1 //! Lowers the AST to the HIR.
3 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
4 //! much like a fold. Where lowering involves a bit more work things get more
5 //! interesting and there are some invariants you should know about. These mostly
6 //! concern spans and IDs.
8 //! Spans are assigned to AST nodes during parsing and then are modified during
9 //! expansion to indicate the origin of a node and the process it went through
10 //! being expanded. IDs are assigned to AST nodes just before lowering.
12 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
13 //! expansion we do not preserve the process of lowering in the spans, so spans
14 //! should not be modified here. When creating a new node (as opposed to
15 //! 'folding' an existing one), then you create a new ID using `next_id()`.
17 //! You must ensure that IDs are unique. That means that you should only use the
18 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
19 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
20 //! If you do, you must then set the new node's ID to a fresh one.
22 //! Spans are used for error messages and for tools to map semantics back to
23 //! source code. It is therefore not as important with spans as IDs to be strict
24 //! about use (you can't break the compiler by screwing up a span). Obviously, a
25 //! HIR node can only have a single span. But multiple nodes can have the same
26 //! span and spans don't need to be kept in order, etc. Where code is preserved
27 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
28 //! new it is probably best to give a span for the whole AST node being lowered.
29 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
30 //! get confused if the spans from leaf AST nodes occur in multiple places
31 //! in the HIR, especially for multiple identifiers.
33 #![feature(array_value_iter)]
34 #![feature(crate_visibility_modifier)]
36 use rustc::arena::Arena;
37 use rustc::dep_graph::DepGraph;
38 use rustc::hir::map::definitions::{DefKey, DefPathData, Definitions};
39 use rustc::hir::map::Map;
41 use rustc::lint::builtin;
42 use rustc::middle::cstore::CrateStore;
43 use rustc::util::captures::Captures;
44 use rustc::{bug, span_bug};
45 use rustc_data_structures::fx::FxHashSet;
46 use rustc_data_structures::sync::Lrc;
47 use rustc_error_codes::*;
48 use rustc_errors::struct_span_err;
50 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
51 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
52 use rustc_hir::intravisit;
53 use rustc_hir::{ConstArg, GenericArg, ParamName};
54 use rustc_index::vec::IndexVec;
55 use rustc_session::config::nightly_options;
56 use rustc_session::node_id::NodeMap;
57 use rustc_session::Session;
58 use rustc_span::hygiene::ExpnId;
59 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind};
60 use rustc_span::symbol::{kw, sym, Symbol};
65 use syntax::print::pprust;
66 use syntax::sess::ParseSess;
67 use syntax::token::{self, Nonterminal, Token};
68 use syntax::tokenstream::{TokenStream, TokenTree};
69 use syntax::visit::{self, Visitor};
70 use syntax::walk_list;
72 use log::{debug, trace};
73 use smallvec::{smallvec, SmallVec};
74 use std::collections::BTreeMap;
77 macro_rules! arena_vec {
78 ($this:expr; $($x:expr),*) => ({
80 $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<T>(
437 owner: Option<NodeId>,
438 f: impl FnOnce(&mut Self) -> T,
440 let old = mem::replace(&mut self.hir_id_owner, owner);
442 self.hir_id_owner = old;
447 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
448 fn visit_pat(&mut self, p: &'tcx Pat) {
449 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
450 // Doesn't generate a HIR node
451 } else if let Some(owner) = self.hir_id_owner {
452 self.lctx.lower_node_id_with_owner(p.id, owner);
455 visit::walk_pat(self, p)
458 fn visit_item(&mut self, item: &'tcx Item) {
459 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
462 ItemKind::Struct(_, ref generics)
463 | ItemKind::Union(_, ref generics)
464 | ItemKind::Enum(_, ref generics)
465 | ItemKind::TyAlias(_, ref generics)
466 | ItemKind::Trait(_, _, ref generics, ..) => {
467 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
471 .filter(|param| match param.kind {
472 ast::GenericParamKind::Lifetime { .. } => true,
476 self.lctx.type_def_lifetime_params.insert(def_id, count);
478 ItemKind::Use(ref use_tree) => {
479 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
484 self.with_hir_id_owner(Some(item.id), |this| {
485 visit::walk_item(this, item);
489 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
490 self.lctx.allocate_hir_id_counter(item.id);
493 AssocItemKind::Fn(_, None) => {
494 // Ignore patterns in trait methods without bodies
495 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
497 _ => self.with_hir_id_owner(Some(item.id), |this| {
498 visit::walk_trait_item(this, item);
503 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
504 self.lctx.allocate_hir_id_counter(item.id);
505 self.with_hir_id_owner(Some(item.id), |this| {
506 visit::walk_impl_item(this, item);
510 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
511 // Ignore patterns in foreign items
512 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
515 fn visit_ty(&mut self, t: &'tcx Ty) {
517 // Mirrors the case in visit::walk_ty
518 TyKind::BareFn(ref f) => {
519 walk_list!(self, visit_generic_param, &f.generic_params);
520 // Mirrors visit::walk_fn_decl
521 for parameter in &f.decl.inputs {
522 // We don't lower the ids of argument patterns
523 self.with_hir_id_owner(None, |this| {
524 this.visit_pat(¶meter.pat);
526 self.visit_ty(¶meter.ty)
528 self.visit_fn_ret_ty(&f.decl.output)
530 _ => visit::walk_ty(self, t),
535 self.lower_node_id(CRATE_NODE_ID);
536 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
538 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
539 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
541 let module = self.lower_mod(&c.module);
542 let attrs = self.lower_attrs(&c.attrs);
543 let body_ids = body_ids(&self.bodies);
545 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
551 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
552 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
554 trait_items: self.trait_items,
555 impl_items: self.impl_items,
558 trait_impls: self.trait_impls,
559 modules: self.modules,
563 fn insert_item(&mut self, item: hir::Item<'hir>) {
564 let id = item.hir_id;
565 // FIXME: Use `debug_asset-rt`.
566 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
567 self.items.insert(id, item);
568 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
571 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
572 // Set up the counter if needed.
573 self.item_local_id_counters.entry(owner).or_insert(0);
574 // Always allocate the first `HirId` for the owner itself.
575 let lowered = self.lower_node_id_with_owner(owner, owner);
576 debug_assert_eq!(lowered.local_id.as_u32(), 0);
580 fn lower_node_id_generic(
583 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
585 if ast_node_id == DUMMY_NODE_ID {
586 return hir::DUMMY_HIR_ID;
589 let min_size = ast_node_id.as_usize() + 1;
591 if min_size > self.node_id_to_hir_id.len() {
592 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
595 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
597 if existing_hir_id == hir::DUMMY_HIR_ID {
598 // Generate a new `HirId`.
