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 dep_graph::DepNode;
  22 use hir::map::Map;
  23 use session::Session;
  24 use hir::def::{Def, DefMap};
  25 use hir::def_id::DefId;
  26 use middle::region;
  27 use ty;
  28 use std::mem::replace;
  29 use syntax::ast;
  30 use syntax::symbol::keywords;
  31 use syntax_pos::Span;
  32 use util::nodemap::NodeMap;
  33
  34 use rustc_data_structures::fx::FxHashSet;
  35 use hir;
  36 use hir::print::lifetime_to_string;
  37 use hir::intravisit::{self, Visitor, FnKind};
  38
  39 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
  40 pub enum DefRegion {
  41     DefStaticRegion,
  42     DefEarlyBoundRegion(/* index */ u32,
  43                         /* lifetime decl */ ast::NodeId),
  44     DefLateBoundRegion(ty::DebruijnIndex,
  45                        /* lifetime decl */ ast::NodeId),
  46     DefFreeRegion(region::CallSiteScopeData,
  47                   /* lifetime decl */ ast::NodeId),
  48 }
  49
  50 // Maps the id of each lifetime reference to the lifetime decl
  51 // that it corresponds to.
  52 pub struct NamedRegionMap {
  53     // maps from every use of a named (not anonymous) lifetime to a
  54     // `DefRegion` describing how that region is bound
  55     pub defs: NodeMap<DefRegion>,
  56
  57     // the set of lifetime def ids that are late-bound; late-bound ids
  58     // are named regions appearing in fn arguments that do not appear
  59     // in where-clauses
  60     pub late_bound: NodeMap<ty::Issue32330>,
  61 }
  62
  63 struct LifetimeContext<'a, 'tcx: 'a> {
  64     sess: &'a Session,
  65     hir_map: &'a Map<'tcx>,
  66     map: &'a mut NamedRegionMap,
  67     scope: Scope<'a>,
  68     def_map: &'a DefMap,
  69     // Deep breath. Our representation for poly trait refs contains a single
  70     // binder and thus we only allow a single level of quantification. However,
  71     // the syntax of Rust permits quantification in two places, e.g., `T: for <'a> Foo<'a>`
  72     // and `for <'a, 'b> &'b T: Foo<'a>`. In order to get the de Bruijn indices
  73     // correct when representing these constraints, we should only introduce one
  74     // scope. However, we want to support both locations for the quantifier and
  75     // during lifetime resolution we want precise information (so we can't
  76     // desugar in an earlier phase).
  77
  78     // SO, if we encounter a quantifier at the outer scope, we set
  79     // trait_ref_hack to true (and introduce a scope), and then if we encounter
  80     // a quantifier at the inner scope, we error. If trait_ref_hack is false,
  81     // then we introduce the scope at the inner quantifier.
  82
  83     // I'm sorry.
  84     trait_ref_hack: bool,
  85
  86     // List of labels in the function/method currently under analysis.
  87     labels_in_fn: Vec<(ast::Name, Span)>,
  88 }
  89
  90 #[derive(PartialEq, Debug)]
  91 enum ScopeChain<'a> {
  92     /// EarlyScope(['a, 'b, ...], start, s) extends s with early-bound
  93     /// lifetimes, with consecutive parameter indices from `start`.
  94     /// That is, 'a has index `start`, 'b has index `start + 1`, etc.
  95     /// Indices before `start` correspond to other generic parameters
  96     /// of a parent item (trait/impl of a method), or `Self` in traits.
  97     EarlyScope(&'a [hir::LifetimeDef], u32, Scope<'a>),
  98     /// LateScope(['a, 'b, ...], s) extends s with late-bound
  99     /// lifetimes introduced by the declaration binder_id.
 100     LateScope(&'a [hir::LifetimeDef], Scope<'a>),
 101
 102     /// lifetimes introduced by a fn are scoped to the call-site for that fn.
 103     FnScope { fn_id: ast::NodeId, body_id: ast::NodeId, s: Scope<'a> },
 104     RootScope
 105 }
 106
 107 type Scope<'a> = &'a ScopeChain<'a>;
 108
 109 static ROOT_SCOPE: ScopeChain<'static> = RootScope;
 110
 111 pub fn krate(sess: &Session,
 112              hir_map: &Map,
 113              def_map: &DefMap)
 114              -> Result<NamedRegionMap, usize> {
 115     let _task = hir_map.dep_graph.in_task(DepNode::ResolveLifetimes);
 116     let krate = hir_map.krate();
 117     let mut map = NamedRegionMap {
 118         defs: NodeMap(),
 119         late_bound: NodeMap(),
 120     };
 121     sess.track_errors(|| {
 122         intravisit::walk_crate(&mut LifetimeContext {
 123             sess: sess,
 124             hir_map: hir_map,
 125             map: &mut map,
 126             scope: &ROOT_SCOPE,
 127             def_map: def_map,
 128             trait_ref_hack: false,
 129             labels_in_fn: vec![],
 130         }, krate);
 131     })?;
 132     Ok(map)
 133 }
 134
 135 impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
 136     // Override the nested functions -- lifetimes follow lexical scope,
 137     // so it's convenient to walk the tree in lexical order.
