src/librustc/hir/lowering.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Lowers the AST to the HIR.
  12 //!
  13 //! Since the AST and HIR are fairly similar, this is mostly a simple procedure,
  14 //! much like a fold. Where lowering involves a bit more work things get more
  15 //! interesting and there are some invariants you should know about. These mostly
  16 //! concern spans and ids.
  17 //!
  18 //! Spans are assigned to AST nodes during parsing and then are modified during
  19 //! expansion to indicate the origin of a node and the process it went through
  20 //! being expanded. Ids are assigned to AST nodes just before lowering.
  21 //!
  22 //! For the simpler lowering steps, ids and spans should be preserved. Unlike
  23 //! expansion we do not preserve the process of lowering in the spans, so spans
  24 //! should not be modified here. When creating a new node (as opposed to
  25 //! 'folding' an existing one), then you create a new id using `next_id()`.
  26 //!
  27 //! You must ensure that ids are unique. That means that you should only use the
  28 //! id from an AST node in a single HIR node (you can assume that AST node ids
  29 //! are unique). Every new node must have a unique id. Avoid cloning HIR nodes.
  30 //! If you do, you must then set the new node's id to a fresh one.
  31 //!
  32 //! Spans are used for error messages and for tools to map semantics back to
  33 //! source code. It is therefore not as important with spans as ids to be strict
  34 //! about use (you can't break the compiler by screwing up a span). Obviously, a
  35 //! HIR node can only have a single span. But multiple nodes can have the same
  36 //! span and spans don't need to be kept in order, etc. Where code is preserved
  37 //! by lowering, it should have the same span as in the AST. Where HIR nodes are
  38 //! new it is probably best to give a span for the whole AST node being lowered.
  39 //! All nodes should have real spans, don't use dummy spans. Tools are likely to
  40 //! get confused if the spans from leaf AST nodes occur in multiple places
  41 //! in the HIR, especially for multiple identifiers.
  42
  43 use dep_graph::DepGraph;
  44 use hir::{self, ParamName};
  45 use hir::HirVec;
  46 use hir::map::{DefKey, DefPathData, Definitions};
  47 use hir::def_id::{DefId, DefIndex, DefIndexAddressSpace, CRATE_DEF_INDEX};
  48 use hir::def::{Def, PathResolution, PerNS};
  49 use hir::GenericArg;
  50 use lint::builtin::{self, PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES};
  51 use middle::cstore::CrateStore;
  52 use rustc_data_structures::indexed_vec::IndexVec;
  53 use session::Session;
  54 use util::common::FN_OUTPUT_NAME;
  55 use util::nodemap::{DefIdMap, FxHashMap, NodeMap};
  56
  57 use std::collections::{BTreeMap, HashSet};
  58 use std::fmt::Debug;
  59 use std::iter;
  60 use std::mem;
  61 use syntax::attr;
  62 use syntax::ast;
  63 use syntax::ast::*;
  64 use syntax::errors;
  65 use syntax::ext::hygiene::{Mark, SyntaxContext};
  66 use syntax::print::pprust;
  67 use syntax::ptr::P;
  68 use syntax::codemap::{self, respan, CompilerDesugaringKind, Spanned};
  69 use syntax::std_inject;
  70 use syntax::symbol::{keywords, Symbol};
  71 use syntax::tokenstream::{Delimited, TokenStream, TokenTree};
  72 use syntax::parse::token::Token;
  73 use syntax::util::small_vector::SmallVector;
  74 use syntax::visit::{self, Visitor};
  75 use syntax_pos::Span;
  76
  77 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
  78
  79 pub struct LoweringContext<'a> {
  80     crate_root: Option<&'static str>,
  81
  82     // Use to assign ids to hir nodes that do not directly correspond to an ast node
  83     sess: &'a Session,
  84
  85     cstore: &'a CrateStore,
  86
  87     resolver: &'a mut Resolver,
  88     name_map: FxHashMap<Ident, Name>,
  89
  90     /// The items being lowered are collected here.
  91     items: BTreeMap<NodeId, hir::Item>,
  92
  93     trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
  94     impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
  95     bodies: BTreeMap<hir::BodyId, hir::Body>,
  96     exported_macros: Vec<hir::MacroDef>,
  97
  98     trait_impls: BTreeMap<DefId, Vec<NodeId>>,
  99     trait_auto_impl: BTreeMap<DefId, NodeId>,
 100
 101     is_generator: bool,
 102
 103     catch_scopes: Vec<NodeId>,
 104     loop_scopes: Vec<NodeId>,
 105     is_in_loop_condition: bool,
 106     is_in_trait_impl: bool,
 107
 108     /// What to do when we encounter either an "anonymous lifetime
 109     /// reference". The term "anonymous" is meant to encompass both
 110     /// `'_` lifetimes as well as fully elided cases where nothing is
 111     /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
 112     anonymous_lifetime_mode: AnonymousLifetimeMode,
 113
 114     // This is a list of in-band type definitions being generated by
 115     // Argument-position `impl Trait`.
 116     // When traversing a signature such as `fn foo(x: impl Trait)`,
 117     // we record `impl Trait` as a new type parameter, then later
 118     // add it on to `foo`s generics.
 119     in_band_ty_params: Vec<hir::GenericParam>,
 120
 121     // Used to create lifetime definitions from in-band lifetime usages.
 122     // e.g. `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
 123     // When a named lifetime is encountered in a function or impl header and
 124     // has not been defined
 125     // (i.e. it doesn't appear in the in_scope_lifetimes list), it is added
 126     // to this list. The results of this list are then added to the list of
 127     // lifetime definitions in the corresponding impl or function generics.
 128     lifetimes_to_define: Vec<(Span, ParamName)>,
 129
 130     // Whether or not in-band lifetimes are being collected. This is used to
 131     // indicate whether or not we're in a place where new lifetimes will result
 132     // in in-band lifetime definitions, such a function or an impl header.
 133     // This will always be false unless the `in_band_lifetimes` feature is
 134     // enabled.
 135     is_collecting_in_band_lifetimes: bool,
 136
 137     // Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
 138     // When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
 139     // against this list to see if it is already in-scope, or if a definition
 140     // needs to be created for it.
 141     in_scope_lifetimes: Vec<Name>,
 142
 143     type_def_lifetime_params: DefIdMap<usize>,
 144
 145     current_hir_id_owner: Vec<(DefIndex, u32)>,
 146     item_local_id_counters: NodeMap<u32>,
 147     node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
 148 }
 149
 150 pub trait Resolver {
 151     /// Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
 152     fn resolve_hir_path(&mut self, path: &mut hir::Path, is_value: bool);
 153
 154     /// Obtain the resolution for a node id
 155     fn get_resolution(&mut self, id: NodeId) -> Option<PathResolution>;
 156
 157     /// Obtain the possible resolutions for the given `use` statement.
 158     fn get_import(&mut self, id: NodeId) -> PerNS<Option<PathResolution>>;
 159
 160     /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
 161     /// This should only return `None` during testing.
 162     fn definitions(&mut self) -> &mut Definitions;
 163
 164     /// Given suffix ["b","c","d"], creates a HIR path for `[::crate_root]::b::c::d` and resolves
 165     /// it based on `is_value`.
 166     fn resolve_str_path(
 167         &mut self,
 168         span: Span,
 169         crate_root: Option<&str>,
 170         components: &[&str],
 171         is_value: bool,
 172     ) -> hir::Path;
 173 }
 174
 175 #[derive(Clone, Copy, Debug)]
 176 enum ImplTraitContext {
 177     /// Treat `impl Trait` as shorthand for a new universal generic parameter.
 178     /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
 179     /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
 180     ///
 181     /// We store a DefId here so we can look up necessary information later
 182     Universal(DefId),
 183
 184     /// Treat `impl Trait` as shorthand for a new universal existential parameter.
 185     /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
 186     /// equivalent to a fresh existential parameter like `abstract type T; fn foo() -> T`.
 187     ///
 188     /// We store a DefId here so we can look up necessary information later
 189     Existential(DefId),
 190
 191     /// `impl Trait` is not accepted in this position.
 192     Disallowed,
 193 }
 194
 195 pub fn lower_crate(
 196     sess: &Session,
 197     cstore: &CrateStore,
 198     dep_graph: &DepGraph,
 199     krate: &Crate,
 200     resolver: &mut Resolver,
 201 ) -> hir::Crate {
 202     // We're constructing the HIR here; we don't care what we will
 203     // read, since we haven't even constructed the *input* to
 204     // incr. comp. yet.
 205     dep_graph.assert_ignored();
 206
 207     LoweringContext {
 208         crate_root: std_inject::injected_crate_name(),
 209         sess,
 210         cstore,
 211         resolver,
 212         name_map: FxHashMap(),
 213         items: BTreeMap::new(),
 214         trait_items: BTreeMap::new(),
 215         impl_items: BTreeMap::new(),
 216         bodies: BTreeMap::new(),
 217         trait_impls: BTreeMap::new(),
 218         trait_auto_impl: BTreeMap::new(),
 219         exported_macros: Vec::new(),
 220         catch_scopes: Vec::new(),
 221         loop_scopes: Vec::new(),
 222         is_in_loop_condition: false,
 223         anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
 224         type_def_lifetime_params: DefIdMap(),
 225         current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
 226         item_local_id_counters: NodeMap(),
 227         node_id_to_hir_id: IndexVec::new(),
 228         is_generator: false,
 229         is_in_trait_impl: false,
 230         in_band_ty_params: Vec::new(),
 231         lifetimes_to_define: Vec::new(),
 232         is_collecting_in_band_lifetimes: false,
 233         in_scope_lifetimes: Vec::new(),
 234     }.lower_crate(krate)
 235 }
 236
 237 #[derive(Copy, Clone, PartialEq, Eq)]
 238 enum ParamMode {
 239     /// Any path in a type context.
 240     Explicit,
 241     /// The `module::Type` in `module::Type::method` in an expression.
 242     Optional,
 243 }
 244
 245 #[derive(Debug)]
 246 struct LoweredNodeId {
 247     node_id: NodeId,
 248     hir_id: hir::HirId,
 249 }
 250
 251 enum ParenthesizedGenericArgs {
 252     Ok,
 253     Warn,
 254     Err,
 255 }
 256
 257 /// What to do when we encounter an **anonymous** lifetime
 258 /// reference. Anonymous lifetime references come in two flavors.  You
 259 /// have implicit, or fully elided, references to lifetimes, like the
 260 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
 261 /// or `Ref<'_, T>`.  These often behave the same, but not always:
 262 ///
 263 /// - certain usages of implicit references are deprecated, like
 264 ///   `Ref<T>`, and we sometimes just give hard errors in those cases
 265 ///   as well.
 266 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
 267 ///   the same as `Box<dyn Foo + '_>`.
 268 ///
 269 /// We describe the effects of the various modes in terms of three cases:
 270 ///
 271 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
 272 ///   of a `&` (e.g., the missing lifetime in something like `&T`)
 273 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
 274 ///   there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
 275 ///   elided bounds follow special rules. Note that this only covers
 276 ///   cases where *nothing* is written; the `'_` in `Box<dyn Foo +
 277 ///   '_>` is a case of "modern" elision.
 278 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
 279 ///   parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
 280 ///   non-deprecated equivalent.
 281 ///
 282 /// Currently, the handling of lifetime elision is somewhat spread out
 283 /// between HIR lowering and -- as described below -- the
 284 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
 285 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
 286 /// everything into HIR lowering.
 287 #[derive(Copy, Clone)]
 288 enum AnonymousLifetimeMode {
 289     /// For **Modern** cases, create a new anonymous region parameter
 290     /// and reference that.
 291     ///
 292     /// For **Dyn Bound** cases, pass responsibility to
 293     /// `resolve_lifetime` code.
 294     ///
 295     /// For **Deprecated** cases, report an error.
 296     CreateParameter,
 297
 298     /// Pass responsibility to `resolve_lifetime` code for all cases.
 299     PassThrough,
 300 }
 301
 302 impl<'a> LoweringContext<'a> {
 303     fn lower_crate(mut self, c: &Crate) -> hir::Crate {
 304         /// Full-crate AST visitor that inserts into a fresh
 305         /// `LoweringContext` any information that may be
 306         /// needed from arbitrary locations in the crate.
 307         /// E.g. The number of lifetime generic parameters
 308         /// declared for every type and trait definition.
 309         struct MiscCollector<'lcx, 'interner: 'lcx> {
 310             lctx: &'lcx mut LoweringContext<'interner>,
 311         }
 312
 313         impl<'lcx, 'interner> Visitor<'lcx> for MiscCollector<'lcx, 'interner> {
 314             fn visit_item(&mut self, item: &'lcx Item) {
 315                 self.lctx.allocate_hir_id_counter(item.id, item);
 316
 317                 match item.node {
 318                     ItemKind::Struct(_, ref generics)
 319                     | ItemKind::Union(_, ref generics)
 320                     | ItemKind::Enum(_, ref generics)
 321                     | ItemKind::Ty(_, ref generics)
 322                     | ItemKind::Trait(_, _, ref generics, ..) => {
 323                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
 324                         let count = generics
 325                             .params
 326                             .iter()
 327                             .filter(|param| match param.kind {
 328                                 ast::GenericParamKind::Lifetime { .. } => true,
 329                                 _ => false,
 330                             })
 331                             .count();
 332                         self.lctx.type_def_lifetime_params.insert(def_id, count);
 333                     }
 334                     _ => {}
 335                 }
 336                 visit::walk_item(self, item);
 337             }
 338
 339             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 340                 self.lctx.allocate_hir_id_counter(item.id, item);
 341                 visit::walk_trait_item(self, item);
 342             }
 343
 344             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 345                 self.lctx.allocate_hir_id_counter(item.id, item);
 346                 visit::walk_impl_item(self, item);
 347             }
 348         }
 349
 350         struct ItemLowerer<'lcx, 'interner: 'lcx> {
 351             lctx: &'lcx mut LoweringContext<'interner>,
 352         }
 353
 354         impl<'lcx, 'interner> ItemLowerer<'lcx, 'interner> {
 355             fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
 356             where
 357                 F: FnOnce(&mut Self),
 358             {
 359                 let old = self.lctx.is_in_trait_impl;
 360                 self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
 361                     false
 362                 } else {
 363                     true
 364                 };
 365                 f(self);
 366                 self.lctx.is_in_trait_impl = old;
 367             }
 368         }
 369
 370         impl<'lcx, 'interner> Visitor<'lcx> for ItemLowerer<'lcx, 'interner> {
 371             fn visit_item(&mut self, item: &'lcx Item) {
 372                 let mut item_lowered = true;
 373                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 374                     if let Some(hir_item) = lctx.lower_item(item) {
 375                         lctx.items.insert(item.id, hir_item);
 376                     } else {
 377                         item_lowered = false;
 378                     }
 379                 });
 380
 381                 if item_lowered {
 382                     let item_generics = match self.lctx.items.get(&item.id).unwrap().node {
 383                         hir::Item_::ItemImpl(_, _, _, ref generics, ..)
 384                         | hir::Item_::ItemTrait(_, _, ref generics, ..) => {
 385                             generics.params.clone()
 386                         }
 387                         _ => HirVec::new(),
 388                     };
 389
 390                     self.lctx.with_parent_impl_lifetime_defs(&item_generics, |this| {
 391                         let this = &mut ItemLowerer { lctx: this };
 392                         if let ItemKind::Impl(_, _, _, _, ref opt_trait_ref, _, _) = item.node {
 393                             this.with_trait_impl_ref(opt_trait_ref, |this| {
 394                                 visit::walk_item(this, item)
 395                             });
 396                         } else {
 397                             visit::walk_item(this, item);
 398                         }
 399                     });
 400                 }
 401             }
 402
 403             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 404                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 405                     let id = hir::TraitItemId { node_id: item.id };
 406                     let hir_item = lctx.lower_trait_item(item);
 407                     lctx.trait_items.insert(id, hir_item);
 408                 });
 409
 410                 visit::walk_trait_item(self, item);
 411             }
 412
 413             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 414                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 415                     let id = hir::ImplItemId { node_id: item.id };
 416                     let hir_item = lctx.lower_impl_item(item);
 417                     lctx.impl_items.insert(id, hir_item);
 418                 });
 419                 visit::walk_impl_item(self, item);
 420             }
 421         }
 422
 423         self.lower_node_id(CRATE_NODE_ID);
 424         debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
 425
 426         visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
 427         visit::walk_crate(&mut ItemLowerer { lctx: &mut self }, c);
 428
 429         let module = self.lower_mod(&c.module);
 430         let attrs = self.lower_attrs(&c.attrs);
 431         let body_ids = body_ids(&self.bodies);
 432
 433         self.resolver
 434             .definitions()
 435             .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
 436
 437         hir::Crate {
 438             module,
 439             attrs,
 440             span: c.span,
 441             exported_macros: hir::HirVec::from(self.exported_macros),
 442             items: self.items,
 443             trait_items: self.trait_items,
 444             impl_items: self.impl_items,
 445             bodies: self.bodies,
 446             body_ids,
 447             trait_impls: self.trait_impls,
 448             trait_auto_impl: self.trait_auto_impl,
 449         }
 450     }
 451
 452     fn allocate_hir_id_counter<T: Debug>(&mut self, owner: NodeId, debug: &T) {
 453         if self.item_local_id_counters.insert(owner, 0).is_some() {
 454             bug!(
 455                 "Tried to allocate item_local_id_counter for {:?} twice",
 456                 debug
 457             );
 458         }
 459         // Always allocate the first HirId for the owner itself
 460         self.lower_node_id_with_owner(owner, owner);
 461     }
 462
 463     fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> LoweredNodeId
 464     where
 465         F: FnOnce(&mut Self) -> hir::HirId,
 466     {
 467         if ast_node_id == DUMMY_NODE_ID {
 468             return LoweredNodeId {
 469                 node_id: DUMMY_NODE_ID,
 470                 hir_id: hir::DUMMY_HIR_ID,
 471             };
 472         }
 473
 474         let min_size = ast_node_id.as_usize() + 1;
 475
 476         if min_size > self.node_id_to_hir_id.len() {
 477             self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
 478         }
 479
 480         let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
 481
 482         if existing_hir_id == hir::DUMMY_HIR_ID {
 483             // Generate a new HirId
 484             let hir_id = alloc_hir_id(self);
 485             self.node_id_to_hir_id[ast_node_id] = hir_id;
 486             LoweredNodeId {
 487                 node_id: ast_node_id,
 488                 hir_id,
 489             }
 490         } else {
 491             LoweredNodeId {
 492                 node_id: ast_node_id,
 493                 hir_id: existing_hir_id,
 494             }
 495         }
 496     }
 497
 498     fn with_hir_id_owner<F, T>(&mut self, owner: NodeId, f: F) -> T
 499     where
 500         F: FnOnce(&mut Self) -> T,
 501     {
 502         let counter = self.item_local_id_counters
 503             .insert(owner, HIR_ID_COUNTER_LOCKED)
 504             .unwrap();
 505         let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
 506         self.current_hir_id_owner.push((def_index, counter));
 507         let ret = f(self);
 508         let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
 509
 510         debug_assert!(def_index == new_def_index);
 511         debug_assert!(new_counter >= counter);
 512
 513         let prev = self.item_local_id_counters
 514             .insert(owner, new_counter)
 515             .unwrap();
 516         debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
 517         ret
 518     }
 519
 520     /// This method allocates a new HirId for the given NodeId and stores it in
 521     /// the LoweringContext's NodeId => HirId map.
 522     /// Take care not to call this method if the resulting HirId is then not
 523     /// actually used in the HIR, as that would trigger an assertion in the
 524     /// HirIdValidator later on, which makes sure that all NodeIds got mapped
 525     /// properly. Calling the method twice with the same NodeId is fine though.
