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;
40 use rustc::lint::builtin;
41 use rustc::{bug, span_bug};
42 use rustc_data_structures::captures::Captures;
43 use rustc_data_structures::fx::FxHashSet;
44 use rustc_data_structures::sync::Lrc;
45 use rustc_error_codes::*;
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::{BuiltinLintDiagnostics, LintBuffer};
55 use rustc_session::node_id::NodeMap;
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::print::pprust;
65 use syntax::sess::ParseSess;
66 use syntax::token::{self, Nonterminal, Token};
67 use syntax::tokenstream::{TokenStream, TokenTree};
68 use syntax::visit::{self, Visitor};
69 use syntax::walk_list;
71 use log::{debug, trace};
72 use smallvec::{smallvec, SmallVec};
73 use std::collections::BTreeMap;
76 macro_rules! arena_vec {
77 ($this:expr; $($x:expr),*) => ({
79 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
88 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
90 struct LoweringContext<'a, 'hir: 'a> {
91 crate_root: Option<Symbol>,
93 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
96 resolver: &'a mut dyn Resolver,
98 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
99 /// if we don't have this function pointer. To avoid that dependency so that
100 /// librustc is independent of the parser, we use dynamic dispatch here.
101 nt_to_tokenstream: NtToTokenstream,
103 /// Used to allocate HIR nodes
104 arena: &'hir Arena<'hir>,
106 /// The items being lowered are collected here.
107 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
109 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
110 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
111 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
112 exported_macros: Vec<hir::MacroDef<'hir>>,
113 non_exported_macro_attrs: Vec<ast::Attribute>,
115 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
117 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
119 generator_kind: Option<hir::GeneratorKind>,
121 /// Used to get the current `fn`'s def span to point to when using `await`
122 /// outside of an `async fn`.
123 current_item: Option<Span>,
125 catch_scopes: Vec<NodeId>,
126 loop_scopes: Vec<NodeId>,
127 is_in_loop_condition: bool,
128 is_in_trait_impl: bool,
129 is_in_dyn_type: bool,
131 /// What to do when we encounter either an "anonymous lifetime
132 /// reference". The term "anonymous" is meant to encompass both
133 /// `'_` lifetimes as well as fully elided cases where nothing is
134 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
135 anonymous_lifetime_mode: AnonymousLifetimeMode,
137 /// Used to create lifetime definitions from in-band lifetime usages.
138 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
139 /// When a named lifetime is encountered in a function or impl header and
140 /// has not been defined
141 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
142 /// to this list. The results of this list are then added to the list of
143 /// lifetime definitions in the corresponding impl or function generics.
144 lifetimes_to_define: Vec<(Span, ParamName)>,
146 /// `true` if in-band lifetimes are being collected. This is used to
147 /// indicate whether or not we're in a place where new lifetimes will result
148 /// in in-band lifetime definitions, such a function or an impl header,
149 /// including implicit lifetimes from `impl_header_lifetime_elision`.
150 is_collecting_in_band_lifetimes: bool,
152 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
153 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
154 /// against this list to see if it is already in-scope, or if a definition
155 /// needs to be created for it.
157 /// We always store a `modern()` version of the param-name in this
159 in_scope_lifetimes: Vec<ParamName>,
161 current_module: hir::HirId,
163 type_def_lifetime_params: DefIdMap<usize>,
165 current_hir_id_owner: Vec<(DefIndex, u32)>,
166 item_local_id_counters: NodeMap<u32>,
167 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
169 allow_try_trait: Option<Lrc<[Symbol]>>,
170 allow_gen_future: Option<Lrc<[Symbol]>>,
174 fn def_key(&mut self, id: DefId) -> DefKey;
176 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
178 /// Obtains resolution for a `NodeId` with a single resolution.
179 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
181 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
182 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
184 /// Obtains resolution for a label with the given `NodeId`.
185 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
187 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
188 /// This should only return `None` during testing.
189 fn definitions(&mut self) -> &mut Definitions;
191 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
192 /// resolves it based on `is_value`.
196 crate_root: Option<Symbol>,
197 components: &[Symbol],
199 ) -> (ast::Path, Res<NodeId>);
201 fn lint_buffer(&mut self) -> &mut LintBuffer;
203 fn next_node_id(&mut self) -> NodeId;
206 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
208 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
209 /// and if so, what meaning it has.
211 enum ImplTraitContext<'b, 'a> {
212 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
213 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
214 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
216 /// Newly generated parameters should be inserted into the given `Vec`.
217 Universal(&'b mut Vec<hir::GenericParam<'a>>),
219 /// Treat `impl Trait` as shorthand for a new opaque type.
220 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
221 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
223 /// We optionally store a `DefId` for the parent item here so we can look up necessary
224 /// information later. It is `None` when no information about the context should be stored
225 /// (e.g., for consts and statics).
226 OpaqueTy(Option<DefId> /* fn def-ID */),
228 /// `impl Trait` is not accepted in this position.
229 Disallowed(ImplTraitPosition),
232 /// Position in which `impl Trait` is disallowed.
233 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
234 enum ImplTraitPosition {
235 /// Disallowed in `let` / `const` / `static` bindings.
238 /// All other posiitons.
242 impl<'a> ImplTraitContext<'_, 'a> {
244 fn disallowed() -> Self {
245 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
248 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
249 use self::ImplTraitContext::*;
251 Universal(params) => Universal(params),
252 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
253 Disallowed(pos) => Disallowed(*pos),
258 pub fn lower_crate<'a, 'hir>(
260 dep_graph: &'a DepGraph,
262 resolver: &'a mut dyn Resolver,
263 nt_to_tokenstream: NtToTokenstream,
264 arena: &'hir Arena<'hir>,
265 ) -> hir::Crate<'hir> {
266 // We're constructing the HIR here; we don't care what we will
267 // read, since we haven't even constructed the *input* to
269 dep_graph.assert_ignored();
271 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
274 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
279 items: BTreeMap::new(),
280 trait_items: BTreeMap::new(),
281 impl_items: BTreeMap::new(),
282 bodies: BTreeMap::new(),
283 trait_impls: BTreeMap::new(),
284 modules: BTreeMap::new(),
285 exported_macros: Vec::new(),
286 non_exported_macro_attrs: Vec::new(),
287 catch_scopes: Vec::new(),
288 loop_scopes: Vec::new(),
289 is_in_loop_condition: false,
290 is_in_trait_impl: false,
291 is_in_dyn_type: false,
292 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
293 type_def_lifetime_params: Default::default(),
294 current_module: hir::CRATE_HIR_ID,
295 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
296 item_local_id_counters: Default::default(),
297 node_id_to_hir_id: IndexVec::new(),
298 generator_kind: None,
300 lifetimes_to_define: Vec::new(),
301 is_collecting_in_band_lifetimes: false,
302 in_scope_lifetimes: Vec::new(),
303 allow_try_trait: Some([sym::try_trait][..].into()),
304 allow_gen_future: Some([sym::gen_future][..].into()),
309 #[derive(Copy, Clone, PartialEq)]
311 /// Any path in a type context.
313 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
315 /// The `module::Type` in `module::Type::method` in an expression.
319 enum ParenthesizedGenericArgs {
324 /// What to do when we encounter an **anonymous** lifetime
325 /// reference. Anonymous lifetime references come in two flavors. You
326 /// have implicit, or fully elided, references to lifetimes, like the
327 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
328 /// or `Ref<'_, T>`. These often behave the same, but not always:
330 /// - certain usages of implicit references are deprecated, like
331 /// `Ref<T>`, and we sometimes just give hard errors in those cases
333 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
334 /// the same as `Box<dyn Foo + '_>`.
