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     sess.abort_if_new_errors(|| {
  99         krate.visit_all_items(&mut LifetimeContext {
 100             sess: sess,
 101             named_region_map: &mut named_region_map,
 102             scope: &ROOT_SCOPE,
 103             def_map: def_map,
 104             trait_ref_hack: false,
 105             labels_in_fn: vec![],
 106         });
 107     });
 108     named_region_map
 109 }
 110
 111 impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
 112     fn visit_item(&mut self, item: &hir::Item) {
 113         assert!(self.labels_in_fn.is_empty());
 114
 115         // Items always introduce a new root scope
 116         self.with(RootScope, |_, this| {
 117             match item.node {
 118                 hir::ItemFn(..) => {
 119                     // Fn lifetimes get added in visit_fn below:
 120                     intravisit::walk_item(this, item);
 121                 }
 122                 hir::ItemExternCrate(_) |
 123                 hir::ItemUse(_) |
 124                 hir::ItemMod(..) |
 125                 hir::ItemDefaultImpl(..) |
 126                 hir::ItemForeignMod(..) |
 127                 hir::ItemStatic(..) |
 128                 hir::ItemConst(..) => {
 129                     // These sorts of items have no lifetime parameters at all.
 130                     intravisit::walk_item(this, item);
 131                 }
 132                 hir::ItemTy(_, ref generics) |
 133                 hir::ItemEnum(_, ref generics) |
 134                 hir::ItemStruct(_, ref generics) |
 135                 hir::ItemTrait(_, ref generics, _, _) |
 136                 hir::ItemImpl(_, _, ref generics, _, _, _) => {
 137                     // These kinds of items have only early bound lifetime parameters.
 138                     let lifetimes = &generics.lifetimes;
 139                     let early_scope = EarlyScope(subst::TypeSpace, lifetimes, &ROOT_SCOPE);
 140                     this.with(early_scope, |old_scope, this| {
 141                         this.check_lifetime_defs(old_scope, lifetimes);
 142                         intravisit::walk_item(this, item);
 143                     });
 144                 }
 145             }
 146         });
 147
 148         // Done traversing the item; remove any labels it created
 149         self.labels_in_fn.truncate(0);
 150     }
 151
 152     fn visit_foreign_item(&mut self, item: &hir::ForeignItem) {
 153         // Items save/restore the set of labels. This way inner items
 154         // can freely reuse names, be they loop labels or lifetimes.
 155         let saved = replace(&mut self.labels_in_fn, vec![]);
 156
 157         // Items always introduce a new root scope
 158         self.with(RootScope, |_, this| {
 159             match item.node {
 160                 hir::ForeignItemFn(_, ref generics) => {
 161                     this.visit_early_late(subst::FnSpace, generics, |this| {
 162                         intravisit::walk_foreign_item(this, item);
 163                     })
 164                 }
 165                 hir::ForeignItemStatic(..) => {
 166                     intravisit::walk_foreign_item(this, item);
 167                 }
 168             }
 169         });
 170
 171         // Done traversing the item; restore saved set of labels.
 172         replace(&mut self.labels_in_fn, saved);
 173     }
 174
 175     fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
 176                 b: &'v hir::Block, s: Span, _: ast::NodeId) {
 177         match fk {
 178             FnKind::ItemFn(_, generics, _, _, _, _) => {
 179                 self.visit_early_late(subst::FnSpace, generics, |this| {
 180                     this.walk_fn(fk, fd, b, s)
 181                 })
 182             }
 183             FnKind::Method(_, sig, _) => {
 184                 self.visit_early_late(subst::FnSpace, &sig.generics, |this| {
 185                     this.walk_fn(fk, fd, b, s)
 186                 })
 187             }
 188             FnKind::Closure => {
 189                 self.walk_fn(fk, fd, b, s)
 190             }
 191         }
 192     }
 193
 194     fn visit_ty(&mut self, ty: &hir::Ty) {
 195         match ty.node {
 196             hir::TyBareFn(ref c) => {
 197                 self.with(LateScope(&c.lifetimes, self.scope), |old_scope, this| {
 198                     // a bare fn has no bounds, so everything
 199                     // contained within is scoped within its binder.