 526     fn lower_node_id(&mut self, ast_node_id: NodeId) -> LoweredNodeId {
 527         self.lower_node_id_generic(ast_node_id, |this| {
 528             let &mut (def_index, ref mut local_id_counter) =
 529                 this.current_hir_id_owner.last_mut().unwrap();
 530             let local_id = *local_id_counter;
 531             *local_id_counter += 1;
 532             hir::HirId {
 533                 owner: def_index,
 534                 local_id: hir::ItemLocalId(local_id),
 535             }
 536         })
 537     }
 538
 539     fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> LoweredNodeId {
 540         self.lower_node_id_generic(ast_node_id, |this| {
 541             let local_id_counter = this
 542                 .item_local_id_counters
 543                 .get_mut(&owner)
 544                 .expect("called lower_node_id_with_owner before allocate_hir_id_counter");
 545             let local_id = *local_id_counter;
 546
 547             // We want to be sure not to modify the counter in the map while it
 548             // is also on the stack. Otherwise we'll get lost updates when writing
 549             // back from the stack to the map.
 550             debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
 551
 552             *local_id_counter += 1;
 553             let def_index = this
 554                 .resolver
 555                 .definitions()
 556                 .opt_def_index(owner)
 557                 .expect("You forgot to call `create_def_with_parent` or are lowering node ids \
 558                          that do not belong to the current owner");
 559
 560             hir::HirId {
 561                 owner: def_index,
 562                 local_id: hir::ItemLocalId(local_id),
 563             }
 564         })
 565     }
 566
 567     fn record_body(&mut self, value: hir::Expr, decl: Option<&FnDecl>) -> hir::BodyId {
 568         let body = hir::Body {
 569             arguments: decl.map_or(hir_vec![], |decl| {
 570                 decl.inputs.iter().map(|x| self.lower_arg(x)).collect()
 571             }),
 572             is_generator: self.is_generator,
 573             value,
 574         };
 575         let id = body.id();
 576         self.bodies.insert(id, body);
 577         id
 578     }
 579
 580     fn next_id(&mut self) -> LoweredNodeId {
 581         self.lower_node_id(self.sess.next_node_id())
 582     }
 583
 584     fn expect_full_def(&mut self, id: NodeId) -> Def {
 585         self.resolver.get_resolution(id).map_or(Def::Err, |pr| {
 586             if pr.unresolved_segments() != 0 {
 587                 bug!("path not fully resolved: {:?}", pr);
 588             }
 589             pr.base_def()
 590         })
 591     }
 592
 593     fn expect_full_def_from_use(&mut self, id: NodeId) -> impl Iterator<Item=Def> {
 594         self.resolver.get_import(id).present_items().map(|pr| {
 595             if pr.unresolved_segments() != 0 {
 596                 bug!("path not fully resolved: {:?}", pr);
 597             }
 598             pr.base_def()
 599         })
 600     }
 601
 602     fn diagnostic(&self) -> &errors::Handler {
 603         self.sess.diagnostic()
 604     }
 605
 606     fn str_to_ident(&self, s: &'static str) -> Name {
 607         Symbol::gensym(s)
 608     }
 609
 610     fn allow_internal_unstable(&self, reason: CompilerDesugaringKind, span: Span) -> Span {
 611         let mark = Mark::fresh(Mark::root());
 612         mark.set_expn_info(codemap::ExpnInfo {
 613             call_site: span,
 614             callee: codemap::NameAndSpan {
 615                 format: codemap::CompilerDesugaring(reason),
 616                 span: Some(span),
 617                 allow_internal_unstable: true,
 618                 allow_internal_unsafe: false,
 619                 edition: codemap::hygiene::default_edition(),
 620             },
 621         });
 622         span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
 623     }
 624
 625     fn with_anonymous_lifetime_mode<R>(
 626         &mut self,
 627         anonymous_lifetime_mode: AnonymousLifetimeMode,
 628         op: impl FnOnce(&mut Self) -> R,
 629     ) -> R {
 630         let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
 631         self.anonymous_lifetime_mode = anonymous_lifetime_mode;
 632         let result = op(self);
 633         self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
 634         result
 635     }
 636
 637     /// Creates a new hir::GenericParam for every new lifetime and
 638     /// type parameter encountered while evaluating `f`. Definitions
 639     /// are created with the parent provided. If no `parent_id` is
 640     /// provided, no definitions will be returned.
 641     ///
 642     /// Presuming that in-band lifetimes are enabled, then
 643     /// `self.anonymous_lifetime_mode` will be updated to match the
 644     /// argument while `f` is running (and restored afterwards).
 645     fn collect_in_band_defs<T, F>(
 646         &mut self,
 647         parent_id: DefId,
 648         anonymous_lifetime_mode: AnonymousLifetimeMode,
 649         f: F,
 650     ) -> (Vec<hir::GenericParam>, T)
 651     where
 652         F: FnOnce(&mut LoweringContext) -> T,
 653     {
 654         assert!(!self.is_collecting_in_band_lifetimes);
 655         assert!(self.lifetimes_to_define.is_empty());
 656         let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
 657
 658         self.is_collecting_in_band_lifetimes = self.sess.features_untracked().in_band_lifetimes;
 659         if self.is_collecting_in_band_lifetimes {
 660             self.anonymous_lifetime_mode = anonymous_lifetime_mode;
 661         }
 662
 663         assert!(self.in_band_ty_params.is_empty());
 664         let res = f(self);
 665
 666         self.is_collecting_in_band_lifetimes = false;
 667         self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
 668
 669         let in_band_ty_params = self.in_band_ty_params.split_off(0);
 670         let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
 671
 672         let params = lifetimes_to_define
 673             .into_iter()
 674             .map(|(span, hir_name)| {
 675                 let def_node_id = self.next_id().node_id;
 676
 677                 // Get the name we'll use to make the def-path. Note
 678                 // that collisions are ok here and this shouldn't
 679                 // really show up for end-user.
 680                 let str_name = match hir_name {
 681                     ParamName::Plain(name) => name.as_str(),
 682                     ParamName::Fresh(_) => keywords::UnderscoreLifetime.name().as_str(),
 683                 };
 684
 685                 // Add a definition for the in-band lifetime def
 686                 self.resolver.definitions().create_def_with_parent(
 687                     parent_id.index,
 688                     def_node_id,
 689                     DefPathData::LifetimeParam(str_name.as_interned_str()),
 690                     DefIndexAddressSpace::High,
 691                     Mark::root(),
 692                     span,
 693                 );
 694
 695                 hir::GenericParam {
 696                     id: def_node_id,
 697                     name: hir_name,
 698                     attrs: hir_vec![],
 699                     bounds: hir_vec![],
 700                     span,
 701                     pure_wrt_drop: false,
 702                     kind: hir::GenericParamKind::Lifetime { in_band: true }
 703                 }
 704             })
 705             .chain(in_band_ty_params.into_iter())
 706             .collect();
 707
 708         (params, res)
 709     }
 710
 711     /// When there is a reference to some lifetime `'a`, and in-band
 712     /// lifetimes are enabled, then we want to push that lifetime into
 713     /// the vector of names to define later. In that case, it will get
 714     /// added to the appropriate generics.
 715     fn maybe_collect_in_band_lifetime(&mut self, span: Span, name: Name) {
 716         if !self.is_collecting_in_band_lifetimes {
 717             return;
 718         }
 719
 720         if self.in_scope_lifetimes.contains(&name) {
 721             return;
 722         }
 723
 724         let hir_name = ParamName::Plain(name);
 725
 726         if self.lifetimes_to_define.iter().any(|(_, lt_name)| *lt_name == hir_name) {
 727             return;
 728         }
 729
 730         self.lifetimes_to_define.push((span, hir_name));
 731     }
 732
 733     /// When we have either an elided or `'_` lifetime in an impl
 734     /// header, we convert it to
 735     fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> ParamName {
 736         assert!(self.is_collecting_in_band_lifetimes);
 737         let index = self.lifetimes_to_define.len();
 738         let hir_name = ParamName::Fresh(index);
 739         self.lifetimes_to_define.push((span, hir_name));
 740         hir_name
 741     }
 742
 743     // Evaluates `f` with the lifetimes in `params` in-scope.
 744     // This is used to track which lifetimes have already been defined, and
 745     // which are new in-band lifetimes that need to have a definition created
 746     // for them.
 747     fn with_in_scope_lifetime_defs<T, F>(&mut self, params: &Vec<GenericParam>, f: F) -> T
 748     where
 749         F: FnOnce(&mut LoweringContext) -> T,
 750     {
 751         let old_len = self.in_scope_lifetimes.len();
 752         let lt_def_names = params.iter().filter_map(|param| match param.kind {
 753             GenericParamKind::Lifetime { .. } => Some(param.ident.name),
 754             _ => None,
 755         });
 756         self.in_scope_lifetimes.extend(lt_def_names);
 757
 758         let res = f(self);
 759
 760         self.in_scope_lifetimes.truncate(old_len);
 761         res
 762     }
 763
 764     // Same as the method above, but accepts `hir::GenericParam`s
 765     // instead of `ast::GenericParam`s.
 766     // This should only be used with generics that have already had their
 767     // in-band lifetimes added. In practice, this means that this function is
 768     // only used when lowering a child item of a trait or impl.
 769     fn with_parent_impl_lifetime_defs<T, F>(&mut self,
 770         params: &HirVec<hir::GenericParam>,
 771         f: F
 772     ) -> T where
 773         F: FnOnce(&mut LoweringContext) -> T,
 774     {
 775         let old_len = self.in_scope_lifetimes.len();
 776         let lt_def_names = params.iter().filter_map(|param| match param.kind {
 777             hir::GenericParamKind::Lifetime { .. } => Some(param.name.name()),
 778             _ => None,
 779         });
 780         self.in_scope_lifetimes.extend(lt_def_names);
 781
 782         let res = f(self);
 783
 784         self.in_scope_lifetimes.truncate(old_len);
 785         res
 786     }
 787
 788     /// Appends in-band lifetime defs and argument-position `impl
 789     /// Trait` defs to the existing set of generics.
 790     ///
 791     /// Presuming that in-band lifetimes are enabled, then
 792     /// `self.anonymous_lifetime_mode` will be updated to match the
 793     /// argument while `f` is running (and restored afterwards).
 794     fn add_in_band_defs<F, T>(
 795         &mut self,
 796         generics: &Generics,
 797         parent_id: DefId,
 798         anonymous_lifetime_mode: AnonymousLifetimeMode,
 799         f: F,
 800     ) -> (hir::Generics, T)
 801     where
 802         F: FnOnce(&mut LoweringContext) -> T,
 803     {
 804         let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
 805             &generics.params,
 806             |this| {
 807                 let itctx = ImplTraitContext::Universal(parent_id);
 808                 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
 809                     (this.lower_generics(generics, itctx), f(this))
 810                 })
 811             },
 812         );
 813
 814         lowered_generics.params = lowered_generics
 815             .params
 816             .iter()
 817             .cloned()
 818             .chain(in_band_defs)
 819             .collect();
 820
 821         (lowered_generics, res)
 822     }
 823
 824     fn with_catch_scope<T, F>(&mut self, catch_id: NodeId, f: F) -> T
 825     where
 826         F: FnOnce(&mut LoweringContext) -> T,
 827     {
 828         let len = self.catch_scopes.len();
 829         self.catch_scopes.push(catch_id);
 830
 831         let result = f(self);
 832         assert_eq!(
 833             len + 1,
 834             self.catch_scopes.len(),
 835             "catch scopes should be added and removed in stack order"
 836         );
 837
 838         self.catch_scopes.pop().unwrap();
 839
 840         result
 841     }
 842
 843     fn lower_body<F>(&mut self, decl: Option<&FnDecl>, f: F) -> hir::BodyId
 844     where
 845         F: FnOnce(&mut LoweringContext) -> hir::Expr,
 846     {
 847         let prev = mem::replace(&mut self.is_generator, false);
 848         let result = f(self);
 849         let r = self.record_body(result, decl);
 850         self.is_generator = prev;
 851         return r;
 852     }
 853
 854     fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
 855     where
 856         F: FnOnce(&mut LoweringContext) -> T,
 857     {
 858         // We're no longer in the base loop's condition; we're in another loop.
 859         let was_in_loop_condition = self.is_in_loop_condition;
 860         self.is_in_loop_condition = false;
 861
 862         let len = self.loop_scopes.len();
 863         self.loop_scopes.push(loop_id);
 864
 865         let result = f(self);
 866         assert_eq!(
 867             len + 1,
 868             self.loop_scopes.len(),
 869             "Loop scopes should be added and removed in stack order"
 870         );
 871
 872         self.loop_scopes.pop().unwrap();
 873
 874         self.is_in_loop_condition = was_in_loop_condition;
 875
 876         result
 877     }
 878
 879     fn with_loop_condition_scope<T, F>(&mut self, f: F) -> T
 880     where
 881         F: FnOnce(&mut LoweringContext) -> T,
 882     {
 883         let was_in_loop_condition = self.is_in_loop_condition;
 884         self.is_in_loop_condition = true;
 885
 886         let result = f(self);
 887
 888         self.is_in_loop_condition = was_in_loop_condition;
 889
 890         result
 891     }
 892
 893     fn with_new_scopes<T, F>(&mut self, f: F) -> T
 894     where
 895         F: FnOnce(&mut LoweringContext) -> T,
 896     {
 897         let was_in_loop_condition = self.is_in_loop_condition;
 898         self.is_in_loop_condition = false;
 899
 900         let catch_scopes = mem::replace(&mut self.catch_scopes, Vec::new());
 901         let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
 902         let result = f(self);
 903         self.catch_scopes = catch_scopes;
 904         self.loop_scopes = loop_scopes;
 905
 906         self.is_in_loop_condition = was_in_loop_condition;
 907
 908         result
 909     }
 910
 911     fn def_key(&mut self, id: DefId) -> DefKey {
 912         if id.is_local() {
 913             self.resolver.definitions().def_key(id.index)
 914         } else {
 915             self.cstore.def_key(id)
 916         }
 917     }
 918
 919     fn lower_ident(&mut self, ident: Ident) -> Name {
 920         let ident = ident.modern();
 921         if ident.span.ctxt() == SyntaxContext::empty() {
 922             return ident.name;
 923         }
 924         *self.name_map
 925             .entry(ident)
 926             .or_insert_with(|| Symbol::from_ident(ident))
 927     }
 928
 929     fn lower_label(&mut self, label: Option<Label>) -> Option<hir::Label> {
 930         label.map(|label| hir::Label {
 931             name: label.ident.name,
 932             span: label.ident.span,
 933         })
 934     }
 935
 936     fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
 937         match destination {
 938             Some((id, label)) => {
 939                 let target_id = if let Def::Label(loop_id) = self.expect_full_def(id) {
 940                     Ok(self.lower_node_id(loop_id).node_id)
 941                 } else {
 942                     Err(hir::LoopIdError::UnresolvedLabel)
 943                 };
 944                 hir::Destination {
 945                     label: self.lower_label(Some(label)),
 946                     target_id,
 947                 }
 948             }
 949             None => {
 950                 let target_id = self.loop_scopes
 951                     .last()
 952                     .map(|innermost_loop_id| *innermost_loop_id)
 953                     .map(|id| Ok(self.lower_node_id(id).node_id))
 954                     .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope))
 955                     .into();
 956
 957                 hir::Destination {
 958                     label: None,
 959                     target_id,
 960                 }
 961             }
 962         }
 963     }
 964
 965     fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
 966         attrs
 967             .iter()
 968             .map(|a| self.lower_attr(a))
 969             .collect::<Vec<_>>()
 970             .into()
 971     }
 972
 973     fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
 974         Attribute {
 975             id: attr.id,
 976             style: attr.style,
 977             path: attr.path.clone(),
 978             tokens: self.lower_token_stream(attr.tokens.clone()),
 979             is_sugared_doc: attr.is_sugared_doc,
 980             span: attr.span,
 981         }
 982     }
 983
 984     fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
 985         tokens
 986             .into_trees()
 987             .flat_map(|tree| self.lower_token_tree(tree).into_trees())
 988             .collect()
 989     }
 990
 991     fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
 992         match tree {
 993             TokenTree::Token(span, token) => self.lower_token(token, span),
 994             TokenTree::Delimited(span, delimited) => TokenTree::Delimited(
 995                 span,
 996                 Delimited {
 997                     delim: delimited.delim,
 998                     tts: self.lower_token_stream(delimited.tts.into()).into(),
 999                 },
1000             ).into(),
1001         }
1002     }
1003
1004     fn lower_token(&mut self, token: Token, span: Span) -> TokenStream {
1005         match token {
1006             Token::Interpolated(_) => {}
1007             other => return TokenTree::Token(span, other).into(),
1008         }
1009
1010         let tts = token.interpolated_to_tokenstream(&self.sess.parse_sess, span);
1011         self.lower_token_stream(tts)
1012     }
1013
1014     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm {
1015         hir::Arm {
1016             attrs: self.lower_attrs(&arm.attrs),
1017             pats: arm.pats.iter().map(|x| self.lower_pat(x)).collect(),
1018             guard: arm.guard.as_ref().map(|ref x| P(self.lower_expr(x))),
1019             body: P(self.lower_expr(&arm.body)),
1020         }
1021     }
1022
1023     fn lower_ty_binding(&mut self, b: &TypeBinding, itctx: ImplTraitContext) -> hir::TypeBinding {
1024         hir::TypeBinding {
1025             id: self.lower_node_id(b.id).node_id,
1026             name: self.lower_ident(b.ident),
1027             ty: self.lower_ty(&b.ty, itctx),
1028             span: b.span,
1029         }
1030     }
1031
1032     fn lower_generic_arg(&mut self,
1033                         arg: &ast::GenericArg,
1034                         itctx: ImplTraitContext)
1035                         -> hir::GenericArg {
1036         match arg {
1037             ast::GenericArg::Lifetime(lt) => GenericArg::Lifetime(self.lower_lifetime(&lt)),
1038             ast::GenericArg::Type(ty) => GenericArg::Type(self.lower_ty(&ty, itctx)),
1039         }
1040     }
1041
1042     fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext) -> P<hir::Ty> {
1043         let kind = match t.node {
1044             TyKind::Infer => hir::TyInfer,
1045             TyKind::Err => hir::TyErr,
1046             TyKind::Slice(ref ty) => hir::TySlice(self.lower_ty(ty, itctx)),
1047             TyKind::Ptr(ref mt) => hir::TyPtr(self.lower_mt(mt, itctx)),
1048             TyKind::Rptr(ref region, ref mt) => {
1049                 let span = t.span.shrink_to_lo();
1050                 let lifetime = match *region {
1051                     Some(ref lt) => self.lower_lifetime(lt),
1052                     None => self.elided_ref_lifetime(span),
1053                 };
1054                 hir::TyRptr(lifetime, self.lower_mt(mt, itctx))
1055             }
1056             TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1057                 &f.generic_params,
1058                 |this| {
1059                     this.with_anonymous_lifetime_mode(
1060                         AnonymousLifetimeMode::PassThrough,
1061                         |this| {
1062                             hir::TyBareFn(P(hir::BareFnTy {
1063                                 generic_params: this.lower_generic_params(
1064                                     &f.generic_params,
1065                                     &NodeMap(),
1066                                     ImplTraitContext::Disallowed,
1067                                 ),
1068                                 unsafety: this.lower_unsafety(f.unsafety),
1069                                 abi: f.abi,
1070                                 decl: this.lower_fn_decl(&f.decl, None, false),
1071                                 arg_names: this.lower_fn_args_to_names(&f.decl),
1072                             }))
1073                         },
1074                     )
1075                 },
1076             ),
1077             TyKind::Never => hir::TyNever,
1078             TyKind::Tup(ref tys) => {
1079                 hir::TyTup(tys.iter().map(|ty| self.lower_ty(ty, itctx)).collect())
1080             }
1081             TyKind::Paren(ref ty) => {
1082                 return self.lower_ty(ty, itctx);
1083             }
1084             TyKind::Path(ref qself, ref path) => {
1085                 let id = self.lower_node_id(t.id);
1086                 let qpath = self.lower_qpath(t.id, qself, path, ParamMode::Explicit, itctx);
1087                 let ty = self.ty_path(id, t.span, qpath);
1088                 if let hir::TyTraitObject(..) = ty.node {
1089                     self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1090                 }
1091                 return ty;
1092             }
1093             TyKind::ImplicitSelf => hir::TyPath(hir::QPath::Resolved(
1094                 None,
1095                 P(hir::Path {
1096                     def: self.expect_full_def(t.id),
1097                     segments: hir_vec![hir::PathSegment::from_name(keywords::SelfType.name())],
1098                     span: t.span,
1099                 }),
1100             )),
1101             TyKind::Array(ref ty, ref length) => {
1102                 hir::TyArray(self.lower_ty(ty, itctx), self.lower_anon_const(length))
1103             }
1104             TyKind::Typeof(ref expr) => {
1105                 hir::TyTypeof(self.lower_anon_const(expr))
1106             }
1107             TyKind::TraitObject(ref bounds, kind) => {
1108                 let mut lifetime_bound = None;
1109                 let bounds = bounds
1110                     .iter()
1111                     .filter_map(|bound| match *bound {
1112                         Trait(ref ty, TraitBoundModifier::None) => {
1113                             Some(self.lower_poly_trait_ref(ty, itctx))
1114                         }
1115                         Trait(_, TraitBoundModifier::Maybe) => None,
1116                         Outlives(ref lifetime) => {
1117                             if lifetime_bound.is_none() {
1118                                 lifetime_bound = Some(self.lower_lifetime(lifetime));
1119                             }
1120                             None
1121                         }
1122                     })
1123                     .collect();
1124                 let lifetime_bound =
1125                     lifetime_bound.unwrap_or_else(|| self.elided_dyn_bound(t.span));
1126                 if kind != TraitObjectSyntax::Dyn {
1127                     self.maybe_lint_bare_trait(t.span, t.id, false);
1128                 }
1129                 hir::TyTraitObject(bounds, lifetime_bound)
1130             }
1131             TyKind::ImplTrait(ref bounds) => {
1132                 let span = t.span;
1133                 match itctx {
1134                     ImplTraitContext::Existential(fn_def_id) => {
1135
1136                         // We need to manually repeat the code of `next_id` because the lowering
1137                         // needs to happen while the owner_id is pointing to the item itself,
1138                         // because items are their own owners
1139                         let exist_ty_node_id = self.sess.next_node_id();
1140
1141                         // Make sure we know that some funky desugaring has been going on here.
