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::{bug, span_bug};
41 use rustc_data_structures::captures::Captures;
42 use rustc_data_structures::fx::FxHashSet;
43 use rustc_data_structures::sync::Lrc;
44 use rustc_errors::struct_span_err;
46 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
47 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
48 use rustc_hir::intravisit;
49 use rustc_hir::{ConstArg, GenericArg, ParamName};
50 use rustc_index::vec::IndexVec;
51 use rustc_session::config::nightly_options;
52 use rustc_session::lint::{builtin, BuiltinLintDiagnostics, LintBuffer};
53 use rustc_session::node_id::NodeMap;
54 use rustc_session::Session;
55 use rustc_span::hygiene::ExpnId;
56 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind};
57 use rustc_span::symbol::{kw, sym, Symbol};
62 use syntax::print::pprust;
63 use syntax::sess::ParseSess;
64 use syntax::token::{self, Nonterminal, Token};
65 use syntax::tokenstream::{TokenStream, TokenTree};
66 use syntax::visit::{self, Visitor};
67 use syntax::walk_list;
69 use log::{debug, trace};
70 use smallvec::{smallvec, SmallVec};
71 use std::collections::BTreeMap;
74 macro_rules! arena_vec {
75 ($this:expr; $($x:expr),*) => ({
77 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
86 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
88 struct LoweringContext<'a, 'hir: 'a> {
89 crate_root: Option<Symbol>,
91 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
94 resolver: &'a mut dyn Resolver,
96 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
97 /// if we don't have this function pointer. To avoid that dependency so that
98 /// librustc is independent of the parser, we use dynamic dispatch here.
99 nt_to_tokenstream: NtToTokenstream,
101 /// Used to allocate HIR nodes
102 arena: &'hir Arena<'hir>,
104 /// The items being lowered are collected here.
105 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
107 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
108 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
109 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
110 exported_macros: Vec<hir::MacroDef<'hir>>,
111 non_exported_macro_attrs: Vec<ast::Attribute>,
113 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
115 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
117 generator_kind: Option<hir::GeneratorKind>,
119 /// Used to get the current `fn`'s def span to point to when using `await`
120 /// outside of an `async fn`.
121 current_item: Option<Span>,
123 catch_scopes: Vec<NodeId>,
124 loop_scopes: Vec<NodeId>,
125 is_in_loop_condition: bool,
126 is_in_trait_impl: bool,
127 is_in_dyn_type: bool,
129 /// What to do when we encounter either an "anonymous lifetime
130 /// reference". The term "anonymous" is meant to encompass both
131 /// `'_` lifetimes as well as fully elided cases where nothing is
132 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
133 anonymous_lifetime_mode: AnonymousLifetimeMode,
135 /// Used to create lifetime definitions from in-band lifetime usages.
136 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
137 /// When a named lifetime is encountered in a function or impl header and
138 /// has not been defined
139 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
140 /// to this list. The results of this list are then added to the list of
141 /// lifetime definitions in the corresponding impl or function generics.
142 lifetimes_to_define: Vec<(Span, ParamName)>,
144 /// `true` if in-band lifetimes are being collected. This is used to
145 /// indicate whether or not we're in a place where new lifetimes will result
146 /// in in-band lifetime definitions, such a function or an impl header,
147 /// including implicit lifetimes from `impl_header_lifetime_elision`.
148 is_collecting_in_band_lifetimes: bool,
150 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
151 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
152 /// against this list to see if it is already in-scope, or if a definition
153 /// needs to be created for it.
155 /// We always store a `modern()` version of the param-name in this
157 in_scope_lifetimes: Vec<ParamName>,
159 current_module: hir::HirId,
161 type_def_lifetime_params: DefIdMap<usize>,
163 current_hir_id_owner: Vec<(DefIndex, u32)>,
164 item_local_id_counters: NodeMap<u32>,
165 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
167 allow_try_trait: Option<Lrc<[Symbol]>>,
168 allow_gen_future: Option<Lrc<[Symbol]>>,
172 fn def_key(&mut self, id: DefId) -> DefKey;
174 fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize;
176 /// Obtains resolution for a `NodeId` with a single resolution.
177 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
179 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
180 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
182 /// Obtains resolution for a label with the given `NodeId`.
183 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
185 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
186 /// This should only return `None` during testing.
187 fn definitions(&mut self) -> &mut Definitions;
189 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
190 /// resolves it based on `is_value`.
194 crate_root: Option<Symbol>,
195 components: &[Symbol],
197 ) -> (ast::Path, Res<NodeId>);
199 fn lint_buffer(&mut self) -> &mut LintBuffer;
201 fn next_node_id(&mut self) -> NodeId;
204 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
206 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
207 /// and if so, what meaning it has.
209 enum ImplTraitContext<'b, 'a> {
210 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
211 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
212 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
214 /// Newly generated parameters should be inserted into the given `Vec`.
215 Universal(&'b mut Vec<hir::GenericParam<'a>>),
217 /// Treat `impl Trait` as shorthand for a new opaque type.
218 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
219 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
221 /// We optionally store a `DefId` for the parent item here so we can look up necessary
222 /// information later. It is `None` when no information about the context should be stored
223 /// (e.g., for consts and statics).
224 OpaqueTy(Option<DefId> /* fn def-ID */),
226 /// `impl Trait` is not accepted in this position.
227 Disallowed(ImplTraitPosition),
230 /// Position in which `impl Trait` is disallowed.
231 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
232 enum ImplTraitPosition {
233 /// Disallowed in `let` / `const` / `static` bindings.
236 /// All other posiitons.
240 impl<'a> ImplTraitContext<'_, 'a> {
242 fn disallowed() -> Self {
243 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
246 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
247 use self::ImplTraitContext::*;
249 Universal(params) => Universal(params),
250 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
251 Disallowed(pos) => Disallowed(*pos),
256 pub fn lower_crate<'a, 'hir>(
258 dep_graph: &'a DepGraph,
260 resolver: &'a mut dyn Resolver,
261 nt_to_tokenstream: NtToTokenstream,
262 arena: &'hir Arena<'hir>,
263 ) -> hir::Crate<'hir> {
264 // We're constructing the HIR here; we don't care what we will
265 // read, since we haven't even constructed the *input* to
267 dep_graph.assert_ignored();
269 let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering");
272 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
277 items: BTreeMap::new(),
278 trait_items: BTreeMap::new(),
279 impl_items: BTreeMap::new(),
280 bodies: BTreeMap::new(),
281 trait_impls: BTreeMap::new(),
282 modules: BTreeMap::new(),
283 exported_macros: Vec::new(),
284 non_exported_macro_attrs: Vec::new(),
285 catch_scopes: Vec::new(),
286 loop_scopes: Vec::new(),
287 is_in_loop_condition: false,
288 is_in_trait_impl: false,
289 is_in_dyn_type: false,
290 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
291 type_def_lifetime_params: Default::default(),
292 current_module: hir::CRATE_HIR_ID,
293 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
294 item_local_id_counters: Default::default(),
295 node_id_to_hir_id: IndexVec::new(),
296 generator_kind: None,
298 lifetimes_to_define: Vec::new(),
299 is_collecting_in_band_lifetimes: false,
300 in_scope_lifetimes: Vec::new(),
301 allow_try_trait: Some([sym::try_trait][..].into()),
302 allow_gen_future: Some([sym::gen_future][..].into()),
307 #[derive(Copy, Clone, PartialEq)]
309 /// Any path in a type context.
311 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
313 /// The `module::Type` in `module::Type::method` in an expression.