 138     fn nested_visit_map(&mut self) -> Option<&hir::map::Map<'tcx>> {
 139         Some(&self.hir_map)
 140     }
 141
 142     fn visit_item(&mut self, item: &'tcx hir::Item) {
 143         // Save labels for nested items.
 144         let saved_labels_in_fn = replace(&mut self.labels_in_fn, vec![]);
 145
 146         // Items always introduce a new root scope
 147         self.with(RootScope, |_, this| {
 148             match item.node {
 149                 hir::ItemFn(..) => {
 150                     // Fn lifetimes get added in visit_fn below:
 151                     intravisit::walk_item(this, item);
 152                 }
 153                 hir::ItemExternCrate(_) |
 154                 hir::ItemUse(_) |
 155                 hir::ItemMod(..) |
 156                 hir::ItemDefaultImpl(..) |
 157                 hir::ItemForeignMod(..) |
 158                 hir::ItemStatic(..) |
 159                 hir::ItemConst(..) => {
 160                     // These sorts of items have no lifetime parameters at all.
 161                     intravisit::walk_item(this, item);
 162                 }
 163                 hir::ItemTy(_, ref generics) |
 164                 hir::ItemEnum(_, ref generics) |
 165                 hir::ItemStruct(_, ref generics) |
 166                 hir::ItemUnion(_, ref generics) |
 167                 hir::ItemTrait(_, ref generics, ..) |
 168                 hir::ItemImpl(_, _, ref generics, ..) => {
 169                     // These kinds of items have only early bound lifetime parameters.
 170                     let lifetimes = &generics.lifetimes;
 171                     let start = if let hir::ItemTrait(..) = item.node {
 172                         1 // Self comes before lifetimes
 173                     } else {
 174                         0
 175                     };
 176                     this.with(EarlyScope(lifetimes, start, &ROOT_SCOPE), |old_scope, this| {
 177                         this.check_lifetime_defs(old_scope, lifetimes);
 178                         intravisit::walk_item(this, item);
 179                     });
 180                 }
 181             }
 182         });
 183
 184         // Done traversing the item; remove any labels it created
 185         self.labels_in_fn = saved_labels_in_fn;
 186     }
 187
 188     fn visit_foreign_item(&mut self, item: &'tcx hir::ForeignItem) {
 189         // Items save/restore the set of labels. This way inner items
 190         // can freely reuse names, be they loop labels or lifetimes.
 191         let saved = replace(&mut self.labels_in_fn, vec![]);
 192
 193         // Items always introduce a new root scope
 194         self.with(RootScope, |_, this| {
 195             match item.node {
 196                 hir::ForeignItemFn(ref decl, ref generics) => {
 197                     this.visit_early_late(item.id, decl, generics, |this| {
 198                         intravisit::walk_foreign_item(this, item);
 199                     })
 200                 }
 201                 hir::ForeignItemStatic(..) => {
 202                     intravisit::walk_foreign_item(this, item);
 203                 }
 204             }
 205         });
 206
 207         // Done traversing the item; restore saved set of labels.
 208         replace(&mut self.labels_in_fn, saved);
 209     }
 210
 211     fn visit_fn(&mut self, fk: FnKind<'tcx>, decl: &'tcx hir::FnDecl,
 212                 b: &'tcx hir::Expr, s: Span, fn_id: ast::NodeId) {
 213         match fk {
 214             FnKind::ItemFn(_, generics, ..) => {
 215                 self.visit_early_late(fn_id,decl, generics, |this| {
 216                     this.add_scope_and_walk_fn(fk, decl, b, s, fn_id)
 217                 })
 218             }
 219             FnKind::Method(_, sig, ..) => {
 220                 self.visit_early_late(
 221                     fn_id,
 222                     decl,
 223                     &sig.generics,
 224                     |this| this.add_scope_and_walk_fn(fk, decl, b, s, fn_id));
 225             }
 226             FnKind::Closure(_) => {
 227                 // Closures have their own set of labels, save labels just
 228                 // like for foreign items above.
 229                 let saved = replace(&mut self.labels_in_fn, vec![]);
 230                 let result = self.add_scope_and_walk_fn(fk, decl, b, s, fn_id);
 231                 replace(&mut self.labels_in_fn, saved);
 232                 result
 233             }
 234         }
 235     }
 236
 237     fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
 238         match ty.node {
 239             hir::TyBareFn(ref c) => {
 240                 self.with(LateScope(&c.lifetimes, self.scope), |old_scope, this| {
 241                     // a bare fn has no bounds, so everything
 242                     // contained within is scoped within its binder.
