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::common::FN_OUTPUT_NAME;
50 use crate::util::nodemap::{DefIdMap, NodeMap};
51 use errors::Applicability;
52 use rustc_data_structures::fx::FxHashSet;
53 use rustc_data_structures::sync::Lrc;
54 use rustc_index::vec::IndexVec;
56 use smallvec::SmallVec;
57 use std::collections::BTreeMap;
63 use syntax::print::pprust;
64 use syntax::ptr::P as AstP;
65 use syntax::sess::ParseSess;
66 use syntax::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
67 use syntax::symbol::{kw, sym, Symbol};
68 use syntax::token::{self, Nonterminal, Token};
69 use syntax::tokenstream::{TokenStream, TokenTree};
70 use syntax::visit::{self, Visitor};
71 use syntax_pos::hygiene::ExpnId;
74 use rustc_error_codes::*;
76 macro_rules! arena_vec {
80 ($this:expr; $($x:expr),*) => (
81 $this.arena.alloc_from_iter(vec![$($x),*])
88 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
90 pub struct LoweringContext<'a, 'hir: 'a> {
91 crate_root: Option<Symbol>,
93 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
96 resolver: &'a mut dyn Resolver,
98 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
99 /// if we don't have this function pointer. To avoid that dependency so that
100 /// librustc is independent of the parser, we use dynamic dispatch here.
101 nt_to_tokenstream: NtToTokenstream,
103 /// Used to allocate HIR nodes
104 arena: &'hir Arena<'hir>,
106 /// The items being lowered are collected here.
107 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
109 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
110 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
111 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
112 exported_macros: Vec<hir::MacroDef<'hir>>,
113 non_exported_macro_attrs: Vec<ast::Attribute>,
115 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
117 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
119 generator_kind: Option<hir::GeneratorKind>,
121 /// Used to get the current `fn`'s def span to point to when using `await`
122 /// outside of an `async fn`.
123 current_item: Option<Span>,
125 catch_scopes: Vec<NodeId>,
126 loop_scopes: Vec<NodeId>,
127 is_in_loop_condition: bool,
128 is_in_trait_impl: bool,
129 is_in_dyn_type: bool,
131 /// What to do when we encounter either an "anonymous lifetime
132 /// reference". The term "anonymous" is meant to encompass both
133 /// `'_` lifetimes as well as fully elided cases where nothing is
134 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
135 anonymous_lifetime_mode: AnonymousLifetimeMode,
137 /// Used to create lifetime definitions from in-band lifetime usages.
138 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
139 /// When a named lifetime is encountered in a function or impl header and
140 /// has not been defined
141 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
142 /// to this list. The results of this list are then added to the list of
143 /// lifetime definitions in the corresponding impl or function generics.
144 lifetimes_to_define: Vec<(Span, ParamName)>,
146 /// `true` if in-band lifetimes are being collected. This is used to
147 /// indicate whether or not we're in a place where new lifetimes will result
148 /// in in-band lifetime definitions, such a function or an impl header,
149 /// including implicit lifetimes from `impl_header_lifetime_elision`.
150 is_collecting_in_band_lifetimes: bool,
152 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
153 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
154 /// against this list to see if it is already in-scope, or if a definition
155 /// needs to be created for it.
157 /// We always store a `modern()` version of the param-name in this
159 in_scope_lifetimes: Vec<ParamName>,
161 current_module: hir::HirId,
163 type_def_lifetime_params: DefIdMap<usize>,
165 current_hir_id_owner: Vec<(DefIndex, u32)>,
166 item_local_id_counters: NodeMap<u32>,
167 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
169 allow_try_trait: Option<Lrc<[Symbol]>>,
170 allow_gen_future: Option<Lrc<[Symbol]>>,
174 fn cstore(&self) -> &dyn CrateStore;
176 /// Obtains resolution for a `NodeId` with a single resolution.
177 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
179 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
180 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
182 /// Obtains resolution for a label with the given `NodeId`.
183 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
185 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
186 /// This should only return `None` during testing.
187 fn definitions(&mut self) -> &mut Definitions;
189 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
190 /// resolves it based on `is_value`.
194 crate_root: Option<Symbol>,
195 components: &[Symbol],
197 ) -> (ast::Path, Res<NodeId>);
199 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
201 fn next_node_id(&mut self) -> NodeId;
204 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
206 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
207 /// and if so, what meaning it has.
209 enum ImplTraitContext<'a> {
210 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
211 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
212 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
214 /// Newly generated parameters should be inserted into the given `Vec`.
215 Universal(&'a mut Vec<hir::GenericParam>),
217 /// Treat `impl Trait` as shorthand for a new opaque type.
218 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
219 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
221 /// We optionally store a `DefId` for the parent item here so we can look up necessary
222 /// information later. It is `None` when no information about the context should be stored
223 /// (e.g., for consts and statics).
224 OpaqueTy(Option<DefId> /* fn def-ID */),
226 /// `impl Trait` is not accepted in this position.
227 Disallowed(ImplTraitPosition),
230 /// Position in which `impl Trait` is disallowed.
231 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
232 enum ImplTraitPosition {
233 /// Disallowed in `let` / `const` / `static` bindings.
236 /// All other posiitons.
240 impl<'a> ImplTraitContext<'a> {
242 fn disallowed() -> Self {
243 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
246 fn reborrow(&'b mut self) -> ImplTraitContext<'b> {
247 use self::ImplTraitContext::*;
249 Universal(params) => Universal(params),
250 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
251 Disallowed(pos) => Disallowed(*pos),
256 pub fn lower_crate<'a, 'hir>(
258 dep_graph: &'a DepGraph,
260 resolver: &'a mut dyn Resolver,
261 nt_to_tokenstream: NtToTokenstream,
262 arena: &'hir Arena<'hir>,
263 ) -> hir::Crate<'hir> {
264 // We're constructing the HIR here; we don't care what we will
265 // read, since we haven't even constructed the *input* to
267 dep_graph.assert_ignored();
269 let _prof_timer = sess.prof.generic_activity("hir_lowering");
272 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
277 items: BTreeMap::new(),
278 trait_items: BTreeMap::new(),
279 impl_items: BTreeMap::new(),
280 bodies: BTreeMap::new(),
281 trait_impls: BTreeMap::new(),
282 modules: BTreeMap::new(),
283 exported_macros: Vec::new(),
284 non_exported_macro_attrs: Vec::new(),
285 catch_scopes: Vec::new(),
286 loop_scopes: Vec::new(),
287 is_in_loop_condition: false,
288 is_in_trait_impl: false,
289 is_in_dyn_type: false,
290 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
291 type_def_lifetime_params: Default::default(),
292 current_module: hir::CRATE_HIR_ID,
293 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
294 item_local_id_counters: Default::default(),
295 node_id_to_hir_id: IndexVec::new(),
296 generator_kind: None,
298 lifetimes_to_define: Vec::new(),
299 is_collecting_in_band_lifetimes: false,
300 in_scope_lifetimes: Vec::new(),
301 allow_try_trait: Some([sym::try_trait][..].into()),
302 allow_gen_future: Some([sym::gen_future][..].into()),
307 #[derive(Copy, Clone, PartialEq)]
309 /// Any path in a type context.
311 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
313 /// The `module::Type` in `module::Type::method` in an expression.
317 enum ParenthesizedGenericArgs {
322 /// What to do when we encounter an **anonymous** lifetime
323 /// reference. Anonymous lifetime references come in two flavors. You
324 /// have implicit, or fully elided, references to lifetimes, like the
325 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
326 /// or `Ref<'_, T>`. These often behave the same, but not always:
328 /// - certain usages of implicit references are deprecated, like
329 /// `Ref<T>`, and we sometimes just give hard errors in those cases
331 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
332 /// the same as `Box<dyn Foo + '_>`.
334 /// We describe the effects of the various modes in terms of three cases:
336 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
337 /// of a `&` (e.g., the missing lifetime in something like `&T`)
338 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
339 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
340 /// elided bounds follow special rules. Note that this only covers
341 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
342 /// '_>` is a case of "modern" elision.
343 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
344 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
345 /// non-deprecated equivalent.
347 /// Currently, the handling of lifetime elision is somewhat spread out
348 /// between HIR lowering and -- as described below -- the
349 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
350 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
351 /// everything into HIR lowering.
352 #[derive(Copy, Clone, Debug)]
353 enum AnonymousLifetimeMode {
354 /// For **Modern** cases, create a new anonymous region parameter
355 /// and reference that.
357 /// For **Dyn Bound** cases, pass responsibility to
358 /// `resolve_lifetime` code.
360 /// For **Deprecated** cases, report an error.
363 /// Give a hard error when either `&` or `'_` is written. Used to
364 /// rule out things like `where T: Foo<'_>`. Does not imply an
365 /// error on default object bounds (e.g., `Box<dyn Foo>`).
368 /// Pass responsibility to `resolve_lifetime` code for all cases.
