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::HirVec;
42 use crate::hir::{self, ParamName};
43 use crate::hir::{ConstArg, GenericArg};
45 use crate::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
46 use crate::middle::cstore::CrateStore;
47 use crate::session::config::nightly_options;
48 use crate::session::Session;
49 use crate::util::captures::Captures;
50 use crate::util::common::FN_OUTPUT_NAME;
51 use crate::util::nodemap::{DefIdMap, NodeMap};
52 use errors::Applicability;
53 use rustc_data_structures::fx::FxHashSet;
54 use rustc_data_structures::sync::Lrc;
55 use rustc_index::vec::IndexVec;
57 use smallvec::SmallVec;
58 use std::collections::BTreeMap;
64 use syntax::print::pprust;
65 use syntax::ptr::P as AstP;
66 use syntax::sess::ParseSess;
67 use syntax::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
68 use syntax::symbol::{kw, sym, Symbol};
69 use syntax::token::{self, Nonterminal, Token};
70 use syntax::tokenstream::{TokenStream, TokenTree};
71 use syntax::visit::{self, Visitor};
72 use syntax_pos::hygiene::ExpnId;
75 use rustc_error_codes::*;
77 macro_rules! arena_vec {
81 ($this:expr; $($x:expr),*) => (
82 $this.arena.alloc_from_iter(vec![$($x),*])
89 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
91 pub struct LoweringContext<'a, 'hir: 'a> {
92 crate_root: Option<Symbol>,
94 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
97 resolver: &'a mut dyn Resolver,
99 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
100 /// if we don't have this function pointer. To avoid that dependency so that
101 /// librustc is independent of the parser, we use dynamic dispatch here.
102 nt_to_tokenstream: NtToTokenstream,
104 /// Used to allocate HIR nodes
105 arena: &'hir Arena<'hir>,
107 /// The items being lowered are collected here.
108 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
110 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
111 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
112 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
113 exported_macros: Vec<hir::MacroDef<'hir>>,
114 non_exported_macro_attrs: Vec<ast::Attribute>,
116 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
118 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
120 generator_kind: Option<hir::GeneratorKind>,
122 /// Used to get the current `fn`'s def span to point to when using `await`
123 /// outside of an `async fn`.
124 current_item: Option<Span>,
126 catch_scopes: Vec<NodeId>,
127 loop_scopes: Vec<NodeId>,
128 is_in_loop_condition: bool,
129 is_in_trait_impl: bool,
130 is_in_dyn_type: bool,
132 /// What to do when we encounter either an "anonymous lifetime
133 /// reference". The term "anonymous" is meant to encompass both
134 /// `'_` lifetimes as well as fully elided cases where nothing is
135 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
136 anonymous_lifetime_mode: AnonymousLifetimeMode,
138 /// Used to create lifetime definitions from in-band lifetime usages.
139 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
140 /// When a named lifetime is encountered in a function or impl header and
141 /// has not been defined
142 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
143 /// to this list. The results of this list are then added to the list of
144 /// lifetime definitions in the corresponding impl or function generics.
145 lifetimes_to_define: Vec<(Span, ParamName)>,
147 /// `true` if in-band lifetimes are being collected. This is used to
148 /// indicate whether or not we're in a place where new lifetimes will result
149 /// in in-band lifetime definitions, such a function or an impl header,
150 /// including implicit lifetimes from `impl_header_lifetime_elision`.
151 is_collecting_in_band_lifetimes: bool,
153 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
154 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
155 /// against this list to see if it is already in-scope, or if a definition
156 /// needs to be created for it.
158 /// We always store a `modern()` version of the param-name in this
160 in_scope_lifetimes: Vec<ParamName>,
162 current_module: hir::HirId,
164 type_def_lifetime_params: DefIdMap<usize>,
166 current_hir_id_owner: Vec<(DefIndex, u32)>,
167 item_local_id_counters: NodeMap<u32>,
168 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
170 allow_try_trait: Option<Lrc<[Symbol]>>,
171 allow_gen_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()),
308 #[derive(Copy, Clone, PartialEq)]
310 /// Any path in a type context.
312 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
314 /// The `module::Type` in `module::Type::method` in an expression.
318 enum ParenthesizedGenericArgs {
323 /// What to do when we encounter an **anonymous** lifetime
324 /// reference. Anonymous lifetime references come in two flavors. You
325 /// have implicit, or fully elided, references to lifetimes, like the
326 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
327 /// or `Ref<'_, T>`. These often behave the same, but not always:
329 /// - certain usages of implicit references are deprecated, like
330 /// `Ref<T>`, and we sometimes just give hard errors in those cases
332 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
333 /// the same as `Box<dyn Foo + '_>`.
335 /// We describe the effects of the various modes in terms of three cases:
337 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
338 /// of a `&` (e.g., the missing lifetime in something like `&T`)
339 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
340 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
341 /// elided bounds follow special rules. Note that this only covers
342 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
343 /// '_>` is a case of "modern" elision.
344 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
345 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
346 /// non-deprecated equivalent.
348 /// Currently, the handling of lifetime elision is somewhat spread out
349 /// between HIR lowering and -- as described below -- the
350 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
351 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
352 /// everything into HIR lowering.
353 #[derive(Copy, Clone, Debug)]
354 enum AnonymousLifetimeMode {
355 /// For **Modern** cases, create a new anonymous region parameter
356 /// and reference that.
358 /// For **Dyn Bound** cases, pass responsibility to
359 /// `resolve_lifetime` code.
361 /// For **Deprecated** cases, report an error.
364 /// Give a hard error when either `&` or `'_` is written. Used to
365 /// rule out things like `where T: Foo<'_>`. Does not imply an
366 /// error on default object bounds (e.g., `Box<dyn Foo>`).
369 /// Pass responsibility to `resolve_lifetime` code for all cases.
373 struct ImplTraitTypeIdVisitor<'a> {
374 ids: &'a mut SmallVec<[NodeId; 1]>,
377 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
378 fn visit_ty(&mut self, ty: &'a Ty) {
380 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
382 TyKind::ImplTrait(id, _) => self.ids.push(id),
385 visit::walk_ty(self, ty);
388 fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment) {
389 if let Some(ref p) = path_segment.args {
390 if let GenericArgs::Parenthesized(_) = **p {
394 visit::walk_path_segment(self, path_span, path_segment)
398 impl<'a, 'hir> LoweringContext<'a, 'hir> {
399 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
400 /// Full-crate AST visitor that inserts into a fresh
401 /// `LoweringContext` any information that may be
402 /// needed from arbitrary locations in the crate,
403 /// e.g., the number of lifetime generic parameters
404 /// declared for every type and trait definition.
405 struct MiscCollector<'tcx, 'lowering, 'hir> {
406 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
407 hir_id_owner: Option<NodeId>,
410 impl MiscCollector<'_, '_, '_> {
411 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
413 UseTreeKind::Simple(_, id1, id2) => {
414 for &id in &[id1, id2] {
415 self.lctx.resolver.definitions().create_def_with_parent(
422 self.lctx.allocate_hir_id_counter(id);
425 UseTreeKind::Glob => (),
426 UseTreeKind::Nested(ref trees) => {
427 for &(ref use_tree, id) in trees {
428 let hir_id = self.lctx.allocate_hir_id_counter(id);
429 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
435 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
437 F: FnOnce(&mut Self) -> T,
439 let old = mem::replace(&mut self.hir_id_owner, owner);
441 self.hir_id_owner = old;
446 impl<'tcx, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
447 fn visit_pat(&mut self, p: &'tcx Pat) {
448 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
449 // Doesn't generate a HIR node
450 } else if let Some(owner) = self.hir_id_owner {
451 self.lctx.lower_node_id_with_owner(p.id, owner);
454 visit::walk_pat(self, p)
457 fn visit_item(&mut self, item: &'tcx Item) {
458 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
461 ItemKind::Struct(_, ref generics)
462 | ItemKind::Union(_, ref generics)
463 | ItemKind::Enum(_, ref generics)
464 | ItemKind::TyAlias(_, ref generics)
465 | ItemKind::Trait(_, _, ref generics, ..) => {
466 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
470 .filter(|param| match param.kind {
471 ast::GenericParamKind::Lifetime { .. } => true,
475 self.lctx.type_def_lifetime_params.insert(def_id, count);
477 ItemKind::Use(ref use_tree) => {
478 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
483 self.with_hir_id_owner(Some(item.id), |this| {
484 visit::walk_item(this, item);
488 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
489 self.lctx.allocate_hir_id_counter(item.id);
492 AssocItemKind::Fn(_, None) => {
493 // Ignore patterns in trait methods without bodies
494 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
496 _ => self.with_hir_id_owner(Some(item.id), |this| {
497 visit::walk_trait_item(this, item);
502 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
503 self.lctx.allocate_hir_id_counter(item.id);
504 self.with_hir_id_owner(Some(item.id), |this| {
505 visit::walk_impl_item(this, item);
509 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
510 // Ignore patterns in foreign items
511 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
514 fn visit_ty(&mut self, t: &'tcx Ty) {
516 // Mirrors the case in visit::walk_ty
517 TyKind::BareFn(ref f) => {
518 walk_list!(self, visit_generic_param, &f.generic_params);
519 // Mirrors visit::walk_fn_decl
520 for parameter in &f.decl.inputs {
521 // We don't lower the ids of argument patterns
522 self.with_hir_id_owner(None, |this| {
523 this.visit_pat(¶meter.pat);
525 self.visit_ty(¶meter.ty)
527 self.visit_fn_ret_ty(&f.decl.output)
529 _ => visit::walk_ty(self, t),
534 self.lower_node_id(CRATE_NODE_ID);
535 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
537 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
538 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
540 let module = self.lower_mod(&c.module);
541 let attrs = self.arena.alloc_from_iter(self.lower_attrs(&c.attrs).into_iter());
542 let body_ids = body_ids(&self.bodies);
544 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
550 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
551 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
553 trait_items: self.trait_items,
554 impl_items: self.impl_items,
557 trait_impls: self.trait_impls,
558 modules: self.modules,
562 fn insert_item(&mut self, item: hir::Item<'hir>) {
563 let id = item.hir_id;
564 // FIXME: Use `debug_asset-rt`.
