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 use crate::arena::Arena;
36 use crate::dep_graph::DepGraph;
37 use crate::hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
38 use crate::hir::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
39 use crate::hir::map::{DefKey, DefPathData, Definitions};
40 use crate::hir::ptr::P;
41 use crate::hir::{self, ParamName};
42 use crate::hir::{ConstArg, GenericArg};
44 use crate::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
45 use crate::middle::cstore::CrateStore;
46 use crate::session::config::nightly_options;
47 use crate::session::Session;
48 use crate::util::captures::Captures;
49 use crate::util::common::FN_OUTPUT_NAME;
50 use crate::util::nodemap::{DefIdMap, NodeMap};
51 use errors::Applicability;
52 use rustc_data_structures::fx::FxHashSet;
53 use rustc_data_structures::sync::Lrc;
54 use rustc_index::vec::IndexVec;
56 use smallvec::SmallVec;
57 use std::collections::BTreeMap;
63 use syntax::print::pprust;
64 use syntax::ptr::P as AstP;
65 use syntax::sess::ParseSess;
66 use syntax::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
67 use syntax::symbol::{kw, sym, Symbol};
68 use syntax::token::{self, Nonterminal, Token};
69 use syntax::tokenstream::{TokenStream, TokenTree};
70 use syntax::visit::{self, Visitor};
71 use syntax_pos::hygiene::ExpnId;
74 use rustc_error_codes::*;
76 macro_rules! arena_vec {
80 ($this:expr; $($x:expr),*) => (
81 $this.arena.alloc_from_iter(vec![$($x),*])
88 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
90 pub struct LoweringContext<'a, 'hir: 'a> {
91 crate_root: Option<Symbol>,
93 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
96 resolver: &'a mut dyn Resolver,
98 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
99 /// if we don't have this function pointer. To avoid that dependency so that
100 /// librustc is independent of the parser, we use dynamic dispatch here.
101 nt_to_tokenstream: NtToTokenstream,
103 /// Used to allocate HIR nodes
104 arena: &'hir Arena<'hir>,
106 /// The items being lowered are collected here.
107 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
109 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
110 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
111 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
112 exported_macros: Vec<hir::MacroDef<'hir>>,
113 non_exported_macro_attrs: Vec<ast::Attribute>,
115 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
117 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
119 generator_kind: Option<hir::GeneratorKind>,
121 /// Used to get the current `fn`'s def span to point to when using `await`
122 /// outside of an `async fn`.
123 current_item: Option<Span>,
125 catch_scopes: Vec<NodeId>,
126 loop_scopes: Vec<NodeId>,
127 is_in_loop_condition: bool,
128 is_in_trait_impl: bool,
129 is_in_dyn_type: bool,
131 /// What to do when we encounter either an "anonymous lifetime
132 /// reference". The term "anonymous" is meant to encompass both
133 /// `'_` lifetimes as well as fully elided cases where nothing is
134 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
135 anonymous_lifetime_mode: AnonymousLifetimeMode,
137 /// Used to create lifetime definitions from in-band lifetime usages.
138 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
139 /// When a named lifetime is encountered in a function or impl header and
140 /// has not been defined
141 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
142 /// to this list. The results of this list are then added to the list of
143 /// lifetime definitions in the corresponding impl or function generics.
144 lifetimes_to_define: Vec<(Span, ParamName)>,
146 /// `true` if in-band lifetimes are being collected. This is used to
147 /// indicate whether or not we're in a place where new lifetimes will result
148 /// in in-band lifetime definitions, such a function or an impl header,
149 /// including implicit lifetimes from `impl_header_lifetime_elision`.
150 is_collecting_in_band_lifetimes: bool,
152 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
153 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
154 /// against this list to see if it is already in-scope, or if a definition
155 /// needs to be created for it.
157 /// We always store a `modern()` version of the param-name in this
159 in_scope_lifetimes: Vec<ParamName>,
161 current_module: hir::HirId,
163 type_def_lifetime_params: DefIdMap<usize>,
165 current_hir_id_owner: Vec<(DefIndex, u32)>,
166 item_local_id_counters: NodeMap<u32>,
167 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
169 allow_try_trait: Option<Lrc<[Symbol]>>,
170 allow_gen_future: Option<Lrc<[Symbol]>>,
171 allow_into_future: Option<Lrc<[Symbol]>>,
175 fn cstore(&self) -> &dyn CrateStore;
177 /// Obtains resolution for a `NodeId` with a single resolution.
178 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
180 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
181 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
183 /// Obtains resolution for a label with the given `NodeId`.
184 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
186 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
187 /// This should only return `None` during testing.
188 fn definitions(&mut self) -> &mut Definitions;
190 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
191 /// resolves it based on `is_value`.
195 crate_root: Option<Symbol>,
196 components: &[Symbol],
198 ) -> (ast::Path, Res<NodeId>);
200 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
202 fn next_node_id(&mut self) -> NodeId;
205 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
207 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
208 /// and if so, what meaning it has.
210 enum ImplTraitContext<'b, 'a> {
211 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
212 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
213 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
215 /// Newly generated parameters should be inserted into the given `Vec`.
216 Universal(&'b mut Vec<hir::GenericParam<'a>>),
218 /// Treat `impl Trait` as shorthand for a new opaque type.
219 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
220 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
222 /// We optionally store a `DefId` for the parent item here so we can look up necessary
223 /// information later. It is `None` when no information about the context should be stored
224 /// (e.g., for consts and statics).
225 OpaqueTy(Option<DefId> /* fn def-ID */),
227 /// `impl Trait` is not accepted in this position.
228 Disallowed(ImplTraitPosition),
231 /// Position in which `impl Trait` is disallowed.
