//! Lowers the AST to the HIR. //! //! Since the AST and HIR are fairly similar, this is mostly a simple procedure, //! much like a fold. Where lowering involves a bit more work things get more //! interesting and there are some invariants you should know about. These mostly //! concern spans and IDs. //! //! Spans are assigned to AST nodes during parsing and then are modified during //! expansion to indicate the origin of a node and the process it went through //! being expanded. IDs are assigned to AST nodes just before lowering. //! //! For the simpler lowering steps, IDs and spans should be preserved. Unlike //! expansion we do not preserve the process of lowering in the spans, so spans //! should not be modified here. When creating a new node (as opposed to //! 'folding' an existing one), then you create a new ID using `next_id()`. //! //! You must ensure that IDs are unique. That means that you should only use the //! ID from an AST node in a single HIR node (you can assume that AST node-IDs //! are unique). Every new node must have a unique ID. Avoid cloning HIR nodes. //! If you do, you must then set the new node's ID to a fresh one. //! //! Spans are used for error messages and for tools to map semantics back to //! source code. It is therefore not as important with spans as IDs to be strict //! about use (you can't break the compiler by screwing up a span). Obviously, a //! HIR node can only have a single span. But multiple nodes can have the same //! span and spans don't need to be kept in order, etc. Where code is preserved //! by lowering, it should have the same span as in the AST. Where HIR nodes are //! new it is probably best to give a span for the whole AST node being lowered. //! All nodes should have real spans, don't use dummy spans. Tools are likely to //! get confused if the spans from leaf AST nodes occur in multiple places //! in the HIR, especially for multiple identifiers. #![feature(array_value_iter)] #![feature(crate_visibility_modifier)] #![feature(or_patterns)] #![recursion_limit = "256"] use rustc_ast::node_id::NodeMap; use rustc_ast::token::{self, DelimToken, Nonterminal, Token}; use rustc_ast::tokenstream::{CanSynthesizeMissingTokens, DelimSpan, TokenStream, TokenTree}; use rustc_ast::visit::{self, AssocCtxt, Visitor}; use rustc_ast::walk_list; use rustc_ast::{self as ast, *}; use rustc_ast_pretty::pprust; use rustc_data_structures::captures::Captures; use rustc_data_structures::fx::FxHashSet; use rustc_data_structures::sync::Lrc; use rustc_errors::struct_span_err; use rustc_hir as hir; use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res}; use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX}; use rustc_hir::definitions::{DefKey, DefPathData, Definitions}; use rustc_hir::intravisit; use rustc_hir::{ConstArg, GenericArg, ParamName}; use rustc_index::vec::{Idx, IndexVec}; use rustc_session::lint::{builtin::BARE_TRAIT_OBJECTS, BuiltinLintDiagnostics, LintBuffer}; use rustc_session::parse::ParseSess; use rustc_session::Session; use rustc_span::hygiene::ExpnId; use rustc_span::source_map::{respan, DesugaringKind}; use rustc_span::symbol::{kw, sym, Ident, Symbol}; use rustc_span::Span; use smallvec::{smallvec, SmallVec}; use std::collections::BTreeMap; use std::mem; use tracing::{debug, trace}; macro_rules! arena_vec { ($this:expr; $($x:expr),*) => ({ let a = [$($x),*]; $this.arena.alloc_from_iter(std::array::IntoIter::new(a)) }); } mod expr; mod item; mod pat; mod path; const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF; rustc_hir::arena_types!(rustc_arena::declare_arena, [], 'tcx); struct LoweringContext<'a, 'hir: 'a> { /// Used to assign IDs to HIR nodes that do not directly correspond to AST nodes. sess: &'a Session, resolver: &'a mut dyn ResolverAstLowering, /// HACK(Centril): there is a cyclic dependency between the parser and lowering /// if we don't have this function pointer. To avoid that dependency so that /// librustc_middle is independent of the parser, we use dynamic dispatch here. nt_to_tokenstream: NtToTokenstream, /// Used to allocate HIR nodes arena: &'hir Arena<'hir>, /// The items being lowered are collected here. items: BTreeMap>, trait_items: BTreeMap>, impl_items: BTreeMap>, foreign_items: BTreeMap>, bodies: BTreeMap>, exported_macros: Vec>, non_exported_macro_attrs: Vec, trait_impls: BTreeMap>, modules: BTreeMap, generator_kind: Option, /// When inside an `async` context, this is the `HirId` of the /// `task_context` local bound to the resume argument of the generator. task_context: Option, /// Used to get the current `fn`'s def span to point to when using `await` /// outside of an `async fn`. current_item: Option, catch_scopes: Vec, loop_scopes: Vec, is_in_loop_condition: bool, is_in_trait_impl: bool, is_in_dyn_type: bool, /// What to do when we encounter either an "anonymous lifetime /// reference". The term "anonymous" is meant to encompass both /// `'_` lifetimes as well as fully elided cases where nothing is /// written at all (e.g., `&T` or `std::cell::Ref`). anonymous_lifetime_mode: AnonymousLifetimeMode, /// Used to create lifetime definitions from in-band lifetime usages. /// e.g., `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8` /// When a named lifetime is encountered in a function or impl header and /// has not been defined /// (i.e., it doesn't appear in the in_scope_lifetimes list), it is added /// to this list. The results of this list are then added to the list of /// lifetime definitions in the corresponding impl or function generics. lifetimes_to_define: Vec<(Span, ParamName)>, /// `true` if in-band lifetimes are being collected. This is used to /// indicate whether or not we're in a place where new lifetimes will result /// in in-band lifetime definitions, such a function or an impl header, /// including implicit lifetimes from `impl_header_lifetime_elision`. is_collecting_in_band_lifetimes: bool, /// Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB. /// When `is_collecting_in_band_lifetimes` is true, each lifetime is checked /// against this list to see if it is already in-scope, or if a definition /// needs to be created for it. /// /// We always store a `normalize_to_macros_2_0()` version of the param-name in this /// vector. in_scope_lifetimes: Vec, current_module: hir::HirId, type_def_lifetime_params: DefIdMap, current_hir_id_owner: Vec<(LocalDefId, u32)>, item_local_id_counters: NodeMap, node_id_to_hir_id: IndexVec>, allow_try_trait: Option>, allow_gen_future: Option>, } pub trait ResolverAstLowering { fn def_key(&mut self, id: DefId) -> DefKey; fn item_generics_num_lifetimes(&self, def: DefId, sess: &Session) -> usize; /// Obtains resolution for a `NodeId` with a single resolution. fn get_partial_res(&mut self, id: NodeId) -> Option; /// Obtains per-namespace resolutions for `use` statement with the given `NodeId`. fn get_import_res(&mut self, id: NodeId) -> PerNS>>; /// Obtains resolution for a label with the given `NodeId`. fn get_label_res(&mut self, id: NodeId) -> Option; /// We must keep the set of definitions up to date as we add nodes that weren't in the AST. /// This should only return `None` during testing. fn definitions(&mut self) -> &mut Definitions; fn lint_buffer(&mut self) -> &mut LintBuffer; fn next_node_id(&mut self) -> NodeId; fn trait_map(&self) -> &NodeMap>; fn opt_local_def_id(&self, node: NodeId) -> Option; fn local_def_id(&self, node: NodeId) -> LocalDefId; fn create_def( &mut self, parent: LocalDefId, node_id: ast::NodeId, data: DefPathData, expn_id: ExpnId, span: Span, ) -> LocalDefId; } type NtToTokenstream = fn(&Nonterminal, &ParseSess, CanSynthesizeMissingTokens) -> TokenStream; /// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree, /// and if so, what meaning it has. #[derive(Debug)] enum ImplTraitContext<'b, 'a> { /// Treat `impl Trait` as shorthand for a new universal generic parameter. /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually /// equivalent to a fresh universal parameter like `fn foo(x: T)`. /// /// Newly generated parameters should be inserted into the given `Vec`. Universal(&'b mut Vec>), /// Treat `impl Trait` as shorthand for a new opaque type. /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`. /// ReturnPositionOpaqueTy { /// `DefId` for the parent function, used to look up necessary /// information later. fn_def_id: DefId, /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn, origin: hir::OpaqueTyOrigin, }, /// Impl trait in type aliases, consts and statics. OtherOpaqueTy { /// Set of lifetimes that this opaque type can capture, if it uses /// them. This includes lifetimes bound since we entered this context. /// For example, in /// /// type A<'b> = impl for<'a> Trait<'a, Out = impl Sized + 'a>; /// /// the inner opaque type captures `'a` because it uses it. It doesn't /// need to capture `'b` because it already inherits the lifetime /// parameter from `A`. // FIXME(impl_trait): but `required_region_bounds` will ICE later // anyway. capturable_lifetimes: &'b mut FxHashSet, /// Origin: Either OpaqueTyOrigin::Misc or OpaqueTyOrigin::Binding, origin: hir::OpaqueTyOrigin, }, /// `impl Trait` is not accepted in this position. Disallowed(ImplTraitPosition), } /// Position in which `impl Trait` is disallowed. #[derive(Debug, Copy, Clone, PartialEq, Eq)] enum ImplTraitPosition { /// Disallowed in `let` / `const` / `static` bindings. Binding, /// All other positions. Other, } impl<'a> ImplTraitContext<'_, 'a> { #[inline] fn disallowed() -> Self { ImplTraitContext::Disallowed(ImplTraitPosition::Other) } fn reborrow<'this>(&'this mut self) -> ImplTraitContext<'this, 'a> { use self::ImplTraitContext::*; match self { Universal(params) => Universal(params), ReturnPositionOpaqueTy { fn_def_id, origin } => { ReturnPositionOpaqueTy { fn_def_id: *fn_def_id, origin: *origin } } OtherOpaqueTy { capturable_lifetimes, origin } => { OtherOpaqueTy { capturable_lifetimes, origin: *origin } } Disallowed(pos) => Disallowed(*pos), } } } pub fn lower_crate<'a, 'hir>( sess: &'a Session, krate: &'a Crate, resolver: &'a mut dyn ResolverAstLowering, nt_to_tokenstream: NtToTokenstream, arena: &'hir Arena<'hir>, ) -> hir::Crate<'hir> { let _prof_timer = sess.prof.verbose_generic_activity("hir_lowering"); LoweringContext { sess, resolver, nt_to_tokenstream, arena, items: BTreeMap::new(), trait_items: BTreeMap::new(), impl_items: