src/librustc/middle/resolve_lifetime.rs

   1 // Copyright 2012-2013 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 //! Name resolution for lifetimes.
  12 //!
  13 //! Name resolution for lifetimes follows MUCH simpler rules than the
  14 //! full resolve. For example, lifetime names are never exported or
  15 //! used between functions, and they operate in a purely top-down
  16 //! way. Therefore we break lifetime name resolution into a separate pass.
  17
  18 pub use self::DefRegion::*;
  19 use self::ScopeChain::*;
  20
  21 use session::Session;
  22 use middle::def::{self, DefMap};
  23 use middle::region;
  24 use middle::subst;
  25 use middle::ty;
  26 use std::fmt;
  27 use std::mem::replace;
  28 use syntax::ast;
  29 use syntax::codemap::Span;
  30 use syntax::parse::token::special_idents;
  31 use util::nodemap::NodeMap;
  32
  33 use rustc_front::hir;
  34 use rustc_front::print::pprust::lifetime_to_string;
  35 use rustc_front::intravisit::{self, Visitor, FnKind};
  36
  37 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
  38 pub enum DefRegion {
  39     DefStaticRegion,
  40     DefEarlyBoundRegion(/* space */ subst::ParamSpace,
  41                         /* index */ u32,
  42                         /* lifetime decl */ ast::NodeId),
  43     DefLateBoundRegion(ty::DebruijnIndex,
  44                        /* lifetime decl */ ast::NodeId),
  45     DefFreeRegion(/* block scope */ region::DestructionScopeData,
  46                   /* lifetime decl */ ast::NodeId),
  47 }
  48
  49 // Maps the id of each lifetime reference to the lifetime decl
  50 // that it corresponds to.
  51 pub type NamedRegionMap = NodeMap<DefRegion>;
  52
  53 struct LifetimeContext<'a> {
  54     sess: &'a Session,
  55     named_region_map: &'a mut NamedRegionMap,
  56     scope: Scope<'a>,
  57     def_map: &'a DefMap,
  58     // Deep breath. Our representation for poly trait refs contains a single
  59     // binder and thus we only allow a single level of quantification. However,
  60     // the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
  61     // and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the de Bruijn indices
  62     // correct when representing these constraints, we should only introduce one
  63     // scope. However, we want to support both locations for the quantifier and
  64     // during lifetime resolution we want precise information (so we can't
  65     // desugar in an earlier phase).
  66
  67     // SO, if we encounter a quantifier at the outer scope, we set
  68     // trait_ref_hack to true (and introduce a scope), and then if we encounter
  69     // a quantifier at the inner scope, we error. If trait_ref_hack is false,
  70     // then we introduce the scope at the inner quantifier.
  71
  72     // I'm sorry.
  73     trait_ref_hack: bool,
  74
  75     // List of labels in the function/method currently under analysis.
  76     labels_in_fn: Vec<(ast::Name, Span)>,
  77 }
  78
  79 enum ScopeChain<'a> {
  80     /// EarlyScope(i, ['a, 'b, ...], s) extends s with early-bound
  81     /// lifetimes, assigning indexes 'a => i, 'b => i+1, ... etc.
  82     EarlyScope(subst::ParamSpace, &'a Vec<hir::LifetimeDef>, Scope<'a>),
  83     /// LateScope(['a, 'b, ...], s) extends s with late-bound
  84     /// lifetimes introduced by the declaration binder_id.
  85     LateScope(&'a Vec<hir::LifetimeDef>, Scope<'a>),
  86     /// lifetimes introduced by items within a code block are scoped
  87     /// to that block.
