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.
35 #![feature(array_value_iter)]
37 use rustc::arena::Arena;
38 use rustc::dep_graph::DepGraph;
39 use rustc::hir::intravisit;
40 use rustc::hir::map::{DefKey, DefPathData, Definitions};
42 use rustc::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
43 use rustc::middle::cstore::CrateStore;
44 use rustc::util::captures::Captures;
45 use rustc::util::common::FN_OUTPUT_NAME;
46 use rustc::{bug, span_bug};
47 use rustc_data_structures::fx::FxHashSet;
48 use rustc_data_structures::sync::Lrc;
49 use rustc_error_codes::*;
50 use rustc_errors::{struct_span_err, Applicability};
52 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
53 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
54 use rustc_hir::{ConstArg, GenericArg, ParamName};
55 use rustc_index::vec::IndexVec;
56 use rustc_session::config::nightly_options;
57 use rustc_session::node_id::NodeMap;
58 use rustc_session::Session;
59 use rustc_span::hygiene::ExpnId;
60 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
61 use rustc_span::symbol::{kw, sym, Symbol};
66 use syntax::print::pprust;
67 use syntax::ptr::P as AstP;
68 use syntax::sess::ParseSess;
69 use syntax::token::{self, Nonterminal, Token};
70 use syntax::tokenstream::{TokenStream, TokenTree};
71 use syntax::visit::{self, Visitor};
72 use syntax::walk_list;
74 use log::{debug, trace};
75 use smallvec::{smallvec, SmallVec};
76 use std::collections::BTreeMap;
79 macro_rules! arena_vec {
80 ($this:expr; $($x:expr),*) => ({
82 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
89 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
91 struct LoweringContext<'a, 'hir: 'a> {
92 crate_root: Option<Symbol>,
94 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
97 resolver: &'a mut dyn Resolver,
99 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
100 /// if we don't have this function pointer. To avoid that dependency so that
101 /// librustc is independent of the parser, we use dynamic dispatch here.
102 nt_to_tokenstream: NtToTokenstream,
104 /// Used to allocate HIR nodes
105 arena: &'hir Arena<'hir>,
107 /// The items being lowered are collected here.
108 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
110 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
111 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
112 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
113 exported_macros: Vec<hir::MacroDef<'hir>>,
114 non_exported_macro_attrs: Vec<ast::Attribute>,
116 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
118 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
120 generator_kind: Option<hir::GeneratorKind>,
122 /// Used to get the current `fn`'s def span to point to when using `await`
123 /// outside of an `async fn`.
124 current_item: Option<Span>,
126 catch_scopes: Vec<NodeId>,
127 loop_scopes: Vec<NodeId>,
128 is_in_loop_condition: bool,
129 is_in_trait_impl: bool,
130 is_in_dyn_type: bool,
132 /// What to do when we encounter either an "anonymous lifetime
133 /// reference". The term "anonymous" is meant to encompass both
134 /// `'_` lifetimes as well as fully elided cases where nothing is
135 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
136 anonymous_lifetime_mode: AnonymousLifetimeMode,
138 /// Used to create lifetime definitions from in-band lifetime usages.
139 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
140 /// When a named lifetime is encountered in a function or impl header and
141 /// has not been defined
142 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
143 /// to this list. The results of this list are then added to the list of
144 /// lifetime definitions in the corresponding impl or function generics.
145 lifetimes_to_define: Vec<(Span, ParamName)>,
147 /// `true` if in-band lifetimes are being collected. This is used to
148 /// indicate whether or not we're in a place where new lifetimes will result
149 /// in in-band lifetime definitions, such a function or an impl header,
150 /// including implicit lifetimes from `impl_header_lifetime_elision`.
151 is_collecting_in_band_lifetimes: bool,
153 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
154 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
155 /// against this list to see if it is already in-scope, or if a definition
156 /// needs to be created for it.
158 /// We always store a `modern()` version of the param-name in this
160 in_scope_lifetimes: Vec<ParamName>,
162 current_module: hir::HirId,
164 type_def_lifetime_params: DefIdMap<usize>,
166 current_hir_id_owner: Vec<(DefIndex, u32)>,
167 item_local_id_counters: NodeMap<u32>,
168 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
170 allow_try_trait: Option<Lrc<[Symbol]>>,
171 allow_gen_future: Option<Lrc<[Symbol]>>,
175 fn cstore(&self) -> &dyn CrateStore;
177 /// Obtains resolution for a `NodeId` with a single resolution.
178 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
180 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
181 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
183 /// Obtains resolution for a label with the given `NodeId`.
184 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
186 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
187 /// This should only return `None` during testing.
188 fn definitions(&mut self) -> &mut Definitions;
190 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
191 /// resolves it based on `is_value`.
195 crate_root: Option<Symbol>,
196 components: &[Symbol],
198 ) -> (ast::Path, Res<NodeId>);
200 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
202 fn next_node_id(&mut self) -> NodeId;
205 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
207 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
208 /// and if so, what meaning it has.
210 enum ImplTraitContext<'b, 'a> {
211 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
212 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
213 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
215 /// Newly generated parameters should be inserted into the given `Vec`.
216 Universal(&'b mut Vec<hir::GenericParam<'a>>),
218 /// Treat `impl Trait` as shorthand for a new opaque type.
219 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
220 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
222 /// We optionally store a `DefId` for the parent item here so we can look up necessary
223 /// information later. It is `None` when no information about the context should be stored
224 /// (e.g., for consts and statics).
225 OpaqueTy(Option<DefId> /* fn def-ID */),
227 /// `impl Trait` is not accepted in this position.
228 Disallowed(ImplTraitPosition),
231 /// Position in which `impl Trait` is disallowed.
232 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
233 enum ImplTraitPosition {
234 /// Disallowed in `let` / `const` / `static` bindings.
237 /// All other posiitons.
241 impl<'a> ImplTraitContext<'_, 'a> {
243 fn disallowed() -> Self {
244 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
247 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
248 use self::ImplTraitContext::*;
250 Universal(params) => Universal(params),
251 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
252 Disallowed(pos) => Disallowed(*pos),
257 pub fn lower_crate<'a, 'hir>(
259 dep_graph: &'a DepGraph,
261 resolver: &'a mut dyn Resolver,
262 nt_to_tokenstream: NtToTokenstream,
263 arena: &'hir Arena<'hir>,
264 ) -> hir::Crate<'hir> {
265 // We're constructing the HIR here; we don't care what we will
266 // read, since we haven't even constructed the *input* to
268 dep_graph.assert_ignored();
270 let _prof_timer = sess.prof.generic_activity("hir_lowering");
273 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
278 items: BTreeMap::new(),
279 trait_items: BTreeMap::new(),
280 impl_items: BTreeMap::new(),
281 bodies: BTreeMap::new(),
282 trait_impls: BTreeMap::new(),
283 modules: BTreeMap::new(),
284 exported_macros: Vec::new(),
285 non_exported_macro_attrs: Vec::new(),
286 catch_scopes: Vec::new(),
287 loop_scopes: Vec::new(),
288 is_in_loop_condition: false,
289 is_in_trait_impl: false,
290 is_in_dyn_type: false,
291 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
292 type_def_lifetime_params: Default::default(),
293 current_module: hir::CRATE_HIR_ID,
294 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
295 item_local_id_counters: Default::default(),
296 node_id_to_hir_id: IndexVec::new(),
297 generator_kind: None,
299 lifetimes_to_define: Vec::new(),
300 is_collecting_in_band_lifetimes: false,
301 in_scope_lifetimes: Vec::new(),
302 allow_try_trait: Some([sym::try_trait][..].into()),
303 allow_gen_future: Some([sym::gen_future][..].into()),
308 #[derive(Copy, Clone, PartialEq)]
310 /// Any path in a type context.
312 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
314 /// The `module::Type` in `module::Type::method` in an expression.
318 enum ParenthesizedGenericArgs {
323 /// What to do when we encounter an **anonymous** lifetime
324 /// reference. Anonymous lifetime references come in two flavors. You
325 /// have implicit, or fully elided, references to lifetimes, like the
326 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
327 /// or `Ref<'_, T>`. These often behave the same, but not always:
329 /// - certain usages of implicit references are deprecated, like
330 /// `Ref<T>`, and we sometimes just give hard errors in those cases
332 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
333 /// the same as `Box<dyn Foo + '_>`.
335 /// We describe the effects of the various modes in terms of three cases:
337 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
338 /// of a `&` (e.g., the missing lifetime in something like `&T`)
339 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
340 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
341 /// elided bounds follow special rules. Note that this only covers
342 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
343 /// '_>` is a case of "modern" elision.
344 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
345 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
346 /// non-deprecated equivalent.
348 /// Currently, the handling of lifetime elision is somewhat spread out
349 /// between HIR lowering and -- as described below -- the
350 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
351 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
352 /// everything into HIR lowering.
353 #[derive(Copy, Clone, Debug)]
354 enum AnonymousLifetimeMode {
355 /// For **Modern** cases, create a new anonymous region parameter
356 /// and reference that.
358 /// For **Dyn Bound** cases, pass responsibility to
359 /// `resolve_lifetime` code.
361 /// For **Deprecated** cases, report an error.
