1 // ignore-tidy-filelength
3 //! Lowers the AST to the HIR.
5 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
6 //! much like a fold. Where lowering involves a bit more work things get more
7 //! interesting and there are some invariants you should know about. These mostly
8 //! concern spans and IDs.
10 //! Spans are assigned to AST nodes during parsing and then are modified during
11 //! expansion to indicate the origin of a node and the process it went through
12 //! being expanded. IDs are assigned to AST nodes just before lowering.
14 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
15 //! expansion we do not preserve the process of lowering in the spans, so spans
16 //! should not be modified here. When creating a new node (as opposed to
17 //! 'folding' an existing one), then you create a new ID using `next_id()`.
19 //! You must ensure that IDs are unique. That means that you should only use the
20 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
21 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
22 //! If you do, you must then set the new node's ID to a fresh one.
24 //! Spans are used for error messages and for tools to map semantics back to
25 //! source code. It is therefore not as important with spans as IDs to be strict
26 //! about use (you can't break the compiler by screwing up a span). Obviously, a
27 //! HIR node can only have a single span. But multiple nodes can have the same
28 //! span and spans don't need to be kept in order, etc. Where code is preserved
29 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
30 //! new it is probably best to give a span for the whole AST node being lowered.
31 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
32 //! get confused if the spans from leaf AST nodes occur in multiple places
33 //! in the HIR, especially for multiple identifiers.
35 #![feature(array_value_iter)]
37 use rustc::arena::Arena;
38 use rustc::dep_graph::DepGraph;
39 use rustc::hir::map::definitions::{DefKey, DefPathData, Definitions};
40 use rustc::hir::map::Map;
42 use rustc::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
43 use rustc::middle::cstore::CrateStore;
44 use rustc::util::captures::Captures;
45 use rustc::util::common::FN_OUTPUT_NAME;
46 use rustc::{bug, span_bug};
47 use rustc_data_structures::fx::FxHashSet;
48 use rustc_data_structures::sync::Lrc;
49 use rustc_error_codes::*;
50 use rustc_errors::{struct_span_err, Applicability};
52 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
53 use rustc_hir::def_id::{DefId, DefIdMap, DefIndex, CRATE_DEF_INDEX};
54 use rustc_hir::intravisit;
55 use rustc_hir::{ConstArg, GenericArg, ParamName};
56 use rustc_index::vec::IndexVec;
57 use rustc_session::config::nightly_options;
58 use rustc_session::node_id::NodeMap;
59 use rustc_session::Session;
60 use rustc_span::hygiene::ExpnId;
61 use rustc_span::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
62 use rustc_span::symbol::{kw, sym, Symbol};
67 use syntax::print::pprust;
68 use syntax::ptr::P as AstP;
69 use syntax::sess::ParseSess;
70 use syntax::token::{self, Nonterminal, Token};
71 use syntax::tokenstream::{TokenStream, TokenTree};
72 use syntax::visit::{self, Visitor};
73 use syntax::walk_list;
75 use log::{debug, trace};
76 use smallvec::{smallvec, SmallVec};
77 use std::collections::BTreeMap;
80 macro_rules! arena_vec {
81 ($this:expr; $($x:expr),*) => ({
83 $this.arena.alloc_from_iter(std::array::IntoIter::new(a))
90 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
92 struct LoweringContext<'a, 'hir: 'a> {
93 crate_root: Option<Symbol>,
95 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
98 resolver: &'a mut dyn Resolver,
100 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
101 /// if we don't have this function pointer. To avoid that dependency so that
102 /// librustc is independent of the parser, we use dynamic dispatch here.
103 nt_to_tokenstream: NtToTokenstream,
105 /// Used to allocate HIR nodes
106 arena: &'hir Arena<'hir>,
108 /// The items being lowered are collected here.
109 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
111 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
112 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
113 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
114 exported_macros: Vec<hir::MacroDef<'hir>>,
115 non_exported_macro_attrs: Vec<ast::Attribute>,
117 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
119 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
121 generator_kind: Option<hir::GeneratorKind>,
123 /// Used to get the current `fn`'s def span to point to when using `await`
124 /// outside of an `async fn`.
125 current_item: Option<Span>,
127 catch_scopes: Vec<NodeId>,
128 loop_scopes: Vec<NodeId>,
129 is_in_loop_condition: bool,
130 is_in_trait_impl: bool,
131 is_in_dyn_type: bool,
133 /// What to do when we encounter either an "anonymous lifetime
134 /// reference". The term "anonymous" is meant to encompass both
135 /// `'_` lifetimes as well as fully elided cases where nothing is
136 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
137 anonymous_lifetime_mode: AnonymousLifetimeMode,
139 /// Used to create lifetime definitions from in-band lifetime usages.
140 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
141 /// When a named lifetime is encountered in a function or impl header and
142 /// has not been defined
143 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
144 /// to this list. The results of this list are then added to the list of
145 /// lifetime definitions in the corresponding impl or function generics.
146 lifetimes_to_define: Vec<(Span, ParamName)>,
148 /// `true` if in-band lifetimes are being collected. This is used to
149 /// indicate whether or not we're in a place where new lifetimes will result
150 /// in in-band lifetime definitions, such a function or an impl header,
151 /// including implicit lifetimes from `impl_header_lifetime_elision`.
152 is_collecting_in_band_lifetimes: bool,
154 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
155 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
156 /// against this list to see if it is already in-scope, or if a definition
157 /// needs to be created for it.
159 /// We always store a `modern()` version of the param-name in this
161 in_scope_lifetimes: Vec<ParamName>,
163 current_module: hir::HirId,
165 type_def_lifetime_params: DefIdMap<usize>,
167 current_hir_id_owner: Vec<(DefIndex, u32)>,
168 item_local_id_counters: NodeMap<u32>,
169 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
171 allow_try_trait: Option<Lrc<[Symbol]>>,
172 allow_gen_future: Option<Lrc<[Symbol]>>,
176 fn cstore(&self) -> &dyn CrateStore;
178 /// Obtains resolution for a `NodeId` with a single resolution.
179 fn get_partial_res(&mut self, id: NodeId) -> Option<PartialRes>;
181 /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`.
182 fn get_import_res(&mut self, id: NodeId) -> PerNS<Option<Res<NodeId>>>;
184 /// Obtains resolution for a label with the given `NodeId`.
185 fn get_label_res(&mut self, id: NodeId) -> Option<NodeId>;
187 /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
188 /// This should only return `None` during testing.
189 fn definitions(&mut self) -> &mut Definitions;
191 /// Given suffix `["b", "c", "d"]`, creates an AST path for `[::crate_root]::b::c::d` and
192 /// resolves it based on `is_value`.
196 crate_root: Option<Symbol>,
197 components: &[Symbol],
199 ) -> (ast::Path, Res<NodeId>);
201 fn lint_buffer(&mut self) -> &mut lint::LintBuffer;
203 fn next_node_id(&mut self) -> NodeId;
206 type NtToTokenstream = fn(&Nonterminal, &ParseSess, Span) -> TokenStream;
208 /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
209 /// and if so, what meaning it has.
211 enum ImplTraitContext<'b, 'a> {
212 /// Treat `impl Trait` as shorthand for a new universal generic parameter.
213 /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
214 /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
216 /// Newly generated parameters should be inserted into the given `Vec`.
217 Universal(&'b mut Vec<hir::GenericParam<'a>>),
219 /// Treat `impl Trait` as shorthand for a new opaque type.
220 /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
221 /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
223 /// We optionally store a `DefId` for the parent item here so we can look up necessary
224 /// information later. It is `None` when no information about the context should be stored
225 /// (e.g., for consts and statics).
226 OpaqueTy(Option<DefId> /* fn def-ID */),
228 /// `impl Trait` is not accepted in this position.
229 Disallowed(ImplTraitPosition),
232 /// Position in which `impl Trait` is disallowed.
233 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
234 enum ImplTraitPosition {
235 /// Disallowed in `let` / `const` / `static` bindings.
238 /// All other posiitons.
242 impl<'a> ImplTraitContext<'_, 'a> {
244 fn disallowed() -> Self {
245 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
248 fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> {
249 use self::ImplTraitContext::*;
251 Universal(params) => Universal(params),
252 OpaqueTy(fn_def_id) => OpaqueTy(*fn_def_id),
253 Disallowed(pos) => Disallowed(*pos),
258 pub fn lower_crate<'a, 'hir>(
260 dep_graph: &'a DepGraph,
262 resolver: &'a mut dyn Resolver,
263 nt_to_tokenstream: NtToTokenstream,
264 arena: &'hir Arena<'hir>,
265 ) -> hir::Crate<'hir> {
266 // We're constructing the HIR here; we don't care what we will
267 // read, since we haven't even constructed the *input* to
269 dep_graph.assert_ignored();
271 let _prof_timer = sess.prof.generic_activity("hir_lowering");
274 crate_root: sess.parse_sess.injected_crate_name.try_get().copied(),
279 items: BTreeMap::new(),
280 trait_items: BTreeMap::new(),
281 impl_items: BTreeMap::new(),
282 bodies: BTreeMap::new(),
283 trait_impls: BTreeMap::new(),
284 modules: BTreeMap::new(),
285 exported_macros: Vec::new(),
286 non_exported_macro_attrs: Vec::new(),
287 catch_scopes: Vec::new(),
288 loop_scopes: Vec::new(),
289 is_in_loop_condition: false,
290 is_in_trait_impl: false,
291 is_in_dyn_type: false,
292 anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
293 type_def_lifetime_params: Default::default(),
294 current_module: hir::CRATE_HIR_ID,
295 current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
296 item_local_id_counters: Default::default(),
297 node_id_to_hir_id: IndexVec::new(),
298 generator_kind: None,
300 lifetimes_to_define: Vec::new(),
301 is_collecting_in_band_lifetimes: false,
302 in_scope_lifetimes: Vec::new(),
303 allow_try_trait: Some([sym::try_trait][..].into()),
304 allow_gen_future: Some([sym::gen_future][..].into()),
309 #[derive(Copy, Clone, PartialEq)]
311 /// Any path in a type context.
