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;
  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};
  49 use lint::builtin::{self, PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES};
  50 use middle::cstore::CrateStore;
  51 use rustc_data_structures::indexed_vec::IndexVec;
  52 use session::Session;
  53 use util::common::FN_OUTPUT_NAME;
  54 use util::nodemap::{DefIdMap, FxHashMap, NodeMap};
  55
  56 use std::collections::{BTreeMap, HashSet};
  57 use std::fmt::Debug;
  58 use std::iter;
  59 use std::mem;
  60 use syntax::attr;
  61 use syntax::ast::*;
  62 use syntax::errors;
  63 use syntax::ext::hygiene::{Mark, SyntaxContext};
  64 use syntax::print::pprust;
  65 use syntax::ptr::P;
  66 use syntax::codemap::{self, respan, CompilerDesugaringKind, Spanned};
  67 use syntax::std_inject;
  68 use syntax::symbol::{keywords, Symbol};
  69 use syntax::tokenstream::{Delimited, TokenStream, TokenTree};
  70 use syntax::parse::token::Token;
  71 use syntax::util::small_vector::SmallVector;
  72 use syntax::visit::{self, Visitor};
  73 use syntax_pos::Span;
  74
  75 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
  76
  77 pub struct LoweringContext<'a> {
  78     crate_root: Option<&'static str>,
  79
  80     // Use to assign ids to hir nodes that do not directly correspond to an ast node
  81     sess: &'a Session,
  82
  83     cstore: &'a CrateStore,
  84
  85     // As we walk the AST we must keep track of the current 'parent' def id (in
  86     // the form of a DefIndex) so that if we create a new node which introduces
  87     // a definition, then we can properly create the def id.
  88     parent_def: Option<DefIndex>,
  89     resolver: &'a mut Resolver,
  90     name_map: FxHashMap<Ident, Name>,
  91
  92     /// The items being lowered are collected here.
  93     items: BTreeMap<NodeId, hir::Item>,
  94
  95     trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
  96     impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
  97     bodies: BTreeMap<hir::BodyId, hir::Body>,
  98     exported_macros: Vec<hir::MacroDef>,
  99
 100     trait_impls: BTreeMap<DefId, Vec<NodeId>>,
 101     trait_auto_impl: BTreeMap<DefId, NodeId>,
 102
 103     is_generator: bool,
 104
 105     catch_scopes: Vec<NodeId>,
 106     loop_scopes: Vec<NodeId>,
 107     is_in_loop_condition: bool,
 108     is_in_trait_impl: bool,
 109
 110     /// What to do when we encounter either an "anonymous lifetime
 111     /// reference". The term "anonymous" is meant to encompass both
 112     /// `'_` lifetimes as well as fully elided cases where nothing is
 113     /// written at all (e.g., `&T` or `std::cell::Ref<T>`).
 114     anonymous_lifetime_mode: AnonymousLifetimeMode,
 115
 116     // This is a list of in-band type definitions being generated by
 117     // Argument-position `impl Trait`.
 118     // When traversing a signature such as `fn foo(x: impl Trait)`,
 119     // we record `impl Trait` as a new type parameter, then later
 120     // add it on to `foo`s generics.
 121     in_band_ty_params: Vec<hir::TyParam>,
 122
 123     // Used to create lifetime definitions from in-band lifetime usages.
 124     // e.g. `fn foo(x: &'x u8) -> &'x u8` to `fn foo<'x>(x: &'x u8) -> &'x u8`
 125     // When a named lifetime is encountered in a function or impl header and
 126     // has not been defined
 127     // (i.e. it doesn't appear in the in_scope_lifetimes list), it is added
 128     // to this list. The results of this list are then added to the list of
 129     // lifetime definitions in the corresponding impl or function generics.
 130     lifetimes_to_define: Vec<(Span, hir::LifetimeName)>,
 131
 132     // Whether or not in-band lifetimes are being collected. This is used to
 133     // indicate whether or not we're in a place where new lifetimes will result
 134     // in in-band lifetime definitions, such a function or an impl header.
 135     // This will always be false unless the `in_band_lifetimes` feature is
 136     // enabled.
 137     is_collecting_in_band_lifetimes: bool,
 138
 139     // Currently in-scope lifetimes defined in impl headers, fn headers, or HRTB.
 140     // When `is_collectin_in_band_lifetimes` is true, each lifetime is checked
 141     // against this list to see if it is already in-scope, or if a definition
 142     // needs to be created for it.
 143     in_scope_lifetimes: Vec<Name>,
 144
 145     type_def_lifetime_params: DefIdMap<usize>,
 146
 147     current_hir_id_owner: Vec<(DefIndex, u32)>,
 148     item_local_id_counters: NodeMap<u32>,
 149     node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
 150 }
 151
 152 pub trait Resolver {
 153     /// Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
 154     fn resolve_hir_path(&mut self, path: &mut hir::Path, is_value: bool);
 155
 156     /// Obtain the resolution for a node id
 157     fn get_resolution(&mut self, id: NodeId) -> Option<PathResolution>;
 158
 159     /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
 160     /// This should only return `None` during testing.
 161     fn definitions(&mut self) -> &mut Definitions;
 162
 163     /// Given suffix ["b","c","d"], creates a HIR path for `[::crate_root]::b::c::d` and resolves
 164     /// it based on `is_value`.
 165     fn resolve_str_path(
 166         &mut self,
 167         span: Span,
 168         crate_root: Option<&str>,
 169         components: &[&str],
 170         is_value: bool,
 171     ) -> hir::Path;
 172 }
 173
 174 #[derive(Clone, Copy, Debug)]
 175 enum ImplTraitContext {
 176     /// Treat `impl Trait` as shorthand for a new universal generic parameter.
 177     /// Example: `fn foo(x: impl Debug)`, where `impl Debug` is conceptually
 178     /// equivalent to a fresh universal parameter like `fn foo<T: Debug>(x: T)`.
 179     ///
 180     /// We store a DefId here so we can look up necessary information later
 181     Universal(DefId),
 182
 183     /// Treat `impl Trait` as shorthand for a new universal existential parameter.
 184     /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
 185     /// equivalent to a fresh existential parameter like `abstract type T; fn foo() -> T`.
 186     Existential,
 187
 188     /// `impl Trait` is not accepted in this position.
 189     Disallowed,
 190 }
 191
 192 pub fn lower_crate(
 193     sess: &Session,
 194     cstore: &CrateStore,
 195     dep_graph: &DepGraph,
 196     krate: &Crate,
 197     resolver: &mut Resolver,
 198 ) -> hir::Crate {
 199     // We're constructing the HIR here; we don't care what we will
 200     // read, since we haven't even constructed the *input* to
 201     // incr. comp. yet.
 202     dep_graph.assert_ignored();
 203
 204     LoweringContext {
 205         crate_root: std_inject::injected_crate_name(),
 206         sess,
 207         cstore,
 208         parent_def: None,
 209         resolver,
 210         name_map: FxHashMap(),
 211         items: BTreeMap::new(),
 212         trait_items: BTreeMap::new(),
 213         impl_items: BTreeMap::new(),
 214         bodies: BTreeMap::new(),
 215         trait_impls: BTreeMap::new(),
 216         trait_auto_impl: BTreeMap::new(),
 217         exported_macros: Vec::new(),
 218         catch_scopes: Vec::new(),
 219         loop_scopes: Vec::new(),
 220         is_in_loop_condition: false,
 221         anonymous_lifetime_mode: AnonymousLifetimeMode::PassThrough,
 222         type_def_lifetime_params: DefIdMap(),
 223         current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
 224         item_local_id_counters: NodeMap(),
 225         node_id_to_hir_id: IndexVec::new(),
 226         is_generator: false,
 227         is_in_trait_impl: false,
 228         in_band_ty_params: Vec::new(),
 229         lifetimes_to_define: Vec::new(),
 230         is_collecting_in_band_lifetimes: false,
 231         in_scope_lifetimes: Vec::new(),
 232     }.lower_crate(krate)
 233 }
 234
 235 #[derive(Copy, Clone, PartialEq, Eq)]
 236 enum ParamMode {
 237     /// Any path in a type context.
 238     Explicit,
 239     /// The `module::Type` in `module::Type::method` in an expression.
 240     Optional,
 241 }
 242
 243 struct LoweredNodeId {
 244     node_id: NodeId,
 245     hir_id: hir::HirId,
 246 }
 247
 248 enum ParenthesizedGenericArgs {
 249     Ok,
 250     Warn,
 251     Err,
 252 }
 253
 254 /// What to do when we encounter an **anonymous** lifetime
 255 /// reference. Anonymous lifetime references come in two flavors.  You
 256 /// have implicit, or fully elided, references to lifetimes, like the
 257 /// one in `&T` or `Ref<T>`, and you have `'_` lifetimes, like `&'_ T`
 258 /// or `Ref<'_, T>`.  These often behave the same, but not always:
 259 ///
 260 /// - certain usages of implicit references are deprecated, like
 261 ///   `Ref<T>`, and we sometimes just give hard errors in those cases
 262 ///   as well.
 263 /// - for object bounds there is a difference: `Box<dyn Foo>` is not
 264 ///   the same as `Box<dyn Foo + '_>`.
 265 ///
 266 /// We describe the effects of the various modes in terms of three cases:
 267 ///
 268 /// - **Modern** -- includes all uses of `'_`, but also the lifetime arg
 269 ///   of a `&` (e.g., the missing lifetime in something like `&T`)
 270 /// - **Dyn Bound** -- if you have something like `Box<dyn Foo>`,
 271 ///   there is an elided lifetime bound (`Box<dyn Foo + 'X>`). These
 272 ///   elided bounds follow special rules. Note that this only covers
 273 ///   cases where *nothing* is written; the `'_` in `Box<dyn Foo +
 274 ///   '_>` is a case of "modern" elision.
 275 /// - **Deprecated** -- this coverse cases like `Ref<T>`, where the lifetime
 276 ///   parameter to ref is completely elided. `Ref<'_, T>` would be the modern,
 277 ///   non-deprecated equivalent.
 278 ///
 279 /// Currently, the handling of lifetime elision is somewhat spread out
 280 /// between HIR lowering and -- as described below -- the
 281 /// `resolve_lifetime` module. Often we "fallthrough" to that code by generating
 282 /// an "elided" or "underscore" lifetime name. In the future, we probably want to move
 283 /// everything into HIR lowering.
 284 #[derive(Copy, Clone)]
 285 enum AnonymousLifetimeMode {
 286     /// For **Modern** cases, create a new anonymous region parameter
 287     /// and reference that.
 288     ///
 289     /// For **Dyn Bound** cases, pass responsibility to
 290     /// `resolve_lifetime` code.
 291     ///
 292     /// For **Deprecated** cases, report an error.
 293     CreateParameter,
 294
 295     /// Pass responsibility to `resolve_lifetime` code for all cases.
 296     PassThrough,
 297 }
 298
 299 impl<'a> LoweringContext<'a> {
 300     fn lower_crate(mut self, c: &Crate) -> hir::Crate {
 301         /// Full-crate AST visitor that inserts into a fresh
 302         /// `LoweringContext` any information that may be
 303         /// needed from arbitrary locations in the crate.
 304         /// E.g. The number of lifetime generic parameters
 305         /// declared for every type and trait definition.
 306         struct MiscCollector<'lcx, 'interner: 'lcx> {
 307             lctx: &'lcx mut LoweringContext<'interner>,
 308         }
 309
 310         impl<'lcx, 'interner> Visitor<'lcx> for MiscCollector<'lcx, 'interner> {
 311             fn visit_item(&mut self, item: &'lcx Item) {
 312                 self.lctx.allocate_hir_id_counter(item.id, item);
 313
 314                 match item.node {
 315                     ItemKind::Struct(_, ref generics)
 316                     | ItemKind::Union(_, ref generics)
 317                     | ItemKind::Enum(_, ref generics)
 318                     | ItemKind::Ty(_, ref generics)
 319                     | ItemKind::Trait(_, _, ref generics, ..) => {
 320                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
 321                         let count = generics
 322                             .params
 323                             .iter()
 324                             .filter(|param| param.is_lifetime_param())
 325                             .count();
 326                         self.lctx.type_def_lifetime_params.insert(def_id, count);
 327                     }
 328                     _ => {}
 329                 }
 330                 visit::walk_item(self, item);
 331             }
 332
 333             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 334                 self.lctx.allocate_hir_id_counter(item.id, item);
 335                 visit::walk_trait_item(self, item);
 336             }
 337
 338             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 339                 self.lctx.allocate_hir_id_counter(item.id, item);
 340                 visit::walk_impl_item(self, item);
 341             }
 342         }
 343
 344         struct ItemLowerer<'lcx, 'interner: 'lcx> {
 345             lctx: &'lcx mut LoweringContext<'interner>,
 346         }
 347
 348         impl<'lcx, 'interner> ItemLowerer<'lcx, 'interner> {
 349             fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
 350             where
 351                 F: FnOnce(&mut Self),
 352             {
 353                 let old = self.lctx.is_in_trait_impl;
 354                 self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
 355                     false
 356                 } else {
 357                     true
 358                 };
 359                 f(self);
 360                 self.lctx.is_in_trait_impl = old;
 361             }
 362         }
 363
 364         impl<'lcx, 'interner> Visitor<'lcx> for ItemLowerer<'lcx, 'interner> {
 365             fn visit_item(&mut self, item: &'lcx Item) {
 366                 let mut item_lowered = true;
 367                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 368                     if let Some(hir_item) = lctx.lower_item(item) {
 369                         lctx.items.insert(item.id, hir_item);
 370                     } else {
 371                         item_lowered = false;
 372                     }
 373                 });
 374
 375                 if item_lowered {
 376                     let item_lifetimes = match self.lctx.items.get(&item.id).unwrap().node {
 377                         hir::Item_::ItemImpl(_, _, _, ref generics, ..)
 378                         | hir::Item_::ItemTrait(_, _, ref generics, ..) => {
 379                             generics.lifetimes().cloned().collect::<Vec<_>>()
 380                         }
 381                         _ => Vec::new(),
 382                     };
 383
 384                     self.lctx
 385                         .with_parent_impl_lifetime_defs(&item_lifetimes, |this| {
 386                             let this = &mut ItemLowerer { lctx: this };
 387                             if let ItemKind::Impl(_, _, _, _, ref opt_trait_ref, _, _) = item.node {
 388                                 this.with_trait_impl_ref(opt_trait_ref, |this| {
 389                                     visit::walk_item(this, item)
 390                                 });
 391                             } else {
 392                                 visit::walk_item(this, item);
 393                             }
 394                         });
 395                 }
 396             }
 397
 398             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 399                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 400                     let id = hir::TraitItemId { node_id: item.id };
 401                     let hir_item = lctx.lower_trait_item(item);
 402                     lctx.trait_items.insert(id, hir_item);
 403                 });
 404
 405                 visit::walk_trait_item(self, item);
 406             }
 407
 408             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 409                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 410                     let id = hir::ImplItemId { node_id: item.id };
 411                     let hir_item = lctx.lower_impl_item(item);
 412                     lctx.impl_items.insert(id, hir_item);
 413                 });
 414                 visit::walk_impl_item(self, item);
 415             }
 416         }
 417
 418         self.lower_node_id(CRATE_NODE_ID);
 419         debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
 420
 421         visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
 422         visit::walk_crate(&mut ItemLowerer { lctx: &mut self }, c);
 423
 424         let module = self.lower_mod(&c.module);
 425         let attrs = self.lower_attrs(&c.attrs);
 426         let body_ids = body_ids(&self.bodies);
 427
 428         self.resolver
 429             .definitions()
 430             .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
 431
 432         hir::Crate {
 433             module,
 434             attrs,
 435             span: c.span,
 436             exported_macros: hir::HirVec::from(self.exported_macros),
 437             items: self.items,
 438             trait_items: self.trait_items,
 439             impl_items: self.impl_items,
 440             bodies: self.bodies,
 441             body_ids,
 442             trait_impls: self.trait_impls,
 443             trait_auto_impl: self.trait_auto_impl,
 444         }
 445     }
 446
 447     fn allocate_hir_id_counter<T: Debug>(&mut self, owner: NodeId, debug: &T) {
 448         if self.item_local_id_counters.insert(owner, 0).is_some() {
 449             bug!(
 450                 "Tried to allocate item_local_id_counter for {:?} twice",
 451                 debug
 452             );
 453         }
 454         // Always allocate the first HirId for the owner itself
 455         self.lower_node_id_with_owner(owner, owner);
 456     }
 457
 458     fn lower_node_id_generic<F>(&mut self, ast_node_id: NodeId, alloc_hir_id: F) -> LoweredNodeId
 459     where
 460         F: FnOnce(&mut Self) -> hir::HirId,
 461     {
 462         if ast_node_id == DUMMY_NODE_ID {
 463             return LoweredNodeId {
 464                 node_id: DUMMY_NODE_ID,
 465                 hir_id: hir::DUMMY_HIR_ID,
 466             };
 467         }
 468
 469         let min_size = ast_node_id.as_usize() + 1;
 470
 471         if min_size > self.node_id_to_hir_id.len() {
 472             self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
 473         }
 474
 475         let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
 476
 477         if existing_hir_id == hir::DUMMY_HIR_ID {
 478             // Generate a new HirId
 479             let hir_id = alloc_hir_id(self);
 480             self.node_id_to_hir_id[ast_node_id] = hir_id;
 481             LoweredNodeId {
 482                 node_id: ast_node_id,
 483                 hir_id,
 484             }
 485         } else {
 486             LoweredNodeId {
 487                 node_id: ast_node_id,
 488                 hir_id: existing_hir_id,
 489             }
 490         }
 491     }
 492
 493     fn with_hir_id_owner<F>(&mut self, owner: NodeId, f: F)
 494     where
 495         F: FnOnce(&mut Self),
 496     {
 497         let counter = self.item_local_id_counters
 498             .insert(owner, HIR_ID_COUNTER_LOCKED)
 499             .unwrap();
 500         let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
 501         self.current_hir_id_owner.push((def_index, counter));
 502         f(self);
 503         let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
 504
 505         debug_assert!(def_index == new_def_index);
 506         debug_assert!(new_counter >= counter);
 507
 508         let prev = self.item_local_id_counters
 509             .insert(owner, new_counter)
 510             .unwrap();
 511         debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
 512     }
 513
 514     /// This method allocates a new HirId for the given NodeId and stores it in
 515     /// the LoweringContext's NodeId => HirId map.
 516     /// Take care not to call this method if the resulting HirId is then not
 517     /// actually used in the HIR, as that would trigger an assertion in the
 518     /// HirIdValidator later on, which makes sure that all NodeIds got mapped
 519     /// properly. Calling the method twice with the same NodeId is fine though.
 520     fn lower_node_id(&mut self, ast_node_id: NodeId) -> LoweredNodeId {
 521         self.lower_node_id_generic(ast_node_id, |this| {
 522             let &mut (def_index, ref mut local_id_counter) =
 523                 this.current_hir_id_owner.last_mut().unwrap();
 524             let local_id = *local_id_counter;
 525             *local_id_counter += 1;
 526             hir::HirId {
 527                 owner: def_index,
 528                 local_id: hir::ItemLocalId(local_id),
 529             }
 530         })
 531     }
 532
 533     fn lower_node_id_with_owner(&mut self, ast_node_id: NodeId, owner: NodeId) -> LoweredNodeId {
 534         self.lower_node_id_generic(ast_node_id, |this| {
 535             let local_id_counter = this.item_local_id_counters.get_mut(&owner).unwrap();
 536             let local_id = *local_id_counter;
 537
 538             // We want to be sure not to modify the counter in the map while it
 539             // is also on the stack. Otherwise we'll get lost updates when writing
 540             // back from the stack to the map.