 243                     this.check_lifetime_defs(old_scope, &c.lifetimes);
 244                     intravisit::walk_ty(this, ty);
 245                 });
 246             }
 247             hir::TyPath(hir::QPath::Resolved(None, ref path)) => {
 248                 // if this path references a trait, then this will resolve to
 249                 // a trait ref, which introduces a binding scope.
 250                 match self.def_map.get(&ty.id).map(|d| (d.base_def, d.depth)) {
 251                     Some((Def::Trait(..), 0)) => {
 252                         self.with(LateScope(&[], self.scope), |_, this| {
 253                             this.visit_path(path, ty.id);
 254                         });
 255                     }
 256                     _ => {
 257                         intravisit::walk_ty(self, ty);
 258                     }
 259                 }
 260             }
 261             _ => {
 262                 intravisit::walk_ty(self, ty)
 263             }
 264         }
 265     }
 266
 267     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
 268         // We reset the labels on every trait item, so that different
 269         // methods in an impl can reuse label names.
 270         let saved = replace(&mut self.labels_in_fn, vec![]);
 271
 272         if let hir::MethodTraitItem(ref sig, None) = trait_item.node {
 273             self.visit_early_late(
 274                 trait_item.id,
 275                 &sig.decl, &sig.generics,
 276                 |this| intravisit::walk_trait_item(this, trait_item))
 277         } else {
 278             intravisit::walk_trait_item(self, trait_item);
 279         }
 280
 281         replace(&mut self.labels_in_fn, saved);
 282     }
 283
 284     fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
 285         if lifetime_ref.name == keywords::StaticLifetime.name() {
 286             self.insert_lifetime(lifetime_ref, DefStaticRegion);
 287             return;
 288         }
 289         self.resolve_lifetime_ref(lifetime_ref);
 290     }
 291
 292     fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
 293         for ty_param in generics.ty_params.iter() {
 294             walk_list!(self, visit_ty_param_bound, &ty_param.bounds);
 295             if let Some(ref ty) = ty_param.default {
 296                 self.visit_ty(&ty);
 297             }
 298         }
 299         for predicate in &generics.where_clause.predicates {
 300             match predicate {
 301                 &hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate{ ref bounded_ty,
 302                                                                                ref bounds,
 303                                                                                ref bound_lifetimes,
 304                                                                                .. }) => {
 305                     if !bound_lifetimes.is_empty() {
 306                         self.trait_ref_hack = true;
 307                         let result = self.with(LateScope(bound_lifetimes, self.scope),
 308                                                |old_scope, this| {
 309                             this.check_lifetime_defs(old_scope, bound_lifetimes);
 310                             this.visit_ty(&bounded_ty);
 311                             walk_list!(this, visit_ty_param_bound, bounds);
 312                         });
 313                         self.trait_ref_hack = false;
 314                         result
 315                     } else {
 316                         self.visit_ty(&bounded_ty);
 317                         walk_list!(self, visit_ty_param_bound, bounds);
 318                     }
 319                 }
 320                 &hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate{ref lifetime,
 321                                                                                 ref bounds,
 322                                                                                 .. }) => {
 323
 324                     self.visit_lifetime(lifetime);
 325                     for bound in bounds {
 326                         self.visit_lifetime(bound);
 327                     }
 328                 }
 329                 &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate{ id,
 330                                                                          ref path,
 331                                                                          ref ty,
 332                                                                          .. }) => {
 333                     self.visit_path(path, id);
 334                     self.visit_ty(&ty);
 335                 }
 336             }
 337         }
 338     }
 339
 340     fn visit_poly_trait_ref(&mut self,
 341                             trait_ref: &'tcx hir::PolyTraitRef,
 342                             _modifier: &'tcx hir::TraitBoundModifier) {
 343         debug!("visit_poly_trait_ref trait_ref={:?}", trait_ref);
 344
 345         if !self.trait_ref_hack || !trait_ref.bound_lifetimes.is_empty() {
 346             if self.trait_ref_hack {
 347                 span_err!(self.sess, trait_ref.span, E0316,
 348                           "nested quantification of lifetimes");
 349             }
 350             self.with(LateScope(&trait_ref.bound_lifetimes, self.scope), |old_scope, this| {
 351                 this.check_lifetime_defs(old_scope, &trait_ref.bound_lifetimes);
 352                 for lifetime in &trait_ref.bound_lifetimes {
 353                     this.visit_lifetime_def(lifetime);
 354                 }
 355                 intravisit::walk_path(this, &trait_ref.trait_ref.path)
 356             })
 357         } else {
 358             self.visit_trait_ref(&trait_ref.trait_ref)
 359         }
 360     }
 361 }
 362
 363 #[derive(Copy, Clone, PartialEq)]
 364 enum ShadowKind { Label, Lifetime }
 365 struct Original { kind: ShadowKind, span: Span }
 366 struct Shadower { kind: ShadowKind, span: Span }
 367
 368 fn original_label(span: Span) -> Original {
 369     Original { kind: ShadowKind::Label, span: span }
 370 }
 371 fn shadower_label(span: Span) -> Shadower {
 372     Shadower { kind: ShadowKind::Label, span: span }
 373 }
 374 fn original_lifetime(l: &hir::Lifetime) -> Original {
 375     Original { kind: ShadowKind::Lifetime, span: l.span }
 376 }
 377 fn shadower_lifetime(l: &hir::Lifetime) -> Shadower {
 378     Shadower { kind: ShadowKind::Lifetime, span: l.span }
 379 }
 380
 381 impl ShadowKind {
 382     fn desc(&self) -> &'static str {
 383         match *self {
 384             ShadowKind::Label => "label",
 385             ShadowKind::Lifetime => "lifetime",
 386         }
 387     }
 388 }
 389
 390 fn signal_shadowing_problem(sess: &Session, name: ast::Name, orig: Original, shadower: Shadower) {
 391     let mut err = if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
 392         // lifetime/lifetime shadowing is an error
 393         struct_span_err!(sess, shadower.span, E0496,
 394                          "{} name `{}` shadows a \
 395                           {} name that is already in scope",
 396                          shadower.kind.desc(), name, orig.kind.desc())
 397     } else {
 398         // shadowing involving a label is only a warning, due to issues with
 399         // labels and lifetimes not being macro-hygienic.