372 struct ImplTraitTypeIdVisitor<'a> {
373 ids: &'a mut SmallVec<[NodeId; 1]>,
376 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
377 fn visit_ty(&mut self, ty: &'a Ty) {
379 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
381 TyKind::ImplTrait(id, _) => self.ids.push(id),
384 visit::walk_ty(self, ty);
387 fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment) {
388 if let Some(ref p) = path_segment.args {
389 if let GenericArgs::Parenthesized(_) = **p {
393 visit::walk_path_segment(self, path_span, path_segment)
397 impl<'a, 'hir> LoweringContext<'a, 'hir> {
398 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
399 /// Full-crate AST visitor that inserts into a fresh
400 /// `LoweringContext` any information that may be
401 /// needed from arbitrary locations in the crate,
402 /// e.g., the number of lifetime generic parameters
403 /// declared for every type and trait definition.
404 struct MiscCollector<'tcx, 'lowering, 'hir> {
405 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
406 hir_id_owner: Option<NodeId>,
409 impl MiscCollector<'_, '_, '_> {
410 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
412 UseTreeKind::Simple(_, id1, id2) => {
413 for &id in &[id1, id2] {
414 self.lctx.resolver.definitions().create_def_with_parent(
421 self.lctx.allocate_hir_id_counter(id);
424 UseTreeKind::Glob => (),
425 UseTreeKind::Nested(ref trees) => {
426 for &(ref use_tree, id) in trees {
427 let hir_id = self.lctx.allocate_hir_id_counter(id);
428 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
434 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
436 F: FnOnce(&mut Self) -> T,
438 let old = mem::replace(&mut self.hir_id_owner, owner);
440 self.hir_id_owner = old;
445 impl<'tcx, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
446 fn visit_pat(&mut self, p: &'tcx Pat) {
447 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
448 // Doesn't generate a HIR node
449 } else if let Some(owner) = self.hir_id_owner {
450 self.lctx.lower_node_id_with_owner(p.id, owner);
453 visit::walk_pat(self, p)
456 fn visit_item(&mut self, item: &'tcx Item) {
457 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
460 ItemKind::Struct(_, ref generics)
461 | ItemKind::Union(_, ref generics)
462 | ItemKind::Enum(_, ref generics)
463 | ItemKind::TyAlias(_, ref generics)
464 | ItemKind::Trait(_, _, ref generics, ..) => {
465 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
469 .filter(|param| match param.kind {
470 ast::GenericParamKind::Lifetime { .. } => true,
474 self.lctx.type_def_lifetime_params.insert(def_id, count);
476 ItemKind::Use(ref use_tree) => {
477 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
482 self.with_hir_id_owner(Some(item.id), |this| {
483 visit::walk_item(this, item);
487 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
488 self.lctx.allocate_hir_id_counter(item.id);
491 AssocItemKind::Fn(_, None) => {
492 // Ignore patterns in trait methods without bodies
493 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
495 _ => self.with_hir_id_owner(Some(item.id), |this| {
496 visit::walk_trait_item(this, item);
501 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
502 self.lctx.allocate_hir_id_counter(item.id);
503 self.with_hir_id_owner(Some(item.id), |this| {
504 visit::walk_impl_item(this, item);
508 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
509 // Ignore patterns in foreign items
510 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
513 fn visit_ty(&mut self, t: &'tcx Ty) {
515 // Mirrors the case in visit::walk_ty
516 TyKind::BareFn(ref f) => {
517 walk_list!(self, visit_generic_param, &f.generic_params);
518 // Mirrors visit::walk_fn_decl
519 for parameter in &f.decl.inputs {
520 // We don't lower the ids of argument patterns
521 self.with_hir_id_owner(None, |this| {
522 this.visit_pat(¶meter.pat);
524 self.visit_ty(¶meter.ty)
526 self.visit_fn_ret_ty(&f.decl.output)
528 _ => visit::walk_ty(self, t),
533 self.lower_node_id(CRATE_NODE_ID);
534 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
536 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
537 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
539 let module = self.lower_mod(&c.module);
540 let attrs = self.arena.alloc_from_iter(self.lower_attrs(&c.attrs).into_iter());
541 let body_ids = body_ids(&self.bodies);
543 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
549 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
550 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
552 trait_items: self.trait_items,
553 impl_items: self.impl_items,
556 trait_impls: self.trait_impls,
557 modules: self.modules,
561 fn insert_item(&mut self, item: hir::Item<'hir>) {
562 let id = item.hir_id;
563 // FIXME: Use `debug_asset-rt`.
564 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
565 self.items.insert(id, item);
566 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
569 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
570 // Set up the counter if needed.
571 self.item_local_id_counters.entry(owner).or_insert(0);
572 // Always allocate the first `HirId` for the owner itself.
573 let lowered = self.lower_node_id_with_owner(owner, owner);
574 debug_assert_eq!(lowered.local_id.as_u32(), 0);
578 fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
580 F: FnOnce(&mut Self) -> hir::HirId,
582 if ast_node_id == DUMMY_NODE_ID {
583 return hir::DUMMY_HIR_ID;
586 let min_size = ast_node_id.as_usize() + 1;
588 if min_size > self.node_id_to_hir_id.len() {
589 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
592 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
594 if existing_hir_id == hir::DUMMY_HIR_ID {
595 // Generate a new `HirId`.
596 let hir_id = alloc_hir_id(self);
597 self.node_id_to_hir_id[ast_node_id] = hir_id;
605 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
607 F: FnOnce(&mut Self) -> T,
610 .item_local_id_counters
611 .insert(owner, HIR_ID_COUNTER_LOCKED)
612 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
613 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
614 self.current_hir_id_owner.push((def_index, counter));
616 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
618 debug_assert!(def_index == new_def_index);
619 debug_assert!(new_counter >= counter);
621 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
622 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
626 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
627 /// the `LoweringContext`'s `NodeId => HirId` map.
628 /// Take care not to call this method if the resulting `HirId` is then not
629 /// actually used in the HIR, as that would trigger an assertion in the
630 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
631 /// properly. Calling the method twice with the same `NodeId` is fine though.
632 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
633 self.lower_node_id_generic(ast_node_id, |this| {
634 let &mut (def_index, ref mut local_id_counter) =
635 this.current_hir_id_owner.last_mut().unwrap();
636 let local_id = *local_id_counter;
637 *local_id_counter += 1;
638 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
642 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
643 self.lower_node_id_generic(ast_node_id, |this| {
644 let local_id_counter = this
645 .item_local_id_counters
647 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
648 let local_id = *local_id_counter;
650 // We want to be sure not to modify the counter in the map while it
651 // is also on the stack. Otherwise we'll get lost updates when writing
652 // back from the stack to the map.
653 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
655 *local_id_counter += 1;
656 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
657 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
658 that do not belong to the current owner",
661 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
665 fn next_id(&mut self) -> hir::HirId {
666 let node_id = self.resolver.next_node_id();
667 self.lower_node_id(node_id)
670 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
672 self.lower_node_id_generic(id, |_| {
673 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
678 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
679 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
680 if pr.unresolved_segments() != 0 {
681 bug!("path not fully resolved: {:?}", pr);
687 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
688 self.resolver.get_import_res(id).present_items()
691 fn diagnostic(&self) -> &errors::Handler {
692 self.sess.diagnostic()
695 /// Reuses the span but adds information like the kind of the desugaring and features that are
696 /// allowed inside this span.
697 fn mark_span_with_reason(
699 reason: DesugaringKind,
701 allow_internal_unstable: Option<Lrc<[Symbol]>>,
703 span.fresh_expansion(ExpnData {
704 allow_internal_unstable,
705 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
709 fn with_anonymous_lifetime_mode<R>(
711 anonymous_lifetime_mode: AnonymousLifetimeMode,
712 op: impl FnOnce(&mut Self) -> R,
715 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
716 anonymous_lifetime_mode,
718 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
719 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
720 let result = op(self);
721 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
723 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
724 old_anonymous_lifetime_mode
729 /// Creates a new `hir::GenericParam` for every new lifetime and
730 /// type parameter encountered while evaluating `f`. Definitions
731 /// are created with the parent provided. If no `parent_id` is
732 /// provided, no definitions will be returned.
734 /// Presuming that in-band lifetimes are enabled, then
735 /// `self.anonymous_lifetime_mode` will be updated to match the
736 /// parameter while `f` is running (and restored afterwards).
737 fn collect_in_band_defs<T, F>(
740 anonymous_lifetime_mode: AnonymousLifetimeMode,
742 ) -> (Vec<hir::GenericParam>, T)
744 F: FnOnce(&mut LoweringContext<'_, '_>) -> (Vec<hir::GenericParam>, T),
746 assert!(!self.is_collecting_in_band_lifetimes);
747 assert!(self.lifetimes_to_define.is_empty());
748 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
750 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
751 self.is_collecting_in_band_lifetimes = true;
753 let (in_band_ty_params, res) = f(self);
755 self.is_collecting_in_band_lifetimes = false;
756 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
758 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
760 let params = lifetimes_to_define
762 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
763 .chain(in_band_ty_params.into_iter())
769 /// Converts a lifetime into a new generic parameter.