  88     BlockScope(region::DestructionScopeData, Scope<'a>),
  89     RootScope
  90 }
  91
  92 type Scope<'a> = &'a ScopeChain<'a>;
  93
  94 static ROOT_SCOPE: ScopeChain<'static> = RootScope;
  95
  96 pub fn krate(sess: &Session, krate: &hir::Crate, def_map: &DefMap) -> NamedRegionMap {
  97     let mut named_region_map = NodeMap();
  98     krate.visit_all_items(&mut LifetimeContext {
  99         sess: sess,
 100         named_region_map: &mut named_region_map,
 101         scope: &ROOT_SCOPE,
 102         def_map: def_map,
 103         trait_ref_hack: false,
 104         labels_in_fn: vec![],
 105     });
 106     sess.abort_if_errors();
 107     named_region_map
 108 }
 109
 110 impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
 111     fn visit_item(&mut self, item: &hir::Item) {
 112         assert!(self.labels_in_fn.is_empty());
 113
 114         // Items always introduce a new root scope
 115         self.with(RootScope, |_, this| {
 116             match item.node {
 117                 hir::ItemFn(..) => {
 118                     // Fn lifetimes get added in visit_fn below:
 119                     intravisit::walk_item(this, item);
 120                 }
 121                 hir::ItemExternCrate(_) |
 122                 hir::ItemUse(_) |
 123                 hir::ItemMod(..) |
 124                 hir::ItemDefaultImpl(..) |
 125                 hir::ItemForeignMod(..) |
 126                 hir::ItemStatic(..) |
 127                 hir::ItemConst(..) => {
 128                     // These sorts of items have no lifetime parameters at all.
 129                     intravisit::walk_item(this, item);
 130                 }
 131                 hir::ItemTy(_, ref generics) |
 132                 hir::ItemEnum(_, ref generics) |
 133                 hir::ItemStruct(_, ref generics) |
 134                 hir::ItemTrait(_, ref generics, _, _) |
 135                 hir::ItemImpl(_, _, ref generics, _, _, _) => {
 136                     // These kinds of items have only early bound lifetime parameters.
 137                     let lifetimes = &generics.lifetimes;
 138                     let early_scope = EarlyScope(subst::TypeSpace, lifetimes, &ROOT_SCOPE);
 139                     this.with(early_scope, |old_scope, this| {
 140                         this.check_lifetime_defs(old_scope, lifetimes);
 141                         intravisit::walk_item(this, item);
 142                     });
 143                 }
 144             }
 145         });
 146
 147         // Done traversing the item; remove any labels it created
 148         self.labels_in_fn.truncate(0);
 149     }
 150
 151     fn visit_foreign_item(&mut self, item: &hir::ForeignItem) {
 152         // Items save/restore the set of labels. This way inner items
 153         // can freely reuse names, be they loop labels or lifetimes.
 154         let saved = replace(&mut self.labels_in_fn, vec![]);
 155
 156         // Items always introduce a new root scope
 157         self.with(RootScope, |_, this| {
 158             match item.node {
 159                 hir::ForeignItemFn(_, ref generics) => {
 160                     this.visit_early_late(subst::FnSpace, generics, |this| {
 161                         intravisit::walk_foreign_item(this, item);
 162                     })
 163                 }
 164                 hir::ForeignItemStatic(..) => {
 165                     intravisit::walk_foreign_item(this, item);
 166                 }
 167             }
 168         });
 169
 170         // Done traversing the item; restore saved set of labels.
 171         replace(&mut self.labels_in_fn, saved);
 172     }
 173
 174     fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
 175                 b: &'v hir::Block, s: Span, _: ast::NodeId) {
 176         match fk {
 177             FnKind::ItemFn(_, generics, _, _, _, _) => {
 178                 self.visit_early_late(subst::FnSpace, generics, |this| {
 179                     this.walk_fn(fk, fd, b, s)
 180                 })
 181             }
 182             FnKind::Method(_, sig, _) => {
 183                 self.visit_early_late(subst::FnSpace, &sig.generics, |this| {
 184                     this.walk_fn(fk, fd, b, s)
 185                 })
 186             }
 187             FnKind::Closure(..) => {
 188                 self.walk_fn(fk, fd, b, s)
 189             }
 190         }
 191     }
 192
 193     fn visit_ty(&mut self, ty: &hir::Ty) {
 194         match ty.node {
 195             hir::TyBareFn(ref c) => {
 196                 self.with(LateScope(&c.lifetimes, self.scope), |old_scope, this| {
 197                     // a bare fn has no bounds, so everything
 198                     // contained within is scoped within its binder.
 199                     this.check_lifetime_defs(old_scope, &c.lifetimes);
 200                     intravisit::walk_ty(this, ty);
 201                 });
 202             }
 203             hir::TyPath(None, ref path) => {
 204                 // if this path references a trait, then this will resolve to
 205                 // a trait ref, which introduces a binding scope.