599 let hir_id = alloc_hir_id(self);
600 self.node_id_to_hir_id[ast_node_id] = hir_id;
608 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
610 .item_local_id_counters
611 .insert(owner, HIR_ID_COUNTER_LOCKED)
612 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
613 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
614 self.current_hir_id_owner.push((def_index, counter));
616 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
618 debug_assert!(def_index == new_def_index);
619 debug_assert!(new_counter >= counter);
621 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
622 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
626 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
627 /// the `LoweringContext`'s `NodeId => HirId` map.
628 /// Take care not to call this method if the resulting `HirId` is then not
629 /// actually used in the HIR, as that would trigger an assertion in the
630 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
631 /// properly. Calling the method twice with the same `NodeId` is fine though.
632 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
633 self.lower_node_id_generic(ast_node_id, |this| {
634 let &mut (def_index, ref mut local_id_counter) =
635 this.current_hir_id_owner.last_mut().unwrap();
636 let local_id = *local_id_counter;
637 *local_id_counter += 1;
638 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
642 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
643 self.lower_node_id_generic(ast_node_id, |this| {
644 let local_id_counter = this
645 .item_local_id_counters
647 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
648 let local_id = *local_id_counter;
650 // We want to be sure not to modify the counter in the map while it
651 // is also on the stack. Otherwise we'll get lost updates when writing
652 // back from the stack to the map.
653 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
655 *local_id_counter += 1;
656 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
657 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
658 that do not belong to the current owner",
661 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
665 fn next_id(&mut self) -> hir::HirId {
666 let node_id = self.resolver.next_node_id();
667 self.lower_node_id(node_id)
670 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
672 self.lower_node_id_generic(id, |_| {
673 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
678 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
679 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
680 if pr.unresolved_segments() != 0 {
681 bug!("path not fully resolved: {:?}", pr);
687 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
688 self.resolver.get_import_res(id).present_items()
691 fn diagnostic(&self) -> &rustc_errors::Handler {
692 self.sess.diagnostic()
695 /// Reuses the span but adds information like the kind of the desugaring and features that are
696 /// allowed inside this span.
697 fn mark_span_with_reason(
699 reason: DesugaringKind,
701 allow_internal_unstable: Option<Lrc<[Symbol]>>,
703 span.fresh_expansion(ExpnData {
704 allow_internal_unstable,
705 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
709 fn with_anonymous_lifetime_mode<R>(
711 anonymous_lifetime_mode: AnonymousLifetimeMode,
712 op: impl FnOnce(&mut Self) -> R,
715 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
716 anonymous_lifetime_mode,
718 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
719 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
720 let result = op(self);
721 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
723 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
724 old_anonymous_lifetime_mode
729 /// Creates a new `hir::GenericParam` for every new lifetime and
730 /// type parameter encountered while evaluating `f`. Definitions
731 /// are created with the parent provided. If no `parent_id` is
732 /// provided, no definitions will be returned.
734 /// Presuming that in-band lifetimes are enabled, then
735 /// `self.anonymous_lifetime_mode` will be updated to match the
736 /// parameter while `f` is running (and restored afterwards).
737 fn collect_in_band_defs<T>(
740 anonymous_lifetime_mode: AnonymousLifetimeMode,
741 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
742 ) -> (Vec<hir::GenericParam<'hir>>, T) {
743 assert!(!self.is_collecting_in_band_lifetimes);
744 assert!(self.lifetimes_to_define.is_empty());
745 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
747 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
748 self.is_collecting_in_band_lifetimes = true;
750 let (in_band_ty_params, res) = f(self);
752 self.is_collecting_in_band_lifetimes = false;
753 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
755 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
757 let params = lifetimes_to_define
759 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
760 .chain(in_band_ty_params.into_iter())
766 /// Converts a lifetime into a new generic parameter.
767 fn lifetime_to_generic_param(
771 parent_index: DefIndex,
772 ) -> hir::GenericParam<'hir> {
773 let node_id = self.resolver.next_node_id();
775 // Get the name we'll use to make the def-path. Note
776 // that collisions are ok here and this shouldn't
777 // really show up for end-user.
778 let (str_name, kind) = match hir_name {
779 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
780 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
781 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
784 // Add a definition for the in-band lifetime def.
785 self.resolver.definitions().create_def_with_parent(
788 DefPathData::LifetimeNs(str_name),
794 hir_id: self.lower_node_id(node_id),
799 pure_wrt_drop: false,
800 kind: hir::GenericParamKind::Lifetime { kind },
804 /// When there is a reference to some lifetime `'a`, and in-band
805 /// lifetimes are enabled, then we want to push that lifetime into
806 /// the vector of names to define later. In that case, it will get
807 /// added to the appropriate generics.
808 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
809 if !self.is_collecting_in_band_lifetimes {
813 if !self.sess.features_untracked().in_band_lifetimes {
817 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
821 let hir_name = ParamName::Plain(ident);
823 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
828 self.lifetimes_to_define.push((ident.span, hir_name));
831 /// When we have either an elided or `'_` lifetime in an impl
832 /// header, we convert it to an in-band lifetime.
833 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
834 assert!(self.is_collecting_in_band_lifetimes);
835 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
836 let hir_name = ParamName::Fresh(index);
837 self.lifetimes_to_define.push((span, hir_name));
841 // Evaluates `f` with the lifetimes in `params` in-scope.
842 // This is used to track which lifetimes have already been defined, and
843 // which are new in-band lifetimes that need to have a definition created
845 fn with_in_scope_lifetime_defs<T>(
847 params: &[GenericParam],
848 f: impl FnOnce(&mut Self) -> T,
850 let old_len = self.in_scope_lifetimes.len();
851 let lt_def_names = params.iter().filter_map(|param| match param.kind {
852 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
855 self.in_scope_lifetimes.extend(lt_def_names);
859 self.in_scope_lifetimes.truncate(old_len);
863 /// Appends in-band lifetime defs and argument-position `impl
864 /// Trait` defs to the existing set of generics.
866 /// Presuming that in-band lifetimes are enabled, then
867 /// `self.anonymous_lifetime_mode` will be updated to match the
868 /// parameter while `f` is running (and restored afterwards).
869 fn add_in_band_defs<T>(
873 anonymous_lifetime_mode: AnonymousLifetimeMode,
874 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
875 ) -> (hir::Generics<'hir>, T) {
876 let (in_band_defs, (mut lowered_generics, res)) =
877 self.with_in_scope_lifetime_defs(&generics.params, |this| {
878 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
879 let mut params = Vec::new();
880 // Note: it is necessary to lower generics *before* calling `f`.
