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