 400         sess.struct_span_warn(shadower.span,
 401                               &format!("{} name `{}` shadows a \
 402                                         {} name that is already in scope",
 403                                        shadower.kind.desc(), name, orig.kind.desc()))
 404     };
 405     err.span_label(orig.span, &"first declared here");
 406     err.span_label(shadower.span,
 407                    &format!("lifetime {} already in scope", name));
 408     err.emit();
 409 }
 410
 411 // Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
 412 // if one of the label shadows a lifetime or another label.
 413 fn extract_labels(ctxt: &mut LifetimeContext, b: &hir::Expr) {
 414     struct GatherLabels<'a> {
 415         sess: &'a Session,
 416         scope: Scope<'a>,
 417         labels_in_fn: &'a mut Vec<(ast::Name, Span)>,
 418     }
 419
 420     let mut gather = GatherLabels {
 421         sess: ctxt.sess,
 422         scope: ctxt.scope,
 423         labels_in_fn: &mut ctxt.labels_in_fn,
 424     };
 425     gather.visit_expr(b);
 426     return;
 427
 428     impl<'v, 'a> Visitor<'v> for GatherLabels<'a> {
 429         fn visit_expr(&mut self, ex: &'v hir::Expr) {
 430             // do not recurse into closures defined in the block
 431             // since they are treated as separate fns from the POV of
 432             // labels_in_fn
 433             if let hir::ExprClosure(..) = ex.node {
 434                 return
 435             }
 436             if let Some((label, label_span)) = expression_label(ex) {
 437                 for &(prior, prior_span) in &self.labels_in_fn[..] {
 438                     // FIXME (#24278): non-hygienic comparison
 439                     if label == prior {
 440                         signal_shadowing_problem(self.sess,
 441                                                  label,
 442                                                  original_label(prior_span),
 443                                                  shadower_label(label_span));
 444                     }
 445                 }
 446
 447                 check_if_label_shadows_lifetime(self.sess,
 448                                                 self.scope,
 449                                                 label,
 450                                                 label_span);
 451
 452                 self.labels_in_fn.push((label, label_span));
 453             }
 454             intravisit::walk_expr(self, ex)
 455         }
 456
 457         fn visit_item(&mut self, _: &hir::Item) {
 458             // do not recurse into items defined in the block
 459         }
 460     }
 461
 462     fn expression_label(ex: &hir::Expr) -> Option<(ast::Name, Span)> {
 463         match ex.node {
 464             hir::ExprWhile(.., Some(label)) |
 465             hir::ExprLoop(_, Some(label), _) => Some((label.node, label.span)),
 466             _ => None,
 467         }
 468     }
 469
 470     fn check_if_label_shadows_lifetime<'a>(sess: &'a Session,
 471                                            mut scope: Scope<'a>,
 472                                            label: ast::Name,
 473                                            label_span: Span) {
 474         loop {
 475             match *scope {
 476                 FnScope { s, .. } => { scope = s; }
 477                 RootScope => { return; }
 478
 479                 EarlyScope(lifetimes, _, s) |
 480                 LateScope(lifetimes, s) => {
 481                     for lifetime_def in lifetimes {
 482                         // FIXME (#24278): non-hygienic comparison
 483                         if label == lifetime_def.lifetime.name {
 484                             signal_shadowing_problem(
 485                                 sess,
 486                                 label,
 487                                 original_lifetime(&lifetime_def.lifetime),
 488                                 shadower_label(label_span));
 489                             return;
 490                         }
 491                     }
 492                     scope = s;
 493                 }
 494             }
 495         }
 496     }
 497 }
 498
 499 impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
 500     fn add_scope_and_walk_fn(&mut self,
 501                              fk: FnKind<'tcx>,
 502                              fd: &'tcx hir::FnDecl,
 503                              fb: &'tcx hir::Expr,
 504                              _span: Span,
 505                              fn_id: ast::NodeId) {
 506         match fk {
 507             FnKind::ItemFn(_, generics, ..) => {
 508                 intravisit::walk_fn_decl(self, fd);
 509                 self.visit_generics(generics);
 510             }
 511             FnKind::Method(_, sig, ..) => {
 512                 intravisit::walk_fn_decl(self, fd);
 513                 self.visit_generics(&sig.generics);
 514             }
 515             FnKind::Closure(_) => {
 516                 intravisit::walk_fn_decl(self, fd);
 517             }
 518         }
 519
 520         // After inpsecting the decl, add all labels from the body to
 521         // `self.labels_in_fn`.