881 // When lowering `async fn`, there's a final step when lowering
882 // the return type that assumes that all in-scope lifetimes have
883 // already been added to either `in_scope_lifetimes` or
884 // `lifetimes_to_define`. If we swapped the order of these two,
885 // in-band-lifetimes introduced by generics or where-clauses
886 // wouldn't have been added yet.
888 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
889 let res = f(this, &mut params);
890 (params, (generics, res))
894 let mut lowered_params: Vec<_> =
895 lowered_generics.params.into_iter().chain(in_band_defs).collect();
897 // FIXME(const_generics): the compiler doesn't always cope with
898 // unsorted generic parameters at the moment, so we make sure
899 // that they're ordered correctly here for now. (When we chain
900 // the `in_band_defs`, we might make the order unsorted.)
901 lowered_params.sort_by_key(|param| match param.kind {
902 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
903 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
904 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
907 lowered_generics.params = lowered_params.into();
909 let lowered_generics = lowered_generics.into_generics(self.arena);
910 (lowered_generics, res)
913 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
914 let was_in_dyn_type = self.is_in_dyn_type;
915 self.is_in_dyn_type = in_scope;
917 let result = f(self);
919 self.is_in_dyn_type = was_in_dyn_type;
924 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
925 let was_in_loop_condition = self.is_in_loop_condition;
926 self.is_in_loop_condition = false;
928 let catch_scopes = mem::take(&mut self.catch_scopes);
929 let loop_scopes = mem::take(&mut self.loop_scopes);
931 self.catch_scopes = catch_scopes;
932 self.loop_scopes = loop_scopes;
934 self.is_in_loop_condition = was_in_loop_condition;
939 fn def_key(&mut self, id: DefId) -> DefKey {
941 self.resolver.definitions().def_key(id.index)
943 self.resolver.cstore().def_key(id)
947 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
948 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
951 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
952 // Note that we explicitly do not walk the path. Since we don't really
953 // lower attributes (we use the AST version) there is nowhere to keep
954 // the `HirId`s. We don't actually need HIR version of attributes anyway.
955 let kind = match attr.kind {
956 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
957 path: item.path.clone(),
958 args: self.lower_mac_args(&item.args),
960 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
963 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
966 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
968 MacArgs::Empty => MacArgs::Empty,
969 MacArgs::Delimited(dspan, delim, ref tokens) => {
970 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
972 MacArgs::Eq(eq_span, ref tokens) => {
973 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
978 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
979 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
982 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
984 TokenTree::Token(token) => self.lower_token(token),
985 TokenTree::Delimited(span, delim, tts) => {
986 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
991 fn lower_token(&mut self, token: Token) -> TokenStream {
993 token::Interpolated(nt) => {
994 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
995 self.lower_token_stream(tts)
997 _ => TokenTree::Token(token).into(),
1001 /// Given an associated type constraint like one of these:
1004 /// T: Iterator<Item: Debug>
1006 /// T: Iterator<Item = Debug>
1010 /// returns a `hir::TypeBinding` representing `Item`.
1011 fn lower_assoc_ty_constraint(
1013 constraint: &AssocTyConstraint,
1014 itctx: ImplTraitContext<'_, 'hir>,
1015 ) -> hir::TypeBinding<'hir> {
1016 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1018 let kind = match constraint.kind {
1019 AssocTyConstraintKind::Equality { ref ty } => {
1020 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1022 AssocTyConstraintKind::Bound { ref bounds } => {
1023 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1024 let (desugar_to_impl_trait, itctx) = match itctx {
1025 // We are in the return position:
1027 // fn foo() -> impl Iterator<Item: Debug>
1031 // fn foo() -> impl Iterator<Item = impl Debug>
1032 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1034 // We are in the argument position, but within a dyn type:
1036 // fn foo(x: dyn Iterator<Item: Debug>)
1040 // fn foo(x: dyn Iterator<Item = impl Debug>)
1041 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1043 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1044 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1045 // "impl trait context" to permit `impl Debug` in this position (it desugars
1046 // then to an opaque type).
1048 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1049 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1050 (true, ImplTraitContext::OpaqueTy(None))
1053 // We are in the parameter position, but not within a dyn type:
1055 // fn foo(x: impl Iterator<Item: Debug>)
1057 // so we leave it as is and this gets expanded in astconv to a bound like
1058 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1060 _ => (false, itctx),
1063 if desugar_to_impl_trait {
1064 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1065 // constructing the HIR for `impl bounds...` and then lowering that.
1067 let impl_trait_node_id = self.resolver.next_node_id();
1068 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1069 self.resolver.definitions().create_def_with_parent(
1072 DefPathData::ImplTrait,
1077 self.with_dyn_type_scope(false, |this| {
1078 let node_id = this.resolver.next_node_id();
1079 let ty = this.lower_ty(
1082 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1083 span: constraint.span,
1088 hir::TypeBindingKind::Equality { ty }
1091 // Desugar `AssocTy: Bounds` into a type binding where the
1092 // later desugars into a trait predicate.
1093 let bounds = self.lower_param_bounds(bounds, itctx);
1095 hir::TypeBindingKind::Constraint { bounds }
1101 hir_id: self.lower_node_id(constraint.id),
1102 ident: constraint.ident,
1104 span: constraint.span,
1108 fn lower_generic_arg(
1110 arg: &ast::GenericArg,
1111 itctx: ImplTraitContext<'_, 'hir>,
1112 ) -> hir::GenericArg<'hir> {
1114 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1115 ast::GenericArg::Type(ty) => {
1116 // We parse const arguments as path types as we cannot distiguish them durring
1117 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1118 // type and value namespaces. If we resolved the path in the value namespace, we
1119 // transform it into a generic const argument.
1120 if let TyKind::Path(ref qself, ref path) = ty.kind {
1121 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1122 let res = partial_res.base_res();
1123 if !res.matches_ns(Namespace::TypeNS) {
1125 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1129 // Construct a AnonConst where the expr is the "ty"'s path.
1131 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1132 let node_id = self.resolver.next_node_id();
1134 // Add a definition for the in-band const def.