317 enum ParenthesizedGenericArgs {
322 /// What to do when we encounter an **anonymous** lifetime
323 /// reference. Anonymous lifetime references come in two flavors. You
324 /// have implicit, or fully elided, references to lifetimes, like the
325 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
326 /// or `Ref<'_, T>`. These often behave the same, but not always:
328 /// - certain usages of implicit references are deprecated, like
329 /// `Ref<T>`, and we sometimes just give hard errors in those cases
331 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
332 /// the same as `Box<dyn Foo + '_>`.
334 /// We describe the effects of the various modes in terms of three cases:
336 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
337 /// of a `&` (e.g., the missing lifetime in something like `&T`)
338 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
339 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
340 /// elided bounds follow special rules. Note that this only covers
341 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
342 /// '_>` is a case of "modern" elision.
343 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
344 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
345 /// non-deprecated equivalent.
347 /// Currently, the handling of lifetime elision is somewhat spread out
348 /// between HIR lowering and -- as described below -- the
349 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
350 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
351 /// everything into HIR lowering.
352 #[derive(Copy, Clone, Debug)]
353 enum AnonymousLifetimeMode {
354 /// For **Modern** cases, create a new anonymous region parameter
355 /// and reference that.
357 /// For **Dyn Bound** cases, pass responsibility to
358 /// `resolve_lifetime` code.
360 /// For **Deprecated** cases, report an error.
363 /// Give a hard error when either `&` or `'_` is written. Used to
364 /// rule out things like `where T: Foo<'_>`. Does not imply an
365 /// error on default object bounds (e.g., `Box<dyn Foo>`).
368 /// Pass responsibility to `resolve_lifetime` code for all cases.
372 struct ImplTraitTypeIdVisitor<'a> {
373 ids: &'a mut SmallVec<[NodeId; 1]>,
376 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
377 fn visit_ty(&mut self, ty: &Ty) {
379 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
381 TyKind::ImplTrait(id, _) => self.ids.push(id),
384 visit::walk_ty(self, ty);
387 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
388 if let Some(ref p) = path_segment.args {
389 if let GenericArgs::Parenthesized(_) = **p {
393 visit::walk_path_segment(self, path_span, path_segment)
397 impl<'a, 'hir> LoweringContext<'a, 'hir> {
398 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
399 /// Full-crate AST visitor that inserts into a fresh
400 /// `LoweringContext` any information that may be
401 /// needed from arbitrary locations in the crate,
402 /// e.g., the number of lifetime generic parameters
403 /// declared for every type and trait definition.
404 struct MiscCollector<'tcx, 'lowering, 'hir> {
405 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
406 hir_id_owner: Option<NodeId>,
409 impl MiscCollector<'_, '_, '_> {
410 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
412 UseTreeKind::Simple(_, id1, id2) => {
413 for &id in &[id1, id2] {
414 self.lctx.resolver.definitions().create_def_with_parent(
421 self.lctx.allocate_hir_id_counter(id);
424 UseTreeKind::Glob => (),
425 UseTreeKind::Nested(ref trees) => {
426 for &(ref use_tree, id) in trees {
427 let hir_id = self.lctx.allocate_hir_id_counter(id);
428 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
434 fn with_hir_id_owner<T>(
436 owner: Option<NodeId>,
437 f: impl FnOnce(&mut Self) -> T,
439 let old = mem::replace(&mut self.hir_id_owner, owner);
441 self.hir_id_owner = old;
446 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
447 fn visit_pat(&mut self, p: &'tcx Pat) {
448 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
449 // Doesn't generate a HIR node
450 } else if let Some(owner) = self.hir_id_owner {
451 self.lctx.lower_node_id_with_owner(p.id, owner);
454 visit::walk_pat(self, p)
457 fn visit_item(&mut self, item: &'tcx Item) {
458 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
461 ItemKind::Struct(_, ref generics)
462 | ItemKind::Union(_, ref generics)
463 | ItemKind::Enum(_, ref generics)
464 | ItemKind::TyAlias(_, ref generics)
465 | ItemKind::Trait(_, _, ref generics, ..) => {
466 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
470 .filter(|param| match param.kind {
471 ast::GenericParamKind::Lifetime { .. } => true,
475 self.lctx.type_def_lifetime_params.insert(def_id, count);
477 ItemKind::Use(ref use_tree) => {
478 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
483 self.with_hir_id_owner(Some(item.id), |this| {
484 visit::walk_item(this, item);
488 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
489 self.lctx.allocate_hir_id_counter(item.id);
492 AssocItemKind::Fn(_, None) => {
493 // Ignore patterns in trait methods without bodies
494 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
496 _ => self.with_hir_id_owner(Some(item.id), |this| {
497 visit::walk_trait_item(this, item);
502 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
503 self.lctx.allocate_hir_id_counter(item.id);
504 self.with_hir_id_owner(Some(item.id), |this| {
505 visit::walk_impl_item(this, item);
509 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
510 // Ignore patterns in foreign items
511 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
514 fn visit_ty(&mut self, t: &'tcx Ty) {
516 // Mirrors the case in visit::walk_ty
517 TyKind::BareFn(ref f) => {
518 walk_list!(self, visit_generic_param, &f.generic_params);
519 // Mirrors visit::walk_fn_decl
520 for parameter in &f.decl.inputs {
521 // We don't lower the ids of argument patterns
522 self.with_hir_id_owner(None, |this| {
523 this.visit_pat(¶meter.pat);
525 self.visit_ty(¶meter.ty)
527 self.visit_fn_ret_ty(&f.decl.output)
529 _ => visit::walk_ty(self, t),
534 self.lower_node_id(CRATE_NODE_ID);
535 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
537 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
538 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
540 let module = self.lower_mod(&c.module);
541 let attrs = self.lower_attrs(&c.attrs);
542 let body_ids = body_ids(&self.bodies);
544 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
550 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
551 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
553 trait_items: self.trait_items,
554 impl_items: self.impl_items,
557 trait_impls: self.trait_impls,
558 modules: self.modules,
562 fn insert_item(&mut self, item: hir::Item<'hir>) {
563 let id = item.hir_id;
564 // FIXME: Use `debug_asset-rt`.
565 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
566 self.items.insert(id, item);
567 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
570 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
571 // Set up the counter if needed.
572 self.item_local_id_counters.entry(owner).or_insert(0);
573 // Always allocate the first `HirId` for the owner itself.
574 let lowered = self.lower_node_id_with_owner(owner, owner);
575 debug_assert_eq!(lowered.local_id.as_u32(), 0);
579 fn lower_node_id_generic(
582 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
584 if ast_node_id == DUMMY_NODE_ID {
585 return hir::DUMMY_HIR_ID;
588 let min_size = ast_node_id.as_usize() + 1;
590 if min_size > self.node_id_to_hir_id.len() {
591 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
594 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
596 if existing_hir_id == hir::DUMMY_HIR_ID {
597 // Generate a new `HirId`.
598 let hir_id = alloc_hir_id(self);
599 self.node_id_to_hir_id[ast_node_id] = hir_id;
607 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
609 .item_local_id_counters
610 .insert(owner, HIR_ID_COUNTER_LOCKED)
611 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
612 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
613 self.current_hir_id_owner.push((def_index, counter));
615 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
617 debug_assert!(def_index == new_def_index);
618 debug_assert!(new_counter >= counter);
620 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
621 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
625 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
626 /// the `LoweringContext`'s `NodeId => HirId` map.
627 /// Take care not to call this method if the resulting `HirId` is then not
628 /// actually used in the HIR, as that would trigger an assertion in the
629 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
630 /// properly. Calling the method twice with the same `NodeId` is fine though.
