, we might make the order unsorted.)
897 lowered_params.sort_by_key(|param| match param.kind {
898 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
899 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
900 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
903 lowered_generics.params = lowered_params.into();
905 (lowered_generics, res)
908 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
910 F: FnOnce(&mut LoweringContext<'_, '_>) -> T,
912 let was_in_dyn_type = self.is_in_dyn_type;
913 self.is_in_dyn_type = in_scope;
915 let result = f(self);
917 self.is_in_dyn_type = was_in_dyn_type;
922 fn with_new_scopes<T, F>(&mut self, f: F) -> T
924 F: FnOnce(&mut LoweringContext<'_, '_>) -> T,
926 let was_in_loop_condition = self.is_in_loop_condition;
927 self.is_in_loop_condition = false;
929 let catch_scopes = mem::take(&mut self.catch_scopes);
930 let loop_scopes = mem::take(&mut self.loop_scopes);
932 self.catch_scopes = catch_scopes;
933 self.loop_scopes = loop_scopes;
935 self.is_in_loop_condition = was_in_loop_condition;
940 fn def_key(&mut self, id: DefId) -> DefKey {
942 self.resolver.definitions().def_key(id.index)
944 self.resolver.cstore().def_key(id)
948 fn lower_attrs_arena(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
949 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
952 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
953 attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into()
956 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
957 // Note that we explicitly do not walk the path. Since we don't really
958 // lower attributes (we use the AST version) there is nowhere to keep
959 // the `HirId`s. We don't actually need HIR version of attributes anyway.
960 let kind = match attr.kind {
961 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
962 path: item.path.clone(),
963 args: self.lower_mac_args(&item.args),
965 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
968 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
971 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
973 MacArgs::Empty => MacArgs::Empty,
974 MacArgs::Delimited(dspan, delim, ref tokens) => {
975 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
977 MacArgs::Eq(eq_span, ref tokens) => {
978 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
983 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
984 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
987 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
989 TokenTree::Token(token) => self.lower_token(token),
990 TokenTree::Delimited(span, delim, tts) => {
991 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
996 fn lower_token(&mut self, token: Token) -> TokenStream {
998 token::Interpolated(nt) => {
999 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1000 self.lower_token_stream(tts)
1002 _ => TokenTree::Token(token).into(),
1006 /// Given an associated type constraint like one of these:
1009 /// T: Iterator<Item: Debug>
1011 /// T: Iterator<Item = Debug>
1015 /// returns a `hir::TypeBinding` representing `Item`.
1016 fn lower_assoc_ty_constraint(
1018 constraint: &AssocTyConstraint,
1019 itctx: ImplTraitContext<'_>,
1020 ) -> hir::TypeBinding {
1021 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1023 let kind = match constraint.kind {
1024 AssocTyConstraintKind::Equality { ref ty } => {
1025 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1027 AssocTyConstraintKind::Bound { ref bounds } => {
1028 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1029 let (desugar_to_impl_trait, itctx) = match itctx {
1030 // We are in the return position:
1032 // fn foo() -> impl Iterator<Item: Debug>
1036 // fn foo() -> impl Iterator<Item = impl Debug>
1037 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1039 // We are in the argument position, but within a dyn type:
1041 // fn foo(x: dyn Iterator<Item: Debug>)
1045 // fn foo(x: dyn Iterator<Item = impl Debug>)
1046 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1048 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1049 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1050 // "impl trait context" to permit `impl Debug` in this position (it desugars
1051 // then to an opaque type).
1053 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1054 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1055 (true, ImplTraitContext::OpaqueTy(None))
1058 // We are in the parameter position, but not within a dyn type:
1060 // fn foo(x: impl Iterator<Item: Debug>)
1062 // so we leave it as is and this gets expanded in astconv to a bound like
1063 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1065 _ => (false, itctx),
1068 if desugar_to_impl_trait {
1069 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1070 // constructing the HIR for `impl bounds...` and then lowering that.
1072 let impl_trait_node_id = self.resolver.next_node_id();
1073 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1074 self.resolver.definitions().create_def_with_parent(
1077 DefPathData::ImplTrait,
1082 self.with_dyn_type_scope(false, |this| {
1083 let node_id = this.resolver.next_node_id();
1084 let ty = this.lower_ty(
1087 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1088 span: constraint.span,
1093 hir::TypeBindingKind::Equality { ty }
1096 // Desugar `AssocTy: Bounds` into a type binding where the
1097 // later desugars into a trait predicate.
1098 let bounds = self.lower_param_bounds(bounds, itctx);
1100 hir::TypeBindingKind::Constraint { bounds }
1106 hir_id: self.lower_node_id(constraint.id),
1107 ident: constraint.ident,
1109 span: constraint.span,
1113 fn lower_generic_arg(
1115 arg: &ast::GenericArg,
1116 itctx: ImplTraitContext<'_>,
1117 ) -> hir::GenericArg {
1119 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1120 ast::GenericArg::Type(ty) => {
1121 // We parse const arguments as path types as we cannot distiguish them durring
1122 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1123 // type and value namespaces. If we resolved the path in the value namespace, we
1124 // transform it into a generic const argument.
1125 if let TyKind::Path(ref qself, ref path) = ty.kind {
1126 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1127 let res = partial_res.base_res();
1128 if !res.matches_ns(Namespace::TypeNS) {
1130 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1134 // Construct a AnonConst where the expr is the "ty"'s path.
1136 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1137 let node_id = self.resolver.next_node_id();
1139 // Add a definition for the in-band const def.