336 /// We describe the effects of the various modes in terms of three cases:
338 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
339 /// of a `&` (e.g., the missing lifetime in something like `&T`)
340 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
341 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
342 /// elided bounds follow special rules. Note that this only covers
343 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
344 /// '_>` is a case of "modern" elision.
345 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
346 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
347 /// non-deprecated equivalent.
349 /// Currently, the handling of lifetime elision is somewhat spread out
350 /// between HIR lowering and -- as described below -- the
351 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
352 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
353 /// everything into HIR lowering.
354 #[derive(Copy, Clone, Debug)]
355 enum AnonymousLifetimeMode {
356 /// For **Modern** cases, create a new anonymous region parameter
357 /// and reference that.
359 /// For **Dyn Bound** cases, pass responsibility to
360 /// `resolve_lifetime` code.
362 /// For **Deprecated** cases, report an error.
365 /// Give a hard error when either `&` or `'_` is written. Used to
366 /// rule out things like `where T: Foo<'_>`. Does not imply an
367 /// error on default object bounds (e.g., `Box<dyn Foo>`).
370 /// Pass responsibility to `resolve_lifetime` code for all cases.
374 struct ImplTraitTypeIdVisitor<'a> {
375 ids: &'a mut SmallVec<[NodeId; 1]>,
378 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
379 fn visit_ty(&mut self, ty: &Ty) {
381 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
383 TyKind::ImplTrait(id, _) => self.ids.push(id),
386 visit::walk_ty(self, ty);
389 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
390 if let Some(ref p) = path_segment.args {
391 if let GenericArgs::Parenthesized(_) = **p {
395 visit::walk_path_segment(self, path_span, path_segment)
399 impl<'a, 'hir> LoweringContext<'a, 'hir> {
400 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
401 /// Full-crate AST visitor that inserts into a fresh
402 /// `LoweringContext` any information that may be
403 /// needed from arbitrary locations in the crate,
404 /// e.g., the number of lifetime generic parameters
405 /// declared for every type and trait definition.
406 struct MiscCollector<'tcx, 'lowering, 'hir> {
407 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
408 hir_id_owner: Option<NodeId>,
411 impl MiscCollector<'_, '_, '_> {
412 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
414 UseTreeKind::Simple(_, id1, id2) => {
415 for &id in &[id1, id2] {
416 self.lctx.resolver.definitions().create_def_with_parent(
423 self.lctx.allocate_hir_id_counter(id);
426 UseTreeKind::Glob => (),
427 UseTreeKind::Nested(ref trees) => {
428 for &(ref use_tree, id) in trees {
429 let hir_id = self.lctx.allocate_hir_id_counter(id);
430 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
436 fn with_hir_id_owner<T>(
438 owner: Option<NodeId>,
439 f: impl FnOnce(&mut Self) -> T,
441 let old = mem::replace(&mut self.hir_id_owner, owner);
443 self.hir_id_owner = old;
448 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
449 fn visit_pat(&mut self, p: &'tcx Pat) {
450 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
451 // Doesn't generate a HIR node
452 } else if let Some(owner) = self.hir_id_owner {
453 self.lctx.lower_node_id_with_owner(p.id, owner);
456 visit::walk_pat(self, p)
459 fn visit_item(&mut self, item: &'tcx Item) {
460 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
463 ItemKind::Struct(_, ref generics)
464 | ItemKind::Union(_, ref generics)
465 | ItemKind::Enum(_, ref generics)
466 | ItemKind::TyAlias(_, ref generics)
467 | ItemKind::Trait(_, _, ref generics, ..) => {
468 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
472 .filter(|param| match param.kind {
473 ast::GenericParamKind::Lifetime { .. } => true,
477 self.lctx.type_def_lifetime_params.insert(def_id, count);
479 ItemKind::Use(ref use_tree) => {
480 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
485 self.with_hir_id_owner(Some(item.id), |this| {
486 visit::walk_item(this, item);
490 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
491 self.lctx.allocate_hir_id_counter(item.id);
494 AssocItemKind::Fn(_, None) => {
495 // Ignore patterns in trait methods without bodies
496 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
498 _ => self.with_hir_id_owner(Some(item.id), |this| {
499 visit::walk_trait_item(this, item);
504 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
505 self.lctx.allocate_hir_id_counter(item.id);
506 self.with_hir_id_owner(Some(item.id), |this| {
507 visit::walk_impl_item(this, item);
511 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
512 // Ignore patterns in foreign items
513 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
516 fn visit_ty(&mut self, t: &'tcx Ty) {
518 // Mirrors the case in visit::walk_ty
519 TyKind::BareFn(ref f) => {
520 walk_list!(self, visit_generic_param, &f.generic_params);
521 // Mirrors visit::walk_fn_decl
522 for parameter in &f.decl.inputs {
523 // We don't lower the ids of argument patterns
524 self.with_hir_id_owner(None, |this| {
525 this.visit_pat(¶meter.pat);
527 self.visit_ty(¶meter.ty)
529 self.visit_fn_ret_ty(&f.decl.output)
531 _ => visit::walk_ty(self, t),
536 self.lower_node_id(CRATE_NODE_ID);
537 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
539 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
540 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
542 let module = self.lower_mod(&c.module);
543 let attrs = self.lower_attrs(&c.attrs);
544 let body_ids = body_ids(&self.bodies);
546 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
552 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
553 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
555 trait_items: self.trait_items,
556 impl_items: self.impl_items,
559 trait_impls: self.trait_impls,
560 modules: self.modules,
564 fn insert_item(&mut self, item: hir::Item<'hir>) {
565 let id = item.hir_id;
566 // FIXME: Use `debug_asset-rt`.
567 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
568 self.items.insert(id, item);
569 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
572 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
573 // Set up the counter if needed.
574 self.item_local_id_counters.entry(owner).or_insert(0);
575 // Always allocate the first `HirId` for the owner itself.
576 let lowered = self.lower_node_id_with_owner(owner, owner);
577 debug_assert_eq!(lowered.local_id.as_u32(), 0);
581 fn lower_node_id_generic(
584 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
586 if ast_node_id == DUMMY_NODE_ID {
587 return hir::DUMMY_HIR_ID;
590 let min_size = ast_node_id.as_usize() + 1;
592 if min_size > self.node_id_to_hir_id.len() {
593 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
596 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
598 if existing_hir_id == hir::DUMMY_HIR_ID {
599 // Generate a new `HirId`.
600 let hir_id = alloc_hir_id(self);
601 self.node_id_to_hir_id[ast_node_id] = hir_id;
609 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
611 .item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
623 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
627 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
628 /// the `LoweringContext`'s `NodeId => HirId` map.
629 /// Take care not to call this method if the resulting `HirId` is then not
630 /// actually used in the HIR, as that would trigger an assertion in the
631 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
632 /// properly. Calling the method twice with the same `NodeId` is fine though.
633 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let &mut (def_index, ref mut local_id_counter) =
636 this.current_hir_id_owner.last_mut().unwrap();
637 let local_id = *local_id_counter;
638 *local_id_counter += 1;
639 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
643 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
644 self.lower_node_id_generic(ast_node_id, |this| {
645 let local_id_counter = this
646 .item_local_id_counters
648 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
649 let local_id = *local_id_counter;
651 // We want to be sure not to modify the counter in the map while it
652 // is also on the stack. Otherwise we'll get lost updates when writing
653 // back from the stack to the map.