232 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
233 enum ImplTraitPosition {
234 /// Disallowed in `let` / `const` / `static` bindings.
237 /// All other posiitons.
241 impl<'b, 'a> ImplTraitContext<'b, 'a> {
243 fn disallowed() -> Self {
244 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
247 fn reborrow(&'c mut self) -> ImplTraitContext<'c, 'a> {
248 use self::ImplTraitContext::*;
250 Universal(params) => Universal(params),
251 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
252 Disallowed(pos) => Disallowed(*pos),
257 pub fn lower_crate<'a, 'hir>(
259 dep_graph: &'a DepGraph,
261 resolver: &'a mut dyn Resolver,
262 nt_to_tokenstream: NtToTokenstream,
263 arena: &'hir Arena<'hir>,
264 ) -> hir::Crate<'hir> {
265 // We're constructing the HIR here; we don't care what we will
266 // read, since we haven't even constructed the *input* to
268 dep_graph.assert_ignored();
270 let _prof_timer = sess.prof.generic_activity("hir_lowering");
273 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
278 items: BTreeMap::new(),
279 trait_items: BTreeMap::new(),
280 impl_items: BTreeMap::new(),
281 bodies: BTreeMap::new(),
282 trait_impls: BTreeMap::new(),
283 modules: BTreeMap::new(),
284 exported_macros: Vec::new(),
285 non_exported_macro_attrs: Vec::new(),
286 catch_scopes: Vec::new(),
287 loop_scopes: Vec::new(),
288 is_in_loop_condition: false,
289 is_in_trait_impl: false,
290 is_in_dyn_type: false,
291 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
292 type_def_lifetime_params: Default::default(),
293 current_module: hir::CRATE_HIR_ID,
294 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
295 item_local_id_counters: Default::default(),
296 node_id_to_hir_id: IndexVec::new(),
297 generator_kind: None,
299 lifetimes_to_define: Vec::new(),
300 is_collecting_in_band_lifetimes: false,
301 in_scope_lifetimes: Vec::new(),
302 allow_try_trait: Some([sym::try_trait][..].into()),
303 allow_gen_future: Some([sym::gen_future][..].into()),
304 allow_into_future: Some([sym::into_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<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
379 fn visit_ty(&mut self, ty: &'a 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: &'v 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) -> &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()
1353 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1354 attributes to enable"
1362 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1363 TyKind::CVarArgs => {
1364 self.sess.delay_span_bug(
1366 "`TyKind::CVarArgs` should have been handled elsewhere",
1372 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1375 fn lower_opaque_impl_trait(
1378 fn_def_id: Option<DefId>,
1379 opaque_ty_node_id: NodeId,
1380 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1381 ) -> hir::TyKind<'hir> {
1383 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1384 fn_def_id, opaque_ty_node_id, span,
1387 // Make sure we know that some funky desugaring has been going on here.
1388 // This is a first: there is code in other places like for loop
1389 // desugaring that explicitly states that we don't want to track that.
1390 // Not tracking it makes lints in rustc and clippy very fragile, as
1391 // frequently opened issues show.
1392 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1394 let opaque_ty_def_index =
1395 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1397 self.allocate_hir_id_counter(opaque_ty_node_id);
1399 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1401 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1403 opaque_ty_def_index,
1407 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1409 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1411 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1412 let opaque_ty_item = hir::OpaqueTy {
1413 generics: hir::Generics {
1414 params: lifetime_defs,
1415 where_clause: hir::WhereClause { predicates: &[], span },
1419 impl_trait_fn: fn_def_id,
1420 origin: hir::OpaqueTyOrigin::FnReturn,
1423 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1425 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1427 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1428 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1432 /// Registers a new opaque type with the proper `NodeId`s and
1433 /// returns the lowered node-ID for the opaque type.
1434 fn generate_opaque_type(
1436 opaque_ty_node_id: NodeId,
1437 opaque_ty_item: hir::OpaqueTy<'hir>,
1439 opaque_ty_span: Span,
1441 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1442 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1443 // Generate an `type Foo = impl Trait;` declaration.
1444 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1445 let opaque_ty_item = hir::Item {
1446 hir_id: opaque_ty_id,
1447 ident: Ident::invalid(),
1448 attrs: Default::default(),
1449 kind: opaque_ty_item_kind,
1450 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1451 span: opaque_ty_span,
1454 // Insert the item into the global item list. This usually happens
1455 // automatically for all AST items. But this opaque type item
1456 // does not actually exist in the AST.
1457 self.insert_item(opaque_ty_item);
1461 fn lifetimes_from_impl_trait_bounds(
1463 opaque_ty_id: NodeId,
1464 parent_index: DefIndex,
1465 bounds: hir::GenericBounds<'hir>,
1466 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1468 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1469 parent_index={:?}, \
1471 opaque_ty_id, parent_index, bounds,
1474 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1475 // appear in the bounds, excluding lifetimes that are created within the bounds.
1476 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1477 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1478 context: &'r mut LoweringContext<'a, 'hir>,
1480 opaque_ty_id: NodeId,
1481 collect_elided_lifetimes: bool,
1482 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1483 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1484 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1485 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1488 impl<'r, 'a, 'v, 'hir> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1489 fn nested_visit_map<'this>(
1491 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1492 hir::intravisit::NestedVisitorMap::None
1495 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1496 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1497 if parameters.parenthesized {
1498 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1499 self.collect_elided_lifetimes = false;
1500 hir::intravisit::walk_generic_args(self, span, parameters);
1501 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1503 hir::intravisit::walk_generic_args(self, span, parameters);
1507 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1508 // Don't collect elided lifetimes used inside of `fn()` syntax.