364 /// Give a hard error when either `&` or `'_` is written. Used to
365 /// rule out things like `where T: Foo<'_>`. Does not imply an
366 /// error on default object bounds (e.g., `Box<dyn Foo>`).
369 /// Pass responsibility to `resolve_lifetime` code for all cases.
373 struct ImplTraitTypeIdVisitor<'a> {
374 ids: &'a mut SmallVec<[NodeId; 1]>,
377 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
378 fn visit_ty(&mut self, ty: &Ty) {
380 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
382 TyKind::ImplTrait(id, _) => self.ids.push(id),
385 visit::walk_ty(self, ty);
388 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
389 if let Some(ref p) = path_segment.args {
390 if let GenericArgs::Parenthesized(_) = **p {
394 visit::walk_path_segment(self, path_span, path_segment)
398 impl<'a, 'hir> LoweringContext<'a, 'hir> {
399 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
400 /// Full-crate AST visitor that inserts into a fresh
401 /// `LoweringContext` any information that may be
402 /// needed from arbitrary locations in the crate,
403 /// e.g., the number of lifetime generic parameters
404 /// declared for every type and trait definition.
405 struct MiscCollector<'tcx, 'lowering, 'hir> {
406 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
407 hir_id_owner: Option<NodeId>,
410 impl MiscCollector<'_, '_, '_> {
411 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
413 UseTreeKind::Simple(_, id1, id2) => {
414 for &id in &[id1, id2] {
415 self.lctx.resolver.definitions().create_def_with_parent(
422 self.lctx.allocate_hir_id_counter(id);
425 UseTreeKind::Glob => (),
426 UseTreeKind::Nested(ref trees) => {
427 for &(ref use_tree, id) in trees {
428 let hir_id = self.lctx.allocate_hir_id_counter(id);
429 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
435 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
437 F: FnOnce(&mut Self) -> T,
439 let old = mem::replace(&mut self.hir_id_owner, owner);
441 self.hir_id_owner = old;
446 impl<'tcx, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
447 fn visit_pat(&mut self, p: &'tcx Pat) {
448 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
449 // Doesn't generate a HIR node
450 } else if let Some(owner) = self.hir_id_owner {
451 self.lctx.lower_node_id_with_owner(p.id, owner);
454 visit::walk_pat(self, p)
457 fn visit_item(&mut self, item: &'tcx Item) {
458 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
461 ItemKind::Struct(_, ref generics)
462 | ItemKind::Union(_, ref generics)
463 | ItemKind::Enum(_, ref generics)
464 | ItemKind::TyAlias(_, ref generics)
465 | ItemKind::Trait(_, _, ref generics, ..) => {
466 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
470 .filter(|param| match param.kind {
471 ast::GenericParamKind::Lifetime { .. } => true,
475 self.lctx.type_def_lifetime_params.insert(def_id, count);
477 ItemKind::Use(ref use_tree) => {
478 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
483 self.with_hir_id_owner(Some(item.id), |this| {
484 visit::walk_item(this, item);
488 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
489 self.lctx.allocate_hir_id_counter(item.id);
492 AssocItemKind::Fn(_, None) => {
493 // Ignore patterns in trait methods without bodies
494 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
496 _ => self.with_hir_id_owner(Some(item.id), |this| {
497 visit::walk_trait_item(this, item);
502 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
503 self.lctx.allocate_hir_id_counter(item.id);
504 self.with_hir_id_owner(Some(item.id), |this| {
505 visit::walk_impl_item(this, item);
509 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
510 // Ignore patterns in foreign items
511 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
514 fn visit_ty(&mut self, t: &'tcx Ty) {
516 // Mirrors the case in visit::walk_ty
517 TyKind::BareFn(ref f) => {
518 walk_list!(self, visit_generic_param, &f.generic_params);
519 // Mirrors visit::walk_fn_decl
520 for parameter in &f.decl.inputs {
521 // We don't lower the ids of argument patterns
522 self.with_hir_id_owner(None, |this| {
523 this.visit_pat(¶meter.pat);
525 self.visit_ty(¶meter.ty)
527 self.visit_fn_ret_ty(&f.decl.output)
529 _ => visit::walk_ty(self, t),
534 self.lower_node_id(CRATE_NODE_ID);
535 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
537 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
538 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
540 let module = self.lower_mod(&c.module);
541 let attrs = self.lower_attrs(&c.attrs);
542 let body_ids = body_ids(&self.bodies);
544 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
550 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
551 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
553 trait_items: self.trait_items,
554 impl_items: self.impl_items,
557 trait_impls: self.trait_impls,
558 modules: self.modules,
562 fn insert_item(&mut self, item: hir::Item<'hir>) {
563 let id = item.hir_id;
564 // FIXME: Use `debug_asset-rt`.
565 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
566 self.items.insert(id, item);
567 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
570 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
571 // Set up the counter if needed.
572 self.item_local_id_counters.entry(owner).or_insert(0);
573 // Always allocate the first `HirId` for the owner itself.
574 let lowered = self.lower_node_id_with_owner(owner, owner);
575 debug_assert_eq!(lowered.local_id.as_u32(), 0);
579 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
581 F: FnOnce(&mut Self) -> hir::HirId,
583 if ast_node_id == DUMMY_NODE_ID {
584 return hir::DUMMY_HIR_ID;
587 let min_size = ast_node_id.as_usize() + 1;
589 if min_size > self.node_id_to_hir_id.len() {
590 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
593 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
595 if existing_hir_id == hir::DUMMY_HIR_ID {
596 // Generate a new `HirId`.
597 let hir_id = alloc_hir_id(self);
598 self.node_id_to_hir_id[ast_node_id] = hir_id;
606 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
608 F: FnOnce(&mut Self) -> T,
611 .item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
623 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
627 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
628 /// the `LoweringContext`'s `NodeId => HirId` map.
629 /// Take care not to call this method if the resulting `HirId` is then not
630 /// actually used in the HIR, as that would trigger an assertion in the
631 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
632 /// properly. Calling the method twice with the same `NodeId` is fine though.
633 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let &mut (def_index, ref mut local_id_counter) =
636 this.current_hir_id_owner.last_mut().unwrap();
637 let local_id = *local_id_counter;
638 *local_id_counter += 1;
639 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
643 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
644 self.lower_node_id_generic(ast_node_id, |this| {
645 let local_id_counter = this
646 .item_local_id_counters
648 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
649 let local_id = *local_id_counter;
651 // We want to be sure not to modify the counter in the map while it
652 // is also on the stack. Otherwise we'll get lost updates when writing
653 // back from the stack to the map.
654 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
656 *local_id_counter += 1;
657 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
658 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
659 that do not belong to the current owner",
662 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
666 fn next_id(&mut self) -> hir::HirId {
667 let node_id = self.resolver.next_node_id();
668 self.lower_node_id(node_id)
671 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
673 self.lower_node_id_generic(id, |_| {
674 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
679 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
680 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
681 if pr.unresolved_segments() != 0 {
682 bug!("path not fully resolved: {:?}", pr);
688 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
689 self.resolver.get_import_res(id).present_items()
692 fn diagnostic(&self) -> &rustc_errors::Handler {
693 self.sess.diagnostic()
696 /// Reuses the span but adds information like the kind of the desugaring and features that are
697 /// allowed inside this span.
698 fn mark_span_with_reason(
700 reason: DesugaringKind,
702 allow_internal_unstable: Option<Lrc<[Symbol]>>,
704 span.fresh_expansion(ExpnData {
705 allow_internal_unstable,
706 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
710 fn with_anonymous_lifetime_mode<R>(
712 anonymous_lifetime_mode: AnonymousLifetimeMode,
713 op: impl FnOnce(&mut Self) -> R,
716 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
717 anonymous_lifetime_mode,
719 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
720 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
721 let result = op(self);
722 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
724 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
725 old_anonymous_lifetime_mode
730 /// Creates a new `hir::GenericParam` for every new lifetime and
731 /// type parameter encountered while evaluating `f`. Definitions
732 /// are created with the parent provided. If no `parent_id` is
733 /// provided, no definitions will be returned.
735 /// Presuming that in-band lifetimes are enabled, then
736 /// `self.anonymous_lifetime_mode` will be updated to match the
737 /// parameter while `f` is running (and restored afterwards).
738 fn collect_in_band_defs<T, F>(
741 anonymous_lifetime_mode: AnonymousLifetimeMode,
743 ) -> (Vec<hir::GenericParam<'hir>>, T)
745 F: FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
747 assert!(!self.is_collecting_in_band_lifetimes);
748 assert!(self.lifetimes_to_define.is_empty());
749 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
751 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
752 self.is_collecting_in_band_lifetimes = true;
754 let (in_band_ty_params, res) = f(self);
756 self.is_collecting_in_band_lifetimes = false;
757 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
759 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
761 let params = lifetimes_to_define
763 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
764 .chain(in_band_ty_params.into_iter())
770 /// Converts a lifetime into a new generic parameter.
771 fn lifetime_to_generic_param(
775 parent_index: DefIndex,
776 ) -> hir::GenericParam<'hir> {
777 let node_id = self.resolver.next_node_id();
779 // Get the name we'll use to make the def-path. Note
780 // that collisions are ok here and this shouldn't
781 // really show up for end-user.
782 let (str_name, kind) = match hir_name {
783 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
784 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
785 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
788 // Add a definition for the in-band lifetime def.