1135 self.resolver.definitions().create_def_with_parent(
1138 DefPathData::AnonConst,
1143 let path_expr = Expr {
1145 kind: ExprKind::Path(qself.clone(), path.clone()),
1147 attrs: AttrVec::new(),
1150 let ct = self.with_new_scopes(|this| hir::AnonConst {
1151 hir_id: this.lower_node_id(node_id),
1152 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1154 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1158 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1160 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1161 value: self.lower_anon_const(&ct),
1162 span: ct.value.span,
1167 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1168 self.arena.alloc(self.lower_ty_direct(t, itctx))
1174 qself: &Option<QSelf>,
1176 param_mode: ParamMode,
1177 itctx: ImplTraitContext<'_, 'hir>,
1178 ) -> hir::Ty<'hir> {
1179 let id = self.lower_node_id(t.id);
1180 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1181 let ty = self.ty_path(id, t.span, qpath);
1182 if let hir::TyKind::TraitObject(..) = ty.kind {
1183 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1188 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1189 hir::Ty { hir_id: self.next_id(), kind, span }
1192 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1193 self.ty(span, hir::TyKind::Tup(tys))
1196 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1197 let kind = match t.kind {
1198 TyKind::Infer => hir::TyKind::Infer,
1199 TyKind::Err => hir::TyKind::Err,
1200 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1201 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1202 TyKind::Rptr(ref region, ref mt) => {
1203 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1204 let lifetime = match *region {
1205 Some(ref lt) => self.lower_lifetime(lt),
1206 None => self.elided_ref_lifetime(span),
1208 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1210 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1211 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1212 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1213 generic_params: this.lower_generic_params(
1215 &NodeMap::default(),
1216 ImplTraitContext::disallowed(),
1218 unsafety: f.unsafety,
1219 abi: this.lower_extern(f.ext),
1220 decl: this.lower_fn_decl(&f.decl, None, false, None),
1221 param_names: this.lower_fn_params_to_names(&f.decl),
1225 TyKind::Never => hir::TyKind::Never,
1226 TyKind::Tup(ref tys) => {
1227 hir::TyKind::Tup(self.arena.alloc_from_iter(
1228 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1231 TyKind::Paren(ref ty) => {
1232 return self.lower_ty_direct(ty, itctx);
1234 TyKind::Path(ref qself, ref path) => {
1235 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1237 TyKind::ImplicitSelf => {
1238 let res = self.expect_full_res(t.id);
1239 let res = self.lower_res(res);
1240 hir::TyKind::Path(hir::QPath::Resolved(
1242 self.arena.alloc(hir::Path {
1244 segments: arena_vec![self; hir::PathSegment::from_ident(
1245 Ident::with_dummy_span(kw::SelfUpper)
1251 TyKind::Array(ref ty, ref length) => {
1252 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1254 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1255 TyKind::TraitObject(ref bounds, kind) => {
1256 let mut lifetime_bound = None;
1257 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1259 this.arena.alloc_from_iter(bounds.iter().filter_map(
1260 |bound| match *bound {
1261 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1262 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1264 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1265 GenericBound::Outlives(ref lifetime) => {
1266 if lifetime_bound.is_none() {
1267 lifetime_bound = Some(this.lower_lifetime(lifetime));
1273 let lifetime_bound =
1274 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1275 (bounds, lifetime_bound)
1277 if kind != TraitObjectSyntax::Dyn {
1278 self.maybe_lint_bare_trait(t.span, t.id, false);
1280 hir::TyKind::TraitObject(bounds, lifetime_bound)
1282 TyKind::ImplTrait(def_node_id, ref bounds) => {
1285 ImplTraitContext::OpaqueTy(fn_def_id) => {
1286 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1287 this.lower_param_bounds(bounds, itctx)
1290 ImplTraitContext::Universal(in_band_ty_params) => {
1291 // Add a definition for the in-band `Param`.
1293 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1295 let hir_bounds = self.lower_param_bounds(
1297 ImplTraitContext::Universal(in_band_ty_params),
1299 // Set the name to `impl Bound1 + Bound2`.
1300 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1301 in_band_ty_params.push(hir::GenericParam {
1302 hir_id: self.lower_node_id(def_node_id),
1303 name: ParamName::Plain(ident),
1304 pure_wrt_drop: false,
1308 kind: hir::GenericParamKind::Type {
1310 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1314 hir::TyKind::Path(hir::QPath::Resolved(
1316 self.arena.alloc(hir::Path {
1318 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1319 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1323 ImplTraitContext::Disallowed(pos) => {
1324 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1325 "bindings or function and inherent method return types"
1327 "function and inherent method return types"
1329 let mut err = struct_span_err!(
1333 "`impl Trait` not allowed outside of {}",
1336 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1339 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1340 attributes to enable",
1348 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1349 TyKind::CVarArgs => {
1350 self.sess.delay_span_bug(
1352 "`TyKind::CVarArgs` should have been handled elsewhere",
1358 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1361 fn lower_opaque_impl_trait(
1364 fn_def_id: Option<DefId>,
1365 opaque_ty_node_id: NodeId,
1366 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1367 ) -> hir::TyKind<'hir> {
1369 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1370 fn_def_id, opaque_ty_node_id, span,
1373 // Make sure we know that some funky desugaring has been going on here.
1374 // This is a first: there is code in other places like for loop
1375 // desugaring that explicitly states that we don't want to track that.
1376 // Not tracking it makes lints in rustc and clippy very fragile, as
1377 // frequently opened issues show.
1378 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1380 let opaque_ty_def_index =
1381 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1383 self.allocate_hir_id_counter(opaque_ty_node_id);
1385 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1387 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1389 opaque_ty_def_index,
1393 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1395 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1397 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1398 let opaque_ty_item = hir::OpaqueTy {
1399 generics: hir::Generics {
1400 params: lifetime_defs,
1401 where_clause: hir::WhereClause { predicates: &[], span },
1405 impl_trait_fn: fn_def_id,
1406 origin: hir::OpaqueTyOrigin::FnReturn,
1409 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1411 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1413 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1414 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1418 /// Registers a new opaque type with the proper `NodeId`s and
1419 /// returns the lowered node-ID for the opaque type.
1420 fn generate_opaque_type(
1422 opaque_ty_node_id: NodeId,
1423 opaque_ty_item: hir::OpaqueTy<'hir>,
1425 opaque_ty_span: Span,
1427 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1428 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1429 // Generate an `type Foo = impl Trait;` declaration.
1430 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1431 let opaque_ty_item = hir::Item {
1432 hir_id: opaque_ty_id,
1433 ident: Ident::invalid(),
1434 attrs: Default::default(),
1435 kind: opaque_ty_item_kind,
1436 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1437 span: opaque_ty_span,
1440 // Insert the item into the global item list. This usually happens
1441 // automatically for all AST items. But this opaque type item
1442 // does not actually exist in the AST.