1140 self.resolver.definitions().create_def_with_parent(
1143 DefPathData::AnonConst,
1148 let path_expr = Expr {
1150 kind: ExprKind::Path(qself.clone(), path.clone()),
1152 attrs: AttrVec::new(),
1155 let ct = self.with_new_scopes(|this| hir::AnonConst {
1156 hir_id: this.lower_node_id(node_id),
1157 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1159 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1163 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1165 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1166 value: self.lower_anon_const(&ct),
1167 span: ct.value.span,
1172 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1173 P(self.lower_ty_direct(t, itctx))
1179 qself: &Option<QSelf>,
1181 param_mode: ParamMode,
1182 itctx: ImplTraitContext<'_>,
1184 let id = self.lower_node_id(t.id);
1185 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1186 let ty = self.ty_path(id, t.span, qpath);
1187 if let hir::TyKind::TraitObject(..) = ty.kind {
1188 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1193 fn ty(&mut self, span: Span, kind: hir::TyKind) -> hir::Ty {
1194 hir::Ty { hir_id: self.next_id(), kind, span }
1197 fn ty_tup(&mut self, span: Span, tys: HirVec<hir::Ty>) -> hir::Ty {
1198 self.ty(span, hir::TyKind::Tup(tys))
1201 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1202 let kind = match t.kind {
1203 TyKind::Infer => hir::TyKind::Infer,
1204 TyKind::Err => hir::TyKind::Err,
1205 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1206 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1207 TyKind::Rptr(ref region, ref mt) => {
1208 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1209 let lifetime = match *region {
1210 Some(ref lt) => self.lower_lifetime(lt),
1211 None => self.elided_ref_lifetime(span),
1213 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1215 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1216 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1217 hir::TyKind::BareFn(P(hir::BareFnTy {
1218 generic_params: this.lower_generic_params(
1220 &NodeMap::default(),
1221 ImplTraitContext::disallowed(),
1223 unsafety: f.unsafety,
1224 abi: this.lower_extern(f.ext),
1225 decl: this.lower_fn_decl(&f.decl, None, false, None),
1226 param_names: this.lower_fn_params_to_names(&f.decl),
1230 TyKind::Never => hir::TyKind::Never,
1231 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1232 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())).collect(),
1234 TyKind::Paren(ref ty) => {
1235 return self.lower_ty_direct(ty, itctx);
1237 TyKind::Path(ref qself, ref path) => {
1238 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1240 TyKind::ImplicitSelf => {
1241 let res = self.expect_full_res(t.id);
1242 let res = self.lower_res(res);
1243 hir::TyKind::Path(hir::QPath::Resolved(
1247 segments: hir_vec![hir::PathSegment::from_ident(Ident::with_dummy_span(
1254 TyKind::Array(ref ty, ref length) => {
1255 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1257 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1258 TyKind::TraitObject(ref bounds, kind) => {
1259 let mut lifetime_bound = None;
1260 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1263 .filter_map(|bound| match *bound {
1264 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1265 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1267 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1268 GenericBound::Outlives(ref lifetime) => {
1269 if lifetime_bound.is_none() {
1270 lifetime_bound = Some(this.lower_lifetime(lifetime));
1276 let lifetime_bound =
1277 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1278 (bounds, lifetime_bound)
1280 if kind != TraitObjectSyntax::Dyn {
1281 self.maybe_lint_bare_trait(t.span, t.id, false);
1283 hir::TyKind::TraitObject(bounds, lifetime_bound)
1285 TyKind::ImplTrait(def_node_id, ref bounds) => {
1288 ImplTraitContext::OpaqueTy(fn_def_id) => {
1289 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1290 this.lower_param_bounds(bounds, itctx)
1293 ImplTraitContext::Universal(in_band_ty_params) => {
1294 // Add a definition for the in-band `Param`.
1296 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1298 let hir_bounds = self.lower_param_bounds(
1300 ImplTraitContext::Universal(in_band_ty_params),
1302 // Set the name to `impl Bound1 + Bound2`.
1303 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1304 in_band_ty_params.push(hir::GenericParam {
1305 hir_id: self.lower_node_id(def_node_id),
1306 name: ParamName::Plain(ident),
1307 pure_wrt_drop: false,
1311 kind: hir::GenericParamKind::Type {
1313 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1317 hir::TyKind::Path(hir::QPath::Resolved(
1321 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1322 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1326 ImplTraitContext::Disallowed(pos) => {
1327 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1328 "bindings or function and inherent method return types"
1330 "function and inherent method return types"
1332 let mut err = struct_span_err!(
1336 "`impl Trait` not allowed outside of {}",
1339 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1343 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1344 attributes to enable"
1352 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1353 TyKind::CVarArgs => {
1354 self.sess.delay_span_bug(
1356 "`TyKind::CVarArgs` should have been handled elsewhere",
1362 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1365 fn lower_opaque_impl_trait(
1368 fn_def_id: Option<DefId>,
1369 opaque_ty_node_id: NodeId,
1370 lower_bounds: impl FnOnce(&mut LoweringContext<'_, '_>) -> hir::GenericBounds,
1373 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1374 fn_def_id, opaque_ty_node_id, span,
1377 // Make sure we know that some funky desugaring has been going on here.
1378 // This is a first: there is code in other places like for loop
1379 // desugaring that explicitly states that we don't want to track that.
1380 // Not tracking it makes lints in rustc and clippy very fragile, as
1381 // frequently opened issues show.
1382 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1384 let opaque_ty_def_index =
1385 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1387 self.allocate_hir_id_counter(opaque_ty_node_id);
1389 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1391 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1393 opaque_ty_def_index,
1397 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1399 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1401 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1402 let opaque_ty_item = hir::OpaqueTy {
1403 generics: hir::Generics {
1404 params: lifetime_defs,
1405 where_clause: hir::WhereClause { predicates: hir_vec![], span },
1409 impl_trait_fn: fn_def_id,
1410 origin: hir::OpaqueTyOrigin::FnReturn,
1413 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1415 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1417 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1418 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1422 /// Registers a new opaque type with the proper `NodeId`s and
1423 /// returns the lowered node-ID for the opaque type.
1424 fn generate_opaque_type(
1426 opaque_ty_node_id: NodeId,
1427 opaque_ty_item: hir::OpaqueTy,
1429 opaque_ty_span: Span,
1431 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1432 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1433 // Generate an `type Foo = impl Trait;` declaration.
1434 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1435 let opaque_ty_item = hir::Item {
1436 hir_id: opaque_ty_id,
1437 ident: Ident::invalid(),
1438 attrs: Default::default(),
1439 kind: opaque_ty_item_kind,
1440 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1441 span: opaque_ty_span,
1444 // Insert the item into the global item list. This usually happens
1445 // automatically for all AST items. But this opaque type item
1446 // does not actually exist in the AST.
1447 self.insert_item(opaque_ty_item);
1451 fn lifetimes_from_impl_trait_bounds(
1453 opaque_ty_id: NodeId,
1454 parent_index: DefIndex,
1455 bounds: &hir::GenericBounds,
1456 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1458 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1459 parent_index={:?}, \
1461 opaque_ty_id, parent_index, bounds,
1464 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1465 // appear in the bounds, excluding lifetimes that are created within the bounds.
1466 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1467 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1468 context: &'r mut LoweringContext<'a, 'hir>,
1470 opaque_ty_id: NodeId,
1471 collect_elided_lifetimes: bool,
1472 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1473 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1474 output_lifetimes: Vec<hir::GenericArg>,
1475 output_lifetime_params: Vec<hir::GenericParam>,
1478 impl<'r, 'a, 'v, 'hir> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1479 fn nested_visit_map<'this>(
1481 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1482 hir::intravisit::NestedVisitorMap::None
1485 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1486 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1487 if parameters.parenthesized {
1488 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1489 self.collect_elided_lifetimes = false;
1490 hir::intravisit::walk_generic_args(self, span, parameters);
1491 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1493 hir::intravisit::walk_generic_args(self, span, parameters);
1497 fn visit_ty(&mut self, t: &'v hir::Ty) {
1498 // Don't collect elided lifetimes used inside of `fn()` syntax.
