1 // ignore-tidy-filelength
3 //! Lowers the AST to the HIR.
5 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
6 //! much like a fold. Where lowering involves a bit more work things get more
7 //! interesting and there are some invariants you should know about. These mostly
8 //! concern spans and IDs.
10 //! Spans are assigned to AST nodes during parsing and then are modified during
11 //! expansion to indicate the origin of a node and the process it went through
12 //! being expanded. IDs are assigned to AST nodes just before lowering.
14 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
15 //! expansion we do not preserve the process of lowering in the spans, so spans
16 //! should not be modified here. When creating a new node (as opposed to
17 //! 'folding' an existing one), then you create a new ID using `next_id()`.
19 //! You must ensure that IDs are unique. That means that you should only use the
20 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
21 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
22 //! If you do, you must then set the new node's ID to a fresh one.
24 //! Spans are used for error messages and for tools to map semantics back to
25 //! source code. It is therefore not as important with spans as IDs to be strict
26 //! about use (you can't break the compiler by screwing up a span). Obviously, a
27 //! HIR node can only have a single span. But multiple nodes can have the same
28 //! span and spans don't need to be kept in order, etc. Where code is preserved
29 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
30 //! new it is probably best to give a span for the whole AST node being lowered.
31 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
32 //! get confused if the spans from leaf AST nodes occur in multiple places
33 //! in the HIR, especially for multiple identifiers.
35 #![feature(array_value_iter)]
37 use rustc::arena::Arena;
38 use rustc::dep_graph::DepGraph;
39 use rustc::hir::map::definitions::{DefKey, DefPathData, Definitions};
40 use rustc::hir::map::Map;
42 use rustc::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
43 use rustc::middle::cstore::CrateStore;
44 use rustc::util::captures::Captures;
45 use rustc::util::common::FN_OUTPUT_NAME;
46 use rustc::{bug, span_bug};
47 use rustc_data_structures::fx::FxHashSet;
48 use rustc_data_structures::sync::Lrc;
49 use rustc_error_codes::*;
50 use rustc_errors::{struct_span_err, Applicability};
52 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
53 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
54 use rustc_hir::intravisit;
55 use rustc_hir::{ConstArg, GenericArg, ParamName};
56 use rustc_index::vec::IndexVec;
57 use rustc_session::config::nightly_options;
58 use rustc_session::node_id::NodeMap;
59 use rustc_session::Session;
60 use rustc_span::hygiene::ExpnId;
61 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
62 use rustc_span::symbol::{kw, sym, Symbol};
67 use syntax::print::pprust;
68 use syntax::ptr::P as AstP;
69 use syntax::sess::ParseSess;
70 use syntax::token::{self, Nonterminal, Token};
71 use syntax::tokenstream::{TokenStream, TokenTree};
72 use syntax::visit::{self, Visitor};
73 use syntax::walk_list;
75 use log::{debug, trace};
76 use smallvec::{smallvec, SmallVec};
77 use std::collections::BTreeMap;
80 macro_rules! arena_vec {
81 ($this:expr; $($x:expr),*) => ({
83 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
90 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
92 struct LoweringContext<'a, 'hir: 'a> {
93 crate_root: Option<Symbol>,
95 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
98 resolver: &'a mut dyn Resolver,
100 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
101 /// if we don't have this function pointer. To avoid that dependency so that
102 /// librustc is independent of the parser, we use dynamic dispatch here.
103 nt_to_tokenstream: NtToTokenstream,
105 /// Used to allocate HIR nodes
106 arena: &'hir Arena<'hir>,
108 /// The items being lowered are collected here.
109 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
111 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
112 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
113 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
114 exported_macros: Vec<hir::MacroDef<'hir>>,
115 non_exported_macro_attrs: Vec<ast::Attribute>,
117 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
119 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
121 generator_kind: Option<hir::GeneratorKind>,
123 /// Used to get the current `fn`'s def span to point to when using `await`
124 /// outside of an `async fn`.
125 current_item: Option<Span>,
127 catch_scopes: Vec<NodeId>,
128 loop_scopes: Vec<NodeId>,
129 is_in_loop_condition: bool,
130 is_in_trait_impl: bool,
131 is_in_dyn_type: bool,
133 /// What to do when we encounter either an "anonymous lifetime
134 /// reference". The term "anonymous" is meant to encompass both
135 /// `'_` lifetimes as well as fully elided cases where nothing is
136 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
137 anonymous_lifetime_mode: AnonymousLifetimeMode,
139 /// Used to create lifetime definitions from in-band lifetime usages.
140 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
141 /// When a named lifetime is encountered in a function or impl header and
142 /// has not been defined
143 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
144 /// to this list. The results of this list are then added to the list of
145 /// lifetime definitions in the corresponding impl or function generics.
146 lifetimes_to_define: Vec<(Span, ParamName)>,
148 /// `true` if in-band lifetimes are being collected. This is used to
149 /// indicate whether or not we're in a place where new lifetimes will result
150 /// in in-band lifetime definitions, such a function or an impl header,
151 /// including implicit lifetimes from `impl_header_lifetime_elision`.
152 is_collecting_in_band_lifetimes: bool,
154 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
155 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
156 /// against this list to see if it is already in-scope, or if a definition
157 /// needs to be created for it.
159 /// We always store a `modern()` version of the param-name in this
161 in_scope_lifetimes: Vec<ParamName>,
163 current_module: hir::HirId,
165 type_def_lifetime_params: DefIdMap<usize>,
167 current_hir_id_owner: Vec<(DefIndex, u32)>,
168 item_local_id_counters: NodeMap<u32>,
169 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
171 allow_try_trait: Option<Lrc<[Symbol]>>,
172 allow_gen_future: Option<Lrc<[Symbol]>>,
176 fn cstore(&self) -> &dyn CrateStore;
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 lint::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.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<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
438 F: FnOnce(&mut Self) -> T,
440 let old = mem::replace(&mut self.hir_id_owner, owner);
442 self.hir_id_owner = old;
447 impl<'tcx, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
448 fn visit_pat(&mut self, p: &'tcx Pat) {
449 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
450 // Doesn't generate a HIR node
451 } else if let Some(owner) = self.hir_id_owner {
452 self.lctx.lower_node_id_with_owner(p.id, owner);
455 visit::walk_pat(self, p)
458 fn visit_item(&mut self, item: &'tcx Item) {
459 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
462 ItemKind::Struct(_, ref generics)
463 | ItemKind::Union(_, ref generics)
464 | ItemKind::Enum(_, ref generics)
465 | ItemKind::TyAlias(_, ref generics)
466 | ItemKind::Trait(_, _, ref generics, ..) => {
467 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
471 .filter(|param| match param.kind {
472 ast::GenericParamKind::Lifetime { .. } => true,
476 self.lctx.type_def_lifetime_params.insert(def_id, count);
478 ItemKind::Use(ref use_tree) => {
479 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
484 self.with_hir_id_owner(Some(item.id), |this| {
485 visit::walk_item(this, item);
489 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
490 self.lctx.allocate_hir_id_counter(item.id);
493 AssocItemKind::Fn(_, None) => {
494 // Ignore patterns in trait methods without bodies
495 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
497 _ => self.with_hir_id_owner(Some(item.id), |this| {
498 visit::walk_trait_item(this, item);
503 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
504 self.lctx.allocate_hir_id_counter(item.id);
505 self.with_hir_id_owner(Some(item.id), |this| {
506 visit::walk_impl_item(this, item);
510 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
511 // Ignore patterns in foreign items
512 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
515 fn visit_ty(&mut self, t: &'tcx Ty) {
517 // Mirrors the case in visit::walk_ty
518 TyKind::BareFn(ref f) => {
519 walk_list!(self, visit_generic_param, &f.generic_params);
520 // Mirrors visit::walk_fn_decl
521 for parameter in &f.decl.inputs {
522 // We don't lower the ids of argument patterns
523 self.with_hir_id_owner(None, |this| {
524 this.visit_pat(¶meter.pat);
526 self.visit_ty(¶meter.ty)
528 self.visit_fn_ret_ty(&f.decl.output)
530 _ => visit::walk_ty(self, t),
535 self.lower_node_id(CRATE_NODE_ID);
536 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
538 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
539 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
541 let module = self.lower_mod(&c.module);
542 let attrs = self.lower_attrs(&c.attrs);
543 let body_ids = body_ids(&self.bodies);
545 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
551 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
552 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
554 trait_items: self.trait_items,
555 impl_items: self.impl_items,
558 trait_impls: self.trait_impls,
559 modules: self.modules,
563 fn insert_item(&mut self, item: hir::Item<'hir>) {
564 let id = item.hir_id;
565 // FIXME: Use `debug_asset-rt`.