1509 if let hir::TyKind::BareFn(_) = t.kind {
1510 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1511 self.collect_elided_lifetimes = false;
1513 // Record the "stack height" of `for<'a>` lifetime bindings
1514 // to be able to later fully undo their introduction.
1515 let old_len = self.currently_bound_lifetimes.len();
1516 hir::intravisit::walk_ty(self, t);
1517 self.currently_bound_lifetimes.truncate(old_len);
1519 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1521 hir::intravisit::walk_ty(self, t)
1525 fn visit_poly_trait_ref(
1527 trait_ref: &'v hir::PolyTraitRef<'v>,
1528 modifier: hir::TraitBoundModifier,
1530 // Record the "stack height" of `for<'a>` lifetime bindings
1531 // to be able to later fully undo their introduction.
1532 let old_len = self.currently_bound_lifetimes.len();
1533 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1534 self.currently_bound_lifetimes.truncate(old_len);
1537 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1538 // Record the introduction of 'a in `for<'a> ...`.
1539 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1540 // Introduce lifetimes one at a time so that we can handle
1541 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1542 let lt_name = hir::LifetimeName::Param(param.name);
1543 self.currently_bound_lifetimes.push(lt_name);
1546 hir::intravisit::walk_generic_param(self, param);
1549 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1550 let name = match lifetime.name {
1551 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1552 if self.collect_elided_lifetimes {
1553 // Use `'_` for both implicit and underscore lifetimes in
1554 // `type Foo<'_> = impl SomeTrait<'_>;`.
1555 hir::LifetimeName::Underscore
1560 hir::LifetimeName::Param(_) => lifetime.name,
1562 // Refers to some other lifetime that is "in
1563 // scope" within the type.
1564 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1566 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1569 if !self.currently_bound_lifetimes.contains(&name)
1570 && !self.already_defined_lifetimes.contains(&name)
1572 self.already_defined_lifetimes.insert(name);
1574 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1575 hir_id: self.context.next_id(),
1576 span: lifetime.span,
1580 let def_node_id = self.context.resolver.next_node_id();
1582 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1583 self.context.resolver.definitions().create_def_with_parent(
1586 DefPathData::LifetimeNs(name.ident().name),
1591 let (name, kind) = match name {
1592 hir::LifetimeName::Underscore => (
1593 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1594 hir::LifetimeParamKind::Elided,
1596 hir::LifetimeName::Param(param_name) => {
1597 (param_name, hir::LifetimeParamKind::Explicit)
1599 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1602 self.output_lifetime_params.push(hir::GenericParam {
1605 span: lifetime.span,
1606 pure_wrt_drop: false,
1609 kind: hir::GenericParamKind::Lifetime { kind },
1615 let mut lifetime_collector = ImplTraitLifetimeCollector {
1617 parent: parent_index,
1619 collect_elided_lifetimes: true,
1620 currently_bound_lifetimes: Vec::new(),
1621 already_defined_lifetimes: FxHashSet::default(),
1622 output_lifetimes: Vec::new(),
1623 output_lifetime_params: Vec::new(),
1626 for bound in bounds {
1627 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1630 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1634 self.arena.alloc_from_iter(output_lifetimes),
1635 self.arena.alloc_from_iter(output_lifetime_params),
1642 qself: &Option<QSelf>,
1644 param_mode: ParamMode,
1645 mut itctx: ImplTraitContext<'_, 'hir>,
1646 ) -> hir::QPath<'hir> {
1647 let qself_position = qself.as_ref().map(|q| q.position);
1648 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1651 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1653 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1654 let path = self.arena.alloc(hir::Path {
1655 res: self.lower_res(partial_res.base_res()),
1656 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1658 let param_mode = match (qself_position, param_mode) {
1659 (Some(j), ParamMode::Optional) if i < j => {
1660 // This segment is part of the trait path in a
1661 // qualified path - one of `a`, `b` or `Trait`
1662 // in `<X as a::b::Trait>::T::U::method`.
1668 // Figure out if this is a type/trait segment,
1669 // which may need lifetime elision performed.
1670 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1671 krate: def_id.krate,
1672 index: this.def_key(def_id).parent.expect("missing parent"),
1674 let type_def_id = match partial_res.base_res() {
1675 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1676 Some(parent_def_id(self, def_id))
1678 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1679 Some(parent_def_id(self, def_id))
1681 Res::Def(DefKind::Struct, def_id)
1682 | Res::Def(DefKind::Union, def_id)
1683 | Res::Def(DefKind::Enum, def_id)
1684 | Res::Def(DefKind::TyAlias, def_id)
1685 | Res::Def(DefKind::Trait, def_id)
1686 if i + 1 == proj_start =>
1692 let parenthesized_generic_args = match partial_res.base_res() {
1693 // `a::b::Trait(Args)`
1694 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1695 ParenthesizedGenericArgs::Ok
1697 // `a::b::Trait(Args)::TraitItem`
1698 Res::Def(DefKind::Method, _)
1699 | Res::Def(DefKind::AssocConst, _)
1700 | Res::Def(DefKind::AssocTy, _)
1701 if i + 2 == proj_start =>
1703 ParenthesizedGenericArgs::Ok
1705 // Avoid duplicated errors.
1706 Res::Err => ParenthesizedGenericArgs::Ok,
1708 _ => ParenthesizedGenericArgs::Err,
1711 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1712 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1715 assert!(!def_id.is_local());
1716 let item_generics = self
1719 .item_generics_cloned_untracked(def_id, self.sess);
1720 let n = item_generics.own_counts().lifetimes;
1721 self.type_def_lifetime_params.insert(def_id, n);
1724 self.lower_path_segment(
1729 parenthesized_generic_args,
1738 // Simple case, either no projections, or only fully-qualified.