1443 self.insert_item(opaque_ty_item);
1447 fn lifetimes_from_impl_trait_bounds(
1449 opaque_ty_id: NodeId,
1450 parent_index: DefIndex,
1451 bounds: hir::GenericBounds<'hir>,
1452 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1454 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1455 parent_index={:?}, \
1457 opaque_ty_id, parent_index, bounds,
1460 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1461 // appear in the bounds, excluding lifetimes that are created within the bounds.
1462 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1463 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1464 context: &'r mut LoweringContext<'a, 'hir>,
1466 opaque_ty_id: NodeId,
1467 collect_elided_lifetimes: bool,
1468 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1469 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1470 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1471 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1474 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1477 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1478 intravisit::NestedVisitorMap::None
1481 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1482 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1483 if parameters.parenthesized {
1484 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1485 self.collect_elided_lifetimes = false;
1486 intravisit::walk_generic_args(self, span, parameters);
1487 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1489 intravisit::walk_generic_args(self, span, parameters);
1493 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1494 // Don't collect elided lifetimes used inside of `fn()` syntax.
1495 if let hir::TyKind::BareFn(_) = t.kind {
1496 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1497 self.collect_elided_lifetimes = false;
1499 // Record the "stack height" of `for<'a>` lifetime bindings
1500 // to be able to later fully undo their introduction.
1501 let old_len = self.currently_bound_lifetimes.len();
1502 intravisit::walk_ty(self, t);
1503 self.currently_bound_lifetimes.truncate(old_len);
1505 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1507 intravisit::walk_ty(self, t)
1511 fn visit_poly_trait_ref(
1513 trait_ref: &'v hir::PolyTraitRef<'v>,
1514 modifier: hir::TraitBoundModifier,
1516 // Record the "stack height" of `for<'a>` lifetime bindings
1517 // to be able to later fully undo their introduction.
1518 let old_len = self.currently_bound_lifetimes.len();
1519 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1520 self.currently_bound_lifetimes.truncate(old_len);
1523 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1524 // Record the introduction of 'a in `for<'a> ...`.
1525 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1526 // Introduce lifetimes one at a time so that we can handle
1527 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1528 let lt_name = hir::LifetimeName::Param(param.name);
1529 self.currently_bound_lifetimes.push(lt_name);
1532 intravisit::walk_generic_param(self, param);
1535 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1536 let name = match lifetime.name {
1537 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1538 if self.collect_elided_lifetimes {
1539 // Use `'_` for both implicit and underscore lifetimes in
1540 // `type Foo<'_> = impl SomeTrait<'_>;`.
1541 hir::LifetimeName::Underscore
1546 hir::LifetimeName::Param(_) => lifetime.name,
1548 // Refers to some other lifetime that is "in
1549 // scope" within the type.
1550 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1552 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1555 if !self.currently_bound_lifetimes.contains(&name)
1556 && !self.already_defined_lifetimes.contains(&name)
1558 self.already_defined_lifetimes.insert(name);
1560 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1561 hir_id: self.context.next_id(),
1562 span: lifetime.span,
1566 let def_node_id = self.context.resolver.next_node_id();
1568 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1569 self.context.resolver.definitions().create_def_with_parent(
1572 DefPathData::LifetimeNs(name.ident().name),
1577 let (name, kind) = match name {
1578 hir::LifetimeName::Underscore => (
1579 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1580 hir::LifetimeParamKind::Elided,
1582 hir::LifetimeName::Param(param_name) => {
1583 (param_name, hir::LifetimeParamKind::Explicit)
1585 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1588 self.output_lifetime_params.push(hir::GenericParam {
1591 span: lifetime.span,
1592 pure_wrt_drop: false,
1595 kind: hir::GenericParamKind::Lifetime { kind },
1601 let mut lifetime_collector = ImplTraitLifetimeCollector {
1603 parent: parent_index,
1605 collect_elided_lifetimes: true,
1606 currently_bound_lifetimes: Vec::new(),
1607 already_defined_lifetimes: FxHashSet::default(),
1608 output_lifetimes: Vec::new(),
1609 output_lifetime_params: Vec::new(),
1612 for bound in bounds {
1613 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1616 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1620 self.arena.alloc_from_iter(output_lifetimes),
1621 self.arena.alloc_from_iter(output_lifetime_params),
1625 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1626 let mut ids = SmallVec::<[NodeId; 1]>::new();
1627 if self.sess.features_untracked().impl_trait_in_bindings {
1628 if let Some(ref ty) = l.ty {
1629 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1630 visitor.visit_ty(ty);
1633 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
1634 let ty = l.ty.as_ref().map(|t| {
1637 if self.sess.features_untracked().impl_trait_in_bindings {
1638 ImplTraitContext::OpaqueTy(Some(parent_def_id))
1640 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1644 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1647 hir_id: self.lower_node_id(l.id),
1649 pat: self.lower_pat(&l.pat),
1652 attrs: l.attrs.clone(),
1653 source: hir::LocalSource::Normal,
1659 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1660 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1661 // as they are not explicit in HIR/Ty function signatures.
1662 // (instead, the `c_variadic` flag is set to `true`)
1663 let mut inputs = &decl.inputs[..];
1664 if decl.c_variadic() {
1665 inputs = &inputs[..inputs.len() - 1];
1667 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1668 PatKind::Ident(_, ident, _) => ident,
1669 _ => Ident::new(kw::Invalid, param.pat.span),
1673 // Lowers a function declaration.
1675 // `decl`: the unlowered (AST) function declaration.
1676 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1677 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1678 // `make_ret_async` is also `Some`.
1679 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1680 // This guards against trait declarations and implementations where `impl Trait` is
1682 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1683 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1684 // return type `impl Trait` item.
1688 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1689 impl_trait_return_allow: bool,
1690 make_ret_async: Option<NodeId>,
1691 ) -> &'hir hir::FnDecl<'hir> {
1695 in_band_ty_params: {:?}, \
1696 impl_trait_return_allow: {}, \
1697 make_ret_async: {:?})",
1698 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1700 let lt_mode = if make_ret_async.is_some() {
1701 // In `async fn`, argument-position elided lifetimes
1702 // must be transformed into fresh generic parameters so that
1703 // they can be applied to the opaque `impl Trait` return type.
1704 AnonymousLifetimeMode::CreateParameter
1706 self.anonymous_lifetime_mode
1709 let c_variadic = decl.c_variadic();
1711 // Remember how many lifetimes were already around so that we can
1712 // only look at the lifetime parameters introduced by the arguments.
1713 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1714 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1715 // as they are not explicit in HIR/Ty function signatures.
