1 // ignore-tidy-filelength
3 //! Lowers the AST to the HIR.
5 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
6 //! much like a fold. Where lowering involves a bit more work things get more
7 //! interesting and there are some invariants you should know about. These mostly
8 //! concern spans and IDs.
10 //! Spans are assigned to AST nodes during parsing and then are modified during
11 //! expansion to indicate the origin of a node and the process it went through
12 //! being expanded. IDs are assigned to AST nodes just before lowering.
14 //! For the simpler lowering steps, IDs and spans should be preserved. Unlike
15 //! expansion we do not preserve the process of lowering in the spans, so spans
16 //! should not be modified here. When creating a new node (as opposed to
17 //! 'folding' an existing one), then you create a new ID using `next_id()`.
19 //! You must ensure that IDs are unique. That means that you should only use the
20 //! ID from an AST node in a single HIR node (you can assume that AST node-IDs
21 //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes.
22 //! If you do, you must then set the new node's ID to a fresh one.
24 //! Spans are used for error messages and for tools to map semantics back to
25 //! source code. It is therefore not as important with spans as IDs to be strict
26 //! about use (you can't break the compiler by screwing up a span). Obviously, a
27 //! HIR node can only have a single span. But multiple nodes can have the same
28 //! span and spans don't need to be kept in order, etc. Where code is preserved
29 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
30 //! new it is probably best to give a span for the whole AST node being lowered.
31 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
32 //! get confused if the spans from leaf AST nodes occur in multiple places
33 //! in the HIR, especially for multiple identifiers.
35 use crate::arena::Arena;
36 use crate::dep_graph::DepGraph;
37 use crate::hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
38 use crate::hir::def_id::{DefId, DefIndex, CRATE_DEF_INDEX};
39 use crate::hir::map::{DefKey, DefPathData, Definitions};
40 use crate::hir::ptr::P;
41 use crate::hir::HirVec;
42 use crate::hir::{self, ParamName};
43 use crate::hir::{ConstArg, GenericArg};
45 use crate::lint::builtin::{self, ELIDED_LIFETIMES_IN_PATHS};
46 use crate::middle::cstore::CrateStore;
47 use crate::session::config::nightly_options;
48 use crate::session::Session;
49 use crate::util::captures::Captures;
50 use crate::util::common::FN_OUTPUT_NAME;
51 use crate::util::nodemap::{DefIdMap, NodeMap};
52 use errors::Applicability;
53 use rustc_data_structures::fx::FxHashSet;
54 use rustc_data_structures::sync::Lrc;
55 use rustc_index::vec::IndexVec;
57 use smallvec::SmallVec;
58 use std::collections::BTreeMap;
64 use syntax::print::pprust;
65 use syntax::ptr::P as AstP;
66 use syntax::sess::ParseSess;
67 use syntax::source_map::{respan, DesugaringKind, ExpnData, ExpnKind, Spanned};
68 use syntax::symbol::{kw, sym, Symbol};
69 use syntax::token::{self, Nonterminal, Token};
70 use syntax::tokenstream::{TokenStream, TokenTree};
71 use syntax::visit::{self, Visitor};
72 use syntax_pos::hygiene::ExpnId;
75 use rustc_error_codes::*;
77 macro_rules! arena_vec {
81 ($this:expr; $($x:expr),*) => (
82 $this.arena.alloc_from_iter(vec![$($x),*])
89 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
91 pub struct LoweringContext<'a, 'hir: 'a> {
92 crate_root: Option<Symbol>,
94 /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes.
97 resolver: &'a mut dyn Resolver,
99 /// HACK(Centril): there is a cyclic dependency between the parser and lowering
100 /// if we don't have this function pointer. To avoid that dependency so that
101 /// librustc is independent of the parser, we use dynamic dispatch here.
102 nt_to_tokenstream: NtToTokenstream,
104 /// Used to allocate HIR nodes
105 arena: &'hir Arena<'hir>,
107 /// The items being lowered are collected here.
108 items: BTreeMap<hir::HirId, hir::Item<'hir>>,
110 trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem<'hir>>,
111 impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem<'hir>>,
112 bodies: BTreeMap<hir::BodyId, hir::Body<'hir>>,
113 exported_macros: Vec<hir::MacroDef<'hir>>,
114 non_exported_macro_attrs: Vec<ast::Attribute>,
116 trait_impls: BTreeMap<DefId, Vec<hir::HirId>>,
118 modules: BTreeMap<hir::HirId, hir::ModuleItems>,
120 generator_kind: Option<hir::GeneratorKind>,
122 /// Used to get the current `fn`'s def span to point to when using `await`
123 /// outside of an `async fn`.
124 current_item: Option<Span>,
126 catch_scopes: Vec<NodeId>,
127 loop_scopes: Vec<NodeId>,
128 is_in_loop_condition: bool,
129 is_in_trait_impl: bool,
130 is_in_dyn_type: bool,
132 /// What to do when we encounter either an "anonymous lifetime
133 /// reference". The term "anonymous" is meant to encompass both
134 /// `'_` lifetimes as well as fully elided cases where nothing is
135 /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
136 anonymous_lifetime_mode: AnonymousLifetimeMode,
138 /// Used to create lifetime definitions from in-band lifetime usages.
139 /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
140 /// When a named lifetime is encountered in a function or impl header and
141 /// has not been defined
142 /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added
143 /// to this list. The results of this list are then added to the list of
144 /// lifetime definitions in the corresponding impl or function generics.
145 lifetimes_to_define: Vec<(Span, ParamName)>,
147 /// `true` if in-band lifetimes are being collected. This is used to
148 /// indicate whether or not we're in a place where new lifetimes will result
149 /// in in-band lifetime definitions, such a function or an impl header,
150 /// including implicit lifetimes from `impl_header_lifetime_elision`.
151 is_collecting_in_band_lifetimes: bool,
153 /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
154 /// When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
155 /// against this list to see if it is already in-scope, or if a definition
156 /// needs to be created for it.
158 /// We always store a `modern()` version of the param-name in this
160 in_scope_lifetimes: Vec<ParamName>,
162 current_module: hir::HirId,
164 type_def_lifetime_params: DefIdMap<usize>,
166 current_hir_id_owner: Vec<(DefIndex, u32)>,
167 item_local_id_counters: NodeMap<u32>,
168 node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
170 allow_try_trait: Option<Lrc<[Symbol]>>,
171 allow_gen_future: Option<Lrc<[Symbol]>>,
172 allow_into_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<'b, 'a> ImplTraitContext<'b, 'a> {
244 fn disallowed() -> Self {
245 ImplTraitContext::Disallowed(ImplTraitPosition::Other)
248 fn reborrow(&'c mut self) -> ImplTraitContext<'c, '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()),
305 allow_into_future: Some([sym::into_future][..].into()),
310 #[derive(Copy, Clone, PartialEq)]
312 /// Any path in a type context.
314 /// Path in a type definition, where the anonymous lifetime `'_` is not allowed.
316 /// The `module::Type` in `module::Type::method` in an expression.
320 enum ParenthesizedGenericArgs {
325 /// What to do when we encounter an **anonymous** lifetime
326 /// reference. Anonymous lifetime references come in two flavors. You
327 /// have implicit, or fully elided, references to lifetimes, like the
328 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
329 /// or `Ref<'_, T>`. These often behave the same, but not always:
331 /// - certain usages of implicit references are deprecated, like
332 /// `Ref<T>`, and we sometimes just give hard errors in those cases
334 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
335 /// the same as `Box<dyn Foo + '_>`.
337 /// We describe the effects of the various modes in terms of three cases:
339 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
340 /// of a `&` (e.g., the missing lifetime in something like `&T`)
341 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
342 /// there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
343 /// elided bounds follow special rules. Note that this only covers
344 /// cases where *nothing* is written; the `'_` in `Box<dyn Foo +
345 /// '_>` is a case of "modern" elision.
346 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
347 /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
348 /// non-deprecated equivalent.
350 /// Currently, the handling of lifetime elision is somewhat spread out
351 /// between HIR lowering and -- as described below -- the
352 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
353 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
354 /// everything into HIR lowering.
355 #[derive(Copy, Clone, Debug)]
356 enum AnonymousLifetimeMode {
357 /// For **Modern** cases, create a new anonymous region parameter
358 /// and reference that.
360 /// For **Dyn Bound** cases, pass responsibility to
361 /// `resolve_lifetime` code.
363 /// For **Deprecated** cases, report an error.
366 /// Give a hard error when either `&` or `'_` is written. Used to
367 /// rule out things like `where T: Foo<'_>`. Does not imply an
368 /// error on default object bounds (e.g., `Box<dyn Foo>`).
371 /// Pass responsibility to `resolve_lifetime` code for all cases.
375 struct ImplTraitTypeIdVisitor<'a> {
376 ids: &'a mut SmallVec<[NodeId; 1]>,
379 impl<'a, 'b> Visitor<'a> for ImplTraitTypeIdVisitor<'b> {
380 fn visit_ty(&mut self, ty: &'a Ty) {
382 TyKind::Typeof(_) | TyKind::BareFn(_) => return,
384 TyKind::ImplTrait(id, _) => self.ids.push(id),
387 visit::walk_ty(self, ty);
390 fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment) {
391 if let Some(ref p) = path_segment.args {
392 if let GenericArgs::Parenthesized(_) = **p {
396 visit::walk_path_segment(self, path_span, path_segment)
400 impl<'a, 'hir> LoweringContext<'a, 'hir> {
401 fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> {
402 /// Full-crate AST visitor that inserts into a fresh
403 /// `LoweringContext` any information that may be
404 /// needed from arbitrary locations in the crate,
405 /// e.g., the number of lifetime generic parameters
406 /// declared for every type and trait definition.
407 struct MiscCollector<'tcx, 'lowering, 'hir> {
408 lctx: &'tcx mut LoweringContext<'lowering, 'hir>,
409 hir_id_owner: Option<NodeId>,
412 impl MiscCollector<'_, '_, '_> {
413 fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: DefIndex) {
415 UseTreeKind::Simple(_, id1, id2) => {
416 for &id in &[id1, id2] {
417 self.lctx.resolver.definitions().create_def_with_parent(
424 self.lctx.allocate_hir_id_counter(id);
427 UseTreeKind::Glob => (),
428 UseTreeKind::Nested(ref trees) => {
429 for &(ref use_tree, id) in trees {
430 let hir_id = self.lctx.allocate_hir_id_counter(id);
431 self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner);
437 fn with_hir_id_owner<F, T>(&mut self, owner: Option<NodeId>, f: F) -> T
439 F: FnOnce(&mut Self) -> T,
441 let old = mem::replace(&mut self.hir_id_owner, owner);
443 self.hir_id_owner = old;
448 impl<'tcx, 'lowering, 'hir> Visitor<'tcx> for MiscCollector<'tcx, 'lowering, 'hir> {
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.arena.alloc_from_iter(self.lower_attrs(&c.attrs).into_iter());
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<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> hir::HirId
583 F: FnOnce(&mut Self) -> hir::HirId,
585 if ast_node_id == DUMMY_NODE_ID {
586 return hir::DUMMY_HIR_ID;
589 let min_size = ast_node_id.as_usize() + 1;
591 if min_size > self.node_id_to_hir_id.len() {
592 self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
595 let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
597 if existing_hir_id == hir::DUMMY_HIR_ID {
598 // Generate a new `HirId`.