654 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
656 *local_id_counter += 1;
657 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
658 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
659 that do not belong to the current owner",
662 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
666 fn next_id(&mut self) -> hir::HirId {
667 let node_id = self.resolver.next_node_id();
668 self.lower_node_id(node_id)
671 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
673 self.lower_node_id_generic(id, |_| {
674 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
679 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
680 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
681 if pr.unresolved_segments() != 0 {
682 bug!("path not fully resolved: {:?}", pr);
688 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
689 self.resolver.get_import_res(id).present_items()
692 fn diagnostic(&self) -> &rustc_errors::Handler {
693 self.sess.diagnostic()
696 /// Reuses the span but adds information like the kind of the desugaring and features that are
697 /// allowed inside this span.
698 fn mark_span_with_reason(
700 reason: DesugaringKind,
702 allow_internal_unstable: Option<Lrc<[Symbol]>>,
704 span.fresh_expansion(ExpnData {
705 allow_internal_unstable,
706 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
710 fn with_anonymous_lifetime_mode<R>(
712 anonymous_lifetime_mode: AnonymousLifetimeMode,
713 op: impl FnOnce(&mut Self) -> R,
716 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
717 anonymous_lifetime_mode,
719 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
720 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
721 let result = op(self);
722 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
724 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
725 old_anonymous_lifetime_mode
730 /// Creates a new `hir::GenericParam` for every new lifetime and
731 /// type parameter encountered while evaluating `f`. Definitions
732 /// are created with the parent provided. If no `parent_id` is
733 /// provided, no definitions will be returned.
735 /// Presuming that in-band lifetimes are enabled, then
736 /// `self.anonymous_lifetime_mode` will be updated to match the
737 /// parameter while `f` is running (and restored afterwards).
738 fn collect_in_band_defs<T>(
741 anonymous_lifetime_mode: AnonymousLifetimeMode,
742 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
743 ) -> (Vec<hir::GenericParam<'hir>>, T) {
744 assert!(!self.is_collecting_in_band_lifetimes);
745 assert!(self.lifetimes_to_define.is_empty());
746 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
748 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
749 self.is_collecting_in_band_lifetimes = true;
751 let (in_band_ty_params, res) = f(self);
753 self.is_collecting_in_band_lifetimes = false;
754 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
756 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
758 let params = lifetimes_to_define
760 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
761 .chain(in_band_ty_params.into_iter())
767 /// Converts a lifetime into a new generic parameter.
768 fn lifetime_to_generic_param(
772 parent_index: DefIndex,
773 ) -> hir::GenericParam<'hir> {
774 let node_id = self.resolver.next_node_id();
776 // Get the name we'll use to make the def-path. Note
777 // that collisions are ok here and this shouldn't
778 // really show up for end-user.
779 let (str_name, kind) = match hir_name {
780 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
781 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
782 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
785 // Add a definition for the in-band lifetime def.
786 self.resolver.definitions().create_def_with_parent(
789 DefPathData::LifetimeNs(str_name),
795 hir_id: self.lower_node_id(node_id),
800 pure_wrt_drop: false,
801 kind: hir::GenericParamKind::Lifetime { kind },
805 /// When there is a reference to some lifetime `'a`, and in-band
806 /// lifetimes are enabled, then we want to push that lifetime into
807 /// the vector of names to define later. In that case, it will get
808 /// added to the appropriate generics.
809 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
810 if !self.is_collecting_in_band_lifetimes {
814 if !self.sess.features_untracked().in_band_lifetimes {
818 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
822 let hir_name = ParamName::Plain(ident);
824 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
829 self.lifetimes_to_define.push((ident.span, hir_name));
832 /// When we have either an elided or `'_` lifetime in an impl
833 /// header, we convert it to an in-band lifetime.
834 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
835 assert!(self.is_collecting_in_band_lifetimes);
836 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
837 let hir_name = ParamName::Fresh(index);
838 self.lifetimes_to_define.push((span, hir_name));
842 // Evaluates `f` with the lifetimes in `params` in-scope.
843 // This is used to track which lifetimes have already been defined, and
844 // which are new in-band lifetimes that need to have a definition created
846 fn with_in_scope_lifetime_defs<T>(
848 params: &[GenericParam],
849 f: impl FnOnce(&mut Self) -> T,
851 let old_len = self.in_scope_lifetimes.len();
852 let lt_def_names = params.iter().filter_map(|param| match param.kind {
853 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
856 self.in_scope_lifetimes.extend(lt_def_names);
860 self.in_scope_lifetimes.truncate(old_len);
864 /// Appends in-band lifetime defs and argument-position `impl
865 /// Trait` defs to the existing set of generics.
867 /// Presuming that in-band lifetimes are enabled, then
868 /// `self.anonymous_lifetime_mode` will be updated to match the
869 /// parameter while `f` is running (and restored afterwards).
870 fn add_in_band_defs<T>(
874 anonymous_lifetime_mode: AnonymousLifetimeMode,
875 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
876 ) -> (hir::Generics<'hir>, T) {
877 let (in_band_defs, (mut lowered_generics, res)) =
878 self.with_in_scope_lifetime_defs(&generics.params, |this| {
879 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
880 let mut params = Vec::new();
881 // Note: it is necessary to lower generics *before* calling `f`.
882 // When lowering `async fn`, there's a final step when lowering
883 // the return type that assumes that all in-scope lifetimes have
884 // already been added to either `in_scope_lifetimes` or
885 // `lifetimes_to_define`. If we swapped the order of these two,
886 // in-band-lifetimes introduced by generics or where-clauses
887 // wouldn't have been added yet.
889 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
890 let res = f(this, &mut params);
891 (params, (generics, res))
895 let mut lowered_params: Vec<_> =
896 lowered_generics.params.into_iter().chain(in_band_defs).collect();
898 // FIXME(const_generics): the compiler doesn't always cope with
899 // unsorted generic parameters at the moment, so we make sure
900 // that they're ordered correctly here for now. (When we chain
901 // the `in_band_defs`, we might make the order unsorted.)
902 lowered_params.sort_by_key(|param| match param.kind {
903 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
904 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
905 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
908 lowered_generics.params = lowered_params.into();
910 let lowered_generics = lowered_generics.into_generics(self.arena);
911 (lowered_generics, res)
914 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
915 let was_in_dyn_type = self.is_in_dyn_type;
916 self.is_in_dyn_type = in_scope;
918 let result = f(self);
920 self.is_in_dyn_type = was_in_dyn_type;
925 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
926 let was_in_loop_condition = self.is_in_loop_condition;
927 self.is_in_loop_condition = false;
929 let catch_scopes = mem::take(&mut self.catch_scopes);
930 let loop_scopes = mem::take(&mut self.loop_scopes);
932 self.catch_scopes = catch_scopes;
933 self.loop_scopes = loop_scopes;
935 self.is_in_loop_condition = was_in_loop_condition;
940 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
941 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
944 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
945 // Note that we explicitly do not walk the path. Since we don't really
946 // lower attributes (we use the AST version) there is nowhere to keep
947 // the `HirId`s. We don't actually need HIR version of attributes anyway.