1716 // (instead, the `c_variadic` flag is set to `true`)
1717 let mut inputs = &decl.inputs[..];
1719 inputs = &inputs[..inputs.len() - 1];
1721 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1722 if let Some((_, ibty)) = &mut in_band_ty_params {
1723 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1725 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1730 let output = if let Some(ret_id) = make_ret_async {
1731 self.lower_async_fn_ret_ty(
1733 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1738 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
1739 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
1740 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
1742 _ => hir::FunctionRetTy::Return(
1743 self.lower_ty(ty, ImplTraitContext::disallowed()),
1746 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
1750 self.arena.alloc(hir::FnDecl {
1754 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1755 let is_mutable_pat = match arg.pat.kind {
1756 PatKind::Ident(BindingMode::ByValue(mt), _, _)
1757 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
1762 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1763 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1764 // Given we are only considering `ImplicitSelf` types, we needn't consider
1765 // the case where we have a mutable pattern to a reference as that would
1766 // no longer be an `ImplicitSelf`.
1767 TyKind::Rptr(_, ref mt)
1768 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1770 hir::ImplicitSelfKind::MutRef
1772 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1773 hir::ImplicitSelfKind::ImmRef
1775 _ => hir::ImplicitSelfKind::None,
1781 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1782 // combined with the following definition of `OpaqueTy`:
1784 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1786 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1787 // `output`: unlowered output type (`T` in `-> T`)
1788 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1789 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1790 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1791 fn lower_async_fn_ret_ty(
1793 output: &FunctionRetTy,
1795 opaque_ty_node_id: NodeId,
1796 ) -> hir::FunctionRetTy<'hir> {
1798 "lower_async_fn_ret_ty(\
1801 opaque_ty_node_id={:?})",
1802 output, fn_def_id, opaque_ty_node_id,
1805 let span = output.span();
1807 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1809 let opaque_ty_def_index =
1810 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1812 self.allocate_hir_id_counter(opaque_ty_node_id);
1814 // When we create the opaque type for this async fn, it is going to have
1815 // to capture all the lifetimes involved in the signature (including in the
1816 // return type). This is done by introducing lifetime parameters for:
1818 // - all the explicitly declared lifetimes from the impl and function itself;
1819 // - all the elided lifetimes in the fn arguments;
1820 // - all the elided lifetimes in the return type.
1822 // So for example in this snippet:
1825 // impl<'a> Foo<'a> {
1826 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1827 // // ^ '0 ^ '1 ^ '2
1828 // // elided lifetimes used below
1833 // we would create an opaque type like:
1836 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1839 // and we would then desugar `bar` to the equivalent of:
1842 // impl<'a> Foo<'a> {
1843 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1847 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1848 // this is because the elided lifetimes from the return type
1849 // should be figured out using the ordinary elision rules, and
1850 // this desugaring achieves that.
1852 // The variable `input_lifetimes_count` tracks the number of
1853 // lifetime parameters to the opaque type *not counting* those
1854 // lifetimes elided in the return type. This includes those
1855 // that are explicitly declared (`in_scope_lifetimes`) and
1856 // those elided lifetimes we found in the arguments (current
1857 // content of `lifetimes_to_define`). Next, we will process
1858 // the return type, which will cause `lifetimes_to_define` to
1860 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
1862 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
1863 // We have to be careful to get elision right here. The
1864 // idea is that we create a lifetime parameter for each
1865 // lifetime in the return type. So, given a return type
1866 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1867 // Future<Output = &'1 [ &'2 u32 ]>`.
1869 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1870 // hence the elision takes place at the fn site.
1871 let future_bound = this
1872 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
1873 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1876 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1878 // Calculate all the lifetimes that should be captured
1879 // by the opaque type. This should include all in-scope
1880 // lifetime parameters, including those defined in-band.
1882 // Note: this must be done after lowering the output type,
1883 // as the output type may introduce new in-band lifetimes.
1884 let lifetime_params: Vec<(Span, ParamName)> = this
1888 .map(|name| (name.ident().span, name))
1889 .chain(this.lifetimes_to_define.iter().cloned())
1892 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
1893 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
1894 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
1896 let generic_params =
1897 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
1898 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
1901 let opaque_ty_item = hir::OpaqueTy {
1902 generics: hir::Generics {
1903 params: generic_params,
1904 where_clause: hir::WhereClause { predicates: &[], span },
1907 bounds: arena_vec![this; future_bound],
1908 impl_trait_fn: Some(fn_def_id),
1909 origin: hir::OpaqueTyOrigin::AsyncFn,
1912 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
1914 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1916 (opaque_ty_id, lifetime_params)
1919 // As documented above on the variable
1920 // `input_lifetimes_count`, we need to create the lifetime
1921 // arguments to our opaque type. Continuing with our example,
1922 // we're creating the type arguments for the return type:
1925 // Bar<'a, 'b, '0, '1, '_>
1928 // For the "input" lifetime parameters, we wish to create
1929 // references to the parameters themselves, including the
1930 // "implicit" ones created from parameter types (`'a`, `'b`,
1933 // For the "output" lifetime parameters, we just want to
1935 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
1937 .map(|&(span, hir_name)| {
1938 // Input lifetime like `'a` or `'1`:
1939 GenericArg::Lifetime(hir::Lifetime {
1940 hir_id: self.next_id(),
1942 name: hir::LifetimeName::Param(hir_name),
1946 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
1947 // Output lifetime like `'_`.
1948 GenericArg::Lifetime(hir::Lifetime {
1949 hir_id: self.next_id(),
1951 name: hir::LifetimeName::Implicit,
1953 let generic_args = self.arena.alloc_from_iter(generic_args);
1955 // Create the `Foo<...>` reference itself. Note that the `type
1956 // Foo = impl Trait` is, internally, created as a child of the
1957 // async fn, so the *type parameters* are inherited. It's
1958 // only the lifetime parameters that we must supply.
1959 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
1960 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1961 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
1964 /// Transforms `-> T` into `Future<Output = T>`
1965 fn lower_async_fn_output_type_to_future_bound(
1967 output: &FunctionRetTy,
1970 ) -> hir::GenericBound<'hir> {
1971 // Compute the `T` in `Future<Output = T>` from the return type.