1739 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1740 if partial_res.unresolved_segments() == 0 {
1741 return hir::QPath::Resolved(qself, path);
1744 // Create the innermost type that we're projecting from.
1745 let mut ty = if path.segments.is_empty() {
1746 // If the base path is empty that means there exists a
1747 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1748 qself.expect("missing QSelf for <T>::...")
1750 // Otherwise, the base path is an implicit `Self` type path,
1751 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1752 // `<I as Iterator>::Item::default`.
1753 let new_id = self.next_id();
1754 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1757 // Anything after the base path are associated "extensions",
1758 // out of which all but the last one are associated types,
1759 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1760 // * base path is `std::vec::Vec<T>`
1761 // * "extensions" are `IntoIter`, `Item` and `clone`
1762 // * type nodes are:
1763 // 1. `std::vec::Vec<T>` (created above)
1764 // 2. `<std::vec::Vec<T>>::IntoIter`
1765 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1766 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1767 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1768 let segment = self.arena.alloc(self.lower_path_segment(
1773 ParenthesizedGenericArgs::Err,
1777 let qpath = hir::QPath::TypeRelative(ty, segment);
1779 // It's finished, return the extension of the right node type.
1780 if i == p.segments.len() - 1 {
1784 // Wrap the associated extension in another type node.
1785 let new_id = self.next_id();
1786 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1789 // We should've returned in the for loop above.
1792 "lower_qpath: no final extension segment in {}..{}",
1798 fn lower_path_extra(
1802 param_mode: ParamMode,
1803 explicit_owner: Option<NodeId>,
1804 ) -> hir::Path<'hir> {
1807 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1808 self.lower_path_segment(
1813 ParenthesizedGenericArgs::Err,
1814 ImplTraitContext::disallowed(),
1822 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path<'hir> {
1823 let res = self.expect_full_res(id);
1824 let res = self.lower_res(res);
1825 self.lower_path_extra(res, p, param_mode, None)
1828 fn lower_path_segment(
1831 segment: &PathSegment,
1832 param_mode: ParamMode,
1833 expected_lifetimes: usize,
1834 parenthesized_generic_args: ParenthesizedGenericArgs,
1835 itctx: ImplTraitContext<'_, 'hir>,
1836 explicit_owner: Option<NodeId>,
1837 ) -> hir::PathSegment<'hir> {
1838 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1839 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1840 match **generic_args {
1841 GenericArgs::AngleBracketed(ref data) => {
1842 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1844 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1845 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1846 ParenthesizedGenericArgs::Err => {
1847 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1848 err.span_label(data.span, "only `Fn` traits may use parentheses");
1849 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1850 // Do not suggest going from `Trait()` to `Trait<>`
1851 if data.inputs.len() > 0 {
1852 if let Some(split) = snippet.find('(') {
1853 let trait_name = &snippet[0..split];
1854 let args = &snippet[split + 1..snippet.len() - 1];
1855 err.span_suggestion(
1857 "use angle brackets instead",
1858 format!("{}<{}>", trait_name, args),
1859 Applicability::MaybeIncorrect,
1866 self.lower_angle_bracketed_parameter_data(
1867 &data.as_angle_bracketed_args(),
1878 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1881 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1882 GenericArg::Lifetime(_) => true,
1885 let first_generic_span = generic_args
1889 .chain(generic_args.bindings.iter().map(|b| b.span))
1891 if !generic_args.parenthesized && !has_lifetimes {
1892 generic_args.args = self
1893 .elided_path_lifetimes(path_span, expected_lifetimes)
1895 .map(|lt| GenericArg::Lifetime(lt))
1896 .chain(generic_args.args.into_iter())
1898 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1899 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1900 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1901 let no_bindings = generic_args.bindings.is_empty();
1902 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1903 // If there are no (non-implicit) generic args or associated type
1904 // bindings, our suggestion includes the angle brackets.
1905 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1907 // Otherwise (sorry, this is kind of gross) we need to infer the
1908 // place to splice in the `'_, ` from the generics that do exist.
1909 let first_generic_span = first_generic_span
1910 .expect("already checked that non-lifetime args or bindings exist");
1911 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1913 match self.anonymous_lifetime_mode {
1914 // In create-parameter mode we error here because we don't want to support
1915 // deprecated impl elision in new features like impl elision and `async fn`,
1916 // both of which work using the `CreateParameter` mode:
1918 // impl Foo for std::cell::Ref<u32> // note lack of '_
1919 // async fn foo(_: std::cell::Ref<u32>) { ... }
1920 AnonymousLifetimeMode::CreateParameter => {
1921 let mut err = struct_span_err!(
1925 "implicit elided lifetime not allowed here"
1927 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1938 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1939 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1940 ELIDED_LIFETIMES_IN_PATHS,
1943 "hidden lifetime parameters in types are deprecated",
1944 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1957 let res = self.expect_full_res(segment.id);
1958 let id = if let Some(owner) = explicit_owner {
1959 self.lower_node_id_with_owner(segment.id, owner)
1961 self.lower_node_id(segment.id)
1964 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1965 segment.ident, segment.id, id,
1969 ident: segment.ident,
1971 res: Some(self.lower_res(res)),
1973 args: if generic_args.is_empty() {
1976 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
1981 fn lower_angle_bracketed_parameter_data(
1983 data: &AngleBracketedArgs,
1984 param_mode: ParamMode,
1985 mut itctx: ImplTraitContext<'_, 'hir>,
1986 ) -> (GenericArgsCtor<'hir>, bool) {
1987 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1988 let has_non_lt_args = args.iter().any(|arg| match arg {
1989 ast::GenericArg::Lifetime(_) => false,
1990 ast::GenericArg::Type(_) => true,
1991 ast::GenericArg::Const(_) => true,
1995 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1996 bindings: self.arena.alloc_from_iter(
1997 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
1999 parenthesized: false,
2001 !has_non_lt_args && param_mode == ParamMode::Optional,
2005 fn lower_parenthesized_parameter_data(
2007 data: &ParenthesizedArgs,
2008 ) -> (GenericArgsCtor<'hir>, bool) {
2009 // Switch to `PassThrough` mode for anonymous lifetimes; this
2010 // means that we permit things like `&Ref<T>`, where `Ref` has
2011 // a hidden lifetime parameter. This is needed for backwards
2012 // compatibility, even in contexts like an impl header where
2013 // we generally don't permit such things (see #51008).
