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 hir;
  44 use hir::map::{Definitions, DefKey};
  45 use hir::def_id::{DefIndex, DefId, CRATE_DEF_INDEX};
  46 use hir::def::{Def, PathResolution};
  47 use lint::builtin::PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES;
  48 use rustc_data_structures::indexed_vec::IndexVec;
  49 use session::Session;
  50 use util::common::FN_OUTPUT_NAME;
  51 use util::nodemap::{DefIdMap, FxHashMap, NodeMap};
  52
  53 use std::collections::BTreeMap;
  54 use std::fmt::Debug;
  55 use std::iter;
  56 use std::mem;
  57 use syntax::attr;
  58 use syntax::ast::*;
  59 use syntax::errors;
  60 use syntax::ext::hygiene::{Mark, SyntaxContext};
  61 use syntax::ptr::P;
  62 use syntax::codemap::{self, respan, Spanned, CompilerDesugaringKind};
  63 use syntax::std_inject;
  64 use syntax::symbol::{Symbol, keywords};
  65 use syntax::util::small_vector::SmallVector;
  66 use syntax::visit::{self, Visitor};
  67 use syntax_pos::Span;
  68
  69 const HIR_ID_COUNTER_LOCKED: u32 = 0xFFFFFFFF;
  70
  71 pub struct LoweringContext<'a> {
  72     crate_root: Option<&'static str>,
  73
  74     // Use to assign ids to hir nodes that do not directly correspond to an ast node
  75     sess: &'a Session,
  76
  77     // As we walk the AST we must keep track of the current 'parent' def id (in
  78     // the form of a DefIndex) so that if we create a new node which introduces
  79     // a definition, then we can properly create the def id.
  80     parent_def: Option<DefIndex>,
  81     resolver: &'a mut Resolver,
  82     name_map: FxHashMap<Ident, Name>,
  83
  84     /// The items being lowered are collected here.
  85     items: BTreeMap<NodeId, hir::Item>,
  86
  87     trait_items: BTreeMap<hir::TraitItemId, hir::TraitItem>,
  88     impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
  89     bodies: BTreeMap<hir::BodyId, hir::Body>,
  90     exported_macros: Vec<hir::MacroDef>,
  91
  92     trait_impls: BTreeMap<DefId, Vec<NodeId>>,
  93     trait_default_impl: BTreeMap<DefId, NodeId>,
  94
  95     is_generator: bool,
  96
  97     catch_scopes: Vec<NodeId>,
  98     loop_scopes: Vec<NodeId>,
  99     is_in_loop_condition: bool,
 100
 101     type_def_lifetime_params: DefIdMap<usize>,
 102
 103     current_hir_id_owner: Vec<(DefIndex, u32)>,
 104     item_local_id_counters: NodeMap<u32>,
 105     node_id_to_hir_id: IndexVec<NodeId, hir::HirId>,
 106 }
 107
 108 pub trait Resolver {
 109     /// Resolve a hir path generated by the lowerer when expanding `for`, `if let`, etc.
 110     fn resolve_hir_path(&mut self, path: &mut hir::Path, is_value: bool);
 111
 112     /// Obtain the resolution for a node id
 113     fn get_resolution(&mut self, id: NodeId) -> Option<PathResolution>;
 114
 115     /// We must keep the set of definitions up to date as we add nodes that weren't in the AST.
 116     /// This should only return `None` during testing.
 117     fn definitions(&mut self) -> &mut Definitions;
 118 }
 119
 120 pub fn lower_crate(sess: &Session,
 121                    krate: &Crate,
 122                    resolver: &mut Resolver)
 123                    -> hir::Crate {
 124     // We're constructing the HIR here; we don't care what we will
 125     // read, since we haven't even constructed the *input* to
 126     // incr. comp. yet.
 127     let _ignore = sess.dep_graph.in_ignore();
 128
 129     LoweringContext {
 130         crate_root: std_inject::injected_crate_name(krate),
 131         sess,
 132         parent_def: None,
 133         resolver,
 134         name_map: FxHashMap(),
 135         items: BTreeMap::new(),
 136         trait_items: BTreeMap::new(),
 137         impl_items: BTreeMap::new(),
 138         bodies: BTreeMap::new(),
 139         trait_impls: BTreeMap::new(),
 140         trait_default_impl: BTreeMap::new(),
 141         exported_macros: Vec::new(),
 142         catch_scopes: Vec::new(),
 143         loop_scopes: Vec::new(),
 144         is_in_loop_condition: false,
 145         type_def_lifetime_params: DefIdMap(),
 146         current_hir_id_owner: vec![(CRATE_DEF_INDEX, 0)],
 147         item_local_id_counters: NodeMap(),
 148         node_id_to_hir_id: IndexVec::new(),
 149         is_generator: false,
 150     }.lower_crate(krate)
 151 }
 152
 153 #[derive(Copy, Clone, PartialEq, Eq)]
 154 enum ParamMode {
 155     /// Any path in a type context.
 156     Explicit,
 157     /// The `module::Type` in `module::Type::method` in an expression.
 158     Optional
 159 }
 160
 161 struct LoweredNodeId {
 162     node_id: NodeId,
 163     hir_id: hir::HirId,
 164 }
 165
 166 enum ParenthesizedGenericArgs {
 167     Ok,
 168     Warn,
 169     Err,
 170 }
 171
 172 impl<'a> LoweringContext<'a> {
 173     fn lower_crate(mut self, c: &Crate) -> hir::Crate {
 174         /// Full-crate AST visitor that inserts into a fresh
 175         /// `LoweringContext` any information that may be
 176         /// needed from arbitrary locations in the crate.
 177         /// E.g. The number of lifetime generic parameters
 178         /// declared for every type and trait definition.
 179         struct MiscCollector<'lcx, 'interner: 'lcx> {
 180             lctx: &'lcx mut LoweringContext<'interner>,
 181         }
 182
 183         impl<'lcx, 'interner> Visitor<'lcx> for MiscCollector<'lcx, 'interner> {
 184             fn visit_item(&mut self, item: &'lcx Item) {
 185                 self.lctx.allocate_hir_id_counter(item.id, item);
 186
 187                 match item.node {
 188                     ItemKind::Struct(_, ref generics) |
 189                     ItemKind::Union(_, ref generics) |
 190                     ItemKind::Enum(_, ref generics) |
 191                     ItemKind::Ty(_, ref generics) |
 192                     ItemKind::Trait(_, ref generics, ..) => {
 193                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
 194                         let count = generics.lifetimes.len();
 195                         self.lctx.type_def_lifetime_params.insert(def_id, count);
 196                     }
 197                     _ => {}
 198                 }
 199                 visit::walk_item(self, item);
 200             }
 201
 202             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 203                 self.lctx.allocate_hir_id_counter(item.id, item);
 204                 visit::walk_trait_item(self, item);
 205             }
 206
 207             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 208                 self.lctx.allocate_hir_id_counter(item.id, item);
 209                 visit::walk_impl_item(self, item);
 210             }
 211         }
 212
 213         struct ItemLowerer<'lcx, 'interner: 'lcx> {
 214             lctx: &'lcx mut LoweringContext<'interner>,
 215         }
 216
 217         impl<'lcx, 'interner> Visitor<'lcx> for ItemLowerer<'lcx, 'interner> {
 218             fn visit_item(&mut self, item: &'lcx Item) {
 219                 let mut item_lowered = true;
 220                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 221                     if let Some(hir_item) = lctx.lower_item(item) {
 222                         lctx.items.insert(item.id, hir_item);
 223                     } else {
 224                         item_lowered = false;
 225                     }
 226                 });
 227
 228                 if item_lowered {
 229                     visit::walk_item(self, item);
 230                 }
 231             }
 232
 233             fn visit_trait_item(&mut self, item: &'lcx TraitItem) {
 234                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 235                     let id = hir::TraitItemId { node_id: item.id };
 236                     let hir_item = lctx.lower_trait_item(item);
 237                     lctx.trait_items.insert(id, hir_item);
 238                 });
 239
 240                 visit::walk_trait_item(self, item);
 241             }
 242
 243             fn visit_impl_item(&mut self, item: &'lcx ImplItem) {
 244                 self.lctx.with_hir_id_owner(item.id, |lctx| {
 245                     let id = hir::ImplItemId { node_id: item.id };
 246                     let hir_item = lctx.lower_impl_item(item);
 247                     lctx.impl_items.insert(id, hir_item);
 248                 });
 249                 visit::walk_impl_item(self, item);
 250             }
 251         }
 252
 253         self.lower_node_id(CRATE_NODE_ID);
 254         debug_assert!(self.node_id_to_hir_id[CRATE_NODE_ID] == hir::CRATE_HIR_ID);
 255
 256         visit::walk_crate(&mut MiscCollector { lctx: &mut self }, c);
 257         visit::walk_crate(&mut ItemLowerer { lctx: &mut self }, c);
 258
 259         let module = self.lower_mod(&c.module);
 260         let attrs = self.lower_attrs(&c.attrs);
 261         let body_ids = body_ids(&self.bodies);
 262
 263         self.resolver
 264             .definitions()
 265             .init_node_id_to_hir_id_mapping(self.node_id_to_hir_id);
 266
 267         hir::Crate {
 268             module,
 269             attrs,
 270             span: c.span,
 271             exported_macros: hir::HirVec::from(self.exported_macros),
 272             items: self.items,
 273             trait_items: self.trait_items,
 274             impl_items: self.impl_items,
 275             bodies: self.bodies,
 276             body_ids,
 277             trait_impls: self.trait_impls,
 278             trait_default_impl: self.trait_default_impl,
 279         }
 280     }
 281
 282     fn allocate_hir_id_counter<T: Debug>(&mut self,
 283                                          owner: NodeId,
 284                                          debug: &T) {
 285         if self.item_local_id_counters.insert(owner, 0).is_some() {
 286             bug!("Tried to allocate item_local_id_counter for {:?} twice", debug);
 287         }
 288         // Always allocate the first HirId for the owner itself
 289         self.lower_node_id_with_owner(owner, owner);
 290     }
 291
 292     fn lower_node_id_generic<F>(&mut self,
 293                                 ast_node_id: NodeId,
 294                                 alloc_hir_id: F)
 295                                 -> LoweredNodeId
 296         where F: FnOnce(&mut Self) -> hir::HirId
 297     {
 298         if ast_node_id == DUMMY_NODE_ID {
 299             return LoweredNodeId {
 300                 node_id: DUMMY_NODE_ID,
 301                 hir_id: hir::DUMMY_HIR_ID,
 302             }
 303         }
 304
 305         let min_size = ast_node_id.as_usize() + 1;
 306
 307         if min_size > self.node_id_to_hir_id.len() {
 308             self.node_id_to_hir_id.resize(min_size, hir::DUMMY_HIR_ID);
 309         }
 310
 311         let existing_hir_id = self.node_id_to_hir_id[ast_node_id];
 312
 313         if existing_hir_id == hir::DUMMY_HIR_ID {
 314             // Generate a new HirId
 315             let hir_id = alloc_hir_id(self);
 316             self.node_id_to_hir_id[ast_node_id] = hir_id;
 317             LoweredNodeId {
 318                 node_id: ast_node_id,
 319                 hir_id,
 320             }
 321         } else {
 322             LoweredNodeId {
 323                 node_id: ast_node_id,
 324                 hir_id: existing_hir_id,
 325             }
 326         }
 327     }
 328
 329     fn with_hir_id_owner<F>(&mut self, owner: NodeId, f: F)
 330         where F: FnOnce(&mut Self)
 331     {
 332         let counter = self.item_local_id_counters
 333                           .insert(owner, HIR_ID_COUNTER_LOCKED)
 334                           .unwrap();
 335         let def_index = self.resolver.definitions().opt_def_index(owner).unwrap();
 336         self.current_hir_id_owner.push((def_index, counter));
 337         f(self);
 338         let (new_def_index, new_counter) = self.current_hir_id_owner.pop().unwrap();
 339
 340         debug_assert!(def_index == new_def_index);
 341         debug_assert!(new_counter >= counter);
 342
 343         let prev = self.item_local_id_counters.insert(owner, new_counter).unwrap();
 344         debug_assert!(prev == HIR_ID_COUNTER_LOCKED);
 345     }
 346
 347     /// This method allocates a new HirId for the given NodeId and stores it in
 348     /// the LoweringContext's NodeId => HirId map.
 349     /// Take care not to call this method if the resulting HirId is then not
 350     /// actually used in the HIR, as that would trigger an assertion in the
 351     /// HirIdValidator later on, which makes sure that all NodeIds got mapped
 352     /// properly. Calling the method twice with the same NodeId is fine though.
 353     fn lower_node_id(&mut self, ast_node_id: NodeId) -> LoweredNodeId {
 354         self.lower_node_id_generic(ast_node_id, |this| {
 355             let &mut (def_index, ref mut local_id_counter) = this.current_hir_id_owner
 356                                                                  .last_mut()
 357                                                                  .unwrap();
 358             let local_id = *local_id_counter;
 359             *local_id_counter += 1;
 360             hir::HirId {
 361                 owner: def_index,
 362                 local_id: hir::ItemLocalId(local_id),
 363             }
 364         })
 365     }
 366
 367     fn lower_node_id_with_owner(&mut self,
 368                                 ast_node_id: NodeId,
 369                                 owner: NodeId)
 370                                 -> LoweredNodeId {
 371         self.lower_node_id_generic(ast_node_id, |this| {
 372             let local_id_counter = this.item_local_id_counters
 373                                        .get_mut(&owner)
 374                                        .unwrap();
 375             let local_id = *local_id_counter;
 376
 377             // We want to be sure not to modify the counter in the map while it
 378             // is also on the stack. Otherwise we'll get lost updates when writing
 379             // back from the stack to the map.
