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)]
35 #![recursion_limit = "256"]
37 use rustc::arena::Arena;
38 use rustc::dep_graph::DepGraph;
39 use rustc::hir::map::definitions::{DefKey, DefPathData, Definitions};
40 use rustc::hir::map::Map;
41 use rustc::{bug, span_bug};
42 use rustc_ast_pretty::pprust;
43 use rustc_data_structures::captures::Captures;
44 use rustc_data_structures::fx::FxHashSet;
45 use rustc_data_structures::sync::Lrc;
46 use rustc_errors::struct_span_err;
48 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
49 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
50 use rustc_hir::intravisit;
51 use rustc_hir::{ConstArg, GenericArg, ParamName};
52 use rustc_index::vec::IndexVec;
53 use rustc_session::config::nightly_options;
54 use rustc_session::lint::{builtin::BARE_TRAIT_OBJECTS, BuiltinLintDiagnostics, LintBuffer};
55 use rustc_session::parse::ParseSess;
56 use rustc_session::Session;
57 use rustc_span::hygiene::ExpnId;
58 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind};
59 use rustc_span::symbol::{kw, sym, Symbol};
64 use syntax::node_id::NodeMap;
65 use syntax::token::{self, Nonterminal, Token};
66 use syntax::tokenstream::{TokenStream, TokenTree};
67 use syntax::visit::{self, AssocCtxt, Visitor};
68 use syntax::walk_list;
70 use log::{debug, trace};
71 use smallvec::{smallvec, SmallVec};
72 use std::collections::BTreeMap;
75 macro_rules! arena_vec {
76 ($this:expr; $($x:expr),*) => ({
78 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
87 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
89 struct LoweringContext<'a, 'hir: 'a> {
90 crate_root: Option<Symbol>,
92 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
95 resolver: &'a mut dyn Resolver,
97 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
98 /// if we don't have this function pointer. To avoid that dependency so that
99 /// librustc is independent of the parser, we use dynamic dispatch here.
100 nt_to_tokenstream: NtToTokenstream,
102 /// Used to allocate HIR nodes
103 arena: &'hir Arena<'hir>,
105 /// The items being lowered are collected here.
106 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
108 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
109 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
110 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
111 exported_macros: Vec<hir::MacroDef<'hir>>,
112 non_exported_macro_attrs: Vec<ast::Attribute>,
114 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
116 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
118 generator_kind: Option<hir::GeneratorKind>,
120 /// Used to get the current `fn`'s def span to point to when using `await`
121 /// outside of an `async fn`.
122 current_item: Option<Span>,
124 catch_scopes: Vec<NodeId>,
125 loop_scopes: Vec<NodeId>,
126 is_in_loop_condition: bool,
127 is_in_trait_impl: bool,
128 is_in_dyn_type: bool,
130 /// What to do when we encounter either an "anonymous lifetime
131 /// reference". The term "anonymous" is meant to encompass both
132 /// `'_` lifetimes as well as fully elided cases where nothing is
133 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
134 anonymous_lifetime_mode: AnonymousLifetimeMode,
136 /// Used to create lifetime definitions from in-band lifetime usages.
137 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
138 /// When a named lifetime is encountered in a function or impl header and
139 /// has not been defined
140 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
141 /// to this list. The results of this list are then added to the list of
142 /// lifetime definitions in the corresponding impl or function generics.
143 lifetimes_to_define: Vec<(Span, ParamName)>,
145 /// `true` if in-band lifetimes are being collected. This is used to
146 /// indicate whether or not we're in a place where new lifetimes will result
147 /// in in-band lifetime definitions, such a function or an impl header,
148 /// including implicit lifetimes from `impl_header_lifetime_elision`.
149 is_collecting_in_band_lifetimes: bool,
151 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
152 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
153 /// against this list to see if it is already in-scope, or if a definition
154 /// needs to be created for it.
156 /// We always store a `modern()` version of the param-name in this
158 in_scope_lifetimes: Vec<ParamName>,
160 current_module: hir::HirId,
162 type_def_lifetime_params: DefIdMap<usize>,
164 current_hir_id_owner: Vec<(DefIndex, u32)>,
165 item_local_id_counters: NodeMap<u32>,
166 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
168 allow_try_trait: Option<Lrc<[Symbol]>>,
169 allow_gen_future: Option<Lrc<[Symbol]>>,
173 fn def_key(&mut self, id: DefId) -> DefKey;
175 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
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 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 */, hir::OpaqueTyOrigin),
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, origin) => OpaqueTy(*fn_def_id, *origin),
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.verbose_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_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) {
490 self.lctx.allocate_hir_id_counter(item.id);
491 let owner = match (&item.kind, ctxt) {
492 // Ignore patterns in trait methods without bodies.
493 (AssocItemKind::Fn(_, _, None), AssocCtxt::Trait) => None,
496 self.with_hir_id_owner(owner, |this| visit::walk_assoc_item(this, item, ctxt));
499 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
500 // Ignore patterns in foreign items
501 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
504 fn visit_ty(&mut self, t: &'tcx Ty) {
506 // Mirrors the case in visit::walk_ty
507 TyKind::BareFn(ref f) => {
508 walk_list!(self, visit_generic_param, &f.generic_params);
509 // Mirrors visit::walk_fn_decl
510 for parameter in &f.decl.inputs {
511 // We don't lower the ids of argument patterns
512 self.with_hir_id_owner(None, |this| {
513 this.visit_pat(¶meter.pat);
515 self.visit_ty(¶meter.ty)
517 self.visit_fn_ret_ty(&f.decl.output)
519 _ => visit::walk_ty(self, t),
524 self.lower_node_id(CRATE_NODE_ID);
525 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
527 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
528 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
530 let module = self.lower_mod(&c.module);
531 let attrs = self.lower_attrs(&c.attrs);
532 let body_ids = body_ids(&self.bodies);
533 let proc_macros = c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id]).collect();
535 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
541 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
542 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
544 trait_items: self.trait_items,
545 impl_items: self.impl_items,
548 trait_impls: self.trait_impls,
549 modules: self.modules,
554 fn insert_item(&mut self, item: hir::Item<'hir>) {
555 let id = item.hir_id;
556 // FIXME: Use `debug_asset-rt`.
557 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
558 self.items.insert(id, item);
559 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
562 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
563 // Set up the counter if needed.
564 self.item_local_id_counters.entry(owner).or_insert(0);
565 // Always allocate the first `HirId` for the owner itself.
566 let lowered = self.lower_node_id_with_owner(owner, owner);
567 debug_assert_eq!(lowered.local_id.as_u32(), 0);
571 fn lower_node_id_generic(
574 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
576 if ast_node_id == DUMMY_NODE_ID {
577 return hir::DUMMY_HIR_ID;
580 let min_size = ast_node_id.as_usize() + 1;
582 if min_size > self.node_id_to_hir_id.len() {
583 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
586 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
588 if existing_hir_id == hir::DUMMY_HIR_ID {
589 // Generate a new `HirId`.