565 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
566 self.items.insert(id, item);
567 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
570 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
571 // Set up the counter if needed.
572 self.item_local_id_counters.entry(owner).or_insert(0);
573 // Always allocate the first `HirId` for the owner itself.
574 let lowered = self.lower_node_id_with_owner(owner, owner);
575 debug_assert_eq!(lowered.local_id.as_u32(), 0);
579 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
581 F: FnOnce(&mut Self) -> hir::HirId,
583 if ast_node_id == DUMMY_NODE_ID {
584 return hir::DUMMY_HIR_ID;
587 let min_size = ast_node_id.as_usize() + 1;
589 if min_size > self.node_id_to_hir_id.len() {
590 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
593 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
595 if existing_hir_id == hir::DUMMY_HIR_ID {
596 // Generate a new `HirId`.
597 let hir_id = alloc_hir_id(self);
598 self.node_id_to_hir_id[ast_node_id] = hir_id;
606 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
608 F: FnOnce(&mut Self) -> T,
611 .item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
623 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
627 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
628 /// the `LoweringContext`'s `NodeId => HirId` map.
629 /// Take care not to call this method if the resulting `HirId` is then not
630 /// actually used in the HIR, as that would trigger an assertion in the
631 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
632 /// properly. Calling the method twice with the same `NodeId` is fine though.
633 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let &mut (def_index, ref mut local_id_counter) =
636 this.current_hir_id_owner.last_mut().unwrap();
637 let local_id = *local_id_counter;
638 *local_id_counter += 1;
639 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
643 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
644 self.lower_node_id_generic(ast_node_id, |this| {
645 let local_id_counter = this
646 .item_local_id_counters
648 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
649 let local_id = *local_id_counter;
651 // We want to be sure not to modify the counter in the map while it
652 // is also on the stack. Otherwise we'll get lost updates when writing
653 // back from the stack to the map.
654 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
656 *local_id_counter += 1;
657 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
658 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
659 that do not belong to the current owner",
662 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
666 fn next_id(&mut self) -> hir::HirId {
667 let node_id = self.resolver.next_node_id();
668 self.lower_node_id(node_id)
671 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
673 self.lower_node_id_generic(id, |_| {
674 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
679 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
680 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
681 if pr.unresolved_segments() != 0 {
682 bug!("path not fully resolved: {:?}", pr);
688 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
689 self.resolver.get_import_res(id).present_items()
692 fn diagnostic(&self) -> &errors::Handler {
693 self.sess.diagnostic()
696 /// Reuses the span but adds information like the kind of the desugaring and features that are
697 /// allowed inside this span.
698 fn mark_span_with_reason(
700 reason: DesugaringKind,
702 allow_internal_unstable: Option<Lrc<[Symbol]>>,
704 span.fresh_expansion(ExpnData {
705 allow_internal_unstable,
706 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
710 fn with_anonymous_lifetime_mode<R>(
712 anonymous_lifetime_mode: AnonymousLifetimeMode,
713 op: impl FnOnce(&mut Self) -> R,
716 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
717 anonymous_lifetime_mode,
719 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
720 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
721 let result = op(self);
722 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
724 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
725 old_anonymous_lifetime_mode
730 /// Creates a new `hir::GenericParam` for every new lifetime and
731 /// type parameter encountered while evaluating `f`. Definitions
732 /// are created with the parent provided. If no `parent_id` is
733 /// provided, no definitions will be returned.
735 /// Presuming that in-band lifetimes are enabled, then
736 /// `self.anonymous_lifetime_mode` will be updated to match the
737 /// parameter while `f` is running (and restored afterwards).
738 fn collect_in_band_defs<T, F>(
741 anonymous_lifetime_mode: AnonymousLifetimeMode,
743 ) -> (Vec<hir::GenericParam<'hir>>, T)
745 F: FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
747 assert!(!self.is_collecting_in_band_lifetimes);
748 assert!(self.lifetimes_to_define.is_empty());
749 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
751 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
752 self.is_collecting_in_band_lifetimes = true;
754 let (in_band_ty_params, res) = f(self);
756 self.is_collecting_in_band_lifetimes = false;
757 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
759 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
761 let params = lifetimes_to_define
763 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
764 .chain(in_band_ty_params.into_iter())
770 /// Converts a lifetime into a new generic parameter.
771 fn lifetime_to_generic_param(
775 parent_index: DefIndex,
776 ) -> hir::GenericParam<'hir> {
777 let node_id = self.resolver.next_node_id();
779 // Get the name we'll use to make the def-path. Note
780 // that collisions are ok here and this shouldn't
781 // really show up for end-user.
782 let (str_name, kind) = match hir_name {
783 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
784 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
785 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
788 // Add a definition for the in-band lifetime def.
789 self.resolver.definitions().create_def_with_parent(
792 DefPathData::LifetimeNs(str_name),
798 hir_id: self.lower_node_id(node_id),
803 pure_wrt_drop: false,
804 kind: hir::GenericParamKind::Lifetime { kind },
808 /// When there is a reference to some lifetime `'a`, and in-band
809 /// lifetimes are enabled, then we want to push that lifetime into
810 /// the vector of names to define later. In that case, it will get
811 /// added to the appropriate generics.
812 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
813 if !self.is_collecting_in_band_lifetimes {
817 if !self.sess.features_untracked().in_band_lifetimes {
821 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
825 let hir_name = ParamName::Plain(ident);
827 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
832 self.lifetimes_to_define.push((ident.span, hir_name));
835 /// When we have either an elided or `'_` lifetime in an impl
836 /// header, we convert it to an in-band lifetime.
837 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
838 assert!(self.is_collecting_in_band_lifetimes);
839 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
840 let hir_name = ParamName::Fresh(index);
841 self.lifetimes_to_define.push((span, hir_name));
845 // Evaluates `f` with the lifetimes in `params` in-scope.
846 // This is used to track which lifetimes have already been defined, and
847 // which are new in-band lifetimes that need to have a definition created
849 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
851 F: FnOnce(&mut Self) -> T,
853 let old_len = self.in_scope_lifetimes.len();
854 let lt_def_names = params.iter().filter_map(|param| match param.kind {
855 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
858 self.in_scope_lifetimes.extend(lt_def_names);
862 self.in_scope_lifetimes.truncate(old_len);
866 /// Appends in-band lifetime defs and argument-position `impl
867 /// Trait` defs to the existing set of generics.
869 /// Presuming that in-band lifetimes are enabled, then
870 /// `self.anonymous_lifetime_mode` will be updated to match the
871 /// parameter while `f` is running (and restored afterwards).
872 fn add_in_band_defs<F, T>(
876 anonymous_lifetime_mode: AnonymousLifetimeMode,
878 ) -> (hir::Generics<'hir>, T)
880 F: FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
882 let (in_band_defs, (mut lowered_generics, res)) =
883 self.with_in_scope_lifetime_defs(&generics.params, |this| {
884 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
885 let mut params = Vec::new();
886 // Note: it is necessary to lower generics *before* calling `f`.
887 // When lowering `async fn`, there's a final step when lowering
888 // the return type that assumes that all in-scope lifetimes have
889 // already been added to either `in_scope_lifetimes` or
890 // `lifetimes_to_define`. If we swapped the order of these two,
891 // in-band-lifetimes introduced by generics or where-clauses
892 // wouldn't have been added yet.