 380             debug_assert!(local_id != HIR_ID_COUNTER_LOCKED);
 381
 382             *local_id_counter += 1;
 383             let def_index = this.resolver.definitions().opt_def_index(owner).unwrap();
 384
 385             hir::HirId {
 386                 owner: def_index,
 387                 local_id: hir::ItemLocalId(local_id),
 388             }
 389         })
 390     }
 391
 392     fn record_body(&mut self, value: hir::Expr, decl: Option<&FnDecl>)
 393                    -> hir::BodyId {
 394         let body = hir::Body {
 395             arguments: decl.map_or(hir_vec![], |decl| {
 396                 decl.inputs.iter().map(|x| self.lower_arg(x)).collect()
 397             }),
 398             is_generator: self.is_generator,
 399             value,
 400         };
 401         let id = body.id();
 402         self.bodies.insert(id, body);
 403         id
 404     }
 405
 406     fn next_id(&mut self) -> LoweredNodeId {
 407         self.lower_node_id(self.sess.next_node_id())
 408     }
 409
 410     fn expect_full_def(&mut self, id: NodeId) -> Def {
 411         self.resolver.get_resolution(id).map_or(Def::Err, |pr| {
 412             if pr.unresolved_segments() != 0 {
 413                 bug!("path not fully resolved: {:?}", pr);
 414             }
 415             pr.base_def()
 416         })
 417     }
 418
 419     fn diagnostic(&self) -> &errors::Handler {
 420         self.sess.diagnostic()
 421     }
 422
 423     fn str_to_ident(&self, s: &'static str) -> Name {
 424         Symbol::gensym(s)
 425     }
 426
 427     fn allow_internal_unstable(&self, reason: CompilerDesugaringKind, span: Span) -> Span
 428     {
 429         let mark = Mark::fresh(Mark::root());
 430         mark.set_expn_info(codemap::ExpnInfo {
 431             call_site: span,
 432             callee: codemap::NameAndSpan {
 433                 format: codemap::CompilerDesugaring(reason),
 434                 span: Some(span),
 435                 allow_internal_unstable: true,
 436                 allow_internal_unsafe: false,
 437             },
 438         });
 439         span.with_ctxt(SyntaxContext::empty().apply_mark(mark))
 440     }
 441
 442     fn with_catch_scope<T, F>(&mut self, catch_id: NodeId, f: F) -> T
 443         where F: FnOnce(&mut LoweringContext) -> T
 444     {
 445         let len = self.catch_scopes.len();
 446         self.catch_scopes.push(catch_id);
 447
 448         let result = f(self);
 449         assert_eq!(len + 1, self.catch_scopes.len(),
 450             "catch scopes should be added and removed in stack order");
 451
 452         self.catch_scopes.pop().unwrap();
 453
 454         result
 455     }
 456
 457     fn lower_body<F>(&mut self, decl: Option<&FnDecl>, f: F) -> hir::BodyId
 458         where F: FnOnce(&mut LoweringContext) -> hir::Expr
 459     {
 460         let prev = mem::replace(&mut self.is_generator, false);
 461         let result = f(self);
 462         let r = self.record_body(result, decl);
 463         self.is_generator = prev;
 464         return r
 465     }
 466
 467     fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
 468         where F: FnOnce(&mut LoweringContext) -> T
 469     {
 470         // We're no longer in the base loop's condition; we're in another loop.
 471         let was_in_loop_condition = self.is_in_loop_condition;
 472         self.is_in_loop_condition = false;
 473
 474         let len = self.loop_scopes.len();
 475         self.loop_scopes.push(loop_id);
 476
 477         let result = f(self);
 478         assert_eq!(len + 1, self.loop_scopes.len(),
 479             "Loop scopes should be added and removed in stack order");
 480
 481         self.loop_scopes.pop().unwrap();
 482
 483         self.is_in_loop_condition = was_in_loop_condition;
 484
 485         result
 486     }
 487
 488     fn with_loop_condition_scope<T, F>(&mut self, f: F) -> T
 489         where F: FnOnce(&mut LoweringContext) -> T
 490     {
 491         let was_in_loop_condition = self.is_in_loop_condition;
 492         self.is_in_loop_condition = true;
 493
 494         let result = f(self);
 495
 496         self.is_in_loop_condition = was_in_loop_condition;
 497
 498         result
 499     }
 500
 501     fn with_new_scopes<T, F>(&mut self, f: F) -> T
 502         where F: FnOnce(&mut LoweringContext) -> T
 503     {
 504         let was_in_loop_condition = self.is_in_loop_condition;
 505         self.is_in_loop_condition = false;
 506
 507         let catch_scopes = mem::replace(&mut self.catch_scopes, Vec::new());
 508         let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
 509         let result = f(self);
 510         self.catch_scopes = catch_scopes;
 511         self.loop_scopes = loop_scopes;
 512
 513         self.is_in_loop_condition = was_in_loop_condition;
 514
 515         result
 516     }
 517
 518     fn with_parent_def<T, F>(&mut self, parent_id: NodeId, f: F) -> T
 519         where F: FnOnce(&mut LoweringContext) -> T
 520     {
 521         let old_def = self.parent_def;
 522         self.parent_def = {
 523             let defs = self.resolver.definitions();
 524             Some(defs.opt_def_index(parent_id).unwrap())
 525         };
 526
 527         let result = f(self);
 528
 529         self.parent_def = old_def;
 530         result
 531     }
 532
 533     fn def_key(&mut self, id: DefId) -> DefKey {
 534         if id.is_local() {
 535             self.resolver.definitions().def_key(id.index)
 536         } else {
 537             self.sess.cstore.def_key(id)
 538         }
 539     }
 540
 541     fn lower_ident(&mut self, ident: Ident) -> Name {
 542         let ident = ident.modern();
 543         if ident.ctxt == SyntaxContext::empty() {
 544             return ident.name;
 545         }
 546         *self.name_map.entry(ident).or_insert_with(|| Symbol::from_ident(ident))
 547     }
 548
 549     fn lower_opt_sp_ident(&mut self, o_id: Option<Spanned<Ident>>) -> Option<Spanned<Name>> {
 550         o_id.map(|sp_ident| respan(sp_ident.span, sp_ident.node.name))
 551     }
 552
 553     fn lower_loop_destination(&mut self, destination: Option<(NodeId, Spanned<Ident>)>)
 554         -> hir::Destination
 555     {
 556         match destination {
 557             Some((id, label_ident)) => {
 558                 let target = if let Def::Label(loop_id) = self.expect_full_def(id) {
 559                     hir::LoopIdResult::Ok(self.lower_node_id(loop_id).node_id)
 560                 } else {
 561                     hir::LoopIdResult::Err(hir::LoopIdError::UnresolvedLabel)
 562                 };
 563                 hir::Destination {
 564                     ident: Some(label_ident),
 565                     target_id: hir::ScopeTarget::Loop(target),
 566                 }
 567             },
 568             None => {
 569                 let loop_id = self.loop_scopes
 570                                   .last()
 571                                   .map(|innermost_loop_id| *innermost_loop_id);
 572
 573                 hir::Destination {
 574                     ident: None,
 575                     target_id: hir::ScopeTarget::Loop(
 576                         loop_id.map(|id| Ok(self.lower_node_id(id).node_id))
 577                                .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope))
 578                                .into())
 579                 }
 580             }
 581         }
 582     }
 583
 584     fn lower_attrs(&mut self, attrs: &Vec<Attribute>) -> hir::HirVec<Attribute> {
 585         attrs.clone().into()
 586     }
 587
 588     fn lower_arm(&mut self, arm: &Arm) -> hir::Arm {
 589         hir::Arm {
 590             attrs: self.lower_attrs(&arm.attrs),
 591             pats: arm.pats.iter().map(|x| self.lower_pat(x)).collect(),
 592             guard: arm.guard.as_ref().map(|ref x| P(self.lower_expr(x))),
 593             body: P(self.lower_expr(&arm.body)),
 594         }
 595     }
 596
 597     fn lower_ty_binding(&mut self, b: &TypeBinding) -> hir::TypeBinding {
 598         hir::TypeBinding {
 599             id: self.lower_node_id(b.id).node_id,
 600             name: self.lower_ident(b.ident),
 601             ty: self.lower_ty(&b.ty),
 602             span: b.span,
 603         }
 604     }
 605
 606     fn lower_ty(&mut self, t: &Ty) -> P<hir::Ty> {
 607         let kind = match t.node {
 608             TyKind::Infer => hir::TyInfer,
 609             TyKind::Err => hir::TyErr,
 610             TyKind::Slice(ref ty) => hir::TySlice(self.lower_ty(ty)),
 611             TyKind::Ptr(ref mt) => hir::TyPtr(self.lower_mt(mt)),
 612             TyKind::Rptr(ref region, ref mt) => {
 613                 let span = t.span.with_hi(t.span.lo());
 614                 let lifetime = match *region {
 615                     Some(ref lt) => self.lower_lifetime(lt),
 616                     None => self.elided_lifetime(span)
 617                 };
 618                 hir::TyRptr(lifetime, self.lower_mt(mt))
 619             }
 620             TyKind::BareFn(ref f) => {
 621                 hir::TyBareFn(P(hir::BareFnTy {
 622                     lifetimes: self.lower_lifetime_defs(&f.lifetimes),
 623                     unsafety: self.lower_unsafety(f.unsafety),
 624                     abi: f.abi,
 625                     decl: self.lower_fn_decl(&f.decl),
 626                 }))
 627             }
 628             TyKind::Never => hir::TyNever,
 629             TyKind::Tup(ref tys) => {
 630                 hir::TyTup(tys.iter().map(|ty| self.lower_ty(ty)).collect())
 631             }
 632             TyKind::Paren(ref ty) => {
 633                 return self.lower_ty(ty);
 634             }
 635             TyKind::Path(ref qself, ref path) => {
 636                 let id = self.lower_node_id(t.id).node_id;
 637                 let qpath = self.lower_qpath(t.id, qself, path, ParamMode::Explicit);
 638                 return self.ty_path(id, t.span, qpath);
 639             }
 640             TyKind::ImplicitSelf => {
 641                 hir::TyPath(hir::QPath::Resolved(None, P(hir::Path {
 642                     def: self.expect_full_def(t.id),
 643                     segments: hir_vec![hir::PathSegment {
 644                         name: keywords::SelfType.name(),
 645                         parameters: hir::PathParameters::none()
 646                     }],
 647                     span: t.span,
 648                 })))
 649             }
 650             TyKind::Array(ref ty, ref length) => {
 651                 let length = self.lower_body(None, |this| this.lower_expr(length));
 652                 hir::TyArray(self.lower_ty(ty), length)
 653             }
 654             TyKind::Typeof(ref expr) => {
 655                 let expr = self.lower_body(None, |this| this.lower_expr(expr));
 656                 hir::TyTypeof(expr)
 657             }
 658             TyKind::TraitObject(ref bounds) => {
 659                 let mut lifetime_bound = None;
 660                 let bounds = bounds.iter().filter_map(|bound| {
 661                     match *bound {
 662                         TraitTyParamBound(ref ty, TraitBoundModifier::None) => {
 663                             Some(self.lower_poly_trait_ref(ty))
 664                         }
 665                         TraitTyParamBound(_, TraitBoundModifier::Maybe) => None,
 666                         RegionTyParamBound(ref lifetime) => {
 667                             if lifetime_bound.is_none() {
 668                                 lifetime_bound = Some(self.lower_lifetime(lifetime));
 669                             }
 670                             None
 671                         }
 672                     }
 673                 }).collect();
 674                 let lifetime_bound = lifetime_bound.unwrap_or_else(|| {
 675                     self.elided_lifetime(t.span)
 676                 });
 677                 hir::TyTraitObject(bounds, lifetime_bound)
 678             }
 679             TyKind::ImplTrait(ref bounds) => {
 680                 hir::TyImplTrait(self.lower_bounds(bounds))
 681             }
 682             TyKind::Mac(_) => panic!("TyMac should have been expanded by now."),
 683         };
 684
 685         P(hir::Ty {
 686             id: self.lower_node_id(t.id).node_id,
 687             node: kind,
 688             span: t.span,
 689         })
 690     }
 691
 692     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
 693         hir::ForeignMod {
 694             abi: fm.abi,
 695             items: fm.items.iter().map(|x| self.lower_foreign_item(x)).collect(),
 696         }
 697     }
 698
 699     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
 700         P(hir::GlobalAsm {
 701             asm: ga.asm,
 702             ctxt: ga.ctxt,
 703         })
 704     }
 705
 706     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
 707         Spanned {
 708             node: hir::Variant_ {
 709                 name: v.node.name.name,
 710                 attrs: self.lower_attrs(&v.node.attrs),
 711                 data: self.lower_variant_data(&v.node.data),
 712                 disr_expr: v.node.disr_expr.as_ref().map(|e| {
 713                     self.lower_body(None, |this| this.lower_expr(e))
 714                 }),
 715             },
 716             span: v.span,
 717         }
 718     }
 719
 720     fn lower_qpath(&mut self,
 721                    id: NodeId,
 722                    qself: &Option<QSelf>,
 723                    p: &Path,
 724                    param_mode: ParamMode)
 725                    -> hir::QPath {
 726         let qself_position = qself.as_ref().map(|q| q.position);
 727         let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty));
 728
 729         let resolution = self.resolver.get_resolution(id)
 730                                       .unwrap_or(PathResolution::new(Def::Err));
 731
 732         let proj_start = p.segments.len() - resolution.unresolved_segments();
 733         let path = P(hir::Path {
 734             def: resolution.base_def(),
 735             segments: p.segments[..proj_start].iter().enumerate().map(|(i, segment)| {
 736                 let param_mode = match (qself_position, param_mode) {
 737                     (Some(j), ParamMode::Optional) if i < j => {
 738                         // This segment is part of the trait path in a
 739                         // qualified path - one of `a`, `b` or `Trait`
 740                         // in `<X as a::b::Trait>::T::U::method`.
 741                         ParamMode::Explicit
 742                     }
 743                     _ => param_mode
 744                 };
 745
 746                 // Figure out if this is a type/trait segment,
 747                 // which may need lifetime elision performed.
 748                 let parent_def_id = |this: &mut Self, def_id: DefId| {
 749                     DefId {
 750                         krate: def_id.krate,
 751                         index: this.def_key(def_id).parent.expect("missing parent")
 752                     }
 753                 };
 754                 let type_def_id = match resolution.base_def() {
 755                     Def::AssociatedTy(def_id) if i + 2 == proj_start => {
 756                         Some(parent_def_id(self, def_id))
 757                     }
 758                     Def::Variant(def_id) if i + 1 == proj_start => {
 759                         Some(parent_def_id(self, def_id))
 760                     }
 761                     Def::Struct(def_id) |
 762                     Def::Union(def_id) |
 763                     Def::Enum(def_id) |
 764                     Def::TyAlias(def_id) |
 765                     Def::Trait(def_id) if i + 1 == proj_start => Some(def_id),
 766                     _ => None
 767                 };
 768                 let parenthesized_generic_args = match resolution.base_def() {
 769                     // `a::b::Trait(Args)`
 770                     Def::Trait(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Ok,
 771                     // `a::b::Trait(Args)::TraitItem`
 772                     Def::Method(..) |
 773                     Def::AssociatedConst(..) |
 774                     Def::AssociatedTy(..) if i + 2 == proj_start => ParenthesizedGenericArgs::Ok,
 775                     // Avoid duplicated errors
 776                     Def::Err => ParenthesizedGenericArgs::Ok,
 777                     // An error
 778                     Def::Struct(..) | Def::Enum(..) | Def::Union(..) | Def::TyAlias(..) |
 779                     Def::Variant(..) if i + 1 == proj_start => ParenthesizedGenericArgs::Err,
 780                     // A warning for now, for compatibility reasons
 781                     _ => ParenthesizedGenericArgs::Warn,
 782                 };
 783
 784                 let num_lifetimes = type_def_id.map_or(0, |def_id| {
 785                     if let Some(&n) = self.type_def_lifetime_params.get(&def_id) {
 786                         return n;
 787                     }
 788                     assert!(!def_id.is_local());
 789                     let n = self.sess.cstore.item_generics_cloned_untracked(def_id).regions.len();
 790                     self.type_def_lifetime_params.insert(def_id, n);
 791                     n
 792                 });
 793                 self.lower_path_segment(p.span, segment, param_mode, num_lifetimes,
 794                                         parenthesized_generic_args)
 795             }).collect(),
 796             span: p.span,
 797         });
 798
 799         // Simple case, either no projections, or only fully-qualified.
 800         // E.g. `std::mem::size_of` or `<I as Iterator>::Item`.