1499 if let hir::TyKind::BareFn(_) = t.kind {
1500 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1501 self.collect_elided_lifetimes = false;
1503 // Record the "stack height" of `for<'a>` lifetime bindings
1504 // to be able to later fully undo their introduction.
1505 let old_len = self.currently_bound_lifetimes.len();
1506 hir::intravisit::walk_ty(self, t);
1507 self.currently_bound_lifetimes.truncate(old_len);
1509 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1511 hir::intravisit::walk_ty(self, t)
1515 fn visit_poly_trait_ref(
1517 trait_ref: &'v hir::PolyTraitRef,
1518 modifier: hir::TraitBoundModifier,
1520 // Record the "stack height" of `for<'a>` lifetime bindings
1521 // to be able to later fully undo their introduction.
1522 let old_len = self.currently_bound_lifetimes.len();
1523 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1524 self.currently_bound_lifetimes.truncate(old_len);
1527 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1528 // Record the introduction of 'a in `for<'a> ...`.
1529 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1530 // Introduce lifetimes one at a time so that we can handle
1531 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1532 let lt_name = hir::LifetimeName::Param(param.name);
1533 self.currently_bound_lifetimes.push(lt_name);
1536 hir::intravisit::walk_generic_param(self, param);
1539 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1540 let name = match lifetime.name {
1541 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1542 if self.collect_elided_lifetimes {
1543 // Use `'_` for both implicit and underscore lifetimes in
1544 // `type Foo<'_> = impl SomeTrait<'_>;`.
1545 hir::LifetimeName::Underscore
1550 hir::LifetimeName::Param(_) => lifetime.name,
1552 // Refers to some other lifetime that is "in
1553 // scope" within the type.
1554 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1556 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1559 if !self.currently_bound_lifetimes.contains(&name)
1560 && !self.already_defined_lifetimes.contains(&name)
1562 self.already_defined_lifetimes.insert(name);
1564 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1565 hir_id: self.context.next_id(),
1566 span: lifetime.span,
1570 let def_node_id = self.context.resolver.next_node_id();
1572 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1573 self.context.resolver.definitions().create_def_with_parent(
1576 DefPathData::LifetimeNs(name.ident().name),
1581 let (name, kind) = match name {
1582 hir::LifetimeName::Underscore => (
1583 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1584 hir::LifetimeParamKind::Elided,
1586 hir::LifetimeName::Param(param_name) => {
1587 (param_name, hir::LifetimeParamKind::Explicit)
1589 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1592 self.output_lifetime_params.push(hir::GenericParam {
1595 span: lifetime.span,
1596 pure_wrt_drop: false,
1599 kind: hir::GenericParamKind::Lifetime { kind },
1605 let mut lifetime_collector = ImplTraitLifetimeCollector {
1607 parent: parent_index,
1609 collect_elided_lifetimes: true,
1610 currently_bound_lifetimes: Vec::new(),
1611 already_defined_lifetimes: FxHashSet::default(),
1612 output_lifetimes: Vec::new(),
1613 output_lifetime_params: Vec::new(),
1616 for bound in bounds {
1617 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1621 lifetime_collector.output_lifetimes.into(),
1622 lifetime_collector.output_lifetime_params.into(),
1629 qself: &Option<QSelf>,
1631 param_mode: ParamMode,
1632 mut itctx: ImplTraitContext<'_>,
1634 let qself_position = qself.as_ref().map(|q| q.position);
1635 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1638 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1640 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1641 let path = P(hir::Path {
1642 res: self.lower_res(partial_res.base_res()),
1643 segments: p.segments[..proj_start]
1646 .map(|(i, segment)| {
1647 let param_mode = match (qself_position, param_mode) {
1648 (Some(j), ParamMode::Optional) if i < j => {
1649 // This segment is part of the trait path in a
1650 // qualified path - one of `a`, `b` or `Trait`
1651 // in `<X as a::b::Trait>::T::U::method`.
1657 // Figure out if this is a type/trait segment,
1658 // which may need lifetime elision performed.
1659 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1660 krate: def_id.krate,
1661 index: this.def_key(def_id).parent.expect("missing parent"),
1663 let type_def_id = match partial_res.base_res() {
1664 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1665 Some(parent_def_id(self, def_id))
1667 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1668 Some(parent_def_id(self, def_id))
1670 Res::Def(DefKind::Struct, def_id)
1671 | Res::Def(DefKind::Union, def_id)
1672 | Res::Def(DefKind::Enum, def_id)
1673 | Res::Def(DefKind::TyAlias, def_id)
1674 | Res::Def(DefKind::Trait, def_id)
1675 if i + 1 == proj_start =>
1681 let parenthesized_generic_args = match partial_res.base_res() {
1682 // `a::b::Trait(Args)`
1683 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1684 ParenthesizedGenericArgs::Ok
1686 // `a::b::Trait(Args)::TraitItem`
1687 Res::Def(DefKind::Method, _)
1688 | Res::Def(DefKind::AssocConst, _)
1689 | Res::Def(DefKind::AssocTy, _)
1690 if i + 2 == proj_start =>
1692 ParenthesizedGenericArgs::Ok
1694 // Avoid duplicated errors.
1695 Res::Err => ParenthesizedGenericArgs::Ok,
1697 _ => ParenthesizedGenericArgs::Err,
1700 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1701 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1704 assert!(!def_id.is_local());
1705 let item_generics = self
1708 .item_generics_cloned_untracked(def_id, self.sess);
1709 let n = item_generics.own_counts().lifetimes;
1710 self.type_def_lifetime_params.insert(def_id, n);
1713 self.lower_path_segment(
1718 parenthesized_generic_args,
1727 // Simple case, either no projections, or only fully-qualified.
1728 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1729 if partial_res.unresolved_segments() == 0 {
1730 return hir::QPath::Resolved(qself, path);
1733 // Create the innermost type that we're projecting from.
1734 let mut ty = if path.segments.is_empty() {
1735 // If the base path is empty that means there exists a
1736 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1737 qself.expect("missing QSelf for <T>::...")
1739 // Otherwise, the base path is an implicit `Self` type path,
1740 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1741 // `<I as Iterator>::Item::default`.