789 self.resolver.definitions().create_def_with_parent(
792 DefPathData::LifetimeNs(str_name),
798 hir_id: self.lower_node_id(node_id),
803 pure_wrt_drop: false,
804 kind: hir::GenericParamKind::Lifetime { kind },
808 /// When there is a reference to some lifetime `'a`, and in-band
809 /// lifetimes are enabled, then we want to push that lifetime into
810 /// the vector of names to define later. In that case, it will get
811 /// added to the appropriate generics.
812 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
813 if !self.is_collecting_in_band_lifetimes {
817 if !self.sess.features_untracked().in_band_lifetimes {
821 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
825 let hir_name = ParamName::Plain(ident);
827 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
832 self.lifetimes_to_define.push((ident.span, hir_name));
835 /// When we have either an elided or `'_` lifetime in an impl
836 /// header, we convert it to an in-band lifetime.
837 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
838 assert!(self.is_collecting_in_band_lifetimes);
839 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
840 let hir_name = ParamName::Fresh(index);
841 self.lifetimes_to_define.push((span, hir_name));
845 // Evaluates `f` with the lifetimes in `params` in-scope.
846 // This is used to track which lifetimes have already been defined, and
847 // which are new in-band lifetimes that need to have a definition created
849 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
851 F: FnOnce(&mut Self) -> T,
853 let old_len = self.in_scope_lifetimes.len();
854 let lt_def_names = params.iter().filter_map(|param| match param.kind {
855 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
858 self.in_scope_lifetimes.extend(lt_def_names);
862 self.in_scope_lifetimes.truncate(old_len);
866 /// Appends in-band lifetime defs and argument-position `impl
867 /// Trait` defs to the existing set of generics.
869 /// Presuming that in-band lifetimes are enabled, then
870 /// `self.anonymous_lifetime_mode` will be updated to match the
871 /// parameter while `f` is running (and restored afterwards).
872 fn add_in_band_defs<F, T>(
876 anonymous_lifetime_mode: AnonymousLifetimeMode,
878 ) -> (hir::Generics<'hir>, T)
880 F: FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
882 let (in_band_defs, (mut lowered_generics, res)) =
883 self.with_in_scope_lifetime_defs(&generics.params, |this| {
884 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
885 let mut params = Vec::new();
886 // Note: it is necessary to lower generics *before* calling `f`.
887 // When lowering `async fn`, there's a final step when lowering
888 // the return type that assumes that all in-scope lifetimes have
889 // already been added to either `in_scope_lifetimes` or
890 // `lifetimes_to_define`. If we swapped the order of these two,
891 // in-band-lifetimes introduced by generics or where-clauses
892 // wouldn't have been added yet.
894 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
895 let res = f(this, &mut params);
896 (params, (generics, res))
900 let mut lowered_params: Vec<_> =
901 lowered_generics.params.into_iter().chain(in_band_defs).collect();
903 // FIXME(const_generics): the compiler doesn't always cope with
904 // unsorted generic parameters at the moment, so we make sure
905 // that they're ordered correctly here for now. (When we chain
906 // the `in_band_defs`, we might make the order unsorted.)
907 lowered_params.sort_by_key(|param| match param.kind {
908 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
909 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
910 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
913 lowered_generics.params = lowered_params.into();
915 let lowered_generics = lowered_generics.into_generics(self.arena);
916 (lowered_generics, res)
919 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
921 F: FnOnce(&mut Self) -> T,
923 let was_in_dyn_type = self.is_in_dyn_type;
924 self.is_in_dyn_type = in_scope;
926 let result = f(self);
928 self.is_in_dyn_type = was_in_dyn_type;
933 fn with_new_scopes<T, F>(&mut self, f: F) -> T
935 F: FnOnce(&mut Self) -> T,
937 let was_in_loop_condition = self.is_in_loop_condition;
938 self.is_in_loop_condition = false;
940 let catch_scopes = mem::take(&mut self.catch_scopes);
941 let loop_scopes = mem::take(&mut self.loop_scopes);
943 self.catch_scopes = catch_scopes;
944 self.loop_scopes = loop_scopes;
946 self.is_in_loop_condition = was_in_loop_condition;
951 fn def_key(&mut self, id: DefId) -> DefKey {
953 self.resolver.definitions().def_key(id.index)
955 self.resolver.cstore().def_key(id)
959 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
960 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
963 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
964 // Note that we explicitly do not walk the path. Since we don't really
965 // lower attributes (we use the AST version) there is nowhere to keep
966 // the `HirId`s. We don't actually need HIR version of attributes anyway.
967 let kind = match attr.kind {
968 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
969 path: item.path.clone(),
970 args: self.lower_mac_args(&item.args),
972 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
975 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
978 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
980 MacArgs::Empty => MacArgs::Empty,
981 MacArgs::Delimited(dspan, delim, ref tokens) => {
982 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
984 MacArgs::Eq(eq_span, ref tokens) => {
985 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
990 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
991 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
994 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
996 TokenTree::Token(token) => self.lower_token(token),
997 TokenTree::Delimited(span, delim, tts) => {
998 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
1003 fn lower_token(&mut self, token: Token) -> TokenStream {
1005 token::Interpolated(nt) => {
1006 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1007 self.lower_token_stream(tts)
1009 _ => TokenTree::Token(token).into(),
1013 /// Given an associated type constraint like one of these:
1016 /// T: Iterator<Item: Debug>
1018 /// T: Iterator<Item = Debug>
1022 /// returns a `hir::TypeBinding` representing `Item`.
1023 fn lower_assoc_ty_constraint(
1025 constraint: &AssocTyConstraint,
1026 itctx: ImplTraitContext<'_, 'hir>,
1027 ) -> hir::TypeBinding<'hir> {
1028 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1030 let kind = match constraint.kind {
1031 AssocTyConstraintKind::Equality { ref ty } => {
1032 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1034 AssocTyConstraintKind::Bound { ref bounds } => {
1035 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1036 let (desugar_to_impl_trait, itctx) = match itctx {
1037 // We are in the return position:
1039 // fn foo() -> impl Iterator<Item: Debug>
1043 // fn foo() -> impl Iterator<Item = impl Debug>
1044 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1046 // We are in the argument position, but within a dyn type:
1048 // fn foo(x: dyn Iterator<Item: Debug>)
1052 // fn foo(x: dyn Iterator<Item = impl Debug>)
1053 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1055 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1056 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1057 // "impl trait context" to permit `impl Debug` in this position (it desugars
1058 // then to an opaque type).
1060 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1061 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1062 (true, ImplTraitContext::OpaqueTy(None))
1065 // We are in the parameter position, but not within a dyn type:
1067 // fn foo(x: impl Iterator<Item: Debug>)
1069 // so we leave it as is and this gets expanded in astconv to a bound like
1070 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1072 _ => (false, itctx),
1075 if desugar_to_impl_trait {
1076 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1077 // constructing the HIR for `impl bounds...` and then lowering that.
1079 let impl_trait_node_id = self.resolver.next_node_id();
1080 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1081 self.resolver.definitions().create_def_with_parent(
1084 DefPathData::ImplTrait,
1089 self.with_dyn_type_scope(false, |this| {
1090 let node_id = this.resolver.next_node_id();
1091 let ty = this.lower_ty(
1094 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1095 span: constraint.span,
1100 hir::TypeBindingKind::Equality { ty }
1103 // Desugar `AssocTy: Bounds` into a type binding where the
1104 // later desugars into a trait predicate.
1105 let bounds = self.lower_param_bounds(bounds, itctx);
1107 hir::TypeBindingKind::Constraint { bounds }
1113 hir_id: self.lower_node_id(constraint.id),
1114 ident: constraint.ident,
1116 span: constraint.span,
1120 fn lower_generic_arg(
1122 arg: &ast::GenericArg,
1123 itctx: ImplTraitContext<'_, 'hir>,
1124 ) -> hir::GenericArg<'hir> {
1126 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1127 ast::GenericArg::Type(ty) => {
1128 // We parse const arguments as path types as we cannot distiguish them durring
1129 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1130 // type and value namespaces. If we resolved the path in the value namespace, we
1131 // transform it into a generic const argument.
1132 if let TyKind::Path(ref qself, ref path) = ty.kind {
1133 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1134 let res = partial_res.base_res();
1135 if !res.matches_ns(Namespace::TypeNS) {
1137 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1141 // Construct a AnonConst where the expr is the "ty"'s path.
1143 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1144 let node_id = self.resolver.next_node_id();
1146 // Add a definition for the in-band const def.