1972 let output_ty = match output {
1973 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
1974 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1978 let future_params = self.arena.alloc(hir::GenericArgs {
1980 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1981 parenthesized: false,
1984 // ::std::future::Future<future_params>
1986 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
1988 hir::GenericBound::Trait(
1990 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
1991 bound_generic_params: &[],
1994 hir::TraitBoundModifier::None,
1998 fn lower_param_bound(
2001 itctx: ImplTraitContext<'_, 'hir>,
2002 ) -> hir::GenericBound<'hir> {
2004 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2005 self.lower_poly_trait_ref(ty, itctx),
2006 self.lower_trait_bound_modifier(modifier),
2008 GenericBound::Outlives(ref lifetime) => {
2009 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2014 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2015 let span = l.ident.span;
2017 ident if ident.name == kw::StaticLifetime => {
2018 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2020 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2021 AnonymousLifetimeMode::CreateParameter => {
2022 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2023 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2026 AnonymousLifetimeMode::PassThrough => {
2027 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2030 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2033 self.maybe_collect_in_band_lifetime(ident);
2034 let param_name = ParamName::Plain(ident);
2035 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2040 fn new_named_lifetime(
2044 name: hir::LifetimeName,
2045 ) -> hir::Lifetime {
2046 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2049 fn lower_generic_params_mut<'s>(
2051 params: &'s [GenericParam],
2052 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2053 mut itctx: ImplTraitContext<'s, 'hir>,
2054 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2057 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2060 fn lower_generic_params(
2062 params: &[GenericParam],
2063 add_bounds: &NodeMap<Vec<GenericBound>>,
2064 itctx: ImplTraitContext<'_, 'hir>,
2065 ) -> &'hir [hir::GenericParam<'hir>] {
2066 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2069 fn lower_generic_param(
2071 param: &GenericParam,
2072 add_bounds: &NodeMap<Vec<GenericBound>>,
2073 mut itctx: ImplTraitContext<'_, 'hir>,
2074 ) -> hir::GenericParam<'hir> {
2075 let mut bounds: Vec<_> = self
2076 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2077 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2080 let (name, kind) = match param.kind {
2081 GenericParamKind::Lifetime => {
2082 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2083 self.is_collecting_in_band_lifetimes = false;
2086 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2087 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2089 let param_name = match lt.name {
2090 hir::LifetimeName::Param(param_name) => param_name,
2091 hir::LifetimeName::Implicit
2092 | hir::LifetimeName::Underscore
2093 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2094 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2097 "object-lifetime-default should not occur here",
2100 hir::LifetimeName::Error => ParamName::Error,
2104 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2106 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2110 GenericParamKind::Type { ref default, .. } => {
2111 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2112 if !add_bounds.is_empty() {
2113 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2114 bounds.extend(params);
2117 let kind = hir::GenericParamKind::Type {
2120 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2124 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2125 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2129 (hir::ParamName::Plain(param.ident), kind)
2131 GenericParamKind::Const { ref ty } => (
2132 hir::ParamName::Plain(param.ident),
2133 hir::GenericParamKind::Const {
2134 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2140 hir_id: self.lower_node_id(param.id),
2142 span: param.ident.span,
2143 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2144 attrs: self.lower_attrs(¶m.attrs),
2145 bounds: self.arena.alloc_from_iter(bounds),
2153 itctx: ImplTraitContext<'_, 'hir>,
2154 ) -> hir::TraitRef<'hir> {
2155 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2156 hir::QPath::Resolved(None, path) => path,
2157 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2159 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2162 fn lower_poly_trait_ref(
2165 mut itctx: ImplTraitContext<'_, 'hir>,
2166 ) -> hir::PolyTraitRef<'hir> {
2167 let bound_generic_params = self.lower_generic_params(
2168 &p.bound_generic_params,
2169 &NodeMap::default(),
2172 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2173 this.lower_trait_ref(&p.trait_ref, itctx)
2176 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2179 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2180 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2183 fn lower_param_bounds(
2185 bounds: &[GenericBound],
2186 itctx: ImplTraitContext<'_, 'hir>,
2187 ) -> hir::GenericBounds<'hir> {
2188 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2191 fn lower_param_bounds_mut<'s>(
2193 bounds: &'s [GenericBound],
2194 mut itctx: ImplTraitContext<'s, 'hir>,
2195 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2196 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2199 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2200 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2203 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2204 let mut stmts = vec![];
2205 let mut expr: Option<&'hir _> = None;
2207 for (index, stmt) in b.stmts.iter().enumerate() {
2208 if index == b.stmts.len() - 1 {
2209 if let StmtKind::Expr(ref e) = stmt.kind {
2210 expr = Some(self.lower_expr(e));
2212 stmts.extend(self.lower_stmt(stmt));
2215 stmts.extend(self.lower_stmt(stmt));
2220 hir_id: self.lower_node_id(b.id),
2221 stmts: self.arena.alloc_from_iter(stmts),
2223 rules: self.lower_block_check_mode(&b.rules),
2229 /// Lowers a block directly to an expression, presuming that it
2230 /// has no attributes and is not targeted by a `break`.
2231 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2232 let block = self.lower_block(b, false);
2233 self.expr_block(block, AttrVec::new())
2236 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2237 self.with_new_scopes(|this| hir::AnonConst {
2238 hir_id: this.lower_node_id(c.id),
2239 body: this.lower_const_body(c.value.span, Some(&c.value)),
2243 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2244 let kind = match s.kind {
2245 StmtKind::Local(ref l) => {
2246 let (l, item_ids) = self.lower_local(l);
2247 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2250 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2251 self.stmt(s.span, hir::StmtKind::Item(item_id))
2256 hir_id: self.lower_node_id(s.id),
2257 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2263 StmtKind::Item(ref it) => {
2264 // Can only use the ID once.
2265 let mut id = Some(s.id);
2272 .map(|id| self.lower_node_id(id))
2273 .unwrap_or_else(|| self.next_id());
2275 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2279 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2280 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2281 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2283 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2286 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2288 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2289 BlockCheckMode::Unsafe(u) => {
2290 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2295 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2297 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2298 UserProvided => hir::UnsafeSource::UserProvided,
2302 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2304 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2305 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2309 // Helper methods for building HIR.
2311 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2312 hir::Stmt { span, kind, hir_id: self.next_id() }
2315 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2316 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2323 init: Option<&'hir hir::Expr<'hir>>,
2324 pat: &'hir hir::Pat<'hir>,
2325 source: hir::LocalSource,
2326 ) -> hir::Stmt<'hir> {
2327 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2328 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2331 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2332 self.block_all(expr.span, &[], Some(expr))
2338 stmts: &'hir [hir::Stmt<'hir>],
2339 expr: Option<&'hir hir::Expr<'hir>>,
2340 ) -> &'hir hir::Block<'hir> {
2341 let blk = hir::Block {
2344 hir_id: self.next_id(),
2345 rules: hir::BlockCheckMode::DefaultBlock,
2347 targeted_by_break: false,
2349 self.arena.alloc(blk)
2352 /// Constructs a `true` or `false` literal pattern.