 200                     this.check_lifetime_defs(old_scope, &c.lifetimes);
 201                     intravisit::walk_ty(this, ty);
 202                 });
 203             }
 204             hir::TyPath(None, ref path) => {
 205                 // if this path references a trait, then this will resolve to
 206                 // a trait ref, which introduces a binding scope.
 207                 match self.def_map.get(&ty.id).map(|d| (d.base_def, d.depth)) {
 208                     Some((def::DefTrait(..), 0)) => {
 209                         self.with(LateScope(&Vec::new(), self.scope), |_, this| {
 210                             this.visit_path(path, ty.id);
 211                         });
 212                     }
 213                     _ => {
 214                         intravisit::walk_ty(self, ty);
 215                     }
 216                 }
 217             }
 218             _ => {
 219                 intravisit::walk_ty(self, ty)
 220             }
 221         }
 222     }
 223
 224     fn visit_trait_item(&mut self, trait_item: &hir::TraitItem) {
 225         // We reset the labels on every trait item, so that different
 226         // methods in an impl can reuse label names.
 227         let saved = replace(&mut self.labels_in_fn, vec![]);
 228
 229         if let hir::MethodTraitItem(ref sig, None) = trait_item.node {
 230             self.visit_early_late(
 231                 subst::FnSpace, &sig.generics,
 232                 |this| intravisit::walk_trait_item(this, trait_item))
 233         } else {
 234             intravisit::walk_trait_item(self, trait_item);
 235         }
 236
 237         replace(&mut self.labels_in_fn, saved);
 238     }
 239
 240     fn visit_block(&mut self, b: &hir::Block) {
 241         self.with(BlockScope(region::DestructionScopeData::new(b.id),
 242                              self.scope),
 243                   |_, this| intravisit::walk_block(this, b));
 244     }
 245
 246     fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
 247         if lifetime_ref.name == special_idents::static_lifetime.name {
 248             self.insert_lifetime(lifetime_ref, DefStaticRegion);
 249             return;
 250         }
 251         self.resolve_lifetime_ref(lifetime_ref);
 252     }
 253
 254     fn visit_generics(&mut self, generics: &hir::Generics) {
 255         for ty_param in generics.ty_params.iter() {
 256             walk_list!(self, visit_ty_param_bound, &ty_param.bounds);
 257             match ty_param.default {
 258                 Some(ref ty) => self.visit_ty(&**ty),
 259                 None => {}
 260             }
 261         }
 262         for predicate in &generics.where_clause.predicates {
 263             match predicate {
 264                 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate{ ref bounded_ty,
 265                                                                                ref bounds,
 266                                                                                ref bound_lifetimes,
 267                                                                                .. }) => {
 268                     if !bound_lifetimes.is_empty() {
 269                         self.trait_ref_hack = true;
 270                         let result = self.with(LateScope(bound_lifetimes, self.scope),
 271                                                |old_scope, this| {
 272                             this.check_lifetime_defs(old_scope, bound_lifetimes);
 273                             this.visit_ty(&**bounded_ty);
 274                             walk_list!(this, visit_ty_param_bound, bounds);
 275                         });
 276                         self.trait_ref_hack = false;
 277                         result
 278                     } else {
 279                         self.visit_ty(&**bounded_ty);
 280                         walk_list!(self, visit_ty_param_bound, bounds);
 281                     }
 282                 }
 283                 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate{ref lifetime,
 284                                                                                 ref bounds,
 285                                                                                 .. }) => {
 286
 287                     self.visit_lifetime(lifetime);
 288                     for bound in bounds {
 289                         self.visit_lifetime(bound);
 290                     }
 291                 }
 292                 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate{ id,
 293                                                                          ref path,
 294                                                                          ref ty,
 295                                                                          .. }) => {
 296                     self.visit_path(path, id);