 541             debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
 542
 543             *local_id_counter += 1;
 544             let def_index = this.resolver.definitions().opt_def_index(owner).unwrap();
 545
 546             hir::HirId {
 547                 owner: def_index,
 548                 local_id: hir::ItemLocalId(local_id),
 549             }
 550         })
 551     }
 552
 553     fn record_body(&mut self, value: hir::Expr, decl: Option<&FnDecl>) -> hir::BodyId {
 554         let body = hir::Body {
 555             arguments: decl.map_or(hir_vec![], |decl| {
 556                 decl.inputs.iter().map(|x| self.lower_arg(x)).collect()
 557             }),
 558             is_generator: self.is_generator,
 559             value,
 560         };
 561         let id = body.id();
 562         self.bodies.insert(id, body);
 563         id
 564     }
 565
 566     fn next_id(&mut self) -> LoweredNodeId {
 567         self.lower_node_id(self.sess.next_node_id())
 568     }
 569
 570     fn expect_full_def(&mut self, id: NodeId) -> Def {
 571         self.resolver.get_resolution(id).map_or(Def::Err, |pr| {
 572             if pr.unresolved_segments() != 0 {
 573                 bug!("path not fully resolved: {:?}", pr);
 574             }
 575             pr.base_def()
 576         })
 577     }
 578
 579     fn diagnostic(&self) -> &errors::Handler {
 580         self.sess.diagnostic()
 581     }
 582
 583     fn str_to_ident(&self, s: &'static str) -> Name {
 584         Symbol::gensym(s)
 585     }
 586
 587     fn allow_internal_unstable(&self, reason: CompilerDesugaringKind, span: Span) -> Span {
 588         let mark = Mark::fresh(Mark::root());
 589         mark.set_expn_info(codemap::ExpnInfo {
 590             call_site: span,
 591             callee: codemap::NameAndSpan {
 592                 format: codemap::CompilerDesugaring(reason),
 593                 span: Some(span),
 594                 allow_internal_unstable: true,
 595                 allow_internal_unsafe: false,
 596             },
 597         });
 598         span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
 599     }
 600
 601     /// Creates a new hir::GenericParam for every new lifetime and
 602     /// type parameter encountered while evaluating `f`. Definitions
 603     /// are created with the parent provided. If no `parent_id` is
 604     /// provided, no definitions will be returned.
 605     ///
 606     /// Presuming that in-band lifetimes are enabled, then
 607     /// `self.anonymous_lifetime_mode` will be updated to match the
 608     /// argument while `f` is running (and restored afterwards).
 609     fn collect_in_band_defs<T, F>(
 610         &mut self,
 611         parent_id: DefId,
 612         anonymous_lifetime_mode: AnonymousLifetimeMode,
 613         f: F,
 614     ) -> (Vec<hir::GenericParam>, T)
 615     where
 616         F: FnOnce(&mut LoweringContext) -> T,
 617     {
 618         assert!(!self.is_collecting_in_band_lifetimes);
 619         assert!(self.lifetimes_to_define.is_empty());
 620         let old_anonymous_lifetime_mode = self.anonymous_lifetime_mode;
 621
 622         self.is_collecting_in_band_lifetimes = self.sess.features_untracked().in_band_lifetimes;
 623         if self.is_collecting_in_band_lifetimes {
 624             self.anonymous_lifetime_mode = anonymous_lifetime_mode;
 625         }
 626
 627         assert!(self.in_band_ty_params.is_empty());
 628         let res = f(self);
 629
 630         self.is_collecting_in_band_lifetimes = false;
 631         self.anonymous_lifetime_mode = old_anonymous_lifetime_mode;
 632
 633         let in_band_ty_params = self.in_band_ty_params.split_off(0);
 634         let lifetimes_to_define = self.lifetimes_to_define.split_off(0);
 635
 636         let params = lifetimes_to_define
 637             .into_iter()
 638             .map(|(span, hir_name)| {
 639                 let def_node_id = self.next_id().node_id;
 640
 641                 // Get the name we'll use to make the def-path. Note
 642                 // that collisions are ok here and this shouldn't
 643                 // really show up for end-user.
 644                 let str_name = match hir_name {
 645                     hir::LifetimeName::Name(n) => n.as_str(),
 646                     hir::LifetimeName::Fresh(_) => keywords::UnderscoreLifetime.name().as_str(),
 647                     hir::LifetimeName::Implicit
 648                     | hir::LifetimeName::Underscore
 649                     | hir::LifetimeName::Static => {
 650                         span_bug!(span, "unexpected in-band lifetime name: {:?}", hir_name)
 651                     }
 652                 };
 653
 654                 // Add a definition for the in-band lifetime def
 655                 self.resolver.definitions().create_def_with_parent(
 656                     parent_id.index,
 657                     def_node_id,
 658                     DefPathData::LifetimeDef(str_name.as_interned_str()),
 659                     DefIndexAddressSpace::High,
 660                     Mark::root(),
 661                     span,
 662                 );
 663
 664                 hir::GenericParam::Lifetime(hir::LifetimeDef {
 665                     lifetime: hir::Lifetime {
 666                         id: def_node_id,
 667                         span,
 668                         name: hir_name,
 669                     },
 670                     bounds: Vec::new().into(),
 671                     pure_wrt_drop: false,
 672                     in_band: true,
 673                 })
 674             })
 675             .chain(
 676                 in_band_ty_params
 677                     .into_iter()
 678                     .map(|tp| hir::GenericParam::Type(tp)),
 679             )
 680             .collect();
 681
 682         (params, res)
 683     }
 684
 685     /// When there is a reference to some lifetime `'a`, and in-band
 686     /// lifetimes are enabled, then we want to push that lifetime into
 687     /// the vector of names to define later. In that case, it will get
 688     /// added to the appropriate generics.
 689     fn maybe_collect_in_band_lifetime(&mut self, span: Span, name: Name) {
 690         if !self.is_collecting_in_band_lifetimes {
 691             return;
 692         }
 693
 694         if self.in_scope_lifetimes.contains(&name) {
 695             return;
 696         }
 697
 698         let hir_name = hir::LifetimeName::Name(name);
 699
 700         if self.lifetimes_to_define
 701             .iter()
 702             .any(|(_, lt_name)| *lt_name == hir_name)
 703         {
 704             return;
 705         }
 706
 707         self.lifetimes_to_define.push((span, hir_name));
 708     }
 709
 710     /// When we have either an elided or `'_` lifetime in an impl
 711     /// header, we convert it to
 712     fn collect_fresh_in_band_lifetime(&mut self, span: Span) -> hir::LifetimeName {
 713         assert!(self.is_collecting_in_band_lifetimes);
 714         let index = self.lifetimes_to_define.len();
 715         let hir_name = hir::LifetimeName::Fresh(index);
 716         self.lifetimes_to_define.push((span, hir_name));
 717         hir_name
 718     }
 719
 720     // Evaluates `f` with the lifetimes in `lt_defs` in-scope.
 721     // This is used to track which lifetimes have already been defined, and
 722     // which are new in-band lifetimes that need to have a definition created
 723     // for them.
 724     fn with_in_scope_lifetime_defs<'l, T, F>(
 725         &mut self,
 726         lt_defs: impl Iterator<Item = &'l LifetimeDef>,
 727         f: F,
 728     ) -> T
 729     where
 730         F: FnOnce(&mut LoweringContext) -> T,
 731     {
 732         let old_len = self.in_scope_lifetimes.len();
 733         let lt_def_names = lt_defs.map(|lt_def| lt_def.lifetime.ident.name);
 734         self.in_scope_lifetimes.extend(lt_def_names);
 735
 736         let res = f(self);
 737
 738         self.in_scope_lifetimes.truncate(old_len);
 739         res
 740     }
 741
 742     // Same as the method above, but accepts `hir::LifetimeDef`s
 743     // instead of `ast::LifetimeDef`s.
 744     // This should only be used with generics that have already had their
 745     // in-band lifetimes added. In practice, this means that this function is
 746     // only used when lowering a child item of a trait or impl.
 747     fn with_parent_impl_lifetime_defs<T, F>(&mut self, lt_defs: &[hir::LifetimeDef], 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 = lt_defs.iter().map(|lt_def| lt_def.lifetime.name.name());
 753         self.in_scope_lifetimes.extend(lt_def_names);
 754
 755         let res = f(self);
 756
 757         self.in_scope_lifetimes.truncate(old_len);
 758         res
 759     }
 760
 761     /// Appends in-band lifetime defs and argument-position `impl
 762     /// Trait` defs to the existing set of generics.
 763     ///
 764     /// Presuming that in-band lifetimes are enabled, then
 765     /// `self.anonymous_lifetime_mode` will be updated to match the
 766     /// argument while `f` is running (and restored afterwards).
 767     fn add_in_band_defs<F, T>(
 768         &mut self,
 769         generics: &Generics,
 770         parent_id: DefId,
 771         anonymous_lifetime_mode: AnonymousLifetimeMode,
 772         f: F,
 773     ) -> (hir::Generics, T)
 774     where
 775         F: FnOnce(&mut LoweringContext) -> T,
 776     {
 777         let (in_band_defs, (mut lowered_generics, res)) = self.with_in_scope_lifetime_defs(
 778             generics.params.iter().filter_map(|p| match p {
 779                 GenericParam::Lifetime(ld) => Some(ld),
 780                 _ => None,
 781             }),
 782             |this| {
 783                 let itctx = ImplTraitContext::Universal(parent_id);
 784                 this.collect_in_band_defs(parent_id, anonymous_lifetime_mode, |this| {
 785                     (this.lower_generics(generics, itctx), f(this))
 786                 })
 787             },
 788         );
 789
 790         lowered_generics.params = lowered_generics
 791             .params
 792             .iter()
 793             .cloned()
 794             .chain(in_band_defs)
 795             .collect();
 796
 797         (lowered_generics, res)
 798     }
 799
 800     fn with_catch_scope<T, F>(&mut self, catch_id: NodeId, f: F) -> T
 801     where
 802         F: FnOnce(&mut LoweringContext) -> T,
 803     {
 804         let len = self.catch_scopes.len();
 805         self.catch_scopes.push(catch_id);
 806
 807         let result = f(self);
 808         assert_eq!(
 809             len + 1,
 810             self.catch_scopes.len(),
 811             "catch scopes should be added and removed in stack order"
 812         );
 813
 814         self.catch_scopes.pop().unwrap();
 815
 816         result
 817     }
 818
 819     fn lower_body<F>(&mut self, decl: Option<&FnDecl>, f: F) -> hir::BodyId
 820     where
 821         F: FnOnce(&mut LoweringContext) -> hir::Expr,
 822     {
 823         let prev = mem::replace(&mut self.is_generator, false);
 824         let result = f(self);
 825         let r = self.record_body(result, decl);
 826         self.is_generator = prev;
 827         return r;
 828     }
 829
 830     fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
 831     where
 832         F: FnOnce(&mut LoweringContext) -> T,
 833     {
 834         // We're no longer in the base loop's condition; we're in another loop.
 835         let was_in_loop_condition = self.is_in_loop_condition;
 836         self.is_in_loop_condition = false;
 837
 838         let len = self.loop_scopes.len();
 839         self.loop_scopes.push(loop_id);
 840
 841         let result = f(self);
 842         assert_eq!(
 843             len + 1,
 844             self.loop_scopes.len(),
 845             "Loop scopes should be added and removed in stack order"
 846         );
 847
 848         self.loop_scopes.pop().unwrap();
 849
 850         self.is_in_loop_condition = was_in_loop_condition;
 851
 852         result
 853     }
 854
 855     fn with_loop_condition_scope<T, F>(&mut self, f: F) -> T
 856     where
 857         F: FnOnce(&mut LoweringContext) -> T,
 858     {
 859         let was_in_loop_condition = self.is_in_loop_condition;
 860         self.is_in_loop_condition = true;
 861
 862         let result = f(self);
 863
 864         self.is_in_loop_condition = was_in_loop_condition;
 865
 866         result
 867     }
 868
 869     fn with_new_scopes<T, F>(&mut self, f: F) -> T
 870     where
 871         F: FnOnce(&mut LoweringContext) -> T,
 872     {
 873         let was_in_loop_condition = self.is_in_loop_condition;
 874         self.is_in_loop_condition = false;
 875
 876         let catch_scopes = mem::replace(&mut self.catch_scopes, Vec::new());
 877         let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
 878         let result = f(self);
 879         self.catch_scopes = catch_scopes;
 880         self.loop_scopes = loop_scopes;
 881
 882         self.is_in_loop_condition = was_in_loop_condition;
 883
 884         result
 885     }
 886
 887     fn with_parent_def<T, F>(&mut self, parent_id: NodeId, f: F) -> T
 888     where
 889         F: FnOnce(&mut LoweringContext) -> T,
 890     {
 891         let old_def = self.parent_def;
 892         self.parent_def = {
 893             let defs = self.resolver.definitions();
 894             Some(defs.opt_def_index(parent_id).unwrap())
 895         };
 896
 897         let result = f(self);
 898
 899         self.parent_def = old_def;
 900         result
 901     }
 902
 903     fn def_key(&mut self, id: DefId) -> DefKey {
 904         if id.is_local() {
 905             self.resolver.definitions().def_key(id.index)
 906         } else {
 907             self.cstore.def_key(id)
 908         }
 909     }
 910
 911     fn lower_ident(&mut self, ident: Ident) -> Name {
 912         let ident = ident.modern();
 913         if ident.span.ctxt() == SyntaxContext::empty() {
 914             return ident.name;
 915         }
 916         *self.name_map
 917             .entry(ident)
 918             .or_insert_with(|| Symbol::from_ident(ident))
 919     }
 920
 921     fn lower_label(&mut self, label: Option<Label>) -> Option<hir::Label> {
 922         label.map(|label| hir::Label {
 923             name: label.ident.name,
 924             span: label.ident.span,
 925         })
 926     }
 927
 928     fn lower_loop_destination(&mut self, destination: Option<(NodeId, Label)>) -> hir::Destination {
 929         match destination {
 930             Some((id, label)) => {
 931                 let target = if let Def::Label(loop_id) = self.expect_full_def(id) {
 932                     hir::LoopIdResult::Ok(self.lower_node_id(loop_id).node_id)
 933                 } else {
 934                     hir::LoopIdResult::Err(hir::LoopIdError::UnresolvedLabel)
 935                 };
 936                 hir::Destination {
 937                     label: self.lower_label(Some(label)),
 938                     target_id: hir::ScopeTarget::Loop(target),
 939                 }
 940             }
 941             None => {
 942                 let loop_id = self.loop_scopes
 943                     .last()
 944                     .map(|innermost_loop_id| *innermost_loop_id);
 945
 946                 hir::Destination {
 947                     label: None,
 948                     target_id: hir::ScopeTarget::Loop(
 949                         loop_id
 950                             .map(|id| Ok(self.lower_node_id(id).node_id))
 951                             .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope))
 952                             .into(),
 953                     ),
 954                 }
 955             }
 956         }
 957     }
 958
 959     fn lower_attrs(&mut self, attrs: &[Attribute]) -> hir::HirVec<Attribute> {
 960         attrs
 961             .iter()
 962             .map(|a| self.lower_attr(a))
 963             .collect::<Vec<_>>()
 964             .into()
 965     }
 966
 967     fn lower_attr(&mut self, attr: &Attribute) -> Attribute {
 968         Attribute {
 969             id: attr.id,
 970             style: attr.style,
 971             path: attr.path.clone(),
 972             tokens: self.lower_token_stream(attr.tokens.clone()),
 973             is_sugared_doc: attr.is_sugared_doc,
 974             span: attr.span,
 975         }
 976     }
 977
 978     fn lower_token_stream(&mut self, tokens: TokenStream) -> TokenStream {
 979         tokens
 980             .into_trees()
 981             .flat_map(|tree| self.lower_token_tree(tree).into_trees())
 982             .collect()
 983     }
 984
 985     fn lower_token_tree(&mut self, tree: TokenTree) -> TokenStream {
 986         match tree {
 987             TokenTree::Token(span, token) => self.lower_token(token, span),
 988             TokenTree::Delimited(span, delimited) => TokenTree::Delimited(
 989                 span,
 990                 Delimited {
 991                     delim: delimited.delim,
 992                     tts: self.lower_token_stream(delimited.tts.into()).into(),
 993                 },
 994             ).into(),
 995         }
 996     }
 997
 998     fn lower_token(&mut self, token: Token, span: Span) -> TokenStream {
 999         match token {
1000             Token::Interpolated(_) => {}
1001             other => return TokenTree::Token(span, other).into(),
1002         }
1003
1004         let tts = token.interpolated_to_tokenstream(&self.sess.parse_sess, span);
1005         self.lower_token_stream(tts)
1006     }
1007
1008     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm {
1009         hir::Arm {
1010             attrs: self.lower_attrs(&arm.attrs),
1011             pats: arm.pats.iter().map(|x| self.lower_pat(x)).collect(),
1012             guard: arm.guard.as_ref().map(|ref x| P(self.lower_expr(x))),
1013             body: P(self.lower_expr(&arm.body)),
1014         }
1015     }
1016
1017     fn lower_ty_binding(&mut self, b: &TypeBinding, itctx: ImplTraitContext) -> hir::TypeBinding {
1018         hir::TypeBinding {
1019             id: self.lower_node_id(b.id).node_id,
1020             name: self.lower_ident(b.ident),
1021             ty: self.lower_ty(&b.ty, itctx),
1022             span: b.span,
1023         }
1024     }
1025
1026     fn lower_ty(&mut self, t: &Ty, itctx: ImplTraitContext) -> P<hir::Ty> {
1027         let kind = match t.node {
1028             TyKind::Infer => hir::TyInfer,
1029             TyKind::Err => hir::TyErr,
1030             TyKind::Slice(ref ty) => hir::TySlice(self.lower_ty(ty, itctx)),
1031             TyKind::Ptr(ref mt) => hir::TyPtr(self.lower_mt(mt, itctx)),
1032             TyKind::Rptr(ref region, ref mt) => {
1033                 let span = t.span.shrink_to_lo();
1034                 let lifetime = match *region {
1035                     Some(ref lt) => self.lower_lifetime(lt),
1036                     None => self.elided_ref_lifetime(span),
1037                 };
1038                 hir::TyRptr(lifetime, self.lower_mt(mt, itctx))
1039             }
1040             TyKind::BareFn(ref f) => self.with_in_scope_lifetime_defs(
1041                 f.generic_params.iter().filter_map(|p| match p {
1042                     GenericParam::Lifetime(ld) => Some(ld),
1043                     _ => None,
1044                 }),
1045                 |this| {
1046                     hir::TyBareFn(P(hir::BareFnTy {
1047                         generic_params: this.lower_generic_params(
1048                             &f.generic_params,
1049                             &NodeMap(),
1050                             ImplTraitContext::Disallowed,
1051                         ),
1052                         unsafety: this.lower_unsafety(f.unsafety),
1053                         abi: f.abi,
1054                         decl: this.lower_fn_decl(&f.decl, None, false),
1055                         arg_names: this.lower_fn_args_to_names(&f.decl),
1056                     }))
1057                 },
1058             ),
1059             TyKind::Never => hir::TyNever,
1060             TyKind::Tup(ref tys) => {
1061                 hir::TyTup(tys.iter().map(|ty| self.lower_ty(ty, itctx)).collect())
1062             }
1063             TyKind::Paren(ref ty) => {
1064                 return self.lower_ty(ty, itctx);
1065             }
1066             TyKind::Path(ref qself, ref path) => {
1067                 let id = self.lower_node_id(t.id);
1068                 let qpath = self.lower_qpath(t.id, qself, path, ParamMode::Explicit, itctx);
1069                 let ty = self.ty_path(id, t.span, qpath);
1070                 if let hir::TyTraitObject(..) = ty.node {
1071                     self.maybe_lint_bare_trait(t.span, t.id, qself.is_none() && path.is_global());
1072                 }
1073                 return ty;
1074             }
1075             TyKind::ImplicitSelf => hir::TyPath(hir::QPath::Resolved(
1076                 None,
1077                 P(hir::Path {
1078                     def: self.expect_full_def(t.id),
1079                     segments: hir_vec![hir::PathSegment::from_name(keywords::SelfType.name())],
1080                     span: t.span,
1081                 }),
1082             )),
1083             TyKind::Array(ref ty, ref length) => {
1084                 let length = self.lower_body(None, |this| this.lower_expr(length));
1085                 hir::TyArray(self.lower_ty(ty, itctx), length)
1086             }
1087             TyKind::Typeof(ref expr) => {
1088                 let expr = self.lower_body(None, |this| this.lower_expr(expr));
1089                 hir::TyTypeof(expr)
1090             }
1091             TyKind::TraitObject(ref bounds, kind) => {
1092                 let mut lifetime_bound = None;
1093                 let bounds = bounds
1094                     .iter()
1095                     .filter_map(|bound| match *bound {
1096                         TraitTyParamBound(ref ty, TraitBoundModifier::None) => {
1097                             Some(self.lower_poly_trait_ref(ty, itctx))
1098                         }
1099                         TraitTyParamBound(_, TraitBoundModifier::Maybe) => None,
1100                         RegionTyParamBound(ref lifetime) => {
1101                             if lifetime_bound.is_none() {
1102                                 lifetime_bound = Some(self.lower_lifetime(lifetime));
1103                             }
1104                             None
1105                         }
1106                     })
1107                     .collect();
1108                 let lifetime_bound =
1109                     lifetime_bound.unwrap_or_else(|| self.elided_dyn_bound(t.span));
1110                 if kind != TraitObjectSyntax::Dyn {
1111                     self.maybe_lint_bare_trait(t.span, t.id, false);
1112                 }
1113                 hir::TyTraitObject(bounds, lifetime_bound)
1114             }
1115             TyKind::ImplTrait(ref bounds) => {
1116                 let span = t.span;
1117                 match itctx {
1118                     ImplTraitContext::Existential => {
1119                         let def_index = self.resolver.definitions().opt_def_index(t.id).unwrap();
1120                         let hir_bounds = self.lower_bounds(bounds, itctx);
1121                         let (lifetimes, lifetime_defs) =
1122                             self.lifetimes_from_impl_trait_bounds(def_index, &hir_bounds);
1123
1124                         hir::TyImplTraitExistential(
1125                             hir::ExistTy {
1126                                 generics: hir::Generics {
1127                                     params: lifetime_defs,
1128                                     where_clause: hir::WhereClause {
1129                                         id: self.next_id().node_id,
1130                                         predicates: Vec::new().into(),
1131                                     },
1132                                     span,
1133                                 },
1134                                 bounds: hir_bounds,
1135                             },
1136                             lifetimes,
1137                         )
1138                     }
1139                     ImplTraitContext::Universal(def_id) => {
1140                         let def_node_id = self.next_id().node_id;
1141
1142                         // Add a definition for the in-band TyParam
1143                         let def_index = self.resolver.definitions().create_def_with_parent(
1144                             def_id.index,
1145                             def_node_id,
1146                             DefPathData::ImplTrait,
1147                             DefIndexAddressSpace::High,
1148                             Mark::root(),
1149                             span,
1150                         );
1151
1152                         let hir_bounds = self.lower_bounds(bounds, itctx);
1153                         // Set the name to `impl Bound1 + Bound2`
1154                         let name = Symbol::intern(&pprust::ty_to_string(t));
1155                         self.in_band_ty_params.push(hir::TyParam {
1156                             name,
1157                             id: def_node_id,
1158                             bounds: hir_bounds,
1159                             default: None,
1160                             span,
1161                             pure_wrt_drop: false,
1162                             synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
1163                             attrs: P::new(),
1164                         });
1165
1166                         hir::TyPath(hir::QPath::Resolved(
1167                             None,
1168                             P(hir::Path {
1169                                 span,
1170                                 def: Def::TyParam(DefId::local(def_index)),
1171                                 segments: hir_vec![hir::PathSegment::from_name(name)],
1172                             }),
1173                         ))
1174                     }
1175                     ImplTraitContext::Disallowed => {
1176                         span_err!(
1177                             self.sess,
1178                             t.span,
1179                             E0562,
1180                             "`impl Trait` not allowed outside of function \
1181                              and inherent method return types"
1182                         );
1183                         hir::TyErr
1184                     }
1185                 }
1186             }
1187             TyKind::Mac(_) => panic!("TyMac should have been expanded by now."),
1188         };
1189
1190         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(t.id);
1191         P(hir::Ty {
1192             id: node_id,
1193             node: kind,
1194             span: t.span,
1195             hir_id,
1196         })
1197     }
1198
1199     fn lifetimes_from_impl_trait_bounds(
1200         &mut self,
1201         parent_index: DefIndex,
1202         bounds: &hir::TyParamBounds,
1203     ) -> (HirVec<hir::Lifetime>, HirVec<hir::GenericParam>) {
1204         // This visitor walks over impl trait bounds and creates defs for all lifetimes which
1205         // appear in the bounds, excluding lifetimes that are created within the bounds.