566 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
567 self.items.insert(id, item);
568 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
571 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
572 // Set up the counter if needed.
573 self.item_local_id_counters.entry(owner).or_insert(0);
574 // Always allocate the first `HirId` for the owner itself.
575 let lowered = self.lower_node_id_with_owner(owner, owner);
576 debug_assert_eq!(lowered.local_id.as_u32(), 0);
580 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
582 F: 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<F, T>(&mut self, owner: NodeId, f: F) -> T
609 F: FnOnce(&mut Self) -> T,
612 .item_local_id_counters
613 .insert(owner, HIR_ID_COUNTER_LOCKED)
614 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
615 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
616 self.current_hir_id_owner.push((def_index, counter));
618 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
620 debug_assert!(def_index == new_def_index);
621 debug_assert!(new_counter >= counter);
623 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
624 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
628 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
629 /// the `LoweringContext`'s `NodeId => HirId` map.
630 /// Take care not to call this method if the resulting `HirId` is then not
631 /// actually used in the HIR, as that would trigger an assertion in the
632 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
633 /// properly. Calling the method twice with the same `NodeId` is fine though.
634 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
635 self.lower_node_id_generic(ast_node_id, |this| {
636 let &mut (def_index, ref mut local_id_counter) =
637 this.current_hir_id_owner.last_mut().unwrap();
638 let local_id = *local_id_counter;
639 *local_id_counter += 1;
640 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
644 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
645 self.lower_node_id_generic(ast_node_id, |this| {
646 let local_id_counter = this
647 .item_local_id_counters
649 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
650 let local_id = *local_id_counter;
652 // We want to be sure not to modify the counter in the map while it
653 // is also on the stack. Otherwise we'll get lost updates when writing
654 // back from the stack to the map.
655 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
657 *local_id_counter += 1;
658 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
659 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
660 that do not belong to the current owner",
663 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
667 fn next_id(&mut self) -> hir::HirId {
668 let node_id = self.resolver.next_node_id();
669 self.lower_node_id(node_id)
672 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
674 self.lower_node_id_generic(id, |_| {
675 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
680 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
681 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
682 if pr.unresolved_segments() != 0 {
683 bug!("path not fully resolved: {:?}", pr);
689 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
690 self.resolver.get_import_res(id).present_items()
693 fn diagnostic(&self) -> &rustc_errors::Handler {
694 self.sess.diagnostic()
697 /// Reuses the span but adds information like the kind of the desugaring and features that are
698 /// allowed inside this span.
699 fn mark_span_with_reason(
701 reason: DesugaringKind,
703 allow_internal_unstable: Option<Lrc<[Symbol]>>,
705 span.fresh_expansion(ExpnData {
706 allow_internal_unstable,
707 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
711 fn with_anonymous_lifetime_mode<R>(
713 anonymous_lifetime_mode: AnonymousLifetimeMode,
714 op: impl FnOnce(&mut Self) -> R,
717 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
718 anonymous_lifetime_mode,
720 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
721 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
722 let result = op(self);
723 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
725 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
726 old_anonymous_lifetime_mode
731 /// Creates a new `hir::GenericParam` for every new lifetime and
732 /// type parameter encountered while evaluating `f`. Definitions
733 /// are created with the parent provided. If no `parent_id` is
734 /// provided, no definitions will be returned.
736 /// Presuming that in-band lifetimes are enabled, then
737 /// `self.anonymous_lifetime_mode` will be updated to match the
738 /// parameter while `f` is running (and restored afterwards).
739 fn collect_in_band_defs<T, F>(
742 anonymous_lifetime_mode: AnonymousLifetimeMode,
744 ) -> (Vec<hir::GenericParam<'hir>>, T)
746 F: FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
748 assert!(!self.is_collecting_in_band_lifetimes);
749 assert!(self.lifetimes_to_define.is_empty());
750 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
752 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
753 self.is_collecting_in_band_lifetimes = true;
755 let (in_band_ty_params, res) = f(self);
757 self.is_collecting_in_band_lifetimes = false;
758 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
760 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
762 let params = lifetimes_to_define
764 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
765 .chain(in_band_ty_params.into_iter())
771 /// Converts a lifetime into a new generic parameter.
772 fn lifetime_to_generic_param(
776 parent_index: DefIndex,
777 ) -> hir::GenericParam<'hir> {
778 let node_id = self.resolver.next_node_id();
780 // Get the name we'll use to make the def-path. Note
781 // that collisions are ok here and this shouldn't
782 // really show up for end-user.
783 let (str_name, kind) = match hir_name {
784 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
785 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
786 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
789 // Add a definition for the in-band lifetime def.
790 self.resolver.definitions().create_def_with_parent(
793 DefPathData::LifetimeNs(str_name),
799 hir_id: self.lower_node_id(node_id),
804 pure_wrt_drop: false,
805 kind: hir::GenericParamKind::Lifetime { kind },
809 /// When there is a reference to some lifetime `'a`, and in-band
810 /// lifetimes are enabled, then we want to push that lifetime into
811 /// the vector of names to define later. In that case, it will get
812 /// added to the appropriate generics.
813 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
814 if !self.is_collecting_in_band_lifetimes {
818 if !self.sess.features_untracked().in_band_lifetimes {
822 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
826 let hir_name = ParamName::Plain(ident);
828 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
833 self.lifetimes_to_define.push((ident.span, hir_name));
836 /// When we have either an elided or `'_` lifetime in an impl
837 /// header, we convert it to an in-band lifetime.
838 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
839 assert!(self.is_collecting_in_band_lifetimes);
840 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
841 let hir_name = ParamName::Fresh(index);
842 self.lifetimes_to_define.push((span, hir_name));
846 // Evaluates `f` with the lifetimes in `params` in-scope.
847 // This is used to track which lifetimes have already been defined, and
848 // which are new in-band lifetimes that need to have a definition created
850 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
852 F: FnOnce(&mut Self) -> T,
854 let old_len = self.in_scope_lifetimes.len();
855 let lt_def_names = params.iter().filter_map(|param| match param.kind {
856 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
859 self.in_scope_lifetimes.extend(lt_def_names);
863 self.in_scope_lifetimes.truncate(old_len);
867 /// Appends in-band lifetime defs and argument-position `impl
868 /// Trait` defs to the existing set of generics.
870 /// Presuming that in-band lifetimes are enabled, then
871 /// `self.anonymous_lifetime_mode` will be updated to match the
872 /// parameter while `f` is running (and restored afterwards).
873 fn add_in_band_defs<F, T>(
877 anonymous_lifetime_mode: AnonymousLifetimeMode,
879 ) -> (hir::Generics<'hir>, T)
881 F: FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
883 let (in_band_defs, (mut lowered_generics, res)) =
884 self.with_in_scope_lifetime_defs(&generics.params, |this| {
885 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
886 let mut params = Vec::new();
887 // Note: it is necessary to lower generics *before* calling `f`.
888 // When lowering `async fn`, there's a final step when lowering
889 // the return type that assumes that all in-scope lifetimes have
890 // already been added to either `in_scope_lifetimes` or
891 // `lifetimes_to_define`. If we swapped the order of these two,
892 // in-band-lifetimes introduced by generics or where-clauses
893 // wouldn't have been added yet.
895 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
896 let res = f(this, &mut params);
897 (params, (generics, res))
901 let mut lowered_params: Vec<_> =
902 lowered_generics.params.into_iter().chain(in_band_defs).collect();
904 // FIXME(const_generics): the compiler doesn't always cope with
905 // unsorted generic parameters at the moment, so we make sure
906 // that they're ordered correctly here for now. (When we chain
907 // the `in_band_defs`, we might make the order unsorted.)
908 lowered_params.sort_by_key(|param| match param.kind {
909 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
910 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
911 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
914 lowered_generics.params = lowered_params.into();
916 let lowered_generics = lowered_generics.into_generics(self.arena);
917 (lowered_generics, res)
920 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
922 F: FnOnce(&mut Self) -> T,
924 let was_in_dyn_type = self.is_in_dyn_type;
925 self.is_in_dyn_type = in_scope;
927 let result = f(self);
929 self.is_in_dyn_type = was_in_dyn_type;
934 fn with_new_scopes<T, F>(&mut self, f: F) -> T
936 F: FnOnce(&mut Self) -> T,
938 let was_in_loop_condition = self.is_in_loop_condition;
939 self.is_in_loop_condition = false;
941 let catch_scopes = mem::take(&mut self.catch_scopes);
942 let loop_scopes = mem::take(&mut self.loop_scopes);
944 self.catch_scopes = catch_scopes;
945 self.loop_scopes = loop_scopes;
947 self.is_in_loop_condition = was_in_loop_condition;
952 fn def_key(&mut self, id: DefId) -> DefKey {
954 self.resolver.definitions().def_key(id.index)
956 self.resolver.cstore().def_key(id)
960 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
961 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
964 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
965 // Note that we explicitly do not walk the path. Since we don't really
966 // lower attributes (we use the AST version) there is nowhere to keep
967 // the `HirId`s. We don't actually need HIR version of attributes anyway.