894 this.lower_generics(generics, ImplTraitContext::Universal(&mut params));
895 let res = f(this, &mut params);
896 (params, (generics, res))
900 let mut lowered_params: Vec<_> =
901 lowered_generics.params.into_iter().chain(in_band_defs).collect();
903 // FIXME(const_generics): the compiler doesn't always cope with
904 // unsorted generic parameters at the moment, so we make sure
905 // that they're ordered correctly here for now. (When we chain
906 // the `in_band_defs`, we might make the order unsorted.)
907 lowered_params.sort_by_key(|param| match param.kind {
908 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
909 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
910 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
913 lowered_generics.params = lowered_params.into();
915 (lowered_generics, res)
918 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
920 F: FnOnce(&mut Self) -> T,
922 let was_in_dyn_type = self.is_in_dyn_type;
923 self.is_in_dyn_type = in_scope;
925 let result = f(self);
927 self.is_in_dyn_type = was_in_dyn_type;
932 fn with_new_scopes<T, F>(&mut self, f: F) -> T
934 F: FnOnce(&mut Self) -> T,
936 let was_in_loop_condition = self.is_in_loop_condition;
937 self.is_in_loop_condition = false;
939 let catch_scopes = mem::take(&mut self.catch_scopes);
940 let loop_scopes = mem::take(&mut self.loop_scopes);
942 self.catch_scopes = catch_scopes;
943 self.loop_scopes = loop_scopes;
945 self.is_in_loop_condition = was_in_loop_condition;
950 fn def_key(&mut self, id: DefId) -> DefKey {
952 self.resolver.definitions().def_key(id.index)
954 self.resolver.cstore().def_key(id)
958 fn lower_attrs_arena(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
959 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
962 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
963 attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into()
966 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
967 // Note that we explicitly do not walk the path. Since we don't really
968 // lower attributes (we use the AST version) there is nowhere to keep
969 // the `HirId`s. We don't actually need HIR version of attributes anyway.
970 let kind = match attr.kind {
971 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
972 path: item.path.clone(),
973 args: self.lower_mac_args(&item.args),
975 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
978 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
981 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
983 MacArgs::Empty => MacArgs::Empty,
984 MacArgs::Delimited(dspan, delim, ref tokens) => {
985 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
987 MacArgs::Eq(eq_span, ref tokens) => {
988 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
993 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
994 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
997 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
999 TokenTree::Token(token) => self.lower_token(token),
1000 TokenTree::Delimited(span, delim, tts) => {
1001 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
1006 fn lower_token(&mut self, token: Token) -> TokenStream {
1008 token::Interpolated(nt) => {
1009 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1010 self.lower_token_stream(tts)
1012 _ => TokenTree::Token(token).into(),
1016 /// Given an associated type constraint like one of these:
1019 /// T: Iterator<Item: Debug>
1021 /// T: Iterator<Item = Debug>
1025 /// returns a `hir::TypeBinding` representing `Item`.
1026 fn lower_assoc_ty_constraint(
1028 constraint: &AssocTyConstraint,
1029 itctx: ImplTraitContext<'_, 'hir>,
1030 ) -> hir::TypeBinding<'hir> {
1031 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1033 let kind = match constraint.kind {
1034 AssocTyConstraintKind::Equality { ref ty } => {
1035 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1037 AssocTyConstraintKind::Bound { ref bounds } => {
1038 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1039 let (desugar_to_impl_trait, itctx) = match itctx {
1040 // We are in the return position:
1042 // fn foo() -> impl Iterator<Item: Debug>
1046 // fn foo() -> impl Iterator<Item = impl Debug>
1047 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1049 // We are in the argument position, but within a dyn type:
1051 // fn foo(x: dyn Iterator<Item: Debug>)
1055 // fn foo(x: dyn Iterator<Item = impl Debug>)
1056 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1058 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1059 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1060 // "impl trait context" to permit `impl Debug` in this position (it desugars
1061 // then to an opaque type).
1063 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1064 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1065 (true, ImplTraitContext::OpaqueTy(None))
1068 // We are in the parameter position, but not within a dyn type:
1070 // fn foo(x: impl Iterator<Item: Debug>)
1072 // so we leave it as is and this gets expanded in astconv to a bound like
1073 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1075 _ => (false, itctx),
1078 if desugar_to_impl_trait {
1079 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1080 // constructing the HIR for `impl bounds...` and then lowering that.
1082 let impl_trait_node_id = self.resolver.next_node_id();
1083 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1084 self.resolver.definitions().create_def_with_parent(
1087 DefPathData::ImplTrait,
1092 self.with_dyn_type_scope(false, |this| {
1093 let node_id = this.resolver.next_node_id();
1094 let ty = this.lower_ty(
1097 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1098 span: constraint.span,
1103 hir::TypeBindingKind::Equality { ty }
1106 // Desugar `AssocTy: Bounds` into a type binding where the
1107 // later desugars into a trait predicate.
1108 let bounds = self.lower_param_bounds(bounds, itctx);
1110 hir::TypeBindingKind::Constraint { bounds }
1116 hir_id: self.lower_node_id(constraint.id),
1117 ident: constraint.ident,
1119 span: constraint.span,
1123 fn lower_generic_arg(
1125 arg: &ast::GenericArg,
1126 itctx: ImplTraitContext<'_, 'hir>,
1127 ) -> hir::GenericArg<'hir> {
1129 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1130 ast::GenericArg::Type(ty) => {
1131 // We parse const arguments as path types as we cannot distiguish them durring
1132 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1133 // type and value namespaces. If we resolved the path in the value namespace, we
1134 // transform it into a generic const argument.
1135 if let TyKind::Path(ref qself, ref path) = ty.kind {
1136 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1137 let res = partial_res.base_res();
1138 if !res.matches_ns(Namespace::TypeNS) {
1140 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1144 // Construct a AnonConst where the expr is the "ty"'s path.
1146 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1147 let node_id = self.resolver.next_node_id();
1149 // Add a definition for the in-band const def.
1150 self.resolver.definitions().create_def_with_parent(
1153 DefPathData::AnonConst,
1158 let path_expr = Expr {
1160 kind: ExprKind::Path(qself.clone(), path.clone()),
1162 attrs: AttrVec::new(),
1165 let ct = self.with_new_scopes(|this| hir::AnonConst {
1166 hir_id: this.lower_node_id(node_id),
1167 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1169 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1173 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1175 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1176 value: self.lower_anon_const(&ct),
1177 span: ct.value.span,
1182 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1183 self.arena.alloc(self.lower_ty_direct(t, itctx))
1189 qself: &Option<QSelf>,
1191 param_mode: ParamMode,
1192 itctx: ImplTraitContext<'_, 'hir>,
1193 ) -> hir::Ty<'hir> {
1194 let id = self.lower_node_id(t.id);
1195 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1196 let ty = self.ty_path(id, t.span, qpath);
1197 if let hir::TyKind::TraitObject(..) = ty.kind {
1198 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1203 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1204 hir::Ty { hir_id: self.next_id(), kind, span }
1207 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1208 self.ty(span, hir::TyKind::Tup(tys))
1211 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1212 let kind = match t.kind {
1213 TyKind::Infer => hir::TyKind::Infer,
1214 TyKind::Err => hir::TyKind::Err,
1215 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1216 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1217 TyKind::Rptr(ref region, ref mt) => {
1218 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1219 let lifetime = match *region {
1220 Some(ref lt) => self.lower_lifetime(lt),
1221 None => self.elided_ref_lifetime(span),
1223 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1225 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1226 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1227 hir::TyKind::BareFn(
1228 this.arena.alloc(hir::BareFnTy {
1229 generic_params: this.arena.alloc_from_iter(
1230 this.lower_generic_params(
1232 &NodeMap::default(),
1233 ImplTraitContext::disallowed(),
1237 unsafety: f.unsafety,
1238 abi: this.lower_extern(f.ext),
1239 decl: this.lower_fn_decl(&f.decl, None, false, None),
1240 param_names: this.arena.alloc_from_iter(
1241 this.lower_fn_params_to_names(&f.decl).into_iter(),
1247 TyKind::Never => hir::TyKind::Never,
1248 TyKind::Tup(ref tys) => {
1249 hir::TyKind::Tup(self.arena.alloc_from_iter(
1250 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1253 TyKind::Paren(ref ty) => {
1254 return self.lower_ty_direct(ty, itctx);
1256 TyKind::Path(ref qself, ref path) => {
1257 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1259 TyKind::ImplicitSelf => {
1260 let res = self.expect_full_res(t.id);
1261 let res = self.lower_res(res);
1262 hir::TyKind::Path(hir::QPath::Resolved(
1264 self.arena.alloc(hir::Path {
1266 segments: arena_vec![self; hir::PathSegment::from_ident(
1267 Ident::with_dummy_span(kw::SelfUpper)
1273 TyKind::Array(ref ty, ref length) => {
1274 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1276 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1277 TyKind::TraitObject(ref bounds, kind) => {
1278 let mut lifetime_bound = None;
1279 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1281 this.arena.alloc_from_iter(bounds.iter().filter_map(
1282 |bound| match *bound {
1283 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1284 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1286 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1287 GenericBound::Outlives(ref lifetime) => {
1288 if lifetime_bound.is_none() {
1289 lifetime_bound = Some(this.lower_lifetime(lifetime));
1295 let lifetime_bound =
1296 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1297 (bounds, lifetime_bound)
1299 if kind != TraitObjectSyntax::Dyn {
1300 self.maybe_lint_bare_trait(t.span, t.id, false);
1302 hir::TyKind::TraitObject(bounds, lifetime_bound)
1304 TyKind::ImplTrait(def_node_id, ref bounds) => {
1307 ImplTraitContext::OpaqueTy(fn_def_id) => {
1308 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1309 this.lower_param_bounds(bounds, itctx)
1312 ImplTraitContext::Universal(in_band_ty_params) => {
1313 // Add a definition for the in-band `Param`.