 297                     self.visit_ty(&**ty);
 298                 }
 299             }
 300         }
 301     }
 302
 303     fn visit_poly_trait_ref(&mut self,
 304                             trait_ref: &hir::PolyTraitRef,
 305                             _modifier: &hir::TraitBoundModifier) {
 306         debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
 307
 308         if !self.trait_ref_hack || !trait_ref.bound_lifetimes.is_empty() {
 309             if self.trait_ref_hack {
 310                 println!("{:?}", trait_ref.span);
 311                 span_err!(self.sess, trait_ref.span, E0316,
 312                           "nested quantification of lifetimes");
 313             }
 314             self.with(LateScope(&trait_ref.bound_lifetimes, self.scope), |old_scope, this| {
 315                 this.check_lifetime_defs(old_scope, &trait_ref.bound_lifetimes);
 316                 for lifetime in &trait_ref.bound_lifetimes {
 317                     this.visit_lifetime_def(lifetime);
 318                 }
 319                 intravisit::walk_path(this, &trait_ref.trait_ref.path)
 320             })
 321         } else {
 322             self.visit_trait_ref(&trait_ref.trait_ref)
 323         }
 324     }
 325 }
 326
 327 #[derive(Copy, Clone, PartialEq)]
 328 enum ShadowKind { Label, Lifetime }
 329 struct Original { kind: ShadowKind, span: Span }
 330 struct Shadower { kind: ShadowKind, span: Span }
 331
 332 fn original_label(span: Span) -> Original {
 333     Original { kind: ShadowKind::Label, span: span }
 334 }
 335 fn shadower_label(span: Span) -> Shadower {
 336     Shadower { kind: ShadowKind::Label, span: span }
 337 }
 338 fn original_lifetime(l: &hir::Lifetime) -> Original {
 339     Original { kind: ShadowKind::Lifetime, span: l.span }
 340 }
 341 fn shadower_lifetime(l: &hir::Lifetime) -> Shadower {
 342     Shadower { kind: ShadowKind::Lifetime, span: l.span }
 343 }
 344
 345 impl ShadowKind {
 346     fn desc(&self) -> &'static str {
 347         match *self {
 348             ShadowKind::Label => "label",
 349             ShadowKind::Lifetime => "lifetime",
 350         }
 351     }
 352 }
 353
 354 fn signal_shadowing_problem(
 355     sess: &Session, name: ast::Name, orig: Original, shadower: Shadower) {
 356     if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
 357         // lifetime/lifetime shadowing is an error
 358         span_err!(sess, shadower.span, E0496,
 359                   "{} name `{}` shadows a \
 360                    {} name that is already in scope",
 361                   shadower.kind.desc(), name, orig.kind.desc());
 362     } else {
 363         // shadowing involving a label is only a warning, due to issues with
 364         // labels and lifetimes not being macro-hygienic.
 365         sess.span_warn(shadower.span,
 366                       &format!("{} name `{}` shadows a \
 367                                 {} name that is already in scope",
 368                                shadower.kind.desc(), name, orig.kind.desc()));
 369     }
 370     sess.span_note(orig.span,
 371                    &format!("shadowed {} `{}` declared here",
 372                             orig.kind.desc(), name));
 373 }
 374
 375 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
 376 // if one of the label shadows a lifetime or another label.
 377 fn extract_labels<'v, 'a>(ctxt: &mut LifetimeContext<'a>, b: &'v hir::Block) {
 378
 379     struct GatherLabels<'a> {
 380         sess: &'a Session,
 381         scope: Scope<'a>,
 382         labels_in_fn: &'a mut Vec<(ast::Name, Span)>,
 383     }
 384
 385     let mut gather = GatherLabels {
 386         sess: ctxt.sess,
 387         scope: ctxt.scope,
 388         labels_in_fn: &mut ctxt.labels_in_fn,
 389     };
 390     gather.visit_block(b);
 391     return;
 392
 393     impl<'v, 'a> Visitor<'v> for GatherLabels<'a> {
 394         fn visit_expr(&mut self, ex: &'v hir::Expr) {
 395             // do not recurse into closures defined in the block
 396             // since they are treated as separate fns from the POV of
 397             // labels_in_fn
 398             if let hir::ExprClosure(..) = ex.node {
 399                 return
 400             }
 401             if let Some(label) = expression_label(ex) {
 402                 for &(prior, prior_span) in &self.labels_in_fn[..] {
 403                     // FIXME (#24278): non-hygienic comparison
 404                     if label == prior {
 405                         signal_shadowing_problem(self.sess,
 406                                                  label,
 407                                                  original_label(prior_span),
 408                                                  shadower_label(ex.span));
 409                     }
 410                 }
 411
 412                 check_if_label_shadows_lifetime(self.sess,