770 fn lifetime_to_generic_param(
774 parent_index: DefIndex,
775 ) -> hir::GenericParam {
776 let node_id = self.resolver.next_node_id();
778 // Get the name we'll use to make the def-path. Note
779 // that collisions are ok here and this shouldn't
780 // really show up for end-user.
781 let (str_name, kind) = match hir_name {
782 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
783 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
784 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
787 // Add a definition for the in-band lifetime def.
788 self.resolver.definitions().create_def_with_parent(
791 DefPathData::LifetimeNs(str_name),
797 hir_id: self.lower_node_id(node_id),
802 pure_wrt_drop: false,
803 kind: hir::GenericParamKind::Lifetime { kind },
807 /// When there is a reference to some lifetime `'a`, and in-band
808 /// lifetimes are enabled, then we want to push that lifetime into
809 /// the vector of names to define later. In that case, it will get
810 /// added to the appropriate generics.
811 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
812 if !self.is_collecting_in_band_lifetimes {
816 if !self.sess.features_untracked().in_band_lifetimes {
820 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
824 let hir_name = ParamName::Plain(ident);
826 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
831 self.lifetimes_to_define.push((ident.span, hir_name));
834 /// When we have either an elided or `'_` lifetime in an impl
835 /// header, we convert it to an in-band lifetime.
836 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
837 assert!(self.is_collecting_in_band_lifetimes);
838 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
839 let hir_name = ParamName::Fresh(index);
840 self.lifetimes_to_define.push((span, hir_name));
844 // Evaluates `f` with the lifetimes in `params` in-scope.
845 // This is used to track which lifetimes have already been defined, and
846 // which are new in-band lifetimes that need to have a definition created
848 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
850 F: FnOnce(&mut LoweringContext<'_, 'hir>) -> T,
852 let old_len = self.in_scope_lifetimes.len();
853 let lt_def_names = params.iter().filter_map(|param| match param.kind {
854 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
857 self.in_scope_lifetimes.extend(lt_def_names);
861 self.in_scope_lifetimes.truncate(old_len);
865 /// Appends in-band lifetime defs and argument-position `impl
866 /// Trait` defs to the existing set of generics.
868 /// Presuming that in-band lifetimes are enabled, then
869 /// `self.anonymous_lifetime_mode` will be updated to match the
870 /// parameter while `f` is running (and restored afterwards).
871 fn add_in_band_defs<F, T>(
875 anonymous_lifetime_mode: AnonymousLifetimeMode,
877 ) -> (hir::Generics, T)
879 F: FnOnce(&mut LoweringContext<'_, '_>, &mut Vec<hir::GenericParam>) -> T,
881 let (in_band_defs, (mut lowered_generics, res)) =
882 self.with_in_scope_lifetime_defs(&generics.params, |this| {
883 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
884 let mut params = Vec::new();
885 // Note: it is necessary to lower generics *before* calling `f`.
886 // When lowering `async fn`, there's a final step when lowering
887 // the return type that assumes that all in-scope lifetimes have
888 // already been added to either `in_scope_lifetimes` or
889 // `lifetimes_to_define`. If we swapped the order of these two,
890 // in-band-lifetimes introduced by generics or where-clauses
891 // wouldn't have been added yet.
893 this.lower_generics(generics, ImplTraitContext::Universal(&mut params));
894 let res = f(this, &mut params);
895 (params, (generics, res))
899 let mut lowered_params: Vec<_> =
900 lowered_generics.params.into_iter().chain(in_band_defs).collect();
902 // FIXME(const_generics): the compiler doesn't always cope with
903 // unsorted generic parameters at the moment, so we make sure
904 // that they're ordered correctly here for now. (When we chain
905 // the `in_band_defs`, we might make the order unsorted.)
906 lowered_params.sort_by_key(|param| match param.kind {
907 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
908 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
909 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
912 lowered_generics.params = lowered_params.into();
914 (lowered_generics, res)
917 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
919 F: FnOnce(&mut LoweringContext<'_, '_>) -> T,
921 let was_in_dyn_type = self.is_in_dyn_type;
922 self.is_in_dyn_type = in_scope;
924 let result = f(self);
926 self.is_in_dyn_type = was_in_dyn_type;
931 fn with_new_scopes<T, F>(&mut self, f: F) -> T
933 F: FnOnce(&mut Self) -> T,
935 let was_in_loop_condition = self.is_in_loop_condition;
936 self.is_in_loop_condition = false;
938 let catch_scopes = mem::take(&mut self.catch_scopes);
939 let loop_scopes = mem::take(&mut self.loop_scopes);
941 self.catch_scopes = catch_scopes;
942 self.loop_scopes = loop_scopes;
944 self.is_in_loop_condition = was_in_loop_condition;
949 fn def_key(&mut self, id: DefId) -> DefKey {
951 self.resolver.definitions().def_key(id.index)
953 self.resolver.cstore().def_key(id)
957 fn lower_attrs_arena(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
958 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
961 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
962 attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into()
965 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
966 // Note that we explicitly do not walk the path. Since we don't really
967 // lower attributes (we use the AST version) there is nowhere to keep
968 // the `HirId`s. We don't actually need HIR version of attributes anyway.
969 let kind = match attr.kind {
970 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
971 path: item.path.clone(),
972 args: self.lower_mac_args(&item.args),
974 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
977 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
980 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
982 MacArgs::Empty => MacArgs::Empty,
983 MacArgs::Delimited(dspan, delim, ref tokens) => {
984 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
986 MacArgs::Eq(eq_span, ref tokens) => {
987 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
992 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
993 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
996 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
998 TokenTree::Token(token) => self.lower_token(token),
999 TokenTree::Delimited(span, delim, tts) => {
1000 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
1005 fn lower_token(&mut self, token: Token) -> TokenStream {
1007 token::Interpolated(nt) => {
1008 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1009 self.lower_token_stream(tts)
1011 _ => TokenTree::Token(token).into(),
1015 /// Given an associated type constraint like one of these:
1018 /// T: Iterator<Item: Debug>
1020 /// T: Iterator<Item = Debug>
1024 /// returns a `hir::TypeBinding` representing `Item`.
1025 fn lower_assoc_ty_constraint(
1027 constraint: &AssocTyConstraint,
1028 itctx: ImplTraitContext<'_>,
1029 ) -> hir::TypeBinding {
1030 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1032 let kind = match constraint.kind {
1033 AssocTyConstraintKind::Equality { ref ty } => {
1034 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1036 AssocTyConstraintKind::Bound { ref bounds } => {
1037 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1038 let (desugar_to_impl_trait, itctx) = match itctx {
1039 // We are in the return position:
1041 // fn foo() -> impl Iterator<Item: Debug>
1045 // fn foo() -> impl Iterator<Item = impl Debug>
1046 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1048 // We are in the argument position, but within a dyn type:
1050 // fn foo(x: dyn Iterator<Item: Debug>)
1054 // fn foo(x: dyn Iterator<Item = impl Debug>)
1055 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1057 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1058 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1059 // "impl trait context" to permit `impl Debug` in this position (it desugars
1060 // then to an opaque type).
1062 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1063 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1064 (true, ImplTraitContext::OpaqueTy(None))
1067 // We are in the parameter position, but not within a dyn type:
1069 // fn foo(x: impl Iterator<Item: Debug>)
1071 // so we leave it as is and this gets expanded in astconv to a bound like
1072 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1074 _ => (false, itctx),
1077 if desugar_to_impl_trait {
1078 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1079 // constructing the HIR for `impl bounds...` and then lowering that.
1081 let impl_trait_node_id = self.resolver.next_node_id();
1082 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1083 self.resolver.definitions().create_def_with_parent(
1086 DefPathData::ImplTrait,
1091 self.with_dyn_type_scope(false, |this| {
1092 let node_id = this.resolver.next_node_id();
1093 let ty = this.lower_ty(
1096 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1097 span: constraint.span,
1102 hir::TypeBindingKind::Equality { ty }
1105 // Desugar `AssocTy: Bounds` into a type binding where the
1106 // later desugars into a trait predicate.
1107 let bounds = self.lower_param_bounds(bounds, itctx);
1109 hir::TypeBindingKind::Constraint { bounds }
1115 hir_id: self.lower_node_id(constraint.id),
1116 ident: constraint.ident,
1118 span: constraint.span,
1122 fn lower_generic_arg(
1124 arg: &ast::GenericArg,
1125 itctx: ImplTraitContext<'_>,
1126 ) -> hir::GenericArg {
1128 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1129 ast::GenericArg::Type(ty) => {
1130 // We parse const arguments as path types as we cannot distiguish them durring
1131 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1132 // type and value namespaces. If we resolved the path in the value namespace, we
1133 // transform it into a generic const argument.