1315 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1317 let hir_bounds = self.lower_param_bounds(
1319 ImplTraitContext::Universal(in_band_ty_params),
1321 // Set the name to `impl Bound1 + Bound2`.
1322 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1323 in_band_ty_params.push(hir::GenericParam {
1324 hir_id: self.lower_node_id(def_node_id),
1325 name: ParamName::Plain(ident),
1326 pure_wrt_drop: false,
1330 kind: hir::GenericParamKind::Type {
1332 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1336 hir::TyKind::Path(hir::QPath::Resolved(
1338 self.arena.alloc(hir::Path {
1340 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1341 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1345 ImplTraitContext::Disallowed(pos) => {
1346 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1347 "bindings or function and inherent method return types"
1349 "function and inherent method return types"
1351 let mut err = struct_span_err!(
1355 "`impl Trait` not allowed outside of {}",
1358 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1362 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1363 attributes to enable"
1371 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1372 TyKind::CVarArgs => {
1373 self.sess.delay_span_bug(
1375 "`TyKind::CVarArgs` should have been handled elsewhere",
1381 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1384 fn lower_opaque_impl_trait(
1387 fn_def_id: Option<DefId>,
1388 opaque_ty_node_id: NodeId,
1389 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1390 ) -> hir::TyKind<'hir> {
1392 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1393 fn_def_id, opaque_ty_node_id, span,
1396 // Make sure we know that some funky desugaring has been going on here.
1397 // This is a first: there is code in other places like for loop
1398 // desugaring that explicitly states that we don't want to track that.
1399 // Not tracking it makes lints in rustc and clippy very fragile, as
1400 // frequently opened issues show.
1401 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1403 let opaque_ty_def_index =
1404 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1406 self.allocate_hir_id_counter(opaque_ty_node_id);
1408 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1410 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1412 opaque_ty_def_index,
1416 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1418 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1420 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1421 let opaque_ty_item = hir::OpaqueTy {
1422 generics: hir::Generics {
1423 params: lifetime_defs,
1424 where_clause: hir::WhereClause { predicates: &[], span },
1428 impl_trait_fn: fn_def_id,
1429 origin: hir::OpaqueTyOrigin::FnReturn,
1432 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1434 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1436 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1437 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1441 /// Registers a new opaque type with the proper `NodeId`s and
1442 /// returns the lowered node-ID for the opaque type.
1443 fn generate_opaque_type(
1445 opaque_ty_node_id: NodeId,
1446 opaque_ty_item: hir::OpaqueTy<'hir>,
1448 opaque_ty_span: Span,
1450 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1451 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1452 // Generate an `type Foo = impl Trait;` declaration.
1453 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1454 let opaque_ty_item = hir::Item {
1455 hir_id: opaque_ty_id,
1456 ident: Ident::invalid(),
1457 attrs: Default::default(),
1458 kind: opaque_ty_item_kind,
1459 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1460 span: opaque_ty_span,
1463 // Insert the item into the global item list. This usually happens
1464 // automatically for all AST items. But this opaque type item
1465 // does not actually exist in the AST.
1466 self.insert_item(opaque_ty_item);
1470 fn lifetimes_from_impl_trait_bounds(
1472 opaque_ty_id: NodeId,
1473 parent_index: DefIndex,
1474 bounds: hir::GenericBounds<'hir>,
1475 ) -> (&'hir [hir::GenericArg<'hir>], HirVec<hir::GenericParam<'hir>>) {
1477 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1478 parent_index={:?}, \
1480 opaque_ty_id, parent_index, bounds,
1483 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1484 // appear in the bounds, excluding lifetimes that are created within the bounds.
1485 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1486 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1487 context: &'r mut LoweringContext<'a, 'hir>,
1489 opaque_ty_id: NodeId,
1490 collect_elided_lifetimes: bool,
1491 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1492 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1493 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1494 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1497 impl<'r, 'a, 'v, 'hir> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1498 fn nested_visit_map<'this>(
1500 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1501 hir::intravisit::NestedVisitorMap::None
1504 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1505 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1506 if parameters.parenthesized {
1507 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1508 self.collect_elided_lifetimes = false;
1509 hir::intravisit::walk_generic_args(self, span, parameters);
1510 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1512 hir::intravisit::walk_generic_args(self, span, parameters);
1516 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1517 // Don't collect elided lifetimes used inside of `fn()` syntax.
1518 if let hir::TyKind::BareFn(_) = t.kind {
1519 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1520 self.collect_elided_lifetimes = false;
1522 // Record the "stack height" of `for<'a>` lifetime bindings
1523 // to be able to later fully undo their introduction.
1524 let old_len = self.currently_bound_lifetimes.len();
1525 hir::intravisit::walk_ty(self, t);
1526 self.currently_bound_lifetimes.truncate(old_len);
1528 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1530 hir::intravisit::walk_ty(self, t)
1534 fn visit_poly_trait_ref(
1536 trait_ref: &'v hir::PolyTraitRef<'v>,
1537 modifier: hir::TraitBoundModifier,
1539 // Record the "stack height" of `for<'a>` lifetime bindings
1540 // to be able to later fully undo their introduction.
1541 let old_len = self.currently_bound_lifetimes.len();
1542 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1543 self.currently_bound_lifetimes.truncate(old_len);
1546 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1547 // Record the introduction of 'a in `for<'a> ...`.
1548 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1549 // Introduce lifetimes one at a time so that we can handle
1550 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1551 let lt_name = hir::LifetimeName::Param(param.name);
1552 self.currently_bound_lifetimes.push(lt_name);
1555 hir::intravisit::walk_generic_param(self, param);
1558 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1559 let name = match lifetime.name {
1560 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1561 if self.collect_elided_lifetimes {
1562 // Use `'_` for both implicit and underscore lifetimes in
1563 // `type Foo<'_> = impl SomeTrait<'_>;`.
1564 hir::LifetimeName::Underscore
1569 hir::LifetimeName::Param(_) => lifetime.name,
1571 // Refers to some other lifetime that is "in
1572 // scope" within the type.
1573 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1575 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1578 if !self.currently_bound_lifetimes.contains(&name)
1579 && !self.already_defined_lifetimes.contains(&name)
1581 self.already_defined_lifetimes.insert(name);
1583 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1584 hir_id: self.context.next_id(),
1585 span: lifetime.span,
1589 let def_node_id = self.context.resolver.next_node_id();
1591 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1592 self.context.resolver.definitions().create_def_with_parent(
1595 DefPathData::LifetimeNs(name.ident().name),
1600 let (name, kind) = match name {
1601 hir::LifetimeName::Underscore => (
1602 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1603 hir::LifetimeParamKind::Elided,
1605 hir::LifetimeName::Param(param_name) => {
1606 (param_name, hir::LifetimeParamKind::Explicit)
1608 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1611 self.output_lifetime_params.push(hir::GenericParam {
1614 span: lifetime.span,
1615 pure_wrt_drop: false,
1618 kind: hir::GenericParamKind::Lifetime { kind },
1624 let mut lifetime_collector = ImplTraitLifetimeCollector {
1626 parent: parent_index,
1628 collect_elided_lifetimes: true,
1629 currently_bound_lifetimes: Vec::new(),
1630 already_defined_lifetimes: FxHashSet::default(),
1631 output_lifetimes: Vec::new(),
1632 output_lifetime_params: Vec::new(),
1635 for bound in bounds {
1636 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1639 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1642 (self.arena.alloc_from_iter(output_lifetimes), output_lifetime_params.into())
1648 qself: &Option<QSelf>,
1650 param_mode: ParamMode,
1651 mut itctx: ImplTraitContext<'_, 'hir>,
1652 ) -> hir::QPath<'hir> {
1653 let qself_position = qself.as_ref().map(|q| q.position);
1654 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1657 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1659 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1660 let path = self.arena.alloc(hir::Path {
1661 res: self.lower_res(partial_res.base_res()),
1662 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1664 let param_mode = match (qself_position, param_mode) {
1665 (Some(j), ParamMode::Optional) if i < j => {
1666 // This segment is part of the trait path in a
1667 // qualified path - one of `a`, `b` or `Trait`
1668 // in `<X as a::b::Trait>::T::U::method`.