1142                         // This is a first: there is code in other places like for loop
1143                         // desugaring that explicitly states that we don't want to track that.
1144                         // Not tracking it makes lints in rustc and clippy very fragile as
1145                         // frequently opened issues show.
1146                         let exist_ty_span = self.allow_internal_unstable(
1147                             CompilerDesugaringKind::ExistentialReturnType,
1148                             t.span,
1149                         );
1150
1151                         // Pull a new definition from the ether
1152                         let exist_ty_def_index = self
1153                             .resolver
1154                             .definitions()
1155                             .create_def_with_parent(
1156                             fn_def_id.index,
1157                             exist_ty_node_id,
1158                             DefPathData::ExistentialImplTrait,
1159                             DefIndexAddressSpace::High,
1160                             Mark::root(),
1161                             exist_ty_span,
1162                         );
1163
1164                         // the `t` is just for printing debug messages
1165                         self.allocate_hir_id_counter(exist_ty_node_id, t);
1166
1167                         let hir_bounds = self.with_hir_id_owner(exist_ty_node_id, |lctx| {
1168                             lctx.lower_bounds(bounds, itctx)
1169                         });
1170
1171                         let (lifetimes, lifetime_defs) = self.lifetimes_from_impl_trait_bounds(
1172                             exist_ty_node_id,
1173                             exist_ty_def_index,
1174                             &hir_bounds,
1175                         );
1176
1177                         self.with_hir_id_owner(exist_ty_node_id, |lctx| {
1178                             let exist_ty_item_kind = hir::ItemExistential(hir::ExistTy {
1179                                 generics: hir::Generics {
1180                                     params: lifetime_defs,
1181                                     where_clause: hir::WhereClause {
1182                                         id: lctx.next_id().node_id,
1183                                         predicates: Vec::new().into(),
1184                                     },
1185                                     span,
1186                                 },
1187                                 bounds: hir_bounds,
1188                                 impl_trait_fn: Some(fn_def_id),
1189                             });
1190                             let exist_ty_id = lctx.lower_node_id(exist_ty_node_id);
1191                             // Generate an `existential type Foo: Trait;` declaration
1192                             trace!("creating existential type with id {:#?}", exist_ty_id);
1193                             // Set the name to `impl Bound1 + Bound2`
1194                             let exist_ty_name = Symbol::intern(&pprust::ty_to_string(t));
1195
1196                             trace!("exist ty def index: {:#?}", exist_ty_def_index);
1197                             let exist_ty_item = hir::Item {
1198                                 id: exist_ty_id.node_id,
1199                                 hir_id: exist_ty_id.hir_id,
1200                                 name: exist_ty_name,
1201                                 attrs: Default::default(),
1202                                 node: exist_ty_item_kind,
1203                                 vis: hir::Visibility::Inherited,
1204                                 span: exist_ty_span,
1205                             };
1206
1207                             // Insert the item into the global list. This usually happens
1208                             // automatically for all AST items. But this existential type item
1209                             // does not actually exist in the AST.
1210                             lctx.items.insert(exist_ty_id.node_id, exist_ty_item);
1211
1212                             // `impl Trait` now just becomes `Foo<'a, 'b, ..>`
1213                             hir::TyImplTraitExistential(
1214                                 hir::ItemId {
1215                                     id: exist_ty_id.node_id
1216                                 },
1217                                 DefId::local(exist_ty_def_index),
1218                                 lifetimes,
1219                             )
1220                         })
1221                     }
1222                     ImplTraitContext::Universal(def_id) => {
1223                         let def_node_id = self.next_id().node_id;
1224
1225                         // Add a definition for the in-band TyParam
1226                         let def_index = self.resolver.definitions().create_def_with_parent(
1227                             def_id.index,
1228                             def_node_id,
1229                             DefPathData::UniversalImplTrait,
1230                             DefIndexAddressSpace::High,
1231                             Mark::root(),
1232                             span,
1233                         );
1234
1235                         let hir_bounds = self.lower_param_bounds(bounds, itctx);
1236                         // Set the name to `impl Bound1 + Bound2`
1237                         let name = Symbol::intern(&pprust::ty_to_string(t));
1238                         self.in_band_ty_params.push(hir::GenericParam {
1239                             id: def_node_id,
1240                             name: ParamName::Plain(name),
1241                             span,
1242                             pure_wrt_drop: false,
1243                             attrs: hir_vec![],
1244                             bounds: hir_bounds,
1245                             kind: hir::GenericParamKind::Type {
1246                                 default: None,
1247                                 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1248                             }
1249                         });
1250
1251                         hir::TyPath(hir::QPath::Resolved(
1252                             None,
1253                             P(hir::Path {
1254                                 span,
1255                                 def: Def::TyParam(DefId::local(def_index)),
1256                                 segments: hir_vec![hir::PathSegment::from_name(name)],
1257                             }),
1258                         ))
1259                     }
1260                     ImplTraitContext::Disallowed => {
1261                         span_err!(
1262                             self.sess,
1263                             t.span,
1264                             E0562,
1265                             "`impl Trait` not allowed outside of function \
1266                              and inherent method return types"
1267                         );
1268                         hir::TyErr
1269                     }
1270                 }
1271             }
1272             TyKind::Mac(_) => panic!("TyMac should have been expanded by now."),
1273         };
1274
1275         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(t.id);
1276         P(hir::Ty {
1277             id: node_id,
1278             node: kind,
1279             span: t.span,
1280             hir_id,
1281         })
1282     }
1283
1284     fn lifetimes_from_impl_trait_bounds(
1285         &mut self,
1286         exist_ty_id: NodeId,
1287         parent_index: DefIndex,
1288         bounds: &hir::GenericBounds,
1289     ) -> (HirVec<hir::Lifetime>, HirVec<hir::GenericParam>) {
1290         // This visitor walks over impl trait bounds and creates defs for all lifetimes which
1291         // appear in the bounds, excluding lifetimes that are created within the bounds.
1292         // e.g. 'a, 'b, but not 'c in `impl for<'c> SomeTrait<'a, 'b, 'c>`
1293         struct ImplTraitLifetimeCollector<'r, 'a: 'r> {
1294             context: &'r mut LoweringContext<'a>,
1295             parent: DefIndex,
1296             exist_ty_id: NodeId,
1297             collect_elided_lifetimes: bool,
1298             currently_bound_lifetimes: Vec<hir::LifetimeName>,
1299             already_defined_lifetimes: HashSet<hir::LifetimeName>,
1300             output_lifetimes: Vec<hir::Lifetime>,
1301             output_lifetime_params: Vec<hir::GenericParam>,
1302         }
1303
1304         impl<'r, 'a: 'r, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1305             fn nested_visit_map<'this>(
1306                 &'this mut self,
1307             ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1308                 hir::intravisit::NestedVisitorMap::None
1309             }
1310
1311             fn visit_generic_args(&mut self, span: Span, parameters: &'v hir::GenericArgs) {
1312                 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1313                 if parameters.parenthesized {
1314                     let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1315                     self.collect_elided_lifetimes = false;
1316                     hir::intravisit::walk_generic_args(self, span, parameters);
1317                     self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1318                 } else {
1319                     hir::intravisit::walk_generic_args(self, span, parameters);
1320                 }
1321             }
1322
1323             fn visit_ty(&mut self, t: &'v hir::Ty) {
1324                 // Don't collect elided lifetimes used inside of `fn()` syntax
1325                 if let &hir::Ty_::TyBareFn(_) = &t.node {
1326                     let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1327                     self.collect_elided_lifetimes = false;
1328
1329                     // Record the "stack height" of `for<'a>` lifetime bindings
1330                     // to be able to later fully undo their introduction.
1331                     let old_len = self.currently_bound_lifetimes.len();
1332                     hir::intravisit::walk_ty(self, t);
1333                     self.currently_bound_lifetimes.truncate(old_len);
1334
1335                     self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1336                 } else {
1337                     hir::intravisit::walk_ty(self, t);
1338                 }
1339             }
1340
1341             fn visit_poly_trait_ref(
1342                 &mut self,
1343                 trait_ref: &'v hir::PolyTraitRef,
1344                 modifier: hir::TraitBoundModifier,
1345             ) {
1346                 // Record the "stack height" of `for<'a>` lifetime bindings
1347                 // to be able to later fully undo their introduction.
1348                 let old_len = self.currently_bound_lifetimes.len();
1349                 hir::intravisit::walk_poly_trait_ref(self, trait_ref, modifier);
1350                 self.currently_bound_lifetimes.truncate(old_len);
1351             }
1352
1353             fn visit_generic_param(&mut self, param: &'v hir::GenericParam) {
1354                 // Record the introduction of 'a in `for<'a> ...`
1355                 if let hir::GenericParamKind::Lifetime { .. } = param.kind {
1356                     // Introduce lifetimes one at a time so that we can handle
1357                     // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`
1358                     let lt_name = hir::LifetimeName::Param(param.name);
1359                     self.currently_bound_lifetimes.push(lt_name);
1360                 }
1361
1362                 hir::intravisit::walk_generic_param(self, param);
1363             }
1364
1365             fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1366                 let name = match lifetime.name {
1367                     hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1368                         if self.collect_elided_lifetimes {
1369                             // Use `'_` for both implicit and underscore lifetimes in
1370                             // `abstract type Foo<'_>: SomeTrait<'_>;`
1371                             hir::LifetimeName::Underscore
1372                         } else {
1373                             return;
1374                         }
1375                     }
1376                     hir::LifetimeName::Param(_) => lifetime.name,
1377                     hir::LifetimeName::Static => return,
1378                 };
1379
1380                 if !self.currently_bound_lifetimes.contains(&name)
1381                     && !self.already_defined_lifetimes.contains(&name) {
1382                     self.already_defined_lifetimes.insert(name);
1383
1384                     self.output_lifetimes.push(hir::Lifetime {
1385                         id: self.context.next_id().node_id,
1386                         span: lifetime.span,
1387                         name,
1388                     });
1389
1390                     // We need to manually create the ids here, because the
1391                     // definitions will go into the explicit `existential type`
1392                     // declaration and thus need to have their owner set to that item
1393                     let def_node_id = self.context.sess.next_node_id();
1394                     let _ = self.context.lower_node_id_with_owner(def_node_id, self.exist_ty_id);
1395                     self.context.resolver.definitions().create_def_with_parent(
1396                         self.parent,
1397                         def_node_id,
1398                         DefPathData::LifetimeParam(name.name().as_interned_str()),
1399                         DefIndexAddressSpace::High,
1400                         Mark::root(),
1401                         lifetime.span,
1402                     );
1403
1404                     let name = match name {
1405                         hir::LifetimeName::Underscore => {
1406                             hir::ParamName::Plain(keywords::UnderscoreLifetime.name())
1407                         }
1408                         hir::LifetimeName::Param(param_name) => param_name,
1409                         _ => bug!("expected LifetimeName::Param or ParamName::Plain"),
1410                     };
1411
1412                     self.output_lifetime_params.push(hir::GenericParam {
1413                         id: def_node_id,
1414                         name,
1415                         span: lifetime.span,
1416                         pure_wrt_drop: false,
1417                         attrs: hir_vec![],
1418                         bounds: hir_vec![],
1419                         kind: hir::GenericParamKind::Lifetime {
1420                             in_band: false,
1421                         }
1422                     });
1423                 }
1424             }
1425         }
1426
1427         let mut lifetime_collector = ImplTraitLifetimeCollector {
1428             context: self,
1429             parent: parent_index,
1430             exist_ty_id,
1431             collect_elided_lifetimes: true,
1432             currently_bound_lifetimes: Vec::new(),
1433             already_defined_lifetimes: HashSet::new(),
1434             output_lifetimes: Vec::new(),
1435             output_lifetime_params: Vec::new(),
1436         };
1437
1438         for bound in bounds {
1439             hir::intravisit::walk_param_bound(&mut lifetime_collector, &bound);
1440         }
1441
1442         (
1443             lifetime_collector.output_lifetimes.into(),
1444             lifetime_collector.output_lifetime_params.into(),
1445         )
1446     }
1447
1448     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
1449         hir::ForeignMod {
1450             abi: fm.abi,
1451             items: fm.items
1452                 .iter()
1453                 .map(|x| self.lower_foreign_item(x))
1454                 .collect(),
1455         }
1456     }
1457
1458     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
1459         P(hir::GlobalAsm {
1460             asm: ga.asm,
1461             ctxt: ga.ctxt,
1462         })
1463     }
1464
1465     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
1466         Spanned {
1467             node: hir::Variant_ {
1468                 name: v.node.ident.name,
1469                 attrs: self.lower_attrs(&v.node.attrs),
1470                 data: self.lower_variant_data(&v.node.data),
1471                 disr_expr: v.node.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
1472             },
1473             span: v.span,
1474         }
1475     }
1476
1477     fn lower_qpath(
1478         &mut self,
1479         id: NodeId,
1480         qself: &Option<QSelf>,
1481         p: &Path,
1482         param_mode: ParamMode,
1483         itctx: ImplTraitContext,
1484     ) -> hir::QPath {
1485         let qself_position = qself.as_ref().map(|q| q.position);
1486         let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx));
1487
1488         let resolution = self.resolver
1489             .get_resolution(id)
1490             .unwrap_or(PathResolution::new(Def::Err));
1491
1492         let proj_start = p.segments.len() - resolution.unresolved_segments();
1493         let path = P(hir::Path {
1494             def: resolution.base_def(),
1495             segments: p.segments[..proj_start]
1496                 .iter()
1497                 .enumerate()
1498                 .map(|(i, segment)| {
1499                     let param_mode = match (qself_position, param_mode) {
1500                         (Some(j), ParamMode::Optional) if i < j => {
1501                             // This segment is part of the trait path in a
1502                             // qualified path - one of `a`, `b` or `Trait`
1503                             // in `<X as a::b::Trait>::T::U::method`.
1504                             ParamMode::Explicit
1505                         }
1506                         _ => param_mode,
1507                     };
1508
1509                     // Figure out if this is a type/trait segment,
1510                     // which may need lifetime elision performed.
1511                     let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1512                         krate: def_id.krate,
1513                         index: this.def_key(def_id).parent.expect("missing parent"),
1514                     };
1515                     let type_def_id = match resolution.base_def() {
1516                         Def::AssociatedTy(def_id) if i + 2 == proj_start => {
1517                             Some(parent_def_id(self, def_id))
1518                         }
1519                         Def::Variant(def_id) if i + 1 == proj_start => {
1520                             Some(parent_def_id(self, def_id))
1521                         }
1522                         Def::Struct(def_id)
1523                         | Def::Union(def_id)
1524                         | Def::Enum(def_id)
1525                         | Def::TyAlias(def_id)
1526                         | Def::Trait(def_id) if i + 1 == proj_start =>
1527                         {
1528                             Some(def_id)
1529                         }
1530                         _ => None,
1531                     };
1532                     let parenthesized_generic_args = match resolution.base_def() {
1533                         // `a::b::Trait(Args)`
1534                         Def::Trait(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Ok,
1535                         // `a::b::Trait(Args)::TraitItem`
1536                         Def::Method(..) | Def::AssociatedConst(..) | Def::AssociatedTy(..)
1537                             if i + 2 == proj_start =>
1538                         {
1539                             ParenthesizedGenericArgs::Ok
1540                         }
1541                         // Avoid duplicated errors
1542                         Def::Err => ParenthesizedGenericArgs::Ok,
1543                         // An error
1544                         Def::Struct(..)
1545                         | Def::Enum(..)
1546                         | Def::Union(..)
1547                         | Def::TyAlias(..)
1548                         | Def::Variant(..) if i + 1 == proj_start =>
1549                         {
1550                             ParenthesizedGenericArgs::Err
1551                         }
1552                         // A warning for now, for compatibility reasons
1553                         _ => ParenthesizedGenericArgs::Warn,
1554                     };
1555
1556                     let num_lifetimes = type_def_id.map_or(0, |def_id| {
1557                         if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1558                             return n;
1559                         }
1560                         assert!(!def_id.is_local());
1561                         let item_generics =
1562                             self.cstore.item_generics_cloned_untracked(def_id, self.sess);
1563                         let n = item_generics.own_counts().lifetimes;
1564                         self.type_def_lifetime_params.insert(def_id, n);
1565                         n
1566                     });
1567                     self.lower_path_segment(
1568                         p.span,
1569                         segment,
1570                         param_mode,
1571                         num_lifetimes,
1572                         parenthesized_generic_args,
1573                         itctx,
1574                     )
1575                 })
1576                 .collect(),
1577             span: p.span,
1578         });
1579
1580         // Simple case, either no projections, or only fully-qualified.
1581         // E.g. `std::mem::size_of` or `<I as Iterator>::Item`.
1582         if resolution.unresolved_segments() == 0 {
1583             return hir::QPath::Resolved(qself, path);
1584         }
1585
1586         // Create the innermost type that we're projecting from.
1587         let mut ty = if path.segments.is_empty() {
1588             // If the base path is empty that means there exists a
1589             // syntactical `Self`, e.g. `&i32` in `<&i32>::clone`.
1590             qself.expect("missing QSelf for <T>::...")
1591         } else {
1592             // Otherwise, the base path is an implicit `Self` type path,
1593             // e.g. `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1594             // `<I as Iterator>::Item::default`.