631 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
632 self.lower_node_id_generic(ast_node_id, |this| {
633 let &mut (def_index, ref mut local_id_counter) =
634 this.current_hir_id_owner.last_mut().unwrap();
635 let local_id = *local_id_counter;
636 *local_id_counter += 1;
637 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
641 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
642 self.lower_node_id_generic(ast_node_id, |this| {
643 let local_id_counter = this
644 .item_local_id_counters
646 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
647 let local_id = *local_id_counter;
649 // We want to be sure not to modify the counter in the map while it
650 // is also on the stack. Otherwise we'll get lost updates when writing
651 // back from the stack to the map.
652 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
654 *local_id_counter += 1;
655 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
656 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
657 that do not belong to the current owner",
660 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
664 fn next_id(&mut self) -> hir::HirId {
665 let node_id = self.resolver.next_node_id();
666 self.lower_node_id(node_id)
669 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
671 self.lower_node_id_generic(id, |_| {
672 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
677 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
678 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
679 if pr.unresolved_segments() != 0 {
680 bug!("path not fully resolved: {:?}", pr);
686 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
687 self.resolver.get_import_res(id).present_items()
690 fn diagnostic(&self) -> &rustc_errors::Handler {
691 self.sess.diagnostic()
694 /// Reuses the span but adds information like the kind of the desugaring and features that are
695 /// allowed inside this span.
696 fn mark_span_with_reason(
698 reason: DesugaringKind,
700 allow_internal_unstable: Option<Lrc<[Symbol]>>,
702 span.fresh_expansion(ExpnData {
703 allow_internal_unstable,
704 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
708 fn with_anonymous_lifetime_mode<R>(
710 anonymous_lifetime_mode: AnonymousLifetimeMode,
711 op: impl FnOnce(&mut Self) -> R,
714 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
715 anonymous_lifetime_mode,
717 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
718 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
719 let result = op(self);
720 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
722 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
723 old_anonymous_lifetime_mode
728 /// Creates a new `hir::GenericParam` for every new lifetime and
729 /// type parameter encountered while evaluating `f`. Definitions
730 /// are created with the parent provided. If no `parent_id` is
731 /// provided, no definitions will be returned.
733 /// Presuming that in-band lifetimes are enabled, then
734 /// `self.anonymous_lifetime_mode` will be updated to match the
735 /// parameter while `f` is running (and restored afterwards).
736 fn collect_in_band_defs<T>(
739 anonymous_lifetime_mode: AnonymousLifetimeMode,
740 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
741 ) -> (Vec<hir::GenericParam<'hir>>, T) {
742 assert!(!self.is_collecting_in_band_lifetimes);
743 assert!(self.lifetimes_to_define.is_empty());
744 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
746 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
747 self.is_collecting_in_band_lifetimes = true;
749 let (in_band_ty_params, res) = f(self);
751 self.is_collecting_in_band_lifetimes = false;
752 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
754 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
756 let params = lifetimes_to_define
758 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
759 .chain(in_band_ty_params.into_iter())
765 /// Converts a lifetime into a new generic parameter.
766 fn lifetime_to_generic_param(
770 parent_index: DefIndex,
771 ) -> hir::GenericParam<'hir> {
772 let node_id = self.resolver.next_node_id();
774 // Get the name we'll use to make the def-path. Note
775 // that collisions are ok here and this shouldn't
776 // really show up for end-user.
777 let (str_name, kind) = match hir_name {
778 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
779 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
780 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
783 // Add a definition for the in-band lifetime def.
784 self.resolver.definitions().create_def_with_parent(
787 DefPathData::LifetimeNs(str_name),
793 hir_id: self.lower_node_id(node_id),
798 pure_wrt_drop: false,
799 kind: hir::GenericParamKind::Lifetime { kind },
803 /// When there is a reference to some lifetime `'a`, and in-band
804 /// lifetimes are enabled, then we want to push that lifetime into
805 /// the vector of names to define later. In that case, it will get
806 /// added to the appropriate generics.
807 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
808 if !self.is_collecting_in_band_lifetimes {
812 if !self.sess.features_untracked().in_band_lifetimes {
816 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
820 let hir_name = ParamName::Plain(ident);
822 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
827 self.lifetimes_to_define.push((ident.span, hir_name));
830 /// When we have either an elided or `'_` lifetime in an impl
831 /// header, we convert it to an in-band lifetime.
832 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
833 assert!(self.is_collecting_in_band_lifetimes);
834 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
835 let hir_name = ParamName::Fresh(index);
836 self.lifetimes_to_define.push((span, hir_name));
840 // Evaluates `f` with the lifetimes in `params` in-scope.
841 // This is used to track which lifetimes have already been defined, and
842 // which are new in-band lifetimes that need to have a definition created
844 fn with_in_scope_lifetime_defs<T>(
846 params: &[GenericParam],
847 f: impl FnOnce(&mut Self) -> T,
849 let old_len = self.in_scope_lifetimes.len();
850 let lt_def_names = params.iter().filter_map(|param| match param.kind {
851 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
854 self.in_scope_lifetimes.extend(lt_def_names);
858 self.in_scope_lifetimes.truncate(old_len);
862 /// Appends in-band lifetime defs and argument-position `impl
863 /// Trait` defs to the existing set of generics.
865 /// Presuming that in-band lifetimes are enabled, then
866 /// `self.anonymous_lifetime_mode` will be updated to match the
867 /// parameter while `f` is running (and restored afterwards).
868 fn add_in_band_defs<T>(
872 anonymous_lifetime_mode: AnonymousLifetimeMode,
873 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
874 ) -> (hir::Generics<'hir>, T) {
875 let (in_band_defs, (mut lowered_generics, res)) =
876 self.with_in_scope_lifetime_defs(&generics.params, |this| {
877 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
878 let mut params = Vec::new();
879 // Note: it is necessary to lower generics *before* calling `f`.
880 // When lowering `async fn`, there's a final step when lowering
881 // the return type that assumes that all in-scope lifetimes have
882 // already been added to either `in_scope_lifetimes` or
883 // `lifetimes_to_define`. If we swapped the order of these two,
884 // in-band-lifetimes introduced by generics or where-clauses
885 // wouldn't have been added yet.
887 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
888 let res = f(this, &mut params);
889 (params, (generics, res))
893 let mut lowered_params: Vec<_> =
894 lowered_generics.params.into_iter().chain(in_band_defs).collect();
896 // FIXME(const_generics): the compiler doesn't always cope with
897 // unsorted generic parameters at the moment, so we make sure
898 // that they're ordered correctly here for now. (When we chain
899 // the `in_band_defs`, we might make the order unsorted.)
900 lowered_params.sort_by_key(|param| match param.kind {
901 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
902 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
903 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
906 lowered_generics.params = lowered_params.into();
908 let lowered_generics = lowered_generics.into_generics(self.arena);
909 (lowered_generics, res)
912 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
913 let was_in_dyn_type = self.is_in_dyn_type;
914 self.is_in_dyn_type = in_scope;
916 let result = f(self);
918 self.is_in_dyn_type = was_in_dyn_type;
923 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
924 let was_in_loop_condition = self.is_in_loop_condition;
925 self.is_in_loop_condition = false;
927 let catch_scopes = mem::take(&mut self.catch_scopes);
928 let loop_scopes = mem::take(&mut self.loop_scopes);
930 self.catch_scopes = catch_scopes;
931 self.loop_scopes = loop_scopes;
933 self.is_in_loop_condition = was_in_loop_condition;
938 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
939 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
942 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
943 // Note that we explicitly do not walk the path. Since we don't really
944 // lower attributes (we use the AST version) there is nowhere to keep
945 // the `HirId`s. We don't actually need HIR version of attributes anyway.