2353 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2354 let expr = self.expr_bool(span, val);
2355 self.pat(span, hir::PatKind::Lit(expr))
2358 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2359 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
2362 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2363 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
2366 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2367 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
2370 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2371 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
2377 components: &[Symbol],
2378 subpats: &'hir [&'hir hir::Pat<'hir>],
2379 ) -> &'hir hir::Pat<'hir> {
2380 let path = self.std_path(span, components, None, true);
2381 let qpath = hir::QPath::Resolved(None, path);
2382 let pt = if subpats.is_empty() {
2383 hir::PatKind::Path(qpath)
2385 hir::PatKind::TupleStruct(qpath, subpats, None)
2390 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2391 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2394 fn pat_ident_binding_mode(
2398 bm: hir::BindingAnnotation,
2399 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2400 let hir_id = self.next_id();
2403 self.arena.alloc(hir::Pat {
2405 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2412 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2413 self.pat(span, hir::PatKind::Wild)
2416 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2417 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
2420 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
2421 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
2422 /// The path is also resolved according to `is_value`.
2426 components: &[Symbol],
2427 params: Option<&'hir hir::GenericArgs<'hir>>,
2429 ) -> &'hir hir::Path<'hir> {
2430 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
2431 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
2433 let mut segments: Vec<_> = path
2437 let res = self.expect_full_res(segment.id);
2439 ident: segment.ident,
2440 hir_id: Some(self.lower_node_id(segment.id)),
2441 res: Some(self.lower_res(res)),
2447 segments.last_mut().unwrap().args = params;
2449 self.arena.alloc(hir::Path {
2451 res: res.map_id(|_| panic!("unexpected `NodeId`")),
2452 segments: self.arena.alloc_from_iter(segments),
2458 mut hir_id: hir::HirId,
2460 qpath: hir::QPath<'hir>,
2461 ) -> hir::Ty<'hir> {
2462 let kind = match qpath {
2463 hir::QPath::Resolved(None, path) => {
2464 // Turn trait object paths into `TyKind::TraitObject` instead.
2466 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
2467 let principal = hir::PolyTraitRef {
2468 bound_generic_params: &[],
2469 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2473 // The original ID is taken by the `PolyTraitRef`,
2474 // so the `Ty` itself needs a different one.
2475 hir_id = self.next_id();
2476 hir::TyKind::TraitObject(
2477 arena_vec![self; principal],
2478 self.elided_dyn_bound(span),
2481 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2484 _ => hir::TyKind::Path(qpath),
2487 hir::Ty { hir_id, kind, span }
2490 /// Invoked to create the lifetime argument for a type `&T`
2491 /// with no explicit lifetime.
2492 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2493 match self.anonymous_lifetime_mode {
2494 // Intercept when we are in an impl header or async fn and introduce an in-band
2496 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2498 AnonymousLifetimeMode::CreateParameter => {
2499 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2501 hir_id: self.next_id(),
2503 name: hir::LifetimeName::Param(fresh_name),
2507 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2509 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2513 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2514 /// return a "error lifetime".
2515 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2516 let (id, msg, label) = match id {
2517 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2520 self.resolver.next_node_id(),
2521 "`&` without an explicit lifetime name cannot be used here",
2522 "explicit lifetime name needed here",
2526 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2527 err.span_label(span, label);
2530 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2533 /// Invoked to create the lifetime argument(s) for a path like
2534 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2535 /// sorts of cases are deprecated. This may therefore report a warning or an
2536 /// error, depending on the mode.
2537 fn elided_path_lifetimes<'s>(
2541 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2542 (0..count).map(move |_| self.elided_path_lifetime(span))
2545 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2546 match self.anonymous_lifetime_mode {
2547 AnonymousLifetimeMode::CreateParameter => {
2548 // We should have emitted E0726 when processing this path above
2550 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2551 let id = self.resolver.next_node_id();
2552 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2554 // `PassThrough` is the normal case.
2555 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2556 // is unsuitable here, as these can occur from missing lifetime parameters in a
2557 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2558 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2559 // later, at which point a suitable error will be emitted.
2560 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2561 self.new_implicit_lifetime(span)
2566 /// Invoked to create the lifetime argument(s) for an elided trait object
2567 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2568 /// when the bound is written, even if it is written with `'_` like in
2569 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2570 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2571 match self.anonymous_lifetime_mode {
2572 // NB. We intentionally ignore the create-parameter mode here.
2573 // and instead "pass through" to resolve-lifetimes, which will apply
2574 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2575 // do not act like other elided lifetimes. In other words, given this:
2577 // impl Foo for Box<dyn Debug>
2579 // we do not introduce a fresh `'_` to serve as the bound, but instead
2580 // ultimately translate to the equivalent of:
2582 // impl Foo for Box<dyn Debug + 'static>
2584 // `resolve_lifetime` has the code to make that happen.
2585 AnonymousLifetimeMode::CreateParameter => {}
2587 AnonymousLifetimeMode::ReportError => {
2588 // ReportError applies to explicit use of `'_`.
2591 // This is the normal case.
2592 AnonymousLifetimeMode::PassThrough => {}
2595 let r = hir::Lifetime {
2596 hir_id: self.next_id(),
2598 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2600 debug!("elided_dyn_bound: r={:?}", r);
2604 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2605 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2608 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2609 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2610 // call site which do not have a macro backtrace. See #61963.
2611 let is_macro_callsite = self
2614 .span_to_snippet(span)
2615 .map(|snippet| snippet.starts_with("#["))
2617 if !is_macro_callsite {
2618 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2619 builtin::BARE_TRAIT_OBJECTS,
2622 "trait objects without an explicit `dyn` are deprecated",
2623 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2629 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2630 // Sorting by span ensures that we get things in order within a
2631 // file, and also puts the files in a sensible order.
2632 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2633 body_ids.sort_by_key(|b| bodies[b].value.span);
2637 /// Helper struct for delayed construction of GenericArgs.
2638 struct GenericArgsCtor<'hir> {
2639 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2640 bindings: &'hir [hir::TypeBinding<'hir>],
2641 parenthesized: bool,
2644 impl<'hir> GenericArgsCtor<'hir> {
2645 fn is_empty(&self) -> bool {
2646 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2649 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2651 args: arena.alloc_from_iter(self.args),
2652 bindings: self.bindings,
2653 parenthesized: self.parenthesized,