 522         extract_labels(self, fb);
 523
 524         self.with(FnScope { fn_id: fn_id, body_id: fb.id, s: self.scope },
 525                   |_old_scope, this| this.visit_expr(fb))
 526     }
 527
 528     // FIXME(#37666) this works around a limitation in the region inferencer
 529     fn hack<F>(&mut self, f: F) where
 530         F: for<'b> FnOnce(&mut LifetimeContext<'b, 'tcx>),
 531     {
 532         f(self)
 533     }
 534
 535     fn with<F>(&mut self, wrap_scope: ScopeChain, f: F) where
 536         F: for<'b> FnOnce(Scope, &mut LifetimeContext<'b, 'tcx>),
 537     {
 538         let LifetimeContext {sess, hir_map, ref mut map, ..} = *self;
 539         let mut this = LifetimeContext {
 540             sess: sess,
 541             hir_map: hir_map,
 542             map: *map,
 543             scope: &wrap_scope,
 544             def_map: self.def_map,
 545             trait_ref_hack: self.trait_ref_hack,
 546             labels_in_fn: self.labels_in_fn.clone(),
 547         };
 548         debug!("entering scope {:?}", this.scope);
 549         f(self.scope, &mut this);
 550         debug!("exiting scope {:?}", this.scope);
 551     }
 552
 553     /// Visits self by adding a scope and handling recursive walk over the contents with `walk`.
 554     ///
 555     /// Handles visiting fns and methods. These are a bit complicated because we must distinguish
 556     /// early- vs late-bound lifetime parameters. We do this by checking which lifetimes appear
 557     /// within type bounds; those are early bound lifetimes, and the rest are late bound.
 558     ///
 559     /// For example:
 560     ///
 561     ///    fn foo<'a,'b,'c,T:Trait<'b>>(...)
 562     ///
 563     /// Here `'a` and `'c` are late bound but `'b` is early bound. Note that early- and late-bound
 564     /// lifetimes may be interspersed together.
 565     ///
 566     /// If early bound lifetimes are present, we separate them into their own list (and likewise
 567     /// for late bound). They will be numbered sequentially, starting from the lowest index that is
 568     /// already in scope (for a fn item, that will be 0, but for a method it might not be). Late
 569     /// bound lifetimes are resolved by name and associated with a binder id (`binder_id`), so the
 570     /// ordering is not important there.
 571     fn visit_early_late<F>(&mut self,
 572                            fn_id: ast::NodeId,
 573                            decl: &'tcx hir::FnDecl,
 574                            generics: &'tcx hir::Generics,
 575                            walk: F) where
 576         F: for<'b, 'c> FnOnce(&'b mut LifetimeContext<'c, 'tcx>),
 577     {
 578         let fn_def_id = self.hir_map.local_def_id(fn_id);
 579         insert_late_bound_lifetimes(self.map,
 580                                     fn_def_id,
 581                                     decl,
 582                                     generics);
 583
 584         let (late, early): (Vec<_>, _) =
 585             generics.lifetimes
 586                     .iter()
 587                     .cloned()
 588                     .partition(|l| self.map.late_bound.contains_key(&l.lifetime.id));
 589
 590         // Find the start of nested early scopes, e.g. in methods.
 591         let mut start = 0;
 592         if let EarlyScope(..) = *self.scope {
 593             let parent = self.hir_map.expect_item(self.hir_map.get_parent(fn_id));
 594             if let hir::ItemTrait(..) = parent.node {
 595                 start += 1; // Self comes first.
 596             }
 597             match parent.node {
 598                 hir::ItemTrait(_, ref generics, ..) |
 599                 hir::ItemImpl(_, _, ref generics, ..) => {
 600                     start += generics.lifetimes.len() + generics.ty_params.len();
 601                 }
 602                 _ => {}
 603             }
 604         }
 605
 606         self.with(EarlyScope(&early, start as u32, self.scope), move |old_scope, this| {
 607             this.with(LateScope(&late, this.scope), move |_, this| {
 608                 this.check_lifetime_defs(old_scope, &generics.lifetimes);
 609                 this.hack(walk); // FIXME(#37666) workaround in place of `walk(this)`
 610             });
 611         });
 612     }
 613
 614     fn resolve_lifetime_ref(&mut self, lifetime_ref: &hir::Lifetime) {
 615         // Walk up the scope chain, tracking the number of fn scopes
 616         // that we pass through, until we find a lifetime with the
 617         // given name or we run out of scopes. If we encounter a code
 618         // block, then the lifetime is not bound but free, so switch
 619         // over to `resolve_free_lifetime_ref()` to complete the
 620         // search.