968 let kind = match attr.kind {
969 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
970 path: item.path.clone(),
971 args: self.lower_mac_args(&item.args),
973 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
976 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
979 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
981 MacArgs::Empty => MacArgs::Empty,
982 MacArgs::Delimited(dspan, delim, ref tokens) => {
983 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
985 MacArgs::Eq(eq_span, ref tokens) => {
986 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
991 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
992 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
995 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
997 TokenTree::Token(token) => self.lower_token(token),
998 TokenTree::Delimited(span, delim, tts) => {
999 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
1004 fn lower_token(&mut self, token: Token) -> TokenStream {
1006 token::Interpolated(nt) => {
1007 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1008 self.lower_token_stream(tts)
1010 _ => TokenTree::Token(token).into(),
1014 /// Given an associated type constraint like one of these:
1017 /// T: Iterator<Item: Debug>
1019 /// T: Iterator<Item = Debug>
1023 /// returns a `hir::TypeBinding` representing `Item`.
1024 fn lower_assoc_ty_constraint(
1026 constraint: &AssocTyConstraint,
1027 itctx: ImplTraitContext<'_, 'hir>,
1028 ) -> hir::TypeBinding<'hir> {
1029 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1031 let kind = match constraint.kind {
1032 AssocTyConstraintKind::Equality { ref ty } => {
1033 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1035 AssocTyConstraintKind::Bound { ref bounds } => {
1036 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1037 let (desugar_to_impl_trait, itctx) = match itctx {
1038 // We are in the return position:
1040 // fn foo() -> impl Iterator<Item: Debug>
1044 // fn foo() -> impl Iterator<Item = impl Debug>
1045 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1047 // We are in the argument position, but within a dyn type:
1049 // fn foo(x: dyn Iterator<Item: Debug>)
1053 // fn foo(x: dyn Iterator<Item = impl Debug>)
1054 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1056 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1057 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1058 // "impl trait context" to permit `impl Debug` in this position (it desugars
1059 // then to an opaque type).
1061 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1062 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1063 (true, ImplTraitContext::OpaqueTy(None))
1066 // We are in the parameter position, but not within a dyn type:
1068 // fn foo(x: impl Iterator<Item: Debug>)
1070 // so we leave it as is and this gets expanded in astconv to a bound like
1071 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1073 _ => (false, itctx),
1076 if desugar_to_impl_trait {
1077 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1078 // constructing the HIR for `impl bounds...` and then lowering that.
1080 let impl_trait_node_id = self.resolver.next_node_id();
1081 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1082 self.resolver.definitions().create_def_with_parent(
1085 DefPathData::ImplTrait,
1090 self.with_dyn_type_scope(false, |this| {
1091 let node_id = this.resolver.next_node_id();
1092 let ty = this.lower_ty(
1095 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1096 span: constraint.span,
1101 hir::TypeBindingKind::Equality { ty }
1104 // Desugar `AssocTy: Bounds` into a type binding where the
1105 // later desugars into a trait predicate.
1106 let bounds = self.lower_param_bounds(bounds, itctx);
1108 hir::TypeBindingKind::Constraint { bounds }
1114 hir_id: self.lower_node_id(constraint.id),
1115 ident: constraint.ident,
1117 span: constraint.span,
1121 fn lower_generic_arg(
1123 arg: &ast::GenericArg,
1124 itctx: ImplTraitContext<'_, 'hir>,
1125 ) -> hir::GenericArg<'hir> {
1127 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1128 ast::GenericArg::Type(ty) => {
1129 // We parse const arguments as path types as we cannot distiguish them durring
1130 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1131 // type and value namespaces. If we resolved the path in the value namespace, we
1132 // transform it into a generic const argument.
1133 if let TyKind::Path(ref qself, ref path) = ty.kind {
1134 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1135 let res = partial_res.base_res();
1136 if !res.matches_ns(Namespace::TypeNS) {
1138 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1142 // Construct a AnonConst where the expr is the "ty"'s path.
1144 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1145 let node_id = self.resolver.next_node_id();
1147 // Add a definition for the in-band const def.
1148 self.resolver.definitions().create_def_with_parent(
1151 DefPathData::AnonConst,
1156 let path_expr = Expr {
1158 kind: ExprKind::Path(qself.clone(), path.clone()),
1160 attrs: AttrVec::new(),
1163 let ct = self.with_new_scopes(|this| hir::AnonConst {
1164 hir_id: this.lower_node_id(node_id),
1165 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1167 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1171 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1173 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1174 value: self.lower_anon_const(&ct),
1175 span: ct.value.span,
1180 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1181 self.arena.alloc(self.lower_ty_direct(t, itctx))
1187 qself: &Option<QSelf>,
1189 param_mode: ParamMode,
1190 itctx: ImplTraitContext<'_, 'hir>,
1191 ) -> hir::Ty<'hir> {
1192 let id = self.lower_node_id(t.id);
1193 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1194 let ty = self.ty_path(id, t.span, qpath);
1195 if let hir::TyKind::TraitObject(..) = ty.kind {
1196 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1201 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1202 hir::Ty { hir_id: self.next_id(), kind, span }
1205 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1206 self.ty(span, hir::TyKind::Tup(tys))
1209 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1210 let kind = match t.kind {
1211 TyKind::Infer => hir::TyKind::Infer,
1212 TyKind::Err => hir::TyKind::Err,
1213 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1214 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1215 TyKind::Rptr(ref region, ref mt) => {
1216 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1217 let lifetime = match *region {
1218 Some(ref lt) => self.lower_lifetime(lt),
1219 None => self.elided_ref_lifetime(span),
1221 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1223 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1224 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1225 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1226 generic_params: this.lower_generic_params(
1228 &NodeMap::default(),
1229 ImplTraitContext::disallowed(),
1231 unsafety: f.unsafety,
1232 abi: this.lower_extern(f.ext),
1233 decl: this.lower_fn_decl(&f.decl, None, false, None),
1234 param_names: this.lower_fn_params_to_names(&f.decl),
1238 TyKind::Never => hir::TyKind::Never,
1239 TyKind::Tup(ref tys) => {
1240 hir::TyKind::Tup(self.arena.alloc_from_iter(
1241 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1244 TyKind::Paren(ref ty) => {
1245 return self.lower_ty_direct(ty, itctx);
1247 TyKind::Path(ref qself, ref path) => {
1248 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1250 TyKind::ImplicitSelf => {
1251 let res = self.expect_full_res(t.id);
1252 let res = self.lower_res(res);
1253 hir::TyKind::Path(hir::QPath::Resolved(
1255 self.arena.alloc(hir::Path {
1257 segments: arena_vec![self; hir::PathSegment::from_ident(
1258 Ident::with_dummy_span(kw::SelfUpper)
1264 TyKind::Array(ref ty, ref length) => {
1265 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1267 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1268 TyKind::TraitObject(ref bounds, kind) => {
1269 let mut lifetime_bound = None;
1270 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1272 this.arena.alloc_from_iter(bounds.iter().filter_map(
1273 |bound| match *bound {
1274 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1275 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1277 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1278 GenericBound::Outlives(ref lifetime) => {
1279 if lifetime_bound.is_none() {
1280 lifetime_bound = Some(this.lower_lifetime(lifetime));
1286 let lifetime_bound =
1287 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1288 (bounds, lifetime_bound)
1290 if kind != TraitObjectSyntax::Dyn {
1291 self.maybe_lint_bare_trait(t.span, t.id, false);
1293 hir::TyKind::TraitObject(bounds, lifetime_bound)
1295 TyKind::ImplTrait(def_node_id, ref bounds) => {
1298 ImplTraitContext::OpaqueTy(fn_def_id) => {
1299 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1300 this.lower_param_bounds(bounds, itctx)
1303 ImplTraitContext::Universal(in_band_ty_params) => {
1304 // Add a definition for the in-band `Param`.
1306 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1308 let hir_bounds = self.lower_param_bounds(
1310 ImplTraitContext::Universal(in_band_ty_params),
1312 // Set the name to `impl Bound1 + Bound2`.