1595             let new_id = self.next_id();
1596             self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path))
1597         };
1598
1599         // Anything after the base path are associated "extensions",
1600         // out of which all but the last one are associated types,
1601         // e.g. for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1602         // * base path is `std::vec::Vec<T>`
1603         // * "extensions" are `IntoIter`, `Item` and `clone`
1604         // * type nodes are:
1605         //   1. `std::vec::Vec<T>` (created above)
1606         //   2. `<std::vec::Vec<T>>::IntoIter`
1607         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1608         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1609         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1610             let segment = P(self.lower_path_segment(
1611                 p.span,
1612                 segment,
1613                 param_mode,
1614                 0,
1615                 ParenthesizedGenericArgs::Warn,
1616                 itctx,
1617             ));
1618             let qpath = hir::QPath::TypeRelative(ty, segment);
1619
1620             // It's finished, return the extension of the right node type.
1621             if i == p.segments.len() - 1 {
1622                 return qpath;
1623             }
1624
1625             // Wrap the associated extension in another type node.
1626             let new_id = self.next_id();
1627             ty = self.ty_path(new_id, p.span, qpath);
1628         }
1629
1630         // Should've returned in the for loop above.
1631         span_bug!(
1632             p.span,
1633             "lower_qpath: no final extension segment in {}..{}",
1634             proj_start,
1635             p.segments.len()
1636         )
1637     }
1638
1639     fn lower_path_extra(
1640         &mut self,
1641         def: Def,
1642         p: &Path,
1643         name: Option<Name>,
1644         param_mode: ParamMode,
1645     ) -> hir::Path {
1646         hir::Path {
1647             def,
1648             segments: p.segments
1649                 .iter()
1650                 .map(|segment| {
1651                     self.lower_path_segment(
1652                         p.span,
1653                         segment,
1654                         param_mode,
1655                         0,
1656                         ParenthesizedGenericArgs::Err,
1657                         ImplTraitContext::Disallowed,
1658                     )
1659                 })
1660                 .chain(name.map(|name| hir::PathSegment::from_name(name)))
1661                 .collect(),
1662             span: p.span,
1663         }
1664     }
1665
1666     fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1667         let def = self.expect_full_def(id);
1668         self.lower_path_extra(def, p, None, param_mode)
1669     }
1670
1671     fn lower_path_segment(
1672         &mut self,
1673         path_span: Span,
1674         segment: &PathSegment,
1675         param_mode: ParamMode,
1676         expected_lifetimes: usize,
1677         parenthesized_generic_args: ParenthesizedGenericArgs,
1678         itctx: ImplTraitContext,
1679     ) -> hir::PathSegment {
1680         let (mut generic_args, infer_types) = if let Some(ref generic_args) = segment.args {
1681             let msg = "parenthesized parameters may only be used with a trait";
1682             match **generic_args {
1683                 GenericArgs::AngleBracketed(ref data) => {
1684                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1685                 }
1686                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
1687                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1688                     ParenthesizedGenericArgs::Warn => {
1689                         self.sess.buffer_lint(
1690                             PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
1691                             CRATE_NODE_ID,
1692                             data.span,
1693                             msg.into(),
1694                         );
1695                         (hir::GenericArgs::none(), true)
1696                     }
1697                     ParenthesizedGenericArgs::Err => {
1698                         struct_span_err!(self.sess, data.span, E0214, "{}", msg)
1699                             .span_label(data.span, "only traits may use parentheses")
1700                             .emit();
1701                         (hir::GenericArgs::none(), true)
1702                     }
1703                 },
1704             }
1705         } else {
1706             self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1707         };
1708
1709         let has_lifetimes = generic_args.args.iter().any(|arg| match arg {
1710             GenericArg::Lifetime(_) => true,
1711             _ => false,
1712         });
1713         if !generic_args.parenthesized && !has_lifetimes {
1714             generic_args.args =
1715                 self.elided_path_lifetimes(path_span, expected_lifetimes)
1716                     .into_iter()
1717                     .map(|lt| GenericArg::Lifetime(lt))
1718                     .chain(generic_args.args.into_iter())
1719                     .collect();
1720         }
1721
1722         hir::PathSegment::new(
1723             self.lower_ident(segment.ident),
1724             generic_args,
1725             infer_types,
1726         )
1727     }
1728
1729     fn lower_angle_bracketed_parameter_data(
1730         &mut self,
1731         data: &AngleBracketedArgs,
1732         param_mode: ParamMode,
1733         itctx: ImplTraitContext,
1734     ) -> (hir::GenericArgs, bool) {
1735         let &AngleBracketedArgs { ref args, ref bindings, .. } = data;
1736         let has_types = args.iter().any(|arg| match arg {
1737             ast::GenericArg::Type(_) => true,
1738             _ => false,
1739         });
1740         (hir::GenericArgs {
1741             args: args.iter().map(|a| self.lower_generic_arg(a, itctx)).collect(),
1742             bindings: bindings.iter().map(|b| self.lower_ty_binding(b, itctx)).collect(),
1743             parenthesized: false,
1744         },
1745         !has_types && param_mode == ParamMode::Optional)
1746     }
1747
1748     fn lower_parenthesized_parameter_data(
1749         &mut self,
1750         data: &ParenthesizedArgData,
1751     ) -> (hir::GenericArgs, bool) {
1752         // Switch to `PassThrough` mode for anonymous lifetimes: this
1753         // means that we permit things like `&Ref<T>`, where `Ref` has
1754         // a hidden lifetime parameter. This is needed for backwards
1755         // compatibility, even in contexts like an impl header where
1756         // we generally don't permit such things (see #51008).
1757         self.with_anonymous_lifetime_mode(
1758             AnonymousLifetimeMode::PassThrough,
1759             |this| {
1760                 const DISALLOWED: ImplTraitContext = ImplTraitContext::Disallowed;
1761                 let &ParenthesizedArgData { ref inputs, ref output, span } = data;
1762                 let inputs = inputs.iter().map(|ty| this.lower_ty(ty, DISALLOWED)).collect();
1763                 let mk_tup = |this: &mut Self, tys, span| {
1764                     let LoweredNodeId { node_id, hir_id } = this.next_id();
1765                     P(hir::Ty { node: hir::TyTup(tys), id: node_id, hir_id, span })
1766                 };
1767
1768                 (
1769                     hir::GenericArgs {
1770                         args: hir_vec![GenericArg::Type(mk_tup(this, inputs, span))],
1771                         bindings: hir_vec![
1772                             hir::TypeBinding {
1773                                 id: this.next_id().node_id,
1774                                 name: Symbol::intern(FN_OUTPUT_NAME),
1775                                 ty: output
1776                                     .as_ref()
1777                                     .map(|ty| this.lower_ty(&ty, DISALLOWED))
1778                                     .unwrap_or_else(|| mk_tup(this, hir::HirVec::new(), span)),
1779                                 span: output.as_ref().map_or(span, |ty| ty.span),
1780                             }
1781                         ],
1782                         parenthesized: true,
1783                     },
1784                     false,
1785                 )
1786             }
1787         )
1788     }
1789
1790     fn lower_local(&mut self, l: &Local) -> P<hir::Local> {
1791         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(l.id);
1792         P(hir::Local {
1793             id: node_id,
1794             hir_id,
1795             ty: l.ty
1796                 .as_ref()
1797                 .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed)),
1798             pat: self.lower_pat(&l.pat),
1799             init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
1800             span: l.span,
1801             attrs: l.attrs.clone(),
1802             source: hir::LocalSource::Normal,
1803         })
1804     }
1805
1806     fn lower_mutability(&mut self, m: Mutability) -> hir::Mutability {
1807         match m {
1808             Mutability::Mutable => hir::MutMutable,
1809             Mutability::Immutable => hir::MutImmutable,
1810         }
1811     }
1812
1813     fn lower_arg(&mut self, arg: &Arg) -> hir::Arg {
1814         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(arg.id);
1815         hir::Arg {
1816             id: node_id,
1817             hir_id,
1818             pat: self.lower_pat(&arg.pat),
1819         }
1820     }
1821
1822     fn lower_fn_args_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Spanned<Name>> {
1823         decl.inputs
1824             .iter()
1825             .map(|arg| match arg.pat.node {
1826                 PatKind::Ident(_, ident, None) => respan(ident.span, ident.name),
1827                 _ => respan(arg.pat.span, keywords::Invalid.name()),
1828             })
1829             .collect()
1830     }
1831
1832     fn lower_fn_decl(
1833         &mut self,
1834         decl: &FnDecl,
1835         fn_def_id: Option<DefId>,
1836         impl_trait_return_allow: bool,
1837     ) -> P<hir::FnDecl> {
1838         // NOTE: The two last parameters here have to do with impl Trait. If fn_def_id is Some,
1839         //       then impl Trait arguments are lowered into generic parameters on the given
1840         //       fn_def_id, otherwise impl Trait is disallowed. (for now)
1841         //
1842         //       Furthermore, if impl_trait_return_allow is true, then impl Trait may be used in
1843         //       return positions as well. This guards against trait declarations and their impls
1844         //       where impl Trait is disallowed. (again for now)
1845         P(hir::FnDecl {
1846             inputs: decl.inputs
1847                 .iter()
1848                 .map(|arg| {
1849                     if let Some(def_id) = fn_def_id {
1850                         self.lower_ty(&arg.ty, ImplTraitContext::Universal(def_id))
1851                     } else {
1852                         self.lower_ty(&arg.ty, ImplTraitContext::Disallowed)
1853                     }
1854                 })
1855                 .collect(),
1856             output: match decl.output {
1857                 FunctionRetTy::Ty(ref ty) => match fn_def_id {
1858                     Some(def_id) if impl_trait_return_allow => {
1859                         hir::Return(self.lower_ty(ty, ImplTraitContext::Existential(def_id)))
1860                     }
1861                     _ => hir::Return(self.lower_ty(ty, ImplTraitContext::Disallowed)),
1862                 },
1863                 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
1864             },
1865             variadic: decl.variadic,
1866             has_implicit_self: decl.inputs.get(0).map_or(false, |arg| match arg.ty.node {
1867                 TyKind::ImplicitSelf => true,
1868                 TyKind::Rptr(_, ref mt) => mt.ty.node == TyKind::ImplicitSelf,
1869                 _ => false,
1870             }),
1871         })
1872     }
1873
1874     fn lower_param_bound(
1875         &mut self,
1876         tpb: &GenericBound,
1877         itctx: ImplTraitContext,
1878     ) -> hir::GenericBound {
1879         match *tpb {
1880             GenericBound::Trait(ref ty, modifier) => hir::GenericBound::Trait(
1881                 self.lower_poly_trait_ref(ty, itctx),
1882                 self.lower_trait_bound_modifier(modifier),
1883             ),
1884             GenericBound::Outlives(ref lifetime) => {
1885                 hir::GenericBound::Outlives(self.lower_lifetime(lifetime))
1886             }
1887         }
1888     }
1889
1890     fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
1891         let span = l.ident.span;
1892         match self.lower_ident(l.ident) {
1893             x if x == "'static" => self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
1894             x if x == "'_" => match self.anonymous_lifetime_mode {
1895                 AnonymousLifetimeMode::CreateParameter => {
1896                     let fresh_name = self.collect_fresh_in_band_lifetime(span);
1897                     self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(fresh_name))
1898                 }
1899
1900                 AnonymousLifetimeMode::PassThrough => {
1901                     self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
1902                 }
1903             },
1904             name => {
1905                 self.maybe_collect_in_band_lifetime(span, name);
1906                 let param_name = ParamName::Plain(name);
1907                 self.new_named_lifetime(l.id, span, hir::LifetimeName::Param(param_name))
1908             }
1909         }
1910     }
1911
1912     fn new_named_lifetime(
1913         &mut self,
1914         id: NodeId,
1915         span: Span,
1916         name: hir::LifetimeName,
1917     ) -> hir::Lifetime {
1918         hir::Lifetime {
1919             id: self.lower_node_id(id).node_id,
1920             span,
1921             name: name,
1922         }
1923     }
1924
1925     fn lower_generic_params(
1926         &mut self,
1927         params: &Vec<GenericParam>,
1928         add_bounds: &NodeMap<Vec<GenericBound>>,
1929         itctx: ImplTraitContext,
1930     ) -> hir::HirVec<hir::GenericParam> {
1931         params.iter().map(|param| self.lower_generic_param(param, add_bounds, itctx)).collect()
1932     }
1933
1934     fn lower_generic_param(&mut self,
1935                            param: &GenericParam,
1936                            add_bounds: &NodeMap<Vec<GenericBound>>,
1937                            itctx: ImplTraitContext)
1938                            -> hir::GenericParam {
1939         let mut bounds = self.lower_param_bounds(&param.bounds, itctx);
1940         match param.kind {
1941             GenericParamKind::Lifetime => {
1942                 let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
1943                 self.is_collecting_in_band_lifetimes = false;
1944
1945                 let lt = self.lower_lifetime(&Lifetime { id: param.id, ident: param.ident });
1946                 let param_name = match lt.name {
1947                     hir::LifetimeName::Param(param_name) => param_name,
1948                     _ => hir::ParamName::Plain(lt.name.name()),
1949                 };
1950                 let param = hir::GenericParam {
1951                     id: lt.id,
1952                     name: param_name,
1953                     span: lt.span,
1954                     pure_wrt_drop: attr::contains_name(&param.attrs, "may_dangle"),
1955                     attrs: self.lower_attrs(&param.attrs),
1956                     bounds,
1957                     kind: hir::GenericParamKind::Lifetime { in_band: false }
1958                 };
1959
1960                 self.is_collecting_in_band_lifetimes = was_collecting_in_band;
1961
1962                 param
1963             }
1964             GenericParamKind::Type { ref default, .. } => {
1965                 let mut name = self.lower_ident(param.ident);
1966
1967                 // Don't expose `Self` (recovered "keyword used as ident" parse error).
1968                 // `rustc::ty` expects `Self` to be only used for a trait's `Self`.
1969                 // Instead, use gensym("Self") to create a distinct name that looks the same.
1970                 if name == keywords::SelfType.name() {
1971                     name = Symbol::gensym("Self");
1972                 }
1973
1974                 let add_bounds = add_bounds.get(&param.id).map_or(&[][..], |x| &x);
1975                 if !add_bounds.is_empty() {
1976                     bounds = bounds.into_iter()
1977                                    .chain(self.lower_param_bounds(add_bounds, itctx).into_iter())
1978                                    .collect();
1979                 }
1980
1981                 hir::GenericParam {
1982                     id: self.lower_node_id(param.id).node_id,
1983                     name: hir::ParamName::Plain(name),
1984                     span: param.ident.span,
1985                     pure_wrt_drop: attr::contains_name(&param.attrs, "may_dangle"),
1986                     attrs: self.lower_attrs(&param.attrs),
1987                     bounds,
1988                     kind: hir::GenericParamKind::Type {
1989                         default: default.as_ref().map(|x| {
1990                             self.lower_ty(x, ImplTraitContext::Disallowed)
1991                         }),
1992                         synthetic: param.attrs.iter()
1993                                               .filter(|attr| attr.check_name("rustc_synthetic"))
1994                                               .map(|_| hir::SyntheticTyParamKind::ImplTrait)
1995                                               .next(),
1996                     }
1997                 }
1998             }
1999         }
2000     }
2001
2002     fn lower_generics(
2003         &mut self,
2004         generics: &Generics,
2005         itctx: ImplTraitContext)
2006         -> hir::Generics
2007     {
2008         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
2009         // FIXME: This could probably be done with less rightward drift. Also looks like two control
2010         //        paths where report_error is called are also the only paths that advance to after
2011         //        the match statement, so the error reporting could probably just be moved there.
2012         let mut add_bounds = NodeMap();
2013         for pred in &generics.where_clause.predicates {
2014             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
2015                 'next_bound: for bound in &bound_pred.bounds {
2016                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
2017                         let report_error = |this: &mut Self| {
2018                             this.diagnostic().span_err(
2019                                 bound_pred.bounded_ty.span,
2020                                 "`?Trait` bounds are only permitted at the \
2021                                  point where a type parameter is declared",
2022                             );
2023                         };
2024                         // Check if the where clause type is a plain type parameter.
2025                         match bound_pred.bounded_ty.node {
2026                             TyKind::Path(None, ref path)
2027                                 if path.segments.len() == 1
2028                                     && bound_pred.bound_generic_params.is_empty() =>
2029                             {
2030                                 if let Some(Def::TyParam(def_id)) = self.resolver
2031                                     .get_resolution(bound_pred.bounded_ty.id)
2032                                     .map(|d| d.base_def())
2033                                 {
2034                                     if let Some(node_id) =
2035                                         self.resolver.definitions().as_local_node_id(def_id)
2036                                     {
2037                                         for param in &generics.params {
2038                                             match param.kind {
2039                                                 GenericParamKind::Type { .. } => {
2040                                                     if node_id == param.id {
2041                                                         add_bounds.entry(param.id)
2042                                                             .or_insert(Vec::new())
2043                                                             .push(bound.clone());
2044                                                         continue 'next_bound;
2045                                                     }
2046                                                 }
2047                                                 _ => {}
2048                                             }
2049                                         }
2050                                     }
2051                                 }
2052                                 report_error(self)
2053                             }
2054                             _ => report_error(self),
2055                         }
2056                     }
2057                 }
2058             }
2059         }
2060
2061         hir::Generics {
2062             params: self.lower_generic_params(&generics.params, &add_bounds, itctx),
2063             where_clause: self.lower_where_clause(&generics.where_clause),
2064             span: generics.span,
2065         }
2066     }
2067
2068     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
2069         hir::WhereClause {
2070             id: self.lower_node_id(wc.id).node_id,
2071             predicates: wc.predicates
2072                 .iter()
2073                 .map(|predicate| self.lower_where_predicate(predicate))
2074                 .collect(),
2075         }
2076     }
2077
2078     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
2079         match *pred {
2080             WherePredicate::BoundPredicate(WhereBoundPredicate {
2081                 ref bound_generic_params,
2082                 ref bounded_ty,
2083                 ref bounds,
2084                 span,
2085             }) => {
2086                 self.with_in_scope_lifetime_defs(
2087                     &bound_generic_params,
2088                     |this| {
2089                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
2090                             bound_generic_params: this.lower_generic_params(
2091                                 bound_generic_params,
2092                                 &NodeMap(),
2093                                 ImplTraitContext::Disallowed,
2094                             ),
2095                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::Disallowed),
2096                             bounds: bounds
2097                                 .iter()
2098                                 .filter_map(|bound| match *bound {
2099                                     // Ignore `?Trait` bounds.
2100                                     // Tthey were copied into type parameters already.