1206         // e.g. 'a, 'b, but not 'c in `impl for<'c> SomeTrait<'a, 'b, 'c>`
1207         struct ImplTraitLifetimeCollector<'r, 'a: 'r> {
1208             context: &'r mut LoweringContext<'a>,
1209             parent: DefIndex,
1210             collect_elided_lifetimes: bool,
1211             currently_bound_lifetimes: Vec<hir::LifetimeName>,
1212             already_defined_lifetimes: HashSet<hir::LifetimeName>,
1213             output_lifetimes: Vec<hir::Lifetime>,
1214             output_lifetime_params: Vec<hir::GenericParam>,
1215         }
1216
1217         impl<'r, 'a: 'r, 'v> hir::intravisit::Visitor<'v> for ImplTraitLifetimeCollector<'r, 'a> {
1218             fn nested_visit_map<'this>(
1219                 &'this mut self,
1220             ) -> hir::intravisit::NestedVisitorMap<'this, 'v> {
1221                 hir::intravisit::NestedVisitorMap::None
1222             }
1223
1224             fn visit_path_parameters(&mut self, span: Span, parameters: &'v hir::PathParameters) {
1225                 // Don't collect elided lifetimes used inside of `Fn()` syntax.
1226                 if parameters.parenthesized {
1227                     let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1228                     self.collect_elided_lifetimes = false;
1229                     hir::intravisit::walk_path_parameters(self, span, parameters);
1230                     self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1231                 } else {
1232                     hir::intravisit::walk_path_parameters(self, span, parameters);
1233                 }
1234             }
1235
1236             fn visit_ty(&mut self, t: &'v hir::Ty) {
1237                 // Don't collect elided lifetimes used inside of `fn()` syntax
1238                 if let &hir::Ty_::TyBareFn(_) = &t.node {
1239                     let old_collect_elided_lifetimes = self.collect_elided_lifetimes;
1240                     self.collect_elided_lifetimes = false;
1241                     hir::intravisit::walk_ty(self, t);
1242                     self.collect_elided_lifetimes = old_collect_elided_lifetimes;
1243                 } else {
1244                     hir::intravisit::walk_ty(self, t);
1245                 }
1246             }
1247
1248             fn visit_poly_trait_ref(
1249                 &mut self,
1250                 polytr: &'v hir::PolyTraitRef,
1251                 _: hir::TraitBoundModifier,
1252             ) {
1253                 let old_len = self.currently_bound_lifetimes.len();
1254
1255                 // Record the introduction of 'a in `for<'a> ...`
1256                 for param in &polytr.bound_generic_params {
1257                     if let hir::GenericParam::Lifetime(ref lt_def) = *param {
1258                         // Introduce lifetimes one at a time so that we can handle
1259                         // cases like `fn foo<'d>() -> impl for<'a, 'b: 'a, 'c: 'b + 'd>`
1260                         self.currently_bound_lifetimes.push(lt_def.lifetime.name);
1261
1262                         // Visit the lifetime bounds
1263                         for lt_bound in &lt_def.bounds {
1264                             self.visit_lifetime(&lt_bound);
1265                         }
1266                     }
1267                 }
1268
1269                 hir::intravisit::walk_trait_ref(self, &polytr.trait_ref);
1270
1271                 self.currently_bound_lifetimes.truncate(old_len);
1272             }
1273
1274             fn visit_lifetime(&mut self, lifetime: &'v hir::Lifetime) {
1275                 let name = match lifetime.name {
1276                     hir::LifetimeName::Implicit | hir::LifetimeName::Underscore => {
1277                         if self.collect_elided_lifetimes {
1278                             // Use `'_` for both implicit and underscore lifetimes in
1279                             // `abstract type Foo<'_>: SomeTrait<'_>;`
1280                             hir::LifetimeName::Underscore
1281                         } else {
1282                             return;
1283                         }
1284                     }
1285                     name @ hir::LifetimeName::Fresh(_) => name,
1286                     name @ hir::LifetimeName::Name(_) => name,
1287                     hir::LifetimeName::Static => return,
1288                 };
1289
1290                 if !self.currently_bound_lifetimes.contains(&name)
1291                     && !self.already_defined_lifetimes.contains(&name)
1292                 {
1293                     self.already_defined_lifetimes.insert(name);
1294
1295                     self.output_lifetimes.push(hir::Lifetime {
1296                         id: self.context.next_id().node_id,
1297                         span: lifetime.span,
1298                         name,
1299                     });
1300
1301                     let def_node_id = self.context.next_id().node_id;
1302                     self.context.resolver.definitions().create_def_with_parent(
1303                         self.parent,
1304                         def_node_id,
1305                         DefPathData::LifetimeDef(name.name().as_interned_str()),
1306                         DefIndexAddressSpace::High,
1307                         Mark::root(),
1308                         lifetime.span,
1309                     );
1310                     let def_lifetime = hir::Lifetime {
1311                         id: def_node_id,
1312                         span: lifetime.span,
1313                         name: name,
1314                     };
1315                     self.output_lifetime_params
1316                         .push(hir::GenericParam::Lifetime(hir::LifetimeDef {
1317                             lifetime: def_lifetime,
1318                             bounds: Vec::new().into(),
1319                             pure_wrt_drop: false,
1320                             in_band: false,
1321                         }));
1322                 }
1323             }
1324         }
1325
1326         let mut lifetime_collector = ImplTraitLifetimeCollector {
1327             context: self,
1328             parent: parent_index,
1329             collect_elided_lifetimes: true,
1330             currently_bound_lifetimes: Vec::new(),
1331             already_defined_lifetimes: HashSet::new(),
1332             output_lifetimes: Vec::new(),
1333             output_lifetime_params: Vec::new(),
1334         };
1335
1336         for bound in bounds {
1337             hir::intravisit::walk_ty_param_bound(&mut lifetime_collector, &bound);
1338         }
1339
1340         (
1341             lifetime_collector.output_lifetimes.into(),
1342             lifetime_collector.output_lifetime_params.into(),
1343         )
1344     }
1345
1346     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
1347         hir::ForeignMod {
1348             abi: fm.abi,
1349             items: fm.items
1350                 .iter()
1351                 .map(|x| self.lower_foreign_item(x))
1352                 .collect(),
1353         }
1354     }
1355
1356     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
1357         P(hir::GlobalAsm {
1358             asm: ga.asm,
1359             ctxt: ga.ctxt,
1360         })
1361     }
1362
1363     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
1364         Spanned {
1365             node: hir::Variant_ {
1366                 name: v.node.ident.name,
1367                 attrs: self.lower_attrs(&v.node.attrs),
1368                 data: self.lower_variant_data(&v.node.data),
1369                 disr_expr: v.node
1370                     .disr_expr
1371                     .as_ref()
1372                     .map(|e| self.lower_body(None, |this| this.lower_expr(e))),
1373             },
1374             span: v.span,
1375         }
1376     }
1377
1378     fn lower_qpath(
1379         &mut self,
1380         id: NodeId,
1381         qself: &Option<QSelf>,
1382         p: &Path,
1383         param_mode: ParamMode,
1384         itctx: ImplTraitContext,
1385     ) -> hir::QPath {
1386         let qself_position = qself.as_ref().map(|q| q.position);
1387         let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx));
1388
1389         let resolution = self.resolver
1390             .get_resolution(id)
1391             .unwrap_or(PathResolution::new(Def::Err));
1392
1393         let proj_start = p.segments.len() - resolution.unresolved_segments();
1394         let path = P(hir::Path {
1395             def: resolution.base_def(),
1396             segments: p.segments[..proj_start]
1397                 .iter()
1398                 .enumerate()
1399                 .map(|(i, segment)| {
1400                     let param_mode = match (qself_position, param_mode) {
1401                         (Some(j), ParamMode::Optional) if i < j => {
1402                             // This segment is part of the trait path in a
1403                             // qualified path - one of `a`, `b` or `Trait`
1404                             // in `<X as a::b::Trait>::T::U::method`.
1405                             ParamMode::Explicit
1406                         }
1407                         _ => param_mode,
1408                     };
1409
1410                     // Figure out if this is a type/trait segment,
1411                     // which may need lifetime elision performed.
1412                     let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
1413                         krate: def_id.krate,
1414                         index: this.def_key(def_id).parent.expect("missing parent"),
1415                     };
1416                     let type_def_id = match resolution.base_def() {
1417                         Def::AssociatedTy(def_id) if i + 2 == proj_start => {
1418                             Some(parent_def_id(self, def_id))
1419                         }
1420                         Def::Variant(def_id) if i + 1 == proj_start => {
1421                             Some(parent_def_id(self, def_id))
1422                         }
1423                         Def::Struct(def_id)
1424                         | Def::Union(def_id)
1425                         | Def::Enum(def_id)
1426                         | Def::TyAlias(def_id)
1427                         | Def::Trait(def_id) if i + 1 == proj_start =>
1428                         {
1429                             Some(def_id)
1430                         }
1431                         _ => None,
1432                     };
1433                     let parenthesized_generic_args = match resolution.base_def() {
1434                         // `a::b::Trait(Args)`
1435                         Def::Trait(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Ok,
1436                         // `a::b::Trait(Args)::TraitItem`
1437                         Def::Method(..) | Def::AssociatedConst(..) | Def::AssociatedTy(..)
1438                             if i + 2 == proj_start =>
1439                         {
1440                             ParenthesizedGenericArgs::Ok
1441                         }
1442                         // Avoid duplicated errors
1443                         Def::Err => ParenthesizedGenericArgs::Ok,
1444                         // An error
1445                         Def::Struct(..)
1446                         | Def::Enum(..)
1447                         | Def::Union(..)
1448                         | Def::TyAlias(..)
1449                         | Def::Variant(..) if i + 1 == proj_start =>
1450                         {
1451                             ParenthesizedGenericArgs::Err
1452                         }
1453                         // A warning for now, for compatibility reasons
1454                         _ => ParenthesizedGenericArgs::Warn,
1455                     };
1456
1457                     let num_lifetimes = type_def_id.map_or(0, |def_id| {
1458                         if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
1459                             return n;
1460                         }
1461                         assert!(!def_id.is_local());
1462                         let n = self.cstore
1463                             .item_generics_cloned_untracked(def_id, self.sess)
1464                             .regions
1465                             .len();
1466                         self.type_def_lifetime_params.insert(def_id, n);
1467                         n
1468                     });
1469                     self.lower_path_segment(
1470                         p.span,
1471                         segment,
1472                         param_mode,
1473                         num_lifetimes,
1474                         parenthesized_generic_args,
1475                         itctx,
1476                     )
1477                 })
1478                 .collect(),
1479             span: p.span,
1480         });
1481
1482         // Simple case, either no projections, or only fully-qualified.
1483         // E.g. `std::mem::size_of` or `<I as Iterator>::Item`.
1484         if resolution.unresolved_segments() == 0 {
1485             return hir::QPath::Resolved(qself, path);
1486         }
1487
1488         // Create the innermost type that we're projecting from.
1489         let mut ty = if path.segments.is_empty() {
1490             // If the base path is empty that means there exists a
1491             // syntactical `Self`, e.g. `&i32` in `<&i32>::clone`.
1492             qself.expect("missing QSelf for <T>::...")
1493         } else {
1494             // Otherwise, the base path is an implicit `Self` type path,
1495             // e.g. `Vec` in `Vec::new` or `<I as Iterator>::Item` in
1496             // `<I as Iterator>::Item::default`.
1497             let new_id = self.next_id();
1498             self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path))
1499         };
1500
1501         // Anything after the base path are associated "extensions",
1502         // out of which all but the last one are associated types,
1503         // e.g. for `std::vec::Vec::<T>::IntoIter::Item::clone`:
1504         // * base path is `std::vec::Vec<T>`
1505         // * "extensions" are `IntoIter`, `Item` and `clone`
1506         // * type nodes are:
1507         //   1. `std::vec::Vec<T>` (created above)
1508         //   2. `<std::vec::Vec<T>>::IntoIter`
1509         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
1510         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
1511         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
1512             let segment = P(self.lower_path_segment(
1513                 p.span,
1514                 segment,
1515                 param_mode,
1516                 0,
1517                 ParenthesizedGenericArgs::Warn,
1518                 itctx,
1519             ));
1520             let qpath = hir::QPath::TypeRelative(ty, segment);
1521
1522             // It's finished, return the extension of the right node type.
1523             if i == p.segments.len() - 1 {
1524                 return qpath;
1525             }
1526
1527             // Wrap the associated extension in another type node.
1528             let new_id = self.next_id();
1529             ty = self.ty_path(new_id, p.span, qpath);
1530         }
1531
1532         // Should've returned in the for loop above.