1313 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1314 in_band_ty_params.push(hir::GenericParam {
1315 hir_id: self.lower_node_id(def_node_id),
1316 name: ParamName::Plain(ident),
1317 pure_wrt_drop: false,
1321 kind: hir::GenericParamKind::Type {
1323 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1327 hir::TyKind::Path(hir::QPath::Resolved(
1329 self.arena.alloc(hir::Path {
1331 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1332 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1336 ImplTraitContext::Disallowed(pos) => {
1337 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1338 "bindings or function and inherent method return types"
1340 "function and inherent method return types"
1342 let mut err = struct_span_err!(
1346 "`impl Trait` not allowed outside of {}",
1349 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1352 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1353 attributes to enable",
1361 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1362 TyKind::CVarArgs => {
1363 self.sess.delay_span_bug(
1365 "`TyKind::CVarArgs` should have been handled elsewhere",
1371 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1374 fn lower_opaque_impl_trait(
1377 fn_def_id: Option<DefId>,
1378 opaque_ty_node_id: NodeId,
1379 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1380 ) -> hir::TyKind<'hir> {
1382 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1383 fn_def_id, opaque_ty_node_id, span,
1386 // Make sure we know that some funky desugaring has been going on here.
1387 // This is a first: there is code in other places like for loop
1388 // desugaring that explicitly states that we don't want to track that.
1389 // Not tracking it makes lints in rustc and clippy very fragile, as
1390 // frequently opened issues show.
1391 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1393 let opaque_ty_def_index =
1394 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1396 self.allocate_hir_id_counter(opaque_ty_node_id);
1398 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1400 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1402 opaque_ty_def_index,
1406 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1408 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1410 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1411 let opaque_ty_item = hir::OpaqueTy {
1412 generics: hir::Generics {
1413 params: lifetime_defs,
1414 where_clause: hir::WhereClause { predicates: &[], span },
1418 impl_trait_fn: fn_def_id,
1419 origin: hir::OpaqueTyOrigin::FnReturn,
1422 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1424 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1426 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1427 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1431 /// Registers a new opaque type with the proper `NodeId`s and
1432 /// returns the lowered node-ID for the opaque type.
1433 fn generate_opaque_type(
1435 opaque_ty_node_id: NodeId,
1436 opaque_ty_item: hir::OpaqueTy<'hir>,
1438 opaque_ty_span: Span,
1440 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1441 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1442 // Generate an `type Foo = impl Trait;` declaration.
1443 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1444 let opaque_ty_item = hir::Item {
1445 hir_id: opaque_ty_id,
1446 ident: Ident::invalid(),
1447 attrs: Default::default(),
1448 kind: opaque_ty_item_kind,
1449 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1450 span: opaque_ty_span,
1453 // Insert the item into the global item list. This usually happens
1454 // automatically for all AST items. But this opaque type item
1455 // does not actually exist in the AST.
1456 self.insert_item(opaque_ty_item);
1460 fn lifetimes_from_impl_trait_bounds(
1462 opaque_ty_id: NodeId,
1463 parent_index: DefIndex,
1464 bounds: hir::GenericBounds<'hir>,
1465 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1467 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1468 parent_index={:?}, \
1470 opaque_ty_id, parent_index, bounds,
1473 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1474 // appear in the bounds, excluding lifetimes that are created within the bounds.
1475 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1476 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1477 context: &'r mut LoweringContext<'a, 'hir>,
1479 opaque_ty_id: NodeId,
1480 collect_elided_lifetimes: bool,
1481 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1482 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1483 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1484 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1487 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1490 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1491 intravisit::NestedVisitorMap::None
1494 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1495 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1496 if parameters.parenthesized {
1497 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1498 self.collect_elided_lifetimes = false;
1499 intravisit::walk_generic_args(self, span, parameters);
1500 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1502 intravisit::walk_generic_args(self, span, parameters);
1506 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1507 // Don't collect elided lifetimes used inside of `fn()` syntax.
1508 if let hir::TyKind::BareFn(_) = t.kind {
1509 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1510 self.collect_elided_lifetimes = false;
1512 // Record the "stack height" of `for<'a>` lifetime bindings
1513 // to be able to later fully undo their introduction.
1514 let old_len = self.currently_bound_lifetimes.len();
1515 intravisit::walk_ty(self, t);
1516 self.currently_bound_lifetimes.truncate(old_len);
1518 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1520 intravisit::walk_ty(self, t)
1524 fn visit_poly_trait_ref(
1526 trait_ref: &'v hir::PolyTraitRef<'v>,
1527 modifier: hir::TraitBoundModifier,
1529 // Record the "stack height" of `for<'a>` lifetime bindings
1530 // to be able to later fully undo their introduction.
1531 let old_len = self.currently_bound_lifetimes.len();
1532 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1533 self.currently_bound_lifetimes.truncate(old_len);
1536 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1537 // Record the introduction of 'a in `for<'a> ...`.
1538 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1539 // Introduce lifetimes one at a time so that we can handle
1540 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1541 let lt_name = hir::LifetimeName::Param(param.name);
1542 self.currently_bound_lifetimes.push(lt_name);
1545 intravisit::walk_generic_param(self, param);
1548 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1549 let name = match lifetime.name {
1550 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1551 if self.collect_elided_lifetimes {
1552 // Use `'_` for both implicit and underscore lifetimes in
1553 // `type Foo<'_> = impl SomeTrait<'_>;`.
1554 hir::LifetimeName::Underscore
1559 hir::LifetimeName::Param(_) => lifetime.name,
1561 // Refers to some other lifetime that is "in
1562 // scope" within the type.
1563 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1565 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1568 if !self.currently_bound_lifetimes.contains(&name)
1569 && !self.already_defined_lifetimes.contains(&name)
1571 self.already_defined_lifetimes.insert(name);
1573 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1574 hir_id: self.context.next_id(),
1575 span: lifetime.span,
1579 let def_node_id = self.context.resolver.next_node_id();
1581 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1582 self.context.resolver.definitions().create_def_with_parent(
1585 DefPathData::LifetimeNs(name.ident().name),
1590 let (name, kind) = match name {
1591 hir::LifetimeName::Underscore => (
1592 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1593 hir::LifetimeParamKind::Elided,
1595 hir::LifetimeName::Param(param_name) => {
1596 (param_name, hir::LifetimeParamKind::Explicit)
1598 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1601 self.output_lifetime_params.push(hir::GenericParam {
1604 span: lifetime.span,
1605 pure_wrt_drop: false,
1608 kind: hir::GenericParamKind::Lifetime { kind },
1614 let mut lifetime_collector = ImplTraitLifetimeCollector {
1616 parent: parent_index,
1618 collect_elided_lifetimes: true,
1619 currently_bound_lifetimes: Vec::new(),
1620 already_defined_lifetimes: FxHashSet::default(),
1621 output_lifetimes: Vec::new(),
1622 output_lifetime_params: Vec::new(),
1625 for bound in bounds {
1626 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1629 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1633 self.arena.alloc_from_iter(output_lifetimes),
1634 self.arena.alloc_from_iter(output_lifetime_params),
1641 qself: &Option<QSelf>,
1643 param_mode: ParamMode,
1644 mut itctx: ImplTraitContext<'_, 'hir>,
1645 ) -> hir::QPath<'hir> {
1646 let qself_position = qself.as_ref().map(|q| q.position);
1647 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1650 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1652 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1653 let path = self.arena.alloc(hir::Path {
1654 res: self.lower_res(partial_res.base_res()),
1655 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1657 let param_mode = match (qself_position, param_mode) {
1658 (Some(j), ParamMode::Optional) if i < j => {
1659 // This segment is part of the trait path in a
1660 // qualified path - one of `a`, `b` or `Trait`
1661 // in `<X as a::b::Trait>::T::U::method`.
1667 // Figure out if this is a type/trait segment,
1668 // which may need lifetime elision performed.
1669 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1670 krate: def_id.krate,
1671 index: this.def_key(def_id).parent.expect("missing parent"),
1673 let type_def_id = match partial_res.base_res() {
1674 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1675 Some(parent_def_id(self, def_id))
1677 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1678 Some(parent_def_id(self, def_id))
1680 Res::Def(DefKind::Struct, def_id)
1681 | Res::Def(DefKind::Union, def_id)
1682 | Res::Def(DefKind::Enum, def_id)
1683 | Res::Def(DefKind::TyAlias, def_id)
1684 | Res::Def(DefKind::Trait, def_id)
1685 if i + 1 == proj_start =>
1691 let parenthesized_generic_args = match partial_res.base_res() {
1692 // `a::b::Trait(Args)`
1693 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1694 ParenthesizedGenericArgs::Ok
1696 // `a::b::Trait(Args)::TraitItem`
1697 Res::Def(DefKind::Method, _)
1698 | Res::Def(DefKind::AssocConst, _)
1699 | Res::Def(DefKind::AssocTy, _)
1700 if i + 2 == proj_start =>
1702 ParenthesizedGenericArgs::Ok
1704 // Avoid duplicated errors.