2014 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2015 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2016 let inputs = this.arena.alloc_from_iter(
2017 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2019 let output_ty = match output {
2020 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2021 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2023 let args = vec![GenericArg::Type(this.ty_tup(span, inputs))];
2024 let binding = hir::TypeBinding {
2025 hir_id: this.next_id(),
2026 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2027 span: output_ty.span,
2028 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2031 GenericArgsCtor { args, bindings: arena_vec![this; binding], parenthesized: true },
2037 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2038 let mut ids = SmallVec::<[NodeId; 1]>::new();
2039 if self.sess.features_untracked().impl_trait_in_bindings {
2040 if let Some(ref ty) = l.ty {
2041 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2042 visitor.visit_ty(ty);
2045 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2046 let ty = l.ty.as_ref().map(|t| {
2049 if self.sess.features_untracked().impl_trait_in_bindings {
2050 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2052 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2056 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2059 hir_id: self.lower_node_id(l.id),
2061 pat: self.lower_pat(&l.pat),
2064 attrs: l.attrs.clone(),
2065 source: hir::LocalSource::Normal,
2071 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
2072 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2073 // as they are not explicit in HIR/Ty function signatures.
2074 // (instead, the `c_variadic` flag is set to `true`)
2075 let mut inputs = &decl.inputs[..];
2076 if decl.c_variadic() {
2077 inputs = &inputs[..inputs.len() - 1];
2079 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
2080 PatKind::Ident(_, ident, _) => ident,
2081 _ => Ident::new(kw::Invalid, param.pat.span),
2085 // Lowers a function declaration.
2087 // `decl`: the unlowered (AST) function declaration.
2088 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2089 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2090 // `make_ret_async` is also `Some`.
2091 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2092 // This guards against trait declarations and implementations where `impl Trait` is
2094 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2095 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2096 // return type `impl Trait` item.
2100 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2101 impl_trait_return_allow: bool,
2102 make_ret_async: Option<NodeId>,
2103 ) -> &'hir hir::FnDecl<'hir> {
2107 in_band_ty_params: {:?}, \
2108 impl_trait_return_allow: {}, \
2109 make_ret_async: {:?})",
2110 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2112 let lt_mode = if make_ret_async.is_some() {
2113 // In `async fn`, argument-position elided lifetimes
2114 // must be transformed into fresh generic parameters so that
2115 // they can be applied to the opaque `impl Trait` return type.
2116 AnonymousLifetimeMode::CreateParameter
2118 self.anonymous_lifetime_mode
2121 let c_variadic = decl.c_variadic();
2123 // Remember how many lifetimes were already around so that we can
2124 // only look at the lifetime parameters introduced by the arguments.
2125 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2126 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2127 // as they are not explicit in HIR/Ty function signatures.
2128 // (instead, the `c_variadic` flag is set to `true`)
2129 let mut inputs = &decl.inputs[..];
2131 inputs = &inputs[..inputs.len() - 1];
2133 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2134 if let Some((_, ibty)) = &mut in_band_ty_params {
2135 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2137 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2142 let output = if let Some(ret_id) = make_ret_async {
2143 self.lower_async_fn_ret_ty(
2145 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2150 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2151 Some((def_id, _)) if impl_trait_return_allow => {
2152 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2154 _ => hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed())),
2156 FunctionRetTy::Default(span) => hir::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>
2400 let future_path = self.arena.alloc(self.std_path(
2402 &[sym::future, sym::Future],
2403 Some(future_params),
2407 hir::GenericBound::Trait(
2409 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2410 bound_generic_params: &[],
2413 hir::TraitBoundModifier::None,
2417 fn lower_param_bound(
2420 itctx: ImplTraitContext<'_, 'hir>,
2421 ) -> hir::GenericBound<'hir> {
2423 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2424 self.lower_poly_trait_ref(ty, itctx),
2425 self.lower_trait_bound_modifier(modifier),
2427 GenericBound::Outlives(ref lifetime) => {
2428 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2433 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2434 let span = l.ident.span;
2436 ident if ident.name == kw::StaticLifetime => {
2437 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2439 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2440 AnonymousLifetimeMode::CreateParameter => {
2441 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2442 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2445 AnonymousLifetimeMode::PassThrough => {
2446 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2449 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2452 self.maybe_collect_in_band_lifetime(ident);
2453 let param_name = ParamName::Plain(ident);
2454 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2459 fn new_named_lifetime(
2463 name: hir::LifetimeName,
2464 ) -> hir::Lifetime {
2465 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2468 fn lower_generic_params_mut(
2470 params: &[GenericParam],
2471 add_bounds: &NodeMap<Vec<GenericBound>>,
2472 mut itctx: ImplTraitContext<'_, 'hir>,
2473 ) -> Vec<hir::GenericParam<'hir>> {
2476 .map(|param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2480 fn lower_generic_params(
2482 params: &[GenericParam],
2483 add_bounds: &NodeMap<Vec<GenericBound>>,
2484 itctx: ImplTraitContext<'_, 'hir>,
2485 ) -> &'hir [hir::GenericParam<'hir>] {
2486 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2489 fn lower_generic_param(
2491 param: &GenericParam,