948 let kind = match attr.kind {
949 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
950 path: item.path.clone(),
951 args: self.lower_mac_args(&item.args),
953 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
956 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
959 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
961 MacArgs::Empty => MacArgs::Empty,
962 MacArgs::Delimited(dspan, delim, ref tokens) => {
963 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
965 MacArgs::Eq(eq_span, ref tokens) => {
966 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
971 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
972 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
975 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
977 TokenTree::Token(token) => self.lower_token(token),
978 TokenTree::Delimited(span, delim, tts) => {
979 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
984 fn lower_token(&mut self, token: Token) -> TokenStream {
986 token::Interpolated(nt) => {
987 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
988 self.lower_token_stream(tts)
990 _ => TokenTree::Token(token).into(),
994 /// Given an associated type constraint like one of these:
997 /// T: Iterator<Item: Debug>
999 /// T: Iterator<Item = Debug>
1003 /// returns a `hir::TypeBinding` representing `Item`.
1004 fn lower_assoc_ty_constraint(
1006 constraint: &AssocTyConstraint,
1007 itctx: ImplTraitContext<'_, 'hir>,
1008 ) -> hir::TypeBinding<'hir> {
1009 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1011 let kind = match constraint.kind {
1012 AssocTyConstraintKind::Equality { ref ty } => {
1013 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1015 AssocTyConstraintKind::Bound { ref bounds } => {
1016 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1017 let (desugar_to_impl_trait, itctx) = match itctx {
1018 // We are in the return position:
1020 // fn foo() -> impl Iterator<Item: Debug>
1024 // fn foo() -> impl Iterator<Item = impl Debug>
1025 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1027 // We are in the argument position, but within a dyn type:
1029 // fn foo(x: dyn Iterator<Item: Debug>)
1033 // fn foo(x: dyn Iterator<Item = impl Debug>)
1034 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1036 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1037 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1038 // "impl trait context" to permit `impl Debug` in this position (it desugars
1039 // then to an opaque type).
1041 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1042 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1043 (true, ImplTraitContext::OpaqueTy(None))
1046 // We are in the parameter position, but not within a dyn type:
1048 // fn foo(x: impl Iterator<Item: Debug>)
1050 // so we leave it as is and this gets expanded in astconv to a bound like
1051 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1053 _ => (false, itctx),
1056 if desugar_to_impl_trait {
1057 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1058 // constructing the HIR for `impl bounds...` and then lowering that.
1060 let impl_trait_node_id = self.resolver.next_node_id();
1061 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1062 self.resolver.definitions().create_def_with_parent(
1065 DefPathData::ImplTrait,
1070 self.with_dyn_type_scope(false, |this| {
1071 let node_id = this.resolver.next_node_id();
1072 let ty = this.lower_ty(
1075 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1076 span: constraint.span,
1081 hir::TypeBindingKind::Equality { ty }
1084 // Desugar `AssocTy: Bounds` into a type binding where the
1085 // later desugars into a trait predicate.
1086 let bounds = self.lower_param_bounds(bounds, itctx);
1088 hir::TypeBindingKind::Constraint { bounds }
1094 hir_id: self.lower_node_id(constraint.id),
1095 ident: constraint.ident,
1097 span: constraint.span,
1101 fn lower_generic_arg(
1103 arg: &ast::GenericArg,
1104 itctx: ImplTraitContext<'_, 'hir>,
1105 ) -> hir::GenericArg<'hir> {
1107 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1108 ast::GenericArg::Type(ty) => {
1109 // We parse const arguments as path types as we cannot distiguish them durring
1110 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1111 // type and value namespaces. If we resolved the path in the value namespace, we
1112 // transform it into a generic const argument.
1113 if let TyKind::Path(ref qself, ref path) = ty.kind {
1114 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1115 let res = partial_res.base_res();
1116 if !res.matches_ns(Namespace::TypeNS) {
1118 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1122 // Construct a AnonConst where the expr is the "ty"'s path.
1124 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1125 let node_id = self.resolver.next_node_id();
1127 // Add a definition for the in-band const def.
1128 self.resolver.definitions().create_def_with_parent(
1131 DefPathData::AnonConst,
1136 let path_expr = Expr {
1138 kind: ExprKind::Path(qself.clone(), path.clone()),
1140 attrs: AttrVec::new(),
1143 let ct = self.with_new_scopes(|this| hir::AnonConst {
1144 hir_id: this.lower_node_id(node_id),
1145 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1147 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1151 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1153 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1154 value: self.lower_anon_const(&ct),
1155 span: ct.value.span,
1160 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1161 self.arena.alloc(self.lower_ty_direct(t, itctx))
1167 qself: &Option<QSelf>,
1169 param_mode: ParamMode,
1170 itctx: ImplTraitContext<'_, 'hir>,
1171 ) -> hir::Ty<'hir> {
1172 let id = self.lower_node_id(t.id);
1173 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1174 let ty = self.ty_path(id, t.span, qpath);
1175 if let hir::TyKind::TraitObject(..) = ty.kind {
1176 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1181 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1182 hir::Ty { hir_id: self.next_id(), kind, span }
1185 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1186 self.ty(span, hir::TyKind::Tup(tys))
1189 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1190 let kind = match t.kind {
1191 TyKind::Infer => hir::TyKind::Infer,
1192 TyKind::Err => hir::TyKind::Err,
1193 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1194 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1195 TyKind::Rptr(ref region, ref mt) => {
1196 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1197 let lifetime = match *region {
1198 Some(ref lt) => self.lower_lifetime(lt),
1199 None => self.elided_ref_lifetime(span),
1201 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1203 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1204 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1205 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1206 generic_params: this.lower_generic_params(
1208 &NodeMap::default(),
1209 ImplTraitContext::disallowed(),
1211 unsafety: f.unsafety,
1212 abi: this.lower_extern(f.ext),
1213 decl: this.lower_fn_decl(&f.decl, None, false, None),
1214 param_names: this.lower_fn_params_to_names(&f.decl),
1218 TyKind::Never => hir::TyKind::Never,
1219 TyKind::Tup(ref tys) => {
1220 hir::TyKind::Tup(self.arena.alloc_from_iter(
1221 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1224 TyKind::Paren(ref ty) => {
1225 return self.lower_ty_direct(ty, itctx);
1227 TyKind::Path(ref qself, ref path) => {
1228 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1230 TyKind::ImplicitSelf => {
1231 let res = self.expect_full_res(t.id);
1232 let res = self.lower_res(res);
1233 hir::TyKind::Path(hir::QPath::Resolved(
1235 self.arena.alloc(hir::Path {
1237 segments: arena_vec![self; hir::PathSegment::from_ident(
1238 Ident::with_dummy_span(kw::SelfUpper)
1244 TyKind::Array(ref ty, ref length) => {
1245 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1247 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1248 TyKind::TraitObject(ref bounds, kind) => {
1249 let mut lifetime_bound = None;
1250 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1252 this.arena.alloc_from_iter(bounds.iter().filter_map(
1253 |bound| match *bound {
1254 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1255 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1257 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1258 GenericBound::Outlives(ref lifetime) => {
1259 if lifetime_bound.is_none() {
1260 lifetime_bound = Some(this.lower_lifetime(lifetime));
1266 let lifetime_bound =
1267 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1268 (bounds, lifetime_bound)
1270 if kind != TraitObjectSyntax::Dyn {
1271 self.maybe_lint_bare_trait(t.span, t.id, false);
1273 hir::TyKind::TraitObject(bounds, lifetime_bound)
1275 TyKind::ImplTrait(def_node_id, ref bounds) => {
1278 ImplTraitContext::OpaqueTy(fn_def_id) => {
1279 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1280 this.lower_param_bounds(bounds, itctx)
1283 ImplTraitContext::Universal(in_band_ty_params) => {
1284 // Add a definition for the in-band `Param`.