1705 Res::Err => ParenthesizedGenericArgs::Ok,
1707 _ => ParenthesizedGenericArgs::Err,
1710 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1711 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1714 assert!(!def_id.is_local());
1715 let item_generics = self
1718 .item_generics_cloned_untracked(def_id, self.sess);
1719 let n = item_generics.own_counts().lifetimes;
1720 self.type_def_lifetime_params.insert(def_id, n);
1723 self.lower_path_segment(
1728 parenthesized_generic_args,
1737 // Simple case, either no projections, or only fully-qualified.
1738 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1739 if partial_res.unresolved_segments() == 0 {
1740 return hir::QPath::Resolved(qself, path);
1743 // Create the innermost type that we're projecting from.
1744 let mut ty = if path.segments.is_empty() {
1745 // If the base path is empty that means there exists a
1746 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1747 qself.expect("missing QSelf for <T>::...")
1749 // Otherwise, the base path is an implicit `Self` type path,
1750 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1751 // `<I as Iterator>::Item::default`.
1752 let new_id = self.next_id();
1753 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1756 // Anything after the base path are associated "extensions",
1757 // out of which all but the last one are associated types,
1758 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1759 // * base path is `std::vec::Vec<T>`
1760 // * "extensions" are `IntoIter`, `Item` and `clone`
1761 // * type nodes are:
1762 // 1. `std::vec::Vec<T>` (created above)
1763 // 2. `<std::vec::Vec<T>>::IntoIter`
1764 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1765 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1766 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1767 let segment = self.arena.alloc(self.lower_path_segment(
1772 ParenthesizedGenericArgs::Err,
1776 let qpath = hir::QPath::TypeRelative(ty, segment);
1778 // It's finished, return the extension of the right node type.
1779 if i == p.segments.len() - 1 {
1783 // Wrap the associated extension in another type node.
1784 let new_id = self.next_id();
1785 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1788 // We should've returned in the for loop above.
1791 "lower_qpath: no final extension segment in {}..{}",
1797 fn lower_path_extra(
1801 param_mode: ParamMode,
1802 explicit_owner: Option<NodeId>,
1803 ) -> &'hir hir::Path<'hir> {
1804 self.arena.alloc(hir::Path {
1806 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1807 self.lower_path_segment(
1812 ParenthesizedGenericArgs::Err,
1813 ImplTraitContext::disallowed(),
1821 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> &'hir hir::Path<'hir> {
1822 let res = self.expect_full_res(id);
1823 let res = self.lower_res(res);
1824 self.lower_path_extra(res, p, param_mode, None)
1827 fn lower_path_segment(
1830 segment: &PathSegment,
1831 param_mode: ParamMode,
1832 expected_lifetimes: usize,
1833 parenthesized_generic_args: ParenthesizedGenericArgs,
1834 itctx: ImplTraitContext<'_, 'hir>,
1835 explicit_owner: Option<NodeId>,
1836 ) -> hir::PathSegment<'hir> {
1837 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1838 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1839 match **generic_args {
1840 GenericArgs::AngleBracketed(ref data) => {
1841 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1843 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1844 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1845 ParenthesizedGenericArgs::Err => {
1846 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1847 err.span_label(data.span, "only `Fn` traits may use parentheses");
1848 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1849 // Do not suggest going from `Trait()` to `Trait<>`
1850 if data.inputs.len() > 0 {
1851 if let Some(split) = snippet.find('(') {
1852 let trait_name = &snippet[0..split];
1853 let args = &snippet[split + 1..snippet.len() - 1];
1854 err.span_suggestion(
1856 "use angle brackets instead",
1857 format!("{}<{}>", trait_name, args),
1858 Applicability::MaybeIncorrect,
1865 self.lower_angle_bracketed_parameter_data(
1866 &data.as_angle_bracketed_args(),
1877 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1880 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1881 GenericArg::Lifetime(_) => true,
1884 let first_generic_span = generic_args
1888 .chain(generic_args.bindings.iter().map(|b| b.span))
1890 if !generic_args.parenthesized && !has_lifetimes {
1891 generic_args.args = self
1892 .elided_path_lifetimes(path_span, expected_lifetimes)
1893 .map(|lt| GenericArg::Lifetime(lt))
1894 .chain(generic_args.args.into_iter())
1896 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1897 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1898 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1899 let no_bindings = generic_args.bindings.is_empty();
1900 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1901 // If there are no (non-implicit) generic args or associated type
1902 // bindings, our suggestion includes the angle brackets.
1903 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1905 // Otherwise (sorry, this is kind of gross) we need to infer the
1906 // place to splice in the `'_, ` from the generics that do exist.
1907 let first_generic_span = first_generic_span
1908 .expect("already checked that non-lifetime args or bindings exist");
1909 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1911 match self.anonymous_lifetime_mode {
1912 // In create-parameter mode we error here because we don't want to support
1913 // deprecated impl elision in new features like impl elision and `async fn`,
1914 // both of which work using the `CreateParameter` mode:
1916 // impl Foo for std::cell::Ref<u32> // note lack of '_
1917 // async fn foo(_: std::cell::Ref<u32>) { ... }
1918 AnonymousLifetimeMode::CreateParameter => {
1919 let mut err = struct_span_err!(
1923 "implicit elided lifetime not allowed here"
1925 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1936 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1937 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1938 ELIDED_LIFETIMES_IN_PATHS,
1941 "hidden lifetime parameters in types are deprecated",
1942 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1955 let res = self.expect_full_res(segment.id);
1956 let id = if let Some(owner) = explicit_owner {
1957 self.lower_node_id_with_owner(segment.id, owner)
1959 self.lower_node_id(segment.id)
1962 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1963 segment.ident, segment.id, id,
1967 ident: segment.ident,
1969 res: Some(self.lower_res(res)),
1971 args: if generic_args.is_empty() {
1974 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
1979 fn lower_angle_bracketed_parameter_data(
1981 data: &AngleBracketedArgs,
1982 param_mode: ParamMode,
1983 mut itctx: ImplTraitContext<'_, 'hir>,
1984 ) -> (GenericArgsCtor<'hir>, bool) {
1985 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1986 let has_non_lt_args = args.iter().any(|arg| match arg {
1987 ast::GenericArg::Lifetime(_) => false,
1988 ast::GenericArg::Type(_) => true,
1989 ast::GenericArg::Const(_) => true,
1993 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1994 bindings: self.arena.alloc_from_iter(
1995 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
1997 parenthesized: false,
1999 !has_non_lt_args && param_mode == ParamMode::Optional,
2003 fn lower_parenthesized_parameter_data(
2005 data: &ParenthesizedArgs,
2006 ) -> (GenericArgsCtor<'hir>, bool) {
2007 // Switch to `PassThrough` mode for anonymous lifetimes; this
2008 // means that we permit things like `&Ref<T>`, where `Ref` has
2009 // a hidden lifetime parameter. This is needed for backwards
2010 // compatibility, even in contexts like an impl header where
2011 // we generally don't permit such things (see #51008).
2012 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2013 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2014 let inputs = this.arena.alloc_from_iter(
2015 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2017 let output_ty = match output {
2018 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2019 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2021 let args = smallvec![GenericArg::Type(this.ty_tup(span, inputs))];
2022 let binding = hir::TypeBinding {
2023 hir_id: this.next_id(),
2024 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2025 span: output_ty.span,
2026 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2029 GenericArgsCtor { args, bindings: arena_vec![this; binding], parenthesized: true },
2035 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2036 let mut ids = SmallVec::<[NodeId; 1]>::new();
2037 if self.sess.features_untracked().impl_trait_in_bindings {
2038 if let Some(ref ty) = l.ty {
2039 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2040 visitor.visit_ty(ty);
2043 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2044 let ty = l.ty.as_ref().map(|t| {
2047 if self.sess.features_untracked().impl_trait_in_bindings {
2048 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2050 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2054 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2057 hir_id: self.lower_node_id(l.id),
2059 pat: self.lower_pat(&l.pat),
2062 attrs: l.attrs.clone(),
2063 source: hir::LocalSource::Normal,
2069 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
2070 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2071 // as they are not explicit in HIR/Ty function signatures.