599 let hir_id = alloc_hir_id(self);
600 self.node_id_to_hir_id[ast_node_id] = hir_id;
608 fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
610 F: FnOnce(&mut Self) -> T,
613 .item_local_id_counters
614 .insert(owner, HIR_ID_COUNTER_LOCKED)
615 .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner));
616 let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
617 self.current_hir_id_owner.push((def_index, counter));
619 let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
621 debug_assert!(def_index == new_def_index);
622 debug_assert!(new_counter >= counter);
624 let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
625 debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
629 /// This method allocates a new `HirId` for the given `NodeId` and stores it in
630 /// the `LoweringContext`'s `NodeId => HirId` map.
631 /// Take care not to call this method if the resulting `HirId` is then not
632 /// actually used in the HIR, as that would trigger an assertion in the
633 /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped
634 /// properly. Calling the method twice with the same `NodeId` is fine though.
635 fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId {
636 self.lower_node_id_generic(ast_node_id, |this| {
637 let &mut (def_index, ref mut local_id_counter) =
638 this.current_hir_id_owner.last_mut().unwrap();
639 let local_id = *local_id_counter;
640 *local_id_counter += 1;
641 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
645 fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId {
646 self.lower_node_id_generic(ast_node_id, |this| {
647 let local_id_counter = this
648 .item_local_id_counters
650 .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`");
651 let local_id = *local_id_counter;
653 // We want to be sure not to modify the counter in the map while it
654 // is also on the stack. Otherwise we'll get lost updates when writing
655 // back from the stack to the map.
656 debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
658 *local_id_counter += 1;
659 let def_index = this.resolver.definitions().opt_def_index(owner).expect(
660 "you forgot to call `create_def_with_parent` or are lowering node-IDs \
661 that do not belong to the current owner",
664 hir::HirId { owner: def_index, local_id: hir::ItemLocalId::from_u32(local_id) }
668 fn next_id(&mut self) -> hir::HirId {
669 let node_id = self.resolver.next_node_id();
670 self.lower_node_id(node_id)
673 fn lower_res(&mut self, res: Res<NodeId>) -> Res {
675 self.lower_node_id_generic(id, |_| {
676 panic!("expected `NodeId` to be lowered already for res {:#?}", res);
681 fn expect_full_res(&mut self, id: NodeId) -> Res<NodeId> {
682 self.resolver.get_partial_res(id).map_or(Res::Err, |pr| {
683 if pr.unresolved_segments() != 0 {
684 bug!("path not fully resolved: {:?}", pr);
690 fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator<Item = Res<NodeId>> {
691 self.resolver.get_import_res(id).present_items()
694 fn diagnostic(&self) -> &errors::Handler {
695 self.sess.diagnostic()
698 /// Reuses the span but adds information like the kind of the desugaring and features that are
699 /// allowed inside this span.
700 fn mark_span_with_reason(
702 reason: DesugaringKind,
704 allow_internal_unstable: Option<Lrc<[Symbol]>>,
706 span.fresh_expansion(ExpnData {
707 allow_internal_unstable,
708 ..ExpnData::default(ExpnKind::Desugaring(reason), span, self.sess.edition())
712 fn with_anonymous_lifetime_mode<R>(
714 anonymous_lifetime_mode: AnonymousLifetimeMode,
715 op: impl FnOnce(&mut Self) -> R,
718 "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})",
719 anonymous_lifetime_mode,
721 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
722 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
723 let result = op(self);
724 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
726 "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}",
727 old_anonymous_lifetime_mode
732 /// Creates a new `hir::GenericParam` for every new lifetime and
733 /// type parameter encountered while evaluating `f`. Definitions
734 /// are created with the parent provided. If no `parent_id` is
735 /// provided, no definitions will be returned.
737 /// Presuming that in-band lifetimes are enabled, then
738 /// `self.anonymous_lifetime_mode` will be updated to match the
739 /// parameter while `f` is running (and restored afterwards).
740 fn collect_in_band_defs<T, F>(
743 anonymous_lifetime_mode: AnonymousLifetimeMode,
745 ) -> (Vec<hir::GenericParam<'hir>>, T)
747 F: FnOnce(&mut Self) -> (Vec<hir::GenericParam<'hir>>, T),
749 assert!(!self.is_collecting_in_band_lifetimes);
750 assert!(self.lifetimes_to_define.is_empty());
751 let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
753 self.anonymous_lifetime_mode = anonymous_lifetime_mode;
754 self.is_collecting_in_band_lifetimes = true;
756 let (in_band_ty_params, res) = f(self);
758 self.is_collecting_in_band_lifetimes = false;
759 self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
761 let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
763 let params = lifetimes_to_define
765 .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_id.index))
766 .chain(in_band_ty_params.into_iter())
772 /// Converts a lifetime into a new generic parameter.
773 fn lifetime_to_generic_param(
777 parent_index: DefIndex,
778 ) -> hir::GenericParam<'hir> {
779 let node_id = self.resolver.next_node_id();
781 // Get the name we'll use to make the def-path. Note
782 // that collisions are ok here and this shouldn't
783 // really show up for end-user.
784 let (str_name, kind) = match hir_name {
785 ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand),
786 ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided),
787 ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error),
790 // Add a definition for the in-band lifetime def.
791 self.resolver.definitions().create_def_with_parent(
794 DefPathData::LifetimeNs(str_name),
800 hir_id: self.lower_node_id(node_id),
805 pure_wrt_drop: false,
806 kind: hir::GenericParamKind::Lifetime { kind },
810 /// When there is a reference to some lifetime `'a`, and in-band
811 /// lifetimes are enabled, then we want to push that lifetime into
812 /// the vector of names to define later. In that case, it will get
813 /// added to the appropriate generics.
814 fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) {
815 if !self.is_collecting_in_band_lifetimes {
819 if !self.sess.features_untracked().in_band_lifetimes {
823 if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.modern())) {
827 let hir_name = ParamName::Plain(ident);
829 if self.lifetimes_to_define.iter().any(|(_, lt_name)| lt_name.modern() == hir_name.modern())
834 self.lifetimes_to_define.push((ident.span, hir_name));
837 /// When we have either an elided or `'_` lifetime in an impl
838 /// header, we convert it to an in-band lifetime.
839 fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
840 assert!(self.is_collecting_in_band_lifetimes);
841 let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len();
842 let hir_name = ParamName::Fresh(index);
843 self.lifetimes_to_define.push((span, hir_name));
847 // Evaluates `f` with the lifetimes in `params` in-scope.
848 // This is used to track which lifetimes have already been defined, and
849 // which are new in-band lifetimes that need to have a definition created
851 fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &[GenericParam], f: F) -> T
853 F: FnOnce(&mut Self) -> T,
855 let old_len = self.in_scope_lifetimes.len();
856 let lt_def_names = params.iter().filter_map(|param| match param.kind {
857 GenericParamKind::Lifetime { .. } => Some(ParamName::Plain(param.ident.modern())),
860 self.in_scope_lifetimes.extend(lt_def_names);
864 self.in_scope_lifetimes.truncate(old_len);
868 /// Appends in-band lifetime defs and argument-position `impl
869 /// Trait` defs to the existing set of generics.
871 /// Presuming that in-band lifetimes are enabled, then
872 /// `self.anonymous_lifetime_mode` will be updated to match the
873 /// parameter while `f` is running (and restored afterwards).
874 fn add_in_band_defs<F, T>(
878 anonymous_lifetime_mode: AnonymousLifetimeMode,
880 ) -> (hir::Generics<'hir>, T)
882 F: FnOnce(&mut Self, &mut Vec<hir::GenericParam<'hir>>) -> T,
884 let (in_band_defs, (mut lowered_generics, res)) =
885 self.with_in_scope_lifetime_defs(&generics.params, |this| {
886 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
887 let mut params = Vec::new();
888 // Note: it is necessary to lower generics *before* calling `f`.
889 // When lowering `async fn`, there's a final step when lowering
890 // the return type that assumes that all in-scope lifetimes have
891 // already been added to either `in_scope_lifetimes` or
892 // `lifetimes_to_define`. If we swapped the order of these two,
893 // in-band-lifetimes introduced by generics or where-clauses
894 // wouldn't have been added yet.
896 this.lower_generics(generics, ImplTraitContext::Universal(&mut params));
897 let res = f(this, &mut params);
898 (params, (generics, res))
902 let mut lowered_params: Vec<_> =
903 lowered_generics.params.into_iter().chain(in_band_defs).collect();
905 // FIXME(const_generics): the compiler doesn't always cope with
906 // unsorted generic parameters at the moment, so we make sure
907 // that they're ordered correctly here for now. (When we chain
908 // the `in_band_defs`, we might make the order unsorted.)
909 lowered_params.sort_by_key(|param| match param.kind {
910 hir::GenericParamKind::Lifetime { .. } => ParamKindOrd::Lifetime,
911 hir::GenericParamKind::Type { .. } => ParamKindOrd::Type,
912 hir::GenericParamKind::Const { .. } => ParamKindOrd::Const,
915 lowered_generics.params = lowered_params.into();
917 (lowered_generics, res)
920 fn with_dyn_type_scope<T, F>(&mut self, in_scope: bool, f: F) -> T
922 F: FnOnce(&mut Self) -> T,
924 let was_in_dyn_type = self.is_in_dyn_type;
925 self.is_in_dyn_type = in_scope;
927 let result = f(self);
929 self.is_in_dyn_type = was_in_dyn_type;
934 fn with_new_scopes<T, F>(&mut self, f: F) -> T
936 F: FnOnce(&mut Self) -> T,
938 let was_in_loop_condition = self.is_in_loop_condition;
939 self.is_in_loop_condition = false;
941 let catch_scopes = mem::take(&mut self.catch_scopes);
942 let loop_scopes = mem::take(&mut self.loop_scopes);
944 self.catch_scopes = catch_scopes;
945 self.loop_scopes = loop_scopes;
947 self.is_in_loop_condition = was_in_loop_condition;
952 fn def_key(&mut self, id: DefId) -> DefKey {
954 self.resolver.definitions().def_key(id.index)
956 self.resolver.cstore().def_key(id)
960 fn lower_attrs_arena(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] {
961 self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a)))
964 fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
965 attrs.iter().map(|a| self.lower_attr(a)).collect::<Vec<_>>().into()
968 fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
969 // Note that we explicitly do not walk the path. Since we don't really
970 // lower attributes (we use the AST version) there is nowhere to keep
971 // the `HirId`s. We don't actually need HIR version of attributes anyway.