1286 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1288 let hir_bounds = self.lower_param_bounds(
1290 ImplTraitContext::Universal(in_band_ty_params),
1292 // Set the name to `impl Bound1 + Bound2`.
1293 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1294 in_band_ty_params.push(hir::GenericParam {
1295 hir_id: self.lower_node_id(def_node_id),
1296 name: ParamName::Plain(ident),
1297 pure_wrt_drop: false,
1301 kind: hir::GenericParamKind::Type {
1303 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1307 hir::TyKind::Path(hir::QPath::Resolved(
1309 self.arena.alloc(hir::Path {
1311 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1312 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1316 ImplTraitContext::Disallowed(pos) => {
1317 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1318 "bindings or function and inherent method return types"
1320 "function and inherent method return types"
1322 let mut err = struct_span_err!(
1326 "`impl Trait` not allowed outside of {}",
1329 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1332 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1333 attributes to enable",
1341 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1342 TyKind::CVarArgs => {
1343 self.sess.delay_span_bug(
1345 "`TyKind::CVarArgs` should have been handled elsewhere",
1351 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1354 fn lower_opaque_impl_trait(
1357 fn_def_id: Option<DefId>,
1358 opaque_ty_node_id: NodeId,
1359 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1360 ) -> hir::TyKind<'hir> {
1362 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1363 fn_def_id, opaque_ty_node_id, span,
1366 // Make sure we know that some funky desugaring has been going on here.
1367 // This is a first: there is code in other places like for loop
1368 // desugaring that explicitly states that we don't want to track that.
1369 // Not tracking it makes lints in rustc and clippy very fragile, as
1370 // frequently opened issues show.
1371 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1373 let opaque_ty_def_index =
1374 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1376 self.allocate_hir_id_counter(opaque_ty_node_id);
1378 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1380 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1382 opaque_ty_def_index,
1386 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1388 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1390 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1391 let opaque_ty_item = hir::OpaqueTy {
1392 generics: hir::Generics {
1393 params: lifetime_defs,
1394 where_clause: hir::WhereClause { predicates: &[], span },
1398 impl_trait_fn: fn_def_id,
1399 origin: hir::OpaqueTyOrigin::FnReturn,
1402 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1404 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1406 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1407 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1411 /// Registers a new opaque type with the proper `NodeId`s and
1412 /// returns the lowered node-ID for the opaque type.
1413 fn generate_opaque_type(
1415 opaque_ty_node_id: NodeId,
1416 opaque_ty_item: hir::OpaqueTy<'hir>,
1418 opaque_ty_span: Span,
1420 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1421 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1422 // Generate an `type Foo = impl Trait;` declaration.
1423 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1424 let opaque_ty_item = hir::Item {
1425 hir_id: opaque_ty_id,
1426 ident: Ident::invalid(),
1427 attrs: Default::default(),
1428 kind: opaque_ty_item_kind,
1429 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1430 span: opaque_ty_span,
1433 // Insert the item into the global item list. This usually happens
1434 // automatically for all AST items. But this opaque type item
1435 // does not actually exist in the AST.
1436 self.insert_item(opaque_ty_item);
1440 fn lifetimes_from_impl_trait_bounds(
1442 opaque_ty_id: NodeId,
1443 parent_index: DefIndex,
1444 bounds: hir::GenericBounds<'hir>,
1445 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1447 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1448 parent_index={:?}, \
1450 opaque_ty_id, parent_index, bounds,
1453 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1454 // appear in the bounds, excluding lifetimes that are created within the bounds.
1455 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1456 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1457 context: &'r mut LoweringContext<'a, 'hir>,
1459 opaque_ty_id: NodeId,
1460 collect_elided_lifetimes: bool,
1461 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1462 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1463 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1464 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1467 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1470 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1471 intravisit::NestedVisitorMap::None
1474 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1475 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1476 if parameters.parenthesized {
1477 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1478 self.collect_elided_lifetimes = false;
1479 intravisit::walk_generic_args(self, span, parameters);
1480 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1482 intravisit::walk_generic_args(self, span, parameters);
1486 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1487 // Don't collect elided lifetimes used inside of `fn()` syntax.
1488 if let hir::TyKind::BareFn(_) = t.kind {
1489 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1490 self.collect_elided_lifetimes = false;
1492 // Record the "stack height" of `for<'a>` lifetime bindings
1493 // to be able to later fully undo their introduction.
1494 let old_len = self.currently_bound_lifetimes.len();
1495 intravisit::walk_ty(self, t);
1496 self.currently_bound_lifetimes.truncate(old_len);
1498 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1500 intravisit::walk_ty(self, t)
1504 fn visit_poly_trait_ref(
1506 trait_ref: &'v hir::PolyTraitRef<'v>,
1507 modifier: hir::TraitBoundModifier,
1509 // Record the "stack height" of `for<'a>` lifetime bindings
1510 // to be able to later fully undo their introduction.
1511 let old_len = self.currently_bound_lifetimes.len();
1512 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1513 self.currently_bound_lifetimes.truncate(old_len);
1516 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1517 // Record the introduction of 'a in `for<'a> ...`.
1518 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1519 // Introduce lifetimes one at a time so that we can handle
1520 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1521 let lt_name = hir::LifetimeName::Param(param.name);
1522 self.currently_bound_lifetimes.push(lt_name);
1525 intravisit::walk_generic_param(self, param);
1528 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1529 let name = match lifetime.name {
1530 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1531 if self.collect_elided_lifetimes {
1532 // Use `'_` for both implicit and underscore lifetimes in
1533 // `type Foo<'_> = impl SomeTrait<'_>;`.
1534 hir::LifetimeName::Underscore
1539 hir::LifetimeName::Param(_) => lifetime.name,
1541 // Refers to some other lifetime that is "in
1542 // scope" within the type.
1543 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1545 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1548 if !self.currently_bound_lifetimes.contains(&name)
1549 && !self.already_defined_lifetimes.contains(&name)
1551 self.already_defined_lifetimes.insert(name);
1553 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1554 hir_id: self.context.next_id(),
1555 span: lifetime.span,
1559 let def_node_id = self.context.resolver.next_node_id();
1561 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1562 self.context.resolver.definitions().create_def_with_parent(
1565 DefPathData::LifetimeNs(name.ident().name),
1570 let (name, kind) = match name {
1571 hir::LifetimeName::Underscore => (
1572 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1573 hir::LifetimeParamKind::Elided,
1575 hir::LifetimeName::Param(param_name) => {
1576 (param_name, hir::LifetimeParamKind::Explicit)
1578 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1581 self.output_lifetime_params.push(hir::GenericParam {
1584 span: lifetime.span,
1585 pure_wrt_drop: false,
1588 kind: hir::GenericParamKind::Lifetime { kind },
1594 let mut lifetime_collector = ImplTraitLifetimeCollector {
1596 parent: parent_index,
1598 collect_elided_lifetimes: true,
1599 currently_bound_lifetimes: Vec::new(),
1600 already_defined_lifetimes: FxHashSet::default(),
1601 output_lifetimes: Vec::new(),
1602 output_lifetime_params: Vec::new(),
1605 for bound in bounds {
1606 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1609 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1613 self.arena.alloc_from_iter(output_lifetimes),
1614 self.arena.alloc_from_iter(output_lifetime_params),
1618 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1619 let mut ids = SmallVec::<[NodeId; 1]>::new();
1620 if self.sess.features_untracked().impl_trait_in_bindings {
1621 if let Some(ref ty) = l.ty {
1622 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1623 visitor.visit_ty(ty);
1626 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
1627 let ty = l.ty.as_ref().map(|t| {
1630 if self.sess.features_untracked().impl_trait_in_bindings {
1631 ImplTraitContext::OpaqueTy(Some(parent_def_id))
1633 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1637 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1640 hir_id: self.lower_node_id(l.id),
1642 pat: self.lower_pat(&l.pat),
1645 attrs: l.attrs.clone(),
1646 source: hir::LocalSource::Normal,
1652 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1653 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1654 // as they are not explicit in HIR/Ty function signatures.