1533         span_bug!(
1534             p.span,
1535             "lower_qpath: no final extension segment in {}..{}",
1536             proj_start,
1537             p.segments.len()
1538         )
1539     }
1540
1541     fn lower_path_extra(
1542         &mut self,
1543         id: NodeId,
1544         p: &Path,
1545         name: Option<Name>,
1546         param_mode: ParamMode,
1547     ) -> hir::Path {
1548         hir::Path {
1549             def: self.expect_full_def(id),
1550             segments: p.segments
1551                 .iter()
1552                 .map(|segment| {
1553                     self.lower_path_segment(
1554                         p.span,
1555                         segment,
1556                         param_mode,
1557                         0,
1558                         ParenthesizedGenericArgs::Err,
1559                         ImplTraitContext::Disallowed,
1560                     )
1561                 })
1562                 .chain(name.map(|name| hir::PathSegment::from_name(name)))
1563                 .collect(),
1564             span: p.span,
1565         }
1566     }
1567
1568     fn lower_path(&mut self, id: NodeId, p: &Path, param_mode: ParamMode) -> hir::Path {
1569         self.lower_path_extra(id, p, None, param_mode)
1570     }
1571
1572     fn lower_path_segment(
1573         &mut self,
1574         path_span: Span,
1575         segment: &PathSegment,
1576         param_mode: ParamMode,
1577         expected_lifetimes: usize,
1578         parenthesized_generic_args: ParenthesizedGenericArgs,
1579         itctx: ImplTraitContext,
1580     ) -> hir::PathSegment {
1581         let (mut parameters, infer_types) = if let Some(ref parameters) = segment.parameters {
1582             let msg = "parenthesized parameters may only be used with a trait";
1583             match **parameters {
1584                 PathParameters::AngleBracketed(ref data) => {
1585                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
1586                 }
1587                 PathParameters::Parenthesized(ref data) => match parenthesized_generic_args {
1588                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
1589                     ParenthesizedGenericArgs::Warn => {
1590                         self.sess.buffer_lint(
1591                             PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
1592                             CRATE_NODE_ID,
1593                             data.span,
1594                             msg.into(),
1595                         );
1596                         (hir::PathParameters::none(), true)
1597                     }
1598                     ParenthesizedGenericArgs::Err => {
1599                         struct_span_err!(self.sess, data.span, E0214, "{}", msg)
1600                             .span_label(data.span, "only traits may use parentheses")
1601                             .emit();
1602                         (hir::PathParameters::none(), true)
1603                     }
1604                 },
1605             }
1606         } else {
1607             self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode, itctx)
1608         };
1609
1610         if !parameters.parenthesized && parameters.lifetimes.is_empty() {
1611             parameters.lifetimes = self.elided_path_lifetimes(path_span, expected_lifetimes);
1612         }
1613
1614         hir::PathSegment::new(
1615             self.lower_ident(segment.ident),
1616             parameters,
1617             infer_types,
1618         )
1619     }
1620
1621     fn lower_angle_bracketed_parameter_data(
1622         &mut self,
1623         data: &AngleBracketedParameterData,
1624         param_mode: ParamMode,
1625         itctx: ImplTraitContext,
1626     ) -> (hir::PathParameters, bool) {
1627         let &AngleBracketedParameterData {
1628             ref lifetimes,
1629             ref types,
1630             ref bindings,
1631             ..
1632         } = data;
1633         (
1634             hir::PathParameters {
1635                 lifetimes: self.lower_lifetimes(lifetimes),
1636                 types: types.iter().map(|ty| self.lower_ty(ty, itctx)).collect(),
1637                 bindings: bindings
1638                     .iter()
1639                     .map(|b| self.lower_ty_binding(b, itctx))
1640                     .collect(),
1641                 parenthesized: false,
1642             },
1643             types.is_empty() && param_mode == ParamMode::Optional,
1644         )
1645     }
1646
1647     fn lower_parenthesized_parameter_data(
1648         &mut self,
1649         data: &ParenthesizedParameterData,
1650     ) -> (hir::PathParameters, bool) {
1651         const DISALLOWED: ImplTraitContext = ImplTraitContext::Disallowed;
1652         let &ParenthesizedParameterData {
1653             ref inputs,
1654             ref output,
1655             span,
1656         } = data;
1657         let inputs = inputs
1658             .iter()
1659             .map(|ty| self.lower_ty(ty, DISALLOWED))
1660             .collect();
1661         let mk_tup = |this: &mut Self, tys, span| {
1662             let LoweredNodeId { node_id, hir_id } = this.next_id();
1663             P(hir::Ty {
1664                 node: hir::TyTup(tys),
1665                 id: node_id,
1666                 hir_id,
1667                 span,
1668             })
1669         };
1670
1671         (
1672             hir::PathParameters {
1673                 lifetimes: hir::HirVec::new(),
1674                 types: hir_vec![mk_tup(self, inputs, span)],
1675                 bindings: hir_vec![
1676                     hir::TypeBinding {
1677                         id: self.next_id().node_id,
1678                         name: Symbol::intern(FN_OUTPUT_NAME),
1679                         ty: output
1680                             .as_ref()
1681                             .map(|ty| self.lower_ty(&ty, DISALLOWED))
1682                             .unwrap_or_else(|| mk_tup(self, hir::HirVec::new(), span)),
1683                         span: output.as_ref().map_or(span, |ty| ty.span),
1684                     }
1685                 ],
1686                 parenthesized: true,
1687             },
1688             false,
1689         )
1690     }
1691
1692     fn lower_local(&mut self, l: &Local) -> P<hir::Local> {
1693         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(l.id);
1694         P(hir::Local {
1695             id: node_id,
1696             hir_id,
1697             ty: l.ty
1698                 .as_ref()
1699                 .map(|t| self.lower_ty(t, ImplTraitContext::Disallowed)),
1700             pat: self.lower_pat(&l.pat),
1701             init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
1702             span: l.span,
1703             attrs: l.attrs.clone(),
1704             source: hir::LocalSource::Normal,
1705         })
1706     }
1707
1708     fn lower_mutability(&mut self, m: Mutability) -> hir::Mutability {
1709         match m {
1710             Mutability::Mutable => hir::MutMutable,
1711             Mutability::Immutable => hir::MutImmutable,
1712         }
1713     }
1714
1715     fn lower_arg(&mut self, arg: &Arg) -> hir::Arg {
1716         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(arg.id);
1717         hir::Arg {
1718             id: node_id,
1719             hir_id,
1720             pat: self.lower_pat(&arg.pat),
1721         }
1722     }
1723
1724     fn lower_fn_args_to_names(&mut self, decl: &FnDecl) -> hir::HirVec<Spanned<Name>> {
1725         decl.inputs
1726             .iter()
1727             .map(|arg| match arg.pat.node {
1728                 PatKind::Ident(_, ident, None) => respan(ident.span, ident.name),
1729                 _ => respan(arg.pat.span, keywords::Invalid.name()),
1730             })
1731             .collect()
1732     }
1733
1734     fn lower_fn_decl(
1735         &mut self,
1736         decl: &FnDecl,
1737         fn_def_id: Option<DefId>,
1738         impl_trait_return_allow: bool,
1739     ) -> P<hir::FnDecl> {
1740         // NOTE: The two last parameters here have to do with impl Trait. If fn_def_id is Some,
1741         //       then impl Trait arguments are lowered into generic parameters on the given
1742         //       fn_def_id, otherwise impl Trait is disallowed. (for now)
1743         //
1744         //       Furthermore, if impl_trait_return_allow is true, then impl Trait may be used in
1745         //       return positions as well. This guards against trait declarations and their impls
1746         //       where impl Trait is disallowed. (again for now)
1747         P(hir::FnDecl {
1748             inputs: decl.inputs
1749                 .iter()
1750                 .map(|arg| {
1751                     if let Some(def_id) = fn_def_id {
1752                         self.lower_ty(&arg.ty, ImplTraitContext::Universal(def_id))
1753                     } else {
1754                         self.lower_ty(&arg.ty, ImplTraitContext::Disallowed)
1755                     }
1756                 })
1757                 .collect(),
1758             output: match decl.output {
1759                 FunctionRetTy::Ty(ref ty) => match fn_def_id {
1760                     Some(_) if impl_trait_return_allow => {
1761                         hir::Return(self.lower_ty(ty, ImplTraitContext::Existential))
1762                     }
1763                     _ => hir::Return(self.lower_ty(ty, ImplTraitContext::Disallowed)),
1764                 },
1765                 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
1766             },
1767             variadic: decl.variadic,
1768             has_implicit_self: decl.inputs.get(0).map_or(false, |arg| match arg.ty.node {
1769                 TyKind::ImplicitSelf => true,
1770                 TyKind::Rptr(_, ref mt) => mt.ty.node == TyKind::ImplicitSelf,
1771                 _ => false,
1772             }),
1773         })
1774     }
1775
1776     fn lower_ty_param_bound(
1777         &mut self,
1778         tpb: &TyParamBound,
1779         itctx: ImplTraitContext,
1780     ) -> hir::TyParamBound {
1781         match *tpb {
1782             TraitTyParamBound(ref ty, modifier) => hir::TraitTyParamBound(
1783                 self.lower_poly_trait_ref(ty, itctx),
1784                 self.lower_trait_bound_modifier(modifier),
1785             ),
1786             RegionTyParamBound(ref lifetime) => {
1787                 hir::RegionTyParamBound(self.lower_lifetime(lifetime))
1788             }
1789         }
1790     }
1791
1792     fn lower_ty_param(
1793         &mut self,
1794         tp: &TyParam,
1795         add_bounds: &[TyParamBound],
1796         itctx: ImplTraitContext,
1797     ) -> hir::TyParam {
1798         let mut name = self.lower_ident(tp.ident);
1799
1800         // Don't expose `Self` (recovered "keyword used as ident" parse error).
1801         // `rustc::ty` expects `Self` to be only used for a trait's `Self`.
1802         // Instead, use gensym("Self") to create a distinct name that looks the same.
1803         if name == keywords::SelfType.name() {
1804             name = Symbol::gensym("Self");
1805         }
1806
1807         let mut bounds = self.lower_bounds(&tp.bounds, itctx);
1808         if !add_bounds.is_empty() {
1809             bounds = bounds
1810                 .into_iter()
1811                 .chain(self.lower_bounds(add_bounds, itctx).into_iter())
1812                 .collect();
1813         }
1814
1815         hir::TyParam {
1816             id: self.lower_node_id(tp.id).node_id,
1817             name,
1818             bounds,
1819             default: tp.default
1820                 .as_ref()
1821                 .map(|x| self.lower_ty(x, ImplTraitContext::Disallowed)),
1822             span: tp.ident.span,
1823             pure_wrt_drop: attr::contains_name(&tp.attrs, "may_dangle"),
1824             synthetic: tp.attrs
1825                 .iter()
1826                 .filter(|attr| attr.check_name("rustc_synthetic"))
1827                 .map(|_| hir::SyntheticTyParamKind::ImplTrait)
1828                 .nth(0),
1829             attrs: self.lower_attrs(&tp.attrs),
1830         }
1831     }
1832
1833     fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
1834         let span = l.ident.span;
1835         match self.lower_ident(l.ident) {
1836             x if x == "'static" => self.new_named_lifetime(l.id, span, hir::LifetimeName::Static),
1837             x if x == "'_" => match self.anonymous_lifetime_mode {
1838                 AnonymousLifetimeMode::CreateParameter => {
1839                     let fresh_name = self.collect_fresh_in_band_lifetime(span);
1840                     self.new_named_lifetime(l.id, span, fresh_name)
1841                 }
1842
1843                 AnonymousLifetimeMode::PassThrough => {
1844                     self.new_named_lifetime(l.id, span, hir::LifetimeName::Underscore)
1845                 }
1846             },
1847             name => {
1848                 self.maybe_collect_in_band_lifetime(span, name);
1849                 self.new_named_lifetime(l.id, span, hir::LifetimeName::Name(name))
1850             }
1851         }
1852     }
1853
1854     fn new_named_lifetime(
1855         &mut self,
1856         id: NodeId,
1857         span: Span,
1858         name: hir::LifetimeName,
1859     ) -> hir::Lifetime {
1860         hir::Lifetime {
1861             id: self.lower_node_id(id).node_id,
1862             span,
1863             name: name,
1864         }
1865     }
1866
1867     fn lower_lifetime_def(&mut self, l: &LifetimeDef) -> hir::LifetimeDef {
1868         let was_collecting_in_band = self.is_collecting_in_band_lifetimes;
1869         self.is_collecting_in_band_lifetimes = false;
1870
1871         let def = hir::LifetimeDef {
1872             lifetime: self.lower_lifetime(&l.lifetime),
1873             bounds: self.lower_lifetimes(&l.bounds),
1874             pure_wrt_drop: attr::contains_name(&l.attrs, "may_dangle"),
1875             in_band: false,
1876         };
1877
1878         self.is_collecting_in_band_lifetimes = was_collecting_in_band;
1879
1880         def
1881     }
1882
1883     fn lower_lifetimes(&mut self, lts: &Vec<Lifetime>) -> hir::HirVec<hir::Lifetime> {
1884         lts.iter().map(|l| self.lower_lifetime(l)).collect()
1885     }
1886
1887     fn lower_generic_params(
1888         &mut self,
1889         params: &Vec<GenericParam>,
1890         add_bounds: &NodeMap<Vec<TyParamBound>>,
1891         itctx: ImplTraitContext,
1892     ) -> hir::HirVec<hir::GenericParam> {
1893         params
1894             .iter()
1895             .map(|param| match *param {
1896                 GenericParam::Lifetime(ref lifetime_def) => {
1897                     hir::GenericParam::Lifetime(self.lower_lifetime_def(lifetime_def))
1898                 }
1899                 GenericParam::Type(ref ty_param) => hir::GenericParam::Type(self.lower_ty_param(
1900                     ty_param,
1901                     add_bounds.get(&ty_param.id).map_or(&[][..], |x| &x),
1902                     itctx,
1903                 )),
1904             })
1905             .collect()
1906     }
1907
1908     fn lower_generics(&mut self, g: &Generics, itctx: ImplTraitContext) -> hir::Generics {
1909         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1910         // FIXME: This could probably be done with less rightward drift. Also looks like two control
1911         //        paths where report_error is called are also the only paths that advance to after
1912         //        the match statement, so the error reporting could probably just be moved there.
1913         let mut add_bounds = NodeMap();
1914         for pred in &g.where_clause.predicates {
1915             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1916                 'next_bound: for bound in &bound_pred.bounds {
1917                     if let TraitTyParamBound(_, TraitBoundModifier::Maybe) = *bound {
1918                         let report_error = |this: &mut Self| {
1919                             this.diagnostic().span_err(
1920                                 bound_pred.bounded_ty.span,
1921                                 "`?Trait` bounds are only permitted at the \
1922                                  point where a type parameter is declared",
1923                             );
1924                         };
1925                         // Check if the where clause type is a plain type parameter.
1926                         match bound_pred.bounded_ty.node {
1927                             TyKind::Path(None, ref path)
1928                                 if path.segments.len() == 1
1929                                     && bound_pred.bound_generic_params.is_empty() =>
1930                             {
1931                                 if let Some(Def::TyParam(def_id)) = self.resolver
1932                                     .get_resolution(bound_pred.bounded_ty.id)
1933                                     .map(|d| d.base_def())
1934                                 {
1935                                     if let Some(node_id) =
1936                                         self.resolver.definitions().as_local_node_id(def_id)
1937                                     {
1938                                         for param in &g.params {
1939                                             if let GenericParam::Type(ref ty_param) = *param {
1940                                                 if node_id == ty_param.id {
1941                                                     add_bounds
1942                                                         .entry(ty_param.id)
1943                                                         .or_insert(Vec::new())
1944                                                         .push(bound.clone());
1945                                                     continue 'next_bound;
1946                                                 }
1947                                             }
1948                                         }
1949                                     }
1950                                 }
1951                                 report_error(self)
1952                             }
1953                             _ => report_error(self),
1954                         }
1955                     }
1956                 }
1957             }
1958         }
1959
1960         hir::Generics {
1961             params: self.lower_generic_params(&g.params, &add_bounds, itctx),
1962             where_clause: self.lower_where_clause(&g.where_clause),
1963             span: g.span,
1964         }
1965     }
1966
1967     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1968         hir::WhereClause {
1969             id: self.lower_node_id(wc.id).node_id,
1970             predicates: wc.predicates
1971                 .iter()
1972                 .map(|predicate| self.lower_where_predicate(predicate))
1973                 .collect(),
1974         }
1975     }
1976
1977     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1978         match *pred {
1979             WherePredicate::BoundPredicate(WhereBoundPredicate {
1980                 ref bound_generic_params,
1981                 ref bounded_ty,
1982                 ref bounds,
1983                 span,
1984             }) => {
1985                 self.with_in_scope_lifetime_defs(
1986                     bound_generic_params.iter().filter_map(|p| match p {
1987                         GenericParam::Lifetime(ld) => Some(ld),
1988                         _ => None,
1989                     }),
1990                     |this| {
1991                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1992                             bound_generic_params: this.lower_generic_params(
1993                                 bound_generic_params,
1994                                 &NodeMap(),
1995                                 ImplTraitContext::Disallowed,
1996                             ),
1997                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::Disallowed),
1998                             bounds: bounds
1999                                 .iter()
2000                                 .filter_map(|bound| match *bound {
2001                                     // Ignore `?Trait` bounds.
2002                                     // Tthey were copied into type parameters already.