1147 self.resolver.definitions().create_def_with_parent(
1150 DefPathData::AnonConst,
1155 let path_expr = Expr {
1157 kind: ExprKind::Path(qself.clone(), path.clone()),
1159 attrs: AttrVec::new(),
1162 let ct = self.with_new_scopes(|this| hir::AnonConst {
1163 hir_id: this.lower_node_id(node_id),
1164 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1166 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1170 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1172 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1173 value: self.lower_anon_const(&ct),
1174 span: ct.value.span,
1179 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1180 self.arena.alloc(self.lower_ty_direct(t, itctx))
1186 qself: &Option<QSelf>,
1188 param_mode: ParamMode,
1189 itctx: ImplTraitContext<'_, 'hir>,
1190 ) -> hir::Ty<'hir> {
1191 let id = self.lower_node_id(t.id);
1192 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1193 let ty = self.ty_path(id, t.span, qpath);
1194 if let hir::TyKind::TraitObject(..) = ty.kind {
1195 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1200 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1201 hir::Ty { hir_id: self.next_id(), kind, span }
1204 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1205 self.ty(span, hir::TyKind::Tup(tys))
1208 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1209 let kind = match t.kind {
1210 TyKind::Infer => hir::TyKind::Infer,
1211 TyKind::Err => hir::TyKind::Err,
1212 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1213 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1214 TyKind::Rptr(ref region, ref mt) => {
1215 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1216 let lifetime = match *region {
1217 Some(ref lt) => self.lower_lifetime(lt),
1218 None => self.elided_ref_lifetime(span),
1220 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1222 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1223 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1224 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1225 generic_params: this.lower_generic_params(
1227 &NodeMap::default(),
1228 ImplTraitContext::disallowed(),
1230 unsafety: f.unsafety,
1231 abi: this.lower_extern(f.ext),
1232 decl: this.lower_fn_decl(&f.decl, None, false, None),
1233 param_names: this.lower_fn_params_to_names(&f.decl),
1237 TyKind::Never => hir::TyKind::Never,
1238 TyKind::Tup(ref tys) => {
1239 hir::TyKind::Tup(self.arena.alloc_from_iter(
1240 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1243 TyKind::Paren(ref ty) => {
1244 return self.lower_ty_direct(ty, itctx);
1246 TyKind::Path(ref qself, ref path) => {
1247 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1249 TyKind::ImplicitSelf => {
1250 let res = self.expect_full_res(t.id);
1251 let res = self.lower_res(res);
1252 hir::TyKind::Path(hir::QPath::Resolved(
1254 self.arena.alloc(hir::Path {
1256 segments: arena_vec![self; hir::PathSegment::from_ident(
1257 Ident::with_dummy_span(kw::SelfUpper)
1263 TyKind::Array(ref ty, ref length) => {
1264 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1266 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1267 TyKind::TraitObject(ref bounds, kind) => {
1268 let mut lifetime_bound = None;
1269 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1271 this.arena.alloc_from_iter(bounds.iter().filter_map(
1272 |bound| match *bound {
1273 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1274 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1276 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1277 GenericBound::Outlives(ref lifetime) => {
1278 if lifetime_bound.is_none() {
1279 lifetime_bound = Some(this.lower_lifetime(lifetime));
1285 let lifetime_bound =
1286 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1287 (bounds, lifetime_bound)
1289 if kind != TraitObjectSyntax::Dyn {
1290 self.maybe_lint_bare_trait(t.span, t.id, false);
1292 hir::TyKind::TraitObject(bounds, lifetime_bound)
1294 TyKind::ImplTrait(def_node_id, ref bounds) => {
1297 ImplTraitContext::OpaqueTy(fn_def_id) => {
1298 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1299 this.lower_param_bounds(bounds, itctx)
1302 ImplTraitContext::Universal(in_band_ty_params) => {
1303 // Add a definition for the in-band `Param`.
1305 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1307 let hir_bounds = self.lower_param_bounds(
1309 ImplTraitContext::Universal(in_band_ty_params),
1311 // Set the name to `impl Bound1 + Bound2`.
1312 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1313 in_band_ty_params.push(hir::GenericParam {
1314 hir_id: self.lower_node_id(def_node_id),
1315 name: ParamName::Plain(ident),
1316 pure_wrt_drop: false,
1320 kind: hir::GenericParamKind::Type {
1322 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1326 hir::TyKind::Path(hir::QPath::Resolved(
1328 self.arena.alloc(hir::Path {
1330 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1331 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1335 ImplTraitContext::Disallowed(pos) => {
1336 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1337 "bindings or function and inherent method return types"
1339 "function and inherent method return types"
1341 let mut err = struct_span_err!(
1345 "`impl Trait` not allowed outside of {}",
1348 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1351 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1352 attributes to enable",
1360 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1361 TyKind::CVarArgs => {
1362 self.sess.delay_span_bug(
1364 "`TyKind::CVarArgs` should have been handled elsewhere",
1370 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1373 fn lower_opaque_impl_trait(
1376 fn_def_id: Option<DefId>,
1377 opaque_ty_node_id: NodeId,
1378 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1379 ) -> hir::TyKind<'hir> {
1381 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1382 fn_def_id, opaque_ty_node_id, span,
1385 // Make sure we know that some funky desugaring has been going on here.
1386 // This is a first: there is code in other places like for loop
1387 // desugaring that explicitly states that we don't want to track that.
1388 // Not tracking it makes lints in rustc and clippy very fragile, as
1389 // frequently opened issues show.
1390 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1392 let opaque_ty_def_index =
1393 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1395 self.allocate_hir_id_counter(opaque_ty_node_id);
1397 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1399 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1401 opaque_ty_def_index,
1405 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1407 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1409 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1410 let opaque_ty_item = hir::OpaqueTy {
1411 generics: hir::Generics {
1412 params: lifetime_defs,
1413 where_clause: hir::WhereClause { predicates: &[], span },
1417 impl_trait_fn: fn_def_id,
1418 origin: hir::OpaqueTyOrigin::FnReturn,
1421 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1423 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1425 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1426 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1430 /// Registers a new opaque type with the proper `NodeId`s and
1431 /// returns the lowered node-ID for the opaque type.
1432 fn generate_opaque_type(
1434 opaque_ty_node_id: NodeId,
1435 opaque_ty_item: hir::OpaqueTy<'hir>,
1437 opaque_ty_span: Span,
1439 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1440 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1441 // Generate an `type Foo = impl Trait;` declaration.
1442 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1443 let opaque_ty_item = hir::Item {
1444 hir_id: opaque_ty_id,
1445 ident: Ident::invalid(),
1446 attrs: Default::default(),
1447 kind: opaque_ty_item_kind,
1448 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1449 span: opaque_ty_span,
1452 // Insert the item into the global item list. This usually happens
1453 // automatically for all AST items. But this opaque type item
1454 // does not actually exist in the AST.
1455 self.insert_item(opaque_ty_item);
1459 fn lifetimes_from_impl_trait_bounds(
1461 opaque_ty_id: NodeId,
1462 parent_index: DefIndex,
1463 bounds: hir::GenericBounds<'hir>,
1464 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1466 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1467 parent_index={:?}, \
1469 opaque_ty_id, parent_index, bounds,
1472 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1473 // appear in the bounds, excluding lifetimes that are created within the bounds.
1474 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1475 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1476 context: &'r mut LoweringContext<'a, 'hir>,
1478 opaque_ty_id: NodeId,
1479 collect_elided_lifetimes: bool,
1480 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1481 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1482 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1483 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1486 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1487 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'v> {
1488 intravisit::NestedVisitorMap::None
1491 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1492 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1493 if parameters.parenthesized {
1494 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1495 self.collect_elided_lifetimes = false;
1496 intravisit::walk_generic_args(self, span, parameters);
1497 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1499 intravisit::walk_generic_args(self, span, parameters);
1503 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1504 // Don't collect elided lifetimes used inside of `fn()` syntax.
1505 if let hir::TyKind::BareFn(_) = t.kind {
1506 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1507 self.collect_elided_lifetimes = false;
1509 // Record the "stack height" of `for<'a>` lifetime bindings
1510 // to be able to later fully undo their introduction.
1511 let old_len = self.currently_bound_lifetimes.len();
1512 intravisit::walk_ty(self, t);
1513 self.currently_bound_lifetimes.truncate(old_len);
1515 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1517 intravisit::walk_ty(self, t)
1521 fn visit_poly_trait_ref(
1523 trait_ref: &'v hir::PolyTraitRef<'v>,
1524 modifier: hir::TraitBoundModifier,
1526 // Record the "stack height" of `for<'a>` lifetime bindings
1527 // to be able to later fully undo their introduction.
1528 let old_len = self.currently_bound_lifetimes.len();
1529 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1530 self.currently_bound_lifetimes.truncate(old_len);
1533 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1534 // Record the introduction of 'a in `for<'a> ...`.
1535 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1536 // Introduce lifetimes one at a time so that we can handle
1537 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1538 let lt_name = hir::LifetimeName::Param(param.name);
1539 self.currently_bound_lifetimes.push(lt_name);
1542 intravisit::walk_generic_param(self, param);
1545 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1546 let name = match lifetime.name {
1547 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1548 if self.collect_elided_lifetimes {
1549 // Use `'_` for both implicit and underscore lifetimes in
1550 // `type Foo<'_> = impl SomeTrait<'_>;`.
1551 hir::LifetimeName::Underscore
1556 hir::LifetimeName::Param(_) => lifetime.name,
1558 // Refers to some other lifetime that is "in
1559 // scope" within the type.