1674 // Figure out if this is a type/trait segment,
1675 // which may need lifetime elision performed.
1676 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1677 krate: def_id.krate,
1678 index: this.def_key(def_id).parent.expect("missing parent"),
1680 let type_def_id = match partial_res.base_res() {
1681 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1682 Some(parent_def_id(self, def_id))
1684 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1685 Some(parent_def_id(self, def_id))
1687 Res::Def(DefKind::Struct, def_id)
1688 | Res::Def(DefKind::Union, def_id)
1689 | Res::Def(DefKind::Enum, def_id)
1690 | Res::Def(DefKind::TyAlias, def_id)
1691 | Res::Def(DefKind::Trait, def_id)
1692 if i + 1 == proj_start =>
1698 let parenthesized_generic_args = match partial_res.base_res() {
1699 // `a::b::Trait(Args)`
1700 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1701 ParenthesizedGenericArgs::Ok
1703 // `a::b::Trait(Args)::TraitItem`
1704 Res::Def(DefKind::Method, _)
1705 | Res::Def(DefKind::AssocConst, _)
1706 | Res::Def(DefKind::AssocTy, _)
1707 if i + 2 == proj_start =>
1709 ParenthesizedGenericArgs::Ok
1711 // Avoid duplicated errors.
1712 Res::Err => ParenthesizedGenericArgs::Ok,
1714 _ => ParenthesizedGenericArgs::Err,
1717 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1718 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1721 assert!(!def_id.is_local());
1722 let item_generics = self
1725 .item_generics_cloned_untracked(def_id, self.sess);
1726 let n = item_generics.own_counts().lifetimes;
1727 self.type_def_lifetime_params.insert(def_id, n);
1730 self.lower_path_segment(
1735 parenthesized_generic_args,
1744 // Simple case, either no projections, or only fully-qualified.
1745 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1746 if partial_res.unresolved_segments() == 0 {
1747 return hir::QPath::Resolved(qself, path);
1750 // Create the innermost type that we're projecting from.
1751 let mut ty = if path.segments.is_empty() {
1752 // If the base path is empty that means there exists a
1753 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1754 qself.expect("missing QSelf for <T>::...")
1756 // Otherwise, the base path is an implicit `Self` type path,
1757 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1758 // `<I as Iterator>::Item::default`.
1759 let new_id = self.next_id();
1760 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1763 // Anything after the base path are associated "extensions",
1764 // out of which all but the last one are associated types,
1765 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1766 // * base path is `std::vec::Vec<T>`
1767 // * "extensions" are `IntoIter`, `Item` and `clone`
1768 // * type nodes are:
1769 // 1. `std::vec::Vec<T>` (created above)
1770 // 2. `<std::vec::Vec<T>>::IntoIter`
1771 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1772 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1773 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1774 let segment = self.arena.alloc(self.lower_path_segment(
1779 ParenthesizedGenericArgs::Err,
1783 let qpath = hir::QPath::TypeRelative(ty, segment);
1785 // It's finished, return the extension of the right node type.
1786 if i == p.segments.len() - 1 {
1790 // Wrap the associated extension in another type node.
1791 let new_id = self.next_id();
1792 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1795 // We should've returned in the for loop above.
1798 "lower_qpath: no final extension segment in {}..{}",
1804 fn lower_path_extra(
1808 param_mode: ParamMode,
1809 explicit_owner: Option<NodeId>,
1810 ) -> hir::Path<'hir> {
1813 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1814 self.lower_path_segment(
1819 ParenthesizedGenericArgs::Err,
1820 ImplTraitContext::disallowed(),
1828 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path<'hir> {
1829 let res = self.expect_full_res(id);
1830 let res = self.lower_res(res);
1831 self.lower_path_extra(res, p, param_mode, None)
1834 fn lower_path_segment(
1837 segment: &PathSegment,
1838 param_mode: ParamMode,
1839 expected_lifetimes: usize,
1840 parenthesized_generic_args: ParenthesizedGenericArgs,
1841 itctx: ImplTraitContext<'_, 'hir>,
1842 explicit_owner: Option<NodeId>,
1843 ) -> hir::PathSegment<'hir> {
1844 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1845 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1846 match **generic_args {
1847 GenericArgs::AngleBracketed(ref data) => {
1848 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1850 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1851 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1852 ParenthesizedGenericArgs::Err => {
1853 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1854 err.span_label(data.span, "only `Fn` traits may use parentheses");
1855 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1856 // Do not suggest going from `Trait()` to `Trait<>`
1857 if data.inputs.len() > 0 {
1858 if let Some(split) = snippet.find('(') {
1859 let trait_name = &snippet[0..split];
1860 let args = &snippet[split + 1..snippet.len() - 1];
1861 err.span_suggestion(
1863 "use angle brackets instead",
1864 format!("{}<{}>", trait_name, args),
1865 Applicability::MaybeIncorrect,
1872 self.lower_angle_bracketed_parameter_data(
1873 &data.as_angle_bracketed_args(),
1884 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1887 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1888 GenericArg::Lifetime(_) => true,
1891 let first_generic_span = generic_args
1895 .chain(generic_args.bindings.iter().map(|b| b.span))
1897 if !generic_args.parenthesized && !has_lifetimes {
1898 generic_args.args = self
1899 .elided_path_lifetimes(path_span, expected_lifetimes)
1901 .map(|lt| GenericArg::Lifetime(lt))
1902 .chain(generic_args.args.into_iter())
1904 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1905 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1906 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1907 let no_bindings = generic_args.bindings.is_empty();
1908 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1909 // If there are no (non-implicit) generic args or associated type
1910 // bindings, our suggestion includes the angle brackets.
1911 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1913 // Otherwise (sorry, this is kind of gross) we need to infer the
1914 // place to splice in the `'_, ` from the generics that do exist.
1915 let first_generic_span = first_generic_span
1916 .expect("already checked that non-lifetime args or bindings exist");
1917 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1919 match self.anonymous_lifetime_mode {
1920 // In create-parameter mode we error here because we don't want to support
1921 // deprecated impl elision in new features like impl elision and `async fn`,
1922 // both of which work using the `CreateParameter` mode:
1924 // impl Foo for std::cell::Ref<u32> // note lack of '_
1925 // async fn foo(_: std::cell::Ref<u32>) { ... }
1926 AnonymousLifetimeMode::CreateParameter => {
1927 let mut err = struct_span_err!(
1931 "implicit elided lifetime not allowed here"
1933 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1944 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1945 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1946 ELIDED_LIFETIMES_IN_PATHS,
1949 "hidden lifetime parameters in types are deprecated",
1950 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1963 let res = self.expect_full_res(segment.id);
1964 let id = if let Some(owner) = explicit_owner {
1965 self.lower_node_id_with_owner(segment.id, owner)
1967 self.lower_node_id(segment.id)
1970 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1971 segment.ident, segment.id, id,
1975 ident: segment.ident,
1977 res: Some(self.lower_res(res)),
1979 args: if generic_args.is_empty() { None } else { Some(self.arena.alloc(generic_args)) },
1983 fn lower_angle_bracketed_parameter_data(
1985 data: &AngleBracketedArgs,
1986 param_mode: ParamMode,
1987 mut itctx: ImplTraitContext<'_, 'hir>,
1988 ) -> (hir::GenericArgs<'hir>, bool) {
1989 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1990 let has_non_lt_args = args.iter().any(|arg| match arg {
1991 ast::GenericArg::Lifetime(_) => false,
1992 ast::GenericArg::Type(_) => true,
1993 ast::GenericArg::Const(_) => true,
1997 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1998 bindings: self.arena.alloc_from_iter(
1999 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
2001 parenthesized: false,
2003 !has_non_lt_args && param_mode == ParamMode::Optional,
2007 fn lower_parenthesized_parameter_data(
2009 data: &ParenthesizedArgs,
2010 ) -> (hir::GenericArgs<'hir>, bool) {
2011 // Switch to `PassThrough` mode for anonymous lifetimes; this
2012 // means that we permit things like `&Ref<T>`, where `Ref` has
2013 // a hidden lifetime parameter. This is needed for backwards
2014 // compatibility, even in contexts like an impl header where
2015 // we generally don't permit such things (see #51008).