946 let kind = match attr.kind {
947 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
948 path: item.path.clone(),
949 args: self.lower_mac_args(&item.args),
951 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
954 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
957 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
959 MacArgs::Empty => MacArgs::Empty,
960 MacArgs::Delimited(dspan, delim, ref tokens) => {
961 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
963 MacArgs::Eq(eq_span, ref tokens) => {
964 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
969 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
970 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
973 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
975 TokenTree::Token(token) => self.lower_token(token),
976 TokenTree::Delimited(span, delim, tts) => {
977 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
982 fn lower_token(&mut self, token: Token) -> TokenStream {
984 token::Interpolated(nt) => {
985 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
986 self.lower_token_stream(tts)
988 _ => TokenTree::Token(token).into(),
992 /// Given an associated type constraint like one of these:
995 /// T: Iterator<Item: Debug>
997 /// T: Iterator<Item = Debug>
1001 /// returns a `hir::TypeBinding` representing `Item`.
1002 fn lower_assoc_ty_constraint(
1004 constraint: &AssocTyConstraint,
1005 itctx: ImplTraitContext<'_, 'hir>,
1006 ) -> hir::TypeBinding<'hir> {
1007 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1009 let kind = match constraint.kind {
1010 AssocTyConstraintKind::Equality { ref ty } => {
1011 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1013 AssocTyConstraintKind::Bound { ref bounds } => {
1014 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1015 let (desugar_to_impl_trait, itctx) = match itctx {
1016 // We are in the return position:
1018 // fn foo() -> impl Iterator<Item: Debug>
1022 // fn foo() -> impl Iterator<Item = impl Debug>
1023 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1025 // We are in the argument position, but within a dyn type:
1027 // fn foo(x: dyn Iterator<Item: Debug>)
1031 // fn foo(x: dyn Iterator<Item = impl Debug>)
1032 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1034 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1035 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1036 // "impl trait context" to permit `impl Debug` in this position (it desugars
1037 // then to an opaque type).
1039 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1040 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1041 (true, ImplTraitContext::OpaqueTy(None))
1044 // We are in the parameter position, but not within a dyn type:
1046 // fn foo(x: impl Iterator<Item: Debug>)
1048 // so we leave it as is and this gets expanded in astconv to a bound like
1049 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1051 _ => (false, itctx),
1054 if desugar_to_impl_trait {
1055 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1056 // constructing the HIR for `impl bounds...` and then lowering that.
1058 let impl_trait_node_id = self.resolver.next_node_id();
1059 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1060 self.resolver.definitions().create_def_with_parent(
1063 DefPathData::ImplTrait,
1068 self.with_dyn_type_scope(false, |this| {
1069 let node_id = this.resolver.next_node_id();
1070 let ty = this.lower_ty(
1073 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1074 span: constraint.span,
1079 hir::TypeBindingKind::Equality { ty }
1082 // Desugar `AssocTy: Bounds` into a type binding where the
1083 // later desugars into a trait predicate.
1084 let bounds = self.lower_param_bounds(bounds, itctx);
1086 hir::TypeBindingKind::Constraint { bounds }
1092 hir_id: self.lower_node_id(constraint.id),
1093 ident: constraint.ident,
1095 span: constraint.span,
1099 fn lower_generic_arg(
1101 arg: &ast::GenericArg,
1102 itctx: ImplTraitContext<'_, 'hir>,
1103 ) -> hir::GenericArg<'hir> {
1105 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1106 ast::GenericArg::Type(ty) => {
1107 // We parse const arguments as path types as we cannot distiguish them durring
1108 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1109 // type and value namespaces. If we resolved the path in the value namespace, we
1110 // transform it into a generic const argument.
1111 if let TyKind::Path(ref qself, ref path) = ty.kind {
1112 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1113 let res = partial_res.base_res();
1114 if !res.matches_ns(Namespace::TypeNS) {
1116 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1120 // Construct a AnonConst where the expr is the "ty"'s path.
1122 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1123 let node_id = self.resolver.next_node_id();
1125 // Add a definition for the in-band const def.
1126 self.resolver.definitions().create_def_with_parent(
1129 DefPathData::AnonConst,
1134 let path_expr = Expr {
1136 kind: ExprKind::Path(qself.clone(), path.clone()),
1138 attrs: AttrVec::new(),
1141 let ct = self.with_new_scopes(|this| hir::AnonConst {
1142 hir_id: this.lower_node_id(node_id),
1143 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1145 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1149 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1151 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1152 value: self.lower_anon_const(&ct),
1153 span: ct.value.span,
1158 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1159 self.arena.alloc(self.lower_ty_direct(t, itctx))
1165 qself: &Option<QSelf>,
1167 param_mode: ParamMode,
1168 itctx: ImplTraitContext<'_, 'hir>,
1169 ) -> hir::Ty<'hir> {
1170 let id = self.lower_node_id(t.id);
1171 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1172 let ty = self.ty_path(id, t.span, qpath);
1173 if let hir::TyKind::TraitObject(..) = ty.kind {
1174 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1179 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1180 hir::Ty { hir_id: self.next_id(), kind, span }
1183 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1184 self.ty(span, hir::TyKind::Tup(tys))
1187 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1188 let kind = match t.kind {
1189 TyKind::Infer => hir::TyKind::Infer,
1190 TyKind::Err => hir::TyKind::Err,
1191 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1192 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1193 TyKind::Rptr(ref region, ref mt) => {
1194 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1195 let lifetime = match *region {
1196 Some(ref lt) => self.lower_lifetime(lt),
1197 None => self.elided_ref_lifetime(span),
1199 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1201 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1202 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1203 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1204 generic_params: this.lower_generic_params(
1206 &NodeMap::default(),
1207 ImplTraitContext::disallowed(),
1209 unsafety: f.unsafety,
1210 abi: this.lower_extern(f.ext),
1211 decl: this.lower_fn_decl(&f.decl, None, false, None),
1212 param_names: this.lower_fn_params_to_names(&f.decl),
1216 TyKind::Never => hir::TyKind::Never,
1217 TyKind::Tup(ref tys) => {
1218 hir::TyKind::Tup(self.arena.alloc_from_iter(
1219 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1222 TyKind::Paren(ref ty) => {
1223 return self.lower_ty_direct(ty, itctx);
1225 TyKind::Path(ref qself, ref path) => {
1226 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1228 TyKind::ImplicitSelf => {
1229 let res = self.expect_full_res(t.id);
1230 let res = self.lower_res(res);
1231 hir::TyKind::Path(hir::QPath::Resolved(
1233 self.arena.alloc(hir::Path {
1235 segments: arena_vec![self; hir::PathSegment::from_ident(
1236 Ident::with_dummy_span(kw::SelfUpper)
1242 TyKind::Array(ref ty, ref length) => {
1243 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1245 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1246 TyKind::TraitObject(ref bounds, kind) => {
1247 let mut lifetime_bound = None;
1248 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1250 this.arena.alloc_from_iter(bounds.iter().filter_map(
1251 |bound| match *bound {
1252 GenericBound::Trait(ref ty, TraitBoundModifier::None)
1253 | GenericBound::Trait(ref ty, TraitBoundModifier::MaybeConst) => {
1254 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1256 // `?const ?Bound` will cause an error during AST validation
1257 // anyways, so treat it like `?Bound` as compilation proceeds.