 621         let mut late_depth = 0;
 622         let mut scope = self.scope;
 623         loop {
 624             match *scope {
 625                 FnScope {fn_id, body_id, s } => {
 626                     return self.resolve_free_lifetime_ref(
 627                         region::CallSiteScopeData { fn_id: fn_id, body_id: body_id },
 628                         lifetime_ref,
 629                         s);
 630                 }
 631
 632                 RootScope => {
 633                     break;
 634                 }
 635
 636                 EarlyScope(lifetimes, start, s) => {
 637                     match search_lifetimes(lifetimes, lifetime_ref) {
 638                         Some((index, lifetime_def)) => {
 639                             let decl_id = lifetime_def.id;
 640                             let def = DefEarlyBoundRegion(start + index, decl_id);
 641                             self.insert_lifetime(lifetime_ref, def);
 642                             return;
 643                         }
 644                         None => {
 645                             scope = s;
 646                         }
 647                     }
 648                 }
 649
 650                 LateScope(lifetimes, s) => {
 651                     match search_lifetimes(lifetimes, lifetime_ref) {
 652                         Some((_index, lifetime_def)) => {
 653                             let decl_id = lifetime_def.id;
 654                             let debruijn = ty::DebruijnIndex::new(late_depth + 1);
 655                             let def = DefLateBoundRegion(debruijn, decl_id);
 656                             self.insert_lifetime(lifetime_ref, def);
 657                             return;
 658                         }
 659
 660                         None => {
 661                             late_depth += 1;
 662                             scope = s;
 663                         }
 664                     }
 665                 }
 666             }
 667         }
 668
 669         self.unresolved_lifetime_ref(lifetime_ref);
 670     }
 671
 672     fn resolve_free_lifetime_ref(&mut self,
 673                                  scope_data: region::CallSiteScopeData,
 674                                  lifetime_ref: &hir::Lifetime,
 675                                  scope: Scope) {
 676         debug!("resolve_free_lifetime_ref \
 677                 scope_data: {:?} lifetime_ref: {:?} scope: {:?}",
 678                scope_data, lifetime_ref, scope);
 679
 680         // Walk up the scope chain, tracking the outermost free scope,
 681         // until we encounter a scope that contains the named lifetime
 682         // or we run out of scopes.
 683         let mut scope_data = scope_data;
 684         let mut scope = scope;
 685         let mut search_result = None;
 686         loop {
 687             debug!("resolve_free_lifetime_ref \
 688                     scope_data: {:?} scope: {:?} search_result: {:?}",
 689                    scope_data, scope, search_result);
 690             match *scope {
 691                 FnScope { fn_id, body_id, s } => {
 692                     scope_data = region::CallSiteScopeData {
 693                         fn_id: fn_id, body_id: body_id
 694                     };
 695                     scope = s;
 696                 }
 697
 698                 RootScope => {
 699                     break;
 700                 }
 701
 702                 EarlyScope(lifetimes, _, s) |
 703                 LateScope(lifetimes, s) => {
 704                     search_result = search_lifetimes(lifetimes, lifetime_ref);
 705                     if search_result.is_some() {
 706                         break;
 707                     }
 708                     scope = s;
 709                 }
 710             }
 711         }
 712
 713         match search_result {
 714             Some((_depth, lifetime)) => {
 715                 let def = DefFreeRegion(scope_data, lifetime.id);
 716                 self.insert_lifetime(lifetime_ref, def);
 717             }
 718
 719             None => {
 720                 self.unresolved_lifetime_ref(lifetime_ref);
 721             }
 722         }
 723
 724     }
 725
 726     fn unresolved_lifetime_ref(&self, lifetime_ref: &hir::Lifetime) {
 727         struct_span_err!(self.sess, lifetime_ref.span, E0261,
 728             "use of undeclared lifetime name `{}`", lifetime_ref.name)
 729             .span_label(lifetime_ref.span, &format!("undeclared lifetime"))
 730             .emit();
 731     }
 732
 733     fn check_lifetime_defs(&mut self, old_scope: Scope, lifetimes: &[hir::LifetimeDef]) {
 734         for i in 0..lifetimes.len() {
 735             let lifetime_i = &lifetimes[i];
 736
 737             for lifetime in lifetimes {
 738                 if lifetime.lifetime.name == keywords::StaticLifetime.name() {
 739                     let lifetime = lifetime.lifetime;
 740                     let mut err = struct_span_err!(self.sess, lifetime.span, E0262,
 741                                   "invalid lifetime parameter name: `{}`", lifetime.name);
 742                     err.span_label(lifetime.span,
 743                                    &format!("{} is a reserved lifetime name", lifetime.name));
 744                     err.emit();
 745                 }
 746             }
 747
 748             // It is a hard error to shadow a lifetime within the same scope.