2072 // (instead, the `c_variadic` flag is set to `true`)
2073 let mut inputs = &decl.inputs[..];
2074 if decl.c_variadic() {
2075 inputs = &inputs[..inputs.len() - 1];
2077 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
2078 PatKind::Ident(_, ident, _) => ident,
2079 _ => Ident::new(kw::Invalid, param.pat.span),
2083 // Lowers a function declaration.
2085 // `decl`: the unlowered (AST) function declaration.
2086 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2087 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2088 // `make_ret_async` is also `Some`.
2089 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2090 // This guards against trait declarations and implementations where `impl Trait` is
2092 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2093 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2094 // return type `impl Trait` item.
2098 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2099 impl_trait_return_allow: bool,
2100 make_ret_async: Option<NodeId>,
2101 ) -> &'hir hir::FnDecl<'hir> {
2105 in_band_ty_params: {:?}, \
2106 impl_trait_return_allow: {}, \
2107 make_ret_async: {:?})",
2108 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2110 let lt_mode = if make_ret_async.is_some() {
2111 // In `async fn`, argument-position elided lifetimes
2112 // must be transformed into fresh generic parameters so that
2113 // they can be applied to the opaque `impl Trait` return type.
2114 AnonymousLifetimeMode::CreateParameter
2116 self.anonymous_lifetime_mode
2119 let c_variadic = decl.c_variadic();
2121 // Remember how many lifetimes were already around so that we can
2122 // only look at the lifetime parameters introduced by the arguments.
2123 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2124 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2125 // as they are not explicit in HIR/Ty function signatures.
2126 // (instead, the `c_variadic` flag is set to `true`)
2127 let mut inputs = &decl.inputs[..];
2129 inputs = &inputs[..inputs.len() - 1];
2131 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2132 if let Some((_, ibty)) = &mut in_band_ty_params {
2133 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2135 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2140 let output = if let Some(ret_id) = make_ret_async {
2141 self.lower_async_fn_ret_ty(
2143 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2148 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2149 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
2150 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
2152 _ => hir::FunctionRetTy::Return(
2153 self.lower_ty(ty, ImplTraitContext::disallowed()),
2156 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
2160 self.arena.alloc(hir::FnDecl {
2164 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2165 let is_mutable_pat = match arg.pat.kind {
2166 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2167 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2172 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2173 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2174 // Given we are only considering `ImplicitSelf` types, we needn't consider
2175 // the case where we have a mutable pattern to a reference as that would
2176 // no longer be an `ImplicitSelf`.
2177 TyKind::Rptr(_, ref mt)
2178 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2180 hir::ImplicitSelfKind::MutRef
2182 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2183 hir::ImplicitSelfKind::ImmRef
2185 _ => hir::ImplicitSelfKind::None,
2191 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2192 // combined with the following definition of `OpaqueTy`:
2194 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2196 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2197 // `output`: unlowered output type (`T` in `-> T`)
2198 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2199 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2200 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2201 fn lower_async_fn_ret_ty(
2203 output: &FunctionRetTy,
2205 opaque_ty_node_id: NodeId,
2206 ) -> hir::FunctionRetTy<'hir> {
2208 "lower_async_fn_ret_ty(\
2211 opaque_ty_node_id={:?})",
2212 output, fn_def_id, opaque_ty_node_id,
2215 let span = output.span();
2217 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2219 let opaque_ty_def_index =
2220 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2222 self.allocate_hir_id_counter(opaque_ty_node_id);
2224 // When we create the opaque type for this async fn, it is going to have
2225 // to capture all the lifetimes involved in the signature (including in the
2226 // return type). This is done by introducing lifetime parameters for:
2228 // - all the explicitly declared lifetimes from the impl and function itself;
2229 // - all the elided lifetimes in the fn arguments;
2230 // - all the elided lifetimes in the return type.
2232 // So for example in this snippet:
2235 // impl<'a> Foo<'a> {
2236 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2237 // // ^ '0 ^ '1 ^ '2
2238 // // elided lifetimes used below
2243 // we would create an opaque type like:
2246 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2249 // and we would then desugar `bar` to the equivalent of:
2252 // impl<'a> Foo<'a> {
2253 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2257 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2258 // this is because the elided lifetimes from the return type
2259 // should be figured out using the ordinary elision rules, and
2260 // this desugaring achieves that.
2262 // The variable `input_lifetimes_count` tracks the number of
2263 // lifetime parameters to the opaque type *not counting* those
2264 // lifetimes elided in the return type. This includes those
2265 // that are explicitly declared (`in_scope_lifetimes`) and
2266 // those elided lifetimes we found in the arguments (current
2267 // content of `lifetimes_to_define`). Next, we will process
2268 // the return type, which will cause `lifetimes_to_define` to
2270 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2272 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2273 // We have to be careful to get elision right here. The
2274 // idea is that we create a lifetime parameter for each
2275 // lifetime in the return type. So, given a return type
2276 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2277 // Future<Output = &'1 [ &'2 u32 ]>`.
2279 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2280 // hence the elision takes place at the fn site.
2281 let future_bound = this
2282 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2283 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2286 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2288 // Calculate all the lifetimes that should be captured
2289 // by the opaque type. This should include all in-scope
2290 // lifetime parameters, including those defined in-band.
2292 // Note: this must be done after lowering the output type,
2293 // as the output type may introduce new in-band lifetimes.
2294 let lifetime_params: Vec<(Span, ParamName)> = this
2298 .map(|name| (name.ident().span, name))
2299 .chain(this.lifetimes_to_define.iter().cloned())
2302 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2303 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2304 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2306 let generic_params =
2307 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2308 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
2311 let opaque_ty_item = hir::OpaqueTy {
2312 generics: hir::Generics {
2313 params: generic_params,
2314 where_clause: hir::WhereClause { predicates: &[], span },
2317 bounds: arena_vec![this; future_bound],
2318 impl_trait_fn: Some(fn_def_id),
2319 origin: hir::OpaqueTyOrigin::AsyncFn,
2322 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2324 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2326 (opaque_ty_id, lifetime_params)
2329 // As documented above on the variable
2330 // `input_lifetimes_count`, we need to create the lifetime
2331 // arguments to our opaque type. Continuing with our example,
2332 // we're creating the type arguments for the return type:
2335 // Bar<'a, 'b, '0, '1, '_>
2338 // For the "input" lifetime parameters, we wish to create
2339 // references to the parameters themselves, including the
2340 // "implicit" ones created from parameter types (`'a`, `'b`,
2343 // For the "output" lifetime parameters, we just want to
2345 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2347 .map(|&(span, hir_name)| {
2348 // Input lifetime like `'a` or `'1`:
2349 GenericArg::Lifetime(hir::Lifetime {
2350 hir_id: self.next_id(),
2352 name: hir::LifetimeName::Param(hir_name),
2356 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2357 // Output lifetime like `'_`.
2358 GenericArg::Lifetime(hir::Lifetime {
2359 hir_id: self.next_id(),
2361 name: hir::LifetimeName::Implicit,
2363 let generic_args = self.arena.alloc_from_iter(generic_args);
2365 // Create the `Foo<...>` reference itself. Note that the `type
2366 // Foo = impl Trait` is, internally, created as a child of the
2367 // async fn, so the *type parameters* are inherited. It's
2368 // only the lifetime parameters that we must supply.
2369 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
2370 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2371 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
2374 /// Transforms `-> T` into `Future<Output = T>`
2375 fn lower_async_fn_output_type_to_future_bound(
2377 output: &FunctionRetTy,
2380 ) -> hir::GenericBound<'hir> {
2381 // Compute the `T` in `Future<Output = T>` from the return type.