313 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
315 /// The `module::Type` in `module::Type::method` in an expression.
319 enum ParenthesizedGenericArgs {
324 /// What to do when we encounter an **anonymous** lifetime
325 /// reference. Anonymous lifetime references come in two flavors. You
326 /// have implicit, or fully elided, references to lifetimes, like the
327 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
328 /// or `Ref<'_, T>`. These often behave the same, but not always:
330 /// - certain usages of implicit references are deprecated, like
331 /// `Ref<T>`, and we sometimes just give hard errors in those cases
333 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
334 /// the same as `Box<dyn Foo + '_>`.
336 /// We describe the effects of the various modes in terms of three cases:
338 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
339 /// of a `&` (e.g., the missing lifetime in something like `&T`)
340 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
341 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
342 /// elided bounds follow special rules. Note that this only covers
343 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
344 /// '_>` is a case of "modern" elision.
345 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
346 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
347 /// non-deprecated equivalent.
349 /// Currently, the handling of lifetime elision is somewhat spread out
350 /// between HIR lowering and -- as described below -- the
351 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
352 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
353 /// everything into HIR lowering.
354 #[derive(Copy, Clone, Debug)]
355 enum AnonymousLifetimeMode {
356 /// For **Modern** cases, create a new anonymous region parameter
357 /// and reference that.
359 /// For **Dyn Bound** cases, pass responsibility to
360 /// `resolve_lifetime` code.
362 /// For **Deprecated** cases, report an error.
365 /// Give a hard error when either `&` or `'_` is written. Used to
366 /// rule out things like `where T: Foo<'_>`. Does not imply an
367 /// error on default object bounds (e.g., `Box<dyn Foo>`).
370 /// Pass responsibility to `resolve_lifetime` code for all cases.
374 struct ImplTraitTypeIdVisitor<'a> {
375 ids: &'a mut SmallVec<[NodeId; 1]>,
378 impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> {
379 fn visit_ty(&mut self, ty: &Ty) {
381 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
383 TyKind::ImplTrait(id, _) => self.ids.push(id),
386 visit::walk_ty(self, ty);
389 fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) {
390 if let Some(ref p) = path_segment.args {
391 if let GenericArgs::Parenthesized(_) = **p {
395 visit::walk_path_segment(self, path_span, path_segment)
399 impl<'a, 'hir> LoweringContext<'a, 'hir> {
400 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
401 /// Full-crate AST visitor that inserts into a fresh
402 /// `LoweringContext` any information that may be
403 /// needed from arbitrary locations in the crate,
404 /// e.g., the number of lifetime generic parameters
405 /// declared for every type and trait definition.
406 struct MiscCollector<'tcx, 'lowering, 'hir> {
407 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
408 hir_id_owner: Option<NodeId>,
411 impl MiscCollector<'_, '_, '_> {
412 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
414 UseTreeKind::Simple(_, id1, id2) => {
415 for &id in &[id1, id2] {
416 self.lctx.resolver.definitions().create_def_with_parent(
423 self.lctx.allocate_hir_id_counter(id);
426 UseTreeKind::Glob => (),
427 UseTreeKind::Nested(ref trees) => {
428 for &(ref use_tree, id) in trees {
429 let hir_id = self.lctx.allocate_hir_id_counter(id);
430 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
436 fn with_hir_id_owner<T>(
438 owner: Option<NodeId>,
439 f: impl FnOnce(&mut Self) -> T,
441 let old = mem::replace(&mut self.hir_id_owner, owner);
443 self.hir_id_owner = old;
448 impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> {
449 fn visit_pat(&mut self, p: &'tcx Pat) {
450 if let PatKind::Paren(..) | PatKind::Rest = p.kind {
451 // Doesn't generate a HIR node
452 } else if let Some(owner) = self.hir_id_owner {
453 self.lctx.lower_node_id_with_owner(p.id, owner);
456 visit::walk_pat(self, p)
459 fn visit_item(&mut self, item: &'tcx Item) {
460 let hir_id = self.lctx.allocate_hir_id_counter(item.id);
463 ItemKind::Struct(_, ref generics)
464 | ItemKind::Union(_, ref generics)
465 | ItemKind::Enum(_, ref generics)
466 | ItemKind::TyAlias(_, ref generics)
467 | ItemKind::Trait(_, _, ref generics, ..) => {
468 let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
472 .filter(|param| match param.kind {
473 ast::GenericParamKind::Lifetime { .. } => true,
477 self.lctx.type_def_lifetime_params.insert(def_id, count);
479 ItemKind::Use(ref use_tree) => {
480 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
485 self.with_hir_id_owner(Some(item.id), |this| {
486 visit::walk_item(this, item);
490 fn visit_trait_item(&mut self, item: &'tcx AssocItem) {
491 self.lctx.allocate_hir_id_counter(item.id);
494 AssocItemKind::Fn(_, None) => {
495 // Ignore patterns in trait methods without bodies
496 self.with_hir_id_owner(None, |this| visit::walk_trait_item(this, item));
498 _ => self.with_hir_id_owner(Some(item.id), |this| {
499 visit::walk_trait_item(this, item);
504 fn visit_impl_item(&mut self, item: &'tcx AssocItem) {
505 self.lctx.allocate_hir_id_counter(item.id);
506 self.with_hir_id_owner(Some(item.id), |this| {
507 visit::walk_impl_item(this, item);
511 fn visit_foreign_item(&mut self, i: &'tcx ForeignItem) {
512 // Ignore patterns in foreign items
513 self.with_hir_id_owner(None, |this| visit::walk_foreign_item(this, i));
516 fn visit_ty(&mut self, t: &'tcx Ty) {
518 // Mirrors the case in visit::walk_ty
519 TyKind::BareFn(ref f) => {
520 walk_list!(self, visit_generic_param, &f.generic_params);
521 // Mirrors visit::walk_fn_decl
522 for parameter in &f.decl.inputs {
523 // We don't lower the ids of argument patterns
524 self.with_hir_id_owner(None, |this| {
525 this.visit_pat(¶meter.pat);
527 self.visit_ty(¶meter.ty)
529 self.visit_fn_ret_ty(&f.decl.output)
531 _ => visit::walk_ty(self, t),
536 self.lower_node_id(CRATE_NODE_ID);
537 debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
539 visit::walk_crate(&mut MiscCollector { lctx: &mut self, hir_id_owner: None }, c);
540 visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c);
542 let module = self.lower_mod(&c.module);
543 let attrs = self.lower_attrs(&c.attrs);
544 let body_ids = body_ids(&self.bodies);
546 self.resolver.definitions().init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
552 exported_macros: self.arena.alloc_from_iter(self.exported_macros),
553 non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs),
555 trait_items: self.trait_items,
556 impl_items: self.impl_items,
559 trait_impls: self.trait_impls,
560 modules: self.modules,
564 fn insert_item(&mut self, item: hir::Item<'hir>) {
565 let id = item.hir_id;
566 // FIXME: Use `debug_asset-rt`.
567 assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0));
568 self.items.insert(id, item);
569 self.modules.get_mut(&self.current_module).unwrap().items.insert(id);
572 fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId {
573 // Set up the counter if needed.
574 self.item_local_id_counters.entry(owner).or_insert(0);
575 // Always allocate the first `HirId` for the owner itself.
576 let lowered = self.lower_node_id_with_owner(owner, owner);
577 debug_assert_eq!(lowered.local_id.as_u32(), 0);
581 fn lower_node_id_generic(
584 alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId,
586 if ast_node_id == DUMMY_NODE_ID {
587 return hir::DUMMY_HIR_ID;
590 let min_size = ast_node_id.as_usize() + 1;
592 if min_size > self.node_id_to_hir_id.len() {
593 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
596 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
598 if existing_hir_id == hir::DUMMY_HIR_ID {
599 // Generate a new `HirId`.
600 let hir_id = alloc_hir_id(self);
601 self.node_id_to_hir_id[ast_node_id] = hir_id;
609 fn with_hir_id_owner<T>(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T {
611 .item_local_id_counters
612 .insert(owner, HIR_ID_COUNTER_LOCKED)
613 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
614 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
615 self.current_hir_id_owner.push((def_index, counter));
617 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
619 debug_assert!(def_index == new_def_index);
620 debug_assert!(new_counter >= counter);
622 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
623 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
627 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
628 /// the `LoweringContext`'s `NodeId => HirId` map.
629 /// Take care not to call this method if the resulting `HirId` is then not
630 /// actually used in the HIR, as that would trigger an assertion in the
631 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
632 /// properly. Calling the method twice with the same `NodeId` is fine though.
633 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
634 self.lower_node_id_generic(ast_node_id, |this| {
635 let &mut (def_index, ref mut local_id_counter) =
636 this.current_hir_id_owner.last_mut().unwrap();
637 let local_id = *local_id_counter;
638 *local_id_counter += 1;
639 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
643 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
644 self.lower_node_id_generic(ast_node_id, |this| {
645 let local_id_counter = this
646 .item_local_id_counters
648 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
649 let local_id = *local_id_counter;
651 // We want to be sure not to modify the counter in the map while it
652 // is also on the stack. Otherwise we'll get lost updates when writing
653 // back from the stack to the map.
654 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
656 *local_id_counter += 1;
657 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
658 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
659 that do not belong to the current owner",
662 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
666 fn next_id(&mut self) -> hir::HirId {
667 let node_id = self.resolver.next_node_id();
668 self.lower_node_id(node_id)
671 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
673 self.lower_node_id_generic(id, |_| {
674 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
679 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
680 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
681 if pr.unresolved_segments() != 0 {
682 bug!("path not fully resolved: {:?}", pr);
688 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
689 self.resolver.get_import_res(id).present_items()
692 fn diagnostic(&self) -> &rustc_errors::Handler {
693 self.sess.diagnostic()
696 /// Reuses the span but adds information like the kind of the desugaring and features that are
697 /// allowed inside this span.