 206                 match self.def_map.get(&ty.id).map(|d| (d.base_def, d.depth)) {
 207                     Some((def::DefTrait(..), 0)) => {
 208                         self.with(LateScope(&Vec::new(), self.scope), |_, this| {
 209                             this.visit_path(path, ty.id);
 210                         });
 211                     }
 212                     _ => {
 213                         intravisit::walk_ty(self, ty);
 214                     }
 215                 }
 216             }
 217             _ => {
 218                 intravisit::walk_ty(self, ty)
 219             }
 220         }
 221     }
 222
 223     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
 224         // We reset the labels on every trait item, so that different
 225         // methods in an impl can reuse label names.
 226         let saved = replace(&mut self.labels_in_fn, vec![]);
 227
 228         if let hir::MethodTraitItem(ref sig, None) = trait_item.node {
 229             self.visit_early_late(
 230                 subst::FnSpace, &sig.generics,
 231                 |this| intravisit::walk_trait_item(this, trait_item))
 232         } else {
 233             intravisit::walk_trait_item(self, trait_item);
 234         }
 235
 236         replace(&mut self.labels_in_fn, saved);
 237     }
 238
 239     fn visit_block(&mut self, b: &hir::Block) {
 240         self.with(BlockScope(region::DestructionScopeData::new(b.id),
 241                              self.scope),
 242                   |_, this| intravisit::walk_block(this, b));
 243     }
 244
 245     fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
 246         if lifetime_ref.name == special_idents::static_lifetime.name {
 247             self.insert_lifetime(lifetime_ref, DefStaticRegion);
 248             return;
 249         }
 250         self.resolve_lifetime_ref(lifetime_ref);
 251     }
 252
 253     fn visit_generics(&mut self, generics: &hir::Generics) {
 254         for ty_param in generics.ty_params.iter() {
 255             walk_list!(self, visit_ty_param_bound, &ty_param.bounds);
 256             match ty_param.default {
 257                 Some(ref ty) => self.visit_ty(&**ty),
 258                 None => {}
 259             }
 260         }
 261         for predicate in &generics.where_clause.predicates {
 262             match predicate {
 263                 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate{ ref bounded_ty,
 264                                                                                ref bounds,
 265                                                                                ref bound_lifetimes,
 266                                                                                .. }) => {
 267                     if !bound_lifetimes.is_empty() {
 268                         self.trait_ref_hack = true;
 269                         let result = self.with(LateScope(bound_lifetimes, self.scope),
 270                                                |old_scope, this| {
 271                             this.check_lifetime_defs(old_scope, bound_lifetimes);
 272                             this.visit_ty(&**bounded_ty);
 273                             walk_list!(this, visit_ty_param_bound, bounds);
 274                         });
 275                         self.trait_ref_hack = false;
 276                         result
 277                     } else {
 278                         self.visit_ty(&**bounded_ty);
 279                         walk_list!(self, visit_ty_param_bound, bounds);
 280                     }
 281                 }
 282                 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate{ref lifetime,
 283                                                                                 ref bounds,
 284                                                                                 .. }) => {
 285
 286                     self.visit_lifetime(lifetime);
 287                     for bound in bounds {
 288                         self.visit_lifetime(bound);
 289                     }
 290                 }
 291                 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate{ id,
 292                                                                          ref path,
 293                                                                          ref ty,
 294                                                                          .. }) => {
 295                     self.visit_path(path, id);
 296                     self.visit_ty(&**ty);
 297                 }
 298             }
 299         }
 300     }
 301
 302     fn visit_poly_trait_ref(&mut self,
 303                             trait_ref: &hir::PolyTraitRef,