2101                                     GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
2102                                     _ => Some(this.lower_param_bound(
2103                                         bound,
2104                                         ImplTraitContext::Disallowed,
2105                                     )),
2106                                 })
2107                                 .collect(),
2108                             span,
2109                         })
2110                     },
2111                 )
2112             }
2113             WherePredicate::RegionPredicate(WhereRegionPredicate {
2114                 ref lifetime,
2115                 ref bounds,
2116                 span,
2117             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
2118                 span,
2119                 lifetime: self.lower_lifetime(lifetime),
2120                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::Disallowed),
2121             }),
2122             WherePredicate::EqPredicate(WhereEqPredicate {
2123                 id,
2124                 ref lhs_ty,
2125                 ref rhs_ty,
2126                 span,
2127             }) => hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
2128                 id: self.lower_node_id(id).node_id,
2129                 lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::Disallowed),
2130                 rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::Disallowed),
2131                 span,
2132             }),
2133         }
2134     }
2135
2136     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
2137         match *vdata {
2138             VariantData::Struct(ref fields, id) => hir::VariantData::Struct(
2139                 fields
2140                     .iter()
2141                     .enumerate()
2142                     .map(|f| self.lower_struct_field(f))
2143                     .collect(),
2144                 self.lower_node_id(id).node_id,
2145             ),
2146             VariantData::Tuple(ref fields, id) => hir::VariantData::Tuple(
2147                 fields
2148                     .iter()
2149                     .enumerate()
2150                     .map(|f| self.lower_struct_field(f))
2151                     .collect(),
2152                 self.lower_node_id(id).node_id,
2153             ),
2154             VariantData::Unit(id) => hir::VariantData::Unit(self.lower_node_id(id).node_id),
2155         }
2156     }
2157
2158     fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext) -> hir::TraitRef {
2159         let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2160             hir::QPath::Resolved(None, path) => path.and_then(|path| path),
2161             qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2162         };
2163         hir::TraitRef {
2164             path,
2165             ref_id: self.lower_node_id(p.ref_id).node_id,
2166         }
2167     }
2168
2169     fn lower_poly_trait_ref(
2170         &mut self,
2171         p: &PolyTraitRef,
2172         itctx: ImplTraitContext,
2173     ) -> hir::PolyTraitRef {
2174         let bound_generic_params =
2175             self.lower_generic_params(&p.bound_generic_params, &NodeMap(), itctx);
2176         let trait_ref = self.with_parent_impl_lifetime_defs(
2177             &bound_generic_params,
2178             |this| this.lower_trait_ref(&p.trait_ref, itctx),
2179         );
2180
2181         hir::PolyTraitRef {
2182             bound_generic_params,
2183             trait_ref,
2184             span: p.span,
2185         }
2186     }
2187
2188     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
2189         hir::StructField {
2190             span: f.span,
2191             id: self.lower_node_id(f.id).node_id,
2192             ident: match f.ident {
2193                 Some(ident) => ident,
2194                 // FIXME(jseyfried) positional field hygiene
2195                 None => Ident::new(Symbol::intern(&index.to_string()), f.span),
2196             },
2197             vis: self.lower_visibility(&f.vis, None),
2198             ty: self.lower_ty(&f.ty, ImplTraitContext::Disallowed),
2199             attrs: self.lower_attrs(&f.attrs),
2200         }
2201     }
2202
2203     fn lower_field(&mut self, f: &Field) -> hir::Field {
2204         hir::Field {
2205             id: self.next_id().node_id,
2206             ident: f.ident,
2207             expr: P(self.lower_expr(&f.expr)),
2208             span: f.span,
2209             is_shorthand: f.is_shorthand,
2210         }
2211     }
2212
2213     fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy {
2214         hir::MutTy {
2215             ty: self.lower_ty(&mt.ty, itctx),
2216             mutbl: self.lower_mutability(mt.mutbl),
2217         }
2218     }
2219
2220     fn lower_param_bounds(&mut self, bounds: &[GenericBound], itctx: ImplTraitContext)
2221         -> hir::GenericBounds {
2222         bounds.iter().map(|bound| self.lower_param_bound(bound, itctx)).collect()
2223     }
2224
2225     fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2226         let mut expr = None;
2227
2228         let mut stmts = vec![];
2229
2230         for (index, stmt) in b.stmts.iter().enumerate() {
2231             if index == b.stmts.len() - 1 {
2232                 if let StmtKind::Expr(ref e) = stmt.node {
2233                     expr = Some(P(self.lower_expr(e)));
2234                 } else {
2235                     stmts.extend(self.lower_stmt(stmt));
2236                 }
2237             } else {
2238                 stmts.extend(self.lower_stmt(stmt));
2239             }
2240         }
2241
2242         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(b.id);
2243
2244         P(hir::Block {
2245             id: node_id,
2246             hir_id,
2247             stmts: stmts.into(),
2248             expr,
2249             rules: self.lower_block_check_mode(&b.rules),
2250             span: b.span,
2251             targeted_by_break,
2252             recovered: b.recovered,
2253         })
2254     }
2255
2256     fn lower_item_kind(
2257         &mut self,
2258         id: NodeId,
2259         name: &mut Name,
2260         attrs: &hir::HirVec<Attribute>,
2261         vis: &mut hir::Visibility,
2262         i: &ItemKind,
2263     ) -> hir::Item_ {
2264         match *i {
2265             ItemKind::ExternCrate(orig_name) => hir::ItemExternCrate(orig_name),
2266             ItemKind::Use(ref use_tree) => {
2267                 // Start with an empty prefix
2268                 let prefix = Path {
2269                     segments: vec![],
2270                     span: use_tree.span,
2271                 };
2272
2273                 self.lower_use_tree(use_tree, &prefix, id, vis, name, attrs)
2274             }
2275             ItemKind::Static(ref t, m, ref e) => {
2276                 let value = self.lower_body(None, |this| this.lower_expr(e));
2277                 hir::ItemStatic(
2278                     self.lower_ty(t, ImplTraitContext::Disallowed),
2279                     self.lower_mutability(m),
2280                     value,
2281                 )
2282             }
2283             ItemKind::Const(ref t, ref e) => {
2284                 let value = self.lower_body(None, |this| this.lower_expr(e));
2285                 hir::ItemConst(self.lower_ty(t, ImplTraitContext::Disallowed), value)
2286             }
2287             ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
2288                 let fn_def_id = self.resolver.definitions().local_def_id(id);
2289                 self.with_new_scopes(|this| {
2290                     let body_id = this.lower_body(Some(decl), |this| {
2291                         let body = this.lower_block(body, false);
2292                         this.expr_block(body, ThinVec::new())
2293                     });
2294                     let (generics, fn_decl) = this.add_in_band_defs(
2295                         generics,
2296                         fn_def_id,
2297                         AnonymousLifetimeMode::PassThrough,
2298                         |this| this.lower_fn_decl(decl, Some(fn_def_id), true),
2299                     );
2300
2301                     hir::ItemFn(
2302                         fn_decl,
2303                         this.lower_unsafety(unsafety),
2304                         this.lower_constness(constness),
2305                         abi,
2306                         generics,
2307                         body_id,
2308                     )
2309                 })
2310             }
2311             ItemKind::Mod(ref m) => hir::ItemMod(self.lower_mod(m)),
2312             ItemKind::ForeignMod(ref nm) => hir::ItemForeignMod(self.lower_foreign_mod(nm)),
2313             ItemKind::GlobalAsm(ref ga) => hir::ItemGlobalAsm(self.lower_global_asm(ga)),
2314             ItemKind::Ty(ref t, ref generics) => hir::ItemTy(
2315                 self.lower_ty(t, ImplTraitContext::Disallowed),
2316                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2317             ),
2318             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemEnum(
2319                 hir::EnumDef {
2320                     variants: enum_definition
2321                         .variants
2322                         .iter()
2323                         .map(|x| self.lower_variant(x))
2324                         .collect(),
2325                 },
2326                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2327             ),
2328             ItemKind::Struct(ref struct_def, ref generics) => {
2329                 let struct_def = self.lower_variant_data(struct_def);
2330                 hir::ItemStruct(
2331                     struct_def,
2332                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2333                 )
2334             }
2335             ItemKind::Union(ref vdata, ref generics) => {
2336                 let vdata = self.lower_variant_data(vdata);
2337                 hir::ItemUnion(
2338                     vdata,
2339                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2340                 )
2341             }
2342             ItemKind::Impl(
2343                 unsafety,
2344                 polarity,
2345                 defaultness,
2346                 ref ast_generics,
2347                 ref trait_ref,
2348                 ref ty,
2349                 ref impl_items,
2350             ) => {
2351                 let def_id = self.resolver.definitions().local_def_id(id);
2352
2353                 // Lower the "impl header" first. This ordering is important
2354                 // for in-band lifetimes! Consider `'a` here:
2355                 //
2356                 //     impl Foo<'a> for u32 {
2357                 //         fn method(&'a self) { .. }
2358                 //     }
2359                 //
2360                 // Because we start by lowering the `Foo<'a> for u32`
2361                 // part, we will add `'a` to the list of generics on
2362                 // the impl. When we then encounter it later in the
2363                 // method, it will not be considered an in-band
2364                 // lifetime to be added, but rather a reference to a
2365                 // parent lifetime.
2366                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
2367                     ast_generics,
2368                     def_id,
2369                     AnonymousLifetimeMode::CreateParameter,
2370                     |this| {
2371                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
2372                             this.lower_trait_ref(trait_ref, ImplTraitContext::Disallowed)
2373                         });
2374
2375                         if let Some(ref trait_ref) = trait_ref {
2376                             if let Def::Trait(def_id) = trait_ref.path.def {
2377                                 this.trait_impls.entry(def_id).or_insert(vec![]).push(id);
2378                             }
2379                         }
2380
2381                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::Disallowed);
2382
2383                         (trait_ref, lowered_ty)
2384                     },
2385                 );
2386
2387                 let new_impl_items = self.with_in_scope_lifetime_defs(
2388                     &ast_generics.params,
2389                     |this| {
2390                         impl_items
2391                             .iter()
2392                             .map(|item| this.lower_impl_item_ref(item))
2393                             .collect()
2394                     },
2395                 );
2396
2397                 hir::ItemImpl(
2398                     self.lower_unsafety(unsafety),
2399                     self.lower_impl_polarity(polarity),
2400                     self.lower_defaultness(defaultness, true /* [1] */),
2401                     generics,
2402                     trait_ref,
2403                     lowered_ty,
2404                     new_impl_items,
2405                 )
2406             }
2407             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
2408                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::Disallowed);
2409                 let items = items
2410                     .iter()
2411                     .map(|item| self.lower_trait_item_ref(item))
2412                     .collect();
2413                 hir::ItemTrait(
2414                     self.lower_is_auto(is_auto),
2415                     self.lower_unsafety(unsafety),
2416                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2417                     bounds,
2418                     items,
2419                 )
2420             }
2421             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemTraitAlias(
2422                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2423                 self.lower_param_bounds(bounds, ImplTraitContext::Disallowed),
2424             ),
2425             ItemKind::MacroDef(..) | ItemKind::Mac(..) => panic!("Shouldn't still be around"),
2426         }
2427
2428         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
2429         //     not cause an assertion failure inside the `lower_defaultness` function
2430     }
2431
2432     fn lower_use_tree(
2433         &mut self,
2434         tree: &UseTree,
2435         prefix: &Path,
2436         id: NodeId,
2437         vis: &mut hir::Visibility,
2438         name: &mut Name,
2439         attrs: &hir::HirVec<Attribute>,
2440     ) -> hir::Item_ {
2441         let path = &tree.prefix;
2442
2443         match tree.kind {
2444             UseTreeKind::Simple(rename, id1, id2) => {
2445                 *name = tree.ident().name;
2446
2447                 // First apply the prefix to the path
2448                 let mut path = Path {
2449                     segments: prefix
2450                         .segments
2451                         .iter()
2452                         .chain(path.segments.iter())
2453                         .cloned()
2454                         .collect(),
2455                     span: path.span,
2456                 };
2457
2458                 // Correctly resolve `self` imports
2459                 if path.segments.len() > 1
2460                     && path.segments.last().unwrap().ident.name == keywords::SelfValue.name()
2461                 {
2462                     let _ = path.segments.pop();
2463                     if rename.is_none() {
2464                         *name = path.segments.last().unwrap().ident.name;
2465                     }
2466                 }
2467
2468                 let parent_def_index = self.current_hir_id_owner.last().unwrap().0;
2469                 let mut defs = self.expect_full_def_from_use(id);
2470                 // we want to return *something* from this function, so hang onto the first item
2471                 // for later
2472                 let mut ret_def = defs.next().unwrap_or(Def::Err);
2473
2474                 for (def, &new_node_id) in defs.zip([id1, id2].iter()) {
2475                     let vis = vis.clone();
2476                     let name = name.clone();
2477                     let span = path.span;
2478                     self.resolver.definitions().create_def_with_parent(
2479                         parent_def_index,
2480                         new_node_id,
2481                         DefPathData::Misc,
2482                         DefIndexAddressSpace::High,
2483                         Mark::root(),
2484                         span);
2485                     self.allocate_hir_id_counter(new_node_id, &path);
2486
2487                     self.with_hir_id_owner(new_node_id, |this| {
2488                         let new_id = this.lower_node_id(new_node_id);
2489                         let path = this.lower_path_extra(def, &path, None, ParamMode::Explicit);
2490                         let item = hir::ItemUse(P(path), hir::UseKind::Single);
2491                         let vis = match vis {
2492                             hir::Visibility::Public => hir::Visibility::Public,
2493                             hir::Visibility::Crate(sugar) => hir::Visibility::Crate(sugar),
2494                             hir::Visibility::Inherited => hir::Visibility::Inherited,
2495                             hir::Visibility::Restricted { ref path, id: _ } => {
2496                                 hir::Visibility::Restricted {
2497                                     path: path.clone(),
2498                                     // We are allocating a new NodeId here
2499                                     id: this.next_id().node_id,
2500                                 }
2501                             }
2502                         };
2503
2504                         this.items.insert(
2505                             new_id.node_id,
2506                             hir::Item {
2507                                 id: new_id.node_id,
2508                                 hir_id: new_id.hir_id,
2509                                 name: name,
2510                                 attrs: attrs.clone(),
2511                                 node: item,
2512                                 vis,
2513                                 span,
2514                             },
2515                         );
2516                     });
2517                 }
2518
2519                 let path = P(self.lower_path_extra(ret_def, &path, None, ParamMode::Explicit));
2520                 hir::ItemUse(path, hir::UseKind::Single)
2521             }
2522             UseTreeKind::Glob => {
2523                 let path = P(self.lower_path(
2524                     id,
2525                     &Path {
2526                         segments: prefix
2527                             .segments
2528                             .iter()
2529                             .chain(path.segments.iter())
2530                             .cloned()
2531                             .collect(),
2532                         span: path.span,
2533                     },
2534                     ParamMode::Explicit,
2535                 ));
2536                 hir::ItemUse(path, hir::UseKind::Glob)
2537             }
2538             UseTreeKind::Nested(ref trees) => {
2539                 let prefix = Path {
2540                     segments: prefix
2541                         .segments
2542                         .iter()
2543                         .chain(path.segments.iter())
2544                         .cloned()
2545                         .collect(),
2546                     span: prefix.span.to(path.span),
2547                 };
2548
2549                 // Add all the nested PathListItems in the HIR
2550                 for &(ref use_tree, id) in trees {
2551                     self.allocate_hir_id_counter(id, &use_tree);
2552                     let LoweredNodeId {
2553                         node_id: new_id,
2554                         hir_id: new_hir_id,
2555                     } = self.lower_node_id(id);
2556
2557                     let mut vis = vis.clone();
2558                     let mut name = name.clone();
2559                     let item =
2560                         self.lower_use_tree(use_tree, &prefix, new_id, &mut vis, &mut name, &attrs);
2561
2562                     self.with_hir_id_owner(new_id, |this| {
2563                         let vis = match vis {
2564                             hir::Visibility::Public => hir::Visibility::Public,
2565                             hir::Visibility::Crate(sugar) => hir::Visibility::Crate(sugar),
2566                             hir::Visibility::Inherited => hir::Visibility::Inherited,
2567                             hir::Visibility::Restricted { ref path, id: _ } => {
2568                                 hir::Visibility::Restricted {
2569                                     path: path.clone(),
2570                                     // We are allocating a new NodeId here
2571                                     id: this.next_id().node_id,
2572                                 }
2573                             }
2574                         };
2575
2576                         this.items.insert(
2577                             new_id,
2578                             hir::Item {
2579                                 id: new_id,
2580                                 hir_id: new_hir_id,
2581                                 name: name,
2582                                 attrs: attrs.clone(),
2583                                 node: item,
2584                                 vis,
2585                                 span: use_tree.span,
2586                             },
2587                         );
2588                     });
2589                 }
2590
2591                 // Privatize the degenerate import base, used only to check
2592                 // the stability of `use a::{};`, to avoid it showing up as
2593                 // a re-export by accident when `pub`, e.g. in documentation.