BTreeMap::new(), foreign_items: BTreeMap::new(), bodies: BTreeMap::new(), trait_impls: BTreeMap::new(), modules: BTreeMap::new(), exported_macros: Vec::new(), non_exported_macro_attrs: Vec::new(), catch_scopes: Vec::new(), loop_scopes: Vec::new(), is_in_loop_condition: false, is_in_trait_impl: false, is_in_dyn_type: false, anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough, type_def_lifetime_params: Default::default(), current_module: hir::CRATE_HIR_ID, current_hir_id_owner: vec![(LocalDefId { local_def_index: CRATE_DEF_INDEX }, 0)], item_local_id_counters: Default::default(), node_id_to_hir_id: IndexVec::new(), generator_kind: None, task_context: None, current_item: None, lifetimes_to_define: Vec::new(), is_collecting_in_band_lifetimes: false, in_scope_lifetimes: Vec::new(), allow_try_trait: Some([sym::try_trait][..].into()), allow_gen_future: Some([sym::gen_future][..].into()), } .lower_crate(krate) } #[derive(Copy, Clone, PartialEq)] enum ParamMode { /// Any path in a type context. Explicit, /// Path in a type definition, where the anonymous lifetime `'_` is not allowed. ExplicitNamed, /// The `module::Type` in `module::Type::method` in an expression. Optional, } enum ParenthesizedGenericArgs { Ok, Err, } /// What to do when we encounter an **anonymous** lifetime /// reference. Anonymous lifetime references come in two flavors. You /// have implicit, or fully elided, references to lifetimes, like the /// one in `&T` or `Ref`, and you have `'_` lifetimes, like `&'_ T` /// or `Ref<'_, T>`. These often behave the same, but not always: /// /// - certain usages of implicit references are deprecated, like /// `Ref`, and we sometimes just give hard errors in those cases /// as well. /// - for object bounds there is a difference: `Box` is not /// the same as `Box`. /// /// We describe the effects of the various modes in terms of three cases: /// /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg /// of a `&` (e.g., the missing lifetime in something like `&T`) /// - **Dyn Bound** -- if you have something like `Box`, /// there is an elided lifetime bound (`Box`). These /// elided bounds follow special rules. Note that this only covers /// cases where *nothing* is written; the `'_` in `Box` is a case of "modern" elision. /// - **Deprecated** -- this covers cases like `Ref`, where the lifetime /// parameter to ref is completely elided. `Ref<'_, T>` would be the modern, /// non-deprecated equivalent. /// /// Currently, the handling of lifetime elision is somewhat spread out /// between HIR lowering and -- as described below -- the /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating /// an "elided" or "underscore" lifetime name. In the future, we probably want to move /// everything into HIR lowering. #[derive(Copy, Clone, Debug)] enum AnonymousLifetimeMode { /// For **Modern** cases, create a new anonymous region parameter /// and reference that. /// /// For **Dyn Bound** cases, pass responsibility to /// `resolve_lifetime` code. /// /// For **Deprecated** cases, report an error. CreateParameter, /// Give a hard error when either `&` or `'_` is written. Used to /// rule out things like `where T: Foo<'_>`. Does not imply an /// error on default object bounds (e.g., `Box`). ReportError, /// Pass responsibility to `resolve_lifetime` code for all cases. PassThrough, } struct TokenStreamLowering<'a> { parse_sess: &'a ParseSess, synthesize_tokens: CanSynthesizeMissingTokens, nt_to_tokenstream: NtToTokenstream, } impl<'a> TokenStreamLowering<'a> { fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream { tokens.into_trees().flat_map(|tree| self.lower_token_tree(tree).into_trees()).collect() } fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream { match tree { TokenTree::Token(token) => self.lower_token(token), TokenTree::Delimited(span, delim, tts) => { TokenTree::Delimited(span, delim, self.lower_token_stream(tts)).into() } } } fn lower_token(&mut self, token: Token) -> TokenStream { match token.kind { token::Interpolated(nt) => { let tts = (self.nt_to_tokenstream)(&nt, self.parse_sess, self.synthesize_tokens); TokenTree::Delimited( DelimSpan::from_single(token.span), DelimToken::NoDelim, self.lower_token_stream(tts), ) .into() } _ => TokenTree::Token(token).into(), } } } struct ImplTraitTypeIdVisitor<'a> { ids: &'a mut SmallVec<[NodeId; 1]>, } impl Visitor<'_> for ImplTraitTypeIdVisitor<'_> { fn visit_ty(&mut self, ty: &Ty) { match ty.kind { TyKind::Typeof(_) | TyKind::BareFn(_) => return, TyKind::ImplTrait(id, _) => self.ids.push(id), _ => {} } visit::walk_ty(self, ty); } fn visit_path_segment(&mut self, path_span: Span, path_segment: &PathSegment) { if let Some(ref p) = path_segment.args { if let GenericArgs::Parenthesized(_) = **p { return; } } visit::walk_path_segment(self, path_span, path_segment) } } impl<'a, 'hir> LoweringContext<'a, 'hir> { fn lower_crate(mut self, c: &Crate) -> hir::Crate<'hir> { /// Full-crate AST visitor that inserts into a fresh /// `LoweringContext` any information that may be /// needed from arbitrary locations in the crate, /// e.g., the number of lifetime generic parameters /// declared for every type and trait definition. struct MiscCollector<'tcx, 'lowering, 'hir> { lctx: &'tcx mut LoweringContext<'lowering, 'hir>, } impl MiscCollector<'_, '_, '_> { fn allocate_use_tree_hir_id_counters(&mut self, tree: &UseTree, owner: LocalDefId) { match tree.kind { UseTreeKind::Simple(_, id1, id2) => { for &id in &[id1, id2] { self.lctx.resolver.create_def( owner, id, DefPathData::Misc, ExpnId::root(), tree.prefix.span, ); self.lctx.allocate_hir_id_counter(id); } } UseTreeKind::Glob => (), UseTreeKind::Nested(ref trees) => { for &(ref use_tree, id) in trees { let hir_id = self.lctx.allocate_hir_id_counter(id); self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner); } } } } } impl<'tcx> Visitor<'tcx> for MiscCollector<'tcx, '_, '_> { fn visit_item(&mut self, item: &'tcx Item) { let hir_id = self.lctx.allocate_hir_id_counter(item.id); match item.kind { ItemKind::Struct(_, ref generics) | ItemKind::Union(_, ref generics) | ItemKind::Enum(_, ref generics) | ItemKind::TyAlias(_, ref generics, ..) | ItemKind::Trait(_, _, ref generics, ..) => { let def_id = self.lctx.resolver.local_def_id(item.id); let count = generics .params .iter() .filter(|param| matches!(param.kind, ast::GenericParamKind::Lifetime { .. })) .count(); self.lctx.type_def_lifetime_params.insert(def_id.to_def_id(), count); } ItemKind::Use(ref use_tree) => { self.allocate_use_tree_hir_id_counters(use_tree, hir_id.owner); } _ => {} } visit::walk_item(self, item); } fn visit_assoc_item(&mut self, item: &'tcx AssocItem, ctxt: AssocCtxt) { self.lctx.allocate_hir_id_counter(item.id); visit::walk_assoc_item(self, item, ctxt); } fn visit_foreign_item(&mut self, item: &'tcx ForeignItem) { self.lctx.allocate_hir_id_counter(item.id); visit::walk_foreign_item(self, item); } fn visit_ty(&mut self, t: &'tcx Ty) { match t.kind { // Mirrors the case in visit::walk_ty TyKind::BareFn(ref f) => { walk_list!(self, visit_generic_param, &f.generic_params); // Mirrors visit::walk_fn_decl for parameter in &f.decl.inputs { // We don't lower the ids of argument patterns self.visit_pat(¶meter.pat); self.visit_ty(¶meter.ty) } self.visit_fn_ret_ty(&f.decl.output) } TyKind::ImplTrait(def_node_id, _) => { self.lctx.allocate_hir_id_counter(def_node_id); visit::walk_ty(self, t); } _ => visit::walk_ty(self, t), } } } self.lower_node_id(CRATE_NODE_ID); debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == Some(hir::CRATE_HIR_ID)); visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c); visit::walk_crate(&mut item::ItemLowerer { lctx: &mut self }, c); let module = self.lower_mod(&c.module); let attrs = self.lower_attrs(&c.attrs); let body_ids = body_ids(&self.bodies); let proc_macros = c.proc_macros.iter().map(|id| self.node_id_to_hir_id[*id].unwrap()).collect(); let trait_map = self .resolver .trait_map() .iter() .filter_map(|(&k, v)| { self.node_id_to_hir_id.get(k).and_then(|id| id.as_ref()).map(|id| (*id, v.clone())) }) .collect(); let mut def_id_to_hir_id = IndexVec::default(); for (node_id, hir_id) in self.node_id_to_hir_id.into_iter_enumerated() { if let Some(def_id) = self.resolver.opt_local_def_id(node_id) { if def_id_to_hir_id.len() <= def_id.index() { def_id_to_hir_id.resize(def_id.index() + 1, None); } def_id_to_hir_id[def_id] = hir_id; } } self.resolver.definitions().init_def_id_to_hir_id_mapping(def_id_to_hir_id); hir::Crate { item: hir::CrateItem { module, attrs, span: c.span }, exported_macros: self.arena.alloc_from_iter(self.exported_macros), non_exported_macro_attrs: self.arena.alloc_from_iter(self.non_exported_macro_attrs), items: self.items, trait_items: self.trait_items, impl_items: self.impl_items, foreign_items: self.foreign_items, bodies: self.bodies, body_ids, trait_impls: self.trait_impls, modules: self.modules, proc_macros, trait_map, } } fn insert_item(&mut self, item: hir::Item<'hir>) { let id = item.hir_id; // FIXME: Use `debug_asset-rt`. assert_eq!(id.local_id, hir::ItemLocalId::from_u32(0)); self.items.insert(id, item); self.modules.get_mut(&self.current_module).unwrap().items.insert(id); } fn allocate_hir_id_counter(&mut self, owner: NodeId) -> hir::HirId { // Set up the counter if needed. self.item_local_id_counters.entry(owner).or_insert(0); // Always allocate the first `HirId` for the owner itself. let lowered = self.lower_node_id_with_owner(owner, owner); debug_assert_eq!(lowered.local_id.as_u32(), 0); lowered } fn lower_node_id_generic( &mut self, ast_node_id: NodeId, alloc_hir_id: impl FnOnce(&mut Self) -> hir::HirId, ) -> hir::HirId { assert_ne!(ast_node_id, DUMMY_NODE_ID); let min_size = ast_node_id.as_usize() + 1; if min_size > self.node_id_to_hir_id.len() { self.node_id_to_hir_id.resize(min_size, None); } if let Some(existing_hir_id) = self.node_id_to_hir_id[ast_node_id] { existing_hir_id } else { // Generate a new `HirId`. let hir_id = alloc_hir_id(self); self.node_id_to_hir_id[ast_node_id] = Some(hir_id); hir_id } } fn with_hir_id_owner(&mut self, owner: NodeId, f: impl FnOnce(&mut Self) -> T) -> T { let counter = self .item_local_id_counters .insert(owner, HIR_ID_COUNTER_LOCKED) .unwrap_or_else(|| panic!("no `item_local_id_counters` entry for {:?