 304                             _modifier: &hir::TraitBoundModifier) {
 305         debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
 306
 307         if !self.trait_ref_hack || !trait_ref.bound_lifetimes.is_empty() {
 308             if self.trait_ref_hack {
 309                 println!("{:?}", trait_ref.span);
 310                 span_err!(self.sess, trait_ref.span, E0316,
 311                           "nested quantification of lifetimes");
 312             }
 313             self.with(LateScope(&trait_ref.bound_lifetimes, self.scope), |old_scope, this| {
 314                 this.check_lifetime_defs(old_scope, &trait_ref.bound_lifetimes);
 315                 for lifetime in &trait_ref.bound_lifetimes {
 316                     this.visit_lifetime_def(lifetime);
 317                 }
 318                 intravisit::walk_path(this, &trait_ref.trait_ref.path)
 319             })
 320         } else {
 321             self.visit_trait_ref(&trait_ref.trait_ref)
 322         }
 323     }
 324 }
 325
 326 #[derive(Copy, Clone, PartialEq)]
 327 enum ShadowKind { Label, Lifetime }
 328 struct Original { kind: ShadowKind, span: Span }
 329 struct Shadower { kind: ShadowKind, span: Span }
 330
 331 fn original_label(span: Span) -> Original {
 332     Original { kind: ShadowKind::Label, span: span }
 333 }
 334 fn shadower_label(span: Span) -> Shadower {
 335     Shadower { kind: ShadowKind::Label, span: span }
 336 }
 337 fn original_lifetime(l: &hir::Lifetime) -> Original {
 338     Original { kind: ShadowKind::Lifetime, span: l.span }
 339 }
 340 fn shadower_lifetime(l: &hir::Lifetime) -> Shadower {
 341     Shadower { kind: ShadowKind::Lifetime, span: l.span }
 342 }
 343
 344 impl ShadowKind {
 345     fn desc(&self) -> &'static str {
 346         match *self {
 347             ShadowKind::Label => "label",
 348             ShadowKind::Lifetime => "lifetime",
 349         }
 350     }
 351 }
 352
 353 fn signal_shadowing_problem(
 354     sess: &Session, name: ast::Name, orig: Original, shadower: Shadower) {
 355     if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
 356         // lifetime/lifetime shadowing is an error
 357         span_err!(sess, shadower.span, E0496,
 358                   "{} name `{}` shadows a \
 359                    {} name that is already in scope",
 360                   shadower.kind.desc(), name, orig.kind.desc());
 361     } else {
 362         // shadowing involving a label is only a warning, due to issues with
 363         // labels and lifetimes not being macro-hygienic.
 364         sess.span_warn(shadower.span,
 365                       &format!("{} name `{}` shadows a \
 366                                 {} name that is already in scope",
 367                                shadower.kind.desc(), name, orig.kind.desc()));
 368     }
 369     sess.span_note(orig.span,
 370                    &format!("shadowed {} `{}` declared here",
 371                             orig.kind.desc(), name));
 372 }
 373
 374 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
 375 // if one of the label shadows a lifetime or another label.
 376 fn extract_labels<'v, 'a>(ctxt: &mut LifetimeContext<'a>, b: &'v hir::Block) {
 377
 378     struct GatherLabels<'a> {
 379         sess: &'a Session,
 380         scope: Scope<'a>,
 381         labels_in_fn: &'a mut Vec<(ast::Name, Span)>,
 382     }
 383
 384     let mut gather = GatherLabels {
 385         sess: ctxt.sess,
 386         scope: ctxt.scope,
 387         labels_in_fn: &mut ctxt.labels_in_fn,
 388     };
 389     gather.visit_block(b);
 390     return;
 391
 392     impl<'v, 'a> Visitor<'v> for GatherLabels<'a> {
 393         fn visit_expr(&mut self, ex: &'v hir::Expr) {
 394             // do not recurse into closures defined in the block
 395             // since they are treated as separate fns from the POV of
 396             // labels_in_fn
 397             if let hir::ExprClosure(..) = ex.node {
 398                 return
 399             }
 400             if let Some(label) = expression_label(ex) {
 401                 for &(prior, prior_span) in &self.labels_in_fn[..] {
 402                     // FIXME (#24278): non-hygienic comparison
 403                     if label == prior {
 404                         signal_shadowing_problem(self.sess,
 405                                                  label,
 406                                                  original_label(prior_span),
 407                                                  shadower_label(ex.span));
 408                     }
 409                 }
 410
 411                 check_if_label_shadows_lifetime(self.sess,
 412                                                 self.scope,
 413                                                 label,