1258 GenericBound::Trait(_, TraitBoundModifier::Maybe)
1259 | GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
1262 GenericBound::Outlives(ref lifetime) => {
1263 if lifetime_bound.is_none() {
1264 lifetime_bound = Some(this.lower_lifetime(lifetime));
1270 let lifetime_bound =
1271 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1272 (bounds, lifetime_bound)
1274 if kind != TraitObjectSyntax::Dyn {
1275 self.maybe_lint_bare_trait(t.span, t.id, false);
1277 hir::TyKind::TraitObject(bounds, lifetime_bound)
1279 TyKind::ImplTrait(def_node_id, ref bounds) => {
1282 ImplTraitContext::OpaqueTy(fn_def_id) => {
1283 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1284 this.lower_param_bounds(bounds, itctx)
1287 ImplTraitContext::Universal(in_band_ty_params) => {
1288 // Add a definition for the in-band `Param`.
1290 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1292 let hir_bounds = self.lower_param_bounds(
1294 ImplTraitContext::Universal(in_band_ty_params),
1296 // Set the name to `impl Bound1 + Bound2`.
1297 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1298 in_band_ty_params.push(hir::GenericParam {
1299 hir_id: self.lower_node_id(def_node_id),
1300 name: ParamName::Plain(ident),
1301 pure_wrt_drop: false,
1305 kind: hir::GenericParamKind::Type {
1307 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1311 hir::TyKind::Path(hir::QPath::Resolved(
1313 self.arena.alloc(hir::Path {
1315 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1316 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1320 ImplTraitContext::Disallowed(pos) => {
1321 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1322 "bindings or function and inherent method return types"
1324 "function and inherent method return types"
1326 let mut err = struct_span_err!(
1330 "`impl Trait` not allowed outside of {}",
1333 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1336 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1337 attributes to enable",
1345 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1346 TyKind::CVarArgs => {
1347 self.sess.delay_span_bug(
1349 "`TyKind::CVarArgs` should have been handled elsewhere",
1355 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1358 fn lower_opaque_impl_trait(
1361 fn_def_id: Option<DefId>,
1362 opaque_ty_node_id: NodeId,
1363 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1364 ) -> hir::TyKind<'hir> {
1366 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1367 fn_def_id, opaque_ty_node_id, span,
1370 // Make sure we know that some funky desugaring has been going on here.
1371 // This is a first: there is code in other places like for loop
1372 // desugaring that explicitly states that we don't want to track that.
1373 // Not tracking it makes lints in rustc and clippy very fragile, as
1374 // frequently opened issues show.
1375 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1377 let opaque_ty_def_index =
1378 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1380 self.allocate_hir_id_counter(opaque_ty_node_id);
1382 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1384 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1386 opaque_ty_def_index,
1390 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1392 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1394 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1395 let opaque_ty_item = hir::OpaqueTy {
1396 generics: hir::Generics {
1397 params: lifetime_defs,
1398 where_clause: hir::WhereClause { predicates: &[], span },
1402 impl_trait_fn: fn_def_id,
1403 origin: hir::OpaqueTyOrigin::FnReturn,
1406 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1408 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1410 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1411 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1415 /// Registers a new opaque type with the proper `NodeId`s and
1416 /// returns the lowered node-ID for the opaque type.
1417 fn generate_opaque_type(
1419 opaque_ty_node_id: NodeId,
1420 opaque_ty_item: hir::OpaqueTy<'hir>,
1422 opaque_ty_span: Span,
1424 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1425 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1426 // Generate an `type Foo = impl Trait;` declaration.
1427 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1428 let opaque_ty_item = hir::Item {
1429 hir_id: opaque_ty_id,
1430 ident: Ident::invalid(),
1431 attrs: Default::default(),
1432 kind: opaque_ty_item_kind,
1433 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1434 span: opaque_ty_span,
1437 // Insert the item into the global item list. This usually happens
1438 // automatically for all AST items. But this opaque type item
1439 // does not actually exist in the AST.
1440 self.insert_item(opaque_ty_item);
1444 fn lifetimes_from_impl_trait_bounds(
1446 opaque_ty_id: NodeId,
1447 parent_index: DefIndex,
1448 bounds: hir::GenericBounds<'hir>,
1449 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1451 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1452 parent_index={:?}, \
1454 opaque_ty_id, parent_index, bounds,
1457 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1458 // appear in the bounds, excluding lifetimes that are created within the bounds.
1459 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1460 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1461 context: &'r mut LoweringContext<'a, 'hir>,
1463 opaque_ty_id: NodeId,
1464 collect_elided_lifetimes: bool,
1465 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1466 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1467 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1468 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1471 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1474 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1475 intravisit::NestedVisitorMap::None
1478 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1479 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1480 if parameters.parenthesized {
1481 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1482 self.collect_elided_lifetimes = false;
1483 intravisit::walk_generic_args(self, span, parameters);
1484 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1486 intravisit::walk_generic_args(self, span, parameters);
1490 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1491 // Don't collect elided lifetimes used inside of `fn()` syntax.
1492 if let hir::TyKind::BareFn(_) = t.kind {
1493 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1494 self.collect_elided_lifetimes = false;
1496 // Record the "stack height" of `for<'a>` lifetime bindings
1497 // to be able to later fully undo their introduction.
1498 let old_len = self.currently_bound_lifetimes.len();
1499 intravisit::walk_ty(self, t);
1500 self.currently_bound_lifetimes.truncate(old_len);
1502 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1504 intravisit::walk_ty(self, t)
1508 fn visit_poly_trait_ref(
1510 trait_ref: &'v hir::PolyTraitRef<'v>,
1511 modifier: hir::TraitBoundModifier,
1513 // Record the "stack height" of `for<'a>` lifetime bindings
1514 // to be able to later fully undo their introduction.
1515 let old_len = self.currently_bound_lifetimes.len();
1516 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1517 self.currently_bound_lifetimes.truncate(old_len);
1520 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1521 // Record the introduction of 'a in `for<'a> ...`.
1522 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1523 // Introduce lifetimes one at a time so that we can handle
1524 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1525 let lt_name = hir::LifetimeName::Param(param.name);
1526 self.currently_bound_lifetimes.push(lt_name);
1529 intravisit::walk_generic_param(self, param);
1532 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1533 let name = match lifetime.name {
1534 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1535 if self.collect_elided_lifetimes {
1536 // Use `'_` for both implicit and underscore lifetimes in
1537 // `type Foo<'_> = impl SomeTrait<'_>;`.
1538 hir::LifetimeName::Underscore
1543 hir::LifetimeName::Param(_) => lifetime.name,
1545 // Refers to some other lifetime that is "in
1546 // scope" within the type.
1547 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1549 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1552 if !self.currently_bound_lifetimes.contains(&name)
1553 && !self.already_defined_lifetimes.contains(&name)
1555 self.already_defined_lifetimes.insert(name);
1557 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1558 hir_id: self.context.next_id(),
1559 span: lifetime.span,
1563 let def_node_id = self.context.resolver.next_node_id();
1565 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1566 self.context.resolver.definitions().create_def_with_parent(
1569 DefPathData::LifetimeNs(name.ident().name),
1574 let (name, kind) = match name {
1575 hir::LifetimeName::Underscore => (
1576 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1577 hir::LifetimeParamKind::Elided,
1579 hir::LifetimeName::Param(param_name) => {
1580 (param_name, hir::LifetimeParamKind::Explicit)
1582 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1585 self.output_lifetime_params.push(hir::GenericParam {
1588 span: lifetime.span,
1589 pure_wrt_drop: false,
1592 kind: hir::GenericParamKind::Lifetime { kind },
1598 let mut lifetime_collector = ImplTraitLifetimeCollector {
1600 parent: parent_index,
1602 collect_elided_lifetimes: true,
1603 currently_bound_lifetimes: Vec::new(),
1604 already_defined_lifetimes: FxHashSet::default(),
1605 output_lifetimes: Vec::new(),
1606 output_lifetime_params: Vec::new(),
1609 for bound in bounds {
1610 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1613 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1617 self.arena.alloc_from_iter(output_lifetimes),
1618 self.arena.alloc_from_iter(output_lifetime_params),
1622 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
1623 let mut ids = SmallVec::<[NodeId; 1]>::new();
1624 if self.sess.features_untracked().impl_trait_in_bindings {
1625 if let Some(ref ty) = l.ty {
1626 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
1627 visitor.visit_ty(ty);
1630 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
1631 let ty = l.ty.as_ref().map(|t| {
1634 if self.sess.features_untracked().impl_trait_in_bindings {
1635 ImplTraitContext::OpaqueTy(Some(parent_def_id))
1637 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
1641 let init = l.init.as_ref().map(|e| self.lower_expr(e));
1644 hir_id: self.lower_node_id(l.id),
1646 pat: self.lower_pat(&l.pat),
1649 attrs: l.attrs.clone(),
1650 source: hir::LocalSource::Normal,
1656 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
1657 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1658 // as they are not explicit in HIR/Ty function signatures.