2492 add_bounds: &NodeMap<Vec<GenericBound>>,
2493 mut itctx: ImplTraitContext<'_, 'hir>,
2494 ) -> hir::GenericParam<'hir> {
2495 let mut bounds: Vec<_> = self
2496 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2497 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2500 let (name, kind) = match param.kind {
2501 GenericParamKind::Lifetime => {
2502 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2503 self.is_collecting_in_band_lifetimes = false;
2506 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2507 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2509 let param_name = match lt.name {
2510 hir::LifetimeName::Param(param_name) => param_name,
2511 hir::LifetimeName::Implicit
2512 | hir::LifetimeName::Underscore
2513 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2514 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2517 "object-lifetime-default should not occur here",
2520 hir::LifetimeName::Error => ParamName::Error,
2524 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2526 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2530 GenericParamKind::Type { ref default, .. } => {
2531 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2532 if !add_bounds.is_empty() {
2533 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2534 bounds.extend(params);
2537 let kind = hir::GenericParamKind::Type {
2540 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2544 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2545 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2549 (hir::ParamName::Plain(param.ident), kind)
2551 GenericParamKind::Const { ref ty } => (
2552 hir::ParamName::Plain(param.ident),
2553 hir::GenericParamKind::Const {
2554 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2560 hir_id: self.lower_node_id(param.id),
2562 span: param.ident.span,
2563 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2564 attrs: self.lower_attrs(¶m.attrs),
2565 bounds: self.arena.alloc_from_iter(bounds),
2573 itctx: ImplTraitContext<'_, 'hir>,
2574 ) -> hir::TraitRef<'hir> {
2575 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2576 hir::QPath::Resolved(None, path) => path,
2577 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2579 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2582 fn lower_poly_trait_ref(
2585 mut itctx: ImplTraitContext<'_, 'hir>,
2586 ) -> hir::PolyTraitRef<'hir> {
2587 let bound_generic_params = self.lower_generic_params(
2588 &p.bound_generic_params,
2589 &NodeMap::default(),
2592 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2593 this.lower_trait_ref(&p.trait_ref, itctx)
2596 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2599 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2600 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2603 fn lower_param_bounds(
2605 bounds: &[GenericBound],
2606 itctx: ImplTraitContext<'_, 'hir>,
2607 ) -> hir::GenericBounds<'hir> {
2608 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2611 fn lower_param_bounds_mut<'s>(
2613 bounds: &'s [GenericBound],
2614 mut itctx: ImplTraitContext<'s, 'hir>,
2615 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2616 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2619 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2620 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2623 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2624 let mut stmts = vec![];
2625 let mut expr: Option<&'hir _> = None;
2627 for (index, stmt) in b.stmts.iter().enumerate() {
2628 if index == b.stmts.len() - 1 {
2629 if let StmtKind::Expr(ref e) = stmt.kind {
2630 expr = Some(self.lower_expr(e));
2632 stmts.extend(self.lower_stmt(stmt));
2635 stmts.extend(self.lower_stmt(stmt));
2640 hir_id: self.lower_node_id(b.id),
2641 stmts: self.arena.alloc_from_iter(stmts),
2643 rules: self.lower_block_check_mode(&b.rules),
2649 /// Lowers a block directly to an expression, presuming that it
2650 /// has no attributes and is not targeted by a `break`.
2651 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2652 let block = self.lower_block(b, false);
2653 self.expr_block(block, AttrVec::new())
2656 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2657 let node = match p.kind {
2658 PatKind::Wild => hir::PatKind::Wild,
2659 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2660 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2661 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2664 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2665 PatKind::TupleStruct(ref path, ref pats) => {
2666 let qpath = self.lower_qpath(
2670 ParamMode::Optional,
2671 ImplTraitContext::disallowed(),
2673 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2674 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2676 PatKind::Or(ref pats) => {
2677 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2679 PatKind::Path(ref qself, ref path) => {
2680 let qpath = self.lower_qpath(
2684 ParamMode::Optional,
2685 ImplTraitContext::disallowed(),
2687 hir::PatKind::Path(qpath)
2689 PatKind::Struct(ref path, ref fields, etc) => {
2690 let qpath = self.lower_qpath(
2694 ParamMode::Optional,
2695 ImplTraitContext::disallowed(),
2698 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2699 hir_id: self.next_id(),
2701 pat: self.lower_pat(&f.pat),
2702 is_shorthand: f.is_shorthand,
2705 hir::PatKind::Struct(qpath, fs, etc)
2707 PatKind::Tuple(ref pats) => {
2708 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2709 hir::PatKind::Tuple(pats, ddpos)
2711 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2712 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2713 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2714 self.lower_expr(e1),
2715 self.lower_expr(e2),
2716 self.lower_range_end(end),
2718 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2720 // If we reach here the `..` pattern is not semantically allowed.
2721 self.ban_illegal_rest_pat(p.span)
2723 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2724 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2727 self.pat_with_node_id_of(p, node)
2734 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2735 let mut elems = Vec::with_capacity(pats.len());
2736 let mut rest = None;
2738 let mut iter = pats.iter().enumerate();
2739 for (idx, pat) in iter.by_ref() {
2740 // Interpret the first `..` pattern as a sub-tuple pattern.
2741 // Note that unlike for slice patterns,
2742 // where `xs @ ..` is a legal sub-slice pattern,
2743 // it is not a legal sub-tuple pattern.