698 fn mark_span_with_reason(
700 reason: DesugaringKind,
702 allow_internal_unstable: Option<Lrc<[Symbol]>>,
704 span.fresh_expansion(ExpnData {
705 allow_internal_unstable,
706 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
710 fn with_anonymous_lifetime_mode<R>(
712 anonymous_lifetime_mode: AnonymousLifetimeMode,
713 op: impl FnOnce(&mut Self) -> R,
716 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
717 anonymous_lifetime_mode,
719 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
720 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
721 let result = op(self);
722 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
724 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
725 old_anonymous_lifetime_mode
730 /// Creates a new `hir::GenericParam` for every new lifetime and
731 /// type parameter encountered while evaluating `f`. Definitions
732 /// are created with the parent provided. If no `parent_id` is
733 /// provided, no definitions will be returned.
735 /// Presuming that in-band lifetimes are enabled, then
736 /// `self.anonymous_lifetime_mode` will be updated to match the
737 /// parameter while `f` is running (and restored afterwards).
738 fn collect_in_band_defs<T>(
741 anonymous_lifetime_mode: AnonymousLifetimeMode,
742 f: impl FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
743 ) -> (Vec<hir::GenericParam<'hir>>, T) {
744 assert!(!self.is_collecting_in_band_lifetimes);
745 assert!(self.lifetimes_to_define.is_empty());
746 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
748 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
749 self.is_collecting_in_band_lifetimes = true;
751 let (in_band_ty_params, res) = f(self);
753 self.is_collecting_in_band_lifetimes = false;
754 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
756 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
758 let params = lifetimes_to_define
760 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
761 .chain(in_band_ty_params.into_iter())
767 /// Converts a lifetime into a new generic parameter.
768 fn lifetime_to_generic_param(
772 parent_index: DefIndex,
773 ) -> hir::GenericParam<'hir> {
774 let node_id = self.resolver.next_node_id();
776 // Get the name we'll use to make the def-path. Note
777 // that collisions are ok here and this shouldn't
778 // really show up for end-user.
779 let (str_name, kind) = match hir_name {
780 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
781 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
782 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
785 // Add a definition for the in-band lifetime def.
786 self.resolver.definitions().create_def_with_parent(
789 DefPathData::LifetimeNs(str_name),
795 hir_id: self.lower_node_id(node_id),
800 pure_wrt_drop: false,
801 kind: hir::GenericParamKind::Lifetime { kind },
805 /// When there is a reference to some lifetime `'a`, and in-band
806 /// lifetimes are enabled, then we want to push that lifetime into
807 /// the vector of names to define later. In that case, it will get
808 /// added to the appropriate generics.
809 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
810 if !self.is_collecting_in_band_lifetimes {
814 if !self.sess.features_untracked().in_band_lifetimes {
818 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
822 let hir_name = ParamName::Plain(ident);
824 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
829 self.lifetimes_to_define.push((ident.span, hir_name));
832 /// When we have either an elided or `'_` lifetime in an impl
833 /// header, we convert it to an in-band lifetime.
834 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
835 assert!(self.is_collecting_in_band_lifetimes);
836 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
837 let hir_name = ParamName::Fresh(index);
838 self.lifetimes_to_define.push((span, hir_name));
842 // Evaluates `f` with the lifetimes in `params` in-scope.
843 // This is used to track which lifetimes have already been defined, and
844 // which are new in-band lifetimes that need to have a definition created
846 fn with_in_scope_lifetime_defs<T>(
848 params: &[GenericParam],
849 f: impl FnOnce(&mut Self) -> T,
851 let old_len = self.in_scope_lifetimes.len();
852 let lt_def_names = params.iter().filter_map(|param| match param.kind {
853 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
856 self.in_scope_lifetimes.extend(lt_def_names);
860 self.in_scope_lifetimes.truncate(old_len);
864 /// Appends in-band lifetime defs and argument-position `impl
865 /// Trait` defs to the existing set of generics.
867 /// Presuming that in-band lifetimes are enabled, then
868 /// `self.anonymous_lifetime_mode` will be updated to match the
869 /// parameter while `f` is running (and restored afterwards).
870 fn add_in_band_defs<T>(
874 anonymous_lifetime_mode: AnonymousLifetimeMode,
875 f: impl FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
876 ) -> (hir::Generics<'hir>, T) {
877 let (in_band_defs, (mut lowered_generics, res)) =
878 self.with_in_scope_lifetime_defs(&generics.params, |this| {
879 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
880 let mut params = Vec::new();
881 // Note: it is necessary to lower generics *before* calling `f`.
882 // When lowering `async fn`, there's a final step when lowering
883 // the return type that assumes that all in-scope lifetimes have
884 // already been added to either `in_scope_lifetimes` or
885 // `lifetimes_to_define`. If we swapped the order of these two,
886 // in-band-lifetimes introduced by generics or where-clauses
887 // wouldn't have been added yet.
889 this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params));
890 let res = f(this, &mut params);
891 (params, (generics, res))
895 let mut lowered_params: Vec<_> =
896 lowered_generics.params.into_iter().chain(in_band_defs).collect();
898 // FIXME(const_generics): the compiler doesn't always cope with
899 // unsorted generic parameters at the moment, so we make sure
900 // that they're ordered correctly here for now. (When we chain
901 // the `in_band_defs`, we might make the order unsorted.)
902 lowered_params.sort_by_key(|param| match param.kind {
903 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
904 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
905 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
908 lowered_generics.params = lowered_params.into();
910 let lowered_generics = lowered_generics.into_generics(self.arena);
911 (lowered_generics, res)
914 fn with_dyn_type_scope<T>(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T {
915 let was_in_dyn_type = self.is_in_dyn_type;
916 self.is_in_dyn_type = in_scope;
918 let result = f(self);
920 self.is_in_dyn_type = was_in_dyn_type;
925 fn with_new_scopes<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> T {
926 let was_in_loop_condition = self.is_in_loop_condition;
927 self.is_in_loop_condition = false;
929 let catch_scopes = mem::take(&mut self.catch_scopes);
930 let loop_scopes = mem::take(&mut self.loop_scopes);
932 self.catch_scopes = catch_scopes;
933 self.loop_scopes = loop_scopes;
935 self.is_in_loop_condition = was_in_loop_condition;
940 fn def_key(&mut self, id: DefId) -> DefKey {
942 self.resolver.definitions().def_key(id.index)
944 self.resolver.cstore().def_key(id)
948 fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
949 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
952 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
953 // Note that we explicitly do not walk the path. Since we don't really
954 // lower attributes (we use the AST version) there is nowhere to keep
955 // the `HirId`s. We don't actually need HIR version of attributes anyway.
956 let kind = match attr.kind {
957 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
958 path: item.path.clone(),
959 args: self.lower_mac_args(&item.args),
961 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
964 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
967 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
969 MacArgs::Empty => MacArgs::Empty,
970 MacArgs::Delimited(dspan, delim, ref tokens) => {
971 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
973 MacArgs::Eq(eq_span, ref tokens) => {
974 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
979 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
980 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
983 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
985 TokenTree::Token(token) => self.lower_token(token),
986 TokenTree::Delimited(span, delim, tts) => {
987 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
992 fn lower_token(&mut self, token: Token) -> TokenStream {
994 token::Interpolated(nt) => {
995 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
996 self.lower_token_stream(tts)
998 _ => TokenTree::Token(token).into(),
1002 /// Given an associated type constraint like one of these:
1005 /// T: Iterator<Item: Debug>
1007 /// T: Iterator<Item = Debug>
1011 /// returns a `hir::TypeBinding` representing `Item`.
1012 fn lower_assoc_ty_constraint(
1014 constraint: &AssocTyConstraint,
1015 itctx: ImplTraitContext<'_, 'hir>,
1016 ) -> hir::TypeBinding<'hir> {
1017 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1019 let kind = match constraint.kind {
1020 AssocTyConstraintKind::Equality { ref ty } => {
1021 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1023 AssocTyConstraintKind::Bound { ref bounds } => {
1024 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1025 let (desugar_to_impl_trait, itctx) = match itctx {
1026 // We are in the return position:
1028 // fn foo() -> impl Iterator<Item: Debug>
1032 // fn foo() -> impl Iterator<Item = impl Debug>
1033 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1035 // We are in the argument position, but within a dyn type:
1037 // fn foo(x: dyn Iterator<Item: Debug>)
1041 // fn foo(x: dyn Iterator<Item = impl Debug>)
1042 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1044 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1045 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1046 // "impl trait context" to permit `impl Debug` in this position (it desugars
1047 // then to an opaque type).
1049 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1050 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1051 (true, ImplTraitContext::OpaqueTy(None))
1054 // We are in the parameter position, but not within a dyn type:
1056 // fn foo(x: impl Iterator<Item: Debug>)
1058 // so we leave it as is and this gets expanded in astconv to a bound like
1059 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1061 _ => (false, itctx),
1064 if desugar_to_impl_trait {
1065 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1066 // constructing the HIR for `impl bounds...` and then lowering that.
1068 let impl_trait_node_id = self.resolver.next_node_id();
1069 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1070 self.resolver.definitions().create_def_with_parent(
1073 DefPathData::ImplTrait,
1078 self.with_dyn_type_scope(false, |this| {
1079 let node_id = this.resolver.next_node_id();
1080 let ty = this.lower_ty(
1083 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1084 span: constraint.span,
1089 hir::TypeBindingKind::Equality { ty }
1092 // Desugar `AssocTy: Bounds` into a type binding where the
1093 // later desugars into a trait predicate.