1659 // (instead, the `c_variadic` flag is set to `true`)
1660 let mut inputs = &decl.inputs[..];
1661 if decl.c_variadic() {
1662 inputs = &inputs[..inputs.len() - 1];
1664 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
1665 PatKind::Ident(_, ident, _) => ident,
1666 _ => Ident::new(kw::Invalid, param.pat.span),
1670 // Lowers a function declaration.
1672 // `decl`: the unlowered (AST) function declaration.
1673 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
1674 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
1675 // `make_ret_async` is also `Some`.
1676 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
1677 // This guards against trait declarations and implementations where `impl Trait` is
1679 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
1680 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
1681 // return type `impl Trait` item.
1685 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
1686 impl_trait_return_allow: bool,
1687 make_ret_async: Option<NodeId>,
1688 ) -> &'hir hir::FnDecl<'hir> {
1692 in_band_ty_params: {:?}, \
1693 impl_trait_return_allow: {}, \
1694 make_ret_async: {:?})",
1695 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
1697 let lt_mode = if make_ret_async.is_some() {
1698 // In `async fn`, argument-position elided lifetimes
1699 // must be transformed into fresh generic parameters so that
1700 // they can be applied to the opaque `impl Trait` return type.
1701 AnonymousLifetimeMode::CreateParameter
1703 self.anonymous_lifetime_mode
1706 let c_variadic = decl.c_variadic();
1708 // Remember how many lifetimes were already around so that we can
1709 // only look at the lifetime parameters introduced by the arguments.
1710 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
1711 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
1712 // as they are not explicit in HIR/Ty function signatures.
1713 // (instead, the `c_variadic` flag is set to `true`)
1714 let mut inputs = &decl.inputs[..];
1716 inputs = &inputs[..inputs.len() - 1];
1718 this.arena.alloc_from_iter(inputs.iter().map(|param| {
1719 if let Some((_, ibty)) = &mut in_band_ty_params {
1720 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
1722 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
1727 let output = if let Some(ret_id) = make_ret_async {
1728 self.lower_async_fn_ret_ty(
1730 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
1735 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
1736 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
1737 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
1739 _ => hir::FunctionRetTy::Return(
1740 self.lower_ty(ty, ImplTraitContext::disallowed()),
1743 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
1747 self.arena.alloc(hir::FnDecl {
1751 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
1752 let is_mutable_pat = match arg.pat.kind {
1753 PatKind::Ident(BindingMode::ByValue(mt), _, _)
1754 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
1759 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
1760 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
1761 // Given we are only considering `ImplicitSelf` types, we needn't consider
1762 // the case where we have a mutable pattern to a reference as that would
1763 // no longer be an `ImplicitSelf`.
1764 TyKind::Rptr(_, ref mt)
1765 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
1767 hir::ImplicitSelfKind::MutRef
1769 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
1770 hir::ImplicitSelfKind::ImmRef
1772 _ => hir::ImplicitSelfKind::None,
1778 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
1779 // combined with the following definition of `OpaqueTy`:
1781 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
1783 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
1784 // `output`: unlowered output type (`T` in `-> T`)
1785 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
1786 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
1787 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
1788 fn lower_async_fn_ret_ty(
1790 output: &FunctionRetTy,
1792 opaque_ty_node_id: NodeId,
1793 ) -> hir::FunctionRetTy<'hir> {
1795 "lower_async_fn_ret_ty(\
1798 opaque_ty_node_id={:?})",
1799 output, fn_def_id, opaque_ty_node_id,
1802 let span = output.span();
1804 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
1806 let opaque_ty_def_index =
1807 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1809 self.allocate_hir_id_counter(opaque_ty_node_id);
1811 // When we create the opaque type for this async fn, it is going to have
1812 // to capture all the lifetimes involved in the signature (including in the
1813 // return type). This is done by introducing lifetime parameters for:
1815 // - all the explicitly declared lifetimes from the impl and function itself;
1816 // - all the elided lifetimes in the fn arguments;
1817 // - all the elided lifetimes in the return type.
1819 // So for example in this snippet:
1822 // impl<'a> Foo<'a> {
1823 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
1824 // // ^ '0 ^ '1 ^ '2
1825 // // elided lifetimes used below
1830 // we would create an opaque type like:
1833 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
1836 // and we would then desugar `bar` to the equivalent of:
1839 // impl<'a> Foo<'a> {
1840 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
1844 // Note that the final parameter to `Bar` is `'_`, not `'2` --
1845 // this is because the elided lifetimes from the return type
1846 // should be figured out using the ordinary elision rules, and
1847 // this desugaring achieves that.
1849 // The variable `input_lifetimes_count` tracks the number of
1850 // lifetime parameters to the opaque type *not counting* those
1851 // lifetimes elided in the return type. This includes those
1852 // that are explicitly declared (`in_scope_lifetimes`) and
1853 // those elided lifetimes we found in the arguments (current
1854 // content of `lifetimes_to_define`). Next, we will process
1855 // the return type, which will cause `lifetimes_to_define` to
1857 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
1859 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
1860 // We have to be careful to get elision right here. The
1861 // idea is that we create a lifetime parameter for each
1862 // lifetime in the return type. So, given a return type
1863 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
1864 // Future<Output = &'1 [ &'2 u32 ]>`.
1866 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
1867 // hence the elision takes place at the fn site.
1868 let future_bound = this
1869 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
1870 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
1873 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
1875 // Calculate all the lifetimes that should be captured
1876 // by the opaque type. This should include all in-scope
1877 // lifetime parameters, including those defined in-band.
1879 // Note: this must be done after lowering the output type,
1880 // as the output type may introduce new in-band lifetimes.
1881 let lifetime_params: Vec<(Span, ParamName)> = this
1885 .map(|name| (name.ident().span, name))
1886 .chain(this.lifetimes_to_define.iter().cloned())
1889 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
1890 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
1891 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
1893 let generic_params =
1894 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
1895 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
1898 let opaque_ty_item = hir::OpaqueTy {
1899 generics: hir::Generics {
1900 params: generic_params,
1901 where_clause: hir::WhereClause { predicates: &[], span },
1904 bounds: arena_vec![this; future_bound],
1905 impl_trait_fn: Some(fn_def_id),
1906 origin: hir::OpaqueTyOrigin::AsyncFn,
1909 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
1911 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1913 (opaque_ty_id, lifetime_params)
1916 // As documented above on the variable
1917 // `input_lifetimes_count`, we need to create the lifetime
1918 // arguments to our opaque type. Continuing with our example,
1919 // we're creating the type arguments for the return type:
1922 // Bar<'a, 'b, '0, '1, '_>
1925 // For the "input" lifetime parameters, we wish to create
1926 // references to the parameters themselves, including the
1927 // "implicit" ones created from parameter types (`'a`, `'b`,
1930 // For the "output" lifetime parameters, we just want to
1932 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
1934 .map(|&(span, hir_name)| {
1935 // Input lifetime like `'a` or `'1`:
1936 GenericArg::Lifetime(hir::Lifetime {
1937 hir_id: self.next_id(),
1939 name: hir::LifetimeName::Param(hir_name),
1943 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
1944 // Output lifetime like `'_`.