1742 let new_id = self.next_id();
1743 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1746 // Anything after the base path are associated "extensions",
1747 // out of which all but the last one are associated types,
1748 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1749 // * base path is `std::vec::Vec<T>`
1750 // * "extensions" are `IntoIter`, `Item` and `clone`
1751 // * type nodes are:
1752 // 1. `std::vec::Vec<T>` (created above)
1753 // 2. `<std::vec::Vec<T>>::IntoIter`
1754 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1755 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1756 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1757 let segment = P(self.lower_path_segment(
1762 ParenthesizedGenericArgs::Err,
1766 let qpath = hir::QPath::TypeRelative(ty, segment);
1768 // It's finished, return the extension of the right node type.
1769 if i == p.segments.len() - 1 {
1773 // Wrap the associated extension in another type node.
1774 let new_id = self.next_id();
1775 ty = P(self.ty_path(new_id, p.span, qpath));
1778 // We should've returned in the for loop above.
1781 "lower_qpath: no final extension segment in {}..{}",
1787 fn lower_path_extra(
1791 param_mode: ParamMode,
1792 explicit_owner: Option<NodeId>,
1800 self.lower_path_segment(
1805 ParenthesizedGenericArgs::Err,
1806 ImplTraitContext::disallowed(),
1815 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1816 let res = self.expect_full_res(id);
1817 let res = self.lower_res(res);
1818 self.lower_path_extra(res, p, param_mode, None)
1821 fn lower_path_segment(
1824 segment: &PathSegment,
1825 param_mode: ParamMode,
1826 expected_lifetimes: usize,
1827 parenthesized_generic_args: ParenthesizedGenericArgs,
1828 itctx: ImplTraitContext<'_>,
1829 explicit_owner: Option<NodeId>,
1830 ) -> hir::PathSegment {
1831 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1832 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1833 match **generic_args {
1834 GenericArgs::AngleBracketed(ref data) => {
1835 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1837 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1838 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1839 ParenthesizedGenericArgs::Err => {
1840 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1841 err.span_label(data.span, "only `Fn` traits may use parentheses");
1842 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1843 // Do not suggest going from `Trait()` to `Trait<>`
1844 if data.inputs.len() > 0 {
1845 if let Some(split) = snippet.find('(') {
1846 let trait_name = &snippet[0..split];
1847 let args = &snippet[split + 1..snippet.len() - 1];
1848 err.span_suggestion(
1850 "use angle brackets instead",
1851 format!("{}<{}>", trait_name, args),
1852 Applicability::MaybeIncorrect,
1859 self.lower_angle_bracketed_parameter_data(
1860 &data.as_angle_bracketed_args(),
1871 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1874 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1875 GenericArg::Lifetime(_) => true,
1878 let first_generic_span = generic_args
1882 .chain(generic_args.bindings.iter().map(|b| b.span))
1884 if !generic_args.parenthesized && !has_lifetimes {
1885 generic_args.args = self
1886 .elided_path_lifetimes(path_span, expected_lifetimes)
1888 .map(|lt| GenericArg::Lifetime(lt))
1889 .chain(generic_args.args.into_iter())
1891 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1892 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1893 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1894 let no_bindings = generic_args.bindings.is_empty();
1895 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1896 // If there are no (non-implicit) generic args or associated type
1897 // bindings, our suggestion includes the angle brackets.
1898 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1900 // Otherwise (sorry, this is kind of gross) we need to infer the
1901 // place to splice in the `'_, ` from the generics that do exist.
1902 let first_generic_span = first_generic_span
1903 .expect("already checked that non-lifetime args or bindings exist");
1904 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1906 match self.anonymous_lifetime_mode {
1907 // In create-parameter mode we error here because we don't want to support
1908 // deprecated impl elision in new features like impl elision and `async fn`,
1909 // both of which work using the `CreateParameter` mode:
1911 // impl Foo for std::cell::Ref<u32> // note lack of '_
1912 // async fn foo(_: std::cell::Ref<u32>) { ... }
1913 AnonymousLifetimeMode::CreateParameter => {
1914 let mut err = struct_span_err!(
1918 "implicit elided lifetime not allowed here"
1920 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1931 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1932 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1933 ELIDED_LIFETIMES_IN_PATHS,
1936 "hidden lifetime parameters in types are deprecated",
1937 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1950 let res = self.expect_full_res(segment.id);
1951 let id = if let Some(owner) = explicit_owner {
1952 self.lower_node_id_with_owner(segment.id, owner)
1954 self.lower_node_id(segment.id)
1957 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1958 segment.ident, segment.id, id,
1961 hir::PathSegment::new(
1964 Some(self.lower_res(res)),
1970 fn lower_angle_bracketed_parameter_data(
1972 data: &AngleBracketedArgs,
1973 param_mode: ParamMode,
1974 mut itctx: ImplTraitContext<'_>,
1975 ) -> (hir::GenericArgs, bool) {
1976 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1977 let has_non_lt_args = args.iter().any(|arg| match arg {
1978 ast::GenericArg::Lifetime(_) => false,
1979 ast::GenericArg::Type(_) => true,
1980 ast::GenericArg::Const(_) => true,
1984 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1985 bindings: constraints
1987 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
1989 parenthesized: false,
1991 !has_non_lt_args && param_mode == ParamMode::Optional,
1995 fn lower_parenthesized_parameter_data(
1997 data: &ParenthesizedArgs,
1998 ) -> (hir::GenericArgs, bool) {
1999 // Switch to `PassThrough` mode for anonymous lifetimes; this
2000 // means that we permit things like `&Ref<T>`, where `Ref` has
2001 // a hidden lifetime parameter. This is needed for backwards
2002 // compatibility, even in contexts like an impl header where
2003 // we generally don't permit such things (see #51008).
2004 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2005 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2008 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2010 let output_ty = match output {
2011 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2012 FunctionRetTy::Default(_) => P(this.ty_tup(span, hir::HirVec::new())),
2014 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2015 let binding = hir::TypeBinding {
2016 hir_id: this.next_id(),
2017 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2018 span: output_ty.span,
2019 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2021 (hir::GenericArgs { args, bindings: hir_vec![binding], parenthesized: true }, false)
2025 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2026 let mut ids = SmallVec::<[NodeId; 1]>::new();
2027 if self.sess.features_untracked().impl_trait_in_bindings {
2028 if let Some(ref ty) = l.ty {
2029 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2030 visitor.visit_ty(ty);
2033 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2036 hir_id: self.lower_node_id(l.id),
2037 ty: l.ty.as_ref().map(|t| {
2040 if self.sess.features_untracked().impl_trait_in_bindings {
2041 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2043 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2047 pat: self.lower_pat(&l.pat),
2048 init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
2050 attrs: l.attrs.clone(),
2051 source: hir::LocalSource::Normal,
2057 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2058 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2059 // as they are not explicit in HIR/Ty function signatures.