1560 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1562 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1565 if !self.currently_bound_lifetimes.contains(&name)
1566 && !self.already_defined_lifetimes.contains(&name)
1568 self.already_defined_lifetimes.insert(name);
1570 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1571 hir_id: self.context.next_id(),
1572 span: lifetime.span,
1576 let def_node_id = self.context.resolver.next_node_id();
1578 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1579 self.context.resolver.definitions().create_def_with_parent(
1582 DefPathData::LifetimeNs(name.ident().name),
1587 let (name, kind) = match name {
1588 hir::LifetimeName::Underscore => (
1589 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1590 hir::LifetimeParamKind::Elided,
1592 hir::LifetimeName::Param(param_name) => {
1593 (param_name, hir::LifetimeParamKind::Explicit)
1595 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1598 self.output_lifetime_params.push(hir::GenericParam {
1601 span: lifetime.span,
1602 pure_wrt_drop: false,
1605 kind: hir::GenericParamKind::Lifetime { kind },
1611 let mut lifetime_collector = ImplTraitLifetimeCollector {
1613 parent: parent_index,
1615 collect_elided_lifetimes: true,
1616 currently_bound_lifetimes: Vec::new(),
1617 already_defined_lifetimes: FxHashSet::default(),
1618 output_lifetimes: Vec::new(),
1619 output_lifetime_params: Vec::new(),
1622 for bound in bounds {
1623 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1626 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1630 self.arena.alloc_from_iter(output_lifetimes),
1631 self.arena.alloc_from_iter(output_lifetime_params),
1638 qself: &Option<QSelf>,
1640 param_mode: ParamMode,
1641 mut itctx: ImplTraitContext<'_, 'hir>,
1642 ) -> hir::QPath<'hir> {
1643 let qself_position = qself.as_ref().map(|q| q.position);
1644 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1647 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1649 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1650 let path = self.arena.alloc(hir::Path {
1651 res: self.lower_res(partial_res.base_res()),
1652 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1654 let param_mode = match (qself_position, param_mode) {
1655 (Some(j), ParamMode::Optional) if i < j => {
1656 // This segment is part of the trait path in a
1657 // qualified path - one of `a`, `b` or `Trait`
1658 // in `<X as a::b::Trait>::T::U::method`.
1664 // Figure out if this is a type/trait segment,
1665 // which may need lifetime elision performed.
1666 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1667 krate: def_id.krate,
1668 index: this.def_key(def_id).parent.expect("missing parent"),
1670 let type_def_id = match partial_res.base_res() {
1671 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1672 Some(parent_def_id(self, def_id))
1674 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1675 Some(parent_def_id(self, def_id))
1677 Res::Def(DefKind::Struct, def_id)
1678 | Res::Def(DefKind::Union, def_id)
1679 | Res::Def(DefKind::Enum, def_id)
1680 | Res::Def(DefKind::TyAlias, def_id)
1681 | Res::Def(DefKind::Trait, def_id)
1682 if i + 1 == proj_start =>
1688 let parenthesized_generic_args = match partial_res.base_res() {
1689 // `a::b::Trait(Args)`
1690 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1691 ParenthesizedGenericArgs::Ok
1693 // `a::b::Trait(Args)::TraitItem`
1694 Res::Def(DefKind::Method, _)
1695 | Res::Def(DefKind::AssocConst, _)
1696 | Res::Def(DefKind::AssocTy, _)
1697 if i + 2 == proj_start =>
1699 ParenthesizedGenericArgs::Ok
1701 // Avoid duplicated errors.
1702 Res::Err => ParenthesizedGenericArgs::Ok,
1704 _ => ParenthesizedGenericArgs::Err,
1707 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1708 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1711 assert!(!def_id.is_local());
1712 let item_generics = self
1715 .item_generics_cloned_untracked(def_id, self.sess);
1716 let n = item_generics.own_counts().lifetimes;
1717 self.type_def_lifetime_params.insert(def_id, n);
1720 self.lower_path_segment(
1725 parenthesized_generic_args,
1734 // Simple case, either no projections, or only fully-qualified.
1735 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1736 if partial_res.unresolved_segments() == 0 {
1737 return hir::QPath::Resolved(qself, path);
1740 // Create the innermost type that we're projecting from.
1741 let mut ty = if path.segments.is_empty() {
1742 // If the base path is empty that means there exists a
1743 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1744 qself.expect("missing QSelf for <T>::...")
1746 // Otherwise, the base path is an implicit `Self` type path,
1747 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1748 // `<I as Iterator>::Item::default`.
1749 let new_id = self.next_id();
1750 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1753 // Anything after the base path are associated "extensions",
1754 // out of which all but the last one are associated types,
1755 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1756 // * base path is `std::vec::Vec<T>`
1757 // * "extensions" are `IntoIter`, `Item` and `clone`
1758 // * type nodes are:
1759 // 1. `std::vec::Vec<T>` (created above)
1760 // 2. `<std::vec::Vec<T>>::IntoIter`
1761 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1762 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1763 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1764 let segment = self.arena.alloc(self.lower_path_segment(
1769 ParenthesizedGenericArgs::Err,
1773 let qpath = hir::QPath::TypeRelative(ty, segment);
1775 // It's finished, return the extension of the right node type.
1776 if i == p.segments.len() - 1 {
1780 // Wrap the associated extension in another type node.
1781 let new_id = self.next_id();
1782 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1785 // We should've returned in the for loop above.
1788 "lower_qpath: no final extension segment in {}..{}",
1794 fn lower_path_extra(
1798 param_mode: ParamMode,
1799 explicit_owner: Option<NodeId>,
1800 ) -> &'hir hir::Path<'hir> {
1801 self.arena.alloc(hir::Path {
1803 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1804 self.lower_path_segment(
1809 ParenthesizedGenericArgs::Err,
1810 ImplTraitContext::disallowed(),
1818 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> &'hir hir::Path<'hir> {
1819 let res = self.expect_full_res(id);
1820 let res = self.lower_res(res);
1821 self.lower_path_extra(res, p, param_mode, None)
1824 fn lower_path_segment(
1827 segment: &PathSegment,
1828 param_mode: ParamMode,
1829 expected_lifetimes: usize,
1830 parenthesized_generic_args: ParenthesizedGenericArgs,
1831 itctx: ImplTraitContext<'_, 'hir>,
1832 explicit_owner: Option<NodeId>,
1833 ) -> hir::PathSegment<'hir> {
1834 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1835 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1836 match **generic_args {
1837 GenericArgs::AngleBracketed(ref data) => {
1838 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1840 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1841 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1842 ParenthesizedGenericArgs::Err => {
1843 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1844 err.span_label(data.span, "only `Fn` traits may use parentheses");
1845 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1846 // Do not suggest going from `Trait()` to `Trait<>`
1847 if data.inputs.len() > 0 {
1848 if let Some(split) = snippet.find('(') {
1849 let trait_name = &snippet[0..split];
1850 let args = &snippet[split + 1..snippet.len() - 1];
1851 err.span_suggestion(
1853 "use angle brackets instead",
1854 format!("{}<{}>", trait_name, args),
1855 Applicability::MaybeIncorrect,
1862 self.lower_angle_bracketed_parameter_data(
1863 &data.as_angle_bracketed_args(),
1874 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1877 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1878 GenericArg::Lifetime(_) => true,
1881 let first_generic_span = generic_args
1885 .chain(generic_args.bindings.iter().map(|b| b.span))
1887 if !generic_args.parenthesized && !has_lifetimes {
1888 generic_args.args = self
1889 .elided_path_lifetimes(path_span, expected_lifetimes)
1890 .map(|lt| GenericArg::Lifetime(lt))
1891 .chain(generic_args.args.into_iter())
1893 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1894 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1895 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1896 let no_bindings = generic_args.bindings.is_empty();
1897 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1898 // If there are no (non-implicit) generic args or associated type
1899 // bindings, our suggestion includes the angle brackets.
1900 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1902 // Otherwise (sorry, this is kind of gross) we need to infer the
1903 // place to splice in the `'_, ` from the generics that do exist.
1904 let first_generic_span = first_generic_span
1905 .expect("already checked that non-lifetime args or bindings exist");
1906 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1908 match self.anonymous_lifetime_mode {
1909 // In create-parameter mode we error here because we don't want to support
1910 // deprecated impl elision in new features like impl elision and `async fn`,
1911 // both of which work using the `CreateParameter` mode:
1913 // impl Foo for std::cell::Ref<u32> // note lack of '_
1914 // async fn foo(_: std::cell::Ref<u32>) { ... }
1915 AnonymousLifetimeMode::CreateParameter => {
1916 let mut err = struct_span_err!(
1920 "implicit elided lifetime not allowed here"
1922 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1933 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1934 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1935 ELIDED_LIFETIMES_IN_PATHS,
1938 "hidden lifetime parameters in types are deprecated",
1939 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1952 let res = self.expect_full_res(segment.id);
1953 let id = if let Some(owner) = explicit_owner {
1954 self.lower_node_id_with_owner(segment.id, owner)
1956 self.lower_node_id(segment.id)
1959 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1960 segment.ident, segment.id, id,
1964 ident: segment.ident,
1966 res: Some(self.lower_res(res)),
1968 args: if generic_args.is_empty() {
1971 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
1976 fn lower_angle_bracketed_parameter_data(
1978 data: &AngleBracketedArgs,
1979 param_mode: ParamMode,
1980 mut itctx: ImplTraitContext<'_, 'hir>,
1981 ) -> (GenericArgsCtor<'hir>, bool) {
1982 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1983 let has_non_lt_args = args.iter().any(|arg| match arg {
1984 ast::GenericArg::Lifetime(_) => false,
1985 ast::GenericArg::Type(_) => true,
1986 ast::GenericArg::Const(_) => true,
1990 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1991 bindings: self.arena.alloc_from_iter(
1992 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
1994 parenthesized: false,
1996 !has_non_lt_args && param_mode == ParamMode::Optional,
2000 fn lower_parenthesized_parameter_data(
2002 data: &ParenthesizedArgs,
2003 ) -> (GenericArgsCtor<'hir>, bool) {
2004 // Switch to `PassThrough` mode for anonymous lifetimes; this
2005 // means that we permit things like `&Ref<T>`, where `Ref` has
2006 // a hidden lifetime parameter. This is needed for backwards
2007 // compatibility, even in contexts like an impl header where
2008 // we generally don't permit such things (see #51008).