590 let hir_id = alloc_hir_id(self);
591 self.node_id_to_hir_id[ast_node_id] = hir_id;
599 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
601 .item_local_id_counters
602 .insert(owner, HIR_ID_COUNTER_LOCKED)
603 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
604 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
605 self.current_hir_id_owner.push((def_index, counter));
607 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
609 debug_assert!(def_index == new_def_index);
610 debug_assert!(new_counter >= counter);
612 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
613 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
617 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
618 /// the `LoweringContext`'s `NodeId => HirId` map.
619 /// Take care not to call this method if the resulting `HirId` is then not
620 /// actually used in the HIR, as that would trigger an assertion in the
621 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
622 /// properly. Calling the method twice with the same `NodeId` is fine though.
623 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
624 self.lower_node_id_generic(ast_node_id, |this| {
625 let &mut (def_index, ref mut local_id_counter) =
626 this.current_hir_id_owner.last_mut().unwrap();
627 let local_id = *local_id_counter;
628 *local_id_counter += 1;
629 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
633 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let local_id_counter = this
636 .item_local_id_counters
638 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
639 let local_id = *local_id_counter;
641 // We want to be sure not to modify the counter in the map while it
642 // is also on the stack. Otherwise we'll get lost updates when writing
643 // back from the stack to the map.
644 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
646 *local_id_counter += 1;
647 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
648 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
649 that do not belong to the current owner",
652 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
656 fn next_id(&mut self) -> hir::HirId {
657 let node_id = self.resolver.next_node_id();
658 self.lower_node_id(node_id)
661 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
663 self.lower_node_id_generic(id, |_| {
664 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
669 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
670 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
671 if pr.unresolved_segments() != 0 {
672 bug!("path not fully resolved: {:?}", pr);
678 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
679 self.resolver.get_import_res(id).present_items()
682 fn diagnostic(&self) -> &rustc_errors::Handler {
683 self.sess.diagnostic()
686 /// Reuses the span but adds information like the kind of the desugaring and features that are
687 /// allowed inside this span.
688 fn mark_span_with_reason(
690 reason: DesugaringKind,
692 allow_internal_unstable: Option<Lrc<[Symbol]>>,
694 span.fresh_expansion(ExpnData {
695 allow_internal_unstable,
696 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
700 fn with_anonymous_lifetime_mode<R>(
702 anonymous_lifetime_mode: AnonymousLifetimeMode,
703 op: impl FnOnce(&mut Self) -> R,
706 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
707 anonymous_lifetime_mode,
709 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
710 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
711 let result = op(self);
712 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
714 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
715 old_anonymous_lifetime_mode
720 /// Creates a new `hir::GenericParam` for every new lifetime and
721 /// type parameter encountered while evaluating `f`. Definitions
722 /// are created with the parent provided. If no `parent_id` is
723 /// provided, no definitions will be returned.
725 /// Presuming that in-band lifetimes are enabled, then
726 /// `self.anonymous_lifetime_mode` will be updated to match the
727 /// parameter while `f` is running (and restored afterwards).
728 fn collect_in_band_defs<T>(
731 anonymous_lifetime_mode: AnonymousLifetimeMode,
732 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
733 ) -> (Vec<hir::GenericParam<'hir>>, T) {
734 assert!(!self.is_collecting_in_band_lifetimes);
735 assert!(self.lifetimes_to_define.is_empty());
736 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
738 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
739 self.is_collecting_in_band_lifetimes = true;
741 let (in_band_ty_params, res) = f(self);
743 self.is_collecting_in_band_lifetimes = false;
744 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
746 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
748 let params = lifetimes_to_define
750 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
751 .chain(in_band_ty_params.into_iter())
757 /// Converts a lifetime into a new generic parameter.
758 fn lifetime_to_generic_param(
762 parent_index: DefIndex,
763 ) -> hir::GenericParam<'hir> {
764 let node_id = self.resolver.next_node_id();
766 // Get the name we'll use to make the def-path. Note
767 // that collisions are ok here and this shouldn't
768 // really show up for end-user.
769 let (str_name, kind) = match hir_name {
770 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
771 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
772 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
775 // Add a definition for the in-band lifetime def.
776 self.resolver.definitions().create_def_with_parent(
779 DefPathData::LifetimeNs(str_name),
785 hir_id: self.lower_node_id(node_id),
790 pure_wrt_drop: false,
791 kind: hir::GenericParamKind::Lifetime { kind },
795 /// When there is a reference to some lifetime `'a`, and in-band
796 /// lifetimes are enabled, then we want to push that lifetime into
797 /// the vector of names to define later. In that case, it will get
798 /// added to the appropriate generics.
799 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
800 if !self.is_collecting_in_band_lifetimes {
804 if !self.sess.features_untracked().in_band_lifetimes {
808 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
812 let hir_name = ParamName::Plain(ident);
814 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
819 self.lifetimes_to_define.push((ident.span, hir_name));
822 /// When we have either an elided or `'_` lifetime in an impl
823 /// header, we convert it to an in-band lifetime.
824 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
825 assert!(self.is_collecting_in_band_lifetimes);
826 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
827 let hir_name = ParamName::Fresh(index);
828 self.lifetimes_to_define.push((span, hir_name));
832 // Evaluates `f` with the lifetimes in `params` in-scope.
833 // This is used to track which lifetimes have already been defined, and
834 // which are new in-band lifetimes that need to have a definition created
836 fn with_in_scope_lifetime_defs<T>(
838 params: &[GenericParam],
839 f: impl FnOnce(&mut Self) -> T,
841 let old_len = self.in_scope_lifetimes.len();
842 let lt_def_names = params.iter().filter_map(|param| match param.kind {
843 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
846 self.in_scope_lifetimes.extend(lt_def_names);
850 self.in_scope_lifetimes.truncate(old_len);
854 /// Appends in-band lifetime defs and argument-position `impl
855 /// Trait` defs to the existing set of generics.
857 /// Presuming that in-band lifetimes are enabled, then
858 /// `self.anonymous_lifetime_mode` will be updated to match the
859 /// parameter while `f` is running (and restored afterwards).
860 fn add_in_band_defs<T>(
864 anonymous_lifetime_mode: AnonymousLifetimeMode,
865 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
866 ) -> (hir::Generics<'hir>, T) {
867 let (in_band_defs, (mut lowered_generics, res)) =
868 self.with_in_scope_lifetime_defs(&generics.params, |this| {
869 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
870 let mut params = Vec::new();
871 // Note: it is necessary to lower generics *before* calling `f`.