}", owner)); let def_id = self.resolver.local_def_id(owner); self.current_hir_id_owner.push((def_id, counter)); let ret = f(self); let (new_def_id, new_counter) = self.current_hir_id_owner.pop().unwrap(); debug_assert!(def_id == new_def_id); debug_assert!(new_counter >= counter); let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap(); debug_assert!(prev == HIR_ID_COUNTER_LOCKED); ret } /// This method allocates a new `HirId` for the given `NodeId` and stores it in /// the `LoweringContext`'s `NodeId => HirId` map. /// Take care not to call this method if the resulting `HirId` is then not /// actually used in the HIR, as that would trigger an assertion in the /// `HirIdValidator` later on, which makes sure that all `NodeId`s got mapped /// properly. Calling the method twice with the same `NodeId` is fine though. fn lower_node_id(&mut self, ast_node_id: NodeId) -> hir::HirId { self.lower_node_id_generic(ast_node_id, |this| { let &mut (owner, ref mut local_id_counter) = this.current_hir_id_owner.last_mut().unwrap(); let local_id = *local_id_counter; *local_id_counter += 1; hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) } }) } fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> hir::HirId { self.lower_node_id_generic(ast_node_id, |this| { let local_id_counter = this .item_local_id_counters .get_mut(&owner) .expect("called `lower_node_id_with_owner` before `allocate_hir_id_counter`"); let local_id = *local_id_counter; // We want to be sure not to modify the counter in the map while it // is also on the stack. Otherwise we'll get lost updates when writing // back from the stack to the map. debug_assert!(local_id != HIR_ID_COUNTER_LOCKED); *local_id_counter += 1; let owner = this.resolver.opt_local_def_id(owner).expect( "you forgot to call `create_def` or are lowering node-IDs \ that do not belong to the current owner", ); hir::HirId { owner, local_id: hir::ItemLocalId::from_u32(local_id) } }) } fn next_id(&mut self) -> hir::HirId { let node_id = self.resolver.next_node_id(); self.lower_node_id(node_id) } fn lower_res(&mut self, res: Res) -> Res { res.map_id(|id| { self.lower_node_id_generic(id, |_| { panic!("expected `NodeId` to be lowered already for res {:#?}", res); }) }) } fn expect_full_res(&mut self, id: NodeId) -> Res { self.resolver.get_partial_res(id).map_or(Res::Err, |pr| { if pr.unresolved_segments() != 0 { panic!("path not fully resolved: {:?}", pr); } pr.base_res() }) } fn expect_full_res_from_use(&mut self, id: NodeId) -> impl Iterator> { self.resolver.get_import_res(id).present_items() } fn diagnostic(&self) -> &rustc_errors::Handler { self.sess.diagnostic() } /// Reuses the span but adds information like the kind of the desugaring and features that are /// allowed inside this span. fn mark_span_with_reason( &self, reason: DesugaringKind, span: Span, allow_internal_unstable: Option>, ) -> Span { span.mark_with_reason(allow_internal_unstable, reason, self.sess.edition()) } fn with_anonymous_lifetime_mode( &mut self, anonymous_lifetime_mode: AnonymousLifetimeMode, op: impl FnOnce(&mut Self) -> R, ) -> R { debug!( "with_anonymous_lifetime_mode(anonymous_lifetime_mode={:?})", anonymous_lifetime_mode, ); let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode; self.anonymous_lifetime_mode = anonymous_lifetime_mode; let result = op(self); self.anonymous_lifetime_mode = old_anonymous_lifetime_mode; debug!( "with_anonymous_lifetime_mode: restoring anonymous_lifetime_mode={:?}", old_anonymous_lifetime_mode ); result } /// Creates a new `hir::GenericParam` for every new lifetime and /// type parameter encountered while evaluating `f`. Definitions /// are created with the parent provided. If no `parent_id` is /// provided, no definitions will be returned. /// /// Presuming that in-band lifetimes are enabled, then /// `self.anonymous_lifetime_mode` will be updated to match the /// parameter while `f` is running (and restored afterwards). fn collect_in_band_defs( &mut self, parent_def_id: LocalDefId, anonymous_lifetime_mode: AnonymousLifetimeMode, f: impl FnOnce(&mut Self) -> (Vec>, T), ) -> (Vec>, T) { assert!(!self.is_collecting_in_band_lifetimes); assert!(self.lifetimes_to_define.is_empty()); let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode; self.anonymous_lifetime_mode = anonymous_lifetime_mode; self.is_collecting_in_band_lifetimes = true; let (in_band_ty_params, res) = f(self); self.is_collecting_in_band_lifetimes = false; self.anonymous_lifetime_mode = old_anonymous_lifetime_mode; let lifetimes_to_define = self.lifetimes_to_define.split_off(0); let params = lifetimes_to_define .into_iter() .map(|(span, hir_name)| self.lifetime_to_generic_param(span, hir_name, parent_def_id)) .chain(in_band_ty_params.into_iter()) .collect(); (params, res) } /// Converts a lifetime into a new generic parameter. fn lifetime_to_generic_param( &mut self, span: Span, hir_name: ParamName, parent_def_id: LocalDefId, ) -> hir::GenericParam<'hir> { let node_id = self.resolver.next_node_id(); // Get the name we'll use to make the def-path. Note // that collisions are ok here and this shouldn't // really show up for end-user. let (str_name, kind) = match hir_name { ParamName::Plain(ident) => (ident.name, hir::LifetimeParamKind::InBand), ParamName::Fresh(_) => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Elided), ParamName::Error => (kw::UnderscoreLifetime, hir::LifetimeParamKind::Error), }; // Add a definition for the in-band lifetime def. self.resolver.create_def( parent_def_id, node_id, DefPathData::LifetimeNs(str_name), ExpnId::root(), span, ); hir::GenericParam { hir_id: self.lower_node_id(node_id), name: hir_name, attrs: &[], bounds: &[], span, pure_wrt_drop: false, kind: hir::GenericParamKind::Lifetime { kind }, } } /// When there is a reference to some lifetime `'a`, and in-band /// lifetimes are enabled, then we want to push that lifetime into /// the vector of names to define later. In that case, it will get /// added to the appropriate generics. fn maybe_collect_in_band_lifetime(&mut self, ident: Ident) { if !self.is_collecting_in_band_lifetimes { return; } if !self.sess.features_untracked().in_band_lifetimes { return; } if self.in_scope_lifetimes.contains(&ParamName::Plain(ident.normalize_to_macros_2_0())) { return; } let hir_name = ParamName::Plain(ident); if self.lifetimes_to_define.iter().any(|(_, lt_name)| { lt_name.normalize_to_macros_2_0() == hir_name.normalize_to_macros_2_0() }) { return; } self.lifetimes_to_define.push((ident.span, hir_name)); } /// When we have either an elided or `'_` lifetime in an impl /// header, we convert it to an in-band lifetime. fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName { assert!(self.is_collecting_in_band_lifetimes); let index = self.lifetimes_to_define.len() + self.in_scope_lifetimes.len(); let hir_name = ParamName::Fresh(index); self.lifetimes_to_define.push((span, hir_name)); hir_name } // Evaluates `f` with the lifetimes in `params` in-scope. // This is used to track which lifetimes have already been defined, and // which are new in-band lifetimes that need to have a definition created // for them. fn with_in_scope_lifetime_defs( &mut self, params: &[GenericParam], f: impl FnOnce(&mut Self) -> T, ) -> T { let old_len = self.in_scope_lifetimes.len(); let lt_def_names = params.iter().filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => { Some(ParamName::Plain(param.ident.normalize_to_macros_2_0())) } _ => None, }); self.in_scope_lifetimes.extend(lt_def_names); let res = f(self); self.in_scope_lifetimes.truncate(old_len); res } /// Appends in-band lifetime defs and argument-position `impl /// Trait` defs to the existing set of generics. /// /// Presuming that in-band lifetimes are enabled, then /// `self.anonymous_lifetime_mode` will be updated to match the /// parameter while `f` is running (and restored afterwards). fn add_in_band_defs( &mut self, generics: &Generics, parent_def_id: LocalDefId, anonymous_lifetime_mode: AnonymousLifetimeMode, f: impl FnOnce(&mut Self, &mut Vec>) -> T, ) -> (hir::Generics<'hir>, T) { let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(&generics.params, |this| { this.collect_in_band_defs(parent_def_id, anonymous_lifetime_mode, |this| { let mut params = Vec::new(); // Note: it is necessary to lower generics *before* calling `f`. // When lowering `async fn`, there's a final step when lowering // the return type that assumes that all in-scope lifetimes have // already been added to either `in_scope_lifetimes` or // `lifetimes_to_define`. If we swapped the order of these two, // in-band-lifetimes introduced by generics or where-clauses // wouldn't have been added yet. let generics = this.lower_generics_mut(generics, ImplTraitContext::Universal(&mut params)); let res = f(this, &mut params); (params, (generics, res)) }) }); lowered_generics.params.extend(in_band_defs); let lowered_generics = lowered_generics.into_generics(self.arena); (lowered_generics, res) } fn with_dyn_type_scope(&mut self, in_scope: bool, f: impl FnOnce(&mut Self) -> T) -> T { let was_in_dyn_type = self.is_in_dyn_type; self.is_in_dyn_type = in_scope; let result = f(self); self.is_in_dyn_type = was_in_dyn_type; result } fn with_new_scopes(&mut self, f: impl FnOnce(&mut Self) -> T) -> T { let was_in_loop_condition = self.is_in_loop_condition; self.is_in_loop_condition = false; let catch_scopes = mem::take(&mut self.catch_scopes); let loop_scopes = mem::take(&mut self.loop_scopes); let ret = f(self); self.catch_scopes = catch_scopes; self.loop_scopes = loop_scopes; self.is_in_loop_condition = was_in_loop_condition; ret } fn lower_attrs(&mut self, attrs: &[Attribute]) -> &'hir [Attribute] { self.arena.alloc_from_iter(attrs.iter().map(|a| self.lower_attr(a))) } fn lower_attr(&mut self, attr: &Attribute) -> Attribute { // Note that we explicitly do not walk the path. Since we don't really // lower attributes (we use the AST version) there is nowhere to keep // the `HirId`s. We don't actually need HIR version of attributes anyway. // Tokens are also not needed after macro expansion and parsing. let kind = match attr.kind { AttrKind::Normal(ref item, _) => AttrKind::Normal( AttrItem { path: item.path.clone(), args: self.lower_mac_args(&item.args), tokens: None, }, None, ), AttrKind::DocComment(comment_kind, data) => AttrKind::DocComment(comment_kind, data), }; Attribute { kind, id: attr.id, style: attr.style, span: attr.span } } fn lower_mac_args(&mut self, args: &MacArgs) -> MacArgs { match *args { MacArgs::Empty => MacArgs::Empty, MacArgs::Delimited(dspan, delim, ref tokens) => { // This is either a non-key-value attribute, or a `macro_rules!