 414                                                 ex.span);
 415
 416                 self.labels_in_fn.push((label, ex.span));
 417             }
 418             intravisit::walk_expr(self, ex)
 419         }
 420
 421         fn visit_item(&mut self, _: &hir::Item) {
 422             // do not recurse into items defined in the block
 423         }
 424     }
 425
 426     fn expression_label(ex: &hir::Expr) -> Option<ast::Name> {
 427         match ex.node {
 428             hir::ExprWhile(_, _, Some(label)) |
 429             hir::ExprLoop(_, Some(label)) => Some(label.name),
 430             _ => None,
 431         }
 432     }
 433
 434     fn check_if_label_shadows_lifetime<'a>(sess: &'a Session,
 435                                            mut scope: Scope<'a>,
 436                                            label: ast::Name,
 437                                            label_span: Span) {
 438         loop {
 439             match *scope {
 440                 BlockScope(_, s) => { scope = s; }
 441                 RootScope => { return; }
 442
 443                 EarlyScope(_, lifetimes, s) |
 444                 LateScope(lifetimes, s) => {
 445                     for lifetime_def in lifetimes {
 446                         // FIXME (#24278): non-hygienic comparison
 447                         if label == lifetime_def.lifetime.name {
 448                             signal_shadowing_problem(
 449                                 sess,
 450                                 label,
 451                                 original_lifetime(&lifetime_def.lifetime),
 452                                 shadower_label(label_span));
 453                             return;
 454                         }
 455                     }
 456                     scope = s;
 457                 }
 458             }
 459         }
 460     }
 461 }
 462
 463 impl<'a> LifetimeContext<'a> {
 464     // This is just like intravisit::walk_fn, except that it extracts the
 465     // labels of the function body and swaps them in before visiting
 466     // the function body itself.
 467     fn walk_fn<'b>(&mut self,
 468                    fk: FnKind,
 469                    fd: &hir::FnDecl,
 470                    fb: &'b hir::Block,
 471                    _span: Span) {
 472         match fk {
 473             FnKind::ItemFn(_, generics, _, _, _, _) => {
 474                 intravisit::walk_fn_decl(self, fd);
 475                 self.visit_generics(generics);
 476             }
 477             FnKind::Method(_, sig, _) => {
 478                 intravisit::walk_fn_decl(self, fd);
 479                 self.visit_generics(&sig.generics);
 480                 self.visit_explicit_self(&sig.explicit_self);
 481             }
 482             FnKind::Closure(..) => {
 483                 intravisit::walk_fn_decl(self, fd);
 484             }
 485         }
 486
 487         // After inpsecting the decl, add all labels from the body to
 488         // `self.labels_in_fn`.
 489         extract_labels(self, fb);
 490
 491         self.visit_block(fb);
 492     }
 493
 494     fn with<F>(&mut self, wrap_scope: ScopeChain, f: F) where
 495         F: FnOnce(Scope, &mut LifetimeContext),
 496     {
 497         let LifetimeContext {sess, ref mut named_region_map, ..} = *self;
 498         let mut this = LifetimeContext {
 499             sess: sess,
 500             named_region_map: *named_region_map,
 501             scope: &wrap_scope,
 502             def_map: self.def_map,
 503             trait_ref_hack: self.trait_ref_hack,
 504             labels_in_fn: self.labels_in_fn.clone(),
 505         };
 506         debug!("entering scope {:?}", this.scope);
 507         f(self.scope, &mut this);
 508         debug!("exiting scope {:?}", this.scope);
 509     }
 510
 511     /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
 512     ///
 513     /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
 514     /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
 515     /// within type bounds; those are early bound lifetimes, and the rest are late bound.
 516     ///
 517     /// For example:
 518     ///
 519     ///    fn foo<'a,'b,'c,T:Trait<'b>>(...)
 520     ///
 521     /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
 522     /// lifetimes may be interspersed together.
 523     ///
 524     /// If early bound lifetimes are present, we separate them into their own list (and likewise
 525     /// for late bound). They will be numbered sequentially, starting from the lowest index that is
 526     /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
 527     /// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
 528     /// ordering is not important there.