872 // When lowering `async fn`, there's a final step when lowering
873 // the return type that assumes that all in-scope lifetimes have
874 // already been added to either `in_scope_lifetimes` or
875 // `lifetimes_to_define`. If we swapped the order of these two,
876 // in-band-lifetimes introduced by generics or where-clauses
877 // wouldn't have been added yet.
879 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
880 let res = f(this, &mut params);
881 (params, (generics, res))
885 let mut lowered_params: Vec<_> =
886 lowered_generics.params.into_iter().chain(in_band_defs).collect();
888 // FIXME(const_generics): the compiler doesn't always cope with
889 // unsorted generic parameters at the moment, so we make sure
890 // that they're ordered correctly here for now. (When we chain
891 // the `in_band_defs`, we might make the order unsorted.)
892 lowered_params.sort_by_key(|param| match param.kind {
893 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
894 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
895 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
898 lowered_generics.params = lowered_params.into();
900 let lowered_generics = lowered_generics.into_generics(self.arena);
901 (lowered_generics, res)
904 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
905 let was_in_dyn_type = self.is_in_dyn_type;
906 self.is_in_dyn_type = in_scope;
908 let result = f(self);
910 self.is_in_dyn_type = was_in_dyn_type;
915 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
916 let was_in_loop_condition = self.is_in_loop_condition;
917 self.is_in_loop_condition = false;
919 let catch_scopes = mem::take(&mut self.catch_scopes);
920 let loop_scopes = mem::take(&mut self.loop_scopes);
922 self.catch_scopes = catch_scopes;
923 self.loop_scopes = loop_scopes;
925 self.is_in_loop_condition = was_in_loop_condition;
930 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
931 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
934 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
935 // Note that we explicitly do not walk the path. Since we don't really
936 // lower attributes (we use the AST version) there is nowhere to keep
937 // the `HirId`s. We don't actually need HIR version of attributes anyway.
938 let kind = match attr.kind {
939 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
940 path: item.path.clone(),
941 args: self.lower_mac_args(&item.args),
943 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
946 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
949 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
951 MacArgs::Empty => MacArgs::Empty,
952 MacArgs::Delimited(dspan, delim, ref tokens) => {
953 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
955 MacArgs::Eq(eq_span, ref tokens) => {
956 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
961 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
962 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
965 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
967 TokenTree::Token(token) => self.lower_token(token),
968 TokenTree::Delimited(span, delim, tts) => {
969 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
974 fn lower_token(&mut self, token: Token) -> TokenStream {
976 token::Interpolated(nt) => {
977 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
978 self.lower_token_stream(tts)
980 _ => TokenTree::Token(token).into(),
984 /// Given an associated type constraint like one of these:
987 /// T: Iterator<Item: Debug>
989 /// T: Iterator<Item = Debug>
993 /// returns a `hir::TypeBinding` representing `Item`.
994 fn lower_assoc_ty_constraint(
996 constraint: &AssocTyConstraint,
997 itctx: ImplTraitContext<'_, 'hir>,
998 ) -> hir::TypeBinding<'hir> {
999 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1001 let kind = match constraint.kind {
1002 AssocTyConstraintKind::Equality { ref ty } => {
1003 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1005 AssocTyConstraintKind::Bound { ref bounds } => {
1006 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1007 let (desugar_to_impl_trait, itctx) = match itctx {
1008 // We are in the return position:
1010 // fn foo() -> impl Iterator<Item: Debug>
1014 // fn foo() -> impl Iterator<Item = impl Debug>
1015 ImplTraitContext::OpaqueTy(..) => (true, itctx),
1017 // We are in the argument position, but within a dyn type:
1019 // fn foo(x: dyn Iterator<Item: Debug>)
1023 // fn foo(x: dyn Iterator<Item = impl Debug>)
1024 ImplTraitContext::Universal(..) if self.is_in_dyn_type => (true, itctx),
1026 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1027 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1028 // "impl trait context" to permit `impl Debug` in this position (it desugars
1029 // then to an opaque type).
1031 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1032 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1033 (true, ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc))
1036 // We are in the parameter position, but not within a dyn type:
1038 // fn foo(x: impl Iterator<Item: Debug>)
1040 // so we leave it as is and this gets expanded in astconv to a bound like
1041 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1043 _ => (false, itctx),
1046 if desugar_to_impl_trait {
1047 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1048 // constructing the HIR for `impl bounds...` and then lowering that.
1050 let impl_trait_node_id = self.resolver.next_node_id();
1051 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1052 self.resolver.definitions().create_def_with_parent(
1055 DefPathData::ImplTrait,
1060 self.with_dyn_type_scope(false, |this| {
1061 let node_id = this.resolver.next_node_id();
1062 let ty = this.lower_ty(
1065 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1066 span: constraint.span,
1071 hir::TypeBindingKind::Equality { ty }
1074 // Desugar `AssocTy: Bounds` into a type binding where the
1075 // later desugars into a trait predicate.
1076 let bounds = self.lower_param_bounds(bounds, itctx);
1078 hir::TypeBindingKind::Constraint { bounds }
1084 hir_id: self.lower_node_id(constraint.id),
1085 ident: constraint.ident,
1087 span: constraint.span,
1091 fn lower_generic_arg(
1093 arg: &ast::GenericArg,
1094 itctx: ImplTraitContext<'_, 'hir>,
1095 ) -> hir::GenericArg<'hir> {
1097 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1098 ast::GenericArg::Type(ty) => {
1099 // We parse const arguments as path types as we cannot distiguish them durring
1100 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1101 // type and value namespaces. If we resolved the path in the value namespace, we
1102 // transform it into a generic const argument.
1103 if let TyKind::Path(ref qself, ref path) = ty.kind {
1104 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1105 let res = partial_res.base_res();
1106 if !res.matches_ns(Namespace::TypeNS) {
1108 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1112 // Construct a AnonConst where the expr is the "ty"'s path.
1114 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1115 let node_id = self.resolver.next_node_id();
1117 // Add a definition for the in-band const def.