 801         if resolution.unresolved_segments() == 0 {
 802             return hir::QPath::Resolved(qself, path);
 803         }
 804
 805         // Create the innermost type that we're projecting from.
 806         let mut ty = if path.segments.is_empty() {
 807             // If the base path is empty that means there exists a
 808             // syntactical `Self`, e.g. `&i32` in `<&i32>::clone`.
 809             qself.expect("missing QSelf for <T>::...")
 810         } else {
 811             // Otherwise, the base path is an implicit `Self` type path,
 812             // e.g. `Vec` in `Vec::new` or `<I as Iterator>::Item` in
 813             // `<I as Iterator>::Item::default`.
 814             let new_id = self.next_id().node_id;
 815             self.ty_path(new_id, p.span, hir::QPath::Resolved(qself, path))
 816         };
 817
 818         // Anything after the base path are associated "extensions",
 819         // out of which all but the last one are associated types,
 820         // e.g. for `std::vec::Vec::<T>::IntoIter::Item::clone`:
 821         // * base path is `std::vec::Vec<T>`
 822         // * "extensions" are `IntoIter`, `Item` and `clone`
 823         // * type nodes are:
 824         //   1. `std::vec::Vec<T>` (created above)
 825         //   2. `<std::vec::Vec<T>>::IntoIter`
 826         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
 827         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
 828         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
 829             let segment = P(self.lower_path_segment(p.span, segment, param_mode, 0,
 830                                                     ParenthesizedGenericArgs::Warn));
 831             let qpath = hir::QPath::TypeRelative(ty, segment);
 832
 833             // It's finished, return the extension of the right node type.
 834             if i == p.segments.len() - 1 {
 835                 return qpath;
 836             }
 837
 838             // Wrap the associated extension in another type node.
 839             let new_id = self.next_id().node_id;
 840             ty = self.ty_path(new_id, p.span, qpath);
 841         }
 842
 843         // Should've returned in the for loop above.
 844         span_bug!(p.span, "lower_qpath: no final extension segment in {}..{}",
 845                   proj_start, p.segments.len())
 846     }
 847
 848     fn lower_path_extra(&mut self,
 849                         id: NodeId,
 850                         p: &Path,
 851                         name: Option<Name>,
 852                         param_mode: ParamMode,
 853                         defaults_to_global: bool)
 854                         -> hir::Path {
 855         let mut segments = p.segments.iter();
 856         if defaults_to_global && p.is_global() {
 857             segments.next();
 858         }
 859
 860         hir::Path {
 861             def: self.expect_full_def(id),
 862             segments: segments.map(|segment| {
 863                 self.lower_path_segment(p.span, segment, param_mode, 0,
 864                                         ParenthesizedGenericArgs::Err)
 865             }).chain(name.map(|name| {
 866                 hir::PathSegment {
 867                     name,
 868                     parameters: hir::PathParameters::none()
 869                 }
 870             })).collect(),
 871             span: p.span,
 872         }
 873     }
 874
 875     fn lower_path(&mut self,
 876                   id: NodeId,
 877                   p: &Path,
 878                   param_mode: ParamMode,
 879                   defaults_to_global: bool)
 880                   -> hir::Path {
 881         self.lower_path_extra(id, p, None, param_mode, defaults_to_global)
 882     }
 883
 884     fn lower_path_segment(&mut self,
 885                           path_span: Span,
 886                           segment: &PathSegment,
 887                           param_mode: ParamMode,
 888                           expected_lifetimes: usize,
 889                           parenthesized_generic_args: ParenthesizedGenericArgs)
 890                           -> hir::PathSegment {
 891         let mut parameters = if let Some(ref parameters) = segment.parameters {
 892             let msg = "parenthesized parameters may only be used with a trait";
 893             match **parameters {
 894                 PathParameters::AngleBracketed(ref data) => {
 895                     self.lower_angle_bracketed_parameter_data(data, param_mode)
 896                 }
 897                 PathParameters::Parenthesized(ref data) => match parenthesized_generic_args {
 898                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
 899                     ParenthesizedGenericArgs::Warn => {
 900                         self.sess.buffer_lint(PARENTHESIZED_PARAMS_IN_TYPES_AND_MODULES,
 901                                               CRATE_NODE_ID, data.span, msg.into());
 902                         hir::PathParameters::none()
 903                     }
 904                     ParenthesizedGenericArgs::Err => {
 905                         struct_span_err!(self.sess, data.span, E0214, "{}", msg)
 906                             .span_label(data.span, "only traits may use parentheses").emit();
 907                         hir::PathParameters::none()
 908                     }
 909                 }
 910             }
 911         } else {
 912             self.lower_angle_bracketed_parameter_data(&Default::default(), param_mode)
 913         };
 914
 915         if !parameters.parenthesized && parameters.lifetimes.is_empty() {
 916             parameters.lifetimes = (0..expected_lifetimes).map(|_| {
 917                 self.elided_lifetime(path_span)
 918             }).collect();
 919         }
 920
 921         hir::PathSegment {
 922             name: self.lower_ident(segment.identifier),
 923             parameters,
 924         }
 925     }
 926
 927     fn lower_angle_bracketed_parameter_data(&mut self,
 928                                             data: &AngleBracketedParameterData,
 929                                             param_mode: ParamMode)
 930                                             -> hir::PathParameters {
 931         let &AngleBracketedParameterData { ref lifetimes, ref types, ref bindings, .. } = data;
 932         hir::PathParameters {
 933             lifetimes: self.lower_lifetimes(lifetimes),
 934             types: types.iter().map(|ty| self.lower_ty(ty)).collect(),
 935             infer_types: types.is_empty() && param_mode == ParamMode::Optional,
 936             bindings: bindings.iter().map(|b| self.lower_ty_binding(b)).collect(),
 937             parenthesized: false,
 938         }
 939     }
 940
 941     fn lower_parenthesized_parameter_data(&mut self,
 942                                           data: &ParenthesizedParameterData)
 943                                           -> hir::PathParameters {
 944         let &ParenthesizedParameterData { ref inputs, ref output, span } = data;
 945         let inputs = inputs.iter().map(|ty| self.lower_ty(ty)).collect();
 946         let mk_tup = |this: &mut Self, tys, span| {
 947             P(hir::Ty { node: hir::TyTup(tys), id: this.next_id().node_id, span })
 948         };
 949
 950         hir::PathParameters {
 951             lifetimes: hir::HirVec::new(),
 952             types: hir_vec![mk_tup(self, inputs, span)],
 953             infer_types: false,
 954             bindings: hir_vec![hir::TypeBinding {
 955                 id: self.next_id().node_id,
 956                 name: Symbol::intern(FN_OUTPUT_NAME),
 957                 ty: output.as_ref().map(|ty| self.lower_ty(&ty))
 958                                    .unwrap_or_else(|| mk_tup(self, hir::HirVec::new(), span)),
 959                 span: output.as_ref().map_or(span, |ty| ty.span),
 960             }],
 961             parenthesized: true,
 962         }
 963     }
 964
 965     fn lower_local(&mut self, l: &Local) -> P<hir::Local> {
 966         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(l.id);
 967         P(hir::Local {
 968             id: node_id,
 969             hir_id,
 970             ty: l.ty.as_ref().map(|t| self.lower_ty(t)),
 971             pat: self.lower_pat(&l.pat),
 972             init: l.init.as_ref().map(|e| P(self.lower_expr(e))),
 973             span: l.span,
 974             attrs: l.attrs.clone(),
 975             source: hir::LocalSource::Normal,
 976         })
 977     }
 978
 979     fn lower_mutability(&mut self, m: Mutability) -> hir::Mutability {
 980         match m {
 981             Mutability::Mutable => hir::MutMutable,
 982             Mutability::Immutable => hir::MutImmutable,
 983         }
 984     }
 985
 986     fn lower_arg(&mut self, arg: &Arg) -> hir::Arg {
 987         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(arg.id);
 988         hir::Arg {
 989             id: node_id,
 990             hir_id,
 991             pat: self.lower_pat(&arg.pat),
 992         }
 993     }
 994
 995     fn lower_fn_args_to_names(&mut self, decl: &FnDecl)
 996                               -> hir::HirVec<Spanned<Name>> {
 997         decl.inputs.iter().map(|arg| {
 998             match arg.pat.node {
 999                 PatKind::Ident(_, ident, None) => {
1000                     respan(ident.span, ident.node.name)
1001                 }
1002                 _ => respan(arg.pat.span, keywords::Invalid.name()),
1003             }
1004         }).collect()
1005     }
1006
1007     fn lower_fn_decl(&mut self, decl: &FnDecl) -> P<hir::FnDecl> {
1008         P(hir::FnDecl {
1009             inputs: decl.inputs.iter().map(|arg| self.lower_ty(&arg.ty)).collect(),
1010             output: match decl.output {
1011                 FunctionRetTy::Ty(ref ty) => hir::Return(self.lower_ty(ty)),
1012                 FunctionRetTy::Default(span) => hir::DefaultReturn(span),
1013             },
1014             variadic: decl.variadic,
1015             has_implicit_self: decl.inputs.get(0).map_or(false, |arg| {
1016                 match arg.ty.node {
1017                     TyKind::ImplicitSelf => true,
1018                     TyKind::Rptr(_, ref mt) => mt.ty.node == TyKind::ImplicitSelf,
1019                     _ => false
1020                 }
1021             })
1022         })
1023     }
1024
1025     fn lower_ty_param_bound(&mut self, tpb: &TyParamBound) -> hir::TyParamBound {
1026         match *tpb {
1027             TraitTyParamBound(ref ty, modifier) => {
1028                 hir::TraitTyParamBound(self.lower_poly_trait_ref(ty),
1029                                        self.lower_trait_bound_modifier(modifier))
1030             }
1031             RegionTyParamBound(ref lifetime) => {
1032                 hir::RegionTyParamBound(self.lower_lifetime(lifetime))
1033             }
1034         }
1035     }
1036
1037     fn lower_ty_param(&mut self, tp: &TyParam, add_bounds: &[TyParamBound]) -> hir::TyParam {
1038         let mut name = self.lower_ident(tp.ident);
1039
1040         // Don't expose `Self` (recovered "keyword used as ident" parse error).
1041         // `rustc::ty` expects `Self` to be only used for a trait's `Self`.
1042         // Instead, use gensym("Self") to create a distinct name that looks the same.
1043         if name == keywords::SelfType.name() {
1044             name = Symbol::gensym("Self");
1045         }
1046
1047         let mut bounds = self.lower_bounds(&tp.bounds);
1048         if !add_bounds.is_empty() {
1049             bounds = bounds.into_iter().chain(self.lower_bounds(add_bounds).into_iter()).collect();
1050         }
1051
1052         hir::TyParam {
1053             id: self.lower_node_id(tp.id).node_id,
1054             name,
1055             bounds,
1056             default: tp.default.as_ref().map(|x| self.lower_ty(x)),
1057             span: tp.span,
1058             pure_wrt_drop: tp.attrs.iter().any(|attr| attr.check_name("may_dangle")),
1059         }
1060     }
1061
1062     fn lower_ty_params(&mut self, tps: &Vec<TyParam>, add_bounds: &NodeMap<Vec<TyParamBound>>)
1063                        -> hir::HirVec<hir::TyParam> {
1064         tps.iter().map(|tp| {
1065             self.lower_ty_param(tp, add_bounds.get(&tp.id).map_or(&[][..], |x| &x))
1066         }).collect()
1067     }
1068
1069     fn lower_lifetime(&mut self, l: &Lifetime) -> hir::Lifetime {
1070         hir::Lifetime {
1071             id: self.lower_node_id(l.id).node_id,
1072             name: self.lower_ident(l.ident),
1073             span: l.span,
1074         }
1075     }
1076
1077     fn lower_lifetime_def(&mut self, l: &LifetimeDef) -> hir::LifetimeDef {
1078         hir::LifetimeDef {
1079             lifetime: self.lower_lifetime(&l.lifetime),
1080             bounds: self.lower_lifetimes(&l.bounds),
1081             pure_wrt_drop: l.attrs.iter().any(|attr| attr.check_name("may_dangle")),
1082         }
1083     }
1084
1085     fn lower_lifetimes(&mut self, lts: &Vec<Lifetime>) -> hir::HirVec<hir::Lifetime> {
1086         lts.iter().map(|l| self.lower_lifetime(l)).collect()
1087     }
1088
1089     fn lower_lifetime_defs(&mut self, lts: &Vec<LifetimeDef>) -> hir::HirVec<hir::LifetimeDef> {
1090         lts.iter().map(|l| self.lower_lifetime_def(l)).collect()
1091     }
1092
1093     fn lower_generics(&mut self, g: &Generics) -> hir::Generics {
1094         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1095         let mut add_bounds = NodeMap();
1096         for pred in &g.where_clause.predicates {
1097             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1098                 'next_bound: for bound in &bound_pred.bounds {
1099                     if let TraitTyParamBound(_, TraitBoundModifier::Maybe) = *bound {
1100                         let report_error = |this: &mut Self| {
1101                             this.diagnostic().span_err(bound_pred.bounded_ty.span,
1102                                                        "`?Trait` bounds are only permitted at the \
1103                                                         point where a type parameter is declared");
1104                         };
1105                         // Check if the where clause type is a plain type parameter.
1106                         match bound_pred.bounded_ty.node {
1107                             TyKind::Path(None, ref path)
1108                                     if path.segments.len() == 1 &&
1109                                        bound_pred.bound_lifetimes.is_empty() => {
1110                                 if let Some(Def::TyParam(def_id)) =
1111                                         self.resolver.get_resolution(bound_pred.bounded_ty.id)
1112                                                      .map(|d| d.base_def()) {
1113                                     if let Some(node_id) =
1114                                             self.resolver.definitions().as_local_node_id(def_id) {
1115                                         for ty_param in &g.ty_params {
1116                                             if node_id == ty_param.id {
1117                                                 add_bounds.entry(ty_param.id).or_insert(Vec::new())
1118                                                                             .push(bound.clone());
1119                                                 continue 'next_bound;
1120                                             }
1121                                         }
1122                                     }
1123                                 }
1124                                 report_error(self)
1125                             }
1126                             _ => report_error(self)
1127                         }
1128                     }
1129                 }
1130             }
1131         }
1132
1133         hir::Generics {
1134             ty_params: self.lower_ty_params(&g.ty_params, &add_bounds),
1135             lifetimes: self.lower_lifetime_defs(&g.lifetimes),
1136             where_clause: self.lower_where_clause(&g.where_clause),
1137             span: g.span,
1138         }
1139     }
1140
1141     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1142         hir::WhereClause {
1143             id: self.lower_node_id(wc.id).node_id,
1144             predicates: wc.predicates
1145                           .iter()
1146                           .map(|predicate| self.lower_where_predicate(predicate))
1147                           .collect(),
1148         }
1149     }
1150
1151     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1152         match *pred {
1153             WherePredicate::BoundPredicate(WhereBoundPredicate{ ref bound_lifetimes,
1154                                                                 ref bounded_ty,
1155                                                                 ref bounds,
1156                                                                 span}) => {
1157                 hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1158                     bound_lifetimes: self.lower_lifetime_defs(bound_lifetimes),
1159                     bounded_ty: self.lower_ty(bounded_ty),
1160                     bounds: bounds.iter().filter_map(|bound| match *bound {
1161                         // Ignore `?Trait` bounds, they were copied into type parameters already.