1134 if let TyKind::Path(ref qself, ref path) = ty.kind {
1135 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1136 let res = partial_res.base_res();
1137 if !res.matches_ns(Namespace::TypeNS) {
1139 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1143 // Construct a AnonConst where the expr is the "ty"'s path.
1145 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1146 let node_id = self.resolver.next_node_id();
1148 // Add a definition for the in-band const def.
1149 self.resolver.definitions().create_def_with_parent(
1152 DefPathData::AnonConst,
1157 let path_expr = Expr {
1159 kind: ExprKind::Path(qself.clone(), path.clone()),
1161 attrs: AttrVec::new(),
1164 let ct = self.with_new_scopes(|this| hir::AnonConst {
1165 hir_id: this.lower_node_id(node_id),
1166 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1168 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1172 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1174 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1175 value: self.lower_anon_const(&ct),
1176 span: ct.value.span,
1181 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_>) -> P<hir::Ty> {
1182 P(self.lower_ty_direct(t, itctx))
1188 qself: &Option<QSelf>,
1190 param_mode: ParamMode,
1191 itctx: ImplTraitContext<'_>,
1193 let id = self.lower_node_id(t.id);
1194 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1195 let ty = self.ty_path(id, t.span, qpath);
1196 if let hir::TyKind::TraitObject(..) = ty.kind {
1197 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1202 fn ty(&mut self, span: Span, kind: hir::TyKind) -> hir::Ty {
1203 hir::Ty { hir_id: self.next_id(), kind, span }
1206 fn ty_tup(&mut self, span: Span, tys: HirVec<hir::Ty>) -> hir::Ty {
1207 self.ty(span, hir::TyKind::Tup(tys))
1210 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_>) -> hir::Ty {
1211 let kind = match t.kind {
1212 TyKind::Infer => hir::TyKind::Infer,
1213 TyKind::Err => hir::TyKind::Err,
1214 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1215 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1216 TyKind::Rptr(ref region, ref mt) => {
1217 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1218 let lifetime = match *region {
1219 Some(ref lt) => self.lower_lifetime(lt),
1220 None => self.elided_ref_lifetime(span),
1222 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1224 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1225 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1226 hir::TyKind::BareFn(P(hir::BareFnTy {
1227 generic_params: this.lower_generic_params(
1229 &NodeMap::default(),
1230 ImplTraitContext::disallowed(),
1232 unsafety: f.unsafety,
1233 abi: this.lower_extern(f.ext),
1234 decl: this.lower_fn_decl(&f.decl, None, false, None),
1235 param_names: this.lower_fn_params_to_names(&f.decl),
1239 TyKind::Never => hir::TyKind::Never,
1240 TyKind::Tup(ref tys) => hir::TyKind::Tup(
1241 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())).collect(),
1243 TyKind::Paren(ref ty) => {
1244 return self.lower_ty_direct(ty, itctx);
1246 TyKind::Path(ref qself, ref path) => {
1247 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1249 TyKind::ImplicitSelf => {
1250 let res = self.expect_full_res(t.id);
1251 let res = self.lower_res(res);
1252 hir::TyKind::Path(hir::QPath::Resolved(
1256 segments: hir_vec![hir::PathSegment::from_ident(Ident::with_dummy_span(
1263 TyKind::Array(ref ty, ref length) => {
1264 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1266 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1267 TyKind::TraitObject(ref bounds, kind) => {
1268 let mut lifetime_bound = None;
1269 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1272 .filter_map(|bound| match *bound {
1273 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1274 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1276 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1277 GenericBound::Outlives(ref lifetime) => {
1278 if lifetime_bound.is_none() {
1279 lifetime_bound = Some(this.lower_lifetime(lifetime));
1285 let lifetime_bound =
1286 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1287 (bounds, lifetime_bound)
1289 if kind != TraitObjectSyntax::Dyn {
1290 self.maybe_lint_bare_trait(t.span, t.id, false);
1292 hir::TyKind::TraitObject(bounds, lifetime_bound)
1294 TyKind::ImplTrait(def_node_id, ref bounds) => {
1297 ImplTraitContext::OpaqueTy(fn_def_id) => {
1298 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1299 this.lower_param_bounds(bounds, itctx)
1302 ImplTraitContext::Universal(in_band_ty_params) => {
1303 // Add a definition for the in-band `Param`.
1305 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1307 let hir_bounds = self.lower_param_bounds(
1309 ImplTraitContext::Universal(in_band_ty_params),
1311 // Set the name to `impl Bound1 + Bound2`.
1312 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1313 in_band_ty_params.push(hir::GenericParam {
1314 hir_id: self.lower_node_id(def_node_id),
1315 name: ParamName::Plain(ident),
1316 pure_wrt_drop: false,
1320 kind: hir::GenericParamKind::Type {
1322 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1326 hir::TyKind::Path(hir::QPath::Resolved(
1330 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1331 segments: hir_vec![hir::PathSegment::from_ident(ident)],
1335 ImplTraitContext::Disallowed(pos) => {
1336 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1337 "bindings or function and inherent method return types"
1339 "function and inherent method return types"
1341 let mut err = struct_span_err!(
1345 "`impl Trait` not allowed outside of {}",
1348 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1352 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1353 attributes to enable"
1361 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1362 TyKind::CVarArgs => {
1363 self.sess.delay_span_bug(
1365 "`TyKind::CVarArgs` should have been handled elsewhere",
1371 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1374 fn lower_opaque_impl_trait(
1377 fn_def_id: Option<DefId>,
1378 opaque_ty_node_id: NodeId,
1379 lower_bounds: impl FnOnce(&mut LoweringContext<'_, '_>) -> hir::GenericBounds,
1382 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1383 fn_def_id, opaque_ty_node_id, span,
1386 // Make sure we know that some funky desugaring has been going on here.
1387 // This is a first: there is code in other places like for loop
1388 // desugaring that explicitly states that we don't want to track that.
1389 // Not tracking it makes lints in rustc and clippy very fragile, as
1390 // frequently opened issues show.
1391 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1393 let opaque_ty_def_index =
1394 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1396 self.allocate_hir_id_counter(opaque_ty_node_id);
1398 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1400 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1402 opaque_ty_def_index,
1406 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1408 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1410 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1411 let opaque_ty_item = hir::OpaqueTy {
1412 generics: hir::Generics {
1413 params: lifetime_defs,
1414 where_clause: hir::WhereClause { predicates: hir_vec![], span },
1418 impl_trait_fn: fn_def_id,
1419 origin: hir::OpaqueTyOrigin::FnReturn,
1422 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1424 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1426 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1427 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1431 /// Registers a new opaque type with the proper `NodeId`s and
1432 /// returns the lowered node-ID for the opaque type.
1433 fn generate_opaque_type(
1435 opaque_ty_node_id: NodeId,
1436 opaque_ty_item: hir::OpaqueTy,
1438 opaque_ty_span: Span,
1440 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1441 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1442 // Generate an `type Foo = impl Trait;` declaration.
1443 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1444 let opaque_ty_item = hir::Item {
1445 hir_id: opaque_ty_id,
1446 ident: Ident::invalid(),
1447 attrs: Default::default(),
1448 kind: opaque_ty_item_kind,
1449 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1450 span: opaque_ty_span,
1453 // Insert the item into the global item list. This usually happens
1454 // automatically for all AST items. But this opaque type item
1455 // does not actually exist in the AST.
1456 self.insert_item(opaque_ty_item);
1460 fn lifetimes_from_impl_trait_bounds(
1462 opaque_ty_id: NodeId,
1463 parent_index: DefIndex,
1464 bounds: &hir::GenericBounds,
1465 ) -> (HirVec<hir::GenericArg>, HirVec<hir::GenericParam>) {
1467 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1468 parent_index={:?}, \
1470 opaque_ty_id, parent_index, bounds,
1473 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1474 // appear in the bounds, excluding lifetimes that are created within the bounds.
1475 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1476 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1477 context: &'r mut LoweringContext<'a, 'hir>,
1479 opaque_ty_id: NodeId,
1480 collect_elided_lifetimes: bool,
1481 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1482 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1483 output_lifetimes: Vec<hir::GenericArg>,
1484 output_lifetime_params: Vec<hir::GenericParam>,
1487 impl<'r, 'a, 'v, 'hir> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1488 fn nested_visit_map<'this>(
1490 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1491 hir::intravisit::NestedVisitorMap::None
1494 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1495 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1496 if parameters.parenthesized {
1497 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1498 self.collect_elided_lifetimes = false;
1499 hir::intravisit::walk_generic_args(self, span, parameters);
1500 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1502 hir::intravisit::walk_generic_args(self, span, parameters);
1506 fn visit_ty(&mut self, t: &'v hir::Ty) {
1507 // Don't collect elided lifetimes used inside of `fn()` syntax.
1508 if let hir::TyKind::BareFn(_) = t.kind {
1509 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1510 self.collect_elided_lifetimes = false;
1512 // Record the "stack height" of `for<'a>` lifetime bindings
1513 // to be able to later fully undo their introduction.