 413                                                 self.scope,
 414                                                 label,
 415                                                 ex.span);
 416
 417                 self.labels_in_fn.push((label, ex.span));
 418             }
 419             intravisit::walk_expr(self, ex)
 420         }
 421
 422         fn visit_item(&mut self, _: &hir::Item) {
 423             // do not recurse into items defined in the block
 424         }
 425     }
 426
 427     fn expression_label(ex: &hir::Expr) -> Option<ast::Name> {
 428         match ex.node {
 429             hir::ExprWhile(_, _, Some(label)) |
 430             hir::ExprLoop(_, Some(label)) => Some(label.unhygienic_name),
 431             _ => None,
 432         }
 433     }
 434
 435     fn check_if_label_shadows_lifetime<'a>(sess: &'a Session,
 436                                            mut scope: Scope<'a>,
 437                                            label: ast::Name,
 438                                            label_span: Span) {
 439         loop {
 440             match *scope {
 441                 BlockScope(_, s) => { scope = s; }
 442                 RootScope => { return; }
 443
 444                 EarlyScope(_, lifetimes, s) |
 445                 LateScope(lifetimes, s) => {
 446                     for lifetime_def in lifetimes {
 447                         // FIXME (#24278): non-hygienic comparison
 448                         if label == lifetime_def.lifetime.name {
 449                             signal_shadowing_problem(
 450                                 sess,
 451                                 label,
 452                                 original_lifetime(&lifetime_def.lifetime),
 453                                 shadower_label(label_span));
 454                             return;
 455                         }
 456                     }
 457                     scope = s;
 458                 }
 459             }
 460         }
 461     }
 462 }
 463
 464 impl<'a> LifetimeContext<'a> {
 465     // This is just like intravisit::walk_fn, except that it extracts the
 466     // labels of the function body and swaps them in before visiting
 467     // the function body itself.
 468     fn walk_fn<'b>(&mut self,
 469                    fk: FnKind,
 470                    fd: &hir::FnDecl,
 471                    fb: &'b hir::Block,
 472                    _span: Span) {
 473         match fk {
 474             FnKind::ItemFn(_, generics, _, _, _, _) => {
 475                 intravisit::walk_fn_decl(self, fd);
 476                 self.visit_generics(generics);
 477             }
 478             FnKind::Method(_, sig, _) => {
 479                 intravisit::walk_fn_decl(self, fd);
 480                 self.visit_generics(&sig.generics);
 481                 self.visit_explicit_self(&sig.explicit_self);
 482             }
 483             FnKind::Closure => {
 484                 intravisit::walk_fn_decl(self, fd);
 485             }
 486         }
 487
 488         // After inpsecting the decl, add all labels from the body to
 489         // `self.labels_in_fn`.
 490         extract_labels(self, fb);
 491
 492         self.visit_block(fb);
 493     }
 494
 495     fn with<F>(&mut self, wrap_scope: ScopeChain, f: F) where
 496         F: FnOnce(Scope, &mut LifetimeContext),
 497     {
 498         let LifetimeContext {sess, ref mut named_region_map, ..} = *self;
 499         let mut this = LifetimeContext {
 500             sess: sess,
 501             named_region_map: *named_region_map,
 502             scope: &wrap_scope,
 503             def_map: self.def_map,
 504             trait_ref_hack: self.trait_ref_hack,
 505             labels_in_fn: self.labels_in_fn.clone(),
 506         };
 507         debug!("entering scope {:?}", this.scope);
 508         f(self.scope, &mut this);
 509         debug!("exiting scope {:?}", this.scope);
 510     }
 511
 512     /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
 513     ///
 514     /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
 515     /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
 516     /// within type bounds; those are early bound lifetimes, and the rest are late bound.
 517     ///
 518     /// For example:
 519     ///
 520     ///    fn foo<'a,'b,'c,T:Trait<'b>>(...)
 521     ///
 522     /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
 523     /// lifetimes may be interspersed together.
 524     ///
 525     /// If early bound lifetimes are present, we separate them into their own list (and likewise
 526     /// for late bound). They will be numbered sequentially, starting from the lowest index that is
 527     /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
 528     /// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
 529     /// ordering is not important there.