1945 GenericArg::Lifetime(hir::Lifetime {
1946 hir_id: self.next_id(),
1948 name: hir::LifetimeName::Implicit,
1950 let generic_args = self.arena.alloc_from_iter(generic_args);
1952 // Create the `Foo<...>` reference itself. Note that the `type
1953 // Foo = impl Trait` is, internally, created as a child of the
1954 // async fn, so the *type parameters* are inherited. It's
1955 // only the lifetime parameters that we must supply.
1956 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
1957 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
1958 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
1961 /// Transforms `-> T` into `Future<Output = T>`
1962 fn lower_async_fn_output_type_to_future_bound(
1964 output: &FunctionRetTy,
1967 ) -> hir::GenericBound<'hir> {
1968 // Compute the `T` in `Future<Output = T>` from the return type.
1969 let output_ty = match output {
1970 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
1971 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
1975 let future_params = self.arena.alloc(hir::GenericArgs {
1977 bindings: arena_vec![self; self.output_ty_binding(span, output_ty)],
1978 parenthesized: false,
1981 // ::std::future::Future<future_params>
1983 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
1985 hir::GenericBound::Trait(
1987 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
1988 bound_generic_params: &[],
1991 hir::TraitBoundModifier::None,
1995 fn lower_param_bound(
1998 itctx: ImplTraitContext<'_, 'hir>,
1999 ) -> hir::GenericBound<'hir> {
2001 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2002 self.lower_poly_trait_ref(ty, itctx),
2003 self.lower_trait_bound_modifier(modifier),
2005 GenericBound::Outlives(ref lifetime) => {
2006 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2011 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2012 let span = l.ident.span;
2014 ident if ident.name == kw::StaticLifetime => {
2015 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2017 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2018 AnonymousLifetimeMode::CreateParameter => {
2019 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2020 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2023 AnonymousLifetimeMode::PassThrough => {
2024 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2027 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2030 self.maybe_collect_in_band_lifetime(ident);
2031 let param_name = ParamName::Plain(ident);
2032 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2037 fn new_named_lifetime(
2041 name: hir::LifetimeName,
2042 ) -> hir::Lifetime {
2043 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2046 fn lower_generic_params_mut<'s>(
2048 params: &'s [GenericParam],
2049 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2050 mut itctx: ImplTraitContext<'s, 'hir>,
2051 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2054 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2057 fn lower_generic_params(
2059 params: &[GenericParam],
2060 add_bounds: &NodeMap<Vec<GenericBound>>,
2061 itctx: ImplTraitContext<'_, 'hir>,
2062 ) -> &'hir [hir::GenericParam<'hir>] {
2063 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2066 fn lower_generic_param(
2068 param: &GenericParam,
2069 add_bounds: &NodeMap<Vec<GenericBound>>,
2070 mut itctx: ImplTraitContext<'_, 'hir>,
2071 ) -> hir::GenericParam<'hir> {
2072 let mut bounds: Vec<_> = self
2073 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2074 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2077 let (name, kind) = match param.kind {
2078 GenericParamKind::Lifetime => {
2079 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2080 self.is_collecting_in_band_lifetimes = false;
2083 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2084 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2086 let param_name = match lt.name {
2087 hir::LifetimeName::Param(param_name) => param_name,
2088 hir::LifetimeName::Implicit
2089 | hir::LifetimeName::Underscore
2090 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2091 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2094 "object-lifetime-default should not occur here",
2097 hir::LifetimeName::Error => ParamName::Error,
2101 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2103 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2107 GenericParamKind::Type { ref default, .. } => {
2108 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2109 if !add_bounds.is_empty() {
2110 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2111 bounds.extend(params);
2114 let kind = hir::GenericParamKind::Type {
2117 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2121 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2122 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2126 (hir::ParamName::Plain(param.ident), kind)
2128 GenericParamKind::Const { ref ty } => {
2130 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2131 this.lower_ty(&ty, ImplTraitContext::disallowed())
2134 (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty })
2139 hir_id: self.lower_node_id(param.id),
2141 span: param.ident.span,
2142 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2143 attrs: self.lower_attrs(¶m.attrs),
2144 bounds: self.arena.alloc_from_iter(bounds),
2152 itctx: ImplTraitContext<'_, 'hir>,
2153 ) -> hir::TraitRef<'hir> {
2154 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2155 hir::QPath::Resolved(None, path) => path,
2156 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2158 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2161 fn lower_poly_trait_ref(
2164 mut itctx: ImplTraitContext<'_, 'hir>,
2165 ) -> hir::PolyTraitRef<'hir> {
2166 let bound_generic_params = self.lower_generic_params(
2167 &p.bound_generic_params,
2168 &NodeMap::default(),
2171 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2172 this.lower_trait_ref(&p.trait_ref, itctx)
2175 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2178 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2179 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2182 fn lower_param_bounds(
2184 bounds: &[GenericBound],
2185 itctx: ImplTraitContext<'_, 'hir>,
2186 ) -> hir::GenericBounds<'hir> {
2187 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2190 fn lower_param_bounds_mut<'s>(
2192 bounds: &'s [GenericBound],
2193 mut itctx: ImplTraitContext<'s, 'hir>,
2194 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2195 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2198 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2199 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2202 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2203 let mut stmts = vec![];
2204 let mut expr: Option<&'hir _> = None;
2206 for (index, stmt) in b.stmts.iter().enumerate() {
2207 if index == b.stmts.len() - 1 {
2208 if let StmtKind::Expr(ref e) = stmt.kind {
2209 expr = Some(self.lower_expr(e));
2211 stmts.extend(self.lower_stmt(stmt));
2214 stmts.extend(self.lower_stmt(stmt));
2219 hir_id: self.lower_node_id(b.id),
2220 stmts: self.arena.alloc_from_iter(stmts),
2222 rules: self.lower_block_check_mode(&b.rules),
2228 /// Lowers a block directly to an expression, presuming that it
2229 /// has no attributes and is not targeted by a `break`.
2230 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2231 let block = self.lower_block(b, false);
2232 self.expr_block(block, AttrVec::new())
2235 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2236 self.with_new_scopes(|this| hir::AnonConst {
2237 hir_id: this.lower_node_id(c.id),
2238 body: this.lower_const_body(c.value.span, Some(&c.value)),
2242 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2243 let kind = match s.kind {
2244 StmtKind::Local(ref l) => {
2245 let (l, item_ids) = self.lower_local(l);
2246 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2249 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2250 self.stmt(s.span, hir::StmtKind::Item(item_id))
2255 hir_id: self.lower_node_id(s.id),
2256 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2262 StmtKind::Item(ref it) => {
2263 // Can only use the ID once.
2264 let mut id = Some(s.id);
2271 .map(|id| self.lower_node_id(id))
2272 .unwrap_or_else(|| self.next_id());
2274 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2278 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2279 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2280 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2282 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2285 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2287 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2288 BlockCheckMode::Unsafe(u) => {
2289 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2294 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2296 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2297 UserProvided => hir::UnsafeSource::UserProvided,
2301 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2303 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2304 TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
2306 // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
2307 // placeholder for compilation to proceed.