1514 let old_len = self.currently_bound_lifetimes.len();
1515 hir::intravisit::walk_ty(self, t);
1516 self.currently_bound_lifetimes.truncate(old_len);
1518 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1520 hir::intravisit::walk_ty(self, t)
1524 fn visit_poly_trait_ref(
1526 trait_ref: &'v hir::PolyTraitRef,
1527 modifier: hir::TraitBoundModifier,
1529 // Record the "stack height" of `for<'a>` lifetime bindings
1530 // to be able to later fully undo their introduction.
1531 let old_len = self.currently_bound_lifetimes.len();
1532 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1533 self.currently_bound_lifetimes.truncate(old_len);
1536 fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1537 // Record the introduction of 'a in `for<'a> ...`.
1538 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1539 // Introduce lifetimes one at a time so that we can handle
1540 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1541 let lt_name = hir::LifetimeName::Param(param.name);
1542 self.currently_bound_lifetimes.push(lt_name);
1545 hir::intravisit::walk_generic_param(self, param);
1548 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1549 let name = match lifetime.name {
1550 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1551 if self.collect_elided_lifetimes {
1552 // Use `'_` for both implicit and underscore lifetimes in
1553 // `type Foo<'_> = impl SomeTrait<'_>;`.
1554 hir::LifetimeName::Underscore
1559 hir::LifetimeName::Param(_) => lifetime.name,
1561 // Refers to some other lifetime that is "in
1562 // scope" within the type.
1563 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1565 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1568 if !self.currently_bound_lifetimes.contains(&name)
1569 && !self.already_defined_lifetimes.contains(&name)
1571 self.already_defined_lifetimes.insert(name);
1573 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1574 hir_id: self.context.next_id(),
1575 span: lifetime.span,
1579 let def_node_id = self.context.resolver.next_node_id();
1581 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1582 self.context.resolver.definitions().create_def_with_parent(
1585 DefPathData::LifetimeNs(name.ident().name),
1590 let (name, kind) = match name {
1591 hir::LifetimeName::Underscore => (
1592 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1593 hir::LifetimeParamKind::Elided,
1595 hir::LifetimeName::Param(param_name) => {
1596 (param_name, hir::LifetimeParamKind::Explicit)
1598 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1601 self.output_lifetime_params.push(hir::GenericParam {
1604 span: lifetime.span,
1605 pure_wrt_drop: false,
1608 kind: hir::GenericParamKind::Lifetime { kind },
1614 let mut lifetime_collector = ImplTraitLifetimeCollector {
1616 parent: parent_index,
1618 collect_elided_lifetimes: true,
1619 currently_bound_lifetimes: Vec::new(),
1620 already_defined_lifetimes: FxHashSet::default(),
1621 output_lifetimes: Vec::new(),
1622 output_lifetime_params: Vec::new(),
1625 for bound in bounds {
1626 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1630 lifetime_collector.output_lifetimes.into(),
1631 lifetime_collector.output_lifetime_params.into(),
1638 qself: &Option<QSelf>,
1640 param_mode: ParamMode,
1641 mut itctx: ImplTraitContext<'_>,
1643 let qself_position = qself.as_ref().map(|q| q.position);
1644 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1647 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1649 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1650 let path = P(hir::Path {
1651 res: self.lower_res(partial_res.base_res()),
1652 segments: p.segments[..proj_start]
1655 .map(|(i, segment)| {
1656 let param_mode = match (qself_position, param_mode) {
1657 (Some(j), ParamMode::Optional) if i < j => {
1658 // This segment is part of the trait path in a
1659 // qualified path - one of `a`, `b` or `Trait`
1660 // in `<X as a::b::Trait>::T::U::method`.
1666 // Figure out if this is a type/trait segment,
1667 // which may need lifetime elision performed.
1668 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1669 krate: def_id.krate,
1670 index: this.def_key(def_id).parent.expect("missing parent"),
1672 let type_def_id = match partial_res.base_res() {
1673 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1674 Some(parent_def_id(self, def_id))
1676 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1677 Some(parent_def_id(self, def_id))
1679 Res::Def(DefKind::Struct, def_id)
1680 | Res::Def(DefKind::Union, def_id)
1681 | Res::Def(DefKind::Enum, def_id)
1682 | Res::Def(DefKind::TyAlias, def_id)
1683 | Res::Def(DefKind::Trait, def_id)
1684 if i + 1 == proj_start =>
1690 let parenthesized_generic_args = match partial_res.base_res() {
1691 // `a::b::Trait(Args)`
1692 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1693 ParenthesizedGenericArgs::Ok
1695 // `a::b::Trait(Args)::TraitItem`
1696 Res::Def(DefKind::Method, _)
1697 | Res::Def(DefKind::AssocConst, _)
1698 | Res::Def(DefKind::AssocTy, _)
1699 if i + 2 == proj_start =>
1701 ParenthesizedGenericArgs::Ok
1703 // Avoid duplicated errors.
1704 Res::Err => ParenthesizedGenericArgs::Ok,
1706 _ => ParenthesizedGenericArgs::Err,
1709 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1710 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1713 assert!(!def_id.is_local());
1714 let item_generics = self
1717 .item_generics_cloned_untracked(def_id, self.sess);
1718 let n = item_generics.own_counts().lifetimes;
1719 self.type_def_lifetime_params.insert(def_id, n);
1722 self.lower_path_segment(
1727 parenthesized_generic_args,
1736 // Simple case, either no projections, or only fully-qualified.
1737 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1738 if partial_res.unresolved_segments() == 0 {
1739 return hir::QPath::Resolved(qself, path);
1742 // Create the innermost type that we're projecting from.
1743 let mut ty = if path.segments.is_empty() {
1744 // If the base path is empty that means there exists a
1745 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1746 qself.expect("missing QSelf for <T>::...")
1748 // Otherwise, the base path is an implicit `Self` type path,
1749 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1750 // `<I as Iterator>::Item::default`.
1751 let new_id = self.next_id();
1752 P(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1755 // Anything after the base path are associated "extensions",
1756 // out of which all but the last one are associated types,
1757 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1758 // * base path is `std::vec::Vec<T>`
1759 // * "extensions" are `IntoIter`, `Item` and `clone`
1760 // * type nodes are:
1761 // 1. `std::vec::Vec<T>` (created above)
1762 // 2. `<std::vec::Vec<T>>::IntoIter`
1763 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1764 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1765 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1766 let segment = P(self.lower_path_segment(
1771 ParenthesizedGenericArgs::Err,
1775 let qpath = hir::QPath::TypeRelative(ty, segment);
1777 // It's finished, return the extension of the right node type.
1778 if i == p.segments.len() - 1 {
1782 // Wrap the associated extension in another type node.
1783 let new_id = self.next_id();
1784 ty = P(self.ty_path(new_id, p.span, qpath));
1787 // We should've returned in the for loop above.
1790 "lower_qpath: no final extension segment in {}..{}",
1796 fn lower_path_extra(
1800 param_mode: ParamMode,
1801 explicit_owner: Option<NodeId>,
1809 self.lower_path_segment(
1814 ParenthesizedGenericArgs::Err,
1815 ImplTraitContext::disallowed(),
1824 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1825 let res = self.expect_full_res(id);
1826 let res = self.lower_res(res);
1827 self.lower_path_extra(res, p, param_mode, None)
1830 fn lower_path_segment(
1833 segment: &PathSegment,
1834 param_mode: ParamMode,
1835 expected_lifetimes: usize,
1836 parenthesized_generic_args: ParenthesizedGenericArgs,
1837 itctx: ImplTraitContext<'_>,
1838 explicit_owner: Option<NodeId>,
1839 ) -> hir::PathSegment {
1840 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1841 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1842 match **generic_args {
1843 GenericArgs::AngleBracketed(ref data) => {
1844 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1846 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1847 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1848 ParenthesizedGenericArgs::Err => {
1849 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1850 err.span_label(data.span, "only `Fn` traits may use parentheses");
1851 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1852 // Do not suggest going from `Trait()` to `Trait<>`
1853 if data.inputs.len() > 0 {
1854 if let Some(split) = snippet.find('(') {
1855 let trait_name = &snippet[0..split];
1856 let args = &snippet[split + 1..snippet.len() - 1];
1857 err.span_suggestion(
1859 "use angle brackets instead",
1860 format!("{}<{}>", trait_name, args),
1861 Applicability::MaybeIncorrect,
1868 self.lower_angle_bracketed_parameter_data(
1869 &data.as_angle_bracketed_args(),
1880 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1883 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1884 GenericArg::Lifetime(_) => true,
1887 let first_generic_span = generic_args
1891 .chain(generic_args.bindings.iter().map(|b| b.span))
1893 if !generic_args.parenthesized && !has_lifetimes {
1894 generic_args.args = self
1895 .elided_path_lifetimes(path_span, expected_lifetimes)
1897 .map(|lt| GenericArg::Lifetime(lt))
1898 .chain(generic_args.args.into_iter())
1900 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1901 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1902 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1903 let no_bindings = generic_args.bindings.is_empty();
1904 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1905 // If there are no (non-implicit) generic args or associated type
1906 // bindings, our suggestion includes the angle brackets.