1162                         TraitTyParamBound(_, TraitBoundModifier::Maybe) => None,
1163                         _ => Some(self.lower_ty_param_bound(bound))
1164                     }).collect(),
1165                     span,
1166                 })
1167             }
1168             WherePredicate::RegionPredicate(WhereRegionPredicate{ ref lifetime,
1169                                                                   ref bounds,
1170                                                                   span}) => {
1171                 hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1172                     span,
1173                     lifetime: self.lower_lifetime(lifetime),
1174                     bounds: bounds.iter().map(|bound| self.lower_lifetime(bound)).collect(),
1175                 })
1176             }
1177             WherePredicate::EqPredicate(WhereEqPredicate{ id,
1178                                                           ref lhs_ty,
1179                                                           ref rhs_ty,
1180                                                           span}) => {
1181                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1182                     id: self.lower_node_id(id).node_id,
1183                     lhs_ty: self.lower_ty(lhs_ty),
1184                     rhs_ty: self.lower_ty(rhs_ty),
1185                     span,
1186                 })
1187             }
1188         }
1189     }
1190
1191     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
1192         match *vdata {
1193             VariantData::Struct(ref fields, id) => {
1194                 hir::VariantData::Struct(fields.iter()
1195                                                .enumerate()
1196                                                .map(|f| self.lower_struct_field(f))
1197                                                .collect(),
1198                                          self.lower_node_id(id).node_id)
1199             }
1200             VariantData::Tuple(ref fields, id) => {
1201                 hir::VariantData::Tuple(fields.iter()
1202                                               .enumerate()
1203                                               .map(|f| self.lower_struct_field(f))
1204                                               .collect(),
1205                                         self.lower_node_id(id).node_id)
1206             }
1207             VariantData::Unit(id) => hir::VariantData::Unit(self.lower_node_id(id).node_id),
1208         }
1209     }
1210
1211     fn lower_trait_ref(&mut self, p: &TraitRef) -> hir::TraitRef {
1212         let path = match self.lower_qpath(p.ref_id, &None, &p.path, ParamMode::Explicit) {
1213             hir::QPath::Resolved(None, path) => path.and_then(|path| path),
1214             qpath => bug!("lower_trait_ref: unexpected QPath `{:?}`", qpath)
1215         };
1216         hir::TraitRef {
1217             path,
1218             ref_id: self.lower_node_id(p.ref_id).node_id,
1219         }
1220     }
1221
1222     fn lower_poly_trait_ref(&mut self, p: &PolyTraitRef) -> hir::PolyTraitRef {
1223         hir::PolyTraitRef {
1224             bound_lifetimes: self.lower_lifetime_defs(&p.bound_lifetimes),
1225             trait_ref: self.lower_trait_ref(&p.trait_ref),
1226             span: p.span,
1227         }
1228     }
1229
1230     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
1231         hir::StructField {
1232             span: f.span,
1233             id: self.lower_node_id(f.id).node_id,
1234             name: self.lower_ident(match f.ident {
1235                 Some(ident) => ident,
1236                 // FIXME(jseyfried) positional field hygiene
1237                 None => Ident { name: Symbol::intern(&index.to_string()), ctxt: f.span.ctxt() },
1238             }),
1239             vis: self.lower_visibility(&f.vis, None),
1240             ty: self.lower_ty(&f.ty),
1241             attrs: self.lower_attrs(&f.attrs),
1242         }
1243     }
1244
1245     fn lower_field(&mut self, f: &Field) -> hir::Field {
1246         hir::Field {
1247             name: respan(f.ident.span, self.lower_ident(f.ident.node)),
1248             expr: P(self.lower_expr(&f.expr)),
1249             span: f.span,
1250             is_shorthand: f.is_shorthand,
1251         }
1252     }
1253
1254     fn lower_mt(&mut self, mt: &MutTy) -> hir::MutTy {
1255         hir::MutTy {
1256             ty: self.lower_ty(&mt.ty),
1257             mutbl: self.lower_mutability(mt.mutbl),
1258         }
1259     }
1260
1261     fn lower_bounds(&mut self, bounds: &[TyParamBound]) -> hir::TyParamBounds {
1262         bounds.iter().map(|bound| self.lower_ty_param_bound(bound)).collect()
1263     }
1264
1265     fn lower_block(&mut self, b: &Block, targeted_by_break: bool) -> P<hir::Block> {
1266         let mut expr = None;
1267
1268         let mut stmts = vec![];
1269
1270         for (index, stmt) in b.stmts.iter().enumerate() {
1271             if index == b.stmts.len() - 1 {
1272                 if let StmtKind::Expr(ref e) = stmt.node {
1273                     expr = Some(P(self.lower_expr(e)));
1274                 } else {
1275                     stmts.extend(self.lower_stmt(stmt));
1276                 }
1277             } else {
1278                 stmts.extend(self.lower_stmt(stmt));
1279             }
1280         }
1281
1282         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(b.id);
1283
1284         P(hir::Block {
1285             id: node_id,
1286             hir_id,
1287             stmts: stmts.into(),
1288             expr,
1289             rules: self.lower_block_check_mode(&b.rules),
1290             span: b.span,
1291             targeted_by_break,
1292         })
1293     }
1294
1295     fn lower_item_kind(&mut self,
1296                        id: NodeId,
1297                        name: &mut Name,
1298                        attrs: &hir::HirVec<Attribute>,
1299                        vis: &mut hir::Visibility,
1300                        i: &ItemKind)
1301                        -> hir::Item_ {
1302         match *i {
1303             ItemKind::ExternCrate(string) => hir::ItemExternCrate(string),
1304             ItemKind::Use(ref view_path) => {
1305                 let path = match view_path.node {
1306                     ViewPathSimple(_, ref path) => path,
1307                     ViewPathGlob(ref path) => path,
1308                     ViewPathList(ref path, ref path_list_idents) => {
1309                         for &Spanned { node: ref import, span } in path_list_idents {
1310                             // `use a::{self as x, b as y};` lowers to
1311                             // `use a as x; use a::b as y;`
1312                             let mut ident = import.name;
1313                             let suffix = if ident.name == keywords::SelfValue.name() {
1314                                 if let Some(last) = path.segments.last() {
1315                                     ident = last.identifier;
1316                                 }
1317                                 None
1318                             } else {
1319                                 Some(ident.name)
1320                             };
1321
1322                             let mut path = self.lower_path_extra(import.id, path, suffix,
1323                                                                  ParamMode::Explicit, true);
1324                             path.span = span;
1325
1326                             self.allocate_hir_id_counter(import.id, import);
1327                             let LoweredNodeId {
1328                                 node_id: import_node_id,
1329                                 hir_id: import_hir_id,
1330                             } = self.lower_node_id(import.id);
1331
1332                             self.with_hir_id_owner(import_node_id, |this| {
1333                                 let vis = match *vis {
1334                                     hir::Visibility::Public => hir::Visibility::Public,
1335                                     hir::Visibility::Crate => hir::Visibility::Crate,
1336                                     hir::Visibility::Inherited => hir::Visibility::Inherited,
1337                                     hir::Visibility::Restricted { ref path, id: _ } => {
1338                                         hir::Visibility::Restricted {
1339                                             path: path.clone(),
1340                                             // We are allocating a new NodeId here
1341                                             id: this.next_id().node_id,
1342                                         }
1343                                     }
1344                                 };
1345
1346                                 this.items.insert(import_node_id, hir::Item {
1347                                     id: import_node_id,
1348                                     hir_id: import_hir_id,
1349                                     name: import.rename.unwrap_or(ident).name,
1350                                     attrs: attrs.clone(),
1351                                     node: hir::ItemUse(P(path), hir::UseKind::Single),
1352                                     vis,
1353                                     span,
1354                                 });
1355                             });
1356                         }
1357                         path
1358                     }
1359                 };
1360                 let path = P(self.lower_path(id, path, ParamMode::Explicit, true));
1361                 let kind = match view_path.node {
1362                     ViewPathSimple(ident, _) => {
1363                         *name = ident.name;
1364                         hir::UseKind::Single
1365                     }
1366                     ViewPathGlob(_) => {
1367                         hir::UseKind::Glob
1368                     }
1369                     ViewPathList(..) => {
1370                         // Privatize the degenerate import base, used only to check
1371                         // the stability of `use a::{};`, to avoid it showing up as
1372                         // a reexport by accident when `pub`, e.g. in documentation.
1373                         *vis = hir::Inherited;
1374                         hir::UseKind::ListStem
1375                     }
1376                 };
1377                 hir::ItemUse(path, kind)
1378             }
1379             ItemKind::Static(ref t, m, ref e) => {
1380                 let value = self.lower_body(None, |this| this.lower_expr(e));
1381                 hir::ItemStatic(self.lower_ty(t),
1382                                 self.lower_mutability(m),
1383                                 value)
1384             }
1385             ItemKind::Const(ref t, ref e) => {
1386                 let value = self.lower_body(None, |this| this.lower_expr(e));
1387                 hir::ItemConst(self.lower_ty(t), value)
1388             }
1389             ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
1390                 self.with_new_scopes(|this| {
1391                     let body_id = this.lower_body(Some(decl), |this| {
1392                         let body = this.lower_block(body, false);
1393                         this.expr_block(body, ThinVec::new())
1394                     });
1395                     hir::ItemFn(this.lower_fn_decl(decl),
1396                                               this.lower_unsafety(unsafety),
1397                                               this.lower_constness(constness),
1398                                               abi,
1399                                               this.lower_generics(generics),
1400                                               body_id)
1401                 })
1402             }
1403             ItemKind::Mod(ref m) => hir::ItemMod(self.lower_mod(m)),
1404             ItemKind::ForeignMod(ref nm) => hir::ItemForeignMod(self.lower_foreign_mod(nm)),
1405             ItemKind::GlobalAsm(ref ga) => hir::ItemGlobalAsm(self.lower_global_asm(ga)),
1406             ItemKind::Ty(ref t, ref generics) => {
1407                 hir::ItemTy(self.lower_ty(t), self.lower_generics(generics))
1408             }
1409             ItemKind::Enum(ref enum_definition, ref generics) => {
1410                 hir::ItemEnum(hir::EnumDef {
1411                                   variants: enum_definition.variants
1412                                                            .iter()
1413                                                            .map(|x| self.lower_variant(x))
1414                                                            .collect(),
1415                               },
1416                               self.lower_generics(generics))
1417             }
1418             ItemKind::Struct(ref struct_def, ref generics) => {
1419                 let struct_def = self.lower_variant_data(struct_def);
1420                 hir::ItemStruct(struct_def, self.lower_generics(generics))
1421             }
1422             ItemKind::Union(ref vdata, ref generics) => {
1423                 let vdata = self.lower_variant_data(vdata);
1424                 hir::ItemUnion(vdata, self.lower_generics(generics))
1425             }
1426             ItemKind::DefaultImpl(unsafety, ref trait_ref) => {
1427                 let trait_ref = self.lower_trait_ref(trait_ref);
1428
1429                 if let Def::Trait(def_id) = trait_ref.path.def {
1430                     self.trait_default_impl.insert(def_id, id);
1431                 }
1432
1433                 hir::ItemDefaultImpl(self.lower_unsafety(unsafety),
1434                                      trait_ref)
1435             }
1436             ItemKind::Impl(unsafety,
1437                            polarity,
1438                            defaultness,
1439                            ref generics,
1440                            ref ifce,
1441                            ref ty,
1442                            ref impl_items) => {
1443                 let new_impl_items = impl_items.iter()
1444                                                .map(|item| self.lower_impl_item_ref(item))
1445                                                .collect();
1446                 let ifce = ifce.as_ref().map(|trait_ref| self.lower_trait_ref(trait_ref));
1447
1448                 if let Some(ref trait_ref) = ifce {
1449                     if let Def::Trait(def_id) = trait_ref.path.def {
1450                         self.trait_impls.entry(def_id).or_insert(vec![]).push(id);
1451                     }
1452                 }
1453
1454                 hir::ItemImpl(self.lower_unsafety(unsafety),
1455                               self.lower_impl_polarity(polarity),
1456                               self.lower_defaultness(defaultness, true /* [1] */),
1457                               self.lower_generics(generics),
1458                               ifce,
1459                               self.lower_ty(ty),
1460                               new_impl_items)
1461             }
1462             ItemKind::Trait(unsafety, ref generics, ref bounds, ref items) => {
1463                 let bounds = self.lower_bounds(bounds);
1464                 let items = items.iter().map(|item| self.lower_trait_item_ref(item)).collect();
1465                 hir::ItemTrait(self.lower_unsafety(unsafety),
1466                                self.lower_generics(generics),
1467                                bounds,
1468                                items)
1469             }
1470             ItemKind::MacroDef(..) | ItemKind::Mac(..) => panic!("Shouldn't still be around"),
1471         }
1472
1473         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
1474         //     not cause an assertion failure inside the `lower_defaultness` function
1475     }
1476
1477     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {
1478         self.with_parent_def(i.id, |this| {
1479             let LoweredNodeId { node_id, hir_id } = this.lower_node_id(i.id);
1480
1481             hir::TraitItem {
1482                 id: node_id,
1483                 hir_id,
1484                 name: this.lower_ident(i.ident),
1485                 attrs: this.lower_attrs(&i.attrs),
1486                 node: match i.node {
1487                     TraitItemKind::Const(ref ty, ref default) => {
1488                         hir::TraitItemKind::Const(this.lower_ty(ty),