` body. // We either not have any nonterminals present (in the case of an attribute), // or have tokens available for all nonterminals in the case of a nested // `macro_rules`: e.g: // // ```rust // macro_rules! outer { // ($e:expr) => { // macro_rules! inner { // () => { $e } // } // } // } // ``` // // In both cases, we don't want to synthesize any tokens MacArgs::Delimited( dspan, delim, self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::No), ) } // This is an inert key-value attribute - it will never be visible to macros // after it gets lowered to HIR. Therefore, we can synthesize tokens with fake // spans to handle nonterminals in `#[doc]` (e.g. `#[doc = $e]`). MacArgs::Eq(eq_span, ref tokens) => MacArgs::Eq( eq_span, self.lower_token_stream(tokens.clone(), CanSynthesizeMissingTokens::Yes), ), } } fn lower_token_stream( &self, tokens: TokenStream, synthesize_tokens: CanSynthesizeMissingTokens, ) -> TokenStream { TokenStreamLowering { parse_sess: &self.sess.parse_sess, synthesize_tokens, nt_to_tokenstream: self.nt_to_tokenstream, } .lower_token_stream(tokens) } /// Given an associated type constraint like one of these: /// /// ``` /// T: Iterator /// ^^^^^^^^^^^ /// T: Iterator /// ^^^^^^^^^^^^ /// ``` /// /// returns a `hir::TypeBinding` representing `Item`. fn lower_assoc_ty_constraint( &mut self, constraint: &AssocTyConstraint, itctx: ImplTraitContext<'_, 'hir>, ) -> hir::TypeBinding<'hir> { debug!("lower_assoc_ty_constraint(constraint={:?}, itctx={:?})", constraint, itctx); if let Some(ref gen_args) = constraint.gen_args { self.sess.span_fatal( gen_args.span(), "generic associated types in trait paths are currently not implemented", ); } let kind = match constraint.kind { AssocTyConstraintKind::Equality { ref ty } => { hir::TypeBindingKind::Equality { ty: self.lower_ty(ty, itctx) } } AssocTyConstraintKind::Bound { ref bounds } => { let mut capturable_lifetimes; // Piggy-back on the `impl Trait` context to figure out the correct behavior. let (desugar_to_impl_trait, itctx) = match itctx { // We are in the return position: // // fn foo() -> impl Iterator // // so desugar to // // fn foo() -> impl Iterator ImplTraitContext::ReturnPositionOpaqueTy { .. } | ImplTraitContext::OtherOpaqueTy { .. } => (true, itctx), // We are in the argument position, but within a dyn type: // // fn foo(x: dyn Iterator) // // so desugar to // // fn foo(x: dyn Iterator) ImplTraitContext::Universal(..) if self.is_in_dyn_type => (true, itctx), // In `type Foo = dyn Iterator` we desugar to // `type Foo = dyn Iterator` but we have to override the // "impl trait context" to permit `impl Debug` in this position (it desugars // then to an opaque type). // // FIXME: this is only needed until `impl Trait` is allowed in type aliases. ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => { capturable_lifetimes = FxHashSet::default(); ( true, ImplTraitContext::OtherOpaqueTy { capturable_lifetimes: &mut capturable_lifetimes, origin: hir::OpaqueTyOrigin::Misc, }, ) } // We are in the parameter position, but not within a dyn type: // // fn foo(x: impl Iterator) // // so we leave it as is and this gets expanded in astconv to a bound like // `::Item: Debug` where `T` is the type parameter for the // `impl Iterator`. _ => (false, itctx), }; if desugar_to_impl_trait { // Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by // constructing the HIR for `impl bounds...` and then lowering that. let impl_trait_node_id = self.resolver.next_node_id(); let parent_def_id = self.current_hir_id_owner.last().unwrap().0; self.resolver.create_def( parent_def_id, impl_trait_node_id, DefPathData::ImplTrait, ExpnId::root(), constraint.span, ); self.with_dyn_type_scope(false, |this| { let node_id = this.resolver.next_node_id(); let ty = this.lower_ty( &Ty { id: node_id, kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()), span: constraint.span, tokens: None, }, itctx, ); hir::TypeBindingKind::Equality { ty } }) } else { // Desugar `AssocTy: Bounds` into a type binding where the // later desugars into a trait predicate. let bounds = self.lower_param_bounds(bounds, itctx); hir::TypeBindingKind::Constraint { bounds } } } }; hir::TypeBinding { hir_id: self.lower_node_id(constraint.id), ident: constraint.ident, kind, span: constraint.span, } } fn lower_generic_arg( &mut self, arg: &ast::GenericArg, itctx: ImplTraitContext<'_, 'hir>, ) -> hir::GenericArg<'hir> { match arg { ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(<)), ast::GenericArg::Type(ty) => { // We parse const arguments as path types as we cannot distinguish them during // parsing. We try to resolve that ambiguity by attempting resolution in both the // type and value namespaces. If we resolved the path in the value namespace, we // transform it into a generic const argument. if let TyKind::Path(ref qself, ref path) = ty.kind { if let Some(partial_res) = self.resolver.get_partial_res(ty.id) { let res = partial_res.base_res(); if !res.matches_ns(Namespace::TypeNS) { debug!( "lower_generic_arg: Lowering type argument as const argument: {:?}", ty, ); // Construct a AnonConst where the expr is the "ty"'s path. let parent_def_id = self.current_hir_id_owner.last().unwrap().0; let node_id = self.resolver.next_node_id(); // Add a definition for the in-band const def. self.resolver.create_def( parent_def_id, node_id, DefPathData::AnonConst, ExpnId::root(), ty.span, ); let path_expr = Expr { id: ty.id, kind: ExprKind::Path(qself.clone(), path.clone()), span: ty.span, attrs: AttrVec::new(), tokens: None, }; let ct = self.with_new_scopes(|this| hir::AnonConst { hir_id: this.lower_node_id(node_id), body: this.lower_const_body(path_expr.span, Some(&path_expr)), }); return GenericArg::Const(ConstArg { value: ct, span: ty.span }); } } } GenericArg::Type(self.lower_ty_direct(&ty, itctx)) } ast::GenericArg::Const(ct) => GenericArg::Const(ConstArg { value: self.lower_anon_const(&ct), span: ct.value.span, }), } } fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext<'_, 'hir>) -> &'hir hir::Ty<'hir> { self.arena.alloc(self.lower_ty_direct(t, itctx)) } fn lower_path_ty( &mut self, t: &Ty, qself: &Option, path: &Path, param_mode: ParamMode, itctx: ImplTraitContext<'_, 'hir>, ) -> hir::Ty<'hir> { let id = self.lower_node_id(t.id); let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx); let ty = self.ty_path(id, t.span, qpath); if let hir::TyKind::TraitObject(..) = ty.kind { self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global()); } ty } fn ty(&mut self, span: Span, kind: hir::TyKind<'hir>) -> hir::Ty<'hir> { hir::Ty { hir_id: self.next_id(), kind, span } } fn ty_tup(&mut self, span: Span, tys: &'hir [hir::Ty<'hir>]) -> hir::Ty<'hir> { self.ty(span, hir::TyKind::Tup(tys)) } fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) -> hir::Ty<'hir> { let kind = match t.kind { TyKind::Infer => hir::TyKind::Infer, TyKind::Err => hir::TyKind::Err, TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)), TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)), TyKind::Rptr(ref region, ref mt) => { let span = self.sess.source_map().next_point(t.span.shrink_to_lo()); let lifetime = match *region { Some(ref lt) => self.lower_lifetime(lt), None => self.elided_ref_lifetime(span), }; hir::TyKind::Rptr(lifetime, self.lower_mt(mt, itctx)) } TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(&f.generic_params, |this| { this.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| { hir::TyKind::BareFn(this.arena.alloc(hir::BareFnTy { generic_params: this.lower_generic_params( &f.generic_params, &NodeMap::default(), ImplTraitContext::disallowed(), ), unsafety: this.lower_unsafety(f.unsafety), abi: this.lower_extern(f.ext), decl: this.lower_fn_decl(&f.decl, None, false, None), param_names: this.lower_fn_params_to_names(&f.decl), })) }) }), TyKind::Never => hir::TyKind::Never, TyKind::Tup(ref tys) => { hir::TyKind::Tup(self.arena.alloc_from_iter( tys.iter().map(|ty| self.lower_ty_direct(ty, itctx.reborrow())), )) } TyKind::Paren(ref ty) => { return self.lower_ty_direct(ty, itctx); } TyKind::Path(ref qself, ref path) => { return self.lower_path_ty(t, qself, path, ParamMode::Explicit, itctx); } TyKind::ImplicitSelf => { let res = self.expect_full_res(t.id); let res = self.lower_res(res); hir::TyKind::Path(hir::QPath::Resolved( None, self.arena.alloc(hir::Path { res, segments: arena_vec![self; hir::PathSegment::from_ident( Ident::with_dummy_span(kw::SelfUpper) )], span: t.span, }), )) } TyKind::Array(ref ty, ref length) => { hir::TyKind::Array(self.lower_ty(ty, itctx), self.lower_anon_const(length)) } TyKind::Typeof(ref expr) => hir::TyKind::Typeof(self.lower_anon_const(expr)), TyKind::TraitObject(ref bounds, kind) => { let mut lifetime_bound = None; let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| { let bounds = this.arena.alloc_from_iter(bounds.iter().filter_map( |bound| match *bound { GenericBound::Trait( ref ty, TraitBoundModifier::None | TraitBoundModifier::MaybeConst, ) => Some(this.lower_poly_trait_ref(ty, itctx.reborrow())), // `?const ?Bound` will cause an error during AST validation // anyways, so treat it like `?Bound` as compilation proceeds. GenericBound::Trait( _, TraitBoundModifier::Maybe | TraitBoundModifier::MaybeConstMaybe, ) => None, GenericBound::Outlives(ref lifetime) => { if lifetime_bound.is_none() { lifetime_bound = Some(this.lower_lifetime(lifetime)); } None } }, )); let lifetime_bound = lifetime_bound.unwrap_or_else(|| this.elided_dyn_bound(t.span)); (bounds, lifetime_bound) }); if kind != TraitObjectSyntax::Dyn { self.maybe_lint_bare_trait(t.span, t.id, false); } hir::TyKind::TraitObject(bounds, lifetime_bound) } TyKind::ImplTrait(def_node_id, ref bounds) => { let span = t.span; match itctx { ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin } => self .lower_opaque_impl_trait( span, Some(fn_def_id), origin, def_node_id, None, |this| this.lower_param_bounds(bounds, itctx), ), ImplTraitContext::OtherOpaqueTy { ref capturable_lifetimes, origin } => { // Reset capturable lifetimes, any nested impl trait // types will inherit lifetimes from this opaque type, // so don't need to capture them again. let nested_itctx = ImplTraitContext::OtherOpaqueTy { capturable_lifetimes: &mut FxHashSet::default(), origin, }; self.lower_opaque_impl_trait( span, None, origin, def_node_id, Some(capturable_lifetimes), |this| this.lower_param_bounds(bounds, nested_itctx), ) } ImplTraitContext::Universal(in_band_ty_params) => { // Add a definition for the in-band `Param`. let def_id = self.resolver.local_def_id(def_node_id); self.allocate_hir_id_counter(def_node_id); let hir_bounds = self.with_hir_id_owner(def_node_id, |this| { this.lower_param_bounds( bounds, ImplTraitContext::Universal(in_band_ty_params), ) }); // Set the name to `impl Bound1 + Bound2`. let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span); in_band_ty_params.push(hir::GenericParam { hir_id: self.lower_node_id(def_node_id), name: ParamName::Plain(ident), pure_wrt_drop: false, attrs: &[], bounds: hir_bounds, span, kind: hir::GenericParamKind::Type { default: None, synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), }, }); hir::TyKind::Path(hir::QPath::Resolved( None, self.arena.alloc(hir::Path { span, res: Res::Def(DefKind::TyParam, def_id.to_def_id()), segments: arena_vec![self; hir::PathSegment::from_ident(ident)], }), )) } ImplTraitContext::Disallowed(pos) => { let allowed_in = if self.sess.features_untracked().impl_trait_in_bindings { "bindings or function and inherent method return types" } else { "function and inherent method return types" }; let mut err = struct_span_err!