1907 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1909 // Otherwise (sorry, this is kind of gross) we need to infer the
1910 // place to splice in the `'_, ` from the generics that do exist.
1911 let first_generic_span = first_generic_span
1912 .expect("already checked that non-lifetime args or bindings exist");
1913 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1915 match self.anonymous_lifetime_mode {
1916 // In create-parameter mode we error here because we don't want to support
1917 // deprecated impl elision in new features like impl elision and `async fn`,
1918 // both of which work using the `CreateParameter` mode:
1920 // impl Foo for std::cell::Ref<u32> // note lack of '_
1921 // async fn foo(_: std::cell::Ref<u32>) { ... }
1922 AnonymousLifetimeMode::CreateParameter => {
1923 let mut err = struct_span_err!(
1927 "implicit elided lifetime not allowed here"
1929 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1940 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1941 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1942 ELIDED_LIFETIMES_IN_PATHS,
1945 "hidden lifetime parameters in types are deprecated",
1946 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1959 let res = self.expect_full_res(segment.id);
1960 let id = if let Some(owner) = explicit_owner {
1961 self.lower_node_id_with_owner(segment.id, owner)
1963 self.lower_node_id(segment.id)
1966 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1967 segment.ident, segment.id, id,
1970 hir::PathSegment::new(
1973 Some(self.lower_res(res)),
1979 fn lower_angle_bracketed_parameter_data(
1981 data: &AngleBracketedArgs,
1982 param_mode: ParamMode,
1983 mut itctx: ImplTraitContext<'_>,
1984 ) -> (hir::GenericArgs, bool) {
1985 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1986 let has_non_lt_args = args.iter().any(|arg| match arg {
1987 ast::GenericArg::Lifetime(_) => false,
1988 ast::GenericArg::Type(_) => true,
1989 ast::GenericArg::Const(_) => true,
1993 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1994 bindings: constraints
1996 .map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow()))
1998 parenthesized: false,
2000 !has_non_lt_args && param_mode == ParamMode::Optional,
2004 fn lower_parenthesized_parameter_data(
2006 data: &ParenthesizedArgs,
2007 ) -> (hir::GenericArgs, bool) {
2008 // Switch to `PassThrough` mode for anonymous lifetimes; this
2009 // means that we permit things like `&Ref<T>`, where `Ref` has
2010 // a hidden lifetime parameter. This is needed for backwards
2011 // compatibility, even in contexts like an impl header where
2012 // we generally don't permit such things (see #51008).
2013 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2014 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2017 .map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed()))
2019 let output_ty = match output {
2020 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2021 FunctionRetTy::Default(_) => P(this.ty_tup(span, hir::HirVec::new())),
2023 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2024 let binding = hir::TypeBinding {
2025 hir_id: this.next_id(),
2026 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2027 span: output_ty.span,
2028 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2030 (hir::GenericArgs { args, bindings: hir_vec![binding], parenthesized: true }, false)
2034 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2035 let mut ids = SmallVec::<[NodeId; 1]>::new();
2036 if self.sess.features_untracked().impl_trait_in_bindings {
2037 if let Some(ref ty) = l.ty {
2038 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2039 visitor.visit_ty(ty);
2042 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2043 let ty = l.ty.as_ref().map(|t| {
2046 if self.sess.features_untracked().impl_trait_in_bindings {
2047 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2049 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2053 let ty = ty.map(|ty| &*self.arena.alloc(ty.into_inner()));
2054 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2057 hir_id: self.lower_node_id(l.id),
2059 pat: self.lower_pat(&l.pat),
2062 attrs: l.attrs.clone(),
2063 source: hir::LocalSource::Normal,
2069 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2070 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2071 // as they are not explicit in HIR/Ty function signatures.
2072 // (instead, the `c_variadic` flag is set to `true`)
2073 let mut inputs = &decl.inputs[..];
2074 if decl.c_variadic() {
2075 inputs = &inputs[..inputs.len() - 1];
2079 .map(|param| match param.pat.kind {
2080 PatKind::Ident(_, ident, _) => ident,
2081 _ => Ident::new(kw::Invalid, param.pat.span),
2086 // Lowers a function declaration.
2088 // `decl`: the unlowered (AST) function declaration.
2089 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2090 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2091 // `make_ret_async` is also `Some`.
2092 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2093 // This guards against trait declarations and implementations where `impl Trait` is
2095 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2096 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2097 // return type `impl Trait` item.
2101 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam>)>,
2102 impl_trait_return_allow: bool,
2103 make_ret_async: Option<NodeId>,
2104 ) -> P<hir::FnDecl> {
2108 in_band_ty_params: {:?}, \
2109 impl_trait_return_allow: {}, \
2110 make_ret_async: {:?})",
2111 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2113 let lt_mode = if make_ret_async.is_some() {
2114 // In `async fn`, argument-position elided lifetimes
2115 // must be transformed into fresh generic parameters so that
2116 // they can be applied to the opaque `impl Trait` return type.
2117 AnonymousLifetimeMode::CreateParameter
2119 self.anonymous_lifetime_mode
2122 let c_variadic = decl.c_variadic();
2124 // Remember how many lifetimes were already around so that we can
2125 // only look at the lifetime parameters introduced by the arguments.
2126 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2127 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2128 // as they are not explicit in HIR/Ty function signatures.
2129 // (instead, the `c_variadic` flag is set to `true`)
2130 let mut inputs = &decl.inputs[..];
2132 inputs = &inputs[..inputs.len() - 1];
2137 if let Some((_, ibty)) = &mut in_band_ty_params {
2138 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2140 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2143 .collect::<HirVec<_>>()
2146 let output = if let Some(ret_id) = make_ret_async {
2147 self.lower_async_fn_ret_ty(
2149 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2154 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2155 Some((def_id, _)) if impl_trait_return_allow => {
2156 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2158 _ => hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed())),
2160 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2168 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2169 let is_mutable_pat = match arg.pat.kind {
2170 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2171 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2176 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2177 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2178 // Given we are only considering `ImplicitSelf` types, we needn't consider
2179 // the case where we have a mutable pattern to a reference as that would
2180 // no longer be an `ImplicitSelf`.
2181 TyKind::Rptr(_, ref mt)
2182 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2184 hir::ImplicitSelfKind::MutRef
2186 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2187 hir::ImplicitSelfKind::ImmRef
2189 _ => hir::ImplicitSelfKind::None,
2195 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2196 // combined with the following definition of `OpaqueTy`:
2198 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2200 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2201 // `output`: unlowered output type (`T` in `-> T`)
2202 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2203 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2204 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2205 fn lower_async_fn_ret_ty(
2207 output: &FunctionRetTy,
2209 opaque_ty_node_id: NodeId,
2210 ) -> hir::FunctionRetTy {
2212 "lower_async_fn_ret_ty(\
2215 opaque_ty_node_id={:?})",
2216 output, fn_def_id, opaque_ty_node_id,
2219 let span = output.span();
2221 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2223 let opaque_ty_def_index =
2224 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2226 self.allocate_hir_id_counter(opaque_ty_node_id);
2228 // When we create the opaque type for this async fn, it is going to have
2229 // to capture all the lifetimes involved in the signature (including in the
2230 // return type). This is done by introducing lifetime parameters for:
2232 // - all the explicitly declared lifetimes from the impl and function itself;
2233 // - all the elided lifetimes in the fn arguments;
2234 // - all the elided lifetimes in the return type.
2236 // So for example in this snippet:
2239 // impl<'a> Foo<'a> {
2240 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2241 // // ^ '0 ^ '1 ^ '2
2242 // // elided lifetimes used below
2247 // we would create an opaque type like:
2250 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2253 // and we would then desugar `bar` to the equivalent of:
2256 // impl<'a> Foo<'a> {
2257 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2261 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2262 // this is because the elided lifetimes from the return type
2263 // should be figured out using the ordinary elision rules, and
2264 // this desugaring achieves that.
2266 // The variable `input_lifetimes_count` tracks the number of
2267 // lifetime parameters to the opaque type *not counting* those
2268 // lifetimes elided in the return type. This includes those
2269 // that are explicitly declared (`in_scope_lifetimes`) and
2270 // those elided lifetimes we found in the arguments (current
2271 // content of `lifetimes_to_define`). Next, we will process
2272 // the return type, which will cause `lifetimes_to_define` to
2274 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2276 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2277 // We have to be careful to get elision right here. The
2278 // idea is that we create a lifetime parameter for each
2279 // lifetime in the return type. So, given a return type
2280 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2281 // Future<Output = &'1 [ &'2 u32 ]>`.
2283 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2284 // hence the elision takes place at the fn site.