1655 // (instead, the `c_variadic` flag is set to `true`)
1656 let mut inputs = &decl.inputs[..];
1657 if decl.c_variadic() {
1658 inputs = &inputs[..inputs.len() - 1];
1660 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1661 PatKind::Ident(_, ident, _) => ident,
1662 _ => Ident::new(kw::Invalid, param.pat.span),
1666 // Lowers a function declaration.
1668 // `decl`: the unlowered (AST) function declaration.
1669 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1670 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1671 // `make_ret_async` is also `Some`.
1672 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1673 // This guards against trait declarations and implementations where `impl Trait` is
1675 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1676 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1677 // return type `impl Trait` item.
1681 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1682 impl_trait_return_allow: bool,
1683 make_ret_async: Option<NodeId>,
1684 ) -> &'hir hir::FnDecl<'hir> {
1688 in_band_ty_params: {:?}, \
1689 impl_trait_return_allow: {}, \
1690 make_ret_async: {:?})",
1691 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1693 let lt_mode = if make_ret_async.is_some() {
1694 // In `async fn`, argument-position elided lifetimes
1695 // must be transformed into fresh generic parameters so that
1696 // they can be applied to the opaque `impl Trait` return type.
1697 AnonymousLifetimeMode::CreateParameter
1699 self.anonymous_lifetime_mode
1702 let c_variadic = decl.c_variadic();
1704 // Remember how many lifetimes were already around so that we can
1705 // only look at the lifetime parameters introduced by the arguments.
1706 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1707 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1708 // as they are not explicit in HIR/Ty function signatures.
1709 // (instead, the `c_variadic` flag is set to `true`)
1710 let mut inputs = &decl.inputs[..];
1712 inputs = &inputs[..inputs.len() - 1];
1714 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1715 if let Some((_, ibty)) = &mut in_band_ty_params {
1716 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1718 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1723 let output = if let Some(ret_id) = make_ret_async {
1724 self.lower_async_fn_ret_ty(
1726 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1731 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
1732 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
1733 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
1735 _ => hir::FunctionRetTy::Return(
1736 self.lower_ty(ty, ImplTraitContext::disallowed()),
1739 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
1743 self.arena.alloc(hir::FnDecl {
1747 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1748 let is_mutable_pat = match arg.pat.kind {
1749 PatKind::Ident(BindingMode::ByValue(mt), _, _)
1750 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
1755 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1756 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1757 // Given we are only considering `ImplicitSelf` types, we needn't consider
1758 // the case where we have a mutable pattern to a reference as that would
1759 // no longer be an `ImplicitSelf`.
1760 TyKind::Rptr(_, ref mt)
1761 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1763 hir::ImplicitSelfKind::MutRef
1765 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1766 hir::ImplicitSelfKind::ImmRef
1768 _ => hir::ImplicitSelfKind::None,
1774 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1775 // combined with the following definition of `OpaqueTy`:
1777 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1779 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1780 // `output`: unlowered output type (`T` in `-> T`)
1781 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1782 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1783 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1784 fn lower_async_fn_ret_ty(
1786 output: &FunctionRetTy,
1788 opaque_ty_node_id: NodeId,
1789 ) -> hir::FunctionRetTy<'hir> {
1791 "lower_async_fn_ret_ty(\
1794 opaque_ty_node_id={:?})",
1795 output, fn_def_id, opaque_ty_node_id,
1798 let span = output.span();
1800 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1802 let opaque_ty_def_index =
1803 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1805 self.allocate_hir_id_counter(opaque_ty_node_id);
1807 // When we create the opaque type for this async fn, it is going to have
1808 // to capture all the lifetimes involved in the signature (including in the
1809 // return type). This is done by introducing lifetime parameters for:
1811 // - all the explicitly declared lifetimes from the impl and function itself;
1812 // - all the elided lifetimes in the fn arguments;
1813 // - all the elided lifetimes in the return type.
1815 // So for example in this snippet:
1818 // impl<'a> Foo<'a> {
1819 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1820 // // ^ '0 ^ '1 ^ '2
1821 // // elided lifetimes used below
1826 // we would create an opaque type like:
1829 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1832 // and we would then desugar `bar` to the equivalent of:
1835 // impl<'a> Foo<'a> {
1836 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1840 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1841 // this is because the elided lifetimes from the return type
1842 // should be figured out using the ordinary elision rules, and
1843 // this desugaring achieves that.
1845 // The variable `input_lifetimes_count` tracks the number of
1846 // lifetime parameters to the opaque type *not counting* those
1847 // lifetimes elided in the return type. This includes those
1848 // that are explicitly declared (`in_scope_lifetimes`) and
1849 // those elided lifetimes we found in the arguments (current
1850 // content of `lifetimes_to_define`). Next, we will process
1851 // the return type, which will cause `lifetimes_to_define` to
1853 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
1855 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
1856 // We have to be careful to get elision right here. The
1857 // idea is that we create a lifetime parameter for each
1858 // lifetime in the return type. So, given a return type
1859 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1860 // Future<Output = &'1 [ &'2 u32 ]>`.
1862 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1863 // hence the elision takes place at the fn site.
1864 let future_bound = this
1865 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
1866 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1869 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1871 // Calculate all the lifetimes that should be captured
1872 // by the opaque type. This should include all in-scope
1873 // lifetime parameters, including those defined in-band.
1875 // Note: this must be done after lowering the output type,
1876 // as the output type may introduce new in-band lifetimes.
1877 let lifetime_params: Vec<(Span, ParamName)> = this
1881 .map(|name| (name.ident().span, name))
1882 .chain(this.lifetimes_to_define.iter().cloned())
1885 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
1886 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
1887 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
1889 let generic_params =
1890 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
1891 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
1894 let opaque_ty_item = hir::OpaqueTy {
1895 generics: hir::Generics {
1896 params: generic_params,
1897 where_clause: hir::WhereClause { predicates: &[], span },
1900 bounds: arena_vec![this; future_bound],
1901 impl_trait_fn: Some(fn_def_id),
1902 origin: hir::OpaqueTyOrigin::AsyncFn,
1905 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
1907 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1909 (opaque_ty_id, lifetime_params)
1912 // As documented above on the variable
1913 // `input_lifetimes_count`, we need to create the lifetime
1914 // arguments to our opaque type. Continuing with our example,
1915 // we're creating the type arguments for the return type:
1918 // Bar<'a, 'b, '0, '1, '_>
1921 // For the "input" lifetime parameters, we wish to create
1922 // references to the parameters themselves, including the
1923 // "implicit" ones created from parameter types (`'a`, `'b`,
1926 // For the "output" lifetime parameters, we just want to
1928 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
1930 .map(|&(span, hir_name)| {
1931 // Input lifetime like `'a` or `'1`:
1932 GenericArg::Lifetime(hir::Lifetime {
1933 hir_id: self.next_id(),
1935 name: hir::LifetimeName::Param(hir_name),
1939 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
1940 // Output lifetime like `'_`.