2009 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2010 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2011 let inputs = this.arena.alloc_from_iter(
2012 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2014 let output_ty = match output {
2015 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2016 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2018 let args = smallvec![GenericArg::Type(this.ty_tup(span, inputs))];
2019 let binding = hir::TypeBinding {
2020 hir_id: this.next_id(),
2021 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2022 span: output_ty.span,
2023 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2026 GenericArgsCtor { args, bindings: arena_vec![this; binding], parenthesized: true },
2032 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2033 let mut ids = SmallVec::<[NodeId; 1]>::new();
2034 if self.sess.features_untracked().impl_trait_in_bindings {
2035 if let Some(ref ty) = l.ty {
2036 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2037 visitor.visit_ty(ty);
2040 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2041 let ty = l.ty.as_ref().map(|t| {
2044 if self.sess.features_untracked().impl_trait_in_bindings {
2045 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2047 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2051 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2054 hir_id: self.lower_node_id(l.id),
2056 pat: self.lower_pat(&l.pat),
2059 attrs: l.attrs.clone(),
2060 source: hir::LocalSource::Normal,
2066 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
2067 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2068 // as they are not explicit in HIR/Ty function signatures.
2069 // (instead, the `c_variadic` flag is set to `true`)
2070 let mut inputs = &decl.inputs[..];
2071 if decl.c_variadic() {
2072 inputs = &inputs[..inputs.len() - 1];
2074 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
2075 PatKind::Ident(_, ident, _) => ident,
2076 _ => Ident::new(kw::Invalid, param.pat.span),
2080 // Lowers a function declaration.
2082 // `decl`: the unlowered (AST) function declaration.
2083 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2084 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2085 // `make_ret_async` is also `Some`.
2086 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2087 // This guards against trait declarations and implementations where `impl Trait` is
2089 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2090 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2091 // return type `impl Trait` item.
2095 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2096 impl_trait_return_allow: bool,
2097 make_ret_async: Option<NodeId>,
2098 ) -> &'hir hir::FnDecl<'hir> {
2102 in_band_ty_params: {:?}, \
2103 impl_trait_return_allow: {}, \
2104 make_ret_async: {:?})",
2105 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2107 let lt_mode = if make_ret_async.is_some() {
2108 // In `async fn`, argument-position elided lifetimes
2109 // must be transformed into fresh generic parameters so that
2110 // they can be applied to the opaque `impl Trait` return type.
2111 AnonymousLifetimeMode::CreateParameter
2113 self.anonymous_lifetime_mode
2116 let c_variadic = decl.c_variadic();
2118 // Remember how many lifetimes were already around so that we can
2119 // only look at the lifetime parameters introduced by the arguments.
2120 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2121 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2122 // as they are not explicit in HIR/Ty function signatures.
2123 // (instead, the `c_variadic` flag is set to `true`)
2124 let mut inputs = &decl.inputs[..];
2126 inputs = &inputs[..inputs.len() - 1];
2128 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2129 if let Some((_, ibty)) = &mut in_band_ty_params {
2130 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2132 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2137 let output = if let Some(ret_id) = make_ret_async {
2138 self.lower_async_fn_ret_ty(
2140 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2145 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2146 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
2147 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
2149 _ => hir::FunctionRetTy::Return(
2150 self.lower_ty(ty, ImplTraitContext::disallowed()),
2153 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
2157 self.arena.alloc(hir::FnDecl {
2161 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2162 let is_mutable_pat = match arg.pat.kind {
2163 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2164 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2169 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2170 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2171 // Given we are only considering `ImplicitSelf` types, we needn't consider
2172 // the case where we have a mutable pattern to a reference as that would
2173 // no longer be an `ImplicitSelf`.
2174 TyKind::Rptr(_, ref mt)
2175 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2177 hir::ImplicitSelfKind::MutRef
2179 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2180 hir::ImplicitSelfKind::ImmRef
2182 _ => hir::ImplicitSelfKind::None,
2188 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2189 // combined with the following definition of `OpaqueTy`:
2191 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2193 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2194 // `output`: unlowered output type (`T` in `-> T`)
2195 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2196 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2197 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2198 fn lower_async_fn_ret_ty(
2200 output: &FunctionRetTy,
2202 opaque_ty_node_id: NodeId,
2203 ) -> hir::FunctionRetTy<'hir> {
2205 "lower_async_fn_ret_ty(\
2208 opaque_ty_node_id={:?})",
2209 output, fn_def_id, opaque_ty_node_id,
2212 let span = output.span();
2214 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2216 let opaque_ty_def_index =
2217 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2219 self.allocate_hir_id_counter(opaque_ty_node_id);
2221 // When we create the opaque type for this async fn, it is going to have
2222 // to capture all the lifetimes involved in the signature (including in the
2223 // return type). This is done by introducing lifetime parameters for:
2225 // - all the explicitly declared lifetimes from the impl and function itself;
2226 // - all the elided lifetimes in the fn arguments;
2227 // - all the elided lifetimes in the return type.
2229 // So for example in this snippet:
2232 // impl<'a> Foo<'a> {
2233 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2234 // // ^ '0 ^ '1 ^ '2
2235 // // elided lifetimes used below
2240 // we would create an opaque type like:
2243 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2246 // and we would then desugar `bar` to the equivalent of:
2249 // impl<'a> Foo<'a> {
2250 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2254 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2255 // this is because the elided lifetimes from the return type
2256 // should be figured out using the ordinary elision rules, and
2257 // this desugaring achieves that.
2259 // The variable `input_lifetimes_count` tracks the number of
2260 // lifetime parameters to the opaque type *not counting* those
2261 // lifetimes elided in the return type. This includes those
2262 // that are explicitly declared (`in_scope_lifetimes`) and
2263 // those elided lifetimes we found in the arguments (current
2264 // content of `lifetimes_to_define`). Next, we will process
2265 // the return type, which will cause `lifetimes_to_define` to
2267 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2269 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2270 // We have to be careful to get elision right here. The
2271 // idea is that we create a lifetime parameter for each
2272 // lifetime in the return type. So, given a return type
2273 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2274 // Future<Output = &'1 [ &'2 u32 ]>`.
2276 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2277 // hence the elision takes place at the fn site.
2278 let future_bound = this
2279 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2280 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2283 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2285 // Calculate all the lifetimes that should be captured
2286 // by the opaque type. This should include all in-scope
2287 // lifetime parameters, including those defined in-band.
2289 // Note: this must be done after lowering the output type,
2290 // as the output type may introduce new in-band lifetimes.
2291 let lifetime_params: Vec<(Span, ParamName)> = this
2295 .map(|name| (name.ident().span, name))
2296 .chain(this.lifetimes_to_define.iter().cloned())
2299 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2300 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2301 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2303 let generic_params =
2304 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2305 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
2308 let opaque_ty_item = hir::OpaqueTy {
2309 generics: hir::Generics {
2310 params: generic_params,
2311 where_clause: hir::WhereClause { predicates: &[], span },
2314 bounds: arena_vec![this; future_bound],
2315 impl_trait_fn: Some(fn_def_id),
2316 origin: hir::OpaqueTyOrigin::AsyncFn,
2319 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2321 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2323 (opaque_ty_id, lifetime_params)
2326 // As documented above on the variable
2327 // `input_lifetimes_count`, we need to create the lifetime
2328 // arguments to our opaque type. Continuing with our example,
2329 // we're creating the type arguments for the return type:
2332 // Bar<'a, 'b, '0, '1, '_>
2335 // For the "input" lifetime parameters, we wish to create
2336 // references to the parameters themselves, including the
2337 // "implicit" ones created from parameter types (`'a`, `'b`,
2340 // For the "output" lifetime parameters, we just want to
2342 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2344 .map(|&(span, hir_name)| {
2345 // Input lifetime like `'a` or `'1`:
2346 GenericArg::Lifetime(hir::Lifetime {
2347 hir_id: self.next_id(),
2349 name: hir::LifetimeName::Param(hir_name),
2353 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2354 // Output lifetime like `'_`.
2355 GenericArg::Lifetime(hir::Lifetime {
2356 hir_id: self.next_id(),
2358 name: hir::LifetimeName::Implicit,
2360 let generic_args = self.arena.alloc_from_iter(generic_args);
2362 // Create the `Foo<...>` reference itself. Note that the `type
2363 // Foo = impl Trait` is, internally, created as a child of the
2364 // async fn, so the *type parameters* are inherited. It's
2365 // only the lifetime parameters that we must supply.