2594                 let path = P(self.lower_path(id, &prefix, ParamMode::Explicit));
2595                 *vis = hir::Inherited;
2596                 hir::ItemUse(path, hir::UseKind::ListStem)
2597             }
2598         }
2599     }
2600
2601     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {
2602         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(i.id);
2603         let trait_item_def_id = self.resolver.definitions().local_def_id(node_id);
2604
2605         let (generics, node) = match i.node {
2606             TraitItemKind::Const(ref ty, ref default) => (
2607                 self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2608                 hir::TraitItemKind::Const(
2609                     self.lower_ty(ty, ImplTraitContext::Disallowed),
2610                     default
2611                         .as_ref()
2612                         .map(|x| self.lower_body(None, |this| this.lower_expr(x))),
2613                 ),
2614             ),
2615             TraitItemKind::Method(ref sig, None) => {
2616                 let names = self.lower_fn_args_to_names(&sig.decl);
2617                 self.add_in_band_defs(
2618                     &i.generics,
2619                     trait_item_def_id,
2620                     AnonymousLifetimeMode::PassThrough,
2621                     |this| {
2622                         hir::TraitItemKind::Method(
2623                             this.lower_method_sig(sig, trait_item_def_id, false),
2624                             hir::TraitMethod::Required(names),
2625                         )
2626                     },
2627                 )
2628             }
2629             TraitItemKind::Method(ref sig, Some(ref body)) => {
2630                 let body_id = self.lower_body(Some(&sig.decl), |this| {
2631                     let body = this.lower_block(body, false);
2632                     this.expr_block(body, ThinVec::new())
2633                 });
2634
2635                 self.add_in_band_defs(
2636                     &i.generics,
2637                     trait_item_def_id,
2638                     AnonymousLifetimeMode::PassThrough,
2639                     |this| {
2640                         hir::TraitItemKind::Method(
2641                             this.lower_method_sig(sig, trait_item_def_id, false),
2642                             hir::TraitMethod::Provided(body_id),
2643                         )
2644                     },
2645                 )
2646             }
2647             TraitItemKind::Type(ref bounds, ref default) => (
2648                 self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2649                 hir::TraitItemKind::Type(
2650                     self.lower_param_bounds(bounds, ImplTraitContext::Disallowed),
2651                     default
2652                         .as_ref()
2653                         .map(|x| self.lower_ty(x, ImplTraitContext::Disallowed)),
2654                 ),
2655             ),
2656             TraitItemKind::Macro(..) => panic!("Shouldn't exist any more"),
2657         };
2658
2659         hir::TraitItem {
2660             id: node_id,
2661             hir_id,
2662             name: self.lower_ident(i.ident),
2663             attrs: self.lower_attrs(&i.attrs),
2664             generics,
2665             node,
2666             span: i.span,
2667         }
2668     }
2669
2670     fn lower_trait_item_ref(&mut self, i: &TraitItem) -> hir::TraitItemRef {
2671         let (kind, has_default) = match i.node {
2672             TraitItemKind::Const(_, ref default) => {
2673                 (hir::AssociatedItemKind::Const, default.is_some())
2674             }
2675             TraitItemKind::Type(_, ref default) => {
2676                 (hir::AssociatedItemKind::Type, default.is_some())
2677             }
2678             TraitItemKind::Method(ref sig, ref default) => (
2679                 hir::AssociatedItemKind::Method {
2680                     has_self: sig.decl.has_self(),
2681                 },
2682                 default.is_some(),
2683             ),
2684             TraitItemKind::Macro(..) => unimplemented!(),
2685         };
2686         hir::TraitItemRef {
2687             id: hir::TraitItemId { node_id: i.id },
2688             name: self.lower_ident(i.ident),
2689             span: i.span,
2690             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
2691             kind,
2692         }
2693     }
2694
2695     fn lower_impl_item(&mut self, i: &ImplItem) -> hir::ImplItem {
2696         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(i.id);
2697         let impl_item_def_id = self.resolver.definitions().local_def_id(node_id);
2698
2699         let (generics, node) = match i.node {
2700             ImplItemKind::Const(ref ty, ref expr) => {
2701                 let body_id = self.lower_body(None, |this| this.lower_expr(expr));
2702                 (
2703                     self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2704                     hir::ImplItemKind::Const(
2705                         self.lower_ty(ty, ImplTraitContext::Disallowed),
2706                         body_id,
2707                     ),
2708                 )
2709             }
2710             ImplItemKind::Method(ref sig, ref body) => {
2711                 let body_id = self.lower_body(Some(&sig.decl), |this| {
2712                     let body = this.lower_block(body, false);
2713                     this.expr_block(body, ThinVec::new())
2714                 });
2715                 let impl_trait_return_allow = !self.is_in_trait_impl;
2716
2717                 self.add_in_band_defs(
2718                     &i.generics,
2719                     impl_item_def_id,
2720                     AnonymousLifetimeMode::PassThrough,
2721                     |this| {
2722                         hir::ImplItemKind::Method(
2723                             this.lower_method_sig(
2724                                 sig,
2725                                 impl_item_def_id,
2726                                 impl_trait_return_allow,
2727                             ),
2728                             body_id,
2729                         )
2730                     },
2731                 )
2732             }
2733             ImplItemKind::Type(ref ty) => (
2734                 self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2735                 hir::ImplItemKind::Type(self.lower_ty(ty, ImplTraitContext::Disallowed)),
2736             ),
2737             ImplItemKind::Macro(..) => panic!("Shouldn't exist any more"),
2738         };
2739
2740         hir::ImplItem {
2741             id: node_id,
2742             hir_id,
2743             name: self.lower_ident(i.ident),
2744             attrs: self.lower_attrs(&i.attrs),
2745             generics,
2746             vis: self.lower_visibility(&i.vis, None),
2747             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
2748             node,
2749             span: i.span,
2750         }
2751
2752         // [1] since `default impl` is not yet implemented, this is always true in impls
2753     }
2754
2755     fn lower_impl_item_ref(&mut self, i: &ImplItem) -> hir::ImplItemRef {
2756         hir::ImplItemRef {
2757             id: hir::ImplItemId { node_id: i.id },
2758             name: self.lower_ident(i.ident),
2759             span: i.span,
2760             vis: self.lower_visibility(&i.vis, Some(i.id)),
2761             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
2762             kind: match i.node {
2763                 ImplItemKind::Const(..) => hir::AssociatedItemKind::Const,
2764                 ImplItemKind::Type(..) => hir::AssociatedItemKind::Type,
2765                 ImplItemKind::Method(ref sig, _) => hir::AssociatedItemKind::Method {
2766                     has_self: sig.decl.has_self(),
2767                 },
2768                 ImplItemKind::Macro(..) => unimplemented!(),
2769             },
2770         }
2771
2772         // [1] since `default impl` is not yet implemented, this is always true in impls
2773     }
2774
2775     fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
2776         hir::Mod {
2777             inner: m.inner,
2778             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
2779         }
2780     }
2781
2782     fn lower_item_id(&mut self, i: &Item) -> SmallVector<hir::ItemId> {
2783         match i.node {
2784             ItemKind::Use(ref use_tree) => {
2785                 let mut vec = SmallVector::one(hir::ItemId { id: i.id });
2786                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
2787                 return vec;
2788             }
2789             ItemKind::MacroDef(..) => return SmallVector::new(),
2790             _ => {}
2791         }
2792         SmallVector::one(hir::ItemId { id: i.id })
2793     }
2794
2795     fn lower_item_id_use_tree(&mut self,
2796                               tree: &UseTree,
2797                               base_id: NodeId,
2798                               vec: &mut SmallVector<hir::ItemId>)
2799     {
2800         match tree.kind {
2801             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
2802                 vec.push(hir::ItemId { id });
2803                 self.lower_item_id_use_tree(nested, id, vec);
2804             },
2805             UseTreeKind::Glob => {}
2806             UseTreeKind::Simple(_, id1, id2) => {
2807                 for (_, &id) in self.expect_full_def_from_use(base_id)
2808                                     .skip(1)
2809                                     .zip([id1, id2].iter())
2810                 {
2811                     vec.push(hir::ItemId { id });
2812                 }
2813             },
2814         }
2815     }
2816
2817     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
2818         let mut name = i.ident.name;
2819         let mut vis = self.lower_visibility(&i.vis, None);
2820         let attrs = self.lower_attrs(&i.attrs);
2821         if let ItemKind::MacroDef(ref def) = i.node {
2822             if !def.legacy || attr::contains_name(&i.attrs, "macro_export") {
2823                 let body = self.lower_token_stream(def.stream());
2824                 self.exported_macros.push(hir::MacroDef {
2825                     name,
2826                     vis,
2827                     attrs,
2828                     id: i.id,
2829                     span: i.span,
2830                     body,
2831                     legacy: def.legacy,
2832                 });
2833             }
2834             return None;
2835         }
2836
2837         let node = self.lower_item_kind(i.id, &mut name, &attrs, &mut vis, &i.node);
2838
2839         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(i.id);
2840
2841         Some(hir::Item {
2842             id: node_id,
2843             hir_id,
2844             name,
2845             attrs,
2846             node,
2847             vis,
2848             span: i.span,
2849         })
2850     }
2851
2852     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
2853         let node_id = self.lower_node_id(i.id).node_id;
2854         let def_id = self.resolver.definitions().local_def_id(node_id);
2855         hir::ForeignItem {
2856             id: node_id,
2857             name: i.ident.name,
2858             attrs: self.lower_attrs(&i.attrs),
2859             node: match i.node {
2860                 ForeignItemKind::Fn(ref fdec, ref generics) => {
2861                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
2862                         generics,
2863                         def_id,
2864                         AnonymousLifetimeMode::PassThrough,
2865                         |this| {
2866                             (
2867                                 // Disallow impl Trait in foreign items
2868                                 this.lower_fn_decl(fdec, None, false),
2869                                 this.lower_fn_args_to_names(fdec),
2870                             )
2871                         },
2872                     );
2873
2874                     hir::ForeignItemFn(fn_dec, fn_args, generics)
2875                 }
2876                 ForeignItemKind::Static(ref t, m) => {
2877                     hir::ForeignItemStatic(self.lower_ty(t, ImplTraitContext::Disallowed), m)
2878                 }
2879                 ForeignItemKind::Ty => hir::ForeignItemType,
2880                 ForeignItemKind::Macro(_) => panic!("shouldn't exist here"),
2881             },
2882             vis: self.lower_visibility(&i.vis, None),
2883             span: i.span,
2884         }
2885     }
2886
2887     fn lower_method_sig(
2888         &mut self,
2889         sig: &MethodSig,
2890         fn_def_id: DefId,
2891         impl_trait_return_allow: bool,
2892     ) -> hir::MethodSig {
2893         hir::MethodSig {
2894             abi: sig.abi,
2895             unsafety: self.lower_unsafety(sig.unsafety),
2896             constness: self.lower_constness(sig.constness),
2897             decl: self.lower_fn_decl(&sig.decl, Some(fn_def_id), impl_trait_return_allow),
2898         }
2899     }
2900
2901     fn lower_is_auto(&mut self, a: IsAuto) -> hir::IsAuto {
2902         match a {
2903             IsAuto::Yes => hir::IsAuto::Yes,
2904             IsAuto::No => hir::IsAuto::No,
2905         }
2906     }
2907
2908     fn lower_unsafety(&mut self, u: Unsafety) -> hir::Unsafety {
2909         match u {
2910             Unsafety::Unsafe => hir::Unsafety::Unsafe,
2911             Unsafety::Normal => hir::Unsafety::Normal,
2912         }
2913     }
2914
2915     fn lower_constness(&mut self, c: Spanned<Constness>) -> hir::Constness {
2916         match c.node {
2917             Constness::Const => hir::Constness::Const,
2918             Constness::NotConst => hir::Constness::NotConst,
2919         }
2920     }
2921
2922     fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
2923         match u {
2924             UnOp::Deref => hir::UnDeref,
2925             UnOp::Not => hir::UnNot,
2926             UnOp::Neg => hir::UnNeg,
2927         }
2928     }
2929
2930     fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
2931         Spanned {
2932             node: match b.node {
2933                 BinOpKind::Add => hir::BiAdd,
2934                 BinOpKind::Sub => hir::BiSub,
2935                 BinOpKind::Mul => hir::BiMul,
2936                 BinOpKind::Div => hir::BiDiv,
2937                 BinOpKind::Rem => hir::BiRem,
2938                 BinOpKind::And => hir::BiAnd,
2939                 BinOpKind::Or => hir::BiOr,
2940                 BinOpKind::BitXor => hir::BiBitXor,
2941                 BinOpKind::BitAnd => hir::BiBitAnd,
2942                 BinOpKind::BitOr => hir::BiBitOr,
2943                 BinOpKind::Shl => hir::BiShl,
2944                 BinOpKind::Shr => hir::BiShr,
2945                 BinOpKind::Eq => hir::BiEq,
2946                 BinOpKind::Lt => hir::BiLt,
2947                 BinOpKind::Le => hir::BiLe,
2948                 BinOpKind::Ne => hir::BiNe,
2949                 BinOpKind::Ge => hir::BiGe,
2950                 BinOpKind::Gt => hir::BiGt,
2951             },
2952             span: b.span,
2953         }
2954     }
2955
2956     fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2957         let node = match p.node {
2958             PatKind::Wild => hir::PatKind::Wild,
2959             PatKind::Ident(ref binding_mode, ident, ref sub) => {
2960                 match self.resolver.get_resolution(p.id).map(|d| d.base_def()) {
2961                     // `None` can occur in body-less function signatures
2962                     def @ None | def @ Some(Def::Local(_)) => {
2963                         let canonical_id = match def {
2964                             Some(Def::Local(id)) => id,
2965                             _ => p.id,
2966                         };
2967                         hir::PatKind::Binding(
2968                             self.lower_binding_mode(binding_mode),
2969                             canonical_id,
2970                             respan(ident.span, ident.name),
2971                             sub.as_ref().map(|x| self.lower_pat(x)),
2972                         )
2973                     }
2974                     Some(def) => hir::PatKind::Path(hir::QPath::Resolved(
2975                         None,
2976                         P(hir::Path {
2977                             span: ident.span,
2978                             def,
2979                             segments: hir_vec![hir::PathSegment::from_name(ident.name)],
2980                         }),
2981                     )),
2982                 }
2983             }
2984             PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2985             PatKind::TupleStruct(ref path, ref pats, ddpos) => {
2986                 let qpath = self.lower_qpath(
2987                     p.id,
2988                     &None,
2989                     path,
2990                     ParamMode::Optional,
2991                     ImplTraitContext::Disallowed,
2992                 );
2993                 hir::PatKind::TupleStruct(
2994                     qpath,
2995                     pats.iter().map(|x| self.lower_pat(x)).collect(),
2996                     ddpos,
2997                 )
2998             }
2999             PatKind::Path(ref qself, ref path) => hir::PatKind::Path(self.lower_qpath(
3000                 p.id,
3001                 qself,
3002                 path,
3003                 ParamMode::Optional,
3004                 ImplTraitContext::Disallowed,
3005             )),
3006             PatKind::Struct(ref path, ref fields, etc) => {
3007                 let qpath = self.lower_qpath(
3008                     p.id,
3009                     &None,
3010                     path,
3011                     ParamMode::Optional,
3012                     ImplTraitContext::Disallowed,
3013                 );
3014
3015                 let fs = fields
3016                     .iter()
3017                     .map(|f| Spanned {
3018                         span: f.span,
3019                         node: hir::FieldPat {
3020                             id: self.next_id().node_id,
3021                             ident: f.node.ident,
3022                             pat: self.lower_pat(&f.node.pat),
3023                             is_shorthand: f.node.is_shorthand,
3024                         },
3025                     })
3026                     .collect();
3027                 hir::PatKind::Struct(qpath, fs, etc)
3028             }
3029             PatKind::Tuple(ref elts, ddpos) => {
3030                 hir::PatKind::Tuple(elts.iter().map(|x| self.lower_pat(x)).collect(), ddpos)
3031             }
3032             PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
3033             PatKind::Ref(ref inner, mutbl) => {
3034                 hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
3035             }
3036             PatKind::Range(ref e1, ref e2, ref end) => hir::PatKind::Range(
3037                 P(self.lower_expr(e1)),
3038                 P(self.lower_expr(e2)),
3039                 self.lower_range_end(end),
3040             ),
3041             PatKind::Slice(ref before, ref slice, ref after) => hir::PatKind::Slice(
3042                 before.iter().map(|x| self.lower_pat(x)).collect(),
3043                 slice.as_ref().map(|x| self.lower_pat(x)),
3044                 after.iter().map(|x| self.lower_pat(x)).collect(),
3045             ),
3046             PatKind::Paren(ref inner) => return self.lower_pat(inner),
3047             PatKind::Mac(_) => panic!("Shouldn't exist here"),
3048         };
3049
3050         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(p.id);
3051         P(hir::Pat {
3052             id: node_id,
3053             hir_id,
3054             node,
3055             span: p.span,
3056         })
3057     }
3058
3059     fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
3060         match *e {
3061             RangeEnd::Included(_) => hir::RangeEnd::Included,
3062             RangeEnd::Excluded => hir::RangeEnd::Excluded,
3063         }
3064     }
3065
3066     fn lower_anon_const(&mut self, c: &AnonConst) -> hir::AnonConst {
3067         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(c.id);
3068
3069         hir::AnonConst {
3070             id: node_id,
3071             hir_id,
3072             body: self.lower_body(None, |this| this.lower_expr(&c.value)),
3073         }
3074     }
3075
3076     fn lower_expr(&mut self, e: &Expr) -> hir::Expr {
3077         let kind = match e.node {
3078             ExprKind::Box(ref inner) => hir::ExprBox(P(self.lower_expr(inner))),
3079             ExprKind::ObsoleteInPlace(..) => {
3080                 self.sess.abort_if_errors();
3081                 span_bug!(e.span, "encountered ObsoleteInPlace expr during lowering");
3082             }
3083             ExprKind::Array(ref exprs) => {
3084                 hir::ExprArray(exprs.iter().map(|x| self.lower_expr(x)).collect())
3085             }
3086             ExprKind::Repeat(ref expr, ref count) => {
3087                 let expr = P(self.lower_expr(expr));
3088                 let count = self.lower_anon_const(count);
3089                 hir::ExprRepeat(expr, count)
3090             }
3091             ExprKind::Tup(ref elts) => {
3092                 hir::ExprTup(elts.iter().map(|x| self.lower_expr(x)).collect())
3093             }
3094             ExprKind::Call(ref f, ref args) => {
3095                 let f = P(self.lower_expr(f));
3096                 hir::ExprCall(f, args.iter().map(|x| self.lower_expr(x)).collect())
3097             }
3098             ExprKind::MethodCall(ref seg, ref args) => {
3099                 let hir_seg = self.lower_path_segment(
3100                     e.span,
3101                     seg,
3102                     ParamMode::Optional,
3103                     0,
3104                     ParenthesizedGenericArgs::Err,
3105                     ImplTraitContext::Disallowed,
3106                 );
3107                 let args = args.iter().map(|x| self.lower_expr(x)).collect();
3108                 hir::ExprMethodCall(hir_seg, seg.ident.span, args)
3109             }
3110             ExprKind::Binary(binop, ref lhs, ref rhs) => {
3111                 let binop = self.lower_binop(binop);
3112                 let lhs = P(self.lower_expr(lhs));
3113                 let rhs = P(self.lower_expr(rhs));
3114                 hir::ExprBinary(binop, lhs, rhs)
3115             }
3116             ExprKind::Unary(op, ref ohs) => {
3117                 let op = self.lower_unop(op);
3118                 let ohs = P(self.lower_expr(ohs));
3119                 hir::ExprUnary(op, ohs)
3120             }
3121             ExprKind::Lit(ref l) => hir::ExprLit(P((**l).clone())),
3122             ExprKind::Cast(ref expr, ref ty) => {
3123                 let expr = P(self.lower_expr(expr));
3124                 hir::ExprCast(expr, self.lower_ty(ty, ImplTraitContext::Disallowed))
3125             }
3126             ExprKind::Type(ref expr, ref ty) => {
3127                 let expr = P(self.lower_expr(expr));
3128                 hir::ExprType(expr, self.lower_ty(ty, ImplTraitContext::Disallowed))
3129             }
3130             ExprKind::AddrOf(m, ref ohs) => {
3131                 let m = self.lower_mutability(m);
3132                 let ohs = P(self.lower_expr(ohs));
3133                 hir::ExprAddrOf(m, ohs)
3134             }
3135             // More complicated than you might expect because the else branch
3136             // might be `if let`.
3137             ExprKind::If(ref cond, ref blk, ref else_opt) => {
3138                 let else_opt = else_opt.as_ref().map(|els| {
3139                     match els.node {
3140                         ExprKind::IfLet(..) => {
3141                             // wrap the if-let expr in a block
3142                             let span = els.span;
3143                             let els = P(self.lower_expr(els));
3144                             let LoweredNodeId { node_id, hir_id } = self.next_id();
3145                             let blk = P(hir::Block {
3146                                 stmts: hir_vec![],
3147                                 expr: Some(els),
3148                                 id: node_id,
3149                                 hir_id,
3150                                 rules: hir::DefaultBlock,
3151                                 span,
3152                                 targeted_by_break: false,
3153                                 recovered: blk.recovered,
3154                             });
3155                             P(self.expr_block(blk, ThinVec::new()))
3156                         }
3157                         _ => P(self.lower_expr(els)),
3158                     }
3159                 });
3160
3161                 let then_blk = self.lower_block(blk, false);
3162                 let then_expr = self.expr_block(then_blk, ThinVec::new());
3163
3164                 hir::ExprIf(P(self.lower_expr(cond)), P(then_expr), else_opt)
3165             }
3166             ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
3167                 hir::ExprWhile(
3168                     this.with_loop_condition_scope(|this| P(this.lower_expr(cond))),
3169                     this.lower_block(body, false),
3170                     this.lower_label(opt_label),
3171                 )
3172             }),
3173             ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
3174                 hir::ExprLoop(
3175                     this.lower_block(body, false),
3176                     this.lower_label(opt_label),
3177                     hir::LoopSource::Loop,
3178                 )
3179             }),
3180             ExprKind::Catch(ref body) => {
3181                 self.with_catch_scope(body.id, |this| {
3182                     let unstable_span =
3183                         this.allow_internal_unstable(CompilerDesugaringKind::Catch, body.span);
3184                     let mut block = this.lower_block(body, true).into_inner();
3185                     let tail = block.expr.take().map_or_else(
3186                         || {
3187                             let LoweredNodeId { node_id, hir_id } = this.next_id();
3188                             let span = this.sess.codemap().end_point(unstable_span);
3189                             hir::Expr {
3190                                 id: node_id,
3191                                 span,
3192                                 node: hir::ExprTup(hir_vec![]),
3193                                 attrs: ThinVec::new(),
3194                                 hir_id,
3195                             }
3196                         },
3197                         |x: P<hir::Expr>| x.into_inner(),
3198                     );
3199                     block.expr = Some(this.wrap_in_try_constructor(
3200                         "from_ok", tail, unstable_span));
3201                     hir::ExprBlock(P(block), None)
3202                 })
3203             }
3204             ExprKind::Match(ref expr, ref arms) => hir::ExprMatch(
3205                 P(self.lower_expr(expr)),
3206                 arms.iter().map(|x| self.lower_arm(x)).collect(),
3207                 hir::MatchSource::Normal,
3208             ),
3209             ExprKind::Closure(capture_clause, movability, ref decl, ref body, fn_decl_span) => {
3210                 self.with_new_scopes(|this| {
3211                     let mut is_generator = false;
3212                     let body_id = this.lower_body(Some(decl), |this| {
3213                         let e = this.lower_expr(body);
3214                         is_generator = this.is_generator;
3215                         e
3216                     });
3217                     let generator_option = if is_generator {
3218                         if !decl.inputs.is_empty() {
3219                             span_err!(
3220                                 this.sess,
3221                                 fn_decl_span,
3222                                 E0628,
3223                                 "generators cannot have explicit arguments"
3224                             );
3225                             this.sess.abort_if_errors();
3226                         }
3227                         Some(match movability {
3228                             Movability::Movable => hir::GeneratorMovability::Movable,
3229                             Movability::Static => hir::GeneratorMovability::Static,
3230                         })
3231                     } else {
3232                         if movability == Movability::Static {
3233                             span_err!(
3234                                 this.sess,
3235                                 fn_decl_span,
3236                                 E0697,
3237                                 "closures cannot be static"
3238                             );
3239                         }
3240                         None
3241                     };
3242                     hir::ExprClosure(
3243                         this.lower_capture_clause(capture_clause),
3244                         this.lower_fn_decl(decl, None, false),
3245                         body_id,
3246                         fn_decl_span,
3247                         generator_option,
3248                     )
3249                 })
3250             }
3251             ExprKind::Block(ref blk, opt_label) => {
3252                 hir::ExprBlock(self.lower_block(blk,
3253                                                 opt_label.is_some()),
3254                                                 self.lower_label(opt_label))
3255             }
3256             ExprKind::Assign(ref el, ref er) => {
3257                 hir::ExprAssign(P(self.lower_expr(el)), P(self.lower_expr(er)))
3258             }
3259             ExprKind::AssignOp(op, ref el, ref er) => hir::ExprAssignOp(
3260                 self.lower_binop(op),
3261                 P(self.lower_expr(el)),
3262                 P(self.lower_expr(er)),
3263             ),
3264             ExprKind::Field(ref el, ident) => hir::ExprField(P(self.lower_expr(el)), ident),
3265             ExprKind::Index(ref el, ref er) => {
3266                 hir::ExprIndex(P(self.lower_expr(el)), P(self.lower_expr(er)))
3267             }
3268             // Desugar `<start>..=<end>` to `std::ops::RangeInclusive::new(<start>, <end>)`
3269             ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
3270                 // FIXME: Use e.span directly after RangeInclusive::new() is stabilized in stage0.