1094 let bounds = self.lower_param_bounds(bounds, itctx);
1096 hir::TypeBindingKind::Constraint { bounds }
1102 hir_id: self.lower_node_id(constraint.id),
1103 ident: constraint.ident,
1105 span: constraint.span,
1109 fn lower_generic_arg(
1111 arg: &ast::GenericArg,
1112 itctx: ImplTraitContext<'_, 'hir>,
1113 ) -> hir::GenericArg<'hir> {
1115 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1116 ast::GenericArg::Type(ty) => {
1117 // We parse const arguments as path types as we cannot distiguish them durring
1118 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1119 // type and value namespaces. If we resolved the path in the value namespace, we
1120 // transform it into a generic const argument.
1121 if let TyKind::Path(ref qself, ref path) = ty.kind {
1122 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1123 let res = partial_res.base_res();
1124 if !res.matches_ns(Namespace::TypeNS) {
1126 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1130 // Construct a AnonConst where the expr is the "ty"'s path.
1132 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1133 let node_id = self.resolver.next_node_id();
1135 // Add a definition for the in-band const def.
1136 self.resolver.definitions().create_def_with_parent(
1139 DefPathData::AnonConst,
1144 let path_expr = Expr {
1146 kind: ExprKind::Path(qself.clone(), path.clone()),
1148 attrs: AttrVec::new(),
1151 let ct = self.with_new_scopes(|this| hir::AnonConst {
1152 hir_id: this.lower_node_id(node_id),
1153 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1155 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1159 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1161 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1162 value: self.lower_anon_const(&ct),
1163 span: ct.value.span,
1168 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1169 self.arena.alloc(self.lower_ty_direct(t, itctx))
1175 qself: &Option<QSelf>,
1177 param_mode: ParamMode,
1178 itctx: ImplTraitContext<'_, 'hir>,
1179 ) -> hir::Ty<'hir> {
1180 let id = self.lower_node_id(t.id);
1181 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1182 let ty = self.ty_path(id, t.span, qpath);
1183 if let hir::TyKind::TraitObject(..) = ty.kind {
1184 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1189 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1190 hir::Ty { hir_id: self.next_id(), kind, span }
1193 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1194 self.ty(span, hir::TyKind::Tup(tys))
1197 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1198 let kind = match t.kind {
1199 TyKind::Infer => hir::TyKind::Infer,
1200 TyKind::Err => hir::TyKind::Err,
1201 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1202 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1203 TyKind::Rptr(ref region, ref mt) => {
1204 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1205 let lifetime = match *region {
1206 Some(ref lt) => self.lower_lifetime(lt),
1207 None => self.elided_ref_lifetime(span),
1209 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1211 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1212 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1213 hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy {
1214 generic_params: this.lower_generic_params(
1216 &NodeMap::default(),
1217 ImplTraitContext::disallowed(),
1219 unsafety: f.unsafety,
1220 abi: this.lower_extern(f.ext),
1221 decl: this.lower_fn_decl(&f.decl, None, false, None),
1222 param_names: this.lower_fn_params_to_names(&f.decl),
1226 TyKind::Never => hir::TyKind::Never,
1227 TyKind::Tup(ref tys) => {
1228 hir::TyKind::Tup(self.arena.alloc_from_iter(
1229 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1232 TyKind::Paren(ref ty) => {
1233 return self.lower_ty_direct(ty, itctx);
1235 TyKind::Path(ref qself, ref path) => {
1236 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1238 TyKind::ImplicitSelf => {
1239 let res = self.expect_full_res(t.id);
1240 let res = self.lower_res(res);
1241 hir::TyKind::Path(hir::QPath::Resolved(
1243 self.arena.alloc(hir::Path {
1245 segments: arena_vec![self; hir::PathSegment::from_ident(
1246 Ident::with_dummy_span(kw::SelfUpper)
1252 TyKind::Array(ref ty, ref length) => {
1253 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1255 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1256 TyKind::TraitObject(ref bounds, kind) => {
1257 let mut lifetime_bound = None;
1258 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1260 this.arena.alloc_from_iter(bounds.iter().filter_map(
1261 |bound| match *bound {
1262 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1263 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1265 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1266 GenericBound::Outlives(ref lifetime) => {
1267 if lifetime_bound.is_none() {
1268 lifetime_bound = Some(this.lower_lifetime(lifetime));
1274 let lifetime_bound =
1275 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1276 (bounds, lifetime_bound)
1278 if kind != TraitObjectSyntax::Dyn {
1279 self.maybe_lint_bare_trait(t.span, t.id, false);
1281 hir::TyKind::TraitObject(bounds, lifetime_bound)
1283 TyKind::ImplTrait(def_node_id, ref bounds) => {
1286 ImplTraitContext::OpaqueTy(fn_def_id) => {
1287 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1288 this.lower_param_bounds(bounds, itctx)
1291 ImplTraitContext::Universal(in_band_ty_params) => {
1292 // Add a definition for the in-band `Param`.
1294 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1296 let hir_bounds = self.lower_param_bounds(
1298 ImplTraitContext::Universal(in_band_ty_params),
1300 // Set the name to `impl Bound1 + Bound2`.
1301 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1302 in_band_ty_params.push(hir::GenericParam {
1303 hir_id: self.lower_node_id(def_node_id),
1304 name: ParamName::Plain(ident),
1305 pure_wrt_drop: false,
1309 kind: hir::GenericParamKind::Type {
1311 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1315 hir::TyKind::Path(hir::QPath::Resolved(
1317 self.arena.alloc(hir::Path {
1319 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1320 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1324 ImplTraitContext::Disallowed(pos) => {
1325 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1326 "bindings or function and inherent method return types"
1328 "function and inherent method return types"
1330 let mut err = struct_span_err!(
1334 "`impl Trait` not allowed outside of {}",
1337 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1340 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1341 attributes to enable",
1349 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1350 TyKind::CVarArgs => {
1351 self.sess.delay_span_bug(
1353 "`TyKind::CVarArgs` should have been handled elsewhere",
1359 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1362 fn lower_opaque_impl_trait(
1365 fn_def_id: Option<DefId>,
1366 opaque_ty_node_id: NodeId,
1367 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1368 ) -> hir::TyKind<'hir> {
1370 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1371 fn_def_id, opaque_ty_node_id, span,
1374 // Make sure we know that some funky desugaring has been going on here.
1375 // This is a first: there is code in other places like for loop
1376 // desugaring that explicitly states that we don't want to track that.
1377 // Not tracking it makes lints in rustc and clippy very fragile, as
1378 // frequently opened issues show.
1379 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1381 let opaque_ty_def_index =
1382 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1384 self.allocate_hir_id_counter(opaque_ty_node_id);
1386 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1388 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1390 opaque_ty_def_index,
1394 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1396 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1398 self.with_hir_id_owner(opaque_ty_node_id, move |lctx| {
1399 let opaque_ty_item = hir::OpaqueTy {
1400 generics: hir::Generics {
1401 params: lifetime_defs,
1402 where_clause: hir::WhereClause { predicates: &[], span },
1406 impl_trait_fn: fn_def_id,
1407 origin: hir::OpaqueTyOrigin::FnReturn,
1410 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1412 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1414 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1415 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1419 /// Registers a new opaque type with the proper `NodeId`s and
1420 /// returns the lowered node-ID for the opaque type.
1421 fn generate_opaque_type(
1423 opaque_ty_node_id: NodeId,
1424 opaque_ty_item: hir::OpaqueTy<'hir>,
1426 opaque_ty_span: Span,
1428 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1429 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1430 // Generate an `type Foo = impl Trait;` declaration.
1431 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1432 let opaque_ty_item = hir::Item {
1433 hir_id: opaque_ty_id,
1434 ident: Ident::invalid(),
1435 attrs: Default::default(),
1436 kind: opaque_ty_item_kind,
1437 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1438 span: opaque_ty_span,
1441 // Insert the item into the global item list. This usually happens
1442 // automatically for all AST items. But this opaque type item
1443 // does not actually exist in the AST.
1444 self.insert_item(opaque_ty_item);
1448 fn lifetimes_from_impl_trait_bounds(
1450 opaque_ty_id: NodeId,
1451 parent_index: DefIndex,
1452 bounds: hir::GenericBounds<'hir>,
1453 ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) {
1455 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1456 parent_index={:?}, \
1458 opaque_ty_id, parent_index, bounds,
1461 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1462 // appear in the bounds, excluding lifetimes that are created within the bounds.
1463 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1464 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1465 context: &'r mut LoweringContext<'a, 'hir>,
1467 opaque_ty_id: NodeId,
1468 collect_elided_lifetimes: bool,
1469 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1470 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1471 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1472 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1475 impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1478 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
1479 intravisit::NestedVisitorMap::None
1482 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1483 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1484 if parameters.parenthesized {
1485 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1486 self.collect_elided_lifetimes = false;
1487 intravisit::walk_generic_args(self, span, parameters);
1488 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1490 intravisit::walk_generic_args(self, span, parameters);
1494 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1495 // Don't collect elided lifetimes used inside of `fn()` syntax.
1496 if let hir::TyKind::BareFn(_) = t.kind {
1497 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1498 self.collect_elided_lifetimes = false;
1500 // Record the "stack height" of `for<'a>` lifetime bindings
1501 // to be able to later fully undo their introduction.
1502 let old_len = self.currently_bound_lifetimes.len();
1503 intravisit::walk_ty(self, t);
1504 self.currently_bound_lifetimes.truncate(old_len);
1506 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1508 intravisit::walk_ty(self, t)
1512 fn visit_poly_trait_ref(
1514 trait_ref: &'v hir::PolyTraitRef<'v>,
1515 modifier: hir::TraitBoundModifier,
1517 // Record the "stack height" of `for<'a>` lifetime bindings
1518 // to be able to later fully undo their introduction.