972 let kind = match attr.kind {
973 AttrKind::Normal(ref item) => AttrKind::Normal(AttrItem {
974 path: item.path.clone(),
975 args: self.lower_mac_args(&item.args),
977 AttrKind::DocComment(comment) => AttrKind::DocComment(comment),
980 Attribute { kind, id: attr.id, style: attr.style, span: attr.span }
983 fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs {
985 MacArgs::Empty => MacArgs::Empty,
986 MacArgs::Delimited(dspan, delim, ref tokens) => {
987 MacArgs::Delimited(dspan, delim, self.lower_token_stream(tokens.clone()))
989 MacArgs::Eq(eq_span, ref tokens) => {
990 MacArgs::Eq(eq_span, self.lower_token_stream(tokens.clone()))
995 fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
996 tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect()
999 fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
1001 TokenTree::Token(token) => self.lower_token(token),
1002 TokenTree::Delimited(span, delim, tts) => {
1003 TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into()
1008 fn lower_token(&mut self, token: Token) -> TokenStream {
1010 token::Interpolated(nt) => {
1011 let tts = (self.nt_to_tokenstream)(&nt, &self.sess.parse_sess, token.span);
1012 self.lower_token_stream(tts)
1014 _ => TokenTree::Token(token).into(),
1018 /// Given an associated type constraint like one of these:
1021 /// T: Iterator<Item: Debug>
1023 /// T: Iterator<Item = Debug>
1027 /// returns a `hir::TypeBinding` representing `Item`.
1028 fn lower_assoc_ty_constraint(
1030 constraint: &AssocTyConstraint,
1031 itctx: ImplTraitContext<'_, 'hir>,
1032 ) -> hir::TypeBinding<'hir> {
1033 debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx);
1035 let kind = match constraint.kind {
1036 AssocTyConstraintKind::Equality { ref ty } => {
1037 hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) }
1039 AssocTyConstraintKind::Bound { ref bounds } => {
1040 // Piggy-back on the `impl Trait` context to figure out the correct behavior.
1041 let (desugar_to_impl_trait, itctx) = match itctx {
1042 // We are in the return position:
1044 // fn foo() -> impl Iterator<Item: Debug>
1048 // fn foo() -> impl Iterator<Item = impl Debug>
1049 ImplTraitContext::OpaqueTy(_) => (true, itctx),
1051 // We are in the argument position, but within a dyn type:
1053 // fn foo(x: dyn Iterator<Item: Debug>)
1057 // fn foo(x: dyn Iterator<Item = impl Debug>)
1058 ImplTraitContext::Universal(_) if self.is_in_dyn_type => (true, itctx),
1060 // In `type Foo = dyn Iterator<Item: Debug>` we desugar to
1061 // `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
1062 // "impl trait context" to permit `impl Debug` in this position (it desugars
1063 // then to an opaque type).
1065 // FIXME: this is only needed until `impl Trait` is allowed in type aliases.
1066 ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => {
1067 (true, ImplTraitContext::OpaqueTy(None))
1070 // We are in the parameter position, but not within a dyn type:
1072 // fn foo(x: impl Iterator<Item: Debug>)
1074 // so we leave it as is and this gets expanded in astconv to a bound like
1075 // `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
1077 _ => (false, itctx),
1080 if desugar_to_impl_trait {
1081 // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
1082 // constructing the HIR for `impl bounds...` and then lowering that.
1084 let impl_trait_node_id = self.resolver.next_node_id();
1085 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1086 self.resolver.definitions().create_def_with_parent(
1089 DefPathData::ImplTrait,
1094 self.with_dyn_type_scope(false, |this| {
1095 let node_id = this.resolver.next_node_id();
1096 let ty = this.lower_ty(
1099 kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
1100 span: constraint.span,
1105 hir::TypeBindingKind::Equality { ty }
1108 // Desugar `AssocTy: Bounds` into a type binding where the
1109 // later desugars into a trait predicate.
1110 let bounds = self.lower_param_bounds(bounds, itctx);
1112 hir::TypeBindingKind::Constraint { bounds }
1118 hir_id: self.lower_node_id(constraint.id),
1119 ident: constraint.ident,
1121 span: constraint.span,
1125 fn lower_generic_arg(
1127 arg: &ast::GenericArg,
1128 itctx: ImplTraitContext<'_, 'hir>,
1129 ) -> hir::GenericArg<'hir> {
1131 ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)),
1132 ast::GenericArg::Type(ty) => {
1133 // We parse const arguments as path types as we cannot distiguish them durring
1134 // parsing. We try to resolve that ambiguity by attempting resolution in both the
1135 // type and value namespaces. If we resolved the path in the value namespace, we
1136 // transform it into a generic const argument.
1137 if let TyKind::Path(ref qself, ref path) = ty.kind {
1138 if let Some(partial_res) = self.resolver.get_partial_res(ty.id) {
1139 let res = partial_res.base_res();
1140 if !res.matches_ns(Namespace::TypeNS) {
1142 "lower_generic_arg: Lowering type argument as const argument: {:?}",
1146 // Construct a AnonConst where the expr is the "ty"'s path.
1148 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
1149 let node_id = self.resolver.next_node_id();
1151 // Add a definition for the in-band const def.
1152 self.resolver.definitions().create_def_with_parent(
1155 DefPathData::AnonConst,
1160 let path_expr = Expr {
1162 kind: ExprKind::Path(qself.clone(), path.clone()),
1164 attrs: AttrVec::new(),
1167 let ct = self.with_new_scopes(|this| hir::AnonConst {
1168 hir_id: this.lower_node_id(node_id),
1169 body: this.lower_const_body(path_expr.span, Some(&path_expr)),
1171 return GenericArg::Const(ConstArg { value: ct, span: ty.span });
1175 GenericArg::Type(self.lower_ty_direct(&ty, itctx))
1177 ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg {
1178 value: self.lower_anon_const(&ct),
1179 span: ct.value.span,
1184 fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> {
1185 self.arena.alloc(self.lower_ty_direct(t, itctx))
1191 qself: &Option<QSelf>,
1193 param_mode: ParamMode,
1194 itctx: ImplTraitContext<'_, 'hir>,
1195 ) -> hir::Ty<'hir> {
1196 let id = self.lower_node_id(t.id);
1197 let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
1198 let ty = self.ty_path(id, t.span, qpath);
1199 if let hir::TyKind::TraitObject(..) = ty.kind {
1200 self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1205 fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> {
1206 hir::Ty { hir_id: self.next_id(), kind, span }
1209 fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> {
1210 self.ty(span, hir::TyKind::Tup(tys))
1213 fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> {
1214 let kind = match t.kind {
1215 TyKind::Infer => hir::TyKind::Infer,
1216 TyKind::Err => hir::TyKind::Err,
1217 TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
1218 TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
1219 TyKind::Rptr(ref region, ref mt) => {
1220 let span = self.sess.source_map().next_point(t.span.shrink_to_lo());
1221 let lifetime = match *region {
1222 Some(ref lt) => self.lower_lifetime(lt),
1223 None => self.elided_ref_lifetime(span),
1225 hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx))
1227 TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| {
1228 this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
1229 hir::TyKind::BareFn(
1230 this.arena.alloc(hir::BareFnTy {
1231 generic_params: this.arena.alloc_from_iter(
1232 this.lower_generic_params(
1234 &NodeMap::default(),
1235 ImplTraitContext::disallowed(),
1239 unsafety: f.unsafety,
1240 abi: this.lower_extern(f.ext),
1241 decl: this.lower_fn_decl(&f.decl, None, false, None),
1242 param_names: this.arena.alloc_from_iter(
1243 this.lower_fn_params_to_names(&f.decl).into_iter(),
1249 TyKind::Never => hir::TyKind::Never,
1250 TyKind::Tup(ref tys) => {
1251 hir::TyKind::Tup(self.arena.alloc_from_iter(
1252 tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())),
1255 TyKind::Paren(ref ty) => {
1256 return self.lower_ty_direct(ty, itctx);
1258 TyKind::Path(ref qself, ref path) => {
1259 return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx);
1261 TyKind::ImplicitSelf => {
1262 let res = self.expect_full_res(t.id);
1263 let res = self.lower_res(res);
1264 hir::TyKind::Path(hir::QPath::Resolved(
1266 self.arena.alloc(hir::Path {
1268 segments: arena_vec![self; hir::PathSegment::from_ident(
1269 Ident::with_dummy_span(kw::SelfUpper)
1275 TyKind::Array(ref ty, ref length) => {
1276 hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1278 TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)),
1279 TyKind::TraitObject(ref bounds, kind) => {
1280 let mut lifetime_bound = None;
1281 let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
1283 this.arena.alloc_from_iter(bounds.iter().filter_map(
1284 |bound| match *bound {
1285 GenericBound::Trait(ref ty, TraitBoundModifier::None) => {
1286 Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
1288 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1289 GenericBound::Outlives(ref lifetime) => {
1290 if lifetime_bound.is_none() {
1291 lifetime_bound = Some(this.lower_lifetime(lifetime));
1297 let lifetime_bound =
1298 lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span));
1299 (bounds, lifetime_bound)
1301 if kind != TraitObjectSyntax::Dyn {
1302 self.maybe_lint_bare_trait(t.span, t.id, false);
1304 hir::TyKind::TraitObject(bounds, lifetime_bound)
1306 TyKind::ImplTrait(def_node_id, ref bounds) => {
1309 ImplTraitContext::OpaqueTy(fn_def_id) => {
1310 self.lower_opaque_impl_trait(span, fn_def_id, def_node_id, |this| {
1311 this.lower_param_bounds(bounds, itctx)
1314 ImplTraitContext::Universal(in_band_ty_params) => {
1315 // Add a definition for the in-band `Param`.
1317 self.resolver.definitions().opt_def_index(def_node_id).unwrap();
1319 let hir_bounds = self.lower_param_bounds(
1321 ImplTraitContext::Universal(in_band_ty_params),
1323 // Set the name to `impl Bound1 + Bound2`.