2382 let output_ty = match output {
2383 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2384 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2388 let future_params = self.arena.alloc(hir::GenericArgs {
2390 bindings: arena_vec![self; hir::TypeBinding {
2391 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2392 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2393 hir_id: self.next_id(),
2396 parenthesized: false,
2399 // ::std::future::Future<future_params>
2401 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
2403 hir::GenericBound::Trait(
2405 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2406 bound_generic_params: &[],
2409 hir::TraitBoundModifier::None,
2413 fn lower_param_bound(
2416 itctx: ImplTraitContext<'_, 'hir>,
2417 ) -> hir::GenericBound<'hir> {
2419 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2420 self.lower_poly_trait_ref(ty, itctx),
2421 self.lower_trait_bound_modifier(modifier),
2423 GenericBound::Outlives(ref lifetime) => {
2424 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2429 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2430 let span = l.ident.span;
2432 ident if ident.name == kw::StaticLifetime => {
2433 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2435 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2436 AnonymousLifetimeMode::CreateParameter => {
2437 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2438 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2441 AnonymousLifetimeMode::PassThrough => {
2442 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2445 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2448 self.maybe_collect_in_band_lifetime(ident);
2449 let param_name = ParamName::Plain(ident);
2450 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2455 fn new_named_lifetime(
2459 name: hir::LifetimeName,
2460 ) -> hir::Lifetime {
2461 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2464 fn lower_generic_params_mut<'s>(
2466 params: &'s [GenericParam],
2467 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2468 mut itctx: ImplTraitContext<'s, 'hir>,
2469 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2472 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2475 fn lower_generic_params(
2477 params: &[GenericParam],
2478 add_bounds: &NodeMap<Vec<GenericBound>>,
2479 itctx: ImplTraitContext<'_, 'hir>,
2480 ) -> &'hir [hir::GenericParam<'hir>] {
2481 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2484 fn lower_generic_param(
2486 param: &GenericParam,
2487 add_bounds: &NodeMap<Vec<GenericBound>>,
2488 mut itctx: ImplTraitContext<'_, 'hir>,
2489 ) -> hir::GenericParam<'hir> {
2490 let mut bounds: Vec<_> = self
2491 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2492 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2495 let (name, kind) = match param.kind {
2496 GenericParamKind::Lifetime => {
2497 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2498 self.is_collecting_in_band_lifetimes = false;
2501 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2502 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2504 let param_name = match lt.name {
2505 hir::LifetimeName::Param(param_name) => param_name,
2506 hir::LifetimeName::Implicit
2507 | hir::LifetimeName::Underscore
2508 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2509 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2512 "object-lifetime-default should not occur here",
2515 hir::LifetimeName::Error => ParamName::Error,
2519 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2521 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2525 GenericParamKind::Type { ref default, .. } => {
2526 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2527 if !add_bounds.is_empty() {
2528 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2529 bounds.extend(params);
2532 let kind = hir::GenericParamKind::Type {
2535 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2539 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2540 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2544 (hir::ParamName::Plain(param.ident), kind)
2546 GenericParamKind::Const { ref ty } => (
2547 hir::ParamName::Plain(param.ident),
2548 hir::GenericParamKind::Const {
2549 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2555 hir_id: self.lower_node_id(param.id),
2557 span: param.ident.span,
2558 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2559 attrs: self.lower_attrs(¶m.attrs),
2560 bounds: self.arena.alloc_from_iter(bounds),
2568 itctx: ImplTraitContext<'_, 'hir>,
2569 ) -> hir::TraitRef<'hir> {
2570 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2571 hir::QPath::Resolved(None, path) => path,
2572 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2574 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2577 fn lower_poly_trait_ref(
2580 mut itctx: ImplTraitContext<'_, 'hir>,
2581 ) -> hir::PolyTraitRef<'hir> {
2582 let bound_generic_params = self.lower_generic_params(
2583 &p.bound_generic_params,
2584 &NodeMap::default(),
2587 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2588 this.lower_trait_ref(&p.trait_ref, itctx)
2591 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2594 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2595 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2598 fn lower_param_bounds(
2600 bounds: &[GenericBound],
2601 itctx: ImplTraitContext<'_, 'hir>,
2602 ) -> hir::GenericBounds<'hir> {
2603 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2606 fn lower_param_bounds_mut<'s>(
2608 bounds: &'s [GenericBound],
2609 mut itctx: ImplTraitContext<'s, 'hir>,
2610 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2611 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2614 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2615 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2618 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2619 let mut stmts = vec![];
2620 let mut expr: Option<&'hir _> = None;
2622 for (index, stmt) in b.stmts.iter().enumerate() {
2623 if index == b.stmts.len() - 1 {
2624 if let StmtKind::Expr(ref e) = stmt.kind {
2625 expr = Some(self.lower_expr(e));
2627 stmts.extend(self.lower_stmt(stmt));
2630 stmts.extend(self.lower_stmt(stmt));
2635 hir_id: self.lower_node_id(b.id),
2636 stmts: self.arena.alloc_from_iter(stmts),
2638 rules: self.lower_block_check_mode(&b.rules),
2644 /// Lowers a block directly to an expression, presuming that it
2645 /// has no attributes and is not targeted by a `break`.
2646 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2647 let block = self.lower_block(b, false);
2648 self.expr_block(block, AttrVec::new())
2651 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2652 let node = match p.kind {
2653 PatKind::Wild => hir::PatKind::Wild,
2654 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2655 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2656 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2659 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2660 PatKind::TupleStruct(ref path, ref pats) => {
2661 let qpath = self.lower_qpath(
2665 ParamMode::Optional,
2666 ImplTraitContext::disallowed(),
2668 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2669 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2671 PatKind::Or(ref pats) => {
2672 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2674 PatKind::Path(ref qself, ref path) => {
2675 let qpath = self.lower_qpath(
2679 ParamMode::Optional,
2680 ImplTraitContext::disallowed(),
2682 hir::PatKind::Path(qpath)
2684 PatKind::Struct(ref path, ref fields, etc) => {
2685 let qpath = self.lower_qpath(
2689 ParamMode::Optional,
2690 ImplTraitContext::disallowed(),
2693 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2694 hir_id: self.next_id(),
2696 pat: self.lower_pat(&f.pat),
2697 is_shorthand: f.is_shorthand,
2700 hir::PatKind::Struct(qpath, fs, etc)
2702 PatKind::Tuple(ref pats) => {
2703 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2704 hir::PatKind::Tuple(pats, ddpos)
2706 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2707 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2708 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2709 self.lower_expr(e1),
2710 self.lower_expr(e2),
2711 self.lower_range_end(end),
2713 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2715 // If we reach here the `..` pattern is not semantically allowed.
2716 self.ban_illegal_rest_pat(p.span)
2718 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2719 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2722 self.pat_with_node_id_of(p, node)
2729 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2730 let mut elems = Vec::with_capacity(pats.len());
2731 let mut rest = None;
2733 let mut iter = pats.iter().enumerate();
2734 for (idx, pat) in iter.by_ref() {
2735 // Interpret the first `..` pattern as a sub-tuple pattern.
2736 // Note that unlike for slice patterns,
2737 // where `xs @ ..` is a legal sub-slice pattern,
2738 // it is not a legal sub-tuple pattern.
2740 rest = Some((idx, pat.span));
2743 // It was not a sub-tuple pattern so lower it normally.
2744 elems.push(self.lower_pat(pat));
2747 for (_, pat) in iter {
2748 // There was a previous sub-tuple pattern; make sure we don't allow more...
2750 // ...but there was one again, so error.
2751 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2753 elems.push(self.lower_pat(pat));
2757 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2760 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2761 /// `hir::PatKind::Slice(before, slice, after)`.
2763 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2764 /// this is interpreted as a sub-slice pattern semantically.
2765 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2766 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2767 let mut before = Vec::new();
2768 let mut after = Vec::new();
2769 let mut slice = None;
2770 let mut prev_rest_span = None;
2772 let mut iter = pats.iter();
2773 // Lower all the patterns until the first occurence of a sub-slice pattern.
2774 for pat in iter.by_ref() {
2776 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2778 prev_rest_span = Some(pat.span);
2779 slice = Some(self.pat_wild_with_node_id_of(pat));
2782 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2783 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2784 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2785 prev_rest_span = Some(sub.span);
2786 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2787 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2788 slice = Some(self.pat_with_node_id_of(pat, node));
2791 // It was not a subslice pattern so lower it normally.
2792 _ => before.push(self.lower_pat(pat)),
2796 // Lower all the patterns after the first sub-slice pattern.
2798 // There was a previous subslice pattern; make sure we don't allow more.
2799 let rest_span = match pat.kind {
2800 PatKind::Rest => Some(pat.span),
2801 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2802 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2803 after.push(self.pat_wild_with_node_id_of(pat));
2808 if let Some(rest_span) = rest_span {
2809 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2810 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2812 // Lower the pattern normally.
2813 after.push(self.lower_pat(pat));
2817 hir::PatKind::Slice(
2818 self.arena.alloc_from_iter(before),
2820 self.arena.alloc_from_iter(after),
2827 binding_mode: &BindingMode,
2829 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2830 ) -> hir::PatKind<'hir> {
2831 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2832 // `None` can occur in body-less function signatures
2833 res @ None | res @ Some(Res::Local(_)) => {
2834 let canonical_id = match res {
2835 Some(Res::Local(id)) => id,
2839 hir::PatKind::Binding(
2840 self.lower_binding_mode(binding_mode),
2841 self.lower_node_id(canonical_id),
2846 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2848 self.arena.alloc(hir::Path {
2850 res: self.lower_res(res),
2851 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2857 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2858 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2861 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2862 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2863 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2866 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2867 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2869 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2870 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2871 .span_label(prev_sp, "previously used here")
2875 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2876 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2878 .struct_span_err(sp, "`..` patterns are not allowed here")
2879 .note("only allowed in tuple, tuple struct, and slice patterns")
2882 // We're not in a list context so `..` can be reasonably treated
2883 // as `_` because it should always be valid and roughly matches the
2884 // intent of `..` (notice that the rest of a single slot is that slot).