2003                                     TraitTyParamBound(_, TraitBoundModifier::Maybe) => None,
2004                                     _ => Some(this.lower_ty_param_bound(
2005                                         bound,
2006                                         ImplTraitContext::Disallowed,
2007                                     )),
2008                                 })
2009                                 .collect(),
2010                             span,
2011                         })
2012                     },
2013                 )
2014             }
2015             WherePredicate::RegionPredicate(WhereRegionPredicate {
2016                 ref lifetime,
2017                 ref bounds,
2018                 span,
2019             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
2020                 span,
2021                 lifetime: self.lower_lifetime(lifetime),
2022                 bounds: bounds
2023                     .iter()
2024                     .map(|bound| self.lower_lifetime(bound))
2025                     .collect(),
2026             }),
2027             WherePredicate::EqPredicate(WhereEqPredicate {
2028                 id,
2029                 ref lhs_ty,
2030                 ref rhs_ty,
2031                 span,
2032             }) => hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
2033                 id: self.lower_node_id(id).node_id,
2034                 lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::Disallowed),
2035                 rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::Disallowed),
2036                 span,
2037             }),
2038         }
2039     }
2040
2041     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
2042         match *vdata {
2043             VariantData::Struct(ref fields, id) => hir::VariantData::Struct(
2044                 fields
2045                     .iter()
2046                     .enumerate()
2047                     .map(|f| self.lower_struct_field(f))
2048                     .collect(),
2049                 self.lower_node_id(id).node_id,
2050             ),
2051             VariantData::Tuple(ref fields, id) => hir::VariantData::Tuple(
2052                 fields
2053                     .iter()
2054                     .enumerate()
2055                     .map(|f| self.lower_struct_field(f))
2056                     .collect(),
2057                 self.lower_node_id(id).node_id,
2058             ),
2059             VariantData::Unit(id) => hir::VariantData::Unit(self.lower_node_id(id).node_id),
2060         }
2061     }
2062
2063     fn lower_trait_ref(&mut self, p: &TraitRef, itctx: ImplTraitContext) -> hir::TraitRef {
2064         let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit, itctx) {
2065             hir::QPath::Resolved(None, path) => path.and_then(|path| path),
2066             qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath),
2067         };
2068         hir::TraitRef {
2069             path,
2070             ref_id: self.lower_node_id(p.ref_id).node_id,
2071         }
2072     }
2073
2074     fn lower_poly_trait_ref(
2075         &mut self,
2076         p: &PolyTraitRef,
2077         itctx: ImplTraitContext,
2078     ) -> hir::PolyTraitRef {
2079         let bound_generic_params =
2080             self.lower_generic_params(&p.bound_generic_params, &NodeMap(), itctx);
2081         let trait_ref = self.with_parent_impl_lifetime_defs(
2082             &bound_generic_params
2083                 .iter()
2084                 .filter_map(|p| match *p {
2085                     hir::GenericParam::Lifetime(ref ld) => Some(ld.clone()),
2086                     _ => None,
2087                 })
2088                 .collect::<Vec<_>>(),
2089             |this| this.lower_trait_ref(&p.trait_ref, itctx),
2090         );
2091
2092         hir::PolyTraitRef {
2093             bound_generic_params,
2094             trait_ref,
2095             span: p.span,
2096         }
2097     }
2098
2099     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
2100         hir::StructField {
2101             span: f.span,
2102             id: self.lower_node_id(f.id).node_id,
2103             name: self.lower_ident(match f.ident {
2104                 Some(ident) => ident,
2105                 // FIXME(jseyfried) positional field hygiene
2106                 None => Ident::new(Symbol::intern(&index.to_string()), f.span),
2107             }),
2108             vis: self.lower_visibility(&f.vis, None),
2109             ty: self.lower_ty(&f.ty, ImplTraitContext::Disallowed),
2110             attrs: self.lower_attrs(&f.attrs),
2111         }
2112     }
2113
2114     fn lower_field(&mut self, f: &Field) -> hir::Field {
2115         hir::Field {
2116             id: self.next_id().node_id,
2117             name: respan(f.ident.span, self.lower_ident(f.ident)),
2118             expr: P(self.lower_expr(&f.expr)),
2119             span: f.span,
2120             is_shorthand: f.is_shorthand,
2121         }
2122     }
2123
2124     fn lower_mt(&mut self, mt: &MutTy, itctx: ImplTraitContext) -> hir::MutTy {
2125         hir::MutTy {
2126             ty: self.lower_ty(&mt.ty, itctx),
2127             mutbl: self.lower_mutability(mt.mutbl),
2128         }
2129     }
2130
2131     fn lower_bounds(
2132         &mut self,
2133         bounds: &[TyParamBound],
2134         itctx: ImplTraitContext,
2135     ) -> hir::TyParamBounds {
2136         bounds
2137             .iter()
2138             .map(|bound| self.lower_ty_param_bound(bound, itctx))
2139             .collect()
2140     }
2141
2142     fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
2143         let mut expr = None;
2144
2145         let mut stmts = vec![];
2146
2147         for (index, stmt) in b.stmts.iter().enumerate() {
2148             if index == b.stmts.len() - 1 {
2149                 if let StmtKind::Expr(ref e) = stmt.node {
2150                     expr = Some(P(self.lower_expr(e)));
2151                 } else {
2152                     stmts.extend(self.lower_stmt(stmt));
2153                 }
2154             } else {
2155                 stmts.extend(self.lower_stmt(stmt));
2156             }
2157         }
2158
2159         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(b.id);
2160
2161         P(hir::Block {
2162             id: node_id,
2163             hir_id,
2164             stmts: stmts.into(),
2165             expr,
2166             rules: self.lower_block_check_mode(&b.rules),
2167             span: b.span,
2168             targeted_by_break,
2169             recovered: b.recovered,
2170         })
2171     }
2172
2173     fn lower_item_kind(
2174         &mut self,
2175         id: NodeId,
2176         name: &mut Name,
2177         attrs: &hir::HirVec<Attribute>,
2178         vis: &mut hir::Visibility,
2179         i: &ItemKind,
2180     ) -> hir::Item_ {
2181         match *i {
2182             ItemKind::ExternCrate(orig_name) => hir::ItemExternCrate(orig_name),
2183             ItemKind::Use(ref use_tree) => {
2184                 // Start with an empty prefix
2185                 let prefix = Path {
2186                     segments: vec![],
2187                     span: use_tree.span,
2188                 };
2189
2190                 self.lower_use_tree(use_tree, &prefix, id, vis, name, attrs)
2191             }
2192             ItemKind::Static(ref t, m, ref e) => {
2193                 let value = self.lower_body(None, |this| this.lower_expr(e));
2194                 hir::ItemStatic(
2195                     self.lower_ty(t, ImplTraitContext::Disallowed),
2196                     self.lower_mutability(m),
2197                     value,
2198                 )
2199             }
2200             ItemKind::Const(ref t, ref e) => {
2201                 let value = self.lower_body(None, |this| this.lower_expr(e));
2202                 hir::ItemConst(self.lower_ty(t, ImplTraitContext::Disallowed), value)
2203             }
2204             ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
2205                 let fn_def_id = self.resolver.definitions().local_def_id(id);
2206                 self.with_new_scopes(|this| {
2207                     let body_id = this.lower_body(Some(decl), |this| {
2208                         let body = this.lower_block(body, false);
2209                         this.expr_block(body, ThinVec::new())
2210                     });
2211                     let (generics, fn_decl) = this.add_in_band_defs(
2212                         generics,
2213                         fn_def_id,
2214                         AnonymousLifetimeMode::PassThrough,
2215                         |this| this.lower_fn_decl(decl, Some(fn_def_id), true),
2216                     );
2217
2218                     hir::ItemFn(
2219                         fn_decl,
2220                         this.lower_unsafety(unsafety),
2221                         this.lower_constness(constness),
2222                         abi,
2223                         generics,
2224                         body_id,
2225                     )
2226                 })
2227             }
2228             ItemKind::Mod(ref m) => hir::ItemMod(self.lower_mod(m)),
2229             ItemKind::ForeignMod(ref nm) => hir::ItemForeignMod(self.lower_foreign_mod(nm)),
2230             ItemKind::GlobalAsm(ref ga) => hir::ItemGlobalAsm(self.lower_global_asm(ga)),
2231             ItemKind::Ty(ref t, ref generics) => hir::ItemTy(
2232                 self.lower_ty(t, ImplTraitContext::Disallowed),
2233                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2234             ),
2235             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemEnum(
2236                 hir::EnumDef {
2237                     variants: enum_definition
2238                         .variants
2239                         .iter()
2240                         .map(|x| self.lower_variant(x))
2241                         .collect(),
2242                 },
2243                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2244             ),
2245             ItemKind::Struct(ref struct_def, ref generics) => {
2246                 let struct_def = self.lower_variant_data(struct_def);
2247                 hir::ItemStruct(
2248                     struct_def,
2249                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2250                 )
2251             }
2252             ItemKind::Union(ref vdata, ref generics) => {
2253                 let vdata = self.lower_variant_data(vdata);
2254                 hir::ItemUnion(
2255                     vdata,
2256                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2257                 )
2258             }
2259             ItemKind::Impl(
2260                 unsafety,
2261                 polarity,
2262                 defaultness,
2263                 ref ast_generics,
2264                 ref trait_ref,
2265                 ref ty,
2266                 ref impl_items,
2267             ) => {
2268                 let def_id = self.resolver.definitions().local_def_id(id);
2269
2270                 // Lower the "impl header" first. This ordering is important
2271                 // for in-band lifetimes! Consider `'a` here:
2272                 //
2273                 //     impl Foo<'a> for u32 {
2274                 //         fn method(&'a self) { .. }
2275                 //     }
2276                 //
2277                 // Because we start by lowering the `Foo<'a> for u32`
2278                 // part, we will add `'a` to the list of generics on
2279                 // the impl. When we then encounter it later in the
2280                 // method, it will not be considered an in-band
2281                 // lifetime to be added, but rather a reference to a
2282                 // parent lifetime.
2283                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
2284                     ast_generics,
2285                     def_id,
2286                     AnonymousLifetimeMode::CreateParameter,
2287                     |this| {
2288                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
2289                             this.lower_trait_ref(trait_ref, ImplTraitContext::Disallowed)
2290                         });
2291
2292                         if let Some(ref trait_ref) = trait_ref {
2293                             if let Def::Trait(def_id) = trait_ref.path.def {
2294                                 this.trait_impls.entry(def_id).or_insert(vec![]).push(id);
2295                             }
2296                         }
2297
2298                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::Disallowed);
2299
2300                         (trait_ref, lowered_ty)
2301                     },
2302                 );
2303
2304                 let new_impl_items = self.with_in_scope_lifetime_defs(
2305                     ast_generics.params.iter().filter_map(|p| match p {
2306                         GenericParam::Lifetime(ld) => Some(ld),
2307                         _ => None,
2308                     }),
2309                     |this| {
2310                         impl_items
2311                             .iter()
2312                             .map(|item| this.lower_impl_item_ref(item))
2313                             .collect()
2314                     },
2315                 );
2316
2317                 hir::ItemImpl(
2318                     self.lower_unsafety(unsafety),
2319                     self.lower_impl_polarity(polarity),
2320                     self.lower_defaultness(defaultness, true /* [1] */),
2321                     generics,
2322                     trait_ref,
2323                     lowered_ty,
2324                     new_impl_items,
2325                 )
2326             }
2327             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
2328                 let bounds = self.lower_bounds(bounds, ImplTraitContext::Disallowed);
2329                 let items = items
2330                     .iter()
2331                     .map(|item| self.lower_trait_item_ref(item))
2332                     .collect();
2333                 hir::ItemTrait(
2334                     self.lower_is_auto(is_auto),
2335                     self.lower_unsafety(unsafety),
2336                     self.lower_generics(generics, ImplTraitContext::Disallowed),
2337                     bounds,
2338                     items,
2339                 )
2340             }
2341             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemTraitAlias(
2342                 self.lower_generics(generics, ImplTraitContext::Disallowed),
2343                 self.lower_bounds(bounds, ImplTraitContext::Disallowed),
2344             ),
2345             ItemKind::MacroDef(..) | ItemKind::Mac(..) => panic!("Shouldn't still be around"),
2346         }
2347
2348         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
2349         //     not cause an assertion failure inside the `lower_defaultness` function
2350     }
2351
2352     fn lower_use_tree(
2353         &mut self,
2354         tree: &UseTree,
2355         prefix: &Path,
2356         id: NodeId,
2357         vis: &mut hir::Visibility,
2358         name: &mut Name,
2359         attrs: &hir::HirVec<Attribute>,
2360     ) -> hir::Item_ {
2361         let path = &tree.prefix;
2362
2363         match tree.kind {
2364             UseTreeKind::Simple(rename) => {
2365                 *name = tree.ident().name;
2366
2367                 // First apply the prefix to the path
2368                 let mut path = Path {
2369                     segments: prefix
2370                         .segments
2371                         .iter()
2372                         .chain(path.segments.iter())
2373                         .cloned()
2374                         .collect(),
2375                     span: path.span,
2376                 };
2377
2378                 // Correctly resolve `self` imports
2379                 if path.segments.len() > 1
2380                     && path.segments.last().unwrap().ident.name == keywords::SelfValue.name()
2381                 {
2382                     let _ = path.segments.pop();
2383                     if rename.is_none() {
2384                         *name = path.segments.last().unwrap().ident.name;
2385                     }
2386                 }
2387
2388                 let path = P(self.lower_path(id, &path, ParamMode::Explicit));
2389                 hir::ItemUse(path, hir::UseKind::Single)
2390             }
2391             UseTreeKind::Glob => {
2392                 let path = P(self.lower_path(
2393                     id,
2394                     &Path {
2395                         segments: prefix
2396                             .segments
2397                             .iter()
2398                             .chain(path.segments.iter())
2399                             .cloned()
2400                             .collect(),
2401                         span: path.span,
2402                     },
2403                     ParamMode::Explicit,
2404                 ));
2405                 hir::ItemUse(path, hir::UseKind::Glob)
2406             }
2407             UseTreeKind::Nested(ref trees) => {
2408                 let prefix = Path {
2409                     segments: prefix
2410                         .segments
2411                         .iter()
2412                         .chain(path.segments.iter())
2413                         .cloned()
2414                         .collect(),
2415                     span: prefix.span.to(path.span),
2416                 };
2417
2418                 // Add all the nested PathListItems in the HIR
2419                 for &(ref use_tree, id) in trees {
2420                     self.allocate_hir_id_counter(id, &use_tree);
2421                     let LoweredNodeId {
2422                         node_id: new_id,
2423                         hir_id: new_hir_id,
2424                     } = self.lower_node_id(id);
2425
2426                     let mut vis = vis.clone();
2427                     let mut name = name.clone();
2428                     let item =
2429                         self.lower_use_tree(use_tree, &prefix, new_id, &mut vis, &mut name, &attrs);
2430
2431                     self.with_hir_id_owner(new_id, |this| {
2432                         let vis = match vis {
2433                             hir::Visibility::Public => hir::Visibility::Public,
2434                             hir::Visibility::Crate => hir::Visibility::Crate,
2435                             hir::Visibility::Inherited => hir::Visibility::Inherited,
2436                             hir::Visibility::Restricted { ref path, id: _ } => {
2437                                 hir::Visibility::Restricted {
2438                                     path: path.clone(),
2439                                     // We are allocating a new NodeId here
2440                                     id: this.next_id().node_id,
2441                                 }
2442                             }
2443                         };
2444
2445                         this.items.insert(
2446                             new_id,
2447                             hir::Item {
2448                                 id: new_id,
2449                                 hir_id: new_hir_id,
2450                                 name: name,
2451                                 attrs: attrs.clone(),
2452                                 node: item,
2453                                 vis,
2454                                 span: use_tree.span,
2455                             },
2456                         );
2457                     });
2458                 }
2459
2460                 // Privatize the degenerate import base, used only to check
2461                 // the stability of `use a::{};`, to avoid it showing up as
2462                 // a re-export by accident when `pub`, e.g. in documentation.
2463                 let path = P(self.lower_path(id, &prefix, ParamMode::Explicit));
2464                 *vis = hir::Inherited;
2465                 hir::ItemUse(path, hir::UseKind::ListStem)
2466             }
2467         }
2468     }
2469
2470     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {
2471         self.with_parent_def(i.id, |this| {
2472             let LoweredNodeId { node_id, hir_id } = this.lower_node_id(i.id);
2473             let trait_item_def_id = this.resolver.definitions().local_def_id(node_id);
2474
2475             let (generics, node) = match i.node {
2476                 TraitItemKind::Const(ref ty, ref default) => (
2477                     this.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2478                     hir::TraitItemKind::Const(
2479                         this.lower_ty(ty, ImplTraitContext::Disallowed),
2480                         default
2481                             .as_ref()
2482                             .map(|x| this.lower_body(None, |this| this.lower_expr(x))),
2483                     ),
2484                 ),
2485                 TraitItemKind::Method(ref sig, None) => {
2486                     let names = this.lower_fn_args_to_names(&sig.decl);
2487                     this.add_in_band_defs(
2488                         &i.generics,
2489                         trait_item_def_id,
2490                         AnonymousLifetimeMode::PassThrough,
2491                         |this| {
2492                             hir::TraitItemKind::Method(
2493                                 this.lower_method_sig(sig, trait_item_def_id, false),
2494                                 hir::TraitMethod::Required(names),
2495                             )
2496                         },
2497                     )
2498                 }
2499                 TraitItemKind::Method(ref sig, Some(ref body)) => {
2500                     let body_id = this.lower_body(Some(&sig.decl), |this| {
2501                         let body = this.lower_block(body, false);
2502                         this.expr_block(body, ThinVec::new())
2503                     });
2504
2505                     this.add_in_band_defs(
2506                         &i.generics,
2507                         trait_item_def_id,
2508                         AnonymousLifetimeMode::PassThrough,
2509                         |this| {
2510                             hir::TraitItemKind::Method(
2511                                 this.lower_method_sig(sig, trait_item_def_id, false),
2512                                 hir::TraitMethod::Provided(body_id),
2513                             )
2514                         },
2515                     )
2516                 }
2517                 TraitItemKind::Type(ref bounds, ref default) => (
2518                     this.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2519                     hir::TraitItemKind::Type(
2520                         this.lower_bounds(bounds, ImplTraitContext::Disallowed),
2521                         default
2522                             .as_ref()
2523                             .map(|x| this.lower_ty(x, ImplTraitContext::Disallowed)),
2524                     ),
2525                 ),
2526                 TraitItemKind::Macro(..) => panic!("Shouldn't exist any more"),
2527             };
2528
2529             hir::TraitItem {
2530                 id: node_id,
2531                 hir_id,
2532                 name: this.lower_ident(i.ident),
2533                 attrs: this.lower_attrs(&i.attrs),
2534                 generics,
2535                 node,
2536                 span: i.span,
2537             }
2538         })
2539     }
2540
2541     fn lower_trait_item_ref(&mut self, i: &TraitItem) -> hir::TraitItemRef {
2542         let (kind, has_default) = match i.node {
2543             TraitItemKind::Const(_, ref default) => {
2544                 (hir::AssociatedItemKind::Const, default.is_some())
2545             }
2546             TraitItemKind::Type(_, ref default) => {
2547                 (hir::AssociatedItemKind::Type, default.is_some())
2548             }
2549             TraitItemKind::Method(ref sig, ref default) => (
2550                 hir::AssociatedItemKind::Method {
2551                     has_self: sig.decl.has_self(),
2552                 },
2553                 default.is_some(),
2554             ),
2555             TraitItemKind::Macro(..) => unimplemented!(),
2556         };
2557         hir::TraitItemRef {
2558             id: hir::TraitItemId { node_id: i.id },
2559             name: self.lower_ident(i.ident),
2560             span: i.span,
2561             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
2562             kind,
2563         }
2564     }
2565
2566     fn lower_impl_item(&mut self, i: &ImplItem) -> hir::ImplItem {
2567         self.with_parent_def(i.id, |this| {
2568             let LoweredNodeId { node_id, hir_id } = this.lower_node_id(i.id);
2569             let impl_item_def_id = this.resolver.definitions().local_def_id(node_id);
2570
2571             let (generics, node) = match i.node {
2572                 ImplItemKind::Const(ref ty, ref expr) => {
2573                     let body_id = this.lower_body(None, |this| this.lower_expr(expr));
2574                     (
2575                         this.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2576                         hir::ImplItemKind::Const(