1324 let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
1325 in_band_ty_params.push(hir::GenericParam {
1326 hir_id: self.lower_node_id(def_node_id),
1327 name: ParamName::Plain(ident),
1328 pure_wrt_drop: false,
1332 kind: hir::GenericParamKind::Type {
1334 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1338 hir::TyKind::Path(hir::QPath::Resolved(
1340 self.arena.alloc(hir::Path {
1342 res: Res::Def(DefKind::TyParam, DefId::local(def_index)),
1343 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
1347 ImplTraitContext::Disallowed(pos) => {
1348 let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings {
1349 "bindings or function and inherent method return types"
1351 "function and inherent method return types"
1353 let mut err = struct_span_err!(
1357 "`impl Trait` not allowed outside of {}",
1360 if pos == ImplTraitPosition::Binding && nightly_options::is_nightly_build()
1364 "add `#![feature(impl_trait_in_bindings)]` to the crate \
1365 attributes to enable"
1373 TyKind::Mac(_) => bug!("`TyKind::Mac` should have been expanded by now"),
1374 TyKind::CVarArgs => {
1375 self.sess.delay_span_bug(
1377 "`TyKind::CVarArgs` should have been handled elsewhere",
1383 hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) }
1386 fn lower_opaque_impl_trait(
1389 fn_def_id: Option<DefId>,
1390 opaque_ty_node_id: NodeId,
1391 lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>,
1392 ) -> hir::TyKind<'hir> {
1394 "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})",
1395 fn_def_id, opaque_ty_node_id, span,
1398 // Make sure we know that some funky desugaring has been going on here.
1399 // This is a first: there is code in other places like for loop
1400 // desugaring that explicitly states that we don't want to track that.
1401 // Not tracking it makes lints in rustc and clippy very fragile, as
1402 // frequently opened issues show.
1403 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None);
1405 let opaque_ty_def_index =
1406 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
1408 self.allocate_hir_id_counter(opaque_ty_node_id);
1410 let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds);
1412 let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1414 opaque_ty_def_index,
1418 debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes,);
1420 debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs,);
1422 self.with_hir_id_owner(opaque_ty_node_id, |lctx| {
1423 let opaque_ty_item = hir::OpaqueTy {
1424 generics: hir::Generics {
1425 params: lifetime_defs,
1426 where_clause: hir::WhereClause { predicates: &[], span },
1430 impl_trait_fn: fn_def_id,
1431 origin: hir::OpaqueTyOrigin::FnReturn,
1434 trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_index);
1436 lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
1438 // `impl Trait` now just becomes `Foo<'a, 'b, ..>`.
1439 hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, lifetimes)
1443 /// Registers a new opaque type with the proper `NodeId`s and
1444 /// returns the lowered node-ID for the opaque type.
1445 fn generate_opaque_type(
1447 opaque_ty_node_id: NodeId,
1448 opaque_ty_item: hir::OpaqueTy<'hir>,
1450 opaque_ty_span: Span,
1452 let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item);
1453 let opaque_ty_id = self.lower_node_id(opaque_ty_node_id);
1454 // Generate an `type Foo = impl Trait;` declaration.
1455 trace!("registering opaque type with id {:#?}", opaque_ty_id);
1456 let opaque_ty_item = hir::Item {
1457 hir_id: opaque_ty_id,
1458 ident: Ident::invalid(),
1459 attrs: Default::default(),
1460 kind: opaque_ty_item_kind,
1461 vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited),
1462 span: opaque_ty_span,
1465 // Insert the item into the global item list. This usually happens
1466 // automatically for all AST items. But this opaque type item
1467 // does not actually exist in the AST.
1468 self.insert_item(opaque_ty_item);
1472 fn lifetimes_from_impl_trait_bounds(
1474 opaque_ty_id: NodeId,
1475 parent_index: DefIndex,
1476 bounds: hir::GenericBounds<'hir>,
1477 ) -> (&'hir [hir::GenericArg<'hir>], HirVec<hir::GenericParam<'hir>>) {
1479 "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \
1480 parent_index={:?}, \
1482 opaque_ty_id, parent_index, bounds,
1485 // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that
1486 // appear in the bounds, excluding lifetimes that are created within the bounds.
1487 // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`.
1488 struct ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1489 context: &'r mut LoweringContext<'a, 'hir>,
1491 opaque_ty_id: NodeId,
1492 collect_elided_lifetimes: bool,
1493 currently_bound_lifetimes: Vec<hir::LifetimeName>,
1494 already_defined_lifetimes: FxHashSet<hir::LifetimeName>,
1495 output_lifetimes: Vec<hir::GenericArg<'hir>>,
1496 output_lifetime_params: Vec<hir::GenericParam<'hir>>,
1499 impl<'r, 'a, 'v, 'hir> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> {
1500 fn nested_visit_map<'this>(
1502 ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1503 hir::intravisit::NestedVisitorMap::None
1506 fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) {
1507 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1508 if parameters.parenthesized {
1509 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1510 self.collect_elided_lifetimes = false;
1511 hir::intravisit::walk_generic_args(self, span, parameters);
1512 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1514 hir::intravisit::walk_generic_args(self, span, parameters);
1518 fn visit_ty(&mut self, t: &'v hir::Ty<'v>) {
1519 // Don't collect elided lifetimes used inside of `fn()` syntax.
1520 if let hir::TyKind::BareFn(_) = t.kind {
1521 let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1522 self.collect_elided_lifetimes = false;
1524 // Record the "stack height" of `for<'a>` lifetime bindings
1525 // to be able to later fully undo their introduction.
1526 let old_len = self.currently_bound_lifetimes.len();
1527 hir::intravisit::walk_ty(self, t);
1528 self.currently_bound_lifetimes.truncate(old_len);
1530 self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1532 hir::intravisit::walk_ty(self, t)
1536 fn visit_poly_trait_ref(
1538 trait_ref: &'v hir::PolyTraitRef<'v>,
1539 modifier: hir::TraitBoundModifier,
1541 // Record the "stack height" of `for<'a>` lifetime bindings
1542 // to be able to later fully undo their introduction.
1543 let old_len = self.currently_bound_lifetimes.len();
1544 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1545 self.currently_bound_lifetimes.truncate(old_len);
1548 fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) {
1549 // Record the introduction of 'a in `for<'a> ...`.
1550 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1551 // Introduce lifetimes one at a time so that we can handle
1552 // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`.
1553 let lt_name = hir::LifetimeName::Param(param.name);
1554 self.currently_bound_lifetimes.push(lt_name);
1557 hir::intravisit::walk_generic_param(self, param);
1560 fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1561 let name = match lifetime.name {
1562 hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1563 if self.collect_elided_lifetimes {
1564 // Use `'_` for both implicit and underscore lifetimes in
1565 // `type Foo<'_> = impl SomeTrait<'_>;`.
1566 hir::LifetimeName::Underscore
1571 hir::LifetimeName::Param(_) => lifetime.name,
1573 // Refers to some other lifetime that is "in
1574 // scope" within the type.
1575 hir::LifetimeName::ImplicitObjectLifetimeDefault => return,
1577 hir::LifetimeName::Error | hir::LifetimeName::Static => return,
1580 if !self.currently_bound_lifetimes.contains(&name)
1581 && !self.already_defined_lifetimes.contains(&name)
1583 self.already_defined_lifetimes.insert(name);
1585 self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime {
1586 hir_id: self.context.next_id(),
1587 span: lifetime.span,
1591 let def_node_id = self.context.resolver.next_node_id();
1593 self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id);
1594 self.context.resolver.definitions().create_def_with_parent(
1597 DefPathData::LifetimeNs(name.ident().name),
1602 let (name, kind) = match name {
1603 hir::LifetimeName::Underscore => (
1604 hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)),
1605 hir::LifetimeParamKind::Elided,
1607 hir::LifetimeName::Param(param_name) => {
1608 (param_name, hir::LifetimeParamKind::Explicit)
1610 _ => bug!("expected `LifetimeName::Param` or `ParamName::Plain`"),
1613 self.output_lifetime_params.push(hir::GenericParam {
1616 span: lifetime.span,
1617 pure_wrt_drop: false,
1620 kind: hir::GenericParamKind::Lifetime { kind },
1626 let mut lifetime_collector = ImplTraitLifetimeCollector {
1628 parent: parent_index,
1630 collect_elided_lifetimes: true,
1631 currently_bound_lifetimes: Vec::new(),
1632 already_defined_lifetimes: FxHashSet::default(),
1633 output_lifetimes: Vec::new(),
1634 output_lifetime_params: Vec::new(),
1637 for bound in bounds {
1638 hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1641 let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } =
1644 (self.arena.alloc_from_iter(output_lifetimes), output_lifetime_params.into())
1650 qself: &Option<QSelf>,
1652 param_mode: ParamMode,
1653 mut itctx: ImplTraitContext<'_, 'hir>,
1654 ) -> hir::QPath<'hir> {
1655 let qself_position = qself.as_ref().map(|q| q.position);
1656 let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));
1659 self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
1661 let proj_start = p.segments.len() - partial_res.unresolved_segments();
1662 let path = self.arena.alloc(hir::Path {
1663 res: self.lower_res(partial_res.base_res()),
1664 segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
1666 let param_mode = match (qself_position, param_mode) {
1667 (Some(j), ParamMode::Optional) if i < j => {
1668 // This segment is part of the trait path in a
1669 // qualified path - one of `a`, `b` or `Trait`
1670 // in `<X as a::b::Trait>::T::U::method`.
1676 // Figure out if this is a type/trait segment,
1677 // which may need lifetime elision performed.
1678 let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1679 krate: def_id.krate,
1680 index: this.def_key(def_id).parent.expect("missing parent"),
1682 let type_def_id = match partial_res.base_res() {
1683 Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
1684 Some(parent_def_id(self, def_id))
1686 Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
1687 Some(parent_def_id(self, def_id))
1689 Res::Def(DefKind::Struct, def_id)
1690 | Res::Def(DefKind::Union, def_id)
1691 | Res::Def(DefKind::Enum, def_id)
1692 | Res::Def(DefKind::TyAlias, def_id)
1693 | Res::Def(DefKind::Trait, def_id)
1694 if i + 1 == proj_start =>
1700 let parenthesized_generic_args = match partial_res.base_res() {
1701 // `a::b::Trait(Args)`
1702 Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
1703 ParenthesizedGenericArgs::Ok
1705 // `a::b::Trait(Args)::TraitItem`
1706 Res::Def(DefKind::Method, _)
1707 | Res::Def(DefKind::AssocConst, _)
1708 | Res::Def(DefKind::AssocTy, _)
1709 if i + 2 == proj_start =>
1711 ParenthesizedGenericArgs::Ok
1713 // Avoid duplicated errors.
1714 Res::Err => ParenthesizedGenericArgs::Ok,
1716 _ => ParenthesizedGenericArgs::Err,
1719 let num_lifetimes = type_def_id.map_or(0, |def_id| {
1720 if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1723 assert!(!def_id.is_local());
1724 let item_generics = self
1727 .item_generics_cloned_untracked(def_id, self.sess);
1728 let n = item_generics.own_counts().lifetimes;
1729 self.type_def_lifetime_params.insert(def_id, n);
1732 self.lower_path_segment(
1737 parenthesized_generic_args,
1746 // Simple case, either no projections, or only fully-qualified.
1747 // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
1748 if partial_res.unresolved_segments() == 0 {
1749 return hir::QPath::Resolved(qself, path);
1752 // Create the innermost type that we're projecting from.