1118 self.resolver.definitions().create_def_with_parent(
1121 DefPathData::AnonConst,
1126 let path_expr = Expr {
1128 kind: ExprKind::Path(qself.clone(), path.clone()),
1130 attrs: AttrVec::new(),
1133 let ct = self.with_new_scopes(|this| hir::AnonConst {
1134 hir_id: this.lower_node_id(node_id),
1135 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1137 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1141 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1143 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1144 value: self.lower_anon_const(&ct),
1145 span: ct.value.span,
1150 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1151 self.arena.alloc(self.lower_ty_direct(t, itctx))
1157 qself: &Option<QSelf>,
1159 param_mode: ParamMode,
1160 itctx: ImplTraitContext<'_, 'hir>,
1161 ) -> hir::Ty<'hir> {
1162 let id = self.lower_node_id(t.id);
1163 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1164 let ty = self.ty_path(id, t.span, qpath);
1165 if let hir::TyKind::TraitObject(..) = ty.kind {
1166 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1171 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1172 hir::Ty { hir_id: self.next_id(), kind, span }
1175 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1176 self.ty(span, hir::TyKind::Tup(tys))
1179 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1180 let kind = match t.kind {
1181 TyKind::Infer => hir::TyKind::Infer,
1182 TyKind::Err => hir::TyKind::Err,
1183 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1184 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1185 TyKind::Rptr(ref region, ref mt) => {
1186 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1187 let lifetime = match *region {
1188 Some(ref lt) => self.lower_lifetime(lt),
1189 None => self.elided_ref_lifetime(span),
1191 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1193 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1194 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1195 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1196 generic_params: this.lower_generic_params(
1198 &NodeMap::default(),
1199 ImplTraitContext::disallowed(),
1201 unsafety: this.lower_unsafety(f.unsafety),
1202 abi: this.lower_extern(f.ext),
1203 decl: this.lower_fn_decl(&f.decl, None, false, None),
1204 param_names: this.lower_fn_params_to_names(&f.decl),
1208 TyKind::Never => hir::TyKind::Never,
1209 TyKind::Tup(ref tys) => {
1210 hir::TyKind::Tup(self.arena.alloc_from_iter(
1211 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1214 TyKind::Paren(ref ty) => {
1215 return self.lower_ty_direct(ty, itctx);
1217 TyKind::Path(ref qself, ref path) => {
1218 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1220 TyKind::ImplicitSelf => {
1221 let res = self.expect_full_res(t.id);
1222 let res = self.lower_res(res);
1223 hir::TyKind::Path(hir::QPath::Resolved(
1225 self.arena.alloc(hir::Path {
1227 segments: arena_vec![self; hir::PathSegment::from_ident(
1228 Ident::with_dummy_span(kw::SelfUpper)
1234 TyKind::Array(ref ty, ref length) => {
1235 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1237 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1238 TyKind::TraitObject(ref bounds, kind) => {
1239 let mut lifetime_bound = None;
1240 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1242 this.arena.alloc_from_iter(bounds.iter().filter_map(
1243 |bound| match *bound {
1244 GenericBound::Trait(ref ty, TraitBoundModifier::None)
1245 | GenericBound::Trait(ref ty, TraitBoundModifier::MaybeConst) => {
1246 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1248 // `?const ?Bound` will cause an error during AST validation
1249 // anyways, so treat it like `?Bound` as compilation proceeds.
1250 GenericBound::Trait(_, TraitBoundModifier::Maybe)
1251 | GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1254 GenericBound::Outlives(ref lifetime) => {
1255 if lifetime_bound.is_none() {
1256 lifetime_bound = Some(this.lower_lifetime(lifetime));
1262 let lifetime_bound =
1263 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1264 (bounds, lifetime_bound)
1266 if kind != TraitObjectSyntax::Dyn {
1267 self.maybe_lint_bare_trait(t.span, t.id, false);
1269 hir::TyKind::TraitObject(bounds, lifetime_bound)
1271 TyKind::ImplTrait(def_node_id, ref bounds) => {
1274 ImplTraitContext::OpaqueTy(fn_def_id, origin) => {
1275 self.lower_opaque_impl_trait(span, fn_def_id, origin, def_node_id, |this| {
1276 this.lower_param_bounds(bounds, itctx)
1279 ImplTraitContext::Universal(in_band_ty_params) => {
1280 // Add a definition for the in-band `Param`.
1282 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1284 let hir_bounds = self.lower_param_bounds(
1286 ImplTraitContext::Universal(in_band_ty_params),
1288 // Set the name to `impl Bound1 + Bound2`.
1289 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1290 in_band_ty_params.push(hir::GenericParam {
1291 hir_id: self.lower_node_id(def_node_id),
1292 name: ParamName::Plain(ident),
1293 pure_wrt_drop: false,
1297 kind: hir::GenericParamKind::Type {
1299 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1303 hir::TyKind::Path(hir::QPath::Resolved(
1305 self.arena.alloc(hir::Path {
1307 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1308 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1312 ImplTraitContext::Disallowed(pos) => {
1313 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1314 "bindings or function and inherent method return types"
1316 "function and inherent method return types"
1318 let mut err = struct_span_err!(
1322 "`impl Trait` not allowed outside of {}",
1325 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1328 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1329 attributes to enable",
1337 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1338 TyKind::CVarArgs => {
1339 self.sess.delay_span_bug(
1341 "`TyKind::CVarArgs` should have been handled elsewhere",
1347 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1350 fn lower_opaque_impl_trait(
1353 fn_def_id: Option<DefId>,
1354 origin: hir::OpaqueTyOrigin,
1355 opaque_ty_node_id: NodeId,
1356 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1357 ) -> hir::TyKind<'hir> {
1359 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1360 fn_def_id, opaque_ty_node_id, span,
1363 // Make sure we know that some funky desugaring has been going on here.
1364 // This is a first: there is code in other places like for loop
1365 // desugaring that explicitly states that we don't want to track that.
1366 // Not tracking it makes lints in rustc and clippy very fragile, as
1367 // frequently opened issues show.
1368 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1370 let opaque_ty_def_index =
1371 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1373 self.allocate_hir_id_counter(opaque_ty_node_id);
1375 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1377 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1379 opaque_ty_def_index,
1383 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1385 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1387 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1388 let opaque_ty_item = hir::OpaqueTy {
1389 generics: hir::Generics {
1390 params: lifetime_defs,
1391 where_clause: hir::WhereClause { predicates: &[], span },
1395 impl_trait_fn: fn_def_id,
1399 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1401 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1403 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1404 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1408 /// Registers a new opaque type with the proper `NodeId`s and
1409 /// returns the lowered node-ID for the opaque type.
1410 fn generate_opaque_type(
1412 opaque_ty_node_id: NodeId,
1413 opaque_ty_item: hir::OpaqueTy<'hir>,
1415 opaque_ty_span: Span,
1417 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1418 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1419 // Generate an `type Foo = impl Trait;` declaration.
1420 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1421 let opaque_ty_item = hir::Item {
1422 hir_id: opaque_ty_id,
1423 ident: Ident::invalid(),
1424 attrs: Default::default(),
1425 kind: opaque_ty_item_kind,
1426 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1427 span: opaque_ty_span,
1430 // Insert the item into the global item list. This usually happens
1431 // automatically for all AST items. But this opaque type item
1432 // does not actually exist in the AST.