2366 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
2367 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2368 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
2371 /// Transforms `-> T` into `Future<Output = T>`
2372 fn lower_async_fn_output_type_to_future_bound(
2374 output: &FunctionRetTy,
2377 ) -> hir::GenericBound<'hir> {
2378 // Compute the `T` in `Future<Output = T>` from the return type.
2379 let output_ty = match output {
2380 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2381 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2385 let future_params = self.arena.alloc(hir::GenericArgs {
2387 bindings: arena_vec![self; hir::TypeBinding {
2388 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2389 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2390 hir_id: self.next_id(),
2393 parenthesized: false,
2396 // ::std::future::Future<future_params>
2398 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
2400 hir::GenericBound::Trait(
2402 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2403 bound_generic_params: &[],
2406 hir::TraitBoundModifier::None,
2410 fn lower_param_bound(
2413 itctx: ImplTraitContext<'_, 'hir>,
2414 ) -> hir::GenericBound<'hir> {
2416 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2417 self.lower_poly_trait_ref(ty, itctx),
2418 self.lower_trait_bound_modifier(modifier),
2420 GenericBound::Outlives(ref lifetime) => {
2421 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2426 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2427 let span = l.ident.span;
2429 ident if ident.name == kw::StaticLifetime => {
2430 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2432 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2433 AnonymousLifetimeMode::CreateParameter => {
2434 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2435 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2438 AnonymousLifetimeMode::PassThrough => {
2439 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2442 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2445 self.maybe_collect_in_band_lifetime(ident);
2446 let param_name = ParamName::Plain(ident);
2447 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2452 fn new_named_lifetime(
2456 name: hir::LifetimeName,
2457 ) -> hir::Lifetime {
2458 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2461 fn lower_generic_params_mut<'s>(
2463 params: &'s [GenericParam],
2464 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2465 mut itctx: ImplTraitContext<'s, 'hir>,
2466 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2469 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2472 fn lower_generic_params(
2474 params: &[GenericParam],
2475 add_bounds: &NodeMap<Vec<GenericBound>>,
2476 itctx: ImplTraitContext<'_, 'hir>,
2477 ) -> &'hir [hir::GenericParam<'hir>] {
2478 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2481 fn lower_generic_param(
2483 param: &GenericParam,
2484 add_bounds: &NodeMap<Vec<GenericBound>>,
2485 mut itctx: ImplTraitContext<'_, 'hir>,
2486 ) -> hir::GenericParam<'hir> {
2487 let mut bounds: Vec<_> = self
2488 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2489 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2492 let (name, kind) = match param.kind {
2493 GenericParamKind::Lifetime => {
2494 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2495 self.is_collecting_in_band_lifetimes = false;
2498 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2499 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2501 let param_name = match lt.name {
2502 hir::LifetimeName::Param(param_name) => param_name,
2503 hir::LifetimeName::Implicit
2504 | hir::LifetimeName::Underscore
2505 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2506 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2509 "object-lifetime-default should not occur here",
2512 hir::LifetimeName::Error => ParamName::Error,
2516 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2518 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2522 GenericParamKind::Type { ref default, .. } => {
2523 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2524 if !add_bounds.is_empty() {
2525 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2526 bounds.extend(params);
2529 let kind = hir::GenericParamKind::Type {
2532 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2536 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2537 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2541 (hir::ParamName::Plain(param.ident), kind)
2543 GenericParamKind::Const { ref ty } => (
2544 hir::ParamName::Plain(param.ident),
2545 hir::GenericParamKind::Const {
2546 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2552 hir_id: self.lower_node_id(param.id),
2554 span: param.ident.span,
2555 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2556 attrs: self.lower_attrs(¶m.attrs),
2557 bounds: self.arena.alloc_from_iter(bounds),
2565 itctx: ImplTraitContext<'_, 'hir>,
2566 ) -> hir::TraitRef<'hir> {
2567 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2568 hir::QPath::Resolved(None, path) => path,
2569 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2571 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2574 fn lower_poly_trait_ref(
2577 mut itctx: ImplTraitContext<'_, 'hir>,
2578 ) -> hir::PolyTraitRef<'hir> {
2579 let bound_generic_params = self.lower_generic_params(
2580 &p.bound_generic_params,
2581 &NodeMap::default(),
2584 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2585 this.lower_trait_ref(&p.trait_ref, itctx)
2588 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2591 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2592 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2595 fn lower_param_bounds(
2597 bounds: &[GenericBound],
2598 itctx: ImplTraitContext<'_, 'hir>,
2599 ) -> hir::GenericBounds<'hir> {
2600 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2603 fn lower_param_bounds_mut<'s>(
2605 bounds: &'s [GenericBound],
2606 mut itctx: ImplTraitContext<'s, 'hir>,
2607 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2608 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2611 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2612 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2615 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2616 let mut stmts = vec![];
2617 let mut expr: Option<&'hir _> = None;
2619 for (index, stmt) in b.stmts.iter().enumerate() {
2620 if index == b.stmts.len() - 1 {
2621 if let StmtKind::Expr(ref e) = stmt.kind {
2622 expr = Some(self.lower_expr(e));
2624 stmts.extend(self.lower_stmt(stmt));
2627 stmts.extend(self.lower_stmt(stmt));
2632 hir_id: self.lower_node_id(b.id),
2633 stmts: self.arena.alloc_from_iter(stmts),
2635 rules: self.lower_block_check_mode(&b.rules),
2641 /// Lowers a block directly to an expression, presuming that it
2642 /// has no attributes and is not targeted by a `break`.
2643 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2644 let block = self.lower_block(b, false);
2645 self.expr_block(block, AttrVec::new())
2648 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2649 let node = match p.kind {
2650 PatKind::Wild => hir::PatKind::Wild,
2651 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2652 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2653 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2656 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2657 PatKind::TupleStruct(ref path, ref pats) => {
2658 let qpath = self.lower_qpath(
2662 ParamMode::Optional,
2663 ImplTraitContext::disallowed(),
2665 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2666 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2668 PatKind::Or(ref pats) => {
2669 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2671 PatKind::Path(ref qself, ref path) => {
2672 let qpath = self.lower_qpath(
2676 ParamMode::Optional,
2677 ImplTraitContext::disallowed(),
2679 hir::PatKind::Path(qpath)
2681 PatKind::Struct(ref path, ref fields, etc) => {
2682 let qpath = self.lower_qpath(
2686 ParamMode::Optional,
2687 ImplTraitContext::disallowed(),
2690 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2691 hir_id: self.next_id(),
2693 pat: self.lower_pat(&f.pat),
2694 is_shorthand: f.is_shorthand,
2697 hir::PatKind::Struct(qpath, fs, etc)
2699 PatKind::Tuple(ref pats) => {
2700 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2701 hir::PatKind::Tuple(pats, ddpos)
2703 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2704 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2705 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2706 self.lower_expr(e1),
2707 self.lower_expr(e2),
2708 self.lower_range_end(end),
2710 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2712 // If we reach here the `..` pattern is not semantically allowed.
2713 self.ban_illegal_rest_pat(p.span)
2715 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2716 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2719 self.pat_with_node_id_of(p, node)
2726 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2727 let mut elems = Vec::with_capacity(pats.len());
2728 let mut rest = None;
2730 let mut iter = pats.iter().enumerate();
2731 for (idx, pat) in iter.by_ref() {
2732 // Interpret the first `..` pattern as a sub-tuple pattern.
2733 // Note that unlike for slice patterns,
2734 // where `xs @ ..` is a legal sub-slice pattern,
2735 // it is not a legal sub-tuple pattern.
2737 rest = Some((idx, pat.span));
2740 // It was not a sub-tuple pattern so lower it normally.
2741 elems.push(self.lower_pat(pat));
2744 for (_, pat) in iter {
2745 // There was a previous sub-tuple pattern; make sure we don't allow more...
2747 // ...but there was one again, so error.
2748 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2750 elems.push(self.lower_pat(pat));
2754 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2757 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2758 /// `hir::PatKind::Slice(before, slice, after)`.
2760 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2761 /// this is interpreted as a sub-slice pattern semantically.
2762 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2763 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2764 let mut before = Vec::new();
2765 let mut after = Vec::new();
2766 let mut slice = None;
2767 let mut prev_rest_span = None;
2769 let mut iter = pats.iter();
2770 // Lower all the patterns until the first occurence of a sub-slice pattern.
2771 for pat in iter.by_ref() {
2773 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2775 prev_rest_span = Some(pat.span);
2776 slice = Some(self.pat_wild_with_node_id_of(pat));
2779 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2780 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2781 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2782 prev_rest_span = Some(sub.span);
2783 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2784 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2785 slice = Some(self.pat_with_node_id_of(pat, node));
2788 // It was not a subslice pattern so lower it normally.
2789 _ => before.push(self.lower_pat(pat)),
2793 // Lower all the patterns after the first sub-slice pattern.
2795 // There was a previous subslice pattern; make sure we don't allow more.
2796 let rest_span = match pat.kind {
2797 PatKind::Rest => Some(pat.span),
2798 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2799 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2800 after.push(self.pat_wild_with_node_id_of(pat));
2805 if let Some(rest_span) = rest_span {
2806 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2807 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2809 // Lower the pattern normally.