1489                                                   default.as_ref().map(|x| {
1490                             this.lower_body(None, |this| this.lower_expr(x))
1491                         }))
1492                     }
1493                     TraitItemKind::Method(ref sig, None) => {
1494                         let names = this.lower_fn_args_to_names(&sig.decl);
1495                         hir::TraitItemKind::Method(this.lower_method_sig(sig),
1496                                                    hir::TraitMethod::Required(names))
1497                     }
1498                     TraitItemKind::Method(ref sig, Some(ref body)) => {
1499                         let body_id = this.lower_body(Some(&sig.decl), |this| {
1500                             let body = this.lower_block(body, false);
1501                             this.expr_block(body, ThinVec::new())
1502                         });
1503                         hir::TraitItemKind::Method(this.lower_method_sig(sig),
1504                                                    hir::TraitMethod::Provided(body_id))
1505                     }
1506                     TraitItemKind::Type(ref bounds, ref default) => {
1507                         hir::TraitItemKind::Type(this.lower_bounds(bounds),
1508                                                  default.as_ref().map(|x| this.lower_ty(x)))
1509                     }
1510                     TraitItemKind::Macro(..) => panic!("Shouldn't exist any more"),
1511                 },
1512                 span: i.span,
1513             }
1514         })
1515     }
1516
1517     fn lower_trait_item_ref(&mut self, i: &TraitItem) -> hir::TraitItemRef {
1518         let (kind, has_default) = match i.node {
1519             TraitItemKind::Const(_, ref default) => {
1520                 (hir::AssociatedItemKind::Const, default.is_some())
1521             }
1522             TraitItemKind::Type(_, ref default) => {
1523                 (hir::AssociatedItemKind::Type, default.is_some())
1524             }
1525             TraitItemKind::Method(ref sig, ref default) => {
1526                 (hir::AssociatedItemKind::Method {
1527                     has_self: sig.decl.has_self(),
1528                  }, default.is_some())
1529             }
1530             TraitItemKind::Macro(..) => unimplemented!(),
1531         };
1532         hir::TraitItemRef {
1533             id: hir::TraitItemId { node_id: i.id },
1534             name: self.lower_ident(i.ident),
1535             span: i.span,
1536             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
1537             kind,
1538         }
1539     }
1540
1541     fn lower_impl_item(&mut self, i: &ImplItem) -> hir::ImplItem {
1542         self.with_parent_def(i.id, |this| {
1543             let LoweredNodeId { node_id, hir_id } = this.lower_node_id(i.id);
1544
1545             hir::ImplItem {
1546                 id: node_id,
1547                 hir_id,
1548                 name: this.lower_ident(i.ident),
1549                 attrs: this.lower_attrs(&i.attrs),
1550                 vis: this.lower_visibility(&i.vis, None),
1551                 defaultness: this.lower_defaultness(i.defaultness, true /* [1] */),
1552                 node: match i.node {
1553                     ImplItemKind::Const(ref ty, ref expr) => {
1554                         let body_id = this.lower_body(None, |this| this.lower_expr(expr));
1555                         hir::ImplItemKind::Const(this.lower_ty(ty), body_id)
1556                     }
1557                     ImplItemKind::Method(ref sig, ref body) => {
1558                         let body_id = this.lower_body(Some(&sig.decl), |this| {
1559                             let body = this.lower_block(body, false);
1560                             this.expr_block(body, ThinVec::new())
1561                         });
1562                         hir::ImplItemKind::Method(this.lower_method_sig(sig), body_id)
1563                     }
1564                     ImplItemKind::Type(ref ty) => hir::ImplItemKind::Type(this.lower_ty(ty)),
1565                     ImplItemKind::Macro(..) => panic!("Shouldn't exist any more"),
1566                 },
1567                 span: i.span,
1568             }
1569         })
1570
1571         // [1] since `default impl` is not yet implemented, this is always true in impls
1572     }
1573
1574     fn lower_impl_item_ref(&mut self, i: &ImplItem) -> hir::ImplItemRef {
1575         hir::ImplItemRef {
1576             id: hir::ImplItemId { node_id: i.id },
1577             name: self.lower_ident(i.ident),
1578             span: i.span,
1579             vis: self.lower_visibility(&i.vis, Some(i.id)),
1580             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
1581             kind: match i.node {
1582                 ImplItemKind::Const(..) => hir::AssociatedItemKind::Const,
1583                 ImplItemKind::Type(..) => hir::AssociatedItemKind::Type,
1584                 ImplItemKind::Method(ref sig, _) => hir::AssociatedItemKind::Method {
1585                     has_self: sig.decl.has_self(),
1586                 },
1587                 ImplItemKind::Macro(..) => unimplemented!(),
1588             },
1589         }
1590
1591         // [1] since `default impl` is not yet implemented, this is always true in impls
1592     }
1593
1594     fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
1595         hir::Mod {
1596             inner: m.inner,
1597             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
1598         }
1599     }
1600
1601     fn lower_item_id(&mut self, i: &Item) -> SmallVector<hir::ItemId> {
1602         match i.node {
1603             ItemKind::Use(ref view_path) => {
1604                 if let ViewPathList(_, ref imports) = view_path.node {
1605                     return iter::once(i.id).chain(imports.iter().map(|import| import.node.id))
1606                         .map(|id| hir::ItemId { id: id }).collect();
1607                 }
1608             }
1609             ItemKind::MacroDef(..) => return SmallVector::new(),
1610             _ => {}
1611         }
1612         SmallVector::one(hir::ItemId { id: i.id })
1613     }
1614
1615     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
1616         let mut name = i.ident.name;
1617         let mut vis = self.lower_visibility(&i.vis, None);
1618         let attrs = self.lower_attrs(&i.attrs);
1619         if let ItemKind::MacroDef(ref def) = i.node {
1620             if !def.legacy || i.attrs.iter().any(|attr| attr.path == "macro_export") {
1621                 self.exported_macros.push(hir::MacroDef {
1622                     name,
1623                     vis,
1624                     attrs,
1625                     id: i.id,
1626                     span: i.span,
1627                     body: def.stream(),
1628                     legacy: def.legacy,
1629                 });
1630             }
1631             return None;
1632         }
1633
1634         let node = self.with_parent_def(i.id, |this| {
1635             this.lower_item_kind(i.id, &mut name, &attrs, &mut vis, &i.node)
1636         });
1637
1638         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(i.id);
1639
1640         Some(hir::Item {
1641             id: node_id,
1642             hir_id,
1643             name,
1644             attrs,
1645             node,
1646             vis,
1647             span: i.span,
1648         })
1649     }
1650
1651     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
1652         self.with_parent_def(i.id, |this| {
1653             hir::ForeignItem {
1654                 id: this.lower_node_id(i.id).node_id,
1655                 name: i.ident.name,
1656                 attrs: this.lower_attrs(&i.attrs),
1657                 node: match i.node {
1658                     ForeignItemKind::Fn(ref fdec, ref generics) => {
1659                         hir::ForeignItemFn(this.lower_fn_decl(fdec),
1660                                            this.lower_fn_args_to_names(fdec),
1661                                            this.lower_generics(generics))
1662                     }
1663                     ForeignItemKind::Static(ref t, m) => {
1664                         hir::ForeignItemStatic(this.lower_ty(t), m)
1665                     }
1666                 },
1667                 vis: this.lower_visibility(&i.vis, None),
1668                 span: i.span,
1669             }
1670         })
1671     }
1672
1673     fn lower_method_sig(&mut self, sig: &MethodSig) -> hir::MethodSig {
1674         hir::MethodSig {
1675             generics: self.lower_generics(&sig.generics),
1676             abi: sig.abi,
1677             unsafety: self.lower_unsafety(sig.unsafety),
1678             constness: self.lower_constness(sig.constness),
1679             decl: self.lower_fn_decl(&sig.decl),
1680         }
1681     }
1682
1683     fn lower_unsafety(&mut self, u: Unsafety) -> hir::Unsafety {
1684         match u {
1685             Unsafety::Unsafe => hir::Unsafety::Unsafe,
1686             Unsafety::Normal => hir::Unsafety::Normal,
1687         }
1688     }
1689
1690     fn lower_constness(&mut self, c: Spanned<Constness>) -> hir::Constness {
1691         match c.node {
1692             Constness::Const => hir::Constness::Const,
1693             Constness::NotConst => hir::Constness::NotConst,
1694         }
1695     }
1696
1697     fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
1698         match u {
1699             UnOp::Deref => hir::UnDeref,
1700             UnOp::Not => hir::UnNot,
1701             UnOp::Neg => hir::UnNeg,
1702         }
1703     }
1704
1705     fn lower_binop(&mut self, b: BinOp) -> hir::BinOp {
1706         Spanned {
1707             node: match b.node {
1708                 BinOpKind::Add => hir::BiAdd,
1709                 BinOpKind::Sub => hir::BiSub,
1710                 BinOpKind::Mul => hir::BiMul,
1711                 BinOpKind::Div => hir::BiDiv,
1712                 BinOpKind::Rem => hir::BiRem,
1713                 BinOpKind::And => hir::BiAnd,
1714                 BinOpKind::Or => hir::BiOr,
1715                 BinOpKind::BitXor => hir::BiBitXor,
1716                 BinOpKind::BitAnd => hir::BiBitAnd,
1717                 BinOpKind::BitOr => hir::BiBitOr,
1718                 BinOpKind::Shl => hir::BiShl,
1719                 BinOpKind::Shr => hir::BiShr,
1720                 BinOpKind::Eq => hir::BiEq,
1721                 BinOpKind::Lt => hir::BiLt,
1722                 BinOpKind::Le => hir::BiLe,
1723                 BinOpKind::Ne => hir::BiNe,
1724                 BinOpKind::Ge => hir::BiGe,
1725                 BinOpKind::Gt => hir::BiGt,
1726             },
1727             span: b.span,
1728         }
1729     }
1730
1731     fn lower_pat(&mut self, p: &Pat) -> P<hir::Pat> {
1732         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(p.id);
1733
1734         P(hir::Pat {
1735             id: node_id,
1736             hir_id,
1737             node: match p.node {
1738                 PatKind::Wild => hir::PatKind::Wild,
1739                 PatKind::Ident(ref binding_mode, pth1, ref sub) => {
1740                     match self.resolver.get_resolution(p.id).map(|d| d.base_def()) {
1741                         // `None` can occur in body-less function signatures
1742                         def @ None | def @ Some(Def::Local(_)) => {
1743                             let canonical_id = match def {
1744                                 Some(Def::Local(id)) => id,
1745                                 _ => p.id
1746                             };
1747                             hir::PatKind::Binding(self.lower_binding_mode(binding_mode),
1748                                                   canonical_id,
1749                                                   respan(pth1.span, pth1.node.name),
1750                                                   sub.as_ref().map(|x| self.lower_pat(x)))
1751                         }
1752                         Some(def) => {
1753                             hir::PatKind::Path(hir::QPath::Resolved(None, P(hir::Path {
1754                                 span: pth1.span,
1755                                 def,
1756                                 segments: hir_vec![
1757                                     hir::PathSegment::from_name(pth1.node.name)
1758                                 ],
1759                             })))
1760                         }
1761                     }
1762                 }
1763                 PatKind::Lit(ref e) => hir::PatKind::Lit(P(self.lower_expr(e))),
1764                 PatKind::TupleStruct(ref path, ref pats, ddpos) => {
1765                     let qpath = self.lower_qpath(p.id, &None, path, ParamMode::Optional);
1766                     hir::PatKind::TupleStruct(qpath,
1767                                               pats.iter().map(|x| self.lower_pat(x)).collect(),
1768                                               ddpos)
1769                 }
1770                 PatKind::Path(ref qself, ref path) => {
1771                     hir::PatKind::Path(self.lower_qpath(p.id, qself, path, ParamMode::Optional))
1772                 }
1773                 PatKind::Struct(ref path, ref fields, etc) => {
1774                     let qpath = self.lower_qpath(p.id, &None, path, ParamMode::Optional);
1775
1776                     let fs = fields.iter()
1777                                    .map(|f| {
1778                                        Spanned {
1779                                            span: f.span,
1780                                            node: hir::FieldPat {
1781                                                name: self.lower_ident(f.node.ident),
1782                                                pat: self.lower_pat(&f.node.pat),
1783                                                is_shorthand: f.node.is_shorthand,
1784                                            },
1785                                        }
1786                                    })
1787                                    .collect();
1788                     hir::PatKind::Struct(qpath, fs, etc)
1789                 }
1790                 PatKind::Tuple(ref elts, ddpos) => {
1791                     hir::PatKind::Tuple(elts.iter().map(|x| self.lower_pat(x)).collect(), ddpos)
1792                 }
1793                 PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
1794                 PatKind::Ref(ref inner, mutbl) => {
1795                     hir::PatKind::Ref(self.lower_pat(inner), self.lower_mutability(mutbl))
1796                 }
1797                 PatKind::Range(ref e1, ref e2, ref end) => {
1798                     hir::PatKind::Range(P(self.lower_expr(e1)),
1799                                         P(self.lower_expr(e2)),
1800                                         self.lower_range_end(end))
1801                 }
1802                 PatKind::Slice(ref before, ref slice, ref after) => {
1803                     hir::PatKind::Slice(before.iter().map(|x| self.lower_pat(x)).collect(),
1804                                 slice.as_ref().map(|x| self.lower_pat(x)),
1805                                 after.iter().map(|x| self.lower_pat(x)).collect())
1806                 }
1807                 PatKind::Mac(_) => panic!("Shouldn't exist here"),
1808             },
1809             span: p.span,
1810         })
1811     }
1812
1813     fn lower_range_end(&mut self, e: &RangeEnd) -> hir::RangeEnd {
1814         match *e {
1815             RangeEnd::Included => hir::RangeEnd::Included,
1816             RangeEnd::Excluded => hir::RangeEnd::Excluded,
1817         }
1818     }
1819
1820     fn lower_expr(&mut self, e: &Expr) -> hir::Expr {
1821         let kind = match e.node {
1822             // Issue #22181:
1823             // Eventually a desugaring for `box EXPR`
1824             // (similar to the desugaring above for `in PLACE BLOCK`)
1825             // should go here, desugaring
1826             //
1827             // to:
1828             //
1829             // let mut place = BoxPlace::make_place();
1830             // let raw_place = Place::pointer(&mut place);
1831             // let value = $value;
1832             // unsafe {
1833             //     ::std::ptr::write(raw_place, value);
1834             //     Boxed::finalize(place)
1835             // }
1836             //
1837             // But for now there are type-inference issues doing that.