 529     fn visit_early_late<F>(&mut self,
 530                            early_space: subst::ParamSpace,
 531                            generics: &hir::Generics,
 532                            walk: F) where
 533         F: FnOnce(&mut LifetimeContext),
 534     {
 535         let referenced_idents = early_bound_lifetime_names(generics);
 536
 537         debug!("visit_early_late: referenced_idents={:?}",
 538                referenced_idents);
 539
 540         let (early, late): (Vec<_>, _) = generics.lifetimes.iter().cloned().partition(
 541             |l| referenced_idents.iter().any(|&i| i == l.lifetime.name));
 542
 543         self.with(EarlyScope(early_space, &early, self.scope), move |old_scope, this| {
 544             this.with(LateScope(&late, this.scope), move |_, this| {
 545                 this.check_lifetime_defs(old_scope, &generics.lifetimes);
 546                 walk(this);
 547             });
 548         });
 549     }
 550
 551     fn resolve_lifetime_ref(&mut self, lifetime_ref: &hir::Lifetime) {
 552         // Walk up the scope chain, tracking the number of fn scopes
 553         // that we pass through, until we find a lifetime with the
 554         // given name or we run out of scopes. If we encounter a code
 555         // block, then the lifetime is not bound but free, so switch
 556         // over to `resolve_free_lifetime_ref()` to complete the
 557         // search.
 558         let mut late_depth = 0;
 559         let mut scope = self.scope;
 560         loop {
 561             match *scope {
 562                 BlockScope(blk_scope, s) => {
 563                     return self.resolve_free_lifetime_ref(blk_scope, lifetime_ref, s);
 564                 }
 565
 566                 RootScope => {
 567                     break;
 568                 }
 569
 570                 EarlyScope(space, lifetimes, s) => {
 571                     match search_lifetimes(lifetimes, lifetime_ref) {
 572                         Some((index, lifetime_def)) => {
 573                             let decl_id = lifetime_def.id;
 574                             let def = DefEarlyBoundRegion(space, index, decl_id);
 575                             self.insert_lifetime(lifetime_ref, def);
 576                             return;
 577                         }
 578                         None => {
 579                             scope = s;
 580                         }
 581                     }
 582                 }
 583
 584                 LateScope(lifetimes, s) => {
 585                     match search_lifetimes(lifetimes, lifetime_ref) {
 586                         Some((_index, lifetime_def)) => {
 587                             let decl_id = lifetime_def.id;
 588                             let debruijn = ty::DebruijnIndex::new(late_depth + 1);
 589                             let def = DefLateBoundRegion(debruijn, decl_id);
 590                             self.insert_lifetime(lifetime_ref, def);
 591                             return;
 592                         }
 593
 594                         None => {
 595                             late_depth += 1;
 596                             scope = s;
 597                         }
 598                     }
 599                 }
 600             }
 601         }
 602
 603         self.unresolved_lifetime_ref(lifetime_ref);
 604     }
 605
 606     fn resolve_free_lifetime_ref(&mut self,
 607                                  scope_data: region::DestructionScopeData,
 608                                  lifetime_ref: &hir::Lifetime,
 609                                  scope: Scope) {
 610         debug!("resolve_free_lifetime_ref \
 611                 scope_data: {:?} lifetime_ref: {:?} scope: {:?}",
 612                scope_data, lifetime_ref, scope);
 613
 614         // Walk up the scope chain, tracking the outermost free scope,
 615         // until we encounter a scope that contains the named lifetime
 616         // or we run out of scopes.
 617         let mut scope_data = scope_data;
 618         let mut scope = scope;
 619         let mut search_result = None;
 620         loop {
 621             debug!("resolve_free_lifetime_ref \
 622                     scope_data: {:?} scope: {:?} search_result: {:?}",
 623                    scope_data, scope, search_result);
 624             match *scope {
 625                 BlockScope(blk_scope_data, s) => {
 626                     scope_data = blk_scope_data;
 627                     scope = s;
 628                 }
 629
 630                 RootScope => {
 631                     break;
 632                 }
 633
 634                 EarlyScope(_, lifetimes, s) |
 635                 LateScope(lifetimes, s) => {
 636                     search_result = search_lifetimes(lifetimes, lifetime_ref);
 637                     if search_result.is_some() {
 638                         break;
 639                     }
 640                     scope = s;
 641                 }
 642             }
 643         }
 644
 645         match search_result {
 646             Some((_depth, lifetime)) => {
 647                 let def = DefFreeRegion(scope_data, lifetime.id);
 648                 self.insert_lifetime(lifetime_ref, def);
 649             }
 650
 651             None => {
 652                 self.unresolved_lifetime_ref(lifetime_ref);
 653             }
 654         }
 655
 656     }
 657
 658     fn unresolved_lifetime_ref(&self, lifetime_ref: &hir::Lifetime) {
 659         span_err!(self.sess, lifetime_ref.span, E0261,
 660             "use of undeclared lifetime name `{}`",
 661                     lifetime_ref.name);
 662     }
 663
 664     fn check_lifetime_defs(&mut self, old_scope: Scope, lifetimes: &Vec<hir::LifetimeDef>) {
 665         for i in 0..lifetimes.len() {
 666             let lifetime_i = &lifetimes[i];
 667
 668             let special_idents = [special_idents::static_lifetime];
 669             for lifetime in lifetimes {
 670                 if special_idents.iter().any(|&i| i.name == lifetime.lifetime.name) {
 671                     span_err!(self.sess, lifetime.lifetime.span, E0262,
 672                         "invalid lifetime parameter name: `{}`", lifetime.lifetime.name);
 673                 }
 674             }
 675
 676             // It is a hard error to shadow a lifetime within the same scope.