1519 let old_len = self.currently_bound_lifetimes.len();
1520 intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1521 self.currently_bound_lifetimes.truncate(old_len);
1524 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1525 // Record the introduction of 'a in `for<'a> ...`.
1526 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1527 // Introduce lifetimes one at a time so that we can handle
1528 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1529 let lt_name = hir::LifetimeName::Param(param.name);
1530 self.currently_bound_lifetimes.push(lt_name);
1533 intravisit::walk_generic_param(self, param);
1536 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1537 let name = match lifetime.name {
1538 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1539 if self.collect_elided_lifetimes {
1540 // Use `'_` for both implicit and underscore lifetimes in
1541 // `type Foo<'_> = impl SomeTrait<'_>;`.
1542 hir::LifetimeName::Underscore
1547 hir::LifetimeName::Param(_) => lifetime.name,
1549 // Refers to some other lifetime that is "in
1550 // scope" within the type.
1551 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1553 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1556 if !self.currently_bound_lifetimes.contains(&name)
1557 && !self.already_defined_lifetimes.contains(&name)
1559 self.already_defined_lifetimes.insert(name);
1561 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1562 hir_id: self.context.next_id(),
1563 span: lifetime.span,
1567 let def_node_id = self.context.resolver.next_node_id();
1569 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1570 self.context.resolver.definitions().create_def_with_parent(
1573 DefPathData::LifetimeNs(name.ident().name),
1578 let (name, kind) = match name {
1579 hir::LifetimeName::Underscore => (
1580 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1581 hir::LifetimeParamKind::Elided,
1583 hir::LifetimeName::Param(param_name) => {
1584 (param_name, hir::LifetimeParamKind::Explicit)
1586 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1589 self.output_lifetime_params.push(hir::GenericParam {
1592 span: lifetime.span,
1593 pure_wrt_drop: false,
1596 kind: hir::GenericParamKind::Lifetime { kind },
1602 let mut lifetime_collector = ImplTraitLifetimeCollector {
1604 parent: parent_index,
1606 collect_elided_lifetimes: true,
1607 currently_bound_lifetimes: Vec::new(),
1608 already_defined_lifetimes: FxHashSet::default(),
1609 output_lifetimes: Vec::new(),
1610 output_lifetime_params: Vec::new(),
1613 for bound in bounds {
1614 intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1617 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1621 self.arena.alloc_from_iter(output_lifetimes),
1622 self.arena.alloc_from_iter(output_lifetime_params),
1629 qself: &Option<QSelf>,
1631 param_mode: ParamMode,
1632 mut itctx: ImplTraitContext<'_, 'hir>,
1633 ) -> hir::QPath<'hir> {
1634 let qself_position = qself.as_ref().map(|q| q.position);
1635 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1638 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1640 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1641 let path = self.arena.alloc(hir::Path {
1642 res: self.lower_res(partial_res.base_res()),
1643 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1645 let param_mode = match (qself_position, param_mode) {
1646 (Some(j), ParamMode::Optional) if i < j => {
1647 // This segment is part of the trait path in a
1648 // qualified path - one of `a`, `b` or `Trait`
1649 // in `<X as a::b::Trait>::T::U::method`.
1655 // Figure out if this is a type/trait segment,
1656 // which may need lifetime elision performed.
1657 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1658 krate: def_id.krate,
1659 index: this.def_key(def_id).parent.expect("missing parent"),
1661 let type_def_id = match partial_res.base_res() {
1662 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1663 Some(parent_def_id(self, def_id))
1665 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1666 Some(parent_def_id(self, def_id))
1668 Res::Def(DefKind::Struct, def_id)
1669 | Res::Def(DefKind::Union, def_id)
1670 | Res::Def(DefKind::Enum, def_id)
1671 | Res::Def(DefKind::TyAlias, def_id)
1672 | Res::Def(DefKind::Trait, def_id)
1673 if i + 1 == proj_start =>
1679 let parenthesized_generic_args = match partial_res.base_res() {
1680 // `a::b::Trait(Args)`
1681 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1682 ParenthesizedGenericArgs::Ok
1684 // `a::b::Trait(Args)::TraitItem`
1685 Res::Def(DefKind::Method, _)
1686 | Res::Def(DefKind::AssocConst, _)
1687 | Res::Def(DefKind::AssocTy, _)
1688 if i + 2 == proj_start =>
1690 ParenthesizedGenericArgs::Ok
1692 // Avoid duplicated errors.
1693 Res::Err => ParenthesizedGenericArgs::Ok,
1695 _ => ParenthesizedGenericArgs::Err,
1698 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1699 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1702 assert!(!def_id.is_local());
1703 let item_generics = self
1706 .item_generics_cloned_untracked(def_id, self.sess);
1707 let n = item_generics.own_counts().lifetimes;
1708 self.type_def_lifetime_params.insert(def_id, n);
1711 self.lower_path_segment(
1716 parenthesized_generic_args,
1725 // Simple case, either no projections, or only fully-qualified.
1726 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1727 if partial_res.unresolved_segments() == 0 {
1728 return hir::QPath::Resolved(qself, path);
1731 // Create the innermost type that we're projecting from.
1732 let mut ty = if path.segments.is_empty() {
1733 // If the base path is empty that means there exists a
1734 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1735 qself.expect("missing QSelf for <T>::...")
1737 // Otherwise, the base path is an implicit `Self` type path,
1738 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1739 // `<I as Iterator>::Item::default`.
1740 let new_id = self.next_id();
1741 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1744 // Anything after the base path are associated "extensions",
1745 // out of which all but the last one are associated types,
1746 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1747 // * base path is `std::vec::Vec<T>`
1748 // * "extensions" are `IntoIter`, `Item` and `clone`
1749 // * type nodes are:
1750 // 1. `std::vec::Vec<T>` (created above)
1751 // 2. `<std::vec::Vec<T>>::IntoIter`
1752 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1753 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1754 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1755 let segment = self.arena.alloc(self.lower_path_segment(
1760 ParenthesizedGenericArgs::Err,
1764 let qpath = hir::QPath::TypeRelative(ty, segment);
1766 // It's finished, return the extension of the right node type.
1767 if i == p.segments.len() - 1 {
1771 // Wrap the associated extension in another type node.
1772 let new_id = self.next_id();
1773 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1776 // We should've returned in the for loop above.
1779 "lower_qpath: no final extension segment in {}..{}",
1785 fn lower_path_extra(
1789 param_mode: ParamMode,
1790 explicit_owner: Option<NodeId>,
1791 ) -> &'hir hir::Path<'hir> {
1792 self.arena.alloc(hir::Path {
1794 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1795 self.lower_path_segment(
1800 ParenthesizedGenericArgs::Err,
1801 ImplTraitContext::disallowed(),
1809 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> &'hir hir::Path<'hir> {
1810 let res = self.expect_full_res(id);
1811 let res = self.lower_res(res);
1812 self.lower_path_extra(res, p, param_mode, None)
1815 fn lower_path_segment(
1818 segment: &PathSegment,
1819 param_mode: ParamMode,
1820 expected_lifetimes: usize,
1821 parenthesized_generic_args: ParenthesizedGenericArgs,
1822 itctx: ImplTraitContext<'_, 'hir>,
1823 explicit_owner: Option<NodeId>,
1824 ) -> hir::PathSegment<'hir> {
1825 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1826 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1827 match **generic_args {
1828 GenericArgs::AngleBracketed(ref data) => {
1829 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1831 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1832 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1833 ParenthesizedGenericArgs::Err => {
1834 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1835 err.span_label(data.span, "only `Fn` traits may use parentheses");
1836 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1837 // Do not suggest going from `Trait()` to `Trait<>`
1838 if data.inputs.len() > 0 {
1839 if let Some(split) = snippet.find('(') {
1840 let trait_name = &snippet[0..split];
1841 let args = &snippet[split + 1..snippet.len() - 1];
1842 err.span_suggestion(
1844 "use angle brackets instead",
1845 format!("{}<{}>", trait_name, args),
1846 Applicability::MaybeIncorrect,
1853 self.lower_angle_bracketed_parameter_data(
1854 &data.as_angle_bracketed_args(),
1865 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1868 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1869 GenericArg::Lifetime(_) => true,
1872 let first_generic_span = generic_args
1876 .chain(generic_args.bindings.iter().map(|b| b.span))
1878 if !generic_args.parenthesized && !has_lifetimes {
1879 generic_args.args = self
1880 .elided_path_lifetimes(path_span, expected_lifetimes)
1881 .map(|lt| GenericArg::Lifetime(lt))
1882 .chain(generic_args.args.into_iter())
1884 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1885 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1886 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1887 let no_bindings = generic_args.bindings.is_empty();
1888 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1889 // If there are no (non-implicit) generic args or associated type
1890 // bindings, our suggestion includes the angle brackets.
1891 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1893 // Otherwise (sorry, this is kind of gross) we need to infer the
1894 // place to splice in the `'_, ` from the generics that do exist.