1838             ExprKind::Box(ref inner) => {
1839                 hir::ExprBox(P(self.lower_expr(inner)))
1840             }
1841
1842             // Desugar ExprBox: `in (PLACE) EXPR`
1843             ExprKind::InPlace(ref placer, ref value_expr) => {
1844                 // to:
1845                 //
1846                 // let p = PLACE;
1847                 // let mut place = Placer::make_place(p);
1848                 // let raw_place = Place::pointer(&mut place);
1849                 // push_unsafe!({
1850                 //     std::intrinsics::move_val_init(raw_place, pop_unsafe!( EXPR ));
1851                 //     InPlace::finalize(place)
1852                 // })
1853                 let placer_expr = P(self.lower_expr(placer));
1854                 let value_expr = P(self.lower_expr(value_expr));
1855
1856                 let placer_ident = self.str_to_ident("placer");
1857                 let place_ident = self.str_to_ident("place");
1858                 let p_ptr_ident = self.str_to_ident("p_ptr");
1859
1860                 let make_place = ["ops", "Placer", "make_place"];
1861                 let place_pointer = ["ops", "Place", "pointer"];
1862                 let move_val_init = ["intrinsics", "move_val_init"];
1863                 let inplace_finalize = ["ops", "InPlace", "finalize"];
1864
1865                 let unstable_span =
1866                     self.allow_internal_unstable(CompilerDesugaringKind::BackArrow, e.span);
1867                 let make_call = |this: &mut LoweringContext, p, args| {
1868                     let path = P(this.expr_std_path(unstable_span, p, ThinVec::new()));
1869                     P(this.expr_call(e.span, path, args))
1870                 };
1871
1872                 let mk_stmt_let = |this: &mut LoweringContext, bind, expr| {
1873                     this.stmt_let(e.span, false, bind, expr)
1874                 };
1875
1876                 let mk_stmt_let_mut = |this: &mut LoweringContext, bind, expr| {
1877                     this.stmt_let(e.span, true, bind, expr)
1878                 };
1879
1880                 // let placer = <placer_expr> ;
1881                 let (s1, placer_binding) = {
1882                     mk_stmt_let(self, placer_ident, placer_expr)
1883                 };
1884
1885                 // let mut place = Placer::make_place(placer);
1886                 let (s2, place_binding) = {
1887                     let placer = self.expr_ident(e.span, placer_ident, placer_binding);
1888                     let call = make_call(self, &make_place, hir_vec![placer]);
1889                     mk_stmt_let_mut(self, place_ident, call)
1890                 };
1891
1892                 // let p_ptr = Place::pointer(&mut place);
1893                 let (s3, p_ptr_binding) = {
1894                     let agent = P(self.expr_ident(e.span, place_ident, place_binding));
1895                     let args = hir_vec![self.expr_mut_addr_of(e.span, agent)];
1896                     let call = make_call(self, &place_pointer, args);
1897                     mk_stmt_let(self, p_ptr_ident, call)
1898                 };
1899
1900                 // pop_unsafe!(EXPR));
1901                 let pop_unsafe_expr = {
1902                     self.signal_block_expr(hir_vec![],
1903                                            value_expr,
1904                                            e.span,
1905                                            hir::PopUnsafeBlock(hir::CompilerGenerated),
1906                                            ThinVec::new())
1907                 };
1908
1909                 // push_unsafe!({
1910                 //     std::intrinsics::move_val_init(raw_place, pop_unsafe!( EXPR ));
1911                 //     InPlace::finalize(place)
1912                 // })
1913                 let expr = {
1914                     let ptr = self.expr_ident(e.span, p_ptr_ident, p_ptr_binding);
1915                     let call_move_val_init =
1916                         hir::StmtSemi(
1917                             make_call(self, &move_val_init, hir_vec![ptr, pop_unsafe_expr]),
1918                             self.next_id().node_id);
1919                     let call_move_val_init = respan(e.span, call_move_val_init);
1920
1921                     let place = self.expr_ident(e.span, place_ident, place_binding);
1922                     let call = make_call(self, &inplace_finalize, hir_vec![place]);
1923                     P(self.signal_block_expr(hir_vec![call_move_val_init],
1924                                              call,
1925                                              e.span,
1926                                              hir::PushUnsafeBlock(hir::CompilerGenerated),
1927                                              ThinVec::new()))
1928                 };
1929
1930                 let block = self.block_all(e.span, hir_vec![s1, s2, s3], Some(expr));
1931                 hir::ExprBlock(P(block))
1932             }
1933
1934             ExprKind::Array(ref exprs) => {
1935                 hir::ExprArray(exprs.iter().map(|x| self.lower_expr(x)).collect())
1936             }
1937             ExprKind::Repeat(ref expr, ref count) => {
1938                 let expr = P(self.lower_expr(expr));
1939                 let count = self.lower_body(None, |this| this.lower_expr(count));
1940                 hir::ExprRepeat(expr, count)
1941             }
1942             ExprKind::Tup(ref elts) => {
1943                 hir::ExprTup(elts.iter().map(|x| self.lower_expr(x)).collect())
1944             }
1945             ExprKind::Call(ref f, ref args) => {
1946                 let f = P(self.lower_expr(f));
1947                 hir::ExprCall(f, args.iter().map(|x| self.lower_expr(x)).collect())
1948             }
1949             ExprKind::MethodCall(ref seg, ref args) => {
1950                 let hir_seg = self.lower_path_segment(e.span, seg, ParamMode::Optional, 0,
1951                                                       ParenthesizedGenericArgs::Err);
1952                 let args = args.iter().map(|x| self.lower_expr(x)).collect();
1953                 hir::ExprMethodCall(hir_seg, seg.span, args)
1954             }
1955             ExprKind::Binary(binop, ref lhs, ref rhs) => {
1956                 let binop = self.lower_binop(binop);
1957                 let lhs = P(self.lower_expr(lhs));
1958                 let rhs = P(self.lower_expr(rhs));
1959                 hir::ExprBinary(binop, lhs, rhs)
1960             }
1961             ExprKind::Unary(op, ref ohs) => {
1962                 let op = self.lower_unop(op);
1963                 let ohs = P(self.lower_expr(ohs));
1964                 hir::ExprUnary(op, ohs)
1965             }
1966             ExprKind::Lit(ref l) => hir::ExprLit(P((**l).clone())),
1967             ExprKind::Cast(ref expr, ref ty) => {
1968                 let expr = P(self.lower_expr(expr));
1969                 hir::ExprCast(expr, self.lower_ty(ty))
1970             }
1971             ExprKind::Type(ref expr, ref ty) => {
1972                 let expr = P(self.lower_expr(expr));
1973                 hir::ExprType(expr, self.lower_ty(ty))
1974             }
1975             ExprKind::AddrOf(m, ref ohs) => {
1976                 let m = self.lower_mutability(m);
1977                 let ohs = P(self.lower_expr(ohs));
1978                 hir::ExprAddrOf(m, ohs)
1979             }
1980             // More complicated than you might expect because the else branch
1981             // might be `if let`.
1982             ExprKind::If(ref cond, ref blk, ref else_opt) => {
1983                 let else_opt = else_opt.as_ref().map(|els| {
1984                     match els.node {
1985                         ExprKind::IfLet(..) => {
1986                             // wrap the if-let expr in a block
1987                             let span = els.span;
1988                             let els = P(self.lower_expr(els));
1989                             let LoweredNodeId {
1990                                 node_id,
1991                                 hir_id,
1992                             } = self.next_id();
1993                             let blk = P(hir::Block {
1994                                 stmts: hir_vec![],
1995                                 expr: Some(els),
1996                                 id: node_id,
1997                                 hir_id,
1998                                 rules: hir::DefaultBlock,
1999                                 span,
2000                                 targeted_by_break: false,
2001                             });
2002                             P(self.expr_block(blk, ThinVec::new()))
2003                         }
2004                         _ => P(self.lower_expr(els)),
2005                     }
2006                 });
2007
2008                 let then_blk = self.lower_block(blk, false);
2009                 let then_expr = self.expr_block(then_blk, ThinVec::new());
2010
2011                 hir::ExprIf(P(self.lower_expr(cond)), P(then_expr), else_opt)
2012             }
2013             ExprKind::While(ref cond, ref body, opt_ident) => {
2014                 self.with_loop_scope(e.id, |this|
2015                     hir::ExprWhile(
2016                         this.with_loop_condition_scope(|this| P(this.lower_expr(cond))),
2017                         this.lower_block(body, false),
2018                         this.lower_opt_sp_ident(opt_ident)))
2019             }
2020             ExprKind::Loop(ref body, opt_ident) => {
2021                 self.with_loop_scope(e.id, |this|
2022                     hir::ExprLoop(this.lower_block(body, false),
2023                                   this.lower_opt_sp_ident(opt_ident),
2024                                   hir::LoopSource::Loop))
2025             }
2026             ExprKind::Catch(ref body) => {
2027                 self.with_catch_scope(body.id, |this|
2028                     hir::ExprBlock(this.lower_block(body, true)))
2029             }
2030             ExprKind::Match(ref expr, ref arms) => {
2031                 hir::ExprMatch(P(self.lower_expr(expr)),
2032                                arms.iter().map(|x| self.lower_arm(x)).collect(),
2033                                hir::MatchSource::Normal)
2034             }
2035             ExprKind::Closure(capture_clause, ref decl, ref body, fn_decl_span) => {
2036                 self.with_new_scopes(|this| {
2037                     this.with_parent_def(e.id, |this| {
2038                         let mut is_generator = false;
2039                         let body_id = this.lower_body(Some(decl), |this| {
2040                             let e = this.lower_expr(body);
2041                             is_generator = this.is_generator;
2042                             e
2043                         });
2044                         if is_generator && !decl.inputs.is_empty() {
2045                             span_err!(this.sess, fn_decl_span, E0628,
2046                                       "generators cannot have explicit arguments");
2047                             this.sess.abort_if_errors();
2048                         }
2049                         hir::ExprClosure(this.lower_capture_clause(capture_clause),
2050                                          this.lower_fn_decl(decl),
2051                                          body_id,
2052                                          fn_decl_span,
2053                                          is_generator)
2054                     })
2055                 })
2056             }
2057             ExprKind::Block(ref blk) => hir::ExprBlock(self.lower_block(blk, false)),
2058             ExprKind::Assign(ref el, ref er) => {
2059                 hir::ExprAssign(P(self.lower_expr(el)), P(self.lower_expr(er)))
2060             }
2061             ExprKind::AssignOp(op, ref el, ref er) => {
2062                 hir::ExprAssignOp(self.lower_binop(op),
2063                                   P(self.lower_expr(el)),
2064                                   P(self.lower_expr(er)))
2065             }
2066             ExprKind::Field(ref el, ident) => {
2067                 hir::ExprField(P(self.lower_expr(el)),
2068                                respan(ident.span, self.lower_ident(ident.node)))
2069             }
2070             ExprKind::TupField(ref el, ident) => {
2071                 hir::ExprTupField(P(self.lower_expr(el)), ident)
2072             }
2073             ExprKind::Index(ref el, ref er) => {
2074                 hir::ExprIndex(P(self.lower_expr(el)), P(self.lower_expr(er)))
2075             }
2076             ExprKind::Range(ref e1, ref e2, lims) => {
2077                 use syntax::ast::RangeLimits::*;
2078
2079                 let path = match (e1, e2, lims) {
2080                     (&None, &None, HalfOpen) => "RangeFull",
2081                     (&Some(..), &None, HalfOpen) => "RangeFrom",
2082                     (&None, &Some(..), HalfOpen) => "RangeTo",
2083                     (&Some(..), &Some(..), HalfOpen) => "Range",
2084                     (&None, &Some(..), Closed) => "RangeToInclusive",
2085                     (&Some(..), &Some(..), Closed) => "RangeInclusive",
2086                     (_, &None, Closed) =>
2087                         panic!(self.diagnostic().span_fatal(
2088                             e.span, "inclusive range with no end")),
2089                 };
2090
2091                 let fields =
2092                     e1.iter().map(|e| ("start", e)).chain(e2.iter().map(|e| ("end", e)))
2093                     .map(|(s, e)| {
2094                         let expr = P(self.lower_expr(&e));
2095                         let unstable_span =
2096                             self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
2097                         self.field(Symbol::intern(s), expr, unstable_span)
2098                     }).collect::<P<[hir::Field]>>();
2099
2100                 let is_unit = fields.is_empty();
2101                 let unstable_span =
2102                     self.allow_internal_unstable(CompilerDesugaringKind::DotFill, e.span);
2103                 let struct_path =
2104                     iter::once("ops").chain(iter::once(path))
2105                     .collect::<Vec<_>>();
2106                 let struct_path = self.std_path(unstable_span, &struct_path, is_unit);
2107                 let struct_path = hir::QPath::Resolved(None, P(struct_path));
2108
2109                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
2110
2111                 return hir::Expr {
2112                     id: node_id,
2113                     hir_id,
2114                     node: if is_unit {
2115                         hir::ExprPath(struct_path)
2116                     } else {
2117                         hir::ExprStruct(struct_path, fields, None)
2118                     },
2119                     span: unstable_span,
2120                     attrs: e.attrs.clone(),
2121                 };
2122             }
2123             ExprKind::Path(ref qself, ref path) => {
2124                 hir::ExprPath(self.lower_qpath(e.id, qself, path, ParamMode::Optional))
2125             }
2126             ExprKind::Break(opt_ident, ref opt_expr) => {
2127                 let label_result = if self.is_in_loop_condition && opt_ident.is_none() {
2128                     hir::Destination {
2129                         ident: opt_ident,
2130                         target_id: hir::ScopeTarget::Loop(
2131                                 Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into()),
2132                     }
2133                 } else {
2134                     self.lower_loop_destination(opt_ident.map(|ident| (e.id, ident)))
2135                 };
2136                 hir::ExprBreak(
2137                         label_result,
2138                         opt_expr.as_ref().map(|x| P(self.lower_expr(x))))
2139             }
2140             ExprKind::Continue(opt_ident) =>
2141                 hir::ExprAgain(
2142                     if self.is_in_loop_condition && opt_ident.is_none() {
2143                         hir::Destination {
2144                             ident: opt_ident,
2145                             target_id: hir::ScopeTarget::Loop(Err(
2146                                 hir::LoopIdError::UnlabeledCfInWhileCondition).into()),
2147                         }
2148                     } else {
2149                         self.lower_loop_destination(opt_ident.map( |ident| (e.id, ident)))
2150                     }),
2151             ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
2152             ExprKind::InlineAsm(ref asm) => {
2153                 let hir_asm = hir::InlineAsm {
2154                     inputs: asm.inputs.iter().map(|&(ref c, _)| c.clone()).collect(),
2155                     outputs: asm.outputs.iter().map(|out| {
2156                         hir::InlineAsmOutput {
2157                             constraint: out.constraint.clone(),
2158                             is_rw: out.is_rw,
2159                             is_indirect: out.is_indirect,
2160                         }
2161                     }).collect(),
2162                     asm: asm.asm.clone(),
2163                     asm_str_style: asm.asm_str_style,
2164                     clobbers: asm.clobbers.clone().into(),
2165                     volatile: asm.volatile,
2166                     alignstack: asm.alignstack,
2167                     dialect: asm.dialect,
2168                     ctxt: asm.ctxt,
2169                 };
2170                 let outputs =
2171                     asm.outputs.iter().map(|out| self.lower_expr(&out.expr)).collect();
2172                 let inputs =
2173                     asm.inputs.iter().map(|&(_, ref input)| self.lower_expr(input)).collect();
2174                 hir::ExprInlineAsm(P(hir_asm), outputs, inputs)
2175             }
2176             ExprKind::Struct(ref path, ref fields, ref maybe_expr) => {
2177                 hir::ExprStruct(self.lower_qpath(e.id, &None, path, ParamMode::Optional),
2178                                 fields.iter().map(|x| self.lower_field(x)).collect(),
2179                                 maybe_expr.as_ref().map(|x| P(self.lower_expr(x))))
2180             }
2181             ExprKind::Paren(ref ex) => {
2182                 let mut ex = self.lower_expr(ex);
2183                 // include parens in span, but only if it is a super-span.
2184                 if e.span.contains(ex.span) {
2185                     ex.span = e.span;
2186                 }
2187                 // merge attributes into the inner expression.