 530     fn visit_early_late<F>(&mut self,
 531                            early_space: subst::ParamSpace,
 532                            generics: &hir::Generics,
 533                            walk: F) where
 534         F: FnOnce(&mut LifetimeContext),
 535     {
 536         let referenced_idents = early_bound_lifetime_names(generics);
 537
 538         debug!("visit_early_late: referenced_idents={:?}",
 539                referenced_idents);
 540
 541         let (early, late): (Vec<_>, _) = generics.lifetimes.iter().cloned().partition(
 542             |l| referenced_idents.iter().any(|&i| i == l.lifetime.name));
 543
 544         self.with(EarlyScope(early_space, &early, self.scope), move |old_scope, this| {
 545             this.with(LateScope(&late, this.scope), move |_, this| {
 546                 this.check_lifetime_defs(old_scope, &generics.lifetimes);
 547                 walk(this);
 548             });
 549         });
 550     }
 551
 552     fn resolve_lifetime_ref(&mut self, lifetime_ref: &hir::Lifetime) {
 553         // Walk up the scope chain, tracking the number of fn scopes
 554         // that we pass through, until we find a lifetime with the
 555         // given name or we run out of scopes. If we encounter a code
 556         // block, then the lifetime is not bound but free, so switch
 557         // over to `resolve_free_lifetime_ref()` to complete the
 558         // search.
 559         let mut late_depth = 0;
 560         let mut scope = self.scope;
 561         loop {
 562             match *scope {
 563                 BlockScope(blk_scope, s) => {
 564                     return self.resolve_free_lifetime_ref(blk_scope, lifetime_ref, s);
 565                 }
 566
 567                 RootScope => {
 568                     break;
 569                 }
 570
 571                 EarlyScope(space, lifetimes, s) => {
 572                     match search_lifetimes(lifetimes, lifetime_ref) {
 573                         Some((index, lifetime_def)) => {
 574                             let decl_id = lifetime_def.id;
 575                             let def = DefEarlyBoundRegion(space, index, decl_id);
 576                             self.insert_lifetime(lifetime_ref, def);
 577                             return;
 578                         }
 579                         None => {
 580                             scope = s;
 581                         }
 582                     }
 583                 }
 584
 585                 LateScope(lifetimes, s) => {
 586                     match search_lifetimes(lifetimes, lifetime_ref) {
 587                         Some((_index, lifetime_def)) => {
 588                             let decl_id = lifetime_def.id;
 589                             let debruijn = ty::DebruijnIndex::new(late_depth + 1);
 590                             let def = DefLateBoundRegion(debruijn, decl_id);
 591                             self.insert_lifetime(lifetime_ref, def);
 592                             return;
 593                         }
 594
 595                         None => {
 596                             late_depth += 1;
 597                             scope = s;
 598                         }
 599                     }
 600                 }
 601             }
 602         }
 603
 604         self.unresolved_lifetime_ref(lifetime_ref);
 605     }
 606
 607     fn resolve_free_lifetime_ref(&mut self,
 608                                  scope_data: region::DestructionScopeData,
 609                                  lifetime_ref: &hir::Lifetime,
 610                                  scope: Scope) {
 611         debug!("resolve_free_lifetime_ref \
 612                 scope_data: {:?} lifetime_ref: {:?} scope: {:?}",
 613                scope_data, lifetime_ref, scope);
 614
 615         // Walk up the scope chain, tracking the outermost free scope,
 616         // until we encounter a scope that contains the named lifetime
 617         // or we run out of scopes.