( self.sess, t.span, E0562, "`impl Trait` not allowed outside of {}", allowed_in, ); if pos == ImplTraitPosition::Binding && self.sess.is_nightly_build() { err.help( "add `#![feature(impl_trait_in_bindings)]` to the crate \ attributes to enable", ); } err.emit(); hir::TyKind::Err } } } TyKind::MacCall(_) => panic!("`TyKind::MacCall` should have been expanded by now"), TyKind::CVarArgs => { self.sess.delay_span_bug( t.span, "`TyKind::CVarArgs` should have been handled elsewhere", ); hir::TyKind::Err } }; hir::Ty { kind, span: t.span, hir_id: self.lower_node_id(t.id) } } fn lower_opaque_impl_trait( &mut self, span: Span, fn_def_id: Option, origin: hir::OpaqueTyOrigin, opaque_ty_node_id: NodeId, capturable_lifetimes: Option<&FxHashSet>, lower_bounds: impl FnOnce(&mut Self) -> hir::GenericBounds<'hir>, ) -> hir::TyKind<'hir> { debug!( "lower_opaque_impl_trait(fn_def_id={:?}, opaque_ty_node_id={:?}, span={:?})", fn_def_id, opaque_ty_node_id, span, ); // Make sure we know that some funky desugaring has been going on here. // This is a first: there is code in other places like for loop // desugaring that explicitly states that we don't want to track that. // Not tracking it makes lints in rustc and clippy very fragile, as // frequently opened issues show. let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::OpaqueTy, span, None); let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id); self.allocate_hir_id_counter(opaque_ty_node_id); let hir_bounds = self.with_hir_id_owner(opaque_ty_node_id, lower_bounds); let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds( opaque_ty_node_id, opaque_ty_def_id, &hir_bounds, capturable_lifetimes, ); debug!("lower_opaque_impl_trait: lifetimes={:#?}", lifetimes); debug!("lower_opaque_impl_trait: lifetime_defs={:#?}", lifetime_defs); self.with_hir_id_owner(opaque_ty_node_id, move |lctx| { let opaque_ty_item = hir::OpaqueTy { generics: hir::Generics { params: lifetime_defs, where_clause: hir::WhereClause { predicates: &[], span }, span, }, bounds: hir_bounds, impl_trait_fn: fn_def_id, origin, }; trace!("lower_opaque_impl_trait: {:#?}", opaque_ty_def_id); let opaque_ty_id = lctx.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span); // `impl Trait` now just becomes `Foo<'a, 'b, ..>`. hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, lifetimes) }) } /// Registers a new opaque type with the proper `NodeId`s and /// returns the lowered node-ID for the opaque type. fn generate_opaque_type( &mut self, opaque_ty_node_id: NodeId, opaque_ty_item: hir::OpaqueTy<'hir>, span: Span, opaque_ty_span: Span, ) -> hir::HirId { let opaque_ty_item_kind = hir::ItemKind::OpaqueTy(opaque_ty_item); let opaque_ty_id = self.lower_node_id(opaque_ty_node_id); // Generate an `type Foo = impl Trait;` declaration. trace!("registering opaque type with id {:#?}", opaque_ty_id); let opaque_ty_item = hir::Item { hir_id: opaque_ty_id, ident: Ident::invalid(), attrs: Default::default(), kind: opaque_ty_item_kind, vis: respan(span.shrink_to_lo(), hir::VisibilityKind::Inherited), span: opaque_ty_span, }; // Insert the item into the global item list. This usually happens // automatically for all AST items. But this opaque type item // does not actually exist in the AST. self.insert_item(opaque_ty_item); opaque_ty_id } fn lifetimes_from_impl_trait_bounds( &mut self, opaque_ty_id: NodeId, parent_def_id: LocalDefId, bounds: hir::GenericBounds<'hir>, lifetimes_to_include: Option<&FxHashSet>, ) -> (&'hir [hir::GenericArg<'hir>], &'hir [hir::GenericParam<'hir>]) { debug!( "lifetimes_from_impl_trait_bounds(opaque_ty_id={:?}, \ parent_def_id={:?}, \ bounds={:#?})", opaque_ty_id, parent_def_id, bounds, ); // This visitor walks over `impl Trait` bounds and creates defs for all lifetimes that // appear in the bounds, excluding lifetimes that are created within the bounds. // E.g., `'a`, `'b`, but not `'c` in `impl for<'c> SomeTrait<'a, 'b, 'c>`. struct ImplTraitLifetimeCollector<'r, 'a, 'hir> { context: &'r mut LoweringContext<'a, 'hir>, parent: LocalDefId, opaque_ty_id: NodeId, collect_elided_lifetimes: bool, currently_bound_lifetimes: Vec, already_defined_lifetimes: FxHashSet, output_lifetimes: Vec>, output_lifetime_params: Vec>, lifetimes_to_include: Option<&'r FxHashSet>, } impl<'r, 'a, 'v, 'hir> intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a, 'hir> { type Map = intravisit::ErasedMap<'v>; fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap { intravisit::NestedVisitorMap::None } fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs<'v>) { // Don't collect elided lifetimes used inside of `Fn()` syntax. if parameters.parenthesized { let old_collect_elided_lifetimes = self.collect_elided_lifetimes; self.collect_elided_lifetimes = false; intravisit::walk_generic_args(self, span, parameters); self.collect_elided_lifetimes = old_collect_elided_lifetimes; } else { intravisit::walk_generic_args(self, span, parameters); } } fn visit_ty(&mut self, t: &'v hir::Ty<'v>) { // Don't collect elided lifetimes used inside of `fn()` syntax. if let hir::TyKind::BareFn(_) = t.kind { let old_collect_elided_lifetimes = self.collect_elided_lifetimes; self.collect_elided_lifetimes = false; // Record the "stack height" of `for<'a>` lifetime bindings // to be able to later fully undo their introduction. let old_len = self.currently_bound_lifetimes.len(); intravisit::walk_ty(self, t); self.currently_bound_lifetimes.truncate(old_len); self.collect_elided_lifetimes = old_collect_elided_lifetimes; } else { intravisit::walk_ty(self, t) } } fn visit_poly_trait_ref( &mut self, trait_ref: &'v hir::PolyTraitRef<'v>, modifier: hir::TraitBoundModifier, ) { // Record the "stack height" of `for<'a>` lifetime bindings // to be able to later fully undo their introduction. let old_len = self.currently_bound_lifetimes.len(); intravisit::walk_poly_trait_ref(self, trait_ref, modifier); self.currently_bound_lifetimes.truncate(old_len); } fn visit_generic_param(&mut self, param: &'v hir::GenericParam<'v>) { // Record the introduction of 'a in `for<'a> ...`. if let hir::GenericParamKind::Lifetime { .. } = param.kind { // Introduce lifetimes one at a time so that we can handle // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`. let lt_name = hir::LifetimeName::Param(param.name); self.currently_bound_lifetimes.push(lt_name); } intravisit::walk_generic_param(self, param); } fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) { let name = match lifetime.name { hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => { if self.collect_elided_lifetimes { // Use `'_` for both implicit and underscore lifetimes in // `type Foo<'_> = impl SomeTrait<'_>;`. hir::LifetimeName::Underscore } else { return; } } hir::LifetimeName::Param(_) => lifetime.name, // Refers to some other lifetime that is "in // scope" within the type. hir::LifetimeName::ImplicitObjectLifetimeDefault => return, hir::LifetimeName::Error | hir::LifetimeName::Static => return, }; if !self.currently_bound_lifetimes.contains(&name) && !self.already_defined_lifetimes.contains(&name) && self.lifetimes_to_include.map_or(true, |lifetimes| lifetimes.contains(&name)) { self.already_defined_lifetimes.insert(name); self.output_lifetimes.push(hir::GenericArg::Lifetime(hir::Lifetime { hir_id: self.context.next_id(), span: lifetime.span, name, })); let def_node_id = self.context.resolver.next_node_id(); let hir_id = self.context.lower_node_id_with_owner(def_node_id, self.opaque_ty_id); self.context.resolver.create_def( self.parent, def_node_id, DefPathData::LifetimeNs(name.ident().name), ExpnId::root(), lifetime.span, ); let (name, kind) = match name { hir::LifetimeName::Underscore => ( hir::ParamName::Plain(Ident::with_dummy_span(kw::UnderscoreLifetime)), hir::LifetimeParamKind::Elided, ), hir::LifetimeName::Param(param_name) => { (param_name, hir::LifetimeParamKind::Explicit) } _ => panic!("expected `LifetimeName::Param` or `ParamName::Plain`"), }; self.output_lifetime_params.push(hir::GenericParam { hir_id, name, span: lifetime.span, pure_wrt_drop: false, attrs: &[], bounds: &[], kind: hir::GenericParamKind::Lifetime { kind }, }); } } } let mut lifetime_collector = ImplTraitLifetimeCollector { context: self, parent: parent_def_id, opaque_ty_id, collect_elided_lifetimes: true, currently_bound_lifetimes: Vec::new(), already_defined_lifetimes: FxHashSet::default(), output_lifetimes: Vec::new(), output_lifetime_params: Vec::new(), lifetimes_to_include, }; for bound in bounds { intravisit::walk_param_bound(&mut lifetime_collector, &bound); } let ImplTraitLifetimeCollector { output_lifetimes, output_lifetime_params, .. } = lifetime_collector; ( self.arena.alloc_from_iter(output_lifetimes), self.arena.alloc_from_iter(output_lifetime_params), ) } fn lower_local(&mut self, l: &Local) -> (hir::Local<'hir>, SmallVec<[NodeId; 1]>) { let mut ids = SmallVec::<[NodeId; 1]>::new(); if self.sess.features_untracked().impl_trait_in_bindings { if let Some(ref ty) = l.ty { let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids }; visitor.visit_ty(ty); } } let ty = l.ty.as_ref().map(|t| { let mut capturable_lifetimes; self.lower_ty( t, if self.sess.features_untracked().impl_trait_in_bindings { capturable_lifetimes = FxHashSet::default(); ImplTraitContext::OtherOpaqueTy { capturable_lifetimes: &mut capturable_lifetimes, origin: hir::OpaqueTyOrigin::Binding, } } else { ImplTraitContext::Disallowed(ImplTraitPosition::Binding) }, ) }); let init = l.init.as_ref().map(|e| self.lower_expr(e)); ( hir::Local { hir_id: self.lower_node_id(l.id), ty, pat: self.lower_pat(&l.pat), init, span: l.span, attrs: l.attrs.iter().map(|a| self.lower_attr(a)).collect::>().into(), source: hir::LocalSource::Normal, }, ids, ) } fn lower_fn_params_to_names(&mut self, decl: &FnDecl) -> &'hir [Ident] { // Skip the `...