2745 rest = Some((idx, pat.span));
2748 // It was not a sub-tuple pattern so lower it normally.
2749 elems.push(self.lower_pat(pat));
2752 for (_, pat) in iter {
2753 // There was a previous sub-tuple pattern; make sure we don't allow more...
2755 // ...but there was one again, so error.
2756 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2758 elems.push(self.lower_pat(pat));
2762 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2765 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2766 /// `hir::PatKind::Slice(before, slice, after)`.
2768 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2769 /// this is interpreted as a sub-slice pattern semantically.
2770 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2771 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2772 let mut before = Vec::new();
2773 let mut after = Vec::new();
2774 let mut slice = None;
2775 let mut prev_rest_span = None;
2777 let mut iter = pats.iter();
2778 // Lower all the patterns until the first occurence of a sub-slice pattern.
2779 for pat in iter.by_ref() {
2781 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2783 prev_rest_span = Some(pat.span);
2784 slice = Some(self.pat_wild_with_node_id_of(pat));
2787 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2788 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2789 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2790 prev_rest_span = Some(sub.span);
2791 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2792 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2793 slice = Some(self.pat_with_node_id_of(pat, node));
2796 // It was not a subslice pattern so lower it normally.
2797 _ => before.push(self.lower_pat(pat)),
2801 // Lower all the patterns after the first sub-slice pattern.
2803 // There was a previous subslice pattern; make sure we don't allow more.
2804 let rest_span = match pat.kind {
2805 PatKind::Rest => Some(pat.span),
2806 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2807 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2808 after.push(self.pat_wild_with_node_id_of(pat));
2813 if let Some(rest_span) = rest_span {
2814 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2815 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2817 // Lower the pattern normally.
2818 after.push(self.lower_pat(pat));
2822 hir::PatKind::Slice(
2823 self.arena.alloc_from_iter(before),
2825 self.arena.alloc_from_iter(after),
2832 binding_mode: &BindingMode,
2834 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2835 ) -> hir::PatKind<'hir> {
2836 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2837 // `None` can occur in body-less function signatures
2838 res @ None | res @ Some(Res::Local(_)) => {
2839 let canonical_id = match res {
2840 Some(Res::Local(id)) => id,
2844 hir::PatKind::Binding(
2845 self.lower_binding_mode(binding_mode),
2846 self.lower_node_id(canonical_id),
2851 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2853 self.arena.alloc(hir::Path {
2855 res: self.lower_res(res),
2856 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2862 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2863 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2866 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2867 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2868 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2871 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2872 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2874 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2875 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2876 .span_label(prev_sp, "previously used here")
2880 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2881 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2883 .struct_span_err(sp, "`..` patterns are not allowed here")
2884 .note("only allowed in tuple, tuple struct, and slice patterns")
2887 // We're not in a list context so `..` can be reasonably treated
2888 // as `_` because it should always be valid and roughly matches the
2889 // intent of `..` (notice that the rest of a single slot is that slot).
2893 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2895 RangeEnd::Included(_) => hir::RangeEnd::Included,
2896 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2900 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2901 self.with_new_scopes(|this| hir::AnonConst {
2902 hir_id: this.lower_node_id(c.id),
2903 body: this.lower_const_body(c.value.span, Some(&c.value)),
2907 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2908 let kind = match s.kind {
2909 StmtKind::Local(ref l) => {
2910 let (l, item_ids) = self.lower_local(l);
2911 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2914 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2915 self.stmt(s.span, hir::StmtKind::Item(item_id))
2920 hir_id: self.lower_node_id(s.id),
2921 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2927 StmtKind::Item(ref it) => {
2928 // Can only use the ID once.
2929 let mut id = Some(s.id);
2936 .map(|id| self.lower_node_id(id))
2937 .unwrap_or_else(|| self.next_id());
2939 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2943 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2944 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2945 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2947 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2950 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2952 BlockCheckMode::Default => hir::DefaultBlock,
2953 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2957 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2959 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2960 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2961 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2962 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2966 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2968 CompilerGenerated => hir::CompilerGenerated,
2969 UserProvided => hir::UserProvided,
2973 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2975 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2976 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2980 // Helper methods for building HIR.
2982 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2983 hir::Stmt { span, kind, hir_id: self.next_id() }
2986 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2987 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2994 init: Option<&'hir hir::Expr<'hir>>,
2995 pat: &'hir hir::Pat<'hir>,
2996 source: hir::LocalSource,
2997 ) -> hir::Stmt<'hir> {
2998 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2999 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
3002 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
3003 self.block_all(expr.span, &[], Some(expr))
3009 stmts: &'hir [hir::Stmt<'hir>],
3010 expr: Option<&'hir hir::Expr<'hir>>,
3011 ) -> &'hir hir::Block<'hir> {
3012 let blk = hir::Block {
3015 hir_id: self.next_id(),
3016 rules: hir::DefaultBlock,
3018 targeted_by_break: false,
3020 self.arena.alloc(blk)
3023 /// Constructs a `true` or `false` literal pattern.
3024 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3025 let expr = self.expr_bool(span, val);
3026 self.pat(span, hir::PatKind::Lit(expr))
3029 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3030 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3033 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3034 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3037 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3038 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3041 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3042 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3048 components: &[Symbol],
3049 subpats: &'hir [&'hir hir::Pat<'hir>],
3050 ) -> &'hir hir::Pat<'hir> {
3051 let path = self.std_path(span, components, None, true);
3052 let qpath = hir::QPath::Resolved(None, self.arena.alloc(path));
3053 let pt = if subpats.is_empty() {
3054 hir::PatKind::Path(qpath)
3056 hir::PatKind::TupleStruct(qpath, subpats, None)
3061 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3062 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3065 fn pat_ident_binding_mode(
3069 bm: hir::BindingAnnotation,
3070 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3071 let hir_id = self.next_id();
3074 self.arena.alloc(hir::Pat {
3076 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3083 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3084 self.pat(span, hir::PatKind::Wild)
3087 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3088 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3091 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3092 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3093 /// The path is also resolved according to `is_value`.