 749             for j in i + 1..lifetimes.len() {
 750                 let lifetime_j = &lifetimes[j];
 751
 752                 if lifetime_i.lifetime.name == lifetime_j.lifetime.name {
 753                     struct_span_err!(self.sess, lifetime_j.lifetime.span, E0263,
 754                                      "lifetime name `{}` declared twice in the same scope",
 755                                      lifetime_j.lifetime.name)
 756                         .span_label(lifetime_j.lifetime.span,
 757                                     &format!("declared twice"))
 758                         .span_label(lifetime_i.lifetime.span,
 759                                    &format!("previous declaration here"))
 760                         .emit();
 761                 }
 762             }
 763
 764             // It is a soft error to shadow a lifetime within a parent scope.
 765             self.check_lifetime_def_for_shadowing(old_scope, &lifetime_i.lifetime);
 766
 767             for bound in &lifetime_i.bounds {
 768                 self.resolve_lifetime_ref(bound);
 769             }
 770         }
 771     }
 772
 773     fn check_lifetime_def_for_shadowing(&self,
 774                                         mut old_scope: Scope,
 775                                         lifetime: &hir::Lifetime)
 776     {
 777         for &(label, label_span) in &self.labels_in_fn {
 778             // FIXME (#24278): non-hygienic comparison
 779             if lifetime.name == label {
 780                 signal_shadowing_problem(self.sess,
 781                                          lifetime.name,
 782                                          original_label(label_span),
 783                                          shadower_lifetime(&lifetime));
 784                 return;
 785             }
 786         }
 787
 788         loop {
 789             match *old_scope {
 790                 FnScope { s, .. } => {
 791                     old_scope = s;
 792                 }
 793
 794                 RootScope => {
 795                     return;
 796                 }
 797
 798                 EarlyScope(lifetimes, _, s) |
 799                 LateScope(lifetimes, s) => {
 800                     if let Some((_, lifetime_def)) = search_lifetimes(lifetimes, lifetime) {
 801                         signal_shadowing_problem(
 802                             self.sess,
 803                             lifetime.name,
 804                             original_lifetime(&lifetime_def),
 805                             shadower_lifetime(&lifetime));
 806                         return;
 807                     }
 808
 809                     old_scope = s;
 810                 }
 811             }
 812         }
 813     }
 814
 815     fn insert_lifetime(&mut self,
 816                        lifetime_ref: &hir::Lifetime,
 817                        def: DefRegion) {
 818         if lifetime_ref.id == ast::DUMMY_NODE_ID {
 819             span_bug!(lifetime_ref.span,
 820                       "lifetime reference not renumbered, \
 821                        probably a bug in syntax::fold");
 822         }
 823
 824         debug!("lifetime_ref={:?} id={:?} resolved to {:?} span={:?}",
 825                lifetime_to_string(lifetime_ref),
 826                lifetime_ref.id,
 827                def,
 828                self.sess.codemap().span_to_string(lifetime_ref.span));
 829         self.map.defs.insert(lifetime_ref.id, def);
 830     }
 831 }
 832
 833 fn search_lifetimes<'a>(lifetimes: &'a [hir::LifetimeDef],
 834                     lifetime_ref: &hir::Lifetime)
 835                     -> Option<(u32, &'a hir::Lifetime)> {
 836     for (i, lifetime_decl) in lifetimes.iter().enumerate() {
 837         if lifetime_decl.lifetime.name == lifetime_ref.name {
 838             return Some((i as u32, &lifetime_decl.lifetime));
 839         }
 840     }
 841     return None;
 842 }
 843
 844 ///////////////////////////////////////////////////////////////////////////
 845
 846 /// Detects late-bound lifetimes and inserts them into
 847 /// `map.late_bound`.
 848 ///
 849 /// A region declared on a fn is **late-bound** if:
 850 /// - it is constrained by an argument type;
 851 /// - it does not appear in a where-clause.
 852 ///
 853 /// "Constrained" basically means that it appears in any type but
 854 /// not amongst the inputs to a projection.  In other words, `<&'a
 855 /// T as Trait<''b>>::Foo` does not constrain `'a` or `'b`.