2577                             this.lower_ty(ty, ImplTraitContext::Disallowed),
2578                             body_id,
2579                         ),
2580                     )
2581                 }
2582                 ImplItemKind::Method(ref sig, ref body) => {
2583                     let body_id = this.lower_body(Some(&sig.decl), |this| {
2584                         let body = this.lower_block(body, false);
2585                         this.expr_block(body, ThinVec::new())
2586                     });
2587                     let impl_trait_return_allow = !this.is_in_trait_impl;
2588
2589                     this.add_in_band_defs(
2590                         &i.generics,
2591                         impl_item_def_id,
2592                         AnonymousLifetimeMode::PassThrough,
2593                         |this| {
2594                             hir::ImplItemKind::Method(
2595                                 this.lower_method_sig(
2596                                     sig,
2597                                     impl_item_def_id,
2598                                     impl_trait_return_allow,
2599                                 ),
2600                                 body_id,
2601                             )
2602                         },
2603                     )
2604                 }
2605                 ImplItemKind::Type(ref ty) => (
2606                     this.lower_generics(&i.generics, ImplTraitContext::Disallowed),
2607                     hir::ImplItemKind::Type(this.lower_ty(ty, ImplTraitContext::Disallowed)),
2608                 ),
2609                 ImplItemKind::Macro(..) => panic!("Shouldn't exist any more"),
2610             };
2611
2612             hir::ImplItem {
2613                 id: node_id,
2614                 hir_id,
2615                 name: this.lower_ident(i.ident),
2616                 attrs: this.lower_attrs(&i.attrs),
2617                 generics,
2618                 vis: this.lower_visibility(&i.vis, None),
2619                 defaultness: this.lower_defaultness(i.defaultness, true /* [1] */),
2620                 node,
2621                 span: i.span,
2622             }
2623         })
2624
2625         // [1] since `default impl` is not yet implemented, this is always true in impls
2626     }
2627
2628     fn lower_impl_item_ref(&mut self, i: &ImplItem) -> hir::ImplItemRef {
2629         hir::ImplItemRef {
2630             id: hir::ImplItemId { node_id: i.id },
2631             name: self.lower_ident(i.ident),
2632             span: i.span,
2633             vis: self.lower_visibility(&i.vis, Some(i.id)),
2634             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
2635             kind: match i.node {
2636                 ImplItemKind::Const(..) => hir::AssociatedItemKind::Const,
2637                 ImplItemKind::Type(..) => hir::AssociatedItemKind::Type,
2638                 ImplItemKind::Method(ref sig, _) => hir::AssociatedItemKind::Method {
2639                     has_self: sig.decl.has_self(),
2640                 },
2641                 ImplItemKind::Macro(..) => unimplemented!(),
2642             },
2643         }
2644
2645         // [1] since `default impl` is not yet implemented, this is always true in impls
2646     }
2647
2648     fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
2649         hir::Mod {
2650             inner: m.inner,
2651             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
2652         }
2653     }
2654
2655     fn lower_item_id(&mut self, i: &Item) -> SmallVector<hir::ItemId> {
2656         match i.node {
2657             ItemKind::Use(ref use_tree) => {
2658                 let mut vec = SmallVector::one(hir::ItemId { id: i.id });
2659                 self.lower_item_id_use_tree(use_tree, &mut vec);
2660                 return vec;
2661             }
2662             ItemKind::MacroDef(..) => return SmallVector::new(),
2663             _ => {}
2664         }
2665         SmallVector::one(hir::ItemId { id: i.id })
2666     }
2667
2668     fn lower_item_id_use_tree(&self, tree: &UseTree, vec: &mut SmallVector<hir::ItemId>) {
2669         match tree.kind {
2670             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
2671                 vec.push(hir::ItemId { id });
2672                 self.lower_item_id_use_tree(nested, vec);
2673             },
2674             UseTreeKind::Glob => {}
2675             UseTreeKind::Simple(..) => {}
2676         }
2677     }
2678
2679     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
2680         let mut name = i.ident.name;
2681         let mut vis = self.lower_visibility(&i.vis, None);
2682         let attrs = self.lower_attrs(&i.attrs);
2683         if let ItemKind::MacroDef(ref def) = i.node {
2684             if !def.legacy || attr::contains_name(&i.attrs, "macro_export") {
2685                 let body = self.lower_token_stream(def.stream());
2686                 self.exported_macros.push(hir::MacroDef {
2687                     name,
2688                     vis,
2689                     attrs,
2690                     id: i.id,
2691                     span: i.span,
2692                     body,
2693                     legacy: def.legacy,
2694                 });
2695             }
2696             return None;
2697         }
2698
2699         let node = self.with_parent_def(i.id, |this| {
2700             this.lower_item_kind(i.id, &mut name, &attrs, &mut vis, &i.node)
2701         });
2702
2703         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(i.id);
2704
2705         Some(hir::Item {
2706             id: node_id,
2707             hir_id,
2708             name,
2709             attrs,
2710             node,
2711             vis,
2712             span: i.span,
2713         })
2714     }
2715
2716     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
2717         self.with_parent_def(i.id, |this| {
2718             let node_id = this.lower_node_id(i.id).node_id;
2719             let def_id = this.resolver.definitions().local_def_id(node_id);
2720             hir::ForeignItem {
2721                 id: node_id,
2722                 name: i.ident.name,
2723                 attrs: this.lower_attrs(&i.attrs),
2724                 node: match i.node {
2725                     ForeignItemKind::Fn(ref fdec, ref generics) => {
2726                         let (generics, (fn_dec, fn_args)) = this.add_in_band_defs(
2727                             generics,
2728                             def_id,
2729                             AnonymousLifetimeMode::PassThrough,
2730                             |this| {
2731                                 (
2732                                     // Disallow impl Trait in foreign items
2733                                     this.lower_fn_decl(fdec, None, false),
2734                                     this.lower_fn_args_to_names(fdec),
2735                                 )
2736                             },
2737                         );
2738
2739                         hir::ForeignItemFn(fn_dec, fn_args, generics)
2740                     }
2741                     ForeignItemKind::Static(ref t, m) => {
2742                         hir::ForeignItemStatic(this.lower_ty(t, ImplTraitContext::Disallowed), m)
2743                     }
2744                     ForeignItemKind::Ty => hir::ForeignItemType,
2745                     ForeignItemKind::Macro(_) => panic!("shouldn't exist here"),
2746                 },
2747                 vis: this.lower_visibility(&i.vis, None),
2748                 span: i.span,
2749             }
2750         })
2751     }
2752
2753     fn lower_method_sig(
2754         &mut self,
2755         sig: &MethodSig,
2756         fn_def_id: DefId,
2757         impl_trait_return_allow: bool,
2758     ) -> hir::MethodSig {
2759         hir::MethodSig {
2760             abi: sig.abi,
2761             unsafety: self.lower_unsafety(sig.unsafety),
2762             constness: self.lower_constness(sig.constness),
2763             decl: self.lower_fn_decl(&sig.decl, Some(fn_def_id), impl_trait_return_allow),
2764         }
2765     }
2766
2767     fn lower_is_auto(&mut self, a: IsAuto) -> hir::IsAuto {
2768         match a {
2769             IsAuto::Yes => hir::IsAuto::Yes,
2770             IsAuto::No => hir::IsAuto::No,
2771         }
2772     }
2773
2774     fn lower_unsafety(&mut self, u: Unsafety) -> hir::Unsafety {
2775         match u {
2776             Unsafety::Unsafe => hir::Unsafety::Unsafe,
2777             Unsafety::Normal => hir::Unsafety::Normal,
2778         }
2779     }
2780
2781     fn lower_constness(&mut self, c: Spanned<Constness>) -> hir::Constness {
2782         match c.node {
2783             Constness::Const => hir::Constness::Const,
2784             Constness::NotConst => hir::Constness::NotConst,
2785         }
2786     }
2787
2788     fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
2789         match u {
2790             UnOp::Deref => hir::UnDeref,
2791             UnOp::Not => hir::UnNot,
2792             UnOp::Neg => hir::UnNeg,
2793         }
2794     }
2795
2796     fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
2797         Spanned {
2798             node: match b.node {
2799                 BinOpKind::Add => hir::BiAdd,
2800                 BinOpKind::Sub => hir::BiSub,
2801                 BinOpKind::Mul => hir::BiMul,
2802                 BinOpKind::Div => hir::BiDiv,
2803                 BinOpKind::Rem => hir::BiRem,
2804                 BinOpKind::And => hir::BiAnd,
2805                 BinOpKind::Or => hir::BiOr,
2806                 BinOpKind::BitXor => hir::BiBitXor,
2807                 BinOpKind::BitAnd => hir::BiBitAnd,
2808                 BinOpKind::BitOr => hir::BiBitOr,
2809                 BinOpKind::Shl => hir::BiShl,
2810                 BinOpKind::Shr => hir::BiShr,
2811                 BinOpKind::Eq => hir::BiEq,
2812                 BinOpKind::Lt => hir::BiLt,
2813                 BinOpKind::Le => hir::BiLe,
2814                 BinOpKind::Ne => hir::BiNe,
2815                 BinOpKind::Ge => hir::BiGe,
2816                 BinOpKind::Gt => hir::BiGt,
2817             },
2818             span: b.span,
2819         }
2820     }
2821
2822     fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
2823         let node = match p.node {
2824             PatKind::Wild => hir::PatKind::Wild,
2825             PatKind::Ident(ref binding_mode, ident, ref sub) => {
2826                 match self.resolver.get_resolution(p.id).map(|d| d.base_def()) {
2827                     // `None` can occur in body-less function signatures
2828                     def @ None | def @ Some(Def::Local(_)) => {
2829                         let canonical_id = match def {
2830                             Some(Def::Local(id)) => id,
2831                             _ => p.id,
2832                         };
2833                         hir::PatKind::Binding(
2834                             self.lower_binding_mode(binding_mode),
2835                             canonical_id,
2836                             respan(ident.span, ident.name),
2837                             sub.as_ref().map(|x| self.lower_pat(x)),
2838                         )
2839                     }
2840                     Some(def) => hir::PatKind::Path(hir::QPath::Resolved(
2841                         None,
2842                         P(hir::Path {
2843                             span: ident.span,
2844                             def,
2845                             segments: hir_vec![hir::PathSegment::from_name(ident.name)],
2846                         }),
2847                     )),
2848                 }
2849             }
2850             PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
2851             PatKind::TupleStruct(ref path, ref pats, ddpos) => {
2852                 let qpath = self.lower_qpath(
2853                     p.id,
2854                     &None,
2855                     path,
2856                     ParamMode::Optional,
2857                     ImplTraitContext::Disallowed,
2858                 );
2859                 hir::PatKind::TupleStruct(
2860                     qpath,
2861                     pats.iter().map(|x| self.lower_pat(x)).collect(),
2862                     ddpos,
2863                 )
2864             }
2865             PatKind::Path(ref qself, ref path) => hir::PatKind::Path(self.lower_qpath(
2866                 p.id,
2867                 qself,
2868                 path,
2869                 ParamMode::Optional,
2870                 ImplTraitContext::Disallowed,
2871             )),
2872             PatKind::Struct(ref path, ref fields, etc) => {
2873                 let qpath = self.lower_qpath(
2874                     p.id,
2875                     &None,
2876                     path,
2877                     ParamMode::Optional,
2878                     ImplTraitContext::Disallowed,
2879                 );
2880
2881                 let fs = fields
2882                     .iter()
2883                     .map(|f| Spanned {
2884                         span: f.span,
2885                         node: hir::FieldPat {
2886                             id: self.next_id().node_id,
2887                             name: self.lower_ident(f.node.ident),
2888                             pat: self.lower_pat(&f.node.pat),
2889                             is_shorthand: f.node.is_shorthand,
2890                         },
2891                     })
2892                     .collect();
2893                 hir::PatKind::Struct(qpath, fs, etc)
2894             }
2895             PatKind::Tuple(ref elts, ddpos) => {
2896                 hir::PatKind::Tuple(elts.iter().map(|x| self.lower_pat(x)).collect(), ddpos)
2897             }
2898             PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
2899             PatKind::Ref(ref inner, mutbl) => {
2900                 hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
2901             }
2902             PatKind::Range(ref e1, ref e2, ref end) => hir::PatKind::Range(
2903                 P(self.lower_expr(e1)),
2904                 P(self.lower_expr(e2)),
2905                 self.lower_range_end(end),
2906             ),
2907             PatKind::Slice(ref before, ref slice, ref after) => hir::PatKind::Slice(
2908                 before.iter().map(|x| self.lower_pat(x)).collect(),
2909                 slice.as_ref().map(|x| self.lower_pat(x)),
2910                 after.iter().map(|x| self.lower_pat(x)).collect(),
2911             ),
2912             PatKind::Paren(ref inner) => return self.lower_pat(inner),
2913             PatKind::Mac(_) => panic!("Shouldn't exist here"),
2914         };
2915
2916         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(p.id);
2917         P(hir::Pat {
2918             id: node_id,
2919             hir_id,
2920             node,
2921             span: p.span,
2922         })
2923     }
2924
2925     fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
2926         match *e {
2927             RangeEnd::Included(_) => hir::RangeEnd::Included,
2928             RangeEnd::Excluded => hir::RangeEnd::Excluded,
2929         }
2930     }
2931
2932     fn lower_expr(&mut self, e: &Expr) -> hir::Expr {
2933         let kind = match e.node {
2934             ExprKind::Box(ref inner) => hir::ExprBox(P(self.lower_expr(inner))),
2935
2936             ExprKind::Array(ref exprs) => {
2937                 hir::ExprArray(exprs.iter().map(|x| self.lower_expr(x)).collect())
2938             }
2939             ExprKind::Repeat(ref expr, ref count) => {
2940                 let expr = P(self.lower_expr(expr));
2941                 let count = self.lower_body(None, |this| this.lower_expr(count));
2942                 hir::ExprRepeat(expr, count)
2943             }
2944             ExprKind::Tup(ref elts) => {
2945                 hir::ExprTup(elts.iter().map(|x| self.lower_expr(x)).collect())
2946             }
2947             ExprKind::Call(ref f, ref args) => {
2948                 let f = P(self.lower_expr(f));
2949                 hir::ExprCall(f, args.iter().map(|x| self.lower_expr(x)).collect())
2950             }
2951             ExprKind::MethodCall(ref seg, ref args) => {
2952                 let hir_seg = self.lower_path_segment(
2953                     e.span,
2954                     seg,
2955                     ParamMode::Optional,
2956                     0,
2957                     ParenthesizedGenericArgs::Err,
2958                     ImplTraitContext::Disallowed,
2959                 );
2960                 let args = args.iter().map(|x| self.lower_expr(x)).collect();
2961                 hir::ExprMethodCall(hir_seg, seg.ident.span, args)
2962             }
2963             ExprKind::Binary(binop, ref lhs, ref rhs) => {
2964                 let binop = self.lower_binop(binop);
2965                 let lhs = P(self.lower_expr(lhs));
2966                 let rhs = P(self.lower_expr(rhs));
2967                 hir::ExprBinary(binop, lhs, rhs)
2968             }
2969             ExprKind::Unary(op, ref ohs) => {
2970                 let op = self.lower_unop(op);
2971                 let ohs = P(self.lower_expr(ohs));
2972                 hir::ExprUnary(op, ohs)
2973             }
2974             ExprKind::Lit(ref l) => hir::ExprLit(P((**l).clone())),
2975             ExprKind::Cast(ref expr, ref ty) => {
2976                 let expr = P(self.lower_expr(expr));
2977                 hir::ExprCast(expr, self.lower_ty(ty, ImplTraitContext::Disallowed))
2978             }
2979             ExprKind::Type(ref expr, ref ty) => {
2980                 let expr = P(self.lower_expr(expr));
2981                 hir::ExprType(expr, self.lower_ty(ty, ImplTraitContext::Disallowed))
2982             }
2983             ExprKind::AddrOf(m, ref ohs) => {
2984                 let m = self.lower_mutability(m);
2985                 let ohs = P(self.lower_expr(ohs));
2986                 hir::ExprAddrOf(m, ohs)
2987             }
2988             // More complicated than you might expect because the else branch
2989             // might be `if let`.
2990             ExprKind::If(ref cond, ref blk, ref else_opt) => {
2991                 let else_opt = else_opt.as_ref().map(|els| {
2992                     match els.node {
2993                         ExprKind::IfLet(..) => {
2994                             // wrap the if-let expr in a block
2995                             let span = els.span;
2996                             let els = P(self.lower_expr(els));
2997                             let LoweredNodeId { node_id, hir_id } = self.next_id();
2998                             let blk = P(hir::Block {
2999                                 stmts: hir_vec![],
3000                                 expr: Some(els),
3001                                 id: node_id,
3002                                 hir_id,
3003                                 rules: hir::DefaultBlock,
3004                                 span,
3005                                 targeted_by_break: false,
3006                                 recovered: blk.recovered,
3007                             });
3008                             P(self.expr_block(blk, ThinVec::new()))
3009                         }
3010                         _ => P(self.lower_expr(els)),
3011                     }
3012                 });
3013
3014                 let then_blk = self.lower_block(blk, false);
3015                 let then_expr = self.expr_block(then_blk, ThinVec::new());
3016
3017                 hir::ExprIf(P(self.lower_expr(cond)), P(then_expr), else_opt)
3018             }
3019             ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
3020                 hir::ExprWhile(
3021                     this.with_loop_condition_scope(|this| P(this.lower_expr(cond))),
3022                     this.lower_block(body, false),
3023                     this.lower_label(opt_label),
3024                 )
3025             }),
3026             ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
3027                 hir::ExprLoop(
3028                     this.lower_block(body, false),
3029                     this.lower_label(opt_label),
3030                     hir::LoopSource::Loop,
3031                 )
3032             }),
3033             ExprKind::Catch(ref body) => {
3034                 self.with_catch_scope(body.id, |this| {
3035                     let unstable_span =
3036                         this.allow_internal_unstable(CompilerDesugaringKind::Catch, body.span);
3037                     let mut block = this.lower_block(body, true).into_inner();
3038                     let tail = block.expr.take().map_or_else(
3039                         || {
3040                             let LoweredNodeId { node_id, hir_id } = this.next_id();
3041                             let span = this.sess.codemap().end_point(unstable_span);
3042                             hir::Expr {
3043                                 id: node_id,
3044                                 span,
3045                                 node: hir::ExprTup(hir_vec![]),
3046                                 attrs: ThinVec::new(),
3047                                 hir_id,
3048                             }
3049                         },
3050                         |x: P<hir::Expr>| x.into_inner(),
3051                     );
3052                     block.expr = Some(this.wrap_in_try_constructor(
3053                         "from_ok", tail, unstable_span));
3054                     hir::ExprBlock(P(block))
3055                 })
3056             }
3057             ExprKind::Match(ref expr, ref arms) => hir::ExprMatch(
3058                 P(self.lower_expr(expr)),
3059                 arms.iter().map(|x| self.lower_arm(x)).collect(),
3060                 hir::MatchSource::Normal,
3061             ),
3062             ExprKind::Closure(capture_clause, movability, ref decl, ref body, fn_decl_span) => {
3063                 self.with_new_scopes(|this| {
3064                     this.with_parent_def(e.id, |this| {
3065                         let mut is_generator = false;
3066                         let body_id = this.lower_body(Some(decl), |this| {
3067                             let e = this.lower_expr(body);
3068                             is_generator = this.is_generator;
3069                             e
3070                         });
3071                         let generator_option = if is_generator {
3072                             if !decl.inputs.is_empty() {
3073                                 span_err!(
3074                                     this.sess,
3075                                     fn_decl_span,
3076                                     E0628,
3077                                     "generators cannot have explicit arguments"
3078                                 );
3079                                 this.sess.abort_if_errors();
3080                             }
3081                             Some(match movability {
3082                                 Movability::Movable => hir::GeneratorMovability::Movable,
3083                                 Movability::Static => hir::GeneratorMovability::Static,
3084                             })
3085                         } else {
3086                             if movability == Movability::Static {
3087                                 span_err!(
3088                                     this.sess,
3089                                     fn_decl_span,
3090                                     E0906,
3091                                     "closures cannot be static"
3092                                 );
3093                             }
3094                             None
3095                         };
3096                         hir::ExprClosure(
3097                             this.lower_capture_clause(capture_clause),
3098                             this.lower_fn_decl(decl, None, false),
3099                             body_id,
3100                             fn_decl_span,
3101                             generator_option,
3102                         )
3103                     })
3104                 })
3105             }
3106             ExprKind::Block(ref blk) => hir::ExprBlock(self.lower_block(blk, false)),
3107             ExprKind::Assign(ref el, ref er) => {
3108                 hir::ExprAssign(P(self.lower_expr(el)), P(self.lower_expr(er)))
3109             }
3110             ExprKind::AssignOp(op, ref el, ref er) => hir::ExprAssignOp(
3111                 self.lower_binop(op),
3112                 P(self.lower_expr(el)),
3113                 P(self.lower_expr(er)),
3114             ),
3115             ExprKind::Field(ref el, ident) => hir::ExprField(
3116                 P(self.lower_expr(el)),
3117                 respan(ident.span, self.lower_ident(ident)),
3118             ),
3119             ExprKind::Index(ref el, ref er) => {
3120                 hir::ExprIndex(P(self.lower_expr(el)), P(self.lower_expr(er)))
3121             }
3122             // Desugar `<start>..=<end>` to `std::ops::RangeInclusive::new(<start>, <end>)`
3123             ExprKind::Range(Some(ref e1), Some(ref e2), RangeLimits::Closed) => {
3124                 // FIXME: Use head_sp directly after RangeInclusive::new() is stabilized in stage0.