1753 let mut ty = if path.segments.is_empty() {
1754 // If the base path is empty that means there exists a
1755 // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
1756 qself.expect("missing QSelf for <T>::...")
1758 // Otherwise, the base path is an implicit `Self` type path,
1759 // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1760 // `<I as Iterator>::Item::default`.
1761 let new_id = self.next_id();
1762 self.arena.alloc(self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path)))
1765 // Anything after the base path are associated "extensions",
1766 // out of which all but the last one are associated types,
1767 // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1768 // * base path is `std::vec::Vec<T>`
1769 // * "extensions" are `IntoIter`, `Item` and `clone`
1770 // * type nodes are:
1771 // 1. `std::vec::Vec<T>` (created above)
1772 // 2. `<std::vec::Vec<T>>::IntoIter`
1773 // 3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1774 // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1775 for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1776 let segment = self.arena.alloc(self.lower_path_segment(
1781 ParenthesizedGenericArgs::Err,
1785 let qpath = hir::QPath::TypeRelative(ty, segment);
1787 // It's finished, return the extension of the right node type.
1788 if i == p.segments.len() - 1 {
1792 // Wrap the associated extension in another type node.
1793 let new_id = self.next_id();
1794 ty = self.arena.alloc(self.ty_path(new_id, p.span, qpath));
1797 // We should've returned in the for loop above.
1800 "lower_qpath: no final extension segment in {}..{}",
1806 fn lower_path_extra(
1810 param_mode: ParamMode,
1811 explicit_owner: Option<NodeId>,
1812 ) -> hir::Path<'hir> {
1815 segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
1816 self.lower_path_segment(
1821 ParenthesizedGenericArgs::Err,
1822 ImplTraitContext::disallowed(),
1830 fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path<'hir> {
1831 let res = self.expect_full_res(id);
1832 let res = self.lower_res(res);
1833 self.lower_path_extra(res, p, param_mode, None)
1836 fn lower_path_segment(
1839 segment: &PathSegment,
1840 param_mode: ParamMode,
1841 expected_lifetimes: usize,
1842 parenthesized_generic_args: ParenthesizedGenericArgs,
1843 itctx: ImplTraitContext<'_, 'hir>,
1844 explicit_owner: Option<NodeId>,
1845 ) -> hir::PathSegment<'hir> {
1846 let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
1847 let msg = "parenthesized type parameters may only be used with a `Fn` trait";
1848 match **generic_args {
1849 GenericArgs::AngleBracketed(ref data) => {
1850 self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1852 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1853 ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1854 ParenthesizedGenericArgs::Err => {
1855 let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
1856 err.span_label(data.span, "only `Fn` traits may use parentheses");
1857 if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
1858 // Do not suggest going from `Trait()` to `Trait<>`
1859 if data.inputs.len() > 0 {
1860 if let Some(split) = snippet.find('(') {
1861 let trait_name = &snippet[0..split];
1862 let args = &snippet[split + 1..snippet.len() - 1];
1863 err.span_suggestion(
1865 "use angle brackets instead",
1866 format!("{}<{}>", trait_name, args),
1867 Applicability::MaybeIncorrect,
1874 self.lower_angle_bracketed_parameter_data(
1875 &data.as_angle_bracketed_args(),
1886 self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1889 let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1890 GenericArg::Lifetime(_) => true,
1893 let first_generic_span = generic_args
1897 .chain(generic_args.bindings.iter().map(|b| b.span))
1899 if !generic_args.parenthesized && !has_lifetimes {
1900 generic_args.args = self
1901 .elided_path_lifetimes(path_span, expected_lifetimes)
1903 .map(|lt| GenericArg::Lifetime(lt))
1904 .chain(generic_args.args.into_iter())
1906 if expected_lifetimes > 0 && param_mode == ParamMode::Explicit {
1907 let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
1908 let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
1909 let no_bindings = generic_args.bindings.is_empty();
1910 let (incl_angl_brckt, insertion_sp, suggestion) = if no_non_lt_args && no_bindings {
1911 // If there are no (non-implicit) generic args or associated type
1912 // bindings, our suggestion includes the angle brackets.
1913 (true, path_span.shrink_to_hi(), format!("<{}>", anon_lt_suggestion))
1915 // Otherwise (sorry, this is kind of gross) we need to infer the
1916 // place to splice in the `'_, ` from the generics that do exist.
1917 let first_generic_span = first_generic_span
1918 .expect("already checked that non-lifetime args or bindings exist");
1919 (false, first_generic_span.shrink_to_lo(), format!("{}, ", anon_lt_suggestion))
1921 match self.anonymous_lifetime_mode {
1922 // In create-parameter mode we error here because we don't want to support
1923 // deprecated impl elision in new features like impl elision and `async fn`,
1924 // both of which work using the `CreateParameter` mode:
1926 // impl Foo for std::cell::Ref<u32> // note lack of '_
1927 // async fn foo(_: std::cell::Ref<u32>) { ... }
1928 AnonymousLifetimeMode::CreateParameter => {
1929 let mut err = struct_span_err!(
1933 "implicit elided lifetime not allowed here"
1935 crate::lint::builtin::add_elided_lifetime_in_path_suggestion(
1946 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
1947 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
1948 ELIDED_LIFETIMES_IN_PATHS,
1951 "hidden lifetime parameters in types are deprecated",
1952 builtin::BuiltinLintDiagnostics::ElidedLifetimesInPaths(
1965 let res = self.expect_full_res(segment.id);
1966 let id = if let Some(owner) = explicit_owner {
1967 self.lower_node_id_with_owner(segment.id, owner)
1969 self.lower_node_id(segment.id)
1972 "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
1973 segment.ident, segment.id, id,
1977 ident: segment.ident,
1979 res: Some(self.lower_res(res)),
1981 args: if generic_args.is_empty() { None } else { Some(self.arena.alloc(generic_args)) },
1985 fn lower_angle_bracketed_parameter_data(
1987 data: &AngleBracketedArgs,
1988 param_mode: ParamMode,
1989 mut itctx: ImplTraitContext<'_, 'hir>,
1990 ) -> (hir::GenericArgs<'hir>, bool) {
1991 let &AngleBracketedArgs { ref args, ref constraints, .. } = data;
1992 let has_non_lt_args = args.iter().any(|arg| match arg {
1993 ast::GenericArg::Lifetime(_) => false,
1994 ast::GenericArg::Type(_) => true,
1995 ast::GenericArg::Const(_) => true,
1999 args: args.iter().map(|a| self.lower_generic_arg(a, itctx.reborrow())).collect(),
2000 bindings: self.arena.alloc_from_iter(
2001 constraints.iter().map(|b| self.lower_assoc_ty_constraint(b, itctx.reborrow())),
2003 parenthesized: false,
2005 !has_non_lt_args && param_mode == ParamMode::Optional,
2009 fn lower_parenthesized_parameter_data(
2011 data: &ParenthesizedArgs,
2012 ) -> (hir::GenericArgs<'hir>, bool) {
2013 // Switch to `PassThrough` mode for anonymous lifetimes; this
2014 // means that we permit things like `&Ref<T>`, where `Ref` has
2015 // a hidden lifetime parameter. This is needed for backwards
2016 // compatibility, even in contexts like an impl header where
2017 // we generally don't permit such things (see #51008).
2018 self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
2019 let &ParenthesizedArgs { ref inputs, ref output, span } = data;
2020 let inputs = this.arena.alloc_from_iter(
2021 inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
2023 let output_ty = match output {
2024 FunctionRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
2025 FunctionRetTy::Default(_) => this.arena.alloc(this.ty_tup(span, &[])),
2027 let args = hir_vec![GenericArg::Type(this.ty_tup(span, inputs))];
2028 let binding = hir::TypeBinding {
2029 hir_id: this.next_id(),
2030 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2031 span: output_ty.span,
2032 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2035 hir::GenericArgs { args, bindings: arena_vec![this; binding], parenthesized: true },
2041 fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) {
2042 let mut ids = SmallVec::<[NodeId; 1]>::new();
2043 if self.sess.features_untracked().impl_trait_in_bindings {
2044 if let Some(ref ty) = l.ty {
2045 let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
2046 visitor.visit_ty(ty);
2049 let parent_def_id = DefId::local(self.current_hir_id_owner.last().unwrap().0);
2050 let ty = l.ty.as_ref().map(|t| {
2053 if self.sess.features_untracked().impl_trait_in_bindings {
2054 ImplTraitContext::OpaqueTy(Some(parent_def_id))
2056 ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
2060 let init = l.init.as_ref().map(|e| self.lower_expr(e));
2063 hir_id: self.lower_node_id(l.id),
2065 pat: self.lower_pat(&l.pat),
2068 attrs: l.attrs.clone(),
2069 source: hir::LocalSource::Normal,
2075 fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Ident> {
2076 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2077 // as they are not explicit in HIR/Ty function signatures.
2078 // (instead, the `c_variadic` flag is set to `true`)
2079 let mut inputs = &decl.inputs[..];
2080 if decl.c_variadic() {
2081 inputs = &inputs[..inputs.len() - 1];
2085 .map(|param| match param.pat.kind {
2086 PatKind::Ident(_, ident, _) => ident,
2087 _ => Ident::new(kw::Invalid, param.pat.span),
2092 // Lowers a function declaration.
2094 // `decl`: the unlowered (AST) function declaration.
2095 // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the
2096 // given DefId, otherwise impl Trait is disallowed. Must be `Some` if
2097 // `make_ret_async` is also `Some`.
2098 // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position.
2099 // This guards against trait declarations and implementations where `impl Trait` is
2101 // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future<Output = T>` in the
2102 // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the
2103 // return type `impl Trait` item.
2107 mut in_band_ty_params: Option<(DefId, &mut Vec<hir::GenericParam<'hir>>)>,
2108 impl_trait_return_allow: bool,
2109 make_ret_async: Option<NodeId>,
2110 ) -> &'hir hir::FnDecl<'hir> {
2114 in_band_ty_params: {:?}, \
2115 impl_trait_return_allow: {}, \
2116 make_ret_async: {:?})",
2117 decl, in_band_ty_params, impl_trait_return_allow, make_ret_async,
2119 let lt_mode = if make_ret_async.is_some() {
2120 // In `async fn`, argument-position elided lifetimes
2121 // must be transformed into fresh generic parameters so that
2122 // they can be applied to the opaque `impl Trait` return type.
2123 AnonymousLifetimeMode::CreateParameter
2125 self.anonymous_lifetime_mode
2128 let c_variadic = decl.c_variadic();
2130 // Remember how many lifetimes were already around so that we can
2131 // only look at the lifetime parameters introduced by the arguments.
2132 let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| {
2133 // Skip the `...` (`CVarArgs`) trailing arguments from the AST,
2134 // as they are not explicit in HIR/Ty function signatures.