2016 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2017 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2018 let inputs = this.arena.alloc_from_iter(
2019 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2021 let output_ty = match output {
2022 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2023 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2025 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2026 let binding = hir::TypeBinding {
2027 hir_id: this.next_id(),
2028 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2029 span: output_ty.span,
2030 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2033 hir::GenericArgs { args, bindings: arena_vec![this; binding], parenthesized: true },
2039 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2040 let mut ids = SmallVec::<[NodeId; 1]>::new();
2041 if self.sess.features_untracked().impl_trait_in_bindings {
2042 if let Some(ref ty) = l.ty {
2043 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2044 visitor.visit_ty(ty);
2047 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2048 let ty = l.ty.as_ref().map(|t| {
2051 if self.sess.features_untracked().impl_trait_in_bindings {
2052 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2054 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2058 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2061 hir_id: self.lower_node_id(l.id),
2063 pat: self.lower_pat(&l.pat),
2066 attrs: l.attrs.clone(),
2067 source: hir::LocalSource::Normal,
2073 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2074 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2075 // as they are not explicit in HIR/Ty function signatures.
2076 // (instead, the `c_variadic` flag is set to `true`)
2077 let mut inputs = &decl.inputs[..];
2078 if decl.c_variadic() {
2079 inputs = &inputs[..inputs.len() - 1];
2083 .map(|param| match param.pat.kind {
2084 PatKind::Ident(_, ident, _) => ident,
2085 _ => Ident::new(kw::Invalid, param.pat.span),
2090 // Lowers a function declaration.
2092 // `decl`: the unlowered (AST) function declaration.
2093 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2094 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2095 // `make_ret_async` is also `Some`.
2096 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2097 // This guards against trait declarations and implementations where `impl Trait` is
2099 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2100 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2101 // return type `impl Trait` item.
2105 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2106 impl_trait_return_allow: bool,
2107 make_ret_async: Option<NodeId>,
2108 ) -> &'hir hir::FnDecl<'hir> {
2112 in_band_ty_params: {:?}, \
2113 impl_trait_return_allow: {}, \
2114 make_ret_async: {:?})",
2115 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2117 let lt_mode = if make_ret_async.is_some() {
2118 // In `async fn`, argument-position elided lifetimes
2119 // must be transformed into fresh generic parameters so that
2120 // they can be applied to the opaque `impl Trait` return type.
2121 AnonymousLifetimeMode::CreateParameter
2123 self.anonymous_lifetime_mode
2126 let c_variadic = decl.c_variadic();
2128 // Remember how many lifetimes were already around so that we can
2129 // only look at the lifetime parameters introduced by the arguments.
2130 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2131 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2132 // as they are not explicit in HIR/Ty function signatures.
2133 // (instead, the `c_variadic` flag is set to `true`)
2134 let mut inputs = &decl.inputs[..];
2136 inputs = &inputs[..inputs.len() - 1];
2138 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2139 if let Some((_, ibty)) = &mut in_band_ty_params {
2140 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2142 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2147 let output = if let Some(ret_id) = make_ret_async {
2148 self.lower_async_fn_ret_ty(
2150 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2155 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2156 Some((def_id, _)) if impl_trait_return_allow => {
2157 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2159 _ => hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed())),
2161 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2165 self.arena.alloc(hir::FnDecl {
2169 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2170 let is_mutable_pat = match arg.pat.kind {
2171 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2172 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2177 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2178 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2179 // Given we are only considering `ImplicitSelf` types, we needn't consider
2180 // the case where we have a mutable pattern to a reference as that would
2181 // no longer be an `ImplicitSelf`.
2182 TyKind::Rptr(_, ref mt)
2183 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2185 hir::ImplicitSelfKind::MutRef
2187 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2188 hir::ImplicitSelfKind::ImmRef
2190 _ => hir::ImplicitSelfKind::None,
2196 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2197 // combined with the following definition of `OpaqueTy`:
2199 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2201 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2202 // `output`: unlowered output type (`T` in `-> T`)
2203 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2204 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2205 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2206 fn lower_async_fn_ret_ty(
2208 output: &FunctionRetTy,
2210 opaque_ty_node_id: NodeId,
2211 ) -> hir::FunctionRetTy<'hir> {
2213 "lower_async_fn_ret_ty(\
2216 opaque_ty_node_id={:?})",
2217 output, fn_def_id, opaque_ty_node_id,
2220 let span = output.span();
2222 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2224 let opaque_ty_def_index =
2225 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2227 self.allocate_hir_id_counter(opaque_ty_node_id);
2229 // When we create the opaque type for this async fn, it is going to have
2230 // to capture all the lifetimes involved in the signature (including in the
2231 // return type). This is done by introducing lifetime parameters for:
2233 // - all the explicitly declared lifetimes from the impl and function itself;
2234 // - all the elided lifetimes in the fn arguments;
2235 // - all the elided lifetimes in the return type.
2237 // So for example in this snippet:
2240 // impl<'a> Foo<'a> {
2241 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2242 // // ^ '0 ^ '1 ^ '2
2243 // // elided lifetimes used below
2248 // we would create an opaque type like:
2251 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2254 // and we would then desugar `bar` to the equivalent of:
2257 // impl<'a> Foo<'a> {
2258 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2262 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2263 // this is because the elided lifetimes from the return type
2264 // should be figured out using the ordinary elision rules, and
2265 // this desugaring achieves that.
2267 // The variable `input_lifetimes_count` tracks the number of
2268 // lifetime parameters to the opaque type *not counting* those
2269 // lifetimes elided in the return type. This includes those
2270 // that are explicitly declared (`in_scope_lifetimes`) and
2271 // those elided lifetimes we found in the arguments (current
2272 // content of `lifetimes_to_define`). Next, we will process
2273 // the return type, which will cause `lifetimes_to_define` to
2275 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2277 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2278 // We have to be careful to get elision right here. The
2279 // idea is that we create a lifetime parameter for each
2280 // lifetime in the return type. So, given a return type
2281 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2282 // Future<Output = &'1 [ &'2 u32 ]>`.
2284 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2285 // hence the elision takes place at the fn site.
2286 let future_bound = this
2287 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2288 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2291 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2293 // Calculate all the lifetimes that should be captured
2294 // by the opaque type. This should include all in-scope
2295 // lifetime parameters, including those defined in-band.
2297 // Note: this must be done after lowering the output type,
2298 // as the output type may introduce new in-band lifetimes.
2299 let lifetime_params: Vec<(Span, ParamName)> = this
2303 .map(|name| (name.ident().span, name))
2304 .chain(this.lifetimes_to_define.iter().cloned())
2307 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2308 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2309 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2311 let generic_params = lifetime_params
2313 .map(|(span, hir_name)| {
2314 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
2318 let opaque_ty_item = hir::OpaqueTy {
2319 generics: hir::Generics {
2320 params: generic_params,
2321 where_clause: hir::WhereClause { predicates: &[], span },
2324 bounds: arena_vec![this; future_bound],
2325 impl_trait_fn: Some(fn_def_id),
2326 origin: hir::OpaqueTyOrigin::AsyncFn,
2329 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2331 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2333 (opaque_ty_id, lifetime_params)
2336 // As documented above on the variable
2337 // `input_lifetimes_count`, we need to create the lifetime
2338 // arguments to our opaque type. Continuing with our example,
2339 // we're creating the type arguments for the return type:
2342 // Bar<'a, 'b, '0, '1, '_>
2345 // For the "input" lifetime parameters, we wish to create
2346 // references to the parameters themselves, including the
2347 // "implicit" ones created from parameter types (`'a`, `'b`,
2350 // For the "output" lifetime parameters, we just want to
2352 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2354 .map(|&(span, hir_name)| {
2355 // Input lifetime like `'a` or `'1`:
2356 GenericArg::Lifetime(hir::Lifetime {
2357 hir_id: self.next_id(),
2359 name: hir::LifetimeName::Param(hir_name),
2363 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2364 // Output lifetime like `'_`.
2365 GenericArg::Lifetime(hir::Lifetime {
2366 hir_id: self.next_id(),
2368 name: hir::LifetimeName::Implicit,
2370 let generic_args = self.arena.alloc_from_iter(generic_args);
2372 // Create the `Foo<...>` reference itself. Note that the `type
2373 // Foo = impl Trait` is, internally, created as a child of the
2374 // async fn, so the *type parameters* are inherited. It's
2375 // only the lifetime parameters that we must supply.
2376 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
2377 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2378 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
2381 /// Transforms `-> T` into `Future<Output = T>`
2382 fn lower_async_fn_output_type_to_future_bound(
2384 output: &FunctionRetTy,
2387 ) -> hir::GenericBound<'hir> {
2388 // Compute the `T` in `Future<Output = T>` from the return type.