3125                 let span = self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3126                 let id = self.lower_node_id(e.id);
3127                 let e1 = self.lower_expr(e1);
3128                 let e2 = self.lower_expr(e2);
3129                 let ty_path = P(self.std_path(span, &["ops", "RangeInclusive"], false));
3130                 let ty = self.ty_path(id, span, hir::QPath::Resolved(None, ty_path));
3131                 let new_seg = P(hir::PathSegment::from_name(Symbol::intern("new")));
3132                 let new_path = hir::QPath::TypeRelative(ty, new_seg);
3133                 let new = P(self.expr(span, hir::ExprPath(new_path), ThinVec::new()));
3134                 hir::ExprCall(new, hir_vec![e1, e2])
3135             }
3136             ExprKind::Range(ref e1, ref e2, lims) => {
3137                 use syntax::ast::RangeLimits::*;
3138
3139                 let path = match (e1, e2, lims) {
3140                     (&None, &None, HalfOpen) => "RangeFull",
3141                     (&Some(..), &None, HalfOpen) => "RangeFrom",
3142                     (&None, &Some(..), HalfOpen) => "RangeTo",
3143                     (&Some(..), &Some(..), HalfOpen) => "Range",
3144                     (&None, &Some(..), Closed) => "RangeToInclusive",
3145                     (&Some(..), &Some(..), Closed) => unreachable!(),
3146                     (_, &None, Closed) => self.diagnostic()
3147                         .span_fatal(e.span, "inclusive range with no end")
3148                         .raise(),
3149                 };
3150
3151                 let fields = e1.iter()
3152                     .map(|e| ("start", e))
3153                     .chain(e2.iter().map(|e| ("end", e)))
3154                     .map(|(s, e)| {
3155                         let expr = P(self.lower_expr(&e));
3156                         let unstable_span =
3157                             self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3158                         self.field(Symbol::intern(s), expr, unstable_span)
3159                     })
3160                     .collect::<P<[hir::Field]>>();
3161
3162                 let is_unit = fields.is_empty();
3163                 let unstable_span =
3164                     self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
3165                 let struct_path = iter::once("ops")
3166                     .chain(iter::once(path))
3167                     .collect::<Vec<_>>();
3168                 let struct_path = self.std_path(unstable_span, &struct_path, is_unit);
3169                 let struct_path = hir::QPath::Resolved(None, P(struct_path));
3170
3171                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3172
3173                 return hir::Expr {
3174                     id: node_id,
3175                     hir_id,
3176                     node: if is_unit {
3177                         hir::ExprPath(struct_path)
3178                     } else {
3179                         hir::ExprStruct(struct_path, fields, None)
3180                     },
3181                     span: unstable_span,
3182                     attrs: e.attrs.clone(),
3183                 };
3184             }
3185             ExprKind::Path(ref qself, ref path) => hir::ExprPath(self.lower_qpath(
3186                 e.id,
3187                 qself,
3188                 path,
3189                 ParamMode::Optional,
3190                 ImplTraitContext::Disallowed,
3191             )),
3192             ExprKind::Break(opt_label, ref opt_expr) => {
3193                 let destination = if self.is_in_loop_condition && opt_label.is_none() {
3194                     hir::Destination {
3195                         label: None,
3196                         target_id: hir::ScopeTarget::Loop(
3197                             Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
3198                         ),
3199                     }
3200                 } else {
3201                     self.lower_loop_destination(opt_label.map(|label| (e.id, label)))
3202                 };
3203                 hir::ExprBreak(
3204                     destination,
3205                     opt_expr.as_ref().map(|x| P(self.lower_expr(x))),
3206                 )
3207             }
3208             ExprKind::Continue(opt_label) => {
3209                 hir::ExprAgain(if self.is_in_loop_condition && opt_label.is_none() {
3210                     hir::Destination {
3211                         label: None,
3212                         target_id: hir::ScopeTarget::Loop(
3213                             Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
3214                         ),
3215                     }
3216                 } else {
3217                     self.lower_loop_destination(opt_label.map(|label| (e.id, label)))
3218                 })
3219             }
3220             ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
3221             ExprKind::InlineAsm(ref asm) => {
3222                 let hir_asm = hir::InlineAsm {
3223                     inputs: asm.inputs.iter().map(|&(ref c, _)| c.clone()).collect(),
3224                     outputs: asm.outputs
3225                         .iter()
3226                         .map(|out| hir::InlineAsmOutput {
3227                             constraint: out.constraint.clone(),
3228                             is_rw: out.is_rw,
3229                             is_indirect: out.is_indirect,
3230                         })
3231                         .collect(),
3232                     asm: asm.asm.clone(),
3233                     asm_str_style: asm.asm_str_style,
3234                     clobbers: asm.clobbers.clone().into(),
3235                     volatile: asm.volatile,
3236                     alignstack: asm.alignstack,
3237                     dialect: asm.dialect,
3238                     ctxt: asm.ctxt,
3239                 };
3240                 let outputs = asm.outputs
3241                     .iter()
3242                     .map(|out| self.lower_expr(&out.expr))
3243                     .collect();
3244                 let inputs = asm.inputs
3245                     .iter()
3246                     .map(|&(_, ref input)| self.lower_expr(input))
3247                     .collect();
3248                 hir::ExprInlineAsm(P(hir_asm), outputs, inputs)
3249             }
3250             ExprKind::Struct(ref path, ref fields, ref maybe_expr) => hir::ExprStruct(
3251                 self.lower_qpath(
3252                     e.id,
3253                     &None,
3254                     path,
3255                     ParamMode::Optional,
3256                     ImplTraitContext::Disallowed,
3257                 ),
3258                 fields.iter().map(|x| self.lower_field(x)).collect(),
3259                 maybe_expr.as_ref().map(|x| P(self.lower_expr(x))),
3260             ),
3261             ExprKind::Paren(ref ex) => {
3262                 let mut ex = self.lower_expr(ex);
3263                 // include parens in span, but only if it is a super-span.
3264                 if e.span.contains(ex.span) {
3265                     ex.span = e.span;
3266                 }
3267                 // merge attributes into the inner expression.
3268                 let mut attrs = e.attrs.clone();
3269                 attrs.extend::<Vec<_>>(ex.attrs.into());
3270                 ex.attrs = attrs;
3271                 return ex;
3272             }
3273
3274             ExprKind::Yield(ref opt_expr) => {
3275                 self.is_generator = true;
3276                 let expr = opt_expr
3277                     .as_ref()
3278                     .map(|x| self.lower_expr(x))
3279                     .unwrap_or_else(|| self.expr(e.span, hir::ExprTup(hir_vec![]), ThinVec::new()));
3280                 hir::ExprYield(P(expr))
3281             }
3282
3283             // Desugar ExprIfLet
3284             // From: `if let <pat> = <sub_expr> <body> [<else_opt>]`
3285             ExprKind::IfLet(ref pats, ref sub_expr, ref body, ref else_opt) => {
3286                 // to:
3287                 //
3288                 //   match <sub_expr> {
3289                 //     <pat> => <body>,
3290                 //     _ => [<else_opt> | ()]
3291                 //   }
3292
3293                 let mut arms = vec![];
3294
3295                 // `<pat> => <body>`
3296                 {
3297                     let body = self.lower_block(body, false);
3298                     let body_expr = P(self.expr_block(body, ThinVec::new()));
3299                     let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
3300                     arms.push(self.arm(pats, body_expr));
3301                 }
3302
3303                 // _ => [<else_opt>|()]
3304                 {
3305                     let wildcard_arm: Option<&Expr> = else_opt.as_ref().map(|p| &**p);
3306                     let wildcard_pattern = self.pat_wild(e.span);
3307                     let body = if let Some(else_expr) = wildcard_arm {
3308                         P(self.lower_expr(else_expr))
3309                     } else {
3310                         self.expr_tuple(e.span, hir_vec![])
3311                     };
3312                     arms.push(self.arm(hir_vec![wildcard_pattern], body));
3313                 }
3314
3315                 let contains_else_clause = else_opt.is_some();
3316
3317                 let sub_expr = P(self.lower_expr(sub_expr));
3318
3319                 hir::ExprMatch(
3320                     sub_expr,
3321                     arms.into(),
3322                     hir::MatchSource::IfLetDesugar {
3323                         contains_else_clause,
3324                     },
3325                 )
3326             }
3327
3328             // Desugar ExprWhileLet
3329             // From: `[opt_ident]: while let <pat> = <sub_expr> <body>`
3330             ExprKind::WhileLet(ref pats, ref sub_expr, ref body, opt_label) => {
3331                 // to:
3332                 //
3333                 //   [opt_ident]: loop {
3334                 //     match <sub_expr> {
3335                 //       <pat> => <body>,
3336                 //       _ => break
3337                 //     }
3338                 //   }
3339
3340                 // Note that the block AND the condition are evaluated in the loop scope.
3341                 // This is done to allow `break` from inside the condition of the loop.
3342                 let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| {
3343                     (
3344                         this.lower_block(body, false),
3345                         this.expr_break(e.span, ThinVec::new()),
3346                         this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
3347                     )
3348                 });
3349
3350                 // `<pat> => <body>`
3351                 let pat_arm = {
3352                     let body_expr = P(self.expr_block(body, ThinVec::new()));
3353                     let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
3354                     self.arm(pats, body_expr)
3355                 };
3356
3357                 // `_ => break`
3358                 let break_arm = {
3359                     let pat_under = self.pat_wild(e.span);
3360                     self.arm(hir_vec![pat_under], break_expr)
3361                 };
3362
3363                 // `match <sub_expr> { ... }`
3364                 let arms = hir_vec![pat_arm, break_arm];
3365                 let match_expr = self.expr(
3366                     sub_expr.span,
3367                     hir::ExprMatch(sub_expr, arms, hir::MatchSource::WhileLetDesugar),
3368                     ThinVec::new(),
3369                 );
3370
3371                 // `[opt_ident]: loop { ... }`
3372                 let loop_block = P(self.block_expr(P(match_expr)));
3373                 let loop_expr = hir::ExprLoop(
3374                     loop_block,
3375                     self.lower_label(opt_label),
3376                     hir::LoopSource::WhileLet,
3377                 );
3378                 // add attributes to the outer returned expr node
3379                 loop_expr
3380             }
3381
3382             // Desugar ExprForLoop
3383             // From: `[opt_ident]: for <pat> in <head> <body>`
3384             ExprKind::ForLoop(ref pat, ref head, ref body, opt_label) => {
3385                 // to:
3386                 //
3387                 //   {
3388                 //     let result = match ::std::iter::IntoIterator::into_iter(<head>) {
3389                 //       mut iter => {
3390                 //         [opt_ident]: loop {
3391                 //           let mut __next;
3392                 //           match ::std::iter::Iterator::next(&mut iter) {
3393                 //             ::std::option::Option::Some(val) => __next = val,
3394                 //             ::std::option::Option::None => break
3395                 //           };
3396                 //           let <pat> = __next;
3397                 //           StmtExpr(<body>);
3398                 //         }
3399                 //       }
3400                 //     };
3401                 //     result
3402                 //   }
3403
3404                 // expand <head>
3405                 let head = self.lower_expr(head);
3406                 let head_sp = head.span;
3407
3408                 let iter = self.str_to_ident("iter");
3409
3410                 let next_ident = self.str_to_ident("__next");
3411                 let next_pat = self.pat_ident_binding_mode(
3412                     pat.span,
3413                     next_ident,
3414                     hir::BindingAnnotation::Mutable,
3415                 );
3416
3417                 // `::std::option::Option::Some(val) => next = val`
3418                 let pat_arm = {
3419                     let val_ident = self.str_to_ident("val");
3420                     let val_pat = self.pat_ident(pat.span, val_ident);
3421                     let val_expr = P(self.expr_ident(pat.span, val_ident, val_pat.id));
3422                     let next_expr = P(self.expr_ident(pat.span, next_ident, next_pat.id));
3423                     let assign = P(self.expr(
3424                         pat.span,
3425                         hir::ExprAssign(next_expr, val_expr),
3426                         ThinVec::new(),
3427                     ));
3428                     let some_pat = self.pat_some(pat.span, val_pat);
3429                     self.arm(hir_vec![some_pat], assign)
3430                 };
3431
3432                 // `::std::option::Option::None => break`
3433                 let break_arm = {
3434                     let break_expr =
3435                         self.with_loop_scope(e.id, |this| this.expr_break(e.span, ThinVec::new()));
3436                     let pat = self.pat_none(e.span);
3437                     self.arm(hir_vec![pat], break_expr)
3438                 };
3439
3440                 // `mut iter`
3441                 let iter_pat =
3442                     self.pat_ident_binding_mode(head_sp, iter, hir::BindingAnnotation::Mutable);
3443
3444                 // `match ::std::iter::Iterator::next(&mut iter) { ... }`
3445                 let match_expr = {
3446                     let iter = P(self.expr_ident(head_sp, iter, iter_pat.id));
3447                     let ref_mut_iter = self.expr_mut_addr_of(head_sp, iter);
3448                     let next_path = &["iter", "Iterator", "next"];
3449                     let next_path = P(self.expr_std_path(head_sp, next_path, ThinVec::new()));
3450                     let next_expr = P(self.expr_call(head_sp, next_path, hir_vec![ref_mut_iter]));
3451                     let arms = hir_vec![pat_arm, break_arm];
3452
3453                     P(self.expr(
3454                         head_sp,
3455                         hir::ExprMatch(next_expr, arms, hir::MatchSource::ForLoopDesugar),
3456                         ThinVec::new(),
3457                     ))
3458                 };
3459                 let match_stmt = respan(head_sp, hir::StmtExpr(match_expr, self.next_id().node_id));
3460
3461                 let next_expr = P(self.expr_ident(head_sp, next_ident, next_pat.id));
3462
3463                 // `let mut __next`
3464                 let next_let =
3465                     self.stmt_let_pat(head_sp, None, next_pat, hir::LocalSource::ForLoopDesugar);
3466
3467                 // `let <pat> = __next`
3468                 let pat = self.lower_pat(pat);
3469                 let pat_let = self.stmt_let_pat(
3470                     head_sp,
3471                     Some(next_expr),
3472                     pat,
3473                     hir::LocalSource::ForLoopDesugar,
3474                 );
3475
3476                 let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body, false));
3477                 let body_expr = P(self.expr_block(body_block, ThinVec::new()));
3478                 let body_stmt = respan(body.span, hir::StmtExpr(body_expr, self.next_id().node_id));
3479
3480                 let loop_block = P(self.block_all(
3481                     e.span,
3482                     hir_vec![next_let, match_stmt, pat_let, body_stmt],
3483                     None,
3484                 ));
3485
3486                 // `[opt_ident]: loop { ... }`
3487                 let loop_expr = hir::ExprLoop(
3488                     loop_block,
3489                     self.lower_label(opt_label),
3490                     hir::LoopSource::ForLoop,
3491                 );
3492                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3493                 let loop_expr = P(hir::Expr {
3494                     id: node_id,
3495                     hir_id,
3496                     node: loop_expr,
3497                     span: e.span,
3498                     attrs: ThinVec::new(),
3499                 });
3500
3501                 // `mut iter => { ... }`
3502                 let iter_arm = self.arm(hir_vec![iter_pat], loop_expr);
3503
3504                 // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
3505                 let into_iter_expr = {
3506                     let into_iter_path = &["iter", "IntoIterator", "into_iter"];
3507                     let into_iter = P(self.expr_std_path(head_sp, into_iter_path, ThinVec::new()));
3508                     P(self.expr_call(head_sp, into_iter, hir_vec![head]))
3509                 };
3510
3511                 let match_expr = P(self.expr_match(
3512                     head_sp,
3513                     into_iter_expr,
3514                     hir_vec![iter_arm],
3515                     hir::MatchSource::ForLoopDesugar,
3516                 ));
3517
3518                 // `{ let _result = ...; _result }`
3519                 // underscore prevents an unused_variables lint if the head diverges
3520                 let result_ident = self.str_to_ident("_result");
3521                 let (let_stmt, let_stmt_binding) =
3522                     self.stmt_let(e.span, false, result_ident, match_expr);
3523
3524                 let result = P(self.expr_ident(e.span, result_ident, let_stmt_binding));
3525                 let block = P(self.block_all(e.span, hir_vec![let_stmt], Some(result)));
3526                 // add the attributes to the outer returned expr node
3527                 return self.expr_block(block, e.attrs.clone());
3528             }
3529
3530             // Desugar ExprKind::Try
3531             // From: `<expr>?`
3532             ExprKind::Try(ref sub_expr) => {
3533                 // to:
3534                 //
3535                 // match Try::into_result(<expr>) {
3536                 //     Ok(val) => #[allow(unreachable_code)] val,
3537                 //     Err(err) => #[allow(unreachable_code)]
3538                 //                 // If there is an enclosing `catch {...}`
3539                 //                 break 'catch_target Try::from_error(From::from(err)),
3540                 //                 // Otherwise
3541                 //                 return Try::from_error(From::from(err)),
3542                 // }
3543
3544                 let unstable_span =
3545                     self.allow_internal_unstable(CompilerDesugaringKind::QuestionMark, e.span);
3546
3547                 // Try::into_result(<expr>)
3548                 let discr = {
3549                     // expand <expr>
3550                     let sub_expr = self.lower_expr(sub_expr);
3551
3552                     let path = &["ops", "Try", "into_result"];
3553                     let path = P(self.expr_std_path(unstable_span, path, ThinVec::new()));
3554                     P(self.expr_call(e.span, path, hir_vec![sub_expr]))
3555                 };
3556
3557                 // #[allow(unreachable_code)]
3558                 let attr = {
3559                     // allow(unreachable_code)
3560                     let allow = {
3561                         let allow_ident = Ident::from_str("allow").with_span_pos(e.span);
3562                         let uc_ident = Ident::from_str("unreachable_code").with_span_pos(e.span);
3563                         let uc_nested = attr::mk_nested_word_item(uc_ident);
3564                         attr::mk_list_item(e.span, allow_ident, vec![uc_nested])
3565                     };
3566                     attr::mk_spanned_attr_outer(e.span, attr::mk_attr_id(), allow)
3567                 };
3568                 let attrs = vec![attr];
3569
3570                 // Ok(val) => #[allow(unreachable_code)] val,
3571                 let ok_arm = {
3572                     let val_ident = self.str_to_ident("val");
3573                     let val_pat = self.pat_ident(e.span, val_ident);
3574                     let val_expr = P(self.expr_ident_with_attrs(
3575                         e.span,
3576                         val_ident,
3577                         val_pat.id,
3578                         ThinVec::from(attrs.clone()),
3579                     ));
3580                     let ok_pat = self.pat_ok(e.span, val_pat);
3581
3582                     self.arm(hir_vec![ok_pat], val_expr)
3583                 };
3584
3585                 // Err(err) => #[allow(unreachable_code)]
3586                 //             return Try::from_error(From::from(err)),
3587                 let err_arm = {
3588                     let err_ident = self.str_to_ident("err");
3589                     let err_local = self.pat_ident(e.span, err_ident);
3590                     let from_expr = {
3591                         let path = &["convert", "From", "from"];
3592                         let from = P(self.expr_std_path(e.span, path, ThinVec::new()));
3593                         let err_expr = self.expr_ident(e.span, err_ident, err_local.id);
3594
3595                         self.expr_call(e.span, from, hir_vec![err_expr])
3596                     };
3597                     let from_err_expr =
3598                         self.wrap_in_try_constructor("from_error", from_expr, unstable_span);
3599                     let thin_attrs = ThinVec::from(attrs);
3600                     let catch_scope = self.catch_scopes.last().map(|x| *x);
3601                     let ret_expr = if let Some(catch_node) = catch_scope {
3602                         P(self.expr(
3603                             e.span,
3604                             hir::ExprBreak(
3605                                 hir::Destination {
3606                                     label: None,
3607                                     target_id: hir::ScopeTarget::Block(catch_node),
3608                                 },
3609                                 Some(from_err_expr),
3610                             ),
3611                             thin_attrs,
3612                         ))
3613                     } else {
3614                         P(self.expr(e.span, hir::Expr_::ExprRet(Some(from_err_expr)), thin_attrs))
3615                     };
3616
3617                     let err_pat = self.pat_err(e.span, err_local);
3618                     self.arm(hir_vec![err_pat], ret_expr)
3619                 };
3620
3621                 hir::ExprMatch(
3622                     discr,
3623                     hir_vec![err_arm, ok_arm],
3624                     hir::MatchSource::TryDesugar,
3625                 )
3626             }
3627
3628             ExprKind::Mac(_) => panic!("Shouldn't exist here"),
3629         };
3630
3631         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
3632
3633         hir::Expr {
3634             id: node_id,
3635             hir_id,
3636             node: kind,
3637             span: e.span,
3638             attrs: e.attrs.clone(),
3639         }
3640     }
3641
3642     fn lower_stmt(&mut self, s: &Stmt) -> SmallVector<hir::Stmt> {
3643         SmallVector::one(match s.node {
3644             StmtKind::Local(ref l) => Spanned {
3645                 node: hir::StmtDecl(
3646                     P(Spanned {
3647                         node: hir::DeclLocal(self.lower_local(l)),
3648                         span: s.span,
3649                     }),
3650                     self.lower_node_id(s.id).node_id,
3651                 ),
3652                 span: s.span,
3653             },
3654             StmtKind::Item(ref it) => {
3655                 // Can only use the ID once.