2135 // (instead, the `c_variadic` flag is set to `true`)
2136 let mut inputs = &decl.inputs[..];
2138 inputs = &inputs[..inputs.len() - 1];
2140 this.arena.alloc_from_iter(inputs.iter().map(|param| {
2141 if let Some((_, ibty)) = &mut in_band_ty_params {
2142 this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty))
2144 this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed())
2149 let output = if let Some(ret_id) = make_ret_async {
2150 self.lower_async_fn_ret_ty(
2152 in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0,
2157 FunctionRetTy::Ty(ref ty) => match in_band_ty_params {
2158 Some((def_id, _)) if impl_trait_return_allow => {
2159 hir::Return(self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(def_id))))
2161 _ => hir::Return(self.lower_ty(ty, ImplTraitContext::disallowed())),
2163 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
2167 self.arena.alloc(hir::FnDecl {
2171 implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| {
2172 let is_mutable_pat = match arg.pat.kind {
2173 PatKind::Ident(BindingMode::ByValue(mt), _, _)
2174 | PatKind::Ident(BindingMode::ByRef(mt), _, _) => mt == Mutability::Mut,
2179 TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut,
2180 TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm,
2181 // Given we are only considering `ImplicitSelf` types, we needn't consider
2182 // the case where we have a mutable pattern to a reference as that would
2183 // no longer be an `ImplicitSelf`.
2184 TyKind::Rptr(_, ref mt)
2185 if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut =>
2187 hir::ImplicitSelfKind::MutRef
2189 TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => {
2190 hir::ImplicitSelfKind::ImmRef
2192 _ => hir::ImplicitSelfKind::None,
2198 // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }`
2199 // combined with the following definition of `OpaqueTy`:
2201 // type OpaqueTy<generics_from_parent_fn> = impl Future<Output = T>;
2203 // `inputs`: lowered types of parameters to the function (used to collect lifetimes)
2204 // `output`: unlowered output type (`T` in `-> T`)
2205 // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition)
2206 // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created
2207 // `elided_lt_replacement`: replacement for elided lifetimes in the return type
2208 fn lower_async_fn_ret_ty(
2210 output: &FunctionRetTy,
2212 opaque_ty_node_id: NodeId,
2213 ) -> hir::FunctionRetTy<'hir> {
2215 "lower_async_fn_ret_ty(\
2218 opaque_ty_node_id={:?})",
2219 output, fn_def_id, opaque_ty_node_id,
2222 let span = output.span();
2224 let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None);
2226 let opaque_ty_def_index =
2227 self.resolver.definitions().opt_def_index(opaque_ty_node_id).unwrap();
2229 self.allocate_hir_id_counter(opaque_ty_node_id);
2231 // When we create the opaque type for this async fn, it is going to have
2232 // to capture all the lifetimes involved in the signature (including in the
2233 // return type). This is done by introducing lifetime parameters for:
2235 // - all the explicitly declared lifetimes from the impl and function itself;
2236 // - all the elided lifetimes in the fn arguments;
2237 // - all the elided lifetimes in the return type.
2239 // So for example in this snippet:
2242 // impl<'a> Foo<'a> {
2243 // async fn bar<'b>(&self, x: &'b Vec<f64>, y: &str) -> &u32 {
2244 // // ^ '0 ^ '1 ^ '2
2245 // // elided lifetimes used below
2250 // we would create an opaque type like:
2253 // type Bar<'a, 'b, '0, '1, '2> = impl Future<Output = &'2 u32>;
2256 // and we would then desugar `bar` to the equivalent of:
2259 // impl<'a> Foo<'a> {
2260 // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec<f64>, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_>
2264 // Note that the final parameter to `Bar` is `'_`, not `'2` --
2265 // this is because the elided lifetimes from the return type
2266 // should be figured out using the ordinary elision rules, and
2267 // this desugaring achieves that.
2269 // The variable `input_lifetimes_count` tracks the number of
2270 // lifetime parameters to the opaque type *not counting* those
2271 // lifetimes elided in the return type. This includes those
2272 // that are explicitly declared (`in_scope_lifetimes`) and
2273 // those elided lifetimes we found in the arguments (current
2274 // content of `lifetimes_to_define`). Next, we will process
2275 // the return type, which will cause `lifetimes_to_define` to
2277 let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len();
2279 let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| {
2280 // We have to be careful to get elision right here. The
2281 // idea is that we create a lifetime parameter for each
2282 // lifetime in the return type. So, given a return type
2283 // like `async fn foo(..) -> &[&u32]`, we lower to `impl
2284 // Future<Output = &'1 [ &'2 u32 ]>`.
2286 // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and
2287 // hence the elision takes place at the fn site.
2288 let future_bound = this
2289 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| {
2290 this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span)
2293 debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound);
2295 // Calculate all the lifetimes that should be captured
2296 // by the opaque type. This should include all in-scope
2297 // lifetime parameters, including those defined in-band.
2299 // Note: this must be done after lowering the output type,
2300 // as the output type may introduce new in-band lifetimes.
2301 let lifetime_params: Vec<(Span, ParamName)> = this
2305 .map(|name| (name.ident().span, name))
2306 .chain(this.lifetimes_to_define.iter().cloned())
2309 debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes);
2310 debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define);
2311 debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params);
2313 let generic_params = lifetime_params
2315 .map(|(span, hir_name)| {
2316 this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_index)
2320 let opaque_ty_item = hir::OpaqueTy {
2321 generics: hir::Generics {
2322 params: generic_params,
2323 where_clause: hir::WhereClause { predicates: &[], span },
2326 bounds: arena_vec![this; future_bound],
2327 impl_trait_fn: Some(fn_def_id),
2328 origin: hir::OpaqueTyOrigin::AsyncFn,
2331 trace!("exist ty from async fn def index: {:#?}", opaque_ty_def_index);
2333 this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span);
2335 (opaque_ty_id, lifetime_params)
2338 // As documented above on the variable
2339 // `input_lifetimes_count`, we need to create the lifetime
2340 // arguments to our opaque type. Continuing with our example,
2341 // we're creating the type arguments for the return type:
2344 // Bar<'a, 'b, '0, '1, '_>
2347 // For the "input" lifetime parameters, we wish to create
2348 // references to the parameters themselves, including the
2349 // "implicit" ones created from parameter types (`'a`, `'b`,
2352 // For the "output" lifetime parameters, we just want to
2354 let mut generic_args: Vec<_> = lifetime_params[..input_lifetimes_count]
2356 .map(|&(span, hir_name)| {
2357 // Input lifetime like `'a` or `'1`:
2358 GenericArg::Lifetime(hir::Lifetime {
2359 hir_id: self.next_id(),
2361 name: hir::LifetimeName::Param(hir_name),
2365 generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)|
2366 // Output lifetime like `'_`.
2367 GenericArg::Lifetime(hir::Lifetime {
2368 hir_id: self.next_id(),
2370 name: hir::LifetimeName::Implicit,
2372 let generic_args = self.arena.alloc_from_iter(generic_args);
2374 // Create the `Foo<...>` reference itself. Note that the `type
2375 // Foo = impl Trait` is, internally, created as a child of the
2376 // async fn, so the *type parameters* are inherited. It's
2377 // only the lifetime parameters that we must supply.
2378 let opaque_ty_ref = hir::TyKind::Def(hir::ItemId { id: opaque_ty_id }, generic_args);
2379 let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref);
2380 hir::FunctionRetTy::Return(self.arena.alloc(opaque_ty))
2383 /// Transforms `-> T` into `Future<Output = T>`
2384 fn lower_async_fn_output_type_to_future_bound(
2386 output: &FunctionRetTy,
2389 ) -> hir::GenericBound<'hir> {
2390 // Compute the `T` in `Future<Output = T>` from the return type.