2188                 let mut attrs = e.attrs.clone();
2189                 attrs.extend::<Vec<_>>(ex.attrs.into());
2190                 ex.attrs = attrs;
2191                 return ex;
2192             }
2193
2194             ExprKind::Yield(ref opt_expr) => {
2195                 self.is_generator = true;
2196                 let expr = opt_expr.as_ref().map(|x| self.lower_expr(x)).unwrap_or_else(|| {
2197                     self.expr(e.span, hir::ExprTup(hir_vec![]), ThinVec::new())
2198                 });
2199                 hir::ExprYield(P(expr))
2200             }
2201
2202             // Desugar ExprIfLet
2203             // From: `if let <pat> = <sub_expr> <body> [<else_opt>]`
2204             ExprKind::IfLet(ref pat, ref sub_expr, ref body, ref else_opt) => {
2205                 // to:
2206                 //
2207                 //   match <sub_expr> {
2208                 //     <pat> => <body>,
2209                 //     _ => [<else_opt> | ()]
2210                 //   }
2211
2212                 let mut arms = vec![];
2213
2214                 // `<pat> => <body>`
2215                 {
2216                     let body = self.lower_block(body, false);
2217                     let body_expr = P(self.expr_block(body, ThinVec::new()));
2218                     let pat = self.lower_pat(pat);
2219                     arms.push(self.arm(hir_vec![pat], body_expr));
2220                 }
2221
2222                 // _ => [<else_opt>|()]
2223                 {
2224                     let wildcard_arm: Option<&Expr> = else_opt.as_ref().map(|p| &**p);
2225                     let wildcard_pattern = self.pat_wild(e.span);
2226                     let body = if let Some(else_expr) = wildcard_arm {
2227                         P(self.lower_expr(else_expr))
2228                     } else {
2229                         self.expr_tuple(e.span, hir_vec![])
2230                     };
2231                     arms.push(self.arm(hir_vec![wildcard_pattern], body));
2232                 }
2233
2234                 let contains_else_clause = else_opt.is_some();
2235
2236                 let sub_expr = P(self.lower_expr(sub_expr));
2237
2238                 hir::ExprMatch(
2239                     sub_expr,
2240                     arms.into(),
2241                     hir::MatchSource::IfLetDesugar {
2242                         contains_else_clause,
2243                     })
2244             }
2245
2246             // Desugar ExprWhileLet
2247             // From: `[opt_ident]: while let <pat> = <sub_expr> <body>`
2248             ExprKind::WhileLet(ref pat, ref sub_expr, ref body, opt_ident) => {
2249                 // to:
2250                 //
2251                 //   [opt_ident]: loop {
2252                 //     match <sub_expr> {
2253                 //       <pat> => <body>,
2254                 //       _ => break
2255                 //     }
2256                 //   }
2257
2258                 // Note that the block AND the condition are evaluated in the loop scope.
2259                 // This is done to allow `break` from inside the condition of the loop.
2260                 let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| (
2261                     this.lower_block(body, false),
2262                     this.expr_break(e.span, ThinVec::new()),
2263                     this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
2264                 ));
2265
2266                 // `<pat> => <body>`
2267                 let pat_arm = {
2268                     let body_expr = P(self.expr_block(body, ThinVec::new()));
2269                     let pat = self.lower_pat(pat);
2270                     self.arm(hir_vec![pat], body_expr)
2271                 };
2272
2273                 // `_ => break`
2274                 let break_arm = {
2275                     let pat_under = self.pat_wild(e.span);
2276                     self.arm(hir_vec![pat_under], break_expr)
2277                 };
2278
2279                 // `match <sub_expr> { ... }`
2280                 let arms = hir_vec![pat_arm, break_arm];
2281                 let match_expr = self.expr(e.span,
2282                                            hir::ExprMatch(sub_expr,
2283                                                           arms,
2284                                                           hir::MatchSource::WhileLetDesugar),
2285                                            ThinVec::new());
2286
2287                 // `[opt_ident]: loop { ... }`
2288                 let loop_block = P(self.block_expr(P(match_expr)));
2289                 let loop_expr = hir::ExprLoop(loop_block, self.lower_opt_sp_ident(opt_ident),
2290                                               hir::LoopSource::WhileLet);
2291                 // add attributes to the outer returned expr node
2292                 loop_expr
2293             }
2294
2295             // Desugar ExprForLoop
2296             // From: `[opt_ident]: for <pat> in <head> <body>`
2297             ExprKind::ForLoop(ref pat, ref head, ref body, opt_ident) => {
2298                 // to:
2299                 //
2300                 //   {
2301                 //     let result = match ::std::iter::IntoIterator::into_iter(<head>) {
2302                 //       mut iter => {
2303                 //         [opt_ident]: loop {
2304                 //           let mut __next;
2305                 //           match ::std::iter::Iterator::next(&mut iter) {
2306                 //             ::std::option::Option::Some(val) => __next = val,
2307                 //             ::std::option::Option::None => break
2308                 //           };
2309                 //           let <pat> = __next;
2310                 //           StmtExpr(<body>);
2311                 //         }
2312                 //       }
2313                 //     };
2314                 //     result
2315                 //   }
2316
2317                 // expand <head>
2318                 let head = self.lower_expr(head);
2319
2320                 let iter = self.str_to_ident("iter");
2321
2322                 let next_ident = self.str_to_ident("__next");
2323                 let next_pat = self.pat_ident_binding_mode(e.span,
2324                                                            next_ident,
2325                                                            hir::BindingAnnotation::Mutable);
2326
2327                 // `::std::option::Option::Some(val) => next = val`
2328                 let pat_arm = {
2329                     let val_ident = self.str_to_ident("val");
2330                     let val_pat = self.pat_ident(e.span, val_ident);
2331                     let val_expr = P(self.expr_ident(e.span, val_ident, val_pat.id));
2332                     let next_expr = P(self.expr_ident(e.span, next_ident, next_pat.id));
2333                     let assign = P(self.expr(e.span,
2334                                              hir::ExprAssign(next_expr, val_expr),
2335                                              ThinVec::new()));
2336                     let some_pat = self.pat_some(e.span, val_pat);
2337                     self.arm(hir_vec![some_pat], assign)
2338                 };
2339
2340                 // `::std::option::Option::None => break`
2341                 let break_arm = {
2342                     let break_expr = self.with_loop_scope(e.id, |this|
2343                         this.expr_break(e.span, ThinVec::new()));
2344                     let pat = self.pat_none(e.span);
2345                     self.arm(hir_vec![pat], break_expr)
2346                 };
2347
2348                 // `mut iter`
2349                 let iter_pat = self.pat_ident_binding_mode(e.span,
2350                                                            iter,
2351                                                            hir::BindingAnnotation::Mutable);
2352
2353                 // `match ::std::iter::Iterator::next(&mut iter) { ... }`
2354                 let match_expr = {
2355                     let iter = P(self.expr_ident(e.span, iter, iter_pat.id));
2356                     let ref_mut_iter = self.expr_mut_addr_of(e.span, iter);
2357                     let next_path = &["iter", "Iterator", "next"];
2358                     let next_path = P(self.expr_std_path(e.span, next_path, ThinVec::new()));
2359                     let next_expr = P(self.expr_call(e.span, next_path,
2360                                       hir_vec![ref_mut_iter]));
2361                     let arms = hir_vec![pat_arm, break_arm];
2362
2363                     P(self.expr(e.span,
2364                                 hir::ExprMatch(next_expr, arms,
2365                                                hir::MatchSource::ForLoopDesugar),
2366                                 ThinVec::new()))
2367                 };
2368                 let match_stmt = respan(e.span, hir::StmtExpr(match_expr, self.next_id().node_id));
2369
2370                 let next_expr = P(self.expr_ident(e.span, next_ident, next_pat.id));
2371
2372                 // `let mut __next`
2373                 let next_let = self.stmt_let_pat(e.span,
2374                     None,
2375                     next_pat,
2376                     hir::LocalSource::ForLoopDesugar);
2377
2378                 // `let <pat> = __next`
2379                 let pat = self.lower_pat(pat);
2380                 let pat_let = self.stmt_let_pat(e.span,
2381                     Some(next_expr),
2382                     pat,
2383                     hir::LocalSource::ForLoopDesugar);
2384
2385                 let body_block = self.with_loop_scope(e.id,
2386                                                         |this| this.lower_block(body, false));
2387                 let body_expr = P(self.expr_block(body_block, ThinVec::new()));
2388                 let body_stmt = respan(e.span, hir::StmtExpr(body_expr, self.next_id().node_id));
2389
2390                 let loop_block = P(self.block_all(e.span,
2391                                                   hir_vec![next_let,
2392                                                            match_stmt,
2393                                                            pat_let,
2394                                                            body_stmt],
2395                                                   None));
2396
2397                 // `[opt_ident]: loop { ... }`
2398                 let loop_expr = hir::ExprLoop(loop_block, self.lower_opt_sp_ident(opt_ident),
2399                                               hir::LoopSource::ForLoop);
2400                 let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
2401                 let loop_expr = P(hir::Expr {
2402                     id: node_id,
2403                     hir_id,
2404                     node: loop_expr,
2405                     span: e.span,
2406                     attrs: ThinVec::new(),
2407                 });
2408
2409                 // `mut iter => { ... }`
2410                 let iter_arm = self.arm(hir_vec![iter_pat], loop_expr);
2411
2412                 // `match ::std::iter::IntoIterator::into_iter(<head>) { ... }`
2413                 let into_iter_expr = {
2414                     let into_iter_path = &["iter", "IntoIterator", "into_iter"];
2415                     let into_iter = P(self.expr_std_path(e.span, into_iter_path,
2416                                                          ThinVec::new()));
2417                     P(self.expr_call(e.span, into_iter, hir_vec![head]))
2418                 };
2419
2420                 let match_expr = P(self.expr_match(e.span,
2421                                                    into_iter_expr,
2422                                                    hir_vec![iter_arm],
2423                                                    hir::MatchSource::ForLoopDesugar));
2424
2425                 // `{ let _result = ...; _result }`
2426                 // underscore prevents an unused_variables lint if the head diverges
2427                 let result_ident = self.str_to_ident("_result");
2428                 let (let_stmt, let_stmt_binding) =
2429                     self.stmt_let(e.span, false, result_ident, match_expr);
2430
2431                 let result = P(self.expr_ident(e.span, result_ident, let_stmt_binding));
2432                 let block = P(self.block_all(e.span, hir_vec![let_stmt], Some(result)));
2433                 // add the attributes to the outer returned expr node
2434                 return self.expr_block(block, e.attrs.clone());
2435             }
2436
2437             // Desugar ExprKind::Try
2438             // From: `<expr>?`
2439             ExprKind::Try(ref sub_expr) => {
2440                 // to:
2441                 //
2442                 // match Try::into_result(<expr>) {
2443                 //     Ok(val) => #[allow(unreachable_code)] val,
2444                 //     Err(err) => #[allow(unreachable_code)]
2445                 //                 // If there is an enclosing `catch {...}`
2446                 //                 break 'catch_target Try::from_error(From::from(err)),
2447                 //                 // Otherwise
2448                 //                 return Try::from_error(From::from(err)),
2449                 // }
2450
2451                 let unstable_span =
2452                     self.allow_internal_unstable(CompilerDesugaringKind::QuestionMark, e.span);
2453
2454                 // Try::into_result(<expr>)
2455                 let discr = {
2456                     // expand <expr>
2457                     let sub_expr = self.lower_expr(sub_expr);
2458
2459                     let path = &["ops", "Try", "into_result"];
2460                     let path = P(self.expr_std_path(unstable_span, path, ThinVec::new()));
2461                     P(self.expr_call(e.span, path, hir_vec![sub_expr]))
2462                 };
2463
2464                 // #[allow(unreachable_code)]
2465                 let attr = {
2466                     // allow(unreachable_code)
2467                     let allow = {
2468                         let allow_ident = self.str_to_ident("allow");
2469                         let uc_ident = self.str_to_ident("unreachable_code");
2470                         let uc_meta_item = attr::mk_spanned_word_item(e.span, uc_ident);
2471                         let uc_nested = NestedMetaItemKind::MetaItem(uc_meta_item);
2472                         let uc_spanned = respan(e.span, uc_nested);
2473                         attr::mk_spanned_list_item(e.span, allow_ident, vec![uc_spanned])
2474                     };
2475                     attr::mk_spanned_attr_outer(e.span, attr::mk_attr_id(), allow)
2476                 };
2477                 let attrs = vec![attr];
2478
2479                 // Ok(val) => #[allow(unreachable_code)] val,
2480                 let ok_arm = {
2481                     let val_ident = self.str_to_ident("val");
2482                     let val_pat = self.pat_ident(e.span, val_ident);
2483                     let val_expr = P(self.expr_ident_with_attrs(e.span,
2484                                                                 val_ident,
2485                                                                 val_pat.id,
2486                                                                 ThinVec::from(attrs.clone())));
2487                     let ok_pat = self.pat_ok(e.span, val_pat);
2488
2489                     self.arm(hir_vec![ok_pat], val_expr)
2490                 };
2491
2492                 // Err(err) => #[allow(unreachable_code)]
2493                 //             return Carrier::from_error(From::from(err)),
2494                 let err_arm = {
2495                     let err_ident = self.str_to_ident("err");
2496                     let err_local = self.pat_ident(e.span, err_ident);
2497                     let from_expr = {
2498                         let path = &["convert", "From", "from"];
2499                         let from = P(self.expr_std_path(e.span, path, ThinVec::new()));
2500                         let err_expr = self.expr_ident(e.span, err_ident, err_local.id);
2501
2502                         self.expr_call(e.span, from, hir_vec![err_expr])
2503                     };
2504                     let from_err_expr = {
2505                         let path = &["ops", "Try", "from_error"];
2506                         let from_err = P(self.expr_std_path(unstable_span, path,
2507                                                             ThinVec::new()));
2508                         P(self.expr_call(e.span, from_err, hir_vec![from_expr]))
2509                     };
2510
2511                     let thin_attrs = ThinVec::from(attrs);
2512                     let catch_scope = self.catch_scopes.last().map(|x| *x);
2513                     let ret_expr = if let Some(catch_node) = catch_scope {
2514                         P(self.expr(
2515                             e.span,
2516                             hir::ExprBreak(
2517                                 hir::Destination {
2518                                     ident: None,
2519                                     target_id: hir::ScopeTarget::Block(catch_node),
2520                                 },
2521                                 Some(from_err_expr)
2522                             ),
2523                             thin_attrs))
2524                     } else {
2525                         P(self.expr(e.span,
2526                                     hir::Expr_::ExprRet(Some(from_err_expr)),
2527                                     thin_attrs))
2528                     };
2529
2530
2531                     let err_pat = self.pat_err(e.span, err_local);
2532                     self.arm(hir_vec![err_pat], ret_expr)
2533                 };
2534
2535                 hir::ExprMatch(discr,
2536                                hir_vec![err_arm, ok_arm],
2537                                hir::MatchSource::TryDesugar)
2538             }
2539
2540             ExprKind::Mac(_) => panic!("Shouldn't exist here"),
2541         };
2542
2543         let LoweredNodeId { node_id, hir_id } = self.lower_node_id(e.id);
2544
2545         hir::Expr {
2546             id: node_id,
2547             hir_id,
2548             node: kind,
2549             span: e.span,
2550             attrs: e.attrs.clone(),
2551         }
2552     }
2553
2554     fn lower_stmt(&mut self, s: &Stmt) -> SmallVector<hir::Stmt> {
2555         SmallVector::one(match s.node {
2556             StmtKind::Local(ref l) => Spanned {
2557                 node: hir::StmtDecl(P(Spanned {
2558                     node: hir::DeclLocal(self.lower_local(l)),
2559                     span: s.span,
2560                 }), self.lower_node_id(s.id).node_id),
2561                 span: s.span,
2562             },
2563             StmtKind::Item(ref it) => {
2564                 // Can only use the ID once.