1433 self.insert_item(opaque_ty_item);
1437 fn lifetimes_from_impl_trait_bounds(
1439 opaque_ty_id: NodeId,
1440 parent_index: DefIndex,
1441 bounds: hir::GenericBounds<'hir>,
1442 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1444 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1445 parent_index={:?}, \
1447 opaque_ty_id, parent_index, bounds,
1450 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1451 // appear in the bounds, excluding lifetimes that are created within the bounds.
1452 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1453 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1454 context: &'r mut LoweringContext<'a, 'hir>,
1456 opaque_ty_id: NodeId,
1457 collect_elided_lifetimes: bool,
1458 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1459 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1460 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1461 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1464 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1467 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1468 intravisit::NestedVisitorMap::None
1471 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1472 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1473 if parameters.parenthesized {
1474 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1475 self.collect_elided_lifetimes = false;
1476 intravisit::walk_generic_args(self, span, parameters);
1477 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1479 intravisit::walk_generic_args(self, span, parameters);
1483 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1484 // Don't collect elided lifetimes used inside of `fn()` syntax.
1485 if let hir::TyKind::BareFn(_) = t.kind {
1486 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1487 self.collect_elided_lifetimes = false;
1489 // Record the "stack height" of `for<'a>` lifetime bindings
1490 // to be able to later fully undo their introduction.
1491 let old_len = self.currently_bound_lifetimes.len();
1492 intravisit::walk_ty(self, t);
1493 self.currently_bound_lifetimes.truncate(old_len);
1495 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1497 intravisit::walk_ty(self, t)
1501 fn visit_poly_trait_ref(
1503 trait_ref: &'v hir::PolyTraitRef<'v>,
1504 modifier: hir::TraitBoundModifier,
1506 // Record the "stack height" of `for<'a>` lifetime bindings
1507 // to be able to later fully undo their introduction.
1508 let old_len = self.currently_bound_lifetimes.len();
1509 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1510 self.currently_bound_lifetimes.truncate(old_len);
1513 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1514 // Record the introduction of 'a in `for<'a> ...`.
1515 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1516 // Introduce lifetimes one at a time so that we can handle
1517 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1518 let lt_name = hir::LifetimeName::Param(param.name);
1519 self.currently_bound_lifetimes.push(lt_name);
1522 intravisit::walk_generic_param(self, param);
1525 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1526 let name = match lifetime.name {
1527 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1528 if self.collect_elided_lifetimes {
1529 // Use `'_` for both implicit and underscore lifetimes in
1530 // `type Foo<'_> = impl SomeTrait<'_>;`.
1531 hir::LifetimeName::Underscore
1536 hir::LifetimeName::Param(_) => lifetime.name,
1538 // Refers to some other lifetime that is "in
1539 // scope" within the type.
1540 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1542 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1545 if !self.currently_bound_lifetimes.contains(&name)
1546 && !self.already_defined_lifetimes.contains(&name)
1548 self.already_defined_lifetimes.insert(name);
1550 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1551 hir_id: self.context.next_id(),
1552 span: lifetime.span,
1556 let def_node_id = self.context.resolver.next_node_id();
1558 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1559 self.context.resolver.definitions().create_def_with_parent(
1562 DefPathData::LifetimeNs(name.ident().name),
1567 let (name, kind) = match name {
1568 hir::LifetimeName::Underscore => (
1569 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1570 hir::LifetimeParamKind::Elided,
1572 hir::LifetimeName::Param(param_name) => {
1573 (param_name, hir::LifetimeParamKind::Explicit)
1575 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1578 self.output_lifetime_params.push(hir::GenericParam {
1581 span: lifetime.span,
1582 pure_wrt_drop: false,
1585 kind: hir::GenericParamKind::Lifetime { kind },
1591 let mut lifetime_collector = ImplTraitLifetimeCollector {
1593 parent: parent_index,
1595 collect_elided_lifetimes: true,
1596 currently_bound_lifetimes: Vec::new(),
1597 already_defined_lifetimes: FxHashSet::default(),
1598 output_lifetimes: Vec::new(),
1599 output_lifetime_params: Vec::new(),
1602 for bound in bounds {
1603 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1606 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1610 self.arena.alloc_from_iter(output_lifetimes),
1611 self.arena.alloc_from_iter(output_lifetime_params),
1615 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1616 let mut ids = SmallVec::<[NodeId; 1]>::new();
1617 if self.sess.features_untracked().impl_trait_in_bindings {
1618 if let Some(ref ty) = l.ty {
1619 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1620 visitor.visit_ty(ty);
1623 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
1624 let ty = l.ty.as_ref().map(|t| {
1627 if self.sess.features_untracked().impl_trait_in_bindings {
1628 ImplTraitContext::OpaqueTy(Some(parent_def_id), hir::OpaqueTyOrigin::Misc)
1630 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1634 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1637 hir_id: self.lower_node_id(l.id),
1639 pat: self.lower_pat(&l.pat),
1642 attrs: l.attrs.clone(),
1643 source: hir::LocalSource::Normal,
1649 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1650 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1651 // as they are not explicit in HIR/Ty function signatures.
1652 // (instead, the `c_variadic` flag is set to `true`)
1653 let mut inputs = &decl.inputs[..];
1654 if decl.c_variadic() {
1655 inputs = &inputs[..inputs.len() - 1];
1657 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1658 PatKind::Ident(_, ident, _) => ident,
1659 _ => Ident::new(kw::Invalid, param.pat.span),
1663 // Lowers a function declaration.
1665 // `decl`: the unlowered (AST) function declaration.
1666 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1667 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1668 // `make_ret_async` is also `Some`.
1669 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1670 // This guards against trait declarations and implementations where `impl Trait` is
1672 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1673 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1674 // return type `impl Trait` item.
1678 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1679 impl_trait_return_allow: bool,
1680 make_ret_async: Option<NodeId>,
1681 ) -> &'hir hir::FnDecl<'hir> {
1685 in_band_ty_params: {:?}, \
1686 impl_trait_return_allow: {}, \
1687 make_ret_async: {:?})",
1688 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1690 let lt_mode = if make_ret_async.is_some() {
1691 // In `async fn`, argument-position elided lifetimes
1692 // must be transformed into fresh generic parameters so that
1693 // they can be applied to the opaque `impl Trait` return type.
1694 AnonymousLifetimeMode::CreateParameter
1696 self.anonymous_lifetime_mode
1699 let c_variadic = decl.c_variadic();
1701 // Remember how many lifetimes were already around so that we can
1702 // only look at the lifetime parameters introduced by the arguments.
1703 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1704 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1705 // as they are not explicit in HIR/Ty function signatures.