2060 // (instead, the `c_variadic` flag is set to `true`)
2061 let mut inputs = &decl.inputs[..];
2062 if decl.c_variadic() {
2063 inputs = &inputs[..inputs.len() - 1];
2067 .map(|param| match param.pat.kind {
2068 PatKind::Ident(_, ident, _) => ident,
2069 _ => Ident::new(kw::Invalid, param.pat.span),
2074 // Lowers a function declaration.
2076 // `decl`: the unlowered (AST) function declaration.
2077 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2078 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2079 // `make_ret_async` is also `Some`.
2080 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2081 // This guards against trait declarations and implementations where `impl Trait` is
2083 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2084 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2085 // return type `impl Trait` item.
2089 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2090 impl_trait_return_allow: bool,
2091 make_ret_async: Option<NodeId>,
2092 ) -> P<hir::FnDecl> {
2096 in_band_ty_params: {:?}, \
2097 impl_trait_return_allow: {}, \
2098 make_ret_async: {:?})",
2099 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2101 let lt_mode = if make_ret_async.is_some() {
2102 // In `async fn`, argument-position elided lifetimes
2103 // must be transformed into fresh generic parameters so that
2104 // they can be applied to the opaque `impl Trait` return type.
2105 AnonymousLifetimeMode::CreateParameter
2107 self.anonymous_lifetime_mode
2110 let c_variadic = decl.c_variadic();
2112 // Remember how many lifetimes were already around so that we can
2113 // only look at the lifetime parameters introduced by the arguments.
2114 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2115 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2116 // as they are not explicit in HIR/Ty function signatures.
2117 // (instead, the `c_variadic` flag is set to `true`)
2118 let mut inputs = &decl.inputs[..];
2120 inputs = &inputs[..inputs.len() - 1];
2125 if let Some((_, ibty)) = &mut in_band_ty_params {
2126 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2128 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2131 .collect::<HirVec<_>>()
2134 let output = if let Some(ret_id) = make_ret_async {
2135 self.lower_async_fn_ret_ty(
2137 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2142 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2143 Some((def_id, _)) if impl_trait_return_allow => {
2144 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2146 _ => hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed())),
2148 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2156 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2157 let is_mutable_pat = match arg.pat.kind {
2158 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2159 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2164 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2165 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2166 // Given we are only considering `ImplicitSelf` types, we needn't consider
2167 // the case where we have a mutable pattern to a reference as that would
2168 // no longer be an `ImplicitSelf`.
2169 TyKind::Rptr(_, ref mt)
2170 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2172 hir::ImplicitSelfKind::MutRef
2174 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2175 hir::ImplicitSelfKind::ImmRef
2177 _ => hir::ImplicitSelfKind::None,
2183 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2184 // combined with the following definition of `OpaqueTy`:
2186 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2188 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2189 // `output`: unlowered output type (`T` in `-> T`)
2190 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2191 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2192 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2193 fn lower_async_fn_ret_ty(
2195 output: &FunctionRetTy,
2197 opaque_ty_node_id: NodeId,
2198 ) -> hir::FunctionRetTy {
2200 "lower_async_fn_ret_ty(\
2203 opaque_ty_node_id={:?})",
2204 output, fn_def_id, opaque_ty_node_id,
2207 let span = output.span();
2209 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2211 let opaque_ty_def_index =
2212 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2214 self.allocate_hir_id_counter(opaque_ty_node_id);
2216 // When we create the opaque type for this async fn, it is going to have
2217 // to capture all the lifetimes involved in the signature (including in the
2218 // return type). This is done by introducing lifetime parameters for:
2220 // - all the explicitly declared lifetimes from the impl and function itself;
2221 // - all the elided lifetimes in the fn arguments;
2222 // - all the elided lifetimes in the return type.
2224 // So for example in this snippet:
2227 // impl<'a> Foo<'a> {
2228 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2229 // // ^ '0 ^ '1 ^ '2
2230 // // elided lifetimes used below
2235 // we would create an opaque type like:
2238 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2241 // and we would then desugar `bar` to the equivalent of:
2244 // impl<'a> Foo<'a> {
2245 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2249 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2250 // this is because the elided lifetimes from the return type
2251 // should be figured out using the ordinary elision rules, and
2252 // this desugaring achieves that.
2254 // The variable `input_lifetimes_count` tracks the number of
2255 // lifetime parameters to the opaque type *not counting* those
2256 // lifetimes elided in the return type. This includes those
2257 // that are explicitly declared (`in_scope_lifetimes`) and
2258 // those elided lifetimes we found in the arguments (current
2259 // content of `lifetimes_to_define`). Next, we will process
2260 // the return type, which will cause `lifetimes_to_define` to
2262 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2264 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2265 // We have to be careful to get elision right here. The
2266 // idea is that we create a lifetime parameter for each
2267 // lifetime in the return type. So, given a return type
2268 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2269 // Future<Output = &'1 [ &'2 u32 ]>`.
2271 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2272 // hence the elision takes place at the fn site.
2273 let future_bound = this
2274 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2275 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2278 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2280 // Calculate all the lifetimes that should be captured
2281 // by the opaque type. This should include all in-scope
2282 // lifetime parameters, including those defined in-band.
2284 // Note: this must be done after lowering the output type,
2285 // as the output type may introduce new in-band lifetimes.
2286 let lifetime_params: Vec<(Span, ParamName)> = this
2290 .map(|name| (name.ident().span, name))
2291 .chain(this.lifetimes_to_define.iter().cloned())
2294 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2295 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2296 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2298 let generic_params = lifetime_params
2301 .map(|(span, hir_name)| {
2302 this.lifetime_to_generic_param(span, hir_name, opaque_ty_def_index)
2306 let opaque_ty_item = hir::OpaqueTy {
2307 generics: hir::Generics {
2308 params: generic_params,
2309 where_clause: hir::WhereClause { predicates: hir_vec![], span },
2312 bounds: hir_vec![future_bound],
2313 impl_trait_fn: Some(fn_def_id),
2314 origin: hir::OpaqueTyOrigin::AsyncFn,
2317 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2319 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2321 (opaque_ty_id, lifetime_params)
2324 // As documented above on the variable
2325 // `input_lifetimes_count`, we need to create the lifetime
2326 // arguments to our opaque type. Continuing with our example,
2327 // we're creating the type arguments for the return type:
2330 // Bar<'a, 'b, '0, '1, '_>
2333 // For the "input" lifetime parameters, we wish to create
2334 // references to the parameters themselves, including the
2335 // "implicit" ones created from parameter types (`'a`, `'b`,
2338 // For the "output" lifetime parameters, we just want to
2340 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2342 .map(|&(span, hir_name)| {
2343 // Input lifetime like `'a` or `'1`:
2344 GenericArg::Lifetime(hir::Lifetime {
2345 hir_id: self.next_id(),
2347 name: hir::LifetimeName::Param(hir_name),
2351 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)| {
2352 // Output lifetime like `'_`.