2389 let output_ty = match output {
2390 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2391 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2395 let future_params = self.arena.alloc(hir::GenericArgs {
2396 args: HirVec::new(),
2397 bindings: arena_vec![self; hir::TypeBinding {
2398 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2399 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2400 hir_id: self.next_id(),
2403 parenthesized: false,
2406 // ::std::future::Future<future_params>
2407 let future_path = self.arena.alloc(self.std_path(
2409 &[sym::future, sym::Future],
2410 Some(future_params),
2414 hir::GenericBound::Trait(
2416 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2417 bound_generic_params: &[],
2420 hir::TraitBoundModifier::None,
2424 fn lower_param_bound(
2427 itctx: ImplTraitContext<'_, 'hir>,
2428 ) -> hir::GenericBound<'hir> {
2430 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2431 self.lower_poly_trait_ref(ty, itctx),
2432 self.lower_trait_bound_modifier(modifier),
2434 GenericBound::Outlives(ref lifetime) => {
2435 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2440 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2441 let span = l.ident.span;
2443 ident if ident.name == kw::StaticLifetime => {
2444 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2446 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2447 AnonymousLifetimeMode::CreateParameter => {
2448 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2449 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2452 AnonymousLifetimeMode::PassThrough => {
2453 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2456 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2459 self.maybe_collect_in_band_lifetime(ident);
2460 let param_name = ParamName::Plain(ident);
2461 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2466 fn new_named_lifetime(
2470 name: hir::LifetimeName,
2471 ) -> hir::Lifetime {
2472 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2475 fn lower_generic_params(
2477 params: &[GenericParam],
2478 add_bounds: &NodeMap<Vec<GenericBound>>,
2479 mut itctx: ImplTraitContext<'_, 'hir>,
2480 ) -> HirVec<hir::GenericParam<'hir>> {
2483 .map(|param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2487 fn lower_generic_param(
2489 param: &GenericParam,
2490 add_bounds: &NodeMap<Vec<GenericBound>>,
2491 mut itctx: ImplTraitContext<'_, 'hir>,
2492 ) -> hir::GenericParam<'hir> {
2493 let mut bounds: Vec<_> = self
2494 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2495 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2498 let (name, kind) = match param.kind {
2499 GenericParamKind::Lifetime => {
2500 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2501 self.is_collecting_in_band_lifetimes = false;
2504 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2505 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2507 let param_name = match lt.name {
2508 hir::LifetimeName::Param(param_name) => param_name,
2509 hir::LifetimeName::Implicit
2510 | hir::LifetimeName::Underscore
2511 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2512 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2515 "object-lifetime-default should not occur here",
2518 hir::LifetimeName::Error => ParamName::Error,
2522 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2524 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2528 GenericParamKind::Type { ref default, .. } => {
2529 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2530 if !add_bounds.is_empty() {
2531 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2532 bounds.extend(params);
2535 let kind = hir::GenericParamKind::Type {
2538 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2542 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2543 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2547 (hir::ParamName::Plain(param.ident), kind)
2549 GenericParamKind::Const { ref ty } => (
2550 hir::ParamName::Plain(param.ident),
2551 hir::GenericParamKind::Const {
2552 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2558 hir_id: self.lower_node_id(param.id),
2560 span: param.ident.span,
2561 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2562 attrs: self.lower_attrs_arena(¶m.attrs),
2563 bounds: self.arena.alloc_from_iter(bounds),
2571 itctx: ImplTraitContext<'_, 'hir>,
2572 ) -> hir::TraitRef<'hir> {
2573 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2574 hir::QPath::Resolved(None, path) => path,
2575 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2577 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2580 fn lower_poly_trait_ref(
2583 mut itctx: ImplTraitContext<'_, 'hir>,
2584 ) -> hir::PolyTraitRef<'hir> {
2585 let bound_generic_params = self.lower_generic_params(
2586 &p.bound_generic_params,
2587 &NodeMap::default(),
2590 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2591 this.lower_trait_ref(&p.trait_ref, itctx)
2595 bound_generic_params: self.arena.alloc_from_iter(bound_generic_params.into_iter()),
2601 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2602 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2605 fn lower_param_bounds(
2607 bounds: &[GenericBound],
2608 itctx: ImplTraitContext<'_, 'hir>,
2609 ) -> hir::GenericBounds<'hir> {
2610 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2613 fn lower_param_bounds_mut<'s>(
2615 bounds: &'s [GenericBound],
2616 mut itctx: ImplTraitContext<'s, 'hir>,
2617 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2618 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2621 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2622 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2625 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2626 let mut stmts = vec![];
2627 let mut expr: Option<&'hir _> = None;
2629 for (index, stmt) in b.stmts.iter().enumerate() {
2630 if index == b.stmts.len() - 1 {
2631 if let StmtKind::Expr(ref e) = stmt.kind {
2632 expr = Some(self.lower_expr(e));
2634 stmts.extend(self.lower_stmt(stmt));
2637 stmts.extend(self.lower_stmt(stmt));
2642 hir_id: self.lower_node_id(b.id),
2643 stmts: self.arena.alloc_from_iter(stmts),
2645 rules: self.lower_block_check_mode(&b.rules),
2651 /// Lowers a block directly to an expression, presuming that it
2652 /// has no attributes and is not targeted by a `break`.
2653 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2654 let block = self.lower_block(b, false);
2655 self.expr_block(block, AttrVec::new())
2658 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2659 let node = match p.kind {
2660 PatKind::Wild => hir::PatKind::Wild,
2661 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2662 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2663 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2666 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2667 PatKind::TupleStruct(ref path, ref pats) => {
2668 let qpath = self.lower_qpath(
2672 ParamMode::Optional,
2673 ImplTraitContext::disallowed(),
2675 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2676 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2678 PatKind::Or(ref pats) => {
2679 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2681 PatKind::Path(ref qself, ref path) => {
2682 let qpath = self.lower_qpath(
2686 ParamMode::Optional,
2687 ImplTraitContext::disallowed(),
2689 hir::PatKind::Path(qpath)
2691 PatKind::Struct(ref path, ref fields, etc) => {
2692 let qpath = self.lower_qpath(
2696 ParamMode::Optional,
2697 ImplTraitContext::disallowed(),
2700 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2701 hir_id: self.next_id(),
2703 pat: self.lower_pat(&f.pat),
2704 is_shorthand: f.is_shorthand,
2707 hir::PatKind::Struct(qpath, fs, etc)
2709 PatKind::Tuple(ref pats) => {
2710 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2711 hir::PatKind::Tuple(pats, ddpos)
2713 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2714 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2715 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2716 self.lower_expr(e1),
2717 self.lower_expr(e2),
2718 self.lower_range_end(end),
2720 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2722 // If we reach here the `..` pattern is not semantically allowed.
2723 self.ban_illegal_rest_pat(p.span)
2725 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2726 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2729 self.pat_with_node_id_of(p, node)
2736 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2737 let mut elems = Vec::with_capacity(pats.len());
2738 let mut rest = None;
2740 let mut iter = pats.iter().enumerate();
2741 for (idx, pat) in iter.by_ref() {
2742 // Interpret the first `..` pattern as a sub-tuple pattern.
2743 // Note that unlike for slice patterns,
2744 // where `xs @ ..` is a legal sub-slice pattern,
2745 // it is not a legal sub-tuple pattern.
2747 rest = Some((idx, pat.span));
2750 // It was not a sub-tuple pattern so lower it normally.
2751 elems.push(self.lower_pat(pat));
2754 for (_, pat) in iter {
2755 // There was a previous sub-tuple pattern; make sure we don't allow more...
2757 // ...but there was one again, so error.
2758 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2760 elems.push(self.lower_pat(pat));
2764 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2767 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2768 /// `hir::PatKind::Slice(before, slice, after)`.
2770 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2771 /// this is interpreted as a sub-slice pattern semantically.
2772 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2773 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2774 let mut before = Vec::new();
2775 let mut after = Vec::new();
2776 let mut slice = None;
2777 let mut prev_rest_span = None;
2779 let mut iter = pats.iter();
2780 // Lower all the patterns until the first occurence of a sub-slice pattern.
2781 for pat in iter.by_ref() {
2783 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2785 prev_rest_span = Some(pat.span);
2786 slice = Some(self.pat_wild_with_node_id_of(pat));
2789 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2790 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2791 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2792 prev_rest_span = Some(sub.span);
2793 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2794 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2795 slice = Some(self.pat_with_node_id_of(pat, node));
2798 // It was not a subslice pattern so lower it normally.
2799 _ => before.push(self.lower_pat(pat)),
2803 // Lower all the patterns after the first sub-slice pattern.
2805 // There was a previous subslice pattern; make sure we don't allow more.
2806 let rest_span = match pat.kind {
2807 PatKind::Rest => Some(pat.span),
2808 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2809 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2810 after.push(self.pat_wild_with_node_id_of(pat));
2815 if let Some(rest_span) = rest_span {
2816 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2817 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2819 // Lower the pattern normally.