3656                 let mut id = Some(s.id);
3657                 return self.lower_item_id(it)
3658                     .into_iter()
3659                     .map(|item_id| Spanned {
3660                         node: hir::StmtDecl(
3661                             P(Spanned {
3662                                 node: hir::DeclItem(item_id),
3663                                 span: s.span,
3664                             }),
3665                             id.take()
3666                                 .map(|id| self.lower_node_id(id).node_id)
3667                                 .unwrap_or_else(|| self.next_id().node_id),
3668                         ),
3669                         span: s.span,
3670                     })
3671                     .collect();
3672             }
3673             StmtKind::Expr(ref e) => Spanned {
3674                 node: hir::StmtExpr(P(self.lower_expr(e)), self.lower_node_id(s.id).node_id),
3675                 span: s.span,
3676             },
3677             StmtKind::Semi(ref e) => Spanned {
3678                 node: hir::StmtSemi(P(self.lower_expr(e)), self.lower_node_id(s.id).node_id),
3679                 span: s.span,
3680             },
3681             StmtKind::Mac(..) => panic!("Shouldn't exist here"),
3682         })
3683     }
3684
3685     fn lower_capture_clause(&mut self, c: CaptureBy) -> hir::CaptureClause {
3686         match c {
3687             CaptureBy::Value => hir::CaptureByValue,
3688             CaptureBy::Ref => hir::CaptureByRef,
3689         }
3690     }
3691
3692     /// If an `explicit_owner` is given, this method allocates the `HirId` in
3693     /// the address space of that item instead of the item currently being
3694     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
3695     /// lower a `Visibility` value although we haven't lowered the owning
3696     /// `ImplItem` in question yet.
3697     fn lower_visibility(
3698         &mut self,
3699         v: &Visibility,
3700         explicit_owner: Option<NodeId>,
3701     ) -> hir::Visibility {
3702         match v.node {
3703             VisibilityKind::Public => hir::Public,
3704             VisibilityKind::Crate(..) => hir::Visibility::Crate,
3705             VisibilityKind::Restricted { ref path, id, .. } => hir::Visibility::Restricted {
3706                 path: P(self.lower_path(id, path, ParamMode::Explicit)),
3707                 id: if let Some(owner) = explicit_owner {
3708                     self.lower_node_id_with_owner(id, owner).node_id
3709                 } else {
3710                     self.lower_node_id(id).node_id
3711                 },
3712             },
3713             VisibilityKind::Inherited => hir::Inherited,
3714         }
3715     }
3716
3717     fn lower_defaultness(&mut self, d: Defaultness, has_value: bool) -> hir::Defaultness {
3718         match d {
3719             Defaultness::Default => hir::Defaultness::Default {
3720                 has_value: has_value,
3721             },
3722             Defaultness::Final => {
3723                 assert!(has_value);
3724                 hir::Defaultness::Final
3725             }
3726         }
3727     }
3728
3729     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
3730         match *b {
3731             BlockCheckMode::Default => hir::DefaultBlock,
3732             BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
3733         }
3734     }
3735
3736     fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
3737         match *b {
3738             BindingMode::ByValue(Mutability::Immutable) => hir::BindingAnnotation::Unannotated,
3739             BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
3740             BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
3741             BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
3742         }
3743     }
3744
3745     fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
3746         match u {
3747             CompilerGenerated => hir::CompilerGenerated,
3748             UserProvided => hir::UserProvided,
3749         }
3750     }
3751
3752     fn lower_impl_polarity(&mut self, i: ImplPolarity) -> hir::ImplPolarity {
3753         match i {
3754             ImplPolarity::Positive => hir::ImplPolarity::Positive,
3755             ImplPolarity::Negative => hir::ImplPolarity::Negative,
3756         }
3757     }
3758
3759     fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
3760         match f {
3761             TraitBoundModifier::None => hir::TraitBoundModifier::None,
3762             TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
3763         }
3764     }
3765
3766     // Helper methods for building HIR.
3767
3768     fn arm(&mut self, pats: hir::HirVec<P<hir::Pat>>, expr: P<hir::Expr>) -> hir::Arm {
3769         hir::Arm {
3770             attrs: hir_vec![],
3771             pats,
3772             guard: None,
3773             body: expr,
3774         }
3775     }
3776
3777     fn field(&mut self, name: Name, expr: P<hir::Expr>, span: Span) -> hir::Field {
3778         hir::Field {
3779             id: self.next_id().node_id,
3780             name: Spanned { node: name, span },
3781             span,
3782             expr,
3783             is_shorthand: false,
3784         }
3785     }
3786
3787     fn expr_break(&mut self, span: Span, attrs: ThinVec<Attribute>) -> P<hir::Expr> {
3788         let expr_break = hir::ExprBreak(self.lower_loop_destination(None), None);
3789         P(self.expr(span, expr_break, attrs))
3790     }
3791
3792     fn expr_call(
3793         &mut self,
3794         span: Span,
3795         e: P<hir::Expr>,
3796         args: hir::HirVec<hir::Expr>,
3797     ) -> hir::Expr {
3798         self.expr(span, hir::ExprCall(e, args), ThinVec::new())
3799     }
3800
3801     fn expr_ident(&mut self, span: Span, id: Name, binding: NodeId) -> hir::Expr {
3802         self.expr_ident_with_attrs(span, id, binding, ThinVec::new())
3803     }
3804
3805     fn expr_ident_with_attrs(
3806         &mut self,
3807         span: Span,
3808         id: Name,
3809         binding: NodeId,
3810         attrs: ThinVec<Attribute>,
3811     ) -> hir::Expr {
3812         let expr_path = hir::ExprPath(hir::QPath::Resolved(
3813             None,
3814             P(hir::Path {
3815                 span,
3816                 def: Def::Local(binding),
3817                 segments: hir_vec![hir::PathSegment::from_name(id)],
3818             }),
3819         ));
3820
3821         self.expr(span, expr_path, attrs)
3822     }
3823
3824     fn expr_mut_addr_of(&mut self, span: Span, e: P<hir::Expr>) -> hir::Expr {
3825         self.expr(span, hir::ExprAddrOf(hir::MutMutable, e), ThinVec::new())
3826     }
3827
3828     fn expr_std_path(
3829         &mut self,
3830         span: Span,
3831         components: &[&str],
3832         attrs: ThinVec<Attribute>,
3833     ) -> hir::Expr {
3834         let path = self.std_path(span, components, true);
3835         self.expr(
3836             span,
3837             hir::ExprPath(hir::QPath::Resolved(None, P(path))),
3838             attrs,
3839         )
3840     }
3841
3842     fn expr_match(
3843         &mut self,
3844         span: Span,
3845         arg: P<hir::Expr>,
3846         arms: hir::HirVec<hir::Arm>,
3847         source: hir::MatchSource,
3848     ) -> hir::Expr {
3849         self.expr(span, hir::ExprMatch(arg, arms, source), ThinVec::new())
3850     }
3851
3852     fn expr_block(&mut self, b: P<hir::Block>, attrs: ThinVec<Attribute>) -> hir::Expr {
3853         self.expr(b.span, hir::ExprBlock(b), attrs)
3854     }
3855
3856     fn expr_tuple(&mut self, sp: Span, exprs: hir::HirVec<hir::Expr>) -> P<hir::Expr> {
3857         P(self.expr(sp, hir::ExprTup(exprs), ThinVec::new()))
3858     }
3859
3860     fn expr(&mut self, span: Span, node: hir::Expr_, attrs: ThinVec<Attribute>) -> hir::Expr {
3861         let LoweredNodeId { node_id, hir_id } = self.next_id();
3862         hir::Expr {
3863             id: node_id,
3864             hir_id,
3865             node,
3866             span,
3867             attrs,
3868         }
3869     }
3870
3871     fn stmt_let_pat(
3872         &mut self,
3873         sp: Span,
3874         ex: Option<P<hir::Expr>>,
3875         pat: P<hir::Pat>,
3876         source: hir::LocalSource,
3877     ) -> hir::Stmt {
3878         let LoweredNodeId { node_id, hir_id } = self.next_id();
3879
3880         let local = P(hir::Local {
3881             pat,
3882             ty: None,
3883             init: ex,
3884             id: node_id,
3885             hir_id,
3886             span: sp,
3887             attrs: ThinVec::new(),
3888             source,
3889         });
3890         let decl = respan(sp, hir::DeclLocal(local));
3891         respan(sp, hir::StmtDecl(P(decl), self.next_id().node_id))
3892     }
3893
3894     fn stmt_let(
3895         &mut self,
3896         sp: Span,
3897         mutbl: bool,
3898         ident: Name,
3899         ex: P<hir::Expr>,
3900     ) -> (hir::Stmt, NodeId) {
3901         let pat = if mutbl {
3902             self.pat_ident_binding_mode(sp, ident, hir::BindingAnnotation::Mutable)
3903         } else {
3904             self.pat_ident(sp, ident)
3905         };
3906         let pat_id = pat.id;
3907         (
3908             self.stmt_let_pat(sp, Some(ex), pat, hir::LocalSource::Normal),
3909             pat_id,
3910         )
3911     }
3912
3913     fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
3914         self.block_all(expr.span, hir::HirVec::new(), Some(expr))
3915     }
3916
3917     fn block_all(
3918         &mut self,
3919         span: Span,
3920         stmts: hir::HirVec<hir::Stmt>,
3921         expr: Option<P<hir::Expr>>,
3922     ) -> hir::Block {
3923         let LoweredNodeId { node_id, hir_id } = self.next_id();
3924
3925         hir::Block {
3926             stmts,
3927             expr,
3928             id: node_id,
3929             hir_id,
3930             rules: hir::DefaultBlock,
3931             span,
3932             targeted_by_break: false,
3933             recovered: false,
3934         }
3935     }
3936
3937     fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3938         self.pat_std_enum(span, &["result", "Result", "Ok"], hir_vec![pat])
3939     }
3940
3941     fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3942         self.pat_std_enum(span, &["result", "Result", "Err"], hir_vec![pat])
3943     }
3944
3945     fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
3946         self.pat_std_enum(span, &["option", "Option", "Some"], hir_vec![pat])
3947     }
3948
3949     fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
3950         self.pat_std_enum(span, &["option", "Option", "None"], hir_vec![])
3951     }
3952
3953     fn pat_std_enum(
3954         &mut self,
3955         span: Span,
3956         components: &[&str],
3957         subpats: hir::HirVec<P<hir::Pat>>,
3958     ) -> P<hir::Pat> {
3959         let path = self.std_path(span, components, true);
3960         let qpath = hir::QPath::Resolved(None, P(path));
3961         let pt = if subpats.is_empty() {
3962             hir::PatKind::Path(qpath)
3963         } else {
3964             hir::PatKind::TupleStruct(qpath, subpats, None)
3965         };
3966         self.pat(span, pt)
3967     }
3968
3969     fn pat_ident(&mut self, span: Span, name: Name) -> P<hir::Pat> {
3970         self.pat_ident_binding_mode(span, name, hir::BindingAnnotation::Unannotated)
3971     }
3972
3973     fn pat_ident_binding_mode(
3974         &mut self,
3975         span: Span,
3976         name: Name,
3977         bm: hir::BindingAnnotation,
3978     ) -> P<hir::Pat> {
3979         let LoweredNodeId { node_id, hir_id } = self.next_id();
3980
3981         P(hir::Pat {
3982             id: node_id,
3983             hir_id,
3984             node: hir::PatKind::Binding(bm, node_id, Spanned { span, node: name }, None),
3985             span,
3986         })
3987     }
3988
3989     fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
3990         self.pat(span, hir::PatKind::Wild)
3991     }
3992
3993     fn pat(&mut self, span: Span, pat: hir::PatKind) -> P<hir::Pat> {
3994         let LoweredNodeId { node_id, hir_id } = self.next_id();
3995         P(hir::Pat {
3996             id: node_id,
3997             hir_id,
3998             node: pat,
3999             span,
4000         })
4001     }
4002
4003     /// Given suffix ["b","c","d"], returns path `::std::b::c::d` when
4004     /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
4005     /// The path is also resolved according to `is_value`.
4006     fn std_path(&mut self, span: Span, components: &[&str], is_value: bool) -> hir::Path {
4007         self.resolver
4008             .resolve_str_path(span, self.crate_root, components, is_value)
4009     }
4010
4011     fn ty_path(&mut self, id: LoweredNodeId, span: Span, qpath: hir::QPath) -> P<hir::Ty> {
4012         let mut id = id;
4013         let node = match qpath {
4014             hir::QPath::Resolved(None, path) => {
4015                 // Turn trait object paths into `TyTraitObject` instead.
4016                 if let Def::Trait(_) = path.def {
4017                     let principal = hir::PolyTraitRef {
4018                         bound_generic_params: hir::HirVec::new(),
4019                         trait_ref: hir::TraitRef {
4020                             path: path.and_then(|path| path),
4021                             ref_id: id.node_id,
4022                         },
4023                         span,
4024                     };
4025
4026                     // The original ID is taken by the `PolyTraitRef`,
4027                     // so the `Ty` itself needs a different one.
4028                     id = self.next_id();
4029                     hir::TyTraitObject(hir_vec![principal], self.elided_dyn_bound(span))
4030                 } else {
4031                     hir::TyPath(hir::QPath::Resolved(None, path))
4032                 }
4033             }
4034             _ => hir::TyPath(qpath),
4035         };
4036         P(hir::Ty {
4037             id: id.node_id,
4038             hir_id: id.hir_id,
4039             node,
4040             span,
4041         })
4042     }
4043
4044     /// Invoked to create the lifetime argument for a type `&T`
4045     /// with no explicit lifetime.
4046     fn elided_ref_lifetime(&mut self, span: Span) -> hir::Lifetime {
4047         match self.anonymous_lifetime_mode {
4048             // Intercept when we are in an impl header and introduce an in-band lifetime.
4049             // Hence `impl Foo for &u32` becomes `impl<'f> Foo for &'f u32` for some fresh
4050             // `'f`.
4051             AnonymousLifetimeMode::CreateParameter => {
4052                 let fresh_name = self.collect_fresh_in_band_lifetime(span);
4053                 hir::Lifetime {
4054                     id: self.next_id().node_id,
4055                     span,
4056                     name: fresh_name,
4057                 }
4058             }
4059
4060             AnonymousLifetimeMode::PassThrough => self.new_implicit_lifetime(span),
4061         }
4062     }
4063
4064     /// Invoked to create the lifetime argument(s) for a path like
4065     /// `std::cell::Ref<T>`; note that implicit lifetimes in these
4066     /// sorts of cases are deprecated. This may therefore report a warning or an
4067     /// error, depending on the mode.
4068     fn elided_path_lifetimes(&mut self, span: Span, count: usize) -> P<[hir::Lifetime]> {
4069         match self.anonymous_lifetime_mode {
4070             // NB. We intentionally ignore the create-parameter mode here
4071             // and instead "pass through" to resolve-lifetimes, which will then
4072             // report an error. This is because we don't want to support
4073             // impl elision for deprecated forms like
4074             //
4075             //     impl Foo for std::cell::Ref<u32> // note lack of '_
4076             AnonymousLifetimeMode::CreateParameter => {}
4077
4078             // This is the normal case.
4079             AnonymousLifetimeMode::PassThrough => {}
4080         }
4081
4082         (0..count)
4083             .map(|_| self.new_implicit_lifetime(span))
4084             .collect()
4085     }
4086
4087     /// Invoked to create the lifetime argument(s) for an elided trait object
4088     /// bound, like the bound in `Box<dyn Debug>`. This method is not invoked
4089     /// when the bound is written, even if it is written with `'_` like in
4090     /// `Box<dyn Debug + '_>`. In those cases, `lower_lifetime` is invoked.
4091     fn elided_dyn_bound(&mut self, span: Span) -> hir::Lifetime {
4092         match self.anonymous_lifetime_mode {
4093             // NB. We intentionally ignore the create-parameter mode here.
4094             // and instead "pass through" to resolve-lifetimes, which will apply
4095             // the object-lifetime-defaulting rules. Elided object lifetime defaults
4096             // do not act like other elided lifetimes. In other words, given this:
4097             //
4098             //     impl Foo for Box<dyn Debug>
4099             //
4100             // we do not introduce a fresh `'_` to serve as the bound, but instead
4101             // ultimately translate to the equivalent of:
4102             //
4103             //     impl Foo for Box<dyn Debug + 'static>
4104             //
4105             // `resolve_lifetime` has the code to make that happen.
4106             AnonymousLifetimeMode::CreateParameter => {}
4107
4108             // This is the normal case.
4109             AnonymousLifetimeMode::PassThrough => {}
4110         }
4111
4112         self.new_implicit_lifetime(span)
4113     }
4114
4115     fn new_implicit_lifetime(&mut self, span: Span) -> hir::Lifetime {
4116         hir::Lifetime {
4117             id: self.next_id().node_id,
4118             span,
4119             name: hir::LifetimeName::Implicit,
4120         }
4121     }
4122
4123     fn maybe_lint_bare_trait(&self, span: Span, id: NodeId, is_global: bool) {
4124         self.sess.buffer_lint_with_diagnostic(
4125             builtin::BARE_TRAIT_OBJECT,
4126             id,
4127             span,
4128             "trait objects without an explicit `dyn` are deprecated",
4129             builtin::BuiltinLintDiagnostics::BareTraitObject(span, is_global),
4130         )
4131     }
4132
4133     fn wrap_in_try_constructor(
4134         &mut self,
4135         method: &'static str,
4136         e: hir::Expr,
4137         unstable_span: Span,
4138     ) -> P<hir::Expr> {
4139         let path = &["ops", "Try", method];
4140         let from_err = P(self.expr_std_path(unstable_span, path,
4141                                             ThinVec::new()));
4142         P(self.expr_call(e.span, from_err, hir_vec![e]))
4143     }
4144 }
4145
4146 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
4147     // Sorting by span ensures that we get things in order within a
4148     // file, and also puts the files in a sensible order.
4149     let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
4150     body_ids.sort_by_key(|b| bodies[b].value.span);
4151     body_ids
4152 }