2353 GenericArg::Lifetime(hir::Lifetime {
2354 hir_id: self.next_id(),
2356 name: hir::LifetimeName::Implicit,
2360 // Create the `Foo<...>` reference itself. Note that the `type
2361 // Foo = impl Trait` is, internally, created as a child of the
2362 // async fn, so the *type parameters* are inherited. It's
2363 // only the lifetime parameters that we must supply.
2364 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args.into());
2365 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2366 hir::FunctionRetTy::Return(P(opaque_ty))
2369 /// Transforms `-> T` into `Future<Output = T>`
2370 fn lower_async_fn_output_type_to_future_bound(
2372 output: &FunctionRetTy,
2375 ) -> hir::GenericBound {
2376 // Compute the `T` in `Future<Output = T>` from the return type.
2377 let output_ty = match output {
2378 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2379 FunctionRetTy::Default(ret_ty_span) => P(self.ty_tup(*ret_ty_span, hir_vec![])),
2383 let future_params = P(hir::GenericArgs {
2385 bindings: hir_vec![hir::TypeBinding {
2386 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2387 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2388 hir_id: self.next_id(),
2391 parenthesized: false,
2394 // ::std::future::Future<future_params>
2396 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2398 hir::GenericBound::Trait(
2400 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2401 bound_generic_params: hir_vec![],
2404 hir::TraitBoundModifier::None,
2408 fn lower_param_bound(
2411 itctx: ImplTraitContext<'_>,
2412 ) -> hir::GenericBound {
2414 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2415 self.lower_poly_trait_ref(ty, itctx),
2416 self.lower_trait_bound_modifier(modifier),
2418 GenericBound::Outlives(ref lifetime) => {
2419 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2424 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2425 let span = l.ident.span;
2427 ident if ident.name == kw::StaticLifetime => {
2428 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2430 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2431 AnonymousLifetimeMode::CreateParameter => {
2432 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2433 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2436 AnonymousLifetimeMode::PassThrough => {
2437 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2440 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2443 self.maybe_collect_in_band_lifetime(ident);
2444 let param_name = ParamName::Plain(ident);
2445 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2450 fn new_named_lifetime(
2454 name: hir::LifetimeName,
2455 ) -> hir::Lifetime {
2456 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2459 fn lower_generic_params(
2461 params: &[GenericParam],
2462 add_bounds: &NodeMap<Vec<GenericBound>>,
2463 mut itctx: ImplTraitContext<'_>,
2464 ) -> hir::HirVec<hir::GenericParam> {
2467 .map(|param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2471 fn lower_generic_param(
2473 param: &GenericParam,
2474 add_bounds: &NodeMap<Vec<GenericBound>>,
2475 mut itctx: ImplTraitContext<'_>,
2476 ) -> hir::GenericParam {
2477 let mut bounds = self
2478 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2479 this.lower_param_bounds(¶m.bounds, itctx.reborrow())
2482 let (name, kind) = match param.kind {
2483 GenericParamKind::Lifetime => {
2484 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2485 self.is_collecting_in_band_lifetimes = false;
2488 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2489 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2491 let param_name = match lt.name {
2492 hir::LifetimeName::Param(param_name) => param_name,
2493 hir::LifetimeName::Implicit
2494 | hir::LifetimeName::Underscore
2495 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2496 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2499 "object-lifetime-default should not occur here",
2502 hir::LifetimeName::Error => ParamName::Error,
2506 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2508 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2512 GenericParamKind::Type { ref default, .. } => {
2513 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2514 if !add_bounds.is_empty() {
2515 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2516 bounds = bounds.into_iter().chain(params).collect();
2519 let kind = hir::GenericParamKind::Type {
2522 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2526 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2527 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2531 (hir::ParamName::Plain(param.ident), kind)
2533 GenericParamKind::Const { ref ty } => (
2534 hir::ParamName::Plain(param.ident),
2535 hir::GenericParamKind::Const {
2536 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2542 hir_id: self.lower_node_id(param.id),
2544 span: param.ident.span,
2545 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2546 attrs: self.lower_attrs(¶m.attrs),
2552 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2553 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2554 hir::QPath::Resolved(None, path) => path,
2555 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2557 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2560 fn lower_poly_trait_ref(
2563 mut itctx: ImplTraitContext<'_>,
2564 ) -> hir::PolyTraitRef {
2565 let bound_generic_params = self.lower_generic_params(
2566 &p.bound_generic_params,
2567 &NodeMap::default(),
2570 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2571 this.lower_trait_ref(&p.trait_ref, itctx)
2574 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2577 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2578 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2581 fn lower_param_bounds(
2583 bounds: &[GenericBound],
2584 mut itctx: ImplTraitContext<'_>,
2585 ) -> hir::GenericBounds {
2586 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2589 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block<'hir>> {
2590 let mut stmts = vec![];
2591 let mut expr = None;
2593 for (index, stmt) in b.stmts.iter().enumerate() {
2594 if index == b.stmts.len() - 1 {
2595 if let StmtKind::Expr(ref e) = stmt.kind {
2596 expr = Some(P(self.lower_expr(e)));
2598 stmts.extend(self.lower_stmt(stmt));
2601 stmts.extend(self.lower_stmt(stmt));
2606 hir_id: self.lower_node_id(b.id),
2607 stmts: stmts.into(),
2609 rules: self.lower_block_check_mode(&b.rules),
2615 /// Lowers a block directly to an expression, presuming that it
2616 /// has no attributes and is not targeted by a `break`.
2617 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2618 let block = self.lower_block(b, false);
2619 self.expr_block(block, AttrVec::new())
2622 fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat<'hir>> {
2623 let node = match p.kind {
2624 PatKind::Wild => hir::PatKind::Wild,
2625 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2626 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2627 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2630 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2631 PatKind::TupleStruct(ref path, ref pats) => {
2632 let qpath = self.lower_qpath(
2636 ParamMode::Optional,
2637 ImplTraitContext::disallowed(),
2639 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2640 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2642 PatKind::Or(ref pats) => {
2643 hir::PatKind::Or(pats.iter().map(|x| self.lower_pat(x)).collect())
2645 PatKind::Path(ref qself, ref path) => {
2646 let qpath = self.lower_qpath(
2650 ParamMode::Optional,
2651 ImplTraitContext::disallowed(),
2653 hir::PatKind::Path(qpath)
2655 PatKind::Struct(ref path, ref fields, etc) => {
2656 let qpath = self.lower_qpath(
2660 ParamMode::Optional,
2661 ImplTraitContext::disallowed(),
2666 .map(|f| hir::FieldPat {
2667 hir_id: self.next_id(),
2669 pat: self.lower_pat(&f.pat),
2670 is_shorthand: f.is_shorthand,
2674 hir::PatKind::Struct(qpath, fs, etc)
2676 PatKind::Tuple(ref pats) => {
2677 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2678 hir::PatKind::Tuple(pats, ddpos)
2680 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2681 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2682 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2683 P(self.lower_expr(e1)),
2684 P(self.lower_expr(e2)),
2685 self.lower_range_end(end),
2687 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2689 // If we reach here the `..` pattern is not semantically allowed.