3271                 let span = self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3272                 let id = self.next_id();
3273                 let e1 = self.lower_expr(e1);
3274                 let e2 = self.lower_expr(e2);
3275                 let ty_path = P(self.std_path(span, &["ops", "RangeInclusive"], false));
3276                 let ty = self.ty_path(id, span, hir::QPath::Resolved(None, ty_path));
3277                 let new_seg = P(hir::PathSegment::from_name(Symbol::intern("new")));
3278                 let new_path = hir::QPath::TypeRelative(ty, new_seg);
3279                 let new = P(self.expr(span, hir::ExprPath(new_path), ThinVec::new()));
3280                 hir::ExprCall(new, hir_vec![e1, e2])
3281             }
3282             ExprKind::Range(ref e1, ref e2, lims) => {
3283                 use syntax::ast::RangeLimits::*;
3284
3285                 let path = match (e1, e2, lims) {
3286                     (&None, &None, HalfOpen) => "RangeFull",
3287                     (&Some(..), &None, HalfOpen) => "RangeFrom",
3288                     (&None, &Some(..), HalfOpen) => "RangeTo",
3289                     (&Some(..), &Some(..), HalfOpen) => "Range",
3290                     (&None, &Some(..), Closed) => "RangeToInclusive",
3291                     (&Some(..), &Some(..), Closed) => unreachable!(),
3292                     (_, &None, Closed) => self.diagnostic()
3293                         .span_fatal(e.span, "inclusive range with no end")
3294                         .raise(),
3295                 };
3296
3297                 let fields = e1.iter()
3298                     .map(|e| ("start", e))
3299                     .chain(e2.iter().map(|e| ("end", e)))
3300                     .map(|(s, e)| {
3301                         let expr = P(self.lower_expr(&e));
3302                         let unstable_span =
3303                             self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3304                         let ident = Ident::new(Symbol::intern(s), unstable_span);
3305                         self.field(ident, expr, unstable_span)
3306                     })
3307                     .collect::<P<[hir::Field]>>();
3308
3309                 let is_unit = fields.is_empty();
3310                 let unstable_span =
3311                     self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3312                 let struct_path = iter::once("ops")
3313                     .chain(iter::once(path))
3314                     .collect::<Vec<_>>();
3315                 let struct_path = self.std_path(unstable_span, &struct_path, is_unit);
3316                 let struct_path = hir::QPath::Resolved(None, P(struct_path));
3317
3318                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3319
3320                 return hir::Expr {
3321                     id: node_id,
3322                     hir_id,
3323                     node: if is_unit {
3324                         hir::ExprPath(struct_path)
3325                     } else {
3326                         hir::ExprStruct(struct_path, fields, None)
3327                     },
3328                     span: unstable_span,
3329                     attrs: e.attrs.clone(),
3330                 };
3331             }
3332             ExprKind::Path(ref qself, ref path) => hir::ExprPath(self.lower_qpath(
3333                 e.id,
3334                 qself,
3335                 path,
3336                 ParamMode::Optional,
3337                 ImplTraitContext::Disallowed,
3338             )),
3339             ExprKind::Break(opt_label, ref opt_expr) => {
3340                 let destination = if self.is_in_loop_condition && opt_label.is_none() {
3341                     hir::Destination {
3342                         label: None,
3343                         target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
3344                     }
3345                 } else {
3346                     self.lower_loop_destination(opt_label.map(|label| (e.id, label)))
3347                 };
3348                 hir::ExprBreak(
3349                     destination,
3350                     opt_expr.as_ref().map(|x| P(self.lower_expr(x))),
3351                 )
3352             }
3353             ExprKind::Continue(opt_label) => {
3354                 hir::ExprAgain(if self.is_in_loop_condition && opt_label.is_none() {
3355                     hir::Destination {
3356                         label: None,
3357                         target_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
3358                     }
3359                 } else {
3360                     self.lower_loop_destination(opt_label.map(|label| (e.id, label)))
3361                 })
3362             }
3363             ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
3364             ExprKind::InlineAsm(ref asm) => {
3365                 let hir_asm = hir::InlineAsm {
3366                     inputs: asm.inputs.iter().map(|&(ref c, _)| c.clone()).collect(),
3367                     outputs: asm.outputs
3368                         .iter()
3369                         .map(|out| hir::InlineAsmOutput {
3370                             constraint: out.constraint.clone(),
3371                             is_rw: out.is_rw,
3372                             is_indirect: out.is_indirect,
3373                         })
3374                         .collect(),
3375                     asm: asm.asm.clone(),
3376                     asm_str_style: asm.asm_str_style,
3377                     clobbers: asm.clobbers.clone().into(),
3378                     volatile: asm.volatile,
3379                     alignstack: asm.alignstack,
3380                     dialect: asm.dialect,
3381                     ctxt: asm.ctxt,
3382                 };
3383                 let outputs = asm.outputs
3384                     .iter()
3385                     .map(|out| self.lower_expr(&out.expr))
3386                     .collect();
3387                 let inputs = asm.inputs
3388                     .iter()
3389                     .map(|&(_, ref input)| self.lower_expr(input))
3390                     .collect();
3391                 hir::ExprInlineAsm(P(hir_asm), outputs, inputs)
3392             }
3393             ExprKind::Struct(ref path, ref fields, ref maybe_expr) => hir::ExprStruct(
3394                 self.lower_qpath(
3395                     e.id,
3396                     &None,
3397                     path,
3398                     ParamMode::Optional,
3399                     ImplTraitContext::Disallowed,
3400                 ),
3401                 fields.iter().map(|x| self.lower_field(x)).collect(),
3402                 maybe_expr.as_ref().map(|x| P(self.lower_expr(x))),
3403             ),
3404             ExprKind::Paren(ref ex) => {
3405                 let mut ex = self.lower_expr(ex);
3406                 // include parens in span, but only if it is a super-span.
3407                 if e.span.contains(ex.span) {
3408                     ex.span = e.span;
3409                 }
3410                 // merge attributes into the inner expression.
3411                 let mut attrs = e.attrs.clone();
3412                 attrs.extend::<Vec<_>>(ex.attrs.into());
3413                 ex.attrs = attrs;
3414                 return ex;
3415             }
3416
3417             ExprKind::Yield(ref opt_expr) => {
3418                 self.is_generator = true;
3419                 let expr = opt_expr
3420                     .as_ref()
3421                     .map(|x| self.lower_expr(x))
3422                     .unwrap_or_else(|| self.expr(e.span, hir::ExprTup(hir_vec![]), ThinVec::new()));
3423                 hir::ExprYield(P(expr))
3424             }
3425
3426             // Desugar ExprIfLet
3427             // From: `if let <pat> = <sub_expr> <body> [<else_opt>]`
3428             ExprKind::IfLet(ref pats, ref sub_expr, ref body, ref else_opt) => {
3429                 // to:
3430                 //
3431                 //   match <sub_expr> {
3432                 //     <pat> => <body>,
3433                 //     _ => [<else_opt> | ()]
3434                 //   }
3435
3436                 let mut arms = vec![];
3437
3438                 // `<pat> => <body>`
3439                 {
3440                     let body = self.lower_block(body, false);
3441                     let body_expr = P(self.expr_block(body, ThinVec::new()));
3442                     let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
3443                     arms.push(self.arm(pats, body_expr));
3444                 }
3445
3446                 // _ => [<else_opt>|()]
3447                 {
3448                     let wildcard_arm: Option<&Expr> = else_opt.as_ref().map(|p| &**p);
3449                     let wildcard_pattern = self.pat_wild(e.span);
3450                     let body = if let Some(else_expr) = wildcard_arm {
3451                         P(self.lower_expr(else_expr))
3452                     } else {
3453                         self.expr_tuple(e.span, hir_vec![])
3454                     };
3455                     arms.push(self.arm(hir_vec![wildcard_pattern], body));
3456                 }
3457
3458                 let contains_else_clause = else_opt.is_some();
3459
3460                 let sub_expr = P(self.lower_expr(sub_expr));
3461
3462                 hir::ExprMatch(
3463                     sub_expr,
3464                     arms.into(),
3465                     hir::MatchSource::IfLetDesugar {
3466                         contains_else_clause,
3467                     },
3468                 )
3469             }
3470
3471             // Desugar ExprWhileLet
3472             // From: `[opt_ident]: while let <pat> = <sub_expr> <body>`
3473             ExprKind::WhileLet(ref pats, ref sub_expr, ref body, opt_label) => {
3474                 // to:
3475                 //
3476                 //   [opt_ident]: loop {
3477                 //     match <sub_expr> {
3478                 //       <pat> => <body>,
3479                 //       _ => break
3480                 //     }
3481                 //   }
3482
3483                 // Note that the block AND the condition are evaluated in the loop scope.
3484                 // This is done to allow `break` from inside the condition of the loop.
3485                 let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| {
3486                     (
3487                         this.lower_block(body, false),
3488                         this.expr_break(e.span, ThinVec::new()),
3489                         this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
3490                     )
3491                 });
3492
3493                 // `<pat> => <body>`
3494                 let pat_arm = {
3495                     let body_expr = P(self.expr_block(body, ThinVec::new()));
3496                     let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
3497                     self.arm(pats, body_expr)
3498                 };
3499
3500                 // `_ => break`
3501                 let break_arm = {
3502                     let pat_under = self.pat_wild(e.span);
3503                     self.arm(hir_vec![pat_under], break_expr)
3504                 };
3505
3506                 // `match <sub_expr> { ... }`
3507                 let arms = hir_vec![pat_arm, break_arm];
3508                 let match_expr = self.expr(
3509                     sub_expr.span,
3510                     hir::ExprMatch(sub_expr, arms, hir::MatchSource::WhileLetDesugar),
3511                     ThinVec::new(),
3512                 );
3513
3514                 // `[opt_ident]: loop { ... }`
3515                 let loop_block = P(self.block_expr(P(match_expr)));
3516                 let loop_expr = hir::ExprLoop(
3517                     loop_block,
3518                     self.lower_label(opt_label),
3519                     hir::LoopSource::WhileLet,
3520                 );
3521                 // add attributes to the outer returned expr node
3522                 loop_expr
3523             }
3524
3525             // Desugar ExprForLoop
3526             // From: `[opt_ident]: for <pat> in <head> <body>`
3527             ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
3528                 // to:
3529                 //
3530                 //   {
3531                 //     let result = match ::std::iter::IntoIterator::into_iter(<head>) {
3532                 //       mut iter => {
3533                 //         [opt_ident]: loop {
3534                 //           let mut __next;
3535                 //           match ::std::iter::Iterator::next(&mut iter) {
3536                 //             ::std::option::Option::Some(val) => __next = val,
3537                 //             ::std::option::Option::None => break
3538                 //           };
3539                 //           let <pat> = __next;
3540                 //           StmtExpr(<body>);
3541                 //         }
3542                 //       }
3543                 //     };
3544                 //     result
3545                 //   }
3546
3547                 // expand <head>
3548                 let head = self.lower_expr(head);
3549                 let head_sp = head.span;
3550
3551                 let iter = self.str_to_ident("iter");
3552
3553                 let next_ident = self.str_to_ident("__next");
3554                 let next_pat = self.pat_ident_binding_mode(
3555                     pat.span,
3556                     next_ident,
3557                     hir::BindingAnnotation::Mutable,
3558                 );
3559
3560                 // `::std::option::Option::Some(val) => next = val`
3561                 let pat_arm = {
3562                     let val_ident = self.str_to_ident("val");
3563                     let val_pat = self.pat_ident(pat.span, val_ident);
3564                     let val_expr = P(self.expr_ident(pat.span, val_ident, val_pat.id));
3565                     let next_expr = P(self.expr_ident(pat.span, next_ident, next_pat.id));
3566                     let assign = P(self.expr(
3567                         pat.span,
3568                         hir::ExprAssign(next_expr, val_expr),
3569                         ThinVec::new(),
3570                     ));
3571                     let some_pat = self.pat_some(pat.span, val_pat);
3572                     self.arm(hir_vec![some_pat], assign)
3573                 };
3574
3575                 // `::std::option::Option::None => break`
3576                 let break_arm = {
3577                     let break_expr =
3578                         self.with_loop_scope(e.id, |this| this.expr_break(e.span, ThinVec::new()));
3579                     let pat = self.pat_none(e.span);
3580                     self.arm(hir_vec![pat], break_expr)
3581                 };
3582
3583                 // `mut iter`
3584                 let iter_pat =
3585                     self.pat_ident_binding_mode(head_sp, iter, hir::BindingAnnotation::Mutable);
3586
3587                 // `match ::std::iter::Iterator::next(&mut iter) { ... }`
3588                 let match_expr = {
3589                     let iter = P(self.expr_ident(head_sp, iter, iter_pat.id));
3590                     let ref_mut_iter = self.expr_mut_addr_of(head_sp, iter);
3591                     let next_path = &["iter", "Iterator", "next"];
3592                     let next_path = P(self.expr_std_path(head_sp, next_path, ThinVec::new()));
3593                     let next_expr = P(self.expr_call(head_sp, next_path, hir_vec![ref_mut_iter]));
3594                     let arms = hir_vec![pat_arm, break_arm];
3595
3596                     P(self.expr(
3597                         head_sp,
3598                         hir::ExprMatch(next_expr, arms, hir::MatchSource::ForLoopDesugar),
3599                         ThinVec::new(),
3600                     ))
3601                 };
3602                 let match_stmt = respan(head_sp, hir::StmtExpr(match_expr, self.next_id().node_id));
3603
3604                 let next_expr = P(self.expr_ident(head_sp, next_ident, next_pat.id));
3605
3606                 // `let mut __next`
3607                 let next_let =
3608                     self.stmt_let_pat(head_sp, None, next_pat, hir::LocalSource::ForLoopDesugar);
3609
3610                 // `let <pat> = __next`
3611                 let pat = self.lower_pat(pat);
3612                 let pat_let = self.stmt_let_pat(
3613                     head_sp,
3614                     Some(next_expr),
3615                     pat,
3616                     hir::LocalSource::ForLoopDesugar,
3617                 );
3618
3619                 let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
3620                 let body_expr = P(self.expr_block(body_block, ThinVec::new()));
3621                 let body_stmt = respan(body.span, hir::StmtExpr(body_expr, self.next_id().node_id));
3622
3623                 let loop_block = P(self.block_all(
3624                     e.span,
3625                     hir_vec![next_let, match_stmt, pat_let, body_stmt],
3626                     None,
3627                 ));
3628
3629                 // `[opt_ident]: loop { ... }`
3630                 let loop_expr = hir::ExprLoop(
3631                     loop_block,
3632                     self.lower_label(opt_label),
3633                     hir::LoopSource::ForLoop,
3634                 );
3635                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3636                 let loop_expr = P(hir::Expr {
3637                     id: node_id,
3638                     hir_id,
3639                     node: loop_expr,
3640                     span: e.span,
3641                     attrs: ThinVec::new(),
3642                 });
3643
3644                 // `mut iter => { ... }`
3645                 let iter_arm = self.arm(hir_vec![iter_pat], loop_expr);
3646
3647                 // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
3648                 let into_iter_expr = {
3649                     let into_iter_path = &["iter", "IntoIterator", "into_iter"];
3650                     let into_iter = P(self.expr_std_path(head_sp, into_iter_path, ThinVec::new()));
3651                     P(self.expr_call(head_sp, into_iter, hir_vec![head]))
3652                 };
3653
3654                 let match_expr = P(self.expr_match(
3655                     head_sp,
3656                     into_iter_expr,
3657                     hir_vec![iter_arm],
3658                     hir::MatchSource::ForLoopDesugar,
3659                 ));
3660
3661                 // `{ let _result = ...; _result }`
3662                 // underscore prevents an unused_variables lint if the head diverges
3663                 let result_ident = self.str_to_ident("_result");
3664                 let (let_stmt, let_stmt_binding) =
3665                     self.stmt_let(e.span, false, result_ident, match_expr);
3666
3667                 let result = P(self.expr_ident(e.span, result_ident, let_stmt_binding));
3668                 let block = P(self.block_all(e.span, hir_vec![let_stmt], Some(result)));
3669                 // add the attributes to the outer returned expr node
3670                 return self.expr_block(block, e.attrs.clone());
3671             }
3672
3673             // Desugar ExprKind::Try
3674             // From: `<expr>?`
3675             ExprKind::Try(ref sub_expr) => {
3676                 // to:
3677                 //
3678                 // match Try::into_result(<expr>) {
3679                 //     Ok(val) => #[allow(unreachable_code)] val,
3680                 //     Err(err) => #[allow(unreachable_code)]
3681                 //                 // If there is an enclosing `catch {...}`
3682                 //                 break 'catch_target Try::from_error(From::from(err)),
3683                 //                 // Otherwise
3684                 //                 return Try::from_error(From::from(err)),
3685                 // }
3686
3687                 let unstable_span =
3688                     self.allow_internal_unstable(CompilerDesugaringKind::QuestionMark, e.span);
3689
3690                 // Try::into_result(<expr>)
3691                 let discr = {
3692                     // expand <expr>
3693                     let sub_expr = self.lower_expr(sub_expr);
3694
3695                     let path = &["ops", "Try", "into_result"];
3696                     let path = P(self.expr_std_path(unstable_span, path, ThinVec::new()));
3697                     P(self.expr_call(e.span, path, hir_vec![sub_expr]))
3698                 };
3699
3700                 // #[allow(unreachable_code)]
3701                 let attr = {
3702                     // allow(unreachable_code)
3703                     let allow = {
3704                         let allow_ident = Ident::from_str("allow").with_span_pos(e.span);
3705                         let uc_ident = Ident::from_str("unreachable_code").with_span_pos(e.span);
3706                         let uc_nested = attr::mk_nested_word_item(uc_ident);
3707                         attr::mk_list_item(e.span, allow_ident, vec![uc_nested])
3708                     };
3709                     attr::mk_spanned_attr_outer(e.span, attr::mk_attr_id(), allow)
3710                 };
3711                 let attrs = vec![attr];
3712
3713                 // Ok(val) => #[allow(unreachable_code)] val,
3714                 let ok_arm = {
3715                     let val_ident = self.str_to_ident("val");
3716                     let val_pat = self.pat_ident(e.span, val_ident);
3717                     let val_expr = P(self.expr_ident_with_attrs(
3718                         e.span,
3719                         val_ident,
3720                         val_pat.id,
3721                         ThinVec::from(attrs.clone()),
3722                     ));
3723                     let ok_pat = self.pat_ok(e.span, val_pat);
3724
3725                     self.arm(hir_vec![ok_pat], val_expr)
3726                 };
3727
3728                 // Err(err) => #[allow(unreachable_code)]
3729                 //             return Try::from_error(From::from(err)),
3730                 let err_arm = {
3731                     let err_ident = self.str_to_ident("err");
3732                     let err_local = self.pat_ident(e.span, err_ident);
3733                     let from_expr = {
3734                         let path = &["convert", "From", "from"];
3735                         let from = P(self.expr_std_path(e.span, path, ThinVec::new()));
3736                         let err_expr = self.expr_ident(e.span, err_ident, err_local.id);
3737
3738                         self.expr_call(e.span, from, hir_vec![err_expr])
3739                     };
3740                     let from_err_expr =
3741                         self.wrap_in_try_constructor("from_error", from_expr, unstable_span);
3742                     let thin_attrs = ThinVec::from(attrs);
3743                     let catch_scope = self.catch_scopes.last().map(|x| *x);
3744                     let ret_expr = if let Some(catch_node) = catch_scope {
3745                         P(self.expr(
3746                             e.span,
3747                             hir::ExprBreak(
3748                                 hir::Destination {
3749                                     label: None,
3750                                     target_id: Ok(catch_node),
3751                                 },
3752                                 Some(from_err_expr),
3753                             ),
3754                             thin_attrs,
3755                         ))
3756                     } else {
3757                         P(self.expr(e.span, hir::Expr_::ExprRet(Some(from_err_expr)), thin_attrs))
3758                     };
3759
3760                     let err_pat = self.pat_err(e.span, err_local);
3761                     self.arm(hir_vec![err_pat], ret_expr)
3762                 };
3763
3764                 hir::ExprMatch(
3765                     discr,
3766                     hir_vec![err_arm, ok_arm],
3767                     hir::MatchSource::TryDesugar,
3768                 )
3769             }
3770
3771             ExprKind::Mac(_) => panic!("Shouldn't exist here"),
3772         };
3773
3774         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3775
3776         hir::Expr {
3777             id: node_id,
3778             hir_id,
3779             node: kind,
3780             span: e.span,
3781             attrs: e.attrs.clone(),
3782         }
3783     }
3784
3785     fn lower_stmt(&mut self, s: &Stmt) -> SmallVector<hir::Stmt> {
3786         SmallVector::one(match s.node {
3787             StmtKind::Local(ref l) => Spanned {
3788                 node: hir::StmtDecl(
3789                     P(Spanned {
3790                         node: hir::DeclLocal(self.lower_local(l)),
3791                         span: s.span,
3792                     }),
3793                     self.lower_node_id(s.id).node_id,
3794                 ),
3795                 span: s.span,
3796             },
3797             StmtKind::Item(ref it) => {
3798                 // Can only use the ID once.