 856 fn insert_late_bound_lifetimes(map: &mut NamedRegionMap,
 857                                fn_def_id: DefId,
 858                                decl: &hir::FnDecl,
 859                                generics: &hir::Generics) {
 860     debug!("insert_late_bound_lifetimes(decl={:?}, generics={:?})", decl, generics);
 861
 862     let mut constrained_by_input = ConstrainedCollector { regions: FxHashSet() };
 863     for arg in &decl.inputs {
 864         constrained_by_input.visit_ty(&arg.ty);
 865     }
 866
 867     let mut appears_in_output = AllCollector {
 868         regions: FxHashSet(),
 869         impl_trait: false
 870     };
 871     intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
 872
 873     debug!("insert_late_bound_lifetimes: constrained_by_input={:?}",
 874            constrained_by_input.regions);
 875
 876     // Walk the lifetimes that appear in where clauses.
 877     //
 878     // Subtle point: because we disallow nested bindings, we can just
 879     // ignore binders here and scrape up all names we see.
 880     let mut appears_in_where_clause = AllCollector {
 881         regions: FxHashSet(),
 882         impl_trait: false
 883     };
 884     for ty_param in generics.ty_params.iter() {
 885         walk_list!(&mut appears_in_where_clause,
 886                    visit_ty_param_bound,
 887                    &ty_param.bounds);
 888     }
 889     walk_list!(&mut appears_in_where_clause,
 890                visit_where_predicate,
 891                &generics.where_clause.predicates);
 892     for lifetime_def in &generics.lifetimes {
 893         if !lifetime_def.bounds.is_empty() {
 894             // `'a: 'b` means both `'a` and `'b` are referenced
 895             appears_in_where_clause.visit_lifetime_def(lifetime_def);
 896         }
 897     }
 898
 899     debug!("insert_late_bound_lifetimes: appears_in_where_clause={:?}",
 900            appears_in_where_clause.regions);
 901
 902     // Late bound regions are those that:
 903     // - appear in the inputs
 904     // - do not appear in the where-clauses
 905     // - are not implicitly captured by `impl Trait`
 906     for lifetime in &generics.lifetimes {
 907         let name = lifetime.lifetime.name;
 908
 909         // appears in the where clauses? early-bound.
 910         if appears_in_where_clause.regions.contains(&name) { continue; }
 911
 912         // any `impl Trait` in the return type? early-bound.
 913         if appears_in_output.impl_trait { continue; }
 914
 915         // does not appear in the inputs, but appears in the return
 916         // type? eventually this will be early-bound, but for now we
 917         // just mark it so we can issue warnings.
 918         let constrained_by_input = constrained_by_input.regions.contains(&name);
 919         let appears_in_output = appears_in_output.regions.contains(&name);
 920         let will_change = !constrained_by_input && appears_in_output;
 921         let issue_32330 = if will_change {
 922             ty::Issue32330::WillChange {
 923                 fn_def_id: fn_def_id,
 924                 region_name: name,
 925             }
 926         } else {
 927             ty::Issue32330::WontChange
 928         };
 929
 930         debug!("insert_late_bound_lifetimes: \
 931                 lifetime {:?} with id {:?} is late-bound ({:?}",
 932                lifetime.lifetime.name, lifetime.lifetime.id, issue_32330);
 933
 934         let prev = map.late_bound.insert(lifetime.lifetime.id, issue_32330);
 935         assert!(prev.is_none(), "visited lifetime {:?} twice", lifetime.lifetime.id);
 936     }
 937
 938     return;
 939
 940     struct ConstrainedCollector {
 941         regions: FxHashSet<ast::Name>,
 942     }
 943
 944     impl<'v> Visitor<'v> for ConstrainedCollector {
 945         fn visit_ty(&mut self, ty: &'v hir::Ty) {
 946             match ty.node {
 947                 hir::TyPath(hir::QPath::Resolved(Some(_), _)) |
 948                 hir::TyPath(hir::QPath::TypeRelative(..)) => {
 949                     // ignore lifetimes appearing in associated type
 950                     // projections, as they are not *constrained*
 951                     // (defined above)
 952                 }
 953
 954                 hir::TyPath(hir::QPath::Resolved(None, ref path)) => {
 955                     // consider only the lifetimes on the final
 956                     // segment; I am not sure it's even currently
 957                     // valid to have them elsewhere, but even if it
 958                     // is, those would be potentially inputs to
 959                     // projections
 960                     if let Some(last_segment) = path.segments.last() {
 961                         self.visit_path_segment(path.span, last_segment);
 962                     }
 963                 }
 964
 965                 _ => {
 966                     intravisit::walk_ty(self, ty);
 967                 }
 968             }
 969         }
 970
 971         fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
 972             self.regions.insert(lifetime_ref.name);
 973         }
 974     }
 975
 976     struct AllCollector {
 977         regions: FxHashSet<ast::Name>,
 978         impl_trait: bool
 979     }
 980
 981     impl<'v> Visitor<'v> for AllCollector {
 982         fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
 983             self.regions.insert(lifetime_ref.name);
 984         }
 985
 986         fn visit_ty(&mut self, ty: &hir::Ty) {
 987             if let hir::TyImplTrait(_) = ty.node {
 988                 self.impl_trait = true;
 989             }
 990             intravisit::walk_ty(self, ty);
 991         }
 992     }
 993 }