2690 self.ban_illegal_rest_pat(p.span)
2692 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2693 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2696 self.pat_with_node_id_of(p, node)
2703 ) -> (HirVec<P<hir::Pat<'hir>>>, Option<usize>) {
2704 let mut elems = Vec::with_capacity(pats.len());
2705 let mut rest = None;
2707 let mut iter = pats.iter().enumerate();
2708 for (idx, pat) in iter.by_ref() {
2709 // Interpret the first `..` pattern as a sub-tuple pattern.
2710 // Note that unlike for slice patterns,
2711 // where `xs @ ..` is a legal sub-slice pattern,
2712 // it is not a legal sub-tuple pattern.
2714 rest = Some((idx, pat.span));
2717 // It was not a sub-tuple pattern so lower it normally.
2718 elems.push(self.lower_pat(pat));
2721 for (_, pat) in iter {
2722 // There was a previous sub-tuple pattern; make sure we don't allow more...
2724 // ...but there was one again, so error.
2725 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2727 elems.push(self.lower_pat(pat));
2731 (elems.into(), rest.map(|(ddpos, _)| ddpos))
2734 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2735 /// `hir::PatKind::Slice(before, slice, after)`.
2737 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2738 /// this is interpreted as a sub-slice pattern semantically.
2739 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2740 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2741 let mut before = Vec::new();
2742 let mut after = Vec::new();
2743 let mut slice = None;
2744 let mut prev_rest_span = None;
2746 let mut iter = pats.iter();
2747 // Lower all the patterns until the first occurence of a sub-slice pattern.
2748 for pat in iter.by_ref() {
2750 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2752 prev_rest_span = Some(pat.span);
2753 slice = Some(self.pat_wild_with_node_id_of(pat));
2756 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2757 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2758 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2759 prev_rest_span = Some(sub.span);
2760 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2761 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2762 slice = Some(self.pat_with_node_id_of(pat, node));
2765 // It was not a subslice pattern so lower it normally.
2766 _ => before.push(self.lower_pat(pat)),
2770 // Lower all the patterns after the first sub-slice pattern.
2772 // There was a previous subslice pattern; make sure we don't allow more.
2773 let rest_span = match pat.kind {
2774 PatKind::Rest => Some(pat.span),
2775 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2776 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2777 after.push(self.pat_wild_with_node_id_of(pat));
2782 if let Some(rest_span) = rest_span {
2783 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2784 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2786 // Lower the pattern normally.
2787 after.push(self.lower_pat(pat));
2791 hir::PatKind::Slice(before.into(), slice, after.into())
2797 binding_mode: &BindingMode,
2799 lower_sub: impl FnOnce(&mut Self) -> Option<P<hir::Pat<'hir>>>,
2800 ) -> hir::PatKind<'hir> {
2801 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2802 // `None` can occur in body-less function signatures
2803 res @ None | res @ Some(Res::Local(_)) => {
2804 let canonical_id = match res {
2805 Some(Res::Local(id)) => id,
2809 hir::PatKind::Binding(
2810 self.lower_binding_mode(binding_mode),
2811 self.lower_node_id(canonical_id),
2816 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2820 res: self.lower_res(res),
2821 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2827 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> P<hir::Pat<'hir>> {
2828 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2831 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2832 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> P<hir::Pat<'hir>> {
2833 P(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2836 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2837 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2839 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2840 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2841 .span_label(prev_sp, "previously used here")
2845 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2846 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2848 .struct_span_err(sp, "`..` patterns are not allowed here")
2849 .note("only allowed in tuple, tuple struct, and slice patterns")
2852 // We're not in a list context so `..` can be reasonably treated
2853 // as `_` because it should always be valid and roughly matches the
2854 // intent of `..` (notice that the rest of a single slot is that slot).
2858 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2860 RangeEnd::Included(_) => hir::RangeEnd::Included,
2861 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2865 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2866 self.with_new_scopes(|this| hir::AnonConst {
2867 hir_id: this.lower_node_id(c.id),
2868 body: this.lower_const_body(c.value.span, Some(&c.value)),
2872 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2873 let kind = match s.kind {
2874 StmtKind::Local(ref l) => {
2875 let (l, item_ids) = self.lower_local(l);
2876 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2879 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2880 self.stmt(s.span, hir::StmtKind::Item(item_id))
2885 hir_id: self.lower_node_id(s.id),
2886 kind: hir::StmtKind::Local(P(l)),
2892 StmtKind::Item(ref it) => {
2893 // Can only use the ID once.
2894 let mut id = Some(s.id);
2901 .map(|id| self.lower_node_id(id))
2902 .unwrap_or_else(|| self.next_id());
2904 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2908 StmtKind::Expr(ref e) => hir::StmtKind::Expr(P(self.lower_expr(e))),
2909 StmtKind::Semi(ref e) => hir::StmtKind::Semi(P(self.lower_expr(e))),
2910 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2912 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2915 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2917 BlockCheckMode::Default => hir::DefaultBlock,
2918 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2922 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2924 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2925 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2926 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2927 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2931 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2933 CompilerGenerated => hir::CompilerGenerated,
2934 UserProvided => hir::UserProvided,
2938 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2940 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2941 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2945 // Helper methods for building HIR.
2947 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2948 hir::Stmt { span, kind, hir_id: self.next_id() }
2951 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2952 self.stmt(span, hir::StmtKind::Expr(P(expr)))
2959 init: Option<P<hir::Expr<'hir>>>,
2960 pat: P<hir::Pat<'hir>>,
2961 source: hir::LocalSource,
2962 ) -> hir::Stmt<'hir> {
2963 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2964 self.stmt(span, hir::StmtKind::Local(P(local)))
2967 fn block_expr(&mut self, expr: P<hir::Expr<'hir>>) -> hir::Block<'hir> {
2968 self.block_all(expr.span, hir::HirVec::new(), Some(expr))
2974 stmts: hir::HirVec<hir::Stmt<'hir>>,
2975 expr: Option<P<hir::Expr<'hir>>>,
2976 ) -> hir::Block<'hir> {
2980 hir_id: self.next_id(),
2981 rules: hir::DefaultBlock,
2983 targeted_by_break: false,
2987 /// Constructs a `true` or `false` literal pattern.