1706 // (instead, the `c_variadic` flag is set to `true`)
1707 let mut inputs = &decl.inputs[..];
1709 inputs = &inputs[..inputs.len() - 1];
1711 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1712 if let Some((_, ibty)) = &mut in_band_ty_params {
1713 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1715 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1720 let output = if let Some(ret_id) = make_ret_async {
1721 self.lower_async_fn_ret_ty(
1723 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1728 FnRetTy::Ty(ref ty) => {
1729 let context = match in_band_ty_params {
1730 Some((def_id, _)) if impl_trait_return_allow => {
1731 ImplTraitContext::OpaqueTy(Some(def_id), hir::OpaqueTyOrigin::FnReturn)
1733 _ => ImplTraitContext::disallowed(),
1735 hir::FnRetTy::Return(self.lower_ty(ty, context))
1737 FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span),
1741 self.arena.alloc(hir::FnDecl {
1745 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1746 let is_mutable_pat = match arg.pat.kind {
1747 PatKind::Ident(BindingMode::ByValue(mt), _, _)
1748 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
1753 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1754 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1755 // Given we are only considering `ImplicitSelf` types, we needn't consider
1756 // the case where we have a mutable pattern to a reference as that would
1757 // no longer be an `ImplicitSelf`.
1758 TyKind::Rptr(_, ref mt)
1759 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1761 hir::ImplicitSelfKind::MutRef
1763 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1764 hir::ImplicitSelfKind::ImmRef
1766 _ => hir::ImplicitSelfKind::None,
1772 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1773 // combined with the following definition of `OpaqueTy`:
1775 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1777 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1778 // `output`: unlowered output type (`T` in `-> T`)
1779 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1780 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1781 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1782 fn lower_async_fn_ret_ty(
1786 opaque_ty_node_id: NodeId,
1787 ) -> hir::FnRetTy<'hir> {
1789 "lower_async_fn_ret_ty(\
1792 opaque_ty_node_id={:?})",
1793 output, fn_def_id, opaque_ty_node_id,
1796 let span = output.span();
1798 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1800 let opaque_ty_def_index =
1801 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1803 self.allocate_hir_id_counter(opaque_ty_node_id);
1805 // When we create the opaque type for this async fn, it is going to have
1806 // to capture all the lifetimes involved in the signature (including in the
1807 // return type). This is done by introducing lifetime parameters for:
1809 // - all the explicitly declared lifetimes from the impl and function itself;
1810 // - all the elided lifetimes in the fn arguments;
1811 // - all the elided lifetimes in the return type.
1813 // So for example in this snippet:
1816 // impl<'a> Foo<'a> {
1817 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1818 // // ^ '0 ^ '1 ^ '2
1819 // // elided lifetimes used below
1824 // we would create an opaque type like:
1827 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1830 // and we would then desugar `bar` to the equivalent of:
1833 // impl<'a> Foo<'a> {
1834 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1838 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1839 // this is because the elided lifetimes from the return type
1840 // should be figured out using the ordinary elision rules, and
1841 // this desugaring achieves that.
1843 // The variable `input_lifetimes_count` tracks the number of
1844 // lifetime parameters to the opaque type *not counting* those
1845 // lifetimes elided in the return type. This includes those
1846 // that are explicitly declared (`in_scope_lifetimes`) and
1847 // those elided lifetimes we found in the arguments (current
1848 // content of `lifetimes_to_define`). Next, we will process
1849 // the return type, which will cause `lifetimes_to_define` to
1851 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
1853 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
1854 // We have to be careful to get elision right here. The
1855 // idea is that we create a lifetime parameter for each
1856 // lifetime in the return type. So, given a return type
1857 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1858 // Future<Output = &'1 [ &'2 u32 ]>`.
1860 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1861 // hence the elision takes place at the fn site.
1862 let future_bound = this
1863 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
1864 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1867 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1869 // Calculate all the lifetimes that should be captured
1870 // by the opaque type. This should include all in-scope
1871 // lifetime parameters, including those defined in-band.
1873 // Note: this must be done after lowering the output type,
1874 // as the output type may introduce new in-band lifetimes.
1875 let lifetime_params: Vec<(Span, ParamName)> = this
1879 .map(|name| (name.ident().span, name))
1880 .chain(this.lifetimes_to_define.iter().cloned())
1883 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
1884 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
1885 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
1887 let generic_params =
1888 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
1889 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
1892 let opaque_ty_item = hir::OpaqueTy {
1893 generics: hir::Generics {
1894 params: generic_params,
1895 where_clause: hir::WhereClause { predicates: &[], span },
1898 bounds: arena_vec![this; future_bound],
1899 impl_trait_fn: Some(fn_def_id),
1900 origin: hir::OpaqueTyOrigin::AsyncFn,
1903 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
1905 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1907 (opaque_ty_id, lifetime_params)
1910 // As documented above on the variable
1911 // `input_lifetimes_count`, we need to create the lifetime
1912 // arguments to our opaque type. Continuing with our example,
1913 // we're creating the type arguments for the return type:
1916 // Bar<'a, 'b, '0, '1, '_>
1919 // For the "input" lifetime parameters, we wish to create
1920 // references to the parameters themselves, including the
1921 // "implicit" ones created from parameter types (`'a`, `'b`,
1924 // For the "output" lifetime parameters, we just want to
1926 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
1928 .map(|&(span, hir_name)| {
1929 // Input lifetime like `'a` or `'1`:
1930 GenericArg::Lifetime(hir::Lifetime {
1931 hir_id: self.next_id(),
1933 name: hir::LifetimeName::Param(hir_name),
1937 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
1938 // Output lifetime like `'_`.
1939 GenericArg::Lifetime(hir::Lifetime {
1940 hir_id: self.next_id(),
1942 name: hir::LifetimeName::Implicit,
1944 let generic_args = self.arena.alloc_from_iter(generic_args);
1946 // Create the `Foo<...>` reference itself. Note that the `type
1947 // Foo = impl Trait` is, internally, created as a child of the
1948 // async fn, so the *type parameters* are inherited. It's
1949 // only the lifetime parameters that we must supply.
1950 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
1951 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1952 hir::FnRetTy::Return(self.arena.alloc(opaque_ty))
1955 /// Transforms `-> T` into `Future<Output = T>`
1956 fn lower_async_fn_output_type_to_future_bound(
1961 ) -> hir::GenericBound<'hir> {
1962 // Compute the `T` in `Future<Output = T>` from the return type.