1895 let first_generic_span = first_generic_span
1896 .expect("already checked that non-lifetime args or bindings exist");
1897 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1899 match self.anonymous_lifetime_mode {
1900 // In create-parameter mode we error here because we don't want to support
1901 // deprecated impl elision in new features like impl elision and `async fn`,
1902 // both of which work using the `CreateParameter` mode:
1904 // impl Foo for std::cell::Ref<u32> // note lack of '_
1905 // async fn foo(_: std::cell::Ref<u32>) { ... }
1906 AnonymousLifetimeMode::CreateParameter => {
1907 let mut err = struct_span_err!(
1911 "implicit elided lifetime not allowed here"
1913 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1924 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1925 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1926 ELIDED_LIFETIMES_IN_PATHS,
1929 "hidden lifetime parameters in types are deprecated",
1930 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1943 let res = self.expect_full_res(segment.id);
1944 let id = if let Some(owner) = explicit_owner {
1945 self.lower_node_id_with_owner(segment.id, owner)
1947 self.lower_node_id(segment.id)
1950 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1951 segment.ident, segment.id, id,
1955 ident: segment.ident,
1957 res: Some(self.lower_res(res)),
1959 args: if generic_args.is_empty() {
1962 Some(self.arena.alloc(generic_args.into_generic_args(self.arena)))
1967 fn lower_angle_bracketed_parameter_data(
1969 data: &AngleBracketedArgs,
1970 param_mode: ParamMode,
1971 mut itctx: ImplTraitContext<'_, 'hir>,
1972 ) -> (GenericArgsCtor<'hir>, bool) {
1973 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1974 let has_non_lt_args = args.iter().any(|arg| match arg {
1975 ast::GenericArg::Lifetime(_) => false,
1976 ast::GenericArg::Type(_) => true,
1977 ast::GenericArg::Const(_) => true,
1981 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
1982 bindings: self.arena.alloc_from_iter(
1983 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
1985 parenthesized: false,
1987 !has_non_lt_args && param_mode == ParamMode::Optional,
1991 fn lower_parenthesized_parameter_data(
1993 data: &ParenthesizedArgs,
1994 ) -> (GenericArgsCtor<'hir>, bool) {
1995 // Switch to `PassThrough` mode for anonymous lifetimes; this
1996 // means that we permit things like `&Ref<T>`, where `Ref` has
1997 // a hidden lifetime parameter. This is needed for backwards
1998 // compatibility, even in contexts like an impl header where
1999 // we generally don't permit such things (see #51008).
2000 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2001 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2002 let inputs = this.arena.alloc_from_iter(
2003 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2005 let output_ty = match output {
2006 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2007 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2009 let args = smallvec![GenericArg::Type(this.ty_tup(span, inputs))];
2010 let binding = hir::TypeBinding {
2011 hir_id: this.next_id(),
2012 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2013 span: output_ty.span,
2014 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2017 GenericArgsCtor { args, bindings: arena_vec![this; binding], parenthesized: true },
2023 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2024 let mut ids = SmallVec::<[NodeId; 1]>::new();
2025 if self.sess.features_untracked().impl_trait_in_bindings {
2026 if let Some(ref ty) = l.ty {
2027 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2028 visitor.visit_ty(ty);
2031 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2032 let ty = l.ty.as_ref().map(|t| {
2035 if self.sess.features_untracked().impl_trait_in_bindings {
2036 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2038 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2042 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2045 hir_id: self.lower_node_id(l.id),
2047 pat: self.lower_pat(&l.pat),
2050 attrs: l.attrs.clone(),
2051 source: hir::LocalSource::Normal,
2057 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] {
2058 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2059 // as they are not explicit in HIR/Ty function signatures.
2060 // (instead, the `c_variadic` flag is set to `true`)
2061 let mut inputs = &decl.inputs[..];
2062 if decl.c_variadic() {
2063 inputs = &inputs[..inputs.len() - 1];
2065 self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind {
2066 PatKind::Ident(_, ident, _) => ident,
2067 _ => Ident::new(kw::Invalid, param.pat.span),
2071 // Lowers a function declaration.
2073 // `decl`: the unlowered (AST) function declaration.
2074 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2075 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2076 // `make_ret_async` is also `Some`.
2077 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2078 // This guards against trait declarations and implementations where `impl Trait` is
2080 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2081 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2082 // return type `impl Trait` item.
2086 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2087 impl_trait_return_allow: bool,
2088 make_ret_async: Option<NodeId>,
2089 ) -> &'hir hir::FnDecl<'hir> {
2093 in_band_ty_params: {:?}, \
2094 impl_trait_return_allow: {}, \
2095 make_ret_async: {:?})",
2096 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2098 let lt_mode = if make_ret_async.is_some() {
2099 // In `async fn`, argument-position elided lifetimes
2100 // must be transformed into fresh generic parameters so that
2101 // they can be applied to the opaque `impl Trait` return type.
2102 AnonymousLifetimeMode::CreateParameter
2104 self.anonymous_lifetime_mode
2107 let c_variadic = decl.c_variadic();
2109 // Remember how many lifetimes were already around so that we can
2110 // only look at the lifetime parameters introduced by the arguments.
2111 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2112 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2113 // as they are not explicit in HIR/Ty function signatures.
2114 // (instead, the `c_variadic` flag is set to `true`)
2115 let mut inputs = &decl.inputs[..];
2117 inputs = &inputs[..inputs.len() - 1];
2119 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2120 if let Some((_, ibty)) = &mut in_band_ty_params {
2121 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2123 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2128 let output = if let Some(ret_id) = make_ret_async {
2129 self.lower_async_fn_ret_ty(
2131 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2136 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2137 Some((def_id, _)) if impl_trait_return_allow => hir::FunctionRetTy::Return(
2138 self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))),
2140 _ => hir::FunctionRetTy::Return(
2141 self.lower_ty(ty, ImplTraitContext::disallowed()),
2144 FunctionRetTy::Default(span) => hir::FunctionRetTy::DefaultReturn(span),
2148 self.arena.alloc(hir::FnDecl {
2152 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2153 let is_mutable_pat = match arg.pat.kind {
2154 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2155 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2160 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2161 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2162 // Given we are only considering `ImplicitSelf` types, we needn't consider
2163 // the case where we have a mutable pattern to a reference as that would
2164 // no longer be an `ImplicitSelf`.
2165 TyKind::Rptr(_, ref mt)
2166 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2168 hir::ImplicitSelfKind::MutRef
2170 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2171 hir::ImplicitSelfKind::ImmRef
2173 _ => hir::ImplicitSelfKind::None,
2179 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2180 // combined with the following definition of `OpaqueTy`:
2182 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2184 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2185 // `output`: unlowered output type (`T` in `-> T`)
2186 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2187 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2188 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2189 fn lower_async_fn_ret_ty(
2191 output: &FunctionRetTy,
2193 opaque_ty_node_id: NodeId,
2194 ) -> hir::FunctionRetTy<'hir> {
2196 "lower_async_fn_ret_ty(\
2199 opaque_ty_node_id={:?})",
2200 output, fn_def_id, opaque_ty_node_id,
2203 let span = output.span();
2205 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2207 let opaque_ty_def_index =
2208 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2210 self.allocate_hir_id_counter(opaque_ty_node_id);
2212 // When we create the opaque type for this async fn, it is going to have
2213 // to capture all the lifetimes involved in the signature (including in the
2214 // return type). This is done by introducing lifetime parameters for:
2216 // - all the explicitly declared lifetimes from the impl and function itself;
2217 // - all the elided lifetimes in the fn arguments;
2218 // - all the elided lifetimes in the return type.
2220 // So for example in this snippet:
2223 // impl<'a> Foo<'a> {
2224 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2225 // // ^ '0 ^ '1 ^ '2
2226 // // elided lifetimes used below
2231 // we would create an opaque type like:
2234 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2237 // and we would then desugar `bar` to the equivalent of:
2240 // impl<'a> Foo<'a> {
2241 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2245 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2246 // this is because the elided lifetimes from the return type
2247 // should be figured out using the ordinary elision rules, and
2248 // this desugaring achieves that.
2250 // The variable `input_lifetimes_count` tracks the number of
2251 // lifetime parameters to the opaque type *not counting* those
2252 // lifetimes elided in the return type. This includes those
2253 // that are explicitly declared (`in_scope_lifetimes`) and
2254 // those elided lifetimes we found in the arguments (current
2255 // content of `lifetimes_to_define`). Next, we will process
2256 // the return type, which will cause `lifetimes_to_define` to
2258 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2260 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2261 // We have to be careful to get elision right here. The
2262 // idea is that we create a lifetime parameter for each
2263 // lifetime in the return type. So, given a return type
2264 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2265 // Future<Output = &'1 [ &'2 u32 ]>`.
2267 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2268 // hence the elision takes place at the fn site.
2269 let future_bound = this
2270 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2271 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2274 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2276 // Calculate all the lifetimes that should be captured
2277 // by the opaque type. This should include all in-scope
2278 // lifetime parameters, including those defined in-band.
2280 // Note: this must be done after lowering the output type,
2281 // as the output type may introduce new in-band lifetimes.
2282 let lifetime_params: Vec<(Span, ParamName)> = this
2286 .map(|name| (name.ident().span, name))
2287 .chain(this.lifetimes_to_define.iter().cloned())
2290 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2291 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2292 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2294 let generic_params =
2295 this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| {
2296 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
2299 let opaque_ty_item = hir::OpaqueTy {
2300 generics: hir::Generics {
2301 params: generic_params,
2302 where_clause: hir::WhereClause { predicates: &[], span },
2305 bounds: arena_vec![this; future_bound],
2306 impl_trait_fn: Some(fn_def_id),
2307 origin: hir::OpaqueTyOrigin::AsyncFn,
2310 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2312 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2314 (opaque_ty_id, lifetime_params)
2317 // As documented above on the variable
2318 // `input_lifetimes_count`, we need to create the lifetime
2319 // arguments to our opaque type. Continuing with our example,
2320 // we're creating the type arguments for the return type:
2323 // Bar<'a, 'b, '0, '1, '_>
2326 // For the "input" lifetime parameters, we wish to create
2327 // references to the parameters themselves, including the
2328 // "implicit" ones created from parameter types (`'a`, `'b`,
2331 // For the "output" lifetime parameters, we just want to
2333 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2335 .map(|&(span, hir_name)| {
2336 // Input lifetime like `'a` or `'1`:
2337 GenericArg::Lifetime(hir::Lifetime {
2338 hir_id: self.next_id(),
2340 name: hir::LifetimeName::Param(hir_name),
2344 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2345 // Output lifetime like `'_`.