1941 GenericArg::Lifetime(hir::Lifetime {
1942 hir_id: self.next_id(),
1944 name: hir::LifetimeName::Implicit,
1946 let generic_args = self.arena.alloc_from_iter(generic_args);
1948 // Create the `Foo<...>` reference itself. Note that the `type
1949 // Foo = impl Trait` is, internally, created as a child of the
1950 // async fn, so the *type parameters* are inherited. It's
1951 // only the lifetime parameters that we must supply.
1952 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
1953 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1954 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
1957 /// Transforms `-> T` into `Future<Output = T>`
1958 fn lower_async_fn_output_type_to_future_bound(
1960 output: &FunctionRetTy,
1963 ) -> hir::GenericBound<'hir> {
1964 // Compute the `T` in `Future<Output = T>` from the return type.
1965 let output_ty = match output {
1966 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
1967 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1971 let future_params = self.arena.alloc(hir::GenericArgs {
1973 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1974 parenthesized: false,
1977 // ::std::future::Future<future_params>
1979 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
1981 hir::GenericBound::Trait(
1983 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
1984 bound_generic_params: &[],
1987 hir::TraitBoundModifier::None,
1991 fn lower_param_bound(
1994 itctx: ImplTraitContext<'_, 'hir>,
1995 ) -> hir::GenericBound<'hir> {
1997 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
1998 self.lower_poly_trait_ref(ty, itctx),
1999 self.lower_trait_bound_modifier(modifier),
2001 GenericBound::Outlives(ref lifetime) => {
2002 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2007 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2008 let span = l.ident.span;
2010 ident if ident.name == kw::StaticLifetime => {
2011 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2013 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2014 AnonymousLifetimeMode::CreateParameter => {
2015 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2016 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2019 AnonymousLifetimeMode::PassThrough => {
2020 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2023 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2026 self.maybe_collect_in_band_lifetime(ident);
2027 let param_name = ParamName::Plain(ident);
2028 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2033 fn new_named_lifetime(
2037 name: hir::LifetimeName,
2038 ) -> hir::Lifetime {
2039 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2042 fn lower_generic_params_mut<'s>(
2044 params: &'s [GenericParam],
2045 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2046 mut itctx: ImplTraitContext<'s, 'hir>,
2047 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2050 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2053 fn lower_generic_params(
2055 params: &[GenericParam],
2056 add_bounds: &NodeMap<Vec<GenericBound>>,
2057 itctx: ImplTraitContext<'_, 'hir>,
2058 ) -> &'hir [hir::GenericParam<'hir>] {
2059 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2062 fn lower_generic_param(
2064 param: &GenericParam,
2065 add_bounds: &NodeMap<Vec<GenericBound>>,
2066 mut itctx: ImplTraitContext<'_, 'hir>,
2067 ) -> hir::GenericParam<'hir> {
2068 let mut bounds: Vec<_> = self
2069 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2070 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2073 let (name, kind) = match param.kind {
2074 GenericParamKind::Lifetime => {
2075 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2076 self.is_collecting_in_band_lifetimes = false;
2079 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2080 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2082 let param_name = match lt.name {
2083 hir::LifetimeName::Param(param_name) => param_name,
2084 hir::LifetimeName::Implicit
2085 | hir::LifetimeName::Underscore
2086 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2087 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2090 "object-lifetime-default should not occur here",
2093 hir::LifetimeName::Error => ParamName::Error,
2097 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2099 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2103 GenericParamKind::Type { ref default, .. } => {
2104 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2105 if !add_bounds.is_empty() {
2106 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2107 bounds.extend(params);
2110 let kind = hir::GenericParamKind::Type {
2113 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2117 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2118 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2122 (hir::ParamName::Plain(param.ident), kind)
2124 GenericParamKind::Const { ref ty } => (
2125 hir::ParamName::Plain(param.ident),
2126 hir::GenericParamKind::Const {
2127 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2133 hir_id: self.lower_node_id(param.id),
2135 span: param.ident.span,
2136 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2137 attrs: self.lower_attrs(¶m.attrs),
2138 bounds: self.arena.alloc_from_iter(bounds),
2146 itctx: ImplTraitContext<'_, 'hir>,
2147 ) -> hir::TraitRef<'hir> {
2148 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2149 hir::QPath::Resolved(None, path) => path,
2150 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2152 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2155 fn lower_poly_trait_ref(
2158 mut itctx: ImplTraitContext<'_, 'hir>,
2159 ) -> hir::PolyTraitRef<'hir> {
2160 if p.trait_ref.constness.is_some() {
2161 self.diagnostic().span_err(p.span, "`?const` on trait bounds is not yet implemented");
2164 let bound_generic_params = self.lower_generic_params(
2165 &p.bound_generic_params,
2166 &NodeMap::default(),
2169 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2170 this.lower_trait_ref(&p.trait_ref, itctx)
2173 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2176 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2177 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2180 fn lower_param_bounds(
2182 bounds: &[GenericBound],
2183 itctx: ImplTraitContext<'_, 'hir>,
2184 ) -> hir::GenericBounds<'hir> {
2185 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2188 fn lower_param_bounds_mut<'s>(
2190 bounds: &'s [GenericBound],
2191 mut itctx: ImplTraitContext<'s, 'hir>,
2192 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2193 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2196 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2197 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2200 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2201 let mut stmts = vec![];
2202 let mut expr: Option<&'hir _> = None;
2204 for (index, stmt) in b.stmts.iter().enumerate() {
2205 if index == b.stmts.len() - 1 {
2206 if let StmtKind::Expr(ref e) = stmt.kind {
2207 expr = Some(self.lower_expr(e));
2209 stmts.extend(self.lower_stmt(stmt));
2212 stmts.extend(self.lower_stmt(stmt));
2217 hir_id: self.lower_node_id(b.id),
2218 stmts: self.arena.alloc_from_iter(stmts),
2220 rules: self.lower_block_check_mode(&b.rules),
2226 /// Lowers a block directly to an expression, presuming that it
2227 /// has no attributes and is not targeted by a `break`.
2228 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2229 let block = self.lower_block(b, false);
2230 self.expr_block(block, AttrVec::new())
2233 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2234 self.with_new_scopes(|this| hir::AnonConst {
2235 hir_id: this.lower_node_id(c.id),
2236 body: this.lower_const_body(c.value.span, Some(&c.value)),
2240 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2241 let kind = match s.kind {
2242 StmtKind::Local(ref l) => {
2243 let (l, item_ids) = self.lower_local(l);
2244 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2247 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2248 self.stmt(s.span, hir::StmtKind::Item(item_id))
2253 hir_id: self.lower_node_id(s.id),
2254 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2260 StmtKind::Item(ref it) => {
2261 // Can only use the ID once.