1963 let output_ty = match output {
1964 FnRetTy::Ty(ty) => {
1965 // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the
1966 // `impl Future` opaque type that `async fn` implicitly
1969 ImplTraitContext::OpaqueTy(Some(fn_def_id), hir::OpaqueTyOrigin::FnReturn);
1970 self.lower_ty(ty, context)
1972 FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1976 let future_params = self.arena.alloc(hir::GenericArgs {
1978 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1979 parenthesized: false,
1982 // ::std::future::Future<future_params>
1984 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
1986 hir::GenericBound::Trait(
1988 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
1989 bound_generic_params: &[],
1992 hir::TraitBoundModifier::None,
1996 fn lower_param_bound(
1999 itctx: ImplTraitContext<'_, 'hir>,
2000 ) -> hir::GenericBound<'hir> {
2002 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2003 self.lower_poly_trait_ref(ty, itctx),
2004 self.lower_trait_bound_modifier(modifier),
2006 GenericBound::Outlives(ref lifetime) => {
2007 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2012 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2013 let span = l.ident.span;
2015 ident if ident.name == kw::StaticLifetime => {
2016 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2018 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2019 AnonymousLifetimeMode::CreateParameter => {
2020 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2021 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2024 AnonymousLifetimeMode::PassThrough => {
2025 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2028 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2031 self.maybe_collect_in_band_lifetime(ident);
2032 let param_name = ParamName::Plain(ident);
2033 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2038 fn new_named_lifetime(
2042 name: hir::LifetimeName,
2043 ) -> hir::Lifetime {
2044 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2047 fn lower_generic_params_mut<'s>(
2049 params: &'s [GenericParam],
2050 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2051 mut itctx: ImplTraitContext<'s, 'hir>,
2052 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2055 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2058 fn lower_generic_params(
2060 params: &[GenericParam],
2061 add_bounds: &NodeMap<Vec<GenericBound>>,
2062 itctx: ImplTraitContext<'_, 'hir>,
2063 ) -> &'hir [hir::GenericParam<'hir>] {
2064 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2067 fn lower_generic_param(
2069 param: &GenericParam,
2070 add_bounds: &NodeMap<Vec<GenericBound>>,
2071 mut itctx: ImplTraitContext<'_, 'hir>,
2072 ) -> hir::GenericParam<'hir> {
2073 let mut bounds: Vec<_> = self
2074 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2075 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2078 let (name, kind) = match param.kind {
2079 GenericParamKind::Lifetime => {
2080 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2081 self.is_collecting_in_band_lifetimes = false;
2084 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2085 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2087 let param_name = match lt.name {
2088 hir::LifetimeName::Param(param_name) => param_name,
2089 hir::LifetimeName::Implicit
2090 | hir::LifetimeName::Underscore
2091 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2092 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2095 "object-lifetime-default should not occur here",
2098 hir::LifetimeName::Error => ParamName::Error,
2102 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2104 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2108 GenericParamKind::Type { ref default, .. } => {
2109 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2110 if !add_bounds.is_empty() {
2111 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2112 bounds.extend(params);
2115 let kind = hir::GenericParamKind::Type {
2116 default: default.as_ref().map(|x| {
2119 ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc),
2125 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2126 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2130 (hir::ParamName::Plain(param.ident), kind)
2132 GenericParamKind::Const { ref ty } => {
2134 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2135 this.lower_ty(&ty, ImplTraitContext::disallowed())
2138 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty })
2143 hir_id: self.lower_node_id(param.id),
2145 span: param.ident.span,
2146 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2147 attrs: self.lower_attrs(¶m.attrs),
2148 bounds: self.arena.alloc_from_iter(bounds),
2156 itctx: ImplTraitContext<'_, 'hir>,
2157 ) -> hir::TraitRef<'hir> {
2158 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2159 hir::QPath::Resolved(None, path) => path,
2160 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2162 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2165 fn lower_poly_trait_ref(
2168 mut itctx: ImplTraitContext<'_, 'hir>,
2169 ) -> hir::PolyTraitRef<'hir> {
2170 let bound_generic_params = self.lower_generic_params(
2171 &p.bound_generic_params,
2172 &NodeMap::default(),
2175 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2176 this.lower_trait_ref(&p.trait_ref, itctx)
2179 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2182 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2183 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2186 fn lower_param_bounds(
2188 bounds: &[GenericBound],
2189 itctx: ImplTraitContext<'_, 'hir>,
2190 ) -> hir::GenericBounds<'hir> {
2191 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2194 fn lower_param_bounds_mut<'s>(
2196 bounds: &'s [GenericBound],
2197 mut itctx: ImplTraitContext<'s, 'hir>,
2198 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2199 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2202 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2203 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2206 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2207 let mut stmts = vec![];
2208 let mut expr: Option<&'hir _> = None;
2210 for (index, stmt) in b.stmts.iter().enumerate() {
2211 if index == b.stmts.len() - 1 {
2212 if let StmtKind::Expr(ref e) = stmt.kind {
2213 expr = Some(self.lower_expr(e));
2215 stmts.extend(self.lower_stmt(stmt));
2218 stmts.extend(self.lower_stmt(stmt));
2223 hir_id: self.lower_node_id(b.id),
2224 stmts: self.arena.alloc_from_iter(stmts),
2226 rules: self.lower_block_check_mode(&b.rules),
2232 /// Lowers a block directly to an expression, presuming that it
2233 /// has no attributes and is not targeted by a `break`.
2234 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2235 let block = self.lower_block(b, false);
2236 self.expr_block(block, AttrVec::new())
2239 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2240 self.with_new_scopes(|this| hir::AnonConst {
2241 hir_id: this.lower_node_id(c.id),
2242 body: this.lower_const_body(c.value.span, Some(&c.value)),
2246 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2247 let kind = match s.kind {
2248 StmtKind::Local(ref l) => {
2249 let (l, item_ids) = self.lower_local(l);
2250 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2253 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2254 self.stmt(s.span, hir::StmtKind::Item(item_id))
2259 hir_id: self.lower_node_id(s.id),
2260 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2266 StmtKind::Item(ref it) => {
2267 // Can only use the ID once.
2268 let mut id = Some(s.id);
2275 .map(|id| self.lower_node_id(id))
2276 .unwrap_or_else(|| self.next_id());
2278 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2282 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2283 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2284 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2286 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2289 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2291 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2292 BlockCheckMode::Unsafe(u) => {
2293 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2298 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2300 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2301 UserProvided => hir::UnsafeSource::UserProvided,
2305 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2307 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2308 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2310 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2311 // placeholder for compilation to proceed.
2312 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2313 hir::TraitBoundModifier::Maybe
2318 // Helper methods for building HIR.