2285 let future_bound = this
2286 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2287 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2290 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2292 // Calculate all the lifetimes that should be captured
2293 // by the opaque type. This should include all in-scope
2294 // lifetime parameters, including those defined in-band.
2296 // Note: this must be done after lowering the output type,
2297 // as the output type may introduce new in-band lifetimes.
2298 let lifetime_params: Vec<(Span, ParamName)> = this
2302 .map(|name| (name.ident().span, name))
2303 .chain(this.lifetimes_to_define.iter().cloned())
2306 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2307 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2308 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2310 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: hir_vec![], span },
2324 bounds: hir_vec![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,
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.into());
2377 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2378 hir::FunctionRetTy::Return(P(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 {
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) => P(self.ty_tup(*ret_ty_span, hir_vec![])),
2395 let future_params = P(hir::GenericArgs {
2397 bindings: hir_vec![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>
2408 P(self.std_path(span, &[sym::future, sym::Future], Some(future_params), false));
2410 hir::GenericBound::Trait(
2412 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2413 bound_generic_params: hir_vec![],
2416 hir::TraitBoundModifier::None,
2420 fn lower_param_bound(
2423 itctx: ImplTraitContext<'_>,
2424 ) -> hir::GenericBound {
2426 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2427 self.lower_poly_trait_ref(ty, itctx),
2428 self.lower_trait_bound_modifier(modifier),
2430 GenericBound::Outlives(ref lifetime) => {
2431 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2436 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2437 let span = l.ident.span;
2439 ident if ident.name == kw::StaticLifetime => {
2440 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2442 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2443 AnonymousLifetimeMode::CreateParameter => {
2444 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2445 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2448 AnonymousLifetimeMode::PassThrough => {
2449 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2452 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2455 self.maybe_collect_in_band_lifetime(ident);
2456 let param_name = ParamName::Plain(ident);
2457 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2462 fn new_named_lifetime(
2466 name: hir::LifetimeName,
2467 ) -> hir::Lifetime {
2468 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2471 fn lower_generic_params(
2473 params: &[GenericParam],
2474 add_bounds: &NodeMap<Vec<GenericBound>>,
2475 mut itctx: ImplTraitContext<'_>,
2476 ) -> hir::HirVec<hir::GenericParam> {
2479 .map(|param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2483 fn lower_generic_param(
2485 param: &GenericParam,
2486 add_bounds: &NodeMap<Vec<GenericBound>>,
2487 mut itctx: ImplTraitContext<'_>,
2488 ) -> hir::GenericParam {
2489 let mut bounds = self
2490 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2491 this.lower_param_bounds(¶m.bounds, itctx.reborrow())
2494 let (name, kind) = match param.kind {
2495 GenericParamKind::Lifetime => {
2496 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2497 self.is_collecting_in_band_lifetimes = false;
2500 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2501 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2503 let param_name = match lt.name {
2504 hir::LifetimeName::Param(param_name) => param_name,
2505 hir::LifetimeName::Implicit
2506 | hir::LifetimeName::Underscore
2507 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2508 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2511 "object-lifetime-default should not occur here",
2514 hir::LifetimeName::Error => ParamName::Error,
2518 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2520 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2524 GenericParamKind::Type { ref default, .. } => {
2525 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2526 if !add_bounds.is_empty() {
2527 let params = self.lower_param_bounds(add_bounds, itctx.reborrow()).into_iter();
2528 bounds = bounds.into_iter().chain(params).collect();
2531 let kind = hir::GenericParamKind::Type {
2534 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2538 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2539 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2543 (hir::ParamName::Plain(param.ident), kind)
2545 GenericParamKind::Const { ref ty } => (
2546 hir::ParamName::Plain(param.ident),
2547 hir::GenericParamKind::Const {
2548 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2554 hir_id: self.lower_node_id(param.id),
2556 span: param.ident.span,
2557 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2558 attrs: self.lower_attrs(¶m.attrs),
2564 fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext<'_>) -> hir::TraitRef {
2565 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2566 hir::QPath::Resolved(None, path) => path,
2567 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2569 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2572 fn lower_poly_trait_ref(
2575 mut itctx: ImplTraitContext<'_>,
2576 ) -> hir::PolyTraitRef {
2577 let bound_generic_params = self.lower_generic_params(
2578 &p.bound_generic_params,
2579 &NodeMap::default(),
2582 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2583 this.lower_trait_ref(&p.trait_ref, itctx)
2586 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2589 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_>) -> hir::MutTy {
2590 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2593 fn lower_param_bounds(
2595 bounds: &[GenericBound],
2596 mut itctx: ImplTraitContext<'_>,
2597 ) -> hir::GenericBounds {
2598 bounds.iter().map(|bound| self.lower_param_bound(bound, itctx.reborrow())).collect()
2601 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2602 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2605 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2606 let mut stmts = vec![];
2607 let mut expr: Option<&'hir _> = None;
2609 for (index, stmt) in b.stmts.iter().enumerate() {
2610 if index == b.stmts.len() - 1 {
2611 if let StmtKind::Expr(ref e) = stmt.kind {
2612 expr = Some(self.lower_expr(e));
2614 stmts.extend(self.lower_stmt(stmt));
2617 stmts.extend(self.lower_stmt(stmt));
2622 hir_id: self.lower_node_id(b.id),
2623 stmts: self.arena.alloc_from_iter(stmts),
2625 rules: self.lower_block_check_mode(&b.rules),
2631 /// Lowers a block directly to an expression, presuming that it
2632 /// has no attributes and is not targeted by a `break`.
2633 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2634 let block = self.lower_block(b, false);
2635 self.expr_block(block, AttrVec::new())
2638 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2639 let node = match p.kind {
2640 PatKind::Wild => hir::PatKind::Wild,
2641 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2642 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2643 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2646 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2647 PatKind::TupleStruct(ref path, ref pats) => {
2648 let qpath = self.lower_qpath(
2652 ParamMode::Optional,
2653 ImplTraitContext::disallowed(),
2655 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2656 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2658 PatKind::Or(ref pats) => {
2659 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2661 PatKind::Path(ref qself, ref path) => {
2662 let qpath = self.lower_qpath(
2666 ParamMode::Optional,
2667 ImplTraitContext::disallowed(),
2669 hir::PatKind::Path(qpath)
2671 PatKind::Struct(ref path, ref fields, etc) => {
2672 let qpath = self.lower_qpath(
2676 ParamMode::Optional,
2677 ImplTraitContext::disallowed(),
2680 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2681 hir_id: self.next_id(),
2683 pat: self.lower_pat(&f.pat),
2684 is_shorthand: f.is_shorthand,
2687 hir::PatKind::Struct(qpath, fs, etc)
2689 PatKind::Tuple(ref pats) => {
2690 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2691 hir::PatKind::Tuple(pats, ddpos)
2693 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2694 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2695 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2696 self.lower_expr(e1),
2697 self.lower_expr(e2),
2698 self.lower_range_end(end),
2700 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2702 // If we reach here the `..` pattern is not semantically allowed.
2703 self.ban_illegal_rest_pat(p.span)
2705 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2706 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2709 self.pat_with_node_id_of(p, node)
2716 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2717 let mut elems = Vec::with_capacity(pats.len());
2718 let mut rest = None;
2720 let mut iter = pats.iter().enumerate();
2721 for (idx, pat) in iter.by_ref() {
2722 // Interpret the first `..` pattern as a sub-tuple pattern.
2723 // Note that unlike for slice patterns,
2724 // where `xs @ ..` is a legal sub-slice pattern,
2725 // it is not a legal sub-tuple pattern.
2727 rest = Some((idx, pat.span));
2730 // It was not a sub-tuple pattern so lower it normally.
2731 elems.push(self.lower_pat(pat));
2734 for (_, pat) in iter {
2735 // There was a previous sub-tuple pattern; make sure we don't allow more...
2737 // ...but there was one again, so error.
2738 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2740 elems.push(self.lower_pat(pat));
2744 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2747 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2748 /// `hir::PatKind::Slice(before, slice, after)`.
2750 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2751 /// this is interpreted as a sub-slice pattern semantically.
2752 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2753 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2754 let mut before = Vec::new();
2755 let mut after = Vec::new();
2756 let mut slice = None;
2757 let mut prev_rest_span = None;
2759 let mut iter = pats.iter();
2760 // Lower all the patterns until the first occurence of a sub-slice pattern.
2761 for pat in iter.by_ref() {
2763 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2765 prev_rest_span = Some(pat.span);
2766 slice = Some(self.pat_wild_with_node_id_of(pat));
2769 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2770 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2771 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2772 prev_rest_span = Some(sub.span);
2773 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2774 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2775 slice = Some(self.pat_with_node_id_of(pat, node));
2778 // It was not a subslice pattern so lower it normally.
2779 _ => before.push(self.lower_pat(pat)),
2783 // Lower all the patterns after the first sub-slice pattern.
2785 // There was a previous subslice pattern; make sure we don't allow more.