` (`CVarArgs`) trailing arguments from the AST, // as they are not explicit in HIR/Ty function signatures. // (instead, the `c_variadic` flag is set to `true`) let mut inputs = &decl.inputs[..]; if decl.c_variadic() { inputs = &inputs[..inputs.len() - 1]; } self.arena.alloc_from_iter(inputs.iter().map(|param| match param.pat.kind { PatKind::Ident(_, ident, _) => ident, _ => Ident::new(kw::Empty, param.pat.span), })) } // Lowers a function declaration. // // `decl`: the unlowered (AST) function declaration. // `fn_def_id`: if `Some`, impl Trait arguments are lowered into generic parameters on the // given DefId, otherwise impl Trait is disallowed. Must be `Some` if // `make_ret_async` is also `Some`. // `impl_trait_return_allow`: determines whether `impl Trait` can be used in return position. // This guards against trait declarations and implementations where `impl Trait` is // disallowed. // `make_ret_async`: if `Some`, converts `-> T` into `-> impl Future` in the // return type. This is used for `async fn` declarations. The `NodeId` is the ID of the // return type `impl Trait` item. fn lower_fn_decl( &mut self, decl: &FnDecl, mut in_band_ty_params: Option<(DefId, &mut Vec>)>, impl_trait_return_allow: bool, make_ret_async: Option, ) -> &'hir hir::FnDecl<'hir> { debug!( "lower_fn_decl(\ fn_decl: {:?}, \ in_band_ty_params: {:?}, \ impl_trait_return_allow: {}, \ make_ret_async: {:?})", decl, in_band_ty_params, impl_trait_return_allow, make_ret_async, ); let lt_mode = if make_ret_async.is_some() { // In `async fn`, argument-position elided lifetimes // must be transformed into fresh generic parameters so that // they can be applied to the opaque `impl Trait` return type. AnonymousLifetimeMode::CreateParameter } else { self.anonymous_lifetime_mode }; let c_variadic = decl.c_variadic(); // Remember how many lifetimes were already around so that we can // only look at the lifetime parameters introduced by the arguments. let inputs = self.with_anonymous_lifetime_mode(lt_mode, |this| { // Skip the `...` (`CVarArgs`) trailing arguments from the AST, // as they are not explicit in HIR/Ty function signatures. // (instead, the `c_variadic` flag is set to `true`) let mut inputs = &decl.inputs[..]; if c_variadic { inputs = &inputs[..inputs.len() - 1]; } this.arena.alloc_from_iter(inputs.iter().map(|param| { if let Some((_, ibty)) = &mut in_band_ty_params { this.lower_ty_direct(¶m.ty, ImplTraitContext::Universal(ibty)) } else { this.lower_ty_direct(¶m.ty, ImplTraitContext::disallowed()) } })) }); let output = if let Some(ret_id) = make_ret_async { self.lower_async_fn_ret_ty( &decl.output, in_band_ty_params.expect("`make_ret_async` but no `fn_def_id`").0, ret_id, ) } else { match decl.output { FnRetTy::Ty(ref ty) => { let context = match in_band_ty_params { Some((def_id, _)) if impl_trait_return_allow => { ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id: def_id, origin: hir::OpaqueTyOrigin::FnReturn, } } _ => ImplTraitContext::disallowed(), }; hir::FnRetTy::Return(self.lower_ty(ty, context)) } FnRetTy::Default(span) => hir::FnRetTy::DefaultReturn(span), } }; self.arena.alloc(hir::FnDecl { inputs, output, c_variadic, implicit_self: decl.inputs.get(0).map_or(hir::ImplicitSelfKind::None, |arg| { use BindingMode::{ByRef, ByValue}; let is_mutable_pat = matches!( arg.pat.kind, PatKind::Ident(ByValue(Mutability::Mut) | ByRef(Mutability::Mut), ..) ); match arg.ty.kind { TyKind::ImplicitSelf if is_mutable_pat => hir::ImplicitSelfKind::Mut, TyKind::ImplicitSelf => hir::ImplicitSelfKind::Imm, // Given we are only considering `ImplicitSelf` types, we needn't consider // the case where we have a mutable pattern to a reference as that would // no longer be an `ImplicitSelf`. TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() && mt.mutbl == ast::Mutability::Mut => { hir::ImplicitSelfKind::MutRef } TyKind::Rptr(_, ref mt) if mt.ty.kind.is_implicit_self() => { hir::ImplicitSelfKind::ImmRef } _ => hir::ImplicitSelfKind::None, } }), }) } // Transforms `-> T` for `async fn` into `-> OpaqueTy { .. }` // combined with the following definition of `OpaqueTy`: // // type OpaqueTy = impl Future; // // `inputs`: lowered types of parameters to the function (used to collect lifetimes) // `output`: unlowered output type (`T` in `-> T`) // `fn_def_id`: `DefId` of the parent function (used to create child impl trait definition) // `opaque_ty_node_id`: `NodeId` of the opaque `impl Trait` type that should be created // `elided_lt_replacement`: replacement for elided lifetimes in the return type fn lower_async_fn_ret_ty( &mut self, output: &FnRetTy, fn_def_id: DefId, opaque_ty_node_id: NodeId, ) -> hir::FnRetTy<'hir> { debug!( "lower_async_fn_ret_ty(\ output={:?}, \ fn_def_id={:?}, \ opaque_ty_node_id={:?})", output, fn_def_id, opaque_ty_node_id, ); let span = output.span(); let opaque_ty_span = self.mark_span_with_reason(DesugaringKind::Async, span, None); let opaque_ty_def_id = self.resolver.local_def_id(opaque_ty_node_id); self.allocate_hir_id_counter(opaque_ty_node_id); // When we create the opaque type for this async fn, it is going to have // to capture all the lifetimes involved in the signature (including in the // return type). This is done by introducing lifetime parameters for: // // - all the explicitly declared lifetimes from the impl and function itself; // - all the elided lifetimes in the fn arguments; // - all the elided lifetimes in the return type. // // So for example in this snippet: // // ```rust // impl<'a> Foo<'a> { // async fn bar<'b>(&self, x: &'b Vec, y: &str) -> &u32 { // // ^ '0 ^ '1 ^ '2 // // elided lifetimes used below // } // } // ``` // // we would create an opaque type like: // // ``` // type Bar<'a, 'b, '0, '1, '2> = impl Future; // ``` // // and we would then desugar `bar` to the equivalent of: // // ```rust // impl<'a> Foo<'a> { // fn bar<'b, '0, '1>(&'0 self, x: &'b Vec, y: &'1 str) -> Bar<'a, 'b, '0, '1, '_> // } // ``` // // Note that the final parameter to `Bar` is `'_`, not `'2` -- // this is because the elided lifetimes from the return type // should be figured out using the ordinary elision rules, and // this desugaring achieves that. // // The variable `input_lifetimes_count` tracks the number of // lifetime parameters to the opaque type *not counting* those // lifetimes elided in the return type. This includes those // that are explicitly declared (`in_scope_lifetimes`) and // those elided lifetimes we found in the arguments (current // content of `lifetimes_to_define`). Next, we will process // the return type, which will cause `lifetimes_to_define` to // grow. let input_lifetimes_count = self.in_scope_lifetimes.len() + self.lifetimes_to_define.len(); let (opaque_ty_id, lifetime_params) = self.with_hir_id_owner(opaque_ty_node_id, |this| { // We have to be careful to get elision right here. The // idea is that we create a lifetime parameter for each // lifetime in the return type. So, given a return type // like `async fn foo(..) -> &[&u32]`, we lower to `impl // Future`. // // Then, we will create `fn foo(..) -> Foo<'_, '_>`, and // hence the elision takes place at the fn site. let future_bound = this .with_anonymous_lifetime_mode(AnonymousLifetimeMode::CreateParameter, |this| { this.lower_async_fn_output_type_to_future_bound(output, fn_def_id, span) }); debug!("lower_async_fn_ret_ty: future_bound={:#?}", future_bound); // Calculate all the lifetimes that should be captured // by the opaque type. This should include all in-scope // lifetime parameters, including those defined in-band. // // Note: this must be done after lowering the output type, // as the output type may introduce new in-band lifetimes. let lifetime_params: Vec<(Span, ParamName)> = this .in_scope_lifetimes .iter() .cloned() .map(|name| (name.ident().span, name)) .chain(this.lifetimes_to_define.iter().cloned()) .collect(); debug!("lower_async_fn_ret_ty: in_scope_lifetimes={:#?}", this.in_scope_lifetimes); debug!("lower_async_fn_ret_ty: lifetimes_to_define={:#?}", this.lifetimes_to_define); debug!("lower_async_fn_ret_ty: lifetime_params={:#?}", lifetime_params); let generic_params = this.arena.alloc_from_iter(lifetime_params.iter().map(|(span, hir_name)| { this.lifetime_to_generic_param(*span, *hir_name, opaque_ty_def_id) })); let opaque_ty_item = hir::OpaqueTy { generics: hir::Generics { params: generic_params, where_clause: hir::WhereClause { predicates: &[], span }, span, }, bounds: arena_vec![this; future_bound], impl_trait_fn: Some(fn_def_id), origin: hir::OpaqueTyOrigin::AsyncFn, }; trace!("exist ty from async fn def id: {:#?}", opaque_ty_def_id); let opaque_ty_id = this.generate_opaque_type(opaque_ty_node_id, opaque_ty_item, span, opaque_ty_span); (opaque_ty_id, lifetime_params) }); // As documented above on the variable // `input_lifetimes_count`, we need to create the lifetime // arguments to our opaque type. Continuing with our example, // we're creating the type arguments for the return type: // // ``` // Bar<'a, 'b, '0, '1, '_> // ``` // // For the "input" lifetime parameters, we wish to create // references to the parameters themselves, including the // "implicit" ones created from parameter types (`'a`, `'b`, // '`0`, `'1`). // // For the "output" lifetime parameters, we just want to // generate `'_`. let mut generic_args = Vec::with_capacity(lifetime_params.len()); generic_args.extend(lifetime_params[..input_lifetimes_count].iter().map( |&(span, hir_name)| { // Input lifetime like `'a` or `'1`: GenericArg::Lifetime(hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Param(hir_name), }) }, )); generic_args.extend(lifetime_params[input_lifetimes_count..].iter().map(|&(span, _)| // Output lifetime like `'_`. GenericArg::Lifetime(hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit, }))); let generic_args = self.arena.alloc_from_iter(generic_args); // Create the `Foo<...