2320 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2321 hir::Stmt { span, kind, hir_id: self.next_id() }
2324 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2325 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2332 init: Option<&'hir hir::Expr<'hir>>,
2333 pat: &'hir hir::Pat<'hir>,
2334 source: hir::LocalSource,
2335 ) -> hir::Stmt<'hir> {
2336 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2337 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2340 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2341 self.block_all(expr.span, &[], Some(expr))
2347 stmts: &'hir [hir::Stmt<'hir>],
2348 expr: Option<&'hir hir::Expr<'hir>>,
2349 ) -> &'hir hir::Block<'hir> {
2350 let blk = hir::Block {
2353 hir_id: self.next_id(),
2354 rules: hir::BlockCheckMode::DefaultBlock,
2356 targeted_by_break: false,
2358 self.arena.alloc(blk)
2361 /// Constructs a `true` or `false` literal pattern.
2362 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2363 let expr = self.expr_bool(span, val);
2364 self.pat(span, hir::PatKind::Lit(expr))
2367 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2368 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
2371 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2372 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
2375 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2376 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
2379 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2380 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
2386 components: &[Symbol],
2387 subpats: &'hir [&'hir hir::Pat<'hir>],
2388 ) -> &'hir hir::Pat<'hir> {
2389 let path = self.std_path(span, components, None, true);
2390 let qpath = hir::QPath::Resolved(None, path);
2391 let pt = if subpats.is_empty() {
2392 hir::PatKind::Path(qpath)
2394 hir::PatKind::TupleStruct(qpath, subpats, None)
2399 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2400 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2403 fn pat_ident_binding_mode(
2407 bm: hir::BindingAnnotation,
2408 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2409 let hir_id = self.next_id();
2412 self.arena.alloc(hir::Pat {
2414 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2421 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2422 self.pat(span, hir::PatKind::Wild)
2425 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2426 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
2429 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
2430 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
2431 /// The path is also resolved according to `is_value`.
2435 components: &[Symbol],
2436 params: Option<&'hir hir::GenericArgs<'hir>>,
2438 ) -> &'hir hir::Path<'hir> {
2439 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
2440 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
2442 let mut segments: Vec<_> = path
2446 let res = self.expect_full_res(segment.id);
2448 ident: segment.ident,
2449 hir_id: Some(self.lower_node_id(segment.id)),
2450 res: Some(self.lower_res(res)),
2456 segments.last_mut().unwrap().args = params;
2458 self.arena.alloc(hir::Path {
2460 res: res.map_id(|_| panic!("unexpected `NodeId`")),
2461 segments: self.arena.alloc_from_iter(segments),
2467 mut hir_id: hir::HirId,
2469 qpath: hir::QPath<'hir>,
2470 ) -> hir::Ty<'hir> {
2471 let kind = match qpath {
2472 hir::QPath::Resolved(None, path) => {
2473 // Turn trait object paths into `TyKind::TraitObject` instead.
2475 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
2476 let principal = hir::PolyTraitRef {
2477 bound_generic_params: &[],
2478 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2482 // The original ID is taken by the `PolyTraitRef`,
2483 // so the `Ty` itself needs a different one.
2484 hir_id = self.next_id();
2485 hir::TyKind::TraitObject(
2486 arena_vec![self; principal],
2487 self.elided_dyn_bound(span),
2490 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2493 _ => hir::TyKind::Path(qpath),
2496 hir::Ty { hir_id, kind, span }
2499 /// Invoked to create the lifetime argument for a type `&T`
2500 /// with no explicit lifetime.
2501 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2502 match self.anonymous_lifetime_mode {
2503 // Intercept when we are in an impl header or async fn and introduce an in-band
2505 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2507 AnonymousLifetimeMode::CreateParameter => {
2508 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2510 hir_id: self.next_id(),
2512 name: hir::LifetimeName::Param(fresh_name),
2516 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2518 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2522 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2523 /// return a "error lifetime".
2524 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2525 let (id, msg, label) = match id {
2526 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2529 self.resolver.next_node_id(),
2530 "`&` without an explicit lifetime name cannot be used here",
2531 "explicit lifetime name needed here",
2535 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2536 err.span_label(span, label);
2539 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2542 /// Invoked to create the lifetime argument(s) for a path like
2543 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2544 /// sorts of cases are deprecated. This may therefore report a warning or an
2545 /// error, depending on the mode.
2546 fn elided_path_lifetimes<'s>(
2550 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2551 (0..count).map(move |_| self.elided_path_lifetime(span))
2554 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2555 match self.anonymous_lifetime_mode {
2556 AnonymousLifetimeMode::CreateParameter => {
2557 // We should have emitted E0726 when processing this path above
2559 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2560 let id = self.resolver.next_node_id();
2561 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2563 // `PassThrough` is the normal case.
2564 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2565 // is unsuitable here, as these can occur from missing lifetime parameters in a
2566 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2567 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2568 // later, at which point a suitable error will be emitted.
2569 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2570 self.new_implicit_lifetime(span)
2575 /// Invoked to create the lifetime argument(s) for an elided trait object
2576 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2577 /// when the bound is written, even if it is written with `'_` like in
2578 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2579 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2580 match self.anonymous_lifetime_mode {
2581 // NB. We intentionally ignore the create-parameter mode here.
2582 // and instead "pass through" to resolve-lifetimes, which will apply
2583 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2584 // do not act like other elided lifetimes. In other words, given this:
2586 // impl Foo for Box<dyn Debug>
2588 // we do not introduce a fresh `'_` to serve as the bound, but instead
2589 // ultimately translate to the equivalent of:
2591 // impl Foo for Box<dyn Debug + 'static>
2593 // `resolve_lifetime` has the code to make that happen.
2594 AnonymousLifetimeMode::CreateParameter => {}
2596 AnonymousLifetimeMode::ReportError => {
2597 // ReportError applies to explicit use of `'_`.
2600 // This is the normal case.
2601 AnonymousLifetimeMode::PassThrough => {}
2604 let r = hir::Lifetime {
2605 hir_id: self.next_id(),
2607 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2609 debug!("elided_dyn_bound: r={:?}", r);
2613 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2614 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2617 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2618 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2619 // call site which do not have a macro backtrace. See #61963.
2620 let is_macro_callsite = self
2623 .span_to_snippet(span)
2624 .map(|snippet| snippet.starts_with("#["))
2626 if !is_macro_callsite {
2627 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2631 "trait objects without an explicit `dyn` are deprecated",
2632 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2638 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2639 // Sorting by span ensures that we get things in order within a
2640 // file, and also puts the files in a sensible order.
2641 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2642 body_ids.sort_by_key(|b| bodies[b].value.span);
2646 /// Helper struct for delayed construction of GenericArgs.
2647 struct GenericArgsCtor<'hir> {
2648 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2649 bindings: &'hir [hir::TypeBinding<'hir>],
2650 parenthesized: bool,
2653 impl<'hir> GenericArgsCtor<'hir> {
2654 fn is_empty(&self) -> bool {
2655 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2658 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2660 args: arena.alloc_from_iter(self.args),
2661 bindings: self.bindings,
2662 parenthesized: self.parenthesized,