 618         let mut scope_data = scope_data;
 619         let mut scope = scope;
 620         let mut search_result = None;
 621         loop {
 622             debug!("resolve_free_lifetime_ref \
 623                     scope_data: {:?} scope: {:?} search_result: {:?}",
 624                    scope_data, scope, search_result);
 625             match *scope {
 626                 BlockScope(blk_scope_data, s) => {
 627                     scope_data = blk_scope_data;
 628                     scope = s;
 629                 }
 630
 631                 RootScope => {
 632                     break;
 633                 }
 634
 635                 EarlyScope(_, lifetimes, s) |
 636                 LateScope(lifetimes, s) => {
 637                     search_result = search_lifetimes(lifetimes, lifetime_ref);
 638                     if search_result.is_some() {
 639                         break;
 640                     }
 641                     scope = s;
 642                 }
 643             }
 644         }
 645
 646         match search_result {
 647             Some((_depth, lifetime)) => {
 648                 let def = DefFreeRegion(scope_data, lifetime.id);
 649                 self.insert_lifetime(lifetime_ref, def);
 650             }
 651
 652             None => {
 653                 self.unresolved_lifetime_ref(lifetime_ref);
 654             }
 655         }
 656
 657     }
 658
 659     fn unresolved_lifetime_ref(&self, lifetime_ref: &hir::Lifetime) {
 660         span_err!(self.sess, lifetime_ref.span, E0261,
 661             "use of undeclared lifetime name `{}`",
 662                     lifetime_ref.name);
 663     }
 664
 665     fn check_lifetime_defs(&mut self, old_scope: Scope, lifetimes: &Vec<hir::LifetimeDef>) {
 666         for i in 0..lifetimes.len() {
 667             let lifetime_i = &lifetimes[i];
 668
 669             let special_idents = [special_idents::static_lifetime];
 670             for lifetime in lifetimes {
 671                 if special_idents.iter().any(|&i| i.name == lifetime.lifetime.name) {
 672                     span_err!(self.sess, lifetime.lifetime.span, E0262,
 673                         "invalid lifetime parameter name: `{}`", lifetime.lifetime.name);
 674                 }
 675             }
 676
 677             // It is a hard error to shadow a lifetime within the same scope.
 678             for j in i + 1..lifetimes.len() {
 679                 let lifetime_j = &lifetimes[j];
 680
 681                 if lifetime_i.lifetime.name == lifetime_j.lifetime.name {
 682                     span_err!(self.sess, lifetime_j.lifetime.span, E0263,
 683                         "lifetime name `{}` declared twice in \
 684                                 the same scope",
 685                                 lifetime_j.lifetime.name);
 686                 }
 687             }
 688
 689             // It is a soft error to shadow a lifetime within a parent scope.
 690             self.check_lifetime_def_for_shadowing(old_scope, &lifetime_i.lifetime);
 691
 692             for bound in &lifetime_i.bounds {
 693                 self.resolve_lifetime_ref(bound);
 694             }
 695         }
 696     }
 697
 698     fn check_lifetime_def_for_shadowing(&self,
 699                                         mut old_scope: Scope,
 700                                         lifetime: &hir::Lifetime)
 701     {
 702         for &(label, label_span) in &self.labels_in_fn {
 703             // FIXME (#24278): non-hygienic comparison
 704             if lifetime.name == label {
 705                 signal_shadowing_problem(self.sess,
 706                                          lifetime.name,
 707                                          original_label(label_span),
 708                                          shadower_lifetime(&lifetime));
 709                 return;
 710             }
 711         }
 712
 713         loop {
 714             match *old_scope {
 715                 BlockScope(_, s) => {
 716                     old_scope = s;
 717                 }
 718
 719                 RootScope => {
 720                     return;
 721                 }
 722
 723                 EarlyScope(_, lifetimes, s) |
 724                 LateScope(lifetimes, s) => {
 725                     if let Some((_, lifetime_def)) = search_lifetimes(lifetimes, lifetime) {
 726                         signal_shadowing_problem(
 727                             self.sess,
 728                             lifetime.name,
 729                             original_lifetime(&lifetime_def),
 730                             shadower_lifetime(&lifetime));
 731                         return;
 732                     }
 733
 734                     old_scope = s;
 735                 }
 736             }
 737         }
 738     }
 739
 740     fn insert_lifetime(&mut self,
 741                        lifetime_ref: &hir::Lifetime,
 742                        def: DefRegion) {
 743         if lifetime_ref.id == ast::DUMMY_NODE_ID {
 744             self.sess.span_bug(lifetime_ref.span,
 745                                "lifetime reference not renumbered, \
 746                                probably a bug in syntax::fold");
 747         }
 748
 749         debug!("lifetime_ref={:?} id={:?} resolved to {:?}",
 750                 lifetime_to_string(lifetime_ref),
 751                 lifetime_ref.id,
 752                 def);
 753         self.named_region_map.insert(lifetime_ref.id, def);
 754     }
 755 }
 756
 757 fn search_lifetimes<'a>(lifetimes: &'a Vec<hir::LifetimeDef>,
 758                     lifetime_ref: &hir::Lifetime)
 759                     -> Option<(u32, &'a hir::Lifetime)> {
 760     for (i, lifetime_decl) in lifetimes.iter().enumerate() {
 761         if lifetime_decl.lifetime.name == lifetime_ref.name {
 762             return Some((i as u32, &lifetime_decl.lifetime));
 763         }
 764     }
 765     return None;
 766 }
 767
 768 ///////////////////////////////////////////////////////////////////////////
 769
 770 pub fn early_bound_lifetimes<'a>(generics: &'a hir::Generics) -> Vec<hir::LifetimeDef> {
 771     let referenced_idents = early_bound_lifetime_names(generics);
 772     if referenced_idents.is_empty() {
 773         return Vec::new();
 774     }
 775
 776     generics.lifetimes.iter()
 777         .filter(|l| referenced_idents.iter().any(|&i| i == l.lifetime.name))
 778         .cloned()
 779         .collect()
 780 }
 781
 782 /// Given a set of generic declarations, returns a list of names containing all early bound
 783 /// lifetime names for those generics. (In fact, this list may also contain other names.)