>` reference itself. Note that the `type // Foo = impl Trait` is, internally, created as a child of the // async fn, so the *type parameters* are inherited. It's // only the lifetime parameters that we must supply. let opaque_ty_ref = hir::TyKind::OpaqueDef(hir::ItemId { id: opaque_ty_id }, generic_args); let opaque_ty = self.ty(opaque_ty_span, opaque_ty_ref); hir::FnRetTy::Return(self.arena.alloc(opaque_ty)) } /// Transforms `-> T` into `Future` fn lower_async_fn_output_type_to_future_bound( &mut self, output: &FnRetTy, fn_def_id: DefId, span: Span, ) -> hir::GenericBound<'hir> { // Compute the `T` in `Future` from the return type. let output_ty = match output { FnRetTy::Ty(ty) => { // Not `OpaqueTyOrigin::AsyncFn`: that's only used for the // `impl Future` opaque type that `async fn` implicitly // generates. let context = ImplTraitContext::ReturnPositionOpaqueTy { fn_def_id, origin: hir::OpaqueTyOrigin::FnReturn, }; self.lower_ty(ty, context) } FnRetTy::Default(ret_ty_span) => self.arena.alloc(self.ty_tup(*ret_ty_span, &[])), }; // "" let future_args = self.arena.alloc(hir::GenericArgs { args: &[], bindings: arena_vec![self; self.output_ty_binding(span, output_ty)], parenthesized: false, }); hir::GenericBound::LangItemTrait( // ::std::future::Future hir::LangItem::Future, span, self.next_id(), future_args, ) } fn lower_param_bound( &mut self, tpb: &GenericBound, itctx: ImplTraitContext<'_, 'hir>, ) -> hir::GenericBound<'hir> { match *tpb { GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait( self.lower_poly_trait_ref(ty, itctx), self.lower_trait_bound_modifier(modifier), ), GenericBound::Outlives(ref lifetime) => { hir::GenericBound::Outlives(self.lower_lifetime(lifetime)) } } } fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime { let span = l.ident.span; match l.ident { ident if ident.name == kw::StaticLifetime => { self.new_named_lifetime(l.id, span, hir::LifetimeName::Static) } ident if ident.name == kw::UnderscoreLifetime => match self.anonymous_lifetime_mode { AnonymousLifetimeMode::CreateParameter => { let fresh_name = self.collect_fresh_in_band_lifetime(span); self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name)) } AnonymousLifetimeMode::PassThrough => { self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore) } AnonymousLifetimeMode::ReportError => self.new_error_lifetime(Some(l.id), span), }, ident => { self.maybe_collect_in_band_lifetime(ident); let param_name = ParamName::Plain(ident); self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name)) } } } fn new_named_lifetime( &mut self, id: NodeId, span: Span, name: hir::LifetimeName, ) -> hir::Lifetime { hir::Lifetime { hir_id: self.lower_node_id(id), span, name } } fn lower_generic_params_mut<'s>( &'s mut self, params: &'s [GenericParam], add_bounds: &'s NodeMap>, mut itctx: ImplTraitContext<'s, 'hir>, ) -> impl Iterator> + Captures<'a> + Captures<'s> { params .iter() .map(move |param| self.lower_generic_param(param, add_bounds, itctx.reborrow())) } fn lower_generic_params( &mut self, params: &[GenericParam], add_bounds: &NodeMap>, itctx: ImplTraitContext<'_, 'hir>, ) -> &'hir [hir::GenericParam<'hir>] { self.arena.alloc_from_iter(self.lower_generic_params_mut(params, add_bounds, itctx)) } fn lower_generic_param( &mut self, param: &GenericParam, add_bounds: &NodeMap>, mut itctx: ImplTraitContext<'_, 'hir>, ) -> hir::GenericParam<'hir> { let mut bounds: Vec<_> = self .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| { this.lower_param_bounds_mut(¶m.bounds, itctx.reborrow()).collect() }); let (name, kind) = match param.kind { GenericParamKind::Lifetime => { let was_collecting_in_band = self.is_collecting_in_band_lifetimes; self.is_collecting_in_band_lifetimes = false; let lt = self .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| { this.lower_lifetime(&Lifetime { id: param.id, ident: param.ident }) }); let param_name = match lt.name { hir::LifetimeName::Param(param_name) => param_name, hir::LifetimeName::Implicit | hir::LifetimeName::Underscore | hir::LifetimeName::Static => hir::ParamName::Plain(lt.name.ident()), hir::LifetimeName::ImplicitObjectLifetimeDefault => { self.sess.diagnostic().span_bug( param.ident.span, "object-lifetime-default should not occur here", ); } hir::LifetimeName::Error => ParamName::Error, }; let kind = hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit }; self.is_collecting_in_band_lifetimes = was_collecting_in_band; (param_name, kind) } GenericParamKind::Type { ref default, .. } => { let add_bounds = add_bounds.get(¶m.id).map_or(&[][..], |x| &x); if !add_bounds.is_empty() { let params = self.lower_param_bounds_mut(add_bounds, itctx.reborrow()); bounds.extend(params); } let kind = hir::GenericParamKind::Type { default: default.as_ref().map(|x| { self.lower_ty( x, ImplTraitContext::OtherOpaqueTy { capturable_lifetimes: &mut FxHashSet::default(), origin: hir::OpaqueTyOrigin::Misc, }, ) }), synthetic: param .attrs .iter() .filter(|attr| self.sess.check_name(attr, sym::rustc_synthetic)) .map(|_| hir::SyntheticTyParamKind::FromAttr) .next(), }; (hir::ParamName::Plain(param.ident), kind) } GenericParamKind::Const { ref ty, kw_span: _, ref default } => { let ty = self .with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| { this.lower_ty(&ty, ImplTraitContext::disallowed()) }); let default = default.as_ref().map(|def| self.lower_anon_const(def)); (hir::ParamName::Plain(param.ident), hir::GenericParamKind::Const { ty, default }) } }; hir::GenericParam { hir_id: self.lower_node_id(param.id), name, span: param.ident.span, pure_wrt_drop: self.sess.contains_name(¶m.attrs, sym::may_dangle), attrs: self.lower_attrs(¶m.attrs), bounds: self.arena.alloc_from_iter(bounds), kind, } } fn lower_trait_ref( &mut self, p: &TraitRef, itctx: ImplTraitContext<'_, 'hir>, ) -> hir::TraitRef<'hir> { let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) { hir::QPath::Resolved(None, path) => path, qpath => panic!("lower_trait_ref: unexpected QPath `{:?}`", qpath), }; hir::TraitRef { path, hir_ref_id: self.lower_node_id(p.ref_id) } } fn lower_poly_trait_ref( &mut self, p: &PolyTraitRef, mut itctx: ImplTraitContext<'_, 'hir>, ) -> hir::PolyTraitRef<'hir> { let bound_generic_params = self.lower_generic_params( &p.bound_generic_params, &NodeMap::default(), itctx.reborrow(), ); let trait_ref = self.with_in_scope_lifetime_defs(&p.bound_generic_params, |this| { // Any impl Trait types defined within this scope can capture // lifetimes bound on this predicate. let lt_def_names = p.bound_generic_params.iter().filter_map(|param| match param.kind { GenericParamKind::Lifetime { .. } => Some(hir::LifetimeName::Param( ParamName::Plain(param.ident.normalize_to_macros_2_0()), )), _ => None, }); if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx { capturable_lifetimes.extend(lt_def_names.clone()); } let res = this.lower_trait_ref(&p.trait_ref, itctx.reborrow()); if let ImplTraitContext::OtherOpaqueTy { ref mut capturable_lifetimes, .. } = itctx { for param in lt_def_names { capturable_lifetimes.remove(¶m); } } res }); hir::PolyTraitRef { bound_generic_params, trait_ref, span: p.span } } fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext<'_, 'hir>) -> hir::MutTy<'hir> { hir::MutTy { ty: self.lower_ty(&mt.ty, itctx), mutbl: mt.mutbl } } fn lower_param_bounds( &mut self, bounds: &[GenericBound], itctx: ImplTraitContext<'_, 'hir>, ) -> hir::GenericBounds<'hir> { self.arena.alloc_from_iter(self.lower_param_bounds_mut(bounds, itctx)) } fn lower_param_bounds_mut<'s>( &'s mut self, bounds: &'s [GenericBound], mut itctx: ImplTraitContext<'s, 'hir>, ) -> impl Iterator> + Captures<'s> + Captures<'a> { bounds.iter().map(move |bound| self.lower_param_bound(bound, itctx.reborrow())) } fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> &'hir hir::Block<'hir> { self.arena.alloc(self.lower_block_noalloc(b, targeted_by_break)) } fn lower_block_noalloc(&mut self, b: &Block, targeted_by_break: bool) -> hir::Block<'hir> { let mut expr: Option<&'hir _> = None; let stmts = self.arena.alloc_from_iter( b.stmts .iter() .enumerate() .filter_map(|(index, stmt)| { if index == b.stmts.len() - 1 { if let StmtKind::Expr(ref e) = stmt.kind { expr = Some(self.lower_expr(e)); None } else { Some(self.lower_stmt(stmt)) } } else { Some(self.lower_stmt(stmt)) } }) .flatten(), ); let rules = self.lower_block_check_mode(&b.rules); let hir_id = self.lower_node_id(b.id); hir::Block { hir_id, stmts, expr, rules, span: b.span, targeted_by_break } } /// Lowers a block directly to an expression, presuming that it /// has no attributes and is not targeted by a `break`. fn lower_block_expr(&mut self, b: &Block) -> hir::Expr<'hir> { let block = self.lower_block(b, false); self.expr_block(block, AttrVec::new()) } fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst { self.with_new_scopes(|this| hir::AnonConst { hir_id: this.lower_node_id(c.id), body: this.lower_const_body(c.value.span, Some(&c.value)), }) } fn lower_stmt(&mut self, s: &Stmt) -> SmallVec<[hir::Stmt<'hir>; 1]> { let kind = match s.kind { StmtKind::Local(ref l) => { let (l, item_ids) = self.lower_local(l); let mut ids: SmallVec<[hir::Stmt<'hir>; 1]> = item_ids .into_iter() .map(|item_id| { let item_id = hir::ItemId { id: self.lower_node_id(item_id) }; self.stmt(s.span, hir::StmtKind::Item(item_id)) }) .collect(); ids.push({ hir::Stmt { hir_id: self.lower_node_id(s.id), kind: hir::StmtKind::Local(self.arena.alloc(l)), span: s.span, } }); return ids; } StmtKind::Item(ref it) => { // Can only use the ID once. let mut id = Some(s.id); return self .lower_item_id(it) .into_iter() .map(|item_id| { let hir_id = id .take() .map(|id| self.lower_node_id(id)) .unwrap_or_else(|| self.next_id()); hir::Stmt { hir_id, kind: hir::StmtKind::Item(item_id), span: s.span } }) .collect(); } StmtKind::Expr(ref e) => hir::StmtKind::Expr(self.lower_expr(e)), StmtKind::Semi(ref e) => hir::StmtKind::Semi(self.lower_expr(e)), StmtKind::Empty => return smallvec![], StmtKind::MacCall(..) => panic!