2391 let output_ty = match output {
2392 FunctionRetTy::Ty(ty) => self.lower_ty(ty, ImplTraitContext::OpaqueTy(Some(fn_def_id))),
2393 FunctionRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])),
2397 let future_params = self.arena.alloc(hir::GenericArgs {
2398 args: HirVec::new(),
2399 bindings: arena_vec![self; hir::TypeBinding {
2400 ident: Ident::with_dummy_span(FN_OUTPUT_NAME),
2401 kind: hir::TypeBindingKind::Equality { ty: output_ty },
2402 hir_id: self.next_id(),
2405 parenthesized: false,
2408 // ::std::future::Future<future_params>
2409 let future_path = self.arena.alloc(self.std_path(
2411 &[sym::future, sym::Future],
2412 Some(future_params),
2416 hir::GenericBound::Trait(
2418 trait_ref: hir::TraitRef { path: future_path, hir_ref_id: self.next_id() },
2419 bound_generic_params: &[],
2422 hir::TraitBoundModifier::None,
2426 fn lower_param_bound(
2429 itctx: ImplTraitContext<'_, 'hir>,
2430 ) -> hir::GenericBound<'hir> {
2432 GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
2433 self.lower_poly_trait_ref(ty, itctx),
2434 self.lower_trait_bound_modifier(modifier),
2436 GenericBound::Outlives(ref lifetime) => {
2437 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
2442 fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
2443 let span = l.ident.span;
2445 ident if ident.name == kw::StaticLifetime => {
2446 self.new_named_lifetime(l.id, span, hir::LifetimeName::Static)
2448 ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode {
2449 AnonymousLifetimeMode::CreateParameter => {
2450 let fresh_name = self.collect_fresh_in_band_lifetime(span);
2451 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
2454 AnonymousLifetimeMode::PassThrough => {
2455 self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
2458 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span),
2461 self.maybe_collect_in_band_lifetime(ident);
2462 let param_name = ParamName::Plain(ident);
2463 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
2468 fn new_named_lifetime(
2472 name: hir::LifetimeName,
2473 ) -> hir::Lifetime {
2474 hir::Lifetime { hir_id: self.lower_node_id(id), span, name }
2477 fn lower_generic_params(
2479 params: &[GenericParam],
2480 add_bounds: &NodeMap<Vec<GenericBound>>,
2481 mut itctx: ImplTraitContext<'_, 'hir>,
2482 ) -> HirVec<hir::GenericParam<'hir>> {
2485 .map(|param| self.lower_generic_param(param, add_bounds, itctx.reborrow()))
2489 fn lower_generic_param(
2491 param: &GenericParam,
2492 add_bounds: &NodeMap<Vec<GenericBound>>,
2493 mut itctx: ImplTraitContext<'_, 'hir>,
2494 ) -> hir::GenericParam<'hir> {
2495 let mut bounds: Vec<_> = self
2496 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2497 this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect()
2500 let (name, kind) = match param.kind {
2501 GenericParamKind::Lifetime => {
2502 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
2503 self.is_collecting_in_band_lifetimes = false;
2506 .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
2507 this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident })
2509 let param_name = match lt.name {
2510 hir::LifetimeName::Param(param_name) => param_name,
2511 hir::LifetimeName::Implicit
2512 | hir::LifetimeName::Underscore
2513 | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()),
2514 hir::LifetimeName::ImplicitObjectLifetimeDefault => {
2517 "object-lifetime-default should not occur here",
2520 hir::LifetimeName::Error => ParamName::Error,
2524 hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
2526 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
2530 GenericParamKind::Type { ref default, .. } => {
2531 let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x);
2532 if !add_bounds.is_empty() {
2533 let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow());
2534 bounds.extend(params);
2537 let kind = hir::GenericParamKind::Type {
2540 .map(|x| self.lower_ty(x, ImplTraitContext::OpaqueTy(None))),
2544 .filter(|attr| attr.check_name(sym::rustc_synthetic))
2545 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
2549 (hir::ParamName::Plain(param.ident), kind)
2551 GenericParamKind::Const { ref ty } => (
2552 hir::ParamName::Plain(param.ident),
2553 hir::GenericParamKind::Const {
2554 ty: self.lower_ty(&ty, ImplTraitContext::disallowed()),
2560 hir_id: self.lower_node_id(param.id),
2562 span: param.ident.span,
2563 pure_wrt_drop: attr::contains_name(¶m.attrs, sym::may_dangle),
2564 attrs: self.lower_attrs_arena(¶m.attrs),
2565 bounds: self.arena.alloc_from_iter(bounds),
2573 itctx: ImplTraitContext<'_, 'hir>,
2574 ) -> hir::TraitRef<'hir> {
2575 let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2576 hir::QPath::Resolved(None, path) => path,
2577 qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2579 hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) }
2582 fn lower_poly_trait_ref(
2585 mut itctx: ImplTraitContext<'_, 'hir>,
2586 ) -> hir::PolyTraitRef<'hir> {
2587 let bound_generic_params = self.lower_generic_params(
2588 &p.bound_generic_params,
2589 &NodeMap::default(),
2592 let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| {
2593 this.lower_trait_ref(&p.trait_ref, itctx)
2597 bound_generic_params: self.arena.alloc_from_iter(bound_generic_params.into_iter()),
2603 fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> {
2604 hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl }
2607 fn lower_param_bounds(
2609 bounds: &[GenericBound],
2610 itctx: ImplTraitContext<'_, 'hir>,
2611 ) -> hir::GenericBounds<'hir> {
2612 self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx))
2615 fn lower_param_bounds_mut<'s>(
2617 bounds: &'s [GenericBound],
2618 mut itctx: ImplTraitContext<'s, 'hir>,
2619 ) -> impl Iterator<Item = hir::GenericBound<'hir>> + Captures<'s> + Captures<'a> {
2620 bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow()))
2623 fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> {
2624 self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break))
2627 fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> {
2628 let mut stmts = vec![];
2629 let mut expr: Option<&'hir _> = None;
2631 for (index, stmt) in b.stmts.iter().enumerate() {
2632 if index == b.stmts.len() - 1 {
2633 if let StmtKind::Expr(ref e) = stmt.kind {
2634 expr = Some(self.lower_expr(e));
2636 stmts.extend(self.lower_stmt(stmt));
2639 stmts.extend(self.lower_stmt(stmt));
2644 hir_id: self.lower_node_id(b.id),
2645 stmts: self.arena.alloc_from_iter(stmts),
2647 rules: self.lower_block_check_mode(&b.rules),
2653 /// Lowers a block directly to an expression, presuming that it
2654 /// has no attributes and is not targeted by a `break`.
2655 fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> {
2656 let block = self.lower_block(b, false);
2657 self.expr_block(block, AttrVec::new())
2660 fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2661 let node = match p.kind {
2662 PatKind::Wild => hir::PatKind::Wild,
2663 PatKind::Ident(ref binding_mode, ident, ref sub) => {
2664 let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
2665 let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
2668 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
2669 PatKind::TupleStruct(ref path, ref pats) => {
2670 let qpath = self.lower_qpath(
2674 ParamMode::Optional,
2675 ImplTraitContext::disallowed(),
2677 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
2678 hir::PatKind::TupleStruct(qpath, pats, ddpos)
2680 PatKind::Or(ref pats) => {
2681 hir::PatKind::Or(self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))))
2683 PatKind::Path(ref qself, ref path) => {
2684 let qpath = self.lower_qpath(
2688 ParamMode::Optional,
2689 ImplTraitContext::disallowed(),
2691 hir::PatKind::Path(qpath)
2693 PatKind::Struct(ref path, ref fields, etc) => {
2694 let qpath = self.lower_qpath(
2698 ParamMode::Optional,
2699 ImplTraitContext::disallowed(),
2702 let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
2703 hir_id: self.next_id(),
2705 pat: self.lower_pat(&f.pat),
2706 is_shorthand: f.is_shorthand,
2709 hir::PatKind::Struct(qpath, fs, etc)
2711 PatKind::Tuple(ref pats) => {
2712 let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
2713 hir::PatKind::Tuple(pats, ddpos)
2715 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2716 PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
2717 PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => hir::PatKind::Range(
2718 self.lower_expr(e1),
2719 self.lower_expr(e2),
2720 self.lower_range_end(end),
2722 PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
2724 // If we reach here the `..` pattern is not semantically allowed.
2725 self.ban_illegal_rest_pat(p.span)
2727 PatKind::Paren(ref inner) => return self.lower_pat(inner),
2728 PatKind::Mac(_) => panic!("Shouldn't exist here"),
2731 self.pat_with_node_id_of(p, node)
2738 ) -> (&'hir [&'hir hir::Pat<'hir>], Option<usize>) {
2739 let mut elems = Vec::with_capacity(pats.len());
2740 let mut rest = None;
2742 let mut iter = pats.iter().enumerate();
2743 for (idx, pat) in iter.by_ref() {
2744 // Interpret the first `..` pattern as a sub-tuple pattern.
2745 // Note that unlike for slice patterns,
2746 // where `xs @ ..` is a legal sub-slice pattern,
2747 // it is not a legal sub-tuple pattern.
2749 rest = Some((idx, pat.span));
2752 // It was not a sub-tuple pattern so lower it normally.
2753 elems.push(self.lower_pat(pat));
2756 for (_, pat) in iter {
2757 // There was a previous sub-tuple pattern; make sure we don't allow more...
2759 // ...but there was one again, so error.
2760 self.ban_extra_rest_pat(pat.span, rest.unwrap().1, ctx);
2762 elems.push(self.lower_pat(pat));
2766 (self.arena.alloc_from_iter(elems), rest.map(|(ddpos, _)| ddpos))
2769 /// Lower a slice pattern of form `[pat_0, ..., pat_n]` into
2770 /// `hir::PatKind::Slice(before, slice, after)`.
2772 /// When encountering `($binding_mode $ident @)? ..` (`slice`),
2773 /// this is interpreted as a sub-slice pattern semantically.
2774 /// Patterns that follow, which are not like `slice` -- or an error occurs, are in `after`.
2775 fn lower_pat_slice(&mut self, pats: &[AstP<Pat>]) -> hir::PatKind<'hir> {
2776 let mut before = Vec::new();
2777 let mut after = Vec::new();
2778 let mut slice = None;
2779 let mut prev_rest_span = None;
2781 let mut iter = pats.iter();
2782 // Lower all the patterns until the first occurence of a sub-slice pattern.
2783 for pat in iter.by_ref() {
2785 // Found a sub-slice pattern `..`. Record, lower it to `_`, and stop here.
2787 prev_rest_span = Some(pat.span);
2788 slice = Some(self.pat_wild_with_node_id_of(pat));
2791 // Found a sub-slice pattern `$binding_mode $ident @ ..`.
2792 // Record, lower it to `$binding_mode $ident @ _`, and stop here.
2793 PatKind::Ident(ref bm, ident, Some(ref sub)) if sub.is_rest() => {
2794 prev_rest_span = Some(sub.span);
2795 let lower_sub = |this: &mut Self| Some(this.pat_wild_with_node_id_of(sub));
2796 let node = self.lower_pat_ident(pat, bm, ident, lower_sub);
2797 slice = Some(self.pat_with_node_id_of(pat, node));
2800 // It was not a subslice pattern so lower it normally.
2801 _ => before.push(self.lower_pat(pat)),
2805 // Lower all the patterns after the first sub-slice pattern.
2807 // There was a previous subslice pattern; make sure we don't allow more.
2808 let rest_span = match pat.kind {
2809 PatKind::Rest => Some(pat.span),
2810 PatKind::Ident(.., Some(ref sub)) if sub.is_rest() => {
2811 // The `HirValidator` is merciless; add a `_` pattern to avoid ICEs.
2812 after.push(self.pat_wild_with_node_id_of(pat));
2817 if let Some(rest_span) = rest_span {
2818 // We have e.g., `[a, .., b, ..]`. That's no good, error!
2819 self.ban_extra_rest_pat(rest_span, prev_rest_span.unwrap(), "slice");
2821 // Lower the pattern normally.
2822 after.push(self.lower_pat(pat));
2826 hir::PatKind::Slice(
2827 self.arena.alloc_from_iter(before),
2829 self.arena.alloc_from_iter(after),
2836 binding_mode: &BindingMode,
2838 lower_sub: impl FnOnce(&mut Self) -> Option<&'hir hir::Pat<'hir>>,
2839 ) -> hir::PatKind<'hir> {
2840 match self.resolver.get_partial_res(p.id).map(|d| d.base_res()) {
2841 // `None` can occur in body-less function signatures
2842 res @ None | res @ Some(Res::Local(_)) => {
2843 let canonical_id = match res {
2844 Some(Res::Local(id)) => id,
2848 hir::PatKind::Binding(
2849 self.lower_binding_mode(binding_mode),
2850 self.lower_node_id(canonical_id),
2855 Some(res) => hir::PatKind::Path(hir::QPath::Resolved(
2857 self.arena.alloc(hir::Path {
2859 res: self.lower_res(res),
2860 segments: arena_vec![self; hir::PathSegment::from_ident(ident)],
2866 fn pat_wild_with_node_id_of(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
2867 self.pat_with_node_id_of(p, hir::PatKind::Wild)
2870 /// Construct a `Pat` with the `HirId` of `p.id` lowered.
2871 fn pat_with_node_id_of(&mut self, p: &Pat, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
2872 self.arena.alloc(hir::Pat { hir_id: self.lower_node_id(p.id), kind, span: p.span })
2875 /// Emit a friendly error for extra `..` patterns in a tuple/tuple struct/slice pattern.
2876 fn ban_extra_rest_pat(&self, sp: Span, prev_sp: Span, ctx: &str) {
2878 .struct_span_err(sp, &format!("`..` can only be used once per {} pattern", ctx))
2879 .span_label(sp, &format!("can only be used once per {} pattern", ctx))
2880 .span_label(prev_sp, "previously used here")
2884 /// Used to ban the `..` pattern in places it shouldn't be semantically.