3097 components: &[Symbol],
3098 params: Option<&'hir hir::GenericArgs<'hir>>,
3100 ) -> hir::Path<'hir> {
3101 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3102 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3104 let mut segments: Vec<_> = path
3108 let res = self.expect_full_res(segment.id);
3110 ident: segment.ident,
3111 hir_id: Some(self.lower_node_id(segment.id)),
3112 res: Some(self.lower_res(res)),
3118 segments.last_mut().unwrap().args = params;
3122 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3123 segments: self.arena.alloc_from_iter(segments),
3129 mut hir_id: hir::HirId,
3131 qpath: hir::QPath<'hir>,
3132 ) -> hir::Ty<'hir> {
3133 let kind = match qpath {
3134 hir::QPath::Resolved(None, path) => {
3135 // Turn trait object paths into `TyKind::TraitObject` instead.
3137 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3138 let principal = hir::PolyTraitRef {
3139 bound_generic_params: &[],
3140 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3144 // The original ID is taken by the `PolyTraitRef`,
3145 // so the `Ty` itself needs a different one.
3146 hir_id = self.next_id();
3147 hir::TyKind::TraitObject(
3148 arena_vec![self; principal],
3149 self.elided_dyn_bound(span),
3152 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3155 _ => hir::TyKind::Path(qpath),
3158 hir::Ty { hir_id, kind, span }
3161 /// Invoked to create the lifetime argument for a type `&T`
3162 /// with no explicit lifetime.
3163 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3164 match self.anonymous_lifetime_mode {
3165 // Intercept when we are in an impl header or async fn and introduce an in-band
3167 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3169 AnonymousLifetimeMode::CreateParameter => {
3170 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3172 hir_id: self.next_id(),
3174 name: hir::LifetimeName::Param(fresh_name),
3178 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3180 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3184 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3185 /// return a "error lifetime".
3186 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3187 let (id, msg, label) = match id {
3188 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3191 self.resolver.next_node_id(),
3192 "`&` without an explicit lifetime name cannot be used here",
3193 "explicit lifetime name needed here",
3197 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3198 err.span_label(span, label);
3201 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3204 /// Invoked to create the lifetime argument(s) for a path like
3205 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3206 /// sorts of cases are deprecated. This may therefore report a warning or an
3207 /// error, depending on the mode.
3208 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3209 (0..count).map(|_| self.elided_path_lifetime(span)).collect()
3212 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3213 match self.anonymous_lifetime_mode {
3214 AnonymousLifetimeMode::CreateParameter => {
3215 // We should have emitted E0726 when processing this path above
3217 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3218 let id = self.resolver.next_node_id();
3219 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3221 // `PassThrough` is the normal case.
3222 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3223 // is unsuitable here, as these can occur from missing lifetime parameters in a
3224 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3225 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3226 // later, at which point a suitable error will be emitted.
3227 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3228 self.new_implicit_lifetime(span)
3233 /// Invoked to create the lifetime argument(s) for an elided trait object
3234 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3235 /// when the bound is written, even if it is written with `'_` like in
3236 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3237 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3238 match self.anonymous_lifetime_mode {
3239 // NB. We intentionally ignore the create-parameter mode here.
3240 // and instead "pass through" to resolve-lifetimes, which will apply
3241 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3242 // do not act like other elided lifetimes. In other words, given this:
3244 // impl Foo for Box<dyn Debug>
3246 // we do not introduce a fresh `'_` to serve as the bound, but instead
3247 // ultimately translate to the equivalent of:
3249 // impl Foo for Box<dyn Debug + 'static>
3251 // `resolve_lifetime` has the code to make that happen.
3252 AnonymousLifetimeMode::CreateParameter => {}
3254 AnonymousLifetimeMode::ReportError => {
3255 // ReportError applies to explicit use of `'_`.
3258 // This is the normal case.
3259 AnonymousLifetimeMode::PassThrough => {}
3262 let r = hir::Lifetime {
3263 hir_id: self.next_id(),
3265 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3267 debug!("elided_dyn_bound: r={:?}", r);
3271 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3272 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3275 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3276 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3277 // call site which do not have a macro backtrace. See #61963.
3278 let is_macro_callsite = self
3281 .span_to_snippet(span)
3282 .map(|snippet| snippet.starts_with("#["))
3284 if !is_macro_callsite {
3285 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3286 builtin::BARE_TRAIT_OBJECTS,
3289 "trait objects without an explicit `dyn` are deprecated",
3290 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3296 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId> {
3297 // Sorting by span ensures that we get things in order within a
3298 // file, and also puts the files in a sensible order.
3299 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3300 body_ids.sort_by_key(|b| bodies[b].value.span);
3304 /// Helper struct for delayed construction of GenericArgs.
3305 struct GenericArgsCtor<'hir> {
3306 args: Vec<hir::GenericArg<'hir>>,
3307 bindings: &'hir [hir::TypeBinding<'hir>],
3308 parenthesized: bool,
3311 impl GenericArgsCtor<'hir> {
3312 fn is_empty(&self) -> bool {
3313 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
3316 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
3318 args: arena.alloc_from_iter(self.args),
3319 bindings: self.bindings,
3320 parenthesized: self.parenthesized,