2346 GenericArg::Lifetime(hir::Lifetime {
2347 hir_id: self.next_id(),
2349 name: hir::LifetimeName::Implicit,
2351 let generic_args = self.arena.alloc_from_iter(generic_args);
2353 // Create the `Foo<...>` reference itself. Note that the `type
2354 // Foo = impl Trait` is, internally, created as a child of the
2355 // async fn, so the *type parameters* are inherited. It's
2356 // only the lifetime parameters that we must supply.
2357 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
2358 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2359 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
2362 /// Transforms `-> T` into `Future<Output = T>`
2363 fn lower_async_fn_output_type_to_future_bound(
2365 output: &FunctionRetTy,
2368 ) -> hir::GenericBound<'hir> {
2369 // Compute the `T` in `Future<Output = T>` from the return type.
2370 let output_ty = match output {
2371 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2372 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2376 let future_params = self.arena.alloc(hir::GenericArgs {
2378 bindings: arena_vec![self; hir::TypeBinding {
2379 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2380 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2381 hir_id: self.next_id(),
2384 parenthesized: false,
2387 // ::std::future::Future<future_params>
2389 self.std_path(span, &[sym::future, sym::Future], Some(future_params), false);
2391 hir::GenericBound::Trait(
2393 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2394 bound_generic_params: &[],
2397 hir::TraitBoundModifier::None,
2401 fn lower_param_bound(
2404 itctx: ImplTraitContext<'_, 'hir>,
2405 ) -> hir::GenericBound<'hir> {
2407 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2408 self.lower_poly_trait_ref(ty, itctx),
2409 self.lower_trait_bound_modifier(modifier),
2411 GenericBound::Outlives(ref lifetime) => {
2412 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2417 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2418 let span = l.ident.span;
2420 ident if ident.name == kw::StaticLifetime => {
2421 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2423 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2424 AnonymousLifetimeMode::CreateParameter => {
2425 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2426 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2429 AnonymousLifetimeMode::PassThrough => {
2430 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2433 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2436 self.maybe_collect_in_band_lifetime(ident);
2437 let param_name = ParamName::Plain(ident);
2438 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2443 fn new_named_lifetime(
2447 name: hir::LifetimeName,
2448 ) -> hir::Lifetime {
2449 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2452 fn lower_generic_params_mut<'s>(
2454 params: &'s [GenericParam],
2455 add_bounds: &'s NodeMap<Vec<GenericBound>>,
2456 mut itctx: ImplTraitContext<'s, 'hir>,
2457 ) -> impl Iterator<Item = hir::GenericParam<'hir>> + Captures<'a> + Captures<'s> {
2460 .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2463 fn lower_generic_params(
2465 params: &[GenericParam],
2466 add_bounds: &NodeMap<Vec<GenericBound>>,
2467 itctx: ImplTraitContext<'_, 'hir>,
2468 ) -> &'hir [hir::GenericParam<'hir>] {
2469 self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx))
2472 fn lower_generic_param(
2474 param: &GenericParam,
2475 add_bounds: &NodeMap<Vec<GenericBound>>,
2476 mut itctx: ImplTraitContext<'_, 'hir>,
2477 ) -> hir::GenericParam<'hir> {
2478 let mut bounds: Vec<_> = self
2479 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2480 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2483 let (name, kind) = match param.kind {
2484 GenericParamKind::Lifetime => {
2485 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2486 self.is_collecting_in_band_lifetimes = false;
2489 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2490 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2492 let param_name = match lt.name {
2493 hir::LifetimeName::Param(param_name) => param_name,
2494 hir::LifetimeName::Implicit
2495 | hir::LifetimeName::Underscore
2496 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2497 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2500 "object-lifetime-default should not occur here",
2503 hir::LifetimeName::Error => ParamName::Error,
2507 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2509 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2513 GenericParamKind::Type { ref default, .. } => {
2514 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2515 if !add_bounds.is_empty() {
2516 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2517 bounds.extend(params);
2520 let kind = hir::GenericParamKind::Type {
2523 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2527 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2528 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2532 (hir::ParamName::Plain(param.ident), kind)
2534 GenericParamKind::Const { ref ty } => (
2535 hir::ParamName::Plain(param.ident),
2536 hir::GenericParamKind::Const {
2537 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2543 hir_id: self.lower_node_id(param.id),
2545 span: param.ident.span,
2546 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2547 attrs: self.lower_attrs(¶m.attrs),
2548 bounds: self.arena.alloc_from_iter(bounds),
2556 itctx: ImplTraitContext<'_, 'hir>,
2557 ) -> hir::TraitRef<'hir> {
2558 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2559 hir::QPath::Resolved(None, path) => path,
2560 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2562 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2565 fn lower_poly_trait_ref(
2568 mut itctx: ImplTraitContext<'_, 'hir>,
2569 ) -> hir::PolyTraitRef<'hir> {
2570 let bound_generic_params = self.lower_generic_params(
2571 &p.bound_generic_params,
2572 &NodeMap::default(),
2575 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2576 this.lower_trait_ref(&p.trait_ref, itctx)
2579 hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span }
2582 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2583 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2586 fn lower_param_bounds(
2588 bounds: &[GenericBound],
2589 itctx: ImplTraitContext<'_, 'hir>,
2590 ) -> hir::GenericBounds<'hir> {
2591 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2594 fn lower_param_bounds_mut<'s>(
2596 bounds: &'s [GenericBound],
2597 mut itctx: ImplTraitContext<'s, 'hir>,
2598 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2599 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2602 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2603 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2606 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2607 let mut stmts = vec![];
2608 let mut expr: Option<&'hir _> = None;
2610 for (index, stmt) in b.stmts.iter().enumerate() {
2611 if index == b.stmts.len() - 1 {
2612 if let StmtKind::Expr(ref e) = stmt.kind {
2613 expr = Some(self.lower_expr(e));
2615 stmts.extend(self.lower_stmt(stmt));
2618 stmts.extend(self.lower_stmt(stmt));
2623 hir_id: self.lower_node_id(b.id),
2624 stmts: self.arena.alloc_from_iter(stmts),
2626 rules: self.lower_block_check_mode(&b.rules),
2632 /// Lowers a block directly to an expression, presuming that it
2633 /// has no attributes and is not targeted by a `break`.
2634 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2635 let block = self.lower_block(b, false);
2636 self.expr_block(block, AttrVec::new())
2639 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2640 let node = match p.kind {
2641 PatKind::Wild => hir::PatKind::Wild,
2642 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2643 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2644 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2647 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2648 PatKind::TupleStruct(ref path, ref pats) => {
2649 let qpath = self.lower_qpath(
2653 ParamMode::Optional,
2654 ImplTraitContext::disallowed(),
2656 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2657 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2659 PatKind::Or(ref pats) => {
2660 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2662 PatKind::Path(ref qself, ref path) => {
2663 let qpath = self.lower_qpath(
2667 ParamMode::Optional,
2668 ImplTraitContext::disallowed(),
2670 hir::PatKind::Path(qpath)
2672 PatKind::Struct(ref path, ref fields, etc) => {
2673 let qpath = self.lower_qpath(
2677 ParamMode::Optional,
2678 ImplTraitContext::disallowed(),
2681 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2682 hir_id: self.next_id(),
2684 pat: self.lower_pat(&f.pat),
2685 is_shorthand: f.is_shorthand,
2688 hir::PatKind::Struct(qpath, fs, etc)
2690 PatKind::Tuple(ref pats) => {
2691 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2692 hir::PatKind::Tuple(pats, ddpos)
2694 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2695 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2696 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2697 self.lower_expr(e1),
2698 self.lower_expr(e2),
2699 self.lower_range_end(end),
2701 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2703 // If we reach here the `..` pattern is not semantically allowed.
2704 self.ban_illegal_rest_pat(p.span)
2706 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2707 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2710 self.pat_with_node_id_of(p, node)
2717 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2718 let mut elems = Vec::with_capacity(pats.len());
2719 let mut rest = None;
2721 let mut iter = pats.iter().enumerate();
2722 for (idx, pat) in iter.by_ref() {
2723 // Interpret the first `..` pattern as a sub-tuple pattern.
2724 // Note that unlike for slice patterns,
2725 // where `xs @ ..` is a legal sub-slice pattern,
2726 // it is not a legal sub-tuple pattern.
2728 rest = Some((idx, pat.span));
2731 // It was not a sub-tuple pattern so lower it normally.
2732 elems.push(self.lower_pat(pat));
2735 for (_, pat) in iter {
2736 // There was a previous sub-tuple pattern; make sure we don't allow more...
2738 // ...but there was one again, so error.
2739 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2741 elems.push(self.lower_pat(pat));
2745 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2748 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2749 /// `hir::PatKind::Slice(before, slice, after)`.
2751 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2752 /// this is interpreted as a sub-slice pattern semantically.
2753 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2754 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2755 let mut before = Vec::new();
2756 let mut after = Vec::new();
2757 let mut slice = None;
2758 let mut prev_rest_span = None;
2760 let mut iter = pats.iter();
2761 // Lower all the patterns until the first occurence of a sub-slice pattern.
2762 for pat in iter.by_ref() {
2764 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2766 prev_rest_span = Some(pat.span);
2767 slice = Some(self.pat_wild_with_node_id_of(pat));
2770 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2771 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2772 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2773 prev_rest_span = Some(sub.span);
2774 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2775 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2776 slice = Some(self.pat_with_node_id_of(pat, node));
2779 // It was not a subslice pattern so lower it normally.
2780 _ => before.push(self.lower_pat(pat)),
2784 // Lower all the patterns after the first sub-slice pattern.
2786 // There was a previous subslice pattern; make sure we don't allow more.
2787 let rest_span = match pat.kind {
2788 PatKind::Rest => Some(pat.span),
2789 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2790 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2791 after.push(self.pat_wild_with_node_id_of(pat));
2796 if let Some(rest_span) = rest_span {
2797 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2798 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2800 // Lower the pattern normally.