2786 let rest_span = match pat.kind {
2787 PatKind::Rest => Some(pat.span),
2788 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2789 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2790 after.push(self.pat_wild_with_node_id_of(pat));
2795 if let Some(rest_span) = rest_span {
2796 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2797 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2799 // Lower the pattern normally.
2800 after.push(self.lower_pat(pat));
2804 hir::PatKind::Slice(
2805 self.arena.alloc_from_iter(before),
2807 self.arena.alloc_from_iter(after),
2814 binding_mode: &BindingMode,
2816 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2817 ) -> hir::PatKind<'hir> {
2818 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2819 // `None` can occur in body-less function signatures
2820 res @ None | res @ Some(Res::Local(_)) => {
2821 let canonical_id = match res {
2822 Some(Res::Local(id)) => id,
2826 hir::PatKind::Binding(
2827 self.lower_binding_mode(binding_mode),
2828 self.lower_node_id(canonical_id),
2833 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2837 res: self.lower_res(res),
2838 segments: hir_vec![hir::PathSegment::from_ident(ident)],
2844 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2845 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2848 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2849 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2850 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2853 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2854 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2856 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2857 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2858 .span_label(prev_sp, "previously used here")
2862 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2863 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2865 .struct_span_err(sp, "`..` patterns are not allowed here")
2866 .note("only allowed in tuple, tuple struct, and slice patterns")
2869 // We're not in a list context so `..` can be reasonably treated
2870 // as `_` because it should always be valid and roughly matches the
2871 // intent of `..` (notice that the rest of a single slot is that slot).
2875 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2877 RangeEnd::Included(_) => hir::RangeEnd::Included,
2878 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2882 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2883 self.with_new_scopes(|this| hir::AnonConst {
2884 hir_id: this.lower_node_id(c.id),
2885 body: this.lower_const_body(c.value.span, Some(&c.value)),
2889 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2890 let kind = match s.kind {
2891 StmtKind::Local(ref l) => {
2892 let (l, item_ids) = self.lower_local(l);
2893 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2896 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2897 self.stmt(s.span, hir::StmtKind::Item(item_id))
2902 hir_id: self.lower_node_id(s.id),
2903 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2909 StmtKind::Item(ref it) => {
2910 // Can only use the ID once.
2911 let mut id = Some(s.id);
2918 .map(|id| self.lower_node_id(id))
2919 .unwrap_or_else(|| self.next_id());
2921 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2925 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2926 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2927 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2929 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2932 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2934 BlockCheckMode::Default => hir::DefaultBlock,
2935 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2939 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2941 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2942 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2943 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2944 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2948 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2950 CompilerGenerated => hir::CompilerGenerated,
2951 UserProvided => hir::UserProvided,
2955 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2957 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2958 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2962 // Helper methods for building HIR.
2964 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2965 hir::Stmt { span, kind, hir_id: self.next_id() }
2968 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2969 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2976 init: Option<&'hir hir::Expr<'hir>>,
2977 pat: &'hir hir::Pat<'hir>,
2978 source: hir::LocalSource,
2979 ) -> hir::Stmt<'hir> {
2980 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2981 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2984 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2985 self.block_all(expr.span, &[], Some(expr))
2991 stmts: &'hir [hir::Stmt<'hir>],
2992 expr: Option<&'hir hir::Expr<'hir>>,
2993 ) -> &'hir hir::Block<'hir> {
2994 let blk = hir::Block {
2997 hir_id: self.next_id(),
2998 rules: hir::DefaultBlock,
3000 targeted_by_break: false,
3002 self.arena.alloc(blk)
3005 /// Constructs a `true` or `false` literal pattern.
3006 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3007 let expr = self.expr_bool(span, val);
3008 self.pat(span, hir::PatKind::Lit(expr))
3011 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3012 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3015 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3016 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3019 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3020 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3023 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3024 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3030 components: &[Symbol],
3031 subpats: &'hir [&'hir hir::Pat<'hir>],
3032 ) -> &'hir hir::Pat<'hir> {
3033 let path = self.std_path(span, components, None, true);
3034 let qpath = hir::QPath::Resolved(None, P(path));
3035 let pt = if subpats.is_empty() {
3036 hir::PatKind::Path(qpath)
3038 hir::PatKind::TupleStruct(qpath, subpats, None)
3043 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3044 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3047 fn pat_ident_binding_mode(
3051 bm: hir::BindingAnnotation,
3052 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3053 let hir_id = self.next_id();
3056 self.arena.alloc(hir::Pat {
3058 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3065 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3066 self.pat(span, hir::PatKind::Wild)
3069 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3070 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3073 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3074 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3075 /// The path is also resolved according to `is_value`.
3079 components: &[Symbol],
3080 params: Option<P<hir::GenericArgs>>,
3083 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3084 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3086 let mut segments: Vec<_> = path
3090 let res = self.expect_full_res(segment.id);
3092 ident: segment.ident,
3093 hir_id: Some(self.lower_node_id(segment.id)),
3094 res: Some(self.lower_res(res)),
3100 segments.last_mut().unwrap().args = params;
3104 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3105 segments: segments.into(),
3109 fn ty_path(&mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath) -> hir::Ty {
3110 let kind = match qpath {
3111 hir::QPath::Resolved(None, path) => {
3112 // Turn trait object paths into `TyKind::TraitObject` instead.
3114 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3115 let principal = hir::PolyTraitRef {
3116 bound_generic_params: hir::HirVec::new(),
3117 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3121 // The original ID is taken by the `PolyTraitRef`,
3122 // so the `Ty` itself needs a different one.
3123 hir_id = self.next_id();
3124 hir::TyKind::TraitObject(hir_vec![principal], self.elided_dyn_bound(span))
3126 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3129 _ => hir::TyKind::Path(qpath),
3132 hir::Ty { hir_id, kind, span }
3135 /// Invoked to create the lifetime argument for a type `&T`
3136 /// with no explicit lifetime.
3137 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3138 match self.anonymous_lifetime_mode {
3139 // Intercept when we are in an impl header or async fn and introduce an in-band
3141 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3143 AnonymousLifetimeMode::CreateParameter => {
3144 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3146 hir_id: self.next_id(),
3148 name: hir::LifetimeName::Param(fresh_name),
3152 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3154 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3158 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3159 /// return a "error lifetime".
3160 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3161 let (id, msg, label) = match id {
3162 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3165 self.resolver.next_node_id(),
3166 "`&` without an explicit lifetime name cannot be used here",
3167 "explicit lifetime name needed here",
3171 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3172 err.span_label(span, label);
3175 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3178 /// Invoked to create the lifetime argument(s) for a path like
3179 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3180 /// sorts of cases are deprecated. This may therefore report a warning or an
3181 /// error, depending on the mode.
3182 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3183 (0..count).map(|_| self.elided_path_lifetime(span)).collect()
3186 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3187 match self.anonymous_lifetime_mode {
3188 AnonymousLifetimeMode::CreateParameter => {
3189 // We should have emitted E0726 when processing this path above
3191 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3192 let id = self.resolver.next_node_id();
3193 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3195 // `PassThrough` is the normal case.
3196 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3197 // is unsuitable here, as these can occur from missing lifetime parameters in a
3198 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3199 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3200 // later, at which point a suitable error will be emitted.
3201 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3202 self.new_implicit_lifetime(span)
3207 /// Invoked to create the lifetime argument(s) for an elided trait object
3208 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3209 /// when the bound is written, even if it is written with `'_` like in
3210 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3211 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3212 match self.anonymous_lifetime_mode {
3213 // NB. We intentionally ignore the create-parameter mode here.
3214 // and instead "pass through" to resolve-lifetimes, which will apply
3215 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3216 // do not act like other elided lifetimes. In other words, given this:
3218 // impl Foo for Box<dyn Debug>
3220 // we do not introduce a fresh `'_` to serve as the bound, but instead
3221 // ultimately translate to the equivalent of:
3223 // impl Foo for Box<dyn Debug + 'static>
3225 // `resolve_lifetime` has the code to make that happen.
3226 AnonymousLifetimeMode::CreateParameter => {}
3228 AnonymousLifetimeMode::ReportError => {
3229 // ReportError applies to explicit use of `'_`.
3232 // This is the normal case.
3233 AnonymousLifetimeMode::PassThrough => {}
3236 let r = hir::Lifetime {
3237 hir_id: self.next_id(),
3239 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3241 debug!("elided_dyn_bound: r={:?}", r);
3245 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3246 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3249 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3250 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3251 // call site which do not have a macro backtrace. See #61963.
3252 let is_macro_callsite = self
3255 .span_to_snippet(span)
3256 .map(|snippet| snippet.starts_with("#["))
3258 if !is_macro_callsite {
3259 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3260 builtin::BARE_TRAIT_OBJECTS,
3263 "trait objects without an explicit `dyn` are deprecated",
3264 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3270 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId> {
3271 // Sorting by span ensures that we get things in order within a
3272 // file, and also puts the files in a sensible order.
3273 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3274 body_ids.sort_by_key(|b| bodies[b].value.span);