2820 after.push(self.lower_pat(pat));
2824 hir::PatKind::Slice(
2825 self.arena.alloc_from_iter(before),
2827 self.arena.alloc_from_iter(after),
2834 binding_mode: &BindingMode,
2836 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2837 ) -> hir::PatKind<'hir> {
2838 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2839 // `None` can occur in body-less function signatures
2840 res @ None | res @ Some(Res::Local(_)) => {
2841 let canonical_id = match res {
2842 Some(Res::Local(id)) => id,
2846 hir::PatKind::Binding(
2847 self.lower_binding_mode(binding_mode),
2848 self.lower_node_id(canonical_id),
2853 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2855 self.arena.alloc(hir::Path {
2857 res: self.lower_res(res),
2858 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2864 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2865 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2868 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2869 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2870 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2873 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2874 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2876 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2877 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2878 .span_label(prev_sp, "previously used here")
2882 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2883 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2885 .struct_span_err(sp, "`..` patterns are not allowed here")
2886 .note("only allowed in tuple, tuple struct, and slice patterns")
2889 // We're not in a list context so `..` can be reasonably treated
2890 // as `_` because it should always be valid and roughly matches the
2891 // intent of `..` (notice that the rest of a single slot is that slot).
2895 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2897 RangeEnd::Included(_) => hir::RangeEnd::Included,
2898 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2902 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2903 self.with_new_scopes(|this| hir::AnonConst {
2904 hir_id: this.lower_node_id(c.id),
2905 body: this.lower_const_body(c.value.span, Some(&c.value)),
2909 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2910 let kind = match s.kind {
2911 StmtKind::Local(ref l) => {
2912 let (l, item_ids) = self.lower_local(l);
2913 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2916 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2917 self.stmt(s.span, hir::StmtKind::Item(item_id))
2922 hir_id: self.lower_node_id(s.id),
2923 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2929 StmtKind::Item(ref it) => {
2930 // Can only use the ID once.
2931 let mut id = Some(s.id);
2938 .map(|id| self.lower_node_id(id))
2939 .unwrap_or_else(|| self.next_id());
2941 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2945 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2946 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2947 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2949 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2952 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2954 BlockCheckMode::Default => hir::DefaultBlock,
2955 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2959 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2961 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2962 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2963 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2964 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2968 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2970 CompilerGenerated => hir::CompilerGenerated,
2971 UserProvided => hir::UserProvided,
2975 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2977 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2978 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2982 // Helper methods for building HIR.
2984 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2985 hir::Stmt { span, kind, hir_id: self.next_id() }
2988 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2989 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2996 init: Option<&'hir hir::Expr<'hir>>,
2997 pat: &'hir hir::Pat<'hir>,
2998 source: hir::LocalSource,
2999 ) -> hir::Stmt<'hir> {
3000 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
3001 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
3004 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
3005 self.block_all(expr.span, &[], Some(expr))
3011 stmts: &'hir [hir::Stmt<'hir>],
3012 expr: Option<&'hir hir::Expr<'hir>>,
3013 ) -> &'hir hir::Block<'hir> {
3014 let blk = hir::Block {
3017 hir_id: self.next_id(),
3018 rules: hir::DefaultBlock,
3020 targeted_by_break: false,
3022 self.arena.alloc(blk)
3025 /// Constructs a `true` or `false` literal pattern.
3026 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3027 let expr = self.expr_bool(span, val);
3028 self.pat(span, hir::PatKind::Lit(expr))
3031 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3032 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3035 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3036 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3039 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3040 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3043 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3044 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3050 components: &[Symbol],
3051 subpats: &'hir [&'hir hir::Pat<'hir>],
3052 ) -> &'hir hir::Pat<'hir> {
3053 let path = self.std_path(span, components, None, true);
3054 let qpath = hir::QPath::Resolved(None, self.arena.alloc(path));
3055 let pt = if subpats.is_empty() {
3056 hir::PatKind::Path(qpath)
3058 hir::PatKind::TupleStruct(qpath, subpats, None)
3063 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3064 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3067 fn pat_ident_binding_mode(
3071 bm: hir::BindingAnnotation,
3072 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3073 let hir_id = self.next_id();
3076 self.arena.alloc(hir::Pat {
3078 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3085 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3086 self.pat(span, hir::PatKind::Wild)
3089 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3090 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3093 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3094 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3095 /// The path is also resolved according to `is_value`.
3099 components: &[Symbol],
3100 params: Option<&'hir hir::GenericArgs<'hir>>,
3102 ) -> hir::Path<'hir> {
3103 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3104 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3106 let mut segments: Vec<_> = path
3110 let res = self.expect_full_res(segment.id);
3112 ident: segment.ident,
3113 hir_id: Some(self.lower_node_id(segment.id)),
3114 res: Some(self.lower_res(res)),
3120 segments.last_mut().unwrap().args = params;
3124 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3125 segments: self.arena.alloc_from_iter(segments),
3131 mut hir_id: hir::HirId,
3133 qpath: hir::QPath<'hir>,
3134 ) -> hir::Ty<'hir> {
3135 let kind = match qpath {
3136 hir::QPath::Resolved(None, path) => {
3137 // Turn trait object paths into `TyKind::TraitObject` instead.
3139 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3140 let principal = hir::PolyTraitRef {
3141 bound_generic_params: &[],
3142 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3146 // The original ID is taken by the `PolyTraitRef`,
3147 // so the `Ty` itself needs a different one.
3148 hir_id = self.next_id();
3149 hir::TyKind::TraitObject(
3150 arena_vec![self; principal],
3151 self.elided_dyn_bound(span),
3154 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3157 _ => hir::TyKind::Path(qpath),
3160 hir::Ty { hir_id, kind, span }
3163 /// Invoked to create the lifetime argument for a type `&T`
3164 /// with no explicit lifetime.
3165 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3166 match self.anonymous_lifetime_mode {
3167 // Intercept when we are in an impl header or async fn and introduce an in-band
3169 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3171 AnonymousLifetimeMode::CreateParameter => {
3172 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3174 hir_id: self.next_id(),
3176 name: hir::LifetimeName::Param(fresh_name),
3180 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3182 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3186 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3187 /// return a "error lifetime".
3188 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3189 let (id, msg, label) = match id {
3190 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3193 self.resolver.next_node_id(),
3194 "`&` without an explicit lifetime name cannot be used here",
3195 "explicit lifetime name needed here",
3199 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3200 err.span_label(span, label);
3203 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3206 /// Invoked to create the lifetime argument(s) for a path like
3207 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3208 /// sorts of cases are deprecated. This may therefore report a warning or an
3209 /// error, depending on the mode.
3210 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3211 (0..count).map(|_| self.elided_path_lifetime(span)).collect()
3214 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3215 match self.anonymous_lifetime_mode {
3216 AnonymousLifetimeMode::CreateParameter => {
3217 // We should have emitted E0726 when processing this path above
3219 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3220 let id = self.resolver.next_node_id();
3221 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3223 // `PassThrough` is the normal case.
3224 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3225 // is unsuitable here, as these can occur from missing lifetime parameters in a
3226 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3227 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3228 // later, at which point a suitable error will be emitted.
3229 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3230 self.new_implicit_lifetime(span)
3235 /// Invoked to create the lifetime argument(s) for an elided trait object
3236 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3237 /// when the bound is written, even if it is written with `'_` like in
3238 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3239 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3240 match self.anonymous_lifetime_mode {
3241 // NB. We intentionally ignore the create-parameter mode here.
3242 // and instead "pass through" to resolve-lifetimes, which will apply
3243 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3244 // do not act like other elided lifetimes. In other words, given this:
3246 // impl Foo for Box<dyn Debug>
3248 // we do not introduce a fresh `'_` to serve as the bound, but instead
3249 // ultimately translate to the equivalent of:
3251 // impl Foo for Box<dyn Debug + 'static>
3253 // `resolve_lifetime` has the code to make that happen.
3254 AnonymousLifetimeMode::CreateParameter => {}
3256 AnonymousLifetimeMode::ReportError => {
3257 // ReportError applies to explicit use of `'_`.
3260 // This is the normal case.
3261 AnonymousLifetimeMode::PassThrough => {}
3264 let r = hir::Lifetime {
3265 hir_id: self.next_id(),
3267 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3269 debug!("elided_dyn_bound: r={:?}", r);
3273 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3274 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3277 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3278 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3279 // call site which do not have a macro backtrace. See #61963.
3280 let is_macro_callsite = self
3283 .span_to_snippet(span)
3284 .map(|snippet| snippet.starts_with("#["))
3286 if !is_macro_callsite {
3287 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3288 builtin::BARE_TRAIT_OBJECTS,
3291 "trait objects without an explicit `dyn` are deprecated",
3292 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3298 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId> {
3299 // Sorting by span ensures that we get things in order within a
3300 // file, and also puts the files in a sensible order.
3301 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3302 body_ids.sort_by_key(|b| bodies[b].value.span);