2801 after.push(self.lower_pat(pat));
2805 hir::PatKind::Slice(
2806 self.arena.alloc_from_iter(before),
2808 self.arena.alloc_from_iter(after),
2815 binding_mode: &BindingMode,
2817 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2818 ) -> hir::PatKind<'hir> {
2819 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2820 // `None` can occur in body-less function signatures
2821 res @ None | res @ Some(Res::Local(_)) => {
2822 let canonical_id = match res {
2823 Some(Res::Local(id)) => id,
2827 hir::PatKind::Binding(
2828 self.lower_binding_mode(binding_mode),
2829 self.lower_node_id(canonical_id),
2834 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2836 self.arena.alloc(hir::Path {
2838 res: self.lower_res(res),
2839 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2845 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2846 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2849 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2850 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2851 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2854 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2855 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2857 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2858 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2859 .span_label(prev_sp, "previously used here")
2863 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2864 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2866 .struct_span_err(sp, "`..` patterns are not allowed here")
2867 .note("only allowed in tuple, tuple struct, and slice patterns")
2870 // We're not in a list context so `..` can be reasonably treated
2871 // as `_` because it should always be valid and roughly matches the
2872 // intent of `..` (notice that the rest of a single slot is that slot).
2876 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2878 RangeEnd::Included(_) => hir::RangeEnd::Included,
2879 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2883 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2884 self.with_new_scopes(|this| hir::AnonConst {
2885 hir_id: this.lower_node_id(c.id),
2886 body: this.lower_const_body(c.value.span, Some(&c.value)),
2890 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2891 let kind = match s.kind {
2892 StmtKind::Local(ref l) => {
2893 let (l, item_ids) = self.lower_local(l);
2894 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2897 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2898 self.stmt(s.span, hir::StmtKind::Item(item_id))
2903 hir_id: self.lower_node_id(s.id),
2904 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2910 StmtKind::Item(ref it) => {
2911 // Can only use the ID once.
2912 let mut id = Some(s.id);
2919 .map(|id| self.lower_node_id(id))
2920 .unwrap_or_else(|| self.next_id());
2922 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2926 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2927 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2928 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2930 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2933 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2935 BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock,
2936 BlockCheckMode::Unsafe(u) => {
2937 hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u))
2942 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2944 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2945 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2946 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2947 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2951 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2953 CompilerGenerated => hir::UnsafeSource::CompilerGenerated,
2954 UserProvided => hir::UnsafeSource::UserProvided,
2958 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2960 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2961 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2965 // Helper methods for building HIR.
2967 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2968 hir::Stmt { span, kind, hir_id: self.next_id() }
2971 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2972 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2979 init: Option<&'hir hir::Expr<'hir>>,
2980 pat: &'hir hir::Pat<'hir>,
2981 source: hir::LocalSource,
2982 ) -> hir::Stmt<'hir> {
2983 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
2984 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
2987 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
2988 self.block_all(expr.span, &[], Some(expr))
2994 stmts: &'hir [hir::Stmt<'hir>],
2995 expr: Option<&'hir hir::Expr<'hir>>,
2996 ) -> &'hir hir::Block<'hir> {
2997 let blk = hir::Block {
3000 hir_id: self.next_id(),
3001 rules: hir::BlockCheckMode::DefaultBlock,
3003 targeted_by_break: false,
3005 self.arena.alloc(blk)
3008 /// Constructs a `true` or `false` literal pattern.
3009 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3010 let expr = self.expr_bool(span, val);
3011 self.pat(span, hir::PatKind::Lit(expr))
3014 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3015 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3018 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3019 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3022 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3023 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3026 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3027 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3033 components: &[Symbol],
3034 subpats: &'hir [&'hir hir::Pat<'hir>],
3035 ) -> &'hir hir::Pat<'hir> {
3036 let path = self.std_path(span, components, None, true);
3037 let qpath = hir::QPath::Resolved(None, path);
3038 let pt = if subpats.is_empty() {
3039 hir::PatKind::Path(qpath)
3041 hir::PatKind::TupleStruct(qpath, subpats, None)
3046 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3047 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3050 fn pat_ident_binding_mode(
3054 bm: hir::BindingAnnotation,
3055 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3056 let hir_id = self.next_id();
3059 self.arena.alloc(hir::Pat {
3061 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3068 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3069 self.pat(span, hir::PatKind::Wild)
3072 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3073 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3076 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3077 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3078 /// The path is also resolved according to `is_value`.
3082 components: &[Symbol],
3083 params: Option<&'hir hir::GenericArgs<'hir>>,
3085 ) -> &'hir hir::Path<'hir> {
3086 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3087 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3089 let mut segments: Vec<_> = path
3093 let res = self.expect_full_res(segment.id);
3095 ident: segment.ident,
3096 hir_id: Some(self.lower_node_id(segment.id)),
3097 res: Some(self.lower_res(res)),
3103 segments.last_mut().unwrap().args = params;
3105 self.arena.alloc(hir::Path {
3107 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3108 segments: self.arena.alloc_from_iter(segments),
3114 mut hir_id: hir::HirId,
3116 qpath: hir::QPath<'hir>,
3117 ) -> hir::Ty<'hir> {
3118 let kind = match qpath {
3119 hir::QPath::Resolved(None, path) => {
3120 // Turn trait object paths into `TyKind::TraitObject` instead.
3122 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3123 let principal = hir::PolyTraitRef {
3124 bound_generic_params: &[],
3125 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3129 // The original ID is taken by the `PolyTraitRef`,
3130 // so the `Ty` itself needs a different one.
3131 hir_id = self.next_id();
3132 hir::TyKind::TraitObject(
3133 arena_vec![self; principal],
3134 self.elided_dyn_bound(span),
3137 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3140 _ => hir::TyKind::Path(qpath),
3143 hir::Ty { hir_id, kind, span }
3146 /// Invoked to create the lifetime argument for a type `&T`
3147 /// with no explicit lifetime.
3148 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3149 match self.anonymous_lifetime_mode {
3150 // Intercept when we are in an impl header or async fn and introduce an in-band
3152 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3154 AnonymousLifetimeMode::CreateParameter => {
3155 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3157 hir_id: self.next_id(),
3159 name: hir::LifetimeName::Param(fresh_name),
3163 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3165 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3169 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3170 /// return a "error lifetime".
3171 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3172 let (id, msg, label) = match id {
3173 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3176 self.resolver.next_node_id(),
3177 "`&` without an explicit lifetime name cannot be used here",
3178 "explicit lifetime name needed here",
3182 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3183 err.span_label(span, label);
3186 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3189 /// Invoked to create the lifetime argument(s) for a path like
3190 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3191 /// sorts of cases are deprecated. This may therefore report a warning or an
3192 /// error, depending on the mode.
3193 fn elided_path_lifetimes<'s>(
3197 ) -> impl Iterator<Item = hir::Lifetime> + Captures<'a> + Captures<'s> + Captures<'hir> {
3198 (0..count).map(move |_| self.elided_path_lifetime(span))
3201 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3202 match self.anonymous_lifetime_mode {
3203 AnonymousLifetimeMode::CreateParameter => {
3204 // We should have emitted E0726 when processing this path above
3206 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3207 let id = self.resolver.next_node_id();
3208 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3210 // `PassThrough` is the normal case.
3211 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3212 // is unsuitable here, as these can occur from missing lifetime parameters in a
3213 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3214 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3215 // later, at which point a suitable error will be emitted.
3216 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3217 self.new_implicit_lifetime(span)
3222 /// Invoked to create the lifetime argument(s) for an elided trait object
3223 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3224 /// when the bound is written, even if it is written with `'_` like in
3225 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3226 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3227 match self.anonymous_lifetime_mode {
3228 // NB. We intentionally ignore the create-parameter mode here.
3229 // and instead "pass through" to resolve-lifetimes, which will apply
3230 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3231 // do not act like other elided lifetimes. In other words, given this:
3233 // impl Foo for Box<dyn Debug>
3235 // we do not introduce a fresh `'_` to serve as the bound, but instead
3236 // ultimately translate to the equivalent of:
3238 // impl Foo for Box<dyn Debug + 'static>
3240 // `resolve_lifetime` has the code to make that happen.
3241 AnonymousLifetimeMode::CreateParameter => {}
3243 AnonymousLifetimeMode::ReportError => {
3244 // ReportError applies to explicit use of `'_`.
3247 // This is the normal case.
3248 AnonymousLifetimeMode::PassThrough => {}
3251 let r = hir::Lifetime {
3252 hir_id: self.next_id(),
3254 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3256 debug!("elided_dyn_bound: r={:?}", r);
3260 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3261 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3264 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3265 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3266 // call site which do not have a macro backtrace. See #61963.
3267 let is_macro_callsite = self
3270 .span_to_snippet(span)
3271 .map(|snippet| snippet.starts_with("#["))
3273 if !is_macro_callsite {
3274 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3275 builtin::BARE_TRAIT_OBJECTS,
3278 "trait objects without an explicit `dyn` are deprecated",
3279 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3285 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'_>>) -> Vec<hir::BodyId> {
3286 // Sorting by span ensures that we get things in order within a
3287 // file, and also puts the files in a sensible order.
3288 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3289 body_ids.sort_by_key(|b| bodies[b].value.span);
3293 /// Helper struct for delayed construction of GenericArgs.
3294 struct GenericArgsCtor<'hir> {
3295 args: SmallVec<[hir::GenericArg<'hir>; 4]>,
3296 bindings: &'hir [hir::TypeBinding<'hir>],
3297 parenthesized: bool,
3300 impl<'hir> GenericArgsCtor<'hir> {
3301 fn is_empty(&self) -> bool {
3302 self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized
3305 fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> {
3307 args: arena.alloc_from_iter(self.args),
3308 bindings: self.bindings,
3309 parenthesized: self.parenthesized,