2885 fn ban_illegal_rest_pat(&self, sp: Span) -> hir::PatKind<'hir> {
2887 .struct_span_err(sp, "`..` patterns are not allowed here")
2888 .note("only allowed in tuple, tuple struct, and slice patterns")
2891 // We're not in a list context so `..` can be reasonably treated
2892 // as `_` because it should always be valid and roughly matches the
2893 // intent of `..` (notice that the rest of a single slot is that slot).
2897 fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2899 RangeEnd::Included(_) => hir::RangeEnd::Included,
2900 RangeEnd::Excluded => hir::RangeEnd::Excluded,
2904 fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
2905 self.with_new_scopes(|this| hir::AnonConst {
2906 hir_id: this.lower_node_id(c.id),
2907 body: this.lower_const_body(c.value.span, Some(&c.value)),
2911 fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> {
2912 let kind = match s.kind {
2913 StmtKind::Local(ref l) => {
2914 let (l, item_ids) = self.lower_local(l);
2915 let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids
2918 let item_id = hir::ItemId { id: self.lower_node_id(item_id) };
2919 self.stmt(s.span, hir::StmtKind::Item(item_id))
2924 hir_id: self.lower_node_id(s.id),
2925 kind: hir::StmtKind::Local(self.arena.alloc(l)),
2931 StmtKind::Item(ref it) => {
2932 // Can only use the ID once.
2933 let mut id = Some(s.id);
2940 .map(|id| self.lower_node_id(id))
2941 .unwrap_or_else(|| self.next_id());
2943 hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span }
2947 StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)),
2948 StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)),
2949 StmtKind::Mac(..) => panic!("shouldn't exist here"),
2951 smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }]
2954 fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2956 BlockCheckMode::Default => hir::DefaultBlock,
2957 BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2961 fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2963 BindingMode::ByValue(Mutability::Not) => hir::BindingAnnotation::Unannotated,
2964 BindingMode::ByRef(Mutability::Not) => hir::BindingAnnotation::Ref,
2965 BindingMode::ByValue(Mutability::Mut) => hir::BindingAnnotation::Mutable,
2966 BindingMode::ByRef(Mutability::Mut) => hir::BindingAnnotation::RefMut,
2970 fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2972 CompilerGenerated => hir::CompilerGenerated,
2973 UserProvided => hir::UserProvided,
2977 fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2979 TraitBoundModifier::None => hir::TraitBoundModifier::None,
2980 TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2984 // Helper methods for building HIR.
2986 fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> {
2987 hir::Stmt { span, kind, hir_id: self.next_id() }
2990 fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> {
2991 self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr)))
2998 init: Option<&'hir hir::Expr<'hir>>,
2999 pat: &'hir hir::Pat<'hir>,
3000 source: hir::LocalSource,
3001 ) -> hir::Stmt<'hir> {
3002 let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None };
3003 self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local)))
3006 fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> {
3007 self.block_all(expr.span, &[], Some(expr))
3013 stmts: &'hir [hir::Stmt<'hir>],
3014 expr: Option<&'hir hir::Expr<'hir>>,
3015 ) -> &'hir hir::Block<'hir> {
3016 let blk = hir::Block {
3019 hir_id: self.next_id(),
3020 rules: hir::DefaultBlock,
3022 targeted_by_break: false,
3024 self.arena.alloc(blk)
3027 /// Constructs a `true` or `false` literal pattern.
3028 fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> {
3029 let expr = self.expr_bool(span, val);
3030 self.pat(span, hir::PatKind::Lit(expr))
3033 fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3034 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Ok], arena_vec![self; pat])
3037 fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3038 self.pat_std_enum(span, &[sym::result, sym::Result, sym::Err], arena_vec![self; pat])
3041 fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
3042 self.pat_std_enum(span, &[sym::option, sym::Option, sym::Some], arena_vec![self; pat])
3045 fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3046 self.pat_std_enum(span, &[sym::option, sym::Option, sym::None], &[])
3052 components: &[Symbol],
3053 subpats: &'hir [&'hir hir::Pat<'hir>],
3054 ) -> &'hir hir::Pat<'hir> {
3055 let path = self.std_path(span, components, None, true);
3056 let qpath = hir::QPath::Resolved(None, self.arena.alloc(path));
3057 let pt = if subpats.is_empty() {
3058 hir::PatKind::Path(qpath)
3060 hir::PatKind::TupleStruct(qpath, subpats, None)
3065 fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3066 self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated)
3069 fn pat_ident_binding_mode(
3073 bm: hir::BindingAnnotation,
3074 ) -> (&'hir hir::Pat<'hir>, hir::HirId) {
3075 let hir_id = self.next_id();
3078 self.arena.alloc(hir::Pat {
3080 kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None),
3087 fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> {
3088 self.pat(span, hir::PatKind::Wild)
3091 fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> {
3092 self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span })
3095 /// Given a suffix `["b", "c", "d"]`, returns path `::std::b::c::d` when
3096 /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
3097 /// The path is also resolved according to `is_value`.
3101 components: &[Symbol],
3102 params: Option<&'hir hir::GenericArgs<'hir>>,
3104 ) -> hir::Path<'hir> {
3105 let ns = if is_value { Namespace::ValueNS } else { Namespace::TypeNS };
3106 let (path, res) = self.resolver.resolve_str_path(span, self.crate_root, components, ns);
3108 let mut segments: Vec<_> = path
3112 let res = self.expect_full_res(segment.id);
3114 ident: segment.ident,
3115 hir_id: Some(self.lower_node_id(segment.id)),
3116 res: Some(self.lower_res(res)),
3122 segments.last_mut().unwrap().args = params;
3126 res: res.map_id(|_| panic!("unexpected `NodeId`")),
3127 segments: self.arena.alloc_from_iter(segments),
3133 mut hir_id: hir::HirId,
3135 qpath: hir::QPath<'hir>,
3136 ) -> hir::Ty<'hir> {
3137 let kind = match qpath {
3138 hir::QPath::Resolved(None, path) => {
3139 // Turn trait object paths into `TyKind::TraitObject` instead.
3141 Res::Def(DefKind::Trait, _) | Res::Def(DefKind::TraitAlias, _) => {
3142 let principal = hir::PolyTraitRef {
3143 bound_generic_params: &[],
3144 trait_ref: hir::TraitRef { path, hir_ref_id: hir_id },
3148 // The original ID is taken by the `PolyTraitRef`,
3149 // so the `Ty` itself needs a different one.
3150 hir_id = self.next_id();
3151 hir::TyKind::TraitObject(
3152 arena_vec![self; principal],
3153 self.elided_dyn_bound(span),
3156 _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)),
3159 _ => hir::TyKind::Path(qpath),
3162 hir::Ty { hir_id, kind, span }
3165 /// Invoked to create the lifetime argument for a type `&T`
3166 /// with no explicit lifetime.
3167 fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
3168 match self.anonymous_lifetime_mode {
3169 // Intercept when we are in an impl header or async fn and introduce an in-band
3171 // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
3173 AnonymousLifetimeMode::CreateParameter => {
3174 let fresh_name = self.collect_fresh_in_band_lifetime(span);
3176 hir_id: self.next_id(),
3178 name: hir::LifetimeName::Param(fresh_name),
3182 AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span),
3184 AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
3188 /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime;
3189 /// return a "error lifetime".
3190 fn new_error_lifetime(&mut self, id: Option<NodeId>, span: Span) -> hir::Lifetime {
3191 let (id, msg, label) = match id {
3192 Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"),
3195 self.resolver.next_node_id(),
3196 "`&` without an explicit lifetime name cannot be used here",
3197 "explicit lifetime name needed here",
3201 let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,);
3202 err.span_label(span, label);
3205 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3208 /// Invoked to create the lifetime argument(s) for a path like
3209 /// `std::cell::Ref<T>`; note that implicit lifetimes in these
3210 /// sorts of cases are deprecated. This may therefore report a warning or an
3211 /// error, depending on the mode.
3212 fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
3213 (0..count).map(|_| self.elided_path_lifetime(span)).collect()
3216 fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime {
3217 match self.anonymous_lifetime_mode {
3218 AnonymousLifetimeMode::CreateParameter => {
3219 // We should have emitted E0726 when processing this path above
3221 .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error");
3222 let id = self.resolver.next_node_id();
3223 self.new_named_lifetime(id, span, hir::LifetimeName::Error)
3225 // `PassThrough` is the normal case.
3226 // `new_error_lifetime`, which would usually be used in the case of `ReportError`,
3227 // is unsuitable here, as these can occur from missing lifetime parameters in a
3228 // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit
3229 // lifetime. Instead, we simply create an implicit lifetime, which will be checked
3230 // later, at which point a suitable error will be emitted.
3231 AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => {
3232 self.new_implicit_lifetime(span)
3237 /// Invoked to create the lifetime argument(s) for an elided trait object
3238 /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
3239 /// when the bound is written, even if it is written with `'_` like in
3240 /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
3241 fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
3242 match self.anonymous_lifetime_mode {
3243 // NB. We intentionally ignore the create-parameter mode here.
3244 // and instead "pass through" to resolve-lifetimes, which will apply
3245 // the object-lifetime-defaulting rules. Elided object lifetime defaults
3246 // do not act like other elided lifetimes. In other words, given this:
3248 // impl Foo for Box<dyn Debug>
3250 // we do not introduce a fresh `'_` to serve as the bound, but instead
3251 // ultimately translate to the equivalent of:
3253 // impl Foo for Box<dyn Debug + 'static>
3255 // `resolve_lifetime` has the code to make that happen.
3256 AnonymousLifetimeMode::CreateParameter => {}
3258 AnonymousLifetimeMode::ReportError => {
3259 // ReportError applies to explicit use of `'_`.
3262 // This is the normal case.
3263 AnonymousLifetimeMode::PassThrough => {}
3266 let r = hir::Lifetime {
3267 hir_id: self.next_id(),
3269 name: hir::LifetimeName::ImplicitObjectLifetimeDefault,
3271 debug!("elided_dyn_bound: r={:?}", r);
3275 fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
3276 hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit }
3279 fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) {
3280 // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
3281 // call site which do not have a macro backtrace. See #61963.
3282 let is_macro_callsite = self
3285 .span_to_snippet(span)
3286 .map(|snippet| snippet.starts_with("#["))
3288 if !is_macro_callsite {
3289 self.resolver.lint_buffer().buffer_lint_with_diagnostic(
3290 builtin::BARE_TRAIT_OBJECTS,
3293 "trait objects without an explicit `dyn` are deprecated",
3294 builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
3300 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body<'hir>>) -> Vec<hir::BodyId> {
3301 // Sorting by span ensures that we get things in order within a
3302 // file, and also puts the files in a sensible order.
3303 let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
3304 body_ids.sort_by_key(|b| bodies[b].value.span);