("shouldn't exist here"), }; smallvec![hir::Stmt { hir_id: self.lower_node_id(s.id), kind, span: s.span }] } fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode { match *b { BlockCheckMode::Default => hir::BlockCheckMode::DefaultBlock, BlockCheckMode::Unsafe(u) => { hir::BlockCheckMode::UnsafeBlock(self.lower_unsafe_source(u)) } } } fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource { match u { CompilerGenerated => hir::UnsafeSource::CompilerGenerated, UserProvided => hir::UnsafeSource::UserProvided, } } fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier { match f { TraitBoundModifier::None => hir::TraitBoundModifier::None, TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst, // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a // placeholder for compilation to proceed. TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => { hir::TraitBoundModifier::Maybe } } } // Helper methods for building HIR. fn stmt(&mut self, span: Span, kind: hir::StmtKind<'hir>) -> hir::Stmt<'hir> { hir::Stmt { span, kind, hir_id: self.next_id() } } fn stmt_expr(&mut self, span: Span, expr: hir::Expr<'hir>) -> hir::Stmt<'hir> { self.stmt(span, hir::StmtKind::Expr(self.arena.alloc(expr))) } fn stmt_let_pat( &mut self, attrs: AttrVec, span: Span, init: Option<&'hir hir::Expr<'hir>>, pat: &'hir hir::Pat<'hir>, source: hir::LocalSource, ) -> hir::Stmt<'hir> { let local = hir::Local { attrs, hir_id: self.next_id(), init, pat, source, span, ty: None }; self.stmt(span, hir::StmtKind::Local(self.arena.alloc(local))) } fn block_expr(&mut self, expr: &'hir hir::Expr<'hir>) -> &'hir hir::Block<'hir> { self.block_all(expr.span, &[], Some(expr)) } fn block_all( &mut self, span: Span, stmts: &'hir [hir::Stmt<'hir>], expr: Option<&'hir hir::Expr<'hir>>, ) -> &'hir hir::Block<'hir> { let blk = hir::Block { stmts, expr, hir_id: self.next_id(), rules: hir::BlockCheckMode::DefaultBlock, span, targeted_by_break: false, }; self.arena.alloc(blk) } /// Constructs a `true` or `false` literal pattern. fn pat_bool(&mut self, span: Span, val: bool) -> &'hir hir::Pat<'hir> { let expr = self.expr_bool(span, val); self.pat(span, hir::PatKind::Lit(expr)) } fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> { let field = self.single_pat_field(span, pat); self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field) } fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> { let field = self.single_pat_field(span, pat); self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field) } fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> { let field = self.single_pat_field(span, pat); self.pat_lang_item_variant(span, hir::LangItem::OptionSome, field) } fn pat_none(&mut self, span: Span) -> &'hir hir::Pat<'hir> { self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[]) } fn single_pat_field( &mut self, span: Span, pat: &'hir hir::Pat<'hir>, ) -> &'hir [hir::FieldPat<'hir>] { let field = hir::FieldPat { hir_id: self.next_id(), ident: Ident::new(sym::integer(0), span), is_shorthand: false, pat, span, }; arena_vec![self; field] } fn pat_lang_item_variant( &mut self, span: Span, lang_item: hir::LangItem, fields: &'hir [hir::FieldPat<'hir>], ) -> &'hir hir::Pat<'hir> { let qpath = hir::QPath::LangItem(lang_item, span); self.pat(span, hir::PatKind::Struct(qpath, fields, false)) } fn pat_ident(&mut self, span: Span, ident: Ident) -> (&'hir hir::Pat<'hir>, hir::HirId) { self.pat_ident_binding_mode(span, ident, hir::BindingAnnotation::Unannotated) } fn pat_ident_binding_mode( &mut self, span: Span, ident: Ident, bm: hir::BindingAnnotation, ) -> (&'hir hir::Pat<'hir>, hir::HirId) { let hir_id = self.next_id(); ( self.arena.alloc(hir::Pat { hir_id, kind: hir::PatKind::Binding(bm, hir_id, ident.with_span_pos(span), None), span, default_binding_modes: true, }), hir_id, ) } fn pat_wild(&mut self, span: Span) -> &'hir hir::Pat<'hir> { self.pat(span, hir::PatKind::Wild) } fn pat(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> { self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span, default_binding_modes: true, }) } fn pat_without_dbm(&mut self, span: Span, kind: hir::PatKind<'hir>) -> &'hir hir::Pat<'hir> { self.arena.alloc(hir::Pat { hir_id: self.next_id(), kind, span, default_binding_modes: false, }) } fn ty_path( &mut self, mut hir_id: hir::HirId, span: Span, qpath: hir::QPath<'hir>, ) -> hir::Ty<'hir> { let kind = match qpath { hir::QPath::Resolved(None, path) => { // Turn trait object paths into `TyKind::TraitObject` instead. match path.res { Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => { let principal = hir::PolyTraitRef { bound_generic_params: &[], trait_ref: hir::TraitRef { path, hir_ref_id: hir_id }, span, }; // The original ID is taken by the `PolyTraitRef`, // so the `Ty` itself needs a different one. hir_id = self.next_id(); hir::TyKind::TraitObject( arena_vec![self; principal], self.elided_dyn_bound(span), ) } _ => hir::TyKind::Path(hir::QPath::Resolved(None, path)), } } _ => hir::TyKind::Path(qpath), }; hir::Ty { hir_id, kind, span } } /// Invoked to create the lifetime argument for a type `&T` /// with no explicit lifetime. fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime { match self.anonymous_lifetime_mode { // Intercept when we are in an impl header or async fn and introduce an in-band // lifetime. // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh // `'f`. AnonymousLifetimeMode::CreateParameter => { let fresh_name = self.collect_fresh_in_band_lifetime(span); hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Param(fresh_name), } } AnonymousLifetimeMode::ReportError => self.new_error_lifetime(None, span), AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span), } } /// Report an error on illegal use of `'_` or a `&T` with no explicit lifetime; /// return a "error lifetime". fn new_error_lifetime(&mut self, id: Option, span: Span) -> hir::Lifetime { let (id, msg, label) = match id { Some(id) => (id, "`'_` cannot be used here", "`'_` is a reserved lifetime name"), None => ( self.resolver.next_node_id(), "`&` without an explicit lifetime name cannot be used here", "explicit lifetime name needed here", ), }; let mut err = struct_span_err!(self.sess, span, E0637, "{}", msg,); err.span_label(span, label); err.emit(); self.new_named_lifetime(id, span, hir::LifetimeName::Error) } /// Invoked to create the lifetime argument(s) for a path like /// `std::cell::Ref`; note that implicit lifetimes in these /// sorts of cases are deprecated. This may therefore report a warning or an /// error, depending on the mode. fn elided_path_lifetimes<'s>( &'s mut self, span: Span, count: usize, ) -> impl Iterator + Captures<'a> + Captures<'s> + Captures<'hir> { (0..count).map(move |_| self.elided_path_lifetime(span)) } fn elided_path_lifetime(&mut self, span: Span) -> hir::Lifetime { match self.anonymous_lifetime_mode { AnonymousLifetimeMode::CreateParameter => { // We should have emitted E0726 when processing this path above self.sess .delay_span_bug(span, "expected 'implicit elided lifetime not allowed' error"); let id = self.resolver.next_node_id(); self.new_named_lifetime(id, span, hir::LifetimeName::Error) } // `PassThrough` is the normal case. // `new_error_lifetime`, which would usually be used in the case of `ReportError`, // is unsuitable here, as these can occur from missing lifetime parameters in a // `PathSegment`, for which there is no associated `'_` or `&T` with no explicit // lifetime. Instead, we simply create an implicit lifetime, which will be checked // later, at which point a suitable error will be emitted. AnonymousLifetimeMode::PassThrough | AnonymousLifetimeMode::ReportError => { self.new_implicit_lifetime(span) } } } /// Invoked to create the lifetime argument(s) for an elided trait object /// bound, like the bound in `Box`. This method is not invoked /// when the bound is written, even if it is written with `'_` like in /// `Box`. In those cases, `lower_lifetime` is invoked. fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime { match self.anonymous_lifetime_mode { // NB. We intentionally ignore the create-parameter mode here. // and instead "pass through" to resolve-lifetimes, which will apply // the object-lifetime-defaulting rules. Elided object lifetime defaults // do not act like other elided lifetimes. In other words, given this: // // impl Foo for Box // // we do not introduce a fresh `'_` to serve as the bound, but instead // ultimately translate to the equivalent of: // // impl Foo for Box // // `resolve_lifetime` has the code to make that happen. AnonymousLifetimeMode::CreateParameter => {} AnonymousLifetimeMode::ReportError => { // ReportError applies to explicit use of `'_`. } // This is the normal case. AnonymousLifetimeMode::PassThrough => {} } let r = hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::ImplicitObjectLifetimeDefault, }; debug!("elided_dyn_bound: r={:?}", r); r } fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime { hir::Lifetime { hir_id: self.next_id(), span, name: hir::LifetimeName::Implicit } } fn maybe_lint_bare_trait(&mut self, span: Span, id: NodeId, is_global: bool) { // FIXME(davidtwco): This is a hack to detect macros which produce spans of the // call site which do not have a macro backtrace. See #61963. let is_macro_callsite = self .sess .source_map() .span_to_snippet(span) .map(|snippet| snippet.starts_with("#[")) .unwrap_or(true); if !is_macro_callsite { self.resolver.lint_buffer().buffer_lint_with_diagnostic( BARE_TRAIT_OBJECTS, id, span, "trait objects without an explicit `dyn` are deprecated", BuiltinLintDiagnostics::BareTraitObject(span, is_global), ) } } } fn body_ids(bodies: &BTreeMap>) -> Vec { // Sorting by span ensures that we get things in order within a // file, and also puts the files in a sensible order. let mut body_ids: Vec<_> = bodies.keys().cloned().collect(); body_ids.sort_by_key(|b| bodies[b].value.span); body_ids } /// Helper struct for delayed construction of GenericArgs. struct GenericArgsCtor<'hir> { args: SmallVec<[hir::GenericArg<'hir>; 4]>, bindings: &'hir [hir::TypeBinding<'hir>], parenthesized: bool, } impl<'hir> GenericArgsCtor<'hir> { fn is_empty(&self) -> bool { self.args.is_empty() && self.bindings.is_empty() && !self.parenthesized } fn into_generic_args(self, arena: &'hir Arena<'hir>) -> hir::GenericArgs<'hir> { hir::GenericArgs { args: arena.alloc_from_iter(self.args), bindings: self.bindings, parenthesized: self.parenthesized, } } }