 784 fn early_bound_lifetime_names(generics: &hir::Generics) -> Vec<ast::Name> {
 785     // Create two lists, dividing the lifetimes into early/late bound.
 786     // Initially, all of them are considered late, but we will move
 787     // things from late into early as we go if we find references to
 788     // them.
 789     let mut early_bound = Vec::new();
 790     let mut late_bound = generics.lifetimes.iter()
 791                                            .map(|l| l.lifetime.name)
 792                                            .collect();
 793
 794     // Any lifetime that appears in a type bound is early.
 795     {
 796         let mut collector =
 797             FreeLifetimeCollector { early_bound: &mut early_bound,
 798                                     late_bound: &mut late_bound };
 799         for ty_param in generics.ty_params.iter() {
 800             walk_list!(&mut collector, visit_ty_param_bound, &ty_param.bounds);
 801         }
 802         for predicate in &generics.where_clause.predicates {
 803             match predicate {
 804                 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate{ref bounds,
 805                                                                               ref bounded_ty,
 806                                                                               ..}) => {
 807                     collector.visit_ty(&**bounded_ty);
 808                     walk_list!(&mut collector, visit_ty_param_bound, bounds);
 809                 }
 810                 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate{ref lifetime,
 811                                                                                 ref bounds,
 812                                                                                 ..}) => {
 813                     collector.visit_lifetime(lifetime);
 814
 815                     for bound in bounds {
 816                         collector.visit_lifetime(bound);
 817                     }
 818                 }
 819                 &hir::WherePredicate::EqPredicate(_) => unimplemented!()
 820             }
 821         }
 822     }
 823
 824     // Any lifetime that either has a bound or is referenced by a
 825     // bound is early.
 826     for lifetime_def in &generics.lifetimes {
 827         if !lifetime_def.bounds.is_empty() {
 828             shuffle(&mut early_bound, &mut late_bound,
 829                     lifetime_def.lifetime.name);
 830             for bound in &lifetime_def.bounds {
 831                 shuffle(&mut early_bound, &mut late_bound,
 832                         bound.name);
 833             }
 834         }
 835     }
 836     return early_bound;
 837
 838     struct FreeLifetimeCollector<'a> {
 839         early_bound: &'a mut Vec<ast::Name>,
 840         late_bound: &'a mut Vec<ast::Name>,
 841     }
 842
 843     impl<'a, 'v> Visitor<'v> for FreeLifetimeCollector<'a> {
 844         fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
 845             shuffle(self.early_bound, self.late_bound,
 846                     lifetime_ref.name);
 847         }
 848     }
 849
 850     fn shuffle(early_bound: &mut Vec<ast::Name>,
 851                late_bound: &mut Vec<ast::Name>,
 852                name: ast::Name) {
 853         match late_bound.iter().position(|n| *n == name) {
 854             Some(index) => {
 855                 late_bound.swap_remove(index);
 856                 early_bound.push(name);
 857             }
 858             None => { }
 859         }
 860     }
 861 }
 862
 863 impl<'a> fmt::Debug for ScopeChain<'a> {
 864     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
 865         match *self {
 866             EarlyScope(space, defs, _) => write!(fmt, "EarlyScope({:?}, {:?})", space, defs),
 867             LateScope(defs, _) => write!(fmt, "LateScope({:?})", defs),
 868             BlockScope(id, _) => write!(fmt, "BlockScope({:?})", id),
 869             RootScope => write!(fmt, "RootScope"),
 870         }
 871     }
 872 }