2810 after.push(self.lower_pat(pat));
2814 hir::PatKind::Slice(
2815 self.arena.alloc_from_iter(before),
2817 self.arena.alloc_from_iter(after),
2824 binding_mode: &BindingMode,
2826 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2827 ) -> hir::PatKind<'hir> {
2828 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2829 // `None` can occur in body-less function signatures
2830 res @ None | res @ Some(Res::Local(_)) => {
2831 let canonical_id = match res {
2832 Some(Res::Local(id)) => id,
2836 hir::PatKind::Binding(
2837 self.lower_binding_mode(binding_mode),
2838 self.lower_node_id(canonical_id),
2843 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2845 self.arena.alloc(hir::Path {
2847 res: self.lower_res(res),
2848 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2854 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2855 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2858 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2859 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2860 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2863 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2864 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2866 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2867 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2868 .span_label(prev_sp, "previously used here")
2872 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2873 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2875 .struct_span_err(sp, "`..` patterns are not allowed here")
2876 .note("only allowed in tuple, tuple struct, and slice patterns")
2879 // We're not in a list context so `..` can be reasonably treated
2880 // as `_` because it should always be valid and roughly matches the
2881 // intent of `..` (notice that the rest of a single slot is that slot).
2885 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2887 RangeEnd::Included(_) => hir::RangeEnd::Included,
2888 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2892 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2893 self.with_new_scopes(|this| hir::AnonConst {
2894 hir_id: this.lower_node_id(c.id),
2895 body: this.lower_const_body(c.value.span, Some(&c.value)),
2899 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2900 let kind = match s.kind {
2901 StmtKind::Local(ref l) => {
2902 let (l, item_ids) = self.lower_local(l);
2903 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2906 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2907 self.stmt(s.span, hir::StmtKind::Item(item_id))
2912 hir_id: self.lower_node_id(s.id),
2913 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2919 StmtKind::Item(ref it) => {
2920 // Can only use the ID once.
2921 let mut id = Some(s.id);
2928 .map(|id| self.lower_node_id(id))
2929 .unwrap_or_else(|| self.next_id());
2931 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2935 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2936 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2937 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2939 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2942 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2944 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2945 BlockCheckMode::Unsafe(u) => {
2946 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2951 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2953 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2954 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2955 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2956 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2960 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2962 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2963 UserProvided => hir::UnsafeSource::UserProvided,
2967 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2969 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2970 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2974 // Helper methods for building HIR.
2976 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2977 hir::Stmt { span, kind, hir_id: self.next_id() }
2980 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2981 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2988 init: Option<&'hir hir::Expr<'hir>>,
2989 pat: &'hir hir::Pat<'hir>,
2990 source: hir::LocalSource,
2991 ) -> hir::Stmt<'hir> {
2992 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2993 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2996 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2997 self.block_all(expr.span, &[], Some(expr))
3003 stmts: &'hir [hir::Stmt<'hir>],
3004 expr: Option<&'hir hir::Expr<'hir>>,
3005 ) -> &'hir hir::Block<'hir> {
3006 let blk = hir::Block {
3009 hir_id: self.next_id(),
3010 rules: hir::BlockCheckMode::DefaultBlock,
3012 targeted_by_break: false,
3014 self.arena.alloc(blk)
3017 /// Constructs a `true` or `false` literal pattern.
3018 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3019 let expr = self.expr_bool(span, val);
3020 self.pat(span, hir::PatKind::Lit(expr))
3023 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3024 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3027 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3028 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3031 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3032 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3035 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3036 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3042 components: &[Symbol],
3043 subpats: &'hir [&'hir hir::Pat<'hir>],
3044 ) -> &'hir hir::Pat<'hir> {
3045 let path = self.std_path(span, components, None, true);
3046 let qpath = hir::QPath::Resolved(None, path);
3047 let pt = if subpats.is_empty() {
3048 hir::PatKind::Path(qpath)
3050 hir::PatKind::TupleStruct(qpath, subpats, None)
3055 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3056 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3059 fn pat_ident_binding_mode(
3063 bm: hir::BindingAnnotation,
3064 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3065 let hir_id = self.next_id();
3068 self.arena.alloc(hir::Pat {
3070 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3077 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3078 self.pat(span, hir::PatKind::Wild)
3081 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3082 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3085 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3086 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3087 /// The path is also resolved according to `is_value`.
3091 components: &[Symbol],
3092 params: Option<&'hir hir::GenericArgs<'hir>>,
3094 ) -> &'hir hir::Path<'hir> {
3095 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3096 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3098 let mut segments: Vec<_> = path
3102 let res = self.expect_full_res(segment.id);
3104 ident: segment.ident,
3105 hir_id: Some(self.lower_node_id(segment.id)),
3106 res: Some(self.lower_res(res)),
3112 segments.last_mut().unwrap().args = params;
3114 self.arena.alloc(hir::Path {
3116 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3117 segments: self.arena.alloc_from_iter(segments),
3123 mut hir_id: hir::HirId,
3125 qpath: hir::QPath<'hir>,
3126 ) -> hir::Ty<'hir> {
3127 let kind = match qpath {
3128 hir::QPath::Resolved(None, path) => {
3129 // Turn trait object paths into `TyKind::TraitObject` instead.
3131 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3132 let principal = hir::PolyTraitRef {
3133 bound_generic_params: &[],
3134 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3138 // The original ID is taken by the `PolyTraitRef`,
3139 // so the `Ty` itself needs a different one.
3140 hir_id = self.next_id();
3141 hir::TyKind::TraitObject(
3142 arena_vec![self; principal],
3143 self.elided_dyn_bound(span),
3146 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3149 _ => hir::TyKind::Path(qpath),
3152 hir::Ty { hir_id, kind, span }
3155 /// Invoked to create the lifetime argument for a type `&T`
3156 /// with no explicit lifetime.
3157 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3158 match self.anonymous_lifetime_mode {
3159 // Intercept when we are in an impl header or async fn and introduce an in-band
3161 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3163 AnonymousLifetimeMode::CreateParameter => {
3164 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3166 hir_id: self.next_id(),
3168 name: hir::LifetimeName::Param(fresh_name),
3172 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3174 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3178 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3179 /// return a "error lifetime".
3180 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3181 let (id, msg, label) = match id {
3182 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3185 self.resolver.next_node_id(),
3186 "`&` without an explicit lifetime name cannot be used here",
3187 "explicit lifetime name needed here",
3191 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3192 err.span_label(span, label);
3195 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3198 /// Invoked to create the lifetime argument(s) for a path like
3199 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3200 /// sorts of cases are deprecated. This may therefore report a warning or an
3201 /// error, depending on the mode.
3202 fn elided_path_lifetimes<'s>(
3206 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
3207 (0..count).map(move |_| self.elided_path_lifetime(span))
3210 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3211 match self.anonymous_lifetime_mode {
3212 AnonymousLifetimeMode::CreateParameter => {
3213 // We should have emitted E0726 when processing this path above
3215 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3216 let id = self.resolver.next_node_id();
3217 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3219 // `PassThrough` is the normal case.
3220 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3221 // is unsuitable here, as these can occur from missing lifetime parameters in a
3222 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3223 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3224 // later, at which point a suitable error will be emitted.
3225 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3226 self.new_implicit_lifetime(span)
3231 /// Invoked to create the lifetime argument(s) for an elided trait object
3232 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3233 /// when the bound is written, even if it is written with `'_` like in
3234 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3235 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3236 match self.anonymous_lifetime_mode {
3237 // NB. We intentionally ignore the create-parameter mode here.
3238 // and instead "pass through" to resolve-lifetimes, which will apply
3239 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3240 // do not act like other elided lifetimes. In other words, given this:
3242 // impl Foo for Box<dyn Debug>
3244 // we do not introduce a fresh `'_` to serve as the bound, but instead
3245 // ultimately translate to the equivalent of:
3247 // impl Foo for Box<dyn Debug + 'static>
3249 // `resolve_lifetime` has the code to make that happen.
3250 AnonymousLifetimeMode::CreateParameter => {}
3252 AnonymousLifetimeMode::ReportError => {
3253 // ReportError applies to explicit use of `'_`.
3256 // This is the normal case.
3257 AnonymousLifetimeMode::PassThrough => {}
3260 let r = hir::Lifetime {
3261 hir_id: self.next_id(),
3263 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3265 debug!("elided_dyn_bound: r={:?}", r);
3269 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3270 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3273 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3274 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3275 // call site which do not have a macro backtrace. See #61963.
3276 let is_macro_callsite = self
3279 .span_to_snippet(span)
3280 .map(|snippet| snippet.starts_with("#["))
3282 if !is_macro_callsite {
3283 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3284 builtin::BARE_TRAIT_OBJECTS,
3287 "trait objects without an explicit `dyn` are deprecated",
3288 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3294 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
3295 // Sorting by span ensures that we get things in order within a
3296 // file, and also puts the files in a sensible order.
3297 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3298 body_ids.sort_by_key(|b| bodies[b].value.span);
3302 /// Helper struct for delayed construction of GenericArgs.
3303 struct GenericArgsCtor<'hir> {
3304 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
3305 bindings: &'hir [hir::TypeBinding<'hir>],
3306 parenthesized: bool,
3309 impl<'hir> GenericArgsCtor<'hir> {
3310 fn is_empty(&self) -> bool {
3311 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
3314 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
3316 args: arena.alloc_from_iter(self.args),
3317 bindings: self.bindings,
3318 parenthesized: self.parenthesized,