2565                 let mut id = Some(s.id);
2566                 return self.lower_item_id(it).into_iter().map(|item_id| Spanned {
2567                     node: hir::StmtDecl(P(Spanned {
2568                         node: hir::DeclItem(item_id),
2569                         span: s.span,
2570                     }), id.take()
2571                           .map(|id| self.lower_node_id(id).node_id)
2572                           .unwrap_or_else(|| self.next_id().node_id)),
2573                     span: s.span,
2574                 }).collect();
2575             }
2576             StmtKind::Expr(ref e) => {
2577                 Spanned {
2578                     node: hir::StmtExpr(P(self.lower_expr(e)),
2579                                           self.lower_node_id(s.id).node_id),
2580                     span: s.span,
2581                 }
2582             }
2583             StmtKind::Semi(ref e) => {
2584                 Spanned {
2585                     node: hir::StmtSemi(P(self.lower_expr(e)),
2586                                           self.lower_node_id(s.id).node_id),
2587                     span: s.span,
2588                 }
2589             }
2590             StmtKind::Mac(..) => panic!("Shouldn't exist here"),
2591         })
2592     }
2593
2594     fn lower_capture_clause(&mut self, c: CaptureBy) -> hir::CaptureClause {
2595         match c {
2596             CaptureBy::Value => hir::CaptureByValue,
2597             CaptureBy::Ref => hir::CaptureByRef,
2598         }
2599     }
2600
2601     /// If an `explicit_owner` is given, this method allocates the `HirId` in
2602     /// the address space of that item instead of the item currently being
2603     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
2604     /// lower a `Visibility` value although we haven't lowered the owning
2605     /// `ImplItem` in question yet.
2606     fn lower_visibility(&mut self,
2607                         v: &Visibility,
2608                         explicit_owner: Option<NodeId>)
2609                         -> hir::Visibility {
2610         match *v {
2611             Visibility::Public => hir::Public,
2612             Visibility::Crate(_) => hir::Visibility::Crate,
2613             Visibility::Restricted { ref path, id } => {
2614                 hir::Visibility::Restricted {
2615                     path: P(self.lower_path(id, path, ParamMode::Explicit, true)),
2616                     id: if let Some(owner) = explicit_owner {
2617                         self.lower_node_id_with_owner(id, owner).node_id
2618                     } else {
2619                         self.lower_node_id(id).node_id
2620                     }
2621                 }
2622             }
2623             Visibility::Inherited => hir::Inherited,
2624         }
2625     }
2626
2627     fn lower_defaultness(&mut self, d: Defaultness, has_value: bool) -> hir::Defaultness {
2628         match d {
2629             Defaultness::Default => hir::Defaultness::Default { has_value: has_value },
2630             Defaultness::Final => {
2631                 assert!(has_value);
2632                 hir::Defaultness::Final
2633             }
2634         }
2635     }
2636
2637     fn lower_block_check_mode(&mut self, b: &BlockCheckMode) -> hir::BlockCheckMode {
2638         match *b {
2639             BlockCheckMode::Default => hir::DefaultBlock,
2640             BlockCheckMode::Unsafe(u) => hir::UnsafeBlock(self.lower_unsafe_source(u)),
2641         }
2642     }
2643
2644     fn lower_binding_mode(&mut self, b: &BindingMode) -> hir::BindingAnnotation {
2645         match *b {
2646             BindingMode::ByValue(Mutability::Immutable) =>
2647                 hir::BindingAnnotation::Unannotated,
2648             BindingMode::ByRef(Mutability::Immutable) => hir::BindingAnnotation::Ref,
2649             BindingMode::ByValue(Mutability::Mutable) => hir::BindingAnnotation::Mutable,
2650             BindingMode::ByRef(Mutability::Mutable) => hir::BindingAnnotation::RefMut,
2651         }
2652     }
2653
2654     fn lower_unsafe_source(&mut self, u: UnsafeSource) -> hir::UnsafeSource {
2655         match u {
2656             CompilerGenerated => hir::CompilerGenerated,
2657             UserProvided => hir::UserProvided,
2658         }
2659     }
2660
2661     fn lower_impl_polarity(&mut self, i: ImplPolarity) -> hir::ImplPolarity {
2662         match i {
2663             ImplPolarity::Positive => hir::ImplPolarity::Positive,
2664             ImplPolarity::Negative => hir::ImplPolarity::Negative,
2665         }
2666     }
2667
2668     fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBoundModifier {
2669         match f {
2670             TraitBoundModifier::None => hir::TraitBoundModifier::None,
2671             TraitBoundModifier::Maybe => hir::TraitBoundModifier::Maybe,
2672         }
2673     }
2674
2675     // Helper methods for building HIR.
2676
2677     fn arm(&mut self, pats: hir::HirVec<P<hir::Pat>>, expr: P<hir::Expr>) -> hir::Arm {
2678         hir::Arm {
2679             attrs: hir_vec![],
2680             pats,
2681             guard: None,
2682             body: expr,
2683         }
2684     }
2685
2686     fn field(&mut self, name: Name, expr: P<hir::Expr>, span: Span) -> hir::Field {
2687         hir::Field {
2688             name: Spanned {
2689                 node: name,
2690                 span,
2691             },
2692             span,
2693             expr,
2694             is_shorthand: false,
2695         }
2696     }
2697
2698     fn expr_break(&mut self, span: Span, attrs: ThinVec<Attribute>) -> P<hir::Expr> {
2699         let expr_break = hir::ExprBreak(self.lower_loop_destination(None), None);
2700         P(self.expr(span, expr_break, attrs))
2701     }
2702
2703     fn expr_call(&mut self, span: Span, e: P<hir::Expr>, args: hir::HirVec<hir::Expr>)
2704                  -> hir::Expr {
2705         self.expr(span, hir::ExprCall(e, args), ThinVec::new())
2706     }
2707
2708     fn expr_ident(&mut self, span: Span, id: Name, binding: NodeId) -> hir::Expr {
2709         self.expr_ident_with_attrs(span, id, binding, ThinVec::new())
2710     }
2711
2712     fn expr_ident_with_attrs(&mut self, span: Span,
2713                                         id: Name,
2714                                         binding: NodeId,
2715                                         attrs: ThinVec<Attribute>) -> hir::Expr {
2716         let expr_path = hir::ExprPath(hir::QPath::Resolved(None, P(hir::Path {
2717             span,
2718             def: Def::Local(binding),
2719             segments: hir_vec![hir::PathSegment::from_name(id)],
2720         })));
2721
2722         self.expr(span, expr_path, attrs)
2723     }
2724
2725     fn expr_mut_addr_of(&mut self, span: Span, e: P<hir::Expr>) -> hir::Expr {
2726         self.expr(span, hir::ExprAddrOf(hir::MutMutable, e), ThinVec::new())
2727     }
2728
2729     fn expr_std_path(&mut self,
2730                      span: Span,
2731                      components: &[&str],
2732                      attrs: ThinVec<Attribute>)
2733                      -> hir::Expr {
2734         let path = self.std_path(span, components, true);
2735         self.expr(span, hir::ExprPath(hir::QPath::Resolved(None, P(path))), attrs)
2736     }
2737
2738     fn expr_match(&mut self,
2739                   span: Span,
2740                   arg: P<hir::Expr>,
2741                   arms: hir::HirVec<hir::Arm>,
2742                   source: hir::MatchSource)
2743                   -> hir::Expr {
2744         self.expr(span, hir::ExprMatch(arg, arms, source), ThinVec::new())
2745     }
2746
2747     fn expr_block(&mut self, b: P<hir::Block>, attrs: ThinVec<Attribute>) -> hir::Expr {
2748         self.expr(b.span, hir::ExprBlock(b), attrs)
2749     }
2750
2751     fn expr_tuple(&mut self, sp: Span, exprs: hir::HirVec<hir::Expr>) -> P<hir::Expr> {
2752         P(self.expr(sp, hir::ExprTup(exprs), ThinVec::new()))
2753     }
2754
2755     fn expr(&mut self, span: Span, node: hir::Expr_, attrs: ThinVec<Attribute>) -> hir::Expr {
2756         let LoweredNodeId { node_id, hir_id } = self.next_id();
2757         hir::Expr {
2758             id: node_id,
2759             hir_id,
2760             node,
2761             span,
2762             attrs,
2763         }
2764     }
2765
2766     fn stmt_let_pat(&mut self,
2767                     sp: Span,
2768                     ex: Option<P<hir::Expr>>,
2769                     pat: P<hir::Pat>,
2770                     source: hir::LocalSource)
2771                     -> hir::Stmt {
2772         let LoweredNodeId { node_id, hir_id } = self.next_id();
2773
2774         let local = P(hir::Local {
2775             pat,
2776             ty: None,
2777             init: ex,
2778             id: node_id,
2779             hir_id,
2780             span: sp,
2781             attrs: ThinVec::new(),
2782             source,
2783         });
2784         let decl = respan(sp, hir::DeclLocal(local));
2785         respan(sp, hir::StmtDecl(P(decl), self.next_id().node_id))
2786     }
2787
2788     fn stmt_let(&mut self, sp: Span, mutbl: bool, ident: Name, ex: P<hir::Expr>)
2789                 -> (hir::Stmt, NodeId) {
2790         let pat = if mutbl {
2791             self.pat_ident_binding_mode(sp, ident, hir::BindingAnnotation::Mutable)
2792         } else {
2793             self.pat_ident(sp, ident)
2794         };
2795         let pat_id = pat.id;
2796         (self.stmt_let_pat(sp, Some(ex), pat, hir::LocalSource::Normal), pat_id)
2797     }
2798
2799     fn block_expr(&mut self, expr: P<hir::Expr>) -> hir::Block {
2800         self.block_all(expr.span, hir::HirVec::new(), Some(expr))
2801     }
2802
2803     fn block_all(&mut self, span: Span, stmts: hir::HirVec<hir::Stmt>, expr: Option<P<hir::Expr>>)
2804                  -> hir::Block {
2805         let LoweredNodeId { node_id, hir_id } = self.next_id();
2806
2807         hir::Block {
2808             stmts,
2809             expr,
2810             id: node_id,
2811             hir_id,
2812             rules: hir::DefaultBlock,
2813             span,
2814             targeted_by_break: false,
2815         }
2816     }
2817
2818     fn pat_ok(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
2819         self.pat_std_enum(span, &["result", "Result", "Ok"], hir_vec![pat])
2820     }
2821
2822     fn pat_err(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
2823         self.pat_std_enum(span, &["result", "Result", "Err"], hir_vec![pat])
2824     }
2825
2826     fn pat_some(&mut self, span: Span, pat: P<hir::Pat>) -> P<hir::Pat> {
2827         self.pat_std_enum(span, &["option", "Option", "Some"], hir_vec![pat])
2828     }
2829
2830     fn pat_none(&mut self, span: Span) -> P<hir::Pat> {
2831         self.pat_std_enum(span, &["option", "Option", "None"], hir_vec![])
2832     }
2833
2834     fn pat_std_enum(&mut self,
2835                     span: Span,
2836                     components: &[&str],
2837                     subpats: hir::HirVec<P<hir::Pat>>)
2838                     -> P<hir::Pat> {
2839         let path = self.std_path(span, components, true);
2840         let qpath = hir::QPath::Resolved(None, P(path));
2841         let pt = if subpats.is_empty() {
2842             hir::PatKind::Path(qpath)
2843         } else {
2844             hir::PatKind::TupleStruct(qpath, subpats, None)
2845         };
2846         self.pat(span, pt)
2847     }
2848
2849     fn pat_ident(&mut self, span: Span, name: Name) -> P<hir::Pat> {
2850         self.pat_ident_binding_mode(span, name, hir::BindingAnnotation::Unannotated)
2851     }
2852
2853     fn pat_ident_binding_mode(&mut self, span: Span, name: Name, bm: hir::BindingAnnotation)
2854                               -> P<hir::Pat> {
2855         let LoweredNodeId { node_id, hir_id } = self.next_id();
2856
2857         P(hir::Pat {
2858             id: node_id,
2859             hir_id,
2860             node: hir::PatKind::Binding(bm,
2861                                         node_id,
2862                                         Spanned {
2863                                             span,
2864                                             node: name,
2865                                         },
2866                                         None),
2867             span,
2868         })
2869     }
2870
2871     fn pat_wild(&mut self, span: Span) -> P<hir::Pat> {
2872         self.pat(span, hir::PatKind::Wild)
2873     }
2874
2875     fn pat(&mut self, span: Span, pat: hir::PatKind) -> P<hir::Pat> {
2876         let LoweredNodeId { node_id, hir_id } = self.next_id();
2877         P(hir::Pat {
2878             id: node_id,
2879             hir_id,
2880             node: pat,
2881             span,
2882         })
2883     }
2884
2885     /// Given suffix ["b","c","d"], returns path `::std::b::c::d` when
2886     /// `fld.cx.use_std`, and `::core::b::c::d` otherwise.
2887     /// The path is also resolved according to `is_value`.
2888     fn std_path(&mut self, span: Span, components: &[&str], is_value: bool) -> hir::Path {
2889         let mut path = hir::Path {
2890             span,
2891             def: Def::Err,
2892             segments: iter::once(keywords::CrateRoot.name()).chain({
2893                 self.crate_root.into_iter().chain(components.iter().cloned()).map(Symbol::intern)
2894             }).map(hir::PathSegment::from_name).collect(),
2895         };
2896
2897         self.resolver.resolve_hir_path(&mut path, is_value);
2898         path
2899     }
2900
2901     fn signal_block_expr(&mut self,
2902                          stmts: hir::HirVec<hir::Stmt>,
2903                          expr: P<hir::Expr>,
2904                          span: Span,
2905                          rule: hir::BlockCheckMode,
2906                          attrs: ThinVec<Attribute>)
2907                          -> hir::Expr {
2908         let LoweredNodeId { node_id, hir_id } = self.next_id();
2909
2910         let block = P(hir::Block {
2911             rules: rule,
2912             span,
2913             id: node_id,
2914             hir_id,
2915             stmts,
2916             expr: Some(expr),
2917             targeted_by_break: false,
2918         });
2919         self.expr_block(block, attrs)
2920     }
2921
2922     fn ty_path(&mut self, id: NodeId, span: Span, qpath: hir::QPath) -> P<hir::Ty> {
2923         let mut id = id;
2924         let node = match qpath {
2925             hir::QPath::Resolved(None, path) => {
2926                 // Turn trait object paths into `TyTraitObject` instead.
2927                 if let Def::Trait(_) = path.def {
2928                     let principal = hir::PolyTraitRef {
2929                         bound_lifetimes: hir_vec![],
2930                         trait_ref: hir::TraitRef {
2931                             path: path.and_then(|path| path),
2932                             ref_id: id,
2933                         },
2934                         span,
2935                     };
2936
2937                     // The original ID is taken by the `PolyTraitRef`,
2938                     // so the `Ty` itself needs a different one.
2939                     id = self.next_id().node_id;
2940
2941                     hir::TyTraitObject(hir_vec![principal], self.elided_lifetime(span))
2942                 } else {
2943                     hir::TyPath(hir::QPath::Resolved(None, path))
2944                 }
2945             }
2946             _ => hir::TyPath(qpath)
2947         };
2948         P(hir::Ty { id, node, span })
2949     }
2950
2951     fn elided_lifetime(&mut self, span: Span) -> hir::Lifetime {
2952         hir::Lifetime {
2953             id: self.next_id().node_id,
2954             span,
2955             name: keywords::Invalid.name()
2956         }
2957     }
2958 }
2959
2960 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {
2961     // Sorting by span ensures that we get things in order within a
2962     // file, and also puts the files in a sensible order.
2963     let mut body_ids: Vec<_> = bodies.keys().cloned().collect();
2964     body_ids.sort_by_key(|b| bodies[b].value.span);
2965     body_ids
2966 }