 677             for j in i + 1..lifetimes.len() {
 678                 let lifetime_j = &lifetimes[j];
 679
 680                 if lifetime_i.lifetime.name == lifetime_j.lifetime.name {
 681                     span_err!(self.sess, lifetime_j.lifetime.span, E0263,
 682                         "lifetime name `{}` declared twice in \
 683                                 the same scope",
 684                                 lifetime_j.lifetime.name);
 685                 }
 686             }
 687
 688             // It is a soft error to shadow a lifetime within a parent scope.
 689             self.check_lifetime_def_for_shadowing(old_scope, &lifetime_i.lifetime);
 690
 691             for bound in &lifetime_i.bounds {
 692                 self.resolve_lifetime_ref(bound);
 693             }
 694         }
 695     }
 696
 697     fn check_lifetime_def_for_shadowing(&self,
 698                                         mut old_scope: Scope,
 699                                         lifetime: &hir::Lifetime)
 700     {
 701         for &(label, label_span) in &self.labels_in_fn {
 702             // FIXME (#24278): non-hygienic comparison
 703             if lifetime.name == label {
 704                 signal_shadowing_problem(self.sess,
 705                                          lifetime.name,
 706                                          original_label(label_span),
 707                                          shadower_lifetime(&lifetime));
 708                 return;
 709             }
 710         }
 711
 712         loop {
 713             match *old_scope {
 714                 BlockScope(_, s) => {
 715                     old_scope = s;
 716                 }
 717
 718                 RootScope => {
 719                     return;
 720                 }
 721
 722                 EarlyScope(_, lifetimes, s) |
 723                 LateScope(lifetimes, s) => {
 724                     if let Some((_, lifetime_def)) = search_lifetimes(lifetimes, lifetime) {
 725                         signal_shadowing_problem(
 726                             self.sess,
 727                             lifetime.name,
 728                             original_lifetime(&lifetime_def),
 729                             shadower_lifetime(&lifetime));
 730                         return;
 731                     }
 732
 733                     old_scope = s;
 734                 }
 735             }
 736         }
 737     }
 738
 739     fn insert_lifetime(&mut self,
 740                        lifetime_ref: &hir::Lifetime,
 741                        def: DefRegion) {
 742         if lifetime_ref.id == ast::DUMMY_NODE_ID {
 743             self.sess.span_bug(lifetime_ref.span,
 744                                "lifetime reference not renumbered, \
 745                                probably a bug in syntax::fold");
 746         }
 747
 748         debug!("lifetime_ref={:?} id={:?} resolved to {:?}",
 749                 lifetime_to_string(lifetime_ref),
 750                 lifetime_ref.id,
 751                 def);
 752         self.named_region_map.insert(lifetime_ref.id, def);
 753     }
 754 }
 755
 756 fn search_lifetimes<'a>(lifetimes: &'a Vec<hir::LifetimeDef>,
 757                     lifetime_ref: &hir::Lifetime)
 758                     -> Option<(u32, &'a hir::Lifetime)> {
 759     for (i, lifetime_decl) in lifetimes.iter().enumerate() {
 760         if lifetime_decl.lifetime.name == lifetime_ref.name {
 761             return Some((i as u32, &lifetime_decl.lifetime));
 762         }
 763     }
 764     return None;
 765 }
 766
 767 ///////////////////////////////////////////////////////////////////////////
 768
 769 pub fn early_bound_lifetimes<'a>(generics: &'a hir::Generics) -> Vec<hir::LifetimeDef> {
 770     let referenced_idents = early_bound_lifetime_names(generics);
 771     if referenced_idents.is_empty() {
 772         return Vec::new();
 773     }
 774
 775     generics.lifetimes.iter()
 776         .filter(|l| referenced_idents.iter().any(|&i| i == l.lifetime.name))
 777         .cloned()
 778         .collect()
 779 }
 780
 781 /// Given a set of generic declarations, returns a list of names containing all early bound
 782 /// lifetime names for those generics. (In fact, this list may also contain other names.)