2988 fn pat_bool(&mut self, span: Span, val: bool) -> P<hir::Pat<'hir>> {
2989 let expr = self.expr_bool(span, val);
2990 self.pat(span, hir::PatKind::Lit(P(expr)))
2993 fn pat_ok(&mut self, span: Span, pat: P<hir::Pat<'hir>>) -> P<hir::Pat<'hir>> {
2994 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], hir_vec![pat])
2997 fn pat_err(&mut self, span: Span, pat: P<hir::Pat<'hir>>) -> P<hir::Pat<'hir>> {
2998 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], hir_vec![pat])
3001 fn pat_some(&mut self, span: Span, pat: P<hir::Pat<'hir>>) -> P<hir::Pat<'hir>> {
3002 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], hir_vec![pat])
3005 fn pat_none(&mut self, span: Span) -> P<hir::Pat<'hir>> {
3006 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], hir_vec![])
3012 components: &[Symbol],
3013 subpats: hir::HirVec<P<hir::Pat<'hir>>>,
3014 ) -> P<hir::Pat<'hir>> {
3015 let path = self.std_path(span, components, None, true);
3016 let qpath = hir::QPath::Resolved(None, P(path));
3017 let pt = if subpats.is_empty() {
3018 hir::PatKind::Path(qpath)
3020 hir::PatKind::TupleStruct(qpath, subpats, None)
3025 fn pat_ident(&mut self, span: Span, ident: Ident) -> (P<hir::Pat<'hir>>, hir::HirId) {
3026 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3029 fn pat_ident_binding_mode(
3033 bm: hir::BindingAnnotation,
3034 ) -> (P<hir::Pat<'hir>>, hir::HirId) {
3035 let hir_id = self.next_id();
3040 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3047 fn pat_wild(&mut self, span: Span) -> P<hir::Pat<'hir>> {
3048 self.pat(span, hir::PatKind::Wild)
3051 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> P<hir::Pat<'hir>> {
3052 P(hir::Pat { hir_id: self.next_id(), kind, span })
3055 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3056 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3057 /// The path is also resolved according to `is_value`.
3061 components: &[Symbol],
3062 params: Option<P<hir::GenericArgs>>,
3065 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3066 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3068 let mut segments: Vec<_> = path
3072 let res = self.expect_full_res(segment.id);
3074 ident: segment.ident,
3075 hir_id: Some(self.lower_node_id(segment.id)),
3076 res: Some(self.lower_res(res)),
3082 segments.last_mut().unwrap().args = params;
3086 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3087 segments: segments.into(),
3091 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3092 let kind = match qpath {
3093 hir::QPath::Resolved(None, path) => {
3094 // Turn trait object paths into `TyKind::TraitObject` instead.
3096 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3097 let principal = hir::PolyTraitRef {
3098 bound_generic_params: hir::HirVec::new(),
3099 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3103 // The original ID is taken by the `PolyTraitRef`,
3104 // so the `Ty` itself needs a different one.
3105 hir_id = self.next_id();
3106 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3108 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3111 _ => hir::TyKind::Path(qpath),
3114 hir::Ty { hir_id, kind, span }
3117 /// Invoked to create the lifetime argument for a type `&T`
3118 /// with no explicit lifetime.
3119 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3120 match self.anonymous_lifetime_mode {
3121 // Intercept when we are in an impl header or async fn and introduce an in-band
3123 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3125 AnonymousLifetimeMode::CreateParameter => {
3126 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3128 hir_id: self.next_id(),
3130 name: hir::LifetimeName::Param(fresh_name),
3134 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3136 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3140 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3141 /// return a "error lifetime".
3142 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3143 let (id, msg, label) = match id {
3144 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3147 self.resolver.next_node_id(),
3148 "`&` without an explicit lifetime name cannot be used here",
3149 "explicit lifetime name needed here",
3153 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3154 err.span_label(span, label);
3157 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3160 /// Invoked to create the lifetime argument(s) for a path like
3161 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3162 /// sorts of cases are deprecated. This may therefore report a warning or an
3163 /// error, depending on the mode.
3164 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3165 (0..count).map(|_| self.elided_path_lifetime(span)).collect()
3168 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3169 match self.anonymous_lifetime_mode {
3170 AnonymousLifetimeMode::CreateParameter => {
3171 // We should have emitted E0726 when processing this path above
3173 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3174 let id = self.resolver.next_node_id();
3175 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3177 // `PassThrough` is the normal case.
3178 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3179 // is unsuitable here, as these can occur from missing lifetime parameters in a
3180 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3181 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3182 // later, at which point a suitable error will be emitted.
3183 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3184 self.new_implicit_lifetime(span)
3189 /// Invoked to create the lifetime argument(s) for an elided trait object
3190 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3191 /// when the bound is written, even if it is written with `'_` like in
3192 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3193 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3194 match self.anonymous_lifetime_mode {
3195 // NB. We intentionally ignore the create-parameter mode here.
3196 // and instead "pass through" to resolve-lifetimes, which will apply
3197 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3198 // do not act like other elided lifetimes. In other words, given this:
3200 // impl Foo for Box<dyn Debug>
3202 // we do not introduce a fresh `'_` to serve as the bound, but instead
3203 // ultimately translate to the equivalent of:
3205 // impl Foo for Box<dyn Debug + 'static>
3207 // `resolve_lifetime` has the code to make that happen.
3208 AnonymousLifetimeMode::CreateParameter => {}
3210 AnonymousLifetimeMode::ReportError => {
3211 // ReportError applies to explicit use of `'_`.
3214 // This is the normal case.
3215 AnonymousLifetimeMode::PassThrough => {}
3218 let r = hir::Lifetime {
3219 hir_id: self.next_id(),
3221 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3223 debug!("elided_dyn_bound: r={:?}", r);
3227 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3228 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3231 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3232 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3233 // call site which do not have a macro backtrace. See #61963.
3234 let is_macro_callsite = self
3237 .span_to_snippet(span)
3238 .map(|snippet| snippet.starts_with("#["))
3240 if !is_macro_callsite {
3241 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3242 builtin::BARE_TRAIT_OBJECTS,
3245 "trait objects without an explicit `dyn` are deprecated",
3246 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3252 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId> {
3253 // Sorting by span ensures that we get things in order within a
3254 // file, and also puts the files in a sensible order.
3255 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3256 body_ids.sort_by_key(|b| bodies[b].value.span);