2308 TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
2309 hir::TraitBoundModifier::Maybe
2314 // Helper methods for building HIR.
2316 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2317 hir::Stmt { span, kind, hir_id: self.next_id() }
2320 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2321 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2328 init: Option<&'hir hir::Expr<'hir>>,
2329 pat: &'hir hir::Pat<'hir>,
2330 source: hir::LocalSource,
2331 ) -> hir::Stmt<'hir> {
2332 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2333 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2336 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2337 self.block_all(expr.span, &[], Some(expr))
2343 stmts: &'hir [hir::Stmt<'hir>],
2344 expr: Option<&'hir hir::Expr<'hir>>,
2345 ) -> &'hir hir::Block<'hir> {
2346 let blk = hir::Block {
2349 hir_id: self.next_id(),
2350 rules: hir::BlockCheckMode::DefaultBlock,
2352 targeted_by_break: false,
2354 self.arena.alloc(blk)
2357 /// Constructs a `true` or `false` literal pattern.
2358 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
2359 let expr = self.expr_bool(span, val);
2360 self.pat(span, hir::PatKind::Lit(expr))
2363 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2364 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
2367 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2368 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
2371 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
2372 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
2375 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2376 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
2382 components: &[Symbol],
2383 subpats: &'hir [&'hir hir::Pat<'hir>],
2384 ) -> &'hir hir::Pat<'hir> {
2385 let path = self.std_path(span, components, None, true);
2386 let qpath = hir::QPath::Resolved(None, path);
2387 let pt = if subpats.is_empty() {
2388 hir::PatKind::Path(qpath)
2390 hir::PatKind::TupleStruct(qpath, subpats, None)
2395 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2396 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
2399 fn pat_ident_binding_mode(
2403 bm: hir::BindingAnnotation,
2404 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
2405 let hir_id = self.next_id();
2408 self.arena.alloc(hir::Pat {
2410 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
2417 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
2418 self.pat(span, hir::PatKind::Wild)
2421 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2422 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
2425 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
2426 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
2427 /// The path is also resolved according to `is_value`.
2431 components: &[Symbol],
2432 params: Option<&'hir hir::GenericArgs<'hir>>,
2434 ) -> &'hir hir::Path<'hir> {
2435 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
2436 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
2438 let mut segments: Vec<_> = path
2442 let res = self.expect_full_res(segment.id);
2444 ident: segment.ident,
2445 hir_id: Some(self.lower_node_id(segment.id)),
2446 res: Some(self.lower_res(res)),
2452 segments.last_mut().unwrap().args = params;
2454 self.arena.alloc(hir::Path {
2456 res: res.map_id(|_| panic!("unexpected `NodeId`")),
2457 segments: self.arena.alloc_from_iter(segments),
2463 mut hir_id: hir::HirId,
2465 qpath: hir::QPath<'hir>,
2466 ) -> hir::Ty<'hir> {
2467 let kind = match qpath {
2468 hir::QPath::Resolved(None, path) => {
2469 // Turn trait object paths into `TyKind::TraitObject` instead.
2471 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
2472 let principal = hir::PolyTraitRef {
2473 bound_generic_params: &[],
2474 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
2478 // The original ID is taken by the `PolyTraitRef`,
2479 // so the `Ty` itself needs a different one.
2480 hir_id = self.next_id();
2481 hir::TyKind::TraitObject(
2482 arena_vec![self; principal],
2483 self.elided_dyn_bound(span),
2486 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
2489 _ => hir::TyKind::Path(qpath),
2492 hir::Ty { hir_id, kind, span }
2495 /// Invoked to create the lifetime argument for a type `&T`
2496 /// with no explicit lifetime.
2497 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
2498 match self.anonymous_lifetime_mode {
2499 // Intercept when we are in an impl header or async fn and introduce an in-band
2501 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
2503 AnonymousLifetimeMode::CreateParameter => {
2504 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2506 hir_id: self.next_id(),
2508 name: hir::LifetimeName::Param(fresh_name),
2512 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
2514 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
2518 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
2519 /// return a "error lifetime".
2520 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
2521 let (id, msg, label) = match id {
2522 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
2525 self.resolver.next_node_id(),
2526 "`&` without an explicit lifetime name cannot be used here",
2527 "explicit lifetime name needed here",
2531 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
2532 err.span_label(span, label);
2535 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2538 /// Invoked to create the lifetime argument(s) for a path like
2539 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
2540 /// sorts of cases are deprecated. This may therefore report a warning or an
2541 /// error, depending on the mode.
2542 fn elided_path_lifetimes<'s>(
2546 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
2547 (0..count).map(move |_| self.elided_path_lifetime(span))
2550 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
2551 match self.anonymous_lifetime_mode {
2552 AnonymousLifetimeMode::CreateParameter => {
2553 // We should have emitted E0726 when processing this path above
2555 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
2556 let id = self.resolver.next_node_id();
2557 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
2559 // `PassThrough` is the normal case.
2560 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
2561 // is unsuitable here, as these can occur from missing lifetime parameters in a
2562 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
2563 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
2564 // later, at which point a suitable error will be emitted.
2565 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
2566 self.new_implicit_lifetime(span)
2571 /// Invoked to create the lifetime argument(s) for an elided trait object
2572 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
2573 /// when the bound is written, even if it is written with `'_` like in
2574 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
2575 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
2576 match self.anonymous_lifetime_mode {
2577 // NB. We intentionally ignore the create-parameter mode here.
2578 // and instead "pass through" to resolve-lifetimes, which will apply
2579 // the object-lifetime-defaulting rules. Elided object lifetime defaults
2580 // do not act like other elided lifetimes. In other words, given this:
2582 // impl Foo for Box<dyn Debug>
2584 // we do not introduce a fresh `'_` to serve as the bound, but instead
2585 // ultimately translate to the equivalent of:
2587 // impl Foo for Box<dyn Debug + 'static>
2589 // `resolve_lifetime` has the code to make that happen.
2590 AnonymousLifetimeMode::CreateParameter => {}
2592 AnonymousLifetimeMode::ReportError => {
2593 // ReportError applies to explicit use of `'_`.
2596 // This is the normal case.
2597 AnonymousLifetimeMode::PassThrough => {}
2600 let r = hir::Lifetime {
2601 hir_id: self.next_id(),
2603 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
2605 debug!("elided_dyn_bound: r={:?}", r);
2609 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
2610 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
2613 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
2614 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
2615 // call site which do not have a macro backtrace. See #61963.
2616 let is_macro_callsite = self
2619 .span_to_snippet(span)
2620 .map(|snippet| snippet.starts_with("#["))
2622 if !is_macro_callsite {
2623 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
2624 builtin::BARE_TRAIT_OBJECTS,
2627 "trait objects without an explicit `dyn` are deprecated",
2628 BuiltinLintDiagnostics::BareTraitObject(span, is_global),
2634 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
2635 // Sorting by span ensures that we get things in order within a
2636 // file, and also puts the files in a sensible order.
2637 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2638 body_ids.sort_by_key(|b| bodies[b].value.span);
2642 /// Helper struct for delayed construction of GenericArgs.
2643 struct GenericArgsCtor<'hir> {
2644 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
2645 bindings: &'hir [hir::TypeBinding<'hir>],
2646 parenthesized: bool,
2649 impl<'hir> GenericArgsCtor<'hir> {
2650 fn is_empty(&self) -> bool {
2651 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
2654 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
2656 args: arena.alloc_from_iter(self.args),
2657 bindings: self.bindings,
2658 parenthesized: self.parenthesized,