 783 fn early_bound_lifetime_names(generics: &hir::Generics) -> Vec<ast::Name> {
 784     // Create two lists, dividing the lifetimes into early/late bound.
 785     // Initially, all of them are considered late, but we will move
 786     // things from late into early as we go if we find references to
 787     // them.
 788     let mut early_bound = Vec::new();
 789     let mut late_bound = generics.lifetimes.iter()
 790                                            .map(|l| l.lifetime.name)
 791                                            .collect();
 792
 793     // Any lifetime that appears in a type bound is early.
 794     {
 795         let mut collector =
 796             FreeLifetimeCollector { early_bound: &mut early_bound,
 797                                     late_bound: &mut late_bound };
 798         for ty_param in generics.ty_params.iter() {
 799             walk_list!(&mut collector, visit_ty_param_bound, &ty_param.bounds);
 800         }
 801         for predicate in &generics.where_clause.predicates {
 802             match predicate {
 803                 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate{ref bounds,
 804                                                                               ref bounded_ty,
 805                                                                               ..}) => {
 806                     collector.visit_ty(&**bounded_ty);
 807                     walk_list!(&mut collector, visit_ty_param_bound, bounds);
 808                 }
 809                 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate{ref lifetime,
 810                                                                                 ref bounds,
 811                                                                                 ..}) => {
 812                     collector.visit_lifetime(lifetime);
 813
 814                     for bound in bounds {
 815                         collector.visit_lifetime(bound);
 816                     }
 817                 }
 818                 &hir::WherePredicate::EqPredicate(_) => unimplemented!()
 819             }
 820         }
 821     }
 822
 823     // Any lifetime that either has a bound or is referenced by a
 824     // bound is early.
 825     for lifetime_def in &generics.lifetimes {
 826         if !lifetime_def.bounds.is_empty() {
 827             shuffle(&mut early_bound, &mut late_bound,
 828                     lifetime_def.lifetime.name);
 829             for bound in &lifetime_def.bounds {
 830                 shuffle(&mut early_bound, &mut late_bound,
 831                         bound.name);
 832             }
 833         }
 834     }
 835     return early_bound;
 836
 837     struct FreeLifetimeCollector<'a> {
 838         early_bound: &'a mut Vec<ast::Name>,
 839         late_bound: &'a mut Vec<ast::Name>,
 840     }
 841
 842     impl<'a, 'v> Visitor<'v> for FreeLifetimeCollector<'a> {
 843         fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
 844             shuffle(self.early_bound, self.late_bound,
 845                     lifetime_ref.name);
 846         }
 847     }
 848
 849     fn shuffle(early_bound: &mut Vec<ast::Name>,
 850                late_bound: &mut Vec<ast::Name>,
 851                name: ast::Name) {
 852         match late_bound.iter().position(|n| *n == name) {
 853             Some(index) => {
 854                 late_bound.swap_remove(index);
 855                 early_bound.push(name);
 856             }
 857             None => { }
 858         }
 859     }
 860 }
 861
 862 impl<'a> fmt::Debug for ScopeChain<'a> {
 863     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
 864         match *self {
 865             EarlyScope(space, defs, _) => write!(fmt, "EarlyScope({:?}, {:?})", space, defs),
 866             LateScope(defs, _) => write!(fmt, "LateScope({:?})", defs),
 867             BlockScope(id, _) => write!(fmt, "BlockScope({:?})", id),
 868             RootScope => write!(fmt, "RootScope"),
 869         }
 870     }
 871 }