3799                 let mut id = Some(s.id);
3800                 return self.lower_item_id(it)
3801                     .into_iter()
3802                     .map(|item_id| Spanned {
3803                         node: hir::StmtDecl(
3804                             P(Spanned {
3805                                 node: hir::DeclItem(item_id),
3806                                 span: s.span,
3807                             }),
3808                             id.take()
3809                                 .map(|id| self.lower_node_id(id).node_id)
3810                                 .unwrap_or_else(|| self.next_id().node_id),
3811                         ),
3812                         span: s.span,
3813                     })
3814                     .collect();
3815             }
3816             StmtKind::Expr(ref e) => Spanned {
3817                 node: hir::StmtExpr(P(self.lower_expr(e)), self.lower_node_id(s.id).node_id),
3818                 span: s.span,
3819             },
3820             StmtKind::Semi(ref e) => Spanned {
3821                 node: hir::StmtSemi(P(self.lower_expr(e)), self.lower_node_id(s.id).node_id),
3822                 span: s.span,
3823             },
3824             StmtKind::Mac(..) => panic!("Shouldn't exist here"),
3825         })
3826     }
3827
3828     fn lower_capture_clause(&mut self, c: CaptureBy) -> hir::CaptureClause {
3829         match c {
3830             CaptureBy::Value => hir::CaptureByValue,
3831             CaptureBy::Ref => hir::CaptureByRef,
3832         }
3833     }
3834
3835     /// If an `explicit_owner` is given, this method allocates the `HirId` in
3836     /// the address space of that item instead of the item currently being
3837     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
3838     /// lower a `Visibility` value although we haven't lowered the owning
3839     /// `ImplItem` in question yet.
3840     fn lower_visibility(
3841         &mut self,
3842         v: &Visibility,
3843         explicit_owner: Option<NodeId>,
3844     ) -> hir::Visibility {
3845         match v.node {
3846             VisibilityKind::Public => hir::Public,
3847             VisibilityKind::Crate(sugar) => hir::Visibility::Crate(sugar),
3848             VisibilityKind::Restricted { ref path, id, .. } => hir::Visibility::Restricted {
3849                 path: P(self.lower_path(id, path, ParamMode::Explicit)),
3850                 id: if let Some(owner) = explicit_owner {
3851                     self.lower_node_id_with_owner(id, owner).node_id
3852                 } else {
3853                     self.lower_node_id(id).node_id
3854                 },
3855             },
3856             VisibilityKind::Inherited => hir::Inherited,
3857         }
3858     }
3859
3860     fn lower_defaultness(&mut self, d: Defaultness, has_value: bool) -> hir::Defaultness {
3861         match d {
3862             Defaultness::Default => hir::Defaultness::Default {
3863                 has_value: has_value,
3864             },
3865             Defaultness::Final => {
3866                 assert!(has_value);
3867                 hir::Defaultness::Final
3868             }
3869         }
3870     }
3871
3872     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
3873         match *b {
3874             BlockCheckMode::Default => hir::DefaultBlock,
3875             BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
3876         }
3877     }
3878
3879     fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
3880         match *b {
3881             BindingMode::ByValue(Mutability::Immutable) => hir::BindingAnnotation::Unannotated,
3882             BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
3883             BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
3884             BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
3885         }
3886     }
3887
3888     fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3889         match u {
3890             CompilerGenerated => hir::CompilerGenerated,
3891             UserProvided => hir::UserProvided,
3892         }
3893     }
3894
3895     fn lower_impl_polarity(&mut self, i: ImplPolarity) -> hir::ImplPolarity {
3896         match i {
3897             ImplPolarity::Positive => hir::ImplPolarity::Positive,
3898             ImplPolarity::Negative => hir::ImplPolarity::Negative,
3899         }
3900     }
3901
3902     fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3903         match f {
3904             TraitBoundModifier::None => hir::TraitBoundModifier::None,
3905             TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3906         }
3907     }
3908
3909     // Helper methods for building HIR.
3910
3911     fn arm(&mut self, pats: hir::HirVec<P<hir::Pat>>, expr: P<hir::Expr>) -> hir::Arm {
3912         hir::Arm {
3913             attrs: hir_vec![],
3914             pats,
3915             guard: None,
3916             body: expr,
3917         }
3918     }
3919
3920     fn field(&mut self, ident: Ident, expr: P<hir::Expr>, span: Span) -> hir::Field {
3921         hir::Field {
3922             id: self.next_id().node_id,
3923             ident,
3924             span,
3925             expr,
3926             is_shorthand: false,
3927         }
3928     }
3929
3930     fn expr_break(&mut self, span: Span, attrs: ThinVec<Attribute>) -> P<hir::Expr> {
3931         let expr_break = hir::ExprBreak(self.lower_loop_destination(None), None);
3932         P(self.expr(span, expr_break, attrs))
3933     }
3934
3935     fn expr_call(
3936         &mut self,
3937         span: Span,
3938         e: P<hir::Expr>,
3939         args: hir::HirVec<hir::Expr>,
3940     ) -> hir::Expr {
3941         self.expr(span, hir::ExprCall(e, args), ThinVec::new())
3942     }
3943
3944     fn expr_ident(&mut self, span: Span, id: Name, binding: NodeId) -> hir::Expr {
3945         self.expr_ident_with_attrs(span, id, binding, ThinVec::new())
3946     }
3947
3948     fn expr_ident_with_attrs(
3949         &mut self,
3950         span: Span,
3951         id: Name,
3952         binding: NodeId,
3953         attrs: ThinVec<Attribute>,
3954     ) -> hir::Expr {
3955         let expr_path = hir::ExprPath(hir::QPath::Resolved(
3956             None,
3957             P(hir::Path {
3958                 span,
3959                 def: Def::Local(binding),
3960                 segments: hir_vec![hir::PathSegment::from_name(id)],
3961             }),
3962         ));
3963
3964         self.expr(span, expr_path, attrs)
3965     }
3966
3967     fn expr_mut_addr_of(&mut self, span: Span, e: P<hir::Expr>) -> hir::Expr {
3968         self.expr(span, hir::ExprAddrOf(hir::MutMutable, e), ThinVec::new())
3969     }
3970
3971     fn expr_std_path(
3972         &mut self,
3973         span: Span,
3974         components: &[&str],
3975         attrs: ThinVec<Attribute>,
3976     ) -> hir::Expr {
3977         let path = self.std_path(span, components, true);
3978         self.expr(
3979             span,
3980             hir::ExprPath(hir::QPath::Resolved(None, P(path))),
3981             attrs,
3982         )
3983     }
3984
3985     fn expr_match(
3986         &mut self,
3987         span: Span,
3988         arg: P<hir::Expr>,
3989         arms: hir::HirVec<hir::Arm>,
3990         source: hir::MatchSource,
3991     ) -> hir::Expr {
3992         self.expr(span, hir::ExprMatch(arg, arms, source), ThinVec::new())
3993     }
3994
3995     fn expr_block(&mut self, b: P<hir::Block>, attrs: ThinVec<Attribute>) -> hir::Expr {
3996         self.expr(b.span, hir::ExprBlock(b, None), attrs)
3997     }
3998
3999     fn expr_tuple(&mut self, sp: Span, exprs: hir::HirVec<hir::Expr>) -> P<hir::Expr> {
4000         P(self.expr(sp, hir::ExprTup(exprs), ThinVec::new()))
4001     }
4002
4003     fn expr(&mut self, span: Span, node: hir::Expr_, attrs: ThinVec<Attribute>) -> hir::Expr {
4004         let LoweredNodeId { node_id, hir_id } = self.next_id();
4005         hir::Expr {
4006             id: node_id,
4007             hir_id,
4008             node,
4009             span,
4010             attrs,
4011         }
4012     }
4013
4014     fn stmt_let_pat(
4015         &mut self,
4016         sp: Span,
4017         ex: Option<P<hir::Expr>>,
4018         pat: P<hir::Pat>,
4019         source: hir::LocalSource,
4020     ) -> hir::Stmt {
4021         let LoweredNodeId { node_id, hir_id } = self.next_id();
4022
4023         let local = P(hir::Local {
4024             pat,
4025             ty: None,
4026             init: ex,
4027             id: node_id,
4028             hir_id,
4029             span: sp,
4030             attrs: ThinVec::new(),
4031             source,
4032         });
4033         let decl = respan(sp, hir::DeclLocal(local));
4034         respan(sp, hir::StmtDecl(P(decl), self.next_id().node_id))
4035     }
4036
4037     fn stmt_let(
4038         &mut self,
4039         sp: Span,
4040         mutbl: bool,
4041         ident: Name,
4042         ex: P<hir::Expr>,
4043     ) -> (hir::Stmt, NodeId) {
4044         let pat = if mutbl {
4045             self.pat_ident_binding_mode(sp, ident, hir::BindingAnnotation::Mutable)
4046         } else {
4047             self.pat_ident(sp, ident)
4048         };
4049         let pat_id = pat.id;
4050         (
4051             self.stmt_let_pat(sp, Some(ex), pat, hir::LocalSource::Normal),
4052             pat_id,
4053         )
4054     }
4055
4056     fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
4057         self.block_all(expr.span, hir::HirVec::new(), Some(expr))
4058     }
4059
4060     fn block_all(
4061         &mut self,
4062         span: Span,
4063         stmts: hir::HirVec<hir::Stmt>,
4064         expr: Option<P<hir::Expr>>,
4065     ) -> hir::Block {
4066         let LoweredNodeId { node_id, hir_id } = self.next_id();
4067
4068         hir::Block {
4069             stmts,
4070             expr,
4071             id: node_id,
4072             hir_id,
4073             rules: hir::DefaultBlock,
4074             span,
4075             targeted_by_break: false,
4076             recovered: false,
4077         }
4078     }
4079
4080     fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
4081         self.pat_std_enum(span, &["result", "Result", "Ok"], hir_vec![pat])
4082     }
4083
4084     fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
4085         self.pat_std_enum(span, &["result", "Result", "Err"], hir_vec![pat])
4086     }
4087
4088     fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
4089         self.pat_std_enum(span, &["option", "Option", "Some"], hir_vec![pat])
4090     }
4091
4092     fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
4093         self.pat_std_enum(span, &["option", "Option", "None"], hir_vec![])
4094     }
4095
4096     fn pat_std_enum(
4097         &mut self,
4098         span: Span,
4099         components: &[&str],
4100         subpats: hir::HirVec<P<hir::Pat>>,
4101     ) -> P<hir::Pat> {
4102         let path = self.std_path(span, components, true);
4103         let qpath = hir::QPath::Resolved(None, P(path));
4104         let pt = if subpats.is_empty() {
4105             hir::PatKind::Path(qpath)
4106         } else {
4107             hir::PatKind::TupleStruct(qpath, subpats, None)
4108         };
4109         self.pat(span, pt)
4110     }
4111
4112     fn pat_ident(&mut self, span: Span, name: Name) -> P<hir::Pat> {
4113         self.pat_ident_binding_mode(span, name, hir::BindingAnnotation::Unannotated)
4114     }
4115
4116     fn pat_ident_binding_mode(
4117         &mut self,
4118         span: Span,
4119         name: Name,
4120         bm: hir::BindingAnnotation,
4121     ) -> P<hir::Pat> {
4122         let LoweredNodeId { node_id, hir_id } = self.next_id();
4123
4124         P(hir::Pat {
4125             id: node_id,
4126             hir_id,
4127             node: hir::PatKind::Binding(bm, node_id, Spanned { span, node: name }, None),
4128             span,
4129         })
4130     }
4131
4132     fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
4133         self.pat(span, hir::PatKind::Wild)
4134     }
4135
4136     fn pat(&mut self, span: Span, pat: hir::PatKind) -> P<hir::Pat> {
4137         let LoweredNodeId { node_id, hir_id } = self.next_id();
4138         P(hir::Pat {
4139             id: node_id,
4140             hir_id,
4141             node: pat,
4142             span,
4143         })
4144     }
4145
4146     /// Given suffix ["b","c","d"], returns path `::std::b::c::d` when
4147     /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
4148     /// The path is also resolved according to `is_value`.
4149     fn std_path(&mut self, span: Span, components: &[&str], is_value: bool) -> hir::Path {
4150         self.resolver
4151             .resolve_str_path(span, self.crate_root, components, is_value)
4152     }
4153
4154     fn ty_path(&mut self, id: LoweredNodeId, span: Span, qpath: hir::QPath) -> P<hir::Ty> {
4155         let mut id = id;
4156         let node = match qpath {
4157             hir::QPath::Resolved(None, path) => {
4158                 // Turn trait object paths into `TyTraitObject` instead.
4159                 if let Def::Trait(_) = path.def {
4160                     let principal = hir::PolyTraitRef {
4161                         bound_generic_params: hir::HirVec::new(),
4162                         trait_ref: hir::TraitRef {
4163                             path: path.and_then(|path| path),
4164                             ref_id: id.node_id,
4165                         },
4166                         span,
4167                     };
4168
4169                     // The original ID is taken by the `PolyTraitRef`,
4170                     // so the `Ty` itself needs a different one.
4171                     id = self.next_id();
4172                     hir::TyTraitObject(hir_vec![principal], self.elided_dyn_bound(span))
4173                 } else {
4174                     hir::TyPath(hir::QPath::Resolved(None, path))
4175                 }
4176             }
4177             _ => hir::TyPath(qpath),
4178         };
4179         P(hir::Ty {
4180             id: id.node_id,
4181             hir_id: id.hir_id,
4182             node,
4183             span,
4184         })
4185     }
4186
4187     /// Invoked to create the lifetime argument for a type `&T`
4188     /// with no explicit lifetime.
4189     fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
4190         match self.anonymous_lifetime_mode {
4191             // Intercept when we are in an impl header and introduce an in-band lifetime.
4192             // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
4193             // `'f`.
4194             AnonymousLifetimeMode::CreateParameter => {
4195                 let fresh_name = self.collect_fresh_in_band_lifetime(span);
4196                 hir::Lifetime {
4197                     id: self.next_id().node_id,
4198                     span,
4199                     name: hir::LifetimeName::Param(fresh_name),
4200                 }
4201             }
4202
4203             AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
4204         }
4205     }
4206
4207     /// Invoked to create the lifetime argument(s) for a path like
4208     /// `std::cell::Ref<T>`; note that implicit lifetimes in these
4209     /// sorts of cases are deprecated. This may therefore report a warning or an
4210     /// error, depending on the mode.
4211     fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
4212         match self.anonymous_lifetime_mode {
4213             // NB. We intentionally ignore the create-parameter mode here
4214             // and instead "pass through" to resolve-lifetimes, which will then
4215             // report an error. This is because we don't want to support
4216             // impl elision for deprecated forms like
4217             //
4218             //     impl Foo for std::cell::Ref<u32> // note lack of '_
4219             AnonymousLifetimeMode::CreateParameter => {}
4220
4221             // This is the normal case.
4222             AnonymousLifetimeMode::PassThrough => {}
4223         }
4224
4225         (0..count)
4226             .map(|_| self.new_implicit_lifetime(span))
4227             .collect()
4228     }
4229
4230     /// Invoked to create the lifetime argument(s) for an elided trait object
4231     /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
4232     /// when the bound is written, even if it is written with `'_` like in
4233     /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
4234     fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
4235         match self.anonymous_lifetime_mode {
4236             // NB. We intentionally ignore the create-parameter mode here.
4237             // and instead "pass through" to resolve-lifetimes, which will apply
4238             // the object-lifetime-defaulting rules. Elided object lifetime defaults
4239             // do not act like other elided lifetimes. In other words, given this:
4240             //
4241             //     impl Foo for Box<dyn Debug>
4242             //
4243             // we do not introduce a fresh `'_` to serve as the bound, but instead
4244             // ultimately translate to the equivalent of:
4245             //
4246             //     impl Foo for Box<dyn Debug + 'static>
4247             //
4248             // `resolve_lifetime` has the code to make that happen.
4249             AnonymousLifetimeMode::CreateParameter => {}
4250
4251             // This is the normal case.
4252             AnonymousLifetimeMode::PassThrough => {}
4253         }
4254
4255         self.new_implicit_lifetime(span)
4256     }
4257
4258     fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
4259         hir::Lifetime {
4260             id: self.next_id().node_id,
4261             span,
4262             name: hir::LifetimeName::Implicit,
4263         }
4264     }
4265
4266     fn maybe_lint_bare_trait(&self, span: Span, id: NodeId, is_global: bool) {
4267         self.sess.buffer_lint_with_diagnostic(
4268             builtin::BARE_TRAIT_OBJECTS,
4269             id,
4270             span,
4271             "trait objects without an explicit `dyn` are deprecated",
4272             builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
4273         )
4274     }
4275
4276     fn wrap_in_try_constructor(
4277         &mut self,
4278         method: &'static str,
4279         e: hir::Expr,
4280         unstable_span: Span,
4281     ) -> P<hir::Expr> {
4282         let path = &["ops", "Try", method];
4283         let from_err = P(self.expr_std_path(unstable_span, path,
4284                                             ThinVec::new()));
4285         P(self.expr_call(e.span, from_err, hir_vec![e]))
4286     }
4287 }
4288
4289 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
4290     // Sorting by span ensures that we get things in order within a
4291     // file, and also puts the files in a sensible order.
4292     let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
4293     body_ids.sort_by_key(|b| bodies[b].value.span);
4294     body_ids
4295 }