2262 let mut id = Some(s.id);
2269 .map(|id| self.lower_node_id(id))
2270 .unwrap_or_else(|| self.next_id());
2272 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2276 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2277 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2278 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2280 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2283 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2285 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2286 BlockCheckMode::Unsafe(u) => {
2287 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2292 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2294 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2295 UserProvided => hir::UnsafeSource::UserProvided,
2299 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2301 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2302 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2306 // Helper methods for building HIR.
2308 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2309 hir::Stmt { span, kind, hir_id: self.next_id() }
2312 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2313 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2320 init: Option<&'hir hir::Expr<'hir>>,
2321 pat: &'hir hir::Pat<'hir>,
2322 source: hir::LocalSource,
2323 ) -> hir::Stmt<'hir> {
2324 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2325 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2328 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2329 self.block_all(expr.span, &[], Some(expr))
2335 stmts: &'hir [hir::Stmt<'hir>],
2336 expr: Option<&'hir hir::Expr<'hir>>,
2337 ) -> &'hir hir::Block<'hir> {
2338 let blk = hir::Block {
2341 hir_id: self.next_id(),
2342 rules: hir::BlockCheckMode::DefaultBlock,
2344 targeted_by_break: false,
2346 self.arena.alloc(blk)
2349 /// Constructs a `true` or `false` literal pattern.
2350 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2351 let expr = self.expr_bool(span, val);
2352 self.pat(span, hir::PatKind::Lit(expr))
2355 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2356 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
2359 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2360 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
2363 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2364 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
2367 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2368 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
2374 components: &[Symbol],
2375 subpats: &'hir [&'hir hir::Pat<'hir>],
2376 ) -> &'hir hir::Pat<'hir> {
2377 let path = self.std_path(span, components, None, true);
2378 let qpath = hir::QPath::Resolved(None, path);
2379 let pt = if subpats.is_empty() {
2380 hir::PatKind::Path(qpath)
2382 hir::PatKind::TupleStruct(qpath, subpats, None)
2387 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2388 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2391 fn pat_ident_binding_mode(
2395 bm: hir::BindingAnnotation,
2396 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2397 let hir_id = self.next_id();
2400 self.arena.alloc(hir::Pat {
2402 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2409 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2410 self.pat(span, hir::PatKind::Wild)
2413 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2414 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
2417 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
2418 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
2419 /// The path is also resolved according to `is_value`.
2423 components: &[Symbol],
2424 params: Option<&'hir hir::GenericArgs<'hir>>,
2426 ) -> &'hir hir::Path<'hir> {
2427 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
2428 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
2430 let mut segments: Vec<_> = path
2434 let res = self.expect_full_res(segment.id);
2436 ident: segment.ident,
2437 hir_id: Some(self.lower_node_id(segment.id)),
2438 res: Some(self.lower_res(res)),
2444 segments.last_mut().unwrap().args = params;
2446 self.arena.alloc(hir::Path {
2448 res: res.map_id(|_| panic!("unexpected `NodeId`")),
2449 segments: self.arena.alloc_from_iter(segments),
2455 mut hir_id: hir::HirId,
2457 qpath: hir::QPath<'hir>,
2458 ) -> hir::Ty<'hir> {
2459 let kind = match qpath {
2460 hir::QPath::Resolved(None, path) => {
2461 // Turn trait object paths into `TyKind::TraitObject` instead.
2463 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
2464 let principal = hir::PolyTraitRef {
2465 bound_generic_params: &[],
2466 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2470 // The original ID is taken by the `PolyTraitRef`,
2471 // so the `Ty` itself needs a different one.
2472 hir_id = self.next_id();
2473 hir::TyKind::TraitObject(
2474 arena_vec![self; principal],
2475 self.elided_dyn_bound(span),
2478 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2481 _ => hir::TyKind::Path(qpath),
2484 hir::Ty { hir_id, kind, span }
2487 /// Invoked to create the lifetime argument for a type `&T`
2488 /// with no explicit lifetime.
2489 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2490 match self.anonymous_lifetime_mode {
2491 // Intercept when we are in an impl header or async fn and introduce an in-band
2493 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2495 AnonymousLifetimeMode::CreateParameter => {
2496 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2498 hir_id: self.next_id(),
2500 name: hir::LifetimeName::Param(fresh_name),
2504 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2506 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2510 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2511 /// return a "error lifetime".
2512 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2513 let (id, msg, label) = match id {
2514 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2517 self.resolver.next_node_id(),
2518 "`&` without an explicit lifetime name cannot be used here",
2519 "explicit lifetime name needed here",
2523 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2524 err.span_label(span, label);
2527 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2530 /// Invoked to create the lifetime argument(s) for a path like
2531 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2532 /// sorts of cases are deprecated. This may therefore report a warning or an
2533 /// error, depending on the mode.
2534 fn elided_path_lifetimes<'s>(
2538 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2539 (0..count).map(move |_| self.elided_path_lifetime(span))
2542 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2543 match self.anonymous_lifetime_mode {
2544 AnonymousLifetimeMode::CreateParameter => {
2545 // We should have emitted E0726 when processing this path above
2547 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2548 let id = self.resolver.next_node_id();
2549 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2551 // `PassThrough` is the normal case.
2552 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2553 // is unsuitable here, as these can occur from missing lifetime parameters in a
2554 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2555 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2556 // later, at which point a suitable error will be emitted.
2557 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2558 self.new_implicit_lifetime(span)
2563 /// Invoked to create the lifetime argument(s) for an elided trait object
2564 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2565 /// when the bound is written, even if it is written with `'_` like in
2566 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2567 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2568 match self.anonymous_lifetime_mode {
2569 // NB. We intentionally ignore the create-parameter mode here.
2570 // and instead "pass through" to resolve-lifetimes, which will apply
2571 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2572 // do not act like other elided lifetimes. In other words, given this:
2574 // impl Foo for Box<dyn Debug>
2576 // we do not introduce a fresh `'_` to serve as the bound, but instead
2577 // ultimately translate to the equivalent of:
2579 // impl Foo for Box<dyn Debug + 'static>
2581 // `resolve_lifetime` has the code to make that happen.
2582 AnonymousLifetimeMode::CreateParameter => {}
2584 AnonymousLifetimeMode::ReportError => {
2585 // ReportError applies to explicit use of `'_`.
2588 // This is the normal case.
2589 AnonymousLifetimeMode::PassThrough => {}
2592 let r = hir::Lifetime {
2593 hir_id: self.next_id(),
2595 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2597 debug!("elided_dyn_bound: r={:?}", r);
2601 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2602 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2605 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2606 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2607 // call site which do not have a macro backtrace. See #61963.
2608 let is_macro_callsite = self
2611 .span_to_snippet(span)
2612 .map(|snippet| snippet.starts_with("#["))
2614 if !is_macro_callsite {
2615 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2616 builtin::BARE_TRAIT_OBJECTS,
2619 "trait objects without an explicit `dyn` are deprecated",
2620 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2626 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2627 // Sorting by span ensures that we get things in order within a
2628 // file, and also puts the files in a sensible order.
2629 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2630 body_ids.sort_by_key(|b| bodies[b].value.span);
2634 /// Helper struct for delayed construction of GenericArgs.
2635 struct GenericArgsCtor<'hir> {
2636 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2637 bindings: &'hir [hir::TypeBinding<'hir>],
2638 parenthesized: bool,
2641 impl<'hir> GenericArgsCtor<'hir> {
2642 fn is_empty(&self) -> bool {
2643 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2646 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2648 args: arena.alloc_from_iter(self.args),
2649 bindings: self.bindings,
2650 parenthesized: self.parenthesized,