2888 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2890 RangeEnd::Included(_) => hir::RangeEnd::Included,
2891 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2895 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2896 self.with_new_scopes(|this| hir::AnonConst {
2897 hir_id: this.lower_node_id(c.id),
2898 body: this.lower_const_body(c.value.span, Some(&c.value)),
2902 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2903 let kind = match s.kind {
2904 StmtKind::Local(ref l) => {
2905 let (l, item_ids) = self.lower_local(l);
2906 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2909 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2910 self.stmt(s.span, hir::StmtKind::Item(item_id))
2915 hir_id: self.lower_node_id(s.id),
2916 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2922 StmtKind::Item(ref it) => {
2923 // Can only use the ID once.
2924 let mut id = Some(s.id);
2931 .map(|id| self.lower_node_id(id))
2932 .unwrap_or_else(|| self.next_id());
2934 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2938 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2939 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2940 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2942 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2945 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2947 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2948 BlockCheckMode::Unsafe(u) => {
2949 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2954 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2956 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2957 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2958 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2959 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2963 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2965 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2966 UserProvided => hir::UnsafeSource::UserProvided,
2970 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2972 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2973 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2977 // Helper methods for building HIR.
2979 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2980 hir::Stmt { span, kind, hir_id: self.next_id() }
2983 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2984 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2991 init: Option<&'hir hir::Expr<'hir>>,
2992 pat: &'hir hir::Pat<'hir>,
2993 source: hir::LocalSource,
2994 ) -> hir::Stmt<'hir> {
2995 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2996 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2999 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
3000 self.block_all(expr.span, &[], Some(expr))
3006 stmts: &'hir [hir::Stmt<'hir>],
3007 expr: Option<&'hir hir::Expr<'hir>>,
3008 ) -> &'hir hir::Block<'hir> {
3009 let blk = hir::Block {
3012 hir_id: self.next_id(),
3013 rules: hir::BlockCheckMode::DefaultBlock,
3015 targeted_by_break: false,
3017 self.arena.alloc(blk)
3020 /// Constructs a `true` or `false` literal pattern.
3021 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3022 let expr = self.expr_bool(span, val);
3023 self.pat(span, hir::PatKind::Lit(expr))
3026 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3027 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3030 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3031 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3034 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3035 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3038 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3039 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3045 components: &[Symbol],
3046 subpats: &'hir [&'hir hir::Pat<'hir>],
3047 ) -> &'hir hir::Pat<'hir> {
3048 let path = self.std_path(span, components, None, true);
3049 let qpath = hir::QPath::Resolved(None, path);
3050 let pt = if subpats.is_empty() {
3051 hir::PatKind::Path(qpath)
3053 hir::PatKind::TupleStruct(qpath, subpats, None)
3058 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3059 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3062 fn pat_ident_binding_mode(
3066 bm: hir::BindingAnnotation,
3067 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3068 let hir_id = self.next_id();
3071 self.arena.alloc(hir::Pat {
3073 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3080 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3081 self.pat(span, hir::PatKind::Wild)
3084 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3085 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3088 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3089 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3090 /// The path is also resolved according to `is_value`.
3094 components: &[Symbol],
3095 params: Option<&'hir hir::GenericArgs<'hir>>,
3097 ) -> &'hir hir::Path<'hir> {
3098 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3099 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3101 let mut segments: Vec<_> = path
3105 let res = self.expect_full_res(segment.id);
3107 ident: segment.ident,
3108 hir_id: Some(self.lower_node_id(segment.id)),
3109 res: Some(self.lower_res(res)),
3115 segments.last_mut().unwrap().args = params;
3117 self.arena.alloc(hir::Path {
3119 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3120 segments: self.arena.alloc_from_iter(segments),
3126 mut hir_id: hir::HirId,
3128 qpath: hir::QPath<'hir>,
3129 ) -> hir::Ty<'hir> {
3130 let kind = match qpath {
3131 hir::QPath::Resolved(None, path) => {
3132 // Turn trait object paths into `TyKind::TraitObject` instead.
3134 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3135 let principal = hir::PolyTraitRef {
3136 bound_generic_params: &[],
3137 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3141 // The original ID is taken by the `PolyTraitRef`,
3142 // so the `Ty` itself needs a different one.
3143 hir_id = self.next_id();
3144 hir::TyKind::TraitObject(
3145 arena_vec![self; principal],
3146 self.elided_dyn_bound(span),
3149 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3152 _ => hir::TyKind::Path(qpath),
3155 hir::Ty { hir_id, kind, span }
3158 /// Invoked to create the lifetime argument for a type `&T`
3159 /// with no explicit lifetime.
3160 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3161 match self.anonymous_lifetime_mode {
3162 // Intercept when we are in an impl header or async fn and introduce an in-band
3164 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3166 AnonymousLifetimeMode::CreateParameter => {
3167 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3169 hir_id: self.next_id(),
3171 name: hir::LifetimeName::Param(fresh_name),
3175 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3177 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3181 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3182 /// return a "error lifetime".
3183 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3184 let (id, msg, label) = match id {
3185 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3188 self.resolver.next_node_id(),
3189 "`&` without an explicit lifetime name cannot be used here",
3190 "explicit lifetime name needed here",
3194 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3195 err.span_label(span, label);
3198 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3201 /// Invoked to create the lifetime argument(s) for a path like
3202 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3203 /// sorts of cases are deprecated. This may therefore report a warning or an
3204 /// error, depending on the mode.
3205 fn elided_path_lifetimes<'s>(
3209 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
3210 (0..count).map(move |_| self.elided_path_lifetime(span))
3213 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3214 match self.anonymous_lifetime_mode {
3215 AnonymousLifetimeMode::CreateParameter => {
3216 // We should have emitted E0726 when processing this path above
3218 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3219 let id = self.resolver.next_node_id();
3220 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3222 // `PassThrough` is the normal case.
3223 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3224 // is unsuitable here, as these can occur from missing lifetime parameters in a
3225 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3226 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3227 // later, at which point a suitable error will be emitted.
3228 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3229 self.new_implicit_lifetime(span)
3234 /// Invoked to create the lifetime argument(s) for an elided trait object
3235 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3236 /// when the bound is written, even if it is written with `'_` like in
3237 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3238 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3239 match self.anonymous_lifetime_mode {
3240 // NB. We intentionally ignore the create-parameter mode here.
3241 // and instead "pass through" to resolve-lifetimes, which will apply
3242 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3243 // do not act like other elided lifetimes. In other words, given this:
3245 // impl Foo for Box<dyn Debug>
3247 // we do not introduce a fresh `'_` to serve as the bound, but instead
3248 // ultimately translate to the equivalent of:
3250 // impl Foo for Box<dyn Debug + 'static>
3252 // `resolve_lifetime` has the code to make that happen.
3253 AnonymousLifetimeMode::CreateParameter => {}
3255 AnonymousLifetimeMode::ReportError => {
3256 // ReportError applies to explicit use of `'_`.
3259 // This is the normal case.
3260 AnonymousLifetimeMode::PassThrough => {}
3263 let r = hir::Lifetime {
3264 hir_id: self.next_id(),
3266 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3268 debug!("elided_dyn_bound: r={:?}", r);
3272 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3273 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3276 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3277 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3278 // call site which do not have a macro backtrace. See #61963.
3279 let is_macro_callsite = self
3282 .span_to_snippet(span)
3283 .map(|snippet| snippet.starts_with("#["))
3285 if !is_macro_callsite {
3286 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3287 builtin::BARE_TRAIT_OBJECTS,
3290 "trait objects without an explicit `dyn` are deprecated",
3291 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3297 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
3298 // Sorting by span ensures that we get things in order within a
3299 // file, and also puts the files in a sensible order.
3300 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3301 body_ids.sort_by_key(|b| bodies[b].value.span);
3305 /// Helper struct for delayed construction of GenericArgs.
3306 struct GenericArgsCtor<'hir> {
3307 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
3308 bindings: &'hir [hir::TypeBinding<'hir>],
3309 parenthesized: bool,
3312 impl<'hir> GenericArgsCtor<'hir> {
3313 fn is_empty(&self) -> bool {
3314 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
3317 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
3319 args: arena.alloc_from_iter(self.args),
3320 bindings: self.bindings,
3321 parenthesized: self.parenthesized,